Safety valve, battery case, and method for forming a safety valve

Abstract

To provide a safety valve that can be easily manufactured without requiring a high-precision facility and a manufacturing technology, a battery case provided with the safety valve, and a forming method for forming the safety valve.SOLUTION: A safety valve partially formed thin in a battery case includes a flat portion and a groove portion formed on the periphery of the flat portion and recessed toward the inside of the battery case. When internal pressure in the battery case becomes a predetermined explosion-proof pressure or more, the groove portion is opened by inverting the recessed shape of the groove portion so as to protrude outward from the battery case and forming a crack.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a safety valve for a battery, a battery case provided with the safety valve, and a forming method for forming the safety valve.

Background Art

[0002] As a power source for devices such as mobile phones, digital cameras, and notebook computers, secondary batteries such as lithium-ion secondary batteries are widely used. In order to prevent leakage of the internal electrolyte and intrusion of moisture from the outside, the battery case, which is the exterior of such a secondary battery, has a highly airtight structure.

[0003] On the other hand, in this type of battery, when a temperature rise due to deterioration or overcharging due to an excessive voltage occurs, the electrolyte in the electrolyte volatilizes or decomposes to generate gas. When this gas is confined in a closed space, there is a risk that the pressure (internal pressure) inside the battery case will rise rapidly, causing the battery case to expand, deform, and rupture.

[0004] To solve such problems, this type of battery is often provided with a safety valve that opens due to an increase in internal pressure in order to efficiently discharge the gas generated inside the battery case. For example, Patent Document 1 describes that in a safety valve, a notch having a very small thickness compared to other parts of the safety valve is formed, and the gas generated inside the battery case is discharged through the opening of the notch.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in order to control the internal pressure (explosion-proof pressure) when the safety valve described in Patent Document 1 opens, it is necessary to adjust the thickness of the notch to be small within an allowable range of 10 to several tens of μm. Therefore, since this safety valve is difficult to manufacture, high-precision equipment and manufacturing technology are required.

[0007] In addition, it is difficult to improve the productivity of this safety valve, such as a decrease in yield until the size (dimension) of its thickness stabilizes. Also, when manufacturing a notch with a very small thickness, cracks are likely to occur, and it is difficult to inspect such notches.

[0008] The present invention has been made in view of the above circumstances, and an example of the problem is to solve the above-described problems. That is, an example of the problem of the present invention is to provide a safety valve that can be easily manufactured without requiring high-precision equipment and manufacturing technology, a battery case provided with the safety valve, and a forming method for forming the safety valve.

Means for Solving the Problem

[0009] The safety valve according to the present invention is a safety valve formed to be partially thin-walled in a battery case, and has a flat portion and a groove portion formed at the periphery of the flat portion and recessed toward the inside of the battery case. In a vertical view of the flat portion, the flat portion is substantially circular or substantially elliptical. The groove portion is characterized in that when the internal pressure in the battery case becomes equal to or higher than a predetermined explosion-proof pressure, the concave shape of the groove portion is reversed so as to protrude toward the outside of the battery case, and a crack occurs to open.

[0010] The battery case according to the present invention is provided with the safety valve according to the present invention.

[0011] The forming method of the safety valve according to the present invention is a forming method for forming a safety valve to be partially thin-walled in a battery case, and includes a forming step of forming the safety valve having a flat portion and a groove portion recessed toward the inside of the battery case at the periphery of the flat portion by applying pressure using a mold in the thickness direction of the battery case. In a vertical view of the flat portion, the flat portion is substantially circular or substantially elliptical. When the internal pressure inside the battery case becomes equal to or higher than a predetermined explosion-proof pressure, the groove portion opens by the concave shape of the groove portion being inverted and cracked so as to protrude toward the outside of the battery case.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide a safety valve that can be easily manufactured without requiring high-precision equipment and manufacturing techniques, a battery case provided with the safety valve, and a forming method for forming the safety valve.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments (this embodiment) of the present invention will be described with reference to the drawings. [Battery case] The battery case (battery exterior) 1 shown in FIG. 1 is formed into a rectangular battery case for a secondary battery by press forming a metal plate material such as aluminum or an aluminum alloy by combining drawing, ironing, etc. The material forming the battery case 1 is not limited to aluminum or an aluminum alloy, and may be, for example, other metal materials such as stainless steel, or other materials.

[0015] As shown in FIG. 1, the battery case 1 includes a housing portion 11 for housing a power generation element (electrode, electrolyte, etc.) of the secondary battery, and a lid portion 12 in which a safety valve 13 described later is formed. The housing portion 11 includes a front surface 11a and a back surface 11b, side surfaces 11c and 11d, and a bottom surface 11e, and has a box-shaped configuration having a space capable of housing the power generation element of the secondary battery therein. In this housing portion 11, the front surface 11a and the back surface 11b have a larger area than the side surfaces 11c and 11d.

[0016] The opening side of the housing portion 11 is sealed by joining the lid portion 12 by welding or the like. The battery case 1 becomes a battery case (battery exterior) having a completely sealed space blocked from the outside by providing the lid portion 12 on the housing portion 11 in this way. In fact, the battery case 1 becomes a secondary battery such as a lithium-ion secondary battery by housing the power generation element of the secondary battery in the housing portion 11 and sealing the opening side of the housing portion 11 with the lid portion 12.

[0017] [Lid portion] The lid portion 12, which is an end plate of the battery case 1, is formed by processing a metal plate material such as aluminum or an aluminum alloy. As shown in FIGS. 1 and 2, a safety valve 13 is formed at a substantially central position in the plane longitudinal direction of the lid portion 12. In the lid portion 12, the safety valve 13 is preferably formed at a substantially central position in the plane longitudinal direction of the lid portion 12 so as not to be affected by welding or the like when joining the lid portion 12 and the housing portion 11, but is not limited thereto, and may be formed at other positions in the lid portion 12.

[0018] The longitudinal length N1 of the lid portion 12 is not particularly limited, and may be, for example, 100 mm to 150 mm. The lateral length N2 of the lid portion 12 is not particularly limited, and may be, for example, 10 mm to 30 mm.

[0019] The plate thickness T of the lid portion 12 is not particularly limited, and may be, for example, 1.5 mm to 2.0 mm.

[0020] Although not shown in the figure, the lid portion 12 may be provided with other components (such as terminals) of the secondary battery at positions different from the safety valve 13.

[0021] [Safety Valve] The safety valve 13 shown in FIG. 3 is a structure for efficiently discharging the gas generated in the battery case 1 to the outside to prevent an explosion, and operates when the pressure (internal pressure) in the battery case 1 becomes equal to or higher than a predetermined explosion-proof pressure. The safety valve 13 is partially formed thinner in the lid portion 12 by press-forming a metal plate material constituting the lid portion 12, and has a flat portion 131 and a groove portion 132 formed at the periphery of the flat portion 131 and recessed toward the inside of the battery case 1.

[0022] Note that the value of the predetermined explosion-proof pressure is not particularly limited, and may be controlled by various sizes (the length N1 and length N2 of the lid portion 12, plate thickness T, plate thickness t, diameter D1, diameter D2, angle θ1, angle θ2, size H1, size H2, groove width L, R dimension, etc.) and the shape of the safety valve 13 described in this embodiment. This predetermined explosion-proof pressure may be, for example, a value in the range of 0.5 MPa to 2 MPa, and may be, for example, 1 MPa.

[0023] As shown in FIG. 3, depending on the shape and formed position of the groove portion 132 in the safety valve 13, a recess portion 133 may be formed further outside the groove portion 132 with respect to the flat portion 131.

[0024] As shown in FIG. 4, the plate thickness t of the safety valve 13 formed thinner than the lid portion 12 is not particularly limited. However, when the plate thickness T of the lid portion 12 is 1.5 mm to 2.0 mm as described above, the plate thickness t may be, for example, 0.1 mm to 0.5 mm. Note that the plate thickness T of the lid portion 12 and the plate thickness t of the safety valve 13 can be appropriately adjusted according to the explosion-proof pressure of the battery case 1. Further, the plate thickness t of the safety valve 13 may or may not be uniform over the entire safety valve 13.

[0025] As shown in FIGS. 3 and 4, the shape of the safety valve 13 (that is, the shape of the outer edge of the recess 133) is a substantially circular shape centered on the center point O. The diameter D1 of the substantially circular safety valve 13 is not particularly limited, but may be, for example, 7 mm to 15 mm.

[0026] The flat portion 131 has a substantially circular shape centered on the center point O. The flat portion 131 is a thin and substantially circular panel. Therefore, when gas is generated inside the battery case 1, the surface (inner surface) of the flat portion 131 on the inner side of the battery case 1 receives the internal pressure that rises due to the generation of the gas, and thus deforms to be convex in the outer direction of the battery case 1.

[0027] Since the flat portion 131 has a substantially circular shape without corners, its inner surface can achieve uniform stress with respect to the internal pressure in the battery case 1. If the shape of the flat portion 131 is a rectangular shape with corners, it is not preferable because the stress with respect to the internal pressure concentrates at the corners on the inner surface of the flat portion 131.

[0028] The diameter D2 of the substantially circular shape of the flat portion 131 is not particularly limited, but may be, for example, 5 mm to 10 mm.

[0029] As shown in FIG. 4, the groove portion 132 has an inner peripheral side portion 132a connected to the flat portion 131, a bottom portion 132b connected to the inner peripheral side portion 132a, and an outer peripheral side portion 132c connected to the bottom portion 132b. As shown in FIG. 4, the recess 133 has an inner peripheral side portion 133a, a bottom portion 133b connected to the inner peripheral side portion 133a, and an outer peripheral side portion 133c connected to the bottom portion 133b.

[0030] When the internal pressure in the battery case 1 rises, the groove portion 132 deforms so that the depth of its recess becomes smaller. When the internal pressure in the battery case 1 reaches or exceeds a predetermined explosion-proof pressure, the concave shape of the groove portion 132 is reversed and cracks occur so as to protrude toward the outside of the battery case 1, and thus it opens. By discharging gas to the outside from this opening portion, it is possible to prevent the battery case 1 from being greatly damaged.

[0031] Note that, unlike the examples shown in FIGS. 1 to 4, as will be described later, the safety valve 13 formed to be thin may form only the groove portion 132 at the outer edge of the flat portion 131 (see FIG. 7(a)). Alternatively, the safety valve 13 may form the groove portion 132 at the outer edge of the flat portion 131, and further form an outer-edge flat portion having a plane direction substantially parallel to the plane direction of the flat portion 131 at the outer edge thereof (see FIGS. 6(c) to 6(e)).

[0032] [Configuration Examples of Safety Valve] Next, several examples will be given and described regarding the specific configuration of the safety valve 13. FIGS. 5(a) to 5(d), FIGS. 6(a) to (e), FIGS. 7(a), (b), FIGS. 8(a) to (c), FIGS. 9(a) to (c), and FIGS. 10(a) to (f) each show a part of a cross-section passing through the central axis O' (an axis passing through the center point O and perpendicular to the flat portion 131) of the safety valve 13 for each shape example of the safety valve 13.

[0033] In the safety valve 13-1 shown in FIG. 5(a), a groove portion 132-1 is formed at the outer edge of the flat portion 131, and a recess portion 133-1 is formed at the outer edge of the groove portion 132-1. The groove portion 132-1 has an inner peripheral side portion 132-1a connected to the flat portion 131, a bottom portion 132-1b connected to the inner peripheral side portion 132-1a, and an outer peripheral side portion 132-1c connected to the bottom portion 132-1b. The recess portion 133-1 has an inner peripheral side portion 133-1a, a bottom portion 133-1b connected to the inner peripheral side portion 133-1a, and an outer peripheral side portion 133-1c connected to the bottom portion 133-1b. The outer peripheral side portion 132-1c of the groove portion 132-1 and the inner peripheral side portion 133-1a of the recess portion 133-1 are connected by a connection point 134-1.

[0034] Also, in a cross-sectional view passing through the central axis O', the shape of the boundary portion 136-1 between the outer peripheral side portion 132-1c of the groove portion 132-1, which includes the connection point 134-1, and the inner peripheral side portion 133-1a of the recessed portion 133-1 formed on the outer edge of the groove portion 132-1, is a curved shape without corners.

[0035] Thus, in a cross-sectional view passing through the central axis O', the shape of the boundary portion between the outer peripheral side portion 132c of the groove portion 132 and the inner peripheral side portion 133a of the recessed portion 133 of the safety valve 13 is a curved shape without corners. In this safety valve 13, in a cross-sectional view passing through the central axis O', the R dimension (radius of curvature R-a) inside the curved shape of the boundary portion between the outer peripheral side portion 132c of the groove portion 132 and the inner peripheral side portion 133a of the recessed portion 133 (boundary portion 136-1 in the safety valve 13-1) may or may not be uniform. The R dimension (radius of curvature R-a) inside this curved shape is preferably 0.2 mm to 0.5 mm.

[0036] In a cross-sectional view passing through the central axis O', when using the plate thickness t of the safety valve 13, the groove width L, which is the distance between the straight portion of the outer peripheral side portion 132c and the straight portion of the inner peripheral side portion 132a inside the groove portion 132 of the safety valve 13 (the distance between the straight portion of the outer peripheral side portion 132-1c and the straight portion of the inner peripheral side portion 132-1a in the safety valve 13-1), may be 0 mm to t×10 mm (that is, a length 10 times the plate thickness t). In the groove portion 132-1 of the safety valve 13-1 shown in Fig. 5(a), the groove width L may be 0.4 mm.

[0037] Also, in a cross-sectional view passing through the central axis O', the bottom portion 132b (bottom portion 132-1b in the safety valve 13-1) is a curved shape without corners. The R dimension (radius of curvature R-b) inside the bottom portion 132b, which is an index of the curved shape of the bottom portion 132b (bottom portion 132-1b in the safety valve 13-1), may be 0.1 mm to 1.0 mm. In the groove portion 132-1 of the safety valve 13-1, the straight portion of the outer peripheral side portion 132-1c and the straight portion of the inner peripheral side portion 132-1a are parallel, and thus, in the thickness direction, the groove width L may be uniform. Also, in the safety valve 13-1, the R dimension (radius of curvature R-b) may be uniform inside the curved bottom portion 132b of the groove portion 132-1.

[0038] The smaller the groove width L is, the more likely cracks are to occur in the groove portion 132. Similarly, the smaller the R dimension (curvature radius R-b) is, the more likely cracks are to occur in the groove portion 132. However, considering the compatibility between the likelihood of crack occurrence and the pressure resistance strength described later, as described above, the groove width L is preferably 0 mm to t × 10 mm, and the R dimension (curvature radius R-b) is preferably 0.1 mm to 1.0 mm.

[0039] Also, in a cross-sectional view passing through the central axis O' shown in Fig. 5(a), the shape of the boundary portion 137-1 connecting to the flat portion 131 in the inner peripheral side portion 132-1a of the groove portion 132-1 is a curved shape without corners.

[0040] Thus, in a cross-sectional view passing through the central axis O' of the safety valve 13, the shape of the boundary portion (boundary portion 137-1 in the safety valve 13-1) connecting to the flat portion 131 in the inner peripheral side portion 132a (inner peripheral side portion 132-1a in the safety valve 13-1) of the groove portion 132 is a curved shape without corners. In this safety valve 13, in a cross-sectional view passing through the central axis O', the R dimension (curvature radius R-c) inside the curved shape of the boundary portion (boundary portion 137-1 in the safety valve 13-1) connecting to the flat portion 131 in the inner peripheral side portion 132a (inner peripheral side portion 132-1a in the safety valve 13-1) of the groove portion 132 may or may not be uniform. The R dimension (curvature radius R-c) inside this curved shape is preferably 0.1 mm to 0.4 mm.

[0041] That is, in a cross-sectional view passing through the central axis O' of the safety valve 13, the shape of the boundary portion between the outer peripheral side portion 132c of the groove portion 132 and the inner peripheral side portion 133a of the concave portion 133 (boundary portion 136-1 in the safety valve 13-1), the shape of the bottom portion 132b (bottom portion 132-1b in the safety valve 13-1), and the shape of the boundary portion connecting to the flat portion 131 in the inner peripheral side portion 132a (inner peripheral side portion 132-1a in the safety valve 13-1) of the groove portion 132 are all curved shapes without corners.

[0042] The safety valve 13-2 shown in Fig. 5(b) has a groove portion 132-2 on the outer edge of the flat portion 131 and a recess portion 133-2 on its outer edge. This groove portion 132-2 may have a groove width L, which is the distance between the straight portion of the outer peripheral side portion 132-2c and the straight portion of the inner peripheral side portion 132-2a that are parallel to each other in a cross-sectional view passing through the central axis O', of 0.4 mm as in Fig. 5(a). However, in this groove portion 132-2, as shown in Fig. 5(b), on the inner side of the bottom portion 132-2b, the R dimension (curvature radius R-d) on the outer peripheral side portion 132-2c side may be 0.1 mm, and the R dimension (curvature radius R-e) on the inner peripheral side portion 132-2a side may be 0.3 mm.

[0043] In this regard, the safety valve 13-2 in Fig. 5(b) is different from the safety valve 13-1 in Fig. 5(a), and otherwise, it may have the same configuration as the safety valve 13-1. Thus, the R dimension inside the bottom portion 132b may vary depending on the position inside the bottom portion 132b.

[0044] The safety valve 13-3 shown in Fig. 5(c) has a groove portion 132-3 on the outer edge of the flat portion 131 and a recess portion 133-3 on its outer edge. This groove portion 132-3 has the outer peripheral side portion 132-3c and the inner peripheral side portion 132-3a that are close to each other on the inner side and connected to the bottom portion 132-3b in a cross-sectional view passing through the central axis O'. The groove width L, which is the distance between the outer peripheral side portion 132-3c and the inner peripheral side portion 132-3a on the inner side of the groove portion 132-3, is not particularly limited, but may be a very small value of 0.1 mm or less, for example. Alternatively, in a cross-sectional view passing through the central axis O', the outer peripheral side portion 132-3c and the inner peripheral side portion 132-3a may be in contact with each other.

[0045] In this regard, the safety valve 13-3 in Fig. 5(c) is different from the safety valve 13-1 in Fig. 5(a), and otherwise, it may have the same configuration as the safety valve 13-1.

[0046] The safety valve 13-4 shown in Fig. 5(d) has a groove portion 132-4 on the outer edge of the flat portion 131 and a recess portion 133-4 on its outer edge. This groove portion 132-4, on its inner side, in a cross-sectional view passing through the central axis O’, has a groove width L, which is the distance between the outer peripheral side portion 132-4c and the inner peripheral side portion 132-4a, gradually increasing from the bottom 132-4b toward the opening side. Thus, the groove width L may vary depending on the position in the thickness direction within the groove portion 132. In this regard, the safety valve 13-4 in Fig. 5(d) is different from the safety valve 13-1 in Fig. 5(a), and otherwise, it may have the same configuration as the safety valve 13-1.

[0047] Fig. 6(a) shows the safety valve 13-1 shown in Fig. 5(a). In a cross-sectional view passing through the central axis O’, both the thickness direction size H1 of the inner peripheral side portion 132a inside the groove portion 132 and the thickness direction size H2 of the outer peripheral side portion 132c inside the groove portion 132 increase as the pressure resistance strength against the internal pressure in the battery case 1 increases. The thickness direction size H1 of the inner peripheral side portion 132a (inner peripheral side portion 132-1a in the safety valve 13-1) inside the groove portion 132 may be, for example, 0.8 mm to 1.7 mm, and the thickness direction size H2 of the outer peripheral side portion 132c (outer peripheral side portion 132-1c in the safety valve 13-1) inside the groove portion 132 may be, for example, 0 mm to 1.7 mm.

[0048] Also, the closer the horizontal position of the groove portion 132 of the safety valve 13 is to the central axis O’, the higher the pressure resistance strength against the internal pressure. This means that by adjusting the size of the diameter D2 of the flat portion 131, the horizontal position of the groove portion 132 can be adjusted.

[0049] The safety valve 13-5 shown in Fig. 6(b) has a groove portion 132-5 formed on the outer edge of the flat portion 131, and a recess portion 133-5 formed on the outer edge of the groove portion 132-5. The groove portion 132-5 has an inner peripheral side portion 132-5a connected to the flat portion 131, a bottom portion 132-5b connected to the inner peripheral side portion 132-5a, and an outer peripheral side portion 132-5c connected to the bottom portion 132-5b. The recess portion 133-5 has an inner peripheral side portion 133-5a, a bottom portion 133-5b connected to the inner peripheral side portion 133-5a, and an outer peripheral side portion 133-5c connected to the bottom portion 133-5b. The outer peripheral side portion 132-5c of the groove portion 132-5 and the inner peripheral side portion 133-5a of the recess portion 133-5 are connected by a connection point 134-5.

[0050] In the example of Fig. 6(a), the position (the position of the bottom portion 133-1b of the recess portion 133-1) press-formed at the outermost in the radial direction of the safety valve 13-1 is the lowest position in the thickness direction of the lid portion 12. On the other hand, in the example of Fig. 6(b), the position (the position of the bottom portion 133-5b of the recess portion 133-5) press-formed at the outermost in the radial direction of the safety valve 13-5 is the substantially central position in the thickness direction of the lid portion 12. Thus, the safety valve 13-1 shown in Fig. 6(a) has a recess portion 133-1 with a larger dent than the recess portion 133-5 of the safety valve 13-5 shown in Fig. 6(b). In this regard, the safety valve 13-5 in Fig. 6(b) is different from the safety valve 13-1 in Fig. 6(a), and other than that, it may have the same configuration as the safety valve 13-1.

[0051] The safety valve 13-6 shown in Fig. 6(c) forms a groove portion 132-6 on the outer edge of the flat portion 131. However, in the example of Fig. 6(c), an outer edge flat portion 135-6 having a plane direction substantially parallel to the plane direction of the flat portion 131 is formed on the outer edge of the groove portion 132-6.

[0052] Also, in the example of Fig. 6(c), the position of press forming in the thickness direction of the lid portion 12 is the substantially central position in the thickness direction of the lid portion 12. Thereby, the groove portion 132-6 slightly protrudes below the lower surface of the lid portion 12. In these respects, the safety valve 13-6 in Fig. 6(c) is different from the safety valve 13-1 in Fig. 6(a), and other than that, it may have the same configuration as the safety valve 13-1.

[0053] In the outer peripheral side portion 132-6c of the groove portion 132-6, the shape of the boundary portion 136-6 connected to the outer edge flat portion 135-6 is a curved shape without corners.

[0054] In this way, when the outer edge flat portion is formed on the outer edge of the groove portion 132 in a cross-sectional view passing through the central axis O', in the outer peripheral side portion 132c of the groove portion 132 of the safety valve 13, the shape of the boundary portion (boundary portion 136-6 in the safety valve 13-6) connected to the outer edge flat portion is a curved shape without corners. In this safety valve 13, in a cross-sectional view passing through the central axis O', the R dimension (curvature radius R-f) inside the curved shape of the boundary portion (boundary portion 136-6 in the safety valve 13-6) connected to the outer edge flat portion in the outer peripheral side portion 132c of the groove portion 132 may or may not be uniform. The R dimension (curvature radius R-f) inside this curved shape is preferably 0.2 mm to 0.5 mm.

[0055] The safety valve 13-7 shown in FIG. 6(d) has substantially the same configuration as the safety valve 13-6 in FIG. 6(c), with a groove portion 132-7 formed on the outer edge of the flat portion 131 and an outer edge flat portion 135-7 formed on its outer edge.

[0056] However, it is different from the safety valve 13-6 in FIG. 6(c) in that the position of the press forming in the thickness direction of the lid portion 12 is the lowest position in the thickness direction of the lid portion 12. As a result, the groove portion 132-7 of the safety valve 13-7 protrudes significantly below the lower surface of the lid portion 12.

[0057] Also, the safety valve 13-8 shown in FIG. 6(e) has substantially the same configuration as the safety valve 13-6 in FIG. 6(c), with a groove portion 132-8 formed on the outer edge of the flat portion 131 and an outer edge flat portion 135-8 formed on its outer edge.

[0058] However, it is different from the safety valve 13-6 in FIG. 6(c) in that the position of the press forming in the thickness direction of the lid portion 12 is the highest position in the thickness direction of the lid portion 12. As a result, the groove portion 132-8 of the safety valve 13-8 has a structure that does not protrude below the lower surface of the lid portion 12.

[0059] As the safety valve 13, it is preferable that the structure is such that it is not broken by an external impact and does not interfere with the power generation elements or the like inside the battery case 1. Therefore, among the various safety valves 13 shown in FIGS. 6(a) to 6(e), those in which the components of the safety valve 13 do not protrude above the upper surface of the lid portion 12 and do not protrude below the lower surface of the lid portion 12 in the thickness direction (for example, FIGS. 6(a), 6(b), and 6(e)) are particularly preferable.

[0060] In the safety valve 13-9 shown in FIG. 7(a), only the groove portion 132-9 is formed at the outer edge of the flat portion 131. The groove portion 132-9 has an inner peripheral side portion 132-9a connected to the flat portion 131, a bottom portion 132-9b connected to the inner peripheral side portion 132-9a, and an outer peripheral side portion 132-9c connected to the bottom portion 132-9b. In this regard, the safety valve 13-9 in FIG. 7(a) is different from the safety valve 13-1 in FIG. 5(a), and other than that, it may have the same configuration as the safety valve 13-1. The shape of the boundary portion 136-9 connected to the lid portion 12 in the outer peripheral side portion 132-9c of the groove portion 132-9 is a curved shape without corners.

[0061] Thus, when the lid portion 12 is formed at the outer edge of the groove portion 132 in a cross-sectional view passing through the central axis O', the shape of the boundary portion (boundary portion 136-9 in the safety valve 13-9) connected to the lid portion 12 in the outer peripheral side portion 132c of the groove portion 132 is a curved shape without corners in the safety valve 13. In this safety valve 13, in a cross-sectional view passing through the central axis O', the R dimension (curvature radius R-g) inside the curved shape of the boundary portion (boundary portion 136-9 in the safety valve 13-9) connected to the lid portion 12 in the outer peripheral side portion 132c of the groove portion 132 may or may not be uniform. The R dimension (curvature radius R-g) inside this curved shape is preferably 0.2 mm to 0.5 mm.

[0062] As shown in FIG. 7(a), in a cross-sectional view passing through the central axis O', the distance between the inner peripheral side portion 132-9a and the outer peripheral side portion 132-9c gradually increases from the bottom portion 132-9b toward the opening side. Therefore, the groove portion 132-9 has a larger opening than the examples in FIGS. 6(a) to 6(e).

[0063] The safety valve 13-10 shown in FIG. 7(b) has only a groove portion 132-10 formed outside the flat portion 131. The groove portion 132-10 has a shape obtained by processing the bottom portion 132-9b and the outer peripheral side portion 132-9c of the groove portion 132-9 shown in FIG. 7(a), and has an inner peripheral side portion 132-10a, a bottom portion 132-10b, a first outer peripheral side portion 132-10c, and a second outer peripheral side portion 132-10d.

[0064] In a cross-sectional view passing through the central axis O', in the safety valve 13-9 shown in FIG. 7(a), the outer peripheral side portion 132-9c of the groove portion 132-9 is substantially linear. In contrast, in the safety valve 13-10 shown in FIG. 7(b), the outer peripheral side portion of the groove portion 132-10 has a bent shape formed by the first outer peripheral side portion 132-10c and the second outer peripheral side portion 132-10d, and forms a bottom portion 132-10b having the same shape as the bottom portion 132-1b in FIG. 5(a). The safety valve 13-10 having such a groove portion 132-10 has a higher pressure resistance strength than the safety valve 13-9 having the groove portion 132-9 in FIG. 7(a). In this regard, the safety valve 13-10 in FIG. 7(b) is different from the safety valve 13-9 in FIG. 7(a), and may have the same configuration as the safety valve 13-9 in other respects.

[0065] FIG. 8(a) shows the safety valve 13-1 shown in FIG. 5(a). In this safety valve 13-1, the height position of the flat portion 131 in the thickness direction is substantially the same as the height position of the connection point 134-1 between the outer peripheral side portion 132-1c of the groove portion 132-1 and the inner peripheral side portion 133-1a of the recess portion 133-1 (that is, the size H1 of the inner peripheral side portion 132-1a is approximately equal to the size H2 of the outer peripheral side portion 132-1c).

[0066] In contrast, for the safety valve 13-11 shown in Fig. 8(b), the height position of the connection point 134-11 between the outer peripheral side portion 132-11c of the groove portion 132-11 and the inner peripheral side portion 133-11a of the concave portion 133-11 is higher than the height position of the flat portion 131 in the thickness direction (that is, the size H1 of the inner peripheral side portion 132-11a < the size H2 of the outer peripheral side portion 132-11c). In this regard, the safety valve 13-11 in Fig. 8(b) is different from the safety valve 13-1 in Fig. 8(a), and other than this, it may have the same configuration as the safety valve 13-1.

[0067] Also, for the safety valve 13-12 shown in Fig. 8(c), the height position of the flat portion 131 is higher than the height position of the connection point 134-12 between the outer peripheral side portion 132-12c of the groove portion 132-12 and the inner peripheral side portion 133-12a of the concave portion 133-12 in the thickness direction (that is, the size H2 of the outer peripheral side portion 132-12c < the size H1 of the inner peripheral side portion 132-12a). In this regard, the safety valve 13-12 in Fig. 8(c) is different from the safety valve 13-1 in Fig. 8(a), and other than this, it may have the same configuration as the safety valve 13-1.

[0068] None of the safety valves 13-1, 13-11, and 13-12 shown in Figs. 8(a) to 8(c) protrude above the upper surface of the lid portion 12 or below the lower surface of the lid portion 12 in the thickness direction. For these safety valves 13-1, 13-11, and 13-12, the size H1 in the thickness direction of any of the inner peripheral side portions 132-1a of the groove portion 132-1, the inner peripheral side portions 132-11a of the groove portion 132-11, and the inner peripheral side portions 132-12a of the groove portion 132-12 is substantially the same. On the other hand, among the safety valves 13-1, 13-11, and 13-12, the groove portion 132-11 of the safety valve 13-11 has the largest size H2 in the thickness direction of its outer peripheral side portion 132-11c. Also, the groove portion 132-12 of the safety valve 13-12 has the smallest size H2 in the thickness direction of its outer peripheral side portion 132-12c.

[0069] As a result, among the safety valves 13-1, 13-11, and 13-12 shown in FIGS. 8(a) to 8(c), the safety valve 13-11 having the groove portion 132-11 has the highest pressure resistance, and the safety valve 13-12 having the groove portion 132-12 has the lowest pressure resistance.

[0070] The safety valve 13-13 shown in FIG. 9(a) forms a groove portion 132-13 having the same shape as the groove portion 132-1 shown in FIG. 5(a) at the outer edge of the flat portion 131, and forms a concave portion 133-13 at its outer edge. However, the safety valve 13-13 in FIG. 9(a) has a different shape of the concave portion 133-13 from that of the concave portion 133-1 in FIG. 5(a), and other than that, it may have the same configuration as the safety valve 13-1.

[0071] The safety valve 13-14 shown in FIG. 9(b) also forms a groove portion 132-14 having the same shape as the groove portion 132-13 in FIG. 9(a) at the outer edge of the flat portion 131. However, the groove portion 132-14 is closer to the central axis O' than the groove portion 132-13 of the safety valve 13-13 in FIG. 9(a) in the horizontal direction of the safety valve 13-14. Therefore, the safety valve 13-14 shown in FIG. 9(b) has a higher pressure resistance against the internal pressure in the battery case 1 than the safety valve 13-13 shown in FIG. 9(a). Also, as a result, the safety valve 13-14 forms a concave portion 133-14 having a larger internal space than the concave portion 133-13 of the safety valve 13-13. In this regard, the safety valve 13-14 in FIG. 9(b) is different from the safety valve 13-13 in FIG. 9(a), and other than that, it may have the same configuration as the safety valve 13-13.

[0072] Note that, as in the case of the safety valve 13-15 shown in FIG. 9(c), only a groove portion 132-15 having the same shape as the groove portion 132-13 in FIG. 9(a) may be formed at the outer edge of the flat portion 131, and no concave portion may be formed at the outer edge of the groove portion 132-15. As a result, the outer diameter D1 of the safety valve 13-15 in FIG. 9(c) becomes smaller than the outer diameter D1 of the safety valve 13-13 in FIG. 9(a). In this regard, the safety valve 13-15 in FIG. 9(c) is different from the safety valve 13-13 in FIG. 9(a), and other than that, it may have the same configuration as the safety valve 13-13.

[0073] Figures 10(a) to 10(f) show a plurality of safety valves 13 with different shapes of the groove portion 132. The safety valve 13-16 shown in Figure 10(a) has a groove portion 132-16 at the outer edge of the flat portion 131 and a recess 133-16 at its outer edge.

[0074] In a cross-sectional view passing through the central axis O’, this groove portion 132-16 has a shape in which the opening side of the inner peripheral side portion 132-16a is inclined to the side opposite to the central axis O’ side, so that its opening diameter is smaller than the diameter of the inner space of the bottom portion 132-16b. In this regard, the safety valve 13-16 in this Figure 10(a) is different from the safety valve 13-1 in Figure 5(a), and otherwise, it may have the same configuration as the safety valve 13-1. For example, in a cross-sectional view passing through the central axis O’, the angle θ1 formed by the outer peripheral side portion 132-16c (the straight portion) and the inner peripheral side portion 132-16a (the straight portion) around the bottom portion 132-16b of the groove portion 132-16 may be -30°. In this case, in the safety valve 13-16, in a cross-sectional view passing through the central axis O’, the angle θ2 formed by the flat portion 131 and the inner peripheral side portion 132-16a (the straight portion) may be 60°.

[0075] Figure 10(b) shows the safety valve 13-1 shown in Figure 5(a). As described above, the groove portion 132-1 of the safety valve 13-1 may have the straight portion of the outer peripheral side portion 132-1c and the straight portion of the inner peripheral side portion 132-1a parallel to each other. That is, in a cross-sectional view passing through the central axis O’, the angle θ1 formed by the outer peripheral side portion 132-1c (the straight portion) and the inner peripheral side portion 132-1a (the straight portion) around the bottom portion 132-1b of the groove portion 132-1 may be 0°. Also, in the safety valve 13-1, in a cross-sectional view passing through the central axis O’, the angle θ2 formed by the flat portion 131 and the inner peripheral side portion 132-1a (the straight portion) may be 90°.

[0076] The safety valves 13-17 shown in FIG. 10(c) have grooves 132-17 on the outer edge of the flat portion 131 and recesses 133-17 on the outer edge thereof. This groove 132-17 has a shape in which the opening side of the inner peripheral side portion 132-1a of the groove 132-1 in FIG. 10(b) is inclined toward the central axis O' in a cross-sectional view passing through the central axis O'. Thereby, the distance (groove width L) between the inner peripheral side portion 132-17a and the outer peripheral side portion 132-17c of the groove 132-17 gradually increases from the bottom 132-17b toward the opening side (that is, the opening diameter is larger than the diameter of the inner space at the bottom 132-17b). For example, in a cross-sectional view passing through the central axis O', the angle θ1 formed by the outer peripheral side portion 132-17c (linear portion) and the inner peripheral side portion 132-17a (linear portion) of the groove 132-17 centered on the bottom 132-17b of the groove 132-17 may be 10°. In this case, in the safety valve 13-17, in a cross-sectional view passing through the central axis O', the angle θ2 formed by the flat portion 131 and the inner peripheral side portion 132-17a (linear portion) may be 100°. In this regard, the safety valve 13-17 in FIG. 10(c) is different from the safety valve 13-1 in FIG. 10(b), and other than that, it may have the same configuration as the safety valve 13-1.

[0077] The safety valve 13-18 shown in FIG. 10(d) has a groove 132-18 on the outer edge of the flat portion 131 and a recess 133-18 on the outer edge thereof. The straight portion of the outer peripheral side portion 132-18c and the straight portion of the inner peripheral side portion 132-18a of this groove 132-18 may be parallel. That is, in a cross-sectional view passing through the central axis O', the angle θ1 formed by the outer peripheral side portion 132-18c (linear portion) and the inner peripheral side portion 132-18a (linear portion) of the groove 132-18 centered on the bottom 132-18b of the groove 132-18 may be 0°. However, the opening side of this groove 132-18 is inclined toward the central axis O' direction. Specifically, in the safety valve 13-18, in a cross-sectional view passing through the central axis O', the angle θ2 formed by the flat portion 131 and the inner peripheral side portion 132-18a (linear portion) may be 100°. In this regard, the safety valve 13-18 in FIG. 10(d) is different from the safety valve 13-1 in FIG. 10(b), and other than that, it may have the same configuration as the safety valve 13-1.

[0078] The safety valves 13 - 19 shown in Fig. 10(e) have a groove portion 132 - 19 on the outer edge of the flat portion 131 and a recessed portion 133 - 19 on its outer edge. This groove portion 132 - 19 may have a straight portion of the outer peripheral side portion 132 - 19c and a straight portion of the inner peripheral side portion 132 - 19a that are parallel. That is, in a cross-sectional view passing through the central axis O’, the angle θ1 formed by the outer peripheral side portion 132 - 19c (the straight portion) and the inner peripheral side portion 132 - 19a (the straight portion) around the bottom 132 - 19b of the groove portion 132 - 19 may be 0°. However, this groove portion 132 - 19 has its opening side inclined in a direction opposite to the central axis O’ direction. Specifically, in the safety valve 13 - 19, in a cross-sectional view passing through the central axis O’, the angle θ2 formed by the flat portion 131 and the inner peripheral side portion 132 - 19a (the straight portion) may be 80°. In this regard, the safety valve 13 - 19 in Fig. 10(e) is different from the safety valve 13 - 1 in Fig. 10(b), and otherwise, it may have the same configuration as the safety valve 13 - 1.

[0079] The safety valve 13 - 20 shown in Fig. 10(f) has a groove portion 132 - 20 on the outer edge of the flat portion 131 and a recessed portion 133 - 20 on its outer edge. This groove portion 132 - 20 has a shape in which the opening side of the outer peripheral side portion 132 - 1c of the groove portion 132 - 1 in Fig. 10(b) is inclined in a direction opposite to the central axis O’ direction. As a result, the distance (groove width L) between the inner peripheral side portion 132 - 20a and the outer peripheral side portion 132 - 20c of the groove portion 132 - 20 gradually increases from the bottom 132 - 20b toward the opening side. For example, in a cross-sectional view passing through the central axis O’, the angle θ1 formed by the outer peripheral side portion 132 - 20c (the straight portion) and the inner peripheral side portion 132 - 20a (the straight portion) around the bottom 132 - 20b of the groove portion 132 - 20 may be 10°. In this case, in the safety valve 13 - 20, in a cross-sectional view passing through the central axis O’, the angle θ2 formed by the flat portion 131 and the inner peripheral side portion 132 - 20a (the straight portion) may be 90°. In this regard, the safety valve 13 - 20 in Fig. 10(f) is different from the safety valve 13 - 1 in Fig. 10(b), and otherwise, it may have the same configuration as the safety valve 13 - 1.

[0080] Based on FIGS. 10(a) to 10(f) as described above, in a cross-sectional view passing through the central axis O' of the safety valve 13, for example, the angle θ1 formed by the outer peripheral side portion 132c (the straight portion thereof) and the inner peripheral side portion 132a (the straight portion thereof) centered on the bottom portion 132b of the groove portion 132 may be -45° to 60°, and the angle θ2 formed by the flat portion 131 and the inner peripheral side portion 132a (the straight portion thereof) may be 45° to 135°. The smaller the angle θ1, the more difficult it is for the inner peripheral side portion 132a and the outer peripheral side portion 132c to open with respect to the bottom portion 132b of the groove portion 132, and the higher the pressure resistance strength against the internal pressure. However, considering the ease of manufacturing the groove portion 132, it is preferable that the angle θ1 is 0° and the angle θ2 is 90°.

[0081] [Deformation and Opening of the Safety Valve] Next, an example of the operation when the safety valve 13 deforms and opens under the internal pressure in the battery case 1 will be described with reference to FIG. 11.

[0082] FIGS. 11(a) to 11(d) show cross-sectional views passing through the central axis O' of the safety valve 13 formed in the lid portion 12. As shown in FIG. 11(a), the lid portion 12 is formed with a safety valve 13 having a flat portion 131, a groove portion 132, and a recess portion 133. Note that the angle θ1 formed by the outer peripheral side portion 132c (the straight portion thereof) and the inner peripheral side portion 132a (the straight portion thereof) centered on the bottom portion 132b of the groove portion 132 shown in FIG. 11(a) may be, for example, 0°.

[0083] When the internal pressure in the battery case 1 provided with such a lid portion 12 rises, as shown in FIG. 11(b), the inner surface of the flat portion 131 receives the rising internal pressure and deforms so as to be convex outward of the lid portion 12 in a cross-sectional view passing through the central axis O'. Further, the groove portion 132 deforms such that the angle θ1 formed by the outer peripheral side portion 132c (the straight portion thereof) and the inner peripheral side portion 132a (the straight portion thereof) centered on the bottom portion 132b of the groove portion 132 increases in a cross-sectional view passing through the central axis O' as the bottom portion 132b of the groove portion 132 receives the rising internal pressure. As a result, the depth of the recess of the groove portion 132 formed by the inner peripheral side portion 132a, the bottom portion 132b, and the outer peripheral side portion 132c becomes smaller. Note that the angle θ1 shown in FIG. 11(b) may be, for example, 20°.

[0084] As shown in FIG. 11(b), until the internal pressure in the battery case 1 rises to a predetermined explosion-proof pressure, large plastic deformation is prevented by the rigidity of the groove portion 132. Thereafter, when the internal pressure in the battery case 1 becomes equal to or higher than the predetermined explosion-proof pressure, as shown in FIG. 11(c), the concave shape of the groove portion 132 is inverted (buckled) so that the groove portion 132 protrudes toward the outside of the battery case 1, and at this time, the groove portion 132 is greatly plastically deformed. (The angle θ1 shown in FIG. 11(c) may be, for example, 230°). As a result, a crack occurs in the groove portion 132 and it opens as shown in FIG. 11(d). Then, from the portion opened by this crack in the groove portion 132, the opening (size) spreads around the groove portion 132.

[0085] As described above, in a cross-sectional view passing through the central axis O', the shape of the boundary portion between the outer peripheral side portion 132c of the groove portion 132 and the portion formed at the outer edge of the groove portion 132 connected to the outer peripheral side portion 132c (for example, the shape of the boundary portion between the outer peripheral side portion 132c of the groove portion 132 and the inner peripheral side portion 133a of the concave portion 133) of the safety valve 13 is a curved shape without corners. As the internal pressure in the battery case 1 increases, in the process of changing from the state of FIG. 11(a) to the state of FIG. 11(c) via the state of FIG. 11(b), the curved shape of this boundary portion gradually expands, and the depth of the recess of the curved shape gradually decreases. At this time, since this curved shape has no corners, the stress on the internal pressure in the battery case 1 does not concentrate on the corners. Therefore, when this curved shape gradually expands due to the increase in the internal pressure, it expands smoothly without generating cracks.

[0086] Further, in a cross-sectional view passing through the central axis O', not only the shape of the boundary portion between the outer peripheral side portion 132c of the groove portion 132 and the portion formed at the outer edge of the groove portion 132 connected to the outer peripheral side portion 132c (for example, the shape of the boundary portion between the outer peripheral side portion 132c of the groove portion 132 and the inner peripheral side portion 133a of the concave portion 133), but also the shape of the bottom portion 132b and the shape of the boundary portion at the inner peripheral side portion 132a of the groove portion 132 connected to the flat portion 131 are curved shapes without corners.

[0087] As a result, until the internal pressure in the battery case 1 rises to a predetermined explosion-proof pressure, the safety valve 13 has no stress concentration at the corners of the boundary between the outer peripheral side portion 132c of the groove portion 132 and the portion formed at the outer edge of the groove portion 132 connected to this outer peripheral side portion 132c (for example, the boundary between the outer peripheral side portion 132c of the groove portion 132 and the inner peripheral side portion 133a of the concave portion 133), the bottom portion 132b, and the boundary connected to the flat portion 131 in the inner peripheral side portion 132a. Therefore, the curved shape gradually and smoothly expands without cracking.

[0088] When the internal pressure in the battery case 1 reaches the predetermined explosion-proof pressure, the groove portion 132 in the state where the groove portion 132 has expanded without cracking smoothly inverts, and a crack occurs due to large plastic deformation, causing it to open.

[0089] In addition, due to the opening caused by this crack, the flat portion 131 also remains in an integral state without separating from the portion connected to the groove portion 132 of the safety valve 13. Therefore, since the flat portion 131 does not separate and fly off during opening, safety can be ensured.

[0090] The gas generated in the battery case 1 is discharged to the outside of the battery case 1 through this opening portion. In this way, the battery case 1 is prevented from being greatly damaged, ensuring the safety of the secondary battery.

[0091] Even if the safety valve 13 of this embodiment does not have a structure such as a conventional notch, by adjusting the above-mentioned various sizes (diameter D1, diameter D2, angle θ1, angle θ2, size H1, size H2, groove width L, R dimension, etc.) and shape, it is possible to maintain the pressure resistance strength against the internal pressure in the battery case 1 and surely cause a crack when the internal pressure exceeds the predetermined explosion-proof pressure. That is, in the safety valve 13, problems such as no crack occurring when in the state shown in FIG. 11(c) or a crack occurring before reaching the state shown in FIG. 11(c) do not occur.

[0092] [Formation of safety valve] The safety valve 13 of this embodiment can be formed by, for example, the following press forming. First, prepare a metal plate such as aluminum or an aluminum alloy that constitutes the lid portion 12. Next, attach a pair of press dies (forming dies) consisting of a male die and a female die having the shape of the safety valve 13 to a press machine.

[0093] Next, sandwich the lid portion 12 between the male die and the female die so that the upper plane of the lid portion 12 faces the male die and the lower plane faces the female die, and apply pressure at a predetermined pressure in the vertical direction of the plane of the lid portion 12 at a substantially central position in the plane longitudinal direction of the lid portion 12. By such press forming, the lid portion 12 is bent and stretched, and as shown in FIG. 2, the safety valve 13 is formed at a substantially central position in the plane longitudinal direction of the lid portion 12. The predetermined pressure during this pressurization is not particularly limited, but can be, for example, 500 MPa to 1500 MPa.

[0094] As described above, when the internal pressure in the battery case 1 becomes equal to or higher than a predetermined explosion-proof pressure, the safety valve 13 of this embodiment opens by the concave shape being inverted so that the groove portion 132 protrudes outward from the battery case 1 and cracks occur. Therefore, unlike, for example, a conventional safety valve with a notch, in order to control the internal pressure (explosion-proof pressure) when opening, it is not necessary to adjust the thickness of the safety valve within an allowable range of 10 to several tens of μm, and it can be easily manufactured without high-precision equipment and manufacturing technology.

[0095] As a result, in the manufacture of this safety valve 13, there are no problems such as a decrease in yield until the size (dimension) of the thickness is stabilized, so productivity can be improved. Since it does not have a complicated structure with a small thickness, generation of cracks and the like can be suppressed, and inspection can also be easily performed.

[0096] [Modification example] In the above-described embodiments, the technologies of each embodiment can be applied to one another, including modifications. The above-described embodiments do not limit the content of the present invention, and modifications can be made without departing from the scope of the claims.

[0097] The shape of the safety valve 13 is not limited to the above-described substantially circular example, and other shapes may be used. For example, as shown in FIG. 12, it may be substantially elliptical.

[0098] The safety valve 13m shown in FIG. 12 is substantially elliptical with the center point Om as the center. This safety valve 13m has a substantially elliptical flat portion 131m, a groove portion 132m formed on its outer edge, and a concave portion 133m formed on its outer edge. The minor axis D3 passing through the center point Om of the safety valve 13m is not particularly limited, but may be, for example, 7 mm to 15 mm. Also, the major axis D4 passing through the center point Om of this safety valve 13m is not particularly limited, but may be, for example, 12 mm to 20 mm. Further, the minor axis D31 passing through the center point Om of the flat portion 131m is not particularly limited, but may be, for example, 5 mm to 10 mm. Also, the major axis D41 passing through the center point Om of this flat portion 131m is not particularly limited, but may be, for example, 10 mm to 15 mm.

[0099] Also in this substantially elliptical safety valve 13m, similar to the above-described substantially circular safety valve 13, when the internal pressure in the battery case 1 becomes equal to or higher than a predetermined explosion-proof pressure, the groove portion 132m opens by reversing its concave shape so as to protrude toward the outside of the battery case 1 and cracks occur. At this time, in the groove portion 132m, the portions that first open may be the minor axis end portions 132m-a and 132m-b having the largest radius of curvature in the substantially elliptical shape.

[0100] Note that the shape of the safety valve 13 is not limited to the above-described substantially circular and substantially elliptical shapes as long as it has no corners as described above, and other shapes may be used.

[0101] Also, in the above-described embodiment, the safety valve 13 is formed on the lid portion 12 which is an end plate of the battery case (battery exterior body) 1, but is not limited thereto, and may be formed on any of the front surface 11a, back surface 11b, side surface 11c, side surface 11d, and bottom surface 11e of the housing portion 11 of the battery case 1. Note that the basic configuration such as the formation material and plate thickness of the front surface 11a, back surface 11b, side surface 11c, side surface 11d, and bottom surface 11e of the housing portion 11 may be the same as that of the above-described lid portion 12.

Explanation of Signs

[0102] 1 Battery case, 11 Housing portion, 12 Lid portion, 13 Safety valve, 131 Flat portion, 132 Groove portion, 132a Inner peripheral side portion, 132b Bottom portion, 132c Outer peripheral side portion, 133 Concave portion, 133a Inner peripheral side portion, 133b Bottom portion, 133c Outer peripheral side portion, 13m Safety valve, 131m Flat portion, 132m Groove portion, 133m Concave portion

Claims

1. A safety valve partially formed to be thin-walled in a battery case, a flat portion, a groove portion formed at a periphery of the flat portion and recessed toward an inside of the battery case, and having, in a vertical view with respect to the flat portion, the flat portion being substantially circular or substantially elliptical, the groove portion, when an internal pressure in the battery case becomes equal to or higher than a predetermined explosion-proof pressure, the concave shape of the groove portion is inverted so as to protrude toward an outside of the battery case and cracks are generated to open a safety valve characterized by the above.

2. The groove portion, has an inner peripheral side portion connected to the flat portion, a bottom portion connected to the inner peripheral side portion, and an outer peripheral side portion connected to the bottom portion, due to an increase in the internal pressure in the battery case, in a cross-sectional view passing through a central axis of the safety valve, deforms such that an angle formed by the outer peripheral side portion and the inner peripheral side portion of the groove portion around the bottom portion of the groove portion increases a safety valve according to claim 1, characterized by the above.

3. In a cross-sectional view passing through a central axis of the safety valve, a shape of a boundary portion between the outer peripheral side portion of the groove portion and a portion formed at an outer edge of the groove portion connected to the outer peripheral side portion has a curved shape without corners a safety valve according to claim 2, characterized by the above.

4. In a cross-sectional view passing through a central axis of the safety valve, an angle formed by the outer peripheral side portion and the inner peripheral side portion in the groove portion is -45° to 60°, an angle formed by the flat portion and the inner peripheral side portion is 45° to 135° a safety valve according to claim 2 or 3, characterized by the above.

5. The safety valve is formed at a substantially central position in a plane longitudinal direction of a lid portion of the battery case a safety valve according to any one of claims 1 to 4, characterized by the above.

6. The safety valve is formed in a housing portion of the battery case a safety valve according to any one of claims 1 to 4, characterized by the above.

7. A battery case provided with the safety valve according to any one of claims 1 to 6.

8. A forming method for partially forming a thin-walled safety valve in a battery case, including a forming step of forming the safety valve having a flat portion and a groove portion recessed toward an inside of the battery case at a periphery of the flat portion by performing pressurization using a mold with respect to a thickness direction of the battery case, in a vertical view with respect to the flat portion, the flat portion being substantially circular or substantially elliptical, the groove portion, when an internal pressure in the battery case becomes equal to or higher than a predetermined explosion-proof pressure, the concave shape of the groove portion is inverted so as to protrude toward an outside of the battery case and cracks are generated to open A method for forming a safety valve, characterized by the above.

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