Sealed battery

Abstract

To provide a sealed battery in which a gas discharge hole formed at a metallic wall part of a battery case is sealed with a resin safety valve member formed of a resin and the resin safety valve member is opened when an inner pressure of the battery case reaches a valve open pressure.SOLUTION: A battery case 30 has a metallic wall part 15 formed with a gas discharge hole 12. An annular hole peripheral surface 13, which surrounds an opening 12b of the gas discharge hole 12, of an outer surface 15b of the metallic wall part 15 includes an annular seal surface 14 which surrounds the opening 12b of the gas discharge hole 12. A resin safety valve member 18 which closes the gas discharge hole 12 in a manner that the resin safety valve member 18 covers the hole peripheral surface 13 has an annular joint part 18b which is joined to the annular seal surface 14 in an air-tight manner. When an inner pressure of the battery case 30 reaches a valve open pressure, the resin safety valve member 18 is opened by destruction of the annular joint part 18b.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a sealed battery comprising an electrode assembly and a metal battery case that houses the electrode assembly. The battery case comprises a rectangular box-shaped case body with an opening and a metal lid member that closes the opening of the case body. The case body and the lid member are integrated by welding to form the battery case. A safety valve is provided in the center of the lid member. The safety valve is formed integrally with the lid member.

[0003] The safety valve is thinner than the other parts of the lid member and has a groove formed on its top surface. This allows the safety valve to activate when the internal pressure inside the battery case reaches a predetermined pressure (valve opening pressure). In other words, when the internal pressure of the battery case reaches the valve opening pressure, the groove ruptures, opening the safety valve and releasing the gas inside the battery case to the outside. This prevents the internal pressure of the battery case from rising too high (reaching a dangerous internal pressure). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2018-041668 Summary of the Invention [Problem to be solved by the invention]

[0005] The above-mentioned safety valve is formed integrally with an aluminum lid member. Specifically, the safety valve is formed simultaneously with the lid member by press-molding an aluminum plate. However, this method of forming the safety valve in the lid member by press-molding places restrictions on the thickness and material of the metal plate constituting the lid member, making it difficult to accommodate a wide variety of sealed batteries.

[0006] For this reason, there has been a demand for a safety valve formed as a separate member from the metal wall portion (such as a lid member) that constitutes the battery case. Specifically, there has been a demand for a battery case having a metal wall portion in which a gas vent hole is formed, and for the safety valve to be a safety valve member that closes the gas vent hole by covering the annular hole-peripheral surface of the metal wall portion that surrounds the opening of the gas vent hole, and for this safety valve member to properly seal the gas vent hole. Furthermore, there has been a demand for a safety valve member that is made of resin in order to easily form the safety valve member. That is, there has been a demand for a sealed battery in which the gas vent hole formed in the metal wall portion of the battery case is sealed by a resin safety valve member, and the resin safety valve member opens when the internal pressure of the battery case reaches a valve-opening pressure.

[0007] The present invention has been made in consideration of the current situation, and aims to provide a sealed battery in which a gas exhaust hole formed in a metal wall portion of a battery case is sealed by a resin safety valve member made of resin, and the resin safety valve member opens when the internal pressure of the battery case reaches the valve opening pressure. [Means for solving the problem]

[0008] (1) One aspect of the present invention is a sealed battery comprising: a battery case having a metal wall portion in which a gas release hole is formed; and a safety valve member that covers an annular hole-peripheral surface of the outer surface of the metal wall portion that surrounds the opening of the gas release hole and closes the gas release hole; the safety valve member is a resin safety valve member made of resin, and the hole-peripheral surface surrounds the opening of the gas release hole and includes an annular roughened surface having an uneven shape; the resin safety valve member has an annular joint that is airtightly joined to the annular roughened surface, and the resin that forms the annular joint enters into a recess in the annular roughened surface, and when the internal pressure of the battery case reaches a valve-opening pressure, the annular joint closes the resin forming the annular roughened surface penetrates into the recesses of the annular roughened surface. The resin safety valve member is a sealed battery in which the resin safety valve member opens when the portion of the battery that forms the smallest width between the inner periphery and the outer periphery is destroyed.

[0009] The sealed battery described above has a safety valve member that closes the gas vent hole by covering an annular hole-peripheral surface that surrounds the opening of the gas vent hole on the outer surface of the metal wall of the battery case. The safety valve member is a resin safety valve member made of resin. The resin safety valve member has an annular joint that is airtightly joined to an annular sealing surface (a portion included in the hole-peripheral surface) that surrounds the opening of the gas vent hole. By having such an annular joint, the resin safety valve member is airtightly joined to the metal wall, and the gas vent hole is sealed by the resin safety valve member.

[0010] Furthermore, in this sealed battery, when the internal pressure of the battery case reaches the valve-opening pressure, the annular joint of the resin safety valve member breaks, thereby opening the resin safety valve member (i.e., the sealing of the gas vent hole by the resin safety valve member is released). More specifically, when the internal pressure of the battery case reaches the valve-opening pressure, the stress generated in the annular joint by the internal pressure of the battery case reaches the breaking strength of the annular joint, causing the annular joint to break and releasing the sealing of the gas vent hole by the resin safety valve member. In this way, while the inside of the battery case is kept airtight by hermetically joining the annular joint of the resin safety valve member to the annular sealing surface of the metal wall portion, when the internal pressure of the battery case reaches the valve-opening pressure, the resin safety valve member opens, thereby releasing the gas inside the battery case to the outside and preventing the internal pressure of the battery case from rising too much.

[0011] As described above, the above-mentioned sealed battery is a sealed battery in which the gas exhaust hole formed in the metal wall portion of the battery case is sealed by a resin safety valve member made of resin, and the resin safety valve member opens when the internal pressure of the battery case reaches the valve opening pressure.

[0013] In the sealed battery described above, the resin forming the annular joint penetrates into the recesses of the annular roughened surface of the metal wall, and the annular joint of the resin safety valve member is hermetically joined to the annular roughened surface. In other words, the annular joint of the resin safety valve member is hermetically joined to the annular roughened surface by an anchor effect caused by the protrusions of the annular roughened surface of the metal wall biting into the annular joint of the resin safety valve member. This increases the airtightness between the annular joint of the resin safety valve member and the annular roughened surface of the metal wall, thereby improving the airtightness of the sealed battery.

[0014] (2) Furthermore, in the sealed battery of (1) above, it is preferable that the minimum width of the annular joint is 0.3 mm or more and 1.3 mm or less. (3) Furthermore, in the sealed battery of (1) or (2), the battery case may comprise a case body having an opening and a metal lid body that closes the opening of the case body, and the metal lid body may be a sealed battery having the metal wall portion.

[0015] In the sealed battery described above, the metal lid has a metal wall. That is, a gas exhaust hole is formed in the metal lid that closes the opening of the case body of the battery case, and the portion of the outer surface of the metal lid that surrounds the opening of the gas exhaust hole forms an annular sealing surface. Therefore, the sealed battery described above is a sealed battery in which a resin safety valve is provided in the metal lid such that the annular joint of the resin safety valve member is airtightly joined to the annular sealing surface of the metal lid.

[0016] (4) Furthermore, in the sealed battery of (3), it is preferable that the metal lid body and the resin safety valve member are integrally molded by insert molding.

[0017] In the above-described sealed battery, the metal lid body and the resin safety valve member are integrally molded by insert molding. That is, the metal lid body is used as an insert part, and the resin safety valve member is molded by resin injection molding, thereby integrally molding the metal lid body and the resin safety valve member. In other words, the metal lid body and the resin safety valve member constitute an insert-molded product in which the resin safety valve member is integrally molded with the metal lid body. In this way, by using an insert-molded product in which the metal lid body and the resin safety valve member are integrally molded by insert molding, it is possible to easily and appropriately manufacture a sealed battery in which the gas exhaust hole formed in the metal lid body is sealed with the resin safety valve member.

[0018] (5) Furthermore, in the sealed battery of any of (1) to (4), the annular joint has a minimum width joint that is a circumferential part of the annular joint and has a width dimension smaller than other parts of the annular joint in a plan view, and when the internal pressure of the battery case reaches a valve opening pressure, the minimum width joint breaks, thereby opening the resin safety valve member.

[0019] The smaller the width of the annular joint of the resin safety valve member, the more susceptible it is to breakage. Here, the width of the annular joint refers to the distance between the inner and outer peripheries of the annular joint in a plan view. Therefore, in an annular joint having a minimum-width joint at a portion of its circumference, where the width is smaller than other portions, the minimum-width joint is the portion of the annular joint that is most susceptible to breakage. Therefore, by providing a minimum-width joint at a portion of the circumference of the annular joint, the valve opening position (the position at which the annular joint breaks) when the internal pressure of the battery case reaches the valve-opening pressure can be determined at the minimum-width joint. This allows the valve-opening pressure to be set with precision. Therefore, the above-described sealed battery is a sealed battery with a precisely set valve-opening pressure.

[0020] (6) Furthermore, in the sealed battery of any one of (1) to (4), the annular joint may have an elliptical or oval ring shape in a plan view.

[0021] In an elliptical or oval annular joint, when a pressure acts on the resin safety valve member due to an increase in the internal pressure of the battery case, stress concentrates on the area located on the minor axis of the ellipse or oval that forms the outer periphery of the annular joint (referred to as the "minor axis area"). Therefore, the area on the minor axis of the annular joint is more susceptible to destruction than other areas. Therefore, by making the annular joint shaped as an elliptical or oval annular joint in plan view, the valve opening position (the position where the annular joint will be destroyed) when the internal pressure of the battery case reaches the valve opening pressure can be determined at the minor axis area. This allows the valve opening pressure to be set with precision. Therefore, the above-described sealed battery has a precisely set valve opening pressure. An ellipse is a figure consisting of two parallel lines, an arc connecting one end of the lines, and an arc connecting the other end of the lines.

[0022] (7) Furthermore, in the sealed battery of (5), the annular joint has an elliptical or oval ring shape in a plan view, and the minimum width joint is preferably located on the minor axis of the ellipse or oval that forms the outer periphery of the annular joint.

[0023] In an elliptical or oval annular joint, by providing a minimum-width joint on the minor axis where stress is concentrated when a pressing force acts on the resin safety valve member due to an increase in internal pressure of the battery case, the valve opening position (the position where the annular joint breaks) when the internal pressure of the battery case reaches the valve opening pressure can be determined at the minimum-width joint. This allows the valve opening pressure to be set with precision. Therefore, the above-mentioned sealed battery is a sealed battery with a valve opening pressure set with precision. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a plan view (top view) of a sealed battery according to an embodiment. [Figure 2] FIG. [Figure 3] 2 is a cross-sectional view of FIG. 1 taken along line B-B. [Figure 4] 6A and 6B are enlarged views of a portion C in FIG. 3 and a portion G in FIG. 6B, respectively. [Figure 5] FIG. 2 is a plan view of a lid body (insert molding product) with a safety valve. [Figure 6] FIG. 6 is a cross-sectional view taken along the line DD in FIG. 5. [Figure 7] FIG. [Figure 8] 8 is a cross-sectional view of FIG. 7 taken along line E-E. [Figure 9] FIG. 9 is an enlarged view of part F in FIG. 8. DETAILED DESCRIPTION OF THE INVENTION

[0025] Next, an embodiment of the present invention will be described. The sealed battery 1 of this embodiment is a lithium ion secondary battery, and includes a battery case 30, an electrode assembly 50 housed in the battery case 30, a positive electrode terminal 41, and a negative electrode terminal 42 (see FIGS. 1 to 3). The battery case 30 is a hard case made of metal, and has a rectangular box shape. The battery case 30 includes a metal case body 21 in the shape of a rectangular cylinder with a bottom, and a rectangular flat metal lid body 11 that closes the opening 21b of the case body 21 (see FIGS. 1 to 3). The metal lid body 11 has a metal wall portion 15 in which a gas exhaust hole 12 is formed. The metal wall portion 15 is a part of the metal lid body 11.

[0026] Two rectangular cylindrical through-holes 16 and 17 are formed in the metal lid 11 (see FIGS. 5 and 7). A positive electrode terminal 41 is inserted into the through-hole 16, and a negative electrode terminal 42 is inserted into the through-hole 17 (see FIGS. 1 and 2). Cylindrical insulating members (not shown) are interposed between the inner peripheral surface of the through-hole 16 in the metal lid 11 and the outer peripheral surface of the positive electrode terminal 41, and between the inner peripheral surface of the through-hole 17 in the metal lid 11 and the outer peripheral surface of the negative electrode terminal 42. Furthermore, a cylindrical gas exhaust hole 12 is formed in the metal lid 11 (more specifically, in the metal wall portion 15) and penetrates the metal lid 11 in the thickness direction (see FIG. 3).

[0027] The electrode assembly 50 includes a positive electrode plate 60, a negative electrode plate 70, and a separator 80 interposed between the positive electrode plate 60 and the negative electrode plate 70. More specifically, the electrode assembly 50 includes a plurality of positive electrode plates 60, a plurality of negative electrode plates 70, and a plurality of separators 80, and is a laminated electrode assembly in which the positive electrode plates 60 and the negative electrode plates 70 are alternately stacked in a stacking direction DL with the separators 80 interposed therebetween (see FIG. 3). An electrolyte (not shown) is contained inside the electrode assembly 50. An electrolyte (not shown) is also contained on the bottom side of the interior of the battery case 30. The positive electrode plate 60 of the electrode assembly 50 is connected to the positive electrode terminal 41 via a positive electrode current collector tab (not shown). The negative electrode plate 70 is connected to the negative electrode terminal 42 via a negative electrode current collector tab (not shown).

[0028] The sealed battery 1 further includes a resin safety valve member 18 that closes the gas discharge hole 12 by covering the annular hole-peripheral surface 13 surrounding the opening 12b of the gas discharge hole 12 on the outer surface 11b of the metal lid 11 (specifically, the outer surface 15b of the metal wall portion 15) (see FIGS. 1 to 3). The resin safety valve member 18 is disc-shaped and has a disc-shaped first portion 18c located inside the gas discharge hole 12 and a disc-shaped second portion 18d that is larger in diameter than the first portion 18c and contacts the hole-peripheral surface 13 of the metal lid 11 (see FIG. 3). The resin safety valve member 18 is preferably formed from a resin with low electrolyte permeability, such as PPS (polyphenylene sulfide), PAS (polyarylene sulfide), an olefin resin, or a fluororesin. In this embodiment, the resin safety valve member 18 is formed from PPS.

[0029] The hole-surrounding surface 13 of the metal cover 11 includes an annular sealing surface 14 that surrounds the opening 12b of the gas discharge hole 12 (see FIGS. 7 to 9). The second portion 18d of the resin safety valve member 18 has an annular joint portion 18b that is airtightly joined to the annular sealing surface 14 (see FIGS. 3 and 4). The annular joint portion 18b has an annular shape in a plan view. By having such an annular joint portion 18b, the resin safety valve member 18 is airtightly joined to the metal cover 11 (more specifically, the metal wall portion 15), and the gas discharge hole 12 is sealed by the resin safety valve member 18. The first portion 18c of the resin safety valve member 18 and the inner circumferential surface 12c that forms the gas discharge hole 12 are not airtightly joined, allowing gas to enter.

[0030] In particular, in this embodiment, the annular sealing surface 14 of the metal cover 11 (specifically, the metal wall portion 15) is an annular roughened surface 14 having an uneven shape (see FIGS. 8 and 9). This annular roughened surface 14 has a circular ring shape in a plan view (see FIG. 7). The resin safety valve member 18 is airtightly joined to the annular roughened surface 14 in such a manner that the resin forming the annular joint 18b enters the recessed portion 14b of the annular roughened surface 14 (see FIG. 4). In other words, the protruding portion 14c of the annular roughened surface 14 of the metal wall portion 15 bites into the annular joint 18b of the resin safety valve member 18, creating an anchor effect, thereby airtightly joining the annular joint 18b of the resin safety valve member 18 to the annular roughened surface 14. This improves the airtightness between the annular joint 18b of the resin safety valve member 18 and the annular roughened surface 14 of the metal wall portion 15, thereby improving the airtightness of the sealed battery 1.

[0031] The annular roughened surface 14 can be formed by performing a known surface roughening treatment on the hole periphery surface 13 of the outer surface 11b of the metal lid 11. Examples of surface roughening treatments include laser surface treatment, sandblasting, and anodizing. Among these, an example of the laser surface treatment is the laser surface treatment disclosed in Japanese Patent Application Laid-Open No. 2022-28587. In this embodiment, the hole periphery surface 13 of the metal lid 11 is made into the annular roughened surface 14 by laser surface treatment.

[0032] Furthermore, the metal lid 11 and the resin safety valve member 18 are integrally molded by insert molding. Specifically, the metal lid 11 and the resin safety valve member 18 constitute a safety valve-equipped lid 10 (insert molded product) in which the resin safety valve member 18 is integrally molded into the metal lid 11 by insert molding (see FIGS. 5 and 6). This safety valve-equipped lid 10 is produced as follows. Specifically, first, a metal lid 11 having an annular roughened surface 14 (see FIGS. 7 to 9) is prepared. Next, the resin safety valve member 18 is molded by resin injection molding using this metal lid 11 as an insert part, thereby producing a safety valve-equipped lid 10 (insert molded product, see FIGS. 5 and 6) in which the metal lid 11 and the resin safety valve member 18 are integrally molded.

[0033] In this way, by using the safety valve-equipped lid 10 in which the metal lid 11 and the resin safety valve member 18 are integrally molded by insert molding, it is possible to easily and appropriately manufacture a sealed battery 1 in which the gas release hole 12 formed in the metal lid 11 is sealed with the resin safety valve member 18. Note that a portion of the resin injected to mold the resin safety valve member 18 (the resin that becomes the annular joint 18b) enters the recess 14b of the annular roughened surface 14 of the metal lid 11, thereby airtightly joining the annular joint 18b of the resin safety valve member 18 to the annular roughened surface 14 of the metal lid 11 (see FIG. 4).

[0034] Furthermore, in the sealed battery 1, when the internal pressure of the battery case 30 reaches the valve-opening pressure, the annular joint 18b of the resin safety valve member 18 is broken, thereby opening the resin safety valve member 18 (i.e., the sealing of the gas release hole 12 by the resin safety valve member 18 is released). More specifically, when the internal pressure of the battery case 30 increases due to gas generation inside the battery case 30, a force pushing up the lower surface 18f of the resin safety valve member 18 increases, and stress generated in the annular joint 18b increases (see FIG. 3 ). Then, when the internal pressure of the battery case 30 reaches the valve-opening pressure, the stress generated in the annular joint 18b reaches the breaking strength of the annular joint 18b, causing the annular joint 18b to break, and the sealing of the gas release hole 12 by the resin safety valve member 18 is released. For example, a circumferential portion of the annular joint 18b is broken, forming a gas release path in the annular joint 18b. This allows gas inside the battery case 30 to be discharged to the outside of the battery case 30 through the gas discharge hole 12, thereby preventing the internal pressure of the battery case 30 from rising too much.

[0035] As described above, in the sealed battery 1 of this embodiment, the annular joint portion 18b of the resin safety valve member 18 is airtightly joined to the annular seal surface 14 of the metal lid body 11 (more specifically, the metal wall portion 15), thereby keeping the interior of the battery case 30 airtight, and when the internal pressure of the battery case 30 reaches the valve-opening pressure, the resin safety valve member 18 opens to discharge gas inside the battery case 30 to the outside, thereby preventing an excessive increase in the internal pressure of the battery case 30. Therefore, the sealed battery 1 is a sealed battery in which the gas vent hole 12 formed in the metal wall portion 15 of the battery case 30 is sealed by the resin safety valve member 18 made of resin, and the resin safety valve member 18 opens when the internal pressure of the battery case 30 reaches the valve-opening pressure.

[0036] In this embodiment, the valve opening pressure of the resin safety valve member 18 is determined by the minimum width W of the annular joint 18b of the resin safety valve member 18. Here, the width of the annular joint 18b is the distance between the inner and outer peripheries of the annular joint 18b in a plan view, and can be referred to as the "seal length." The minimum width W of the annular joint 18b is the shortest distance between the inner and outer peripheries of the annular joint 18b in a plan view (see FIGS. 3 and 5), and can be referred to as the "minimum seal length." In this embodiment, the annular joint 18b has a circular ring shape in a plan view, and the inner and outer peripheries of the annular joint 18b are concentric. Therefore, the width of the annular joint 18b is constant, and the width of the annular joint 18b is the minimum width W.

[0037] The valve opening pressure of the resin safety valve member 18 is the internal pressure of the battery case 30 when the sealing of the gas discharge hole 12 by the resin safety valve member 18 is released due to the destruction of the annular joint 18b of the resin safety valve member 18. Therefore, the larger the minimum width dimension W of the annular joint 18b, the less likely it is that the sealing of the gas discharge hole 12 will be released due to the destruction of the annular joint 18b of the resin safety valve member 18, and the greater the value of the valve opening pressure.

[0038] [Table 1]

[0039] Table 1 is a correspondence table showing the minimum width W (mm) of the annular joint 18b and the valve-opening pressure (MPa). As shown in Table 1, for example, in a sealed battery 1 in which the minimum width W of the annular joint 18b is 0.5 mm, the valve-opening pressure can be set to 1.4 MPa. Also, in a sealed battery 1 in which the minimum width W of the annular joint 18b is 0.9 mm, the valve-opening pressure can be set to 3.0 MPa. In this way, the valve-opening pressure of the resin safety valve member 18 can be determined by the minimum width W of the annular joint 18b of the resin safety valve member 18.

[0040] Although the present invention has been described above in accordance with an embodiment, it goes without saying that the present invention is not limited to the above embodiment and can be modified and applied as appropriate within the scope of the gist of the present invention.

[0041] For example, in the embodiment, a safety valve lid 10 is used in which a resin safety valve member 18 is integrally molded into a metal lid 11 by insert molding. However, a safety valve lid in which a resin safety valve member made of a resin film is welded to the metal lid 11 may also be used. This safety valve lid can be produced as follows. Specifically, first, a metal lid 11 (see FIGS. 7 to 9) having an annular roughened surface 14 is prepared. A resin safety valve member made of a resin film is also prepared. Next, the metal lid 11 is heated to 200°C, and the surface of the resin safety valve member that comes into contact with the annular roughened surface 14 is softened or melted by heating, and the resin safety valve member is welded to the annular roughened surface 14 of the metal lid 11. At this time, a portion of the resin forming the resin safety valve member (the resin that becomes the annular joint) penetrates into the recess 14b of the annular roughened surface 14 of the metal lid body 11, thereby hermetically joining the annular joint of the resin safety valve member to the annular roughened surface 14 of the metal lid body 11.

[0042] In the embodiment, the annular joint 18b has a circular shape in a plan view and a constant width. However, the annular joint may have a minimum-width joint portion in a circumferential portion of the annular joint, the minimum width being smaller than the remaining portions in a plan view. In this annular joint, the width of the minimum-width joint portion is the minimum width W of the annular joint. Therefore, in a sealed battery having this annular joint, when the internal pressure of the battery case reaches the valve-opening pressure, the minimum-width joint portion breaks, opening the resin safety valve member. This is because the minimum-width joint portion is the portion of the annular joint that is most susceptible to breakage. By providing the minimum-width joint portion in a circumferential portion of the annular joint, the valve-opening position (the position at which the annular joint breaks) when the internal pressure of the battery case reaches the valve-opening pressure can be determined at the minimum-width joint portion. This allows the valve-opening pressure to be set accurately. Therefore, a sealed battery having this annular joint has a precisely set valve-opening pressure.

[0043] Although the annular joint 18b has a circular ring shape in plan view in the embodiment, it may also have an elliptical or oval ring shape in plan view. In this case, the shape of the gas release hole and the annular roughened surface may also be elliptical or oval ring shape in plan view, similar to the shape of the annular joint. In an annular joint having an elliptical or oval ring shape in plan view, when a pressure acts on the resin safety valve member due to an increase in the internal pressure of the battery case, stress concentrates on the portion located on the minor axis of the ellipse or oval forming the outer periphery of the annular joint (referred to as the minor axis portion). Therefore, the minor axis portion of the annular joint is more susceptible to fracture than other portions. Therefore, by making the annular joint have an elliptical or oval ring shape in plan view, the valve opening position (the position at which the annular joint fractures) when the internal pressure of the battery case reaches the valve opening pressure can be determined to be the minor axis portion. This allows for precise valve opening pressure setting. Therefore, a sealed battery having this annular joint has a precisely set valve opening pressure. An ellipse is a figure made up of two parallel straight lines, an arc connecting one end of each of the straight lines, and another arc connecting the other end of each of the straight lines.

[0044] The annular joint may also have an elliptical or oval shape in plan view, with the minimum-width joint located on the minor axis of the ellipse or oval that defines the outer periphery of the annular joint. In an annular joint that has an elliptical or oval shape in plan view, the minimum-width joint is located on the minor axis where stress concentrates when a pressure acts on the resin safety valve member due to an increase in the internal pressure of the battery case. This allows the valve opening position (the position where the annular joint breaks) when the internal pressure of the battery case reaches the valve opening pressure to be determined at the minimum-width joint. This allows the valve opening pressure to be set with precision. Therefore, a sealed battery having this annular joint is a sealed battery with a precisely set valve opening pressure.

[0045] In the embodiment, the sealed battery 1 is shown as having a gas exhaust hole 12 formed in the metal wall portion 15 of the metal lid body 11 and a resin safety valve member 18 that closes this gas exhaust hole 12. However, the present invention also includes a sealed battery in which a gas exhaust hole is formed in the metal wall portion of the case body 21 and a resin safety valve member that closes this gas exhaust hole. [Explanation of symbols]

[0046] 1 sealed battery 11 Metal lid 11b Outer surface of metal lid 12 Gas exhaust hole 12b Gas exhaust hole opening 13 Hole periphery surface 14 Annular roughened surface (annular sealing surface) 14b Recess 15 Metal wall 15b Outer surface of metal wall 18 Resin safety valve components (safety valve components) 18b Annular joint 21 Case body 30 Battery case

Claims

1. a battery case having a metal wall portion with a gas exhaust hole formed therein; a safety valve member that covers an annular hole-periphery surface of the outer surface of the metal wall portion that surrounds the opening of the gas discharge hole and closes the gas discharge hole. In sealed batteries, the safety valve member is a resin safety valve member made of resin, the hole-surrounding surface includes an annular roughened surface having an uneven shape, the annular roughened surface surrounding the opening of the gas discharge hole; The resin safety valve member is an annular joint portion that is airtightly joined to the annular roughened surface, and the resin that forms the annular joint portion enters a recess in the annular roughened surface, and the resin is airtightly joined to the annular roughened surface, When the internal pressure of the battery case reaches a valve-opening pressure, the resin safety valve member opens due to destruction of a portion of the resin forming the annular joint that has entered into a recess in the annular roughened surface, the portion being the smallest width between the inner and outer peripheries. Sealed battery.

2. The sealed battery according to claim 1, The minimum width of the annular joint is 0.3 mm or more and 1.3 mm or less. Sealed battery.

3. The sealed battery according to claim 1 or 2, The battery case is a case body having an opening; a metal cover that closes the opening of the case body, The metal cover has the metal wall portion. Sealed battery.

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