Sealed battery

Abstract

To provide a sealed battery including a safety valve made of a resin, the safety valve being capable of quickly exhausting gas inside a battery case if the internal pressure of the battery case increases to reach a valve opening pressure.SOLUTION: In a sealed battery 1 including an electrode body 50 and a battery case 30 housing the electrode body 50, the battery case 50 includes a case body 21 having an opening 21b and housing the electrode body 50, and a plate-shaped lid body 10 closing an opening 21b of the case body 21. The lid body 10 includes a safety valve 18 made of a resin. In the safety valve 18, there is formed an annular groove 18m that has an annular shape in plan view and that is concave in a thickness direction of the lid body 10. A portion with an annular shape in plan view, where a bottom 18t of the annular groove 18m is formed, of the safety valve 18 is an annular thinnest portion 18s having a thinnest thickness of the safety valve 18.SELECTED DRAWING: Figure 5

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. This safety valve is made of metal and is integral 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 portion of the safety valve where the groove is formed (the portion that overlaps with the bottom of the groove in a plan view) 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 groove formed in the safety valve is linear in plan view. Therefore, when the internal pressure of the battery case reaches the valve-opening pressure, the linear portion of the safety valve where the groove is formed breaks, forming a slit-shaped gas vent hole, through which gas is released to the outside of the battery case. However, it is difficult to quickly release gas from inside the battery case with a slit-shaped gas vent hole. Therefore, there has been a demand for a safety valve that can quickly release gas from inside the battery case to the outside. Furthermore, there has been a demand for a safety valve made of resin in order to easily and appropriately form safety valves for a wide variety of sealed batteries.

[0006] The present invention has been made in consideration of the current situation, and aims to provide a sealed battery having a safety valve made of resin that can quickly release gas inside the battery case to the outside when the internal pressure of the battery case increases and reaches the valve opening pressure. [Means for solving the problem]

[0007] (1) One aspect of the present invention is a sealed battery comprising an electrode assembly and a battery case that houses the electrode assembly, the battery case having an opening and including a case body that houses the electrode assembly and a plate-shaped lid body that closes the opening of the case body, the lid body having a safety valve made of resin. a through hole penetrating the lid body in a thickness direction; and an annular seal surface surrounding an opening of the through hole. the safety valve an annular joint portion that closes the through hole and is airtightly joined to the annular seal surface; and a flat plate-shaped portion that is located inside the through hole in a plan view. a groove recessed in the thickness direction of the lid body and having an annular shape in a plan view; and, a portion of the safety valve that is annular in plan view and in which the bottom of the annular groove is formed is an annular thinnest portion that is the thinnest in thickness of the safety valve, the annular groove and the annular thinnest part are formed in the flat plate-like portion, The thinnest annular portion of the sealed battery is configured so that when the internal pressure of the battery case reaches the valve-opening pressure, the thinnest annular portion ruptures, forming a cylindrical gas exhaust hole surrounded by the ruptured surface of the thinnest annular portion.

[0008] In the above-described sealed battery, the annular portion of the safety valve where the bottom of the annular groove is formed in a planar view is the annular thinnest portion, which is the thinnest part of the safety valve. That is, the annular portion of the safety valve that overlaps with the bottom of the annular groove in a planar view is the annular thinnest portion, which is the thinnest part of the safety valve. Therefore, when the internal pressure of the battery case reaches the valve opening pressure and the safety valve ruptures, the annular thinnest portion ruptures, forming a cylindrical gas vent hole surrounded by the fracture surface of the annular thinnest portion. For example, in the case of a safety valve in which the annular groove is circular in a planar view, the annular thinnest portion is an annular thinnest portion having a circular shape in a planar view equivalent to the bottom of the annular groove. Therefore, when the safety valve ruptures, the annular thinnest portion ruptures, forming a cylindrical (or approximately cylindrical) gas vent hole surrounded by the fracture surface of the annular thinnest portion.

[0009] As described above, in the sealed battery, when the internal pressure of the battery case reaches the valve-opening pressure, the annular thinnest part of the safety valve ruptures, forming a cylindrical gas vent hole, which makes it easier for gas inside the battery case to be released to the outside. Therefore, when the internal pressure of the battery case increases due to gas generated inside the battery case and reaches the valve-opening pressure, the gas inside the battery case can be quickly released to the outside through the cylindrical gas vent hole, and the internal pressure of the battery case can be quickly reduced.

[0010] Examples of the annular groove include a circular groove having a circular ring shape in a plan view and an elliptical groove having an elliptical ring shape in a plan view. The safety valve may have not only an annular groove but also other grooves (for example, linear grooves) formed therein. In this case, the thinnest part of the safety valve may include not only the annular thinnest part but also the part of the safety valve where the bottom of the other groove is formed. In other words, the thinnest part of the safety valve may be the annular thinnest part and the other thinnest part formed by the other groove.

[0011] The lid may be, for example, a lid body made of a metal plate having a cylindrical through-hole penetrating the lid body in the thickness direction, and a safety valve for closing the through-hole.The lid may also be a resin lid body made of resin and including a safety valve as part of the resin lid body.

[0012] (2) Furthermore, in the sealed battery of (1), the annular groove may be an annular groove having a circular ring shape in a planar view, and the annular thinnest portion may be an annular thinnest portion having a circular ring shape in a planar view.

[0013] By configuring the annular thinnest portion as a circular annular thinnest portion, when the safety valve ruptures, the circular annular thinnest portion breaks, thereby forming a cylindrical (or approximately cylindrical) gas vent hole surrounded by the fracture surface of the circular annular thinnest portion, which allows gas inside the battery case to be quickly discharged to the outside and the internal pressure of the battery case to be quickly reduced.

[0014] (3) Furthermore, in the sealed battery of (1) or (2), in addition to the annular groove, the safety valve also has a linear groove that is linear in plan view and divides the area surrounded by the annular groove into two equal parts in plan view, and the thinnest part of the safety valve is preferably the linear thinnest part, which is a linear part in plan view where the bottom of the linear groove is formed in the safety valve, and the annular thinnest part.

[0015] In the above-described sealed battery, the thinnest part of the safety valve has a linear thinnest part in addition to the annular thinnest part. The linear thinnest part is a linear thinnest part in plan view that bisects the area surrounded by the annular thinnest part in plan view. Therefore, when the safety valve ruptures, both the linear thinnest part and the annular thinnest part rupture. This makes it possible to form a gas vent hole more quickly than when only the annular thinnest part ruptures to form a gas vent hole, allowing gas inside the battery case to be quickly released to the outside and quickly reducing the internal pressure of the battery case.

[0016] (4) Furthermore, in the sealed battery of any one of (1) to (3), it is preferable that the annular groove has a V-shaped cross section in which the width dimension of the groove decreases from the opening of the groove toward the bottom.

[0017] Because the width of the bottom of a V-shaped cross-section groove is extremely small, the width of the annular thinnest part (the distance between the inner and outer circumferences of the annular thinnest part, the dimension perpendicular to the thickness direction) is also extremely small. This increases the positional accuracy of the fracture surface formed by fracture of the annular thinnest part, and therefore increases the dimensional accuracy of the cylindrical gas release hole surrounded by the fracture surface. This reduces the variation in the size of the gas release hole among multiple batteries, thereby reducing the variation in gas release rate.

[0018] (5) Furthermore, in the sealed battery of any of (1) to (4), the lid body is a lid main body made of a metal plate, and includes a lid main body having a cylindrical through-hole penetrating the lid main body in a thickness direction, and the safety valve closing the through-hole, the lid main body including an annular sealing surface surrounding the opening of the through-hole, the safety valve having an annular joint hermetically joined to the annular sealing surface and a flat portion located inside the through-hole in a plan view, the annular groove and the annular thinnest portion are formed in the flat portion, and when the internal pressure of the battery case reaches a valve opening pressure, the annular thinnest portion breaks, forming a cylindrical gas release hole surrounded by the fracture surface of the annular thinnest portion, which is a preferred sealed battery.

[0019] In the sealed battery described above, the safety valve is a safety valve that closes a through-hole in a lid body made of a metal plate. This safety valve has an annular joint that is airtightly joined to an annular sealing surface of the lid body that surrounds the opening of the through-hole. By having such an annular joint, the safety valve is airtightly joined to the lid body and the through-hole is sealed by the safety valve. Furthermore, in this safety valve, the annular groove and the annular thinnest portion are formed in a flat portion located inside the through hole in a plan view. Therefore, when the internal pressure of the battery case reaches the valve-opening pressure, the annular thinnest portion ruptures, forming a cylindrical gas vent hole surrounded by the fractured surface of the annular thinnest portion at a position inside the through hole in a plan view. This allows gas inside the battery case to be discharged to the outside through the entire cylindrical gas vent hole surrounded by the fractured surface of the annular thinnest portion.

[0020] (6) Furthermore, in the sealed battery of (5), the annular sealing surface is preferably an annular roughened surface having an uneven shape, and the safety valve is preferably a sealed battery that is hermetically joined to the annular roughened surface in such a manner that the resin forming the annular joint enters into the recess of the annular roughened surface.

[0021] In the sealed battery described above, the resin forming the annular joint penetrates into the recesses of the annular roughened surface of the lid body, and the annular joint of the safety valve is hermetically joined to the annular roughened surface. In other words, the annular joint of the safety valve is hermetically joined to the annular roughened surface by an anchor effect caused by the protrusions of the annular roughened surface of the lid body biting into the annular joint of the safety valve. This increases the airtightness between the annular joint of the safety valve and the annular roughened surface of the lid body, thereby improving the airtightness of the sealed battery. [Brief explanation of the drawings]

[0022] [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] FIG. 4 is an enlarged view of part C in FIG. 3. [Figure 5] FIG. 4 is an enlarged bottom view of a portion of the lid body including a safety valve. [Figure 6] FIG. 2 is a cross-sectional view of FIG. 1 . [Figure 7] FIG. [Figure 8]FIG. 8 is a cross-sectional view taken along the line DD in FIG. 7. [Figure 9] FIG. 2 is a plan view (top view) of the lid main body. [Figure 10] 10 is a cross-sectional view of FIG. 9 taken along line E-E. [Figure 11] FIG. 11 is an enlarged view of part F in FIG. [Figure 12] FIG. 10 is an explanatory diagram of the safety valve of the embodiment when it is torn open. [Figure 13] 10 is an enlarged bottom view of a portion of the cover according to Comparative Example 1 that includes a safety valve. FIG. [Figure 14] FIG. 2 is an enlarged cross-sectional view of a portion of the lid including a safety valve. [Figure 15] FIG. 10 is an explanatory view of the safety valve of Comparative Example 1 when it is ruptured. DETAILED DESCRIPTION OF THE INVENTION

[0023] 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 in the shape of a rectangular parallelepiped box. The battery case 30 includes a metal case body 21 in the shape of a rectangular cylinder with a bottom, and a rectangular flat plate-like lid body 10 that closes the opening 21b of the case body 21 (see FIGS. 1 to 3). The lid body 10 includes a flat plate-like lid main body portion 11 made of metal, and a safety valve 18 made of resin.

[0024] The lid main body 11 is formed with two rectangular cylindrical through holes, a first through hole 16 and a second through hole 17 (see FIGS. 7 and 9). A positive terminal 41 is inserted into the first through hole 16, and a negative terminal 42 is inserted into the second through hole 17 (see FIGS. 1 and 2). Cylindrical insulating members (not shown) are interposed between the inner circumferential surface of the first through hole 16 of the lid main body 11 and the outer circumferential surface of the positive terminal 41, and between the inner circumferential surface of the second through hole 17 of the lid main body 11 and the outer circumferential surface of the negative terminal 42. Furthermore, the lid main body 11 is formed with a cylindrical third through hole 12 penetrating the lid main body 11 in the thickness direction (see FIG. 3). This third through hole 12 penetrates between the outer surface 11b (upper surface) and the inner surface 11c (lower surface) of the lid main body 11.

[0025] 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).

[0026] The lid main body 11 also includes an annular sealing surface 15 that surrounds the opening 12b of the third through hole 12 (see FIGS. 9 to 11). In this embodiment, the annular hole peripheral surface 13 that surrounds the opening 12b of the third through hole 12 on the outer surface 11b of the lid main body 11 serves as the annular sealing surface 15.

[0027] The lid 10 further includes a safety valve 18 that closes the third through-hole 12 of the lid main body 11. The safety valve 18 has a bottomed, cylindrical shape with a flange, an annular joint portion 18b that is airtightly joined to the annular seal surface 15, and an inner portion 18c located inside the third through-hole 12 in a plan view (see FIGS. 3 and 4). The inner portion 18c includes a cylindrical portion 18j that extends in the thickness direction of the lid main body 11 (the vertical direction in FIG. 3) and a disk-shaped, flat portion 18h that is located radially inward from the inner circumferential surface of the cylindrical portion 18j. In this embodiment, the safety valve 18 includes a first portion 18d that is cylindrical and has a bottom, and an annular second portion 18f that is located radially outward from the outer circumferential surface of the first portion 18d. The first portion 18d is the inner portion 18c, and the portion of the second portion 18f that is close to the annular seal surface 15 is the annular joint portion 18b.

[0028] The safety valve 18 is preferably made of a resin with low permeability to the electrolyte, such as PPS (polyphenylene sulfide), PAS (polyarylene sulfide), an olefin resin, or a fluororesin. In this embodiment, the safety valve 18 is made of PPS.

[0029] As described above, the safety valve 18 has the annular joint portion 18b that is airtightly joined to the annular seal surface 15 (see FIGS. 3 and 4). The annular joint portion 18b has a circular ring shape in plan view (see FIG. 9). By having such an annular joint portion 18b, the safety valve 18 is airtightly joined to the lid main body 11, and the third through-hole 12 is sealed by the safety valve 18.

[0030] In particular, in this embodiment, the annular sealing surface 15 of the lid main body 11 is an annular roughened surface 14 having an uneven shape (see FIGS. 10 and 11). This annular roughened surface 14 has a circular ring shape in a plan view (see FIG. 9). The safety valve 18 is airtightly joined to the annular roughened surface 14 in such a manner that the resin forming the annular joint 18b enters the recess 14b of the annular roughened surface 14 (see FIG. 4). In other words, the annular joint 18b of the safety valve 18 is airtightly joined to the annular roughened surface 14 by an anchor effect caused by the protrusion 14c of the annular roughened surface 14 biting into the annular joint 18b of the safety valve 18. This increases the airtightness between the annular joint 18b and the annular roughened surface 14, 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 lid main body 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 lid main body 11 is made into the annular roughened surface 14 by laser surface treatment.

[0032] The lid main body 11 and the safety valve 18 are integrally molded by insert molding. Specifically, the lid main body 11 and the safety valve 18 constitute a lid 10 (insert molded product) in which the safety valve 18 is integrally molded into the lid main body 11 by insert molding (see FIGS. 7 and 8). The lid 10 is produced as follows. Specifically, first, a lid main body 11 (see FIGS. 9 to 11) having an annular roughened surface 14 is prepared. Next, the safety valve 18 is molded by resin injection molding using the lid main body 11 as an insert part, thereby producing a lid 10 (insert molded product, see FIGS. 7 and 8) in which the lid main body 11 and the safety valve 18 are integrally molded.

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

[0034] Meanwhile, an annular groove 18m, which is a groove recessed in the thickness direction of the lid body 10 and the lid main body 11 and has an annular shape in plan view, is formed on the underside 18g of the flat plate-shaped portion 18h of the safety valve 18 (see FIGS. 5 and 6). Furthermore, the portion of the safety valve 18 that has an annular shape in plan view where the bottom 18t of the annular groove 18m is formed is the annular thinnest portion 18s that has the thinnest thickness in the safety valve 18. In other words, the annular portion of the safety valve 18 that overlaps with the bottom 18t of the annular groove 18m in plan view is the annular thinnest portion 18s that has the thinnest thickness in the safety valve 18 (see FIGS. 5 and 6).

[0035] Therefore, when the internal pressure of the battery case 30 reaches the valve opening pressure and the safety valve 18 ruptures, the annular thinnest part 18s ruptures, forming a cylindrical (or approximately cylindrical) gas exhaust hole GH1 surrounded by the fracture surface 18v of the annular thinnest part 18s (see Figure 12).

[0036] As described above, in the sealed battery 1 of this embodiment, when the internal pressure of the battery case 30 reaches the valve-opening pressure, the annular thinnest portion 18s of the safety valve 18 ruptures, forming a cylindrical gas vent hole GH1, which facilitates the release of gas to the outside within the battery case 30. Therefore, when the internal pressure of the battery case 30 increases due to gas generated within the battery case 30 and reaches the valve-opening pressure, the gas within the battery case 30 can be quickly released to the outside through the cylindrical gas vent hole GH1, and the internal pressure of the battery case 30 can be quickly reduced.

[0037] Moreover, in addition to the annular groove 18m, the safety valve 18 of this embodiment also has a linear groove 18n that is linear in plan view and that bisects the area SA surrounded by the annular groove 18m in plan view (see FIGS. 5 and 6). The thinnest portions of the safety valve 18 are linear thinnest portion 18r, which is a linear portion in plan view where the bottom 18u of the linear groove 18n of the safety valve 18 is formed, and annular thinnest portion 18s. That is, the thinnest portion of the safety valve 18 includes linear thinnest portion 18r in addition to annular thinnest portion 18s. The linear thinnest portion 18r is a thinnest portion that is linear in plan view and that bisects the area surrounded by the annular thinnest portion 18s in plan view.

[0038] Therefore, when the safety valve 18 ruptures, the linear thinnest portion 18r and the annular thinnest portion 18s rupture. This allows the gas vent hole GH1 to be formed more quickly than when the gas vent hole GH1 is formed by rupturing only the annular thinnest portion 18s, and allows the gas inside the battery case 30 to be quickly released to the outside, thereby quickly reducing the internal pressure of the battery case 30.

[0039] Furthermore, in this embodiment, the annular groove 18m has a V-shaped cross section in which the width of the annular groove 18m decreases from the opening of the annular groove 18m toward the bottom 18t. Because the width of the bottom 18t of the annular groove 18m having such a V-shaped cross section is extremely small, the width of the annular thinnest portion 18s (the distance between the inner and outer peripheries of the annular thinnest portion 18s, the dimension perpendicular to the thickness direction) is also extremely small. This increases the positional accuracy of the fractured surfaces 18v formed by the fracture of the annular thinnest portion 18s, thereby increasing the dimensional accuracy of the cylindrical gas release hole GH1 surrounded by the fractured surfaces 18v. This reduces variation in the size of the gas release hole GH1 among multiple sealed batteries 1, thereby reducing variation in the gas release rate.

[0040] As described above, in the sealed battery 1 of this embodiment, the inside of the battery case 30 is made airtight by hermetically joining the annular joint portion 18b of the safety valve 18 to the annular sealing surface 15 of the lid main body portion 11, and when the internal pressure of the battery case 30 reaches the valve opening pressure, the safety valve 18 opens to discharge the gas inside the battery case 30 to the outside, thereby preventing the internal pressure of the battery case 30 from rising too much.

[0041] Incidentally, it is possible to adjust the valve opening pressure of the safety valve 18 by adjusting the thicknesses of the annular thinnest portion 18s and the linear thinnest portion 18r of the safety valve 18. This is because the breaking strength of the annular thinnest portion 18s and the linear thinnest portion 18r varies depending on the thicknesses of the annular thinnest portion 18s and the linear thinnest portion 18r. The valve opening pressure of the safety valve 18 is the internal pressure of the battery case 30 when the annular thinnest portion 18s and the linear thinnest portion 18r of the safety valve 18 break to form the gas release hole GH1.

[0042] In the sealed battery 1 of this embodiment, the valve opening pressure of the safety valve 18 is determined by the thickness T of the annular thinnest portion 18s and the linear thinnest portion 18r. By setting the valve opening pressure in this way using the thickness T of the annular thinnest portion 18s and the linear thinnest portion 18r, the valve opening pressure can be set with high precision.

[0043] [Table 1]

[0044] Table 1 shows the relationship between the thickness T (mm) of the annular thinnest portion 18s and the linear thinnest portion 18r and the valve-opening pressure (MPa). As shown in Table 1, for example, in a sealed battery 1 in which the thickness T of the annular thinnest portion 18s and the linear thinnest portion 18r is 0.06 mm, the valve-opening pressure can be set to 1.4 MPa. In addition, in a sealed battery 1 in which the thickness T of the annular thinnest portion 18s and the linear thinnest portion 18r is 0.10 mm, the valve-opening pressure can be set to 2.0 MPa. In addition, in a sealed battery 1 in which the thickness T of the annular thinnest portion 18s and the linear thinnest portion 18r is 0.15 mm, the valve-opening pressure can be set to 2.7 MPa. Thus, the valve-opening pressure of the safety valve 18 can be determined by the thickness T of the annular thinnest portion 18s and the linear thinnest portion 18r of the safety valve 18.

[0045] <Example 1 and Comparative Example 1> As Example 1, a sealed battery 1 was prepared in which the thickness T of the annular thinnest portion 18s and the linear thinnest portion 18r was 0.06 mm. As Comparative Example 1, a sealed battery was prepared that differed from the sealed battery 1 of Example 1 only in the safety valve. Specifically, as shown in FIGS. 13 and 14 , the safety valve 118 of Comparative Example 1 differs from the safety valve 18 of Example 1 in that it has only a linear groove 118n without an annular groove 18m and only a linear thinnest portion 118r without an annular thinnest portion 18s. The other differences are the same. The sealed battery of Comparative Example 1, like the sealed battery 1 of Example 1, has a thickness T of the linear thinnest portion 118r of 0.06 mm. Therefore, the valve opening pressure of the sealed battery of Comparative Example 1 is set to 1.4 MPa, like the sealed battery 1 of Example 1.

[0046] <Gas Emission Test> A gas discharge test was conducted on the sealed batteries of Example 1 and Comparative Example 1. Specifically, each sealed battery was overcharged by charging it until the battery voltage reached 5.0 V, generating gas inside the battery case. This increased the internal pressure of each sealed battery to the valve opening pressure of 1.4 MPa, causing the safety valve to open. Then, for each sealed battery, the time from when the safety valve opened until the gas inside the battery case was completely discharged (referred to as the gas discharge time) was measured. That is, the gas discharge time was measured from when gas began to be discharged from the battery case due to the safety valve opening until gas discharge from the battery case was completed.

[0047] The gas discharge time was 12.0 seconds for the sealed battery of Comparative Example 1. In contrast, the gas discharge time was 4.2 seconds for the sealed battery 1 of Example 1, which was able to reduce the gas discharge time to about one-third of that of the sealed battery of Comparative Example 1. The reasons for this result are as follows.

[0048] The sealed battery of Comparative Example 1 has only linear grooves 118n as grooves and only linear thinnest portions 118r as thinnest portions in the flat portion 118h of the safety valve 118 (FIGS. 13 and 14). Therefore, in the sealed battery of Comparative Example 1, when the internal pressure of the battery case reaches the valve-opening pressure, the linear thinnest portion 118r of the safety valve 118 ruptures, as shown in FIG. 15, forming a slit-shaped gas vent hole GH2 through which gas is released to the outside of the battery case. However, it is difficult to quickly release gas from inside the battery case with the slit-shaped gas vent hole GH2.

[0049] In contrast, the sealed battery 1 of Example 1 has an annular groove 18m as a groove in the flat portion 18h of the safety valve 18, and an annular thinnest portion 18s as the thinnest portion (see FIGS. 5 and 6). Therefore, in the sealed battery 1 of Example 1, when the internal pressure of the battery case 30 reaches the valve-opening pressure, the annular thinnest portion 18s of the safety valve 18 ruptures, forming a cylindrical gas vent hole GH1. This makes it easier for gas inside the battery case 30 to be discharged to the outside than in the sealed battery of Comparative Example 1, which has a slit-shaped gas vent hole GH2. Therefore, in the sealed battery 1 of Example 1, the gas discharge time was reduced to approximately one-third of that of the sealed battery of Comparative Example 1.

[0050] 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.

[0051] For example, in the embodiment, the lid 10 is a lid 10 in which the safety valve 18 is integrally molded into the lid main body 11 by insert molding. However, a lid in which a resin safety valve made of a resin film is welded to the lid main body 11 may also be used. Furthermore, a resin lid made of resin and including a safety valve as part of the resin lid may also be used. This resin lid can be produced, for example, by injection molding of resin.

[0052] Furthermore, in the safety valve 18 of the embodiment, annular groove 18m and linear groove 18n are provided as grooves, and annular thinnest portion 18s and linear thinnest portion 18r are provided as thinnest portions. However, only annular groove 18m may be provided as a groove, and only annular thinnest portion 18s may be provided as the thinnest portion. Furthermore, in the safety valve 18 of the embodiment, annular groove 18m is provided as the annular groove, and annular thinnest portion 18s is provided as the annular thinnest portion. However, annular grooves of other shapes, such as elliptical grooves that are elliptical in plan view, may be provided as the annular groove, and annular thinnest portions of other shapes, such as elliptical thinnest portions, may be provided as the annular thinnest portions. [Explanation of symbols]

[0053] 1 sealed battery 10 Lid 11 Lid main body 12 Third through hole 14 Annular roughened surface (annular sealing surface) 14b Recess 18 Safety valve 18b Annular joint 18h Flat plate area 18m circular groove (circular groove) 18n Straight groove 18t,18u bottom 18r Linear thinnest part 18s Thinnest part of annular ring (thinnest part of annular ring) 21 Case body 21b opening 30 Battery case 50 Electrode body GH1 Gas Vent

Claims

1. A sealed battery comprising an electrode assembly and a battery case that houses the electrode assembly, The battery case is a case body having an opening and accommodating the electrode body; a plate-shaped lid that closes the opening of the case body, The lid body is a safety valve made of resin; a through hole penetrating the lid body in a thickness direction; an annular sealing surface surrounding the opening of the through hole; The safety valve is The through hole is closed, an annular joint portion that is airtightly joined to the annular seal surface; a flat plate-like portion located inside the through hole in a plan view; a groove recessed in the thickness direction of the lid body and having an annular shape in a plan view; a portion of the safety valve that is annular in plan view and in which the bottom of the annular groove is formed is an annular thinnest portion that is the thinnest in thickness of the safety valve, the annular groove and the annular thinnest portion are formed in the flat plate-like portion, The annular thinnest portion is configured so that, when the internal pressure of the battery case reaches a valve-opening pressure, the annular thinnest portion is broken to form a cylindrical gas release hole surrounded by the broken surface of the annular thinnest portion. Sealed battery.

2. The sealed battery according to claim 1, The annular sealing surface is an annular roughened surface having an uneven shape, The safety valve is airtightly joined to the annular roughened surface in such a manner that the resin forming the annular joint enters into the recess of the annular roughened surface. Sealed battery.

Images