Secondary battery

Abstract

To provide a sealed secondary battery in which a safety valve is easily operated properly by securing a gas passage to the safety valve covered with an insulating member when gas pressure or gas temperature rises to a predetermined value or higher in a battery case.SOLUTION: A sealed secondary battery 10 includes a battery case 1, an electrode body 2 housed in the battery case in a sealed manner, an insulating member 3 interposed between the battery case and the electrode body, and a safety valve 4 provided in the battery case at a position facing the insulating member so that gas GS whose gas pressure or gas temperature has risen to a predetermined value or higher in the battery case can be released to the outside of the battery case. The safety vent includes an openable valving element 41 and a valving element support 42 that supports an outer periphery 411 of the valving element 41 in an annular shape and is connected to the battery case, and a gas flow path forming portion 43 that forms a gas flow path 44 communicating with the valving element side is provided between the insulating member pushed out to the valving element side by the gas and the valving element support on an 42N of a case inner surface located inside the case from the valving element of the valving element support.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a secondary battery. [Background technology]

[0002] In general, when a sealed secondary battery containing an electrode assembly housed in a battery case is charged with a high voltage or a large current, gas is generated as the battery temperature rises, and there is a risk that the gas pressure or gas temperature inside the battery case may rise above a predetermined value. Therefore, many sealed secondary batteries are equipped with a safety valve in the battery case that releases the gas inside the battery case to the outside of the battery case when the gas pressure or gas temperature inside the battery case rises above a predetermined value. In addition, when the battery case is made of metal, it is known to interpose an insulating member between the electrode assembly and the battery case for the purpose of improving electrical insulation between the electrode assembly and the battery case.

[0003] For example, Patent Document 1 discloses a secondary battery in which a safety valve is provided on the lid of a battery case, and an end of an insulating film (insulating member) interposed between an electrode body and the battery case extends toward the lid. Patent Document 2 also discloses a battery in which an electrode group is housed in a battery case shaped like a rectangular cylinder with a bottom, and a negative electrode lead connected to a negative electrode plate is electrically connected via an upper insulating plate (insulating member) to an internal terminal of a sealing body having a safety valve, and the upper insulating plate extends to a position covering the safety valve. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-095836 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-31263 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the secondary battery of Patent Document 1 and the battery of Patent Document 2 have a problem in that when the gas pressure or gas temperature inside the battery case rises above a predetermined value, and even though it is desired to release the gas outside the battery case, the insulating member (insulating film, upper insulating plate) may obstruct the flow of gas to the safety valve, preventing the safety valve from operating properly.

[0006] The disclosed technology has been made in consideration of such problems, and aims to provide a sealed secondary battery that ensures a gas flow path to a safety valve covered with an insulating member when the gas pressure or gas temperature inside the battery case rises above a predetermined value, thereby making it easy for the safety valve to operate properly. [Means for solving the problem]

[0007] (1) One aspect of the disclosed technology for solving the above problems is a sealed secondary battery including a battery case, an electrode body hermetically stored within the battery case, an insulating member interposed between the battery case and the electrode body, and a safety valve provided in the battery case at a position facing the insulating member so as to be able to release gas to the outside of the battery case when the gas pressure or gas temperature within the battery case rises to or exceeds a predetermined value, wherein the safety valve includes an openable valve body and a valve body support part that supports the outer periphery of the valve body in an annular shape and is connected to the battery case, and the secondary battery is provided with a gas flow path forming part on the inner surface of the case located more inward than the valve body of the valve body support part, between the insulating member pushed toward the valve body side by the gas and the valve body support part, forming a gas flow path that communicates with the valve body side.

[0008] (2) In the secondary battery described in (1), it is preferable that the gas flow path forming portion has a recessed groove portion formed on the inner surface of the case of the valve body support portion.

[0009] (3) In the secondary battery described in (1), it is preferable that the gas flow path forming portion has a protrusion formed on the inner surface of the case of the valve body support portion.

[0010] (4) In the secondary battery according to any one of (1) to (3), the valve body support portion is preferably a resin valve body support portion formed of a thermoplastic resin material.

[0011] (5) In the secondary battery described in any one of (1) to (4), it is preferable that the valve body is formed of a material whose tensile strength is smaller than that of the battery case, and the valve body support portion is connected to the battery case via an annular member made of the same material as the battery case. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic cross-sectional view of a secondary battery according to one aspect of the present embodiment. [Figure 2] 2 is an enlarged cross-sectional view of part A shown in FIG. 1, illustrating one state when the valve body is opened. FIG. [Figure 3] 1, and is an explanatory view of another state when the valve body is opened. FIG. [Figure 4] 1, and is an enlarged cross-sectional view of part A shown in FIG. 1, illustrating yet another state when the valve body is opened. [Figure 5] 2 is a perspective view of the safety valve and an annular member joined to a valve body support portion of the safety valve in the secondary battery shown in FIG. 1, as viewed from inside the case. FIG. [Figure 6] FIG. 6 is a cross-sectional view of the BB portion shown in FIG. 5. [Figure 7] 1. FIG. 4 is a perspective view of a safety valve and an annular member joined to a valve body support portion of the safety valve in a first modified example of the secondary battery shown in FIG. 1, as viewed from inside the case. [Figure 8] 1. FIG. 6 is a perspective view of a safety valve and an annular member joined to a valve body support portion of the safety valve in a second modified example of the secondary battery shown in FIG. 1, as viewed from inside the case. [Figure 9] 10 is an enlarged cross-sectional view of a portion A in a third modified example of the secondary battery shown in FIG. 1, illustrating a state when the valve body is open. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0013] <Description of this secondary battery> Next, a secondary battery according to one aspect of the embodiment of the disclosed technology will be described in detail with reference to the drawings. FIG. 1 shows a schematic cross-sectional view of a secondary battery according to one aspect of the present embodiment. FIG. 2 is an enlarged cross-sectional view of portion A shown in FIG. 1, illustrating one state when the valve body is open. FIG. 3 is an enlarged cross-sectional view of portion A shown in FIG. 1, illustrating another state when the valve body is open. FIG. 4 is an enlarged cross-sectional view of portion A shown in FIG. 1, illustrating yet another state when the valve body is open. FIG. 5 shows a perspective view of the safety valve and the annular member joined to the valve body support portion of the safety valve in the secondary battery shown in FIG. 1, viewed from the inside of the case. FIG. 6 shows a partial cross-sectional view taken along line B-B shown in FIG. 5. FIG. 6 is a partial cross-sectional view of the intermediate portion between the inner and outer circumferential sides of the valve body support portion, viewed horizontally from the inner circumferential side, in an arc-shaped manner. Note that in FIGS. 1 to 4, the X direction indicates the longitudinal direction of the battery case, the Y direction indicates the lateral direction (width direction) of the battery case, and the Z direction indicates the up-down direction of the battery case.

[0014] As shown in Figures 1 to 6, this secondary battery 10 is a sealed secondary battery 10 including a battery case 1, an electrode body 2 hermetically housed within the battery case 1, an insulating member 3 interposed between the battery case 1 and the electrode body 2, and a safety valve 4 provided in the battery case 1 at a position opposite the insulating member 3 so as to be able to release gas GS to the outside of the battery case 1 when the gas pressure or gas temperature within the battery case 1 rises to or exceeds a predetermined value.

[0015] Here, the battery case 1 includes a rectangular cylindrical case body 11 having rectangular openings 114 (114A, 114B) at both ends in the longitudinal direction (X direction), and plate-like lids 12 (12A, 12B) that seal the openings 114 (114A, 114B) of the case body 11. The battery case 1 may be formed, for example, from a stainless steel plate (e.g., JIS standard: SUS304, etc.) with excellent pressure resistance, but this is not necessarily limited to this. The case body 11 and the lid 12 are formed from the same metal member and are joined in a watertight manner by laser welding or the like. The predetermined value of the gas pressure is a reference value determined, for example, based on the deformation amount of the battery case 1, and the predetermined value of the gas temperature is a reference value determined, for example, based on the melting point of the insulating member 3. The battery case 1 is not limited to the above shapes and may, for example, be a battery case consisting of a rectangular cylindrical case body with a bottom and one opening and a lid that seals the opening.

[0016] The battery case 1 contains an electrode body 2, which is hermetically sealed and includes a positive electrode body 21 and a negative electrode body 22 stacked with a separator 23 sandwiched therebetween. The electrode body 2 is formed by winding the strip-shaped positive electrode body 21 and the negative electrode body 22 in a direction perpendicular to the longitudinal direction (X direction) with the strip-shaped separator 23 sandwiched between them, and then compressing them in the short direction (Y direction) to stack them flat. Therefore, at both longitudinal (X direction) edge portions 2T of the electrode body 2, the ends of the positive electrode body 21, the negative electrode body 22, and the separator 23 are open. Therefore, if a short circuit occurs between the positive electrode body 21 and the negative electrode body 22, high-temperature gas GS and the like will be ejected primarily from the longitudinal (X direction) edge portions 2T of the electrode body 2.

[0017] To ensure electrical insulation between the battery case 1 and the electrode assembly 2, an insulating member 3 made of an insulating film is interposed between the battery case 1 and the electrode assembly 2. The insulating member 3 is formed as a cylindrical body whose longitudinal length (X direction) is longer than that of the electrode assembly 2 and whose both longitudinal edge portions 3T are open. High-temperature gas GS and the like ejected from the longitudinal edge portion 2T of the electrode assembly 2 is separated by the insulating member 3 into the battery case 1 side and the electrode assembly 2 side and moves toward the safety valve 4 side. Here, the insulating member 3 is open along both longitudinal edge portions 3T, but this is not necessarily limited thereto; only the vicinity of the current collecting terminal 5 and the injection port 122, which will be described later, may be open. The insulating member 3 may be formed, for example, from polypropylene (PP) resin or the like.

[0018] A current collecting terminal 5 electrically connected to the current collecting foil of the electrode body 2 is fixed to the lid body 12 in a watertight manner via an insulating resin portion 6. The insulating resin portion 6 can be formed of, for example, polyphenylene sulfide (PPS) resin. A positive electrode current collecting terminal 5 (5A) joined to a tab of the current collecting foil 211 of the positive electrode body 21 is fixed to one lid body 12 (12A) shown in FIG. 1 via an insulating resin portion 6 (6A). A negative electrode current collecting terminal 5 (5B) joined to a tab of the current collecting foil 221 of the negative electrode body 22 is fixed to another lid body 12 (12B) shown in FIG. 1 via an insulating resin portion 6 (6B). An injection port 122 for injecting the electrolyte 7 is formed in one lid body 12 (12A), and the injection port 122 is sealed with a stopper 123 after the electrolyte 7 is injected.

[0019] An insertion hole 111 for the safety valve 4 is formed in the upper end of the case body 11. The safety valve 4 includes an openable valve element 41 and a valve element support portion 42 that supports the outer circumferential portion 411 of the valve element 41 in an annular shape and is connected to the battery case 1 (112). The outer circumferential portion 411 of the valve element 41 is formed to be thicker than the inner circumferential portion. The lower end portion 411K of the outer circumferential portion 411 is embedded and fixed to the upper end portion of the annular valve element support portion 42. In addition, a V-shaped groove 412 for cleavage is formed in an X-shape on the inner circumferential side of the outer circumferential portion 411 of the valve element 41. The shape of the V-shaped groove 412 shown in FIG. 5 is merely an example, and shapes other than those shown in FIG. 5 may be used. Here, the safety valve 4 is formed in an overall circular shape, but this is not necessarily limited thereto and may be formed in, for example, an oval or elliptical shape.

[0020] The lower part of the valve body support part 42 is inserted into the insertion hole 111 of the battery case 1 (case main body 11) and protrudes inward from the battery case 1. The annular member 112 of the battery case 1 is connected to the outer periphery of the valve body support part 42. The annular member 112 is made of the same metal plate (e.g., stainless steel plate) as the battery case 1. The annular member 112 is joined to the case main body 11 by a weld 113 formed continuously on the outer periphery of the insertion hole 111, and is part of the battery case 1. The weld 113 can be formed, for example, by laser welding.

[0021] Additionally, a gas flow path forming portion 43 is provided on the case inner surface 42N of the valve element support portion 42, located inward of the valve element 41. The gas flow path 44 is formed between the valve element support portion 42 and the insulating member 3, which is pushed toward the valve element 41 by the gas GS whose gas pressure or gas temperature inside the battery case 1 exceeds a predetermined value. When the gas pressure or gas temperature inside the battery case 1 exceeds a predetermined value, the gas GS flowing through the battery case 1 is supplied to the valve element 41 through the gas flow path 44 formed between the insulating member 3, which is pushed toward the valve element 41 by the gas GS on the electrode body 2 side, and the valve element support portion 42. Preferably, multiple gas flow path forming portions 43 are formed at predetermined intervals along the case inner surface 42N of the annular valve element support portion 42, extending from the outer periphery toward the inner periphery. In this case, multiple gas flow paths 44 are formed from the outer periphery of the valve element support portion 42 toward the valve element 41.

[0022] Then, the valve element 41 is opened by the gas GS supplied from the gas flow path 44 to the valve element 41 side, and the safety valve 4 with the valve element 41 opened can release the gas GS to the outside of the battery case 1. As a result, when the gas pressure or gas temperature inside the battery case 1 rises to or exceeds a predetermined value, the gas flow path 44 that supplies the gas GS to the safety valve 4 covered with the insulating member 3 is secured, and a sealed secondary battery 10 can be provided in which the safety valve 4 is likely to operate properly.

[0023] The gas flow path forming portion 43 can be formed in various shapes, but here, it has a groove portion 431 formed in the case inner surface 42N of the valve body support portion 42. The groove portion 431 is formed with a U-shaped cross section. The groove portion 431 is continuously formed, bending in an L-shape in the vertical direction (Z direction) and radial direction from the outer periphery to the inner periphery of the case inner surface 42N of the valve body support portion 42. The groove portions 431 are formed at equal intervals in the circumferential direction of the valve body support portion 42. Therefore, when the insulating member 3 is pushed toward the valve body 41 by the gas GS in the battery case 1, part of the insulating member 3 enters the groove portion 431, and wavy folds are formed in the insulating member 3 covering the safety valve 4, as shown in FIGS. 2 and 6.

[0024] In this case, gaps are likely to occur between the insulating member 3 and the recessed groove portion 431, and between the insulating member 3 and the case inner surface 42N of the valve body support portion 42. This makes it even easier to form gas flow paths 44 through which the gas GS inside the battery case 1 flows toward the valve body 41 side. As a result, as shown in FIG. 2 , the gas GS supplied from the gas flow paths 44 toward the valve body 41 side cleaves the V-shaped groove 412 of the valve body 41, opening the valve body 41. Then, the gas GS can be released to the outside of the battery case 1 from the safety valve 4 with the valve body 41 opened.

[0025] The valve element support portion 42 is preferably a resin valve element support portion 42J made of a thermoplastic resin material. The valve element 41 is joined to the resin valve element support portion 42J by insert molding. The resin valve element support portion 42J can be made of, for example, polyphenylene sulfide (PPS) resin. In this case, when the gas temperature rises above a predetermined value before the gas pressure rises above a predetermined value, the joint portion of the resin valve element support portion 42J with the valve element 41 softens or melts, and as shown in FIG. 3, the outer periphery 411 of the valve element 41 can be separated from the resin valve element support portion 42J before the V-groove 412 of the valve element 41 ruptures. Therefore, even if the gas pressure rises slowly and the amount of gas GS supplied from the gas flow path 44 to the valve element 41 side is small, the valve element 41 can be stably opened.

[0026] 4, the resin valve element support portion 42J may be formed from resin materials with different melting points. For example, the resin valve element support portion 42J may be formed by laminating a first resin material 42J1 having a high melting point that bonds with the valve element 41 and the annular member 112, and a second resin material 42J2 having a lower melting point than the first resin material 42J1 and sandwiched between the first resin material 42J1. For example, the first resin material 42J1 may be formed from polyphenylene sulfide (PPS) resin having a melting point of about 290°C, and the second resin material 42J2 may be formed from polypropylene (PP) resin having a melting point of about 170°C.

[0027] In this case, when the gas temperature rises to the melting point or softening temperature of the second resin material 42J2, the outer circumferential portion 411 of the valve element 41 can be separated from the resin valve element support portion 42J, as shown in Fig. 4. Therefore, even if the amount of gas GS supplied from the gas flow path 44 to the valve element 41 side is small, the valve element 41 can be stably opened at a lower temperature.

[0028] In the present secondary battery 10, the valve body 41 is preferably formed of a material having a tensile strength lower than that of the battery case 1, and the valve body support portion 42 is preferably connected to the battery case 1 via an annular member 112 made of the same material as the battery case 1. The valve body 41 may be made of, for example, annealed aluminum (tensile strength: 70 to 100 N / mm 2 The battery case 1 and the annular member 112 are made of, for example, austenitic stainless steel (tensile strength: 590 N / mm 2 It can be formed to a degree.

[0029] In this case, the pressure resistance performance of the battery case 1 against the gas GS is improved, and even if the amount of gas GS supplied to the valve body 41 from the gas flow path 44 formed between the insulating member 3 and the valve body support portion 42 is small when the gas pressure rises, the valve body 41, which has a low tensile strength, can be stably opened.

[0030] In a lithium ion secondary battery, which is an example of the secondary battery 10, the current collector foil 211 of the cathode body 21 is made of, for example, aluminum foil, and the active material applied thereto is, for example, lithium transition metal oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 The current collector foil 221 of the negative electrode body 22 may be made of, for example, copper foil, and the active material coated thereon may be, for example, graphite, hard carbon, soft carbon, or the like. The separator 23 may be made of, for example, a porous sheet of polypropylene resin or polyethylene resin. The electrolyte 7 may be a known non-aqueous electrolyte. The positive electrode current collector terminal 5A is made of, for example, aluminum, and the negative electrode current collector terminal 5B is made of, for example, copper.

[0031] The secondary battery 10 can be manufactured by the following procedure: The electrode body 2 surrounded by the insulating member 3 is housed in the case body 11 of the battery case 1, the current collecting foils 211, 221 of the electrode body 2 are connected to the current collecting terminals 5 (5A, 5B) fixed to the lid 12, and the opening 114 of the case body 11 is sealed with the lid 12 to assemble the battery. After that, the electrolyte 7 is poured in, and initial charging, aging, etc. are performed to manufacture the battery.

[0032] <Modification> The above-described embodiment is merely illustrative and does not limit the present disclosure. Therefore, various improvements and modifications are possible within the spirit and scope of the present disclosure. FIG. 7 shows a perspective view of a safety valve and an annular member joined to a valve body support portion of the safety valve in a first modification of the secondary battery shown in FIG. 1 , viewed from the inside of the case. FIG. 8 shows a perspective view of a safety valve and an annular member joined to a valve body support portion of the safety valve in a second modification of the secondary battery shown in FIG. 1 , viewed from the inside of the case. FIG. 9 is an enlarged cross-sectional view of portion A in a third modification of the secondary battery shown in FIG. 1 , illustrating the state when the valve body is open.

[0033] In the present secondary battery 10, as shown in Figures 2 to 5, the gas flow path forming portion 43 formed on the case inner surface 42N of the valve body support portion 42 is a recessed groove portion 431 formed continuously, bending in an L-shape in the vertical direction (Z direction) and radial direction from the outer periphery to the inner periphery of the case inner surface 42N of the valve body support portion 42, but this does not necessarily have to be limited to this.

[0034] For example, as in a secondary battery 10B of a first modified example shown in FIG. 7 , the gas flow path forming portion 43B formed in the valve element support portion 42B of the safety valve 4B may be a groove portion 431B formed linearly in the vertical direction (Z direction) only on the inner circumferential side of the case inner surface 42N of the valve element support portion 42B. Even in this case, when the insulating member 3 is pushed toward the valve element 41 by the gas GS inside the battery case 1, a part of the insulating member 3 enters the groove portion 431B, forming a wavy fold in the insulating member 3 covering the safety valve 4. Gaps are likely to form between the insulating member 3 and the groove portion 431B and between the insulating member 3 and the case inner surface 42N of the valve element support portion 42, and a gas flow path 44 through which the gas GS inside the battery case 1 flows toward the valve element 41 may be formed.

[0035] Furthermore, as in a secondary battery 10C of a second modified example shown in FIG. 8 , the gas flow path forming portion 43C formed on the case inner surface 42N of the valve element support portion 42C of the safety valve 4C may be a convex portion 431C formed on the case inner surface 42N of the valve element support portion 42C. The convex portion 431C protrudes downward in the vertical direction (Z direction). Even in this case, when the insulating member 3 is pushed toward the valve element 41 by the gas GS in the battery case 1, a portion of the insulating member 3 is pressed downward by the convex portion 431C, forming a wavy fold in the insulating member 3 covering the safety valve 4. As a result, gaps are likely to form between the insulating member 3 and the convex portion 431C and between the insulating member 3 and the case inner surface 42N of the valve element support portion 42. A gas flow path 44 through which the gas GS in the battery case 1 flows toward the valve element 41 may be formed through the gap. Note that although the convex portion 431C is formed in a hemispherical shape in FIG. 8 , it may also be formed in a rectangular cylindrical or triangular pyramidal shape, for example. Furthermore, the gas flow path forming portion 43C formed on the case inner surface 42N of the valve element support portion 42C may include both the recessed groove portion 431 and the protruding portion 431C.

[0036] Furthermore, in the present secondary battery 10, the annular member 112 of the battery case 1 is connected to the outer periphery of the valve element support portion 42 of the safety valve 4, but this is not necessarily limited to this. For example, as in a secondary battery 10D of a third modified example shown in FIG. 9 , the outer periphery of the valve element support portion 42D of the safety valve 4D may be directly connected to the battery case 1 (case body 11). The gas flow path forming portion 43D formed on the case inner surface 42N of the valve element support portion 42D may include a recessed groove portion 431D formed on the case inner surface 42N of the valve element support portion 42D. Even in this case, when the insulating member 3 is pushed toward the valve element 41D by the gas GS in the battery case 1, a part of the insulating member 3 enters the recessed groove portion 431D, and a wavy fold is formed in the insulating member 3 covering the safety valve 4. As a result, gaps are likely to form between the insulating member 3 and the recessed groove portion 431D, and between the insulating member 3 and the case inner surface 42N of the valve body support portion 42D, and a gas flow path 44D may be formed through the gap, through which the gas GS inside the battery case 1 flows toward the valve body 41D. The valve body support portion 42D is a resin valve body support portion 42DJ made of a thermoplastic resin material, and the battery case 1 (case body 11) and the outer periphery 411D of the valve body 41D are joined to the resin valve body support portion 42DJ by insert molding. [Explanation of symbols]

[0037] 1 Battery case 2 Electrode body 3. Insulating materials 4, 4B, 4C, 4D Safety valve 5, 5A, 5B current collector terminal 10, 10B, 10C, 10D secondary battery 41, 41D Valve body 42, 42B, 42C, 42D Valve support part 42N Case interior 42J, 42DJ Resin valve body support part 43, 43B, 43C, 43D Gas flow path forming section 44, 44D Gas flow path 112 Annular member 411, 411D outer periphery 431, 431B, 431D Concave groove part 431C convex part GS Gas

Claims

1. A battery case and an electrode assembly hermetically housed in the battery case; an insulating member interposed between the battery case and the electrode body; a safety valve provided in the battery case at a position facing the insulating member so as to be able to release gas to the outside of the battery case when the gas pressure or gas temperature inside the battery case has risen to or exceeds a predetermined value, the safety valve includes an openable valve body and a valve body support portion that annularly supports an outer periphery of the valve body and is connected to the battery case; A gas flow path forming portion is provided on the inner surface of the case located inward of the valve body of the valve body support portion, between the insulating member pushed out toward the valve body side by the gas and the valve body support portion, to form a gas flow path communicating with the valve body side. Secondary battery.

2. 2. The secondary battery according to claim 1, The gas flow path forming portion includes a recessed groove portion formed on the inner surface of the case of the valve body support portion. Secondary battery.

3. 2. The secondary battery according to claim 1, The gas flow path forming portion has a protrusion formed on the inner surface of the case of the valve body support portion. Secondary battery.

4. 2. The secondary battery according to claim 1, The valve body support portion is a resin valve body support portion formed from a thermoplastic resin material. Secondary battery.

5. The secondary battery according to any one of claims 1 to 4, the valve body is formed of a material having a tensile strength lower than that of the battery case, The valve body support portion is connected to the battery case via an annular member made of the same material as the battery case. Secondary battery.

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