Secondary battery and secondary battery module

Abstract

The present invention provides a secondary battery and a secondary battery module having excellent welding strength between an opening part of an outer can and a lid member.　The secondary battery according to an embodiment has the outer can with a bottom wall, a side wall, and the opening part, an electrode group housed in the outer can, and the lid member fixed to the opening part of the outer can by a welded part. In a cross section taken along the housing direction of the electrode group, the welded part has a first connection part that connects, on the inside of the outer can, the side wall to a bottom face of the lid member. The first connection part is recessed toward the outer can exterior of the welded part.

Description

Secondary Battery and Secondary Battery Module

[0001] Embodiments of the present invention relate to a secondary battery and a secondary battery module.

[0002] In recent years, secondary batteries such as lead-acid batteries and nickel-metal hydride batteries have been used as power sources represented by electric vehicles, hybrid vehicles, electric motorcycles, and forklifts. Recently, development towards the adoption of lithium-ion secondary batteries with high energy density has been actively carried out, and development has been carried out while considering long life, safety, etc.

[0003] As one form of a general lithium-ion secondary battery (hereinafter referred to as a secondary battery), there is a secondary battery including an exterior can having an opening, an electrode group housed in the exterior can, and a lid member disposed at the opening of the exterior can, and the opening of the exterior can and the lid member are welded in a closely attached state. In such a secondary battery, an acute boundary portion may occur on the outside of the exterior can at the welded portion. Also, when gas is generated from the electrode group during charge and discharge, the generated gas accumulates inside the secondary battery, and the pressure inside the secondary battery increases. Then, when such an acute boundary portion is present, the welding strength of this welded portion may decrease.

[0004] Japanese Patent Application Laid-Open No. 2006-324160, Japanese Patent Application Laid-Open No. 2013-211178

[0005] The problem to be solved by the present invention is to provide a secondary battery and a secondary battery module having excellent welding strength between the opening of the exterior can and the lid member.

[0006] In order to solve the above problems, the secondary battery of the embodiment has an exterior can having a bottom wall, a side wall, and an opening, an electrode group housed in the exterior can, and a lid member fixed by a welded portion to the opening of the exterior can. The welded portion has a first connecting portion that connects the side wall inside the exterior can and the bottom surface of the lid member in a cross section along the housing direction of the electrode group. The first connecting portion is concave toward the outside of the exterior can of the welded portion.

[0007] A schematic perspective view showing a secondary battery according to the first embodiment. A partial cross-sectional view of the YZ plane along line I-I in Figure 1, including the welded portion of the secondary battery according to the first embodiment. A partial cross-sectional view in Figure 2, illustrating the angle formed by the interface between the outer casing and the side wall and the interface with the lid member. A partial cross-sectional view of the YZ plane along line I-I in Figure 1, including the welded portion of a modified example of the secondary battery 1 according to the first embodiment. A schematic perspective view showing a secondary battery module according to the second embodiment.

[0008] The secondary battery and secondary battery module of the embodiment will be described below with reference to the drawings.

[0009] (First Embodiment) The secondary battery 1 of the first embodiment will be described with reference to Figure 1. Figure 1 is a schematic perspective view showing the secondary battery 1 according to the first embodiment. As shown in Figure 1, the secondary battery 1 comprises an outer casing 3 and an electrode group 8 inside the outer casing 3. The outer casing 3 is, for example, cylindrical in shape with a bottom wall 10 and side walls 15. The outer casing 3 has an internal cavity (not shown) and an opening 9 is provided on its top surface. A lid member 7 is placed in the opening 9, and the outer casing 3 and the lid member 7 are made of a metal such as aluminum, aluminum alloy, iron, copper, or stainless steel.

[0010] The outer periphery of the opening 9 of the outer can 3 and the outer periphery of the lid member 7 are welded together around their entire circumference, and for example, a laser beam is used for this welding. Through this welding, a welded joint 37 is formed at the outer periphery of the opening 9 of the outer can 3 and the outer periphery of the lid member 7 as the outer can 3 and lid member 7 melt and solidify. The lid member 7 is fixed to the opening 9 of the outer can 3 via this welded joint 37.

[0011] A gas discharge valve 21 may be provided on the surface of the lid member 7 together with the sealing plate 19. Furthermore, for example, a pair of positive external terminals 23a and negative external terminals 23b are attached to the surface of the lid member 7, and the external terminals 23a and 23b are electrically connected to the electrode group 8, respectively. A terminal insulator 35 may be provided between the external terminals 23a and 23b and the lid member 7 to maintain insulation between them.

[0012] The welded portion 37 formed on the outer casing 3 and the lid member 7 will be described with reference to Figure 2. Figure 2 is a partial cross-sectional view of the welded portion 37 of the secondary battery 1 according to the first embodiment, in the YZ plane (a plane along the direction of housing the electrode group 8) along the line I-I in Figure 1. As shown in Figure 2, the welded portion 37 has a first connecting portion 100 that connects the side wall 15 of the outer casing 3 and the bottom surface 20 of the lid member 7 on the inside of the outer casing 3. Here, the first connecting portion 100 is concave toward the outside of the outer casing 3 of the welded portion 37.

[0013] As a result, for example, even if gas generated from the electrode group during charging and discharging of the secondary battery 1 accumulates inside the secondary battery 1 and the internal pressure of the secondary battery 1 rises, the first connecting portion 100 is concave toward the outside of the outer casing 3 of the welded portion 37, which allows the stress inside the secondary battery 1 to be distributed. Furthermore, the concave portion of the first connecting portion 100 gently connects the side wall 15 of the outer casing 3 and the bottom surface 20 of the lid member 7 in a continuous arc shape, allowing the stress inside the secondary battery 1 to be distributed over a wide area connecting the side wall 15 of the outer casing 3 and the bottom surface 20 of the lid member 7. Because the stress inside the secondary battery 1 can be distributed by the first connecting portion 100, the welding strength of the welded portion 37 between the opening of the outer casing 3 and the lid member 7 can be improved. This further suppresses the fracture of the welded portion 37 due to the rise in internal pressure of the secondary battery 1.

[0014] The welded portion 37 having the first connecting portion 100 can be formed by creating a gap between the opening 9 of the outer can 3 and the lid member 7 before welding the opening 9 of the outer can 3 to the lid member 7. The gap between the opening 9 of the outer can 3 and the lid member 7 allows the molten portions of the outer can 3 and the lid member 7 to flow into the gap and solidify during welding, connecting the side wall 15 of the outer can 3 and the bottom surface 20 of the lid member 7. Specifically, when the thickness of the side wall 15 of the outer can 3 is approximately 0.4 mm to 0.7 mm, the gap is preferably approximately 0.2 mm. The gap is approximately 0.35 to 0.5 times the thickness of the side wall 15 of the outer can 3.

[0015] Here, it is preferable that the welded portion 37 having the first connecting portion 100 be provided around the entire circumference of the lid member 7. This is because it is possible to suppress the fracture of the welded portion 37 due to the pressure rise inside the secondary battery 1 around the entire circumference of the lid member 7.

[0016] In the secondary battery 1 of this embodiment, it is sufficient if the opening 9 of the outer casing 3 and the lid member 7 are welded around the entire circumference, but the opening 9 of the outer casing 3 may be rectangular in shape with a long side 2 and a short side 4. Here, a rectangular shape does not mean that there are no corners at the four vertices of the rectangle.

[0017] When the opening 9 of the outer can 3 is rectangular, it is preferable that the welded portion 37 having the first connecting portion 100 be provided around the entire circumference of the lid member 7, but it may also be provided on at least one of the side walls 15 on the short side 4 side of the outer can 3. This is because, when welding the opening 9 of the outer can 3 and the lid member 7, the side walls 15 on the long side 2 side of the outer can 3 may be fixed with a jig from both sides (X direction) for ease of welding, and in that case, a gap is easily created between the short side 4 of the opening 9 of the outer can 3 and the lid member 7.

[0018] Furthermore, from the viewpoint of strength, the side wall 15 of the outer can 3 may be formed thicker on the side wall 15 on the short side 4 than on the side wall 15 on the long side 2. As a result, the side wall 15 on the short side 4 of the outer can 3 may be more difficult to weld to the lid member 7 than the side wall 15 on the long side 2 of the outer can 3. For this reason, it is preferable to provide a welded portion 37 having a first connecting portion 100 on the side wall 15 on the short side 4 of the outer can 3 to increase the welding strength.

[0019] The welded portion 37 of this embodiment will be further described with reference to Figure 3. Figure 3 is a partial cross-sectional view illustrating the angle formed by the interface between the side wall 15 of the outer can 3 and the interface with the lid member 7 in the partial cross-sectional view of Figure 2. As shown in the welded portion 37 of Figure 3, the welded portion 37 has a first interface 11 with the side wall 15 of the outer can 3 and a second interface 12 with the lid member 7. In the welded portion 37, there is a first virtual boundary line 110 connecting the outer end 30 and the inner end 32 of the outer can at the first interface 11, and a second virtual boundary line 120 connecting the outer end 70 and the inner end 72 of the lid member at the second interface 12. The angle R formed by the first virtual boundary line 110 and the second virtual boundary line 120 is preferably 90° or less.

[0020] Here, the first interface 11 and the second interface 12 are defined by cross-sectional observation through a destructive test of the welded joint 37. The procedure for cross-sectional observation through a destructive test of the welded joint 37 is described below. First, the outer can 3 is cut in the XY plane, dividing it into a portion including the lid member 7 which is on the upper side in the Z direction and a portion not including the lid member 7 which is on the lower side in the Z direction. Next, the portion including the lid member 7 which is on the upper side in the Z direction is further cut in the XZ plane around the outer terminal 23a to divide it into the portion around the outer terminal 23a including the observation area, and is embedded in resin. With the portion embedded in resin, the center of the outer terminal 23a, which is the observation area, is further cut in the YZ plane. The resulting cut surface is polished, and after polishing, it is etched using an etching solution to obtain a sample for cross-sectional observation. The obtained sample is observed with an optical microscope, and the portion having a different shading from the outer can 3 and lid member 7 is defined as the welded portion 37. The boundary between the outer can 3 and the welded portion 37 is defined as the first interface 11, and the boundary between the lid member 7 and the welded portion 37 is defined as the second interface 12.

[0021] Here, the reason why the density of the welded portion 37 differs from that of the outer can 3 and the lid member 7 is that the welded portion 37 is formed when the outer can 3 and the lid member 7 melt and solidify, and the crystallinity of the welded portion 37 differs from that of the outer can 3 and the lid member 7.

[0022] Furthermore, the outer end 30 of the outer can is the outermost part of the outer can 3 at the first interface 11, and the inner end 32 of the outer can is the innermost part of the outer can 3 at the first interface 11. Also, the outer end 70 of the lid member is the outermost part of the lid member 7 at the second interface 12, and the inner end 72 of the lid member is the innermost part of the lid member 7 at the second interface 12.

[0023] In the welded joint 37, the angle R formed by the first virtual boundary line 110 and the second virtual boundary line 120 is preferably 90° or less. Here, the angle R is defined as the angle formed at the intersection point where the extension of the first virtual boundary line 110 and the extension of the second virtual boundary line 120 intersect.

[0024] If stress from inside the secondary battery 1 concentrates in the welded joint 37, there is a risk that the welded joint 37 may fracture at the first virtual boundary line 110 or the second virtual boundary line 120. Therefore, it is preferable to maintain a long length for the first virtual boundary line 110 and the second virtual boundary line 120. By having an angle R of 90° or less in the welded joint 37, the lengths of the first virtual boundary line 110 and the second virtual boundary line 120 can be made long. This makes it possible to suppress fracture of the welded joint 37 from the first virtual boundary line 110 or the second virtual boundary line 120, even if stress from inside the secondary battery 1 concentrates in the welded joint 37.

[0025] Furthermore, the welded portion 37 of this embodiment has a second connecting portion 200 that connects the side wall 15 of the outer can 3 and the upper surface 25 of the lid member 7 on the outside of the outer can 3. Here, the second connecting portion 200 is convex toward the outside of the outer can 3 of the welded portion 37, but more preferably it is concave toward the inside of the outer can 3 of the welded portion 37.

[0026] The effect of the second connecting portion 200 of the welded portion 37 being concave toward the inside of the outer casing 3 of the welded portion 37 will be explained by comparing Figures 2 and 4. Figure 4 is a modified example (welded portion 37') of the welded portion 37 of the secondary battery 1 according to the first embodiment, and is a partial cross-sectional view of the YZ plane (plane along the direction of housing the electrode group 8) along the line I-I in Figure 1. In the welded portion 37' in Figure 4, the second connecting portion 200' of the welded portion 37' is concave toward the inside of the outer casing 3 of the welded portion 37'.

[0027] In Figure 4, the welded portion 37' has a first connecting portion 100. Since the first connecting portion 100 is concave toward the outside of the outer casing 3 of the welded portion 37, the stress inside the secondary battery 1 is distributed by the first connecting portion 100, thereby suppressing fracture of the welded portion 37' due to pressure rise inside the secondary battery 1 and preventing damage to the secondary battery 1. Furthermore, since the second connecting portion 200' of the welded portion 37' is concave toward the inside of the outer casing 3 of the welded portion 37', the possibility of the welded portion 37' protruding above the upper surface 25 of the lid member 7 is reduced. Therefore, for example, when designing a secondary battery module by combining multiple secondary batteries 1, the design becomes easier. When designing a secondary battery module by combining multiple secondary batteries 1, the secondary batteries 1 may be connected to each other with connecting members, and it is preferable to keep the maximum height of the secondary batteries 1 in the Z direction constant. Therefore, by preventing the welded portion 37' from protruding above the upper surface 25 of the lid member 7, the maximum height of the secondary battery 1 in the Z direction can be kept constant, and the connection of secondary batteries 1 to each other becomes easier.

[0028] Furthermore, when designing a secondary battery module by combining multiple secondary batteries 1, the secondary batteries 1 may be connected to each other with connecting members. In this case, by ensuring that the welded portion 37' does not protrude above the upper surface 25 of the lid member 7, a sufficient insulating distance can be maintained between the connecting member and the welded portion 37', thereby suppressing short circuits between the connecting member and the welded portion 37'.

[0029] Furthermore, in the welded portion 37' shown in Figure 4, the second connecting portion 200' of the welded portion 37' is concave toward the inside of the outer can 3 of the welded portion 37'. Therefore, the length of the first virtual boundary line 110 connecting the outer end 30 and the inner end 32 of the outer can at the first interface 11 can be increased, and the strength of the welded portion 37' can be sufficiently maintained. If stress from inside the secondary battery 1 concentrates in the welded portion 37', there is a risk that the welded portion 37' may break at the first virtual boundary line 110 or the second virtual boundary line 120, so it is preferable to form the first virtual boundary line 110 and the second virtual boundary line 120 to be long.

[0030] Furthermore, in the welded portions 37 and 37' of this embodiment, it is preferable that the shortest distance S between the first connecting portion 100 and the second connecting portion 200 is longer than the thickness T of the side wall 15 of the outer casing 3. This also allows the strength of the welded portions 37 and 37' to be maintained more sufficiently, and prevents fracture of the welded portions 37 and 37' due to pressure rise inside the secondary battery 1.

[0031] According to the secondary battery 1 of at least one embodiment described above, the welded portion 37 has a first connecting portion 100 that connects the side wall 15 of the outer casing 3 and the bottom surface 20 of the lid member 7 on the inside of the outer casing 3, and the first connecting portion 100 is concave toward the outside of the outer casing 3 of the welded portion 37. As a result, for example, even if gas generated from the electrode group 8 during charging and discharging of the secondary battery 1 accumulates inside the secondary battery 1 and the internal pressure of the secondary battery 1 rises, the first connecting portion 100 being concave toward the outside of the outer casing 3 of the welded portion 37 allows the stress inside the secondary battery 1 to be distributed. Furthermore, because the first connecting portion 100 loosely connects the side wall 15 of the outer casing 3 and the bottom surface 20 of the lid member 7, the stress inside the secondary battery 1 can be distributed over a wide area connecting the side wall 15 of the outer casing 3 and the bottom surface 20 of the lid member 7. The first connecting portion 100 can distribute stress inside the secondary battery 1, thereby suppressing fracture of the welded portion 37 due to pressure rise inside the secondary battery 1 and preventing damage to the secondary battery 1. Therefore, a secondary battery 1 with excellent weld strength between the opening of the outer casing and the lid member can be provided.

[0032] (Second Embodiment) The secondary battery module 50 of the second embodiment will be described with reference to Figure 5. Figure 5 is a schematic perspective view showing the secondary battery module 50 according to the second embodiment. The secondary battery module 50 of the second embodiment is equipped with a plurality of secondary batteries 1 of the first embodiment. The secondary battery module 50 is equipped with connecting members 52 such as busbars for electrically connecting external terminals 23a and 23b. The connection of the secondary batteries 1 is not limited to series, but can also be in parallel. In addition, the secondary batteries 1 of the first embodiment may be connected, or the secondary batteries 1 may be connected to other secondary batteries different from the secondary batteries 1.

[0033] The secondary battery module 50 of this embodiment is equipped with the secondary battery 1 of the first embodiment. Therefore, even if gas generated from the electrode group 8 during charging and discharging of the secondary battery 1 accumulates inside the secondary battery 1 and the internal pressure of the secondary battery 1 rises, the first connecting portion 100 is concave toward the outside of the outer casing 3 of the welded portion 37, which allows the stress inside the secondary battery 1 to be distributed. Because the stress inside the secondary battery 1 can be distributed by the first connecting portion 100, fracture of the welded portion 37 due to the rise in internal pressure of the secondary battery 1 can be suppressed, and damage to the secondary battery 1 can be prevented. Thus, a secondary battery module 50 equipped with a secondary battery 1 with excellent welding strength between the opening of the outer casing and the lid member can be provided.

[0034] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents.

[0035] (Examples) Examples are described below, but the present invention is not limited to the examples listed below, unless it exceeds the spirit of the present invention.

[0036] [Confirmation of the pressure resistance effect of the welded joint 37] The pressure resistance effect of the welded joint 37 in this embodiment was verified by a pressure resistance test. The welded joint 37 was formed by welding the opening 9 of the outer can 3 and the lid member 7 around the entire circumference to create the secondary battery 1. Then, a liquid injection hole was formed in the secondary battery 1, and water was injected into the inside of the secondary battery 1 from the liquid injection hole. The welded joint 37 was observed in cross-section when the internal pressure of the secondary battery 1 reached 1.0 MPa. The method of cross-sectional observation was the same as the cross-sectional observation procedure using the destructive test described above.

[0037] Examples 1 to 6, Comparative Example 1, and Comparative Example 2 are shown below.

[0038] (Example 1) The first connecting portion 100 was formed in a concave shape toward the outside of the outer can 3 of the welded portion 37, and the angle R at the welded portion 37 was set to 60°. Also, the second connecting portion 200 was formed in a convex shape toward the inside of the outer can 3 of the welded portion 37. Further, the welded portion 37 was formed such that the shortest distance S between the first connecting portion 100 and the second connecting portion 200 was longer than the thickness T of the side wall 15 of the outer can 3.

[0039] (Example 2) The angle R at the welded portion 37 was set to 30°. Other conditions were the same as in Example 1.

[0040] (Example 3) The angle R at the welded portion 37 was set to 90°. Other conditions were the same as in Example 1.

[0041] (Example 4) The angle R at the welded portion 37 was set to 120°. Other conditions were the same as in Example 1.

[0042] (Example 5) The second connecting portion 200 was formed in a concave shape toward the inside of the outer can 3 of the welded portion 37. Other conditions were the same as in Example 1.

[0043] (Example 6) The welded portion 37 was formed such that the shortest distance S between the first connecting portion 100 and the second connecting portion 200 was shorter than the thickness T of the side wall 15 of the outer can 3. Other conditions were the same as in Example 1.

[0044] (Comparative Example 1) The first connecting portion 100 was not formed, and the angle R at the welded portion 37 was set to 60°. Other conditions were the same as in Example 1.

[0045] (Comparative Example 2) The first connecting portion 100 was not formed, and the second connecting portion 200 was formed in a concave shape toward the inside of the outer can 3 of the welded portion 37. Other conditions were the same as in Comparative Example 1.

[0046]

[0047] Table 1 shows the cross-sectional states of the welded part 37 in each example and each comparative example. Here, "◎" indicates that no cracks or fractures were observed in the welded part 37, and "〇" indicates that minute cracks were observed in the welded part 37. Further, "△" indicates that although the welded part 37 did not reach the point of cracking, cracks were observed in the welded part 37.

[0048] As shown in Table 1, the examples and the comparative examples are compared. Then, by forming the first connecting part 100 of the welded part 37 and forming the first connecting part 100 in a concave shape toward the outside of the outer can 3 of the welded part 37, even when the pressure inside the secondary battery 1 increases, it has been verified that the stress inside the secondary battery 1 can be dispersed by the first connecting part 100 and the breakage of the welded part 37 can be suppressed.

[0049] Also, by comparing Example 1 to Example 4, it has been verified that the angle R of the welded part 37 is preferably 90° or less. By having the angle R in the welded part 37 be 90° or less, the lengths of the first virtual boundary line 110 and the second virtual boundary line 120 in the welded part 37 can be made longer. Thereby, it has been verified that even when the stress inside the secondary battery 1 concentrates in the welded part 37, the breakage of the welded part 37 from the first virtual boundary line 110 or the second virtual boundary line 120 can be suppressed.

[0050] Furthermore, by comparing Example 1 and Example 6, it has been verified that the shortest distance S between the first connecting part 100 and the second connecting part 200 is preferably longer than the thickness T of the side wall 15 of the outer can 3. Thereby, it has been verified that the strength of the welded part 37 can be maintained more sufficiently and the breakage of the welded part 37 due to the increase in pressure inside the secondary battery 1 can be suppressed.

[0051] The results of the above pressure resistance test are used in the secondary battery 1 of this embodiment. Specifically, the welded portion 37 has a first connecting portion 100 that connects the side wall 15 of the outer casing 3 and the bottom surface 20 of the lid member 7 on the inside of the outer casing 3. Furthermore, the first connecting portion 100 is concave toward the outside of the outer casing 3 of the welded portion 37. As a result, for example, even if gas generated from the electrode group 8 accumulates inside the secondary battery 1 due to charging and discharging of the secondary battery 1, and the pressure inside the secondary battery 1 rises, the first connecting portion 100 being concave toward the outside of the outer casing 3 of the welded portion 37 allows the stress inside the secondary battery 1 to be distributed. In addition, because the first connecting portion 100 loosely connects the side wall 15 of the outer casing 3 and the bottom surface 20 of the lid member 7, the stress inside the secondary battery 1 can be distributed over a wide area connecting the side wall 15 of the outer casing 3 and the bottom surface 20 of the lid member 7. The first connecting portion 100 can distribute stress inside the secondary battery 1, thereby suppressing fracture of the welded portion 37 due to pressure rise inside the secondary battery 1 and preventing damage to the secondary battery 1. Therefore, a secondary battery 1 with excellent weld strength between the opening of the outer casing and the lid member can be provided.

[0052] 1...Secondary battery, 2...Long side, 3...Outer casing, 4...Short side, 7...Lid member, 8...Electrode group, 9...Opening, 10...Bottom wall, 11...First interface, 12...Second interface, 15...Side wall, 19...Sealing plate, 20...Bottom surface, 21...Gas discharge valve, 23...External terminal, 23a...Positive electrode external terminal, 23b...Negative electrode external terminal, 25...Top surface, 30...Outer end of outer casing, 32...Inner end of outer casing, 35...Terminal insulator, 37...Welded part, 50...Secondary battery module, 52...Connecting member, 70...Outer end of lid member, 72...Inner end of lid member, 100...First connecting part, 110...First virtual boundary line, 120...Second virtual boundary line, 200...Second connecting part.

Claims

1. A secondary battery comprising: an outer casing having a bottom wall, side walls and an opening; a group of electrodes housed in the outer casing; and a lid member fixed to the opening of the outer casing by a weld, wherein the weld has a first connecting portion in a cross section along the direction in which the electrode group is housed, connecting the side wall and the bottom surface of the lid member on the inside of the outer casing, and the first connecting portion is concave toward the outside of the outer casing.

2. The secondary battery according to claim 1, wherein the opening is rectangular in shape with a long side and a short side, and the first connecting portion of the welded part is located on at least one of the side walls on the short side of the outer casing.

3. The secondary battery according to claim 1, wherein the welded portion has, in a cross-section along the direction of housing the electrode group, a first interface with the side wall of the outer can and a second interface with the lid member, and the angle formed by a first virtual boundary line connecting the outer end and inner end of the outer can of the first interface and a second virtual boundary line connecting the outer end and inner end of the lid member of the second interface is 90° or less.

4. The secondary battery according to claim 1, wherein the welded portion has a second connecting portion in a cross section along the housing direction of the electrode group, which connects the side wall and the upper surface of the lid member on the outside of the outer casing, and the second connecting portion is concave toward the inside of the outer casing of the welded portion.

5. The secondary battery according to claim 1, wherein the welded portion has a cross section along the housing direction of the electrode group, and has a second connecting portion that connects the side wall and the upper surface of the lid member on the outside of the outer casing, and the shortest distance between the first connecting portion and the second connecting portion is longer than the thickness of the side wall of the outer casing.

6. A secondary battery module comprising: a secondary battery according to claim 1; an external terminal provided on the secondary battery; and a connecting member electrically connected to the external terminal.

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