Secondary battery

Abstract

According to one embodiment, a secondary battery includes: an exterior case having an opening; an electrode group accommodated in the exterior case and including a positive electrode and a negative electrode; a lid member disposed in the opening and having a through-hole; an external terminal disposed on the lid member and having a shaft portion disposed in the through-hole; and an insulating member disposed between an inner wall of the through-hole and the shaft portion of the external terminal. The lid member has a first surface facing the electrode group and a second surface facing the first surface. At least one protrusion and at least one recess are provided on at least one of the first surface and the second surface.

Description

secondary battery

[0001] FIELD An embodiment of the present invention relates to a secondary battery.

[0002] In recent years, secondary batteries such as lead-acid batteries and nickel-metal hydride batteries have been used as power sources for electric vehicles, hybrid vehicles, electric motorcycles, forklifts, etc. Recently, there has been active development toward the adoption of lithium-ion secondary batteries, which have high energy density, and development is being carried out while taking into consideration factors such as long life and safety.

[0003] For example, a lithium-ion secondary battery (hereinafter referred to as a "secondary battery") is manufactured by housing an electrode group in an exterior case and welding the opening of the exterior case to a lid member. The opening of the exterior case and the lid member are welded together by laser welding, resistance welding, or the like. In laser welding, which is one example of a welding method, a laser beam is irradiated onto the opening of the exterior case and the outer peripheral edge of the lid member and allowed to proceed, whereby the opening of the exterior case and the outer peripheral edge of the lid member are melted by the heat of the laser beam, and the melted portion solidifies, joining the exterior case and the lid member.

[0004] In this type of secondary battery, a pair of external terminals is disposed on the lid member. To ensure insulation between the lid member and the external terminals, an insulating member may be disposed between the lid member and the external terminals. If the lid member is welded to the opening of the outer case, the welding heat generated during welding between the lid member and the opening of the outer case may be transferred to the insulating member through the lid member. This may damage the insulating member, deteriorating the adhesion between the external terminals and the insulating member and reducing the airtightness of the secondary battery.

[0005] JP 2015-99681 A Japanese Patent No. 6171943 A

[0006] The problem to be solved by the present invention is to provide a secondary battery that ensures airtightness at the external terminal portion.

[0007] To achieve the above object, a secondary battery according to an embodiment includes an outer case having an opening, an electrode group including a positive electrode and a negative electrode housed in the outer case, a lid member disposed in the opening and having a through hole, an external terminal having a shaft portion disposed in the through hole and disposed in the lid member, and an insulating member disposed between an inner wall of the through hole and the shaft portion of the external terminal. The lid member has a first surface facing the electrode group and a second surface facing the first surface, and at least one of the first surface and the second surface is provided with at least one protrusion and at least one recess.

[0008] FIG. 1 is a perspective view schematically illustrating a secondary battery according to a first embodiment. FIG. 2 is an exploded perspective view schematically illustrating the secondary battery according to the first embodiment in a disassembled state, with each component disassembled. FIG. 3 is a cross-sectional view in the Z direction taken along line II in FIG. 1 of the terminal structure of the secondary battery according to the first embodiment. FIG. 4 is a cross-sectional view in the Z direction taken along line II in FIG. 1 of a modified terminal structure of the secondary battery according to the first embodiment. FIG. 5 is a cross-sectional view in the Z direction taken along line II in FIG. 1 of another modified terminal structure of the secondary battery according to the first embodiment. FIG. 6 is a plan view of a first surface of a lid member used in the secondary battery according to the first embodiment. FIG. 7 is an enlarged view of the first surface of the lid member of FIG. 6 used in the secondary battery according to the first embodiment. FIG. 8 is a plan view of the first surface of a first modified lid member used in the secondary battery according to the first embodiment. FIG. 9 is an enlarged view of the first surface of a first modified lid member used in the secondary battery according to the first embodiment. FIG. 10 is a plan view of the first surface of a second modified lid member used in the secondary battery according to the first embodiment. FIG. 11 is a diagram showing the maximum temperature reduction rate of the insulating member in each example and each comparative example.

[0009] Hereinafter, a secondary battery according to an embodiment of the present invention will be described with reference to the drawings. The disclosure is merely an example, and appropriate modifications that are easily conceivable by those skilled in the art while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, in order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and are not intended to limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings are given the same reference numerals, and detailed descriptions may be appropriately simplified or omitted.

[0010] First Embodiment A secondary battery 1 according to a first embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view schematically illustrating the secondary battery 1 according to the first embodiment, and FIG. 2 is an exploded perspective view schematically illustrating the secondary battery 1 according to the first embodiment, disassembled into individual components. As shown in FIGS. 1 and 2, the secondary battery 1 includes an outer case 3 and an electrode group 5. The outer case 3 is, for example, cylindrical, having side walls and a bottom wall. The outer case 3 has an internal cavity and an opening 9 on its top surface. A lid member 7 is disposed in the opening 9, for example. The outer case 3 and the lid member 7 are formed of a metal such as aluminum, an aluminum alloy, iron, copper, or stainless steel. In this embodiment, the lid member 7 is rectangular, having long sides 90 and short sides 92, but the shape is not limited thereto. The rectangular shape may also include curved corners. The secondary battery 1 may include the outer case 3 and the electrode group 5; however, the bottom wall and the opening 9 are not limited to being rectangular, and the outer case 3 is not limited to being cylindrical.

[0011] The electrode group 5 is housed in the internal cavity of the exterior case 3. The electrode group 5 is manufactured, for example, by sandwiching a separator (not shown) between the positive electrode 13 and the negative electrode 15, winding them around an axis, and then pressure-molding the entire assembly into a flat shape. The positive electrode 13 has a positive electrode current collector 13a and a positive electrode active material support portion (not shown) supported on one or both sides of the positive electrode current collector 13a. The positive electrode current collector 13a has a positive electrode current collector tab 70a as an uncoated portion of the positive electrode active material support portion. Meanwhile, the negative electrode 15 has a negative electrode current collector 15a and a negative electrode active material support portion (not shown) supported on one or both sides of the negative electrode current collector 15a. The negative electrode current collector 15a has a negative electrode current collector tab 70b as an uncoated portion of the negative electrode active material support portion. The electrode group 5 may have a stack structure in which a plurality of positive electrodes 13 and a plurality of negative electrodes 15 are alternately stacked, with a separator provided between the positive electrodes 13 and the negative electrodes 15. When using an electrode group 5 with a stack structure, the connection structure with the outer case 3 is changed as appropriate. Furthermore, the electrode group 5 is not limited to a wound structure or a stack structure.

[0012] In this embodiment, the electrode group 5 is a wound body, and multiple layers of positive electrode current collector tabs 70a and negative electrode current collector tabs 70b are provided at at least one end of the electrode group 5. In this embodiment, the positive electrode current collector tabs 70a and negative electrode current collector tabs 70b are provided at both ends of the electrode group 5. The positive electrode current collector tabs 70a protrude in the opposite direction to the protruding direction of the negative electrode current collector tabs 70b. The multiple layers of positive electrode current collector tabs 70a and negative electrode current collector tabs 70b are preferably integrated by bundling them with a metal member 16. The protruding directions of the positive electrode current collector tabs 70a and negative electrode current collector tabs 70b are not limited to these. For example, both current collector tabs 70 may protrude in the same direction, and the current collector tab 70 may be provided at one end of the electrode group 5.

[0013] The positive electrode 13 is produced by applying a slurry containing a positive electrode active material to a positive electrode current collector 13a made of aluminum foil, aluminum alloy foil, or the like. Examples of the positive electrode active material include, but are not limited to, oxides, sulfides, and polymers thereof that can occlude and release lithium ions. Preferred positive electrode active materials include lithium manganese composite oxide, lithium nickel composite oxide, lithium cobalt composite oxide, and lithium iron phosphate.

[0014] The negative electrode 15 is produced by applying a slurry containing a negative electrode active material to a negative electrode current collector 15a made of aluminum foil, aluminum alloy foil, copper foil, or the like. Examples of the negative electrode active material include, but are not limited to, metal oxides, metal sulfides, metal nitrides, and carbon materials capable of absorbing and releasing lithium ions. Preferred negative electrode active materials include titanium oxide, lithium titanium oxide, niobium titanium oxide, niobium oxide, tungsten oxide, amorphous tin oxide, tin silicon oxide, silicon oxide, and silicon.

[0015] Inside the exterior case 3, the electrode group 5 is impregnated with an electrolyte solution (not shown). The electrolyte solution is poured, for example, through a liquid filling port 17 provided in the lid member 7. After the electrolyte solution is poured, the liquid filling port 17 is closed with a sealing plate 19. The electrolyte solution used is a non-aqueous electrolyte solution prepared by dissolving an electrolyte (e.g., a lithium salt) in a non-aqueous solvent. The non-aqueous solvent may be used alone or in combination of two or more types.

[0016] A liquid inlet 17 and a gas exhaust valve 21 are formed on the surface of the lid member 7. The liquid inlet 17 and the gas exhaust valve 21 do not necessarily have to be provided on the lid member 7. Furthermore, for example, a pair of external terminals 23 are attached to the surface of the lid member 7, and the external terminals 23 are made of a conductive material such as metal. One of the external terminals 23 is a positive electrode external terminal 23a, and the other is a negative electrode external terminal 23b.

[0017] The external terminal 23 has a head 230 and a shaft 232. The shaft 232 of the external terminal 23 is disposed in a through hole 20 provided in the cover member 7. An insulating member 29 is provided between the inner wall of the through hole 20 in the cover member 7 and the shaft 232 of the external terminal 23 to ensure insulation between the cover member 7 and the external terminal 23. The external terminal 23 is disposed in close contact with the cover member 7 via the insulating member 29. The positive electrode external terminal 23a and the negative electrode external terminal 23b are further connected to a positive electrode lead 31a and a negative electrode lead 31b, respectively.

[0018] The positive electrode lead 31a and the negative electrode lead 31b are joined to metal members 16 that bundle the positive electrode current collecting tab 70a and the negative electrode current collecting tab 70b, respectively, and the electrode group 5 is electrically connected to an external terminal 23. Furthermore, an internal insulating member 33 may be provided between the cover member 7 and the lead 31, electrically insulating the cover member 7 and the lead 31. Furthermore, the lead 31 and the current collecting tab 70 are each electrically insulated from the exterior case 3 by, for example, an insulating guard 34. The insulating guard 34 is fixed to the electrode group 5 by insulating tape 36. A terminal insulator 35 may be provided between the external terminal 23 and the cover member 7, electrically insulating the external terminal 23 and the cover member 7.

[0019] The lid member 7 used in the secondary battery 1 according to the first embodiment will be described with reference to Figures 3 to 5. Figure 3 is a cross-sectional view of the terminal structure of the secondary battery 1 according to the first embodiment, taken along line II in Figure 1 in the Z direction. Here, the surface of the lid member 7 facing the electrode group 5 is referred to as a first surface 71, and the surface facing the first surface 71 is referred to as a second surface 72.

[0020] As shown in FIG. 3 , the lid member 7 has a protrusion 80 and a recess 82 provided on the first surface 71. When the opening 9 of the outer case 3 and the outer peripheral edge of the lid member 7 are laser-welded by the protrusion 80 and the recess 82, the welding heat generated by the welding is transmitted to the insulating member 29 via the first thin portion 84 at the position where the recess 82 is formed and the thick portion 86 at the position where the protrusion 80 is formed. In other words, when the lid member 7 is provided with the protrusion 80 and the recess 82, the heat transfer path from the laser irradiation position of the welding heat applied to the lid member 7 by laser welding to the insulating member 29 is longer than the heat transfer path when the lid member 7 does not have the protrusion 80 and the recess 82. Therefore, by providing the lid member 7 with the protrusion 80 and the recess 82, it is possible to prevent the welding heat generated when the opening 9 of the outer case 3 and the lid member 7 are welded together from being transferred to the insulating member 29 provided between the lid member 7 and the external terminal 23.

[0021] Furthermore, simulation results have verified that when the first surface 71 is provided with the convex portions 80 and the concave portions 82, the transfer of welding heat to the insulating member 29 is suppressed compared to when the first surface 71 is provided with neither the convex portions 80 nor the concave portions 82, or when only the concave portions 82 are provided. The simulation results and method will be described later. This makes it possible to suppress deterioration of the adhesion between the external terminal 23 and the insulating member 29 due to damage such as deformation of the insulating member 29 caused by the welding heat, and to provide a secondary battery 1 that ensures airtightness at the external terminal portion.

[0022] The protrusions 80 and the recesses 82 may be provided on the second surface 72 of the lid member 7. Even if the protrusions 80 and the recesses 82 are provided on the second surface 72, it is possible to prevent the transfer of welding heat generated when the opening 9 of the exterior case 3 and the lid member 7 are welded together to the insulating member 29 provided between the lid member 7 and the external terminals 23. However, if the protrusions 80 are provided on the second surface 72, they may protrude outward and be damaged during handling of the secondary battery 1. To reduce the possibility of this damage, it is preferable to provide the protrusions 80 inside the secondary battery 1, i.e., on the first surface 71 where the lid member 7 faces the electrode group 5.

[0023] FIG. 4 is a cross-sectional view of a modified terminal structure of a secondary battery according to the first embodiment taken along line II in FIG. 1 in the Z direction. Preferably, the protrusion 80 and recess 82 of the lid member 7 are adjacent to each other, as shown in FIGS. 3 and 4 . After cutting out the first surface 71 of the lid member 7 to form the recess 82, the cutout portion is provided as the protrusion 80 at a position adjacent to the recess 82, thereby easily providing the protrusion 80 and recess 82 adjacent to each other. For example, the recess 82 and protrusion 80 are provided by press-molding the lid member 7. In the case of press-molding, the volume cut out by the recess 82 tends to escape to the portion of the lid member 7 adjacent to the recess 82. This allows the protrusion 80 to be easily provided adjacent to the recess 82 by utilizing the volume cut out by the recess 82.

[0024] The method of providing the protrusions 80 and recesses 82 is not limited to these. The recesses 82 may be provided after the protrusions 80 are provided, or the cut-out portions of the first surface 71 do not have to be used as the protrusions 80. The protrusions 80 may be provided between the recesses 82 and the external terminals 23 as shown in FIG. 3, or between the recesses 82 and the long sides 90 as shown in FIG. 4. FIG. 5 is a cross-sectional view in the Z direction taken along line II in FIG. 1, showing another modified example of the terminal structure of the secondary battery according to the first embodiment. The protrusions 80 and recesses 82 of the lid member 7 may be spaced apart as shown in FIG. 5.

[0025] The cross-sectional shapes of the convex portions 80 and the concave portions 82 are not limited to the rectangular shapes shown in Figures 3 to 5. As long as the convex portions 80 and the concave portions 82 are provided on the cover member 7, the cross-sectional shapes of the convex portions 80 and the concave portions 82 may be semicircular or polygonal.

[0026] In this embodiment, the head 230 of the external terminal 23 is disposed to protrude and face the second surface 72 of the lid member 7, and a step 40 facing the head 230 is provided on the second surface 72 of the lid member 7. The area of ​​the lid member 7 where the step 40 is provided forms a second thin portion 88 that is thinner than other portions. By providing the step 40, when laser welding the opening 9 of the outer case 3 and the outer peripheral edge of the lid member 7, the welding heat generated by welding is transmitted to the insulating member 29 via the first thin portion 84, the thick portion 86, and the second thin portion 88. When the lid member 7 is provided with the protrusion 80, the recess 82, and the step 40, the heat transfer path of the welding heat passes not only through the first thin portion 84 and the thick portion 86 but also through the second thin portion 88. Therefore, the heat transfer path of the welding heat is longer than when the lid member 7 is provided with only the protrusion 80 and the recess 82. As a result, by providing the convex portion 80, the concave portion 82 and the step portion 40 on the cover member 7, it is possible to further prevent the welding heat generated when welding the opening 9 of the outer case 3 to the cover member 7 from being transmitted to the insulating member 29 provided between the cover member 7 and the external terminal 23.

[0027] It is sufficient that one or more convex portions 80 and one or more concave portions 82 are provided on at least one of the first surface 71 and the second surface 72 of the lid member 7. Furthermore, it is preferable that the number of convex portions 80 and the number of concave portions 82 on each surface are equal, because after forming the concave portions 82 by cutting out the first surface 71 or the second surface 72, the cut-out portions can be provided as convex portions 80 in positions adjacent to the concave portions 82, thereby making it possible to easily provide the convex portions 80 and the concave portions 82 in positions adjacent to each other. However, the numbers of convex portions 80 and the concave portions 82 are not limited to these, and the number of convex portions 80 on each surface of the lid member 7 may be more or less than the number of concave portions 82.

[0028] Specific locations of the protrusions 80 and recesses 82 in this embodiment will be described with reference to FIGS. 6 and 7 . FIG. 6 is a plan view of the first surface 71 of the lid member 7 used in the secondary battery 1 according to the first embodiment. FIG. 7 is an enlarged view of the first surface 71 of the lid member 7 used in the secondary battery 1 according to the first embodiment. As shown in FIGS. 6 and 7 , the protrusions 80 and recesses 82 are provided on the first surface 71 of the lid member 7. When the lid member 7 is rectangular as in this embodiment, the protrusions 80 and recesses 82 are preferably provided parallel to the long side 90 in a region R between the long side 90 and a position (point P) closest to the long side 90 at the outer periphery of the through hole 20 of the lid member 7. Note that the protrusions 80 and recesses 82 do not necessarily have to be parallel to the long side 90, as long as they are provided in the region R.

[0029] Because the insulating member 29 is provided in close contact with the shaft portion 232 of the external terminal 23, the position of the insulating member 29 is determined by the position of the shaft portion 232 of the external terminal 23. The external terminal 23 may be designed to be large so as to allow a large current to flow, and may be located closer to the long side 90 than to the short side 92. Therefore, the insulating member 29 may also be located closer to the long side 90 than to the short side 92. Accordingly, the insulating member 29 is more susceptible to the effect of the welding heat of the laser light irradiated on the long side 90 than to the laser light irradiated on the short side 92. Therefore, by providing the convex portion 80 and the concave portion 82 in the region R, it is possible to suppress the transmission of the welding heat of the laser light irradiated on the long side 90 to the insulating member 29.

[0030] Each set of protrusions 80 and recesses 82 is preferably provided symmetrically with respect to a line Q that passes through the center of the through hole 20 in the lid member 7 and is parallel to the long sides of the lid member 7. This makes it possible to suppress the transfer of welding heat from the laser light irradiated on the two long sides 90 to the insulating member 29, and also to maintain the strength and balance of the lid member 7. The positions at which each set of protrusions 80 and recesses 82 is provided are not limited to these, and multiple sets of protrusions 80 and recesses 82 may be provided in the region R, or just one set. Furthermore, in terms of the strength and balance of the lid member 7, it is preferable that the protrusions 80 and recesses 82 provided on the positive electrode external terminal 23a side are also similarly provided on the negative electrode external terminal 23b side, but this is not limited thereto.

[0031] 7 , where A denotes the length of the protrusions 80 and recesses 82 in the direction of the long side 90, and B denotes the diameter of the through hole 20 in the cover member 7, simulation results have verified that it is preferable for A / B to satisfy the relationship of 0.3 to 1.7. The results of the simulation and the method thereof will be described later. When A / B is 0.3 or more, even small lengths of the protrusions 80 and recesses 82 can suppress the transfer of welding heat of the laser beam to the insulating member 29. More preferably, A / B is 0.6 or more. Simulation results have verified that when A / B is 0.6 or more, the maximum temperature of the insulating member 29 during welding is reduced by approximately 2% or more compared to when the cover member 7 does not have the protrusions 80 and recesses 82.

[0032] Furthermore, when A / B is 1.7 or less, the welding heat in the portion of the long side 90 irradiated with the laser light that is close to the insulating member 29 can be appropriately dispersed by the convex portions 80 and concave portions 82 of sufficient length, thereby suppressing the transmission of the welding heat to the insulating member 29. Convex portions 80 and concave portions 82 provided at positions away from the insulating member 29 in the Y direction do not significantly contribute to suppressing the transmission of the welding heat to the insulating member 29, so the convex portions 80 and concave portions 82 are preferably provided at positions close to the insulating member 29. When the convex portions 80 and concave portions 82 are provided extending in the Y direction, the tips of the convex portions 80 and concave portions 82 are distant from the insulating member 29, so they do not significantly contribute to suppressing the transmission of the welding heat to the insulating member 29. Therefore, when A / B is 1.7 or less, there is no need to provide the convex portions 80 and concave portions 82 at positions away from the insulating member 29, and the transmission of the welding heat to the insulating member 29 can be reliably suppressed.

[0033] A first modification of this embodiment will be described with reference to FIGS. 8 and 9 . FIG. 8 is a top view of a first surface 71 of a first modification of the lid member 7 used in the secondary battery 1 according to the first embodiment. FIG. 9 is an enlarged view of the first surface 71 of the first modification of the lid member 7 used in the secondary battery 1 according to the first embodiment. In the first modification, as shown in FIGS. 8 and 9 , in addition to providing a protrusion 80 and a recess 82 in a region R of the first surface 71 of the lid member 7, the protrusion 80 and the recess 82 are provided parallel to the short side 92 in a region T between the short side 92 and a position (point S) closest to the short side 92 at the outer periphery of the through hole 20 of the lid member 7. The protrusion 80 and the recess 82 do not necessarily have to be parallel to the short side 92, as long as they are provided in the region T.

[0034] As described above, the insulating member 29 may be positioned closer to the long side 90 than to the short side 92. Accordingly, the insulating member 29 is more susceptible to the effect of the welding heat of the laser light irradiated onto the long side 90 than to the laser light irradiated onto the short side 92. However, since the insulating member 29 is also affected by the welding heat of the laser light irradiated onto the short side 92, providing the convex portion 80 and the concave portion 82 in the region T can suppress the welding heat of the laser light irradiated onto the short side 92 from being transmitted to the insulating member 29. In the first modification of this embodiment, the welding heat of the laser light irradiated onto both the long side 90 and the short side 92 can be suppressed from being transmitted to the insulating member 29.

[0035] The positions where a pair of convex portion 80 and concave portion 82 is provided are not limited to these, and multiple pairs may be provided in region T, or just one pair may be provided.

[0036] In FIG. 9 , when the length of the convex portions 80 and the concave portions 82 in the direction of the short side 92 is C and the diameter of the through hole 20 in the lid member 7 is B, simulation results have verified that it is preferable for C / B to satisfy the relationship of 0.3 to 1.7. The simulation results and the simulation method will be described later. When C / B is 0.3 or more, even the convex portions 80 and the concave portions 82 having small lengths can suppress the transfer of welding heat of the laser beam to the insulating member 29. More preferably, C / B is 0.6 or more. Simulation results have verified that when C / B is 0.6 or more, the maximum temperature of the insulating member 29 during welding is reduced by approximately 2% or more compared to when the lid member 7 does not have the convex portions 80 and the concave portions 82.

[0037] Furthermore, when C / B is 1.7 or less, the welding heat in the portion of the long side 90 irradiated with the laser light that is close to the insulating member 29 can be appropriately dispersed by the convex portions 80 and concave portions 82 of sufficient length, thereby suppressing the transmission of the welding heat to the insulating member 29. Convex portions 80 and concave portions 82 provided at positions away from the insulating member 29 in the X direction do not significantly contribute to suppressing the transmission of the welding heat to the insulating member 29, so the convex portions 80 and concave portions 82 are preferably provided at positions close to the insulating member 29. For example, when the convex portions 80 and concave portions 82 are provided extending in the X direction, the tips of the convex portions 80 and concave portions 82 are distant from the insulating member 29 and therefore do not significantly contribute to suppressing the transmission of the welding heat to the insulating member 29. Therefore, when C / B is 1.7 or less, there is no need to provide the convex portions 80 and concave portions 82 at positions away from the insulating member 29, and the transmission of the welding heat to the insulating member 29 can be reliably suppressed.

[0038] A second modification of this embodiment will be described with reference to Fig. 10 . Fig. 10 is a conceptual diagram of a first surface 71 of a second modification of the lid member 7 used in the secondary battery 1 according to the first embodiment. In the second modification, as shown in Fig. 10 , the convex portion 80 and the concave portion 82 are provided on the first surface 71 of the lid member 7 in a rectangular ring shape surrounding the through hole 20 of the lid member 7. This makes it possible to suppress the transfer of welding heat from the laser beam irradiated on both the long side 90 and the short side 92 to the insulating member 29 over the entire circumference of the insulating member 29.

[0039] According to at least one embodiment of the secondary battery 1 described above, by providing the convex portion 80 and the concave portion 82 on the first surface 71 of the lid member 7, the heat transfer path from the laser irradiation position of the welding heat applied to the lid member 7 by laser welding to the insulating member 29 is longer than the heat transfer path when the lid member 7 does not have the convex portion 80 and the concave portion 82. Therefore, it is possible to prevent the welding heat generated when the opening 9 of the exterior case 3 and the lid member 7 are welded together from being transferred to the insulating member 29 provided between the lid member 7 and the external terminal 23. This prevents deterioration of the adhesion between the external terminal 23 and the insulating member 29 due to damage such as deformation of the insulating member 29 caused by the welding heat, and it is possible to provide a secondary battery 1 that ensures airtightness at the external terminal portion.

[0040] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope and spirit of the invention, and are also within the scope of the inventions described in the claims and their equivalents.

[0041] Examples will be described below, but the present invention is not limited to the examples listed below as long as they do not depart from the gist of the present invention.

[0042] "Confirmation of the effect of the convex portions and concave portions in suppressing heat transfer to the insulating member" The effect of the convex portions 80 and concave portions 82 in suppressing heat transfer to the insulating member 29 was determined by simulation. In the simulation, a thermal analysis model was applied to determine the maximum temperature of the insulating member 29 when laser light was irradiated onto the short side 92 of the lid member 7. The maximum temperature was determined at the position of the insulating member 29 closest to the long side 90 of the lid member 7.

[0043] Examples 1 and 2, and Comparative Examples 1 and 2 are shown below. The length A of the convex portion 80 and the concave portion 82 was 5.9 mm, and the diameter B of the through hole 20 of the lid member 7 was 4.8 mm. In this case, the ratio A / B was 1.2.

[0044] As shown in Fig. 6, the convex portion 80 and the concave portion 82 were provided parallel to the long side 90 in a region R between the long side 90 and the position (point P) closest to the long side 90 on the outer peripheral edge of the through hole 20 of the lid member 7. Furthermore, as shown in Fig. 6, one set of the convex portion 80 and the concave portion 82 was provided symmetrically with respect to a line Q parallel to the long side of the lid member 7.

[0045] Example 1 As shown in FIG. 3, a convex portion 80 and a concave portion 82 were provided adjacent to each other on the first surface 71 of the cover member 7, and the concave portion 82 was provided closer to the long side 90 than the convex portion 80.

[0046] Example 2 As shown in FIG. 4, a convex portion 80 and a concave portion 82 were provided adjacent to each other on the first surface 71 of the cover member 7, and the convex portion 80 was provided closer to the long side 90 than the concave portion 82.

[0047] Comparative Example 1 Only the recess 82 was provided in the region R of the first surface 71 of the lid member 7 .

[0048] Comparative Example 2 The cover member 7 was not provided with the convex portion 80 and the concave portion 82 .

[0049]

[0050] Table 1 shows the A / B ratio and the maximum temperature reduction rate of the insulating member 29 in Examples 1 and 2 and Comparative Examples 1 and 2. This maximum temperature reduction rate was based on the conditions of Comparative Example 2. As shown in Table 1, it was verified that providing the convex portion 80 and the concave portion 82 on the first surface 71 of the cover member 7 reduced the maximum temperature of the insulating member 29 by approximately 4%. Furthermore, Comparative Example 1 verified that providing the concave portion 82 on the first surface 71 of the cover member 7 alone reduced the maximum temperature reduction rate of the insulating member 29 by only approximately 1%, thereby verifying the necessity of providing the convex portion 80 and the concave portion 82 on the first surface 71 of the cover member 7 in order to suppress the transmission of welding heat of the laser beam to the insulating member 29.

[0051] "Confirmation of the effect of suppressing heat transfer to the insulating member depending on the length of the convex portion and the concave portion" The effect of suppressing heat transfer to the insulating member 29 depending on the length A of the convex portion 80 and the concave portion 82 was determined by simulation. In the simulation, a thermal analysis model was applied to determine the maximum temperature of the insulating member 29 when laser light was irradiated onto the short side 92 of the lid member 7. The maximum temperature was determined at the position of the insulating member 29 closest to the long side 90 of the lid member 7.

[0052] Examples 3 and 4, and Comparative Examples 3 and 4 are shown below. The diameter B of the through-hole 20 of the lid member 7 was set to 4.8 mm.

[0053] Example 3 Under the same conditions as in Example 1, the length A of the convex portion 80 and the concave portion was set to 3 mm, and the ratio A / B was 0.6.

[0054] Example 4 The length A of the convex portion 80 and the concave portion was set to 8 mm under the same conditions as in Example 1. In this case, A / B was 1.7.

[0055] Comparative Example 3 The length A of the convex portion 80 and the concave portion was set to 1 mm under the same conditions as in Example 1. In this case, A / B was 0.2.

[0056] Comparative Example 4 The length A of the convex portion 80 and the concave portion was set to 10 mm under the same conditions as in Example 1. In this case, A / B was 2.1.

[0057]

[0058] Table 2 and FIG. 11 show the A / B ratios and the maximum temperature reduction rates of the insulating member 29 in Examples 3 and 4 and Comparative Examples 3 and 4. These maximum temperature reduction rates were based on the conditions of Comparative Example 2. As shown in Table 2 and FIG. 11 , it was verified that providing the convex portions 80 and the concave portions 82 on the first surface 71 of the cover member 7 and setting the A / B ratio to 0.3 or greater and 1.7 or less reduced the maximum temperature of the insulating member 29 by approximately 1-4%. It was more preferable that the A / B ratio be 0.6 or greater, which reduced the maximum temperature of the insulating member 29 by approximately 2%. It was also verified that even with a small A / B ratio of 0.3 or greater, more preferably 0.6 or greater, the transmission of welding heat from the laser beam to the insulating member 29 could be suppressed. Furthermore, it was verified that when A / B is 1.7 or less, the welding heat in the portion of the long side 90 irradiated with the laser light that is close to the insulating member 29 can be appropriately dispersed to the convex portion 80 and the concave portion 82 of sufficient length, thereby suppressing the transmission of the welding heat to the insulating member 29.

[0059] The results of the above simulations are used for the secondary battery 1 of this embodiment. Specifically, by providing the protrusions 80 and recesses 82 on the first surface 71 of the lid member 7, the heat transfer path from the laser irradiation position of the welding heat applied to the lid member 7 by laser welding to the insulating member 29 is made longer than the heat transfer path when the lid member 7 does not have the protrusions 80 and recesses 82. Here, if the length of the protrusions 80 and recesses 82 in the direction of the long side 90 is A and the diameter of the through hole 20 in the lid member 7 is B, then A / B satisfies the relationship of 0.3 to 1.7. This makes it possible to prevent the transfer of welding heat generated when the opening 9 of the exterior case 3 and the lid member 7 are welded together from being transferred to the insulating member 29 provided between the lid member 7 and the external terminal 23, thereby providing a secondary battery 1 that ensures airtightness at the external terminal.

[0060] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are within the scope and spirit of the invention, as well as the scope of the invention and its equivalents as set forth in the claims. For example, the electrode assembly is not limited to a so-called wound-type electrode assembly in which electrode plates are wound, but a so-called stacked-type electrode assembly in which multiple electrode plates are stacked in the thickness direction may also be applied. The materials, shapes, sizes, etc. of the elements constituting the secondary battery are not limited to the above-described embodiments and can be variously modified as needed.

Claims

1. A secondary battery comprising: an outer case having an opening; an electrode group including a positive electrode and a negative electrode housed within the outer case; a lid member disposed in the opening and having a through hole; an external terminal disposed in the lid member and having a shaft portion disposed in the through hole; and an insulating member disposed between an inner wall of the through hole and the shaft portion of the external terminal, wherein the lid member has a first surface facing the electrode group and a second surface facing the first surface, and at least one of the first surface and the second surface is provided with at least one or more protrusions and at least one or more recesses.

2. The secondary battery according to claim 1, wherein the protrusions and recesses are provided on the first surface.

3. The secondary battery according to claim 1, wherein the protrusion and the recess are provided adjacent to each other.

4. The secondary battery according to claim 1, wherein the number of said protrusions and said recesses is equal.

5. A secondary battery as described in claim 1, wherein the external terminal has a head that protrudes to face the second surface of the lid member, and the second surface of the lid member is provided with a stepped portion that faces the head of the external terminal.

6. A secondary battery according to any one of claims 1 to 5, wherein the lid member is rectangular with long and short sides, and at least one of the protrusions and recesses is provided parallel to the long sides and between the long sides and a position on the outer periphery of the through hole closest to the long sides.

7. The secondary battery according to claim 6, wherein a length A of the protrusion or recess in the long side direction and a diameter B of the through hole satisfy the relationship of the following formula (1): 0.3≦A / B≦1.7 (1) 8. The secondary battery according to claim 6, wherein the recessed portion is provided closer to the long side than the protruding portion.

9. A secondary battery as described in claim 6, wherein at least one of the protrusions and recesses is provided parallel to the short side, between the short side and a position on the outer peripheral edge of the through hole closest to the short side.

10. The secondary battery according to claim 9, wherein a length C of the convex portion or the concave portion in the short side direction and a diameter B of the through hole satisfy the relationship of the following formula (2): 0.3≦C / B≦1.7 (2) 11. The secondary battery according to claim 9, wherein the recess is provided closer to the shorter side than the protrusion.

12. The secondary battery according to claim 9, wherein at least one of the plurality of protrusions and the plurality of recesses is provided in a rectangular ring shape surrounding the through hole.

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