Method of manufacturing secondary battery and secondary battery

Abstract

To provide a method of manufacturing a secondary battery which has high weld stability between an outer can and a lid member and improves weld efficiency while suppressing heat which is conducted to an insulation gasket during weld, and a secondary battery.SOLUTION: A method of manufacturing a secondary battery includes: a storage step of storing an electrode group in an outer can including a rectangular opening having long sides and short sides; an arrangement step of arranging a lid member in the opening; and a weld step of welding the opening and the lid member by irradiating the opening and the lid member with laser beams. A beam shape at an irradiation position of the laser beams has a longest first distance A in a first direction which is parallel to a long-side direction of the opening and a longest second distance B in a second direction which is parallel to a short-side direction of the opening, and the first distance A is longer than the second distance B.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] FIELD Embodiments of the present invention relate to a method for manufacturing a secondary battery and a secondary battery. [Background technology]

[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 aimed at adopting secondary batteries with 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 is manufactured by housing an electrode group in an outer can and welding the opening of the outer can to a lid member. The welding of the outer can opening to the lid member is performed by laser welding, resistance welding, or the like. In laser welding, which is one example of a welding method, when a laser beam is irradiated onto the outer can opening and the lid member and allowed to proceed, a molten pool is formed in the direction of the laser beam, where the outer can and the lid member are melted by the heat of the laser beam. This molten pool then solidifies in a state where it is integrated with the outer can opening and the lid member, and the outer can opening and the lid member are welded together.

[0004] The sidewall of the outer can is sometimes formed thick from the viewpoint of strength, etc., and when the opening of the outer can and the lid member are welded together, the thick sidewall of the outer can causes the outer peripheral edge of the opening of the outer can and the outer peripheral edge of the lid member to become thin, which may result in poor welding between the opening of the outer can and the lid member. One way to avoid this poor welding is to increase the energy of the laser beam.

[0005] In this type of secondary battery, a pair of external terminals is disposed on the lid member, and an insulating gasket is sometimes provided in close contact with the external terminals. When the opening of the outer can and the lid member are laser-welded, the heat of the laser beam is transferred from the lid member to the terminal insulator (made of resin) and the insulating gasket. When the laser beam irradiation position is close to the insulating gasket or when the laser beam energy is high, the insulating gasket is easily affected by the heat of the laser beam. This weakens the adhesion between the insulating gasket and the external terminals or between the insulating gasket and the lid member, and in some cases, the airtightness of the secondary battery may not be ensured. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-44543 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-219590 Summary of the Invention [Problem to be solved by the invention]

[0007] The problem to be solved by the present invention is to provide a method for manufacturing a secondary battery and a secondary battery that reduce welding defects between the outer can and the lid member, suppress heat transfer to the insulating gasket during welding, and improve welding efficiency. [Means for solving the problem]

[0008] To achieve the above object, a method for manufacturing a secondary battery according to an embodiment includes a housing step of housing an electrode group in an outer can having a rectangular opening with long sides and short sides, a placement step of placing a lid member in the opening, and a welding step of welding the opening and the lid member by irradiating a laser beam. The beam shape at the irradiation position of the laser beam has a first longest distance A in a first direction parallel to the long side of the opening and a second longest distance B in a second direction parallel to the short side of the opening, and the first distance A is longer than the second distance B. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a perspective view schematically showing a secondary battery to which the method for manufacturing a secondary battery according to a first embodiment is applied; [Figure 2] 1 is a perspective view schematically showing a secondary battery to which the method for manufacturing a secondary battery according to a first embodiment is applied, in a state where the secondary battery is disassembled into components; [Figure 3] 2 is a cross-sectional view of the terminal structure of the secondary battery to which the manufacturing method for the secondary battery according to the first embodiment is applied, taken along line II in FIG. 1 in the Z direction. [Figure 4] 2 is a cross-sectional view of the terminal structure of the secondary battery to which the manufacturing method for the secondary battery according to the first embodiment is applied, taken along the line II-II in FIG. 1 in the Z direction. [Figure 5] 3 is a plan view showing the secondary battery to which the method for manufacturing a secondary battery according to the first embodiment is applied, viewed from the side where the lid member is located in the Z direction. FIG. [Figure 6] 3 is a cross-sectional view of a welded portion of the secondary battery to which the manufacturing method for a secondary battery according to the first embodiment is applied, taken along line III-III in FIG. 1 in the Z direction. [Figure 7] 1 shows a beam shape at a position irradiated with laser light applied in the method for manufacturing a secondary battery according to the first embodiment. [Figure 8] 4 is a welding path diagram showing a state viewed from the side where the lid member is located in the Z direction in the laser welding step applied to the manufacturing method of the secondary battery according to the first embodiment. FIG. [Figure 9]5 is a cross-sectional view taken along the Z direction showing a state in which a molten pool is formed in the laser welding step applied to the method for manufacturing the secondary battery according to the first embodiment. FIG. [Figure 10] 10 shows a beam shape at a position irradiated with laser light applied in a method for manufacturing a secondary battery according to a second embodiment. [Figure 11] FIG. 10 is a welding path diagram showing a state viewed from the side where the lid member is located in the Z direction in the laser welding step applied to the manufacturing method of the secondary battery according to the second embodiment. [Figure 12] Computational models in simulation testing. [Figure 13] Cross-sectional shape of the weld on the Z3-X3 plane in the simulation test. [Figure 14] 1 shows simulation results for Example 1, Example 2, and Comparative Example 1. [Figure 15] Simulation results for Examples 1 to 6, Comparative Examples 1 and 2. [Figure 16] Simulation results for Examples 7 to 11, Comparative Examples 1 and 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, a method for manufacturing a secondary battery and a secondary battery according to an embodiment will be described with reference to the drawings.

[0011] (First embodiment) A secondary battery 1 to which the manufacturing method for a secondary battery according to the first embodiment is applied will be described with reference to FIGS. 1 and 2. FIG. 1 is a perspective view schematically illustrating the secondary battery 1 to which the manufacturing method for a secondary battery according to the first embodiment is applied, and FIG. 2 is a perspective view schematically illustrating the secondary battery 1 to which the manufacturing method for a secondary battery according to the first embodiment is applied, disassembled into its components. As shown in FIGS. 1 and 2, the secondary battery 1 includes an outer can 3 and an electrode group 5. The outer can 3 has an internal cavity 11 therein and a rectangular cylindrical shape with an outer can opening 9 provided on the top surface. The outer can opening 9 is rectangular with long and short sides, and a lid member 7 is disposed in the outer can opening 9. Here, the process of disposing the lid member 7 in the outer can opening 9 is referred to as the disposing process. Furthermore, the four corners of the outer can opening 9 may be provided with curved portions. The outer can 3 and the lid member 7 are formed from a metal such as aluminum, an aluminum alloy, iron, copper, or stainless steel. From the viewpoint of strength, the thickness of the side wall on the short side of the outer can 3 may be formed to be thicker than that on the long side of the outer can 3. Specifically, the thickness of the side wall on the short side of the outer can 3 is preferably 0.5 mm or more and 0.7 mm or less, but is not limited to these values.

[0012] The electrode group 5 is housed in the internal cavity 11 of the outer can 3. Here, the process of housing the electrode group 5 in the internal cavity 11 of the outer can 3 is referred to as the housing process. The electrode group 5 is manufactured by sandwiching a separator (not shown) between the positive electrode 13 and the negative electrode 15, spirally winding them, 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 layer (not shown) laminated 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 13b as a portion where the positive electrode active material layer is not applied. Meanwhile, the negative electrode 15 has a negative electrode current collector 15a and a negative electrode active material layer (not shown) laminated 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 15b as a portion where the negative electrode active material layer is not applied. These positive electrode current collecting tabs 13b and negative electrode current collecting tabs 15b are each clamped by two pairs of clips (backup leads 16) arranged inside the outer can 3. 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 separators 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 can 3 is changed as appropriate. The electrode group 5 is not limited to a wound type or a stack structure.

[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] The separator is made of an electrically insulating material, such as cellulose, polyethylene, polypropylene, ethylene-propylene copolymer, or ethylene-butene copolymer.

[0016] Inside the exterior can 3, the electrode group 5 is impregnated with an electrolyte solution (not shown). The electrolyte solution is poured through a pouring hole 17 provided in the lid member 7, and after the electrolyte solution has been poured, the pouring hole 17 is closed with a sealing plate 19. The electrolyte solution used is a non-aqueous electrolyte solution prepared by dissolving an electrolyte (for example, a lithium salt) in a non-aqueous solvent. The non-aqueous solvent may be used alone or in combination of two or more types.

[0017] A liquid inlet 17 and a gas release valve 21 are formed on the surface of the lid member 7. The liquid inlet 17 and the gas release valve 21 do not necessarily have to be provided on the lid member 7. Furthermore, a pair of external terminals 23 are attached to the outer surface of the lid member 7. 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. The external terminals 23 have a rectangular head 25 and a shaft 27 extending downward from the head. The shaft 27 of the external terminal 23 is disposed in close contact with the lid member 7 via an insulating gasket 29. The shaft 27 of the external terminal 23 is further connected to a lead 31, thereby electrically connecting the electrode group 5 to the external terminal 23 via the lead 31. Furthermore, an internal insulating member 33 is provided between the lid member 7 and the lead 31, electrically insulating the lid member 7 and the lead 31. Furthermore, the lead 31, the positive electrode current collector tab 13b, and the negative electrode current collector tab 15b are each electrically insulated from the outer casing 3 by an insulating guard 34. The insulating guard 34 is fixed to the electrode group 5 by an insulating tape 36. A terminal insulator 35 is provided between the external terminal 23 and the lid member 7, and the external terminal 23 and the lid member 7 are electrically insulated from each other.

[0018] The terminal structure of a secondary battery 1 to which the manufacturing method for a secondary battery according to the first embodiment is applied will be described with reference to Figures 3 and 4. Figure 3 is a cross-sectional view in the Z direction along line II in Figure 1 of the terminal structure of a secondary battery to which the manufacturing method for a secondary battery according to the first embodiment is applied. Figure 4 is a cross-sectional view in the Z direction along line II-II in Figure 1 of the terminal structure of a secondary battery to which the manufacturing method for a secondary battery according to the first embodiment is applied. As shown in Figures 3 and 4, the shaft portion 27 of the external terminal 23 is in close contact with the insulating gasket 29 and is fixed to the lid member 7.

[0019] The positions of the pair of external terminals 23 on the outer surface of the lid member 7 will be described with reference to FIG. 5 . FIG. 5 is a plan view showing a secondary battery 1 to which the manufacturing method for a secondary battery according to the first embodiment is applied, viewed from the side where the lid member 7 is located, in the Z direction of FIG. 1 . In FIGS. 3 and 5 , the minimum distance from the end 29 a of the insulating gasket 29 to the sidewall of the short side of the outer can 3 is defined as length Q. Here, length Q is the minimum distance in a direction parallel to the long side of the outer can 3, i.e., in the Y direction. Also, in FIGS. 4 and 5 , the minimum distance from the end 29 b of the insulating gasket 29 to the sidewall of the long side of the outer can 3 is defined as length R. Here, length R is the minimum distance in a direction parallel to the short side of the outer can 3, i.e., in the X direction. The insulating gasket 29 may be any insulator that is disposed in close contact with the shaft portion 27 of the external terminal 23, and is not limited to an O-ring shape as in this embodiment. If the shape of the insulating gasket 29 differs from that of this embodiment, the ends 29a and 29b of the insulating gasket 29 are the ends of the portion that is disposed in close contact with the shaft portion 27 of the external terminal 23.

[0020] 3 to 5, length Q is longer than length R, and at least one external terminal 23 is disposed at a position where length Q is longer than length R. In this embodiment, the position of this external terminal 23 on the cover member 7 is determined by the structure of the lead 31. Therefore, depending on the structure of the lead 31, at least one external terminal 23 may be disposed at a position where length Q is shorter than or equal to length R. In this embodiment, length R is preferably 2.5 mm or more and 3.5 mm or less, but is not limited to this.

[0021] In the method for manufacturing a secondary battery according to the first embodiment, after the storing step of storing the electrode group 5 in the outer can 3 and the arranging step of arranging the lid member 7 in the outer can opening 9, the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7 are welded together along the entire circumference. This step of welding the outer peripheral edge of the outer can opening 9 to the outer peripheral edge of the lid member 7 along the entire circumference is referred to as the welding step. In the welding step of this embodiment, a laser beam 51 is used, and the laser beam 51 is generated by a laser oscillator (not shown). In the welding step, the outer can 3 and the lid member 7 are melted and solidified to form a weld 37 at the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7. The outer can 3 and the lid member 7 are welded together via this weld 37.

[0022] The welded portion 37 formed on the outer can 3 and the lid member 7 will be described with reference to Fig. 6. Fig. 6 is a cross-sectional view in the Z direction taken along line III-III in Fig. 1 of the welded portion of a secondary battery to which the manufacturing method for a secondary battery according to the first embodiment is applied. As shown in Fig. 6, the welded portion 37 is formed in a convex shape in the Z direction of the outer can 3 and the lid member 7. Here, the longest distance in the X direction of the welded portion 37 is defined as length S. Length S is penetration width 43, which is the width across which the welded portion 37 is formed.

[0023] Furthermore, the longest distance in the Z direction at the boundary surface where the outer can 3 and the lid member 7 come into contact at the weld is defined as length T. Length T is penetration depth 49, which is the depth at which the weld 37 is formed. The weld 37 is not limited to the shape shown in FIG. 6 , and may have any shape as long as there is a portion where the outer can 3 and the lid member 7 are melted and solidified. For example, the weld 37 may be formed in a concave shape in the Z direction of the outer can 3 and the lid member 7.

[0024] The cross-sectional observation procedure for the secondary battery 1 to which the manufacturing method for a secondary battery according to the first embodiment is applied, using a destructive test of the welded portion 37, will be described. First, the outer can 3 is cut in the XY plane to separate it into a portion including the lid member 7, which is the upper portion in the Z direction, and a portion not including the lid member 7, which is the lower portion in the Z direction. Next, the portion including the lid member 7, which is the upper portion in the Z direction, is further cut along the XZ plane around the external terminal 23 to separate it into a portion around the external terminal 23 including an observation portion, and then embedded in resin. While still embedded in resin, the center of the external terminal 23, which is the observation portion, is further cut along the XZ plane. The cut surface obtained here is polished, and after polishing, it is etched using an etchant to obtain a sample for cross-sectional observation. The obtained sample is observed under an optical microscope, and the portion with a different shade from the shade of the outer can 3 and the lid member 7 is identified as the welded portion 37. The reason why the shade of the welded portion 37 differs from the shade of the outer can 3 and the lid member 7 is that the welded portion 37 is formed by melting and solidifying the outer can 3 and the lid member 7, and the crystallinity of the welded portion 37 differs from the crystallinity of the outer can 3 and the lid member 7.

[0025] The beam shape of the laser beam 51 used in the method for manufacturing a secondary battery according to the first embodiment will be described with reference to FIG. 7 . FIG. 7 shows the beam shape of the laser beam 51 at the irradiation position of the laser beam 51 used in the method for manufacturing a secondary battery according to the first embodiment. Here, the irradiation position refers to the surface of the irradiated member when the laser beam 51 is irradiated onto the irradiated member. In this embodiment, the irradiated member is the lid member 7, so the irradiation position in this embodiment refers to the surface of the lid member when the laser beam 51 is irradiated onto the lid member 7. As shown in FIG. 7 , the beam shape of the laser beam 51 at the irradiation position has a first longest distance A in a direction parallel to the Y2 direction and a second longest distance B in a direction parallel to the X2 direction. Here, the first distance A is longer than the second distance B. Specific beam shapes of the laser beam 51 include an elliptical shape shown in FIG. 7( a), a rectangular shape shown in FIG. 7( b), a diamond shape and a polygonal shape shown in FIG. 7( c), etc. However, the beam shape of the laser light 51 is not limited to these, and it is sufficient that the beam shape of the laser light 51 has a first distance A and a second distance B, and the first distance A is longer than the second distance B. Laser light 51 with such a beam shape can be obtained by passing a general circular laser light 51 through a DOE (Diffractive Optical Element).

[0026] A welding process applied to the manufacturing method of the secondary battery according to the first embodiment will be described with reference to FIG. 8 . FIG. 8 is a welding path diagram showing a state viewed from the side where the lid member 7 is located in the Z direction in the welding process applied to the manufacturing method of the secondary battery according to the first embodiment. As shown in FIG. 8 , when laser welding the long side of the outer can 3 and the long side of the lid member 7, the laser beam 51 is irradiated in a direction in which a first distance A of the elliptical laser beam 51 is parallel to the long side direction of the lid member 7, i.e., parallel to the Y direction. On the other hand, when laser welding the short side of the outer can 3 and the short side of the lid member 7, the laser beam 51 is irradiated in a direction in which a second distance B of the elliptical laser beam 51 is parallel to the short side direction of the lid member 7, i.e., parallel to the X direction. In the beam shape at the irradiation position of the laser beam 51, the first distance A of the laser beam 51 is parallel to the long side direction of the lid member 7, and the second distance B of the laser beam 51 is parallel to the short side direction of the lid member 7.

[0027] The entire circumference of the outer can 3 and the lid member 7 are laser welded together while maintaining the parallel relationship between the first distance A of the laser beam 51 and the long side direction of the lid member 7, and the parallel relationship between the second distance B of the laser beam 51 and the short side direction of the lid member 7. If the beam shape at the irradiation position of the elliptical laser beam 51 is changed depending on the traveling direction of the laser beam 51, it is necessary to change the installation direction of the DOE in accordance with the beam shape at the irradiation position of the laser beam 51, which increases the number of steps in the welding. However, in this embodiment, it is not necessary to change the beam shape at the irradiation position of the elliptical laser beam 51 depending on the traveling direction of the laser beam 51, and it is not necessary to change the installation direction of the DOE. This makes it easy to laser weld the outer can 3 and the lid member 7 together in this embodiment.

[0028] 8 uses an elliptical laser beam 51, but the shape of the laser beam 51 is not limited to an elliptical shape and may be rectangular, diamond-shaped, or polygonal. Furthermore, the order in which the long and short sides of the outer can 3 and the lid member 7 are welded is not limited as long as the entire circumference is welded. When a weak-energy laser beam 51 is used, the entire circumference may be welded multiple times, or portions of the long and short sides of the outer can 3 and the lid member 7 may be welded multiple times.

[0029] As described above, in this embodiment, the length R, which is the minimum distance from the end 29b of the insulating gasket 29 to the sidewall on the long side of the outer can 3, is shorter than the length Q, which is the minimum distance from the end 29a of the insulating gasket 29 to the sidewall on the short side of the outer can 3. As a result, the insulating gasket 29 disposed between the external terminal 23 and the lid member 7 is more affected by the heat input from the laser beam 51 irradiated onto the long side of the lid member 7 than by the laser beam 51 irradiated onto the short side of the lid member 7. Therefore, when laser welding the long side of the outer can 3 and the long side of the lid member 7 together, the laser beam 51 is irradiated in a direction parallel to the long side direction of the lid member 7 over a first distance A that is longer than the second distance B of the elliptical laser beam 51. As a result, the heat input from the laser beam 51 to the insulating gasket 29 can be suppressed more than that on the short side.

[0030] Furthermore, by welding the long welding distance between the long side of the outer can 3 and the long side of the lid member 7 in this manner, the first distance A of the laser beam 51 is longer than the second distance B, and therefore, a molten pool 60 of a sufficient length for welding is formed on the long side of the outer can 3 and the long side of the lid member 7 as the laser beam 51 advances. Here, the molten pool 60 formed on the outer can 3 and the lid member 7 as the laser beam 51 advances will be described with reference to FIG. 9. FIG. 9 is a cross-sectional view in the Z direction showing the state of the weld pool formed in the laser welding step applied to the method for manufacturing a secondary battery according to the first embodiment. When welding the opening of the outer can and the lid member, it is preferable that the length of the molten pool 60 (molten pool length U) be long. The reason for this will be explained below.

[0031] When the length of the molten pool 60 in the direction of travel of the laser beam 51 (the melt pool length U) is short, the molten zone solidifies starting from the vicinity of the point irradiated with the laser beam. The convection of the molten metal is strong where the metal is irradiated with the laser beam, and the convection of the molten metal subsides the further away from the irradiated point. Therefore, when the molten pool 60 is long, the molten zone solidifies with low convection of the molten metal. However, when the molten pool 60 is short, the molten zone solidifies with high convection of the molten metal, which is likely to cause disruption of the convection of the molten metal. This can result in spatter 70 of the molten metal from the molten pool 60, potentially creating a hole or defect in the weld 37. Therefore, when welding a particularly long distance, it is preferable to increase the molten pool length U to suppress the generation of spatter 70.

[0032] Therefore, when the elliptical laser beam 51 is irradiated over a long welding distance between the long side of the outer can 3 and the long side of the lid member 7 such that the first distance A of the elliptical laser beam 51 is parallel to the long side direction of the lid member 7, the first distance A of the laser beam 51 is longer than the second distance B, and therefore a molten pool 60 of sufficient length is formed in the welding, and the molten pool 60 formed on the outer can 3 and the lid member 7 slowly solidifies. This makes it possible to suppress spatter 70 of molten metal from the molten pool 60.

[0033] In this embodiment, when laser welding the long side of the outer can 3 and the long side of the lid member 7, the first distance A of the elliptical laser beam 51 is irradiated in a direction parallel to the long side direction of the lid member 7, thereby suppressing heat input from the laser beam 51 to the insulating gasket 29, thereby preventing a weakening of the adhesion between the insulating gasket 29 and the external terminal 23 and between the insulating gasket 29 and the lid member 7 and ensuring the airtightness of the secondary battery 1. Furthermore, welding the long welding distance between the long side of the outer can 3 and the long side of the lid member 7 in this manner suppresses spatter 70 of molten metal generated from the molten pool 60, thereby reducing poor welding between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7 and improving welding efficiency.

[0034] As described above, in this embodiment, the sidewall thickness on the short side of the outer can 3 is thicker than the sidewall thickness on the long side of the outer can 3. As a result, when laser welding the short side of the outer can 3 to the short side of the lid member 7, multiple welding passes may be required compared to when welding the long side of the outer can 3 to the long side of the lid member 7 with the laser beam 51. Therefore, when laser welding the short side of the outer can 3 to the short side of the lid member 7, the elliptical laser beam 51 is irradiated in a direction parallel to the short side direction of the lid member 7, such that the second distance B of the laser beam 51 is parallel to the short side direction of the lid member 7. As a result, the first distance A of the laser beam 51 is longer than the second distance B, and therefore the penetration width 43 formed between the short side of the outer can 3 and the short side of the lid member 7 is wider than the penetration width 43 formed between the long side of the outer can 3 and the long side of the lid member 7. This reduces welding defects caused by insufficient penetration width between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7, improving welding efficiency.

[0035] The first distance A and the second distance B of the beam shape of the laser light 51 preferably satisfy the relationship 1.5≦A / B≦5.0. Here, the units of the first distance A and the second distance B are μm. Simulation results show that when the relationship (A / B) between the first distance A and the second distance B of the beam shape of the laser light 51 is 1.5 or more, the heat input to the insulating gasket 29 on the long side can be suppressed more than when a circular laser light 51 is used, and a wider melting width can be obtained on the short side, resulting in the effect of the elliptical beam shape of the laser light 51. Details of the simulation will be described later.

[0036] The beam shape of the laser light 51 at the irradiation position is defined by a Gaussian distribution. If the energy of the laser light 51 is taken as the vertical axis and the beam diameter (second distance B) of the laser light 51 is taken as the horizontal axis, a Gaussian distribution profile with a centrally symmetrical energy distribution can be drawn. Here, the relative energy when the energy on the central axis is normalized to 1 is 1 / e 2 The distance between the two points at which (≈0.135) is defined as the beam diameter (second distance B) of the laser light 51. The beam diameter (first distance A) of the laser light 51 is defined in the same way.

[0037] Furthermore, the second distance B of the beam shape at the irradiation position of laser beam 51 is preferably 100 μm or more and 300 μm or less. The first distance A and the second distance B of the beam shape of laser beam 51 preferably satisfy the relationship 1.5≦A / B≦5.0, so when the second distance B of the beam shape of laser beam 51 is 100 μm, the minimum first distance A is 150 μm. When the difference between the first distance A and the second distance B of the beam shape of laser beam 51 is 50 μm or more, the heat input to insulating gasket 29 can be suppressed on the long side compared to when a circular laser beam 51 is used, and a wider melting width can be obtained on the short side, resulting in the effect of the elliptical beam shape of laser beam 51.

[0038] Furthermore, it is more preferable that the first distance A and the second distance B of the beam shape at the irradiation position of laser beam 51 satisfy the relationship 1.5≦A / B≦3.0. When laser beam 51 having an elliptical shape is irradiated in a direction parallel to the long side direction of lid member 7, if the relationship (A / B) between the first distance A and the second distance B of the beam shape of laser beam 51 is 1.5 or more, penetration depth 49 is deeper than when circular laser beam 51 is used, and there is an effect that the beam shape of laser beam 51 is elliptical. Furthermore, if the relationship (A / B) between the first distance A and the second distance B of the beam shape of laser beam 51 is 3.0 or less, sufficient penetration width 43 can be ensured in welding.

[0039] When laser welding the short sides of the outer can 3 and the short sides of the lid member 7, the laser beam is irradiated so that the center of the laser beam 51 is positioned at a contact point 53 where the upper surface of the side wall on the short side of the outer can 3 comes into contact with the lid member 7. Here, the contact point 53 is preferably located 50 μm or more and 100 μm or less from the inside of the side wall on the long side and the short side of the outer can 3. Therefore, when the relationship (A / B) between the first distance A and the second distance B of the beam shape of the laser beam 51 is 3.0 or less, it is possible to prevent the first distance A of the beam shape of the laser beam 51 from extending outward from the side wall on the short side of the outer can 3. This makes it possible to prevent insufficient melting of the short side of the outer can 3 by the laser beam 51, and to reduce welding defects due to insufficient penetration width.

[0040] The beam shape of laser light 51 used in the manufacturing method for a secondary battery of this embodiment has a first distance A and a second distance B, and is preferably elliptical, as long as first distance A is longer than second distance B. Since elliptical laser light 51 has no corners, it is possible to suppress spatter 70 that occurs when energy of laser light 51 is concentrated at the corners of laser light 51 when outer can 3 and lid member 7 melt.

[0041] According to this embodiment, when laser welding the long side of the outer can 3 and the long side of the lid member 7, the elliptical laser beam 51 is irradiated in a direction parallel to the long side of the lid member 7, over a first distance A that is longer than the second distance B of the elliptical laser beam 51. This makes it possible to suppress the heat input from the laser beam 51 to the lid member 7 compared to the short side. Therefore, it is possible to suppress the heat input from the laser beam 51 to the insulating gasket 29, prevent weakening of the adhesion between the insulating gasket 29 and the external terminal 23, and between the insulating gasket 29 and the lid member 7, and provide a method for manufacturing a secondary battery and a secondary battery 1 that ensure airtightness.

[0042] Furthermore, with this welding method, first distance A of laser beam 51 is longer than second distance B, and therefore, as laser beam 51 travels, a molten pool length U that is sufficiently long for welding is formed on the long side of outer can 3 and on the long side of lid member 7. Therefore, by welding the long welding distance between the long side of outer can 3 and the long side of lid member 7 in this manner, spatter 70 of molten metal generated from molten pool 60 can be suppressed, thereby reducing welding defects between the outer peripheral edge of outer can opening 9 and the outer peripheral edge of lid member 7, and a secondary battery manufacturing method and secondary battery 1 with improved welding efficiency can be provided.

[0043] Furthermore, according to this embodiment, when laser welding the short side of the outer can 3 and the short side of the lid member 7, the elliptical laser beam 51 is irradiated in a direction parallel to the short side direction of the lid member 7, with the second distance B of the elliptical laser beam 51. As a result, the first distance A of the laser beam 51 is longer than the second distance B, and therefore the penetration width 43 formed between the short side of the outer can 3 and the short side of the lid member 7 is wider than the penetration width 43 formed between the long side of the outer can 3 and the long side of the lid member 7. This makes it possible to prevent welding defects due to narrowing of the welding width on the short side of the outer can 3 and the short side of the lid member 7. Therefore, it is possible to provide a method for manufacturing a secondary battery and a secondary battery 1 that reduce welding defects between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7 and improve welding efficiency.

[0044] When the long side of the outer can 3 and the long side of the lid member 7 are laser welded together, the penetration width 43 formed between the long side of the outer can 3 and the long side of the lid member 7 is narrower than the penetration width 43 formed between the short side of the outer can 3 and the short side of the lid member 7. However, a molten pool length U of sufficient length is formed on the long side of the outer can 3 and on the long side of the lid member 7 during welding. Therefore, a method for manufacturing a secondary battery and a secondary battery 1 can be provided that reduce welding defects between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7. On the other hand, when laser welding the short side of the outer can 3 and the short side of the lid member 7, the molten pool length U formed on the short side of the outer can 3 and the short side of the lid member 7 is shorter than the molten pool length U formed on the long side of the outer can 3 and the long side of the lid member 7, but the penetration width 43 formed on the short side of the outer can 3 and the short side of the lid member 7 is wide, so that poor welding between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7 is reduced, and a method for manufacturing a secondary battery and a secondary battery 1 with improved welding efficiency can be provided.

[0045] (Second embodiment) The beam shape of laser light 51 used in the method for manufacturing a secondary battery according to the second embodiment will be described with reference to FIG. 10 . FIG. 10 shows the beam shape of laser light 51 at the irradiation position of laser light 51 used in the method for manufacturing a secondary battery according to the second embodiment. As shown in FIG. 10 , laser light 51 has a high-density region 55 with a high energy density and a low-density region 57 with a lower energy density than high-density region 55. Low-density region 57 of laser light 51 is formed outside high-density region 55 of laser light 51. Low-density region 57 and high-density region 55 of laser light 51 preferably have a common optical axis, but may have different optical axes. Since low-density region 57 and high-density region 55 of laser light 51 have a common optical axis, only one laser oscillator is required to generate the laser light.

[0046] The beam shape of the low-density region 57 of the laser beam 51 is the same as that of the laser beam 51 applied in the manufacturing method for a secondary battery according to the first embodiment, and a detailed description thereof will be omitted. The specific beam shape of the low-density region 57 of the laser beam 51 is an ellipse, but is not limited thereto and may be a rectangular shape, a diamond shape, a polygonal shape, or the like.

[0047] The beam shape of the high-density region 55 of the laser beam 51 has a third distance C, which is the longest distance in a direction parallel to the Y2 direction, and a fourth distance D, which is the longest distance in a direction parallel to the X2 direction. Here, the third distance C is shorter than or equal to the first distance A, and the fourth distance D is shorter than or equal to the second distance B. Specific beam shapes of the high-density region 55 of the laser beam 51 include an elliptical shape as shown in FIG. 10(a), a rectangular shape as shown in FIG. 10(b), and a diamond or polygonal shape as shown in FIG. 10(c). However, the beam shape of the high-density region 55 of the laser beam 51 is not limited to these. It is sufficient that the beam shape of the high-density region 55 of the laser beam 51 has a third distance C and a fourth distance D, where the third distance C is shorter than or equal to the first distance A, and the fourth distance D is shorter than or equal to the second distance B. The laser beam 51 having such a beam shape can be obtained by passing a circular laser beam 51 through a DOE. The DOE may be located anywhere on the path of the laser beam 51.

[0048] The welding step applied to the manufacturing method of the secondary battery according to the second embodiment will be described with reference to Fig. 11. Fig. 11 is a welding path diagram showing a state viewed from the side where the lid member 7 is located in the Z direction in the welding step applied to the manufacturing method of the secondary battery according to the second embodiment. As shown in Fig. 11, when laser welding the long side of the outer can 3 and the long side of the lid member 7 together, the laser beam 51 having an elliptical shape is irradiated in a direction in which the first distance A and the third distance C of the laser beam 51 are parallel to the long side direction of the lid member 7, that is, in a direction parallel to the Y direction.

[0049] On the other hand, when laser welding the short sides of the outer can 3 and the short sides of the lid member 7, the laser beam 51 is irradiated in a direction parallel to the short side direction of the lid member 7, i.e., parallel to the X direction, such that the second distance B and the fourth distance D of the elliptical laser beam 51 are parallel to the long side direction of the lid member 7. In the beam shape at the irradiation position of the laser beam 51, the first distance A and the third distance C of the laser beam 51 are parallel to the long side direction of the lid member 7, and the second distance B and the fourth distance D of the laser beam 51 are parallel to the short side direction of the lid member 7. Here, in the welding path diagram shown in FIG. 11 , the elliptical laser beam 51 is used in both the low-density region 57 and the high-density region 55 of the laser beam 51, but the shape of the laser beam 51 is not limited thereto. The order in which the long and short sides of the outer can 3 and the lid member 7 are welded is not limited as long as the entire circumference is welded. The entire circumference may be welded multiple times, or portions of the long and short sides of the outer can 3 and the lid member 7 may be welded multiple times.

[0050] When laser welding the long sides of the outer can 3 and the long sides of the lid member 7, the elliptical laser beam 51 is irradiated in a direction parallel to the long side direction of the lid member 7 at a first distance A longer than the second distance B and a third distance C longer than the fourth distance D, and the laser beam 51 has a low-density region 57, so that the heat input from the laser beam 51 to the lid member 7 can be suppressed more than on the short side side. This suppresses the heat input from the laser beam 51 to the insulating gasket 29, preventing a weakening of the adhesion between the insulating gasket 29 and the external terminal 23 and between the insulating gasket 29 and the lid member 7, and ensuring the airtightness of the secondary battery 1.

[0051] Furthermore, with this welding method, first distance A of laser beam 51 is longer than second distance B, and third distance C is longer than fourth distance D. Therefore, as laser beam 51 advances, a molten pool length U of sufficient length is formed on the long side of outer can 3 and the long side of lid member 7 during welding. Therefore, by welding the long side of outer can 3 and the long side of lid member 7 over a long welding distance in this manner, spatter 70 of molten metal generated from molten pool 60 can be suppressed. Furthermore, since laser beam 51 has low-density region 57, the portion irradiated with low-density region 57 of laser beam 51 melts slowly, suppressing spatter 70 of molten metal generated from the surfaces of outer can 3 and lid member 7 during welding, and spatter 70 of molten metal generated from molten pool 60. This reduces welding defects between the outer peripheral edge of outer can opening 9 and the outer peripheral edge of lid member 7, and provides a method for manufacturing a secondary battery and a secondary battery 1 with improved welding efficiency.

[0052] Furthermore, when laser welding the short sides of the outer can 3 and the short sides of the lid member 7, by irradiating the elliptical laser beam 51 in a direction parallel to the short side direction of the lid member 7 such that the second distance B and the fourth distance D of the laser beam 51 are set, the first distance A of the laser beam 51 is longer than the second distance B and the third distance C is longer than the fourth distance D. As a result, the penetration width 43 formed between the short sides of the outer can 3 and the short sides of the lid member 7 is wider than the penetration width 43 formed between the long sides of the outer can 3 and the long sides of the lid member 7. This makes it possible to prevent the short sides of the outer can 3 and the short sides of the lid member 7 from becoming thinner. Furthermore, because the laser beam 51 has the low-density region 57, the portion irradiated with the low-density region 57 of the laser beam 51 melts slowly, making it possible to prevent molten metal spatter 70 from occurring on the surfaces of the outer can 3 and the lid member 7 and from the molten pool 60 during welding. This reduces welding defects between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7, thereby improving welding efficiency, and provides a method for manufacturing a secondary battery and a secondary battery 1. Furthermore, since laser beam 51 has low-density region 57, heat input from laser beam 51 to lid member 7 can be suppressed. This suppresses heat input from laser beam 51 to insulating gasket 29, preventing weakening of the adhesion between insulating gasket 29 and external terminal 23 and between insulating gasket 29 and lid member 7, and ensuring the airtightness of secondary battery 1.

[0053] Similarly to the beam shape of the low-density region 57 of the laser beam 51, the third distance C and the fourth distance D of the beam shape of the high-density region 55 of the laser beam 51 preferably satisfy the relationship 1.5≦C / D≦5.0, and more preferably satisfy the relationship 1.5≦C / D≦3.0. Here, the units of the third distance C and the fourth distance D are μm. This is because, when the relationship (C / D) between the third distance C and the fourth distance D of the beam shape of the high-density region 55 of the laser beam 51 is 1.5 or more, the penetration depth 49 is deeper and the beam shape is elliptical compared to when a perfect circular laser beam 51 is used. Furthermore, when the relationship (C / D) between the third distance C and the fourth distance D of the beam shape of the high-density region 55 of the laser beam 51 is 3.0 or less, a sufficient penetration width can be ensured during welding, and the third distance C of the beam shape of the laser beam 51 can be prevented from extending beyond the short-side sidewall of the outer can 3.

[0054] Furthermore, the beam shape of the high-density region 55 of the laser beam 51 is preferably elliptical. This is because the elliptical laser beam 51 has no corners, and therefore can suppress spatter 70 that occurs when the energy of the laser beam 51 concentrates on the corners of the laser beam 51 when the outer casing 3 and the lid member 7 melt. The beam shapes of both the low-density region 57 and the high-density region 55 of the laser beam 51 are preferably elliptical.

[0055] According to the present embodiment, when laser welding the long sides of the outer can 3 and the long sides of the lid member 7, the elliptical laser beam 51 is irradiated in a direction parallel to the long side direction of the lid member 7 at a first distance A that is longer than the second distance B and a third distance C that is longer than the fourth distance D, and the laser beam 51 has a low-density region 57, so that the heat input from the laser beam 51 to the lid member 7 can be suppressed more than on the short side. This makes it possible to suppress the heat input from the laser beam 51 to the insulating gasket 29, preventing a weakening of the adhesion between the insulating gasket 29 and the external terminal 23 and between the insulating gasket 29 and the lid member 7, and thus providing a method for manufacturing a secondary battery and a secondary battery 1 that ensure airtightness.

[0056] Furthermore, with this welding method, first distance A of laser beam 51 is longer than second distance B, and third distance C is longer than fourth distance D. Therefore, as laser beam 51 travels, a molten pool length U that is long enough for welding is formed on the long sides of outer can 3 and lid member 7. This makes it possible to suppress molten metal spatter 70 from molten pool 60. Furthermore, since laser beam 51 has low-density region 57, it is possible to suppress molten metal spatter 70 from the surfaces of outer can 3 and lid member 7 during welding, and molten metal spatter 70 from molten pool 60. This makes it possible to provide a method for manufacturing a secondary battery and a secondary battery 1 that reduce welding defects between the outer peripheral edge of outer can opening 9 and the outer peripheral edge of lid member 7 and improve welding efficiency.

[0057] Furthermore, when laser welding the short side of the outer can 3 and the short side of the lid member 7, the second distance B and the fourth distance D of the elliptical laser beam 51 are irradiated in a direction parallel to the short side direction of the lid member 7. This makes the first distance A of the laser beam 51 longer than the second distance B and the third distance C longer than the fourth distance D. As a result, the penetration width 43 formed between the short side of the outer can 3 and the short side of the lid member 7 is wider than the penetration width 43 formed between the long side of the outer can 3 and the long side of the lid member 7. This makes it possible to prevent the short side of the outer can 3 and the short side of the lid member 7 from becoming thinner. Furthermore, since the laser beam 51 has the low-density region 57, it is possible to prevent molten metal spatter 70 from occurring on the surfaces of the outer can 3 and the lid member 7 during welding, and to prevent molten metal spatter 70 from occurring in the molten pool 60. This makes it possible to provide a method for manufacturing a secondary battery and a secondary battery 1 that reduce welding defects between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7 and improve welding efficiency. Furthermore, since laser light 51 has low-density region 57, heat input from laser light 51 to lid member 7 can be suppressed. This suppresses heat input from laser light 51 to insulating gasket 29, preventing weakening of the adhesion between insulating gasket 29 and external terminal 23 and between insulating gasket 29 and lid member 7, and providing a method for manufacturing a secondary battery and secondary battery 1 that ensure airtightness.

[0058] When the long side of the outer can 3 and the long side of the lid member 7 are laser welded together, the penetration width 43 formed between the long side of the outer can 3 and the long side of the lid member 7 is narrower than the penetration width 43 formed between the short side of the outer can 3 and the short side of the lid member 7. However, a molten pool length U of sufficient length is formed on the long side of the outer can 3 and on the long side of the lid member 7 during welding. Therefore, a method for manufacturing a secondary battery and a secondary battery 1 can be provided that reduce welding defects between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7. On the other hand, when the short side of the outer can 3 and the short side of the lid member 7 are laser welded together, the length of the molten pool length U formed on the short side of the outer can 3 and the short side of the lid member 7 is shorter than the length of the molten pool length U formed on the long side of the outer can 3 and the long side of the lid member 7. However, since the penetration width 43 formed on the short side of the outer can 3 and the short side of the lid member 7 is wide, poor welding between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7 is reduced, and a method for manufacturing a secondary battery and a secondary battery 1 with improved welding efficiency can be provided.

[0059] (Third embodiment) A secondary battery 1 according to the third embodiment will now be described. Fig. 1 shows the secondary battery 1 manufactured by the method for manufacturing a secondary battery according to the first embodiment. The secondary battery 1 manufactured by the method for manufacturing a secondary battery according to the second embodiment also looks like Fig. 1.

[0060] The insulating gasket 29 disposed in close contact with at least one external terminal 23 of the secondary battery 1 manufactured by the manufacturing method for a secondary battery of the first embodiment is disposed at a position where the length Q is longer than the length R. Furthermore, the insulating gasket 29 disposed in close contact with at least one external terminal 23 of the secondary battery 1 manufactured by the manufacturing method for a secondary battery of the second embodiment is disposed at a position where the length Q is longer than the length R. In this embodiment, the position of the external terminal 23 on the lid member 7 is determined by the structure of the lead 31. Therefore, depending on the structure of the lead 31, the insulating gasket 29 disposed in close contact with at least one external terminal 23 may be disposed at a position where the length Q is shorter than or equal to the length R.

[0061] Furthermore, in the secondary battery 1 manufactured by the manufacturing method for a secondary battery of the first embodiment, the thickness of the side wall on the short side of the outer can 3 is thicker than the thickness of the side wall on the long side of the outer can 3, from the viewpoint of strength, etc. This is also true for the secondary battery 1 manufactured by the manufacturing method for a secondary battery of the second embodiment.

[0062] According to the method for manufacturing a secondary battery of at least one embodiment described above, when laser welding the long side of the outer can 3 and the long side of the lid member 7, the elliptical laser beam 51 is irradiated in a direction parallel to the long side of the lid member 7, over a first distance A that is longer than the second distance B of the elliptical laser beam 51. This makes it possible to suppress heat input from the laser beam 51 to the lid member 7 compared to the short side. Therefore, it is possible to suppress heat input from the laser beam 51 to the insulating gasket 29, and to prevent weakening of the adhesion between the insulating gasket 29 and the external terminal 23 and between the insulating gasket 29 and the lid member 7, thereby providing a method for manufacturing a secondary battery and a secondary battery 1 that ensure airtightness.

[0063] Furthermore, with this welding method, first distance A of laser beam 51 is longer than second distance B, and therefore, as laser beam 51 travels, a sufficiently long molten pool length U is formed on the long side of outer can 3 and on the long side of lid member 7. Therefore, by welding the long side of outer can 3 and the long side of lid member 7 over a long welding distance in this manner, spatter 70 of molten metal generated from molten pool 60 can be suppressed, thereby reducing welding defects between the outer peripheral edge of outer can opening 9 and the outer peripheral edge of lid member 7, and a secondary battery manufacturing method and secondary battery 1 with improved welding efficiency can be provided.

[0064] Furthermore, when laser welding the short sides of the outer can 3 and the short sides of the lid member 7, the elliptical laser beam 51 is irradiated in a direction parallel to the short side direction of the lid member 7, with the second distance B of the elliptical laser beam 51. As a result, the first distance A of the laser beam 51 is longer than the second distance B, and therefore the penetration width 43 formed between the short sides of the outer can 3 and the short sides of the lid member 7 is wider than the penetration width 43 formed between the long sides of the outer can 3 and the long sides of the lid member 7. This makes it possible to prevent the weld width at the short sides of the outer can 3 and the short sides of the lid member 7 from becoming narrower. Therefore, it is possible to provide a method for manufacturing a secondary battery and a secondary battery 1 that reduce welding defects between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7 and improve welding efficiency.

[0065] When the long side of the outer can 3 and the long side of the lid member 7 are laser welded together, the penetration width 43 formed between the long side of the outer can 3 and the long side of the lid member 7 is narrower than the penetration width 43 formed between the short side of the outer can 3 and the short side of the lid member 7. However, a molten pool length U of sufficient length is formed on the long side of the outer can 3 and on the long side of the lid member 7 during welding. Therefore, a method for manufacturing a secondary battery and a secondary battery 1 can be provided that reduce welding defects between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7. On the other hand, when the short side of the outer can 3 and the short side of the lid member 7 are laser welded together, the length of the molten pool length U formed on the short side of the outer can 3 and the short side of the lid member 7 is shorter than the length of the molten pool length U formed on the long side of the outer can 3 and the long side of the lid member 7. However, since the penetration width 43 formed on the short side of the outer can 3 and the short side of the lid member 7 is wide, poor welding between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7 is reduced, and a method for manufacturing a secondary battery and a secondary battery 1 with improved welding efficiency can be provided.

[0066] 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. [Example]

[0067] 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.

[0068] [Relationship between laser beam shape, penetration width, penetration depth, and temperature around the welding position] The relationship between the beam shape of the laser light 51 and the penetration width 43, penetration depth 49, and the temperature around the welding position was determined by a simulation test. In the simulation test, FLOW-3D WELD by FLOW Science JAPAN Co., Ltd. was used.

[0069] The actual phenomenon was assumed to involve welding to a flat plate with a thickness of 2 mm and planar dimensions of 10 cm × 10 cm. However, to shorten the calculation time, the model used for the calculation evaluation was created by cutting out only the weld and its surrounding area from the actual phenomenon, resulting in a flat plate with a thickness (Z3) of 2 mm, a width (X3) of 3.6 mm, and a depth (Y3) of 27 mm. As shown in Figure 12, the calculation model was created by setting one side of the Z3-Y3 plane as a symmetry plane, resulting in a flat plate with a thickness (Z3) of 2 mm, a width (X3) of 1.8 mm, and a depth (Y3) of 27 mm. The initial temperature of the calculation model was 293 K, and the boundary conditions were such that the top and bottom surfaces in the thickness (Z3) direction were radiated to the air at 293 K. Both end faces in the depth (Y3) direction and both end faces in the width (X3) direction were continuous. The laser beam 51 described in the examples and comparative examples was irradiated to the upper part of the symmetry plane on the X3-Y3 top surface and propagated within a range of 1 mm to 16 mm in the depth (Y3) direction. The laser output was 1700 W, and the travel speed was 320 mm / sec. The energy distribution of the laser light 51 at the irradiation position was axially symmetric, and the shape in the radial direction was a Gaussian distribution. When the energy on the central axis was normalized to 1, the relative energy was 1 / e 2 The position where (≒0.135) is defined as the radius and was calculated.

[0070] The weld shape was evaluated for penetration width 43 and penetration depth 49 at a position 6 mm in depth (Y3) after the laser beam 51 had advanced. The 6 mm depth (Y3) position is where the flat plate remains molten after the laser beam 51 has advanced. FIG. 13 shows the cross-sectional shape of a weld 37 on the Z3-X3 plane in a simulation test as an example of the evaluation of penetration width 43 and penetration depth 49. The penetration width 43 is the longest distance in the X3 direction in the weld 37, and the penetration depth 49 is the longest distance in the Z3 direction. Furthermore, the maximum temperature during welding was evaluated at a position 885 μm in the width (X3) direction from the 6 mm depth (Y3) position.

[0071] The effect of welding with an elliptical laser beam 51 will be explained below in comparison with the penetration width 43 and maximum temperature during welding when welding with a circular laser beam 51. Here, the laser beam 51 was irradiated onto a flat plate with the first distance A of the laser beam 51 parallel to the depth (Y3) of the flat plate, and the results are shown in Table 1 and FIG. 14. The verification was also carried out when the penetration depth 49 was 600 μm.

[0072] Example 1 An elliptical laser beam 51 was used, the first distance A was set to 300 μm, the second distance B was set to 150 μm, and A / B=2.0.

[0073] Example 2 An elliptical laser beam 51 was used, the first distance A was set to 150 μm, the second distance B was set to 300 μm, and A / B=0.5.

[0074] (Comparative Example 1) A circular laser beam 51 was used, the first distance A was set to 300 μm, the second distance B was set to 300 μm, and A / B=1.0.

[0075] [Table 1]

[0076] As shown in Table 1 and FIG. 14 , comparing Example 1 and Example 2, the penetration width 43 is about 60 μm wider in Example 2. This is because the second distance B of the laser beam 51 used in Example 2 is longer than the second distance B of the laser beam 51 used in Example 1. Furthermore, comparing Example 1 and Example 2, the maximum temperature during welding is lower by about 15 K in Example 1. This is because the second distance B of the laser beam 51 used in Example 1 is shorter than the second distance B of the laser beam 51 used in Example 2.

[0077] Furthermore, when Example 1 and Comparative Example 1 are compared, the molten pool lengths U are approximately the same, and the maximum temperature during welding is lower by approximately 15 K in Example 1. Therefore, it was verified that by using laser beam 51 with A / B=2.0, the stability during welding can be ensured to the same extent as that of laser beam 51 with a perfect circular shape, while the maximum temperature during welding can be suppressed.

[0078] Furthermore, comparing Example 2 and Comparative Example 1, the penetration width 43 in Example 2 is approximately 20 μm wider. This is because the irradiation area of ​​the laser beam 51 in Example 2 is smaller than that in Comparative Example 1, resulting in a higher energy density of the laser beam 51 and the supply of energy from the laser beam 51 in the X3 direction. Furthermore, in Example 2 and Comparative Example 1, the maximum temperature during welding can be kept equal to or lower than that in Comparative Example 1. From the above, it was verified that, in welding an outer can opening 9 having long and short sides and a lid member 7, by arranging the elliptical laser beam 51 at a first distance A parallel to the first direction parallel to the long side direction of the outer can opening 9 and arranging the elliptical laser beam 51 at a second distance B parallel to the second direction parallel to the short side direction of the outer can opening 9, desired welding characteristics that cannot be obtained with a circular laser beam 51 can be obtained.

[0079] Next, the effective range of A / B of the elliptical laser beam 51 was verified. Using the elliptical laser beam 51, the first distance A was set to 300 μm, and the second distance B was varied from 50 to 250 μm. The melting depth 49, melting width 43, molten pool length U, and maximum temperature during melting at this time will be compared and explained. Here, the laser beam 51 was irradiated onto a flat plate such that the first distance A of the laser beam 51 was parallel to the depth direction (Y3) of the flat plate, and the results are shown in Table 2 and Figure 15.

[0080] Example 3 The second distance B was set to 200 μm, and A / B=1.5.

[0081] Example 4 The second distance B was set to 100 μm, and A / B=3.0.

[0082] Example 5 The second distance B was set to 60 μm, and A / B=5.0.

[0083] (Comparative Example 2) The second distance B was set to 250 μm, and A / B=1.2.

[0084] (Comparative Example 3) The second distance B was set to 50 μm, and A / B=6.0.

[0085] [Table 2]

[0086] As shown in Table 2 and Fig. 15, it was confirmed that as the value of A / B increases, the penetration depth 49 increases, the penetration width 43 decreases, the molten pool length U increases, and the maximum temperature during welding decreases. In particular, it was verified that the maximum temperature during welding decreases significantly when the value of A / B is 1.5 or more, compared to the perfectly circular shape of Comparative Example 1.

[0087] In addition, an elliptical laser beam 51 was used, the second distance B was set to 300 μm, and the first distance A was varied from 50 to 250 μm. The melting depth 49, melting width 43, molten pool length U, and maximum temperature during melting at this time will be compared and explained. Here, the laser beam 51 was irradiated onto the flat plate such that the first distance A of the laser beam 51 was parallel to the depth direction (Y3) of the flat plate, and the results are shown in Table 3 and FIG. 16.

[0088] Example 6 The first distance A was set to 200 μm, and A / B=0.7.

[0089] Example 7 The first distance A was set to 150 μm, and A / B=0.5.

[0090] Example 8 The first distance A was set to 100 μm, and A / B=0.3.

[0091] Example 9 The first distance A was set to 60 μm, and A / B=0.2.

[0092] Comparative Example 4 The first distance A was set to 250 μm, and A / B=0.8.

[0093] (Comparative Example 5) The first distance A was set to 50 μm, and A / B=0.17.

[0094] [Table 3]

[0095] 16, it was confirmed that the smaller the value of A / B, the deeper the penetration depth 49 and the longer the molten pool length U. This is because the shorter the first distance A of the laser beam 51, the smaller the irradiation area of ​​the laser beam 51 and the higher the energy density.

[0096] Tables 2 and 3 show the results when the laser beam 51 was irradiated onto a flat plate such that the first distance A of the laser beam 51 was parallel to the depth direction (Y3) of the flat plate. When the results of this simulation are applied to the present invention, in welding an outer can opening 9 having long sides and short sides to a lid member 7, the elliptical laser beam 51 is arranged parallel to the first direction parallel to the long side direction of the outer can opening 9 at the first distance A, and the elliptical laser beam 51 is arranged parallel to the second direction parallel to the short side direction of the outer can opening 9 at the second distance B. Since it is preferable to use laser beam 51 of a similar shape for the long sides and the short sides, when the laser beam 51 of Example 1 and Examples 3 to 5 is used to weld the long sides, the laser beam 51 is rotated 90° to become the laser beam 51 of Example 2 and Examples 6 to 8, and the short sides are welded.

[0097] Here, Table 4 shows the differences in penetration depth 49, penetration width 43, molten pool length U, and maximum temperature during welding when laser beam 51 of Example 1, Examples 3 to 5 is used to weld the long sides, and laser beam 51 of Example 2, Examples 6 to 8 is used to weld the short sides.

[0098] [Table 4]

[0099] As in Table 2, Table 4 demonstrates that when the A / B value is 1.5 or greater, the difference in maximum temperature during welding is 10 K or greater, effectively suppressing the temperature of the irradiated material. Furthermore, as the A / B value increases, the differences in penetration depth 49, penetration width 43, molten pool length U, and maximum temperature during welding increase. However, if the difference in penetration depth 49 is 100 μm or greater, the welding balance between the long and short sides becomes poor. Therefore, it is preferable that the A / B value be 5.0 or less, and it is preferable that the relationship 1.5≦A / B≦5.0 be satisfied. Furthermore, if the difference in penetration depth 49 is 80 μm or less, the welding balance between the long and short sides is good, so it is even more preferable that the relationship 1.5≦A / B≦3.0 be satisfied.

[0100] The results of the above simulation test are used in the manufacturing method for the secondary battery and the secondary battery 1 of this embodiment. Specifically, when laser welding the long side of the outer can 3 and the long side of the lid member 7, the laser beam 51 is irradiated in a direction parallel to the long side of the lid member 7, with a first distance A longer than the second distance B of the elliptical laser beam 51. This makes it possible to suppress the heat input from the laser beam 51 to the lid member 7 compared to the short side. Therefore, it is possible to suppress the heat input from the laser beam 51 to the insulating gasket 29, prevent weakening of the adhesion between the insulating gasket 29 and the external terminal 23, and provide a manufacturing method for a secondary battery and a secondary battery 1 that ensure airtightness.

[0101] Furthermore, when laser welding the short sides of the outer can 3 and the short sides of the lid member 7, the laser beam 51 is irradiated in a direction perpendicular to the short side direction of the lid member 7, over a first distance A that is longer than the second distance B of the elliptical laser beam 51. As a result, the penetration width 43 formed between the short sides of the outer can 3 and the short sides of the lid member 7 is wider than the penetration width 43 formed between the long sides of the outer can 3 and the long sides of the lid member 7. This makes it possible to prevent the short sides of the outer can 3 and the short sides of the lid member 7 from becoming thinner due to an increase in the number of welding operations. Therefore, it is possible to provide a method for manufacturing a secondary battery and a secondary battery 1 that reduce welding defects between the outer peripheral edge of the outer can opening 9 and the outer peripheral edge of the lid member 7 and improve welding efficiency. [Explanation of symbols]

[0102] 1... secondary battery, 3... outer can, 5... electrode group, 7... lid member, 9... outer can opening, 11... internal cavity, 13... positive electrode, 13a... positive electrode current collector, 13b... positive electrode current collector tab, 15... negative electrode, 15a... negative electrode current collector, 15b... negative electrode current collector tab, 16... backup lead, 17... filling port, 19... sealing plate, 21... gas release valve, 23... external terminal, 23a... positive electrode external terminal, 23b... negative electrode external Terminal, 25...head, 27...shank, 29...insulating gasket, 29a...end, 29b...end, 31...lead, 33...internal insulating member, 34...insulating guard, 35...terminal insulator, 36...insulating tape, 37...weld, 43...penetration width, 49...penetration depth, 51...laser light, 53...contact point, 55...high density area, 57...low density area, 60...molten pool, 70...spatter.

Claims

1. a housing step of housing the electrode group in an outer can having a rectangular opening with long sides and short sides; a placement step of placing a cover member on the opening; a welding step of welding the opening and the lid member by irradiating a laser beam; Equipped with The beam shape at the irradiation position of the laser light is a first distance A that is the longest in a first direction parallel to the long side direction of the opening; a second distance B that is the longest in a second direction parallel to the short side direction of the opening, The method for manufacturing a secondary battery, wherein the first distance A is longer than the second distance B.

2. The method for manufacturing a secondary battery according to claim 1 , wherein the first distance A and the second distance B satisfy the relationship of the following formula (1): 1.5≦A / B≦5.0 (1)

3. The method for manufacturing a secondary battery according to claim 1 , wherein the beam shape is an ellipse.

4. The laser light has a high density region with a high energy density and A low-density region having a lower energy density than the high-density region is provided outside the high-density region. The method for manufacturing the secondary battery according to claim 1 .

5. The method for manufacturing a secondary battery according to claim 4 , wherein the high-density region and the low-density region have a common optical axis.

6. The beam shape at the irradiation position of the high density area is a third distance C that is the longest in the first direction parallel to the long side direction of the opening; a fourth distance D that is the longest in the second direction parallel to the short side direction of the opening, the third distance C is less than or equal to the first distance A; the fourth distance D is less than or equal to the second distance B; The method for manufacturing a secondary battery according to claim 4 .

7. The method for manufacturing a secondary battery according to claim 6 , wherein the third distance C and the fourth distance D satisfy the relationship of the following formula (2): 1.5≦C / D≦5.0 (2)

8. The method for manufacturing a secondary battery according to claim 6 , wherein the beam shape at the irradiation position in the high density region is elliptical.

9. an outer can having a rectangular opening with long and short sides; an electrode group housed in the outer can; a cover member disposed on the opening; a pair of external terminals disposed on the cover member via an insulating gasket; A secondary battery manufactured by the method for manufacturing a secondary battery according to claim 1 .

10. 10. The secondary battery according to claim 9, wherein a minimum distance from an end of at least one of the insulating gaskets to the short side in a first direction parallel to the long side direction of the opening is longer than a minimum distance from the end of the insulating gasket to the long side in a second direction parallel to the short side direction of the opening.

11. The secondary battery according to claim 9 , wherein the thickness of the side wall on the short side of the outer can is thicker than the thickness of the side wall on the long side.

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