Method for manufacturing a secondary battery

Abstract

This invention relates to a method for manufacturing a secondary battery. It improves the welding quality of the opening (41a1) of the casing body (41a) and the sealing plate (41b). The method for manufacturing a secondary battery disclosed herein includes: an installation step in which the sealing plate (41b) is installed into the opening (41a1) of a bottomed casing body (41a); and a welding step in which a laser is scanned along the periphery (41b3) of the sealing plate (41b) to perform laser welding on the casing body (41a) and the sealing plate (41b). Here, in the welding process, the laser irradiating the edge of the opening (41a1) of the housing body (41a) and the periphery (41b3) of the sealing plate (41b) is a pulse oscillating laser composed of a rectangular wave with a pulse width of 400 μm or more and 800 μm or less and a frequency of 1.2 kHz or more and 1.4 kHz or less, and is scanned in such a way that the overlap rate of adjacent lasers that are pulse oscillating is 84.4% or more and 86.6% or less.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a secondary battery. Background Technology

[0002] Japanese Patent Application Publication No. 2011-212711 discloses a method for manufacturing a sealed battery that welds and seals the mating portion of an aluminum-based outer can and an aluminum-based sealing plate disposed at the opening of the outer can by irradiating a laser from a continuous oscillating (CW) laser welding apparatus. In this method, scanning is performed in the welding start region while pulse-modulating the laser output, and then scanning is performed while keeping the laser output constant. According to this method, when welding and sealing an aluminum-based outer can and an aluminum-based sealing plate using a continuous oscillating (CW) laser, welding can be performed stably in both the welding start and welding end regions.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2011-212711 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] However, it is desirable to further improve the welding quality in the welding of the opening of the main body of the shell to the periphery of the sealing plate.

[0008] Solution for solving the problem

[0009] The disclosed method for manufacturing a secondary battery includes: an installation step in which a sealing plate is installed on an opening in a bottomed housing body having an opening on one side facing the bottom; and a welding step in which a laser is scanned along the periphery of the sealing plate to perform laser welding on the housing body and the sealing plate. In the welding step, the laser irradiating the edge of the opening in the housing body and the periphery of the sealing plate is a pulsed oscillating laser composed of a rectangular wave with a pulse width of 400 μm or more and 800 μm or less, and a frequency of 1.2 kHz or more and 1.4 kHz or less. The scanning is performed with an overlap rate of 84.4% or more and 86.6% or less between adjacent pulsed lasers. According to this method for manufacturing a secondary battery, it is easy to achieve a moderately deep weld penetration, thereby improving weld quality.

[0010] Alternatively, during the welding process, the laser is scanned along the periphery of the sealing plate while the peak output of the laser is partially changed.

[0011] For example, the sealing plate before welding could have a grooved portion with a groove formed on the inner side of the periphery and a non-groove portion without a groove. In this case, the peak output of the laser when welding the non-groove portion could be set to be greater than the peak output of the laser when welding the grooved portion during the welding process.

[0012] Alternatively, the sealing plate can be a generally rectangular sheet material having a pair of opposing long sides and a pair of opposing short sides. Alternatively, the opening of the main body of the shell can have a generally rectangular shape corresponding to the sealing plate, and in the welding process, the peak laser output is higher when welding the long sides than when welding the short sides.

[0013] Alternatively, the sealing plate may have an R-section located between the long side and the short side. In this case, the peak laser output during welding of the R-section may be lower than the peak laser output during welding of the short side.

[0014] Alternatively, the peak laser output can gradually increase at the boundaries of the long side, short side, and R-section of the sealing plate. Alternatively, the starting and ending points of the welding process can overlap at the periphery of the sealing plate. Attached Figure Description

[0015] Figure 1 This is a partial cross-sectional view of the lithium-ion secondary battery 10.

[0016] Figure 2 This is a top view showing the upper surface where the sealing plate 41b is installed.

[0017] Figure 3 This is a schematic diagram illustrating the waveform of a pulsed oscillating laser.

[0018] Figure 4 It means Figure 2 A cross-sectional view of section AA.

[0019] Figure 5 It means Figure 2 Cross-sectional view of section BB.

[0020] Explanation of reference numerals in the attached figures

[0021] 10: Lithium-ion secondary battery; 20: Electrode body; 21: Positive electrode sheet; 21a: Positive electrode current collector foil; 21a1: Unformed portion of the positive electrode current collector foil; 21b: Positive electrode active material layer; 22: Negative electrode sheet; 22a: Negative electrode current collector foil; 22a1: Unformed portion of the negative electrode current collector foil; 22b: Negative electrode active material layer; 31, 32: Spacers; 41: Battery casing; 41a: Casing body; 41a1: Opening; 41b: Sealing plate; 41b1: Liquid injection hole; 41b 2: Safety valve; 41b3: Peripheral part; 42: Bottom part; 43, 44: Wide part; 45, 46: Narrow part; 47: Slot part; 47a: Slot; 48: Non-slot part; 50: Positive terminal; 51: External terminal; 55: Internal terminal; 60: Negative terminal; 61: External terminal; 65: Internal terminal; 70: Washer; 80: Insulator; 91, 92: Long side part; 93, 94: Short side part; 95-98: R part; L: Laser. Detailed Implementation

[0022] The following describes one embodiment disclosed herein. This embodiment is not intended to limit the scope of the disclosure. The accompanying drawings are schematic depictions and do not necessarily reflect the actual object. Furthermore, unless specifically mentioned otherwise, expressions such as "A to B" indicating a numerical range mean "A or more and B or less." It should be noted that in the drawings described below, the same reference numerals are used to denote components and parts that produce the same effect, and sometimes repeated descriptions are omitted or simplified. Additionally, in the figures referenced in this specification, reference numeral X indicates the "long side direction," reference numeral Y indicates the "short side direction," and reference numeral Z indicates the "height direction."

[0023] In this specification, "secondary battery" generally refers to an energy storage device that undergoes a charging and discharging reaction by the movement of charge carriers between a pair of electrodes (positive and negative electrodes) via an electrolyte. Besides so-called rechargeable batteries such as lithium-ion batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, secondary batteries also include capacitors such as electric double-layer capacitors. Hereinafter, an embodiment of the manufacturing method of the secondary battery disclosed herein will be described using a lithium-ion secondary battery as an example. Unless otherwise specified, the disclosure herein is not limited to lithium-ion secondary batteries and can be applied to other secondary batteries.

[0024] <Lithium-ion secondary battery 10>

[0025] Figure 1 This is a partial cross-sectional view of the lithium-ion secondary battery 10. Figure 2 This is a top view showing the upper surface where the sealing plate 41b is installed. Figure 1 The image depicts a state where the interior is exposed along a wide surface of one side of the roughly rectangular battery casing 41. Figure 1The lithium-ion secondary battery 10 shown is a so-called sealed battery, in which the battery casing 41 containing the electrode body 20 is sealed.

[0026] like Figure 1 As shown, the lithium-ion secondary battery 10 includes an electrode body 20 and a battery casing 41. The battery casing 41 has a casing body 41a with an opening 41a1 and a sealing plate 41b that blocks the opening 41a1 of the casing body 41a. The electrode body 20 is housed in the casing body 41a. Internal terminals 55 and 65 and external terminals 51 and 61 are mounted on the sealing plate 41b, separated by a gasket 70 and an insulator 80. In this embodiment, the internal terminal 55 is connected to the positive electrode current collector foil 21a of the electrode body 20. The external terminal 51 is connected to the internal terminal 55, forming a positive terminal 50 on the outside of the battery casing 41. In addition, the internal terminal 65 is connected to the negative electrode current collector foil 22a of the electrode body 20. The external terminal 61 is connected to the internal terminal 65, forming a negative terminal 60 on the outside of the battery casing 41.

[0027] <Electrode 20>

[0028] The electrode body 20 is housed in the battery casing 41 covered by an insulating film (not shown). The electrode body 20 includes a positive electrode plate 21 as a positive electrode element, a negative electrode plate 22 as a negative electrode element, and spacers 31 and 32 as spacers. The positive electrode plate 21, the first spacer 31, the negative electrode plate 22, and the second spacer 32 are all longitudinally elongated strip-shaped components.

[0029] The positive electrode sheet 21 has a positive electrode active material layer 21b containing positive electrode active material formed on two surfaces of a positive electrode current collector foil 21a (e.g., aluminum foil) of predetermined width and thickness, except for an unformed portion 21a1 of a certain width at one end in the width direction. In lithium-ion secondary batteries, the positive electrode active material is, for example, a material that can release lithium ions during charging and absorb lithium ions during discharging, such as a lithium transition metal composite material. Regarding the positive electrode active material, various solutions have been proposed in general, except for lithium transition metal composite materials, and there is no particular limitation.

[0030] The negative electrode sheet 22 has a negative electrode active material layer 22b formed on both sides of a negative electrode current collector foil 22a (in this case, a copper foil) of predetermined width and thickness, except for an unformed portion 22a1 of a certain width set at one edge in the width direction. This layer contains the negative electrode active material. In lithium-ion secondary batteries, the negative electrode active material is, for example, a material like natural graphite that can absorb lithium ions during charging and release the absorbed lithium ions during discharging. Various alternatives to natural graphite have been proposed for the negative electrode active material, and there is no particular limitation.

[0031] Spacers 31 and 32 may be made of porous resin sheets, for example, through which an electrolyte with the required heat resistance can pass. Various designs for spacers 31 and 32 have also been proposed, and there are no particular limitations.

[0032] Here, the width of the negative electrode active material layer 22b is, for example, wider than that of the positive electrode active material layer 21b. The widths of the spacers 31 and 32 are wider than that of the negative electrode active material layer 22b. The unformed portions 21a1 of the positive electrode current collector foil 21a and the unformed portions 22a1 of the negative electrode current collector foil 22a face opposite sides in the width direction. Furthermore, the positive electrode sheet 21, the first spacer 31, the negative electrode sheet 22, and the second spacer 32 are aligned in the length direction and are sequentially overlapped and wound. The negative electrode active material layer 22b covers the positive electrode active material layer 21b with the spacers 31 and 32 in between. The negative electrode active material layer 22b is covered by the spacers 31 and 32. The unformed portions 21a1 of the positive electrode current collector foil 21a extend from one side of the spacers 31 and 32 in the width direction. The unformed portions 22a1 of the negative electrode current collector foil 22a extend from the spacers 31 and 32 on the opposite side in the width direction.

[0033] like Figure 1 As shown, the electrode body 20 is configured to be flat along a plane including the winding axis so that it can be housed in the housing body 41a of the battery housing 41. Furthermore, along the winding axis of the electrode body 20, an unformed portion 21a1 of the positive electrode current collector foil 21a is disposed on one side, and an unformed portion 22a1 of the negative electrode current collector foil 22a is disposed on the opposite side.

[0034] <Battery casing 41>

[0035] The battery casing 41 houses the electrode body 20. The battery casing 41 has a casing body 41a and a sealing plate 41b. The casing body 41a is a bottomed member with an opening 41a1 on one side facing the bottom; in this embodiment, it has a generally rectangular shape with an opening on one side. The sealing plate 41b is a sheet material installed in the opening 41a1 of the casing body 41a. In this embodiment, from the viewpoint of ensuring lightweight and the required rigidity, the casing body 41a and the sealing plate 41b are respectively formed of aluminum or an aluminum-based alloy. It should be noted that... Figure 1 In the illustrated embodiment, a wound electrode body 20 is shown, but the structure of the electrode body 20 is not limited to this method. For example, the electrode body 20 can also be constructed as a stacked structure in which positive and negative electrode sheets are alternately stacked with spacers between them. Alternatively, multiple electrode bodies 20 may be housed within the battery casing 41.

[0036] The battery casing 41 may also contain an electrolyte (not shown) together with the electrode body 20. As the electrolyte, a non-aqueous electrolyte containing a supporting salt dissolved in a non-aqueous solvent can be used. Examples of non-aqueous solvents include carbonate solvents such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of supporting salts include fluorinated lithium salts such as LiPF6.

[0037] <Shell Body 41a>

[0038] The main body 41a has a generally rectangular, cuboid shape with an opening on one side. The main body 41a has a bottom portion 42 forming a generally rectangular base, and a pair of wide portions 43 and 44 (see reference). Figure 2 A pair of narrow faces 45 and 46 are formed on one side of the body 41a. A pair of wide faces 43 and 44 rise from the long side of the bottom face 42. A pair of narrow faces 45 and 46 rise from the short side of the bottom face 42. An opening 41a1 surrounded by a pair of wide faces 43 and 44 and a pair of narrow faces 45 and 46 is formed on one side of the body 41a.

[0039] <Sealing plate 41b>

[0040] The sealing plate 41b seals the opening 41a1 of the housing body 41a. In this embodiment, as... Figure 2 As shown, the sealing plate 41b is rectangular in shape when viewed from above. In this embodiment, the sealing plate 41b is provided with an injection hole 41b1 and a safety valve 41b2. After the sealing plate 41b is installed in the opening 41a1 of the housing body 41a and electrolyte is injected into the housing body 41a, a sealing member is installed to close the injection hole 41b1. It should be noted that in Figure 2 The diagram shows the state in which the sealing plate 41b is assembled and welded to the opening 41a1 of the housing body 41a. Figure 2 In this case, no sealing component is installed on the sealing plate 41b. The safety valve 41b2 is thin-walled and is the part that breaks when the pressure inside the battery housing 41 exceeds a predetermined value.

[0041] A positive terminal 50 and a negative terminal 60 are mounted on a sealing plate 41b. The positive terminal 50 has an external terminal 51 and an internal terminal 55. The negative terminal 60 has an external terminal 61 and an internal terminal 65. The internal terminals 55 and 65 are mounted on the inner side of the sealing plate 41b, separated by an insulator 80. The external terminals 51 and 61 are mounted on the outer side of the sealing plate 41b, separated by a gasket 70. The internal terminals 55 and 65 extend inside the housing body 41a. The unformed portions 21a1 of the positive current collector foil 21a and 22a1 of the negative current collector foil 22a of the electrode body 20 are mounted on the internal terminals 55 and 65, which are respectively mounted on both sides in the long side direction of the sealing plate 41b.

[0042] The internal terminals 55 and 65 are made of metal. For the positive terminal 55, from the viewpoint of improving the bonding strength with the positive current collector foil 21a, aluminum or an aluminum alloy can be used, for example. For the negative terminal 65, from the viewpoint of improving the bonding strength with the negative current collector foil 22a, and also from the viewpoint of possessing the required resistance to electrolytes, oxidation, etc., copper or a copper alloy can be used, for example.

[0043] External terminals 51 and 61 are made of metal. The metal used for external terminals 51 and 61 is appropriately selected according to the type of external connection components such as busbars. For example, aluminum, aluminum alloy, copper, and copper alloy can be used as external terminals 51 and 61. External terminals 51 and 61 can also be constructed by joining multiple metals, for example, by joining dissimilar metals. Although not shown in the figure, a mounting hole is formed in the sealing plate 41b. An insulator 80 is mounted on the inner side of the sealing plate 41b in the mounting hole, and a washer 70 is mounted on the outer side of the sealing plate 41b. One of the internal terminals 55 and 65 and the external terminals 51 and 61 has a shaft portion that passes through the mounting hole through the washer 70 and the insulator 80. The internal terminals 55 and 65 and the external terminals 51 and 61 are joined by the shaft portion passing through the mounting hole.

[0044] Materials with excellent chemical resistance and weather resistance are preferred for both gasket 70 and insulator 80. In this embodiment, gasket 70 is made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). It should be noted that the material used for gasket 70 is not limited to PFA. Gasket 70 can also be made of, for example, polypropylene (PP), polyethylene (PE), polyphenylene sulfide resin (PPS), etc. Insulator 80 is made of polyphenylene sulfide resin (PPS). It should be noted that the material used for insulator 80 is not limited to PPS.

[0045] Here, as an example of electrode body 20, a so-called wound electrode body is shown, in which the positive electrode 21, the first spacer 31, the negative electrode 22, and the second spacer 32 are all aligned in the same longitudinal direction and are sequentially overlapped and wound. Electrode body 20 is not limited to such a wound electrode body. Alternatively, multiple electrode bodies 20 may be housed in the battery casing 41. The internal terminals 55 and 65, the external terminals 51 and 61, the gasket 70, and the insulator 80 can adopt various structures. For example, it is preferable that the internal terminals 55 and 65, the external terminals 51 and 61, the gasket 70, and the insulator 80 adopt appropriate structures depending on the structure of the housed electrode body 20. In addition, a mechanism (CID (Current Interrupt Device)) may be provided in one of the positive terminal 50 and the negative terminal 60 such that, during overcharging, the internal pressure rises due to the generation of gas inside, thereby cutting off the current.

[0046] Regarding the lithium-ion secondary battery 10, during manufacturing, with the gasket 70 and insulator 80 installed on the sealing plate 41b, the positive terminal 50 and negative terminal 60 are installed. Next, the electrode body 20 is installed on the positive terminal 50 and negative terminal 60. Next, the sealing plate 41b is installed onto a pair of wide facets 43, 44 (see reference). Figure 2 The opening 41a1 of the shell body 41a, which is surrounded by the long side of the shell and the short sides of a pair of narrow facets 45 and 46 (see reference). Figure 1 ). And, as Figure 2 As shown, the peripheral portion 41b3 of the sealing plate 41b is joined to the edge of the opening 41a1 of the housing body 41a. This joining is preferably performed, for example, by a gapless, continuous weld. This weld can be achieved, for example, by laser welding.

[0047] However, in such sealed batteries, there is a tendency to reduce the ineffective space inside the secondary battery in order to achieve high energy density. If the ineffective space inside the secondary battery is small, the internal pressure of the secondary battery will increase when gas is generated inside, etc. Therefore, it is preferable that the laser-welded part between the casing body and the sealing plate has high pressure resistance.

[0048] The manufacturing method of the secondary battery disclosed herein includes: an installation step of installing a sealing plate 41b into the opening 41a1 of the housing body 41a; and a welding step of scanning a laser along the periphery 41b3 of the sealing plate 41b and performing laser welding on the housing body 41a and the sealing plate 41b.

[0049] During the welding process, the laser irradiating the edge of the opening 41a1 of the housing body 41a and the periphery 41b3 of the sealing plate 41b is a pulsed oscillating laser composed of rectangular waves with a pulse width of 400μm to 800μm and a frequency of 1.2kHz to 1.4kHz. Scanning is performed with an overlap rate of 84.4% to 86.6% between adjacent laser pulses.

[0050] Figure 3 This is a schematic diagram illustrating the waveform of a pulsed, oscillating laser. Here, the laser waveform is depicted as a rectangular wave, but the rise of a rectangular wave can also have a slope.

[0051] The pulse width is the distance that the laser scans on the object being irradiated during a certain period of laser output.

[0052] Frequency is the reciprocal of the pulse period, and is used in Hz as the unit.

[0053] The overlap ratio is the proportion of the overlapping area of ​​the melting traces of adjacent lasers when scanning an object irradiated by a laser in a pulsed oscillating manner.

[0054] According to this welding process, a laser pulses out. The energy of a pulsed laser is higher than that of a CW (Continuous Wave) laser, which emits a constant peak output. Furthermore, in this embodiment, the pulse frequency is high. Therefore, adjacent pulsed lasers overlap to a greater extent. Thus, adjacent lasers are emitted with moderate overlap before the molten pool of the first emitted laser completely solidifies. In this embodiment, the molten pools of the pulsed lasers are deeper, the pulse frequency is faster, and adjacent pulsed lasers overlap to a greater extent. Therefore, the weld penetration is more easily and moderately deepened, the weld quality is significantly improved, and the compressive strength is increased.

[0055] In this case, during the welding process, it is preferable to partially change the peak output of the laser while scanning the laser along the periphery 41b3 of the sealing plate 41b. For example, when the internal pressure in the battery casing 41 increases, the force acting on the weld formed on the periphery 41b3 of the sealing plate 41b may vary locally. When scanning the laser along the periphery 41b3 of the sealing plate 41b, the heat capture method may differ. Therefore, from the viewpoint of achieving the required weld penetration and endurance when the internal pressure in the battery casing 41 increases, it is preferable to appropriately adjust the peak output of the laser in a partially controlled manner.

[0056] For example, in Figure 2In the illustrated configuration, the opening 41a1 of the housing body 41a is a generally rectangular opening with rounded corners, and the sealing plate 41b is also a generally rectangular plate with rounded corners, corresponding to the opening 41a1 of the housing body 41a. During the installation process, the sealing plate 41b is held in a state where it is installed in the opening 41a1 of the housing body 41a. In this case, for example, a step for supporting the installed sealing plate 41b may be provided on the inner surface of the opening 41a1 of the housing body 41a. It is preferable that the step supporting the sealing plate 41b is located on a portion of the inner surface of the opening 41a1 of the housing body 41a; for example, it may be located at a corner of the rectangular opening 41a1. Alternatively, the step supporting the sealing plate 41b may also be located on the inner surface of the rectangular opening 41a1. Alternatively, with the sealing plate 41b installed in the opening 41a1 of the housing body 41a, the sealing plate 41b can be held in the opening 41a1 of the housing body 41a by clamping the sidewalls of a pair of long sides of the opening 41a1. It should be noted that, here, the opening 41a1 of the housing body 41a and the sealing plate 41b are approximately rectangular, but unless otherwise specified, the opening 41a1 of the housing body 41a and the sealing plate 41b are not limited to rectangles. For example, the opening 41a1 of the housing body 41a and the sealing plate 41b can also be circular or elliptical.

[0057] In this embodiment, the sealing plate 41b before welding has a groove portion 47 on the inner side of the peripheral portion 41b3 where a groove 47a is formed, and a non-groove portion 48 on the inner side of the peripheral portion 41b3 where no groove 47a is formed. The non-groove portion 48 is provided in the peripheral portion 41b3 of the sealing plate 41b near the location where the washer 70 is disposed. In this embodiment, the groove 47a is formed on the inner side of the peripheral portion 41b3, except for the location near the location where the washer 70 is disposed. Figure 4 It means Figure 2 A cross-sectional view of section AA. In Figure 4 The cross-section of the groove portion 47 is shown in the figure. Figure 5 It means Figure 2 Cross-sectional view of section BB. Figure 5 The cross-section of the non-groove portion 48 is shown. Figure 4 and Figure 5The diagram schematically depicts a laser L irradiating the edge of the opening 41a1 of the housing body 41a and the periphery 41b3 of the sealing plate 41b. If a groove 47a is formed, melting along the periphery 41b3 of the sealing plate 41b is easily generated at the outer edge of the groove 47a, making it easier to control the formation of the molten pool. On the other hand, if a groove 47a is formed at the location where the gasket 70 is disposed, the gasket 70 may melt due to the laser L reflected from the groove 47a. Therefore, in this embodiment, a groove 47a is not formed at the location close to the location where the gasket 70 is disposed.

[0058] In this case, in the non-groove portion 48, compared to the groove portion 47, heat tends to escape more easily from the periphery 41b3 of the sealing plate 41b. Therefore, when the periphery 41b3 of the sealing plate 41b has both the groove portion 47 and the non-groove portion 48, it is preferable to set the peak output of the laser L when welding the non-groove portion 48 to be larger than the peak output of the laser L when welding the groove portion 47 during the welding process. Thus, by setting the peak output of the laser L when welding the non-groove portion 48 to be larger, the difference between the molten pools formed in the groove portion 47 and the non-groove portion 48 becomes smaller, allowing the target molten pool to be approached throughout the entire circumference. Therefore, if the periphery 41b3 of the sealing plate 41b before welding has a groove portion 47 with a groove 47a formed on the inner side of the periphery 41b3 and a non-groove portion 48 without a groove 47a, and other conditions are approximately the same, it is preferable to set the peak output of the laser L when welding the non-groove portion 48 to be larger. For example, as... Figure 2 As shown, when there are groove portions 47 and non-groove portions 48 in the same long side portions 91 and 92, it is better to set the peak output of laser L when welding the non-groove portion 48 to be larger.

[0059] In addition, such as Figure 2 As shown, the sealing plate 41b is a rectangular component, having a pair of opposing long sides 91, 92 and a pair of opposing short sides 93, 94. The opening 41a1 of the housing body 41a has a generally rectangular shape corresponding to that of the sealing plate 41b.

[0060] According to the inventors' insights, when the sealing plate 41b is installed and held in the opening 41a1 of the housing body 41a at the short sides 93 and 94, small gaps may sometimes occur. If gaps occur, there is a possibility of localized laser leakage, and the weld penetration may become shallow. On the other hand, when the internal pressure inside the battery housing 41 increases, the deformation of the wide sides 43 and 44 tends to be significantly greater than that of the narrow sides 45 and 46. Therefore, at the welded area of ​​the peripheral portion 41b3 of the sealing plate 41b, the stress of the long sides 91 and 92 tends to be higher than that of the short sides 93 and 94.

[0061] In this embodiment, during the welding process, the peak laser output is set higher when welding the long sides 91 and 92 than when welding the short sides 93 and 94. Therefore, even when the internal pressure within the battery casing 41 increases, the required strength corresponding to the stress difference between the welded portions acting on the long sides 91 and 92 and the short sides 93 and 94 can be obtained. Thus, the required joint strength is ensured throughout the circumference of the sealing plate 41b. Furthermore, in the short sides 93 and 94, the weld penetration does not exceed the required depth, and the laser output is suppressed. Therefore, the overall power consumption during the welding process is reduced.

[0062] In addition, in this embodiment, such as Figure 2 As shown, the sealing plate 41b has R-sections 95 to 98 located between the long sides 91 and 92 and the short sides 93 and 94. In this embodiment, during the welding process, the peak laser output when welding the R-sections 95 to 98 is set lower than the peak laser output when welding the short sides 93 and 94. This is because, regarding the R-sections 95 to 98, even if the internal pressure in the battery casing 41 increases, stress is less likely to act on the welded portion. Consequently, in the R-sections 95 to 98, the weld penetration is not as deep as required, and the laser output is suppressed. Therefore, the overall power consumption during the welding process is suppressed to a lower level.

[0063] Furthermore, during the welding process, a laser is scanned along the periphery 41b3 of the sealing plate 41b. In this embodiment, as described above, the peak output of the laser is varied in the groove portion 47 and non-groove portion 48 of the long sides 91 and 92, the short sides 93 and 94, and the R-sections 95 to 98. At this time, the peak output of the laser gradually increases at each boundary portion. In this embodiment, the molten pools of the pulsed lasers are relatively deep, and the pulse frequency is relatively fast, so adjacent pulsed lasers overlap to a high extent. Moreover, adjacent lasers are emitted with moderate overlap before the molten pool of the first emitted laser completely solidifies. Therefore, when the peak output of the laser is varied, the peak output of the laser gradually increases at its boundary portion, thereby allowing the weld depth to change smoothly and without interruption. Therefore, the weld quality is significantly improved, and the compressive strength is increased.

[0064] Furthermore, in this embodiment, the portion where welding begins overlaps with the portion where welding ends on the periphery 41b3 of the sealing plate 41b. At the beginning of welding, the opening 41a1 of the housing body 41a and the sealing plate 41b are at low temperatures, tending to result in shallow weld penetration. By overlapping the beginning and end of welding, the weld penetration at the beginning of welding increases, improving weld quality.

[0065] Here, it is preferable to predetermine the peak laser output based on the materials used for the main body 41a and the sealing plate 41b in order to obtain an appropriate weld penetration. However, according to the inventors, if the peak laser output is constant, the weld penetration at the welded area will be unstable. In particular, in this case, when using a high frequency laser with a pulse width of 400μm to 800μm and a frequency of 1.2kHz to 1.4kHz and scanning at a constant speed, it is preferable to appropriately adjust the peak laser output from the viewpoint of stabilizing the weld penetration at the welded area. If the peak laser output is too high, sputtering is likely to occur; if it is too low, the weld penetration becomes too shallow. From this viewpoint, it is preferable to set the peak laser output in the range of 3.0kW to 5.0kW during the welding process to a level that minimizes sputtering and prevents excessively shallow weld penetration.

[0066] If the peak output of the laser is in the range of 3.0kW to 5.0kW, then, for example, when aluminum steel sheets are used for the housing body 41a and the sealing plate 41b, a weld with appropriate penetration depth can be formed. Based on this, it is preferable to locally change the peak output of the laser while scanning, depending on the shape of the opening 41a1 of the sealing plate 41b and the housing body 41a, and whether the sealing plate 41b has a groove, etc. For example, when the housing body 41a is made of A3003 aluminum steel sheet and the sealing plate 41b is made of A1050 aluminum steel sheet, according to the inventor's understanding, it is preferable to adjust it to a range of 3380W to 3950W, where sputtering is less likely to occur and the penetration depth is not too shallow. Thus, it is preferable to appropriately set the peak output of the laser according to the materials used for the housing body 41a and the sealing plate 41b.

[0067] The invention disclosed herein has been described above in various ways. Unless otherwise specified, the embodiments listed herein are not intended to limit the invention. Furthermore, various modifications can be made to the embodiments of the invention disclosed herein, and the constituent elements and processes mentioned herein can be appropriately omitted or combined without causing particular problems.

Claims

1. A method for manufacturing a secondary battery, wherein, The manufacturing method of this secondary battery includes: The installation process involves installing a sealing plate onto the opening in the bottomed housing body, which has an opening on one side opposite the bottom surface; and In the welding process, a laser is scanned along the periphery of the sealing plate to perform laser welding on the shell body and the sealing plate. In the welding process, the laser irradiating the edge of the opening of the housing body and the periphery of the sealing plate is a pulsed oscillating laser composed of rectangular waves with a pulse width of 400 μm or more and 800 μm or less, and a frequency of 1.2 kHz or more and 1.4 kHz or less. In the welding process, scanning is performed with the overlap rate of adjacent lasers undergoing pulse oscillation being 84.4% or more and 86.6% or less. The sealing plate before welding has a grooved portion with a groove formed on the inner side of the periphery and a non-groove portion without the groove. In the welding process, the peak output of the laser when welding the non-groove portion is set to be greater than the peak output of the laser when welding the groove portion.

2. The method for manufacturing a secondary battery according to claim 1, wherein, During the welding process, the laser is scanned along the periphery of the sealing plate while the peak output of the laser is partially altered.

3. The method for manufacturing a secondary battery according to claim 1, wherein, The sealing plate is a generally rectangular sheet material having a pair of opposing long sides and a pair of opposing short sides. The opening in the main body of the housing has a generally rectangular shape corresponding to the sealing plate. In the welding process, the peak output of the laser when welding the long side is higher than the peak output of the laser when welding the short side.

4. The method for manufacturing a secondary battery according to claim 3, wherein, The sealing plate has an R-shaped portion located between the long side and the short side. In the welding process, the peak output of the laser when welding the R-section is lower than the peak output of the laser when welding the short side section.

5. The method for manufacturing a secondary battery according to claim 4, wherein, At the periphery of the sealing plate, and at the boundaries of the long side, the short side, and the R-section, the peak output of the laser gradually increases.

6. The method for manufacturing a secondary battery according to any one of claims 1 to 5, wherein, At the periphery of the sealing plate, the part where welding begins overlaps with the part where welding ends.

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