Manufacturing method of secondary battery

Abstract

To provide a manufacturing method of a secondary battery capable of suppressing occurrence of a deposition defect caused by enlargement of a gap between a sealing member and an opening of a liquid injection port when sealing the liquid injection port.SOLUTION: Provided is a manufacturing method of a secondary battery. A sealing member 40 is a member in a circular plate shape and comprises an extension part 41 which is formed in a circumferential direction radially inside of an outer peripheral part and can be extended in a direction crossing the circumferential direction. The manufacturing method includes a sealing step including a position fixing step and a weld step. The position fixing step is the step of: setting two or more weld regions R1 and R2 by dividing a boundary portion between an opening 16a of a liquid injection port 16 and an outer peripheral part 42 of the sealing member 40 into at least two or more regions in the circumferential direction; and, regarding the weld regions R1 and R2, pulse-welding a part of the boundary portion. The weld step is the step of: regarding one weld regions R1 of the two or more weld regions, laser welding the boundary portion and, regarding the other weld region R2, successively laser-welding the boundary portion.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a secondary battery.

Background Art

[0002] Conventionally, secondary batteries used in electric vehicles such as electric cars and hybrid cars that use a motor as a drive source include an electrode body, an electrolytic solution, a case that houses the electrode body and the electrolytic solution, battery terminals electrically connected to the electrode body, and the like. In this type of secondary battery, usually, with the electrode body housed in the case, the electrolytic solution is injected through a liquid injection port formed in the case, and then the liquid injection port is sealed with a sealing member to seal the inside of the case. Thus, as a method of sealing the liquid injection port with a sealing member, for example, a method for manufacturing a sealed battery disclosed in Patent Document 1 has been proposed.

[0003] In the method for manufacturing a sealed battery described in Patent Document 1, after injecting the electrolytic solution into the case through a liquid injection port formed in the lid portion of the case, the entire circumference of the boundary portion between the lid portion and the sealing material for closing the liquid injection port is laser welded to seal the liquid injection port. And in this manufacturing method, in order to prevent welding defects (formation of cavities inside the welding bead) caused by an increase in the internal pressure of the case due to vaporization of the electrolytic solution adhering to the inner surface of the lid portion or the like during laser welding, when laser welding the lid portion and the sealing material, the welding of the entire circumference of the above boundary portion is performed in at least two separate times, and at least two weldings are performed at a predetermined time interval from each other. Thereby, until the liquid injection port is completely sealed by the sealing material, the electrolytic solution vaporized during laser welding is discharged to the outside of the case, suppressing an increase in the internal pressure of the case, and thus suppressing the occurrence of welding defects during laser welding.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when performing laser welding around the entire circumference of the boundary between the lid portion and the sealing material in multiple steps as in the manufacturing method of the sealed battery described in Patent Document 1, there are the following problems.

[0006] For example, if the sealing material thermally contracts due to the heat generated during the first laser welding, a gap is formed between the lid portion and the sealing material, and as the gap expands, the melting amount decreases during subsequent laser welding, resulting in a decrease in welding strength or the occurrence of welding defects.

[0007] Here, as a method for preventing the expansion of the gap between the lid portion and the sealing material, before performing the first laser welding, a part of the portion to be subjected to subsequent laser welding is pulse-welded with less heat input to fix the position of the sealing material with respect to the lid portion. However, even when such a method is adopted, the load of thermal contraction of the sealing material during laser welding is large, and there is a risk that the pulse-welded portion will be destroyed during subsequent laser welding. Therefore, welding defects due to the expansion of the gap between the lid portion and the sealing material may still occur.

[0008] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for manufacturing a secondary battery that can suppress the occurrence of welding defects caused by the expansion of the gap between the sealing member and the opening of the liquid injection port during liquid injection port sealing.

Means for Solving the Problems

[0009] A characteristic configuration of the method for manufacturing a secondary battery according to the present invention for achieving the above object is a method for manufacturing a sealed secondary battery having a metal battery case formed with a liquid injection port for injecting an electrolytic solution therein and a metal sealing member for sealing the liquid injection port, wherein the sealing member is a circular plate-shaped member, having an extension portion formed along the circumferential direction radially inward of the outer peripheral portion and capable of extending in a direction intersecting the circumferential direction, The sealing process includes a positioning process and a welding process, In the positioning process, at least two or more welding regions are set by dividing the boundary portion between the opening of the liquid injection port and the outer peripheral portion of the sealing member into at least two or more in the circumferential direction, and for each of the welding regions, a part of the boundary portion is pulse-welded. In the welding process, after laser-welding the boundary portion for one of the two or more welding regions, the boundary portion is sequentially laser-welded for the other welding regions.

[0010] According to the above characteristic configuration, in the first welding process, when the boundary portion is welded for one of the two or more welding regions, even if the sealing member thermally contracts, the extension portion extends in a direction intersecting the circumferential direction. Therefore, the load applied to the pulse-welded portion in the other welding regions is reduced. Thus, the pulse-welded portion is less likely to be damaged, and the gap between the sealing member and the opening of the liquid injection port is less likely to expand, so the occurrence of welding defects due to the expansion of the gap is suppressed.

[0011] A further characteristic configuration of the method for manufacturing a secondary battery according to the present invention is The extension portion is formed over the entire circumference in the circumferential direction.

[0012] According to the above characteristic configuration, regardless of the position of the pulse-welded portion and the state of thermal contraction of the sealing member, the load applied to the pulse-welded portion is easily dispersed and reduced.

[0013] A further characteristic configuration of the method for manufacturing a secondary battery according to the present invention is The extension portion is formed by bending a plurality of thin-walled portions having a thickness thinner than other portions a plurality of times, and extends by elastic deformation.

[0014] According to the above characteristic configuration, an extension portion that can extend in a direction intersecting the circumferential direction with a simple configuration can be realized.

Effects of the Invention

[0015] As described above, according to the method for manufacturing a secondary battery according to the present invention, the occurrence of welding defects due to the expansion of the gap between the sealing member and the opening of the liquid injection port during liquid injection port sealing can be suppressed.

Brief Description of the Drawings

[0016]

Figure 1

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Figure 9

Embodiments for Carrying Out the Invention

[0017] Hereinafter, a method for manufacturing a secondary battery according to an embodiment of the present invention will be described with reference to the drawings. In the following, an aspect of manufacturing a lithium-ion secondary battery will be described as an example. Also, in the following, for the sake of clarity, each description and each drawing are appropriately simplified.

[0018] 〔Outline of Secondary Battery 1〕 FIG. 1 is a perspective view of a secondary battery 1 manufactured by the manufacturing method according to the present embodiment. FIG. 2 is a cross-sectional view showing a schematic configuration of the secondary battery 1 according to the present embodiment. In the following description, the direction parallel to the height direction of the secondary battery 1 is defined as the Z-axis direction, the direction parallel to the longitudinal direction of the electrode body 20 is defined as the X-axis direction, and the direction parallel to the thickness direction of the electrode body 20 is defined as the Y-axis direction. The Z-axis direction is parallel to the vertical direction, the X-axis direction and the Y-axis direction are orthogonal to each other, and are parallel to the horizontal direction.

[0019] First, the schematic configuration of the secondary battery 1 to be manufactured will be described. As shown in FIGS. 1 and 2, the secondary battery 1 includes a battery case 10 composed of a case body 11 and a sealing plate 12, battery terminals PS and NS, an electrode body 20, and the like. The secondary battery 1 houses the electrode body 20 and a part of the battery terminals PS and NS inside the case body 11, seals the opening of the case body 11 with the sealing plate 12, and then injects an electrolytic solution into the case body 11 as described later, which is a sealed secondary battery.

[0020] 〔Configuration of Battery Case 10〕 As shown in FIGS. 1 and 2, the battery case 10 of the present embodiment is composed of a case body 11 with an open top and a sealing plate 12 that seals the opening of the case body 11. In the battery case 10 of the present embodiment, both the case body 11 and the sealing plate 12 are made of aluminum, but it is not limited thereto. Various metals and alloys can be used as the materials of the case body 11 and the sealing plate 12.

[0021] In the present embodiment, the case body 11 has a substantially rectangular parallelepiped shape. The case body 11 has a pair of side walls 11a provided opposite to each other along the longitudinal direction (X-axis direction), a pair of end side walls 11b that connect the ends of the side walls 11a in the longitudinal direction (X-axis direction), and a bottom portion 11c that closes the bottom.

[0022] The sealing plate 12 has a shape corresponding to the shape of the opening of the case body 11 and is configured to seal the opening of the case body 11. In the present embodiment, the sealing plate 12 is composed of a flat plate member having a substantially rectangular shape when viewed in the Z-axis direction. On the sealing plate 12, a positive electrode attachment port (not shown) to which the positive electrode battery terminal PS is attached is formed on one end side in the longitudinal direction (one end side in the X-axis direction), and a negative electrode attachment port (not shown) to which the negative electrode battery terminal NS is attached is formed on the other end side in the longitudinal direction (the other end side in the X-axis direction).

[0023] Further, on the sealing plate 12, an explosion-proof valve 15 that opens when the pressure in the battery case 10 increases is formed between the positive electrode attachment port and the negative electrode attachment port when viewed in the Z-axis direction. Furthermore, on the sealing plate 12, a liquid injection port 16 through which the electric liquid E can be injected into the battery case 10 is formed between the explosion-proof valve 15 and the positive electrode attachment port when viewed in the Z-axis direction, and the liquid injection port 16 is sealed by a sealing member 40.

[0024] Hereinafter, the liquid injection port 16 and the sealing member 40 will be described in detail with reference to FIGS. 1 to 4. Note that FIG. 3 is an enlarged view of part A in FIG. 2. Further, FIG. 4 is a view showing the sealing member 40, (a) is a top view, and (b) is a longitudinal sectional view.

[0025] The liquid injection port 16 is a through hole that opens circularly on the front and back surfaces (upper and lower surfaces) of the sealing plate 12, and has a large diameter portion 17, a middle diameter portion 18 that is coaxial with the large diameter portion 17 and has a smaller diameter than the large diameter portion 17, and a small diameter portion 19 that is coaxial with the middle diameter portion 18 and has a smaller diameter than the middle diameter portion 18, from the side of the surface 12a of the sealing plate 12 toward the side of the back surface 12b. Note that between the large diameter portion 17 and the middle diameter portion 18 and between the middle diameter portion 18 and the small diameter portion 19, there are a first transition surface 17a and a second transition surface 18a parallel to the front and back surfaces of the sealing plate 12.

[0026] The sealing member 40 is made of a metal plate material and is a member having a circular shape in a top view. The sealing member 40 has an annular extension 41 formed along the circumferential direction C on the side of the center O in the radial direction D rather than the outer peripheral surface 40a in a top view. Further, the extension 41 is extendable along the radial direction D. In the present embodiment, the portion including the outer peripheral surface 40a of the sealing member 40 and outside the extension 41 in the radial direction D is the outer peripheral portion 42, and the portion inside the extension 41 is the inner peripheral portion 43. That is, the extension 41 is a portion formed over the entire circumference of the circumferential direction C inside the outer peripheral portion 42 of the sealing member 40 in the radial direction D and is extendable along a direction intersecting the circumferential direction C.

[0027] Specifically, the extension 41 of the present embodiment is a portion formed by bending so that a thin-walled portion 44 having a thickness thinner than that of the outer peripheral portion 42 and the inner peripheral portion 43 protrudes upward. When a load acts outward in the radial direction D, the extension 41 extends by elastic deformation and elongation of the thin-walled portion 44 along the radial direction D. The sealing member 40 having such an extension 41 can be manufactured, for example, by pressing a metal plate.

[0028] Although details will be described later, in the secondary battery 1 of the present embodiment, the sealing member 40 is disposed in the large-diameter portion 17 so that the back surface of the outer peripheral portion 42 abuts against the first transition surface 17a of the liquid injection port 16, and the boundary portion between the opening 16a of the liquid injection port 16 (the opening of the large-diameter portion 17) and the outer peripheral portion 42 of the sealing member 40 is laser welded. In addition, the reference numeral M2 in FIG. 3 is the laser welded portion.

[0029] 〔Configuration of the electrode body 20〕 The electrode body 20 is formed by laminating a positive electrode material and a negative electrode material with a separator interposed therebetween, and is housed in the case body 11. The electrode body 20 of the present embodiment is composed of a wound body in which long strip-shaped positive and negative electrode materials are wound in a state of being laminated via a strip-shaped separator and compressed into a flat shape. As shown in FIGS. 1 and 2, the electrode body 20 is substantially rectangular in a thickness direction view (Y-axis direction view), and a positive electrode terminal joint portion 21 where the positive electrode material is collected and foiled is formed on one end side in the longitudinal direction (X-axis direction) in the thickness direction view, and a negative electrode terminal joint portion 22 where the negative electrode material is collected and foiled is formed on the other end side. The electrode body 20 is housed inside the case body 11 in a posture where the thickness direction and the longitudinal direction are parallel to the horizontal direction, and is insulated from the case body 11 by an insulating film or the like as appropriate. Note that the structure of the electrode body 20 is not particularly limited, and various structures used in general sealed secondary batteries can be adopted. Further, in the present embodiment, aluminum is used for the positive electrode material and copper is used for the negative electrode material.

[0030] 〔Configuration of positive electrode side and negative electrode side〕 In the present embodiment, the secondary battery 1 includes a positive electrode external terminal 25 and a negative electrode external terminal 26 as external terminals, and a positive electrode current collecting terminal 27 and a negative electrode current collecting terminal 28 as current collecting terminals. The positive electrode battery terminal PS is composed of the positive electrode external terminal 25 and the positive electrode current collecting terminal 27, and the negative electrode battery terminal NS is composed of the negative electrode external terminal 26 and the negative electrode current collecting terminal 28. In the present embodiment, the positive electrode external terminal 25 and the positive electrode current collecting terminal 27 are made of aluminum, and the negative electrode external terminal 26 and the negative electrode current collecting terminal 28 are made of copper. However, the materials of these terminals are not particularly limited, and various metals and alloys with good conductivity can be used.

[0031] Further, in the present embodiment, the secondary battery 1 has a positive electrode insulating member 29, a negative electrode insulating member 30, a positive electrode gasket 31, and a negative electrode gasket 32, all of which are made of a material having insulating properties. In the present embodiment, a PFA resin is used as the material having insulating properties, but the present invention is not limited thereto.

[0032] Although detailed description is omitted, in the secondary battery 1 of the present embodiment, the positive electrode external terminal 25 and the negative electrode external terminal 26 and the sealing plate 12 are insulated by the positive electrode gasket 31 and the negative electrode gasket 32 respectively, and the positive electrode current collecting terminal 27 and the negative electrode current collecting terminal 28 and the sealing plate 12 are insulated by the positive electrode insulating member 29 and the negative electrode insulating member 30 respectively. Further, each of the current collecting terminals 27, 28 has connection portions 27a, 28a, and the connection portions 27a, 28a are joined to the terminal joining portions 21, 22.

[0033] 〔Method for manufacturing the secondary battery 1〕 Next, a method for manufacturing the secondary battery 1 according to the present embodiment will be described. The method for manufacturing the secondary battery 1 includes a sealing process including a position fixing process and a welding process.

[0034] Hereinafter, it will be described while referring to FIGS. 5 to 7. Note that FIG. 5 is a schematic diagram for explaining the position fixing process. FIGS. 6 and 7 are schematic diagrams for explaining the welding process. In FIGS. 5 to 7, (a) is a top view and (b) is a longitudinal sectional view.

[0035] As described above, the sealing process is a process including a position fixing process and a welding process. Prior to the position fixing process, the outer peripheral surface 40a of the sealing member 40 and the inner wall surface 17b of the large diameter portion 17 at the liquid injection port 16 face each other, and the back surface of the outer peripheral portion 42 of the sealing member 40 abuts on the first transition surface 17a, so that the sealing member 40 is disposed in the large diameter portion 17 of the liquid injection port 16. In the position fixing process, first, welding regions R1, R2 are set at the boundary portion between the opening 16a of the liquid injection port 16 (more specifically, the opening of the large diameter portion 17) and the outer peripheral portion 42 of the sealing member 40. Specifically, the boundary portion is bisected in the circumferential direction C to set a first welding region R1 and a second welding region R2 in a semi-circular arc shape in a top view.

[0036] Next, in the position fixing process, a part of the boundary portion in each of the two welding regions R1, R2 set as described above is pulse welded. Specifically, portions of the boundary portions of the welding regions R1, R2 that face each other with the center O interposed therebetween are pulse welded, and one pulse welded portion M1 is formed for each of the welding regions R1, R2 (see FIG. 5).

[0037] Next, a welding process is performed. In the present embodiment, first, as shown in FIG. 6, the boundary portion in the first welding region R1 is laser welded. Specifically, a laser is irradiated onto the boundary portion located at one end of the first welding region R1, and while continuing the laser irradiation, the laser irradiation position is moved along the boundary portion to the boundary portion located at the other end of the first welding region R1 (arrow J in FIG. 6). As a result, the portion irradiated with the laser melts, and a laser welded portion M2 (weld bead) is formed.

[0038] Here, in the present embodiment, even when the sealing member 40 thermally contracts during the laser welding of the boundary portion in the first welding region R1, the thin-walled portion 44 elastically deforms so that the extension portion 41 extends in the radial direction D. Therefore, the load applied to the pulse welded portion M1 in the second welding region R2 is reduced, and breakage of the pulse welded portion M1 is suppressed.

[0039] Thereafter, the boundary portion in the second welding region R2 is laser welded. Specifically, as shown in FIG. 7, the laser irradiation position is moved from the boundary portion located at one end of the second welding region R2 to the boundary portion located at the other end (arrow K in FIG. 7), and a laser welded portion M2 is formed.

[0040] As a result, the boundary portion between the opening 16a of the liquid injection port 16 and the outer peripheral portion 42 of the sealing member 40 is laser welded over the entire circumference, and the liquid injection port 16 is sealed by the sealing member 40.

[0041] Here, as described above, during laser welding of the boundary portion in the first welding region R1, breakage of the pulse welding portion M1 in the second welding region R2 is suppressed. Therefore, in the second welding region R2, an increase in the gap between the sealing member 40 and the opening 16a of the liquid injection port 16 is suppressed, and the occurrence of welding defects due to the increase in the gap is suppressed. In particular, in the present embodiment, the extension portion 41 is formed over the entire circumference in the circumferential direction C. Therefore, even if the state of the load applied to the pulse welding portion M1 changes depending on the positional relationship between the pulse welding portion M1 and the portion being laser welded and the state of thermal contraction of the sealing member 40, the load is easily dispersed. Therefore, in the present embodiment, compared with the case where the extension portion 41 is not formed or the extension portion 41 is formed only partially, the load applied to the pulse welding portion M1 can be further reduced, and the pulse welding portion M1 is less likely to break, so the occurrence of welding defects due to the increase in the gap is further suppressed.

[0042] As described above, according to the method for manufacturing the secondary battery 1 according to the present embodiment, since the extension portion 41 that can extend in the radial direction D is formed over the entire circumference in the circumferential direction C on the sealing member 40, when the boundary portion is divided into a plurality of welding regions (two in the present embodiment, the first welding region R1 and the second welding region R2) and sequentially laser welded in order to seal the liquid injection port 16 with the sealing member 40, the occurrence of welding defects due to an increase in the gap between the sealing member 40 and the opening 16a of the liquid injection port 16 can be suppressed.

[0043] 〔Alternative Embodiment〕 〔1〕In the above embodiment, in the position fixing step, the mode of setting two welding regions R1 and R2 by dividing the boundary portion between the opening of the liquid injection port 16 and the outer peripheral portion 42 of the sealing member 40 into two in the circumferential direction C has been described. However, the present invention is not limited to such a mode. Any mode may be used as long as at least two welding regions are set. FIG. 8 is a schematic diagram for explaining a setting mode of a welding region in a position fixing step in a method for manufacturing a secondary battery according to another embodiment. As shown in FIG. 8, a mode may be adopted in which a boundary portion between an opening of the liquid injection port 16 and an outer peripheral portion 42 of the sealing member 40 is divided into three to set three welding regions Ra, Rb, and Rc. Even in such a mode, in the position fixing step, for each of the welding regions Ra, Rb, and Rc, a part of the boundary portion is pulse welded to form a pulse welded portion M1, and after fixing the position of the sealing member 40, in the welding step, the boundary portions in the respective welding regions Ra, Rb, and Rc are sequentially laser welded, so that the liquid injection port 16 can be sealed with the sealing member 40 while reducing the load on the pulse welded portion M1 due to the elongation of the extension portion 41.

[0044] 〔2〕In the above embodiment, the mode in which the extension portion 41 is formed over the entire circumference in the circumferential direction C has been described, but the present invention is not limited to such a mode, and a mode in which the extension portion is formed in a part of the circumferential direction C may also be adopted. For example, if the extension portion is formed in a part in the circumferential direction and a pulse welded portion is formed at a location near the extension portion among the boundary portions between the opening of the liquid injection port and the outer peripheral portion of the sealing member, the load applied to the pulse welded portion during laser welding can be reduced as compared with the case where the extension portion is not formed.

[0045] 〔3〕In the above embodiment, the mode in which the extension portion 41 is a portion formed by being bent a plurality of times so that the thin wall portion 44 protrudes upward has been described, but the present invention is not limited to such a mode. FIG. 9 is a cross-sectional view showing a sealing member 50 according to another embodiment. As shown in FIG. 9, the extension portion 51 may be a portion formed by being bent a plurality of times so as to have a portion where the thin wall portion 52 protrudes upward and downward. Note that the extension portion does not have to be a mode formed by bending the thin wall portion a plurality of times as long as it is configured to be extensible in a direction intersecting the circumferential direction of the sealing member.

[0046] In addition, the configurations disclosed in the above embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with the configurations disclosed in other embodiments as long as there is no contradiction. Also, the embodiments disclosed in this specification are examples, and the embodiments of the present invention are not limited thereto, and can be appropriately modified within the scope not departing from the object of the present invention.

Explanation of Reference Numerals

[0047] 1: Secondary battery 10: Battery case 16: Liquid injection port 16a: Opening 17: Large-diameter part (liquid injection port) 18: Medium-diameter part (liquid injection port) 19: Small-diameter part (liquid injection port) 40: Sealing member 41: Extension part 42: Outer peripheral part 44: Thin part R1, R2: Welding area C: Circumferential direction D: Radial direction

Claims

1. A method for manufacturing a sealed secondary battery having a metal battery case formed with a liquid injection port for injecting an electrolytic solution therein and a metal sealing member for sealing the liquid injection port, comprising: The sealing member is a circular plate-shaped member, having an extension portion formed along the circumferential direction radially inward of the outer peripheral portion and extendable in a direction intersecting the circumferential direction, including a sealing step including a position fixing step and a welding step, The position fixing step is a step of setting two or more welding regions obtained by dividing at least two or more boundary portions between the opening of the liquid injection port and the outer peripheral portion of the sealing member in the circumferential direction, and pulse-welding a part of the boundary portion for each of the welding regions, The welding step is a step of laser-welding the boundary portion for one of the two or more welding regions and then sequentially laser-welding the boundary portion for the other welding regions. A method for manufacturing a secondary battery.

2. The method for manufacturing a secondary battery according to claim 1, wherein the extension portion is formed over the entire circumference in the circumferential direction.

3. The method for manufacturing a secondary battery according to claim 1 or 2, wherein the extension portion is formed by bending a plurality of thin-wall portions having a thinner plate thickness than other portions a plurality of times and extends by elastic deformation.

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