Electricity storage device manufacturing method and electricity storage device

Abstract

To prevent laser beam loss by a simple method. [Solution] A manufacturing method for an electricity storage device includes the steps of preparing a rectangular case 11 with a rectangular opening, preparing a sealing plate 13 to be attached to the opening along the edge of the opening, an assembly step of attaching the sealing plate 13 to the opening of the case 11, and a main welding step of laser welding the case 11 and the sealing plate 13 together around the entire periphery of the peripheral edge 13a of the sealing plate 13. In the main welding step, laser welding around the entire periphery of the peripheral edge 13a of the sealing plate 13a is performed in at least four separate steps.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an electricity storage device and an electricity storage device. [Background technology]

[0002] Japanese Patent Application Laid-Open Publication No. 2013-187087 discloses a method for sealing a sealed battery case, in which a lid is joined to the opening of the battery case by welding. A step into which the lid fits is formed on a portion of the inner surface of the opening of the battery case. The lid is fitted into the opening of the battery case. In this welding method, laser welding begins at the joint where the inner surface with the step is joined to the lid. Japanese Patent Application Laid-Open Publication No. 2013-187087 claims that this welding method can prevent laser penetration. Laser penetration is a phenomenon in which a laser penetrates the joint between the battery case and the lid and enters the interior of the battery case.

[0003] Furthermore, Japanese Patent Application Laid-Open Publication No. 2013-187087 discloses a method for welding a sealed battery can in which a sealed battery is divided into a front region and a rear region and then welded. In this welding method, a holding jig is used to press the lid located in the front region of the sealed battery against the battery case from above to below, and laser welding is then initiated to weld the battery case and the lid in the rear region. Next, the holding jig is removed, and the battery case and the lid in the front region of the sealed battery are welded. According to Japanese Patent Application Laid-Open Publication No. 2013-187087, this welding method can prevent the lid from lifting off the battery case during welding. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-187087 Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors of the present invention would like to prevent laser beam omission in a simple manner. [Means for solving the problem]

[0006] The method for manufacturing an electricity storage device disclosed herein includes the steps of: preparing a rectangular case having an opening; preparing a sealing plate to be attached to the opening along the edge of the opening; assembling the case to attach the sealing plate to the opening; and laser welding the case and the sealing plate along the entire periphery of the sealing plate. In the welding step, laser welding is performed along the entire periphery of the sealing plate in at least four separate steps. This manufacturing method provides a simple method for preventing laser welding. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view schematically illustrating an electricity storage device. [Figure 2] FIG. 2 is an exploded perspective view of the electricity storage device. [Figure 3] FIG. 3 is a flowchart showing an example of a method for manufacturing an electricity storage device. [Figure 4] FIG. 4 is a plan view schematically showing the case and the sealing plate after the pre-welding step has been completed. [Figure 5] FIG. 5 is an enlarged view showing a schematic diagram of the boundary portion between the case and the sealing plate according to a reference example. [Figure 6] FIG. 6 is a diagram illustrating a main welding step according to one embodiment. [Figure 7] FIG. 7 is a diagram schematically showing the vicinity of the starting point of the first laser welding. [Figure 8] FIG. 8 is a diagram schematically showing the vicinity of the starting point of the second laser welding. [Figure 9] FIG. 9 is a diagram schematically showing the vicinity of the starting point of the third laser welding. [Figure 10] FIG. 10 is a diagram schematically showing the vicinity of the starting point of the fourth laser welding. [Figure 11]FIG. 11 is a plan view schematically showing the case and the sealing plate after the main welding step has been completed. [Figure 12] FIG. 12 is a diagram for explaining the main welding process according to another embodiment. [Figure 13] FIG. 13 is a diagram for explaining the main welding step according to another embodiment. [Figure 14] FIG. 14 is a diagram for explaining the main welding process according to another embodiment. [Figure 15] FIG. 15 is a diagram for explaining the main welding process according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment of the technology disclosed herein will be described below with reference to the drawings. The embodiments described herein are, of course, not intended to limit the present invention. The drawings are schematic and do not necessarily reflect the actual product. Furthermore, identical reference numerals are used to designate components and parts that perform the same function, and redundant descriptions will be omitted where appropriate. The reference numerals F, Rr, L, R, U, and D in the drawings represent front, rear, left, right, top, and bottom, respectively. The reference numerals X, Y, and Z in the drawings represent the front-to-back direction, left-to-right direction, and top-to-bottom direction, respectively. The Y direction is perpendicular to the X direction. The Z direction is perpendicular to the X and Y directions. However, these directions are merely used for convenience of explanation and do not limit the installation configuration of the battery. Furthermore, in this specification, a numerical range such as "X to Y" means "X or greater and Y or less" unless otherwise specified.

[0009] In this specification, the term "electricity storage device" refers to a device that can be charged and discharged. Electricity storage devices include batteries generally referred to as lithium ion batteries and lithium secondary batteries, as well as batteries such as lithium polymer batteries and nickel-metal hydride batteries. A secondary battery generally refers to a battery that can be repeatedly charged and discharged through the movement of charge carriers between the positive and negative electrodes. An electrolytic solution or a solid electrolyte may be used in an electricity storage device. For example, the secondary battery may be a secondary battery that uses a so-called liquid electrolyte, or a so-called all-solid-state battery that uses a solid electrolyte. Electricity storage devices also include capacitors such as electric double layer capacitors and lithium ion capacitors.

[0010] Fig. 1 is a perspective view that schematically shows an electricity storage device 10. Fig. 2 is an exploded perspective view of the electricity storage device 10. As shown in Figs. 1 and 2, the electricity storage device 10 includes a case 11, a sealing plate 13, and an electrode assembly 20.

[0011] The case 11 is a rectangular case formed in a substantially rectangular parallelepiped shape. When viewed from above, the case 11 has short sides extending in the X direction and long sides extending in the Y direction. The case 11 has a bottom surface 11a, a pair of narrow sides 11b, and a pair of wide sides 11c. The bottom surface 11a extends in the X and Y directions. The pair of narrow sides 11b face each other in the Y direction. The pair of narrow sides 11b extend upward from both ends of the bottom surface 11a in the Y direction. The pair of wide sides 11c face each other in the X direction. The pair of wide sides 11c extend upward from both ends of the bottom surface 11a in the X direction. The pair of narrow sides 11b and the pair of wide sides 11c form side surfaces of the case 11. From the viewpoints of ensuring lightweight and required rigidity, the case 11 is formed of, for example, aluminum or an aluminum alloy mainly containing aluminum.

[0012] As shown in FIG. 2, the case 11 has a rectangular opening 11d at the top. The opening 11d is surrounded by a rear edge 11d1, a front edge 11d2, a left edge 11d3, and a right edge 11d4. The rear edge 11d1 and the front edge 11d2 extend in the Y direction. The rear edge 11d1 is located rearward of the front edge 11d2. The left edge 11d3 and the right edge 11d4 extend in the X direction. The left edge 11d3 is located leftward of the right edge 11d4. The left edge 11d3 connects the left end of the rear edge 11d1 to the left end of the front edge 11d2. The right edge 11d4 connects the right end of the rear edge 11d1 to the right end of the front edge 11d2. In the following description, the rear edge 11d1, the front edge 11d2, the left edge 11d3, and the right edge 11d4 may be collectively referred to simply as "the edges of the opening 11d."

[0013] Sealing plate 13 is a member for closing opening 11d of case 11. Sealing plate 13 is attached to opening 11d along the edge of opening 11d of case 11. In the embodiment shown in FIG. 1, sealing plate 13 is a flat plate formed in a rectangular shape. Sealing plate 13 may be made of the same material as case 11. Sealing plate 13 may be made of, for example, aluminum or an aluminum alloy mainly containing aluminum.

[0014] The sealing plate 13 has a gas exhaust valve 14 for exhausting gas inside the case 11. The gas exhaust valve 14 is located in the center of the sealing plate 13 in the Y direction. The gas exhaust valve 14 is, for example, a thin-walled portion designed to break when the pressure inside the case 11 rises above a predetermined value. When the pressure inside the case 11 reaches or exceeds the predetermined value, the gas exhaust valve 14 breaks, and the gas inside the case 11 is exhausted to the outside of the case 11.

[0015] The sealing plate 13 is provided with a pair of electrode terminals 17, 18. The pair of electrode terminals 17, 18 are arranged at both ends of the sealing plate 13 in the Y direction. The method for attaching the electrode terminals 17, 18 to the sealing plate 13 is not particularly limited. For example, the electrode terminals 17, 18 may be attached to the sealing plate 13 by using a crimping process. The electrode terminals 17, 18 may be integrally formed with the sealing plate 13. The electrode terminal 17 includes an external terminal 17a and an internal terminal 17b. The external terminal 17a is attached to the upper side of the sealing plate 13. The internal terminal 17b is attached to the lower side of the sealing plate 13. Similarly, the electrode terminal 18 includes an external terminal 18a and an internal terminal 18b.

[0016] The electrode body 20 shown in FIG. 2 is housed inside the case 11 in the form shown in FIG. 1. Although not shown, the electrode body 20 has a positive electrode and a negative electrode. The positive electrode of the electrode body 20 is connected to the internal terminal 17b of the electrode terminal 17. Therefore, the electrode terminal 17 is a positive electrode terminal electrically connected to the positive electrode of the electrode body 20. The negative electrode of the electrode body 20 is connected to the internal terminal 18b of the electrode terminal 18. Therefore, the electrode terminal 18 is a negative electrode terminal electrically connected to the negative electrode of the electrode body 20. The configuration of the electrode body 20 is not particularly limited. Various conventionally known electrode bodies can be used for the electrode body 20.

[0017] Next, a method for manufacturing the electricity storage device 10 will be described. Fig. 3 is a flowchart showing an example of the method for manufacturing the electricity storage device 10. The method for manufacturing the electricity storage device 10 includes a case preparation step S01, a sealing plate preparation step S02, an assembly step S03, a temporary welding step S04, and a main welding step S05. The method for manufacturing the electricity storage device 10 may include steps other than these, but descriptions thereof will be omitted here.

[0018] In the case preparation step S01, a rectangular case 11 having an opening 11d is prepared. The method for preparing the case 11 in the case preparation step S01 is not particularly limited. The case 11 is prepared, for example, by bending and shaping a single rectangular flat plate. The width of the case 11 prepared in the case preparation step S01 may be 30 cm or more. Note that in this specification, the width of the case 11 refers to the length of the case 11 in the Y direction. By preparing such a relatively large case, a relatively large electrode assembly can be accommodated inside the case 11, and therefore a high-capacity electricity storage device can be obtained.

[0019] In the sealing plate preparation step S02, a sealing plate 13 to be attached to the opening 11d of the case 11 is prepared along the edge of the opening 11d. The method for preparing the sealing plate 13 in the sealing plate preparation step S02 is not particularly limited. The sealing plate 13 is prepared, for example, by machining a rectangular flat plate, such as by drilling holes, and then attaching electrode terminals 17, 18, etc. The sealing plate 13 may also be prepared by being integrally molded with the electrode terminals 17, 18, etc. The sealing plate preparation step S02 may be performed before or after the case preparation step S01. The sealing plate preparation step S02 may also be performed simultaneously with the case preparation step S01.

[0020] 2, in the assembly step S03, the electrode body 20 is connected to the electrode terminals 17 and 18. More specifically, the positive electrode of the electrode body 20 is connected to the internal terminal 17b of the electrode terminal 17, and the negative electrode of the electrode body 20 is connected to the internal terminal 18b of the electrode terminal 18. Next, in the assembly step S03, with the electrode body 20 connected to the electrode terminals 17 and 18, the sealing plate 13 is attached to the opening 11d of the case 11. In this way, the electrode body 20 is housed inside the case 11, and the sealing plate 13 is attached to the opening 11d.

[0021] In the temporary welding step S04, the case 11 and the sealing plate 13 are temporarily welded together at a predetermined position on the boundary between the case 11 and the sealing plate 13. The temporary welding step S04 is performed with the sealing plate 13 attached to the opening 11d. The temporary welding is performed to position the sealing plate 13 relative to the case 11. In the temporary welding step S04, the case 11 and the sealing plate 13 are intermittently welded together. The welding device used in the temporary welding step S04 may be the same as or different from the welding device used in the main welding step S05. Various conventionally known welding devices may be used in the temporary welding step S04.

[0022] FIG. 4 is a plan view schematically showing the case 11 and the sealing plate 13 after the tack welding step S04. Reference symbols W1 to W16 in FIG. 4 indicate tack welds formed by tack welding. The tack welds W1 to W16 are the portions where the case 11 and the sealing plate 13 are joined. In the configuration shown in FIG. 4, the case 11 and the sealing plate 13 are tack welded at multiple positions. Specifically, the case 11 and the sealing plate 13 are tack welded at 16 predetermined positions. The tack welds W1 to W12 are formed along the rear edge 11d1 or the front edge 11d2 of the opening 11d of the case 11. The tack welds W13 and W14 are formed along the left edge 11d3 of the opening 11d of the case 11. The tack welds W15 and W16 are formed along the right edge 11d4. In the embodiment shown in Fig. 4, predetermined positions near gas release valve 14 on the boundary between case 11 and sealing plate 13 are tack-welded to form tack-welded joints W1 to W4. In the embodiment shown in Fig. 4, predetermined positions near electrode terminal 17 on the boundary between case 11 and sealing plate 13 are tack-welded to form tack-welded joints W5 to W8. In the embodiment shown in Fig. 4, predetermined positions near electrode terminal 18 on the boundary between case 11 and sealing plate 13 are tack-welded to form tack-welded joints W9 to W12. However, the positions and number of tack-welded joints are not limited to those shown in Fig. 4 and can be changed as appropriate depending on the dimensions of case 11 and sealing plate 13, etc.

[0023] The symbol L1 in FIG. 4 indicates the spacing between tack welds W1 and W2. The symbol L2 in FIG. 4 indicates the spacing between tack welds W1 and W6. The symbol L3 in FIG. 4 indicates the spacing between tack welds W5 and W6. In the configuration shown in FIG. 4, the tack welds W1 to W16 are arranged symmetrically in the X and Y directions, so the spacing between tack welds W3 and W4 is equal to the spacing L1 between tack welds W1 and W2. The spacing between tack welds W4 and W7, the spacing between tack welds W2 and W9, and the spacing between tack welds W3 and W12 are equal to the spacing L2 between tack welds W1 and W6. The spacing between tack welds W7 and W8, the spacing between tack welds W9 and W10, and the spacing between tack welds W11 and W12 are equal to the spacing L3 between tack welds W5 and W6.

[0024] In the embodiment shown in FIG. 4, the relationship between the distance L1 between the tack welds W1 and W2, the distance L2 between the tack welds W1 and W6, and the distance L3 between the tack welds W5 and W6 is L2 > L3 = L1. That is, in the embodiment shown in FIG. 4, the distance L1 between the tack welds W1 and W2 is equal to the distance L3 between the tack welds W5 and W6. The distance L2 between the tack welds W1 and W6 is longer than the distance L1 between the tack welds W1 and W2 and the distance L3 between the tack welds W5 and W6. Specifically, in the embodiment shown in FIG. 4, L1 = 40 mm, L2 = 80 mm, and L3 = 40 mm. Therefore, in the embodiment shown in FIG. 4, the case 11 has four portions along the edge of the opening 11d where the distances between the tack welds W1 to W16 are longer than 40 mm. Here, "portions where the spacing between pre-welded portions W1 to W16 is longer than 40 mm" refers to portions where the spacing between pre-welded portions W1 to W16 is longer than a predetermined length. Here, this "pre-determined length" is 40 mm, but this "pre-determined length" can be changed as appropriate in accordance with changes in the dimensions of case 11, etc.

[0025] In the main welding step S05, the case 11 and the sealing plate 13 are main-welded together. This main welding is performed to seal the opening 11d. In the main welding step S05, the case 11 and the sealing plate 13 are laser-welded together along the entire periphery of the peripheral edge 13a of the sealing plate 13. In the main welding step S05, various conventionally known laser welding devices are used. For example, in the main welding step S05, a laser welding device using a fiber laser capable of continuous oscillation can be suitably used.

[0026] However, if a gap exists between the case 11 and the sealing plate 13, so-called laser leakage may occur when laser welding is performed in the main welding step S05. Laser leakage is a phenomenon in which laser light penetrates the gap between the case 11 and the sealing plate 13 and enters the inside of the case 11. Laser leakage can cause welding defects. Therefore, in the main welding step S05, it is preferable to perform laser welding so as to prevent laser leakage. The present inventors wish to prevent laser leakage using a simple method. Therefore, the present inventors conducted various studies to determine under what welding conditions laser leakage is likely to occur. As a result, the present inventors discovered the following problem.

[0027] FIG. 5 is an enlarged view schematically illustrating the boundary between the case 11 and the sealing plate 13 according to a reference example. FIG. 5 illustrates the case 11 and the sealing plate 13 as viewed from above. The arrows labeled WT in FIG. 5 indicate the welding path of the laser welding. In the main welding step S05, the temperature of the case 11 rises, causing the case 11 to expand. This expansion of the case 11 causes the case 11 to deform outward, as shown in FIG. 5, which may locally widen the gap between the case 11 and the sealing plate 13. According to the inventors' findings, as the main welding step S05 progresses, the gap between the case 11 and the sealing plate 13 widens, making laser leakage more likely to occur. This is thought to be because the temperature of the case 11 rises as the main welding step S05 progresses. Furthermore, according to the inventors' findings, the gap between the case 11 and the sealing plate 13 is more likely to widen and laser leakage is more likely to occur in areas where the temporary welds W1 to W16 are relatively long. Specifically, according to the knowledge of the inventors of the present application, laser voids are particularly likely to occur in areas where the spacing between the pre-welded portions W1 to W16 is 40 mm or more.

[0028] Furthermore, according to the findings of the present inventors, laser voids are particularly likely to occur when manufacturing a relatively large electricity storage device 10, such as when the width of the case 11 is 30 cm or more. The present inventors believe the cause of this is as follows: When manufacturing a relatively large electricity storage device 10, the dimensional tolerances of the case 11 and the sealing plate 13 are likely to be large, which makes it easy for a relatively large gap to form between the case 11 and the sealing plate 13. According to the findings of the present inventors, for example, when the width of the case 11 is approximately 30 cm, a gap of approximately 0.2 mm may form between the case 11 and the sealing plate 13. Furthermore, according to the findings of the present inventors, since there are likely to be portions where the spacing between the temporary welds W1 to W16 is relatively long, there are likely to be portions where the gap between the case 11 and the sealing plate 13 is likely to widen in the main welding step S05.

[0029] Therefore, in the method of manufacturing electricity storage device 10 disclosed herein, in main welding step S05, laser welding is performed in at least four steps along the entire periphery of peripheral edge portion 13a of sealing plate 13. Here, a case where laser welding is performed in four steps will be described. However, in main welding step S05, laser welding may be performed in five or more steps.

[0030] Fig. 6 is a diagram illustrating the main welding step S05 according to this embodiment. Fig. 6 illustrates the case 11 and the sealing plate 13 as viewed from above. The arrow indicated by the symbol WT1 in Fig. 6 indicates the welding trajectory of the first laser welding. The arrow indicated by the symbol WT2 indicates the welding trajectory of the second laser welding. The arrow indicated by the symbol WT3 indicates the welding trajectory of the third laser welding. The arrow indicated by the symbol WT4 indicates the welding trajectory of the fourth laser welding.

[0031] FIG. 7 is a schematic diagram illustrating the vicinity of the start point of the first laser welding. In FIG. 7, the start point of the first laser welding is indicated by the symbol P1. In the following description, the start point of the first laser welding may be simply referred to as start point P1. In the embodiment illustrated in FIG. 7, start point P1 is set inside peripheral edge 13a of sealing plate 13. Specifically, start point P1 is set at the same position as pre-welded portion W2 in the Y direction and forward of pre-welded portion W2 in the X direction. Start point P1 may be set at a position, for example, approximately 0.5 mm to 1.5 mm away from pre-welded portion W2 in the X direction. However, the position of start point P1 can be changed as appropriate depending on conditions such as the output value of the laser used for laser welding, the material of sealing plate 13, and the welding speed.

[0032] In the first laser welding, welding is performed along the welding path WT1 shown in FIG. 6. As shown in FIG. 7, in the first laser welding, laser welding is performed from the starting point P1 toward the tack weld W2. When the laser welding position reaches the tack weld W2, laser welding is then performed along the peripheral edge 13a of the sealing plate 13. In the configuration shown in FIG. 7, laser welding is performed from the tack weld W2 to the left. The end point of the first laser welding is set at the position where the tack weld W14 is formed. In the first laser welding, as shown in FIG. 6, laser welding is performed via the tack welds W1, W6, W5, and W13 to the tack weld W14. When the laser welding position reaches the tack weld W14, the first laser welding is completed. As a result, in the first laser welding, mainly the left half of the rear edge 11d1 and the rear half of the left edge 11d3 of the opening 11d of the case 11 are welded to the peripheral edge 13a of the sealing plate 13.

[0033] After the first laser welding is completed, the second laser welding is performed. The time from the end of the first laser welding to the start of the second laser welding is not particularly limited. The second laser welding may be started, for example, about 4 to 10 seconds, or about 5 to 9 seconds after the end of the first laser welding. In this embodiment, the second laser welding is started 7 seconds after the end of the first laser welding.

[0034] FIG. 8 is a schematic diagram illustrating the vicinity of the start point of the second laser welding. In FIG. 8, the start point of the second laser welding is indicated by the symbol P2. In the following description, the start point of the second laser welding may be simply referred to as start point P2. In the embodiment shown in FIG. 8, start point P2 is set inside peripheral edge 13a of sealing plate 13. Specifically, start point P2 is set at the same position as pre-welded portion W1 in the Y direction and forward of pre-welded portion W1 in the X direction. Start point P2 may be set at a position, for example, approximately 0.5 mm to 1.5 mm away from pre-welded portion W1 in the X direction. However, the position of start point P2 can be changed as appropriate depending on conditions such as the output value of the laser used for laser welding, the material of sealing plate 13, and the welding speed.

[0035] In the second laser welding, welding is performed along the welding path WT2 shown in FIG. 6. As shown in FIG. 8, in the second laser welding, laser welding is first performed from the starting point P2 toward the tack weld W1. When the laser welding position reaches the tack weld W1, laser welding is then performed along the peripheral edge 13a of the sealing plate 13. In the configuration shown in FIG. 8, laser welding is performed from the tack weld W1 to the right. The end point of the second laser welding is set at the position where the tack weld W16 is formed. In the second laser welding, as shown in FIG. 6, laser welding is performed via tack welds W2, W9, W10, and W15 to the tack weld W16. When the laser welding position reaches the tack weld W16, the second laser welding is completed. As a result, in the second laser welding, mainly the right half of the rear edge 11d1 and the rear half of the right edge 11d4 of the opening 11d of the case 11 are welded to the peripheral edge 13a of the sealing plate 13.

[0036] After the second laser welding is completed, the third laser welding is performed. The time from the end of the second laser welding to the start of the third laser welding is not particularly limited. The time from the end of the second laser welding to the start of the third laser welding may be the same as the time from the end of the first laser welding to the start of the second laser welding. The third laser welding may be started, for example, about 4 to 10 seconds, or about 5 to 9 seconds after the end of the second laser welding. In this embodiment, the third laser welding is started 7 seconds after the end of the second laser welding.

[0037] FIG. 9 is a schematic diagram showing the vicinity of the start point of the third laser welding. In FIG. 9, the start point of the third laser welding is indicated by the symbol P3. In the following description, the start point of the third laser welding may be simply referred to as start point P3. In the embodiment shown in FIG. 9, start point P3 is set inside peripheral edge 13a of sealing plate 13. Specifically, start point P3 is set at the same position as pre-welded portion W3 in the Y direction and at a position rearward of pre-welded portion W3 in the X direction. Start point P3 may be set at a position, for example, approximately 0.5 mm to 1.5 mm away from pre-welded portion W3 in the X direction. However, the position of start point P3 can be changed as appropriate depending on conditions such as the output value of the laser used for laser welding, the material of sealing plate 13, and the welding speed.

[0038] In the third laser welding, welding is performed along the welding path WT3 shown in FIG. 6. As shown in FIG. 9, in the third laser welding, laser welding is first performed from the starting point P3 toward the tack weld W3. When the laser welding position reaches the tack weld W3, laser welding is then performed along the peripheral edge 13a of the sealing plate 13. In the configuration shown in FIG. 9, laser welding is performed from the tack weld W3 to the left. The end point of the third laser welding is set at the position where the tack weld W13 is formed. In the third laser welding, as shown in FIG. 6, laser welding is performed via tack welds W4, W7, W8, and W14 to the tack weld W13. When the laser welding position reaches the tack weld W13, the third laser welding is completed. As a result, in the third laser welding, mainly the left half of the front edge 11d2 and the front half of the left edge 11d3 of the opening 11d of the case 11 are welded to the peripheral edge 13a of the sealing plate 13.

[0039] After the third laser welding is completed, the fourth laser welding is performed. The time from the end of the third laser welding to the start of the fourth laser welding is not particularly limited. The time from the end of the third laser welding to the start of the fourth laser welding may be the same as the time from the end of the first laser welding to the start of the second laser welding. The fourth laser welding may be started, for example, about 4 to 10 seconds, or about 5 to 9 seconds after the end of the third laser welding. In this embodiment, the fourth laser welding is started 7 seconds after the end of the third laser welding.

[0040] FIG. 10 is a schematic diagram illustrating the vicinity of the start point of the fourth laser welding. In FIG. 10, the start point of the fourth laser welding is indicated by the symbol P4. In the following description, the start point of the fourth laser welding may be simply referred to as start point P4. In the embodiment illustrated in FIG. 10, start point P4 is set inside peripheral edge 13a of sealing plate 13. Specifically, start point P4 is set at the same position as pre-welded portion W4 in the Y direction and at a position rearward of pre-welded portion W4 in the X direction. Start point P4 may be set at a position, for example, approximately 0.5 mm to 1.5 mm away from pre-welded portion W4 in the X direction. However, the position of start point P4 can be changed as appropriate depending on conditions such as the output value of the laser used for laser welding, the material of sealing plate 13, and the welding speed.

[0041] In the fourth laser welding, welding is performed along the welding path WT4 shown in FIG. 6. As shown in FIG. 10, in the fourth laser welding, laser welding is first performed from start point P4 toward tack weld W4. When the laser welding position reaches tack weld W4, laser welding is then performed along the peripheral edge 13a of the sealing plate 13. In the configuration shown in FIG. 10, laser welding is performed from tack weld W4 to the right. The end point of the fourth laser welding is set at the position where tack weld W15 is formed. In the fourth laser welding, as shown in FIG. 6, laser welding is performed via tack welds W3, W12, W11, and W16 to tack weld W15. When the laser welding position reaches tack weld W15, the fourth laser welding ends. As a result, in the fourth laser welding, mainly the right half of the front edge 11d2 and the front half of the right edge 11d4 of the opening 11d of the case 11 are welded to the peripheral edge 13a of the sealing plate 13.

[0042] The main welding step S05 is completed when the fourth laser welding is completed. When the main welding step S05 is completed, the case 11 and the sealing plate 13 are welded together around the entire periphery of the peripheral edge 13a of the sealing plate 13. This seals the inside of the case 11. When the main welding step S05 is completed, various steps are performed as appropriate, such as a liquid injection step of injecting the electrolyte into the case 11, an aging step of charging the electricity storage device 10 and leaving it for a predetermined period of time, and an inspection step of inspecting the electricity storage device 10 for internal short circuits, etc., to manufacture the electricity storage device 10.

[0043] FIG. 11 is a plan view schematically illustrating the case 11 and the sealing plate 13 after the completion of the main welding step S05. In FIG. 11, the hatched areas indicate weld marks 30 formed by the laser welding performed in the main welding step S05. In FIG. 11, the weld marks 30 are exaggerated. The weld marks 30 are formed around the entire periphery of the peripheral edge 13a of the sealing plate 13. The weld marks 30 have four inner protrusions 30a and a main body 30b. As shown in FIG. 11, the main body 30b is formed in an annular shape along the entire periphery of the peripheral edge 13a of the sealing plate 13. The inner protrusions 30a protrude from the main body 30b. The inner protrusions 30a protrude inward from the peripheral edge 13a of the sealing plate 13. The inner protrusions 30a are formed by starting the first through fourth laser welding processes from inside the peripheral edge 13a of the sealing plate 13.

[0044] As described above, according to the findings of the present inventors, as main welding step S05 progresses, the temperature of case 11 increases, widening the gap between case 11 and sealing plate 13 and making laser leakage more likely to occur. Therefore, if laser welding is performed in a single step along the entire periphery of peripheral edge 13a of sealing plate 13 in main welding step S05, laser leakage is likely to occur. However, according to the method for manufacturing electricity storage device 10 of this embodiment, main welding step S05 involves laser welding the entire periphery of peripheral edge 13a of sealing plate 13 in four separate steps. This allows main welding to be performed while suppressing the temperature rise of case 11 compared to when laser welding the entire periphery of peripheral edge 13a of sealing plate 13 in a single step, thereby preventing laser leakage.

[0045] According to this embodiment, the method for manufacturing electricity storage device 10 includes a pre-welding step S04 of pre-welding case 11 and sealing plate 13 at a predetermined position on the boundary between case 11 and sealing plate 13. As a result, final welding is performed in final welding step S05 with sealing plate 13 positioned relative to case 11, and therefore the positional relationship between sealing plate 13 and case 11 is less likely to shift during final welding.

[0046] Specifically, in this embodiment, in the temporary welding step S04, predetermined positions near the gas discharge valve 14 are tack-welded. As a result, final welding can be performed while the vicinity of the gas discharge valve 14 is fixed, and therefore the position of the gas discharge valve 14 is less likely to vary after final welding. Also, in this embodiment, in the temporary welding step S04, predetermined positions near the electrode terminals 17, 18 are tack-welded. As a result, final welding can be performed while the vicinity of the electrode terminals 17, 18 is fixed, and therefore the positions of the electrode terminals 17, 18 are less likely to vary after final welding.

[0047] As described above, according to the inventors' findings, the gap between the case 11 and the sealing plate 13 tends to widen in areas where the spacing between the pre-welded portions W1 to W16 is greater than 40 mm, making laser welding particularly likely to occur. In the embodiment shown in FIG. 6 , the spacing between the pre-welded portions W1 and W6, the spacing between the pre-welded portions W2 and W9, the spacing between the pre-welded portions W4 and W7, and the spacing between the pre-welded portions W3 and W12 are all 80 mm, and the case 11 has four areas where the spacing between the pre-welded portions W1 to W16 is greater than 40 mm. Therefore, in this embodiment, in the main welding step S05, the four areas where the spacing between the pre-welded portions W1 to W16 is greater than 40 mm are welded in separate welding passes. Specifically, in the first laser welding pass, the area between the pre-welded portions W1 and W6 is welded. In the second laser welding pass, the area between the pre-welded portions W2 and W9 is welded. In the third laser welding pass, the area between the pre-welded portions W4 and W7 is welded. In the fourth laser welding, the portion between pre-welded portions W3 and W12 is welded. In this way, by welding the portions of pre-welded portions W1 to W16 where the intervals are relatively long in separate welding operations, it is possible to prevent the gap between case 11 and sealing plate 13 from widening even in the portion where the gap is likely to widen, and therefore laser welding is less likely to occur.

[0048] In the main welding step S05 of this embodiment, the start section and end section of each welding trajectory WT1-WT4 in the four laser welding runs overlap with either the start section or the end section of the welding trajectory WT1-WT4 of another run. Here, the start section refers to, for example, the section on each welding trajectory WT1-WT4 between the start point P1-P4 and the temporary weld W1-W16 that is second closest to the start point P1-P4. The end section refers to, for example, the section on each welding trajectory WT1-WT4 between the end point and the temporary weld W1-W16 that is closest to the end point.

[0049] Specifically, in the embodiment shown in FIG. 6, the start section of the first laser welding is the section between the start point P1 and the tack weld W1 on the welding trajectory WT1. The end section of the first laser welding is the section between the tack weld W13 and the tack weld W14 on the welding trajectory WT1. The start section of the second laser welding is the section between the start point P2 and the tack weld W2 on the welding trajectory WT2. The end section of the second laser welding is the section between the tack weld W15 and the tack weld W16 on the welding trajectory WT2. The start section of the third laser welding is the section between the start point P3 and the tack weld W4 on the welding trajectory WT3. The end section of the third laser welding is the section between the tack weld W13 and the tack weld W14 on the welding trajectory WT3. The start section of the fourth laser welding is the section between the start point P4 and the tack weld W3 on the welding trajectory WT4. The end section of the fourth laser welding is the section between the tack weld W15 and the tack weld W16 on the welding track WT4.

[0050] In the configuration shown in FIG. 6, the start section of the first laser weld overlaps with the start section of the second laser weld. The end section of the first laser weld overlaps with the end section of the third laser weld. The end section of the second laser weld overlaps with the end section of the fourth laser weld. The start section of the third laser weld overlaps with the start section of the fourth laser weld. As a result, the start section and end section of each welding trajectory WT1 to WT4 are welded in an overlapping manner, so that welding can be performed around the entire circumference of peripheral edge portion 13a of sealing plate 13 without any omissions.

[0051] In the main welding step S05 of this embodiment, start points P2 to P4 of the second and subsequent laser welding are set at positions distant from the end point of the previous laser welding. Here, "distant positions" refers to positions that are distant, for example, by at least one-third of the width of the case 11. Specifically, in the embodiment shown in FIG. 6, start point P2 is distant from the position where temporary weld W14, which is the end point of the first laser welding, is formed by at least one-third of the width of the case 11. Start point P3 is distant from the position where temporary weld W16, which is the end point of the second laser welding, is formed by at least one-third of the width of the case 11. Start point P4 is distant from the position where temporary weld W13, which is the end point of the third laser welding, is formed by at least one-third of the width of the case 11. This allows laser welding to begin at a position where the temperature is relatively low in each laser welding, effectively preventing laser welding failure.

[0052] In the main welding step S05 of this embodiment, the second or subsequent laser welding is started 4 to 10 seconds after the previous laser welding is completed. Specifically, in this embodiment, the second or subsequent laser welding is started 7 seconds after the previous laser welding is completed. This allows the laser welding to be started after the temperature of the case 11 has dropped to a certain level, thereby effectively preventing laser welding failure.

[0053] According to the findings of the present inventors, laser leakage can occur even immediately after the start of laser welding. The present inventors believe the cause of this is as follows: As laser welding progresses, the temperatures of case 11 and sealing plate 13 rise, making case 11 and sealing plate 13 more likely to melt. Therefore, as laser welding progresses, a molten pool is more likely to form. This molten pool penetrates into the gap between case 11 and sealing plate 13 and seals the gap, making laser leakage less likely to occur. However, immediately after the start of laser welding, the temperatures of case 11 and sealing plate 13 have not risen sufficiently, making it difficult for a molten pool to form. Therefore, it is believed that laser leakage can occur even immediately after the start of laser welding.

[0054] However, in the main welding step S05 of this embodiment, the start points P1 to P4 of the welding tracks WT1 to WT4 of each of the at least four laser welding runs are set inside the peripheral edge 13a of the sealing plate 13. This makes it easier to increase the temperature of the sealing plate 13 and form a molten pool even immediately after the start of laser welding. This also makes it possible to prevent laser welding from occurring immediately after the start of laser welding.

[0055] As described above, according to the findings of the present inventors, laser leakage is particularly likely to occur when manufacturing a relatively large electricity storage device 10 in which the width of the case 11 is 30 cm or more. This is because a relatively large gap is likely to occur between the case 11 and the sealing plate 13 in a relatively large electricity storage device 10, and the gap between the case 11 and the sealing plate 13 is likely to widen in the main welding step S05. However, according to the manufacturing method of this embodiment, even in the latter half of the main welding step S05 in which the temperature of the case 11 is likely to rise, main welding is performed while suppressing the temperature rise of the case 11, so laser leakage can be prevented. Therefore, the manufacturing method of this embodiment can be used effectively, particularly when manufacturing a relatively large electricity storage device 10.

[0056] Although one embodiment of the technology proposed here has been described above, the above embodiment is merely an example and the technology can be implemented in other modes.

[0057] 12 to 15 are views for explaining main welding step S05 according to another embodiment. For simplicity of explanation, the embodiments shown in Fig. 12 to 15 will be described assuming that the starting point of the welding path for each laser welding is set at peripheral edge 13a of sealing plate 13. However, the starting point of the welding path for each laser welding may be set further inward than peripheral edge 13a of sealing plate 13, as in the embodiment shown in Fig. 6.

[0058] In the embodiment shown in FIG. 12, in the first laser welding, as indicated by the symbol WT1, laser welding is started from the tack weld W1, and laser welding is performed via tack welds W2, W9, W10, and W15 to tack weld W16. In the second laser welding, as indicated by the symbol WT2, laser welding is started from the tack weld W2, and laser welding is performed via tack welds W1, W6, W5, and W13 to tack weld W14. In the third laser welding, as indicated by the symbol WT3, laser welding is started from the tack weld W3, and laser welding is performed via tack welds W4, W7, W8, and W14 to tack weld W13. In the fourth laser welding, as indicated by the symbol WT4, laser welding is started from the tack weld W4, and laser welding is performed via tack welds W3, W12, W11, and W16 to tack weld W15. Therefore, in the configuration shown in FIG. 12, compared to the configuration shown in FIG. 6, the welding trajectory WT1 of the first laser welding and the welding trajectory WT2 of the second laser welding are interchanged and main welding is performed.

[0059] In the embodiment shown in FIG. 13, in the first laser welding, as indicated by the symbol WT1, laser welding is started from the tack weld W2, and laser welding is performed via tack welds W1, W6, W5, and W13 to tack weld W14. In the second laser welding, as indicated by the symbol WT2, laser welding is started from the tack weld W4, and laser welding is performed via tack welds W3, W12, W11, and W16 to tack weld W15. In the third laser welding, as indicated by the symbol WT3, laser welding is started from the tack weld W3, and laser welding is performed via tack welds W4, W7, W8, and W14 to tack weld W13. In the fourth laser welding, as indicated by the symbol WT4, laser welding is started from the tack weld W1, and laser welding is performed via tack welds W2, W9, W10, and W15 to tack weld W16. Therefore, in the configuration shown in FIG. 13, compared to the configuration shown in FIG. 6, the welding trajectory WT2 of the second laser welding and the welding trajectory WT4 of the fourth laser welding are interchanged and main welding is performed.

[0060] In the embodiment shown in FIG. 14, in the first laser welding, as indicated by the symbol WT1, laser welding begins at tack weld W14, and continues through tack welds W13, W5, W6, and W1 to tack W2. In the second laser welding, as indicated by the symbol WT2, laser welding begins at tack weld W16, and continues through tack welds W15, W10, W9, and W2 to tack W1. In the third laser welding, as indicated by the symbol WT3, laser welding begins at tack weld W13, and continues through tack welds W14, W8, W7, and W4 to tack W3. In the fourth laser welding, as indicated by the symbol WT4, laser welding begins at tack weld W15, and continues through tack welds W16, W11, W12, and W3 to tack W4. Therefore, in the configuration shown in FIG. 14, the direction of travel of the welding trajectories WT1 to WT4 is reversed in each welding run, as compared with the configuration shown in FIG.

[0061] In the embodiment shown in Fig. 15, laser welding is performed six times in the main welding step S05. The arrows indicated by the symbols WT1 to WT4 in Fig. 15 indicate the welding trajectories of the first to fourth laser welding, respectively. The arrow indicated by the symbol WT5 indicates the welding trajectory of the fifth laser welding. The arrow indicated by the symbol WT6 indicates the welding trajectory of the sixth laser welding.

[0062] In the embodiment shown in FIG. 15, in the first laser welding, as indicated by the symbol WT1, laser welding is started from the tack weld W2, and laser welding is performed via tack welds W1 and W6 to tack W5. In the second laser welding, as indicated by the symbol WT2, laser welding is started from the tack weld W1, and laser welding is performed via tack welds W2 and W9 to tack W10. In the third laser welding, as indicated by the symbol WT3, laser welding is started from the tack weld W6, and laser welding is performed via tack welds W5, W13, W14, and W8 to tack W7. In the fourth laser welding, as indicated by the symbol WT4, laser welding is started from the tack weld W9, and laser welding is performed via tack welds W10, W15, W16, and W11 to tack W12. In the fifth laser welding, as indicated by the symbol WT5, laser welding starts from the tack weld W3, passes through the tack welds W4 and W7, and continues to the tack weld W8. In the sixth laser welding, as indicated by the symbol WT6, laser welding starts from the tack weld W4, passes through the tack welds W3 and W12, and continues to the tack weld W11.

[0063] The method for manufacturing the electricity storage device 10 may include steps other than those described above. For example, the method for manufacturing the electricity storage device 10 may include a clamping step of pressing the case 11 against the sealing plate 13 before the main welding step S05. This can further prevent laser voids from occurring. Similarly, the method for manufacturing the electricity storage device 10 may also include a clamping step before the temporary welding step S04.

[0064] The technology disclosed herein has been described in various ways. Unless otherwise specified, the embodiments and the like described herein do not limit the present invention. Furthermore, the technology disclosed herein can be modified in various ways, and as long as no particular problems arise, each component and each process described herein can be omitted or combined as appropriate. Furthermore, this specification includes the disclosures described in the following sections.

[0065] Section 1: providing a rectangular case having an opening; preparing a sealing plate to be attached to the opening along an edge of the opening; an assembly process of attaching the sealing plate to the opening of the case; a main welding process of laser welding the case and the sealing plate along the entire periphery of the sealing plate; Including, In the main welding process, The method for manufacturing an electricity storage device includes laser welding the entire periphery of the peripheral edge portion of the sealing plate in at least four separate steps.

[0066] Section 2: Item 2. The method for manufacturing an electricity storage device according to item 1, further comprising a pre-welding step of pre-welding the case and the sealing plate at a predetermined position on the boundary between the case and the sealing plate.

[0067] Section 3: the sealing plate prepared in the step of preparing the sealing plate is provided with an electrode terminal; In the temporary welding step, 3. The method for manufacturing an electricity storage device according to item 2, wherein the boundary between the case and the sealing plate is pre-welded at a predetermined position near the electrode terminal.

[0068] Section 4: the sealing plate prepared in the step of preparing the sealing plate has a gas exhaust valve for exhausting gas inside the case, In the temporary welding step, Item 4. The method for manufacturing an electricity storage device according to item 2 or 3, wherein the boundary between the case and the sealing plate is pre-welded at a predetermined position near the gas release valve.

[0069] Section 5: In the pre-welding step, the case and the sealing plate are pre-welded at a plurality of positions, The case that is pre-welded to the sealing plate in the pre-welding step has a plurality of portions along an edge of the opening where intervals between pre-welded portions formed by the pre-welding are longer than a predetermined length, In the main welding process, Item 5. The method for manufacturing an electricity storage device according to any one of items 2 to 4, wherein the portions of the plurality of temporary welds where the intervals between the temporary welds are longer than the predetermined length are welded to different turns.

[0070] Item 6: In the main welding process, Item 6. The method for manufacturing an electricity storage device according to any one of items 1 to 5, wherein a start section and an end section of a welding trajectory of each of at least four laser welding runs overlap with either a start section or an end section of a welding trajectory of another run.

[0071] Section 7: In the main welding process, Item 7. The method for manufacturing an electricity storage device according to any one of items 1 to 6, wherein a start point of a second or subsequent laser welding is set at a position away from an end point of the previous laser welding.

[0072] Section 8: In the main welding process, 8. The method for manufacturing an electricity storage device according to any one of items 1 to 7, wherein the second or subsequent laser welding is started 4 to 10 seconds after the previous laser welding is completed.

[0073] Section 9: Item 9. The method for manufacturing an electricity storage device according to any one of items 1 to 8, wherein the case prepared in the case preparation step has a width of 30 cm or more.

[0074] Section 10: In the main welding process, Item 10. The method for manufacturing an electricity storage device according to any one of items 1 to 9, wherein a starting point of each welding path of at least four laser welding steps is set inside the peripheral edge of the sealing plate.

[0075] Section 11: An electricity storage device obtained by the electricity storage device manufacturing method according to item 10, a welding mark is formed along the entire periphery of the peripheral edge portion of the sealing plate, The welding mark has an inward protruding portion that protrudes inward beyond the peripheral edge portion of the sealing plate. [Explanation of symbols]

[0076] 10. Energy storage devices 11 cases 11d aperture 13 Sealing plate 13a Periphery of sealing plate 14 Gas exhaust valve 17, 18 Electrode terminal 30 Weld marks 30a Inner protrusion S01 Case preparation process S02 Sealing plate preparation process S03 Assembly process S04 Temporary welding process S05 Main welding process W1~W16 Temporary welds P1~P4 Starting points of laser welding WT1~WT6 welding track

Claims

1. providing a rectangular case having an opening; preparing a sealing plate to be attached to the opening along an edge of the opening; an assembly process of attaching the sealing plate to the opening of the case; a main welding process of laser welding the case and the sealing plate along the entire periphery of the sealing plate; Including, In the main welding process, The method for manufacturing an electricity storage device includes laser welding the entire periphery of the peripheral edge portion of the sealing plate in at least four separate steps.

2. The method for manufacturing an electricity storage device according to claim 1 , further comprising a pre-welding step of pre-welding the case and the sealing plate at a predetermined position in a boundary between the case and the sealing plate.

3. the sealing plate prepared in the step of preparing the sealing plate is provided with an electrode terminal; In the temporary welding step, The method for manufacturing an electricity storage device according to claim 2 , wherein the boundary between the case and the sealing plate is pre-welded at a predetermined position near the electrode terminal.

4. the sealing plate prepared in the step of preparing the sealing plate has a gas exhaust valve for exhausting gas inside the case, In the temporary welding step, The method for manufacturing an electricity storage device according to claim 2 , wherein the boundary between the case and the sealing plate is pre-welded at a predetermined position near the gas release valve.

5. In the pre-welding step, the case and the sealing plate are pre-welded at a plurality of positions, The case that is pre-welded to the sealing plate in the pre-welding step has a plurality of portions along an edge of the opening where intervals between pre-welded portions formed by the pre-welding are longer than a predetermined length, In the main welding process, The method for manufacturing an electricity storage device according to claim 2 , wherein portions of the plurality of temporary welds where the interval between the temporary welds is longer than the predetermined length are welded in separate welding runs.

6. In the main welding process, 2. The method for manufacturing an electricity storage device according to claim 1, wherein a start section and an end section of a welding trajectory of each of at least four laser welding runs overlap with either a start section or an end section of a welding trajectory of another run.

7. In the main welding process, The method for manufacturing an electricity storage device according to claim 1 , wherein a start point of the second or subsequent laser welding is set at a position away from an end point of the previous laser welding.

8. In the main welding process, 2. The method for manufacturing an electricity storage device according to claim 1, wherein the second or subsequent laser welding is started 4 to 10 seconds after the previous laser welding is completed.

9. The method for manufacturing an electricity storage device according to claim 1 , wherein the case prepared in the case preparation step has a width of 30 cm or more.

10. In the main welding process, The method for manufacturing an electricity storage device according to claim 1 , wherein a start point of each welding path of at least four laser welding runs is set inside the peripheral edge portion of the sealing plate.

11. An electricity storage device obtained by the electricity storage device manufacturing method according to claim 10, a welding mark is formed around the entire periphery of the peripheral edge portion of the sealing plate, The welding mark has an inward protruding portion that protrudes inward beyond the peripheral edge portion of the sealing plate.

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