Method for manufacturing energy storage devices

Abstract

Ensure a stable welding depth. [Solution] The method for manufacturing an energy storage device includes a first preparation step S1 of preparing a case body having an opening, a second preparation step S2 of preparing a sealing plate to seal the opening of the case body, an assembly step S4 of attaching the sealing plate to the opening of the case body, and a welding step S6 of welding by irradiating laser light along the space between the case body and the sealing plate. The sealing plate prepared in the second preparation step S2 has a recess that is indented downward at the peripheral edge of the upper surface of the sealing plate. In the welding step S6, welding is performed by irradiating laser light toward the recess of the sealing plate.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a power storage device.

Background Art

[0002] For example, Japanese Patent Application Laid-Open No. 2018-202478 discloses a laser sealing device including means for splitting one laser beam into two and means for translating the two split laser beams in parallel along the bonding interface of two members. In this laser sealing device, the two split laser beams are configured to be symmetrically arranged at positions equidistant from the bonding interface so that the two split laser beams do not enter the bonding interface.

[0003] When welding two members, it is said that high-quality welding can be achieved by using this laser sealing device. For example, in the manufacture of a lithium battery including a container having an opening and a lid attached to the opening and welded to the container, it is said that the generation of sputtering can be suppressed by using the above laser sealing device.

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 the present inventors weld the case body of a power storage device and a sealing plate, they consider ensuring a stable welding depth and suppressing the occurrence of laser penetration.

Means for Solving the Problems

[0006] A method for manufacturing an energy storage device disclosed herein comprises a first preparation step, a second preparation step, an assembly step, and a welding step. In the first preparation step, a case body having an opening is prepared. In the second preparation step, a sealing plate is prepared to seal the opening of the case body. In the assembly step, the sealing plate is fitted into the opening of the case body. In the welding step, the case body and the sealing plate are welded by irradiating them with laser light along the gap between them. The sealing plate prepared in the second preparation step has a recess that is indented downward at the peripheral end of the upper surface of the sealing plate. In the welding step, the sealing plate is welded by irradiating it with laser light toward the recess.

[0007] According to the manufacturing method of the energy storage device disclosed herein, a molten weld mark is formed in a recessed area that is lowered at the peripheral edge of the sealing plate, thereby ensuring a stable welding depth. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic perspective view showing an energy storage device according to an embodiment. [Figure 2] Figure 2 is an exploded perspective view of the energy storage device according to this embodiment. [Figure 3] Figure 3 is a flowchart showing an example of a method for manufacturing an energy storage device. [Figure 4] Figure 4 is a cross-sectional view showing the fracture surface of the sealing plate prepared in the preparation process. [Figure 5] Figure 5 shows the correlation between the fracture surface area and the weld depth. [Figure 6] Figure 6 is a plan view showing the sealing plate prepared in the second preparation step. [Figure 7] Figure 7 is a cross-sectional view showing the sealing plate prepared in the second preparation step. [Figure 8] Figure 8 is a cross-sectional view showing the sealing plate prepared in the second preparation step in the modified example. [Figure 9] Figure 9 is a cross-sectional view showing the case body and the sealing plate welded together. [Figure 10] Figure 10 shows the correlation between the depth of the recess and the welding depth. [Figure 11] Figure 11 shows the correlation between the width of the recess and the welding depth. [Modes for carrying out the invention]

[0009] Hereinafter, an embodiment of the technology disclosed herein will be described with reference to the drawings. Naturally, the embodiment described herein is not intended to particularly limit the present invention. Each figure is a schematic diagram and does not necessarily faithfully reflect an actual implementation. Furthermore, components and parts that perform the same function are appropriately denoted by the same reference numerals, and redundant explanations are omitted as appropriate.

[0010] In this specification, "energy storage device" refers to a device that can be charged and discharged. Energy 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 is a general term for a battery that can be repeatedly charged and discharged by the movement of charge carriers between the positive and negative electrodes. Energy storage devices may use either an electrolyte or a solid electrolyte. For example, a secondary battery may be a secondary battery that uses a so-called liquid electrolyte, or it may be a so-called all-solid-state battery that uses a solid electrolyte. Energy storage devices also include capacitors such as electric double-layer capacitors and lithium-ion capacitors.

[0011] Figure 1 is a schematic perspective view of the energy storage device 10. Figure 2 is an exploded perspective view of the energy storage device 10. In this embodiment, the energy storage device 10 is a so-called lithium-ion secondary battery. In this embodiment, the symbols F, Rr, L, R, U, and D in the drawings indicate the front, back, left, right, top, and bottom of the energy storage device 10, respectively. The symbols X, Y, and Z in the drawings indicate the thickness direction, width direction, and height direction of the energy storage device 10, respectively. Here, the thickness direction X is the front-to-back direction. The width direction Y is the direction perpendicular to the thickness direction X. The width direction Y is the left-to-right direction. The height direction Z is the direction perpendicular to the thickness direction X and the width direction Y. The height direction Z is the up-and-down direction. However, these directions are defined for the convenience of explanation and do not limit in any way the installation configuration of the energy storage device 10 disclosed herein.

[0012] As shown in Figure 1, the energy storage device 10 comprises a case body 11, a sealing plate 13, and an electrode body 20 (see Figure 2). As shown in Figure 2, the case body 11 is a rectangular case having an opening 11d. The opening 11d is formed at the top of the case body 11. The case body 11 is formed in a substantially rectangular parallelepiped shape. The shape of the opening 11d is rectangular. However, the shape of the opening 11d is not particularly limited.

[0013] In this embodiment, the case body 11 has, in plan view, a short side extending in the thickness direction X and a long side extending in the width direction Y. Here, as shown in Figure 2, the case body 11 has a bottom surface 11a, a pair of narrow surfaces 11b, and a pair of wide surfaces 11c. The bottom surface 11a constitutes the bottom of the case body 11 and faces the opening 11d. The bottom surface 11a is formed in a rectangular shape with a short side and a long side. The pair of narrow surfaces 11b face the width direction Y. The pair of narrow surfaces 11b extend upward from both ends of the bottom surface 11a in the width direction Y (in other words, the short sides of the bottom surface 11a). The pair of wide surfaces 11c face the thickness direction X. The pair of wide surfaces 11c extend upward from both ends of the bottom surface 11a in the thickness direction X (in other words, the long sides of the bottom surface 11a). The pair of wide surfaces 11c and the pair of narrow surfaces 11b are continuous. The case body 11 is made of, for example, aluminum or an aluminum alloy mainly composed of aluminum, in order to ensure lightness and the required rigidity.

[0014] As shown in Figure 2, the opening 11d is enclosed by a rear edge 11d1, a front edge 11d2, a left edge 11d3, and a right edge 11d4. The rear edge 11d1, front edge 11d2, left edge 11d3, and right edge 11d4 constitute the upper end of the case body 11. The rear edge 11d1 and front edge 11d2 extend in the width direction Y. The rear edge 11d1 is located behind the front edge 11d2. The left edge 11d3 and right edge 11d4 extend in the thickness direction X. The left edge 11d3 is located to the left of the right edge 11d4. The left edge 11d3 is connected to the left end of the rear edge 11d1 and the left end of the front edge 11d2. The right edge 11d4 is connected to the right end of the rear edge 11d1 and the right end of the front edge 11d2. In the following explanation, the rear edge 11d1, the front edge 11d2, the left edge 11d3, and the right edge 11d4 are also referred to as the edges of the opening 11d.

[0015] The sealing plate 13 is a member for sealing the opening 11d of the case body 11. The sealing plate 13 is attached to the opening 11d along the edge of the opening 11d of the case body 11. The sealing plate 13 has a shape corresponding to the opening 11d. Here, the sealing plate 13 is a flat plate formed in a rectangular shape in plan view. Here, the sealing plate 13 has a peripheral end portion 13a. The peripheral end portion 13a constitutes the front end, the rear end, the left end, and the right end of the sealing plate 13. The peripheral end portion 13a is provided along the circumferential direction of the sealing plate 13 over the entire circumference in the circumferential direction. Although details will be described later, the opening 11d is sealed by laser welding the peripheral end portion 13a of the sealing plate 13 along the edge of the opening 11d. The sealing plate 13 may be formed of the same material as the case body 11. Here, for example, the sealing plate 13 is formed of aluminum or an aluminum alloy mainly composed of aluminum.

[0016] In the present embodiment, as shown in FIG. 2, the sealing plate 13 has a gas discharge valve 14 for discharging the gas inside the case body 11. The gas discharge valve 14 is provided at the central portion in the width direction Y of the sealing plate 13. The gas discharge valve 14 is, for example, a thin-walled portion designed to break when the pressure inside the case body 11 rises above a predetermined value. When the pressure inside the case body 11 becomes equal to or higher than the predetermined value, the gas inside the case body 11 is discharged to the outside of the case body 11 by the breaking of the gas discharge valve 14.

[0017] In this embodiment, a pair of electrode terminals 17 and 18 are provided on the sealing plate 13. The pair of electrode terminals 17 and 18 are arranged at both ends in the width direction Y of the sealing plate 13. Note that the method of attaching the electrode terminals 17 and 18 to the sealing plate 13 is not particularly limited. For example, the electrode terminals 17 and 18 may be attached to the sealing plate 13 by caulking. The electrode terminals 17 and 18 may be integrally formed with the sealing plate 13. Here, as shown in FIG. 2, the electrode terminal 17 has 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. The electrode terminal 18, similarly to the electrode terminal 17, has an external terminal 18a attached to the upper side of the sealing plate 13 and an internal terminal 18b attached to the lower side of the sealing plate 13.

[0018] As shown in FIG. 2, the electrode body 20 is housed inside the case body 11. The electrode body 20 has a flat shape. Although not shown, the electrode body 具有 a positive electrode and a negative electrode. The electrode body 20 is, for example, a wound electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are laminated via a strip-shaped separator and wound in the longitudinal direction around a winding shaft. However, the configuration of the electrode body is not particularly limited. As the electrode body 20, various conventionally known electrode bodies can be used. For example, the electrode body 20 may be a laminated electrode body in which a rectangular positive electrode and a rectangular negative electrode are stacked in an insulated state. Here, the electrode body 20 is housed in the case body 11 with the winding shaft substantially parallel to the width direction Y. Note that the electrode body 20 may be housed in the case body 11 with the winding shaft substantially parallel to the height direction Z. The number of electrode bodies 要 which are housed in the case body 11 may be one or two or more.

[0019] In this embodiment, the positive electrode of the electrode body 20 is connected to the internal terminal 17b of the electrode terminal 17 shown in FIG. 2. 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.

[0020] Although not shown in the diagram, the positive electrode of the electrode body 20 has a positive electrode current collector and a positive electrode composite layer fixed on the positive electrode current collector. The positive electrode current collector is made of a conductive metal such as aluminum, aluminum alloy, nickel, or stainless steel. In this case, the positive electrode current collector is made of aluminum. The positive electrode composite layer typically contains a positive electrode active material (e.g., lithium transition metal composite oxide) capable of reversibly intercepting and releasing charge carriers, and a binder (e.g., polyvinylidene fluoride (PVdF)).

[0021] Although not shown in the diagram, the negative electrode of the electrode body 20 has a negative electrode current collector and a negative electrode composite layer fixed on the negative electrode current collector. The negative electrode current collector is made of a conductive metal such as copper, copper alloy, nickel, or stainless steel. In this case, the negative electrode current collector is made of copper. The negative electrode composite layer typically contains a negative electrode active material (e.g., a carbon material such as graphite) that can reversibly absorb and release charge carriers and a binder (e.g., styrene-butadiene rubber (SBR) or carboxymethylcellulose (CMC)).

[0022] In this embodiment, the electrode body 20 is impregnated with an electrolyte (not shown). Here, the electrolyte is a non-aqueous liquid electrolyte (non-aqueous electrolyte) containing a non-aqueous solvent and a supporting salt. The non-aqueous solvent includes, for example, carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The supporting salt is, for example, a fluorine-containing lithium salt such as LiPF6. However, the electrolyte may be in solid form (a so-called solid electrolyte) and may be integrated with the electrode body 20. Furthermore, any excess electrolyte that cannot be impregnated into the electrode body 20 may be stored inside the case body 11.

[0023] The configuration of the energy storage device 10 according to this embodiment has been described above. Next, the manufacturing method of the energy storage device 10 will be described. Figure 3 is a flowchart of an example of a manufacturing method of the energy storage device 10. As shown in Figure 3, the manufacturing method of the energy storage device 10 includes a first preparation step S1, a second preparation step S2, a third preparation step S3, an assembly step S4, a tack welding step S5, and a main welding step S6. The manufacturing method of the energy storage device 10 may include other steps, but their explanation will be omitted here. In the manufacturing method of the energy storage device 10 shown in Figure 3, the case body 11 (see Figure 2) and the peripheral end 13a of the sealing plate 13 (see Figure 2) are laser-welded. Hereinafter, laser welding will also be simply referred to as welding.

[0024] The first preparation step S1 in Figure 3 is the step of preparing a rectangular case body 11 (see Figure 2) having an opening 11d. The method of preparing the case body 11 in the first preparation step S1 is not particularly limited. The case body 11 can be prepared, for example, by bending a rectangular metal plate (a plate made of aluminum or an aluminum alloy).

[0025] Next, the second preparation step S2 shown in Figure 3 is performed. The second preparation step S2 is the step of preparing a sealing plate 13 (see Figure 2) that seals the opening 11d of the case body 11. In the second preparation step S2, the sealing plate 13 is prepared with the electrode terminals 17 and 18 provided. In this embodiment, as shown in Figure 3, the second preparation step S2 includes the preparation step S21, the forming step S22, and the mounting step S23. By performing the preparation step S21, the forming step S22, and the mounting step S23 in order, the sealing plate 13 can be prepared in the second preparation step S2.

[0026] In preparation step S21 of Figure 3, a sealing plate 13 formed in a predetermined shape (for example, rectangular) is prepared. In this embodiment, for example, the sealing plate 13 is prepared by processing a single rectangular flat plate. Here, in order to prepare a sealing plate 13 formed in a predetermined shape from the above-mentioned flat plate, a punching process is performed. Although not shown in the figure, in the punching process, the above-mentioned flat plate is sandwiched between a so-called punching die and a punching plate, and pressure is applied to the flat plate to manufacture a sealing plate 13 of a predetermined shape.

[0027] Figure 4 is a cross-sectional view showing the fracture surface 30 of the sealing plate 13 prepared in preparation step S21. The cross-sectional view shown in Figure 4 is a longitudinal cross-sectional view of the peripheral end 13a of the sealing plate 13 along the height direction Z. In this embodiment, by performing the punching process described above, a fracture surface 30 may be formed on the sealing plate 13, as shown in Figure 4. The fracture surface 30 is formed, for example, on the peripheral end 13a of the sealing plate 13, in other words, on the side surface of the sealing plate 13. The fracture surface 30 is formed along the circumferential direction of the sealing plate 13. The fracture surface 30 can be formed on the upper part of the side surface of the sealing plate 13 by punching a rectangular flat plate by applying pressure in the vertical direction. Here, in a plan view, the direction toward the center of the sealing plate 13 is called the inward direction, and the direction opposite to the inward direction is called the outward direction. In this embodiment, the fracture surface 30 refers to the surface of the sealing plate 13 that is formed by the punching process and is recessed toward the inward direction on the side surface of the sealing plate 13. The fracture surface 30 is formed along the circumferential direction of the sealing plate 13, but the shape of the fracture surface 30 is not uniform and may differ depending on its position in the circumferential direction of the sealing plate 13. The "shape of the fracture surface 30" here includes the degree of inward indentation, the degree to which it is indented inward from the sealing plate 13, and the length in the height direction Z.

[0028] In this embodiment, as shown in Figure 4, the shear surface 31 is the side surface of the sealing plate 13 that is not indented inward like the fracture surface 30. The shear surface 31 is located, for example, below the fracture surface 30.

[0029] Furthermore, in this embodiment, as shown in Figure 4, a chamfered edge 33 is formed on the sealing plate 13 prepared in preparation step S21. Here, the chamfered edge 33 is formed on the peripheral edge 13a of the lower surface of the sealing plate 13. The chamfered edge 33 is formed on the sealing plate 13 so as to chamfer the lower corner of the sealing plate 13. The chamfered edge 33 is formed along the circumferential direction of the sealing plate 13 and is formed around the entire circumference of the sealing plate 13. In this embodiment, the chamfered edge 33 is provided below the fracture surface 30 and below the shear surface 31. The chamfered edge 33 is formed in preparation step S21 by machining the sealing plate 13, such as by cutting. However, the chamfered edge 33 may be formed on the sealing plate 13 in advance. Note that the chamfered edge 33 is not shown in Figure 2.

[0030] By the way, when laser welding the case body 11 (more specifically the edge of the opening 11d) and the peripheral edge 13a of the sealing plate 13 from above, it is preferable to ensure a stable welding depth. This welding depth refers to the depth of the weld from the upper surface of the sealing plate 13 when the case body 11 and the sealing plate 13 are laser welded together. In other words, by laser welding, a weld mark is formed between the case body 11 and the sealing plate 13. The welding depth is the length of the weld mark in the height direction Z (hereinafter also simply referred to as the length of the weld mark). The weld mark is formed along the peripheral edge 13a of the sealing plate 13, extending over the entire circumference of the sealing plate 13. Here, "stable welding depth" refers to a state in which the welding depth along the peripheral edge 13a of the sealing plate 13 is within a predetermined range. For example, if the length of the weld mark along the peripheral edge 13a of the sealing plate 13 is within a predetermined range, it can be said that a stable welding depth is ensured. A narrow predetermined range is preferable. In this way, by ensuring a stable welding depth during laser welding, the welding strength can be uniformly ensured around the entire circumference.

[0031] However, conventionally, it has been difficult to ensure a stable welding depth when laser welding the case body 11 and the peripheral edge 13a of the sealing plate 13. Therefore, the inventors of this application have investigated various reasons why it is difficult to ensure a stable welding depth when manufacturing the energy storage device 10. As a result, they have found that a stable welding depth can be ensured by processing the peripheral edge 13a of the upper surface of the sealing plate 13 so as to form a gap between the sealing plate 13 and the edge of the opening 11d of the case body 11 when the sealing plate 13 is attached to the opening 11d of the case body 11 before laser welding.

[0032] Furthermore, the inventors of this application have found that when laser welding is performed on the sealing plate 13 with a fracture surface 30 as shown in Figure 4, it is difficult to ensure a stable welding depth. As described above, the shape of the fracture surface 30 may differ depending on the circumferential position of the sealing plate 13. Therefore, during laser welding, variations in the welding depth occur due to differences in the shape of the fracture surface 30 depending on the circumferential position of the sealing plate 13. As a result, it is considered difficult to ensure a stable welding depth.

[0033] Figure 5 shows the correlation between the fracture surface area of ​​the fracture surface 30 and the welding depth. The inventors of this application investigated the correlation between the size of the fracture surface area of ​​the fracture surface 30 formed on the sealing plate 13 and the welding depth. Here, "fracture surface area of ​​the fracture surface 30" refers to the fracture surface area 30a formed by the indentation of the fracture surface 30 formed by punching, as shown in Figure 4. As shown in Figure 5, the fracture surface area of ​​the fracture surface 30 is approximately 0.04 mm 2 ~0.16mm 2Within this range, the welding depth can be in the range of 1.0 mm to 1.5 mm. A narrower range of welding depth is preferable, and a welding depth of approximately 1.2 mm to 1.4 mm can be considered stable. Here, if the shape of the fracture surface 30 differs depending on the circumferential position of the sealing plate 13, the range of fracture surface space area in the fracture surface 30 becomes wider. Thus, because the shape of the fracture surface 30 differs depending on the circumferential position of the sealing plate 13, the range of possible welding depths widens, making it difficult to ensure a stable welding depth.

[0034] Figure 6 is a plan view showing the sealing plate 13 prepared in the second preparation step S2. Figure 7 is a cross-sectional view of the sealing plate 13 prepared in the second preparation step S2. Figure 7 is a cross-sectional view of the peripheral end 13a of the sealing plate 13 along the height direction Z, and corresponds to Figure 4. Figure 7 shows the sealing plate 13 installed in the opening 11d of the case body 11. In this embodiment, in order to solve the above problem, in the second preparation step S2, a sealing plate 13 is prepared in which a recess 40 is formed on the peripheral end 13a of the upper surface of the sealing plate 13, as shown in Figure 7. The sealing plate 13 prepared in the second preparation step S2 has a recess 40 that is recessed downward at the peripheral end 13a of the upper surface of the sealing plate 13. By forming such a recess 40 in the sealing plate 13, a gap can be formed between the sealing plate 13 and the case body 11 when the sealing plate 13 is installed in the opening 11d of the case body 11. Furthermore, by forming a recess 40 at the peripheral edge 13a of the sealing plate 13, the fracture surface 30 (see Figure 4) can be removed. Then, during laser welding, a stable welding depth can be ensured by irradiating the recess 40 with laser light. Note that the recess 40 is not shown in Figures 1 and 2.

[0035] In this embodiment, the recess 40 is formed on the peripheral edge 13a of the sealing plate 13 in the forming step S22 shown in Figure 3. The forming step S22 is a step performed after the preparation step S21. In the forming step S22, the recess 40 is formed on the sealing plate 13 prepared in the preparation step S21. In the forming step S22, the recess 40 is formed so as to be recessed downward from the peripheral edge 13a of the upper surface of the sealing plate 13. At this time, as shown in Figure 6, the recess 40 is formed along the circumferential direction of the sealing plate 13, extending over the entire circumference of the sealing plate 13. In this embodiment, the recess 40 is formed on the sealing plate 13 (see Figure 4) in which the fracture surface 30 was formed in the preparation step S21, by cutting away the fracture surface 30. For example, as shown in Figure 4, the recess 40 is formed by cutting away the peripheral edge 13a of the sealing plate 13 to the position indicated by the dashed lines indicated by reference numerals C1 and C2. Here, it is preferable that the sealing plate 13 in which the recess 40 is formed in the forming step S22 does not have a fracture surface 30 formed in the preparation step S21. However, the sealing plate 13 in which the recess 40 is formed in the forming step S22 may have a small portion of the fracture surface 30 remaining, or another portion of the fracture surface 30 may be removed. The method for forming the recess 40 in the sealing plate 13 in the forming step S22 is not particularly limited. Here, the recess 40 is formed along the circumferential direction of the sealing plate 13 by removing the peripheral edge 13a of the upper surface of the sealing plate 13 and the fracture surface 30 by machining (for example, milling).

[0036] As shown in Figure 7, the sealing plate 13 prepared in the second preparation step S2 has a thickened portion 41 provided below the recess 40. Therefore, the recess 40 is formed so as not to penetrate the sealing plate 13 in the height direction Z. Here, the thickened portion 41 and the chamfered surface 33 are provided below the recess 40. The thickened portion 41 constitutes the chamfered surface 33. The chamfered surface 33 is formed on the peripheral end 13a of the lower surface of the thickened portion 41.

[0037] In this embodiment, the cross-sectional shape of the recess 40 is rectangular. However, the cross-sectional shape of the recess 40 is not particularly limited. For example, as shown in the modified example in Figure 8, the cross-sectional shape of the recess 40 may be triangular. Here, "cross-sectional shape of the recess 40" refers to the shape of the recess 40 when it is cut radially along the height direction Z so as to pass through the center of the sealing plate 13.

[0038] In this embodiment, as shown in Figure 7, the depth L11 of the recess 40 is greater than the width L12 of the recess 40. Here, the depth L11 of the recess 40 is less than or equal to the average welding depth of the portion welded in this welding process S6. Figure 9 is a cross-sectional view showing the state in which the case body 11 and the sealing plate 13 have been welded together. Figure 9 is a cross-sectional view of the peripheral end 13a of the sealing plate 13 along the height direction Z, and corresponds to Figure 4. As shown in Figure 9, when the case body 11 and the sealing plate 13 are welded together, a weld mark 45 is formed between the case body 11 and the sealing plate 13. After welding, it is preferable that no gap is formed between the weld mark 45 and the thick portion 41. That is, it is preferable that the recess 40 is filled with the weld mark 45. In order to make it difficult for a gap to be formed between the weld mark 45 and the thick portion 41, it is preferable to set the depth L11 of the recess 40 to less than or equal to the average welding depth of the portion welded in this welding process S6. In this embodiment, as shown in Figure 7, the height L2 of the thickened portion 41 is smaller than the depth L11 of the recess 40. However, the height L2 of the thickened portion 41 may be the same as the depth L11 of the recess 40, or it may be larger than the depth L11 of the recess 40. The height L2 of the thickened portion 41 is set according to the thickness of the sealing plate 13 and the depth L11 of the recess 40.

[0039] For example, the depth L11 of the recess 40 is 1.0 mm or more and 2.0 mm or less, preferably 1.0 mm or more and 1.5 mm or less. If the depth L11 of the recess 40 is greater than 2.0 mm, a gap may easily form between the weld mark 45 and the thickened portion 41 after welding. The depth L11 of the recess 40 can be set within a range that produces an effect. Also, for example, the width L12 of the recess 40 is 0.2 mm or less, preferably 0.1 mm or more and 0.2 mm or less. The width L12 of the recess 40 can be set within a range that produces an effect.

[0040] The inventors of this application investigated the correlation between the depth L11 of the recess 40 and the welding depth, and the correlation between the width L12 of the recess 40 and the welding depth. Here, an aluminum sealing plate 13 was prepared with a thickness X length of 38 mm, a width Y length of 306 mm, and a height Z length of 2.5 mm. The height Z length of the C-face 33 of this sealing plate 13 is 0.4 mm. A machining process was performed to form a recess 40 on a sealing plate 13 of this size. At this time, the welding depth after laser welding was calculated when the width L12 of the recess 40 was kept constant (for example, 0.2 mm) and recesses 40 with depths L11 of 0.0 mm, 0.5 mm, 1.0 mm, 1.5 mm, and 2.0 mm were formed. The correlation between the depth L11 of the recess 40 and the welding depth is shown in Figure 10.

[0041] Next, for an aluminum sealing plate 13 having a thickness X of 38 mm, a width Y of 306 mm, and a height Z of 2.5 mm, as described above, the welding depth after laser welding was calculated when the depth L11 of the recess 40 was kept constant (for example, 2.0 mm) and recesses 40 with widths L12 of 0.00 mm, 0.05 mm, 0.10 mm, 0.15 mm, and 0.20 mm were formed. The correlation between the width L12 of the recess 40 and the welding depth is shown in Figure 11.

[0042] As shown in Figure 10, the relationship between the depth L11 of the recess 40 and the welding depth (the equation showing the approximate dashed line in Figure 10) had a slope of 0.3 and a correlation coefficient of 0.93. On the other hand, as shown in Figure 11, the relationship between the width L12 of the recess 40 and the welding depth (the equation showing the approximate dashed line in Figure 11) had a slope of 2.6 and a correlation coefficient of 0.97. Thus, it can be seen that increasing the width L12 of the recess 40 tends to increase the welding depth more easily compared to increasing the depth L11 of the recess 40. In other words, for the same amount of change in depth L11 and width L12 of the recess 40, the width L12 has a greater influence on the welding depth than the depth L11. Therefore, in this embodiment, the depth L11 of the recess 40 is made larger than the width L12 of the recess 40. Note that by making the recess 40 larger, multiple reflections are more likely to occur within the recess 40 when laser light is irradiated into the recess 40. As a result, the amount of laser light energy absorbed in the welded area increases, which is thought to lead to a greater welding depth.

[0043] As described above, after forming the recess 40 in the sealing plate 13 in the forming step S22 of Figure 3, the mounting step S23 of Figure 3 is performed. In the mounting step S23, the electrode terminals 17 and 18 are attached to the sealing plate 13 as shown in Figure 2. The method of attaching the electrode terminals 17 and 18 to the sealing plate 13 is not particularly limited. Here, for example, insertion holes are formed at both ends of the sealing plate 13 in the width direction Y by drilling holes in the sealing plate 13. Then, after inserting the electrode terminals 17 and 18 into each insertion hole, the electrode terminals 17 and 18 can be attached to the sealing plate 13 by using a crimping process.

[0044] In this embodiment, as shown in Figure 3, the mounting process S23 is performed after the forming process S22. However, the mounting process S23 may be performed before the forming process S22, or for example, simultaneously with the preparation process S21. That is, the attachment of the electrode terminals 17 and 18 to the sealing plate 13 may be performed after the recess 40 is formed in the sealing plate 13, or before the recess 40 is formed in the sealing plate 13.

[0045] As described above, after the sealing plate 13 (see Figure 7) with the recess 40 formed therein is prepared in the second preparation step S2 of Figure 3, the third preparation step S3 of Figure 3 is performed. The third preparation step S3 is a step of preparing a flat electrode body 20 (see Figure 2) to be housed in the case body 11. The method of preparing the electrode body 20 in the third preparation step S3 is not particularly limited. As mentioned above, for example, the electrode body 20 is manufactured by laminating and winding a positive electrode, a negative electrode, and a separator. In the third preparation step S3, the electrode body 20 manufactured in this manner is prepared.

[0046] The order in which the first preparation step S1, the second preparation step S2, and the third preparation step S3 are executed is not particularly limited. Any of the first preparation step S1, the second preparation step S2, and the third preparation step S3 may be executed first, or any of them may be executed last.

[0047] After the first preparation steps S1 to the third preparation steps S3 are performed, the assembly step S4 shown in Figure 3 is executed. In the assembly step S4, the energy storage device 10 is assembled. Here, as shown in Figure 2, the electrode body 20 is attached to the sealing plate 13. More specifically, the electrode body 20 is attached to the electrode terminals 17 and 18 provided on the sealing plate 13. For example, the positive electrode of the electrode body 20 is electrically connected to the internal terminal 17b of the electrode terminal 17 of the sealing plate 13 by laser welding. The negative electrode of the electrode body 20 is electrically connected to the internal terminal 18b of the electrode terminal 18 of the sealing plate 13 by laser welding. After that, the electrode body 20 connected to the sealing plate 13 is housed in the case body 11, and the sealing plate 13 is attached to the opening 11d of the case body 11. At this time, the sealing plate 13 is sandwiched between a pair of narrow surfaces 11b and a pair of wide surfaces 11c of the case body 11. Alternatively, in assembly step S4, after housing the electrode body 20 in the case body 11, the electrode body 20 may be connected to the electrode terminals 17 and 18 of the sealing plate 13, and the sealing plate 13 may be attached to the opening 11d of the case body 11.

[0048] Next, the tack welding process S5 shown in Figure 3 is performed. In the tack welding process S5, the sealing plate 13 is tack-welded to the case body 11 with the sealing plate 13 attached to the opening 11d of the case body 11. In the tack welding process S5, tack welding is performed to position the sealing plate 13 relative to the case body 11. Here, laser light is irradiated from above the sealing plate 13 to predetermined portions of the boundary between the case body 11 and the sealing plate 13 (here, recesses 40 formed along the circumferential direction of the sealing plate 13), thereby tack-welding the case body 11 and the sealing plate 13. For example, in the tack welding process S5, the case body 11 and the sealing plate 13 are welded intermittently. Here, tack welding is performed to multiple predetermined locations of the boundary between the case body 11 and the sealing plate 13 (here, recesses 40 of the sealing plate 13). In the tack welding process S5, the case body 11 and the sealing plate 13 are tack welded using various conventionally known welding devices. The tack welding is performed under conditions such as a laser beam diameter of 0.6 mm, a laser output of 3000 W, and a laser beam movement speed of 150 mm / s. However, the conditions for tack welding are not particularly limited. The tack welding process S5 may be omitted.

[0049] After the tack welding process S5 is performed in this manner, the main welding process S6 shown in Figure 3 is performed. The main welding process S6 is an example of a welding process. In the main welding process S6, a laser beam is irradiated along the gap between the case body 11 and the sealing plate 13 to perform welding. Here, the laser beam is irradiated along the boundary between the case body 11 and the peripheral edge 13a of the sealing plate 13, welding the case body 11 and the sealing plate 13 around their entire circumference. In this embodiment, a recess 40 is formed on the peripheral edge 13a of the upper surface of the sealing plate 13. Therefore, in the main welding process S6, the laser beam is irradiated toward the recess 40 of the sealing plate 13 to perform welding. At this time, the area around the recess 40 melts due to the laser beam, and a weld mark 45 (see Figure 9) is formed in the area where the recess 40 was formed. In the main welding process S6, various conventionally known welding devices are used to perform the main welding of the case body 11 and the sealing plate 13. The welding equipment used in the main welding process S6 may be the same as or different from the welding equipment used in the tack welding process S5. The main welding in the main welding process S6 is performed under conditions such as a laser beam diameter of 0.8 mm to 1.0 mm, a laser output of 6000 W, and a laser beam movement speed of 300 mm / s. However, the conditions for the main welding are not particularly limited.

[0050] When the main welding process S6 is completed, the case body 11 and the sealing plate 13 are welded together along the entire circumference of the peripheral edge 13a of the sealing plate 13. This seals the inside of the case body 11. Although not shown in the diagram, after the main welding process S6 is completed, an electrolyte injection process is performed to inject electrolyte into the case body 11, an aging process is performed to charge the energy storage device 10 and leave it for a predetermined time, and an inspection process is performed to check for internal short circuits in the energy storage device 10, etc., as appropriate, and the energy storage device 10 is manufactured.

[0051] In this embodiment, the method for manufacturing the energy storage device 10 includes a first preparation step S1, a second preparation step S2, an assembly step S4, and a main welding step S6, as shown in Figure 3. In the first preparation step S1, a case body 11 (see Figure 2) having an opening 11d is prepared. In the second preparation step S2, a sealing plate 13 (see Figure 6) that seals the opening 11d of the case body 11 is prepared. In the assembly step S4, the sealing plate 13 is attached to the opening 11d of the case body 11. In the main welding step S6, laser light is irradiated along the gap between the case body 11 and the sealing plate 13 to perform welding. Here, the sealing plate 13 prepared in the second preparation step S2 has a recess 40 that is indented downward at the peripheral end 13a of the upper surface of the sealing plate 13, as shown in Figure 7. In the main welding step S6, laser light is irradiated toward the recess 40 of the sealing plate 13 to perform welding. In this way, a recess 40 is formed in the peripheral edge 13a of the upper surface of the sealing plate 13, and by irradiating laser light toward the recess 40, a weld mark 45 (see Figure 9) is formed in the recess 40. The weld mark 45 formed in the recess 40 tends to have a uniform length in the height direction Z. Therefore, a stable welding depth can be ensured.

[0052] In this embodiment, as shown in Figure 3, the second preparation step S2 includes the preparation step S21 and the forming step S22. In the preparation step S21, a sealing plate 13 formed in a predetermined shape (here, a sealing plate 13 without the recess 40 formed) is prepared. In the forming step S22, a recess 40 (see Figure 7) is formed in the sealing plate 13 prepared in the preparation step S21. This allows the operator to appropriately set the depth L11 and width L12 of the recess 40 according to the size of the sealing plate 13 (length in the thickness direction X, width direction Y, and height direction Z). Therefore, even if the size of the sealing plate 13 is different, it is easier to ensure a stable welding depth.

[0053] In this embodiment, in preparation step S21 in Figure 3, a sealing plate 13 is prepared by punching out a fracture surface 30 (see Figure 4) formed on its side surface. In forming step S22 in Figure 3, a recess 40 is formed in the sealing plate 13 by grinding away the fracture surface 30. As described above, if the case body 11 and the sealing plate 13 are welded together with the fracture surface 30 having different shapes depending on the circumferential position of the sealing plate 13, variations in welding depth are likely to occur. Therefore, in this embodiment, by forming a recess 40 in the sealing plate 13 by grinding away the fracture surface 30, the sealing plate 13 from which the fracture surface 30 has been removed can be welded to the case body 11. Thus, welding is performed without being affected by the different shapes of the fracture surface 30, and a stable welding depth can be ensured.

[0054] In this embodiment, the sealing plate 13 prepared in the second preparation step S2 has a thickened portion 41 located below the recess 40, as shown in Figure 7. This prevents laser beam penetration and subsequent laser beam dropout when the laser beam is irradiated into the recess 40 during the welding step S6.

[0055] As described above, as shown in Figures 10 and 11, for the same amount of change, the width L12 of the recess 40 has a greater impact on the welding depth than the depth L11. Therefore, in this embodiment, by making the depth L11 of the recess 40 larger than the width L12 of the recess 40, it is easier to suppress variations in welding depth. Consequently, it is easier to ensure a stable welding depth.

[0056] In this embodiment, as shown in Figure 7, the cross-sectional shape of the recess 40 is rectangular. The width L12 of the recess 40 is 0.2 mm or less. The depth L11 of the recess 40 is 2.0 mm or less. By using this shape and size of the recess 40, it is possible to ensure a stable welding depth while suppressing the occurrence of laser penetration.

[0057] In this embodiment, the depth L11 of the recess 40 is less than or equal to the average welding depth of the portion welded in the welding process S6. This makes it difficult to form a gap within the recess 40 when the recess 40 is welded by irradiating it with laser light. In other words, after welding, as shown in Figure 9, it is difficult to form a gap between the weld mark 45 and the thickened portion 41.

[0058] In this embodiment, the recess 40 was formed in the sealing plate 13 during the forming step S22 of the second preparation step S2. However, the recess 40 may already be formed when the sealing plate 13 is prepared in the preparation step S21, without performing the operation of forming the recess 40 on the sealing plate 13. That is, in the preparation step S21, a sealing plate 13 with the recess 40 already formed may be prepared. In this case, the forming step S22 may be omitted.

[0059] As described above, this specification includes the disclosures set forth in the following sections.

[0060] Section 1: A first preparation step involves preparing a case body having an opening, A second preparation step involves preparing a sealing plate to seal the opening of the case body, An assembly step of attaching the sealing plate to the opening of the case body, A welding process in which a laser beam is irradiated along the space between the case body and the sealing plate to weld them together, It includes, The sealing plate prepared in the second preparation step has a recess that is indented downward at the peripheral end of the upper surface of the sealing plate, A method for manufacturing an energy storage device, wherein the welding process involves irradiating a laser beam toward the recess of the sealing plate and welding it.

[0061] Section 2: The second preparation step is, A preparation step of preparing the sealing plate formed in a predetermined shape, A forming step in which the recess is formed in the sealing plate prepared in the preparation step, A method for manufacturing an energy storage device as described in item 1, including the method described in item 1.

[0062] Section 3: In the preparation step described above, the sealing plate is prepared by punching, which forms a fracture surface on its side. The method for manufacturing an energy storage device according to item 2, wherein in the forming step, the recess is formed in the sealing plate so as to shave off the fracture surface.

[0063] Section 4: A method for manufacturing an energy storage device as described in any one of items 1 to 3, wherein the cross-sectional shape of the recess is rectangular.

[0064] Section 5: A method for manufacturing an energy storage device as described in any one of items 1 to 4, wherein the sealing plate prepared in the second preparation step has a thickened portion provided below the recess.

[0065] Item 6: A method for manufacturing an energy storage device as described in any one of items 1 to 5, wherein the depth of the recess is greater than the width of the recess.

[0066] Section 7: A method for manufacturing an energy storage device as described in any one of items 1 to 6, wherein the width of the recess is 0.2 mm or less.

[0067] Section 8: A method for manufacturing an energy storage device as described in any one of items 1 to 7, wherein the depth of the recess is 2.0 mm or less.

[0068] Section 9: A method for manufacturing an energy storage device according to any one of items 1 to 8, wherein the depth of the recess is less than or equal to the average welding depth of the portion welded in the welding process. [Explanation of symbols]

[0069] 10 Energy Storage Devices 11 Case body 11d aperture 13 Sealing board 13a Peripheral end 30 fracture surface 40 recess 41 Thick flesh part S1 first purpose project S2 Second Project S21 Intentional Engineering S22 Formation Engineering S23 Collection and payment of projects S3 Third Project S4 Assembly Project S5 welding project S6 This welding project (welding project)

Claims

1. A first preparation step involves preparing a case body having an opening, A second preparation step involves preparing a sealing plate to seal the opening of the case body, An assembly step of attaching the sealing plate to the opening of the case body, A welding process in which a laser beam is irradiated along the space between the case body and the sealing plate to weld them together, It includes, The sealing plate prepared in the second preparation step has a recess that is indented downward at the peripheral end of the upper surface of the sealing plate. A method for manufacturing an energy storage device, wherein the welding process involves irradiating a laser beam toward the recess of the sealing plate and welding it.

2. The second preparation step is, A preparation step of preparing the sealing plate formed in a predetermined shape, A forming step in which the recess is formed in the sealing plate prepared in the preparation step, A method for manufacturing an energy storage device according to claim 1, comprising:

3. In the preparation step described above, the sealing plate is prepared by punching, which forms a fracture surface on its side. The method for manufacturing an energy storage device according to claim 2, wherein in the forming step, the recess is formed in the sealing plate so as to shave off the fracture surface.

4. The method for manufacturing an energy storage device according to claim 1, wherein the cross-sectional shape of the recess is rectangular.

5. The method for manufacturing an energy storage device according to claim 1, wherein the sealing plate prepared in the second preparation step has a thickened portion provided below the recess.

6. A method for manufacturing an energy storage device according to claim 1, wherein the depth of the recess is greater than the width of the recess.

7. The method for manufacturing an energy storage device according to claim 1, wherein the width of the recess is 0.2 mm or less.

8. The method for manufacturing an energy storage device according to claim 1, wherein the depth of the recess is 2.0 mm or less.

9. The method for manufacturing an energy storage device according to claim 1, wherein the depth of the recess is less than or equal to the average welding depth of the portion welded in the welding process.

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