Manufacturing method of power storage device

Abstract

To provide a manufacturing method of a power storage device capable of preventing wrinkles from being generated in a current collector while ensuring airtightness between the current collector and a sealing member by welding the sealing member by laser irradiation.SOLUTION: The manufacturing method of a power storage device includes a step of (a) fusing a sealing member to a current collector by laser irradiation. The step (a) includes: a step of (a1) welding the sealing member to a laminate that has a structure in which the current collector is sandwiched between a set of sealing members by irradiating at least a first region of the current collector with a first laser beam with a laser intensity I1; and step of (a2) welding the sealing member to the laminate by irradiating a second region of the current collector with a second laser beam with a laser intensity I2. The second region is bounded in a frame shape extending inward from the outer edge of the current collector while the first region is bounded inside the second region and adjacent to the second region in the frame shape, and I2>I1.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Regarding a manufacturing method for an electricity storage device, Patent Document 1 describes a manufacturing method for an electricity storage device, which includes: a preparation step of preparing a laminate including a plurality of current collectors each having an active material layer provided thereon, and a plurality of sealing members each having a frame shape surrounding the active material layer when viewed in the thickness direction of the current collector and an extending portion extending outward from the outer edge of the current collector, such that the sealing members are disposed between the plurality of current collectors; a melting step of melting the plurality of sealing members to form a side surface including a communication port connecting the inside and the outside of the laminate; and a molding step of forming a molding surface against which an equipment-side nozzle is pressed, in a region of the side surface formed by melting the plurality of sealing members and surrounding the communication port, wherein in the melting step, the plurality of sealing members are melted by non-contact heating, and in the molding step, while the sealing members are in a molten state, a pressing member having a temperature lower than the melting point of the sealing members is pressed against the side surface to form the molding surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-000059 A Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 describes an infrared heater as an example of a non-contact heating means for melting the sealing member. However, from the viewpoints of the accuracy of the heating position, the processing speed, and the energy efficiency, it is preferable to use laser irradiation as the non-contact heating means. In addition, since the sealing member after welding is required to cover the end of the current collector for airtightness between the current collector and the sealing member, it is preferable that the sealing member is sufficiently heated. However, when the sealing member is welded by laser irradiation, if the laser output is increased so that the sealing member after welding covers the end of the current collector, wrinkles are likely to occur in the current collector.

[0005] The present invention provides a method for manufacturing an electricity storage device that can suppress the occurrence of wrinkles in the current collector while ensuring airtightness between the current collector and the sealing member by welding the sealing member by laser irradiation. [Means for solving the problem]

[0006] The present invention includes the following embodiments [1] to [3]. [1] A method for manufacturing an electricity storage device, the electricity storage device comprising: A plurality of stacked current collectors, each of which has an active material layer provided on a surface thereof; a plurality of sealing members formed of a resin material and welded to peripheral portions of the plurality of current collectors, each of which has a frame-like shape surrounding the active material layer when viewed in a thickness direction of the current collector, and which has a covering portion overlapping the current collector and an extending portion extending outward from an outer edge of the current collector; The manufacturing method includes: (a) welding the sealing member to the current collector by laser irradiation; The step (a) (a1) a step of irradiating a first laser beam at a first laser intensity per unit area to a laminate having a structure in which the current collector is sandwiched between a pair of the sealing members, thereby welding the sealing members, the first laser beam being transmitted through one of the pair of sealing members and irradiated onto at least a first region of the current collector; (a2) irradiating the laminate with a second laser light at a second laser intensity per unit area to weld the sealing member, the second laser light passing through one of the pair of sealing members and irradiating a second region of the current collector; The second region is defined in a frame shape from an outer edge of the current collector toward the inside, the first region is defined in a frame shape inside the second region of the current collector and adjacent to the second region, In the step (a1), the first laser light may also be irradiated onto the second region of the current collector, A method for manufacturing an electricity storage device, wherein the second laser intensity per unit area is greater than the first laser intensity per unit area.

[0007] [2] The method for producing an electricity storage device according to [1], wherein in the step (a), the step (a2) is carried out after the step (a1).

[0008] [3] The method for producing an electricity storage device according to [1], wherein in the step (a), the step (a1) and the step (a2) are carried out simultaneously. Effect of the Invention

[0009] According to the method for manufacturing an electricity storage device of the present invention, the laser intensity per unit area of ​​the laser light irradiated to the second region is greater than the laser intensity per unit area of ​​the laser light irradiated to the first region. Therefore, when the sealing member is welded by laser irradiation, the welded sealing member can be welded so as to cover the end of the current collector, thereby ensuring airtightness between the current collector and the sealing member while suppressing the occurrence of wrinkles in the current collector. [Brief description of the drawings]

[0010] [Figure 1] 1(a) to 1(g) are cross-sectional views that typically show an example of a manufacturing process for an electricity storage device. [Diagram 2]Fig. 2(A) is a cross-sectional view, which is a reprint of Fig. 1(a), for illustrating a laminate 10 having a structure in which a current collector 1 having active material layers 2 and 3 provided on its surface is sandwiched between a pair of sealing members 4 and 4. Fig. 2(B) is a perspective plan view taken along the arrow BB in Fig. 2(A). [Diagram 3] 3(A) and (B) are schematic partial enlarged views of the vicinity of the outer edge of the current collector 1 before and after irradiation with laser light in step (a), where FIG. 3(A) shows the state before laser light irradiation and FIG. 3(B) shows the state after laser light irradiation. [Figure 4] FIG. 4 is a perspective plan view for explaining a schematic configuration of a test piece and a laser beam. [Diagram 5] FIG. 5 is an example of a micrograph of a cross section of a test piece prepared in an example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments. The drawings do not necessarily reflect accurate dimensions. In addition, some symbols may be omitted in the drawings. In this specification, unless otherwise specified, the expression "A to B" for numerical values ​​A and B means "A or more and B or less." In such an expression, when a unit is added only to numerical value B, the unit is also applied to numerical value A. Furthermore, the words "or" and "or" mean a logical sum unless otherwise specified. Furthermore, the expression "E1 and / or E2" for elements E1 and E2 means "E1 or E2, or a combination thereof," and the expression "E1 and / or E2" for elements E1, ..., E N (N is an integer of 3 or more) for E1, ..., E N-1 , and / or E N " is written as "E1, ..., E N-1 , or E N ", or a combination thereof."

[0012] <Method of manufacturing electricity storage device> 1(a) to 1(g) are cross-sectional views that typically show an example of a manufacturing process for an electricity storage device. FIG. 1(a) is a cross-sectional view that typically explains a laminate 10 having a structure in which a current collector 1, on whose surface active material layers 2 and 3 are provided, is sandwiched between a pair of sealing members 4 and 4 (hereinafter sometimes simply referred to as "sealing member 4"). The current collector 1 is a sheet-like conductive member, and has a first surface 1a and a second surface 1b. A positive electrode active material layer 2 is provided on the surface of the first surface 1a of the current collector 1, and a negative electrode active material layer 3 is provided on the surface of the second surface 1b.

[0013] The current collector 1 is made of, for example, a metal foil or an alloy foil. Examples of the metal foil include copper foil, aluminum foil, titanium foil, and nickel foil. Examples of the alloy foil include stainless steel foil (e.g., SUS304, SUS316, SUS301, etc., as specified in JIS G 4305:2015), plated steel plate (e.g., cold-rolled steel plate (SPCC, etc.) as specified in JIS G 3141:2005), and plated stainless steel plate. The alloy foil may be an alloy foil of the metal exemplified as the material of the metal foil. The current collector 1 may be formed by integrating or laminating a plurality of metal foils, or may be formed by plating another metal on the surface of a metal foil. In one embodiment, the current collector 1 may be, for example, an Al-Cu alloy foil having an aluminum layer and a copper layer, and the Al layer appears on the first surface 1a and the Cu layer appears on the second surface 1b. The Al-Cu alloy foil may be a clad foil in which an aluminum foil and a copper foil are bonded together. The aluminum layer on the first surface 1a of the current collector 1 may be chromated. The copper layer on the second surface 1b of the current collector 1 may be nickel-plated. In this case, the nickel-plated layer may be a roughened surface that is a protruding plated surface having fine protrusions on its surface.

[0014] The positive electrode active material layer 2 is a layered member containing a positive electrode active material, a conductive assistant, and a binder. Examples of the positive electrode active material include a composite oxide, metallic lithium, and sulfur. The composition of the composite oxide includes at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, and lithium. Examples of the composite oxide include olivine-type lithium iron phosphate (LiFePO4), LiCoO2, and LiNiMnCoO2.

[0015] The binder serves to bind the active material or conductive assistant to the surface of the current collector 1 and maintain the conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, acrylic resins containing monomer units such as acrylic acid and methacrylic acid, styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates such as sodium alginate and ammonium alginate, water-soluble cellulose ester crosslinked bodies, and starch-acrylic acid graft polymers. These binders can be used alone or in combination. Examples of the conductive assistant include acetylene black, carbon black, and graphite. The positive electrode active material layer 2 may contain a viscosity adjusting solvent such as N-methyl-2-pyrrolidone (NMP).

[0016] The negative electrode active material layer 3 is a layered member containing a negative electrode active material, a conductive assistant, and a binder. Examples of the negative electrode active material include carbon such as graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, and soft carbon, metal compounds, elements that can be alloyed with lithium or compounds of the elements, and boron-added carbon. Examples of elements that can be alloyed with lithium include silicon and tin. The conductive assistant and binder may be the same as those used in the positive electrode active material layer 22.

[0017] To form the positive electrode active material layer 2 and the negative electrode active material layer 3 on the current collector 1, a conventionally known method such as roll coating, die coating, dip coating, doctor blade, spray coating, curtain coating, etc. is used. Specifically, an active material, a solvent, and optionally a binder and a conductive assistant are mixed to produce a slurry-like active material layer forming composition, which is then applied to the first surface 1a and the second surface 1b and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The dried product may be compressed to increase the electrode density.

[0018] Further, reference is made to Figures 2(A) and (B). Figure 2(A) is a cross-sectional view for explaining a laminate 10 having a structure in which a current collector 1 having active material layers 2 and 3 on its surface is sandwiched between a pair of sealing members 4 and 4, and is a reprint of Figure 1(a). Figure 2(B) is a perspective plan view seen from the arrow BB in Figure 2(A). The sealing member 4 is formed of an electrically insulating resin material that is transparent to the first laser beam and the second laser beam used in step (a) described later, and has a frame-like shape surrounding the active material layers 2 and 3 as viewed from the thickness direction of the current collector 1. As viewed from the thickness direction of the current collector 1, the outer edge 4o of the sealing member 4 is located outside the outer edge 1c of the current collector 1, and the inner edge 4i of the sealing member 4 is located inside the outer edge 1c of the current collector 1. The sealing member 4 includes a covering portion 4a overlapping with the current collector 1 when viewed in the thickness direction of the current collector 1, and an extending portion 4b extending outward from an outer edge 1c of the current collector 1. Examples of materials for the sealing member 4 include optically transparent and electrically insulating thermoplastic resins such as polypropylene, polyethylene, polystyrene, ABS resin, modified polypropylene, and acrylonitrile-styrene resin.

[0019] Referring again to FIG. 1(a), the manufacturing method of the electricity storage device of the present invention includes a step (a) of welding sealing members 4, 4 to a current collector 1 by laser irradiation (hereinafter, sometimes referred to as "step (a)" or "welding step"). By carrying out step (a), a bipolar unit 11 having a sealing member 41 welded to the current collector 1 is obtained (FIG. 1(b)). In the bipolar unit 11, a pair of sealing members 4, 4 are welded to the current collector 1 to form the sealing member 41. A separator 5 is laminated on the bipolar unit 11 (FIG. 1(c)), and the peripheral portion of the separator 5 is welded to the sealing member 41 to obtain a bipolar unit 12 (FIG. 1(d)).

[0020] The separator 5 is a sheet-like member, and the outer edge of the planar shape is located outside the inner edge 4i of the sealing member 4 and inside the outer edge 4o of the sealing member 4o when viewed from the stacking direction. The separator 5 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains an electrolyte. Examples of materials constituting the separator 5 include polypropylene, polyethylene, polyolefin, and polyester. The separator 5 may have a single-layer structure or a multilayer structure. In the case of a multilayer structure, the separator 5 may include, for example, a base material layer and a pair of adhesive layers, and may be bonded and fixed to the positive electrode active material layer 2 and the negative electrode active material layer 2 by the pair of adhesive layers. The separator 5 may include a ceramic layer that serves as a heat-resistant layer. The separator 5 may be reinforced with a vinylidene fluoride resin compound. When welding the peripheral portion of the separator 5 to the sealing member 41, a known heating means such as resistance heating can be used.

[0021] Examples of the electrolyte impregnated in the separator 5 include a liquid electrolyte (electrolytic solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, and a polymer gel electrolyte containing an electrolyte held in a polymer matrix. When the separator 5 is impregnated with an electrolyte, known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 can be used as the electrolyte salt. In addition, known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers can be used as the non-aqueous solvent. Two or more of these known solvent materials may be used in combination. In another embodiment, the separator 5 may contain a solid electrolyte, and in one such embodiment, the separator 5 may not be impregnated with a non-solid electrolyte.

[0022] The bipolar units 12 and the spacers 6 are alternately stacked to obtain a bipolar unit laminate 13 (FIGS. 1(e)-(g)). A positive electrode end unit 14 and a negative electrode end unit 15 are further stacked on the bipolar unit laminate 13 (FIG. 1(g)), to form a cell stack 16 (FIG. 1(h)). In the cell stack 16, adjacent pairs of sealing members 41 and separators 5 are thermally welded (thermal welded portions 7a, 7b), to obtain an electricity storage device 17, which is a laminated battery in which the stacked structure of the cell stack 16 is fixed (FIG. 1(h)). At this time, the unwelded portions inside the sealing members 41 can be further welded (thermal welded portion 7c).

[0023] The configuration of the positive electrode end unit 14 can be the same as that of the bipolar unit 12, except that it does not have the negative electrode active material layer 3. The configuration of the negative electrode end unit 15 can be the same as that of the bipolar unit 12, except that it does not have the positive electrode active material layer 2 and the separator 5.

[0024] The spacer 6 is a frame-shaped member surrounding the active material layers 2, 3 when viewed from the thickness direction of the current collector 1. The spacers 6, 6, ... are respectively arranged between adjacent pairs of bipolar units 12, 12, ..., between the bipolar unit 12 present at the end of the bipolar unit stack 13 where the negative electrode active material layer 3 faces outward and the positive electrode end unit 14, and between the bipolar unit 12 present at the end of the bipolar unit stack 13 where the positive electrode active material layer 2 faces outward and the negative electrode end unit 15.

[0025] The outer edges of each sealing member 41 and each spacer 6 are aligned or approximately aligned with each other when viewed from the stacking direction (hereinafter simply referred to as the "stacking direction") of the bipolar unit 12, the positive electrode end unit 14, and the negative electrode end unit 15. The inner edges of each sealing member 4, 41 are aligned or approximately aligned with each other when viewed from the stacking direction. The inner edges of each spacer 6 are aligned or approximately aligned with each other when viewed from the stacking direction. The inner edges of each spacer 6 are located outside the inner edges of each sealing member 41 when viewed from the stacking direction. The inner edges of each protruding member 35 are aligned or approximately aligned with each other when viewed from the Z-axis direction. In one preferred embodiment, the materials of the sealing members 4, 41, and the spacer 6 may be the same.

[0026] Referring again to Fig. 1(a), Fig. 1(b), and Fig. 2(B), step (a): the step of welding the sealing members 4, 4 to the current collector 1 by laser irradiation includes a step (a1) of welding the sealing members 4, 4 by irradiating a first laser beam L1 at a first laser intensity I1 per unit area to a laminate 10 having a structure in which the current collector 1 is sandwiched between a pair of sealing members 4, 4 (hereinafter, this step may be referred to as "step (a1)" or "first welding step"); and a step (a2) of welding the sealing members 4, 4 by irradiating a second laser beam L2 at a second laser intensity I2 per unit area to the laminate 10 (hereinafter, this step may be referred to as "step (a2)" or "second welding step"). In step (a1), the first laser beam L1 is transmitted through one of the pair of sealing members 4, 4 and irradiated to at least a first region R1 of the current collector. In step (a2), the second laser light L2 is transmitted through one of the pair of sealing members 4, 4 and irradiated onto the second region R2 of the current collector 1. FIG. 2(B) shows the first region R1 and the second region R2 of the current collector 1. The second region R2 is defined in a frame shape from the outer edge 1c of the current collector 1 toward the inside. The first region R1 is defined in a frame shape inside the second region R2 of the current collector 1 and adjacent to the second region R2. From the viewpoint of increasing the amount of the melt of the sealing members 4, 4 to make it easier for the melt to wrap around the end face of the outer edge 1c of the current collector 1, the width of the second region R2 can be preferably, for example, 1 mm or more or 2 mm or more from the outer edge 1c of the current collector 1, and can be 1 to 5 mm, or 2 to 5 mm in one embodiment.

[0027] 3(A) and (B) are schematic partial enlarged views of the vicinity of the outer edge of the current collector 1 before and after the laser beam irradiation in step (a), in which FIG. 3(A) shows the state before the laser beam irradiation and FIG. 3(B) shows the state after the laser beam irradiation. Referring to FIG. 3(A), in step (a), the laminate 10 is placed on a base 101, and at least a region of the laminate 10 including the sealing members 4, 4 is sandwiched between the base 101 and a pressing plate 102. By applying a pressure P between the base 101 and the pressing plate 102, the pressing plate 102 comes into contact with at least the covering portion 4a (see FIG. 2(B)) of the sealing member 4 that overlaps with the current collector 1 without any gaps. The first laser beam L1 and the second laser beam L2 are irradiated through the pressing plate 102.

[0028] FIG. 3(A) shows the first region R1 and the second region R2 of the current collector 1, and the irradiation range of the first laser light L1 (arrow L1) and the irradiation range of the second laser light L2 (arrow L2). In step (a1), the first laser light L1 is irradiated to at least the first region R1 of the current collector 1, and may also be irradiated to the second region R2, and may also be irradiated to the extended portion 4b of the sealing member 4 (see FIG. 2(B)). In step (a2), the second laser light L2 is irradiated to the second region R2, and may also be irradiated to the extended portion 4b of the sealing member 4 (see also FIG. 2(B)). In steps (a1) and (a2), the irradiated laser lights L1 and L2 are absorbed by the current collector 1 and become thermal energy, respectively, and partially melt the adjacent sealing members 4 and 4. The molten sealing members 4, 4 weld the sealing members 4, 4 to the current collector 1. Furthermore, in step (a2), the molten sealing members 4, 4 flow and flow out to the outside of the outer edge 1c of the current collector 1, and weld the extended portions 4b, 4b of the sealing members 4, 4 so as to cover the end faces of the outer edge 1c of the current collector 1, and the sealing members 4, 4 become an integrated sealing member 41 (FIG. 3(B)). From the viewpoint of ensuring airtightness, in the laminate 11 after steps (a1) and (a2) (see also FIG. 1(b)), the width W1 (in a plan view of the laminate 11) of the region where the sealing members 4, 4 are welded to each other is preferably 100 μm or more.

[0029] The base 101 may be made of, for example, glass, metal, or a heat-resistant elastomer such as silicone resin. The pressing plate 102 may be made of a material such as reinforced glass that is transparent to the first and second laser beams L1 and L2 and can withstand the applied pressure P. A transparent silicone resin member or the like that has high laser light transparency may be sandwiched between the pressing plate and the sealing member.

[0030] The first laser intensity I1 per unit area can be set to an intensity capable of welding the sealing members 4, 4 to the first region R1 of the current collector 1. Such a laser intensity I1 per unit area is preferably, for example, 0.5 to 5.0 W / mm 2 The second laser intensity I2 per unit area can be set to an intensity capable of welding the sealing members 4, 4 to the second region R2 of the current collector 1, and welding the extended portions 4b, 4b of the sealing members 4, 4 to the molten material of the sealing members 4, 4 so as to cover the end face of the outer edge 1c of the current collector 1. Such a laser intensity I2 per unit area is preferably, for example, 0.5 to 6.0 W / mm 2 In one embodiment, the 2 or more than 3.8W / mm 2 In steps (a1) and (a2), the second laser intensity per unit area I2 is greater than the first laser intensity per unit area I1 (I2>I1). This allows the sealing members 4, 4 to be welded to cover the end faces of the current collector 1.

[0031] The wavelengths of the first laser light L1 and the second laser light L1 may be the same or different from each other, and may preferably be, for example, 250 to 1200 nm. Irradiating (at least) the entire first region R1 with the first laser light L1 and irradiating the entire second region R2 with the second laser light L2 may be performed by irradiating the entire frame-shaped regions with a frame-shaped laser light, or by scanning each region with a laser light having a predetermined beam width. The total energy density (i.e., time integral of the laser intensity) of the first laser light L1 irradiated to the same location is preferably, for example, 0.05 to 0.40 J / mm from the viewpoint of facilitating welding of the sealing members 4, 4 to the first region R1 of the current collector 1. 2 The total energy density of the second laser light L2 irradiated to the same location is preferably, for example, 0.05 to 0.40 J / mm from the viewpoint of facilitating welding of the extended portions 4b, 4b of the sealing members 4, 4 to the molten material of the sealing members 4, 4 so as to cover the end face of the outer edge 1c of the current collector 1. 2 The beam shape and the linear scanning speed can be adjusted so that the total energy density falls within these ranges. In step (a1), the irradiation time per point of the first laser light L1 (the time from the start to the end of the irradiation of the laser light to a certain point) can be preferably, for example, 20 ms or more from the viewpoint of ensuring a sufficient time for the sealing member 4 to be fused to the first region R1 of the current collector 1, and can be, for example, 500 ms or less from the viewpoint of laser intensity and productivity. In step (a2), the irradiation time per point of the second laser light L2 can be preferably, for example, 35 ms or more, 70 ms or more, or 84 ms or more from the viewpoint of ensuring a sufficient time for the molten sealing member 4 to flow and wrap around the outer edge 1c end face of the current collector 1, and can be, for example, 200 ms or less from the viewpoint of laser intensity and productivity.

[0032] In one preferred embodiment, in step (a), step (a2) is performed after step (a1). According to this embodiment, the welding of the first region R1 is performed before the welding of the second region R2. This is preferable from the viewpoint of welding the sealing members 4, 4 so as to cover the end faces of the current collector 1, since it suppresses the flow of the molten material of the sealing members 4, 4 to the first region R1 side during welding of the second region R2.

[0033] In one preferred embodiment, in step (a), step (a1) and step (a2) are performed simultaneously. According to this embodiment, since the first welding step (a1) and the second welding step (a2) are performed simultaneously, the time required for welding can be shortened and productivity can be increased.

[0034] In step (a2), it is preferable that either of the following requirements (i) and (ii) is satisfied: (i) the total energy density of the second laser light L2 irradiated to the same location is 0.35 J / mm 2 The laser intensity I2 per unit area of ​​the second laser light L2 is 3.3 W / mm 2 or more, the irradiation time per point of the second laser beam L2 is 70 ms or more, and the width of the second region R2 is 2 mm or more; or (ii) the total energy density of the second laser beam L2 irradiated to the same point is 0.40 J / mm 2 The laser intensity I2 per unit area of ​​the second laser light L2 is 3.8 W / mm 2 As described above, the irradiation time per point of the second laser light L2 is 70 ms or more, and the width of the second region R2 is 1 mm or more. By satisfying either of the requirements (i) or (ii) in the step (a2), it is possible to further increase the amount of the molten material of the sealing member 4 that wraps around the end face of the outer edge 1c of the current collector 1, and further increase the width W1 over which the sealing members 4, 4 are welded to each other, thereby further improving the airtightness. EXAMPLES

[0035] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0036] 4 is a perspective plan view for explaining the shape of the test piece and the laser beam. Eleven test pieces 110 were prepared by sandwiching the end vicinity of the current collector 1 (Al-Cu laminated foil, length 27.5 mm, width 110 mm, thickness 70 μm) between a pair of sealing members 4, 4 (polyethylene, length 30.5 mm, width 120 mm, thickness 120 μm). For each test piece 110, the test piece 110 was sandwiched between a base 101 and a pressing plate 102 (made of reinforced glass) as shown in FIG. 3(A), and the same conditions (semiconductor laser, beam width 23 mm, depth in the beam traveling direction 42 mm, laser wavelength 1020 nm, output 2000 W, linear velocity of beam scanning 400 mm / s, irradiation time per point 105 ms, laser intensity per unit area 2.0704 W / mm 2 , Total energy density: 0.2174J / mm 2 ) was used for the laser irradiation in step (a1). Thereafter, the laser irradiation in step (a2) was performed under various different conditions (semiconductor laser, beam width 6 mm, depth in the beam travel direction 42 mm, laser wavelength 1020 nm). As shown in FIG. 4, for each sample, a second region R2 of a predetermined width was defined from the outer edge 1c of the current collector 1, and a first region R1 was defined adjacent to the inner side of the second region R2. In step (a1), the first laser light L1 was irradiated over the entire region where the current collector 1 exists (i.e., over the entire covered portion of the sealing member 4). In step (a2), the second laser light L2 was irradiated over the entire second region R2 and the extended portion of the sealing member 4. The irradiation region of the first laser light L1 and the irradiation region of the second laser light L2 overlap in the second region R2. After irradiation was completed, the sample was cut at 15 points spaced at equal intervals (5 mm) along the outer edge 1c of the current collector 1, and the width W1 (see FIG. 3(B)) of the portion where the sealing members 4, 4 were welded together was measured by observing the cut with a digital microscope (HRX-01 manufactured by Hirox Corporation, zoom lens HR-5000E), and the average value of the 15 points was calculated. The results are shown in Table 1 together with the irradiation conditions of step (a2). One of the digital microscope photographs of the sample cross section is shown in FIG. 5.

[0037] [Table 1]

[0038] In all of Samples No. 1 to 11, the second laser intensity per unit area I2 was 2.0704 W / mm 2 In all of Samples No. 1 to 11, the width W1 of the portion where the sealing members 4, 4 are welded together was stably ensured. In particular, when the total energy density of the second laser beam L2 was 0.40 J / mm 2 Particularly good sealing was obtained in Samples Nos. 7 to 9, which were above the above value, and Samples Nos. 10 and 11, in which the width of the second region R2 was 2 mm or more. [Explanation of symbols]

[0039] 1: current collector, 1a: first surface, 1b: second surface, 1c: outer edge (end portion), 2: positive electrode active material layer, 3: negative electrode active material layer, 4, 41: sealing member, 4a: coated portion, 4b: outer extension portion, 4i: inner edge, 4o: outer edge, R1: first region, R2: second region, 5: separator, 6: spacer, 7a, 7b, 7c: heat-sealed portion, 11, 12: laminate, 13: bipolar unit laminate, 14: positive electrode end unit, 15: negative electrode end unit, 101: base, 102: pressing plate, L1: first laser beam, L2: second laser beam, W1: width of region where sealing members 4, 4 are welded to each other

Claims

1. A method for manufacturing an electricity storage device, comprising: The power storage device is A plurality of stacked current collectors, each of which has an active material layer provided on a surface thereof; a plurality of sealing members formed of a resin material and welded to respective peripheral portions of the plurality of current collectors, each of the sealing members having a frame-like shape surrounding the active material layer when viewed in a thickness direction of the current collector, and each of the sealing members having a covering portion overlapping the current collector and an extending portion extending outward from an outer edge of the current collector; Equipped with The manufacturing method includes: (a) a step of welding the sealing member to the current collector by laser irradiation; Including, The step (a) (a1) a step of irradiating a first laser beam at a first laser intensity per unit area to a laminate having a structure in which the current collector is sandwiched between a pair of the sealing members, thereby welding the sealing members, the first laser beam being transmitted through one of the pair of sealing members and being irradiated onto at least a first region of the current collector; (a2) irradiating the laminate with a second laser light at a second laser intensity per unit area to weld the sealing member, the second laser light passing through one of the pair of sealing members and irradiating a second region of the current collector; Including, The second region is defined in a frame shape from an outer edge of the current collector toward the inside, the first region is defined in a frame shape inside the second region of the current collector and adjacent to the second region, In the step (a1), the first laser light may also be irradiated onto the second region of the current collector, A method for manufacturing an electricity storage device, wherein the second laser intensity per unit area is greater than the first laser intensity per unit area.

2. The method for producing an electricity storage device according to claim 1 , wherein in the step (a), the step (a2) is performed after the step (a1).

3. The method for producing an electricity storage device according to claim 1 , wherein in the step (a), the step (a1) and the step (a2) are carried out simultaneously.

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