JP7816318B2 - Method for manufacturing an electricity storage device - Google Patents

Description

This application relates to a method for manufacturing an electricity storage device.

Regarding a method for manufacturing an electric storage device, Patent Document 1 describes a method for manufacturing an electric storage device, comprising: 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 extending outward from the outer edge of the current collector, with the sealing members disposed between the plurality of current collectors; a melting step of melting the plurality of sealing members to form a side surface composed of the plurality of sealing members and including a communication port connecting the inside and outside of the laminate; and a molding step of forming a molding surface against which an equipment-side nozzle is pressed in an area of the side surface formed by melting the plurality of sealing members and surrounding the communication port; wherein the melting step melts the plurality of sealing members using non-contact heating; and the molding step, while the sealing members are in a molten state, presses a pressing member having a temperature lower than the melting point of the sealing members against the side surface to form the molding surface.

Japanese Patent Application Laid-Open No. 2023-000059

Patent Document 1 describes an infrared heater as an example of a non-contact heating means for melting the sealing member. However, from the standpoints of heating position accuracy, processing speed, and energy efficiency, it is preferable to use laser irradiation as the non-contact heating means. Furthermore, since the sealing member after welding is required to cover the edge of the current collector to ensure airtightness between the current collector and the sealing member, it is desirable for the sealing member to be heated sufficiently. However, when welding the sealing member using laser irradiation, increasing the laser output so that the welded sealing member covers the edge of the current collector is likely to cause wrinkles in the current collector.

The present invention provides a method for manufacturing an electricity storage device that can suppress wrinkles in the current collector while ensuring airtightness between the current collector and the sealing member by welding the sealing member using laser irradiation.

The present invention includes the following embodiments [1] to [3].
[1] A manufacturing method of an electricity storage device, the electricity storage device comprising:
a plurality of stacked current collectors, each having an active material layer provided on a surface of the current collector;
a plurality of sealing members formed of a resin material and welded to peripheral edges of the plurality of current collectors, each of which has a frame 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 laminate having a structure in which the current collector is sandwiched between a pair of the sealing members with a first laser light at a first laser intensity per unit area, thereby welding the sealing members, wherein the first laser light is transmitted through one of the pair of sealing members and is irradiated onto at least a first region of the current collector;
(a2) irradiating the laminate with a second laser beam at a second laser intensity per unit area to weld the sealing member, wherein the second laser beam passes through one of the pair of sealing members and is irradiated onto a second region of the current collector;
the second region is defined in a frame shape extending inward from an outer edge of the current collector,
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 manufacturing an electricity storage device described in [1], wherein, in step (a), step (a2) is performed after step (a1).

[3] The method for manufacturing an electricity storage device described in [1], wherein, in step (a), steps (a1) and (a2) are performed simultaneously.

According to the manufacturing method for an electricity storage device of the present invention, the laser intensity per unit area of the laser light irradiated onto the second region is greater than the laser intensity per unit area of the laser light irradiated onto the first region. Therefore, when the sealing member is welded by laser irradiation, the welded sealing member is welded so that it covers the end of the current collector, ensuring airtightness between the current collector and the sealing member while suppressing the occurrence of wrinkles in the current collector.

1A to 1G are cross-sectional views that schematically show an example of a manufacturing process for an electricity storage device. Fig. 2(A) is a cross-sectional view, reproducing Fig. 1(a), that schematically illustrates a laminate 10 having a structure in which a current collector 1 having active material layers 2 and 3 formed 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 line B-B in Fig. 2(A). 3(A) and 3(B) are schematic enlarged partial views of the vicinity of the outer edge of the current collector 1 before and after the laser light irradiation in step (a), where FIG. 3(A) shows the state before the laser light irradiation and FIG. 3(B) shows the state after the laser light irradiation. FIG. 4 is a perspective plan view for schematically explaining the shape of the test piece and the laser beam. FIG. 5 is an example of a micrograph of a cross section of a test piece prepared in an example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments. Note that the drawings do not necessarily reflect accurate dimensions. In addition, some reference numerals may be omitted in the drawings. In this specification, unless otherwise specified, the notation "A to B" for numerical values A and B means "greater than or equal to A and less than or equal to B." In such notation, if a unit is assigned only to numerical value B, the unit also applies to numerical value A. Furthermore, the words "or" and "or" mean a logical sum unless otherwise specified. Furthermore, the notation " _E1 and/or E2" for elements _{E1 and E2} means " _E1 or _E2 , or a combination thereof," and the notation " _E1 , ..., E N-1, and/or E _N " for elements _E1 , ..., E _{N-1 (} N is an integer of 3 or more) means " _E1 , ..., E _N-1 , or E _N , or a combination thereof."

<Method of manufacturing electricity storage device>
1(a) to 1(g) are cross-sectional views schematically illustrating an example of a manufacturing process for an electricity storage device. FIG. 1(a) is a cross-sectional view schematically 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 (hereinafter sometimes simply referred to as "sealing member 4"). The current collector 1 is a sheet-like conductive member having 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.

The current collector 1 is composed of, for example, a metal foil or alloy foil. Examples of metal foils include copper foil, aluminum foil, titanium foil, and nickel foil. Examples of alloy foils include stainless steel foil (e.g., SUS304, SUS316, SUS301, etc., as defined in JIS G 4305:2015), plated steel sheet (e.g., cold-rolled steel sheet (SPCC, etc.) as defined in JIS G 3141:2005), and plated stainless steel sheet. The alloy foil may be an alloy foil of the metals listed above as examples of the metal foil material. The current collector 1 may be formed by integrating or laminating multiple metal foils, or by plating the surface of a metal foil with another metal. In one embodiment, the current collector 1 may be, for example, an Al-Cu alloy foil having an aluminum layer and a copper layer, with the Al layer appearing on the first surface 1a and the Cu layer appearing on the second surface 1b. The Al-Cu alloy foil may be a clad foil in which aluminum foil and copper foil are bonded together. The aluminum layer on the first surface 1a of the current collector 1 may be chromate-treated. 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 with fine protrusions on its surface.

The positive electrode active material layer 2 is a layered member containing a positive electrode active material, a conductive additive, and a binder. Examples of the positive electrode active material include a composite oxide, metallic lithium, and sulfur. The composite oxide contains lithium and at least one of iron, manganese, titanium, nickel, cobalt, and aluminum. Examples of the composite oxide include olivine-type lithium iron phosphate ( _LiFePO4 ), _LiCoO2 , and _LiNiMnCoO2 .

The binder serves to anchor the active material or conductive additive to the surface of the current collector 1 and maintain the conductive network within the electrode. Examples of binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; 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 crosslinks; and starch-acrylic acid graft polymers. These binders can be used alone or in combination. Examples of conductive additives 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).

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

To form the positive electrode active material layer 2 and the negative electrode active material layer 3 on the current collector 1, conventional methods such as roll coating, die coating, dip coating, doctor blade coating, spray coating, and curtain coating are used. Specifically, an active material, a solvent, and, if necessary, a binder and a conductive additive are mixed to produce a slurry-like active material layer-forming composition. This active material layer-forming composition is then applied to the first surface 1a and the second surface 1b and dried. Examples of solvents include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The dried electrode may be compressed to increase electrode density.

Referring further to Figures 2(A) and (B). Figure 2(A) is a cross-sectional view, reproducing Figure 1(a), that schematically illustrates a laminate 10 having a structure in which a current collector 1, on the surface of which active material layers 2 and 3 are provided, is sandwiched between a pair of sealing members 4 and 4. Figure 2(B) is a perspective plan view taken along the arrows B-B in Figure 2(A). The sealing member 4 is formed of an electrically insulating resin material that is transparent to the first and second laser beams used in step (a) described below, and has a frame-like shape that surrounds the active material layers 2 and 3 when viewed through the thickness of the current collector 1. When viewed through the thickness 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. When viewed in the thickness direction of the current collector 1, the sealing member 4 includes a covering portion 4a that overlaps the current collector 1 and an extending portion 4b that extends outward from the outer edge 1c of the current collector 1. Examples of materials for the sealing member 4 include optically transparent, electrically insulating thermoplastic resins such as polypropylene, polyethylene, polystyrene, ABS resin, modified polypropylene, and acrylonitrile-styrene resin.

Referring again to Figure 1(a), the manufacturing method for the energy storage device of the present invention includes (a) a step 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 performing step (a), a bipolar unit 11 is obtained, which includes a sealing member 41 welded to the current collector 1 (Figure 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 stacked on the bipolar unit 11 (Figure 1(c)), and the peripheral portion of the separator 5 is welded to the sealing member 41 to obtain a bipolar unit 12 (Figure 1(d)).

The separator 5 is a sheet-like member, and the outer edge of its 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 electrolyte. Examples of materials that make up 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 substrate layer and a pair of adhesive layers, and may be bonded 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 also include a ceramic layer that serves as a heat-resistant layer. The separator 5 may be reinforced with a vinylidene fluoride resin compound. Known heating methods, such as resistance heating, can be used to weld the peripheral portion of the separator 5 to the sealing member 41.

Examples of the electrolyte impregnated into the separator 5 include a liquid electrolyte (electrolytic solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, or 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 LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN(FSO ₂ ) ₂ , and LiN(CF ₃ SO ₂ ) ₂ can be used as the electrolyte salt. Also, 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. In such an embodiment, the separator 5 may not be impregnated with a non-solid electrolyte.

By alternately stacking bipolar units 12 and spacers 6, a bipolar unit stack 13 is obtained (Figures 1(e)-(g)). By further stacking positive end units 14 and negative end units 15 on the bipolar unit stack 13 (Figure 1(g)), a cell stack 16 is constructed (Figure 1(h)). By heat-welding adjacent pairs of sealing members 41 and separators 5 in the cell stack 16 (heat-welded portions 7a, 7b), a power storage device 17, which is a stacked battery with a fixed stack structure of the cell stack 16, is obtained (Figure 1(h)). At this time, previously unwelded portions of the sealing members 41 can be further welded (heat-welded portion 7c).

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. Furthermore, 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 or separator 5.

The spacer 6 is a frame-shaped member that surrounds the active material layers 2 and 3 when viewed in the thickness direction of the current collector 1. The spacers 6 are arranged between adjacent pairs of bipolar units 12, 12, between the bipolar unit 12 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 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.

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, positive electrode end unit 14, and 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 sealing members 4, 41, and spacers 6 may be made of the same material.

Referring again to Figures 1(a), 1(b), and 2(B). Step (a): The step of welding the sealing members 4, 4 to the current collector 1 by laser irradiation includes: (a1) a step of irradiating a laminate 10 having a structure in which the current collector 1 is sandwiched between a pair of sealing members 4, 4 with a first laser beam L1 at a first laser intensity per unit area I1 to weld the sealing members 4, 4 (hereinafter, this step may be referred to as "step (a1)" or "first welding step"); and (a2) a step of irradiating the laminate 10 with a second laser beam L2 at a second laser intensity per unit area I2 to weld the sealing members 4, 4 (hereinafter, this step may be referred to as "step (a2)" or "second welding step"). In step (a1), the first laser beam L1 passes through one of the pair of sealing members 4, 4 and is irradiated onto at least a first region R1 of the current collector. In step (a2), the second laser beam L2 passes through one of the pair of sealing members 4, 4 and is 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 extending inward from the outer edge 1c of the current collector 1. 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 perspective of increasing the amount of molten material in the sealing members 4, 4 and making it easier for the molten material 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 in one embodiment, can be 1 to 5 mm or 2 to 5 mm.

3(A) and (B) are schematic enlarged partial views of the vicinity of the outer edge of the current collector 1 before and after irradiation with laser light in step (a). FIG. 3(A) shows the state before laser light irradiation, and FIG. 3(B) shows the state after laser light irradiation. Referring to FIG. 3(A), in step (a), the laminate 10 is placed on a base 101, and an area of the laminate 10 including at least the sealing members 4, 4 is sandwiched between the base 101 and a presser plate 102. By applying pressure P between the base 101 and the presser plate 102, the presser plate 102 comes into tight contact with at least the covered portion 4a of the sealing member 4 that overlaps with the current collector 1 (see FIG. 2(B)). A first laser beam L1 and a second laser beam L2 are irradiated through the presser plate 102.

3(A) shows the first region R1 and the second region R2 of the current collector 1, as well as the irradiation range of the first laser beam L1 (arrow L1) and the irradiation range of the second laser beam L2 (arrow L2). In step (a1), the first laser beam L1 is irradiated onto at least the first region R1 of the current collector 1, and may also be irradiated onto the second region R2, and may also be irradiated onto the extended portion 4b of the sealing member 4 (see FIG. 2(B)). In step (a2), the second laser beam L2 is irradiated onto the second region R2, and may also be irradiated onto the extended portion 4b of the sealing member 4 (see also FIG. 2(B)). In steps (a1) and (a2), the irradiated laser beams L1 and L2 are absorbed by the current collector 1 and converted into thermal energy, respectively, which partially melts the nearby sealing members 4 and 4. The molten sealing members 4, 4 fuse to the current collector 1. Furthermore, in step (a2), the molten sealing members 4, 4 flow and flow outside the outer edge 1c of the current collector 1, welding 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)). To ensure airtightness, the width W1 (in a plan view of the laminate 11) of the region where the sealing members 4, 4 are welded together in the laminate 11 (see also FIG. 1(b)) after steps (a1) and (a2) is preferably 100 μm or greater.

The base 101 can be made of, for example, glass, metal, or a heat-resistant elastomer such as silicone resin. The pressure plate 102 can be made of a material such as tempered glass that is transparent to the first and second laser beams L1 and L2 and can withstand the applied pressure P. Alternatively, a transparent silicone resin member or other material with high laser light transparency can be sandwiched between the pressure plate and the sealing member.

The first laser intensity per unit area I1 can be set to an intensity sufficient to weld the sealing members 4, 4 to the first region R1 of the current collector 1. Such laser intensity per unit area I1 can be preferably set to, for example, 0.5 to 5.0 W/ ^mm² . The second laser intensity per unit area I2 can be set to an intensity sufficient to weld the sealing members 4, 4 to the second region R2 of the current collector 1 and to weld 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 faces of the outer edges 1c of the current collector 1. Such laser intensity per unit area I2 can be preferably set to, for example, 0.5 to 6.0 W/ ^mm² , and in one embodiment, can be set to 3.3 W/ ^mm² or more, or 3.8 W/ ^mm² or more. 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 so as to cover the end faces of the current collector 1.

The wavelengths of the first laser light L1 and the second laser light L1 may be the same or different, 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 the entire second region R2 with the second laser light L2 may be performed by irradiating each frame-shaped region 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., the time integral of the laser intensity) of the first laser light L1 irradiated to the same location may be, for example, 0.05 to 0.40 J/ ^mm² , from the viewpoint of facilitating welding of the sealing members 4, 4 to the first region R1 of the current collector 1. The total energy density of the second laser beam L2 irradiated to the same location can be preferably, for example, 0.05 to 0.40 J/ ^mm² , from the viewpoint of facilitating welding of the extending 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 faces of the outer edges 1c of the current collector 1. The beam shape and the scanning linear velocity 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 beam L1 (the time from the start to the end of irradiation of a point with the laser beam) can be preferably, for example, 20 ms or more, from the viewpoint of ensuring sufficient time for welding the sealing member 4 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 set to, for example, 35 ms or more, 70 ms or more, or 84 ms or more, from the viewpoint of ensuring sufficient time for the molten material of the sealing member 4 to flow and wrap around the end face of the outer edge 1c of the current collector 1, and can be set to, for example, 200 ms or less, from the viewpoint of laser intensity and productivity.

In one preferred embodiment, in step (a), step (a2) is performed after step (a1). According to this embodiment, welding of the first region R1 is performed before welding of the second region R2. This prevents the molten material of the sealing members 4, 4 from flowing toward the first region R1 when welding the second region R2, which is advantageous from the perspective of welding the sealing members 4, 4 so as to cover the end faces of the current collector 1.

In one preferred embodiment, in step (a), steps (a1) and (a2) are performed simultaneously. According to this embodiment, the first welding step (a1) and the second welding step (a2) are performed simultaneously, thereby shortening the time required for welding and increasing productivity.

In step (a2), it is preferable that either of the following requirements (i) and (ii) be satisfied: (i) the total energy density of the second laser light L2 irradiated to the same location is 0.35 J/ ^mm2 or more, the laser intensity I2 per unit area of the second laser light L2 is 3.3 W/ ^mm2 or more, 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 2 mm or more; or (ii) the total energy density of the second laser light L2 irradiated to the same location is 0.40 J/ ^mm2 or more, the laser intensity I2 per unit area of the second laser light L2 is 3.8 W/ ^mm2 or more, 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 becomes 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, further increase the width W1 over which the sealing members 4, 4 are welded to each other, and further improve the airtightness.

The present invention will be explained in more detail below based on examples. However, the present invention is not limited to these examples.

4 is a perspective plan view that schematically illustrates the shapes of the test pieces and the laser beam. Eleven test pieces 110 were fabricated by sandwiching the vicinity of an end of a current collector 1 (Al-Cu clad 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 presser plate 102 (made of tempered glass) as shown in FIG. 3(A), and laser irradiation in step (a1) was performed from the presser plate 102 side under 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: 0.2174 J/mm ² ). Thereafter, laser irradiation in step (a2) (semiconductor laser, beam width 6 mm, depth in the beam traveling direction 42 mm, laser wavelength 1020 nm) was performed under various different conditions. 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 and inside the second region R2. In step (a1), the first laser beam L1 was irradiated over the entire region where the current collector 1 was present (i.e., the entire portion covered by the sealing member 4). In step (a2), the second laser beam L2 was irradiated over the entire second region R2 and the extended portion of the sealing member 4. The region irradiated with the first laser beam L1 and the region irradiated with the second laser beam L2 overlapped in the second region R2. After irradiation was completed, the sample was cut at 15 points spaced equally apart (5 mm) along the outer edge 1c of the current collector 1. The width W1 (see FIG. 3(B)) of the portion where the sealing members 4, 4 were welded together was measured by observing the cuts with a digital microscope (HRX-01 manufactured by Hirox Corporation, zoom lens HR-5000E), and the average value of the 15 cuts was calculated. The results, along with the irradiation conditions for step (a2), are shown in Table 1. One of the digital microscope photographs of the sample cross section is shown in FIG. 5.

In all of Samples No. 1 to 11, the second laser intensity per unit area I2 was greater than the first laser intensity per unit area I1 (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 were welded together was stably secured. Among them, Samples No. 7 to 9, in which the total energy density of the second laser light L2 was 0.40 J/mm ² or more, and Samples No. 10 and 11, in which the width of the second region R2 was 2 mm or more, achieved particularly good sealing.

1: Current collector, 1a: First surface, 1b: Second surface, 1c: Outer edge (end), 2: Positive electrode active material layer, 3: Negative electrode active material layer, 4, 41: Sealing member, 4a: Covering portion, 4b: Outer extension portion, 4i: Inner edge, 4o: Outer edge, R1: First region, R2: Second region, 5: Separator, 6: Spacer, 7a, 7b, 7c: Thermally welded portion, 11, 12: Laminate, 13: Bipolar unit laminate, 14: Positive electrode end unit, 15: Negative electrode end unit, 101: Base, 102: Presser plate, L1: First laser beam, L2: Second laser beam, W1: Width of the region where the sealing members 4 and 4 are welded together

Claims (3)

A method for manufacturing an electricity storage device, comprising:
The power storage device is
a plurality of stacked current collectors, each having an active material layer provided on a surface of the current collector;
a plurality of sealing members formed of a resin material and welded to peripheral edges of the plurality of current collectors, each of which has a frame 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 laminate having a structure in which the current collector is sandwiched between a pair of the sealing members with a first laser light at a first laser intensity per unit area, thereby welding the sealing members, wherein the first laser light is transmitted through one of the pair of sealing members and is irradiated onto at least a first region of the current collector;
(a2) irradiating the laminate with a second laser beam at a second laser intensity per unit area to weld the sealing member, wherein the second laser beam passes through one of the pair of sealing members and is irradiated onto a second region of the current collector;
Including,
the second region is defined in a frame shape extending inward from an outer edge of the current collector,
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. The method for manufacturing an electricity storage device according to claim 1, wherein in step (a), step (a2) is performed after step (a1). The method for manufacturing an electricity storage device according to claim 1, wherein in step (a), steps (a1) and (a2) are performed simultaneously.