Method for manufacturing an electricity storage device

Abstract

To provide a manufacturing method of a power storage device, capable of suppressing fusing of a current collector foil.SOLUTION: A manufacturing method of a power storage device disclosed herein is a manufacturing method of a power storage device that includes a positive electrode 40 and a negative electrode 60. The manufacturing method includes: overlapping a current collector and a plurality of laminated current collector foils, in at least one of the positive electrode 40 and the negative electrode 60; disposing a laser light transmitting member 200 comprising YAG or Y2O3 on the overlapped current collector foils; and allowing laser light L to pass through the laser light transmitting member 200 to irradiate the plurality of overlapped current collector foils with the laser light L and welding the current collector and the plurality of overlapped current collector foils, while holding the laser light transmitting member 200 toward a side of the current collector.SELECTED DRAWING: Figure 5

Description

[Technical Field]

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

[0002] Conventionally, resistance welding or ultrasonic welding has been widely used to join multiple current collecting foils and current collectors of each electrode in an electrode assembly. Meanwhile, from the perspective of cost reduction, technological developments have been made to join multiple current collecting foils and current collectors by laser welding. For example, Patent Document 1 discloses a laser welding technique that includes temporary joining to improve adhesion of metal foils. Furthermore, Patent Documents 2 to 4 disclose techniques for laser welding in which the periphery of the metal foil to be laser welded is pressed with a jig. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-140890 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-136242 [Patent Document 3] Japanese Patent Application Laid-Open No. 2016-030280 [Patent Document 4] Japanese Patent Application Publication No. 2019-067570 Summary of the Invention [Problem to be solved by the invention]

[0004] When laser welding multiple stacked current collecting foils and a current collector, it is desirable to reduce the gaps between the current collecting foils in the areas to be welded. If there are gaps between the current collecting foils, the current collecting foils may melt and cut when irradiated with laser light (resulting in current collecting foils that are not joined to the current collector at the laser welded area).

[0005] A main object of the present disclosure is to provide a method for manufacturing an electricity storage device that can suppress meltdown of the current collecting foil. [Means for solving the problem]

[0006] The disclosed method for manufacturing an electricity storage device includes a positive electrode including a plurality of stacked positive electrode current collector foils and a positive electrode current collector connected to the stacked positive electrode current collector foils, and a negative electrode including a plurality of stacked negative electrode current collector foils and a negative electrode current collector connected to the stacked negative electrode current collector foils. The manufacturing method includes overlapping the plurality of stacked current collector foils and the current collector for at least one of the positive electrode and the negative electrode. The manufacturing method also includes placing a laser light transmitting member made of YAG or YO on the overlapped current collector foils. The manufacturing method also includes pressing the laser light transmitting member toward the current collector, and irradiating the overlapped plurality of current collector foils with a laser light passing through the laser light transmitting member, thereby welding the overlapped plurality of current collector foils to the current collector. According to this manufacturing method, the laser light transmitting member is pressed against the stacked current collecting foils, thereby reducing the gaps between the pressed current collecting foils. Furthermore, by irradiating the current collecting foils with laser light passing through the laser light transmitting member, laser welding can be performed while maintaining the reduced gaps between the current collecting foils. This makes it possible to prevent melting of the current collecting foils, which may occur due to the gaps between the foils. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the general configuration of a nonaqueous electrolyte secondary battery according to one embodiment. [Figure 2] FIG. 2 is an exploded view schematically showing the configuration of an electrode assembly of a nonaqueous electrolyte secondary battery according to one embodiment. [Figure 3] FIG. 3 is a side view schematically showing a laser welding method according to one embodiment. [Figure 4]FIG. 4 is a schematic diagram showing a cross section of the vicinity of the laser welded portion after irradiation with laser light L. [Figure 5] FIG. 5 is a cross-sectional SEM image of the vicinity of the laser weld in the example. [Figure 6] FIG. 6 is a cross-sectional SEM image of the vicinity of the laser weld in the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present technology will be described in detail below. Matters necessary for implementing the present technology (e.g., a method for assembling an electricity storage device) other than those specifically mentioned in this specification (e.g., a method for laser welding a current collecting foil and a current collector) can be understood as design matters for a person skilled in the art based on prior art in the relevant field. The content of the present technology can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field.

[0009] Each drawing is a schematic drawing, and the dimensional relationships (length, width, thickness, etc.) do not necessarily reflect the actual dimensional relationships. Furthermore, in the drawings described below, the same reference numerals are used to designate components and parts that perform the same functions, and redundant explanations may be omitted or simplified. Furthermore, in this specification, when a numerical range is described as "A to B (where A and B are any numerical values)," this means "A or more and B or less," and also encompasses the meanings of "greater than A and less than B," "greater than A and B or less," and "greater than A and less than B."

[0010] In this specification, the term "electricity storage device" refers to a device that can be charged and discharged. Electricity storage devices include batteries such as primary batteries and secondary batteries (e.g., lithium ion secondary batteries and nickel-metal hydride batteries), and capacitors (physical batteries) such as electric double layer capacitors. Below, a non-aqueous electrolyte secondary battery, which is one embodiment of an electricity storage device manufactured by the manufacturing method disclosed herein, will be described. Note that the electricity storage device manufactured by the present technology is not limited to a non-aqueous electrolyte secondary battery.

[0011] 1 is a schematic cross-sectional view roughly illustrating the configuration of a nonaqueous electrolyte secondary battery 100 according to one embodiment. The nonaqueous electrolyte secondary battery 100 includes an electrode assembly 20, a case 30, a positive electrode 40, a negative electrode plate 70, and a nonaqueous electrolyte (not shown). The positive electrode 40 includes a positive electrode terminal 42, a positive electrode current collector 44, and a positive electrode plate 50. The negative electrode 60 includes a negative electrode terminal 62, a negative electrode current collector 64, and the negative electrode plate 70. Although not particularly limited, in this embodiment, the nonaqueous electrolyte secondary battery 100 is a lithium-ion secondary battery.

[0012] As shown in FIG. 1, the nonaqueous electrolyte secondary battery 100 is a rectangular sealed battery constructed by housing a flat electrode assembly (wound electrode assembly) 20 and a nonaqueous electrolyte (not shown) inside a case 30. The case 30 includes a case body 32 having an opening and a sealing member 34 that seals the opening. In this example, the sealing member 34 is plate-shaped. The sealing member 34 is provided with a positive electrode terminal 42 and a negative electrode terminal 62 for external connection. The sealing member 34 also includes a thin-walled safety valve 36 that is designed to release internal pressure in the case 30 when the internal pressure rises above a predetermined level. The case 30 also includes an injection port (not shown) for injecting the nonaqueous electrolyte. The case 30 is preferably made of a metal material that is high in strength, lightweight, and has good thermal conductivity. Examples of such metal materials include aluminum and steel.

[0013] FIG. 2 is an exploded view schematically illustrating the configuration of an electrode assembly 20 of a nonaqueous electrolyte secondary battery 100 according to one embodiment. In FIG. 2, the electrode assembly 20 is a wound electrode assembly in which a long sheet-like positive electrode plate 50 and a long sheet-like negative electrode plate 70 are stacked with two long sheet-like separators 80 interposed between them so that their longitudinal directions are aligned, and then wound around a winding axis WL. The positive electrode plate 50 includes a positive electrode current collector foil 52 and a positive electrode active material layer 54 arranged in the longitudinal direction on one or both sides (both sides in this case) of the positive electrode current collector foil 52. One edge of the positive electrode current collector foil 52 in the direction of the winding axis WL (i.e., the sheet width direction perpendicular to the longitudinal direction) is provided with a strip-shaped portion along the edge where the positive electrode active material layer 54 is not formed and the positive electrode current collector foil 52 is exposed (i.e., a positive electrode current collector foil exposed portion 52a). The negative electrode plate 70 includes a negative electrode current collector foil 72 and a negative electrode active material layer 74 arranged in the longitudinal direction on one or both sides (both sides in this case) of the negative electrode current collector foil 72. The other edge of the negative electrode current collector foil 72 in the winding axis WL direction (i.e., the edge opposite the positive electrode current collector foil exposed portion 52a) has a strip-shaped portion along the edge where the negative electrode active material layer 74 is not formed and the negative electrode current collector foil 72 is exposed (i.e., the negative electrode current collector foil exposed portion 72a).

[0014] The wound positive current collector foil 52 has a plurality of stacked positive current collector foil exposed portions 52a in the thickness direction of the electrode body 20. The stacked positive current collector foil exposed portions 52a are joined to the positive current collector 44 by laser welding (a laser weld 90 shown in FIG. 4, which will be described later, is provided). The wound negative current collector foil 72 has a plurality of stacked negative current collector foil exposed portions 72a in the thickness direction of the electrode body 20. The stacked negative current collector foil exposed portions 72a are joined to the negative current collector 64 by laser welding (i.e., a laser weld is provided). The positive current collector 44 is electrically connected to the positive terminal 42 for external connection, thereby realizing electrical continuity between the inside and outside of the case 30 (see FIG. 1). Similarly, the negative current collector 64 is electrically connected to the negative terminal 62 for external connection, thereby realizing electrical continuity between the inside and outside of the case 30 (see FIG. 1). The positive electrode current collector foil exposed portion 52a and / or the negative electrode current collector foil exposed portion 72a may be tab-shaped, or a plurality of such tabs may be stacked. The shape of the tab is not particularly limited, and may be, for example, trapezoidal, rectangular, or the like in a plan view.

[0015] The portion of the positive electrode current collector 44 where the laser welded portion to be joined to the positive electrode current collector foil exposed portion 52a is provided is preferably plate-shaped. Alternatively, the entire positive electrode current collector 44 may be plate-shaped. The thickness of the portion of the positive electrode current collector 44 joined to the positive electrode current collector foil exposed portion 52a may be, for example, 0.5 mm to 3 mm. The negative electrode current collector 64 preferably has a plate-like portion at which a laser welded portion to be joined to the negative electrode current collector foil exposed portion 72a is provided. The entire negative electrode current collector 64 may also be plate-like. For example, it may be plate-like. The thickness of the portion of the negative electrode current collector 64 to be joined to the negative electrode current collector foil exposed portion 72a may be, for example, 0.5 mm to 3 mm.

[0016] An insulating member (not shown) for insulating the positive electrode terminal 42 from the sealing member 34 can be disposed between the positive electrode terminal 42 and the sealing member 34. The insulating member is made of, for example, a resin member having electrical insulation properties. Examples of such resins include polyolefin resins such as polypropylene (PP), fluorinated resins such as perfluoroalkoxyethylene copolymer (PFA) and polytetrafluoroethylene (PTFE), and polyphenylene sulfide (PPS). The insulating members may also be disposed between the negative electrode terminal 62 and the sealing member 34, between the positive electrode current collector 44 and the sealing member 34, and between the negative electrode current collector 64 and the sealing member 34.

[0017] The positive electrode current collector foil 52 may be, for example, an aluminum foil. The thickness of the positive electrode current collector foil 52 may be, for example, 5 μm to 20 μm. The positive electrode active material layer 54 includes a positive electrode active material. As the positive electrode active material, a known positive electrode active material used in lithium ion secondary batteries may be used, for example, a lithium composite metal oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 Examples of the positive electrode active material layer 54 include LiCrMnO4, LiCrMnO4, LiFePO4, etc. The positive electrode active material layer 54 may also include a conductive material, a binder, etc. Suitable conductive materials include carbon black such as acetylene black (AB) and other carbon materials (such as graphite). Suitable binders include polyvinylidene fluoride (PVDF), for example. The positive electrode active material layer 54 can be formed by dispersing the positive electrode active material and materials (such as a conductive material and a binder) used as needed in an appropriate solvent (for example, N-methyl-2-pyrrolidone: NMP) to prepare a paste-like (or slurry-like) composition (positive electrode mixture paste), applying an appropriate amount of the composition to the surface of the positive electrode current collector foil 52, and drying the composition.

[0018] The negative electrode current collector foil 72 may be, for example, a copper foil. The thickness of the negative electrode current collector foil 72 may be, for example, 5 μm to 20 μm. The negative electrode active material layer 74 includes a negative electrode active material. As the negative electrode active material, for example, a carbon material such as graphite, hard carbon, or soft carbon may be used. The negative electrode active material layer 74 may further include a binder, a thickener, or the like. As the binder, for example, styrene butadiene rubber (SBR) or the like may be used. As the thickener, for example, carboxymethyl cellulose (CMC) or the like may be used. The negative electrode active material layer 74 can be formed, for example, by dispersing the negative electrode active material and materials (such as a binder) used as needed in an appropriate solvent (such as ion-exchanged water) to prepare a paste-like (or slurry-like) composition, applying an appropriate amount of the composition to the surface of the negative electrode current collector foil 72, and drying it.

[0019] As the separator 80, various conventional microporous sheets can be used, such as microporous resin sheets made of resins such as polyethylene (PE) and polypropylene (PP). Such microporous resin sheets may have a single-layer structure or a multi-layer structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). Separator 80 may also have a heat-resistant layer (HRL).

[0020] Conventional nonaqueous electrolytes can be used, for example, nonaqueous electrolytes containing a supporting salt in an organic solvent (nonaqueous solvent). Nonaqueous solvents include aprotic solvents such as carbonates, esters, and ethers. Among these, carbonates, such as ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC), are preferred. Alternatively, fluorine-based solvents, such as fluorinated carbonates, such as monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC), are preferred. These nonaqueous solvents can be used alone or in appropriate combinations of two or more. Lithium salts, such as LiPF, LiBF, and LiClO, are preferred as supporting salts. The concentration of the supporting salt is not particularly limited, but is preferably about 0.7 mol / L or more and 1.3 mol / L or less. The nonaqueous electrolyte may contain components other than the nonaqueous solvent and supporting salt described above, as long as the effects of the present technology are not significantly impaired. For example, the nonaqueous electrolyte may contain various additives such as a gas generating agent, a film-forming agent, a dispersant, and a thickener.

[0021] An electricity storage device such as the nonaqueous electrolyte secondary battery 100 can be used for various purposes, and can be suitably used, for example, as a power source (driving power source) for a motor mounted on a vehicle such as a passenger car, a truck, etc. The type of vehicle is not particularly limited, and examples thereof include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and a battery electric vehicle (BEV).

[0022] The shape of the electricity storage device disclosed herein is not limited to a rectangular shape, and may be a coin shape, a button shape, a cylindrical shape, or the like. The electricity storage device may also be configured as a power storage device including a laminated case. The electricity storage device disclosed herein may be a polymer battery using a polymer electrolyte instead of a nonaqueous electrolyte, an all-solid-state battery using a solid electrolyte, or the like.

[0023] A method for manufacturing the electricity storage device disclosed herein is described below. The manufacturing method disclosed herein includes a laminating step, which includes placing a positive or negative electrode current collector foil, a current collector, and a laser light transparent member on the current collector foil, and a welding step, which laser-welds the current collector foil and the current collector by irradiating the current collector foil with a laser light passing through the laser light transparent member while pressing the laser light transparent member toward the current collector. In addition to the welding step, the manufacturing method disclosed herein may also include, in any order as necessary, a preparation step, an assembly step, a housing step, a sealing step, a liquid injection step, and the like.

[0024] In the manufacturing method disclosed herein, the laser light transmitting member is pressed against the stacked current collecting foils, thereby reducing the gaps between the pressed current collecting foils. Furthermore, by irradiating the current collecting foils with a laser light passing through the laser light transmitting member, laser welding can be performed while maintaining the reduced gaps between the current collecting foils. This makes it possible to prevent melting of the current collecting foils, which can occur due to the gaps between the foils.

[0025] An embodiment of the manufacturing method disclosed herein will now be described.

[0026] In the preparation step, for example, an electrode body is prepared. The electrode body may be a wound electrode body such as the electrode body 20 described above, or a laminated electrode body in which multiple positive electrode plates and multiple negative electrode plates are alternately stacked with separators interposed therebetween. Here, the above-described electrode body 20 will be used as an example for explanation. The electrode body 20 can be produced by a conventionally known procedure.

[0027] The overlapping step includes overlapping a current collector with multiple stacked current collector foils (exposed current collector foil portions) of the electrode body 20 in at least one of the positive electrode 40 and the negative electrode 60, and placing a laser light transmitting member on the multiple stacked current collector foils. Here, the positive electrode 40 will be described as an example.

[0028] FIG. 3 is a side view schematically illustrating a laser welding method according to one embodiment. For ease of explanation, FIG. 3 omits components of the electricity storage device other than the positive current collector foil 52 (positive current collector foil exposed portion 52a) and the positive current collector 44 (the same applies to FIG. 4 described later). In this embodiment, as shown in FIG. 3 , multiple stacked positive current collector foils 52 (specifically, the positive current collector foil exposed portion 52a) located at the end of the electrode assembly 20 are stacked on the surface 44a of the positive current collector 44. The number of stacked positive current collector foils 52 is not particularly limited, but may be, for example, approximately 10 to 120 sheets or 20 to 100 sheets. Although not limited thereto, the stacking direction of the positive current collector foils 52 is preferably vertical. This facilitates reducing gaps between the foils of the positive current collector foils 52 due to gravity.

[0029] Next, the laser light transmitting member 200 is placed on top (on the uppermost surface) of the stacked positive current collector foils 52. In other words, the plurality of stacked positive current collector foils 52 are sandwiched between the laser light transmitting member 200 and the positive current collector 44. At this time, the laser light transmitting member 200 is placed so as to cover the to-be-welded portions 400 (portions to be irradiated with laser) of the positive current collector foils 52. It is preferable to smooth out any wrinkles in the to-be-welded portions 400 of the positive current collector foils 52 before placing the laser light transmitting member 200. This reduces gaps between the stacked positive current collector foils 52, thereby suppressing melting during laser welding.

[0030] The laser beam transmitting member 200 is preferably arranged so that the to-be-welded portion 400 of the positive current collecting foil 52 is located at or near the center in a plan view. This allows the laser beam transmitting member 200 to press the periphery of the to-be-welded portion 400, thereby reducing the gap between the positive current collecting foils near the to-be-welded portion 400.

[0031] The shape of the laser light transmitting member 200 is not particularly limited, but is plate-shaped here. The laser light transmitting member 200 can be circular, elliptical, rectangular, or polygonal in plan view. By having the laser light transmitting member 200 in a plate shape, when the laser light transmitting member 200 is pressed against the positive current collector foil 52, the positive current collector foil 52 can be pressed with a more uniform force, thereby more uniformly reducing the gaps between the foils. The size of the laser light transmitting member 200 is not particularly limited as long as it can cover the to-be-welded portion 400 of the positive current collector foil 52.

[0032] The thickness of the portion of the laser light transmitting member 200 through which the laser light L passes may be, for example, 5 mm or less, preferably 4 mm or less, more preferably 3 mm or less, and even more preferably 2 mm or less. The shorter the distance that the laser light L passes through the laser light transmitting member 200, the more the diffusion of the laser light L is suppressed, and the more accurate the laser welding may be. The thickness of the portion of the laser light transmitting member 200 through which the laser light L passes may be, for example, 0.2 mm or more, preferably 0.5 mm or more, more preferably 0.8 mm or more, and even more preferably 1 mm or more. If the thickness of the laser light transmitting member 200 is too small, the strength may be insufficient. The thickness of the portion of the laser light transmitting member 200 through which the laser light L passes may be, for example, the thickness in the stacking direction of the multiple stacked positive electrode current collecting foils 52.

[0033] The laser light transmitting member 200 may be made of a material that can transmit the laser light L used in laser welding. The laser light transmitting member 200 may be transparent, for example. The transmittance of the laser light wavelength of the laser light transmitting member 200 is, for example, 70% or more, preferably 75% or more, and more preferably 80% or more. The higher the transmittance of the laser light wavelength of the laser light transmitting member 200, the more accurately the laser light L reaches the to-be-welded portion 400 of the positive electrode current collecting foil 52, thereby improving the laser welding accuracy. The laser light wavelength may be measured according to the wavelength of the laser light to be used, and may be, for example, the transmittance for a laser light wavelength of 900 nm to 1200 nm (e.g., 1070 nm). In this specification, the transmittance of a laser light wavelength is calculated as the ratio of the energy measured by a power meter when a laser beam is passed through a laser beam transmitting member in the thickness direction of a test piece having a thickness of 2 mm to the energy measured by a power meter when the laser beam is irradiated onto the power meter for a predetermined time, where the energy measured by the power meter when the laser beam is irradiated onto the power meter for a predetermined time is taken as 100%.

[0034] Laser light transmitting member 200 is preferably made of a material that can withstand the heat generated during laser welding of the current collecting foil and the current collector. In other words, laser light transmitting member 200 is preferably made of a material that has a melting point higher than the melting point of the current collecting foil. The melting point of laser light transmitting member 200 is, for example, 800°C or higher, and can be 1200°C or higher, 1600°C or higher, 1700°C or higher, 1800°C or higher, 1900°C or higher, 2000°C or higher, 2100°C or higher, 2200°C or higher, 2300°C or higher, or 2400°C or higher.

[0035] Examples of materials that constitute laser light transmitting member 200 include YAG (yttrium aluminate, melting point: approximately 1970°C), Y2O3 (yttrium oxide, melting point: approximately 2425°C), sapphire (melting point: approximately 2040°C), and quartz glass (melting point: approximately 1723°C). Among these, it is preferable that laser light transmitting member 200 is constituted by YAG or Y2O3. Among the above examples, YAG and Y2O3 have relatively high densities. For example, when laser light transmitting member 200 is constituted by YAG or Y2O3, the density is 4 g / cm. 3 or more, preferably 4.5 g / cm 3 More preferably, 5 g / cm 3 As a result, for example, when the laser light transmitting member 200, the plurality of positive current collecting foils 52, and the positive current collector 44 are arranged along the vertical direction, the weight of the laser light transmitting member 200 makes it easier to reduce the gaps between the plurality of positive current collecting foils 52. The material that can constitute laser beam transmitting member 200 described above may be any material that is a main component of laser beam transmitting member 200, and may include, for example, a material doped with another element. The proportion of the doped element may be, for example, 5 mol % or less, 3 mol % or less, or 1 mol % or less of the total.

[0036] The welding step includes pressing laser light transmitting member 200 toward positive electrode current collector 44. This reduces the gaps between the foils of multiple laminated positive electrode current collector foils 52 arranged between laser light transmitting member 200 and positive electrode current collector 44.

[0037] The method for holding the laser light transmitting member 200 is not particularly limited. In this embodiment, the laser light transmitting member 200 is held using a jig 300 as shown in FIG. 3 . The jig 300 includes a lower plate 310, an upper plate 320, and a pressure control unit 330. Here, a positive electrode current collector 44 is disposed on the lower plate 310, a plurality of stacked positive electrode current collector foils 52 are disposed on the positive electrode current collector 44, and the laser light transmitting member 200 is disposed on the positive electrode current collector foil 52. The positive electrode current collector 44, the plurality of stacked positive electrode current collector foils 52, and the laser light transmitting member 200 are disposed between the lower plate 310 and the upper plate 320. The upper plate 320 is in contact with the upper surface of the laser light transmitting member 200. The upper plate 320 is not disposed on a portion of the upper surface of the laser light transmitting member 200 that passes through the laser light L.

[0038] The pressure control unit 330 is a part that adjusts the distance between the lower plate 310 and the upper plate 320. Here, the pressure control unit 330 is configured to be able to move the upper plate 320 toward the lower plate 310. By moving the upper plate 320 toward the lower plate 310, the upper plate 320 can press the laser light transmitting member 200 toward the positive electrode current collector 44 side.

[0039] It is preferable that by holding down the laser light transmitting member 200, gaps between the positive current collector foils 52 in the stacking direction of the portions 400 to be welded of the positive current collector foils 52 are substantially eliminated. For example, when the total thickness of the multiple stacked positive current collector foils 52 (the thickness of each positive current collector foil 52 multiplied by the number of stacked foils) is taken as 100%, the thickness of the positive current collector foils 52 in the stacking direction at the portions to be welded when the laser light transmitting member 200 is being held down is preferably 110% or less, more preferably 105% or less, and even more preferably 100% or less. This prevents the current collector foils from melting during laser welding. Note that there is no particular lower limit to the thickness of the positive current collector foils 52 in the stacking direction at the portions to be welded when the laser light transmitting member 200 is being held down, as long as the current collector foils are not broken by the pressure of the laser light transmitting member 200. Since the positive electrode current collector foil 52 is made of metal, it may become thinner than the original thickness, so the lower limit may be, for example, 90% or more, or 95% or more.

[0040] The pressure with which laser light transmitting member 200 is pressed (applied) against positive electrode current collector 44 is not particularly limited, but is, for example, 10N to 200N, and preferably 100N to 200N.

[0041] Next, while pressing the laser light transmitting member 200 toward the positive electrode current collector 44, laser light L is irradiated toward the to-be-welded portion 400 of the positive electrode current collector foil 52. Because the to-be-welded portion 400 is covered with the laser light transmitting member 200, the laser light L passes through the laser light transmitting member 200. It is preferable to irradiate the laser light L from the thickness direction of the laser light transmitting member 200, for example.

[0042] The type of laser beam L is not particularly limited and can be appropriately selected depending on the constituent materials of the current collecting foil and the current collector. Examples of the type of laser beam L include a YAG laser, a CO2 laser, a semiconductor laser, a disk laser, and a fiber laser. The irradiation diameter of the laser beam L can be set to, for example, 0.5 mm to 1.0 mm. The conditions of the laser beam L, such as the irradiation diameter, output, and irradiation time, can be set appropriately depending on, for example, the materials of the current collecting foil and current collector to be laser welded, the number of layers of current collecting foil, and the like.

[0043] The laser beam L may be irradiated onto a single point on the surface of the positive current collector foil 52, or onto two or more points. That is, the positive current collector foil 52 may have one or more to-be-welded portions 400. The to-be-welded portions 400 do not have to be points, but may be lines. When the to-be-welded portions 400 are lines, the laser may be irradiated while moving the laser beam L or the positive current collector foil 52 in a predetermined direction. In this case, the area of ​​the laser weld becomes larger, and the positive current collector foil 52 and the positive current collector 44 can be welded more firmly.

[0044] 4 is a schematic diagram showing a cross section of the vicinity of a laser weld after irradiation with laser light L. By irradiating the to-be-welded portion 400 of the positive current collector foil 52 with laser light L, a laser weld 90 is formed in the to-be-welded portion 400. The laser weld 90 is, for example, a portion where the positive current collector foil 52 and the positive current collector 44 are melted and solidified to be joined to each other. The laser weld 90 joins the multiple stacked positive current collector foils 52 from the top layer to the bottom layer (i.e., it is not melted). This effect may be achieved by using the laser light transmitting member 200 to press the to-be-welded portion 400 of the positive current collector foil 52 to reduce the gap between the foils.

[0045] A recess 92 may be formed in a portion corresponding to the portion to be welded 400 after irradiation with the laser beam L. The recess 92 is recessed from the positive current collector foil 52 side toward the positive current collector 44 side at the laser welded portion 90. The periphery of the recess 92 connects the positive current collector foil 52 and the positive current collector 44 by laser welding. The depth of the recess 92 may vary depending on the laser irradiation conditions (output, irradiation time, etc.). For example, the bottom 92b of the recess 92 may be located above (on the positive current collector foil 52 side) the boundary between the positive current collector foil 52 and the positive current collector 44 (the surface 44a of the positive current collector 44). The bottom 92b of the recess 92 may be located below (on the positive current collector 44 side) the boundary between the positive current collector foil 52 and the positive current collector 44. The position of the bottom 92b of the recess 92 can be confirmed, for example, by a cross-sectional SEM image taken along the stacking direction of the positive current collector foil 52.

[0046] The upper surface 90a of the laser weld 90 (the surface opposite the positive current collector 44; the surface on which the laser light transmitting member 200 was disposed) may be approximately parallel to the interface (surface 44a of the positive current collector 44) between the positive current collector foil 52 and the positive current collector 44. For example, the upper surface 90a of the laser weld 90 may be at an angle of 10° or less, 5° or less, or 1° or less, or may be 0° (i.e., parallel) relative to the interface between the positive current collector foil 52 and the positive current collector 44.

[0047] The above-described laser welding method can be similarly applied to the negative electrode 60. In this embodiment, the negative electrode current collector foil 72 and the negative electrode current collector 64 are laser welded together.

[0048] In the assembly process, for example, a positive electrode current collector 44 attached to the electrode body 20 is joined to a positive electrode terminal 42 attached to the sealing member 34, and a negative electrode current collector 64 attached to the electrode body 20 is joined to a negative electrode terminal 62 attached to the sealing member 34, thereby constructing an assembly including the sealing member 34, electrode body 20, positive electrode terminal 42, positive electrode current collector 44, negative electrode terminal 62, and negative electrode current collector 64. The attachment method for each component may be according to a known method, and the components can be joined by, for example, crimping, laser welding, ultrasonic welding, resistance welding, or the like. Note that the current collector and terminal of each electrode do not need to be joined after the welding process, and may be joined in advance before the welding process.

[0049] In the accommodation step, for example, the electrode body 20 is accommodated inside the case body 12. Here, the electrode body 20 of the assembled structure constructed above is accommodated in the case body 12, and the sealing member 34 is overlapped with the opening of the case body 12. At this time, an insulating film that has been formed into a bag or box shape in advance may be placed between the electrode body 20 and the case body 12.

[0050] In the sealing step, for example, the overlapping portion of the sealing member 34 and the case body 12 is welded to seal the case body 12. The welding method may be a conventionally known method, for example, laser welding.

[0051] In the liquid injection step, a non-aqueous electrolyte is injected according to a conventionally known method through an injection port provided in the case 30. Note that depending on the type of electricity storage device, the liquid injection step may be omitted.

[0052] Thereafter, for example, initial charging, aging treatment, and the like are performed under predetermined conditions to produce a usable non-aqueous electrolyte secondary battery 100 (electricity storage device).

[0053] The technology disclosed herein has been described above, but the above-described embodiment is merely an example. The technology can be implemented in various other forms. In other embodiments, if a technical feature is not essential, it can be deleted as appropriate.

[0054] Specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A positive electrode including a plurality of stacked positive electrode current collector foils and a positive electrode current collector connected to the stacked positive electrode current collector foils; a negative electrode including a plurality of stacked negative electrode current collector foils and a negative electrode current collector connected to the stacked negative electrode current collector foils; A method for manufacturing an electricity storage device comprising: overlapping the plurality of stacked current collecting foils with the current collector in at least one of the positive electrode and the negative electrode; disposing a laser light transmitting member made of YAG or Y2O3 on the overlapped current collecting foils; and irradiating the overlapped plurality of current collecting foils with a laser beam passing through the laser beam transmitting member while pressing the laser beam transmitting member toward the current collector, thereby welding the overlapped plurality of current collecting foils to the current collector; A method for manufacturing an electricity storage device, comprising: Item 2: The manufacturing method according to Item 1, wherein a test piece of the laser beam transmitting member having a thickness of 2 mm has a transmittance of 80% or more at the wavelength of the laser beam in the thickness direction. Item 3: The density of the laser light transmitting member is 4 g / cm 3 Item 3. The method for producing a product according to Item 1 or 2. Item 4: The manufacturing method according to any one of Items 1 to 3, wherein the thickness of the laser beam transmitting member at the portion through which the laser beam passes is 5 mm or less. Item 5: The manufacturing method according to any one of Items 1 to 4, wherein the laser beam transmitting member is in the form of a plate.

[0055] Test examples of the technology disclosed herein will be described below, although the technology disclosed herein is not limited to those shown in the test examples.

[0056] <Example> An aluminum plate-shaped positive electrode current collector and multiple aluminum positive electrode current collector foils were prepared. A 1-2 mm thick plate-shaped quartz glass (melting point: 1723°C, laser wavelength transmittance: 82%) was prepared as a laser beam transmitting member. A jig with the configuration shown in Figure 3 was prepared. The positive electrode current collector, positive electrode current collector foil, and laser beam transmitting member were set in the jig as in Figure 3, and the laser beam transmitting member was pressed toward the positive electrode current collector. While maintaining this state, a YAG laser (output: 2000 W, irradiation time: 0.005 s, laser heat input: 10 J) was irradiated from the thickness direction of the laser beam transmitting member through the laser beam transmitting member onto the surface of the positive electrode current collector foil, thereby laser welding the positive electrode current collector foil and the positive electrode current collector. A cross-sectional SEM image of the vicinity of the laser weld is shown in Figure 5.

[0057] <Comparative Example> An aluminum plate-shaped positive electrode current collector and multiple aluminum positive electrode current collector foils were overlapped and welded using the YAG laser without using a laser beam transmitting member. Figure 6 shows a cross-sectional SEM image of the vicinity of the laser weld.

[0058] In the comparative example shown in Fig. 6, the positive electrode current collector foil is melted and not bonded to the positive electrode current collector (the component at the bottom of the image). On the other hand, in the example shown in Fig. 5, the positive electrode current collector foil is not melted at the laser welded portion and is bonded to the positive electrode current collector.

[0059] Although specific examples of the present technology have been described above, the present technology is not limited to these. The technology described in the claims includes various modifications and alterations of the above-described exemplary embodiments. [Explanation of symbols]

[0060] 20 Electrode body 30 cases 40 positive electrode 42 Positive terminal 44 Positive electrode current collector 50 positive electrode plate 52 Positive electrode current collector foil 52a Positive electrode current collector foil exposed part 60 negative electrode 62 Negative terminal 64 Negative electrode current collector 70 negative electrode plate 72 Negative electrode current collecting foil 72a Exposed part of negative electrode current collector foil 80 Separator 90 Laser welded section 92 recess 100 Nonaqueous electrolyte secondary battery 200 Laser light transmitting member 300 Jig 400 Part to be welded

Claims

1. a positive electrode including a plurality of stacked positive electrode current collector foils and a positive electrode current collector connected to the stacked positive electrode current collector foils; a negative electrode including a plurality of stacked negative electrode current collector foils and a negative electrode current collector connected to the stacked negative electrode current collector foils; A method for manufacturing an electricity storage device comprising: preparing a jig including a lower plate and an upper plate, and arranging the current collector and the plurality of stacked current collecting foils in a superimposed manner on the lower plate in the order of the current collector and the plurality of stacked current collecting foils from the side closest to the lower plate, for at least one of the positive electrode and the negative electrode; YAG or Y ２ O ３ a plate-shaped laser beam transmitting member configured as follows: placing the upper plate on the laser light transparent member, and in a state in which the overlapping current collectors, the plurality of stacked current collecting foils, and the laser transparent member are sandwiched between the upper plate and the lower plate, while pressing the laser light transparent member toward the current collectors, irradiating a laser beam that passes through the laser light transparent member onto the overlapping plurality of current collecting foils, thereby welding the overlapping plurality of current collecting foils and the current collector; Including, The pressure applied to the laser beam transmitting member toward the current collector is 100 N or more and 200 N or less. A method for manufacturing an electricity storage device.

2. 2. The manufacturing method according to claim 1, wherein a test piece of the laser beam transmitting member having a thickness of 2 mm has a transmittance of 80% or more at the wavelength of the laser beam in the thickness direction.

3. The density of the laser light transmitting member is 4 g / cm ３ The manufacturing method according to claim 1 or 2, wherein the above is performed.

4. The manufacturing method according to claim 1 or 2, wherein the thickness of the laser beam transmitting member at the portion through which the laser beam passes is 5 mm or less.

5. The portion of the current collector that is superimposed on the plurality of stacked current collecting foils is a plate-like portion having a thickness of 0.5 mm or more and 3 mm or less, The thickness of each of the plurality of stacked current collecting foils is 5 μm or more and 20 μm or less, The method for manufacturing an electricity storage device according to claim 1 , wherein the plate-shaped portion of the current collector has a thickness four or more times greater than the total thickness of the plurality of stacked current collecting foils.

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