Method for manufacturing an electricity storage device

Abstract

To provide a manufacturing method of a power storage device, capable of suppressing melting of a current collector foil.SOLUTION: A manufacturing method disclosed herein is a manufacturing method of a power storage device, having a positive electrode 40 and a negative electrode 60. The method includes, in at least one electrode of the positive electrode 40 and the negative electrode 60, overlapping a plurality of current collector foils and a plurality of collectors that are laminated. The manufacturing method contains a step of arranging a laser beam transmission member 200 onto the overlapped current collector foils. Here, one part of the laser beam transmission member 200 is arranged at a position deviated from an end part of each overlapped current collector foil. In addition, the manufacturing method includes steps of: passing a laser beam L through the laser beam transmission member 200; irradiating a region containing the end part of the plurality of current collector foils overlapped with the laser beam; and welding the plurality of current collector foils and the plurality of collectors that are overlapped.SELECTED DRAWING: Figure 3

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 technology that includes temporary joining to improve adhesion of metal foils. Furthermore, Patent Documents 2 to 4 disclose technologies for laser welding in which a jig is used to press the periphery of the area of ​​the metal foil to be laser welded. [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] However, when multiple stacked current collecting foils and current collectors are laser welded together, depressions may occur mainly in the areas irradiated with the laser light. These depressions may reach the interface between the current collecting foils and current collectors, reducing the joint width where the current collectors are welded to the current collecting foils.

[0005] Therefore, a main object of the present disclosure is to provide a technique that can improve the bonding strength between a current collecting foil and a current collector. [Means for solving the problem]

[0006] The present disclosure provides a method for manufacturing an electricity storage device including 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. One aspect of the manufacturing method disclosed herein 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 on the overlapped current collector foils, where a portion of the laser light transmitting member is positioned to extend beyond the edge of the overlapped current collector foils. The manufacturing method further includes irradiating a laser light, which passes through the laser light transmitting member, onto a region of the overlapped plurality of current collector foils including the edge, thereby welding the overlapped plurality of current collector foils and the current collector.

[0007] Through research by the present inventors, it was discovered that one of the reasons why dents occur in the area irradiated with laser light when multiple stacked current collecting foils and a current collector are laser welded together is that metal vapor generated in the area irradiated with laser light remains in place. According to the above manufacturing method, since the laser light is irradiated to an area including the ends of multiple stacked current collecting foils, the metal vapor generated by laser welding does not remain in the area irradiated with laser light L, but can diffuse (escape) into the adjacent space. This makes it possible to suppress loss of weld width (joint section) in the laser weld formed between the current collecting foil and the current collector. [Brief explanation of the drawings]

[0008] [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 schematic diagram showing a laser welding method according to one embodiment. [Figure 4] FIG. 4 is a schematic diagram showing a cross section in the vicinity of a laser weld according to one embodiment. [Figure 5] FIG. 5 is a schematic diagram showing a laser welding method according to a modified example. [Figure 6] FIG. 6 is a cross-sectional SEM image of the vicinity of the laser weld in Example 1. [Figure 7] FIG. 7 is a cross-sectional SEM image of the vicinity of the laser weld in Example 2. [Figure 8] FIG. 8 is a cross-sectional SEM image of the vicinity of the laser weld in the comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] 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 of 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.

[0010] 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."

[0011] 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.

[0012] 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 60, 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 a negative electrode plate 70. Although not particularly limited, in this embodiment, the nonaqueous electrolyte secondary battery 100 is a lithium-ion secondary battery.

[0013] 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.

[0014] 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 longitudinally 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 disposed longitudinally 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).

[0015] The electrode body 20 has a laminated portion 52s in which a plurality of positive current collector foil exposed portions 52a are laminated in the thickness direction of the electrode body 20. The laminated portion 52s is formed, for example, by winding the positive current collector foil 52. A portion of the laminated portion 52s is joined to the positive current collector 44 by laser welding. That is, the laminated portion 52s and the positive current collector 44 are connected (joined) via a laser weld. The laser weld is provided, for example, at an end 52e of the laminated portion 52s (the end on the left side of the electrode body 20 in FIG. 1). The laser weld will be described later (see laser weld 90 in FIG. 4, which will be described later). The number of laminations of the positive current collector foil 52 (positive current collector foil exposed portions 52a) in the laminated portion 52s can be, for example, 10 to 120, or 20 to 100. The negative electrode current collector foil 72 has a laminated portion 72s in which a plurality of negative electrode current collector exposed portions 72a are laminated in the thickness direction of the electrode body 20. A portion of the laminated portion 72s is joined to the negative electrode current collector 64 by, for example, laser welding. That is, the laminated portion 72s and the negative electrode current collector 64 may be connected (joined) via a laser welded portion. The number of laminations of the negative electrode current collector foil 72 (negative electrode current collector exposed portions 72a) in the laminated portion 72s may be, for example, approximately 10 to 120 or 20 to 100. The joining between the current collector foil and the current collector in the negative electrode 60 may be the same as or different from that in the positive electrode 40. For example, the joining between the current collector foil and the current collector in the negative electrode 60 may be an ultrasonic joint, a resistance weld, or the like.

[0016] The positive current collector foil 52 may have a tab extending from an end portion in the short direction of the positive current collector foil 52. The shape of the tab is not particularly limited and may be, for example, trapezoidal or rectangular in a plan view. The tab may be provided with, for example, a positive current collector foil exposed portion 52a. In this case, the electrode body 20 may be provided with a laminated portion 52s in which a plurality of such tabs are laminated. The negative current collector foil 72 may also be provided with a tab. The configuration of the tab may be the same as that of the tab of the positive current collector foil 52 described above.

[0017] 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 weld is formed to be joined to the negative electrode current collector foil exposed portion 72a. 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 joined to the negative electrode current collector foil exposed portion 72a may be, for example, 0.5 to 3 mm.

[0018] 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.

[0019] 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 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 1.5Examples 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.

[0020] 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 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.

[0021] 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).

[0022] 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.

[0023] 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).

[0024] 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.

[0025] A method for manufacturing the electricity storage device disclosed herein will be described below. The manufacturing method disclosed herein includes, for example, a laminating step for laminating a current collecting foil, a current collector, and a laser light transmitting member for the positive electrode or the negative electrode, and a welding step for laser welding the current collecting foil and the current collector by irradiating the current collecting foil with a laser light passing through the laser light transmitting member. In addition to the welding step, the manufacturing method disclosed herein may also include, for example, a preparation step, an assembly step, a housing step, a sealing step, a liquid injection step, and the like, in any order as needed. One embodiment of the manufacturing method disclosed herein will be described below.

[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 plurality of stacked current collecting foils (exposed portions of the current collecting foils) with a current collector in at least one of the positive electrode 40 and the negative electrode 60, and disposing a laser light transmitting member on the plurality of stacked current collecting foils. In the following explanation, the positive electrode 40 will be used as an example.

[0028] Fig. 3 is a schematic diagram showing a laser welding method according to one embodiment. Fig. 4 is a schematic diagram showing a cross section in the vicinity of a laser weld according to one embodiment. Fig. 4 may be, for example, a schematic diagram of a laser weld formed by the laser welding method shown in Fig. 3. Fig. 4 is a schematic diagram showing the configuration in the vicinity of a laser weld 90 between the laminated portion 52s of the positive electrode current collector foil 52 and the positive electrode current collector 44 of the nonaqueous electrolyte secondary battery 100 described above.

[0029] 3, in this embodiment, a jig is used that includes a lower plate 310 and an upper plate 320. Although not shown in the figure, the lower plate 310 and the upper plate 320 are configured so that the distance between the lower plate 310 and the upper plate 320 can be adjusted (fixed) as desired.

[0030] In the overlapping step, for example, first, the positive current collector 44 is placed on the lower plate 310. Next, the laminated portion 52s of the positive current collector foil 52 of the electrode body 20 is overlapped on the surface 44a of the positive current collector 44. At this time, the end 52e of the laminated portion 52s in the winding axis WL direction of the electrode body 20 is placed on the positive current collector 44. Here, at the end 52e of the laminated portion 52s, the ends of the overlapping positive current collector foils 52 of the laminated portion 52s are aligned along the stacking direction of the laminated portion 52s.

[0031] The laminated portion 52s has a region to be welded 400. The region to be welded 400 is a region to be irradiated with laser light L in a welding step described below. In the present embodiment, the region to be welded 400 is a region that includes an end portion 52e of the laminated portion 52s. The region to be welded 400 is melted by irradiation with laser light L. This forms a laser weld that joins the laminated portion 52s and the positive electrode current collector 44.

[0032] Next, the laser light transmitting member 200 is placed on top (the uppermost surface) of the laminated portion 52s. At this time, a portion of the laser light transmitting member 200 is placed at a position that protrudes from the end portion 52e of the laminated portion 52s. In other words, the laser light transmitting member 200 is placed so that the laminated portion 52s is sandwiched between a portion of the laser light transmitting member 200 and the positive electrode current collector 44. The laser light transmitting member 200 is also placed so as to cover the intended welding region 400. This allows the laser light transmitting member 200 to directly press the intended welding region 400 from the stacking direction of the laminated portion 52s. This reduces gaps between the laminated foils of the laminated positive electrode current collecting foil 52 in the intended welding region 400. Note that when placing the laser light transmitting member 200, it is preferable to smooth out any wrinkles in the intended welding region 400 of the positive electrode current collecting foil 52 before placing the laser light transmitting member 200. This reduces gaps between the laminated foils of the laminated portion 52s and suppresses melting during laser welding.

[0033] As shown in FIG. 3 , a space 500 is provided between a portion of the laser beam transmitting member 200 that protrudes from the end 52e of the laminated portion 52s and the positive electrode current collector 44 that faces the portion, through which metal vapor A generated from the portion irradiated with the laser beam L can pass. The metal vapor A is generated, for example, from the positive electrode current collector foil 52 or the positive electrode current collector 44 that has been irradiated with the laser beam L or melted by the heat of the laser beam L. The direction of the arrow of the metal vapor A in the figure indicates an example of the direction in which the metal vapor A diffuses. The space 500 is preferably a space that communicates from the end 52e of the laminated portion 52s to the end of the laser beam transmitting member 200.

[0034] In the present technology, by providing the space 500, the metal vapor A does not remain in the portion irradiated with the laser light L, but can be diffused (escaped) into the space 500. In the present technology, the laser light L is irradiated onto a region including the end 52e of the laminated portion 52s, and therefore the metal vapor A is generated at the end 52e of the laminated portion 52s, and the metal vapor A is likely to diffuse into the space 500. According to the study by the present inventors, by diffusing (escaped) the metal vapor A from the portion irradiated with the laser light L, it is possible to suppress loss of the weld width (joined section) of the laser weld formed between the current collecting foil and the current collector (see test examples described later (e.g., FIGS. 6 to 8 described later)).

[0035] The shape of the laser light transmitting member 200 is not particularly limited, but in this embodiment, it is plate-shaped. The laser light transmitting member 200 can be circular, elliptical, rectangular, or polygonal in plan view. Since the laser light transmitting member 200 is plate-shaped, when the laser light transmitting member 200 is pressed against the positive electrode current collector 44, the positive electrode current collector foil 52 sandwiched between the laser light transmitting member 200 and the positive electrode current collector 44 can be pressed with a more uniform force, thereby more uniformly reducing the gap 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 region 400 of the laminated portion 52s (positive electrode current collector foil 52).

[0036] Next, the upper plate 320 is placed on the laser light transmitting member 200. As a result, the positive electrode current collector 44, the laminated portion 52s, and the laser light transmitting member 200 are sandwiched between the lower plate 310 and the upper plate 320. This allows the positive electrode current collector 44, the laminated portion 52s, and the laser light transmitting member 200 to be fixed. Furthermore, although not limited thereto, it is preferable that the stacking direction of the laminated portion 52s be along the vertical direction. This makes it easier to reduce gaps between the laminated foils of the laminated portion 52s due to gravity.

[0037] In the overlapping step, the order in which the positive electrode current collector 44, the laminated portion 52s, the laser light transmitting member 200, and the jig (here, the lower plate 310 and the upper plate 320) are overlapped is not particularly limited. In this embodiment, these are overlapped one by one in order starting from the lower plate 310, but, for example, they may be overlapped simultaneously, or items other than the jig may be overlapped and then fixed to the jig.

[0038] 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 laminated portions 52s.

[0039] 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 transmitting member 200 at the laser wavelength is, for example, 70% or more, preferably 75% or more, and more preferably 80% or more. The higher the transmittance of the laser light transmitting member 200 at the laser wavelength, the more accurately the laser light L reaches the to-be-welded region 400 of the positive electrode current collecting foil 52, thereby improving the laser welding accuracy. The laser 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 wavelength of 900 nm to 1200 nm (e.g., 1070 nm). Note that the transmittance refers to the transmittance of a portion of the laser light transmitting member 200 that passes the laser light L. In this specification, the transmittance of a laser wavelength is calculated as the ratio of the energy measured by a power meter when laser light is passed through a laser light transmitting member and irradiated onto the power meter, assuming that the energy measured by the power meter when laser light is irradiated onto the power meter for a predetermined period of time is 100%.

[0040] 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.

[0041] Examples of materials that constitute laser light transmitting member 200 include YAG (melting point: approximately 1970°C), Y2O3 (melting point: approximately 2425°C), sapphire (melting point: approximately 2040°C), and quartz glass (melting point: approximately 1723°C). Among the above examples, YAG and Y2O3 have a relatively high theoretical density. For example, when laser light transmitting member 200 is made of 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 laser light transmitting member 200 is placed on laminated unit 52s in the vertical direction, the weight of laser light transmitting member 200 makes it easier to reduce gaps between the foils of laminated unit 52s. 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.

[0042] In the welding step, for example, a region to be welded 400 of the laminated portion 52s is irradiated with laser light L. At this time, the laser light L is irradiated so that the laser light L passes through the laser light transmitting member 200 that covers the region to be welded 400. For example, the laser light L can be irradiated onto the region to be welded 400 from the thickness direction of the laser light transmitting member 200, thereby reducing the gap between the positive electrode current collecting foils 52 in the region to be welded 400.

[0043] When irradiating laser beam L, it is preferable to press laser beam transmitting member 200 toward positive electrode current collector 44. For example, pressing can be achieved by sandwiching positive electrode current collector 44, laminated portion 52s, and laser beam transmitting member 200 between lower plate 310 and upper plate 320. This reduces gaps between the foils in laminated portion 52s disposed between laser beam transmitting member 200 and positive electrode current collector 44, improving bonding strength.

[0044] By pressing the laser light transmitting member 200 toward the positive current collector 44, it is preferable to substantially eliminate gaps between the positive current collecting foils 52 in the lamination direction of the region 400 to be welded of the laminated portion 52s. For example, when the total thickness of the multiple stacked positive current collecting foils 52 in the laminated portion 52s (the thickness of each positive current collecting foil 52 multiplied by the number of stacked foils) is taken as 100%, the thickness of the laminated portion 52s in the lamination direction in the region 400 to be welded that is pressed by the laser light transmitting member 200 is preferably 110% or less, more preferably 105% or less, and even more preferably 100% or less. This suppresses melting of the current collecting foil during laser welding and improves bonding strength. Note that there is no particular lower limit to the thickness of the laminated portion 52s in the lamination direction in the region 400 to be welded that is pressed by the laser light transmitting member 200, as long as the current collecting foil does not break due to 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 its original thickness. Therefore, the lower limit of the thickness in the stacking direction of the laminated portion 52s in the region to be welded 400 pressed by the laser light transmitting member 200 may be, for example, 90% or more, or 95% or more.

[0045] The pressure with which laser light transmitting member 200 is pressed against positive electrode current collector 44 is not particularly limited, but is, for example, 10N to 200N, and preferably 100N to 200N.

[0046] The laser light L may be irradiated onto one region of the laminated portion 52s (positive electrode current collecting foil 52), or onto two or more separate locations. That is, the laminated portion 52s may have one or more regions 400 to be welded.

[0047] Furthermore, the region to be welded 400 may be a point or a line having a diameter approximately equal to the irradiation diameter of the laser beam L. When the region to be welded 400 is a line, the laser beam L or the positive current collector foil 52 may be irradiated with the laser while moving (scanning) 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.

[0048] When the laser beam L is irradiated onto the region to be welded 400, it is preferable to irradiate the laser beam L from the end 52e of the laminated portion 52s within the region to be welded 400. In other words, it is preferable to scan the laser beam L starting from the end 52e of the laminated portion 52s. This makes it easier for the metal vapor A to flow into the space 500 adjacent to the end 52e of the laminated portion 52s, improving the bondability.

[0049] Although the scanning direction of the laser light L is not particularly limited, it is preferable to scan the laser light L along the end 52e of the laminated portion 52s, for example. This allows any generated metal vapor A to easily flow into the space 500 adjacent to the end 52e of the laminated portion 52s, thereby improving the bonding performance.

[0050] 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.

[0051] 4, by irradiating a laser beam L onto a region 400 of the positive current collector foil 52 to be welded, a laser weld 90 is formed at a position corresponding to the region 400 (including the surrounding area). 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 together. 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).

[0052] 4, the laser weld 90 is provided at the end 52e of the laminate 52s (the end of the positive current collector foil 52). The laser weld 90 has an inclined portion 92 that is inclined outward from the top surface (the outer surface farther from the positive current collector 44) of the laminate 52s toward the positive current collector 44. The inclined portion 92 may be a structure formed when the positive current collector foil 52 at the end 52e of the laminate 52s melts, flows toward the positive current collector 44, and solidifies.

[0053] 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 in the same manner as the positive electrode 40.

[0054] 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.

[0055] In the accommodation step, for example, the electrode body 20 is accommodated inside the case body 32. Here, the electrode body 20 of the assembled structure constructed above is accommodated in the case body 32, and the sealing member 34 is overlapped with the opening of the case body 32. 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 32.

[0056] In the sealing step, for example, the overlapping portion of the sealing member 34 and the case body 32 is welded to seal the case body 32. The welding method may be a conventionally known method, for example, laser welding.

[0057] 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.

[0058] 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).

[0059] 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. The technology described in the claims includes various modifications and alterations of the above-described exemplary embodiments. For example, it is possible to replace part of the above-described embodiment with other modified embodiments, and it is also possible to add other modified embodiments to the above-described embodiment. Furthermore, if a technical feature is not described as essential, it can also be deleted as appropriate.

[0060] Modifications of the present technology will be described below. FIG. 5 is a schematic diagram of a laser welding method according to a modification. In the embodiment described above, as shown in FIG. 3, the ends of the positive current collector foils 52 stacked in the laminated portion 52s are aligned at the end 52e of the laminated portion 52s. However, an inclined portion 52b may be provided at the end 52e of the laminated portion 52s. The inclined portion 52b is provided so that the positive current collector foil 52 in the bottom layer of the laminated portion 52s (the positive current collector foil 52 in contact with the positive current collector 44) extends further than the positive current collector foil 52 in the top layer of the laminated portion 52s (the positive current collector foil 52 in contact with the laser light transmitting member 200). The inclined portion 52b is preferably configured so that the positive current collector foil 52 of the laminated portion 52s extends more in the stacking direction of the laminated portion 52s as it approaches the positive current collector 44. For example, the inclined portion 52b is provided in a stepped shape. At the inclined portion 52b, a gap (a space continuous with the space 500) is created between the extended positive electrode current collector foil 52 and the laser light transmitting member 200, which facilitates diffusion of the metal vapor A generated when irradiated with the laser light L. This suppresses loss of the joining width between the current collector foil and the current collector, improving the joining property.

[0061] In this modification, the laser beam L is irradiated onto a region including the inclined portion 52b of the end 52e of the laminated portion 52s. The direction in which the laser beam L is scanned is not particularly limited. For example, as shown in FIG. 5, it is preferable to scan the laser beam L along the inclined portion 52b from the extending portion (end) of the positive current collector foil 52 that is in contact with the positive current collector 44 to the end of the positive current collector foil 52 that is in contact with the laser beam transmitting member 200 (scanning the laser beam L in the direction of the arrow in FIG. 5 to the position of the laser beam L′ indicated by the dashed line). This facilitates diffusion of the metal vapor A, improving bonding. Note that the structure of the portion of the inclined portion 52b that is not irradiated with the laser beam L can be maintained inside the manufactured nonaqueous electrolyte secondary battery.

[0062] The angle of the inclined portion 52b with respect to the surface 44a on which the laminated portion 52s of the positive electrode current collector 44 is disposed is not particularly limited, but is, for example, 30° or greater, preferably 45° or greater, and more preferably 60° or greater. If the angle of the inclined portion 52b is too small, the overall thickness of the inclined portion 52b becomes small, which may make the positive electrode current collector foil 52 more susceptible to melting. The upper limit of the angle of the inclined portion 52b is not particularly limited, but may be, for example, 80° or less, 75° or less, or 70° or less. The angle of the inclined portion 52b refers to the angle formed by a line connecting the end of the topmost positive current collector foil 52 and the end of the bottommost positive current collector foil 52, and the surface 44a of the positive current collector 44, in a cross section along the extension direction of the positive current collector foil 52.

[0063] In the above-described embodiment, the upper plate 320 is disposed on the region of the laser light transmitting member 200 in contact with the laminated unit 52s, and is not disposed on the portion of the laser light transmitting member 200 that extends beyond the end 52e of the laminated unit 52s. However, this is not limited thereto. The upper plate 320 may be disposed on the region of the laser light transmitting member 200 in contact with the laminated unit 52s, as well as on the portion of the laser light transmitting member 200 that extends beyond the end 52e of the laminated unit 52s. For example, two or more upper plates 320 may be prepared, and an upper plate having an area (e.g., a through hole) through which the laser light L can pass may be prepared. This can suitably reduce gaps between the foils of the laminated unit 52s at the end 52e of the laminated unit 52s.

[0064] 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.

[0065] Example 1 An aluminum plate-shaped positive electrode current collector and multiple aluminum positive electrode current collector foils were prepared. A 1 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. As in Figure 3, the positive electrode current collector, multiple positive electrode current collector foils, and the laser beam transmitting member were stacked and set in the jig, 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 edge of the positive electrode current collector foil, and the YAG laser was scanned along the edge of the positive electrode current collector foil. This resulted in laser welding between the positive electrode current collector and the positive electrode current collector. Figure 6 shows a cross-sectional SEM image of the vicinity of the laser weld. In FIG. 6, the area surrounded by a thick dashed line indicates the laser welded portion (the same applies to FIGS. 7 and 8).

[0066] <Example 2> The same positive electrode current collector, multiple positive electrode current collector foils, and laser light transmitting member as in Example 1 were prepared. The multiple positive electrode current collector foils were stacked so that their ends formed a stepped inclined portion. As in FIG. 5, the positive electrode current collector, multiple positive electrode current collector foils, and laser light transmitting member were stacked and set in a jig. A YAG laser was scanned under the same conditions as in Example 1 from the bottom end (the end of the positive electrode current collector foil that contacts the positive electrode current collector) to the top end (the end of the positive electrode current collector foil that contacts the laser light transmitting member) of the inclined portions of the multiple positive electrode current collector foils, performing laser welding. FIG. 7 shows a cross-sectional SEM image of the multiple positive electrode current collector foils 52 near the laser weld, taken in a direction perpendicular to the direction in which the inclined portions extend.

[0067] <Comparative Example> Laser welding was performed in the same manner as in Example 1, except that the YAG laser was irradiated not at the edge of the positive electrode current collector foil but at the center of the positive electrode current collector foil (a region not including the edge). A cross-sectional SEM image of the vicinity of the laser weld is shown in Figure 8.

[0068] As shown in Fig. 8, in the comparative example, the positive electrode current collector foil was not melted, but a recess was formed in the laser weld that was recessed from the positive electrode current collector foil side toward the positive electrode current collector side. The recess was formed beyond the surface of the positive electrode current collector on which the positive electrode current collector foil was located, resulting in a section where part of the joint between the positive electrode current collector foil and the positive electrode current collector was lost. On the other hand, as shown in Figs. 6 and 7, in examples 1 and 2, no recess was formed in the laser weld like in the comparative example, and the joint between the positive electrode current collector foil and the positive electrode current collector was not lost.

[0069] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Section 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 on the overlapped current collecting foils, wherein a portion of the laser light transmitting member is disposed at a position that protrudes from an end of the overlapped current collecting foils; and irradiating a laser beam onto a region including the end portions of the overlapping plurality of current collecting foils by passing the laser beam through the laser beam transmitting member, thereby welding the overlapping plurality of current collecting foils and the current collector; A method for manufacturing an electricity storage device, comprising: Item 2: The manufacturing method according to Item 1, wherein the welding is performed while pressing the laser beam transmitting member toward the current collector. Item 3: The manufacturing method according to item 1 or 2, wherein the end of the overlapped current collecting foil has an inclined portion configured such that the current collecting foil in contact with the current collector extends further than the current collecting foil in contact with the laser light transmitting member. Item 4: The manufacturing method according to Item 3, which includes performing the welding by scanning the laser light from an extended portion of the current collecting foil that contacts the current collector side of the inclined portion to a portion of the inclined portion that contacts the laser light transmitting member. Item 5: The manufacturing method according to any one of Items 1 to 4, 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 6: The manufacturing method according to any one of Items 1 to 5, wherein the thickness of the laser beam transmitting member at the portion through which the laser beam passes is 5 mm or less. Section 7: 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; An electricity storage device comprising: at least one of the positive electrode and the negative electrode has a laser welded portion where the current collector foil is joined to the current collector in a state where a plurality of the current collector foils are stacked, Here, the laser welded portion is provided at an end portion of the current collecting foil. Energy storage device. Section 8: the current collector and the plurality of stacked current collecting foils are stacked in the stacking direction, Item 8. The electricity storage device according to item 7, wherein the end of the plurality of stacked current collecting foils on the side where the laser welded portion is provided includes an inclined portion in which the current collecting foil extends in the stacking direction as it approaches the current collector. [Explanation of symbols]

[0070] 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 52b Slope 52e end 52s laminated section 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 Slope 100 Nonaqueous electrolyte secondary battery 200 Laser light transmitting member 400 Planned welding area

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: overlapping the plurality of stacked current collecting foils and the current collector in at least one of the positive electrode and the negative electrode; disposing a laser light transmitting member on the overlapped current collecting foils, wherein a portion of the laser light transmitting member is disposed at a position that protrudes from an end of the overlapped current collecting foils; and irradiating a laser beam onto a region including the end portions of the overlapping plurality of current collecting foils by passing the laser beam through the laser beam transmitting member, thereby welding the overlapping plurality of current collecting foils and the current collector; A method for manufacturing an electricity storage device, comprising:

2. The manufacturing method according to claim 1 , wherein the welding is performed while pressing the laser beam transmitting member toward the current collector.

3. 3. The manufacturing method according to claim 1, wherein the end of the overlapping current collecting foil has an inclined portion configured so that the current collecting foil in contact with the current collector extends further than the current collecting foil in contact with the laser light transmitting member.

4. 4. The manufacturing method according to claim 3, further comprising: performing the welding by scanning the laser light from an extended portion of the current collecting foil that is in contact with the current collector side of the inclined portion to a portion of the inclined portion that is in contact with the laser light transmitting member.

5. 3. 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.

6. 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.

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