Manufacturing method for secondary battery

Abstract

To provide a manufacturing method for a secondary battery, in which the occurrence of liquid leak can be suppressed.SOLUTION: A method for manufacturing a secondary battery including a plurality of stacked bipolar electrodes each including a current collector, a first active material layer stacked on one surface of the current collector, and a second active material layer stacked on the other surface of the current collector includes the steps of: manufacturing a spacer integrated sealing member in which a sealing member and a spacer member are welded together; and disposing the sealing member of the manufactured spacer integrated sealing member on one surface and another sealing member on the other surface at an outer peripheral end part of the current collector and additionally welding the sealing member and the other sealing member.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present disclosure relates to a method for manufacturing a secondary battery. [Background technology]

[0002] Patent Document 1 discloses a bipolar battery in which a seal member for a current collector has a low-rigidity region. Patent Document 2 discloses that a resin member constituting a frame that holds the peripheral portion of the current collector has a core portion with a smaller thermal expansion coefficient than the resin member. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-045564 A [Patent Document 2] JP 2018-106962 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, liquid leakage sometimes occurs between the spacer and the sealant at the outer periphery of the sealing portion.

[0005] Therefore, an object of the present disclosure is to provide a method for manufacturing a secondary battery capable of suppressing the occurrence of electrolyte leakage. [Means for solving the problem]

[0006] As a result of intensive research, the inventors found that the occurrence of such leakage is due to the fact that, in the sealing arranged around the outer periphery of the secondary battery, heat is applied to the current collector and the sealant / spacer material over two processes, the process of welding the sealant to the current collector and the process of welding the spacer material to the sealant, and the difference in the linear expansion coefficient between these processes exerts a force on the current collector, causing wrinkles. Based on this finding, the inventors embodied a solution and completed the invention according to the present disclosure.

[0007] The present application discloses a method for manufacturing a secondary battery including a plurality of stacked bipolar electrodes each including a current collector, a first active material layer stacked on one side of the current collector, and a second active material layer stacked on the other side of the current collector, the method including the steps of: preparing a spacer-integrated sealing member by integrating a sealing member and a spacer member by welding; and placing the sealing member of the prepared spacer-integrated sealing member on one side, at the outer peripheral end of the current collector, and placing another sealing member on the other side, and further welding the sealing member to the other sealing member.

[0008] The method may further include a step of welding a separator so as to bridge the second active material layer and another sealing member. Effect of the Invention

[0009] According to the manufacturing method of the secondary battery disclosed herein, the sealing member and the spacer member are integrally formed and then welded to the current collector, thereby reducing the number of times that heat is applied to the sealing member and the spacer member during the manufacture of the secondary battery, thereby reducing expansion and contraction due to heat, suppressing the occurrence of wrinkles in the current collector, and suppressing the occurrence of liquid leakage. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a schematic external view of a secondary battery 10. As shown in FIG. [Diagram 2] FIG. 2 is a cross-sectional view that diagrammatically illustrates the electricity storage module 20. As shown in FIG. [Diagram 3] FIG. 3 is a cross-sectional view illustrating one embodiment of the first seal member 31. As shown in FIG. [Figure 4] FIG. 4 is a cross-sectional view for explaining an example of the spacer-integrated second seal member 32. As shown in FIG. [Diagram 5] FIG. 5 is a diagram for explaining a conventional manufacturing example. [Figure 6] FIG. 6 is a diagram illustrating a manufacturing example of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, the present disclosure will be described with reference to the accompanying drawings. For ease of understanding, some of the repeated reference symbols may be omitted. In addition, the drawings are shown to indicate the corresponding directions of a three-dimensional orthogonal coordinate system (x-axis, y-axis, z-axis).

[0012] 1. Structure of secondary batteries First, the structure of a secondary battery according to one example of the present disclosure will be described. Fig. 1 is a side view showing a schematic diagram of the secondary battery according to the example. Although Fig. 1 is a side view, hatching is added to make it easier to distinguish between components. The secondary battery 10 can be used as a battery mounted on a vehicle such as a hybrid vehicle or an electric vehicle. The secondary battery 10 includes a module stack 11, connection members 12 and 13, a pair of end plates 14, and a fastening member 15.

[0013] 1.1. Module stack 11 The module stack 11 is formed by stacking a plurality of power storage modules 20 and a plurality of conductive plates 19 alternately in the z-axis direction. The number of times the stacking is repeated is set appropriately depending on the required battery capacity, the arrangement space for the secondary batteries, etc. Both ends of the module stack 11 in the stacking direction are made of conductive plates 19.

[0014] 1.1.1.Conductive plate The conductive plate 19 is electrically connected to the electrodes constituting the power storage modules 20, and electrically connects the two power storage modules 20 arranged with the conductive plate 19 in between. Here, adjacent power storage modules 20 are connected in series by the conductive plate 19.

[0015] A flow path (not shown) for circulating a cooling medium such as air may be provided inside the conductive plate 19. By circulating a cooling medium through the flow path in the conductive plate 19, the conductive plate 19 also functions as a heat exchanger that discharges heat generated in the power storage module 20 to the outside.

[0016] 1.1.2. Energy storage module The power storage module 20 is a flat-plate-shaped cell that is thinner in the z-axis direction than in the x-axis and y-axis directions. Fig. 2(a) shows a schematic cross-sectional view of the layer structure of the power storage module 20. The power storage module 20 of this embodiment is a bipolar lithium-ion secondary battery. The energy storage module 20 includes an electrode stack 21 formed by stacking a plurality of bipolar electrodes 22, and a plurality of sealing bodies 30 provided for each bipolar electrode 22. In the electrode stack 21, a plurality of bipolar electrodes 22 are stacked along the z-axis direction, and a sealing body 30 is disposed for each bipolar electrode 22. Fig. 2(b) shows one bipolar electrode 22 and the sealing body 30 provided thereon, extracted from Fig. 2(a).

[0017] 1.1.2a. Electrode stack [Bipolar electrode] In the following explanation of each component, the terms "upper surface" and "lower surface" may be used, but in the coordinate system shown in Figures 1 and 2, the "upper surface" refers to the xy surface on the larger side in the z-axis direction, and the "lower surface" refers to the xy surface on the smaller side in the z-axis direction. Although these terms are used for convenience, the "upper surface" can also be referred to as the "first surface" and the "lower surface" as the "second surface." The bipolar electrode 22 includes a current collector 23, a positive electrode active material layer 24 (first active material layer) provided on the lower surface of the current collector 23, a negative electrode active material layer 25 (second active material layer) provided on the upper surface of the current collector 23, and a separator 26.

[0018] In this embodiment, the current collector 23 is a sheet-like conductive member having a rectangular shape in a plan view (xy plane), and the current collector 23 is made of, for example, a metal foil or an alloy foil. Examples of the metal foil include copper foil, aluminum foil, titanium foil, and nickel foil. Examples of the alloy foil include stainless steel foil (e.g., SUS304, SUS316, SUS301, etc., as specified in JIS G 4305:2015), plated steel plate (e.g., cold-rolled steel plate (SPCC, etc.) as specified in JIS G 3141:2005), and plated stainless steel plate. The alloy foil may be an alloy foil of the metals exemplified as the material of the metal foil. The current collector 23 may be formed by integrating or laminating a plurality of metal foils, or may be formed by plating another metal on the surface of a metal foil. The current collector 23 may be, for example, a foil in which an aluminum foil and a copper foil are laminated together, so that the upper surface is an aluminum layer and the lower surface is a copper layer.

[0019] The positive electrode active material layer 24 constitutes the positive electrode of the bipolar electrode 22, and in this embodiment is disposed on the lower surface of the current collector 23 via an adhesive layer such as acetylene black. The positive electrode active material layer 24 can include a positive electrode active material, a conductive assistant, and a binder. Examples of the positive electrode active material include a composite oxide, metallic lithium, and sulfur. The composition of the composite oxide includes at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, and lithium. Examples of the composite oxide include olivine-type lithium iron phosphate (LiFePO4), LiCoO2, and LiNiMnCoO2. The binder serves to bind the active material or conductive assistant to the surface of the current collector 23 and maintain the conductive network in the electrode. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resins, acrylic resins containing monomer units such as acrylic acid and methacrylic acid, styrene-butadiene rubber (SBR), carboxymethyl cellulose, alginates such as sodium alginate and ammonium alginate, water-soluble cellulose ester crosslinked bodies, and starch-acrylic acid graft polymers. These binders can be used alone or in combination. Examples of the conductive assistant include acetylene black, carbon black, and graphite.

[0020] The negative electrode active material layer 25 constitutes the negative electrode of the bipolar electrode 22, and is disposed on the upper surface of the current collector 23 in this embodiment. The negative electrode active material layer 25 may contain a negative electrode active material, a conductive additive, and a binder. The conductive additive and the binder may be considered to be similar to those of the positive electrode active material layer 24. Examples of the negative electrode active material include carbon such as graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, and soft carbon, metal compounds, elements capable of being alloyed with lithium or compounds of such elements, boron-doped carbon, etc. Examples of elements capable of being alloyed with lithium include silicon and tin.

[0021] The separator 26 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains an electrolyte, and is placed on the upper surface of the negative electrode active material layer 25 in this embodiment. Examples of materials constituting the separator 26 include polypropylene, polyethylene, polyolefin, polyester, etc. The separator 26 may have a single-layer structure or a multi-layer structure. Examples of the electrolyte absorbed and held in the separator 26 include a liquid electrolyte (electrolytic solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, and a polymer gel electrolyte containing an electrolyte held in a polymer matrix. When the separator 26 is impregnated with an electrolyte, known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 can be used as the electrolyte salt. In addition, known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers can be used as the non-aqueous solvent.

[0022] The current collector 23, the positive electrode active material layer 24, the negative electrode active material layer 25, and the separator 26 are configured to have different sizes in a plan view. More specifically, the current collector 23 is the largest, the separator 26 is the next largest, the negative electrode active material layer 25 is the next largest, and the positive electrode active material layer 24 is the smallest. As can be seen from FIG. 2, the current collector 23, the positive electrode active material layer 24, the negative electrode active material layer 25, and the separator 26 are arranged with their centers aligned in a plan view, and the difference in size is expressed by the degree of protrusion (overhang) of the edges. Therefore, the edge of the current collector 23 protrudes the most, and the edges of the separator 26, the negative electrode active material layer 25, and the positive electrode active material layer 24 protrude in this order so as to be inside the current collector 23.

[0023] To form the positive electrode active material layer 24 and the negative electrode active material layer 25 on the current collector 23, a conventionally known method such as roll coating, die coating, dip coating, doctor blade, spray coating, curtain coating, etc. is used. Specifically, an active material, a solvent, and optionally a binder and a conductive assistant are mixed to produce a slurry-like active material layer forming composition, which is then applied to the upper and lower surfaces of the current collector 23 and dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water.

[0024] [Layer structure of electrode laminate] In the electrode laminate 21, bipolar electrodes 22 adjacent to each other in the z-axis direction (stacking direction) are laminated such that the positive electrode active material layer 24 of one bipolar electrode 22 and the separator 26 of the other bipolar electrode 22 overlap.

[0025] In addition, the electrode stack 21 has a positive terminal electrode 27 at its upper end (the larger side in the z-axis direction) and a negative terminal electrode 28 at its lower end (the smaller side in the z-axis direction) at the stacking direction end of the stack made of bipolar electrodes 22. The positive terminal electrode 27 has a current collector 23 and a positive active material layer 24 provided on the lower surface of the current collector 23, with the positive active material layer 24 laminated on the adjacent bipolar electrode 22 and the current collector 23 laminated on its upper surface. The negative terminal electrode 28 has a current collector 23, a negative electrode active material layer 25 provided on the upper surface of the current collector 23, and a separator 26 laminated on the upper surface thereof. The separator 26 is laminated on the adjacent bipolar electrode 22, and the negative electrode active material layer 25 is laminated on its lower surface, and the current collector 23 is laminated on its lower surface. The positive terminal electrode 27 and the negative terminal electrode 28 are each laminated on the adjacent conductive plate 19 (see FIG. 1) with the current collector 23 thereon.

[0026] 1.1.2b.Encapsulation The sealing body 30 is a member that is disposed on the outer peripheral end of the bipolar electrode 22 to seal the bipolar electrode 22. This also serves to seal the space between adjacent bipolar electrodes 22 in the stacking direction. In this embodiment, the sealing body 30 has a first sealing member 31 and a second sealing member 32 integrated with a spacer.

[0027] [First sealing member] The first sealing member 31 is a frame-shaped member that is disposed along the outer peripheral end (outer edge) of the bipolar electrode 22. Specifically, as can be seen from Figures 2(a) and 2(b), the first sealing member 31 is disposed and joined between the upper surface of the current collector 23 and the lower surface of the separator 26 at the outer peripheral end of the bipolar electrode 22, thereby disposing the negative electrode active material layer 25 within the frame. In this embodiment, a predetermined gap is provided between the inner edge of the first sealing member 31 and the negative electrode active material layer 25 to form a space S1. On the other hand, the outer edge of the first sealing member 31 is configured so that the first sealing member 31 protrudes outward beyond the current collector 23.

[0028] The first sealing member 31 has electrical insulation properties and can be made of a known material, for example, an electrolyte-resistant resin material such as acid-modified polyethylene (acid-modified PE), acid-modified polypropylene (acid-modified PP), polyethylene, or polypropylene.

[0029] The first seal member 31 can be made of known materials as described above, but in this embodiment, the first seal member 31 is made as follows. An explanatory diagram is shown in Fig. 3. Fig. 3 is a cross-sectional view of Fig. 2(b) focusing on the first seal member 31. As can be seen from Fig. 3, in this embodiment, the first seal member 31 is made up of a resin member 31a and a low linear expansion coefficient member 31b.

[0030] The resin member 31a forms the outer shape of the first seal member 31, and is the same as a known first seal member except that the low linear expansion coefficient member 31b is provided inside the resin member 31a. Therefore, the material thereof can be an electrolyte-resistant resin material such as acid-modified polyethylene (acid-modified PE), acid-modified polypropylene (acid-modified PP), polyethylene, or polypropylene, as described above.

[0031] The low linear expansion coefficient member 31b is a low linear expansion coefficient material contained in the resin member 31a. The low linear expansion coefficient member 31b is also a frame-shaped member extending along the frame shape of the first seal member 31, and is smaller in the z-axis direction than in the x-axis and y-axis directions. The material constituting the low linear expansion coefficient member 31b is a material having a linear expansion coefficient lower than that of the material constituting the resin member 31a. For example, when acid-modified polyethylene (a type of polyolefin) is used as the resin member 31a, the linear expansion coefficient should be lower than that of the resin member 31a. Specific examples of the material include metal materials such as aluminum, copper, nickel, stainless steel, and iron, ceramic materials such as glass wool, silica cloth, rock wool, alkaline earth silicate wool, and alumina fiber, and resins such as cellulose, polytetrafluoroethylene, and polyimide that have a linear expansion coefficient lower than that of polyolefin resin.

[0032] In the first seal member 31 having such a resin member 31a and a low linear expansion coefficient member 31b, the thickness (size in the z-axis direction, thinnest part) of the resin member on the upper and lower surfaces of the low linear expansion coefficient member 31b in the thickness direction shown by Tj in Fig. 3 is preferably 5 µm or more, more preferably 10 µm or more. If the thickness of the resin member is less than 5 µm, there is a risk that the adhesive strength will be insufficient when bonding (heat sealing) for sealing is performed. 3 is preferably 5% or more, and more preferably 10% or more, of the thickness (size in the z-axis direction, thinnest part) Tz of the first seal member 31. By making it 5% or more, the linear expansion coefficient of the entire first seal member 31 can be more reliably reduced by the low linear expansion member 31b.

[0033] The first seal member 31, in which the resin member 31a contains the low linear expansion coefficient member 31b, can be manufactured by so-called extrusion lamination. That is, while feeding a strip-shaped base material, a molten material constituting one half of the thickness direction of the resin member 31a is supplied onto the base material, and the material to become the strip-shaped low linear expansion coefficient member 31b is sequentially layered on the molten material. Further, the molten material constituting the other half of the thickness direction of the resin member 31a is supplied onto the material to become the low linear expansion coefficient member 31b, and cooled.

[0034] [Spacer integrated second seal member] The spacer-integrated second sealing member 32 is a frame-shaped member that is disposed along the outer peripheral edge of the bipolar electrode 22. Specifically, as can be seen from Figures 2(a) and 2(b), the spacer-integrated second sealing member 32 is disposed and joined between the current collector 23 and the upper surface of the separator 26 of the adjacent bipolar electrode 22 below, at the outer peripheral edge of the bipolar electrode 22, thereby disposing the positive electrode active material layer 24 within the frame. In this embodiment, the outer edge of the spacer-integrated second seal member 32 is configured so that the spacer-integrated second seal member 32 protrudes outward beyond the current collector 23 . In the spacer-integrated second seal member 32, the second seal member 33 and the spacer member 34 are integrally formed in the z-axis direction.

[0035] The second sealing member 33 is a frame-shaped member that is disposed along the outer peripheral edge of the bipolar electrode 22. Specifically, as can be seen from Figures 2(a) and 2(b), the second sealing member 33 is combined with the spacer member 34, so that the second sealing member 33 is disposed and joined between the lower surface of the current collector 23 and the upper surface of the spacer member 34 at the outer peripheral edge of the bipolar electrode 22, and the positive electrode active material layer 24 is disposed within the frame. In this embodiment, a predetermined gap is provided between the inner edge of the second seal member 33 and the positive electrode active material layer 24 to form a space S2. On the other hand, the outer edge of the second seal member 33 is configured so that the second seal member 33 protrudes outward from the current collector 23. The inner edge and outer edge of the second seal member 33 are positioned at approximately the same positions as the inner edge and outer edge of the first seal member 31 in the xy directions.

[0036] The spacer member 34 is a frame-shaped member that is disposed along the outer peripheral edge of the bipolar electrode 22. Specifically, as can be seen from Figures 2(a) and 2(b), the spacer member 34 is combined with the second seal member 33, so that the spacer member 34 is disposed and joined between the lower surface of the second seal member 33 and the upper surface of the separator 26 of the adjacent bipolar electrode 22 at the outer peripheral edge of the bipolar electrode 22, and the positive electrode active material layer 24 is disposed within the frame. In this embodiment, the inner edge of the spacer member 34 extends so as to contact the positive electrode active material layer 24, and protrudes toward the positive electrode active material layer 24 in the xy directions further than the inner edge of the second seal member 33. On the other hand, the outer edge of the spacer member 34 protrudes outward from the current collector 23, and is positioned at approximately the same position as the outer edge of the second seal member 33 in the xy directions.

[0037] The second sealing member 33 and the spacer member 34 (i.e., the spacer-integrated second sealing member 32) are electrically insulating and can be made of a known material, such as an electrolyte-resistant resin material such as acid-modified polyethylene (acid-modified PE), acid-modified polypropylene (acid-modified PP), polyethylene, or polypropylene.

[0038] The spacer-integrated second seal member 32 can be made of known materials as described above, but in this embodiment, it may be made of a resin material and a material with a low linear expansion coefficient as described for the first seal member 31. An explanatory diagram is shown in Figure 4. Figure 4 is a cross-sectional view of Figure 2(b) focusing on the spacer-integrated second seal member 32. FIG. 4(a) shows an example in which both the second seal member 33 and the spacer member 34 are made of resin members 33a, 34a and low linear expansion coefficient members 33b, 34b. FIG. 4(b) shows an example in which the spacer member 34 is made up of a resin member 34a and a low linear expansion coefficient member 34b. FIG. 4(c) shows an example in which the second seal member 33 is made of a resin member 33a and a low linear expansion coefficient member 33b.

[0039] The material, shape, and preparation of the resin members 33a, 34a and the low expansion coefficient members 33b, 34b can be considered to be similar to those of the resin members 31a, 31b described above. However, the spacer-integrated second seal member 32 as a whole preferably has a linear expansion coefficient of 5 times or less than that of the current collector 23. More preferably, it is 3 times or less. This makes it possible to more reliably prevent the occurrence of wrinkles in the current collector 23, which will be described later. The second seal member 33 and the spacer member 34 can be joined together by, for example, heat lamination (heat roll).

[0040] [Encapsulation composition] The first seal member 31 is joined to the separator 26 at a portion of its upper surface that contacts the separator 26, and is joined to the current collector 23 at a portion of its lower surface that contacts the current collector 23. In addition, a portion of the lower surface of the first seal member 31 that protrudes outward beyond the current collector 23 is joined to a portion of the upper surface of the second seal member 33 of the spacer-integrated second seal member 32 that protrudes outward beyond the current collector 23. The spacer-integrated second seal member 32 is joined to the current collector 23 at a portion of the upper surface of the second seal member 33 that contacts the current collector 23. In addition, a portion of the upper surface of the second seal member 33 that protrudes outward beyond the current collector 23 is joined to a portion of the lower surface of the first seal member 31 that protrudes outward beyond the current collector 23.

[0041] In a configuration in which multiple bipolar electrodes 22 and sealing bodies 30 are stacked, a portion of the underside of the spacer member 34 of the spacer-integrated second sealing member 32 provided in one sealing body 30, which protrudes outward beyond the separator 26, is overlapped and joined to a portion of the underside of the first sealing member 31 provided in an adjacent sealing body 30, which protrudes outward beyond the separator 26.

[0042] It is also preferable that at least one of the first seal member 31, the second seal member 33, and the spacer member 34 is made of a resin member and a low linear expansion coefficient member. Among them, it is more preferable that at least the spacer member 34 is made of a resin member 34a and a low linear expansion coefficient member 34b. If the spacer member 34 is made of the resin member 34a and the low linear expansion coefficient member 34b, the effect can be more reliably achieved even if the first seal member 31 and the second seal member 33 are not made of a resin member and a low linear expansion coefficient member (even if they are made of only resin).

[0043] 1.2.Connecting members Returning to FIG. 1, the connecting members 12 and 13 will be described. The connection members 12 and 13 are conductive members that function as a positive electrode terminal and a negative electrode terminal of the secondary battery 10. The connection members 12 and 13 are electrically connected to a conductive plate 19 that serves as a positive electrode, and the connection member 13 is electrically connected to a conductive plate 19 that serves as a negative electrode. The connection members 12 and 13 are formed of, for example, a metal material or an alloy material. Examples of the metal material include copper, aluminum, titanium, and nickel. Examples of the alloy material include stainless steel and alloys of the above metal materials.

[0044] 1.3. End plates, fastening members The pair of end plates 14 and the fastening members 15 are restraining members that apply a restraining load to the module stack 11 in the stacking direction. The pair of end plates 14, 14 are plate-like members arranged to sandwich the module stack 11 from both sides in the stacking direction, and are formed, for example, from metal plates. Examples of the metal material constituting the end plates 14 include alloys such as copper, aluminum, titanium, nickel, and stainless steel. As can be seen from FIG. 1, the end plate 14 is larger in the xy directions than the module stack 11 , and its outer periphery end projects beyond the module stack 11 . In addition, an electrical insulating sheet 11 a is disposed between the end plate 14 and the module stack 11 .

[0045] The fastening members 15 are composed of, for example, bolts 15a and nuts 15b. The bolts 15a are passed through insertion holes (not shown) provided in the protruding portions of the outer circumferential ends of the pair of end plates 14, and the pair of end plates 14, 14 are fastened together by screwing in the nuts 15b. As a result, a restraining load is applied to the module stack 11 in the stacking direction via the pair of end plates 14, 14.

[0046] 2. Effects etc. According to the secondary battery 10 described above, in the sealing portion 30, as will be described later in the manufacturing method, the second seal member 33 and the spacer member 34 are already formed before being placed in the secondary battery. Since they are integrated as the spacer-integrated second sealing member 32, the number of times that heat is applied to the sealing member and spacer member during the manufacture of the secondary battery 10 can be reduced (for example, from two times to one time), thereby reducing expansion and contraction due to heat, suppressing the occurrence of wrinkles in the current collector, and thereby suppressing the occurrence of liquid leakage.

[0047] Furthermore, by disposing a low linear expansion coefficient material in at least a part of the components constituting the plug 30, the difference in linear expansion coefficient between the current collector 23 and the entire plug 30 can be reduced, and further the occurrence of wrinkles in the current collector 23 can be suppressed.

[0048] 3. Manufacturing method of secondary battery The method for manufacturing a secondary battery will be described below. Here, the method for manufacturing a secondary battery will be described with a focus on the steps related to bonding of the sealing body 30. The other steps in the method for manufacturing a secondary battery are publicly known.

[0049] 3.1. Conventional examples Before describing the manufacturing method of the present disclosure, a conventional method will be described. A diagram for explanation is shown in Fig. 5. Fig. 5 is a view from the same perspective as Fig. 2(b) and corresponds to the right half. Conventionally, the joining of sealing bodies has typically been performed in the order shown in Figures 5(a) to 5(c). That is, first, as shown in Figure 5(a), a first sealing member is placed on the top surface of the end of the current collector, and a second sealing member is placed on the bottom surface, and the end of the current collector is sandwiched between these sealing members and welded. Next, as shown in Fig. 5(b), a separator is welded so as to span the upper surface of the negative electrode active material layer and the upper surface of the first sealing member, and then, as shown in Fig. 5(c), a spacer member is welded so as to span the upper surface of the separator and the upper surface of the first sealing member. Then, a plurality of bipolar electrodes and sealing bodies are stacked to form a power storage module. In this manner, conventionally, welding was carried out multiple times while the current collector was included.

[0050] 3.2. Examples according to the present disclosure Fig. 6 is a diagram for explaining the manufacturing method of the present disclosure. Fig. 6 is a diagram from the same perspective as Fig. 5. Note that this manufacturing method presupposes the step of manufacturing the spacer-integrated second seal member 32 by joining the second seal member 33 and the spacer member 34 together as described above. In the manufacturing method of the present disclosure, first, as shown in FIG. 6(a), a first sealing member 31 is placed on the upper surface of the end of the current collector 23, and a second sealing member 33 having an integrated spacer 32 is placed on the lower surface, and the end of the current collector 23 is sandwiched between these sealing members (sealing body 30) and welded. Next, as shown in FIG. 6(b), the separator 26 is welded to span the upper surface of the negative electrode active material layer 25 and the upper surface of the first sealing member 31. Thereafter, a plurality of bipolar electrodes 22 and sealing bodies 30 are stacked to form the energy storage module 20 as shown in Fig. 2(a). Note that, at the stage of Fig. 6(b), the spacer member 34 is straight in the x-axis direction (y-axis direction), but when a plurality of module stacks 11 are stacked, the inner edge side of the spacer member 34 is pushed by the separator 26 of the adjacent bipolar electrode 22, moves in the z-axis direction, and becomes bent, as shown in Fig. 2(a).

[0051] As described above, in the present disclosure, the number of times welding is performed while the current collector 23 is included can be reduced, and the occurrence of wrinkles in the current collector 23 can be suppressed. It is also possible to shorten the process of attaching the sealing member and assembling the plurality of bipolar electrodes and the sealing body. Furthermore, by preparing the spacer-integrated second seal member 32 in advance, the welding between the second seal member 33 and the spacer member 34 is highly uniform and strong, thereby preventing liquid leakage (sealing failure) from between the second seal member 33 and the spacer member 34.

[0052] 4. Test Example As Test Example 1, the bonding of the sealing body according to the conventional example explained with reference to FIG. 5 was tested, and as Test Examples 2 and 3, the bonding of the sealing body according to the example explained with reference to FIG.

[0053] 4.1. Sealed body of Test Example 1 In test example 1, the first seal member, the second seal member, and the spacer member were prepared separately and joined following the example of Fig. 5. The first seal member, the second seal member, and the spacer member were all made of acid-modified polyethylene, and had a thickness (size in the z-axis direction) of 120 µm.

[0054] 4.2. Sealing body of Test Example 2 In Test Example 2, the first seal member was the same as in Test Example 1, and the spacer-integrated second seal member was used following the example in Fig. 4(a). That is, in Test Example 2, in the spacer-integrated second seal member, both the second seal member and the spacer member had a resin member and a low linear expansion coefficient member. In both the second seal member and the spacer member, the resin member was made of acid-modified polyethylene, and the low linear expansion coefficient member was made of aluminum foil. Before bonding, both the second seal member and the spacer member had a layer of modified polyethylene of 35 μm / layer of aluminum of 50 μm / layer of modified polyethylene of 35 μm in the thickness direction (z-axis direction) to give a total thickness of 120 μm.

[0055] 4.3. Sealing body of Test Example 3 In Test Example 3, the first seal member was the same as in Test Example 1, and the spacer-integrated second seal member was used following the example in Fig. 4(b). That is, in Test Example 3, the spacer member in the spacer-integrated second seal member has a resin member and a low linear expansion coefficient member. In this test example, the second seal member of the spacer-integrated second seal member was the same as the first seal member, and the spacer member was the same as in Test Example 2.

[0056] Test Method A current collector having a thickness of 40 μm (aluminum foil having a thickness of 30 μm and copper foil having a thickness of 10 μm laminated with an adhesive) was prepared. In Test Example 1, following the example of FIG. 5, a first seal member and a second seal member were welded to the top and bottom surfaces of a current collector by an impulse sealer, and then a separator was further welded to the first seal member. In Test Examples 2 and 3, following the example of FIG. 6, a first seal member was welded to the upper surface of the current collector, and a spacer-integrated second seal member was welded to the lower surface by an impulse sealer.

[0057] 4.5. Evaluation method and results 4.5.1. Visual evaluation during welding After welding was completed for each test example, the current collector was visually evaluated for the presence or absence of wrinkles. As a result, wrinkles were generated on the current collector in test example 1, but no wrinkles were generated on the current collector in test examples 2 and 3.

[0058] 4.5.2. Visual evaluation after thermal shock test A thermal shock test was performed on each test specimen, and the current collector was then visually evaluated for wrinkles. The thermal shock test consisted of 100 cycles of holding at 65°C for 1 hour, cooling to -40°C over 2 hours, holding at -40°C for 1 hour, and then heating to 65°C over 2 hours. As a result, in Test Example 1, wrinkles larger than those found in the visual evaluation at the time of welding were generated in the current collector, but in Test Examples 2 and 3, no wrinkles were generated in the current collector. [Explanation of symbols]

[0059] DESCRIPTION OF SYMBOLS 10... secondary battery, 11... module laminate, 20... power storage module, 21... electrode laminate, 22... bipolar electrode, 23... current collector, 24... positive electrode active material layer (first active material layer), 25... negative electrode active material layer (second active material layer), 26... separator, 30... sealing body, 31... first sealing member, 32... spacer-integrated second sealing member, 33... second sealing member, 34... spacer member

Claims

1. A method for manufacturing a secondary battery including a plurality of bipolar electrodes stacked together, the bipolar electrodes including a current collector, a first active material layer stacked on one surface of the current collector, and a second active material layer stacked on the other surface of the current collector, the method comprising the steps of: a step of manufacturing a spacer-integrated seal member by integrating the seal member and the spacer member by welding; and disposing the seal member of the spacer-integrated seal member prepared on one surface of the outer peripheral end portion of the current collector, disposing another seal member on the other surface of the current collector, and further fusing the seal member and the other seal member together. A method for manufacturing a secondary battery.

2. The method for producing a secondary battery according to claim 1 , further comprising the step of welding a separator so as to bridge the second active material layer and the other sealing member.

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