Electricity storage device

Abstract

A power storage device is provided with a laminated body (2) and a sealing body (3). The bipolar electrode (21) has: a current collector (24) that includes a surface (24a) and a surface (24b) on the opposite side from the surface (24a); a positive electrode active material layer (25) provided on the surface (24a); and a negative electrode active material layer (26) provided on the surface (24b). The closing body (3) has a sealing member (4). The collector (24) has a rectangular shape in which at least one side has a length of more than 1 m when viewed from the lamination direction (D) of the laminate (2), and has: a first metal foil (241) including a surface (24a); a second metal foil (242) that includes a surface (24b) and is thinner than the first metal foil (241); and an adhesive layer (243) that is provided between the first metal foil (241) and the second metal foil (242) and that adheres the first metal foil (241) and the second metal foil (242) to each other. The adhesive layer (243) is thinner than the second metal foil (242).

Description

Technical Field

[0001] The present disclosure relates to a power storage device. Background Art

[0002] A power storage device is known that includes: a stack including stacked bipolar electrodes; and a sealing body that seals the side surfaces of the stack, wherein the bipolar electrodes have a current collector formed by integrating two metal foils of different thicknesses through a conductive resin layer (for example, see Patent Document 1).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2010-277862 Summary of the invention

[0006] Problem that the invention aims to solve

[0007] In the above-mentioned power storage device, a resin sealing member having a larger linear expansion coefficient than the metal foil is sometimes bonded to the surface of the current collector. In this case, due to temperature changes during the use of the power storage device, the metal foil may be repeatedly stretched or compressed by the sealing member, resulting in fatigue damage. In particular, in a large-area current collector with at least one side exceeding 1m, the difference in expansion and contraction between the sealing member and the metal foil is large, and the metal foil is easily fatigued.

[0008] In the current collector of Patent Document 1, one of the two metal foils is formed thinner than the other metal foil. Therefore, when a sealing member is joined to the current collector, the one metal foil is particularly likely to be fatigue-damaged.

[0009] An object of the present disclosure is to provide a power storage device in which fatigue damage of two metal foils having different thicknesses can be suppressed in a current collector formed by integrating the two metal foils via a conductive resin layer.

[0010] Solutions for solving problems

[0011] The power storage device disclosed in the present invention comprises: a stack including stacked bipolar electrodes; and a sealing body that seals the stack, wherein the bipolar electrode comprises: a current collector including a first main surface and a second main surface on the side opposite to the first main surface; a first active material layer arranged on the first main surface; and a second active material layer arranged on the second main surface, the sealing body comprises a sealing member made of resin, the sealing member is bonded to the outer edge of at least one of the first main surface and the second main surface, the current collector is rectangular in shape with at least one side being longer than 1 m when viewed from the stacking direction of the stack, and comprises: a first metal foil including the first main surface; a second metal foil including the second main surface and being thinner than the first metal foil; and a conductive adhesive layer arranged between the first metal foil and the second metal foil to bond the first metal foil to the second metal foil, the conductive adhesive layer being thinner than the second metal foil.

[0012] In the power storage device, the current collector has a conductive adhesive layer disposed between a first metal foil and a second metal foil, bonding the first metal foil to the second metal foil. Here, the second metal foil is thinner than the first metal foil and is therefore easily damaged. However, the conductive adhesive layer is thinner than the second metal foil, so even if the conductive adhesive layer is softer than the first metal foil and the second metal foil, the thin second metal foil can be reinforced by the thick first metal foil. Therefore, fatigue damage of the two metal foils, especially the second metal foil, can be suppressed.

[0013] The thickness of the conductive adhesive layer may be 5 μm or less. In this case, since the metal foils can be more easily reinforced, fatigue damage of the two metal foils can be further suppressed.

[0014] The thickness of the conductive adhesive layer may be less than 1 / 2 of the thickness of the second metal foil. In this case, since the metal foils can more easily be reinforced, fatigue damage of the two metal foils can be further suppressed.

[0015] Alternatively, the thickness of the second metal foil may be less than 10 μm. In this case, since the second metal foil is thin, the size of the current collector can be suppressed. Even if the second metal foil is as thin as this, it can be reinforced by the first metal foil, so fatigue damage to the second metal foil is suppressed.

[0016] The Young's modulus of the conductive adhesive layer may be higher than that of the sealing member. In this case, fatigue damage of the metal foil caused by expansion and contraction of the sealing member can be suppressed compared to a configuration in which the Young's modulus of the conductive adhesive layer is lower than that of the sealing member.

[0017] Alternatively, the sealing member is bonded to the outer edge of each of the first main surface and the second main surface. In this case, the tensile and compressive stresses applied by the sealing member to the collector are increased compared to the configuration in which the sealing member is bonded to the outer edge of any one of the first main surface and the second main surface. Therefore, the configuration in which the metal foils can reinforce each other is particularly effective.

[0018] Effects of the Invention

[0019] According to the present disclosure, it is possible to provide a power storage device in which fatigue damage of two metal foils having different thicknesses can be suppressed in a current collector formed by integrating the two metal foils via a conductive resin layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic cross-sectional view of the power storage device according to the embodiment.

[0021] Figure 2 yes Figure 1 A partial enlarged view of . DETAILED DESCRIPTION

[0022] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In each of the drawings, the same or corresponding parts are denoted by the same reference numerals, and repeated descriptions are omitted.

[0023] Figure 1 The power storage device 1 shown is, for example, a power storage module used in batteries of forklifts, hybrid vehicles, electric vehicles, etc. The power storage device 1 is, for example, a secondary battery such as a nickel-hydrogen secondary battery or a lithium-ion secondary battery. In the present embodiment, the power storage device 1 is a lithium-ion secondary battery.

[0024] like Figure 1 As shown, the power storage device 1 includes a stack 2 and a sealing body 3. The stack 2 includes a bipolar electrode 21, a positive terminal electrode 22, and a negative terminal electrode 23 stacked in a stacking direction D. In the present embodiment, the stack 2 includes a plurality of bipolar electrodes 21. The bipolar electrode 21 includes a current collector 24, a positive active material layer 25, and a negative active material layer 26.

[0025] The collector 24 is rectangular in shape with at least one side exceeding 1 meter (m) in length when viewed from the stacking direction D. In the present embodiment, the collector 24 is rectangular in shape with each side exceeding 1m in length when viewed from the stacking direction D. When viewed from the stacking direction D, for example, the length of the long side of the collector 24 is 1.5m, and the length of the short side is 1.2m. The collector 24 includes a surface (first surface) 24a, and a surface (second surface) 24b on the side opposite to the surface 24a. The positive electrode active material layer 25 is provided on the surface 24a. When viewed from the stacking direction D, the positive electrode active material layer 25 is, for example, rectangular in shape. The surface 24a includes an uncoated area where the positive electrode active material layer 25 is not provided. The uncoated area surrounds the positive electrode active material layer 25 when viewed from the stacking direction D.

[0026] The negative electrode active material layer 26 is provided on the surface 24b. When viewed from the stacking direction D, the negative electrode active material layer 26 is, for example, rectangular. The surface 24b includes an uncoated area where the negative electrode active material layer 26 is not provided. The uncoated area surrounds the negative electrode active material layer 26 when viewed from the stacking direction D. The plurality of bipolar electrodes 21 are stacked in such a manner that the positive electrode active material layer 25 of one bipolar electrode 21 faces the negative electrode active material layer 26 of another bipolar electrode 21. That is, the plurality of bipolar electrodes 21 are stacked in such a manner that the surface 24a of the collector 24 of one bipolar electrode 21 faces the surface 24b of the collector 24 of another bipolar electrode 21 among the adjacent bipolar electrodes 21.

[0027] The positive terminal electrode 22 is arranged on one side in the stacking direction D with respect to the plurality of bipolar electrodes 21. The positive terminal electrode 22 has a current collector 24 and a positive electrode active material layer 25. The positive terminal electrode 22 is different from the bipolar electrode 21 in that it does not have a negative electrode active material layer 26. The other configurations of the positive terminal electrode 22 are the same as those of the bipolar electrode 21. The positive terminal electrode 22 is arranged so that the positive electrode active material layer 25 of the positive terminal electrode 22 faces the negative electrode active material layer 26 of the bipolar electrode 21. That is, the positive terminal electrode 22 is stacked so that the surface 24a of the current collector 24 of the positive terminal electrode 22 faces the surface 24b of the current collector 24 of the bipolar electrode 21 adjacent to the positive terminal electrode 22.

[0028] The negative terminal electrode 23 is arranged on the other side of the plurality of bipolar electrodes 21 in the stacking direction D. The negative terminal electrode 23 has a current collector 24 and a negative active material layer 26. The negative terminal electrode 23 is different from the bipolar electrode 21 in that it does not have a positive active material layer 25. The other configurations of the negative terminal electrode 23 are the same as those of the bipolar electrode 21. The negative terminal electrode 23 is arranged so that the negative active material layer 26 of the negative terminal electrode 23 faces the positive active material layer 25 of the bipolar electrode 21. That is, the negative terminal electrode 23 is stacked so that the surface 24b of the current collector 24 of the negative terminal electrode 23 faces the surface 24a of the current collector 24 of the bipolar electrode 21 adjacent to the negative terminal electrode 23. An internal space S containing an electrolyte is formed between the bipolar electrodes 21, between the bipolar electrode 21 and the positive terminal electrode 22, and between the bipolar electrode 21 and the negative terminal electrode 23.

[0029] The stack 2 includes a plurality of separators 27. The separators 27 are arranged between the bipolar electrodes 21, between the bipolar electrode 21 and the positive terminal electrode 22, and between the bipolar electrode 21 and the negative terminal electrode 23. The separator 27 is located between the positive electrode active material layer 25 and the negative electrode active material layer 26 facing each other. The separator 27 is, for example, in the form of a sheet. When the separator 27 is viewed from the stacking direction D, for example, it is in the form of a rectangle. When viewed from the stacking direction D, the outer edge of the separator 27 is located at a position closer to the outside than the outer edge of the positive electrode active material layer 25 and the outer edge of the negative electrode active material layer 26. The peripheral edge of the separator 27 is located between the sealing member 4 and the spacer 5 described later. The separator 27 is a member that allows charge carriers such as lithium ions to pass through. The separator 27 isolates the electrodes 21, 22, and 23 that are adjacent to each other. As a result, an electrical short circuit caused by contact between the electrodes 21, 22, and 23 can be prevented.

[0030] The current collector 24 is a chemically inert electrical conductor for allowing current to continue to flow through the positive electrode active material layer 25 and the negative electrode active material layer 26 during the discharge or charge of the power storage device 1. The current collector 24 may be in the form of a plate, foil, sheet, or film, for example. When the current collector 24 is in the form of a foil, the thickness of the current collector 24 may be in the range of 10 μm or more and 200 μm or less.

[0031] The positive electrode active material layer 25 contains a positive electrode active material that can absorb and release charge carriers such as lithium ions. Examples of the positive electrode active material include composite oxides, metallic lithium, and sulfur. The composite oxide contains, for example, at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, as well as lithium. Examples of the composite oxide include olivine-type lithium iron phosphate (LiFePO 4 ), LiCoO 2 、LiNiMnCoO2 wait.

[0032] The negative electrode active material layer 26 contains a negative electrode active material that can absorb and release charge carriers such as lithium ions. Examples of the negative electrode active material include graphite, artificial graphite, highly oriented graphite (graphite), mesocarbon microbeads, hard carbon, soft carbon and other carbons, metal compounds, elements or compounds thereof that can alloy with lithium, and carbon to which boron is added. Examples of elements that can alloy with lithium include silicon and tin.

[0033] In addition to the active material, each of the positive electrode active material layer 25 and the negative electrode active material layer 26 can also contain a binder and a conductive aid. The binder serves to bind the active material or the conductive aid to each other and maintain the conductive network in the electrode. As a binder, fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, fluorine rubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamide-imide, resins containing alkoxysilyl groups, acrylic acid resins such as polyacrylic acid and polymethacrylic acid, styrene-butadiene rubber, carboxymethyl cellulose, sodium alginate, alginate such as ammonium alginate, water-soluble cellulose ester crosslinked products, starch-acrylic acid graft copolymers can be exemplified. These binders can be used alone or in combination. Conductive aids are conductive materials such as acetylene black, carbon black, and graphite, which can improve electrical conductivity. Viscosity adjustment solvents, for example, use N-methyl-2-pyrrolidone.

[0034] The formation of the positive electrode active material layer 25 on the surface 24a and the formation of the negative electrode active material layer 26 on the surface 24b are, for example, formed by a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, a curtain coating method, and other conventionally known methods. Specifically, the active material, the solvent, and the binder and the conductive aid as required are mixed to produce a slurry-like active material layer-forming composition, which is applied to the surface 24a or the surface 24b and then dried. The solvent is, for example, N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, it can also be compressed after drying.

[0035] The separator 27 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains electrolytes. The material of the separator 27 is, for example, polypropylene, polyethylene, polyolefin, polyester, etc. The separator 27 can be a single-layer structure or a multi-layer structure. In the case where the separator 27 is a multi-layer structure, the separator 27 can, for example, include a substrate layer and a pair of adhesive layers, and is bonded and fixed to the positive electrode active material layer 25 and the negative electrode active material layer 26 by the pair of adhesive layers. The separator 27 can also include a ceramic layer that becomes a heat-resistant layer. The separator 27 can also be reinforced with a vinylidene fluoride resin compound.

[0036] As the electrolyte impregnated into the separator 27, for example, a liquid electrolyte (electrolyte) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, or a polymer gel electrolyte containing an electrolyte retained in a polymer matrix, etc. can be cited. In the case where the electrolyte is impregnated into the separator 13, as the electrolyte salt, LiClO 4 、LiAsF 6 、LiPF 6 , LiBF 4 、LiCF 3 SO 3 、LiN(FSO 2 ) 2 、LiN(CF 3 SO 2 ) 2 The non-aqueous solvent may be a known lithium salt such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, ethers, etc. In addition, a combination of two or more of these known solvent materials may be used. In the present embodiment, the electrolyte impregnated into the separator 27 is an electrolyte solution.

[0037] The sealing body 3 is a member that seals the internal space S. The sealing body 3 is provided on the side of the stacked body 2. The sealing body 3 seals the side of the stacked body 2. The sealing body 3 is, for example, in the shape of a rectangular cylinder, and has electrical insulation. The sealing body 3 has a plurality of sealing members 4, a plurality of spacers 5, and a welded portion 6.

[0038] The sealing member 4 is arranged on the surface of the collector 24 in a manner of surrounding the positive electrode active material layer 25 and the negative electrode active material layer 26 when viewed from the stacking direction (direction perpendicular to the surface 24a). The sealing member 4 is made of resin. The sealing member 4 is joined to the outer edge of at least one of the surface 24a and the surface 24b. That is, the sealing member 4 is joined to at least one of the outer edge 24d of the surface 24a and the outer edge 24e of the surface 24b. In the present embodiment, the sealing member 4 is joined to the outer edge of each of the surface 24a and the surface 24b. That is, the sealing member 4 is joined to each of the outer edge 24d of the surface 24a and the outer edge 24e of the surface 24b.

[0039] The spacer 5 is provided between the electrodes 21, 22, 23 adjacent to each other in the stacking direction D. The spacer 5 is, for example, in the shape of a rectangular frame. The spacer 5 is, for example, made of resin. The welded portion 6 is, for example, in the shape of a rectangular cylinder. The welded portion 6 reaches both ends of the stacked body 2 in the stacking direction D. The welded portion 6 is formed integrally.

[0040] like Figure 2As shown, the current collector 24 includes a first metal foil 241, a second metal foil 242 and an adhesive layer (conductive adhesive layer) 243. The current collector 24 is a laminated foil formed by laminating the first metal foil 241 and the second metal foil 242. The first metal foil 241 includes a surface 24a. The surface 24a of the current collector 24 is the surface of the positive electrode active material layer 25 side of the first metal foil 241. The first metal foil 241 is, for example, rectangular in shape when viewed from the stacking direction D. The first metal foil 241 includes aluminum, for example, aluminum foil. The first metal foil 241 may also be, for example, nickel foil, titanium foil, or stainless steel foil. The first metal foil 241 may also be an alloy foil of the above metals. A coating layer may also be formed on the surface 24a of the first metal foil 241 by a known method such as plating or spraying.

[0041] The second metal foil 242 is arranged on the side opposite to the positive electrode active material layer 25 relative to the first metal foil 241. The second metal foil 242 includes a surface 24b. The surface 24b of the collector 24 is the surface of the negative electrode active material layer 26 side of the second metal foil 242. The second metal foil 242 is, for example, rectangular when viewed from the stacking direction D. When viewed from the stacking direction D, the side (outer edge) 242c of the second metal foil 242 is roughly consistent with the side (outer edge) 241c of the first metal foil 241. In the present embodiment, the second metal foil 242 includes copper, for example, copper foil. The second metal foil 242 may also be, for example, nickel foil, titanium foil, or stainless steel foil. The second metal foil 242 may also be an alloy foil of the above metals. A coating layer may also be formed on the surface 24b of the second metal foil 242 by a known method such as plating or spraying.

[0042] The adhesive layer 243 is provided between the first metal foil 241 and the second metal foil 242. The adhesive layer 243 is, for example, rectangular in shape when viewed from the stacking direction D. When viewed from the stacking direction D, the side surface (outer edge) 243c of the adhesive layer 243 is substantially consistent with the side surface 241c of the first metal foil 241 and the side surface 242c of the second metal foil 242. The side surface (outer edge) 24c of the collector 24 is composed of the side surface 241c, the side surface 242c, and the side surface 243c.

[0043] The adhesive layer 243 bonds the first metal foil 241 and the second metal foil 242. The adhesive layer 243 is bonded to each of the first metal foil 241 and the second metal foil 242. The adhesive layer 243 is a conductive adhesive layer having conductivity. The adhesive layer 243 includes, for example, a conductive resin material. As the conductive resin material, for example, a conductive polymer material or a resin obtained by adding a conductive filler to a non-conductive polymer material can be cited.

[0044] In the present embodiment, the adhesive layer 243 includes an adhesive component and a conductive component. The adhesive component functions as an adhesive for bonding the first metal foil 241 and the second metal foil 242. The adhesive component is, for example, a thermosetting resin or a thermoplastic resin. The resin of the adhesive component is, for example, an olefin resin such as polypropylene or polyethylene, an acrylic resin such as polyacrylic acid, etc. In the case where the adhesive component is a thermosetting resin, the adhesive component may also include a curing agent such as an isocyanate curing agent or an epoxy curing agent. In the case where the first metal foil 241 and the second metal foil 242 are bonded by the adhesive layer 243 with an olefin resin as the adhesive component, an epoxy curing agent with less gas generation accompanying the curing reaction of the adhesive component may be used. The adhesive component may have electrolyte resistance. In this case, even if the electrolyte intrudes between the first metal foil 241 and the second metal foil 242 due to pinhole defects or the like in one of the first metal foil 241 and the second metal foil 242, the electrolyte can be inhibited from reaching the other of the first metal foil 241 and the second metal foil 242 by the adhesive layer 243, thereby preventing a short circuit. The conductive component is, for example, conductive particles dispersed in the adhesive component. The conductive component electrically connects the first metal foil 241 and the second metal foil 242. The material of the conductive component is, for example, graphite or metal. The conductive particles are, for example, graphite particles or metal particles. The conductive particles can be composed of the above-mentioned materials alone, or can be composed by coating the above-mentioned materials on the surface of resin particles or the like. As conductive particles, spherical particles formed by forming a metal film on the surface of core particles composed of resin or ceramics or the like can also be used.

[0045] The thickness of the first metal foil 241 (the length of the first metal foil 241 in the stacking direction D) is, for example, not less than 20 μm and not more than 150 μm. The second metal foil 242 is thinner than the first metal foil 241. The thickness of the second metal foil 242 (the length of the second metal foil 242 in the stacking direction D) is, for example, less than 10 μm. The adhesive layer 243 is thinner than the second metal foil 242. The thickness of the adhesive layer 243 (the length of the adhesive layer 243 in the stacking direction D) is, for example, not more than 1 / 2 of the thickness of the first metal foil 241. The thickness of the adhesive layer 243 is, for example, not more than 5 μm, and may be, for example, not more than 3 μm.

[0046] It is known that, generally, in the metal foil used for the current collector 24, the thicker the metal foil, the higher the strength of the metal foil against fatigue damage. In the present embodiment, the thickness of the first metal foil 241 as the aluminum foil is twice as large as the thickness of the second metal foil 242 as the copper foil, and therefore, the strength of the first metal foil 241 against fatigue damage alone is higher than the strength of the second metal foil 242 against fatigue damage alone. That is, the strength of the second metal foil 242 against fatigue damage alone is lower than the strength of the first metal foil 241 against fatigue damage alone.

[0047] The sealing member 4 includes a sealing portion 41, a sealing portion 42, and a sealing portion 43. The sealing portion 41 is provided on the surface 24a. The sealing portion 41 is, for example, in a rectangular frame shape when viewed from the stacking direction D. The sealing portion 41 surrounds the positive electrode active material layer 25 and the negative electrode active material layer 26 when viewed from the stacking direction D. The outer edge 41c of the sealing portion 41 is substantially consistent with the side surface 24c of the collector 24 when viewed from the stacking direction D. The inner edge 41d of the sealing portion 41 is separated from the positive electrode active material layer 25. The sealing portion 41 is bonded to the outer edge portion 24d of the surface 24a.

[0048] The sealing portion 42 is provided on the surface 24b. The sealing portion 42 is, for example, in a rectangular frame shape when viewed from the stacking direction D. The sealing portion 42 surrounds the positive electrode active material layer 25 and the negative electrode active material layer 26 when viewed from the stacking direction D. The outer edge 42c of the sealing portion 42 is substantially consistent with the side surface 24c of the collector 24 when viewed from the stacking direction D. The inner edge 42d of the sealing portion 42 is separated from the negative electrode active material layer 26. The sealing portion 42 is bonded to the outer edge 24e of the surface 24b. The inner edge 42d of the sealing portion 42 is substantially consistent with the inner edge 41d of the sealing portion 41 when viewed from the stacking direction D. The thickness of the sealing portion 42 (the length of the sealing portion 42 in the stacking direction D) is, for example, substantially consistent with the thickness of the sealing portion 41 (the length of the sealing portion 41 in the stacking direction D), and is 80 μm or more and 160 μm or less. The thickness of the sealing portion 41 and the sealing portion 42 are each greater than the thickness of the first metal foil 241 and greater than the thickness of the second metal foil 242 .

[0049] The sealing portion 43 is provided on the side surface 24c of the current collector 24. The sealing portion 43 is located outside the side surface 24c of the current collector 24, the outer edge 41c of the sealing portion 41, and the outer edge 42c of the sealing portion 42. The sealing portion 43 is connected to each of the sealing portion 41 and the sealing portion 42. The sealing portion 43 covers the side surface 24c of the current collector 24. The sealing portion 43 covers each of the side surface 241c of the first metal foil 241, the side surface 242c of the second metal foil 242, and the side surface 243c of the adhesive layer 243.

[0050] The sealing portion 43 is bonded to the side surface 24c of the current collector 24. The sealing portion 43 is bonded to each of the side surface 241c of the first metal foil 241, the side surface 242c of the second metal foil 242, and the side surface 243c of the adhesive layer 243. The sealing portion 43 seals the side surface 24c of the current collector 24. The sealing portion 41, the sealing portion 42, and the sealing portion 43 are each a partial region of the sealing member 4 formed integrally from the same material.

[0051] The spacer 5 is provided between the sealing members 4 adjacent to each other in the stacking direction D. The spacer 5 is, for example, in the shape of a rectangular frame. When viewed from the stacking direction D, the inner edge 5d of the spacer 5 is farther from the positive electrode active material layer 25 or the negative electrode active material layer 26 than the inner edge 41d of the sealing portion 41 and the inner edge 42d of the sealing portion 42. That is, when viewed from the stacking direction D, the inner edge 41d of the sealing portion 41 is located between the positive electrode active material layer 25 and the inner edge 5d of the spacer 5, and the inner edge 42d of the sealing portion 42 is located between the negative electrode active material layer 26 and the inner edge 5d of the spacer 5. The spacer 5 is a member independent of the sealing member 4.

[0052] The spacer 5 is sandwiched by a pair of sealing members 4 adjacent to each other in the stacking direction D. The spacer 5 is in contact with the sealing member 4. The spacer 5 forms an internal space S for accommodating an electrolyte together with a pair of bipolar electrodes 21 adjacent to each other in the stacking direction D and a pair of sealing members 4 adjacent to each other in the stacking direction D. In addition, a liquid injection port for injecting an electrolyte into the internal space S is formed in the spacer 5.

[0053] The thickness of the spacer 5 (the length of the spacer 5 in the stacking direction D) is greater than the thickness of each of the sealing portion 41 and the sealing portion 42. The thickness of the spacer 5 is, for example, more than twice the thickness of the sealing portion 41 or the thickness of the sealing portion 42. The thickness of the spacer 5 is thinner than the thickness of the sealing member 4 (the length of the sealing member 4 in the stacking direction D). That is, the thickness of the spacer 5 is smaller than the sum of the thickness of the first metal foil 241, the thickness of the second metal foil 242, the thickness of the adhesive layer 243, the thickness of the sealing portion 41, and the thickness of the sealing portion 42.

[0054] The separator 5 is welded to the sealing member 4 at the outer side (i.e., welded portion 6) than the side surface 24c of the current collector 24. Specifically, the outer edge portions of the sealing member 4 and the separator 5 are melted and then solidified again to form the welded portion 6. That is, the welded portion 6 is formed by mutually welding the outer edge portions of the sealing member 4 and the separator 5.

[0055] Here, the outer edge of each of the sealing member 4 and the spacer 5 refers to the outer edge of each of the sealing member 4 and the spacer 5 before welding. The outer edge of the sealing member 4 is a portion located on the opposite side of the collector 24 relative to the sealing portion 43 in the sealing member 4 before welding. The outer edge of the spacer 5 is a portion overlapping with the outer edge of the sealing member 4 in the spacer 5 before welding when viewed from the stacking direction D. The welded portion 6 does not reach the side 24c of the collector 24. The welded portion 6 is separated from the side 24c of the collector 24. In addition, a liquid injection port connected to the liquid injection port of the spacer 5 is formed in the welded portion 6. The welded portion 6 can also be formed to reach the side 24c of the collector 24. In this case, the sealing portion 43 in the sealing member 4 after welding is not formed.

[0056] The sealing member 4 and the spacer 5 each contain a thermoplastic resin. The materials of the sealing member 4 and the spacer 5 are, for example, acid-modified polyethylene (acid-modified PE), acid-modified polypropylene (acid-modified PP), polyethylene or polypropylene, etc. The sealing member 4 and the spacer 5 each have electrolyte resistance. The materials of the sealing member 4 and the spacer 5 can be the same or different from each other. In the present embodiment, the material of the sealing member 4 is, for example, acid-modified polyethylene or acid-modified polypropylene. In the present embodiment, the material of the spacer 5 is, for example, polyethylene or polypropylene. The sealing portion 41, the sealing portion 42 and the spacer 5 can also be composed of a plurality of resin layers. In this case, different materials can be used in each resin layer.

[0057] Acid-modified polyethylene and acid-modified polypropylene are easier to bond with metal than un-acid-modified polyethylene and un-acid-modified polypropylene. Since the first metal foil 241 and the second metal foil 242 of the current collector 24 are each made of metal, the sealing portions 41, 42, 43 are formed of acid-modified polyethylene or acid-modified polypropylene, so that the bonding strength of the sealing portions 41, 42, 43 to the first metal foil 241 or the second metal foil 242 can be improved.

[0058] The Young's modulus of the adhesive layer 243 is higher than that of the sealing member 4. The Young's modulus of the adhesive layer 243 is higher than that of each of the sealing portion 41 and the sealing portion 42. In the present embodiment, since the sealing member 4 is integrally formed of the same material, the sealing portion 41 and the sealing portion 42 have the same Young's modulus.

[0059] The Young's modulus of the adhesive layer 243 is lower than the Young's modulus of the first metal foil 241 and the second metal foil 242. As an example, the Young's modulus of the first metal foil 241 and the second metal foil 242 is about 100 times or more relative to the Young's modulus of the adhesive layer 243. The linear expansion coefficient of the sealing member 4 (sealing portions 41, 42) is greater than the linear expansion coefficient of the first metal foil 241 and the second metal foil 242. As an example, the linear expansion coefficient of the sealing portion 41 and the sealing portion 42 is about 5 times or more relative to the linear expansion coefficient of the first metal foil 241 and the second metal foil 242.

[0060] The heat-resistant temperature of the adhesive layer 243 (hereinafter, sometimes referred to as "heat-resistant temperature") is higher than the melting point of each of the sealing portion 41, the sealing portion 42, the sealing portion 43, and the spacer 5. Specifically, the heat-resistant temperature of the adhesive component of the adhesive layer 243 is higher than the melting point of each of the sealing portion 41, the sealing portion 42, the sealing portion 43, and the spacer 5. The melting point of each of the sealing portion 41, the sealing portion 42, the sealing portion 43, and the spacer 5 is, for example, lower than 150 degrees. The heat-resistant temperature of the adhesive layer 243 is, for example, 150 degrees or more.

[0061] The heat-resistant temperature of the adhesive layer 243 is a limit temperature at which a good bonding state between the first metal foil 241 and the second metal foil 242 can be maintained. Specifically, the heat-resistant temperature of the adhesive layer 243 is a limit temperature at which the bonding strength between the first metal foil 241 and the second metal foil 242 brought by the adhesive layer 243 becomes above a predetermined threshold. The predetermined threshold may be, for example, 1% of the bonding strength of the adhesive layer 243 at room temperature. Generally speaking, when the temperature of the adhesive layer 243 rises due to heating, there is a tendency that the bonding strength of the adhesive layer 243 decreases compared to before heating. Furthermore, when the temperature of the adhesive layer 243 becomes higher than the heat-resistant temperature, the bonding strength of the adhesive layer 243 decreases to a value lower than the above-defined threshold. When the bonding strength of the adhesive layer 243 becomes lower than the above-defined threshold, a good bonding state between the first metal foil 241 and the second metal foil 242 cannot be maintained, and as a result, damage to the collector 24 may occur. In the present embodiment, since the heat-resistant temperature of the adhesive layer 243 is higher than the melting points of the sealing portion 41, the sealing portion 42, the sealing portion 43, and the spacer 5, the current collector 24 is not easily damaged even if the temperature of the adhesive layer 243 reaches the melting point of the sealing portion 41, the sealing portion 42, the sealing portion 43, or the spacer 5 during the welding. Examples of damage to the current collector 24 include peeling of the first metal foil 241 or the second metal foil 242, a change in the relative position of the first metal foil 241 and the second metal foil 242 (positional deviation of the first metal foil 241 and the second metal foil 242), or deformation of the first metal foil 241 or the second metal foil 242 (e.g., wrinkles, etc.).

[0062] In the present embodiment, the adhesive strength of the adhesive layer 243 after being heated to the heat-resistant temperature (hereinafter referred to as "high temperature strength") is 1% or more of the adhesive strength of the adhesive layer 243 at room temperature (hereinafter referred to as "room temperature strength"). If the adhesive strength of the heated adhesive layer 243 is 1% or more of the room temperature strength, the good bonding state of the first metal foil 241 and the second metal foil 242 brought by the adhesive layer 243 will be maintained. When the temperature of the adhesive layer 243 is below the heat-resistant temperature, the adhesive strength of the adhesive layer 243 becomes 1% or more of the room temperature strength, and the good bonding state of the first metal foil 241 and the second metal foil 242 is maintained. In the present embodiment, since the heat-resistant temperature of the adhesive layer 243 is higher than the melting points of the sealing portion 41, the sealing portion 42, the sealing portion 43, and the spacer 5, respectively, during the fusion of the sealing portion 41, the sealing portion 42, the sealing portion 43, or the spacer 5, even if the temperature of the adhesive layer 243 reaches the melting point of the sealing portion 41, the sealing portion 42, the sealing portion 43, or the spacer 5, the bonding strength of the adhesive layer 243 is 1% or more of the strength at room temperature. That is, even if the temperature of the adhesive layer 243 reaches the melting point of the sealing portion 41, the sealing portion 42, the sealing portion 43, or the spacer 5, since the good bonding state of the first metal foil 241 and the second metal foil 242 is maintained by the adhesive layer 243, the current collector 24 is not easily damaged.

[0063] The room temperature strength is measured, for example, as follows. That is, first, prepare the collector 24 (the collector 24 without any of the positive electrode active material layer 25, the negative electrode active material layer 26 and the sealing member 4). Next, at room temperature, for example, by a 180-degree peel strength test (as an example, in accordance with JIS Z 0237:2009), the peel strength when the first metal foil 241 is peeled off from the second metal foil 242 is measured as the room temperature strength. The high temperature strength is measured, for example, as follows. That is, first, prepare the collector 24 in the same manner as the measurement of the room temperature strength. Next, heat the collector 24 to a heat-resistant temperature. Next, while maintaining the temperature of the collector 24 heated to the heat-resistant temperature, the peel strength when the first metal foil 241 is peeled off from the second metal foil 242 is measured as the high temperature strength in the same manner as the measurement of the room temperature strength.

[0064] The current collector 24 is formed, for example, by bonding the first metal foil 241 and the second metal foil 242 with an adhesive layer 243 by a dry lamination method. In the dry lamination method, first, an adhesive solution is applied to the first metal foil 241. Then, the adhesive solution is dried to form a uniform adhesive on the surface of the first metal foil 241. Next, the first metal foil 241 formed with the adhesive is bonded to the second metal foil 242 by thermocompression bonding. The thermocompression bonding is performed using a pair of heating rollers at a constant pressure. One of the heating rollers is a movable roller. By moving the movable roller, the interval between the pair of heating rollers can be adjusted, and the pressure during thermocompression bonding can be adjusted. As a result of bonding, a current collector 24 in which the first metal foil 241 and the second metal foil 242 are bonded by the adhesive layer 243 can be obtained.

[0065] The thickness tolerance of the first metal foil 241 and the second metal foil 242 is large. If the thickness of the adhesive layer 243 is measured by measuring the thickness of the collector 24 in the state where the first metal foil 241 and the second metal foil 242 are bonded, the thickness of the adhesive layer 243 cannot be accurately measured because the thickness tolerance of the first metal foil 241 and the second metal foil 242 has a great influence on the measurement result. Therefore, the management of the thickness of the adhesive layer 243 is carried out by measuring the thickness of the adhesive formed on the surface of the first metal foil 241 before bonding. For example, it is determined whether the thickness of the adhesive is included in the numerical range of qualified products. If it is not included in the numerical range, the part is removed from the production line before bonding, or the part is cut off after bonding. In addition, before bonding, the adhesive is not covered by the second metal foil 242, so it is possible to measure the thickness of only the adhesive. Here, when the first metal foil 241 and the second metal foil 242 are thermocompressed, the adhesive (adhesive layer 243) which is much softer than the first metal foil 241 and the second metal foil 242 is compressed. Therefore, when the first metal foil 241 and the second metal foil 242 are thermocompressed at a constant pressure, by investigating in advance the correlation between the thickness of the adhesive layer 243 after thermocompression bonding with a predetermined pressure and the thickness of the adhesive before bonding, the thickness of the adhesive layer 243 after bonding can be appropriately managed based on the thickness of the adhesive applied to the first metal foil 241.

[0066] As described above, in the power storage device 1, the sealing member 4 having a larger linear expansion coefficient than the first metal foil 241 and the second metal foil 242 of the collector 24 is joined to the collector 24. Therefore, due to repeated temperature changes during the use of the power storage device 1, the sealing member 4 expands and contracts more than the first metal foil 241 and the second metal foil 242, and tensile and compressive stresses are repeatedly applied to the first metal foil 241 and the second metal foil 242. The collector 24 has an adhesive layer 243 that is arranged between the first metal foil 241 and the second metal foil 242 and bonds the first metal foil 241 and the second metal foil 242. Here, as mentioned above, the second metal foil 242 is thinner than the first metal foil 241, so it is easy to be fatigued and damaged. However, the adhesive layer 243 is thinner than the second metal foil 242. Therefore, even if the Young's modulus of the adhesive layer 243 is lower than that of the first metal foil 241 and the second metal foil 242, the adhesive layer 243 is softer than the first metal foil 241 and the second metal foil 242, and the tensile and compressive stress of the sealing member 4 to the first metal foil 241 and the second metal foil 242 is not easily absorbed by the adhesive layer 243. Thus, the effect of the first metal foil 241 and the second metal foil 242 mutually reinforcing the strength can be obtained. Specifically, the thin second metal foil 242 can be strengthened by the thick first metal foil 241. Thus, the fatigue damage of both the first metal foil 241 and the second metal foil 242, especially the second metal foil 242, is suppressed. Since it is not necessary to ensure the strength of the first metal foil 241 and the second metal foil 242 to withstand the repeated tensile and compressive stress brought by the sealing member 4, the enlargement of the collector 24 can be suppressed. As a result of suppressing the increase in size of the current collector 24 , the power storage device 1 can be reduced in size.

[0067] The results of a thermal shock test (in accordance with JISC 60068-2-14: 2011) on multiple test pieces simulating the power storage device involved in the experimental example are described. Each test piece is formed by setting a sealing member 4 on a collector 24. The length of the long side of the collector 24 is 1.5m, and the length of the short side is 1.2m. The collector 24 is composed of aluminum foil (JIS A3003) as the first metal foil 241, copper foil (electrolytic copper foil) as the second metal foil 242, and olefin resin as the adhesive layer 243. As the material of the sealing member 4, acid-modified polyethylene is used, and the thickness of the portion corresponding to the sealing portion 41 and the sealing portion 42 is set to 120μm. Multiple test pieces are respectively composed of collectors 24 in which the thickness of the copper foil is fixed to 7.8μm, the thickness of the olefin resin is fixed to 3μm, and the thickness of the aluminum foil is changed to 40μm, 45μm, and 50μm. A plurality of test pieces were formed under the same conditions except for the thickness of the aluminum foil.

[0068] Table 1 shows the results of the thermal shock test. In Table 1, for the cases where the thickness of the aluminum foil is set to 40μm, 45μm and 50μm, the number of times until the copper foil breaks is shown with the case where the thickness of the aluminum foil is 40μm as the benchmark (1 times). The number of times until the copper foil breaks is the number of thermal shocks (thermal cycle number) until the copper foil breaks. The copper foil breaks earlier than the aluminum foil. As shown in Table 1, when the thickness of the aluminum foil is increased, the number of times until the copper foil breaks also increases. Through this result, it was confirmed that the reinforcing effect of the aluminum foil on the copper foil can be obtained.

[0069] [Table 1]

[0070] Aluminum foil thickness 40μm 45μm 50μm The number of times until the copper foil breaks 1x 1.3 times 1.6 times

[0071] Since the thickness of the second metal foil 242 is less than 10 μm, it is possible to further suppress the increase in size of the current collector 24. Even if the second metal foil 242 is so thin, the first metal foil 241 can reinforce the second metal foil 242, so fatigue damage to the second metal foil 242 is suppressed.

[0072] The thickness of the adhesive layer 243 is equal to or less than 1 / 2 of the thickness of the second metal foil 242. This makes it easier to obtain the mutual reinforcement effect between the first metal foil 241 and the second metal foil 242. Therefore, fatigue damage of the second metal foil 242 can be further suppressed.

[0073] The Young's modulus of the adhesive layer 243 is higher than that of the sealing member 4. Thus, since the adhesive layer 243 is harder than the sealing member 4, the deformation of the collector 24 caused by the expansion and contraction of the sealing member 4 is suppressed compared with a configuration in which the Young's modulus of the adhesive layer 243 is lower than that of the sealing member 4 and the adhesive layer 243 is softer than the sealing member 4. Therefore, fatigue damage of the first metal foil 241 and the second metal foil 242 can be suppressed.

[0074] The sealing member 4 includes a sealing portion 41 joined to the outer edge portion 24d of the surface 24a of the current collector 24, and a sealing portion 42 joined to the outer edge portion 24e of the surface 24b of the current collector 24. Therefore, the tensile and compressive stresses applied by the sealing member 4 to the current collector 24 are increased compared to a configuration in which the sealing member 4 includes any one of the sealing portion 41 and the sealing portion 42. Therefore, a configuration of the power storage device 1 in which the first metal foil 241 and the second metal foil 242 can reinforce each other is particularly effective.

[0075] The present disclosure is not limited to the above-described embodiments.

[0076] In the embodiment, an example is shown in which the collectors 24 of the bipolar electrode 21, the positive terminal electrode 22, and the negative terminal electrode 23 are the same, but the collectors 24 of the positive terminal electrode 22 and the negative terminal electrode 23 may be different in material or thickness from the collectors 24 of the bipolar electrode 21. For example, the collectors 24 of the positive terminal electrode 22 and the negative terminal electrode 23 may be current collectors made of a single metal foil instead of a laminated foil.

[0077] In the embodiment, the example in which the sealing member 4 includes the sealing portion 41, the sealing portion 42, and the sealing portion 43 is shown, but the sealing member 4 only needs to include at least the sealing portion 41 or the sealing portion 42. That is, the sealing member 4 only needs to be bonded to at least the outer edge portion 24d of the surface 24a of the collector 24 or the outer edge portion 24e of the surface 24b.

[0078] In the embodiment, the example in which the peripheral edge of the spacer 27 is located between the sealing member 4 and the spacer 5 is shown, but the peripheral edge of the spacer 27 may not reach the spacer 5. The peripheral edge of the spacer 27 may be welded to the sealing member 4.

[0079] In the embodiment, the first metal foil 241 and the second metal foil 242 are directly bonded to the bonding layer 243, but may be bonded to the bonding layer 243 via a carbon coating (not shown). That is, the current collector 24 may also include a carbon coating disposed between the first metal foil 241 and the bonding layer 243 and between the second metal foil 242 and the bonding layer 243, respectively. The carbon coating has conductivity. The carbon coating includes, for example, a binder and graphite. The carbon coating may also be disposed between the first metal foil 241 and the bonding layer 243 and between the second metal foil 242 and the bonding layer 243. That is, the carbon coating only needs to be disposed on at least one of the first metal foil 241 and the bonding layer 243 and between the second metal foil 242 and the bonding layer 243. According to such a configuration, for example, compared with the case where the first metal foil 241 or the second metal foil 242 is directly bonded to the bonding layer 243, since the binder resin contained in the carbon coating layer is firmly bonded via the bonding layer 243, the bonding strength between the first metal foil 241 and the bonding layer 243 or the bonding strength between the second metal foil 242 and the bonding layer 243 can be more reliably ensured. In addition, for example, even if pinholes are formed in the first metal foil 241, the second metal foil 242, or the bonding layer 243, the liquid interface between the adjacent internal spaces S can be suppressed by the carbon coating layer. In addition, the carbon coating layer may also be provided on the surface 24a or the surface 24b of the collector 24. In this case, the carbon coating layer is also interposed between the surface 24a and the sealing portion 41 or between the surface 24b and the sealing portion 42.

[0080] The inner edge 5d of the separator 5 may be arranged closer to the positive electrode active material layer 25 or the negative electrode active material layer 26 than the inner edge 41d of the sealing portion 41 and the inner edge 42d of the sealing portion 42, respectively, when viewed from the stacking direction D. That is, when viewed from the stacking direction D, the inner edge 5d of the separator 5 may be located between the positive electrode active material layer 25 and the inner edge 41d of the sealing portion 41, or between the negative electrode active material layer 26 and the inner edge 42d of the sealing portion 42.

[0081] Description of Reference Numerals

[0082] 1...power storage device, 2...stacked body, 3...sealing body, 4...sealing member, 21...bipolar electrode, 24...current collector, 24a...surface (first main surface), 24b...surface (second main surface), 24d...outer edge, 24e...outer edge, 25...positive electrode active material layer (first active material layer), 26...negative electrode active material layer (second active material layer), 241...first metal foil, 242...second metal foil, 243...adhesive layer (conductive adhesive layer).

Claims

1. A power storage device comprising: a stacked body comprising stacked bipolar electrodes; and a closing body, which closes the stacked body, The power storage device is characterized in that The bipolar electrode has: a current collector including a first main surface and a second main surface opposite to the first main surface; a first active material layer provided on the first main surface; and a second active material layer provided on the second main surface, The sealing body has a sealing member made of resin, and the sealing member is bonded to an outer edge portion of at least one of the first main surface and the second main surface. The current collector The stacked body is in a rectangular shape with at least one side exceeding 1 m in length when viewed in the stacking direction, and has: a first metal foil including the first main surface; a second metal foil including the second main surface and being thinner than the first metal foil; and a conductive adhesive layer provided between the first metal foil and the second metal foil to bond the first metal foil to the second metal foil; The conductive adhesive layer is thinner than the second metal foil.

2. The power storage device according to claim 1, wherein The conductive adhesive layer has a thickness of 5 μm or less.

3. The power storage device according to claim 1 or 2, wherein: The thickness of the conductive adhesive layer is equal to or less than 1 / 2 of the thickness of the second metal foil.

4. The power storage device according to any one of claims 1 to 3, wherein: The second metal foil has a thickness of less than 10 μm.

5. The power storage device according to any one of claims 1 to 4, wherein: The Young's modulus of the conductive adhesive layer is higher than the Young's modulus of the sealing member.

6. The power storage device according to any one of claims 1 to 5, wherein: The sealing member is bonded to outer edge portions of the first main surface and the second main surface.

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