Energy storage device

Abstract

This power storage device comprises a laminate 2 and a sealing body 3. A bipolar electrode 21 has: a current collector 24 comprising a surface 24a and a surface 24b on the reverse 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 sealing body 3 has a seal member 4. Viewed from the lamination direction D of the laminate 2, the current collector 24 has a rectangular shape in which the length of at least one side exceeds 1 m, and has: a first metal foil 241 that constitutes the surface 24a; a second metal foil 242 that constitutes the 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 adheres the first metal foil 241 and the second metal foil 242. 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] There is known a power storage device including a laminate including laminated bipolar electrodes and a sealing body that seals a side surface of the laminate, in which the bipolar electrode has a current collector in which two metal foils having different thicknesses are integrated by a conductive resin layer (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the power storage device as described above, a resin seal member having a linear expansion coefficient larger than that of the metal foil may be joined to the surface of the current collector. In this case, due to a temperature change during use of the power storage device, the metal foil may be repeatedly pulled or compressed by the seal member, and there is a risk of fatigue damage. In particular, in a current collector having a large area with at least one side exceeding 1 m, the difference in the amount of expansion and contraction between the seal member and the metal foil is large, and the metal foil is likely to be fatigued and damaged.

[0005] 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 seal member is joined to the current collector, there is a risk that the one metal foil will be particularly fatigued and damaged.

[0006] An object of the present disclosure is to provide a power storage device capable of suppressing fatigue damage to both metal foils in a current collector in which two metal foils having different thicknesses are integrated by a conductive resin layer.

Means for Solving the Problems

[0007] The energy storage device of the present disclosure comprises a laminate including stacked bipolar electrodes and a sealant that seals the laminate, wherein the bipolar electrodes include 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 sealant has a resin sealing member joined to the outer edge of at least one of the first and second main surfaces, the current collector has a rectangular shape with at least one side length exceeding 1 m when viewed from the stacking direction of the laminate and includes a first metal foil including the first main surface, a second metal foil including the second main surface and 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 and the second metal foil, the conductive adhesive layer being thinner than the second metal foil.

[0008] In this energy storage device, the current collector is provided between the first metal foil and the second metal foil, and has a conductive adhesive layer that bonds the first and second metal foils together. Here, the second metal foil is thinner than the first metal foil and therefore more susceptible to damage. However, since the conductive adhesive layer is even thinner than the second metal foil, even if the conductive adhesive layer is softer than both the first and second metal foils, the thinner second metal foil can be reinforced by the thicker first metal foil. Thus, fatigue damage to both metal foils, especially the second metal foil, can be suppressed.

[0009] The thickness of the conductive adhesive layer may be 5 μm or less. In this case, the reinforcing effect between the metal foils can be further enhanced, thereby further suppressing fatigue damage to both metal foils.

[0010] The thickness of the conductive adhesive layer may be less than or equal to half the thickness of the second metal foil. In this case, the reinforcing effect between the metal foils is more easily obtained, and fatigue damage to both metal foils can be further suppressed.

[0011] The thickness of the second metal foil may be less than 10 μm. In this case, since the second metal foil is thin, it is possible to suppress the size of the current collector. Even if the second metal foil is thin in this way, reinforcement by the first metal foil is possible, so fatigue damage to the second metal foil is suppressed.

[0012] The Young's modulus of the conductive adhesive layer may be higher than that of the sealing member. In this case, compared to a configuration where the Young's modulus of the conductive adhesive layer is lower than that of the sealing member, fatigue damage to the metal foil due to expansion and contraction of the sealing member can be suppressed.

[0013] The sealing member may be joined to the outer edges of the first and second main surfaces. In this case, the tensile and compressive stress that the sealing member imparts to the current collector increases compared to a configuration in which the sealing member is joined to the outer edge of either the first or second surface. Therefore, a configuration that allows for reinforcement between the metal foils is particularly effective. [Effects of the Invention]

[0014] According to this disclosure, it is possible to provide an energy storage device in which fatigue damage to both metal foils can be suppressed in a current collector in which two metal foils of different thicknesses are integrated by a conductive resin layer. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 is a schematic cross-sectional view of an energy storage device according to an embodiment. [Figure 2] Figure 2 is a magnified view of a portion of Figure 1. [Modes for carrying out the invention]

[0016] Embodiments of this disclosure will be described in detail below with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and redundant descriptions are omitted.

[0017] The energy storage device 1 shown in Figure 1 is an energy storage module used in batteries for, for example, forklifts, hybrid vehicles, electric vehicles, etc. The energy storage device 1 is a secondary battery, such as a nickel-metal hydride secondary battery or a lithium-ion secondary battery. In this embodiment, the energy storage device 1 is a lithium-ion secondary battery.

[0018] As shown in Figure 1, the energy storage device 1 comprises a laminate 2 and a sealing body 3. The laminate 2 includes bipolar electrodes 21 stacked in the stacking direction D, a positive terminal electrode 22, and a negative terminal electrode 23. In this embodiment, the laminate 2 includes a plurality of bipolar electrodes 21. The bipolar electrode 21 has a current collector 24, a positive electrode active material layer 25, and a negative electrode active material layer 26.

[0019] The current collector 24 has a rectangular shape, with at least one side having a length of 1 m or more, when viewed from the stacking direction D. In this embodiment, the current collector 24 has a rectangular shape, with each side having a length of 1 m or more, when viewed from the stacking direction D. When viewed from the stacking direction D, for example, the length of the long side of the current collector 24 is 1.5 m, and the length of the short side is 1.2 m. The current collector 24 includes a surface (first surface) 24a and a surface (second surface) 24b opposite to surface 24a. The positive electrode active material layer 25 is provided on surface 24a. The positive electrode active material layer 25 has a rectangular shape, for example, when viewed from the stacking direction D. 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.

[0020] The negative electrode active material layer 26 is provided on the surface 24b. The negative electrode active material layer 26 has, for example, a rectangular shape when viewed in the stacking direction D. The surface 24b includes an uncoated region where the negative electrode active material layer 26 is not provided. The uncoated region surrounds the negative electrode active material layer 26 when viewed in the stacking direction D. The plurality of bipolar electrodes 21 are stacked such 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 such that, among adjacent bipolar electrodes 21, the surface 24a of the current collector 24 of one bipolar electrode 21 faces the surface 24b of the current collector 24 of the other bipolar electrode 21.

[0021] The positive terminal electrode 22 is disposed 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. Other configurations of the positive terminal electrode 22 are the same as those of the bipolar electrode 21. The positive terminal electrode 22 is disposed such 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 such 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.

[0022] The negative terminal electrode 23 is disposed on the other side in the stacking direction D with respect to the plurality of bipolar electrodes 21. The negative terminal electrode 23 has a current collector 24 and a negative electrode active material layer 26. The negative terminal electrode 23 is different from the bipolar electrode 21 in that it does not have a positive electrode active material layer 25. 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 such that the negative electrode active material layer 26 of the negative terminal electrode 23 faces the positive electrode active material layer 25 of the bipolar electrode 21. That is, the negative terminal electrode 23 is stacked such 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 electrolytic solution is formed between each bipolar electrode 21, between the bipolar electrode 21 and the positive terminal electrode 22, and between the bipolar electrode 21 and the negative terminal electrode 23.

[0023] The laminate 2 includes a plurality of separators 27. The separators 27 are disposed between each bipolar electrode 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 a sheet shape. The separator 27 is, for example, rectangular when viewed in the stacking direction D. When viewed in the stacking direction D, the outer edge of the separator 27 is located outside each of the outer edges of the positive electrode active material layer 25 and the negative electrode active material layer 26. The peripheral portion of the separator 27 is located between a seal member 4 and a spacer 5, which will be described later. The separator 27 is a member that allows charge carriers such as lithium ions to pass through. The separator 27 isolates the adjacent electrodes 21, 22, 23 from each other. Thereby, an electrical short circuit due to contact of the electrodes 21, 22, 23 is prevented.

[0024] The current collector 24 is a chemically inert electrical conductor that allows current to continue flowing through the positive electrode active material layer 25 and the negative electrode active material layer 26 during the discharge or charging of the energy storage device 1. The current collector 24 may be in the form of a plate, foil, sheet, film, etc. If the current collector 24 is foil-shaped, its thickness may be in the range of 10 μm to 200 μm.

[0025] The positive electrode active material layer 25 contains a positive electrode active material capable of intercepting and releasing charge carriers such as lithium ions. Examples of positive electrode active materials include composite oxides, metallic lithium, and sulfur. The composition of the composite oxide includes, for example, at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, and lithium. Examples of composite oxides include olivine-type lithium iron phosphate (LiFePO4), LiCoO2, and LiNiMnCoO2.

[0026] The negative electrode active material layer 26 contains a negative electrode active material capable of intercalating and releasing charge carriers such as lithium ions. Examples of negative electrode active materials include graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, soft carbon and other carbons, metal compounds, elements or compounds thereof that can alloy with lithium, and boron-doped carbon. Examples of elements that can alloy with lithium include silicon and tin.

[0027] Each of the positive electrode active material layer 25 and the negative electrode active material layer 26 may contain an active material, a binder, and a conductive additive. The binder plays a role in maintaining the conductive network in the electrode by binding the active material or conductive additive together. Examples of binders include fluororesins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; thermoplastic resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; alkoxysilyl group-containing resins; acrylic resins such as polyacrylic acid and polymethacrylic acid; styrene-butadiene rubber; alginates such as carboxymethylcellulose, sodium alginate, and ammonium alginate; water-soluble cellulose ester crosslinked polymers; and starch-acrylic acid graft polymers. These binders may be used alone or in combination. Conductive additives are conductive materials such as acetylene black, carbon black, and graphite, which can enhance electrical conductivity. Viscosity-adjusting solvents such as N-methyl-2-pyrrolidone can be used.

[0028] Conventional methods such as roll coating, die coating, dip coating, doctor blade coating, spray coating, and curtain coating are used to form the positive electrode active material layer 25 on surface 24a and the negative electrode active material layer 26 on surface 24b. Specifically, an active material, solvent, and optionally a binder and conductive additive are mixed to produce a slurry-like active material layer forming composition. This active material layer forming composition is then applied to surface 24a or surface 24b and dried. Examples of solvents include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The dried material may be compressed to increase electrode density.

[0029] 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 may have a single-layer structure or a multilayer structure. If the separator 27 has a multilayer structure, it may include, for example, a base layer and a pair of adhesive layers, and may be 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 may also include a ceramic layer that serves as a heat-resistant layer. The separator 27 may be reinforced with a vinylidene fluoride resin compound.

[0030] Examples of electrolytes impregnated into the separator 27 include a liquid electrolyte (electrolyte solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, or a polymer gel electrolyte containing an electrolyte held in a polymer matrix. 27 When an electrolyte is impregnated into the separator 27, 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, linear carbonates, linear esters, and ethers can be used as the non-aqueous solvent. Two or more of these known solvent materials may be used in combination. In this embodiment, the electrolyte impregnated into the separator 27 is an electrolyte solution.

[0031] The sealing body 3 is a member that seals the internal space S. The sealing body 3 is provided on the side surface of the laminate 2. The sealing body 3 seals the side surface of the laminate 2. The sealing body 3 is, for example, rectangular cylindrical in shape. The sealing body 3 has electrical insulating properties. The sealing body 3 has a plurality of sealing members 4, a plurality of spacers 5, and a welded portion 6.

[0032] The sealing member 4 is provided on the surface of the current collector 24 so as to surround 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) D. The sealing member 4 is made of resin. The sealing member 4 is joined to the outer edge of at least one of the surfaces 24a and 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 this embodiment, the sealing member 4 is joined to the respective outer edges of the surfaces 24a and 24b. That is, the sealing member 4 is joined to the respective outer edge 24d of the surface 24a and the outer edge 24e of the surface 24b.

[0033] Spacer 5 is provided between adjacent electrodes 21, 22, and 23 in the stacking direction D. Spacer 5 has, for example, a rectangular frame shape. Spacer 5 is made of, for example, resin. The welded portion 6 has, for example, a rectangular cylindrical shape. The welded portion 6 extends to both ends of the laminate 2 in the stacking direction D. The welded portion 6 is formed integrally.

[0034] As shown in Figure 2, 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 bonding the first metal foil 241 and the second metal foil 242 together. The first metal foil 241 includes a surface 24a. The surface 24a of the current collector 24 is the surface of the first metal foil 241 on the side facing the positive electrode active material layer 25. The first metal foil 241 has a rectangular shape when viewed from the lamination direction D. The first metal foil 241 contains aluminum, and is, for example, an aluminum foil. The first metal foil 241 may be, for example, a nickel foil, a titanium foil, or a stainless steel foil. The first metal foil 241 may be an alloy foil of the above metals. A coating layer may be formed on the surface 24a of the first metal foil 241 by a known method such as plating or spray coating.

[0035] The second metal foil 242 is provided 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 current collector 24 is the surface of the second metal foil 242 on the side facing the negative electrode active material layer 26. When viewed from the lamination direction D, the second metal foil 242 has, for example, a rectangular shape. When viewed from the lamination direction D, the side surface (outer edge) 242c of the second metal foil 242 substantially coincides with the side surface (outer edge) 241c of the first metal foil 241. In this embodiment, the second metal foil 242 contains copper, and is, for example, a copper foil. The second metal foil 242 may be, for example, a nickel foil, a titanium foil, or a stainless steel foil. The second metal foil 242 may be an alloy foil of the above metals. A coating layer may be formed on the surface 24b of the second metal foil 242 by a known method such as plating or spray coating.

[0036] The adhesive layer 243 is provided between the first metal foil 241 and the second metal foil 242. When viewed from the lamination direction D, the adhesive layer 243 has, for example, a rectangular shape. When viewed from the lamination direction D, the side surface (outer edge) 243c of the adhesive layer 243 substantially coincides with the side surface 241c of the first metal foil 241 and the side surface 242c of the second metal foil 242, respectively. The side surface (outer edge) 24c of the current collector 24 is composed of side surfaces 241c, 242c, and 243c.

[0037] The adhesive layer 243 adheres the first metal foil 241 and the second metal foil 242. The adhesive layer 243 is adhered to both the first metal foil 241 and the second metal foil 242. The adhesive layer 243 is a conductive adhesive layer having electrical conductivity. The adhesive layer 243 contains, for example, a conductive resin material. Examples of conductive resin materials include conductive polymer materials, or resins in which conductive fillers are added to non-conductive polymer materials.

[0038] In this embodiment, the adhesive layer 243 contains an adhesive component and a conductive component. The adhesive component functions as an adhesive that bonds 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, or an acrylic resin such as polyacrylic acid. If the adhesive component is a thermosetting resin, the adhesive component may further contain a curing agent such as an isocyanate-based curing agent or an epoxy-based curing agent. When the first metal foil 241 and the second metal foil 242 are joined with an adhesive layer 243 having an olefin resin as the adhesive component, an epoxy-based curing agent that generates less gas during the curing reaction of the adhesive component may be used. The adhesive component may also have electrolyte resistance. In this case, even if an electrolyte penetrates between the first metal foil 241 and the second metal foil 242 due to a pinhole defect or the like occurring in one of the first metal foil 241 and the second metal foil 242, the adhesive layer 243 can prevent the electrolyte from reaching the other metal foil 241 and the second metal foil 242, 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 may be composed of the aforementioned material alone, or they may be composed by coating the surface of resin particles or the like with the aforementioned material. As conductive particles, spherical particles with a metal film formed on the surface of core particles made of resin or ceramic may be used.

[0039] The thickness of the first metal foil 241 (length D in the lamination direction of the first metal foil 241) is, for example, 20 μm or more and 150 μm or less. The second metal foil 242 is thinner than the first metal foil 241. The thickness of the second metal foil 242 (length D in the lamination direction of the second metal foil 242) 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 (length D in the lamination direction of the adhesive layer 243) is, for example, 1 / 2 or less of the thickness of the first metal foil 241. The thickness of the adhesive layer 243 is, for example, 5 μm or less, and may be 3 μm or less.

[0040] Here, it is generally known that in metal foils used in current collectors 24, the strength against fatigue damage of the metal foil increases as the thickness of the metal foil increases. In this embodiment, the thickness of the first metal foil 241, which is aluminum foil, is greater than twice the thickness of the second metal foil 242, which is copper foil. Therefore, the strength against fatigue damage of the first metal foil 241 alone is higher than the strength against fatigue damage of the second metal foil 242 alone. That is, the strength against fatigue damage of the second metal foil 242 alone is lower than the strength against fatigue damage of the first metal foil 241 alone.

[0041] 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. When viewed from the stacking direction D, the sealing portion 41 has, for example, 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. The outer edge 41c of the sealing portion 41 substantially coincides with the side surface 24c of the current 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 joined to the outer edge 24d of the surface 24a.

[0042] The sealing portion 42 is provided on the surface 24b. When viewed from the stacking direction D, the sealing portion 42 has, for example, 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. The outer edge 42c of the sealing portion 42 is approximately the same as the side surface 24c of the current 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 joined to the outer edge 24e of the surface 24b. When viewed from the stacking direction D, the inner edge 42d of the sealing portion 42 is approximately the same as the inner edge 41d of the sealing portion 41. The thickness of the sealing portion 42 (length of the sealing portion 42 in the stacking direction D) is, for example, approximately the same as the thickness of the sealing portion 41 (length of the sealing portion 41 in the stacking direction D), and is between 80 μm and 160 μm. The thickness of the sealing portion 41 and the thickness of the sealing portion 42 are both greater than the thickness of the first metal foil 241 and greater than the thickness of the second metal foil 242.

[0043] 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 the sealing portion 41 and the sealing portion 42, respectively. The sealing portion 43 covers the side surface 24c of the current collector 24. The sealing portion 43 covers 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, respectively.

[0044] The sealing portion 43 is bonded to the side surface 24c of the current collector 24. The sealing portion 43 is bonded to 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. Each of the sealing portions 41, 42, and 43 is a part of the sealing member 4, which is integrally formed from the same material.

[0045] Spacer 5 is provided between adjacent sealing members 4 in the stacking direction D. Spacer 5 has, for example, a rectangular frame shape. When viewed from the stacking direction D, the inner edge 5d of spacer 5 is further away from the positive electrode active material layer 25 or the negative electrode active material layer 26 than the inner edge 41d of sealing portion 41 and the inner edge 42d of sealing portion 42, respectively. In other words, when viewed from the stacking direction D, the inner edge 41d of sealing portion 41 is located between the positive electrode active material layer 25 and the inner edge 5d of spacer 5, and the inner edge 42d of sealing portion 42 is located between the negative electrode active material layer 26 and the inner edge 5d of spacer 5. Spacer 5 is a separate component from the sealing members 4.

[0046] The spacer 5 is sandwiched between a pair of adjacent sealing members 4 in the stacking direction D. The spacer 5 is in contact with the sealing members 4. Together with a pair of adjacent bipolar electrodes 21 in the stacking direction D and a pair of adjacent sealing members 4 in the stacking direction D, the spacer 5 forms an internal space S for containing the electrolyte. The spacer 5 has an injection port for injecting the electrolyte into the internal space S.

[0047] The thickness of spacer 5 (the length D in the stacking direction of spacer 5) is greater than the thickness of the sealing portion 41 and sealing portion 42, respectively. For example, the thickness of spacer 5 is at least twice the thickness of sealing portion 41 or sealing portion 42. The thickness of spacer 5 is thinner than the thickness of sealing member 4 (the length D in the stacking direction of sealing member 4). In other words, the thickness of spacer 5 is less than the sum of the thickness of the first metal foil 241, the second metal foil 242, the adhesive layer 243, the sealing portion 41, and the sealing portion 42.

[0048] The spacer 5 is welded to the sealing member 4 outside the side surface 24c of the current collector 24 (i.e., the welded portion 6). Specifically, the welded portion 6 is formed when the outer edges of the sealing member 4 and the spacer 5 are melted and then solidified again. In other words, the welded portion 6 is formed when the outer edges of the sealing member 4 and the spacer 5 are welded to each other.

[0049] Here, the outer edges of the sealing member 4 and the spacer 5 refer to the outer edges of the sealing member 4 and the spacer 5 before welding. The outer edge of the sealing member 4 is the portion of the sealing member 4 before welding that is located on the opposite side from the current collector 24 to the sealing portion 43. The outer edge of the spacer 5 is the portion of the spacer 5 before welding that overlaps with the outer edge of the sealing member 4 when viewed from the stacking direction D. The welded portion 6 does not reach the side surface 24c of the current collector 24. The welded portion 6 is separated from the side surface 24c of the current collector 24. Note that the welded portion 6 has an injection port that communicates with the injection port of the spacer 5. The welded portion 6 may be formed to extend to the side surface 24c of the current collector 24. In this case, the sealing portion 43 of the sealing member 4 after welding is not formed.

[0050] Each of the sealing member 4 and the spacer 5 contains 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. Each of the sealing member 4 and the spacer 5 has electrolyte resistance. The materials of the sealing member 4 and the spacer 5 may be the same or different. In this embodiment, the material of the sealing member 4 is, for example, acid-modified polyethylene or acid-modified polypropylene. In this 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 may be composed of multiple resin layers. In this case, different materials may be used for each resin layer.

[0051] Acid-modified polyethylene and acid-modified polypropylene bond to metals more easily than un-acid-modified polyethylene and un-acid-modified polypropylene. Since the materials of the first metal foil 241 and the second metal foil 242 of the current collector 24 are metal, the bonding strength of the sealing portions 41, 42, and 43 to the first metal foil 241 or the second metal foil 242 can be improved by constructing the sealing portions 41, 42, and 43 from acid-modified polyethylene or acid-modified polypropylene.

[0052] 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 the sealing portion 41 and the sealing portion 42, respectively. In this embodiment, since the sealing member 4 is integrally formed from the same material, the sealing portion 41 and the sealing portion 42 have the same Young's modulus.

[0053] 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. For example, the Young's modulus of the first metal foil 241 and the second metal foil is approximately 100 times or more than that of the adhesive layer 243. The coefficient of linear expansion of the sealing member 4 (sealing portions 41, 42) is greater than that of the first metal foil 241 and the second metal foil 242. For example, the coefficient of linear expansion of the sealing portions 41, 42 is approximately 5 times or more than that of the first metal foil 241 and the second metal foil 242.

[0054] The heat resistance temperature of the adhesive layer 243 (hereinafter sometimes simply referred to as "heat resistance temperature") is higher than the melting points of the sealing portion 41, sealing portion 42, sealing portion 43, and spacer 5. Specifically, the heat resistance temperature of the adhesive component of the adhesive layer 243 is higher than the melting points of the sealing portion 41, sealing portion 42, sealing portion 43, and spacer 5. The melting points of the sealing portion 41, sealing portion 42, sealing portion 43, and spacer 5 are, for example, lower than 150 degrees. The heat resistance temperature of the adhesive layer 243 is, for example, 150 degrees or higher.

[0055] The heat resistance temperature of the adhesive layer 243 is the limit temperature at which a good bonding state between the first metal foil 241 and the second metal foil 242 is maintained. Specifically, the heat resistance temperature of the adhesive layer 243 is the limit temperature at which the adhesive strength between the first metal foil 241 and the second metal foil 242 by the adhesive layer 243 exceeds a predetermined threshold. The predetermined threshold may be, for example, 1% of the adhesive strength of the adhesive layer 243 at room temperature. Generally, when the temperature of the adhesive layer 243 rises due to heating, the adhesive strength of the adhesive layer 243 tends to decrease compared to before heating. Furthermore, when the temperature of the adhesive layer 243 exceeds the heat resistance temperature, the adhesive strength of the adhesive layer 243 decreases to a value lower than the predetermined threshold. If the adhesive strength of the adhesive layer 243 falls below the predetermined 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 current collector 24 may occur. In this embodiment, since the heat resistance temperature of the adhesive layer 243 is higher than the melting points of the sealing portion 41, sealing portion 42, sealing portion 43, and spacer 5, damage to the current collector 24 is unlikely to occur even if the temperature of the adhesive layer 243 reaches the melting point of the sealing portion 41, sealing portion 42, sealing portion 43, or spacer 5 during welding. Damage to the current collector 24 can include, for example, 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 (misalignment 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).

[0056] In this embodiment, the adhesive strength of the adhesive layer 243 heated to its heat resistance 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, a good bond between the first metal foil 241 and the second metal foil 242 is maintained by the adhesive layer 243. If the temperature of the adhesive layer 243 is below the heat resistance temperature, the adhesive strength of the adhesive layer 243 will be 1% or more of the room temperature strength, and a good bond between the first metal foil 241 and the second metal foil 242 will be maintained. In this embodiment, since the heat resistance temperature of the adhesive layer 243 is greater than the melting points of the sealing portion 41, sealing portion 42, sealing portion 43, and spacer 5, even if the temperature of the adhesive layer 243 reaches the melting point of the sealing portion 41, sealing portion 42, sealing portion 43, or spacer 5 during welding, the adhesive strength of the adhesive layer 243 will be 1% or more of the strength at room temperature. In other words, even if the temperature of the adhesive layer 243 reaches the melting point of the sealing portion 41, sealing portion 42, sealing portion 43, or spacer 5, a good bonding state between the first metal foil 241 and the second metal foil 242 by the adhesive layer 243 is maintained, so damage to the current collector 24 is less likely to occur.

[0057] Room temperature strength is measured, for example, as follows: First, a current collector 24 (a current collector 24 without a positive electrode active material layer 25, a negative electrode active material layer 26, or a sealing member 4) is prepared. Next, at room temperature, the peel strength when the first metal foil 241 is peeled from the second metal foil 242 is measured as room temperature strength, for example, by a 180-degree peel strength test (as an example, in accordance with JIS Z 0237:2009). High temperature strength is measured, for example, as follows: First, a current collector 24 is prepared in the same manner as for measuring room temperature strength. Next, the current collector 24 is heated to its heat resistance temperature. Next, while maintaining the temperature of the current collector 24 heated to its heat resistance temperature, the peel strength when the first metal foil 241 is peeled from the second metal foil 242 is measured as high temperature strength, in the same manner as for measuring room temperature strength.

[0058] The current collector 24 is formed by bonding a first metal foil 241 and a second metal foil 242 with an adhesive layer 243, for example, by a dry lamination method. In the dry lamination method, first, an adhesive solution is applied to the first metal foil 241. Next, the adhesive solution is dried to form a uniform adhesive on the surface of the first metal foil 241. Subsequently, the second metal foil 242 is bonded to the first metal foil 241, which has the adhesive formed on it, by heat-pressure bonding. Heat-pressure bonding is performed at a constant pressure using a pair of heating rollers. One of the heating rollers is a movable roller. By moving the movable roller, the distance between the pair of heating rollers can be adjusted, and the pressure during heat-pressure bonding can be adjusted. As a result of bonding, a current collector 24 is obtained in which the first metal foil 241 and the second metal foil 242 are bonded together by the adhesive layer 243.

[0059] The first metal foil 241 and the second metal foil 242 have large thickness tolerances. If the thickness of the adhesive layer 243 is measured by measuring the thickness of the current collector 24 after the first metal foil 241 and the second metal foil 242 have been bonded together, the thickness tolerances of the first metal foil 241 and the second metal foil 242 greatly affect the measurement result of the thickness of the current collector 24, making it impossible to accurately measure the thickness of the adhesive layer 243. Therefore, the thickness of the adhesive layer 243 is controlled 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 falls within the numerical range of a good product, and if it does not, the relevant part is removed from the line before bonding, or the relevant part is cut off after bonding. Note that before bonding, the adhesive is not covered by the second metal foil 242, so the thickness of the adhesive alone can be measured. Here, when performing heat-pressure bonding between the first metal foil 241 and the second metal foil 242, the adhesive (adhesive layer 243), which is sufficiently softer than the first metal foil 241 and the second metal foil 242, is primarily compressed. Therefore, when performing heat-pressure bonding between the first metal foil 241 and the second metal foil 242 at a constant pressure, by investigating in advance the correlation between the thickness of the adhesive layer 243 after heat-pressure bonding and the thickness of the adhesive before bonding when a predetermined pressure is applied, the thickness of the adhesive layer 243 after bonding can be appropriately controlled based on the thickness of the adhesive applied to the first metal foil 241.

[0060] As explained above, in the energy storage device 1, a sealing member 4 having a larger coefficient of linear expansion than the first metal foil 241 and the second metal foil 242 of the current collector 24 is joined to the current collector 24. Therefore, due to repeated temperature changes during use of the energy storage device 1, the sealing member 4 expands and contracts more than the first metal foil 241 and the second metal foil 242, applying repeated tensile and compressive stress to the first metal foil 241 and the second metal foil 242. The current collector 24 has an adhesive layer 243 provided between the first metal foil 241 and the second metal foil 242, which adheres the first metal foil 241 and the second metal foil 242 together. Here, as mentioned above, the second metal foil 242 is thinner than the first metal foil 241 and is therefore more susceptible to fatigue damage. However, the adhesive layer 243 is even 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, and the adhesive layer 243 is softer than the first metal foil 241 and the second metal foil 242, the tensile and compressive stress of the sealing member 4 on the first metal foil 241 and the second metal foil 242 is not easily absorbed by the adhesive layer 243. Thus, the effect of mutually reinforcing the strength of the first metal foil 241 and the second metal foil 242 is obtained. Specifically, the thinner second metal foil 242 can be reinforced by the thicker first metal foil 241. As a result, fatigue damage to 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 sufficient strength in each of the first metal foil 241 and the second metal foil 242 to withstand the repeated tensile and compressive stress of the sealing member 4, the size of the current collector 24 can be suppressed. As a result of suppressing the size of the current collector 24, the energy storage device 1 can be miniaturized.

[0061] This section describes the results of thermal shock tests (in accordance with JIS C 60068-2-14:2011) conducted on multiple test pieces simulating the energy storage device related to the experimental example. Each test piece was formed by providing a sealing member 4 to a single current collector 24. The length of the long side of the current collector 24 was 1.5 m, and the length of the short side was 1.2 m. The current collector 24 was constructed using 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. Acid-modified polyethylene was used as the material for the sealing member 4, and the thickness of the parts corresponding to the sealing portion 41 and sealing portion 42 was set to 120 μm. Multiple test pieces were constructed using current collectors 24 with a fixed copper foil thickness of 7.8 μm and an olefin resin thickness of 3 μm, while varying the aluminum foil thickness to 40 μm, 45 μm, and 50 μm. The multiple test pieces were constructed under identical conditions except for the aluminum foil thickness.

[0062] Table 1 shows the results of the thermal shock test. Table 1 shows the number of cycles until the copper foil broke for aluminum foil thicknesses of 40 μm, 45 μm, and 50 μm, expressed as a ratio with the 40 μm aluminum foil thickness as the baseline (1x). The number of cycles until the copper foil broke represents the number of thermal shocks (thermal cycles) required for the copper foil to break. The copper foil broke faster than the aluminum foil. As shown in Table 1, increasing the thickness of the aluminum foil also increased the number of cycles until the copper foil broke. This result confirms that the aluminum foil provides a reinforcing effect on the copper foil.

[0063] [Table 1]

[0064] Since the thickness of the second metal foil 242 is less than 10 μm, the size of the current collector 24 can be further suppressed. Even though the second metal foil 242 is thin, it can be reinforced by the first metal foil 241, thus suppressing fatigue damage to the second metal foil 242.

[0065] The thickness of the adhesive layer 243 is less than half the thickness of the second metal foil 242. This makes it easier to obtain a reinforcing effect between the first metal foil 241 and the second metal foil 242. Therefore, fatigue damage to the second metal foil 242 can be further suppressed.

[0066] The Young's modulus of the adhesive layer 243 is higher than that of the sealing member 4. Since the adhesive layer 243 is harder than the sealing member 4, the deformation of the current collector 24 due to the expansion and contraction of the sealing member 4 is suppressed compared to a configuration where 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 to the first metal foil 241 and the second metal foil 242 can be suppressed.

[0067] The sealing member 4 includes a sealing portion 41 joined to the outer edge 24d of the surface 24a of the current collector 24, and a sealing portion 42 joined to the outer edge 24e of the surface 24b. Therefore, compared to a configuration in which the sealing member 4 includes either the sealing portion 41 or the sealing portion 42, the tensile and compressive stress that the sealing member 4 imparts to the current collector 24 is increased. Thus, the configuration of the energy storage device 1 in which the first metal foil 241 and the second metal foil 242 can be reinforced together is particularly effective.

[0068] This disclosure is not limited to the embodiments described above.

[0069] In this embodiment, an example is shown where the current collectors 24 for the bipolar electrode 21, the positive terminal electrode 22, and the negative terminal electrode 23 are all the same. However, the current collectors 24 for the positive terminal electrode 22 and the negative terminal electrode 23 may differ from the current collector 24 for the bipolar electrode 21 in terms of material and thickness. The current collectors 24 for the positive terminal electrode 22 and the negative terminal electrode 23 may be made of a single metal foil, rather than, for example, a laminated foil.

[0070] In the embodiment, the sealing member 4 is shown to include sealing portions 41, 42, and 43, but the sealing member 4 only needs to include at least sealing portion 41 or sealing portion 42. That is, the sealing member 4 only needs to be joined to at least the outer edge portion 24d of the surface 24a or the outer edge portion 24e of the surface 24b of the current collector 24.

[0071] In this embodiment, an example is shown where the peripheral edge of the separator 27 is located between the sealing member 4 and the spacer 5, but the peripheral edge of the separator 27 does not necessarily have to reach the spacer 5. The peripheral edge of the separator 27 may also be welded to the sealing member 4.

[0072] In this embodiment, the first metal foil 241 and the second metal foil 242 are directly bonded to the adhesive layer 243, but they may also be bonded to the adhesive layer 243 via a carbon coat layer (not shown). That is, the current collector 24 may further include carbon coat layers provided between the first metal foil 241 and the adhesive layer 243, and between the second metal foil 242 and the adhesive layer 243. The carbon coat layer is conductive. The carbon coat layer contains, for example, a binder and graphite. The carbon coat layer may be provided between the first metal foil 241 and the adhesive layer 243, or between the second metal foil 242 and the adhesive layer 243. In other words, the carbon coat layer only needs to be provided between the first metal foil 241 and the adhesive layer 243, and between the second metal foil 242 and the adhesive layer 243. With this configuration, for example, compared to the case where the first metal foil 241 or the second metal foil 242 is directly bonded to the adhesive layer 243, the binder resin contained in the carbon coat layer is more firmly bonded by the adhesive layer 243, thus ensuring a more reliable bond between the first metal foil 241 and the adhesive layer 243, or between the second metal foil 242 and the adhesive layer 243. Furthermore, even if pinholes are formed in the first metal foil 241, the second metal foil 242, or the adhesive layer 243, the carbon coat layer can suppress liquid junctions between adjacent internal spaces S. The carbon coat layer may also be further provided on the surface 24a or surface 24b of the current collector 24. In this case, the carbon coat layer is also interposed between surface 24a and the sealing portion 41, or between surface 24b and the sealing portion 42.

[0073] The inner edge 5d of the spacer 5 may be positioned closer to the positive electrode active material layer 25 or the negative electrode active material layer 26 than the inner edge 41d of the seal portion 41 and the inner edge 42d of the seal portion 42, respectively, when viewed from the stacking direction D. In other words, when viewed from the stacking direction D, the inner edge 5d of the spacer 5 may be located between the positive electrode active material layer 25 and the inner edge 41d of the seal portion 41, or between the negative electrode active material layer 26 and the inner edge 42d of the seal portion 42. [Explanation of Symbols]

[0074] 1...Energy storage device, 2...Laminate, 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 laminate containing stacked bipolar electrodes, A power storage device comprising a sealant for sealing the laminate, The bipolar electrode is A current collector comprising a first main surface and a second main surface opposite to the first main surface, The first active material layer provided on the first main surface, The second main surface is provided with a second active material layer, The sealing body has a resin sealing member joined to the outer edge of at least one of the first main surface and the second main surface. The aforementioned current collector is A first metal foil including the first main surface, A second metal foil, which includes the second main surface and is thinner than the first metal foil, It comprises a conductive adhesive layer provided between the first metal foil and the second metal foil, which adheres the first metal foil and the second metal foil together. The conductive adhesive layer is thinner than the second metal foil. The Young's modulus of the conductive adhesive layer is higher than that of the sealing member. The thickness of the first metal foil is greater than twice the thickness of the second metal foil. Energy storage device.

2. A laminate containing stacked bipolar electrodes, A power storage device comprising a sealant for sealing the laminate, The bipolar electrode is A current collector comprising a first main surface and a second main surface opposite to the first main surface, The first active material layer provided on the first main surface, The second main surface is provided with a second active material layer, The sealing body has a resin sealing member joined to the outer edge of at least one of the first main surface and the second main surface. The aforementioned current collector is A first metal foil including the first main surface, A second metal foil, which includes the second main surface and is thinner than the first metal foil, It comprises a conductive adhesive layer provided between the first metal foil and the second metal foil, which adheres the first metal foil and the second metal foil together. The conductive adhesive layer is thinner than the second metal foil. The Young's modulus of the conductive adhesive layer is higher than that of the sealing member. The conductive adhesive layer comprises an olefin resin and an epoxy curing agent. Energy storage device.

3. The thickness of the conductive adhesive layer is 1 / 2 or less of the thickness of the second metal foil. The energy storage device according to claim 1 or 2.

4. The thickness of the second metal foil is less than 10 μm. The energy storage device according to claim 1 or 2.

5. The thickness of the conductive adhesive layer is 3 μm or less. The energy storage device according to claim 1 or 2.

6. The sealing member is joined to the outer edges of the first main surface and the second main surface, The energy storage device according to claim 1 or 2.

7. The current collector further has a side surface connecting the first main surface and the second main surface, The sealing member is provided on the side surface, The energy storage device according to claim 6.

8. The heat resistance temperature of the conductive adhesive layer is higher than the melting point of the sealing member. The energy storage device according to claim 1 or 2.

9. The heat resistance temperature of the conductive adhesive layer is 150 degrees Celsius or higher. The energy storage device according to claim 8.

10. The adhesive strength of the conductive adhesive layer after being heated to its heat-resistant temperature is 1% or more of the adhesive strength of the conductive adhesive layer at room temperature. The energy storage device according to claim 1 or 2.

11. The current collector has a rectangular shape, with at least one side having a length of 1 m or more, when viewed from the stacking direction of the laminate. The energy storage device according to claim 1 or 2.

12. The thickness of the first metal foil is 40 μm or more and 150 μm or less. The energy storage device according to claim 1 or 2.

13. The conductive adhesive layer comprises conductive particles, The energy storage device according to claim 1 or 2.

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