Power storage device

Abstract

To provide a power storage device capable of suppressing deterioration of battery performance by moisture permeation.SOLUTION: A power storage device 1 has an electrode laminate 3 including a plurality of electrodes 5, separators 13, and a resin sealing part 4. The plurality of electrodes 5 have bipolar electrodes 8. The bipolar electrode 8 has collectors 21 and 22, a positive electrode active substance layer 23, and a negative electrode active substance layer 24. The sealing part 4 has first adhesive parts 31 bonded to the collectors 21, second adhesive parts 32 bonded to the collectors 22, first reinforcement parts 33 bonded to the first adhesive parts 31, second reinforcement parts 34 bonded to the second adhesive parts 32, and an end face weld part 36. Vapor permeability of the end face weld part 36 is lower than each of vapor permeability of the first adhesive part 31 and vapor permeability of the second adhesive part 32.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electricity storage device. [Background technology]

[0002] Known as an electricity storage device is a bipolar battery equipped with a bipolar electrode in which a positive electrode active material layer is formed on one surface of a current collector and a negative electrode active material layer is formed on the other surface (see, for example, Patent Document 1). In this bipolar battery, a power generation element formed by alternately stacking bipolar electrodes and electrolyte layers (separators) is sealed inside a battery exterior material. A sealant is arranged around the outer periphery of the cell layer in the power generation element to prevent liquid junctions due to leakage of electrolyte from the electrolyte layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-204386 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide an electricity storage device that can suppress deterioration of battery performance due to moisture permeation. [Means for solving the problem]

[0005] An energy storage device according to one aspect of the present disclosure includes an electrode stack including a plurality of electrodes stacked in a first direction, a separator disposed between the electrodes, and a resin sealing portion that surrounds the electrode stack as viewed from the first direction and seals the space between the electrodes, the plurality of electrodes having bipolar electrodes, the bipolar electrode having a current collector, a first active material layer provided on a first surface of the current collector, and a second active material layer provided on a second surface of the current collector, and the sealing portion includes a first resin portion provided on an edge of the first surface so as to surround the first active material layer as viewed from the first direction, and a second active material layer provided on an edge of the second active material layer as viewed from the first direction. and an end face welded portion formed by welding the outer edges of a plurality of resin portions, including the first resin portion and the second resin portion, together. The first resin portion has a first adhesive portion welded to the first surface and a first reinforcing portion integrated with the surface of the first adhesive portion opposite the current collector. The second resin portion has a second adhesive portion welded to the second surface and a second reinforcing portion integrated with the surface of the second adhesive portion opposite the current collector. The water vapor permeability of the end face welded portion is lower than that of both the first adhesive portion and the second adhesive portion.

[0006] In the above-described energy storage device, a resin sealing portion seals the space between the multiple electrodes stacked in the first direction. The sealing portion includes a first resin portion, a second resin portion, and an end surface weld portion. To ensure sealing performance, a resin with high adhesion to the current collector may be used for the first adhesive portion of the first resin portion and the second adhesive portion of the second resin portion. Even in this case, the water vapor permeability of the end surface weld portion is lower than that of the first adhesive portion and that of the second adhesive portion. Therefore, even if the first adhesive portion and the second adhesive portion are made of a resin with high adhesion to the current collector and high water vapor permeability, moisture is prevented from permeating through the end surface weld portion in a direction intersecting the first direction and entering the space between the electrodes. As a result, degradation of battery performance due to moisture permeation is suppressed.

[0007] The degree of acid modification of the resin in the edge welded portion may be lower than the degree of acid modification of the resin in the first adhesive portion and the degree of acid modification of the resin in the second adhesive portion, respectively. In this case, the water vapor permeability of the edge welded portion can be lower than the water vapor permeability of the first adhesive portion and the water vapor permeability of the second adhesive portion.

[0008] The crystallinity of the resin in the end face welded portion may be higher than the crystallinity of the resin in the first adhesive portion and the crystallinity of the resin in the second adhesive portion. In this case, the water vapor permeability of the resin in the end face welded portion can be lower than the water vapor permeability of the resin in the first adhesive portion and the water vapor permeability of the resin in the second adhesive portion. Furthermore, in this case, the acid-modified degree of the resin in the end face welded portion can be lower than the acid-modified degree of the resin in the first adhesive portion and the acid-modified degree of the resin in the second adhesive portion.

[0009] The water vapor permeability of the first reinforcing portion may be lower than that of the first adhesive portion and that of the second adhesive portion, and the water vapor permeability of the second reinforcing portion may be lower than that of the first adhesive portion and that of the second adhesive portion, respectively. In this case, it is easy to make the water vapor permeability of the end surface welded portion lower than that of the first adhesive portion and that of the second adhesive portion.

[0010] The ratio of the total thickness of the first adhesive portion and the second adhesive portion to the thickness of the multiple resin portions may be 5% or more and 50% or less. This allows the ratio of the total volume of the first adhesive portion and the second adhesive portion to the volume of the end face weld portion to be 5% or more and 50% or less. Degraded gases, such as hydrogen and methane, generated in the space between the electrodes permeate the sealing portion and are released to the outside. The first adhesive portion and the second adhesive portion are more permeable to degraded gases than the first reinforcing portion and the second reinforcing portion. Therefore, by setting the ratio to 5% or more, a path for degraded gases to permeate the sealing portion can be secured. Furthermore, by setting the ratio to 50% or less, the ratio of the total volume of the first reinforcing portion and the second reinforcing portion to the volume of the end face weld portion can be maintained at a value higher than 50%. This reduces the path for water vapor to permeate the end face weld portion, thereby suppressing deterioration of battery performance.

[0011] The sealing portion may further include a spacer disposed between the first reinforcing portion and the second reinforcing portion in the first direction, and the spacer may be surface-bonded to each of the first reinforcing portion and the second reinforcing portion at the end surface welded portion, and the water vapor permeability of the spacer may be lower than the water vapor permeability of each of the first adhesive portion and the second adhesive portion. In this case, the water vapor permeability of the end surface welded portion may be lower than the water vapor permeability of each of the first adhesive portion and the second adhesive portion.

[0012] Each current collector may include a first current collector having a first surface and a second current collector having a second surface, which is a separate member from the first current collector. In this case, the thickness, material, and surface treatment of the current collector can be configured in any desired combination. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide an electricity storage device that can suppress deterioration of battery performance due to moisture permeation. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the electricity storage device according to the first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of the energy storage cell shown in FIG. [Figure 3] FIG. 3 is a schematic cross-sectional view illustrating a method for forming a bipolar electrode unit. [Figure 4] FIG. 4 is a schematic cross-sectional view showing the electricity storage device according to the second embodiment. [Figure 5] FIG. 5 is a schematic cross-sectional view of the energy storage cell shown in FIG. [Figure 6] FIG. 6 is a schematic cross-sectional view showing an electricity storage device according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0016] (Configuration of the power storage device) FIG. 1 is a schematic cross-sectional view showing a power storage device according to a first embodiment. The power storage device 1 shown in FIG. 1 is a power storage module used in batteries for various vehicles such as forklifts, hybrid vehicles, and electric vehicles. The power storage device 1 is a secondary battery such as a nickel-metal hydride secondary battery or a lithium-ion secondary battery. The power storage device 1 may be an electric double layer capacitor or an all-solid-state battery. In this embodiment, the case where the power storage device 1 is a lithium-ion secondary battery is exemplified.

[0017] The energy storage device 1 includes an electrode stack 3, a separator 13, and a sealing portion 4. The electrode stack 3 includes multiple electrodes 5 stacked in direction D. The separator 13 is disposed between adjacent electrodes 5 in direction D. The sealing portion 4 surrounds the electrode stack 3 and seals the space S between adjacent electrodes 5 in direction D. The multiple electrodes 5 include a positive terminal electrode 6, a negative terminal electrode 7, and multiple bipolar electrodes 8. The positive terminal electrode 6 is disposed at one end in the stacking direction (direction D). The negative terminal electrode 7 is disposed at the other end in the stacking direction. The multiple bipolar electrodes 8 are disposed between the positive terminal electrode 6 and the negative terminal electrode 7.

[0018] The positive terminal electrode 6 includes a current collector 21 having a first surface 21a and a second surface 21b facing opposite to each other, and a positive electrode active material layer 23 provided on the first surface 21a. The negative terminal electrode 7 includes a current collector 22 having a first surface 22a and a second surface 22b facing opposite to each other, and a negative electrode active material layer 24 provided on the second surface 22b. The bipolar electrode 8 includes a current collector 10 having a first surface 10a and a second surface 10b facing opposite to each other, a positive electrode active material layer 23 (first active material layer) provided on the first surface 10a, and a negative electrode active material layer 24 (second active material layer) provided on the second surface 10b. The first surface 10a, together with the positive electrode active material layer 23, constitutes a positive electrode 11. The second surface 10b, together with the negative electrode active material layer 24, constitutes a negative electrode 12. Hereinafter, the current collectors 10, 21, and 22 may be collectively referred to as "current collectors."

[0019] The positive electrode 11 and the negative electrode 12 are arranged such that the positive electrode active material layer 23 and the negative electrode active material layer 24 face each other in direction D with the separator 13 interposed therebetween. In this embodiment, the positive electrode active material layer 23 and the negative electrode active material layer 24 are both formed in a rectangular shape when viewed from direction D. The negative electrode active material layer 24 is formed to be slightly larger than the positive electrode active material layer 23. When viewed from direction D, the entire positive electrode active material layer 23 is located inside the outer edge of the negative electrode active material layer 24.

[0020] The energy storage device 1 is a cell stack having a plurality of storage cells 2 stacked in a direction D. Each storage cell 2 has a positive electrode 11 and a negative electrode 12 that face each other in the direction D with a separator 13 interposed therebetween. The plurality of storage cells 2 are stacked such that a pair of storage cells 2 adjacent to each other in the direction D share the same current collector 10. This allows the plurality of storage cells 2 to be electrically connected in series.

[0021] Fig. 2 is a schematic cross-sectional view of the energy storage cell shown in Fig. 1. As shown in Figs. 1 and 2, no active material layer is provided on either the first surface 10a side or the second surface 10b side of the edge portion 10c of the current collector 10 of the bipolar electrode 8. In other words, the first surface 10a and the second surface 10b have regions in the edge portion 10c where no active material layer is provided. When viewed from direction D, the edge portion 10c is located outside the region of the current collector 10 where the positive electrode active material layer 23 or the negative electrode active material layer 24 is provided.

[0022] The current collector is a chemically inactive electrical conductor that allows current to continue to flow through the positive electrode active material layer and the negative electrode active material layer during charging or discharging of the lithium ion secondary battery. For example, a metal material can be used as the material for the current collector. The current collector may be formed by laminating one or more layers containing a conductive resin material or a conductive inorganic material on a layer of the aforementioned metal material. A coating layer may be formed on the surface of the current collector by a known method such as plating or spray coating. The current collector may be formed in the form of, for example, a plate, foil, sheet, film, mesh, or the like.

[0023] When the current collectors 10, 21, and 22 are metal foils, examples of such foils include aluminum foil, copper foil, nickel foil, titanium foil, and stainless steel foil. The current collectors 10, 21, and 22 may also be alloy foils or clad foils of the above metals. When the current collectors 10, 21, and 22 are foil-shaped, the thickness of the current collectors 10, 21, and 22 may be in the range of 1 μm to 100 μm. The current collectors 10, 21, and 22 may be integrated by, for example, copper plating one side of an aluminum foil. In this embodiment, the current collector 10 of the bipolar electrode is an integrated current collector formed by bonding two different metal foils, namely, aluminum foil and copper foil. The first surface 10a is formed by the surface of the aluminum foil, and the second surface 10b is formed by the surface of the copper foil. Alternatively, the current collectors 21 and 22 may be integrated by bonding two different metal foils, namely, aluminum foil and copper foil.

[0024] The positive electrode active material layer 23 includes a positive electrode active material capable of absorbing and releasing charge carriers such as lithium ions. Examples of the positive electrode active material include composite oxides, metallic lithium, and sulfur. The composite oxides include lithium and at least one of iron, manganese, titanium, nickel, cobalt, and aluminum. Examples of the composite oxides include olivine-type lithium iron phosphate (LiFePO4), LiCoO2, and LiNiMnCoO2.

[0025] The negative electrode active material layer 24 includes a negative electrode active material capable of absorbing and releasing charge carriers such as lithium ions. Examples of the negative electrode active material include graphite, artificial graphite, highly oriented graphite, mesocarbon microbeads, hard carbon, soft carbon, and other carbons, metal compounds, elements or compounds thereof that can be alloyed with lithium, and boron-doped carbon. Examples of elements that can be alloyed with lithium include silicon and tin.

[0026] In addition to the active material, the positive electrode active material layer 23 and the negative electrode active material layer 24 may contain a binder and a conductive additive. The binder serves to connect the active material or conductive additive to each other and maintain the conductive network within the electrode. Examples of binders include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber; thermoplastic resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; alkoxysilyl group-containing resins; acrylic resins such as polyacrylic acid and polymethacrylic acid; styrene-butadiene rubber; carboxymethyl cellulose; alginates such as sodium alginate and ammonium alginate; water-soluble cellulose ester crosslinked bodies; and starch-acrylic acid graft polymers. These binders may be used alone or in combination. The conductive additive is, for example, a conductive material such as acetylene black, carbon black, or graphite, and can enhance electrical conductivity. Examples of viscosity-adjusting solvents include N-methyl-2-pyrrolidone.

[0027] To form the positive electrode active material layer 23 and the negative electrode active material layer 24 on the current collectors 10, 21, and 22, conventional methods such as roll coating, die coating, dip coating, doctor blade coating, spray coating, and curtain coating are used. Specifically, an active material, a solvent, and, if necessary, a binder and a conductive additive are mixed to produce a slurry-like active material layer-forming composition. The active material layer-forming composition is then applied to the current collectors 10, 21, and 22 and dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The dried electrode may be compressed to increase electrode density.

[0028] The separator 13 is interposed between the positive electrode 11 and the negative electrode 12. The separator 13 is a component that separates adjacent positive electrodes 11 and negative electrodes 12 when multiple electrodes 5 are stacked, thereby preventing an electrical short circuit due to contact between the electrodes while allowing charge carriers such as lithium ions to pass through.

[0029] The separator 13 has a rectangular shape that is slightly larger than the positive electrode active material layer 23 and the negative electrode active material layer 24 and slightly smaller than the current collectors 10, 21, and 22 when viewed from the direction D. The end portion 13a of the separator 13 is disposed outside the positive electrode active material layer 23 and the negative electrode active material layer 24 when viewed from the direction D. The end portion 13a of the separator 13 does not overlap either the positive electrode active material layer 23 or the negative electrode active material layer 24 when viewed from the direction D. The end portion 13a of the separator 13 is fixed to the sealing portion 4.

[0030] The separator 13 is formed, for example, in a sheet shape. The separator 13 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains an electrolyte. Examples of materials constituting the separator 13 include polyolefins such as polypropylene or polyethylene, or polyesters. The separator 13 may have a single-layer structure or a multi-layer structure. In the case of a multi-layer structure, the separator 13 may include, for example, a substrate layer and a pair of adhesive layers, and may be bonded and fixed to the positive electrode active material layer 23 and the negative electrode active material layer 24 by the pair of adhesive layers. The separator 13 may also include a ceramic layer that serves as a heat-resistant layer. The separator 13 may also be reinforced with a vinylidene fluoride resin compound.

[0031] Examples of the electrolyte impregnated into the separator 13 include a liquid electrolyte (electrolytic solution) containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent, and a polymer gel electrolyte containing an electrolyte held in a polymer matrix. When the separator 13 is impregnated with an electrolyte, known lithium salts such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCF3SO3, LiN(FSO2)2, and LiN(CF3SO2)2 can be used as the electrolyte salt. Also, known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers can be used as the non-aqueous solvent. Two or more of these known solvent materials may be used in combination.

[0032] The sealing portion 4 is a resin member that seals the electrode stack 3. The sealing portion 4 has a rectangular frame shape when viewed from direction D. When viewed from direction D, the sealing portion 4 may be spaced apart from the positive electrode active material layer 23 and the negative electrode active material layer 24. In the energy storage cell 2, a space S is defined by the current collectors and the sealing portion 4. The sealing portion 4 seals the space S between adjacent current collectors. An electrolyte (not shown) is accommodated in the space S. The sealing portion 4 seals the electrolyte in the space S.

[0033] The sealing portion 4 is made of an electrically insulating resin material to prevent short circuits between adjacent current collectors. Examples of materials that can be used to form the sealing portion 4 include polyolefins such as polypropylene and polyethylene. The sealing portion 4 is bonded (attached) to the edge portion 10c of the first surface 10a and the edge portion 10c of the second surface 10b. The sealing portion 4 is disposed between adjacent current collectors, thereby maintaining a gap between the adjacent current collectors. The sealing portion 4 is made of an electrolyte-resistant resin material to prevent leakage of the electrolyte, which is sealed inside the energy storage cell 2 together with the active material layer, to the outside.

[0034] The sealing portion 4 includes multiple resin portions and an end surface weld portion 36 formed by welding the outer edges of the multiple resin portions together. The multiple resin portions include multiple first resin portions R1, multiple second resin portions R2, and multiple spacers 35. The first resin portion R1 is a sealing member provided on the first surface 10a of the current collector 10 so as to surround the positive electrode active material layer 23 when viewed from direction D. The first resin portion R1 is also provided on the first surface 21a of the current collector 21 and the first surface 22a of the current collector 22. The second resin portion R2 is a sealing member provided on the second surface 10b of the current collector 10 so as to surround the negative electrode active material layer 24 when viewed from direction D. The second resin portion R2 is also provided on the second surface 21b of the current collector 21 and the second surface 22b of the current collector 22. The spacer 35 is sandwiched between adjacent first resin portions R1 and second resin portions R2. Each of the multiple resin portions has a rectangular frame shape when viewed from the direction D. Hereinafter, the first resin portion R1 and the second resin portion R2 may be collectively referred to as a "sealing member."

[0035] To improve the sealing performance of the sealing portion 4, it is necessary to construct the sealing portion 4 from a resin that has high adhesion to the current collector. Among resin materials of the same type, resins containing acid-modified groups (e.g., acid-modified polyethylene) have higher adhesion to metals than resins without acid-modified groups (e.g., polyethylene). Meanwhile, the acid modification degree of a resin (the proportion of resins containing acid-modified groups in a resin material) correlates with the water vapor permeability of the resin. Among resin materials of the same type, the water vapor permeability of a resin with a high acid modification degree (e.g., acid-modified polyethylene) is higher than that of a resin with a low acid modification degree (e.g., polyethylene). If moisture permeates the sealing portion 4 and enters the space S, battery performance may be degraded. Therefore, the sealing portion 4 must be able to both seal and suppress moisture permeation. The acid modification degree is the proportion (content, mass %, volume %, compounding ratio, mixing ratio, etc.) of compounds containing acid-modified groups in the resin components. The acid modification degree can be measured, for example, using a known infrared absorption spectroscopy method. Water vapor transmission rate (WVTR) is the amount of water vapor that passes through a test piece per unit area in a unit of time under specified temperature and humidity conditions. Water vapor transmission rate is expressed as the number of grams of water vapor that permeates per square meter of area in 24 hours [g / (m 2 ·24h).

[0036] Acid-modifying a resin reduces its crystallinity due to substitution by acid-modified groups. The increase in the amount of amorphous polymers or additives in the resin also reduces its crystallinity. Crystallinity refers to the ratio (mass %, volume %, compounding ratio, or mixture ratio) of the crystalline portion of a crystalline substance to the entire substance. Therefore, as the crystallinity of a resin decreases, the proportion of crystalline polymer in the overall resin material decreases. As a result, intermolecular gaps are more likely to form than when a high amount of crystalline polymer is blended, and these gaps become pathways for liquids and gases to pass through. Therefore, as the crystallinity of a resin decreases, its liquid resistance decreases and its water vapor permeability increases. Crystallinity is generally determined by the diffraction intensity (peak height) of X-ray diffraction. This method allows the diffraction angle to determine the main composition of the resin. Crystallinity can also be measured from the intensity of the crystalline band in the infrared absorption spectrum. The degree of crystallinity of only the main component of a resin can also be estimated by examining the crystallization temperature of the resin using differential scanning calorimetry (DSC). This method allows us to estimate the relative crystallinity of the main component for multiple resins whose crystallinity is changed by varying the blending ratio of amorphous polymer or additives while keeping the main component constant.

[0037] The first resin portion R1 is bonded to the edge of the first surface 10a of the current collector 10, the edge of the first surface 21a of the current collector 21, and the edge of the first surface 22a of the current collector 22. The first resin portion R1 has a first adhesive portion 31 that abuts on and is bonded to the current collector, and a first reinforcing portion 33 that is integrated with the surface of the first adhesive portion 31 that is opposite the current collector. The second resin portion R2 is bonded to the edge of the second surface 10b of the current collector 10, the edge of the second surface 21b of the current collector 21, and the edge of the second surface 22b of the current collector 22. The second resin portion R2 has a second adhesive portion 32 that is bonded to the current collector, and a second reinforcing portion 34 that is integrated with the surface of the second adhesive portion 32 that is opposite the current collector. The edges of the current collector 10 are reinforced by the first resin portion R1 and the second resin portion R2 bonded to the first surface 10a and the second surface 10b of the current collector 10, respectively. As a result, the rigidity of the bipolar electrode unit described below is increased, making it easier to handle during manufacturing. Similarly, by reinforcing the edges of the current collector 21, the rigidity of the positive terminal electrode unit described below is increased, making it easier to handle during manufacturing. Furthermore, by reinforcing the edges of the current collector 22, the rigidity of the negative terminal electrode unit described below is increased, making it easier to handle during manufacturing.

[0038] The first adhesive portion 31 and the second adhesive portion 32 are layers for adhering the first resin portion R1 and the second resin portion R2 to the current collector. Therefore, the first adhesive portion 31 and the second adhesive portion 32 are made of a resin material that has high adhesive strength to the current collector. For example, when the current collector is made of a metal foil, the first adhesive portion 31 and the second adhesive portion 32 are made of a resin having an acid-modified group, such as acid-modified polyethylene (acid-modified PE) or acid-modified polypropylene (acid-modified PP), which has good adhesion to metals. When comparing resin materials of the same type, resins having an acid-modified group, such as acid-modified PE and acid-modified PP (acid-modified resins), have higher adhesion to metals than resins without acid-modified groups, such as polyethylene (PE) and polypropylene (PP). The first adhesive portion 31 may be welded to the first surface 10a of the current collector 10, the first surface 21a of the current collector 21, and the first surface 22a of the current collector 22. The second adhesive portion 32 may be welded to the second surface 10b of the current collector 10, the second surface 21b of the current collector 21, and the second surface 22b of the current collector 22.

[0039] The thicknesses of the first adhesive portion 31 and the second adhesive portion 32 are set to a minimum thickness sufficient to ensure the adhesive strength required to bond the first resin portion R1 and the second resin portion R2 to the current collector. On the other hand, to prevent moisture from penetrating from the outside, the thicknesses of the first adhesive portion 31 and the second adhesive portion 32 are set to be less than necessary. Resins containing acid-modified groups, such as acid-modified PE and acid-modified PP, which have good adhesion to metals, tend to have higher water vapor permeability than resins without acid-modified groups, such as PE and PP. For example, the thicknesses of the first adhesive portion 31 and the second adhesive portion 32 are 20 μm or more and 200 μm or less. By setting the thickness to 20 μm or more, the adhesive portions 31 and 32 of the sealing member adhere to the corresponding current collectors, sealing the gap between adjacent current collectors. By setting the thickness to 200 μm or less, the moisture permeation path can be narrowed, thereby preventing moisture permeation. In this embodiment, the thicknesses of the first adhesive portion 31 and the second adhesive portion 32 are 50 μm.

[0040] The first reinforcing portion 33 is a resin layer that increases the rigidity of the first resin portion R1 and ensures the pressure resistance of the sealing portion 4. For this reason, a resin material having a higher Young's modulus than that of the first adhesive portion 31 is used for the first reinforcing portion 33. The first reinforcing portion 33 may also function as a resin layer for enhancing the moisture permeation suppression effect of the sealing portion 4 including the first resin portion R1. In this case, a resin material having a water vapor permeability lower than that of the first adhesive portion 31 is used for the first reinforcing portion 33. The first adhesive portion 31 and the first reinforcing portion 33 are formed of the same type of resin material and are surface-bonded to each other to form an integrated body. The first reinforcing portion 33 is surface-bonded to the first adhesive portion 31 by, for example, co-extrusion or thermal lamination, with the interface welded.

[0041] The second reinforcing portion 34 is a resin layer that increases the rigidity of the second resin portion R2 and ensures the pressure resistance of the sealing portion 4. For this reason, a resin material having a higher Young's modulus than that of the second adhesive portion 32 is used for the second reinforcing portion 34. The second reinforcing portion 34 may also function as a resin layer for enhancing the moisture permeation suppression effect of the sealing portion 4 including the second resin portion R2. In this case, a resin material having a water vapor permeability lower than that of the second adhesive portion 32 is used for the second reinforcing portion 34. The second adhesive portion 32 and the second reinforcing portion 34 are formed of the same type of resin material and are surface-bonded to each other to form an integrated body. The second reinforcing portion 34 is surface-bonded to the second adhesive portion 32, for example, by co-extrusion or thermal lamination, with the interface welded.

[0042] The thickness of the first reinforcement portion 33 and the second reinforcement portion 34 is, for example, 20 μm or more and 200 μm or less. In this embodiment, the thickness of the first reinforcement portion 33 and the second reinforcement portion 34 is 120 μm. When viewed from direction D, the outer edges of the first adhesive portion 31, the second adhesive portion 32, the first reinforcement portion 33, and the second reinforcement portion 34 overlap each other at the end face weld portion 36 of the sealing portion 4.

[0043] To enhance the moisture permeation suppression effect of the sealing portion 4, the first reinforcement portion 33 and the second reinforcement portion 34 may be formed of a resin having a water vapor permeability lower than that of at least the first adhesive portion 31 and the second adhesive portion 32. Generally, among the same type of resin material, the water vapor permeability of a resin having an acid-modified group is higher than that of a resin not having an acid-modified group. Therefore, if the first adhesive portion 31 and the second adhesive portion 32 are formed of a resin material having an acid-modified group, such as acid-modified PE or acid-modified PP, which has good adhesion to metal foil, the first reinforcement portion 33 and the second reinforcement portion 34 are formed of a resin material such as non-acid-modified polyethylene (PE) or non-acid-modified polypropylene (PP). The first reinforcement portion 33 and the second reinforcement portion 34 may be formed of the same type of resin material as the first adhesive portion 31 and the second adhesive portion 32. For example, when acid-modified PE is used for the first adhesive portion 31 and the second adhesive portion 32, non-acid-modified polyethylene is used for the first reinforcing portion 33 and the second reinforcing portion 34. When acid-modified PP is used for the first adhesive portion 31 and the second adhesive portion 32, non-acid-modified polypropylene is used for the first reinforcing portion 33 and the second reinforcing portion 34. The first reinforcing portion 33 and the second reinforcing portion 34 may also be made of the same resin material as the first adhesive portion 31 and the second adhesive portion 32, such as acid-modified PE or acid-modified PP. In this case, the degree of acid modification is adjusted, or the material properties are adjusted by additives or the like, so that at least the Young's modulus is higher than that of the first adhesive portion 31 and the second adhesive portion 32.

[0044] The spacer 35 is disposed between the first reinforcing portion 33 of the first resin portion R1 and the second reinforcing portion 34 of the second resin portion R2 in the direction D. The end portion 13a of the separator 13 may be welded and fixed to the spacer 35 or the sealing member. The end portion 13a of the separator 13 may be sandwiched and fixed between the spacer 35 and the sealing member. The outer edge portion 35a of the spacer 35 is welded to the outer edge portions R1a, R2a of the sealing member and integrated as an end surface weld portion 36.

[0045] Like the first reinforcing portion 33 and the second reinforcing portion 34, the spacer 35 may be formed of a resin having a water vapor permeability lower than that of the first adhesive portion 31 and the second adhesive portion 32, respectively, to enhance the moisture permeation suppression effect of the sealing portion 4. The spacer 35 may be formed of a resin material such as non-acid-modified polyethylene (PE) or non-acid-modified polypropylene (PP). The spacer 35 may be formed of the same material as the first reinforcing portion 33 and the second reinforcing portion 34. In this case, the spacer 35 is sandwiched between the first reinforcing portion 33 and the second reinforcing portion 34, which are made of the same material, and therefore is easily compatible when forming the end face weld portion 36. As a result, the end face weld portion 36 is easily formed. The spacer 35 may also be formed of the same type of resin material as the first adhesive portion 31 and the second adhesive portion 32. For example, if the first adhesive portion 31 and the second adhesive portion 32 are made of acid-modified polyethylene (PE), the spacer 35 may be formed of non-acid-modified polyethylene. When the first adhesive portion 31 and the second adhesive portion 32 are made of acid-modified polypropylene (PP), the spacer 35 may be made of non-acid-modified polypropylene. Alternatively, the spacer 35 may be made of the same resin material as the first adhesive portion 31 and the second adhesive portion 32, such as acid-modified PE or acid-modified PP. In this case, the degree of acid modification of the spacer 35 is adjusted, or the material properties of the spacer 35 are adjusted with additives or the like, so that the water vapor permeability of the spacer 35 is lower than at least the water vapor permeability of the first adhesive portion 31 and the water vapor permeability of the second adhesive portion 32.

[0046] The thickness of the spacer 35 is adjusted according to the film thickness of the active material layers (positive electrode active material layer 23 and negative electrode active material layer 24) disposed between the opposing electrodes. In FIGS. 1 and 2, the spacer 35 is in surface contact with each of the first reinforcing portion 33 and the second reinforcing portion 34, even inside the end face weld portion 36. If the thickness of the spacer 35 is, for example, 50 μm or more and 600 μm or less, the film thickness of the active material layer can be ensured. Furthermore, the thicker the spacer 35, the lower the water vapor permeability of the end face weld portion 36 that can be provided. In this embodiment, the thickness of the spacer 35 is 500 μm.

[0047] When viewed from direction D, the inner edge of the spacer 35 may be located outside the inner edges of the first adhesive portion 31, the second adhesive portion 32, the first reinforcing portion 33, and the second reinforcing portion 34. The inner edge of the spacer 35 is located, for example, 1 mm or more outside the inner edges of the first adhesive portion 31, the second adhesive portion 32, the first reinforcing portion 33, and the second reinforcing portion 34. When viewed from direction D, the outer edge of the spacer 35 coincides with the outer edges of the first adhesive portion 31, the second adhesive portion 32, the first reinforcing portion 33, and the second reinforcing portion 34.

[0048] The end face welded portion 36 is formed by welding and integrating the outer edges of multiple resin portions, i.e., the outer edge R1a of the first resin portion R1, the outer edge R2a of the second resin portion R2, and the outer edge 35a of the spacer 35. In the end face welded portion 36, the multiple resin portions are stacked in a state where adjacent resin portions in the stacking direction (direction D) are melted and surface-welded. The ratio of the total thickness of the first adhesive portion 31 and the second adhesive portion 32 to the thickness of the multiple resin portions is 5% or more and 50% or less. The average water vapor permeability of the end face welded portion 36 is lower than the water vapor permeability of the first adhesive portion 31 and the water vapor permeability of the second adhesive portion 32, respectively. Here, the average water vapor permeability of the end face welded portion 36 is the average amount of water vapor per unit area that passes through the end face welded portion 36 per unit time under specified temperature and humidity conditions. The average acid modification degree of the resin in the end face welded portion 36 is lower than the acid modification degree of the resin in the first adhesive portion 31 and the acid modification degree of the resin in the second adhesive portion 32. The average crystallinity degree of the resin in the end face welded portion 36 is higher than the crystallinity of the resin in the first adhesive portion 31 and the crystallinity of the resin in the second adhesive portion 32. Here, the average crystallinity of the resin in the end face welded portion 36 refers to the ratio (mass %, volume %, compounding ratio, mixing ratio) of the crystalline portion contained in the end face welded portion 36 to the entire end face welded portion 36.

[0049] In this embodiment, the inner edge of the end surface weld 36 is spaced apart from the end surface of the current collector, but the end surface weld 36 may be in contact with the end surface of the current collector. The end surface weld 36 may also be provided up to the inside of the end surface of the current collector.

[0050] (Method of manufacturing an electricity storage device) An example of a manufacturing method for the energy storage device 1 will be described. First, a positive terminal electrode 6, a negative terminal electrode 7, a plurality of bipolar electrodes 8, a plurality of first resin parts R1, and a plurality of second resin parts R2 are prepared. Next, a plurality of bipolar electrode units, a positive terminal electrode unit, and a negative terminal electrode unit are formed, respectively.

[0051] 3 is a schematic cross-sectional view illustrating a method for forming a bipolar electrode unit. As shown in FIG. 3, a first resin portion R1, an edge portion 10c of a current collector 10 of a bipolar electrode 8, and a second resin portion R2 are arranged to overlap in direction D. At this time, the first resin portion R1 is arranged on the first surface 10a of the current collector 10 so that the inner edge portion R1b of the first resin portion R1 contacts the edge portion 10c and the outer edge portion R1a of the first resin portion R1 extends beyond the edge portion 10c as viewed in the stacking direction (direction D). Furthermore, the second resin portion R2 is arranged on the second surface 10b of the current collector 10 so that the inner edge portion R2b of the second resin portion R2 contacts the edge portion 10c and the outer edge portion R2a of the second resin portion R2 extends beyond the edge portion 10c as viewed in the stacking direction (direction D).

[0052] Subsequently, the inner edge portion R1b of the first resin portion R1 and the inner edge portion R2b of the second resin portion R2 are bonded to the edge portion 10c by applying heat and pressure in the direction D. This forms a bipolar electrode unit.

[0053] Although not shown in the figures, the positive electrode terminal electrode unit is formed by overlapping a first resin part R1, a positive electrode terminal electrode 6, and a second resin part R2 in direction D and applying heat and pressure in direction D. The negative electrode terminal electrode unit is formed by overlapping a first resin part R1, a negative electrode terminal electrode 7, and a second resin part R2 in direction D and applying heat and pressure in direction D.

[0054] Next, the positive electrode terminal electrode unit, the plurality of bipolar electrode units, and the negative electrode terminal electrode unit are stacked in direction D. At this time, separators 13 and spacers 35 are placed between adjacent units. This forms the electrode stack 3. Next, an end face weld 36 is formed using a heating device. The heating device is, for example, an infrared heater. Pressure is applied from direction D to the outer edges R1a, R2a of the stacked sealing members and the outer edge 35a of the spacer 35, and heat is input from the surface direction (direction perpendicular to the stacking direction) to the stack end faces of the outer edges R1a, R2a of the stacked sealing members and the outer edge 35a of the spacer 35. This causes the outer edges R1a, R2a of the sealing members that protrude outward from the edge 10c to be welded to each other, forming the end face weld 36. In this manner, the energy storage device 1 is manufactured.

[0055] FIG. 4 is a schematic cross-sectional view showing an energy storage device according to a second embodiment. FIG. 5 is a schematic cross-sectional view of the energy storage cell shown in FIG. 4. As shown in FIGS. 4 and 5, the energy storage device 1A according to the second embodiment differs from the energy storage device 1 according to the first embodiment (see FIG. 1) in that it includes a sealing portion 4A. The sealing portion 4 (see FIG. 1) has a structure in which a first resin portion R1, a spacer 35, and a second resin portion R2 are stacked one on top of the other, but the sealing portion 4A has a structure in which the first resin portion R1 and the second resin portion R2 are stacked one on top of the other without the spacer 35 interposed therebetween. In this embodiment, the sealing member has three portions: an adhesive portion formed by the first adhesive portion 31 or the second adhesive portion 32, a reinforcing portion formed by the first reinforcing portion 33 or the second reinforcing portion 34, and a welded portion formed by the end face welded portion 36. The energy storage device 1A has a plurality of energy storage cells 2A stacked in direction D.

[0056] The first resin portion R1 and the second resin portion R2 are surface-welded to each other at the end surface welded portion 36, but are not surface-welded to each other inside the end surface welded portion 36 as viewed from the stacking direction (direction D). In FIGS. 4 and 5, even inside the end surface welded portion 36 as viewed from the stacking direction (direction D), adjacent seal members may have the end portion 13a of the separator 13 interposed between them. The first reinforcing portion 33 and the second reinforcing portion 34 of the sealing portion 4A are formed thicker than the first reinforcing portion 33 and the second reinforcing portion 34 of the sealing portion 4 to ensure a space S according to the thickness of the positive and negative electrode active material layers. The thickness of the first reinforcing portion 33 and the second reinforcing portion 34 of the sealing portion 4A is, for example, 200 μm or more and 400 μm or less. In this embodiment, the thickness of the first reinforcing portion 33 and the second reinforcing portion 34 is 250 μm. An end 13a of the separator 13 is welded and fixed to a sealing member.

[0057] (Action and effect) As described above, in the energy storage device 1, 1A, the sealing portion 4, 4A seals the space S between the multiple electrodes 5 stacked in the direction D. The sealing portion 4, 4A includes at least the first resin portion R1, the second resin portion R2, and the end surface weld portion 36. To ensure sealing performance, a resin with high adhesion to the current collector must be used for the first adhesive portion 31 of the first resin portion R1 and the second adhesive portion 32 of the second resin portion R2. Even in this case, the water vapor permeability of the end surface weld portion 36 is lower than the water vapor permeability of the first adhesive portion 31 and the second adhesive portion 32, respectively. Therefore, even if the first adhesive portion 31 and the second adhesive portion 32 are made of a resin with high adhesion to the current collector and high water vapor permeability, moisture is prevented from permeating through the sealing portion 4, 4A in a direction intersecting (e.g., perpendicular to) the direction D and entering the space S within the energy storage cell 2. As a result, degradation of battery performance due to moisture permeation is suppressed.

[0058] In the battery described in Patent Document 1, the sealing material is not welded to the edges, and the entire power generating element is enclosed in a laminate film under reduced pressure. As described above, the energy storage device 1, 1A has the edge welded parts 36 with low water vapor permeability, and therefore, even if the entire device is not covered with a laminate film, the edge welded parts 36 can suppress moisture permeation.

[0059] In a large battery, the area of the side surface of the electrode stack 3 along direction D is large, so the cross-sectional area (opening area) for moisture permeation is large. In the energy storage device 1, 1A, the end face welded portion 36 can prevent moisture from permeating the sealing portion 4, 4A in a direction intersecting direction D. Therefore, the energy storage device 1, 1A is particularly effective for a large battery.

[0060] The degree of acid modification (e.g., average degree of acid modification) of the resin of the end face welded portion 36 is lower than the degree of acid modification (e.g., average degree of acid modification) of the resin of the adhesive portion of the sealing member. Therefore, the water vapor permeability of the end face welded portion 36 can be lower than the water vapor permeability of the adhesive portion of the sealing member.

[0061] The water vapor permeability of the reinforcing portion consisting of the first reinforcing portion 33 or the second reinforcing portion 34 of the sealing member is lower than the water vapor permeability of the adhesive portion of the sealing member. Therefore, it is easy to make the water vapor permeability of the end face welded portion 36 lower than the water vapor permeability of the adhesive portion of the sealing member.

[0062] In the end face welded portions 36 of the energy storage devices 1, 1A, multiple resin parts including a sealing member are stacked, and adjacent resin parts are surface-welded to each other. The end face welded portions 36 of the energy storage device 1 are a composite material in which outer edge portions R1a, R2a of the sealing member, which are made of an adhesive portion and a reinforcing portion, and an outer edge portion 35a of the spacer 35 are melted and integrated. The end face welded portions 36 of the energy storage device 1A are a composite material in which outer edge portions R1a, R2a of the sealing member, which are made of an adhesive portion and a reinforcing portion, are melted and integrated. These end face welded portions 36 may be formed by melting multiple resin layers until no boundaries remain between the resin layers.

[0063] The ratio of the total thickness of the first adhesive portion 31 and the second adhesive portion 32 to the thickness of the multiple resin portions is 5% or more and 50% or less. This allows the ratio of the total volume of the first adhesive portion 31 and the second adhesive portion 32 to the volume of the end face weld portion 36 to be 5% or more and 50% or less. Degraded gases, such as hydrogen and methane, generated inside the energy storage cell 2 permeate the sealing portion 4 and are released to the outside. The adhesive portion of the sealing member allows degraded gases to permeate more easily than the reinforcing portion of the sealing member. That is, the first adhesive portion 31 and the second adhesive portion 32 allow degraded gases to permeate more easily than the first reinforcing portion 33 and the second reinforcing portion 34. Setting the ratio to 5% or more ensures a path for degraded gases to permeate the sealing portion 4. This suppresses an increase in internal pressure. Furthermore, setting the total occupancy rate to 50% or less allows the ratio of the total volume of the first reinforcing portion 33 and the second reinforcing portion 34 to the volume of the end face weld portion 36 to be maintained at a value higher than 50%. This reduces the path for water vapor to pass through end surface welds 36, preventing deterioration of battery performance. Furthermore, because end surface welds 36 are integrated, they are rigid, allowing the pressure resistance of sealing portions 4, 4A to be maintained.

[0064] In the energy storage device 1, the inner edge of the spacer 35 is located outside the inner edges of the first adhesive portion 31, the second adhesive portion 32, the first reinforcing portion 33, and the second reinforcing portion 34 when viewed from direction D. This allows the space S to be kept large. This makes it possible to ensure, for example, excess space capable of accommodating gas generated in the space S due to various electrochemical reactions accompanying charge and discharge. As a result, the long-term pressure resistance (creep pressure resistance) of the energy storage device 1 can be improved.

[0065] A current collector formed by bonding together an aluminum foil having a first surface 10a and a copper foil having a second surface 10b is used as the current collector 10 of the bipolar electrode. Because the current collector 10 includes two separate metal foils, the thickness, material, and surface treatment of the current collector 10 can be configured in any desired combination.

[0066] When viewed from direction D, the inner edge of the welded region between the seal member and spacer 35 is located outside the inner edge of the joint region between the seal member and current collector. Therefore, part of the stress generated by deformation of the current collector moves from the inner edge of the joint region between the seal member and current collector to the inner edge of the welded region between the seal member and spacer 35. Because the stress can be dispersed in this way, peeling of the sealing portion 4 from the current collector can be prevented even if the internal pressure of the space S increases. As a result, deterioration of sealing performance can be prevented.

[0067] The present disclosure is not limited to the above embodiments.

[0068] In the energy storage devices 1, 1A, the first surface 22a of the negative electrode terminal electrode 7 is provided with a first resin portion R1, but the first resin portion R1 may not be provided, or only the first adhesive portion 31 may be provided. The second surface 21b of the positive electrode terminal electrode 6 is provided with a second resin portion R2, but the second resin portion R2 may not be provided, or only the second adhesive portion 32 may be provided.

[0069] The end face welded portion 36 of the energy storage device 1 may be formed by pressing a hot plate against the outer edge portions R1a, R2a of the sealing member and the outer edge portion 35a of the spacer 35. The end face welded portion 36 of the energy storage device 1A may be formed by pressing a hot plate against the outer edge portions R1a, R2a of the sealing member.

[0070] In the energy storage device 1, 1A, at least one laminate film may be attached to all or part of the side surface that is made up of the end face welded portion 36 and extends in direction D, thereby covering all or part of the side surface of the end face welded portion 36 that extends in direction D with the laminate film. Also, in the energy storage device 1, 1A, a laminate film may be attached to all or part of the surface of the first resin portion R1 that is provided on the first surface 22a of the negative terminal electrode 7, opposite to the first surface 22a, thereby covering all or part of the surface of the first resin portion R1 that is opposite to the first surface 22a with the laminate film. Furthermore, in the energy storage device 1, 1A, a laminate film may be attached to all or part of the surface of the second resin portion R2 opposite the second surface 21b of the positive terminal electrode 6, the surface being opposite the second surface 21b. This configuration further suppresses moisture permeation. However, the laminate film is provided so that the second surface 21b of the positive terminal electrode 6 and the first surface 22a of the negative terminal electrode 7, which serve as electrode outlets, are exposed. The laminate film may be, for example, a known composite laminate film in which a metal foil and a resin layer are bonded together. The metal foil of the composite laminate film may be made of a metal such as aluminum, an aluminum alloy, stainless steel, or a nickel alloy. The resin layer of the composite laminate film may be made of a resin such as polyethylene, ethylene vinyl acetate, or polyethylene terephthalate.

[0071] The spacer 35 may have a laminated structure in which multiple resin layers are stacked. By stacking multiple resin layers, the thickness of the spacer can be easily adjusted. Similarly, the first adhesive portion 31, the second adhesive portion 32, the first reinforcing portion 33, and the second reinforcing portion 34 may each have a laminated structure in which multiple resin layers are stacked and welded together. Since they can be created by stacking and welding multiple resin layers, the height can be easily adjusted.

[0072] In the energy storage device 1, 1A, the first adhesive portion 31 and the first reinforcing portion 33 may be formed of different resin materials. For example, the first adhesive portion 31 may be formed of acid-modified PE, and the first reinforcing portion 33 may be formed of PP. The second adhesive portion 32 and the second reinforcing portion 34 may be formed of different resin materials. For example, the second adhesive portion 32 may be formed of acid-modified PE, and the second reinforcing portion 34 may be formed of PP.

[0073] FIG. 6 is a schematic cross-sectional view showing a power storage device according to a modified example. As shown in FIG. 6, the power storage device 1B according to the modified example differs from the power storage device 1 (see FIG. 1) mainly in that the first resin portion R1 further includes a third adhesive portion 37 and the second resin portion R2 further includes a fourth adhesive portion 38. The third adhesive portion 37 is integrated with the surface of the first reinforcing portion 33 opposite to the first adhesive portion 31. The fourth adhesive portion 38 is integrated with the surface of the second reinforcing portion 34 opposite to the second adhesive portion 32. The power storage device 1B also differs from the power storage device 1 in that the current collectors 21 and 22 are formed by bonding and integrating two different metal foils, namely, aluminum foil and copper foil. The current collectors 21 and 22 may be formed of a single metal foil.

[0074] The average water vapor permeability of the end face welded portion 36 is lower than the water vapor permeability of each of the third adhesive portion 37 and the fourth adhesive portion 38. In this case, the average water vapor permeability of the end face welded portion 36 is lower than the average water vapor permeability of the resin in the entire adhesive portion of the sealing member (for example, the average water vapor permeability of the resin in all adhesive portions including the first adhesive portion 31, the second adhesive portion 32, the third adhesive portion 37, and the fourth adhesive portion 38). The third adhesive portion 37 and the fourth adhesive portion 38 may be made of an acid-modified resin material. In this case, the acid modification degrees of the third adhesive portion 37 and the fourth adhesive portion 38 may be adjusted so that the acid modification degrees (for example, the average acid modification degree) of the resin in the end face welded portion 36 are lower than the acid modification degrees of the resin in the third adhesive portion 37 and the acid modification degrees of the resin in the fourth adhesive portion 38, respectively. In addition, the degree of acid modification of the end face welded portion 36 may be adjusted so that it is lower than the degree of acid modification of the resin in the entire adhesive portion of the sealing member (for example, the average acid modification degree of the resin in all adhesive portions of the first adhesive portion 31, the second adhesive portion 32, the third adhesive portion 37, and the fourth adhesive portion 38 combined).

[0075] The crystallinity of the third adhesive portion 37 and the fourth adhesive portion 38 may be adjusted so that the crystallinity (for example, average crystallinity) of the resin of the end face welded portion 36 is higher than the crystallinity of the resin of the third adhesive portion 37 and the crystallinity of the resin of the fourth adhesive portion 38. Furthermore, the crystallinity of the end face welded portion 36 may be adjusted so that it is higher than the crystallinity of the resin of the entire adhesive portion of the sealing member (for example, the average crystallinity of the resin of all adhesive portions combined, i.e., the first adhesive portion 31, the second adhesive portion 32, the third adhesive portion 37, and the fourth adhesive portion 38).

[0076] In this case, the third adhesive portion 37 and the fourth adhesive portion 38 may be formed of the same type of resin material as the first adhesive portion 31 and the second adhesive portion 32, or may be formed of a different type of resin material from the first adhesive portion 31 and the second adhesive portion 32. For example, the first adhesive portion 31 and the second adhesive portion 32 may be formed of acid-modified PE, and the third adhesive portion 37 and the fourth adhesive portion 38 may be formed of acid-modified PP. When the third adhesive portion 37 and the fourth adhesive portion 38 are formed of the same type of resin material and to the same thickness as the first adhesive portion 31 and the second adhesive portion 32, sandwiching the reinforcing portion made of the first reinforcing portion 33 or the second reinforcing portion 34 between adhesive portions made of the same material and the same thickness suppresses warping of the first resin portion R1 or the second resin portion R2, and suppresses poor welding when welding the first resin portion R1 or the second resin portion R2 to the current collector 10 as shown in FIG. 3 .

[0077] The above-described embodiments and modifications may be combined as appropriate.

[0078] As can be understood from the above description of the embodiments and modifications, this specification includes disclosure of the following aspects. (Appendix 1) an electrode stack including a plurality of electrodes stacked in a first direction; a separator disposed between the electrodes; a resin sealing portion that surrounds the electrode stack when viewed from the first direction and seals the space between the electrodes, the plurality of electrodes includes bipolar electrodes; The bipolar electrode is A current collector; a first active material layer provided on a first surface of the current collector; a second active material layer provided on a second surface of the current collector, The sealing portion is a first resin portion provided on an edge portion of the first surface so as to surround the first active material layer when viewed from the first direction; a second resin portion provided on an edge portion of the second surface so as to surround the second active material layer when viewed from the first direction; an end surface welded portion formed by welding outer edge portions of a plurality of resin portions including the first resin portion and the second resin portion together, the first resin portion has a first adhesive portion adhered to the first surface and a first reinforcing portion integrated with a surface of the first adhesive portion opposite to the current collector, the second resin portion has a second adhesive portion adhered to the second surface and a second reinforcing portion integrated with a surface of the second adhesive portion opposite to the current collector, the water vapor permeability of the end surface welded portion is lower than the water vapor permeability of the first adhesive portion and the water vapor permeability of the second adhesive portion; Energy storage device. (Appendix 2) the degree of acid modification of the resin in the end surface welded portion is lower than the degree of acid modification of the resin in the first adhesive portion and the degree of acid modification of the resin in the second adhesive portion; 2. The power storage device according to claim 1. (Appendix 3) the degree of crystallinity of the resin in the end surface welded portion is higher than the degree of crystallinity of the resin in the first adhesive portion and the degree of crystallinity of the resin in the second adhesive portion; 3. The power storage device according to claim 1 or 2. (Appendix 4) the water vapor permeability of the first reinforcing portion is lower than the water vapor permeability of the first adhesive portion and the water vapor permeability of the second adhesive portion; The water vapor permeability of the second reinforcing portion is lower than the water vapor permeability of the first adhesive portion and the water vapor permeability of the second adhesive portion. 4. The electricity storage device according to any one of claims 1 to 3. (Appendix 5) a ratio of a total thickness of the first adhesive portion and the second adhesive portion to a thickness of the plurality of resin portions is 5% or more and 50% or less; 5. The electricity storage device according to any one of Supplementary notes 1 to 4. (Appendix 6) the sealing portion further includes a spacer disposed between the first reinforcing portion and the second reinforcing portion in a first direction, At the end surface welded portion, the spacer is surface-bonded to each of the first reinforcing portion and the second reinforcing portion, The water vapor permeability of the spacer is lower than the water vapor permeability of the first adhesive portion and the water vapor permeability of the second adhesive portion. 6. The electricity storage device according to any one of appendices 1 to 5. (Appendix 7) Each of the current collectors includes a first current collector having the first surface and a second current collector having the second surface and being a separate member from the first current collector. 7. The electricity storage device according to any one of appendices 1 to 6. [Explanation of symbols]

[0079] 1,1A...electricity storage device, 4,4A...sealing portion, 5...electrode, 8...bipolar electrode, 10...current collector, 10a...first surface, 10b...second surface, 10c...edge portion, 13...separator, 21...current collector, 21a...first surface, 21b...second surface, 22...current collector, 22a...first surface, 22b...second surface, 23...positive electrode active material layer (first active material layer), 24...negative electrode active material layer (second active material layer), 31...first adhesive portion, 32...second adhesive portion, 33...first reinforcing portion, 34...second reinforcing portion, 35...spacer, 35a...outer edge portion, 36...end surface welded portion, R1...first resin portion, R1a...outer edge portion, R2...second resin portion, R2a...outer edge portion, S...space.

Claims

1. an electrode stack including a plurality of electrodes stacked in a first direction; a separator disposed between the electrodes; a resin sealing portion that surrounds the electrode stack when viewed from the first direction and seals the space between the electrodes, the plurality of electrodes includes bipolar electrodes; The bipolar electrode is A current collector; a first active material layer provided on a first surface of the current collector; a second active material layer provided on a second surface of the current collector, The sealing portion is a first resin portion provided on an edge portion of the first surface so as to surround the first active material layer when viewed from the first direction; a second resin portion provided on an edge portion of the second surface so as to surround the second active material layer when viewed from the first direction; an end surface welded portion formed by welding outer edge portions of a plurality of resin portions including the first resin portion and the second resin portion together, the first resin portion has a first adhesive portion adhered to the first surface and a first reinforcing portion integrated with a surface of the first adhesive portion opposite to the current collector, the second resin portion has a second adhesive portion bonded to the second surface and a second reinforcing portion integrated with a surface of the second adhesive portion opposite to the current collector, the water vapor permeability of the end surface welded portion is lower than the water vapor permeability of the first adhesive portion and the water vapor permeability of the second adhesive portion; Energy storage device.

2. the degree of acid modification of the resin in the end surface welded portion is lower than the degree of acid modification of the resin in the first adhesive portion and the degree of acid modification of the resin in the second adhesive portion; The power storage device according to claim 1 .

3. the degree of crystallinity of the resin in the end surface welded portion is higher than the degree of crystallinity of the resin in the first adhesive portion and the degree of crystallinity of the resin in the second adhesive portion; The power storage device according to claim 1 or 2.

4. the water vapor permeability of the first reinforcing portion is lower than the water vapor permeability of the first adhesive portion and the water vapor permeability of the second adhesive portion; The water vapor permeability of the second reinforcing portion is lower than the water vapor permeability of the first adhesive portion and the water vapor permeability of the second adhesive portion. The power storage device according to claim 1 or 2.

5. a ratio of a total thickness of the first adhesive portion and the second adhesive portion to a thickness of the plurality of resin portions is 5% or more and 50% or less; The power storage device according to claim 1 or 2.

6. the sealing portion further includes a spacer disposed between the first reinforcing portion and the second reinforcing portion in a first direction; At the end surface welded portion, the spacer is surface-bonded to each of the first reinforcing portion and the second reinforcing portion, the water vapor permeability of the spacer is lower than the water vapor permeability of the first adhesive portion and the water vapor permeability of the second adhesive portion; The power storage device according to claim 1 or 2.

7. Each of the current collectors includes a first current collector having the first surface and a second current collector having the second surface and being a separate member from the first current collector. The power storage device according to claim 1 or 2.

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