JP7722249B2 - Power storage device - Google Patents

Description

This disclosure relates to an electricity storage device.

A known type of energy storage device is a bipolar battery equipped with bipolar electrodes in which a positive electrode active material layer is formed on one side of a current collector and a negative electrode active material layer is formed on the other side (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 casing. A sealant is placed 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.

JP 2011-204386 A

The purpose of this disclosure is to provide an energy storage device that can suppress degradation of battery performance due to moisture permeation.

An energy storage device according to one aspect of the present disclosure comprises 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 include bipolar electrodes, and the bipolar electrode includes 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. 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 the edge of the first surface so as to seal the second active material layer as viewed from the first direction. a second resin portion provided on the edge of the second surface so as to surround the resin layer; and an end surface welded portion formed by welding and integrating the outer edges of multiple resin portions including the first resin portion and the second resin portion; 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; and the water vapor permeability of the end surface welded portion is lower than the water vapor permeability of both the first adhesive portion and the second adhesive portion.

In the above-described energy storage device, a resin sealing portion seals the space between 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, respectively. 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.

The degree of acid modification of the resin in the end face 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. In this case, the water vapor permeability of the end face 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.

The crystallinity of the resin in the end 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 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 modification degree of the resin in the end welded portion can be lower than the acid modification degree of the resin in the first adhesive portion and the acid modification degree of the resin in the second adhesive portion.

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

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. Degradation 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 degradation gases than the first reinforcing portion and the second reinforcing portion. Therefore, by setting this ratio to 5% or more, a path for degradation gases to permeate the sealing portion can be secured. Furthermore, by setting this 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, suppressing deterioration of battery performance.

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

Each current collector may include a first current collector having a first surface and a second current collector having a second surface and made of a separate material 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.

This disclosure provides an energy storage device that can suppress degradation of battery performance due to moisture permeation.

FIG. 1 is a schematic cross-sectional view showing the electricity storage device according to the first embodiment. FIG. 2 is a schematic cross-sectional view of the storage cell shown in FIG. FIG. 3 is a schematic cross-sectional view illustrating a method for forming a bipolar electrode unit. FIG. 4 is a schematic cross-sectional view showing the power storage device according to the second embodiment. FIG. 5 is a schematic cross-sectional view of the storage cell shown in FIG. FIG. 6 is a schematic cross-sectional view showing a power storage device according to a modified example.

Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements will be designated by the same reference numerals, and duplicate descriptions will be omitted.

(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, a case where the power storage device 1 is a lithium-ion secondary battery is illustrated.

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 of the stacking direction (direction D). The negative terminal electrode 7 is disposed at the other end of the stacking direction. The multiple bipolar electrodes 8 are disposed between the positive terminal electrode 6 and the negative terminal electrode 7.

The positive terminal electrode 6 includes a current collector 21 having a first surface 21a and a second surface 21b facing opposite 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 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 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 the positive electrode 11. The second surface 10b, together with the negative electrode active material layer 24, constitutes the negative electrode 12. Hereinafter, current collectors 10, 21, and 22 may be collectively referred to as "current collectors."

The positive electrode 11 and negative electrode 12 are arranged so that the positive electrode active material layer 23 and negative electrode active material layer 24 face each other in direction D with the separator 13 interposed between them. In this embodiment, the positive electrode active material layer 23 and 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.

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

Figure 2 is a schematic cross-sectional view of the energy storage cell shown in Figure 1. As shown in Figures 1 and 2, the edge portion 10c of the current collector 10 of the bipolar electrode 8 does not have an active material layer on either the first surface 10a side or the second surface 10b side. In other words, the first surface 10a and the second surface 10b have areas on the edge portion 10c where no active material layer is provided. When viewed from direction D, the edge portion 10c is located outside the area of the current collector 10 where the positive electrode active material layer 23 or the negative electrode active material layer 24 is provided.

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 onto 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.

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, for example, by copper plating one side of the 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, 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. Furthermore, the current collectors 21 and 22 may also be integrated by bonding two different metal foils, aluminum foil and copper foil.

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 at least one of iron, manganese, titanium, nickel, cobalt, and aluminum, and lithium. Examples of the composite oxides include olivine-type lithium iron phosphate ( _LiFePO4 ), _LiCoO2 , and _LiNiMnCoO2 .

The negative electrode active material layer 24 contains a negative electrode active material capable of absorbing 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 be alloyed with lithium, and boron-doped carbon. Examples of elements that can be alloyed with lithium include silicon and tin.

In addition to the active material, the positive electrode active material layer 23 and the negative electrode active material layer 24 may also 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 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; 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 a conductive material such as acetylene black, carbon black, or graphite, which can enhance electrical conductivity. Examples of viscosity-adjusting solvents include N-methyl-2-pyrrolidone.

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. This active material layer-forming composition is then applied to the current collectors 10, 21, and 22 and dried. Examples of solvents include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. The dried electrode may be compressed to increase electrode density.

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, preventing electrical short circuits due to contact between the electrodes while allowing charge carriers such as lithium ions to pass through.

When viewed from direction D, 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, but slightly smaller than the current collectors 10, 21, and 22. When viewed from direction D, the end 13a of the separator 13 is positioned outside the positive electrode active material layer 23 and the negative electrode active material layer 24. When viewed from direction D, the end 13a of the separator 13 does not overlap either the positive electrode active material layer 23 or the negative electrode active material layer 24. The end 13a of the separator 13 is fixed to the sealing portion 4.

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 electrolyte. Materials constituting the separator 13 include, for example, polyolefins such as polypropylene or polyethylene, or polyester. 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 adhered 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.

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. Furthermore, 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.

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 contained in the space S. The sealing portion 4 seals the electrolyte in the space S.

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 make the sealing portion 4 include polyolefins such as polypropylene or polyethylene. The sealing portion 4 is adhered (bonded) to the edge portion 10c of the first surface 10a and the edge portion 10c of the second surface 10b. By being positioned between adjacent current collectors, the sealing portion 4 maintains the spacing 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.

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 and second resin parts R1 and R2. When viewed from direction D, each of the multiple resin parts has a rectangular frame shape. Hereinafter, the first and second resin parts R1 and R2 may be collectively referred to as the "sealing member."

To improve the sealing performance of the sealing portion 4, the sealing portion 4 must be made of a resin that has high adhesion to the current collector. Among the same type of resin material, 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 resin's water vapor permeability. Among the same type of resin material, 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 deteriorate. Therefore, the sealing portion 4 must achieve both sealing performance and moisture permeation suppression. 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 is 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 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/( ^m2 ·24h)].

Acid-modifying a resin reduces its crystallinity due to substitution by acid-modifying 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 in resins with a high crystalline polymer content, 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 resin's crystallization temperature using DSC (differential scanning calorimetry). This method allows the relative crystallinity of the main component to be estimated for multiple resins whose main component is fixed and whose crystallinity is changed by varying the blending ratio of amorphous polymer or additive.

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 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 faces away from 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 faces away from the current collector. The edges of the current collector 10 are reinforced by the first resin portion R1 and the second resin portion R2, which are 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 electrode terminal 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 electrode terminal unit (described below) is increased, making it easier to handle during manufacturing.

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 with high adhesive strength to the current collector. For example, if the current collector is made of 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 acid-modified groups (acid-modified resins), such as acid-modified PE and acid-modified PP, have higher adhesion to metals than resins without acid-modified groups (non-acid-modified resins), 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.

The thicknesses of the first adhesive portion 31 and the second adhesive portion 32 are set to at least the minimum thickness necessary 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, from the perspective of suppressing moisture penetration from the outside, the thicknesses of the first adhesive portion 31 and the second adhesive portion 32 are set to be not thicker than necessary. Resins containing acid-modified groups, such as acid-modified PE and acid-modified PP, which have good adhesion to metal, tend to have higher water vapor permeability than resins without acid-modified groups, such as PE and PP. For example, the thickness of the first adhesive portion 31 and the second adhesive portion 32 is 20 μm or more and 200 μm or less. By setting the thickness to 20 μm or more, each adhesive portion 31, 32 of the sealing member adheres to the corresponding current collector, sealing the space between adjacent current collectors. By setting the thickness to 200 μm or less, the moisture permeation path can be narrowed, thereby suppressing moisture permeation. In this embodiment, the thickness of the first adhesive portion 31 and the second adhesive portion 32 is 50 μm.

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 with 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 with 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 from the same type of resin material and are surface-bonded to each other to form an integrated unit. The first reinforcing portion 33 is surface-bonded to the first adhesive portion 31, for example, by co-extrusion or thermal lamination, with the interface welded.

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 with 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 with 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 from the same type of resin material and are surface-bonded to each other to form an integrated unit. 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.

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.

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 from 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, for 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 from 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 from a resin material such as unacid-modified polyethylene (PE) or unacid-modified polypropylene (PP). The first reinforcement portion 33 and the second reinforcement portion 34 may be formed from the same type of resin material as the first adhesive portion 31 and the second adhesive portion 32. For example, if 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 reinforcement portion 33 and the second reinforcement portion 34. If 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 reinforcement portion 33 and the second reinforcement portion 34. The first reinforcement portion 33 and the second reinforcement 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 may be adjusted, or the material properties may be adjusted using additives, etc., so that the Young's modulus is at least higher than that of the first adhesive portion 31 and the second adhesive portion 32.

The spacer 35 is disposed in direction D between the first reinforcing portion 33 of the first resin portion R1 and the second reinforcing portion 34 of the second resin portion R2. 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 the end surface weld portion 36.

Like the first reinforcement portion 33 and the second reinforcement 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 reinforcement portion 33 and the second reinforcement portion 34. In this case, the spacer 35 is sandwiched between the first reinforcement portion 33 and the second reinforcement portion 34, which are made of the same material, making them more compatible when forming the end face weld portion 36. As a result, the end face weld portion 36 is easier to form. The spacer 35 may also be formed of the same 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. If 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.

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 Figures 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 surface weld 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 surface weld 36 that can be provided. In this embodiment, the thickness of the spacer 35 is 500 μm.

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 reinforcement portion 33, and the second reinforcement 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 reinforcement portion 33, and the second reinforcement 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 reinforcement portion 33, and the second reinforcement portion 34.

The end face weld 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 weld 36, the multiple resin portions are stacked in a state where adjacent resin portions are melted and surface-welded in the stacking direction (direction D). 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 weld 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 weld 36 is the average amount of water vapor per unit area that passes through the end face weld 36 per unit time under specified temperature and humidity conditions. The average acid modification degree of the resin in the end face weld 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 weld 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 weld 36 refers to the ratio (mass %, volume %, compounding ratio, mixing ratio) of the crystalline portion contained in the end face weld 36 to the entire end face weld 36.

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 also 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.

(Method for 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 portions R1, and a plurality of second resin portions R2 are prepared. Next, a plurality of bipolar electrode units, a positive terminal electrode unit, and a negative terminal electrode unit are formed, respectively.

Figure 3 is a schematic cross-sectional view illustrating a method for forming a bipolar electrode unit. As shown in Figure 3, the first resin portion R1, the edge portion 10c of the current collector 10 of the bipolar electrode 8, and the second resin portion R2 are arranged in a stacked manner in direction D. 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 when viewed from the stacking direction (direction D). 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 when viewed from the stacking direction (direction D).

Next, heat and pressure in direction D are applied to bond the inner edge portion R1b of the first resin portion R1 and the inner edge portion R2b of the second resin portion R2 to the edge portion 10c. This forms a bipolar electrode unit.

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

Next, the positive electrode terminal unit, multiple bipolar electrode units, and negative electrode terminal unit are stacked in direction D. Separators 13 and spacers 35 are placed between adjacent units, thereby forming the electrode stack 3. Next, an edge 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 applied from the surface direction (direction perpendicular to the stacking direction) to the stacked end surfaces of the outer edges R1a, R2a of the stacked sealing members and the outer edge 35a of the spacer 35. This welds the outer edges R1a, R2a of the sealing members that protrude outward from the edge 10c to each other, forming the edge weld 36. In this way, the energy storage device 1 is manufactured.

Figure 4 is a schematic cross-sectional view showing a power storage device according to the second embodiment. Figure 5 is a schematic cross-sectional view of the power storage cell shown in Figure 4. As shown in Figures 4 and 5, the power storage device 1A according to the second embodiment differs from the power storage device 1 according to the first embodiment (see Figure 1) in that it includes a sealing portion 4A. While the sealing portion 4 (see Figure 1) has a structure in which the first resin portion R1, the spacer 35, and the second resin portion R2 are stacked, the sealing portion 4A has a structure in which the first resin portion R1 and the second resin portion R2 are stacked without the spacer 35 interposed therebetween. In this embodiment, the sealing member has three portions: an adhesive portion consisting of the first adhesive portion 31 or the second adhesive portion 32; a reinforcing portion consisting of the first reinforcing portion 33 or the second reinforcing portion 34; and a welded portion consisting of the end surface welded portion 36. The power storage device 1A has a plurality of power storage cells 2A stacked in direction D.

The first resin portion R1 and the second resin portion R2 are surface-welded to each other at the end-face welded portion 36, but are not surface-welded to each other inside the end-face welded portion 36 as viewed from the stacking direction (direction D). In Figures 4 and 5, even inside the end-face welded portion 36 as viewed from the stacking direction (direction D), adjacent seal members may have the end 13a of the separator 13 interposed between them. The first reinforcement portion 33 and the second reinforcement portion 34 of the sealing portion 4A are formed thicker than the first reinforcement portion 33 and the second reinforcement portion 34 of the sealing portion 4 to ensure space S depending on the thickness of the positive and negative electrode active material layers. The thickness of the first reinforcement portion 33 and the second reinforcement 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 reinforcement portion 33 and the second reinforcement portion 34 is 250 μm. The end 13a of the separator 13 is welded and fixed to the sealing member.

(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. 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.

In the battery described in Patent Document 1, the sealing material is not welded to the edges, and the entire power generating element is vacuum-encapsulated within a laminate film. As described above, the energy storage device 1, 1A has an edge weld 36 with low water vapor permeability, so the edge weld 36 can suppress moisture permeation even without covering the entire device with a laminate film.

In large batteries, the side surface area of the electrode stack 3 along direction D is large, resulting in a large cross-sectional area (opening area) for moisture permeation. In the energy storage devices 1 and 1A, the end surface welds 36 prevent moisture from permeating the sealing portions 4 and 4A in a direction intersecting direction D. Therefore, the energy storage devices 1 and 1A are particularly effective for large batteries.

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

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 surface weld portion 36 lower than the water vapor permeability of the adhesive portion of the sealing member.

The end surface welds 36 of the energy storage devices 1 and 1A are made by laminating multiple resin parts, including sealing material, and surface welding adjacent resin parts together. The end surface welds 36 of the energy storage device 1 are made of a composite material in which the outer edge portions R1a, R2a of the sealing material, which are made of adhesive and reinforcing parts, and the outer edge portion 35a of the spacer 35 are fused together. The end surface welds 36 of the energy storage device 1A are made of a composite material in which the outer edge portions R1a, R2a of the sealing material, which are made of adhesive and reinforcing parts, are fused together. These end surface welds 36 may be made by melting the multiple resin layers until no boundaries remain between the resin layers.

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 is more permeable to degraded gases than the reinforcing portion of the sealing member. That is, the first adhesive portion 31 and the second adhesive portion 32 are more permeable to degraded gases than the first reinforcing portion 33 and the second reinforcing portion 34. By setting this ratio at 5% or more, a path for degraded gases to permeate the sealing portion 4 can be secured. This prevents an increase in internal pressure. Furthermore, by setting the total occupancy rate to 50% or less, 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 can be maintained at a value greater than 50%. This reduces the path for water vapor to pass through the end surface weld 36, preventing deterioration of battery performance. Furthermore, because the end surface weld 36 is integrated, it provides rigidity, thereby maintaining the pressure resistance strength of the sealing portions 4, 4A.

In the energy storage device 1, when viewed from direction D, 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. This allows the space S to be kept large. This ensures, for example, excess space capable of accommodating gas generated in the space S due to various electrochemical reactions associated with charging and discharging. As a result, the long-term pressure resistance (creep pressure resistance) of the energy storage device 1 can be improved.

The current collector 10 of the bipolar electrode is made by bonding together an aluminum foil having a first surface 10a and a copper foil having a second surface 10b. Because the current collector 10 comprises two separate metal foils, the thickness, material, and surface treatment of the current collector 10 can be configured in any desired combination.

When viewed from direction D, the inner edge of the welded area between the seal member and spacer 35 is located outside the inner edge of the joint area between the seal member and current collector. As a result, part of the stress generated by deformation of the current collector moves from the inner edge of the joint area between the seal member and current collector to the inner edge of the welded area between the seal member and spacer 35. Because 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 space S increases. As a result, deterioration of sealing performance can be prevented.

This disclosure is not limited to the above embodiments.

In the energy storage device 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.

The end surface welds 36 of the energy storage device 1 may be formed by pressing a heat plate against the outer edge portions R1a, R2a of the sealing member and the outer edge portion 35a of the spacer 35. The end surface welds 36 of the energy storage device 1A may be formed by pressing a heat plate against the outer edge portions R1a, R2a of the sealing member.

In the energy storage device 1, 1A, at least one laminate film may be attached to all or part of the side surface of the end surface weld 36 extending in direction D, thereby covering all or part of the side surface of the end surface weld 36 extending 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 provided on the first surface 22a of the negative terminal electrode 7 opposite the first surface 22a, thereby covering all or part of the surface of the first resin portion R1 opposite 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 reduces 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.

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. Because they can be created by stacking and welding multiple resin layers, the height can be easily adjusted.

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

Figure 6 is a schematic cross-sectional view showing a modified energy storage device. As shown in Figure 6, the modified energy storage device 1B differs from the energy storage device 1 (see Figure 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 the first adhesive portion 31. The fourth adhesive portion 38 is integrated with the surface of the second reinforcing portion 34 opposite the second adhesive portion 32. The energy storage device 1B also differs from the energy storage device 1 in that the current collectors 21, 22 are formed by bonding together two different metal foils, namely, aluminum foil and copper foil. The current collectors 21, 22 may alternatively be a single metal foil.

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 (e.g., 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 (e.g., average acid modification degrees) 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. The degree of acid modification of the end face weld portion 36 may also 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).

The crystallinity of the third adhesive portion 37 and the fourth adhesive portion 38 may be adjusted so that the crystallinity (e.g., average crystallinity) of the resin in the end surface weld portion 36 is higher than the crystallinity of the resin in the third adhesive portion 37 and the crystallinity of the resin in the fourth adhesive portion 38. Furthermore, the crystallinity of the end surface weld portion 36 may be adjusted so that it is higher than the crystallinity of the resin in the entire adhesive portion of the sealing member (e.g., the average crystallinity 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).

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

The above embodiments and variations may be combined as appropriate.

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 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.
(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 power storage device according to claim 1.
(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 power storage device according to claim 1.
(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 power 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 power storage device according to any one of claims 1 to 6.

REFERENCE SIGNS LIST 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 (7)

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. 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 . 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. 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. 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. 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. 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.