Power storage device

Abstract

This power storage device (10) comprises a power storage cell (20) that is comprised of a positive electrode (21), a negative electrode (22), a separator (23), and a sealing part (24) that forms a sealed space for housing a liquid electrolyte between the positive electrode (21) and the negative electrode (22). The positive electrode (21) has a positive electrode active material layer (21b) that is formed on a first surface (21a1) of a positive electrode current collector (21a). The first surface (21a1) of the positive electrode current collector (21a) is formed of aluminum. The sealing part (24) is formed of an acid-modified polyolefin resin, and is bonded to the first surface (21a1) of the positive electrode current collector (21a). The positive electrode (21) comprises a carbon coating layer (M) that is provided, at a bonded portion with the sealing part (24), on the first surface (21a1) of the positive electrode current collector (21a). The carbon coating layer (M) contains carbon particles and a coating layer binding agent. The basis weight of the carbon coating layer M is 0.2 g / m2 or more.

Description

Power storage device

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

[0002] Patent Document 1 discloses a flat-type energy storage device constructed by stacking a plurality of individually manufactured energy storage cells in series. The energy storage cell includes a positive electrode having a positive electrode active material layer formed in the center of one side of a foil-shaped positive electrode current collector, a negative electrode having a negative electrode active material layer formed in the center of one side of a foil-shaped negative electrode current collector, the negative electrode active material layer being disposed so as to face the positive electrode active material layer of the positive electrode, and a separator disposed between the positive electrode and the negative electrode.

[0003] The energy storage cell further includes a seal portion disposed between the positive electrode and the negative electrode and on the outer circumferential side of the positive electrode active material layer and the negative electrode active material layer. The seal portion maintains a gap between the positive electrode current collector and the negative electrode current collector to prevent short circuits between the current collectors, and also liquid-tightly seals the gap between the positive electrode current collector and the negative electrode current collector, thereby forming an enclosed space for accommodating a liquid electrolyte between the positive electrode current collector and the negative electrode current collector.

[0004] JP 2017-16825 A

[0005] In conventional energy storage devices, when a load is applied to the adhesive portion between the current collector and the seal, such as when the internal pressure of the sealed space increases, the seal may peel off from the current collector. Peeling of the seal can cause a short circuit between the current collectors and leakage of the liquid electrolyte.

[0006] One aspect of the present disclosure provides an energy storage device including an energy storage cell. The energy storage cell is composed of a positive electrode, a negative electrode, a separator, and a sealing portion. In the positive electrode, a positive electrode active material layer is provided on a first surface of a positive electrode current collector. In the negative electrode, a negative electrode active material layer is provided on a first surface of a negative electrode current collector, and the negative electrode active material layer is disposed so as to face the positive electrode active material layer of the positive electrode. A separator is disposed between the positive electrode active material layer and the negative electrode active material layer. A sealing portion is disposed between the positive electrode and the negative electrode so as to surround the periphery of the positive electrode active material layer and the negative electrode active material layer. The sealing portion is bonded to the first surfaces of the positive electrode current collector and the negative electrode current collector, respectively, to form an enclosed space for containing a liquid electrolyte between the positive electrode and the negative electrode. The sealing portion is composed of an acid-modified polyolefin resin. The first surface of the positive electrode current collector is composed of aluminum. The positive electrode includes a carbon coating layer provided on the first surface of the positive electrode current collector at an adhesive portion where the positive electrode current collector is bonded to the sealing portion. The carbon coating layer includes carbon particles and a coating layer binder. The carbon coating layer has a basis weight of 0.2 g / m. ２ That's all.

[0007] In the electricity storage device, the carbon coating layer has a coating weight of 1.0 g / m ２ In the electricity storage device, the coating layer binder preferably contains a resin having a carboxyl group.

[0008] In the above-described energy storage device, it is preferable that the carbon coating layer is provided on the entire first surface of the positive electrode current collector. In the above-described energy storage device, it is preferable that a plurality of the energy storage cells are stacked, and that a bipolar electrode is provided in which a surface of the positive electrode current collector of the positive electrode constituting one of the adjacent energy storage cells opposite to the first surface is joined to a surface of the negative electrode current collector of the negative electrode constituting the other of the adjacent energy storage cells opposite to the first surface.

[0009] In the above energy storage device, the first surface of the negative electrode current collector of the bipolar electrode is preferably made of copper. In the above energy storage device, the bipolar electrode preferably has the following configuration: The positive electrode current collector is aluminum foil. The negative electrode current collector of the bipolar electrode is copper foil. In the bipolar electrode, the positive electrode current collector and the negative electrode current collector are bonded together with a conductive adhesive layer. The conductive adhesive layer includes an adhesive and conductive particles. The conductive particles have a resin core and a conductive layer located on the surface of the core. The content of the conductive particles in the conductive adhesive layer is 0.1% by volume or more and 1.0% by volume or less.

[0010] In the above-described power storage device, the bipolar electrode preferably has the carbon coating layer provided on both the first surface of the positive electrode current collector and the first surface of the negative electrode current collector.

[0011] According to the present invention, the adhesive strength of the seal portion to the current collector can be improved.

[0012] FIG. 1 is a cross-sectional view of the electricity storage device.

[0013] An embodiment of the present invention will be described below with reference to the drawings. The power storage device 10 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 10 is, for example, a secondary battery, such as a nickel-metal hydride secondary battery or a lithium-ion secondary battery. The power storage device 10 may also be an electric double layer capacitor. In this embodiment, the power storage device 10 is a lithium-ion secondary battery.

[0014] 1, the energy storage device 10 includes a cell stack 30 (laminated body) in which a plurality of energy storage cells 20 are stacked in a stacking direction. Hereinafter, the stacking direction of the plurality of energy storage cells 20 will be simply referred to as the stacking direction. Each energy storage cell 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and a seal portion 24.

[0015] The positive electrode 21 includes a positive electrode current collector 21 a and a positive electrode active material layer 21 b provided on a first surface 21 a 1 of the positive electrode current collector 21 a. In this embodiment, the positive electrode 21, the positive electrode current collector 21 a, and the positive electrode active material layer 21 b correspond to an electrode, a current collector, and an active material layer, respectively.

[0016] In a plan view seen from the stacking direction (hereinafter simply referred to as a plan view), the positive electrode active material layer 21b is formed in the central portion of the first surface 21a1 of the positive electrode current collector 21a. The peripheral portion of the first surface 21a1 of the positive electrode current collector 21a in the plan view is a positive electrode uncoated portion 21c where the positive electrode active material layer 21b is not provided. The positive electrode uncoated portion 21c is arranged so as to surround the periphery of the positive electrode active material layer 21b in the plan view.

[0017] The negative electrode 22 includes a negative electrode current collector 22a and a negative electrode active material layer 22b provided on a first surface 22a1 of the negative electrode current collector 22a. In a plan view, the negative electrode active material layer 22b is formed in the center of the first surface 22a1 of the negative electrode current collector 22a. In a plan view, the peripheral portion of the first surface 22a1 of the negative electrode current collector 22a is a negative electrode uncoated portion 22c where the negative electrode active material layer 22b is not provided. In a plan view, the negative electrode uncoated portion 22c is arranged to surround the periphery of the negative electrode active material layer 22b.

[0018] The positive electrode 21 and the negative electrode 22 are arranged such that the positive electrode active material layer 21b and the negative electrode active material layer 22b face each other in the stacking direction. That is, the facing direction of the positive electrode 21 and the negative electrode 22 coincides with the stacking direction. The negative electrode active material layer 22b is formed to be slightly larger than the positive electrode active material layer 21b, and in a plan view seen from the stacking direction, the entire formation region of the positive electrode active material layer 21b is located within the formation region of the negative electrode active material layer 22b.

[0019] Here, the positive electrode current collector 21a has a second surface 21a2 located opposite to the first surface 21a1, and the negative electrode current collector 22a has a second surface 22a2 located opposite to the first surface 22a1. The cell stack 30 has a structure in which a plurality of power storage cells 20 are stacked such that the second surface 21a2 of the positive electrode current collector 21a and the second surface 22a2 of the negative electrode current collector 22a are in contact with each other. In this way, the plurality of power storage cells 20 constituting the cell stack 30 are connected in series.

[0020] In the cell stack 30, two adjacent energy storage cells 20 in the stacking direction form a pseudo bipolar electrode 25 in which the mutually contacting positive electrode current collector 21 a and negative electrode current collector 22 a are regarded as a single current collector. The pseudo bipolar electrode 25 includes a current collector having a structure in which the positive electrode current collector 21 a and the negative electrode current collector 22 a are stacked, a positive electrode active material layer 21 b formed on one surface of the current collector, and a negative electrode active material layer 22 b formed on the other surface.

[0021] Alternatively, the positive electrode current collector 21a and the negative electrode current collector 22a may form a bipolar current collector in which the second surface 21a2 of the positive electrode current collector 21a and the second surface 22a2 of the negative electrode current collector 22a are joined together. In this case, the positive electrode 21 and the negative electrode 22 form a bipolar electrode 25 including a single bipolar current collector in which the positive electrode current collector 21a and the negative electrode current collector 22a are joined together. In other words, the bipolar electrode 25 is formed by joining a surface of the positive electrode current collector 21a of the positive electrode 21 constituting one of the adjacent energy storage cells 20 opposite to the first surface 21a1 and a surface of the negative electrode current collector 22a of the negative electrode 22 constituting the other of the adjacent energy storage cells 20 opposite to the first surface 22a1.

[0022] The separator 23 is disposed between the positive electrode 21 and the negative electrode 22, and is a component that separates the positive electrode 21 and the negative electrode 22 to prevent short circuits due to contact between the two electrodes, while allowing charge carriers such as lithium ions to pass through.

[0023] The separator 23 is, for example, a porous sheet or nonwoven fabric containing a polymer that absorbs and retains the liquid electrolyte. Examples of materials that form the separator 23 include polypropylene, polyethylene, polyolefin, and polyester. The separator 23 may have a single-layer structure or a multi-layer structure. The multi-layer structure may include, for example, an adhesive layer, a ceramic layer as a heat-resistant layer, and the like.

[0024] The seal portion 24 is disposed between the first surface 22a1 of the positive electrode current collector 21a of the positive electrode 21 and the first surface 22a1 of the negative electrode current collector 22a of the negative electrode 22, and is disposed on the outer circumferential side of the positive electrode active material layer 21b and the negative electrode active material layer 22b, and is adhered to both the positive electrode current collector 21a and the negative electrode current collector 22a. The seal portion 24 insulates the positive electrode current collector 21a from the negative electrode current collector 22a, thereby preventing a short circuit between the current collectors.

[0025] The sealing portion 24 extends along the peripheral edges of the positive electrode current collector 21 a and the negative electrode current collector 22 a in a plan view, and is formed in a frame shape surrounding the peripheries of the positive electrode active material layer 21 b and the negative electrode active material layer 22 b. The sealing portion 24 is disposed between the positive electrode uncoated portion 21 c on the first surface 21 a 1 of the positive electrode current collector 21 a and the negative electrode uncoated portion 22 c on the first surface 22 a 1 of the negative electrode current collector 22 a.

[0026] An enclosed space S is formed inside the energy storage cell 20 and is surrounded by a frame-shaped seal portion 24, the positive electrode 21, and the negative electrode 22. A separator 23 and a liquid electrolyte are housed in the enclosed space S. The peripheral portion of the separator 23 is embedded in the seal portion 24.

[0027] The seal portion 24 can prevent the liquid electrolyte contained in the sealed space S from permeating to the outside by sealing the sealed space S between the positive electrode 21 and the negative electrode 22. The seal portion 24 can also prevent moisture from entering the sealed space S from the outside of the energy storage device 10. Furthermore, the seal portion 24 can prevent gas generated from the positive electrode 21 or the negative electrode 22 due to, for example, a charge / discharge reaction, from leaking to the outside of the energy storage device 10.

[0028] The seal portion 24 of each storage cell 20 has an outer peripheral portion 24a that extends outward beyond the edges of the positive electrode current collector 21a and the negative electrode current collector 22a. When viewed from the stacking direction, the outer peripheral portion 24a protrudes beyond the edges of the positive electrode current collector 21a and the negative electrode current collector 22a in a direction perpendicular to the stacking direction. Adjacent storage cells 20 in the stacking direction are integrated by bonding the outer peripheral portions 24a of the seal portions 24 together. Examples of methods for bonding adjacent seal portions 24 together include known welding methods such as heat welding, ultrasonic welding, and infrared welding.

[0029] The energy storage device 10 includes a pair of current-carrying bodies, consisting of a positive electrode current-carrying plate 40 and a negative electrode current-carrying plate 50, which are arranged to sandwich the cell stack 30 in the stacking direction of the cell stack 30. The positive electrode current-carrying plate 40 and the negative electrode current-carrying plate 50 are each made of a material with excellent conductivity.

[0030] The positive electrode current-carrying plate 40 is electrically connected to the second surface 21a2 of the positive electrode current collector 21a of the positive electrode 21 arranged outermost at one end in the stacking direction. The negative electrode current-carrying plate 50 is electrically connected to the second surface 22a2 of the negative electrode current collector 22a of the negative electrode 22 arranged outermost at the other end in the stacking direction.

[0031] The energy storage device 10 is charged and discharged through terminals provided on the positive electrode current-carrying plate 40 and the negative electrode current-carrying plate 50. The material constituting the positive electrode current-carrying plate 40 may be, for example, the same material as the material constituting the positive electrode current collector 21a. The positive electrode current-carrying plate 40 may be formed of a metal plate that is thicker than the positive electrode current collector 21a used in the cell stack 30. The material constituting the negative electrode current-carrying plate 50 may be, for example, the same material as the material constituting the negative electrode current collector 22a. The negative electrode current-carrying plate 50 may be formed of a metal plate that is thicker than the negative electrode current collector 22a used in the cell stack 30.

[0032] Next, the positive electrode current collector 21a, the negative electrode current collector 22a, the positive electrode active material layer 21b, the negative electrode active material layer 22b, the liquid electrolyte, and the seal portion 24 will be described in detail. <Positive Electrode Current Collector and Negative Electrode Current Collector> The positive electrode current collector 21a is a chemically inactive electrical conductor that continuously passes current through the positive electrode active material layer 21b during discharge or charge of the lithium-ion secondary battery. An example of the positive electrode current collector 21a is an aluminum current collector whose surface, which becomes the first surface 21a1, is made of aluminum. The aluminum current collector may be a single body made entirely of aluminum, or a composite having a portion made of aluminum and a portion made of a material other than aluminum. Examples of such a single body include aluminum foil such as rolled aluminum foil. Examples of such a composite include a multilayer structure in which the layer making up the first surface 21a1 is an aluminum layer, and a substrate whose surface, including the first surface 21a1, is coated with an aluminum film.

[0033] Examples of materials other than aluminum include metal materials, conductive resin materials, and conductive inorganic materials. Examples of metal materials include copper, nickel, titanium, and stainless steel (e.g., SUS304, SUS316, SUS301, SUS304, etc., as defined in JIS G 4305:2015). Examples of conductive resin materials include resins obtained by adding a conductive filler to a conductive polymer material or a non-conductive polymer material as needed. The aluminum current collector may be in the form of, for example, a foil, a sheet, or a film. The thickness of the aluminum current collector is, for example, 1 to 100 μm.

[0034] The negative electrode current collector 22a is a chemically inactive electrical conductor that continues to pass current through the negative electrode active material layer 22b during discharge or charge of the lithium-ion secondary battery. An example of the negative electrode current collector 22a is a copper current collector whose surface, which becomes the first surface 22a1, is made of copper. The copper current collector may be a simple substance made entirely of copper, or a composite having a portion made of copper and a portion made of a material other than copper. Examples of the simple substance include copper foil, such as electrolytic copper foil. Examples of the composite include a multilayer structure in which the layer making up the first surface 22a1 is a copper layer, and a substrate whose surface, including the first surface 22a1, is coated with a copper film.

[0035] Examples of materials other than copper include metal materials, conductive resin materials, and conductive inorganic materials. Examples of metal materials include aluminum, nickel, titanium, and stainless steel (e.g., SUS304, SUS316, SUS301, SUS304, etc., as defined in JIS G 4305:2015). Examples of conductive resin materials include resins obtained by adding a conductive filler to a conductive polymer material or a non-conductive polymer material as needed. The copper current collector may be in the form of, for example, a foil, a sheet, or a film. The aluminum current collector may have a thickness of, for example, 1 to 100 μm.

[0036] A preferred example of a combination of the positive electrode current collector 21 a and the negative electrode current collector 22 a is a combination in which the positive electrode current collector 21 a is made of aluminum foil, which is an aluminum current collector, and the negative electrode current collector 22 a is made of copper foil, which is a copper current collector. Examples of the bipolar current collector include a current collector in which two aluminum foils are bonded together, a current collector in which an aluminum foil and a copper foil are bonded together, and a current collector in which copper is plated on the surface of an aluminum foil.

[0037] The positive electrode current collector 21a and the negative electrode current collector 22a constituting the bipolar current collector are bonded together via, for example, an adhesive layer. The adhesive layer is conductive and electrically connects the positive electrode current collector 21a and the negative electrode current collector 22a. The adhesive layer includes, for example, an adhesive component and a conductive component dispersed in the adhesive component. Examples of the adhesive component include polyolefin-based resins such as polypropylene and polyethylene. The adhesive component may be a single type or a combination of two or more types. The adhesive component may include a curing agent such as an isocyanate-based curing agent or an epoxy-based curing agent. An example of the adhesive component includes a polyolefin-based resin and an epoxy-based curing agent. In this case, gas generation associated with the curing reaction can be suppressed. Examples of the conductive component include conductive particles and conductive fillers. Examples of the conductive particles include metal particles such as aluminum particles, nickel particles, SUS particles, silver particles, gold particles, copper particles, titanium particles, and alloy particles, and carbon particles such as graphite particles. The conductive particles may also be spherical particles having a metal coating formed on the surface of a core particle such as a resin or ceramic. Examples of conductive fillers include carbon nanotubes. The conductive component may be a single type or a combination of two or more types. The adhesive component may also be a conductive adhesive component. Examples of conductive adhesive components include conductive polymer materials. In this case, if the adhesive component is conductive, the conductive component dispersed in the adhesive component may be omitted.

[0038] A carbon coating layer M is provided on the first surface 21a1 of the positive electrode current collector 21a. Details of the carbon coating layer M will be described later. <Positive Electrode Active Material Layer and Negative Electrode Active Material Layer> The positive electrode active material layer 21b contains a positive electrode active material capable of absorbing and releasing charge carriers such as lithium ions. As the positive electrode active material, any material that can be used as a positive electrode active material for a lithium ion secondary battery, such as a lithium composite metal oxide having a layered rock salt structure, a metal oxide having a spinel structure, or a polyanion-based compound, may be used. Two or more types of positive electrode active materials may also be used in combination. In this embodiment, the positive electrode active material layer 21b contains an olivine-type lithium iron phosphate (LiFePO ), which is a polyanion-based compound. ４ ) is included.

[0039] The negative electrode active material layer 22b can be made of any element, alloy, or compound capable of absorbing and releasing charge carriers such as lithium ions. Examples of the negative electrode active material include Li, carbon, metal compounds, and elements or compounds thereof that can be alloyed with lithium. Examples of carbon include natural graphite, artificial graphite, hard carbon (non-graphitizable carbon), and soft carbon (easily graphitizable carbon). Examples of artificial graphite include highly oriented graphite and mesocarbon microbeads. Examples of elements that can be alloyed with lithium include silicon and tin. In this embodiment, the negative electrode active material layer 22b contains graphite as a carbon-based material.

[0040] The positive electrode active material layer 21 b and the negative electrode active material layer 22 b (hereinafter also simply referred to as the active material layer) may each further contain, as necessary, a conductive aid for increasing electrical conductivity, a binder, an electrolyte (a polymer matrix, an ion-conductive polymer, a liquid electrolyte, etc.), an electrolyte supporting salt (lithium salt) for increasing ion conductivity, etc. The components contained in the active material layer, the blending ratio of these components, and the thickness of the active material layer are not particularly limited, and conventionally known knowledge about lithium ion secondary batteries may be referred to as appropriate.

[0041] The conductive additive is added to enhance the conductivity of the positive electrode 21 or the negative electrode 22. Examples of the conductive additive include acetylene black, carbon black, and graphite. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluorine rubber; thermoplastic resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamideimide; alkoxysilyl group-containing resins; acrylic resins such as poly(meth)acrylic 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 can be used alone or in combination. Examples of the solvent or dispersion medium include water and N-methyl-2-pyrrolidone.

[0042] The method for forming the active material layer on the surface of the positive electrode current collector 21 a and the negative electrode current collector 22 a is not particularly limited, and a conventionally known method such as roll coating can be used. In order to improve the thermal stability of the positive electrode 21 or the negative electrode 22, the heat-resistant layer may be provided on the surface of the active material layer.

[0043] The basis weight of the active material layer is not particularly limited, and conventionally known knowledge about lithium ion secondary batteries can be referred to as appropriate. However, from the viewpoint of increasing the energy density of the storage cell 20, it is preferable to increase the basis weight of the active material layer. The basis weight of the positive electrode active material layer 21b is, for example, 55 to 90 mg / cm. ２ and 60 mg / cm ２ It is preferable that the concentration is 70 mg / cm or more. ２ The weight of the negative electrode active material layer 22b is, for example, 25 to 45 mg / cm ２ and 30 mg / cm ２ It is preferable that this is equal to or greater than this.

[0044] <Sealing portion> The sealing portion 24 is made of an acid-modified polyolefin resin. Examples of acid-modified polyolefin resins include acid-modified polyethylene, acid-modified polypropylene, acid-modified isoprene, and acid-modified polybutene. Examples of acid-modified groups include carboxylic acid groups, maleic acid groups, and maleic anhydride groups. The acid-modified polyolefin resin constituting the sealing portion 24 may be one type or a combination of two or more types. The acid-modified polyolefin resin constituting the sealing portion 24 may be a thermoplastic resin or a thermosetting resin.

[0045] The melting point Tm1 of the acid-modified polyolefin resin constituting the seal portion 24 is, for example, 90° C. or higher and 170° C. or lower. The thickness of the seal portion 24 is, for example, preferably 50 μm or higher and 1000 μm or lower, and more preferably 100 μm or higher and 800 μm or lower. The thickness of the seal portion 24 refers to the thickness of a portion located between the first surface 21 a1 of the positive electrode current collector 21 a and the first surface 22 a1 of the negative electrode current collector 22 a.

[0046] The sealing portion 24 is adhered to the first surface 21a1 of the positive electrode current collector 21a, more specifically, to the carbon coating layer M provided on the first surface 21a1. The sealing portion 24 is also adhered to the first surface 22a1 of the negative electrode current collector 22a.

[0047] <Liquid Electrolyte> The liquid electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The electrolyte salt is LiClO ４ , LiAsF ６ , LiPF ６ , LiBF ４ , LiCF ３ SO ３ , LiN(FSO ２ ) ２ , LiN(CF ３ SO ２ ) ２ Known lithium salts such as those listed above can be used. Furthermore, known solvents such as cyclic carbonates, cyclic esters, chain carbonates, chain esters, and ethers can be used as the non-aqueous solvent. These known solvent materials may be used in combination of two or more.

[0048] <Carbon Coating Layer> Next, the carbon coating layer M provided on the first surface 21a1 of the positive electrode current collector 21a will be described.

[0049] In the present embodiment, the carbon coating layer M is provided on the entire first surface 21a1 of the positive electrode current collector 21a. Therefore, the first surface 21a1 of the positive electrode current collector 21a is bonded to the sealing portion 24 via the carbon coating layer M. In other words, the sealing portion 24 is bonded to the carbon coating layer M provided on the first surface 21a1 of the positive electrode current collector 21a.

[0050] The carbon coating layer M contains carbon particles and a coating layer binder. As the carbon particles, known carbon materials applicable to carbon coating layers, such as graphite and acetylene black, can be used.

[0051] Examples of materials constituting the coating layer binder include resins having a carboxyl group such as acrylic resins and carboxy-modified styrene-butadiene rubbers. The material constituting the coating layer binder is preferably an acrylic resin.

[0052] Examples of the acrylic resin include homopolymers of acrylic monomers such as acrylic acid, methacrylic acid, and (meth)acrylic acid esters, and (meth)acrylic copolymers containing the above acrylic monomers. In this embodiment, (meth)acrylic acid refers to acrylic acid or methacrylic acid.

[0053] Examples of the (meth)acrylic acid ester include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, and isobutyl (meth)acrylate.

[0054] In the (meth)acrylic copolymer, other comonomers copolymerized with the acrylic monomer include α-olefin, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile, and vinyl acetate. These comonomers can be present in the acrylic resin in the form of random copolymers, graft copolymers, or block copolymers. Examples of the (meth)acrylic copolymer include silicon-modified acrylic-styrene resins, carboxy-modified acrylic-styrene resins, and hydroxyl-modified acrylic resins. The material constituting the coating layer binder may be one type, or a combination of two or more types.

[0055] The carbon coating layer M is preferably formed so that many carboxyl groups are present on the surface. For example, a small contact angle of water with the surface of the carbon coating layer M is an indication of the presence of many carboxyl groups on the surface. The contact angle of water with the surface of the carbon coating layer M is, for example, 40° or less, and preferably 30° or less.

[0056] The glass transition temperature Tg2 of the coating layer binder is, for example, 0°C or higher and 150°C or lower. When the seal portion 24 is bonded by thermal welding, it is preferable to heat the sealing material forming the seal portion 24 at a temperature higher than the glass transition temperature Tg2 of the coating layer binder and at a temperature equal to or higher than the melting point Tm1 of the acid-modified polyolefin resin constituting the seal portion 24. In this case, the heating required to bond the seal portion 24 softens the coating layer binder contained in the carbon coating layer M, thereby making the coating layer binder and the seal portion 24 more compatible. Therefore, it is preferable that the glass transition temperature Tg2 of the coating layer binder be lower than the melting point Tm1 of the acid-modified polyolefin resin constituting the seal portion 24 (Tg2<Tm1). The difference between the melting point Tm1 of the acid-modified polyolefin resin and the glass transition temperature Tg2 of the coating layer binder (melting point Tm1-Tg2) is, for example, 5°C or higher and 100°C or lower.

[0057] The weight of the carbon coating layer M is 0.2 g / m ２ or more, and preferably 0.3 g / m ２ More preferably, it is 0.4 g / m or more. ２ The weight per unit area is 0.2 g / m ２ As a result of the above, the carbon coating layer M is interposed between the first surface 21a1 of the positive electrode current collector 21a and the seal portion 24, thereby improving the adhesive strength.

[0058] The weight of the carbon coating layer M is, for example, 1.2 g / m ２ and preferably 1.0 g / m or less. ２ The weight of the carbon coating layer M is 0.2 g / m or less. ２ Within the above range, the effect of improving the adhesive strength tends to decrease as the basis weight increases. ２ When the weight per unit area is 1.0 g / m or less, the effect of improving the adhesive strength can be suppressed from decreasing. Furthermore, when the weight per unit area is increased, a thicker carbon coating layer M is formed. When the carbon coating layer M is excessively thick, the liquid electrolyte may permeate through the carbon coating layer M, which may cause leakage of the liquid electrolyte through the carbon coating layer M. ... ２If it is equal to or less than this, leakage of the liquid electrolyte through the carbon coating layer M to the outside of the storage cell 20 can be suppressed.

[0059] The thickness of the carbon coating layer M is, for example, 0.1 μm or more and 5 μm or less, and preferably 0.5 μm or more and 2 μm or less. The content of carbon particles in the carbon coating layer M is, for example, 13 mass% or more, and preferably 30 mass% or more. The content of carbon particles in the carbon coating layer M is, for example, 90 mass% or less, and preferably 70 mass% or less.

[0060] The content of the coating layer binder in the carbon coating layer M is, for example, 10% by mass or more, and preferably 30% by mass or more. The content of the coating layer binder in the carbon coating layer M is, for example, 87% by mass or less, and preferably 70% by mass or less. The mass ratio of the carbon particles to the coating layer binder in the carbon coating layer M (carbon particles:coating layer binder) is, for example, 13:87 to 90:10.

[0061] The carbon coating layer M may also contain other components such as a dispersant. Examples of dispersants include carboxyethyl cellulose. The other components refer to components other than the carbon particles and the coating layer binder. The content of the other components in the carbon coating layer M is, for example, 20% by mass or less, and preferably 15% by mass or less. In other words, the total content of the carbon particles and the coating layer binder in the carbon coating layer M is, for example, 80% by mass or more, and preferably 85% by mass or more.

[0062] Next, a method for manufacturing the energy storage device 10 of this embodiment will be described. The energy storage device 10 is manufactured by sequentially performing an electrode formation process, an energy storage cell formation process, and a cell stack formation process. Here, as an example, a case will be described in which the positive electrode current collector 21 a is made of aluminum foil and the negative electrode current collector 22 a is made of copper foil.

[0063] <Electrode Forming Step> The electrode forming step includes a positive electrode forming step of forming the positive electrode 21 and a negative electrode forming step of forming the negative electrode 22 .

[0064] In the positive electrode formation step, first, a carbon coating layer M is formed on the entire first surface 21a1 of the aluminum foil serving as the positive electrode current collector 21a. Prior to the formation of the carbon coating layer M, the first surface 21a1 of the aluminum foil is subjected to a corona discharge treatment. The corona discharge treatment forms hydrophilic groups (OH groups) on the first surface 21a1 of the aluminum foil. The carbon coating layer M can be formed by any known method applicable to the formation of coatings, such as a solution-based process or a vapor deposition-based process.

[0065] An example of a solution-based process is described below. First, a carbon paste is prepared by kneading carbon particles, a coating layer binder, and an aqueous solvent. A coating film is formed by applying the carbon paste to the entire first surface 21a1 of the positive electrode current collector 21a to a predetermined thickness. The formed coating film is dried and solidified to form the carbon coating layer M. Examples of processes for solidifying the carbon paste coating include drying to volatilize the solvent, heating to a temperature equal to or higher than the glass transition temperature Tg2 of the coating layer binder, and then cooling to solidify. Examples of aqueous solvents used in the carbon paste include water and mixed solvents of water and an organic solvent. Examples of organic solvents used in the mixed solvent include N-methyl-2-pyrrolidone (NMP).

[0066] When forming a bipolar electrode 25 having a bipolar current collector, instead of aluminum foil as the positive electrode current collector 21a, a current collector made of aluminum foils bonded together, a current collector made of aluminum foil and copper foil bonded together, a current collector made of aluminum foil with copper plated on the surface, etc. is used.

[0067] An example of a bipolar current collector in which a positive electrode current collector 21a and a negative electrode current collector 22a are bonded together is described below. The bipolar current collector is formed by bonding a positive electrode current collector 21a and a negative electrode current collector 22a together with a conductive adhesive layer. In this case, the positive electrode current collector 21a is, for example, an aluminum foil having a thickness of 20 μm to 100 μm, and the negative electrode current collector 22a is, for example, a copper foil having a thickness of 5 μm to 10 μm.

[0068] The conductive adhesive layer includes an adhesive and conductive particles. The adhesive is not particularly limited, and any known adhesive used for bonding metals can be used. One example of an adhesive is an adhesive containing a polyolefin resin and an epoxy curing agent. In this case, the adhesive has high electrolyte resistance, so it can maintain good bonding strength for a long period of time. In addition, by using an epoxy curing agent as a curing agent in combination with the polyolefin resin, gas generation caused by the curing reaction between the polyolefin resin and the curing agent during the production of the bipolar current collector can be effectively reduced.

[0069] The conductive particles are contained in the conductive adhesive layer to impart conductivity. The aluminum foil and the copper foil bonded together by the conductive adhesive layer are electrically connected through the conductive particles. An example of the conductive particles is a particle having a resin core and a conductive layer located on the surface of the core.

[0070] The conductive layer is, for example, a metal layer. Examples of metals constituting the conductive layer include gold, silver, copper, platinum, nickel, palladium, and aluminum. The metal constituting the conductive layer may be an alloy. One example of the conductive layer covers the entire surface of the core.

[0071] The content of the conductive particles in the conductive adhesive layer is, for example, 0.1% by volume or more and 1.0% by volume or less. In this case, the internal resistance of the bipolar current collector can be reduced while ensuring the bonding strength between the aluminum foil and the copper foil via the conductive adhesive layer. Furthermore, since the content is 1.0% by volume or less, i.e., the content of the adhesive in the conductive adhesive layer is high, a conductive adhesive layer with flat surfaces on both sides can be formed.

[0072] The average particle diameter of the conductive particles in the thickness direction of the conductive adhesive layer (hereinafter referred to as the average particle diameter of the conductive particles) is larger than the average thickness of the conductive adhesive layer, for example, 1 to 1.3 times the average thickness of the conductive adhesive layer.

[0073] The average thickness of the conductive adhesive layer is, for example, 2.0 μm or more and 5.0 μm or less. The average particle diameter of the conductive particles is the average value of particle diameters (maximum length) in the thickness direction of the conductive adhesive layer. The average particle diameter of the conductive particles and the average thickness of the conductive adhesive layer can be measured, for example, by observing a cross section of the conductive adhesive layer using an electron microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0074] The coefficient of variation, which indicates the variation in the particle size distribution of the conductive particles, is, for example, 10% or less, preferably 5% or less. A lower coefficient of variation means a narrower particle size distribution of the conductive particles. By using a material with a small coefficient of variation, deformation of the aluminum foil and copper foil can be suppressed. This improves the surface smoothness of the aluminum foil and copper foil.

[0075] Next, a cathode composite material that will become the cathode active material layer 21b upon solidification is adhered to a central portion of the first surface 21a1 of the aluminum foil on which the carbon coating layer M has been formed, to a predetermined thickness. A solidification treatment appropriate for the cathode composite material is then performed to form the cathode active material layer 21b. Similarly, a negative electrode composite material that will become the anode active material layer 22b upon solidification is adhered to a central portion of the first surface 22a1 of the copper foil serving as the anode current collector 22a, to a predetermined thickness, and a solidification treatment appropriate for the anode composite material is then performed to form the anode active material layer 22b.

[0076] <Storage Cell Formation Process> In the storage cell formation process, first, the positive electrode 21 and the negative electrode 22 are arranged such that the positive electrode active material layer 21b and the negative electrode active material layer 22b face each other in the stacking direction with the separator 23 sandwiched therebetween. In addition, a sealing material that will become the sealing portion 24 is arranged between the positive electrode 21 and the negative electrode 22 and on the outer periphery of the positive electrode current collector 21a and the negative electrode current collector 22a. The sealing material is a resin sheet made of an acid-modified polyolefin resin cut into the same shape as the sealing portion 24 in a planar view. At this time, the sealing material is arranged so as to contact the carbon coating layer M on the first surface 21a1 of the positive electrode current collector 21a.

[0077] Thereafter, the positive electrode 21, the negative electrode 22, the separator 23, and the sealing material are welded together to form an assembly in which the positive electrode 21, the negative electrode 22, the separator 23, and the sealing portion 24 are integrated together. Examples of methods for bonding the sealing material include known welding methods such as heat welding, ultrasonic welding, and infrared welding.

[0078] When the seal portion 24 is formed by thermal welding, the seal material may be heated to a temperature equal to or higher than the melting point Tm1 of the acid-modified polyolefin resin that constitutes the seal material, and then cooled to solidify. In this case, if the glass transition temperature Tg2 of the coating layer binder is lower than the melting point Tm1 of the acid-modified polyolefin resin, the coating layer binder also softens, and the coating layer binder and the acid-modified polyolefin resin become more compatible with each other.

[0079] Next, a liquid electrolyte is injected into the sealed space S inside the assembly through an injection port provided in a part of the seal portion 24, and the injection port is then sealed. This forms the energy storage cell 20. <Cell Stack Forming Process> In the cell stack forming process, first, the plurality of energy storage cells 20 are stacked on top of each other so that the second surfaces 21a2 of the positive electrode current collectors 21a and the second surfaces 22a2 of the negative electrode current collectors 22a face each other. Thereafter, the plurality of energy storage cells 20 are integrated by bonding the outer circumferential portions 24a of the seal portions 24 of the energy storage cells 20 adjacent to each other in the stacking direction.

[0080] Next, a positive electrode current-carrying plate 40 is overlapped and fixed in an electrically connected state to the second surface 21a2 of the positive electrode current collector 21a of the positive electrode 21 arranged outermost at one end in the stacking direction. Similarly, a negative electrode current-carrying plate 50 is overlapped and fixed in an electrically connected state to the second surface 22a2 of the negative electrode current collector 22a of the negative electrode 22 arranged outermost at the other end in the stacking direction.

[0081] <Function> Next, the function of this embodiment will be described. In the electricity storage device 10 of this embodiment, the carbon coating layer M is provided on the entire first surface 21a1 of the positive electrode current collector 21a. The sealing portion 24 made of an acid-modified polyolefin resin is adhered to the carbon coating layer M provided on the first surface 21a1 of the positive electrode current collector 21a.

[0082] In this configuration, the first surface 21a1 of the positive electrode current collector 21a is bonded to the coating layer binder contained in the carbon coating layer M. This bond is considered to be either an ester bond or a hydrogen bond, or both. The ester bond is formed when the coating layer binder contains a resin having a carboxyl group.

[0083] The ester bond is, for example, a bonding structure (-COOMe) in which a hydroxyl group (Me-OH) on the first surface 21a1 of the positive electrode current collector 21a is ester-bonded to a carboxyl group (-COOH) of the coating layer binder. "Me" refers to the metal constituting the current collector. The hydrogen bond is a bonding structure in which a hydroxyl group (Me-OH) on the first surface 21a1 of the positive electrode current collector 21a is hydrogen-bonded to either or both of a hydroxyl group and a carboxyl group of a material constituting the carbon coating layer M. The hydroxyl group is either or both of a hydroxyl group (C-OH) on the surface of the carbon particle and a hydroxyl group (C-OH) of the coating layer binder.

[0084] Furthermore, at the interface between the sealing portion 24 and the carbon coating layer M, the acid-modified polyolefin resin of the sealing portion 24 is bonded to the carbon particles contained in the carbon coating layer M. This bond is thought to be either an ester bond or a hydrogen bond, or both. The ester bond is a bonding structure (-COOC) in which a hydroxyl group (C-OH) on the surface of the carbon particle is ester-bonded to a carboxyl group (-COOH) of the acid-modified polyolefin resin. The hydrogen bond is a bonding structure in which either or both of a hydroxyl group and a carboxyl group of a material constituting the carbon coating layer M is hydrogen-bonded to a carboxyl group (-COOH) of the acid-modified polyolefin resin. The hydroxyl group is either or both of a hydroxyl group (C-OH) on the surface of the carbon particle and a hydroxyl group (C-OH) of the coating layer binder. The above-mentioned bonding structure is formed at the interface between the positive electrode current collector 21a and the carbon coating layer M, and at the interface between the sealing portion 24 and the carbon coating layer M, so that the sealing portion 24 is adhered to the first surface 21a1 of the positive electrode current collector 21a via the carbon coating layer M.

[0085] As described above, according to the configuration of this embodiment, a bond structure is formed at each of the interface between the first surface 21a1 of the positive electrode current collector 21a and the carbon coating layer M, and at the interface between the sealing portion 24 and the carbon coating layer M. In addition, the coating layer binder contained in the carbon coating layer M is compatible with and tightly adheres to the sealing portion 24, thereby improving the adhesive strength of the sealing portion 24 to the positive electrode current collector 21a. More specifically, because the carbon coating layer M contains carbon particles, the surface of the carbon coating layer M has a rough surface with finer irregularities than the first surface 21a1 of the positive electrode current collector 21a. In this case, a bond structure is also formed at the interface between the sealing portion 24 and the carbon coating layer M based on the anchor effect, whereby the resin of the sealing portion 24 penetrates into the irregularities on the surface of the carbon coating layer M. As a result, the adhesive strength of the sealing portion 24 to the positive electrode current collector 21a is improved.

[0086] The effect of improving the adhesive strength due to the carbon coating layer M being interposed between the first surface 21a1 of the positive electrode current collector 21a and the seal portion 24 is as follows: ２ The carbon coating layer M has a coating weight of 0.2 g / m or more. ２ As a result, the first surface 21a1 of the positive electrode current collector 21a can be appropriately covered with the carbon coating layer M. In other words, the surface state of the interface between the positive electrode current collector 21a and the seal portion 24 can be changed from a state in which properties based on the first surface 21a1 of the positive electrode current collector 21a are primarily exhibited to a state in which properties based on the carbon coating layer M are primarily exhibited. The above properties include, for example, surface wettability and smoothness.

[0087] <Effects> According to this embodiment, the following effects can be obtained. (1) The energy storage device 10 includes a plurality of energy storage cells 20. Each energy storage cell 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and a seal portion 24. In the positive electrode 21, a positive electrode active material layer 21b is formed on the first surface 21a1 of the positive electrode current collector 21a. In the negative electrode 22, a negative electrode active material layer 22b is formed on the first surface 22a1 of the negative electrode current collector 22a. The separator 23 is disposed between the positive electrode active material layer 21b and the negative electrode active material layer 22b. The seal portion 24 is bonded to the first surfaces 21a1, 22a1 of the positive electrode current collector 21a and the negative electrode current collector 22a, respectively, to form an enclosed space for accommodating a liquid electrolyte between the positive electrode 21 and the negative electrode 22. The seal portion 24 is made of an acid-modified polyolefin resin. The first surface 21a1 of the positive electrode current collector 21a is made of aluminum. The positive electrode 21 includes a carbon coating layer M provided on the adhesive portion of the first surface 21a1 of the positive electrode current collector 21a with the seal portion 24. The carbon coating layer M contains carbon particles and a coating layer binder. The coating weight of the carbon coating layer M is 0.2 g / m ２ That's all.

[0088] According to the above configuration, a bond structure is formed at the interface between the first surface 21a1 of the positive electrode current collector 21a and the carbon coating layer M, and at the interface between the sealing portion 24 and the carbon coating layer M. In addition, the coating layer binder contained in the carbon coating layer M and the sealing portion 24 are compatible with each other and tightly bonded together, thereby improving the adhesive strength of the sealing portion 24 to the positive electrode current collector 21a.

[0089] (2) The weight of the carbon coating layer is 1.0 g / m ２ According to the above configuration, leakage of the liquid electrolyte due to permeation through the carbon coating layer M can be suppressed.

[0090] (3) The coating layer binder contains a resin having a carboxyl group. According to the above configuration, an ester bond is formed at the interface between the first surface 21a1 of the positive electrode current collector 21a and the carbon coating layer M, and at the interface between the seal portion 24 and the carbon coating layer M. This makes the effect of (1) above more pronounced.

[0091] (4) The carbon coating layer M is provided on the entire first surface 21a1 of the positive electrode current collector 21a. According to the above configuration, the process of forming the carbon coating layer M can be simplified compared to a configuration in which the carbon coating layer M is provided on only a part of the first surface 21a1 of the positive electrode current collector 21a.

[0092] (5) The energy storage device 10 includes a plurality of stacked energy storage cells 20, and includes a bipolar electrode 25 in which a positive electrode current collector 21a of a positive electrode 21 constituting one of adjacent energy storage cells 20 is joined to a negative electrode current collector 22a of a negative electrode 22 constituting the other of adjacent energy storage cells 20. The bipolar electrode 25 is joined to a surface (second surface 21a2) of the positive electrode current collector 21a opposite to the first surface 21a1 and a surface (second surface 22a2) of the negative electrode current collector 22a opposite to the first surface 22a1.

[0093] According to the above configuration, it is possible to improve the adhesive strength of the seal portion 24 in the power storage device 10 including the bipolar electrode 25. (6) The first surface 22a1 of the negative electrode current collector 22a is made of copper.

[0094] Aluminum has a higher standard electrode potential than copper. Therefore, the first surface 21a1 of the positive electrode collector 21a, which is made of aluminum, is more susceptible to oxidation than the first surface 22a1 of the negative electrode collector 22a, which is made of copper. Therefore, by providing a carbon coating layer M on the first surface 21a1 of the positive electrode collector 21a, which is made of aluminum, oxidation of the first surface 21a1 of the positive electrode collector 21a due to heat applied during the manufacturing process of the electricity storage device 10 can be suppressed. Examples of processes in which heat is applied include heating when bonding the positive electrode collector 21a and the negative electrode collector 22a together and heating when solidifying the positive electrode active material layer 21b.

[0095] (7) The positive electrode current collector 21a of the bipolar electrode 25 is aluminum foil, and the negative electrode current collector 22a is copper foil. In the bipolar electrode 25, the positive electrode current collector 21a and the negative electrode current collector 22a are bonded together with a conductive adhesive layer. The conductive adhesive layer contains an adhesive and conductive particles. The conductive particles have a resin core and a conductive layer located on the surface of the core. The content of the conductive particles in the conductive adhesive layer is 0.1% by volume or more and 1.0% by volume or less.

[0096] The high adhesive content in the conductive adhesive layer and the use of conductive particles with a resin core allow for the formation of a conductive adhesive layer with flat surfaces on both sides. This improves the smoothness of the surface of the aluminum foil placed along the conductive adhesive layer. In this case, it becomes easier to uniformly form the carbon coating layer M on the surface of the aluminum foil that is the positive electrode current collector 21a. By being able to uniformly form the carbon coating layer M, the above-mentioned effect (1) based on the carbon coating layer M can be more reliably achieved.

[0097] This embodiment can be modified as follows. This embodiment and the following modifications can be implemented in combination as long as there is no technical contradiction. The carbon coating layer M may be provided on at least a portion of the first surface 21a1 of the positive electrode current collector 21a that is bonded to the seal portion 24. For example, the carbon coating layer M may be absent from a portion of the first surface 21a1 of the positive electrode current collector 21a that is bonded to the seal portion 24. However, it is preferable that the carbon coating layer M is formed in a ring shape surrounding the sealed space S in a plan view on the portion of the first surface 21a1 of the positive electrode current collector 21a that is bonded to the seal portion 24. Furthermore, the carbon coating layer M may be absent from a portion or the entirety of the portion of the first surface 21a1 of the positive electrode current collector 21a that is not bonded to the seal portion 24.

[0098] The carbon coating layer M may be provided on the first surface 22a1 of the negative electrode current collector 22a instead of on the first surface 21a1 of the positive electrode current collector 21a. Alternatively, the carbon coating layer M may be provided on both the first surface 21a1 of the positive electrode current collector 21a and the first surface 22a1 of the negative electrode current collector 22a. In these cases, the adhesive strength of the seal portion 24 to the first surface 22a1 of the negative electrode current collector 22a is improved.

[0099] The planar shapes of the positive electrode current collector 21 a and the positive electrode active material layer 21 b are not particularly limited. They may be polygonal, such as rectangular, or may be circular or elliptical. The same applies to the negative electrode current collector 22 a and the negative electrode active material layer 22 b.

[0100] The planar shape of the seal portion 24 is not particularly limited and may be a polygonal shape such as a rectangle, or may be a circle or an ellipse. A conductive layer that adheres closely to the positive electrode current collector 21a may be disposed between the positive electrode current-carrying plate 40 and the positive electrode current collector 21a to improve the conductive contact between the two components. Examples of the conductive layer include a layer containing carbon such as acetylene black or graphite, or a layer with a lower hardness than the positive electrode current collector 21a, such as a plating layer containing Au. A similar conductive layer may also be disposed between the negative electrode current-carrying plate 50 and the negative electrode current collector 22a.

[0101] The number of storage cells 20 constituting the energy storage device 10 is not particularly limited. The number of storage cells 20 constituting the energy storage device 10 may be one. The positive electrode active material layer 21b or the negative electrode active material layer 22b may be provided on the second surface 21a2 of the positive electrode current collector 21a. Furthermore, the positive electrode active material layer 21b or the negative electrode active material layer 22b may be provided on the second surface 22a2 of the negative electrode current collector 22a.

[0102] The energy storage device 10 may include a restraining member that restrains the cell stack 30. The restraining member applies a restraining load to the region where the energy storage cells 20 face each other in the stacking direction of the cell stack 30, particularly to the region where the area where the positive electrode active material layer 21 b is provided overlaps with the area where the negative electrode active material layer 22 b is provided in a plan view.

[0103] The specific configuration of the restraining member is not particularly limited as long as it is capable of applying a restraining load to the cell stack 30. For example, the restraining member may be configured to include plate-shaped restraining plates disposed at both ends of the cell stack 30 in the stacking direction so as to sandwich the cell stack 30, and fastening members made of bolts and nuts that fasten the restraining plates together. In the case of a restraining member configured as described above, the fastening members urge the restraining plates in directions that bring them closer to each other, thereby applying a restraining load to the cell stack 30 in the stacking direction.

[0104] Examples that further embody the above-described embodiment will be described below. (Test Examples 1 to 5) Aluminum foil having a thickness of 30 μm was prepared, and one surface of the aluminum foil was subjected to a corona discharge treatment to hydrophilize the surface of the aluminum foil. A coating film was formed by applying a carbon paste to the entire hydrophilized surface of the aluminum foil. The formed coating film was dried. Thereafter, the sheet was heated at 150°C for 10 seconds and then cooled to form a carbon coating layer. The obtained sheet materials were designated as Test Examples 1 to 5.

[0105] The carbon paste was a mixture of carbon particles, a coating layer binder, carboxyethyl cellulose (CMC), and water. Acetylene black was used as the carbon particles. An acrylic resin was used as the coating layer binder. The mass ratio of the solid contents in the carbon paste was 50:37.5:12.5 (carbon particles: coating layer binder: CMC). The solvent content in the carbon paste was such that the solid content ratio was 85% by mass. Test Examples 1 to 5 each had a different basis weight of the carbon coating layer. The basis weights of the carbon coating layers of the sheet materials in Test Examples 1 to 5 are as shown in Table 1.

[0106] (Contact Angle Measurement) A 4 μL drop of water was dropped onto the surface of the carbon coating layer of the sheet material of Test Example 4 using a dropper, and the contact angle of the water drop formed on the surface of the carbon coating layer was measured. The contact angle of water with the surface of the carbon coating layer was 27.4°. From this result, it can be inferred that carboxyl groups are present on the surface of the carbon coating layer to an extent that the contact angle of water can be reduced to 40° or less, or even 30° or less.

[0107] (Measurement of adhesive strength) Rectangular sheet materials measuring 10 mm long x 50 mm wide were cut out from the sheet materials of Test Examples 1 to 5. Also, rectangular sealing materials measuring 10 mm long x 50 mm wide were prepared. An acid-modified polyethylene sheet having a thickness of 120 μm and a melting point of 120°C was used as the sealing material. A laminate was obtained by laminating the sealing material onto the sheet material so that the edges were aligned. The laminate was heated at 150°C for 10 seconds using an impulse sealer, and then cooled to prepare a measurement sample in which the sheet material and sealing material were bonded together.

[0108] The measurement sample was immersed in a liquid electrolyte for 240 hours at 60° C. The liquid electrolyte used was a non-aqueous electrolyte prepared by dissolving lithium hexafluorophosphate to a concentration of 1.2 M in a mixed solvent of ethylene carbonate and methyl propionate in a volume ratio of 15:85.

[0109] The measurement sample after the immersion treatment was subjected to a 180-degree peel test under conditions of a pulling speed of 10 mm / min and a temperature of 25°C. The peel strength of the measurement sample was calculated by dividing the strength measured in the 180-degree peel test by the line width of 10 mm, and this calculated value was taken as the adhesive strength. The results are shown in Table 1. Note that the conditions of the immersion treatment were adjusted to conditions that made peeling easier than in actual cases so that the adhesive strength of Test Example 1 would be 0 N / mm in the 180-degree peel test.

[0110]

[0111] As shown in Table 1, the weight of the carbon coating layer was 0.1 g / m ２In the case of Test Example 2 below, an increase in adhesive strength due to the provision of the carbon coating layer was not confirmed compared to Test Example 1. The basis weight of the carbon coating layer was 0.2 g / m ２ In the case of Test Examples 3 to 5, the adhesive strength was significantly increased compared to Test Example 1. In addition, when the coating weight of the carbon coating layer was 0.2 g / m ２ Within the above range, there was a tendency for the adhesive strength to gradually decrease as the basis weight increased. ２ From the tendency for the adhesive strength to decrease with increasing basis weight of the carbon coating layer in the range of (Test Examples 3 to 5), it was found that the basis weight was 1.0 g / m ２ If the weight is less than this, the maximum weight is 0.22 g / m ２ In this case, the degree of decrease in adhesive strength can be suppressed to 25% or less.

[0112] M... Carbon coating layer S... Sealed space 10... Energy storage device 20... Energy storage cell 21... Positive electrode 21a... Positive electrode current collector 21b... Positive electrode active material layer 22... Negative electrode 22a... Negative electrode current collector 22b... Negative electrode active material layer 23... Separator 24... Seal portion 25... Bipolar electrode 30... Cell stack

Claims

1. An electricity storage device including an electricity storage cell including: a positive electrode having a positive electrode active material layer provided on a first surface of a positive electrode current collector; a negative electrode having a negative electrode active material layer provided on a first surface of a negative electrode current collector, the negative electrode active material layer being disposed so as to face the positive electrode active material layer of the positive electrode; a separator disposed between the positive electrode active material layer and the negative electrode active material layer; and a seal portion disposed between the positive electrode and the negative electrode so as to surround the periphery of the positive electrode active material layer and the negative electrode active material layer, and bonded to each first surface of the positive electrode current collector and the negative electrode current collector to form an enclosed space for accommodating a liquid electrolyte between the positive electrode and the negative electrode, wherein the seal portion is made of an acid-modified polyolefin resin; the first surface of the positive electrode current collector is made of aluminum; and the positive electrode has a carbon coating layer provided on the adhesion portion of the first surface of the positive electrode current collector with the seal portion, The carbon coating layer contains carbon particles and a coating layer binder, and the carbon coating layer has a basis weight of 0.2 g / m ２ That's all about the energy storage device.

2. The weight of the carbon coating layer is 1.0 g / m ２ The power storage device according to claim 1 , wherein:

3. The electricity storage device according to claim 1 or 2, wherein the coating layer binder contains a resin having a carboxyl group.

4. The electricity storage device according to any one of claims 1 to 3, wherein the carbon coating layer is provided on the entire first surface of the positive electrode current collector.

5. The energy storage device according to any one of claims 1 to 4, comprising a bipolar electrode in which a plurality of the energy storage cells are stacked and a surface of the positive electrode current collector of the positive electrode constituting one of the adjacent energy storage cells opposite to the first surface of the positive electrode current collector of the negative electrode constituting the other of the adjacent energy storage cells is joined to a surface of the negative electrode current collector of the negative electrode constituting the other of the adjacent energy storage cells opposite to the first surface of the negative electrode current collector.

6. The electricity storage device according to claim 5, wherein the first surface of the negative electrode current collector of the bipolar electrode is made of copper.

7. The energy storage device according to claim 5 or 6, wherein the positive electrode current collector of the bipolar electrode is an aluminum foil, the negative electrode current collector of the bipolar electrode is a copper foil, the bipolar electrode has the positive electrode current collector and the negative electrode current collector bonded together with a conductive adhesive layer, the conductive adhesive layer contains an adhesive and conductive particles, the conductive particles have a resin core and a conductive layer located on a surface of the core, and the conductive particle content in the conductive adhesive layer is 0.1 vol % or more and 1.0 vol % or less.

8. The energy storage device according to any one of claims 5 to 7, wherein the bipolar electrode has a carbon coating layer provided on both the first surface of the positive electrode collector and the first surface of the negative electrode collector.

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