Energy storage device

Abstract

An energy storage device (10) includes an energy storage unit (20) comprising a positive electrode (21), a negative electrode (22), a separator (23), and a sealing portion (24) forming a sealed space for containing 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) 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 made of aluminum. The sealing portion (24) is made 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) has a carbon coating (M) disposed on the bonding portion of the first surface (21a1) of the positive electrode current collector (21a) with the sealing portion (24). The carbon coating (M) comprises carbon particles and a coating binder. The carbon coating (M) has a unit area weight of 0.2 g / m². 2 above.

Description

Technical Field

[0001] This disclosure relates to energy storage devices. Background Technology

[0002] Patent Document 1 discloses a flat energy storage device constructed by stacking multiple independently manufactured energy storage units in series. The energy storage unit comprises: a positive electrode, which is formed by forming a positive active material layer on the central portion of one side of a foil-shaped positive current collector; a negative electrode, which is formed by forming a negative active material layer on the central portion of one side of a foil-shaped negative current collector, arranged such that the negative active material layer faces the positive active material layer of the positive electrode; and a separator disposed between the positive and negative electrodes.

[0003] Furthermore, the aforementioned energy storage unit includes a sealing portion disposed between the positive and negative electrodes and further outward than the positive and negative active material layers. The sealing portion maintains the distance between the positive and negative current collectors to prevent short circuits between the current collectors, and liquid-tightly seals the space between the positive and negative current collectors to form a sealed space for containing the liquid electrolyte between them. Existing technical documents Patent documents

[0004] Patent Document 1: Japanese Patent Application Publication No. 2017-16825 Summary of the Invention The problem the invention aims to solve

[0005] In existing energy storage devices, when a load is applied to the bonded portion between the current collector and the seal, such as in a situation where the internal pressure of a confined space increases, the seal may sometimes detach from the current collector. This detachment of the seal can lead to short circuits between current collectors and leakage of the liquid electrolyte. Solution for solving the problem

[0006] In one aspect of this disclosure, an energy storage device with an energy storage unit is provided. The energy storage unit includes a positive electrode, a negative electrode, a separator, and a sealing portion. The positive electrode is formed by depositing a positive active material layer on the first surface of a positive current collector. The negative electrode is formed by depositing a negative active material layer on the first surface of a negative current collector, arranged such that the negative active material layer faces the positive active material layer of the positive electrode. The separator is disposed between the positive and negative active material layers. The sealing portion is disposed between the positive and negative electrodes in a manner that surrounds the positive and negative active material layers. The sealing portion forms a sealed space for containing a liquid electrolyte between the positive and negative electrodes by being bonded to the first surfaces of the positive and negative current collectors. The sealing portion is made of an acid-modified polyolefin resin. The first surface of the positive current collector is made of aluminum. The positive electrode has a carbon coating disposed on the bonding portion of the first surface of the positive current collector with the sealing portion. The carbon coating comprises carbon particles and a coating binder. The weight per unit area of ​​the carbon coating is 0.2 g / m². 2 above.

[0007] In the aforementioned energy storage device, the preferred unit area weight of the carbon coating is 1.0 g / m². 2 the following. In the above-mentioned energy storage device, the coating adhesive preferably comprises a resin having carboxyl groups.

[0008] In the above-mentioned energy storage device, the carbon coating is preferably disposed on the entire first surface of the positive electrode current collector. In the above-mentioned energy storage device, a plurality of energy storage units are stacked, and each unit has a bipolar electrode. The bipolar electrode is formed by joining the surface of the positive current collector of the positive electrode of one of the adjacent energy storage units, located on the opposite side of the first surface, with the surface of the negative current collector of the negative electrode of the other adjacent energy storage unit, located on the opposite side of the first surface.

[0009] In the above-mentioned energy storage device, preferably, the first surface of the negative current collector of the bipolar electrode is made of copper. In the above-described energy storage device, the bipolar electrode preferably has the following configuration: The positive current collector is aluminum foil. The negative current collector of the bipolar electrode is copper foil. The bipolar electrode is formed by bonding the positive current collector and the negative current collector together with a conductive adhesive layer. The conductive adhesive layer comprises 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-mentioned energy storage device, preferably, the bipolar electrode is provided with the carbon coating on both the first surface of the positive current collector and the first surface of the negative current collector. Invention Effects

[0011] According to the present invention, the adhesion strength of the sealing portion relative to the current collector can be improved. Attached Figure Description

[0012] Figure 1 This is a cross-sectional view of the energy storage device. Detailed Implementation

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Figure 1 The energy storage device 10 shown is, for example, an energy storage module used in the batteries of various vehicles such as forklifts, hybrid vehicles, and electric vehicles. The energy storage device 10 is, for example, a nickel-metal hydride secondary battery or a lithium-ion secondary battery. The energy storage device 10 may also be an electric double-layer capacitor. In this embodiment, the case where the energy storage device 10 is a lithium-ion secondary battery is illustrated.

[0014] <Electric Storage Devices> like Figure 1 As shown, the energy storage device 10 is configured as a unit stack 30 (stack) comprising multiple energy storage units 20 stacked in a stacking direction. Hereinafter, the stacking direction of the multiple energy storage units 20 will be simply referred to as the stacking direction. Each energy storage unit 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and a sealing portion 24.

[0015] The positive electrode 21 includes a positive current collector 21a and a positive active material layer 21b disposed on the first surface 21a1 of the positive current collector 21a. In this embodiment, the positive electrode 21, the positive current collector 21a, and the positive active material layer 21b are respectively equivalent to an electrode, a current collector, and an active material layer.

[0016] In a top view (hereinafter referred to as top view) viewed from the stacking direction, the positive electrode active material layer 21b is formed at the center of the first surface 21a1 of the positive electrode current collector 21a. The periphery of the first surface 21a1 of the positive electrode current collector 21a in the top view is the uncoated positive electrode portion 21c, where the positive electrode active material layer 21b is not provided. The uncoated positive electrode portion 21c is arranged in a manner that surrounds the positive electrode active material layer 21b in the top view.

[0017] The negative electrode 22 includes a negative electrode current collector 22a and a negative electrode active material layer 22b disposed on a first surface 22a1 of the negative electrode current collector 22a. In plan view, the negative electrode active material layer 22b is formed at the center of the first surface 22a1 of the negative electrode current collector 22a. In plan view, the peripheral portion of the first surface 22a1 of the negative electrode current collector 22a is an uncoated negative electrode portion 22c where the negative electrode active material layer 22b is not disposed. In plan view, the uncoated negative electrode portion 22c is arranged to surround 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 are opposite to each other in the stacking direction. That is, the direction in which the positive electrode 21 and the negative electrode 22 face each other is consistent with the stacking direction. The negative electrode active material layer 22b is formed to be one size larger than the positive electrode active material layer 21b, and when viewed from above in the stacking direction, the entire formation area of ​​the positive electrode active material layer 21b is located within the formation area of ​​the negative electrode active material layer 22b.

[0019] Here, the positive current collector 21a has a second surface 21a2 located on the opposite side of the first surface 21a1, and the negative current collector 22a has a second surface 22a2 located on the opposite side of the first surface 22a1. The unit stack 30 has a structure in which multiple energy storage units 20 are stacked in such a way that the second surface 21a2 of the positive current collector 21a and the second surface 22a2 of the negative current collector 22a are in contact. Thus, the multiple energy storage units 20 constituting the unit stack 30 are connected in series.

[0020] In the unit stack 30, two adjacent energy storage units 20 in the stacking direction form a suspected bipolar electrode 25 that treats the positive current collector 21a and the negative current collector 22a in contact with each other as a single current collector. The suspected bipolar electrode 25 includes: a current collector, which is a structure formed by stacking the positive current collector 21a and the negative current collector 22a; a positive active material layer 21b, which is formed on one side of the current collector; and a negative active material layer 22b, which is formed on the other side of the current collector.

[0021] Alternatively, the positive current collector 21a and the negative current collector 22a can also form a bipolar current collector by joining the second surface 21a2 of the positive current collector 21a and the second surface 22a2 of the negative current collector 22a. In this case, the positive electrode 21 and the negative electrode 22 form a bipolar electrode 25 having a bipolar current collector formed by joining the positive current collector 21a and the negative current collector 22a. In other words, the bipolar electrode 25 is formed by joining the surface of the positive current collector 21a of the positive electrode 21 of one of the adjacent energy storage units 20, located opposite to the first surface 21a1, with the surface of the negative current collector 22a of the negative electrode 22 of the other energy storage unit 20, located opposite to the first surface 22a1.

[0022] The separator 23 is a component disposed between the positive electrode 21 and the negative electrode 22, which prevents short circuits caused by contact between the two electrodes by isolating the positive electrode 21 and the negative electrode 22 and allows 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 constituting the separator 23 include polypropylene, polyethylene, polyolefins, and polyester. The separator 23 can have a single-layer or multi-layer structure. A multi-layer structure may include, for example, an adhesive layer, a ceramic layer as a heat-resistant layer, etc.

[0024] The sealing portion 24 is disposed between the first surface 22a1 of the positive current collector 21a of the positive electrode 21 and the first surface 22a1 of the negative current collector 22a of the negative electrode 22, and at a position further outward than the positive active material layer 21b and the negative active material layer 22b, and is adhered to both the positive current collector 21a and the negative current collector 22a. The sealing portion 24 prevents short circuits between the current collectors by insulating the positive current collector 21a and the negative current collector 22a.

[0025] When viewed from above, the sealing portion 24 is formed as a frame extending along the periphery of the positive electrode current collector 21a and the negative electrode current collector 22a, and surrounding the periphery of the positive electrode active material layer 21b and the negative electrode active material layer 22b. The sealing portion 24 is disposed between the positive electrode uncoated portion 21c of the first surface 21a1 of the positive electrode current collector 21a and the negative electrode uncoated portion 22c of the first surface 22a1 of the negative electrode current collector 22a.

[0026] Inside the energy storage unit 20, a sealed space S is formed, surrounded by a frame-shaped sealing portion 24, a positive electrode 21, and a negative electrode 22. The sealed space S houses a separator 23 and a liquid electrolyte. Furthermore, the periphery of the separator 23 is embedded within the sealing portion 24.

[0027] The sealing portion 24, by sealing the enclosed space S between the positive electrode 21 and the negative electrode 22, can suppress the permeation of the liquid electrolyte contained in the enclosed space S to the outside. In addition, the sealing portion 24 can prevent moisture from entering the enclosed space S from the outside of the energy storage device 10. Moreover, the sealing portion 24 can, for example, prevent the leakage of gas generated from the positive electrode 21 or the negative electrode 22 due to charging and discharging reactions to the outside of the energy storage device 10.

[0028] Each energy storage cell 20 has a sealing portion 24 that extends outward from the edges of the positive current collector 21a and the negative current collector 22a. When viewed from the stacking direction, the outer peripheral portion 24a protrudes in a direction orthogonal to the stacking direction from the edges of the positive current collector 21a and the negative current collector 22a. Adjacent energy storage cells 20 in the stacking direction are integrated by bonding them together with the outer peripheral portions 24a of their respective sealing portions 24. Known welding methods such as thermal welding, ultrasonic welding, or infrared welding can be used as methods for bonding adjacent sealing portions 24 together.

[0029] The energy storage device 10 includes a pair of current-carrying bodies, including a positive electrode current-carrying plate 40 and a negative electrode current-carrying plate 50, arranged in the stacking direction of the unit stack 30 in such a way that they sandwich the unit 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 energizing plate 40 is electrically connected to the second surface 21a2 of the positive current collector 21a, which is located on the outermost side of the positive electrode 21 in the stacking direction. The negative electrode energizing plate 50 is electrically connected to the second surface 22a2 of the negative current collector 22a, which is located on the outermost side of the negative electrode 22 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, respectively. For example, the same material as the material constituting the positive electrode current-carrying plate 40 can be used to construct the positive electrode current-carrying member 21a. The positive electrode current-carrying plate 40 may also be constructed of a metal plate thicker than the positive electrode current-carrying member 21a used in the unit stack 30. For example, the same material as the material constituting the negative electrode current-carrying member 22a can be used to construct the negative electrode current-carrying plate 50. The negative electrode current-carrying plate 50 may also be constructed of a metal plate thicker than the negative electrode current-carrying member 22a used in the unit stack 30.

[0032] Next, the details of the positive current collector 21a, the negative current collector 22a, the positive active material layer 21b, the negative active material layer 22b, the liquid electrolyte, and the sealing part 24 will be explained. <Positive and negative current collectors> The positive electrode current collector 21a is a chemically inert conductor used to continuously allow current to flow through the positive electrode active material layer 21b during the discharge or charging of a lithium-ion secondary battery. An example of the positive electrode current collector 21a is an aluminum current collector whose first surface 21a1 is made of aluminum. The aluminum current collector can be a single material entirely composed of aluminum, or a composite material having portions made of aluminum and portions made of materials other than aluminum. Examples of such single materials include, for example, rolled aluminum foil. Examples of such composite materials include multilayer structures where the first surface 21a1 is an aluminum layer, and substrates containing the first surface 21a1 covered by an aluminum film.

[0033] Materials other than aluminum can include, for example, metallic materials, conductive resin materials, and conductive inorganic materials. Examples of metallic materials include, for example, copper, nickel, titanium, and stainless steel (e.g., SUS304, SUS316, SUS301, SUS304, etc. as specified in JIS G 4305:2015). Examples of conductive resin materials include, for example, conductive polymer materials or resins formed by adding conductive fillers to non-conductive polymer materials as needed. The form of the aluminum current collector is, for example, foil, sheet, or 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 inert conductor used to continuously allow current to flow through the negative electrode active material layer 22b during the discharge or charging of a lithium-ion secondary battery. An example of the negative electrode current collector 22a is a copper current collector whose first surface 22a1 is made of copper. The copper current collector can be a single element entirely composed of copper, or a composite having portions made of copper and portions made of materials other than copper. Examples of such single elements include copper foil, such as electrolytic copper foil. Examples of such composites include multilayer structures where the first surface 22a1 is a copper layer, and substrates containing the first surface 22a1 covered by a copper film.

[0035] Materials other than copper can include, for example, metallic materials, conductive resin materials, and conductive inorganic materials. Examples of metallic materials include, for example, aluminum, nickel, titanium, and stainless steel (e.g., SUS304, SUS316, SUS301, SUS304, etc. as specified in JIS G 4305:2015). Examples of conductive resin materials include, for example, conductive polymer materials or resins formed by adding conductive fillers to non-conductive polymer materials as needed. The form of the copper current collector is, for example, foil, sheet, or film. The thickness of the aluminum current collector is, for example, 1–100 μm.

[0036] As an example of a preferred combination of the positive current collector 21a and the negative current collector 22a, the positive current collector 21a can be made of aluminum foil, which is an aluminum current collector, and the negative current collector 22a can be made of copper foil, which is a copper current collector. Furthermore, as examples of the aforementioned bipolar current collector, a current collector formed by bonding aluminum foils together, a current collector formed by bonding aluminum foil and copper foil together, and a current collector formed by plating copper onto the surface of aluminum foil can be described.

[0037] The positive current collector 21a and the negative current collector 22a constituting the bipolar current collector are bonded together, for example, via an adhesive layer. The adhesive layer is conductive, electrically connecting the positive current collector 21a and the negative current collector 22a. The adhesive layer may contain, for example, an adhesive component and a conductive component dispersed within the adhesive component. Examples of adhesive components include polyolefin resins such as polypropylene and polyethylene. The adhesive component may be one type or a combination of two or more types. The adhesive component may also contain curing agents such as isocyanate-based curing agents and epoxy-based curing agents. An example of an adhesive component includes a polyolefin resin and an epoxy-based curing agent. In this case, the generation of gases accompanying the curing reaction can be suppressed. Examples of conductive components include conductive particles and conductive fillers. Examples of conductive particles include metal particles such as aluminum particles, nickel particles, SUS particles, silver particles, gold particles, copper particles, titanium particles, and alloy particles, as well as carbon particles such as graphite particles. Alternatively, conductive particles can also be spherical particles formed by forming a metal film on the surface of core particles such as resin or ceramics. Examples of conductive fillers include carbon nanotubes. The conductive component can be one type or a combination of two or more. Furthermore, the adhesive component can also be a conductive adhesive component. Examples of conductive adhesive components include conductive polymers. In this case, if the adhesive component is conductive, the conductive component dispersed in the adhesive component can be omitted.

[0038] In addition, a carbon coating M is provided on the first surface 21a1 of the positive current collector 21a. Details about the carbon coating 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 suitable for use as a positive electrode active material in lithium-ion secondary batteries, such as lithium composite metal oxides with a layered rock salt structure, metal oxides with a spinel structure, or polyanionic compounds, can be used. Alternatively, two or more positive electrode active materials can be used in combination. In this embodiment, the positive electrode active material layer 21b contains olivine-type lithium iron phosphate (LiFePO4) as a polyanionic compound.

[0039] The negative electrode active material layer 22b can be any element, alloy, or compound capable of absorbing and releasing charge carriers such as lithium ions, and is not particularly limited in its use. Examples of negative electrode active materials include lithium (Li), carbon, metal compounds, elements or compounds that can alloy with lithium, etc. Examples of carbon include natural graphite, artificial graphite, or hard carbon (difficult-to-graphitize carbon) or soft carbon (easily-graphitize carbon). Examples of artificial graphite include highly oriented graphite, mesophase carbon microspheres, etc. Examples of elements that can alloy 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 21b and the negative electrode active material layer 22b (hereinafter referred to as active material layers) may each contain conductive additives, binders, electrolytes (polymer matrix, ion-conducting polymer, liquid electrolyte, etc.), and electrolyte support salts (lithium salts) to improve ion conductivity, as needed. The components contained in the active material layers, the mixing ratio of these components, and the thickness of the active material layers are not particularly limited and can be appropriately referenced to previously known insights regarding lithium-ion secondary batteries.

[0041] Conductive additives are added to improve the conductivity of the positive electrode 21 or the negative electrode 22. Examples of conductive additives include acetylene black, carbon black, and graphite. Examples of adhesives include fluorinated resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber; thermoplastic resins such as polypropylene and polyethylene; imide resins such as polyimide and polyamide-imide; resins containing alkoxysilyl groups; 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 crosslinks; and starch-acrylic acid graft polymers. These adhesives can be used alone or in combination. Examples of solvents or dispersion media include water and N-methyl-2-pyrrolidone.

[0042] There are no particular limitations on the method for forming active material layers on the surfaces of the positive current collector 21a and the negative current collector 22a, and conventionally known methods such as roller coating can be used. To improve the thermal stability of the positive electrode 21 or the negative electrode 22, the aforementioned heat-resistant layer can also be provided on the surface of the active material layer.

[0043] The weight per unit area of ​​the active material layer is not particularly limited, and can be appropriately referenced to previously known insights regarding lithium-ion secondary batteries. However, from the viewpoint of increasing the energy density of the energy storage unit 20, it is preferable to increase the weight per unit area of ​​the active material layer. For example, the weight per unit area of ​​the positive electrode active material layer 21b is 55–90 mg / cm³. 2The preferred concentration is 60 mg / cm³. 2 The above, more preferably 70 mg / cm³ 2 The above. The weight per unit area of ​​the negative electrode active material layer 22b is, for example, 25–45 mg / cm³. 2 The preferred concentration is 30 mg / cm³. 2 above.

[0044] <Sealing section> 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-modifying groups include carboxylic acid groups, maleic acid groups, and maleic anhydride groups. The acid-modified polyolefin resin constituting the sealing portion 24 can be one type or a combination of two or more types. The acid-modified polyolefin resin constituting the sealing portion 24 can be a thermoplastic resin or a thermosetting resin.

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

[0046] The sealing part 24 is bonded to the first surface 21a1 of the positive current collector 21a, and more specifically, to the carbon coating M provided on the first surface 21a1. Additionally, the sealing part 24 is bonded to the first surface 22a1 of the negative current collector 22a.

[0047] <Liquid Electrolytes> Liquid electrolytes comprise a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. 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. In addition, combinations of two or more of these known solvent materials can be used.

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

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

[0050] The carbon coating M consists of carbon particles and a coating binder. As carbon particles, known carbon materials such as graphite and acetylene black, which are used in carbon coatings, can be used.

[0051] Materials constituting the coating adhesive include, for example, acrylic resins and carboxyl-modified styrene-butadiene rubber, which are resins containing carboxyl groups. Acrylic resins are preferred as the materials constituting the coating adhesive.

[0052] Examples of acrylic resins include homopolymers of acrylic monomers such as acrylic acid, methacrylic acid, and (meth)acrylates, or (meth)acrylate copolymers containing the aforementioned acrylic monomers. In this embodiment, (meth)acrylate means acrylic acid or methacrylic acid.

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

[0054] In the aforementioned (meth)acrylic acid copolymers, other comonomers that copolymerize with acrylic monomers include α-olefins, styrene, α-methylstyrene, vinyltoluene, acrylonitrile, methacrylonitrile, and vinyl acetate. These comonomers can exist in the acrylic resin in the form of random copolymers, graft copolymers, or block copolymers. Examples of the aforementioned (meth)acrylic acid copolymers include, for example, silicone-modified styrene-acrylic acid resins, carboxyl-modified styrene-acrylic acid resins, and hydroxyl-modified acrylic acid resins. The materials constituting the coating adhesive can be one or a combination of two or more.

[0055] The carbon coating M is preferably formed with a large number of carboxyl groups on its surface. For example, as a benchmark for the presence of a large number of carboxyl groups on the surface, a small contact angle of water with respect to the surface of the carbon coating M can be cited. The contact angle of water with respect to the surface of the carbon coating M is, for example, 40° or less, preferably 30° or less.

[0056] The glass transition temperature Tg2 of the coating adhesive is, for example, 0°C or higher and 150°C or lower. When the sealing portion 24 is bonded by heat fusion, it is preferable to heat the sealing element, which is the material forming the sealing portion 24, at a temperature exceeding the glass transition temperature Tg2 of the coating adhesive and at a temperature exceeding the melting point Tm1 of the acid-modified polyolefin resin constituting the sealing portion 24. In this case, the coating adhesive contained in the carbon coating M softens due to the heating used to bond the sealing portion 24, thus making the coating adhesive readily compatible with the sealing portion 24. Therefore, the glass transition temperature Tg2 of the coating adhesive is preferably a temperature lower than the melting point Tm1 of the acid-modified polyolefin resin constituting the sealing 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 adhesive (melting point Tm1 - Tg2) is, for example, 5°C or higher and 100°C or lower.

[0057] The carbon coating M has a unit area weight of 0.2 g / m². 2 The preferred value is 0.3g / m 2 The above, more preferably 0.4 g / m 2 The above. By making the weight per unit area 0.2g / m² 2 The above results in improved adhesion strength due to the carbon coating M being located between the first surface 21a1 of the positive current collector 21a and the sealing portion 24.

[0058] The weight per unit area of ​​the carbon coating M is, for example, 1.2 g / m². 2 The preferred value is 1.0 g / m 2 The following is an example: The weight per unit area of ​​the carbon coating M is 0.2 g / m². 2 Within the above range, the improvement in adhesive strength tends to decrease with increasing unit area weight. At a unit area weight of 1.2 g / m²... 2 The reduction in the aforementioned bond strength enhancement effect can be suppressed under the following conditions. Furthermore, increasing the weight per unit area results in a thicker carbon coating M. When the carbon coating M becomes excessively thick, leakage may occur due to the liquid electrolyte permeating through the carbon coating M. This is possible when the weight per unit area is 1.0 g / m². 2 Under the following conditions, leakage of liquid electrolyte through the carbon coating M to the outside of the energy storage unit 20 can be suppressed.

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

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

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

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

[0063] <Electrode Forming Process> The electrode forming process includes a positive electrode forming process for forming a positive electrode 21 and a negative electrode forming process for forming a negative electrode 22.

[0064] In the positive electrode formation process, firstly, a carbon coating M is formed on the entire first surface 21a1 of the aluminum foil, which serves as the positive electrode current collector 21a. Before forming the carbon coating M, a corona discharge treatment is performed on the first surface 21a1 of the aluminum foil. Through the corona discharge treatment, hydrophilic groups (OH groups) are formed on the first surface 21a1 of the aluminum foil. As a method for forming the carbon coating M, known methods applied to the formation of coatings, such as solution-based processes or vapor deposition processes, can be used.

[0065] The following describes an example of a solution-based process. First, carbon paste is prepared by mixing carbon particles, a coating binder, and an aqueous solvent. A coating film is formed by attaching the carbon paste to the entire first surface 21a1 of the positive electrode current collector 21a at a predetermined thickness. A carbon coating M is formed by drying and curing the formed coating film. For example, the process for curing the carbon paste coating film can be described as follows: after drying to evaporate the solvent, the mixture is heated to a temperature above the glass transition temperature Tg2 of the coating binder, and then cooled to cure. Examples of aqueous solvents used in the carbon paste include water and mixtures of water and organic solvents. Examples of organic solvents used in the mixture include N-methyl-2-pyrrolidone (NMP).

[0066] Furthermore, when forming a bipolar electrode 25 with a bipolar current collector, instead of aluminum foil as the positive current collector 21a, a current collector formed by bonding aluminum foils together, a current collector formed by bonding aluminum foil and copper foil together, or a current collector formed by plating copper on the surface of aluminum foil can be used.

[0067] The following describes an example of a bipolar current collector formed by bonding the positive current collector 21a and the negative current collector 22a together. The bipolar current collector is formed by bonding a positive current collector 21a and a negative current collector 22a together with a conductive adhesive layer. In this case, the positive current collector 21a is, for example, an aluminum foil with a thickness of 20 μm or more and 100 μm or less, and the negative current collector 22a is, for example, a copper foil with a thickness of 5 μm or more and 10 μm or less.

[0068] The conductive adhesive layer comprises an adhesive and conductive particles. There are no particular limitations on the adhesive; any known adhesive used in bonding metals can be used. One example of an adhesive is one comprising a polyolefin resin and an epoxy curing agent. In this case, the adhesive exhibits high electrolyte resistance, thus maintaining good bond strength over a long period. Furthermore, by using an epoxy curing agent in combination with the polyolefin resin, the generation of gas caused by the curing reaction between the polyolefin resin and the curing agent can be significantly reduced during the manufacture of bipolar current collectors.

[0069] Conductive particles are included to impart conductivity to the conductive adhesive layer. The aluminum and copper foils, bonded together by the conductive adhesive layer, are electrically connected by the conductive particles. An example of conductive particles is those having a resin core and a conductive layer 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 can also be an alloy. An example of a conductive layer is that it covers the entire surface of the core.

[0071] The content of 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 bonding strength between the aluminum foil and the copper foil via the conductive adhesive layer can be ensured, and the internal resistance of the bipolar current collector can be further reduced. Furthermore, by making the content of the above-mentioned adhesive content less than 1.0% by volume, that is, by having a high content of adhesive in the conductive adhesive layer, it is possible to form a conductive adhesive layer with flat surfaces on both sides.

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

[0073] The average thickness of the conductive adhesive layer is, for example, greater than 2.0 μm and less than 5.0 μm. The average particle size of the conductive particles is the average of the particle sizes (maximum lengths) along the thickness direction of the conductive adhesive layer. The average particle size and the average thickness of the conductive adhesive layer can be determined, for example, by observing the cross-section of the conductive adhesive layer using electron microscopes such as scanning electron microscopes (SEM) and transmission electron microscopes (TEM).

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

[0075] Next, the positive electrode composite material, which has been cured to become the positive electrode active material layer 21b, is attached to the center of the first surface 21a1 of the aluminum foil with the carbon coating M to a predetermined thickness. Then, a curing process corresponding to the positive electrode composite material is performed to form the positive electrode active material layer 21b. Similarly, after attaching the negative electrode composite material, which has been cured to become the negative electrode active material layer 22b, to the center of the first surface 22a1 of the copper foil serving as the negative electrode current collector 22a to a predetermined thickness, a curing process corresponding to the negative electrode composite material is performed to form the negative electrode active material layer 22b.

[0076] <Energy Storage Unit Formation Process> In the energy storage cell formation process, firstly, the positive electrode 21 and the negative electrode 22 are arranged such that the separator 23 is sandwiched between the positive electrode active material layer 21b and the negative electrode active material layer 22b, and they are opposite each other in the stacking direction. Furthermore, a sealing member, forming a sealing portion 24, is disposed between the positive electrode 21 and the negative electrode 22, and on the outer periphery side of the positive electrode current collector 21a and the negative electrode current collector 22a. As the sealing member, a resin sheet comprising an acid-modified polyolefin resin is cut into a shape identical to the top view shape of the sealing portion 24. At this time, the sealing member is arranged in contact with the carbon coating M in the first surface 21a1 of the positive electrode current collector 21a.

[0077] Subsequently, the positive electrode 21, negative electrode 22, and separator 23 are bonded to the sealing element by welding, thereby forming an assembly in which the positive electrode 21, negative electrode 22, separator 23, and sealing element 24 are integrated. Commonly known welding methods such as thermal welding, ultrasonic welding, and infrared welding can be cited as examples of methods for bonding the sealing element.

[0078] When the sealing part 24 is formed by heat fusion, one example is the process of heating the seal to a temperature above the melting point Tm1 of the acid-modified polyolefin resin constituting the seal and then cooling it to cure it. In this case, if the glass transition temperature Tg2 of the coating adhesive is lower than the melting point Tm1 of the acid-modified polyolefin resin, the coating adhesive will also soften, thus the coating adhesive is readily compatible with the acid-modified polyolefin resin.

[0079] Next, after injecting liquid electrolyte into the sealed space S inside the assembly through an injection port provided in a part of the sealing section 24, the injection port is sealed. Thus, the energy storage unit 20 is formed. <Unit Stack Formation Process> In the cell stacking process, firstly, multiple energy storage cells 20 are stacked such that the second surface 21a2 of the positive current collector 21a faces the second surface 22a2 of the negative current collector 22a. Then, the multiple energy storage cells 20 are integrated by bonding the outer peripheral portions 24a of the sealing portions 24 in adjacent energy storage cells 20 in the stacking direction to each other.

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

[0081] <Function> Next, the function of this embodiment will be explained. In the energy storage device 10 of this embodiment, a carbon coating M is provided on the entire first surface 21a1 of the positive electrode current collector 21a. Furthermore, a sealing part 24 made of acid-modified polyolefin resin is bonded to the carbon coating 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 current collector 21a is bonded to the coating binder contained in the carbon coating M. This bonding is considered to be either ester bonding or hydrogen bonding, or both. Ester bonding is formed when the coating binder contains a resin having carboxyl groups.

[0083] The aforementioned ester bonding is, for example, a bonding structure (-COOMe) formed by the ester bonding of the hydroxyl group (Me-OH) on the first face 21a1 of the positive electrode current collector 21a with the carboxyl group (-COOH) of the coating binder. "Me" signifies the metal constituting the current collector. The aforementioned hydrogen bonding is a bonding structure formed by the hydrogen bonding of the hydroxyl group (Me-OH) on the first face 21a1 of the positive electrode current collector 21a with either or both of the hydroxyl and carboxyl groups of the substance constituting the carbon coating M. The aforementioned hydroxyl group can be either or both of the hydroxyl group (C-OH) on the surface of the carbon particles and the hydroxyl group (C-OH) of the coating binder.

[0084] Furthermore, at the interface between the sealing portion 24 and the carbon coating M, the acid-modified polyolefin resin serving as the sealing portion 24 is bonded to the carbon particles contained in the carbon coating M. This bonding is considered to be either ester bonding or hydrogen bonding, or both. The aforementioned ester bonding is a bond structure (-COOC) formed by the ester bonding of hydroxyl groups (C-OH) on the surface of the carbon particles with carboxyl groups (-COOH) of the acid-modified polyolefin resin. The aforementioned hydrogen bonding is a bond structure formed by the hydrogen bonding of either or both of the hydroxyl and carboxyl groups of the substance constituting the carbon coating M with the carboxyl groups (-COOH) of the acid-modified polyolefin resin. The aforementioned hydroxyl groups are either or both of the hydroxyl groups (C-OH) on the surface of the carbon particles and the hydroxyl groups (C-OH) of the coating adhesive. By forming the aforementioned bonding structures at the interface between the positive electrode current collector 21a and the carbon coating M, and at the interface between the sealing portion 24 and the carbon coating M, the sealing portion 24 is adhered to the first surface 21a1 of the positive electrode current collector 21a via the carbon coating M.

[0085] Thus, according to the configuration of this embodiment, bonding structures are formed at the interface between the first surface 21a1 of the positive current collector 21a and the carbon coating M, and at the interface between the sealing portion 24 and the carbon coating M. Furthermore, the coating adhesive contained in the carbon coating M is compatible with and tightly bonded to the sealing portion 24, resulting in increased bonding strength between the sealing portion 24 and the positive current collector 21a. In detail, since the carbon coating M contains carbon particles, its surface has a slightly rougher texture compared to the first surface 21a1 of the positive current collector 21a. In this case, a bonding structure based on the anchoring effect caused by the resin of the sealing portion 24 penetrating the surface of the carbon coating M is also formed at the interface between the sealing portion 24 and the carbon coating M. As a result, the bonding strength between the sealing portion 24 and the positive current collector 21a is increased.

[0086] The aforementioned improvement in adhesive strength resulting from the carbon coating M being located between the first surface 21a1 of the positive current collector 21a and the sealing portion 24 results in a carbon coating M with a unit area weight of 0.2 g / m². 2 The above conditions were met. The carbon coating M was made to have a unit area weight of 0.2 g / m². 2 The above allows the first surface 21a1 of the positive current collector 21a to be suitably covered by the carbon coating M. In other words, it allows the surface state of the interface between the positive current collector 21a and the sealing portion 24 to change from a state that primarily exhibits properties based on the first surface 21a1 of the positive current collector 21a to a state that primarily exhibits properties based on the carbon coating M. These properties include, for example, surface wettability and smoothness.

[0087] <Effect> According to this embodiment, the following effects can be obtained. (1) The energy storage device 10 includes multiple energy storage units 20. Each energy storage unit 20 includes a positive electrode 21, a negative electrode 22, a separator 23, and a sealing 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 sealing portion 24 is bonded to the first surfaces 21a1 and 22a1 of the positive electrode current collector 21a and the negative electrode current collector 22a, forming a sealed space for containing liquid electrolyte between the positive electrode 21 and the negative electrode 22. The sealing 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 has a carbon coating M disposed on the bonding portion with the sealing portion 24 in the first surface 21a1 of the positive electrode current collector 21a. The carbon coating M comprises carbon particles and a coating binder. The weight per unit area of ​​the carbon coating M is 0.2 g / m². 2 above.

[0088] According to the above configuration, bonding structures are formed at the interface between the first surface 21a1 of the positive current collector 21a and the carbon coating M, and at the interface between the sealing portion 24 and the carbon coating M. Furthermore, the coating adhesive contained in the carbon coating M is compatible with and tightly bonded to the sealing portion 24, resulting in improved bonding strength of the sealing portion 24 relative to the positive current collector 21a.

[0089] (2) The unit area weight of the carbon coating is 1.0 g / m². 2 the following. Based on the above configuration, leakage of liquid electrolyte caused by the permeation of the carbon coating M can be suppressed.

[0090] (3) The coating adhesive contains a resin with carboxyl groups. According to the above configuration, ester bonds are formed at the interface between the first surface 21a1 of the positive current collector 21a and the carbon coating M, and at the interface between the sealing part 24 and the carbon coating M. As a result, the effect of (1) described above can be obtained more significantly.

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

[0092] (5) The energy storage device 10 has multiple energy storage units 20 stacked on top of each other, and has a bipolar electrode 25 formed by joining a positive current collector 21a of the positive electrode 21 of one of the adjacent energy storage units 20 with a negative current collector 22a of the negative electrode 22 of another adjacent energy storage unit 20. The bipolar electrode 25 is formed by joining the surface of the positive current collector 21a located on the opposite side of the first surface 21a1 (the second surface 21a2) with the surface of the negative current collector 22a located on the opposite side of the first surface 22a1 (the second surface 22a2).

[0093] According to the above configuration, in the energy storage device 10 equipped with bipolar electrodes 25, the bonding strength of the sealing portion 24 can be improved. (6) The first surface 22a1 of the negative 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 current collector 21a made of aluminum is more prone to oxidation than the first surface 22a1 of the negative current collector 22a made of copper. Therefore, by providing a carbon coating M on the first surface 21a1 of the positive current collector 21a made of aluminum, oxidation of the first surface 21a1 of the positive current collector 21a due to heat applied during the manufacturing process of the energy storage device 10 can be suppressed. Examples of the heat-applied processes include heating when bonding the positive current collector 21a and the negative current collector 22a, and heating when curing the positive active material layer 21b.

[0095] (7) The positive current collector 21a of the bipolar electrode 25 is aluminum foil, and the negative current collector 22a is copper foil. The bipolar electrode 25 is formed by bonding the positive current collector 21a and the negative current collector 22a 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 on the surface of the core. The content of conductive particles in the conductive adhesive layer is more than 0.1% by volume and less than 1.0% by volume.

[0096] By increasing the amount of adhesive in the conductive adhesive layer and using conductive particles with resin cores, a conductive adhesive layer with flat surfaces on both sides can be formed. This improves the smoothness of the surface of the aluminum foil arranged along the conductive adhesive layer. In this case, it becomes easier to uniformly form a carbon coating M on the surface of the aluminum foil serving as the positive current collector 21a. Since the carbon coating M can be uniformly formed, the aforementioned effect (1) based on the carbon coating M can be obtained more reliably.

[0097] Furthermore, this embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other within the scope of technical non-inconsistency. In the first surface 21a1 of the positive current collector 21a, the carbon coating M only needs to be provided on at least a portion of the part that is bonded to the sealing portion 24. For example, in the portion of the first surface 21a1 of the positive current collector 21a bonded to the sealing portion 24, there may be portions where the carbon coating M is not provided. However, it is preferable that the carbon coating M is formed in a ring shape surrounding the sealed space S in the portion of the first surface 21a1 of the positive current collector 21a bonded to the sealing portion 24 when viewed from above. In addition, in the portion of the first surface 21a1 of the positive current collector 21a that is not bonded to the sealing portion 24, there may be portions where the carbon coating M is not provided, either partially or entirely.

[0098] Alternatively, the carbon coating M can be provided on the first surface 22a1 of the negative current collector 22a instead of the first surface 21a1 of the positive current collector 21a. Alternatively, the carbon coating M can be provided on both the first surface 21a1 of the positive current collector 21a and the first surface 22a1 of the negative current collector 22a. In these cases, the adhesion strength of the sealing portion 24 relative to the first surface 22a1 of the negative current collector 22a is improved.

[0099] The top-view shape of the positive current collector 21a and the positive active material layer 21b is not particularly limited. It can be rectangular or polygonal, or circular or elliptical. The same applies to the negative current collector 22a and the negative active material layer 22b.

[0100] The top view shape of the sealing part 24 is not particularly limited; it can be a rectangle or other polygonal shape, or it can be a circle or an ellipse. To ensure good conductive contact between the positive electrode current-carrying plate 40 and the positive electrode current collector 21a, a conductive layer in close contact with the positive electrode current collector 21a can be disposed between the two components. Examples of conductive layers include carbon-containing layers such as acetylene black or graphite, and plating layers containing Au, which have a lower hardness than the positive electrode current collector 21a. Alternatively, the same conductive layer can be disposed between the negative electrode current-carrying plate 50 and the negative electrode current collector 22a.

[0101] The number of energy storage units 20 constituting the energy storage device 10 is not particularly limited. The number of energy storage units 20 constituting the energy storage device 10 may also be one. Alternatively, a positive electrode active material layer 21b or a negative electrode active material layer 22b may be provided on the second surface 21a2 of the positive electrode current collector 21a. Alternatively, a positive electrode active material layer 21b or a 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 also be an energy storage device having a constraint member of the constraint unit stack 30. The constraint member applies a constraint load to the area where the energy storage units 20 are opposite to each other in the stacking direction of the unit stack 30, especially in the area where the positive electrode active material layer 21b is provided and the area where the negative electrode active material layer 22b is provided when viewed from above.

[0103] The specific configuration of the constraint member is not particularly limited, as long as it can impart a constraint load to the unit stack 30. Examples of constraint members include a plate-shaped constraint plate disposed at both ends of the unit stack 30 in the stacking direction, clamping the unit stack 30, and a fastening member including bolts and nuts to fasten the constraint plate to each other. In the case of the constraint member configured as described above, a constraint load in the stacking direction is imparted to the unit stack 30 by applying force from the fastening member in the direction in which the constraint plates approach each other. Example

[0104] The following describes embodiments that further specify the above-described implementation methods. (Experimental Examples 1-5) An aluminum foil with a thickness of 30 μm was prepared, and one side of its surface was subjected to corona discharge treatment to hydrophilize that side. A coating was formed by adhering carbon paste to the entire hydrophilized surface of the aluminum foil. The formed coating was then dried. Subsequently, it was heated at 150°C for 10 seconds and then cooled to form a carbon coating. The resulting sheets were designated as Test Examples 1 to 5.

[0105] The carbon paste used was a mixture of carbon particles, a coating binder, carboxyethyl cellulose (CMC), and water. Acetylene black was used as the carbon particles. An acrylic resin was used as the coating binder. The mass ratio of the solid components in the carbon paste was set to 50:37.5:12.5 (carbon particles: coating binder: CMC). The solvent content in the carbon paste was set to an amount that made the solid component ratio 85% by mass. The unit area weight of the carbon coatings in Test Examples 1-5 were different. The unit area weight of the carbon coatings on the sheets of Test Examples 1-5 is shown in Table 1.

[0106] (Determination of contact angle) A 4 μL drop of water was dropped onto the carbon coating surface of the sheet in Test Example 4 using a dropper, and the contact angle of the water droplet formed on the surface of the carbon coating was measured. The contact angle of water relative to the surface of the carbon coating was 27.4°. From this result, it can be inferred that there are carboxyl groups on the surface of the carbon coating that can reduce the contact angle of water to less than 40°, and further to less than 30°.

[0107] (Determination of adhesive strength) Rectangular sheets measuring 10 mm in length and 50 mm in width were cut from the sheets used in Examples 1-5. Seals also measuring 10 mm in length and 50 mm in width were prepared. An acid-modified polyethylene sheet with a thickness of 120 μm and a melting point of 120 °C was used as the seal. A laminate was obtained by stacking the seals on the sheets with the ends aligned. A test sample was prepared by heating the laminate at 150 °C for 10 seconds using a pulse sealing machine and then cooling it.

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

[0109] For the test samples after impregnation treatment, a 180-degree peel test was conducted at a tensile speed of 10 mm / min and a temperature of 25°C. The peel strength of the test sample was calculated by dividing the strength determined by the 180-degree peel test by 10 mm, which is the line width, and this calculated value was taken as the adhesive strength. The results are shown in Table 1. Furthermore, the impregnation treatment conditions were adjusted to conditions that were easier to peel than actually, so that the adhesive strength of Test Example 1 was 0 N / mm in the 180-degree peel test.

[0110] [Table 1]

[0111] As shown in Table 1, the weight per unit area of ​​the carbon coating is 0.1 g / m². 2 In the case of Test Example 2 below, compared with Test Example 1, no increase in bond strength due to the application of the carbon coating was observed. The carbon coating had a unit area weight of 0.2 g / m². 2 In the cases of Test Examples 3-5 above, the bond strength was significantly increased compared to Test Example 1. Furthermore, the weight per unit area of ​​the carbon coating was 0.2 g / m². 2 Within the above range, the bond strength tends to gradually decrease with increasing weight per unit area. This ranges from 0.22 to 1.05 g / m². 2 Looking at the decreasing trend of adhesive strength with increasing unit area weight of carbon coatings within the range of (Examples 3-5), if the unit area weight is set to 1.0 g / m²... 2 The following can be calculated from the maximum unit area weight of 0.22 g / m². 2 Under these conditions, the decrease in bond strength is suppressed to less than 25%. Explanation of reference numerals in the attached figures

[0112] M…carbon coating S…enclosed space 10…Electric Storage Devices 20… Energy Storage Unit 21… Positive electrode 21a…Positive current collector 21b… Positive electrode active material layer 22… Negative electrode 22a… Negative current collector 22b…Negative electrode active material layer 23…isolation materials 24…Sealing part 25…bipolar electrode 30… Unit stack.

Claims

1. An energy storage device comprising an energy storage unit, the energy storage unit comprising: The positive electrode is formed by depositing a layer of positive electrode active material on the first surface of the positive electrode current collector; The negative electrode is formed by providing a negative electrode active material layer on the first surface of the negative electrode current collector, and the negative electrode active material layer is arranged opposite to 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 sealing portion is disposed between the positive electrode and the negative electrode in a manner that surrounds the positive electrode active material layer and the negative electrode active material layer, and forms a sealed space for containing liquid electrolyte between the positive electrode and the negative electrode by being adhered to the first surface of each of the positive electrode current collector and the negative electrode current collector. The energy storage device is characterized in that... The sealing part is made of acid-modified polyolefin resin. The first surface of the positive current collector is made of aluminum. The positive electrode has a carbon coating disposed on the first surface of the positive electrode current collector at the bonding portion with the sealing portion. The carbon coating comprises carbon particles and a coating binder. The carbon coating has a unit area weight of 0.2 g / m². 2 above.

2. The energy storage device according to claim 1, wherein, The carbon coating has a unit area weight of 1.0 g / m². 2 the following.

3. The energy storage device according to claim 1 or 2, wherein, The coating adhesive comprises a resin having carboxyl groups.

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

5. The energy storage device according to any one of claims 1 to 4, wherein, Multiple energy storage units are stacked together. The device is equipped with a bipolar electrode, wherein the bipolar electrode is formed by joining the face of the positive current collector of the positive electrode of one of the adjacent energy storage units, located on the opposite side of the first surface, to the face of the negative current collector of the negative electrode of the other adjacent energy storage unit, located on the opposite side of the first surface.

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

7. The energy storage device according to claim 5 or 6, wherein, The positive current collector of the bipolar electrode is aluminum foil. The negative current collector of the bipolar electrode is a copper foil. The bipolar electrode is formed by bonding the positive current collector and the negative current collector together with a conductive adhesive layer. The conductive adhesive layer comprises an adhesive and conductive particles. The conductive particles have a resin core and a conductive layer on the surface of the core. The content of the conductive particles in the conductive adhesive layer is more than 0.1% by volume and less than 1.0% by volume.

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

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