Current collector, electrode structure, power storage device, and method for manufacturing current collector

Abstract

To further improve safety in a bipolar power storage device when an internal short circuit occurs.SOLUTION: A current collector according to the present disclosure is a current collector used in a bipolar power storage device, and includes an insulating portion formed in a grid pattern and a conductive portion arranged on the grid of the insulating portion and having a size larger than the grid. The current collector has a structure that prevents electrolyte from passing through in the thickness direction, and the gap between adjacent conductive portions is smaller than the width of the grid.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This specification discloses a current collector, an electrode structure, an electricity storage device, and a method for manufacturing the current collector. [Background technology]

[0002] Conventionally, a proposed electricity storage device is one in which a laminated conductive sheet is obtained by preparing a support substrate, forming a conductive layer on the front side of the support substrate, and transferring the conductive layer to the front and back sides of a resin-containing sheet, and the resulting sheet is used as a current collector for a bipolar battery used as a lithium ion secondary battery (see, for example, Patent Document 1). This electricity storage device is said to reduce manufacturing costs. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-254727 Summary of the Invention [Problem to be solved by the invention]

[0004] However, although Patent Document 1 realizes a bipolar lithium-ion secondary battery using a current collector in which conductive layers are formed on both sides of a resin-containing sheet, it does not consider safety in the event of an internal short circuit. Thus, there has been a demand for a current collection structure that can deal with internal short circuits in bipolar electricity storage devices.

[0005] The present disclosure has been made to solve such problems, and its main object is to provide a current collector, an electrode structure, a current storage device, and a method for manufacturing a current collector that can further improve safety in the event of an internal short circuit in a bipolar type power storage device. [Means for solving the problem]

[0006] In order to achieve the above-mentioned object, the inventors conducted extensive research and discovered that arranging a conductive portion larger than the grid on a grid-shaped insulating portion can further improve safety in the event of an internal short circuit in a bipolar energy storage device, and have thus completed the invention disclosed in this specification.

[0007] That is, the current collector disclosed in the present specification is A current collector used in a bipolar electricity storage device, an insulating portion formed in a grid pattern; a conductive portion disposed on the grid of the insulating portion and having a size larger than the grid, The current collector has a structure that prevents the electrolyte from passing through in the thickness direction, and the gap between adjacent conductive portions is smaller than the width of the grid.

[0008] The electrode structure disclosed herein comprises: The current collector described above; a positive electrode mixture layer formed on a surface of the current collector on which the conductive portion is disposed on the insulating portion; and a negative electrode mixture layer formed on the other surface of the current collector.

[0009] The electricity storage device disclosed in this specification comprises: The electrode structure is formed by stacking the above-mentioned electrode structures.

[0010] The method for producing a current collector disclosed in the present specification includes the steps of: A method for manufacturing a current collector used in a bipolar electricity storage device, comprising: A conductive portion having a size larger than the grid is disposed on the grid of an insulating portion formed in a grid shape, a fixing step of fixing the conductive portion to the insulating portion by either gluing the conductive portion to an edge of an opening of the lattice of the insulating portion or by thermocompression bonding the conductive portion to the edge of an opening of the lattice of the insulating portion; It includes: [Effects of the Invention]

[0011] The present disclosure can further improve safety in bipolar energy storage devices in the event of an internal short circuit. The reason for this effect is presumed to be as follows. For example, in bipolar energy storage devices, when an internal short circuit occurs, current flows in a planar direction within the current collector from the entire short-circuited electrode toward the local short circuit, which can cause current concentration and heat generation at the short-circuited area. On the other hand, in the current collector of the present disclosure, the conductive portion is disposed on the lattice of the insulating portion, which can further suppress current concentration in a planar direction in the event of an internal short circuit, thereby suppressing heat generation and further improving safety. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram showing an example of an electricity storage device 10. FIG. [Figure 2] FIG. 2 is a schematic diagram showing an example of a current collector 20. [Figure 3] FIG. 3 is a schematic diagram showing an example of a current collector 20B. [Figure 4] 1 is a schematic diagram showing an example of a cross section of an electricity storage device 10. FIG. [Figure 5] FIG. 3 is an explanatory diagram showing a current flow in the electricity storage device 10 when an internal short circuit occurs. [Figure 6] FIG. 4 is an explanatory diagram showing the flow of current in the current collector 20 when an internal short circuit occurs. [Figure 7] An electrical circuit diagram that simulates an internal short circuit in a bipolar battery. [Figure 8] The results of examining the relationship between the conductive and insulating parts of the current collector using calculation model 1. [Figure 9] The results of examining the relationship between the conductive and insulating parts of the current collector using calculation model 2. [Figure 10] The results of examining the relationship between the conductive and insulating parts of the current collector using calculation model 3. DETAILED DESCRIPTION OF THE INVENTION

[0013] The current collector, electrode structure, electricity storage device, and method for manufacturing a current collector described in the embodiments of the present disclosure relate to a bipolar electricity storage device. This electricity storage device may be, for example, an electric double layer capacitor, a hybrid capacitor, a pseudo-electric double layer capacitor, an alkali metal secondary battery, or an alkali metal ion battery. Examples of carrier ions in the electricity storage device include Group 1 (alkali metal) ions such as lithium ions, sodium ions, and potassium ions, and Group 2 ions such as magnesium ions, strontium ions, and calcium ions. The electricity storage device may also be, for example, an all-solid-state secondary battery using a solid electrolyte. For ease of explanation, the following description will be given mainly as an example of a lithium ion secondary battery in which the electricity storage device uses lithium ions as a carrier.

[0014] (current collector) The current collector of the present disclosure described in the embodiments is a sheet-like current collector used in an electricity storage device, specifically a current collector used in a bipolar electricity storage device. This current collector has an insulating portion formed in a grid pattern and a conductive portion disposed on the grid of the insulating portion and larger in size than the grid. This current collector has a structure that prevents electrolyte from passing through in the thickness direction, and the gap between adjacent conductive portions is smaller than the width of the grid. That is, the conductive portion may be sized to overlap the opening edge of the grid of the insulating portion. In this current collector, it is preferable that the gap between adjacent conductive portions is 2 mm or less and the width of the grid of the insulating portion is 5 mm or less.

[0015] In the current collector, the area S per conductive portion is not particularly limited, but is, for example, 50 mm 2 It may be more than 100mm 2 It may be more than 200mm 2 The area SL may be, for example, 10,000 mm 2 It may be less than 5000mm 2 It may be less than 1000mm 2The current collector may have 20 or more conductive portions. The number of conductive portions may be 50 or more, or more than 100. The number of conductive portions may be 1000 or less, 500 or less, or 200 or less. The conductive portions may be arranged in a single row, or in multiple rows. In the current collector, the conductive portions may all have the same shape, or some or all of them may have different shapes.

[0016] In the current collector, the length of one side of the conductive portion is preferably as small as possible from the viewpoint of further enhancing safety, for example, preferably 50 mm or less, preferably 40 mm or less, and more preferably 30 mm or less. The length of one side of the conductive portion may be, for example, 5 mm or more, 10 mm or more, or 20 mm or more. With regard to the length of one side of the conductive portion, the length in the vertical direction and the length in the horizontal direction may be the same or different.

[0017] In the current collector, the material of the conductive portion is not particularly limited, but is preferably, for example, a metal such as Cu, Ni, stainless steel, Ti, or Al, and among these, a metal foil of one or more of Al, Cu, and stainless steel is preferred. The material of the conductive portion may also be carbon, baked carbon, a conductive polymer, conductive glass, an Al-Cd alloy, or the like. Examples of conductive polymers include polymer materials such as polythiophene, polyacetylene, polyaniline, and polypyrrole. The conductive portion may also be a solidified resin in which metal particles or carbon particles are dispersed as a conductive material. Examples of the metal conductive material include noble metals such as silver.

[0018] The conductive portion may be fixed to the insulating portion by adhesion to the edge of the opening of the lattice of the insulating portion and / or by thermocompression bonding to the edge of the opening of the lattice. When the conductive portion is fixed by adhesion, the adhesive may be a liquid adhesive, such as a latex adhesive, an emulsion adhesive, a solvent adhesive, or a reactive adhesive. Examples of such adhesives include acrylic resin adhesives, epoxy adhesives, and styrene-butadiene rubber adhesives. When the conductive portion is fixed by thermocompression bonding, the lattice of the insulating portion may be formed from a thermoplastic resin, or a thermoplastic resin may be disposed on the insulating portion and then thermocompression bonded.

[0019] The insulating portion is formed in a lattice shape. The lattice is not particularly limited as long as it has polygonal openings, but examples include rectangular, hexagonal, and triangular shapes, with rectangular shapes being preferred as they are easier to handle. The insulating portion is not particularly limited as long as it has high insulating properties, but may be made of a resin material, for example. Examples of resin materials include one or more of polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polyimide (PI). The material of the insulating portion is not particularly limited, but may be, for example, a metal oxide such as anodized aluminum, a metal nitride, or a metal boride.

[0020] In the current collector, the width of the grid of the insulating portion is preferably as small as possible to further suppress deterioration of battery performance due to the introduction of the insulating portion, for example, preferably 5 mm or less, more preferably 3 mm or less, and even more preferably 2.5 mm or less. The width of the grid of the insulating portion may be, for example, 0.1 mm or more, 0.5 mm or more, or 1 mm or more. The vertical width and horizontal width of the grid of the insulating portion may be the same or different.

[0021] In the current collector, the resistance between adjacent conductive portions is preferably 0.5 Ω or more, and may be 1 Ω or more, or 5 Ω or more. When this resistance is 0.5 Ω or more, safety in the event of an internal short circuit can be further improved. Note that, if the resistance between adjacent conductive portions is 0.5 Ω or more, the conductive portions may be electrically connected to each other.

[0022] The thickness of the current collector is not particularly limited, but from the viewpoint of improving the energy density of the electricity storage device, a thinner thickness is preferable, for example, 100 μm or less is preferable, 50 μm or less is more preferable, and 30 μm or less is even more preferable. From the viewpoint of ensuring impermeability to the ion conductive medium, the thickness of the current collector may be, for example, 5 μm or more, 10 μm or more, or 20 μm or more.

[0023] (Manufacturing method of current collector) This current collector manufacturing method may be a method for manufacturing a current collector used in a bipolar energy storage device, and may be a method for manufacturing the current collector described above. This manufacturing method includes a fixing step of placing a conductive portion larger than the lattice of an insulating portion formed in a lattice pattern on the lattice of the insulating portion, and fixing the conductive portion to the insulating portion by either gluing the conductive portion to the opening edge of the lattice of the insulating portion or by thermocompression bonding the conductive portion to the opening edge of the lattice of the insulating portion. When bonding the conductive portion in this step, a liquid adhesive may be used, such as a latex adhesive, an emulsion adhesive, a solvent adhesive, or a reactive adhesive. Examples of such adhesives include an acrylic resin adhesive, an epoxy adhesive, and a styrene-butadiene rubber adhesive. Furthermore, when fixing the conductive portion by thermocompression bonding, the lattice of the insulating portion may be formed from a thermoplastic resin, or a thermoplastic resin may be placed on the insulating portion and then thermocompression bonded.

[0024] (Electricity storage device) The electricity storage device of the present disclosure is formed by stacking electrode structures including the above-described current collector, a positive electrode composite layer formed on the surface of the current collector on which the conductive portion is disposed in the insulating portion, and a negative electrode composite layer formed on the other surface of the current collector. The electricity storage device is a so-called bipolar secondary battery. The electrode structure includes the above-described current collector, a positive electrode composite layer formed on the surface of the current collector on which the conductive portion is disposed in the insulating portion, and a negative electrode composite layer formed on the other surface of the current collector.

[0025] The electricity storage device disclosed in this embodiment will be described with reference to the drawings. FIG. 1 is a schematic diagram showing an example of an electricity storage device 10. FIG. 2 is a schematic cross-sectional view showing an example of a current collector 20. FIG. 3 is a schematic cross-sectional view showing an example of another current collector 20B. FIG. 4 is a cross-sectional view showing an example of an electricity storage device 10, and is an explanatory diagram showing the flow of current in the electricity storage device 10 during normal charging and discharging. FIG. 5 is an explanatory diagram showing the flow of current in the electricity storage device 10 when an internal short circuit occurs.

[0026] The electricity storage device 10 includes a stack 40 in which unit cells 30 are stacked in multiple stages, and a pair of external current collectors 50. The unit cells 30 include a current collector 20, a positive electrode composite layer 32, a negative electrode composite layer 34, and an ion conductive medium 36 interposed between the positive electrode composite layer 32 and the negative electrode composite layer 34. Here, the ion conductive medium 36 is impregnated into a separator 38 interposed between the positive electrode composite layer 32 and the negative electrode composite layer 34. The current collector 20 is the current collector described above, and includes insulating portions 22 formed in a lattice pattern and conductive portions 21 formed within each lattice of the insulating portion 22. The stack 40 is stacked in multiple stages so that the unit cells 30 are connected in series via the current collector 20 serving as an internal current collector, i.e., so that the positive electrode composite layers 32 and the negative electrode composite layers 34 alternate. This laminate 40 has a structure in which electrode structures 15 are stacked, each of which has a positive electrode composite layer 32 on one surface of a current collector 20 and a negative electrode composite layer 34 on the other surface. The laminate 40 and external current collector 50 are housed in an exterior case 60.

[0027] The current collector 20 includes a conductive portion 21 and an insulating portion 22. The insulating portion 22 is formed in a lattice pattern. As shown in FIG. 2, the conductive portion 21 is disposed on the lattice of the insulating portion 22 and has a length W1 that is larger than the length L2 of the opening of the lattice. The current collector 20 has a structure that prevents the electrolyte from passing through in the thickness direction, and the length L1 of the gap between adjacent conductive portions 21 is smaller than the width W2 of the lattice. The length W1 of the conductive portion 21 is larger than the lengths L1 and L2. The length W1 of the conductive portion 21 is preferably 10 cm or less, for example, and may be 5 cm or less. The length W1 may be 1 cm or more. Note that the length W1 refers to the length of one side if the conductive portion 21 is polygonal, and refers to the diameter or major axis if the conductive portion 21 is circular or elliptical. The width W2 of the lattice of the insulating portion 22 is preferably 5 mm or less, for example, and may be 4 mm or less. The length W2 may be 1 mm or more. The length L1, which is the distance between the conductive portions 21, is preferably 2 mm or less, more preferably 1 mm or less. This length L1 is preferably 0.1 mm or more to facilitate the arrangement of the conductive portions 21. The length L2 of the lattice is preferably 9.8 cm or less, more preferably 4.8 cm or less. This length L2 is preferably 0.8 cm or more in consideration of the contact area with the negative electrode. Note that the length L2 is the length of one side if the lattice is polygonal, and the diameter or major axis if the lattice is circular or elliptical. The thickness t1 of the conductive portion 21 may be the same as or different from the thickness T2 of the insulating portion 22. The thickness t1 of the conductive portion 21 may be in the range of 5 μm to 100 μm, or in the range of 10 μm to 50 μm. The thickness t2 of the insulating portion 22 may be in the range of 5 μm to 100 μm, or in the range of 10 μm to 50 μm.

[0028] As shown in FIG. 3, the current collector 20B has a structure in which a conductive portion 24 is disposed within the lattice of the insulating portion 22. The length W3 of the conductive portion 24 may be the same as the length L2 of the opening of the lattice. The thickness t3 of the conductive portion 24 may be the same as or different from the thickness t2 of the insulating portion 22. When the potential of the negative electrode is higher than 0.75 V relative to the lithium potential, aluminum foil can be used for the conductive portion 21. However, when the potential of the negative electrode is lower than 0.75 V, a Cu layer or a conductive portion 24 made of stainless steel current collecting foil may be formed on the back side of the conductive portion 21. The thickness of the Cu layer or stainless steel current collecting foil can be, for example, in the range of 5 μm to 25 μm. The Cu layer may be formed by electrolytic plating.

[0029] The positive electrode mixture layer 32 contains a positive electrode active material. The positive electrode mixture layer 32 is preferably disposed on the surface of the current collector 20 on which the conductive portion 21 is disposed on the insulating portion 22. Because the positive electrode mixture layer 32 has lower conductivity than the negative electrode mixture layer 34, it is preferably formed on the surface of the current collector 20 that has a large contact area with the conductive portion 21. The positive electrode mixture layer 32 may be formed, for example, by mixing a positive electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like positive electrode mixture, applying the paste to the mixture layer formation region 23 on one side of the current collector 20, drying the mixture, and compressing it as necessary to increase electrode density. Examples of the positive electrode active material that can be used include sulfides containing transition metal elements and oxides containing lithium and transition metal elements. Examples of the former include transition metal sulfides such as TiS2, TiS3, MoS3, and FeS2. Examples of the latter include lithium-manganese composite oxide, lithium-cobalt composite oxide, lithium-nickel composite oxide, lithium-nickel-cobalt-manganese composite oxide, lithium-vanadium composite oxide, and lithium-iron phosphate compounds. Examples of conductive materials include graphite, such as natural graphite (scale graphite and flake graphite) and artificial graphite, acetylene black, carbon black, Ketjen black, carbon whiskers, needle coke, carbon fiber, and metals (copper, nickel, aluminum, silver, gold, etc.), either singly or in combination. Examples of binders include fluorine-containing resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and fluororubber; thermoplastic resins such as polypropylene and polyethylene; ethylene propylene diene monomer (EPDM) rubber; sulfonated EPDM rubber; and natural butyl rubber (NBR), either singly or in combination. Examples of the solvent that can be used include organic solvents such as N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethylenetriamine, N,N-dimethylaminopropylamine, ethylene oxide, and tetrahydrofuran.

[0030] The negative electrode mixture layer 34 includes a negative electrode active material. The negative electrode mixture layer 34 is preferably disposed on the surface of the current collector 20 on which the insulating portion 22 does not include the conductive portion 21. The negative electrode mixture layer 34 may be formed, for example, by mixing a negative electrode active material, a conductive material, and a binder, adding an appropriate solvent to form a paste-like negative electrode mixture, applying the paste to the mixture layer formation region 23 on the other surface of the current collector 20, drying the mixture, and compressing it as needed to increase electrode density. The negative electrode mixture layer 34 may also be formed by adhering the negative electrode active material to the mixture layer formation region 23 on the other surface of the current collector 20. The negative electrode active material is preferably one that can be used as a current collector using aluminum, and for example, the charge / discharge potential is preferably 0.75 V or higher, preferably 0.8 V or higher, 1.0 V or higher, or 1.2 V or higher relative to lithium. Examples of negative electrode active materials include composite oxides containing multiple elements, composite materials, and conductive polymers capable of absorbing and releasing lithium ions. Examples of composite oxides include lithium titanium composite oxide and lithium vanadium composite oxide. Examples of composite materials include layered structures having an organic framework layer containing an aromatic compound that is a dicarboxylate anion having two or more aromatic ring structures, and an alkali metal element layer in which an alkali metal element is coordinated to oxygen contained in the carboxylate anion to form a framework. Examples of layered structures include dilithium naphthalenedicarboxylate and dilithium biphenyldicarboxylate. The same conductive materials, binders, and solvents as those used in the positive electrode composite layer 32 can be used.

[0031] The ion-conducting medium 36 may be a non-aqueous electrolyte solution containing a supporting salt, a non-aqueous gel electrolyte solution, or an aqueous electrolyte solution. Examples of solvents for non-aqueous electrolyte solutions include carbonates, esters, ethers, nitriles, furans, sulfolanes, and dioxolanes, which may be used alone or in combination. Specific examples of carbonates include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, vinylene carbonate, butylene carbonate, and chloroethylene carbonate; chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate, ethyl-n-butyl carbonate, methyl-t-butyl carbonate, di-i-propyl carbonate, and t-butyl-i-propyl carbonate; and γ-butyl carbonate. Examples of supporting salts include cyclic esters such as lactone and γ-valerolactone, chain esters such as methyl formate, methyl acetate, ethyl acetate, and methyl butyrate, ethers such as dimethoxyethane, ethoxymethoxyethane, and diethoxyethane, nitriles such as acetonitrile and benzonitrile, furans such as tetrahydrofuran and methyltetrahydrofuran, sulfolanes such as sulfolane and tetramethylsulfolane, and dioxolanes such as 1,3-dioxolane and methyldioxolane. Examples of supporting salts include LiPF, LiBF, LiAsF, LiCF, LiN(CF,SO), LiC(CF,SO), LiSbF, LiSiF, LiAlF, LiSCN, LiClO, LiCl, LiF, LiBr, LiI, and LiAlCl. The concentration of this supporting salt in the electrolyte is preferably 0.1 mol / L to 5 mol / L, and more preferably 0.5 mol / L to 2 mol / L.

[0032] The separator 38 insulates the positive electrode composite layer 32 from the negative electrode composite layer 34 without impeding ion conduction of carrier ions. In other words, the separator 38 is configured to allow carrier ions to pass through but not electrons. The separator 38 may be made of any material having a composition that can withstand the range of use of the power storage device 10. Examples of the separator 38 include polymer nonwoven fabrics such as polypropylene nonwoven fabrics and polyphenylene sulfide nonwoven fabrics, and thin microporous membranes made of olefin resins such as polyethylene and polypropylene. These may be used alone or in combination. The thickness of the separator 38 is preferably 5 μm or more, more preferably 8 μm or more, and may be 10 μm or more. A thickness of 5 μm or more is preferable for ensuring insulation. The thickness of the separator 38 is preferably 15 μm or less, and more preferably 10 μm or less. A thickness of 15 μm or less is preferable in that a decrease in ion conductivity can be suppressed and the volume occupied by the cell can be further reduced.

[0033] A pair of external current collectors 50 are provided so as to contact the outer electrode layers of each of the two unit cells 30 located at both ends of the stack 40. The external current collectors 50 may have a structure similar to that of the current collector 20 to further enhance safety in the event of an internal short circuit. Alternatively, the external current collector 50 may have a structure different from that of the current collector 20, such as being composed of a continuous conductor, to facilitate normal charging and discharging. In this case, the external current collector 50 may be made of, for example, copper, nickel, stainless steel, titanium, aluminum, baked carbon, conductive polymers, conductive glass, Al-Cd alloys, or copper whose surface has been treated with carbon, nickel, titanium, silver, or the like to improve adhesion, conductivity, and reduction resistance. The external current collector 50 may be made of the same material as or a different material from the conductive portion 21 of the current collector 20. The external current collector 50 may be in the form of a sheet, a net, a punched or expanded material, a lath, a porous material, a foam, a fiber group, or the like. The thickness of the external current collector 50 is preferably the same as or thicker than the thickness T of the conductive portion 21 of the current collector 20. The thickness of the external current collector 50 may be, for example, 500 μm or less. One and the other external current collectors 50 may be made of the same material and shape, or may be different in at least one of the material and shape.

[0034] The exterior case 60 houses the laminate 40 and the external current collectors 50 and has openings that expose portions of each external current collector 50. The exterior case 60 is formed, for example, in a cylindrical shape. The material of the exterior case 60 may be, for example, a laminate film, or may be, for example, a polymer-metal composite film in which a heat-sealable resin film, a metal foil, and a rigid resin film are laminated in this order from the inside to the outside. Examples of the heat-sealable resin film include polyethylene, ionomer, and ethylene vinyl acetate. Examples of the metal foil include aluminum foil and nickel foil. Examples of the rigid resin include polyethylene terephthalate and nylon. The current collector 20 may be fixed to the exterior case 60 by, for example, heat-sealing the heat-sealable resin film.

[0035] In this electricity storage device 10, during normal charging and discharging, current flows in the thickness direction of the current collector 20 as shown in FIG. 4 (see the outline arrow). When an internal short circuit occurs in a bipolar battery, current flows in a planar direction within the current collector foil from the entire short-circuited electrode toward the local short circuit, causing the current to concentrate at the short-circuited area and generate heat. The degree of heat generation varies depending on the short-circuit resistance, but in some cases the temperature rises and there is a risk of fire. When a conventional current collector foil 120 is used instead of the current collector 20, current flows from the entire surface of the current collector foil 120 to the short-circuited area (indicated by a star) when an internal short circuit occurs, as shown in FIG. 6A. On the other hand, the electricity storage device 10 of the present disclosure has a current collector 20, which includes insulating portions 22 formed in a lattice pattern and conductive portions 21 formed within each lattice of the insulating portions 22. In this current collector 20, if an internal short circuit occurs in the electricity storage device 10, as shown in FIG. 6B, current flows from the conductive portions 21 in the lattice that include the shorted area toward the shorted area. However, the current is significantly suppressed from the other conductive portions 21 by the insulating portions 22, thereby suppressing the temperature rise and reducing the risk of fire (see the dotted arrows in FIG. 5). In the example of FIG. 6B, the electrodes are divided into 36 sections by the lattice. Therefore, even if an internal short circuit occurs, only energy equivalent to 1 / 36 of the capacity is supplied to the shorted area, thereby further suppressing the temperature rise in the shorted area. Because the charge / discharge current of a bipolar electricity storage device flows in the stacked electrode direction (FIG. 4), the current flow within the current collector is in the thickness direction. Therefore, even if a lattice-shaped insulating portion is introduced into the current collector and the resistance of that portion increases, the current does not flow in-plane through the conductive portions but only in the thickness direction, so charging and discharging are hardly hindered. Therefore, the electricity storage device 10 and current collector 20 can further suppress deterioration of charge / discharge function while further improving safety in the event of an internal short circuit.

[0036] In this electricity storage device 10, from the viewpoint of suppressing a decrease in battery performance due to the introduction of an insulating portion, the IV resistance during normal charging and discharging is preferably 110% or less, and more preferably 105% or less, when the IV resistance when a continuous foil is used as the current collector is normalized to 100%. This IV resistance may be greater than 100% or may be 102% or more. Furthermore, in this electricity storage device 10, from the viewpoint of enhancing safety in the event of an internal short circuit, the resistance of the short-circuit portion is preferably 0.5 Ω or more, preferably 0.8 Ω or more, and more preferably 1 Ω or more. The resistance of the short-circuit portion may be, for example, 1.95 Ω or less, or 1.9 Ω or less.

[0037] The current collector 20 and the electricity storage device 10 described above can further improve safety in the event of an internal short circuit in a bipolar electricity storage device. The reason for this effect is presumed to be as follows. For example, in a bipolar electricity storage device 10, when an internal short circuit occurs, current flows in a planar direction within the current collector from the entire short-circuited electrode toward the local short circuit, which can cause current concentration and heat generation at the short-circuited area. On the other hand, in the current collector 20 of the present disclosure, the insulating portions 22 are present between regions of the conductive portions 21, which can further suppress current concentration in a planar direction during an internal short circuit, thereby suppressing heat generation and further improving safety. Furthermore, the current collector 20 has conductive portions 21 that are arranged on the lattice of the insulating portions 22, which are formed in a lattice pattern, and are larger than the lattice. In this current collector 20, the conductive portions 21 are larger than the lattice, making it easier to fix the conductive portions 21 on the lattice. Furthermore, the current collector 20 has a structure that prevents the electrolyte from passing through in the thickness direction, and the length L1 of the gap between adjacent conductive portions 21 is smaller than the width W2 of the grid, making it easy to fix the conductive portions 21 on the grid.

[0038] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure.

[0039] For example, in the above embodiment, the insulating portion 22 is formed in a rectangular grid shape, and the conductive portion 21 has a rectangular region, but it may be formed in a polygonal shape such as a circle, an ellipse, a hexagon, or an octagon.

[0040] In the above-described embodiment, the positive electrode active material is a positive electrode active material for a lithium ion secondary battery, but is not particularly limited thereto, and may be, for example, a carbon material used in a capacitor. The carbon material is not particularly limited, but examples thereof include activated carbons, cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbon fibers, carbon nanotubes, and polyacenes. Of these, activated carbons exhibiting a high specific surface area are preferred. Activated carbons as carbon materials have a specific surface area of 1000 m 2 / g or more, and 1500 m 2 / g or more is more preferable. 2 / g or more, the discharge capacity can be further increased. The specific surface area of this activated carbon is 3000 m 2 / g or less, and 2000m 2 / g or less is more preferable. The positive electrode is considered to store electricity by adsorbing and desorbing at least one of anions and cations contained in the ionically conductive medium, but may also store electricity by inserting and desorbing at least one of anions and cations contained in the ionically conductive medium.

[0041] The present disclosure may be any of the following [1] to

[10] . [1] A current collector used in a bipolar electricity storage device, an insulating portion formed in a grid pattern; a conductive portion disposed on the grid of the insulating portion and having a size larger than the grid, the current collector has a structure that prevents the electrolyte from passing through in a thickness direction, and a gap between adjacent conductive portions is smaller than a width of the grid; Current collector. [2] The current collector according to [1], wherein the gap between adjacent conductive portions is 2 mm or less, and the width of the grid of the insulating portion is 5 mm or less. [3] The current collector according to [1] or [2], wherein the conductive portion is fixed to the insulating portion by adhesion to the opening edge of the lattice of the insulating portion and / or by thermocompression bonding to the opening edge of the lattice. [4] The current collector according to any one of [1] to [3], wherein the insulating portion is a resin member and the conductive portion is a metal foil. [5] The conductive portion is a metal foil of one or more of Al, Cu, and stainless steel, The current collector according to any one of [1] to [4], wherein the insulating portion is made of one or more resin members selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polyimide (PI). [6] The current collector according to any one of [1] to [5], wherein the resistance between the conductive portions of the current collector is 0.5 Ω or more. [7] The current collector according to any one of [1] to [6], wherein the insulating portion is a resin member, the conductive portion is an Al foil as a metal foil, and a Cu foil as a metal layer is disposed inside the lattice. [8] An electrode structure for use in a bipolar electricity storage device, The current collector according to any one of [1] to [7], a positive electrode mixture layer formed on a surface of the current collector on which the conductive portion is disposed on the insulating portion; and a negative electrode mixture layer formed on the other surface of the current collector. [9] An electricity storage device formed by stacking the electrode structure according to [8].

[10] A method for manufacturing a current collector used in a bipolar electricity storage device, comprising: A conductive portion having a size larger than the grid is disposed on the grid of an insulating portion formed in a grid shape, a fixing step of fixing the conductive portion to the insulating portion by either gluing the conductive portion to an edge of an opening of the lattice of the insulating portion or by thermocompression bonding the conductive portion to the edge of an opening of the lattice of the insulating portion; A method for producing a current collector comprising: [Example]

[0042] An example in which the above-described power storage device was experimentally examined will be described below as an experimental example.

[0043] (Electrical circuit calculation) In bipolar batteries, current flows in the thickness direction of the current collector during normal charging and discharging, but in the event of an internal short circuit, current flows in the in-plane direction of the current collector. Figure 7 is an electrical circuit diagram that simulates the internal short circuit in a bipolar battery.

[0044] Figure 7A is an electrical circuit diagram simulating an internal short circuit in a bipolar battery with a continuous foil current collector. Here, the bipolar battery is assumed to consist of N unit cells connected in series, each with a voltage of V and an internal resistance of Ri. Assuming an internal short circuit occurs in the unit cell indicated by the dashed line, the short-circuit current Isn flowing through the short-circuited part was calculated, and the heat generation amount Wsn at the short-circuited part was also calculated. Note that the heat generation at the short-circuited part is maximized when Ri = Rs (the internal resistance of the battery is equal to the short-circuit resistance) (see, for example, NTT Facilities Research Institute Report No. 28, June 2017, pp. 44-46). The results are shown in the following equations (3) and (4). Isn=V·(1 / (2Ri)-(1 / 2)·(N-1 / 2) / (3.5Ri+Rt))…(1) Wsn=(Isn) 2 ×Ri …(2)

[0045] Fig. 7B is an electrical circuit diagram simulating the internal short circuit of a bipolar battery equipped with a divided foil as a current collector, which has a structure in which the conductive part is divided into n parts by a lattice-shaped insulating part. When such a divided foil is used, a "single cell with voltage V and internal resistance Ri" becomes is a state in which "divided cells with voltage V and internal resistance nRi are connected in parallel", and N of these are connected in series. Assuming that an internal short circuit has occurred in the divided cell indicated by the dashed line, the short-circuit current Isb flowing through the short-circuited part was calculated, and further, the amount of heat generated at the short-circuited part Wsb was calculated. Note that the heat generated at the short-circuited part was calculated using Ri = Rs, as in the case of using continuous foil. The results were as shown in the following formulas (3) and (4). Isb=V·(1 / (2Ri)-(1 / 2)·(N-1 / 2) / (3.5Ri+Rt)) / n …(3) Wsb=(Isb) 2 ×nRi …(4)

[0046] From the above, it was found that the resistance and heat generation at the short circuit area for continuous foil and divided foil are related by the following formulas (5) and (6). From this relationship, it was found that the current value and heat generation at the short circuit area can be controlled and suppressed according to the number of divisions n. Furthermore, the values calculated by substituting the resistance value and voltage into these formulas matched the values calculated using a commercially available electric circuit simulator (e.g., TopSpice). Isb / Isn=1 / n (7) Wsb / Wsn=1 / n (8)

[0047] (Evaluation of short-circuit resistance and heat generation) The resistance and heat generation of the short-circuited area during an internal short circuit were calculated using the above equations (1) to (6). Table 1 shows the results of a simulation of the energy consumption at the local short circuit when an internal short occurs between the positive and negative electrodes in a bipolar battery using a standard current collector foil and a grid-shaped current collector foil (a standard current collector foil divided into 10 vertical and 10 horizontal sections). The grid-shaped current collector foil is made of a grid-shaped polymer film with a metal foil larger than the grid attached within it. Table 1 also shows the calculated cell voltage (V), short-circuit resistance Rs (Ω), single-cell impedance Ri (Ω), heat flow rate Wi (W) of the entire cell immediately after the short circuit, heat flow rate Ws (W) at the local short circuit immediately after the short circuit, energy consumed at Ws (Wh) for a 10 Ah standard current collector foil, and energy consumed at Ws (Wh) for a 10 Ah grid-shaped current collector foil (10 × 10) cell. When a bipolar battery with a single cell voltage of 2.7V, capacity of 10 Ah, and single cell impedance Ri of 50 mΩ is short-circuited with a short-circuit resistance Rs of 0 to 50 Ω, the heat flow rate (Wi) of the entire cell (excluding the short-circuited area) immediately after the short circuit and the heat flow rate (Ws) of the short-circuited area immediately after the short circuit vary depending on the ratio of Rs to Ri. Ws is highest at 36.5 W when Rs is the same as Ri. At this time, the heating rate of the short-circuited area during an internal short circuit is at its highest. With a standard current collector foil, this heating continues for only 13.5 Wh of energy, making it highly likely to lead to thermal runaway. In contrast, when a grid-shaped current collector foil is used, dividing the cell into 100 sections with a resistance of 0.5 Ω or more, Ws remains unchanged at 36.5 W immediately after the short circuit, but this heating only continues for 0.1 to 0.2 Wh of energy, making it highly unlikely to lead to thermal runaway.

[0048] [Table 1]

[0049] Figure 8 shows the results of a study using calculation model 1 to examine the relationship between the conductive portion of the current collector and the grid-like insulating portion. Figure 8A shows calculation model 1, Figure 8B shows the relationship between grid width and capacity retention during 4C discharge, and Figure 8C shows the relationship between grid width and capacity retention during 4C charge. As shown in Figure 8A, a quarter of the current collecting metal and grid structural unit was cut out to set a symmetrical boundary. Blue indicates the current collecting metal, and white indicates the grid. Al is the conductive portion on the positive electrode side, Cu is the conductive portion on the negative electrode side, and the grid corresponds to the insulating portion. In calculation model 1, grids are set on Al and Cu. Furthermore, the relationship between the conductive portion of the current collector and the grid-like insulating portion was evaluated for one cell layer. As shown in Figure 8B, the relationship between the grid width and the discharge capacity retention indicates that the capacity can be maintained even if the metal area is large, even if the grid width is widened. Furthermore, as shown in Figure 8C, the capacity retention rate during charging was found to be lower than that during discharging. The grid width was set when the area of the current collecting foil was 10 2 mm 2 ~80 2 mm 2 (100mm 2 ~6400mm 2 ) it was presumed that 2.5 mm or less is preferable, 2 mm or less is more preferable, and 1 mm or less is even more preferable.

[0050] Figure 9 shows the results of examining the relationship between the conductive part of the current collector and the grid-shaped insulating part using calculation model 2. Figure 9A is an explanatory diagram of calculation model 2, Figure 9B is a diagram showing the relationship between the grid width and capacity retention rate during 4C discharge, and Figure 9C is a diagram showing the relationship between the grid width and capacity retention rate during 4C charge. As in Figure 8A, Figure 9A cuts out 1 / 4 of the current collecting metal and grid structural unit and sets the symmetric boundary. Blue indicates the current collecting metal, and white indicates the grid. In calculation model 2, a grid was set only on Cu. As shown in Figure 9B, the grid set on Cu did not affect the discharge capacity. On the other hand, as shown in Figure 9C, the grid placed on Cu slightly reduced the charge capacity. The gaps in the Cu foil were larger when the area of the current collecting foil was 10 2 mm 2 ~80 2 mm 2 It was presumed that within this range, 5 mm or less is preferable, 2.5 mm or less is more preferable, and 2 mm or less is even more preferable.

[0051] Figure 10 shows the results of examining the relationship between the conductive part of the current collector and the grid-shaped insulating part as calculation model 3, where Figure 10A is an explanatory diagram of calculation model 3, Figure 10B is a diagram showing the relationship between the grid width and capacity retention rate during 4C discharge, and Figure 10C is a diagram showing the relationship between the grid width and capacity retention rate during 4C charge. As shown in Figure 10A, in calculation model 3, the grid was set only on Al. As shown in Figure 10B, the grid set on Al reduced the discharge capacity. Furthermore, as shown in Figure 10C, the grid set on Al significantly reduced the charge capacity. The gaps in the Al foil were formed when the area of the current collector foil was 10 2 mm 2 ~80 2 mm 2 It was estimated that within this range, 3 mm or less is preferable, 2 mm or less is more preferable, and 1 mm or less is even more preferable.

[0052] It goes without saying that the present disclosure is not limited to the above-described embodiments, and can be embodied in various forms as long as they fall within the technical scope of the present disclosure. [Industrial Applicability]

[0053] The present disclosure is applicable to the technical field of electricity storage devices. [Explanation of symbols]

[0054] 10 electricity storage device, 15 electrode structure, 20 current collector, 21 conductive portion, 22 insulating portion, 23 composite layer forming region, 24 conductive portion, 30 single cell, 32 positive electrode composite layer, 34 negative electrode composite layer, 36 ion conductive medium, 38 separator, 40 laminate, 50 external current collector, 60 outer case, 120 current collecting foil, L1, L2, W1 length, W2 width, t1 to t3 thickness.

Claims

1. A current collector used in a bipolar electricity storage device, an insulating portion formed in a grid pattern; a conductive portion disposed on the grid of the insulating portion and having a size larger than the grid, the current collector has a structure that prevents the electrolyte from passing through in a thickness direction, and a gap between adjacent conductive portions is smaller than a width of the grid; Current collector.

2. 2. The current collector according to claim 1, wherein the gap between adjacent conductive portions is 2 mm or less, and the grid width of the insulating portion is 5 mm or less.

3. The current collector according to claim 1 or 2, wherein the conductive portion is fixed to the insulating portion by adhesion to an edge of an opening of the lattice of the insulating portion and / or by thermocompression bonding to the edge of the opening of the lattice.

4. The current collector according to claim 1 or 2, wherein the insulating portion is a resin member, and the conductive portion is a metal foil.

5. the conductive portion is a metal foil of one or more of Al, Cu, and stainless steel, The current collector according to claim 1 or 2, wherein the insulating portion is made of one or more resin members selected from the group consisting of polyethylene terephthalate (PET), polypropylene (PP), polyethylene (PE), and polyimide (PI).

6. The current collector according to claim 1 or 2, wherein the resistance between the conductive portions of the current collector is 0.5 Ω or more.

7. the insulating portion is a resin member, the conductive portion is an Al foil as a metal foil, The current collector according to claim 1 or 2, wherein a Cu foil is disposed as a metal layer inside the grid.

8. An electrode structure used in a bipolar electricity storage device, The current collector according to claim 1 or 2; a positive electrode mixture layer formed on a surface of the current collector on which the conductive portion is disposed on the insulating portion; and a negative electrode mixture layer formed on the other surface of the current collector.

9. An electricity storage device comprising a stack of electrode structures according to claim 8 .

10. A method for manufacturing a current collector used in a bipolar electricity storage device, comprising: A conductive portion having a size larger than the grid is disposed on the grid of an insulating portion formed in a grid shape, a fixing step of fixing the conductive portion to the insulating portion by either gluing the conductive portion to an edge of an opening of the lattice of the insulating portion or by thermocompression bonding the conductive portion to the edge of an opening of the lattice of the insulating portion; A method for producing a current collector comprising:

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