Sheet-like object for current collector, current collector, power storage element, secondary battery, electric automobile, and electric flying object

Abstract

Provided is a sheet-like object for a current collector capable of achieving both light weight and good battery characteristics at low cost. This sheet-like object for a current collector includes a base material layer, and layers containing organic resin A on both surfaces of the base material layer. The organic resin A is composed only of a polymer having LUMO of -0.5 eV or more.

Description

Current collector sheet material, current collector, power storage element, secondary battery, electric vehicle, and electric flying object

[0001] The present invention relates to a sheet material for a current collector, a current collector, an electricity storage element, a secondary battery, an electric vehicle, and an electric flying object.

[0002] In recent years, reducing carbon dioxide emissions has become a pressing need for environmental protection. The automotive industry is focused on reducing carbon dioxide emissions through the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs). Therefore, active development of secondary batteries for motor drive, which hold the key to their practical application, is underway. Secondary batteries include lithium-ion batteries, which can achieve high energy density and high power density, as well as next-generation batteries such as lithium-ion batteries using metallic lithium anodes, all-solid-state batteries, and air-air batteries. In addition to automobiles, the development of next-generation mobility technologies such as drones, flying cars, and flying communication base stations is also accelerating, necessitating the development of lightweight, high-energy-density secondary batteries. Therefore, to promote the widespread use of these battery-powered automobiles and flying cars, it is essential to provide low-cost battery components.

[0003] In secondary batteries such as lithium-ion batteries, metal foils have traditionally been used as current collectors, but in recent years, film current collectors made of resin films have been proposed as an alternative to metal foils. Film current collectors are lighter than metal current collector foils, and are therefore expected to improve energy density.

[0004] On the other hand, in the case of a film current collector, sufficient adhesion and bonding between the metal layer and the film are important. For example, in Patent Document 1, an adhesive layer containing an acid-modified polyolefin resin, a polyester resin, and an epoxy resin is formed on the surface of a resin film as a current collector reinforcing film, thereby ensuring the adhesion and bonding between the metal layer and the film.

[0005] In addition, Patent Document 2 discloses a negative electrode current collector having a polymer material and a conductive layer, which defines the sheet resistance increase rate and volume resistivity within a predetermined range, thereby improving battery characteristics. Patent Document 3 discloses the development of a separator having an organic-inorganic hybrid layer. The battery characteristics are improved by comprehensively adjusting the adaptive combination relationship of the median particle diameters of the first inorganic particles and the second inorganic particles and controlling the rational combination of particles on the order of micrometers and nanometers.

[0006] Japanese Patent Application Laid-Open No. 2023-145049 Japanese Patent Application Laid-Open No. 2020-184515 Special Publication No. 2023-539970

[0007] However, although Patent Document 1 provides good adhesion and bonding, the inclusion of a polyester resin in the adhesive layer is expected to result in a deterioration in battery performance due to reduced resistance to reduction. Patent Document 2 specifies various polymeric materials, but it is expected that it will be difficult to achieve both battery performance and high productivity costs. Furthermore, Patent Document 3 aims to improve battery performance through the separator, but to use this separator as a current collector, a metal layer must be formed on a microporous separator. However, it is difficult to form a uniform metal layer, and measures to slow the metal layer formation rate are necessary, which is expected to result in high processing costs.

[0008] As mentioned above, when applying a film current collector, not only is it required to improve energy density by reducing weight, but it is also essential that the film current collector has good battery characteristics and that it be provided at low cost.

[0009] In view of the above problems, an object of the present invention is to provide a current collector sheet material that is lightweight and has good battery characteristics at low cost.

[0010] Therefore, the present inventors have discovered that a sheet-like current collector having good battery characteristics can be produced at low cost by providing a base layer and layers containing organic resin A on both sides of the base layer and specifying the range of LUMO energy (lowest unoccupied molecular orbital) of the polymer constituting organic resin A, thereby suppressing decomposition of the base layer.

[0011] In order to solve the above problems, the current collector sheet of the present invention has the following configuration: (1) A current collector sheet comprising a base layer and layers containing an organic resin A on both sides of the base layer, the organic resin A being composed solely of a polymer having a LUMO of −0.5 eV or more. (2) A current collector sheet comprising a base layer and layers containing an organic resin A on both sides of the base layer, the organic resin A comprising at least one organic resin selected from the group consisting of styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylpyrrolidone, N-vinylpyrrolidone, (meth)acrylate, polyethylene, polypropylene, cyclic polyolefin copolymer, cyclic polyolefin, acid-modified polyolefin, polycarbonate, and propylene carbonate. (3) The current collector sheet according to (2), wherein the organic resin A comprises at least one organic resin selected from the group consisting of styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride. (4) The current collector sheet according to (1) or (2), wherein at least one of the base layers comprises two or more types of thermoplastic resins. (5) The current collector sheet according to (1) or (2), wherein the base layer comprises a polyester resin. (6) The current collector sheet according to (1) or (2), wherein the base layer has at least one resin layer having a domain structure with a thickness direction length of 1.0 μm or less and an aspect ratio of 5 or more in a cross section in the direction perpendicular to the main orientation—thickness direction. (7) The current collector sheet according to (1) or (2), wherein the layer containing the organic resin A has a water contact angle of 20° or more and 80° or less. (8) The sheet material for a current collector according to (1) or (2), wherein the layer containing organic resin A has a thickness of 0.1 μm or more and 4.0 μm or less. (9) The sheet material for a current collector according to (1) or (2), wherein the thickness of the base layer is 1 μm or more and 30 μm or less. (10) The sheet material for a current collector according to (1) or (2), wherein the maximum strength in at least one of the longitudinal direction and the width direction of the sheet material for a current collector is 200 MPa or more. (11) The water vapor permeability of the base layer at 40° C. and 90% RH is 200 g / (m２ (12) A current collector having the sheet material for a current collector according to (1) or (2) and a layer (M layer) containing a metal and / or a metal-based compound, wherein the metal and / or metal-based compound is in contact with a layer containing organic resin A. (13) The sheet material for a current collector according to (12), wherein the adhesion strength between the layer containing organic resin A and the M layer is 1 N / 15 mm or more and 5 N / 15 mm or less. (14) A current collector having a maximum reduction current peak intensity of 0.000 mA / cm in CV measurement (0.01 V to 2.0 V, 10 cycles). ２ 0.050mA / cm or more ２ (15) The sheet material for a current collector according to (12), wherein at least one of the M layers in contact with the layer containing organic resin A has a layer containing elemental copper on at least one surface side, and the layer containing copper is in contact with the layer containing organic resin A. (16) The sheet material for a current collector according to (12), wherein at least one of the M layers in contact with the layer containing organic resin A has a layer containing elemental aluminum on at least one surface side, and the layer containing aluminum is in contact with the layer containing organic resin A. (17) The current collector for a bipolar battery according to (12), wherein one of the M layers in contact with the layer containing organic resin A has a layer containing elemental copper on one surface side, and the layer containing copper is in contact with the layer containing organic resin A, and the other M layer has a layer containing elemental aluminum on one surface side, and the layer containing aluminum is in contact with the layer containing organic resin A. (18) An electric storage element comprising the current collector according to (12). (19) A secondary battery comprising the electric storage element according to (18). (20) An electric vehicle equipped with the secondary battery according to (19). (21) An electric flying object equipped with the secondary battery according to (20).

[0012] According to the present invention, a current collector sheet material that is both lightweight and has good battery characteristics can be provided at low cost.

[0013] The current collector sheet of the present invention comprises a substrate layer and layers containing an organic resin A on both sides of the substrate layer, wherein the organic resin A is composed solely of a polymer having a LUMO of −0.5 eV or more.

[0014] The current collector sheet material of the present invention will be described in detail below.

[0015] [Layer containing organic resin A] In the present invention, the layer containing organic resin A refers to a layer that improves the battery characteristics by providing a dispersion containing organic resin A on both sides of a substrate layer, thereby improving reduction resistance.

[0016] (1) Organic Resin A Organic Resin A in the present invention preferably has reduction resistance. A parameter indicating reduction resistance is the LUMO energy (Lowest Unoccupied Molecular Orbital) calculated using the PM3 method with a Hamiltonian in a semi-empirical molecular orbital calculation. As is well known to those skilled in the art, the LUMO energy can be calculated using the PM3 method with a Hamiltonian in a semi-empirical molecular orbital calculation. (It can be easily calculated on a computer using MOPAC: see, for example, JP-A-6-333576).

[0017] The LUMO energy of the polymer constituting organic resin A is preferably −0.5 eV or more. More preferably, it is 1 eV or more, and even more preferably 2 eV or more. By making it −0.5 eV or more, electrons are less likely to be introduced into the lowest unoccupied molecular orbital, and when the secondary battery of the present invention is configured, the reduction resistance is improved, and the battery characteristics are also improved.

[0018] The organic resin A preferably contains at least one organic resin selected from the group consisting of styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylpyrrolidone, N-vinylpyrrolidone, (meth)acrylate, polyethylene, polypropylene, cyclic polyolefin copolymer, cyclic polyolefin, acid-modified polyolefin, polycarbonate, and propylene carbonate. These organic resins may be used alone, or two or more may be used in combination in any ratio. Among these, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride (PVDF), which are easily prepared as dispersions using these organic resins and water as a solvent, are particularly preferred from the standpoints of environmental friendliness, safety, and economy. Furthermore, styrene butadiene rubber, carboxymethyl cellulose, and sodium carboxymethyl cellulose have functional groups that trap lithium salts in the electrolyte, thereby suppressing the penetration of the electrolyte into the substrate layer, thereby suppressing reductive decomposition of the substrate and improving battery characteristics. (Examples: ethylene groups in styrene butadiene rubber, carboxy groups in carboxymethyl cellulose and sodium carboxymethyl cellulose.) The type of organic resin polymer contained in organic resin A can be measured using known methods. For example, the current collector sheet is impregnated with an organic solvent such as water or alcohol, or an ultrasonic homogenizer is used in water to remove the layer containing organic resin A, and the organic solvent such as water or alcohol is thoroughly dried to obtain the components contained in the layer containing organic resin A. An organic solvent that dissolves the organic resin components is added to the obtained components to dissolve only the organic resin components. Next, the organic solvent is dried from the solution in which the organic resin components have been dissolved, and only the organic resin components are extracted. The obtained organic resin components are used for nuclear magnetic resonance (NMR) analysis. １ H-NMR, １９ F-NMR, １３The amount of the organic resin A can be calculated from the signal intensity indicating various organic resins by using techniques such as C-NMR, infrared absorption spectroscopy (IR), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence analysis (EDX), elemental analysis, pyrolysis gas chromatograph mass spectrometer (pyrolysis GC / MS), etc. In particular, after confirming the presence or absence of organic resin polymer contained in organic resin A by pyrolysis GC / MS, １３ By C-NMR (filling a solid-state NMR sample tube with the organic resin component and an appropriate amount of solvent (deuterated chloroform), leaving it to stand overnight, and then measuring by DD / MAS), it is possible to determine the structural unit and content of at least one organic resin.

[0019] (2) Binder In order to improve the adhesion between the layer containing organic resin A and the substrate layer in the present invention, the layer containing organic resin A may contain a binder. As the binder, a resin that is electrochemically stable within the range of use of the battery is preferred. In addition, examples of the binder include a binder soluble in an organic solvent, a water-soluble binder, and an emulsion binder. The binder may be used alone or in combination of two or more types.

[0020] When using a binder soluble in an organic solvent or a water-soluble binder, the viscosity of the binder itself is preferably 10,000 mPa·s or less at a concentration of 15% by mass. It is more preferably 8,000 mPa·s or less, and even more preferably 5,000 mPa·s or less. By keeping the viscosity at 10,000 mPa·s or less at a concentration of 15% by mass, the viscosity of the coating agent can be suppressed from increasing. This improves the coatability of the layer containing organic resin A.

[0021] Furthermore, when an emulsion binder is used, the dispersant may be water or an organic solvent, such as an alcohol solvent such as ethanol or a ketone solvent such as acetone, but an aqueous dispersion is preferred in terms of ease of handling and miscibility with other components. The particle size of the emulsion binder is 30 to 1000 nm, preferably 50 to 500 nm, more preferably 70 to 400 nm, and even more preferably 80 to 300 nm. By setting the particle size of the emulsion binder to 30 nm or more, an increase in air permeability can be suppressed, resulting in good battery characteristics. Furthermore, by setting the particle size to 1000 nm or less, the adhesion between the substrate layer and the layer containing organic resin A is improved.

[0022] Examples of resins used in the binder include polyamide, polyamideimide, polyimide, polyetherimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polysulfone, polyketone, polyetherketone, polycarbonate, polyacetal, polyvinyl alcohol, polyethylene glycol, cellulose ether, acrylic resin, polyethylene, polypropylene, polystyrene, and urethane. Among these, acrylic resins are particularly preferred because stronger adhesion can be obtained through interaction with the organic resin A. These resins may be used alone or in combination of two or more, as necessary.

[0023] When a water-soluble binder is used, the amount added is preferably 0.5% by mass or more relative to the total amount of organic resin A and inorganic particles. More preferably, it is 1% by mass or more, and even more preferably, it is 1.5% by mass or more. Also, it is preferably 10% by mass or less. More preferably, it is 8% by mass or less, and even more preferably, it is 6% by mass or less. By setting the amount of water-soluble binder to 0.5% by mass or more, sufficient adhesion to the base layer and the layer containing organic resin A can be obtained. Furthermore, by setting it to 10% by mass or less, the content of organic resin A in the layer increases, and as a result, reduction resistance is improved and battery characteristics are improved.

[0024] (3) Formation of Layer Containing Organic Resin A The method for forming the layer containing organic resin A will be described below.

[0025] The coating method is not particularly limited, but a typical coating method will be described below.

[0026] (i) First, a coating liquid is prepared by dispersing organic resin A to a predetermined concentration. The coating liquid is prepared by dispersing, suspending, or emulsifying organic resin A in a solvent. The solvent for the aqueous dispersion coating liquid is not necessarily limited, but is not particularly limited as long as it does not dissolve water or the organic resin and can disperse, suspend, or emulsify it in a solid state. Examples of organic solvents include methanol, ethanol, 2-propanol, acetone, tetrahydrofuran, methyl ethyl ketone, ethyl acetate, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and the like. From the standpoints of low environmental impact, safety, and economy, aqueous emulsions in which an organic resin is emulsified in water or a mixture of water and alcohol are also preferred. When water is used, a solvent other than water may be further added.

[0027] The solids concentration of the coating liquid is preferably 2% or more and 50% or less. By setting the solids concentration within this range, both coating stability and uneven surface distribution during coating and drying can be achieved. Furthermore, the solution viscosity of the coating liquid is preferably 5 mPa·s or more and 100 mPa·s or less. By setting the solids concentration within this range, organic resin A can be uniformly present in the layer containing organic resin A.

[0028] If necessary, the coating liquid may contain additives such as a film-forming aid, a dispersant, a thickener, a stabilizer, an antifoaming agent, and a leveling agent.

[0029] Examples of methods for dispersing the coating liquid include a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, an ultrasonic homogenizer, a high-pressure homogenizer, an ultrasonic device, and a paint shaker. Among these, selecting a dispersing method that applies high pressure to the inorganic particles and organic resin during dispersion (bead mill, sand mill) improves the dispersibility of the coating liquid containing organic resin A. A plurality of these mixer-dispersers may be combined to perform dispersion in stages.

[0030] (ii) Next, the obtained coating liquid is applied to a substrate. Examples of coating methods that can be used include dip coating, gravure coating, slit die coating, knife coating, comma coating, kiss coating, roll coating, bar coating, spray coating, immersion coating, spin coating, screen printing, inkjet printing, pad printing, and other types of printing. The coating method is not limited to these, and can be selected according to preferred conditions such as the organic resin, binder, dispersant, leveling agent, solvent, and substrate used.

[0031] (iii) Thereafter, the solvent in the coating liquid is dried to form a layer containing organic resin A. The drying temperature is preferably 40°C or higher and 120°C or lower. This allows the layer containing organic resin A to dry uniformly, resulting in a uniform film thickness, suppressing the occurrence of cracks, and improving the battery characteristics as a result of the improved reduction resistance. If the drying temperature is lower than 40°C, the solvent in the coating liquid may not dry. On the other hand, if the drying temperature is higher than 120°C, the amount of heat generated during drying may increase, which may cause the substrate to shrink and deteriorate the appearance of the current collector sheet material. Therefore, by setting the drying temperature within the specified range, it is possible to achieve both battery characteristics, coating and drying properties, and cost reduction due to improved drying speed.

[0032] [Characteristics of Layer Containing Organic Resin A] (1) Water Contact Angle The water contact angle of the layer containing organic resin A is preferably 20° or more, more preferably 30° or more, and even more preferably 40° or more. It is also preferably 80° or less, more preferably 70° or less, and even more preferably 60° or less. By making the water contact angle of the layer containing organic resin A 20° or more, the coatability when coating the layer containing organic resin A is improved and the adhesive strength with the substrate is also improved, which is preferable. Furthermore, by making it 80° or less, the solvent for the coating liquid of the layer containing organic resin A can be water, which is preferable from the viewpoints of low environmental impact, safety, and economy.

[0033] (2) Film Thickness The film thickness of the layer containing organic resin A is preferably 0.1 μm or more, more preferably 0.5 μm or more, and even more preferably 1 μm or more. It is also preferably 4.0 μm or less, more preferably 3.0 μm or less, and even more preferably 2.0 μm or less. Here, the film thickness of the layer containing organic resin A refers to the film thickness of the layer containing organic resin A when the current collector sheet has a layer containing organic resin A on one side of the substrate, or the sum of the film thicknesses of both layers containing organic resin A when the current collector sheet has layers containing organic resin A on both sides of the substrate. By making the film thickness of the layer containing organic resin A 0.1 μm or more, good thermal dimensional stability and improved reduction resistance are achieved, resulting in good battery characteristics. Furthermore, by making the film thickness 4.0 μm or less, the adhesion strength is maintained at a certain level. This improves the preferable reduction resistance and battery characteristics, which also contributes to improving yield when forming a layer containing a metal and / or metal-based compound (M layer) and then coating and drying a positive electrode active material or a negative electrode active material to produce a battery electrode, as described below. It may also be advantageous in terms of cost.

[0034] [Substrate Layer] (1) Main Component of the Substrate Layer In the present invention, the substrate layer (hereinafter sometimes referred to as the substrate) may be, for example, polyamide, polyester, such as polyethylene terephthalate, polyimide, polyolefin, such as polyethylene (PE), polypropylene (PP), polystyrene, polyvinyl chloride, acrylonitrile, butadiene-styrene copolymer, polyparaphenylene terephthalamide, ethylene-propylene rubber, polyoxymethylene, epoxy resin, phenolic resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, or polycarbonate. Among these, the use of polyester increases the strength and elongation of the substrate layer, thereby improving the yield in the manufacturing process. In addition, the adhesion strength with the layer containing a metal and / or metal-based compound (M layer), which will be described later, is easily increased.

[0035] Here, the case where polyester is used will be described in detail. The polyester resin in the present invention is obtained by polycondensation of a dicarboxylic acid component and a diol component. In the present invention, the component of the polyester resin refers to the smallest unit that can be obtained by hydrolysis. In the present invention, the polyester resin obtained by polycondensation of a dicarboxylic acid component and a diol component is sometimes referred to as a polyester resin containing a dicarboxylic acid component and a diol component.

[0036] Examples of diol constituent components constituting such polyester resins include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol; alicyclic diols such as 1,4-cyclohexanedimethanol, 1,3-cyclobutanedimethanol, 2,2,4,4-tetramethyl-1,3-cyclobutanedimethanol, and spiroglycol; and diols in which a plurality of the above-mentioned diol components are connected together.

[0037] Examples of dicarboxylic acid components constituting such polyester resins include aromatic dicarboxylic acids such as terephthalic acid, isophthalic acid, phthalic acid, 1,4-naphthalenedicarboxylic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, 1,8-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, and 4,4'-diphenyletherdicarboxylic acid.

[0038] Examples of polyester resins containing such dicarboxylic acid components and diol components include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polycyclohexylene dimethylene terephthalate (PCT), polyethylene naphthalate (PEN), etc. These polyester resins may be copolymerized with isophthalic acid or naphthalenedicarboxylic acid as part of the dicarboxylic acid component of the polyester, and with 1,3-butanediol, 1,4-cyclohexanedimethanol, or 2,2,4,4-tetramethyl-1,3-cyclobutanedimethanol as part of the diol component, to the extent that the effects of the present invention are not affected.

[0039] Among these, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), and polyethylene naphthalate (PEN) are particularly preferred in the present invention from the viewpoints of the maximum point strength of the current collector (described later) and the adhesive strength with the layer containing a metal and / or metal-based compound (M layer), because the reduction resistance can be improved by providing a layer containing organic resin A.

[0040] The quantitative analysis method for the resin components constituting the substrate is not limited, but an example is shown below. The layer containing metal and / or metal-based compounds (M layer) and the layer containing organic resin A are removed from the current collector sheet of the present invention using water and an organic solvent such as alcohol, yielding only the substrate. The substrate is then immersed in 1,1,1,2,2,2-hexafluoro-2-isopropanol (HFIP), the soluble portion is separated by centrifugation, and the supernatant is collected to extract the components contained in the polyester resin. The extract is then measured by matrix-assisted laser desorption / ionization mass spectrometry (MALDI-MS). The structure of the resin components is identified from the obtained mass spectrum and the nuclear magnetic resonance (1H-NMR) spectrum described below.

[0041] (1H-NMR measurement conditions) Apparatus used: ECA-400 (manufactured by JEOL RESONANCE) Measurement method: single pulse Observation frequency: 399.8 MHz Pulse width: 6.45 s (45 pulses) Lock solvent: HFIP-d2 Chemical shift reference: residual protons in heavy solvent (4.41 ppm) Observation width: approximately 8000 Hz (approximately -2 ppm to 18 ppm) Number of data points: 32768 Waiting time: 30 seconds Number of accumulations: 128 Measurement temperature: room temperature (21°C) Sample rotation speed: 15 Hz.

[0042] (2) Biaxial Orientation: The polyester film used as the substrate for the current collector sheet of the present invention is preferably biaxially oriented from the viewpoint of improving mechanical strength and thermal dimensional stability. Biaxial orientation here refers to a film that exhibits a biaxially oriented pattern in wide-angle X-ray diffraction. Biaxially oriented polyester films can generally be obtained by stretching an unstretched polyester film in the axial direction of the film-forming machine (hereinafter sometimes referred to as the longitudinal direction) and the width direction, followed by heat treatment to complete the oriented crystallization.

[0043] (3) Structure of the Base Material Layer The base material layer of the present invention preferably has at least one resin layer having a domain structure in which, in a cross section in the direction perpendicular to the main orientation-thickness direction, the thickness direction length is 1.0 μm or less and the aspect ratio is 5 or more. The main orientation direction here refers to the direction showing the highest value when Young's modulus is measured in each direction forming an angle of 0° to 175° in 5° increments relative to an arbitrary direction in the plane of the resin film, with the arbitrary direction being set to 0°, and the direction perpendicular to the main orientation refers to the direction perpendicular to the main orientation direction in the plane of the resin film. The method for evaluating Young's modulus will be described later.

[0044] By providing at least one resin layer with a flat domain structure on the substrate, even if strong stress is applied during a peel test, the stress is alleviated by the domain structure within the resin layer, thereby suppressing cohesive failure of the substrate. Furthermore, it has been found that providing a flat domain structure improves reduction resistance. When a substrate having this resin layer is used as a current collector, reducing agent by-products such as lithium methoxide and methanol are generated in the electrolyte. If these reducing agent by-products attack the bonding portions of the resin structure in the substrate (e.g., ester groups when the substrate is made of polyester resin), the substrate may deteriorate, resulting in problems such as a decrease in battery capacity retention. Providing a flat domain structure in the resin layer of the current collector can suppress infiltration of the electrolyte from the substrate surface and the reducing agent by-products in the electrolyte. Furthermore, the presence of a flat domain structure within the substrate is thought to delay the diffusion of reducing agent by-products within the resin layer, thereby suppressing deterioration and improving reduction resistance. While at least one resin layer with a flat domain structure is required, two or more layers may be provided.

[0045] To form a flat domain structure, for example, a method of adjusting the kneading conditions or raw material composition of the raw materials, a method of setting the film-forming conditions within the ranges described below, etc. can be used in appropriate combination. In particular, it is effective to select the intrinsic viscosities of two or more thermoplastic resins within a predetermined range, to knead and use two or more thermoplastic resins, to select a domain resin having a glass transition temperature (Tg) lower than that of the matrix resin, and to perform longitudinal stretching in a temperature range between the Tg of the domain resin and the Tg of the matrix resin.

[0046] The matrix resin herein refers to the resin with the largest content among the resin components constituting the resin layer having a domain structure, and the domain resin refers to the resin with the largest content among the components constituting the domain structure.

[0047] To set the size and aspect ratio of the domain structure within the above ranges, for example, methods of adjusting the kneading conditions or raw material composition of the raw materials, methods of setting the film-forming conditions within the ranges described below, etc. can be used in appropriate combination. In particular, it is effective to select the intrinsic viscosities of two or more thermoplastic resins within a predetermined range, to use compound raw materials pre-kneaded under predetermined conditions to uniformly disperse the domains, to select a domain resin having a glass transition temperature (Tg) lower than that of the matrix resin, and to perform high-temperature preheating just below the crystallization temperature (Tc) of the domain resin in the preheating step for longitudinal stretching, and then stretch in a temperature range between the Tg of the domain resin and the Tg of the matrix resin, thereby uniformly and highly elongating the domains.

[0048] The upper limit of the domain length in the thickness direction is more preferably 0.8 μm, even more preferably 0.6 μm, even more preferably 0.4 μm, and most preferably 0.1 μm. By keeping the domain length in the thickness direction at 1 μm or less, the mechanical strength of the resin film can be maintained high, and defects such as resin film breakage can be suppressed even if strong tension is applied during the processing step in producing the current collector. From the above viewpoint, the lower limit of the domain length in the thickness direction is not particularly limited, but 0.001 μm is a substantial lower limit.

[0049] The lower limit of the length of the domain in the direction perpendicular to the main orientation is preferably 0.1 μm, more preferably 0.5 μm, and the upper limit is preferably 1.0 μm, more preferably 3.0 μm.

[0050] The lower limit of the aspect ratio is more preferably 10, even more preferably 20, even more preferably 40, and most preferably 70. When the aspect ratio is 5 or more, voids are less likely to form at the domain structure interface during film formation of the substrate, and swelling of the substrate in the electrolyte can be suppressed. From the above viewpoint, the upper limit of the aspect ratio is not particularly limited, but 500 is a substantial upper limit.

[0051] (4) Method for Producing Substrate Next, a method for producing a biaxially oriented polyester film as a substrate for the current collector sheet of the present invention will be described, but the present invention is not limited to the product obtained by this example.

[0052] A biaxially oriented polyester film can be obtained as a substrate for the current collector sheet of the present invention by a conventional polymerization method. For example, the biaxially oriented polyester film can be obtained by subjecting the dicarboxylic acid component or its ester-forming derivative and the diol component or its ester-forming derivative to a transesterification or esterification reaction using a known method, followed by a melt polymerization reaction. If necessary, the polyester resin obtained by the melt polymerization reaction can be subjected to a solid-state polymerization reaction at a temperature below the melting point of the polyester resin.

[0053] The biaxially oriented polyester film used as the substrate for the current collector sheet of the present invention can be produced by any conventionally known production method. Specifically, a method (melt casting method) can be used in which dried raw materials are heated and melted in an extruder, extruded through a die onto a cooled casting drum, and processed into a sheet. Another method that can be used is a method (solution casting method) in which the raw materials are dissolved in a solvent, the solution is extruded through a die onto a support such as a casting drum or endless belt to form a film, and the solvent is then dried and removed from the film layer to form a sheet.

[0054] The drying of the polyester resin is preferably carried out at a temperature of 100°C or higher, which is the boiling point of water, under reduced pressure, since this allows for the removal of trace amounts of moisture present in the raw materials of the substrate. More preferably, the drying is carried out at a temperature of 120°C or higher under reduced pressure. From the viewpoint of increasing the drying efficiency of the polyester resin, it is even more preferable to place the resin raw materials in a rotating metal container and dry them at a drying temperature of 120°C or higher under reduced pressure. In addition, in the step of melt-extruding the polyester resin, it is also a preferred method to simultaneously melt the polyester resin and remove the contained moisture by reducing the pressure inside the extruder. By removing moisture by drying the raw materials and / or extrusion under reduced pressure, the moisture content of the polyester resin can be controlled within a preferred range.

[0055] When a substrate having two or more layers is produced by the melt-casting method, a method (co-extrusion method) is preferably used in which an extruder is used for each layer constituting the biaxially oriented substrate, the raw materials for each layer are melted, and these are laminated in the molten state in a confluence device provided between the extrusion device and the die, and then introduced into the die, and extruded from the die onto a casting drum cooled to a surface temperature of 20°C or higher and 60°C or lower, and processed into a sheet to form an unstretched substrate.

[0056] (Sequential Biaxial Stretching) With regard to the stretching conditions when an unstretched substrate is biaxially stretched, when the substrate of the current collector sheet of the present invention is mainly composed of a polyester resin, the longitudinal stretching is preferably performed by stretching the unstretched substrate film in the longitudinal direction with a group of rolls heated to 70°C or higher, and then cooling with a group of rolls set at a temperature of 20°C or higher and 50°C or lower.

[0057] The lower limit of the heating roll temperature during longitudinal stretching is not particularly limited as long as it does not impair the stretchability of the sheet, but it is preferable that it exceeds the glass transition temperature of the polyester resin used. Furthermore, the preferred range of the longitudinal stretching ratio is 2 to 5 times, and a more preferred range is 3 to 4 times. When the longitudinal stretching ratio is 2 times or more, orientation crystallization progresses, and film strength can be improved. On the other hand, by setting the stretching ratio to 5 times or less, orientation crystallization of the polyester resin due to stretching progresses excessively, making the film brittle and causing breakage during film formation.

[0058] The process film (uniaxially stretched film) stretched in the longitudinal direction is then stretched in the direction perpendicular to the longitudinal direction (width direction). The uniaxially stretched film is preferably guided into a tenter while being held at both ends with clips, and stretched 2 to 5 times in the direction perpendicular to the longitudinal direction (width direction) in an atmosphere heated to a temperature of 70 to 160°C.

[0059] The stretched film is then preferably heat-treated to stabilize the internal orientation structure. The thermal history temperature of the film during heat treatment can be confirmed by the temperature of a small endothermic peak (sometimes referred to as Tmeta) that appears just below the melting point temperature measured using a differential scanning calorimeter (DSC) described below. The tenter apparatus temperature setting is preferably set so that the maximum temperature inside the tenter is 150°C or higher and 270°C or lower when polyester (melting point 280°C (in the case of PET)) is the main component, and is preferably set to a temperature between the resin melting point (°C) and the resin melting point (°C) -70°C or higher and the resin melting point (°C) -10°C or lower when another thermoplastic resin is the main component. Setting the heat treatment temperature to 150°C or higher can improve the dimensional stability of the substrate of the biaxially oriented current collector sheet. Furthermore, setting the heat treatment temperature to 270°C or lower, for example, for PET, can suppress substrate tearing due to resin melting, allowing for efficient production. A more preferable range of the heat treatment temperature is 180°C or higher and 250°C or lower.

[0060] For the reasons mentioned above, the temperature range of Tmeta, which represents the thermal history temperature of the film during heat treatment, is preferably 200°C or higher and 260°C or lower when the film is mainly composed of PET. A more preferred temperature range for Tmeta is 210°C or higher and 240°C or lower.

[0061] Furthermore, in order to impart dimensional stability after the heat treatment, a relaxation treatment may be carried out in the range of 1% to 6%. A relaxation treatment of 1% or more can improve the dimensional stability when the biaxially oriented substrate is used in a high-temperature environment, and a relaxation treatment of 6% or less can continue to apply an appropriate tension to the biaxially oriented substrate, preventing thickness unevenness from worsening.

[0062] The stretching ratio is preferably 2 to 5 times in both the longitudinal and width directions, but the area ratio (stretching ratio in the longitudinal direction × stretching ratio in the width direction) is preferably 4 to 22 times, more preferably 9 to 20 times. By setting the area ratio to 4 times or more, it is possible to promote molecular orientation of the obtained biaxially oriented substrate and improve its durability, and by setting the area ratio to 22 times or less, it is possible to suppress the occurrence of tearing during stretching.

[0063] (4) Thickness of the Substrate The thickness of the substrate is preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 4 μm or more. It is also preferably 30 μm or less, more preferably 20 μm or less, and even more preferably 10 μm or less. By making the thickness 1 μm or more, it is possible to process the film without tearing in the step of providing the M layer described below. It also becomes tensile-resistant, and can maintain its performance as a current collector even when deformed during processing as a battery component. Furthermore, by making the thickness 30 μm or less, it is possible to suppress an increase in the weight and thickness of the battery itself, even when used as a lithium-ion battery component.

[0064] (5) Water Vapor Permeability The water vapor permeability of the substrate layer in the present invention is 200 g / (m ２ ・day) or less is preferable. More preferably, it is 150 g / (m ２ ・day) or less, more preferably 100 g / (m ２ ・day) or less. ２ By setting the maximum strength of the substrate layer at 1000 kJ / cm2 or less, the yield of the battery can be improved by setting the maximum strength of the substrate layer at 1000 kJ / cm2 or more.

[0065] [Layer containing metal and / or metal-based compound (M layer)] As the current collector in a secondary battery, a current collector having a layer containing the current collector sheet material of the present invention and a layer containing a metal and / or metal-based compound (M layer), in which the layer containing the metal and / or metal-based compound (M layer) is in contact with a layer containing organic resin A, is preferred.

[0066] At least one layer of the M layer is a layer containing copper element, and the copper element-containing layer is in contact with the layer containing organic resin A, thereby improving reduction resistance, and therefore the M layer is suitable for use in a negative electrode current collector for a secondary battery.

[0067] Furthermore, at least one layer of the M layer is a layer containing aluminum element, and the layer containing aluminum element is in contact with the layer containing organic resin A, thereby improving oxidation resistance, and therefore, the M layer is suitable for use as a positive electrode current collector for a secondary battery.

[0068] Furthermore, the M layer has a layer containing copper element on one side and a layer containing aluminum element on the opposite side, and is in contact with the layer containing organic resin A, so that the M layer can also be suitably used as a current collector for a bipolar battery.

[0069] In the case where the current collector sheet has the M layer on both surfaces, when a layer containing organic resin A is formed on only one surface of the base layer, an M layer will be present that is not on the side of the layer containing organic resin A. In this case, the M layer described for the side of the layer containing organic resin A can be applied.

[0070] (1) Method for Forming the M Layer The method for forming the M layer in the present invention is not particularly limited, and examples thereof include deposition, sputtering, or electroplating under vacuum conditions or reduced pressure conditions in which an inert gas such as argon gas is sealed (hereinafter these may be collectively referred to as deposition methods), a method in which a metal foil or a foil of a metal compound is bonded to a current collector sheet directly or via an adhesive layer, and a method in which a metal layer is formed by an electrochemical reaction using a solution containing a metal salt (electrolytic plating method, electroless plating method).Of these, deposition is preferred from the viewpoint of continuously forming the M layer on a film using a roll of current collector sheet.

[0071] Examples of sputtering methods include radio frequency sputtering, magnetron sputtering, bipolar sputtering, DC sputtering, and reactive sputtering. However, radio frequency sputtering is preferred from the viewpoints that the equipment is simple, a metal layer can be formed on an insulating sample, and the sample is relatively little damaged.

[0072] In the case of using the vacuum deposition method, a preferred embodiment is to place a current collector sheet roll in a vacuum chamber in advance, and then adhere the heated and vaporized metal and / or metal compound to the surface of the current collector sheet while bringing the unwound film into close contact with a cooling roll, thereby forming an M layer, and then winding the film up again into a film roll.

[0073] Here, the inside of the vacuum chamber is 9.0 × 10 －３ The pressure is reduced to 9.0 × 10 Pa or less under vacuum conditions, or an inert gas such as argon gas is sealed in the chamber. －３ Pa or more 1×10 －１ Any of the conditions under which the pressure is reduced to or below Pa can be suitably used. The M layer may also be formed by successively carrying out two or more vapor deposition steps, for example, by providing a first M layer by sputtering and then providing a second M layer by vacuum deposition.

[0074] Vacuum deposition methods include induction heating deposition, resistance heating deposition, laser beam deposition, and electron beam deposition, among which electron beam deposition, laser beam deposition, and induction heating deposition, which have a large calorific value of the deposition source, are preferably used. The calorific value of the deposition source must be increased until an M layer of the desired thickness is formed, and the substrate surface temperature must be sufficiently high. However, since this is difficult to measure, whether the calorific value is sufficient is determined by confirming that the M layer after deposition has the desired thickness.

[0075] However, if the heat output of the deposition source is increased to the required heat output, the temperature of the current collector sheet will rise if the cooling function is controlled as in a normal vacuum deposition method, and the mechanical properties of the current collector sheet will decrease due to thermal damage, and there is also the risk of the current collector sheet melting. Therefore, it is preferable to perform deposition while controlling the cooling function so that the current collector sheet can be uniformly cooled so that the temperature does not rise too much during deposition. Specifically, it is preferable to cool the current collector sheet uniformly from the back side of the deposition surface using a cooling mechanism consisting of a metal plate or metal roll that is sufficiently cooled with a refrigerant.

[0076] When the M layer in the present invention is to have a desired metal layer thickness, a method of forming it by a single vapor deposition (a set of unwinding, vapor deposition, and winding is defined as one vapor deposition) is preferred from the viewpoints of productivity, resistance characteristics, and grade and quality, but, for example, thin film vapor deposition to form an aluminum vapor deposition layer of 50 nm thickness in one vapor deposition may be repeated 20 times (the above set is repeated 20 times) to form an aluminum metal layer of a total thickness of 1 μm. Furthermore, when the M layer is provided on the surface of the current collector sheet material of the present invention, the surface of the current collector sheet material may be modified by vacuum plasma treatment, atmospheric pressure plasma treatment, etc., for the purpose of improving the adhesion between the M layer and the current collector sheet material.

[0077] Examples of metal elements constituting the M layer include gold, silver, copper, zinc, lead, nickel, iron, aluminum, titanium, cobalt, manganese, cadmium, and palladium, and the M layer may be a metal layer consisting of a simple metal element, or a layer consisting of a metal compound in which the metal element is mixed with oxygen, nitrogen, fluorine, carbon, boron, chlorine, sulfur, or phosphorus. The metal elements of the M layer provided on both sides of the current collector sheet may be the same or different.

[0078] (2) Thickness of the M Layer In the present invention, the thickness of the M layer is preferably 0.1 μm or more, because when used as a resin current collector, this prevents a decrease in electrical properties due to uneven thickness of the metal layer, particularly an increase in resistance when incorporated into a battery cell. The thickness of the M layer is more preferably 0.2 μm or more. Furthermore, by setting the thickness of the M layer to 5.0 μm or less, this prevents an increase in battery weight when used as a resin current collector for a battery. The thickness of the M layer is more preferably 3.0 μm or less. Furthermore, when the M layer is present on both sides of the current collector sheet, it is even more preferable that the thickness of each M layer is 0.2 μm or more. Furthermore, when the M layer is present on both sides of the current collector sheet, it is even more preferable that the thickness of each M layer is 3.0 μm or less.

[0079] (3) Adhesion Strength of M Layer In the current collector sheet material of the present invention, the adhesion strength between the layer containing the organic resin A and the M layer is preferably 1 N / 15 mm or more. More preferably, it is 2 N / 15 mm or more, and even more preferably, it is 3 N / 15 mm or more. It is also preferably 5 N / 15 mm or less. A strength of 1 N / 15 mm or more is preferable from the viewpoint of preventing peeling of the M layer and short-circuiting of the battery when the current collector of the present invention is incorporated into a battery. It is also preferable from the viewpoint of improving the yield when a positive electrode active material or a negative electrode active material is coated and dried on the M layer to produce an electrode for a battery.

[0080] Preferred means for improving the adhesion strength include a method in which the organic resin A contains an organic resin having a polar group, or a method in which a metal layer having good affinity with the M layer is previously provided on the surface of the current collector sheet by sputtering or the like.

[0081] (4) Maximum Point Strength: The maximum point strength of the current collector sheet material of the present invention is preferably 200 MPa or less in at least one of the longitudinal and width directions within the plane of the sheet material. A maximum point strength of 200 MPa or more is preferable because, when the current collector sheet material of the present invention is incorporated as a current collector in an electric storage element, a slight impact during transportation of the electric storage element can prevent the current collector sheet material from reaching a maximum point, thereby preventing a decrease in performance as an electric storage element. This is also preferable from the viewpoint of improving yield when a positive electrode active material or a negative electrode active material is coated and dried on the M layer to produce a battery electrode. A more preferable range for the maximum point strength in at least one of the longitudinal and width directions within the plane of the sheet material is 250 MPa or more in at least one direction within the plane, and even more preferably 300 MPa or more in at least one direction within the plane.

[0082] With respect to the maximum point strength of the current collector sheet of the present invention, when the unwinding direction of the current collector sheet is defined as the longitudinal direction and the direction rotated 90° in-plane from the longitudinal direction is defined as the width direction of the current collector sheet, it is more preferable that the maximum point strength in at least one of the longitudinal direction and the width direction satisfies the above-mentioned preferred range. It is even more preferable that the maximum point strength in both the longitudinal direction and the width direction satisfies the above-mentioned preferred range.

[0083] The CV measurement is as described below.

[0084] When the current collector sheet of the present invention has an M layer on both surfaces, a copper metal layer is formed on one surface of the current collector sheet by sputtering, and then the sheet is punched out into a circle with a diameter of 16 mm. The copper metal layer, a polyethylene separator with a diameter of 18 mm, a metallic lithium foil with a diameter of 16.1 mm, and two stainless steel plates (made of SUS304) are arranged in this order, and the electrolyte is sealed inside to prepare a 2032-type coin cell.

[0085] When the sheet material for current collector of the present invention has an M layer on one surface thereof, a copper metal layer is formed by sputtering on the surface not having the M layer, and then the evaluation is carried out in the same manner.

[0086] The above-mentioned potential sweep operation is performed to evaluate the maximum reduction current peak intensity. When the M layer is present on both surfaces of the current collector sheet of the present invention, the above-mentioned coin cell preparation and potential sweep operation are performed on each of the surfaces to evaluate the reduction current peaks, and the maximum value thereof is used.

[0087] In this CV measurement, the area of ​​the sample (2.01 cm ) observed during potential sweep with the redox potential of lithium metal set as the reference 0 V was ２ ) the maximum reduction current peak intensity normalized by 0.050 mA / cm ２ or less indicates that no current resulting from an oxidation-reduction reaction is observed at the interface between the current collector sheet material and the M layer. When the observed current value is a positive value, it indicates that an oxidation reaction has occurred at the interface between the current collector sheet material and the M layer, and when the current value is a negative value, it indicates that a reduction reaction has occurred at the interface between the current collector sheet material and the M layer.

[0088] In particular, the minimum observed current value is −0.050 mA / cm ２ 0.000mA / cm or more ２ When the maximum reduction current peak intensity is less than 0.000 mA / cm, it indicates that reductive decomposition is unlikely to occur at the interface between the M layer and the current collector sheet, even when the M layer laminated on the current collector sheet undergoes an oxidation reaction due to a potential sweep operation and serves as a negative electrode in a coin cell. A more preferable range of the maximum reduction current peak intensity is 0.000 mA / cm. ２ 0.010mA / cm or more ２ The minimum current value is -0.010 mA / cm ２ 0.000mA / cm or more ２ The most preferred range of the maximum reduction current peak intensity is less than 0.000 mA / cm ２ 0.006mA / cm or more ２ The minimum current value is −0.006 mA / cm ２ 0.000mA / cm or more ２ The current collector sheet of the present invention has two surfaces, and it is preferable that the maximum reduction current peak intensity in the above-mentioned CV measurement is less than 0.000 mA / cm on at least one surface. ２ 0.050mA / cm or more２ The maximum reduction current peak intensity in CV measurement on both surfaces is 0.000 mA / cm ２ 0.050mA / cm or more ２ More preferably, it is:

[0089] It is generally known that when polyester is used as the substrate of a current collector sheet, the ester bonds connecting the molecular chains of the polyester react with water molecules or hydrogen ions, causing the bonds to be broken and decomposed, i.e., a hydrolysis reaction.

[0090] For this reason, although the reaction pathway of the current collector sheet when voltage is applied is unclear, it is believed that trace amounts of water molecules remaining in the current collector sheet and hydrogen ions formed by ionization of hydrogen atoms present in carboxyl groups at the ends of polyester molecular chains may cause ester bond cleavage decomposition reactions similar to hydrolysis. It is also possible that lithium ions from the electrolyte solution penetrate into the current collector sheet and then coordinate, inducing ester bond cleavage. Therefore, it is believed that by laminating a layer containing organic resin A on the substrate, it is possible to suppress the penetration of the electrolyte solution and thereby suppress ester bond cleavage even when the substrate is a polyester film.

[0091] [Electricity storage element] The electric storage element of the present invention comprises an electrode assembly including a positive electrode and a negative electrode. It may contain an electrolytic solution, in which case it preferably contains a separator interposed between the positive electrode and the negative electrode. An electric storage element made of a solid electrolyte that does not contain an electrolytic solution is also a preferred example. It may also comprise a battery case that houses the electrode assembly.

[0092] Such an electric storage element includes, for example, a primary battery, a secondary battery, an electric double layer capacitor, an aluminum electrolytic capacitor, etc., but it refers to the secondary battery of the present invention.

[0093] Examples of secondary batteries include lithium secondary batteries, lead storage batteries, nickel-cadmium batteries, nickel-metal hydride batteries, nickel-iron storage batteries, silver oxide-zinc storage batteries, manganese dioxide-lithium secondary batteries, lithium cobalt oxide-carbonate secondary batteries, and vanadium-lithium secondary batteries.

[0094] Among these, secondary batteries are preferred because they can be used for a long period of time, and lithium secondary batteries are more preferred because they achieve high energy density by using organic solvents.

[0095] Examples of battery cases that can be used include aluminum cases, iron cases with nickel-plated interiors, and cases made of aluminum laminate film. Examples of battery case shapes include pouch-type, cylindrical, rectangular, and coin-type. Among these, pouch-type cases are preferred because they can achieve high energy density and can be freely designed into different shapes at low cost.

[0096] The positive electrode is formed by laminating a positive electrode material, which is made of an active material, a binder resin, and a conductive additive, on a current collector. ２ , LiNiO ２ , Li(NiCoMn)O ２ Lithium-containing transition metal oxides having a layered structure, such as LiMn ２ O ４ Spinel-type manganese oxides such as LiFePO ４ Examples of the binder resin include iron-based compounds such as fluorine-containing resin, acrylic resin, and styrene-butadiene resin. Examples of the conductive additive include carbon materials such as carbon black and graphite. Metal foil is suitable for the current collector, and aluminum foil is often used in particular.

[0097] The negative electrode is a negative electrode material made of an active material and a binder resin laminated on a current collector. Examples of the active material include carbon materials such as artificial graphite, natural graphite, hard carbon, and soft carbon, lithium alloy materials such as tin and silicon, metal materials such as lithium, and lithium titanate (Li ４ Ti ５ O １２ ) and the like. Examples of binder resins include fluorine-containing resins, acrylic resins, and styrene-butadiene resins. Metal foils are suitable as current collectors, and copper foils are often used in particular, but it is particularly preferable to use the current collector of the present invention.

[0098] When the energy storage element of the present invention contains an electrolytic solution, the electrolytic solution serves as a place for ions to move between a positive electrode and a negative electrode in an electrochemical element such as a secondary battery, and it is preferable that the electrolyte be dissolved in an organic solvent.

[0099] The electrolyte is LiPF ６ , LiBF ４ , and LiClO ４ However, from the viewpoint of solubility in organic solvents and ionic conductivity, LiPF ６ is preferably used.

[0100] Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate. Two or more of these organic solvents may be mixed and used.

[0101] An example of a method for producing a lithium secondary battery, which is preferably used among the energy storage elements, will be described below.

[0102] A lithium secondary battery is fabricated by first dispersing an active material and a conductive additive in a binder resin solution to prepare an electrode coating solution, then applying the coating solution to a current collector and drying the solvent to obtain a positive electrode and a negative electrode. The thickness of the coating film after drying is preferably 50 μm to 500 μm. Furthermore, it is preferable to apply pressure to the active material layer formed on the current collector, preferably by a roll press method or the like, to densify the active material layer and thin the current collector.

[0103] A lithium secondary battery separator is placed between the obtained positive electrode and negative electrode so as to be in contact with the active material layer of each electrode, and the resulting battery is enclosed in an exterior material such as an aluminum laminate film. After injecting an electrolyte, a negative electrode lead and a safety valve are installed, and the exterior material is sealed.

[0104] The lithium secondary battery element thus obtained has high adhesion to the electrodes, has excellent battery characteristics, and can be produced at low cost.

[0105] [Secondary Battery] The energy storage elements produced by the above-described method or the like may be used as a secondary battery by connecting multiple energy storage elements in series to meet the intended use of the energy storage elements and the required battery capacity. In such cases, it is preferable to provide a secondary battery equipped with voltage management, temperature management, and safety devices. A preferred example of a secondary battery is one in which the energy storage elements are connected to each other with tab leads (current extraction wires) and housed in a resin or metal module case.

[0106] [Electric Vehicles] Secondary batteries produced by the above-described methods and other methods have excellent battery characteristics and durability. When the secondary battery contains a polyester film with a lower specific gravity than metal, it is lightweight and has improved weight-weight energy density, making it a preferred form for use in electric vehicles. An electric vehicle is a vehicle in which some or all of the driving energy required for running is supplied from a secondary battery. Examples of electric vehicles include BEVs (Battery Electric Vehicles) equipped only with secondary battery batteries, HEVs (Hybrid Electric Vehicles) equipped with both fossil fuels such as gasoline and secondary battery batteries, and PHEVs (Plug-in Hybrid Electric Vehicles). The secondary battery of the present invention can be suitably used in any of these applications.

[0107] [Electric Air Vehicle] The secondary battery produced by the above-described method or the like has excellent battery characteristics and durability. When the secondary battery contains a polyester film with a lower specific gravity than metal, it is lightweight and has improved weight-weight energy density, making it a preferred form for use in an electric air vehicle. An electric air vehicle is one in which some or all of the driving energy required during flight is supplied from a secondary battery. Specific examples include electric aircraft such as drones, stratospheric platform aircraft (HAPS), air metro systems, and air taxis. The secondary battery of the present invention can be suitably used in any of these applications.

[0108] [Various Evaluation Methods] (1) Thickness of Substrate: The layer containing organic resin A was removed from the current collector sheet using water and an organic solvent such as alcohol to obtain a substrate alone. Then, the thickness of a sample cut to 100 mm x 100 mm was measured using a contact thickness meter (a Litematic manufactured by Mitutoyo Corporation, contact pressure 0.01 N, 10.5 mm diameter probe). The above measurement was performed on five samples, and the measured values ​​were averaged.

[0109] (2) Water Vapor Permeability The water vapor permeability was measured in an atmosphere of 40°C temperature and 90% RH by the calcium corrosion method described in Japanese Patent No. 4407466. Two samples were used for measuring the water vapor permeability, and the measurement was carried out five times for each sample. The average of the 10 measurements was taken as the water vapor permeability (g / (m ２ ・Sun)

[0110] (3) Thickness of Layer Containing Organic Resin A A current collector sheet material was cut into a size of 100 mm x 100 mm, and a cross section of the sample was cut out using a microtome at the center of the sample. The cross section was observed at a magnification of 10,000 times using a field emission scanning electron microscope (S-800 manufactured by Hitachi, Ltd., accelerating voltage 26 kV), and the distance from the interface with the substrate to the highest point on the surface was measured. In the case of a single-sided sample, only one side was measured, and in the case of a double-sided sample, both sides were measured, and the total was taken as the thickness of the layer containing organic resin A. The above measurement was performed on five samples, and the measured values ​​were averaged.

[0111] (4) Water Contact Angle: A layer containing organic resin A is removed from the current collector sheet using water and an organic solvent such as alcohol to obtain a substrate. Then, within the range of a sample cut to 50 mm x 50 mm, the contact angle was measured by the sessile drop method using a contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DMo-501 type", control box "DMC-2", control and analysis software "FAMAS (version 5.0.30)") at 23 ° C and 50% RH. The amount of distilled water dropped was 2 μL, and the water contact angle was calculated using the θ / 2 method from the image 5 seconds after the drop. The above measurement was performed on five samples, and the measured values ​​were averaged.

[0112] (5) Maximum Point Strength: A rectangular sample 150 mm long and 10 mm wide was cut out from the current collector sheet, with the unwinding direction of the roll being the longitudinal direction of the current collector sheet, and the long side being in the longitudinal direction. According to the following method specified in ASTM-D882, an Instron-type tensile tester (AMF / RTA-100 manufactured by Orientec Co., Ltd.) was used to set a 10 mm wide sample so that the chuck length was 50 mm, and a tensile test was performed at a tensile speed of 300 mm / min, and the strength at the time of sample break (maximum point strength) was read. Five measurements were taken, and the average value was taken as the maximum point strength in the longitudinal direction.

[0113] In the same manner as in the measurement in the longitudinal direction, the direction rotated 90° in-plane from the longitudinal direction of the current collector sheet was defined as the width direction, and a rectangular sample 150 mm long and 10 mm wide was cut out so that the long side was in the width direction, and the maximum point strength was measured. The measurement was performed five times, and the average value of the measurements was defined as the maximum point strength in the width direction.

[0114] When the longitudinal and width directions of the current collector sheet material are unknown, the maximum point strength is measured in a total of four directions: a specific direction and directions rotated at 45°, 90°, and 135° in-plane from the specific direction. The maximum value of the maximum point elongation and maximum point strength obtained in the four directions is defined as the maximum point strength of the current collector sheet material whose longitudinal and width directions are unknown.

[0115] (6) Adhesion strength, interfacial peel strength: A current collector sheet was cut into a rectangular shape measuring 15 mm in width and 80 mm in length. Cellophane tape No. 29 (15 mm wide) manufactured by Nitto was attached to the M layer of the cut sample as a peeling tape, and the tape was pressed against the M layer using a 2 kg rubber roller. The sample was then conditioned at 23°C and 65% RH for one day.

[0116] The humidity-conditioned sample was subjected to a 180° peel test under the following conditions using a Kyowa Interface Science Co., Ltd. adhesive / film peeling analyzer (VPA-2). The side of the humidity-conditioned sample opposite the tape-attached side was fixed to the device, and the edge of the peeling tape was fixed to the device's load cell for measurement. (Peel test conditions) Peel angle: 180° Tape width: 15 mm Peel rate: 25 mm / min Initial peel force: 0 N Measurement distance: 50 mm The average peel force (N / 15 mm) was calculated for the 15 mm to 35 mm travel distance section of the obtained peel force waveform. Peel force measurements were performed on three different samples, and the peeled surfaces were confirmed. The average value was used as the adhesion strength between the M layer and the current collector sheet. When visual observation revealed interfacial peeling, particularly between the M layer and the layer containing organic resin A, the adhesion strength was recorded as the interfacial peel strength.

[0117] (7) CV Measurement (i) Fabrication of 2032-Type Coin Cells A sample having a copper metal layer formed on the surface of a current collector sheet by sputtering was punched out into a circle with a diameter of 16 mm. A polyethylene separator with a diameter of 18 mm, a metallic lithium foil with a diameter of 16.1 mm, and two SUS plates were laminated in this order on the surface of the copper metal layer of the punched sample, and the following electrolyte solution was sealed inside to fabricate a 2032-type coin cell. The polyethylene separator used had a thickness of 4 μm to 20 μm and an air permeability of 500 seconds or less. (Electrolyte Solution Composition) Electrolyte: 1 mol / L lithium hexafluorophosphate (LiPF ６ Solvent: 1:1 (volume %) mixture of ethylene carbonate (EC) and diethylene carbonate (DEC) Mixing environment: Performed in a dry room with a dew point of -50°C or less.

[0118] (ii) CV Measurement Using the 2032-type coin cell obtained in the above (i), cyclic voltammetry measurement is carried out using a VSP manufactured by Biologic under the following conditions. The current value (mA) observed during the potential sweep operation is calculated based on the sample area (2.01 cm) used. ２ ) to obtain the current value per unit area (mA / cm ２(Measurement conditions) Test temperature: 25°C Pre-reduction treatment: The oxide film on the copper was reduced by holding at a voltage of 0.01 V for 100 hours. Potential sweep range: 0.01-2.0 V (vs. Li ＋ / Li) Sweep rate: 0.1 mV / s Number of cycles: 10 cycles.

[0119] (iii) Maximum reduction current peak intensity per unit area: The current value per unit area (mA / cm) obtained in the above (ii) ２ ), the one with the largest absolute value is defined as the maximum reduction current peak intensity (mA / cm ２ ) was calculated.

[0120] (8) Battery Characteristics (i) Formation of Negative Electrode Current Collector A negative electrode current collector was prepared by providing a copper metal layer on both sides of a current collector sheet by vacuum deposition processing.

[0121] Specifically, a roll of the current collector sheet material was placed in a roll-type vacuum deposition apparatus (EWC-060 manufactured by ULVAC), and a copper ingot was heated by induction heating deposition using a carbon crucible, thereby forming a copper layer by vacuum deposition. Vacuum deposition was performed while adjusting the conveyance speed and output conditions so that the copper layer would have a thickness of 1 μm. Next, the roll of the current collector sheet material with the copper layer provided on one side was placed again in the roll-type vacuum deposition apparatus (EWC-060 manufactured by ULVAC), and a copper layer was formed by vacuum deposition on the surface of the current collector sheet material opposite the surface on which the copper layer was provided, by heating the copper ingot by induction heating deposition using a carbon crucible. Vacuum deposition was performed while adjusting the conveyance speed and output conditions so that the copper layer would have a thickness of 1 μm.

[0122] (ii) Preparation of Positive Electrode 94 parts by mass of nickel-cobalt-manganese composite oxide NMC (Ni:Co:Mn = 6:2:2 (element ratio)) as the positive electrode active material, 3 parts by mass of carbon black as a conductive material, and 3 parts by mass of polyvinylidene fluoride (PVDF) as a resin binder were mixed in a ratio of 1 / 4, and these were dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was uniformly applied to one side of a 20 μm thick aluminum foil that served as a positive electrode current collector, dried, and then compression molded using a roll press. At this time, the amount of positive electrode mixture applied to one side was 170 g / m ２ , density is 3.0 g / cm ３ After fabricating the cathode ray tube, it was cut into a size of 28 mm × 44 mm. One side of the tube was 28 mm × 5 mm, which was an uncoated portion for connecting a tab, and the coated portion of the tube was 28 mm × 39 mm. An aluminum positive electrode tab was then joined to the uncoated portion by ultrasonic welding.

[0123] (iii) Preparation of Negative Electrode and Its Yield: 97 parts by mass of artificial graphite as the negative electrode active material, 1 part by mass of carboxymethyl cellulose and 2 parts by mass of styrene-butadiene copolymer latex as the resin binder were mixed and dispersed in purified water to prepare a slurry. This slurry was uniformly applied to one side of a 10 μm thick copper foil serving as a negative electrode current collector, or the negative electrode current collector, and dried at 80°C, followed by compression molding using a roll press. At this time, the amount of negative electrode mixture applied to one side was 100 g / m. ２ , density is 1.5 g / cm ３ After fabricating the negative electrode, a 30 mm × 46 mm piece was cut out. One side of the 30 mm × 5 mm piece was an uncoated portion for connecting a tab, and the coated portion of the slurry was 30 mm × 41 mm. A copper negative electrode tab was then joined to the uncoated portion by ultrasonic welding.

[0124] The yield during coating and drying of the slurry consisting of the negative electrode active material and resin binder was evaluated as follows: Excellent: Wrinkles or peeling of the layer containing metal and / or metal-based compounds (M layer) occurred on the negative electrode current collector in two or fewer out of ten sheets. Good: Wrinkles or peeling of the layer containing metal and / or metal-based compounds (M layer) occurred on the negative electrode current collector in three to five out of ten sheets. Fair: Wrinkles or peeling of the layer containing metal and / or metal-based compounds (M layer) occurred on the negative electrode current collector in six to eight out of ten sheets. Poor: Wrinkles or peeling of the layer containing metal and / or metal-based compounds (M layer) occurred on the negative electrode current collector in nine or more out of ten sheets.

[0125] (iv) Polyolefin microporous membrane The method for producing a polyolefin microporous membrane is not particularly limited, and any known method for producing a polyolefin microporous membrane can be used. In this example, a polyolefin microporous membrane was produced with reference to the method described in Japanese Patent No. 4,460,028. The produced microporous membrane was cut into a size of 38 mm x 49 mm.

[0126] (v) Electrolyte: A mixed solvent of ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate = 3:3:4 (volume ratio) containing LiPF as a solute. ６ was dissolved to a concentration of 1.0 mol / L. One part by mass of vinylene carbonate was added to 100 parts by mass of this solution to prepare an electrolyte solution.

[0127] (vi) Preparation of Evaluation Battery The above positive electrode and negative electrode were stacked in the order of positive electrode / polyolefin microporous membrane / negative electrode to prepare a laminated electrode body. This laminated electrode body was sandwiched between aluminum laminate films and sealed, leaving a partial opening. After drying in a vacuum oven at 60°C for 6 hours, the above nonaqueous electrolyte solution was poured into the laminated electrode body and sealed with a vacuum sealer. After initial charge / discharge and final charge / discharge, a laminated battery was prepared.

[0128] (vii) Discharge Load Characteristics The discharge load characteristics were tested according to the following procedure and evaluated in terms of discharge capacity retention. Using the above laminated battery, the discharge capacity when discharged at 0.5 C and 5 C at 35°C was measured, and the discharge capacity retention was calculated by (discharge capacity at 5 C) / (discharge capacity at 0.5 C) × 100. The charge conditions were a constant current charge of 0.5 C and 4.2 V, and the discharge conditions were a constant current discharge of 3.0 V. Five laminated batteries were produced, and the results with the highest and lowest discharge capacity retention rates were removed. The average of the three measurement results was used as the capacity retention rate. A discharge capacity retention rate of less than 40% was rated as "unacceptable," 45% to less than 50% as "acceptable," 50% to less than 55% as "good," and 55% or more as "excellent."

[0129] (viii) Life Characteristics: The life characteristics were tested according to the following procedure and evaluated by the discharge capacity retention rate. <1st to 300th Cycles> One cycle consisted of charge and discharge, with the charge condition being a constant current charge of 1C and 4.2V, and the discharge condition being a constant current discharge of 1C and 3.9V. The charge and discharge cycle was repeated 300 times at 35°C. <Calculation of Discharge Capacity Retention Rate> The discharge capacity retention rate was calculated by (discharge capacity at the 300th cycle) / (discharge capacity at the 1st cycle) × 100. Five laminated batteries were produced, and the results with the highest and lowest discharge capacity retention rates were removed. The average of the three measurement results was taken as the capacity retention rate. A discharge capacity retention rate of less than 50% was rated as poor life characteristics, 50% to less than 60% as fair life characteristics, 60% to less than 70% as good life characteristics, 70% to less than 80% as excellent life characteristics, and 80% or more as excellent life characteristics.

[0130] (9) Cross-section evaluation (i) Domain structure analysis: A cross section of the current collector sheet of the present invention was cut out with a microtome in a direction parallel to the direction perpendicular to the main orientation of the resin layer. After subjecting the cross section to a sputtering treatment using platinum-palladium, a cross-sectional image (image dimensions: vertical 18.5 μm × horizontal 25 μm) was observed at a magnification of 5000 times using a scanning electron microscope (JEOL Ltd., JSM-6700). The size and aspect ratio of the domain structure were determined by the following analysis using image analysis software (Planetron Corporation, Image-Pro Plus Version 4.0 for “Windows” (registered trademark)).

[0131] (Image analysis conditions) After the cross-sectional image is captured using software, 8-bit grayscale processing is performed by executing the "Gray Scale 8" command under the "Conversion" menu. Next, the "Spatial Calibration" command under the "Calibration" menu is used to set the width of the captured image to 25 μm. After that, binarization processing is performed using the "Binarization" command under the "Processing" menu.

[0132] (Binarization processing conditions) - Select "3x3" - Threshold setting: Press the auto-detect button located to the right of the numerical input field once and use the obtained value - Preview conditions: The background is displayed in white, and detected particles are displayed in black After performing binarization processing, open the "Count / Size" command screen under the "Measurement" menu, set the following particle detection conditions and particle analysis conditions, and run "Count" to analyze the detected particles.

[0133] (Domain detection conditions) ・Brightness range selection: Select "Automatically extract dark objects" ・Check "Measure objects" (Object extraction option conditions) ・4-connected / 8-connected: Select 4-connected ・Check only "Pre-select" and "Fill holes" ・Smoothing: 0 ・Exclude on boundaries: Select "All boundaries".

[0134] (Method for Measuring the Thickness Direction Length of Domains) A square measuring 1 μm square is drawn on the obtained image with a pair of sides parallel to the thickness direction, and the domain structure passing through a pair of sides of the square in the thickness direction is identified. Then, a line passing through the intersection of the diagonals of the square and parallel to the thickness direction is drawn, and the thickness direction length of each identified domain is measured on that line. The thickness direction length of the domains is measured by drawing lines at the top and bottom of all domain structures passing through a pair of sides parallel to the thickness direction of the square, passing through the intersection of the diagonals of the square and parallel to the thickness direction, and measuring the distance between them. The average value of the thickness direction lengths of the domains thus obtained is then calculated. The position of the squares is further changed arbitrarily, and similar measurements are performed a total of 10 times (at this time, the squares are set so that all 10 do not overlap). The average value of the thickness direction lengths of the domains measured for each measurement is then calculated, and the resulting value is the average value of the thickness direction length of the domains (unit: nm).

[0135] (Method of Measuring Aspect Ratio of Domain) For the image obtained in the above item (i), the aspect ratio of the domain structure in the image obtained is determined using the aspect ratio (aspect value) in the "Count / Size" command screen.

[0136] A count histogram is created by plotting the obtained aspect ratios on the horizontal axis in 0.5 intervals for the intervals of 1 to 10 and in 10 intervals for the intervals of 10 or more for the five different fields of view. If a maximum value exists in the region of the number histogram where the aspect ratio is 1 to less than 5, the minimum value in the interval showing that maximum value (for example, if the maximum value is in the region of 2 to 2.5, 2 is used as the maximum value) is taken as the aspect ratio of the domain (domain 1) existing in the region where the aspect ratio is 1 to less than 5. If multiple maximum peaks exist in the region where the aspect ratio is 1 to less than 5, the weighted average of those vertical axis values ​​is taken as the aspect ratio of the domain (domain 1) existing in the region where the aspect ratio is 1 to less than 5.

[0137] Similarly, if a maximum value exists in a region where the aspect ratio is 5 or more, that maximum value is taken as the aspect ratio of the domain (domain 2) existing in the region where the aspect ratio is 5 or more. If multiple maximum peaks exist in the region where the aspect ratio is 5 or more, the weighted average of those vertical axis values ​​is taken as the aspect ratio of the domain (domain 2) existing in the region where the aspect ratio is 5 or more.

[0138] For each of the five different visual fields, the aspect ratios of the domains (domain 1) present in the region with an aspect ratio of 1 or more and less than 5, and the domains (domain 2) present in the region with an aspect ratio of 5 or more, are determined, and the average value of the five visual fields in each region is taken as the aspect ratio of domain 1 and domain 2 in the resin layer.

[0139] The present invention will be described below with reference to examples, but the present invention is not necessarily limited to these examples.

[0140] Example 1 [Production of Base Layer] 1.9 moles of ethylene glycol were added per mole of dimethyl terephthalate (DMT), and 0.05 parts by mass of magnesium acetate tetrahydrate and 0.015 parts by mass of phosphoric acid were added per 100 parts by mass of dimethyl terephthalate (DMT) to carry out thermal transesterification. Subsequently, 0.025 parts by mass of antimony trioxide was added, and the mixture was heated to an elevated temperature and subjected to polycondensation under highly reduced pressure to obtain polyethylene terephthalate resin pellets. The glass transition temperature was 78°C, the melting peak temperature was 255°C, the intrinsic viscosity was 0.70 dl / g, and the moisture content was 4,300 ppm by mass.

[0141] Next, after drying under reduced pressure at 180 ° C. for 2 hours and 30 minutes, the film was fed to an extruder, melt-extruded, and filtered through a filter. The film was then wrapped around a cooled cast roll maintained at 25 ° C. using an electrostatic casting method via a T-die and cooled to solidify, resulting in an unstretched substrate. This unstretched substrate was then guided to a group of stretching rolls heated to 60 ° C. to 120 ° C. in the longitudinal direction according to the film-forming conditions in the table, and stretched 3.0 times by a stretching operation. Thereafter, the uniaxially stretched film was guided to a tenter and preheated to 90 ° C., and then stretched 3.0 times in the width direction at a temperature of 100 ° C. to 130 ° C., and then heat-treated at 230 ° C. at a constant length and subjected to a 4% relaxation treatment in the width direction to obtain a biaxially oriented polyethylene terephthalate (PET) substrate having a thickness of 5 μm.

[0142] [Formation of Layer Containing Organic Resin A] A water dispersion of styrene butadiene rubber (SBR) (component (1) in Table 1) was used as the organic resin A, and an acrylic emulsion binder was used as the binder. They were dispersed in water so that the SBR was 95% by volume, the acrylic emulsion binder was 5% by volume, and the solids concentration of the coating liquid was 20% by mass, and mixed with a stirrer. The obtained coating liquid was applied to both sides of the substrate layer using a #10 wire bar, and dried in a hot air oven (drying temperature set at 60°C) for 1 minute, and the contained solvent was evaporated to form a layer containing organic resin A.

[0143] [Formation of Layer (M Layer) Containing Metal and / or Metal-Based Compound] Metal layers (M layers) were formed by vacuum deposition on both surfaces of the obtained substrate layer / layer containing organic resin A so that the thicknesses of the metal layers were as shown in the table, and the metal species were as shown in Table 1, thereby producing current collector sheets. The results of the above evaluations of these sheets are shown in Tables 1 and 2.

[0144]

[0145]

[0146] Example 2 A current collector sheet was produced and evaluated in the same manner as in Example 1, except that polyethylene naphthalate (PEN) resin pellets were produced as follows for the substrate layer.

[0147] [Production of Base Layer] PEN resin pellets were obtained in the same manner as in Example 1, except that 1.9 mol of ethylene glycol was added per 1 mol of 2,6-dimethylnaphthalate (2,6DMN). The PEN resin obtained by adjusting the polymerization time had a glass transition temperature of 115°C, a melting peak temperature of 265°C, an intrinsic viscosity of 0.86 dl / g, and a water content of 2200 ppm by mass.

[0148] (Example 3) A current collector sheet was prepared in the same manner as in Example 1, except that a #5 wire bar was used to form the layer containing organic resin A to a thickness as shown in Table 1, and evaluation was similarly performed.

[0149] Example 4 A current collector sheet was prepared in the same manner as in Example 1, except that the substrate layer was prepared as follows, and the evaluation was similarly carried out.

[0150] [Production of the base layer] Polypropylene (PP) was fed into a single-screw melt extruder, melt-extruded at 240 ° C, and after removing foreign matter with a 60 μm cut-off sintered filter, it was discharged onto a casting drum whose surface temperature was controlled at 30 ° C and adhered to the casting drum with an air knife. The sheet on the non-cooled drum surface on the casting drum was then cooled by spraying compressed air at a temperature of 30 ° C and a pressure of 0.3 MPa to obtain an unstretched sheet. The sheet was then preheated to 140 ° C using a ceramic roll and stretched 4.0 times in the longitudinal direction of the film between rolls at 140 ° C with a peripheral speed difference. The film was then introduced into a tenter-type stretching machine with its edges clamped with clips, preheated at 170°C for 3 seconds, stretched 8.0 times at 165°C, and heat-treated at 150°C while providing 10% relaxation in the width direction. After a cooling step at 100°C, the film was introduced to the outside of the tenter, and the clips on the film edges were released to obtain a substrate film with a thickness of 8 μm.

[0151] Example 5 A current collector sheet was prepared in the same manner as in Example 5, except that polyethylene was used instead of polypropylene, and the evaluation was similarly carried out.

[0152] (Example 6) A current collector sheet was prepared in the same manner as in Example 1, except that carboxymethyl cellulose (CMC) was used as the organic resin A to form a layer containing the organic resin A as shown below, and the current collector sheet was evaluated in the same manner.

[0153] [Formation of Layer Containing Organic Resin A] An aqueous dispersion of carboxymethyl cellulose (CMC) was used as the organic resin A, and an acrylic emulsion binder was used as the binder. They were dispersed in water so that the CMC was 95% by volume, the acrylic emulsion binder was 5% by volume, and the solids concentration of the coating liquid was 5% by mass, and mixed with a stirrer. The obtained coating liquid was applied to both sides of the substrate layer using a #5 wire bar, and dried in a hot air oven (drying temperature set at 60°C) for 1 minute, and the contained solvent was volatilized to form a layer containing organic resin A.

[0154] Example 7 A current collector sheet was prepared in the same manner as in Example 7, except that the wire bar used in forming the layer containing organic resin A was #18, and the evaluation was similarly performed.

[0155] Example 8 A current collector sheet was prepared in the same manner as in Example 8, except that carboxymethyl cellulose sodium (CMC-Na) was used as the organic resin A, and the current collector sheet was evaluated in the same manner.

[0156] (Example 9) A current collector sheet was prepared in the same manner as in Example 1, except that polypropylene (PP) was used as organic resin A and a layer containing organic resin A was formed as shown below, and evaluation was performed in the same manner.

[0157] [Formation of Layer Containing Organic Resin A] A water dispersion of polypropylene (PP) was used as the organic resin A, and an acrylic emulsion binder was used as the binder. They were dispersed in water to a solids concentration of 20 mass% (PP 95% by volume, acrylic emulsion binder 5% by volume), and mixed with a stirrer. The obtained coating liquid was coated on both sides of the substrate layer using a #10 wire bar, and dried in a hot air oven (drying temperature set at 60°C) for 1 minute, and the contained solvent was evaporated to form a layer containing organic resin A.

[0158] Example 10 A current collector sheet was prepared in the same manner as in Example 1, except that polyethylene (PE) was used as the organic resin A, and the current collector sheet was evaluated in the same manner.

[0159] Example 11 A current collector sheet was prepared in the same manner as in Example 1, except that propylene carbonate was used as the organic resin A, and the resulting sheet was evaluated in the same manner.

[0160] Example 12 A current collector sheet was prepared in the same manner as in Example 1, except that polyvinylidene fluoride was used as the organic resin A, and the resulting sheet was evaluated in the same manner.

[0161] Example 13 A current collector sheet was prepared in the same manner as in Example 1, except that (meth)acrylate was used as the organic resin A, and the resulting sheet was evaluated in the same manner.

[0162] Example 14 A current collector sheet was prepared in the same manner as in Example 1, except that polytetrafluoroethylene was used as the organic resin A, and the resulting sheet was evaluated in the same manner.

[0163] Example 15 A current collector sheet was prepared in the same manner as in Example 1, except that the base layer was stretched 4.5 times in the width direction, and was evaluated in the same manner.

[0164] Example 16 A current collector sheet was prepared in the same manner as in Example 1, except that the base layer was stretched 2.0 times in the width direction, and was evaluated in the same manner.

[0165] Example 17 A current collector sheet was prepared in the same manner as in Example 1, except that a styrene butadiene rubber (SBR) (component (1) in Table 1) and carboxymethyl cellulose (component (2) in Table 1) were used in combination as organic resin A, and a layer containing organic resin A was formed as shown below, and evaluation was similarly performed.

[0166] [Formation of Layer Containing Organic Resin A] As the organic resin A, an aqueous dispersion of styrene butadiene rubber (SBR) and an aqueous dispersion of carboxymethyl cellulose (CMC) were used, and as the binder, an acrylic emulsion binder was used, and the SBR was 48% by volume, the CMC was 47% by volume, and the acrylic emulsion binder was 5% by volume. These were dispersed in water so that the solid content concentration of the coating liquid was 20% by mass, and mixed with a stirrer. The obtained coating liquid was coated on both sides of the substrate layer using a #10 wire bar, and dried in a hot air oven (drying temperature set at 60°C) for 1 minute, and the contained solvent was evaporated to form a layer containing organic resin A.

[0167] Example 18 A current collector sheet was prepared in the same manner as in Example 1, except that the substrate layer was prepared as follows, and the evaluation was similarly carried out.

[0168] [Production of Base Layer] First, thermoplastic resin 1 and thermoplastic resin 2 were produced by the following method.

[0169] [Production of Thermoplastic Resin 1] To 1 mole of a dicarboxylic acid component consisting of 0.90 moles of dimethyl terephthalate (DMT) and 0.10 moles of dimethyl isophthalate, 1.9 moles of cyclohexanedimethanol were added, and 0.05 part by mass of magnesium acetate tetrahydrate and 0.015 part by mass of phosphoric acid were added to 100 parts by mass of the dicarboxylic acid component to carry out thermal transesterification. Subsequently, 0.025 part by mass of antimony trioxide was added, and the mixture was heated to an elevated temperature and subjected to polycondensation under highly reduced pressure to obtain pellets of Thermoplastic Resin 1, a copolymerized polycyclohexadimethylene terephthalate resin substantially free of particles.

[0170] [Production of Thermoplastic Resin 2] 100 g of the solid titanium catalyst component, 131 mL of triethylaluminum, 37.3 ml of diethylaminotriethoxysilane, and 14.3 L of heptane were charged into a 20 L autoclave equipped with a stirrer, and 1000 g of propylene was charged while maintaining the internal temperature at 15 to 20°C. The reaction was carried out with stirring for 120 minutes. After polymerization was completed, the solid component was allowed to settle, and the supernatant was removed and washed twice with heptane. The resulting prepolymerized catalyst was resuspended in purified heptane to a solid catalyst component concentration of 1.0 g / L, yielding a catalyst slurry. Next, propylene was continuously fed at 40 kg / h, hydrogen at 222 NL / h, the catalyst slurry (solid catalyst component) at 0.42 g / h, triethylaluminum at 3.0 ml / h, and diethylaminotriethoxysilane at 1.1 ml / h into a jacketed tubular polymerization reactor with an internal volume of 58 L. Polymerization was carried out in a liquid-filled state with no gas phase present, yielding a slurry. The temperature of the tubular polymerization reactor was 70°C, and the pressure was 3.57 MPa / G. The resulting slurry was transferred to a 100 L vessel polymerization reactor equipped with a stirrer, where further polymerization was carried out. Propylene was fed at 15 kg / h to the polymerization reactor, and hydrogen was fed so that the hydrogen concentration in the gas phase was 8.5 mol%. Polymerization was carried out under conditions of a polymerization temperature of 69°C and a pressure of 3.39 MPa / G. The obtained slurry was transferred to a liquid transfer tube with an internal volume of 2.4 L, and the slurry was gasified and subjected to gas-solid separation. Thereafter, a polypropylene homopolymer powder was sent to a gas-phase polymerization reactor with an internal volume of 480 L and vacuum dried at 80°C to obtain pellets of thermoplastic resin 2, which was a polypropylene resin.

[0171] Then, 95 parts by weight of thermoplastic resin 1 and 5 parts by weight of thermoplastic resin 2 were dehumidified and dried for 5 hours, and then fed into a vented twin-screw extruder (L / D = 40, vent hole vacuum level of 200 Pa) equipped with a twin-screw, three-stage screw (kneading plasticization zone / Dalmage kneading zone / reverse-threaded Dalmage fine dispersion compatibilization zone) heated to 290 ° C. and melt-extruded for a residence time of 3 minutes to obtain blend chips A. This blend chip A was dried under reduced pressure at 180 ° C. for 2 hours and 30 minutes, fed into the extruder, melt-extruded, filtered, and then wrapped around a cooled cast roll maintained at 25 ° C. via a T-die using an electrostatic casting method, cooled, and solidified to obtain an unstretched film. This unstretched film was first heated to 105 ° C. with a preheated roll, and then stretched 4.1 times in the longitudinal direction at 80 ° C. according to the film-forming conditions in the table. The uniaxially stretched film was then introduced into a tenter and preheated to 90°C, after which it was stretched 4.1 times in the width direction at a temperature of 130°C, and then heat-treated at 230°C to perform a relaxation treatment of 7% in the width direction, thereby obtaining a single-layer biaxially oriented resin film with a thickness of 8 μm.

[0172] (Example 19) A current collector sheet was prepared in the same manner as in Example 18, except that the proportions of the thermoplastic resins were 92 parts by mass of thermoplastic resin 1 and 8 parts by mass of thermoplastic resin 2, and the current collector sheet was evaluated in the same manner.

[0173] Example 20 A current collector sheet was prepared in the same manner as in Example 18, except that the proportion of the thermoplastic resin was 100 parts by mass of Thermoplastic Resin 1, and the current collector sheet was evaluated in the same manner.

[0174] Comparative Example 1 A current collector sheet was prepared in the same manner as in Example 1, except that the layer containing organic resin A was not formed, and the same evaluation was carried out.

[0175] Comparative Example 2 A current collector sheet was prepared in the same manner as in Example 2, except that the layer containing organic resin A was not formed, and the current collector sheet was evaluated in the same manner.

[0176] Comparative Example 3 A current collector sheet was prepared in the same manner as in Example 1, except that polyacrylonitrile was used as the organic resin A, and the resulting sheet was evaluated in the same manner.

[0177] [Formation of layer containing organic resin A] As organic resin A, an aqueous dispersion of polyacrylonitrile and an aqueous dispersion of carboxymethyl cellulose (CMC) were used, and as a binder, an acrylic emulsion binder was used. The polyacrylonitrile was 48% by volume, the CMC was 47% by volume, and the acrylic emulsion binder was 5% by volume. The solid content of the coating liquid was dispersed in water to be 20% by mass, and mixed with a stirrer. The obtained coating liquid was coated on both sides of the substrate layer using a #10 wire bar, and dried in a hot air oven (drying temperature set at 60 ° C.) for 1 minute, and the contained solvent was evaporated to form a layer containing organic resin A.

[0178] As can be seen from Tables 1 and 2, all of Examples 1 to 20 are sheet-like materials for current collectors that include a base layer, a layer containing organic resin A, and a layer containing a metal and / or metal-based compound (M layer) in this order, and the organic resin A is composed only of polymers with a LUMO of −0.5 eV or more, and have excellent yield in electrode production and battery characteristics (discharge load characteristics and life characteristics).

[0179] On the other hand, in Comparative Examples 1 and 2, the maximum reduction current peak intensity in CV is large and the battery characteristics are poor due to reductive decomposition, because the layer containing organic resin A is not included. In Comparative Example 3, the organic resin A is composed only of a polymer with a LUMO of less than −0.5 eV, so the maximum reduction current peak intensity in CV is large and the battery characteristics are poor due to reductive decomposition.

Claims

The current collector sheet comprises a substrate layer and layers containing an organic resin A on both sides of the substrate layer, the organic resin A being composed solely of a polymer having a LUMO of −0.5 eV or more. 　 A sheet-like material for a current collector, comprising: a base layer; and layers containing an organic resin A on both sides of the base layer, wherein the organic resin A contains at least one organic resin selected from the group consisting of styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylpyrrolidone, N-vinylpyrrolidone, (meth)acrylate, polyethylene, polypropylene, cyclic polyolefin copolymer, cyclic polyolefin, acid-modified polyolefin, polycarbonate, and propylene carbonate.

3. The current collector sheet according to claim 2, wherein the organic resin A comprises at least one organic resin selected from the group consisting of styrene-butadiene rubber, carboxymethyl cellulose, sodium carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride. 　 The current collector sheet according to claim 1 or 2, wherein at least one of the base layers contains two or more types of thermoplastic resins. 　 The current collector sheet according to claim 1 or 2, wherein the substrate layer contains a polyester resin.

3. The current collector sheet according to claim 1, wherein the base layer has at least one resin layer having a domain structure in a cross section taken along the direction perpendicular to the main orientation and the thickness direction, the domain structure having a thickness direction length of 1.0 μm or less and an aspect ratio of 5 or more.

3. The current collector sheet according to claim 1, wherein the layer containing the organic resin A has a water contact angle of 20° or more and 80° or less.

3. The current collector sheet according to claim 1, wherein the layer containing the organic resin A has a thickness of 0.1 μm or more and 4.0 μm or less.

3. The current collector sheet according to claim 1, wherein the thickness of the substrate layer is 1 μm or more and 30 μm or less.

3. The current collector sheet according to claim 1, wherein the sheet has a maximum strength of 200 MPa or more in at least one of the longitudinal direction and the width direction. 　 The water vapor permeability of the substrate layer at 40°C and 90% RH is 200 g / (m ２ 3. The current collector sheet material according to claim 1, wherein the temperature is 100°C or less. 　 A current collector having the current collector sheet material according to claim 1 or 2 and a layer (M layer) containing a metal and / or a metal-based compound, wherein the layer (M layer) containing the metal and / or a metal-based compound is in contact with a layer containing organic resin A.

13. The current collector according to claim 12, wherein the adhesion strength between the layer containing the organic resin A and the layer M is 1 N / 15 mm or more. 　 The maximum reduction current peak intensity in CV measurement (0.01 V to 2.0 V, 10 cycles) was 0.000 mA / cm ２ 0.050mA / cm or more ２ 13. The current collector of claim 12, wherein:

13. The negative electrode current collector according to claim 12, wherein at least one of the M layers in contact with the layer containing organic resin A has a layer containing elemental copper as a surface layer on at least one side, and the layer containing elemental copper is in contact with the layer containing organic resin A.

13. The positive electrode current collector according to claim 12, wherein at least one of the M layers in contact with the layer containing organic resin A has a layer containing aluminum element as a surface layer on at least one side, and the layer containing aluminum element is in contact with the layer containing organic resin A.

13. The current collector for a bipolar battery according to claim 12, wherein one of the M layers in contact with the layer containing organic resin A has a layer containing elemental copper as a surface layer on one side, and the layer containing elemental copper is in contact with the layer containing organic resin A, and the other M layer has a layer containing elemental aluminum as a surface layer on one side, and the layer containing elemental aluminum is in contact with the layer containing organic resin A. 　 An electric storage element comprising the current collector according to claim 12. 　 A secondary battery comprising the energy storage element according to claim 18. 　 An electric vehicle equipped with the secondary battery according to claim 19. 　 An electric flying object equipped with the secondary battery according to claim 19.

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