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WO2025033202A1 - Membrane microporeuse de polyoléfine, film séparateur pour dispositifs de stockage d'énergie l'utilisant, et dispositif de stockage d'énergie - Google Patents

Membrane microporeuse de polyoléfine, film séparateur pour dispositifs de stockage d'énergie l'utilisant, et dispositif de stockage d'énergie Download PDF

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Publication number
WO2025033202A1
WO2025033202A1 PCT/JP2024/026674 JP2024026674W WO2025033202A1 WO 2025033202 A1 WO2025033202 A1 WO 2025033202A1 JP 2024026674 W JP2024026674 W JP 2024026674W WO 2025033202 A1 WO2025033202 A1 WO 2025033202A1
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WO
WIPO (PCT)
Prior art keywords
polyolefin microporous
microporous membrane
layer
resin layer
film
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
PCT/JP2024/026674
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English (en)
Japanese (ja)
Inventor
秀悟 中川
昭夫 仁後
剛久 角田
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ube Maxell Kyoto Co Ltd
Ube Corp
Original Assignee
Ube Maxell Kyoto Co Ltd
Ube Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ube Maxell Kyoto Co Ltd, Ube Corp filed Critical Ube Maxell Kyoto Co Ltd
Publication of WO2025033202A1 publication Critical patent/WO2025033202A1/fr
Pending legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B27/00—Layered products comprising a layer of synthetic resin
    • B32B27/32—Layered products comprising a layer of synthetic resin comprising polyolefins
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B32—LAYERED PRODUCTS
    • B32B—LAYERED PRODUCTS, i.e. PRODUCTS BUILT-UP OF STRATA OF FLAT OR NON-FLAT, e.g. CELLULAR OR HONEYCOMB, FORM
    • B32B5/00—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts
    • B32B5/22—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed
    • B32B5/32—Layered products characterised by the non- homogeneity or physical structure, i.e. comprising a fibrous, filamentary, particulate or foam layer; Layered products characterised by having a layer differing constitutionally or physically in different parts characterised by the presence of two or more layers which are next to each other and are fibrous, filamentary, formed of particles or foamed at least two layers being foamed and next to each other
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • H01M50/491—Porosity
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a polyolefin microporous membrane and an electricity storage device.
  • electricity storage devices with high energy density, high electromotive force, and little self-discharge are becoming more common.
  • Examples of electricity storage devices include lithium-ion secondary batteries and lithium-ion capacitors.
  • a separator film is placed between the positive and negative electrodes to prevent them from coming into contact with each other and causing a short circuit.
  • a polyolefin microporous membrane is used for the separator film.
  • a separator film made of a polyolefin microporous membrane can block the pores in the porous membrane to prevent ions from flowing between the two electrodes, thereby increasing the electrical resistance. This stops the function of the electricity storage device, preventing the risk of fire or other dangers caused by an excessive rise in temperature.
  • the function of preventing the risk of fire or other dangers caused by an excessive rise in temperature is extremely important for separator films for electricity storage devices, and is generally called non-porous or shutdown (hereinafter, SD).
  • Patent Document 1 discloses a polyolefin microporous membrane that has a three-layer laminate separator film in a sandwich configuration with both outer layers being polypropylene and an inner layer being polyethylene, and is characterized by a thickness of 7.0 to 50 ⁇ m, a porosity of 30 to 70%, and a surface porosity of 10 to 30%.
  • Patent Document 1 describes air permeability, it does not describe low resistance performance related to liquid resistance.
  • the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polyolefin microporous membrane that maintains a thin film while exhibiting low resistance and excellent safety. Another object of the present invention is to provide an electricity storage device having low resistance and excellent safety, in which the above-mentioned polyolefin microporous membrane is interposed between electrodes.
  • the present invention relates to the following:
  • a polyolefin microporous membrane having a polyethylene-based resin layer containing a polyethylene-based resin and a polypropylene-based resin layer containing a polypropylene-based resin, the content of the polyethylene resin in the total mass of the polyolefin microporous membrane is 5% by mass to 45% by mass,
  • the polyolefin microporous membrane has a porosity of 42% to 62%; the surface porosity of the polypropylene-based resin layer is 5% to 30%, and the surface porosity of the polyethylene-based resin layer is 5% to 20.6%; Polyolefin microporous membrane.
  • the polyolefin microporous membrane has a laminated structure in which the polyethylene-based resin layer and the polypropylene-based resin layer are laminated,
  • a separator film for an electricity storage device comprising the polyolefin microporous membrane according to any one of [1] to [10].
  • An electricity storage device comprising the separator film for an electricity storage device according to [11], a positive electrode, and a negative electrode.
  • the present invention by adjusting the specific material, content, porosity, and surface porosity of the polyolefin microporous membrane, it is possible to provide a polyolefin microporous membrane that has shutdown properties while simultaneously improving low resistance and puncture strength.
  • the polyolefin microporous membrane of the present invention contains at least a polypropylene (hereinafter sometimes referred to as PP)-based resin and a polyethylene (hereinafter sometimes referred to as PE)-based resin as resin materials.
  • the polyolefin microporous membrane has a multilayer structure.
  • the content of the polyethylene resin in the total mass of the polyolefin microporous membrane is 5% by mass or more, preferably 9% by mass or more, more preferably 11% by mass or more, and particularly preferably 13% by mass or more, with the upper limit being 45% by mass or less, preferably 38% by mass or less, more preferably 32% by mass or less, and particularly preferably 29% by mass or less.
  • the porosity of the polyolefin microporous membrane of the present invention is 42% or more and 62% or less from the viewpoint of ensuring sufficient mechanical strength of the polyolefin microporous membrane and further ensuring sufficient ion mobility while suppressing short circuit. It is preferably 43% or more, more preferably 44% or more, even more preferably 45% or more, and particularly preferably 49% or more. On the other hand, it is preferably 60% or less, more preferably 58% or less, and even more preferably 56% or less. If the porosity is as above, a good performance electric storage device can be obtained.
  • the porosity refers to the porosity of the entire polyolefin microporous membrane.
  • the polypropylene resin is a polymer that is contained in the polypropylene resin layer as a main component at a ratio of 80% by mass or more.
  • a polymer may be used alone as the polypropylene resin, or a mixture of multiple types may be used.
  • polypropylene resins generally contain additives such as surfactants, antiaging agents, plasticizers, flame retardants, and colorants for various purposes.
  • the polypropylene resin used in the present invention may also contain these additives.
  • the content of the polypropylene resin in the entire polypropylene resin layer is preferably 85% by mass or more, more preferably 90% by mass or more, and the upper limit is not particularly limited, but is preferably 100% by mass or less.
  • the pentad fraction of the polypropylene resin is preferably 80% or more, more preferably 90% or more, and even more preferably 94% or more. There is no particular upper limit, but it is preferably 100% or less.
  • the zero shear viscosity ⁇ PP (Pa ⁇ s) of the polypropylene resin at 200°C is preferably within the range of 10,000 to 100,000 Pa ⁇ s. If the zero shear viscosity of the polypropylene resin is 10,000 Pa ⁇ s or more, a polyolefin microporous film that can maintain the moldability of PP during shutdown can be obtained. In addition, by using a polypropylene resin having a zero shear viscosity of 100,000 Pa ⁇ s or less, the shape retention characteristics of the laminated structure are improved.
  • the zero shear viscosity of the polypropylene resin at 200°C is more preferably 13,000 to 80,000 Pa ⁇ s, even more preferably 14,000 to 50,000 Pa ⁇ s, and particularly preferably 14,500 to 40,000 Pa ⁇ s.
  • the lower limit of the crystalline melting peak temperature (melting point) of the polypropylene-based resin measured by a differential scanning calorimeter (DSC) is preferably 155°C or higher, more preferably 157°C or higher, even more preferably 159°C or higher, and most preferably 160°C or higher.
  • the upper limit is preferably 175°C or lower, more preferably 173°C or lower, even more preferably 170°C or lower, and most preferably 169°C or lower.
  • the polyethylene resin is a polymer that is contained in the polyethylene resin layer in a proportion of 80% by mass or more as a main component. In the present invention, such a polymer may be used alone as the polyethylene resin, or a mixture of multiple types may be used. In addition, the polyethylene resin generally contains additives such as surfactants, antiaging agents, plasticizers, flame retardants, and colorants for various purposes. The polyethylene resin used in the present invention may also contain these additives.
  • the polyethylene resin in the entire polyethylene resin layer is preferably 85% by mass or more, more preferably 90% by mass or more, and the upper limit is not particularly limited, but is preferably 100% by mass or less.
  • the density of the polyethylene resin is preferably 0.950 g/cm 3 or more and 0.970 g/cm 3 or less.
  • As the polyethylene resin high-density polyethylene having a density of 0.960 g/cm 3 or more is more preferable, but medium-density polyethylene may also be used.
  • the zero shear viscosity of the polyethylene resin at 200°C is preferably within the range of 15,000 to 90,000 Pa ⁇ s. If the zero shear viscosity of the polyethylene resin is 15,000 Pa ⁇ s or more, the polyethylene resin layer will have sufficient strength, which is preferable. Also, if the zero shear viscosity of the polyethylene resin is 90,000 Pa ⁇ s or less, the effect on the shape of the polypropylene resin layer can be reduced, which is preferable.
  • the zero shear viscosity of the polyethylene resin at 200°C is more preferably 20,000 to 70,000 Pa ⁇ s, and even more preferably 25,000 to 50,000 Pa ⁇ s.
  • the melting point of the polyethylene resin is preferably 100°C or higher and 140°C or lower, more preferably 110°C or higher and 138°C or lower, and even more preferably 120°C or higher and 137°C or lower.
  • shutdown occurs at a temperature equal to or higher than the melting point of the polyethylene resin. That is, a phenomenon occurs in which molten polyethylene resin flows into the pores of the polypropylene resin layer, blocking the movement of ions. It is preferable for the melting point of the PE resin used in the polyolefin microporous membrane to be 140°C or lower, since shutdown can be initiated early. It is not easy to use a polyethylene resin with a melting point of less than 100°C as a raw material for the polyolefin microporous membrane.
  • the surface porosity of the polypropylene resin layer of the present invention is 5% or more and 30% or less from the viewpoint of ensuring sufficient ion mobility and effectively suppressing short circuit. It is preferably 5% or more, more preferably 6% or more, and even more preferably 7% or more. On the other hand, it is preferably 28% or less, more preferably 25% or less, even more preferably 20% or less, and particularly preferably 19% or less.
  • the surface porosity of both sides of the polypropylene resin layer i.e., the surface porosity of one surface and the surface porosity of the other surface
  • the polyolefin microporous membrane of the present invention has a plurality of polypropylene resin layers, it is sufficient that the surface porosity of at least one of the plurality of polypropylene resin layers is within the above range, but it is preferable that the surface porosity of all the polypropylene resin layers included in the polyolefin microporous membrane of the present invention is within the above range.
  • the polyolefin microporous membrane of the present invention has two polypropylene-based resin layers, it is sufficient that the surface porosity of at least one of the polypropylene-based resin layers is within the above-mentioned range, but it is preferable that the surface porosity of both polypropylene-based resin layers is within the above-mentioned range.
  • the surface porosity of the polyethylene resin layer of the present invention is 5% or more and 20.6% or less. It is preferably 6% or more, more preferably 7% or more, even more preferably 9% or more, and particularly preferably 12% or more. On the other hand, it is preferably 19.5% or less, more preferably 19% or less, and even more preferably 18.5% or less. By being in the above range, it is possible to simultaneously improve the reduction of electrical resistance and the pin puncture strength while ensuring ion mobility and shutdown characteristics.
  • the surface porosity of both sides of the polyethylene resin layer i.e., the surface porosity of one surface and the surface porosity of the other surface
  • the surface porosity of both sides of the polyethylene resin layer may be the same or may be different as long as they are within the above range.
  • the polyolefin microporous membrane of the present invention has a plurality of polyethylene resin layers, it is sufficient that the surface porosity of at least one of the plurality of polyethylene resin layers is in the above range, but it is preferable that the surface porosity of all the polyethylene resin layers included in the polyolefin microporous membrane of the present invention is in the above range.
  • the surface porosity of the polyethylene resin layer is preferably higher than that of the polypropylene resin layer, and by adopting such an embodiment, the pin puncture strength can be further increased even when the porosity is approximately the same.
  • the difference between the surface porosity of the polyethylene resin layer and the surface porosity of the polypropylene resin layer is preferably 1% or more, more preferably 2% or more, even more preferably 3% or more, preferably 8% or less, more preferably 7% or less, and even more preferably 6% or less.
  • the polyolefin microporous membrane of the present invention is preferably a laminated structure with a polyethylene resin layer as an intermediate layer.
  • a polypropylene resin layer may be present on both sides of the polyethylene resin layer, or a polypropylene resin layer may be present on one surface and a polyethylene resin layer may be present on the remaining surface.
  • the laminated structure referred to here may be a polyethylene resin layer as an intermediate layer, and a polypropylene resin layer may be present on at least one surface of the polyethylene resin layer. The total number of layers in the laminated structure may be 4 or more.
  • the polyolefin microporous membrane of the present invention preferably has a three-layer laminate structure in which a polypropylene-based resin layer is present on both sides of a polyethylene-based resin layer, i.e., a three-layer laminate structure in which a polypropylene-based resin layer/a polyethylene-based resin layer/a polypropylene-based resin layer are laminated in this order.
  • the pin puncture strength and porosity of the polyolefin microporous membrane of the present invention can be measured by the measurement methods described below, and it is preferable that the pin puncture strength (N/ ⁇ m) and porosity (%) per 1 ⁇ m of membrane thickness satisfy the following formula (I). 100 x puncture strength/(100-porosity) ⁇ 0.44...(I) If formula (I) is satisfied, the separator film for an electric storage device can improve the puncture strength while ensuring good ionic conductivity.
  • the left side of formula (I) is preferably 0.44 or more, more preferably 0.45 or more, even more preferably 0.47 or more, and even more preferably 0.48 or more.
  • the upper limit of the value of "100 x puncture strength/(100 - porosity)" is not particularly limited, but is preferably 0.54 (i.e., 100 x puncture strength/(100 - porosity) ⁇ 0.54).
  • Formula (I) is a value indicating the puncture strength per thickness equivalent to the substantial resin component excluding the pore portion, and in formula (I), the unit of puncture strength is "N/ ⁇ m" and the unit of porosity is "%".
  • the polyolefin microporous membrane of the present invention preferably has an electrical resistance of 0.06 ( ⁇ cm 2 / ⁇ m) or less in order to achieve good ion conductivity.
  • the electrical resistance referred to here indicates the electrical resistance per 1 ⁇ m of membrane thickness.
  • the electrical resistance ( ⁇ cm 2 / ⁇ m) is more preferably 0.057 or less, even more preferably 0.055 or less, and even more preferably 0.05 or less, and the lower limit of the electrical resistance ( ⁇ cm 2 / ⁇ m) is not particularly limited, but is preferably 0.01 or more. If it is within the above range, the electrical resistance can be reduced while maintaining the shutdown property and pin puncture strength.
  • the electrical resistance is measured by filling the polyolefin microporous membrane with an electrolyte and measuring the resistance value of the separator filled with the electrolyte.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • the polyolefin microporous membrane of the present invention is preferably as thin as possible because it can make the electricity storage device more compact. If the polyolefin microporous membrane is too thick, it is not preferable because when the membrane is used as a separator in an electricity storage device, the volume ratio of the separator increases, and the capacity per unit volume of the electricity storage device decreases.
  • the thickness of the entire polyolefin microporous membrane is preferably 30 ⁇ m or less, more preferably 25 ⁇ m or less, and even more preferably 20 ⁇ m or less. By making the thickness of the laminated structure 20 ⁇ m or less, the capacity of the electricity storage device using this polyolefin microporous membrane as a separator can be increased.
  • the membrane thickness of the polyolefin microporous membrane can be determined by a method of image analysis of an image of a cross section of the microporous membrane taken by a scanning electron microscope (SEM), or by using a dot-type thickness measuring device, etc.
  • the lower limit of the air permeability (Gurley value) of the polyolefin microporous membrane of the present invention is preferably 80 s/100 cc or more, more preferably 90 s/100 cc or more, even more preferably 95 s/100 cc or more, even more preferably 100 s/100 cc or more, and particularly preferably 130 s/100 cc or more.
  • the upper limit of the air permeability (Gurley value) is preferably 500 s/100 cc or less, more preferably 400 s/100 cc or less, even more preferably 300 s/100 cc or less, and even more preferably 250 s/100 cc or less.
  • the air permeability of the polyolefin microporous membrane is 500s/100cc or less, when this polyolefin microporous membrane is used as a separator for an electricity storage device, the movement of ions is less likely to be suppressed or hindered, which is preferable. Conversely, if the air permeability of the polyolefin microporous membrane is 80s/100cc or more, when this polyolefin microporous membrane is used as a separator for an electricity storage device, the movement of ions is prevented from being too fast, which can prevent a rapid temperature rise in the event of a breakdown in the electricity storage device.
  • the tensile strength of the polyolefin microporous membrane in the MD direction is preferably 130 MPa or more, more preferably 150 MPa or more, even more preferably 170 MPa or more, and even more preferably 180 MPa or more, and the upper limit is preferably 250 MPa or less, more preferably 230 MPa or less, even more preferably 210 MPa or less, and even more preferably 200 MPa or less.
  • the tensile strength in the MD direction is preferably 5 MPa or more, more preferably 6 MPa or more, and even more preferably 7 MPa or more, and the upper limit is preferably 20 MPa or less, more preferably 18 MPa or less, and even more preferably 16 MPa or less.
  • the tensile elongation of the polyolefin microporous membrane is preferably 45% or more, more preferably 50% or more, particularly preferably 60% or more in both MD and TD. If the tensile elongation in MD is 45% or more, the possibility of the separator breaking when the battery is deformed by external force can be reduced. In addition, the polyolefin microporous membrane is distorted in the micro-section generated when the polyolefin microporous membrane and the electrode are laminated in the presence of minute foreign matter, and pinholes are generated, which can reduce the possibility of battery failure due to micro-short circuit.
  • the upper limit of the tensile elongation in MD and/or TD of the polyolefin microporous membrane is not particularly limited.
  • the tortuosity of the polyolefin microporous membrane is preferably 2 or less, more preferably 1.8 or less, even more preferably 1.6 or less, and even more preferably 1.55 or less.
  • the lower limit is preferably 1 or more, more preferably 1.2 or more, even more preferably 1.3 or more, and even more preferably 1.35 or more.
  • the tortuosity can be explained as an index of the tortuous path that ions travel from one side of the porous membrane through the pores of the membrane body to the opposite side of the membrane, and a low tortuosity as described above promotes more or faster movement of ions and electrolytes through the porous battery separator membrane during the charge and discharge cycle of a lithium ion battery compared to a high tortuosity. If it is within the above range, the puncture strength can be improved.
  • a separator film made of a polyolefin microporous membrane can block the pores in the porous membrane to prevent ions from flowing between the two electrodes, thereby increasing the electrical resistance. This stops the function of the electricity storage device, preventing the risk of fire or other dangers caused by an excessive rise in temperature.
  • the function of preventing the risk of fire or other dangers caused by an excessive rise in temperature is extremely important for separator films for electricity storage devices, and is generally called non-porous or shutdown (hereinafter, SD).
  • the shutdown property of the polyolefin microporous membrane of the present invention is such that, when the polyolefin microporous membrane is heated to a temperature equal to or higher than the melting point of the polyethylene resin as described above, all or part of the pores in the polypropylene resin layer are blocked in this temperature range, causing the resistance of the separator film, measured as impedance, to increase, and when it exceeds 1000 ⁇ , it is determined that the shutdown property is present.
  • the puncture strength means the stress of the sample against the force applied by fixing the periphery of the membrane sample and piercing a needle of a specific size from the outer surface of the membrane sample in the thickness direction of the membrane sample.
  • the puncture elongation means the moving distance (elongation) from when the needle contacts the membrane sample to when a hole is made by fixing the periphery of the membrane sample and piercing a needle of a specific size from the outer surface of the membrane sample in the thickness direction of the membrane sample.
  • the puncture strength of the polyolefin microporous membrane is preferably 2N or more, more preferably 3N or more, from the viewpoint of separator productivity and secondary battery safety, and although there is no particular upper limit, it is preferably 10N or less.
  • the puncture elongation of the microporous film is preferably 2.5mm or more, more preferably 3mm or more, even more preferably 3.5mm or more, particularly preferably 4mm or more, and most preferably 5mm or more, and although there is no particular upper limit, it is preferably 10mm or less, from the viewpoint of puncture strength, wettability to non-aqueous solvents, and voltage resistance.
  • the method for producing the polyolefin microporous membrane of the present invention will be described below.
  • the microporous polyolefin membrane of the present invention is preferably produced by a dry process that does not use a solvent during production.
  • the precursor film of the present invention comprises a polyethylene-based resin layer (hereinafter, PE layer) containing the above-mentioned polyethylene-based resin, and a polypropylene-based resin layer (hereinafter, PP layer) containing the above-mentioned polypropylene-based resin.
  • PE layer polyethylene-based resin layer
  • PP layer polypropylene-based resin layer
  • the structure of the precursor film is not particularly limited, but it is sufficient to have a PP layer on the PE layer, for example, a three-layer structure such as PE layer/PP layer/PE layer, PP layer/PE layer/PP layer, a five-layer structure such as PP layer/PE layer/PP layer/PE layer/PP layer, and the like.
  • the laminate structure of the precursor film and the laminate structure of the polyolefin microporous film are basically the same, the laminate structure of the precursor film may be determined according to the laminate structure of the obtained polyolefin microporous film.
  • the precursor film of the present invention can be produced by a method of forming a film by extruding the above-mentioned polyethylene-based resin and the above-mentioned polypropylene-based resin together into a film, that is, a method of forming a film by co-extrusion.
  • a method of forming a film by co-extrusion for example, in the case of producing a precursor film having a PE layer as an intermediate layer and a PP layer provided on both sides thereof, the precursor film can be produced by co-extrusion of the polyethylene-based resin and the polypropylene-based resin so that the PE layer is the intermediate layer and the PP layer is formed on both sides thereof.
  • the apparatus used for co-extrusion is not particularly limited, and conventionally known apparatus can be used.
  • co-extrusion apparatus include a co-extruder equipped with a circular die, and a co-extruder equipped with a feed block or a multi-manifold type T-die.
  • melt molding using a T-die is also a suitable method for forming the raw roll, and when forming the PP film and PE film, which are the raw rolls used for the polyolefin microporous membrane, by melt molding using a T-die, the PP film and PE film may be molded separately.
  • the die temperature is preferably 185 to 240°C, more preferably 190 to 235°C, and even more preferably 195 to 230°C.
  • the die temperature is preferably 185 to 240°C, more preferably 190 to 235°C, and even more preferably 195 to 230°C.
  • the microporous polyolefin membrane of the present invention is produced by stretching the above-mentioned precursor film of the present invention to make it porous.
  • the precursor film When stretching a precursor film to make it porous, it is preferable to previously heat treat the precursor film before stretching it to make it porous.
  • the polyethylene resin and polypropylene resin that make up the precursor film can be crystallized, making the precursor film more suitable for making it porous by stretching, and making it more suitable for making it porous by stretching.
  • the crystallization degree of the precursor film can be controlled by the heat treatment conditions, and by controlling the crystallization degree by the heat treatment conditions, the pore opening characteristics of the porous film obtained by stretching it to make it porous can be adjusted.
  • the heat treatment method may be, for example, a method in which the precursor film is brought into contact with a preheated roll, or a method in which the precursor film is passed through an environment heated to a predetermined temperature, and it is advisable to use an appropriate method.
  • the heat treatment temperature is preferably 110°C or higher and 145°C or lower, more preferably higher than 128°C and 140°C or lower, and even more preferably 130°C or higher and 136°C or lower.
  • a laminated film obtained by thermocompression bonding (lamination process) a laminate of a PP film and a PE film obtained by melt molding using a T-die may be used as the precursor film.
  • each film to be heat-pressed is unwound from an original roll stand, and passed between heated rolls in a state in which a PP film is placed on each side of the PE film. This results in a laminate film in which a PP film is heat-pressed on each side of the PE film.
  • the stretching method used for stretching to make the film porous is not particularly limited, but examples include uniaxial stretching in the machine direction (MD), uniaxial stretching in the width direction (TD) which is approximately perpendicular to the machine direction, sequential biaxial stretching in which the film is stretched in the machine direction (MD) and then in the width direction (TD), simultaneous biaxial stretching in which the film is stretched in the machine direction (MD) and width direction (TD) approximately simultaneously, and tubular biaxial stretching.
  • MD machine direction
  • TD width direction
  • TD sequential biaxial stretching in which the film is stretched in the machine direction (MD) and then in the width direction (TD)
  • simultaneous biaxial stretching in which the film is stretched in the machine direction (MD) and width direction (TD) approximately simultaneously and tubular biaxial stretching.
  • a specific method for making the film porous by stretching is, for example, to obtain a porous film by stretching a heat-treated precursor film at a low temperature in a low-temperature stretching zone, and then stretching the film at a higher temperature in a high-temperature stretching zone to make the film porous. If only one of the low-temperature stretching and high-temperature stretching is used, it may not be possible to make both the polypropylene-based resin and the polyethylene-based resin sufficiently porous, and it may not be possible to form a porous film.
  • the temperature for low-temperature stretching is not particularly limited, but is preferably -20°C or higher and +50°C or lower, and more preferably +20°C or higher and +40°C or lower. If the low-temperature stretching temperature is too low, the precursor film is more likely to break during stretching, which is undesirable. On the other hand, if the low-temperature stretching temperature is too high, the polyethylene resin in the precursor film is less likely to be perforated, which is undesirable.
  • the stretching ratio for low-temperature stretching is not particularly limited, but is preferably in the range of 3% or more and 200% or less, and more preferably in the range of 5% or more and 100% or less. If the stretching ratio for low-temperature stretching is 3% or more, it is easier to obtain a porous film with a sufficiently low Gurley value. On the other hand, if the stretching ratio for low-temperature stretching exceeds 200%, the generated crazes will turn into cracks and cause film rupture. For this reason, it is preferable that the stretching ratio for low-temperature stretching is 200% or less.
  • the temperature of the high-temperature stretching is preferably 70°C or higher and 150°C or lower, and more preferably 80°C or higher and 145°C or lower.
  • the stretching ratio of the high-temperature stretching is not particularly limited, but is preferably in the range of 100% or more and 400% or less. If the stretching ratio of the high-temperature stretching is too low, the Gurley value of the porous film may not be sufficiently low. Also, if the stretching ratio of the high-temperature stretching is too high, the air permeability of the porous film may become too low.
  • the polyolefin microporous membrane of the present invention which has a polyethylene resin layer containing a polyethylene resin and a polypropylene resin layer containing a polypropylene resin.
  • the separator film for an electricity storage device has the polyolefin microporous membrane of the present invention.
  • the separator film for an electricity storage device of the present invention may consist only of the polyolefin microporous membrane of the present invention, that is, the polyolefin microporous membrane of the present invention may be used as it is as a separator film for an electricity storage device without any additional processing.
  • the separator film for an electricity storage device of the present invention may have the polyolefin microporous membrane of the present invention. Therefore, the separator film for an electricity storage device of the present invention may have, for example, at least one layer selected from a heat-resistant porous layer, an adhesive layer, and a functional layer on one or both sides of the polyolefin microporous membrane.
  • the heat-resistant porous layer, adhesive layer, and functional layer may each be a single layer, or may be a laminate of multiple layers.
  • the heat-resistant porous layer, adhesive layer, and functional layer may each be provided individually as a layer having a single function, or may be provided as a layer having the functions of at least two layers selected from the heat-resistant porous layer, adhesive layer, and functional layer.
  • the heat-resistant porous layer, adhesive layer, and functional layer may all be formed using known materials.
  • the heat-resistant porous layer may be, for example, a layer made of heat-resistant fine particles and an organic binder.
  • the adhesive layer may be, for example, a layer made of an organic material such as a fluorine-based resin.
  • An example of the functional layer is a layer containing organic fine particles and a binder.
  • the heat-resistant porous layer, the adhesive layer and the functional layer can all be formed by a method of applying a predetermined coating liquid.
  • a separator film for an electricity storage device having a heat-resistant porous layer, an adhesive layer and a functional layer in this order on one or both sides of a polyolefin microporous membrane it can be formed by the method shown below.
  • a coating liquid containing heat-resistant fine particles and an organic binder is applied to one or both sides of a polyolefin microporous film to form a heat-resistant porous layer.
  • An organic material such as a fluorine-based resin is then applied to the heat-resistant porous layer to form an adhesive layer.
  • a coating liquid containing organic fine particles and a binder is then applied to the adhesive layer.
  • This provides a separator film for an electricity storage device having a heat-resistant porous layer, an adhesive layer and a functional layer in this order on one or both sides of the polyolefin microporous membrane.
  • the heat-resistant porous layer contains heat-resistant fine particles and preferably contains an organic binder.
  • the heat-resistant porous layer contains the heat-resistant fine particles, thereby improving the heat resistance of the separator film for an electricity storage device.
  • the heat-resistant porous layer may be a single layer or a multilayer in which a plurality of layers are laminated.
  • the heat resistance of the heat-resistant fine particles is preferably 200° C. or higher, more preferably 300° C. or higher, and even more preferably 400° C. or higher.
  • the term "heat resistant" means that no change in shape, such as deformation, is visually observed at least at that temperature.
  • the heat-resistant fine particles are preferably inorganic fine particles having electrical insulation.
  • the heat-resistant fine particles include inorganic oxide fine particles such as iron oxide, silica ( SiO2 ), alumina ( Al2O3 ), TiO2 , magnesia, boehmite, BaTiO2, etc.; inorganic nitride fine particles such as aluminum nitride, silicon nitride , etc.; sparingly soluble ionic crystal fine particles such as calcium fluoride, barium fluoride, barium sulfate, etc.; covalent crystal fine particles such as silicon, diamond, etc.; clay fine particles such as montmorillonite, etc.
  • the inorganic oxide fine particles may be fine particles of substances derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or artificial products thereof.
  • the inorganic compounds constituting these inorganic fine particles may be element-substituted or solid-solution-formed as necessary.
  • the inorganic fine particles may be surface-treated.
  • the heat-resistant microparticles may be particles that have been given electrical insulation by coating the surface of a conductive material, such as a metal, a conductive oxide such as SnO 2 or tin-indium oxide (ITO), or a carbonaceous material such as carbon black or graphite, with an electrically insulating material (e.g., the inorganic oxides mentioned above).
  • a conductive material such as a metal, a conductive oxide such as SnO 2 or tin-indium oxide (ITO), or a carbonaceous material such as carbon black or graphite, with an electrically insulating material (e.g., the inorganic oxides mentioned above).
  • organic fine particles may be used as the heat-resistant fine particles.
  • organic fine particles include fine particles of cross-linked polymers such as polyimide, melamine resin, phenolic resin, aromatic polyamide resin, cross-linked polymethyl methacrylate (cross-linked PMMA), cross-linked polystyrene (cross-linked PS), polydivinylbenzene (PDVB), and benzoguanamine-formaldehyde condensates; and fine particles of heat-resistant polymers such as thermoplastic polyimide.
  • the organic resins (polymers) that make up these organic fine particles may be mixtures, modified products, derivatives, copolymers (random copolymers, alternating copolymers, block copolymers, graft copolymers), and cross-linked products (in the case of the heat-resistant polymers) of the above-mentioned materials.
  • the heat-resistant microparticles may be one of the above-mentioned examples, or two or more of them may be used in combination. As described above, inorganic microparticles and organic microparticles can be used as the heat-resistant microparticles, and they may be used appropriately depending on the application.
  • the heat-resistant fine particles it is particularly preferable to use boehmite.
  • the boehmite used has an average particle size of preferably 0.001 ⁇ m or more, more preferably 0.1 ⁇ m or more, and preferably 15 ⁇ m or less, more preferably 3 ⁇ m or less.
  • the average particle size of the heat-resistant fine particles can be defined as the number average particle size measured by dispersing the heat-resistant fine particles in a medium that does not dissolve the heat-resistant fine particles using a laser scattering particle size distribution meter (for example, HORIBA's "LA-920").
  • the shape of the heat-resistant fine particles may be, for example, close to a sphere or plate-like. From the viewpoint of preventing short circuits, it is preferable that the heat-resistant fine particles are plate-like particles.
  • Representative examples of heat-resistant fine particles formed into a plate shape include alumina and boehmite.
  • Organic binder is contained in the heat-resistant porous layer in order to bind the heat-resistant fine particles contained as a main component to each other and to bind the heat-resistant fine particles to the polyolefin microporous film.
  • organic binder There are no particular limitations on the organic binder as long as it can satisfactorily bond the heat-resistant fine particles to each other and to the heat-resistant fine particles and the polyolefin microporous film, and is electrochemically stable and stable to the electrolyte of the electricity storage device.
  • organic binders examples include ethylene-vinyl acetate copolymers (EVA, with 20-35 mol% of structural units derived from vinyl acetate), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymer (EEA), fluororesins [such as polyvinylidene fluoride (PVDF)], fluorine-based rubber, styrene-butadiene rubber (SBR), water-soluble cellulose derivatives such as carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), poly N-vinyl acetamide, cross-linked acrylic resins, polyurethane, epoxy resins, polyimides, etc. These organic binders may be used alone or in combination of two or more types.
  • EVA ethylene-vinyl acetate copolymers
  • ESA
  • heat-resistant resins with a heat resistance of 150°C or higher are preferred, and it is particularly preferable to use highly flexible materials such as ethylene-vinyl acetate copolymer (EVA), ethylene-acrylic acid copolymer, ethylene-ethyl acrylate copolymer (EEA), polyvinyl butyral (PVB), fluorine-based rubber, and styrene-butadiene rubber (SBR). It is also preferable to use a cross-linked acrylic resin (self-cross-linking acrylic resin) with a low glass transition temperature that has a cross-linked structure with butyl acrylate as the main component as the organic binder.
  • EVA ethylene-vinyl acetate copolymer
  • EAA ethylene-acrylic acid copolymer
  • ESA ethylene-ethyl acrylate copolymer
  • PVB polyvinyl butyral
  • SBR styrene-butadiene rubber
  • the heat-resistant porous layer contains heat-resistant fine particles as a main component.
  • "containing heat-resistant fine particles as a main component” means that the heat-resistant fine particles account for 70 mass % or more of the total mass of the components constituting the heat-resistant porous layer.
  • the amount of heat-resistant fine particles in the heat-resistant porous layer is preferably 80% by mass or more, more preferably 85% by mass or more, based on the total mass of the components of the heat-resistant porous layer.
  • the suitable upper limit of the amount of heat-resistant fine particles in the heat-resistant porous layer is, for example, preferably 99% by mass or less based on the total mass of the components of the heat-resistant porous layer.
  • the content of the organic binder in the heat-resistant porous layer is preferably 1.1 to 30 parts by mass per 100 parts by mass of the heat-resistant fine particles. If the content of the organic binder is 30 parts by mass or less, the pores in the heat-resistant porous layer are filled with the organic binder, which is preferable since it does not impede the function of the separator. If the content of the organic binder is 1.1 parts by mass or more, the effect of including the organic binder becomes significant.
  • the thickness of the heat-resistant porous layer is not particularly limited, but is preferably 0.5 ⁇ m or more, more preferably 1 ⁇ m or more, and even more preferably 2 ⁇ m or more.
  • the thickness of the heat-resistant porous layer is preferably 10 ⁇ m or less, more preferably 8 ⁇ m or less, and even more preferably 6 ⁇ m or less.
  • the heat-resistant porous layer is 0.5 ⁇ m or more, the meltdown prevention effect due to the heat-resistant porous layer is sufficiently obtained.
  • the heat-resistant porous layer is 10 ⁇ m or less, defects are unlikely to occur in the heat-resistant porous layer, which is preferable.
  • the heat-resistant porous layer is 10 ⁇ m or less, the heat-resistant porous layer is too thick, and therefore, in a power storage device using a separator film for a power storage device, the amount of electrolyte injected can be increased, which increases the battery manufacturing cost, and the energy density per volume and per mass can be prevented from decreasing, which is preferable.
  • the thickness ratio a/b is preferably 0.5 to 20, more preferably 1 to 10.
  • the thickness of the heat-resistant porous layer relative to the polyolefin microporous membrane is not too thick, and it is possible to prevent an increase in the amount of electrolyte injected into the polyolefin microporous membrane having the heat-resistant porous membrane, which would result in a decrease in energy density.
  • the a/b value is 0.5 or more, the meltdown prevention effect of having the heat-resistant porous layer is sufficiently obtained.
  • the Gurley value (air permeability) of a polyolefin microporous membrane having a heat-resistant porous layer on one or both sides is not particularly limited, but is preferably 80 to 700 seconds/100cc, more preferably 90 to 650 seconds/100cc, and even more preferably 100 to 600 seconds/100cc. If the Gurley value is 700 seconds/100cc or less, the polyolefin microporous membrane having a heat-resistant porous layer will function sufficiently when used as a separator for an electricity storage device. If the Gurley value is 80 seconds/100cc or more, it is preferable because it is easier to ensure uniformity of the internal reaction when used as a separator for an electricity storage device.
  • the power storage device of the present invention includes at least a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and may also include a non-aqueous electrolyte impregnated in the separator.
  • the electricity storage device of the present invention has, as a separator, the polyolefin microporous membrane or the separator film for an electricity storage device of the present invention.
  • the polyolefin microporous membrane or separator film for an electricity storage device of the present invention can be used, for example, as a separator for the first and second electricity storage devices described below.
  • it is preferably used as a separator for a lithium ion battery (first electricity storage device) that uses lithium salt as the electrolyte salt, or a lithium ion capacitor (second electricity storage device), more preferably for a lithium ion battery, and even more preferably for a lithium ion secondary battery.
  • the shape of the separator used in the electricity storage device may be adjusted appropriately depending on, for example, the shape of the lithium ion secondary battery.
  • the shapes of the positive and negative electrodes of the electricity storage device may be adjusted appropriately depending on, for example, the shape of the lithium ion secondary battery.
  • the lithium ion secondary battery as the electricity storage device of the present invention has a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte.
  • the non-aqueous electrolyte used in the electricity storage device of the present invention contains, for example, an electrolyte salt and a non-aqueous solvent.
  • the non-aqueous electrolyte may be in a liquid state or in a gel state.
  • Non-aqueous solvent Suitable examples of the non-aqueous solvent used in the non-aqueous electrolyte include cyclic carbonates and chain esters.
  • the non-aqueous solvent preferably contains a chain ester, more preferably contains a chain carbonate, and most preferably contains both a cyclic carbonate and a chain carbonate, because the electrochemical properties at a wide temperature range, particularly at high temperatures, are improved synergistically.
  • chain ester is used as a concept including chain carbonates and chain carboxylate esters.
  • the cyclic carbonate may be one or more selected from ethylene carbonate (EC), propylene carbonate (PC), and vinylene carbonate (VC), with a combination of EC and PC being particularly preferred.
  • EC ethylene carbonate
  • PC propylene carbonate
  • VC vinylene carbonate
  • the non-aqueous solvent contains ethylene carbonate and/or propylene carbonate, the stability of the coating formed on the electrode is increased, and the high-temperature, high-voltage cycle characteristics are improved, which is preferable.
  • the content of ethylene carbonate and/or propylene carbonate is preferably 3 vol.% or more, more preferably 5 vol.% or more, and even more preferably 7 vol.% or more, based on the total volume of the non-aqueous solvent.
  • the upper limit is preferably 45 vol.% or less, more preferably 35 vol.% or less, and even more preferably 25 vol.% or less.
  • chain esters preferred examples include ethyl methyl carbonate (EMC) as an asymmetric chain carbonate, dimethyl carbonate (DMC) and diethyl carbonate (DEC) as symmetric chain carbonates, and ethyl propionate (hereinafter, EP) as a chain carboxylic acid ester.
  • EMC ethyl methyl carbonate
  • DMC dimethyl carbonate
  • DEC diethyl carbonate
  • EP ethyl propionate
  • chain carboxylic acid ester a combination of asymmetric chain esters containing an ethoxy group, such as EMC and EP, is possible.
  • the amount of the chain ester is not particularly limited, but is preferably in the range of 60 to 90% by volume relative to the total volume of the non-aqueous solvent. If the amount is 60% by volume or more, the viscosity of the non-aqueous electrolyte does not become too high, which is preferable. If the amount is 90% by volume or less, the electrical conductivity of the non-aqueous electrolyte decreases, which is less likely to cause a decrease in the electrochemical properties over a wide temperature range, especially at high temperatures, which is preferable.
  • the volume ratio of EP among the chain esters in the non-aqueous solvent is preferably 1% by volume or more, more preferably 2% by volume or more.
  • the upper limit is preferably 30% by volume or less, and even more preferably 20% by volume or less.
  • the asymmetric chain carbonate more preferably has an ethyl group, and ethyl methyl carbonate is particularly preferred.
  • the ratio of cyclic carbonate to chain ester is preferably 10:90 to 45:55, more preferably 15:85 to 40:60, and particularly preferably 20:80 to 35:65.
  • the electrolyte salt used in the electricity storage device of the present invention is preferably a lithium salt.
  • the lithium salt is preferably one or more selected from the group consisting of LiPF6 , LiBF4 , LiN( SO2F ) 2 , and LiN( SO2CF3 ) 2 , more preferably one or more selected from LiPF6 , LiBF4 , and LiN (SO2F ) 2 , and most preferably LiPF6 .
  • the nonaqueous electrolyte used in the electricity storage device of the present invention can be obtained, for example, by adding an electrolyte salt to a nonaqueous solvent, and, if necessary, adding a composition in which a compound such as a dissolution aid is mixed with the nonaqueous electrolyte at a specific mixing ratio, and mixing them. It is preferable that the compound to be added to the non-aqueous electrolyte solution is previously purified to have as few impurities as possible, within the range that does not significantly reduce productivity.
  • the positive electrode of the lithium ion secondary battery has a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector.
  • the positive electrode mixture layer contains a positive electrode active material, a conductive agent, and a binder.
  • a positive electrode active material for example, a composite metal oxide containing one or more selected from the group consisting of cobalt, manganese, and nickel and lithium is used. These positive electrode active materials may be used alone or in combination of two or more.
  • lithium composite metal oxides examples include LiCoO2 , LiCo1 -xMxO2 (wherein M is one or more elements selected from Sn, Mg, Fe, Ti , Al, Zr, Cr, V , Ga, Zn , and Cu), LiMn2O4 , LiNiO2 , LiCo1 - xNixO2 , LiCo1 / 3Ni1 / 3Mn1 /3O2 , LiNi0.5Mn0.3Co0.2Mn0.3O2 , LiNi0.8Mn0.1Co0.1O2 , LiNi0.8Co0.15Al0.05O2 , Li Suitable examples of the solid solution include a solid solution of Li2MO3 and LiMO2 (wherein M is a transition metal such as Co, Ni, Mn, or Fe) and LiNi1 / 2Mn3 / 2O4 .
  • M is one or more elements selected from Sn, Mg, Fe, Ti , Al, Zr, Cr, V , Ga, Zn ,
  • the conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not undergo chemical changes, and examples thereof include one or more types of carbon black selected from graphite such as natural graphite (e.g., flake graphite) and artificial graphite, and acetylene black.
  • the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), and carboxymethyl cellulose (CMC).
  • the positive electrode current collector may be made of aluminum foil, a stainless steel plate, or the like.
  • the positive electrode can be produced, for example, by the following method.
  • the positive electrode active material is mixed with a conductive agent and a binder, and a solvent is added and kneaded to produce a positive electrode mixture.
  • the positive electrode mixture is then applied to a positive electrode current collector, dried, pressure molded, and heated under specified conditions to form a positive electrode mixture layer.
  • the negative electrode of the lithium ion secondary battery has a current collector and a negative electrode mixture layer formed on the current collector.
  • the negative electrode mixture layer contains a negative electrode active material, a conductive agent, and a binder.
  • the negative electrode active material lithium metal, lithium alloys, carbon materials capable of absorbing and releasing lithium, tin (single element), tin compounds, silicon (single element), silicon compounds, lithium titanate compounds such as Li4Ti5O12 , etc. can be used alone or in combination of two or more.
  • the negative electrode active material it is particularly preferable to use artificial graphite particles having a block structure in which a plurality of flat graphitic fine particles are aggregated or bonded in a non-parallel manner to each other, or particles obtained by spheroidizing flake natural graphite by repeatedly applying mechanical actions such as compressive force, frictional force, and shear force.
  • the conductive agent and binder used in the negative electrode may be the same as the conductive agent and binder used in the positive electrode.
  • the negative electrode current collector may be made of copper foil or the like.
  • the negative electrode can be produced, for example, by the following method: A negative electrode active material is mixed with a conductive agent and a binder, and a solvent is added and kneaded to form a negative electrode mixture. The negative electrode mixture is then applied to a negative electrode current collector, dried, pressure molded, and heated under predetermined conditions to form a negative electrode mixture layer.
  • the structure of the lithium ion secondary battery there is no particular limitation on the structure of the lithium ion secondary battery, and for example, a coin battery, a cylindrical battery, a square battery, or a laminate battery can be used.
  • a wound type lithium ion secondary battery which is an example of a lithium ion secondary battery, has a configuration in which an electrode body is housed in a battery case together with a non-aqueous electrolyte.
  • the electrode body is composed of a positive electrode, a negative electrode, and a separator. At least a portion of the non-aqueous electrolyte is impregnated into the electrode body.
  • the wound lithium ion secondary battery includes, as a positive electrode, a long sheet-like positive electrode current collector, and a positive electrode mixture layer containing a positive electrode active material and provided on the positive electrode current collector, and, as a negative electrode, a long sheet-like negative electrode current collector, and a negative electrode mixture layer containing a negative electrode active material and provided on the negative electrode current collector.
  • the separator like the positive electrode and the negative electrode, is formed in a long sheet shape. The positive electrode and the negative electrode, with the separator interposed therebetween, are wound into a cylindrical shape.
  • the battery case comprises a cylindrical case body with a bottom and a lid that closes the opening of the case body.
  • the lid and case body are made of metal, for example, and are insulated from each other.
  • the lid is electrically connected to the positive electrode current collector, and the case body is electrically connected to the negative electrode current collector.
  • the lid may also serve as the positive electrode terminal, and the case body may also serve as the negative electrode terminal.
  • Lithium ion secondary batteries can be charged and discharged at temperatures between -40 and 100°C, and preferably between -10 and 80°C.
  • a method of providing a safety valve in the battery lid, or a method of making cuts in the battery case body, gasket, and other components can be adopted.
  • a current cut-off mechanism that detects the internal pressure of the battery and cuts off the current can also be provided in the lid.
  • the positive electrode, negative electrode, and separator are each produced. Next, they are stacked and wound into a cylindrical shape to assemble the electrode body. Next, the electrode body is inserted into the case body, and non-aqueous electrolyte is injected into the case body. This causes the electrode body to be impregnated with the non-aqueous electrolyte. After the non-aqueous electrolyte is injected into the case body, a lid is placed on the case body, and the lid and case body are sealed.
  • the shape of the electrode assembly after winding is not limited to a cylindrical shape. For example, after the positive electrode, the separator, and the negative electrode are wound, pressure may be applied from the side to form a flat shape.
  • the lithium ion secondary battery described above can be used as a secondary battery for various applications.
  • it can be mounted on a vehicle such as an automobile and be suitably used as a power source for a driving source such as a motor that drives the vehicle.
  • a driving source such as a motor that drives the vehicle.
  • a driving source such as a motor that drives the vehicle.
  • a driving source such as a motor that drives the vehicle.
  • a driving source such as a motor that drives the vehicle.
  • a driving source such as a motor that drives the vehicle.
  • Such a lithium ion secondary battery can be used alone, or multiple batteries can be connected in series and/or parallel.
  • Laminate lithium-ion secondary battery Although the above describes a wound type lithium ion secondary battery, the present invention is not limited to this, and may be applied to a laminate type lithium ion secondary battery.
  • a laminated lithium ion secondary battery is, for example, a battery in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween, and then laminated (sealed).
  • a laminated lithium-ion secondary battery can be manufactured by the following method.
  • a positive or negative electrode is sandwiched between a pair of separators and packaged.
  • the positive electrode is a bagged electrode.
  • the separator has a size slightly larger than the electrode. While the main body of the electrode is sandwiched between the pair of separators, the tab protruding from the end of the electrode is made to protrude to the outside from the separator.
  • the side edges of the pair of stacked separators are joined together to bag the electrodes, and the electrodes bagged with the separators are alternately stacked and impregnated with an electrolyte to produce a laminated battery.
  • the separators and electrodes may be compressed in the thickness direction to reduce the thickness.
  • Lithium ion capacitor (second power storage device)
  • Another example of the electricity storage device of the present invention is a lithium ion capacitor.
  • the lithium ion capacitor of the present invention comprises a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution.
  • the separator is made of the polyolefin microporous membrane or the separator film for an electricity storage device of the present invention.
  • Lithium ion capacitors can store energy by utilizing the intercalation of lithium ions into a carbon material such as graphite, which is the negative electrode.
  • Examples of the positive electrode include those that utilize an electric double layer between an activated carbon electrode and an electrolyte, and those that utilize a doping/dedoping reaction of a ⁇ -conjugated polymer electrode.
  • the non-aqueous electrolyte contains at least a lithium salt such as LiPF6 .
  • the power storage device of the present invention has low resistance and excellent safety due to the polyolefin microporous membrane of the present invention being sandwiched between the electrodes, and therefore can be suitably mounted in various products such as vehicles, aircraft, and power tools.
  • the surface of the polypropylene-based resin layer and the surface of the polyethylene-based resin layer of the polyolefin microporous membrane were observed by a scanning electron microscope (SEM), the images were binarized, and the surface porosity was calculated by image analysis.
  • the surface porosity was evaluated as a percentage by calculating the total area of the pores by binarization and dividing it by the area subjected to image analysis.
  • the surface porosity of both surfaces of the polypropylene-based resin layer was approximately the same, and the surface porosity of both surfaces of the polyethylene-based resin layer was also approximately the same. Furthermore, the surface porosity between each of the two polypropylene-based resin layers was also approximately the same.
  • Electrode resistance ER is defined as the resistance ( ⁇ cm 2 ) of the separator filled with electrolyte by filling the polyolefin microporous membrane with electrolyte.
  • the unit of electrical resistance is ⁇ cm 2.
  • the resistance of the separator is characterized by cutting small pieces of the separator from the finished material and then placing these pieces between two platinum electrodes.
  • EC ethylene carbonate
  • EMC ethyl methyl carbonate
  • the resistance (R) of the separator in ohms ( ⁇ ) is measured by a four-probe AC impedance method. To reduce measurement errors at the platinum electrode/separator interface, multiple measurements are required by adding more layers.
  • the resistance value per ⁇ m obtained by dividing the obtained Rs by the film thickness is taken as the electrical resistance ER ( ⁇ cm2 / ⁇ m).
  • shutdown characteristics The shutdown characteristic was confirmed using a cell for measuring electrical resistance.
  • the electrolyte solution in which LiPF 6 was dissolved in the mixed solvent to a concentration of 1 mol/L was impregnated into a polyolefin microporous membrane to obtain a separator sample.
  • the separator sample piece impregnated with the electrolyte solution was sandwiched between nickel electrodes and heated at a rate of 10°C/min.
  • the electrical resistance ER was measured using a resistance measuring device (LCR Hi-Tester (manufactured by Hioki Electric Industry Co., Ltd.)) at a measurement frequency of 1 kHz.
  • LCR Hi-Tester manufactured by Hioki Electric Industry Co., Ltd.
  • the polyolefin microporous membrane is heated to a temperature above the melting point of the PE resin, all or part of the pores of the PP resin layer are blocked in this temperature range, and the resistance of the separator film measured as impedance increases, and if it exceeds 1000 ⁇ , it is determined that there is a shutdown characteristic.
  • Tables 1 and 2 the polyolefin microporous membranes that had the shutdown property were marked with ' ⁇ ', and the polyolefin microporous membranes that did not had the shutdown property were marked with ' ⁇ '.
  • a test piece 80 mm wide in the MD direction was taken from the polyolefin microporous membrane, and measurements were performed at three points, the center and the left and right ends (50 mm inside from the end faces), using a B-type Gurley densometer (manufactured by Toyo Seiki Co., Ltd.) in accordance with JIS P8117. The average value of the three points was evaluated as the air permeability value.
  • a rheometer ARES (model: ARES) manufactured by TA Instruments was used to measure the shear dynamic viscoelasticity of the molten PP resin.
  • a cone-parallel plate (cone angle 0.1 rad) was used for the geometry.
  • Dynamic viscoelasticity measurements were performed at four temperatures of 220°C, 200°C, 180°C, and 160°C under the conditions of a frequency range of 400 to 0.01 s-1 (5 points per decade) and strain of 0.1 (10%), and a master curve was created based on the measurement data at 200°C. The viscosity value that became a constant value in the frequency range of 0.01 s-1 or less was taken as the zero shear viscosity.
  • the creation of a master curve based on the measurement data at 200°C and the calculation of the zero shear viscosity based on this master curve are referred to as "200°C conditions".
  • the zero shear viscosity of the PP resin used in Examples 1 to 16 and Comparative Examples 1 to 4 at 200°C was 16,000 Pa ⁇ s.
  • the zero shear viscosity of the PE resin used in Examples 1 to 16 and Comparative Examples 1 to 4 at 200°C was 34,000 Pa ⁇ s.
  • Example 1 Hereinafter, an example of the method for producing the polyolefin microporous membrane of Example 1 will be described.
  • the method for producing the polyolefin microporous membrane of Example 1 is not limited to the method described below, and other methods may be used.
  • the polyolefin microporous membrane of Example 1 may be produced by using unstretched PP raw material or PE raw material and performing a lamination process and a stretching process.
  • a precursor film having a three-layer structure including a PE layer (a three-layer structure of a PP layer/PE layer/PP layer) was obtained by co-extruding a polypropylene resin and a polyethylene resin using a co-extruder equipped with a multi-manifold die at a die temperature (co-extrusion temperature) of (180 to 230)° C., with the PE layer as an intermediate layer and PP layers formed on both sides of the intermediate layer.
  • the content of the PE layer in the precursor film was 12.8% by mass.
  • the obtained precursor film was then heat-treated in a temperature range of 128.0°C to 136.0°C, and the heat-treated precursor film was then low-temperature stretched in a cold stretching zone.
  • the low-temperature stretched precursor film was then high-temperature stretched in a hot stretching zone at 130 to 135°C at a stretch ratio of 180 to 300% (maximum stretch ratio), and then heat-relaxed until the stretch ratio reached 100 to 200% (final stretch ratio). Thereafter, the film was heat-set at a constant temperature to produce a porous film.
  • the precursor film was stretched by uniaxial stretching in the machine direction (MD). The results are shown in Table 1.
  • the PE content, film thickness, surface porosity of the PP layer and PE layer, ER, porosity, puncture strength, puncture strength per thickness equivalent to the substantial resin component excluding pores (formula (1)), puncture elongation, shutdown property, tensile strength, tensile elongation, air permeability, and bending degree of the polyolefin microporous film of Example 1 are shown in Table 1.
  • Example 2 to 16 Comparative Example 1 A polyolefin microporous membrane was produced in the same manner as in Example 1, except that the membrane thickness and PE content were changed to those shown in Table 1 by adjusting the amount of resin discharged during melt extrusion. The results are shown in Tables 1 and 2.
  • a porous film was obtained in which the PE content was controlled to 5% to 45% by mass, the surface porosity of the PP layer was controlled to 5% to 30%, and the surface porosity of the PE layer was controlled to 5% to 20.6%.
  • the porous film thus obtained had an ER of 0.06 ⁇ cm 2 / ⁇ m or less, a puncture strength formula (I) per thickness equivalent to the substantial resin component excluding the pores was 0.44 or more, a puncture elongation of 5.8 mm or more, a shutdown characteristic, and a bending degree of 1.6 or less. From these results, it can be said that the porous films obtained in Examples 1 to 16 have both low resistance and high puncture strength and have shutdown characteristics, and can be suitably used, for example, as separators for lithium ion batteries.
  • Comparative Example 1 which is a porous film in which the PE content was controlled to more than 45% by mass
  • the surface porosity of the PP was 10.0% and the surface porosity of the PE exceeded 20%, but an effective pore path length that could become a through hole was not formed
  • the ER exceeded 0.06 ⁇ cm2 / ⁇ m
  • the tortuosity exceeded 1.6
  • the pin puncture strength formula (I) per thickness equivalent to the substantial resin component excluding the pore portion was 0.44 or less, which was an insufficient result.
  • Comparative Examples 2, 3, and 4 which are PP porous films not containing PE, although the ER was low at 0.046 ⁇ cm2 / ⁇ m or less, the puncture strength formula (I) per thickness equivalent to the substantial resin component excluding the pores was 0.35 or less, the puncture elongation was 4.1 mm or less, and furthermore, they did not have shutdown properties, resulting in unsatisfactory results.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Cell Separators (AREA)

Abstract

L'invention concerne une membrane microporeuse de polyoléfine qui a une couche de résine de polyéthylène contenant une résine de polyéthylène et une couche de résine de polypropylène contenant une résine de polypropylène, le rapport de teneur de la résine de polyéthylène dans la masse totale de la membrane microporeuse de polyoléfine étant de 5 % en masse à 45 % ; la porosité de la membrane microporeuse de polyoléfine est de 42 % à 62 % ; le rapport d'ouverture de surface de la couche de résine de polypropylène est de 5 % à 30 % ; et le rapport d'ouverture de surface de la couche de résine de polyéthylène est de 5 % à 20,6 %.
PCT/JP2024/026674 2023-08-04 2024-07-25 Membrane microporeuse de polyoléfine, film séparateur pour dispositifs de stockage d'énergie l'utilisant, et dispositif de stockage d'énergie Pending WO2025033202A1 (fr)

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JP2008255202A (ja) * 2007-04-04 2008-10-23 Asahi Kasei Chemicals Corp 複合微多孔膜、電池用セパレータ、及び複合微多孔膜の製造方法
JP2014182962A (ja) * 2013-03-19 2014-09-29 Sony Corp セパレータ、電池、電池パック、電子機器、電動車両、蓄電装置および電力システム
JP2015022893A (ja) * 2013-07-19 2015-02-02 積水化学工業株式会社 耐熱性微多孔フィルム及びその製造方法
WO2015166949A1 (fr) * 2014-05-01 2015-11-05 積水化学工業株式会社 Film microporeux en résine synthétique résistant à la chaleur ainsi que procédé de fabrication de celui-ci, séparateur pour batterie secondaire à électrolyte non aqueux, et batterie secondaire à électrolyte non aqueux
WO2017073781A1 (fr) * 2015-10-30 2017-05-04 宇部興産株式会社 Film poreux et dispositif de stockage d'électricité
JP2017141428A (ja) * 2016-02-09 2017-08-17 宇部興産株式会社 ポリオレフィン微多孔膜、蓄電デバイス用セパレータフィルム、及び蓄電デバイス
WO2018155287A1 (fr) * 2017-02-23 2018-08-30 東レ株式会社 Film poreux, séparateur pour batterie rechargeable, et batterie rechargeable
US20200220163A1 (en) * 2019-01-08 2020-07-09 Ningde Amperex Technology Limited Electrode with scaffold-structured composite layer and protection layer for improved battery performance
JP2020104422A (ja) * 2018-12-27 2020-07-09 宇部興産株式会社 ポリオレフィン微多孔膜及び蓄電デバイス
JP2020522094A (ja) * 2017-05-26 2020-07-27 セルガード エルエルシー 新規な又は改良された微多孔膜、電池用セパレータ、コーティングされたセパレータ、電池、及び関連方法

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2008255202A (ja) * 2007-04-04 2008-10-23 Asahi Kasei Chemicals Corp 複合微多孔膜、電池用セパレータ、及び複合微多孔膜の製造方法
JP2014182962A (ja) * 2013-03-19 2014-09-29 Sony Corp セパレータ、電池、電池パック、電子機器、電動車両、蓄電装置および電力システム
JP2015022893A (ja) * 2013-07-19 2015-02-02 積水化学工業株式会社 耐熱性微多孔フィルム及びその製造方法
WO2015166949A1 (fr) * 2014-05-01 2015-11-05 積水化学工業株式会社 Film microporeux en résine synthétique résistant à la chaleur ainsi que procédé de fabrication de celui-ci, séparateur pour batterie secondaire à électrolyte non aqueux, et batterie secondaire à électrolyte non aqueux
WO2017073781A1 (fr) * 2015-10-30 2017-05-04 宇部興産株式会社 Film poreux et dispositif de stockage d'électricité
JP2017141428A (ja) * 2016-02-09 2017-08-17 宇部興産株式会社 ポリオレフィン微多孔膜、蓄電デバイス用セパレータフィルム、及び蓄電デバイス
WO2018155287A1 (fr) * 2017-02-23 2018-08-30 東レ株式会社 Film poreux, séparateur pour batterie rechargeable, et batterie rechargeable
JP2020522094A (ja) * 2017-05-26 2020-07-27 セルガード エルエルシー 新規な又は改良された微多孔膜、電池用セパレータ、コーティングされたセパレータ、電池、及び関連方法
JP2020104422A (ja) * 2018-12-27 2020-07-09 宇部興産株式会社 ポリオレフィン微多孔膜及び蓄電デバイス
US20200220163A1 (en) * 2019-01-08 2020-07-09 Ningde Amperex Technology Limited Electrode with scaffold-structured composite layer and protection layer for improved battery performance

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