WO2019074122A1 - ポリオレフィン微多孔膜及びこれを用いたリチウムイオン二次電池 - Google Patents
ポリオレフィン微多孔膜及びこれを用いたリチウムイオン二次電池 Download PDFInfo
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- WO2019074122A1 WO2019074122A1 PCT/JP2018/038211 JP2018038211W WO2019074122A1 WO 2019074122 A1 WO2019074122 A1 WO 2019074122A1 JP 2018038211 W JP2018038211 W JP 2018038211W WO 2019074122 A1 WO2019074122 A1 WO 2019074122A1
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- polyolefin
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B2307/50—Properties of the layers or laminate having particular mechanical properties
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- B32B2307/518—Oriented bi-axially
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- B32B2307/50—Properties of the layers or laminate having particular mechanical properties
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- B32B2307/00—Properties of the layers or laminate
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B2307/00—Properties of the layers or laminate
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B2307/00—Properties of the layers or laminate
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B32B2457/00—Electrical equipment
- B32B2457/10—Batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- 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
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- 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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to a microporous polyolefin membrane and a lithium ion secondary battery using the same.
- the microporous polyolefin membrane is used for battery separators, capacitor separators, fuel cell materials, precision filtration membranes, and the like, and is particularly used as a separator for lithium ion secondary batteries.
- the separator prevents direct contact between the positive and negative electrodes, and also allows ions to permeate through the electrolyte held in the fine pores.
- lithium ion secondary batteries have been applied not only to small electronic devices such as mobile phones and laptop computers, but also to electric vehicles such as electric vehicles and small electric motorcycles. Since the lithium ion secondary battery for vehicle use tends to have a large capacity per unit cell, the calorific value at the time of abnormal heat generation of the battery also increases. Therefore, improvement in safety has become a more important issue due to the increase in demand for lithium ion secondary batteries in automotive applications. On the other hand, from the viewpoint of increasing the capacity, increasing energy density, reducing the weight, and reducing the thickness of lithium ion secondary batteries, the mainstream of the exterior material of lithium ion secondary batteries is shifting from metal cans to laminate films.
- Laminated batteries are more flexible than the rectangular or cylindrical batteries, and there is concern about battery swelling and distortion due to gas generation.
- separators with an adhesive layer on the surface should be used. After assembling the battery and using it while heating and pressing the battery (herein also referred to as “heat press” in the present specification), an adhesion process of bonding the separator and the electrode is performed.
- Patent Documents 1 to 7 Various raw materials or materials of microporous polyolefin membranes have been studied as a base material of such lithium ion secondary battery separators.
- Patent Document 1 discloses a first microporous layer (surface layer) made of a polyethylene resin containing ultrahigh molecular weight polyethylene and a second microporous layer made of a polyolefin resin containing high density polyethylene and polypropylene (intermediate layer (intermediate layer) Polyolefin multilayer microporous membrane having at least three layers including a layer), a pin puncture strength of 25 g / ⁇ m or more, a static friction coefficient to aluminum foil of 0.40 or more, and a meltdown temperature of 180 ° C. or more It is done.
- Patent Document 2 discloses a first microporous membrane layer including a first polyethylene, a first polypropylene, and a second polypropylene different from the first polypropylene, and a second microporous membrane layer including the first polyethylene and the second polyethylene.
- a multilayer microporous membrane is described which has at least a piercing strength of 3,500 mN or more and an air permeability of 1,000 seconds / cm 3 or less after thermal compression.
- Patent Documents 3 and 4 show a microporous membrane made of polyolefin in which a microporous membrane A having polyethylene and polypropylene as essential components and a microporous membrane of polyethylene B are integrally laminated, and the membrane is occupied by the microporous membrane A of polypropylene.
- a microporous polyolefin film characterized in that the ratio is 3 to 50% by mass and the film thickness is 5 to 20 ⁇ m is described.
- Patent Document 5 includes a first microporous layer containing polypropylene and polyethylene, and a second microporous layer laminated on the first microporous layer, and the first microporous layer has a surface layer.
- a microporous polyolefin membrane is described which is characterized in that it forms and the heat of fusion of polypropylene is 90 J / g or more.
- Patent Document 6 is a microporous polyolefin film comprising polyethylene and polypropylene as essential components and comprising a laminated film of three layers, having an average pore diameter of 0.02 ⁇ m or more and 1 ⁇ m or less, and polypropylene in at least one surface layer.
- a microporous polyolefin membrane is described in which the mixing ratio of is more than 50% by mass and not more than 95% by mass, and the content of polyethylene in the entire membrane is 60% by mass or more and 95% by mass or less.
- Patent Document 7 shows a polyolefin microporous film including a laminated film of two or more layers, wherein at least one surface layer has a thickness of 0.2 ⁇ m to 4 ⁇ m, and 5% by mass to 60% by mass of inorganic particles. % Or less, at least another layer contains at least 50% by weight of polyethylene, air permeability is 50 seconds / 100 cc or more and 1000 seconds / 100 cc or less, and puncture strength is 3.0 N / 20 ⁇ m or more A microporous membrane is described.
- the separators when the heat pressing is performed, the separators may be shrunk to cause winding displacement, deflection, or distortion of the battery.
- the end face of the electrode and the separator may be dislocated or wrinkles may occur during hot pressing.
- the defective rate of the battery is increased due to the occurrence.
- the permeability and cycle characteristics of the battery after the heat pressing may be lowered.
- a separator exhibiting good short circuit resistance in a short circuit test under severe conditions is required.
- an object of the present invention is to provide a microporous polyolefin membrane that can suppress distortion of the battery during hot pressing derived from the separator, and deterioration in permeability and cycle characteristics.
- another object of the present invention is to provide a microporous polyolefin membrane having good short circuit resistance in a short circuit test under severe conditions.
- the inventors have found that the above problems can be solved by setting the laminated structure of the polyolefin microporous membrane, the proportion of polypropylene in each layer, and the TD heat shrinkage in a state where a load is applied to the MD, etc.
- the present invention has been completed. That is, the present invention is as follows.
- a microporous polyolefin membrane having a laminated structure comprising at least one layer of an A layer containing a polyolefin and a layer B containing a polyolefin,
- the polypropylene contained in the layer A is 0% by mass or more and less than 3% by mass
- the polypropylene contained in the layer B is 1% by mass or more and less than 30% by mass
- the proportion of the polypropylene contained in the layer A is PPA (mass %)
- PPB mass % by mass
- PPB PPA
- a microporous polyolefin membrane having a laminated structure comprising an A layer containing polyolefin and at least one B layer containing polyolefin on both sides thereof,
- the polyolefin microporous membrane according to claim 1 wherein the ratio of the thickness of the layer A to the total thickness of the polyolefin microporous membrane is 40% or more and 90% or less.
- the polyolefin microporous film according to claim 1 or 2 wherein the content of inorganic particles in the layer B is less than 5% by mass.
- the proportion of molecules having a molecular weight of 3,000,000 or more in the integral curve of gel permeation chromatography (GPC) measurement of the above microporous polyolefin membrane is 10% by mass or less, and the proportion of molecules having a molecular weight of 30,000 or less is 3.0% by mass or less
- the microporous polyolefin membrane according to any one of claims 1 to 4 which has a melt index of 0.1 g / 10 min or more and 3.0 g / 10 min or less under a load of 21.6 kgf at 190 ° C.
- the melt viscosity under a load of 21.6 kgf at 190 ° C. in the layer A of the microporous polyolefin membrane is 0.01 g / 10 min or more and 0.3 g / 10 min or less.
- Polyolefin microporous membrane as described.
- the melt index under a load of 21.6 kgf at 190 ° C. in the layer B of the microporous polyolefin membrane is more than 0.3 g / 10 min and not more than 2.0 g / 10 min.
- the ratio of the melt index of the layer B to the melt index of the layer A of the microporous polyolefin membrane is 1.5 or more and 20 or less.
- a microporous polyolefin membrane which can provide a separator capable of suppressing distortion of a battery during hot pressing and deterioration of battery characteristics while maintaining safety.
- a microporous polyolefin membrane can be provided which can provide a separator having good short circuit resistance in short circuit test under severe conditions such as nail penetration test.
- FIG. 1 (A) is a schematic view of a shutdown temperature measuring device
- FIG. 1 (B) is a schematic view for illustrating a microporous membrane fixed on a nickel foil in the measurement of the shutdown temperature
- FIG. 1C is a schematic view for explaining masking of a nickel foil in the measurement of the shutdown temperature
- FIG. 2 is a schematic view for explaining a method of measuring the thermal contraction rate (%) of TD in a state where a certain load is applied to the MD.
- this embodiment an embodiment of the present invention
- the present invention is not limited to the present embodiment.
- the upper limit value and the lower limit value of each numerical range can be arbitrarily combined.
- the microporous polyolefin membrane of the present embodiment has a laminated structure of two or more layers including at least one layer of an A layer containing polyolefin and a layer of B containing polyolefin.
- the microporous polyolefin membrane preferably has a laminated structure of three or more layers provided with one B layer each on both sides (both sides) of the A layer.
- the laminated structure is not limited to the two-layer structure of "A-layer-B layer" or the three-layer structure of "B-layer-A-layer-B layer” as long as it has one layer each of the A layer and the B layer.
- the microporous polyolefin membrane may have one or more additional layers formed on either or both of the B layers or between the A and B layers.
- additional layer include a layer containing polyolefin, a heat-resistant layer containing a heat-resistant resin such as inorganic particles and a crosslinkable polymer, and an adhesive layer containing an adhesive polymer.
- the layers A and B contain a polyolefin, preferably composed of a polyolefin.
- the form of the polyolefin of layer A and layer B may be a microporous body of polyolefin, for example, a woven fabric of polyolefin fibers (woven fabric), a nonwoven fabric of polyolefin fibers, and the like.
- polyolefins include homopolymers, copolymers, or multistage polymers obtained using ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, and 1-octene as monomers. These polymers may be used alone or in combination of two or more.
- the polyolefin is preferably at least one selected from the group consisting of polyethylene, polypropylene, and copolymers thereof from the viewpoint of the shutdown and meltdown properties of the separator.
- polyethylene examples include low density polyethylene (LDPE), linear low density polyethylene (LLDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), high molecular weight polyethylene (HMWPE), and ultra high molecular weight polyethylene ( UHMWPE) and the like.
- LDPE low density polyethylene
- LLDPE linear low density polyethylene
- MDPE medium density polyethylene
- HDPE high density polyethylene
- HMWPE high molecular weight polyethylene
- UHMWPE ultra high molecular weight polyethylene
- high density polyethylene refers to polyethylene having a density of 0.942 to 0.970 g / cm 3 .
- the density of polyethylene refers to a value measured according to D) density gradient tube method described in JIS K7112 (1999).
- polypropylene examples include isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene.
- copolymer of ethylene and propylene examples include ethylene-propylene random copolymer and ethylene-propylene rubber.
- the amount of polypropylene contained in layer A is preferably 0% by mass or more and less than 3% by mass, more preferably 0% by mass or more and less than 1% by mass, most preferably, based on the total mass of the resin component constituting layer A.
- a layer does not contain polypropylene. By containing less than 3% by mass of polypropylene in the layer A, the mechanical strength and elongation of the microporous polyolefin membrane become better.
- the amount of polyethylene is preferably 90% by mass to 100% by mass, more preferably 97% by mass to 100% by mass, based on the total mass of the resin component constituting the layer A. % Or less, most preferably, the A layer is composed of polyethylene.
- the high percentage of polyethylene contained in the layer A makes the shutdown function of the microporous polyolefin membrane better.
- the ratio of the thickness of layer A to the total thickness (total thickness) of the microporous polyolefin membrane is 40% or more and 90% or less, preferably 50% or more and 90% or less, more preferably 55% or more and 85% or less Preferably, they are 60% or more and 80% or less.
- the ratio of the thickness of the layer A is 90% or less, the melting point of the entire microporous polyolefin membrane does not become too low, and the thermal contraction of the separator can be suppressed. Moreover, it can suppress that A layer is closed and the permeability falls at the time of a heat press.
- the layer A contains less polypropylene than the layer B, the layer A tends to have higher toughness and a lower melting point than the layer B.
- the layer A plays a role as a base of the microporous polyolefin membrane, and the mechanical strength and elongation of the microporous polyolefin membrane become better, and , Can secure the shutdown function.
- the B layer contains more polypropylene than the A layer. That is, when the proportion of polypropylene contained in the layer A is PPA (mass%) and the proportion of polypropylene contained in the layer B is PPB (mass%), PPB> PPA.
- the lower limit of the amount of polypropylene contained in layer B is preferably 1% by mass or more, more preferably 3% by mass or more, and still more preferably 4% by mass or more, based on the total mass of the resin component constituting layer B. Still more preferably, it is 5% by mass or more, and most preferably 10% by mass or more.
- the upper limit of the amount of polypropylene contained in the layer B is preferably 30% by mass or less, more preferably 27% by mass or less, still more preferably 25% by mass or less, based on the total mass of the resin component constituting the layer B. Still more preferably, it is at most 20% by mass, most preferably at most 18% by mass.
- the range of the amount of polypropylene contained in the layer B is, for example, 1% by mass or more and 30% by mass or less, 1% by mass or more and less than 30% by mass, preferably 5% by mass or more and less than 30% by mass, more preferably 5% by mass % Or more and 25% by mass or less, more preferably 10% by mass or more and 20% by mass or less.
- the layer A secures strength and elongation, and the polypropylene contained in the layer B is in the above range, when heat pressing is performed in a state where a certain tension is applied to the MD of the polyolefin microporous film, TD Since it is possible to suppress heat shrinkage, distortion can be suppressed.
- polypropylene has a melting point higher than that of polyethylene, the presence of polypropylene in the above-mentioned range in layer B prevents the surface layer from melting and the permeability from being lowered at the time of heat pressing while securing the shutdown function of the separator. can do.
- the amount of polyethylene is preferably 60% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 95% by mass based on the total mass of the resin component constituting the B layer. % Or less, more preferably 75% by weight or more and 90% by weight or less, and most preferably the B layer is composed of polypropylene and polyethylene.
- the viscosity average molecular weight of the polyethylene contained in layer A and layer B is preferably 50,000 or more and not more than 100,000, more preferably 100,000 or more and 5,000,000 or less, still more preferably 120,000 or more and 3,000,000 or less, and most preferably 15 More than one million and less than one million.
- the molecular weight is 50,000 or more, a microporous polyolefin membrane having sufficient strength can be obtained, and when it is 10,000,000 or less, the internal stress during stretching does not become too large, so excessive heat shrinkage can be suppressed. it can.
- the molecular weight distribution (Mw / Mn) of polyethylene is preferably 20 or less, more preferably 17 or less, still more preferably 14 or less, still more preferably 10 or less, most preferably 8 or less, preferably 2 or more, More preferably, it is 3 or more, more preferably 4 or more.
- Mw / Mn The molecular weight distribution of polyethylene is preferably 20 or less, more preferably 17 or less, still more preferably 14 or less, still more preferably 10 or less, most preferably 8 or less, preferably 2 or more, More preferably, it is 3 or more, more preferably 4 or more.
- Mw / Mn The molecular weight distribution (Mw / Mn) of polyethylene is preferably 20 or less, more preferably 17 or less, still more preferably 14 or less, still more preferably 10 or less, most preferably 8 or less, preferably 2 or more, More preferably, it is 3 or more, more preferably 4 or more.
- the molecular weight distribution is 20 or less, a
- the A layer contains UHMWPE.
- the amount of UHMWPE is preferably 5% by mass or more, more preferably 10% by mass or more, preferably 70% by mass or less, more preferably, based on the total mass of the polyolefin in the A layer. Is 60 mass% or less.
- the layer A contains UHMWPE, it is possible to improve the breaking elongation of the microporous polyolefin membrane having a laminated structure as a substrate.
- the B layer may contain UHMPWE.
- the amount of UHMWPE is preferably less than 30% by mass, more preferably less than 20% by mass, still more preferably less than 10% by mass, based on the total mass of the polyolefin in the B layer.
- B layer contains UHMWPE, by making the amount of UHMWPE in B layer 30 mass% or less, melt viscosity does not rise too much at the time of temperature rising, and shutdown response time does not become too slow. This effect is remarkable when the B layer includes the structure of B layer-A layer-B layer to which heat is transferred first.
- the proportion of UHMWPE relative to the total mass of the polyolefin throughout the microporous polyolefin membrane is preferably less than 45% by mass, more preferably less than 35% by mass, still more preferably less than 25% by mass.
- the ratio of UHMWPE to the total mass of the polyolefin throughout the microporous polyolefin membrane is less than 45%, it is possible to suppress an increase in thermal contraction due to residual stress.
- the B layer preferably contains LDPE.
- the amount of LDPE is preferably 3% by mass or more, more preferably 5% by mass or more, based on the total mass of the polyolefin in the B layer.
- the inclusion of low LDPE in the layer B can lower the shutdown temperature and shutdown response time. This effect is remarkable when the B layer includes the structure of B layer-A layer-B layer to which heat is transferred first.
- Layer A may contain LDPE.
- the amount of LDPE is preferably 25% by mass or less, more preferably 20% by mass or less, still more preferably 15% by mass or less, based on the total mass of the polyolefin in the layer A Is 10% by mass or less.
- the fall of breaking elongation and mechanical strength can be suppressed by the ratio of LDPE being 25 mass% or less. This effect is remarkable when the layer A includes the structure of the layer B-A layer-B layer which secures mechanical strength as a substrate.
- the ratio of LDPE to the total mass of the polyolefin throughout the microporous polyolefin membrane is preferably 25% by mass or less, more preferably 18% by mass or less, and still more preferably 13% by mass or less.
- the ratio of LDPE to the total mass of the polyolefin in the entire microporous polyolefin membrane is 25% by mass or less, the reduction of excessive crystallinity is prevented, and thermal contraction due to shrinkage of the amorphous portion below the melting point due to residual stress It is possible to suppress the problems of increase and decrease in permeability and cycle characteristics. This effect is remarkable when it is used as a laminate type secondary battery separator which requires a step of fusing a separator having an adhesive layer with an electrode by heat pressing.
- the lower limit value of the viscosity average molecular weight of the polypropylene contained in layer A and layer B is preferably 50,000 or more, more preferably 100,000 or more, further preferably 150,000 or more, still more preferably 300,000 or more, most preferably 35 It is over ten thousand.
- the upper limit value of the viscosity average molecular weight of the polypropylene contained in the layer A and the layer B is preferably 10,000,000 or less, more preferably 5,000,000 or less, still more preferably 1,000,000 or less, and most preferably 800,000 or less.
- the range of viscosity average molecular weight of the polypropylene contained in the layer A and the layer B is 50,000 to 10,000,000, more preferably 100,000 to 5,000,000, and most preferably 150,000 to 1,000,000.
- the melt index of the microporous polyolefin membrane does not become too high, so that melting at the time of heat pressing can be prevented.
- the excellent short circuit resistance of the battery under such severe conditions is advantageous, for example, in the field where a higher degree of safety is required, such as a vehicle battery separator.
- the molecular weight of polypropylene is 10,000,000 or less, the internal stress at the time of stretching does not become too large, so that excessive heat shrinkage can be suppressed.
- the molecular weight distribution (Mw / Mn) of polypropylene is preferably 30 or less, more preferably 24 or less, and most preferably 12 or less.
- the molecular weight distribution of the polypropylene is 30 or less, since the low molecular weight polypropylene component is small, the miscibility with polyethylene becomes good, and a polyolefin microporous film having higher heat resistance derived from polypropylene can be obtained. .
- the polypropylene contained in A layer and B layer is a homopolymer.
- the amount of the homopolymer is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 98% by mass or more, most preferably 100% by mass, based on the total mass of polypropylene in the entire polyolefin microporous membrane (All).
- the homopolymer is 90% by mass or more, it is possible to suppress the further melting of the microporous film due to the temperature rise at the time of short circuit.
- homopolymers have high crystallinity, phase separation with a plasticizer tends to proceed, and a membrane having good porosity and high permeability tends to be obtained.
- the output and cycle characteristics can be favorably affected. Furthermore, since the homopolymer has few amorphous parts, it is possible to suppress an increase in thermal contraction due to shrinkage of the amorphous parts when heat is applied below the melting point or due to residual stress, and shrinkage of the amorphous parts. It is possible to suppress the problem that the permeability and the cycle characteristics are lowered by Although not limited to the application, this effect is remarkable in a laminate type secondary battery separator which requires a step of fusing a separator having an adhesive layer with an electrode by heat pressing.
- the ratio of the thickness of the layer B to the total thickness of the microporous polyolefin membrane is preferably 10% to 50%, more preferably 15% to 45%, and still more preferably 20% to 40%.
- Layers A and B are resins such as polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, nylon, polytetrafluoroethylene, polyvinylidene fluoride, etc. in addition to the above-mentioned polyolefins. May be further included.
- the proportion of molecules having a molecular weight of 3,000,000 or more in the integral curve of gel permeation chromatography (GPC) measurement of the microporous polyolefin membrane is preferably 10% by mass or less, more preferably 9% by mass or less, still more preferably 8% by mass or less Preferably it is 3 mass% or more, More preferably, it is 5 mass% or more.
- the ratio of molecules having a molecular weight of 30,000 or less in the integral curve of gel permeation chromatography (GPC) measurement of the microporous polyolefin membrane is preferably 3% by mass or less, more preferably 2.8% by mass or less, and most preferably Is 2.5 mass% or less, preferably 0.5 mass% or more, more preferably 0.8 mass% or more. If the high molecular weight polyethylene component is 10% by mass or less, the viscosity of the microporous polyolefin membrane does not become too high, and the shutdown function can be secured. In addition, when the low molecular weight polyethylene component is 3.0% by mass or less, the microporous polyolefin membrane can be prevented from being closed during heat pressing to reduce the permeability.
- GPC gel permeation chromatography
- the content of the inorganic particles in the layer B is preferably less than 5% by mass, more preferably less than 3% by mass, and most preferably free of inorganic particles.
- the content of the inorganic particles is less than 5% by mass, blistering and the like of the battery due to gas generation can be effectively suppressed. This effect is more pronounced in laminate type batteries in which the package is susceptible to deformation.
- inorganic particles when inorganic particles are present in an amount of 5% by mass or more in the layer B, the inorganic particles act as a starting point of fracture and the elongation decreases due to deterioration of mechanical safety, and the cycle due to disordered hole uniformity. It is not preferable because deterioration of properties tends to occur.
- the inorganic particles are not particularly limited, and, for example, oxide ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide, etc .; silicon nitride, titanium nitride, boron nitride Silicon carbide, calcium carbonate, aluminum sulfate, barium sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite And bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, kieselguhr, silica sand and other ceramics; and glass fibers. These may be used alone or in combinations of two or more. Among these, from the viewpoint of electrochemical stability, the inorganic particles are preferably at least one selected from the group consisting of silica, alumina
- the microporous polyolefin membrane of the present embodiment has a thermal shrinkage of 10% to 40%, preferably 15% to 35%, at 120 ° C. when measured under a certain load applied to MD. More preferably, they are 20% or more and 30% or less.
- the present inventors for example, in a laminate type battery including a wound body in which a laminate of an electrode and a separator is flatly wound in MD, the separator is wound in MD, and thus heat-pressed in a state of being restrained by MD.
- the thermal shrinkage of TD measured as described above being 40% or less, it is possible to effectively suppress the occurrence of a short circuit during bonding press, and the thermal shrinkage is By 10% or more, it discovered that the deflection
- the TD thermal contraction in the state of being held in the MD is in the above-mentioned range, it is estimated that the short circuit portion around the nail becomes difficult to spread even if the battery temperature rises in the nailing test. Therefore, the voltage drop can be made gentle.
- the microporous polyolefin membrane of the present embodiment preferably has a melt index (MI) under a load of 21.6 kgf at 190 ° C. of preferably 0.01 g / 10 min to 3.0 g / 10 min, more preferably 0.05 g / min. It is preferably 10 min to 1.5 g / 10 min, more preferably 0.1 g / 10 min to 0.6 g / 10 min, and most preferably 0.12 g / 10 min to 0.5 g / 10 min.
- MI melt index
- the melt index is 0.6 g / 10 min or less, the fluidity of the molten separator is low even if the battery is shorted due to a broken film and temperature rise of the battery is prevented, so that the rapid decrease in insulation can be prevented. It is preferable because it is presumed to be possible.
- the MI of the microporous polyolefin membrane can be controlled by the type and ratio of the polyolefin raw material used, the viscosity average molecular weight and the molecular weight distribution.
- the MI of layer A under a load of 21.6 kgf at 190 ° C. is preferably 0.30 g / 10 min or less, and more preferably 0.26 g / 10 min or less
- 0.22 g / 10 min or less is more preferable
- 0.01 g / 10 min or more is preferable
- 0.03 g / 10 min or more is more preferable
- MI of layer B under a load of 21.6 kgf at 190 ° C. preferably exceeds 0.3 g / min, and more preferably exceeds 0.35 g / min. It is further preferable to exceed 0.40 g / min, preferably 2.0 g / min or less, more preferably 1.8 g / min or less, and still more preferably 1.6 g / min or less.
- MI of B layer exceeds 0.3g / min, when short circuit and temperature inside the battery rises, it is presumed that it melts and shuts down quickly, resistance can be increased and heat generation can be suppressed. Ru.
- MI in the B layer is 2.0 g / min or less, the molten resin does not flow when the temperature in the battery rises due to a short circuit, and it is considered that an increase in the short circuit area can be suppressed.
- the ratio of MI of layer B to layer A is preferably 1.5 or more, and more preferably 1.8 or more It is preferably 2.1 or more, more preferably 20.0 or less, more preferably 18.0 or less, and still more preferably 16.0 or less. Since the ratio of MI of layer B to layer A is 1.5 or more, molten B layer penetrates into the pores of layer A when the temperature in the battery rises due to a short circuit, thereby increasing resistance; It is speculated that a sharp voltage drop can be suppressed by holding and supporting the shape of the layer A. When the ratio of MI of layer B to layer A is 20.0 or less, the affinity of the interface between layer A and layer B can be secured, and the layer structure can be stabilized.
- the polyolefin microporous membrane of the present embodiment preferably has a shutdown response time of 8 seconds to 30 seconds, more preferably 12 seconds to 22 seconds, still more preferably 14 seconds to 20 seconds, still more preferably 16 seconds or more. 18 seconds or less.
- “shutdown response time” refers to the time until the electrical resistance value reaches 10 2 ⁇ to 10 3 ⁇ in the shutdown characteristic test described in the examples.
- the shutdown response time is 12 seconds or more, it is possible to suppress that the micropores are closed during heat pressing and the permeability is reduced.
- a shutdown response time of 22 seconds or less is preferable because the safety required for in-vehicle applications can be further enhanced.
- the microporous polyolefin membrane of the present embodiment has a shutdown temperature of preferably 200 ° C. or less, more preferably 170 ° C. or less, still more preferably 150 ° C. or less, preferably 135 ° C. or more, more preferably 138 ° C. or more, further Preferably it is 140 degreeC or more.
- the polyolefin microporous membrane of the present embodiment preferably has a rupture temperature of 100 ° C. or higher, more preferably 130 ° C. or higher, still more preferably 150 ° C. or higher, still more preferably 170 ° C. or higher, and more than 170 ° C. Most preferably, 300 ° C. or less is preferable, and 280 ° C.
- shutdown temperature means the first decimal point of the temperature value when the value of the electrical resistance of the microporous film once reaches 10 3 ⁇ in the shutdown characteristic test described in the examples.
- breakdown temperature means that the temperature is further increased after shutdown in the shutdown characteristic test described in the example, and the blocked membrane breaks and the electric resistance value is again 10 3 ⁇ .
- the temperature below when The shutdown temperature of the microporous polyolefin membrane is 150 ° C. or less, and the rupture temperature exceeds 170 ° C., which is preferable because thermal runaway at the time of internal short circuit of the battery can be prevented.
- the shutdown temperature is 135 ° C. or higher, it is possible to prevent the decrease in permeability during the bonding press.
- the microporous polyolefin film of the present embodiment preferably has a puncture strength (gf / 10 ⁇ m) per 10 ⁇ m of film thickness of preferably 170 gf / 10 ⁇ m or more, more preferably 180 gf / 10 ⁇ m or more, still more preferably 190 gf / 10 ⁇ m or more. Is 1500 gf / 10 ⁇ m or less, more preferably 1300 gf / 10 ⁇ m or less.
- the puncture strength is 170 gf / 10 ⁇ m or more
- the puncture strength is 170 gf / 10 ⁇ m or more
- the microporous polyolefin membrane of the present embodiment has an air permeability (sec / 100 cc) of preferably 30 sec / 100 cc or more, more preferably 40 sec / 100 cc or more, still more preferably 50 sec / 100 cc or more, and preferably 500 sec / 100 cc or less More preferably, it is 400 sec / 100 cc or less, more preferably 300 sec / 100 cc or less, still more preferably 200 sec / 100 cc or less, and most preferably 100 sec / 100 cc or less.
- the air permeability is 30 sec / 100 cc or more, a minute short circuit of the battery can be suppressed.
- the air permeability is 500 sec / 100 cc or less, the output of the battery can be secured.
- Microporous polyolefin membrane of the present embodiment is preferably a tensile strength at break in the TD is 100 kgf / cm 2 or more 5000 kgf / cm 2 or less, more preferably 300 kgf / cm 2 or more 3000 kgf / cm 2 or less, more preferably 500 kgf / cm 2 It is more than 2000 kgf / cm 2 .
- the tensile breaking strength of TD is 100 kgf / cm 2 or more, the possibility of the separator being broken when the battery is deformed by an external force can be reduced.
- a residual stress can be made low as the tensile breaking strength of TD is 5000 kgf / cm ⁇ 2 > or less, and since thermal contraction can be suppressed, it is preferable. This effect is more pronounced in laminate type batteries in which the package is susceptible to deformation.
- the polyolefin microporous membrane of the present embodiment preferably has a tensile elongation of 10% or more and 500% or less, more preferably 30% or more and 300% or less, and still more preferably 50% or more and 200% or less.
- TD tensile elongation
- the microporous polyolefin membrane may be distorted in a minute section generated when laminating the microporous polyolefin membrane and the electrode in the presence of minute foreign substances, and pinholes may be generated to cause a battery failure due to a micro short circuit. Can be reduced.
- TD elongation By setting the TD elongation to 500% or less, it is possible to prevent longitudinal tearing of the separator (tearing of MD) when the battery is deformed by an external force or the like without being excessively oriented to MD. This effect is more pronounced in laminate type batteries in which the package is susceptible to deformation.
- the microporous polyolefin membrane preferably has low electron conductivity, ion conductivity, high resistance to organic solvents, and a fine pore diameter.
- the microporous polyolefin membrane can be used as a lithium ion secondary battery separator, and in particular, can be suitably used as a laminate type lithium ion secondary battery separator.
- the thickness of the microporous polyolefin membrane is preferably 0.1 ⁇ m to 100 ⁇ m, more preferably 1 ⁇ m to 50 ⁇ m, still more preferably 3 ⁇ m to 25 ⁇ m, still more preferably 15 ⁇ m or less, and most preferably 10 ⁇ m or less.
- the thickness of the microporous polyolefin membrane is preferably 0.1 ⁇ m or more from the viewpoint of mechanical strength, and preferably 100 ⁇ m or less from the viewpoint of increasing the capacity of a lithium ion secondary battery.
- the total thickness of the microporous polyolefin membrane can be adjusted, for example, by controlling the die lip spacing, the stretching ratio in the stretching step, and the like.
- the average pore diameter of the microporous polyolefin membrane is preferably 0.03 ⁇ m or more and 0.70 ⁇ m or less, more preferably 0.04 ⁇ m or more and 0.20 ⁇ m or less, and still more preferably 0.05 ⁇ m or more and 0.10 ⁇ m or less.
- the average pore diameter of the microporous polyolefin membrane is preferably 0.03 ⁇ m or more and 0.70 ⁇ m or less from the viewpoint of high ion conductivity and withstand voltage.
- the average pore diameter is controlled by controlling the composition ratio of the polyolefin, the cooling rate of the extruded sheet, the drawing temperature, the drawing ratio, the heat setting temperature, the drawing ratio at the heat setting, and the relaxation rate at the heat setting. It can be adjusted.
- the porosity of the microporous polyolefin membrane is preferably 25% to 95%, more preferably 30% to 65%, and still more preferably 35% to 55%.
- the porosity of the microporous polyolefin membrane is preferably 25% or more from the viewpoint of improving ion conductivity, and is preferably 95% or less from the viewpoint of withstand voltage characteristics.
- the porosity of the microporous polyolefin membrane can be controlled by controlling the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio during heat setting, and the relaxation rate during heat setting, and It can adjust by combining these.
- the viscosity average molecular weight (Mv) of the microporous polyolefin membrane is preferably 30,000 to 12,000,000, more preferably 50,000 to 2,000,000, and still more preferably 100,000 to 1,000. Or less, most preferably 500,000 or more and 900,000 or less.
- Mv The viscosity average molecular weight
- the melt tension at the time of melt molding becomes large and the formability becomes good, and there is a tendency that a high strength polyolefin microporous membrane is obtained by entanglement of polymers. preferable.
- the viscosity average molecular weight is 12,000,000 or less, it is easy to melt and knead uniformly, which is preferable because it tends to be excellent in sheet formability, particularly thickness stability. Further, when the viscosity average molecular weight is 1,000,000 or less, when used as a secondary battery separator, the pores are easily clogged at the time of temperature rise, which is preferable because a favorable fuse function tends to be obtained.
- a method of producing polyolefin microporous membrane is employable. For example, the following method: (1) A method of forming a sheet by melt-kneading a polyolefin resin composition and a pore-forming material, stretching as required, and then extracting the pore-forming material to make it porous; (2) A method in which the polyolefin resin composition is melt-kneaded and extruded at a high draw ratio, and then heat treatment and stretching are performed to peel off the polyolefin crystal interface to make it porous; (3) A method in which the polyolefin resin composition and the inorganic filler are melt-kneaded to be formed on a sheet, and then the interface between the polyolefin and the inorganic filler is peeled off by stretching to make it porous. (4) After dissolving the polyolefin resin composition, it
- the polyolefin resin composition used for layer A and the above-mentioned pore forming material are melt-kneaded to obtain a melt-kneaded product A, and the polyolefin resin composition used for layer B and the above-mentioned hole forming material are melt-kneaded to melt The kneaded material B is obtained.
- a polyolefin resin and, if necessary, other additives are introduced into a resin-kneading apparatus such as an extruder, a kneader, a laboplast mill, a kneading roll, or a Banbury mixer while heating and melting resin components.
- mixing a hole formation material by arbitrary ratios is mentioned.
- the pore forming material can include a plasticizer, an inorganic material, or a combination thereof.
- non-volatile solvent which can form a uniform solution above the melting point of polyolefin.
- non-volatile solvents include, for example, hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol . These plasticizers may be recovered by distillation or the like after extraction and reused.
- the polyolefin resin, the other additives and the plasticizer are preliminarily kneaded at a predetermined ratio in advance using a Henschel mixer or the like. More preferably, in the pre-kneading, only a part of the plasticizer is introduced, and the remaining plasticizer is kneaded while being appropriately heated and side-fed to the resin kneading apparatus.
- the dispersibility of the plasticizer is enhanced, and when the melt-kneaded product of the resin composition and the plasticizer is stretched in the form of a sheet in a later step, high magnification can be achieved without breaking the film. It tends to be able to be stretched.
- liquid paraffin is highly compatible with polyethylene or polypropylene when the polyolefin resin is polyethylene or polypropylene, and even if the melt-kneaded product is stretched, interfacial peeling between the resin and the plasticizer hardly occurs, and uniform stretching is achieved. Is preferable because it tends to be easy to implement.
- the ratio of the polyolefin resin composition to the pore-forming material is not particularly limited as long as it can be melt-kneaded uniformly and molded into a sheet.
- the mass fraction of the pore-forming material in the composition comprising the polyolefin resin composition and the pore-forming material is preferably 20% by mass or more, more preferably 25% by mass or more, and still more preferably 30% by mass or more.
- it is 38 mass% or less, More preferably, it is 36 mass% or less, More preferably, it is 34 mass% or less.
- the mass fraction of the pore-forming material is 38% by mass or less, the melt tension at the time of melt molding tends to be sufficient to improve the formability.
- the mass fraction of the pore forming material is 20% by mass or more, the polyolefin molecular chain is not cut even when the mixture of the polyolefin resin composition and the pore forming material is drawn at a high magnification, and the fine uniform It is easy to form a pore structure and to increase the strength.
- the inorganic material used as the pore-forming material is not particularly limited.
- the proportion of the inorganic material as a pore-forming material in the polyolefin resin composition is preferably 5% by mass or more, and 10% by mass or more based on the total mass of these, from the viewpoint of obtaining good separability. Is more preferably 99% by mass or less, and more preferably 95% by mass or less from the viewpoint of securing high strength.
- melt-kneaded products A and B of the resin composition and the pore-forming material are co-formed into a sheet shape laminated in the order of melt-kneaded product B-melt-kneaded product A-melt-kneaded product B, and sheet-like molding Get the body.
- the melt-kneaded product is co-extruded in a sheet form through a T die or the like, brought into contact with a heat conductor, and cooled to a temperature sufficiently lower than the crystallization temperature of the resin component.
- lifted As a heat conductor used for cooling solidification, metal, water, air, a plasticizer, etc. are mentioned. Among these, it is preferable to use a metal roll because the heat conduction efficiency is high.
- the die lip distance when co-extruding the melt-kneaded product from the T die into a sheet is preferably 200 ⁇ m to 3,000 ⁇ m, and more preferably 500 ⁇ m to 2,500 ⁇ m.
- the die-lip spacing is 200 ⁇ m or more, texture and the like are reduced, the influence on film quality such as streaks and defects is small, and risk of film breakage and the like can be reduced in the subsequent stretching step.
- the die lip distance is 3,000 ⁇ m or less, the cooling rate is fast, cooling unevenness can be prevented, and the thickness stability of the sheet can be maintained.
- the sheet-like formed body may be rolled.
- the rolling can be carried out by, for example, a press method using a double belt press or the like.
- the rolling area magnification is preferably more than one and not more than three times, and more preferably more than one and not more than two times.
- the rolling ratio exceeds 1 time, the plane orientation tends to increase and the film strength of the finally obtained porous film tends to increase.
- the rolling ratio is 3 times or less, the difference in orientation between the surface layer portion and the inside of the center is small, and a uniform porous structure tends to be formed in the thickness direction of the film.
- the pore-forming material is removed from the sheet-like compact to obtain a microporous polyolefin membrane.
- the sheet-like molded object is immersed in an extraction solvent, for example, the method of extracting a hole formation material and making it fully dry is mentioned.
- the method of extracting the pore-forming material may be either a batch system or a continuous system.
- the amount of pore forming material remaining in the porous membrane is preferably less than 1% by mass with respect to the mass of the entire porous membrane.
- an extraction solvent used when extracting the pore-forming material it is preferable to use a solvent which is a poor solvent for the polyolefin resin and a good solvent for the pore-forming material and whose boiling point is lower than the melting point of the polyolefin resin .
- extraction solvents examples include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorinated such as hydrofluoroether and hydrofluorocarbon Halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; and ketones such as acetone and methyl ethyl ketone.
- hydrocarbons such as n-hexane and cyclohexane
- halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane
- non-chlorinated such as hydrofluoroether and hydrofluorocarbon Halogenated solvents
- alcohols such as ethanol and isopropanol
- ethers such as diethyl ether and tetrahydrofuran
- ketones such as ace
- Stretching may be performed before extracting the pore-forming material from the sheet-like compact.
- the stretching method include methods such as uniaxial stretching, simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, multiple stretching, and the like. Simultaneous biaxial stretching is preferable from the viewpoint of improvement in puncture strength, uniformity of stretching, and fuse characteristics.
- simultaneous biaxial stretching refers to a stretching method in which stretching of MD (machine direction of continuous microporous membrane formation) and stretching of TD (direction across MD of microporous membrane at an angle of 90 °) are simultaneously performed. No, the draw ratio in each direction may be different.
- Sequential biaxial stretching refers to a stretching method in which stretching of MD and TD is performed independently, and when MD or TD is stretched, the other direction is fixed in a non-constrained state or a fixed length It will be in the state.
- the stretching temperature of the sheet-like molded product or the microporous polyolefin membrane is preferably 116 ° C. or more, more preferably 118 ° C. or more, and still more preferably 120 ° C. or more.
- the temperature at the time of stretching is preferably 129 ° C. or less, more preferably 127 ° C., and still more preferably 125 ° C. or less.
- the temperature at the time of stretching in particular, the temperature at the time of biaxial stretching to 129 ° C. or less, roughening of the pore size distribution due to melting of the film surface can be prevented, and cycle performance when the charge and discharge of the battery are repeated can be ensured.
- unevenness in the adhesion state is unlikely to occur when the electrode is heat-pressed when the electrode layer is in a state having an adhesive layer, because the surface state becomes uniform.
- this effect is remarkable when it is used as a laminate type secondary battery separator which requires a step of fusing the separator having the adhesive layer with the electrode by heat pressing.
- the stretching ratio is preferably in the range of 20 times to 100 times in terms of area ratio, more preferably in the range of 25 times to 70 times, and still more preferably 30 times to 50 times.
- the stretching ratio in each axial direction is preferably 4 to 10 times in MD, 4 to 10 times in TD, 5 to 8 times in MD, 5 to 8 times in TD Is more preferably in the range of 5 to 7 times in MD, and still more preferably in the range of 5 to 7 times in TD.
- heat setting may be performed after the stretching step or after the microporous polyolefin membrane is formed, and heat setting may be performed.
- the microporous polyolefin membrane may be subjected to post-treatments such as hydrophilization treatment with a surfactant or the like, or crosslinking treatment with an ionizing radiation or the like.
- the microporous polyolefin membrane is preferably heat-treated by heat treatment.
- a stretching operation performed at a predetermined temperature atmosphere and a predetermined stretching ratio, and / or a relaxation operation performed at a predetermined temperature atmosphere and a predetermined relaxation rate for the purpose of reduction of stretching stress can be mentioned.
- the relaxation operation may be performed after the stretching operation.
- the magnification of the stretching operation is preferably 1.1 times or more, more preferably 1.2 times or more, in the MD and / or TD of the membrane. Preferably, it is less than 2.3 times, more preferably less than 2.0 times.
- the product of the draw ratio of MD and TD is less than 3.5 times, More preferably, it is less than 3.0 times.
- the strain rate during stretching is preferably 3% / sec to 15% / sec, more preferably 4% / sec to 13% / sec, and most preferably 5% / sec to 11% / sec. is there.
- a relaxation operation is a reduction operation of the membrane to MD and / or TD.
- the relaxation rate is a value obtained by dividing the dimension of the film after the relaxation operation by the dimension of the film before the relaxation operation. In addition, when both MD and TD are eased, it is the value which multiplied the relaxation rate of MD and the relaxation rate of TD.
- the relaxation rate is preferably less than 1.0, more preferably less than 0.97, still more preferably less than 0.95, and most preferably less than 0.90.
- the relaxation rate is preferably 0.4 or more, more preferably 0.6 or more, and still more preferably 0.8 or more, from the viewpoint of film quality.
- the absolute value of strain rate during relaxation is preferably 0.4% / sec or more and 6.0% / sec or less, more preferably 0.5% / sec or more and 5.0% / sec or less, and most preferably 0.6% / sec or more and 4.0% / sec or less.
- the relaxation operation may be performed in both MD and TD, but may be performed in only one of MD and TD. By performing stretching and relaxation at the above magnification and strain rate, the thermal contraction of MD and / or TD can be controlled within an appropriate range.
- the stretching and relaxation operation after this plasticizer extraction is preferably performed in the TD.
- the temperature in the stretching and relaxation operation is preferably a weighted average value of -10 ° C to + 10 ° C or less of the melting point (hereinafter also referred to as "Tm") of the polyolefin resin contained in the B layer, and more preferably a weighted average value It is ⁇ 9 ° C. to + 5 ° C. or less, more preferably the weighted average value ⁇ 8 ° C. to + 1 ° C. or less.
- the weighted average of the melting points can be determined from the melting point determined by differential scanning calorimetry (DSC) measurement of each material and the weight fraction of each material contained in the B layer.
- DSC differential scanning calorimetry
- thermoplastic resin contained in the adhesive layer is not particularly limited.
- polyolefins such as polyethylene and polypropylene
- fluorine-containing resins such as polyvinylidene fluoride and polytetrafluoroethylene
- vinylidene fluoride-hexafluoropropylene copolymer fluorine Fluorinated rubbers such as vinylidene fluoride-tetrafluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene tetrafluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, etc .
- styrene-butadiene copolymer and its hydride acrylonitrile -Butadiene copolymer and its hydride, acrylonitrile-butadiene-styrene copolymer and its hydride, (meth) acrylic acid ester copolymer, styrene-acrylic acid ester copolymer, acrylonitrile Rubbers such
- the method for forming the adhesive layer on the surface of the microporous polyolefin membrane is not particularly limited, and known methods described in Japanese Patent No. 3839706, Japanese Patent Application Laid-Open No. 2013-203894, or Japanese Patent Application No. 2015-512124 can be used. It can be used.
- the laminate type lithium ion secondary battery of the present embodiment has at least one structure in which a positive electrode and a negative electrode are laminated via the polyolefin porous film of the present embodiment in an outer package made of a laminate film.
- stacked metal foil and the resin film is used, for example, the laminate film comprised from three layers of outer layer resin film / metal foil / inner layer resin film is illustrated.
- the outer layer resin film is for preventing the metal foil from being damaged by contact or the like, and examples thereof include resins such as nylon and polyester.
- the metal foil is for preventing permeation of moisture and gas, and examples thereof include foils of copper, aluminum, stainless steel and the like.
- the inner layer resin film protects the metal foil from the electrolytic solution stored inside, and melts and bonds it when heated to seal it, and examples thereof include polyolefin and acid-modified polyolefin.
- the proportion of polypropylene contained in the microporous polyolefin membrane can be determined by infrared spectroscopy (IR) or Raman spectroscopy.
- IR infrared spectroscopy
- Raman spectroscopy for example, in order to calculate the ratio of polypropylene to polyethylene, calibration was performed using a peak at 1473 cm -1 derived from polyethylene in the IR spectrum and a peak at 1376 cm -1 derived from polypropylene as respective marker bands from samples with known polypropylene content Based on the line, the proportion of polypropylene can be calculated.
- FIG. 2 is a schematic view for explaining a method of measuring the thermal contraction rate (%) of TD in a state where a certain load is applied to the MD. Cut out the sample (1) into a rectangle of 130 mm in MD and 50 mm in TD, fix one side of the short side to a metal frame or metal rod with heat-resistant tape (9) so that no wrinkles will occur, The clip (10) was wider than the long, and was hung down with the clip facing down. A weight was hung on the clip to apply a constant load (11) to the MD. At this time, the distance from the lower end of the tape to the upper end of the clip was fixed to 100 mm.
- Thermal shrinkage of TD (%) (Length of TD before heating (mm)-Length of TD after heating (mm)) / Length of TD before heating (mm) x 100
- MI Melt Index
- MFR Melt Mass Flow Rate
- MVR Melt Volume Flow Rate
- a load of 21.6 kgf was applied at 190 ° C., and the amount (g) of resin which flowed out from an orifice having a diameter of 1 mm and a length of 10 mm in 10 minutes was measured, and the value rounded off to the first decimal place was taken as MI.
- the melt index of layer A or layer B can be measured by peeling off the layer of the laminated microporous polyolefin membrane.
- FIG. 1A shows a schematic view of a device for measuring the shutdown response time, the shutdown temperature, and the film rupture temperature (meltdown temperature).
- symbol 1 shows a microporous film
- symbol 2A and 2B shows a 10-micrometer-thick nickel foil
- symbol 3A and 3B shows a glass plate, respectively.
- Reference numeral 4 denotes an electrical resistance measuring device (LCR meter “AG-4311” (trade name) manufactured by Ando Electric Co., Ltd.), which is connected to the nickel foils 2A and 2B.
- Reference numeral 5 denotes a thermocouple, which is connected to the thermometer 6.
- Reference numeral 7 denotes a data collector, which is connected to the electrical resistance measuring device 4 and the thermometer 6.
- symbol 8 shows an oven and heats the microporous film 1. As shown in FIG.
- the microporous film 1 is superimposed on the nickel foil 2A, and a "Teflon (registered trademark)" tape (figure in the longitudinal direction (direction of the arrow in the figure) It fixed to the nickel foil 2A in the hatched part of.
- a “Teflon (registered trademark)” tape (hatched portion in the figure) is pasted onto the nickel foil 2B, and the nickel foil 2B has a 15 mm ⁇ 10 mm window at its center. I left it and masked it.
- the nickel foil 2A and the nickel foil 2B are stacked in such a manner as to sandwich the microporous film 1 and two nickel foils are further sandwiched by the glass plates 3A and 3B from both sides thereof. At this time, the window portion of the foil 2B and the microporous film 1 were aligned so as to face each other.
- the two glass plates 3A and 3B were fixed by sandwiching them with a commercially available double clip.
- the thermocouple 5 was fixed to the glass plate with "Teflon (registered trademark)" tape.
- the microporous film 1, the nickel foils 2A and 2B, and the glass plates 3A and 3B are heated by the oven 8 with such a measuring apparatus, and the temperature at that time and the electrical resistance between the nickel foils 2A and 2B are obtained. It measured continuously. The temperature was raised from 25 ° C. to 200 ° C. at a rate of 2 ° C./min, and the electrical resistance value was measured with an alternating current of 1 kHz. The value obtained by rounding off the first decimal place of the temperature value when the value of the electrical resistance of the microporous film once reached 10 3 ⁇ was defined as the shutdown temperature. Thereafter, the temperature at which the electrical resistance value falls below 10 3 ⁇ again was taken as the film rupture temperature. However, if the resistance value is greater than 10 3 ⁇ From the beginning, the temperature at which less than 10 3 ⁇ was the rupture temperature. The time required for the electrical resistance value to reach 10 2 ⁇ to 10 3 ⁇ was defined as the shutdown response time.
- TD tensile test The tensile test of TD is performed using a tensile tester (Shimadzu Autograph AG type A), the strength at the time of sample breakage is divided by the sample cross-sectional area before the test, and the TD tensile strength at break (kg / cm 2 ) did. Measurement conditions are: temperature: 23 ⁇ 2 ° C., humidity: 40%, sample shape: width 10 mm ⁇ length 100 mm, distance between chucks: 50 mm, tensile speed: 200 mm / min. The tensile elongation (%) was determined by dividing the amount of elongation (mm) until breakage to the distance between chucks (50 mm) and multiplying by 100.
- ⁇ Melting point (° C)> After the temperature is raised from room temperature to 200 ° C. at a rate of 10 ° C./min (first temperature rising process) using a differential scanning calorimetry (DSC) measurement apparatus “DSC-60” (manufactured by Shimadzu Corporation), 10 ° C./min.
- the temperature is the minimum point of the endothermic peak in the second temperature raising process when the temperature is raised again to 200 ° C. at a rate of 10 ° C./min after the temperature is lowered to 30 ° C. in min (the first temperature lowering process).
- the value obtained by rounding off the first decimal place of the obtained value was taken as the melting point.
- the melting point of each different endothermic peak is taken as the melting point.
- the melting point of polyethylene appears as an endothermic peak in the range of 120 ° C. to 140 ° C. and the melting point of polypropylene in the range of 140 ° C. to 170 ° C.
- Porosity (%) (volume-mass / density) / volume x 100
- Air permeability (sec / 100 cc)> According to JIS P-8117, using a Gurley-type air permeability meter G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd., the air permeability of the microporous polyolefin membrane under an atmosphere of temperature 23 ° C. and humidity 40%. The degree of resistance was measured to determine the air permeability.
- the microporous membrane was fixed with a sample holder with a diameter of 11.3 mm at the opening using a Kato Tech handy compression tester KES-G5 (trademark). Next, the central part of the microporous membrane fixed is subjected to a piercing test at a temperature of 23 ° C. and a humidity of 40% with a curvature of 0.5 mm at the tip of the needle and a piercing speed of 2 mm / sec.
- Raw puncture strength (gf) was obtained as a load.
- the positive electrode, the negative electrode, and the non-aqueous electrolyte were prepared by the following procedures a to c.
- NMP N-methylpyrrolidone
- the slurry is coated on one side of a 20 ⁇ m thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and compression molded using a roll press to obtain a positive electrode. Made.
- the application amount of the positive electrode active material at this time was 109 g / m 2 . b.
- Negative Electrode 87.6% by mass of graphite powder A (density 2.23 g / cm 3 , number average particle diameter 12.7 ⁇ m) as a negative electrode active material and graphite powder B (density 2.27 g / cm 3 , number average particle diameter 9.7% by mass of 6.5 ⁇ m), 1.4% by mass (in terms of solid content) of ammonium salt of carboxymethylcellulose as binder (in solid content concentration 1.83% by mass aqueous solution) and 1.7% by mass of diene rubber latex A slurry was prepared by dispersing solid content (solid content 40% by weight aqueous solution) in purified water.
- the slurry was applied to one side of a 12 ⁇ m thick copper foil serving as a negative electrode current collector by a die coater, dried at 120 ° C. for 3 minutes, and compression molded by a roll press to produce a negative electrode.
- the applied amount of the negative electrode active material at this time was 52 g / m 2 .
- Adhesive Layer An adhesive layer was formed on the microporous polyolefin membranes obtained in the examples and comparative examples according to the following procedure.
- a reaction vessel equipped with a stirrer, a reflux condenser, a dropping tank and a thermometer 64 parts of water and 0.25 parts of Perex SS-L (45% solid content of sodium alkyldiphenyl ether disulfonate by Kao) were charged.
- 0.15 parts of ammonium persulfate (2% aqueous solution) was added to the above reaction vessel while maintaining the temperature of the reaction vessel at 80 ° C. Five minutes after the addition, the emulsion prepared as described below was dropped from the dropping tank to the above reaction container over 150 minutes.
- emulsion 24 parts of methyl methacrylate (MMA), 34 parts of butyl acrylate (BA), 1.5 parts of acrylic acid (AA), 0.1 parts of n-dodecyl mercaptan (nDDM), 1.5 parts of Perex SS-L, ammonium persulfate
- MMA methyl methacrylate
- BA butyl acrylate
- AA acrylic acid
- nDDM n-dodecyl mercaptan
- Perex SS-L ammonium persulfate
- a 25% aqueous ammonia solution is added to the above reaction vessel to adjust the pH to 8.0, water is further added, the solid content is adjusted to 40% by mass, and an acrylic emulsion as an adhesive coating liquid is prepared. Obtained. 7.5 parts by mass of the obtained adhesive coating liquid was uniformly dispersed in 92.5 parts by mass of water to prepare a coating liquid, and the surface was coated with a gravure coater on the surface of the polyolefin resin porous film. Dried at 60 ° C. to remove water. Furthermore, the coating liquid was applied in the same manner on the other side, and dried, to obtain a storage device separator having an adhesive layer. e.
- the surface temperature of the laminated secondary battery was measured, and evaluated as follows based on the highest temperature reached.
- the positive electrode, the negative electrode, and the non-aqueous electrolyte were prepared by the above procedures a to c, and an adhesive layer was formed on the microporous polyolefin membranes obtained in the examples and comparative examples by the above procedure d.
- e. Battery Preparation The separators obtained in each of the examples and the comparative examples were cut into a circle of 24 mm ⁇ , and the positive electrode and the negative electrode were each cut into a circle of 16 mm ⁇ .
- the negative electrode, the separator, and the positive electrode were stacked in this order so that the positive electrode and the active material surface of the negative electrode face each other, and pressed or heat pressed, and the resultant was housed in a stainless steel container with a lid.
- cycle characteristics were evaluated based on the following criteria.
- Evaluation criteria of cycle characteristics A: Capacity retention of 90% or more and 100% or less
- ⁇ Gas generation test> The laminate sheet was cut into a fixed size and made into a pack (6 cm ⁇ 8 cm) by an impulse sealer (hereinafter referred to as “lami pack”). Three polyolefin microporous films cut into 10 cm ⁇ 10 cm were folded, inserted into the laminate pack, and vacuum dried at 80 ° C. for 12 hours. 0.4 mL of an electrolytic solution (LIPASTE-E2MEC / PF1: manufactured by Toyama Pharmaceutical Co., Ltd.) was added, and the opening of the laminate was sealed with a sealer. This was stored in an oven set at 85 ° C. for 3 days, the weight before and after the test was measured, and the volume was calculated by the Archimedes method.
- an electrolytic solution LIPASTE-E2MEC / PF1: manufactured by Toyama Pharmaceutical Co., Ltd.
- the weight was converted at the density of water (20 ° C .: 0.9982 g / cm 3 ).
- the amount of gas generation volume after test-volume before test
- Two measurements were made for each microporous polyolefin membrane, and those with an average gas generation amount of 1.2 mL or more were C, 0.8 mL or more and less than 1.2 mL
- One with B and one with less than 0.8 mL was named A.
- Example 1 ⁇ Production of polyolefin microporous membrane> A microporous polyolefin membrane of a two-kind / three-layer laminated structure (B layer-A layer-B layer) was produced by the following procedure.
- the resin composition of the surface layer (B layer) is 80 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 600,000 and a molecular weight distribution of 6.0, and a homogeneity of a melting point of 160 ° C., a viscosity average molecular weight of 400,000 and a molecular weight distribution of 10.0. It was 20 parts by weight of polymer polypropylene.
- the sheet was dried and stretched 1.5 times at a strain rate of 9.0% / sec in the width direction (TD) at a temperature of 120 ° C. by a tenter stretcher. Then, heat treatment is performed to relax this stretched sheet in the width direction (TD) at a strain rate of 2.0% / sec so as to be 0.9 times the width after transverse stretching at 133 ° C.
- a microporous polyolefin membrane having a two-kind three-layer laminated structure in which the two layers of the layer have the same composition and the intermediate layer (A layer) has a different composition is obtained.
- Example 2 A microporous polyolefin membrane was obtained under the same conditions as in Example 1, except that the ratio of the total thickness of the surface layer to the thickness of the intermediate layer was 20:80 during extrusion from the T-die.
- Example 3 A microporous polyolefin membrane was obtained under the same conditions as in Example 1 except that the resin composition of the surface layer (B layer) was changed to 95 parts by weight of polyethylene and 5 parts by weight of polypropylene.
- Example 4 A microporous polyolefin membrane was obtained under the same conditions as Example 1, except that the resin composition of the surface layer (B layer) was 73 parts by weight of polyethylene and 27 parts by weight of polypropylene, and the temperature during relaxation treatment was 138 ° C.
- the resin composition of the middle layer (A layer) is 98 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 600,000 and a molecular weight distribution of 6.0, and a polypropylene having a melting point of 160 ° C., a viscosity average molecular weight of 400,000 and a molecular weight distribution of 10.0
- a microporous polyolefin membrane was obtained under the same conditions as in Example 1 except that the amount was 2 parts by weight.
- Example 6 Using polyethylene of melting point 135 ° C., viscosity average molecular weight 700,000, molecular weight distribution 3.0, and homopolymer polypropylene of melting point 165 ° C., viscosity average molecular weight 400,000, molecular weight distribution 6.0 for the surface layer (layer B)
- a polyethylene with a melting point of 135 ° C, a viscosity average molecular weight of 700,000 and a molecular weight distribution of 3.0 is used for the middle layer (A layer), the strain rate at the time of stretching with a tenter stretching machine is 12.0% / sec, relaxation treatment
- a microporous polyolefin membrane was obtained under the same conditions as in Example 1 except that the strain rate was 0.5% / sec and the temperature was 132 ° C.
- Example 7 The resin composition of the surface layer (B layer) has a melting point of 135 ° C., a viscosity average molecular weight of 600,000, and 78 parts by weight of polyethylene having a molecular weight distribution of 6.0, and a melting point of 160 ° C., a viscosity average molecular weight of 400,000 and a polypropylene of a molecular weight distribution of 10.0 19 parts by weight, 3 parts by weight of silica “DM10C” (trade mark, manufactured by Tokuyama Co., Ltd .; hydrophobic treatment with dimethyldichlorosilane) having an average primary particle diameter of 15 nm, and the temperature during relaxation treatment was 140 ° C.
- a microporous polyolefin membrane was obtained under the same conditions as in Example 1.
- Example 8 Using polyethylene of melting point 135 ° C., viscosity average molecular weight 500,000, molecular weight distribution 6.0, and homopolymer polypropylene of melting point 155 ° C., viscosity average molecular weight 200,000, molecular weight distribution 6.0 for the surface layer (layer B)
- a polyethylene with a melting point of 135 ° C, a viscosity average molecular weight of 500,000 and a molecular weight distribution of 6.0 is used for the middle layer (A layer), the strain rate at the time of stretching with a tenter stretching machine is 4.0% / sec, relaxation treatment
- a microporous polyolefin membrane was obtained under the same conditions as in Example 1 except that the strain rate was 3.5% / sec and the temperature was 138 ° C.
- Example 9 In the surface layer (B layer), 70 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 700,000 and a molecular weight distribution of 6.0, 20 points of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 250,000 and a molecular weight distribution of 6.0, Using 10 parts by weight of homopolymer polypropylene having a melting point of 160 ° C., a viscosity average molecular weight of 400,000 and a molecular weight distribution of 10.0, an intermediate layer (A layer) has a melting point of 135 ° C., a viscosity average molecular weight of 700,000 and a molecular weight distribution of 6.0 Using polyethylene, inject 300 parts by weight of liquid paraffin into each extruder by side feed, extrude so that the ratio of the total thickness of the surface layer to the thickness of the middle layer is 35: 65, and immediately
- Example 10 >> In the middle layer (layer A), 40 parts by weight of polyethylene having a melting point of 135 ° C., viscosity average molecular weight 2,000,000, molecular weight distribution 7.0, 60 parts by weight of polyethylene having a melting point 135 ° C., viscosity average molecular weight 250,000, molecular weight distribution 6.0 A microporous polyolefin membrane was obtained under the same conditions as in Example 9 except that it was used.
- Example 11 70 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 700,000 and a molecular weight distribution of 6.0, 15 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 250,000 and a molecular weight distribution of 6.0 Melting point 130 ° C, viscosity average molecular weight 150,000, 15 parts by weight of low density polyethylene (LDPE) with molecular weight distribution 5.0, melting point 160 ° C, viscosity average molecular weight 400,000, homopolymer polypropylene 5 parts by weight with molecular weight distribution 10.0
- LDPE low density polyethylene
- Example 12 In the middle layer (layer A), 45 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 2,000,000 and a molecular weight distribution of 7.0, 45 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 250,000 and a molecular weight distribution of 6.0 A microporous polyolefin membrane was obtained under the same conditions as in Example 11 except that 10 parts by weight of low density polyethylene (LDPE) having a viscosity average molecular weight of 150,000 and a molecular weight distribution of 5.0 was used.
- LDPE low density polyethylene
- Example 13 In the surface layer (B layer), 75 parts by weight of polyethylene having a melting point of 135 ° C., viscosity average molecular weight 700,000 and molecular weight distribution 6.0, melting point 135 ° C., 20 parts of polyethylene having viscosity average molecular weight 250,000 and molecular weight distribution 6.0, A microporous polyolefin membrane was obtained under the same conditions as in Example 12, except that 5 parts by weight of homopolymer polypropylene having a melting point of 160 ° C., a viscosity average molecular weight of 400,000, and a molecular weight distribution of 10.0 was used.
- Example 14 By preparing a microporous polyolefin membrane under the same conditions as in Example 10 except that a lamination die capable of coextrusion with two types and two layers is used, a polyolefin fine layer of a two type and two layer lamination structure (A layer-B layer) is produced. A porous membrane was obtained.
- Example 15 A microporous polyolefin membrane of three types and five layers (B layer-C layer-A layer-C layer-B layer) was produced according to the following procedure.
- the resin composition of the layer A is as follows: melting point 135 ° C., viscosity average molecular weight 2,000,000, polyethylene 40 parts by weight molecular weight distribution 7.0, melting point 135 ° C. viscosity average molecular weight 250,000, polyethylene 60 parts by weight molecular weight distribution 6.0
- the 0.3 parts by weight of tetrakis- (methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate) methane was mixed as an antioxidant.
- liquid paraffin kinetic viscosity at 37.78 ° C. 75.90 cSt
- the resin composition of layer B has a melting point of 135 ° C., a viscosity average molecular weight of 700,000, 70 parts by weight of polyethylene with a molecular weight distribution of 6.0, a melting point of 135 ° C., a viscosity average molecular weight of 250,000, a polyethylene of 20 parts with a molecular weight distribution of 6.0, a melting point of 160 C., a viscosity average molecular weight of 400,000, and 10 parts by weight of a homopolymer polypropylene having a molecular weight distribution of 10.0 were used to form a 0.4 mm single layer sheet under the same conditions as in the A layer.
- the resin composition of layer C is 90 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 500,000 and a molecular weight distribution of 6.0, and 10 weight parts of homopolymer polypropylene having a melting point of 160 ° C., a viscosity average molecular weight of 400,000 and a molecular weight distribution of 10.0 It used and shape
- the three types of single-layer sheets thus obtained are stacked to form a three-layer five-layer structure of B-layer-C-layer-A-layer-C-layer-B-layer, under the same conditions as in Example 1 after simultaneous biaxial stretching.
- a microporous polyolefin membrane having a three-kind five-layer laminated structure was obtained.
- Example 16 In the middle layer (layer A), 40 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 2,000,000 and a molecular weight distribution of 7.0, 30 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 700,000 and a molecular weight distribution of 6.0, A microporous polyolefin membrane was obtained under the same conditions as in Example 10, except that 30 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 250,000 and a molecular weight distribution of 6.0 was used.
- Example 17 In the surface layer (B layer), 40 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 700,000 and a molecular weight distribution of 6.0, 20 points of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 250,000 and a molecular weight distribution of 6.0, Melting point 130 ° C, viscosity average molecular weight 150,000, 30 parts by weight of low density polyethylene (LDPE) with molecular weight distribution 5.0, melting point 160 ° C, viscosity average molecular weight 400,000, homopolymer 10 parts by weight with homopolymer polypropylene 10 parts by weight A microporous polyolefin membrane was obtained under the same conditions as in Example 16 except for the above.
- LDPE low density polyethylene
- Example 18 8 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 2,000,000 and a molecular weight distribution of 7.0, 72 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 700,000 and a molecular weight distribution of 6.0 Melting point 135 ° C., viscosity average molecular weight 250,000, 15 parts by weight of polyethylene having a molecular weight distribution of 6.0, melting point 160 ° C., viscosity average molecular weight of 400,000, and 5 parts by weight of homopolymer polypropylene having a molecular weight distribution of 10.0 A microporous polyolefin membrane was obtained under the same conditions as in (16).
- Example 19 A microporous polyolefin membrane was obtained under the same conditions as Example 9, except that the polypropylene contained in the surface layer (B layer) was a homopolymer polypropylene having a melting point of 160 ° C., a viscosity average molecular weight of 1,000,000 and a molecular weight distribution of 10.0. .
- a microporous polyolefin membrane of a single layer (only A layer) was prepared by the following procedure.
- the resin composition is 90 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 500,000 and a molecular weight distribution of 6.0, and 10 parts by weight of homopolymer polypropylene having a melting point of 160 ° C., a viscosity average molecular weight of 400,000 and a molecular weight distribution of 10.0.
- the 0.3 parts by weight of tetrakis- (methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate) methane was mixed as an antioxidant.
- liquid paraffin kinetic viscosity at 37.78 ° C. 75.90 cSt
- the sheet was dried and stretched 1.5 times at a strain rate of 17.0% / sec in the width direction (TD) at a temperature of 120 ° C. by a tenter stretcher. Thereafter, the stretched sheet is heat-treated to relax in the width direction (TD) at a strain rate of 0.3% / sec so as to be 0.9 times the width after transverse stretching at 133 ° C. A microporous membrane was obtained.
- Comparative Example 2 Same as Comparative Example 1 except that biaxial stretching was performed at 124 ° C., strain rate at the time of stretching with a tenter stretching machine was 7.0% / sec, and relaxation treatment was performed at a strain rate of 0.9% / sec.
- the microporous polyolefin membrane was obtained under the following conditions.
- Comparative Example 3 A microporous polyolefin membrane was obtained under the same conditions as in Example 1 except that the resin composition of the surface layer (B layer) was 60 parts by weight of polyethylene and 40 parts by weight of polypropylene, and the temperature during relaxation treatment was 137 ° C.
- Comparative Example 4 A microporous polyolefin membrane was obtained under the same conditions as Example 1, except that the resin composition of the surface layer (B layer) was 20 parts by weight of polyethylene and 80 parts by weight of polypropylene, and the temperature during relaxation treatment was 140 ° C.
- the resin composition of the surface layer (B layer) has a melting point of 135 ° C., a viscosity average molecular weight of 600,000, 24 parts by weight of polyethylene having a molecular weight distribution of 6.0, and a melting point of 160 ° C., a viscosity average molecular weight of 400,000, a polypropylene having a molecular weight distribution of 10.0 70 parts by weight of silica “DM10C” (trademark, manufactured by Tokuyama Co., Ltd .; hydrophobic treatment with dimethyldichlorosilane) having an average primary particle diameter of 15 nm is 6 parts by weight, and the total thickness and intermediate thickness of the surface layer during extrusion from a T-die
- a microporous polyolefin membrane was obtained under the same conditions as in Example 1 except that the layer was extruded so that the ratio to the layer thickness was 25:75, and the temperature during the relaxation treatment was 145 ° C.
- Comparative Example 6 A microporous polyolefin membrane was obtained under the same conditions as in Example 1, except that polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 900,000 and a molecular weight distribution of 6.0 was used as the polyethylene contained in the surface layer and the intermediate layer.
- Comparative Example 7 A microporous polyolefin membrane was obtained under the same conditions as in Example 1 except that the resin composition of the surface layer and the resin composition of the intermediate layer in Example 1 were replaced.
- Comparative Example 8 Using polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 250,000, and a molecular weight distribution of 6.0 as the polyethylene contained in the surface layer and the intermediate layer, 150 parts by weight of liquid paraffin injected into the extruder with respect to 100 parts by weight of resin The extrusion was performed so that the ratio of the total thickness of the surface layer to the thickness of the intermediate layer at the time of extrusion from the T die was 36:64, and the temperature at the relaxation treatment was 120 ° C. A microporous polyolefin membrane was obtained under the conditions.
- Comparative Example 9 Melting point 135 ° C., viscosity average molecular weight 250,000, 38.8 parts by weight of polyethylene having a molecular weight distribution of 6.0, and melting point 160 ° C., viscosity average molecular weight of 400,000, polypropylene of 1.2 parts by weight of molecular weight distribution 10.0, liquid paraffin 60% by weight was melt-kneaded by an extruder equipped with a T-die at the tip and then extruded to form a 1300 ⁇ m-thick sheet. The sheet was stretched simultaneously in the vertical and horizontal directions to produce a sheet having a thickness of 20 ⁇ m.
- This sheet was immersed in methyl ethyl ketone (MEK) to extract and remove liquid paraffin, and then dried to produce a microporous membrane B with a thickness of 18 ⁇ m.
- MEK methyl ethyl ketone
- the sheet was extruded to make a 1300 ⁇ m thick sheet.
- This sheet was stretched 8 times in MD and 8 times in TD to prepare a 20 ⁇ m thick sheet.
- microporous membrane A This sheet was immersed in methyl ethyl ketone (MEK) to extract and remove liquid paraffin, and then dried to produce a microporous membrane A with a thickness of 18 ⁇ m.
- MEK methyl ethyl ketone
- Three sheets were laminated in the form of microporous film B / microporous film A / microporous film B, and stretched by three times in the longitudinal direction while passing through several rolls heated to 110 ° C., and then heated to 122 ° C. A heat treatment was conducted through several rolls to produce three longitudinally laminated films. Subsequently, the longitudinally stretched film is stretched in the lateral direction twice at a strain rate of 4% / sec with a tenter heated to 118 ° C., and then heat treated in the region heated to 128 ° C. in the same tenter The width after stretching was forcibly relaxed to 0.9 times at a strain rate of 0.7% / sec to prepare a 10 ⁇ m thick B /
- the resin composition of the microporous film A has a melting point of 135 ° C., a viscosity average molecular weight of 250,000, 22.5 parts by weight of polyethylene having a molecular weight distribution of 6.0, a viscosity average molecular weight of 150,000, a low density polyethylene (LDPE) having a molecular weight distribution of 5.0 .5 parts by weight, liquid paraffin 55 parts by weight, resin composition of microporous membrane B melting point 135 ° C., viscosity average molecular weight 2,000,000, polyethylene 24 parts by weight molecular weight distribution 7.0, melting point 160 ° C.
- LDPE low density polyethylene
- Comparative Example 11 In the surface layer (B layer), 10 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 2,000,000 and a molecular weight distribution of 7.0, 87 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 250,000 and a molecular weight distribution of 6.0 And 3 parts by weight of a random polymer polypropylene having a melting point of 155 ° C., a viscosity average molecular weight of 100,000, and a molecular weight distribution of 3.0, to an intermediate layer (A layer), a melting point of 135 ° C., a viscosity average molecular weight of 2,000,000, and a molecular weight distribution of 7.0 18 parts by weight of polyethylene, melting point 135 ° C., viscosity average molecular weight 250,000, 82 parts by weight of polyethylene having a molecular weight distribution of 6.0, simultaneous
- Comparative Example 12 In the surface layer (B layer), 97 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 250,000 and a molecular weight distribution of 6.0, and a homopolymer polypropylene 3 having a melting point of 162 ° C., a viscosity average molecular weight of 400,000 and a molecular weight distribution of 10.0 20 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 2,000,000, a molecular weight distribution of 7.0, and a melting point of 135 ° C., a viscosity average molecular weight of 250,000, a molecular weight distribution of 6.0
- Comparative Example 13 In the surface layer (B layer), 92 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 250,000 and a molecular weight distribution of 6.0, and a random polymer polypropylene 8 having a melting point of 155 ° C., a viscosity average molecular weight of 100,000 and a molecular weight distribution of 3.0 30 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 2,000,000 and a molecular weight distribution of 7.0, 30 parts by weight of a melting point of 135 ° C., a viscosity average molecular weight of 250,000, a molecular weight distribution of 6.0 70 parts by weight of polyethylene, the simultaneous biaxial stretching temperature is 115.degree. C., and the relaxation treatment with a tenter stretching machine is 0.86 times after TD stretching at 124.degree. C., and is the same as Comparative Example
- Comparative Example 14 80 parts by weight of polyethylene having a melting point of 135 ° C., a viscosity average molecular weight of 700,000 and a molecular weight distribution of 6.0, and a homopolymer polypropylene 20 having a melting point of 160 ° C., a viscosity average molecular weight of 1.60,000 and a molecular weight distribution of 10.0 in the surface layer (B layer) Parts by weight, in the intermediate layer (layer A), melting point 135 ° C., viscosity average molecular weight 2,000,000, polyethylene 40 parts by weight molecular weight distribution 7.0, melting point 135 ° C.
- the microporous polyolefin membrane of the present embodiment can be suitably used as a lithium ion secondary battery separator, in particular, as a laminate type lithium ion secondary battery separator.
- the separator containing the microporous polyolefin membrane according to the present embodiment is not easily shrunk at the time of heat pressing, and the decrease in permeability due to the closed micropores can be suppressed.
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Abstract
Description
また、一実施形態において、車載用電池用セパレータなどのより高度な安全性が求められる分野においては、過酷な条件での短絡試験で良好な短絡耐性を示すセパレータが求められる。
[1]
ポリオレフィンを含むA層と、ポリオレフィンを含むB層とを少なくとも1層ずつ備える積層構造を有するポリオレフィン微多孔膜であって、
上記A層に含まれるポリプロピレンは0質量%以上3質量%未満であり、上記B層に含まれるポリプロピレンは1質量%以上30質量%未満であり、A層に含まれるポリプロピレンの割合をPPA(質量%)、B層に含まれるポリプロピレンの割合をPPB(質量%)とした場合、PPB>PPAであり、
MDに、下記式:
荷重(gf)=0.01×ポリオレフィン微多孔膜の突刺強度(gf)×ポリオレフィン微多孔膜のTDの長さ(mm)
に基づいて決定される一定の荷重をかけた状態で測定される、120℃でのTDの熱収縮率が10%以上40%以下である、ポリオレフィン微多孔膜。
[2]
ポリオレフィンを含むA層と、その両面にポリオレフィンを含むB層を少なくとも1層ずつ備える積層構造を有するポリオレフィン微多孔膜であって、
上記ポリオレフィン微多孔膜の総厚みに対する上記A層の厚みの割合が40%以上90%以下である、請求項1に記載のポリオレフィン微多孔膜。
[3]
上記B層中の無機粒子の含有率が5質量%未満である、請求項1又は2に記載のポリオレフィン微多孔膜。
[4]
上記ポリオレフィン微多孔膜のゲル浸透クロマトグラフィー(GPC)測定の積分曲線における分子量300万以上の分子の割合が10質量%以下であり、かつ分子量3万以下の分子の割合が3.0質量%以下である、請求項1~3のいずれか一項に記載のポリオレフィン微多孔膜。
[5]
190℃で21.6kgfの荷重下でのメルトインデックスが0.1g/10min以上3.0g/10min以下である、請求項1~4のいずれか一項に記載のポリオレフィン微多孔膜。
[6]
上記ポリオレフィン微多孔膜のA層における、190℃で21.6kgfの荷重下でのメルトインデックスが0.01g/10min以上0.3g/10min以下である、請求項1~5のいずれか一項に記載のポリオレフィン微多孔膜。
[7]
上記ポリオレフィン微多孔膜のB層における、190℃で21.6kgfの荷重下でのメルトインデックスが0.3g/10minを超え、2.0g/10min以下である、請求項1~6のいずれか一項に記載のポリオレフィン微多孔膜。
[8]
上記ポリオレフィン微多孔膜の上記A層におけるメルトインデックスに対する上記B層のメルトインデックスの比率(B層のメルトインデックス/A層のメルトインデックス)が1.5以上20以下である、請求項1~7のいずれか一項に記載のポリオレフィン微多孔膜。
[9]
シャットダウン応答時間が12秒以上22秒以下である、請求項1~8のいずれか一項に記載のポリオレフィン微多孔膜。
[10]
シャットダウン温度が150℃以下であり、破膜温度が170℃を超える、請求項1~9のいずれか一項に記載のポリオレフィン微多孔膜。
[11]
上記ポリオレフィン微多孔膜に含まれるポリプロピレンの粘度平均分子量が30万以上120万以下である、請求項1~10のいずれか一項に記載のポリオレフィン微多孔膜。
[12]
上記ポリオレフィン微多孔膜に含まれるポリプロピレンがホモポリマーである、請求項1~11のいずれか一項に記載のポリオレフィン微多孔膜。
[13]
突刺強度が170gf/10μm以上である、請求項1~12のいずれか一項に記載のポリオレフィン微多孔膜。
[14]
ラミネートフィルムで構成される外装体の中に、正極と負極とが、請求項1~13のいずれか一項に記載のポリオレフィン微多孔膜を介して積層された構造を少なくとも一つ有する、ラミネート型リチウムイオン二次電池。
〈積層構造〉
本実施形態のポリオレフィン微多孔膜は、ポリオレフィンを含むA層と、ポリオレフィンを含むB層とを少なくとも1層ずつ備える2層以上の積層構造を有する。ポリオレフィン微多孔膜は、好ましくは、A層の両側(両面)にB層をそれぞれ1層ずつ備える3層以上の積層構造を有する。積層構造は、上記A層及びB層をそれぞれ1層づつ有する限りにおいて、「A層-B層」の二層構造、又は「B層-A層-B層」の三層構造に限定されない。例えば、ポリオレフィン微多孔膜は、いずれか一方又は両方のB層の上や、A層とB層の間に一つ又は複数の更なる層が形成されていてもよい。更なる層としては、例えば、ポリオレフィンを含む層や、無機粒子や架橋性高分子などの耐熱樹脂を含む耐熱層、接着性高分子を含む接着層等が挙げられる。
[η]=6.77×10-4Mv0.67
一般的に、超高分子量ポリエチレン(UHMWPE)のMvは、100万以上であるため、本願明細書における高分子量ポリエチレン(HMWPE)は、定義上、UHMWPEを包含する。
A層に含まれるポリプロピレンの量は、A層を構成する樹脂成分の全質量を基準として好ましくは0質量%以上3質量%未満、より好ましくは0質量%以上1質量%未満、最も好ましくは、A層はポリプロピレンを含まない。A層に含まれるポリプロピレンが3質量%未満であることによって、ポリオレフィン微多孔膜の機械的強度及び伸度がより良好になる。
B層はA層より多くのポリプロピレンを含む。すなわち、A層に含まれるポリプロピレンの割合をPPA(質量%)、B層に含まれるポリプロピレンの割合をPPB(質量%)とした場合、PPB>PPAである。B層に含まれるポリプロピレンの量の下限値は、B層を構成する樹脂成分の全質量を基準として、好ましくは1質量%以上、より好ましくは3質量%以上、さらに好ましくは4質量%以上、よりさらに好ましくは5質量%以上、最も好ましくは10質量%以上である。B層に含まれるポリプロピレンの量の上限値は、B層を構成する樹脂成分の全質量を基準として、好ましくは30質量%以下、より好ましくは27質量%以下、さらに好ましくは25質量%以下、よりさらに好ましくは20質量%以下、最も好ましくは18質量%以下である。B層に含まれるポリプロピレンの量の範囲は、例えば、1質量%以上30質量%以下、1質量%以上30質量%未満であり、好ましくは5質量%以上30質量%未満、より好ましくは5質量%以上25質量%以下、更に好ましくは10質量%以上20質量%以下である。A層が強度と伸度を担保するとともに、B層に含まれるポリプロピレンが上記範囲内であることにより、ポリオレフィン微多孔膜のMDに一定の張力がかかった状態で熱プレスを行ったとき、TDへの熱収縮を抑制することができるため、歪みを抑制することができる。また、ポリプロピレンはポリエチレンより融点が高いため、B層にポリプロピレンが上記範囲内で存在することにより、セパレータのシャットダウン機能を担保しつつ、熱プレス時に表層が溶融して透過性が低下することを防止することができる。
B層がUHMWPEを含む場合、B層中のUHMWPEの量を30質量%以下とすることにより、昇温時に溶融粘度が上がり過ぎず、シャットダウン応答時間が遅くなり過ぎない。この効果は、B層に先に熱が伝わるB層-A層-B層の構造を含むときに顕著になる。ポリオレフィン微多孔膜全体のポリオレフィンの総質量に対するUHMWPEの割合は、好ましくは45質量%未満、より好ましくは35質量%未満、よりさらに好ましくは25質量%未満である。ポリオレフィン微多孔膜全体のポリオレフィンの総質量に対するUHMWPEの割合が45%未満であることによって、残留応力による熱収縮の増加を抑制することができる。
ポリプロピレンの分子量が5万以上であることにより、ポリオレフィン微多孔膜のメルトインデックスが高くなり過ぎないため熱プレス時の溶融を防ぐことができる。また、釘刺試験において優れた電池の短絡耐性を有するポリオレフィン微多孔膜を提供することができる。その理由としては、理論に限定されないが、破膜によって電池が短絡して電池の昇温が起きても、分子鎖の絡み合いにより溶融したセパレータの流動性が低いため、急激な絶縁性の低下を防ぐことができるからであると考えられる。このような過酷な条件における優れた電池の短絡耐性は、例えば、車載用電池用セパレータ等のより高度な安全性が求められる分野において有利である。
ポリプロピレンの分子量が1000万以下であることにより、延伸時の内部応力が大きくなり過ぎないため過度な熱収縮を抑えることができる。
また、ポリプロピレンの分子量分布(Mw/Mn)は、好ましくは30以下、さらに好ましくは24以下、最も好ましくは12以下である。ポリプロピレンの分子量分布が30以下であることにより、低分子量のポリプロピレン成分が少ないため、ポリエチレンとの混和性が良好になり、ポリプロピレンに由来するより高い耐熱性を有するポリオレフィン微多孔膜を得ることができる。
ポリオレフィン微多孔膜のゲル浸透クロマトグラフィー(GPC)測定の積分曲線における分子量300万以上の分子の割合は、好ましくは10質量%以下、より好ましくは9質量%以下、更に好ましくは8質量%以下であり、好ましくは3質量%以上、より好ましくは5質量%以上である。また、ポリオレフィン微多孔膜のゲル浸透クロマトグラフィー(GPC)測定の積分曲線における分子量3万以下の分子の割合は、好ましくは3質量%以下、より好ましくは2.8質量%以下であり、最も好ましくは2.5質量%以下であり、好ましくは0.5質量%以上、より好ましくは0.8質量%以上である。高分子量のポリエチレン成分が10質量%以下であると、ポリオレフィン微多孔膜の粘度が高くなりすぎず、シャットダウン機能を担保することができる。また、低分子量のポリエチレン成分が3.0質量%以下であると、熱プレス時にポリオレフィン微多孔膜が閉孔して透過性が低下することを抑制することができる。
B層中の無機粒子の含有率は、好ましくは5質量%未満、より好ましくは3質量%未満であり、無機粒子を含まないことが最も好ましい。無機粒子の含有量が5質量%未満であることにより、ガス発生による電池の膨れ等を効果的に抑制することができる。この効果は、外装体が変形を受けやすいラミネート型電池においてより顕著になる。また、無機粒子がB層中に5質量%以上存在すると、無機粒子が破断の起点になって伸度の低下が起こることによる機械的安全性の低下や、孔の均一性が乱れることによるサイクル特性の低下が起こりやすくなるため好ましくない。
本実施形態のポリオレフィン微多孔膜は、MDに一定の荷重をかけた状態で測定される120℃でのTDの熱収縮率が10%以上40%以下であり、好ましくは15%以上35%以下、より好ましくは20%以上30%以下である。発明者らは、例えば、電極及びセパレータの積層体をMDに扁平状に捲回した捲回体を含むラミネート型電池では、セパレータがMDに捲回され、したがってMDに拘束された状態で熱プレスを受けることとなるため、上記のようにして測定されるTDの熱収縮が40%以下であることにより、接着プレス時に短絡が起こることを効果的に抑制することができること、また、熱収縮が10%以上であることにより、ポリオレフィン微多孔膜のたわみや電池成型不良を効果的に抑制することができることを見出した。また、一実施形態において、MDに保持された状態でのTD熱収縮が上記範囲であることにより、釘刺試験において電池の温度が上昇しても釘周辺の短絡部が広がりずらくなると推測されるため、電圧降下を緩やかにすることができる。
本実施形態のポリオレフィン微多孔膜は、190℃で21.6kgfの荷重下でのメルトインデックス(MI)が、好ましくは0.01g/10min以上3.0g/10min以下、より好ましくは0.05g/10min以上1.5g/10min以下、更に好ましくは0.1g/10min以上0.6g/10min以下、最も好ましくは0.12g/10min以上0.5g/10min以下である。メルトインデックスが0.1g/10min以上であると、溶融時の流動性が高くシャットダウン機能がより良好になる。メルトインデックスが0.6g/10min以下であれば、破膜によって電池が短絡して電池の昇温が起きても、溶融したセパレータの流動性が低いため、急激な絶縁性の低下を防ぐことができると推測されるため好ましい。ポリオレフィン微多孔膜のMIは、用いるポリオレフィン原料の種類、割合、粘度平均分子量や分子量分布により制御することができる。
本実施形態のポリオレフィン微多孔膜は、シャットダウン応答時間が好ましくは8秒以上30秒以下、より好ましくは12秒以上22秒以下、更に好ましくは14秒以上20秒以下、より更に好ましくは16秒以上18秒以下である。本願明細書において、「シャットダウン応答時間」とは、実施例に記載のシャットダウン特性試験において、電気抵抗値が102Ωから103Ωに到達するまでの時間をいう。シャットダウン応答時間が12秒以上であると、熱プレス時に微多孔が閉孔して透過性が低下することを抑制することができる。シャットダウン応答時間が22秒以下であれば、車載用途として求められる安全性をより高めることができるため好ましい。
本実施形態のポリオレフィン微多孔膜は、TDの引張破断強度が好ましくは100kgf/cm2以上5000kgf/cm2以下、より好ましくは300kgf/cm2以上3000kgf/cm2以下、更に好ましくは500kgf/cm2以上2000kgf/cm2以下である。TDの引張破断強度が100kgf/cm2以上であると、電池が外力により変形したとき等にセパレータが破膜する可能性を低減することができる。TDの引張破断強度が5000kgf/cm2以下であると、残留応力を低くすることができ、熱収縮を抑制できるため好ましい。この効果は、外装体が変形を受けやすいラミネート型電池においてより顕著になる。
ポリオレフィン微多孔膜は、電子伝導性が小さく、イオン伝導性を有し、有機溶媒に対する耐性が高く、かつ孔径の微細なものが好ましい。また、ポリオレフィン微多孔膜は、リチウムイオン二次電池用セパレータとして利用することができ、特にラミネート型リチウムイオン二次電池用セパレータとして好適に利用することができる。
ポリオレフィン微多孔膜の製造方法としては、特に制限はなく、既知の製造方法を採用することができる。例えば、以下の方法:
(1)ポリオレフィン樹脂組成物と孔形成材とを溶融混練してシート状に成形後、必要に応じて延伸した後、孔形成材を抽出することにより多孔化させる方法;
(2)ポリオレフィン樹脂組成物を溶融混練して高ドロー比で押出した後、熱処理と延伸によってポリオレフィン結晶界面を剥離させることにより多孔化させる方法;
(3)ポリオレフィン樹脂組成物と無機充填材とを溶融混練してシート上に成形した後、延伸によってポリオレフィンと無機充填材との界面を剥離させることにより多孔化させる方法;
(4)ポリオレフィン樹脂組成物を溶解後、ポリオレフィンに対する貧溶媒に浸漬させてポリオレフィンを凝固させると同時に溶剤を除去することにより多孔化させる方法
等が挙げられる。
ラミネート型電池の変形やガス発生による膨れを防ぐため、ポリオレフィン微多孔膜表面に、熱可塑性樹脂を含む接着層を設けることができる。接着層に含まれる熱可塑性樹脂としては特に限定されず、例えば、ポリエチレンやポリプロピレン等のポリオレフィン;ポリフッ化ビニリデン、ポリテトラフルオロエチレン等の含フッ素樹脂;フッ化ビニリデン-ヘキサフルオロプロピレン共重合体、フッ化ビニリデン-テトラフルオロエチレン共重合体、フッ化ビニリデン-ヘキサフルオロプロピレンテトラフルオロエチレン共重合体、エチレン-テトラフルオロエチレン共重合体等の含フッ素ゴム;スチレン-ブタジエン共重合体及びその水素化物、アクリロニトリル-ブタジエン共重合体及びその水素化物、アクリロニトリル-ブタジエン-スチレン共重合体及びその水素化物、(メタ)アクリル酸エステル共重合体、スチレン-アクリル酸エステル共重合体、アクリロニトリル-アクリル酸エステル共重合体、エチレンプロピレンラバー、ポリビニルアルコール、ポリ酢酸ビニル等のゴム類;エチルセルロース、メチルセルロース、ヒドロキシエチルセルロース、カルボキシメチルセルロース等のセルロース誘導体;ポリフェニレンエーテル、ポリスルホン、ポリエーテルスルホン、ポリフェニレンスルフィド、ポリエーテルイミド、ポリアミドイミド、ポリアミド、ポリエステル等の融点及び/又はガラス転移温度が180℃以上の樹脂等が挙げられる。
本実施形態のラミネート型リチウムイオン二次電池は、ラミネートフィルムで構成される外装体の中に、正極と負極とを本実施形態のポリオレフィン多孔膜を介して積層した構造を少なくとも一つ有する。
〈ポリプロピレンの割合〉
ポリオレフィン微多孔膜に含まれるポリプロピレンの割合は、赤外分光法(IR)やラマン分光法により求めることができる。例えば、ポリエチレンに対するポリプロピレンの割合を算出するには、IRスペクトルのポリエチレン由来の1473cm-1のピークとポリプロピレン由来の1376cm-1のピークをそれぞれのマーカーバンドとして、ポリプロピレン含有量既知の試料から作成した検量線に基づいて、ポリプロピレンの割合を算出することができる。中間層(A層)と表面層(B層)とでポリプロピレンの割合が違う場合は、ATR-IR法で表面層のポリプロピレンの割合を算出する方法や、ポリオレフィン微多孔膜断面の顕微IRまたは顕微ラマン分光測定により、それぞれの層のポリプロピレンの割合を求める方法が挙げられる。
・試料の調製
ポリオレフィン微多孔膜に無機粒子が含まれる場合は、90℃に加熱した苛性ソーダ中に30分間浸漬して無機粒子を除去した後、流水で3時間洗浄し、10時間乾燥させたものを試料とした。
試料を秤量し、濃度が1mg/mlになるように溶離液1,2,4-トリクロロベンゼン(TCB)を加えた。高温溶解器を用いて、160℃で30分静置したのち、160℃で1時間揺動させ、試料がすべて溶解したことを目視で確認した。160℃のまま、0.5μmフィルターでろ過し、ろ液をGPC測定試料とした。
・GPC測定
GPC装置として、Agilent社製のPL-GPC220(商標)を用い、東ソー(株)製のTSKgel GMHHR-H(20) HT(商標)の30cmカラム2本を使用し、上記で調整したGPC測定試料500μlを測定機に注入し、160℃にてGPC測定を行った。
なお、標準物質として市販の分子量既知の単分散ポリスチレンを用いて検量線を作成し、求められた各試料のポリスチレン換算の分子量分布データを取得した。これより、各試料の分子量300万以上の分子の割合および分子量3万以下の分子の割合を得た。
図2は、MDに一定の荷重をかけた状態でのTDの熱収縮率(%)の測定方法を説明するための模式図である。サンプル(1)をMDに130mm、TDに50mmの長方形に切り出し、短辺の片側を金枠や金属棒などに耐熱テープ(9)でしわが入らないように固定し、もう片方をサンプルのTD長よりも幅の広いクリップ(10)で挟み、クリップを下側にして垂下した。クリップに重りをぶら下げてMDに一定の荷重(11)を印加した。この時、テープ下端からクリップ上端までの距離が100mmになるように固定した。なお、上記サイズのサンプルが確保できない場合は、可能な限りTD長が50mmに近い形状にサンプルを切り出し、テープ下端からクリップ上端までの距離と、TDの長さとの比率が、上記と同様の比率(100mm/50mm)となるようにサンプルを設置した。また、セル捲回時の張力は膜の強度にしたがって強く設定することから、MDへの一定の荷重は、下記式に従って決定する。
荷重(gf)=0.01×サンプルの突刺強度(gf)×サンプルのTDの長さ(mm)
重りの付いたサンプルを120℃の温度に加熱してある熱風乾燥機に投入した。サンプルは、乾燥機の内壁等に付着しないように、かつサンプル同士が融着しないように設置した。5分後にサンプルを取り出し、重りをぶら下げた状態で室温まで冷却し、TDの長さを求め、下記式に従って熱収縮率を算出した。
TDの熱収縮率(%)=(加熱前のTDの長さ(mm)-加熱後のTDの長さ(mm))/加熱前のTDの長さ(mm)×100
JIS K7210:1999(プラスチック-熱可塑性プラスチックのメルトマスフローレイト(MFR)及びメルトボリュームフローレイト(MVR))に従って、ポリオレフィン微多孔膜のメルトインデックス(MI)を測定した。190℃で21.6kgfの荷重を加えて、直径1mm、長さ10mmのオリフィスから10分で流出した樹脂量(g)を測定し、小数点以下第一位を四捨五入した値をMIとした。A層またはB層のメルトインデックスは、積層されたポリオレフィン微多孔膜の層を剥離することにより、それぞれ測定することができる。
図1(A)に、シャットダウン応答時間、シャットダウン温度、及び破膜温度(メルトダウン温度)の測定装置の概略図を示す。符号1は微多孔性フィルムを示し、符号2A及び2Bは厚さ10μmのニッケル箔、符号3A及び3Bはガラス板をそれぞれ示す。符号4は電気抵抗測定装置(安藤電気製LCRメーター「AG-4311」(商標))を示し、ニッケル箔2A及び2Bと接続されている。符号5は熱電対を示し、温度計6と接続されている。符号7はデーターコレクターを示し、電気抵抗測定装置4及び温度計6と接続されている。符号8はオーブンを示し、微多孔性フィルム1を加熱するものである。
引張試験機(島津オートグラフAG-A型)を用いてTDの引張試験を行い、サンプル破断時の強度を、試験前のサンプル断面積で除し、TD引張破断強度(kg/cm2)とした。測定条件は、温度;23±2℃、湿度:40%、サンプル形状;幅10mm×長さ100mm、チャック間距離;50mm、引張速度;200mm/minである。
引張伸度(%)は、破断に至るまでの伸び量(mm)をチャック間距離(50mm)で除して、100を乗じることにより求めた。
ASTM-D4020に基づき、デカリン溶媒における135℃での極限粘度[η](dl/g)を求めた。
ポリエチレンについては、次式により算出した。
[η]=6.77×10-4Mv0.67
ポリプロピレンについては、次式によりMvを算出した。
[η]=1.10×10-4Mv0.80
示差走査熱量(DSC)測定装置「DSC-60」(島津製作所社製)を用いて、10℃/minの速度で室温から200℃まで昇温(第一昇温過程)したのち、10℃/minで30℃まで降温(第一降温過程)したのち、再度200℃まで10℃/minの速度で昇温した際の第二昇温過程での吸熱ピークの極小点の温度を融点とした。得られた値の小数点以下第一位を四捨五入した値を、融点とした。ポリオレフィンの種類が複数ある場合はそれぞれの異なる吸熱ピークの極小点を融点とした。一般的に、ポリエチレンの融点は120℃から140℃、ポリプロピレンの融点は140℃から170℃の範囲に吸熱ピークとして現れる。
微小測厚器(東洋精機製 タイプKBM)を用いて、室温23℃、湿度40%の雰囲気下で測定した。端子径5mmφの端子を用い、44gfの荷重を印加して測定した。
10cm×10cm角の試料を微多孔膜から切り取り、その体積(cm3)と質量(g)を求め、それらと密度(g/cm3)より、次式を用いて気孔率を計算した。
気孔率(%)=(体積-質量/密度)/体積×100
JIS P-8117に準拠し、東洋精器(株)製のガーレー式透気度計、G-B2(商標)を用いて温度23℃、湿度40%の雰囲気下でポリオレフィン微多孔膜の透気抵抗度を測定し透気度とした。
カトーテック製のハンディー圧縮試験器KES-G5(商標)を用いて、開口部の直径11.3mmの試料ホルダーで微多孔膜を固定した。次に固定された微多孔膜の中央部を、針先端の曲率半径0.5mm、突刺速度2mm/secで、温度23℃、湿度40%の雰囲気下にて突刺試験を行うことにより、最大突刺荷重として生の突刺強度(gf)を得た。
以下の手順a~cにより、正極、負極、及び非水電解液を調整した。
a.正極の作製
正極活物質としてニッケル、マンガン、コバルト複合酸化物(NMC)(Ni:Mn:Co=1:1:1(元素比)、密度4.70g/cm3)を90.4質量%、導電助材としてグラファイト粉末(KS6)(密度2.26g/cm3、数平均粒子径6.5μm)を1.6質量%及びアセチレンブラック粉末(AB)(密度1.95g/cm3、数平均粒子径48nm)を3.8質量%、並びにバインダとしてポリフッ化ビニリデン(PVDF)(密度1.75g/cm3)を4.2質量%の比率で混合し、これらをN-メチルピロリドン(NMP)中に分散させてスラリーを調製した。このスラリーを、正極集電体となる厚さ20μmのアルミニウム箔の片面にダイコーターを用いて塗布し、130℃において3分間乾燥した後、ロールプレス機を用いて圧縮成形することにより、正極を作製した。この時の正極活物質塗布量は109g/m2であった。
b.負極の作製
負極活物質としてグラファイト粉末A(密度2.23g/cm3、数平均粒子径12.7μm)を87.6質量%及びグラファイト粉末B(密度2.27g/cm3、数平均粒子径6.5μm)を9.7質量%、並びにバインダとしてカルボキシメチルセルロースのアンモニウム塩1.4質量%(固形分換算)(固形分濃度1.83質量%水溶液)及びジエンゴム系ラテックス1.7質量%(固形分換算)(固形分濃度40質量%水溶液)を精製水中に分散させてスラリーを調製した。このスラリーを負極集電体となる厚さ12μmの銅箔の片面にダイコーターで塗布し、120℃において3分間乾燥した後、ロールプレス機で圧縮成形することにより、負極を作製した。この時の負極活物質塗布量は52g/m2であった。
c.非水電解液の調製
エチレンカーボネート:エチルメチルカーボネート=1:2(体積比)の混合溶媒に、溶質としてLiPF6を濃度1.0mol/Lとなるように溶解させることにより、非水電解液を調製した。
d.接着層の形成
以下の手順により、実施例及び比較例で得られたポリオレフィン微多孔膜上に、接着層を形成した。
撹拌機、還流冷却器、滴下槽および温度計を取りつけた反応容器に、水64部とペレックスSS-L(花王製アルキルジフェニルエーテルジスルホン酸ナトリウム固形分45%)0.25部とを投入した。さらに、反応容器の温度を80℃に保ったまま、過硫酸アンモニウム(2%水溶液)を0.15部、上記反応容器に添加した。
添加した5分後に、以下のとおり作製した乳化液を、滴下槽から上記反応容器に150分かけて滴下した。
乳化液の作製:
メタクリル酸メチル(MMA)24部、アクリル酸ブチル(BA)34部、アクリル酸(AA)1.5部、n-ドデシルメルカプタン(nDDM)0.1部、ペレックスSS-L1.5部、過硫酸アンモニウム0.15部、および水69部を、ホモミキサーにより6000rpmで5分間混合して乳化液を作製した。
乳化液滴下終了後、反応容器の温度を80℃に保ったまま60分維持し、その後室温まで冷却した。次に、上記反応容器に25%アンモニア水溶液を添加してpHを8.0に調整し、さらに水を加え、固形分含有率を40質量%に調整し、接着塗工液としてのアクリルエマルジョンを得た。
得られた接着塗工液7.5質量部を92.5質量部の水に均一に分散させて塗布液を調製し、ポリオレフィン樹脂多孔膜の表面にグラビアコーターを用いて塗布した。60℃にて乾燥して水を除去した。さらに、もう片面も同様にして塗布液を塗工し、乾燥させることにより、接着層を有する蓄電デバイス用セパレータを得た。
e.電池作製
上記a~cで得られた正極、負極、及び非水電解液、並びに上記dで得られたセパレータを使用して、電流値1A(0.3C)、終止電池電圧4.2Vの条件で3時間定電流定電圧(CCCV)充電したサイズ100mm×60mm、容量3Ahのラミネート型二次電池を作製した。
f.釘刺し評価
ラミネート型二次電池を、防爆ブース内の鉄板上に静置した。ラミネート型二次電池の中央部に、直径2.5mmの鉄製釘を、25℃前後の環境下で、3mm/秒の速度で貫通させ、釘は貫通した状態で維持した。ラミネート型二次電池の表面温度を測定し、その最高到達温度に基づいて以下のように評価した。
A:40℃以下
B:40℃より高く50℃以下
C:50℃より高く80℃以下
D:80℃より高く100℃以下
E:100℃より高い、または発火、爆発
上記の手順a~cにより、正極、負極、及び非水電解液を調整し、上記手順dにより、実施例及び比較例で得られたポリオレフィン微多孔膜上に、接着層を形成した。
e.電池作製
各実施例及び比較例で得られたセパレータを24mmφ、正極及び負極をそれぞれ16mmφの円形に切り出した。正極と負極の活物質面とが対向するように、負極、セパレータ、正極の順に重ね、プレス又はヒートプレスをして、蓋付きステンレス金属製容器に収容した。容器と蓋とは絶縁されており、容器は負極の銅箔と、蓋は正極のアルミニウム箔と、それぞれ接していた。この容器内に上記非水電解液を0.2ml注入して密閉することにより、容量3mAhの簡易電池を組み立てた。
f.サイクル試験
実施例及び比較例で得たセパレータをそれぞれ使用し、上記手順eで得られた簡易電池を用いて、以下の手順でサイクル特性の評価を行った。
(1)前処理
上記簡易電池を、1/3Cの電流値で電圧4.2Vまで定電流充電した後、4.2Vの定電圧充電を8時間行い、その後1/3Cの電流で3.0Vの終止電圧まで放電を行った。次に、1Cの電流値で電圧4.2Vまで定電流充電した後、4.2Vの定電圧充電を3時間行い、更に1Cの電流で3.0Vの終止電圧まで放電を行った。最後に1Cの電流値で4.2Vまで定電流充電をした後、4.2Vの定電圧充電を3時間行った。なお、1Cとは電池の基準容量を1時間で放電する電流値を表す。
(2)サイクル試験
上記前処理を行った電池を、温度25℃の条件下で、放電電流1Cで放電終止電圧3Vまで放電を行った後、充電電流1Cで充電終止電圧4.2Vまで充電を行った。これを1サイクルとして充放電を繰り返した。そして、初期容量(第1回目のサイクルにおける容量)に対する200サイクル後の容量保持率を用いて、以下の基準でサイクル特性を評価した。
(3)サイクル特性の評価基準
A:90%以上100%以下の容量保持率
B:85%以上90%未満の容量保持率
C:80%以上85%未満の容量保持率
D:80%未満の容量保持率
ラミネートシートを一定サイズに切り出し、インパルスシーラーによりパック状(6cm×8cm)にした(以下、「ラミパック」という。)。10cm×10cmに裁断したポリオレフィン微多孔膜3枚を折りたたんでラミパックに挿入し、80℃にて12時間真空乾燥させた。電解液(LIPASTE-E2MEC/PF1:富山薬品工業製)0.4mLを入れてラミパックの開口部をシーラーによりシールした。
これを85℃に設定したオーブンに3日間保存し、試験前後の重量を測定し、アルキメデス法により容積を算出した。重量は水の密度(20℃:0.9982g/cm3)にて換算した。(アルキメデス法:F=-ρVg)
ガス発生量=試験後容積-試験前容積
各ポリオレフィン微多孔膜につき2回の測定を行い、そのガス発生量の平均値が1.2mL以上のものをC、0.8mL以上1.2mL未満のものをB、0.8mL未満のものをAとした。
正極及び負極を、ポリオレフィン微多孔膜を介して積層し、これを扁平状に捲回して捲回積層体を作製し、回積層体をラミネートフィルム内に入れた。これを、圧力1.0MPa、100℃で3分間プレスした際に、不良(反り、シワ、及び端面ずれ)が発生する頻度を目視で検査し、以下のように評価した。
A:0/10個に不良あり(不良なし)
B:1/10個に不良あり
C:2/10個に不良あり
D:3/10以上に不良あり
〈ポリオレフィン微多孔膜の製造〉
二種三層積層構造(B層-A層-B層)のポリオレフィン微多孔膜を、以下の手順で作製した。表面層(B層)の樹脂組成は、融点135℃、粘度平均分子量60万、分子量分布6.0のポリエチレン80重量部、及び融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン20重量部であった。中間層(A層)の樹脂組成は、粘度平均分子量60万、分子量分布6.0のポリエチレン100重量部であった。各層の樹脂組成に、酸化防止剤として、0.3重量部のテトラキス-(メチレン-3-(3’,5’-ジ-t-ブチル-4’-ヒドロキシフェニル)プロピオネート)メタンを混合した。得られた各混合物を、それぞれ、口径25mm、L/D=48の二軸押出機にフィーダーを介して投入した。更に孔形成材として流動パラフィン(37.78℃における動粘度75.90cSt)200重量部をサイドフィードでそれぞれの押出機に注入し、200℃、200rpmの条件で混練し、押出機先端に設置した二種三層で共押出可能なTダイから表面層の合計厚みと中間層の厚みとの比が40:60となるように押出した。押出後、ただちに25℃に冷却したキャストロールで冷却固化させ、厚さ1.3mmのシートを成形した。このシートを同時二軸延伸機で124℃の条件で7×7倍に延伸した後、塩化メチレンに浸漬して流動パラフィンを抽出除去した。その後、シートを乾燥し、テンター延伸機により120℃の条件で幅方向(TD)に歪速度9.0%/secで1.5倍延伸した。その後、この延伸シートを133℃の条件で横延伸後の幅から0.9倍になるように歪速度2.0%/secで幅方向(TD)に緩和する熱処理を行い、表面層(B層)の二層が同一の組成で、中間層(A層)が異なる組成の二種三層積層構造を有するポリオレフィン微多孔膜を得た。
Tダイからの押出時に表面層の合計厚みと中間層の厚みとの比が20:80となるように押出したこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)の樹脂組成をポリエチレン95重量部、ポリプロピレン5重量部としたこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)の樹脂組成をポリエチレン73重量部、ポリプロピレン27重量部とし、緩和処理時の温度を138℃としたこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
中間層(A層)の樹脂組成を、融点135℃、粘度平均分子量60万、分子量分布6.0のポリエチレン98重量部、及び融点160℃、粘度平均分子量40万、分子量分布10.0のポリプロピレン2重量部としたこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量70万、分子量分布3.0のポリエチレン、及び融点165℃、粘度平均分子量40万、分子量分布6.0のホモポリマーポリプロピレンを使用し、中間層(A層)に、融点135℃、粘度平均分子量70万、分子量分布3.0のポリエチレンを使用し、テンター延伸機での延伸時の歪速度を12.0%/sec、緩和処理を、歪速度0.5%/sec、温度132℃で行ったこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)の樹脂組成を、融点135℃、粘度平均分子量60万、分子量分布6.0のポリエチレン78重量部、及び融点160℃、粘度平均分子量40万、分子量分布10.0のポリプロピレン19重量部、平均一次粒径が15nmであるシリカ「DM10C」(商標、トクヤマ社製。ジメチルジクロロシランで疎水処理実施)を3重量部とし、緩和処理時の温度を140℃としたこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量50万、分子量分布6.0のポリエチレン、及び融点155℃、粘度平均分子量20万、分子量分布6.0のホモポリマーポリプロピレンを使用し、中間層(A層)に、融点135℃、粘度平均分子量50万、分子量分布6.0のポリエチレンを使用し、テンター延伸機での延伸時の歪速度を4.0%/sec、緩和処理を、歪速度3.5%/sec、温度138℃で行ったこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレン70重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン20重量部、融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン10重量部を使用し、中間層(A層)に、融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレンを使用し、流動パラフィン300重量部をサイドフィードでそれぞれの押出機に注入し、表面層の合計厚みと中間層の厚みとの比が35:65となるように押出し、押出後、ただちに25℃に冷却したキャストロールで冷却固化させ、厚さ1.7mmのシートを成形した以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
中間層(A層)に、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン40重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン60重量部を使用した以外は実施例9と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレン70重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン15重量部、融点130℃、粘度平均分子量15万、分子量分布5.0の低密度ポリエチレン(LDPE)15重量部、融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン5重量部を使用した以外は実施例10と同様の条件でポリオレフィン微多孔膜を得た。
中間層(A層)に、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン45重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン45重量部、粘度平均分子量15万、分子量分布5.0の低密度ポリエチレン(LDPE)10重量部を使用した以外は実施例11と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレン75重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン20重量部、融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン5重量部を使用した以外は実施例12と同様の条件でポリオレフィン微多孔膜を得た。
二種二層で共押出可能な積層ダイを使用した以外は実施例10と同様の条件でポリオレフィン微多孔膜を作製することで、二種二層積層構造(A層-B層)のポリオレフィン微多孔膜を得た。
三種五層積層構造(B層-C層-A層-C層-B層)のポリオレフィン微多孔膜を、以下の手順で作製した。A層の樹脂組成は、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン40重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン60重量部であった。酸化防止剤として、0.3重量部のテトラキス-(メチレン-3-(3’,5’-ジ-t-ブチル-4’-ヒドロキシフェニル)プロピオネート)メタンを混合した。得られた混合物を、口径25mm、L/D=48の二軸押出機にフィーダーを介して投入した。更に孔形成材として流動パラフィン(37.78℃における動粘度75.90cSt)300重量部をサイドフィードでそれぞれの押出機に注入し、200℃、200rpmの条件で混練し、押出機先端に設置したTダイから押出した。押出後、ただちに25℃に冷却したキャストロールで冷却固化させ、厚さ0.4mmの単層シートを成形した。B層の樹脂組成は融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレン70重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン20重量部、融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン10重量部を使用し、A層と同様の条件で0.4mmの単層シートを成型した。C層の樹脂組成は融点135℃、粘度平均分子量50万、分子量分布6.0のポリエチレン90重量部、及び融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン10重量を使用し、A層と同様の条件で0.4mmの単層シートを成型した。得られた3種類の単層シートをB層-C層-A層-C層-B層の三種五層積層構造になるように重ね、同時二軸延伸以降は実施例1と同様の条件で三種五層積層構造を有するポリオレフィン微多孔膜を得た。
中間層(A層)に、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン40重量部、融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレン30重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン30重量部を使用した以外は実施例10と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレン40重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン20重量部、融点130℃、粘度平均分子量15万、分子量分布5.0の低密度ポリエチレン(LDPE)30重量部、融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン10重量部を使用した以外は実施例16と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン8重量部、融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレン72重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン15重量部、融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン5重量部を使用した以外は実施例16と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に含まれるポリプロピレンを、融点160℃、粘度平均分子量100万、分子量分布10.0のホモポリマーポリプロピレンとした以外は実施例9と同様の条件でポリオレフィン微多孔膜を得た。
単層(A層のみ)のポリオレフィン微多孔膜を、以下の手順で作製した。樹脂組成は、融点135℃、粘度平均分子量50万、分子量分布6.0のポリエチレン90重量部、及び融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン10重量部であった。酸化防止剤として、0.3重量部のテトラキス-(メチレン-3-(3’,5’-ジ-t-ブチル-4’-ヒドロキシフェニル)プロピオネート)メタンを混合した。得られた混合物を、口径25mm、L/D=48の二軸押出機にフィーダーを介して投入した。更に孔形成材として流動パラフィン(37.78℃における動粘度75.90cSt)200重量部をサイドフィードでそれぞれの押出機に注入し、200℃、200rpmの条件で混練し、押出機先端に設置したTダイから押出した。押出後、ただちに25℃に冷却したキャストロールで冷却固化させ、厚さ1.3mmのシートを成形した。このシートを同時二軸延伸機で118℃の条件で7×7倍に延伸した後、塩化メチレンに浸漬して流動パラフィンを抽出除去した。その後、シートを乾燥し、テンター延伸機により120℃の条件で幅方向(TD)に歪速度17.0%/secで1.5倍延伸した。その後、この延伸シートを133℃の条件で横延伸後の幅から0.9倍になるように歪速度0.3%/secで幅方向(TD)に緩和する熱処理を行い、単層のポリオレフィン微多孔膜を得た。
124℃で二軸延伸を行い、テンター延伸機での延伸時の歪速度を7.0%/sec、緩和処理を、歪速度0.9%/secで行ったこと以外は比較例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)の樹脂組成をポリエチレン60重量部、ポリプロピレン40重量部とし、緩和処理時の温度を137℃とした以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)の樹脂組成をポリエチレン20重量部、ポリプロピレン80重量部とし、緩和処理時の温度を140℃とした以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)の樹脂組成を、融点135℃、粘度平均分子量60万、分子量分布6.0のポリエチレン24重量部、及び融点160℃、粘度平均分子量40万、分子量分布10.0のポリプロピレン6重量部、平均一次粒径が15nmであるシリカ「DM10C」(商標、トクヤマ社製。ジメチルジクロロシランで疎水処理実施)を70重量部とし、Tダイからの押出時に表面層の合計厚みと中間層の厚みとの比が25:75となるように押出し、緩和処理時の温度を145℃としたこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層及び中間層に含まれるポリエチレンとして、融点135℃、粘度平均分子量90万、分子量分布6.0のポリエチレンを使用したこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
実施例1における表面層の樹脂組成と中間層の樹脂組成を入れ替えたこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
表面層及び中間層に含まれるポリエチレンとして、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレンを使用し、押出機に注入する流動パラフィンを樹脂100重量部に対して150重量部とし、Tダイからの押出時に表面層の合計厚みと中間層の厚みとの比が36:64となるように押出し、緩和処理時の温度を120℃としたこと以外は実施例1と同様の条件でポリオレフィン微多孔膜を得た。
融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレンを38.8重量部、及び融点160℃、粘度平均分子量40万、分子量分布10.0のポリプロピレン1.2重量部、流動パラフィン60重量部%を先端にT-ダイを装着した押出機で溶融混練した後押し出して、厚さ1300μmのシートを作成した。このシートを縦横同時に延伸し、厚さ20μmのシートを作製した。このシートをメチルエチルケトン(MEK)中に浸漬し流動パラフィンを抽出除去した後で乾燥させて、厚さ18μmの微多孔膜Bを作製した。また、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレンを45.0重量部、流動パラフィン55.0重量部%を先端にT-ダイを装着した押出機で溶融混練した後押出して、厚さ1300μmのシートを作成した。このシートをMDに8倍、TDに8倍延伸し、厚さ20μmのシートを作製した。このシートをメチルエチルケトン(MEK)中に浸漬し流動パラフィンを抽出除去した後で乾燥させて、厚さ18μmの微多孔膜Aを作製した。微多孔膜B/微多孔膜A/微多孔膜Bの形態に3枚積層し、110℃に加熱された数本のロールを通しながら縦方向に3倍延伸し、その後122℃に加熱された数本のロールを通して熱処理を行い3枚積層した縦延伸膜を作製した。続いて、縦延伸膜を118℃に加熱されたテンターにて横方向に歪速度4%/secで2倍に延伸し、続いて同テンター内の128℃に加熱された領域にて熱処理しながら歪速度0.7%/secで延伸後の幅から0.9倍まで強制的に緩和させて厚さ10μmのB/A/B型の3枚積層微多孔膜を作製した。
微多孔膜Aの樹脂組成を融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン22.5重量部、粘度平均分子量15万、分子量分布5.0の低密度ポリエチレン(LDPE)22.5重量部、流動パラフィン55重量部%、微多孔膜Bの樹脂組成を融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン24重量部、融点160℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン16重量部、流動パラフィン60重量部%を使用し、流動パラフィン抽出前の同時二軸延伸倍率をMDに8倍、TDに8倍とし、流動パラフィン抽出後の横延伸時の歪速度を16.0%/sec、横延伸後の緩和を125℃、歪速度を2.8%/secとした以外は比較例9と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン10重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン87重量部、及び融点155℃、粘度平均分子量10万、分子量分布3.0のランダムポリマーポリプロピレン3重量部を使用し、中間層(A層)に、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン18重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン82重量部を使用し、同時二軸延伸を118℃で倍率をMD5倍、TD5倍とし、テンター延伸機でのTD延伸温度を126℃、歪速度4.0%/secで倍率1.3倍とし、緩和処理を、126℃で歪速度3.0%/secでTD延伸後から0.92倍としたこと以外は実施例9と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン97重量部、及び融点162℃、粘度平均分子量40万、分子量分布10.0のホモポリマーポリプロピレン3重量部を使用し、中間層(A層)に、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン20重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン80重量部を使用し、同時二軸延伸温度を117℃とし、テンター延伸機でのTD延伸を倍率1.4倍とし、緩和処理を行わなかったこと以外は比較例11と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン92重量部、及び融点155℃、粘度平均分子量10万、分子量分布3.0のランダムポリマーポリプロピレン8重量部を使用し、中間層(A層)に、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン30重量部、融点135℃、粘度平均分子量25万、分子量分布6.0のポリエチレン70重量部を使用し、同時二軸延伸温度を115℃とし、テンター延伸機での緩和処理を、124℃でTD延伸後から0.86倍としたこと以外は比較例12と同様の条件でポリオレフィン微多孔膜を得た。
表面層(B層)に、融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレン80重量部、及び融点160℃、粘度平均分子量160万、分子量分布10.0のホモポリマーポリプロピレン20重量部を使用し、中間層(A層)に、融点135℃、粘度平均分子量200万、分子量分布7.0のポリエチレン40重量部、融点135℃、粘度平均分子量70万、分子量分布6.0のポリエチレン60重量部を使用し、テンター延伸機でのTD延伸温度を124℃で歪速度を20%/secとし、緩和処理を行わなかったこと以外は比較例13と同様の条件でポリオレフィン微多孔膜を得た。
2A,2B ニッケル箔
3A,3B ガラス板
4 電気抵抗測定装置
5 熱電対
6 温度計
7 データコレクター
8 オーブン
9 耐熱テープ
10 クリップ
11 荷重
Claims (14)
- ポリオレフィンを含むA層と、ポリオレフィンを含むB層とを少なくとも1層ずつ備える積層構造を有するポリオレフィン微多孔膜であって、
前記A層に含まれるポリプロピレンは0質量%以上3質量%未満であり、前記B層に含まれるポリプロピレンは1質量%以上30質量%未満であり、A層に含まれるポリプロピレンの割合をPPA(質量%)、B層に含まれるポリプロピレンの割合をPPB(質量%)とした場合、PPB>PPAであり、
MDに、下記式:
荷重(gf)=0.01×ポリオレフィン微多孔膜の突刺強度(gf)×ポリオレフィン微多孔膜のTDの長さ(mm)
に基づいて決定される一定の荷重をかけた状態で測定される120℃でのTDの熱収縮率が10%以上40%以下である、ポリオレフィン微多孔膜。 - ポリオレフィンを含むA層と、その両面にポリオレフィンを含むB層を少なくとも1層ずつ備える積層構造を有するポリオレフィン微多孔膜であって、
前記ポリオレフィン微多孔膜の総厚みに対する前記A層の厚みの割合が40%以上90%以下である、請求項1に記載のポリオレフィン微多孔膜。 - 前記B層中の無機粒子の含有率が5質量%未満である、請求項1又は2に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜のゲル浸透クロマトグラフィー(GPC)測定の積分曲線における分子量300万以上の分子の割合が10質量%以下であり、かつ分子量3万以下の分子の割合が3.0質量%以下である、請求項1~3のいずれか一項に記載のポリオレフィン微多孔膜。
- 190℃で21.6kgfの荷重下でのメルトインデックスが0.1g/10min以上3.0g/10min以下である、請求項1~4のいずれか一項に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜のA層における、190℃で21.6kgfの荷重下でのメルトインデックスが0.01g/10min以上0.3g/10min以下である、請求項1~5のいずれか一項に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜のB層における、190℃で21.6kgfの荷重下でのメルトインデックスが0.3g/10minを超え、2.0g/10min以下である、請求項1~6のいずれか一項に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜の前記A層におけるメルトインデックスに対する前記B層のメルトインデックスの比率(B層のメルトインデックス/A層のメルトインデックス)が1.5以上20以下である、請求項1~7のいずれか一項に記載のポリオレフィン微多孔膜。
- シャットダウン応答時間が12秒以上22秒以下である、請求項1~8のいずれか一項に記載のポリオレフィン微多孔膜。
- シャットダウン温度が150℃以下であり、破膜温度が170℃を超える、請求項1~9のいずれか一項に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜に含まれるポリプロピレンの粘度平均分子量が30万以上120万以下である、請求項1~10のいずれか一項に記載のポリオレフィン微多孔膜。
- 前記ポリオレフィン微多孔膜に含まれるポリプロピレンがホモポリマーである、請求項1~11のいずれか一項に記載のポリオレフィン微多孔膜。
- 突刺強度が170gf/10μm以上である、請求項1~12のいずれか一項に記載のポリオレフィン微多孔膜。
- ラミネートフィルムで構成される外装体の中に、正極と負極とが、請求項1~13のいずれか一項に記載のポリオレフィン微多孔膜を介して積層された構造を少なくとも一つ有する、ラミネート型リチウムイオン二次電池。
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CN116387757A (zh) * | 2023-05-29 | 2023-07-04 | 合肥长阳新能源科技有限公司 | 一种高孔隙率钠离子电池拉伸隔膜及其制备方法 |
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JP2021091896A (ja) * | 2019-12-10 | 2021-06-17 | 旭化成株式会社 | ポリエチレン樹脂組成物 |
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