WO2009136648A1 - 高出力密度リチウムイオン二次電池用セパレータ - Google Patents
高出力密度リチウムイオン二次電池用セパレータ Download PDFInfo
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- WO2009136648A1 WO2009136648A1 PCT/JP2009/058748 JP2009058748W WO2009136648A1 WO 2009136648 A1 WO2009136648 A1 WO 2009136648A1 JP 2009058748 W JP2009058748 W JP 2009058748W WO 2009136648 A1 WO2009136648 A1 WO 2009136648A1
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- Prior art keywords
- separator
- power density
- ion secondary
- high power
- lithium ion
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Classifications
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion 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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/411—Organic material
- H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
- H01M50/417—Polyolefins
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/463—Separators, membranes or diaphragms characterised by their shape
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/491—Porosity
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
- H01M50/494—Tensile strength
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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
Definitions
- the present invention relates to a separator for high power density lithium ion secondary batteries.
- Polyolefin microporous membranes are widely used as separation of various substances, selective permeation separation membranes, separators and the like, and examples of applications thereof include microfiltration membranes, fuel cells, separators for capacitors, or functional materials
- the base material of the functional film for making it fill in a hole and making a new function appear, the separator for batteries, etc. are mentioned.
- a microporous membrane made of polyolefin is suitably used as a separator for lithium ion batteries widely used in notebook personal computers, mobile phones, digital cameras and the like.
- Lithium-ion secondary batteries used in applications such as power tools, bikes, bicycles, cleaners, carts, and automobiles are required to have higher power density, and conventionally, polyolefins made as electrodes, electrolytes, and separators are used. Improvements have been made to the porous membrane and the electrolyte respectively.
- the power density is a graph showing the relationship between the battery voltage and the discharge current at 50% SOC (State Of Charge), and the line between the discharge end voltage (3.0 V) of the battery and the current-voltage characteristics is out of the discharge end voltage. From the current value (I) when inserted and the battery mass (Wt), it is determined by the following equation.
- High power density means that the power density is 1000 W / kg or more, more preferably 1100 W / kg or more, and particularly preferably 1200 W / kg or more.
- the lithium ion secondary battery which has a high output density, also indicates that it has a high input density in that it enables high-speed lithium ion transfer.
- the term "high power density” as used herein also means that the input density is 800 w / kg or more, more preferably 850 W / kg or more, and particularly preferably 900 W / kg or more.
- Patent Document 1 proposes a microporous film comprising a mixture of high molecular weight polyethylene and high molecular weight polypropylene.
- Patent Document 2 proposes application to a lithium ion secondary battery for high power density applications by dispersing a lithium ion conductive material in a separator to reduce resistance.
- Patent No. 3342755 Patent Document 1 JP 2007-1141591A
- a separator for high output density lithium ion secondary batteries from a viewpoint of realizing high ion permeability, a thing with a large pore size and a high porosity is used.
- the battery is easily discharged due to its "large pore diameter" and "high porosity", and there is still room for improvement from the viewpoint of high rate characteristics.
- “high rate characteristics” indicates the ratio of the battery capacity when discharging to a constant voltage with high current to the battery capacity when discharging to a constant voltage with low current, and it is considered that the higher the value, the better. It can be said.
- the size of the high power density lithium ion secondary battery tends to be larger from the viewpoint of achieving higher power density.
- An object of the present invention is to provide a separator for a high power density lithium ion secondary battery which can realize a lithium ion secondary battery which is suppressed in self-discharge and excellent in high rate characteristics and which is also excellent in homogeneity. Do.
- the present invention is as follows.
- Longitudinal (MD) tensile strength and transverse (TD) tensile strength are each 50 MPa or more
- a separator for a high power density lithium ion secondary battery comprising a microporous polyolefin membrane containing polypropylene and having a total of 20 to 250% of MD tensile elongation and TD tensile elongation.
- [3] The separator for high power density lithium ion secondary batteries as described in said [1] or [2] whose TD thermal contraction rate in 65 degreeC is 1.0% or less.
- [4] The separator for a high power density lithium ion secondary battery according to any one of the above [1] to [3], wherein the porosity is 40% or more.
- [5] The separator for a high power density lithium ion secondary battery according to any one of the above [1] to [4], which has a film thickness of 20 ⁇ m or more.
- a high power density lithium ion secondary battery comprising the separator for a high power density lithium ion secondary battery according to any one of the above [1] to [5], a positive electrode, a negative electrode, and an electrolytic solution.
- the present invention it is possible to realize a lithium ion secondary battery which is suppressed in self-discharge and excellent in high rate characteristics and also has a good homogeneity, and a separator for a high power density lithium ion secondary battery.
- the separator for a high power density lithium ion secondary battery of the present embodiment (hereinafter sometimes simply referred to as “separator”) is a polyolefin microporous film (hereinafter simply referred to as “microporous film”)
- the microporous film has communicating holes in the film thickness direction, and has, for example, a three-dimensional network structure.
- the microporous film has a length direction (same as the material resin discharge direction or the machine direction, hereinafter may be abbreviated as “MD”) tensile strength and width direction (direction orthogonal to the length direction).
- the tensile strength is 50 MPa or more, and the sum of the MD tensile elongation and the TD tensile elongation is 20 to 250%, and contains polypropylene. I assume.
- the separator of the present embodiment can realize good high-rate characteristics and low self-discharge characteristics particularly required for lithium ion secondary batteries with high output density, and also uniformity. Excellent.
- the separator of the present embodiment is suitable as a high power density lithium ion secondary battery separator.
- the porosity of the microporous film is preferably 30% or more, more preferably 35% or more, and still more preferably 40% or more, from the viewpoint of following the rapid movement of lithium ions at high rate. Also, from the viewpoint of film strength and self-discharge, it is preferably 90% or less, more preferably 80% or less, and still more preferably 60% or less.
- the average pore diameter of the microporous film is preferably less than 0.1 ⁇ m (from the viewpoint of preventing self-discharge in the case of the maximum pore diameter by the bubble point method, 0.09 ⁇ m or less) from the viewpoint of preventing self-discharge.
- it is 0.09 micrometer or less, More preferably, it is 0.08 micrometer or less.
- the average pore diameter is less than 0.1 ⁇ m from the viewpoint that self-discharge hardly occurs during storage after charge, particularly in a battery with high power density.
- the lower limit is not particularly limited, but is preferably 0.01 ⁇ m or more, more preferably 0.02 ⁇ m or more, and still more preferably 0.03 ⁇ m or more from the viewpoint of balance of air permeability .
- the air permeability of the microporous film is preferably 1 second or more, more preferably 50 seconds or more, and still more preferably 100 seconds or more, from the viewpoint of the balance between the film thickness, the porosity, and the average pore diameter.
- 400 seconds or less is preferable, and 300 seconds or less is more preferable.
- the tensile strength of the microporous membrane is 50 MPa or more in both MD and TD directions, and more preferably 70 MPa or more. It is preferable to set the tensile strengths of MD and TD to 50 MPa or more from the viewpoint that breakage at the time of slits and battery winding hardly occurs, or from the viewpoint of short circuit caused by foreign matter in the battery hardly occurring. In addition, it is preferable from the viewpoint that the membrane can easily maintain the original pore structure with respect to expansion and contraction of the electrode at the time of the high rate test and the like, and the deterioration of the characteristics can be reduced. On the other hand, the upper limit value is not particularly limited, but from the viewpoint of achieving a low shrinkage ratio, 500 MPa or less is preferable, 300 MPa or less is more preferable, and 200 MPa or less is still more preferable.
- the MD tensile elongation and the TD tensile elongation of the microporous film are each preferably 10 to 150%, and the total is 20 to 250%, more preferably 30 to 200%, and 50 to 50%. Particularly preferred is 200%.
- the total of tensile elongations of MD and TD is 20 to 250%, adequate strength is easily expressed by appropriate orientation, and uniform stretching is easily applied in the stretching step, and the film thickness distribution becomes good. As a result, the battery winding property also tends to be improved.
- the pore structure is less likely to change with respect to expansion and contraction of the electrode in the high rate test and the like, and the characteristics can be easily maintained.
- the stretching unevenness at the time of stretching is reduced and the film thickness distribution is improved, and the uniformity after bending, for example, 1 mm or less. Can achieve an excellent reel.
- the microporous membrane whose tensile strength and tensile elongation are set in the above ranges is the original for use at a high current such as 10 C (10 times the 1-hour rate of rated electrical capacity (1 C) current). It is easy to maintain the pore structure, resulting in the surprising effect that the high rate characteristics and the self-discharge characteristics become good.
- the puncture strength (absolute strength) of the microporous membrane is preferably 3N or more, more preferably 5N or more.
- the puncture strength is 3 N or more, it is preferable from the viewpoint of being able to reduce the occurrence of pinholes and cracks even when the sharp portions of the electrode material and the like pierce the microporous film when used as a battery separator.
- the upper limit is preferably 10 N or less, more preferably 8 N or less, from the viewpoint of achieving a low thermal shrinkage.
- the thickness of the microporous membrane is not particularly limited, but is preferably 1 ⁇ m or more from the viewpoint of membrane strength, and preferably 500 ⁇ m or less from the viewpoint of permeability. 20 ⁇ m or more from the viewpoint of being used for high power density batteries that require relatively high self-discharge characteristics, such as safety tests, etc., with relatively high calorific value, and from the viewpoint of winding performance in a large-sized battery winding machine Is preferable, 22 ⁇ m is more preferable, and 23 ⁇ m or more is particularly preferable.
- the upper limit is preferably 100 ⁇ m or less, more preferably 50 ⁇ m or less.
- Examples of means for forming a microporous film having various properties as described above include, for example, a method for optimizing polymer concentration and stretching ratio during extrusion, and stretching and relaxation operations after extraction, and the like. As the adjustment of the degree, a method of blending polypropylene with polyethylene and the like can be mentioned.
- the aspect of the microporous film may be an aspect of a single layer body or an aspect of a laminate.
- the laminate refers to the lamination of the microporous film and the non-woven fabric or other fine multi-layer film in the present embodiment, or the surface coating of the inorganic component and the organic component.
- the form is not particularly limited as long as the physical properties of the laminate are within the range of the present embodiment.
- a method including the following steps (a) to (d) may be mentioned.
- C A stretching step of extracting a plasticizer and an inorganic material as necessary after the sheet forming step, and further stretching the sheet in the direction of one or more axes.
- D A post-processing step of extracting a plasticizer and an inorganic agent as necessary after the stretching step and further performing a heat treatment.
- polystyrene resin examples include ethylene, a homopolymer of propylene, or ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene, and norbornene.
- Copolymers formed of at least two or more monomers selected from the group consisting of These may be a mixture. The use of a mixture is preferable because control of the fuse temperature and the short circuit temperature is facilitated.
- the ultrahigh molecular weight polyolefin component is considered to have a high property of maintaining the pore structure, enable heat setting at a higher temperature, and reduce the heat shrinkage rate.
- the polyethylene to be blended is preferably a high density homopolymer from the viewpoint that heat setting can be performed at a higher temperature without blocking the pores.
- Mv of the whole microporous film is 100,000 or more and 1.2 million or less. More preferably, it is 300,000 to 800,000. If the Mv is 100,000 or more, the resistance to rupture of the film tends to be easily developed, and if it is 1.2 million or less, the extrusion process tends to be easy, and the contraction force is relaxed during the melting. The heat resistance tends to improve as the temperature becomes faster.
- Blending polypropylene in a polyolefin is effective in reducing tensile elongation because it tends to create an interface between polypropylene and a polyethylene matrix. Therefore, it becomes easy to adjust to a desired tensile elongation, and as a result, a uniform force is easily applied to the whole film at the time of stretching, so that the film thickness distribution is improved.
- polypropylene blends tend to have small pore sizes during phase separation.
- the Mv of the polypropylene to be blended is preferably 100,000 or more from the viewpoint of resistance to breakage at the time of melting, and preferably less than 1,000,000 from the viewpoint of formability.
- the blend amount of the ultrahigh molecular weight polyolefin having a viscosity average molecular weight of 500,000 or more with respect to the entire polyolefin used in the step (a) is preferably 1 to 90% by mass, more preferably 5 to 80% by mass, further preferably Is 10 to 70% by mass.
- the ultrahigh molecular weight component tends to contribute to the high elastic modulus and film thickness uniformity of the film, and the pore structure tends to be easily maintained. .
- the blend amount of the polyolefin having a viscosity average molecular weight of less than 500,000 based on the total weight of the polyolefin used in the step (a) is preferably 1 to 90% by mass, more preferably 5 to 80% by mass, and still more preferably It is 10 to 70% by mass.
- a film having a favorable thickness distribution tends to be easily obtained by forming appropriate entanglement with the ultrahigh molecular weight component.
- the blend amount of polypropylene with respect to the whole polyolefin used in the step (a) is preferably 1 to 80% by mass, more preferably 2 to 50% by mass, still more preferably 3 to 20% by mass, particularly preferably It is 5 to 10% by mass.
- the blend amount of polypropylene is 1% by mass or more, the above-mentioned effects tend to be easily exhibited, and when it is 80% by mass or less, permeability tends to be easily ensured.
- the polyolefin used in the step (a) further includes known additives such as metal soaps such as calcium stearate and zinc stearate, an ultraviolet absorber, a light stabilizer, an antistatic agent, an antifogging agent, a color pigment and the like.
- the agents can be mixed and used.
- the organic compound which can form a uniform solution with polyolefin at the temperature below a boiling point can be mentioned.
- decalin, xylene, dioctyl phthalate, dibutyl phthalate, stearyl alcohol, oleyl alcohol, decyl alcohol, nonyl alcohol, diphenyl ether, n-decane, n-dodecane, paraffin oil and the like can be mentioned.
- paraffin oil and dioctyl phthalate are preferable.
- the proportion of the plasticizer is not particularly limited, but from the viewpoint of the porosity of the resulting microporous film, 20% by mass based on the total mass of the polyolefin, the plasticizer, and the inorganic material optionally blended
- the above is preferable, and 90% by mass or less is preferable from the viewpoint of viscosity.
- it is preferably 50 to 80% by mass, and more preferably 60 to 75% by mass.
- the inorganic material examples include alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, oxide ceramics such as zinc oxide and iron oxide, and nitrides of silicon nitride, titanium nitride, boron nitride and the like.
- Ceramics silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite And ceramics such as calcium silicate, magnesium silicate, kieselguhr, silica sand, glass fibers and the like. These can be used alone or in combination of two or more. Among them, from the viewpoint of electrochemical stability, silica, alumina and titania are more preferable, and silica is particularly preferable.
- a method of kneading for example, first, some or all of the raw materials are pre-mixed using a Henschel mixer, a ribbon blender, a tumbler blender, etc., as necessary. Next, all the raw materials are melt-kneaded by a screw extruder such as a single screw extruder or a twin screw extruder, a kneader, a mixer or the like. The kneaded material is extruded from a T-type die, an annular die or the like. At this time, single-layer extrusion or lamination extrusion may be used.
- a screw extruder such as a single screw extruder or a twin screw extruder, a kneader, a mixer or the like.
- the kneaded material is extruded from a T-type die, an annular die or the like. At this time, single-layer extrusion or lamination extrusion may be used.
- melt-kneading After mixing an antioxidant with a raw material polymer at a predetermined concentration, it is preferable to substitute in a nitrogen atmosphere and perform melt-kneading in a state in which the nitrogen atmosphere is maintained. 160 degreeC or more is preferable and, as for the temperature at the time of melt-kneading, 180 degreeC or more is more preferable. Moreover, less than 300 degreeC is preferable, less than 240 degreeC is more preferable, and less than 230 degreeC is further more preferable.
- a method of solidifying the melt-kneaded and extruded melt by compression cooling may be mentioned.
- a cooling method there is a method of directly contacting with a cooling medium such as cold air or cooling water, a method of contacting with a roll cooled with a refrigerant or a press, and a method of contacting with a roll or a press cooled with a refrigerant And film thickness control is preferable.
- the total area magnification is preferably 8 times or more, more preferably 15 times or more, and still more preferably 30 times or more from the viewpoint of film thickness uniformity and tensile elongation, and the balance between porosity and average pore diameter. When the area magnification is 30 times or more, high strength and low elongation tend to be easily obtained.
- Extraction of the plasticizer and the inorganic material can be performed by a method of immersion in an extraction solvent, showering, or the like.
- the extraction solvent is preferably a poor solvent for polyolefin, and a good solvent for plasticizer and inorganic material, and has a boiling point lower than the melting point of polyolefin.
- Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane, methylene chloride, 1,1,1-trichloroethane, halogenated hydrocarbons such as fluorocarbons, alcohols such as ethanol and isopropanol, and acetone And ketones such as 2-butanone and alkaline water.
- the above solvents can be used alone or in combination.
- the inorganic material may be extracted in whole or in part in any of all the processes, or may be left in the product.
- the order, method and number of extractions are not particularly limited. The extraction of the inorganic material may not be performed as needed.
- Examples of the heat treatment method include a heat setting method in which stretching and relaxation operations are performed using a tenter or a roll stretching machine.
- a relaxation operation is a reduction operation performed at a certain relaxation rate to the film MD and / or TD.
- the relaxation rate is the value obtained by dividing the MD dimension of the film after the relaxation operation by the MD dimension of the film before the operation, or the value obtained by dividing the TD dimension after the relaxation operation by the TD dimension of the film before the operation, or MD, TD When both are relaxed, it is the value which multiplied the relaxation rate of MD and the relaxation rate of TD.
- the predetermined temperature is preferably 100 ° C. or more from the viewpoint of heat shrinkage, and preferably less than 135 ° C. from the viewpoint of porosity and permeability.
- the predetermined relaxation rate is preferably 0.9 or less, more preferably 0.8 or less, from the viewpoint of the thermal contraction rate. Moreover, it is preferable that it is 0.6 or more from a viewpoint of wrinkles prevention, a porosity, and permeability.
- the relaxation operation may be performed in both the MD and TD directions, but it is possible to reduce the thermal contraction rate not only in the operation direction but also in the direction perpendicular to the operation by the relaxation operation of only one of MD and TD.
- a step of stacking a plurality of single layer bodies can be employed as a step for obtaining a laminate.
- surface treatment processes such as electron beam irradiation, plasma irradiation, surfactant coating, chemical modification and the like can be employed.
- the film winding body (hereinafter referred to as "master roll") after the above-mentioned heat setting can be treated at a predetermined temperature (master roll aging operation), and then the master roll can be rewound. This step releases the residual stress of the polyolefin in the master roll.
- a predetermined temperature master roll aging operation
- the preferable temperature which heat-processes a master roll 35 degreeC or more is preferable, 45 degreeC or more is more preferable, and 60 degreeC or more is still more preferable. From the viewpoint of permeability retention, 120 ° C. or less is preferable.
- the heat treatment time is not limited, but is preferably 24 hours or more because the effect is easily exhibited.
- the above-mentioned heat setting is effective for reducing the thermal contraction rate in the region of 100 ° C. or higher, but it is difficult to effectively remove the residual stress at a relatively low temperature such as 65 ° C. by such a method. It is. Therefore, it is preferable to perform the aging operation, for example, since the TD thermal contraction rate at a relatively low temperature of 65 ° C. is easily 1.0% or less, and the separator is hardly shrunk in the battery drying step. If the TD thermal contraction rate at 65 ° C. is 1.0% or less, the possibility that the positive electrode and the negative electrode make a fine contact can be reduced, and the self-discharge characteristics tend to be improved.
- the TD heat shrinkage at 65 ° C. is preferably 0.5% or less, more preferably 0.2% or less.
- the separator made of the microporous polyolefin membrane of the present embodiment has high strength, pore blocking property, low thermal shrinkage, and permeability such as porosity, average pore diameter, strength, and MD / as compared with the conventional separator.
- the balance of TD tensile elongation is improved. Therefore, by using the separator of this embodiment particularly as a separator for a high power density battery, it has excellent high rate characteristics, good self-discharge performance, and excellent battery winding property (homogeneity It is possible to provide good separators.
- the separator for a high power density lithium ion secondary battery according to the present embodiment is particularly suitable for applications requiring high power density characteristics such as an electric power tool, a motorbike, a bicycle, a cart, a scooter, and an automobile. Therefore, it becomes possible to impart battery characteristics more than conventional.
- Porosity (volume-mass / film density) / volume x 100 The film density was calculated at a constant 0.95.
- Air permeability (seconds) In accordance with JIS P-8117, it was measured by a Gurley-type air permeability meter (G-B2 (trademark) manufactured by Toyo Seiki Co., Ltd.).
- 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.
- the tensile strength (MPa) was determined by dividing the strength at break by the sample cross-sectional area before the test.
- the sum (%) of MD tensile elongation degree and TD tensile elongation degree was calculated
- the measurement was carried out at a temperature of 23 ⁇ 2 ° C., a chuck pressure of 0.30 MPa, and a tensile speed of 200 mm / min (strain rate of 400% / min for samples in which the distance between chucks can not be secured 50 mm).
- R gas was determined from the air permeability (sec) using the following equation.
- R gas 0.0001 / (air permeability ⁇ (6.424 ⁇ 10 ⁇ 4 ) ⁇ (0.01276 ⁇ 101325)) Moreover, R liq was calculated
- required using the following formula from water permeability (cm ⁇ 3 > / (cm ⁇ 2 > * sec * Pa)). R liq permeability / 100 The water permeability is determined as follows.
- a microporous membrane previously dipped in alcohol is set in a stainless steel liquid-permeable cell with a diameter of 41 mm, and after the alcohol of the membrane is washed with water, water is allowed to permeate at a differential pressure of about 50000 Pa, and a lapse of 120 seconds
- the water permeation amount per unit time, unit pressure, and unit area was calculated from the water permeation amount (cm 3 ) at the time of carrying out, and this was made into the water permeability.
- a microporous membrane slit at a width of 60 mm and a length of 1000 m was wound on a plastic core having an outer diameter of 8 inches.
- the reel was fed out by 1 m on a flat plate, and the amount of bending (a displacement in the direction of the microporous membrane TD with respect to the MD center line of the strip microporous membrane in the direction of mm) mm at 50 cm in the length direction from the delivery end.
- the amount of bending is an indicator of the homogeneity of the microporous membrane.
- the active material application amount of the positive electrode was 250 g / m 2
- the bulk density of the active material was 3.00 g / cm 3 .
- Preparation of Negative Electrode A slurry was prepared by dispersing 96.9% by mass of artificial graphite as a negative electrode active material, 1.4% by mass of ammonium salt of carboxymethylcellulose as a binder and 1.7% by mass of styrene-butadiene copolymer latex in purified water did. 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.
- the active material application amount of the negative electrode was 106 g / m 2 , and the bulk density of the active material was 1.35 g / cm 3 .
- Battery assembly The separator was cut into a circle of 18 mm in diameter and the positive electrode and the negative electrode in a circle of 16 mm, and the positive electrode, the separator and the negative electrode were stacked in this order so that the active material faces of the positive and negative electrodes face each other.
- the container and the lid were insulated, and the container was in contact with the copper foil of the negative electrode, and the lid was in contact with the aluminum foil of the positive electrode.
- the above-mentioned non-aqueous electrolyte was injected into the container and sealed. After standing at room temperature for 1 day, charge to a battery voltage of 4.2 V at a current value of 3 mA (0.5 C) in a 25 ° C. atmosphere, and after reaching the voltage of 4.2 V, hold down the current value from 3 mA The first charge after making the battery for a total of 6 hours was done in the way of getting started. Subsequently, the battery was discharged to a battery voltage of 3.0 V at a current value of 3 mA (0.5 C). e.
- Self-discharge characteristic / high rate characteristic At 25 ° C atmosphere, charge the battery voltage to 4.2V at a current value of 6mA (1.0C), and keep the 4.2V after reaching, and start the current value from 6mA So, I did charge for a total of 3 hours. Subsequently, the battery was discharged to a battery voltage of 3.0 V at a current value of 6 mA (1.0 C). The battery capacity at that time was X mAh, and was further charged to a battery voltage of 4.2 V at a current value of 6 mA (1.0 C) and left for 24 hours. This operation was performed with a total of 50 cells.
- the proportion (%) of cells maintaining the capacity of 90% or more of X out of 50 cells was calculated as the self-discharge characteristic.
- the battery capable of maintaining the capacity of 90% or more was discharged to a battery voltage of 3.0 V at a current value of 60 mA (10 C).
- the capacity at that time was Y mAh, and Y / X ⁇ 100 (%) was calculated as the high rate characteristic.
- Power Density Measurement A positive electrode and a negative electrode prepared in a and b were stacked in the order of a negative electrode, a separator, a positive electrode and a separator, and spirally wound several times to produce a cylindrical laminate.
- the cylindrical laminate was housed in a stainless steel container, the nickel lead drawn from the negative electrode current collector was connected to the bottom of the container, and the aluminum lead drawn from the positive electrode current collector was connected to the container lid terminal. Furthermore, the non-aqueous electrolyte described above was injected into the container and sealed, and a cylindrical battery having a width of 18 mm and a height of 65 mm was produced. Thereafter, the battery was charged to a battery voltage of 4.2 V at a current value of 1 C, and after reaching the voltage of 4.2 V, the current value was gradually reduced by a method of gradually reducing the current value for a total of 3 hours to 100% SOC.
- the battery voltage after discharge for 10 seconds in (1) to (5) was measured, and each voltage was plotted against the current value.
- the power density was calculated by the following equation from the battery mass (Wt), with a current value at which the approximate straight line by the least squares method intersects the discharge lower limit voltage (V).
- Power density (P) (V ⁇ I) / Wt
- the voltages at d, e and f (4.2 V and 3.0 V) are an example when lithium cobalt composite oxide is used for the positive electrode and graphite is used for the negative electrode, and the measurement is within the operating voltage range of the electrode member. I adjusted it together.
- the battery when lithium iron phosphate is used for the positive electrode and graphite is used for the negative electrode, the battery is charged to 3.6 V and discharged to 2.0 V, and the discharge lower limit voltage is also 2.0 V.
- the battery voltage after charging for 10 seconds in each of (1) to (5) was measured, and each voltage was plotted against the current value.
- the current value at which the approximate straight line by the least squares method intersects with the charge upper limit voltage (V) was taken as (I), and it was calculated similarly to the power density from the battery mass (Wt).
- Example 1 Using a tumbler blender, 47% by mass of homopolymer polyethylene of 700,000 Mv, 46% by mass of homopolymer polyethylene of Mv 300,000, and 7% by mass of polypropylene of Mv 400,000 (PP blend amount 7% by mass) It was dry blended. To 99% by mass of the obtained pure polymer mixture, 1% by mass of pentaerythrityl-tetrakis- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] is added as an antioxidant, and the tumbler is again carried out. A blend of polymers and the like was obtained by dry blending using a blender.
- the resulting mixture of polymers and the like was substituted with nitrogen and then fed to a twin-screw extruder by a feeder under a nitrogen atmosphere.
- liquid paraffin kinetic viscosity 7.59 ⁇ 10 ⁇ 5 m 2 / s at 37.78 ° C.
- PC polymer concentration
- melt-kneading conditions were a set temperature of 200 ° C., a screw rotation speed of 240 rpm, and a discharge amount of 12 kg / h. Subsequently, the melt-kneaded product was extruded and cast on a cooling roll controlled to a surface temperature of 25 ° C. through a T-die to obtain a gel sheet having a raw film thickness of 1400 ⁇ m. Next, it was introduced into a simultaneous biaxial tenter stretching machine and biaxial stretching was performed.
- the set stretching conditions were an MD magnification of 7.0 times, a TD magnification of 7.0 times (that is, 7 ⁇ 7 times), and a biaxial stretching temperature of 125 ° C.
- a TD tenter to perform heat fixation (sometimes abbreviated as “HS”), perform HS at a heat fixation temperature of 125 ° C., a draw ratio of 1.4 times, and then perform a relaxation operation of 0.8 times (Ie, the HS relaxation rate was 0.8 times).
- HS heat fixation
- the master roll (MR) wound to 1000 m was left in a temperature-controlled room at 60 ° C. for 24 hours (that is, with MR aging).
- Examples 2 to 18, Comparative Examples 1 to 6 A microporous film was obtained in the same manner as in Example 1 except for the conditions shown in Table 1 below. Various properties of the obtained microporous membrane were evaluated. The results are shown in Tables 1 and 2 below.
- the polyolefin microporous film of the present invention is particularly suitably used as a separator for lithium ion batteries having a high output density.
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Abstract
Description
出力密度(P)=(V×I)/Wt
ここで、「高出力密度」とは、1000W/kg以上の出力密度であることを意味し、1100W/kg以上がより好ましく、1200W/kg以上が特に好ましい。また、一般的に、高出力密度であるリチウムイオン二次電池は、高速のリチウムイオン伝達を可能にしているという点で、高入力密度であるということも同時に示している。本願でいう「高出力密度」とは、入力密度で800w/kg以上であることをも意味し、850W/kg以上がより好ましく、900W/kg以上が特に好ましい。
また、高出力密度リチウムイオン二次電池の大きさは、より高出力密度を実現する観点からより大きくなる傾向にある。その場合、電池内のセパレータの捲回数も多くなり、セパレータのパスライン長も長くなる傾向にある。長いパスラインでも安定した電池生産を可能とする観点から、セパレータの均質性(曲がりを生じない)という点でも、より一層品質の優れたポリオレフィン製微多孔膜が求められている。
本発明は、自己放電が抑制され、ハイレート特性にも優れたリチウムイオン二次電池を実現し得ると共に、均質性も良好な、高出力密度リチウムイオン二次電池用セパレータを提供することを目的とする。
[1]
長さ方向(MD)引張強度と幅方向(TD)引張強度がそれぞれ50MPa以上であり、
MD引張伸度とTD引張伸度の合計が20~250%であり、かつポリプロピレンを含むポリオレフィン製微多孔膜からなることを特徴とする高出力密度リチウムイオン二次電池用セパレータ。
[2]
平均孔径が0.1μm未満である上記[1]に記載の高出力密度リチウムイオン二次電池用セパレータ。
[3]
65℃でのTD熱収縮率が1.0%以下である上記[1]又は[2]に記載の高出力密度リチウムイオン二次電池用セパレータ。
[4]
気孔率が40%以上である上記[1]~[3]のいずれかに記載の高出力密度リチウムイオン二次電池用セパレータ。
[5]
膜厚が20μm以上である上記[1]~[4]のいずれかに記載の高出力密度リチウムイオン二次電池用セパレータ。
[6]
上記[1]~[5]のいずれかに記載の高出力密度リチウムイオン二次電池用セパレータと、正極と、負極と、電解液とを用いてなる高出力密度リチウムイオン二次電池。
(a)ポリオレフィンと、可塑剤と、必要に応じて無機材とを混練する混練工程。
(b)混練工程の後に混練物を押出し、シート状(単層、積層であることは問わない)に成形して冷却固化させるシート成形工程。
(c)シート成形工程の後、必要に応じて可塑剤や無機材を抽出し、更にシートを一軸以上の方向へ延伸する延伸工程。
(d)延伸工程の後、必要に応じて可塑剤や無機剤を抽出し、更に熱処理を行う後加工工程。
ASTM-D4020に基づき、デカリン溶媒における135℃での極限粘度[η]を求めた。膜がポリエチレンとポリプロピレンとのブレンド物である場合は、以下のポリエチレンの式で算出した。
ポリエチレンのMvは次式により算出した。
[η]=6.77×10-4Mv0.67
ポリプロピレンのMvは次式により算出した。
[η]=1.10×10-4Mv0.80
東洋精機製の微小測厚器、KBM(商標)用いて室温23±2℃で測定した。
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、それらと膜密度(g/cm3)より、次式を用いて計算した。
気孔率=(体積-質量/膜密度)/体積×100
なお、膜密度は0.95と一定にして計算した。
JIS P-8117に準拠し、ガーレー式透気度計(東洋精器(株)製、G-B2(商標))により測定した。
カトーテック製、KES-G5(商標)ハンディー圧縮試験器を用いて、開口部の直径11.3mmの試料ホルダーで針先端の曲率半径0.5mm、突刺速度2mm/secで、23±2℃雰囲気下にて突刺試験を行うことにより、最大突刺荷重(N)を計測し、突刺強度とした。
JIS K7127に準拠し、島津製作所製の引張試験機、オートグラフAG-A型(商標)を用いて、MD及びTDサンプル(形状;幅10mm×長さ100mm)について測定した。また、サンプルはチャック間を50mmとし、サンプルの両端部(各25mm)の片面にセロハンテープ(日東電工包装システム(株)製、商品名:N.29)を貼ったものを用いた。更に、試験中のサンプル滑りを防止するために、引張試験機のチャック内側に、厚み1mmのフッ素ゴムを貼り付けた。
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。
引張強度(MPa)は、破断時の強度を、試験前のサンプル断面積で除することで求めた。また、MD引張伸度とTD引張伸度の値を合計することにより、MD引張伸度とTD引張伸度の合計(%)を求めた。なお、測定は、温度23±2℃、チャック圧0.30MPa、引張速度200mm/分(チャック間距離を50mm確保できないサンプルにあっては、ひずみ速度400%/分)で行った。
キャピラリー内部の流体は、流体の平均自由工程がキャピラリーの孔径より大きいときはクヌーセンの流れに、小さい時はポアズイユの流れに従うことが知られている。そこで、微多孔膜の透気度測定における空気の流れがクヌーセンの流れに、また微多孔膜の透水度測定における水の流れがポアズイユの流れに従うと仮定した。
この場合、平均孔径d(μm)は、空気の透過速度定数Rgas(m3/(m2・sec・Pa))、水の透過速度定数Rliq(m3/(m2・sec・Pa))、空気の分子速度ν(m/sec)、水の粘度η(Pa・sec)、標準圧力Ps(=101325Pa)、気孔率ε(%)、膜厚L(μm)から、次式を用いて求めることができる。
d=2ν×(Rliq/Rgas)×(16η/3Ps)×106
ここで、Rgasは透気度(sec)から次式を用いて求めた。
Rgas=0.0001/(透気度×(6.424×10-4)×(0.01276×101325))
また、Rliqは透水度(cm3/(cm2・sec・Pa))から次式を用いて求めた。
Rliq=透水度/100
なお、透水度は次のように求められる。直径41mmのステンレス製の透液セルに、あらかじめアルコールに浸しておいた微多孔膜をセットし、該膜のアルコールを水で洗浄した後、約50000Paの差圧で水を透過させ、120sec間経過した際の透水量(cm3)より、単位時間・単位圧力・単位面積当たりの透水量を計算し、これを透水度とした。
また、νは気体定数R(=8.314)、絶対温度T(K)、円周率π、空気の平均分子量M(=2.896×10-2kg/mol)から次式を用いて求められる。
ν=((8R×T)/(π×M))1/2
ASTM F316-86に準拠し、エタノール溶媒で測定した。
微多孔膜をMD方向に150mm、TD方向に200mmに切り取り、65℃のオーブン中に5時間静置した。このとき、温風が直接サンプルにあたらないよう、2枚の紙に挟んだ。オーブンから取り出し冷却した後、長さ(mm)を測定し、以下の式にてMD及びTDの熱収縮率を算出した。(サンプル長が確保できないものに関しては、150mm×200mmに入る範囲で、可能な限り長いサンプルとした。)
MD熱収縮率(%)=(150-加熱後のMDの長さ)/150×100
TD熱収縮率(%)=(200-加熱後のTDの長さ)/200×100
外径8インチのプラスチックコアに、60mmの幅で1000mの長さでスリットした微多孔膜を捲回した。そのリールを平面板上で1m繰り出し、繰り出し端から長さ方向50cm部分における曲がり量(短冊状微多孔膜のMD方向中心線に対する、微多孔膜TD方向へのズレ量。mm)を測定した。当該曲がり量は、微多孔膜の均質性の指標である。
a.正極の作製
正極活物質としてリチウムコバルト複合酸化物LiCoO2を92.2質量%、導電材としてリン片状グラファイトとアセチレンブラックをそれぞれ2.3質量%、バインダーとしてポリフッ化ビニリデン(PVDF)3.2質量%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で塗布し、130℃で3分間乾燥後、ロールプレス機で圧縮成形した。このとき、正極の活物質塗布量は250g/m2,活物質嵩密度は3.00g/cm3になるようにした。
b.負極の作製
負極活物質として人造グラファイト96.9質量%、バインダー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%とスチレン-ブタジエン共重合体ラテックス1.7質量%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℃で3分間乾燥後、ロールプレス機で圧縮成形した。このとき、負極の活物質塗布量は106g/m2,活物質嵩密度は1.35g/cm3になるようにした。
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/リットルとなるように溶解させて調製した。
d.電池組立
セパレータを18mmφ,正極及び負極を16mmφの円形に切り出し、正極と負極の活物質面が対向するよう、正極、セパレータ、負極の順に重ね、蓋付きステンレス金属製容器に収納した。容器と蓋とは絶縁されており、容器は負極の銅箔と、蓋は正極のアルミ箔と接していた。この容器内に前記した非水電解液を注入して密閉した。室温にて1日放置した後、25℃雰囲気下、3mA(0.5C)の電流値で電池電圧4.2Vまで充電し、到達後4.2Vを保持するようにして電流値を3mAから絞り始めるという方法で、合計6時間電池作成後の最初の充電を行った。続いて3mA(0.5C)の電流値で電池電圧3.0Vまで放電した。
e.自己放電特性/ハイレート特性
25℃雰囲気下、6mA(1.0C)の電流値で電池電圧4.2Vまで充電し、到達後4.2Vを保持するようにして電流値を6mAから絞り始めるという方法で、合計3時間充電を行った。続いて6mA(1.0C)の電流値で電池電圧3.0Vまで放電した。そのときの電池容量をXmAhとし、更に6mA(1.0C)の電流値で電池電圧4.2Vまで充電し24時間放置した。この操作を合計50セルの電池で行った。その後、50セルのうち、Xの90%以上の容量を維持していたセルの割合(%)を、自己放電特性として算出した。
次に25℃雰囲気下、上記90%以上の容量を維持できた電池を、60mA(10C)の電流値で電池電圧3.0Vまで放電を行った。そのときの容量をYmAhとし、Y/X×100(%)を、ハイレート特性として算出した。
f.出力密度測定 a、bで作成した正極及び負極を、負極,セパレータ,正極,セパレータの順に重ねて渦巻状に複数回捲回することで円筒型積層体を作製した。この円筒型積層体をステンレス金属製容器に収納し、負極集電体から導出したニッケル製リードを容器底に接続し、正極集電体から導出したアルミニウム製リードを容器蓋端子部に接続した。さらに、この容器内に前記した非水電解液を注入して封口し、幅18mm、高さ65mmの円筒型電池を作製した。その後、1Cの電流値で電池電圧4.2Vまで充電し、到達後4.2Vを保持するようにして電流値を徐々に減らす方法で、合計3時間の充電を行い、SOC100%とした。10分休止後、0.3Cの電流値でSOC50%まで放電し、1時間休止した。その後、(1)0.5Cで10秒間放電、1分休止、0.5Cで10秒間充電、1分休止、(2)1Cで10秒間放電、1分休止、1Cで10秒間充電、1分休止、(3)2Cで10秒間放電、1分休止、2Cで10秒間充電、1分休止、(4)3Cで10秒間放電、1分休止、3Cで10秒間充電、1分休止、(5)5Cで10秒間放電、1分休止、5Cで10秒間充電、1分休止という作業を行った。
(1)~(5)における10秒間放電後の電池電圧をそれぞれ計測し、それぞれの電圧を電流値に対してプロットした。最小二乗法による近似直線が放電下限電圧(V)と交差する電流値を(I)とし、電池質量(Wt)とから次式により出力密度を算出した。
出力密度(P)=(V×I)/Wt
なお、d、e、fでの電圧(4.2Vおよび3.0V)は、正極にリチウムコバルト複合酸化物、負極にグラファイトを用いたときの一例であり、測定は電極部材の作動電圧範囲に合わせて調整した。例えば、正極にリン酸鉄リチウム、負極にグラファイトを用いた場合は3.6Vまで充電し、2.0Vまで放電し、放電下限電圧も2.0Vとした。
また、入力密度を算出する場合は、(1)~(5)での各々の10秒間充電後の電池電圧を計測し、それぞれの電圧を電流値に対してプロットした。最小二乗法による近似直線が充電上限電圧(V)と交差する電流値を(I)とし、電池質量(Wt)とから出力密度と同様に算出した。
LIB(リチウムイオン二次電池)への適合性を、下記の基準に従って評価した。
(A)ハイレート特性が86%以下を4、87~90%を6、91~95%を8、96~100%を10とし、(B)自己放電特性が90%以下を4、91~94%を6、95~99%を8、100%を10とし、(C)曲がりが5mm以上を8、1~4mmを9、1mm未満を10としたとき、(A),(B),(C)各項目の合計が、28以上のものを「a」、26~27を「b」、23~25を「c」、21~22を「d」、20以下を「e」と評価した。「a」から順に適合性が高いと判断される。
Mvが70万のホモポリマーのポリエチレンを47質量%、Mv30万のホモポリマーのポリエチレンを46質量%、Mv40万のポリプロピレンを7質量%(PPブレンド量 7質量%)とを、タンブラーブレンダーを用いてドライブレンドした。得られた純ポリマー混合物99質量%に酸化防止剤としてペンタエリスリチル-テトラキス-[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]を1質量%添加し、再度タンブラーブレンダーを用いてドライブレンドすることにより、ポリマー等混合物を得た。得られたポリマー等混合物は窒素で置換を行った後に、二軸押出機へ窒素雰囲気下でフィーダーにより供給した。また流動パラフィン(37.78℃における動粘度7.59×10-5m2/s)を押出機シリンダーにプランジャーポンプにより注入した。
溶融混練し、押し出される全混合物中に占める流動パラフィン量比が65質量%となるように(即ち、ポリマー濃度(「PC」と略記することがある)が35質量%となるように)、フィーダー及びポンプを調整した。溶融混練条件は、設定温度200℃であり、スクリュー回転数240rpm、吐出量12kg/hで行った。
続いて、溶融混練物を、T-ダイを経て表面温度25℃に制御された冷却ロール上に押出しキャストすることにより、原反膜厚1400μmのゲルシートを得た。
次に、同時二軸テンター延伸機に導き、二軸延伸を行った。設定延伸条件は、MD倍率7.0倍、TD倍率7.0倍(即ち、7×7倍)、二軸延伸温度125℃であった。
次に、メチルエチルケトン槽に導き、メチルエチルケトン中に充分に浸漬して流動パラフィンを抽出除去し、その後メチルエチルケトンを乾燥除去した。
次に、熱固定(「HS」と略記することがある)を行なうべくTDテンターに導き、熱固定温度125℃、延伸倍率1.4倍でHSを行い、その後、0.8倍の緩和操作(即ち、HS緩和率が0.8倍)を行った。
その後、1000mに巻取ったマスターロール(MR)を、60℃の恒温室内に24時間放置した(即ち、MRエージング有り)。その後、10kg/mの捲回張力で巻き返しを行い、高出力密度リチウムイオン二次電池用ポリオレフィン製微多孔膜を得た。得られた微多孔膜について、各種特性を評価した。結果を下表1に示す。
下表1に示す条件以外は実施例1と同様にして微多孔膜を得た。得られた微多孔膜について、各種特性を評価した。結果を下表1及び2に示す。
Claims (6)
- 長さ方向(MD)引張強度と幅方向(TD)引張強度がそれぞれ50MPa以上であり、
MD引張伸度とTD引張伸度の合計が20~250%であり、かつポリプロピレンを含むポリオレフィン製微多孔膜からなることを特徴とする高出力密度リチウムイオン二次電池用セパレータ。 - 平均孔径が0.1μm未満である請求項1に記載の高出力密度リチウムイオン二次電池用セパレータ。
- 65℃でのTD熱収縮率が1.0%以下である請求項1又は2に記載の高出力密度リチウムイオン二次電池用セパレータ。
- 気孔率が40%以上である請求項1~3のいずれか1項に記載の高出力密度リチウムイオン二次電池用セパレータ。
- 膜厚が20μm以上である請求項1~4のいずれか1項に記載の高出力密度リチウムイオン二次電池用セパレータ。
- 請求項1~5のいずれか1項に記載の高出力密度リチウムイオン二次電池用セパレータと、正極と、負極と、電解液とを用いてなる高出力密度リチウムイオン二次電池。
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