WO2014021292A1 - 非水電解質電池用セパレータおよび非水電解質電池 - Google Patents
非水電解質電池用セパレータおよび非水電解質電池 Download PDFInfo
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- WO2014021292A1 WO2014021292A1 PCT/JP2013/070540 JP2013070540W WO2014021292A1 WO 2014021292 A1 WO2014021292 A1 WO 2014021292A1 JP 2013070540 W JP2013070540 W JP 2013070540W WO 2014021292 A1 WO2014021292 A1 WO 2014021292A1
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- electrolyte battery
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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
- H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
- H01M50/461—Separators, membranes or diaphragms characterised by their combination with electrodes with adhesive layers between electrodes and separators
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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
-
- 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
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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
- H01M50/426—Fluorocarbon polymers
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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
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
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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
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
- H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
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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
- H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
-
- 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
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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
- H01M50/491—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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
- H01M50/451—Separators, membranes or diaphragms characterised by the material having a layered structure comprising layers of only organic material and layers containing inorganic material
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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 a nonaqueous electrolyte battery and a nonaqueous electrolyte battery.
- Non-aqueous electrolyte batteries such as lithium ion secondary batteries are widely used as power sources for portable electronic devices such as notebook computers, mobile phones, digital cameras, and camcorders. Further, in recent years, these batteries have been studied for application to automobiles and the like because of their high energy density.
- a technique is known that uses a separator in which a porous layer made of a polyvinylidene fluoride resin (hereinafter also referred to as an adhesive porous layer) is formed on a polyolefin microporous film, which is a conventional separator (for example, see Patent Document 1).
- an adhesive porous layer made of a polyvinylidene fluoride resin (hereinafter also referred to as an adhesive porous layer) is formed on a polyolefin microporous film, which is a conventional separator (for example, see Patent Document 1).
- the adhesive porous layer is hot-pressed over the electrode in a state containing the electrolytic solution, the electrode and the separator can be satisfactorily bonded and can function as an adhesive. Therefore, the cycle life of the soft pack battery can be improved.
- a battery element is manufactured by winding the electrode and the separator in an overlapped state, and the element is enclosed in the metal can exterior together with an electrolytic solution. Is made.
- a battery element is produced in the same manner as the battery with the above metal can, and this is put together with the electrolyte in the soft pack exterior.
- a battery is produced by encapsulating and finally adding a hot press process. Therefore, in the case of using the separator having the adhesive porous layer as described above, a battery element can be produced in the same manner as the battery with the above metal can outer case. There is also an advantage that no change is required.
- the shutdown function is a function to prevent the thermal runaway of the battery by blocking the movement of ions by melting the thermoplastic resin and closing the pores of the porous substrate when the battery temperature rises.
- the adhesive porous layer may constrain the pores on the surface of the polyolefin microporous membrane when the shutdown function is manifested, which may inhibit the shutdown function.
- the present invention aims to provide a separator for a nonaqueous electrolyte battery excellent in adhesiveness with an electrode, ion permeability, and shutdown characteristics, and to achieve the object To do.
- a porous substrate comprising a porous substrate comprising a thermoplastic resin and an adhesive porous layer comprising an adhesive resin provided on at least one surface of the porous substrate, and the porous substrate
- the difference between the Gurley value of the material and the Gurley value of the composite film is 75 seconds / 100 cc or less, and the difference between the curvature of the porous substrate and the curvature of the composite film is 0.30 or less.
- ⁇ 2> The separator for a nonaqueous electrolyte battery according to ⁇ 1>, wherein the composite membrane has a ratio of the standard deviation of the Gurley value to the average Gurley value of 0.3 or less.
- ⁇ 3> The separator for a non-aqueous electrolyte battery according to ⁇ 1> or ⁇ 2>, wherein the Gurley value of the porous substrate is 50 seconds / 100 cc or more and 800 seconds / 100 cc.
- ⁇ 4> The separator for a nonaqueous electrolyte battery according to any one of ⁇ 1> to ⁇ 3>, wherein the curvature of the composite film is 1.5 to 2.5.
- ⁇ 5> The separator for a nonaqueous electrolyte battery according to any one of ⁇ 1> to ⁇ 4>, wherein the adhesive porous layer has an average pore diameter of 1 nm to 100 nm.
- the adhesive resin is a polyvinylidene fluoride resin.
- ⁇ 7> The separator for a nonaqueous electrolyte battery according to ⁇ 6>, wherein the polyvinylidene fluoride resin has a weight average molecular weight of 500,000 to 3,000,000.
- the separator for nonaqueous electrolyte batteries excellent in the adhesiveness with an electrode, ion permeability, and a shutdown characteristic can be provided.
- the nonaqueous electrolyte battery separator of the present invention and the nonaqueous electrolyte battery using the same will be described in detail.
- the numerical value range indicated by “ ⁇ ” means a numerical range including an upper limit value and a lower limit value.
- a separator for a nonaqueous electrolyte battery according to the present invention (hereinafter also simply referred to as “separator”) is provided on a porous substrate containing a thermoplastic resin and an adhesive containing an adhesive resin provided on at least one side of the porous substrate. And a porous layer.
- the separator of the present invention composite membrane
- the difference (Gurley difference) between the Gurley value G B of the porous substrate and Gurley value G S of the composite film ⁇ G is not more than 75 seconds / 100 cc
- the difference (curvature difference) ⁇ between the curvature ⁇ B of the substrate and the curvature ⁇ S of the composite film is 0.30 or less.
- the non-aqueous electrolyte battery separator has the above-described configuration, so that it has excellent adhesion to electrodes, ion permeability, and shutdown characteristics. Therefore, by using such a separator, it is possible to provide a high performance non-aqueous electrolyte battery with an aluminum laminate pack that has excellent battery characteristics such as rate characteristics and cycle characteristics, and safety at high temperatures. .
- the separator is interposed between a positive electrode and a negative electrode in a non-aqueous electrolyte battery (hereinafter also simply referred to as “battery”), and prevents permeation of electrodes such as lithium ions in the electrolytic solution. Play a smooth role. At this time, in order to suppress a decrease in the life of the battery, ions are required to permeate uniformly over the entire surface of the separator without being biased toward the separator.
- the separator since the separator has a laminated structure having a porous substrate and an adhesive porous layer, the opening of the hole of the porous substrate is covered with the adhesive porous layer, If the opening of the pores of the porous layer is blocked by the porous substrate, the ion permeability is impaired. Therefore, in order to increase the ion permeability of the separator, it is desirable that the pores of the porous base material communicate with the pores of the adhesive porous layer.
- the Gurley difference ⁇ G (
- ) of the separator is 75 seconds / 100 cc or less
- the curvature difference ⁇ (
- ) is 0.30 or less. If comprised so, it will be thought that the opening part of the hole which a porous base material and an adhesive porous layer have is not blocked
- the opening of the hole of the porous base material is not easily blocked, when the battery is overheated, the hole of the porous base material is easily crushed, and the permeation of ions is quickly blocked. And has excellent shutdown characteristics. Furthermore, since the adhesive porous layer contains an adhesive resin, the adhesiveness between the separator and the electrode is excellent.
- the Gurley difference ⁇ G and the curvature difference ⁇ are, for example, selection of a porous substrate having a specific Gurley value and curvature, the molecular weight of the adhesive resin constituting the adhesive porous layer, and the adhesive porous It can be controlled by adjusting the composition of the material for forming the layer, the formation conditions, and the like.
- the separator of the present invention the difference between the Gurley value G B of the porous substrate and Gurley value G S of the composite membrane (Gurley difference) .DELTA.G is less than 75 seconds / 100 cc.
- the Gurley difference ⁇ G is preferably 70 seconds / 100 cc or less, more preferably 65 seconds / 100 cc or less, and further preferably 60 seconds / 100 cc or less.
- the Gurley value G B of the porous substrate and the Gurley value G S of the composite membrane (separator) can be measured with a Gurley type densometer (G-B2C manufactured by Toyo Seiki Co., Ltd.) according to JIS P8117.
- Gurley value G S of the composite film from the viewpoint of obtaining a sufficient battery performance is preferably in the range of less than 50 seconds / 100 cc to 800 sec / 100 cc. Further, from the viewpoint of enhancing cycle characteristics of homogeneity and cell ion permeability, the standard deviation SD GS ratio [SD GS / AV of Gurley value G S of the composite film to the average value AV GS of Gurley value G S of the composite film GS ] is preferably 0.3 or less. SD GS / AV GS is an index for determining the uniformity of the Gurley value in the entire separator, and the smaller the SD GS / AV GS, the higher the Gurley value in the entire separator.
- the separator plays a role of smoothly transmitting lithium ions and the like in the electrolytic solution.
- ions are biased to a part of the separator.
- SD GS / AV GS is more preferably 0.29 or less, further preferably 0.25 or less, and particularly preferably 0.20 or less.
- the Gurley values of arbitrarily different portions in the separator were measured at 20 points, and the average value and standard deviation thereof were taken as AV GS and SD GS , respectively.
- the average Gale value AV GS is obtained by dividing the sum of the Gurley values measured at 20 points by the number of data (20).
- the standard deviation SD GS of the Gurley value is obtained by subtracting the sum of the squares of the differences between the respective Gurley values and the average value AV GS by “number of data ⁇ 1”, that is, 19 and obtaining the square root.
- SD GS / AV GS is controlled by adjusting the molecular weight of the adhesive resin constituting the adhesive porous layer, the composition of the material for forming the adhesive porous layer, the formation conditions, and the like. Can do.
- the difference (curvature difference) ⁇ between the curvature ⁇ B of the porous substrate and the curvature ⁇ S of the composite film is 0.30 or less.
- the curvature difference ⁇ (
- ) exceeds 0.30, it is considered that the ratio of pore blocking on the surface of the porous substrate is larger than that of the adhesive porous layer.
- the curvature ⁇ S of the separator is preferably in the range of 1.5 to 2.5 from the viewpoint of ensuring good ion permeability.
- the curvature ⁇ is a ratio (L P / L S ) between the length L P of the hole penetrating from one surface of the separator to the opposite surface and the film thickness L S of the separator. Therefore, when the hole is not bent and is a straight line, the curvature is 1, and the curvature is increased as the hole is bent.
- There are several methods for calculating the curvature and specific examples include a method of calculating from the membrane resistance and a method of calculating from the air permeability. When considering battery characteristics, a method of calculating from the membrane resistance is desirable.
- the curvature ⁇ B of the porous substrate and the curvature ⁇ S of the composite membrane are calculated based on the following formula as the curvature when the sample is impregnated with the electrolyte. Value.
- the porosity of the nonaqueous electrolyte battery separator is suitably in the range of 30% or more and 60% or less from the viewpoint of obtaining the effects of the present invention and good mechanical properties of the separator.
- the thickness of the separator is preferably 5 ⁇ m to 35 ⁇ m from the viewpoint of mechanical strength and energy density.
- Membrane resistance of the separator from the viewpoint of ensuring the load characteristics of the sufficient battery, is preferably in the range of 1ohm ⁇ cm 2 ⁇ 10ohm ⁇ cm 2.
- the membrane resistance is a resistance value when the separator is impregnated with the electrolytic solution, and is measured by an alternating current method.
- the porous substrate means a substrate having pores or voids therein.
- a substrate include a microporous film, a porous sheet made of a fibrous material such as a nonwoven fabric and a paper sheet, or one or more other porous layers laminated on the microporous film or the porous sheet.
- the composite porous sheet etc. which were made to be mentioned can be mentioned.
- a microporous membrane is a membrane that has a large number of micropores inside and a structure in which these micropores are connected, and allows gas or liquid to pass from one surface to the other. Means.
- thermoplastic resin is used as the material constituting the porous substrate from the viewpoint of providing a shutdown function.
- thermoplastic resin a thermoplastic resin having a melting point of less than 200 ° C. is suitable, and polyolefin is particularly preferable.
- a polyolefin microporous membrane is suitable as a porous substrate using polyolefin.
- a polyolefin microporous membrane having sufficient mechanical properties and ion permeability and applied to a conventional separator for nonaqueous electrolyte batteries can be used.
- the polyolefin microporous membrane preferably contains polyethylene from the viewpoint of having the shutdown function described above, and the polyethylene content is preferably 95% by mass or more.
- polyethylene and polypropylene are used as materials constituting the porous substrate.
- a polyolefin microporous membrane containing Examples of such a polyolefin microporous membrane include a microporous membrane in which polyethylene and polypropylene are mixed in one membrane.
- Such a microporous membrane preferably contains 95% by mass or more of polyethylene and 5% by mass or less of polypropylene from the viewpoint of achieving both a shutdown function and heat resistance.
- the polyolefin microporous membrane has a structure of at least two layers, and one of the two layers includes polyethylene and the other layer includes polypropylene.
- a polyolefin microporous membrane having a structure is also preferred.
- the weight average molecular weight of polyolefin is preferably 100,000 to 5,000,000. If the weight average molecular weight is less than 100,000, it may be difficult to ensure sufficient mechanical properties. On the other hand, if it exceeds 5 million, the shutdown characteristics may be deteriorated or molding may be difficult.
- Such a polyolefin microporous membrane can be produced, for example, by the following method. That is, (i) a step of extruding a molten polyolefin resin from a T-die to form a sheet, (ii) a step of subjecting the sheet to crystallization treatment, (iii) a step of stretching the sheet, and (iv) heat treatment of the sheet A method of forming the microporous film by sequentially performing the steps is performed.
- a step of melting a polyolefin resin together with a plasticizer such as liquid paraffin, extruding it from a T-die and cooling it to form a sheet (ii) a step of stretching the sheet, (iii) Examples include a method of forming a microporous film by sequentially performing a step of extracting a plasticizer from the sheet, and (iv) a step of heat-treating the sheet.
- a plasticizer such as liquid paraffin
- porous sheet made of a fibrous material a porous sheet made of polyester such as polyethylene terephthalate, a fibrous material made of polyolefin such as polyethylene or polypropylene, or a mixture of these fibrous materials can be used.
- the composite porous sheet a structure in which a functional layer is laminated on a porous sheet made of a microporous film or a fibrous material can be adopted. Such a composite porous sheet is preferable in that a further function can be added by the functional layer.
- a porous layer made of a heat resistant resin or a porous layer made of a heat resistant resin and an inorganic filler can be used.
- the heat resistant resin include one or more heat resistant polymers selected from aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide.
- a metal oxide such as alumina or a metal hydroxide such as magnesium hydroxide can be suitably used.
- the composite method include a method of coating a functional sheet on a porous sheet, a method of bonding with an adhesive, and a method of thermocompression bonding.
- the Gurley value G B of the porous substrate ⁇ G is not limited particularly as long as conditions are satisfied in the above, is preferably 50 sec / 100 cc to 800 sec / 100 cc.
- Gurley value G B of the porous substrate is preferably in view of obtaining a battery short-circuit prevention if 50 seconds / 100 cc or more, more preferably 90 sec / 100 cc or more, it is 120 seconds / 100 cc or more Further preferred.
- the Gurley value G B of the porous substrate is not more than 800 sec / 100 cc have good ion permeability, more preferably at most 500 sec / 100 cc.
- the curvature ⁇ B of the porous substrate is not particularly limited as long as ⁇ satisfies the above-described condition. If ⁇ B is 5.0 or less, it is preferable from the viewpoint of obtaining sufficient ion permeability, more preferably 4.0 or less, and even more preferably 3.0 or less.
- the average pore diameter of the porous substrate is preferably 1 nm or more, more preferably 10 nm or more, and further preferably 20 nm or more. Further, the average pore diameter of the porous substrate is preferably 300 nm or less, more preferably 200 nm or less, and further preferably 100 nm or less.
- the average pore size of the porous substrate d B has a pore surface area S B of the porous substrate which is calculated from the nitrogen gas adsorption, a porous pore volume V B of the substrate to be calculated from porosity Assuming that all the holes are cylindrical, the following equation is used.
- V B pore volume of porous substrate
- S B pore surface area of porous substrate
- the pore surface area S B (m 2 / g) of the porous substrate For the pore surface area S B (m 2 / g) of the porous substrate, first, the specific surface area (m 2 / g) of the porous substrate applied by the nitrogen gas adsorption method is measured. Next, by multiplying the specific surface area of the porous substrate by the basis weight (g / m 2 ) of the porous substrate, the pore surface area S B (m 2 / g) per 1 m 2 of the porous substrate is obtained. Ask.
- the film thickness of the porous substrate is preferably in the range of 5 to 25 ⁇ m from the viewpoint of obtaining good mechanical properties and internal resistance.
- the puncture strength of the porous substrate is preferably 300 g or more from the viewpoint of improving the production yield.
- the adhesive porous layer is provided on at least one surface of the porous substrate and includes an adhesive resin.
- the adhesive porous layer has a large number of micropores inside, and has a structure in which these micropores are connected, so that gas or liquid can pass from one surface to the other. Means layer.
- the adhesive porous layer is provided as the outermost layer of the separator on one side or both sides of the porous substrate, and can be adhered to the electrode by this adhesive porous layer. That is, the adhesive porous layer is a layer that can adhere the separator to the electrode when hot-pressed with the separator and the electrode overlapped.
- the separator for nonaqueous electrolyte batteries of the present invention has an adhesive porous layer only on one side of the porous substrate, the adhesive porous layer is bonded to either the positive electrode or the negative electrode. Moreover, when the separator for nonaqueous electrolyte batteries of this invention has an adhesive porous layer on both sides of the said porous base material, an adhesive porous layer is adhere
- the adhesive resin is not particularly limited as long as it is easily adhered to the electrode, and examples thereof include polyvinylidene fluoride, polyvinylidene fluoride copolymer, styrene-butadiene copolymer, polyvinyl alcohol, acrylonitrile, methacrylonitrile, and the like. Polyvinyl nitrile homopolymers or copolymers, polyethylene oxide, polypropylene oxide and the like are preferred. In particular, polyvinylidene fluoride and a polyvinylidene fluoride copolymer (these are referred to as “polyvinylidene fluoride resins”) are particularly suitable.
- the adhesive porous layer may contain only one type of adhesive resin or two or more types.
- polyvinylidene fluoride-based resin a homopolymer of vinylidene fluoride (that is, polyvinylidene fluoride), a copolymer of vinylidene fluoride and another copolymerizable monomer, or a mixture thereof can be used.
- the monomer copolymerizable with vinylidene fluoride for example, one kind or two or more kinds such as tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichloroethylene, or vinyl fluoride can be used.
- Such a polyvinylidene fluoride resin can be obtained by emulsion polymerization or suspension polymerization.
- a copolymer obtained by copolymerizing at least vinylidene fluoride and hexafluoropropylene is preferable from the viewpoint of adhesion to an electrode, and moreover, a structural unit derived from vinylidene fluoride and a mass standard And more preferably 0.1 to 5 mol% (preferably 0.5 to 2 mol%) of a hexafluoropropylene-derived structural unit.
- the polyvinylidene fluoride resin preferably has a weight average molecular weight in the range of 500,000 to 3,000,000.
- the weight average molecular weight is 500,000 or more, the adhesive porous layer can have mechanical properties sufficient to withstand the adhesion process with the electrode, and sufficient adhesion can be easily obtained.
- the weight average molecular weight of the polyvinylidene fluoride resin is preferably 600,000 or more, more preferably 700,000 or more.
- the weight average molecular weight of the polyvinylidene fluoride resin is 3 million or less, the moldability of the adhesive porous layer is good, and good crystals can be formed in the adhesive porous layer, thereby obtaining a suitable porous structure. Can do.
- the weight average molecular weight of the polyvinylidene fluoride resin is preferably 2.5 million or less, and preferably 2 million or less. If the weight average molecular weight of the polyvinylidene fluoride resin is in the range of 500,000 to 3,000,000, it is also preferable in terms of easy adjustment of the above-mentioned Gurley difference ⁇ G, curvature difference ⁇ , and SD GS / AV GS within the scope of the present invention. .
- the adhesive porous layer may contain a filler made of an inorganic substance or an organic substance or other additives within a range that does not impair the effects of the present invention.
- a filler made of an inorganic substance or an organic substance or other additives within a range that does not impair the effects of the present invention.
- the slipperiness and heat resistance of the separator can be improved.
- the inorganic filler for example, a metal oxide such as alumina, a metal hydroxide such as magnesium hydroxide, or the like can be used.
- the organic filler for example, an acrylic resin, a methacrylic ester resin, or the like can be used.
- the content of the additive in the adhesive porous layer is preferably 1% by mass to 95% by mass with respect to the total mass of the adhesive porous layer.
- the average pore size of the adhesive porous layer is preferably 1 nm to 100 nm. If the average pore size of the adhesive porous layer is 100 nm or less, it becomes easy to have a porous structure in which uniform pores are uniformly dispersed, and the adhesion points with the electrode are uniformly dispersed, so that good adhesion can be obtained. Can do. In that case, since the movement of ions becomes uniform, sufficient cycle characteristics can be obtained, and even better load characteristics can be obtained. On the other hand, the average pore diameter is preferably as small as possible from the viewpoint of uniformity, but it is practically difficult to form a porous structure smaller than 1 nm.
- the polyvinylidene fluoride-based resin swells.
- the average pore diameter is preferably 1 nm or more.
- the average pore size of the adhesive porous layer is more preferably 20 nm to 100 nm.
- the average pore diameter d A of the adhesive porous layer has a pore surface area S A of the adhesive porous layer is calculated from the nitrogen gas adsorption, the pores of the adhesive porous layer is calculated from porosity Using the volume VA , it is calculated from the following equation assuming that all holes are cylindrical.
- a specific surface area of the porous substrate obtained by applying a nitrogen gas adsorption method (m 2 / g)
- was molded adhesive porous layer separator The specific surface area (m 2 / g) is measured. Then, the specific surface area is multiplied by the basis weight (g / m 2 ) to obtain the pore surface area per unit area of the separator, and the pore surface area of the porous substrate is subtracted from the pore surface area of the separator. it is, to calculate the pore surface area S a of the adhesive porous layer.
- the coating amount of the adhesive porous layer is 0.5 g / m as the amount of one side of the porous substrate. 2 to 1.5 g / m 2 is preferable, and 0.7 g / m 2 to 1.3 g / m 2 is more preferable.
- the coating amount is 0.5 g / m 2 or more, the adhesion between the adhesive porous layer and the electrode becomes better.
- the coating amount is 1.5 g / m 2 or less, better ion permeability is easily secured.
- the difference between the coating amount on one side and the coating amount on the other side is 20 masses relative to the total coating amount on both sides. % Or less is preferable.
- the content is 20% by mass or less, the separator is hardly curled. As a result, the handling property is good and the problem that the cycle characteristics are deteriorated hardly occurs.
- the thickness of the adhesive porous layer is preferably 0.3 ⁇ m to 5 ⁇ m on one side of the porous substrate. When the thickness is 0.3 ⁇ m or more, the adhesion to the electrode becomes better. When the thickness is 5 ⁇ m or less, good ion permeability is secured and the load characteristics of the battery are excellent. From this point of view, the thickness of the adhesive porous layer is more preferably 0.5 ⁇ m to 5 ⁇ m, and still more preferably 1 ⁇ m to 2 ⁇ m on one side of the porous substrate.
- the adhesive porous layer preferably has a sufficiently porous structure from the viewpoint of ion permeability.
- the porosity of the adhesive porous layer is preferably 30% to 60%.
- the porosity is 30% or more, the ion permeability is good and the battery characteristics are excellent.
- the porosity is 60% or less, sufficient mechanical properties are obtained such that the porous structure is not crushed when bonded to the electrode by hot pressing.
- the porosity is 60% or less, the surface porosity is lowered and the area occupied by the adhesive resin is increased, so that a better adhesive force can be ensured.
- the porosity of the adhesive porous layer is more preferably in the range of 30 to 50%.
- the fibril diameter of the adhesive resin in the adhesive porous layer is preferably in the range of 10 nm to 1000 nm from the viewpoint of cycle characteristics.
- the separator for a non-aqueous electrolyte battery of the present invention is formed by, for example, applying a coating liquid containing an adhesive resin such as a polyvinylidene fluoride resin on a porous substrate to form a coating layer. It is manufactured by a method in which the adhesive porous layer is integrally formed on the porous substrate by solidifying the resin.
- an adhesive porous layer is formed using a polyvinylidene fluoride resin will be described.
- the adhesive porous layer using the polyvinylidene fluoride resin as the adhesive resin can be suitably formed by, for example, the following wet coating method.
- the wet coating method includes (i) a step of dissolving a polyvinylidene fluoride resin in an appropriate solvent to prepare a coating solution, (ii) a step of applying this coating solution to a porous substrate, (iii) By immersing the porous base material in an appropriate coagulating liquid, a step of solidifying the polyvinylidene fluoride resin while inducing phase separation, (iv) a water washing step, and (v) a drying step are performed to obtain a porous material.
- This is a film forming method for forming a porous layer on a substrate.
- the details of the wet coating method suitable for the present invention are as follows.
- Solvents for dissolving the polyvinylidene fluoride resin used for preparing the coating liquid include polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylformamide. Preferably used. From the viewpoint of forming a good porous structure, it is preferable to mix a phase separation agent that induces phase separation in addition to a good solvent. Examples of the phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol.
- the phase separation agent is preferably added in a range that can ensure a viscosity suitable for coating.
- the solvent is preferably a mixed solvent containing 60% by mass or more of a good solvent and 40% by mass or less of a phase separation agent from the viewpoint of forming a good porous structure.
- the coating liquid preferably contains a polyvinylidene fluoride resin at a concentration of 3% by mass to 10% by mass from the viewpoint of forming a good porous structure. What is necessary is just to mix or dissolve in a coating liquid, when making an adhesive porous layer contain a filler and another component.
- the coagulation liquid is generally composed of a good solvent used for preparing the coating liquid, a phase separation agent, and water. It is preferable in production that the mixing ratio of the good solvent and the phase separation agent is adjusted to the mixing ratio of the mixed solvent used for dissolving the polyvinylidene fluoride resin.
- the water concentration is suitably 40% by mass to 90% by mass from the viewpoint of formation of a porous structure and productivity.
- the conventional coating method such as Meyer bar, die coater, reverse roll coater or gravure coater may be applied to the coating liquid on the porous substrate.
- the adhesive porous layer is formed on both surfaces of the porous substrate, it is preferable from the viewpoint of productivity to apply the coating liquid to both surfaces simultaneously on both surfaces.
- the adhesive porous layer can be produced by a dry coating method other than the wet coating method described above.
- the dry coating method refers to, for example, coating a porous substrate with a coating liquid containing a polyvinylidene fluoride resin and a solvent, and drying the coating layer to volatilize and remove the solvent. It is a method of obtaining a layer.
- the wet coating method is preferred in that a good porous structure can be obtained.
- the separator for a non-aqueous electrolyte battery of the present invention is produced by a method in which an adhesive porous layer is produced as an independent sheet, and this adhesive porous layer is laminated on a porous substrate and combined by thermocompression bonding or an adhesive. Can also be manufactured.
- a method for producing the adhesive porous layer as an independent sheet a coating liquid containing a resin is applied onto a release sheet, and the above-mentioned wet coating method or dry coating method is applied to form the adhesive porous layer.
- the method of forming and peeling an adhesive porous layer from a peeling sheet is mentioned.
- the non-aqueous electrolyte battery of the present invention is a non-aqueous electrolyte battery that obtains an electromotive force by doping or dedoping lithium, and includes a positive electrode, a negative electrode, and the separator for a non-aqueous electrolyte battery of the present invention described above.
- the dope means occlusion, support, adsorption, or insertion, and means a phenomenon in which lithium ions enter the active material of an electrode such as a positive electrode.
- the nonaqueous electrolyte battery has a structure in which a battery element in which a negative electrode and a positive electrode face each other with a separator interposed therebetween is impregnated with an electrolytic solution.
- the nonaqueous electrolyte battery of the present invention is suitable for a nonaqueous electrolyte secondary battery, particularly a lithium ion secondary battery.
- the nonaqueous electrolyte battery of the present invention is provided with the above-described separator for nonaqueous electrolyte batteries of the present invention as a separator, so that the adhesiveness between the electrode and the separator is excellent, and the yield in the manufacturing process is high. It also has excellent retention. Therefore, the nonaqueous electrolyte battery of the present invention exhibits stable cycle characteristics.
- the positive electrode can have a structure in which an active material layer containing a positive electrode active material and a binder resin is formed on a current collector.
- the active material layer may further contain a conductive additive.
- the positive electrode active material include lithium-containing transition metal oxides. Specifically, LiCoO 2 , LiNiO 2 , LiMn 1/2 Ni 1/2 O 2 , LiCo 1/3 Mn 1/3 Ni 1 / 3 O 2, LiMn 2 O 4 , LiFePO 4, LiCo 1/2 Ni 1/2 O 2, LiAl 1/4 Ni 3/4 O 2 and the like.
- the binder resin include polyvinylidene fluoride resins and styrene-butadiene copolymers.
- the conductive aid include carbon materials such as acetylene black, ketjen black, and graphite powder.
- the current collector include aluminum foil, titanium foil, and stainless steel foil having a thickness of 5 ⁇ m to 20 ⁇ m.
- the separator when the separator includes an adhesive porous layer containing a polyvinylidene fluoride resin, and the adhesive porous layer is disposed on the positive electrode side, the polyvinylidene fluoride resin has oxidation resistance. Since it is excellent, it is easy to apply positive electrode active materials such as LiMn 1/2 Ni 1/2 O 2 and LiCo 1/3 Mn 1/3 Ni 1/3 O 2 that can be operated at a high voltage of 4.2 V or more. is there.
- the negative electrode may have a structure in which an active material layer including a negative electrode active material and a binder resin is formed on a current collector.
- the active material layer may further contain a conductive additive.
- the negative electrode active material include materials that can occlude lithium electrochemically, and specifically include carbon materials, silicon, tin, aluminum, wood alloys, and the like.
- the binder resin include polyvinylidene fluoride resins and styrene-butadiene copolymers.
- the conductive aid include carbon materials such as acetylene black, ketjen black, and graphite powder.
- Examples of the current collector include copper foil, nickel foil, and stainless steel foil having a thickness of 5 ⁇ m to 20 ⁇ m. Moreover, it may replace with said negative electrode and may use metal lithium foil as a negative electrode.
- the electrolytic solution is a solution in which a lithium salt is dissolved in a non-aqueous solvent.
- the lithium salt include LiPF 6 , LiBF 4 , LiClO 4, and the like.
- non-aqueous solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted products thereof; ⁇ -butyrolactone And cyclic esters such as ⁇ -valerolactone, and these may be used alone or in combination.
- a solution in which a cyclic carbonate and a chain carbonate are mixed at a mass ratio (cyclic carbonate / chain carbonate) of 20/80 to 40/60 and a lithium salt is dissolved in an amount of 0.5 M to 1.5 M is preferable. is there.
- Examples of the exterior material include a metal can and a pack made of an aluminum laminate film.
- the shape of the battery includes a square shape, a cylindrical shape, a coin shape, and the like, but the nonaqueous electrolyte battery separator of the present invention is suitable for any shape.
- Frm thickness It measured using the contact-type thickness meter (made by LITEMATIC Mitutoyo).
- the measurement terminal was a cylindrical one having a diameter of 5 mm, and was adjusted so that a load of 7 g was applied during the measurement.
- Weight A sample was cut into 10 cm ⁇ 10 cm and its mass was measured. The basis weight was determined by dividing the mass by the area.
- Coating amount of polyvinylidene fluoride resin Using an energy dispersive X-ray fluorescence analyzer (EDX-800HS, Shimadzu Corporation), the coating amount (mass) of the polyvinylidene fluoride resin was measured from the spectrum intensity of FK ⁇ . In this measurement, the mass of the polyvinylidene fluoride resin on the surface irradiated with X-rays is measured. Therefore, when a porous layer made of polyvinylidene fluoride resin is formed on both the front and back surfaces, the weight of each front and back polyvinylidene fluoride resin is measured by measuring each of the front and back surfaces. Mass can be measured.
- EDX-800HS energy dispersive X-ray fluorescence analyzer
- ⁇ ⁇ 1-Ws / (ds ⁇ t) ⁇ ⁇ 100
- ⁇ the porosity (%)
- Ws the basis weight (g / m 2 )
- ds the true density (g / cm 3 )
- t the film thickness ( ⁇ m).
- the porosity ⁇ (%) of a separator in which a polyethylene porous substrate and a porous layer made only of a polyvinylidene fluoride resin were laminated was calculated from the following equation.
- ⁇ ⁇ 1 ⁇ (Wa / 0.95 + Wb / 1.78) / t ⁇ ⁇ 100
- Wa is weight per unit area of the base material (g / m 2)
- Wb is weight of polyvinylidene fluoride resin (g / m 2)
- t represents the thickness ([mu] m).
- Wa 0 (g / m 2 )
- t the thickness of the adhesive porous layer, that is, the thickness of the separator, and the film of the substrate It can be obtained by subtracting the thickness.
- the weight average molecular weight (Dalton) of the polyvinylidene fluoride resin is a molecular weight measured by gel permeation chromatography (hereinafter also referred to as GPC) under the following conditions and converted to polystyrene.
- GPC Alliance GPC 2000 type (manufactured by Waters) Column: TSKgel GMH 6 -HT ⁇ 2 + TSKgel GMH 6 -HTL ⁇ 2 [manufactured by Tosoh Corporation] -Mobile phase solvent: o-dichlorobenzene-Standard sample: Monodispersed polystyrene (manufactured by Tosoh Corporation) -Column temperature: 140 ° C
- ), the porous substrate and a separator tortuosity of ( ⁇ B and ⁇ S ), curvature difference ⁇ (
- Table 1 shows the measurement results of the concentration of the phase separating agent, the concentration of water in the coagulation liquid, and the temperature of the coagulation liquid.
- the separators of the following examples and comparative examples are collectively shown in Table 1.
- Examples 2 to 6 and Comparative Example 1 The separators for nonaqueous electrolyte batteries of Examples 2 to 6 and Comparative Example 1 were obtained in the same manner as in Example 1, except that the phase separation agent concentration, water concentration, and coagulating liquid temperature were changed as shown in Table 1. It was.
- Example 7 to 8 The nonaqueous electrolyte batteries of Examples 7 to 8 were the same as Example 1 except that a vinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 500,000 or 3 million was used as the adhesive resin. A separator was obtained.
- nonaqueous electrolyte battery Using the separators produced in Examples 1 to 8 and Comparative Example 1, nonaqueous electrolyte batteries of Examples 1 to 8 and Comparative Example 1 were produced based on the following procedure.
- a lead tab was welded to the positive electrode and the negative electrode, the positive and negative electrodes were joined via a separator, an electrolyte solution was impregnated, and sealed in an aluminum pack using a vacuum sealer.
- 1 M LiPF 6 ethylene carbonate / ethyl methyl carbonate (3/7 mass ratio) was used as the electrolytic solution.
- a test battery was produced by applying a load of 20 kg per 1 cm 2 of electrode with a hot press machine and performing hot pressing at 90 ° C. for 2 minutes.
- the peel strength when peeling the electrode surface from the adhesive porous layer was determined as follows. That is, based on JIS K 6854, it calculated
- the separator on which an adhesive porous layer made of a styrene-butadiene copolymer was formed was obtained by coating an equal amount on both sides and drying this.
- this separator The physical properties of this separator are as follows: the Gurley value (G s ) is 234 seconds / 100 cc, the SD GS / AV GS is 0.29, the curvature ( ⁇ S ) is 2.25, and the Gurley difference ( ⁇ G) is 74 seconds / 100 cc and the curvature difference ( ⁇ ) was 0.27.
- the Gurley value (G s ) is 234 seconds / 100 cc
- the SD GS / AV GS is 0.29
- the curvature ( ⁇ S ) is 2.25
- the Gurley difference ( ⁇ G) is 74 seconds / 100 cc and the curvature difference ( ⁇ ) was 0.27.
Abstract
Description
<1> 熱可塑性樹脂を含む多孔質基材と、前記多孔質基材の少なくとも片面に設けられ、接着性樹脂を含む接着性多孔質層と、を備えた複合膜からなり、前記多孔質基材のガーレ値と前記複合膜のガーレ値との差が75秒/100cc以下であり、かつ、前記多孔質基材の曲路率と前記複合膜の曲路率との差が0.30以下である非水電解質電池用セパレータ。
<2> 前記複合膜は、ガーレ値の平均値に対するガーレ値の標準偏差の比が0.3以下である<1>に記載の非水電解質電池用セパレータ。
<3> 前記多孔質基材のガーレ値は、50秒/100cc以上800秒/100ccである<1>または<2>に記載の非水電解質電池用セパレータ。
<4> 前記複合膜の曲路率は、1.5~2.5である<1>~<3>のいずれか1項に記載の非水電解質電池用セパレータ。
<5> 前記接着性多孔質層は、平均孔径が1nm以上100nm以下である<1>~<4>のいずれか1項に記載の非水電解質電池用セパレータ。
<6> 前記接着性樹脂が、ポリフッ化ビニリデン系樹脂である<1>~<5>のいずれか1項に記載の非水電解質電池用セパレータ。
<7> 前記ポリフッ化ビニリデン系樹脂は、重量平均分子量が50万以上300万以下である<6>に記載の非水電解質電池用セパレータ。
<8> 正極と、負極と、前記正極及び前記負極の間に配置された<1>~<7>のいずれか1項に記載の非水電解質電池用セパレータと、を備え、リチウムのドープ・脱ドープにより起電力を得る非水電解質電池。
また従来技術に比べて、イオン透過性およびシャットダウン特性に優れた非水電解質電池を提供することができる。
本発明の非水電解質電池用セパレータ(以下、単に「セパレータ」とも称する)は、熱可塑性樹脂を含む多孔質基材と、前記多孔質基材の少なくとも片面に設けられ、接着性樹脂を含む接着性多孔質層と、を備えた複合膜からなる。そして、本発明のセパレータ(複合膜)は、多孔質基材のガーレ値GBと複合膜のガーレ値GSとの差(ガーレ差)ΔGが75秒/100cc以下であり、かつ、多孔質基材の曲路率τBと複合膜の曲路率τSとの差(曲路率差)Δτが0.30以下である。
本発明において、セパレータは、多孔質基材と接着性多孔質層とを有する積層構造であるため、多孔質基材が有する孔の開口部が接着性多孔質層に覆われていたり、接着性多孔質層が有する孔の開口部が多孔質基材によって塞がれていると、イオンの透過性が損なわれる。従って、セパレータのイオン透過性を高めるには、多孔質基材が有する孔と、接着性多孔質層が有する孔とが通じていることが望ましい。
さらには、接着性多孔質層が接着性樹脂を含むため、セパレータと電極との接着性に優れる。
本発明のセパレータは、多孔質基材のガーレ値GBと複合膜のガーレ値GSとの差(ガーレ差)ΔGが75秒/100cc以下である。ガーレ差ΔG(=|GB-GS|)が75秒/100ccを超えると、接着性多孔質層と多孔質基材と間の界面において両層の空孔同士が十分に連通されていないことにより、イオン透過を阻害し、十分な電池の特性が得られない。このような観点では、ガーレ差ΔGは、70秒/100cc以下であることが好ましく、65秒/100cc以下であることがより好ましく、60秒/100cc以下であることがさらに好ましい。
なお、多孔質基材のガーレ値GB、及び複合膜(セパレータ)のガーレ値GSは、JIS P8117に従い、ガーレ式デンソメータ(G-B2C 東洋精機社製)にて測定することができる。
さらに、イオン透過性の均一性および電池のサイクル特性を高める観点から、複合膜のガーレ値GSの平均値AVGSに対する複合膜のガーレ値GSの標準偏差SDGSの比〔SDGS/AVGS〕が0.3以下であることが好ましい。
SDGS/AVGSは、セパレータ全体におけるガーレ値の均一性を判断する指標となり、SDGS/AVGSが小さいほど、セパレータ全体におけるガーレ値の均一性が高いことを示す。
つまり、SDGS/AVGSを0.3以下とすることで、充放電を繰り返した場合にも、電池の容量維持を保つことのできるサイクル特性を高めることができる。このような観点では、SDGS/AVGSは、0.29以下であることがより好ましく、0.25以下であることがさらに好ましく、0.20以下であることが特に好ましい。
また、SDGS/AVGSは、例えば、接着性多孔質層を構成する接着性樹脂の分子量、接着性多孔質層を形成するための材料の組成、形成条件等を調整することにより制御することができる。
本発明のセパレータは、多孔質基材の曲路率τBと複合膜の曲路率τSとの差(曲路率差)Δτが0.30以下である。曲路率差Δτ(=|τB-τS|)が0.30を超えると、接着性多孔質層より、多孔質基材表面の孔の閉塞の割合が多くなると考えられるため、膜抵抗が高くなり、電池のレート特性(充放電容量の維持特性)やサイクル特性が十分に得られない。このような観点では、曲路率差Δτは、0.25以下であることが好ましく、0.20以下であることが好ましい。
本発明においては、多孔質基材の曲路率τB、および複合膜の曲路率τSは、試料に電解液を含浸させたときの曲路率として、下記式に基づき、算出される値である。
τ:試料の曲路率(τBまたはτS)
R(ohm・cm2):電解液を試料に含浸させたときの試料の抵抗
r(ohm・cm):電解液の比抵抗
ε(%):空孔率
t(cm):試料の厚さ
非水電解質電池用セパレータの空孔率は、本発明の効果とセパレータの力学物性を良好に得る観点から、30%以上60%以下の範囲が適当である。
セパレータの膜厚は、機械強度とエネルギー密度の観点から、5μm~35μmが好ましい。
セパレータの膜抵抗は、十分な電池の負荷特性を確保するという観点から、1ohm・cm2~10ohm・cm2の範囲であることが好ましい。
ここで膜抵抗とはセパレータに電解液を含浸させたときの抵抗値であり、交流法にて測定される。当然、電解液の種類、温度によって異なるが、上記の数値は電解液として1M LiBF4 プロピレンカーボネート/エチレンカーボネート(1/1質量比)を用い、20℃にて測定した数値である。
本発明において、多孔質基材とは、内部に空孔ないし空隙を有する基材を意味する。
このような基材としては、微多孔膜や、不織布、紙状シート等の繊維状物からなる多孔性シート、あるいは、これら微多孔膜や多孔性シートに他の多孔性層を1層以上積層させた複合多孔質シート等を挙げることができる。なお、微多孔膜とは、内部に多数の微細孔を有し、これら微細孔が連結された構造となっており、一方の面から他方の面へと気体あるいは液体が通過可能となった膜を意味する。
本発明において、多孔質基材のガーレ値GBはΔGが既述の条件を満たす範囲であれば特に制限されないが、50秒/100cc以上800秒/100ccであることが好ましい。多孔質基材のガーレ値GBが、50秒/100cc以上であれば電池の短絡防止を得る観点で好ましく、90秒/100cc以上であることがより好ましく、120秒/100cc以上であることがさらに好ましい。また、多孔質基材のガーレ値GBは、800秒/100cc以下であればイオン透過性が良好であり、500秒/100cc以下であることがより好ましい。
以上のような観点から、多孔質基材の平均孔径は、1nm以上であることが好ましく、10nm以上であることがより好ましく、20nm以上であることがさらに好ましい。また、多孔質基材の平均孔径は、300nm以下であることが好ましく、200nm以下であることがより好ましく、100nm以下であることがさらに好ましい。
dB:多孔質基材の平均孔径
VB:多孔質基材の空孔体積
SB:多孔質基材の空孔表面積
多孔質基材の突刺強度は、製造歩留まりを向上させる観点から、300g以上が好適である。
接着性多孔質層は、多孔質基材の少なくとも片面に設けられ、接着性樹脂を含んで構成される。接着性多孔質層は、内部に多数の微細孔を有し、これら微細孔が連結された構造となっており、一方の面から他方の面へと気体あるいは液体が通過可能となった多孔質層を意味する。
接着性多孔質層は、多孔質基材の片面又は両面にセパレータの最外層として設けられ、この接着性多孔質層によって電極と接着させることができる。すなわち、接着性多孔質層は、セパレータと電極とを重ねた状態で熱プレスしたときにセパレータを電極に接着させ得る層である。本発明の非水電解質電池用セパレータが前記多孔質基材の片側のみに接着性多孔質層を有する場合、接着性多孔質層は正極又は負極のいずれかに接着される。また、本発明の非水電解質電池用セパレータが前記多孔質基材の両側に接着性多孔質層を有する場合、接着性多孔質層は正極及び負極の双方に接着される。接着性多孔質層を多孔質基材の両面に設けることで、セパレータの両面が接着性多孔質層を介して両電極とよく接着するため、電池のサイクル特性に優れる点で好ましい。
接着性樹脂は、電極との接着し易いものであれば特に制限されず、例えば、ポリフッ化ビニリデン、ポリフッ化ビニリデン共重合体、スチレン-ブタジエン共重合体、ポリビニルアルコール、アクリロニトリル、メタクリロニトリル等のビニルニトリル類の単独重合体又は共重合体、ポリエチレンオキサイド、ポリプロピレンオキサイド等のポリエーテルが好適である。特に、ポリフッ化ビニリデン及びポリフッ化ビニリデン共重合体(これらを「ポリフッ化ビニリデン系樹脂」と称する。)が特に好適である。接着性多孔質層は、接着性樹脂を1種のみ含んでもよく、2種以上を含んでもよい。
接着性多孔質層には、本発明の効果を阻害しない範囲内で、無機物あるいは有機物からなるフィラーやその他添加物を含んでいてもよい。
接着性多孔質層がこのようなフィラーを含むことで、セパレータの滑り性や耐熱性を改善することが可能となる。無機フィラーとしては、例えば、アルミナ等の金属酸化物や、水酸化マグネシウム等の金属水酸化物等を用いることができる。有機フィラーとしては例えばアクリル系樹脂、メタクリル酸エステル系樹脂等を用いることができる。
接着性多孔質層中の添加物の含有量は、接着性多孔質層の全質量に対して1質量%~95質量%であることが好ましい。
本発明において、接着性多孔質層の平均孔径は1nm~100nmであることが好ましい。接着性多孔質層の平均孔径が100nm以下であれば、均一な空孔が均一に分散した多孔質構造になり易く、電極との接着点が均一に分散するため、良好な接着性を得ることができる。また、その場合、イオンの移動も均一となるため、十分なサイクル特性を得ることができ、さらに良好な負荷特性が得られる。一方、平均孔径は均一性という観点では出来るだけ小さいことが好ましいが、1nmより小さい多孔構造を形成することは現実的に困難である。また、接着性多孔質層に電解液を含浸させた場合、ポリフッ化ビニリデン系樹脂は膨潤するが、平均孔径が小さすぎると、膨潤により孔が閉塞し、イオン透過性が阻害されてしまう。このような観点からも平均孔径は1nm以上であることが好ましい。接着性多孔質層の平均孔径は20nm~100nmであればより好ましい。
dA:接着性多孔質層の平均孔径
VA:接着性多孔質層の空孔体積
SA:接着性多孔質層の空孔表面積
本発明の非水電解質電池用セパレータは、例えば、ポリフッ化ビニリデン系樹脂等の接着性樹脂を含む塗工液を多孔質基材上に塗工し塗工層を形成し、次いで塗工層の樹脂を固化させることで、接着性多孔質層を多孔質基材上に一体的に形成する方法で製造される。
以下、接着性多孔質層をポリフッ化ビニリデン系樹脂を用いて形成する場合について、説明する。
湿式塗工法は、(i)ポリフッ化ビニリデン系樹脂を適切な溶媒に溶解させて塗工液を調製する工程、(ii)この塗工液を多孔質基材に塗工する工程、(iii)当該多孔質基材を適切な凝固液に浸漬させることで、相分離を誘発しつつポリフッ化ビニリデン系樹脂を固化させる工程、(iv)水洗工程、および(v)乾燥工程を行って、多孔質基材上に多孔質層を形成する製膜法である。本発明に好適な湿式塗工法の詳細は、以下のとおりである。
良好な多孔構造を形成する観点からは、良溶媒に加えて相分離を誘発させる相分離剤を混合させることが好ましい。相分離剤としては、水、メタノール、エタノール、プロピルアルコール、ブチルアルコール、ブタンジオール、エチレングリコール、プロピレングリコール、トリプロピレングリコール等が挙げられる。相分離剤は、塗工に適切な粘度が確保できる範囲で添加することが好ましい。
溶媒としては、良好な多孔構造を形成する観点から、良溶媒を60質量%以上、相分離剤を40質量%以下含む混合溶媒が好ましい。
接着性多孔質層にフィラーやその他の成分を含有させる場合は、塗工液中に混合あるいは溶解させればよい。
本発明の非水電解質電池は、リチウムのドープ・脱ドープにより起電力を得る非水電解質電池であり、正極と、負極と、既述の本発明の非水電解質電池用セパレータとを設けて構成されている。なお、ドープとは、吸蔵、担持、吸着、又は挿入を意味し、正極等の電極の活物質にリチウムイオンが入る現象を意味する。
正極活物質としては、例えばリチウム含有遷移金属酸化物等が挙げられ、具体的にはLiCoO2、LiNiO2、LiMn1/2Ni1/2O2、LiCo1/3Mn1/3Ni1/3O2、LiMn2O4、LiFePO4、LiCo1/2Ni1/2O2、LiAl1/4Ni3/4O2等が挙げられる。
バインダー樹脂としては、例えば、ポリフッ化ビニリデン系樹脂、スチレン-ブタジエン共重合体などが挙げられる。
導電助剤としては、例えばアセチレンブラック、ケッチェンブラック、黒鉛粉末といった炭素材料が挙げられる。
集電体としては、例えば厚さ5μm~20μmの、アルミ箔、チタン箔、ステンレス箔等が挙げられる。
負極活物質としては、例えばリチウムを電気化学的に吸蔵し得る材料が挙げられ、具体的には炭素材料、シリコン、スズ、アルミニウム、ウッド合金等が挙げられる。
バインダー樹脂としては、例えば、ポリフッ化ビニリデン系樹脂、スチレン-ブタジエン共重合体などが挙げられる。
導電助剤としては、例えばアセチレンブラック、ケッチェンブラック、黒鉛粉末といった炭素材料が挙げられる。
集電体としては、例えば厚さ5μm~20μmの、銅箔、ニッケル箔、ステンレス箔等が挙げられる。
また、上記の負極に代えて、金属リチウム箔を負極として用いてもよい。
リチウム塩としては、例えばLiPF6、LiBF4、LiClO4等が挙げられる。
非水系溶媒としては、例えばエチレンカーボネート、プロピレンカーボネート、フロロエチレンカーボネート、ジフロロエチレンカーボネート等の環状カーボネート;ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート、及びそのフッ素置換体等の鎖状カーボネート;γ-ブチロラクトン、γ-バレロラクトン等の環状エステル;が挙げられ、これらは単独で用いても混合して用いてもよい。
電解液としては、環状カーボネートと鎖状カーボネートとを質量比(環状カーボネート/鎖状カーボネート)20/80~40/60で混合し、リチウム塩を0.5M~1.5M溶解したものが好適である。
電池の形状は角型、円筒型、コイン型等があるが、本発明の非水電解質電池用セパレータはいずれの形状にも好適である。
以下に示す実施例及び比較例で作製したセパレータ及びリチウムイオン二次電池について、以下の測定、評価を行なった。
(ガーレ値)
JIS P8117に従い、ガーレ式デンソメータ(G-B2C 東洋精機社製)にて測定した。
多孔質基材の曲路率τB、および複合膜(セパレータ)の曲路率τSは次のようにして測定した。電解液に1M LiBF4 プロピレンカーボネート/エチレンカーボネート=1/1質量比を用い、この電解液を試料(多孔質基材またはセパレータ)に含浸させた。これをリードタブ付きのアルミ箔電極に挟みアルミパックに封入して試験セルを作製した。この試験セルの抵抗を交流インピーダンス法(測定周波数:100kHz)により20℃、-20℃にて測定した。得られた20℃の抵抗値から以下の式を適用することで、試料の曲路率を算出した。
τ:試料の曲路率
R(ohm・cm2):電解液を試料に含浸させたときの試料の抵抗
r(ohm・cm):電解液の比抵抗
ε(%):空孔率
t(cm):試料の厚さ
複合膜(セパレータ)のガーレ値GSの平均値AVGSに対する複合膜(セパレータ)のガーレ値GSの標準偏差SDGSの比〔SDGS/AVGS〕は、セパレータにおいて、任意の異なる部分のガーレ値を20点測定し、その値からSDGSおよびAVGSを算出した。
接触式の厚み計(LITEMATIC ミツトヨ社製)を用いて測定した。測定端子は直径5mmの円柱状のものを用い、測定中には7gの荷重が印加されるように調整して行った。
サンプルを10cm×10cmに切り出し、その質量を測定した。質量を面積で割ることで目付を求めた。
エネルギー分散型蛍光X線分析装置(EDX-800HS、島津製作所)を用いてFKαのスペクトル強度からポリフッ化ビニリデン系樹脂の塗工量(質量)を測定した。この測定ではX線を照射した面のポリフッ化ビニリデン系樹脂の質量が測定される。よって表裏両面にポリフッ化ビニリデン系樹脂からなる多孔質層を形成した場合、表裏各々の測定を行うことで表裏各々のポリフッ化ビニリデン系樹脂の質量が測定され、それを合計することで表裏合計の質量が測定できる。
セパレータの空孔率は、以下の式によって算出した。
ε={1-Ws/(ds・t)}×100
ここで、εは空孔率(%)、Wsは目付(g/m2)、dsは真密度(g/cm3)、tは膜厚(μm)である。
ε={1―(Wa/0.95+Wb/1.78)/t}×100
ここで、Waは基材の目付(g/m2)、Wbはポリフッ化ビニリデン系樹脂の重量(g/m2)、tは膜厚(μm)である。
接着性多孔質層の空孔率を算出する場合は、上記式において、Wa=0(g/m2)として、tは接着性多孔質層の厚み、すなわちセパレータの膜厚から基材の膜厚を引いた値とすることで、求められる。
ポリフッ化ビニリデン系樹脂の重量平均分子量(ダルトン)は、ゲル浸透クロマトグラフィー(以下、GPCともいう。)により下記の条件で測定し、ポリスチレン換算して表した分子量である。
<条件>
・GPC:Alliance GPC 2000型〔Waters社製〕
・カラム:TSKgel GMH6-HT×2 +TSKgel GMH6-HTL×2〔東ソー(株)製〕
・移動相溶媒:o-ジクロロベンゼン
・標準試料 :単分散ポリスチレン〔東ソー(株)製〕
・カラム温度:140℃
ガス吸着法でBET式を適用することにより、多孔質基材の比表面積(m2/g)と、接着性多孔質層を形成した複合膜の比表面積(m2/g)を測定した。これら比表面積(m2/g)にそれぞれの目付(g/m2)を乗算して、シート1m2当たりの空孔表面積を算出した。多孔質基材の空孔表面積を複合膜の空孔表面積から減算することで、接着性多孔質層1m2当たりの空孔表面積SAを算出した。別途、空孔率からシート1m2当たりの接着性多孔質層の空孔体積VAを算出した。接着性多孔質層の平均孔径dAは、接着性多孔質層の空孔表面積SAと空孔体積VAを用いて、すべての孔が円柱状であることを仮定して、以下の式から算出した。
dA=4×VA/SA
dA:接着性多孔質層の平均孔径
VA:接着性多孔質層の空孔体積
SA:接着性多孔質層の空孔表面積
ポリフッ化ビニリデン系樹脂としてフッ化ビニリデン/ヘキサフロロプロピレン=98.9/1.1モル%、重量平均分子量180万の共重合体を用いた。
該ポリフッ化ビニリデン系樹脂を5質量%の濃度でジメチルアセトアミド/トリプロピレングリコール=7/3質量比である混合溶媒に溶解し、塗工液を作製した。これを膜厚9μm、ガーレ値160秒/100cc、空孔率43%のポリエチレン微多孔膜の両面に等量塗工し、水/ジメチルアセトアミド/トリプロピレングリコール=57/30/13質量比の凝固液(40℃)に浸漬することで固化させた。これを水洗した後、乾燥することでポリオレフィン系微多孔膜の表裏両面にポリフッ化ビニリデン系樹脂からなる接着性多孔質層が形成された本発明の非水電解質電池用セパレータを得た。
このセパレータについて、多孔質基材及びセパレータ(複合膜)のガーレ値(GB及びGS)、ガーレ差ΔG(=|GB-GS|)、多孔質基材およびセパレータの曲路率(τB及びτS)、曲路率差Δτ(=|τB-τS|)、セパレータのSDGS/AVGS、ポリフッ化ビニリデン系樹脂(PVdF)の重量平均分子量(Mw)、塗工液中の相分離剤の濃度、凝固液の水の濃度、ならびに、凝固液の温度の測定結果を表1に示す。
以下の実施例および比較例のセパレータについても同様に、表1にまとめて示す。
相分離剤濃度、水濃度、及び凝固液温度を表1に示すとおり変化させた以外は、実施例1と同様にして、実施例2~6及び比較例1の非水電解質電池用セパレータを得た。
接着性樹脂として、重量平均分子量が50万あるいは300万のフッ化ビニリデン-ヘキサフロロプロピレン共重合体を用いたこと以外は、実施例1と同様にして、実施例7~8の非水電解質電池用セパレータを得た。
既述の曲路率の測定方法に基づき、実施例1および比較例1で作成したセパレータ、ならびに、上記のポリエチレン微多孔膜について、20℃あるいは-20℃において電解液を含浸させたときのセパレータの抵抗測定を実施した。その結果を表2に示す。また、得られた20℃の抵抗値から既述の式を適用することで、セパレータの曲路率を算出した。この結果も表2に示す。
なお、表2に示す、「20℃」および「-20℃」は、20℃および-20℃における試験セルの抵抗であり、「20℃/-20℃」は両者の比である。
表2から、曲路率が高いと膜抵抗が高くなり、低温における抵抗値上昇がより顕著になることがわかる。
実施例1~8及び比較例1で作製したセパレータを用いて、次の手順に基づき、実施例1~8及び比較例1の各非水電解質電池を作製した。
負極活物質である人造黒鉛300g、バインダーであるスチレン-ブタジエン共重合体の変性体を40質量%含む水溶性分散液7.5g、増粘剤であるカルボキシメチルセルロース3g、及び適量の水を双腕式混合機にて攪拌し、負極用スラリーを作製した。この負極用スラリーを負極集電体である厚さ10μmの銅箔に塗布し、乾燥後プレスして、負極活物質層を有する負極を得た。
正極活物質であるコバルト酸リチウム粉末89.5g、導電助剤であるアセチレンブラック4.5g、及びバインダーであるポリフッ化ビニリデン6gを、ポリフッ化ビニリデンの濃度が6質量%となるようにN-メチル-ピロリドン(NMP)に溶解し、双腕式混合機にて攪拌し、正極用スラリーを作製した。この正極用スラリーを正極集電体である厚さ20μmのアルミ箔に塗布し、乾燥後プレスして、正極活物質層を有する正極を得た。
前記の正極と負極にリードタブを溶接し、セパレータを介してこれら正負極を接合させ、電解液をしみ込ませてアルミパック中に真空シーラーを用いて封入した。ここで電解液は1M LiPF6 エチレンカーボネート/エチルメチルカーボネート(3/7質量比)を用いた。これを熱プレス機により電極1cm2当たり20kgの荷重をかけ、90℃、2分の熱プレスを行うことで試験電池を作製した。
負荷特性試験は上記のようにして作製した非水電解質電池を用いて実施した。電池の負荷特性は25℃にて0.2Cの放電容量を基準にした2Cの相対放電容量を測定し、これを指標とした。この試験を、実施例1~8及び比較例1で作製したセパレータを用いた電池について実施した。その結果を表3に示す。
充放電サイクル試験は前記作製した非水電解質電池を用いて実施した。充電条件は1C、4.2Vの定電流定電圧充電、放電条件は1C、2.75Vカットオフの定電流放電としサイクル特性試験を実施した。ここでサイクル特性の指標は100サイクル後の容量維持率とした。この試験を、実施例1~8及び比較例1で作製したセパレータを用いた電池について実施した。その結果を表3に示す。
充放電サイクル試験後の電池を解体し、セパレータと電極の接着性を確認した。接着性は接着力と均一性の観点から確認し、その結果を表3に示す。なお、接着力に関しては、正極側の電極表面および負極側の電極表面のそれぞれについて、実施例1のセパレータを用いた場合の剥離強度を100としたときの相対値を表3に示す。
均一性に関しては、正極側および負極側のそれぞれについて剥離テストを行なった後における、電極表面における接着性多孔質層の付着程度から、次の評価基準に基づき評価した。
A:接着性多孔質層がほぼ全て電極表面に付着していた〔均一性が良好〕。
B:接着性多孔質層の大部分が電極表面に付着しているが一部破損していた〔均一性が中程度〕。
C:接着性多孔質層の大部分が電極表面に付着しておらず著しく破損していた〔均一性が不良〕。
この剥離試験で、正極側および負極側の各電極表面から、セパレータを剥離するときに要した荷重を測定することにより剥離強度を求めた。
実施例1~8及び比較例1で作製した各セパレータについて、次の方法によりシャットダウン特性を評価した。結果を表3に示す。
まず、セパレータを直径19mmに打ち抜き、非イオン性界面活性剤(花王社製;エマルゲン210P)の3重量%メタノール溶液中に浸漬して風乾した。そしてセパレータに電解液を含浸させSUS板(直径15.5mm)に挟んだ。電解液には、プロピレンカーボネートとエチレンカーボネートが1対1の重量比で混合した溶媒に、1mol/LのLiBF4を溶解させた液体を用いた。これを2032型コインセルに封入した。コインセルからリード線をとり、熱電対を付けてオーブンの中に入れた。昇温速度1.6℃/分で昇温させ、同時に振幅10mV、1kHzの周波数の交流を印加することでセルの抵抗を測定した。
上記測定で130~140℃の範囲で抵抗値が103ohm・cm2以上となった場合をAと評価し、140~150℃の範囲で抵抗値が103ohm・cm2以上となった場合をBと評価し、150℃超で抵抗値が103ohm・cm2以上となった場合あるいはいずれの温度領域でも抵抗値が103ohm・cm2以上にならなかった場合をCと評価した。
塗工液として、スチレン-ブタジエン共重合体(スチレン共重合比40質量%):カルボキシルメチルセルロース:水=3:2:95[質量比]の混合物を用い、実施例1で用いたポリエチレン微多孔膜に両面等量塗工し、これを乾燥することでスチレン-ブタジエン共重合体からなる接着性多孔質層が形成されたセパレータを得た。このセパレータの物性値は、ガーレ値(Gs)が234秒/100cc、SDGS/AVGSが0.29、曲路率(τS)が2.25、ガーレ差(ΔG)が74秒/100cc、曲路率差(Δτ)が0.27であった。
なお、この実施例9についても実施例1と同様にして評価を行ったところ、実施例1と同程度の結果が得られた。
Claims (8)
- 熱可塑性樹脂を含む多孔質基材と、
前記多孔質基材の少なくとも片面に設けられ、接着性樹脂を含む接着性多孔質層と、
を備えた複合膜からなり、
前記多孔質基材のガーレ値と前記複合膜のガーレ値との差が75秒/100cc以下であり、かつ、前記多孔質基材の曲路率と前記複合膜の曲路率との差が0.30以下である非水電解質電池用セパレータ。 - 前記複合膜は、ガーレ値の平均値に対するガーレ値の標準偏差の比が0.3以下である請求項1に記載の非水電解質電池用セパレータ。
- 前記多孔質基材のガーレ値は、50秒/100cc以上800秒/100ccである請求項1または請求項2に記載の非水電解質電池用セパレータ。
- 前記複合膜の曲路率は、1.5~2.5である請求項1~請求項3のいずれか1項に記載の非水電解質電池用セパレータ。
- 前記接着性多孔質層は、平均孔径が1nm以上100nm以下である請求項1~請求項4のいずれか1項に記載の非水電解質電池用セパレータ。
- 前記接着性樹脂が、ポリフッ化ビニリデン系樹脂である請求項1~請求項5のいずれか1項に記載の非水電解質電池用セパレータ。
- 前記ポリフッ化ビニリデン系樹脂は、重量平均分子量が50万以上300万以下である請求項6に記載の非水電解質電池用セパレータ。
- 正極と、
負極と、
前記正極及び前記負極の間に配置された請求項1~請求項7のいずれか1項に記載の非水電解質電池用セパレータと、
を備え、リチウムのドープ・脱ドープにより起電力を得る非水電解質電池。
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