CN108305970B - Separator for lithium ion secondary battery, method for producing same, and lithium ion secondary battery - Google Patents
Separator for lithium ion secondary battery, method for producing same, and lithium ion secondary battery Download PDFInfo
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- CN108305970B CN108305970B CN201710674670.5A CN201710674670A CN108305970B CN 108305970 B CN108305970 B CN 108305970B CN 201710674670 A CN201710674670 A CN 201710674670A CN 108305970 B CN108305970 B CN 108305970B
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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
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D133/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides, or nitriles thereof; Coating compositions based on derivatives of such polymers
- C09D133/24—Homopolymers or copolymers of amides or imides
- C09D133/26—Homopolymers or copolymers of acrylamide or methacrylamide
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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
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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
- H01M50/431—Inorganic material
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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
- H01M50/44—Fibrous material
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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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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Abstract
A separator for a lithium ion secondary battery, which has excellent heat resistance, is less likely to cause an internal short circuit even at high temperatures, and can stably exhibit the function of the separator even when the thickness of the separator is reduced, a method for producing the separator, and a lithium ion secondary battery are provided, and the output characteristics of the lithium ion secondary battery are improved by using the separator. The inorganic coating layer can be formed into a uniform coating film without defects such as pinholes, and a separator having stable performance can be produced with good productivity. A separator for a lithium ion secondary battery, comprising a plastic nonwoven fabric having an inorganic coating layer provided on the surface thereof, wherein the synthetic fibers constituting the plastic nonwoven fabric have an average fiber diameter of 1 to 10 [ mu ] m and an average pore diameter (a) of 1 to 20 [ mu ] m, the inorganic coating layer and the nonwoven fabric contain ceramic fine particles (A) having an average particle diameter (B) of 0.1 to 5 [ mu ] m and a water-soluble polymer (B) therein, and the ratio (X) [ (B)/(a) ] of the average particle diameter (B) to the average pore diameter (a) is in the range of 0.05 to 0.5.
Description
Technical Field
The present invention relates to a lithium ion secondary battery separator, a method for manufacturing the lithium ion secondary battery separator, and a lithium ion secondary battery.
Background
As a lithium ion secondary battery separator (hereinafter, sometimes simply referred to as "separator") used in a lithium ion secondary battery (hereinafter, sometimes simply referred to as "battery"), a resin porous film made of a polyolefin resin such as polyethylene or polypropylene has been conventionally used. However, when such a resin porous film is used as a separator, there are the following problems: when the battery is abnormally heated, the battery melts and contracts, and the function of isolating the positive electrode from the negative electrode is lost, thereby generating a significant internal short circuit.
As a separator having heat resistance in which melting and shrinkage are not likely to occur even when the battery abnormally generates heat, a separator in which a layer containing various inorganic pigments is provided on a plastic nonwoven fabric substrate has been proposed (for example, see patent documents 1 to 2).
The separators of patent documents 1 and 2 are produced by applying a coating liquid containing an inorganic pigment on a plastic nonwoven fabric base. However, when the amount of the inorganic pigment to be applied is increased in order to improve heat resistance, the coating liquid may bleed out to the back surface of the nonwoven fabric substrate to contaminate the roll supporting the nonwoven fabric substrate, and when a separator having a small thickness is to be produced in order to reduce internal resistance and the amount of the inorganic pigment to be applied is reduced, pinholes may easily occur in the layer containing the inorganic pigment.
As the high molecular polymer of the separator of patent document 3, carboxymethyl cellulose (CMC) and styrene-butadiene latex are used. However, since two kinds of CMC having different viscosities are used or CMC having a concentration of 1% is prepared and used, there is a problem that the productivity is poor.
As the high molecular polymer of the separator of patent document 4, polyacrylamide-acrylate is used. However, when the thickness of the separator is reduced to reduce the internal resistance, pinholes are likely to occur, and an internal short circuit is likely to occur.
Documents of the prior art
Patent document
Patent document 1: japanese Kokai publication Hei-2005-536857
Patent document 2: japanese laid-open patent publication No. 2009-230975
Patent document 3: japanese patent laid-open publication No. 2013-115031
Patent document 4: japanese Kohyo publication No. 2013-519205
Disclosure of Invention
Problems to be solved by the invention
The present invention is intended to solve the above problems. That is, the first object of the present invention is to provide a separator for a lithium ion secondary battery, which comprises a plastic nonwoven fabric and an inorganic coating layer, has excellent heat resistance, is less likely to cause an internal short circuit even at high temperatures, and can stably exhibit the function of the separator (the function of separating a positive electrode from a negative electrode) even when the thickness of the separator is reduced, and to improve the output characteristics of the lithium ion secondary battery using the separator. Also provided is a method for producing the separator, wherein when the separator is produced by applying a coating agent to a nonwoven fabric and drying the coating agent, a uniform coating film can be formed without defects such as pinholes in the inorganic coating layer, and a separator having stable performance can be produced with good productivity.
Means for solving the problems
The present inventors have found that the above problems can be solved by combining a nonwoven fabric and ceramic fine particles in which the average fiber diameter and average pore diameter of synthetic fibers constituting the nonwoven fabric and the average particle diameter of ceramic fine particles contained in an inorganic coating layer are respectively set to specific ranges and the ratio of the average pore diameter of the synthetic fibers to the average particle diameter of the ceramic fine particles is in a specific relationship in a separator having the inorganic coating layer provided on the surface of the nonwoven fabric.
Namely, the present invention relates to:
a separator for a lithium ion secondary battery, comprising a plastic nonwoven fabric and an inorganic coating layer provided on the surface of the plastic nonwoven fabric, wherein synthetic fibers constituting the plastic nonwoven fabric have an average fiber diameter of 1 to 10 [ mu ] m and an average pore diameter (a) of 1 to 20 [ mu ] m, the coating layer and the interior of the nonwoven fabric contain ceramic fine particles (A) having an average particle diameter (B) of 0.1 to 5 [ mu ] m and a water-soluble polymer (B), and the ratio (X) [ (B)/(a) ] of the average particle diameter (B) to the average pore diameter (a) is in the range of 0.05 to 0.5;
the separator for a lithium ion secondary battery is characterized in that the water-soluble polymer (B) is a poly (meth) acrylamide obtained by copolymerizing a monomer (c) containing a sulfonic acid group-substituted unsaturated hydrocarbon group in an amount of 0.01 to 1 mol%;
the method for producing the separator for a lithium ion secondary battery is characterized in that a coating agent containing ceramic fine particles (A) having an average particle diameter (B) of 0.1 to 5 [ mu ] m, a water-soluble polymer (B) and water and having a B-type viscosity at 25 ℃ in the range of 50 to 1000 mPas is applied to the surface of a plastic nonwoven fabric having an average fiber diameter of 1 to 10 [ mu ] m and an average pore diameter (a) of 1 to 20 [ mu ] m, and the coating agent is dried;
the method for producing a separator for a lithium ion secondary battery, wherein the total concentration of the ceramic fine particles (A) and the water-soluble polymer (B) in the coating agent is 20 to 50 mass%;
a lithium ion secondary battery having the above separator mounted thereon.
Effects of the invention
The separator of the present invention has excellent heat resistance, is less likely to cause internal short circuit due to melting and shrinkage even when the battery abnormally generates heat, can stably exhibit the function of the separator (the function of separating the positive electrode from the negative electrode), and is particularly suitable for separators in which the internal resistance is reduced by reducing the thickness of the separator. Therefore, the lithium ion secondary battery having the separator of the present invention mounted thereon is excellent in battery output characteristics.
According to the method for producing a separator of the present invention, the coating agent can be prevented from leaking (bleeding) to the back surface of the plastic nonwoven fabric, and a uniform coating film free from pinholes and the like can be formed on the nonwoven fabric.
Detailed Description
A lithium ion secondary battery separator (hereinafter simply referred to as a separator) of the present invention is a separator for a lithium ion battery having an inorganic coating layer provided on the surface of a plastic nonwoven fabric, characterized in that the plastic nonwoven fabric has an average fiber diameter of 1 to 10 [ mu ] m and an average pore diameter (a) of 1 to 20 [ mu ] m, the inorganic coating layer and the nonwoven fabric contain ceramic fine particles (A) having an average particle diameter (B) of 0.1 to 5 [ mu ] m and a water-soluble polymer (B) therein, and the ratio (X) [ (B)/(a) ] of the average particle diameter (B) to the average pore diameter (a) is in the range of 0.05 to 0.5.
[ nonwoven Fabric made of Plastic ]
The plastic nonwoven fabric used in the separator of the present invention is a nonwoven fabric composed of synthetic fibers having an average fiber diameter of 1 to 10 μm and an average pore diameter of 1 to 20 μm. The average fiber diameter of the plastic nonwoven fabric is 1 to 10 μm, and more preferably 1 to 9.5 μm. When the average fiber diameter is less than 1 μm, the fibers are too fine to fill the interior of the nonwoven fabric with the ceramic fine particles (a) and the water-soluble polymer (B) described later, and the adhesion between the inorganic coating layer and the nonwoven fabric is insufficient. In addition, the separator may not have a sufficiently high separating function. When the average fiber diameter is larger than 10 μm, it is difficult to reduce the thickness of the nonwoven fabric layer itself and the thickness of the separator.
The average pore diameter of the present invention means the gap between synthetic fibers forming the plastic nonwoven fabric.
The average pore diameter of the plastic nonwoven fabric is 1 to 20 μm, more preferably 3 to 20 μm, and still more preferably 5 to 20 μm. When the average pore diameter is less than 1 μm, the internal resistance increases, and the output characteristics deteriorate. On the other hand, if the average pore diameter is more than 20 μm, internal short-circuiting may occur when lithium dendrite is generated.
The average fiber diameter and the average pore diameter in the present invention are the average of the fiber diameters of 20 fibers and the average of the pore diameters of 20 sites, which are randomly selected by measuring the fiber diameters and the pore diameters of the fibers with a scanning electron microscope photograph.
The nonwoven fabric is preferably composed of only synthetic fibers having an average fiber diameter of 1 to 10 μm and an average pore diameter of 1 to 20 μm, but when the need for reducing the thickness of the separator is not so high, synthetic fibers having an average fiber diameter and an average pore diameter different from those described above may be used in combination as needed. From the same viewpoint, fibers other than synthetic fibers may be used in combination as appropriate. The content of these fibers (synthetic resin fibers having an average fiber diameter and an average pore diameter outside the ranges specified in the present application, fibers other than synthetic fibers) used in combination should be 30 mass% or less, preferably 20 mass% or less, and more preferably 10 mass% or less, from the viewpoint of securing the strength of the nonwoven fabric.
Examples of the synthetic resin used as the synthetic resin fibers include polyolefin resin, polyester resin, polyvinyl acetate resin, ethylene-vinyl acetate copolymer resin, polyamide resin, acrylic resin, polyvinyl chloride resin, polyvinylidene chloride resin, polyvinyl ether resin, polyvinyl ketone resin, polyether resin, polyvinyl alcohol resin, diene resin, polyurethane resin, phenol resin, melamine resin, furan resin, polyester resin, Unsaturated aniline resin, Unsaturated polyester resin, and Unsaturated polyester resin, Fluorine (fluorocarbon) resin, silicone (silicone) resin, polyamideimide (polyamide imide) resin, polyphenylene sulfide (polyphenylene sulfide) resin, polyimide (polyimide) resin, polycarbonate (polycarbonate) resin, polyimide (polyimide) resin, polyamide (polyamide) resin, polyether ether ketone (polyether ether ketone) resin, poly (p-phenylene benzophenones) resin, poly (phenylene ether ketone) resin, poly (phenylene benzophenones) resin, poly (phenylene ether ketone) resin, poly (phenylene benzophenones), poly (phenylene ether ketone) resin, poly (phenylene benzophenones, poly (phenylene benzophenones), poly (phenylene benzophenones, poly (phenylene benzophenones), poly(s), poly (phenylene benzophenones), poly(s), poly (phenylene benzophenones, poly(s), poly (phenylene benzophenones, poly(s), poly(s), and poly(s), poly(s), and poly(s), and s
And a poly-p-phenylene bisoxazole resin, a polybenzimidazole resin, an ethylene-vinyl alcohol copolymer resin, and the like, and among them, a polyester resin, an acrylic resin, and a polyolefin resin are preferably used in order to improve the adhesion to the ceramic fine particles. In addition, when a polyester resin, an acrylic resin, or a polyamide resin is used, the heat resistance of the separator can be improved.
Examples of the polyester resin include resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PPT), polyethylene naphthalate (PEN), polybutylene naphthalate (polybutylene naphthalate) and polyethylene isophthalate (polyethylene isophthalate), and fully aromatic polyester (fully aromatic polyester). In addition, derivatives of these resins may also be used. Among these resins, polyethylene terephthalate resins are preferred in order to improve heat resistance, electrolyte solution resistance, and adhesiveness to ceramic fine particles.
Examples of the acrylic resin include resins composed of a polymer of 100% acrylonitrile, resins obtained by copolymerizing acrylonitrile with (meth) acrylic acid derivatives such as acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters, vinyl acetate, and the like.
Examples of the polyolefin resin include polypropylene, polyethylene, polymethylpentene, ethylene-vinyl alcohol copolymers, and olefin copolymers. From the viewpoint of heat resistance, polypropylene, polymethylpentene, an ethylene-vinyl alcohol copolymer, an olefin copolymer, and the like can be mentioned.
Examples of the polyamide resin include aliphatic polyamides such as nylon, wholly aromatic polyamides such as polyparaphenylene terephthalamide, polyparaphenylene terephthalamide-3, 4-diphenyl ether phthalic diamide, and poly (m-phenylene isophthalamide), and semi-aromatic polyamides having an aliphatic chain in a part of the main chain of the aromatic polyamide.
The semiaromatic group is a substance having, for example, a fatty chain in a part of the main chain. The wholly aromatic polyamide may be either of a para type and an meta type.
The synthetic resin fiber may be a fiber (single fiber) made of a single resin or a fiber (composite fiber) made of two or more resins. Examples of the composite fiber include a core-sheath type, an eccentric type, a side-by-side type, an island-in-sea type, an orange type, and a multilayer metal type.
Examples of the fibers other than the synthetic resin fibers that can be used in combination with the synthetic resin fibers include solvent-spun cellulose, short fibers of regenerated cellulose, fibrillized products, natural cellulose fibers, pulp products or fibrillized products of natural cellulose fibers, and inorganic fibers.
The thickness of the plastic nonwoven fabric is preferably 5 to 25 μm, and more preferably 5 to 15 μm, from the viewpoint of obtaining a separator having a reduced thickness and a low internal resistance.
[ inorganic coating layer ]
The separator for a lithium ion secondary battery of the present invention is characterized in that an inorganic coating layer is provided on the surface of a plastic nonwoven fabric, and the inorganic coating layer and the nonwoven fabric contain ceramic fine particles (A) having an average particle diameter of 0.1 to 5 [ mu ] m and a water-soluble polymer (B) therein.
The inorganic coating layer constituting the separator of the present invention will be explained.
The inorganic coating layer contains ceramic fine particles (A) and a water-soluble polymer (B) as constituent components. The separator of the present invention has a structure in which the inorganic coating layer is formed on the surface of the plastic nonwoven fabric and also penetrates into the interior of the nonwoven fabric, and the inorganic coating layer and the nonwoven fabric layer are firmly adhered to each other. Therefore, the description of the inorganic coating layer described below is also applicable to a portion that enters the inside of the nonwoven fabric.
Examples of the ceramic fine particles (a) include inorganic oxides such as alumina, gibbsite, boehmite, magnesia, magnesium hydroxide, silica, titanium oxide, barium titanate, and zirconia, inorganic nitrides such as aluminum nitride and silicon nitride, aluminum compounds, zeolites, and mica, and boehmite is particularly preferable.
The average particle diameter in the present invention refers to a volume average particle diameter (D50) obtained by particle size distribution measurement by a laser diffraction method.
The ceramic fine particles (A) have an average particle diameter of 0.1 to 5 μm, preferably 0.1 to 4.5 μm, and more preferably 0.1 to 4.0. mu.m. When the average particle size is less than 0.1 μm, the internal resistance increases, the output characteristics decrease, and it is difficult to form a flat and uniform inorganic coating layer. On the other hand, if it exceeds 5 μm, it is difficult to reduce the thickness of the inorganic coating layer and hence the separator. In addition, sufficient heat resistance cannot be obtained, and internal short circuits can easily occur. In addition, it is difficult to uniformly exist the ceramic fine particles (a) and the water-soluble polymer (B) in the nonwoven fabric, and therefore, stable barrier properties and adhesion of the separator cannot be obtained.
The present invention is characterized in that the ratio (X) [ (X) ═ b)/(a) ] of the average particle diameter (b) of the ceramic fine particles to the average pore diameter (a) of the plastic nonwoven fabric is set to be in the range of 0.05 to 0.5. The (X) is more preferably 0.05 to 0.45, and still more preferably 0.05 to 0.4.
By adjusting (X) to a range of 0.05 to 0.5, the ceramic fine particles (a) can be effectively retained in the pore diameter of the plastic nonwoven fabric, thereby effectively preventing internal short circuit and reducing the internal resistance of the separator, and a separator exhibiting a stable separation function can be obtained. In addition, since the adhesion to the inorganic coating layer is secured, stable performance can be exhibited even if the thickness of the separator is reduced.
When (X) is less than 0.05, the average particle diameter (b) of the ceramic fine particles is too small relative to the average pore diameter (a) of the plastic nonwoven fabric, and the applied coating agent penetrates pores of the nonwoven fabric to make strikethrough conspicuous, making it difficult to form an inorganic coating layer. On the other hand, if it exceeds 0.5, the average particle diameter (b) of the ceramic fine particles does not enter the pores of the nonwoven fabric, and therefore, adhesion cannot be obtained.
The water-soluble polymer (B) is not particularly limited as long as it is soluble in water. Specific examples thereof include cellulose compounds, starch, alginic acid, xanthan gum, chitosan, carrageenan, agar, dextrin, gelatin, polyvinyl alcohol, poly (meth) acrylamide, poly (meth) acrylic acid, polysulfonic acid, polyethyleneimine, polyethylene oxide, polyvinylpyrrolidone, polyethylene glycol, polystyrene sulfonic acid, ethylene-acrylic acid copolymers, ethylene-acrylamide-acrylic acid copolymers, polyamidine, polyvinyl imidazoline, and derivatives or salts thereof. Among these, cellulose compounds, polyvinyl alcohol, poly (meth) acrylamide, poly (meth) acrylic acid and derivatives thereof are preferable because they are excellent in thickening and film-forming properties and in dispersing effect of the ceramic fine particles (a). However, cellulose-based compounds are generally commercially available in the form of powder, and it takes a long time to dissolve a high molecular weight cellulose-based compound (a cellulose-based compound having a 1 mass% aqueous solution viscosity of 1000mPa · s or more at 25 ℃) in water, and therefore, it is economically disadvantageous and thus not preferable.
From the viewpoint of ensuring the heat resistance of the separator, poly (meth) acrylamide is most preferable. These water-soluble polymers (B) may be used singly or in combination of two or more.
The poly (meth) acrylamide contains a monomer having a (meth) acrylamide skeleton in the molecule (hereinafter referred to as a component (d)) as a constituent monomer. Specific examples of the component (d) include acrylamide, methacrylamide, N-isopropylacrylamide, N-dimethylacrylamide, N-dimethylmethacrylamide, N-diethylacrylamide, N-diethylmethacrylamide, N-dimethylaminopropylacrylamide, N-dimethylaminopropylmethacrylamide, N-hydroxymethylmethacrylamide, N-hydroxymethylacrylamide, diacetoneacrylamide, maleic acid amide, and acrylamide tert-butylsulfonic acid, and one of them may be used alone or two or more of them may be used in combination. Among these, when (meth) acrylamide, particularly acrylamide, is used, the oxidation resistance of poly (meth) acrylamide is improved.
In the component (d), by selecting (meth) acrylamide, the dispersibility of the ceramic fine particles (a) and the adhesion between the active materials in the electrode interior are improved.
The monomer of the poly (meth) acrylamide may contain a monomer other than the component (d), but in this case, the content of the component (d) is usually 30 mol% or more, preferably 50 mol% or more, based on the total monomers constituting the poly (meth) acrylamide.
Among the water-soluble polymers (B), poly (meth) acrylamide is advantageous in that the viscosity can be adjusted to an appropriate level when an inorganic coating layer is formed by applying the poly (meth) acrylamide to a plastic nonwoven fabric in the form of a water-soluble coating agent as in the production method of the present invention described later. That is, the poly (meth) acrylamide is easily controlled in molecular weight by using a chain transfer agent or the like in combination, and the viscosity of the coating agent is easily adjusted to a viscosity range suitable for penetration into the plastic nonwoven fabric.
As the chain transfer agent, it is most preferable to use a monomer (c) containing a sulfonic acid group-substituted unsaturated hydrocarbon group (hereinafter referred to as component (c)) from the viewpoint of improving the oxidation resistance of the separator. By using the component (c) in combination as a monomer, the oxidation resistance is improved. The separator has improved heat resistance and is particularly suitable for use on the positive electrode side having strong oxidizing properties.
As the component (c), any of various known compounds can be used without particular limitation as long as the compound or salt thereof is one in which the hydrogen of an unsaturated hydrocarbon group is substituted with a sulfonic acid group. Examples of the component (c) include vinylsulfonic acid, allylsulfonic acid, and methacrylsulfonic acid, and salts thereof, and one of them may be used alone or two or more of them may be used in combination. Examples of the salt include organic salts such as organic amine salts; and metal salts including alkali metal salts such as potassium salts and sodium salts, and inorganic salts including ammonium salts. Among them, from the viewpoint of obtaining a coating agent having an appropriate viscosity and water solubility (i.e., water solubility to an extent suitable for the dispersion stability of the component (a) in the coating agent) as a coating agent to be described later, a methacrylic sulfonate salt is preferable, and sodium methallyl sulfonate is particularly preferable.
(c) The content of the component (b) is not particularly limited, and is about 0.01 to about 1 mol%, preferably about 0.05 to about 1 mol%, based on the total monomers constituting the poly (meth) acrylamide.
(c) When the amount of the component (b) is too large, the obtained poly (meth) acrylamide has a low molecular weight, and the flexibility of the separator may be insufficient. On the other hand, when the component (c) is too small, the polymer becomes too high, so that the poly (meth) acrylamide is likely to aggregate, and it is difficult to uniformly disperse the ceramic fine particles (a) in the coating layer, and the separator may have insufficient barrier performance and adhesion.
Further, the monomer used in the poly (meth) acrylamide may contain another monomer (e) (hereinafter referred to as component (e)) copolymerizable with the component (c) and the component (d) within a range not to impair the effects of the present invention. Specific examples of the component (e) include unsaturated carboxylic acids, unsaturated carboxylic acid esters, α, β -unsaturated nitrile compounds, conjugated diene compounds, aromatic vinyl compounds, and the like, and one of them may be used alone or two or more thereof may be used in combination.
Examples of the unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. The unsaturated carboxylic acid content is not particularly limited, but is preferably less than 10 mol% in the total monomers in view of adhesion.
The unsaturated carboxylic acid ester is preferably a (meth) acrylic acid ester, and examples thereof include monofunctional (meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, n-pentyl (meth) acrylate, isoamyl (meth) acrylate, hexyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, n-octyl (meth) acrylate, nonyl (meth) acrylate, and decyl (meth) acrylate; polyfunctional (meth) acrylates such as glycidyl (meth) acrylate, hydroxymethyl (meth) acrylate, hydroxyethyl (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, allyl (meth) acrylate, and vinyl di (meth) acrylate, and one of these may be used alone or two or more of them may be used in combination. The content of the unsaturated carboxylic acid ester is not particularly limited, and is preferably less than 10 mol% in the total monomers in view of oxidation resistance.
The α, β -unsaturated nitrile compound is effective in imparting flexibility to the obtained inorganic coating layer. Specific examples thereof include acrylonitrile, methacrylonitrile, α -chloroacrylonitrile, α -ethylacrylonitrile, and dicyanovinylene, and two or more kinds thereof may be used in combination. Among these, acrylonitrile and/or methacrylonitrile are preferable, and acrylonitrile is particularly preferable. The content of the α, β -unsaturated nitrile compound is not particularly limited, and is more preferably less than 40 mol% in the total monomers in order to maintain the water solubility of the poly (meth) acrylamide.
Examples of the conjugated diene compound include 1, 3-butadiene, 2-methyl-1, 3-butadiene, 2, 3-dimethyl-1, 3-butadiene, 2-chloro-1, 3-butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like. Examples of the aromatic vinyl compound include styrene, α -methylstyrene, p-methylstyrene, vinyltoluene, chlorostyrene, and divinylbenzene. One of them may be used alone or two or more of them may be used in combination. The content of these is not particularly limited, but is preferably less than 10 mol% based on the total monomers of the poly (meth) acrylamide. The binder for a positive electrode is exposed to a high voltage, and therefore oxidation resistance is required. However, since the conjugated diene compound and the aromatic vinyl compound are easily oxidized, the oxidation resistance tends to be lowered. Therefore, on the positive electrode side, it is preferable not to use these substances.
The poly (meth) acrylamide can be synthesized by a radical polymerization method among various known methods. Aqueous solution radical polymerization is preferred. Specifically, a radical polymerization initiator may be added to a mixture of the components (c) and (d) and, if necessary, a monomer containing the component (e), and the mixture may be stirred and subjected to a polymerization reaction at a reaction temperature of about 50 to about 100 ℃. The reaction time is not particularly limited, and is usually about 1 hour to about 10 hours.
As the radical polymerization initiator, various known polymerization initiators can be used without particular limitation. Specifically, examples thereof include: persulfates such as potassium persulfate and ammonium persulfate; a redox polymerization initiator comprising a combination of the persulfate and a reducing agent such as sodium hydrogen sulfite; azo initiators, and the like. The content of the radical polymerization initiator is not particularly limited, and is about 0.05 to about 2% by mass, preferably about 0.1 to about 1.5% by mass, based on the total mass of all monomers used in the synthesis of the poly (meth) acrylamide. In this case, the polymerization reaction can sufficiently proceed, and the poly (meth) acrylamide can be increased in molecular weight.
The pH adjustment may be performed by using a general neutralizing agent such as ammonia, organic amine, potassium hydroxide, sodium hydroxide, or lithium hydroxide before the radical polymerization reaction or when the obtained poly (meth) acrylamide is water-dissolved, in order to improve the production stability. In this case, the pH (25 ℃) is preferably adjusted to a range of about 5 to about 11. In addition, EDTA or a salt thereof, which is a metal ion sealant, may also be used for the same purpose.
The solid content ratio (% by mass) of the ceramic fine particles (a) and the water-soluble polymer (B) in the inorganic coating layer is preferably in the range of 99:1 to 90: 10. When the solid content ratio of the water-soluble polymer (B) is less than 1, the adhesion of the inorganic coating layer cannot be maintained, and the ceramic fine particles (a) are likely to be peeled off. On the other hand, when the amount is 10 or more, the inorganic coating layer covers the entire inorganic coating layer, and therefore, the internal resistance is increased, and the output characteristics of the lithium ion secondary battery may be deteriorated.
The separator for a lithium ion secondary battery of the present invention comprises the above-described constitution, and the thickness of the separator is preferably 10 to 40 μm, more preferably 10 to 30 μm, and further preferably 10 to 25 μm. If the thickness exceeds 40 μm, the internal resistance is increased due to the influence of the thickness, and the output characteristics of the lithium ion secondary battery may be deteriorated, whereas if the thickness is less than 10 μm, it may be difficult to obtain sufficient strength.
[ method for producing separator for lithium ion Secondary Battery ]
The method for producing a separator for a lithium ion secondary battery is characterized in that a coating agent containing the ceramic fine particles (A), a water-soluble polymer (B) and water and having a B-type viscosity at 25 ℃ in the range of 50 to 1000 mPas is applied to the surface of the plastic nonwoven fabric and dried.
The coating agent used in the present invention can suitably permeate into the plastic nonwoven fabric having the above-mentioned average fiber diameter and average pore diameter, and can provide a stable inorganic coating layer on the surface thereof.
The coating agent contains ceramic fine particles (A), a water-soluble polymer (B) and water, and the ceramic fine particles (A) are uniformly and stably dispersed by the water-soluble polymer (B). The water-soluble polymer (B) has a function of dispersing the ceramic fine particles (a), and has an effect as a binder for causing the inorganic coating layer formed on the surface of the plastic nonwoven fabric to adhere to the nonwoven fabric.
The B-type viscosity of the coating agent at 25 ℃ is preferably 50 to 1000 mPas from the viewpoints of ensuring coating stability, adequate permeability into a plastic nonwoven fabric, and the like, such as formation of a uniform and thin coating film. When the viscosity exceeds 1000 mPas, the amount of the coating is too large, and it is difficult to form a thin inorganic coating layer. Further, the coating agent is less likely to penetrate into the nonwoven fabric, and the internal resistance of the separator increases, which may deteriorate the output characteristics of the battery. On the other hand, when the viscosity is less than 50mPa · s, strike-through of the coating agent to the nonwoven fabric substrate occurs at the time of coating, and the ceramic fine particles (a) are hardly held in the pores, and roll contamination or the like occurs, thereby deteriorating productivity.
From the same viewpoint, the total concentration of the ceramic fine particles (a) and the water-soluble polymer (B) is preferably 20 to 50% by mass. From the same viewpoint, the ratio of the ceramic fine particles (a) to the water-soluble polymer (B) in the coating agent is preferably in the range of 20:0.2 to 45:5 in terms of a solid content mass ratio. When the solid content ratio of the water-soluble polymer (B) is less than 0.2, the adhesion of the coating layer cannot be maintained, and the ceramic fine particles (a) are easily peeled off, while when it exceeds 5, the coating layer is entirely covered, so that the internal resistance is increased, and the output characteristics of the lithium ion secondary battery are deteriorated.
The coating agent used in the present invention may contain other additives. Specifically, examples thereof include an aqueous latex, a dispersant, a leveling agent, an antioxidant, an electrolyte decomposition inhibitor, a conductive auxiliary agent, and a thixotropic agent.
Examples of the aqueous latex include styrene-butadiene copolymer latex, butadiene latex, and acrylate latex, and they are used for the purpose of imparting flexibility to the separator. However, these latexes are not preferable because they are resistant to oxidation and are difficult to use on the positive electrode side, and when the amount of the latex added is large, they penetrate pores of the nonwoven fabric during application of the coating agent, and thereby show increased strike-through. Therefore, the content is preferably set to less than 10 parts by mass with respect to 100 parts by mass of the component (B). For the same reason, it is more preferable not to contain it.
Examples of the dispersant include anionic compounds, cationic compounds, nonionic compounds, and polymer compounds. By using the dispersant, the stability of the coating agent of the present invention is improved, and in addition, a smooth electrode layer can be formed using the coating agent, and thus a high battery capacity can be achieved. The amount of the dispersant used is not particularly limited, and is less than 5 parts by mass per 100 parts by mass of the component (B).
Examples of the leveling agent include an alkyl surfactant, a silicon surfactant, a fluorine surfactant, and a metal surfactant. By using a surfactant, the repulsion of the coating agent of the present invention when applied to a plastic nonwoven fabric can be suppressed, and the smoothness of the inorganic coating layer surface can be improved. The amount of the leveling agent used is not particularly limited, and is less than 10 parts by mass per 100 parts by mass of the component (B).
Examples of the antioxidant include phenol compounds, hydroquinone compounds, organic phosphorus compounds, sulfur compounds, phenylenediamine compounds, and polymer-type phenol compounds. The polymer-type phenol compound is a polymer having a phenol structure in a molecule, and has a mass average molecular weight of usually 200 or more, preferably 600 or more, usually 1000 or less, preferably 700 or less. The use of an antioxidant can improve the stability of the coating agent of the present invention, and the battery capacity and cycle characteristics of a secondary battery obtained using the coating agent. The amount of the antioxidant used is not particularly limited, and is less than 5 parts by mass per 100 parts by mass of the component (B).
The amount of the coating agent (weight per unit area) is preferably 3.0 to 40.0g/m per unit area of the nonwoven fabric2More preferably 3.3 to 35.0g/m2More preferably 3.5 to 30.0g/m2. More than 40.0g/m2In the case of this, the internal resistance of the separator for a lithium ion secondary battery is increased, and the output characteristics are sometimes deteriorated to less than 3.0g/m2Sometimes, a short circuit easily occurs.
The method for applying the coating agent to the plastic nonwoven fabric is not particularly limited, and various coating methods such as a doctor blade, a bar, an inversion roller, a doctor blade, a die, a curtain, and an air knife, various printing methods such as a flexible printing method, a screen printing method, an offset printing method, a gravure printing method, and an ink jet printing method, transfer methods such as a roll transfer method and a film transfer method, and a method of scraping the coating liquid on the non-coating surface side by a pulling method such as dipping can be selected as necessary. The coating agent is applied to one surface or both surfaces of the plastic nonwoven fabric by using the above-described various methods.
In the present invention, the basis weight of the lithium ion secondary battery separator is preferably 9.5 to 50.0g/m per unit area of the nonwoven fabric2More preferably 11.0 to 40.0g/m2More preferably 12.5 to 35.0g/m2. More than 50.0g/m2In the case where the amount of the electrolyte is too small, the internal resistance of the separator increases, and the output characteristics of the battery may deteriorate to less than 9.5g/m2In this case, it may be difficult to obtain sufficient strength.
The separator thus obtained was filled between the positive electrode and the negative electrode of the lithium ion secondary battery, and the space between the inside of the separator and the positive electrode or the negative electrode was filled with a supporting electrolyte solution, and the separator was mounted on the lithium ion secondary battery.
The positive electrode active material of the lithium ion secondary battery of the present invention is roughly classified into a positive electrode active material made of an inorganic compound and a positive electrode active material made of an organic compound. Examples of the positive electrode active material composed of an inorganic compound include transition metal oxides, complex oxides of lithium and transition metals, transition metal sulfides, and the like. As the transition metal, Fe, Co, Ni, Mn, Al, or the like is used. Specific examples of the inorganic compound used for the positive electrode active material include: LiCoO2、LiNiO2、LiMnO2、LiMn2O4、LiFePO4、LiNi1/2Mn3/2O4、LiCo1/3Ni1/3Mn1/3O2、Li[Li0.1Al0.1Mn1.9]O4、LiFeVO4And the like lithium-containing composite metal oxides; TiS2、TiS3Amorphous MoS2Isotransition metal sulfides; cu2V2O3Amorphous V2O-P2O5、MoO3、V2O5、V6O13And transition metal oxides; and the like. These compounds may be compounds which have been partially subjected to element substitution. As the positive electrode active material composed of an organic compound, for example, a conductive polymer such as polyacetylene or polyparaphenylene may be used. Since the iron-based oxide having insufficient electrical conductivity contains a carbon source substance during reduction and calcination, it can be used in the form of an electrode active material coated with a carbon material. Further, these compounds may be compounds partially substituted with an element. Among them, LiCoO is preferable from the viewpoint of practicality, electrical characteristics, and long life2、LiNiO2、LiMnO2、LiMn2O4、LiFePO4、LiNi1/2Mn3/2O4、LiCo1/3Ni1/3Mn1/3O2、Li[Li0.1Al0.1Mn1.9]O4。
Examples of the negative electrode active material for a lithium ion secondary battery include: conductive polymers such as polyacene; metals such as silicon, tin, zinc, manganese, iron, and nickel, alloys thereof, and oxides or sulfates thereof; lithium metal, lithium alloys such as Li-Al, Li-Bi-Cd, Li-Sn-Cd, and lithium transition metal nitrides; silicon; carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, pitch-based carbon fibers, and the like. Examples of the raw material of the carbonaceous material include graphite (graphite) such as artificial graphite, natural graphite, and graphite fluoride, and thermal decomposition products of organic substances under various thermal decomposition conditions. Examples of the thermal decomposition products include coal-based coke, petroleum-based coke, carbide of coal-based pitch, carbide of petroleum-based pitch, or carbide obtained by oxidizing these pitches, needle coke, pitch coke, phenol resin, carbide such as crystalline cellulose, carbon material obtained by partially graphitizing these, furnace black, acetylene black, pitch-based carbon fiber, and the like. The negative electrode material may be a carbonaceous material, particularly a graphite material containing artificial graphite, purified natural graphite, pitch, or the like, and these materials may be subjected to various surface treatments.
As a supporting electrolyte solution of a lithium ion secondary battery, for example, LiPF is used6、LiAsF6、LiBF4、LiSbF6、LiAlCl4、LiClO4、CF3SO3Li、C4F9SO3Li、CF3COOLi、(CF3CO)2NLi、(CF3SO2)2NLi、(C2F5SO2)2A solution obtained by dissolving a supporting electrolyte in a nonaqueous solvent such as NLi. As the supporting electrolyte, LiPF6、LiClO4、CF3SO3Li shows a high degree of dissociation and is therefore preferred. Examples of the nonaqueous solvent include: chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, and butylene carbonate; chain ethers such as 1, 2-dimethoxyethane; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane and 1, 3-dioxolane; chain esters such as methyl formate, methyl acetate, and methyl propionate; cyclic esters such as γ -butyrolactone and γ -valerolactone, and acetonitrile. These solvents may be used in combination of two or more kinds, and a combination of a cyclic carbonate and a chain carbonate is particularly preferable.
The form of the lithium ion secondary battery of the present invention is not particularly limited. Examples of the separator include a cylindrical separator having a spiral shape and a sheet electrode, a cylindrical separator having an inside-out (inside-out) structure and a cylindrical separator having a spiral shape and a sheet electrode, and a coin-shaped separator having a sheet electrode and a separator laminated on each other. The batteries of these forms can be used in any shape such as a coin shape, a cylindrical shape, or a rectangular shape by being housed in any outer case.
The procedure for assembling the lithium ion secondary battery of the present invention is also not particularly limited, and the lithium ion secondary battery may be assembled in an appropriate procedure depending on the structure of the battery, and for example, the method described in japanese patent application laid-open No. 2013-89437 may be mentioned. The battery can be formed by providing the outer case with a negative electrode, providing the electrolyte and the separator thereon, placing the positive electrode so as to face the negative electrode, and caulking the positive electrode together with the gasket and the sealing plate.
[ examples ]
The present invention will be described in more detail with reference to examples, but the present invention is not limited to the examples. In the examples, "%" and "parts" represent "% by mass" and "parts by mass", respectively.
Production of Water-soluble Polymer (B)
Production example 1
2300g of ion-exchanged water, 400g (5.63mol) of acrylamide and 9.0g (0.057mol) of sodium methallylsulfonate were charged into a reaction apparatus equipped with a stirrer, a thermometer, a reflux condenser and a nitrogen gas inlet, and nitrogen gas was introduced into the apparatus to remove oxygen in the reaction system, and then the temperature was raised to 50 ℃. 4.0g of 2, 2' -azobis-2-amidinopropane dihydrochloride (product name "NC-32" available from Nippon chemical Co., Ltd.) and 30g of ion-exchanged water were charged thereinto, and the reaction was carried out at 80 ℃ for 1.5 hours. Subsequently, NC-324.0 g and 30g of ion-exchanged water were charged and reacted at 80 ℃ for 1.5 hours to prepare an aqueous solution containing poly (meth) acrylamide having a solid content of 15.0% and a viscosity (25 ℃) of 35000 mPas.
Production examples 2 to 8
An aqueous solution containing poly (meth) acrylamide was prepared in the same manner as in example 1, except that the monomer composition and the amount of the initiator in production example 1 were changed to the substances and numerical values shown in table 1.
[ Table 1]
AM: acrylamide
NMAM: n-methylolacrylamide
ATBS: acrylamide tert-butyl sulfonic acid
SMAS: sodium methallyl sulfonate
MAS: methacrylic acid sulfonic acid
AA: acrylic acid
EA: acrylic acid ethyl ester
HEMA: 2-Hydroxyethyl methacrylate
AN: acrylonitrile
MPA: 3-mercaptopropionic acid
Example 1
An alumina hydrate (boehmite, specific surface area 3.9 m) having an average particle diameter (b) of 2.3 μm2G, net bulk density 0.31g/cm3)100 parts by mass of the aqueous solution containing poly (meth) acrylamide synthesized in production example 1 (nonvolatile content: 15%, viscosity: 35000 mPas at 25 ℃) was added as a water-soluble polymer (B) (5.3 parts by mass in terms of solid content) after dispersing 100 parts by mass of the aqueous solution in 140 parts by mass of water, followed by stirring and mixing, and further adding ion-exchanged water to adjust the viscosity, thereby producing a coating agent. On a PET nonwoven fabric having an average fiber diameter of 5.2 μm and an average pore diameter (a) of 8.7 μm, a dry solid content of 10g/m was applied by a gravure coater2In the embodiment (1), the coating agent is applied to both surfaces of a nonwoven fabric and dried to obtain a separator for a lithium ion secondary battery.
Examples 2 to 12
A separator for a lithium ion secondary battery was obtained in the same manner as in example 1, except that the average fiber diameter and the average pore diameter of the PET nonwoven fabric, the average particle diameter of the ceramic fine particles, and the water-soluble polymer (B) were changed to the materials and values shown in table 2.
Example 13
A separator for a lithium ion secondary battery was obtained in the same manner as in example 1, except that polyvinyl alcohol (PVA, 5% aqueous solution, 40 mPas, average polymerization degree of about 3100 to 3900, partially saponified type, manufactured by Wako pure chemical industries, Ltd.) was used as the water-soluble polymer (B).
Example 14
A separator for a lithium ion secondary battery was obtained in the same manner as in example 1, except that sodium carboxymethylcellulose (CMC, 1% aqueous solution, 7800mPa · s, manufactured by first industrial pharmaceutical co., ltd.) was used as the water-soluble polymer (B).
Comparative examples 1 to 5
A separator for a lithium ion secondary battery was obtained in the same manner as in example 1, except that the average fiber diameter and the average pore diameter of the PET nonwoven fabric, the average particle diameter of the ceramic fine particles, and the water-soluble polymer (B) were changed to the materials and values shown in table 2.
Comparative example 6
A separator for a lithium ion secondary battery was obtained in the same manner as in example 1, except that a latex aqueous solution of styrene-butadiene copolymer latex (SBR) was used as the water-soluble polymer (B).
[ Table 2]
In examples and comparative examples, the viscosity of the coating agent, the stability of the coating agent, the coatability, the evaluation of pinholes in the separator, and the output characteristics in the lithium ion secondary battery were each performed as follows.
< viscosity >
The slurry viscosities of the coating agents of examples and comparative examples were measured at 25 ℃ and 60rpm using a B-type viscometer.
< stability of coating agent >
The coating agents of examples and comparative examples were left standing at 25 ℃ for 6 hours, and the sedimentation state of the ceramic fine particles at this time was visually evaluated by the following criteria.
Very good: the whole was homogeneous paste-like, no liquid separation was observed, and no aggregates were observed.
O: no aggregates were observed at the bottom of the vessel, but a small amount of liquid separation was observed.
And (delta): a small amount of aggregate and slightly more liquid separation was observed at the bottom of the vessel.
X: a large number of clay-like aggregates were observed at the bottom of the vessel, and liquid separation was also observed in many cases.
< coatability of coating agent >
The coating agents of examples and comparative examples were applied to the plastic nonwoven fabric laid on black drawing paper using a bar coater, and when the nonwoven fabric was removed from the drawing paper, traces of the coating agents adhered to the drawing paper were observed and evaluated according to the following criteria.
Very good: there were no traces of coating agent on the drawing paper.
O: there were 2 or less traces of strike-through coating agent on the drawing paper.
And (delta): there are traces of print-through coating agent on the drawing paper.
X: there are multiple traces of print-through coating agent on the graphic paper.
< evaluation of pinhole of separator >
The state of the inorganic coating layer of the separator obtained in examples and comparative examples was observed from the side of the inorganic coating layer by irradiating light from the side of the separator substrate, and evaluated according to the following evaluation criteria.
A: no pinhole generation was observed in visual observation
B: there is a portion where transmitted light is slightly observed
C: multiple transmitted light was clearly observed
< preparation of lithium ion Secondary Battery >
Using the separators obtained in examples and comparative examples, lithium nickel, manganese, and cobalt oxide was used for the positive electrode, graphite was used for the negative electrode, and lithium hexafluorophosphate (LiPF) was used for the electrolyte solution6) A coin-type lithium ion secondary battery was prepared by using a mixed solvent solution of 1mol/L of Ethylene Carbonate (EC)/dimethyl carbonate (DMC) (capacity ratio 3/7).
< output characteristics of lithium ion Secondary Battery >
The lithium ion secondary battery thus produced was charged at 25 ℃ with a voltage of 0.1C and 2.5 to 4.2V, and when the voltage reached 4.2V, the charging was continued with a constant voltage (4.2V), and when the current value reached 0.01C, the charging was completed (cut off). Next, charge and discharge from 1C to 2.5V were repeated for 50 cycles, and the ratio of the 1C discharge capacity at the 50 th cycle to the 1C discharge capacity at the 5 th cycle was calculated as a percentage, and the obtained value was taken as a capacity retention rate. The larger the value, the better the output characteristics.
[ Table 3]
The coating agents obtained in examples 1 to 14 were stable in all cases and also had good coatability. In addition, when the ratio (X) of (a) to (b) is 0.05 to 0.5 in the production of the separator, no offset or pin hole is observed, and a good separator is obtained. Then, the output characteristics were also very good, and the oxidation resistance was excellent.
In comparative example 1, the coating agent obtained was good in coatability and had no pin holes in the separator, but the (X) was large, and therefore, the adhesion was poor and the output characteristics were deteriorated.
In comparative example 2, since the nonwoven fabric had a small average fiber diameter, a large average pore diameter, and a small average particle diameter of the ceramic fine particles, the coating agent was strikethrough, and the coatability was deteriorated. In addition, the generation of pinholes in the separator was also observed.
In comparative example 3, (X) was small, and therefore, the coating agent was strikethrough, and the coatability was deteriorated. In addition, the generation of pinholes in the separator was also observed.
In comparative example 4, since the average particle size of the ceramic fine particles was large, sedimentation was observed in the coating agent, and stability was deteriorated.
In comparative example 5, since the average particle size of the ceramic fine particles was small, (X) became small, and offset occurred in the coating agent, and the coatability was deteriorated. In addition, the generation of pinholes in the separator was also observed.
In comparative example 6, since the latex solution was used as the water-soluble polymer (B), the dispersibility of the coating agent was deteriorated and the coating agent was immediately observed to be deposited, and further, the viscosity of the coating agent was low, and the strike-through was observed. In addition, the generation of pinholes was also observed in a plurality of separators.
Claims (5)
1. A separator for a lithium ion secondary battery, comprising a plastic nonwoven fabric and an inorganic coating layer provided on the surface of the plastic nonwoven fabric, wherein synthetic fibers constituting the plastic nonwoven fabric have an average fiber diameter of 1 to 10 [ mu ] m and an average pore diameter (a) of 1 to 20 [ mu ] m, the inorganic coating layer and the nonwoven fabric contain ceramic fine particles (A) having an average particle diameter (B) of 0.1 to 5 [ mu ] m and a water-soluble polymer (B) therein, the content of an aqueous latex is set to less than 10 parts by mass per 100 parts by mass of the component (B), and the ratio (X) of the average particle diameter (B) to the average pore diameter (a), i.e., (B)/(a), is in the range of 0.05 to 0.5.
2. The separator for a lithium ion secondary battery according to claim 1, wherein the water-soluble polymer (B) is a poly (meth) acrylamide copolymer containing a sulfonic acid group-substituted unsaturated hydrocarbon group-containing monomer (c) in an amount of 0.01 to 1 mol%.
3. The method for producing a separator for a lithium ion secondary battery according to claim 1 or 2, wherein a coating agent containing ceramic fine particles (A) having an average particle diameter (B) of 0.1 to 5 μm, a water-soluble polymer (B) and water and having a B-type viscosity at 25 ℃ of 50 to 1000 mPas is applied to the surface of a plastic nonwoven fabric having an average fiber diameter of 1 to 10 μm and an average pore diameter (a) of 1 to 20 μm, and dried.
4. The method for producing a separator for a lithium-ion secondary battery according to claim 3, wherein the total concentration of the ceramic fine particles (A) and the water-soluble polymer (B) in the coating agent is 20 to 50% by mass.
5. A lithium ion battery comprising the separator according to claim 1 or 2.
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| JP2016157487A JP6579383B2 (en) | 2016-08-10 | 2016-08-10 | Lithium ion secondary battery separator, method for producing lithium ion secondary battery separator, and lithium ion secondary battery |
| JP2016-157487 | 2016-08-10 |
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| KR20200032542A (en) | 2018-09-18 | 2020-03-26 | 삼성에스디아이 주식회사 | Separator for rechargeable lithium battery and rechargeable lithium battery including the same |
| KR102307978B1 (en) * | 2018-12-20 | 2021-09-30 | 삼성에스디아이 주식회사 | Separator for rechargeable lithium battery and rechargeable lithium battery including the same |
| KR102312278B1 (en) * | 2018-12-21 | 2021-10-12 | 삼성에스디아이 주식회사 | Separator for rechargeable lithium battery and rechargeable lithium battery including the same |
| KR102306447B1 (en) * | 2018-12-26 | 2021-09-28 | 삼성에스디아이 주식회사 | Separator for rechargeable lithium battery and rechargeable lithium battery including the same |
| KR102312280B1 (en) * | 2018-12-26 | 2021-10-12 | 삼성에스디아이 주식회사 | Separator for rechargeable lithium battery and rechargeable lithium battery including the same |
| KR102342669B1 (en) * | 2019-01-16 | 2021-12-22 | 삼성에스디아이 주식회사 | Separator for rechargeable lithium battery and rechargeable lithium battery including the same |
| US20220336868A1 (en) * | 2019-09-27 | 2022-10-20 | Zeon Corporation | Slurry composition for non-aqueous secondary battery heat-resistant layer, heat-resistant layer for non-aqueous secondary battery, and non-aqueous secondary battery |
| US20210305659A1 (en) * | 2020-03-20 | 2021-09-30 | Samsung Sdi Co., Ltd. | Composition for coating layer, separator for rechargeable lithium battery including coating layer formed therefrom and rechargeable lithium battery including the same |
| JP2021103676A (en) * | 2020-04-17 | 2021-07-15 | 三井化学株式会社 | Coat material for secondary battery separator |
| JP7151938B2 (en) * | 2020-06-11 | 2022-10-12 | Dic株式会社 | Aqueous Resin Composition for Lithium Ion Secondary Battery Separator Heat-Resistant Layer Binder |
| EP4287298A1 (en) * | 2021-01-29 | 2023-12-06 | Zeon Corporation | Nonaqueous secondary battery |
| CN113131087B (en) * | 2021-04-12 | 2022-09-30 | 中国科学技术大学 | Bio-based lithium battery diaphragm and preparation method thereof |
| CN113122128B (en) * | 2021-04-12 | 2022-05-17 | 中国科学技术大学 | Heat-resistant bio-based lithium battery diaphragm and preparation method thereof |
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| CN108305970A (en) | 2018-07-20 |
| JP2018026266A (en) | 2018-02-15 |
| JP6579383B2 (en) | 2019-09-25 |
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