CN110088943B - Core-shell particles, use thereof, and method for producing same - Google Patents

Core-shell particles, use thereof, and method for producing same Download PDF

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CN110088943B
CN110088943B CN201880005040.1A CN201880005040A CN110088943B CN 110088943 B CN110088943 B CN 110088943B CN 201880005040 A CN201880005040 A CN 201880005040A CN 110088943 B CN110088943 B CN 110088943B
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core
polymer
structural unit
shell
formula
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CN110088943A (en
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冈田佳余子
长泽善幸
及川彩
铃木梦乃
小林正太
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Kureha Corp
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
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    • C08F2/16—Aqueous medium
    • C08F2/22—Emulsion polymerisation
    • C—CHEMISTRY; METALLURGY
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    • C08F214/00—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 a halogen
    • C08F214/18—Monomers containing fluorine
    • C08F214/22—Vinylidene fluoride
    • C—CHEMISTRY; METALLURGY
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    • C08F216/00—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 an alcohol, ether, aldehydo, ketonic, acetal or ketal radical
    • C08F216/12—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 an alcohol, ether, aldehydo, ketonic, acetal or ketal radical by an ether radical
    • C08F216/14—Monomers containing only one unsaturated aliphatic radical
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    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
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    • C08F259/00—Macromolecular compounds obtained by polymerising monomers on to polymers of halogen containing monomers as defined in group C08F14/00
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    • C—CHEMISTRY; METALLURGY
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    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L27/00—Compositions of 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 a halogen; Compositions of derivatives of such polymers
    • C08L27/02—Compositions of 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 a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment
    • C08L27/12—Compositions of 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 a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • C08L27/16—Homopolymers or copolymers or vinylidene fluoride
    • 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
    • C09D127/00—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 a halogen; Coating compositions based on derivatives of such polymers
    • C09D127/02—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 a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment
    • C09D127/12—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 a halogen; Coating compositions based on derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • C09D127/16—Homopolymers or copolymers of vinylidene fluoride
    • 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
    • C09D133/02—Homopolymers or copolymers of acids; Metal or ammonium salts thereof
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    • C09D5/00—Coating compositions, e.g. paints, varnishes or lacquers, characterised by their physical nature or the effects produced; Filling pastes
    • 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
    • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
    • C09D7/40—Additives
    • 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
    • C09D7/00—Features of coating compositions, not provided for in group C09D5/00; Processes for incorporating ingredients in coating compositions
    • C09D7/40—Additives
    • C09D7/43—Thickening agents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • 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
    • H01M50/423—Polyamide resins
    • H—ELECTRICITY
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    • 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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    • 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
    • H01M50/443—Particulate material
    • H—ELECTRICITY
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    • 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
    • H01M50/446—Composite material consisting of a mixture of organic and inorganic materials
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    • 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
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    • 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
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    • H01M50/457—Separators, membranes or diaphragms characterised by the material having a layered structure comprising three or more layers
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    • 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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Abstract

Provided are vinylidene fluoride particles which provide an adhesive layer having sufficient adhesiveness and which can reduce the occurrence of clogging in pores on the surface of a separator even when subjected to a hot-pressing step. The core-shell particle of the present invention includes a core portion including a first polymer having a vinylidene fluoride-derived structural unit as a main structural unit, and a shell portion surrounding the core portion and including a second polymer having a vinylidene fluoride-derived structural unit as a main structural unit, the second polymer further including at least one of a structural unit derived from a compound represented by the following formula (1), a structural unit derived from a compound represented by the following formula (2), and a structural unit derived from a compound represented by the following formula (3). [ chemical formula 1]

Description

Core-shell particles, use thereof, and method for producing same
Technical Field
The present invention relates to a core-shell particle, a dispersion, a coating composition, a separator, a secondary battery, and a method for producing a core-shell particle.
Background
In recent years, development of electronic technology has been remarkable, and high functionality of small portable devices has been advanced. Therefore, power supplies used for these devices are required to be reduced in size and weight, that is, to have high energy density. As a battery having a high energy density, a nonaqueous electrolyte secondary battery represented by a lithium ion secondary battery or the like is widely used.
In addition, from the viewpoint of global environmental problems and energy saving, nonaqueous electrolyte secondary batteries are also used in hybrid vehicles in which a secondary battery is combined with an engine, electric vehicles in which a secondary battery is used as a power source, and the like, and their applications are expanding.
A separator is provided between electrodes (positive electrode and negative electrode) of a nonaqueous electrolyte secondary battery. If a gap is formed between the electrode and the separator, the cycle life may be deteriorated. Therefore, it is required to improve the adhesiveness of the adhesive portion of the electrode, the separator, and the like.
Therefore, a separator having improved adhesion to an electrode has been developed (for example, patent document 1). Patent document 1 discloses a nonaqueous secondary battery separator having excellent ion permeability and handling properties and improved adhesion to an electrode by providing an adhesive layer, which is an aggregate layer containing a predetermined amount of fine particles of a polyvinylidene fluoride (PVDF) resin, on at least one surface of a porous base material.
Documents of the prior art
Patent document
Patent document 1: international publication No. 2013/073503 (published 5 months and 23 days in 2013)
Disclosure of Invention
Problems to be solved by the invention
However, in the separator for a nonaqueous secondary battery described in patent document 1, when hot pressing is performed in the battery production process, fine particles containing a PVDF resin are crushed by melting, and the pores on the surface of the porous base material constituting the separator are clogged. As a result, there is a problem that the ion permeability of the separator is deteriorated.
The present invention has been made in view of the above problems, and an object of the present invention is to provide vinylidene fluoride particles which have high adhesiveness to an electrode and which can reduce clogging of pores on the surface of a separator even after a hot-pressing step.
Technical scheme
In order to solve the above problems, a core-shell particle of the present invention includes a core portion including a first polymer having a vinylidene fluoride-derived structural unit as a main structural unit, and a shell portion surrounding the core portion and including a second polymer having a vinylidene fluoride-derived structural unit as a main structural unit, the second polymer further including at least any one of a structural unit derived from a compound represented by the following formula (1), a structural unit derived from a compound represented by the following formula (2), and a structural unit derived from a compound represented by the following formula (3).
[ chemical formula 1]
Figure BDA0002093732350000021
(in the formula (1), R1、R2And R3Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, X1Is an atomic group having a main chain consisting of 1 to 19 atoms and a molecular weight of 472 or less, and contains at least one hetero atom selected from an oxygen atom and a nitrogen atom)
[ chemical formula 2]
Figure BDA0002093732350000022
(in the formula (2), R4、R5And R6Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, X2Is an atomic group having a main chain consisting of 1 to 19 atoms and having a molecular weight of 484 or less, and containing at least one hetero atom selected from an oxygen atom and a nitrogen atom)
[ chemical formula 3]
Figure BDA0002093732350000031
(in the formula (3), R7、R8And R9Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, R10A hydrogen atom or a hydrocarbon moiety of 1 to 5 carbon atoms containing at least one hydroxyl group)
In addition, a dispersion liquid containing the core-shell particles of the present invention and a dispersion medium is also included in the present invention.
In addition, a coating composition for forming a porous fluororesin layer provided on at least one surface of a separator provided between a negative electrode layer and a positive electrode layer in a secondary battery, the coating composition containing the core-shell particles of the present invention, is also included in the present invention.
Further, a separator having the coating composition of the present invention applied to at least one surface of the separator is also included in the present invention.
Further, a secondary battery provided with a fluororesin layer formed of the coating composition of the present invention, the fluororesin layer having a layer containing the second polymer formed by hot-pressing the negative-electrode layer, the positive-electrode layer and the separator, the layer containing the second polymer containing particles containing the first polymer, is also included in the present invention.
In addition, a coating composition for forming a fluororesin layer provided on at least one surface of at least one of a negative electrode layer and a positive electrode layer in a secondary battery so as to be in contact with a separator provided between the negative electrode layer and the positive electrode layer, the coating composition containing the core-shell particles of the present invention is also included in the present invention.
In order to solve the above problems, a method for producing a core-shell particle according to the present invention is a method for producing a core-shell particle including a core portion and a shell portion surrounding the core portion, the method including: a core portion forming step of forming a core portion including a first polymer having a vinylidene fluoride-derived structural unit as a main structural unit; and a shell section forming step of forming a shell section including a second polymer having a structural unit derived from vinylidene fluoride as a main structural unit, wherein in the shell section forming step, a monomer constituting the second polymer including vinylidene fluoride and at least one of the compound represented by the formula (1), the compound represented by the formula (2), and the compound represented by the formula (3) is subjected to a polymerization reaction in a dispersion liquid including a core section formed in the core section forming step, thereby forming the shell section around the core section.
Advantageous effects
According to the present invention, it is possible to provide vinylidene fluoride particles that provide an adhesive layer having high adhesiveness to an electrode and that can reduce clogging of pores on the surface of a separator even after a hot-pressing step.
Drawings
Fig. 1 is a diagram showing SEM images of examples and comparative examples.
Detailed Description
Hereinafter, one embodiment of the core-shell particles, the dispersion liquid, the coating composition, the separator, the secondary battery, and the method for producing the core-shell particles of the present invention will be described in detail.
[ core-shell type particles ]
In the present embodiment, the "core-shell particle" refers to a particle including a core portion and a shell portion surrounding the core portion.
(core part)
The core portion contains a first polymer having a structural unit derived from vinylidene fluoride as a main structural unit, and the core portion is vinylidene fluoride particles containing the first polymer. In the present specification, the "main structural unit" refers to a structural unit that occupies the largest proportion (mol%) among structural units constituting a polymer. In the present specification, the term "vinylidene fluoride particles" refers to particles of a polymer having a structural unit derived from vinylidene fluoride as a main structural unit, and the polymer includes a homopolymer of vinylidene fluoride and a copolymer of vinylidene fluoride and another monomer.
The proportion of the vinylidene fluoride-derived structural unit in the first polymer is preferably 95 mol% or more, and more preferably 98 mol% or more. In one example, the first polymer is particularly preferably composed only of a structural unit derived from vinylidene fluoride. When the vinylidene fluoride-derived structural unit is used as the main structural unit, it is preferable that the vinylidene fluoride-derived structural unit is 95 mol% or more, and the melting temperature of the first polymer in the presence of the electrolyte is higher than the temperature at which the hot pressing step described later is usually performed. As a result, the core-shell particles of the present embodiment have less core portions crushed (melted) in the hot pressing step. Here, the "melting temperature of the first polymer in the presence of the electrolytic solution" may be a temperature lower by, for example, about 60 ℃ to 70 ℃ than the melting point of the first polymer, although it is also influenced by the composition of the electrolytic solution.
The first polymer may further contain a structural unit derived from a compound other than vinylidene fluoride as another structural unit constituting the first polymer. Examples of compounds other than vinylidene fluoride include: halogenated alkyl vinyl compounds, hydrocarbon monomers, (poly) alkylene glycol dimethacrylate, (poly) alkylene glycol diacrylate, and polyvinyl benzene. Examples of the halogenated alkylvinyl compound include: specific examples of the fluorinated alkyl vinyl compound include: hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene, fluoroalkyl vinyl ether, and the like, among which hexafluoropropylene is preferable. Examples of the hydrocarbon-based monomer include: ethylene, propylene, styrene, and the like.
When a structural unit derived from a compound other than vinylidene fluoride is contained as another structural unit constituting the first polymer, the proportion of the structural unit derived from a compound other than vinylidene fluoride is, for example, preferably 5 mol% or less, and more preferably 2 mol% or less, from the viewpoint of reducing the possibility of impairing oxidation resistance and crystallinity. When the content of the structural unit derived from the halogenated alkyl vinyl compound is 2 mol% or less, the possibility of melt crushing of the core portion can be further reduced in the hot pressing step in the production of the battery.
The core portion may further contain a compound other than the first polymer. Examples of the compound other than the first polymer include: halogenated alkyl vinyl compounds, hydrocarbon monomers, (poly) alkylene glycol dimethacrylate, (poly) alkylene glycol diacrylate, polyvinyl benzene, crosslinking agents, and the like. Examples of the halogenated alkylvinyl compound include fluorinated alkylvinyl compounds, and specifically, include: hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene, fluoroalkyl vinyl ethers, and the like. Examples of the hydrocarbon-based monomer include: ethylene, propylene, styrene, and the like.
From the viewpoint of ion permeability, the melting point of the first polymer is preferably 150 ℃ or higher, more preferably 155 ℃ or higher, and still more preferably 160 ℃ or higher. The method for measuring the melting point of the first polymer of the present embodiment is described in examples described later.
The average particle diameter of the core portion is not particularly limited, and is, for example, 10nm or more and 1 μm or less. The method for measuring the average particle diameter of the core portion in the present embodiment is explained in the examples described later.
(Shell)
The shell portion contains a second polymer having a structural unit derived from vinylidene fluoride as a main structural unit. As the second polymer, a polymer different from the first polymer may be used. The second polymer further contains at least one of a structural unit derived from a compound represented by the following formula (1), a structural unit derived from a compound represented by the following formula (2), and a structural unit derived from a compound represented by the following formula (3).
[ chemical formula 4]
Figure BDA0002093732350000061
(in the formula (1), R1、R2And R3Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, X1Is an atomic group having a main chain consisting of 1 to 19 atoms and a molecular weight of 472 or less, and contains at least one hetero atom selected from an oxygen atom and a nitrogen atom)
[ chemical formula 5]
Figure BDA0002093732350000062
(in the formula (2), R4、R5And R6Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, X2Is an atomic group having a main chain consisting of 1 to 19 atoms and having a molecular weight of 484 or less, and containing at least one hetero atom selected from an oxygen atom and a nitrogen atom)
[ chemical formula 6]
Figure BDA0002093732350000071
(in the formula (3), R7、R8And R9Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, R10A hydrogen atom or a hydrocarbon moiety of 1 to 5 carbon atoms containing at least one hydroxyl group)
In the core-shell particle of the present embodiment, the second polymer further includes at least one of a structural unit derived from the compound represented by formula (1), a structural unit derived from the compound represented by formula (2), and a structural unit derived from the compound represented by formula (3), whereby the adhesion between the electrode and the fluororesin layer described later can be further improved. In addition, when the second polymer contains at least one of the structural unit derived from the compound represented by formula (1) and the structural unit derived from the compound represented by formula (2), the adhesiveness between the separator and the fluororesin layer can be further improved.
[ Compound represented by the formula (1) ]
R1、R2And R3Each independently represents a hydrogen atom, a chlorine atom or an alkyl group having 1 to 5 carbon atoms. Examples of the alkyl group having 1 to 5 carbon atoms include a methyl group, an ethyl group, a propyl group, and an isopropyl group. Wherein R is1Preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom. R2Preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom. R3Preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom.
Form X1The number of atoms of the main chain of (a) is 1 to 19, preferably 1 to 14, more preferably 1 to 9. Examples of the atoms constituting the main chain include carbon atoms and hetero atoms described later. The number of atoms in the main chain does not include the number of atoms of a hydrogen atom. Further, the number of atoms of the main chain means: linked by the smallest number of atoms described by X1The carboxyl group on the right side of (1) and the group shown in X1The left group of (R)1R2C＝CR3-the number of atoms in the backbone of the chain formed by CO-.
X1The molecular weight of the atomic group (b) is 472 or less, more preferably 172 or less. The lower limit of the molecular weight in the case of a radical is not particularly limited, but is usually 15.
Further, X1Containing at least one hetero atom selected from an oxygen atom and a nitrogen atom. The atomic group may contain at least one heteroatom, and may contain a plurality of heteroatoms. The hetero atom is preferably an oxygen atom from the viewpoint of copolymerizability with vinylidene fluoride. The hetero atom may be contained in both the main chain and the side chain of the atomic group, or may be contained in only one of them. In addition, the side chain of the atomic group may contain one or more carboxyl groups.
The compound represented by the formula (1) is preferably a compound represented by the following formula (4).
[ chemical formula 7]
Figure BDA0002093732350000081
(in the formula (4), R1、R2And R3Are respectively reacted with R in the formula (1)1、R2And R3Same as X3Is a group having a main chain of 1 to 18 atoms and a molecular weight of 456 or less)
X constituting the compound represented by the formula (4)3The number of atoms of the main chain of (a) is 1 to 18, preferably 1 to 13, more preferably 1 to 8. Examples of the atoms constituting the main chain include carbon atoms and hetero atoms described later. The number of atoms in the main chain does not include the number of atoms of a hydrogen atom. Further, the number of atoms of the main chain means: linked by the smallest number of atoms described by X3The carboxyl group on the right side of (1) and the group shown in X3The left group of (R)1R2C＝CR3The number of atoms in the skeleton of the chain formed by-CO-O-.
X of the Compound represented by the formula (4)3The molecular weight of the atomic group is 456 or less, preferably 156 or less. The lower limit of the molecular weight in the case of a radical is not particularly limited, but is usually 14.
Further, X3At least one hetero atom selected from an oxygen atom and a nitrogen atom may be contained, and a plurality of hetero atoms may be contained. The hetero atom may be contained in both the main chain and the side chain of the atomic group, or may be contained in only one of them.
Examples of the compound represented by the formula (1) include: acryloxypropylsuccinic acid, acryloxyethylsuccinic acid, methacryloxyethylsuccinic acid, methacryloxypropylsuccinic acid, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, acryloxyethyl phthalate, methacryloxyethyl phthalate, N-carboxyethyl (meth) acrylamide, carboxyethyl thio (meth) acrylate, and the like. The compound represented by formula (1) is preferably acryloxypropylsuccinic acid and/or acryloxyethylsuccinic acid from the viewpoint of adhesiveness between the electrode and the fluororesin layer and adhesiveness between the separator and the fluororesin layer.
[ Compound represented by the formula (2) ]
R4、R5And R6Each independently represents a hydrogen atom, a chlorine atom or an alkyl group having 1 to 5 carbon atoms. Examples of the alkyl group having 1 to 5 carbon atoms include a methyl group, an ethyl group, a propyl group, and an isopropyl group. Wherein R is4Preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom. R5Preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom. R6Preferably a hydrogen atom or a methyl group, more preferably a hydrogen atom.
Form X2The number of atoms of the main chain of (a) is 1 to 19, preferably 1 to 14, more preferably 1 to 9. Examples of the atoms constituting the main chain include carbon atoms and hetero atoms described later. The number of atoms in the main chain does not include the number of atoms of a hydrogen atom. Further, the number of atoms of the main chain means: linked by the smallest number of atoms described by X2The carboxyl group on the right side of (1) and the group shown in X2The left group of (R)4R5C＝CR6The number of atoms in the skeleton of the chain formed by-O-.
X2The molecular weight of the atomic group (b) is 484 or less, preferably 184 or less. The lower limit of the molecular weight in the case of a radical is not particularly limited, but is usually 15.
Further, X2Containing at least one hetero atom selected from an oxygen atom and a nitrogen atom. The atomic group may contain at least one heteroatom, and may contain a plurality of heteroatoms. The hetero atom is preferably an oxygen atom from the viewpoint of copolymerizability with vinylidene fluoride. The hetero atom may be contained in both the main chain and the side chain of the atomic group, or may be contained in only one of them. In addition, the side chain of the atomic group may contain one or more carboxyl groups.
Examples of the compound represented by the formula (2) include vinylcarboxyalkyl ethers, and specifically include: vinyl carboxylmethyl ether, and vinyl carboxyethyl ether.
[ Compound represented by the formula (3) ]
R7、R8And R9Each independently represents a hydrogen atom, a chlorine atom or an alkyl group having 1 to 5 carbon atoms. Examples of the alkyl group having 1 to 5 carbon atoms include a methyl group, an ethyl group, a propyl group, and an isopropyl group. Wherein R is7、R8And R9Each is preferably a hydrogen atom.
R10Is a hydrogen atom or a hydrocarbon moiety of 1 to 5 carbon atoms containing at least one hydroxyl group. Examples of the hydrocarbon moiety having 1 to 5 carbon atoms and including a hydroxyl group include a hydroxyethyl group, a hydroxypropyl group and the like.
Examples of the compound represented by the formula (3) include: acrylic acid, methacrylic acid, hydroxyethyl acrylate, and 2-hydroxypropyl acrylate, and the like. The compound represented by formula (3) is preferably acrylic acid from the viewpoint of adhesiveness between the electrode and the fluororesin layer and adhesiveness between the separator and the fluororesin layer.
[ other structural units ]
As another structural unit constituting the second polymer, the second polymer may further contain a structural unit derived from vinylidene fluoride and a compound other than the compounds represented by the above formulae (1) to (3). Examples of such compounds include: halogenated alkyl vinyl compounds, hydrocarbon monomers, (poly) alkylene glycol dimethacrylate, (poly) alkylene glycol diacrylate, and polyvinyl benzene.
Examples of the halogenated alkylvinyl compound include: specific examples of the fluorinated alkyl vinyl compound include: hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene, fluoroalkyl vinyl ether, and the like, among which hexafluoropropylene is preferable. Examples of the hydrocarbon-based monomer include: ethylene, propylene, styrene, and the like. By containing the halogenated alkyl vinyl compound, adhesiveness can be improved when the electrode is hot-pressed in a state of containing the electrolytic solution.
[ ratio of structural units ]
From the viewpoint of ion permeability, the proportion of the vinylidene fluoride-derived structural unit in the second polymer is preferably 50 mol% or more, more preferably 70 mol% or more, and still more preferably 90 mol% or more. From the viewpoint of adhesion, the content is preferably 99 mol% or less, more preferably 98 mol% or less, and still more preferably 95 mol% or less.
The total proportion of the structural unit derived from the compound represented by the above formula (1), the structural unit derived from the compound represented by the above formula (2), and the structural unit derived from the compound represented by the above formula (3) in the second polymer is not particularly limited, but is preferably 0.01 mol% or more, more preferably 0.02 mol% or more, and further preferably 0.03 mol% or more from the viewpoint of adhesion. From the viewpoint of productivity, the total ratio is preferably 5 mol% or less, more preferably 4 mol% or less, and still more preferably 3 mol% or less.
When a structural unit derived from a halogenated alkyl vinyl compound is contained as another structural unit constituting the second polymer, the proportion of the structural unit derived from the halogenated alkyl vinyl compound is not particularly limited, but from the viewpoint of adhesion, the proportion is preferably 0.5 mol% or more, more preferably 1 mol% or more, and further preferably 2 mol% or more. From the viewpoint of ion permeability, the ratio is preferably 50 mol% or less, more preferably 30 mol% or less, and still more preferably 20 mol% or less.
In addition, the shell portion may further contain a compound other than the second polymer. Examples of the compound other than the second polymer include: halogenated alkyl vinyl compounds, hydrocarbon monomers, (poly) alkylene glycol dimethacrylate, (poly) alkylene glycol diacrylate, polyvinyl benzene, crosslinking agents, and the like. Examples of the halogenated alkylvinyl compound include fluorinated alkylvinyl compounds, and specifically, include: hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene, fluoroalkyl vinyl ethers, and the like. Examples of the hydrocarbon-based monomer include: ethylene, propylene, styrene, and the like.
Structural unit of core-shell particle of the present embodimentCan be determined by detecting19Peak area ratio by F-NMR and absorbance ratio (IR ratio) ARTo obtain the final product. Peak area ratio and absorbance ratio (IR ratio) ARThe detection method (2) is explained in the examples described later.
Further, it is preferable that at least either one of the first polymer and the second polymer contains a structural unit derived from a halogenated alkyl vinyl compound. The proportion of the structural unit derived from the halogenated alkyl vinyl compound in the core-shell particles is not particularly limited, but is preferably 1 mol% or more, and more preferably 1.5 mol% or more. The ratio is preferably 5 mol% or less, and more preferably 3.5 mol% or less.
(melting Point of core-Shell type particle)
Preferably, the melting point of the first polymer is higher than the melting point of the second polymer. Therefore, the melting point of the core-shell particles is lower than that of the first polymer. The melting point of the core-shell particles is preferably 145 ℃ or higher, and preferably lower than 164 ℃. The method for measuring the melting point of the core-shell particles of the present embodiment is described in the examples below.
(particle diameter)
The average particle diameter of the core-shell particles of the present embodiment is not particularly limited, and is, for example, 10nm or more and 1 μm or less. The method for measuring the average particle diameter of the core-shell particles according to the present embodiment is described in the examples below.
(use)
The core-shell particles of the present embodiment are suitably used as a constituent material of a coating composition applied to a separator or an electrode in a secondary battery (particularly, a nonaqueous electrolyte secondary battery), for example.
By incorporating the core-shell particles of the present embodiment in the coating composition, as will be described later, high adhesion to the electrode is achieved, and the vinylidene fluoride particles contained in the core portion can be reduced from being crushed when hot-pressed in the battery production process. Therefore, even after the hot pressing step, the number of holes blocking the surface of the separator can be reduced.
[ method for producing core-shell particles ]
The method for producing core-shell particles of the present embodiment includes: a core portion forming step of forming a core portion including a first polymer; and a shell section forming step of forming a shell section containing a second polymer. In one example, the core-shell particles of the present embodiment described above can be produced by the method for producing core-shell particles of the present embodiment. Therefore, the description of the [ core-shell particle ] can be referred to as appropriate in the description of the [ method for producing core-shell particles ].
In the core portion forming step, vinylidene fluoride, which is a monomer constituting the first polymer, is polymerized. When a structural unit derived from a compound other than vinylidene fluoride is further included as a structural unit constituting the first polymer, the vinylidene fluoride and the other compound are polymerized.
When the total amount of all monomers in the core portion forming step is set to 100 parts by mass, the charge amount of vinylidene fluoride in the core portion forming step is preferably 90 parts by mass or more, more preferably 92 parts by mass or more, and still more preferably 95 parts by mass or more. Furthermore, vinylidene fluoride alone may be used.
When the halogenated alkyl vinyl compound is added as another compound, the amount of the halogenated alkyl vinyl compound charged is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and still more preferably 5 parts by mass or less, from the viewpoint of ion permeability, assuming that the total amount of all monomers in the core portion forming step is 100 parts by mass.
The core part obtained by the above polymerization may be used in the state of a dispersion liquid containing the particles obtained in the core part forming step as it is in the shell part forming step to be performed next, or may be used by being powdered by at least one method selected from salting out, freeze-grinding, spray-drying, freeze-drying and the like. In the case of using the polymer as it is, it may be dispersed in a dispersion medium for polymerization in the core portion forming step, or may be physically or chemically redispersed in a separately prepared dispersion medium such as water. The core portion of the powder may be physically or chemically redispersed in a dispersion medium such as water. The dispersion liquid containing an untreated core part or the dispersion liquid containing a core part treated by the above-mentioned operation or the like may further contain a surfactant, a pH adjuster, an anti-settling agent, a dispersion stabilizer, an anticorrosive agent, an antifungal agent, a wetting agent, or the like, and impurities may be removed by a dialysis membrane, an ion exchange resin, or the like.
In the shell section forming step, in the dispersion liquid containing the core section formed in the core section forming step, a monomer constituting the second polymer, which contains vinylidene fluoride and at least one of the compound represented by the above formula (1), the compound represented by the above formula (2) and the compound represented by the above formula (3), is subjected to a polymerization reaction. The timing of adding these monomers is not particularly limited, and all of the monomers may be added before the start of the polymerization reaction, a part of the monomers may be added after the start of the polymerization reaction, or a combination thereof may be added. In this polymerization, the polymerization is performed so that the monomers do not permeate into the first polymer particles. By doing so, it is possible to polymerize core-shell particles formed so that the second polymer surrounds the first polymer particles, without polymerizing polymer alloy particles having an IPN structure in which the first polymer and the second polymer are entangled with each other. By this polymerization, a shell is formed around the core of the vinylidene fluoride particles.
When the total amount of all monomers in the shell section forming step is 100 parts by mass, the charge amount of vinylidene fluoride in the shell section forming step is preferably 50 parts by mass or more, more preferably 60 parts by mass or more, and still more preferably 70 parts by mass or more.
In addition, from the viewpoint of adhesion, the total amount of the charged compounds of the compound represented by the formula (1), the compound represented by the formula (2), and the compound represented by the formula (3) is preferably 0.03 parts by mass or more, more preferably 0.1 parts by mass or more, and still more preferably 0.3 parts by mass or more, when the total amount of all the monomers in the shell section forming step is 100 parts by mass. From the viewpoint of manufacturability, the total amount of the charged materials is preferably 2 parts by mass or less, more preferably 1 part by mass or less, and still more preferably 0.5 part by mass or less.
When the halogenated alkyl vinyl compound is added as another compound, the amount of the halogenated alkyl vinyl compound charged is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 20 parts by mass or more, from the viewpoint of adhesion, assuming that the total amount of all monomers in the shell section forming step is 100 parts by mass. In addition, the charging amount is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and further preferably 30 parts by mass or less, from the viewpoint of ion permeability.
The core-forming step and the shell-forming step may be performed in the same reactor, or may be performed in separate reactors. When the core-portion forming step and the shell-portion forming step are continuously performed in the same reactor, for example, after the core-portion forming step is completed, the residual gas monomer in the reactor may be purged, and then the monomer or the like used in the shell-portion forming step may be added to the reactor.
In the core section forming step and the shell section forming step, the method of polymerizing the first polymer and the second polymer is not particularly limited, and examples thereof include conventionally known polymerization methods. Examples of the polymerization method include: suspension polymerization, emulsion polymerization, soap-free emulsion polymerization, miniemulsion polymerization, seeded emulsion polymerization, solution polymerization, and the like, and among them, emulsion polymerization, soap-free emulsion polymerization, miniemulsion polymerization, and seeded emulsion polymerization are particularly preferable. The method of polymerizing the first polymer may be the same as or different from the method of polymerizing the second polymer.
Emulsion polymerization is one of radical polymerization methods, and is a polymerization method in which a medium such as water, a monomer that is hardly soluble in the medium, and an emulsifier (hereinafter, also referred to as a surfactant) are mixed, and a polymerization initiator that is soluble in the medium is added thereto. In the emulsion polymerization, a dispersion medium, a surfactant, and a polymerization initiator may be used in addition to vinylidene fluoride and other monomers.
The suspension polymerization is a polymerization method in which an oil-soluble polymerization initiator is dissolved in a water-insoluble monomer in water containing a suspending agent or the like, and the resulting solution is suspended and dispersed by mechanical stirring. In the suspension polymerization, polymerization is carried out in monomer droplets, whereby vinylidene fluoride particles can be obtained.
The soap-free emulsion polymerization is emulsion polymerization performed without using a conventional emulsifier used in the above emulsion polymerization. The vinylidene fluoride particles obtained by soap-free emulsion polymerization are preferable because the emulsifier does not remain in the polymer particles.
The miniemulsion polymerization is a polymerization method in which monomer droplets are finely divided into submicron sizes by applying a strong shearing force using an ultrasonic oscillator or the like. In miniemulsion polymerization, a poorly water-soluble substance called a hydrophobe (hydrophobe) is added in order to stabilize the finely divided monomer droplets. In a preferred miniemulsion polymerization, the monomer droplets are polymerized to form fine particles of the vinylidene fluoride polymer.
The seed emulsion polymerization is a polymerization in which the fine particles obtained by the above-described polymerization method are covered with a polymer composed of another monomer. In the dispersion liquid of the fine particles, vinylidene fluoride, other monomers, a dispersion medium, a surfactant, a polymerization initiator, and the like can be further used.
[ dispersing Medium ]
The usable dispersion medium is not particularly limited, and for example, a conventionally known dispersion medium can be used, but water is preferably used as the dispersion medium.
[ surfactant ]
The surfactant to be used may be any of a nonionic surfactant, a cationic surfactant, an anionic surfactant, and an amphoteric surfactant, or a combination of a plurality of surfactants may be used. As the surfactant, a per-fluorinated surfactant, a partially fluorinated surfactant, a non-fluorinated surfactant, and the like, which have been conventionally used for polymerization of polyvinylidene fluoride, are suitable. Among them, preferred are perfluoroalkyl sulfonic acids and salts thereof, perfluoroalkyl carboxylic acids and salts thereof, and fluorine-based surfactants having fluorocarbon chains or fluoropolyether chains, and more preferred are perfluoroalkyl carboxylic acids and salts thereof. In the present embodiment, one kind or two or more kinds of emulsifiers can be used alone.
The amount of the emulsifier added is preferably 0.005 to 22 parts by mass, more preferably 0.2 to 20 parts by mass, assuming that the total amount of all monomers used for polymerization is 100 parts by mass.
[ polymerization initiator ]
The polymerization initiator that can be used is not particularly limited, and, for example, a conventionally known polymerization initiator can be used. As the polymerization initiator, for example, a water-soluble peroxide, a water-soluble azo compound or a redox initiator system can be used. Examples of the water-soluble peroxide include ammonium persulfate and potassium persulfate. Examples of the water-soluble azo compound include AIBN and AMBN. Examples of the redox initiator system include ascorbic acid-hydrogen peroxide. The polymerization initiator is preferably a water-soluble peroxide. The polymerization initiator may be used singly or in combination of two or more.
The amount of the polymerization initiator added is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 4 parts by mass, assuming that the total amount of all monomers used for polymerization is 100 parts by mass.
[ other ingredients ]
In the emulsion polymerization, a chain transfer agent may be used in order to adjust the degree of polymerization of the obtained core-shell particles. Examples of the chain transfer agent include: ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propionaldehyde, ethyl propionate, carbon tetrachloride, and the like.
Further, a pH adjuster may be used as needed. Examples of the pH adjuster include: electrolyte substances having a buffering capacity such as sodium dihydrogen phosphate, disodium hydrogen phosphate, and potassium dihydrogen phosphate, and alkaline substances such as sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, and ammonia.
Further, a settling inhibitor, a dispersion stabilizer, an anticorrosive agent, a mildewproofing agent, a wetting agent, and the like may be used as necessary.
The amount of the other components added is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 7 parts by mass, assuming that the total amount of all monomers used for polymerization is 100 parts by mass.
(polymerization conditions)
The polymerization temperature may be appropriately selected depending on the kind of the polymerization initiator, and for example, may be set in the range of 0 ℃ to 120 ℃, preferably in the range of 20 ℃ to 110 ℃, and more preferably in the range of 40 ℃ to 100 ℃.
Further, the polymerization pressure may be set, for example, in the range of 0MPa to 10MPa, preferably in the range of 0.5MPa to 8MPa, and more preferably in the range of 1MPa to 6 MPa.
The polymerization time is not particularly limited, but is preferably in the range of 1 hour to 24 hours in view of productivity and the like.
[ Dispersion liquid ]
The dispersion liquid of the present embodiment contains the core-shell particles of the present embodiment and a dispersion medium.
The dispersion medium in the dispersion liquid of the present embodiment is preferably water, for example, but is not particularly limited as long as it is a mixed liquid of water and an arbitrary nonaqueous solvent mixed with water, and it is a liquid that can be dispersed, suspended, or emulsified without dissolving the vinylidene fluoride resin. Examples of the nonaqueous solvent include: amide compounds such as N-methylpyrrolidone, dimethylformamide and N, N-dimethylacetamide; hydrocarbons such as toluene, xylene, n-dodecane, and tetralin; alcohols such as methanol, ethanol, isopropanol, 2-ethyl-1-hexanol, 1-nonanol and lauryl alcohol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, phorone, acetophenone, and isophorone; esters such as benzyl acetate, isoamyl butyrate, methyl lactate, ethyl lactate, and butyl lactate; amine compounds such as o-toluidine, m-toluidine and p-toluidine; lactones such as γ -butyrolactone and-butyrolactone; sulfoxide compounds and sulfone compounds such as dimethyl sulfoxide and sulfolane; and tetrahydrofuran, ethyl acetate, and the like. The nonaqueous solvent can be used by mixing with water at an arbitrary ratio. Water may be used alone or as a mixed dispersion medium obtained by mixing water with one or more nonaqueous solvents.
Further, a pH adjuster, a sedimentation inhibitor, a dispersion stabilizer, an anticorrosive agent, a mildewproofing agent, a wetting agent, and the like may be used as necessary.
The content of the core-shell particles in the dispersion of the present embodiment is preferably 60 parts by mass or less, assuming that the total amount of the dispersion is 100 parts by mass.
[ coating composition ]
The coating composition of the present embodiment is a composition for forming a porous fluororesin layer that improves the adhesion between an electrode and a separator in a secondary battery including a negative electrode layer, a positive electrode layer (electrode), and a separator provided between the negative electrode layer and the positive electrode layer.
The coating composition of the present embodiment includes the core-shell particles of the present embodiment. The coating composition of the present embodiment may contain only the core-shell particles, or may further contain a dispersion medium in which the core-shell particles are dispersed. Specific descriptions of the dispersion medium can be found in the column "dispersion" above. In one example, the coating composition of the present embodiment may be the dispersion liquid described above.
In the preparation of the coating composition of the present embodiment, the core-shell particles may be pulverized by at least one method selected from salting out, freeze-grinding, spray-drying, freeze-drying and the like to be used as a coating composition as it is, or the core-shell particles thus pulverized may be physically or chemically redispersed in a dispersion medium such as water to be used as a coating composition. Alternatively, a dispersion liquid in which the core-shell particles are dispersed in a dispersion medium used for polymerization may be used as it is as a coating composition, or the core-shell particles may be physically or chemically redispersed in a separately prepared dispersion medium such as water as a coating composition.
In the case of using the dispersion medium, the content of the dispersion medium contained in the coating composition is preferably 65 to 3500 parts by mass, more preferably 300 to 2000 parts by mass, assuming that the content of the core-shell particles is 100 parts by mass.
The coating composition of the present embodiment may contain a filler as needed. The heat resistance of the separator can be improved by containing the filler. As the filler, for exampleSuch as the following: silicon dioxide (SiO)2) Alumina (Al)2O3) Titanium dioxide (TiO)2) Calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), magnesium oxide (MgO), zinc oxide (ZnO), barium titanate (BaTiO)3) And oxides, etc.; magnesium hydroxide (Mg (OH)2) Calcium hydroxide (Ca (OH)2) Zinc hydroxide (Zn (OH)2) Aluminum hydroxide (Al (OH)3) Hydroxides such as aluminum metahydroxide (AlO (OH)); calcium carbonate (CaCO)3) And carbonates; sulfates such as barium sulfate; a nitride; a clay mineral; and boehmite, and the like. The filler is preferably alumina, silica, magnesium oxide, magnesium hydroxide, magnesium carbonate, zinc oxide, or boehmite, from the viewpoint of battery safety and coating liquid stability. The filler may be used alone or in combination of two or more.
In addition, the coating composition of the present embodiment may further contain a tackifier. The viscosity of the coating composition can be adjusted and the dispersibility of the core-shell particles and the filler can be improved by containing the thickener. Examples of the thickener include: cellulose compounds such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl cellulose; ammonium salts or alkali metal salts of the above cellulose compounds; polycarboxylic acids such as poly (meth) acrylic acid and modified poly (meth) acrylic acid; alkali metal salts of the above polycarboxylic acids; polyvinyl alcohol (co) polymers such as polyvinyl alcohol, modified polyvinyl alcohol, and ethylene-vinyl alcohol copolymers; and water-soluble polymers such as saponified copolymers of unsaturated carboxylic acids such as (meth) acrylic acid, maleic acid, and fumaric acid with polyvinylpyrrolidone, polyvinyl butyral, and vinyl ester. Among them, cellulose compounds and salts thereof are preferable. The tackifier may be used alone, or two or more thereof may be used.
When the filler is contained, the content of the filler is preferably 10 to 900 parts by mass, assuming that the content of the core-shell particles is 100 parts by mass.
When the thickener is contained, the content of the thickener is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, assuming that the total amount of the core-shell particles, the filler, and the thickener is 100 parts by mass.
The coating composition of the present embodiment may further contain a surfactant, a pH adjuster, an anti-settling agent, an anti-corrosion agent, a dispersion stabilizer, an anti-mold agent, a wetting agent, an antifoaming agent, and the like, as necessary.
[ fluororesin layer ]
The fluororesin layer in the present embodiment is formed by applying the coating composition of the present embodiment to a separator or an electrode and drying the coating composition. Specifically, first, the coating composition is applied to at least one surface of either the separator or the electrode, and the applied coating composition is dried. The dried separator and electrode are stacked, and the stack is placed in a package together with an electrolyte and other necessary members, and the separator and electrode are bonded by hot pressing together with the package. At this stage, the shell portion of the core-shell particle is melted by heat to form a fluororesin layer.
The thickness of the fluororesin layer is not particularly limited, but is preferably 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 9.5 μm or less, and still more preferably 0.3 μm or more and 9 μm or less. The coating composition of the present embodiment is applied so that the film thickness of the fluororesin layer falls within the above range.
Examples of the method for applying the coating composition include: a doctor blade method, a reverse roll method, a comma bar method, an intaglio method, an air knife method, a die coating method, a dip coating method, and the like. The drying treatment of the coating film is preferably performed at a temperature ranging from 40 ℃ to 150 ℃, more preferably from 45 ℃ to 130 ℃, preferably at a treatment time ranging from 1 minute to 500 minutes, more preferably from 2 minutes to 300 minutes.
The fluororesin layer in the present embodiment may be provided between the negative electrode layer and the separator, between the separator and the positive electrode layer, or both.
The fluororesin layer in this embodiment is an adhesive layer. The fluororesin layer in the present embodiment can provide sufficient adhesion between the separator and the electrode by being provided between the separator and the electrode. The peel strength between the electrode and the separator provided with the fluororesin layer in the present embodiment is, for example, 0.2gf/mm to 2.7 gf/mm. The method of measuring the peel strength is described in examples below.
The fluororesin layer in the present embodiment contains a layer containing a molten second polymer after a step of hot pressing, which is a part of the manufacturing steps of the nonaqueous electrolyte battery described later. That is, in one example, the fluororesin layer has a layer containing the second polymer formed by hot-pressing the negative electrode layer, the positive electrode layer, and the separator. The layer comprising the second polymer contains particles comprising the first polymer. With such a structure, even after the hot pressing step, the number of holes blocking the surface of the separator can be reduced. Therefore, the fluororesin layer in the present embodiment is porous. It can be confirmed by SEM observation that: with the fluororesin layer in this embodiment, the pores on the surface of the separator are not clogged. The method for producing the fluororesin layer-coated separator for SEM observation is described in examples described later.
[ diaphragm ]
The separator of the present embodiment is electrically stable and does not have conductivity. In addition, the separator of the present embodiment can use a porous base material having pores or voids inside, and is excellent in ion permeability. Examples of the porous substrate include: single-layer or multilayer porous membranes comprising polyolefin polymers (e.g., polyethylene, polypropylene, etc.), polyester polymers (e.g., polyethylene terephthalate, etc.), polyimide polymers (e.g., aromatic polyamide polymers, polyether imides, etc.), polyether sulfones, polysulfones, polyether ketones, polystyrenes, polyethylene oxides, polycarbonates, polyvinyl chlorides, polyacrylonitriles, polymethyl methacrylates, ceramics, etc., and mixtures of at least two of these; non-woven fabrics; glass; and paper and the like. The polymer may be a modified polymer.
The porous substrate preferably contains a polyolefin polymer (e.g., polyethylene, polypropylene, etc.). The porous substrate more preferably contains polyethylene from the viewpoint of shutdown function, and more preferably contains polyethylene and polypropylene from the viewpoint of both shutdown function and heat resistance, and further preferably contains 95 mass% or more of polyethylene and 5 mass% or less of polypropylene.
From the viewpoint of mechanical properties and internal resistance, the thickness of the porous substrate is preferably 3 μm to 25 μm, and more preferably 5 μm to 25 μm.
The surface of the porous substrate may be subjected to corona treatment, plasma treatment, flame treatment, ultraviolet irradiation treatment, or the like for the purpose of improving wettability with the coating composition.
In one example, the separator of the present embodiment is coated with the coating composition of the present embodiment on at least one of the surfaces facing the negative electrode layer and the positive electrode layer.
[ electrode ]
The negative electrode layer and the positive electrode layer in the present embodiment are not particularly limited, and for example, known negative electrode layers and known positive electrode layers in secondary batteries can be used.
In one example, the negative electrode layer and the positive electrode layer are formed by providing a layer of the electrode mixture on the current collector. The electrode mixture layer may be formed on at least one surface of the current collector.
The electrode material mixture can contain, for example, an electrode active material and a binder composition.
The electrode active material is not particularly limited, and for example, a conventionally known electrode active material for a negative electrode (negative electrode active material) or an electrode active material for a positive electrode (positive electrode active material) can be used.
Examples of the negative electrode active material include: a carbon material such as artificial graphite, natural graphite, non-graphitizable carbon, activated carbon, or a substance obtained by firing and carbonizing a phenol resin, pitch, or the like; metal materials and alloy materials such as Cu, Li, Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr, and Y; and GeO, GeO2、SnO、SnO2PbO and PbO2And the like.
As the positive electrode active material, a lithium-based positive electrode active material containing at least lithium is preferable. Examples of the lithium-based positive electrode active material include: for example from LiCoO2、LiNixCo1-xO2(0≤x≤1)、LiNiCoMnO2Of the general formula LiMY2(M is at least one of transition metals such as Co, Ni, Fe, Mn, Cr, and V, and Y is a chalcogen such as O, S); LiMn2O4And the like, a spinel-structured composite metal oxide; and LiFePO4And other olivine-type lithium compounds.
Examples of the binder composition include: the adhesive composition contains at least one of a cellulose compound such as a vinylidene fluoride polymer, Polytetrafluoroethylene (PTFE), Styrene Butadiene Rubber (SBR), polyacrylic acid, polyimide, and carboxymethyl cellulose, an ammonium salt and an alkali metal salt of the cellulose compound, and Polyacrylonitrile (PAN).
The electrode mixture may further contain a conductive additive such as carbon black, acetylene black, ketjen black, graphite powder, carbon fiber, or carbon nanotube; pigment dispersants such as polyvinylpyrrolidone; and an adhesion promoter such as polyacrylic acid or polymethacrylic acid.
The current collector is a base material of the negative electrode layer and the positive electrode layer, and is a terminal for drawing electricity. The material of the current collector is not particularly limited, and a metal foil, a metal steel, or the like of aluminum, copper, iron, stainless steel, nickel, titanium, or the like can be used. The thickness of the current collector is not particularly limited, and is preferably 5 μm to 100 μm, and more preferably 5 μm to 70 μm.
The thickness of the electrode material mixture layer is not particularly limited, and is usually 6 μm to 1000 μm, preferably 7 μm to 500 μm.
In the electrode of the present embodiment, the fluororesin layer may be provided so as to be in contact with the separator in at least either one of the negative electrode layer and the positive electrode layer, and in one example, is preferably provided in the positive electrode layer. In the electrode according to the present embodiment, in one example, the coating composition according to the present embodiment is applied to at least one surface of at least one of the negative electrode layer and the positive electrode layer.
[ electrolyte ]
The electrolyte used in the secondary battery in the present embodiment is not particularly limited, and for example, a known electrolyte in a secondary battery can be used. Examples of the electrolyte include: LiPF6、LiBF4、LiClO4、LiAsF6、LiSbF6、LiCF3SO3、Li(CF3SO2)2N、LiC4F9SO3、Li(CF3SO2)3C. And LiBPh4And the like. In the secondary battery in the present embodiment, an electrolytic solution in which an electrolyte is dissolved in a nonaqueous solvent can also be used. Examples of the nonaqueous solvent include: cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and difluoroethylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, methylethyl carbonate, and fluoro-substituted products thereof; cyclic esters such as γ -butyrolactone and γ -valerolactone; and mixed solvents thereof, and the like.
[ Secondary Battery ]
The secondary battery of the present embodiment may be provided with a fluororesin layer formed of the coating composition of the present embodiment. In one example, the separator is the separator described above. In one example, the electrode is the electrode described above.
The secondary battery of the present embodiment can be classified according to the type of electrolyte, for example. Specifically, for example, a nonaqueous electrolyte secondary battery, a solid electrolyte secondary battery, and the like are cited, and among them, a nonaqueous electrolyte secondary battery is preferable.
The nonaqueous electrolyte secondary battery of the present embodiment includes, for example, a polymer battery containing a gel electrolyte. Other members of the nonaqueous electrolyte secondary battery are not particularly limited, and, for example, conventionally used members can be used.
Examples of the method for producing the nonaqueous electrolyte secondary battery include: and (3) laminating the negative electrode layer and the positive electrode layer with a diaphragm interposed therebetween, loading the laminated sheets into a battery container, and injecting an electrolyte into the battery container to seal the battery container. In this production method, a part (preferably only the shell portion) of the core-shell particles contained in the coating composition is melted by hot pressing after the electrolyte injection, and the electrode and the separator are bonded to each other through the formed fluororesin layer.
The temperature of the hot pressing is determined by the melting temperature of the first polymer and the melting temperature of the core-shell particles, and may be, for example, 30 ℃ to 150 ℃. The pressure of the hot pressing is not particularly limited, and may be, for example, 1 to 30 MPa.
According to the core-shell particles of the present embodiment, since the melting temperature of the first polymer in the presence of the electrolyte is higher than the temperature of the hot pressing, the possibility of crushing the vinylidene fluoride particles in the core portion by the hot pressing can be reduced.
[ conclusion ]
As described above, the core-shell particle according to one embodiment of the present invention includes a core portion including a first polymer having a vinylidene fluoride-derived structural unit as a main structural unit, and a shell portion surrounding the core portion, the shell portion including a second polymer having a vinylidene fluoride-derived structural unit as a main structural unit, the second polymer further including at least one of a structural unit derived from the compound represented by formula (1), a structural unit derived from the compound represented by formula (2), and a structural unit derived from the compound represented by formula (3).
In the core-shell particle according to an embodiment of the present invention, the compound represented by the formula (1) is preferably a compound represented by the formula (4).
In the core-shell particle according to an embodiment of the present invention, it is preferable that the first polymer contained in the core portion and/or the second polymer contained in the shell portion further contain a structural unit derived from a halogenated alkyl vinyl compound.
In the core-shell particle according to an embodiment of the present invention, the melting point of the core-shell particle is preferably 145 ℃ or higher.
In the core-shell particle according to an embodiment of the present invention, it is preferable that the structural unit of the first polymer is only a structural unit derived from vinylidene fluoride.
An embodiment of the present invention also provides a dispersion liquid including the core-shell particles according to an embodiment of the present invention and a dispersion medium.
An embodiment of the present invention also provides a coating composition for forming a porous fluororesin layer provided on at least one surface of a separator provided between a negative electrode layer and a positive electrode layer in a secondary battery, the coating composition including the core-shell particles according to an embodiment of the present invention.
The coating composition according to an embodiment of the present invention may further contain an adhesion promoter.
The coating composition of an embodiment of the present invention may further contain a filler.
An embodiment of the present invention also provides a separator having the coating composition according to an embodiment of the present invention coated on at least one surface of the separator.
An embodiment of the present invention also provides a secondary battery provided with a fluororesin layer formed from the coating composition of an embodiment of the present invention, the fluororesin layer having a layer containing the second polymer formed by thermally pressing the negative electrode layer, the positive electrode layer and the separator, the layer containing the second polymer containing particles containing the first polymer.
An embodiment of the present invention also provides a coating composition for forming a fluororesin layer provided on at least one surface of at least one of a negative electrode layer and a positive electrode layer in a secondary battery so as to be in contact with a separator provided between the negative electrode layer and the positive electrode layer, the coating composition including the core-shell particles according to an embodiment of the present invention.
A method for producing a core-shell particle according to an embodiment of the present invention is a method for producing a core-shell particle including a core portion and a shell portion surrounding the core portion, the method including: a core portion forming step of forming a core portion including a first polymer having a vinylidene fluoride-derived structural unit as a main structural unit; and a shell section forming step of forming a shell section including a second polymer having a structural unit derived from vinylidene fluoride as a main structural unit, wherein in the shell section forming step, a monomer constituting the second polymer including vinylidene fluoride and at least one of the compound represented by the formula (1), the compound represented by the formula (2), and the compound represented by the formula (3) is subjected to a polymerization reaction in a dispersion liquid including a core section formed in the core section forming step, thereby forming the shell section around the core section.
The following examples are provided to further explain embodiments of the present invention in detail. It is needless to say that the present invention is not limited to the following examples, and various modifications can be made in the details. The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and embodiments obtained by appropriately combining the respective disclosed technical means are also included in the technical scope of the present invention. In addition, the documents described in the present specification are all cited as reference.
Examples
As described below, core-shell particles and vinylidene fluoride particles (hereinafter collectively referred to as fluoropolymer particles) of the present invention were produced, and the physical properties of the fluoropolymer particles were measured. Further, a separator was produced using the fluoropolymer particles, and a peel strength test and SEM observation were performed using the separator. Before describing specific examples, the following description will be made of a method for calculating the "solid content concentration" and the "particle size" in the present specification.
[ concentration of solid component ]
About 5g of a dispersion containing fluoropolymer particles prepared by polymerization (hereinafter also referred to as a latex) was placed in an aluminum cup, dried at 80 ℃ for 3 hours, and the concentration was calculated by measuring the weight before and after drying.
[ particle diameter ]
The particle size of the fluoropolymer particles was calculated by regularization analysis by a dynamic light scattering method. Specifically, the particle size was measured in accordance with JIS Z8828 using "delsa maxcore" manufactured by BECKMAN COULTER corporation, and the larger of the two peaks obtained by regularization analysis was taken as the particle size.
< preparation of fluoropolymer particles >
The following describes the production methods of the fluoropolymer particles in the examples and comparative examples.
[ example 1]
Polymerization of core part: 280 parts by mass of ion-exchanged water was charged into an autoclave, and degassing was performed by bubbling nitrogen gas for 30 minutes. Subsequently, 0.2 parts by mass of disodium hydrogenphosphate and 1.0 parts by mass of perfluorooctanoic acid ammonium salt (PFOA) were charged, and pressurized to 4.5MPa to carry out tertiary nitrogen substitution. Ethyl acetate 0.05 parts by mass and vinylidene fluoride (VDF)35 parts by mass were added to the autoclave. After raising the temperature to 80 ℃ with stirring, a 5 wt% aqueous solution of ammonium persulfate was charged in an amount corresponding to 0.06 part by mass in terms of ammonium persulfate, and polymerization was started. The pot pressure at this time was 4.3 MPa. After the reaction was started, when the pressure was reduced to 2.5MPa, 65 parts by mass of VDF were continuously added so that the pressure in the pot was maintained at 2.5 MPa. After the completion of the addition, the polymerization was terminated when the pressure was reduced to 1.5MPa, and a latex containing particles of a core portion was obtained. The resulting latex had a solid content of 24.0 wt% and a particle diameter of 140 nm.
Polymerization of the shell portion: 700 parts by mass of ion-exchanged water was charged into an autoclave, and degassing was performed by bubbling nitrogen gas for 30 minutes. Then, 100 parts by mass of the water-dispersed core particles and 0.5 part by mass of PFOA were charged, and pressurized to 4.5MPa to carry out nitrogen substitution three times. Ethyl acetate 0.05 parts by mass, VDF 70 parts by mass, Hexafluoropropylene (HFP)30 parts by mass, and acryloxypropylsuccinic Acid (APS)0.06 parts by mass were added to the autoclave. After raising the temperature to 80 ℃ with stirring, a 5 wt% aqueous solution of ammonium persulfate was charged in an amount corresponding to 0.1 part by mass of ammonium persulfate, and polymerization was started. The pot pressure at this time was 3.3 MPa. After the reaction was started, the polymerization of the shell portion was terminated when the pressure was reduced to 1.5MPa, and a latex containing core-shell particles was obtained. The resulting latex had a solid content of 13.5 wt% and a particle diameter of 170 nm.
[ example 2]
Polymerization of core part: vinylidene fluoride particles having a core portion were obtained in the same manner as in example 1.
Polymerization of the shell portion: polymerization was carried out in the same manner as in example 1 except that VDF was changed from 70 parts by mass to 78 parts by mass, HFP was changed from 30 parts by mass to 22 parts by mass, and APS was changed from 0.06 part by mass to 0.1 part by mass, thereby obtaining a latex containing core-shell particles. The resulting latex had a solid content of 13.3 wt% and a particle diameter of 170 nm.
[ example 3]
Polymerization of core part: vinylidene fluoride particles having a core portion were obtained in the same manner as in example 1.
Polymerization of the shell portion: polymerization was carried out in the same manner as in example 2 except that 0.1 part by mass of ammonium persulfate was changed to 0.4 part by mass and 0.1 part by mass of APS was changed to 0.5 part by mass, thereby obtaining a latex containing core-shell particles. The resulting latex had a solid content of 13.3 wt% and a particle diameter of 170 nm.
[ example 4]
Polymerization of core part: vinylidene fluoride particles having a core portion were obtained in the same manner as in example 1.
Polymerization of the shell portion: polymerization was carried out in the same manner as in example 2 except that APS was changed to Acrylic Acid (AA), thereby obtaining a latex containing core-shell particles. The resulting latex had a solid content of 13.6 wt% and a particle diameter of 180 nm.
[ example 5]
Polymerization of core part: polymerization was carried out in the same manner as in example 1 except that VDF added to the autoclave was changed from 35 parts by mass to 30 parts by mass and HFP was further added by 5.0 parts by mass, to obtain a latex containing particles of a core portion. The resulting latex had a solid content of 21.5 wt% and a particle diameter of 140 nm.
Polymerization of the shell portion: polymerization was carried out in the same manner as in example 2 to obtain a latex containing core-shell particles. The resulting latex had a solid content of 13.1 wt% and a particle diameter of 170 nm.
[ example 6]
Polymerization of core part: vinylidene fluoride particles having a core portion were obtained in the same manner as in example 5.
Polymerization of the shell portion: polymerization was carried out in the same manner as in example 4 to obtain a latex containing core-shell particles. The resulting latex had a solid content of 13.2 wt% and a particle diameter of 170 nm.
[ example 7]
Polymerization of core part: polymerization was carried out in the same manner as in example 5 except that VDF added to the autoclave was changed from 30 parts by mass to 25 parts by mass and HFP was changed from 5.0 parts by mass to 10 parts by mass, to obtain a latex containing vinylidene fluoride particles in the core portion. The resulting latex had a solid content of 21.4 wt% and a particle diameter of 140 nm.
Polymerization of the shell portion: polymerization was carried out in the same manner as in example 2 to obtain a latex containing core-shell particles. The resulting latex had a solid content of 13.2 wt% and a particle diameter of 180 nm.
[ comparative example 1]
Polymerization of core part: vinylidene fluoride particles having a core portion were obtained in the same manner as in example 1.
Polymerization of the shell portion: polymerization was carried out in the same manner as in example 1 except that the polymerization of the shell portion was terminated when the pressure was reduced to 1.5MPa after the start of the reaction without adding APS, to obtain a latex containing core-shell particles. The resulting latex had a solid content of 13.5 wt% and a particle diameter of 170 nm.
[ comparative example 2]
Polymerization of core part: vinylidene fluoride particles having a core portion were obtained in the same manner as in example 1.
Polymerization of the shell portion: polymerization was carried out in the same manner as in example 2 except that the polymerization of the shell portion was terminated when the pressure was reduced to 1.5MPa after the start of the reaction without adding APS, to obtain a latex containing core-shell particles. The resulting latex had a solid content of 13.4 wt% and a particle diameter of 170 nm.
[ comparative example 3]
280 parts by mass of ion-exchanged water was charged into an autoclave, and degassing was performed by bubbling nitrogen gas for 30 minutes. Then, 0.5 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged and pressurized to 4.5MPa to conduct nitrogen substitution three times. Ethyl acetate 0.05 parts by mass, vinylidene fluoride (VDF)30 parts by mass, and HFP5.0 parts by mass were added to the autoclave. After raising the temperature to 80 ℃ with stirring, a 5 wt% aqueous solution of ammonium persulfate was charged in an amount corresponding to 0.1 part by mass of ammonium persulfate, and polymerization was started. The pot pressure at this time was 3.1 MPa. After the reaction was started, when the pressure in the pot was reduced to 2.5MPa, 65 parts by mass of VDF was continuously added so that the pressure in the pot was maintained at 2.5 MPa. At the time when 50 mass% or more of VDF was consumed by continuous addition, 0.06 parts by mass of APS was added. After the reaction was started, the polymerization was terminated when the pressure was reduced to 1.5MPa, and a latex containing vinylidene fluoride particles was obtained. The resulting latex had a solid content of 19.6 wt% and a particle diameter of 200 nm.
[ comparative example 4]
Polymerization was carried out in the same manner as in comparative example 3 except that PFOA was changed from 0.5 part by mass to 1.0 part by mass and APS was changed to AA, to obtain a latex containing vinylidene fluoride particles. The resulting latex had a solid content of 21.0 wt% and a particle diameter of 130 nm.
< measurement of physical Properties of fluoropolymer particles >
The measurement methods of the physical properties of the fluoropolymer particles in the examples and comparative examples are described below.
[ HFP introduction amount ]
The amount of HFP introduced into the fluoropolymer particles in the dispersion prepared by polymerization19F-NMR (manufactured by BRUKER) was measured. 40mg of fluoropolymer particles reduced in powder form by salting out was dissolved in acetone-d 69660 6960 mg to prepare a sample for measurement. CF derived from HFP unit3Some of the peaks correspond to two peaks around-70-to 80ppm, derived from the CF of VDF and HFP units (all monomers)2Some of the peaks correspond to peaks of-90 ppm or less. From these peak intensities, the amount of HFP introduced was determined by the following equation.
HFP incorporation [ wt% ], HFP peak area/total monomer peak area X100
[ Absorbance ratio (IR ratio) AR〕
The fluoropolymer particle-containing dispersions obtained in the examples and comparative examples were salted out with 0.5 mass% calcium chloride and dried in an oven at 80 ℃ to be powdered. The powdery fluoropolymer particles were hot-pressed at 200 ℃ to prepare a pressed sheet having a thickness of about 0.01. mu.m. An infrared spectrophotometer FT-730 (manufactured by horiba, Ltd.) was used at 1500cm-1To 4000cm-1IR spectrum of the prepared tabletAnd (4) carrying out measurement. IR ratio ARThe following equation was used.
AR＝A1760/A3020
In the above formula, A1760Is at 1760cm-1The absorbance of the stretching vibration derived from the carbonyl group detected in the vicinity thereof will be 1600cm-1To 1800cm-1The peak detected was regarded as absorbance derived from stretching vibration of the carbonyl group. A. the3020Is at 3020cm-1The absorbance of the stretching vibration derived from CH detected in the vicinity is 2900cm-1To 3100cm-1The peak detected was regarded as absorbance derived from stretching vibration of the carbonyl group. [ melting Point ]
The melting point of the fluoropolymer particles in the dispersion prepared by polymerization was measured in the form of a film. The film was produced by the following procedure. A mold having a length of 5 cm. times.width of 5 cm. times.thickness of 150 μm and about 1g of fluoropolymer particles powdered by salting out were sandwiched between two aluminum foils sprayed with a release agent, and the pressed foils were pressed at 200 ℃. The melting point was measured by using DSC ("DSC-1" manufactured by METTLER corporation) according to ASTM d 3418.
[ Peel Strength test ]
Using the fluoropolymer particles obtained in each example and each comparative example, a fluoropolymer particle-coated separator was produced, and a peel strength test was performed with respect to the electrodes (positive electrode and negative electrode). The following describes in detail the methods for producing the fluoropolymer particle-coated separator and the electrode.
(preparation of coating composition)
Water was added to 100 parts by weight of the fluoropolymer particles and 2 parts by weight of CMC (carboxymethylcellulose) (Celogen 4H, first industrial pharmaceutical product), to prepare a composition having a solid content concentration of 10 mass%, which was used as a coating composition.
(production of fluoropolymer particle-coated separator for measuring peeling Strength)
The coating composition thus obtained was applied to one surface of a separator (HIPORE ND420, manufactured by chemical and chemical industries, inc.) obtained by corona-treating the coating composition with a corona treatment device (manufactured by spring electric company), in a wet application amount of 24 μm (count 12) using a wire bar, and dried at 70 ℃ for 30 minutes. Further heat treatment was carried out at 70 ℃ for 2 hours.
(preparation of Positive electrode for measuring peeling Strength)
Adding N-methyl-2-pyrrolidone to LiNiCoMnO294 parts by weight of MX6UMICORE, 3 parts by weight of a conductive auxiliary (SuperPTIMCAL), and 3 parts by weight of PVDF (polyvinylidene fluoride) (KF #7200, Wuyu corporation), were prepared into a slurry, and the slurry was coated on an Al foil (thickness: 15 μm). After drying, pressing and heat treatment at 120 ℃ for 3 hours, an electrode having a bulk density of 3.0 g/cm was obtained3]The weight per unit area is 103 g/m2]The positive electrode of (1).
(preparation of negative electrode for measuring peeling Strength)
Water was added to 95 parts by weight of BTR918 (manufactured by modified natural graphite BTR), 2 parts by weight of a conductive assistant (manufactured by SuperP timal), 2 parts by weight of SBR (styrene butadiene rubber) latex (manufactured by BM-400 japan ZEON), and 1 part by weight of CMC (manufactured by Celogen 4H first industrial pharmaceutical), to prepare a slurry, which was applied to a Cu foil (thickness 10 μm). After drying, pressing and heat treatment at 150 ℃ for 3 hours, an electrode having a bulk density of 1.6 g/cm was obtained3]The weight per unit area is 50 g/m2]The negative electrode of (1).
(preparation of sample for measuring peeling Strength)
The positive electrode and the negative electrode obtained as described above were cut into pieces of 2.5 × 5.0cm, the fluoropolymer particle-coated separator was cut into pieces of 3.0 × 6.0cm, and the pieces were joined to each other, and immersed in an electrolyte solution (ethylene carbonate (EC)/Ethyl Methyl Carbonate (EMC) ═ 3/7, LiPF)61.2M, VC1 wt%) was added, and the mixture was vacuum degassed, sealed in an Al laminate battery, and allowed to stand overnight.
The Al laminated battery was hot-pressed to obtain a sample for measuring peel strength of the positive electrode and a sample for measuring peel strength of the negative electrode. Specifically, the samples for measuring the peel strength of the positive electrode and the samples for measuring the peel strength of the negative electrode were prepared by hot pressing at 100 ℃ for 2 minutes after 1 minute of residual heat and at a surface pressure of about 4 MPa. In the samples for measuring the peel strength of the positive electrode and the samples for measuring the peel strength of the negative electrode, a fluororesin layer was formed at the interface between the fluoropolymer particle-coated separator and the electrode (positive electrode or negative electrode) by hot pressing.
(measurement of peeling Strength)
The positive electrode and the negative electrode were fixed to the prepared sample for measuring the peel strength to the positive electrode and the sample for measuring the peel strength to the negative electrode, respectively, and a 180 ° peel test was performed at a head speed of 200 mm/min using a tensile tester (STA-1150 unitversasal TESTING MACHINE, manufactured by ORIENTEC corporation) to measure the peel strength.
[ evaluation of porosity by SEM Observation ]
The fluoropolymer particles obtained in each example and each comparative example were used to produce a fluoropolymer particle-coated separator. The electrode (negative electrode) and the fluororesin-coated separator for SEM observation were hot-pressed, and SEM observation was performed on the fluororesin-coated separator after hot-pressing. The following describes in detail the methods for producing the fluoropolymer particle-coated separator and the electrode.
(preparation of coating composition)
A composition prepared by the same method as the method for preparing the coating composition prepared in the peel strength test was used as the coating composition.
(preparation of fluororesin layer-coated separator for SEM Observation)
The coated separator was produced by the same method as that for the coated separator produced in the peel strength test. (preparation of negative electrode for SEM Observation)
The negative electrode was produced in the same manner as the negative electrode for peel strength measurement, and used for SEM observation.
(preparation of sample for SEM Observation and evaluation of porosity)
The negative electrode obtained as described above was cut into 4.0 × 4.0cm, the fluoropolymer particle-coated separator was cut into 4.0 × 4.0cm, and the resultant was joined to each other, and immersed in an electrolyte solution (ethylene carbonate (EC)/Ethyl Methyl Carbonate (EMC) ═ 3/7, LiPF61.2M, VC1 wt%) was added, and 150 μ L was sealed in an Al laminate battery by vacuum degassing and allowed to stand overnight.
After the Al laminated battery was hot-pressed, the separator was peeled off from the negative electrode, and the separator was washed to obtain a sample for SEM observation. Specifically, the sample for SEM observation was hot-pressed at 100 ℃ for 1 minute and a surface pressure of about 3MPa, and a fluororesin layer was formed at the interface between the fluoropolymer particle-coated separator and the electrode (negative electrode). Next, the interface between the coated separator having the fluororesin layer formed and the negative electrode was peeled off, the separator was washed with dimethyl carbonate (DMC), and dried at 70 ℃ for 2 hours to obtain a sample for SEM observation.
The prepared SEM observation sample was imaged with a scanning electron microscope (JSM-6510 LA, manufactured by japan electronics) to obtain an image of the interface between the coated separator having the fluororesin layer formed thereon and the electrode (negative electrode). In the SEM image taken at an acceleration voltage of 5kV and a magnification of 10000 times, the case where each particle contained in the fluororesin layer was confirmed to maintain the particle shape was "porous", and the case where the particle was melted by hot pressing and the particle shape could not be maintained was "non-porous".
< results >
The evaluation results of the particle diameter, IR ratio, melting point, peel strength, and porosity obtained from the SEM image (fig. 1) in each example and each comparative example are shown in tables 1 to 3 together with the charge composition ratio of the fluoropolymer particles in each example and each comparative example.
[ Table 1]
Figure BDA0002093732350000301
[ Table 2]
Figure BDA0002093732350000302
Figure BDA0002093732350000311
[ Table 3]
Figure BDA0002093732350000312
Industrial applicability of the invention
The core-shell particles of the present invention can be suitably used for manufacturing, for example, a secondary battery.

Claims (13)

1. A core-shell particle comprising a core portion and a shell portion surrounding the core portion,
the core portion includes a first polymer having a structural unit derived from vinylidene fluoride as a main structural unit,
the shell portion includes a second polymer having a structural unit derived from vinylidene fluoride as a main structural unit,
the melting point of the first polymer is higher than the melting point of the second polymer,
the second polymer further contains at least one of a structural unit derived from a compound represented by the following formula (1), a structural unit derived from a compound represented by the following formula (2), and a structural unit derived from a compound represented by the following formula (3),
[ chemical formula 1]
Figure DEST_PATH_IMAGE001
In the formula (1), R1、R2And R3Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, X1Is an atomic group having a main chain consisting of 1 to 19 atoms and a molecular weight of 472 or less, and containing at least one hetero atom selected from an oxygen atom and a nitrogen atom,
[ chemical formula 2]
Figure DEST_PATH_IMAGE002
In the formula (2), R4、R5And R6Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, X2Is a main chain composed of atomsA number of 1 to 19 and a molecular weight of 484 or less, and contains at least one hetero atom selected from an oxygen atom and a nitrogen atom,
[ chemical formula 3]
Figure DEST_PATH_IMAGE003
In the formula (3), R7、R8And R9Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, R10Is a hydrogen atom or a hydrocarbon moiety of 1 to 5 carbon atoms containing at least one hydroxyl group.
2. The core-shell particle of claim 1 wherein,
the compound shown in the formula (1) is a compound shown in the following formula (4),
[ chemical formula 4]
Figure DEST_PATH_IMAGE004
In the formula (4), R1、R2And R3Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, X3Is an atomic group having a main chain consisting of 1 to 18 atoms and having a molecular weight of 456 or less.
3. The core-shell particle of claim 1 or 2 wherein,
the first polymer contained in the core portion and/or the second polymer contained in the shell portion further contain a structural unit derived from a halogenated alkyl vinyl compound.
4. The core-shell particle of claim 1 or 2 wherein,
the core-shell particles have a melting point of 145 ℃ or higher.
5. The core-shell particle of claim 1 or 2 wherein,
the structural units of the first polymer are only structural units derived from vinylidene fluoride.
6. A dispersion liquid comprising the core-shell particle according to claim 1 or 2 and a dispersion medium.
7. A coating composition for forming a porous fluororesin layer provided on at least one surface of a separator provided between a negative electrode layer and a positive electrode layer in a secondary battery, the coating composition comprising the core-shell particles according to claim 1 or 2.
8. The coating composition of claim 7, further comprising an adhesion promoter.
9. The coating composition of claim 7, further comprising a filler.
10. A separator coated on at least one side with the coating composition of claim 7.
11. A secondary battery provided with a fluororesin layer formed from the coating composition of claim 7,
the fluororesin layer has a layer containing the second polymer formed by hot-pressing the negative electrode layer and the positive electrode layer and the separator,
the layer comprising the second polymer contains particles comprising the first polymer.
12. A coating composition for forming a fluororesin layer provided on at least one surface of at least either one of a negative electrode layer and a positive electrode layer in a secondary battery so as to be in contact with a separator provided between the negative electrode layer and the positive electrode layer, the coating composition comprising the core-shell type particle according to claim 1 or 2.
13. A method for producing a core-shell particle including a core portion and a shell portion surrounding the core portion, the method comprising:
a core portion forming step of forming a core portion including a first polymer having a vinylidene fluoride-derived structural unit as a main structural unit; and
a shell section forming step of forming a shell section of a second polymer containing a structural unit derived from vinylidene fluoride as a main structural unit,
the melting point of the first polymer is higher than the melting point of the second polymer,
in the shell section forming step, a monomer constituting the second polymer, which contains vinylidene fluoride and at least one of a compound represented by formula (1), a compound represented by formula (2), and a compound represented by formula (3), is polymerized in a dispersion liquid containing a core section formed in the core section forming step, thereby forming the shell section around the core section,
[ chemical formula 5]
Figure DEST_PATH_IMAGE005
In the formula (1), R1、R2And R3Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, X1Is an atomic group having a main chain consisting of 1 to 19 atoms and a molecular weight of 472 or less, and containing at least one hetero atom selected from an oxygen atom and a nitrogen atom,
[ chemical formula 6]
Figure DEST_PATH_IMAGE006
In the formula (2), R4、R5And R6Each independently being a hydrogen atom, a chlorine atom or a carbon atomAlkyl of 1 to 5 atoms, X2Is an atomic group having a main chain consisting of 1 to 19 atoms and having a molecular weight of 484 or less, and containing at least one hetero atom selected from an oxygen atom and a nitrogen atom,
[ chemical formula 7]
Figure DEST_PATH_IMAGE007
In the formula (3), R7、R8And R9Each independently is a hydrogen atom, a chlorine atom or an alkyl group of 1 to 5 carbon atoms, R10Is a hydrogen atom or a hydrocarbon moiety of 1 to 5 carbon atoms containing at least one hydroxyl group.
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