CN112088457A - Adhesive composition, separator structure, electrode structure, nonaqueous electrolyte secondary battery, and method for producing same - Google Patents

Adhesive composition, separator structure, electrode structure, nonaqueous electrolyte secondary battery, and method for producing same Download PDF

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Publication number
CN112088457A
CN112088457A CN201980031083.1A CN201980031083A CN112088457A CN 112088457 A CN112088457 A CN 112088457A CN 201980031083 A CN201980031083 A CN 201980031083A CN 112088457 A CN112088457 A CN 112088457A
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China
Prior art keywords
vinylidene fluoride
mass
adhesive resin
adhesive composition
separator
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CN201980031083.1A
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CN112088457B (en
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铃木梦乃
小林正太
冈田佳余子
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Kureha Corp
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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
    • H01M50/443—Particulate material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
    • H01M50/461—Separators, membranes or diaphragms characterised by their combination with electrodes with adhesive layers between electrodes and separators
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J11/00—Features of adhesives not provided for in group C09J9/00, e.g. additives
    • C09J11/02—Non-macromolecular additives
    • C09J11/06—Non-macromolecular additives organic
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09J—ADHESIVES; NON-MECHANICAL ASPECTS OF ADHESIVE PROCESSES IN GENERAL; ADHESIVE PROCESSES NOT PROVIDED FOR ELSEWHERE; USE OF MATERIALS AS ADHESIVES
    • C09J127/00—Adhesives 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; Adhesives based on derivatives of such polymers
    • C09J127/02—Adhesives 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; Adhesives based on derivatives of such polymers not modified by chemical after-treatment
    • C09J127/12—Adhesives 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; Adhesives based on derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
    • C09J127/16—Homopolymers or copolymers of vinylidene fluoride
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/426—Fluorocarbon polymers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/449—Separators, membranes or diaphragms characterised by the material having a layered structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)
  • Cell Separators (AREA)
  • Adhesives Or Adhesive Processes (AREA)
  • Adhesive Tapes (AREA)

Abstract

The adhesive resin composition is provided on the surface of a separator or an electrode of a non-aqueous electrolyte secondary battery, and comprises an adhesive resin, wherein the adhesive resin comprises at least one vinylidene fluoride copolymer (a) comprising a constituent unit derived from vinylidene fluoride and a constituent unit derived from a monomer copolymerizable with the vinylidene fluoride, the turbidity of an NMP solution of the adhesive resin is 2 to 95 inclusive, the solution viscosity (A) of an acetone solution of the adhesive resin is 350 to 20000 mPas, and the ratio (A)/(B) of the solution viscosity (A) to the solution viscosity (B) of the NMP solution of the adhesive resin is 1 to 15 inclusive.

Description

Adhesive composition, separator structure, electrode structure, nonaqueous electrolyte secondary battery, and method for producing same
Technical Field
The invention relates to an adhesive composition, a separator structure, an electrode structure, a nonaqueous electrolyte secondary battery, and a method for manufacturing the same.
Background
Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries have high voltage and high energy density, and are therefore used as power sources for various applications such as mobile electronic devices such as smartphones and electric vehicles.
The lithium ion secondary battery has a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte solution. The separator plays a role of an ion channel in the battery, and has a function of preventing the positive electrode and the negative electrode from being directly contacted to cause short circuit.
In recent years, as the capacity of lithium ion secondary batteries has increased, importance has been placed on the safety of the batteries. For example, as one of the higher capacities of batteries, it has been studied to increase the charging voltage of the battery, but this tends to make the oxidation environment in the battery more severe, and the separator tends to be oxidized and deteriorated. If the separator is oxidatively deteriorated, a shutdown (shutdown) function and the like are easily damaged, and an internal short circuit and the like are easily generated. Therefore, it is required to improve the oxidation resistance of the separator. Further, when the internal resistance of the battery increases due to expansion and contraction of the electrode active material during charge and discharge of the battery, battery characteristics (particularly cycle characteristics) are likely to decrease. Therefore, it is also required to suppress an increase in the internal resistance of the battery by bonding the separator to the electrode. From the viewpoint of achieving them, studies have been made on: an adhesive composition layer is provided on the surface of the separator or the electrode, and the separator and the electrode are bonded to each other via the adhesive composition layer, whereby the oxidation resistance of the separator and the adhesion between the separator and the electrode are improved.
As a separator having an adhesive composition layer, for example, a separator having an adhesive composition layer of a coating liquid obtained by mixing a dispersion of copolymer particles containing vinylidene fluoride (VDF) and Hexafluoropropylene (HFP) with a CMC aqueous solution is disclosed (for example, patent document 1).
Documents of the prior art
Patent document
Patent document 1: international publication No. 2014/185378
Disclosure of Invention
Problems to be solved by the invention
Further, a battery having such a separator or electrode having an adhesive composition layer may be exposed to a high-temperature environment. Therefore, it is required that the adhesiveness between the separator and the electrode is not lowered even in a high-temperature environment.
For example, a battery having a separator or an electrode provided with an adhesive composition layer is produced by the following steps, taking a laminate battery as an example: 1) laminating the positive electrode and the negative electrode with a separator interposed therebetween to obtain a laminate; 2) sealing the laminate in a laminate battery, immersing the laminate in an electrolyte, and then sealing the laminate; and 3) heating or hot-pressing the packaged laminated battery, and bonding the separator to the positive electrode or the negative electrode via the adhesive composition layer. In the heating or hot-pressing step of 3), the battery is exposed to high-temperature heat, and therefore it is desired that high adhesion between the separator and the electrode be exhibited even when exposed to such high temperature. In the heating or hot-pressing step of 3), strict temperature control is required, and if the temperature is slightly deviated, a defective battery in which the electrode and the separator are not bonded can be easily produced. Therefore, from the viewpoint of reducing the defective rate of the battery, it is required that an allowable heating or hot-pressing temperature range (process window) is as wide as possible.
Even with the separator of patent document 1, it is more desirable than ever to maintain high adhesion of the separator to the electrode when exposed to high temperatures and to have a wide process window. In particular, the adhesiveness between the separator and the negative electrode has not been studied sufficiently in the past.
The present invention has been made in view of the above circumstances, and an object thereof is to provide an adhesive composition containing an adhesive resin, which can maintain high adhesion between a separator and an electrode even when exposed to high temperature and has a wide process window. It is another object of the present invention to provide a separator structure, an electrode structure, a nonaqueous electrolyte secondary battery, and a method for producing the same, each using the adhesive composition.
Technical scheme
The adhesive composition for a nonaqueous electrolyte secondary battery according to the present invention for solving the above problems is an adhesive composition provided on the surface of a separator or an electrode of a nonaqueous electrolyte secondary battery and comprising an adhesive resin, the adhesive resin comprising at least one vinylidene fluoride copolymer (a) comprising a constituent unit derived from vinylidene fluoride and a constituent unit derived from a monomer copolymerizable with the vinylidene fluoride, the adhesive resin having a turbidity of 2 or more and 95 or less when dissolved in N-methyl-2-pyrrolidone (hereinafter, abbreviated as "NMP") so that the concentration in the solution becomes 5 mass%, and a solution viscosity (a) of 350 to 20000mPa · s when dissolved in acetone so that the concentration in the solution becomes 10 mass%, the ratio (A)/(B) of the solution viscosity (A) to the solution viscosity (B) when the adhesive resin is dissolved in NMP so that the concentration of the adhesive resin in the solution becomes 5 mass% is 1 to 15 inclusive.
The separator structure of the present invention comprises: a spacer; and an adhesive composition layer provided on at least one surface of the separator and obtained by using the adhesive composition of the present invention.
The electrode structure of the present invention comprises: an electrode having a current collector and an electrode active material layer containing an electrode active material provided on the current collector; and an adhesive composition layer provided on the surface of the electrode active material layer and obtained by using the adhesive composition of the present invention.
The nonaqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an adhesive composition layer provided between at least one of the separator and the positive electrode and the separator and the negative electrode, and is obtained by using the adhesive composition of the present invention.
The method for manufacturing a nonaqueous electrolyte secondary battery of the present invention includes the steps of:
obtaining a laminate having a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an adhesive composition layer provided between at least one of the separator and the positive electrode and the separator and the negative electrode, the laminate being obtained using the adhesive composition of the present invention; and
the separator is bonded to the positive electrode via the adhesive resin composition layer, and/or the separator is bonded to the negative electrode via the adhesive resin composition layer.
Advantageous effects
According to the present invention, an adhesive composition having a wide process window in a heating or hot-pressing step, which can maintain high adhesion between a separator and an electrode even when exposed to high temperatures, and a separator structure, an electrode structure, and a battery using the adhesive composition, and a method for producing the adhesive composition can be provided.
Detailed Description
It is considered that the high adhesiveness between the separator and the electrode is obtained by "the component of the adhesive composition layer provided between the separator and the electrode does not dissolve in the electrolyte even at a certain temperature or higher, and remains between the separator and the electrode" and "the component of the adhesive composition layer has a high elastic modulus". In addition, it is considered that, for a wide process window, "the components of the adhesive composition layer do not dissolve in the electrolyte solution and remain between the separator and the electrode even at a certain temperature or higher when exposed to a high temperature (in a heating or hot-pressing step, etc.)" is effective. That is, it is considered that 1) the solubility in the electrolytic solution is reduced and 2) the high elastic modulus is effective in order to obtain an adhesive resin which maintains high adhesion of the separator to the electrode even when exposed to high temperature and has a wide process window.
About 1)
A polymer having low solubility in an electrolytic solution generally tends to have low solubility in NMP and high solubility in acetone. When the solubility in NMP is low, the turbidity when dissolving in NMP tends to increase. If the solubility in acetone is high, the solution viscosity (a) when dissolved in acetone tends to be high.
As a result of intensive studies, the present inventors have found that when the turbidity of an adhesive resin containing a vinylidene fluoride copolymer (a) dissolved in NMP is 2 or more and 95 or less, the solubility in an electrolytic solution tends to be moderately low, and when the solution viscosity (a) of the adhesive resin containing a vinylidene fluoride copolymer (a) dissolved in acetone is 350 to 20000mPa · s, the affinity of the adhesive resin for an electrolytic solution can be locally controlled, and the requirement for the solubility (i) of the adhesive resin in an electrolytic solution can be reduced.
About 2)
In contrast, a polymer having a high elastic modulus generally tends to have a high solubility in NMP and a low solubility in acetone. When the solubility in NMP is high, the solution viscosity (B) when dissolved in NMP tends to be high. If the solubility in acetone is low, the solution viscosity (a) when dissolved in acetone tends to be low.
As a result of intensive studies, the present inventors have found that the ratio (a)/(B) of the solution viscosity (a) of an acetone solution of an adhesive resin containing a vinylidene fluoride copolymer (a) to the solution viscosity (B) of an NMP solution of an adhesive resin containing a vinylidene fluoride copolymer (a) is 1 to 15, and thereby the requirements of high elastic modulus and low solubility (ii) in an electrolyte solution can be satisfied in a well-balanced manner.
That is, the adhesive resin containing the vinylidene fluoride copolymer (a) and satisfying the requirements of i) and ii) can reduce the solubility in the electrolytic solution and has a high elastic modulus.
i) The adhesive resin has a turbidity of 2 to 95 inclusive when dissolved in NMP, and has a solution viscosity (A) of 350 to 20000 mPas when dissolved in acetone
ii) the ratio (A)/(B) of the solution viscosity (A) to the solution viscosity (B) obtained by dissolving the adhesive resin in NMP is 1 to 15 inclusive
In the present specification, the case where the adhesive resin is "mixed" with the solvent, and only a part of the adhesive resin is dissolved in the solvent, is also referred to as "dissolved" similarly to the case where the adhesive resin is completely dissolved, and the mixed solution thereof is referred to as "solution".
The turbidity and the solution viscosity (B) when the adhesive resin containing the vinylidene fluoride copolymer (a) is dissolved in NMP and the solution viscosity (a) when the adhesive resin containing the vinylidene fluoride copolymer (a) is dissolved in acetone can be determined by the molecular weight and the branching amount of the vinylidene fluoride copolymer (a); the content of the monomer copolymerizable with vinylidene fluoride (HFP, CTFE) and the crosslinkable monomer in the vinylidene fluoride copolymer (a), and the distribution thereof; the content ratio of the vinylidene fluoride copolymer (a) in the adhesive resin; alkali treatment of the adhesive resin, and the like.
For example, in order to increase the turbidity of the NMP solution and the solution viscosity (a) of the acetone solution in i), it is preferable to perform, for example: the content increase and distribution control of the monomer copolymerizable with vinylidene fluoride (HFP, CTFE) and the crosslinkable monomer in the vinylidene fluoride copolymer (a); increase in molecular weight and branching amount of the vinylidene fluoride copolymer (a); alkali treatment of the adhesive resin. On the other hand, in order to set the viscosity ratio (a)/(B) of ii) to 15 or less, it is preferable, for example, not to excessively increase the contents of the monomer copolymerizable with vinylidene fluoride (HFP, CTFE) and the crosslinking monomer; the molecular weight and the branching amount of the vinylidene fluoride copolymer (a) are not excessively increased; the alkali treatment of the adhesive resin is not excessively performed.
In particular, the positive electrode mostly contains a vinylidene fluoride polymer as a binder, while the negative electrode mostly contains a resin such as carboxymethyl cellulose (CMC) different from the vinylidene fluoride polymer as a binder. Therefore, when an adhesive resin containing a vinylidene fluoride polymer is used, it is difficult to obtain the adhesiveness between the separator and the negative electrode as compared with the adhesiveness between the separator and the positive electrode. On the other hand, the adhesive resin of the present invention satisfying the requirements of i) and ii) above and the adhesive composition containing the same can maintain high adhesion between the separator and the negative electrode even at high temperatures and widen the process window. The present invention has been completed based on such findings.
1. Adhesive composition
The adhesive composition of the present invention contains at least an adhesive resin.
1-1. adhesive resin
The adhesive resin contains at least a vinylidene fluoride copolymer (a).
(vinylidene fluoride copolymer (a))
The vinylidene fluoride copolymer (a) comprises a constituent unit derived from vinylidene fluoride and a constituent unit derived from a monomer copolymerizable with vinylidene fluoride.
Examples of the monomer copolymerizable with vinylidene fluoride include a fluorine-based monomer copolymerizable with vinylidene fluoride, a hydrocarbon-based monomer, and a monomer having a polar functional group having hydrogen bonding property (preferably, a carboxyl group-containing monomer).
Examples of the fluorine-containing monomer copolymerizable with vinylidene fluoride include fluorine-containing alkyl vinyl compounds such as vinyl fluoride, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene, Chlorotrifluoroethylene (CTFE), and Hexafluoropropylene (HFP).
Examples of the hydrocarbon-based monomer copolymerizable with vinylidene fluoride include ethylene, propylene and the like.
Examples of the carboxyl group-containing monomer copolymerizable with vinylidene fluoride include: unsaturated monobasic acids such as acrylic acid, methacrylic acid, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate and the like; unsaturated dibasic acids such as maleic acid and citraconic acid; monoesters of unsaturated dibasic acids such as monomethyl maleate, monoethyl maleate, monomethyl citraconate, and monoethyl citraconate; acryloxyethyl succinate, acryloxypropyl succinate, methacryloxyethyl succinate, methacryloxypropyl succinate.
Among them, from the viewpoint of easier control of crystallinity, a fluorine-based monomer is preferable, tetrafluoroethylene, chlorotrifluoroethylene, and hexafluoropropylene are preferable, and hexafluoropropylene is more preferable.
The content of the structural unit derived from vinylidene fluoride in the vinylidene fluoride copolymer (a) and the content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride differ depending on the form of the adhesive resin, and therefore, the details will be described below.
In addition, the vinylidene fluoride copolymer (a) may be crosslinked from the viewpoint of further lowering the solubility in NMP and further improving the adhesive strength with the surface of the electrode. That is, the vinylidene fluoride copolymer (a) may contain a constituent unit derived from a crosslinkable fluoroalkyl vinyl compound (hereinafter, also simply referred to as "crosslinkable monomer") in addition to vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride.
As the crosslinkable monomer, a polyfunctional monomer may be used, and after obtaining an uncrosslinked copolymer, a crosslinking reaction may be further performed using a polyfunctional monomer.
Examples of the crosslinking monomer include perfluorodivinyl ether, perfluoroalkylene divinyl ether, and the like. It is to be noted that, as the perfluoroalkylene divinyl ether, a compound having the following structure can be used: two vinyl ether groups, all of whose hydrogen atoms are replaced by fluorine atoms, are bonded via a linear or branched divalent perfluoroalkylene group having 1 to 6 carbon atoms.
The content of the constituent unit derived from the crosslinkable monomer in the vinylidene fluoride copolymer (a) is preferably less than 5% by mass, more preferably 0.5 to 4% by mass, and still more preferably 1.2 to 3% by mass, based on the total amount of all the constituent units constituting the vinylidene fluoride copolymer (a).
The form of the adhesive resin is not particularly limited, but for example, when water is used as the dispersion medium, the adhesive resin is preferably in a particulate form from the viewpoint of forming a porous adhesive composition layer. The form of the adhesive resin particles is not particularly limited, but from the viewpoint of easily satisfying the requirements (turbidity of NMP solution, solution viscosity (a) and viscosity ratio (a)/(B) of acetone solution)) of i) and ii) described above, it is preferable that: (1) a core-shell particle comprising a core portion (or shell portion) composed of a vinylidene fluoride copolymer (a) and a shell portion (or core portion) composed of a vinylidene fluoride polymer (b) different from the core portion (or shell portion) and having a content of a structural unit derived from a monomer copolymerizable with vinylidene fluoride lower than that of the vinylidene fluoride polymer (a); or (2) the inclined particles are composed of the vinylidene fluoride copolymer (a).
For example, in the case of (1), after the core is polymerized, monomers and the like necessary for polymerizing the shell are charged again, and the shell is polymerized again outside the core particle to obtain the core-shell particle, whereas in the case of (2), the polymer structure is controlled in one polymerization to give variation in the resin composition, and an adhesive resin having the same physical properties as those of the core-shell particle can be obtained.
Core-shell particles of (1)
The core-shell particles containing the vinylidene fluoride copolymer (a) may have a core portion composed of the vinylidene fluoride copolymer (a) and a shell portion composed of a vinylidene fluoride polymer (b) different from the core portion; the polymer may have a core portion composed of a vinylidene fluoride polymer (b) and a shell portion composed of a vinylidene fluoride copolymer (a). Among them, since a large content of a structural unit derived from a monomer copolymerizable with vinylidene fluoride tends to increase the viscosity, it is preferable to form the shell portion from a vinylidene fluoride polymer (b) having a small content of a structural unit derived from a monomer copolymerizable with vinylidene fluoride, from the viewpoint of improving the stability at the time of coating and winding. That is, the core-shell type particles preferably have a core portion composed of the vinylidene fluoride copolymer (a) and a shell portion composed of the vinylidene fluoride polymer (b) different from the core portion.
The content of the vinylidene fluoride-derived constituent unit in the vinylidene fluoride copolymer (a) constituting the core portion is preferably 20 to 70% by mass, more preferably 30 to 60% by mass, and still more preferably 30 to 50% by mass, assuming that the total amount of the vinylidene fluoride-derived constituent unit and the constituent unit derived from the monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) constituting the core portion is 100% by mass. When the content of the structural unit derived from vinylidene fluoride is not less than a certain level, the solution viscosity (B) of the NMP solution containing the core-shell particles of the vinylidene fluoride copolymer (a) is easily increased, and the solution viscosity (a) of the acetone solution containing the core-shell particles of the vinylidene fluoride copolymer (a) is easily decreased. This makes it easy to set the viscosity ratio (a)/(B) to a constant value or less, and to increase the elastic modulus of the core-shell particles comprising the vinylidene fluoride copolymer (a). On the other hand, if the content of the structural unit derived from vinylidene fluoride is not more than a certain level, the turbidity of the NMP solution containing the core-shell particles of the vinylidene fluoride copolymer (a) and the solution viscosity (a) of the acetone solution do not become excessively low. Thus, the solubility of the core-shell particles containing the vinylidene fluoride copolymer (a) in the electrolyte solution is not excessively increased.
When the total amount of the constituent units derived from vinylidene fluoride and the constituent units derived from a monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) is 100% by mass, the content of the constituent units derived from a monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) is preferably 30 to 80% by mass, more preferably 40 to 70% by mass, and still more preferably 50 to 70% by mass. When the content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride is not less than a certain level, the turbidity of the NMP solution containing the particles of the vinylidene fluoride copolymer (a) and the acetone solution viscosity (a) can be easily increased. This makes it easy to reduce the solubility of the core-shell particles containing the vinylidene fluoride copolymer (a) in the electrolyte solution. On the other hand, if the content of the structural unit derived from the monomer copolymerizable with vinylidene fluoride is a certain level or less, the solution viscosity (B) of the NMP solution containing the core-shell particles of the vinylidene fluoride copolymer (a) is not excessively low, and the solution viscosity (a) of the acetone solution containing the core-shell particles of the vinylidene fluoride copolymer (a) is not excessively high, so that it is easy to set the viscosity ratio (a)/(B) to a certain level or less. Thus, the elastic modulus of the core-shell particles containing the vinylidene fluoride copolymer (a) is not excessively lowered.
In particular, the vinylidene fluoride copolymer (a) may be crosslinked from the viewpoint of further reducing the solubility of the core-shell particles in the electrolyte solution. In addition, from the viewpoint of not impairing the elastic modulus of the core-shell particles, the vinylidene fluoride copolymer (a) may not be crosslinked.
The vinylidene fluoride polymer (b) constituting the shell section contains at least a structural unit derived from vinylidene fluoride.
The vinylidene fluoride-derived structural unit content in the vinylidene fluoride polymer (b) is preferably higher than the vinylidene fluoride-derived structural unit content in the vinylidene fluoride copolymer (a). Specifically, when the total amount of the vinylidene fluoride-derived structural unit in the vinylidene fluoride polymer (b) and the constituent unit derived from an arbitrary monomer copolymerizable with vinylidene fluoride described later is taken as 100% by mass, the content of the vinylidene fluoride-derived structural unit in the vinylidene fluoride polymer (b) is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 95% by mass or more, and may be 100% by mass. When the content of the vinylidene fluoride-derived structural unit in the vinylidene fluoride polymer (B) is 80 mass% or more, the solution viscosity (B) of the NMP solution containing the core-shell particles of the vinylidene fluoride copolymer (a) tends to be high, and the solution viscosity (a) of the acetone solution containing the core-shell particles of the vinylidene fluoride copolymer (a) tends to be low, so that the viscosity ratio (a)/(B) tends to be constant or less. This makes it easy to improve the elastic modulus of the core-shell particles comprising the vinylidene fluoride copolymer (a).
The vinylidene fluoride polymer (b) may further contain a constituent unit derived from a monomer copolymerizable with vinylidene fluoride and a constituent unit derived from a crosslinkable monomer, if necessary. The vinylidene fluoride polymer (b) may be the same as the vinylidene fluoride-copolymerizable monomer and the crosslinkable monomer in the above-mentioned vinylidene fluoride copolymer (a).
In particular, from the viewpoint of further reducing the solubility of the vinylidene fluoride polymer (b) in the electrolyte solution, the vinylidene fluoride polymer (b) may be crosslinked, that is, may further contain a structural unit derived from a crosslinkable monomer. For example, when the content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) constituting the core portion is small (for example, less than 50% by mass), and when the solution viscosity (a) of the acetone solution containing the particles of the vinylidene fluoride copolymer (a) is low (for example, less than 600mPa · s), the turbidity of the NMP solution is not easily increased only by the core portion, and the solubility in the electrolyte solution is not sufficiently lowered. In such a case, the vinylidene fluoride polymer (b) constituting the shell portion is preferably crosslinked.
On the contrary, even when the content of the structural unit derived from the monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) constituting the core portion is large (for example, 50% by mass or more), or when the solution viscosity (a) of the particles containing the vinylidene fluoride copolymer (a) is high (for example, 600mPa · s or more), the turbidity of the NMP solution is easily increased only by the core portion, and the solubility in the electrolyte solution is easily sufficiently lowered. In such a case, the vinylidene fluoride polymer (b) constituting the shell portion may not be crosslinked.
In addition, in forming the adhesive resin composition layer containing inorganic fine particles, the vinylidene fluoride polymer (b) preferably contains a structural unit derived from a monomer having a polar functional group having hydrogen bonding property (preferably, a carboxyl group-containing monomer) which is a monomer copolymerizable with vinylidene fluoride, from the viewpoint of improving dispersion stability between the inorganic fine particles and the adhesive resin and improving coatability.
The content of vinylidene fluoride is preferably 97% by mass or less, more preferably 50 to 97% by mass, and still more preferably 60 to 95% by mass, assuming that the total amount of monomers contained in the core-shell particles is 100% by mass.
In the core-shell particles having a core portion composed of a vinylidene fluoride copolymer (a) and a shell portion composed of a vinylidene fluoride polymer (b), the mass ratio of the core portion to the shell portion is not particularly limited, but for example, the core portion/shell portion is preferably 40/60 to 99/1, more preferably 50/50 to 90/10, and still more preferably 50/50 to 70/30. If the mass ratio of the core portion is high, the solubility in the electrolyte solution is likely to be sufficiently reduced, and if the mass ratio of the shell portion is high, the elastic modulus is likely to be sufficiently increased. The adhesive resin composition layer obtained from such core-shell particles easily maintains high adhesiveness to an electrode even at high temperatures, and also easily widens the process window in the heating or hot-pressing step.
Regarding (2) inclined particles
The inclined particles composed of the vinylidene fluoride copolymer (a) preferably have a variation in composition from the central portion to the surface layer portion of the particles.
For example, the polymer structure can be controlled to obtain tilted particles having a small content of structural units derived from a monomer copolymerizable with vinylidene fluoride on the outside of the particles (tilted particles having a large content of structural units derived from vinylidene fluoride on the outside of the particles). By increasing the amount of the structural units derived from a monomer copolymerizable with vinylidene fluoride in the particles and increasing the amount of vinylidene fluoride outside the particles, the stability during coating and winding can be improved as in the case of the core-shell particles of (1). Such inclined particles can be obtained, for example, by charging a part of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride more than the part of vinylidene fluoride during polymerization, starting the polymerization, reducing the pressure, and then adding the remaining part of vinylidene fluoride and polymerizing.
On the other hand, when the content of the structural unit derived from a monomer copolymerizable with vinylidene fluoride is smaller than that of the core-shell particles, since it is difficult to exhibit viscosity that affects stability during coating and winding, the structural unit derived from vinylidene fluoride may be localized in the particles, and the structure, branched structure, and crosslinked structure derived from a monomer copolymerizable with vinylidene fluoride may be localized in the surface layer portion. This reduces the solubility of the surface layer portion of the inclined particle in the electrolyte solution, and increases the elastic modulus of the central portion. Such inclined particles can be obtained, for example, by polymerizing a monomer copolymerizable with vinylidene fluoride in part of vinylidene fluoride during polymerization when the crosslinked structure is biased to the surface layer, and then adding a crosslinkable monomer and the remainder of vinylidene fluoride to the polymerized product while keeping the pressure constant after reducing the pressure.
In the inclined particles composed of the vinylidene fluoride copolymer (a), the content of the vinylidene fluoride-derived constituent unit in the vinylidene fluoride copolymer (a) is preferably 50 to 99% by mass, more preferably 60 to 95% by mass, and even more preferably 70 to 95% by mass, assuming that the total amount of the vinylidene fluoride-derived constituent unit and the constituent unit derived from the monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) is 100% by mass. When the total amount of the constituent units derived from vinylidene fluoride and the constituent units derived from a monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) is 100% by mass, the content of the constituent units derived from a monomer copolymerizable with vinylidene fluoride in the vinylidene fluoride copolymer (a) is preferably 1 to 50% by mass, more preferably 5 to 40% by mass, and still more preferably 5 to 30% by mass.
Physical Properties of adhesive resin (physical Properties of acetone solution)
(1) Preparation of acetone solution
The powdered adhesive resin was dissolved in acetone so that the concentration in the acetone solution became 10 mass%. Specifically, after dispersing the adhesive resin in a sample bottle containing acetone, the sample bottle is placed in a water bath set at 45 ℃ and stirred for about 2 hours to prepare an acetone solution in which a part or all of the adhesive resin is dissolved. The turbidity and the solution viscosity of the acetone solution are preferably measured immediately after the prepared acetone solution is allowed to cool to room temperature.
(2) Turbidity of water
The turbidity of the acetone solution prepared in the above is preferably 80 or less, more preferably 1 to 60, and further preferably 2 to 55. When the turbidity is 80 or less, the solubility of the adhesive resin in the electrolyte solution tends to be low.
The turbidity of the solution can be measured by a turbidimeter (hazemeter). Specifically, acetone was added to a linear cell (size: 10 × 36 × 55mm) so that the height was 4cm or more and less than 4.5cm, and the mixture was placed in a measuring part of a turbidimeter (NDH 2000, manufactured by nippon electrochromism) and then calibrated (calibration) under conditions of room temperature 20 ± 2 ℃, humidity 50 ± 5%, light source D65 · C, and measuring method 3 (measuring method according to JIS K7136). Then, an acetone solution in which the adhesive resin is dissolved is added to the cell, and the turbidity of the solution is measured under the same conditions.
(3) Viscosity of solution (A)
The solution viscosity (A) of the acetone solution prepared above is preferably 350 to 20000 mPas. When the solution viscosity (a) is 350mPa · s or more, the molecular weight (branching amount) of the adhesive resin is large, and thus the solubility of the adhesive resin in the electrolyte solution is likely to be low, and when the solution viscosity (a) is 20000mPa · s or less, the solubility in NMP is not excessively low. From these viewpoints, the solution viscosity (A) of the adhesive resin is more preferably 200 to 10000 mPas, and still more preferably 500 to 6200 mPas.
The viscosity of the solution can be measured by an E-type viscometer. Specifically, 1.1ml of the solution was added to a measurement part of a viscometer (RE 550 type viscometer manufactured by Toyobo industries Co., Ltd.), and the measurement was carried out at a measurement temperature of 25 ℃ for 300 seconds at a rotation speed of 10rpm with a conical rotor of 1 ℃ 34' XR 24. The viscosity at the time point when 300 seconds passed was set as the solution viscosity.
(physical Properties of NMP solution)
(1) Preparation of NMP solution
The powdery adhesive resin was added to NMP (N-methylpyrrolidone) so that the concentration thereof in the NMP solution became 5 mass%, and a part or the whole of the resin was dissolved. Specifically, an NMP solution was prepared by adding an adhesive resin to a sample bottle containing NMP, dispersing the resin at room temperature, raising the temperature so that the solution temperature became 50 ℃, and stirring the mixture for about 5 hours to dissolve part or all of the adhesive resin.
(2) Turbidity of water
The turbidity of the prepared NMP solution is preferably 2-95. When the turbidity is 2 or more, the solubility of the adhesive resin in the electrolyte solution tends to be low. When the haze is 95 or less, the melting point of the adhesive resin is not excessively lowered. From the above viewpoint, the turbidity of the NMP solution of the adhesive resin is more preferably 2 to 75, and still more preferably 2.5 to 60. The turbidity of the NMP solution can be measured by the same method as described above. Note that the calibration was performed by adding NMP to the cell.
(3) Viscosity of solution (B)
The solution viscosity (B) of the NMP solution prepared as described above may be within a range in which the ratio (a)/(B) of the solution viscosities (a) and (B) falls within a range described below. The solution viscosity (B) can be measured by the same method as described above.
In order to increase the turbidity of the NMP solution and increase the viscosity (a) of the acetone solution, it is preferable to increase the content of the monomer copolymerizable with vinylidene fluoride (HFP, CTFE) and the crosslinking monomer in the vinylidene fluoride copolymer (a) constituting the adhesive resin, to control the distribution, or to increase the molecular weight and the branching amount of the vinylidene fluoride copolymer (a), for example.
(viscosity ratio (A)/(B))
The ratio (a)/(B) of the solution viscosity (a) of the acetone solution of the adhesive resin to the solution viscosity (B) of the NMP solution of the adhesive resin is preferably 1 to 15. When the ratio (a)/(B) is 1 or more, the solution viscosity (B) of the NMP solution tends to be low, and the solution viscosity (a) of the acetone solution tends to be high, that is, the solubility in NMP tends to be low (the solubility in acetone tends to be high). Therefore, the solubility of the adhesive resin in the electrolytic solution is easily reduced. When the ratio (a)/(B) is 15 or less, the solution viscosity (B) of the NMP solution is not too low, and the solution viscosity (a) of the acetone solution is not too high, that is, the solubility in NMP is not too low (the solubility in acetone is not too high), and therefore a high elastic modulus is easily obtained. The ratio (a)/(B) is more preferably 1 to 10.
In order to keep the viscosity ratio (a)/(B) constant or less, it is preferable to keep the monomer copolymerizable with vinylidene fluoride (HFP, CTFE), the content and distribution of the crosslinkable monomer, the molecular weight and the branching amount of the vinylidene fluoride copolymer (a) in the vinylidene fluoride copolymer (a) constituting the adhesive resin constant or less, or the content of the vinylidene fluoride copolymer (a) in the adhesive resin constant or less, for example.
(average particle diameter)
The average particle diameter of the adhesive resin particles is not particularly limited, but is preferably 10nm to 1 μm, more preferably 50 to 500nm, and still more preferably 70 to 300 nm.
When the adhesive resin particles are obtained by emulsion polymerization, the average particle diameter of the adhesive resin particles can be measured by regularization analysis by a dynamic light scattering method in a state where the adhesive resin particles are dispersed in a liquid medium (for example, water) after polymerization. Specifically, the particle size of the polymer particles was measured according to JIS Z8828 using "delsa maxcore" manufactured by BECKMAN COULTER corporation, and the large peak of two large and small peaks obtained by regularization analysis was set as the average particle size. On the other hand, in the case of obtaining an adhesive resin by suspension polymerization, 3000 powdered vinylidene fluoride copolymer particles were photographed, and the average particle diameter was defined as the average particle diameter of the particles assuming that the photographed particles were circular.
(melting Point)
The melting point of the adhesive resin is not particularly limited, but is preferably 90 ℃ or higher, more preferably 100 ℃ or higher, and still more preferably 105 ℃ or higher.
The melting point of the adhesive resin can be measured by the following method. That is, a mold having a length of 5 cm. times.5 cm. times.150. mu.m in width and about 1g of an adhesive resin were sandwiched between two aluminum foils sprayed with a release agent, and pressed at 200 ℃ to obtain a film. The melting point of the obtained film was measured by ASTM d 3418 using DSC ("DSC-1" manufactured by METTLER Co.).
The melting point of the adhesive resin can be adjusted by the monomer composition of the vinylidene fluoride copolymer (a) contained in the adhesive resin. In order to increase the melting point of the adhesive resin, for example, it is preferable to increase the content of the vinylidene fluoride-derived structural unit in the vinylidene fluoride copolymer (a).
(logarithmic viscosity)
The inherent viscosity (. eta.i) of the adhesive resin obtained by the suspension polymerization method is preferably 0.50 to 5.0dl/g, more preferably 1.0 to 4.0dl/g, and still more preferably 1.0 to 3.5dl/g, from the viewpoint of coatability.
The logarithmic viscosity (. eta.i) can be determined as the logarithmic viscosity at 30 ℃ of a solution prepared by dissolving 4g of an adhesive resin in 1 liter of N, N-dimethylformamide (hereinafter, abbreviated as "DMF"). 1-3. Process for producing adhesive resin
The adhesive resin (resin containing vinylidene fluoride copolymer (a)) can be obtained by the following steps: vinylidene fluoride and a monomer copolymerizable with the vinylidene fluoride are polymerized by a known polymerization method including an emulsion polymerization method and a suspension polymerization method.
(emulsion polymerization method)
In the emulsion polymerization method, a polymerization initiator having solubility in a liquid medium is further added to a mixed solution obtained by mixing the above-mentioned liquid medium in which each monomer is hardly soluble, each monomer, an emulsifier, and, if necessary, a chain transfer agent, and the monomers are polymerized.
The liquid medium may be such that each monomer is hardly soluble, and is preferably water, for example.
The emulsifier may be one which can form micelles of the respective monomers in a liquid medium and stably disperse the polymer synthesized by the emulsion polymerization method in the liquid medium, and may be appropriately selected from known surfactants and used. The emulsifier may be a surfactant conventionally used for the synthesis of vinylidene fluoride copolymers, and for example, a perfluorinated surfactant, a partially fluorinated surfactant, a non-fluorinated surfactant, or the like can be used. Among these surfactants, perfluoroalkyl sulfonic acids and salts thereof, perfluoroalkyl carboxylic acids and salts thereof, and fluorine-based surfactants having fluorocarbon chains or fluoropolyether chains are preferable, and perfluoroalkyl carboxylic acids and salts thereof are more preferable.
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.
The polymerization initiator is a polymerization initiator having solubility in a liquid medium, and examples thereof include a water-soluble peroxide, a water-soluble azo compound, and a redox initiator. Examples of the water-soluble peroxide include ammonium persulfate, potassium persulfate and the like. Examples of the water-soluble azo-based compound include 2,2 '-Azobisisobutyronitrile (AIBN), 2' -azobis-2-methylbutyronitrile (AMBN), and the like. Examples of the redox initiator include ascorbic acid-hydrogen peroxide and the like. Among them, the polymerization initiator is preferably a water-soluble peroxide.
The emulsion polymerization method may be a soap-free emulsion polymerization method or a miniemulsion polymerization (miniemulsion polymerization) method.
In the soap-free emulsion polymerization method, a reactive emulsifier which has a polymerizable double bond in the molecule and also functions as an emulsifier is preferably used as the emulsifier. The reactive emulsifier forms micelles in the system at the initial stage of polymerization, but as polymerization proceeds, it is consumed as a monomer for the polymerization reaction, and therefore, it is hardly present in a free state in the reaction system finally obtained. Therefore, the reactive emulsifier is less likely to bleed out to the particle surface of the resulting polymer.
Examples of the reactive emulsifier include polyoxyalkylene alkenyl ether, sodium alkylallyl sulfosuccinate, sodium methacryloxypolyoxypropylene sulfate, and alkoxypolyethylene glycol methacrylate, and the like.
When the monomers are dispersed in a liquid medium even without a reactive emulsifier, soap-free polymerization can be carried out without using a reactive emulsifier.
In the miniemulsion polymerization method, polymerization is carried out by finely dividing micelles into submicron sizes by applying a strong shearing force using an ultrasonic oscillator or the like. At this time, a known hydrophobic substance is added to the mixed solution in order to stabilize the micelle after the miniaturization. In the miniemulsion polymerization method, typically, polymerization reaction occurs only in the respective micelles, and the micelles become fine particles of the polymer, and therefore, the particle size, particle size distribution, and the like of the fine particles of the polymer to be obtained are easily controlled.
(suspension polymerization method)
In the suspension polymerization method, a monomer dispersion liquid obtained by dissolving an oil-soluble polymerization initiator in each monomer is mechanically stirred and heated in water containing a suspending agent, a chain transfer agent, a stabilizer, a dispersant, and the like, thereby suspending and dispersing the monomers and causing a polymerization reaction in suspended monomer droplets. In the suspension polymerization method, typically, the polymerization reaction occurs only in the interior of each of the monomer droplets, and the monomer droplets become polymer fine particles, so that the particle diameter, particle diameter distribution, and the like of the obtained polymer fine particles can be easily controlled.
Examples of the polymerization initiator include diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di-n-fluoropropyl peroxydicarbonate, diisopropyl peroxydicarbonate, isobutyryl peroxide, bis (chlorofluorocarbonyl) peroxide, bis (perfluoroacyl) peroxide, t-butyl peroxypivalate, and the like.
Examples of the suspending agent include methyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, partially saponified polyvinyl acetate, acrylic polymer, and the like.
The chain transfer agent may be the same as described above.
Next, a method for producing the adhesive resin particles will be described for each mode.
1-3-1 cases of core-shell particles
The core-shell particles containing the vinylidene fluoride copolymer (a) can be obtained by sequential polymerization. For example, a core-shell particle having a core portion made of a vinylidene fluoride copolymer (a) and a shell portion made of a vinylidene fluoride polymer (b) can be produced, for example, by the following steps: copolymerizing vinylidene fluoride with a monomer copolymerizable with vinylidene fluoride to form a core part composed of a vinylidene fluoride copolymer (a); and polymerizing at least vinylidene fluoride around the obtained core portion to form a shell portion composed of a vinylidene fluoride copolymer (b).
When the vinylidene fluoride copolymer (a) and the vinylidene fluoride polymer (b) further contain the structural unit derived from the crosslinkable monomer, these monomers may be further copolymerized in the polymerization in each step.
The polymerization in each step can be carried out by a known polymerization method such as the emulsion polymerization method or the suspension polymerization method described above.
1-3-2. case of inclined type particles
The inclined particles composed of the vinylidene fluoride copolymer (a) can be obtained by the following steps: polymerizing vinylidene fluoride with a monomer copolymerizable with vinylidene fluoride. The polymerization can be carried out by a known polymerization method such as an emulsion polymerization method or a suspension polymerization method, as described above.
In addition, from the viewpoint of satisfying the above-mentioned turbidity of the NMP solution, the solution viscosity (a) of the acetone solution, and the viscosity ratio (a)/(B), it is preferable to provide variations in composition and structure from the center portion to the surface layer portion of the particles.
For example, in order to obtain particles having a large content of structural units derived from a monomer copolymerizable with vinylidene fluoride in the particle interior and a large content of structural units derived from vinylidene fluoride in the particle surface layer portion, for example, a monomer copolymerizable with vinylidene fluoride, which is partially vinylidene fluoride and partially more vinylidene fluoride, is charged during polymerization, polymerization is started, and after the pressure is reduced, the remaining part of vinylidene fluoride is added and polymerized.
For example, in order to obtain particles having a crosslinked structure more localized in the surface layer portion, it is preferable that, during polymerization, a part of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride are charged into a polymerization reactor, and after the polymerization is started, the crosslinkable monomer and the remaining part of vinylidene fluoride are polymerized while adding them several times (including continuous addition in which the post-addition is continuously performed) so that the pressure becomes constant after the pressure is reduced (method 1).
The vinylidene fluoride is preferably added after the polymerization has started and after the pressure has been reduced. Specifically, the vinylidene fluoride is preferably added after the polymerization is started and the pressure is reduced. Specifically, the post-addition of vinylidene fluoride is preferably performed at a time point when the pressure in the reactor is reduced by 2% or more, more preferably 15% or more, from the initial pressure.
The monomers to be added later are preferably only vinylidene fluoride and a crosslinkable monomer, and substantially no monomer copolymerizable with vinylidene fluoride (for example, 1% by mass or less, preferably 0% by mass, based on the total of the monomers to be added later). The mass ratio of the later-added vinylidene fluoride to the earlier-added vinylidene fluoride is preferably 1:1 to 10:1 (mass ratio) of the later-added vinylidene fluoride to the earlier-added vinylidene fluoride, and more preferably 2.5:1 to 7:1 (mass ratio) of the later-added vinylidene fluoride to the earlier-added vinylidene fluoride.
The amount of the crosslinkable monomer is preferably 0.1 to 4% by mass, more preferably 1.2 to 3.5% by mass, based on the total amount of the vinylidene fluoride and the monomer copolymerizable with vinylidene fluoride. The amount of vinylidene fluoride blended is preferably 15% by mass or more, more preferably 12% by mass or more, based on the total amount of all monomers constituting the vinylidene fluoride copolymer (a).
When the crosslinkable monomer is not used, the method may be the same as the method 1. That is, as a method for imparting variation in the composition and structure of the particles, it is preferable that, at the time of polymerization, a part of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride are charged into a polymerization vessel, polymerization is started, and after the pressure is reduced, the remaining part of vinylidene fluoride is polymerized while being added thereto in multiple portions so that the pressure becomes constant (including continuous addition in which post-addition is continuously performed). The timing of the post-addition and the mass ratio of the post-added vinylidene fluoride to the pre-added vinylidene fluoride may be the same as in the above method 1.
In order to obtain particles having a branched structure more localized in the surface layer portion, it is preferable to reduce the amount of the chain transfer agent to be added in the step of polymerizing vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride, specifically, to reduce the amount of the chain transfer agent to the total amount of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride (method 2). By reducing the amount of the chain transfer agent incorporated, the molecular weight (branching amount) of the vinylidene fluoride copolymer (a) to be obtained can be increased. This makes it easy for the resulting particles to increase the turbidity of the NMP solution and to increase the viscosity (a) of the acetone solution.
The amount of the chain transfer agent to be incorporated is preferably 0.2% by mass or less, more preferably 0.15% by mass or less, and still more preferably 0.08% by mass or less, based on the total amount of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride.
In these methods 1 and 2, a crosslinked structure or a branched structure can be formed in the surface layer portion of the obtained particles by performing polymerization in an environment containing a large amount of vinylidene fluoride in particular.
Further, another method for imparting variation in composition and structure to the adhesive resin includes: a method (method 3) in which a part of vinylidene fluoride and a monomer copolymerizable with vinylidene fluoride are charged so that the monomer copolymerizable with vinylidene fluoride is larger than vinylidene fluoride (so that the monomer is in excess) at the initial stage of polymerization, and then polymerization is carried out, and the remaining part of vinylidene fluoride is added to the mixture at a stage where the pressure is lower than that at the start of polymerization; a method (method 4) of subjecting an adhesive resin containing the vinylidene fluoride copolymer (a)' to an alkali treatment.
For example, in method 3, the specific timing of the post-addition and the mass ratio of the post-added vinylidene fluoride to the pre-added vinylidene fluoride may be the same as in method 1.
For example, as a method (method 4) of alkali-treating the vinylidene fluoride copolymer (a) ', specifically, the vinylidene fluoride copolymer (a)' is dissolved in NMP (turbidity at this time is less than 2) so that the polymer concentration in the solution becomes 5 parts by mass, and a powder of lithium hydroxide (LiOH) is added thereto and stirred under heating. This can modify (for example, defluorinate) the vinylidene fluoride copolymer (a)' to reduce the solubility in the electrolyte solution.
The content of LiOH in the solution is preferably 0.01 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the vinylidene fluoride copolymer (a).
The heating temperature and the stirring time in the alkali treatment may be set to such an extent that the solubility of the obtained vinylidene fluoride copolymer (a)' in the electrolyte solution is reduced. The heating temperature may be set to 45 to 60 ℃. The stirring time may be, for example, 30 minutes to 12 hours.
1-4. other ingredients
The adhesive resin composition may further contain other components than the adhesive resin. Examples of the other components include water-soluble polymers, inorganic fillers, organic fillers, solvents (dispersion media), and various additives.
The water-soluble polymer can improve the adhesion between the adhesive resin composition layer and the separator and the adhesion between the adhesive resin composition layer and the electrode. The water-soluble polymer is preferably a polymer having adhesiveness to an adhesive resin, an electrode, or a separator.
Examples of the water-soluble polymer include: cellulose compounds such as carboxymethyl cellulose (CMC), methyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl cellulose; ammonium or alkali metal salts of the above cellulose compounds, polyacrylic acid (PAA), polyvinylpyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene oxide (PEO). Among them, carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA) are preferable from the viewpoint of long-term use of the battery.
The content of the water-soluble polymer is preferably 0.01 to 20 parts by mass, more preferably 0.01 to 15 parts by mass, based on 100 parts by mass of the total solid content of the adhesive resin composition.
The inorganic filler prevents short circuit and improves the safety of the battery even when the battery obtained is exposed to a high temperature such as a melting of the separator or the adhesive resin.
Examples of such inorganic fillers include: 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) And the like hydroxides; calcium carbonate (CaCO)3) And carbonates; sulfates such as barium sulfate; a nitride; clay minerals, and the like. One kind of the inorganic filler may be used alone, or two or more kinds may be used in combination. Among them, alumina, silica, magnesium oxide, and zinc oxide are preferable from the viewpoint of safety of the battery and stability of the coating liquid.
The content of the inorganic filler is preferably 0.01 to 99 parts by mass, and more preferably 50 to 95 parts by mass, based on 100 parts by mass of the total solid content of the adhesive resin composition.
The average particle diameter of the inorganic filler is preferably 5nm to 2 μm, more preferably 10nm to 1 μm. The average particle diameter can be measured by the same method as described above.
Examples of the inorganic filler include AKP3000 (manufactured by sumitomo chemical) commercially available as high-purity alumina particles.
Examples of the solvent include water, NMP. The content of the solvent is not particularly limited as long as the coatability is good, but is preferably 30 to 99 parts by mass, and more preferably 35 to 98 parts by mass, based on 100 parts by mass of the total mass of the adhesive resin composition.
2. Spacer structure
The separator structure of the present invention includes a separator and an adhesive resin composition layer provided on at least one surface of the separator.
2-1. spacer
The material of the separator is not particularly limited, but examples thereof include polyolefin resins such as polyethylene and polypropylene; polyester resins such as polyethylene terephthalate; an aromatic polyamide resin; polyimide resins such as polyetherimides; polyethersulfone, polysulfone, polyetherketone, polystyrene, polyethylene oxide, polycarbonate, polyvinyl chloride, polyacrylonitrile, polymethyl methacrylate, ceramics, etc., and mixtures thereof. Among them, a porous film of polyolefin resin (for example, polyethylene or polypropylene) is preferable from the viewpoint of excellent shutdown function and fusing function.
Examples of the porous film of polyolefin resin include single-layer polypropylene separator, single-layer polyethylene separator, and polypropylene/polyethylene/polypropylene three-layer separator commercially available as Celgard (registered trademark, manufactured by Polypore corporation).
2-2. adhesive resin composition layer
The adhesive resin composition layer is provided on at least one surface of the separator. The adhesive resin composition layer is a layer obtained by using at least the above adhesive resin composition, and may contain other components as necessary.
The thickness of the adhesive resin composition layer is not particularly limited as long as the adhesiveness between the separator and the electrode can be maintained well, but is, for example, preferably 0.5 to 25 μm, and more preferably 1 to 20 μm.
The adhesive resin composition layer may be formed through the following steps: drying the adhesive resin composition after coating the adhesive resin composition on a separator; and if necessary, to be made porous. The coating method is not particularly limited, and may be a method of coating by a bar coater, a die coater, a comma coater, or the like.
The drying is preferably performed to such an extent that the solvent in the coating film can be sufficiently removed. For example, the drying temperature is preferably 40 to 180 ℃, and more preferably 50 to 150 ℃. The drying time may be 1 minute to 15 hours.
After drying, a heat treatment may be further performed as necessary. For example, when the adhesive resin composition layer does not contain a water-soluble polymer as another component, the heat treatment is preferably performed. The heat treatment temperature is preferably 40-180 ℃, and more preferably 50-170 ℃. The heat treatment time may be, for example, 1 minute to 5 hours.
3. Electrode structure
The electrode structure has an electrode and an adhesive resin composition layer provided on the surface of the electrode.
3-1. electrode
The electrode has a current collector and an electrode active material layer provided on the surface of the current collector. The electrode may be a positive electrode or a negative electrode.
(Current collector)
Examples of the current collector for the negative electrode include copper. The copper may be metal copper, or may be a material in which a copper foil is applied to the surface of another medium.
Examples of the current collector for the positive electrode include aluminum. The aluminum may be a material in which an aluminum foil is applied to the surface of another medium, or a material in which a mesh-like aluminum is added.
The thickness of the current collector for the negative electrode or the positive electrode is preferably 5 to 100 μm, and more preferably 5 to 20 μm.
(electrode active material layer)
The electrode active material layer contains an electrode active material and a binder, and may further contain a conductive auxiliary agent as needed.
Examples of the electrode active material for the positive electrode include lithium-based positive electrode active materials. Examples of the lithium-based positive electrode active material include: LiCoO2、LiNixCo1-xO2(0<x is less than or equal to 1), etc. are represented by a general formula LiMY2(M is one or more of transition metals such as Co, Ni, Fe, Mn, Cr and V, Y is a chalcogen such as O and S) A complex metal chalcogenide compound of (a); LiMn2O4And the like, a spinel-structured composite metal oxide; and LiFePO4And the like olivine-type lithium compounds. The positive electrode active material may be a commercially available material.
The specific surface area of the active material for the positive electrode is preferably 0.05 to 50m from the viewpoint of suppressing decomposition of the electrolyte and suppressing increase in initial irreversible capacity2A more preferable range is 0.1 to 30 m/g2/g。
Examples of the active material for the negative electrode include carbon materials, metal materials, alloy materials, metal oxides, and the like, which have been conventionally used as active materials for negative electrodes. Among them, carbon materials are preferable from the viewpoint of easily obtaining stable battery characteristics, and artificial graphite, natural graphite, non-graphitizable carbon, and the like are more preferable. Examples of the artificial graphite include artificial graphite obtained by carbonizing an organic material, further performing heat treatment at a high temperature, and performing pulverization and classification. Examples of the non-graphitizable carbon include non-graphitizable carbon obtained by firing a material derived from petroleum pitch at 1000 to 1500 ℃. The negative electrode active material may be a commercially available material.
The specific surface area of the active material for the negative electrode is preferably 0.3 to 10m from the viewpoint of suppressing decomposition of the electrolyte and suppressing increase in initial irreversible capacity2A more preferable range is 0.6 to 6 m/g2/g。
The binder can improve the adhesion between the electrode active materials, the adhesion between the electrode active materials and the conductive assistant, or the adhesion between the electrode active materials and the current collector. The binder is not particularly limited, and binders widely used in lithium ion secondary batteries can be used. Examples of the binder include: fluorine-containing resins such as polytetrafluoroethylene, polyvinylidene fluoride (including vinylidene fluoride (co) polymers such as vinylidene fluoride-monomethyl maleate copolymers), and fluororubbers; styrene butadiene rubber latex (SBR); cellulose compounds (carboxymethyl cellulose and the like); and Polyacrylonitrile (PAN), and the like. Among them, preferable examples of the binder for the positive electrode include vinylidene fluoride (co) polymer, and examples of the binder for the negative electrode include styrene butadiene rubber latex (SBR) and carboxymethyl cellulose (CMC).
The content of the binder is preferably 0.2 to 15 parts by mass, and more preferably 0.5 to 10 parts by mass, based on 100 parts by mass of the total amount of the electrode active material and the binder.
The conductive assistant can further improve the conductivity between the electrode active materials or the conductivity between the electrode active material and the current collector. Examples of the conductive assistant include acetylene black, ketjen black, carbon nanofibers, carbon nanotubes, carbon fibers, and the like.
The content of the conductive additive is preferably 0.5 to 15 parts by mass, and more preferably 0.5 to 5 parts by mass, based on 100 parts by mass of the total amount of the electrode active material and the binder.
The electrode active material layer can be formed by applying a mixture to the current collector and drying the mixture.
The mixture is obtained by mixing the electrode active material, the binder, and if necessary, the conductive additive and the nonaqueous solvent to form a uniform slurry. Examples of the nonaqueous solvent include acetone, dimethyl sulfoxide, ethyl methyl ketone, diisopropyl ketone, cyclohexanone, methylcyclohexane, ethyl acetate, γ -butyrolactone, tetrahydrofuran, acetamide, N-methylpyrrolidone, N-dimethylformamide, propylene carbonate, dimethyl carbonate, ethyl methyl carbonate (ethyl methyl carbonate), diethyl carbonate, and the like.
The coating method is not particularly limited, and a method of coating by a bar coater, a die coater, a comma coater, or the like can be used. The drying after the coating is usually carried out at 50 to 150 ℃ for 1 to 300 minutes. Drying may be carried out several times at different temperatures. In the drying, pressure may be applied, but the drying is usually carried out under atmospheric pressure or reduced pressure. The heat treatment may be performed after drying. The heat treatment is usually carried out at 100 to 300 ℃ for 10 seconds to 300 minutes.
A pressing treatment may be further performed after coating and drying. The pressing treatment is usually carried out at 1 to 200 MPa. By performing the pressing treatment, the electrode density can be increased.
The thickness of the electrode active material layer for the positive electrode is preferably 40 to 500 μm, and more preferably 100 to 400 μm. The thickness of the electrode active material layer for the negative electrode is preferably 20 to 400 μm, and more preferably 40 to 300 μm.
The weight of the electrode active material layer per unit area is preferably 20 to 700g/m2More preferably 30 to 500g/m2。
3-2. adhesive resin composition layer
The adhesive resin composition layer is a layer obtained by using the adhesive resin composition described above, and is provided on the electrode. The composition and the forming method of the adhesive resin composition layer are the same as those of the adhesive resin composition layer described above.
4. Nonaqueous electrolyte secondary battery
The nonaqueous electrolyte secondary battery of the present invention includes: a positive electrode; a negative electrode; a separator disposed between the positive electrode and the negative electrode; and an adhesive resin composition layer provided between the separator and the positive electrode and at least one of the separator and the negative electrode.
The adhesive resin composition layer is a layer obtained from the adhesive resin composition layer, and is provided between the separator and the positive electrode and between the separator and the negative electrode. Among these, the adhesive resin composition layer is preferably provided between the separator and the negative electrode.
Such a nonaqueous electrolyte secondary battery can be manufactured through the following steps: obtaining a laminate having a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and the adhesive resin composition layer provided at least one of between the separator and the negative electrode and between the separator and the positive electrode; and heating or hot-pressing the resulting laminate.
The laminate can be produced by any method. For example, a laminate can be obtained by laminating a positive electrode, a negative electrode, and the separator structure described above; the laminate may be obtained by laminating a negative electrode structure having an adhesive resin composition layer (or a positive electrode structure having an adhesive resin composition layer), a positive electrode (or a negative electrode), and a separator.
The heating or hot pressing of the obtained laminate may be performed before or after the step of immersing the laminate in the electrolyte solution. From the viewpoint of promoting the impregnation of the electrolyte solution into the adhesive resin composition layer and reducing the increase in internal resistance caused by the adhesive resin composition layer when the battery is produced, and from the viewpoint of lowering the temperature at the time of heating or hot pressing, it is preferable that the heating or hot pressing is performed after the obtained laminate is impregnated with the electrolyte solution.
That is, the nonaqueous electrolyte secondary battery of the present invention can be obtained by, for example, a laminate battery through the following steps: 1) obtaining the laminate; 2) the resulting laminate was put into a (pouch-shaped) laminate battery, immersed in an electrolyte, and then the laminate battery was packaged; and 3) heating or hot-pressing the packaged laminated battery to bond the electrode and the separator via the adhesive resin composition layer.
The heating or hot-pressing temperature is not particularly limited as long as the separator and the electrode can be bonded to each other, but is, for example, preferably 40 to 180 ℃, and more preferably 60 to 110 ℃. Thus, the adhesive resin composition layer obtained using the adhesive resin composition of the present invention can easily obtain adhesion between the separator and the electrode in a wide temperature range (for example, 20 to 50 ℃), and has a wide process window. The heating or hot-pressing time is, for example, 20 seconds to 30 minutes. The pressure of the hot pressing is, for example, 1 to 30 MPa.
In this manner, in the heating or hot-pressing step, the adhesive resin composition layer is exposed to a high-temperature environment in the presence of the electrolytic solution. Even at such high temperatures, the adhesive resin composition layer obtained using the adhesive resin composition of the present invention is not easily dissolved in an electrolytic solution even at a certain temperature or higher, and has a high elastic modulus. Thus, not only can high adhesion between the separator and the electrode be maintained, but also the heating or hot-pressing temperature range (process window) can be widened, thereby reducing the fraction defective of the battery.
In particular, a negative electrode containing a resin other than vinylidene fluoride polymer as a binder is less likely to be well bonded to a separator via an adhesive resin composition layer containing vinylidene fluoride polymer, as compared to a positive electrode containing vinylidene fluoride polymer as a binder. Even in such a case, the adhesive resin composition layer obtained using the adhesive resin composition of the present invention can maintain high adhesion between the separator and the negative electrode at high temperatures, and can widen the process window.
Examples
The present invention will be described in more detail below with reference to examples. The scope of the invention is not to be interpreted restrictively according to these examples.
1. Preparation of adhesive resin particles and measurement of physical Properties
< preparation of Polymer particles 1 (core-Shell particles) >
(1) Polymerization of the core
333 parts by mass of ion-exchanged water and 0.53 parts by mass of sodium pyrophosphate as a neutral buffer were added to the autoclave, and degassing was performed by nitrogen bubbling for 30 minutes. Then, 1.3 parts by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. Ethyl acetate 0.125 parts by mass, vinylidene fluoride (VDF)20 parts by mass, and Chlorotrifluoroethylene (CTFE)30 parts by mass were charged into a monomer charging tank (charge pot). A part of 27 parts by mass of this monomer mixture was added to the above autoclave at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.07 part by mass in terms of APS to start the polymerization. After the reaction was started, when the pressure was decreased by 2% or more, 23 parts by mass of the remaining monomer mixture was continuously added so that the pressure became constant. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby a core part comprising the vinylidene fluoride copolymer (a-1) was obtained. The average particle diameter of the obtained core portion was 98 nm.
(2) Polymerization of the Shell
In advance, 50 parts by mass of vinylidene fluoride (VDF) and 0.125 part by mass of ethyl acetate were measured in a monomer feed tank to prepare a monomer mixture. Subsequently, the core portion was emulsion polymerized, and the monomer mixture was continuously supplied at 80 ℃ to maintain the pressure in the autoclave, thereby carrying out polymerization. After the monomer addition was completed, when the pressure in the autoclave was reduced to 2.5MPa, the polymerization of the shell portion was completed, and the shell portion composed of the vinylidene fluoride polymer (b-1) was formed. The average particle diameter of the obtained core-shell polymer particles 1 (adhesive resin particles) was 135 nm.
< preparation of Polymer particles 2 (core-Shell particles) >
(1) Polymerization of the core
330 parts by mass of ion-exchanged water was added to the autoclave, and degassing was performed by 30 minutes of nitrogen bubbling. Then, 1.0 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. To the autoclave were added 0.05 parts by mass of ethyl acetate, 10 parts by mass of vinylidene fluoride (VDF), and 30 parts by mass of Hexafluoropropylene (HFP) all at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.1 part by mass in terms of APS to start the polymerization. The pressure in the autoclave at this time was 2.6 MPa. After the reaction was started, when the pressure was reduced to 2.5MPa, 1 part by mass of perfluorodivinyl ether (PFDVE) as a crosslinkable monomer was charged, and then 60 parts by mass of vinylidene fluoride (VDF) was continuously added so that the pressure in the autoclave was maintained at 2.5 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, and particles having a core portion composed of the vinylidene fluoride copolymer (a-2) were obtained. The average particle diameter of the obtained particles was 158 nm.
(2) Polymerization of the Shell
700 parts by mass of ion-exchanged water and 0.5 part by mass of disodium hydrogen phosphate were added to the autoclave, and degassing was performed by bubbling nitrogen for 30 minutes. Then, 100 parts by mass of the core particles dispersed in water and 0.5 part by mass of PFOA were charged, and pressurized to 4.5MPa to carry out nitrogen substitution three times. To the autoclave were added 0.05 part by mass of ethyl acetate and 100 parts by mass of vinylidene fluoride (VDF) all at once. After raising the temperature to 80 ℃ under stirring, a 5 wt% aqueous solution of APS was added in an amount corresponding to 0.1 part by mass in terms of APS to start polymerization. The pressure in the autoclave at this time was 4.1 MPa. After the reaction was started, polymerization of the shell portion was completed when the pressure was reduced to 1.5MPa, and the shell portion composed of the vinylidene fluoride polymer (b-1) was formed, thereby obtaining core-shell type polymer particles 2. The average particle diameter of the obtained particles was 199 nm.
< preparation of Polymer particles 3 (core-Shell particles) >
(1) Polymerization of the core
333 parts by mass of ion-exchanged water and 0.53 parts by mass of sodium pyrophosphate as a neutral buffer were added to the autoclave, and degassing was performed by nitrogen bubbling for 30 minutes. Then, 1.33 parts by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. Ethyl acetate 0.25 parts by mass, vinylidene fluoride (VDF)29 parts by mass, Chlorotrifluoroethylene (CTFE)21 parts by mass, and perfluorodivinyl ether (PFDVE)0.5 parts by mass as a crosslinkable monomer were charged into a monomer-charging tank. A part of 27 parts by mass of this monomer mixture was added to the above autoclave at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.07 part by mass in terms of APS to start the polymerization. After the reaction was started, when the pressure was decreased by 2% or more, 23 parts by mass of the remaining monomer mixture was continuously added so that the pressure became constant. The polymerization was terminated when the pressure was reduced to 1.5MPa, and the emulsion polymerization of the core part composed of the vinylidene fluoride polymer (a-3) was terminated. The average particle diameter of the obtained core particles was 97 nm.
(2) Polymerization of the Shell
In advance, 50 parts by mass of vinylidene fluoride (VDF) and 0.25 part by mass of ethyl acetate were measured in a monomer feed tank to prepare a monomer mixture. Subsequently, the above-mentioned core emulsion polymerization was carried out by continuously supplying the monomer mixture at 80 ℃ so as to maintain the pressure in the tank at 3.2 MPa. After the monomer addition was completed, when the pressure in the autoclave was reduced to 2.5MPa, the shell was polymerized to form a shell composed of a vinylidene fluoride polymer (b-2), and core-shell polymer particles 3 were obtained. The average particle diameter of the obtained particles was 132 nm.
< preparation of Polymer particles 4 (core-Shell particles) >
(1) Polymerization of the core
333 parts by mass of ion-exchanged water and 0.53 parts by mass of sodium pyrophosphate as a neutral buffer were added to the autoclave, and degassing was performed by nitrogen bubbling for 30 minutes. Then, 1.33 parts by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. Ethyl acetate 0.25 parts by mass, vinylidene fluoride (VDF)15 parts by mass, and Chlorotrifluoroethylene (CTFE)35 parts by mass were charged into a monomer-charging tank. A part of 27 parts by mass of this monomer mixture was added to the above autoclave at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.06 part by mass in terms of APS to start the polymerization. After the reaction was started, when the pressure was decreased by 2% or more, 23 parts by mass of the remaining monomer mixture was continuously added while maintaining the pressure constant. The polymerization was terminated when the pressure was reduced to 1.5MPa, and particles having a core portion composed of the vinylidene fluoride copolymer (a-4) were obtained. The average particle diameter of the obtained core particles was 94 nm.
(2) Polymerization of the Shell
In advance, 50 parts by mass of vinylidene fluoride (VDF) and 0.25 part by mass of ethyl acetate were measured in a monomer feed tank to prepare a monomer mixture. Subsequently, the above-mentioned core emulsion polymerization was carried out by continuously supplying the monomer mixture at 80 ℃ so as to maintain the pressure in the tank at 3.2 MPa. After the monomer addition was completed, when the pressure in the autoclave was reduced to 2.5MPa, the shell was polymerized to form a shell composed of a vinylidene fluoride polymer (b-1), and core-shell polymer particles 4 were obtained. The average particle diameter of the obtained particles was 153 nm.
< preparation of Polymer particles 5 (Tilt particles) >
Into the autoclave were added 330 parts by mass of ion-exchanged water and 0.2 part by mass of disodium hydrogen phosphate, and degassing was performed by bubbling nitrogen for 30 minutes. Then, 1.0 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. 18.0 parts by mass of vinylidene fluoride (VDF) and 7.0 parts by mass of Hexafluoropropylene (HFP) were added to the above autoclave at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.06 part by mass in terms of APS to start the polymerization. The pressure in the autoclave at this time was 2.6 MPa. After the reaction was started, 75.0 parts by mass of vinylidene fluoride (VDF) was continuously added to the autoclave so that the pressure in the autoclave was maintained at 2.5MPa when the pressure was reduced to 2.5 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby polymer particles 5 composed of the vinylidene fluoride copolymer (a-5) were obtained. The average particle diameter of the obtained particles was 146 nm.
< production of Polymer particles 6 (inclined particles) >
(1) Preparation of PVDF/HFP copolymer
An autoclave having an internal volume of 14 liters was charged with 8271g of ion-exchanged water, 1.61g of methylcellulose (SM-100, manufactured by shin-Etsu chemical Co., Ltd.), 12.9g of diisopropyl peroxydicarbonate (IPP), 2936g of vinylidene fluoride (VDF), and 290g of Hexafluoropropylene (HFP), and polymerized at 29 ℃. After completion of the polymerization, the polymer slurry was subjected to heat treatment at 95 ℃ for 60 minutes, then dehydrated, washed with water, and further dried at 80 ℃ for 20 hours, to obtain polymer particles 6 composed of a vinylidene fluoride copolymer (a-6) (vinylidene fluoride/hexafluoropropylene copolymer). The average particle diameter of the obtained particles was 170. mu.m.
(2) Lithium hydroxide treatment-1
The obtained copolymer (PVDF/HFP) was added to NMP at 5 mass%, and heated to 50 ℃ while stirring at room temperature to completely dissolve the copolymer. Lithium hydroxide was added thereto in an amount of 1% by mass relative to the copolymer (PVDF/HFP), and the mixture was stirred at 50 ℃ for 3 hours. Using this solution, the turbidity, viscosity, and peel strength of the NMP solution of the polymer particles 6 were measured.
(3) Lithium hydroxide treatment-2
The obtained copolymer (PVDF/HFP) was added to acetone at 10 mass%, dispersed at room temperature with stirring, and then heated to 45 ℃ in a water bath to dissolve the copolymer. Lithium hydroxide was added thereto in an amount of 1% by mass relative to the copolymer (PVDF/HFP), and the mixture was stirred at 50 ℃ for 3 hours. Using this solution, the turbidity and viscosity of the acetone solution of the polymer particles 6 were measured.
< preparation of Polymer particles 7 (Tilt particles) >
Into the autoclave were added 330 parts by mass of ion-exchanged water and 0.25 part by mass of disodium hydrogen phosphate as a neutral buffer, and degassing was performed by bubbling nitrogen for 30 minutes. Then, 1.0 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. To the autoclave were added 0.2 parts by mass of ethyl acetate, 24.7 parts by mass of vinylidene fluoride (VDF), and 10.0 parts by mass of Hexafluoropropylene (HFP) all at once. After raising the temperature to 80 ℃ under stirring, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.06 part by mass in terms of APS to start polymerization. After the reaction was started and the pressure was reduced by 2% or more, 2 parts by mass of perfluorodivinyl ether (PFDVE) and 63.3 parts by mass of vinylidene fluoride (VDF) were continuously added so that the pressure in the autoclave became constant. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby polymer particles 7 composed of the vinylidene fluoride copolymer (a-7) were obtained. The average particle size of the resulting particles was 154 nm.
< preparation of Polymer particles 8 (Tilt particles) >
An autoclave having an internal volume of 14 liters was charged with 8230g of ion-exchanged water, 0.96g of methylcellulose (SM-100, manufactured by shin-Etsu chemical Co., Ltd.), 27.48g of di-n-propyl peroxydicarbonate, 3146g of vinylidene fluoride (VDF) and 64g of Hexafluoropropylene (HFP), and polymerized at 29 ℃. After completion of the polymerization, the polymer slurry was subjected to heat treatment at 95 ℃ for 60 minutes, then dehydrated, washed with water, and further dried at 80 ℃ for 20 hours to obtain polymer particles 8 composed of a vinylidene fluoride copolymer (c-1) (vinylidene fluoride/hexafluoropropylene copolymer). The average particle diameter of the obtained particles was 173. mu.m.
< preparation of Polymer particles 9 (Tilt particles) >
Into the autoclave were added 330 parts by mass of ion-exchanged water and 0.2 part by mass of disodium hydrogen phosphate, and degassing was performed by bubbling nitrogen for 30 minutes. Then, 0.7 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. 8.0 parts by mass of vinylidene fluoride (VDF) and 47.0 parts by mass of Hexafluoropropylene (HFP) were added to the above autoclave at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.06 part by mass in terms of APS to start the polymerization. The pressure in the autoclave at this time was 3.83 MPa. After the reaction was started, 45.0 parts by mass of vinylidene fluoride (VDF) was continuously added to the autoclave so that the pressure in the autoclave was maintained at 2.5MPa when the pressure was reduced to 2.5 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby polymer particles 9 composed of the vinylidene fluoride copolymer (c-2) were obtained. The average particle diameter of the obtained particles was 187 nm.
< preparation of Polymer particles 10 (Tilt particles) >
An autoclave having an internal volume of 14 liters was charged with 8271g of ion-exchanged water, 1.61g of methylcellulose (SM-100, manufactured by shin-Etsu chemical Co., Ltd.), 12.9g of diisopropyl peroxydicarbonate, 2903g of vinylidene fluoride, and 323g of hexafluoropropylene, and polymerized at 29 ℃. After completion of the polymerization, the polymer slurry was subjected to heat treatment at 95 ℃ for 60 minutes, then dehydrated, washed with water, and further dried at 80 ℃ for 20 hours, to obtain polymer particles 10 composed of a vinylidene fluoride copolymer (c-3) (vinylidene fluoride/hexafluoropropylene copolymer). The average particle size of the obtained particles was 165. mu.m.
< preparation of Polymer particles 11 (Tilt particles) >
Into the autoclave were added 330 parts by mass of ion-exchanged water and 0.2 part by mass of disodium hydrogen phosphate, and degassing was performed by bubbling nitrogen for 30 minutes. Then, 1.0 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. To the autoclave were added 0.25 parts by mass of ethyl acetate, 23.7 parts by mass of vinylidene fluoride (VDF), and 8 parts by mass of Hexafluoropropylene (HFP) all at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.06 part by mass in terms of APS to start the polymerization. The pressure in the autoclave at this time was 3.3 MPa. After the reaction was started, when the pressure was reduced to 2.5MPa, 5 parts by mass of perfluorodivinyl ether (PFDVE) was charged, and 63.3 parts by mass of vinylidene fluoride (VDF) was continuously added to maintain the pressure in the autoclave at 2.5 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby polymer particles 11 composed of the vinylidene fluoride copolymer (c-4) were obtained. The average particle diameter of the obtained particles was 152 nm.
< preparation of Polymer particles 12 (Tilt particles) >
Into the autoclave were added 330 parts by mass of ion-exchanged water and 0.2 part by mass of disodium hydrogen phosphate, and degassing was performed by bubbling nitrogen for 30 minutes. Then, 1.0 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. To the autoclave were added 0.25 parts by mass of ethyl acetate, 28.7 parts by mass of vinylidene fluoride (VDF), and 8.0 parts by mass of Hexafluoropropylene (HFP) all at once. After raising the temperature to 80 ℃ under stirring, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.06 part by mass in terms of APS to start polymerization. The pressure in the autoclave at this time was 3.83 MPa. After the reaction was started, 63.3 parts by mass of vinylidene fluoride (VDF) were continuously added to the autoclave so that the pressure in the autoclave was maintained at 2.5MPa when the pressure was reduced to 2.5 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby polymer particles 12 composed of the vinylidene fluoride copolymer (c-5) were obtained. The average particle diameter of the obtained particles was 187 nm.
< preparation of Polymer particles 13 (Tilt particles) >
250 parts by mass of ion-exchanged water and 0.2 part by mass of sodium pyrophosphate as a neutral buffer were added to the autoclave, and degassing was performed by nitrogen bubbling for 30 minutes. Then, 1.0 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. Ethyl acetate 0.5 parts by mass, vinylidene fluoride (VDF)80 parts by mass, Chlorotrifluoroethylene (CTFE)20 parts by mass, and perfluorodivinyl ether (PFDVE)1 part by mass were charged into a monomer-feeding tank. A part of 20 parts by mass of the monomer mixture was added to the above autoclave at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.08 part by mass in terms of APS to start the polymerization. Immediately after the start of the reaction, 80 parts by mass of the remaining monomer mixture was continuously added with the pressure being maintained constant. The polymerization was terminated when the pressure was reduced to 1.3MPa, whereby polymer particles 13 composed of the vinylidene fluoride copolymer (c-6) were obtained. The average particle size of the resulting particles was 154 nm.
< preparation of Polymer particles 14 (core-Shell particles) >
(1) Polymerization of the core
333 parts by mass of ion-exchanged water and 0.53 parts by mass of sodium pyrophosphate as a neutral buffer were added to the autoclave, and degassing was performed by nitrogen bubbling for 30 minutes. Then, 1.33 parts by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. Ethyl acetate 0.53 parts by mass, vinylidene fluoride (VDF)18 parts by mass, Chlorotrifluoroethylene (CTFE)12 parts by mass, and perfluorodivinyl ether (PFDVE)0.3 parts by mass were charged into a monomer-charging tank. A part of 27 parts by mass of this monomer mixture was added to the above autoclave at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.07 part by mass in terms of APS to start the polymerization. Immediately after the start of the reaction, 3 parts by mass of the remaining monomer mixture was continuously added while maintaining the pressure at 2.6 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, and the emulsion polymerization of the core part composed of the vinylidene fluoride copolymer (a-8) was terminated. The average particle diameter of the obtained particles was 88 nm.
(2) Polymerization of the Shell
In advance, 70 parts by mass of vinylidene fluoride (VDF) and 0.35 part by mass of ethyl acetate were measured in a monomer feed tank to prepare a monomer mixture. Subsequently, the above-mentioned core emulsion polymerization was carried out by continuously supplying the monomer mixture at 80 ℃ so as to maintain the pressure in the tank at 3.2 MPa. After the monomer addition is finished, when the pressure in the kettle is reduced to 2.7MPa, the shell polymerization is finished. Then, after cooling to 40 ℃, the residual monomer was removed to form a shell portion composed of the vinylidene fluoride polymer (b-2), and the core-shell type polymer particles 14 were obtained. The average particle diameter of the obtained particles was 133 nm.
< preparation of Polymer particles 15 (Tilt particles) >
Into the autoclave were added 330 parts by mass of ion-exchanged water and 0.2 part by mass of disodium hydrogen phosphate as a neutral buffer, and degassing was performed by bubbling nitrogen for 30 minutes. Then, 1.0 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. To the autoclave were added 0.25 parts by mass of ethyl acetate, 27.7 parts by mass of vinylidene fluoride (VDF), and 8.0 parts by mass of Hexafluoropropylene (HFP) all at once. After raising the temperature to 80 ℃ under stirring, a 5 wt% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.1 part by mass in terms of APS to start polymerization. The pressure in the autoclave at this time was 3.5 MPa. After the reaction was started, when the pressure was reduced to 2.5MPa, 1 part by mass of perfluorodivinyl ether (PFDVE) was charged, and 63.3 parts by mass of vinylidene fluoride was continuously added to maintain the pressure in the autoclave at 2.5 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby polymer particles 15 composed of the vinylidene fluoride copolymer (c-7) were obtained. The average particle diameter of the obtained particles was 98 nm. < preparation of Polymer particles 16 (core-Shell particles) >
(1) Polymerization of the core
330 parts by mass of ion-exchanged water was added to the autoclave, and degassing was performed by 30 minutes of nitrogen bubbling. Then, 1.0 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. To the autoclave were added 0.05 parts by mass of ethyl acetate, 10 parts by mass of vinylidene fluoride (VDF), and 30 parts by mass of Hexafluoropropylene (HFP) all at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.1 part by mass in terms of APS to start the polymerization. The pressure in the autoclave at this time was 2.5 MPa. After the reaction was started, 60 parts by mass of vinylidene fluoride (VDF) were continuously added to the autoclave so that the pressure in the autoclave was maintained at 2.0MPa when the pressure was reduced to 2.0 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, and particles having a core portion composed of the vinylidene fluoride copolymer (a-9) were obtained. The average particle diameter of the obtained particles was 160 nm.
(2) Polymerization of the Shell
700 parts by mass of ion-exchanged water and 0.5 part by mass of disodium hydrogen phosphate were added to the autoclave, and degassing was performed by bubbling nitrogen for 30 minutes. Then, 100 parts by mass of the core particles dispersed in water and 0.5 part by mass of PFOA were charged, and pressurized to 4.5MPa to carry out nitrogen substitution three times. To the autoclave were added 0.05 part by mass of ethyl acetate and 100 parts by mass of vinylidene fluoride (VDF) all at once. After raising the temperature to 80 ℃ under stirring, a 5 wt% aqueous solution of APS was added in an amount corresponding to 0.1 part by mass in terms of APS to start polymerization. The pressure in the autoclave at this time was 4.0 MPa. After the reaction was started, polymerization of the shell portion was completed when the pressure was reduced to 1.5MPa, and the shell portion composed of the vinylidene fluoride copolymer (b-1) was formed, thereby obtaining core-shell type polymer particles 16. The average particle diameter of the obtained particles was 203 nm.
< preparation of Polymer particles 17 (inclined particles) >
330 parts by mass of ion-exchanged water was added to the autoclave, and degassing was performed by 30 minutes of nitrogen bubbling. Then, 0.7 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. To the autoclave were added 0.1 part by mass of ethyl acetate, 14.7 parts by mass of vinylidene fluoride (VDF), and 22 parts by mass of Hexafluoropropylene (HFP) all at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.06 part by mass in terms of APS to start the polymerization. The pressure in the autoclave at this time was 3.7 MPa. After the reaction was started, 63.3 parts by mass of vinylidene fluoride (VDF) were continuously added to the autoclave so that the pressure in the autoclave was maintained at 2.5MPa when the pressure was reduced to 2.5 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby polymer particles 17 composed of the vinylidene fluoride copolymer (a-10) were obtained. The average particle diameter of the obtained particles was 175 nm.
< preparation of Polymer particles 18 (Tilt particles) >
330 parts by mass of ion-exchanged water was added to the autoclave, and degassing was performed by 30 minutes of nitrogen bubbling. Then, 0.7 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. To the autoclave were added 0.1 part by mass of ethyl acetate, 9.7 parts by mass of vinylidene fluoride (VDF), and 27 parts by mass of Hexafluoropropylene (HFP) all at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.06 part by mass in terms of APS to start the polymerization. The pressure in the autoclave at this time was 3.7 MPa. After the reaction was started, 63.3 parts by mass of vinylidene fluoride (VDF) were continuously added to the autoclave so that the pressure in the autoclave was maintained at 2.5MPa when the pressure was reduced to 2.5 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby polymer particles 18 composed of the vinylidene fluoride copolymer (a-11) were obtained. The average particle diameter of the obtained particles was 183 nm.
< preparation of Polymer particles 19 (Tilt particles) >
330 parts by mass of ion-exchanged water was added to the autoclave, and degassing was performed by 30 minutes of nitrogen bubbling. Then, 0.7 part by mass of perfluorooctanoic acid ammonium salt (PFOA) was charged, and the pressure was increased to 4.5MPa to conduct nitrogen substitution three times. To the autoclave were added 0.1 part by mass of ethyl acetate, 9.5 parts by mass of vinylidene fluoride (VDF), and 27.3 parts by mass of Hexafluoropropylene (HFP) all at once. After raising the temperature to 80 ℃ while stirring the mixture, a 5 mass% aqueous solution of Ammonium Persulfate (APS) was added in an amount corresponding to 0.06 part by mass in terms of APS to start the polymerization. The pressure in the autoclave at this time was 2.6 MPa. Immediately after the reaction was started, 63.4 parts by mass of vinylidene fluoride (VDF) were continuously added to the autoclave so that the pressure in the autoclave was maintained at 2.6 MPa. The polymerization was terminated when the pressure was reduced to 1.5MPa, whereby polymer particles 19 composed of the vinylidene fluoride copolymer (c-8) were obtained. The average particle diameter of the obtained particles was 213 nm.
The melting point, the solution viscosity (a) when dissolved in acetone, the turbidity when dissolved in NMP, the solution viscosity (B) when dissolved in NMP, the inherent viscosity, and the average particle diameter of the obtained polymer particles 1 to 19 were measured by the following methods.
[ melting Point ]
The melting point of the obtained polymer particles was measured in the form of a film. The film was produced by the following method. That is, a mold having a length of 5 cm. times.a width of 5 cm. times.a thickness of 150 μm and about 1g of polymer particles were sandwiched between two aluminum foils sprayed with a release agent, and pressed at 200 ℃. The melting point of the vinylidene fluoride copolymer was measured by using the obtained film according to ASTM d 3418 by DSC ("DSC-1" manufactured by METTLER Co.).
[ solution viscosity (A) of acetone solution ]
(preparation of acetone solution)
The resulting polymer particles were dissolved in acetone. Specifically, the polymer particles were added so that the polymer concentration in the solution became 10 mass%, and after dispersing the polymer particles in acetone at room temperature, the mixture was stirred in a water bath at 45 ℃ to dissolve the vinylidene fluoride copolymer.
(measurement of solution viscosity)
The viscosity of the acetone solution obtained was measured by an E-type viscometer. Specifically, 1.1ml of the acetone solution was added to a measurement part of a viscometer (RE 550 type viscometer manufactured by Toyobo industries Co., Ltd.), and the measurement was carried out at a measurement temperature of 25 ℃ for 300 seconds at a rotation speed of 10rpm with a conical rotor of 1 ℃ 34' XR 24. The viscosity at the time point when 300 seconds passed was set as the acetone solution viscosity.
[ turbidity of NMP solution ]
(preparation of NMP solution)
The obtained polymer particles were dissolved in NMP. Specifically, polymer particles were added so that the polymer concentration in the solution became 5 mass%, and after dispersing the polymer particles in NMP at room temperature, the polymer particles were dissolved by stirring at 50 ℃.
The turbidity of the resulting NMP solution was measured by a turbidimeter (hazemeter). Specifically, NMP was added to a linear square cell (size: 10X 36X 55mm) so that the height became 4cm or more and less than 4.5cm, and the cell was placed in a measuring part of a turbidimeter (NDH 2000, manufactured by Nippon Denshoku industries Co., Ltd.), followed by calibration under conditions of room temperature 20. + -. 2 ℃, humidity 50. + -. 5%, light source D65. C, and measuring method 3 (measuring method according to JIS K7136 (determination method of haze (haze) of plastic-transparent material)). Then, an NMP solution in which the adhesive resin was dissolved was added to the cell, and the turbidity of the solution was measured under the same conditions.
[ solution viscosity (B) of NMP solution ]
(preparation of NMP solution)
An NMP solution was obtained by the same method as described above.
(measurement of solution viscosity)
The viscosity of the NMP solution obtained was measured by the same method as the method for measuring the solution viscosity (a) of the acetone solution.
[ logarithmic viscosity ]
The inherent viscosity of the polymer particles (polymer particles 6, 8 and 10) obtained by the suspension polymerization method was measured. Specifically, 80mg of the obtained polymer particles were dissolved in 20mL of DMF to obtain a solution. The viscosity of the resulting solution and DMF was measured in a constant temperature bath at 30 ℃ using an ubbelohde viscometer, and the inherent viscosity was calculated by the following formula.
ηi＝(1/C)·ln(η/η0)
Eta is the measured viscosity of the solution,. eta.0 is the measured viscosity of DMF, and C is the concentration of particles containing vinylidene fluoride copolymer in the solution, here 0.4(g/dl)
[ average particle diameter ]
The average particle diameter of the polymer particles (polymer particles 1 to 5, 7, 9, and 11 to 19) obtained by the emulsion polymerization method was calculated by regularization analysis by a dynamic light scattering method. Specifically, the particle size of the polymer particles was measured according to JIS Z8828 using "delsa maxcore" manufactured by BECKMAN COULTER corporation, and the large peak of two large and small peaks obtained by regularization analysis was set as the average particle size.
On the other hand, in the case of obtaining polymer particles by suspension polymerization, 3000 powdered polymer particles were photographed, and the average of the particle diameters of the particles in the case where the photographed particles were assumed to be circular was defined as the average particle diameter.
The structures of the obtained polymer particles 1 to 19 are shown in table 1, and the measurement results of the physical properties are shown in table 2. In Table 2, "-" indicates that the measurement was impossible.
[ Table 1]
Figure BDA0002766973180000361
[ Table 2]
Figure BDA0002766973180000362
Figure BDA0002766973180000371
2. Preparation and evaluation of adhesive resin composition
[ examples 1 to 10, comparative examples 1 to 9 ]
The polymer particles (adhesive resin particles) shown in tables 1 and 2 were dispersed in NMP so that the polymer concentration in the solution became 5 mass%, to obtain adhesive resin compositions.
The separator structures having an adhesive resin composition layer were produced using the adhesive resin compositions obtained in examples 1 to 10 and comparative examples 1 to 9, and the peel strength between the separator and the electrode and the bondable temperature range (process window) were measured by the following methods.
[ measurement of peeling Strength ]
(1) Fabrication of spacer Structure
The adhesive resin composition was applied to one surface of a separator (polyethylene single layer separator, thickness 20 μm, porosity 40%, air permeability 300sec, tensile strength (MD)150MPa, (TD)130MPa, tensile elongation (MD) 50%, and (TD) 100%) using a wire bar (wire bar) with a wet application amount of 24 μm (count 12), and then immersed in a coagulation bath (water) at 23 ± 2 ℃ for 3 minutes. Thereafter, the plate was immersed in a cleaning solution (water) for 1 minute, and dried at 70 ℃ under nitrogen for 30 minutes. Further, the resulting laminate was heat-treated at 60 ℃ for 3 hours in a vacuum to obtain a separator structure having an adhesive resin composition layer with a thickness of 2 μm.
(2) Production of negative electrode
Water was added to 95 parts by mass of BTR918 (manufactured by modified natural graphite BTR) as a negative electrode active material, 2 parts by mass of a conductive auxiliary agent (manufactured by SuperP timal), 2 parts by mass of SBR (styrene butadiene rubber) latex (BM-400 manufactured by japan ZEON) as a binder, and 1 part by mass of CMC (carboxymethyl cellulose) (manufactured by CELLOGEN 4H first industrial pharmaceutical chemicals) as a thickener to prepare a slurry, which was applied to a copper foil (thickness 10 μm). The coated slurry was dried, pressed, and heat-treated at 150 ℃ for 3 hours. Thus, an electrode having a bulk density of 1.6g/cm was formed3The weight per unit area is 60g/m2The negative electrode active material layer to obtain a negative electrode.
(3) Production of Al laminated cell
The obtained negative electrode was cut into 2.5X 5.0 cm. The separator thus produced was cut out to 3.0X 6.0 cm. The obtained negative electrode and a separator were stacked and placed in a bag of Al laminated film. To a bag in which an Al laminated film is putThe laminate in (1) was injected with 180 μ L of an electrolyte solution (ethylene carbonate (EC)/Ethyl Methyl Carbonate (EMC) ═ 3/7 (mass ratio), LiPF6: 1.2M, VC: 1 mass%), immersed, vacuum degassed and encapsulated, and left to stand evening.
(4) Hot pressing
The obtained Al laminated battery was hot-pressed to thermally bond the adhesive resin composition layer on the separator and the negative electrode, thereby obtaining a sample for peel strength measurement. Specifically, the obtained Al laminate battery was preheated for 1 minute, and then hot-pressed at 50 ℃ under a surface pressure of about 4MPa for 2 minutes, and the peel strength was measured by the following method.
The laminate of the electrode and the separator was taken out from the obtained sample for measuring peel strength. The negative electrode of the obtained laminate was fixed, and a 180 ° peel test was performed at a head speed of 200 mm/min using a tensile tester (STA-1150 UNIVERSAL TESTING MACHINE, manufactured by ORIENTEC corporation), and the peel strength was measured.
Then, the hot pressing temperature was changed in the range of 50 to 110 ℃ and the same measurement was repeated. Specifically, three samples were prepared at each hot pressing temperature to measure the peel strength, and the average value of these was defined as "peel strength at each hot pressing temperature". Then, the maximum value of the "peel strength at each hot pressing temperature" when the same measurement was repeated while changing the hot pressing temperature within a range of 50 to 110 ℃ was defined as "peel strength".
[ measurement of bondable temperature Range ]
An Al laminated battery was produced in the same manner as in the production of the sample for measuring peel strength. The obtained Al laminated battery was subjected to a residual heat at an arbitrary temperature for 1 minute, and then hot-pressed at a surface pressure of about 4MPa for 2 minutes to thermally bond the adhesive resin composition layer on the separator and the negative electrode, thereby obtaining a sample for measuring peel strength. The peel strength of the obtained sample for peel strength measurement was measured by the same method as described above. The series of operations was repeated while increasing the hot pressing temperature in stages within the range of 50 to 110 ℃ to obtain a temperature range (bondable temperature range, process window) in which the peel strength was 1.0gf/mm or more.
The results of evaluating the peel strength and the bondable temperature ranges of the adhesive resin compositions of examples 1 to 10 and comparative examples 1 to 9 are shown in table 3.
[ Table 3]
Figure BDA0002766973180000391
Figure BDA0002766973180000401
Therefore, the following steps are carried out: in the adhesive resin compositions of examples 1 to 10 using the polymer particles (adhesive resin particles) satisfying the ranges of the turbidity of the NMP solution, the solution concentration (a) of the acetone solution, and the viscosity ratio (a)/(B) of the NMP solution, the peel strength between the separator and the negative electrode was high, and the bondable temperature range was as wide as 20 ℃.
In contrast, it is known that: in the adhesive resin compositions of comparative examples 1, 3, 5 to 7 and 9 using polymer fine particles having a turbidity of at least NMP solution that is too low, comparative example 2 using polymer fine particles having a turbidity of at least NMP solution that is too high, comparative example 4 using polymer particles having a low solution viscosity (a) of acetone solution, and comparative example 8 having a low solution viscosity (a) of acetone solution and a viscosity ratio (a)/(B) of less than 1, the peel strength between the separator and the negative electrode is low, and the bondable temperature range is also narrow to 10 ℃.
The present application claims priority based on japanese patent application 2018, 31/5/2018, 104685. The contents described in the specification of this application are all incorporated in the specification of this application.
Industrial applicability of the invention
According to the present invention, an adhesive resin composition containing adhesive resin particles can be provided which can maintain high adhesion between a separator and an electrode even when exposed to high temperatures and has a wide process window in a heating or hot-pressing step.

Claims (15)

1. An adhesive composition comprising an adhesive resin, which is provided on the surface of a separator or an electrode of a nonaqueous electrolyte secondary battery,
the adhesive resin contains at least one vinylidene fluoride copolymer (a) containing a constituent unit derived from vinylidene fluoride and a constituent unit derived from a monomer copolymerizable with the vinylidene fluoride,
wherein the adhesive resin has a turbidity of 2 to 95 when dissolved in N-methyl-2-pyrrolidone so that the concentration of the adhesive resin in the solution is 5 mass%, and a solution viscosity (A) of 350 to 20000 mPas when dissolved in acetone so that the concentration of the adhesive resin in the solution is 10 mass%,
the ratio (A)/(B) of the solution viscosity (A) to the solution viscosity (B) when the adhesive resin is dissolved in N-methyl-2-pyrrolidone so that the concentration of the adhesive resin in the solution is 5 mass% is 1 to 15.
2. The adhesive composition according to claim 1,
the adhesive resin is particles containing the vinylidene fluoride copolymer (a),
the average particle diameter of the particles is 10nm to 1 μm.
3. The adhesive composition according to claim 2,
the particles are core-shell particles comprising: a core part composed of the vinylidene fluoride copolymer (a); and a shell portion surrounding the core portion and composed of a vinylidene fluoride polymer (b) having a vinylidene fluoride ratio higher than that of the core portion,
the vinylidene fluoride content is 97 mass% or less, assuming that the total monomer content in the core-shell particles is 100 mass%.
4. The adhesive composition according to claim 3,
the vinylidene fluoride copolymer (a) is not crosslinked.
5. The adhesive composition according to claim 3 or 4,
the vinylidene fluoride polymer (b) is not crosslinked.
6. The adhesive composition according to any one of claims 3 to 5, wherein,
the vinylidene fluoride polymer (b) further comprises structural units derived from a carboxyl group-containing monomer.
7. The adhesive composition according to any one of claims 1 to 6, wherein,
the monomer copolymerizable with vinylidene fluoride is at least one of chlorotrifluoroethylene and hexafluoropropylene.
8. The adhesive composition according to any one of claims 1 to 7,
the melting point of the adhesive resin is 90 ℃ or higher.
9. A spacer structure body comprising:
a spacer; and
an adhesive composition layer provided on at least one surface of the separator, the adhesive composition layer being obtained by using the adhesive composition according to any one of claims 1 to 8.
10. An electrode structure body comprising: an electrode having a current collector and an electrode active material layer containing an electrode active material provided on the current collector; and
an adhesive composition layer provided on the surface of the electrode active material layer, the adhesive composition layer being obtained by using the adhesive composition according to any one of claims 1 to 8.
11. A non-aqueous electrolyte secondary battery has
A positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an adhesive composition layer, wherein the adhesive composition layer is provided between the separator and the positive electrode and at least one of the separator and the negative electrode, and is obtained by using the adhesive composition according to any one of claims 1 to 8.
12. A method for manufacturing a nonaqueous electrolyte secondary battery, comprising the steps of:
obtaining a laminate having a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an adhesive composition layer provided between the separator and the positive electrode and/or between the separator and the negative electrode, the laminate being obtained by using the adhesive composition according to any one of claims 1 to 8; and
the separator is bonded to the positive electrode via the adhesive composition and/or the separator is bonded to the negative electrode via the adhesive composition.
13. The method of manufacturing a nonaqueous electrolyte secondary battery according to claim 12,
the bonding step is performed by heating at 40 to 180 ℃.
14. The method of manufacturing a nonaqueous electrolyte secondary battery according to claim 12,
the bonding step is performed by hot pressing at 40 to 180 ℃.
15. The method for manufacturing a nonaqueous electrolyte secondary battery according to any one of claims 12 to 14,
the step of bonding is performed after the laminate is impregnated with an electrolyte.
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