JP6955355B2 - Core-shell type particles and their uses and manufacturing methods - Google Patents

Description

The present invention relates to core-shell particles, dispersions, coating compositions, separators, secondary batteries and methods for producing core-shell particles.

In recent years, the development of electronic technology has been remarkable, and the functionality of small mobile devices has been improved. Therefore, the power supplies used for these are required to be smaller and lighter, that is, to have higher energy density. As a battery having a high energy density, a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery or the like is widely used.

In addition, non-aqueous electrolyte secondary batteries are also used in hybrid vehicles that combine secondary batteries and engines, and electric vehicles that use secondary batteries as a power source, from the viewpoint of global environmental issues and energy saving. Applications are expanding.

A separator is provided between the electrodes (positive electrode and negative electrode) of the non-aqueous electrolyte secondary battery. If a gap is formed between the electrode and the separator, the cycle life may be deteriorated. Therefore, it is required to improve the adhesiveness of the adhesive portion such as the electrode and the separator.

Therefore, a separator having improved adhesiveness to an electrode has been developed (for example, Patent Document 1). Patent Document 1 provides ion permeability and handleability by providing an adhesive layer which is an aggregate layer of a predetermined amount of fine particles containing a polyvinylidene fluoride (PVDF) resin on at least one surface of a porous substrate. A separator for a non-aqueous secondary battery, which is excellent and has improved adhesiveness to an electrode, is disclosed.

International Publication No. 2013/073503 (Released on May 23, 2013)

However, in the separator for a non-aqueous secondary battery described in Patent Document 1, the fine particles containing the PVDF resin are melted and crushed during hot pressing in the battery manufacturing process, and the porous group constituting the separator is formed. The holes on the surface of the material are blocked. As a result, there is a problem that the ion permeability of the separator deteriorates.

The present invention has been made in view of the above problems, and an object of the present invention is to provide vinylidene fluoride particles that provide an adhesive layer with reduced blockage of pores on the surface of a separator even after undergoing a heat pressing step. It is in.

The core-shell type particles according to the present invention include a core portion and a shell portion surrounding the core portion in order to solve the above problems, and the core portion is a constituent unit derived from vinylidene fluoride. The shell portion contains a first polymer containing 98 mol% or more of the above, and the shell portion contains a second polymer different from the first polymer, with the constituent unit derived from vinylidene fluoride as the main constituent unit. The second polymer has a lower melting point than the first polymer.

Further, in the core-shell type particles according to the present invention, the melting point of the core-shell type particles is preferably 145 ° C. or higher.

Further, in the core-shell type particles according to the present invention, the first polymer contained in the core portion and / or the second polymer contained in the shell portion has a configuration derived from a halogenated alkyl vinyl compound. The unit is contained, and it is preferable that the halogenated alkyl vinyl compound is contained in the core-shell type particles in an amount of 0.2 mol% or more and 5 mol% or less.

Further, in the core-shell type particles according to the present invention, the structural unit derived from the halogenated alkyl vinyl compound is the structural unit derived from the fluoroalkyl vinyl compound, and the structural unit derived from the fluoroalkyl vinyl compound is the above. It may be contained in the second polymer.

Further, in the core-shell type particles according to the present invention, the second polymer further contains at least one of a structural unit derived from an unsaturated dibasic acid and a structural unit derived from an unsaturated dibasic acid monoester. Is preferable.

Further, in the core-shell type particles according to the present invention, the structural unit of the first polymer may be only the structural unit derived from vinylidene fluoride.

The present invention also includes a dispersion liquid containing the core-shell type particles and the dispersion medium according to the present invention.

Further, it is a coating composition for forming a porous fluororesin layer provided on at least one surface of a separator provided between a negative electrode layer and a positive electrode layer in a secondary battery, and is a core-shell type according to the present invention. Coating compositions containing particles are also included in the present invention.

In addition, the coating composition according to the present invention may further contain a thickener.

Further, the coating composition according to the present invention may further contain a filler.

The present invention also includes a separator in which the coating composition according to the present invention is applied to at least one surface.

Further, in a secondary battery provided with a fluororesin layer formed from the coating composition according to the present invention, the fluororesin layer is obtained by hot-pressing the negative electrode layer, the positive electrode layer, and the separator. A secondary battery having a layer containing the second polymer formed by the above, and the layer containing the second polymer contains particles containing the first polymer. Is also included in the present invention.

Further, for forming a fluororesin layer provided on at least one surface of the negative electrode layer and the positive electrode layer so as to be in contact with a separator provided between the negative electrode layer and the positive electrode layer in the secondary battery. A coating composition containing core-shell type particles according to the present invention is also included in the present invention.

The method for producing a core-shell type particle according to the present invention is a method for producing a core-shell type particle including a core portion and a shell portion surrounding the core portion in order to solve the above problems. A core portion forming step of forming a core portion containing a first polymer having a constituent unit derived from vinylidene conjugation as a main constituent unit, and a second polymer having a constituent unit derived from vinylidene fluoride as a main constituent unit. In order to form the second polymer in the dispersion liquid containing the core portion formed by the core portion forming step, the shell portion forming step including the shell portion forming step including the above-mentioned shell portion forming step. The shell portion is formed around the core portion by polymerizing the monomers of the above.

INDUSTRIAL APPLICABILITY According to the present invention, vinylidene fluoride particles that provide an adhesive layer with reduced blockage of pores on the surface of a separator even after undergoing a heat pressing step are provided.

Hereinafter, an embodiment of a core-shell type particle, a dispersion liquid, a coating composition, a separator, a secondary battery, and a method for producing the core-shell type particle according to the present invention will be described in detail.

[Core-shell type particles]
In the present embodiment, the “core-shell type particle” refers to a particle including a core portion and a shell portion surrounding the core portion.

(Core part)
The core portion contains a first polymer having a structural unit derived from vinylidene fluoride as a main constituent unit, and the core portion is vinylidene fluoride particles containing the first polymer. As used herein, the term "main structural unit" refers to a structural unit that occupies the largest proportion (mol%) of the structural units that make up the polymer. Further, in the present specification, the “vinylidene fluoride particles” refers to the particles of a polymer having a structural unit derived from vinylidene fluoride as a main constituent unit, and the polymer is a homopolymer of vinylidene fluoride. And copolymers of vinylidene fluoride and other monomers are included.

The proportion of the structural unit derived from vinylidene fluoride in the first polymer is preferably 98 mol% or more. Further, in one example, it is particularly preferable that the first polymer is composed of only the structural units derived from vinylidene fluoride. By setting the constituent unit derived from vinylidene fluoride to 98 mol% or more, the melting temperature of the first polymer in the presence of the electrolytic solution becomes higher than the temperature usually performed in the heat pressing step described later. As a result, in the core-shell type particles according to the present embodiment, the core portion is less likely to be crushed (melted) in the heat pressing process. Here, the "melting temperature of the first polymer in the presence of the electrolytic solution" may be, for example, a temperature about 60 to 70 ° C. lower than the melting point of the first polymer, although it depends on the composition of the electrolytic solution and the like.

The first polymer may further contain a structural unit derived from a compound other than vinylidene fluoride as another structural unit constituting the first polymer. Examples of the compound other than vinylidene fluoride include a halogenated alkyl vinyl compound, a hydrocarbon-based monomer, a dimethacrylic acid (poly) alkylene glycol ester, a diacrylic acid (poly) alkylene glycol ester, and polyvinylbenzene. Examples of the halogenated alkyl vinyl compound include a fluoroalkyl vinyl compound, and specific examples thereof include hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene and fluoroalkyl vinyl ether. Hexafluoropropylene is preferable. Examples of the hydrocarbon-based monomer include ethylene, propylene and styrene.

When a structural unit derived from a compound other than vinylidene fluoride is included as another structural unit constituting the first polymer, the proportion of the structural unit derived from the compound other than vinylidene fluoride has an oxidation resistance and crystallinity. From the viewpoint of reducing the risk of damage, for example, it is preferably 2 mol% or less.

Further, the core portion may further contain a compound other than the first polymer. Compounds other than the first polymer include, for example, halogenated alkyl vinyl compounds, hydrocarbon monomers, dimethacrylic acid (poly) alkylene glycol esters, diacrylic acid (poly) alkylene glycol esters, polyvinylbenzene, and cross-linking agents. And so on. Examples of the halogenated alkyl vinyl compound include a fluoroalkyl vinyl compound, and specific examples thereof include hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene and fluoroalkyl vinyl ether. Can be mentioned. Examples of the hydrocarbon-based monomer include ethylene, propylene and styrene.

The melting point of the first polymer is preferably 150 ° C. or higher, more preferably 155 ° C. or higher, and even more preferably 160 ° C. or higher, from the viewpoint of ion permeability. The method for measuring the melting point of the first polymer according to the present embodiment will be described in Examples described later.

The average particle size of the first polymer is not particularly limited, but is, for example, 10 nm or more and 1 μm or less. The method for measuring the average particle size of the first polymer according to the present embodiment will be described in Examples described later.

(Shell part)
The shell portion contains a second polymer having a structural unit derived from vinylidene fluoride as a main structural unit. As the second polymer, a polymer different from the first polymer is used. Further, the melting point of the second polymer is lower than the melting point of the first polymer. Therefore, the core-shell type particles have a lower melting point than the first polymer. The melting point of the core-shell type particles is preferably 145 ° C. or higher. Further, the melting point of the core-shell type particles is preferably less than 164 ° C. The method for measuring the melting point of the core-shell type particles according to this embodiment will be described in Examples described later.

In addition, the second polymer may further contain a structural unit derived from a compound other than vinylidene fluoride as another structural unit constituting the second polymer. Examples of compounds other than vinylidene fluoride include alkyl vinyl halide compounds, unsaturated dibasic acids, unsaturated dibasic acid monoesters, hydrocarbon-based monomers, dimethacrylic acid (poly) alkylene glycol esters, and diacrylic acids. Examples thereof include (poly) alkylene glycol ester and polyvinylbenzene.

Examples of the halogenated alkyl vinyl compound include a fluoroalkyl vinyl compound, and specific examples thereof include hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene and fluoroalkyl vinyl ether. Hexafluoropropylene is preferable. By containing the halogenated alkyl vinyl compound, the adhesiveness can be improved in hot pressing with the electrode in a state containing the electrolytic solution.

Examples of unsaturated dibasic acids include fumaric acid, maleic acid, citraconic acid and phthalic acid. By containing at least one of these unsaturated dibasic acids, the adhesiveness between the electrode and the fluororesin layer and the adhesiveness between the separator base material and the fluororesin layer are improved.

Examples of the unsaturated dibasic acid monoester include monomethyl fumarate, monoethyl fumarate, monomethyl maleate, monoethyl maleate, monomethyl citraconic acid, monoethyl citraconic acid, monomethyl phthalate and monoethyl phthalate. By containing at least one unsaturated dibasic acid monoester from these, the adhesiveness between the electrode and the fluororesin layer and the adhesiveness between the separator base material and the fluororesin layer are improved.

Examples of the hydrocarbon-based monomer include ethylene, propylene, and styrene.

From the viewpoint of ion permeability, the proportion of the constituent unit derived from vinylidene fluoride in the second polymer is preferably 50 mol% or more, more preferably 70 mol% or more, and 90 mol% or more. The above is more preferable. Further, from the viewpoint of adhesion, it is preferably 99 mol% or less, more preferably 98 mol% or less, and further preferably 95 mol% or less.

When the other structural unit constituting the second polymer includes a structural unit derived from a compound other than vinylidene fluoride, the proportion of the structural unit derived from the compound other than vinylidene fluoride is not particularly limited, but is oxidation resistant. From the viewpoint of sex, it is preferably 12 mol% or less, more preferably 8 mol% or less, and further preferably 3 mol% or less.

When a structural unit derived from an alkylfluorovinyl compound is included as another structural unit constituting the second polymer, the proportion of the structural unit derived from the alkyl vinyl fluoride compound is not particularly limited, but from the viewpoint of adhesion. Therefore, it is preferably 0.5 mol% or more, more preferably 1 mol% or more, and further preferably 2 mol% or more. Further, from the viewpoint of ion permeability, it is preferably 50 mol% or less, more preferably 30 mol% or less, and further preferably 20 mol% or less.

Derived from unsaturated dibasic acid and unsaturated dibasic acid monoester, when other structural units constituting the second polymer include a structural unit derived from unsaturated dibasic acid or unsaturated dibasic acid monoester. The ratio of the constituent units to be formed is not particularly limited, but from the viewpoint of adhesion, it is preferably 0.01 mol% or more, more preferably 0.02 mol% or more, and 0.03 mol% or more. It is more preferable to have. Further, from the viewpoint of productivity, it is preferably 10 mol% or less, more preferably 9 mol% or less, and further preferably 8 mol% or less.

Further, the shell portion may further contain a compound other than the second polymer. Examples of the compound other than the second polymer include a halogenated alkyl vinyl compound, an unsaturated dibasic acid, an unsaturated dibasic acid monoester, a hydrocarbon-based monomer, and a dimethacrylic acid (poly) alkylene glycol ester. Examples thereof include diacrylic acid (poly) alkylene glycol ester, polyvinylbenzene, and a cross-linking agent. Examples of the halogenated alkyl vinyl compound include a fluoroalkyl vinyl compound, and specific examples thereof include hexafluoropropylene, chlorotrifluoroethylene, trifluoroethylene, tetrafluoroethylene, hexafluoroethylene and fluoroalkyl vinyl ether. Can be mentioned. Examples of unsaturated dibasic acids include fumaric acid, maleic acid, citraconic acid and phthalic acid. Examples of the unsaturated dibasic acid monoester include monomethyl fumarate, monoethyl fumarate, monomethyl maleate, monoethyl maleate, monomethyl citraconic acid, monoethyl citraconic acid, monomethyl phthalate and monoethyl phthalate. Examples of the hydrocarbon-based monomer include ethylene, propylene and styrene.

Assignment method of the structural units of the core-shell particles according to the present embodiment, peak area ratio obtained by ^{19 F-NMR} and absorbance ratio (IR ratio) obtained by detecting the A _R. Detection method of the peak area ratio and absorbance ratio (IR ratio) A _R will be described in Examples below.

Further, it is preferable that at least one of the first polymer and the second polymer contains a structural unit derived from the halogenated alkyl vinyl compound. The proportion of the structural unit derived from the halogenated alkyl vinyl compound in the core-shell type particles is not particularly limited, but is preferably 0.2 mol% or more. Further, it is preferably 5 mol% or less.

(Particle size)
The average particle size of the core-shell type particles according to the present embodiment is not particularly limited, but is, for example, 10 nm or more and 1 μm or less. The method for measuring the average particle size of the core-shell type particles according to this embodiment will be described in Examples described later.

(Use)
The core-shell type particles according to the present embodiment are suitably used as a constituent material of a coating composition applied to a separator base material or an electrode in a secondary battery (particularly, a non-aqueous electrolyte secondary battery).

By incorporating the core-shell type particles according to the present embodiment into the coating composition, as will be described later, it is possible to reduce the crushing of vinylidene fluoride particles contained in the core portion during hot pressing in the battery manufacturing process. Can be done. Therefore, it is possible to reduce the blockage of the holes on the surface of the separator even after the heat pressing process.

[Manufacturing method of core-shell type particles]
The method for producing core-shell type particles according to the present embodiment includes a core portion forming step of forming a core portion containing a first polymer and a shell portion forming step of forming a shell portion containing a second polymer. I'm out.

In the core portion forming step, vinylidene fluoride, which is a monomer for forming the first polymer, is polymerized. When the structural unit constituting the first polymer further contains a structural unit derived from a compound other than vinylidene fluoride, vinylidene fluoride and the other compound are polymerized.

The amount of vinylidene fluoride charged in the core portion forming step is preferably 90 parts by mass or more, preferably 92 parts by mass or more, assuming that the total amount of all the monomers in the core portion forming step is 100 parts by mass. More preferably, it is 95 parts by mass or more. Moreover, you may use only vinylidene fluoride.

When the halogenated alkyl vinyl compound is added as another compound, the amount of the halogenated alkyl vinyl compound charged is 10 from the viewpoint of ion permeability, assuming that the total amount of all the monomers in the core portion forming step is 100 parts by mass. It is preferably less than or equal to parts by mass, more preferably less than or equal to 8 parts by mass, and even more preferably less than or equal to 5 parts by mass.

The core portion obtained by the above polymerization may be used as it is in the dispersion liquid containing the particles obtained in the core portion forming step in the subsequent shell portion forming step, or may be salted out, freeze-crushed, or spray-dried. , And freeze-drying, etc., may be powdered and used by at least one method selected. When used as it is, it may remain dispersed in the dispersion medium used for the polymerization in the core portion forming step, or it may be physically or chemically redispersed in a dispersion medium such as water prepared separately. .. Further, the powdered core portion may be used by physically or chemically redispersing it in a dispersion medium such as water. The dispersion liquid containing the untreated core portion or the dispersion liquid containing the core portion treated by the above operation or the like is a surfactant, a pH adjuster, a precipitation inhibitor, a dispersion stabilizer, a corrosion inhibitor, a fungicide, and a wetting agent. An agent or the like may be further contained, or impurities may be removed by a dialysis membrane, an ion exchange resin, or the like.

In the shell portion forming step, the monomer for forming the second polymer is polymerized in the dispersion liquid containing the core portion formed by the core portion forming step. The timing of adding the monomers is not particularly limited, and all the monomers may be added before the start of the polymerization reaction, or some monomers may be added after the start of the polymerization reaction. , They may be combined. In this polymerization, the first polymer particles are polymerized without infiltrating these monomers. By doing so, the second polymer surrounds the first polymer particles instead of the polymer alloy particles such as the IPN structure in which the first polymer and the second polymer are intertwined with each other. The core-shell type particles formed in can be polymerized. By this polymerization, a shell portion is formed around the core portion of the vinylidene fluoride particles.

The amount of vinylidene fluoride charged in the shell portion forming step is preferably 50 parts by mass or more, preferably 60 parts by mass or more, assuming that the total amount of all the monomers in the shell portion forming step is 100 parts by mass. More preferably, it is 70 parts by mass or more.

When the halogenated alkyl vinyl compound is added as another compound, the amount of the halogenated alkyl vinyl compound charged is 5% by mass from the viewpoint of adhesion, assuming that the total amount of all the monomers in the shell portion forming step is 100 parts by mass. It is preferably more than 10 parts by mass, more preferably 10 parts by mass or more, and further preferably 20 parts by mass or more. Further, from the viewpoint of ion permeability, it is preferably 50 parts by mass or less, more preferably 40 parts by mass or less, and further preferably 30 parts by mass or less.

When unsaturated dibasic acid or unsaturated dibasic acid monoester is added as another compound, the amount of unsaturated dibasic acid and unsaturated dibasic acid monoester charged is the amount of all the monomers in the shell part forming step. When the total amount is 100 parts by mass, it is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and further preferably 0.03 parts by mass or more from the viewpoint of adhesion. preferable. Further, from the viewpoint of manufacturability, it is preferably 10 parts by mass or less, more preferably 9 parts by mass or less, and further preferably 8 parts by mass or less.

The core portion forming step and the shell portion forming step may be performed by the same reactor or may be performed by different reactors. When the core portion forming step and the shell portion forming step are continuously performed in the same reactor, for example, the residual gas monomer in the reactor is purged after the completion of the core portion forming step, and then used in the shell portion forming step. Monomers and the like may be added to the reactor.

The method for polymerizing the first polymer and the second polymer in the core portion forming step and the shell portion forming step is not particularly limited, and conventionally known polymerization methods can be used. Examples of the polymerization method include suspension polymerization, emulsion polymerization, soap-free emulsion polymerization, mini-emulsion polymerization, seed emulsion polymerization and solution polymerization, among which emulsion polymerization, soap-free emulsion polymerization, mini-emulsion polymerization and seeds. Emulsion polymerization is particularly preferred.

Emulsion polymerization is a type of radical polymerization in which a medium such as water, a monomer sparingly soluble in the medium and an emulsifier (hereinafter, also referred to as a surfactant) are mixed, and the polymerization is soluble in the medium. This is a polymerization method in which an initiator is added. In emulsion polymerization, in addition to vinylidene fluoride and other monomers, dispersion media, surfactants and polymerization initiators are used.

Suspension polymerization is a polymerization method in which an oil-soluble polymerization initiator is dissolved in a water-insoluble monomer in water containing a suspending agent or the like, and the polymerization initiator is suspended and dispersed by mechanical stirring. In suspension polymerization, vinylidene fluoride particles are obtained by proceeding with the polymerization in the monomer droplets.

The soap-free emulsion polymerization is an emulsion polymerization carried out without using an ordinary emulsifier as used in carrying out the above emulsion polymerization. Vinylidene fluoride particles obtained by soap-free emulsion polymerization are preferable because the emulsifier does not remain in the polymer particles.

Miniemulsion polymerization is a polymerization method in which monomer droplets are refined to a submicron size by applying a strong shearing force using an ultrasonic oscillator or the like. In miniemulsion polymerization, a poorly water-soluble substance called hydrohope is added in order to stabilize the finely divided monomer droplets. In the ideal mini-emulsion polymerization, the monomer droplets are polymerized to form fine particles of vinylidene fluoride polymer.

The seed emulsion polymerization is a polymerization in which fine particles obtained by the above-mentioned polymerization method are coated with a polymer composed of other monomers. Further, vinylidene fluoride and other monomers, a dispersion medium, a surfactant, a polymerization initiator and the like are used as the dispersion liquid of the fine particles.

[Dispersion medium]
The dispersion medium that can be used is not particularly limited, and conventionally known ones can be used, but it is preferable to use water as the dispersion medium.

[Surfactant]
The surfactant to be used may be any of a nonionic surfactant, a cationic surfactant, an anionic surfactant and an amphoteric surfactant, and a plurality of types may be used in combination. As the surfactant, a perfluorinated surfactant, a partially fluorinated surfactant, a non-fluorinated surfactant and the like conventionally used for the polymerization of polyvinylidene fluoride are suitable. Among them, it is preferable to use a perfluoroalkyl sulfonic acid and a salt thereof, a perfluoroalkyl carboxylic acid and a salt thereof, a fluorine-based surfactant having a fluorocarbon chain or a fluoropolyether chain, and the perfluoroalkyl carboxylic acid and its salt. It is more preferable to use salt. In the present embodiment, as the emulsifier, one type alone or two or more types selected from the above can be used.

The amount of the emulsifier added is preferably 0.005 to 22 parts by mass, more preferably 0.2 to 20 parts by mass, assuming that the total amount of all the monomers used in the polymerization is 100 parts by mass.

[Polymerization initiator]
The polymerization initiator that can be used is not particularly limited, and conventionally known ones can be used. As the polymerization initiator, a water-soluble peroxide, a water-soluble azo compound or a redox initiator system is used. Examples of the water-soluble peroxide include ammonium persulfate and potassium persulfate. Examples of the water-soluble azo compound include AIBN and AMBN. Examples of the redox initiator system include ascorbic acid-hydrogen peroxide. The polymerization initiator is preferably a water-soluble peroxide. These polymerization initiators can be used alone or in combination of two or more.

The amount of the polymerization initiator added is preferably 0.01 to 5 parts by mass, more preferably 0.02 to 4 parts by mass, assuming that the total amount of all the monomers used in the polymerization is 100 parts by mass. preferable.

[Other ingredients]
In emulsion polymerization, a chain transfer agent may be used to control the degree of polymerization of the resulting core-shell type particles. Examples of the chain transfer agent include ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propylaldehyde, ethyl propionate, carbon tetrachloride and the like.

Moreover, you may use a pH adjuster if necessary. Examples of the pH adjuster include electrolyte substances having a buffering ability such as sodium dihydrogen phosphate, disodium hydrogen phosphate and potassium dihydrogen phosphate, and sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide and ammonia. And other basic substances.

Further, if necessary, a sedimentation inhibitor, a dispersion stabilizer, a corrosion inhibitor, a fungicide, a wetting agent and the like may be used.

The amount of other components added is preferably 0.01 to 10 parts by mass, more preferably 0.02 to 7 parts by mass, assuming that the total amount of all the monomers used in the polymerization is 100 parts by mass. preferable.

(Polymerization conditions)
The polymerization temperature may be appropriately selected depending on the type of polymerization initiator and the like. For example, it may be in the range of 0 to 120 ° C., preferably in the range of 20 to 110 ° C., and in the range of 40 to 100 ° C. Is more preferable.

The polymerization pressure may be, for example, in the range of 0 to 10 MPa, preferably in the range of 0.5 to 8 MPa, and more preferably in the range of 1 to 6 MPa.

The polymerization time is not particularly limited, but is preferably in the range of 1 to 24 hours in consideration of productivity and the like.

[Dispersion]
The dispersion liquid according to the present embodiment contains the core-shell type particles and the dispersion medium according to the present embodiment.

The dispersion medium in the dispersion liquid according to the present embodiment is preferably water, for example, but is a mixed liquid of any non-aqueous solvent miscible with water and water, which does not dissolve the vinylidene fluoride resin. The liquid is not particularly limited as long as it can be dispersed, suspended, or emulsified. Examples of the non-aqueous solvent include amide compounds such as N-methylpyrrolidone, dimethylformamide, and N, N-dimethylacetamide; hydrocarbons such as toluene, xylene, n-dodecane, and tetralin; methanol, ethanol, isopropyl alcohol, and 2 -Alcohols such as ethyl-1-hexanol, 1-nonanol, lauryl alcohol; ketones such as acetone, methyl ethyl ketone, cyclohexanone, foron, acetophenone, isophorone; esters such as benzyl acetate, isopentyl butyrate, methyl lactate, ethyl lactate, butyl lactate; Examples include amine compounds such as o-toluidine, m-toluidine and p-toluidine; lactones such as γ-butyrolactone and δ-butyrolactone; sulfoxide compounds and sulfone compounds such as dimethylsulfoxide and sulfolane; and tetrahydrofuran and ethyl acetate. These non-aqueous solvents can be used by mixing with water in an arbitrary ratio. Water may be used alone, or may be a mixed dispersion medium in which water and one or more of these non-aqueous solvents are mixed.

Further, if necessary, a pH adjuster, a sedimentation inhibitor, a dispersion stabilizer, a corrosion inhibitor, a fungicide and / or a wetting agent and the like may be used.

The content of the core-shell type particles in the dispersion liquid according to the present embodiment is preferably 60 parts by mass or less, assuming that the total amount of the dispersion liquid is 100 parts by mass.

[Coating composition]
The coating composition according to the present embodiment forms a porous fluororesin layer that improves the adhesiveness between the electrode and the separator in a secondary battery including a negative electrode layer and a positive electrode layer (electrode) and a separator provided between them. It is a composition used for the purpose.

The coating composition according to this embodiment contains core-shell type particles according to this embodiment. The coating composition according to the present embodiment may contain only core-shell type particles, or may further contain a dispersion medium for dispersing core-shell type particles. For a specific description of the dispersion medium, the above [dispersion liquid] column can be referred to. In one example, the coating composition according to this embodiment can be the dispersion liquid described above.

In preparing the coating composition according to the present embodiment, the core-shell type particles may be powdered by at least one method selected from salting out, freeze-grinding, spray-drying, freeze-drying and the like to obtain the coating composition as it is. Alternatively, the core-shell type particles powdered in this way may be physically or chemically redispersed in a dispersion medium such as water to obtain a coating composition. Alternatively, the dispersion liquid in which the core-shell type particles are dispersed in the dispersion medium used for the polymerization may be used as it is as a coating composition, or the core-shell type particles are physically or chemically redispersed in a separately prepared dispersion medium such as water. It may be used as a coating composition.

When a dispersion medium is used, the content of the dispersion medium contained in the coating composition is preferably 65 to 3500 parts by mass, preferably 300 to 2000 parts by mass, assuming that the content of the core-shell type particles is 100 parts by mass. Is more preferable.

In addition, the coating composition according to the present embodiment may contain a filler, if necessary. By including the filler, the heat resistance of the separator can be improved. As the filler, for example, silicon dioxide _(SiO 2), alumina (Al ₂ 〇 _3), titanium _(TiO 2) dioxide, calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), magnesium oxide (MgO ), Oxides such as zinc oxide (ZnO) and barium titanate (BaTIO ₃ ); magnesium hydroxide (Mg (OH) ₂ ), calcium hydroxide (Ca (OH) ₂ ), zinc hydroxide (Zn (OH)) ₂ ), hydroxides such as aluminum hydroxide (Al (OH) ₃ ), aluminum hydroxide (AlO (OH)); carbonates such as calcium carbonate (CaCO ₃ ); sulfates such as barium sulfate; nitrides Clay minerals; and boehmite and the like. As the filler, alumina, silicon dioxide, magnesium oxide, magnesium hydroxide, magnesium carbonate, zinc oxide and boehmite are preferable from the viewpoint of battery safety and coating stability. The filler may be used alone or in combination of two or more.

In addition, the coating composition according to the present embodiment may further contain a thickener. By including the thickener, it is possible to adjust the viscosity of the coating composition and improve the dispersibility of the core-shell type particles and the filler. Examples of the thickener include cellulose compounds such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, and hydroxyethyl cellulose; ammonium salts or alkali metal salts of the above cellulose compounds; poly (meth) acrylic acid, modified poly (meth). ) Polycarboxylic acid such as acrylic acid; alkali metal salt of the above polycarboxylic acid; polyvinyl alcohol-based (co) polymer such as polyvinyl alcohol, modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer; (meth) acrylic acid, malein Examples thereof include water-soluble polymers such as a saponified product of an unsaturated carboxylic acid such as an acid and fumaric acid and a copolymer of polyvinylpyrrolidone, polyvinylbutyral or vinyl ester. Of these, cellulose compounds and salts thereof are preferable.

When the filler is contained, the amount of the filler added is preferably 10 to 900 parts by mass, assuming that the content of the core-shell type particles is 100 parts by mass.

When the thickener is contained, the amount of the thickener added to the coating composition is preferably 10 parts by mass or less, and preferably 5 parts by mass or less of the total amount of the core-shell type particles, the filler and the thickener. More preferred.

Further, the coating composition according to the present embodiment may contain, if necessary, a surfactant, a pH adjuster, an anti-settling agent, an anti-corrosion agent, a dispersion stabilizer, an antifungal agent, a wetting agent and / or an antifoaming agent, etc. May be further included.

[Fluororesin layer]
The fluororesin layer in the present embodiment is formed by applying the coating composition according to the present embodiment to a separator or an electrode and drying it. Specifically, first, the coating composition is applied to at least one surface of either the separator or the electrode, and the applied coating composition is dried. The dried separator and the electrode are overlapped with each other, the electrolytic solution and other necessary members are put into the exterior material, and the exterior material is heat-pressed to bond the separator and the electrode. At this stage, the shell portion of the core-shell particles is melted by heat to form a fluororesin layer.

The film thickness of the fluororesin layer is not particularly limited, but is preferably 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 9.5 μm or less, and 0.3 μm or more and 9 μm or less. Is more preferable. The coating composition according to the present embodiment is applied so that the film thickness of the fluororesin layer falls within the above range.

As a method for applying the coating composition, for example, a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, a die coating method, a dip coating method and the like can be applied. The drying treatment of the coating film is preferably carried out in a temperature range of 40 to 150 ° C., more preferably 45 to 130 ° C., and a treatment time of preferably 1 to 500 minutes, more preferably 2 to 300 minutes.

Further, the fluororesin layer in the present embodiment may be provided between the negative electrode layer and the separator, may be provided between the separator and the positive electrode layer, or may be provided in both of them.

By providing the fluororesin layer in the present embodiment between the separator and the electrode, sufficient adhesiveness can be provided between the separator and the electrode. The peel strength between the separator provided with the fluororesin layer and the electrode in the present embodiment is, for example, 0.2 to 3.5 gf / mm. The method for measuring the peel strength will be described in Examples described later.

The fluororesin layer in the present embodiment includes a layer containing a second polymer that has been melted after the heat pressing step that is a part of the manufacturing step of the non-aqueous electrolyte battery described later is performed. That is, in one example, the fluororesin layer has a layer containing a second polymer formed by hot-pressing the negative electrode layer, the positive electrode layer, and the separator. The layer containing the second polymer contains particles containing the first polymer. By having such a structure, it is reduced that the holes on the surface of the separator are closed even after the heat pressing process. Therefore, the fluororesin layer in this embodiment is porous. The air permeability of the separator provided with the fluororesin layer in the present embodiment is, for example, 2000 s / 100 cc or less. The method for measuring the air permeability will be described in Examples described later.

[Separator]
The separator according to this embodiment is electrically stable and does not have electrical conductivity. Further, the separator according to the present embodiment uses a porous base material having pores or voids inside, and has excellent ion permeability. Examples of the porous substrate include polyolefin-based polymers (for example, polyethylene, polypropylene, etc.), polyester-based polymers (for example, polyethylene terephthalate, etc.), polyimide-based polymers (for example, aromatic polyamide-based polymers, and polyether). (Imid etc.), Polyethersulfone, Polysulfone, Polyesterketone, Polyester, Polyethylene oxide, Polycarbonate, Polyvinyl chloride, Polyacrylonitrile, Polymethylmethacrylate, Ceramics, etc., and a single layer or multilayer consisting of a mixture of at least two of these. Perforated film; non-woven fabric; glass; as well as paper and the like can be mentioned. Examples of the above-mentioned polymer include modified polymers.

As the porous base material, those containing a polyolefin-based polymer (for example, polyethylene, polypropylene, etc.) are preferable. The porous base material more preferably contains polyethylene from the viewpoint of the shutdown function, and more preferably contains polyethylene and polypropylene from the viewpoint of achieving both the shutdown function and heat resistance, and 95% by mass or more of polyethylene. And 5% by mass or less of polypropylene are more preferably contained.

The thickness of the porous substrate is preferably 3 μm or more and 25 μm or less, and more preferably 5 μm or more and 25 μm, from the viewpoint of mechanical properties and internal resistance.

The surface of the porous substrate may be subjected to corona treatment, plasma treatment, flame treatment, ultraviolet irradiation treatment, or the like for the purpose of improving the wettability with the coating composition.

In the separator according to the present embodiment, in one example, the coating composition according to the present embodiment is applied to at least one of the surface facing the negative electrode layer and the positive electrode layer.

〔electrode〕
The negative electrode layer and the positive electrode layer in the present embodiment are not particularly limited, and for example, known negative electrode layers and positive electrode layers in the secondary battery can be used.

In one example, the negative electrode layer and the positive electrode layer have a structure in which a layer of an electrode mixture is provided on a current collector. The electrode mixture layer may be formed on at least one surface of the current collector.

The electrode mixture may contain, for example, an electrode active material and a binder composition.

The electrode active material is not particularly limited, and for example, a conventionally known electrode active material for a negative electrode (negative electrode active material) or an electrode active material for a positive electrode (positive electrode active material) can be used.

Examples of the negative electrode active material include artificial graphite, natural graphite, non-graphitized carbon, easily graphitized carbon, activated carbon, or carbon materials such as phenolic resin and calcined carbonized material; Cu, Li, Mg, B, etc. Metallic and alloying materials such as Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr and Y; and GeO, GeO ₂ , SnO, SnO ₂ , PbO and Examples thereof include metal oxides such as _{PbO 2.}

As the positive electrode active material, a lithium-based positive electrode active material containing at least lithium is preferable. Examples of the lithium-based positive electrode active material include LiCoO ₂ , LiNi _x Co _1-x O ₂ (0 ≦ x ≦ 1), LiNiCoMnO _{2, and} other general formulas LiMY ₂ (M is Co, Ni, Fe, Mn, Cr, At least one kind of transition metal such as V: Y is a chalcogen compound represented by O, S or the like), a composite metal oxide having a spinel structure such as _{LiMn 2} O ₄ , and an olivine type lithium such as _{LiFePO 4.} Examples include compounds.

Examples of the binder composition include cellulose compounds such as vinylidene fluoride polymer, polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), polyacrylic acid, polyimide, and carboxymethyl cellulose, ammonium salts and alkali metal salts of cellulose compounds, and the like. In addition, those containing polyacrylonitrile (PAN) and the like can be mentioned.

The electrode mixture is, for example, a conductive auxiliary agent such as carbon black, acetylene black, ketjen black, graphite powder, carbon fiber, carbon nanotube; a pigment dispersant such as polyvinylpyrrolidone; and adhesion of polyacrylic acid, polymethacrylic acid and the like. Auxiliary agents and the like may be further contained.

The current collector is a base material of the negative electrode layer and the positive electrode layer, and is a terminal for extracting electricity. The material of the current collector is not particularly limited, and metal foils such as aluminum, copper, iron, stainless steel, steel, nickel and titanium, or metal steel can be used. The thickness of the current collector is not particularly limited, but is preferably 5 to 100 μm, and more preferably 5 to 70 μm.

The thickness of the electrode mixture layer is not particularly limited, but is usually 6 to 1000 μm, preferably 7 to 500 μm.

In the electrode of the present embodiment, the fluororesin layer may be provided in contact with the separator in at least one of the negative electrode layer and the positive electrode layer, and in one example, it is preferably provided in the positive electrode layer. Further, in the electrode of the present embodiment, in one example, the coating composition according to the present embodiment is applied to at least one surface of at least one of the negative electrode layer and the positive electrode layer.

〔Electrolytes〕
The electrolyte used in the secondary battery in the present embodiment is not particularly limited, and for example, a known electrolyte in the secondary battery can be used. Examples of the electrolyte include LiPF ₄ , LiBF ₄ , LiClO ₄ , _{LiAsF 6} , LiSbF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ). Examples thereof include _{3 C and LiBPh 4} . In the secondary battery of the present embodiment, an electrolytic solution in which an electrolyte is dissolved in a non-aqueous solvent can also be used. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate and difluoroethylene carbonate, and chain carbonates such as dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate and its fluorine-substituted products. Cyclic esters such as γ-butyrolactone and γ-valerolactone, or a mixed solvent thereof and the like can be mentioned.

[Secondary battery]
The secondary battery according to the present embodiment is provided with a fluororesin layer formed from the coating composition according to the present embodiment. In one example, the separator is the separator described above. Further, in one example, the electrode is the electrode described above.

The secondary battery according to the present embodiment can be classified according to, for example, the type of electrolyte. Specific examples thereof include a non-aqueous electrolyte secondary battery and a solid electrolyte secondary battery, and among them, a non-aqueous electrolyte secondary battery is preferable.

The non-aqueous electrolyte secondary battery according to the present embodiment also includes, for example, a polymer battery containing a gel electrolyte and the like. The other members of the non-aqueous electrolyte secondary battery are not particularly limited, and for example, conventionally used members can be used.

Examples of the method for manufacturing a non-aqueous electrolyte secondary battery include a method in which a negative electrode layer and a positive electrode layer are overlapped with each other via a separator, placed in a battery container, and an electrolytic solution is injected into the battery container to seal the battery. In this manufacturing method, a part of the core-shell type particles (ideally only the shell part) contained in the coating composition is melted by a hot press after injecting the electrolytic solution, and the electrode is formed by the fluororesin layer formed. And the separator adhere.

The temperature of the hot press is determined according to the melting temperature of the first polymer and the melting temperature of the core-shell type particles, and can be, for example, 30 to 150 ° C. The pressure of the hot press is not particularly limited, but can be, for example, 1 to 30 MPa.

According to the core-shell type particles according to the present embodiment, since the melting temperature of the first polymer in the presence of the electrolytic solution is higher than the temperature of the hot press, it is possible to reduce the crushing of vinylidene fluoride particles in the core portion by the hot press. can do.

Examples are shown below, and embodiments of the present invention will be described in more detail. Of course, the present invention is not limited to the following examples, and it goes without saying that various aspects can be used for details. Furthermore, the present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the claims, and the present invention also relates to an embodiment obtained by appropriately combining the disclosed technical means. It is included in the technical scope of the invention. In addition, all the documents described in the present specification are incorporated by reference.

As will be described later, core-shell type particles and vinylidene fluoride particles (hereinafter collectively referred to as fluorine polymer particles) according to the present invention were prepared, and the physical properties of the fluorine polymer particles were measured. In addition, a separator was manufactured using the fluoropolymer particles, and a peel strength test and an air permeability measurement test were conducted using the separator. Prior to the description of specific examples, the calculation method of "solid content concentration" and "particle size" in the present specification will be described below.

[Solid content concentration]
About 5 g of a dispersion liquid (hereinafter, also referred to as latex) containing fluoropolymer particles prepared by polymerization was placed in an aluminum cup, dried at 80 ° C. for 3 hours, and the concentration was calculated by measuring the weight before and after drying.

〔Particle size〕
The particle size of the fluoropolymer particles was calculated by a regularized analysis of the dynamic light scattering method. Specifically, "DelsaMaxCORE" manufactured by BECKMAN COULTER was used, and the measurement was performed in accordance with JIS Z 8828, and the larger peak was defined as the particle size among the two large and small peaks obtained by the regularization analysis.

The method for preparing the fluoropolymer particles in each Example and each Comparative Example is described below.

[Example 1]
Polymerization of core: 280 parts by mass of ion-exchanged water was placed in an autoclave and degassed by nitrogen bubbling for 30 minutes. Next, 0.2 parts by mass of disodium hydrogen phosphate and 1.0 part by mass of ammonium perfluorooctanoate (PFOA) were charged, and the pressure was increased to 4.5 MPa to perform nitrogen substitution three times. 0.05 parts by mass of ethyl acetate and 35 parts by mass of vinylidene fluoride (VDF) were collectively added to the autoclave. After raising the temperature to 80 ° C. under stirring, a 5 wt% ammonium persulfate (APS) aqueous solution was added in an amount corresponding to 0.06 parts by mass in terms of APS to initiate polymerization. The pressure inside the can at this time was 4.3 MPa. After the reaction was started, when the pressure dropped to 2.5 MPa, 65 parts by mass of VDF was continuously added so that the pressure inside the can was maintained at 2.5 MPa. After the addition was completed, the polymerization was completed when the pressure dropped to 1.5 MPa to obtain a latex containing particles in the core portion. The solid content concentration of the obtained latex was 24.0 wt%, and the particle size was 140 nm.
Polymerization of the shell part: 700 parts by mass of ion-exchanged water was placed in an autoclave, and degassing was performed by nitrogen bubbling for 30 minutes. Next, 100 parts by mass of water-dispersed core particles and 0.5 part by mass of PFOA were charged and pressurized to 4.5 MPa to perform nitrogen substitution three times. 0.05 parts by mass of ethyl acetate, 90 parts by mass of vinylidene fluoride (VDF), and 10 parts by mass of hexafluoropropylene (HFP) were added to the autoclave. After raising the temperature to 80 ° C. under stirring, a 5 wt% APS aqueous solution was added in an amount corresponding to 0.1 parts by mass in terms of APS to initiate polymerization. The pressure inside the can at this time was 3.7 MPa. After the reaction was started, the polymerization of the shell portion was completed when the pressure dropped to 1.5 MPa, and a latex containing core-shell type particles was obtained. The solid content concentration of the obtained latex was 13.4 wt%, and the particle size was 180 nm.

[Example 2]
Polymerization of the core portion: Vinyl fluoride particles in the core portion were obtained in the same manner as in Example 1.
Polymerization of shell portion: Polymerization was carried out in the same manner as in Example 1 except that VDF was changed from 90 parts by mass to 88 parts by mass and HFP was changed from 10 parts by mass to 12 parts by mass to obtain a latex containing core-shell type particles. The solid content concentration of the obtained latex was 13.8 wt%, and the particle size was 170 nm.

[Example 3]
Polymerization of the core portion: Vinyl fluoride particles in the core portion were obtained in the same manner as in Example 1.
Polymerization of shell portion: Polymerization was carried out in the same manner as in Example 1 except that VDF was changed from 90 parts by mass to 78 parts by mass and HFP was changed from 10 parts by mass to 22 parts by mass to obtain a latex containing core-shell type particles. The solid content concentration of the obtained latex was 13.4 wt%, and the particle size was 170 nm.

[Example 4]
Polymerization of the core portion: Vinyl fluoride particles in the core portion were obtained in the same manner as in Example 1.
Polymerization of shell portion: Polymerization was carried out in the same manner as in Example 1 except that VDF was changed from 90 parts by mass to 70 parts by mass and HFP was changed from 10 parts by mass to 30 parts by mass to obtain a latex containing core-shell type particles. The solid content concentration of the obtained latex was 13.5 wt%, and the particle size was 170 nm.

[Example 5]
Polymerization of core part: Latex containing particles in the core part by polymerizing in the same manner as in Example 1 except that the VDF to be added to the autoclave at once was changed from 35 parts by mass to 30 parts by mass and 5.0 parts by mass of HFP was further added. Got The solid content concentration of the obtained latex was 21.3 wt%, and the particle size was 130 nm.
Polymerization of shell portion: Polymerization was carried out in the same manner as in Example 3 to obtain a latex containing core-shell type particles. The solid content concentration of the obtained latex was 13.5 wt%, and the particle size was 160 nm.

[Example 6]
Polymerization of the core portion: Vinyl fluoride particles in the core portion were obtained in the same manner as in Example 1.
Polymerization of the shell part: 700 parts by mass of ion-exchanged water was placed in an autoclave, and degassing was performed by nitrogen bubbling for 30 minutes. Next, 100 parts by mass of water-dispersed core particles and 0.5 part by mass of PFOA were charged and pressurized to 4.5 MPa to perform nitrogen substitution three times. 0.05 parts by mass of ethyl acetate, 78 parts by mass of VDF, 22 parts by mass of HFP, and 0.1 part by mass of monomethyl maleate (MMM) were added to the autoclave. After raising the temperature to 80 ° C. under stirring, a 5 wt% APS aqueous solution was added in an amount corresponding to 0.1 parts by mass in terms of APS to initiate polymerization. The pressure inside the can at this time was 3.4 MPa. After the reaction was started, the polymerization of the shell portion was completed when the pressure dropped to 1.5 MPa, and a latex containing core-shell type particles was obtained. The solid content concentration of the obtained latex was 13.3 wt%, and the particle size was 170 nm.

[Comparative Example 1]
Polymerization was carried out in the same manner as in the core portion of Example 1 except that the perfluorooctanoic acid ammonium salt (PFOA) was changed from 1.0 part by mass to 0.6 parts by mass to obtain a latex containing vinylidene fluoride particles. The solid content concentration of the obtained latex was 21.4 wt%, and the particle size was 180 nm.

[Comparative Example 2]
The vinylidene fluoride (VDF) to be added to the autoclave at once was changed from 35 parts by mass to 27 parts by mass, and then polymerized in the same manner as in Comparative Example 1 except that 8.0 parts by mass of hexafluoropropylene (HFP) was added. A latex containing vinylidene fluoride particles was obtained. The solid content concentration of the obtained latex was 21.4 wt%, and the particle size was 190 nm.

[Comparative Example 3]
Except for changing the amount of vinylidene fluoride (VDF) to be added to the autoclave from 35 parts by mass to 5 parts by mass, and further adding 30 parts by mass of hexafluoropropylene (HFP) to set the pressure at the end of polymerization to 2.0 MPa. Polymerization was carried out in the same manner as in Comparative Example 1 to obtain a latex containing vinylidene fluoride particles. The solid content concentration of the obtained latex was 20.7 wt%, and the particle size was 180 nm.

[Comparative Example 4]
Polymerization of core part: Examples except that vinylidene fluoride (VDF) added to the autoclave was changed from 30 parts by mass to 25 parts by mass and hexafluoropropylene (HFP) was changed from 5.0 parts by mass to 10.0 parts by mass. Polymerization was carried out in the same manner as in No. 1 to obtain a latex containing vinylidene fluoride particles in the core portion. The solid content concentration of the obtained latex was 21.3 wt%, and the particle size was 140 nm.
Polymerization of shell portion: Polymerization was carried out in the same manner as in Example 3 to obtain a latex containing core-shell type particles. The solid content concentration of the obtained latex was 13.4 wt%, and the particle size was 170 nm.

The method for measuring the physical properties of the fluoropolymer particles in each Example and each Comparative Example will be described below.

[HFP introduction amount]
The amount of HFP introduced into the fluoropolymer particles in the dispersion prepared by polymerization ^{was measured by 19} F-NMR (manufactured by BURUKAR). 40 mg of fluoropolymer particles pulverized by salting out were dissolved in 960 mg of acetone-d6 to prepare a sample for measurement. _{The peak of CF 3} part derived from HFP unit corresponds to two peaks around -70- to 80 ppm, and _{the peak of CF 2} part derived from VDF and HFP unit (all monomers) is -90 ppm or less. Corresponds to. From these peak areas, the amount of HFP introduced was calculated by the following formula.
HFP introduction amount [wt%] = HFP peak area / total monomer peak area x 100

[Melting point]
The melting point of the fluoropolymer particles in the dispersion prepared by polymerization was measured in the form of a film. The film was prepared by the following operation. A mold having a length of 5 cm, a width of 5 cm, and a thickness of 150 μm and about 1 g of fluoropolymer particles powdered by salting out were sandwiched between two aluminum foils sprayed with a release agent, and pressed at 200 ° C. The melting point was measured using DSC (“DSC-1” manufactured by METTLER) according to ASTM d 3418.

[Absorptance ratio (IR ratio) _AR ]
The dispersion containing the fluoropolymer particles obtained in each Example and each Comparative Example was salted out with 0.5% by mass of calcium chloride and pulverized by drying in an oven at 80 ° C. The powdered fluoropolymer particles were hot-pressed at 200 ° C. to prepare a press sheet having a thickness of about 0.01 μm. The IR spectrum of the press sheets produced, infrared spectrophotometer FT-730 (manufactured by Horiba Ltd.) ^was measured in the range of 1500cm ^-1 ~4000cm -1. IR ratio _{A R} was determined by the following equation.
_{A R} = A 1760 _/ A ₃₀₂₀

In the above _{formula, A 1760} is the absorbance derived from stretching vibration of the carbonyl group to be detected near 1760 cm ^-1, and the absorbance from the peak detected in 1600cm ^-1 ~1800cm -1 on the stretching vibration of the carbonyl group bottom. A ₃₀₂₀ was the absorbance derived from the expansion and contraction vibration of CH detected near ^{3020 cm -1 , and the peak detected at 2900 cm -1 to} 3100 cm ^-1 was defined as the absorbance derived from the expansion and contraction vibration of the carbonyl group.

[Peeling strength test]
A fluoropolymer particle-coated separator was prepared using the fluoropolymer particles obtained in each Example and each Comparative Example, and a peel strength test with an electrode (positive electrode) was performed. The method for manufacturing the fluoropolymer particle-coated separator and the electrode will be described in detail below.

(Preparation of coating composition)
Water was added to 100 parts by weight of fluoropolymer particles and 2 parts by weight of CMC (carboxymethyl cellulose) (Cerogen 4H, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) to prepare a composition having a solid content concentration of 10% by mass, which was used as a coating composition.

(Preparation of fluoropolymer particle coating separator for peel strength measurement)
Using a wire bar with a wet coating amount of 24 μm (count 12) on one side of a separator (Hypore ND420 Asahi Kasei) in which the coating composition obtained above was corona-treated with a corona treatment device (manufactured by Kasuga Denki Co., Ltd.). It was coated sequentially and dried at 70 ° C. for 30 minutes. Further, heat treatment was carried out at 70 ° C. for 2 hours.

(Preparation of positive electrode for peel strength measurement)
Add _{N-methyl-2-pyrrolidone to 94 parts by weight of LiNiComnO 2} (manufactured by MX6 Umicore), 3 parts by weight of conductive aid (manufactured by SuperP TIMCAL), and 3 parts by weight of PVDF (polyvinylidene fluoride) (manufactured by KF # 7200 Kureha). A slurry was prepared and applied to an Al foil (thickness 15 μm). After drying, it was pressed and heat-treated at 120 ° C. for 3 hours to obtain a positive electrode having ^{an electrode bulk density of 3.0 [g / cm 3} ] and a grain size of 103 [g / m ^2].

(Preparation of sample for peel strength measurement and measurement of peel strength)
The positive electrode obtained as described above was cut into 2.5 × 5.0 cm, and the fluoropolymer particle-coated separator was cut into 3.0 × 6.0 cm and bonded to each other, and the electrolytic solution (ethylene carbonate (EC) / ethylmethyl carbonate (ethylene carbonate (EC) / ethylmethyl carbonate) ( After soaking 120 μL of (EMC) = 3/7, LiPF6 1.2M, VC 1 wt%), the mixture was vacuum degassed and sealed in an Al laminate cell and allowed to stand overnight.

By hot-pressing this Al laminate cell, a sample for measuring the peel strength of the positive electrode was obtained. Specifically, the sample for measuring the peel strength of the positive electrode was prepared by performing hot pressing at 100 ° C. for 1 minute of residual heat and then for 2 minutes at a surface pressure of about 4 MPa. In this sample for measuring the peel strength of the positive electrode, a fluororesin layer was formed at the interface between the fluoropolymer particle-coated separator and the electrode (positive electrode) by hot pressing.

For the prepared sample for measuring the peel strength of the positive electrode, the positive electrode 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). , The peel strength was measured.

[Measurement of air permeability]
A fluoropolymer particle-coated separator was prepared using the fluoropolymer particles obtained in each Example and each Comparative Example. A fluororesin layer-coated separator for measuring air permeability after hot pressing with the electrode (negative electrode) was prepared, and the air permeability was measured. The method for manufacturing the fluoropolymer particle-coated separator and the electrode will be described in detail below.

(Preparation of coating composition)
A coating composition prepared by the same method as the method for producing a coating composition prepared in a peel strength test was used as a coating composition.

(Preparation of fluororesin layer coating separator for air permeability measurement)
The wire bar was produced by the same method as the coating separator produced in the peel strength test, except that the wet coating amount was changed from 24 μm (count 12) to 12 μm (count 6).

(Preparation of negative electrode for air permeability measurement)
It was prepared in the same manner as the positive electrode for measuring peel strength, and used as the negative electrode for measuring air permeability.

(Preparation of sample for air permeability measurement and measurement of air permeability)
The negative electrode obtained as described above was cut into 4.0 × 4.0 cm, and the fluoropolymer particle-coated separator was cut into 4.0 × 4.0 cm and bonded to each other, and the electrolytic solution (ethylene carbonate (EC) / ethylmethyl carbonate (ethylene carbonate (EC) / ethylmethyl carbonate) ( After impregnating 150 μL of (EMC) = 3/7, LiPF6 1.2M, VC 1 wt%), the mixture was vacuum degassed and sealed in an Al laminate cell and allowed to stand overnight.

After hot pressing this Al laminate cell, the separator and the negative electrode were peeled off, and the separator was washed to obtain a sample for measuring air permeability. Specifically, the sample for measuring air permeability is hot-pressed at 100 ° C. for 1 minute at a surface pressure of about 3 MPa to form a fluororesin layer at the interface between the fluoropolymer particle-coated separator and the electrode (negative electrode). bottom. Subsequently, the interface between the coating separator on which the fluororesin layer was formed and the negative electrode was peeled off, the separator was washed with dimethyl carbonate (DMC), and dried at 70 ° C. for 2 hours to measure the air permeability. Got

The air permeability of the prepared sample for measuring air permeability was measured using a Garley type densometer (manufactured by Toyo Seiki Seisakusho) in accordance with JIS P8117 and ISO 5636.

<Result>
The results of particle size, IR ratio, melting point, peel strength, and air permeability in each example and each comparative example are shown in Tables 1 to 3 together with the charged composition ratio of the fluoropolymer particles in each example and each comparative example. show.

In Table 3, "unmeasurable" of air permeability means that the fluororesin layer was eluted from the separator base material at the stage of hot pressing, so that the measurement was impossible.

The core-shell type particles according to the present invention can be suitably used, for example, in the production of a secondary battery.

Claims (13)

A core-shell type particle containing a core portion and a shell portion surrounding the core portion.
The core portion contains a first polymer containing 98 mol% or more of a structural unit derived from vinylidene fluoride.
The shell portion contains a structural unit derived from vinylidene fluoride as a main structural unit and contains a second polymer different from the first polymer.
The second polymer, rather low melting point than the first polymer,
Core-shell type particles having a melting point of 145 ° C. or higher . The first polymer contained in the core portion and / or the second polymer contained in the shell portion contains a structural unit derived from an alkyl vinyl halide compound, and is an alkyl vinyl halide. The core-shell type particle according to claim 1, wherein the compound is contained in the core-shell type particle in an amount of 0.2 mol% or more and 5 mol% or less. The structural unit derived from the halogenated alkyl vinyl compound is a structural unit derived from the fluoroalkyl vinyl compound, and the structural unit derived from the fluoroalkyl vinyl compound is contained in the second polymer. The core-shell type particle according to claim 2. The second polymer according to any one of claims 1 to 3 , further comprising at least one of a structural unit derived from an unsaturated dibasic acid and a structural unit derived from an unsaturated dibasic acid monoester. The core-shell type particles described. The core-shell type particle according to any one of claims 1 to 4 , wherein the structural unit of the first polymer is only a structural unit derived from vinylidene fluoride. A dispersion liquid containing the core-shell type particles and the dispersion medium according to any one of claims 1 to 5. A coating composition for forming a porous fluororesin layer provided on at least one surface of a separator provided between a negative electrode layer and a positive electrode layer in a secondary battery.
A coating composition comprising the core-shell type particles according to any one of claims 1 to 5. The coating composition according to claim 7 , further comprising a thickener. The coating composition according to claim 7 or 8 , further comprising a filler. A separator in which the coating composition according to any one of claims 7 to 9 is applied to at least one surface. A secondary battery provided with a fluororesin layer formed from the coating composition according to any one of claims 7 to 9.
The fluororesin layer has a layer containing the second polymer formed by hot-pressing the negative electrode layer, the positive electrode layer, and the separator.
A secondary battery in which particles containing the first polymer are contained in the layer containing the second polymer. Coating composition for forming a fluororesin layer provided on at least one surface of the negative electrode layer and the positive electrode layer so as to be in contact with a separator provided between the negative electrode layer and the positive electrode layer in the secondary battery. It ’s a thing,
A coating composition comprising the core-shell type particles according to any one of claims 1 to 5. The method for producing core-shell type particles according to any one of claims 1 to 5.
A core portion forming step of forming a core portion containing a first polymer having a constituent unit derived from vinylidene fluoride as a main constituent unit, and a core portion forming step.
Includes a shell portion forming step of forming a shell portion containing a second polymer having a constituent unit derived from vinylidene fluoride as a main constituent unit.
In the shell portion forming step, in the dispersion liquid containing the core portion formed by the core portion forming step, a monomer for forming the second polymer is polymerized to react around the core portion. A method for producing core-shell type particles that form the shell portion.