CN116601193A - Separator binder for nonaqueous secondary battery, separator for nonaqueous secondary battery, method for producing separator slurry for nonaqueous secondary battery, and nonaqueous secondary battery - Google Patents

Separator binder for nonaqueous secondary battery, separator for nonaqueous secondary battery, method for producing separator slurry for nonaqueous secondary battery, and nonaqueous secondary battery Download PDF

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CN116601193A
CN116601193A CN202180084547.2A CN202180084547A CN116601193A CN 116601193 A CN116601193 A CN 116601193A CN 202180084547 A CN202180084547 A CN 202180084547A CN 116601193 A CN116601193 A CN 116601193A
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polymer
separator
nonaqueous secondary
structural unit
secondary battery
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高桥健太郎
花崎充
仓田智规
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Lishennoco Co ltd
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Lishennoco Co ltd
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F220/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical or a salt, anhydride ester, amide, imide or nitrile thereof
    • C08F220/02—Monocarboxylic acids having less than ten carbon atoms; Derivatives thereof
    • C08F220/52—Amides or imides
    • C08F220/54—Amides, e.g. N,N-dimethylacrylamide or N-isopropylacrylamide
    • C08F220/56—Acrylamide; Methacrylamide
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/01—Use of inorganic substances as compounding ingredients characterized by their specific function
    • C08K3/013—Fillers, pigments or reinforcing additives
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L29/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical; Compositions of hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Compositions of derivatives of such polymers
    • C08L29/02—Homopolymers or copolymers of unsaturated alcohols
    • C08L29/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
    • C08L33/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and only one being terminated by only one carboxyl radical, or of salts, anhydrides, esters, amides, imides or nitriles thereof; Compositions of derivatives of such polymers
    • C08L33/24—Homopolymers or copolymers of amides or imides
    • C08L33/26—Homopolymers or copolymers of acrylamide or methacrylamide
    • 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
    • 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
    • H01M50/42—Acrylic resins
    • 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 Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Organic Chemistry (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Cell Separators (AREA)

Abstract

The purpose of the present invention is to provide a separator adhesive for nonaqueous secondary batteries and a separator adhesive composition for nonaqueous secondary batteries, which can produce a slurry that has good wettability and coatability to a substrate, can form a coating layer having high peel strength on a separator, and can suppress thermal shrinkage of the separator. The separator binder for nonaqueous secondary batteries comprises a polymer (A) having a polyolefin structure as a main chain and having a first structural unit (a 1) derived from (meth) acrylamide and a second structural unit (a 2) derived from a compound having a hydroxyl group and an ethylenically unsaturated double bond, and a polymer (B) which is a polyvinyl alcohol having a saponification degree of 55mol% or more, wherein the mass ratio between the polymer (A) and the polymer (a 1) is 55.0/45.0 or more and 95.0/5.0 or less, and the mass ratio between the polymer (A) and the polymer (B) is 55.0/45.0 or more and 97.0/3.0 or less.

Description

Separator binder for nonaqueous secondary battery, separator for nonaqueous secondary battery, method for producing separator slurry for nonaqueous secondary battery, and nonaqueous secondary battery
Technical Field
The present application relates to a separator binder for nonaqueous secondary batteries, a separator for nonaqueous secondary batteries, a method for producing a separator slurry for nonaqueous secondary batteries, and a nonaqueous secondary battery.
The present application claims priority from japanese patent application publication No. 2020-214879, 12/24/2020, the contents of which are incorporated herein by reference.
Background
As a typical nonaqueous secondary battery, for example, a lithium ion secondary battery is a secondary battery in which lithium ions move between a positive electrode and a negative electrode to charge and discharge the battery. A lithium ion secondary battery as a main structure, comprising: a positive electrode having a positive electrode active material layer containing a metal oxide such as lithium cobaltate formed on the surface of a current collector such as aluminum; a negative electrode having a negative electrode active material layer containing a material such as graphite formed on a surface of a current collector such as copper; a separator disposed between the positive electrode and the negative electrode; and an electrolyte solution obtained by dissolving an electrolyte such as a lithium salt in a solvent such as a carbonate.
The separator is a member provided to separate the positive electrode from the negative electrode, and a base material such as a porous resin film is widely used as the separator in a nonaqueous secondary battery. When the heat generation amount of the battery increases, the holes of the separator block, the movement of carrier ions is prevented, and the battery is closed. However, in recent years, the energy density of secondary batteries has been increased, and the amount of heat generated by the batteries during use tends to increase. In order to impart heat resistance to the separator, it has been proposed to form a coating layer containing a binder and nonconductive particles on at least one surface of a substrate. The coating typically comprises organic or inorganic particles (fillers) and a binder for fixing the particles to the surface of the substrate.
As such a proposal, for example, patent document 1 describes a method of coating a porous polypropylene sheet with a mixture containing alumina short fibers, polyvinylidene fluoride and N-methylpyrrolidone.
Patent document 2 describes a separator for a nonaqueous electrolyte secondary battery in which a porous film of a water-soluble polymer and a porous film of a polyolefin are laminated, and describes polyvinyl alcohol, carboxymethyl cellulose (CMC), or the like as the water-soluble polymer. In the examples, the coating of a slurry containing CMC and alumina fine particles on a porous film to prepare a separator is described.
Patent document 3 describes a multi-layer porous film comprising a porous layer made of an inorganic filler and polyvinyl alcohol having a saponification degree of 85% or more on at least one surface of a polyolefin resin porous film.
Patent document 4 describes that a binder resin composition containing a water-soluble polymer having a metal carboxylate group and a water-soluble polymer having a hydroxyl group, a carboxyl group or a sulfo group is used to bond filler particles to the surface of a separator substrate for a nonaqueous electrolyte secondary battery. In the examples, examples are described in which carboxymethyl cellulose and polyvinyl alcohol are used as a binder in combination, and water is used as a solvent.
Prior art literature
Patent literature
Patent document 1 Japanese patent No. 3756815
Patent document 2 Japanese patent application laid-open No. 2004-227972
Patent document 3 Japanese patent laid-open No. 2008-186721
Patent document 4 International publication No. 2013/154197
Disclosure of Invention
The invention aims to solve the problems
However, in the structure described in patent document 1, when N-methylpyrrolidone is used as the solvent, it is necessary to raise the drying temperature, and the porous organic film is supported with a large load. In addition, polyvinylidene fluoride lacks hydrophilicity, and it is difficult to satisfy the recent demand for using water as a solvent.
In patent document 2, the CMC resin has poor dispersibility of the inorganic filler, tends to be a slurry having a high viscosity, and tends to be low in coatability. In addition, the slurries using them have poor wettability to polyolefin porous films. The heat resistance of the obtained separator was also insufficient. In addition, since the layer obtained by drying the slurry has poor adhesion to the polyolefin porous film, the produced laminated porous separator is liable to suffer from powder falling.
In patent document 3, the dimensional stability of the porous layer at high temperature is insufficient.
In patent document 4, the slurry containing CMC resin has high viscosity and poor coatability.
Accordingly, an object of the present invention is to provide a separator adhesive for nonaqueous secondary batteries and a separator adhesive composition for nonaqueous secondary batteries, which can produce a slurry having excellent wettability and coatability to a substrate, can form a coating layer having high peel strength on a separator, and can suppress thermal shrinkage of the separator. The present invention also provides a separator for a nonaqueous secondary battery, which has a coating layer having high peel strength to a substrate and has small heat shrinkage.
Means for solving the problems
In order to solve the above problems, the present invention is described in the following [1] to [17 ].
[1] A separator binder for nonaqueous secondary batteries, comprising a polymer (A) and a polymer (B),
the polymer (A) is a polymer of a compound having an ethylenically unsaturated double bond, having a first structural unit (a 1) derived from (meth) acrylamide and a second structural unit (a 2) derived from a compound having a hydroxyl group and an ethylenically unsaturated double bond,
the polymer (B) is polyvinyl alcohol having a saponification degree of 55mol% or more,
the mass ratio between the content of the first structural unit (a 1) and the content of the second structural unit (a 2) in the polymer (a) is 55.0/45.0 or more and 95.0/5.0 or less, and the mass ratio between the content of the polymer (a) and the content of the polymer (B) is 55.0/45.0 or more and 97.0/3.0 or less.
[2] The separator binder for nonaqueous secondary batteries according to [1], which is composed of only the polymer (A) and the polymer (B).
[3] The separator binder for nonaqueous secondary batteries according to [1] or [2], wherein the polymer (A) does not have an anionic functional group.
[4] The separator binder for nonaqueous secondary batteries according to any one of [1] to [3], wherein the saponification degree of the polymer (B) is 65mol% or more.
[5] The separator binder for nonaqueous secondary batteries according to any one of [1] to [4], wherein the polymer (B) has a polymerization degree of 100 to 5000.
[6] The separator for nonaqueous secondary batteries according to any one of [1] to [5], wherein the total content of the first structural unit (a 1) and the second structural unit (a 2) in the polymer (A) is 80 mass% or more.
[7] The separator binder for nonaqueous secondary batteries according to any one of [1] to [6], wherein the polymer (A) is composed of only the first structural unit (a 1) and the second structural unit (a 2).
[8] The separator binder for nonaqueous secondary batteries according to any one of [1] to [7], wherein the second structural unit (a 2) is a structural unit derived from a (meth) acrylate having a hydroxyl group.
[9] The separator binder for nonaqueous secondary batteries according to any one of [1] to [7], wherein the second structural unit (a 2) is a structural unit derived from 2-hydroxyethyl (meth) acrylate.
[10] The separator binder for nonaqueous secondary batteries according to any one of [1] to [7], wherein the second structural unit (a 2) is a structural unit derived from 2-hydroxyethyl methacrylate.
[11] The separator for nonaqueous secondary batteries according to any one of [1] to [10], wherein the polymer (A) has a solubility in 100g of water of 2.0g/100g or more.
[12] A separator binder composition for nonaqueous secondary batteries, comprising the separator binder for nonaqueous secondary batteries described in any one of [1] to [11], and an aqueous medium.
[13] A separator slurry for a nonaqueous secondary battery according to any one of [1] to [11], a filler and an aqueous medium.
[14] A separator for a nonaqueous secondary battery, comprising a substrate as a porous film and a coating layer formed on the surface of the substrate,
the coating layer contains the separator binder for nonaqueous secondary batteries according to any one of [1] to [11], and a filler.
[15] The separator for a nonaqueous secondary battery according to [14], wherein a mass ratio between a content of the separator binder for a nonaqueous secondary battery and a content of the filler in the coating layer is 1.0/99.0 or more and 15.0/85.0 or less.
[16] A method for producing a separator slurry for a nonaqueous secondary battery, comprising:
a first step of mixing the polymer (A) and the filler in an aqueous medium,
a step 2 of adding and mixing the polymer (B) to the mixture obtained in the first step,
the polymer (A) is a polymer of a compound having an ethylenically unsaturated double bond, having a first structural unit (a 1) derived from (meth) acrylamide and a second structural unit (a 2) derived from a compound having a hydroxyl group and an ethylenically unsaturated double bond,
the polymer (B) is polyvinyl alcohol having a saponification degree of 55mol% or more,
the mass ratio between the content of the first structural unit (a 1) and the content of the second structural unit (a 2) in the polymer (A) is 55.0/45.0 or more and 95.0/5.0 or less,
the mass ratio between the amount of the polymer (A) to the amount of the polymer (B) is 55.0/45.0 or more and 97.0/3.0 or less.
[17] A nonaqueous secondary battery comprising the separator for a nonaqueous secondary battery according to [14] or [15 ].
Effects of the invention
According to the present invention, a separator adhesive for nonaqueous secondary batteries and a separator adhesive composition for nonaqueous secondary batteries can be provided, which can produce a slurry having good wettability and coatability to a substrate, can form a coating layer having high peel strength on a separator, and can suppress thermal shrinkage of the separator. Further, according to the present invention, a separator for a nonaqueous secondary battery having a coating layer with high peel strength to a substrate and small heat shrinkage can be provided.
Detailed Description
Hereinafter, as embodiments of the present invention, a separator adhesive for a nonaqueous secondary battery (also referred to as a separator adhesive for a nonaqueous secondary battery), a separator adhesive composition for a nonaqueous secondary battery (also referred to as a separator adhesive composition for a nonaqueous secondary battery), and a separator slurry for a nonaqueous secondary battery (also referred to as a separator slurry for a nonaqueous secondary battery) will be described.
In the embodiments described below, a separator for a nonaqueous secondary battery, in which these are applied to a coating layer, will also be described. That is, in the following description of the embodiments, the separator binder for nonaqueous secondary batteries is a binder suitable for separators for nonaqueous secondary batteries, the separator binder composition for nonaqueous secondary batteries is a binder composition suitable for separators for nonaqueous secondary batteries, and the separator slurry for nonaqueous secondary batteries is a separator slurry suitable for separators for nonaqueous secondary batteries.
However, the description of the present embodiment does not limit the scope of the present invention.
"(meth) acrylic acid" is a generic term for acrylic acid and methacrylic acid, and "(meth) acrylate" is a generic term for acrylate and methacrylate.
The "nonvolatile component" is a component remaining after weighing 1g of the composition in an aluminum dish having a diameter of 5cm and drying at 130℃for 1 hour while circulating air in a dryer at 1 atmosphere (1013 hPa). The form of the composition includes, but is not limited to, a solution, dispersion, slurry. The "nonvolatile content" refers to the mass ratio (mass%) of the nonvolatile content after drying under the above-described conditions to the mass (1 g) of the composition before drying.
"ethylenically unsaturated double bond" refers to an ethylenically unsaturated double bond having free radical polymerization, unless otherwise specified.
The "hydroxyl group" does not include OH of an anionic functional group such as an OH bonded to an atom other than carbon, a carboxyl group, or OH bonded to a carbon atom forming an aromatic ring.
In the polymer of a compound having an ethylenically unsaturated double bond, the chemical structure of a portion other than the ethylenically unsaturated double bond of a certain compound having an ethylenically unsaturated double bond is regarded as the same as the chemical structure of a portion other than the portion of the polymer that forms the main chain of the structural unit. For example, a structural unit derived from acrylamide has CONH as a polymer at a portion other than the main chain 2 Is a structure of (a).
In the case where the chemical structure of the monomer such as a chemical reaction is not matched with the chemical structure of the polymer in a portion other than the main chain after the polymerization, the chemical structure after the polymerization is used as a reference. For example, in the case of saponification after polymerization of vinyl acetate, the structural unit after saponification is a structural unit derived from vinyl alcohol based on the chemical structure of the polymer. According to this definition, polyvinyl alcohol (PVA) obtained by saponifying polyvinyl acetate becomes a copolymer containing a structural unit derived from vinyl acetate and a structural unit derived from vinyl alcohol when the saponification degree is not 100mol%, but in such a copolymer, for example, when 90mol% of a structural unit derived from vinyl alcohol and 10mol% of a structural unit derived from vinyl acetate are contained, it is described as polyvinyl alcohol (PVA) having a saponification degree of 90mol% for convenience.
The anionic functional group is a functional group that releases cations (hydrogen ions, metal ions, ammonium ions, etc.) when dissolved in water at ph 7.0. Examples of the anionic functional group include a carboxyl group, a sulfo group, a phosphate group, and a phenolic hydroxyl group.
In the following description, if not specifically described, the surface means "surface".
<1 > separator Binder for nonaqueous Secondary Battery
The separator binder for a nonaqueous secondary battery according to an embodiment of the present invention contains a polymer (a) and a polymer (B). The separator binder for nonaqueous secondary batteries according to one embodiment of the present invention is preferably composed of only the polymer (a) and the polymer (B). The polymer (A) and the polymer (B) are described below.
[1-1. Polymer (A) ]
The polymer (A) is a polymer of a compound having an ethylenically unsaturated double bond. The polymer (a) is a copolymer comprising a first structural unit (a 1) derived from (meth) acrylamide and a second structural unit (a 2) derived from a compound having a hydroxyl group and an ethylenically unsaturated double bond. The polymer (A) preferably has no anionic functional group. The solubility of the polymer (A) in 100g of water is preferably 2.0g/100g or more, more preferably 5.0g/100g or more, still more preferably 10.0g/100g or more.
The first structural unit (a 1) is a structural unit derived from (meth) acrylamide, and the (meth) acrylamide used to form the first structural unit (a 1) includes acrylamide, methacrylamide, and mixtures thereof.
The second structural unit (a 2) is a structural unit derived from a compound having a hydroxyl group and an ethylenically unsaturated double bond, and is a structural unit containing a hydroxyl group. As the compound having a hydroxyl group and an ethylenically unsaturated double bond, a compound having only 1 hydroxyl group is preferable. The second structural unit (a 2) may be, for example, a structural unit derived from a (meth) acrylate having a hydroxyl group or a vinyl alcohol. The second structural unit (a 2) is preferably a structural unit derived from a (meth) acrylate having a hydroxyl group, more preferably an alkyl (meth) acrylate in which any one of hydrogen atoms of an alkyl group is substituted with a hydroxyl group.
Examples of the (meth) acrylic acid ester having a hydroxyl group include (meth) acrylic acid hydroxyalkyl esters such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, hydroxybutyl (meth) acrylate, hydroxypentyl (meth) acrylate, hydroxyhexyl (meth) acrylate, hydroxyoctyl (meth) acrylate, pentaerythritol tri, di or mono (meth) acrylate, trimethylolpropane di or mono (meth) acrylate, and the like.
Among them, from the viewpoint of reactivity, the second structural unit (a 2) is more preferably a structural unit derived from 2-hydroxyethyl (meth) acrylate, and 2-hydroxypropyl (meth) acrylate, and further preferably 2-hydroxyethyl (meth) acrylate. Among them, 2-hydroxyethyl methacrylate is particularly preferred from the viewpoints of improving the peel strength and reducing the heat shrinkage. The reason why 2-hydroxyethyl methacrylate has a particular effect is not yet determined, but is presumed to be due to a synergistic effect with (meth) acrylamide for forming the first structural unit (a 1). With respect to polymerizability with (meth) acrylamide, 2-hydroxyethyl methacrylate and other compounds such as 2-hydroxyethyl acrylate are different. Compared with 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate can realize an improvement in peel strength and a reduction in heat shrinkage at a higher level because a part of the polymer undergoes microphase separation due to the non-uniformity of the composition ratio of the polymer.
The mass ratio ((content of a 1/(content of a 2)) between the content of the first structural unit (a 1) and the content of the second structural unit (a 2) in the polymer (a) is 55.0/45.0 or more, preferably 65.0/35.0 or more, more preferably 75.0/25.0 or more. This is because, when the binder is applied to a separator for a nonaqueous secondary battery, the heat resistance and electrolyte resistance of the coating layer are improved.
The mass ratio ((content of a 1/(content of a 2)) between the content of the first structural unit (a 1) and the content of the second structural unit (a 2) in the polymer (a) is 95.0/5.0 or less, more preferably 90.0/10.0 or less, still more preferably 85.0/15.0 or less. This is because the compatibility between the polymer (a) and the polymer (B) can be improved, and the viscosity of the slurry to be described later can be suppressed from being increased, thereby improving the coatability.
The polymer (a) may contain structural units derived from other compounds, but the total content of the first structural unit (a 1) and the second structural unit (a 2) in all the structural units in the polymer (a) is preferably 80 mass% or more, more preferably 90 mass% or more, and particularly preferably 100 mass%. That is, the polymer (a) is particularly preferably a copolymer composed of only the first structural unit (a 1) and the second structural unit (a 2). This is because the effect of the object of the present invention by the polymer (A) is further improved. Here, the structural unit in the polymer (A1) does not include a structure of a polymerization initiator, a stopper, a chain transfer agent, or the like used in the production process thereof.
The polymer (a) or a separator binder composition for nonaqueous secondary batteries described later preferably contains no thermally crosslinkable constituent (thermally crosslinkable structural unit or thermally crosslinkable compound). This is to suppress a decrease in dispersibility due to a decrease in wettability of the polymer to the filler when the polymer (a) is applied to a separator slurry for a nonaqueous secondary battery, which will be described later. In addition, when the polymer (a) is applied to a separator for a nonaqueous secondary battery, dimensional changes of the separator due to curing shrinkage or the like of the polymer in the coating layer and a decrease in peel strength of the coating layer with respect to the substrate can be suppressed.
< constituent component for thermal Cross-linking Property >
The thermally crosslinkable component of the present embodiment contains a thermally crosslinkable structural unit or a thermally crosslinkable compound.
Examples of the heat-crosslinkable structural unit include a structural unit derived from a monomer having an epoxy group, a structural unit derived from a polyfunctional (meth) acrylate, and the like. Examples of the monomer that is a source of these structural units include glycidyl methacrylate and ethylene glycol dimethacrylate. In the present embodiment, the first structural unit (a 1) of (meth) acrylamide derived from the polymer (a) and the second structural unit (a 2) derived from the compound having a hydroxyl group and an ethylenically unsaturated double bond do not belong to a thermally crosslinkable structural unit.
Examples of the thermally crosslinkable compound include compounds used as a crosslinking agent, and examples thereof include carbodiimide compounds, epoxy compounds, and isocyanate compounds.
The weight average molecular weight of the polymer (a) is preferably 100000 or more, more preferably 300000 or more, further preferably 350000 or more. This is because, when the binder is applied to a separator for a nonaqueous secondary battery, the electrolyte resistance, strength, and peel strength of the coating layer to the substrate are improved.
The weight average molecular weight of the polymer (a) is preferably 3000000 or less, more preferably 1500000 or less, and further preferably 650000 or less. This is to suppress an increase in viscosity of the slurry to be described later and to improve the coating property of the slurry on the substrate.
The weight average molecular weight is a pullulan equivalent value measured by Gel Permeation Chromatography (GPC).
Examples of the method for synthesizing the polymer (a) include aqueous solution polymerization of a monomer containing (meth) acrylamide and a compound having a hydroxyl group and an ethylenically unsaturated double bond. Examples of the radical polymerization initiator used for the synthesis include ammonium persulfate, potassium persulfate, hydrogen peroxide, t-butyl hydroperoxide, azo compounds, and the like, but are not limited thereto. Examples of azo compounds include 2,2' -azobis (2-methylpropionamidine) 2 hydrochloride. When the polymerization is carried out in water, a water-soluble polymerization initiator is preferably used. In addition, if necessary, a radical polymerization initiator and a reducing agent may be used in combination for redox polymerization. Examples of the reducing agent include sodium bisulphite, rongalite, and ascorbic acid.
[1-2. Polymer (B) ]
The polymer (B) is polyvinyl alcohol (PVA). The saponification degree of the polymer (B) is 55mol% or more, preferably 65mol% or more, more preferably 70mol% or more, and still more preferably 80mol% or more. This is because, when the binder is applied to a separator for a nonaqueous secondary battery, the heat resistance and electrolyte resistance of the coating layer are improved. Here, the saponification degree is a value measured by the measurement method of item 3.5 of JIS K6726 (1994) without using a simple method.
The saponification degree of the polymer (B) may be 100mol% or less, preferably 99mol% or less, more preferably 95mol% or less, and still more preferably 90mol% or less. This is because the compatibility between the polymer (B) and the polymer (a) can be ensured, and the viscosity of the slurry to be described later can be suppressed from increasing, thereby improving the coating property on the substrate.
The polymerization degree of the polymer (B) is preferably 100 or more, more preferably 300 or more, further preferably 1000 or more, and still further preferably 1500 or more. This is because, when the binder is applied to a separator for a nonaqueous secondary battery, the heat resistance and electrolyte resistance of the coating layer are improved. Here, the degree of polymerization is a value measured by the measuring method of item 3.7 of JIS K6726 (1994).
The polymerization degree of the polymer (B) is preferably 5000 or less, more preferably 4000 or less, and further preferably 3000 or less. This is to suppress an increase in viscosity of the slurry to be described later, and to improve the coating property on the substrate.
[1-3. Mixing ratio of Polymer (A) to Polymer (B) ]
The mass ratio between the content of the polymer (a) and the content of the polymer (B) (content of the polymer (a)/content of the polymer (B)) in the separator binder for nonaqueous secondary batteries is 55.0/45.0 or more, preferably 65.0/35.0 or more, more preferably 75.0/25.0 or more. This is because, when the binder is applied to a separator for a nonaqueous secondary battery, the heat resistance of the coating layer is improved.
The mass ratio between the content of the polymer (a) and the content of the polymer (B) in the separator binder for nonaqueous secondary batteries is 97.0/3.0 or less, preferably 93.0/7.0 or less, more preferably 85.0/15.0 or less. This is because, when the porous organic film is used as a substrate, the wettability of the slurry to the substrate is improved. In addition, this is because the peel strength of the coating layer with respect to the substrate is improved when the binder is applied to the separator for a nonaqueous secondary battery.
<2 > separator Binder composition for nonaqueous Secondary Battery
The separator adhesive composition for a nonaqueous secondary battery of the present embodiment contains the separator adhesive for a nonaqueous secondary battery and an aqueous medium. Hereinafter, the separator binder composition for nonaqueous secondary batteries may be referred to as a binder composition. In the adhesive composition, it is preferable that both the polymer (A) and the polymer (B) are dissolved in an aqueous medium. The adhesive composition of the present embodiment may contain, in addition to these components, components derived from the components used for producing the adhesive, and the like, and may further contain polymers other than the polymers contained in the adhesive of the present invention, various additives, and the like.
As the aqueous medium, only water is preferably used, but an organic solvent which is compatible with water may be mixed into water. The boiling point of the organic solvent at atmospheric pressure is preferably 50 to 150 ℃.
Specific examples of the water-miscible organic solvent include alcohols such as methanol, ethanol, n-propanol, and isopropanol; saturated aliphatic ether compounds such as dipropyl ether, diisopropyl ether, dibutyl ether, and diisobutyl ether; tetrahydrofuran, tetrahydropyran, diCyclic ether compounds such as alkanes; organic acid ester compounds such as butyl formate, amyl formate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, and the like; ketone compounds such as acetone, diethyl ketone, and cyclohexanone.
When a mixed solvent of an organic solvent and water is used as the aqueous medium, the content of the organic solvent is not particularly limited, but is preferably 100 parts by mass or less, more preferably 20 parts by mass or less, based on 100 parts by mass of water.
The total content of the polymer (a) and the polymer (B) in the adhesive composition can be appropriately adjusted according to a standard or the like, and is not particularly limited. The total content of the polymer (a) and the polymer (B) in the adhesive composition is preferably 1.0 mass% or more, more preferably 5.0 mass% or more, and still more preferably 10.0 mass% or more. This is because the content of the binder can be sufficiently maintained without removing components such as an aqueous medium in the case of producing a slurry to be described later.
The total content of the polymer (a) and the polymer (B) in the adhesive composition is preferably 70 mass% or less, more preferably 50 mass% or less. This is to suppress the viscosity of the adhesive composition from being excessively high.
<3 > separator slurry for nonaqueous secondary battery
The separator slurry for a nonaqueous secondary battery of the present embodiment contains the separator binder for a nonaqueous secondary battery, a filler, and an aqueous medium. The separator binder for nonaqueous secondary batteries is as described above. Hereinafter, the separator slurry for nonaqueous secondary batteries may be referred to as a slurry. The slurry of the present embodiment may contain, in addition to these components, components derived from the components used for producing the binder, and the like, and may contain binders other than the binder of the present invention, and the like.
The filler may be any of an organic filler and an inorganic filler, or may be used in combination. The filler preferably contains an inorganic filler, and more preferably is composed of an inorganic filler.
Examples of the inorganic filler include calcium carbonate, talc, clay, kaolin, silica, hydrotalcite, diatomaceous earth, magnesium carbonate, barium carbonate, calcium sulfate, magnesium sulfate, barium sulfate, aluminum hydroxide, magnesium hydroxide, calcium oxide, magnesium oxide, titanium oxide, aluminum oxide, mica, zeolite, glass, and the like. The inorganic filler may be particles made of one material or may contain particles of two or more materials. The inorganic filler may be produced by mixing particles having different particle size distributions.
The filler more preferably contains metal oxide particles, and still more preferably contains alumina particles. The alumina particles have excellent affinity with the binder of the present embodiment, and have good dispersibility in kneading, and a slurry having low viscosity and good coatability can be obtained.
The average particle diameter of the constituent filler particles is preferably 3 μm or less, more preferably 1 μm or less. The average particle diameter referred to herein is a number average of primary particle diameters obtained by observation with an SEM (scanning electron microscope). Specifically, 100 filler particles reflected in the SEM were randomly selected, the longest dimension of each particle was measured, and the average value of these measured dimensions was taken as the average particle diameter of the filler.
The mass ratio (binder content/filler content) between the binder content and the filler content in the slurry is preferably 1.0/99.0 or more, more preferably 2.0/98.0 or more, and still more preferably 4.0/96.0 or more. This is to improve the peel strength of the coating made of the slurry to the substrate and to sufficiently fix the filler particles on the coating. In addition, it is also intended to improve the heat resistance of the coating.
The mass ratio between the content of the binder and the content of the filler in the slurry is preferably 15.0/85.0 or less, more preferably 10.0/90.0 or less, and still more preferably 7.0/93.0 or less. This is to sufficiently maintain the air permeability and ion permeability in a separator to be described later, and to obtain a battery having good load characteristics.
The aqueous medium is preferably water alone, but a mixed solvent of water and an organic solvent having a boiling point of 50 to 150 ℃ at 1 atmosphere and being compatible with water may be used. As examples of the organic solvent, the same compounds as exemplified in the item of the adhesive composition are used. When a mixed solvent of an organic solvent and water is used as the aqueous medium, the content of the organic solvent is not particularly limited, but is preferably 100 parts by mass or less, more preferably 20 parts by mass or less, based on 100 parts by mass of water.
The content of the aqueous medium in the slurry is not limited, and may be appropriately adjusted according to a standard or the like. The content of the aqueous medium in the slurry is preferably 80 mass% or less, more preferably 70 mass% or less, and further preferably 60 mass% or less. This is because a coating layer of sufficient thickness can be formed in a smaller amount of the slurry when the slurry is coated on a substrate.
The content of the aqueous medium in the slurry is preferably 20% by mass or more, more preferably 30% by mass or more, and still more preferably 40% by mass or more. This is to bring the viscosity of the slurry within a range suitable for coating.
<4 > method for producing separator slurry for nonaqueous secondary batteries
Examples of the method for producing the slurry include a first method in which the polymer (a) and the polymer (B) are mixed in an aqueous medium, and the mixture is mixed and dispersed after the binder composition is produced; a 2 nd method of mixing the filler and the polymer (A) in an aqueous medium, dispersing the filler, and adding the polymer (B); a 3 rd method of mixing the filler and the polymer (B) in an aqueous medium, dispersing the filler, and adding the polymer (A); a 4 th method of adding the polymer (A) and the polymer (B) after dispersing the filler in the aqueous medium; the 5 th method of dispersing the filler by mixing the filler, the polymer (a) and the polymer (B) in an aqueous medium at the same time is not particularly limited.
Among these methods, the 2 nd method is preferable in order to improve the peel strength of the coating layer described later. On the other hand, the first method of preparing the adhesive composition in advance is sometimes preferable in terms of the manufacturing cost of the slurry and the management cost of the material.
<5 > separator for nonaqueous secondary battery
The separator for a nonaqueous secondary battery of the present embodiment has a substrate as a porous film and a coating layer formed on the surface of the substrate. The coating layer according to the present embodiment may be formed on either one of the surface facing the positive electrode and the surface facing the negative electrode, or may be formed on both surfaces. The separator for nonaqueous secondary batteries may be provided with an adhesive layer, a protective layer, or the like, for example. Hereinafter, the separator for a nonaqueous secondary battery according to the present embodiment may be referred to as a separator.
Examples of the substrate material include thermoplastic resins such as polyolefin, paper sheets such as viscose rayon and natural cellulose, mixed paper sheets obtained by paper sheets of fibers such as cellulose and polyester, electrolytic paper, kraft paper, manila hemp sheets, glass fibers, porous polyesters, aramid fibers, polybutylene terephthalate nonwoven fabrics, para-aramid, vinylidene fluoride, tetrafluoroethylene, copolymers of vinylidene fluoride and hexafluoropropylene, and nonwoven fabrics or porous films of fluorine-containing resins such as fluororubber.
As the material of the base material, polyolefin is preferable. Examples of the polyolefin include homopolymers and copolymers of ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene and the like. Among them, a copolymer mainly composed of ethylene or a homopolymer of ethylene is preferable, and a homopolymer of ethylene, that is, polyethylene is more preferable.
The thickness of the substrate is preferably 5 to 50. Mu.m, more preferably 5 to 30. Mu.m. As the substrate, a commercially available porous film can be used.
The coating layer contains the separator binder for nonaqueous secondary batteries and the filler. The thickness of the coating layer is not particularly limited, but is preferably 10 μm or less. This is to improve the load characteristics of the nonaqueous electrolyte secondary battery including the separator.
<6 > method for producing separator for nonaqueous secondary battery
The method for producing the separator for a nonaqueous secondary battery is not particularly limited, and examples thereof include a method in which the slurry of the present embodiment is applied to the surface of a substrate, and the applied slurry is dried. The substrate may be subjected to a surface treatment such as corona treatment in advance before the slurry is applied to the surface of the substrate.
Examples of the method for applying the slurry to the surface of the substrate include methods generally performed in industry, such as doctor blade coating. The thickness of the coating layer can be controlled by adjusting the coating amount of the slurry, the concentration of the solid component in the slurry, and the like.
The coating is formed by drying a slurry applied to a substrate to remove volatile components from the slurry. Examples of the drying include a method using a heating device such as a drying furnace, a method using a pressure reducing device, and a method of heating and reducing pressure. The conditions such as heating, decompression and drying time may be appropriately selected depending on the material and form of the substrate, the kind of the solvent contained in the volatile component, and the like, and for example, the drying temperature is preferably in the range of the melting point or the glass transition point of the substrate or less. Specifically, the drying temperature of the slurry is preferably 100 ℃ or lower, more preferably 80 ℃ or lower, and even more preferably 70 ℃ or lower. From the viewpoint of productivity, it is preferably 50℃or higher. In addition, as the pressure reducing condition, it is preferable to set the degree to which the coating layer does not generate bubbles or the like while taking the productivity into consideration.
More specifically, as the drying conditions in the case of using a porous film containing a thermoplastic resin such as polypropylene as a base material, drying at 55 to 65℃for 2 to 10 minutes is preferable, and drying at 60℃for 5 minutes is more preferable. This is to prevent the pores in the porous film from being broken due to softening or melting of the thermoplastic resin contained in the porous film.
< 7 > nonaqueous secondary battery
The nonaqueous secondary battery according to an example of the present embodiment has a structure in which a positive electrode, a negative electrode, an electrolyte solution, and a separator are housed in an exterior body. The separator is disposed between the positive electrode and the negative electrode. The positive electrode active material layer of the positive electrode and the negative electrode active material layer of the negative electrode are preferably arranged to face each other with a separator interposed therebetween. The separator has the above-described structure. Here, the case where the nonaqueous secondary battery is a lithium ion secondary battery is described as an example, but the nonaqueous secondary battery is not limited to this, and may be, for example, a potassium ion secondary battery, a sodium ion secondary battery, or the like.
[7-1. Electrodes (Positive and negative electrodes) ]
Hereinafter, the electrode may be referred to as an electrode in some cases, unless the positive electrode and the negative electrode are separately described. The electrode includes a current collector and an electrode active material layer formed on the current collector.
In the case of a lithium ion secondary battery, an aluminum foil is preferably used as a positive electrode, and a copper foil is preferably used as a negative electrode. Examples of the shape of the current collector include a foil, a flat plate, a porous shape, a mesh shape, a plate shape, a punched shape, an embossed shape, a current collector in which these are combined (for example, a porous flat plate, etc.), and the like. The current collector may have irregularities formed on its surface by etching treatment.
The electrode active material layer preferably has a structure in which an electrode active material is fixed to a current collector by an electrode binder. The electrode active material layer may contain an additive such as a conductive additive. The electrode active material can absorb and release ions (lithium ions in the case of a lithium ion secondary battery) as charge carriers, and a material electrochemically more expensive than the negative electrode active material is used as the positive electrode active material.
Examples of the positive electrode active material include nickel-containing lithium composite oxides such as Ni-Co-Mn-based lithium composite oxides, ni-Mn-Al-based lithium composite oxides, and Ni-Co-Al-based lithium composite oxides, lithium cobalt oxide (LiCoO) 2 ) Spinel type lithium manganate (LiMn) 2 O 4 ) Olivine lithium iron phosphate, tiS 2 、MnO 2 、MoO 3 、V 2 O 5 And chalcogenides, etc. As the positive electrode active material, 1 kind of these materials may be used, or 2 or more kinds may be used in combination.
The negative electrode active material includes silicon, silicon oxide (SiO 2 Etc.), carbonaceous materials, metal composite oxides, etc., preferably amorphous carbon, artificial graphite, natural graphite, etc.; a is a x M y O z (wherein A is Li, M is at least one selected from Co, ni, al, sn and Mn, O is an oxygen atom, x, y and z are 1.10.gtoreq. 0.05,4.00.gtoreq.y.gtoreq. 0.85,5.00.gtoreq.z.gtoreq.1.5, and other metal oxides, etc.). The negative electrode active material may be composed of 1 material or may be composed of 2 or more materials.
The electrode binder of the present embodiment may be used, or other resins may be used. Examples of the electrode binder include, but are not limited to, an acrylic copolymer obtained by copolymerizing a monomer containing a (meth) acrylic acid ester and a (meth) acrylic acid, a copolymer of a (meth) acrylic acid salt and N-vinylacetamide, styrene-butadiene rubber, polyvinylidene fluoride, and the like, in addition to the polymer (a) and the polymer (B) described in the present embodiment. In addition, the electrode binder may contain a plurality of materials.
As the conductive auxiliary agent, carbon black, carbon fiber, or the like is preferably used. Examples of the carbon black include furnace black, acetylene black, and taro's oven (registered trademark), and the like (manufactured by taro corporation). The carbon fibers include carbon nanotubes and carbon nanofibers, and VGCF (registered trademark, manufactured by sho and electric company) as a vapor phase method carbon fiber is a preferable example of the carbon nanotubes.
[ 7-2. Electrolyte ]
Examples of the electrolyte solution include a solution in which an electrolyte is dissolved in an organic solvent, and an ionic liquid, and preferably a solution.
The electrolyte may be an alkali metal salt, and may be appropriately selected according to the type of the electrode active material. Examples of the electrolyte include LiClO 4 、LiBF 6 、LiPF 6 、LiCF 3 SO 3 、LiCF 3 CO 2 、LiAsF 6 、LiSbF 6 、LiB 10 Cl 10 、LiAlCl 4 、LiCl、LiBr、LiB(C 2 H 5 ) 4 、CF 3 SO 3 Li、CH 3 SO 3 Li、LiCF 3 SO 3 、LiC 4 F 9 SO 3 、Li(CF 3 SO 2 ) 2 N, lithium aliphatic carboxylate, and the like. In addition, other alkali metal salts may be used as the electrolyte.
The organic solvent for dissolving the electrolyte is not particularly limited, and examples thereof include carbonate compounds such as Ethylene Carbonate (EC), propylene Carbonate (PC), diethyl carbonate (DEC), methyl Ethyl Carbonate (MEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and Vinylene Carbonate (VC), nitrile compounds such as acetonitrile, and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These organic solvents may be used alone or in combination of at least 2 kinds. Among them, a solvent in which a linear carbonate solvent is combined is preferably used. Examples of the linear carbonate solvent include diethyl carbonate, dimethyl carbonate and methylethyl carbonate.
[ 7-3. Outer packaging body ]
As the exterior body, for example, a laminate of aluminum foil and a resin film or the like can be suitably used, but is not limited thereto. The shape of the battery may be any shape such as coin type, button type, sheet type, cylinder type, angle type, flat type, etc.
Examples
The present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In the present embodiment, the abbreviations of the monomers are respectively represented by the following compounds.
Am: acrylamide
HEA 2-hydroxyethyl acrylate
HEMA 2-hydroxyethyl methacrylate
<1. Preparation of aqueous Polymer (A) and aqueous Polymer (CA)
[1-1 ] production of Polymer (A), polymer (CA-1) and aqueous solution of Polymer (CA-2)
As shown in Table 1, polymers (A-1) to (A-6) and polymers (CA-1) and (CA-2) were synthesized. The conditions to be described later for the synthesis, the measurement results of the products, and the structure of the polymer are shown in Table 1.
In the following description, any of the "polymers (A-1) to (A-6)" may be referred to as "polymer (A)". In the following description, the "polymer (CA-1), the" polymer (CA-2) or the "polymer (CA-3) (hereinafter," may be referred to as "polymer (CA)".
TABLE 1
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[ procedure 1]
In the synthesis of each polymer, ion exchange water was charged in an amount shown in column 1 of table 1 in a reaction vessel equipped with a stirrer, a thermometer and a condenser, and the temperature was raised to 80 ℃ while stirring under a nitrogen atmosphere.
[ procedure 2]
An aqueous initiator solution prepared by dissolving 0.50g of ammonium persulfate in 6.6g of ion-exchanged water was charged at once as an initiator at 80 ℃. Simultaneously with the addition of the aqueous initiator solution, the dropwise addition of 50 mass% of the aqueous acrylamide solution, 2-hydroxyethyl acrylate and ion-exchanged water was started in the amounts shown in column 2 of Table 1 for 30 minutes during the synthesis of each polymer. Then, the reaction was carried out at 80℃for 2 hours. In table 1, the individual amount Am is the mass (g) of acrylamide contained in the aqueous acrylamide solution used.
[ procedure 3]
Thereafter, ion-exchanged water was charged in the amount shown in column 3 of table 1 during the synthesis of each polymer.
The nonvolatile components, viscosity, pH and weight average molecular weight of the polymer of the aqueous solution of the product obtained in the above step were measured by the methods described below, and the measurement results are shown in table 1.
[1-2. Preparation of aqueous solution of Polymer (CA-3) ]
970.0g of ion-exchanged water and 30.0g of carboxymethyl cellulose sodium salt (manufactured by Nippon paper Co., ltd., product name. Of Takara Shuzo) (registered trademark) MAC350 HC) as a polymer (CA-3) were charged into a reaction vessel equipped with a stirrer, a thermometer and a condenser, and the mixture was stirred under a nitrogen atmosphere and heated to 80 ℃. The mixture was stirred at 80℃for 3 hours, and carboxymethyl cellulose sodium salt was dissolved to prepare a 3.0 mass% aqueous solution of the polymer (CA-3).
[1-3. Various determinations of Polymer (A) and Polymer (CA) and aqueous solutions thereof ]
[ measurement of nonvolatile component ]
The aqueous solution of the polymer (A) and the aqueous solution of the polymer (CA) were weighed into 1g of an aluminum pan having a diameter of 5cm, and air was circulated in a dryer at 1 air pressure (1013 hPa) while drying at 130℃for 1 hour, and the mass of the remaining components was measured. The mass ratio (mass%) of the component remaining after drying to the mass (1 g) of the adhesive composition before drying was calculated as the amount of the nonvolatile component.
[ measurement of viscosity ]
The viscosities of the aqueous solutions of the polymer (A) and the polymer (CA) were measured by a Brookfield viscometer (manufactured by DONGCHINESE INDUSTRIAL) at a liquid temperature of 23℃and a rotation speed of 10rpm using any one of rotors No.3, no.4 and No. 5. The rotors are selected according to the viscosity of the respective aqueous solutions.
[ measurement of pH ]
The pH value of the aqueous solution of the polymer (a) and the aqueous solution of the polymer (CA) was measured using a pH meter (in the form of a belt) at a liquid temperature of 23 ℃.
[ measurement of weight-average molecular weight ]
The weight average molecular weights of the polymer (a) and the polymer (CA) were measured using Gel Permeation Chromatography (GPC) under the following conditions.
GPC apparatus: GPC-101 (manufactured by Zhao Denko K.K.)
Solvent: 0.1M NaNO 3 Column of aqueous solution sample: shodex Column Ohpak SB-806HQ (8.0 mm I.D.x300 mm). Times.2 reference column: shodex Column Ohpak SB-800RL (8.0 mM I.D.X300 mm). Times.2 column temperature: 40 DEG C
Sample concentration: 0.1 mass%
A detector: RI-71S (Shimadzu corporation)
And (3) a pump: DU-H2000 (Shimadzu corporation)
Pressure: 1.3MPa
Flow rate: 1ml/min
Molecular weight standard: pullulan (P-5, P-10, P-20, P-50, P-100, P-200, P-400, P-800, P-1300, P-2500 (manufactured by Zhaogaku electric Co., ltd.)
[ Structure of Polymer ]
The copolymerization ratio of the resulting polymer, i.e., the mass ratio of the structural unit derived from acrylamide to the structural unit derived from 2-hydroxyethyl acrylate in the polymer, is shown in Table 1. The copolymerization ratio shown here is the mass ratio of acrylamide to 2-hydroxyethyl acrylate used in step 2.
<2 > preparation of aqueous solution of Polymer (B)
For each of the polymers (B-1) to (B-4) as polyvinyl alcohol shown in Table 2, 100.0g of the polymer and 900.0g of ion-exchanged water were charged into a reaction vessel equipped with a stirrer, a thermometer and a condenser, and the temperature was raised to 80℃under nitrogen atmosphere while stirring. The polymer was dissolved by stirring at 80℃for 3 hours. The polyvinyl alcohol used here was manufactured by kurana corporation, and the product grades are shown in table 2. In the following description, the polymer (B-1), the polymer (B-2), the polymer (B-3) or the polymer (B-4) is sometimes referred to as "polymer (B)".
The saponification degree of the polymers (B-1) to (B-4) was measured by the measurement method of item 3.5 of JIS K6726 (1994) (without using a simple method). The polymerization degree of the polymers (B-1) to (B-4) was measured by the measurement method of item 3.7 of JIS K6726 (1994).
The nonvolatile components (mass%) and the viscosity (mPas) of the aqueous solution were measured in the same manner as the aqueous solution of the polymer (A), and the measurement results are shown in Table 2.
TABLE 2
<3 > preparation of slurry
Examples 1 to 8, examples 10 to 12, examples 14 to 21, examples 22 to 25 and comparative examples 1 to 5 (production method I)
(mixing of Polymer (A) and alumina)
The aqueous solution of the polymer (A) or the aqueous solution of the polymer (CA) produced in the above-mentioned step, alumina (AL-45-1, manufactured by Showa electric Co., ltd., average particle size: 2 μm) and ion-exchanged water were put into a rotation-revolution mixer, and the rotation-revolution mixer was stirred and mixed at 2000rpm for 3 times and 2 minutes.
The components and amounts thereof used in each of examples and comparative examples are shown in tables 3 to 6. The amount of the aqueous solution of the polymer (a) or the aqueous solution of the polymer (CA) to be added was adjusted so that the amount of the polymer (a) or the polymer (CA) was as shown in tables 3 to 6. For example, in example 1, 65.5g of a 14.5 mass% aqueous solution of polymer (A-2) (9.5 g of polymer (A-2), 56.0g of water) was added.
The amount of alumina added is shown in tables 3 to 6. For example, in example 1, 190g of alumina was added.
In this step, the amount of ion-exchanged water added was adjusted to 100g with respect to the water contained in the aqueous solution of the polymer (a) or the aqueous solution of the polymer (CA) in examples 1 to 8, 14 to 21 and comparative examples 1 to 4. For example, in example 1, 44.0g of ion-exchanged water was added. In examples 10 to 12, 23 to 25 and comparative example 5, the amount of ion-exchanged water added was adjusted to be 233g as compared with the water contained in the aqueous solution of the polymer (A) or the aqueous solution of the polymer (CA).
(addition and mixing of Polymer (B))
Next, 10.0 mass% aqueous solution of the polymer (B) and ion-exchanged water prepared in the above-described step were added to the aqueous solution of the polymer (a) or the aqueous solution of the polymer (CA) diluted in the above-described step, and the mixture was subjected to revolution stirring at 500rpm for 2 times for 5 minutes, and then, deaeration was performed by revolution stirring at 500rpm for 1 minute, to prepare a slurry.
The types of the aqueous solutions of the polymers (B) used in the examples and comparative examples are shown in tables 3 to 5, and the amounts of the aqueous solutions of the polymers (B) to be added are adjusted so that the amounts of the polymers (B) are shown in tables 3 to 5. For example, in example 1, 5.0g of a 10.0 mass% aqueous solution of the polymer (B-1) (0.50 g of the polymer (B-1), 4.5g of water) was added.
The amount of ion-exchanged water added in this step was adjusted so that the amount of water contained in the aqueous solution of the polymer (B) was 100 g. For example, in example 1, 95.5g of ion-exchanged water was added.
The above-described preparation methods of the slurry are preparation methods I in tables 3 to 5.
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Examples 9, 13, 22 and 26 (preparation method II)
The aqueous solution of the polymer (A) prepared in the step, alumina (AL-45-1), the 10.0 mass% aqueous solution of the polymer (B) prepared in the step, and ion-exchanged water were put into a rotation-revolution mixer, and rotation-revolution mixer was performed 3 times at 2000rpm for 2 minutes.
The types of the aqueous solutions of the polymers (a) used in the examples are shown in tables 3 to 5, and the amounts of the aqueous solutions of the polymers (a) to be added are adjusted so that the amounts of the polymers (a) are shown in tables 3 to 5. For example, in example 9, 55.2g of a 14.5% by mass aqueous solution of polymer (A-2) (8.0 g of polymer (A-2), 47.2g of water) was added.
The amount of alumina added was 190g in example 9 and 323g in example 13.
The types of the aqueous solutions of the polymers (B) used in the examples are shown in tables 3 to 5, and the amounts of the aqueous solutions of the polymers (B) to be added are adjusted so that the amounts of the polymers (B) are shown in tables 3 to 5. For example, in example 9, 20.0g of a 10.0 mass% aqueous solution of the polymer (B-1) (2.0 g of the polymer (B-1), 18.0g of water) was added.
The amount of ion exchange water added was 34.8g in example 9 and 170.9g in example 13.
Then, 100g of ion exchange water was charged, and the slurry was prepared by performing revolution stirring mixing at 500rpm for 2 times for 5 minutes and then performing revolution stirring deaeration at 500rpm for 1 minute.
The above-described preparation method of the slurry is preparation method II in tables 3 to 5.
Comparative example 6
69.0g of a 14.5% by mass aqueous solution of the polymer (A-2) (10.0 g of the polymer (A-2), 59.0g of water), 190g of alumina (AL-45-1) and 41.0g of ion-exchanged water were charged into a rotation/revolution mixer, and rotation/revolution mixing was performed at 2000rpm for 3 times and 2 minutes.
Then, 100g of ion exchange water was charged, and the slurry was prepared by performing revolution stirring mixing at 500rpm for 2 times for 5 minutes and then performing revolution stirring deaeration at 500rpm for 1 minute.
Comparative example 7
A slurry was prepared in the same manner as in comparative example 6, except that a 14.5 mass% aqueous solution of the polymer (CA-1) was used in equal amounts.
Comparative example 8
333g of a 3.0 mass% aqueous solution of the polymer (CA-3) (10.0 g of the polymer (CA-3), 323g of water) and 323g of alumina (AL-45-1) were put into a rotation revolution stirring mixer, and rotation revolution stirring mixing was performed at 2000rpm for 3 times for 2 minutes.
Then, 10g of ion exchange water was charged, and the slurry was prepared by performing revolution stirring mixing at 500rpm for 2 times for 5 minutes and then performing revolution stirring deaeration at 500rpm for 1 minute.
Comparative example 9
100g of a 10.0% by mass aqueous solution of the polymer (B-3) (10.0 g of the polymer (B-3), 90.0g of water), 190g of alumina (AL-45-1) and 10g of ion-exchanged water were put into a rotation-revolution stirring mixer, and rotation-revolution stirring mixing was performed 3 times at 2000rpm for 2 minutes.
Then, 100g of ion exchange water was charged, and the slurry was prepared by performing revolution stirring mixing at 500rpm for 2 times for 5 minutes and then performing revolution stirring deaeration at 500rpm for 1 minute.
Comparative example 10
A slurry was prepared in the same manner as in comparative example 9, except that the same amount of the 10.0% by mass aqueous solution of the polymer (B-4) was used in place of the 10.0% by mass aqueous solution of the polymer (B-3).
Comparative example 11
In comparative example 11, no slurry was prepared, and evaluation was performed using only a separator described later.
<4. Evaluation of separator >
[4-1. Formation of coating (preparation of separator) ]
The slurries prepared in the examples except comparative example 11 were applied to both surfaces of a substrate of a 25 μm polypropylene porous film (ESFINO P, manufactured by water chemical industry Co., ltd.). Coating was performed using a No.8 bar coater having a diameter of 10 mm. Then, the substrate coated with the slurry was dried at 60 ℃ for 5 minutes to obtain a separator having a coating layer formed on the substrate. The thickness of the coating formed on the substrate was 3.5 μm on both sides regardless of the examples and comparative examples (except comparative example 11).
In comparative example 11, the separator was not coated with the slurry, and only the heat shrinkage described later was evaluated.
[4-2. Wettability of the slurry to the substrate ]
The state immediately after the slurry was applied to the substrate was observed, and the wettability of the slurry to the substrate was evaluated as follows.
A: without pits
B: pits were observed at the edges of the coating surface.
C: the entire coating produced pits.
[4-3. Coatability of slurry to substrate ]
The state immediately after the slurry was applied to the substrate was observed, and the coatability of the slurry to the substrate was evaluated as follows.
A: the coating workability was good, and no streaks due to coating were found.
B: the viscosity was high and streaking was observed.
C: the viscosity was very high and significant streaking was observed on the coated surface. Or not coated.
[4-4 peel Strength of coating ]
The peel strength of the coating to the substrate was measured as follows. The separator having a coating on both sides thereof produced by the above procedure was cut into 15mm×100mm sizes to obtain test pieces.
The test piece was attached to an SUS plate having a width of 50mm and a length of 200mm using a double-sided tape (NITTOTAPE (registered trademark) No.5, manufactured by Nitto Denko Co., ltd.) so that the center of the test piece was aligned with the center of the SUS plate. Bonding was performed by reciprocating a 2kg roller 1 time under an atmosphere at 23 ℃. The double-sided tape was attached so as to cover the entire range of the test piece. A transparent adhesive tape (コ, short-cut, T-SE 15N) having a width of 10mm was stuck to a coating layer of a test piece fixed to an SUS plate. The sticking was performed by reciprocating a 2kg roller 1 time under an atmosphere at 23 ℃. After leaving the coated transparent adhesive tape in a state of being adhered to the coating layer for 20 minutes, one end of the transparent adhesive tape was folded back by 180 degrees, and peeled off by pulling at a speed of 100 mm/min toward the other end opposite to the one end, to obtain a graph of peel length (mm) -peel force (mN). Using a tester (Ten RTG-1210; manufactured by Ten corporation), an average value (mN) of the peeling force when the peeling length was 10 to 45mm was calculated in the obtained graph, and a value obtained by dividing the average value of the peeling force by the width of the test piece of 15mm was used as the peeling strength (mN/mm) of the coating layer.
[4-5. Heat shrinkage ]
The separator was cut into rectangles of MD (machine direction) ×td direction (transverse direction) =100 mm×60 mm. The separator was placed on a stainless steel plate having a thickness of 0.8mm×length of 150mm×width of 70mm and a mass of 65g, and a stainless steel plate having the same dimensions and mass was placed on top of the separator. That is, the separator is sandwiched between two stainless steel plates, and the separator is fixed by the weight of the stainless steel plate on the upper side. The separator sandwiched in the stainless steel plate was left to stand in a constant temperature bath at 150℃for 60 minutes. After the separator was taken out, the length in the MD direction was read with a vernier caliper, and the heat shrinkage was calculated according to the following formula.
Heat shrinkage (%) = [ { (100 (mm) -length after heating (mm))/100 (mm) } ×100]
< 5 evaluation results >)
As is clear from tables 3 to 5, in any of the examples, the wettability and coatability of the slurry to the substrate were good. In addition, the coating layer formed on the substrate has high peel strength and the separator has small thermal shrinkage.
In comparative example 1, a polymer (CA-1) containing a large amount of structural units derived from acrylamide (first structural unit (a 1)) was used instead of the polymer (A) to prepare a slurry. However, the resulting slurry could not be coated on a substrate and no coating was formed.
In comparative examples 2 and 3, the amount of polyvinyl alcohol (polymer (B)) contained in the binder was increased, but the heat shrinkage of the separator could not be sufficiently suppressed.
In comparative example 4, the polymer (CA-2) containing a large amount of structural units derived from 2-hydroxyethyl acrylate (second structural unit (a 2)) was used instead of the polymer (A), but the heat shrinkage of the separator could not be sufficiently suppressed.
In comparative example 5, a slurry was prepared using carboxymethyl cellulose sodium salt (polymer (CA-3)) instead of polymer (A). However, the resulting slurry, when applied to a substrate, produced significant streaks on the coating film. In addition, the formed coating layer cannot sufficiently suppress the thermal shrinkage of the separator.
In comparative example 6, the adhesive containing no polymer (B) was used, but the peel strength of the formed coating was insufficient.
In comparative example 7, polymer (CA-1) containing a large amount of structural units derived from acrylamide (first structural unit (a 1)) was used instead of polymer (A), and a slurry containing no polymer (B) was produced. However, the prepared slurry has insufficient wettability to the substrate, and the slurry cannot be applied to the substrate, and thus a coating layer cannot be formed.
In comparative example 8, carboxymethyl cellulose sodium salt (polymer (CA-3)) was used instead of polymer (A), and a slurry containing no polymer (B) was produced. However, if the prepared slurry is coated on a substrate, significant streaks are generated on the coating film. In addition, the peel strength of the formed coating layer was insufficient. Further, the formed coating layer cannot sufficiently suppress the thermal shrinkage of the separator.
In comparative examples 9 and 10, the binder containing no polymer (a) was used, but the formed coating layer could not sufficiently suppress the thermal shrinkage of the separator.
In comparative example 11, the evaluation was performed only with the separator of the base material without forming the coating layer, but the heat shrinkage of the separator was large.
As described above, according to the present invention, a slurry having good wettability and coatability to a substrate can be produced, and a separator adhesive for a nonaqueous secondary battery and a separator adhesive composition for a nonaqueous secondary battery, which can form a coating layer having high peel strength on a separator and can suppress thermal shrinkage of the separator, can be provided. Further, according to the present invention, a separator for a nonaqueous secondary battery having a coating layer with high peel strength to a substrate and small thermal shrinkage can be provided.

Claims (17)

1. A separator binder for nonaqueous secondary batteries, comprising a polymer (A) and a polymer (B),
the polymer (A) is a polymer of a compound having an ethylenically unsaturated double bond, having a first structural unit (a 1) derived from (meth) acrylamide and a second structural unit (a 2) derived from a compound having a hydroxyl group and an ethylenically unsaturated double bond,
the polymer (B) is polyvinyl alcohol having a saponification degree of 55mol% or more,
the mass ratio between the content of the first structural unit (a 1) and the content of the second structural unit (a 2) in the polymer (a) is 55.0/45.0 or more and 95.0/5.0 or less, and the mass ratio between the content of the polymer (a) and the content of the polymer (B) is 55.0/45.0 or more and 97.0/3.0 or less.
2. The separator binder for nonaqueous secondary batteries according to claim 1, which consists of only the polymer (a) and the polymer (B).
3. The separator binder for nonaqueous secondary batteries according to claim 1 or 2, wherein the polymer (a) has no anionic functional group.
4. The separator for nonaqueous secondary batteries according to any one of claims 1 to 3, wherein the polymer (B) has a saponification degree of 65mol% or more.
5. The separator for nonaqueous secondary batteries according to any one of claims 1 to 4, wherein the polymer (B) has a polymerization degree of 100 to 5000.
6. The separator for nonaqueous secondary batteries according to any one of claims 1 to 5, wherein the total content of the first structural unit (a 1) and the second structural unit (a 2) in the polymer (A) is 80 mass% or more.
7. The separator binder for nonaqueous secondary batteries according to any one of claims 1 to 6, wherein the polymer (a) is composed of only the first structural unit (a 1) and the second structural unit (a 2).
8. The separator binder for nonaqueous secondary batteries according to any one of claims 1 to 7, wherein the second structural unit (a 2) is a structural unit derived from a (meth) acrylate having a hydroxyl group.
9. The separator binder for nonaqueous secondary batteries according to any one of claims 1 to 7, wherein the second structural unit (a 2) is a structural unit derived from 2-hydroxyethyl (meth) acrylate.
10. The separator binder for nonaqueous secondary batteries according to any one of claims 1 to 7, wherein the second structural unit (a 2) is a structural unit derived from 2-hydroxyethyl methacrylate.
11. The separator for nonaqueous secondary batteries according to any one of claims 1 to 10, wherein the polymer (a) has a solubility in 100g of water of 2.0g/100g or more.
12. A separator binder composition for nonaqueous secondary batteries, comprising the separator binder for nonaqueous secondary batteries according to any one of claims 1 to 11 and an aqueous medium.
13. A separator slurry for a nonaqueous secondary battery, comprising the separator binder for a nonaqueous secondary battery according to any one of claims 1 to 11, a filler, and an aqueous medium.
14. A separator for a nonaqueous secondary battery, comprising a substrate as a porous film and a coating layer formed on the surface of the substrate,
the coating layer contains the separator binder for nonaqueous secondary batteries according to any one of claims 1 to 11 and a filler.
15. The separator for a nonaqueous secondary battery according to claim 14, wherein a mass ratio between a content of the separator binder for a nonaqueous secondary battery and a content of the filler in the coating layer is 1.0/99.0 or more and 15.0/85.0 or less.
16. A method for producing a separator slurry for a nonaqueous secondary battery, comprising:
a first step of mixing the polymer (A) and the filler in an aqueous medium,
a step 2 of adding and mixing the polymer (B) to the mixture obtained in the first step,
the polymer (A) is a polymer of a compound having an ethylenically unsaturated double bond, having a first structural unit (a 1) derived from (meth) acrylamide and a second structural unit (a 2) derived from a compound having a hydroxyl group and an ethylenically unsaturated double bond,
the polymer (B) is polyvinyl alcohol having a saponification degree of 55mol% or more,
the mass ratio between the content of the first structural unit (a 1) and the content of the second structural unit (a 2) in the polymer (A) is 55.0/45.0 or more and 95.0/5.0 or less,
the mass ratio between the amount of the polymer (A) to the amount of the polymer (B) is 55.0/45.0 or more and 97.0/3.0 or less.
17. A nonaqueous secondary battery comprising the separator for a nonaqueous secondary battery according to claim 14 or 15.
CN202180084547.2A 2020-12-24 2021-12-14 Separator binder for nonaqueous secondary battery, separator for nonaqueous secondary battery, method for producing separator slurry for nonaqueous secondary battery, and nonaqueous secondary battery Pending CN116601193A (en)

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