Binder composition for lithium-ion secondary battery functional layer, slurry composition for lithium-ion secondary battery functional layer, separator having functional layer for lithium-ion secondary battery, and lithium-ion secondary battery

Abstract

Provided is a binder composition for a lithium-ion secondary battery functional layer, the binder composition comprising a granular material that contains at least a particulate polymer A. The volume average particle size of the granular material is 1.0 μm to 10.0 μm. The binder composition has a glass transition temperature of 25°C to less than 60°C and an ash content of less than 3.0 mass%.

Description

Binder composition for functional layer of lithium ion secondary battery, slurry composition for functional layer of lithium ion secondary battery, separator with functional layer for lithium ion secondary battery, and lithium ion secondary battery

[0001] The present invention relates to a binder composition for a functional layer of a lithium ion secondary battery, a slurry composition for a functional layer of a lithium ion secondary battery, a separator with a functional layer for a lithium ion secondary battery, and a lithium ion secondary battery.

[0002] Electrochemical devices such as lithium-ion secondary batteries and electric double-layer capacitors are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Electrochemical devices generally include components such as a positive electrode, a negative electrode, and a separator that separates the positive electrode from the negative electrode to prevent short-circuiting between the positive electrode and the negative electrode.

[0003] Here, in electrochemical elements such as lithium ion secondary batteries, components are used that include a heat-resistant layer for improving heat resistance and strength, an adhesive layer for bonding battery components together, etc. (Hereinafter, these may be collectively referred to as "functional layers for electrochemical elements.") Specifically, an electrode formed by forming a functional layer on an electrode base material formed by providing an electrode mixture layer on a current collector, or a separator formed by forming a functional layer on a separator base material are used as battery components.

[0004] In recent years, further improvements have been investigated in compositions for forming functional layers of electrochemical devices, such as lithium ion secondary batteries, with the aim of further improving the performance of such devices (see Patent Document 1).

[0005] For example, Patent Document 1 proposes that, in an electrochemical element slurry composition containing a particulate polymer having a predetermined core-shell structure, a binder, and heat-resistant fine particles, the particulate polymer has an electrolyte contact angle of 0° or more and 35° or less, and the particulate polymer has a volume average particle diameter of 1.0 μm or more and 10.0 μm or less. Patent Document 1 also discloses that a functional layer obtained using the electrochemical element slurry composition can improve the electrolyte injectability and storage characteristics of electrochemical elements such as lithium ion secondary batteries, and has excellent adhesion (process adhesion) in the manufacturing process of the electrochemical element.

[0006] International Publication No. 2022 / 124126

[0007] However, the conventional compositions for electrochemical device functional layers have room for improvement in terms of achieving both high levels of adhesiveness of the resulting functional layer and high levels of rate characteristics and cycle characteristics of the resulting secondary battery. Therefore, an object of the present invention is to provide a binder composition for a lithium ion secondary battery functional layer, a slurry composition for a lithium ion secondary battery functional layer, and the like (hereinafter, these may be collectively referred to as a lithium ion secondary battery functional layer composition) that can achieve both high levels of adhesiveness of the resulting functional layer and high levels of rate characteristics and cycle characteristics of the resulting secondary battery.

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and have newly discovered that a composition for a lithium ion secondary battery functional layer containing granules containing at least a particulate polymer A can be provided that can simultaneously achieve high levels of adhesiveness of the resulting functional layer, and high levels of rate characteristics and cycle characteristics of the resulting secondary battery, when the volume average particle diameter of the granules and the volume average particle diameter and ash content of the binder composition are each within a predetermined range, thereby completing the present invention.

[0009] The present invention aims to advantageously solve the above-mentioned problems. The present invention provides a binder composition for a functional layer of a lithium ion secondary battery, comprising: [1] a particulate material containing at least a particulate polymer A; wherein the particulate material has a volume average particle diameter of 1.0 μm or more and 10.0 μm or less; the binder composition has a glass transition temperature of 25° C. or more and less than 60° C.; and an ash content of less than 3.0 mass%. The binder composition for a functional layer of a lithium ion secondary battery described above can simultaneously achieve high levels of adhesion of the resulting functional layer and high levels of rate and cycle characteristics of the resulting secondary battery. The volume average particle diameter, glass transition temperature, and ash content can each be measured according to the methods described in the Examples section of this specification.

[0010] [2] Here, it is preferable that the binder composition for a lithium ion secondary battery functional layer of the above [1] further contains a particulate polymer B different from the particulate polymer A. If the binder composition for a lithium ion secondary battery functional layer contains a particulate polymer B different from the particulate polymer A, the adhesiveness of the formed functional layer can be further increased, and the cycle characteristics of a secondary battery having a functional layer formed using the binder composition can be further improved.

[0011] [3] The binder composition for a lithium-ion secondary battery functional layer according to [1] or [2] above preferably has a metal content of less than 1000 ppm by mass. If the metal content of the binder composition for a secondary battery functional layer is less than 1000 ppm by mass, the coating stability of a slurry composition using the binder composition can be improved, and swelling of the secondary battery after repeated charge / discharge can be suppressed. The metal content of the binder composition for a functional layer can be measured according to the method described in the Examples of this specification.

[0012] [4] The present invention also provides a slurry composition for a lithium ion secondary battery functional layer, comprising the binder composition for a lithium ion secondary battery functional layer according to any one of [1] to [3] above and inorganic particles. The slurry composition for a lithium ion secondary battery functional layer described above improves the heat resistance and strength of the functional layer formed using the slurry composition, and allows the functional layer to be formed as a heat-resistant adhesive layer.

[0013] [5] The present invention also provides a separator with a functional layer for a lithium ion secondary battery, comprising a functional layer serving as an adhesive layer formed using the binder composition for a functional layer of a lithium ion secondary battery according to any one of [1] to [3] above, or a functional layer serving as a heat-resistant layer formed using the slurry composition for a functional layer of a lithium ion secondary battery according to [4] above. The separator with a functional layer for a lithium ion secondary battery described above can improve the rate characteristics and cycle characteristics of the lithium ion secondary battery.

[0014] [6] The present invention further provides a lithium ion secondary battery comprising the separator with a functional layer for lithium ion secondary batteries according to [5] above. The lithium ion secondary battery comprising the separator has excellent rate characteristics and cycle characteristics.

[0015] According to the present invention, it is possible to provide a composition for a functional layer of a lithium ion secondary battery (a binder composition for a functional layer of a lithium ion secondary battery and a slurry composition for a functional layer of a lithium ion secondary battery) that can simultaneously achieve high levels of adhesion of the resulting functional layer and high levels of rate characteristics and cycle characteristics of the resulting secondary battery, as well as a separator with a functional layer for a lithium ion secondary battery and a lithium ion secondary battery that use the composition.

[0016] Hereinafter, embodiments of the present invention will be described in detail. Hereinafter, the binder composition for a functional layer of a lithium ion secondary battery and the slurry composition for a functional layer of a lithium ion secondary battery of the present invention (hereinafter, simply referred to as the "binder composition for a functional layer" and the "slurry composition for a functional layer," respectively, and collectively referred to as the "functional layer composition") can be used as materials for forming the functional layer included in the separator with a functional layer for a lithium ion secondary battery of the present invention (hereinafter, simply referred to as the "separator"). The separator of the present invention is characterized by having a functional layer formed using the functional layer composition of the present invention. Furthermore, the lithium ion secondary battery of the present invention (hereinafter, simply referred to as the "secondary battery") includes the separator of the present invention. In this specification, the term "functional layer" collectively refers to an adhesive layer for bonding battery components together and a heat-resistant layer for improving heat resistance and strength. When simply referring to a "functional layer," the term may refer to either a functional layer as an adhesive layer or a heat-resistant layer. Furthermore, in this specification, the term "functional layer composition" collectively refers to the binder composition for a functional layer of the present invention used to form a functional layer as an adhesive layer and the slurry composition for a functional layer of the present invention used to form a functional layer as a heat-resistant layer, and when simply referring to the "functional layer composition," it may refer to either a binder composition for a functional layer or a slurry composition for a functional layer. Furthermore, each of the components disclosed in this specification, as well as the preferred embodiments, numerical ranges, and thresholds defining such numerical ranges, shown for each component, can be independently combined with each other in any manner.

[0017] (Binder composition for lithium ion secondary battery functional layer) The binder composition for lithium ion secondary battery functional layer of the present invention comprises granules containing at least particulate polymer A, and optionally further contains particulate polymer B, a dispersion medium, a dispersant, and other components. Here, the binder composition for functional layer of the present invention is characterized in that the volume average particle diameter of the granules is within a predetermined range, and the glass transition temperature and ash content of the binder composition are each within a predetermined range.

[0018] The binder composition for a functional layer of the present invention satisfies the above-mentioned properties, and therefore, by using the binder composition for a functional layer of the present invention, it is possible to provide the functional layer with excellent adhesion and improve the rate characteristics and cycle characteristics of the resulting secondary battery. Although the reason why the above-mentioned effects are obtained by using the binder composition for a functional layer of the present invention is not clear, it is presumed to be as follows.

[0019] First, in the binder composition for a functional layer of the present invention, the particulate matter containing at least the particulate polymer A has a relatively large volume average particle diameter of 1.0 μm or more and 10.0 μm or less. Therefore, on the thickness direction surface of a functional layer formed using the binder composition for a functional layer of the present invention, the particulate polymer A contained in the binder composition for a functional layer protrudes from materials other than the particulate polymer A, making it easier to contact the electrochemical element components, thereby improving the adhesiveness of the functional layer. In addition, since the glass transition temperature of the binder composition is 25°C or higher, it is believed to have excellent heat shrinkage resistance and act to improve the cycle characteristics and rate characteristics of secondary batteries. Furthermore, since the glass transition temperature is less than 60°C, it is believed to act to improve the adhesiveness of the functional layer. Furthermore, since the ash content is less than 3% by mass, it is believed to act to improve the adhesiveness of the resulting functional layer. The term "adhesion of the functional layer" can be broadly categorized depending on the conditions under which the adhesiveness is exhibited. One of these is the adhesiveness evaluated as "self-binding" in the examples described below. When evaluating "self-adhesion," the functional layers are placed face to face, and the adhesion between the functional layers is evaluated under the following adhesion conditions: a press temperature of 50°C, a press pressure of 2.0 MPa, and a hot press time of 2 minutes. This "self-adhesion" refers to the adhesive retention between the functional layers. A different aspect of adhesion from "self-adhesion" is the adhesion evaluated as "electrode adhesion" in the examples described below. When evaluating "electrode adhesion," an electrode (specifically, a negative electrode) and a functional layer are placed face to face, and the adhesion between the functional layer and the electrode is evaluated under the following adhesion conditions: a press temperature of 60°C, a press pressure of 5 MPa, and a hot press time of 5 seconds. This "electrode adhesion," as evaluated by the evaluation method, refers to the adhesion between the electrode and the functional layer in a secondary battery formed using the functional layer of the present invention. In this specification, the term "adhesion" refers to both of these.

[0020] <Granules> The binder composition for a functional layer of the present invention includes granules containing at least the particulate polymer A. The content of the particulate polymer A in the granules is not particularly limited and may be 100% by mass. Furthermore, when the granules include a component other than the particulate polymer A, the component is not particularly limited, but it is preferable that the component is different from the particulate polymer A in at least one of the properties, such as the amount undissolved in THF, the degree of swelling in an electrolyte, the complex modulus, the maximum compressive strength, the rate of change in maximum compressive strength, and the tan δ ratio, which will be described later.

[0021] <Particulate polymer A> The particulate polymer A has the function of imparting excellent adhesiveness to the functional layer formed using the binder composition for the functional layer. Here, the "particulate polymer" refers to a polymer that is dispersible in an aqueous medium such as water, and exists in the form of particles in the aqueous medium. Usually, the particulate polymer A is water-insoluble. In the present invention, the particles being "water-insoluble" means that when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble content is 90 mass% or more.

[0022] The composition of the particulate polymer A is not particularly limited. In particular, the particulate polymer A preferably contains an aromatic vinyl monomer unit, a crosslinkable monomer unit, and a (meth)acrylic acid ester monomer unit. Note that the particulate polymer A may contain monomer units other than the aromatic vinyl monomer unit, the crosslinkable monomer unit, and the (meth)acrylic acid ester monomer unit (hereinafter referred to as "other monomer units").

[0023] <<Aromatic vinyl monomer unit>> Examples of aromatic vinyl monomers that can form aromatic vinyl monomer units include styrene, α-methylstyrene, p-t-butylstyrene, butoxystyrene, vinyltoluene, chlorostyrene, and vinylnaphthalene. These may be used alone or in combination of two or more. Among these, styrene is preferred.

[0024] The proportion of aromatic vinyl monomer units in the particulate polymer A is preferably 40% by mass or more, more preferably 47% by mass or more, even more preferably 52% by mass or more, particularly preferably 54% by mass or more, and preferably 75% by mass or less, more preferably 69% by mass or less, and even more preferably 64% by mass or less, based on 100% by mass of all monomer units in the particulate polymer A. When the proportion of aromatic vinyl monomer units in the particulate polymer A is equal to or greater than the above-mentioned lower limit, the glass transition temperature of the particulate polymer A is appropriately increased, the coating stability of the slurry composition can be improved, the heat shrinkage resistance of the functional layer can be improved, and the rate characteristics of the resulting secondary battery can be improved. When the proportion of aromatic vinyl monomer units in the particulate polymer A is equal to or less than the above-mentioned upper limit, the glass transition temperature of the particulate polymer can be prevented from becoming excessively high, and the adhesiveness of the resulting functional layer can be improved.

[0025] <<Crosslinkable Monomer Unit>> Examples of crosslinkable monomers that can form crosslinkable monomer units include crosslinkable monomers having a thermally crosslinkable crosslinking group and one olefinic double bond per molecule; and crosslinkable monomers having two or more olefinic double bonds per molecule.

[0026] Examples of the thermally crosslinkable group include an epoxy group, an N-methylolamide group, an oxetanyl group, an oxazoline group, and combinations thereof. Of these, an epoxy group is preferred.

[0027] Examples of crosslinkable monomers having an epoxy group as a thermally crosslinkable crosslinkable group and an olefinic double bond include unsaturated glycidyl ethers such as vinyl glycidyl ether, allyl glycidyl ether, butenyl glycidyl ether, and o-allylphenyl glycidyl ether; diene or polyene monoepoxides such as butadiene monoepoxide, chloroprene monoepoxide, 4,5-epoxy-2-pentene, 3,4-epoxy-1-vinylcyclohexene, and 1,2-epoxy-5,9-cyclododecadiene; 3,4 alkenyl epoxides such as 1,2-epoxy-1-butene, 1,2-epoxy-5-hexene, and 1,2-epoxy-9-decene; and glycidyl esters of unsaturated carboxylic acids such as glycidyl acrylate, glycidyl methacrylate, glycidyl crotonate, glycidyl 4-heptenoate, glycidyl sorbate, glycidyl linoleate, glycidyl 4-methyl-3-pentenoate, glycidyl ester of 3-cyclohexenecarboxylic acid, and glycidyl ester of 4-methyl-3-cyclohexenecarboxylic acid.

[0028] Furthermore, examples of crosslinkable monomers having an N-methylolamide group as a thermally crosslinkable crosslinkable group and having an olefinic double bond include (meth)acrylamides having a methylol group, such as N-methylol(meth)acrylamide. In the present invention, "(meth)acryl" means acrylic and / or methacrylic.

[0029] Furthermore, examples of crosslinkable monomers having an oxetanyl group as a thermally crosslinkable crosslinkable group and having an olefinic double bond include 3-((meth)acryloyloxymethyl)oxetane, 3-((meth)acryloyloxymethyl)-2-trifluoromethyloxetane, 3-((meth)acryloyloxymethyl)-2-phenyloxetane, 2-((meth)acryloyloxymethyl)oxetane, and 2-((meth)acryloyloxymethyl)-4-trifluoromethyloxetane.

[0030] Furthermore, examples of crosslinkable monomers having an oxazoline group as a thermally crosslinkable crosslinkable group and having an olefinic double bond include 2-vinyl-2-oxazoline, 2-vinyl-4-methyl-2-oxazoline, 2-vinyl-5-methyl-2-oxazoline, 2-isopropenyl-2-oxazoline, 2-isopropenyl-4-methyl-2-oxazoline, 2-isopropenyl-5-methyl-2-oxazoline, and 2-isopropenyl-5-ethyl-2-oxazoline.

[0031] Further, examples of crosslinkable monomers having two or more olefinic double bonds per molecule include butadiene, isoprene, allyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane-tri(meth)acrylate, dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane-diallyl ether, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, methylenebisacrylamide, and divinylbenzene. In the present invention, "(meth)acrylate" means acrylate and / or methacrylate.

[0032] The above-mentioned crosslinkable monomers may be used alone or in combination of two or more. Among these, ethylene glycol dimethacrylate, glycidyl methacrylate, and allyl (meth)acrylate are preferred, and ethylene glycol dimethacrylate and glycidyl methacrylate are more preferred.

[0033] The proportion of the crosslinkable monomer units in the particulate polymer A is preferably 1.0% by mass or more, more preferably 3.0% by mass or more, and preferably 20% by mass or less, more preferably 16% by mass or less, and even more preferably 12% by mass or less, based on 100% by mass of all monomer units in the particulate polymer A. If the proportion of the crosslinkable monomer units in the particulate polymer A is equal to or greater than the above lower limit, the elution of the particulate polymer A into the electrolyte can be suppressed, and the rate characteristics of the lithium ion secondary battery can be improved. Furthermore, if the proportion of the crosslinkable monomer units in the particulate polymer A is equal to or less than the above upper limit, the adhesion of the functional layer can be further improved.

[0034] <<(Meth)acrylic Acid Ester Monomer Units>> Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, and 2-ethylhexyl acrylate; alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, and 2-ethylhexyl methacrylate; and the like. These may be used alone or in combination of two or more at any ratio. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are preferred as the (meth)acrylic acid ester monomer.

[0035] The proportion of the (meth)acrylic acid ester monomer units in the particulate polymer A is preferably 15% by mass or more, more preferably 21% by mass or more, and even more preferably 27% by mass or more, and preferably 50% by mass or less, more preferably 43% by mass or less, and even more preferably 38% by mass or less, based on 100% by mass of all monomer units in the particulate polymer A. If the proportion of the (meth)acrylic acid ester monomer units in the particulate polymer A is equal to or greater than the above-mentioned lower limit, the adhesiveness of the functional layer can be further improved. Furthermore, if the proportion of the (meth)acrylic acid ester monomer units in the particulate polymer A is equal to or greater than the above-mentioned lower limit, swelling of the secondary battery after repeated charge and discharge can be suppressed. Furthermore, if the proportion of the (meth)acrylic acid ester monomer units in the particulate polymer A is equal to or less than the above-mentioned upper limit, the coating stability of the slurry composition can be improved, and ultimately the rate characteristics of the resulting secondary battery can be improved.

[0036] <<Other Monomer Units>> Examples of other monomer units include polar group-containing monomer units. The polar group possessed by the polar group-containing monomer unit is not particularly limited, and examples thereof include carboxylic acid groups, nitrile groups, amino groups, sulfonic acid groups, phosphate groups, hydroxyl groups, and amide groups. Specific examples of carboxylic acid group-containing monomers capable of forming carboxylic acid group-containing monomer units include monocarboxylic acids and derivatives thereof, such as (meth)acrylic acid and crotonic acid; and dicarboxylic acids and derivatives thereof, such as maleic acid, fumaric acid, and itaconic acid. These can be used alone or in combination of two or more. Among these, itaconic acid is preferred. The content of other monomer units in the particulate polymer A may be 0% by mass or more, preferably 5% by mass or less, and more preferably 1% by mass or less, based on 100% by mass of all monomer units in the particulate polymer A.

[0037] The particulate polymer A may be particles formed of one kind of polymer (single polymer particles) or particles formed of two or more kinds of polymers (composite polymer particles). Among these, the particulate polymer A is preferably a single polymer particle.

[0038] <<Properties of Particulate Polymer A>> [Amount of Undissolved Tetrahydrofuran] The amount of undissolved tetrahydrofuran in the particulate polymer A (hereinafter abbreviated as "amount of undissolved THF") is preferably 40% by mass or more, more preferably 50% by mass or more, and preferably 99% by mass or less, and more preferably 88% by mass or less. When the amount of undissolved THF in the particulate polymer A is the above-mentioned lower limit or more, the cycle characteristics of the obtained secondary battery can be improved. When the amount of undissolved THF in the particulate polymer A is the above-mentioned upper limit or less, the adhesion of the functional layer can be improved. The amount of undissolved THF in the particulate polymer A can be adjusted, for example, by changing the type and / or amount of the crosslinkable monomer used to prepare the particulate polymer A, or by changing the type and / or amount of the chain transfer agent. Specifically, the amount of undissolved THF can be increased by increasing the amount of crosslinkable monomer, using a polyfunctional crosslinkable monomer, or further by using a plurality of kinds of crosslinkable monomers in combination, and the amount of undissolved THF can be reduced by decreasing the amount of crosslinkable monomer and increasing the amount of chain transfer agent.The amount of undissolved THF of particulate polymer A can be measured according to the method described in the examples of this specification.

[0039] [Electrolyte Swelling Degree] The electrolyte swelling degree of the particulate polymer A is preferably 100% (1.00 times) or more, more preferably 125% (1.25 times) or more, and even more preferably 150% (1.50 times) or more, and is preferably 500% (5.00 times) or less, more preferably 400% (4.00 times) or less, and even more preferably 300% (3.00 times) or less. When the electrolyte swelling degree of the particulate polymer A is the above-mentioned lower limit or more, the rate characteristics of the secondary battery can be further improved. Furthermore, when the electrolyte swelling degree of the particulate polymer A is the above-mentioned upper limit or less, the cycle characteristics of the secondary battery can be further improved. The electrolyte swelling degree of the particulate polymer A can be controlled, for example, by changing the composition of the monomers used to prepare the particulate polymer A. For example, the electrolyte swelling degree can be reduced by increasing the amount of aromatic vinyl monomer blended when preparing the particulate polymer A, and the electrolyte swelling degree can be increased by increasing the amount of (meth)acrylic acid ester monomer. Alternatively, the electrolyte swelling degree can be reduced by increasing the amount of crosslinkable monomer used to prepare the particulate polymer A, and the electrolyte swelling degree can be increased by decreasing the amount.

[0040] [Complex Elastic Modulus] The particulate polymer A preferably has a complex elastic modulus at 40°C of 1 MPa or more, more preferably 15 MPa or more, even more preferably 100 MPa or more, even more preferably 180 MPa or more, particularly preferably 250 MPa or more, and preferably 2000 MPa or less, more preferably 1600 MPa or less, even more preferably 1300 MPa or less, even more preferably 1000 MPa or less, particularly preferably 800 MPa or less. When the complex elastic modulus of the particulate polymer A is within the above range, the adhesiveness of the resulting functional layer can be improved. In particular, when the complex elastic modulus of the particulate polymer A is equal to or greater than the above lower limit, the rate characteristics of the resulting secondary battery can be improved. The complex elastic modulus of the particulate polymer A can be adjusted, for example, by changing the type and / or amount of the (meth)acrylic acid ester monomer used to prepare the particulate polymer A. Specifically, for example, the complex elastic modulus decreases when the amount of the (meth)acrylic acid ester monomer used to prepare the particulate polymer A is increased. Alternatively, the complex modulus can be increased by increasing the amount of metal oxide used in synthesizing the particulate polymer A. The complex modulus of the particulate polymer A can be measured according to the method described in the examples of this specification.

[0041] [Tan δ Ratio] The particulate polymer A has a tan δ ratio calculated by the formula (loss tangent (tan δ) at 60 ° C.) / (loss tangent (tan δ) at 25 ° C.), which is preferably more than 1.00, more preferably 1.10 or more, preferably 10 or more, even more preferably 12 or more, preferably 80 or less, more preferably 70 or less, even more preferably 55 or less, and particularly preferably 45 or less. When the tan δ ratio of the particulate polymer A is equal to or greater than the above lower limit, the coating stability of the resulting slurry composition can be improved and the rate characteristics of the resulting secondary battery can be improved. Furthermore, when the tan δ ratio of the particulate polymer A is equal to or less than the above upper limit, the adhesiveness of the resulting functional layer can be improved and swelling of the secondary battery after repeated charge and discharge can be suppressed. The tan δ ratio of the particulate polymer A can be adjusted, for example, by changing the type and / or amount of the aromatic vinyl monomer and (meth)acrylic acid ester monomer used to prepare the particulate polymer A. Specifically, for example, the tan δ ratio increases by increasing the amount of the aromatic vinyl monomer used to prepare the particulate polymer A, and the tan δ ratio decreases by decreasing the amount. In addition, the tan δ at each temperature can be measured according to the method described in the examples of this specification.

[0042] [Maximum rate of change in compressive strength] The particulate polymer A preferably has a maximum rate of change in compressive strength of 0.50 or more, more preferably 0.65 or more, preferably 1.0 or less, more preferably 0.9 or less, and even more preferably 0.85 or less. In this specification, the maximum rate of change in compressive strength is the maximum compressive strength F at the first repetition when the compressive operation of the particulate polymer A is repeated 10 times. ｍａｘ，１ and the maximum compressive strength F at the 10th repetition ｍａｘ，１０ The ratio F ＊ (F ＊ =F ｍａｘ，１ / F ｍａｘ，１０) When the rate of change in maximum compressive strength of the particulate polymer A is equal to or higher than the lower limit, swelling of the resulting secondary battery after repeated charge and discharge can be suppressed. When the rate of change in maximum compressive strength of the particulate polymer A is equal to or lower than the upper limit, structural change of the particulate polymer A in response to external stimuli is small, and the stability of the particulate polymer A can be improved. The rate of change in maximum compressive strength of the particulate polymer A can be adjusted by the type and / or amount of the crosslinkable monomer used in the synthesis of the particulate polymer A, the polymerization temperature, and the heating time.

[0043] <<Preparation of Particulate Polymer A>> The particulate polymer A can be prepared by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent such as water. Here, the proportion of each monomer in the monomer composition is usually the same as the proportion of each monomer unit in the particulate polymer A.

[0044] The polymerization method is not particularly limited, and any of methods such as suspension polymerization, emulsion polymerization aggregation, and pulverization can be used. Among these, suspension polymerization and emulsion polymerization aggregation are preferred, and suspension polymerization is more preferred. Furthermore, any of reactions such as radical polymerization and living radical polymerization can be used as the polymerization reaction.

[0045] Further, the monomer composition used in preparing the particulate polymer A may contain other additives such as a chain transfer agent, a polymerization regulator, a polymerization reaction retarder, a reactive fluidizing agent, a filler, a flame retardant, an antiaging agent, and a colorant in any blending amount.

[0046] Here, as an example, a method for preparing the particulate polymer A by suspension polymerization will be described.

[0047] [Preparation of Particulate Polymer A by Suspension Polymerization Method] (1) Preparation of Monomer Composition First, the monomers for constituting the polymer and other compounding agents added as necessary are mixed to prepare the monomer composition.

[0048] (2) Preparation of Colloidal Dispersion Next, an aqueous solution containing an inorganic component is prepared, and the aqueous solution is stirred to disperse the solute, thereby preparing a colloidal dispersion. The type of colloidal particles is not particularly limited, but colloidal particles containing, for example, magnesium hydroxide, barium sulfate, silica microparticles, boehmite particles, etc. are preferred. In addition, the concentration and amount of the colloidal dispersion are not particularly limited, but the colloidal particles are preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and preferably 20 parts by mass or less, and more preferably 10 parts by mass or less, based on 100 parts by mass of the total monomer components of the particulate polymer A.

[0049] (3) Formation of droplets The monomer composition is dispersed in the colloidal dispersion, a polymerization initiator is added, and then droplets of the monomer composition are formed. Here, the method for forming the droplets is not particularly limited, and for example, the droplets can be formed by shearing and stirring the colloidal dispersion containing the monomer composition using a disperser such as an emulsifying disperser.

[0050] Examples of the polymerization initiator include oil-soluble polymerization initiators such as t-butylperoxy-2-ethylhexanoate, azobisisobutyronitrile, etc. The polymerization initiator may be added after the monomer composition is dispersed in the colloidal dispersion and before droplets are formed, or may be added to the monomer composition before it is dispersed in the colloidal dispersion.

[0051] (4) Polymerization After droplets of the monomer composition are formed, the temperature of the colloidal dispersion containing the formed droplets is raised to initiate polymerization, thereby forming a particulate polymer in water. Examples of the polymerization initiator used in this process include t-butylperoxy-2-ethylhexanoate. The dispersion of the particulate polymer thus obtained is purified by a reduced pressure treatment using an evaporator, to obtain an aqueous dispersion containing the particulate polymer.

[0052] (5) Washing: The aqueous dispersion of the particulate polymer obtained in the above polymerization step is stirred while adding an acid such as sulfuric acid or hydrochloric acid to perform an acid washing treatment. Next, the aqueous dispersion of the particulate polymer to which the acid has been added is filtered and separated, and the obtained solid content is washed with water. This water washing treatment can be performed once or multiple times. The number of repetitions is, for example, 5 times or less, and may be 3 times or less. Depending on the number of repetitions, the amount of metal remaining in the particulate polymer A can be reduced. Then, the particulate polymer that has been subjected to the water washing treatment is dispersed in water again, and the dispersion is brought into alternate contact with a cation exchange resin and an anion exchange resin, and the particulate polymer A is separated again, thereby obtaining a particulate polymer A with a low metal content.

[0053] <Particulate polymer B> The particulate polymer B, which may be optionally contained in the binder composition for a functional layer of the present invention, is a component that functions as a binder and is usually composed of a polymer having binding ability. When the binder composition for a functional layer contains the particulate polymer B, the room temperature adhesiveness of the functional layer can be further improved. The particulate polymer B is a component different from the above-mentioned particulate polymer A, and is preferably water-insoluble.

[0054] Here, the particulate polymer B is not particularly limited as long as it is a particulate polymer that is different from the above-mentioned particulate polymer A and is water-insoluble and dispersible in a dispersion medium such as water. For example, a conjugated diene polymer or an acrylic polymer can be used. Among these, it is preferable to use an acrylic polymer. Furthermore, the particulate polymer B differs from the above-mentioned particulate polymer A in at least one of the volume average particle size, glass transition temperature, amount of undissolved THF, swelling degree in electrolyte, complex modulus, maximum compressive strength, rate of change in maximum compressive strength, and tan δ ratio. That is, the particulate polymer B does not satisfy at least one of the above-mentioned physical property values ​​(volume average particle size, glass transition temperature, amount of undissolved THF, swelling degree in electrolyte, complex modulus, maximum compressive strength, rate of change in maximum compressive strength, and tan δ ratio) that the particulate polymer A must satisfy. Note that the conjugated diene polymer refers to a polymer containing a conjugated diene monomer unit. Specific examples of the conjugated diene polymer include, but are not limited to, copolymers containing aromatic vinyl monomer units and aliphatic conjugated diene monomer units, such as styrene-butadiene copolymer (SBR), butadiene rubber (BR), acrylic rubber (NBR) (copolymers containing acrylonitrile units and butadiene units), and hydrogenated products thereof. Furthermore, the acrylic polymer refers to a polymer containing (meth)acrylic acid ester monomer units. These may be used alone or in combination of two or more types in any ratio.

[0055] The acrylic polymer that can be preferably used as the particulate polymer B is not particularly limited, and examples thereof include a polymer containing the above-mentioned crosslinkable monomer unit and (meth)acrylic acid ester monomer unit, and an acid group-containing monomer unit described below.

[0056] Examples of the acid group-containing monomer capable of forming the acid group-containing monomer unit include a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, and a monomer having a phosphoric acid group.

[0057] Examples of the monomer having a carboxylic acid group include monocarboxylic acids and dicarboxylic acids. Examples of the monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of the dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid.

[0058] Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth)allyl sulfonic acid, (meth)acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methylpropanesulfonic acid, 3-allyloxy-2-hydroxypropanesulfonic acid, etc. In this specification, "(meth)allyl" means allyl and / or methallyl.

[0059] Examples of the monomer having a phosphate group include 2-(meth)acryloyloxyethyl phosphate, methyl-2-(meth)acryloyloxyethyl phosphate, ethyl-(meth)acryloyloxyethyl phosphate, etc. In this specification, "(meth)acryloyl" means acryloyl and / or methacryloyl.

[0060] The above-mentioned acid group-containing monomers may be used alone or in any combination of two or more kinds in any ratio. Among these, as the acid group-containing monomer, a monomer having a carboxylic acid group is preferred, acrylic acid and methacrylic acid are more preferred, and methacrylic acid is even more preferred.

[0061] The proportion of (meth)acrylic acid ester monomer units in the acrylic polymer is preferably 50% by mass or more, more preferably 55% by mass or more, even more preferably 58% by mass or more, and preferably 98% by mass or less, more preferably 97% by mass or less, even more preferably 96% by mass or less. If the proportion of (meth)acrylic acid ester monomer units in the acrylic polymer is equal to or greater than the above-mentioned lower limit, the room temperature adhesion of the functional layer can be further improved. Furthermore, if the proportion of (meth)acrylic acid ester monomer units in the acrylic polymer is equal to or less than the above-mentioned upper limit, the blocking resistance of the functional layer can be improved.

[0062] The proportion of the acid group-containing monomer units in the acrylic polymer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, even more preferably 0.5% by mass or more, and preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less. When the proportion of the acid group-containing monomer units in the acrylic polymer is equal to or greater than the above-mentioned lower limit, the dispersibility of the particulate polymer B in the binder composition for the functional layer and in the functional layer can be improved, and the room temperature adhesiveness of the functional layer can be further improved. Furthermore, when the proportion of the acid group-containing monomer units in the acrylic polymer is equal to or less than the above-mentioned upper limit, the residual moisture content of the functional layer can be reduced, and the blocking resistance of the functional layer can be improved.

[0063] The proportion of crosslinkable monomer units in the acrylic polymer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and preferably 3% by mass or less, more preferably 2.5% by mass or less. If the proportion of crosslinkable monomer units in the acrylic polymer is equal to or greater than the lower limit, the blocking resistance of the functional layer can be improved. Furthermore, if the proportion of crosslinkable monomer units in the acrylic polymer is equal to or less than the upper limit, the room temperature adhesion of the functional layer can be further improved.

[0064] The acrylic polymer may contain monomer units (other monomer units) other than the (meth)acrylic acid ester monomer units, acid group-containing monomer units and crosslinkable monomer units. and vinyl ester monomers such as vinyl acetate, vinyl propionate, vinyl butyrate, and vinyl benzoate; vinyl ether monomers such as methyl vinyl ether, ethyl vinyl ether, and butyl vinyl ether; vinyl ketone monomers such as methyl vinyl ketone, ethyl vinyl ketone, butyl vinyl ketone, hexyl vinyl ketone, and isopropenyl vinyl ketone; and heterocycle-containing vinyl compound monomers such as N-vinylpyrrolidone, vinylpyridine, and vinylimidazole. Among these, as the other monomer, a nitrile group-containing monomer is preferred, and acrylonitrile is more preferred. Note that these other monomers may be used alone or in combination of two or more types in any ratio. The content ratio of the other monomer units in the acrylic polymer may be appropriately adjusted.

[0065] <<Properties of Particulate Polymer B>> [Volume Average Particle Diameter] The volume average particle diameter of the particulate polymer B is preferably 0.05 μm or more, more preferably 0.10 μm or more, and preferably less than 0.75 μm, more preferably less than 0.50 μm, and even more preferably less than 0.40 μm. If the volume average particle diameter of the particulate polymer B is 0.05 μm or more, the dispersibility of the particulate polymer B can be improved. Furthermore, if the volume average particle diameter of the particulate polymer B is less than 0.75 μm, the binding property of the particulate polymer B can be improved. The volume average particle diameter of the particulate polymer B can be measured using a laser diffraction / scattering measuring device.

[0066] [Glass Transition Temperature] The glass transition temperature (Tg) of the particulate polymer B is preferably -100°C or higher, more preferably -90°C or higher, even more preferably -80°C or higher, and is preferably less than 30°C, more preferably 20°C or lower, and even more preferably 15°C or lower. When the glass transition temperature of the particulate polymer B is equal to or higher than the above lower limit, the room temperature adhesiveness of the functional layer can be further improved. In addition, the blocking resistance of the functional layer can be improved. On the other hand, when the glass transition temperature of the particulate polymer B is equal to or lower than the above upper limit, the flexibility of the functional layer can be increased.

[0067] The mass ratio of the particulate polymer A to the particulate polymer B in the binder composition for the functional layer (particulate polymer A / particulate polymer B) is preferably 1 / 99 or more, more preferably 5 / 95 or more, even more preferably 10 / 90 or more, particularly preferably 50 / 50 or more, and is preferably 99 / 1 or less, more preferably 95 / 5 or less. When the mass ratio of the particulate polymer A to the particulate polymer B is the above-mentioned lower limit or more, the adhesiveness of the functional layer can be further improved. Furthermore, when the mass ratio of the particulate polymer A to the particulate polymer B is the above-mentioned upper limit or less, the rate characteristics of the obtained secondary battery can be improved.

[0068] <<Preparation of Particulate Polymer B>> The particulate polymer B is not particularly limited, and can be prepared, for example, by polymerizing a monomer composition containing the above-mentioned monomers in an aqueous solvent such as water. Here, the ratio of each monomer in the monomer composition is usually the same as the ratio of each monomer unit in the particulate polymer B.

[0069] The polymerization method and polymerization reaction are not particularly limited, and for example, the polymerization methods and polymerization reactions exemplified as the polymerization methods for the particulate polymer A described above can be used.

[0070] <Dispersion medium> The binder composition for a functional layer of the present invention usually contains a dispersion medium. Examples of the dispersion medium include water and organic solvents such as esters, ketones, and alcohols. These may be used alone or in combination of two or more. Among these, water is preferred. That is, the binder composition for a functional layer of the present invention is preferably a slurry composition in which components such as the particulate polymer A described above are dispersed in a dispersion medium containing water.

[0071] <Dispersant> The binder composition for a functional layer of the present invention preferably further contains a dispersant. If the binder composition for a functional layer further contains a dispersant, the room temperature adhesiveness of the functional layer can be further improved.

[0072] Preferred examples of dispersants include polycarboxylic acids such as polyacrylic acid, polymethacrylic acid, and alginic acid. The polycarboxylic acids may form salts with alkali metals, ammonia, or the like. Among these, polyacrylic acid and its salts are preferred. The dispersants may be used alone or in combination of two or more in any ratio.

[0073] The amount of dispersant in the binder composition for functional layer is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.3 parts by mass or more, and is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, relative to 100 parts by mass of the particulate polymer A. When the amount of dispersant in the binder composition for functional layer is equal to or greater than the above-mentioned lower limit, uneven distribution of the particulate polymer A and the particulate polymer B in the functional layer can be suppressed, and the adhesion of the functional layer can be further improved. Furthermore, when the amount of dispersant in the binder composition for functional layer is equal to or less than the above-mentioned upper limit, the rate characteristics of the resulting secondary battery can be improved.

[0074] <Other Components> The binder composition for a functional layer of the present invention may contain any other components in addition to the above-described particulate polymer A, particulate polymer B, dispersion medium, and dispersant. The other components are not particularly limited as long as they do not affect the electrochemical reaction in the electrochemical element, and examples thereof include known additives such as viscosity modifiers such as polyacrylamide (preferably having a weight-average molecular weight of 20,000 or more); wetting agents; and dispersion stabilizers such as sodium dodecylbenzenesulfonate and ammonium polyacrylate. These other components may be used alone or in combination of two or more.

[0075] <Properties of the Binder Composition for Functional Layer> [Volume Average Particle Diameter] As described above, the binder composition for functional layer of the present invention requires that the volume average particle diameter of the granules containing at least the particulate polymer A be 1.0 μm or more and 10.0 μm or less. The volume average particle diameter of the granules is preferably 1.5 μm or more, preferably 9.0 μm or less, and more preferably 7.0 μm or less. It is presumed that if the volume average particle diameter of the granules is equal to or greater than the above-mentioned lower limit, the particulate polymer A can be present as convex portions on the surface of the functional layer, thereby improving the electrode adhesion of the functional layer and improving the heat shrinkage resistance. On the other hand, if the volume average particle diameter of the binder composition for functional layer is equal to or less than the above-mentioned upper limit, it is presumed that a sufficient number of particulate polymers A can be blended into the functional layer, thereby improving the electrode adhesion of the functional layer. Furthermore, if the volume average particle diameter of the granules is within the above-mentioned range, swelling of the secondary battery after repeated charge and discharge can be suppressed. The volume average particle diameter of the binder composition for the functional layer can be adjusted by changing the type and amount of the colloidal dispersion liquid used in preparing the particulate polymer A, as well as the preparation method and preparation conditions for the particulate polymer A.

[0076] Here, the volume average particle diameter of the granules is a value obtained according to the measurement method described in the Examples below. In this measurement method, particles having a particle diameter of 0.4 μm or more are used as measurement objects, and the volume average particle diameter is measured. In this case, when the binder composition for a functional layer does not contain particles having a particle diameter of 0.4 μm or more other than the particulate polymer A, the volume average particle diameter of the granules measured by this measurement method will be equal to that of the particulate polymer A. Therefore, in the present invention, it is preferable that the value of the volume average particle diameter of the particulate polymer A satisfies the above range described for the granules.

[0077] [Particle size distribution] As described above, in the binder composition for functional layer, the particle size distribution of the particulate matter containing at least the particulate polymer A is preferably 2.0 or less, more preferably 1.8 or less. In this specification, the particle size distribution is calculated as the quotient of the volume average particle size divided by the number average particle size. If the particle size distribution is equal to or less than the upper limit, the electrode adhesion of the resulting functional layer can be improved and the heat shrinkage resistance can be improved. The particle size distribution of the particulate matter can be adjusted by changing the type and amount of the colloidal dispersion used in preparing the particulate polymer A, as well as the preparation method and preparation conditions for the particulate polymer A.

[0078] As with the volume average particle size of the particulate material described above, when the binder composition for a functional layer does not contain particles having a particle size of 0.5 μm or more other than the particulate polymer A, the particle size distribution of the particulate material described above is equal to the particle size distribution of the particulate polymer A. Therefore, in the present invention, it is preferable that the particle size distribution of the particulate polymer A satisfies the range described above for the particulate material.

[0079] [Glass Transition Temperature] The glass transition temperature of the binder composition for the functional layer must be 25°C or higher, preferably 30°C or higher, more preferably 42°C or higher, and must be lower than 60°C, preferably 57°C or lower, and even more preferably 54°C or lower. If the glass transition temperature of the binder composition for the functional layer is equal to or higher than the above lower limit, the coating stability of the resulting slurry composition can be improved and the rate characteristics of the resulting secondary battery can be improved. Furthermore, the heat shrinkage resistance of the resulting functional layer can also be improved. Furthermore, if the glass transition temperature of the binder composition for the functional layer is equal to or lower than the above upper limit, the adhesion of the resulting functional layer can be improved. Furthermore, swelling of the secondary battery after repeated charge and discharge can also be suppressed. The glass transition temperature of the binder composition for the functional layer can be adjusted, for example, by changing the type and / or amount of the monomer used to prepare the particulate polymer A.

[0080] Here, the glass transition temperature of the binder composition for the functional layer is a value obtained by obtaining a differential scanning calorimetry (DSC) curve using the binder composition as the measurement target, and when multiple peaks are detected, the peak with the largest displacement is taken as the glass transition temperature of the binder composition, as described in the examples below.Therefore, as in the examples below, when the binder composition for the functional layer contains multiple polymers, the value of the polymer with the largest blending amount will exhibit the peak value, and in the examples, the value of the particulate polymer A, which is the polymer with the largest blending amount, can be detected as the glass transition temperature of the binder composition.Therefore, in the binder composition of the present invention, the value of the glass transition temperature of the binder composition is a value that can coincide with the glass transition temperature of the particulate polymer A.

[0081] [Ash Content] The binder composition for a functional layer must have an ash content of less than 3.0% by mass, preferably 2.9% by mass or less, more preferably 2.0% by mass or less, even more preferably 1.7% by mass or less, even more preferably 1.2% by mass or less, and particularly preferably 0.8% by mass or less, where the total solid content of the binder composition is 100% by mass. When the ash content of the binder composition for a functional layer is equal to or less than the upper limit, the self-binding properties of the resulting functional layer are improved, and the coating stability of the resulting slurry composition can be improved. Furthermore, the cycle characteristics of the resulting secondary battery can be improved. The lower limit of the ash content of the binder composition for a functional layer is not particularly limited. The binder composition for a functional layer may be ash-free, or may have an ash content of, for example, 0.1% by mass or more. The above-mentioned preferred range for the ash content also preferably applies to the particulate polymer A. That is, the ash content of the particulate polymer A must be less than 3.0% by mass, preferably 2.9% by mass or less, more preferably 2.0% by mass or less, even more preferably 1.7% by mass or less, even more preferably 1.2% by mass or less, particularly preferably 0.8% by mass or less, and may be 0% by mass or more, or 0.1% by mass or more, based on the total mass of the particulate polymer A being 100% by mass. The ash content of the binder composition can be adjusted, for example, by changing the concentration and / or amount of the colloidal dispersion used in preparing the particulate polymer A. Specifically, the ash content decreases by reducing the concentration and / or amount of the colloidal dispersion used in preparing the particulate polymer A, and increases by increasing the concentration and / or amount. The ash content of the particulate polymer A can also be adjusted by appropriately selecting and washing the inorganic colloid contained in the particulate polymer A with substances such as solvents, acids, and bases.

[0082] [pH] When the binder composition for a functional layer of the present invention contains water as a dispersion medium, the pH of the binder composition for a functional layer is preferably 5 or more, more preferably 6 or more, and preferably 10.5 or less, more preferably 10.0 or less. If the pH of the binder composition for a functional layer is above the above-mentioned lower limit, the adhesion of the functional layer can be further improved. Furthermore, if the pH of the binder composition for a functional layer is below the above-mentioned upper limit, hydrolysis of viscosity modifiers such as polyacrylamide can be suppressed, and the dispersibility of the binder composition for a functional layer can be improved. The pH of the binder composition for a functional layer can be adjusted by adding a known acidic or basic compound.

[0083] [Solid content concentration] When the binder composition for a functional layer of the present invention contains a dispersion medium, i.e., when it is a slurry composition in which components such as the particulate polymer A described above are dispersed in a dispersion medium, the solid content concentration of the binder composition for a functional layer of the present invention is preferably 5% by mass or more, more preferably 20% by mass or more, and is preferably 50% by mass or less, and more preferably 30% by mass or less. When the solid content concentration of the binder composition for a functional layer is within the above range, it is easy to apply it to a separator substrate.

[0084] [Metal Content] The metal content of the binder composition for functional layer of the present invention is preferably less than 0.10% by mass, more preferably 0.08% by mass or less, and even more preferably 0.06% by mass or less. When the metal content of the binder composition for functional layer is equal to or less than the above upper limit, the coating stability of the resulting slurry composition can be improved, and the cycle characteristics of the resulting secondary battery can be improved. The metal content is not particularly limited, but may be zero (0% by mass) or may be 0.01% by mass or more as the amount of unavoidable impurities. The metal content of the binder composition for functional layer can be adjusted, for example, by changing the concentration and / or amount of the colloidal dispersion used in preparing the particulate polymer A. Specifically, the metal content decreases when the concentration and / or amount of the colloidal dispersion used in preparing the particulate polymer A is reduced, and increases when the concentration and / or amount is increased. Alternatively, the metal content can be increased by reducing the number of washing steps in the preparation of the particulate polymer A. The metal content of the binder composition for the functional layer can be measured according to the method described in the examples of this specification.

[0085] <Method for preparing binder composition for functional layer> The binder composition for functional layer is not particularly limited, and can be prepared, for example, by mixing the above-mentioned particulate polymer A with the particulate polymer B, a dispersion medium, a dispersant, and other components that are used as needed. Note that, when the particulate polymer A or the particulate polymer B is prepared by polymerizing a monomer composition in an aqueous solvent, the particulate polymer A or the particulate polymer B may be mixed with other components as is in the form of an aqueous dispersion. Furthermore, when the particulate polymer A or the particulate polymer B is mixed in the form of an aqueous dispersion, the water in the aqueous dispersion may be used as the dispersion medium.

[0086] Here, the method for mixing the above-mentioned components is not particularly limited, but in order to efficiently disperse each component, it is preferable to use a disperser as a mixing device. The disperser is preferably a device that can uniformly disperse and mix the above-mentioned components. Examples of dispersers include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer.

[0087] (Slurry composition for lithium ion secondary battery functional layer) The slurry composition for lithium ion secondary battery functional layer of the present invention includes the binder composition for lithium ion secondary battery functional layer described above and inorganic particles. The slurry composition for lithium ion secondary battery functional layer of the present invention improves the heat resistance and strength of the functional layer formed using the slurry composition, and can form a functional layer as a heat-resistant adhesive layer.

[0088] <Inorganic Particles> Here, the inorganic particle material is preferably one that is stable in the environment in which the secondary battery is used and is electrochemically stable, and examples thereof include aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH)), gibbsite (Al(OH ３ )), silicon oxide, magnesium oxide (magnesia), magnesium hydroxide, calcium oxide, titanium oxide (titania), barium titanate (BaTiO ３ Examples of inorganic particles include oxide particles such as zirconium oxide (ZrO), and alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystalline particles such as silicon and diamond; sparingly soluble ionic crystalline particles such as barium sulfate, calcium fluoride, and barium fluoride; and clay fine particles such as talc and montmorillonite. Among these, aluminum oxide, aluminum oxide hydrate (boehmite), magnesium hydroxide, and barium sulfate are more preferred, and aluminum oxide hydrate (boehmite) is even more preferred. Furthermore, these particles may be subjected to element substitution, surface treatment, solid solution formation, etc., as necessary. These inorganic particles may be used alone or in combination of two or more types in any ratio.

[0089] <<Volume Average Particle Diameter of Inorganic Particles>> The volume average particle diameter (D50) of the inorganic particles is preferably 0.1 μm or more, more preferably 0.2 μm or more, even more preferably 0.25 μm or more, and preferably 1.5 μm or less, more preferably 1.0 μm or less, and even more preferably 0.8 μm or less. When the volume average particle diameter of the inorganic particles is equal to or greater than the above-mentioned lower limit, the inorganic particles are densely packed in the functional layer. Therefore, the decrease in ionic conductivity in the functional layer can be further suppressed, thereby improving the electrochemical characteristics (particularly, rate characteristics) of the secondary battery. On the other hand, when the volume average particle diameter of the inorganic particles is equal to or less than the above-mentioned upper limit, the functional layer can exhibit excellent heat resistance and strength even when the functional layer is thin, thereby increasing the capacity of the secondary battery. The volume average particle diameter of the inorganic particles can be measured by a laser diffraction / scattering method.

[0090] <<Mixing Ratio of Inorganic Particles and Particulate Polymer A>> The mixing ratio of the inorganic particles to the particulate polymer A in the slurry composition for the functional layer, expressed as a mass ratio (inorganic particles / particulate polymer A), is preferably 40 / 60 or more, more preferably 50 / 50 or more, and even more preferably 60 / 40 or more, and is preferably 99 / 1 or less, more preferably 95 / 5 or less, and even more preferably 90 / 10 or less. If the mass ratio of the inorganic particles to the particulate polymer A is within the above range, the balance between the heat resistance and room temperature adhesion of the functional layer is improved.

[0091] <<Mixing Ratio of Inorganic Particles and Particulate Polymer B>> The mixing ratio of the inorganic particles to the particulate polymer B in the slurry composition for functional layer is preferably 0.1 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.5 parts by mass or more, particularly preferably 1 part by mass or more, per 100 parts by mass of the inorganic particles, and is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 10 parts by mass or less. If the content of the particulate polymer B is not less than the above lower limit, the room temperature adhesion of the functional layer can be further improved. On the other hand, if the content of the particulate polymer B is not more than the above upper limit, the rate characteristics of the obtained secondary battery can be further improved.

[0092] <<Mass Ratio of Particulate Polymer A to Particulate Polymer B>> The mass ratio of the particulate polymer A to the particulate polymer B in the slurry composition for the functional layer is preferably the same as the range described above for the mass ratio of the particulate polymer A to the particulate polymer B in the binder composition for the functional layer.

[0093] <Method for preparing a slurry composition for a functional layer> The slurry composition for a functional layer is not particularly limited, and can be prepared, for example, by adding inorganic particles when mixing the components in the preparation of the binder composition for a functional layer described above. Alternatively, the slurry composition can be prepared by separately preparing a dispersion of inorganic particles and a binder composition for a functional layer and then mixing them. The mixing method can be the same as the method described above in the section on the binder composition for a functional layer.

[0094] (Separator with functional layer for lithium-ion secondary battery) The separator with functional layer for lithium-ion secondary battery of the present invention (hereinafter also simply referred to as "separator") includes a functional layer as an adhesive layer formed using the binder composition for functional layer described above, or a functional layer as a heat-resistant layer formed using the slurry composition for functional layer described above. Because the separator of the present invention includes the functional layer described above, the rate characteristics and cycle characteristics of the resulting secondary battery can be improved.

[0095] <Separator Substrate> The separator of the present invention comprises a separator substrate having the functional layer described above formed on at least one surface thereof. The separator substrate on which the functional layer is formed is not particularly limited, and for example, the substrate described in JP 2012-204303 A can be used. Among these, a microporous film made of a polyolefin resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferred because it allows the overall separator thickness to be thin, thereby increasing the proportion of electrode active material in the lithium ion secondary battery and increasing the capacity per volume. The separator substrate may also include any layer other than the functional layer that can exhibit the desired function.

[0096] <Functional Layer> The functional layer is a functional layer serving as an adhesive layer formed using the functional layer binder composition of the present invention, or a functional layer serving as a heat-resistant layer formed using the functional layer slurry composition of the present invention. Here, the functional layer may be either a functional layer serving as an adhesive layer or a functional layer serving as a heat-resistant layer, or both. The functional layer may be formed as an individual functional layer using the functional layer binder composition and the functional layer slurry composition separately, or as a composite layer by mixing the functional layer binder composition and the functional layer slurry composition. Here, the functional layer contains at least the particulate polymer A described above, and optionally contains particulate polymer B, a dispersant, inorganic particles, and other components. The components contained in the functional layer are those contained in the functional layer binder composition or the functional layer slurry composition (collectively referred to as the "functional layer composition"), and the preferred abundance ratio of each of these components is the same as the preferred abundance ratio of each component in the functional layer composition.

[0097] <<Method of Forming a Functional Layer>> The method of forming a functional layer on a separator substrate using a functional layer composition is not particularly limited, and examples include: 1) a method of applying the functional layer composition to the surface of the separator substrate described above and then drying it; 2) a method of immersing the separator substrate described above in the functional layer composition and then drying it; and 3) a method of applying the functional layer composition to a release substrate and drying it to form a functional layer, and then transferring the resulting functional layer to the surface of the separator substrate described above. Note that the functional layer may be formed on only one side of the separator substrate, or on both sides of the separator substrate. Here, the release substrate is not particularly limited, and known release substrates can be used.

[0098] Among these, the method 1) is preferred because it is easy to control the thickness of the functional layer. The method 1) may include, for example, a step of applying a functional layer composition onto a separator substrate (application step), and a step of drying the functional layer composition applied onto the separator substrate to form a functional layer (functional layer formation step).

[0099] [Coating process] In the coating process, the method for coating the functional layer composition onto the substrate is not particularly limited, and examples thereof include a bar coater method, a doctor blade method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

[0100] [Functional Layer Forming Step] In the functional layer forming step, the method for drying the functional layer composition on the separator substrate is not particularly limited and any known method can be used, such as drying with warm air, hot air, or low-humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams, etc. The drying conditions are not particularly limited, but the drying temperature is preferably 50°C or higher and 150°C or lower, and the drying time is preferably 1 minute or higher and 30 minutes or lower.

[0101] <<Functional Layer Thickness>> The thickness of the functional layer formed using the functional layer composition of the present invention is preferably 0.5 μm or more and preferably 5 μm or less. If the thickness of the functional layer is equal to or greater than the above-mentioned lower limit, the room temperature adhesion of the functional layer can be further improved. Furthermore, if the thickness of the functional layer is equal to or less than the above-mentioned upper limit, the blocking resistance of the functional layer can be improved.

[0102] (Lithium-ion secondary battery) The lithium-ion secondary battery of the present invention (hereinafter also simply referred to as "secondary battery") is characterized by including the separator with functional layer for lithium-ion secondary batteries of the present invention. The lithium-ion secondary battery of the present invention has excellent rate characteristics and cycle characteristics because it uses the separator of the present invention described above.

[0103] <Positive electrode and negative electrode> The positive electrode and negative electrode are not particularly limited, but examples thereof include an electrode base material in which an electrode mixture layer is formed on a current collector. Here, the current collector, the electrode active materials (positive electrode active material, negative electrode active material) and electrode mixture layer binders (positive electrode mixture layer binder, negative electrode mixture layer binder) in the electrode mixture layer, and the method for forming the electrode mixture layer on the current collector can be known methods, and for example, the method described in JP 2013-145763 A can be used.

[0104] <Electrolyte> As the electrolyte, an organic electrolyte solution in which a supporting electrolyte (e.g., a lithium salt) is dissolved in an organic solvent is usually used. Examples of the lithium salt include LiPF ６ , LiAsF ６ , LiBF ４ , LiSbF ６ , LiAlCl ４ , LiClO ４ , C.F. ３ SO ３ Li, C ４ F ９ SO ３ Li, CF ３ COOLi, (CF ３ CO) ２ NLi, (CF ３ SO ２ ) ２ NLi, (C ２ F ５ SO ２ Among them, LiPF is preferred because it is easily soluble in solvents and shows a high degree of dissociation. ６ , LiClO ４ , C.F. ３ SO ３ Li is preferred. The electrolyte may be used alone or in combination of two or more. Generally, the lithium ion conductivity tends to increase as the supporting electrolyte with a higher degree of dissociation is used, so the lithium ion conductivity can be adjusted by the type of supporting electrolyte.

[0105] The organic solvent used in the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte, but suitable examples include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), methyl ethyl carbonate (ethyl methyl carbonate (EMC)), and vinylene carbonate; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like. A mixture of these solvents may also be used.

[0106] Among these, carbonates are preferred because they have a high dielectric constant and a wide stable potential range. Generally, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted by the type of solvent. The concentration of the electrolyte in the electrolyte solution can be adjusted as appropriate. Known additives may also be added to the electrolyte solution.

[0107] <Method for Manufacturing Lithium-Ion Secondary Battery> The method for manufacturing the lithium-ion secondary battery of the present invention is not particularly limited. For example, the lithium-ion secondary battery can be manufactured by stacking a positive electrode and a negative electrode with the separator of the present invention interposed therebetween, rolling or folding the stack as necessary, placing the stack in a battery container, injecting an electrolyte into the battery container, and sealing the battery container. If necessary, an expanded metal, a fuse, an overcurrent prevention element such as a PTC element, a lead plate, or the like may be placed in the battery container to prevent pressure buildup within the battery and overcharging and discharging. The shape of the battery may be any shape, such as a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, or a flat type.

[0108] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, "%" and "parts" representing amounts are based on mass unless otherwise specified. Furthermore, in a polymer produced by polymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer usually coincides with the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, various measurements and evaluations were performed as follows.

[0109] (Physical Property Measurement) <Amount Undissolved in THF> The aqueous dispersion containing the particulate polymer A prepared in each of the Examples and Comparative Examples was dropped into a petri dish so as to give a solid content of 1.5 g, and dried for 24 hours in an environment of 23 to 27°C, and further dried at 110°C for 1 hour to produce a film. For samples in which the dried product did not form a film of 2 mm or more square, 0.2±0.05 g of the sample after the drying was pressed at a temperature of 200°C and a pressure of 5 MPa for 2 minutes to produce a film. The produced film was cut into film pieces of 2.0 to 3.0 mm square, and 0.3±0.05 g was precisely weighed out. The mass of the precisely weighed film pieces was designated W0. Next, the precisely weighed film pieces were immersed in 80 mL of tetrahydrofuran (THF) at 25°C for 24 hours. Thereafter, the film piece was removed from the THF and vacuum-dried at 105°C for 3 hours, and its mass (mass of the insoluble portion) W1 was measured. The amount of insoluble portion in THF (%) was calculated according to the following formula (1): Amount of insoluble portion in THF (%) = W1 / W0 × 100 (1)

[0110] <Electrolyte swelling degree of particulate polymer A> The aqueous dispersions containing particulate polymer A prepared in Examples and Comparative Examples were dried at 80°C to obtain solids, and then approximately 0.2 g of the solids were pressed at 200°C, 1 MPa, and 1 minute to obtain a test piece for measuring the electrolyte swelling degree of particulate polymer A. The mass of the test piece (mass before immersion) was measured. Thereafter, the test piece was immersed in an electrolyte solution at a temperature of 60°C for 72 hours. The immersed test piece was pulled out, the electrolyte solution was wiped off, and the mass (mass after immersion) was immediately measured, and the value ([times]) of (mass after immersion) / (mass before immersion) was taken as the swelling degree. The electrolyte solution was a 3:7 (mass ratio) mixed solvent of ethylene carbonate and ethyl methyl carbonate containing LiPF ６ A solution in which the above was dissolved at a concentration of 1 mol / L was used.

[0111] <Complex modulus by viscoelasticity measurement | G ＊ | and tan δ ratio> The aqueous dispersions containing the particulate polymer A prepared in the examples and comparative examples were each prepared in a 5.3 cm ２The solid content was weighed out to 0.48 g and placed in an aluminum cup, followed by air drying. After air drying, a film consisting of particulate polymer A with a thickness of 70 to 80 μm was obtained. The obtained film was punched out to a diameter of 12 mm, and this was used as a measurement sample. For samples that did not form a film but turned into powder after air drying, approximately 0.1 g of the air-dried powder was weighed out in a tablet press with a diameter of 12 mm, and pressed at 9 kN for 10 seconds to form a tablet (12 mm diameter x 75 μm thickness), which was used as a measurement sample. Then, using a viscoelasticity measuring device (manufactured by Anton Paar, "MCR302") as a dynamic viscoelasticity measuring device, temperature dispersion measurements were performed in the range of 20 to 80 °C with parallel plates (diameter 8 mm), strain 0.01%, frequency 1 Hz, and a heating rate of 10 °C / min, and the following values ​​were obtained. Complex modulus at 40 °C |G ＊ | Tan δ ratio = (tan δ at 60 ° C) / (tan δ at 25 ° C)

[0112] <Maximum compressive strength F and maximum compressive strength change rate F in micro-compression tests ＊ > The aqueous dispersions containing particulate polymer A prepared in the Examples and Comparative Examples were diluted to a solids concentration of 0.1%, and 50 mg of the dispersions were dropped onto the measurement stage of a microcompression tester ("MCT-510" manufactured by Shimadzu Corporation) and dried. For one particle of particulate polymer A, the displacement when a load was applied to the particulate polymer A was recorded. Specifically, at a temperature of 25°C, the load was changed at an application rate of 0.1785 mN / sec up to a maximum test force of 9.8 mN, and the relationship between the test force f (mN) and the displacement d (μm) was obtained. From the obtained results, the compressive strength F = f / d (N / m) was calculated in the section up to the displacement that was 10% of the particle diameter of the particulate polymer A before loading, and the maximum value F in this section, F ｍａｘ This measurement was carried out with n=10, and the average value was taken as the measured value. Other test conditions were as follows: Pressure indenter: Flat indenter with a diameter of 50 μm (material: diamond) Pressure plate: SKS flat plate Measurement mode: Compression test Furthermore, from the relationship between the test force f and displacement d obtained in the above test, the test force f up to the displacement that is 20% of the particle diameter of the particulate polymer A was calculated. ２０ is the maximum test force, and the test force is 0 to the maximum test force f ２０The compression operation was repeated 10 times, and the relationship between the test force f (mN) and the displacement d (μm) was obtained. The compressive strength F = f / d (N / m) was calculated from the obtained results, and the maximum value F of F at the first repetition was ｍａｘ，１ and the maximum value of F after 10 iterations, F ｍａｘ，１０ The maximum compressive strength change rate F ＊ =F ｍａｘ，１ / F ｍａｘ，１０ was calculated.

[0113] <Volume average particle diameter of inorganic colloid dispersion and particulate polymer B> The volume average particle diameter of the inorganic colloid dispersion and particulate polymer B prepared in the examples and comparative examples was measured by a laser diffraction method. Specifically, an aqueous dispersion containing the object to be measured (adjusted to a solid content concentration of 0.1% by mass) was used as a sample. Then, in the particle size distribution (volume basis) measured using a laser diffraction particle size distribution analyzer (manufactured by Shimadzu Corporation, product name "SALD7100"), the particle diameter D50 at which the cumulative volume calculated from the smallest diameter side reached 50% was taken as the volume average particle diameter.

[0114] <Volume Average Particle Diameter and Particle Size Distribution of Granules> A 0.1 g equivalent sample of the binder composition for functional layers prepared in the Examples and Comparative Examples was weighed and placed in a beaker. 0.1 mL of an aqueous alkylbenzene sulfonic acid solution (Fujifilm Corporation, "Drywell") was added as a dispersant. 10-30 mL of a diluent (Beckman Coulter, Inc., "Isoton II") was then added to the beaker, and the mixture was dispersed for 3 minutes using a 20 W (Watt) ultrasonic disperser. The volume average particle diameter (Dv) of the granules was then measured using a particle size analyzer (Beckman Coulter, Inc., "Multisizer") under the following conditions: aperture diameter: 20 μm, medium: Isoton II, and particle count: 100,000. The number average particle diameter (Dp) was also measured, and the particle size distribution (Dv / Dp) was calculated. Under these conditions, the lower limit of the granule particle size measurement was 0.4 μm, and the upper limit was 16 μm. Therefore, the values ​​of the volume average particle size and particle size distribution measured according to this method can substantially correspond to the values ​​of the volume average particle size and particle size distribution of the particulate polymer A.

[0115] <Glass Transition Temperature of Functional Layer Binder Composition and Particulate Polymer B> A powder sample obtained by drying an aqueous dispersion containing the functional layer binder composition and the particulate polymer B at a temperature of 25°C for 48 hours was used as a measurement sample. 10 mg of the measurement sample was weighed into an aluminum pan, and measurement was performed using a differential scanning calorimetry measuring device (manufactured by SII Nanotechnology Inc., product name "EXSTAR DSC6220") under the conditions specified in JIS Z8703, at a temperature range of -100°C to 200°C and a heating rate of 20°C / min, to obtain a differential scanning calorimetry (DSC) curve. An empty aluminum pan was used as a reference. During this heating process, the temperature at which the differential signal (DDSC) peaked was determined as the glass transition temperature (°C). Note that, since multiple peaks were measured for the functional layer binder composition, the temperature showing the peak with the largest displacement was taken as the glass transition temperature of the functional layer binder composition.

[0116] <Ash Content> The functional layer binder compositions prepared in the Examples and Comparative Examples were dropped into a Petri dish to a solid content of 1.5 g and dried for 24 hours at 23-27°C to obtain a dried functional layer binder composition. An empty, clean crucible of appropriate size was heated for 30 minutes in a muffle furnace maintained at 550°C ± 25°C. After heating, the crucible was allowed to cool in a desiccator for 30 minutes, and then its mass W0 was weighed. Approximately 2 g of the dried functional layer binder composition obtained above was weighed into the crucible, and its weight W1 was measured. The crucible and its contents were placed in a muffle furnace maintained at 550°C ± 25°C and heated for 16 hours while supplying sufficient oxygen. After heating, the crucible and its contents were removed from the furnace, allowed to cool to room temperature in a desiccator, and its mass W was weighed. The ash content was calculated using the measured weights according to the following formula (2): (Ash content)=(W-W0) / W1×100(%)...(2)

[0117] <Total Metal Content> Approximately 0.4 g of the functional layer binder composition prepared in the Examples and Comparative Examples was collected and weighed based on the solid content, and incinerated in an electric furnace at 550°C for approximately 3 hours. Approximately 5 mL of concentrated sulfuric acid was then added to dissolve the binder composition, and approximately 5 mL of concentrated nitric acid was gradually added to perform wet decomposition. After decomposition, the acid was concentrated and the volume was adjusted to 10 mL with ultrapure water. The total amounts of Group 2 and Group 13 elements, as well as titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc contained in the functional layer binder composition were measured using an ICP-AES (SPS-5100, manufactured by SII Nanotechnology). The total amount of metals measured was divided by the weight of the functional layer binder composition initially weighed to calculate the total metal content (mass%).

[0118] (Evaluation) <Self-bonding of functional layer> A polyethylene microporous film (thickness: 9 μm) was prepared as a separator substrate. The slurry composition for the heat-resistant layer, which was the slurry composition for the functional layer prepared in the Examples and Comparative Examples, was applied to one side of the separator substrate by a bar coater method. The separator substrate coated with the slurry composition was then dried at 50°C for 2 minutes, and a coating weight of 0.5 g / m was applied to one side of the separator substrate. ２A separator (laminate) with a functional layer was prepared, comprising a heat-resistant adhesive layer as a functional layer. This separator with this functional layer was used as the separator for evaluation. The separator for evaluation was cut into two 10 mm x 50 mm strips. The two cut-out separators for evaluation were stacked with the functional layers facing each other to obtain a pre-press test specimen. This pre-press test specimen was placed in a laminate packaging material, and the packaging material was hot-pressed using a flat press at a temperature of 50°C and a load of 2.0 MPa for 2 minutes. The pressed test specimen was removed from the packaging material, and cellophane tape was attached to one side of the test specimen. The cellophane tape used was specified in JIS Z1522. The cellophane tape was fixed to a horizontal test table. One end of the separator was then pulled vertically upward at a tensile speed of 50 mm / min, and the stress was measured when the separator was peeled off. The same measurement was carried out three times, and the average of the measured values ​​was calculated as the peel strength P1 (N / m) and evaluated according to the following criteria. The higher the peel strength P1, the better the heat-resistant adhesive layer as a functional layer has adhesive retention and self-bonding properties. A: Peel strength P1 is 5.0 N / m or more B: Peel strength P1 is 3.0 N / m or more but less than 5.0 N / m C: Peel strength P1 is 1 N / m or more but less than 3.0 N / m D: Peel strength P1 is less than 1 N / m

[0119] <Electrode Adhesion of Functional Layer> The negative electrodes and separators with functional layers prepared in the Examples and Comparative Examples were each cut to a width of 20 mm and a length of 50 mm. The negative electrodes and separators with functional layers were laminated together and pressed using a flat plate press under conditions of a press temperature of 60°C, a load of 5 kN (press pressure of 5 MPa), and a press time of 5 seconds to obtain an integrated product in which the negative electrode and separator with functional layer were integrated. The resulting integrated product was placed with the current collector side of the negative electrode facing downward, and cellophane tape was attached to the surface of the negative electrode. The cellophane tape used was specified in JIS Z1522. The cellophane tape was fixed to a horizontal test table. The stress was then measured when one end of the separator with functional layer was pulled vertically upward at a pulling rate of 50 mm / min and peeled off. The above-mentioned stress measurement was performed three times for the integrated negative electrode and functional layer-equipped separator, and the average stress was calculated. The average value was defined as the peel strength (N / m). The calculated peel strength was then used to evaluate the adhesion between the positive electrode and the functional layer-equipped separator according to the following criteria. A: Peel strength of 20 N / m or more B: Peel strength of 10 N / m or more but less than 20 N / m C: Peel strength of 5 N / m or more but less than 10 N / m D: Peel strength of less than 5 N / m

[0120] <Coating Stability of Slurry Composition for Functional Layer in Examples 1 to 9 and Comparative Examples 1 to 5> The slurry composition for functional layer prepared in Example 13 was applied onto a separator (made of polyethylene, thickness 9 μm) using a gravure roll (line count 95) at a conveying speed of 50 m / min and a gravure rotation ratio of 200%, and the coated separator was cut out, and the coating amount per unit area M0 (mg / cm ２ ) was calculated. In addition, one hour after the start of application, the application amount M1 (mg / cm ２) was calculated. Then, the coating amount change rate ΔM (%) was calculated using the following formula (3) and evaluated as follows. The smaller this value, the higher the slurry stability of the functional layer slurry composition at high shear. ΔM = (|M0 - M1|) / M0 × 100 (%) ... (3) A: Coating amount change rate ΔM is less than 3% B: Coating amount change rate ΔM is 3% or more and less than 6% C: Coating amount change rate ΔM is 6% or more and less than 9% D: Coating amount change rate ΔM is 9% or more

[0121] <Coating Stability of Functional Layer Composition (Binder Composition) in Example 10> The functional layer binder composition prepared in Example 10 was applied onto a separator (made of polyethylene, thickness 9 μm) using a gravure roll (line count 300) at a conveying speed of 50 m / min and a gravure rotation ratio of 150%, and the coated separator was cut out to measure the coating amount M0 (mg / cm) per unit area. ２ ) was calculated. In addition, one hour after the start of application, the application amount M1 (mg / cm ２ ) was calculated. The coating amount change rate ΔM (%) was then calculated using the following formula (3) and evaluated as follows. The smaller this value, the higher the slurry stability of the binder composition for the functional layer at high shear. ΔM = (|M0 - M1|) / M0 × 100 (%) (3) A: Coating amount change rate ΔM is less than 5% B: Coating amount change rate ΔM is 5% or more but less than 10% C: Coating amount change rate ΔM is 10% or more but less than 20% D: Coating amount change rate ΔM is 20% or more

[0122] <Rate Characteristics of Secondary Battery (-10°C)> After injecting the electrolyte, the lithium ion secondary batteries prepared in the Examples and Comparative Examples were left standing at 25°C for 5 hours. Next, they were charged to a cell voltage of 3.65 V using a constant current method at 0.2 C at 25°C, and then aged for 12 hours at 60°C. Then, they were discharged to a cell voltage of 3.00 V using a constant current method at 0.2 C at 25°C. Then, they were subjected to CC-CV charging (upper limit cell voltage 4.20 V) at a constant current of 0.2 C, and CC discharging at a constant current of 0.2 C to a cell voltage of 3.00 V. This 0.2 C charge-discharge cycle was repeated three times. Next, in an environment at 25°C, constant current charging and discharging was performed at 0.2 C between cell voltages of 4.2 and 3.00 V, and the discharge capacity at this time was defined as C0. Thereafter, similarly, the battery was CC-CV charged at a constant current of 0.2 C, and then discharged to 3.0 V at a constant current of 1.0 C in an environment at a temperature of -10°C, and the discharge capacity at this time was defined as C1. Then, as the rate characteristics, the capacity retention rate expressed as ΔC = (C1 / C0) × 100 (%) was calculated and evaluated according to the following criteria. A larger value of this capacity retention rate ΔC indicates a higher discharge capacity at a high current in a low temperature environment and a lower internal resistance. A: Capacity retention rate ΔC is 70% or more B: Capacity retention rate ΔC is 60% or more but less than 70% C: Capacity retention rate ΔC is 50% or more but less than 60% D: Capacity retention rate ΔC is less than 50%

[0123] <Cycle Characteristics of Secondary Battery (45°C)> After injecting the electrolyte, the lithium ion secondary batteries prepared in the Examples and Comparative Examples were left to stand at 25°C for 2 hours. Next, they were charged to a cell voltage of 3.65 V at a constant current of 0.2 C at 25°C, and then aged for 24 hours at 60°C. Then, they were discharged to a cell voltage of 3.00 V at a constant current of 0.2 C at 25°C. Then, they were subjected to CC-CV charging (upper limit cell voltage 4.20 V) at a constant current of 0.2 C, and CC discharging to 3.00 V at a constant current of 0.2 C. This 0.2 C charge-discharge cycle was repeated three times. Then, in an environment of 45°C, a cycle consisting of charging to 4.20 V at 1 C and discharging to 3.00 V at 1 C was repeated 200 times. At this time, the discharge capacity at the first cycle was defined as X1, and the discharge capacity at the 100th cycle as X2. Using the discharge capacities X1 and X2, the capacity retention rate expressed as ΔC = (X2 / X1) × 100 (%) was calculated and evaluated according to the following criteria. A larger value of the capacity retention rate ΔC indicates that the lithium ion secondary battery has better cycle characteristics. A: Capacity retention rate ΔC is 90% or more B: Capacity retention rate ΔC is 85% or more but less than 90% C: Capacity retention rate ΔC is 80% or more but less than 85% D: Capacity retention rate ΔC is less than 80%

[0124] <Swelling of Secondary Battery After Repeated Charge / Discharge (After Cycles)> The lithium-ion secondary batteries fabricated in the Examples and Comparative Examples were poured with electrolyte and then allowed to stand at 25°C for 5 hours. Next, they were charged to a cell voltage of 3.65 V at 25°C using a constant current method at 0.2 C, and then aged for 12 hours at 60°C. Then, they were discharged to a cell voltage of 3.00 V using a constant current method at 0.2 C at 25°C. Subsequently, they were subjected to CC-CV charging (upper cell voltage 4.20 V) using a constant current method at 0.2 C, and CC discharging to 3.00 V using a constant current method at 0.2 C. This 0.2 C charge / discharge cycle was repeated three times. After that, the batteries were charged to 4.20 V at 0.1 C and discharged to 3.00 V at 0.1 C in a 25°C environment. Then, the batteries were immersed in liquid paraffin, and their volumes (V0) were measured. Furthermore, in a 45°C environment, a cycle of charging to 4.20 V at 1 C and discharging to 3.00 V at 1 C was repeated 200 times. The battery was then immersed in liquid paraffin, and its volume V1 was measured. The volume change ΔV of the battery cell before and after 200 charge / discharge cycles was calculated using the formula "ΔV = (V1 - V0) / V0 × 100 (%)" and evaluated according to the following criteria. The smaller the volume change ΔV, the smaller the swelling of the secondary battery after repeated charge / discharge (after cycling), indicating excellent morphological stability of the lithium-ion secondary battery. A: The ΔV value is less than 18%. B: The ΔV value is 18% or more but less than 22%. C: The ΔV value is 22% or more but less than 26%. D: The ΔV value is 26% or more.

[0125] (Example 1) <Preparation of Particulate Polymer A> [Preparation of Monomer Composition] 31.9 parts of butyl acrylate as a (meth)acrylic acid ester monomer, 8 parts of glycidyl methacrylate as an epoxy group-containing monomer, 0.5 parts of ethylene glycol dimethacrylate as a crosslinkable monomer, and 59.6 parts of styrene as an aromatic-containing monomer were mixed to prepare a monomer composition. [Preparation of Colloidal Dispersion] An aqueous solution of 8.3 parts of sodium hydroxide dissolved in 50 parts of ion-exchanged water was gradually added under stirring to an aqueous solution of 9.9 parts of magnesium chloride dissolved in 200 parts of ion-exchanged water, and stirring was continued for 30 minutes after the addition to prepare a colloidal dispersion containing magnesium hydroxide as a metal hydroxide. The volume average particle diameter of the colloidal dispersion measured as described above was 200 nm. The amount of magnesium hydroxide produced in this step was 6 parts, and in preparing particulate polymer A described below, 6 parts by mass of magnesium hydroxide was used per 100 parts by mass of the solid content of the monomer composition used in the polymerization of particulate polymer A. [Suspension Polymerization Method] Particulate polymer A (unpurified) was prepared by suspension polymerization. Specifically, the monomer composition obtained as described above was added to the colloidal dispersion containing the magnesium hydroxide and further stirred, and then 1.8 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, "Perbutyl O") as a polymerization initiator was added to obtain a mixed solution. The obtained mixed solution was subjected to high-shear stirring at a rotation speed of 12,000 rpm for 1 minute using an in-line emulsifying disperser (manufactured by Pacific Machinery Works, "Cavitron") to form droplets of the monomer composition in the colloidal dispersion containing magnesium hydroxide. The colloidal dispersion containing magnesium hydroxide in which droplets of the monomer composition were formed was placed in a reactor, and the temperature was raised to 90°C, where a polymerization reaction was carried out for 5 hours. The obtained dispersion was purified by subjecting it to reduced pressure treatment at 85°C for 1 hour using an evaporator, to obtain an aqueous dispersion containing particulate polymer A (unpurified). [Washing] While stirring the aqueous dispersion containing particulate polymer A (unpurified) obtained above, 13.5 parts of 20% sulfuric acid (active ingredient amount) was added dropwise at room temperature (25°C), to carry out acid washing.Then, carry out filtration separation, add 100 parts of ion-exchanged water to the obtained solid matter to re-slurry, and repeat water washing treatment (washing, filtration and dehydration) three times, and re-slurry the solid matter after filtration separation so that the solid matter concentration is 25 mass%.After re-slurrying, add a cation exchange resin (HPR1024H, manufactured by Organo) in an amount that corresponds to 10 mass% of the total amount of aqueous dispersion, and after stirring for 30 minutes, use an 80 mesh to separate into an aqueous dispersion containing cation exchange resin and particulate polymer A.Furthermore, add a anion exchange resin (IRA96, manufactured by Organo) in an amount that corresponds to 10 mass% of the total amount of aqueous dispersion, and after stirring for 30 minutes, use an 80 mesh to separate into an aqueous dispersion containing cation exchange resin and particulate polymer A.Then, use a filter material with a pore size of 10 μm to filter the obtained aqueous dispersion containing particulate polymer A, and obtain an aqueous dispersion containing particulate polymer A for evaluation. The resulting aqueous dispersion containing the particulate polymer A was used to measure the amount of undissolved THF, the degree of swelling in the electrolyte, and the complex modulus of elasticity |G determined by viscoelasticity measurement. ＊ | and tanδ ratio; and maximum compressive strength F and maximum compressive strength change rate F by microcompression test ＊ was measured.

[0126] <Preparation of Aqueous Dispersion Containing Particulate Polymer B> 70 parts of ion-exchanged water, 0.15 parts of sodium lauryl sulfate (manufactured by Kao Chemical Corporation, product name "EMAL (registered trademark) 2F") as an emulsifier, and 0.5 parts of ammonium persulfate were each supplied to a reactor equipped with a stirrer, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60°C. Meanwhile, in a separate vessel, 50 parts of ion-exchanged water, 0.5 parts of sodium dodecylbenzenesulfonate, 94.8 parts of n-butyl acrylate as a (meth)acrylic acid ester monomer, 2 parts of acrylonitrile as a nitrile group-containing monomer, 2 parts of methacrylic acid as an acid group-containing monomer, 1 part of allyl glycidyl ether as an epoxy group-containing monomer, and 0.2 parts of allyl methacrylate as a crosslinkable monomer were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor over 4 hours to carry out polymerization. During the addition, the reaction was carried out at 60° C. After the addition was completed, the mixture was further stirred at 70° C. for 3 hours to terminate the reaction, thereby obtaining an aqueous dispersion containing particulate polymer B. The obtained particulate polymer B had a glass transition temperature of −40° C., a volume average particle diameter D50 of 350 nm, and a swelling degree in electrolyte of 390% by mass.

[0127] Preparation of Functional Layer Binder Composition: 93 parts (solids equivalent) of an aqueous dispersion of particulate polymer A, 5 parts (solids equivalent) of an aqueous dispersion of particulate polymer B, 0.2 parts (solids equivalent) of sodium dodecylbenzenesulfonate (manufactured by Kao Chemical Corporation, product name "Neopelex G15"), 1.0 parts (solids equivalent) of ammonium polyacrylate (manufactured by Toagosei, product name "Aron-A30SL"), and ion-exchanged water were mixed, and the pH was adjusted to 8 using a 12% aqueous ammonia solution to obtain a slurry-like functional layer binder composition (solids concentration: 23%). Using this functional layer binder composition, the volume average particle size, ash content, glass transition temperature, total metal content, and amount of metal dissolved into the liquid of the granules were measured. The results are shown in Table 1.

[0128] <Preparation of Slurry Composition for Functional Layer> Boehmite (specific gravity 3 g / m) was used as non-conductive inorganic particles. 3Aqueous solutions containing 90 parts of acrylamide as the (meth)acrylamide monomer, 9 parts of methacrylic acid as the acid group-containing monomer, and 1 part of dimethylacrylamide as the crosslinkable monomer, were prepared. The aqueous solutions were then mixed with 365 parts of ion-exchanged water and 5 parts of isopropyl alcohol and charged to a four-neck flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube. The monomer composition consisted of 90 parts of acrylamide as the (meth)acrylamide monomer, 9 parts of methacrylic acid as the acid group-containing monomer, and 1 part of dimethylacrylamide as the crosslinkable monomer. The reaction system was then deoxygenated with nitrogen gas. Next, with stirring, 3 parts of a 5% aqueous solution of ammonium persulfate and 1.5 parts of a 5% aqueous solution of sodium hydrogen sulfite were added to the flask as polymerization initiators. The mixture was then heated from room temperature to 80°C and maintained at this temperature for 3 hours to polymerize the monomer composition. Then, 162 parts of ion-exchanged water was added, and the pH was adjusted to 5 with a 12% aqueous ammonia solution to obtain an aqueous solution containing a water-soluble polymer with a weight average molecular weight of 250,000, a solids concentration of 15.2%, and a viscosity (25°C, 60 rpm) of 3,050 mPa·s. [Preparation of Slurry Composition for Heat-Resistant Layer] 85 parts of non-conductive inorganic particles, 0.4 parts of dispersant, and ion-exchanged water were mixed and processed in a bead mill (manufactured by Ashizawa Finetech, product name "LMZ015") for 1 hour to obtain a dispersion. Furthermore, 15 parts of the binder composition for the functional layer in terms of solids, 2 parts of particulate polymer B in terms of solids, 1.5 parts of an aqueous solution containing a water-soluble polymer in terms of solids, and 0.2 parts of a polyethylene glycol surfactant (manufactured by San Nopco, product name "Noptex ED-052") were mixed to prepare a slurry composition for the adhesive functional layer for coating with a solids concentration of 35%. The mass ratio of the particulate polymer A to the particulate polymer B in the slurry composition for the heat-resistant layer was 78:22. Here, the layer formed using such a slurry composition for the heat-resistant layer exhibits adhesiveness in addition to heat resistance, and therefore may also be referred to as a heat-resistant adhesive layer.

[0129] <Preparation of separator with functional layer (heat-resistant adhesive layer) on both sides> A polyethylene separator substrate (manufactured by Asahi Kasei Corporation, product name "ND309", thickness: 9 μm) was prepared. The slurry composition for the heat-resistant layer prepared above was applied to the surface of the prepared separator substrate using a bar coater and dried at a temperature of 50°C for 3 minutes to obtain a separator with a heat-resistant adhesive layer of a predetermined weight on one side. The same operation was performed on the other side of the separator substrate to prepare a separator with a functional layer in which a predetermined amount of functional layer as a heat-resistant adhesive layer was applied to both sides.

[0130] <Preparation of Polymer Composition for Cathode> A 10-liter reactor was charged with 100 parts of ion-exchanged water, 35 parts of acrylonitrile as a nitrile group-containing monomer, and 65 parts of 1,3-butadiene as an aliphatic conjugated diene monomer. 2 parts of potassium oleate as an emulsifier, 0.1 parts of potassium phosphate as a stabilizer, and 0.8 parts of tert-dodecyl mercaptan (TDM) as a molecular weight modifier were added. Emulsion polymerization was carried out at a temperature of 5°C in the presence of 0.35 parts of potassium persulfate as a polymerization initiator, and acrylonitrile and 1,3-butadiene were copolymerized. When the polymerization conversion reached 85%, 0.2 parts of hydroxylamine sulfate per 100 parts of monomer was added to terminate the polymerization. Subsequently, the mixture was heated and subjected to steam distillation under reduced pressure at approximately 90°C to recover the residual monomer. Then, 0.1 parts of dibutylhydroxytoluene (BHT) as a substituted phenol was added to obtain an aqueous dispersion of the polymer. Calcium chloride (CaCl) was added as a coagulant in an amount of 3 parts per 100 parts of polymer solids in the resulting aqueous dispersion. ２ A 25% by mass aqueous solution of 2,4-dichloro- ...２ After adding 500 ppm of palladium, a hydrogenation reaction was carried out at a temperature of 60°C for 6 hours under a hydrogen pressure of 3.0 MPa to obtain a hydrogenated reaction product. After completion of the hydrogenation reaction, the palladium and silica were filtered off, and the acetone solvent was removed under reduced pressure to obtain a polymer. The obtained polymer was dissolved in a predetermined amount of NMP to obtain an NMP solution of a polymer composition for a positive electrode having a solids concentration of 8% as a polymer composition.

[0131] <Preparation of Conductive Material Dispersion> Multi-walled carbon nanotubes (BET specific surface area: 250 m) were used as the conductive material. ２ 4 parts of a CNT-containing polymer composition (CNTs) containing 10.0 parts (corresponding to 1 part as solids) of the positive electrode polymer composition obtained above (an NMP solution of the positive electrode polymer composition having a solids concentration of 8%), and 86.0 parts of NMP as a solvent were stirred using a disper (3000 rpm, 10 minutes), and then mixed for 1 hour at a peripheral speed of 12 m / s using a bead mill (LMZ015, manufactured by Ashizawa Fine Tech) using zirconia beads having a diameter of 1 mm, to prepare a conductive material dispersion.

[0132] <Preparation of Slurry for Positive Electrode> A ternary active material (LiNi) having a layered structure as a positive electrode active material was added to the conductive material dispersion liquid obtained as described above. ０．６ Co ０．２ Mn ０．２ O ２ A positive electrode slurry was prepared by adding 98 parts of polyvinylidene fluoride (average particle size: 10 μm), 1 part of polyvinylidene fluoride, 1 part of the conductive material dispersion obtained above (solid content equivalent), and NMP as a solvent, and mixing them with a planetary mixer (60 rpm, 30 minutes). The amount of NMP added was adjusted so that the viscosity of the resulting positive electrode slurry (measured with a single cylindrical rotational viscometer in accordance with JIS Z8803:1991, temperature: 25°C, rotation speed: 60 rpm) was within the range of 4000 mPa s to 5000 mPa s.

[0133] <Preparation of Positive Electrode> The obtained slurry composition for positive electrode composite layer was coated on a 15 μm thick aluminum foil current collector with a comma coater in a coating weight of 22 mg / cm. ２The slurry composition on the aluminum foil was then dried by transporting the aluminum foil at a speed of 500 mm / min through an oven at 120°C for 2 minutes and then through an oven at 130°C for 2 minutes, thereby obtaining a positive electrode blank with a positive electrode composite layer formed on the current collector. Thereafter, the positive electrode composite layer side of the prepared positive electrode blank was roll-pressed under a temperature of 25±3°C and a linear pressure of 14 t (tons), resulting in a positive electrode composite layer with a coating weight of 20.5 mg / cm. ２ , coating density 3.50 g / cm ３ The sheet-like positive electrode was then cut into a piece having a width of 5.0 cm and a length of 52 cm to form a positive electrode for a lithium ion secondary battery.

[0134] <Preparation of Negative Electrode> 33 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 3.5 parts of itaconic acid as an acidic group-containing monomer, 63.5 parts of styrene as an aromatic vinyl monomer, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 50 ° C to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to terminate the polymerization reaction, and a mixture containing a particulate binder (styrene-butadiene copolymer) was obtained. A 5% aqueous sodium hydroxide solution was added to this mixture to adjust the pH to 8, and unreacted monomer was removed by heated vacuum distillation. The mixture was then cooled to 30 ° C or below to obtain an aqueous dispersion containing a binder for the negative electrode. Next, 49.0 parts of artificial graphite as the negative electrode active material, 49.0 parts of natural graphite, and 1 part of carboxymethyl cellulose as a thickener were added to a planetary mixer. The mixture was then diluted with ion-exchanged water to a solids concentration of 60%, and then kneaded for 60 minutes at a rotation speed of 45 rpm. Then, 1 part of the aqueous dispersion containing the negative electrode binder obtained as described above was added in terms of solids content, and the mixture was kneaded for 40 minutes at a rotation speed of 40 rpm. Then, ion-exchanged water was added to obtain a viscosity of 3000±500 mPa·s (measured with a Brookfield viscometer at 25°C and 60 rpm), thereby preparing a negative electrode composite layer slurry. The negative electrode composite layer slurry composition was applied to the surface of a 15 μm-thick copper foil current collector using a comma coater to a predetermined coating amount. The copper foil coated with the slurry composition for the negative electrode composite layer was then transported at a speed of 400 mm / min through an oven at 80°C for 2 minutes and then through an oven at 110°C for 2 minutes to dry the slurry composition on the copper foil, thereby obtaining a negative electrode blank having a negative electrode composite layer formed on a current collector. The negative electrode composite layer side of the prepared negative electrode blank was then roll-pressed under a linear pressure of 11 t (tons) in an environment at a temperature of 25±3°C to obtain a negative electrode composite layer having a coating weight of 11 mg / cm. ２ , coating density 1.60 g / cm ３ The sheet-like negative electrode was then cut into a width of 5.0 cm and a length of 52 cm to form a negative electrode for a lithium ion secondary battery.

[0135] <Preparation of Lithium-Ion Secondary Battery> A flat wound body (equivalent to a discharge capacity of 700 mAh) was prepared using the negative electrode, positive electrode, and functional layer-attached separator described above. It was then pressed using a flat press under conditions of a press temperature of 60°C, a load of 7.5 kN (press pressure of 5 MPa), and a press time of 20 seconds. The pressed flat wound body was placed inside an aluminum laminate sheet exterior. The aluminum packaging was then filled with a 1.0 M LiPF solution (solvent: a mixed solvent of ethylene carbonate (EC) / diethyl carbonate (DEC) = 3 / 7 (volume ratio), additive: containing 2 vol% vinylene carbonate (solvent ratio)) as the electrolyte. The interior of the lithium-ion secondary battery was then reduced in pressure to -95 kPa, held in that state for 1 minute, and then heat-sealed to prepare a lithium-ion secondary battery for various evaluations. This lithium-ion secondary battery was used to evaluate rate characteristics, cycle characteristics, and swelling of the secondary battery after cycling. The results are shown in Table 1.

[0136] (Example 2) When preparing a colloidal dispersion for preparing particulate polymer A, the amount of magnesium chloride was changed from 9.9 parts to 4.5 parts, and the amount of sodium hydroxide was changed from 8.3 parts to 4.2 parts, respectively. In addition, the amount of 20% sulfuric acid used for washing particulate polymer A (unpurified) was changed from 13.5 parts to 6.8 parts as an active ingredient. Except for these points, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0137] (Example 3) When preparing the colloidal dispersion for preparing particulate polymer A, the amount of magnesium chloride was changed from 9.9 parts to 20.0 parts, and the amount of sodium hydroxide was changed from 8.3 parts to 16.6 parts. Furthermore, during suspension polymerization, the time of high-shear stirring treatment using an in-line emulsifying disperser (manufactured by Pacific Machinery Works, "Cavitron") was changed from 1 minute to 2 minutes. Furthermore, the amount of 20% sulfuric acid used for washing particulate polymer A (unpurified) was changed from 13.5 parts to 27.0 parts as an active ingredient. Except for these points, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0138] (Example 4) When preparing particulate polymer A, the blending of the monomer composition was changed from 31.9 parts to 26.5 parts of butyl acrylate as a (meth)acrylic acid ester monomer, and from 59.6 parts to 65 parts of styrene as an aromatic-containing monomer. Except for these points, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0139] (Example 5) When preparing particulate polymer A, the blending of the monomer composition was changed from 31.9 parts to 45.5 parts of butyl acrylate as (meth)acrylic acid ester monomer, and from 59.6 parts to 46 parts of styrene as aromatic-containing monomer. Except for these points, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0140] (Example 6) When washing the particulate polymer A (unpurified) in preparing the particulate polymer A, the number of repetitions of the water washing treatment (washing, filtration and dehydration) was changed from three times to one time. In addition, cation exchange and anion exchange were not performed. Except for these points, various operations, measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0141] Example 7 Suspension polymerization was carried out according to the following procedure to synthesize particulate polymer A without using an inorganic colloid containing a metal hydroxide. Except for this, the same operations, measurements, and evaluations as in Example 1 were carried out. The results are shown in Table 1. <Preparation of Particulate Polymer A> A monomer composition prepared in the same manner as in Example 1 was subjected to suspension polymerization. Specifically, the monomer composition prepared in the same manner as in Example 1 was added to an aqueous solution containing 6.2 parts, in terms of solid content, of polyvinyl alcohol having a degree of polymerization of 3000 to 4000. The mixture was further stirred, and then 1.8 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, "Perbutyl O") as a polymerization initiator was added to obtain a mixed solution. The obtained mixed solution was subjected to high-shear stirring at a rotation speed of 12,000 rpm for 1 minute using an in-line emulsifying disperser (manufactured by Pacific Machinery Works, "Cavitron") to form droplets of the monomer composition. The mixed solution in which droplets of the monomer composition were formed was placed in a reactor, heated to 90°C, and polymerized for 5 hours to obtain an aqueous dispersion containing particulate polymer A. Using the obtained aqueous dispersion containing particulate polymer A, the amount of undissolved THF, the degree of swelling in an electrolyte, and the complex modulus of elasticity measured by viscoelasticity measurement |G ＊ | and tanδ ratio; and maximum compressive strength F and maximum compressive strength change rate F by microcompression test ＊ was measured.

[0142] (Example 8) When preparing particulate polymer A, the blending of the monomer composition was changed from 31.9 parts of butyl acrylate as (meth)acrylic acid ester monomer to 27.9 parts of 2-ethylhexyl acrylate, and from 59.6 parts of styrene as aromatic-containing monomer to 63.5 parts. Except for these points, various operations, measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0143] (Example 9) When preparing particulate polymer A, the blending of the monomer composition was changed from 59.6 parts of styrene as an aromatic group-containing monomer to 59.1 parts, and further, 0.5 parts of itaconic acid as a polar group-containing monomer was blended. Except for these points, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0144] (Example 10) Unlike Examples 1 to 9, a functional layer that was an adhesive layer containing no inorganic particles, rather than a heat-resistant adhesive layer, was mounted in the manner described above. Except for this, the same operations, measurements, and evaluations as in Example 1 were carried out. The results are shown in Table 1. <Preparation of slurry composition for heat-resistant layer> Boehmite (specific gravity 3 g / m) was used as the non-conductive inorganic particles. 3Aqueous solutions containing 90 parts of acrylamide as the (meth)acrylamide monomer, 9 parts of methacrylic acid as the acid group-containing monomer, and 1 part of dimethylacrylamide as the crosslinkable monomer, as well as 365 parts of ion-exchanged water and 5 parts of isopropyl alcohol, were prepared. A four-neck flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet was charged with a monomer composition consisting of 90 parts of acrylamide as the (meth)acrylamide monomer, 9 parts of methacrylic acid as the acid group-containing monomer, and 1 part of dimethylacrylamide as the crosslinkable monomer. The reaction system was then deoxygenated with nitrogen gas. Next, with stirring, 3 parts of a 5% aqueous solution of ammonium persulfate and 1.5 parts of a 5% aqueous solution of sodium hydrogen sulfite were added to the flask as polymerization initiators. The temperature was then raised from room temperature to 80°C and maintained at that temperature for 3 hours to polymerize the monomer composition. Then, 162 parts of ion-exchanged water was added, and the pH was adjusted to 5 with a 48% aqueous sodium hydroxide solution to obtain an aqueous solution containing a water-soluble polymer with a weight average molecular weight of 250,000, a solids concentration of 15.2%, and a viscosity (25°C, 60 rpm) of 3,050 mPa·s. 100 parts of non-conductive inorganic particles, 0.5 parts of dispersant, and ion-exchanged water were mixed and processed for 1 hour in a bead mill (manufactured by Ashizawa Finetech, product name "LMZ015") to obtain a dispersion. Furthermore, 4 parts of particulate polymer B in terms of solids, 1.5 parts of an aqueous solution containing a water-soluble polymer in terms of solids, and 0.2 parts of a polyethylene glycol surfactant (manufactured by San Nopco, product name "Noptex ED-052") were mixed to prepare a slurry composition for a heat-resistant layer with a solids concentration of 35%. <Preparation of separator with heat-resistant layer on both sides> A polyethylene separator substrate (manufactured by Asahi Kasei Corporation, product name "ND309", thickness: 9 μm) was prepared. The coating slurry composition prepared above was applied to the surface of the prepared separator substrate using a bar coater and dried at a temperature of 50°C for 3 minutes to obtain a separator with a heat-resistant layer of a predetermined weight on one side. The same operation was performed on the other side of the separator substrate to prepare a separator with a heat-resistant layer coated on each side with a heat-resistant layer of 2 μm each.<Preparation of separator with adhesive layer and heat-resistant layer, which has adhesive layers on both sides> The binder composition for functional layer prepared in the same manner as in Example 1 was applied to the surface of the separator made of polyethylene and having heat-resistant layers on both sides using a bar coater, and dried at a temperature of 50°C for 3 minutes, and a predetermined basis weight (0.5 g / m) was applied to one side. ２ The same procedure was carried out on the other side of the separator substrate, and a separator with a predetermined basis weight (0.5 g / m per side) was obtained. ２ A separator with an adhesive layer and a heat-resistant layer was obtained.

[0145] (Comparative Example 1) When preparing particulate polymer A, the blending amount of the monomer composition was changed from 31.9 parts to 24.5 parts of butyl acrylate as a (meth)acrylic acid ester monomer, from 59.6 parts to 65 parts of styrene as an aromatic-containing monomer, and from 8 parts to 10 parts of glycidyl methacrylate as an epoxy group-containing monomer. In addition, when preparing the colloidal dispersion when preparing particulate polymer A, the blending amount of magnesium chloride was changed from 9.9 parts to 10.0 parts, and the blending amount of sodium hydroxide was changed from 8.3 parts to 7 parts. Furthermore, during suspension polymerization, the time of high-shear stirring treatment using an in-line emulsifying disperser (manufactured by Pacific Machinery Works, "Cavitron") was changed from 1 minute to 2 minutes, and when purifying the dispersion obtained after polymerization, an evaporator was used to purify it under reduced pressure at 90 ° C for 2 hours, thereby obtaining an aqueous dispersion containing particulate polymer A (unpurified). Then, the particulate polymer A (unpurified) was washed according to the following procedure. [Washing] While stirring the aqueous dispersion containing the particulate polymer A (unpurified), sulfuric acid was added dropwise at room temperature (25°C) to perform acid washing until the pH reached 6.5 or less. Next, filtration and separation were performed, and 500 parts of ion-exchanged water was added to the obtained solid matter to re-slurry it, and the water washing treatment (washing, filtration, and dehydration) was repeated 10 times. Then, filtration and separation were performed, and the obtained solid matter was placed in a container of a dryer and dried at 40°C for 48 hours to obtain a dried particulate polymer. In this step, the cation exchange and anion exchange similar to those in Example 1 were not performed. Except for these points, various operations, measurements, and evaluations similar to those in Example 1 were performed. The results are shown in Table 2.

[0146] (Comparative Example 2) When preparing particulate polymer A, the blending of the monomer composition was changed from 31.9 parts to 48.5 parts of butyl acrylate as (meth)acrylic acid ester monomer, and from 59.6 parts to 43 parts of styrene as aromatic-containing monomer. Except for these points, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 2.

[0147] (Comparative Example 3) When washing particulate polymer A (unpurified) in preparing particulate polymer A, the amount of active ingredient of 20% sulfuric acid dropped was changed from 13.5 parts to 6.5 parts. Furthermore, the number of repetitions of water washing treatment (washing, filtration and dehydration) was changed from 3 times to 1 time. And, cation exchange and anion exchange were not performed. Except for these points, various operations, measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 2.

[0148] (Comparative Example 4) In preparing the colloidal dispersion for preparing particulate polymer A, the amount of magnesium chloride was changed from 9.9 parts to 4.5 parts, and the amount of sodium hydroxide was changed from 8.3 parts to 4.2 parts. Furthermore, in the suspension polymerization, an in-line emulsifying disperser (manufactured by Pacific Machinery Works, "Cavitron") was used instead of an in-line emulsifying disperser (manufactured by Pacific Machinery Works, "Milder"), and the high shear stirring conditions were changed from 12,000 rpm for 1 minute to 6,000 rpm for 1 minute. Furthermore, in washing the particulate polymer A (unpurified) in preparing particulate polymer A, the amount of active ingredient of 20% sulfuric acid dropped was changed from 13.5 parts to 6.8 parts. Except for these points, various operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 2.

[0149] Comparative Example 5 The preparation conditions for particulate polymer A were changed as follows. Except for these changes, the same operations, measurements, and evaluations as in Example 1 were carried out. The results are shown in Table 2. <Preparation of Particulate Polymer A> 110 parts of ion-exchanged water and 0.3 parts of ammonium persulfate were supplied to a reactor equipped with a stirrer, the gas phase was replaced with nitrogen gas, and the temperature was raised to 70°C. Meanwhile, in a separate vessel, 40 parts of ion-exchanged water, 0.2 parts of sodium dodecylbenzenesulfonate as an emulsifier, 31.9 parts of butyl acrylate as a (meth)acrylic acid ester monomer, 8 parts of glycidyl methacrylate as an epoxy group-containing monomer, 0.5 parts of ethylene glycol dimethacrylate as a crosslinkable monomer, 59.1 parts of styrene as an aromatic group-containing monomer, and 0.5 parts of itaconic acid as a polar group-containing monomer were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor over 3 hours, and a polymerization reaction was carried out at 70°C. Polymerization is continued until the polymerization conversion rate reaches 96%, thereby obtaining an aqueous dispersion containing particulate polymer.Subsequently, this aqueous dispersion is heated to 75 ℃, and to this aqueous dispersion, 15.95 parts of butyl acrylate as (meth)acrylic acid ester monomer, 4 parts of glycidyl methacrylate as epoxy group-containing monomer, 0.25 parts of ethylene glycol dimethacrylate as cross-linking monomer, 29.55 parts of styrene as aromatic group-containing monomer, and 0.25 parts of itaconic acid as polar group-containing monomer are mixed and continuously added, and polymerization is continued.When the polymerization conversion rate reaches 96%, cooling is performed to stop the reaction, thereby obtaining an aqueous dispersion containing particulate polymer.

[0150] In Tables 1 and 2 shown below, "ST" represents styrene, "EDMA" represents ethylene glycol dimethacrylate, "GMA" represents glycidyl methacrylate, "2EHA" represents 2-ethylhexyl acrylate, "BA" represents n-butyl acrylate, "IA" represents itaconic acid, "Na-LBS" represents sodium dodecylbenzenesulfonate, and "PAA-NH ４ " indicates polyacrylic acid ammonium salt.

[0151]

[0152]

[0153] Table 1 shows that in Examples 1 to 10, which used compositions for lithium-ion secondary battery functional layers in which the volume average particle size, ash content, and glass transition temperature were all within the specified ranges, the adhesiveness of the resulting functional layer and the rate and cycle characteristics of the resulting secondary battery were simultaneously achieved at high levels. On the other hand, Table 2 shows that in Comparative Example 1, in which the glass transition temperature was 60°C, exceeding the upper limit of the specified range; Comparative Example 2, in which the glass transition temperature was below the lower limit of the specified range; Comparative Example 3, in which the ash content exceeded the upper limit; and Comparative Examples 4 and 5, in which the volume average particle size, ash content, and glass transition temperature all fell outside the specified ranges, the adhesiveness of the resulting functional layer and the rate and cycle characteristics of the resulting secondary battery were simultaneously achieved at high levels.

[0154] According to the present invention, it is possible to provide a binder composition for a functional layer of a lithium ion secondary battery, a slurry composition for a functional layer of a lithium ion secondary battery, and the like, which can simultaneously achieve high levels of adhesiveness of the resulting functional layer and high levels of rate characteristics and cycle characteristics of the resulting secondary battery.

Claims

1. A binder composition for a functional layer of a lithium ion secondary battery, comprising granules containing at least a particulate polymer A, wherein the granules have a volume average particle diameter of 1.0 μm or more and 10.0 μm or less, and the binder composition has a glass transition temperature of 25°C or more and less than 60°C, and an ash content of less than 3.0 mass%.

2. The binder composition for a functional layer of a lithium ion secondary battery according to claim 1, further comprising a particulate polymer B different from the particulate polymer A.

3. The binder composition for a functional layer of a lithium ion secondary battery according to claim 1, wherein the amount of metal contained is less than 1000 ppm by mass.

4. A slurry composition for a functional layer of a lithium ion secondary battery, comprising the binder composition for a functional layer of a lithium ion secondary battery according to claim 1 and inorganic particles.

5. A separator with a functional layer for a lithium ion secondary battery, comprising a functional layer as an adhesive layer formed using the binder composition for a functional layer of a lithium ion secondary battery according to any one of claims 1 to 3, or a functional layer as a heat-resistant layer formed using the slurry composition for a functional layer of a lithium ion secondary battery according to claim 4.

6. A lithium ion secondary battery comprising the separator with functional layer for lithium ion secondary batteries according to claim 5.

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