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

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, wherein the volume average particle size of the granular material and the ash content of the binder composition are each within a prescribed range, and the glass transition temperature of the binder composition is lower than a prescribed temperature.

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 Documents 1 to 3).

[0005] JP 2023-523279 A JP 2023-515152 A JP 2016-183209 A

[0006] However, the conventional compositions for electrochemical device functional layers have room for improvement in terms of further improving room-temperature adhesion and blocking resistance. 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 form a functional layer having excellent room-temperature adhesion and blocking resistance.

[0007] 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 a particulate polymer A can be provided that is capable of forming a functional layer having excellent room-temperature adhesion and blocking resistance when the volume average particle size of the granules and the ash content of the binder composition are each within a predetermined range and the glass transition temperature of the binder composition is less than a predetermined value, thereby completing the present invention.

[0008] That is, the present invention aims to advantageously solve the above-mentioned problems, and the present invention provides [1] a binder composition for a lithium ion secondary battery functional layer, 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 15.0 μm or less, and the binder composition has a glass transition temperature of less than 25° C. and an ash content of 3% by mass or more and 30% by mass or less. The above-mentioned binder composition for a lithium ion secondary battery functional layer can form a functional layer serving as an adhesive layer having excellent room-temperature adhesion and blocking resistance. The volume average particle diameter of the granules, as well as the glass transition temperature and ash content of the binder composition, can be measured according to the methods described in the Examples of this specification.

[0009] [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. When the binder composition for a lithium ion secondary battery functional layer contains a particulate polymer B different from the particulate polymer A, the room temperature adhesiveness of the formed adhesive layer can be further enhanced, and the cycle characteristics of a secondary battery having an adhesive layer formed using the binder composition can be improved.

[0010] [3] The binder composition for a lithium ion secondary battery functional layer according to [1] or [2] above preferably has a metal content of 0.1% by mass or more. When the metal content of the binder composition for a secondary battery functional layer is equal to or greater than the lower limit, the blocking resistance of the adhesive layer formed using the binder composition can be further improved. 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.

[0011] [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.

[0012] [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.

[0013] [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.

[0014] 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 form a functional layer that has excellent room temperature adhesion and blocking resistance, 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.

[0015] 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 functional layer binder composition of the present invention used to form a functional layer as an adhesive layer, and the functional layer slurry composition of the present invention used to form a functional layer as a heat-resistant layer. When simply referring to the "functional layer composition," it may refer to either the functional layer binder composition or the functional layer slurry composition.

[0016] (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 size of the granules and the ash content of the binder composition are each within a predetermined range, and the glass transition temperature of the binder composition is less than a predetermined value.

[0017]

[0033] 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, the functional layer as an adhesive layer can exhibit excellent room temperature adhesion and can also improve blocking resistance. 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.

[0018] 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 15.0 μm or less. Therefore, at 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 and easily comes into contact with the electrochemical device component, thereby improving the adhesiveness of the functional layer as an adhesive layer. In addition, because the glass transition temperature of the binder composition is less than 25°C, the particulate polymer easily deforms at room temperature at the contact surface between the functional layer formed using the binder composition for a functional layer of the present invention and the lithium ion secondary battery component, thereby exhibiting good room temperature adhesive strength. Furthermore, by having an ash content of 3% by mass or more and 30% by mass or less, i.e., by containing a certain amount of inorganic components, it is possible to suppress the particulate polymers from adhering to each other.

[0033] As a result, in a situation where components having functional layers on their surfaces are stacked and stored in a state where the functional layers are adjacent to each other during the manufacturing process of a lithium ion secondary battery, adhesion (blocking) between the functional layers can be suppressed. For the above reasons, it is believed that by using the binder composition for functional layers of the present invention, a functional layer excellent in room temperature adhesion and blocking resistance can be obtained.

[0019] <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.

[0020] <Particulate polymer A> The particulate polymer A has the function of providing excellent adhesiveness to the functional layer, which serves as an adhesive 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.

[0021] 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").

[0022] <<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.

[0023] The proportion of aromatic vinyl monomer units in the particulate polymer A is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more, and is preferably 99% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, particularly preferably 70% by mass or less, and even particularly preferably 40% by mass or less, based on 100% by mass of all monomer units in the particulate polymer A. If 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 increased, and the blocking resistance of the functional layer can be improved. Furthermore, if the proportion of aromatic vinyl monomer units in the particulate polymer A is equal to or greater than the above-mentioned lower limit, the rate characteristics and cycle characteristics of the resulting secondary battery can be improved. Furthermore, if the proportion of aromatic vinyl monomer units in the particulate polymer A is equal to or less than the above-mentioned upper limit, the room temperature adhesion of the functional layer can be further improved.

[0024] <<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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] The proportion of the crosslinkable monomer units in the particulate polymer A is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, even more preferably 0.5% by mass or more, particularly preferably 5.0% by mass or more, and preferably 50% by mass or less, more preferably 30% by mass or less, even more preferably 15% by mass or less, and particularly preferably 10% by mass or less, based on 100% by mass of the total 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 lower limit, the elution of the particulate polymer A into the electrolyte can be suppressed, and the internal resistance of the lithium ion secondary battery can be reduced. Furthermore, if the proportion of the crosslinkable monomer units in the particulate polymer A is equal to or less than the upper limit, the room temperature adhesion of the functional layer can be further improved.

[0033] <<(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.

[0034] The proportion of the (meth)acrylic acid ester monomer units in the particulate polymer A is preferably 1% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, even more preferably 30% by mass or more, and particularly preferably 52% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and particularly preferably 80% 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 lower limit, the room temperature 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 less than the above upper limit, the blocking resistance of the functional layer can be improved, and the rate characteristics and cycle characteristics of the resulting secondary battery can be improved.

[0035] <<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.

[0036] The particulate polymer A may be a particle formed of one type of polymer (single polymer particle) or a particle formed of two or more types of polymers (composite polymer particle). Composite polymer particles are heterophase structures in which different polymer portions exist inside the particle. Here, the heterophase structure refers to a single particle formed by the physical or chemical bonding of two or more different polymers, and is not a particle having a single phase structure formed from a single polymer such as a block polymer. Specific examples of heterophase structures include a core-shell structure in which spherical particles have a core and a shell covering at least a portion of the outer surface of the core, each formed from a different polymer; and a side-by-side structure in which two or more polymers are juxtaposed. Among these, from the viewpoint of further improving the room temperature adhesiveness while improving the blocking resistance of the functional layer, it is preferable that the particulate polymer A has a core-shell structure.

[0037] <<Core-shell structure>> Here, in the particulate polymer A having a core-shell structure, the shell part may cover the entire outer surface of the core part, or may cover the outer surface of the core part partially. Even if the outer surface of the core part appears to be completely covered by the shell part from the outside, as long as holes communicating between the inside and outside of the shell part are formed, the shell part partially covers the outer surface of the core part. Therefore, for example, a particulate polymer A comprising a shell part having pores communicating from the outer surface of the shell part (i.e., the peripheral surface of the particulate polymer A) to the outer surface of the core part corresponds to a particulate polymer A in which the shell part partially covers the outer surface of the core part.

[0038] The particulate polymer A having a core-shell structure may have any constituent element other than the core part and shell part described above, as long as the intended effect is not significantly impaired. Specifically, for example, the particulate polymer A may have a portion formed of a polymer different from the core part inside the core part. As a specific example, the seed particles used when producing the core part by the seed polymerization method may remain inside the core part. However, from the viewpoint of significantly exhibiting the intended effect, it is preferable that the particulate polymer A has only the core part and the shell part.

[0039] [Core Portion] The monomer unit contained in the polymer of the core portion is not particularly limited, but preferred examples include an aromatic vinyl monomer unit, a crosslinkable monomer unit, and a (meth)acrylic acid ester monomer unit. The polymer of the core portion may contain only one type of monomer unit or multiple types.

[0040] -Aromatic vinyl monomer unit- Examples of aromatic vinyl monomers that can form the aromatic vinyl monomer unit in the core polymer include those similar to those described above. These may be used alone or in combination. Among these, styrene is preferred.

[0041] The proportion of aromatic vinyl monomer units contained in the core polymer is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, more preferably 10% by mass or less, preferably 99% by mass or less, more preferably 90% by mass or less, even more preferably 75% by mass or less, particularly preferably 60% by mass or less, and particularly preferably 41% by mass or less, based on 100% by mass of all monomer units contained in the core polymer. If the proportion of aromatic vinyl monomer units in the core polymer is equal to or greater than the lower limit, the glass transition temperature of the core polymer can be increased, thereby improving the blocking resistance of the functional layer. Furthermore, if the proportion of aromatic vinyl monomer units in the core polymer is equal to or greater than the lower limit, the rate characteristics and cycle characteristics of the resulting secondary battery can be improved. Furthermore, if the proportion of aromatic vinyl monomer units in the core polymer is equal to or less than the upper limit, the room temperature adhesion of the functional layer can be further improved.

[0042] Crosslinkable Monomer Units Examples of crosslinkable monomers that can form crosslinkable monomer units in the core polymer include those described above. These may be used alone or in combination. Among these, ethylene glycol dimethacrylate and glycidyl methacrylate are preferred.

[0043] The proportion of crosslinkable monomer units contained in the core polymer is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more, and is preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, based on 100% by mass of all monomer units contained in the core polymer. If the proportion of crosslinkable monomer units in the core polymer is equal to or greater than the lower limit, elution of the particulate polymer A into the electrolyte can be suppressed, and the internal resistance of the lithium ion secondary battery can be reduced. Furthermore, if the proportion of crosslinkable monomer units in the core polymer is equal to or less than the upper limit, the room temperature adhesion of the functional layer can be further improved.

[0044] (Meth)acrylic acid ester monomer units—Examples of (meth)acrylic acid ester monomers that can form the (meth)acrylic acid ester monomer units in the core polymer include the same as those described above. These may be used alone or in combination. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are preferred.

[0045] The proportion of (meth)acrylic acid ester monomer units contained in the core polymer is preferably 1% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, particularly preferably 30% by mass or more, even particularly preferably 50% by mass or more, and preferably 99% by mass or less, more preferably 97% by mass or less, even more preferably 95% by mass or less, and particularly preferably 80% by mass or less, based on 100% by mass of all monomer units contained in the core polymer. If the proportion of (meth)acrylic acid ester monomer units contained in the core polymer is equal to or greater than the lower limit, the room temperature adhesiveness of the functional layer can be further improved. Furthermore, if the proportion of (meth)acrylic acid ester monomer units contained in the core polymer is equal to or less than the upper limit, the blocking resistance of the functional layer can be improved, and the rate and cycle characteristics of the resulting secondary battery can be enhanced.

[0046] —Other Monomer Units— The monomer units (other monomer units) other than the aromatic vinyl monomer units, crosslinkable monomer units, and (meth)acrylic acid ester monomer units that the core polymer may contain are not particularly limited, and examples thereof include the polar group-containing monomer units described above.

[0047] [Shell portion] The monomer unit contained in the polymer of the shell portion is not particularly limited, but preferred examples include crosslinkable monomer units and (meth)acrylic acid ester monomer units. The polymer of the shell portion may contain only one type of monomer unit or multiple types.

[0048] Crosslinkable Monomer Units Examples of crosslinkable monomers that can form crosslinkable monomer units in the polymer of the shell portion include the same ones as those described above. These may be used alone or in combination. Among these, ethylene glycol dimethacrylate is preferred.

[0049] The proportion of the crosslinkable monomer units contained in the polymer of the shell portion is preferably 3% by mass or more, more preferably 5% by mass or more, and even more preferably 7% by mass or more, and preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less, based on 100% by mass of all monomer units contained in the polymer of the shell portion. If the proportion of the crosslinkable monomer units in the polymer of the shell portion is equal to or greater than the lower limit, the elution of the particulate polymer A into the electrolyte can be suppressed, and the internal resistance of the lithium ion secondary battery can be further reduced. If the proportion of the crosslinkable monomer units in the polymer of the shell portion is equal to or less than the upper limit, the room temperature adhesion of the functional layer can be further improved.

[0050] (Meth)acrylic acid ester monomer units—Examples of (meth)acrylic acid ester monomers that can form the (meth)acrylic acid ester monomer units in the shell polymer include the same as those described above and methyl methacrylate. These may be used alone or in combination. Among these, methyl methacrylate is preferred.

[0051] The proportion of (meth)acrylic acid ester monomer units contained in the shell polymer is preferably 50% by mass or more, more preferably 65% ​​by mass or more, and even more preferably 80% by mass or more, and preferably 97% by mass or less, more preferably 95% by mass or less, and even more preferably 93% by mass or less, based on 100% by mass of all monomer units contained in the shell polymer. If the proportion of (meth)acrylic acid ester monomer units in the shell polymer is equal to or greater than the lower limit, the room temperature adhesion of the functional layer can be further improved. If the proportion of (meth)acrylic acid ester monomer units in the shell polymer is equal to or less than the upper limit, the blocking resistance of the functional layer can be improved.

[0052] —Other Monomer Units— The monomer units (other monomer units) other than the crosslinkable monomer units and the (meth)acrylic acid ester monomer units that the shell polymer may contain are not particularly limited, and examples thereof include the aromatic vinyl monomer units and polar group-containing monomer units described above.

[0053] When the particulate polymer A has a core-shell structure, the mass ratio of the core portion to the shell portion (core portion / shell portion) is preferably 0.1 / 99.9 or more, more preferably 1 / 99 or more, even more preferably 10 / 90 or more, particularly preferably 50 / 50 or more, and is preferably 99.9 / 0.1 or less, more preferably 99 / 1 or less, and even more preferably 95 / 5 or less. When the mass ratio of the core portion to the shell portion is the above-mentioned lower limit or more, the room temperature adhesiveness of the functional layer can be further improved. On the other hand, when the mass ratio of the core portion to the shell portion is the above-mentioned upper limit or less, the blocking resistance of the functional layer can be improved.

[0054] Furthermore, when the particulate polymer A has a core-shell structure, the volume average particle diameter of the core portion is preferably 1.0 μm or more, more preferably 1.5 μm or more, and preferably 10.0 μm or less, and more preferably 8.0 μm or less. If the volume average particle diameter of the core portion is not less than the above-mentioned lower limit, the room temperature adhesiveness of the functional layer can be further improved, and if it is not more than the above-mentioned upper limit, the blocking resistance of the functional layer can be improved. The thickness of the shell portion is preferably not less than 0.05 μm, more preferably not less than 0.07 μm, and preferably not more than 1.00 μm, and more preferably not more than 0.50 μm. If the thickness of the shell portion is not less than the above-mentioned lower limit, the blocking resistance of the functional layer can be improved, and if it is not more than the above-mentioned upper limit, the room temperature adhesiveness of the functional layer can be further improved.

[0055] <<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 15% by mass or more, more preferably 50% by mass or more, and preferably 90% by mass or less, and more preferably 85% by mass or less. When the amount of undissolved THF in the particulate polymer A is equal to or greater than the above lower limit, the room temperature adhesion of the functional layer can be improved, and the coating stability of the functional layer composition and the cycle characteristics of the resulting secondary battery can be improved. Furthermore, when the amount of undissolved THF in the particulate polymer A is equal to or less than the above upper limit, the blocking resistance and rate characteristics can be improved. Note that 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. Furthermore, for example, the amount of undissolved THF can be increased by reducing the amount of ash contained in the particulate polymer A, and the amount of undissolved THF can be reduced by increasing the amount of ash contained in the particulate polymer A. The amount of particulate polymer A that is not dissolved in THF can be measured according to the method described in the examples of this specification.

[0056] [Electrolyte Swelling Degree] The electrolyte swelling degree of the particulate polymer A is preferably 100% or more, more preferably 125% or more, even more preferably 150% or more, and preferably 500% or less, more preferably 400% or less, and even more preferably 300% or less. When the electrolyte swelling degree of the particulate polymer A is equal to or greater than the above lower limit, the rate characteristics of the secondary battery can be further improved. When the electrolyte swelling degree of the particulate polymer A is equal to or less than the above upper limit, the cycle characteristics of the secondary battery can be further improved. The electrolyte swelling degree of 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. Specifically, the electrolyte swelling degree decreases when the amount of the crosslinkable monomer used to prepare the particulate polymer A is increased, and increases when the amount is decreased.

[0057] [Complex Elastic Modulus] The particulate polymer A preferably has a complex elastic modulus at 40°C of less than 10 MPa, more preferably 8 MPa or less. The lower limit of the complex elastic modulus of the particulate polymer A is not particularly limited, but is generally preferably 0.05 MPa or more, more preferably 0.1 MPa or more. When the complex elastic modulus of the particulate polymer A is less than the above upper limit, the room temperature adhesiveness of the functional layer can be further improved. Furthermore, when the complex elastic modulus of the particulate polymer A is equal to or greater than the above lower limit, the coating stability of the functional layer composition and the lyophilicity of the resulting separator to the electrolyte 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 aromatic vinyl monomer and (meth)acrylic acid ester monomer used to prepare the particulate polymer A. Specifically, for example, the complex elastic modulus increases when the amount of the aromatic vinyl monomer used to prepare the particulate polymer A is increased, and decreases when the amount is decreased. The complex modulus of the particulate polymer A can be measured according to the method described in the examples of this specification.

[0058] [Tan δ Ratio] The particulate polymer A preferably has a tan δ ratio calculated by the formula (loss tangent (tan δ) at 60°C) / (loss tangent (tan δ) at 25°C) of less than 1.00, more preferably 0.80 or less. The lower limit of the tan δ ratio of the particulate polymer A is not particularly limited, but is generally preferably 0.03 or more, more preferably 0.05 or more. When the tan δ ratio of the particulate polymer A is less than the above upper limit, the room temperature adhesiveness of the functional layer can be further improved. Furthermore, when the tan δ ratio of the particulate polymer A is equal to or greater than the above lower limit, the morphology stability of the particulate polymer A can be maintained. The tan δ ratio of the particulate polymer A can be adjusted, for example, by changing the types and / or amounts 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.

[0059] [Maximum Compressive Strength] The particulate polymer A preferably has a maximum compressive strength of 300 N / m or more, more preferably 500 N / m or more, and preferably 10,000 N / m or less, and more preferably 8,000 N / m or less. If the maximum compressive strength of the particulate polymer A is equal to or greater than the above-mentioned lower limit, the blocking resistance of the functional layer can be further improved. If the maximum compressive strength of the particulate polymer A is equal to or less than the above-mentioned upper limit, the room temperature adhesiveness of the functional layer can be further improved. The maximum compressive strength of the particulate polymer A can be adjusted, for example, by changing the concentration and / or amount of the colloidal dispersion used in preparing the particulate polymer A described below. Specifically, the maximum compressive strength 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. The maximum compressive strength of the particulate polymer A can also be adjusted by appropriately selecting and washing the inorganic colloid contained in the particulate polymer A with a solvent, acid, base, or other substance. The maximum compressive strength of the particulate polymer A can be measured according to the method described in the examples of this specification.

[0060] [Maximum rate of change in compressive strength] The particulate polymer A preferably has a maximum rate of change in compressive strength of 0.1 or more, more preferably 0.2 or more, and preferably 0.8 or less, more preferably 0.7 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) is calculated as follows. When the maximum compressive strength change rate of the particulate polymer A is equal to or greater than the lower limit, the cycle characteristics of the resulting secondary battery can be further improved. When the maximum compressive strength change rate of the particulate polymer A is equal to or less than the upper limit, the blocking resistance of the functional layer can be further increased. The maximum compressive strength change rate of the particulate polymer A can be adjusted, for example, by changing the concentration and / or amount used, and type of the colloidal dispersion used in preparing the particulate polymer A, which will be described later. Specifically, the maximum compressive strength change rate increases by decreasing the concentration and / or amount used of the colloidal dispersion used in preparing the particulate polymer A, and decreases by increasing the concentration and / or amount used. The maximum compressive strength change rate 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.

[0061] <<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.

[0062] 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.

[0063] 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.

[0064] Here, as an example, a method for preparing the particulate polymer A having a core-shell structure by suspension polymerization will be described.

[0065] [Preparation of Particulate Polymer A by Suspension Polymerization Method] (1) Preparation of Core-Forming Monomer Composition First, the monomers constituting the core polymer and other compounding ingredients added as needed are mixed to prepare the core-forming monomer composition.

[0066] (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, a metal hydroxide such as magnesium hydroxide, barium sulfate, silica fine particles, boehmite particles, etc. are preferred. In addition, the concentration and amount used 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 50 parts by mass or less, and more preferably 30 parts by mass or less, based on 100 parts by mass of the total monomer components of the particulate polymer A.

[0067] (3) Formation of droplets The core-forming monomer composition is dispersed in the colloidal dispersion, a polymerization initiator is added, and then droplets of the core-forming monomer composition are formed. 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.

[0068] 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.

[0069] (4) Polymerization After droplets of the core-forming monomer composition are formed, the colloidal dispersion containing the formed droplets is heated to initiate polymerization, thereby forming a particulate polymer constituting the core portion in water. Furthermore, by polymerizing a monomer that forms the shell portion in the presence of the particulate polymer that forms the core portion, the particulate polymer A having the core-shell structure described above can be obtained. The polymerization of the monomer that forms the shell portion can be carried out, for example, by filtering the dispersion containing the particulate polymer that forms the core portion, redispersing the resulting wet cake in water, adding a polymerization initiator and a monomer that forms the shell portion, and then heating the mixture. Examples of the polymerization initiator used in this process include water-soluble thermal radical polymerization initiators such as 2,2'-azobis(2-methylpropionamide) dihydrochloride.

[0070] <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.

[0071] 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 material in volume average particle size, or differs from the above-mentioned particulate polymer A in at least one of the amount of undissolved THF, degree of swelling 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 the above-mentioned volume average particle size value of the particulate material or at least one of the above-mentioned physical property values ​​of the particulate polymer A (amount of undissolved THF, degree of swelling in electrolyte, complex modulus, maximum compressive strength, rate of change in maximum compressive strength, and tan δ ratio). 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] <<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 0.50 μm, 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 increased. Furthermore, if the volume average particle diameter of the particulate polymer B is less than 0.50 μm, the binding property of the particulate polymer B can be increased. The volume average particle diameter of the particulate polymer B can be measured using a laser diffraction / scattering measuring device.

[0083] [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.

[0084] The mass ratio of the particulate polymer A to the particulate polymer B in the 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 room temperature 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.

[0085] <<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.

[0086] 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.

[0087] <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.

[0088] <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.

[0089] 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.

[0090] 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 room temperature 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.

[0091] <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 thickeners such as polyacrylamide; wetting agents; and dispersion stabilizers such as sodium dodecylbenzenesulfonate. These other components may be used alone or in combination of two or more.

[0092] <Properties of the Binder Composition for Functional Layer> [Ash Content] The binder composition for functional layer of the present invention must have an ash content of 3% by mass or more and 30% by mass or less, preferably 5% by mass or more, more preferably 8% by mass or more, preferably 28% by mass or less, and more preferably 25% by mass or less. When the ash content of the binder composition is equal to or greater than the lower limit, the blocking resistance of the functional layer can be improved, and the coating stability of the functional layer composition and the lyophilicity of the resulting separator to the electrolyte can be enhanced. Furthermore, when the ash content of the binder composition is equal to or less than the upper limit, the room-temperature adhesion of the functional layer can be improved, thereby improving the cycle characteristics of the resulting secondary battery. Furthermore, when the ash content of the binder composition is equal to or less than the upper limit, the amount of metal released from the electrode mixture layer in the secondary battery during charge and discharge can be reduced. 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 described below. Specifically, the ash content decreases by decreasing 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 of the colloidal dispersion used in preparing the particulate polymer A. The ash content of the binder composition can also be adjusted by appropriately selecting and washing the inorganic colloid contained in the particulate polymer A with a solvent, acid, base, or other substance.

[0093] [Volume Average Particle Diameter of Granules] As described above, in the binder composition for functional layers of the present invention, the volume average particle diameter of the granules containing at least the particulate polymer A must be 1.0 μm or more and 15.0 μm or less. The volume average particle diameter of the granules is preferably 1.5 μm or more, more preferably 2.0 μm or more, even more preferably 2.5 μm or more, preferably 14.0 μm or less, more preferably 13.0 μm or less, and even more preferably 12.0 μm or less. If the volume average particle diameter of the granules is equal to or greater than the above-mentioned lower limit, the IV resistance can be reduced, improving the rate characteristics of the resulting secondary battery and improving the cycle characteristics of the resulting secondary battery. On the other hand, if the volume average particle diameter of the granules is equal to or less than the above-mentioned upper limit, the room temperature adhesion of the functional layer can be improved and the blocking resistance can be enhanced. The volume average particle diameter of the granules 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.

[0094] 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.

[0095] [Particle size distribution] In the binder composition for functional layer, the particle size distribution of the particulate matter containing at least the particulate polymer A is preferably 1.0 or more, more preferably 1.2 or more, and preferably 2.0 or less, and more preferably 1.8 or less. In this specification, the particle size distribution is calculated as the quotient obtained by dividing the volume average particle size by the number average particle size. If the particle size distribution is equal to or greater than the lower limit, the rate characteristics and cycle characteristics of the resulting secondary battery can be improved. Furthermore, if the particle size distribution is equal to or less than the upper limit, the amount of metal elution after cycling of the resulting secondary battery can be reduced. The particle size distribution of the binder composition for functional layer 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.

[0096] 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.

[0097] [Glass Transition Temperature] The glass transition temperature of the binder composition for the functional layer must be less than 25°C, preferably 10°C or lower, more preferably 0°C or lower, even more preferably -5°C or lower, and preferably -40°C or higher, more preferably -35°C or higher, and even more preferably -30°C or higher. When the glass transition temperature of the binder composition for the functional layer is equal to or higher than the above lower limit, the blocking resistance of the functional layer can be improved. Furthermore, when the glass transition temperature of the binder composition for the functional layer is equal to or lower than the above upper limit, the room temperature adhesiveness of the functional layer can be further improved. 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.

[0098] 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.

[0099] [Ash content] As described above in the section on particulate polymer A, the binder composition of the present invention needs to have an ash content of 3% by mass or more and 30% by mass or less, preferably 5% by mass or more, more preferably 8% by mass or more, preferably 28% by mass or less, and more preferably 25% by mass or less, based on the total solid content of the binder composition being 100% by mass, as described above in the section on particulate polymer A. The effect of and the method for adjusting the ash content of the binder composition are also as described above in the section on particulate polymer A.

[0100] <<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 room temperature 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 thickeners 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.

[0101] <<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.

[0102] <<Metal Content>> The metal content of the binder composition for a functional layer of the present invention is preferably 0.1% by mass or more, more preferably 0.8% by mass or more, and preferably 20.0% by mass or less, and more preferably 10.0% by mass or less. When the metal content of the binder composition for a functional layer is equal to or greater than the above-mentioned lower limit, the blocking resistance of the functional layer can be further improved, and the lyophilicity of the resulting separator to the electrolyte can be improved. Furthermore, when the metal content of the binder composition for a functional layer is equal to or less than the above-mentioned upper limit, the room-temperature adhesion of the functional layer can be improved. The metal content of the binder composition for a 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. 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.

[0103] <<Amount of Metal Dissolved into Liquid>> The binder composition for a functional layer of the present invention preferably has an amount of metal eluted into the liquid of less than 0.10% by mass, more preferably 0.08% by mass or less. The lower limit of the amount of metal eluted into the liquid of the binder composition for a functional layer is not particularly limited and may be 0.00% by mass. When the amount of metal eluted into the liquid of the binder composition for a functional layer is less than the upper limit, the cycle characteristics of the resulting secondary battery can be improved and the coating stability of the resulting functional layer composition can be enhanced. The amount of metal eluted into the liquid of the binder composition for a functional layer can be adjusted, for example, by changing the concentration and / or amount used, as well as the type, of the colloidal dispersion used in preparing the particulate polymer A. Specifically, the amount of metal eluted into the liquid decreases when the concentration and / or amount used of the colloidal dispersion used in preparing the particulate polymer A is reduced, and the amount of metal eluted into the liquid increases when the concentration and / or amount used is increased. The amount of metal eluted into the liquid of the binder composition for a functional layer can be measured according to the method described in the Examples of this specification.

[0104] <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 a particulate material containing the above-mentioned particulate polymer A with the particulate polymer B, a dispersion medium, a dispersant, and other components used as needed. 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. 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.

[0105] 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.

[0106] (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.

[0107] <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 is even more preferred. Furthermore, these particles may be subjected to element substitution, surface treatment, solid solution formation, etc., as necessary. Note that these inorganic particles may be used alone or in combination of two or more types in any ratio.

[0108] <<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, output 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.

[0109] <<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.

[0110] The mixing ratio of the inorganic particles to the particulate polymer B in the slurry composition for the 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 adhesiveness 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 resulting secondary battery can be further improved.

[0111] <<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.

[0112] <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.

[0113] (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.

[0114] <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.

[0115] <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.

[0116] <<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.

[0117] 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).

[0118] [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.

[0119] [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.

[0120] <<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.

[0121] (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.

[0122] <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.

[0123] <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.

[0124] 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.

[0125] 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.

[0126] <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.

[0127] 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.

[0128] (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)

[0129] <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 about 0.2 g of the dispersions were pressed at 200°C, 1 MPa, and 1 minute to obtain test pieces for measuring the electrolyte swelling degree of particulate polymer A. The mass of the test pieces (mass before immersion) was measured. Thereafter, the test pieces were immersed in an electrolyte solution at a temperature of 60°C for 72 hours. The immersed test pieces were pulled out, the electrolyte solution was wiped off, and the mass (mass after immersion) was immediately measured, and the value 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 with LiPF ６ A solution in which the above was dissolved at a concentration of 1 mol / L was used.

[0130] <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 subjected to 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)

[0131] <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.

[0132] <Ash Content> Aqueous dispersions containing the functional layer composition prepared in the Examples and Comparative Examples were dropped into a Petri dish to a solids content of 1.5 g and dried for 24 hours at 23-27°C to obtain a dried functional layer 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 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) Therefore, the value of the ash content measured according to this method can substantially correspond to the value of the ash content of the particulate polymer A.

[0133] <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.

[0134] Particle Size and Particle Size Distribution of Granules Contained in Functional Layer Compositions: For the aqueous dispersions containing the functional layer compositions prepared in the Examples and Comparative Examples, a measurement sample equivalent to 0.1 g was weighed and placed in a beaker. 0.1 mL of an alkylbenzene sulfonic acid aqueous solution (Fujifilm Corporation, "Dry-Well") was added as a dispersant. 10-30 mL of 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 size (Dv) of the granules contained in the functional layer composition 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. Under these conditions, the lower limit of measurement for the granule size was 0.4 μm, and the upper limit was 16 μm. The number average particle diameter (Dp) was also measured, and the particle diameter distribution (Dv / Dp) was calculated. Therefore, the values ​​of the volume average particle diameter and particle diameter distribution measured according to this method can substantially correspond to the values ​​of the volume average particle diameter and particle diameter distribution of the particulate polymer A.

[0135] <Glass Transition Temperature of Functional Layer Composition and Particulate Polymer B> A powder sample obtained by drying an aqueous dispersion containing the functional layer composition and an aqueous dispersion containing 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 composition, the temperature showing the peak with the largest displacement was taken as the glass transition temperature of the functional layer composition.

[0136] <Total Metal Content> Approximately 0.4 g (based on solids) of the aqueous dispersion containing the functional layer composition prepared in each of the Examples and Comparative Examples was collected and weighed, and then 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 mixture, 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 aqueous dispersion containing the functional layer 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 aqueous dispersion containing the functional layer composition initially weighed to calculate the total metal content (mass%).

[0137] <Amount of Metals Dissolved in Liquid> The aqueous dispersions containing the functional layer compositions prepared in the Examples and Comparative Examples were centrifuged (centrifugal acceleration: 32,240 G, 30 minutes, 25°C) to obtain supernatants. Approximately 1 g of the resulting supernatant was collected and weighed, 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 supernatant, 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 aqueous dispersions containing the functional layer compositions were measured using an ICP-AES (SPS-5100, manufactured by SII Nanotechnology). The amount of metals dissolved in the liquid (mass%) was calculated by dividing the measured total amount of metals by the weight of the supernatant of the aqueous dispersion containing the functional layer composition initially weighed.

[0138] (Evaluation) <Blocking Resistance of Separator> A polyethylene microporous film (thickness: 9 μm) was prepared as a separator substrate. The functional layer compositions prepared in Examples and Comparative Examples were applied to one side of this separator substrate by a bar coater method. Next, the separator substrate coated with the functional layer composition was 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. 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 40°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 peeled off. The same measurement was performed 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 smaller the peel strength P1, the more effectively the separators with functional layers can be prevented from sticking together when stored in a rolled state, indicating excellent self-adhesion. A: The separator fell off before the peel strength test. B: Peel strength P1 was less than 0.5 N / m. C: Peel strength P1 was 0.5 N / m or more but less than 1.0 N / m. D: Peel strength P1 was 1 N / m or more.

[0139] <Room Temperature Adhesion of Separators> 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 at a press temperature of 25°C, a load of 2 kN (press pressure of 2 MPa), and a press time of 10 seconds to obtain an integrated product in which the negative electrode and separator with functional layers 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 layers 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 separator with functional layer, 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 negative electrode and the separator with functional layer according to the following criteria. A: Peel strength of 10 N / m or more B: Peel strength of 5 N / m or more but less than 10 N / m C: Peel strength of 2 N / m or more but less than 5 N / m D: Peel strength of less than 2 N / m

[0140] <Lyophilicity to Electrolyte> The positive electrode, negative electrode, and separator with functional layer prepared in the examples and comparative examples were cut into 6.5 x 13.0 cm, 7.0 cm x 13.5 cm, and 7.5 cm x 14.0 cm pieces, respectively. Next, the positive electrode, separator with functional layer, and negative electrode were stacked in this order, and a flat press was used to obtain an integrated product in which the positive electrode, separator with functional layer, and negative electrode were integrated under the following conditions: a press temperature of 25°C, a load of 16.9 kN (press pressure of 2 MPa), and a press time of 10 seconds. The integrated product was then housed in a 9.0 cm x 18.0 cm aluminum laminate sheet exterior. 500 μL of electrolyte was then injected. The interior of the lithium-ion secondary battery was then reduced in pressure to -95 kPa, maintained in that state for 1 minute, and then heat-sealed to obtain a test sample. After 5 minutes, the test sample was disassembled, and the state of electrolyte impregnation in the positive electrode was visually confirmed. The evaluation was carried out according to the following criteria. The larger the area of ​​the positive electrode that is impregnated with the electrolyte, the higher the affinity of the electrolyte to the electrolyte. A: The entire surface of the negative electrode is impregnated with the electrolyte. B: The area of ​​the negative electrode that is not impregnated with the electrolyte is 4 cm or less. ２ C: The part of the negative electrode that is not impregnated with the electrolyte is less than 4 cm ２ Over 8cm ２ D: The part of the negative electrode that is not impregnated with the electrolyte is less than 8 cm ２ That's all that remains.

[0141] <Coating Stability of Functional Layer Compositions in Examples 1-12 and Comparative Examples 1-5> The functional layer binder compositions prepared in Examples 1-12 and Comparative Examples 1-5 were 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, 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. 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

[0142] <Coating Stability of Slurry for Coating in Example 13> 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 to measure 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

[0143] <Rate Characteristics of Secondary Battery> After injecting the electrolyte, the lithium ion secondary batteries prepared in the Examples and Comparative Examples were left to stand at 25°C for 5 hours. Next, they were charged to a cell voltage of 3.65V using a constant current method at 0.2C at 25°C, and then aged for 12 hours at 60°C. Then, they were discharged to a cell voltage of 3.00V using a constant current method at 0.2C at 25°C. Thereafter, CC-CV charging (upper limit cell voltage 4.20V) was performed at a constant current of 0.2C, and CC discharging was performed at a constant current of 0.2C to a cell voltage of 3.00V. This 0.2C charge-discharge cycle was repeated three times. Next, in an environment at 25°C, constant current charging and discharging was performed at 0.2C between cell voltages of 4.2V and 3.00V, 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 0°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 80% or more B: Capacity retention rate ΔC is 70% or more but less than 80% C: Capacity retention rate ΔC is 60% or more but less than 70% D: Capacity retention rate ΔC is less than 60%

[0144] <Cycle Characteristics of Secondary Battery> After injecting the electrolyte, the lithium-ion secondary battery was left standing at 25°C for 1 hour. Next, it was 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, it was discharged to a cell voltage of 3.00 V using a constant current method at 0.2 C at 25°C. Then, it was CC-CV charged (upper limit cell voltage 4.20 V) using a constant current method at 0.2 C, and CC discharged to 3.00 V using a constant current method at 0.2 C. This 0.2 C charge-discharge cycle was repeated three times. Then, 100 cycles of charge-discharge were performed at a charge-discharge rate of 1.0 C at a cell voltage of 4.20-3.00 V under a temperature of 60°C. 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 shown by ΔC = (X2 / X1) × 100 (%) was calculated and evaluated according to the following criteria. A larger value of this capacity retention rate ΔC indicates that the lithium ion secondary battery has better cycle characteristics. A: Capacity retention rate ΔC is 93% or more B: Capacity retention rate ΔC is 90% or more but less than 93% C: Capacity retention rate ΔC is 87% or more but less than 90% D: Capacity retention rate ΔC is less than 87%

[0145] <Metal Leaching Amount After Cycling of Secondary Battery> The lithium-ion secondary batteries prepared in the Examples and Comparative Examples were disassembled after the cycle test, and the amount of metal leaching from the removed negative electrode was measured. Specifically, the lithium-ion secondary batteries after the cycle test were disassembled, and the negative electrode was washed with diethyl carbonate (DEC). The sample scraped off from the copper foil was weighed in a quartz beaker. Sulfuric acid was added thereto, and the mixture was carbonized on a heater and incinerated using a muffle furnace. After cooling, the sample was dissolved by adding fluorine and hydrochloric acid. The volume of the sample was then measured by ICP-AES, and the total amount of Ni, Co, and Mn was calculated to determine the transition metal content. Based on the calculated transition metal content, the following evaluations were performed. A: Transition metal content is less than 150 ppm. B: Transition metal content is 150 ppm or more and less than 250 ppm. C: Transition metal content is 250 ppm or more and less than 400 ppm. D: Transition metal content is 400 ppm or more.

[0146] Example 1 Preparation of an Aqueous Dispersion Containing Particulate Polymer A Preparation of a Monomer Composition 64.0 parts of butyl acrylate as a (meth)acrylic acid ester monomer, 1.0 parts of ethylene glycol dimethacrylate as a crosslinkable monomer, 7.0 parts of glycidyl methacrylate as an epoxy group-containing crosslinkable monomer, and 23.0 parts of styrene as an aromatic vinyl monomer were mixed to prepare a monomer composition. Preparation of a Colloidal Dispersion To an aqueous solution obtained by dissolving 16.0 parts of magnesium chloride in 200 parts of ion-exchanged water, an aqueous solution obtained by dissolving 14.0 parts of sodium hydroxide in 50 parts of ion-exchanged water was gradually added under stirring. 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 by the colloidal precipitation reaction was 10 parts by mass, with the total amount of the monomer components of particulate polymer A being 100 parts by mass. [Formation of Core Portion] Particulate polymer A was prepared by suspension polymerization. Specifically, the monomer composition obtained as described above was added to the colloidal dispersion containing magnesium hydroxide, and after further stirring, 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 had been formed, was placed in a reactor, heated to 90°C, and subjected to a polymerization reaction for 5 hours to obtain an aqueous dispersion containing a particulate polymer constituting the core portion. The content of (meth)acrylic acid ester monomer units in the core portion was 67.4 mass%, the content of crosslinkable monomer units was 8.4 mass%, and the content of aromatic vinyl monomer units was 24.2 mass%. [Formation of Shell Portion] 0.5 parts of hydroxypropyl methylcellulose was dissolved in 200 parts of ion-exchanged water at room temperature to prepare an aqueous hydroxypropyl methylcellulose solution.The aqueous dispersion containing the particulate polymer constituting the core obtained by the suspension polymerization method was filtered using quantitative filter paper (Advantec, No. 5C) to obtain a wet cake containing the particulate polymer. An amount of the obtained wet cake so that the solid content was 31.5 parts was added to the above-mentioned aqueous hydroxypropyl methylcellulose solution and redispersed by stirring at room temperature for 30 minutes. To the redispersed dispersion, 0.15 parts of 2,2'-azobis(2-methylpropionamido) dihydrochloride as a polymerization initiator, 0.5 parts of ethylene glycol dimethacrylate as a crosslinkable monomer, and 4.5 parts of methyl methacrylate as a (meth)acrylic acid ester monomer were added (total (mass ratio) of wet cake solids / shell monomer = 95 / 5), and the temperature was raised to 70°C, and a polymerization reaction was carried out for 6 hours to obtain an aqueous dispersion containing particulate polymer A having a core-shell structure. The content of crosslinkable monomer units in the shell was 10% by mass, and the content of (meth)acrylic acid ester monomer units was 90% by mass. The resulting aqueous dispersion containing particulate polymer A was then filtered using a 400 mesh to obtain an aqueous dispersion containing particulate polymer A for evaluation. Using this particulate polymer A, the amount of undissolved THF, electrolyte swelling degree, complex modulus, maximum compressive strength, maximum compressive strength change rate, tan δ ratio, and ash content were measured. The results are shown in Table 1.

[0147] <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 as a polymerization initiator 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 as a dispersion stabilizer, 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, 0.2 parts of allyl methacrylate as a crosslinkable monomer, and 1.0 parts of allyl glycidyl ether as an epoxy group-containing 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.

[0148] Preparation of Functional Layer Binder Composition: 91.8 parts (solids equivalent) of an aqueous dispersion of particulate polymer A, 7 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") as an additive, 1 part (solids equivalent) of ammonium polyacrylate (manufactured by Toa Gosei, product name "Aron-A30SL") as a water-soluble polymer, and ion-exchanged water were mixed, and the pH was adjusted to 8 with a 12% aqueous ammonia solution to obtain a slurry-like functional layer binder composition (solids concentration: 27%). The aqueous dispersion containing this functional layer binder composition was used to measure the ash content, volume average particle size, glass transition temperature, total metal content, and amount of metal eluted into the liquid. The results are shown in Table 1.

[0149] <Preparation of Slurry Composition for Heat-Resistant Layer> An aqueous solution containing alumina particles (manufactured by Nippon Light Metal Co., Ltd., product name "LS-256", volume average particle diameter: 0.5 μm) as non-conductive inorganic particles, ammonium polyacrylate (manufactured by Toagosei Co., Ltd., Aron A-30SL) as a dispersant, and a water-soluble polymer synthesized as described below as a thickener was prepared. [Synthesis of Aqueous Solution Containing Water-Soluble Polymer] A four-neck flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen gas inlet tube was charged with a monomer composition consisting of 90 parts of acrylamide as a (meth)acrylamide monomer, 9 parts of methacrylic acid as an acid group-containing monomer, and 1 part of dimethylacrylamide as a cross-linkable monomer, as well as 365 parts of ion-exchanged water and 5 parts of isopropyl alcohol, and oxygen was removed from the reaction system with nitrogen gas. Next, 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 under stirring as polymerization initiators, and the mixture was heated from room temperature to 80°C and maintained at that temperature for 3 hours to polymerize the monomer composition. Subsequently, 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 having 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] 100 parts of non-conductive inorganic particles, 0.4 parts of a 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, 3 parts in terms of solid content of the particulate polymer B, 1.5 parts in terms of solid content of the aqueous solution containing the water-soluble polymer, and 0.2 parts of a polyethylene glycol-type surfactant (manufactured by San Nopco, product name "Noptex ED-052") as an additive were mixed, and the pH was adjusted to 9.5 with a 12% aqueous ammonia solution to prepare a slurry composition for a heat-resistant layer having a solid content concentration of 35%.

[0150] <Preparation of Separator> [Preparation of Separator Having Heat-Resistant Layers 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 having a heat-resistant layer 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 heat-resistant layer was applied to each side in a thickness of 2.0 μm. [Preparation of Separator Having Adhesive Layers and Heat-Resistant Layers on Both Sides] The binder composition for the functional layer prepared above was applied to the surface of the polyethylene separator having heat-resistant layers on both sides using a bar coater and dried at a temperature of 50°C for 3 minutes to obtain a separator with a basis weight of 0.5 g / m on one side. ２ The same procedure was carried out on the other side of the separator substrate, and a separator with an adhesive layer and a heat-resistant layer was obtained. ２ A separator with an adhesive layer and a heat-resistant layer was obtained, having an adhesive layer with a basis weight of 1000 on both sides. The separator with the functional layer was used to evaluate blocking resistance, room temperature adhesion, electrolyte affinity, and coating stability of the functional layer composition. The results are shown in Table 1.

[0151] <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 under a hydrogen pressure of 3.0 MPa for 6 hours 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 N-methyl-2-pyrrolidone (NMP) to obtain an NMP solution of a polymer composition for a positive electrode with a solids concentration of 8% as the polymer composition.

[0152] <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.

[0153] <Preparation of Positive Electrode Slurry> 98 parts of a ternary active material having a layered structure (LiNi0.6Co0.2Mn0.2O2, average particle size: 10 μm) as a positive electrode active material, 1 part of polyvinylidene fluoride, 1 part of the conductive material dispersion obtained as described above (solid content equivalent), and NMP as a solvent were added to the conductive material dispersion obtained as described above, and mixed with a planetary mixer (60 rpm, 30 minutes) to prepare a positive electrode slurry. 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 in the range of 4000 mPa s to 5000 mPa s.

[0154] <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. ２ The 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.

[0155] <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 a 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 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, with a coating weight of 11 mg / cm. ２ 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 temperature of 25±3°C and a linear pressure of 11 t (tons), resulting in a negative electrode composite layer having a coating weight of 10 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.

[0156] <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 the following conditions: 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 LiPF6 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 an electrolyte. The interior of the lithium-ion secondary battery was then reduced in pressure to -95 kPa, and the battery was maintained in that state for 1 minute, after which heat sealing was performed to prepare a lithium-ion secondary battery for evaluation. This lithium-ion secondary battery was used to evaluate its rate characteristics, cycle characteristics, and the amount of metal elution after cycling. The results are shown in Table 1.

[0157] (Example 2) In forming the core portion of the particulate polymer A, the stirring conditions were changed from 12,000 rpm for 1 minute using an in-line emulsifying disperser (manufactured by Pacific Machinery & Engineering Co., Ltd., "Cavitron") to 6,000 rpm for 0.5 minutes using an in-line emulsifying disperser (manufactured by Pacific Machinery & Engineering Co., Ltd., "Milder"), and various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0158] (Example 3) In forming the core portion of the particulate polymer A, the stirring time was changed from 1 minute to 10 minutes at a rotation speed of 12,000 rpm using an in-line emulsifying disperser ("Cavitron" manufactured by Pacific Machinery Works, Ltd.) in the same manner as in Example 1, except that the stirring time was changed from 1 minute to 10 minutes. The results are shown in Table 1.

[0159] (Example 4) In the preparation of the particulate polymer A, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the amount of butyl acrylate was changed from 64.0 parts to 46.0 parts and the amount of styrene was changed from 23.0 parts to 41.0 parts when preparing the monomer composition. The results are shown in Table 1. The content of (meth)acrylic acid ester monomer units in the core part of the particulate polymer A was 48.4% by mass, the content of crosslinkable monomer units was 8.4% by mass, and the content of aromatic vinyl monomer units was 43.2% by mass.

[0160] (Example 5) In the preparation of the particulate polymer A, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in the preparation of the monomer composition, the amount of butyl acrylate was changed from 64.0 parts to 76.5 parts, the amount of allyl methacrylate was changed from 0.0 parts to 0.5 parts, and the amount of styrene was changed from 23.0 parts to 10.0 parts. The results are shown in Table 1. The content of (meth)acrylic acid ester monomer units in the core part of the particulate polymer A was 80.5% by mass, the content of crosslinkable monomer units was 8.9% by mass, and the content of aromatic vinyl monomer units was 10.5% by mass.

[0161] (Example 6) In the preparation of the particulate polymer A, the amount of magnesium chloride was changed from 16.0 parts to 32.0 parts when preparing the colloidal dispersion, and the concentration of sodium hydroxide was changed from 14.0 parts of sodium hydroxide to 100 parts of ion-exchanged water to 28.0 parts of sodium hydroxide, except that the amount of magnesium chloride was changed from 16.0 parts to 32.0 parts when preparing the colloidal dispersion, and the concentration of sodium hydroxide was changed from 14.0 parts to 50 parts of ion-exchanged water to 28.0 parts of sodium hydroxide,

[0162] (Example 7) In the preparation of the particulate polymer A, the amount of magnesium chloride was changed from 16.0 parts to 4.5 parts when preparing the colloidal dispersion, the amount of sodium hydroxide was changed from 14.0 parts to 4.2 parts when preparing the colloidal dispersion, and the stirring time was changed from 1 minute to 10 minutes at a rotation speed of 12,000 rpm using an in-line emulsifying disperser (manufactured by Pacific Machinery Works, "Cavitron") when forming the core part of the particulate polymer A. The various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 2.

[0163] (Example 8) In the preparation of the particulate polymer A, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that in the preparation of the monomer composition, the amount of the (meth)acrylic acid ester monomer was changed from 64.0 parts of butyl acrylate to 60.0 parts of 2-ethylhexyl acrylate, and the amount of styrene was changed from 23.0 parts to 27.0 parts. The results are shown in Table 2. The content of (meth)acrylic acid ester monomer units in the core part of the particulate polymer A was 63.2% by mass, the content of crosslinkable monomer units was 8.4% by mass, and the content of aromatic vinyl monomer units was 28.4% by mass.

[0164] (Example 9) In the preparation of the particulate polymer A, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the amount of itaconic acid was changed from 0 parts to 0.5 parts and the amount of styrene was changed from 23.0 parts to 22.5 parts when preparing the monomer composition. The results are shown in Table 2. The content of (meth)acrylic acid ester monomer units in the core part of the particulate polymer A was 67.4% by mass, the content of crosslinkable monomer units was 8.4% by mass, and the content of aromatic vinyl monomer units was 23.7% by mass.

[0165] (Example 10) In the preparation of the particulate polymer A, the type and concentration of the aqueous solution used in the preparation of the colloidal dispersion were changed from 16.0 parts of magnesium chloride to 200 parts of ion-exchanged water to 7.6 parts of sulfuric acid to 100 parts of ion-exchanged water, and from 14.0 parts of sodium hydroxide to 50 parts of ion-exchanged water to 13.3 parts of barium hydroxide to 150 parts of ion-exchanged water, except that various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 2.

[0166] (Example 11) In the preparation of particulate polymer A, a colloidal dispersion containing magnesium hydroxide was not prepared. Instead, when forming the core portion, the monomer composition and 8 parts (based on the solid content) of colloidal silica (Snowtex MP2040, manufactured by Nissan Chemical Industries, Ltd.) were added to 200 parts of ion-exchanged water. Otherwise, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 3.

[0167] (Example 12) In preparing a colloidal dispersion in the preparation of particulate polymer A, 13 parts of cubic boehmite having an average particle size of 300 nm and 100 parts of ion-exchanged water were mixed, and the mixture was treated for 1 hour in a bead mill (manufactured by Ashizawa Fine Tech, product name "LMZ015") while adjusting the pH to 9.5 using ammonia water, to obtain an inorganic colloidal dispersion of boehmite. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 3.

[0168] (Example 13) After producing the binder composition for the functional layer, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that a slurry composition for the functional layer was prepared as follows. The results are shown in Table 3. <Preparation of Slurry Composition for Functional Layer> An aqueous solution containing alumina particles (manufactured by Nippon Light Metal Co., Ltd., product name "LS-256", volume average particle size: 0.5 μm) as non-conductive inorganic particles, ammonium polyacrylate salt (manufactured by Toagosei Co., Ltd., Aron A-30SL) as a dispersant, and a water-soluble polymer synthesized below as a thickener was prepared. [Synthesis of aqueous solution containing water-soluble polymer] A four-necked flask equipped with a stirrer, thermometer, reflux condenser, and nitrogen gas inlet tube was charged with a monomer composition consisting of 90 parts of acrylamide as a (meth)acrylamide monomer, 9 parts of methacrylic acid as an acid group-containing monomer, and 1 part of dimethylacrylamide as a crosslinkable monomer, as well as 365 parts of ion-exchanged water and 5 parts of isopropyl alcohol, and oxygen was removed from the reaction system with nitrogen gas. Next, under stirring, 3 parts of a 5% aqueous ammonium persulfate solution and 1.5 parts of a 5% aqueous sodium hydrogen sulfite solution were added as polymerization initiators to the flask, and the temperature was raised from room temperature to 80 ° C. and kept at 40 ° C. for 3 hours to polymerize the monomer composition. Thereafter, 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 having 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 Functional Layer] 85 parts of non-conductive inorganic particles, 0.4 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, 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 as a thickener (in terms of solids), and 0.2 parts of a polyethylene glycol surfactant (manufactured by San Nopco, product name "Noptex ED-052") were mixed, and the pH was adjusted to 9.5 with a 12% aqueous ammonia solution to prepare a slurry composition for the functional layer with a solids concentration of 35%. <Preparation of Separator with Functional Layer> A polyethylene separator substrate (manufactured by Asahi Kasei Corporation, product name "ND309", thickness: 9 μm) was prepared.The slurry composition for functional 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 give a coating weight of 3.4 g / cm on one side. ２ The same procedure was carried out on the other side of the separator substrate, and a separator having a functional layer of 3.4 g / cm per side was obtained. ２ (3.4 x 10 ４ g / m ２ A separator with functional layers was produced, having functional layers with a basis weight of 1000g on both sides.

[0169] Comparative Example 1 When preparing particulate polymer A, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the following operations were performed. The results are shown in Table 4. <Preparation of Particulate Polymer A> [Preparation of Monomer Composition] A monomer composition was prepared by mixing 24.5 parts of butyl acrylate as a (meth)acrylic acid ester monomer, 0.5 parts of ethylene glycol dimethacrylate as a crosslinkable monomer, 10.0 parts of glycidyl methacrylate as an epoxy group-containing crosslinkable monomer, and 65.0 parts of styrene as an aromatic vinyl monomer. [Preparation of Colloidal Dispersion] An aqueous solution prepared by dissolving 7.0 parts of sodium hydroxide in 50 parts of ion-exchanged water was gradually added under stirring to an aqueous solution prepared by dissolving 10.0 parts of magnesium chloride in 200 parts of ion-exchanged water. Stirring was continued for 30 minutes after the addition to prepare a colloidal dispersion containing magnesium hydroxide as a metal hydroxide. [Suspension Polymerization Method] Particulate polymer A was prepared by suspension polymerization. Specifically, the monomer composition obtained as described above was added to the colloidal dispersion containing magnesium hydroxide, followed by further stirring. Then, 1.8 parts of t-butylperoxy-2-ethylhexanoate ("Perbutyl O," manufactured by NOF Corporation) was added as a polymerization initiator to obtain a mixed solution. The resulting mixed solution was subjected to high-shear stirring at 12,000 rpm for 1 minute using an in-line emulsifying disperser ("Cavitron," manufactured by Pacific Machinery Works, Ltd.) to form droplets of the monomer composition in the colloidal dispersion containing magnesium hydroxide. The colloidal dispersion containing magnesium hydroxide containing the formed droplets of the monomer composition was placed in a reactor, heated to 90°C, and subjected to a polymerization reaction for 5 hours. The resulting dispersion was purified by vacuum treatment at 90°C for 2 hours using an evaporator to obtain an aqueous dispersion containing a particulate polymer. [Washing] While stirring, the aqueous dispersion containing the particulate polymer was subjected to acid washing at room temperature (25°C) until the pH reached 6.5 or less. Then, the solid matter was separated by filtration, and 500 parts of ion-exchanged water was added to the obtained solid matter to form a reslurry, and the water washing treatment (washing, filtration and dehydration) was repeated 10 times. Then, the solid matter was separated by filtration, 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 A.

[0170] (Comparative Example 2) In preparing particulate polymer A, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the following operations were carried out. The results are shown in Table 4. <Preparation of Particulate Polymer A> [Preparation of Monomer Composition] The amount of butyl acrylate was changed from 64.0 parts to 58.9 parts, the amount of ethylene glycol dimethacrylate was changed from 1.0 part to 0.5 part, the amount of glycidyl methacrylate was changed from 7.0 parts to 10.0 parts, and the amount of styrene was changed from 23.0 parts to 20.6 parts. [Formation of Shell Portion] 0.5 parts of hydroxypropyl methylcellulose was dissolved in 200 parts of ion-exchanged water at room temperature to prepare an aqueous hydroxypropyl methylcellulose solution. The aqueous dispersion containing the particulate polymer constituting the core portion obtained by suspension polymerization was centrifuged (10,000 rpm, 10 minutes, 25°C), and the precipitated polymer wet cake was collected. An amount of the obtained wet cake such that the solid content was 30.0 parts was added to the above-mentioned aqueous hydroxypropyl methylcellulose solution, and the mixture was redispersed by stirring at room temperature for 30 minutes. To the redispersed dispersion, 0.15 parts of 2,2'-azobis(2-methylpropionamide) dihydrochloride as a polymerization initiator and 10.0 parts of styrene as an aromatic vinyl monomer were added (total (mass ratio) of wet cake solid content / shell monomer=90 / 10), and the temperature was raised to 70°C, and a polymerization reaction was carried out for 6 hours, thereby obtaining an aqueous dispersion containing a particulate polymer A having a core-shell structure. Thereafter, the obtained aqueous dispersion containing the particulate polymer A was filtered using a 400 mesh to obtain an aqueous dispersion containing a particulate polymer A for evaluation.

[0171] (Comparative Example 3) In the preparation of the particulate polymer A, the amount of magnesium chloride was changed from 16.0 parts to 39.0 parts when preparing the colloidal dispersion, and the concentration of sodium hydroxide was changed from 14.0 parts of sodium hydroxide to 100 parts of ion-exchanged water to 33.0 parts of sodium hydroxide. Except for this, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 4.

[0172] (Comparative Example 4) In the preparation of particulate polymer A, when preparing colloidal dispersion, the amount of magnesium chloride was changed from 16.0 parts to 13.0 parts, the amount of sodium hydroxide was changed from 14.0 parts to 11.0 parts, and when forming the core part of particulate polymer A, the stirring condition was changed from 1 minute at a rotation speed of 12,000 rpm using an in-line type emulsifying disperser (manufactured by Pacific Machinery & Engineering Co., Ltd., "Cavitron") to 0.5 minutes at a rotation speed of 6,000 rpm using an in-line type emulsifying disperser (manufactured by Pacific Machinery & Engineering Co., Ltd., "Milder"), except that various operations, measurements and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 4.

[0173] (Comparative Example 5) In preparing particulate polymer A, various operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that the following operations were carried out. The results are shown in Table 4. <Preparation of Particulate Polymer A> 110 parts of ion-exchanged water and 0.2 parts of ammonium persulfate as a polymerization initiator were fed into a reactor equipped with a stirrer, the gas phase was replaced with nitrogen gas, and the temperature was raised to 80°C. Meanwhile, in a separate vessel, 40 parts of ion-exchanged water, 8 parts (per solid content) of colloidal silica (Nissan Chemical Industries, Ltd., Snowtex ST-50-T), 64.0 parts of butyl acrylate as a (meth)acrylic acid ester monomer, 1.0 part of ethylene glycol dimethacrylate as a crosslinkable monomer, 7.0 parts of glycidyl methacrylate as an epoxy group-containing crosslinkable monomer, and 23.0 parts of styrene as an aromatic vinyl monomer were mixed to obtain a monomer composition. This monomer composition was continuously added to the reactor over 2 hours, and a polymerization reaction was carried out at 80°C. Polymerization was continued until the polymerization conversion rate reached 96%, thereby obtaining an aqueous dispersion containing a particulate polymer constituting the core portion. Next, while maintaining this aqueous dispersion at 80°C, 0.5 parts of ethylene glycol dimethacrylate as a crosslinkable monomer and 4.5 parts of styrene as an aromatic vinyl monomer were continuously added to the aqueous dispersion over 30 minutes, thereby continuing polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to stop the reaction, thereby obtaining an aqueous dispersion containing particulate polymer A.

[0174] In Tables 1 to 4 shown below, "ST" represents styrene, "EDMA" represents ethylene glycol dimethacrylate, "GMA" represents glycidyl methacrylate, "AMA" represents allyl methacrylate, "2EHA" represents 2-ethylhexyl acrylate, "BA" represents n-butyl acrylate, "IA" represents itaconic acid, "MMA" represents methyl methacrylate, "HPMC" represents hydroxypropyl methylcellulose, "Na-LBS" represents sodium dodecylbenzenesulfonate, and "PAA-NH ４ " indicates polyacrylic acid ammonium salt, and "PO / EO" indicates polyethylene glycol type surfactant.

[0175]

[0176]

[0177]

[0178]

[0179] Tables 1-3 show that in Examples 1-13, in which a lithium-ion secondary battery functional layer composition was used in which the volume average particle size of the granules and the ash content of the binder composition were each within the specified range and the glass transition temperature of the binder composition was less than the specified value, functional layers with excellent room-temperature adhesion and blocking resistance were obtained. On the other hand, Table 4 shows that in Comparative Example 1, in which the glass transition temperature of the binder composition was equal to or greater than the specified value and the ash content was outside the specified range, and Comparative Examples 2 and 3, in which the ash content was outside the specified range, the resulting functional layers did not achieve both room-temperature adhesion and blocking resistance compared to Examples 1-13. Furthermore, Comparative Examples 4 and 5, in which the volume average particle size of the granules was outside the specified range, showed inferior blocking resistance compared to Examples 1-13, and Comparative Example 5 also showed inferior room-temperature adhesion.

[0180] According to the present invention, it is possible to provide a composition for a functional layer of a lithium ion secondary battery, which is capable of forming a functional layer having excellent room temperature adhesion and blocking resistance, as well as a separator with a functional layer for a lithium ion secondary battery and a lithium ion secondary battery using the composition.

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 15.0 μm or less, and the binder composition has a glass transition temperature of less than 25°C and an ash content of 3 mass% or more and 30 mass% or less.

2. The binder composition for a lithium ion secondary battery functional layer 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 metal content is 0.1 mass % or more.

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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