Composition for non-aqueous secondary batteries, slurry for porous layer of lithium-ion secondary battery, porous layer of lithium-ion secondary battery, separator for lithium-ion secondary battery, and lithium-ion secondary battery

Abstract

The present invention provides a composition for a non-aqueous secondary battery capable of forming a layer that achieves both good adhesion between the porous film substrate and the porous layer and suppression of separator shrinkage at high temperatures of 150°C or higher, a slurry for a porous layer of a lithium-ion secondary battery containing the non-aqueous secondary battery composition, a porous layer of a lithium-ion secondary battery containing the slurry for a porous layer of a lithium-ion secondary battery, a separator for a lithium-ion secondary battery containing the porous layer of a lithium-ion secondary battery, and a lithium-ion secondary battery. [Solution] A composition for a non-aqueous secondary battery comprising an aqueous medium and a particulate copolymer, wherein the particulate copolymer comprises vinyl monomer units, the vinyl monomer units comprising amide group-containing monomer units and cyano group-containing monomer units, the content of the cyano group-containing monomer units is 5 to 40% by mass relative to the total amount of the particulate copolymer, the average particle size (D1) of the particulate copolymer is 10 to 160 nm, and the glass transition temperature of the particulate copolymer is 10°C or less.

Description

Technical Field

[0001] The present invention relates to a composition for a non-aqueous secondary battery, a slurry for a porous layer of a lithium ion secondary battery, a porous layer of a lithium ion secondary battery, a separator for a lithium ion secondary battery, and a lithium ion secondary battery.

Background Art

[0002] Conventionally, the development of power storage devices typified by lithium ion secondary batteries has been actively carried out. Generally, in the lithium ion secondary battery, a separator made of a microporous membrane is provided between the positive and negative electrodes. The separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to permeate through the electrolytic solution held in the micropores.

[0003] In order to impart various properties to the separator while ensuring the electrical characteristics and safety of the lithium ion secondary battery, a separator in which a layer containing an inorganic filler and a resin binder is disposed on the surface of the base material constituting the separator has been proposed.

[0004] In recent years, further improvement in performance of secondary batteries has been demanded. As one of the performances, when the secondary battery is used in a high-temperature environment, it is required to further ensure safety. The micropores of the separator in the secondary battery have a function of suppressing the runaway of the secondary battery by contracting the pores when the battery generates heat, thereby inhibiting the passage of, for example, lithium ions. However, when the runaway of the secondary battery occurs at a high temperature of about 150°C or higher, there is a problem that the separator contracts and a short circuit of the electrodes occurs. In particular, in recent years, the capacity of the battery has been increasing, and the amount of heat generated during runaway tends to increase. Therefore, a technique for preventing the shrinkage of the separator at high temperatures is required.

[0005] Patent Document 1 discloses a technology relating to a lithium-ion secondary battery in which a resin composition comprising polymer particles formed from a first monomer having an acidic functional group, a second monomer having an amide group, and other third monomers, and an inorganic filler, is coated onto a separator to form a protective layer made of the resin composition on the separator.

[0006] Patent Document 2 discloses a technology relating to a lithium-ion secondary battery in which a porous film with high peel strength is formed on a separator by coating a slurry for a porous film for secondary batteries, which contains a binder containing alkyl (meth)acrylate monomer units and (meth)acrylamide monomer units and non-conductive particles, onto a separator. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2015-088484 [Patent Document 2] Japanese Patent Publication No. 2015-185530 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] Furthermore, conventionally disclosed technologies have the problem that they have not yet achieved sufficient effectiveness in both ensuring good adhesion between the porous film substrate and the porous layer, and suppressing separator shrinkage at high temperatures of 150°C or higher.

[0009] The present invention has been made in view of the problems of the above-mentioned prior art, and aims to provide a composition for a non-aqueous secondary battery, a slurry for a porous layer of a lithium-ion secondary battery containing the non-aqueous secondary battery composition, a porous layer of a lithium-ion secondary battery containing the slurry for a porous layer of a lithium-ion secondary battery, a separator for a lithium-ion secondary battery containing the porous layer of a lithium-ion secondary battery, and a lithium-ion secondary battery, which can form a layer that can achieve both good adhesion between the porous film substrate and the porous layer and suppression of separator shrinkage at high temperatures of 150°C or higher. [Means for solving the problem]

[0010] <1> A composition for a non-aqueous secondary battery comprising an aqueous medium and a particulate copolymer, The particulate copolymer contains vinyl monomer units, The vinyl monomer unit comprises an amide group-containing monomer unit and a cyano group-containing monomer unit. The content of the cyano group-containing monomer units is 5 to 40% by mass relative to the total amount of the particulate copolymer. The average particle size (D1) of the particulate copolymer is 10 to 160 nm. The glass transition temperature of the particulate copolymer is 10°C or lower. Composition for non-aqueous secondary batteries. <2> The aforementioned amide group-containing monomer unit includes a (meth)acrylamide monomer unit. The content of the (meth)acrylamide monomer units is 1 to 30% by mass relative to the total amount of the particulate copolymer. <1> The non-aqueous secondary battery composition described above. <3> The particulate copolymer further comprises (meth)acrylic group-containing monomer units. <1> or <2> The non-aqueous secondary battery composition described above. <4> Water and inorganic fillers, <1> ~ <3> A composition for a non-aqueous secondary battery as described in any one of the following items, Slurry for a porous layer of a lithium-ion secondary battery. <5> The ratio (D2 / D1) of the average particle diameter (D2) of the inorganic filler to the average particle diameter (D1) of the particulate copolymer is 2.00 to 4.00. The slurry for a porous layer of a lithium-ion secondary battery according to <4>. <6> The average particle diameter (D2) of the inorganic filler is 100 to 300 nm. The slurry for a porous layer of a lithium-ion secondary battery according to <4> or <5>. <7> Containing the slurry for a porous layer of a lithium-ion secondary battery according to <4> to <6>. A porous layer of a lithium-ion secondary battery. <8> The thickness of the porous layer of the lithium-ion secondary battery is 0.8 to 2.5 μm. The porous layer of a lithium-ion secondary battery according to <7>. <9> A base material, Containing the porous layer of a lithium-ion secondary battery according to <7> or <8>. A separator for a lithium-ion secondary battery. <10> Containing the separator for a lithium-ion secondary battery according to <9>. A lithium-ion secondary battery.

Advantages of the Invention

[0011] According to the present invention, it is possible to provide a non-aqueous secondary battery composition capable of forming a layer that can achieve both the adhesion between the base material and the porous layer of the porous membrane and the suppression of separator shrinkage at a high temperature of 150°C or higher, a slurry for a porous layer of a lithium-ion secondary battery containing the non-aqueous secondary battery composition, a porous layer of a lithium-ion secondary battery containing the slurry for a porous layer of a lithium-ion secondary battery, a separator for a lithium-ion secondary battery containing the porous layer of a lithium-ion secondary battery, and a lithium-ion secondary battery.

Embodiments for Carrying Out the Invention

[0012] The embodiments of the present invention (hereinafter also referred to as "these embodiments") will be described in detail below. It should be noted that the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of its gist.

[0013] In this specification, the term "monomer" includes all of the monomers that constitute the particulate copolymer of this embodiment. Furthermore, in this specification, when a monomer is incorporated into a polymer, it is referred to as a "monomer unit," and the state before it is incorporated into a polymer is referred to as a "monomer" or "compound."

[0014] In this specification, "(meth)acrylic" means "acrylic" and its corresponding "methacrylic." Furthermore, unless otherwise specified, "~" in this specification includes the values ​​at both ends as the upper and lower limits.

[0015] <Composition for non-aqueous secondary batteries> The non-aqueous secondary battery composition of this embodiment comprises an aqueous medium and a particulate copolymer. The particulate copolymer comprises vinyl monomer units, the vinyl monomer units comprising amide group-containing monomer units and cyano group-containing monomer units, the content of the cyano group-containing monomer units being 5% to 40% by mass relative to the total amount of the particulate copolymer, and the average particle size (D1) of the particulate copolymer being 10 to 160 nm. The glass transition temperature of the particulate copolymer is 10°C or lower.

[0016] According to the non-aqueous secondary battery composition of this embodiment, it is possible to form a layer that can achieve both good adhesion between the porous film substrate and the porous layer, and suppression of separator shrinkage at high temperatures of 150°C or higher.

[0017] Typically, microporous separators for secondary batteries are provided with a layer designed to impart functions such as suppressing thermal shrinkage of the separator. Methods for forming this layer include, for example, coating the separator with a composition containing an inorganic pigment, latex, a dispersant, a thickener, and an aqueous medium. In this case, high adhesion between the separator and the layer (also called the coated layer) is required to prevent delamination. As a result of the inventors' investigations, they found that when the coating layer contains a particulate copolymer comprising amide group-containing monomer units and a predetermined amount of cyano group-containing monomer units as polar components, the average particle size of the particulate copolymer is within a predetermined range, and the glass transition temperature of the particulate copolymer is within a predetermined range, in addition to high adhesion between the substrate and the coating layer, the coating layer exhibits desired behavior at both low and high temperatures, and even at high temperatures such as 150°C, the coating layer can effectively suppress the thermal shrinkage of the separator.

[0018] (aqueous medium) The non-aqueous secondary battery composition of this embodiment includes an aqueous medium. Examples of aqueous media include water, methanol, ethanol, and isopropyl alcohol. The aqueous medium may contain dispersants, lubricants, thickeners, disinfectants, etc.

[0019] (Particulate copolymer) The non-aqueous secondary battery composition of this embodiment includes a particulate copolymer. The particulate copolymer contains vinyl monomer units.

[0020] (Vinyl monomer units) The vinyl compounds, which are raw material monomers for forming the vinyl monomer units that constitute particulate copolymers, are monomers having a vinyl group and include both vinyl compounds (CH2=CHX) and vinylidene compounds (CH2=CXY). Examples include (meth)acrylic acid esters, (meth)acrylic acid, (meth)acrylamide, aromatic vinyl compounds, and acrylonitrile. These will be described in detail below. These may be used individually or in combination of two or more.

[0021] (Amide group-containing monomer unit) Vinyl monomer units include amide group-containing monomer units. Examples of starting monomers for forming amide group-containing monomer units include compounds having an amide group, which will be described in detail below.

[0022] The amide group-containing monomer unit is not particularly limited as long as it contains an amide group, but from the viewpoint of suppressing the thermal shrinkage of the separator using the non-aqueous secondary battery composition of this embodiment, it is preferable that it contains (meth)acrylamide monomer units.

[0023] The particulate copolymer contains vinyl monomer units, and the vinyl monomer units contain amide group-containing monomer units. The content of amide group-containing monomer units is not particularly limited, but is preferably 1 to 30% by mass, more preferably 5 to 25% by mass, and even more preferably 10 to 20% by mass, relative to the total amount of the particulate copolymer. By having the content of amide group-containing monomer units within the above range, the non-aqueous secondary battery composition of this embodiment tends to have improved adhesion at room temperature and to suppress thermal shrinkage of the separator using the non-aqueous secondary battery composition of this embodiment.

[0024] Examples of raw material monomers for forming amide group-containing monomer units include (meth)acrylamide, dimethylacrylamide, diethylacrylamide, diacetoneacrylamide, hydroxyethylacrylamide, hydroxymethylacrylamide, hydroxypropylacrylamide, and hydroxybutylacrylamide. These may be used individually or in combination of two or more in any ratio. From the viewpoint of suppressing the thermal shrinkage of the separator using the non-aqueous secondary battery composition of this embodiment, it is preferable to use methacrylamide and / or acrylamide.

[0025] (Cyano group-containing monomer units) Vinyl monomer units include cyano group-containing monomer units. Examples of starting monomers for forming cyano group-containing monomer units include compounds having a cyano group, which will be described in detail below.

[0026] The particulate copolymer contains vinyl monomer units, and the vinyl monomer units contain cyano group-containing monomer units. The content of cyano group-containing monomer units is 5 to 40% by mass relative to the total amount of particulate copolymer. By having the content of cyano group-containing monomer units within the above range, the non-aqueous secondary battery composition of this embodiment tends to have improved adhesion at room temperature and suppress thermal shrinkage of separators using the non-aqueous secondary battery composition of this embodiment. In addition, the viscosity of the aqueous media dispersion containing the particulate copolymer is suppressed, which tends to improve workability in slurry compounding work. From the above viewpoint, the content of cyano group-containing monomer units is preferably 5 to 30% by mass, more preferably 10 to 25% by mass, and even more preferably 10 to 20% by mass, relative to the total amount of particulate copolymer.

[0027] The particulate copolymer contains vinyl monomer units, and the vinyl monomer units contain amide group-containing monomer units and cyano group-containing monomer units. The ratio of the content of cyano group-containing monomer units to the content of amide group-containing monomer units in the particulate copolymer is not particularly limited, but is preferably 0.1 to 4.0, more preferably 0.3 to 2.7, and even more preferably 0.5 to 2.0. By having the ratio of the content of cyano group-containing monomer units to the content of amide group-containing monomer units within the above range, the non-aqueous secondary battery composition of this embodiment tends to have improved adhesion at room temperature and to suppress thermal shrinkage of the separator using the non-aqueous secondary battery composition of this embodiment.

[0028] Examples of raw material monomers for forming cyano group-containing monomer units include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; and α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile. These may be used individually or in combination of two or more in any ratio. From the viewpoint of improving adhesion at room temperature, it is preferable to use acrylonitrile and / or methacrylonitrile.

[0029] (Other vinyl monomer units) The vinyl monomer units contained in the particulate copolymer of this embodiment may include, in addition to amide group-containing monomer units and cyano group-containing monomer units, other vinyl monomer units. Other vinyl monomer units include monomer units formed from (meth)acrylic group-containing monomers, carboxylic acid group-containing monomers, crosslinkable monomers, etc., excluding the monomers mentioned above.

[0030] ((meth)acrylic group-containing monomer unit) The vinyl monomer units contained in the particulate copolymer of this embodiment may include (meth)acrylic group-containing monomer units in addition to amide group-containing monomer units and cyano group-containing monomer units. In this specification, (meth)acrylic group-containing monomer units are defined as those excluding the amide group-containing monomer units and cyano group-containing monomer units described above.

[0031] The content of (meth)acrylic group-containing monomer units is not particularly limited, but is preferably 30 to 90% by mass, more preferably 45 to 85% by mass, and even more preferably 60 to 80% by mass, relative to the total amount of particulate copolymer. By having the content of (meth)acrylic group-containing monomer units within the above range, the non-aqueous secondary battery composition of this embodiment tends to have improved adhesion at room temperature and to suppress thermal shrinkage of the separator using the non-aqueous secondary battery composition of this embodiment.

[0032] The raw material monomers for forming (meth)acrylic group-containing monomer units are not particularly limited, but include (meth)acrylic acid ester monomers and monomers having a (meth)acrylic group and an acid component.

[0033] Examples of (meth)acrylic acid monomers include (meth)acrylic acid esters having one ethylenically unsaturated bond. In this specification, (meth)acrylic acid esters may also be referred to as (meth)acrylates. (Meth)acrylic acid esters having one ethylenically unsaturated bond are not limited to the following, but include, for example, methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-hexyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, cyclohexyl acrylate, methyl methacrylate (also referred to as methyl methacrylate in this specification), ethyl methacrylate, and propyl methacrylate. Examples include alkyl groups (meth)acrylates such as phosphate, isopropyl acrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, t-butylcyclohexyl acrylate; and aromatic ring (meth)acrylates such as benzyl acrylate, phenyl acrylate, benzyl methacrylate, and phenyl methacrylate. These (meth)acrylic acid ester monomers may be used individually or in combination of two or more in any ratio. The (meth)acrylate having an alkyl group is preferably a (meth)acrylate consisting of an alkyl group and a (meth)acryloyloxy group. The (meth)acrylate having an aromatic ring is preferably a (meth)acrylate consisting of an aromatic ring and a (meth)acryloyloxy group.

[0034] The (meth)acrylic acid ester monomer is more preferably a monomer consisting of an alkyl group having 4 or more carbon atoms and a (meth)acryloyloxy group, even more preferably a monomer consisting of an alkyl group having 6 or more carbon atoms and a (meth)acryloyloxy group, even more preferably one or more selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, and t-butylcyclohexyl acrylate, even more preferably one or more selected from the group consisting of methyl acrylate, methyl methacrylate, cyclohexyl methacrylate, butyl acrylate, butyl methacrylate, and 2-ethylhexyl acrylate, with methyl acrylate and / or butyl acrylate being particularly preferred. Using such a (meth)acrylic acid ester monomer is preferable from the viewpoint of improving polymerization stability during emulsion polymerization and improving adhesion to electrodes.

[0035] Examples of monomers having a (meth)acrylic group and an acid component include acrylic acid and methacrylic acid. One type may be used alone, or two or more types may be used in any ratio. Among these, methacrylic acid is preferred.

[0036] The content of monomer units having (meth)acrylic groups and acid components is not particularly limited, but is preferably 0.1 to 10% by mass, more preferably 0.3 to 5% by mass, and even more preferably 0.5 to 3% by mass, relative to the total amount of particulate copolymer, as this tends to improve adhesion at room temperature and suppress thermal shrinkage of separators using the non-aqueous secondary battery composition of this embodiment.

[0037] (carboxylate group-containing monomer) Examples of monomers containing a carboxylic acid group include, but are not limited to, ethylenically unsaturated monomers having a carboxyl group. In this specification, monomers containing a carboxylic acid group are also referred to as unsaturated carboxylic acids. Examples of ethylenically unsaturated monomers containing a carboxyl group include, but are not limited to, monocarboxylic acid monomers such as half-esters of itaconic acid, maleic acid, and fumaric acid; and dicarboxylic acid monomers such as itaconic acid, fumaric acid, and maleic acid. Carboxylic acid group-containing monomers can be used individually or in combination of two or more.

[0038] (Cross-linkable monomer) Examples of crosslinkable monomers include monomers having two or more radically polymerizable double bonds, and monomers having functional groups that give a self-crosslinking structure during or after polymerization. These can be used individually or in combination of two or more. The crosslinkable monomer constituting the particulate copolymer preferably includes an epoxy group-containing vinyl monomer. The epoxy group-containing vinyl monomer is a monomer having a functional group that gives a self-crosslinking structure during or after polymerization. Examples of epoxy group-containing vinyl monomers include, but are not limited to, glycidyl acrylate, glycidyl methacrylate, allyl glycidyl ether, methyl glycidyl acrylate, and methyl glycidyl methacrylate. These can be used individually or in combination of two or more.

[0039] Besides the epoxy group-containing vinyl monomers mentioned above, examples of monomers having functional groups that give a self-crosslinking structure during or after polymerization include hydroxyl group-containing vinyl monomers containing hydroxyl groups, alkoxymethyl group-containing vinyl monomers containing alkoxymethyl groups, and hydrolyzable silyl group-containing vinyl monomers containing hydrolyzable silyl groups. These can be used individually or in combination of two or more.

[0040] The crosslinkable monomer constituting the particulate copolymer preferably further includes, in addition to the epoxy group-containing vinyl monomer, at least one selected from the group consisting of a monomer having two or more radically polymerizable double bonds, an amino group-containing vinyl monomer, a hydroxyl group-containing vinyl monomer, an alkoxymethyl group-containing vinyl monomer, and a vinyl monomer having a hydrolyzable silyl group. By using the above-mentioned crosslinkable monomer, for example, when a non-aqueous secondary battery binder containing the particulate copolymer of this embodiment is used as an adhesive for electrodes or separators, it tends to have excellent adhesive properties while maintaining appropriate fluidity, thus offering superior handling.

[0041] Examples of monomers having two or more radically polymerizable double bonds include divinylbenzene and polyfunctional (meth)acrylates. Among these monomers having two or more radically polymerizable double bonds, polyfunctional (meth)acrylates are more preferred because they exhibit better resistance to electrolytes even in small amounts.

[0042] The polyfunctional (meth)acrylate may be a difunctional (meth)acrylate, a trifunctional (meth)acrylate, or a tetrafunctional (meth)acrylate. Examples of polyfunctional (meth)acrylates, but not limited to the following, include neopentyl glycol diacrylate, neopentyl glycol dimethacrylate, butanediol diacrylate, butanediol dimethacrylate, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetramethacrylate. These may be used individually or in combination of two or more. Among these, trimethylolpropane triacrylate and trimethylolpropane trimethacrylate are preferred because they exhibit better resistance to electrolytes even in small amounts.

[0043] The amino group-containing vinyl monomer is not limited to the following, but examples include N,N-methylenebisacrylamide, diacetone acrylamide, and N,N-dimethylaminoethylacrylamide.

[0044] The hydroxyl group-containing vinyl monomers are not limited to the following, but examples include hydroxyethyl (meth)acrylates such as 2-hydroxyethyl acrylate and 2-hydroxyethyl methacrylate; hydroxypropyl (meth)acrylates such as 2-hydroxypropyl (meth)acrylate; hydroxybutyl (meth)acrylates such as 2-hydroxybutyl (meth)acrylate and 4-hydroxybutyl (meth)acrylate; 3-chloro-2-hydroxypropyl (meth)acrylate, di-(ethylene glycol) maleate, di-(ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis(2-hydroxyethyl) maleate, and 2-hydroxyethyl methyl fumarate. These hydroxyl group-containing vinyl monomers can be used individually or in combination of two or more. Examples of the hydroxyl group-containing vinyl monomer include, in addition to the compounds described above, methylol group-containing vinyl monomers. Examples of the methylol group-containing vinyl monomer include N-methylolacrylamide, N-methylolmethacrylamide, dimethylolacrylamide, and dimethylolmethacrylamide. These can be used individually or in combination of two or more.

[0045] Examples of alkoxymethyl group-containing vinyl monomers include, but are not limited to, N-methoxymethylacrylamide, N-methoxymethylmethacrylamide, N-butoxymethylacrylamide, and N-butoxymethylmethacrylamide. These can be used individually or in combination of two or more.

[0046] Examples of hydrolyzable silyl group-containing vinyl monomers include, but are not limited to, vinylsilane, vinyltrimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropyltriethoxysilane, 3-(methacryloyloxy)propyltrimethoxysilane, etc. These can be used individually or in combination of two or more.

[0047] The content of monomer units formed by the crosslinkable monomer described above is usually 0.1 parts by mass or more and 30 parts by mass or less, preferably 0.3 parts by mass or more and 10 parts by mass or less, more preferably 0.5 parts by mass or more and 5 parts by mass or less, and even more preferably 0.7 parts by mass or more and 2 parts by mass or less, per 100 parts by mass of the particulate copolymer. By setting the content of monomer units formed by crosslinkable monomers within the above range, a layer containing particulate copolymer provided on the separator of a secondary battery tends to further suppress the thermal shrinkage of the separator.

[0048] (Crosslinkable monomer containing two or more vinyl groups) Among the crosslinkable monomers described above, it is preferable to use a crosslinkable monomer containing two or more vinyl groups. The content of the crosslinkable monomer units containing two or more vinyl groups is preferably 0.1 to 5% by mass, more preferably 0.3 to 3% by mass, and even more preferably 0.5 to 2% by mass, relative to the total amount of the particulate copolymer. By setting the content of the crosslinkable monomer units containing two or more vinyl groups to 0.1% by mass or more relative to the total amount of the particulate copolymer, the electrolyte resistance of the particulate copolymer can be improved. Furthermore, by setting it to 5% by mass or less, the non-aqueous secondary battery composition of this embodiment tends to have improved adhesion at room temperature and to more effectively suppress the shrinkage of the separator even at high temperatures.

[0049] (Form of particulate copolymer) The particulate copolymer of this embodiment may, for example, have the form of a dispersion in which particulate copolymers (also called latex particles) containing the above-mentioned various monomers as monomer units are dispersed in an aqueous medium. Therefore, one embodiment of the non-aqueous secondary battery composition of this embodiment is an aqueous media dispersion containing a particulate copolymer. The solid content concentration in the aqueous media dispersion is not particularly limited, but is usually 10% by mass or more and 60% by mass or less, preferably 30% by mass or more and 50% by mass or less. Setting the solid content concentration to 30% by mass or more increases the degree of freedom in slurry design, such as improving dispersion stability through high solid differentiation of the slurry. Setting it to 50% by mass or less suppresses the viscosity of the aqueous media dispersion containing particulate copolymer, improving workability in slurry compounding operations.

[0050] (Glass transition temperature of particulate copolymers) The glass transition temperature of the particulate copolymer contained in the non-aqueous secondary battery composition of this embodiment is 10°C or lower. The upper limit of the glass transition temperature is preferably 0°C or lower, more preferably -5°C or lower, and even more preferably -10°C or lower. The lower limit of the glass transition temperature is not particularly limited, but is preferably -50°C or higher, more preferably -40°C or higher, and even more preferably -30°C or higher. When the glass transition temperature is within the above range, the slurry for the porous layer of a lithium-ion secondary battery containing the non-aqueous secondary battery composition can be easily coated onto the separator of the secondary battery, and the adhesion between the substrate and the coated layer tends to be improved. The glass transition temperature can be controlled, for example, by adjusting the type and content of monomer units constituting the particulate copolymer. Specifically, it can be controlled to the above-mentioned numerical range by adjusting the content of cyano group-containing monomer units and / or (meth)acrylic group-containing monomer units. The glass transition temperature of particulate copolymers can be measured by the method described in the examples below.

[0051] (Average particle size of particulate copolymer) The average particle size (D1) of the particulate copolymer contained in the non-aqueous secondary battery composition of this embodiment is 10 to 160 nm. The average particle size (D1) of the particulate copolymer refers to the volume average particle size Dv. The average particle size (D1) is preferably 30 to 150 nm, more preferably 50 to 140 nm, and even more preferably 70 to 130 nm. When the average particle size (D1) of the particulate copolymer is within the above range, when the slurry for the porous layer of a lithium-ion secondary battery containing the non-aqueous secondary battery composition of this embodiment is adhered to the separator, it is possible to leave sufficient appropriate voids, maintain the function of the separator in allowing ions in the electrolyte to pass through, and furthermore, improve the adhesion between the substrate and the coating layer. The volume-average particle diameter Dv and number-average particle diameter Dn of the particulate copolymer can be controlled, for example, by manufacturing it using seed latex and surfactant in desired proportions. Generally, increasing the amount of seed latex and surfactant tends to decrease the volume-average particle diameter Dv and number-average particle diameter Dn. The volume-average particle diameter Dv and the number-average particle diameter Dn can be measured by the method described in the examples below.

[0052] In the non-aqueous secondary battery composition of this embodiment, the ratio Dv / Dn of the volume-average particle diameter Dv to the number-average particle diameter Dn of the particulate copolymer is preferably 1 or more and 2.5 or less, more preferably 1 or more and 2 or less, and even more preferably 1 or more and 1.5 or less. The ratio Dv / Dn of the volume-average particle diameter Dv to the number-average particle diameter Dn is an indicator of the particle size distribution of the particulate copolymer. By setting it to 2.5 or less, a dispersion with a narrow particle size distribution without coarse particles can be obtained, resulting in a uniform structure when used as a coating layer, achieving high strength even at high temperatures, and tending to suppress thermal shrinkage of the separator. By improving the dispersion stability of particulate copolymers in an aqueous medium during or after polymerization, the particle size distribution can be narrowed and Dv / Dn can be controlled to the above numerical range. One method for improving dispersion stability is to add a surfactant to the aqueous medium during or after polymerization to increase the steric and electronic repulsion between particulate copolymers. The volume-average particle diameter Dv and the number-average particle diameter Dn can be measured by the method described in the examples below.

[0053] (Method for manufacturing particulate copolymers) The particulate copolymer used in the non-aqueous secondary battery composition of this embodiment can be produced by known polymerization methods. Suitable polymerization methods include, for example, solution polymerization, emulsion polymerization, and bulk polymerization.

[0054] To obtain particulate copolymers as dispersions, emulsion polymerization is preferred as the polymerization method. The emulsion polymerization method is not particularly limited, and conventionally known methods can be used. Examples of emulsion polymerization methods include polymerizing monomers in an aqueous medium in a dispersion system in which amide group-containing monomers, cyano group-containing monomers, (meth)acrylic group-containing monomers, carboxylic acid group-containing monomers, and crosslinkable monomers are used as basic components, as well as radical polymerization initiators, surfactants, and other additive components (e.g., molecular weight modifiers) as needed. During polymerization, various methods can be used as needed, such as keeping the composition of the monomers supplied to the reaction system constant throughout the polymerization process, or sequentially or continuously changing the composition of the supplied monomers during the polymerization process to alter the composition of the particles in the resulting resin dispersion. When particulate copolymers are obtained by emulsion polymerization, for example, the obtained particulate copolymer may be in the form of an aqueous dispersion (latex) containing water and the particulate copolymer dispersed in the water.

[0055] The compounds described above can be used as amide group-containing monomers, cyano group-containing monomers, (meth)acrylic group-containing monomers, carboxylic acid group-containing monomers, and crosslinkable monomers. Radical polymerization initiators initiate the addition polymerization of monomers by radical decomposition using heat or reducing substances. Either inorganic or organic initiators can be used as radical polymerization initiators. As the radical polymerization initiator, a water-soluble or oil-soluble polymerization initiator can be used.

[0056] Examples of water-soluble polymerization initiators include peroxodisulfates, peroxides, water-soluble azobis compounds, and redox systems of peroxides and reducing agents. Examples of peroxodisulfates include ammonium peroxodisulfate (ammonium persulfate), potassium peroxodisulfate (KPS), sodium peroxodisulfate (NPS), and ammonium peroxodisulfate (APS). Examples of peroxides include hydrogen peroxide, t-butyl hydroperoxide, t-butyl peroxymaleic acid, succinic acid peroxide, and benzoyl peroxide. Examples of water-soluble azobis compounds include 2,2-azobis(N-hydroxyethyl isobutylamide), 2,2-azobis(2-amidinopropane)hydrogen chloride, and 4,4-azobis(4-cyanopentanoic acid). Examples of peroxide-reducing agent redox systems include those in which the above-mentioned peroxide is combined with one or more reducing agents such as sodium sulfooxylate formaldehyde, sodium bisulfite, sodium thiosulfate, sodium hydroxymethanesulfinate, L-ascorbic acid and its salts, cuprous salts, and ferrous salts.

[0057] The radical polymerization initiator can preferably be used in an amount of 0.05 to 0.4 parts by mass per 100 parts by mass of the total monomer amount.

[0058] Surfactants form micelles in an aqueous medium, providing a polymerization site for polymerized monomers, and also impart dispersion stability by adsorbing onto the surface of particulate copolymers. Examples of surfactant ionic species include nonionic, anionic, and cationic surfactants, but from the viewpoint of dispersion stability, it is preferable to have nonionic, anionic, or both. Surfactants may have radically polymerizable unsaturated double bonds (e.g., vinyl groups) in their molecular structure. Surfactants having radically polymerizable unsaturated double bonds in their molecular structure will be referred to as reactive surfactants below.

[0059] Nonionic surfactants, which are nonreactive surfactants, include, but are not limited to, nonreactive polyoxyethylene alkyl ethers, polyoxyalkylene alkyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyethylene distyrenated phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid esters, glycerin fatty acid esters, polyoxyethylene fatty acid esters, polyoxyethylene alkylamines, alkyl alkanolamides, and polyoxyethylene alkylphenyl ethers.

[0060] Examples of non-reactive anionic surfactants include, but are not limited to, non-reactive alkyl sulfates, polyoxyethylene alkyl ether sulfates, alkylbenzene sulfons, alkylnaphthalene sulfons, alkyl sulfosuccinates, alkyldiphenyl ether disulfons, naphthalene sulfonic acid formalin condensates, polyoxyethylene polycyclic phenyl ether sulfates, polyoxyethylene distyrenated phenyl ether sulfates, fatty acid salts, alkyl phosphates, and polyoxyethylene alkylphenyl ether sulfates.

[0061] The reactive surfactants, specifically anionic reactive surfactants, are not limited to the following, but are ethylenically unsaturated monomers having a sulfonic acid group, a sulfonate group, or a sulfate ester group and salts thereof, with compounds having a sulfonic acid group or a group that is an ammonium salt or alkali metal salt thereof (ammonium sulfonate group or alkali metal sulfonate group). Examples of such anionic reactive surfactants include, but are not limited to, alkylallyl sulfosuccinates (e.g., "Eleminol® JS-2" and "Eleminol® JS-5" manufactured by Sanyo Chemical Industries; "Latemul® S-120", "Latemul® S-180A", and "Latemul® S-180" manufactured by Kao Corporation); polyoxyethylene alkylpropenylphenyl ether sulfates (e.g., "Aqualon® SR-10" and "Aqualon® SR-1025" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.); ammonium=α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (e.g., "Aqualon® KH-1025" manufactured by Daiichi Kogyo Seiyaku Co., Ltd., and ether sulfate type ammonium salts (e.g., "Adekaria Soap® SR1025" manufactured by ADEKA Corporation)).

[0062] Examples of nonionic reactive surfactants, which are reactive surfactants, include, but are not limited to, α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxypolyoxyethylene (for example, ADEKA Corporation's "Adekaria Soap NE-20", "Adekaria Soap NE-30", "Adekaria Soap (registered trademark) NE-40", etc.); and polyoxyethylene alkylpropenylphenyl ether (for example, Daiichi Kogyo Seiyaku Co., Ltd.'s "Aqualon (registered trademark) RN-10", "Aqualon (registered trademark) RN-20", "Aqualon (registered trademark) RN-30", "Aqualon (registered trademark) RN-50", etc.).

[0063] The surfactant used in the polymerization process of the particulate copolymer preferably includes a reactive surfactant. The reactive surfactant may be used alone or in combination of two or more types. The particulate copolymer contained in the binder for non-aqueous secondary batteries of this embodiment preferably has vinyl monomer units and monomer units derived from a reactive surfactant having a functional group copolymerizable with vinyl groups. Therefore, it is preferable to use a reactive surfactant that exhibits excellent copolymerization with vinyl compounds. From this viewpoint, for example, polyoxyethylene alkylpropenylphenyl ether sulfate salts (e.g., "Aqualon® SR-1025" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) are preferred, and it is also preferable to use ammonium=α-sulfonato-ω-1-(allyloxymethyl)alkyloxypolyoxyethylene (e.g., "Aqualon KH-1025" manufactured by Daiichi Kogyo Seiyaku Co., Ltd.). These are suitably used because the steric repulsion of the polyoxyethylene group and the electronic repulsion due to the anionic nature of the sulfonic acid ester group are effective in improving the stability of the particulate copolymer during and / or after polymerization.

[0064] Reactive surfactants are effective in enhancing the copolymerization of acrylamide monomers, methacrylamide monomers, and other vinyl monomers, thereby producing copolymers with a uniform compositional distribution. The presumed mechanism is as follows: First, a polymer elongation reaction begins between a portion of the methacrylamide monomer dissolved in water and a reactive surfactant. The growing polymer radicals form micelles, into which the remaining methacrylamide monomer and other vinyl monomers enter, and the copolymer grows. The above mechanism suppresses the formation of water-soluble copolymers derived from the homopolymerization of methacrylamide monomers, allowing copolymerization with other vinyl monomers to proceed. The uniformity of the copolymer composition and the suppression of water-soluble copolymer formation are important for increasing the storage modulus of the particulate copolymer and for preventing a decrease in battery performance due to clogging when the slurry is coated onto a separator. From the viewpoint of the opportunity for contact with the methacrylamide monomer in the aqueous layer, it is particularly preferable to use an anionic reactive surfactant.

[0065] Molecular weight modifiers are not limited to the following, but include, for example, halogenated hydrocarbons such as chloroform and carbon tetrachloride, mercaptans such as n-hexymercaptan, n-octylmercaptan, n-dodecylmercaptan, t-dodecylmercaptan, and thioglycolic acid, xanthogens such as dimethylxanthogen disulfide and diisopropylxanthogen disulfide, as well as terpinolene, α-methylstyrene dimer, and all other materials that can be used in ordinary emulsion polymerization. Among these, n-dodecylmercaptan is preferably used.

[0066] The amount of molecular weight adjusting agent used is preferably 5 parts by mass or less per 100 parts by mass of the total amount of monomers used when polymerizing each part.

[0067] (Viscosity of compositions for non-aqueous secondary batteries) The viscosity of the non-aqueous secondary battery composition of this embodiment is not particularly limited, but is usually 2000 mPas or less, and preferably 300 mPas or less. When the viscosity of the binder for the non-aqueous secondary battery of this embodiment is 2000 mPas or less, handling is improved, and for example, workability in slurry compounding operations is improved. Normally, the viscosity of a composition for non-aqueous secondary batteries can be reduced to any value by adding adjusting water, but at the same time, the solid content concentration decreases. Therefore, it is particularly preferable to satisfy the above viscosity range with a solid content concentration of at least 30% by mass or more.

[0068] The non-aqueous secondary battery composition of this embodiment contains particulate copolymer as particles (polymer particles) dispersed in an aqueous medium. In addition to the aqueous medium and copolymer, the aqueous medium dispersion may also contain other solvents, dispersants, lubricants, thickeners, disinfectants, etc.

[0069] (Adhesive for lithium-ion secondary batteries) The non-aqueous secondary battery composition of this embodiment is used as an adhesive for lithium-ion secondary batteries. Adhesives for lithium-ion secondary batteries are used, for example, to bond separators and electrodes. They are also used, for example, to form adhesive layers on the separators and electrodes of lithium-ion secondary batteries. In particular, separators with adhesive layers for lithium-ion secondary batteries can be manufactured by applying lithium-ion secondary battery adhesive to a separator to form an adhesive layer. For more detailed information on the structure of lithium-ion secondary batteries, please refer to, for example, Japanese Patent Publication No. 2015-41603.

[0070] (Binder for porous layers in non-aqueous secondary batteries) The non-aqueous secondary battery composition of this embodiment can be suitably used as a binder for the porous layer in a non-aqueous secondary battery. A binder for porous layers is used, for example, to form a porous layer on a separator by bonding inorganic fillers or the like by point adhesion, thereby improving the heat resistance of the separator while maintaining lithium ion permeability.

[0071] <Slurry for porous layers in lithium-ion secondary batteries> The slurry for the porous layer of the lithium-ion secondary battery of this embodiment comprises water, an inorganic filler, and the non-aqueous secondary battery composition of this embodiment.

[0072] The slurry for the porous layer of a lithium-ion secondary battery in this embodiment is a dispersion used to form a porous layer containing an inorganic filler and a particulate copolymer on the substrate by applying the slurry to, for example, the surface of a separator substrate for an energy storage device, and then drying it. The slurry for the porous layer of a lithium-ion secondary battery in this embodiment may optionally contain a conductive additive, a thickener, a non-aqueous solvent, etc.

[0073] <Porous layer of lithium-ion secondary battery> The porous layer of the lithium-ion secondary battery of this embodiment comprises an inorganic filler and the non-aqueous secondary battery composition of this embodiment.

[0074] (Inorganic filler) The slurry for the porous layer of lithium-ion secondary batteries and the inorganic filler used in the porous layer of lithium-ion secondary batteries are not particularly limited, but those having a melting point of 200°C or higher, high electrical insulation properties, and electrochemical stability within the operating range of lithium-ion secondary batteries are preferred.

[0075] Examples of inorganic fillers include, but are not limited to, oxide-based ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitride-based ceramics such as silicon nitride, titanium nitride, and boron nitride; ceramics such as silicon carbide, calcium carbonate, barium sulfate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, decite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amesite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; and glass fibers. These may be used individually or in any combination of two or more in any ratio.

[0076] Among these, from the viewpoint of improving electrochemical stability and the heat resistance of the separator, it is preferable to use aluminum oxide compounds such as alumina, aluminum hydroxide, and aluminum hydroxide oxide (AlO(OH)); and aluminum silicate compounds that do not have ion exchange ability, such as kaolinite, decite, nacrite, halloysite, and pyrophyllite, or barium sulfate.

[0077] Alumina exists in many crystalline forms, including α-alumina, β-alumina, γ-alumina, and θ-alumina, all of which can be used suitably. Among these, α-alumina is preferred from the viewpoint of thermal and chemical stability.

[0078] As the aluminum oxide compound, aluminum hydroxide oxide (AlO(OH)) is preferred. As aluminum hydroxide oxide, boehmite is more preferred from the viewpoint of preventing internal short circuits caused by the generation of lithium dendrites. By using particles mainly composed of boehmite as the inorganic filler constituting the porous layer of the lithium-ion secondary battery in this embodiment, a very lightweight porous layer of the lithium-ion secondary battery can be obtained while maintaining high permeability. Furthermore, even when a thinner porous layer of the lithium-ion secondary battery is formed, thermal shrinkage of the separator at high temperatures is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite, which can reduce ionic impurities that adversely affect the characteristics of electrochemical devices, is even more preferred.

[0079] As an aluminum silicate compound that does not have ion exchange capacity, kaolin, which is mainly composed of kaolin minerals, is more preferred because it is inexpensive and readily available. Known forms of kaolin include wet kaolin and calcined kaolin, which is obtained by calcining wet kaolin. In this embodiment, calcined kaolin is even more preferred. Calcined kaolin tends to have superior electrochemical stability because crystal water is released during the calcination process, and impurities are also removed.

[0080] (Average particle size of inorganic fillers) The average particle size (D2) of the inorganic filler used in the porous layer of a lithium-ion secondary battery is not particularly limited, but is preferably 100 to 300 nm, more preferably 150 to 290 nm, and even more preferably 200 to 280 nm. Setting the average particle size of the inorganic filler within the above range is preferable from the viewpoint of suppressing thermal shrinkage of the separator at high temperatures, even when the thickness of the porous layer is thin (for example, 2.5 μm or less). As a method for adjusting the average particle size and distribution of the inorganic filler, for example, a method of reducing the particle size by crushing the inorganic filler using an appropriate grinding device such as a ball mill, bead mill, or jet mill. The average particle size of inorganic fillers is expressed as the volume-based D50 particle size. The 50% cumulative diameter D50, obtained from the particle size distribution measurement, is measured using a particle size analyzer based on light scattering (LEED & NORTHRUP, product name "MICROTRAC UPA150"), and this is taken as the average particle size.

[0081] The ratio (D2 / D1) of the average particle diameter (D2) of the inorganic filler to the average particle diameter (D1) of the particulate copolymer is not particularly limited, but from the viewpoint of improving adhesion at room temperature and suppressing thermal shrinkage of the separator using the non-aqueous secondary battery composition of this embodiment, it is preferably 2.00 to 4.00, more preferably 2.00 to 3.50, and even more preferably 2.00 to 3.00.

[0082] Examples of inorganic filler shapes include plate-like, flaky, needle-like, columnar, spherical, polyhedral, and lumpy forms. Multiple types of inorganic fillers having these shapes may be used in combination.

[0083] The proportion of inorganic filler in the porous layer of the lithium-ion secondary battery of this embodiment can be appropriately determined from the viewpoint of the binding properties of the inorganic filler, the permeability of the separator, and the heat resistance. The proportion of inorganic filler in the porous layer of the lithium-ion secondary battery is preferably 20 parts by mass or more and less than 100 parts by mass, more preferably 50 parts by mass or more and 99.99 parts by mass or less, even more preferably 80 parts by mass or more and 99.9 parts by mass or less, and even more preferably 90 parts by mass or more and 99.5 parts by mass or less, when the total amount of inorganic filler and particulate copolymer is 100 parts by mass.

[0084] In this embodiment, the thickness of the porous layer of the lithium-ion secondary battery is preferably 0.8 μm or more, more preferably 1.0 μm or more, and even more preferably 1.2 μm or more, from the viewpoint of improving heat resistance and insulation properties. From the viewpoint of increasing battery capacity and improving permeability, it is preferably 2.5 μm or less, more preferably 2.3 μm or less, and even more preferably 2.0 μm or less. The thickness of the porous layer can be measured by observing a cross-section of the porous layer using a scanning electron microscope (SEM, model JSM-6390LV, manufactured by JEOL Ltd.).

[0085] The layer density of the porous layer in the lithium-ion secondary battery of this embodiment is 0.5 g / cm³. 3 More than 3.0g / cm 3 Preferably, it is 1.0 g / cm³. 3 More than 2.5g / cm 3 The following is more preferable: The layer density of the porous layer of the lithium-ion secondary battery in this embodiment is 0.5 g / cm³. 3 As a result of the above, the thermal shrinkage rate at high temperatures tends to be good. The layer density of the porous layer of the lithium-ion secondary battery in this embodiment is 3.0 g / cm³. 3 The following factors tend to reduce air permeability.

[0086] One method for forming the porous layer of the lithium-ion secondary battery in this embodiment is to coat at least one side of a porous substrate constituting the separator with a coating solution containing an inorganic filler and the non-aqueous secondary battery binder of this embodiment. In this case, the coating solution may contain solvents, dispersants, thickeners, etc., to improve dispersion stability, coating properties, and storage properties.

[0087] <Separator for lithium-ion secondary batteries> The separator for lithium-ion secondary batteries in this embodiment (separator) includes the porous layer for lithium-ion secondary batteries in this embodiment. The separator may include a porous substrate and a porous layer disposed on at least a portion of at least one side of the porous substrate. The porous layer is the porous layer of the lithium-ion secondary battery of this embodiment and contains the particulate copolymer described above. This separator may consist only of a porous substrate and the porous layer of the lithium-ion secondary battery of this embodiment, or it may further have an adhesive layer for contacting the electrodes.

[0088] When a separator for a lithium-ion secondary battery has a porous layer for the lithium-ion secondary battery, the porous layer is arranged on one or both sides of the porous substrate of the separator.

[0089] Preferred embodiments of each component constituting the separator and the method for manufacturing the separator will be described in detail below.

[0090] (Porous base material) A porous substrate is a substrate having voids or cavities inside, and the porous substrate itself can be one that has been conventionally used as a separator in secondary batteries. As a porous substrate, a polyolefin microporous film containing a polyolefin resin as the main component is preferred from the viewpoint of having excellent coating properties when forming a porous layer through a coating process, and from the viewpoint of making the separator film thickness thinner and increasing the active material ratio in energy storage devices such as batteries to increase the capacity per unit volume. Here, "contains as the main component" means containing more than 50% by mass, preferably 75% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more, and may also be 100% by mass.

[0091] Surface treatment of the polyolefin microporous film is preferable because it facilitates the subsequent application of the coating liquid and improves the adhesion between the polyolefin microporous film and the porous layer. Examples of surface treatment methods include corona discharge treatment, plasma treatment, mechanical roughening, solvent treatment, acid treatment, and ultraviolet oxidation.

[0092] (Method for arranging the porous layer of a lithium-ion secondary battery containing inorganic fillers) The lithium-ion secondary battery porous layer of this embodiment can be placed on a porous substrate by coating at least one side of the porous substrate with a coating solution containing, for example, an inorganic filler, a particulate copolymer, and additional components such as a solvent (e.g., water) and a dispersant as needed. The particulate copolymer may be synthesized by emulsion polymerization, and the resulting emulsion may be used directly as a coating solution. The coating solution preferably contains a poor solvent for particulate copolymers, such as water or a mixed solvent of water and a water-soluble organic medium (e.g., methanol or ethanol).

[0093] The method for applying the coating liquid to the porous substrate of the separator is not particularly limited as long as the required layer thickness and coating area can be achieved. Examples of coating methods include gravure coating, small-diameter gravure coating, reverse roll coating, transfer roll coating, kiss coating, dip coating, knife coating, air doctor coating, blade coating, rod coating, squeeze coating, cast coating, die coating, screen printing, spray coating, and inkjet coating. Gravure coating is particularly preferred due to its high degree of freedom in coating shape.

[0094] The method for removing the solvent from the coating film after coating is not limited as long as it does not adversely affect the porous substrate and the porous layer of the lithium-ion secondary battery. Examples include drying at a temperature below the melting point of the substrate while fixing the substrate, and drying under reduced pressure at low temperatures.

[0095] The method for removing the solvent from the coating film after coating is not particularly limited, as long as it does not adversely affect the porous substrate and the porous layer of the lithium-ion secondary battery. Examples include drying the polyolefin porous substrate at a temperature below its melting point while it is fixed, drying under reduced pressure at a low temperature, and immersing the particulate copolymer in a poor solvent to solidify the particulate copolymer into particles while simultaneously extracting the solvent.

[0096] <Lithium-ion rechargeable battery> The lithium-ion secondary battery of this embodiment includes the lithium-ion secondary battery separator of this embodiment. The lithium-ion secondary battery of this embodiment may have the same configuration as conventionally known lithium-ion secondary batteries, except for the inclusion of the separator of this embodiment, as described in, for example, Japanese Patent Application Publication No. 2018-92701.

[0097] The particulate copolymer used in the binder for non-aqueous secondary batteries of this embodiment can be included in the porous layer on the separator, and the film including the separator and the porous layer is called a coated film. The thermal shrinkage rate of the coating film at 150°C is not particularly limited, but is preferably 0% or more and less than 40% for both MD and TD, more preferably 0% or more and 35%, and even more preferably 0% or more and 30%. By having a thermal shrinkage rate of 30% or less at 150°C in both MD and TD directions, it is possible to prevent the separator film from breaking even when the battery overheats abnormally, suppress contact between the positive and negative electrodes, and tend to result in better safety performance. [Examples]

[0098] The embodiment will be described in more detail below with reference to examples, but the embodiment is not limited in any way by these examples. Various physical properties were measured and evaluated using the following measurement and evaluation methods.

[0099] [Solid content concentration] Approximately 1 g of the aqueous dispersion of the particulate copolymer obtained in the examples and comparative examples described later was accurately weighed onto an aluminum dish, and the mass of the aqueous dispersion weighed at this time (g) was denoted as a. It was then dried in a hot air dryer at 130°C for 1 hour, and the dry mass of the copolymer after drying (g) was denoted as b. The solid content concentration was calculated using the following formula. Solid content concentration (%)=b / a×100

[0100] [pH of aqueous dispersion of particulate copolymer] The electrodes of a pH meter (glass electrode type hydrogen ion concentration indicator, manufactured by Toa DDK Corporation) were immersed in an aqueous dispersion of a particulate copolymer with a solid content of approximately 40%, and the displayed value was read.

[0101] [Glass transition temperature of particulate copolymers] An appropriate amount of the aqueous dispersion (solid content concentration 38-42%, pH 8.0) containing the particulate copolymer obtained in the examples and comparative examples described later was placed in an aluminum dish and dried in a hot air dryer at 130°C for 60 minutes. Approximately 17 mg of the dried film was packed into an aluminum container for measurement, and DSC and DDSC curves were obtained under a nitrogen atmosphere using a DSC measuring device (Shimadzu Corporation, model number: DSC6220). The measurements were performed using the following program. (First stage heating program) The temperature started at 70°C and increased at a rate of 15°C per minute. After reaching 110°C, it was maintained for 5 minutes. (Second stage cooling program) The temperature was lowered from 110°C at a rate of 30°C per minute. After reaching -50°C, it was maintained at that temperature for 4 minutes. (3rd stage heating program) The temperature was increased from -50°C to 130°C at a rate of 15°C per minute. DSC and DDSC data were acquired during this third stage of temperature increase. The glass transition temperature (Tg) was defined as the intersection point of a straight line extending the baseline of the obtained DSC curve towards the higher temperature side and the tangent line at the inflection point.

[0102] [Average particle size of particulate copolymer] The 50% particle size (μm) was measured using a light scattering particle size analyzer (LEED & NORTHRUP, product name "MICROTRAC UPA150") and was used as the average particle size. This yielded the average particle diameter (D1) (volume-average particle diameter (Dv)).

[0103] [Viscosity, slurry mixing workability] 100 g of an aqueous dispersion (solid content concentration 30-42%, pH 5.0) containing particulate copolymer obtained in the examples and comparative examples described later was weighed into a polypropylene bottle, and its viscosity was measured using a BM type viscometer (TV-100B, manufactured by Toki Sangyo Co., Ltd.) under conditions of a spindle rotation speed of 60 rpm (viscosity: ηi). Using these measurements, the slurry mixing workability was evaluated according to the following criteria. <Evaluation Criteria for Slurry Mixing Workability> A: ηi is less than 300 mPa·s B:ηi is between 300 mPa·s and less than 2000 mPa·s C:ηi is above 2000 mPa·s

[0104] [Adhesion (Peel Strength)] Using the aqueous dispersions of particulate copolymers obtained in the examples and comparative examples described later, and following the procedure described later (formation of coating film), a dispersion for forming a porous layer was obtained. The porous layer-forming dispersion was applied to the surface of a corona-treated polyethylene porous substrate. A drying process was then performed to form a porous layer, resulting in a coating film with a total thickness of 17 μm. This coating film was attached to a 15mm x 75mm microscope slide using double-sided tape, with the polyethylene porous substrate side facing inwards. Subsequently, a 12mm wide mending tape was applied over the porous layer, and one end of the mending tape was pulled vertically at a speed of 100mm / min. The stress at which it was peeled off was measured. Three measurements were taken, and the average value was calculated and defined as the peel strength. The peel strength value indicates superior adhesion between the polyethylene porous substrate and the porous layer, and this was evaluated according to the following criteria. <Criteria for evaluating adhesion> A:300gf / cm or more B: 150 gf / cm² or more, less than 300 gf / cm² C: Less than 150 gf / cm³

[0105] [Heat shrinkage resistance] A coating film was obtained using the aqueous dispersion of particulate copolymer obtained in the examples and comparative examples described later, and in accordance with the (formation of coating film) described later. The sample was cut to 100 mm in the MD direction and 100 mm in the TD direction, and left to stand in a 150°C oven for 1 hour. During this time, the sample was sandwiched between two sheets of paper to prevent direct contact with the hot air. After removing the sample from the oven and allowing it to cool, its length (mm) was measured, and the thermal shrinkage rate was calculated using the following formula. Measurements were taken in the MD and TD directions, and the larger value was used as the thermal shrinkage coefficient. The thermal shrinkage resistance was evaluated according to the following criteria. Thermal shrinkage rate (%) = {(100 - length after heating) / 100} × 100 <Evaluation Criteria for Heat Shrinkage Resistance> A: Heat shrinkage rate less than 3% B: Thermal shrinkage rate of 3% or more and less than 10% C: Heat shrinkage rate of 10% or more

[0106] [Example 1] (Manufacturing of particulate copolymers) In a reaction vessel equipped with a stirrer, reflux condenser, dropping tank, and thermometer, 65 parts by mass of deionized water, 0.06 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd., also referred to as "KH1025") and 0.06 parts by mass of "Adekaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation, also referred to as "SR1025") were added as surfactants. Next, the temperature inside the reaction vessel was raised to 75°C, and while maintaining the temperature at 75°C, 1.5 parts by mass of a 2% aqueous solution of ammonium persulfate (also referred to as "APS") was added. Five minutes after the addition of the ammonium persulfate aqueous solution was completed, the following emulsion was added dropwise from the dropping tank to the reaction vessel over a period of 150 minutes. The emulsified solution was prepared using the following method. As an amide group-containing monomer; Methacrylamide (also written as "MAAm") 15 parts by mass As a cyano group-containing monomer; Acrylonitrile (also written as "AN") 5 parts by mass As a monomer containing a (meth)acrylic group; Butyl acrylate (also written as "BA") 78 parts by mass Methacrylic acid (also written as "MAA") 1 part by mass As a crosslinkable monomer containing two or more vinyl groups; Trimethylolpropane triacrylate (ATMPT, a product name manufactured by Shin-Nakamura Chemical Industry Co., Ltd., also referred to as "A-TMPT") 2 parts by mass, As a reactive surfactant; 7.5 parts by mass of "Aqualon KH1025" (registered trademark, 25% aqueous solution manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) "Adekaria Soap SR1025" (registered trademark, 25% aqueous solution manufactured by ADEKA Corporation) 7.5 parts by mass, As a polymerization initiator; 0.25 parts by mass of a 2% aqueous solution of ammonium persulfate, And 83.2 parts by mass of ion-exchanged water, The mixture was prepared by mixing it in a homomixer for 5 minutes. After the emulsion was added dropwise, the temperature inside the reaction vessel was raised to 80°C and maintained for 120 minutes, then cooled to room temperature to obtain the emulsion. The resulting emulsion was adjusted to pH 5.0 using an aqueous solution of ammonium hydroxide (25% aqueous solution; also abbreviated as AW) to obtain an aqueous dispersion with a solid content of 40%. The glass transition temperature and average particle size of the particulate copolymer in the obtained aqueous dispersion were measured using the method described above. The evaluation results are shown in Table 1.

[0107] (Formation of coating film) A dispersion for forming a porous layer was prepared by uniformly dispersing 100 parts by mass (50% solid content) of aluminum hydroxide oxide particles (average particle size 250 nm), which are an inorganic filler; 3.0 parts by mass (40% solid content) of an aqueous dispersion containing a synthesized particulate copolymer, which is a resin binder; and 0.5 parts by mass (1% solid content) of polyphosphate amine salt, which is an ion-dissociable inorganic dispersant. The prepared porous layer-forming dispersion was applied to the surface of a pre-corona-treated polyethylene porous substrate using a bar coater. Subsequently, the film was dried at 60°C for 1 minute to remove water, thereby forming a porous layer with a thickness of 1.6 μm on a polyethylene porous substrate, resulting in a coating film with a total thickness of 17 μm. The thickness of the porous layer was measured by observing the cross-section of the porous layer with a scanning electron microscope (SEM, model JSM-6390LV, manufactured by JEOL Ltd.). The adhesion and thermal shrinkage properties of the obtained coating film were evaluated. The evaluation results are listed in Table 1 below. In addition, tripolyphosphate was used as the "polyphosphate" in this study.

[0108] [Examples 2-13, Comparative Examples 1-5] Emulsion polymerization was carried out in the same manner as in Example 1, except that the monomers for forming the particulate copolymer were in the formulations shown in Tables 1 to 6 below, to obtain an aqueous dispersion of the particulate copolymer. Note that in Tables 1 and 2, AAm is acrylamide, MAN is methacrylonitrile, MMA is methyl acrylate. These refer to the respective things. Furthermore, a porous layer was prepared in the same manner as in Example 1, according to the above (formation of coating film). For the particulate copolymer in the obtained aqueous dispersion, the glass transition temperature and average particle size were measured using the method described above, and its adhesion, thermal shrinkage, solution stability, and slurry mixing workability were evaluated. The evaluation results are shown in Tables 1 and 2.

[0109] [Table 1]

[0110] [Table 2]

[0111] Tables 1 and 2 show that, comparing Examples 1 to 13 with Comparative Examples 1 to 5, a non-aqueous secondary battery composition containing a particulate copolymer comprising amide group-containing monomer units and a predetermined amount of cyano group-containing monomer units, wherein the average particle size (D1) of the particulate copolymer is 10 to 160 nm and the glass transition temperature is 10°C or lower, is capable of forming a layer that achieves both good adhesion between the porous film substrate and the porous layer, and suppression of separator shrinkage at high temperatures of 150°C or higher. [Industrial applicability]

[0112] The non-aqueous binder for secondary batteries of the present invention has industrial potential as a material for separators in secondary batteries.

Claims

1. A composition for a non-aqueous secondary battery comprising an aqueous medium and a particulate copolymer, The particulate copolymer contains vinyl monomer units, The vinyl monomer unit comprises an amide group-containing monomer unit and a cyano group-containing monomer unit. The content of the cyano group-containing monomer units is 5 to 40% by mass relative to the total amount of the particulate copolymer. The average particle size (D1) of the particulate copolymer is 10 to 160 nm. The glass transition temperature of the particulate copolymer is 10°C or lower. Composition for non-aqueous secondary batteries.

2. The amide group-containing monomer unit includes a (meth)acrylamide monomer unit. The content of the (meth)acrylamide monomer units is 1 to 30% by mass relative to the total amount of the particulate copolymer. The composition for a non-aqueous secondary battery according to claim 1.

3. The particulate copolymer further comprises (meth)acrylic group-containing monomer units. The composition for a non-aqueous secondary battery according to claim 1.

4. Water and inorganic fillers, A composition for a non-aqueous secondary battery according to any one of claims 1 to 3, comprising Slurry for the porous layer of lithium-ion secondary batteries.

5. The ratio (D2 / D1) of the average particle size (D1) of the inorganic filler to the average particle size (D2) of the particulate copolymer is 2.00 to 4.

00. The slurry for the porous layer of a lithium-ion secondary battery according to claim 4.

6. The average particle size (D2) of the inorganic filler is 100 to 300 nm. The slurry for the porous layer of a lithium-ion secondary battery according to claim 4.

7. The slurry for the porous layer of a lithium-ion secondary battery described in claim 4 comprises Porous layer of lithium-ion secondary battery.

8. The thickness of the porous layer in the lithium-ion secondary battery is 0.8 to 2.5 μm. The porous layer of the lithium-ion secondary battery according to claim 7.

9. Substrate and A lithium-ion secondary battery comprising the porous layer described in claim 7, Separator for lithium-ion secondary batteries.

10. A separator for a lithium-ion secondary battery as described in claim 9, Lithium-ion rechargeable battery.

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