WO2021131813A1 - Copolymer for electrode binder, electrode binder resin composition, and electrode for non-aqueous secondary battery - Google Patents

Abstract

Provided are a copolymer for an electrode binder and an electrode binder resin composition, which are suitable for obtaining an electrode binder having good electrolyte resistance, an electrode containing an electrode active material layer having high peel strength against a current collector, and a non-aqueous secondary battery exhibiting good charge/discharge cycle characteristics. The copolymer for an electrode binder comprises: a structural unit derived from a monomer (a1) such as (meth)acrylic acid alkyl ester; a structural unit derived from a monomer (a2) composed of at least one selected from the group consisting of a carboxylic acid and a salt thereof, the carboxylic acid containing one ethylenically unsaturated bond in a molecule; a structural unit derived from an internal crosslinking agent (a3) such as a compound having at least two ethylenically unsaturated bonds in a molecule; and a structural unit derived from a polymerizable surfactant (a4) such as a compound represented by formula (1).

Description

Copolymers for electrode binders, electrode binder resin compositions, and non-aqueous secondary battery electrodes

The present invention relates to a copolymer for an electrode binder, an electrode binder resin composition, and a non-aqueous secondary battery electrode.
The present application claims priority based on Japanese Patent Application No. 2019-239174 filed in Japan on December 27, 2019, the contents of which are incorporated herein by reference.

A non-aqueous secondary battery has a configuration including a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and an electrolytic solution, and ions move between the positive electrode and the negative electrode. It is a secondary battery in which the battery is charged and discharged.

A typical example is a lithium ion secondary battery as a non-aqueous secondary battery. Non-aqueous secondary batteries are used as power sources for notebook computers, mobile phones, power tools, and electronic / communication devices in terms of miniaturization and weight reduction. Recently, it has also been used for electric vehicles and hybrid vehicles from the viewpoint of application to environmental vehicles. Under these circumstances, there is a strong demand for higher output, higher capacity, longer life, etc. of non-aqueous secondary batteries.

The binder used for the positive electrode and the negative electrode has a role of binding the active materials to each other and the active material to the current collector. Water dispersion binders are being developed to improve the capacity of non-aqueous secondary batteries and protect the working environment. For example, a styrene-butadiene rubber (SBR) -based aqueous dispersion using carboxymethyl cellulose (CMC) as a thickener is known.

In Patent Documents 1 to 5, an ethylenically unsaturated monomer containing styrene, an ethylenically unsaturated carboxylic acid ester, an ethylenically unsaturated carboxylic acid and an internal cross-linking agent is emulsified and polymerized in the presence of a surfactant. The resulting non-aqueous secondary battery electrode binder has been proposed.

Japanese Patent No. 5211794 Japanese Patent No. 5701519 Japanese Patent No. 5991321 JP-A-2017-174804 Chinese Patent Application Publication No. 1048862612

However, when the binders described in Patent Documents 1 to 5 are used, there is room for improvement in charge / discharge cycle characteristics.

INDUSTRIAL APPLICABILITY According to the present invention, an electrode binder having good electrolyte resistance can be obtained, an electrode having an electrode active material layer having high peeling strength against a current collector can be obtained, and a non-aqueous secondary battery having good charge / discharge cycle characteristics can be obtained. An object of the present invention is to provide a obtained copolymer for an electrode binder and an electrode binder resin composition. Further, the present invention includes an electrode binder having good electrolyte resistance, has an electrode active material layer having high peeling strength against a current collector, and can obtain a non-aqueous secondary battery having good charge / discharge cycle characteristics. It is an object of the present invention to provide an aqueous secondary battery electrode.

That is, the configuration of the present invention is as follows [1] to [15].
[1] Selected from the group consisting of a (meth) acrylic acid alkyl ester having one ethylenically unsaturated bond contained in the molecule and a hydrocarbon compound having one ethylenically unsaturated bond contained in the molecule. From at least one selected from the group consisting of a structural unit derived from a monomer (a1) consisting of at least one kind, a carboxylic acid having one ethylenically unsaturated bond contained in the molecule, and a salt thereof. A structural unit derived from the monomer (a2)
A structural unit derived from an internal cross-linking agent (a3) consisting of at least one selected from the group consisting of compounds having two or more ethylenically unsaturated bonds in one molecule, and
A structural unit derived from a polymerizable surfactant (a4) consisting of at least one selected from the group consisting of compounds represented by the following formula (1), and
It is a copolymer containing
The structural unit derived from the monomer (a1) is contained in an amount of 50% by mass or more and 98% by mass or less.
The structural unit derived from the monomer (a2) is contained in an amount of 1.0% by mass or more and 15% by mass or less, and the structural unit derived from the internal cross-linking agent (a3) is contained in an amount of 0.020% by mass or more and 10% by mass or less. Including
A copolymer for an electrode binder, which comprises 0.010% by mass or more and 10% by mass or less of a structural unit derived from the polymerizable surfactant (a4).

In the formula (1), X is a hydrogen atom or SO ₃ NH ₄ , m is an integer of 1 or more and 4 or less, and n is an integer of 5 or more and 40 or less.
[2] The monomer (a1) has a high Tg monomer (a11) having a homopolymer glass transition point Tg of 5 ° C. or higher and a low homopolymer glass transition point Tg of −5 ° C. or lower. The copolymer for an electrode binder according to [1], which contains a Tg monomer (a12).
[3] The mass ratio of the content of the structural unit derived from the high Tg monomer (a11) to the content of the structural unit derived from the low Tg monomer (a12) is 30:70 to 70. : 30. The copolymer for an electrode binder according to [2].
[4] The copolymer for an electrode binder according to any one of [1] to [3], wherein the content of the structural unit derived from the monomer (a1) is 70% by mass or more and 97% by mass or less.
[5] The electrode binder according to any one of [1] to [4], wherein at least a part of the structural unit derived from the monomer (a2) forms a salt of a carboxy group and a basic substance. For copolymers.
[6] The copolymer weight for an electrode binder according to any one of [1] to [5], wherein the content of the structural unit derived from the monomer (a2) is 2.0% by mass or more and 10% by mass or less. Combined.
[7] The electrode binder according to any one of [1] to [6], wherein the content of the structural unit derived from the internal cross-linking agent (a3) is 0.50% by mass or more and 5.0% by mass or less. Copolymer.
[8] In the formula (1), X is the copolymer for an electrode binder according to any one of [1] to [7], which is _{SO 3} NH _4.
[9] The copolymer for an electrode binder according to any one of [1] to [8], wherein n is 8 or more and 25 or less in the formula (1).
[10] The electrode according to any one of [1] to [9], wherein the content of the structural unit derived from the polymerizable surfactant (a4) is 0.10% by mass or more and 3.0% by mass or less. Copolymer for binder.
[11] Further, ethylenically unsaturated, which does not correspond to any of the monomer (a1), the monomer (a2), the internal cross-linking agent (a3), and the polymerizable surfactant (a4). The copolymer for an electrode binder according to any one of [1] to [10], which comprises a structural unit derived from a sulfonic acid having a bond or a salt thereof.
[12] An electrode binder resin composition in which the copolymer for an electrode binder according to any one of [1] to [11] is dispersed in an aqueous medium (B).
[13] An electrode slurry in which the copolymer for an electrode binder according to any one of [1] to [11] and an electrode active material are dispersed in an aqueous medium.
[14] A non-aqueous secondary in which the electrode active material layer containing the electrode binder copolymer and the electrode active material according to any one of [1] to [11] is formed on a current collector made of a metal sheet. Battery electrode.
[15] A non-aqueous secondary battery containing the copolymer for an electrode binder according to any one of [1] to [11] in at least one of a positive electrode and a negative electrode.

According to the present invention, an electrode binder having good electrolyte resistance can be obtained, an electrode having an electrode active material layer having high peeling strength against a current collector can be obtained, and a non-aqueous secondary having good charge / discharge cycle characteristics can be obtained. A copolymer for an electrode binder from which a battery can be obtained and an electrode binder resin composition can be provided. Further, according to the present invention, a non-aqueous secondary battery containing an electrode binder having good electrolyte resistance, having an electrode active material layer having high peeling strength against a current collector, and having good charge / discharge cycle characteristics can be obtained. Non-aqueous secondary battery electrodes can be provided.

"(Meta) acrylic" is a general term for acrylic and methacryl, and "(meth) acrylate" is a general term for acrylate and methacrylate.

The "nonvolatile component" is a component remaining after weighing 1 g of the composition on an aluminum dish having a diameter of 5 cm and drying it at 105 ° C. for 1 hour while circulating air in a dryer at 1 atm (1013 hPa). The form of the composition includes, but is not limited to, a solution, a dispersion, and a slurry.

The "nonvolatile content concentration" is the mass ratio (mass%) of the non-volatile content after drying under the above conditions with respect to the mass (1 g) of the composition before drying.

"Ethylene unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerization unless otherwise specified.

In the polymer of a compound having an ethylenically unsaturated bond, the structural unit derived from the compound having an ethylenically unsaturated bond is the chemical structure of the portion other than the ethylenically unsaturated bond of the compound and its structure in the polymer. It is assumed that the chemical structure of the part other than the part forming the main chain of the unit is the same. For example, a structural unit derived from acrylic acid has a COOH structure in a portion other than the main chain as a polymer.

If the chemical structure of the monomer and the chemical structure of the polymer do not correspond to each other, such as by chemically reacting parts other than the main chain after polymerization, the chemical structure after polymerization is used as a reference. Further, an anionic functional group such as a carboxy group may form a salt. For example, COONH _{4 is} also a carboxy group.

<1. Copolymer for electrode binder (A)>
The copolymer (A) for an electrode binder according to the present invention (hereinafter, may be referred to as a copolymer (A)) has a structural unit derived from the monomer (a1) described later and a monomer described later. It contains a structural unit derived from (a2), a structural unit derived from an internal cross-linking agent (a3) described later, and a structural unit derived from a polymerizable surfactant (a4) described later. The copolymer (A) may contain structural units derived from other monomers (a5).

[1-1. Monomer (a1)]
The monomer (a1) is a (meth) acrylic acid alkyl ester having one ethylenically unsaturated bond contained in the molecule, and a hydrocarbon compound having one ethylenically unsaturated bond contained in the molecule. It consists of at least one type selected from the group consisting of. The (meth) acrylic acid alkyl ester has a hydrocarbon structure except for the (meth) acryloyloxy group. The monomer (a1) preferably contains both the (meth) acrylic acid alkyl ester and the hydrocarbon compound. The monomer (a1) preferably contains an aromatic compound having an ethylenically unsaturated bond from the viewpoint of adhesion between the electrode active material and the copolymer (A).

Examples of aromatic compounds having an ethylenically unsaturated bond include vinyl aromatic compounds such as styrene compounds, vinylnaphthalene compounds, and vinyl biphenyl compounds. As the styrene-based compound, for example, at least one compound selected from the group consisting of styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene is preferable, and styrene, α- Methylstyrene is more preferred, and styrene is even more preferred.

The monomer (a1) is a high Tg monomer (a11) having a homopolymer glass transition point Tg of 5 ° C. or higher, and a low Tg monomer having a homopolymer glass transition point Tg of −5 ° C. or lower. It is preferable to include (a12). This is to control the glass transition point of the copolymer (A) to an appropriate value according to the specifications. The total content of the high Tg monomer (a11) and the low Tg monomer (a12) in the monomer (a1) is preferably 60% by mass or more, preferably 75% by mass or more. More preferably, it is more preferably 90% by mass or more. The monomer (a1) may contain a monomer having a homopolymer glass transition point Tg of less than 5 ° C and more than −5 ° C.

The mass ratio of the content of the structural unit derived from the high Tg monomer (a11) to the content of the structural unit derived from the low Tg monomer (a12) in the copolymer (A) is 30: It is preferably 70 or more, and more preferably 40:60 or more. The mass ratio of the content of the structural unit derived from the high Tg monomer (a11) to the content of the structural unit derived from the low Tg monomer (a12) in the copolymer (A) is 70: It is preferably 30 or less, and more preferably 60:40 or less.

Examples of the high Tg monomer (a11) include styrene (100 ° C.), methyl acrylate (8 ° C.), methyl methacrylate (105 ° C.), ethyl methacrylate (65 ° C.), and n-propyl methacrylate (35 ° C.). , Isopropyl methacrylate (81 ° C), n-butyl methacrylate (20 ° C), isobutyl methacrylate (53 ° C), tert-butyl methacrylate (107 ° C), tert-butyl acrylate (14 ° C), cyclohexyl methacrylate. (83 ° C.), stearyl methacrylate (38 ° C.), stearyl acrylate (10 ° C.), isobornyl methacrylate (155 ° C.), isobornyl acrylate (94 ° C.) and the like, but are not limited thereto. The temperature in parentheses after the compound name given here is the value of Tg of the homopolymer of the compound. Among the compounds listed here, from the viewpoint of ease of emulsion polymerization and elution resistance, the high Tg monomer (a11) is composed of styrene, methyl (meth) acrylate, ethyl methacrylate, and n-butyl methacrylate. It is preferable to include one or more selected species.

Examples of the low Tg monomer (a11) include ethyl acrylate (-22 ° C.), n-propyl acrylate (-48 ° C.), n-butyl acrylate (-52 ° C.), and iso-butyl acrylate (-24 ° C.). ° C.), 2-ethylhexyl methacrylate (-10 ° C.), 2-ethylhexyl acrylate (-70 ° C.), lauryl methacrylate (-65 ° C.) and the like, but are not limited thereto. The temperature in parentheses after the compound name given here is the value of Tg of the homopolymer of the compound. Among the compounds listed here, from the viewpoint of ease of emulsion polymerization and elution resistance, the low Tg monomer (a11) is ethyl acrylate, n-butyl acrylate, 2-ethylhexyl (meth) acrylate, and methacrylic. It is preferable to contain one or more selected from lauryl acid.

[1-2. Monomer (a2)]
The monomer (a2) is composed of at least one selected from the group consisting of a carboxylic acid having one ethylenically unsaturated bond contained in the molecule and a salt thereof. It is more preferable that the monomer (a2) does not contain an alkylene oxide structure having a repetition number of 3 or more.

Examples of the monomer (a2) include unsaturated monocarboxylic acids such as (meth) acrylic acid and crotonic acid, unsaturated dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid, and half esters of unsaturated dicarboxylic acids. Be done. Among these, the monomer (a2) preferably contains at least one of (meth) acrylic acid and itaconic acid.

At least a part of the structural unit derived from the monomer (a2) contained in the copolymer (A) may form a salt of a carboxy group and a basic substance. A salt may be formed by polymerizing using a monomer (a2) containing at least a part of a carboxylic acid salt as a raw material. Further, by adding a basic substance after the synthesis of the copolymer (A), at least a part of the structural units derived from the monomer (a2) contained in the copolymer (A) may be used as a salt.

[1-3. Internal cross-linking agent (a3)]
The internal cross-linking agent (a3) comprises at least one selected from the group consisting of compounds having two or more ethylenically unsaturated bonds in one molecule.

Specific examples of the compound having two or more ethylenically unsaturated bonds in one molecule include divinylbenzene, 1,6-hexanediol diacrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate.

[1-4. Polymerizable surfactant (a4)]
The polymerizable surfactant (a4) comprises at least one selected from the group consisting of compounds having a structure represented by the following formula (1). The monomer having a structure other than the following formula (1) and having a function as a surfactant is referred to as another monomer (a5) in the present invention.

In the formula (1), X is a hydrogen atom or SO ₃ NH ₄ , m is an integer of 1 or more and 4 or less, and n is an integer of 5 or more and 40 or less. X is preferably _{SO 3} NH _4. m is preferably 1 or more and 3 or less. n is preferably 8 or more and 40 or less, more preferably 8 or more and 25 or less, and further preferably 8 or more and 15 or less.

The structural unit derived from the polymerizable surfactant (a4) constitutes a portion of the copolymer (A) having a surface-active effect. When the copolymer (A) is synthesized by emulsion polymerization in an aqueous medium, the stability of the produced particles is improved by the polymerizable surfactant (a4).

Since the copolymer (A) contains a structural unit derived from the polymerizable surfactant (a4), the copolymer (A) exhibits good electrolyte resistance, and the copolymer (A) can be mixed. It has been found in the present invention that the cycle characteristics (cycle capacity retention rate) of the non-aqueous secondary battery used as the electrode binder are improved.

The contact angle of the polymerizable surfactant (a4) with respect to ethyl methyl carbonate (hereinafter, unless otherwise specified, this value is referred to as the contact angle of the polymerizable surfactant (a4)) is 15 ° or less. It is preferably 10 ° or less, more preferably 6 ° or less, and even more preferably 6 ° or less. This is to improve the permeability of the electrolytic solution. For the contact angle, a 20% by mass aqueous solution of the polymerizable surfactant (a4) was applied to a glass plate using a doctor blade and dried at 60 ° C. for 5 minutes to form a film, and ethyl methyl carbonate was applied to this film. It is a static contact angle obtained by the 1 / 2θ method when 4 μL was dropped.

[1-5. Other monomers (a5)]
The other monomers (a5) include the monomer (a1), the monomer (a2), the internal cross-linking agent (a3), the polymerizable surfactant (a4), and ("monomers (a1) to (" It is a compound that does not fall under any of (a4)) and is copolymerizable with the monomers (a1) to (a4). Examples of the other monomer (a5) include a sulfonic acid having an ethylenically unsaturated bond or a salt thereof, a compound having an ethylenically unsaturated bond and a phosphoric acid group or a salt thereof, a glycidyl group and an ethylenically unsaturated bond. Examples thereof include compounds having a hydroxy group and a compound having an ethylenically unsaturated bond.

Specific examples of the sulfonic acid having an ethylenically unsaturated bond include p-styrene sulfonic acid and sodium p-styrene sulfonic acid.

Specific examples of compounds having an ethylenically unsaturated bond and a phosphoric acid group include 2-methchlorooxyethyl acid phosphate, acid phosphooxypolyoxyethylene glycol monomethacrylate, acid phosphooxypolyoxypropylene glycol monomethacrylate, 3-chloro-2. -Acid phosphooxypropyl methacrylate, metachlorooxyethyl acid phosphate monoethanolamine salt and the like can be mentioned.

Specific examples of the compound having a glycidyl group and an ethylenically unsaturated bond include glycidyl (meth) acrylate and the like.

Specific examples of the compound having a hydroxy group and an ethylenically unsaturated bond include 2-hydroxyethyl (meth) acrylate, 4-hydroxybutyl (meth) acrylate and the like.

The other monomer (a5) is a compound having an ethylenically unsaturated bond and having a function as a surfactant, and contains a monomer other than the polymerizable surfactant (a4). May be good. Examples of such monomers include compounds represented by the following chemical formulas (2) to (5).

In formula (2), R ¹ is preferably an alkyl group, and p is preferably an integer of 10 to 40. More preferably the number of carbon atoms of R ¹ is 10 to 40, R ¹ is more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

In the formula (3), R ² is preferably an alkyl group, and q is preferably an integer of 10 to 12. More preferably the number of carbon atoms of R ² is 10-40, R ² is more preferably a straight chain unsubstituted alkyl group having 10 to 40 carbon atoms.

In formula (4), R ³ is preferably an alkyl group, and M ¹ is _{preferably NH 4} or Na. More preferably the number of carbon atoms of R ³ is 10 to 40, R ³ is more preferably a straight chain unsubstituted alkyl group having 10 to 40 carbon atoms.

In formula (5), R ⁴ is preferably an alkyl group, and M ² is _{preferably NH 4} or Na. More preferably the number of carbon atoms of R ⁴ is 10 to 40, R ⁴ is more preferably a straight chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[1-6. Content of each structural unit of copolymer (A)]
The content of the structural unit derived from the monomer (a1) in the copolymer (A) is 50% by mass or more, preferably 70% by mass or more, and preferably 90% by mass or more. More preferred. This is because the peel strength of the electrode active material layer is improved, and the polymerization stability is improved when the copolymer (A) is synthesized by emulsion polymerization.

The content of the structural unit derived from the monomer (a1) in the copolymer (A) is 98% by mass or less, preferably 97% by mass or less, and preferably 96% by mass or less. More preferred. This is to ensure the content of structural units derived from the monomers (a2) to (a4).

The content of the structural unit derived from the monomer (a2) in the copolymer (A) is 1.0% by mass or more, preferably 2.0% by mass or more, preferably 3.0% by mass. % Or more is more preferable. This is because the mechanical stability of the copolymer (A) is improved. This is also because the polymerization stability is improved when the copolymer (A) is synthesized by emulsion polymerization.

The content of the structural unit derived from the monomer (a2) in the copolymer (A) is 15% by mass or less, preferably 10% by mass or less, and 7.0% by mass or less. Is more preferable. This is because the binding property of the electrode active material layer containing the copolymer (A) to the current collector and the binding property between the electrode active materials are improved.

The content of the structural unit derived from the internal cross-linking agent (a3) in the copolymer (A) is 0.020% by mass or more, preferably 0.50% by mass or more, preferably 1.0% by mass. % Or more is more preferable. This is because the electrolytic solution resistance of the electrode containing the copolymer (A) is improved.

The content of the structural unit derived from the internal cross-linking agent (a3) in the copolymer (A) is 10% by mass or less, preferably 5.0% by mass or less, and 3.0% by mass or less. Is more preferable, and 2.0% by mass or less is particularly preferable. This is because the copolymer (A) can be used to produce an electrode exhibiting good flexibility.

The content of the structural unit derived from the polymerizable surfactant (a4) in the copolymer (A) is 0.010% by mass or more, preferably 0.10% by mass or more, and 0. It is more preferably 17% by mass or more. This is because the copolymer (A) exhibits good electrolyte resistance, and the cycle characteristics of the non-aqueous secondary battery using the copolymer (A) as the electrode binder are improved.

The content of the structural unit derived from the polymerizable surfactant (a4) in the copolymer (A) is 10% by mass or less, preferably 3.0% by mass or less, preferably 1.0% by mass. % Or less, more preferably 0.50% by mass or less, and particularly preferably 0.35% by mass or less. This is because an electrode exhibiting good flexibility can be obtained by including the copolymer (A) having such a structure as an electrode binder.

The content of the structural unit derived from the other monomer (a5) in the copolymer (A) is not particularly limited as long as the object of the present invention can be achieved. The content of the structural unit derived from such another monomer (a5) in the copolymer (A) is preferably 10% by mass or less, preferably 5.0% by mass or less. Is more preferable, and 3.0% by mass or less is further preferable.

[1-7. Glass transition point of copolymer (A)]
The Tg of the copolymer (A) is measured by DSC using EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Co., Ltd. at a heating rate of 10 ° C./min in a nitrogen gas atmosphere, and is obtained as a temperature differential of DSC. It is the peak top temperature.

The glass transition point Tg of the copolymer (A) is preferably −30 ° C. or higher, more preferably −10 ° C. or higher, and even more preferably 0 ° C. or higher. This is because the cycle characteristics of the non-aqueous secondary battery using the copolymer (A) as the electrode binder are improved.

The glass transition point Tg of the copolymer (A) is preferably 100 ° C. or lower, more preferably 50 ° C. or lower, and even more preferably 30 ° C. or lower. This is because the adhesion of the electrode active material layer containing the copolymer (A) as an electrode binder to the current collecting foil is improved.

<2. Method for synthesizing copolymer for electrode binder>
The electrode binder copolymer (A) can be obtained by copolymerizing the monomers (a1) to (a4) and, if necessary, another monomer (a5). Here, when the monomer for the copolymer (A) is generically referred to as the monomer (a). That is, the monomer (a) includes the monomers (a1) to (a4) and, if necessary, another monomer (a5). Examples of the polymerization method include emulsion polymerization of the monomer (a) in the aqueous medium (b). Other components used in the synthesis of the copolymer (A) by emulsion polymerization include, for example, a non-polymerizable surfactant (c), a basic substance (d), a polymerization initiator (e), and a chain. The moving agent (f) and the like can be mentioned.

[2-1. Aqueous medium (b)]
The aqueous medium (b) is water, a hydrophilic solvent, or a mixture thereof. Examples of the hydrophilic solvent include methanol, ethanol, isopropyl alcohol, N-methylpyrrolidone and the like. From the viewpoint of polymerization stability, the aqueous medium (b) is preferably water. As the aqueous medium (b), a water to which a hydrophilic solvent is added may be used as long as the polymerization stability is not impaired.

[2-2. Non-polymerizable Surfactant (c)]
In the emulsion polymerization of the monomer (a), a non-polymerizable surfactant (c) may be used. The surfactant (c) can improve the dispersion stability of the dispersion liquid (emulsion) during and / or after the polymerization. As the surfactant (c), it is preferable to use an anionic surfactant or a nonionic surfactant.

Examples of the anionic surfactant include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts.

Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene polycyclic phenyl ether, polyoxyalkylene alkyl ether, sorbitan fatty acid ester, and polyoxyethylene sorbitan fatty acid ester.

The above-mentioned surfactant may be used alone or in combination of two or more.

[2-3. Basic substance (d)]
When the monomer (a) is emulsion-polymerized in the aqueous medium (b), the basic substance (d) may be added. By adding the basic substance (d), the acidic component contained in the monomer (a) and / or the copolymer (A) can be neutralized and the pH can be adjusted. By adjusting the pH, the mechanical stability and chemical stability of the dispersion during and / or after emulsion polymerization can be improved.

The pH of the dispersion at 23 ° C. is preferably 1.5 to 10, more preferably 6.0 to 9.0, and even more preferably 5.0 to 9.0. This is to suppress the sedimentation of the active material in the electrode slurry described later.

Examples of the basic substance (d) include ammonia, triethylamine, sodium hydroxide, lithium hydroxide and the like. These basic substances (d) may be used alone or in combination of two or more.

[2-4. Radical polymerization initiator (e)]
The radical polymerization initiator (e) used in the emulsion polymerization is not particularly limited, and known ones can be used. Examples of the radical polymerization initiator include persulfates such as ammonium persulfate and potassium persulfate; hydrogen peroxide; azo compounds; organic peroxides such as t-butyl hydroperoxide, tert-butyl peroxybenzoate and cumene hydroperoxide. Examples include oxides. Of these, persulfates and organic peroxides are preferred. In the present embodiment, a radical polymerization initiator and a reducing agent such as sodium bisulfite, longalit, and ascorbic acid may be used in combination during emulsion polymerization for redox polymerization.

The amount of the radical polymerization initiator added is preferably 0.10 parts by mass or more, and more preferably 0.80 parts by mass or more with respect to 100 parts by mass of the monomer (a). This is because the conversion rate of the monomer (a) to the copolymer (A) at the time of polymerization can be increased. The amount of the radical polymerization initiator added is preferably 3.0 parts by mass or less, and more preferably 2.0 parts by mass or less with respect to 100 parts by mass of the monomer (a). This is because the molecular weight of the copolymer (A) can be increased and the swelling rate of the electrode active material layer with respect to the electrolytic solution can be reduced.

[2-5. Chain transfer agent (f)]
The chain transfer agent (f) is used to adjust the molecular weight of the copolymer (A) in emulsion polymerization. Examples of the chain transfer agent (f) include n-dodecyl mercaptan, tert-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexylthioglycolate, 2-mercaptoethanol, β-mercaptopropionic acid, methyl alcohol, and n-propyl alcohol. Examples thereof include isopropyl alcohol, t-butyl alcohol and benzyl alcohol.

[2-6. Emulsification polymerization method]
Examples of the emulsion polymerization method include a method of emulsion polymerization while continuously supplying each component used for emulsion polymerization. The temperature of the emulsion polymerization is not particularly limited, but is, for example, 30 to 90 ° C, preferably 50 to 85 ° C, and even more preferably 55 to 80 ° C. Emulsion polymerization is preferably carried out with stirring. Further, it is preferable that the monomer (a) and the radical polymerization initiator are continuously supplied so as to be uniform in the reaction vessel.

<3. Electrode binder resin composition>
In the electrode binder resin composition of the present embodiment (hereinafter, may be referred to as a binder composition), the copolymer for electrode binder (A) is dispersed in the aqueous medium (B). In addition to these components, the binder composition may contain, for example, the above-mentioned components used in the synthesis of the copolymer (A). The binder composition may be a dispersion obtained by the above-mentioned method for synthesizing the copolymer for electrode binder (A), and the copolymer (A) obtained by a method other than emulsion polymerization is used as an aqueous medium (B). It may be a dispersion obtained by dispersing, or may be a dispersion obtained by another method.
The electrode binder resin composition of the present embodiment contains an electrode binder and an aqueous medium (B). The electrode binder contains the above-mentioned copolymer for electrode binder (A), and is preferably the above-mentioned copolymer for electrode binder (A).

[3-1. Aqueous medium (B)]
The aqueous medium (B) is water, a hydrophilic solvent, or a mixture thereof. Examples of the hydrophilic solvent are as described in the description of the aqueous medium (b) in the synthesis of the copolymer (A) for the electrode binder. The aqueous medium (B) may be the same as or different from the aqueous medium (b) used in the synthesis of the copolymer (A).

As the aqueous medium (B), the aqueous medium (b) used for the synthesis of the copolymer (A) may be used as it is, or the aqueous medium (b) may be added with an aqueous solvent, and the copolymer (A) may be used. The aqueous medium (b) may be replaced with a new aqueous solvent after the synthesis of the above. Here, the aqueous solvent to be added or replaced may have the same composition as the solvent used for the synthesis of the copolymer (A), or may have a different composition.

[3-2. Non-volatile content concentration and viscosity of electrode binder resin composition]
The non-volatile content concentration of the binder composition is preferably 20% by mass or more, more preferably 25% by mass or more, and further preferably 30% by mass or more. This is to increase the amount of the active ingredient contained in the binder composition. The non-volatile content concentration of the binder composition can be adjusted by the amount of the aqueous medium (B).

The viscosity of the binder composition is preferably 3000 mPa · s or less, more preferably 1000 mPa · s or less, and even more preferably 80 mPa · s or less. This is to reduce the loss of the binder when producing the electrode slurry, which will be described later, and to shorten the time required for the defoaming step of the slurry. The viscosity of the binder composition was determined by using a Brookfield viscometer at a liquid temperature of 23 ° C., a rotation speed of 60 rpm, and No. 1, No. 2. No. 3 or No. It is a value measured using the rotor of 4. The viscosity of the binder composition is greatly affected by the non-volatile content concentration of the binder composition.

<4. Electrode slurry>
Next, the electrode slurry will be described in detail. The electrode slurry has a structure in which the copolymer (A) and the electrode active material are dispersed in an aqueous medium. In addition to these components, the electrode slurry may contain a thickener, a conductive auxiliary agent, the above-mentioned components used for synthesizing the copolymer (A), and the like.

[4-1. Content of copolymer (A) for electrode binder]
The content of the copolymer (A) is preferably 0.50 parts by mass or more, and more preferably 1.0 parts by mass or more with respect to 100 parts by mass of the electrode active material. This is to fully exhibit the effect of the copolymer (A).

The content of the copolymer (A) is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and 3.0 parts by mass with respect to 100 parts by mass of the electrode active material. More preferably, it is less than or equal to a portion. This is to increase the content of the electrode active material in the electrode active material layer produced by using the electrode slurry.

[4-2. Electrode active material]
The electrode active material is a material capable of inserting / removing ions such as lithium ions that serve as charge carriers. The ion serving as a charge carrier is preferably an alkali metal ion, more preferably a lithium ion, a sodium ion, or a potassium ion, and even more preferably a lithium ion.

When the electrode is a negative electrode, the electrode active material, that is, the negative electrode active material preferably contains at least one of a carbon material, a material containing silicon, and a material containing titanium. Examples of the carbon material used as the electrode active material include coke such as petroleum coke, pitch coke, and coal coke, carbonized organic polymer, artificial graphite, and graphite such as natural graphite. Examples of the material containing silicon include a simple substance of silicon and a silicon compound such as silicon oxide. Examples of the material containing titanium include lithium titanate and the like. These materials may be used alone, or may be mixed or combined.

The negative electrode active material preferably contains at least one of a carbon material and a material containing silicon, and more preferably contains a carbon material. This is because the binder copolymer (A) of the present invention has a very large effect of improving the binding property between the electrode active materials and between the electrode active material and the current collector.

When the electrode is a positive electrode, the electrode active material, that is, the positive electrode active material, uses a material having a higher standard electrode potential than the negative electrode active material. As the positive electrode active material, a lithium composite oxide containing nickel such as a Ni—Co—Mn-based lithium composite oxide, a Ni—Mn—Al based lithium composite oxide, and a Ni—Co—Al based lithium composite oxide. Lithium cobalt oxide (LiCoO ₂ ); spinel-type lithium manganate (LiMn ₂ O ₄ ); olivine-type lithium iron phosphate; TiS ₂ , MnO ₂ , MoO ₃ , V ₂ O _{5, and} other chalcogen compounds. As the positive electrode active material, these substances may be used alone or in combination of two or more.

[4-3. Thickener]
Examples of the thickener include celluloses such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose and hydroxypropyl cellulose, ammonium salts of celluloses, alkali metal salts of celluloses, polyvinyl alcohol, polyvinylpyrrolidone and the like. The thickener preferably contains at least one of carboxymethyl cellulose, an ammonium salt of carboxymethyl cellulose, and an alkali metal salt of carboxymethyl cellulose. This is because the electrode active material is easily dispersed in the electrode slurry.

The content of the thickener in the electrode slurry is preferably 0.50 parts by mass or more, and more preferably 0.80 parts by mass or more with respect to 100 parts by mass of the electrode active material. This is to improve the binding property between the electrode active materials and between the electrode active material and the current collector in the electrode active material layer produced by using the electrode slurry.

The content of the thickener in the electrode slurry is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and 1.5 parts by mass with respect to 100 parts by mass of the electrode active material. The following is more preferable. This is because the coatability of the electrode slurry is improved.

[4-4. Aqueous medium]
The aqueous medium is water, a hydrophilic solvent, or a mixture thereof. Examples of the hydrophilic solvent are as described in the description of the aqueous medium (b) in the synthesis of the copolymer (A) for the electrode binder. The aqueous medium contained in the electrode slurry may be the same as or different from the aqueous medium (B) contained in the electrode binder resin composition or the aqueous medium (b) used for synthesizing the copolymer (A). ..

[4-5. Conductive aid]
As the conductive auxiliary agent, it is preferable to use carbon black, carbon fiber or the like. Examples of carbon black include furnace black, acetylene black, denka black (registered trademark) (manufactured by Denka Co., Ltd.), and Ketjen black (registered trademark) (manufactured by Ketjen Black International Co., Ltd.). Examples of carbon fibers include carbon nanotubes and carbon nanofibers, and examples of carbon nanotubes include VGCF (registered trademark, manufactured by Showa Denko Co., Ltd.), which is a vapor phase carbon fiber.

[4-6. Properties of electrode slurry]
The non-volatile content concentration of the electrode slurry is preferably 20% by mass or more, more preferably 30% by mass or more, and further preferably 40% by mass or more. This is because the concentration of the active ingredient in the electrode slurry becomes high, and a sufficient amount of the electrode active material layer can be formed with a small amount of the electrode slurry. The non-volatile content concentration of the electrode slurry can be adjusted by adjusting the amount of the aqueous medium in the electrode slurry.

The viscosity of the electrode slurry is preferably 20000 mPa · s or less, more preferably 10000 mPa · s or less, and further preferably 5000 mPa · s or less. This is because the applicability of the electrode slurry to the current collector is improved and the productivity of the electrodes is improved. The viscosity of the electrode slurry is greatly affected by the non-volatile content concentration of the electrode slurry and the type and amount of the thickener.

The pH of the electrode slurry at 23 ° C. is preferably 2.0 to 10, more preferably 4.0 to 9.0, and even more preferably 6.0 to 9.0. This is to improve the durability of the battery manufactured by using the electrode slurry.

[4-7. Method of manufacturing electrode slurry]
As a method for preparing the electrode slurry in the present embodiment, a binder composition, an electrode active material, a thickener if necessary, an aqueous medium if necessary, and a conductive auxiliary agent if necessary are required. Mix with other ingredients depending on. The order of the components to be added is not particularly limited and may be appropriately determined. Examples of the mixing method include a method using a mixing device such as a stirring type, a rotary type, and a shaking type.

<5. Non-aqueous secondary battery electrode ＞
The non-aqueous secondary battery electrode (hereinafter, may be referred to as “electrode”) according to the present embodiment includes a current collector and an electrode active material layer formed on the current collector. The shape of the electrode includes, for example, a laminated body and a wound body, but is not particularly limited. Further, the range of forming the electrode active material layer on the current collector is not particularly limited, and it may be formed on the entire surface of the current collector or on a part of the surface of the current collector. When the current collector is in the shape of a plate, foil, or the like, the electrode active material layer may be formed on both sides or only on one side.

[5-1. Current collector]
The current collector is preferably a metal sheet having a thickness of 0.001 mm or more and 0.5 mm or less, and examples of the metal include iron, copper, aluminum, nickel, and stainless steel. The metal sheet may be, for example, a metal foil or a metal plate. When the non-aqueous battery electrode is the negative electrode of the lithium ion secondary battery, the current collector is preferably a copper foil.

[5-2. Electrode active material layer]
The electrode active material layer according to the present embodiment contains a binder copolymer (A) and an electrode active material. The electrode active material layer may contain other components contained in the above-mentioned binder composition, or may contain other components contained in the above-mentioned electrode slurry.

[5-3. Electrode manufacturing method]
As a method for producing an electrode, for example, an electrode slurry is applied onto a current collector, dried to form an electrode active material layer, and then cut into an appropriate size.

The method of applying the electrode slurry onto the current collector is not particularly limited, but for example, the reverse roll method, the direct roll method, the doctor blade method, the knife method, the extrusion method, the curtain method, the gravure method, the bar method, and the dip method. Law, squeeze method, etc. can be mentioned. Among these, the doctor blade method, the knife method, or the extrusion method is preferably used in consideration of various physical properties such as the viscosity of the electrode slurry and the drying property. This is because it is possible to obtain an electrode active material layer having a smooth surface and a small variation in thickness.

The electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. When the electrode slurry is applied to both sides of the current collector, it may be applied sequentially on one side at a time, or on both sides at the same time. Further, the electrode slurry may be continuously applied to the current collector or may be applied intermittently. The coating amount of the electrode slurry can be appropriately determined according to the design capacity of the battery, the composition of the electrode slurry, and the like. The coating amount of the electrode slurry depends on the properties of the electrode slurry, ^{but is preferably 13 mg / cm 2} or less (when coated on both sides, the coating amount per one side). This is because the occurrence of cracks on the electrode surface can be suppressed in the process of drying the electrode slurry.

By drying the electrode slurry applied on the current collector, an electrode active material layer is formed on the current collector. The method for drying the electrode slurry is not particularly limited, and for example, hot air, reduced pressure or vacuum environment, (far) infrared rays, and low temperature air can be used alone or in combination. The drying temperature and drying time of the electrode slurry can be appropriately adjusted depending on the concentration of non-volatile components in the electrode slurry, the amount of coating on the current collector, and the like. The drying temperature is preferably 40 ° C. or higher and 350 ° C. or lower, and more preferably 60 ° C. or higher and 100 ° C. or lower from the viewpoint of productivity. The drying time is preferably 1 minute or more and 30 minutes or less.

The electrode sheet on which the electrode active material layer is formed on the current collector may be cut in order to obtain an appropriate size and shape as an electrode. The method for cutting the electrode sheet is not particularly limited, and for example, a slit, a laser, a wire cut, a cutter, a Thomson, or the like can be used.

If necessary, the electrode sheet may be pressed before or after cutting the electrode sheet. As a result, the electrode active material is firmly bound to the current collector, and the electrode can be made thinner, so that the non-aqueous battery can be miniaturized. As a pressing method, a general method can be used, and it is particularly preferable to use a die pressing method or a roll pressing method. In the case of the die pressing method, the pressing pressure is not particularly limited, but is preferably ^{0.5 t / cm 2} or more and 5 t / cm ^{2 or less.} In the case of the roll press method, the linear pressure is not particularly limited, but is preferably 0.5 t / cm or more and 5 t / cm or less. This is to suppress the insertion and desorption capacity of charge carriers such as lithium ions into the electrode active material while obtaining the above effect by pressing.

<6. Non-aqueous secondary battery ＞
A lithium ion secondary battery will be described as a preferable example of the non-aqueous secondary battery according to the present embodiment, but the battery configuration is not limited to that described here. The non-aqueous secondary battery according to the present embodiment is one in which a positive electrode, a negative electrode, an electrolytic solution, and, if necessary, parts such as a separator are housed in an exterior body, and one of the positive electrode and the negative electrode. Alternatively, the electrodes produced by the above method are used for both. In the non-aqueous secondary battery according to the present embodiment, at least one of the positive electrode and the negative electrode contains the copolymer (A) in the electrode binder, but it is preferable that at least the negative electrode contains the copolymer (A).

[6-1. Electrolyte]
As the electrolytic solution, a non-aqueous liquid having ionic conductivity is used. Examples of the electrolytic solution include a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, and the like, but the former is preferable. This is because a non-aqueous battery having a low manufacturing cost and a low internal resistance can be obtained.

As the electrolyte, an alkali metal salt can be used and can be appropriately selected depending on the type of electrode active material and the like. As the electrolyte, for _{example, LiClO 4, LiBF 6, LiPF} 6, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiB 10 Cl 10, LiAlCl 4, LiCl, LiBr, LiB (C 2 H 5) ₄ , CF ₃ SO ₃ Li, CH ₃ SO ₃ Li, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, lithium aliphatic carboxylate and the like. Further, other alkali metal salts can also be used as the electrolyte.

The organic solvent for dissolving the electrolyte is not particularly limited, but for example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), fluoroethylene carbonate. Carbonic acid ester compounds such as (FEC) and vinylene carbonate (VC); nitrile compounds such as acetonitrile; carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate and propyl propionate. These organic solvents may be used alone or in combination of two or more. Above all, it is preferable to use a combination of linear carbonate-based solvents. Examples of the linear carbonate solvent include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[6-2. Exterior]
As the exterior body, for example, a laminating material of an aluminum foil and a resin film can be appropriately used, but the exterior body is not limited to this. The shape of the battery may be any shape such as a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.

In the following examples, as an example of the configuration of the present invention, a negative electrode of a lithium ion secondary battery and a lithium ion secondary battery are manufactured, and the negative electrode of the lithium ion secondary battery and the lithium ion secondary battery according to the comparative example are used. By comparison, the effect of the present invention is confirmed. The present invention is not limited thereto. Unless otherwise specified, the water used in the following Examples and Comparative Examples is ion-exchanged water.

<1. Synthesis step of copolymer (A) for electrode binder>
[1-1. Example 1]
356 parts by mass of water, 270 parts by mass of styrene, 0.24 parts by mass of methyl methacrylate, 210 parts by mass of 2-ethylhexyl acrylate, 10 parts by mass of itaconic acid, and 80% aqueous solution of acrylic acid. 20 parts by mass (16 parts by mass of acrylic acid and 4.0 parts by mass of water), 6.9 parts by mass of divinylbenzene, and 1.2 parts by mass of Aqualon® AR10 (details are shown in Table 2). 1 part, 3.0 parts by mass of sodium p-styrene sulfonate, and 1 polyoxyethylene alkyl ether sulfate ester salt (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Hytenol 08E) as a non-polymerizable surfactant. A monomer emulsion was prepared by mixing 0.0 parts by mass and 0.10 parts by mass of β-mercaptopropionic acid.

169 parts by mass of water was placed in a separable flask having a cooling tube, a thermometer, a stirrer, and a dropping funnel, and the temperature was raised to 75 ° C. To this separable flask, the above-mentioned monomeric emulsion and an aqueous solution prepared by dissolving 2.2 parts by mass of potassium persulfate as a polymerization initiator in 48 parts by mass of water are added dropwise at 80 ° C. over 4 hours with stirring. And emulsion polymerization. After dropping the monomer emulsified solution and the potassium persulfate aqueous solution, the mixed solution in the separable flask was stirred at 80 ° C. for 60 minutes.

Next, an aqueous solution prepared by dissolving 0.81 parts by mass of tert-butylperoxybenzoate (Kayabutyl B manufactured by Kayaku Akzo Corporation) and 0.52 parts by mass of ascorbic acid in 8.1 parts by mass of water was added. Next, 2.3 parts by mass of tert-butyl hydroperoxide (Kayabutyl H-70 manufactured by Kayaku Akzo Corporation) was dissolved in 15 parts by mass of water, and 2.3 parts by mass of Longalit was added to 15 parts by mass. The aqueous solution dissolved in water and the aqueous solution were stirred for 60 minutes while dropping, and polymerization was carried out. An aqueous emulsion of the copolymer (A) was obtained.

[1-2. Comparative Examples 1 to 3]
Instead of Aqualon AR10, Adecaria Soap (registered trademark) SR10 in Comparative Example 1, Aqualon (registered trademark) KH10 in Comparative Example 2, and Eleminor (registered trademark) JS20 in Comparative Example 3, respectively, with Example 1. Similarly, 1.2 parts by mass was used. Other than this, each Comparative Example is the same as in Example 1. Although all of these components used in Comparative Examples 1 to 3 are monomers having a function as a surfactant, they do not correspond to the polymerizable surfactant (a4).

Table 2 shows the details of Aqualon AR10, Adecaria Soap SR10, Aqualon KH10, and Eleminor JS20.

<2. Preparation process of electrode binder resin composition>
The same was performed in the examples and each comparative example. The obtained aqueous emulsion of the copolymer (A) was cooled to room temperature, and 19 parts by mass of 25% by mass of ammonia water and 155 parts by mass of water were added to a separable flask to neutralize the obtained copolymer (A), and the copolymer weight was equalized. A binder composition containing the coalescence (A) was obtained.

Table 1 shows the amounts of the components used for the synthesis of the copolymer (A) and the preparation of the binder composition. In Table 1, the amount of water is the total amount of water used in the synthesis step and the preparation step, and the water contained in the acrylic acid aqueous solution and the ammonia water is also included in the calculation. Further, in Table 1, the amount of acrylic acid and ammonia added is the amount of only the solute contained in the above aqueous acrylic acid solution and aqueous ammonia.

The contact angles of the components shown in Table 2 were measured as follows. A 20% by mass aqueous solution was prepared for each of the components shown in Table 2. The prepared aqueous solution was applied to a glass plate using a doctor blade and dried at 60 ° C. for 5 minutes to form a film. The static contact angle determined by the 1 / 2θ method when 4 μL of ethylmethyl carbonate was added dropwise to this film was measured. The measurement results are as shown in Table 2.

<3. Evaluation of binder composition>
The binder compositions obtained in Examples and Comparative Examples, and the physical characteristics and performance evaluation tests of the batteries obtained using these binder compositions were carried out by the following methods. The evaluation results are shown in Table 3.

[3-1. Non-volatile content concentration]
1 g of the binder composition was weighed on an aluminum dish having a diameter of 5 cm, dried at 105 ° C. for 1 hour at 1 atm (1013 hPa) while circulating air in a dryer, and the mass of the remaining components was measured. The mass ratio (mass%) of the above-mentioned components remaining after drying with respect to the mass (1 g) of the binder composition before drying was calculated as the non-volatile content concentration.

[3-2. viscosity〕
Using a Brookfield viscometer, the liquid temperature was 23 ° C., the rotation speed was 60 rpm, and No. 1, No. 2. No. 3 or No. It was measured using the rotor of 4.

<4. Evaluation of electrode binder>
The binder composition was cast on a polyethylene sheet, dried at 50 ° C. for 5 hours, and then vacuum dried at 50 ° C. for 1 hour to obtain a film having a thickness of 0.5 mm. The following evaluation was performed using this film. The evaluation results are shown in Table 3.

[4-1. Glass transition point Tg of copolymer (A)]
The obtained film was cut into 2 mm × 2 mm, sealed in an aluminum pan, and DSC measurement was performed using EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Co., Ltd. at a heating rate of 10 ° C./min in a nitrogen gas atmosphere. The peak top temperature of the DDSC chart obtained as the temperature derivative of DSC was measured, and this temperature was defined as the glass transition point Tg (° C.) of the copolymer (A). The measurement temperature range was −40 ° C. to 200 ° C.

[4-2. Electrolyte resistance of electrode binder]
The film was cut out to a size of 30 mm × 10 mm with a cutter knife. The mass M0 of the cut out film was measured. The cut film was immersed in ethyl methyl carbonate (EMC) at 60 ° C. for 24 hours in a closed container, and the film was taken out. The mass M1 of the film immediately after being taken out was measured. Next, the film was vacuum dried at 60 ° C. for 12 hours, and the mass M2 of the dried film was measured. From the measured masses M0, M1 and M2, the swelling rate (mass%) of the electrode binder in the electrolytic solution and the elution rate (mass%) with respect to the electrolytic solution were calculated by the following formulas (6) and (7).

Swelling rate (mass%) = 100 × (M2-M1) / M1 (6)
Elution rate (mass%) = 100 × (M2-M0) / M0 (7)

<5. Evaluation of electrode and battery performance>
Using the binder compositions prepared in each Example and Comparative Example, a negative electrode and a lithium ion secondary battery were prepared and evaluated.

[5-1. Battery production]
[5-1-1. Preparation of positive electrode]
_{A mixture of 94 parts by mass of LiNi 0.6} Mn _0.2 Co _0.2 O ₂ as a positive electrode active material, 3 parts by mass of acetylene black as a conductive auxiliary agent, and 3 parts by mass of polyvinylidene fluoride as a binder is mixed with N-. 50 parts by mass of methylpyrrolidone was added and further mixed to prepare a positive electrode slurry.

A positive electrode slurry was applied to both sides of a 15 μm-thick aluminum foil (positive electrode current collector) by a direct roll method. The amount of the positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described later was 125 μm per side.

The positive electrode slurry applied on the positive electrode current collector was dried at 120 ° C. for 5 minutes and pressed by a roll press (manufactured by Thunk Metal Co., Ltd., press load 5 tons, roll width 7 cm) to form a positive electrode active material layer. A positive electrode sheet was obtained. The obtained positive electrode sheet was cut out to a size of 50 mm × 40 mm, and a conductive tab was attached to prepare a positive electrode.

[5-1-2. Fabrication of negative electrode]
100 parts by mass of artificial graphite (G49, manufactured by Kosai Shiho Technology Co., Ltd.) as the negative electrode active material, and 3.9 parts by mass of the binder composition prepared in each Example and Comparative Example (1.5 parts by mass as a non-volatile content). , And CMC (carboxymethyl cellulose-sodium salt, Sunrose (registered trademark) MAC500LC manufactured by Nippon Paper Chemicals Co., Ltd.) are mixed by 62 parts by mass, and 28 parts by mass of water is further added to prepare a negative electrode slurry. Obtained.

Negative electrode slurry was applied to both sides of a copper foil (negative electrode current collector) having a thickness of 10 μm by the direct roll method. The amount of the negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness after the roll press treatment described later was 170 μm per side.

The negative electrode slurry coated on the negative electrode current collector is dried at 90 ° C. for 10 minutes, pressed by a roll press (manufactured by Thunk Metal Co., Ltd., press load 8 t, roll width 7 cm), and the negative electrode active material layer is placed on the current collector. Was formed to obtain a negative electrode sheet. The obtained negative electrode sheet was cut out to a size of 52 mm × 42 mm, and a conductive tab was attached to prepare a negative electrode.

[5-1-3. Battery production]
An aluminum-laminated exterior body (battery pack) with a separator (made of polyethylene, 25 μm) made of a polyolefin-based porous film interposed between the positive electrode and the negative electrode so that the positive electrode active material layer and the negative electrode active material layer face each other. ). An electrolytic solution was injected into the exterior body, vacuum impregnated, and packed with a vacuum heat sealer to prepare a lithium ion secondary battery for evaluation. _{The electrolytic solution is a solution 99 in which LiPF 6} is dissolved at 1.0 mol / L in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC) = 30/50/20 (volume ratio). It was prepared by mixing 1 part by mass of vinylene carbonate with 1 part by mass of vinylene carbonate.

[5-2. Evaluation of electrodes and batteries]
[5-2-1. Peeling strength of negative electrode active material layer (electrode performance)]
The peel strength of the negative electrode active material layer with respect to the current collector was measured as follows. The negative electrode sheet after pressing in the above negative electrode manufacturing step was cut into a size of 25 mm × 100 mm to obtain a test piece. Using double-sided tape (NITTO TAPE (registered trademark) No. 5, manufactured by Nitto Denko KK), the negative electrode active material layer on the test piece and the SUS plate with a width of 50 mm and a length of 200 mm are used to form the center of the test piece and the center of the SUS plate. It was pasted so that they match. The double-sided tape was attached so as to cover the entire range of the test piece.

After leaving the test piece and the SUS plate bonded together for 10 minutes, the negative electrode active material layer was peeled off by 20 mm in the length direction from one end of the test piece, and the test piece on the copper foil side was folded back 180 ° to this part ( The copper foil side of the part of the test piece from which the negative electrode active material layer was peeled off) was grasped by the chuck on the upper side of the testing machine. Further, one end of the SUS plate on the side where the negative electrode active material layer was peeled off was grasped by the lower chuck. In that state, the copper foil was peeled off from the test piece at a speed of 100 ± 10 mm / min to obtain a graph of peeling length (mm) -peeling force (mN). In the obtained graph, the average value (mN) of the peeling force at a peeling length of 10 to 45 mm was calculated, and the value obtained by dividing the average value of the peeling force by the width of the test piece of 25 mm was the peeling strength (mN / mN / of the negative electrode active material layer. mm). In each of the Examples and Comparative Examples, peeling between the double-sided tape and the SUS plate and interfacial peeling between the double-sided tape and the negative electrode active material layer did not occur during the test.

[5-2-2. Cycle capacity retention rate at high temperature (battery performance)]
The cycle capacity retention rate of the battery at high temperature was repeated in the following steps (i) to (iv) under the condition of 45 ° C. Here, one cycle of a series of operations (i) to (iv) is defined as one cycle.

(I) Charge with a current of 1C until the voltage reaches 4.2V (constant current (CC) charging).
(Ii) Charge at a voltage of 4.2 V until the current reaches 0.05 C (constant voltage (CV) charge). (Iii) Let stand for 30 minutes.
(Iv) Discharge with a current of 1 C until the voltage reaches 2.75 V (constant current (CC) discharge).

The time integral value of the current in the steps (i) and (ii) is the charge capacity, and the time integral value of the current in the step (iv) is the discharge capacity. The discharge capacity of the first cycle and the discharge capacity of the 200th cycle were measured. 100 × (discharge capacity in the 200th cycle) / (discharge capacity in the first cycle) [%] was calculated as the cycle capacity retention rate at high temperature of the battery, and is shown in Table 3.

<6. Evaluation result>
As can be seen from Example 1 of Table 3, an electrode binder resin composition containing a copolymer (A) having a structural unit derived from the polymerizable surfactant (a4) having the structure represented by the formula (1) was used. The electrode binder produced in the above method has good electrolyte resistance. Further, it can be seen that by including this copolymer (A) as an electrode binder, an electrode having an electrode active material layer having high peel strength with respect to the current collector can be obtained. Furthermore, it can be seen that the battery manufactured using this electrode has excellent cycle characteristics.

On the other hand, in Comparative Examples 1 to 3 in which a copolymer containing no structural unit derived from the polymerizable surfactant (a4) having the structure represented by the formula (1) was used as the electrode binder, all of the manufactured batteries The cycle characteristics were inferior.

Claims (15)

1. At least one selected from the group consisting of a (meth) acrylic acid alkyl ester having one ethylenically unsaturated bond contained in the molecule and a hydrocarbon compound having one ethylenically unsaturated bond contained in the molecule. Structural units derived from the type of monomer (a1) and
   A structural unit derived from a monomer (a2) consisting of at least one selected from the group consisting of a carboxylic acid having one ethylenically unsaturated bond contained in the molecule and a salt thereof, and
   A structural unit derived from an internal cross-linking agent (a3) consisting of at least one selected from the group consisting of compounds having two or more ethylenically unsaturated bonds in one molecule, and
   A structural unit derived from a polymerizable surfactant (a4) consisting of at least one selected from the group consisting of compounds represented by the following formula (1), and
   It is a copolymer containing
   The structural unit derived from the monomer (a1) is contained in an amount of 50% by mass or more and 98% by mass or less.
   The structural unit derived from the monomer (a2) is contained in an amount of 1.0% by mass or more and 15% by mass or less.
   The structural unit derived from the internal cross-linking agent (a3) is contained in an amount of 0.020% by mass or more and 10% by mass or less.
   A copolymer for an electrode binder, which comprises 0.010% by mass or more and 10% by mass or less of a structural unit derived from the polymerizable surfactant (a4).
   

   

   In the formula (1), X is a hydrogen atom or SO ₃ NH ₄ , m is an integer of 1 or more and 4 or less, and n is an integer of 5 or more and 40 or less.
2. The monomer (a1) is a high Tg monomer (a11) having a homopolymer glass transition point Tg of 5 ° C. or higher, and a low Tg single amount having a homopolymer glass transition point Tg of −5 ° C. or lower. The copolymer for an electrode binder according to claim 1, which comprises the body (a12).
3. The mass ratio of the content of the structural unit derived from the high Tg monomer (a11) to the content of the structural unit derived from the low Tg monomer (a12) is 30:70 to 70:30. The copolymer for an electrode binder according to claim 2.
4. The copolymer for an electrode binder according to any one of claims 1 to 3, wherein the content of the structural unit derived from the monomer (a1) is 70% by mass or more and 97% by mass or less.
5. The copolymer for an electrode binder according to any one of claims 1 to 4, wherein at least a part of the structural unit derived from the monomer (a2) forms a salt of a carboxy group and a basic substance. Combined.
6. The copolymer for an electrode binder according to any one of claims 1 to 5, wherein the content of the structural unit derived from the monomer (a2) is 2.0% by mass or more and 10% by mass or less.
7. The copolymer for an electrode binder according to any one of claims 1 to 6, wherein the content of the structural unit derived from the internal cross-linking agent (a3) is 0.50% by mass or more and 5.0% by mass or less. ..
8. In the formula (1), X is the copolymer for an electrode binder according to any one of claims 1 to 7, which is _{SO 3} NH _4.
9. The copolymer for an electrode binder according to any one of claims 1 to 8, wherein n is 8 or more and 25 or less in the formula (1).
10. The copoly for the electrode binder according to any one of claims 1 to 9, wherein the content of the structural unit derived from the polymerizable surfactant (a4) is 0.10% by mass or more and 3.0% by mass or less. Polymer.
11. Further, it has an ethylenically unsaturated bond which does not correspond to any of the monomer (a1), the monomer (a2), the internal cross-linking agent (a3), and the polymerizable surfactant (a4). The copolymer for an electrode binder according to any one of claims 1 to 10, which comprises a structural unit derived from sulfonic acid or a salt thereof.
12. An electrode binder resin composition in which the copolymer for an electrode binder according to any one of claims 1 to 11 is dispersed in an aqueous medium (B).
13. An electrode slurry in which the copolymer for an electrode binder according to any one of claims 1 to 11 and an electrode active material are dispersed in an aqueous medium.
14. A non-aqueous secondary battery electrode in which an electrode active material layer containing the copolymer for an electrode binder and the electrode active material according to any one of claims 1 to 11 is formed on a current collector made of a metal sheet.
15. A non-aqueous secondary battery containing the copolymer for an electrode binder according to any one of claims 1 to 11 in at least one of a positive electrode and a negative electrode.