KR102468252B1 - Binder composition for secondary cell electrode, slurry composition for secondary cell electrode, secondary cell electrode, and secondary cell - Google Patents

Abstract

The binder composition of the present invention contains a particulate polymer and water, the particulate polymer has a core-shell structure composed of a core portion and a shell portion, and has a number average particle diameter of 200 nm or more and 600 nm or less, and the core portion is ethylene Polymerization is performed using a monomer composition having an ethylenically unsaturated carboxylic acid monomer content of more than 0.1% by mass and 5.0% by mass or less, and the shell portion has an ethylenically unsaturated carboxylic acid monomer content of 0.1% by mass or more and 3.0% by mass or less Use of a monomer composition and the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition used for polymerization of the core part is greater than the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition used for polymerization of the shell part.

Description

Binder composition for secondary battery electrode, slurry composition for secondary battery electrode, secondary battery electrode and secondary battery

The present invention relates to a binder composition for secondary battery electrodes, a slurry composition for secondary battery electrodes, an electrode for secondary batteries, and a secondary battery.

BACKGROUND ART Secondary batteries such as lithium ion secondary batteries are small and lightweight, have high energy density, and are capable of repeated charging and discharging, and are used in a wide range of applications. Therefore, in recent years, for the purpose of further enhancing the performance of secondary batteries, improvement of battery members such as electrodes has been studied.

Here, an electrode for a secondary battery such as a lithium ion secondary battery usually includes a current collector and an electrode mixture layer formed on the current collector. And the electrode mixture layer is formed by, for example, applying a slurry composition obtained by dispersing an electrode active material and a binder composition containing a binder in a dispersion medium on a current collector, and drying the applied slurry composition.

Accordingly, in recent years, in order to achieve further performance improvement of secondary batteries, an attempt has been made to improve the binder composition used for forming the electrode mixture layer. Specifically, for example, by using a binder composition containing a binder composed of a particulate polymer obtained by polymerizing a monomer composition containing an ethylenically unsaturated carboxylic acid monomer, binding of electrode active materials or electrode active materials and current collector It has been proposed to improve the performance of a secondary battery by increasing its properties.

More specifically, for example, in Patent Document 1, a particulate polymer having a core-shell structure formed by multi-stage polymerization of a monomer composition containing an ethylenically unsaturated carboxylic acid monomer and having a number average particle diameter of 50 to 300 nm is obtained. By using as a binder, while improving the viscosity stability of the slurry composition, a technique of improving the cycle characteristics of a secondary battery by enhancing the binding property between electrode active materials or between electrode active materials and a current collector has been proposed.

Japanese Unexamined Patent Publication No. 2010-192434

However, in a secondary battery using the particulate polymer described in Patent Document 1 as a binder, expansion of the battery cannot be sufficiently suppressed, and secondary battery performance such as rate characteristics and high-temperature cycle characteristics cannot be sufficiently improved. there was

Accordingly, the present invention is to provide a binder composition for a secondary battery electrode and a slurry composition for a secondary battery electrode capable of suppressing expansion of a secondary battery and at the same time exhibiting good rate characteristics and high-temperature cycle characteristics in the secondary battery. do.

Another object of the present invention is to provide a secondary battery electrode capable of suppressing swelling of the secondary battery and at the same time giving the secondary battery good rate characteristics and high-temperature cycle characteristics.

Another object of the present invention is to provide a secondary battery that is excellent in rate characteristics and high-temperature cycle characteristics and is less prone to swelling.

The inventors of the present invention conducted intensive studies for the purpose of solving the above problems. In addition, the inventors of the present invention, in the secondary battery using the particulate polymer having a core-shell structure described in Patent Document 1, since the amount of the ethylenically unsaturated carboxylic acid monomer used for preparation of the particulate polymer is large, the swelling of the battery can be sufficiently suppressed. I found out what I couldn't. In addition, as a result of further studies by the present inventors, it is possible to suppress expansion of the battery by reducing the amount of the ethylenically unsaturated carboxylic acid monomer used for preparation of the particulate polymer, while the amount of the ethylenically unsaturated carboxylic acid monomer It has been found that pinholes are generated in the electrodes when λ is excessively reduced.

Then, the present inventor repeated further studies based on the above findings. Then, the inventors of the present invention, regarding a secondary battery using a particulate polymer having a core-shell structure as a binder, the amount of ethylenically unsaturated carboxylic acid monomer in the monomer composition used for preparing the core portion of the particulate polymer and the amount of the shell portion used for preparation Both expansion of the battery and generation of pinholes in the electrode are suppressed by adjusting the amount of the ethylenically unsaturated carboxylic acid monomer in the monomer composition to be within a predetermined range and at the same time adjusting the number average particle diameter of the particulate polymer to be within a predetermined range Thus, it was found that the rate characteristics and high-temperature cycle characteristics could be sufficiently improved, and the present invention was completed.

That is, this invention aims at advantageously solving the above problems, and the binder composition for secondary battery electrodes of the present invention is a binder composition for secondary battery electrodes containing a particulate polymer and water, wherein the particulate polymer comprises A monomer having a core-shell structure composed of a core portion and a shell portion, and having a number average particle diameter of 200 nm or more and 600 nm or less, and the content of the ethylenically unsaturated carboxylic acid monomer in the core portion is more than 0.1% by mass and 5.0% by mass or less Polymerized using a composition, wherein the shell portion is polymerized using a monomer composition having an ethylenically unsaturated carboxylic acid monomer content of 0.1% by mass or more and 3.0% by mass or less, and the ethylenically unsaturated monomer composition used for polymerization of the core portion It is characterized in that the content of the carboxylic acid monomer is greater than the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition used for polymerization of the shell part. Thus, with respect to the monomer composition used for polymerization of the core portion and the monomer composition used for polymerization of the shell portion, the content of the ethylenically unsaturated carboxylic acid monomer is not more than the above upper limit, and the number average particle size of the particulate polymer is within the above range If so, expansion of the secondary battery produced using the binder composition can be suppressed. Further, with respect to the monomer composition used for polymerization of the core portion and the monomer composition used for polymerization of the shell portion, if the content of the ethylenically unsaturated carboxylic acid monomer is not less than the lower limit and the number average particle diameter of the particulate polymer is within the above range, , the occurrence of pinholes in the electrode can be suppressed. In addition, when the binder composition containing the particulate polymer described above is used, the rate characteristics and high-temperature cycle characteristics of the secondary battery can be sufficiently improved.

On the other hand, in the present invention, the "number average particle diameter of the particulate polymer" can be measured using a laser diffraction/scattering type particle size distribution analyzer. In the present invention, the term "shell portion" refers to a portion polymerized at the final stage when preparing a particulate polymer having a core-shell structure by multistage polymerization, and is usually formed on the surface of the core portion to form the uppermost surface portion of the particulate polymer. refers to the constituent parts. Further, in the present invention, the "core part" may be prepared using one type of monomer composition, or may be prepared by multistage polymerization using two or more types of monomer compositions. On the other hand, when using two or more types of monomer compositions for preparation of the core portion, the content of the ethylenically unsaturated carboxylic acid monomer in each monomer composition needs to be within the above range.

Here, in the binder composition for secondary battery electrodes of the present invention, the amount of ethylenically unsaturated carboxylic acid monomer used for polymerization of the core portion is 0.2 times or more 7.0 times the amount of ethylenically unsaturated carboxylic acid monomer used for polymerization of the shell portion. It is preferable that it is less than twice. When the amount of the ethylenically unsaturated carboxylic acid monomer used for polymerization of the core portion is 0.2 times or more of the amount of the ethylenically unsaturated carboxylic acid monomer used for polymerization of the shell portion, the stability of the slurry composition using the binder composition can be improved, and at the same time It is because generation|occurrence|production of the pinhole with respect to an electrode can fully be suppressed. In addition, if the amount of the ethylenically unsaturated carboxylic acid monomer used for polymerization of the core portion is 7.0 times or less of the amount of the ethylenically unsaturated carboxylic acid monomer used for polymerization of the shell portion, swelling of the secondary battery can be sufficiently suppressed. .

On the other hand, in the present invention, when two or more types of monomer compositions are used for preparation of the core portion, "the amount of ethylenically unsaturated carboxylic acid monomers used for polymerization of the core portion" refers to the total amount of the ethylenically unsaturated carboxylic acid monomers used point

Further, in the binder composition for secondary battery electrodes of the present invention, the particulate polymer preferably contains 0.2% by mass or more and 3.0% by mass or less of an ethylenically unsaturated carboxylic acid monomer unit. It is because generation|occurrence|production of the pinhole with respect to an electrode can fully be suppressed if the quantity of an ethylenically unsaturated carboxylic acid monomeric unit shall be 0.2 mass % or more. In addition, it is because expansion of the secondary battery can be sufficiently suppressed when the amount of the ethylenically unsaturated carboxylic acid monomer unit is 3.0% by mass or less.

On the other hand, in the present invention, "a monomer unit is included" means "a structural unit derived from a monomer is contained in a polymer obtained using the monomer."

And, in the binder composition for secondary battery electrodes of the present invention, it is preferable that the amount of monomers used for polymerization of the core portion is 0.1 times or more and 0.5 times or less of the amount of monomers used for polymerization of the shell portion. When the amount of monomers used for polymerization of the core portion is 0.1 times or more and 0.5 times or less of the amount of monomers used for polymerization of the shell portion, the number average particle diameter of the particulate polymer is set to an appropriate size, and expansion of the secondary battery can be sufficiently suppressed. It is because the peeling strength of the electrode produced using the binder composition can be improved while existing.

On the other hand, in the present invention, when two or more types of monomer compositions are used for preparation of the core part, "amount of monomers used for polymerization of the core part" refers to the total amount of monomers used for preparation of the core part.

In addition, this invention aims at advantageously solving the above problems, and the slurry composition for secondary battery electrodes of the present invention contains any one of the above-mentioned binder compositions for secondary battery electrodes and an electrode active material. to be In this way, when the binder composition described above is used, expansion of a secondary battery produced using the slurry composition can be suppressed. In addition, generation of pinholes in electrodes produced using the slurry composition can be suppressed. In addition, when the slurry composition described above is used, the rate characteristics and high-temperature cycle characteristics of the secondary battery can be sufficiently improved.

Moreover, this invention aims at solving the said subject advantageously, and the electrode for secondary batteries of this invention is characterized by having the electrode mixture layer obtained using the above-mentioned slurry composition for secondary battery electrodes. In this way, when the electrode mixture layer is formed using the above-described slurry composition for secondary battery electrodes, it is possible to suppress expansion of the secondary battery using the electrode while suppressing the occurrence of pinholes, and at the same time, good rate characteristics and high temperature cycles for secondary batteries characteristics can be demonstrated.

Moreover, this invention aims at solving the said subject advantageously, and the secondary battery of this invention is provided with a positive electrode, a negative electrode, an electrolyte solution, and a separator, and at least one of the said positive electrode and the negative electrode is the above-mentioned electrode for secondary batteries It is characterized by being In this way, when the electrode described above is used, it is possible to provide a secondary battery that is excellent in rate characteristics and high-temperature cycle characteristics and is less prone to swelling.

According to the present invention, it is possible to provide a binder composition for a secondary battery electrode and a slurry composition for a secondary battery electrode, which can suppress expansion of a secondary battery and at the same time exhibit good rate characteristics and high-temperature cycle characteristics in the secondary battery.

Further, according to the present invention, it is possible to provide an electrode for a secondary battery capable of suppressing swelling of the secondary battery and at the same time exhibiting good rate characteristics and high-temperature cycle characteristics of the secondary battery.

Further, according to the present invention, it is possible to provide a secondary battery that is excellent in rate characteristics and high-temperature cycle characteristics and is less prone to swelling.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail.

Here, the binder composition for secondary battery electrodes of this invention can be used when preparing the slurry composition for secondary battery electrodes. And the slurry composition for secondary battery electrodes prepared using the binder composition for secondary battery electrodes of this invention can be used when forming the electrode of a secondary battery. Further, the secondary battery of the present invention is characterized by using the electrode for secondary batteries of the present invention.

(Binder composition for secondary battery electrode)

The binder composition for secondary battery electrodes of the present invention is an aqueous binder composition using an aqueous medium as a dispersion medium, and contains a particulate polymer as a binder and water. And, the binder composition for secondary battery electrodes of the present invention is a particulate polymer, a core portion polymerized using a monomer composition having an ethylenically unsaturated carboxylic acid monomer content within a predetermined range, and an ethylenically unsaturated carboxylic acid monomer It is characterized in that it contains a particulate polymer having a core-shell structure composed of shell parts polymerized using a monomer composition in which the content of is within a predetermined range, and the number average particle diameter is within a predetermined range.

<Particulate Polymer>

The particulate polymer is a secondary battery electrode prepared by forming an electrode mixture layer on a current collector using a slurry composition for secondary battery electrodes containing the binder composition and an electrode active material of the present invention, wherein the component contained in the electrode mixture layer is It is a component that can be maintained so as not to detach from the electrode mixture layer. In general, when the particulate polymer in the electrode mixture layer is immersed in an electrolyte solution, it absorbs the electrolyte solution and retains its particulate shape even while swelling, and binds the electrode active materials or the electrode active material and the current collector together, so that the electrode active material prevent falling out of In addition, the particulate polymer binds particles other than the electrode active material included in the electrode mixture layer, and also serves to maintain the strength of the electrode mixture layer.

And, in the binder composition of the present invention, in order to suppress the generation of pinholes in the electrode formed using the binder composition and the expansion of the secondary battery, and to exhibit good rate characteristics and high-temperature cycle characteristics in the secondary battery, predetermined monomers It is characterized by using a particulate polymer having a core-shell structure composed of a core portion and a shell portion formed using the composition and having a number average particle diameter of 200 nm or more and 600 nm or less.

[Core shell structure]

Here, the particulate polymer having a core-shell structure can be prepared by multistage polymerization. Specifically, the particulate polymer is obtained by forming a core portion by one-stage polymerization or multi-stage polymerization using the monomer composition for forming the core portion, and then polymerizing the monomer composition for forming the shell portion in the presence of the core portion to form the shell portion, can be prepared

On the other hand, polymerization of the monomer composition for forming the core portion and the monomer composition for forming the shell portion is not particularly limited, and can be performed in an aqueous solvent such as water. And the content rate of each monomer in the monomer composition used for polymerization is usually the same as the content rate of the repeating unit (monomer unit) in the polymer obtained by superposing|polymerizing the said monomer unit.

The polymerization mode of the core portion and the shell portion is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used, for example. As a polymerization reaction, any reaction, such as ionic polymerization, radical polymerization, and living radical polymerization, can be used, for example. Among them, from the viewpoint of production efficiency, the emulsion polymerization method is particularly preferred. On the other hand, emulsion polymerization can be performed according to a conventional method.

The emulsifier, dispersant, polymerization initiator, polymerization aid, chain transfer agent, etc. used in the polymerization of the core part and the shell part can be generally used, and the amount used is also a generally used amount. In the polymerization of the core portion, seed polymerization may be performed by employing seed particles. In addition, polymerization conditions can also be arbitrarily selected depending on the polymerization method and the type of polymerization initiator.

-Monomer composition for forming core portion-

In the binder composition of the present invention, the core portion of the particulate polymer needs to be polymerized using a monomer composition having an ethylenically unsaturated carboxylic acid monomer content of more than 0.1% by mass and 5.0% by mass or less. Further, the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition used for polymerization of the core portion is required to be greater than the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition used for polymerization of the shell portion.

When the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the core portion is 0.1% by mass or less, the polymerization stability of the core portion is lowered, and the generation of pinholes cannot be suppressed when an electrode is formed using the binder composition. . In addition, when the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the core portion is more than 5.0% by mass, swelling of the secondary battery using the binder composition cannot be suppressed. In addition, when the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the core portion is more than 5.0% by mass, the core-shell structure cannot be formed satisfactorily, and the number average particle size of the particulate polymer may decrease. . On the other hand, when the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the core portion is more than 0.1% by mass and 5.0% by mass or less, both generation of pinholes in the electrode and swelling of the secondary battery are suppressed, resulting in secondary battery can exhibit good rate characteristics and high-temperature cycle characteristics. In addition, if the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the core portion is higher than the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the shell portion, the particle diameter is small and the polymerization stability of the core is likely to decrease. This is because the moiety is favorably polymerized and the occurrence of pinholes in the electrode can be sufficiently suppressed.

On the other hand, from the viewpoint of ensuring the polymerization stability of the core portion and sufficiently suppressing the generation of pinholes in the electrode, the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the core portion is preferably 0.2% by mass or more, and preferably 0.5% by mass. It is more preferable that it is mass % or more, and it is more preferable that it is 2.5 mass % or more. Further, from the viewpoint of sufficiently suppressing expansion of the secondary battery, the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the core portion is preferably 4.0% by mass or less, more preferably 3.5% by mass or less, and 3.0% by mass or less. It is more preferable that it is mass % or less.

Here, as the ethylenically unsaturated carboxylic acid monomer contained in the monomer composition for forming the core portion, monocarboxylic acids and dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, And the anhydride etc. are mentioned. Among them, acrylic acid, methacrylic acid and itaconic acid are preferred. On the other hand, ethylenically unsaturated carboxylic acid monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In addition, the monomers other than the ethylenically unsaturated carboxylic acid monomer contained in the monomer composition for forming the core portion are not particularly limited, and an aliphatic conjugated diene monomer, an aromatic vinyl monomer, a vinyl cyanide monomer, a (meth)acrylic acid ester monomer , known monomers used for preparation of particulate polymers such as unsaturated monomers containing a hydroxyalkyl group and unsaturated carboxylic acid amide monomers. On the other hand, in the present invention, it is important that the amount of the ethylenically unsaturated carboxylic acid monomer contained in the monomer composition is within a predetermined range, and the type and amount of other monomers used for forming the core portion are arbitrary types and amounts can be done with

Here, in this specification, "(meth)acrylic acid" means acrylic acid and/or methacrylic acid.

On the other hand, the aliphatic conjugated diene monomer is not particularly limited, and 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3- butadiene, substituted straight-chain conjugated pentadienes, substituted and side-chain conjugated hexadienes, and the like. Especially, 1,3-butadiene is preferable. On the other hand, an aliphatic conjugated diene monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Moreover, it does not specifically limit as an aromatic vinyl monomer, Styrene, (alpha)-methylstyrene, vinyltoluene, divinylbenzene, etc. are mentioned. Especially, styrene is preferable. On the other hand, an aromatic vinyl monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Moreover, it does not specifically limit as a vinyl cyanide type monomer, Acrylonitrile, methacrylonitrile, (alpha)-chloroacrylonitrile, (alpha)-ethylacrylonitrile, etc. are mentioned. Especially, acrylonitrile and methacrylonitrile are preferable. In addition, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In addition, as a (meth)acrylic acid ester monomer, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, acrylic acid alkyl esters such as hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate and stearyl acrylate; Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate Alkyl methacrylates such as late, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate Ester etc. are mentioned. Especially, methyl acrylate and methyl methacrylate are preferable. In addition, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In addition, as an unsaturated monomer containing a hydroxyalkyl group, for example, β-hydroxyethyl acrylate, β-hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl Acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di-(ethylene glycol) maleate, di-(ethylene glycol) itaconate, 2-hydroxyethyl maleate, Bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate, etc. are mentioned. Especially, (beta)-hydroxyethyl acrylate is preferable. In addition, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Moreover, as an unsaturated carboxylic acid amide monomer, acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N,N- dimethyl acrylamide etc. are mentioned, for example. Especially, acrylamide and methacrylamide are preferable. In addition, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Among them, the monomer composition for forming the core portion preferably contains at least an aliphatic conjugated diene monomer and an aromatic vinyl monomer, and contains 1,3-butadiene as the aliphatic conjugated diene monomer and styrene as the aromatic vinyl monomer. it is more preferable That is, it is preferable that the core portion is constituted of a styrene-butadiene copolymer.

On the other hand, when the core portion is formed by multi-stage polymerization, the composition of the monomer composition used in each polymerization stage may be the same or different.

-Monomer composition for forming shell part-

Further, in the binder composition of the present invention, the shell portion of the particulate polymer needs to be polymerized using a monomer composition having an ethylenically unsaturated carboxylic acid monomer content of 0.1% by mass or more and 3.0% by mass or less.

When the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the shell portion is less than 0.1% by mass, generation of pinholes cannot be suppressed when an electrode is formed using the binder composition. In addition, when the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the shell portion is more than 3.0% by mass, swelling of the secondary battery using the binder composition cannot be suppressed. On the other hand, when the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the shell portion is 0.1% by mass or more and 3.0% by mass or less, both generation of pinholes in the electrode and expansion of the secondary battery are suppressed, resulting in a secondary battery Good rate characteristics and high-temperature cycle characteristics can be exhibited.

On the other hand, from the viewpoint of sufficiently suppressing the occurrence of pinholes in the electrode, the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the shell portion is preferably 0.15% by mass or more, and more preferably 0.2% by mass or more. Further, from the viewpoint of sufficiently suppressing expansion of the secondary battery, the content of the ethylenically unsaturated carboxylic acid monomer in the monomer composition for forming the shell portion is preferably 2.0% by mass or less, more preferably 1.0% by mass or less, and 0.7% by mass % or less is more preferred.

Here, as the ethylenically unsaturated carboxylic acid monomer contained in the monomer composition for forming the shell portion, the same ethylenically unsaturated carboxylic acid monomer as in the monomer composition for forming the core portion can be used. Among them, acrylic acid, methacrylic acid and itaconic acid are preferred. On the other hand, ethylenically unsaturated carboxylic acid monomers may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In addition, the monomers other than the ethylenically unsaturated carboxylic acid monomer contained in the monomer composition for forming the shell portion are not particularly limited, and include aliphatic conjugated diene monomers, aromatic vinyl monomers, vinyl cyanide monomers, (meth)acrylic acid ester monomers, Known monomers used for preparation of particulate polymers, such as an unsaturated monomer containing a hydroxyalkyl group and an unsaturated carboxylic acid amide monomer, are exemplified. Here, in the present invention, it is important that the amount of the ethylenically unsaturated carboxylic acid monomer contained in the monomer composition is within a predetermined range, and the type and amount of other monomers used for forming the shell portion are arbitrary types and amounts can be done with

On the other hand, as the aliphatic conjugated diene monomer, the same aliphatic conjugated diene monomer as the monomer composition for forming the core portion can be used. Especially, 1,3-butadiene is preferable. On the other hand, an aliphatic conjugated diene monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The content of the aliphatic conjugated diene monomer in the monomer composition for forming the shell part is, for example, preferably 17% by mass or more, more preferably 25% by mass or more, preferably 65% by mass or less, and 60% by mass or less. it is more preferable

In addition, as an aromatic vinyl monomer, the same aromatic vinyl monomer as the monomer composition for forming a core part can be used. Especially, styrene is preferable. On the other hand, an aromatic vinyl monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The content of the aromatic vinyl monomer in the monomer composition for forming the shell part is, for example, preferably 27% by mass or more, more preferably 34% by mass or more, preferably 75% by mass or less, and preferably 68% by mass or less. more preferable

In addition, as the vinyl cyanide-based monomer, the same vinyl cyanide-based monomer as the monomer composition for forming the core portion can be used. Especially, acrylonitrile and methacrylonitrile are preferable. In addition, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In addition, as a (meth)acrylic acid ester monomer, the same (meth)acrylic acid ester monomer as the monomer composition for forming a core part can be used. Especially, methyl acrylate and methyl methacrylate are preferable from a viewpoint of speeding up a polymerization rate. In addition, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The content of the (meth)acrylic acid ester monomer in the monomer composition for forming the shell part is, for example, preferably 0.5% by mass or more, more preferably 1% by mass or more, preferably 10% by mass or less, and 7% by mass. It is more preferable that it is % or less.

In addition, as the unsaturated monomer containing a hydroxyalkyl group, the same unsaturated monomer containing a hydroxyalkyl group as the monomer composition for forming the core portion can be used. Especially, (beta)-hydroxyethyl acrylate is preferable. In addition, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

In addition, as the unsaturated carboxylic acid amide monomer, the same unsaturated carboxylic acid amide monomer as the monomer composition for forming the core portion can be used. Especially, acrylamide and methacrylamide are preferable. In addition, these may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Among them, the monomer composition for forming the shell portion preferably contains at least an aliphatic conjugated diene monomer and an aromatic vinyl monomer, and contains 1,3-butadiene as the aliphatic conjugated diene monomer and styrene as the aromatic vinyl monomer. more preferable That is, it is preferable that the shell portion is constituted of a styrene-butadiene copolymer.

-Ratio of usage amount of ethylenically unsaturated carboxylic acid monomer-

Here, in the preparation of the particulate polymer, the amount (total amount) of the ethylenically unsaturated carboxylic acid monomers used for forming the core portion is preferably 0.2 times or more of the amount of the ethylenically unsaturated carboxylic acid monomers used for forming the shell portion. It is more preferably 0.35 times or more, preferably 7.0 times or less, and more preferably 6.0 times or less. When the amount of the ethylenically unsaturated carboxylic acid monomer used for forming the core portion is 0.2 times or more of the amount of the ethylenically unsaturated carboxylic acid monomer used for forming the shell portion, the core portion is formed favorably and the slurry composition using the binder composition This is because the stability of the electrode can be improved and the occurrence of pinholes in the electrode can be sufficiently suppressed. Further, when the amount of the ethylenically unsaturated carboxylic acid monomer used for forming the core portion is 7.0 times or less of the amount of the ethylenically unsaturated carboxylic acid monomer used for forming the shell portion, the amount of the ethylenically unsaturated carboxylic acid monomer used This is because it is possible to reduce the swelling of the secondary battery sufficiently.

-Amount of Ethylenically Unsaturated Carboxylic Acid Monomer Units-

Further, the particulate polymer formed using the above-mentioned monomer composition for forming a core portion and monomer composition for forming a shell portion preferably contains 0.2 mass% or more of ethylenically unsaturated carboxylic acid monomer units, and 0.3 mass% or more It is more preferably included, more preferably 0.5% by mass or more, preferably 3.0% by mass or less, more preferably 1.0% by mass or less, and even more preferably 0.8% by mass or less. When the proportion of the ethylenically unsaturated carboxylic acid monomer unit in all the monomer units of the particulate polymer is 0.2% by mass or more, a sufficient amount of the ethylenically unsaturated carboxylic acid monomer unit is secured and the occurrence of pinholes in the electrode is sufficiently suppressed. Because you can. In addition, if the ratio of the ethylenically unsaturated carboxylic acid monomer unit in all the monomer units of the particulate polymer is 3.0% by mass or less, the amount of the ethylenically unsaturated carboxylic acid monomer unit can be reduced and the expansion of the secondary battery can be sufficiently suppressed. because it can

-Ratio of the amount of monomers-

In addition, in the particulate polymer, the amount of the monomer used for polymerization of the core portion (monomer in the monomer composition for forming the core portion) is 0.1 times or more of the amount of the monomer used for polymerization of the shell portion (monomer in the monomer composition for forming the shell portion). It is preferably 0.2 times or more, more preferably 0.5 times or less, and more preferably 0.3 times or less. When the amount of the monomer used for polymerization of the core portion is 0.1 times or more of the amount of the monomer used for polymerization of the shell portion, the number average particle diameter of the particulate polymer is prevented from becoming excessively large due to a decrease in the number of core portions, and an electrode produced using a binder composition. This is because the peel strength of the can be improved. In addition, when the amount of the monomer used for polymerization of the core portion is 0.5 times or less of the amount of monomer used for polymerization of the shell portion, the number average particle diameter of the particulate polymer is prevented from being too small due to an increase in the number of core portions, and a binder composition is used. It is because generation|occurrence|production of the pinhole with respect to the produced electrode can be suppressed.

[Number Average Particle Diameter]

Further, the particulate polymer having the core-shell structure described above must have a number average particle diameter of 200 nm or more and 600 nm or less, and the number average particle diameter of the particulate polymer is preferably 250 nm or more, more preferably 300 nm or more, It is preferably 550 nm or less, and more preferably 400 nm or less. When the number average particle diameter is less than 200 nm, generation of pinholes in the electrode cannot be suppressed even when the particulate polymer having a core-shell structure is formed using the above-described monomer composition. In addition, when the number average particle diameter is more than 600 nm, expansion of the secondary battery cannot be suppressed, and peeling strength of an electrode produced using the binder composition may decrease.

On the other hand, the number average particle diameter of the particulate polymer can be adjusted to a desired range by, for example, adjusting the amount of the emulsifier, the amount of the monomer, and the like.

[THF gel content]

The particulate polymer used in the binder composition of the present invention preferably has a tetrahydrofuran (THF) gel content of 65% by mass or more, more preferably 70% by mass or more, preferably 95% by mass or less, and 80% by mass. It is more preferable that it is % or less. This is because when the THF gel content of the particulate polymer falls within the above-mentioned range, the expansion of the electrode formed using the binder composition can be sufficiently suppressed and the cycle characteristics of the secondary battery can be sufficiently improved.

On the other hand, in the present invention, the "THF gel content" of the particulate polymer can be measured using the measurement method described in Examples of this specification. In addition, the THF gel content mentioned above can be arbitrarily adjusted also by changing the preparation conditions (for example, the monomer used, polymerization conditions, etc.) of a particulate-form polymer. Specifically, the THF gel content can also be adjusted by changing the polymerization temperature, the type of polymerization initiator, the conversion rate at the time of stopping the reaction (monomer consumption, etc.), and the amount of chain transfer agent used. For example, when the compounding amount of tert-dodecylmercaptan (TDM), which is a chain transfer agent used during polymerization, is reduced, the THF gel content can be increased, and when the amount of TDM is increased, the THF gel content can be decreased.

<Other ingredients>

The binder composition of the present invention may contain components such as a water-soluble polymer, a conductive aid, a reinforcing agent, a leveling agent, a viscosity modifier, and an electrolyte solution additive in addition to the above particulate polymer. These are not particularly limited as long as they do not affect the battery reaction, and known ones such as those described in International Publication No. 2012/115096 can be used. In addition, these components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

<Preparation of Binder Composition>

The binder composition of the present invention can be prepared by dispersing the above components in an aqueous medium as a dispersion medium. Specifically, by mixing the above-described components and an aqueous medium using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, brain grinder, ultrasonic disperser, homogenizer, planetary mixer, fill mix, binder composition can be prepared.

On the other hand, when a particulate polymer is prepared by polymerizing a monomer composition in an aqueous solvent, it can be mixed with other components as it is in the form of an aqueous dispersion. In addition, when mixing a particulate polymer in the state of a water dispersion, you may use water in a water dispersion as said aqueous medium. That is, the binder composition is not particularly limited, and includes a step of preparing an aqueous dispersion of the particulate polymer described above by polymerizing a monomer composition in an aqueous solvent, optionally adding other components and/or water to the aqueous dispersion, It can be prepared using the manufacturing method of the binder composition which further includes the process of mixing.

(Slurry composition for secondary battery electrodes)

The slurry composition for secondary battery electrodes of the present invention is an aqueous slurry composition using an aqueous medium as a dispersion medium, and contains an electrode active material and the binder composition described above. That is, the slurry composition for secondary battery electrodes of this invention contains at least an electrode active material, the above-mentioned particulate polymer, and dispersion mediums, such as water, and optionally further contains other components. And since the slurry composition for secondary battery electrodes of this invention contains the above-mentioned binder composition, while being able to suppress the generation of pinholes in the electrode formed using the said slurry composition, the secondary battery using the said electrode swelling can be suppressed. And, as a result, the rate characteristics and high-temperature cycle characteristics of the secondary battery can be sufficiently improved.

On the other hand, below, as an example, the case where the slurry composition for secondary battery electrodes is a slurry composition for lithium ion secondary battery electrodes will be described, but the present invention is not limited to the following examples.

<Electrode active material>

An electrode active material is a material that exchanges electrons in an electrode (positive electrode, negative electrode) of a lithium ion secondary battery. And as an electrode active material (positive electrode active material, negative electrode active material) of a lithium ion secondary battery, the material which can occlude and discharge|release lithium is normally used.

[Positive Electrode Active Material]

Specifically, as the positive electrode active material, a compound containing a transition metal such as a transition metal oxide, a transition metal sulfide, a composite metal oxide of lithium and transition metal, or the like can be used. On the other hand, as a transition metal, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo etc. are mentioned, for example.

Here, as the transition metal oxide, for example, MnO, MnO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , Cu ₂ V ₂ O ₃ , amorphous V ₂ OP ₂ O ₅ , amorphous MoO ₃ , amorphous V ₂ O ₅ , amorphous V ₆ O ₁₃ and the like.

Examples of the transition metal sulfide include TiS ₂ , TiS ₃ , amorphous MoS ₂ , and FeS.

Examples of the composite metal oxide of lithium and transition metal include a lithium-containing composite metal oxide having a layered structure, a lithium-containing composite metal oxide having a spinel structure, and a lithium-containing composite metal oxide having an olivine structure.

Examples of the lithium-containing composite metal oxide having a layered structure include lithium-containing cobalt oxide (LiCoO ₂ ), lithium-containing nickel oxide (LiNiO ₂ ), and a lithium-containing composite oxide of Co-Ni-Mn (Li(Co Mn Ni ) O ₂ ), a lithium-containing composite oxide of Ni-Mn-Al, a lithium-containing composite oxide of Ni-Co-Al, a solid solution of LiMaO ₂ and Li ₂ MbO ₃ , and the like. On the other hand, examples of the Co-Ni-Mn lithium-containing composite oxide include Li[Ni _0.5 Co _0.2 Mn _0.3 ]O ₂ , Li[Ni _1/3 Co _1/3 Mn _1/3 ]O ₂ , and the like. Moreover, as a solid solution _{of LiMaO2} and _Li2MbO3 , xLiMaO2.( _{1 -} x) _Li2MbO3 etc. are mentioned, for example. Here, x represents a number satisfying 0 < x < 1, Ma represents one or more types of transition metals with an average oxidation state of 3+, and Mb represents one or more types of transition metals with an average oxidation state of 4+. As such a solid solution, Li[Ni _{0 . 17} Li _{0 . 2} Co _{0 . 07} Mn _{0 . 56} ]O ₂ and the like.

In the present specification, the "average oxidation state" indicates the average oxidation state of the above "one or more transition metals", and is calculated from the molar amount and valence of the transition metal. For example, when "one or more types of transition metals" are composed of 50 mol% of Ni ^{2+ and 50 mol% of Mn 4+ ,} the ^average oxidation state of "one or more types of transition metals" is (0.5) × (2+) + (0.5) × (4+) = 3+.

As the lithium-containing composite metal oxide having a spinel structure, for example, lithium manganate (LiMn ₂ O ₄ ) or a compound obtained by substituting a part of Mn of lithium manganate (LiMn ₂ O ₄ ) with another transition metal. can be heard Specific examples include Li _s [Mn _2-t Mc _t ] O ₄ such as LiNi _0.5 Mn _1.5 O ₄ . Here, Mc represents one or more transition metals with an average oxidation state of 4+. Specific examples of Mc include Ni, Co, Fe, Cu, and Cr. Also, t represents a number satisfying 0 < t < 1, and s represents a number satisfying 0 ≤ s ≤ 1. On the other hand, as the positive electrode active material, a lithium-excessive spinel compound represented _{by Li 1+ x Mn 2 - x O 4} (0 < X < 2) or the like can also be used.

Examples of the lithium-containing composite metal oxide having an olivine-type structure include olivine-type lithium phosphate compounds represented by Li _y MdPO ₄ such as olivine-type lithium iron phosphate (LiFePO ₄ ) and olivine-type lithium manganese phosphate (LiMnPO ₄ ). can be heard Here, Md represents one or more transition metals having an average oxidation state of 3+, and examples thereof include Mn, Fe, and Co. Also, y represents a number that satisfies 0 ≤ y ≤ 2. In the olivine-type lithium phosphate compound represented by Li _y MdPO ₄ , Md may be partially substituted with another metal. As a metal which can be substituted, Cu, Mg, Zn, V, Ca, Sr, Ba, Ti, Al, Si, B, and Mo etc. are mentioned, for example.

[negative electrode active material]

Moreover, as a negative electrode active material, a carbon-type negative electrode active material, a metal-type negative electrode active material, the negative electrode active material which combined these, etc. are mentioned, for example.

Here, the carbon-based negative electrode active material refers to an active material having carbon as a main skeleton and capable of intercalating (also referred to as “dope”) lithium, and examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials. have.

A carbonaceous material is a material with a low degree of graphitization (ie, low crystallinity) obtained by carbonizing a carbon precursor by heat treatment at 2000°C or less. On the other hand, although the lower limit of the heat treatment temperature at the time of carbonization is not specifically limited, For example, it can be 500 degreeC or more.

And, as a carbonaceous material, graphitic carbon that easily changes the structure of carbon by heat treatment temperature, for example, graphitic carbon having a structure close to an amorphous structure typified by glassy carbon, which is difficult to graphitize Carbon etc. are mentioned.

Here, as easily graphitic carbon, the carbon material which used tar pitch obtained from petroleum or coal as a raw material is mentioned, for example. Specific examples thereof include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and thermal decomposition vapor-grown carbon fibers.

Moreover, as non-graphitic carbon, a phenol resin sintered body, polyacrylonitrile-type carbon fiber, quasi-isotropic carbon, furfuryl alcohol resin sintered body (PFA), hard carbon etc. are mentioned, for example.

A graphite material is a material having high crystallinity similar to graphite obtained by heat-treating easily graphitic carbon at 2000°C or higher. On the other hand, the upper limit of the heat treatment temperature is not particularly limited, but may be, for example, 5000°C or lower.

And as a graphite material, natural graphite, artificial graphite, etc. are mentioned, for example.

Here, as artificial graphite, for example, artificial graphite obtained by heat-treating carbon containing easily graphitic carbon mainly at 2800 ° C. or higher, graphitized MCMB obtained by heat-treating MCMB at 2000 ° C. or higher, and mesophase pitch-based carbon fiber at 2000 ° C. or higher and graphitized mesophase pitch-based carbon fibers subjected to heat treatment.

In addition, a metal-based negative electrode active material is an active material containing a metal, which usually contains an element capable of intercalating lithium in its structure, and has a theoretical electric capacity per unit mass of 500 mAh/g or more when lithium is intercalated. . Examples of the metal-based active material include, for example, lithium metal and a simple metal capable of forming a lithium alloy (eg, Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, and their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. are used. Among these, as the metal negative electrode active material, an active material containing silicon (silicon negative electrode active material) is preferable. It is because the capacity of a lithium ion secondary battery can be increased by using a silicon type negative electrode active material.

Examples of the silicon-based negative electrode active material include silicon (Si), a silicon-containing alloy, SiO, SiOx, and a composite of a Si-containing material obtained _by coating or combining a Si-containing material with conductive carbon and conductive carbon, and the like. can On the other hand, these silicon-type negative electrode active materials may be used individually by 1 type, and may be used in combination of 2 or more types.

As an alloy containing silicon, the alloy composition containing silicon, aluminum, transition metals, such as iron, and also containing rare-earth elements, such as tin and yttrium, is mentioned, for example.

SiO _x is a compound containing at least one of SiO and SiO ₂ and Si, and x is usually 0.01 or more and less than 2. And, SiO _x can be formed using, for example, a disproportionation reaction of silicon monoxide (SiO). Specifically, SiO _x can be prepared by subjecting SiO to heat treatment in the presence of a polymer such as polyvinyl alcohol, to form silicon and silicon dioxide. On the other hand, the heat treatment can be performed at a temperature of 900°C or higher, preferably 1000°C or higher, in an atmosphere containing organic gas and/or steam after pulverization and mixing of SiO and optionally a polymer.

As the complex of the Si-containing material and the conductive carbon, for example, a pulverized mixture of SiO, a polymer such as polyvinyl alcohol, and optionally a carbon material is heat-treated in an atmosphere containing organic gas and/or steam, for example. and compounds formed by In addition, a method of coating the surface of SiO particles by a chemical vapor deposition method using an organic gas or the like, a method of forming (aggregating) SiO particles and graphite or artificial graphite into composite particles by a mechanochemical method, etc. can also be obtained in this way.

<Binder composition>

As a binder composition that can be blended in the slurry composition for lithium ion secondary battery electrodes, the binder composition for secondary battery electrodes of the present invention containing the above-described particulate polymer and water can be used.

On the other hand, the blending amount of the binder composition is not particularly limited, and for example, the amount of the particulate polymer per 100 parts by mass of the electrode active material, in terms of solid content, can be 0.5 parts by mass or more and 3.0 parts by mass or less.

<Other ingredients>

The other components that can be incorporated into the slurry composition are not particularly limited, and include the same components as the other components that can be incorporated into the binder composition of the present invention. In addition, other components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

<Preparation of slurry composition>

The above-mentioned slurry composition can be prepared by dispersing each of the above components in an aqueous medium as a dispersion medium. Specifically, by mixing the above components and an aqueous medium using a mixer such as a ball mill, sand mill, bead mill, pigment disperser, brain grinder, ultrasonic disperser, homogenizer, planetary mixer, fill mix, slurry composition can be prepared. On the other hand, the mixing of each of the above components and the aqueous medium can usually be performed in the range of room temperature to 80°C for 10 minutes to several hours.

Here, as the aqueous medium, water is usually used, but an aqueous solution of an arbitrary compound or a mixed solution of a small amount of an organic medium and water may be used. On the other hand, the water used as the aqueous medium may also contain water contained in the binder composition.

(electrode for secondary battery)

The said slurry composition for secondary battery electrodes (the slurry composition for negative electrodes and the slurry composition for positive electrodes) prepared using the binder composition for secondary battery electrodes of this invention can be used for manufacture of the electrodes (negative electrode and positive electrode) for secondary batteries.

Here, the electrode for secondary batteries includes a current collector and an electrode mixture layer formed on the current collector, and the electrode mixture layer is formed using the slurry composition for secondary battery electrodes. That is, the electrode mixture layer contains at least the electrode active material and the particulate polymer described above. On the other hand, each component contained in the electrode mixture layer was contained in the slurry composition for secondary battery electrodes, and the appropriate abundance ratio of each component is the same as the appropriate abundance ratio of each component in the slurry composition.

And since the said electrode for secondary batteries is produced using the slurry composition containing the binder composition for secondary battery electrodes of this invention, generation|occurrence|production of a pinhole is suppressed. Further, in a secondary battery using the electrode, expansion of the battery is suppressed. As a result, a secondary battery using the above secondary battery electrode can exhibit good rate characteristics and high-temperature cycle characteristics.

<Method for Manufacturing Electrode for Secondary Battery>

On the other hand, the electrode for a secondary battery of the present invention, for example, the step of applying the above-described slurry composition for a secondary battery electrode onto a current collector (application step), and drying the slurry composition for a secondary battery electrode applied on the current collector to form an electrode mixture layer on the current collector (drying process).

[Coating process]

The method of applying the slurry composition for secondary battery electrodes onto the current collector is not particularly limited, and a known method can be used. Specifically, as a coating method, a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, a brush coating method, or the like can be used. At this time, the slurry composition may be applied only to one side of the current collector, or may be applied to both sides. The thickness of the slurry film on the current collector after application and before drying can be arbitrarily set according to the thickness of the electrode mixture layer obtained by drying.

Here, as the current collector to which the slurry composition is applied, a material having electrical conductivity and electrochemical durability is used. Specifically, as the current collector, a current collector made of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like can be used, for example. Especially, as a collector used for a negative electrode, copper foil is especially preferable. Moreover, as an electrical power collector used for a positive electrode, aluminum foil is especially preferable. In addition, said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[Drying process]

The method for drying the slurry composition on the current collector is not particularly limited, and a known method can be used. For example, drying by warm air, hot air, or low humidity air, vacuum drying, or drying by irradiation with infrared rays or electron beams. can be heard Thus, by drying the slurry composition for electrodes on an electrical power collector, an electrode mixture layer can be formed on an electrical power collector, and the electrode for lithium ion secondary batteries provided with an electrical power collector and an electrode mixture layer can be obtained.

On the other hand, after the drying step, a pressure treatment may be applied to the electrode mixture layer using a mold press, roll press, or the like. The pressure treatment can improve the adhesion between the electrode mixture layer and the current collector.

In addition, when the electrode mixture layer contains a curable polymer, it is preferable to cure the polymer after formation of the electrode mixture layer.

(secondary battery)

The secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolyte solution, and a separator, and uses the electrode for secondary batteries of the present invention as at least one of the positive electrode and the negative electrode. That is, a secondary battery can be manufactured using the electrode for secondary batteries of this invention as at least one of a positive electrode and a negative electrode. And since the secondary battery of this invention is equipped with the electrode for secondary batteries of this invention, it is excellent in rate characteristics and high-temperature cycling characteristics, and it is hard to swell.

Meanwhile, in the following, as an example, a case where the secondary battery is a lithium ion secondary battery will be described, but the present invention is not limited to the following example.

<electrode>

As mentioned above, the electrode for secondary batteries of this invention is used as at least one of a positive electrode and a negative electrode. That is, the positive electrode of the lithium ion secondary battery may be the electrode of the present invention and the negative electrode may be another known negative electrode, the negative electrode of the lithium ion secondary battery may be the electrode of the present invention and the positive electrode may be another known positive electrode, and then the lithium ion secondary battery Both the positive electrode and the negative electrode of may be the electrodes of the present invention.

<Electrolyte>

As the electrolyte solution, an electrolyte solution obtained by dissolving an electrolyte in a solvent can be used.

Here, as the solvent, an organic solvent capable of dissolving the electrolyte can be used. Specifically, as a solvent, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethylmethyl carbonate, dimethyl carbonate in an alkyl carbonate-based solvent such as ethylene carbonate, propylene carbonate, and γ-butyrolactone , methyl acetate, dimethoxyethane, dioxolane, methyl propionate, methyl formate and the like added viscosity adjusting solvent can be used.

As the electrolyte, a lithium salt can be used. As a lithium salt, what was described in Unexamined-Japanese-Patent No. 2012-204303 can be used, for example. Among these lithium salts, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable as electrolytes in view of being easily soluble in organic solvents and exhibiting a high degree of dissociation.

<Separator>

As a separator, the thing of Unexamined-Japanese-Patent No. 2012-204303 can be used, for example. Among these, polyolefin-based resins (polyethylene, polypropylene, A microporous film made of polybutene or polyvinyl chloride) is preferable.

<Method for Manufacturing Lithium Ion Secondary Battery>

In a lithium ion secondary battery, for example, a positive electrode and a negative electrode are stacked with a separator interposed therebetween, and, if necessary, the battery is wound or folded according to the shape of the battery to be placed in a battery container, an electrolyte is injected into the battery container, and the inlet is sealed. can be manufactured by In order to prevent a rise in pressure inside the lithium ion secondary battery, overcharge/discharge, etc., a fuse, an overcurrent prevention element such as a PTC element, an expand metal, a lead plate, or the like may be provided as necessary. The shape of the lithium ion secondary battery may be, for example, a coin shape, a button shape, a sheet shape, a cylindrical shape, a prismatic shape, or a flat shape.

Example

Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. Incidentally, in the following description, "%" and "parts" representing quantities are based on mass unless otherwise specified.

In Examples and Comparative Examples, the number average particle size and THF gel content of the particulate polymer, the stability of the slurry composition, the presence or absence of pinholes and peel strength of the electrode, and the high-temperature cycle characteristics, rate characteristics and expansion resistance of the secondary battery, respectively It was evaluated using the following method.

<Number Average Particle Diameter>

The number average particle diameter of the particulate polymer was measured using a laser diffraction/scattering type particle size distribution analyzer (LS230, manufactured by Beckman Coulter).

Specifically, for the aqueous dispersion containing the particulate polymer, the particle size-number integrated distribution of the particulate polymer is measured using a laser diffraction/scattering type particle size distribution analyzer, and the particle diameter at which the value of the integrated distribution is 50% is counted. It was set as the average particle diameter.

<THF gel content>

An aqueous dispersion containing the particulate polymer was prepared, and the aqueous dispersion was dried in an environment of 50% humidity and 23 to 25° C. to form a film with a thickness of 3±0.3 mm. The formed film was cut into a 1 mm square, and about 1 g was accurately weighed.

Let the mass of the film piece obtained by cutting be w0. This film piece was immersed in 100 g of tetrahydrofuran (THF) at 25°C for 24 hours. Thereafter, the film piece pulled up from THF was vacuum dried at 105°C for 3 hours, and the mass w1 of the insoluble content was measured.

And gel content (mass %) was computed according to the following formula.

Gel content (% by mass) = (w1/w0) × 100

<Stability of slurry composition>

The dispersion stability of the particle|grains in the produced slurry composition for lithium ion secondary battery negative electrodes was evaluated by the gauge (grain gauge) based on JISK5600-2-5:1999 as follows.

The third largest particle size among the occurrence points of streaks observed on the gauge was measured, these measurements were performed 6 times, and the maximum value among the measured values was taken as the particle size in the slurry composition. It shows that dispersion stability of the particle|grains in a slurry composition is so good that a particle size is small.

A: The particle size is less than 30 μm

B: The particle size is 30 μm or more and less than 50 μm

C: particle size of 50 μm or more and less than 70 μm

D: particle size of 70 μm or more

<Presence or absence of pinhole>

A 5 cm × 10 cm test piece was cut out from the negative electrode fabric before roll pressing on which the negative electrode composite material layer was formed, and the number of pinholes (defects) with a diameter of 0.5 mm or more existing on the surface of the test piece was visually measured and evaluated according to the following criteria. did

A: The number of pinholes is 0

B: The number of pinholes is 1 to 4

C: The number of pinholes is 5 to 9

D: The number of pinholes is 10 or more

<Peel strength>

The produced negative electrode for a lithium ion secondary battery was cut into a rectangle having a width of 1.0 cm and a length of 10 cm to obtain a test piece, and the surface of the negative electrode composite material layer side was turned upside down and fixed. Then, a cellophane tape was attached to the surface of the test piece on the negative electrode mixture layer side. At this time, the cellophane tape specified in JIS Z1522 was used. Then, the stress when the cellophane tape was peeled off from one end of the test piece in the 180° direction (the other end side of the test piece) at a speed of 50 mm/min was measured. The measurement was performed 10 times, the average value of the stress was determined, this was regarded as the peel strength (N/m), and the following criteria were evaluated. The higher the peeling strength, the better the binding property of the negative electrode mixture layer to the current collector.

A: 10 N/m or more

B: 8 N/m or more and less than 10 N/m

C: less than 8 N/m

<High temperature cycle characteristics>

The produced lithium ion secondary battery was left still for 24 hours in a 25 ° C environment, then charged to 4.4 V at a charge/discharge rate of 0.2 C and discharged to 3.0 V in a 45 ° C environment. The initial capacity C0 was measured. . Further, a charge/discharge cycle of charging to 4.4 V and discharging to 3.0 V at a charge/discharge rate of 1.0 C was repeated in a 45°C environment, and the capacity C1 after 300 cycles was measured. Then, the high-temperature cycle characteristics were evaluated by the capacity retention rate represented by ΔC = (C1/C0) x 100 (%). The higher the value of this capacity retention ratio, the smaller the decrease in the discharge capacity and the better the high-temperature cycle characteristics.

A: The capacity retention rate ΔC is 80% or more

B: Capacity retention rate ΔC is 75% or more and less than 80%

C: Capacity retention rate ΔC is less than 75%

<Rate characteristics>

After the produced lithium ion secondary battery was left still in a 25°C environment for 24 hours, an operation of charging to 4.4 V and discharging to 3.0 V at a charge/discharge rate of 0.2 C was performed in a 25°C environment. Then, in a 25° C. environment, a charge/discharge cycle of charging to 4.4 V at a charge rate of 0.2 C and discharging to 3.0 V at a discharge rate of 1.0 C, and a charge/discharge cycle of discharging to 3.0 V at a discharge rate of 3.0 C were performed respectively. The ratio of the battery capacity at 3.0 C to the battery capacity at 1.0 C was calculated as a percentage, used as charge/discharge rate characteristics, and evaluated according to the following criteria. The higher the value of the charge/discharge rate characteristic, the smaller the internal resistance, the faster charge/discharge is possible, and the better the rate characteristic.

A: The charge/discharge rate characteristic is 70% or more

B: charge/discharge rate characteristics of 65% or more and less than 70%

C: charge/discharge rate characteristics of 60% or more and less than 65%

D: charge/discharge rate characteristics less than 60%

<Expansion resistance>

The produced lithium ion secondary battery was allowed to stand for 24 hours in a temperature environment of 25°C, and then charged/discharged by charging at 4.35 V and 0.1 C and discharging at 2.75 V and 0.1 C in the environment at a temperature of 25°C. did Then, the cell was immersed in liquid paraffin, and its volume V0 was measured. In addition, 1000 cycles of the charge/discharge operation were repeated in an environment of a temperature of 60°C. Then, the cell was immersed in liquid paraffin, and its volume V1 was measured. Then, the cell volume change rate ΔV (%) = {(V1 - V0)/V0} x 100 before and after the cycle was calculated, and the expansion resistance was evaluated according to the following criteria. The smaller the value of the volume change rate ΔV, the smaller the expansion of the cell, indicating that the expansion resistance is excellent.

A: Volume change rate ΔV is less than 30%

B: Volume change rate ΔV is 30% or more and less than 40%

C: Volume change rate ΔV is 40% or more and less than 50%

D: Volume change rate ΔV is 50% or more

(Example 1)

<Preparation of Binder Composition>

[Formation of Core Portion of Particulate Polymer]

-Preparation of seed particle A-

In a reactor equipped with an agitator, 60.0 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 38.0 parts of styrene as an aromatic vinyl monomer, 2.0 parts of methacrylic acid as an ethylenically unsaturated carboxylic acid monomer, and 4.0 parts of sodium dodecylbenzenesulfonate as an emulsifier , 260 parts of ion-exchanged water, and 0.3 parts of potassium persulfate as a polymerization initiator were added, and polymerization was carried out at a temperature of 60°C for 6 hours. As a result, an aqueous dispersion of seed particles A made of a polymer having a number average particle diameter of 58 nm was obtained.

-Preparation of seed particle B-

In a reactor equipped with an agitator, 2.5 parts of the aqueous dispersion of the seed particles A in terms of solid content, 0.2 parts of sodium dodecylbenzenesulfonate as an emulsifier, 0.5 parts of potassium persulfate as a polymerization initiator, and 100 parts of ion-exchanged water were added and mixed. Thus, a mixture was obtained. Then, the temperature of the mixture was raised to 80°C. On the other hand, in a separate container, 32.60 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 44.64 parts of styrene as an aromatic vinyl monomer, 19.25 parts of methyl methacrylate (methyl methacrylate) as a (meth)acrylic acid ester monomer, ethylenic A monomer dispersion was prepared by mixing 2.73 parts of itaconic acid as an unsaturated carboxylic acid monomer, 0.78 part of acrylamide as an unsaturated carboxylic acid amide monomer, 0.5 part of sodium dodecylbenzenesulfonate as an emulsifier, and 100 parts of ion-exchanged water. A dispersion of this monomer was continuously added to the above mixture over 4 hours to polymerize. The temperature of the reaction system during the continuous addition of the monomer dispersion was maintained at 80°C. After completion of the continuous addition, the reaction was continued at a temperature of 90°C for 3 hours. As a result, an aqueous dispersion of seed particles B (core portion) made of a polymer having a number average particle diameter of 175 nm was obtained.

[Formation of Shell Portion of Particulate Polymer]

In a reactor equipped with an agitator, 25 parts of the aqueous dispersion of the seed particle B in terms of solid content, 0.2 parts of sodium dodecylbenzenesulfonate as an emulsifier, 0.5 parts of potassium persulfate as a polymerization initiator, and 100 parts of ion-exchanged water were added and mixed. Thus, a mixture was obtained. Then, the temperature of the mixture was raised to 80°C. On the other hand, in a separate container, 33.2 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 60.6 parts of styrene as an aromatic vinyl monomer, 0.2 part of acrylic acid as an ethylenically unsaturated carboxylic acid monomer, and methacrylic acid as a (meth)acrylic acid ester monomer 5.0 parts of methyl, 1.0 parts of 2-hydroxyethyl acrylate (β-hydroxyethyl acrylate) as an unsaturated monomer containing a hydroxyalkyl group, 0.5 parts of sodium dodecylbenzenesulfonate as an emulsifier, and 100 parts of ion-exchanged water were mixed. , a dispersion of the monomer was prepared. A dispersion of this monomer was continuously added to the above mixture over 4 hours to polymerize. The temperature of the reaction system during the continuous addition of the monomer dispersion was maintained at 80°C. After completion of the continuous addition, the reaction was continued at a temperature of 90°C for 3 hours. As a result, an aqueous dispersion (binder composition) of the particulate polymer having a core-shell structure was obtained.

And the number average particle diameter and THF gel content of the obtained particulate polymer were evaluated. The results are shown in Table 1.

<Preparation of the slurry composition for lithium ion secondary battery negative electrodes>

In a planetary mixer equipped with a disper, 100 parts of artificial graphite (specific surface area: 3.6 m ² /g, volume average particle diameter: 20 μm) as a negative electrode active material, and carboxymethylcellulose sodium salt (CMC-Na) as a viscosity modifier 1 part of a 1% aqueous solution in terms of solid content was added. And after adjusting these mixtures to 60% of solid content concentration with ion-exchanged water, it mixed at 25 degreeC for 60 minutes.

Next, after adjusting the solid content concentration to 52% with ion-exchanged water, it was further mixed at 25°C for 15 minutes to obtain a liquid mixture.

Subsequently, 1 part of the aqueous dispersion of the particulate polymer (binder composition) in terms of solid content was added to the above mixture, and ion-exchanged water was added to adjust the final solid content concentration to 50%, followed by mixing for another 10 minutes. This was degassed under reduced pressure, and the slurry composition for negative electrodes was obtained.

And stability was evaluated about the produced slurry composition. The results are shown in Table 1.

<Production of Negative Electrode for Lithium Ion Secondary Battery>

The prepared slurry composition for a negative electrode was applied onto a copper foil (current collector) having a thickness of 15 µm using a comma coater in an applied amount of 12.0 mg/cm ² and dried. On the other hand, drying was performed by conveying the copper foil over 2 minutes at a speed of 0.5 m/min in a 70°C oven. Thereafter, a heat treatment was performed at 120° C. for 2 minutes to obtain a negative electrode fabric.

Then, the obtained negative electrode fabric was pressed with a roll press machine so that the negative electrode composite material layer had a density of 1.60 g/cm ³ and a thickness of 75 µm to obtain a negative electrode.

With respect to the produced negative electrode, the presence or absence of a pinhole and peel strength were evaluated. The results are shown in Table 1.

<Production of Positive Electrode for Lithium Ion Secondary Battery>

In a planetary mixer, 100 parts of LiCoO ₂ as a positive electrode active material, 2 parts of acetylene black as a conductive aid (HS-100 manufactured by Denki Chemical Industry Co., Ltd.), PVDF (polyvinylidene fluoride, Kureha Chemical Co., Ltd.) as a binder Production, KF-1100) was charged, and N-methylpyrrolidone was added and mixed so that the total solid content concentration was 67%, thereby obtaining a slurry composition for a positive electrode.

Then, the obtained slurry composition for a positive electrode was applied onto an aluminum foil (current collector) having a thickness of 20 μm with a comma coater, and dried. On the other hand, drying was performed by conveying the aluminum foil over 2 minutes at a speed of 0.5 m/min in a 60°C oven.

Thereafter, a heat treatment was performed at 120°C for 2 minutes to obtain a positive electrode fabric.

Then, the obtained positive electrode fabric was pressed with a roll press to have a density of 3.10 to 3.20 g/cm ³ to obtain a positive electrode.

<Production of Lithium Ion Secondary Battery>

A single-layer polypropylene separator (65 mm wide, 500 mm long, 25 µm thick; manufactured by a dry method; porosity 55%) was prepared and cut into a 5 cm x 5 cm square. In addition, as an exterior of the battery, an aluminum packaging material exterior was prepared.

Then, the prepared positive electrode was cut out into a square of 4 cm x 4 cm, and the surface on the current collector side was placed in contact with the aluminum packaging material exterior. Next, a square separator was disposed on the surface of the positive electrode on the positive electrode mixture layer side. Further, the fabricated negative electrode was cut into a square of 4.2 cm x 4.2 cm, and placed on the separator so that the surface of the negative electrode mixture layer faced the separator. Thereafter, as an electrolyte, a LiPF ₆ solution having a concentration of 1.0 M (the solvent is a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 3/7 (volume ratio), and 2% by weight (solvent ratio) of vinylene carbonate as an additive) was charged. . In addition, in order to seal the opening of the aluminum packaging material exterior, 150 ° C. heat sealing was performed to close the aluminum packaging material exterior, and a lithium ion secondary battery was manufactured.

With respect to the produced lithium ion secondary battery, high-temperature cycle characteristics, rate characteristics, and expansion resistance were evaluated. The results are shown in Table 1.

(Example 2)

Binder composition, negative electrode slurry composition, negative electrode, positive electrode and secondary battery in the same manner as in Example 1 except that the amounts of seed particles B and monomers used in the formation of the shell portion of the particulate polymer were changed as shown in Table 1. was produced. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Example 3)

A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode and a secondary battery were prepared in the same manner as in Example 1 except that the amount of the monomer used in the formation of the seed particles B of the particulate polymer was changed as shown in Table 1. did Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Example 4)

Binder composition for negative electrode, in the same manner as in Example 1, except that the amount of the monomer used when forming the seed particle B of the particulate polymer and the amount of the monomer used when forming the shell portion were changed as shown in Table 1 A slurry composition, a negative electrode, a positive electrode, and a secondary battery were prepared. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Example 5)

Binder composition, negative electrode slurry composition, negative electrode, positive electrode and secondary battery in the same manner as in Example 1 except that the amounts of seed particles B and monomers used in the formation of the shell portion of the particulate polymer were changed as shown in Table 1. was produced. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Example 6)

A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, and a secondary battery were prepared in the same manner as in Example 1, except that the amount of seed particles B used in the formation of the shell portion of the particulate polymer was changed as shown in Table 1. did Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Example 7)

The same as in Example 1 except that the type and amount of the monomer used when forming the seed particle B of the particulate polymer and the amount of the seed particle B and monomer used when forming the shell portion were changed as shown in Table 1. Thus, a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, and a secondary battery were produced. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Example 8)

Binder composition, The slurry composition for negative electrodes, the negative electrode, the positive electrode, and the secondary battery were produced. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Examples 9-10)

A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, and a secondary battery were prepared in the same manner as in Example 1, except that the amount of the monomer used when forming the shell portion of the particulate polymer was changed as shown in Table 1. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Examples 11-12)

A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, and a secondary battery were prepared in the same manner as in Example 2, except that the amount of the monomer used in the formation of the seed particles A of the particulate polymer was changed as shown in Table 1. did Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Example 13)

A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, and a secondary battery were prepared in the same manner as in Example 6, except that the amount of the monomer used when forming the shell portion of the particulate polymer was changed as shown in Table 1. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Examples 1 to 3)

Binder composition, negative electrode slurry composition, negative electrode, positive electrode and secondary battery in the same manner as in Example 1 except that the amounts of seed particles B and monomers used in the formation of the shell portion of the particulate polymer were changed as shown in Table 1. was produced. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 4)

A slurry composition for a negative electrode, a negative electrode, a positive electrode, and a secondary battery were prepared in the same manner as in Example 1 except that the binder composition containing the particulate polymer having no core-shell structure prepared as follows was used. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

<Preparation of Binder Composition>

In a reactor equipped with an agitator, 33.4 parts of 1,3-butadiene as an aliphatic conjugated diene monomer, 61.6 parts of styrene as an aromatic vinyl monomer, 4.0 parts of itaconic acid as an ethylenically unsaturated carboxylic acid monomer, and hydroxyalkyl group-containing unsaturated monomer 1.0 part of 2-hydroxyethyl acrylate (β-hydroxyethyl acrylate), 4.0 parts of sodium dodecylbenzenesulfonate as an emulsifier, 260 parts of ion-exchanged water, and 0.3 part of potassium persulfate as a polymerization initiator were added, and at a temperature of 60°C. Polymerized for 6 hours. As a result, an aqueous dispersion (binder composition) of the particulate polymer having no core-shell structure was obtained.

(Comparative Example 5)

Binder composition, negative electrode slurry composition, negative electrode, positive electrode and secondary battery in the same manner as in Example 1 except that the amounts of seed particles B and monomers used in the formation of the shell portion of the particulate polymer were changed as shown in Table 1. was produced. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 6)

In the same manner as in Example 1 except that the amounts of the monomers used when forming the seed particles B of the particulate polymer and the amounts of seed particles B and monomers used when forming the shell portion were changed as shown in Table 1. , a binder composition, a slurry composition for negative electrodes, a negative electrode, a positive electrode, and a secondary battery were produced. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 7)

The same as in Example 1 except that the type and amount of the monomer used when forming the seed particle B of the particulate polymer and the amount of the seed particle B and monomer used when forming the shell portion were changed as shown in Table 1. Thus, a binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, and a secondary battery were produced. Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Example 8)

A binder composition, a negative electrode slurry composition, a negative electrode, a positive electrode, and a secondary battery were prepared in the same manner as in Example 1, except that the amount of seed particles B used in the formation of the shell portion of the particulate polymer was changed as shown in Table 1. did Then, evaluation was conducted in the same manner as in Example 1. The results are shown in Table 1.

[Table 1]

From Table 1, it can be seen that in Examples 1 to 13, occurrence of pinholes and expansion of the secondary battery can be suppressed, and good rate characteristics and high-temperature cycle characteristics can be exhibited in the secondary battery. On the other hand, in Comparative Examples 1 to 8, it is understood that both the generation of pinholes and the swelling of the secondary battery cannot be simultaneously suppressed. And, as a result, in Comparative Examples 1-8, it turns out that favorable rate characteristics and high-temperature cycle characteristics cannot be exhibited to the secondary battery.

According to the present invention, it is possible to provide a binder composition for a secondary battery electrode and a slurry composition for a secondary battery electrode, which can suppress expansion of a secondary battery and at the same time exhibit good rate characteristics and high-temperature cycle characteristics in the secondary battery.

Further, according to the present invention, it is possible to provide an electrode for a secondary battery capable of suppressing swelling of the secondary battery and at the same time exhibiting good rate characteristics and high-temperature cycle characteristics of the secondary battery.

Further, according to the present invention, it is possible to provide a secondary battery that is excellent in rate characteristics and high-temperature cycle characteristics and is less prone to swelling.

Claims (7)

A binder composition for a secondary battery electrode containing a particulate polymer and water,
The particulate polymer has a core-shell structure composed of a core portion and a shell portion, and has a number average particle diameter of 200 nm or more and 600 nm or less;
The core portion is polymerized using a monomer composition having an ethylenically unsaturated carboxylic acid monomer content of more than 0.1 mass% and 5.0 mass% or less,
The shell part is polymerized using a monomer composition having an ethylenically unsaturated carboxylic acid monomer content of 0.1% by mass or more and 3.0% by mass or less,
The content of the ethylenically unsaturated carboxylic acid monomer in 100 mass% of the monomer composition used for polymerization of the core portion is greater than the content of the ethylenically unsaturated carboxylic acid monomer in 100 mass% of the monomer composition used for polymerization of the shell portion. The binder composition for secondary battery electrodes which is made into. According to claim 1,
A binder composition for secondary battery electrodes, characterized in that the amount of ethylenically unsaturated carboxylic acid monomer used for polymerization of the core part is 0.2 times or more and 7.0 times or less of the amount of ethylenically unsaturated carboxylic acid monomer used for polymerization of the shell part. . According to claim 1,
The binder composition for a secondary battery electrode, wherein the particulate polymer contains 0.2% by mass or more and 3.0% by mass or less of an ethylenically unsaturated carboxylic acid monomer unit. According to claim 1,
The binder composition for secondary battery electrodes, characterized in that the amount of the monomer used for polymerization of the core portion is 0.1 times or more and 0.5 times or less of the amount of the monomer used for polymerization of the shell portion. A slurry composition for secondary battery electrodes comprising the binder composition for secondary battery electrodes according to any one of claims 1 to 4 and an electrode active material. An electrode for secondary batteries characterized by having an electrode mixture layer obtained by using the slurry composition for secondary battery electrodes according to claim 5. A secondary battery comprising a positive electrode, a negative electrode, an electrolyte solution and a separator, wherein at least one of the positive electrode and the negative electrode is the electrode for a secondary battery according to claim 6.