ADHESIVE PRODUCT FOR SECONDARY BATTERIES

Abstract

The invention relates to a secondary battery adhesive product exhibiting low agglomeration tendency in the adhesive composition and enabling the formation of a functional layer with optimal adhesion using the adhesive composition even after long-term storage. The adhesive product consists of a container with a reservoir and the adhesive composition contained within the reservoir space. The inner surface of the reservoir has a contact angle with the water greater than or equal to 80°. The adhesive composition contains an adhesive, a defoamer, and water and has a defoamer content of not less than 0.02 parts by mass and not more than 0.3 parts by mass per 100 parts by mass of the adhesive. The adhesive composition has a surface tension of not less than 20 mN / m and not more than 60 mN / m.

Description

Binder products for secondary batteries

[0001] The present invention relates to a binder product in which a binder composition for a secondary battery is contained in a container.

[0002] Secondary batteries such as lithium-ion secondary batteries are small, lightweight, have high energy density, and can be repeatedly charged and discharged, and are therefore used in a wide range of applications. Secondary batteries generally include battery components such as electrodes (positive and negative electrodes) and a separator that separates the positive and negative electrodes.

[0003] Here, as the battery components of the secondary battery, components having a functional layer containing a binder (binding material) and, optionally, particles (hereinafter referred to as "functional particles") blended to enable the battery components to exhibit a desired function are used. Specifically, as the separator for the secondary battery, a separator having an adhesive layer containing a binder or a porous membrane layer containing a binder and non-conductive particles as functional particles on a separator substrate is used. Furthermore, as the electrode for the secondary battery, an electrode having an electrode mixture layer containing a binder and electrode active material particles as functional particles on a current collector, or an electrode having the above-mentioned adhesive layer or porous membrane layer on an electrode substrate having an electrode mixture layer on a current collector is used.

[0004] Conventionally, binders used in forming battery components are stored in a container as a binder composition obtained by dissolving or dispersing the binder in a solvent such as water (see, for example, Patent Documents 1 and 2).

[0005] International Publication No. 2015 / 029835 Japanese Patent Application Laid-Open No. 2017-220326

[0006] Here, the functional layer is required to exhibit excellent adhesive properties to ensure good adhesion to the substrate supporting the functional layer. For example, in order to ensure good adhesion of the electrode mixture layer serving as the functional layer to the current collector serving as the substrate, a method of reducing the surface tension of the binder composition to increase its affinity with the electrode active material particles and the current collector is conceivable. However, according to the inventors' investigations, when a binder composition with low surface tension (e.g., a surface tension of 60 mN / m or less) is filled into a container and stored in the form of a binder product for a long period of time, a problem occurs in which binder aggregates are formed in the binder composition. If a large amount of such aggregates are formed, the binder is unevenly distributed in the resulting functional layer, impairing the adhesiveness of the functional layer.

[0007] Therefore, an object of the present invention is to provide a binder product for secondary batteries in which the binder composition is less likely to aggregate even after long-term storage, and which can be used to form a functional layer with excellent adhesiveness.

[0008] The present inventors have conducted extensive research to solve the above problems, and have found that filling a container having a storage section whose inner wall surface has a contact angle with water of a predetermined value or more with a predetermined binder composition can suppress the formation of aggregates in the binder composition after long-term storage, and can form a functional layer with excellent adhesiveness even when using a binder composition that has been stored for a long period of time, thereby completing the present invention.

[0009] The present invention aims to advantageously solve the above-mentioned problems. The binder product for a secondary battery of the present invention is a binder product for a secondary battery comprising a container having a storage section and a binder composition contained in the internal space of the storage section, wherein the water contact angle of the inner wall surface of the storage section is 80° or greater, the binder composition includes a binder, an antifoaming agent, and water, the content of the antifoaming agent is 0.02 to 0.3 parts by mass per 100 parts by mass of the binder, and the surface tension of the binder composition is 20 to 60 mN / m. The binder product described above is less likely to form aggregates in the binder composition inside the container even when stored for a long period of time. Furthermore, by using the binder composition contained in the binder product described above, a functional layer with excellent adhesiveness can be formed. In the present invention, both the "water contact angle" and the "surface tension" can be measured using the methods described in the examples.

[0010] In the binder product for a secondary battery of the present invention, the binder preferably has at least one of an amide group and a hydroxyalkyl group. If the binder is a polymer having an amide group and / or a hydroxyalkyl group, the formation of aggregates in the binder composition after long-term storage can be further suppressed, and the adhesiveness of the resulting functional layer can be further improved.

[0011] Furthermore, in the binder product for secondary batteries of the present invention, it is preferable that the binder contains at least one of an amide group-containing monomer unit and a hydroxyalkyl group-containing monomer unit, and the sum of the content of the amide group-containing monomer unit and the content of the hydroxyalkyl group-containing monomer unit in the binder is 0.05% by mass or more and 5% by mass or less. If the binder is a polymer having an amide group and / or a hydroxyalkyl group, the formation of aggregates in the binder composition after long-term storage can be further suppressed, while the adhesion of the resulting functional layer can be further improved. In addition, in the present invention, when a polymer such as a binder "contains a monomer unit," it means that "a polymer obtained using that monomer contains a repeating unit derived from the monomer." In addition, in the present invention, the content ratio of each monomer unit in a polymer such as a binder is １ H-NMR and １３ It can be measured using nuclear magnetic resonance (NMR) techniques such as C-NMR.

[0012] In the binder product for a secondary battery of the present invention, the binder composition preferably further contains a preservative, and the content of the preservative is preferably 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the binder. When the binder composition contains the preservative in an amount within the above range, it is possible to further suppress the formation of aggregates in the binder composition after long-term storage, and further improve the adhesion of the resulting functional layer.

[0013] Furthermore, in the binder product for secondary batteries of the present invention, the volume ratio of voids, which is the internal volume of the container minus the volume occupied by the binder composition in the container, to the internal volume of the container is preferably 10% by volume or less. If the volume ratio of voids to the internal volume of the container (hereinafter referred to as "porosity") is equal to or less than the above value, it is possible to further suppress the formation of aggregates in the binder composition after long-term storage, while further improving the adhesion of the resulting functional layer.

[0014] In the binder product for a secondary battery of the present invention, the solids concentration of the binder composition is preferably 30% by mass or more and 60% by mass or less. When the solids concentration of the binder composition is within the above range, the formation of aggregates in the binder composition after long-term storage can be further suppressed, and the adhesiveness of the resulting functional layer can be further improved.

[0015] In the binder product for secondary batteries of the present invention, the defoaming agent preferably includes a mineral oil-based defoaming agent, which can further suppress the formation of aggregates in the binder composition after long-term storage and further improve the adhesion of the resulting functional layer.

[0016] In the binder product for secondary batteries of the present invention, aggregation of the binder composition is unlikely to occur even after long-term storage, and a functional layer with excellent adhesiveness can be formed using the binder composition.

[0017] 1 is a diagram schematically illustrating the structure of an example of a binder product for a secondary battery of the present invention.

[0018] The binder product for secondary batteries of the present invention will be described below. The binder product of the present invention is a binder composition contained in a container for storage, transportation, etc. of the binder composition. The binder composition contained in the binder product of the present invention can then be removed, and functional particles, etc., can be added as needed to prepare a slurry composition for a functional layer (e.g., a slurry composition for an electrode, a slurry composition for an adhesive layer, or a slurry composition for a porous membrane layer). Such a slurry composition for a functional layer can be used to form a functional layer (e.g., an electrode mixture layer, an adhesive layer, or a porous membrane layer) of a secondary battery.

[0019] Here, in the binder product of the present invention, the container is provided with a storage section whose inner wall surface has a contact angle with water of 80° or more, the surface tension of the binder composition filled in the internal space of the storage section is 20 mN / m or more and 60 mN / m or less, and the binder composition contains an antifoaming agent in an amount of 0.02 parts by mass or more and 0.3 parts by mass or less per 100 parts by mass. Therefore, even when stored for a long period of time, aggregates are unlikely to form in the binder composition, and a functional layer with excellent adhesiveness can be formed using the binder composition.

[0020] (Container) The container has at least a storage section capable of storing the binder composition. The container may be composed of only the storage section, but from the viewpoint of easily filling and removing the binder composition, it is preferable that the container has the storage section and a cap capable of sealing the opening of the storage section to seal the internal space of the storage section. The shape of the container is not particularly limited, and can be any shape such as cylindrical, rectangular, or bag-like.

[0021] An example of the shape of the container will be described with reference to FIG. 1 . In FIG. 1 , a binder product 100 for a secondary battery includes a container 1 and a binder composition 2 accommodated inside the container. In FIG. 1 , the container 1 includes a cap 11 and a storage portion 12. An internal space 14 of the container 1 is defined by an inner wall surface 13 of the storage portion 12 and the cap 11, and the cap 11 seals the opening of the storage portion 12. By removing the cap 11 from the storage portion 12, the binder composition 2 can be taken out from the opening of the storage portion 12.

[0022] <Contact angle with water> As described above, the contact angle with water of the inner wall surface of the storage section of the container must be 80° or more, preferably 100° or more, and more preferably 110° or more. If the contact angle with water of the inner wall surface of the storage section is less than 80°, it is presumed that the affinity between the inner wall surface and the binder composition containing water is excessively increased, promoting the formation of aggregates due to contact between the inner wall surface and the binder composition. However, the formation of aggregates in the binder composition after long-term storage cannot be sufficiently suppressed. The upper limit of the contact angle with water of the inner wall surface of the storage section is not particularly limited, but is, for example, 160° or less. Here, the contact angle with water of the inner wall surface of the storage section can be reduced by changing the material of the storage section or by subjecting the inner wall surface of the storage section to a hydrophobic treatment.

[0023] <Material> The material of the container (in other words, the material of the storage part and / or the cap used optionally) is not particularly limited, and examples thereof include glass, resin, and metal. Among these, resin is preferred, polyethylene, polypropylene, and polycarbonate are more preferred, and polyethylene is even more preferred. That is, the container is preferably made of resin, more preferably made of polyethylene, polypropylene, or polycarbonate, and even more preferably made of polyethylene. Note that the container material may be used alone or in combination of two or more types. For example, a glass storage part having a resin layer on the surface (particularly the inner wall surface) can be used as the storage part constituting the container.

[0024] <Hydrophobic Treatment> Here, examples of hydrophobic treatments that can be used to increase the contact angle of the inner wall surface of the container with water to the above-mentioned predetermined value or more include treatment with a silane coupling agent, treatment with a titanium coupling agent, treatment with an aluminum coupling agent, treatment with a fatty acid ester wax, treatment with a fatty acid ester wax, and treatment with a fluororesin. These may be used alone or in combination of two or more. Among these, treatment with a silane coupling agent and treatment with a fluororesin are preferred from the viewpoint of sufficiently increasing the contact angle of the inner wall surface of the container with water. In other words, it is preferable that the inner wall surface of the container be coated with at least one of a layer (coating) made of a silane coupling agent and a layer (coating) made of a fluororesin.

[0025] <<Treatment with Silane Coupling Agent>> The silane coupling agent is not particularly limited, and examples thereof include sulfur-containing silane coupling agents such as γ-mercaptopropyltrimethoxysilane, γ-mercaptomethyltrimethoxysilane, γ-mercaptomethyltriethoxysilane, γ-mercaptohexamethyldisilazane, bis(3-triethoxysilylpropyl)tetrasulfane, and bis(3-triethoxysilylpropyl)disulfane; γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldimethoxysilane (3-glycidoxypropylmethyldimethoxysilane); silane coupling agents containing an epoxy group, such as N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, 3-aminopropyltrimethoxysilane (γ-aminopropyltriethoxysilane), N-(2-aminoethyl)-3-aminopropyltriethoxysilane, ... amino group-containing silane coupling agents such as γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltris(β-methoxyethoxy)silane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-acryloxypropyltrimethoxysilane, etc. (Meth)acryloxy group-containing silane coupling agents; vinyl group-containing silane coupling agents such as vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris(β-methoxyethoxy)silane, vinyltrichlorosilane, and vinyltriacetoxysilane; chloropropyl group-containing silane coupling agents such as 3-chloropropyltrimethoxysilane; isocyanate group-containing silane coupling agents such as 3-isocyanatepropyltriethoxysilane; styryl group-containing silane coupling agents such as p-styryltrimethoxysilane;Examples of suitable silane coupling agents include ureido group-containing silane coupling agents such as 3-ureidopropyltriethoxysilane; allyl group-containing silane coupling agents such as diallyldimethylsilane; alkoxy group-containing silane coupling agents such as tetraethoxysilane; phenyl group-containing silane coupling agents such as diphenyldimethoxysilane; fluoro group-containing silane coupling agents such as trifluoropropyltrimethoxysilane; and alkyl group-containing silane coupling agents such as isobutyltrimethoxysilane and cyclohexylmethyldimethoxysilane. These may be used alone or in combination of two or more. Among these, epoxy group-containing silane coupling agents are preferred, and 3-glycidoxypropylmethyldimethoxysilane is more preferred, from the viewpoint of further suppressing the formation of aggregates in the binder composition after long-term storage while further improving the adhesion of the resulting functional layer.

[0026] The treatment with the silane coupling agent is not particularly limited as long as it can form a layer made of the silane coupling agent on the inner wall surface of the container, and any known method can be used. For example, a silane coupling agent is dissolved in a solvent such as water or cyclohexane, the resulting solution is applied to the inner wall surface of the container, and then the solution is dried to remove the solvent, thereby forming a layer made of the silane coupling agent on the inner wall surface of the container.

[0027] <<Treatment with Fluorine Resin>> The fluororesin is not particularly limited, and examples thereof include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride, polychlorotrifluoroethylene, ethylene-chlorofluoroethylene copolymer, tetrafluoroethylene-perfluorodioxole copolymer, polyvinyl fluoride, tetrafluoroethylene-propylene copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, acrylic-modified polytetrafluoroethylene, ester-modified polytetrafluoroethylene, epoxy-modified polytetrafluoroethylene, silane-modified polytetrafluoroethylene, and perfluoropolyether group-containing compounds. These may be used alone or in combination of two or more. Among these, perfluoropolyether group-containing compounds are preferred.

[0028] The treatment with the fluororesin is not particularly limited as long as it is possible to form a layer made of the fluororesin on the inner wall surface of the housing portion, and any known method can be used. For example, a layer made of the fluororesin can be formed on the inner wall surface of the housing portion by dissolving the fluororesin in a solvent such as water or cyclohexane, applying the obtained solution to the inner wall surface of the housing portion, and then drying to remove the solvent.

[0029] (Binder Composition) The binder composition contained in the container housing has a surface tension of 20 mN / m or more and 60 mN / m or less. The binder composition contains at least a binder, an antifoaming agent, and water, and optionally contains at least one selected from the group consisting of a preservative, an emulsifier, a wetting agent, and other components.

[0030] <Surface Tension> As described above, the surface tension of the binder composition must be 20 mN / m or more and 60 mN / m or less, preferably 30 mN / m or more, preferably 50 mN / m or less, and more preferably 40 mN / m or less. If the surface tension of the binder composition is less than 20 mN / m, the adhesiveness of the functional layer decreases. Although the reason for this is unclear, it is presumed that if the surface tension of the binder composition is less than 20 mN / m, the binder easily adheres to the inner wall surface of the container in the gap portion. When the adhered binder dries and forms a coating, the coating acts as a starting point to reduce the stability of the slurry composition when it falls into the binder composition. On the other hand, if the surface tension of the binder composition exceeds 60 mN / m, it is presumed that this is due to reduced affinity with the electrode active material particles and the current collector, resulting in reduced adhesiveness of the functional layer. Furthermore, the viscosity stability of the slurry composition prepared using the binder composition is impaired due to reduced affinity with functional particles such as electrode active material particles. The surface tension of the binder composition can be controlled by changing the type and amount of the binder and antifoaming agent, as well as the emulsifier and wetting agent that are optionally used.

[0031] <Binder> The binder is not particularly limited as long as it has binding ability, and any polymer that can be used as a binder can be used. For example, polyethylene, polypropylene, acid-modified polyolefin, fluorine vinyl polymer, hydroxyl group-containing olefin polymer, acrylic acid polymer, acrylic polymer, acrylonitrile polymer, diene polymer, silicon-containing polymer, etc. can be used. These may be used alone or in combination of two or more. Among these, for example, when the binder composition is used to form a negative electrode mixture layer, diene polymers are preferred.

[0032] Furthermore, the binder preferably has at least one of an amide group and a hydroxyalkyl group. According to the inventors' studies, while binders having an amide group and / or a hydroxyalkyl group have excellent binding ability, they tend to foam during storage and transportation, which increases the contact area between the binder composition and the inner wall surface of the storage section, thereby accelerating the formation of aggregates. However, according to the binder product of the present invention, the contact angle of the water on the inner wall surface of the storage section is equal to or greater than a predetermined value, and the binder composition contains a predetermined amount of antifoaming agent. Therefore, even when a polymer having an amide group and / or a hydroxyalkyl group is used as the binder, it is possible to sufficiently suppress the formation of aggregates in the binder composition after long-term storage. Therefore, if the binder used has an amide group and / or a hydroxyalkyl group, it is possible to sufficiently suppress the formation of aggregates in the binder composition after long-term storage, while further improving the adhesion of the resulting functional layer.

[0033] The method for introducing an amide group and / or a hydroxyalkyl group into the binder is not particularly limited, but a method for preparing the binder as a polymer using an amide group-containing monomer and / or a hydroxyalkyl group-containing monomer is preferred. That is, the binder preferably contains at least one of an amide group-containing monomer unit and a hydroxyalkyl group-containing monomer unit. Examples of the hydroxyalkyl group include a hydroxymethyl group, a hydroxyethyl group, and a hydroxypropyl group, and among these, a hydroxyethyl group is preferred.

[0034] <<Amide Group-Containing Monomer Unit>> Examples of amide group-containing monomers that can form amide group-containing monomer units include acrylamide, methacrylamide, dimethylacrylamide, diethylacrylamide, and diacetone acrylamide. These may be used alone or in combination of two or more. Among these, acrylamide is preferred.

[0035] <<Hydroxyalkyl group-containing monomer unit>> Examples of hydroxyalkyl group-containing monomers that can form hydroxyalkyl group-containing monomer units include hydroxymethyl acrylamide, hydroxyethyl acrylamide, hydroxypropyl acrylamide, hydroxymethyl methacrylamide, hydroxyethyl methacrylamide, hydroxypropyl methacrylamide, hydroxymethyl acrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, hydroxymethyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl methacrylate. These may be used alone or in combination of two or more. Among these, hydroxyethyl acrylate is preferred. In the present invention, a monomer having both a hydroxyalkyl group and an amide group is included in the hydroxyalkyl group-containing monomer, but is not included in the amide group-containing monomer.

[0036] <<Content Ratio>> The total content of the amide group-containing monomer units and the hydroxyalkyl group-containing monomer units in the binder is preferably 0.05% by mass or more, preferably 5% by mass or less, more preferably 3% by mass or less, and even more preferably 2% by mass or less, based on 100% by mass of all monomer units contained in the binder. If the total content of the amide group-containing monomer units and the hydroxyalkyl group-containing monomer units is 0.05% by mass or more, the adhesion of the functional layer can be further improved, and if it is 5% by mass or less, foaming of the binder composition can be suppressed, and the formation of aggregates in the binder composition after long-term storage can be sufficiently suppressed.

[0037] <<Diene Polymer>> Here, the composition of a diene polymer suitable as a binder will be described. The diene polymer contains an aliphatic conjugated diene monomer unit, and preferably contains at least one of the above-mentioned amide group-containing monomer unit and the hydroxyalkyl group-containing monomer unit. The diene polymer may optionally contain monomer units (other monomer units) other than the aliphatic conjugated diene monomer unit, the amide group-containing monomer unit, and the hydroxyalkyl group-containing monomer unit.

[0038] [Aliphatic conjugated diene monomer unit] Examples of aliphatic conjugated diene monomers that can form aliphatic conjugated diene monomer units include 1,3-butadiene, 2-methyl-1,3-butadiene (isoprene), and 2,3-dimethyl-1,3-butadiene. These may be used alone or in combination of two or more. Among these, 1,3-butadiene is preferred.

[0039] Here, the content of the aliphatic conjugated diene monomer units in the binder is preferably 25% by mass or more, more preferably 30% by mass or more, and is preferably 60% by mass or less, and more preferably 50% by mass or less, based on 100% by mass of all monomer units contained in the binder.

[0040] [Other Monomer Units] Examples of other monomer units include monomer units derived from known monomers copolymerizable with the above-mentioned aliphatic conjugated diene monomers, amide group-containing monomers, and hydroxyalkyl group-containing monomers. Examples of such monomers include aromatic vinyl monomers, nitrile group-containing monomers, (meth)acrylic acid ester monomers, and carboxylic acid group-containing monomers. These may be used alone or in combination of two or more. Among these, aromatic vinyl monomers, (meth)acrylic acid ester monomers, and carboxylic acid group-containing monomers are preferred, aromatic vinyl monomers and carboxylic acid group-containing monomers are more preferred, and aromatic vinyl monomers are even more preferred. That is, the diene polymer is particularly preferably an aliphatic conjugated diene-aromatic vinyl copolymer containing aliphatic conjugated diene monomer units and aromatic vinyl monomer units. In the present invention, "(meth)acrylic" refers to acrylic and / or methacrylic.

[0041] Examples of aromatic vinyl monomers capable of forming aromatic vinyl monomer units include styrene, α-methylstyrene, vinyltoluene, and divinylbenzene. These may be used alone or in combination of two or more. Among these, styrene is preferred. Here, the content of aromatic vinyl monomer units in the binder is preferably 5% by mass or more, more preferably 10% by mass or more, and preferably 80% by mass or less, and more preferably 70% by mass or less, based on 100% by mass of all monomer units contained in the binder.

[0042] Examples of (meth)acrylic acid ester monomers that can form (meth)acrylic acid ester monomer units include alkyl acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, and 2-ethylhexyl acrylate; and alkyl acrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, and n-butyl methacrylate. Examples of suitable methacrylic acid esters include alkyl methacrylates such as 2-hydroxyethyl acrylate, t-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, and 2-ethylhexyl methacrylate; and hydroxyl group-containing (meth)acrylic acid esters such as 2-hydroxyethyl acrylate, 2-hydroxymethacrylate, 2-hydroxypropyl acrylate, 2-hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, and 3-chloro-2-hydroxypropyl methacrylate. These may be used alone or in combination of two or more. Among these, hydroxyl group-containing (meth)acrylic acid esters are preferred, and 2-hydroxyethyl acrylate is more preferred. Here, the content of the (meth)acrylic acid ester monomer units in the binder is preferably 0.3% by mass or more, more preferably 0.5% by mass or more, and even more preferably 0.6% by mass or more, and is preferably 2% by mass or less, and more preferably 1.5% by mass or less, based on 100% by mass of all monomer units contained in the binder.

[0043] Examples of carboxylic acid group-containing monomers include monocarboxylic acids and their derivatives, dicarboxylic acids and their acid anhydrides, and their derivatives. Examples of monocarboxylic acids include acrylic acid, methacrylic acid, and crotonic acid. Examples of monocarboxylic acid derivatives include 2-ethylacrylic acid, isocrotonic acid, α-acetoxyacrylic acid, β-trans-aryloxyacrylic acid, α-chloro-β-E-methoxyacrylic acid, and β-diaminoacrylic acid. Examples of dicarboxylic acids include maleic acid, fumaric acid, and itaconic acid. Examples of dicarboxylic acid derivatives include methylmaleic acid, dimethylmaleic acid, phenylmaleic acid, chloromaleic acid, dichloromaleic acid, fluoromaleic acid, and maleic acid monoesters such as butyl maleate, nonyl maleate, decyl maleate, dodecyl maleate, octadecyl maleate, and fluoroalkyl maleates. Examples of dicarboxylic acid anhydrides include maleic anhydride, acrylic anhydride, methyl maleic anhydride, dimethyl maleic anhydride, and citraconic anhydride. These may be used alone or in combination of two or more. Among these, dicarboxylic acids and their derivatives and acid anhydrides are preferred, and itaconic acid is more preferred. Here, the content of carboxylic acid group-containing monomer units in the binder is preferably 2% by mass or more, more preferably 3% by mass or more, preferably 8% by mass or less, more preferably 6% by mass or less, and even more preferably 4% by mass or less, based on 100% by mass of all monomer units contained in the binder.

[0044] <<Method for Preparing Binder>> The method for preparing the binder is not particularly limited, and a method of polymerizing a monomer composition containing the above-mentioned monomers by a known method can be used. Here, the ratio of each monomer in the monomer composition is usually the same as the ratio of each monomer unit in the desired binder. The polymerization mode of the binder is not particularly limited, and any method such as solution polymerization, suspension polymerization, bulk polymerization, or emulsion polymerization can be used. The polymerization reaction can be addition polymerization such as ionic polymerization, radical polymerization, or living radical polymerization. Commonly used emulsifiers, dispersants, polymerization initiators, polymerization aids, and the like can be used, and the amounts used can be the same as commonly used amounts. Seed polymerization can also be performed using seed particles. A binder dispersed in an aqueous solvent and produced by suspension polymerization or emulsion polymerization is preferred because of its excellent handleability during transportation and storage.

[0045] <Antifoaming agent> The binder composition needs to contain an antifoaming agent. By containing an antifoaming agent in the binder composition, foaming of the binder composition in the container-mounted portion during long-term storage can be suppressed, and the generation of aggregates due to contact with the inner wall surface of the container-mounted portion can be suppressed.

[0046] Examples of the defoaming agent include silicone-based defoaming agents, mineral oil-based defoaming agents (modified hydrocarbon oils based on mineral oil), and polymer-based defoaming agents. A single defoaming agent may be used alone, or two or more may be used in combination. Mineral oil-based defoaming agents are preferred as defoaming agents, from the viewpoint of further suppressing the formation of aggregates in the binder composition after long-term storage while further improving the adhesion of the functional layer.

[0047] Here, the defoaming agent may be a known defoaming agent, and may be selected from various commercially available defoaming agents. For example, a mineral oil-based defoaming agent such as "DF6351" (manufactured by Seiko PMC Corporation) may be preferably used.

[0048] <<Content>> The amount of antifoaming agent contained in the binder composition must be 0.02 parts by mass or more and 0.3 parts by mass or less per 100 parts by mass of binder, preferably 0.1 parts by mass or less, and more preferably 0.06 parts by mass or less. If the content of the antifoaming agent is less than 0.02 parts by mass per 100 parts by mass of binder, the formation of aggregates in the binder composition after long-term storage cannot be sufficiently suppressed, and the adhesion of the functional layer decreases. On the other hand, if the content of the antifoaming agent is more than 0.3 parts by mass per 100 parts by mass of binder, the adhesion of the binder is presumably inhibited by the presence of the antifoaming agent at the binding interface between electrode active material particles or between the electrode active material particles and the current collector, which reduces the adhesion of the functional layer.

[0049] <Preservative> The binder composition preferably contains a preservative. When the binder composition contains a preservative, bacterial growth is suppressed, and aggregate formation can be further suppressed. The preservative exhibits a particularly effective bacterial growth suppression effect on binders produced by suspension polymerization or emulsion polymerization and dispersed in an aqueous solvent.

[0050] Examples of preservatives include known preservatives such as isothiazolinone compounds and 2-bromo-2-nitro-1,3-propanediol. The isothiazolinone compounds are not particularly limited, and examples include those described in JP 2013-211246 A, JP 2005-097474 A, and JP 2013-206624 A. Preservatives may be used alone or in combination of two or more. Preferred preservatives include 1,2-benzisothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, and 2-bromo-2-nitro-1,3-propanediol, with 1,2-benzisothiazolin-3-one being more preferred.

[0051] The amount of preservative contained in the binder composition is preferably 0.01 parts by mass or more, preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and even more preferably 0.3 parts by mass or less per 100 parts by mass of binder. If the content of the preservative is 0.01 parts by mass or more per 100 parts by mass of binder, the formation of aggregates in the binder composition after long-term storage can be further suppressed, and if it is 0.5 parts by mass or less, the adhesion of the functional layer can be sufficiently improved.

[0052] <Emulsifier> The binder composition preferably contains an emulsifier. By containing an emulsifier in the binder composition, the surface tension of the binder composition can be controlled to an appropriate value, and as a result, the formation of aggregates in the binder composition after long-term storage can be effectively suppressed and the adhesion of the functional layer can be sufficiently improved.

[0053] Examples of emulsifiers include nonionic emulsifiers such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenol ethers, polyoxyethylene alkyl esters, and polyoxyethylene sorbitan alkyl esters; anionic emulsifiers such as alkylbenzenesulfonates (e.g., potassium dodecylbenzenesulfonate, sodium dodecylbenzenesulfonate), higher alcohol sulfates, alkyl sulfosuccinates, sodium β-naphthalenesulfonate-formalin condensates, dodecyldiphenyloxide disulfonates (e.g., sodium dodecyldiphenyloxide disulfonate), and lauryl sulfates (e.g., sodium lauryl sulfate); cationic emulsifiers such as alkyltrimethylammonium chloride, dialkylammonium chloride, and benzylammonium chloride; and copolymerizable emulsifiers such as sulfoesters of α,β-unsaturated carboxylic acids, sulfate esters of α,β-unsaturated carboxylic acids, and sulfoalkylaryl ethers. These emulsifiers may be used singly or in combination of two or more. As the emulsifier, from the viewpoint of further suppressing the formation of aggregates in the binder composition after long-term storage while further improving the adhesion of the functional layer, anionic emulsifiers are preferred, alkylbenzenesulfonates, sodium salt of a β-naphthalenesulfonic acid formalin condensate, dodecyldiphenyloxide disulfonate, and lauryl sulfate are more preferred, and potassium dodecylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium salt of a β-naphthalenesulfonic acid formalin condensate, sodium dodecyldiphenyloxide disulfonate, and sodium lauryl sulfate are even more preferred.

[0054] The amount of emulsifier contained in the binder composition is preferably 0.4 parts by mass or more, preferably 5 parts by mass or less, and more preferably 2 parts by mass or less per 100 parts by mass of binder. If the content of the emulsifier is 0.4 parts by mass or more per 100 parts by mass of binder, the adhesiveness of the functional layer can be further improved while increasing the viscosity stability of the slurry composition prepared using the binder composition. In addition, the viscosity stability of the binder composition can be improved. On the other hand, if the content of the emulsifier is 5 parts by mass or less per 100 parts by mass of binder, the adhesiveness of the functional layer can be sufficiently improved.

[0055] <Solid content concentration> Here, the binder composition preferably has a solid content concentration of 30% by mass or more, more preferably 40% by mass or more, and preferably 60% by mass or less, and more preferably 50% by mass or less. If the solid content concentration of the binder composition is 30% by mass or more, when a slurry composition prepared using the binder composition is dried to form a functional layer, uneven distribution of the binder in the resulting functional layer can be suppressed, allowing the functional layer to exhibit even better adhesion. On the other hand, if the solid content concentration of the binder composition is 60% by mass or less, aggregate formation after long-term storage can be further suppressed.

[0056] <Method for Preparing Binder Composition> The binder composition can be obtained by mixing the above-mentioned components in the presence of water. For example, the binder composition can be prepared by adding an antifoaming agent, and an emulsifier, preservative, and / or other components used as needed, to an aqueous binder solution or aqueous dispersion obtained after the polymerization reaction and mixing the mixture. The antifoaming agent, emulsifier, and other components may be those contained in the aqueous binder solution or aqueous dispersion. As other components, for example, a wetting agent can be used to control the surface tension of the binder composition.

[0057] <Method for manufacturing binder product> The binder product of the present invention is obtained by filling the storage portion of the container with the binder composition. The method for filling the storage portion of the container with the binder composition is not particularly limited, and known methods can be used. Here, the porosity of the binder product is preferably 10% by volume or less. If the porosity is 10% by volume or less, the formation of aggregates in the binder composition after long-term storage can be further suppressed, while the adhesion of the functional layer can be further improved.

[0058] The binder product obtained as described above is preferably stored in an environment with a temperature of 5° C. or higher and 40° C. or lower. Storing the binder product within this temperature range can sufficiently suppress the formation of aggregates in the binder composition while preventing the binder from deteriorating. As a result, the adhesiveness of the resulting functional layer can be further improved.

[0059] (Uses of binder product) The binder composition filled in the storage portion of the container in the binder product of the present invention can be used, for example, to form a functional layer such as an electrode mixture layer. Hereinafter, a case will be described in which an electrode slurry composition is prepared using the binder composition contained in the binder product of the present invention and an electrode is formed, but the present invention is not limited thereto.

[0060] <Slurry Composition for Electrode> The slurry composition for an electrode contains electrode active material particles, the binder composition, and other components used as needed.

[0061] <<Electrode Active Material Particles>> The electrode active material particles may be positive electrode active material particles or negative electrode active material particles. The electrode active material particles are a substance that transfers electrons within a battery. Hereinafter, the case where the electrode active material particles are used in a lithium ion secondary battery will be described.

[0062] The positive electrode active material particles are particles made of a compound (positive electrode active material) capable of absorbing and releasing lithium ions. Positive electrode active materials are broadly classified into those made of inorganic compounds and those made of organic compounds.

[0063] Examples of inorganic positive electrode active materials include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of the transition metals include Fe, Co, Ni, and Mn. Specific examples of inorganic compounds used for the positive electrode active material include LiCoO ２ , LiNiO ２ , LiMnO ２ , LiMn ２ O ４ , LiFePO ４ , LiFeVO ４ Lithium-containing composite metal oxides such as TiS ２ , TiS ３ , amorphous MoS ２ transition metal sulfides such as Cu ２ V ２ O ３ , amorphous V ２ O-P ２ O ５ , MoO ３ , V ２ O ５ , V ６ O １３ These compounds may be partially element-substituted.

[0064] Examples of the positive electrode active material made of an organic compound include polyaniline, polypyrrole, polyacene, disulfide-based compounds, polysulfide-based compounds, and N-fluoropyridinium salts. The positive electrode active material may be a mixture of the inorganic compound and the organic compound. The positive electrode active material particles may be used alone or in combination of two or more.

[0065] Examples of the negative electrode active material constituting the negative electrode active material particles include carbon allotropes such as graphite and coke. The negative electrode active material made of the carbon allotrope can also be used in the form of a mixture or coating with a metal, metal salt, oxide, etc. In addition, examples of the negative electrode active material that can be used include oxides and sulfates of silicon, tin, zinc, manganese, iron, nickel, etc., metallic lithium, lithium alloys such as Li-Al, Li-Bi-Cd, and Li-Sn-Cd, lithium transition metal nitrides, and silicon.

[0066] The negative electrode active material particles may be used alone or in combination of two or more.

[0067] <<Binder Composition>> The binder composition may be the binder composition described above containing a binder. The amount of the binder used is preferably from 0.1 to 50 parts by mass, more preferably from 0.5 to 20 parts by mass, and even more preferably from 1 to 10 parts by mass, relative to 100 parts by mass of the electrode active material particles, from the viewpoint of reducing the internal resistance of the secondary battery while ensuring sufficient adhesiveness of the resulting electrode mixture layer.

[0068] <<Other Components>> Other components that can be blended into the electrode slurry composition are not particularly limited, and examples thereof include known components such as conductive materials, thickeners, etc. The other components may be used alone or in combination of two or more.

[0069] <<Preparation of Slurry Composition for Electrode>> The method for preparing the slurry composition for an electrode is not particularly limited. For example, the slurry composition for an electrode can be prepared by mixing the binder composition, electrode active material particles, and other components used as needed in the presence of a dispersion medium such as water. The mixing method is not particularly limited, and mixing can be performed using a commonly used stirrer or disperser.

[0070] <Electrode> An electrode can be obtained by forming an electrode mixture layer on a current collector using the electrode slurry composition described above. Specifically, the electrode mixture layer can be formed using the following methods: 1) a method of applying the electrode slurry composition to the surface of a current collector and then drying it; 2) a method of immersing a current collector in the electrode slurry composition and then drying it; and 3) a method of applying the electrode slurry composition to a release substrate and drying it to produce an electrode mixture layer, and then transferring the obtained electrode mixture layer to the surface of a current collector. Among these, method 1) is particularly preferred because it makes it easy to control the layer thickness of the electrode mixture layer. Method 1) specifically includes a step of applying the electrode slurry composition to a current collector (application step) and a step of drying the electrode slurry composition applied to the current collector to form an electrode mixture layer on the current collector (drying step).

[0071] <<Coating Step>> The method for applying the electrode slurry composition onto the current collector is not particularly limited, and known methods can be used. Specifically, examples of the application method include a doctor blade method, a dipping method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. In this case, the slurry composition may be applied to only 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 appropriately set depending on the thickness of the electrode mixture layer obtained by drying.

[0072] Here, the current collector to which the electrode slurry composition is applied is made of a material that is electrically conductive and electrochemically durable. Specifically, the current collector may be made of, for example, iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. The above-mentioned materials may be used alone or in combination of two or more.

[0073] <<Drying Step>> The method for drying the electrode slurry composition on the current collector is not particularly limited and any known method can be used, for example, a drying method using warm air, hot air, or low-humidity air, a vacuum drying method, or a drying method using infrared rays, electron beams, etc. By drying the slurry composition on the current collector in this manner, an electrode mixture layer can be formed on the current collector, and an electrode including the current collector and the electrode mixture layer can be obtained.

[0074] After the drying step, the electrode mixture layer may be subjected to a pressure treatment using a mold press or a roll press. The pressure treatment can further improve the adhesiveness of the electrode mixture layer and increase the density of the resulting electrode mixture layer. The electrode obtained as described above can be suitably used as an electrode for a secondary battery such as a lithium-ion secondary battery.

[0075] The present invention will be described in detail below based on examples, but the present invention is not limited to these examples. In the following description, the terms "%" and "parts" used to represent amounts are based on mass unless otherwise specified. In addition, in a polymer produced by polymerizing multiple types of monomers, the proportion of a monomer unit formed by polymerizing a certain monomer in the polymer usually corresponds to the ratio (feed ratio) of that certain monomer to all monomers used in the polymerization of the polymer, unless otherwise specified. In the examples and comparative examples, the water contact angle of the inner wall surface of the container, the surface tension of the binder composition, the suppression of aggregate formation in the binder composition after long-term storage, the viscosity stability of the binder composition, the viscosity stability of the negative electrode slurry composition, and the adhesion of the negative electrode composite layer were evaluated using the following methods.

[0076] <Contact Angle with Water> A contact angle meter (manufactured by Kyowa Interface Science Co., Ltd., product name "DMs-400") was used as the measuring device. Water was dropped onto the inner wall surface of the container, and the image taken from the horizontal direction using the contact angle meter was analyzed using the tangent method to determine the contact angle. <Surface Tension> The surface tension of the binder composition for secondary batteries was measured using an automatic surface tensiometer (manufactured by Kyowa Interface Science Co., Ltd., product name "DY-300") by the platinum plate method in an environment of 25°C. <Suppression of Aggregate Formation> The prepared binder product was placed in a thermostatic chamber capable of adjusting the storage temperature and stored at 60°C for 30 days. Here, the binder product was shaken up and down and left and right on days 0, 10, and 20 of storage. After 30 days of storage, aggregates in the binder composition were captured on a 200-mesh stainless steel wire mesh. The captured aggregates were washed with water and dried in a dryer at 80°C under normal pressure for 1 hour to evaporate the water. The amount of aggregates (mass%) after drying was calculated based on 100% by mass of the solid content of the binder composition before storage, and evaluated according to the following criteria. A smaller amount indicates greater suppression of aggregate formation. A: Amount of aggregates less than 0.05% by mass B: Amount of aggregates 0.05% by mass or more but less than 0.10% by mass C: Amount of aggregates 0.10% by mass or more <Viscosity Stability (Binder Composition)> The viscosity of the prepared binder composition (viscosity before storage) was measured using a Brookfield viscometer at 25°C and 60 rpm. Next, the binder product was stored in the same manner as in <Suppression of Aggregate Formation> above, and then the viscosity of the binder composition (viscosity after storage) was measured using a Brookfield viscometer under the same conditions as above. A viscosity change of more than ±5% from the viscosity before storage was determined to be abnormal, and evaluated according to the following criteria. A: No viscosity abnormality B: Viscosity abnormality <Viscosity Stability (Negative Electrode Slurry Composition)> The viscosity η0 of the prepared negative electrode slurry composition was measured using a Brookfield viscometer at 25°C and 60 rpm. Next, the negative electrode slurry composition was allowed to stand at 25°C for 72 hours, and then the viscosity η1 was measured under the same conditions as for η0. The viscosity change rate, defined by the formula: Δη = |η1 - η0| / η0 × 100 (%), was then determined and evaluated according to the following criteria. A smaller value for the viscosity change rate Δη indicates that the negative electrode slurry composition has better viscosity stability.A: Viscosity change rate Δη is less than 20%. B: Viscosity change rate Δη is 20% or more but less than 50%. C: Viscosity change rate Δη is 50% or more but less than 80%. D: Viscosity change rate Δη is 80% or more. <Adhesion> Cellophane tape (specified in JIS Z1522) was attached to the surface of the negative electrode composite layer of the prepared negative electrode, and one end of the current collector was pulled vertically at a pulling rate of 50 mm / min to measure the stress when peeled off (note that the cellophane tape was fixed to the test table). A total of three measurements were performed, and the average value was calculated as the peel strength, which was evaluated according to the following criteria. A higher peel strength value indicates better adhesion of the negative electrode composite layer and stronger adhesion to the current collector. A: Peel strength of 12 N / m or more. B: Peel strength of 8 N / m or more but less than 12 N / m. C: Peel strength of less than 8 N / m.

[0077] Example 1 <Container Preparation> A polyethylene container (internal volume: 20 liters) consisting of a container and a cap as shown in Figure 1 was prepared. The container had an opening, and the internal space could be sealed by screwing the cap onto the opening. A 2% solution of a silane coupling agent (3-glycidoxypropylmethyldimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd., product name "KBM-402") in weakly acidic water (pH = 4 to 6) was applied to the inner wall surface of the polyethylene container, and the coating was dried at 80°C for 1 hour to perform a hydrophobic treatment, preparing a container to be used in the production of a binder product. The contact angle of water on the inner wall surface of this container was measured. The results are shown in Table 1. <Preparation of Binder Composition and Binder Product> A 5 ​​MPa pressure vessel equipped with a stirrer was charged with 30 parts of 1,3-butadiene, 40 parts of styrene, 9 parts of acrylonitrile, 17 parts of methyl methacrylate, 4 parts of methacrylic acid, 0.5 parts of t-dodecyl mercaptan as a molecular weight modifier, 9 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 1.0 part of potassium persulfate as a polymerization initiator, and after sufficient stirring, the mixture was heated to 50°C to initiate polymerization, thereby obtaining seed particles (particulate diene-based polymer). Furthermore, 4 parts of the seed particles, 45 parts of 1,3-butadiene, 14 parts of styrene, 26 parts of acrylonitrile, 12 parts of methyl methacrylate, 1 part of acrylic acid, 1 part of itaconic acid, 1 part of acrylamide, 1 part of t-dodecyl mercaptan and 0.5 parts of α-methylstyrene dimer as molecular weight modifiers, 1 part of sodium dodecyldiphenyloxide disulfonate and 0.1 parts of β-naphthalenesulfonic acid formalin condensate sodium salt as emulsifiers, 150 parts of ion-exchanged water, and 1.0 part of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 50°C to initiate polymerization. The reaction was terminated by cooling when the polymerization conversion rate reached 96%. A 5% aqueous solution of sodium hydroxide was added to the resulting aqueous dispersion containing the diene polymer to adjust the pH to 8. Subsequently, unreacted monomers were removed by heating and vacuum distillation. The mixture was then cooled to 30°C or below.To the cooled aqueous dispersion containing the diene polymer, 0.05 parts of a mineral oil-based antifoaming agent (manufactured by Seiko PMC Corporation, product name "DF6351") as an antifoaming agent and 0.1 parts of an isothiazolin-based compound (1,2-benzoisothiazolin-3-one) as a preservative were added per 100 parts of binder. The mixture was filtered through a 200-mesh stainless steel wire screen and then filled into the container described above to obtain a binder product containing a binder composition (18 liters). The porosity of this binder product was 10% by volume. The amount of emulsifier contained in the binder composition was 1.4 parts per 100 parts of binder (the total amount of sodium dodecylbenzenesulfonate introduced by the seed particles, and sodium dodecyldiphenyloxide disulfonate and β-naphthalenesulfonic acid formalin condensate sodium salt used in the second-stage polymerization). This binder product was then used to evaluate the suppression of aggregate formation in the binder composition after long-term storage and the viscosity stability of the binder composition. The results are shown in Table 1. <Preparation of Negative Electrode Slurry Composition> A mixture was obtained by adding 100 parts of graphite as negative electrode active material particles, 0.2 parts of carbon black (manufactured by Denka Company, product name "HS-100") as a conductive material, and 1.0 part (solids equivalent) of a 2% aqueous solution of carboxymethyl cellulose (manufactured by Nippon Paper Chemicals Co., Ltd., product name "MAC-500LC") as a water-soluble polymer to a planetary mixer equipped with a disperser. The resulting mixture was adjusted to a solids concentration of 60% with ion-exchanged water and then mixed at 25°C for 60 minutes. Next, the solids concentration was adjusted to 53% with ion-exchanged water and then further mixed at 25°C for 10 minutes to obtain a mixed solution. To the resulting mixture, 2.0 parts (solids equivalent) of the binder composition contained in the binder product after long-term storage under the same conditions as those used to evaluate "inhibition of aggregate formation" and ion-exchanged water were added to adjust the final solids concentration to 48%. After further mixing for 10 minutes, the mixture was degassed under reduced pressure to obtain a negative electrode slurry composition. Viscosity stability was evaluated using this negative electrode slurry composition. The results are shown in Table 1. <Preparation of Negative Electrode> The negative electrode slurry composition was coated using a comma coater onto a 15 μm-thick copper foil current collector to a coating weight of 9 mg / cm after drying. ２The copper foil was then coated and dried so that the density of the negative electrode composite layer became 1.70 g / cm. This drying was performed by conveying the copper foil at a speed of 0.5 m / min through an oven at 60°C for 2 minutes. Thereafter, the copper foil was heat-treated at 120°C for 2 minutes to obtain a negative electrode blank. The negative electrode blank was then rolled using a roll press to obtain a negative electrode composite layer having a density of 1.70 g / cm. ３ The negative electrode was used to evaluate the adhesiveness of the negative electrode mixture layer. The results are shown in Table 1.

[0078] Example 2 A binder composition and a binder product were prepared as follows. Otherwise, a container, a negative electrode slurry composition, and a negative electrode were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1. <Preparation of Binder Composition and Binder Product> 60 parts of 1,3-butadiene, 38 parts of styrene, 2 parts of methacrylic acid, 0.2 parts of t-dodecyl mercaptan as a molecular weight modifier, 4 parts of sodium dodecyldiphenyloxide disulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure-resistant container equipped with a stirrer, and after thorough stirring, the mixture was heated to 50°C to initiate polymerization, yielding seed particles (particulate diene-based polymer). Furthermore, 6 parts of the seed particles, 33 parts of 1,3-butadiene, 62 parts of acrylonitrile, 4 parts of itaconic acid, 1 part of hydroxyethyl acrylate, 0.5 parts of t-dodecyl mercaptan as a molecular weight modifier, 0.5 parts of sodium dodecyldiphenyloxide disulfonate as an emulsifier, 150 parts of ion-exchanged water, and 1.0 part of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 50°C to initiate polymerization. The reaction was terminated by cooling when the polymerization conversion rate reached 96%. A 5% aqueous sodium hydroxide solution was added to the resulting aqueous dispersion containing the diene polymer to adjust the pH to 8. Subsequently, unreacted monomer was removed by heating and vacuum distillation. The mixture was then cooled to 30°C or below. Subsequent operations were the same as in Example 1, and a binder composition and a binder product were obtained. The amount of emulsifier contained in the binder composition was 0.7 parts per 100 parts of binder (the total of sodium dodecyldiphenyloxide disulfonate brought in by the seed particles and sodium dodecyldiphenyloxide disulfonate used in the second-stage polymerization).

[0079] (Examples 3 and 4) In preparing the binder compositions, the amount of the mineral oil-based antifoaming agent used as the antifoaming agent was changed to 0.3 parts (Example 3) and 0.02 parts (Example 4), respectively. Except for this, a container, a binder composition, a binder product, a negative electrode slurry composition, and a negative electrode were prepared and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0080] Example 5 A binder composition and a binder product were prepared as follows. Otherwise, a container, a negative electrode slurry composition, and a negative electrode were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1. <Preparation of Binder Composition and Binder Product> Seed particles (particulate diene polymer) were obtained in the same manner as in Example 1. Furthermore, a 5 MPa pressure-resistant vessel equipped with a stirrer was charged with 4 parts of the seed particles, 45 parts of 1,3-butadiene, 14 parts of styrene, 26 parts of acrylonitrile, 12 parts of methyl methacrylate, 1 part of acrylic acid, 1 part of itaconic acid, 1 part of acrylamide, 1 part of t-dodecyl mercaptan and 0.5 parts of α-methylstyrene dimer as molecular weight modifiers, 0.2 parts of sodium dodecyldiphenyloxide disulfonate as an emulsifier, 150 parts of ion-exchanged water, and 1.0 part of potassium persulfate as a polymerization initiator. After thorough stirring, the mixture was heated to 50°C to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to stop the reaction. A 5% aqueous solution of sodium hydroxide was added to the resulting aqueous dispersion containing the diene polymer to adjust the pH to 8. Unreacted monomers were then removed by heating and vacuum distillation. The mixture was then cooled to 30°C or below. Subsequent operations were the same as in Example 1, yielding a binder composition and a binder product. The amount of emulsifier contained in the binder composition was 0.5 parts per 100 parts of binder (the sum of sodium dodecylbenzenesulfonate introduced by the seed particles and sodium dodecyldiphenyloxidedisulfonate used in the second-stage polymerization).

[0081] (Example 6) A binder composition and a binder product were prepared as follows. Otherwise, a container, a negative electrode slurry composition, and a negative electrode were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1. <Preparation of binder composition and binder product> Seed particles (particulate diene-based polymer) were obtained in the same manner as in Example 1. Furthermore, 4 parts of the seed particles, 45 parts of 1,3-butadiene, 14 parts of styrene, 26 parts of acrylonitrile, 12 parts of methyl methacrylate, 1 part of acrylic acid, 1 part of itaconic acid, 1 part of acrylamide, 1 part of t-dodecyl mercaptan and 0.5 parts of α-methylstyrene dimer as molecular weight modifiers, 4 parts of sodium dodecyldiphenyloxide disulfonate and 0.8 parts of β-naphthalenesulfonic acid formalin condensate sodium salt as emulsifiers, 150 parts of ion-exchanged water, and 1.0 part of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 50°C to initiate polymerization. The reaction was terminated by cooling when the polymerization conversion rate reached 96%. A 5% aqueous solution of sodium hydroxide was added to the resulting aqueous dispersion containing the diene polymer to adjust the pH to 8. Subsequently, unreacted monomers were removed by heating and vacuum distillation. The mixture was then cooled to 30°C or below. A binder composition and a binder product were obtained by the same subsequent operations as in Example 1. The amount of emulsifier contained in the binder composition was 5 parts per 100 parts of binder (the total of sodium dodecylbenzenesulfonate introduced by the seed particles, and sodium dodecyldiphenyloxide disulfonate and β-naphthalenesulfonic acid formalin condensate sodium salt used in the second-stage polymerization).

[0082] Example 7 A binder composition, binder product, negative electrode slurry composition, and negative electrode were prepared and various evaluations were performed in the same manner as in Example 1, except that a container prepared as follows was used. The results are shown in Table 1. <Container Preparation> A container to be used for producing a binder product was prepared by applying a 10% solution of fluororesin (a perfluoropolyether group-containing compound, manufactured by Fluorotechnology Co., Ltd., product name "FS-6130") in water to the inner wall surface of the housing of a polyethylene container similar to that used in Example 1, and drying the resulting mixture at 80°C for 1 hour to perform a hydrophobic treatment.

[0083] Example 8 A binder composition and a binder product were prepared as follows. Otherwise, a container, a negative electrode slurry composition, and a negative electrode were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1. <Preparation of Binder Composition and Binder Product> 38 parts of styrene, 60 parts of 1,3-butadiene, 2 parts of methacrylic acid, 4 parts of sodium lauryl sulfate as an emulsifier, 270 parts of ion-exchanged water, 0.15 parts of tert-dodecyl mercaptan as a chain transfer agent, 0.15 parts of sodium bicarbonate, and 0.3 parts of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure-resistant container A equipped with a stirrer, and after thorough stirring, the mixture was heated to 60°C to initiate polymerization, thereby obtaining seed particles (particulate diene-based polymer). Further, 6 parts of the seed particles, 82 parts of ion-exchanged water, and 0.2 parts of sodium lauryl sulfate as an emulsifier were placed in a 5 MPa pressure vessel B equipped with a stirrer, and the mixture was heated to 75°C, followed by the addition of 18 parts of ion-exchanged water and 1.8 parts of itaconic acid. Furthermore, from another vessel C containing 44 parts of ion-exchanged water, 62 parts of styrene, 33.2 parts of 1,3-butadiene, 2 parts of itaconic acid, 0.2 parts of sodium lauryl sulfate as an emulsifier, and 0.4 parts of sodium bicarbonate, this mixture was continuously added to the pressure vessel B. At the same time, 0.5 parts of potassium persulfate as a polymerization initiator was added to the pressure vessel B to initiate the second-stage polymerization. Furthermore, after the initiation of the second-stage polymerization, 0.3 parts of tert-dodecyl mercaptan as a chain transfer agent was added to the vessel C. Furthermore, after the initiation of the polymerization, a total of 0.5 parts of potassium persulfate as a polymerization initiator was continuously added to the pressure vessel B. Furthermore, 30 minutes before and to coincide with the completion of the addition of the mixture in vessel C, a total of 1.0 part of 2-hydroxyethyl acrylate was continuously added to pressure vessel B. Pressure vessel B was then heated to 90°C, and once the monomer reaction rate reached 96% or more, nitrous acid was added to stop the reaction. A 5% aqueous solution of sodium hydroxide was added to the resulting aqueous dispersion containing the diene polymer, and the pH was adjusted to 8. Unreacted monomers were then removed by heating and distillation under reduced pressure. The mixture was then cooled to 30°C or below. Subsequent operations were the same as in Example 1, and a binder composition and a binder product were obtained.The amount of emulsifier contained in the binder composition was 0.44 parts per 100 parts of binder (the total of sodium lauryl sulfate brought in by the seed particles and sodium lauryl sulfate used in the second-stage polymerization).

[0084] (Comparative Examples 1 and 2) In preparing the binder compositions, the amount of the mineral oil-based antifoaming agent used as the antifoaming agent was changed to 0.01 part (Comparative Example 1) and 0.4 part (Comparative Example 2), respectively. Except for this, a container, a binder composition, a binder product, a negative electrode slurry composition, and a negative electrode were prepared and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0085] Comparative Example 3 A binder composition and a binder product were prepared as follows. Otherwise, a container, a negative electrode slurry composition, and a negative electrode were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1. <Preparation of Binder Composition and Binder Product> Seed particles (particulate diene polymer) were obtained in the same manner as in Example 1. Furthermore, a 5 MPa pressure-resistant vessel equipped with a stirrer was charged with 4 parts of the seed particles, 45 parts of 1,3-butadiene, 14 parts of styrene, 26 parts of acrylonitrile, 12 parts of methyl methacrylate, 1 part of acrylic acid, 1 part of itaconic acid, 1 part of acrylamide, 1 part of t-dodecyl mercaptan and 0.5 parts of α-methylstyrene dimer as molecular weight modifiers, 0.1 parts of sodium dodecyldiphenyloxide disulfonate as an emulsifier, 150 parts of ion-exchanged water, and 1.0 part of potassium persulfate as a polymerization initiator. After thorough stirring, the mixture was heated to 50°C to initiate polymerization. When the polymerization conversion rate reached 96%, the mixture was cooled to stop the reaction. A 5% aqueous solution of sodium hydroxide was added to the resulting aqueous dispersion containing the diene polymer to adjust the pH to 8. Unreacted monomers were then removed by heating and distillation under reduced pressure. The mixture was then cooled to 30°C or below. Subsequent operations were carried out in the same manner as in Example 1 to obtain a binder composition and a binder product. The amount of emulsifier contained in the binder composition was 0.4 parts per 100 parts of binder (the total of sodium dodecylbenzenesulfonate introduced by the seed particles and sodium dodecyldiphenyloxidedisulfonate used in the second-stage polymerization).

[0086] (Comparative Example 4) A binder composition and a binder product were prepared as follows. Otherwise, a container, a negative electrode slurry composition, and a negative electrode were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1. <Preparation of binder composition and binder product> Seed particles (particulate diene-based polymer) were obtained in the same manner as in Example 1. Furthermore, 4 parts of the seed particles, 45 parts of 1,3-butadiene, 14 parts of styrene, 26 parts of acrylonitrile, 12 parts of methyl methacrylate, 1 part of acrylic acid, 1 part of itaconic acid, 1 part of acrylamide, 1 part of t-dodecyl mercaptan and 0.5 parts of α-methylstyrene dimer as molecular weight modifiers, 5 parts of sodium dodecyldiphenyloxide disulfonate and 0.9 parts of β-naphthalenesulfonic acid formalin condensate sodium salt as emulsifiers, 150 parts of ion-exchanged water, and 1.0 part of potassium persulfate as a polymerization initiator were placed in a 5 MPa pressure vessel equipped with a stirrer, and after thorough stirring, the mixture was heated to 50°C to initiate polymerization. The reaction was terminated by cooling when the polymerization conversion rate reached 96%. A 5% aqueous solution of sodium hydroxide was added to the resulting aqueous dispersion containing the diene polymer to adjust the pH to 8. Subsequently, unreacted monomers were removed by heating and vacuum distillation. The mixture was then cooled to 30°C or below. A binder composition and a binder product were obtained by the same subsequent operations as in Example 1. The amount of emulsifier contained in the binder composition was 6 parts per 100 parts of binder (the total of sodium dodecylbenzenesulfonate introduced by the seed particles, and sodium dodecyldiphenyloxide disulfonate and β-naphthalenesulfonic acid formalin condensate sodium salt used in the second-stage polymerization).

[0087] (Comparative Example 5) Except for using a polyethylene container that had not been subjected to a hydrophobic treatment, a binder composition, a binder product, a negative electrode slurry composition, and a negative electrode were prepared and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0088] In Table 1 shown below, "functional group" represents an amide group-containing monomer unit and a hydroxyalkyl group-containing monomer unit, "AAm" represents an acrylamide unit, "HEA" represents a hydroxyethyl acrylate unit, "mineral oil" represents a mineral oil-based defoaming agent, "IST" represents an isothiazolin-based compound (1,2-benzisothiazolin-3-one), "SDBS" represents sodium dodecylbenzenesulfonate, "DSBP" represents sodium dodecyldiphenyloxide disulfonate, "BETA" represents β-naphthalenesulfonic acid formalin condensate sodium salt, "SLS" represents sodium lauryl sulfate, "PE" represents polyethylene, "silane" represents treatment with a silane coupling agent, and "fluorine" represents treatment with a fluororesin.

[0089]

[0090] Table 1 shows that the binder compositions of Examples 1 to 8 are less likely to aggregate even after long-term storage, and that a negative electrode composite layer with excellent adhesiveness can be formed using the binder compositions after long-term storage. Furthermore, it can be seen that in Examples 1 to 8, even when binder compositions after long-term storage are used, negative electrode slurry compositions with excellent viscosity stability can be prepared. Additionally, it can be seen that the binder compositions of Examples 1 to 8 also have excellent viscosity stability.

[0091] In the binder product for secondary batteries of the present invention, aggregation of the binder composition is unlikely to occur even after long-term storage, and a functional layer with excellent adhesiveness can be formed using the binder composition.

[0092] REFERENCE SIGNS LIST 1 container 2 binder composition 11 cap 12 storage section 13 inner wall surface 14 internal space 100 binder product for secondary battery

Claims

1. A binder product for a secondary battery comprising a container having a storage section and a binder composition stored in the internal space of the storage section, wherein the contact angle of the inner wall surface of the storage section with respect to water is 80° or more, the binder composition contains a binder, an antifoaming agent, and water, the content of the antifoaming agent is 0.02 parts by mass or more and 0.3 parts by mass or less per 100 parts by mass of the binder, and the surface tension of the binder composition is 20 mN / m or more and 60 mN / m or less.

2. The binder product for a secondary battery according to claim 1, wherein the binder has at least one of an amide group and a hydroxyalkyl group.

3. A binder product for secondary batteries according to claim 1, wherein the binder contains at least one of an amide group-containing monomer unit and a hydroxyalkyl group-containing monomer unit, and the sum of the content of the amide group-containing monomer unit and the content of the hydroxyalkyl group-containing monomer unit in the binder is 0.05 mass% or more and 5 mass% or less.

4. A binder product for a secondary battery, wherein the binder composition further contains a preservative, and the content of the preservative is 0.01 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the binder.

5. A binder product for secondary batteries according to any one of claims 1 to 4, wherein the volume ratio of void space, which is the volume of the container interior excluding the volume of the binder composition in the container, to the volume of the container interior is 10 volume % or less.

6. The binder product for a secondary battery according to any one of claims 1 to 5, wherein the solid content concentration of the binder composition is 30% by mass or more and 60% by mass or less.

7. The binder product for a secondary battery according to any one of claims 1 to 6, wherein the defoaming agent comprises a mineral oil-based defoaming agent.

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