Water-based binder composition for secondary battery, slurry composition for secondary battery electrode, secondary battery electrode, and secondary battery

Abstract

The present application relates to a water-based binder composition for secondary batteries, a slurry composition for secondary battery electrodes, a secondary battery electrode, and a secondary battery. A water-based binder composition for secondary batteries, comprising polymer particles and 0.001 to 1.0 parts by weight of 1,2-benzisothiazolin-3-one per 100 parts by weight of the polymer particles, the polymer particles comprising monofunctional (meth)acrylate monomer units, ethylenically unsaturated carboxylic acid monomer units, and other monomer units copolymerizable with the monofunctional (meth)acrylate monomer units and the ethylenically unsaturated carboxylic acid monomer units (excluding aliphatic conjugated diene monomer units, amide group-containing monomer units, α,β-unsaturated nitrile monomer units, and monomer units having repeating units from fluorine-containing vinyl monomers), the content of the ethylenically unsaturated carboxylic acid monomer units being 10.5 parts by weight or more per 100 parts by weight of the polymer particles.

Description

Technical Field

[0001] This invention relates to a water-based binder composition for secondary batteries, a slurry composition for secondary battery electrodes, secondary battery electrodes, and secondary batteries. Background Technology

[0002] Electrodes used in lithium-ion secondary batteries typically have a structure in which an electrode active material layer is deposited on a current collector. In addition to the electrode active material, a binder is used in the electrode active material layer to bond the electrode active materials together and to bond them to the current collector. Electrodes are typically manufactured by mixing a binder composition (forming a polymer that serves as the binder dispersed or dissolved in a liquid medium such as water or an organic solvent), the electrode active material, and a conductive material such as conductive carbon (if desired) to obtain a slurry composition. This slurry composition is then coated onto the current collector and dried, thereby manufacturing the electrode.

[0003] Patent Document 1 describes the following: In order to stabilize physical properties such as viscosity over a long period of time, one or more of the following are used: 5-chloro-2-methyl-4-isothiazolin-3-one, 2-methyl-4-isothiazolin-3-one, and 1,2-benzisothiazolin-3-one.

[0004] In addition, Patent Document 2 describes a water-based binder composition for the positive electrode of a secondary battery, which contains a binder and an isothiazolinate compound.

[0005] In addition, Patent Document 3 describes a water-based binder composition for the negative electrode of a secondary battery, which contains a binder and an isothiazolinate compound.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2013-206624

[0009] Patent Document 2: International Publication No. 2012 / 029839

[0010] Patent Document 3: International Publication No. 2012 / 002451 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] However, the aqueous binder compositions described in Patent Documents 1 to 3 are not limited to using 1,2-benzisothiazolin-3-one as the preservative. Furthermore, there are concerns that the dissolution of the preservative's decomposition products into the electrolyte could cause an increase in resistance, potentially negatively impacting cycle performance.

[0013] Furthermore, the aqueous binder compositions described in Patent Documents 1 to 3 are battery electrode compositions containing binders with a large number of olefinic unsaturated carboxylic acid monomer units, so the stability of the binder itself, such as pH and viscosity, cannot be said to be sufficient.

[0014] Therefore, the object of the present invention is to provide a binder composition capable of suppressing the effects of viscosity changes over time caused by preservative decomposition products, and a slurry composition for secondary battery electrodes using the binder composition. Furthermore, the object is to provide a secondary battery with good input / output characteristics and good cycle characteristics by suppressing viscosity changes over time over a long period.

[0015] Methods for solving problems

[0016] Therefore, the inventors conducted research and found that by including a specific amount of 1,2-benzisothiazolin-3-one (hereinafter sometimes referred to as "BIT") in a composition containing a binder with a specific composition, the resulting slurry composition for secondary battery electrodes exhibits good stability over time, while simultaneously improving the input-output characteristics and cycle characteristics of secondary batteries obtained from secondary battery electrodes using this slurry composition for secondary battery electrodes.

[0017] That is, the present invention is as follows. (1)

[0019] A water-based binder composition for secondary batteries comprises polymer particles and 1,2-benzisothiazolin-3-one in an amount of 0.001 to 1.0 parts by weight relative to 100 parts by weight of the polymer particles.

[0020] The polymer particles described above comprise monofunctional (meth)acrylate monomer units, olefinically unsaturated carboxylic acid monomer units, and other monomer units capable of copolymerizing with the monofunctional (meth)acrylate monomer units and the olefinically unsaturated carboxylic acid monomer units (excluding aliphatic conjugated diene monomer units, amide-containing monomer units, α,β-unsaturated nitrile monomer units, and monomer units having repeating units derived from fluorinated vinyl monomers).

[0021] The content of the above-mentioned olefinic unsaturated carboxylic acid monomer units is 10.5 parts by weight or more per 100 parts by weight of the above-mentioned polymer particles. (2)

[0023] The secondary battery water-based binder composition as described in (1) wherein the content of the above-mentioned olefinic unsaturated carboxylic acid monomer unit is 40.0 parts by weight or less relative to 100 parts by weight of the above-mentioned polymer particles. (3)

[0025] The secondary battery aqueous binder composition as described in (1) or (2) wherein the content of the monofunctional (meth)acrylate monomer unit is 20.0 parts by weight or more relative to 100 parts by weight of the polymer particles. (4)

[0027] The secondary battery aqueous binder composition as described in any one of (1) to (3), wherein the content of the monofunctional (meth)acrylate monomer unit is 59.5 parts by weight or more relative to 100 parts by weight of the polymer particles. (5)

[0029] The secondary battery aqueous binder composition as described in any one of (1) to (4), wherein the content of the monofunctional (meth)acrylate monomer unit is 89.0 parts by weight or less relative to 100 parts by weight of the polymer particles. (6)

[0031] The secondary battery water-based binder composition as described in any one of (1) to (5), wherein the weight of the electrolyte-insoluble component of the secondary battery water-based binder composition is 88% by weight or more relative to the weight of the secondary battery water-based binder composition. (7)

[0033] The aqueous binder composition for secondary batteries as described in any one of (1) to (6), wherein the monofunctional (meth)acrylate monomer unit is selected from at least one of the following groups: n-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, n-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate. (8)

[0035] The secondary battery aqueous binder composition as described in any one of (1) to (7), wherein the monofunctional (meth)acrylate monomer unit is at least one selected from the group consisting of heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate and lauryl acrylate. (9)

[0037] The secondary battery water-based binder composition as described in any one of (1) to (8) wherein the content of other monomer units (excluding aliphatic conjugated diene monomer units, amide-containing monomer units, α,β-unsaturated nitrile monomer units, and monomer units having repeating units from fluorinated vinyl monomers) that can copolymerize with the monofunctional (meth)acrylate monomer unit and the olefinic unsaturated carboxylic acid monomer unit is 0.1 parts by weight or more and 79.9 parts by weight or less relative to 100 parts by weight of the polymer particles. (10)

[0039] The secondary battery water-based binder composition as described in any one of (1) to (9) wherein the content of other monomer units (excluding aliphatic conjugated diene monomer units, amide-containing monomer units, α,β-unsaturated nitrile monomer units, and monomer units having repeating units from fluorinated vinyl monomers) that can copolymerize with the monofunctional (meth)acrylate monomer unit and the olefinic unsaturated carboxylic acid monomer unit is 0.5 parts by weight or more and 69.5 parts by weight or less relative to 100 parts by weight of the polymer particles. (11)

[0041] A slurry composition for a secondary battery electrode, comprising:

[0042] The secondary battery aqueous binder composition described in any one of (1) to (10); and

[0043] Negative electrode active material or positive electrode active material. (12)

[0045] A secondary battery electrode having an electrode active material layer formed on a current collector, which is composed of the secondary battery electrode slurry composition described in (11).

[0046] The effects of the invention

[0047] According to the present invention, by using a water-based binder composition for secondary batteries, the resulting slurry composition for secondary battery electrodes exhibits good stability over time. The water-based binder composition comprises polymer particles and 0.001 to 1.0 parts by weight of 1,2-benzisothiazolin-3-one (BIT) relative to 100 parts by weight of the polymer particles. The polymer particles comprise monofunctional (meth)acrylate monomer units, olefinically unsaturated carboxylic acid monomer units, and other monomer units capable of copolymerizing with the monofunctional (meth)acrylate monomer units and the olefinically unsaturated carboxylic acid monomer units (excluding aliphatic conjugated diene monomer units, amide-containing monomer units, α,β-unsaturated nitrile monomer units, and monomer units having repeating units from fluorinated vinyl monomers).

[0048] In addition, the BIT in the binder composition has good affinity with graphite and conductive additives, which can suppress dissolution into the electrolyte. Therefore, it can prevent the increase in resistance caused by BIT and BIT decomposition products, prevent the reduction of input and output characteristics of secondary batteries obtained by using secondary battery electrode slurry composition, and prevent the reduction of cycle characteristics. Detailed Implementation

[0049] The embodiments of the present invention (hereinafter also referred to as "this embodiment") are described in detail below. It should be noted that the present invention is not limited to the following embodiment, and various modifications can be made within the scope of its key points.

[0050] The aqueous binder composition for secondary batteries of the present invention (hereinafter also referred to as the "binder composition") comprises polymer particles and 0.001 to 1.0 parts by weight of 1,2-benzisothiazolin-3-one relative to 100 parts by weight of the polymer particles. The polymer particles comprise a monofunctional (meth)acrylate monomer unit, an olefinic unsaturated carboxylic acid monomer unit, and other monomer units capable of copolymerizing with the monofunctional (meth)acrylate monomer unit and the olefinic unsaturated carboxylic acid monomer unit (excluding aliphatic conjugated diene monomer units, amide-containing monomer units, α,β-unsaturated nitrile monomer units, and monomer units having repeating units from fluorinated vinyl monomers). The content of the olefinic unsaturated carboxylic acid monomer unit is 10.5 parts by weight or more relative to 100 parts by weight of the polymer particles.

[0051] The adhesive composition of the present invention, by containing a specific amount of BIT, can inhibit the growth of bacteria, thereby preventing the generation of odors and thickening of the adhesive composition, and exhibiting excellent stability over time.

[0052] As described below, a slurry composition for a secondary battery electrode containing the aqueous binder composition of the present invention (hereinafter also referred to as "slurry composition") can be obtained using the above-described binder composition. Similar to the above-described binder composition, by containing a specific amount of BIT, it is possible to inhibit the growth of bacteria, thereby preventing the generation of odors and thickening of the binder composition, and exhibiting excellent stability over time.

[0053] In addition, the BIT in the binder composition has good affinity with graphite and conductive additives, which can suppress dissolution into the electrolyte. Therefore, it can prevent the increase in resistance caused by BIT and BIT decomposition products, prevent the reduction of input and output characteristics of the obtained secondary battery, and prevent the reduction of cycle characteristics.

[0054] The BIT content is 0.001 to 1.0 parts by weight, preferably 0.003 to 0.5 parts by weight, relative to 100 parts by weight (converted to solid content) of the polymer particles used as the binder. When the BIT content is less than 0.001 parts by weight, the growth of microorganisms in the binder composition cannot be suppressed, thus reducing the long-term stability of the binder composition. Furthermore, with the growth of microorganisms in the binder composition, the binder composition is modified, its viscosity increases, making it difficult to process, and its peel strength decreases. On the other hand, when the BIT content exceeds 1.0 parts by weight (converted to solid content) relative to 100 parts by weight of the polymer particles, not only can a higher anti-corrosion effect not be expected, but the cycle characteristics of the secondary battery using this binder composition tend to decrease. In other words, by setting the BIT content within the above range, the long-term stability of the binder composition and the slurry composition can be improved, preventing a decrease in the input / output characteristics and cycle characteristics of the resulting secondary battery.

[0055] It should be noted that, in this invention, preservatives other than the aforementioned isothiazolinate compounds may be used within the scope that does not impair the effects of this invention. Such isothiazolinate compounds are not particularly limited, and examples include 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one.

[0056] The BIT content in the adhesive composition can be adjusted by changing the amount of BIT added relative to the adhesive composition.

[0057] The binder in the binder composition of this embodiment is polymer particles, which comprise monofunctional (meth)acrylate monomer units, olefinically unsaturated carboxylic acid monomer units, and other monomer units capable of copolymerizing with the aforementioned monofunctional (meth)acrylate monomer units and olefinically unsaturated carboxylic acid monomer units (excluding aliphatic conjugated diene monomer units, amide-containing monomer units, α,β-unsaturated nitrile monomer units, and monomer units having repeating units from fluorinated vinyl monomers). By using such a binder, electrode active materials can be bonded to each other and to a current collector, enabling its use in the manufacture of secondary battery electrodes and secondary batteries, as described later. The individual monomer units will now be described in detail.

[0058] It should be noted that the above copolymers can be produced by known methods without particular limitation, for example, by the methods described in the examples below.

[0059] (Monofunctional (meth)acrylate monomer unit)

[0060] In this embodiment, "(meth)acrylate monomer" refers to both methacrylate and acrylate.

[0061] There are no particular limitations on the monofunctional (meth)acrylate monomer units, and examples include: methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, and other alkyl acrylates; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, stearyl methacrylate, and other alkyl methacrylates. They can be used alone or in combination of two or more.

[0062] Among these, from the perspective of lithium-ion conductivity exhibited by moderate swelling in the electrolyte without dissolving into it, and the optimal glass transition temperature of the polymer, it is preferably selected from at least one of the following groups: n-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, n-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n-tetradecyl methacrylate, and stearyl methacrylate.

[0063] Furthermore, it is more preferably selected from at least one of the group consisting of heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate and lauryl acrylate, and even more preferably selected from at least one of the group consisting of octyl acrylate, 2-ethylhexyl acrylate and nonyl acrylate.

[0064] The content of monofunctional (meth)acrylate monomer units relative to 100 parts by weight of polymer particles is preferably 20.0 parts by weight or more, more preferably 50.0 parts by weight or more, and even more preferably 59.5 parts by weight or more. By making the content of monofunctional (meth)acrylate monomer units relative to 100 parts by weight of polymer particles 20.0 parts by weight or more, the polymer tends to have lower resistance, better input / output characteristics, and better cycle characteristics.

[0065] Furthermore, the content of monofunctional (meth)acrylate monomer units is preferably 89.0 parts by weight or less relative to 100 parts by weight of polymer particles. By setting the content of monofunctional (meth)acrylate monomer units to 89.0 parts by weight or less relative to 100 parts by weight of polymer particles, there is a tendency for excellent input / output characteristics and cycling characteristics.

[0066] (Alkenyl bond unsaturated carboxylic acid monomer unit)

[0067] Examples of olefinically unsaturated carboxylic acid monomers include monocarboxylic acids or dicarboxylic acids (anhydrides), such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. They can be used individually or in combination of two or more.

[0068] The content of olefinic unsaturated carboxylic acid monomer units is more than 10.5 parts by weight per 100 parts by weight of polymer particles.

[0069] As copolymeric particles, a higher content of acidic units increases the adhesion (peeling) strength of the electrode, thus improving its cycling characteristics. However, this also makes it difficult to process due to increased viscosity variations. In this embodiment, even if the content of olefinic unsaturated carboxylic acid monomer units is 10.5 parts by weight or more per 100 parts by weight of copolymeric particles, the binder composition containing BIT is easy to process, and stable quality can be obtained.

[0070] Furthermore, from the perspective of the viscosity of the adhesive composition and the viscosity of the slurry composition, and the flexibility of the polymer, the content of the olefinic unsaturated carboxylic acid monomer unit is more preferably 50 parts by weight or less, and more preferably 40.0 parts by weight or less, relative to 100 parts by weight of polymer particles.

[0071] There are no particular limitations on the method for adjusting the content of olefinic unsaturated carboxylic acid monomer units. Examples include, for instance, adjusting the amount of each monomer unit added, the polymerization temperature, and / or the polymerization pressure in the copolymerization process.

[0072] (Other monomer units capable of copolymerizing with monofunctional (meth)acrylate monomer units and olefinically unsaturated carboxylic acid monomer units)

[0073] Other monomers capable of copolymerizing with monofunctional (meth)acrylate monomer units and olefinically unsaturated carboxylic acid monomer units do not include aliphatic conjugated diene monomer units, amide-containing monomer units, α,β-unsaturated nitrile monomer units, or monomer units having repeating units derived from fluorinated vinyl monomers. Such other monomer units are not particularly limited, and examples include: aromatic vinyl monomers such as styrene and vinylnaphthalene; monomers containing sulfonic acid groups such as vinylsulfonic acid; aromatic divinyl monomers such as divinylbenzene; ethylene glycol di(meth)acrylate; propylene glycol di(meth)acrylate; 1,4-butanediol di(meth)acrylate; 1,6-hexanediol di(meth)acrylate; 1,9-nonanediol di(meth)acrylate; alkylene glycol di(meth)acrylates; trimethylolpropane di(meth)acrylate; trimethylolpropane tri(meth)acrylate; pentaerythritol di(meth)propylene. Poly(meth)acrylates such as esters, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, etc.; allyl compounds such as diallyl fumarate, diallyl itaconic acid, and triallyl isocyanurate; vinyltrimethoxysilane, vinyltriethoxysilane, p-styryltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltriethoxysilane, etc., silane coupling agents, etc. These can be used individually or in combination of two or more.

[0074] From the perspectives of electrolyte insoluble components, electrolyte swelling degree, strength, and flexibility, the content of other monomer units (excluding aliphatic conjugated diene monomer units, amide-containing monomer units, α,β-unsaturated nitrile monomer units, and monomer units having repeating units from fluorinated vinyl monomers) relative to 100 parts by weight of polymer particles is preferably 0.1 parts by weight or more and 79.9 parts by weight or less, more preferably 0.5 parts by weight or more and 69.5 parts by weight or less.

[0075] (Insoluble components in the electrolyte)

[0076] The electrolyte-insoluble component of the aqueous binder composition for secondary batteries in this embodiment preferably accounts for 88% by weight or more, more preferably 90% by weight or more, further preferably 92% by weight or more, and particularly preferably 94% by weight or more, relative to the weight of the aqueous binder composition for secondary batteries. By ensuring that the electrolyte-insoluble component accounts for 88% by weight or more relative to the weight of the aqueous binder composition for secondary batteries, the components of the binder composition do not dissolve into the electrolyte but moderately swell in the electrolyte, thereby exhibiting lithium-ion conductivity and tending to have superior input / output characteristics and cycle characteristics. Here, the method for calculating the electrolyte-insoluble component can be the same as that described in the embodiments below.

[0077] (use)

[0078] The binder composition of this embodiment may contain any known components other than the polymer particles and BIT in this embodiment, depending on its intended use. As for the use of the binder composition of this embodiment, there are no particular limitations as long as it is used as a material for constructing a non-aqueous secondary battery; for example, it can be used as a negative electrode material, a positive electrode material, and a separator material, etc., and is particularly preferred as a negative electrode material.

[0079] The binder composition of this embodiment can be used in the manufacture of a negative electrode, a positive electrode, or a separator by further including any one of a positive electrode active material, a negative electrode active material, or a separator material. When any one of a positive electrode active material or a negative electrode active material is included as an essential component, it is specifically called a slurry composition for secondary battery electrodes. This slurry composition for secondary battery electrodes can be used in the manufacture of secondary batteries with excellent stability over time, excellent input / output characteristics, and excellent cycle characteristics.

[0080] Here, when using the secondary battery electrode slurry composition to manufacture the negative electrode, the secondary battery electrode slurry composition includes the polymer particles, BIT, and negative electrode active material as described in this embodiment, and may include optional components as needed. Similarly, when using the secondary battery electrode slurry composition to manufacture the positive electrode, the secondary battery electrode slurry composition includes the polymer particles, BIT, and positive electrode active material as described in this embodiment, and may include other components as needed. Furthermore, when using the secondary battery electrode slurry composition to manufacture the separator, the secondary battery electrode slurry composition includes the polymer particles, BIT, and separator raw material as described in this embodiment, and may include other components as needed.

[0081] The secondary battery electrode obtained by the above method has an electrode active material layer formed on the current collector, which is composed of the secondary battery electrode slurry composition of this embodiment. By using this electrode active material layer, a secondary battery with excellent input-output characteristics and cycle characteristics can be obtained.

[0082] On the other hand, the binder composition of this embodiment can also be used as an additive for battery material manufacturing if it does not contain any of the negative electrode active material, positive electrode active material, and separator raw material. Here, when the binder composition of this embodiment is used as a thickener, it is also referred to as a "thickener composition".

[0083] As described above, the binder composition of this embodiment can be used for battery material manufacturing and as a thickener, and in both applications it contains the polymer particles and BIT of this embodiment. Furthermore, in either application, there are no particular limitations on the types and mixing ratios of optional components in the binder composition; they can be appropriately determined according to the application.

[0084] When manufacturing a negative electrode using a slurry composition for secondary battery electrodes, there are no particular limitations on the active material that can be used as the negative electrode, and examples include carbon-based active materials and silicon-based active materials.

[0085] There are no particular limitations on carbon-based active materials; examples include graphite, carbon fiber, coke, hard carbon, mesophase carbon microspheres (MCMB), furfuryl alcohol resin sintered body (PFA), and conductive polymers (poly(p-phenylene oxide), etc.).

[0086] There are no particular limitations on silicon-based active materials; examples include silicon and SiO2. x (0.01≤x<2), alloys of silicon and transition metals, etc.

[0087] When manufacturing a positive electrode using a slurry composition for secondary battery electrodes, there are no particular limitations on the active material that can be used as the positive electrode, and examples include lithium-containing composite oxides, transition metal oxides, transition metal fluorides, and transition metal sulfides.

[0088] There are no particular limitations on lithium-containing composite oxides; examples include LiCoO2, LiMnO2, LiNiO2, LiMn2O4, LiXCoYSnZO2, LiFePO4, and LiXCoYSnZO2.

[0089] There are no particular limitations on transition metal oxides; examples include MnO2, MoO3, V2O5, and V6O. 13 Fe2O3, Fe3O4, etc.

[0090] There are no particular limitations on transition metal fluorides; examples include CuF2 and NiF2.

[0091] There are no particular limitations on transition metal sulfides; examples include TiS2, TiS3, MoS3, and FeS2.

[0092] Furthermore, the adhesive composition of this embodiment may include an antifoaming agent as an optional component. Examples of antifoaming agents include various mineral oil-based, silicone-based, acrylic-based, and polyether-based antifoaming agents. When the adhesive composition includes an antifoaming agent, it tends to have superior defoaming properties. In this case, there are no particular limitations on the type of optional component, the mixing ratio, etc.

[0093] (Method for manufacturing adhesive composition)

[0094] There are no particular limitations on the method used to manufacture the binder composition of this embodiment. For example, it is preferable to manufacture it by the following manufacturing method (hereinafter also referred to as "the manufacturing method of this embodiment"). That is, in order to obtain a composition containing polymer particles as binders, it is preferable to use a monomer or the like as the above-mentioned raw material monomer for emulsion polymerization. Suitable seed particles can be used during polymerization, and the seed particles can also be obtained by conventional emulsion polymerization. In addition, known methods can be used during emulsion polymerization, and polymerization initiators, molecular weight adjusters, chelating agents, pH adjusters, emulsifiers, etc. can be suitably used in an aqueous medium.

[0095] There are no particular limitations on what constitutes an emulsifier; examples include anionic surfactants, nonionic surfactants, amphoteric surfactants, and reactive surfactants. They can be used individually or in combination of two or more.

[0096] There are no particular limitations on anionic surfactants; examples include sulfated esters of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, and sulfated esters of polyethylene glycol alkyl ethers.

[0097] There are no particular limitations for nonionic surfactants; examples include alkyl esters, alkyl ethers, and alkyl phenyl ethers of polyethylene glycol.

[0098] There are no particular limitations on what constitutes an amphoteric surfactant. Examples include betaines such as lauryl betaine and stearyl betaine, and amino acids such as lauryl-β-alanine, stearyl-β-alanine, and lauryl di(aminoethyl)glycine.

[0099] There are no particular limitations on reactive surfactants; examples include polyoxyethylene alkylpropylene phenyl ether and α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxypolyoxyethylene.

[0100] There are no particular limitations on polymerization initiators. Examples include water-soluble polymerization initiators such as sodium persulfate, potassium persulfate, and ammonium persulfate; oil-soluble polymerization initiators such as benzoyl peroxide and lauryl peroxide; and redox polymerization initiators based on combinations with reducing agents. They can be used individually or in combination of two or more.

[0101] In the preparation method of this embodiment, there are no particular limitations on the stirring speed, polymerization temperature, reaction (polymerization) time, etc., as long as the composition of this embodiment can be obtained. For example, the stirring speed can be 50 rpm or more and 500 rpm or less, the polymerization temperature can be 50°C or more and 100°C or less, and the reaction time can be 3 hours or more and 72 hours or less.

[0102] In the preparation method of the binder composition of this embodiment, after obtaining polymer particles as described above, the polymer particles can be dispersed in a dispersion solvent as needed, and optional components can be added to obtain the binder composition of this embodiment. Water can be used as the dispersion solvent, or an organic solvent suitable for mixing the active substance with the binder composition can be used as needed.

[0103] (Non-aqueous secondary battery)

[0104] The non-aqueous secondary battery of this embodiment can be manufactured using the binder composition of this embodiment. That is, the non-aqueous secondary battery of this embodiment includes the binder composition of this embodiment.

[0105] In the case of a lithium-ion secondary battery in this embodiment, typical components include a negative electrode, a negative current collector, a positive electrode, a positive current collector, a separator, and an electrolyte. In this embodiment, at least one of the main components (negative electrode, positive electrode, and separator) is obtained using the aqueous binder composition or electrode slurry composition for secondary batteries of this embodiment. That is, at least one of the main components includes the aforementioned composition, thereby resulting in a lithium-ion secondary battery with excellent input / output characteristics and cycle performance.

[0106] It should be noted that whether each component contains the adhesive composition of this embodiment can be determined by whether the component contains the polymer particles of this embodiment.

[0107] There is no particular limitation on the manufacturing method of the non-aqueous secondary battery in this embodiment. For example, in the case of a lithium-ion secondary battery, the following can be described: after coating the battery material manufacturing composition of this embodiment onto the current collector, heating and drying are performed to form the corresponding electrode, the positive electrode and the negative electrode are placed opposite each other with a separator in between, and electrolyte is injected and sealed, etc.

[0108] There are no particular limitations on the negative electrode current collector; for example, copper foil can be used. Similarly, there are no particular limitations on the positive electrode current collector; for example, aluminum foil can be used. There are no particular limitations on the electrolyte; for example, an electrolyte prepared by dissolving electrolytes such as LiClO4, LiBF4, and LiPF6 in an organic solvent can be used. There are no particular limitations on the organic solvent; examples include ethers, ketones, lactones, nitriles, amines, amides, carbonates, and chlorinated hydrocarbons. Representative examples include tetrahydrofuran, acetonitrile, butyronitrile, propylene carbonate, ethylene carbonate, and diethyl carbonate. One or more of these solvents can be used individually or in combination.

[0109] There are no particular limitations on the coating method; for example, any coating head can be used, such as a reverse roller coater, a comma-shaped bar coater, a gravure coater, or an air knife coater. There are also no particular limitations on the drying method; for example, placement drying, forced air drying, hot air drying, infrared heating, or far-infrared heating can be used. There are no particular limitations on the drying temperature; for example, it can be carried out at 60℃ to 150℃.

[0110] Example

[0111] The following examples and comparative examples illustrate the present invention in detail, but the present invention is not limited to any of the following examples. It should be noted that, in this embodiment, unless otherwise specified, "parts" and "%" refer to parts by weight and percentage by weight, respectively.

[0112] [Example 1]

[0113] 0.3 parts by weight of polyoxyethylene polycyclic phenyl ether sulfate ammonium salt (Newcol 707SF) and 350 parts by weight of deionized water were added to the reactor, and the temperature was raised and maintained at 70°C with stirring. 0.5 parts by weight of sodium persulfate (hereinafter also referred to as "NPS") were added. An emulsion was then added dropwise, which was obtained by emulsifying a mixture of monomer solution (148 parts by weight of 2-ethylhexyl acrylate (hereinafter also referred to as "2-EHA"), 50 parts by weight of methacrylic acid (hereinafter also referred to as "MAA"), and 2 parts by weight of 1,9-nonanediol dimethacrylate (hereinafter also referred to as "1,9-ND"), 1.5 parts by weight of Newcol 707SF, and 350 parts by weight of deionized water in a homogenizer. The addition was carried out dropwise over 2.5 hours while maintaining the temperature at 70°C, followed by continued polymerization for 2 hours.

[0114] The reactor temperature was then increased from 70°C to 85°C and maintained for 1.5 hours to complete the polymerization. At this point, the mixing amounts of each monomer component were as follows: relative to 100 parts by weight of the total monomer components (units 2-EHA, MAA, and 1,9-ND from all olefinically unsaturated carboxylic acid monomers), 2-EHA was 74 parts by weight, MAA was 25 parts by weight, and 1,9-ND was 1 part by weight. Next, 46.5 parts by weight of a 25% sodium hydroxide aqueous solution were added to the resulting polymer particles. Then, relative to 100 parts by weight of the resulting polymer particles, 0.005 parts by weight of BIT as an additive were added, followed by filtration through a 200 μm sieve, thereby preparing the binder composition.

[0115] [Examples 2-4 and Comparative Examples 1 and 2]

[0116] As shown in Table 1, the amount of BIT added in Example 1 was changed, and the adhesive composition containing the polymer was prepared in the same manner as in Example 1.

[0117] [Example 5]

[0118] As shown in Table 1, the mixing amounts of the monomer components in Example 1 were modified, and polymer particles were obtained in the same manner as in Example 1. 22.3 parts by weight of a 25% sodium hydroxide aqueous solution were added to the obtained polymer particles. Next, 0.05 parts by weight of BIT as an additive was added relative to 100 parts by weight of the obtained polymer particles, and the mixture was then filtered through a 200 μm sieve to prepare the binder composition.

[0119] [Example 6]

[0120] As shown in Table 1, the mixing amounts of the monomer components in Example 1 were modified, and polymer particles were obtained in the same manner as in Example 1. 74.4 parts by weight of a 25% sodium hydroxide aqueous solution were added to the obtained polymer particles. Next, 0.05 parts by weight of BIT as an additive was added relative to 100 parts by weight of the obtained polymer particles, and the mixture was then filtered through a 200 μm sieve to prepare the binder composition.

[0121] [Example 7]

[0122] As shown in Table 1, the mixing amounts of the monomer components in Example 1 were modified, and polymer particles were obtained in the same manner as in Example 1. 46.5 parts by weight of a 25% sodium hydroxide aqueous solution were added to the obtained polymer particles. Next, 0.05 parts by weight of BIT as an additive were added relative to 100 parts by weight of the obtained polymer particles, and the mixture was then filtered through a 200 μm sieve to prepare the binder composition.

[0123] [Example 8]

[0124] As shown in Table 1, the mixing amounts of the monomer components in Example 1 were modified, and polymer particles were obtained in the same manner as in Example 1. 55.5 parts by weight of a 25% sodium hydroxide aqueous solution were added to the obtained polymer particles. Next, 0.05 parts by weight of BIT as an additive was added relative to 100 parts by weight of the obtained polymer particles, and the mixture was then filtered through a 200 μm sieve to prepare the binder composition.

[0125] [Comparative Example 3]

[0126] As shown in Table 1, the mixing amounts of the monomer components in Example 1 were modified, and polymer particles were obtained in the same manner as in Example 1. 9.3 parts by weight of a 25% sodium hydroxide aqueous solution were added to the obtained polymer particles. Next, 0.05 parts by weight of 2-methyl-4-isothiazolin-3-one (hereinafter sometimes referred to as MIT) as an additive was added to 100 parts by weight of the obtained polymer particles, followed by filtration through a 200 μm sieve, thereby preparing the binder composition.

[0127] [Comparative Example 4]

[0128] By replacing BIT with MIT in Example 6, a polymer-containing adhesive composition was prepared in the same manner as in Example 6.

[0129] [Comparative Example 5]

[0130] The BIT in Example 6 was replaced with 2-n-octyl-4-isothiazolin-3-one (sometimes referred to as OIT), and the same polymer-containing binder composition was prepared as in Example 6.

[0131] [Comparative Example 6]

[0132] In a temperature-adjustable, pressure-resistant reactor equipped with a stirrer, 300 parts by weight of ion-exchanged water, 0.6 parts by weight of sodium dodecylbenzenesulfonate, 1.0 part by weight of potassium persulfate, 0.5 parts by weight of sodium bisulfite, 0.2 parts by weight of α-methylstyrene dimer, 0.2 parts by weight of dodecyl mercaptan, and the following monomers as shown in Table 1: 40 parts by weight of 1,3-butadiene, 33 parts by weight of styrene, 5 parts by weight of methyl methacrylate, 2 parts by weight of 2-hydroxyethyl methacrylate, 11 parts by weight of acrylic acid, 5 parts by weight of itaconic acid, and 4 parts by weight of acrylonitrile, were added sequentially. The polymerization reaction was carried out at 70°C for 8 hours. Three hours after the addition of the monomers, 1.0 part by weight of α-methylstyrene dimer and 0.3 parts by weight of dodecyl mercaptan were added. The temperature in the reactor was then raised to 80°C, and the reaction was carried out for another 2 hours to obtain a latex. Next, the pH of the latex was adjusted to 7.0, and 5 parts by weight of sodium tripolyphosphate (solid component conversion value, added in the form of a 10% by weight aqueous solution) were added. Then, residual monomers were removed by steam distillation, and the mixture was concentrated under reduced pressure to obtain a composition containing copolymer particles.

[0133] Next, 0.05 parts by weight of BIT as an additive were added relative to 100 parts by weight of the obtained polymer particles, and then the mixture was filtered through a 200 μm sieve to prepare the binder composition.

[0134] [Comparative Example 7]

[0135] Under a nitrogen atmosphere, 7 parts by weight of butyl acrylate, 1 part by weight of methyl methacrylate, 1 part by weight of hydroxyethyl acrylate, 2 parts by weight of itaconic acid, 2 parts by weight of acrylic acid, 0.5 parts by weight of ethylene glycol dimethacrylate, 0.3 parts by weight of cyclohexene, 0.2 parts by weight of sodium dodecylbenzenesulfonate, and 100 parts by weight of deionized water were added to the reactor. The temperature was raised to 65°C, and then 0.8 parts by weight of potassium persulfate was added to initiate polymerization. One hour after polymerization began, 50 parts by weight of butyl acrylate, 13 parts by weight of methyl methacrylate, 11 parts by weight of styrene, 3 parts by weight of acrylamide, 2 parts by weight of hydroxyethyl acrylate, 5 parts by weight of methacrylic acid, 2.5 parts by weight of ethylene glycol dimethacrylate, 0.02 parts by weight of tert-dodecyl mercaptan, 0.5 parts by weight of sodium dodecylbenzenesulfonate, and 20 parts by weight of deionized water were added. The temperature was raised to 70°C, and polymerization continued. Six hours after polymerization began, polymerization was stopped, and the pH was adjusted to 7.5 with an aqueous sodium hydroxide solution. Subsequently, steam distillation was performed at 90°C for 15 hours to remove unreacted monomers and other low-boiling-point compounds, yielding a copolymer latex. Next, 0.05 parts by weight of BIT as an additive were added to 100 parts by weight of the obtained polymer particles, followed by filtration through a 200 μm sieve, thereby preparing the adhesive composition.

[0136] Using the compositions obtained from Examples 1-8 and Comparative Examples 1-7 above, the slurry composition for the negative electrode of a secondary battery, the secondary battery, and the evaluation were carried out as shown below. The results are shown in Table 1.

[0137] (Preparation of slurry composition for the negative electrode of a secondary battery)

[0138] 100 parts by weight of natural graphite as the negative electrode active material and 1.0 parts by weight of carboxymethyl cellulose as a thickener were added to a planetary mixer (manufactured by Primix) and stirred at 40 rpm for 10 minutes, followed by stirring at 60 rpm for 20 minutes. Then, 0.4 parts by weight of carboxymethyl cellulose were added and stirred at 40 rpm for 20 minutes. Afterwards, 1.5 parts by weight of the composition obtained in each example and deionized water were added at a solid content of 55%, and the mixture was stirred at 40 rpm for 10 minutes to prepare a coating solution for a secondary battery negative electrode slurry composition.

[0139] (Making the negative electrode of a secondary battery 1)

[0140] Following a method where the slurry thickness after drying on the day of slurry preparation is 100 μm, the aforementioned secondary battery negative electrode slurry composition is coated onto one side of a copper foil using a die-coating machine, and then dried at 60°C for 60 minutes. After drying at 120°C for 3 minutes, it is compressed and molded using a roller press to obtain the secondary battery negative electrode. The coating amount of the negative electrode active material is 106 g / m². 2 The bulk density of the negative electrode active material is 1.35 g / cm³. 3 .

[0141] (Making the negative electrode of a secondary battery 2)

[0142] After the above-mentioned slurry composition for the secondary battery negative electrode was left at room temperature for one week, it was stirred again at 2000 rpm for 1 minute using an Awatori Rentaro (Thinky Co., Ltd.). The mixture was then coated onto one side of a copper foil using a die-coating machine to achieve a dry thickness of 100 μm. After drying at 60°C for 60 minutes, and then at 120°C for 3 minutes, it was compressed using a roller press to obtain the secondary battery negative electrode. The coating amount of the negative electrode active material was 106 g / m². 2 The bulk density of the negative electrode active material is 1.35 g / cm³. 3 .

[0143] (Making a secondary battery)

[0144] The positive electrode and the negative electrode obtained above are punched into circles. They are then layered in the order of positive electrode, separator, and negative electrode, with the active material surfaces of the positive and negative electrodes facing each other. The layers are then placed in a covered stainless steel container. The container and lid are insulated, with the container in contact with the copper foil of the negative electrode and the lid with the aluminum foil of the positive electrode. Electrolyte is then injected into the container and sealed. The container is left at room temperature for one day to produce the secondary battery.

[0145] Regarding the electrolyte used above, an electrolyte prepared by dissolving LiPF6 as a solute in a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 2 (volume ratio) at a concentration of 1.0 mol / L.

[0146] In addition, the separator mentioned above is a separator made of polyethylene porous membrane. As for the negative electrode of the secondary battery, the negative electrode of the secondary battery is made of the slurry composition of the negative electrode of the secondary battery obtained by the binder composition obtained in Examples 1 to 8 and Comparative Examples 1 to 7.

[0147] Furthermore, the positive electrode of the aforementioned secondary battery is manufactured as follows: A slurry is prepared by dispersing 92.2 wt% of lithium cobalt composite oxide (LiCoO2) as the positive electrode active material, 2.3 wt% each of flake graphite and acetylene black as conductive materials, and 3.2 wt% of polyvinylidene fluoride (PVDF) as a binder in N-methylpyrrolidone (NMP). This slurry is then coated onto one side of a 20 μm thick aluminum foil, which serves as the positive electrode current collector, using a die coater. After drying at 130°C for 3 minutes, it is compressed and molded using a roller press. At this point, the coating weight of the positive electrode active material is 250 g / m². 2 The bulk density of the active substance is 3.00 g / cm³. 3 The electrode obtained in this way is used as the positive electrode of a secondary battery.

[0148] In the examples and comparative examples, various physical properties were evaluated as follows.

[0149] (Viscosity change over time of secondary battery electrode slurry composition (time stability))

[0150] The viscosity of the slurry composition for secondary battery electrodes was measured using a TVB-10M (60 rpm, No. 4 rotor) manufactured by Toki Sangyo Co., Ltd., both immediately after preparation and after standing at room temperature for one week (Type B viscosity). The viscosity change over time, R, of the slurry composition for secondary battery electrodes was calculated using the following formula. It should be noted that for the slurry composition for secondary battery electrodes after standing at room temperature for one week, it was thoroughly stirred until the apparent viscosity remained constant using a spatula at a speed that prevented air bubbles from forming, before measurement.

[0151] R (%) = |Viscosity after 1 week at room temperature - Viscosity immediately after preparation| / Viscosity immediately after preparation

[0152] The evaluation criteria are as follows.

[0153] ◎: R (%) is less than 10%.

[0154] ○: R (%) is 10% or more and less than 30%.

[0155] △: R (%) is 30% or more and less than 50%.

[0156] ×: R (%) is 50% or more.

[0157] (Electrolyte swelling degree)

[0158] The binder composition containing polymer particles was dried by standing in an oven at 130°C for 1 hour. The resulting polymer particle film was cut into 0.5 g pieces. The cut sample was placed in a 50 mL vial with 10 g of a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 2 (by weight). After allowing the mixed solvent to permeate for 1 day at 60°C, the sample was removed, washed with the same mixed solvent, and its weight (Wa: g) was measured. The sample was then placed in an oven at 150°C for 1 hour, and its weight (Wb: g) was measured. The swelling degree of the copolymer with respect to the electrolyte was calculated using the following formula.

[0159] The swelling degree of polymer particles in the electrolyte (times) = 1 + {(Wa - Wb) / (Wb)}

[0160] (Insoluble components in the electrolyte)

[0161] The binder composition containing polymer particles was dried by standing in an oven at 130°C for 1 hour. The resulting polymer particle film was cut into approximately 0.5 g pieces and weighed accurately (W0: g). The cut sample was placed in a 50 mL vial with 10 g of a mixed solvent of ethylene carbonate / ethyl methyl carbonate = 1 / 2 (by weight). After allowing the mixed solvent to permeate for 1 day at 60°C, the sample was removed, washed with the same mixed solvent, and then stood in an oven at 150°C for 1 hour. The sample was then weighed accurately (Wb: g), and the insoluble component of the copolymer in the electrolyte was calculated using the following formula.

[0162] Insoluble component of polymer particles in electrolyte (wt%) = Wb / W0 × 100

[0163] (Input / Output Characteristics)

[0164] After adjusting the secondary batteries obtained in each example to a SOC of 50%, the following operations were performed: (i) charging at 0.1C for 10 seconds, stopping for 10 minutes, discharging at 0.1C for 10 seconds, stopping for 10 minutes; (ii) charging at 0.3C for 10 seconds, stopping for 10 minutes, discharging at 0.3C for 10 seconds, stopping for 10 minutes; (iii) charging at 0.5C for 10 seconds, stopping for 10 minutes, discharging at 0.5C for 10 seconds, stopping for 10 minutes. The voltage after each 10-second charge and discharge cycle was measured. A graph was plotted with the current value on the horizontal axis and the voltage after each 10-second cycle on the vertical axis. The slope of the graph was used to evaluate the input-output characteristics (Ω) during charge and discharge.

[0165] It should be noted that the evaluation uses the secondary battery made using the negative electrode described above (2) for secondary battery negative electrode fabrication.

[0166] The evaluation criteria are as follows.

[0167] ◎: Input / output characteristics (Ω) less than 52Ω.

[0168] ○: Input / output characteristics (Ω) are 52Ω or higher and less than 58Ω.

[0169] △: Input / output characteristics (Ω) are above 58Ω and less than 64Ω.

[0170] ×: Input / output characteristics (Ω) are 64Ω or higher.

[0171] (Cycling characteristics (capacity retention))

[0172] Using the negative electrode of the secondary battery obtained from each example, the manufactured secondary battery was charged at 60°C using a 2C constant current constant voltage charging method to 4.2V, then charged at a constant voltage, and then discharged at a 2C constant current to 3.0V, and this charge-discharge cycle was performed. The cycle test was carried out for 100 cycles, and the ratio of the discharge capacity of the 100th cycle to the initial discharge capacity was used as the capacity retention rate, which was determined according to the following criteria. The larger this value, the less capacity loss caused by repeated charge-discharge cycles.

[0173] The evaluation criteria are as follows.

[0174] 5: Capacity maintenance rate is above 90%.

[0175] 4: Capacity maintenance rate is above 85% and less than 90%.

[0176] 3: Capacity maintenance rate is above 80% and below 85%.

[0177] 2: Capacity maintenance rate is above 70% and below 80%.

[0178] 1: Capacity maintenance rate is less than 70%.

[0179] Regarding the evaluation of the above-mentioned cycle characteristics (capacity retention), secondary batteries made using the negative electrode coated onto copper foil on the day of slurry preparation in (Preparation of secondary battery negative electrode 1) and the negative electrode coated one week after slurry preparation in (Preparation of secondary battery negative electrode 2) were evaluated respectively.

[0180] The evaluation results from the examples and comparative examples are summarized in Table 1.

[0181]

[0182] Industrial applicability

[0183] As described above, the slurry composition for battery electrodes of the present invention can suppress the effects of preservative decomposition products to a low degree, and its viscosity remains stable over a long period, thereby obtaining an electrode with excellent resistive characteristics. As a result, a battery with excellent input / output characteristics, cycle characteristics, and other battery properties can be obtained, which is extremely useful.

Claims

1. A water-based binder composition for secondary batteries, comprising polymer particles and 0.001 to 1.0 parts by weight of 1,2-benzisothiazolin-3-one relative to 100 parts by weight of the polymer particles. The polymer particles contain only monofunctional (meth)acrylate monomer units, olefinically unsaturated carboxylic acid monomer units, and other monomer units capable of copolymerizing with the monofunctional (meth)acrylate monomer units and the olefinically unsaturated carboxylic acid monomer units, wherein... The other monomer units comprise at least alkylene glycol di(meth)acrylate but exclude aliphatic conjugated diene monomer units, amide-containing monomer units, α,β-unsaturated nitrile monomer units, and monomer units having repeating units derived from fluorinated vinyl monomers. The content of the olefinic unsaturated carboxylic acid monomer unit is 10.5 parts by weight or more per 100 parts by weight of the polymer particles. The content of the other monomer units is between 0.1 parts by weight and 1 part by weight relative to 100 parts by weight of the polymer particles.

2. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The content of the olefinic unsaturated carboxylic acid monomer unit is less than 50 parts by weight relative to 100 parts by weight of the polymer particles.

3. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The content of the olefinic unsaturated carboxylic acid monomer unit is less than 40.0 parts by weight per 100 parts by weight of the polymer particles.

4. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The content of the monofunctional (meth)acrylate monomer unit is 20.0 parts by weight or more relative to 100 parts by weight of the polymer particles.

5. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The content of the monofunctional (meth)acrylate monomer unit is 50.0 parts by weight or more relative to 100 parts by weight of the polymer particles.

6. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The content of the monofunctional (meth)acrylate monomer unit is 59.5 parts by weight or more relative to 100 parts by weight of the polymer particles.

7. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The content of the monofunctional (meth)acrylate monomer unit is 89.0 parts by weight or less per 100 parts by weight of the polymer particles.

8. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The electrolyte-insoluble component of the aqueous binder composition for secondary batteries accounts for 88% or more by weight relative to the weight of the aqueous binder composition for secondary batteries.

9. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The monofunctional (meth)acrylate monomer unit is selected from at least one group consisting of n-butyl acrylate, tert-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate, n-butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, hexyl methacrylate, heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl acrylate, n-tetradecyl methacrylate, and stearyl methacrylate.

10. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The monofunctional (meth)acrylate monomer unit is selected from at least one group consisting of heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, and lauryl acrylate.

11. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The content of the other monomer units is more than 0.5 parts by weight and less than 1 part by weight relative to 100 parts by weight of the polymer particles.

12. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The other monomer units also include at least one selected from the group consisting of aromatic vinyl monomers, sulfonic acid-containing monomers, aromatic divinyl monomers, polyol poly(meth)acrylates, allyl compounds, and silane coupling agents.

13. The aqueous binder composition for secondary batteries as described in claim 1, wherein, The content of 1,2-benzisothiazolin-3-one is 0.003 to 0.5 parts by weight relative to 100 parts by weight of the polymer particles.

14. A slurry composition for a secondary battery electrode, comprising: The aqueous binder composition for secondary batteries according to any one of claims 1 to 13; and Negative electrode active material or positive electrode active material.

15. A secondary battery electrode having an electrode active material layer formed on a current collector, comprising the slurry composition for a secondary battery electrode as described in claim 14.

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