Polymer composition for non-aqueous secondary battery and non-aqueous secondary battery

Abstract

A polymer composition for a non-aqueous secondary battery is obtained, which is capable of forming a negative electrode having excellent internal resistance and being resistant to swelling after cycling, and a secondary battery having excellent cycle characteristics. The present invention relates to a (meth)acrylic acid ester monomer unit M1, 1.0% by mass or more and 20% by mass or less of ethylenically unsaturated carboxylic acid monomer units M2; Other crosslinkable monomer units M3 copolymerizable with the M1 and M2 (excluding those having a repeating unit derived from an aliphatic conjugated diene compound) are 0.5% by mass or more and 5% by mass or less; A polymer composition for a non-aqueous secondary battery, comprising copolymer particles having the following: The film made of the nonaqueous polymer composition for a secondary battery was subjected to a test to obtain a film having an SP value of 9.6 (cal / cm) calculated by the Fedors method. 3 ) 1 / 2 The tensile strength of the film swollen by immersion in the solvent at 60°C for 15 hours at an elongation of 10% is 0.08 MPa or more. Polymer composition for non-aqueous secondary batteries.

Description

[Technical Field]

[0001] The present invention relates to a polymer composition for a non-aqueous secondary battery and a non-aqueous secondary battery. [Background technology]

[0002] BACKGROUND ART Research into non-aqueous secondary batteries, particularly lithium ion secondary batteries, has been ongoing as an energy technology that reduces the burden on the environment. Lithium-ion secondary batteries have a larger capacity per unit mass or volume than other batteries, making them suitable for increasing capacity and miniaturization. For example, in the automotive sector, exhaust gas regulations in various countries are becoming stricter every year, and with the shift to electric vehicles, such as EVs, demand for lithium-ion secondary batteries is growing.

[0003] A known method for producing electrodes for use in electrochemical devices such as lithium ion secondary batteries is to apply a liquid composition, in which a binder, a thickener, etc. is added to an electrode active material, to the surface of a current collector and then dry the composition to form an electrode layer on the current collector. Styrene-butadiene copolymer latex is known as a binder that has high adhesive strength with the metal constituting the current collector. The binder functions to improve adhesion between solid electrode active materials, between the electrode active material and the current collector, and between the electrode active material and the separator. However, inside a battery filled with an electrolyte solution, the binder may absorb the electrolyte solution, resulting in insufficient strength of the binder. As described above, if the binder strength is insufficient, the charge-discharge cycle characteristics of the secondary battery tend to be impaired.

[0004] Patent Document 1 discloses a binder that exhibits a predetermined degree of swelling and repeated tensile strength in an electrolyte solution, a composition containing the binder, and a lithium ion secondary battery that uses the composition. Furthermore, Patent Document 2 discloses a technique for adjusting the tensile strength of a copolymer binder wetted with an electrolyte solution to a predetermined range, a composition containing the binder, and a lithium ion secondary battery using the composition. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2013 / 161786 [Patent Document 2] International Publication No. 2018 / 182343 Summary of the Invention [Problem to be solved by the invention]

[0006] However, batteries using the binders proposed so far may have high internal resistance, which impairs the cycle characteristics of the secondary battery during charge and discharge and makes it more susceptible to metallic lithium deposition. For example, according to the composition described in Patent Document 1, it is said that a lithium ion secondary battery with good performance can be obtained by using a binder having a predetermined swelling degree and repeated tensile strength. However, the composition described in Patent Document 1 has the problem that the internal resistance of the battery increases, and there is a possibility that sufficient cycle characteristics cannot be obtained. Furthermore, the composition described in Patent Document 2 is said to be able to exhibit high adhesive strength and mechanical properties and improve the life performance of a battery by using a copolymer binder having a wet strength equal to or greater than a predetermined value. However, the composition described in Patent Document 2 has the problem that the internal resistance of the battery increases, and there is a possibility that sufficient cycle characteristics cannot be obtained.

[0007] Therefore, an object of the present invention is to provide a polymer composition for a non-aqueous secondary battery, which is capable of forming a negative electrode having excellent internal resistance and which is less likely to swell after cycling, and a secondary battery having excellent cycle characteristics, and a non-aqueous secondary battery containing the polymer composition for a non-aqueous secondary battery. [Means for solving the problem]

[0008] As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that, in a polymer composition for a non-aqueous secondary battery containing copolymer particles having (meth)acrylic acid ester monomer units M1, ethylenically unsaturated carboxylic acid monomer units M2, and other crosslinkable monomer units M3 copolymerizable with the (meth)acrylic acid ester monomer units M1 and the ethylenically unsaturated carboxylic acid monomer units M2 (excluding those having a repeating unit derived from an aliphatic conjugated diene compound), a film formed from the polymer composition for a non-aqueous secondary battery has an SP value of 9.6 (cal / cm) calculated by the Fedors method. 3 ) 1 / 2 The inventors have found that the above-mentioned problems of the conventional technology can be solved by specifying a film that has been swollen by immersing it in a solvent such as methyl methacrylate at 60°C for 15 hours and that has a tensile strength at an elongation of 10% of a predetermined value or more, and have thereby completed the present invention. That is, the present invention is as follows.

[0009] [1] (meth)acrylic acid ester monomer units M1; 1.0% by mass or more and 20% by mass or less of ethylenically unsaturated carboxylic acid monomer units M2; other crosslinkable monomer units M3 (excluding those having a repeating unit derived from an aliphatic conjugated diene compound) copolymerizable with the (meth)acrylic acid ester monomer units M1 and the ethylenically unsaturated carboxylic acid monomer units M2 in an amount of 0.5% by mass or more and 5% by mass or less; A polymer composition for a non-aqueous secondary battery, comprising copolymer particles having the following: The film made of the nonaqueous polymer composition for a secondary battery was subjected to a test to obtain a film having an SP value of 9.6 (cal / cm) calculated by the Fedors method. 3 ) 1 / 2 The tensile strength of the film swollen by immersion in the solvent at 60°C for 15 hours at an elongation of 10% is 0.08 MPa or more. Polymer composition for non-aqueous secondary batteries. [2] The crosslinkable monomer unit M3 is The crosslinked monomer unit is composed of at least one compound having three or more unsaturated bonds. The polymer composition for a non-aqueous secondary battery according to [1] above. [3] The glass transition temperature of the nonaqueous polymer composition for secondary batteries is −80° C. or higher and 20° C. or lower. The polymer composition for a non-aqueous secondary battery according to [1] or [2] above. [4] The copolymer particles are Contains 1.0% by mass or more and 12% by mass or less of aromatic vinyl monomer units, The polymer composition for a non-aqueous secondary battery according to any one of [1] to [3] above. [5] A non-aqueous secondary battery containing the polymer composition for non-aqueous secondary batteries according to any one of [1] to [4] above. [Effects of the Invention]

[0010] According to the present invention, there are provided a polymer composition for a nonaqueous secondary battery, which is capable of forming a negative electrode having excellent internal resistance and which is less likely to swell after cycling, and a secondary battery having excellent cycle characteristics, and a nonaqueous secondary battery containing the polymer composition for a nonaqueous secondary battery. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail. The following embodiments are merely examples for explaining the present invention, and are not intended to limit the present invention to the following content. The present invention can be implemented by appropriately modifying it within the scope of the gist thereof.

[0012] In this specification, when the term "monomer" is used, this "monomer" includes all of the monomers that constitute the copolymer particles contained in the polymer composition for a non-aqueous secondary battery of this embodiment. In this specification, when incorporated into a polymer, it is referred to as a "monomer unit", and when not incorporated into a polymer, it is referred to as a "monomer" or a "compound".

[0013] Unless otherwise specified, the expressions "xx or more and xx or less" and "xx to xx" representing a numerical range mean a numerical range including the lower and upper limits, which are the endpoints. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any way.

[0014] In the description of groups (atomic groups) in this specification, when a notation does not specify whether the group is substituted or unsubstituted, it encompasses both unsubstituted and substituted groups. For example, the term "alkyl group" encompasses not only alkyl groups without a substituent (unsubstituted alkyl groups) but also alkyl groups with a substituent (substituted alkyl groups).

[0015] In this specification, "(meth)acrylic" includes both methacrylic and acrylic. In this specification, the content of each component means the total content of the component, unless otherwise specified.

[0016] [Polymer composition for non-aqueous secondary batteries] The polymer composition for non-aqueous secondary batteries of the present embodiment contains copolymer particles having a (meth)acrylic acid ester monomer unit M1, an ethylenically unsaturated carboxylic acid monomer unit M2 in an amount of 1.0 mass% or more and 20 mass% or less, and other crosslinkable monomer units M3 copolymerizable with the (meth)acrylic acid ester monomer unit M1 and the ethylenically unsaturated carboxylic acid monomer unit M2 (excluding those having repeating units derived from aliphatic conjugated diene compounds) in an amount of 0.5 mass% or more and 5 mass% or less. A film made of the polymer composition for non-aqueous secondary batteries of the present embodiment has a tensile strength at 10% elongation of 0.08 MPa or more after swelling by immersing it in a solvent having an SP value of 9.6 (cal / cm 3 ) 1 / 2 at 60°C for 15 hours.

[0017] The SP value calculated by the Fedors method means the solubility parameter δ calculated by the following formula (A) using the cohesive energy density (E) and molar molecular volume (V) of various atomic groups described in "R.F. Fedors: Polym. Eng. Sci., 14[2], 147 - 154 (1974)". δ = ΣE / ΣV Formula (A) (In Formula (A), E and V represent the E and molar volume V of various atomic groups by Fedors, respectively.)

[0018] By incorporating the polymer composition for non-aqueous secondary batteries having the above-described configuration into a non-aqueous secondary battery, a non-aqueous secondary battery with excellent internal resistance and a negative electrode that is difficult to swell after cycling and excellent cycle characteristics can be obtained.

[0019] (Copolymer particles) As described above, the polymer composition for non-aqueous secondary batteries of the present embodiment contains copolymer particles containing monomer units M1, M2, and M3 in predetermined amounts.

[0020] <M1: (meth)acrylic acid ester monomer unit> The copolymer particles used in the polymer composition for a non-aqueous secondary battery of the present embodiment have (meth)acrylate monomer units M1 (hereinafter, may be simply referred to as M1). Examples of the compound forming the (meth)acrylate monomer unit M1 include, but are not limited to, 2-ethylhexyl acrylate, butyl acrylate, 4-hydroxybutyl acrylate, 2-hydroxyethyl methacrylate, cyclohexyl methacrylate, 1,9-nonanediol dimethacrylate, 1,4-butanediol diacrylate, trimethylolpropane triacrylate, methoxypolyethylene glycol acrylate, polypropylene glycol monomethacrylate, and the like. As M1, 2-ethylhexyl acrylate is preferable from the viewpoint of excellent adhesion strength of the electrode and electrolyte resistance. As the compound forming M1, one kind may be used alone, or two or more kinds may be used in combination.

[0021] <M2: ethylenically unsaturated carboxylic acid-based monomer unit> The copolymer particles used in the polymer composition for a non-aqueous secondary battery of the present embodiment have an ethylenically unsaturated carboxylic acid-based monomer unit M2 (hereinafter, may be referred to as M2). The content of M2 in the copolymer particles is 1.0% by mass or more and 20% by mass or less based on the total amount of monomer units derived from all monomers. When the content of M2 is 1.0% by mass or more, the elastic modulus of the copolymer particles can be increased, the expansion of the battery accompanying charge and discharge cycles can be suppressed, and the cycle characteristics tend to be excellent. From the above viewpoints, the content of M2 is preferably 5.0% by mass or more, more preferably 10.0% by mass or more. When the content of M2 is 20% by mass or less, flexibility can be imparted to the copolymer particles to improve the followability to active materials and the like, and the cycle characteristics tend to be excellent. From the above viewpoints, the content of M2 is preferably 18% by mass or less, more preferably 16% by mass or less, and still more preferably 14% by mass or less. Examples of the compound for forming M2 include, but are not limited to, unsaturated carboxylic acids such as (meth)acrylic acid and itaconic acid. In particular, from the viewpoint of excellent swelling suppression and cycle characteristics of the battery, (meth)acrylic acid is preferable as the compound for forming M2. These may be used alone or in combination of two or more.

[0022] <M3: Other crosslinkable monomer units copolymerizable with the M1 and M2> The copolymer particles used in the polymer composition for a non-aqueous secondary battery of the present embodiment include other crosslinkable monomer units (excluding those having repeating units derived from aliphatic conjugated diene compounds) M3 (hereinafter sometimes referred to as M3) copolymerizable with the M1 and M2.

[0023] From the viewpoint of the strength of the polymer composition for a non-aqueous secondary battery of the present embodiment, the M3 preferably contains at least one crosslinking monomer unit composed of a compound having two or more unsaturated bonds, and more preferably contains at least one crosslinking monomer unit composed of a compound having three or more unsaturated bonds.

[0024] The M3 preferably contains at least one of monomer units composed of a compound in which the homopolymer of the compound forming the monomer unit constituting M3 has a glass transition temperature of 60°C or higher. Thereby, the effect of enhancing the strength of the polymer composition for a non-aqueous secondary battery of the present embodiment can be obtained.

[0025] The copolymer particles containing a predetermined amount of the monomer units M1, M2, and M3 contained in the polymer composition for a non-aqueous secondary battery of the present embodiment preferably contain an aromatic vinyl monomer unit in an amount of 1.0% by mass or more and 12% by mass or less. When the content of the aromatic vinyl monomer unit in the copolymer particles is 1.0% by mass or more, the effect of improving the strength of the polymer composition for a non-aqueous secondary battery of the present embodiment can be obtained, and when it is 12% by mass or less, the effect of improving the adhesion due to imparting flexibility can be obtained. The content of the aromatic vinyl monomer unit in the copolymer particles is more preferably 3 to 10% by mass, and further preferably 5 to 8% by mass. The content of the aromatic vinyl monomer unit in the copolymer particles can be controlled within the above-mentioned range by adjusting the amount of aromatic vinyl compound added in the polymerization step and the polymerization time.

[0026] The content of M3 in the copolymer particles contained in the polymer composition for a nonaqueous secondary battery of this embodiment is 0.5 mass % or more and 5 mass % or less with respect to the total amount of monomer units derived from all monomers. When the content of M3 is 0.5% by mass or more, the electrolyte resistance of the copolymer particles can be increased, and battery expansion due to charge / discharge cycles can be suppressed, which tends to result in excellent cycle characteristics. From the above viewpoint, the content of M3 is preferably 0.8% by mass or more, and more preferably 1% by mass or more. When the content of M3 is 5% by mass or less, flexibility is imparted to the copolymer particles, which can improve the ability to conform to the active material and the like, and the cycle characteristics tend to be excellent. From the above viewpoint, the content of M3 is preferably 4% by mass or less, and more preferably 2% by mass or less.

[0027] Examples of compounds that form M3 include, but are not limited to, trimethylolpropane triacrylate, 1,9-nonanediol dimethacrylate, divinylbenzene, ethylene glycol dimethacrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol di(meth)acrylate, pentaerythritol tetra(meth)acrylate, diallyl fumarate, diaryl itaconate, and triallyl isocyanurate. In particular, the compound forming M3 is preferably at least one selected from the group consisting of trimethylolpropane triacrylate, 1,9-nonanediol dimethacrylate, and divinylbenzene, from the viewpoint of achieving excellent electrode adhesive strength and cycle characteristics of nonaqueous secondary batteries. As the compound forming M3, one type may be used alone, or two or more types may be used in combination.

[0028] <Other Monomer Units Other than M1 to M3> The copolymer particles used in the polymer composition for a non-aqueous secondary battery of this embodiment may have other monomer units in addition to M1 to M3. Compounds forming other monomer units other than M1 to M3 include, but are not limited to, (meth)acrylates such as hydroxyethyl methacrylate, ethyl acrylate, and methyl methacrylate; sulfonic acid group-containing monomers such as vinyl sulfonic acid; and the like. The compounds forming the other monomer units other than M1 to M3 may be used singly or in combination of two or more.

[0029] [Physical Properties of Non-Aqueous Polymer Composition for Secondary Batteries] (Tensile strength at 10% elongation of non-aqueous polymer composition film for secondary battery immersed in solvent) The polymer composition for a non-aqueous secondary battery of this embodiment is a polymer composition for a non-aqueous secondary battery, which is formed into a film having an SP value of 9.6 (cal / cm 2 ) calculated by the Fedors method. 3 ) 1 / 2 The film is immersed in the solvent at 60°C for 15 hours to swell it, and the tensile strength at an elongation of 10% is 0.08 MPa or more. This makes it possible to increase the elastic modulus of the polymer composition for a non-aqueous secondary battery and the copolymer particles, thereby suppressing battery expansion due to charge / discharge cycles and tending to result in excellent cycle characteristics. One way to increase the tensile strength of the swollen film to 0.08 MPa or more at 10% elongation is to add a crosslinkable monomer to the copolymer particles in an appropriate range and blend in a small amount of a monomer with a high glass transition temperature of a homopolymer such as styrene or cyclohexyl methacrylate. The tensile strength of the swollen film at 10% elongation is preferably 0.1 MPa or more, more preferably 0.15 MPa or more, and even more preferably 0.2 MPa.

[0030] <Method for measuring tensile strength of film immersed in solvent at 10% elongation> The tensile strength of the film immersed in the solvent at an elongation of 10% can be measured by the following method. The non-aqueous polymer composition for secondary batteries of this embodiment is dried to obtain a film with a thickness of 1 mm. The film is cut into a dumbbell shape No. 6 (JIS-K6251) to obtain a test piece. The test piece has an SP value of 9.6 (cal / cm) calculated by the Fedors method. 3 ) 1 / 2 The film is placed in a sealed container together with 50 g of a solvent containing 10% ethylenediaminetetraacetic acid (E2), and immersed at 60°C for 15 hours. The film is removed from the solvent, the solvent adhering to the surface is wiped off, and then a tensile test is performed at a pulling rate of 30 mm / min and a chuck distance of 60 mm. The tensile strength of the film is calculated from the stress at an elongation of 10%. The solvent used may be any solvent commonly used as an electrolyte for secondary batteries, such as propylene carbonate, ethylene carbonate, diethyl carbonate, ethyl propionate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, vinylene carbonate, acetonitrile, etc. These solvents may be used alone or in combination of two or more.

[0031] (Glass transition temperature (Tg) of polymer composition for non-aqueous secondary battery) The nonaqueous polymer composition for a secondary battery of this embodiment preferably has a glass transition temperature (Tg) of -80°C or higher and 20°C or lower. When the Tg is −80° C. or higher, the copolymer particles contained in the polymer composition for a nonaqueous secondary battery tend to have excellent hardness. From the above viewpoint, the Tg is more preferably −60° C. or higher, and further preferably −50° C. or higher. Furthermore, when the Tg is 20° C. or less, the copolymer particles contained in the polymer composition for a nonaqueous secondary battery tend to have excellent adhesive strength. From the above viewpoint, the Tg is more preferably 10° C. or less, and even more preferably −10° C. or less. The glass transition temperature of the non-aqueous polymer composition for secondary batteries can be controlled within the above-mentioned range by changing the composition ratio of the raw material monomers.

[0032] <Method for measuring glass transition temperature of non-aqueous polymer composition for secondary battery> The glass transition temperature of the nonaqueous polymer composition for a secondary battery of this embodiment can be measured by the following method. The non-aqueous secondary battery polymer composition is adjusted to pH 7.0 and dried to obtain a dried product. Using a differential scanning calorimeter (e.g., Hitachi High-Tech Science Corporation; DSC7020), the temperature is raised at a predetermined rate to obtain a differential scanning calorimetric curve of the non-aqueous secondary battery polymer composition, and the glass transition temperature is determined.

[0033] [Other Components of the Polymer Composition for Non-Aqueous Secondary Batteries] (Isothiazolinone compounds) The nonaqueous polymer composition for a secondary battery of the present embodiment preferably further contains an isothiazolinone compound. The content of the isothiazoline compound is preferably 0.0001 part by mass or more and 1.0 part by mass or less relative to 100 parts by mass of the copolymer particles. When the content is within this range, hysteretic viscosity behavior with respect to shear force can be suppressed, and more stable coating properties tend to be achieved. The isothiazolin-based compound is not limited to the following, and various known compounds can be used, for example, 2-methyl-4-isothiazolin-3-one, 5-chloro-2-methyl-4-isothiazolin-3-one, 1,2-benzisothiazolin-3-one, 2-n-octyl-4-isothiazolin-3-one, 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one, 2-ethyl-4-isothiazolin-3-one, 4,5-dichloro-2-cyclohexyl-4-isothiazolin-3-one, 5-chloro-2-ethyl-4-isothiazolin-3-one, 5-chloro-2-t-octyl-4-isothiazolin-3-one, 4-chloro-2-n-octyl-4-isothiazolin-3-one, Examples of the benzothiazolin-3-one include thiazolin-3-one, 5-chloro-2-n-octyl-4-isothiazolin-3-one, Nn-butyl-1,2-benzisothiazolin-3-one, N-butylbenzisothiazolin-3-one, N-methylbenzisothiazolin-3-one, N-ethylbenzisothiazolin-3-one, N-propylbenzisothiazolin-3-one, N-isobutylbenzisothiazolin-3-one, N-pentylbenzisothiazolin-3-one, N-isopentylbenzisothiazolin-3-one, N-hexylbenzisothiazolin-3-one, N-allylbenzisothiazolin-3-one, and N-(2-butenyl)benzisothiazolin-3-one. 2-Methyl-4-isothiazolin-3-one is particularly preferred.

[0034] (Antifoaming agent) The non-aqueous secondary battery polymer composition of this embodiment may contain an antifoaming agent as an optional component. Examples of the antifoaming agent include, but are not limited to, various mineral oil-based, silicone-based, acrylic-based, and polyether-based antifoaming agents. When an antifoaming agent is contained, the composition tends to have better defoaming properties. The type and blending ratio of the antifoaming agent are not particularly limited.

[0035] (emulsifier) The nonaqueous polymer composition for a secondary battery of the present embodiment may contain an emulsifier as an optional component. Examples of emulsifiers include, but are not limited to, anionic surfactants, nonionic surfactants, amphoteric surfactants, and reactive surfactants. The emulsifier may be used alone or in combination of two or more kinds. Examples of anionic surfactants include, but are not limited to, sulfate esters of higher alcohols, alkylbenzene sulfonates, aliphatic sulfonates, and sulfate esters of polyethylene glycol alkyl ethers. Nonionic surfactants include, but are not limited to, alkyl esters, alkyl ethers, and alkyl phenyl ethers of polyethylene glycol. Examples of amphoteric surfactants include, but are not limited to, betaines such as lauryl betaine and stearyl betaine, and amino acid surfactants such as lauryl-β-alanine, stearyl-β-alanine, and lauryldi(aminoethyl)glycine. Examples of reactive surfactants include, but are not limited to, polyoxyethylene alkylpropenylphenyl ether, α-[1-[(allyloxy)methyl]-2-(nonylphenoxy)ethyl]-ω-hydroxypolyoxyethylene, and the like.

[0036] (Polymerization initiator) The nonaqueous polymer composition for a secondary battery of the present embodiment may contain a polymerization initiator as an optional component. Examples of the polymerization initiator include, but are not limited to, 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-based polymerization initiators in combination with a reducing agent. The polymerization initiator may be used alone or in combination of two or more kinds.

[0037] The polymer composition for a non-aqueous secondary battery of this embodiment is used as a binder for a non-aqueous secondary battery. Depending on the application, it may contain various known optional components in addition to the copolymer particles described above.

[0038] [Uses of polymer composition for non-aqueous secondary batteries] The use of the nonaqueous polymer composition for a secondary battery of this embodiment is not particularly limited as long as it is used as one material of an electrode binder for a secondary battery, for example, as a negative electrode material, a positive electrode material, a separator material, etc.

[0039] [Method for producing polymer composition for non-aqueous secondary battery] The method for producing the non-aqueous polymer composition for secondary batteries of the present embodiment is not particularly limited, but the composition can be produced by the following production method. That is, a method of carrying out emulsion polymerization using the above-mentioned predetermined raw material monomers and the like is preferred. Appropriate seed particles may be used during the polymerization, and the seed particles can also be obtained by ordinary emulsion polymerization. For emulsion polymerization, known methods can be employed, and the production can be carried out in an aqueous medium using a polymerization initiator, a molecular weight modifier, a chelating agent, a pH adjuster, an emulsifier, etc. as appropriate. Conditions such as stirring speed, polymerization temperature, and reaction (polymerization) time are not particularly limited as long as the nonaqueous polymer composition for a secondary battery of this embodiment is obtained. Specifically, the stirring speed can be typically 50 rpm or more and 500 rpm or less, the reaction (polymerization) temperature can be typically 50° C. or more and 100° C. or less, and the reaction (polymerization) time can be typically 3 hours or more and 72 hours or less. In the above-described production method, after obtaining the polymer composition for a nonaqueous secondary battery, optional components can be added as needed to obtain the composition for a nonaqueous secondary battery of the present embodiment. Water can be used as a dispersion medium for the copolymer particles, and an organic solvent suitable for the active material can also be used as needed.

[0040] [Nonaqueous secondary battery] The nonaqueous secondary battery of the present embodiment contains the polymer composition for a nonaqueous secondary battery of the present embodiment described above, and can be produced using the polymer composition for a nonaqueous secondary battery of the present embodiment.

[0041] When the nonaqueous secondary battery of the present embodiment is a lithium ion secondary battery, typical components thereof include a negative electrode, a negative electrode current collector, a positive electrode, a positive electrode current collector, a separator, and an electrolyte. The nonaqueous secondary battery of the present embodiment may have at least one of its main components (negative electrode, positive electrode, and separator) obtained using the polymer composition for a nonaqueous secondary battery of the present embodiment, that is, at least one of its main components contains the polymer composition for a nonaqueous secondary battery of the present embodiment. In the nonaqueous secondary battery of the present embodiment, among the above-mentioned main components, it is preferable that the negative electrode contains the polymer composition for a nonaqueous secondary battery of the present embodiment. The inclusion of each component in the polymer composition for a nonaqueous secondary battery of the present embodiment can be determined by whether or not the polymer composition for a nonaqueous secondary battery of the present embodiment is contained in a predetermined component.

[0042] The method for producing the nonaqueous secondary battery of the present embodiment is not particularly limited. Taking a lithium ion secondary battery as an example, an example includes a method in which the polymer composition for a nonaqueous secondary battery of the present embodiment is applied to a current collector, heated, and dried to form corresponding electrodes, the positive electrode and the negative electrode are arranged to face each other via a separator, an electrolytic solution is injected, and the battery is sealed.

[0043] The negative electrode current collector may be, but is not limited to, a copper foil, for example, and the positive electrode current collector may be, but is not limited to, an aluminum foil, for example. The electrolytic solution is not limited to the following, but examples thereof include those in which an electrolyte such as LiClO4, LiBF4, or LiPF6 is dissolved in an organic solvent. Examples of organic solvents include, but are not limited to, ethers, ketones, lactones, nitriles, amines, amides, carbonates, and chlorinated hydrocarbons. Representative examples include tetrahydrofuran, acetonitrile, butyronitrile, propylene carbonate, ethylene carbonate, and diethyl carbonate. These organic solvents may be used alone or in combination.

[0044] The method for applying the nonaqueous polymer composition for a secondary battery of the present embodiment to a current collector is not limited to the following, but examples thereof include a method using any coater head such as a reverse roll coater, a comma bar coater, a gravure coater, or an air knife coater. The drying method is not limited to the following, and for example, standing drying, air drying, hot air drying, an infrared heater, a far-infrared heater, etc. can be used. The drying temperature is not limited to the following, but can be, for example, 60°C to 150°C.

[0045] When a negative electrode is produced using the polymer composition for a nonaqueous secondary battery of the present embodiment, the negative electrode may contain the polymer composition for a nonaqueous secondary battery of the present embodiment, a negative electrode active material, and, as necessary, optional components. When a positive electrode is produced using the polymer composition for a nonaqueous secondary battery of the present embodiment, the positive electrode may contain the polymer composition for a nonaqueous secondary battery of the present embodiment, a positive electrode active material, and, as necessary, optional components. When a separator is produced using the polymer composition for a nonaqueous secondary battery of the present embodiment, the separator may contain the polymer composition for a nonaqueous secondary battery of the present embodiment, separator raw materials, and optional components as necessary.

[0046] The nonaqueous secondary battery polymer composition of the present embodiment can also be used as an additive for manufacturing battery materials other than negative electrodes, positive electrodes, and separators. All of these applications share the common feature of containing the nonaqueous secondary battery polymer composition of the present embodiment. Furthermore, in all of these applications, when the nonaqueous secondary battery polymer composition of the present embodiment contains optional components, the types, blending ratios, and the like of the optional components are not particularly limited and may be appropriately determined depending on the application.

[0047] When manufacturing a negative electrode containing the polymer composition for a nonaqueous secondary battery of this embodiment, examples of usable negative electrode active materials include, but are not limited to, carbon-based active materials and silicon-based active materials. Examples of carbon-based active materials include, but are not limited to, graphite, carbon fiber, coke, hard carbon, mesocarbon microbeads (MCMB), baked furfuryl alcohol resin (PFA), conductive polymers (poly-p-phenylene, etc.), etc. Examples of silicon-based active materials include, but are not limited to, silicon, SiO x (0.01≦x<2), alloys of silicon and transition metals, etc.

[0048] When producing a positive electrode containing the polymer composition for a nonaqueous secondary battery of the present embodiment, examples of the positive electrode active material that can be used include, but are not limited to, lithium-containing composite oxides, transition metal oxides, transition metal fluorides, and transition metal sulfides. Examples of lithium-containing composite oxides include, but are not limited to, LiCoO2, LiMnO2, LiNiO2, LiMn2O4, Li X Co Y Sn Z O2, LiFePO4, Li X Co Y Sn Z Examples include O2. Examples of transition metal oxides include, but are not limited to, MnO2, MoO3, V2O5, and V6O 13 , Fe2O3, Fe3O4, etc. Examples of transition metal fluorides include, but are not limited to, CuF2, NiF2, and the like. Examples of transition metal sulfides include, but are not limited to, TiS2, TiS3, MoS3, and FeS2. [Example]

[0049] Hereinafter, the present embodiment will be described in more detail using examples and comparative examples, but the present invention is not limited to the following examples and comparative examples. For convenience of explanation, the following examples use terms such as "composition" and "coating liquid," but both of these terms are concepts encompassed by the polymer composition for a non-aqueous secondary battery of the present invention.

[0050] [Measurement of physical properties of polymer composition for non-aqueous secondary battery] (Method for measuring glass transition temperature) The nonaqueous polymer composition for a secondary battery was dried at 130° C. for 30 minutes to obtain a dried product. Using a differential scanning calorimeter (manufactured by Hitachi High-Tech Science Corporation; DSC7020), the temperature was raised from −70° C. to 200° C. at a rate of 20° C. / min to obtain a differential scanning calorimetric curve of the nonaqueous polymer composition for secondary batteries, and the glass transition temperature (° C.) was determined using the attached software.

[0051] (Method for measuring the tensile strength of a film immersed in a solvent at 10% elongation) The nonaqueous polymer composition for a secondary battery was dried in the air at 45° C. for 48 hours to obtain a film having a thickness of 1 mm. The film was cut into a dumbbell-shaped No. 6 (JIS-K6251) specimen. The test piece was placed in a sealed container together with 50 g of a mixed solvent (SP value: 9.6) of ethylene carbonate / propylene carbonate / diethyl carbonate / ethyl propionate = 3 / 1 / 3 / 3 (mass ratio), and immersed at 60°C for 15 hours. The film was removed from the solvent, and the solvent adhering to the surface was wiped off, after which a tensile test was carried out at a tensile speed of 30 mm / min and a chuck distance of 60 mm. The tensile strength (MPa) at an elongation of 10% was calculated from the stress at an elongation of 10% of the film.

[0052] [Evaluation of characteristics of non-aqueous secondary batteries] (Fabrication of non-aqueous secondary battery) <Preparation of secondary battery negative electrode> A coating solution for a secondary battery negative electrode containing a nonaqueous secondary battery polymer composition prepared in Examples and Comparative Examples described below was applied to one side of a copper foil using a die coater so that the thickness after drying would be 100 μm, and then dried at 60° C. for 60 minutes, thereby forming an electrode layer. After drying at 120°C for 3 minutes, the mixture was compression molded using a roll press to obtain a negative electrode active material with a bulk density of 1.49 g / cm. 3 Thus, a secondary battery negative electrode was obtained.

[0053] <Preparation of secondary battery> The secondary battery positive electrode and the secondary battery negative electrode prepared as described above were punched into a circle, and the positive electrode, separator, and negative electrode were stacked in this order so that the active material surfaces of the positive electrode and negative electrode faced each other, and then the stacked electrodes were placed in a stainless steel metal container with a lid. The container and the lid were insulated from each other, and the container was placed so as to be in contact with the copper foil of the negative electrode, and the lid was placed so as to be in contact with the aluminum foil of the positive electrode. The electrolyte solution was poured into the container, which was then sealed and left to stand at room temperature for one day to prepare a secondary battery. The electrolyte used here was prepared by dissolving LiPF6 as a solute in ethylene carbonate / ethyl methyl carbonate = 1 / 2 (volume ratio) (SP value: 9.6) to a concentration of 1.0 mol / L. The separator used was made of a polyethylene porous film, and the negative electrode of the secondary battery used was a negative electrode using the non-aqueous polymer composition for secondary batteries obtained in Examples 1 to 17 and Comparative Examples 1 to 3 described below. Furthermore, the positive electrode of the secondary battery was prepared as follows. A slurry was prepared by dispersing 92.2 parts by mass of lithium cobalt composite oxide (LiCoO2) as the positive electrode active material, 2.3 parts by mass each of flake graphite and acetylene black as the conductive material, and 3.2 parts by mass of polyvinylidene fluoride (PVDF) as the binder in N-methylpyrrolidone (NMP). This slurry was applied to one side of a 20 μm thick aluminum foil that served as the positive electrode current collector using a die coater, dried at 130 °C for 3 minutes, and then compression molded using a roll press. At this time, the amount of applied positive electrode active material was 250 g / m 2 , the bulk density of the active material is 3.00 g / cm 3 The electrode thus obtained was used as a positive electrode for a secondary battery.

[0054] (Method for evaluating the characteristics of non-aqueous secondary batteries) <Non-aqueous secondary battery characteristics> As the non-aqueous secondary battery characteristics, the internal resistance and cycle characteristics were evaluated by the methods described below. [Internal resistance] The fabricated nonaqueous secondary batteries were adjusted to an SOC of 50%, and then (i) charged at 0.1 C for 10 seconds with a 10-minute pause, discharged at 0.1 C for 10 seconds with a 10-minute pause, (ii) charged at 0.3 C for 10 seconds with a 10-minute pause, discharged at 0.3 C for 10 seconds with a 10-minute pause, and (iii) charged at 0.5 C for 10 seconds with a 10-minute pause, discharged at 0.5 C for 10 seconds with a 10-minute pause, and measured the voltage 10 seconds after each charge and discharge. Each current value was plotted on the horizontal axis and the voltage after 10 seconds was plotted on the vertical axis, and the internal resistance (Ω) was evaluated from the slope. The evaluation criteria were as follows: A: Less than 52 ohms B: 52 ohms or more and less than 55 ohms C: 55 ohms or more and less than 58 ohms D: 58Ω or more

[0055] [Cycle characteristics] To evaluate the cycle characteristics of the non-aqueous secondary battery, the following charge / discharge cycle was carried out. The battery was charged at a constant current of 2C at 60°C until the voltage reached 4.2V, then charged at a constant voltage, and then discharged at a constant current of 1C until the voltage reached 3.0V, and this cycle was repeated. The swelling of the electrode after cycling and the capacity retention rate after cycling were evaluated by the methods described below.

[0056] <Swelling of secondary battery negative electrode after cycling> The secondary battery negative electrode prepared as described above was pressed and left to stand for one day, and then the thickness of the electrode layer (the layer formed from the coating liquid for secondary battery negative electrode) was measured. The thickness of the electrode layer was also measured after 100 cycles of charge and discharge as described in the above [Cycle characteristics]. From these measurements, the magnitude of the swelling of the secondary battery negative electrode was calculated according to the following formula. Amount of swelling of secondary battery negative electrode = (thickness of electrode layer after 100 charge / discharge cycles) - (thickness of electrode layer after pressing and leaving for 1 day) The evaluation was based on the following criteria. A: Less than 7 μm B: 7 μm or more and less than 10 μm C: 10 μm or more and less than 13 μm D: 13μm or more

[0057] <Capacity maintenance rate> The cycle test was carried out up to 500 cycles, and the ratio of the discharge capacity at the 500th cycle to the initial discharge capacity was taken as the capacity retention rate, which was evaluated according to the following criteria. The larger this value, the less capacity loss due to repeated charging and discharging. A: 90.0% or more B: 80.0% or more but less than 90.0% C: 70.0% or more and less than 80.0% D: Less than 70.0%

[0058] [Preparation of polymer composition for non-aqueous secondary battery] Example 1 A reactor was charged with 0.9 parts by mass of polyoxyethylene polycyclic phenyl ether sulfate ammonium salt (manufactured by Nippon Nyukazai Co., Ltd., "New Coal 707-SF") and 110 parts by mass of ion-exchanged water, and the mixture was heated to 70°C with stirring and maintained at that temperature. To this was added 1.5 parts by mass of sodium persulfate. A monomer mixture consisting of 243 parts by mass of 2-ethylhexyl acrylate, 36 parts by mass of methacrylic acid, 18 parts by mass of styrene, and 3 parts by mass of trimethylolpropane triacrylate, 3.0 parts by mass of New Coal 707-SF, and 300 parts by mass of ion-exchanged water were added to obtain a mixed liquid. The resulting mixture was emulsified using a homogenizer, and the resulting emulsion was added dropwise. The addition was completed in 2.5 hours while maintaining the temperature at 70°C, and polymerization was continued for 2 hours. The temperature was then raised from 70°C to 80°C and maintained at this temperature for 1 hour to complete the polymerization and obtain copolymer particles. The contents of the units derived from each monomer in the obtained copolymer particles are as shown in Tables 1 and 2 below. To 100 parts by mass of the obtained copolymer particles, 0.0005 parts by mass of 2-methyl-4-isothiazolin-3-one was added as an additive, and the mixture was then filtered using a 200 μm mesh. The polymerization rate was 99%. The obtained copolymer particles were neutralized with 45 parts by mass of a 10% aqueous sodium hydroxide solution to obtain a polymer composition for a non-aqueous secondary battery. The obtained nonaqueous polymer composition for a secondary battery had a pH of 7.5 and a solid content of 40%. The polymerization rate was calculated by adding the solid content rate to the ratio of the amount of residue to the amount of all charged components. To 2.0 parts by solid content by mass of the obtained polymer composition for a nonaqueous secondary battery, 1.0 parts by solid content by mass of carboxymethyl cellulose as a thickener component and 100 parts by mass of natural graphite as a negative electrode active material were further added, and ion-exchanged water was added thereto, followed by stirring with a mechanical stirrer to adjust the total solid content to 60%. This was used as a premix, and then dispersed for 30 seconds at a peripheral speed of 20 m / sec using a thin film rotary high-speed mixer (TK Filmix FM56-L model (product name) manufactured by PRIMIX Corporation) to prepare a coating liquid for secondary battery negative electrodes.

[0059] (Examples 2 to 17) and (Comparative Examples 1 to 3) In each example, the types and / or amounts of monomers and additives, and the content of units derived from each monomer in the resulting copolymer particles are shown in Tables 1 and 2 below. Other conditions were the same as in Example 1, and nonaqueous polymer compositions for secondary batteries of Examples 2 to 17 and Comparative Examples 1 to 3 were prepared, and coating solutions for secondary battery negative electrodes were prepared. The polymer composition for a non-aqueous secondary battery, the negative electrode of the secondary battery, and the non-aqueous secondary battery obtained as described above were subjected to various evaluations. The evaluation results are shown in Tables 1 and 2.

[0060] Details of the components shown in Tables 1 and 2 below are as follows: 2-EHA: 2-ethylhexyl acrylate (M1) HEMA: 2-hydroxyethyl methacrylate (M1) MAA: methacrylic acid (M2) IA: Itaconic acid (M2) Bd: Butadiene (M3) CHMA: Cyclohexyl methacrylate (M1) St: styrene 1,9-ND: 1,9-nonanediol dimethacrylate (M3) 1,4-BDDA: 1,4-butanediol diacrylate (M3) A-TMPT: Trimethylolpropane triacrylate (M3) DVB: Divinylbenzene (M3)

[0061] [Table 1]

[0062] [Table 2]

[0063] The results in Tables 1 and 2 show that Comparative Examples 1 and 2 had poor cycle characteristics, and Comparative Example 3 had high internal resistance. In contrast to this, it was found that in Examples 1 to 17, both low internal resistance and high cycle characteristics were achieved. Furthermore, comparison of Examples 2 to 5 with Examples 1 and 6 to 10 revealed that better cycle characteristics could be obtained by including 1.0 mass % or more and 12 mass % or less of aromatic vinyl monomer units. Furthermore, a comparison between Examples 2 to 5 and Example 11 revealed that better cycle characteristics could be obtained by including a crosslinking monomer having three or more unsaturated bonds. Furthermore, a comparison between Examples 2 to 5 and Example 12 revealed that better cycle characteristics could be obtained by adjusting the glass transition temperature of the nonaqueous polymer composition for secondary batteries to -80°C or more and 10°C or less. [Industrial Applicability]

[0064] The polymer composition for a non-aqueous secondary battery of the present invention has industrial applicability as a constituent material for the negative electrode of a non-aqueous secondary battery.

Claims

1. (meth)acrylic acid ester monomer units M1, 1.0% by mass or more and 20% by mass or less of the ethylenically unsaturated carboxylic acid monomer unit M2; other crosslinkable monomer units M3 (excluding those having a repeating unit derived from an aliphatic conjugated diene compound) copolymerizable with the (meth)acrylic acid ester monomer units M1 and the ethylenically unsaturated carboxylic acid monomer units M2, in an amount of 0.5% by mass or more and 5% by mass or less; A polymer composition for a non-aqueous secondary battery, comprising copolymer particles having the following: The film made of the nonaqueous polymer composition for a secondary battery was subjected to a thermal expansion coefficient (SP) calculation using the Fedors method of 9.6 (cal / cm 3 ) 1 / 2 the tensile strength of the film swollen by immersion in the solvent at 60°C for 15 hours at an elongation of 10% is 0.08 MPa or more, Polymer composition for non-aqueous secondary batteries.

2. The crosslinkable monomer unit M3 is The crosslinked monomer unit is composed of at least one compound having three or more unsaturated bonds. The polymer composition for a non-aqueous secondary battery according to claim 1 .

3. The glass transition temperature of the nonaqueous polymer composition for secondary batteries is −80° C. or higher and 20° C. or lower. The polymer composition for a non-aqueous secondary battery according to claim 1 .

4. The copolymer particles are Contains 1.0% by mass or more and 12% by mass or less of aromatic vinyl monomer units, The polymer composition for a non-aqueous secondary battery according to claim 1 .

5. A non-aqueous secondary battery comprising the polymer composition for non-aqueous secondary batteries according to any one of claims 1 to 4.

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