Binder, binder composition, electrode slurry, electrode, and nonaqueous secondary battery

Abstract

A binder for use as a component of an electrode for a nonaqueous secondary battery, said binder including a polymer X which includes a polymer block A having a glass transition temperature of 25°C or greater, and a polymer block B having a glass transition temperature of 0°C or less.

Description

Binder, binder composition, electrode slurry, electrode, and non-aqueous secondary battery

[0001] This disclosure relates to binders, binder compositions, electrode slurries, electrodes, and non-aqueous secondary batteries.

[0002] Non-aqueous secondary batteries are widely used as power sources for laptop computers, mobile phones, power tools, and electronic communication equipment because they can be made smaller and lighter. In recent years, non-aqueous secondary batteries have also been used as power sources for electric vehicles and hybrid vehicles. A typical example of a non-aqueous secondary battery is the lithium-ion secondary battery.

[0003] A non-aqueous secondary battery comprises a positive electrode and a negative electrode as electrodes, and an electrolyte. The positive electrode and the negative electrode each include a current collector and an electrode active material layer formed on the current collector. The electrode active material layer usually contains a binder, which binds the active materials to each other and to the current collector. Various resins are used as binders in non-aqueous secondary batteries. For example, it has been proposed to use a monomer polymer having ethylenically unsaturated bonds as a binder (see, for example, Patent Documents 1 to 3).

[0004] Japanese Patent Publication No. 2014-239070, Japanese Patent Publication No. 2011-243464, International Publication No. 2023-053863

[0005] Non-aqueous secondary batteries may generate gas inside the battery due to the decomposition of the electrolyte. This gas generation inside the battery may cause the battery to expand in volume (hereinafter also referred to as battery swelling).

[0006] Therefore, this disclosure aims to provide a binder, a binder composition, an electrode slurry, and an electrode that can be used to obtain a non-aqueous secondary battery in which battery swelling is suppressed.

[0007] The present disclosure includes the following aspects. <1> A binder for use as a component of an electrode of a non-aqueous secondary battery, the binder including a polymer X including a polymer block A having a glass transition temperature of 25° C. or higher and a polymer block B having a glass transition temperature of 0° C. or lower. <2> The binder according to <1>, wherein the polymer block A includes a structural unit derived from an alkyl methacrylate, and the polymer block B includes a structural unit derived from an alkyl acrylate. <3> The binder according to <1> or <2>, wherein the polymer X has a molecular structure in which the polymer block A, the polymer block B, and the polymer block A are arranged in this order. <4> The binder according to any one of <1> to <3>, further including a polymer Y not corresponding to the polymer X. <5> The binder according to <4>, wherein the polymer Y is a polymer of a monomer including an ethylenically unsaturated double bond. <6> The binder according to <4> or <5>, wherein the amount of the polymer X is 1 part by mass to 50 parts by mass with respect to 100 parts by mass of the polymer Y. <7> A binder composition including the binder according to any one of <1> to <6> and an aqueous medium. <8> The binder composition according to <7>, wherein particles including the binder are in a dispersed state in the aqueous medium. <9> An electrode slurry including the binder according to any one of <1> to <6>, an electrode active material, and an aqueous medium. <10> An electrode including the binder according to any one of <1> to <6> and an electrode active material. <11> A non-aqueous secondary battery including the electrode according to <10>.

[0008] According to the present disclosure, there are provided a binder, a binder composition, an electrode slurry, and an electrode capable of obtaining a non-aqueous secondary battery in which battery swelling is suppressed. Further, according to the present disclosure, there is provided a non-aqueous secondary battery in which battery swelling is suppressed.

[0009] Hereinafter, embodiments will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components thereof (including element steps and the like) are not essential unless specifically specified. The same applies to numerical values and ranges thereof, which do not limit the present disclosure.

[0010] In the present disclosure, in the numerical range indicated using "~", the numerical values described before and after "~" are respectively included as the minimum value and the maximum value. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described stepwise. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, each component may include a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in a composition or the like, the content or the amount of each component means the total content or the amount of the plurality of substances present in the composition or the like, unless otherwise specified. In the present disclosure, the term "layer" includes not only the case where it is formed over the entire region where the layer exists when observing the region where the layer exists, but also the case where it is formed only in a part of the region.

[0011] In the present disclosure, "(meth)acryl" is a general term for acrylic and methacrylic. "(Meth)acrylate" is a general term for acrylate and methacrylate. In the present disclosure, the term "ethylenically unsaturated bond" means an ethylenically unsaturated bond having radical polymerizability.

[0012] In this disclosure, "polymer of monomers having ethylenically unsaturated bonds" means a compound having a molecular structure as its main chain formed by the bonding of multiple structural units derived from monomers having ethylenically unsaturated bonds. In this disclosure, "structural unit derived from monomers having ethylenically unsaturated bonds" means a site in the main chain of the polymer formed by the reaction of the ethylenically unsaturated bonds of the monomer. In this disclosure, "monomer having ethylenically unsaturated bonds" corresponding to a certain structural unit in the polymer is a compound having a structure in which the bond between the two carbon atoms forming the main chain of the polymer is replaced with an ethylenically unsaturated bond and separated from other structural units. The chemical structure of structural unit A derived from monomer A having ethylenically unsaturated bonds includes the chemical structure of the portion of monomer A from which the ethylenically unsaturated bonds contributing to the formation of the main chain of the polymer have been removed. For example, a structural unit derived from styrene includes the chemical structure of the portion of styrene from which the ethylenically unsaturated bonds have been removed (i.e., the phenyl group). In this disclosure, the chemical structure of a "structural unit derived from a monomer having an ethylenically unsaturated bond" may differ from the chemical structure of the monomer used in the synthesis of the polymer. For example, when a polymer obtained using vinyl acetate as the monomer is saponified, the chemical structure of the structural unit derived from vinyl acetate changes to the chemical structure of vinyl alcohol. In this case, the structural unit is considered to be a "structural unit derived from vinyl alcohol."

[0013] <Binder> The binder of this disclosure is a binder for use as an electrode component of a non-aqueous secondary battery, and comprises a polymer X which includes a polymer block A having a glass transition temperature of 25°C or higher and a polymer block B having a glass transition temperature of 0°C or lower.

[0014] As shown in the examples described later, non-aqueous secondary batteries made using the binder of this disclosure exhibit less battery swelling compared to non-aqueous secondary batteries made using binders other than those of this disclosure. The reason for this effect is not clear, but it is presumed to be as follows. The binder of this disclosure contains polymer X, which includes polymer block A having a glass transition temperature of 25°C or higher, and polymer block B having a glass transition temperature of 0°C or lower. The binder containing polymer X exhibits properties characteristic of elastomers (flexibility, elasticity, etc.). It is thought that this change in the properties of the binder is involved in suppressing the volume expansion of non-aqueous secondary batteries.

[0015] (Polymer X) Polymer X comprises polymer block A having a glass transition temperature of 25°C or higher, and polymer block B having a glass transition temperature of 0°C or lower. In this disclosure, the glass transition temperature (Tg) of polymer block A or polymer block B means the Tg of the polymer constituting polymer block A or polymer block B. That is, if polymer block A or polymer block B consists of only one type of monomer, the Tg of polymer block A or polymer block B is the Tg of the homopolymer obtained by polymerizing that monomer. If polymer block A or polymer block B consists of two or more types of monomers, the Tg of polymer block A or polymer block B is the Tg of the copolymer obtained by polymerizing those two or more types of monomers.

[0016] In this disclosure, the Tg of the polymer is a value measured by differential scanning calorimetry (DSC). Specifically, the measurement is performed at a heating rate of 10°C / min under a nitrogen gas atmosphere, and the peak top temperature of the chart obtained as the temperature derivative is defined as Tg (°C). As the measuring device, for example, an EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Corporation may be used.

[0017] In this disclosure, the Tg of the copolymer may be a value calculated by the following formula (FOX's formula) based on the Tg and mass fraction of the monomers constituting the copolymer.

[0018]

[0019] In the formula, n is the number of types of monomers constituting the copolymer. Tg in the formula is the Tg of the copolymer (unit: K), and Tg １ , Tg ２ and Tg ｎ are the Tg (unit: K) of each of the n types of monomers constituting the copolymer, and C １ , C ２ and C ｎ are the mass fraction of each of the n types of monomers constituting the copolymer (C １ + C ２ + ··· + C ｎ = 1). In the present disclosure, the Tg of the homopolymer obtained using a certain monomer may be referred to as the Tg of the monomer. [[ID=二十]]

[0020] The structure of the polymer block A contained in the polymer X is not particularly limited as long as the Tg of the polymer block A is 25°C or higher. From the viewpoint of the balance of the characteristics as a binder used for the electrode of the non-aqueous secondary battery, the Tg of the polymer block A is preferably 50°C or higher, more preferably 70°C or higher, and even more preferably 90°C or higher. From the viewpoint of the balance of the characteristics as a binder used for the electrode of the non-aqueous secondary battery, the Tg of the polymer block A is preferably 150°C or lower, more preferably 130°C or lower, and even more preferably 120°C or lower.

[0021] Examples of the polymer block A contained in the polymer X include a polymer block containing a structural unit derived from a monomer having a Tg of 25°C or higher.

[0022] When the polymer block A is composed of structural units derived from monomers, the monomer corresponding to the structural unit constituting the polymer block A may be only one type or two or more types. When the polymer block A contains a structural unit derived from a monomer having a Tg of 25°C or higher, the monomer corresponding to the structural unit constituting the polymer block A may be only a monomer having a Tg of 25°C or higher, or a combination of a structural unit derived from a monomer having a Tg of 25°C or higher and a structural unit derived from a monomer having a Tg of less than 25°C.

[0023] The structure of polymer block B contained in polymer X is not particularly limited as long as the structure is such that the Tg of polymer block B is 0°C or lower. From the viewpoint of balancing the properties as a binder used in electrodes of non-aqueous secondary batteries, the Tg of polymer block B is preferably -10°C or lower, more preferably -20°C or lower, and even more preferably -30°C or lower. From the viewpoint of balancing the properties as a binder used in electrodes of non-aqueous secondary batteries, the Tg of polymer block B is preferably -80°C or higher, more preferably -70°C or higher, and even more preferably -60°C or higher.

[0024] Polymer block B contained in polymer X includes polymer blocks that contain structural units derived from monomers with a Tg of 0°C or less.

[0025] When polymer block B is composed of structural units derived from monomers, the monomers corresponding to the structural units constituting polymer block B may be one type or two or more types. When polymer block B includes structural units derived from monomers with a glass transition temperature of 0°C or less, the monomers corresponding to the structural units constituting polymer block B may be only monomers with a glass transition temperature of 0°C or less, or a combination of structural units derived from monomers with a glass transition temperature of 0°C or less and monomers with a glass transition temperature greater than 0°C.

[0026] Polymer X may be a monomer polymer having an ethylenically unsaturated bond. In this case, the monomer having an ethylenically unsaturated bond may contain alkyl (meth)acrylate. That is, polymer X may contain structural units derived from alkyl (meth)acrylate. When polymer X contains structural units derived from alkyl (meth)acrylate, the proportion of structural units derived from alkyl (meth)acrylate is preferably 60% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more of the total structural units constituting polymer X. When polymer X contains structural units derived from alkyl (meth)acrylate, the proportion of structural units derived from alkyl (meth)acrylate may be 100% by mass. In this disclosure, alkyl (meth)acrylate refers to R in the following general formula. Ａ１ is a hydrogen atom or a methyl group, R Ａ２ This refers to compounds having a structure in which is an unsubstituted alkyl group.

[0027]

[0028] R of alkyl (meth)acrylate Ａ２ The number of carbon atoms in the alkyl group represented by is not particularly limited and can be selected according to the desired properties of polymer X. For example, R Ａ２ The number of carbon atoms in the alkyl group represented by may be selected from the range of 1 to 20. Ａ２ The structure of the alkyl group represented by is not particularly limited and can be selected according to the desired properties of polymer X. For example, R Ａ２ The alkyl group represented by may be cyclic or acyclic, and may be branched or unbranched. R of alkyl (meth)acrylate Ａ２ Specific examples of alkyl groups represented by include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, t-butyl group, n-hexyl group, cyclohexyl group, 2-ethylhexyl group, n-octyl group, lauryl group, tridecyl group, stearyl group, isobornyl group, adamantyl group, and the like.

[0029] Polymer block A may contain structural units derived from alkyl methacrylate. If polymer block A contains structural units derived from alkyl methacrylate, the proportion of structural units derived from alkyl methacrylate may be 60% by mass or more, 80% by mass or more, or 90% by mass or more of the total structural units constituting polymer block A. If polymer block A contains structural units derived from alkyl methacrylate, the proportion of structural units derived from alkyl methacrylate may be 100% by mass.

[0030] From the viewpoint of balancing the properties as a binder used in electrodes of non-aqueous secondary batteries, it is preferable that polymer block A contains structural units derived from alkyl methacrylate with a Tg of 25°C or higher. Examples of alkyl methacrylates with a Tg of 25°C or higher include methyl methacrylate (Tg: 105°C), ethyl methacrylate (Tg: 65°C), t-butyl methacrylate (Tg: 107°C), and cyclohexyl methacrylate (Tg: 83°C).

[0031] Polymer block B may contain structural units derived from alkyl acrylate. If polymer block B contains structural units derived from alkyl acrylate, the proportion of structural units derived from alkyl acrylate may be 60% by mass or more, 80% by mass or more, or 90% by mass or more of the total structural units constituting polymer block B. If polymer block B contains structural units derived from alkyl acrylate, the proportion of structural units derived from alkyl acrylate may be 100% by mass. From the viewpoint of balancing the properties as a binder used in electrodes of non-aqueous secondary batteries, it is preferable that polymer block B contains structural units derived from alkyl acrylate with a Tg of 0°C or less.

[0032] Examples of alkyl acrylates with a Tg of 0°C or lower include ethyl acrylate (Tg: -22°C), n-butyl acrylate (Tg: -54°C), 2-ethylhexyl acrylate (Tg: -50°C), and n-octyl acrylate (Tg: -65°C).

[0033] Polymer X may contain structural units derived from monomers that do not correspond to alkyl (meth)acrylates. Examples of monomers that do not correspond to alkyl (meth)acrylates include compounds that do not correspond to alkyl (meth)acrylates, which are exemplified as monomers that can constitute the structural units of polymer Y described later. When polymer X contains structural units derived from alkyl (meth)acrylates and structural units derived from monomers that do not correspond to alkyl (meth)acrylates, the proportion of structural units derived from alkyl (meth)acrylates may be 60% by mass or more, 80% by mass or more, or 90% by mass or more of the total structural units constituting polymer X.

[0034] The molecular structure of polymer X is not particularly limited as long as it contains polymer block A and polymer block B. For example, the molecular structure of polymer X may be represented by any of the following formulas (1) to (3). In the formulas, (A) means polymer block A, (B) means polymer block B, and n is a number of 1 or more. Formula (1): [A - B] ｎ Formula (2): [AB] ｎ - A Equation (3): B - [A - B] ｎ

[0035] In the formula, n is preferably 1 to 5, more preferably 1 to 3, and even more preferably 1 to 2. Polymer X preferably has a molecular structure in which polymer block A, polymer block B, and polymer block A are arranged in this order (a structure in which n is 1 in formula (2), also called an ABA-type triblock structure).

[0036] The mass ratio (A:B) of polymer block A to polymer block B in polymer X is not particularly limited. From the viewpoint of balancing the properties as a binder used in electrodes of non-aqueous secondary batteries, A:B is preferably 5:95 to 60:40, preferably 5:95 to 55:45, and more preferably 10:90 to 35:65.

[0037] If polymer X contains multiple polymer blocks A or polymer blocks B, the ratio is a value based on the total mass of the multiple polymer blocks A or polymer blocks B. For example, polymer X with a mass ratio of A:B of 10:80 may have a molecular structure in which polymer blocks A, polymer block B, and polymer block A are arranged in the order A:B:A = 5:80:5.

[0038] The mass ratio (A:B) of polymer block A to polymer block B in polymer X is not particularly limited. From the viewpoint of balancing the properties as a binder used in electrodes of non-aqueous secondary batteries, A:B is preferably 5:95 to 60:40, preferably 5:95 to 55:45, and more preferably 10:90 to 35:65.

[0039] The weight-average molecular weight (Mw) of polymer X is not particularly limited. From the viewpoint of durability as a binder, the Mw of polymer X is preferably 5,000 or more, more preferably 10,000 or more, and even more preferably 20,000 or more. From the viewpoint of dispersibility of polymer X in an aqueous medium, the Mw of polymer X is preferably 400,000 or less, more preferably 350,000 or less, and even more preferably 300,000 or less. The Mw of polymer X is measured by the method described in the examples below.

[0040] (Method for synthesizing polymer X) The method for synthesizing polymer X is not particularly limited and can be selected from known methods. For example, polymer X may be synthesized by living polymerization of monomers that constitute the structural units of polymer X. Examples of living polymerization methods include living anionic polymerization, RAFT polymerization, ATRP polymerization, and iodine transfer polymerization.

[0041] (Polymer Y) The binder of this disclosure may further contain polymer Y that does not correspond to polymer X. By further containing polymer Y that does not correspond to polymer X in the binder of this disclosure, properties suitable for use as an electrode in a non-aqueous secondary battery can be imparted to the binder.

[0042] When the binder of this disclosure contains polymer X and polymer Y, their mass ratio is not particularly limited. For example, the amount of polymer X in the binder may be selected from the range of 1 to 50 parts by mass per 100 parts by mass of polymer Y. From the viewpoint of exhibiting the effect of including polymer X in the binder, the amount of polymer X in the binder is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and even more preferably 4 parts by mass or more, per 100 parts by mass of polymer Y. From the viewpoint of balancing the properties as a binder used in electrodes of non-aqueous secondary batteries, the amount of polymer X in the binder is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of polymer Y.

[0043] From the viewpoint of balancing the properties of polymer Y as a binder used in electrodes of non-aqueous secondary batteries, the Tg of polymer Y is preferably -50°C or higher, more preferably -40°C or higher, and even more preferably -30°C or higher. From the viewpoint of balancing the properties of polymer Y as a binder used in electrodes of non-aqueous secondary batteries, the Tg of polymer Y is preferably 100°C or lower, more preferably 50°C or lower, even more preferably 30°C or lower, and may be 20°C or lower, or 10°C or lower.

[0044] From the viewpoint of affinity with polymer X in the binder, polymer Y is preferably a monomer polymer having an ethylenically unsaturated double bond. That is, polymer Y preferably contains structural units derived from monomers having an ethylenically unsaturated double bond. When polymer Y is a monomer polymer having an ethylenically unsaturated double bond, the type of monomer, the composition ratio, etc., are not particularly limited and can be selected according to the desired properties of the binder. When polymer Y is a monomer polymer having an ethylenically unsaturated double bond, polymer Y may be a homopolymer or a copolymer. When polymer Y is a copolymer, polymer Y may be a random copolymer or a block copolymer.

[0045] If polymer Y is a monomer polymer having an ethylenically unsaturated double bond, polymer Y may contain structural units (hereinafter also referred to as first structural units) derived from monomer (a1), which is a nonionic compound having only one ethylenically unsaturated bond. Polymer Y may also contain structural units (hereinafter also referred to as second structural units) derived from monomer (a2), which is a compound having only one ethylenically unsaturated bond and a carboxyl group. Polymer Y preferably contains at least the first structural unit, and more preferably contains both the first and second structural units.

[0046] Polymer Y may contain structural units (hereinafter also referred to as third structural units) derived from monomer (a3), which is a compound having multiple independent ethylenically unsaturated bonds. Polymer Y may also contain structural units (hereinafter also referred to as fourth structural units) derived from monomer (a4), which does not fall under any of monomers (a1) to (a3).

[0047] The monomer (a1) constituting the first structural unit is a nonionic compound having only one ethylenically unsaturated bond. That is, monomer (a1) is a compound that does not have either anionic or cationic functional groups. However, silane compounds are not included in monomer (a1). Monomer (a1) may consist of only one compound or a combination of two or more compounds.

[0048] Examples of monomers (a1) include (meth)acrylic acid esters without functional groups, aromatic compounds having ethylenically unsaturated bonds, and compounds having ethylenically unsaturated bonds and nonionic polar functional groups.

[0049] The (meth)acrylate ester without functional groups is more preferably an alkyl (meth)acrylate ester. The number of carbon atoms in the alkyl group of the alkyl (meth)acrylate is preferably 1 to 20. Examples of alkyl (meth)acrylate esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. From the viewpoint of the binder's electrolyte resistance, 2-ethylhexyl acrylate is preferred.

[0050] Aromatic compounds having ethylenically unsaturated bonds include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene. From the viewpoint of dispersibility in aqueous media, styrene is preferred.

[0051] In compounds having an ethylenically unsaturated bond and a nonionic polar functional group, examples of the nonionic polar functional group include a hydroxyl group and a cyano group, with the hydroxyl group being preferred. Specific examples of compounds having an ethylenically unsaturated bond and a nonionic polar functional group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylonitrile. From the viewpoint of polymerization stability, 2-hydroxyethyl methacrylate is preferred.

[0052] Examples of monomers (a1) that do not fall under the above-mentioned compounds include aliphatic hydrocarbon compounds having ethylenically unsaturated bonds and alicyclic hydrocarbon compounds having ethylenically unsaturated bonds.

[0053] The monomer (a2) constituting the second structural unit is a compound having only one ethylenically unsaturated bond and a carboxyl group. Monomer (a2) may be a single compound or a combination of two or more compounds. Monomer (a2) may be a compound having multiple carboxyl groups in one molecule. That is, the second structural unit may contain multiple carboxyl groups in a single structural unit.

[0054] Examples of monomers (a2) include unsaturated monocarboxylic acids such as methacrylic acid, acrylic acid, and crotonic acid; and unsaturated dicarboxylic acids such as itaconic acid and fumaric acid. From the viewpoint of binder binding properties, acrylic acid, methacrylic acid, and itaconic acid are preferred.

[0055] Monomer (a2) may form a salt with a basic substance. That is, at least a portion of the second structural unit may form a salt with a basic substance. Examples of salts with basic substances include metal salts and ammonium salts. Examples of metal salts include salts with alkali metals such as lithium, sodium, and potassium. Examples of monomers (a2) that form a salt with a basic substance include lithium (meth)acrylate, lithium itaconate, dilithium itaconate, sodium (meth)acrylate, sodium itaconate, disodium itaconate, ammonium (meth)acrylate, ammonium itaconate, and diammonium itaconate.

[0056] The monomer (a3) ​​constituting the third structural unit is a compound having multiple independent ethylenically unsaturated bonds. In this disclosure, "a compound having multiple independent ethylenically unsaturated bonds" means a compound having multiple ethylenically unsaturated bonds that are not linked by single bonds. Compounds having conjugated double bonds, such as 1,3-butadiene, do not qualify as monomer (a3). Monomer (a3) ​​is a compound capable of forming a crosslink structure in the molecular structure of polymer Y. Monomer (a3) ​​may consist of only one compound or a combination of two or more compounds.

[0057] Examples of monomers (a3) ​​include compounds having two ethylenically unsaturated bonds, such as divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate, and compounds having three or more ethylenically unsaturated bonds, such as trimethylolpropane tri(meth)acrylate. From the viewpoint of polymerization stability, divinylbenzene and trimethylolpropane triacrylate are preferred.

[0058] The monomer (a4) constituting the fourth structural unit is a monomer that does not fall under any of monomers (a1) to (a3). Examples of monomer (a4) include compounds having only one ethylenically unsaturated bond and an anionic functional group other than a carboxyl group, such as a sulfo group or a phosphate group; surfactants having an ethylenically unsaturated bond and functioning as a surfactant (hereinafter also referred to as "polymerizable surfactants"); and compounds having an ethylenically unsaturated bond and functioning as a silane coupling agent.

[0059] Compounds having only one ethylenically unsaturated bond and a sulfo group include aromatic vinyl compounds having a sulfo group and aromatic vinyl compounds having a sulfo group that forms a salt. From the viewpoint of polymerization stability, parastyrene sulfonic acid and parastyrene sulfonate are preferred, parastyrene sulfonate is more preferred, and sodium parastyrene sulfonate is even more preferred.

[0060] Examples of polymerizable surfactants include compounds represented by the following chemical formulas (1) to (4).

[0061]

[0062] In formula (1), R １ R is an alkyl group. p is an integer between 10 and 40. １ It is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms.

[0063]

[0064] In formula (2), R ２ R is an alkyl group. q is an integer between 10 and 12. ２ The C1 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear unsubstituted alkyl group having 10 to 40 carbon atoms. Examples of compounds represented by formula (2) include polyoxyethylene alkyl ether sulfate salts (for example, Aqualon KH-10, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0065]

[0066] In formula (3), R ３ M is an alkyl group. １ NH ４ Or it is Na. ３ It is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms.

[0067]

[0068] In formula (4), R ４ M is an alkyl group. ２ NH ４ Or it is Na. ４ It is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms.

[0069] Examples of compounds that have an ethylenically unsaturated bond and function as a silane coupling agent include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltriethoxysilane.

[0070] The method for synthesizing polymer Y is not particularly limited and can be selected from known methods. When polymer Y is a monomer polymer having an ethylenically unsaturated double bond, a preferred example of a method for synthesizing polymer Y is a method of polymerizing monomer (a) in the presence of an aqueous medium (b) (hereinafter also referred to as emulsion polymerization). By synthesizing polymer Y by emulsion polymerization, polymer Y (emulsion) can be obtained in which particulate polymer Y is dispersed in an aqueous medium.

[0071] One method for synthesizing polymer Y by emulsion polymerization is to supply each component used for polymerization into a reaction vessel to cause a polymerization reaction of monomer (a). It is preferable to continuously supply monomer (a) and radical polymerization initiator (e) to the reaction vessel so that the concentrations of monomer (a) and radical polymerization initiator (e) in the reaction vessel become uniform. It is preferable to carry out emulsion polymerization while stirring in the reaction vessel. The temperature in the reaction vessel is not particularly limited and may be, for example, 30°C to 90°C, 50°C to 85°C, or 55°C to 80°C.

[0072] When producing polymer Y by emulsion polymerization, in addition to monomers (a) and an aqueous medium (b) as polymerization components, components such as surfactants (c), basic substances (d), radical polymerization initiators (e), and chain transfer agents (f) can be used.

[0073] The aqueous medium (b) is preferably at least one selected from the group consisting of water and hydrophilic organic solvents. From the viewpoint of polymerization stability, the aqueous medium (b) preferably contains water, and more preferably is water. The aqueous medium (b) may also be a mixture of water and a hydrophilic solvent. Specific examples of hydrophilic organic solvents include polar solvents such as methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. The hydrophilic organic solvent used in the synthesis of polymer Y may be one type or two or more types.

[0074] When polymer Y is synthesized by emulsion polymerization, a surfactant (c) may be added to the monomer before polymerization (a) or to the aqueous medium (b) containing polymer Y after polymerization. The surfactant (c) contributes to improving the dispersion stability of polymer Y. It is preferable to use an anionic surfactant or a nonionic surfactant as the surfactant (c). It is preferable that the surfactant (c) does not have ethylenically unsaturated bonds (i.e., does not exhibit polymerizability).

[0075] Examples of anionic surfactants include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts. Examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters. The surfactant (c) used in the synthesis of polymer Y may be one type or two or more types.

[0076] When polymer Y is synthesized by emulsion polymerization, a basic substance (d) may be added to the monomer (a) before polymerization or to the aqueous medium (b) containing polymer Y after polymerization. The basic substance (d) neutralizes the acidic component if the monomer (a) contains an acidic component. As a result, the pH of the dispersion containing polymer Y becomes within an appropriate range, and the stability of the dispersion containing polymer Y is improved.

[0077] Examples of basic substances (d) include ammonia, triethylamine, sodium hydroxide, and lithium hydroxide. The basic substances (d) used in the synthesis of polymer Y may be one or two or more.

[0078] When polymer Y is synthesized by emulsion polymerization, a radical polymerization initiator (e) may be added to the aqueous medium (b) containing the monomer (a) before polymerization. The radical polymerization initiator (e) promotes the polymerization reaction of monomer (a). Specific examples of radical polymerization initiators (e) include persulfates such as ammonium persulfate and potassium persulfate; hydrogen peroxide; azo compounds; and organic peroxides such as t-butyl hydroperoxide, tert-butyl peroxybenzoate, and cumene hydroperoxide.

[0079] When synthesizing polymer Y by emulsion polymerization, redox polymerization may be carried out using a reducing agent together with a radical polymerization initiator (e). Specific examples of reducing agents include sodium bisulfite, longalite, and ascorbic acid.

[0080] The amount of radical polymerization initiator (e) added (including the reducing agent if used in combination) is preferably 0.001 parts by mass or more, more preferably 0.002 parts by mass or more, even more preferably 0.005 parts by mass or more, and particularly preferably 0.01 parts by mass or more, per 100 parts by mass of monomer (a). When the amount of radical polymerization initiator (e) added is within the above range, the conversion rate of monomer (a) to polymer Y tends to improve. The amount of radical polymerization initiator (e) added is preferably 10 parts by mass or less, more preferably 5.0 parts by mass or less, even more preferably 2.0 parts by mass or less, and particularly preferably 1.0 part by mass or less, per 100 parts by mass of monomer (a). When the amount of radical polymerization initiator (e) added is within the above range, the molecular weight of polymer Y tends to increase, and the swelling rate of polymer Y in the electrolyte tends to decrease. The amount of radical polymerization initiator (e) added may be 0.001 to 10 parts by mass, 0.002 to 5.0 parts by mass, 0.005 to 2.0 parts by mass, or 0.01 to 1.0 parts by mass per 100 parts by mass of monomer (a).

[0081] When polymer Y is synthesized by emulsion polymerization, a chain transfer agent (f) may be added to the aqueous medium (b) containing the monomer (a) before polymerization. The chain transfer agent (f) adjusts the molecular weight of polymer Y obtained by polymerization of monomer (a). Specific examples of chain transfer agents (f) include n-dodecyl mercaptan, t-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexyl thioglycolate, 2-mercaptoethanol, β-mercaptopropionic acid, methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, benzyl alcohol, α-methylstyrene dimer, etc.

[0082] <Binder Composition> The binder composition of the present disclosure comprises the binder of the present disclosure and an aqueous medium. The binder composition of the present disclosure is used, for example, in the manufacture of electrodes for non-aqueous secondary batteries.

[0083] The binder composition may contain other components along with the binder and aqueous medium. For example, the binder composition may contain components used during the synthesis of the polymer as a binder, or additives added after the synthesis of the polymer as a binder.

[0084] The binder contained in the binder composition may undergo partial structural changes due to reactions with other components in the binder composition. In this case, the binder in the state reacted with other components in the binder composition is also considered to be the binder of this disclosure.

[0085] The binder composition is preferably in the form of an emulsion, in which particles containing the binder are dispersed in an aqueous medium. The particles containing the binder may consist solely of the binder, or they may contain the binder along with other components (such as surfactants). The binder composition may contain both particles containing the binder and particles that do not contain the binder.

[0086] When a binder composition contains two or more polymers (for example, polymer X and polymer Y), the following cases (1) to (4) are possible states in which the binder-containing particles are dispersed in an aqueous medium: (1) When particles containing polymer X are dispersed in the aqueous medium, and particles containing polymer Y are not dispersed in the aqueous medium. (2) When particles containing polymer Y are dispersed in the aqueous medium, and particles containing polymer X are not dispersed in the aqueous medium. (3) When particles containing polymer X and particles containing polymer Y are each dispersed in the aqueous medium. (4) When particles containing polymer X and polymer Y are dispersed in the aqueous medium.

[0087] A binder composition in which binder-containing particles are dispersed in an aqueous medium may contain particulate binders synthesized by emulsion polymerization, or it may be obtained by dispersing binders obtained by methods other than emulsion polymerization in an aqueous medium.

[0088] The aqueous medium included in the binder composition is preferably at least one selected from the group consisting of water and hydrophilic organic solvents, and is preferably water. The aqueous medium may be a mixture of water and a hydrophilic organic solvent. If the binder composition contains a hydrophilic organic solvent, the binder composition may contain only one or two or more types of hydrophilic organic solvents. The type of hydrophilic organic solvent that can be included in the binder composition is not particularly limited and may be selected from the hydrophilic organic solvents exemplified as the aqueous medium (b) used in the synthesis of the binder.

[0089] The aqueous medium included in the binder composition may be the aqueous medium used during the synthesis of the polymer as a binder, a different aqueous solvent from the aqueous medium used during the synthesis of the polymer as a binder, or a combination thereof.

[0090] The non-volatile content concentration of the binder composition is not particularly limited and can be selected according to the method of use of the binder composition. From the viewpoint of increasing the amount of active ingredients contained in the binder composition, the non-volatile content concentration of the binder composition is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. From the viewpoint of adjusting the viscosity of the binder composition to a viscosity suitable for electrode fabrication, the non-volatile content concentration of the binder composition is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less.

[0091] In this disclosure, the nonvolatile content contained in the binder composition may be a liquid, a solid, or a combination thereof. The nonvolatile content concentration of the binder composition is calculated from the mass of the nonvolatile content measured by the following method: Weigh 1 g of the binder composition and place it on a 5 cm diameter aluminum dish and put it in a drying oven. Then, dry the binder composition while circulating the air in the drying oven (1 atmosphere (1013 hPa), 105°C, 1 hour). The mass of the substance remaining as a solid or liquid after drying is taken as the mass of the nonvolatile content.

[0092] <Electrode Slurry> The electrode slurry of the present disclosure comprises the binder of the present disclosure, an electrode active material, and an aqueous medium. The electrode slurry of the present disclosure is used, for example, to prepare electrodes for non-aqueous secondary batteries.

[0093] The electrode slurry may contain other components along with the binder, electrode active material, and aqueous medium. For example, the electrode slurry may contain components used in the synthesis of polymers as binders, thickeners, conductive additives, etc.

[0094] The binder contained in the electrode slurry may undergo partial structural changes due to reactions with other components in the electrode slurry. In this case, the binder in the state reacted with other components in the electrode slurry is also considered to be the binder of this disclosure.

[0095] The electrode slurry is preferably in which the binder and electrode active material are dispersed in an aqueous medium.

[0096] The aqueous medium contained in the electrode slurry may be the aqueous medium used during the synthesis of the binder, a different aqueous solvent from the aqueous medium used during the synthesis of the binder, or a combination thereof. Examples of aqueous solvents contained in the electrode slurry include water, hydrophilic organic solvents, and combinations thereof. The type of hydrophilic organic solvent is not particularly limited and may be selected from the hydrophilic organic solvents exemplified as the aqueous medium (b) used for the synthesis of the polymer as a binder.

[0097] The binder content in the electrode slurry is preferably 0.5 parts by mass or more, and more preferably 1.0 part by mass or more, per 100 parts by mass of the electrode active material. When the binder content is within the above range, the effects of including the binder tend to be fully expressed.

[0098] The binder content in the electrode slurry is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of electrode active material. When the binder content is within the above range, the content of electrode active material in the electrode slurry is sufficiently ensured, and the electrode obtained using the electrode slurry tends to have excellent charge-discharge characteristics.

[0099] The electrode active material contained in the electrode slurry is a material that allows for the insertion and deintercation of charge carrier ions such as lithium ions. The charge carrier ions are preferably alkali metal ions, more preferably lithium ions, sodium ions, or potassium ions, and even more preferably lithium ions. The electrode active material contained in the electrode slurry may consist of only one type or two or more types.

[0100] When the electrode manufactured using the electrode slurry is a negative electrode, the electrode slurry contains a negative electrode active material as the electrode active material. Preferably, the negative electrode active material contains at least one selected from the group consisting of carbon materials, silicon-containing materials, and titanium-containing materials.

[0101] Carbon materials used as anode active materials include, for example, coke such as petroleum coke, pitch coke, and coal coke, as well as graphite such as organic polymer carbonides, artificial graphite, and natural graphite. Silicon-containing materials used as anode active materials include, for example, elemental silicon and silicon compounds such as silicon oxide. Titanium-containing materials used as anode active materials include, for example, lithium titanate.

[0102] When the electrode for a non-aqueous secondary battery manufactured using an electrode slurry is the positive electrode, the electrode active material is the positive electrode active material. As the positive electrode active material, a material with a higher standard electrode potential than the negative electrode active material is used. Specifically, as the positive electrode active material, nickel-containing lithium composite oxides such as Ni-Co-Mn lithium composite oxides, Ni-Mn-Al lithium composite oxides, and Ni-Co-Al lithium composite oxides, and lithium cobalt oxide (LiCoO) are used. ２ ), spinel-type lithium manganate (LiMn ２ O ４ ), olivine-type lithium iron phosphate, TiS ２ MnO ２ MoO ３ , V ２ O ５ Examples include chalcogen compounds such as those mentioned above. These substances used as positive electrode active materials may be used individually or in combination of two or more.

[0103] The electrode slurry preferably contains at least one electrode active material selected from the group consisting of carbon materials and silicon-containing materials. Compared to other electrode active materials, carbon materials and silicon-containing materials tend to have larger volume changes during ion insertion and deinsertion, and repeated charging and discharging of the battery tends to reduce the bonding between electrode active materials or between the electrode active materials and the current collector. Therefore, if the electrode slurry contains these electrode active materials, the effect of the binder in maintaining good bonding between electrode active materials and between the electrode active materials and the current collector is more effectively exhibited.

[0104] The electrode slurry may contain a thickening agent. Specific examples of thickening agents include cellulose derivatives such as carboxymethylcellulose, hydroxyethylcellulose, and hydroxypropylcellulose; ammonium salts of cellulose derivatives; alkali metal salts of cellulose derivatives; polyvinyl alcohol; polyvinylpyrrolidone; poly(meth)acrylates; poly(meth)acrylamide; and poly(meth)N-hydroxyalkylacrylamide.

[0105] The electrode slurry may contain a conductive additive. Specific examples of conductive additives include conductive substances such as carbon black and carbon fibers.

[0106] [Method for manufacturing electrode slurry] The method for manufacturing the electrode slurry of this disclosure is not particularly limited. For example, the electrode slurry may be manufactured by mixing the components contained in the electrode slurry by known methods.

[0107] <Electrodes> The electrodes of the present disclosure include the binder of the present disclosure and an electrode active material. The electrodes of the present disclosure are used, for example, as electrodes in a non-aqueous secondary battery.

[0108] The electrode of this disclosure may comprise a current collector and an electrode active material layer. In this case, the electrode active material layer includes a binder together with the electrode active material.

[0109] In the electrode of this disclosure, the electrode active material layer is in contact with at least a portion of the surface of the current collector. The electrode active material layer may be formed on the entire surface of the current collector, or on only a portion of the surface of the current collector. If the current collector is in the shape of a sheet or the like, the electrode active material layer may be formed on both sides of the current collector, or on only one side. In this disclosure, "sheet-like" means the shape of an object (including plates, foils, films, membranes, etc.) in which the dimension of thickness relative to the main surface is relatively small. The thickness of a sheet-like current collector may be, for example, in the range of 0.001 mm to 0.5 mm.

[0110] The current collector preferably contains a metal. Examples of metals include iron, copper, aluminum, nickel, and stainless steel. When the electrode of this disclosure is the negative electrode, the current collector may contain copper. When the electrode of this disclosure is the positive electrode, the current collector may contain aluminum.

[0111] The electrode active material layer includes the binder and electrode active material of this disclosure. The electrode active material layer may also contain components other than the binder and electrode active material. For example, the electrode active material layer may contain conductive additives, thickeners, etc. The electrode active material, conductive additives, and thickeners contained in the electrode active material layer may be selected from the electrode active material, conductive additives, and thickeners that can be contained in the electrode slurry described above.

[0112] The binder contained in the electrode may undergo partial structural changes due to reactions with other components in the electrode. In this case, the binder in the state reacted with other components in the electrode is also considered to be the binder of this disclosure.

[0113] The method for manufacturing the electrodes of this disclosure is not particularly limited and can be selected according to the type of non-aqueous secondary battery to which the electrodes are applied. The electrodes of this disclosure are manufactured, for example, by applying the slurry of this disclosure described above to both sides or one side of a sheet-like current collector, and then removing volatile components such as aqueous solvents from the electrode slurry to form an electrode active material layer. The method for applying the electrode slurry is not particularly limited and can be selected from known methods. If necessary, a pressing process may be performed to increase the density of the electrode active material layer formed on both sides or one side of the current collector. The method for performing the pressing process is not particularly limited and can be selected from known methods.

[0114] <Non-aqueous secondary battery> The non-aqueous secondary battery of this disclosure comprises the electrodes of this disclosure. The non-aqueous secondary battery includes, for example, a positive electrode, a negative electrode, and an electrolyte. The non-aqueous secondary battery may include a separator between the positive electrode and the negative electrode, or other components.

[0115] In the non-aqueous secondary battery of this disclosure, it is preferable that at least one of the positive electrode and the negative electrode is an electrode of this disclosure, and at least the negative electrode is an electrode of this disclosure. In the non-aqueous secondary battery of this disclosure, if either the positive electrode or the negative electrode is an electrode of this disclosure, the other electrode may contain a binder different from the binder of this disclosure.

[0116] For non-aqueous secondary batteries, it is preferable to use a non-aqueous liquid with ionic conductivity as the electrolyte. Specific examples of electrolytes include solutions obtained by dissolving the electrolyte in an organic solvent, and ionic liquids.

[0117] The organic solvent used to dissolve the electrolyte is not particularly limited and includes carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC), as well as carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. The organic solvent may be used alone or in combination of two or more. Among these, it is preferable to use two or more linear carbonate solvents in combination as the organic solvent.

[0118] Specifically, the electrolyte in the case where the non-aqueous secondary battery of this disclosure is a lithium-ion secondary battery is LiClO ４ LiBF ６ LiPF ６ LiCF ３ SO ３ LiCF ３ CO ２ LiAsF ６ LiSbF ６ LiB １０ Cl １０ LiAlCl ４ , LiCl, LiBr, LiB(C ２ H ５ ) ４ CF ３ SO ３ Li, CH ３ SO ３ Li, LiCF ３ SO ３ LiC ４ F ９ SO ３ Li(CF ３ SO ２ ) ２ Examples include nitrogen (N) and lithium aliphatic carboxylate.

[0119] The electrolyte may contain additives. The type of additive is not particularly limited and can be selected according to its purpose. Specific examples of additives for the electrolyte include nitrile compounds, sulfur-containing compounds, and boron-containing compounds. Examples of nitrile compounds include succinonitrile and acetonitrile. Examples of sulfur-containing compounds include methyl ethyl sulfone and 1,3-propanesultone, which are compounds having a sulfonyl group, a sulfonate group, or a sultone structure. Examples of boron-containing compounds include boric acid esters.

[0120] Non-aqueous secondary batteries may have a positive electrode, a negative electrode, and an electrolyte housed in an outer casing. The type of outer casing is not particularly limited and can be selected according to the type of non-aqueous secondary battery. In one embodiment, an aluminum laminate material consisting of aluminum foil and a resin film may be used as the outer casing. Since the non-aqueous secondary battery of this disclosure suppresses battery swelling, it is also suitable when using an outer casing that is easily deformable, such as an aluminum laminate material.

[0121] Examples of embodiments of this disclosure will be described below with reference to these examples, but this disclosure is not limited to these embodiments.

[0122] In the following embodiments, the binder of this disclosure is used as the binder for the negative electrode of a lithium-ion secondary battery. In the following embodiments, deionized water is used as the water.

[0123] (1) Preparation of Binder Composition The binder compositions for the examples and comparative examples were prepared by mixing the components shown in Table 1. The polymerization initiators shown in Table 1 are the polymerization initiators used in the synthesis of polymer Y. The binder compositions obtained in the examples were in a state in which the binder-containing particles were dispersed in water (emulsion). The proportion of non-volatile content in the binder composition was adjusted to 40% by mass.

[0124] (2) Preparation of lithium-ion secondary batteries A lithium-ion secondary battery was prepared using the binder composition obtained by the method described above, by the method shown below.

[0125] LiNi as a positive electrode active material ０．６ Mn ０．２ Co０．２ O ２ (94 parts by mass) was mixed with acetylene black (3 parts by mass) as a conductive additive and polyvinylidene fluoride (3 parts by mass) as a binder to obtain a mixture. N-methylpyrrolidone (50 parts by mass) was added to the obtained mixture and mixed further to obtain a positive electrode slurry.

[0126] A 15 μm thick aluminum foil was prepared as the positive electrode current collector. The positive electrode slurry was applied to both sides of the positive electrode current collector using the direct roll method. The positive electrode slurry applied to both sides of the positive electrode current collector was dried (120°C, 5 minutes), and then roll-pressed (5 t / cm) to form a laminate with a positive electrode layer on both sides of the positive electrode current collector (positive electrode density: 3.00 g / cm³). ３ A laminate was obtained. This laminate was cut into a rectangle 50 mm long and 40 mm wide, and conductive tabs were attached to obtain a positive electrode.

[0127] A binder composition (3.6 parts by mass, non-volatile content: 1.4 parts by mass) obtained by the method described above was mixed with artificial graphite (G49, manufactured by Jiangxi Zichen Technology Co., Ltd.) (96.9 parts by mass) as a negative electrode active material and a 2% by mass aqueous solution (60 parts by mass) of sodium salt of CMC (manufactured by Nippon Paper Chemical Co., Ltd., Sunrose MAC500LC) to obtain a mixture. Water (16 parts by mass) was added to this mixture and mixed further to obtain a negative electrode slurry.

[0128] A 10 μm thick copper foil was prepared as the negative electrode current collector. The negative electrode slurry was applied to both sides of the negative electrode current collector using the direct roll method. The negative electrode slurry applied to both sides of the negative electrode current collector was dried (90°C, 10 minutes), and then roll-pressed (8 t / cm) to form a laminate with negative electrode layers on both sides of the negative electrode current collector (negative electrode density: 1.65 g / cm³). ３ A laminate was obtained. This laminate was cut into a rectangle measuring 52 mm in length and 42 mm in width, and conductive tabs were attached to obtain the negative electrode.

[0129] A laminate (layer structure: positive electrode / separator / negative electrode) was fabricated using the positive and negative electrodes obtained by the method described above, and a separator (porous polyethylene film, 25 μm thick). This laminate was housed in an outer casing made of aluminum laminate material. Subsequently, an electrolyte was injected into the outer casing, vacuum impregnation was performed, and the assembly was packed with a vacuum heat sealer to obtain a lithium-ion secondary battery. As the electrolyte, a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC = 30:50:20 was mixed with LiPF at a concentration of 1.0 mol / L. ６ A mixture of a solution containing (99 parts by mass) and vinylene carbonate (1 part by mass) was used.

[0130] (Battery Volume Change) Using the lithium-ion secondary battery obtained by the method described above, the swelling of the battery was evaluated by the method shown below. The results are shown in Table 1. The volume (V1) of the lithium-ion secondary battery obtained by the method described above in a fully charged state was measured. Next, this lithium-ion secondary battery was stored at 60°C for 4 weeks, and the volume (V2) of the lithium-ion secondary battery in a fully charged state after storage was measured. The volume of the lithium-ion secondary battery was measured by Method A (water displacement method) described in JIS K7112:1999 (ISO 1183). The measurement was performed at 23°C using an electronic hydrometer (Alpha Mirage Co., Ltd., MDS-300). From the measured volume of the lithium-ion secondary battery, the volume change of the battery (unit: cm) was calculated using the following formula. ３ The following was calculated: Change in battery volume = V2 - V1

[0131] (Charge / Discharge Characteristics) Under conditions of 45°C, charging and discharging were performed with each cycle consisting of the following steps (i) to (iv). The time integral of the current in steps (i) and (ii) was defined as the charging capacity, and the time integral of the current in step (iv) was defined as the discharging capacity. The discharging capacity after the first cycle and the discharging capacity after 500 cycles were measured, and the discharging capacity retention rate after 500 cycles was calculated using the following formula: Discharging capacity retention rate after 500 cycles (%) = 100 × (Discharging capacity at 500 cycles / Discharging capacity at 1 cycle)

[0132] (i) Charge at a current of 1C until the voltage reaches 4.2V (constant current (CC) charging) (ii) Charge at a voltage of 4.2V until the current reaches 0.05C (constant voltage (CV) charging) (iii) Let stand for 30 minutes (iv) Discharge at a current of 1C until the voltage reaches 2.75V (constant current (CC) discharge)

[0133]

[0134] As polymers X1 to X6 shown in Table 1, the following acrylic block copolymers (all manufactured by Kuraray Co., Ltd.) were used.

[0135] Polymer X1: An ABA-type triblock copolymer comprising polymer block A made of poly(methyl methacrylate) and polymer block B made of poly(n-butyl acrylate) (A:B:A mass ratio = 10:80:10, Mw: 70,000, Clarity LA2140)

[0136] Polymer X2: An ABA-type triblock copolymer comprising polymer block A made of poly(methyl methacrylate) and polymer block B made of poly(n-butyl acrylate) (A:B:A mass ratio = 15:70:15, Mw: 60,000, Clarity LA2250)

[0137] Polymer X3: ABA-type triblock copolymer containing polymer block A made of poly(methyl methacrylate) and polymer block B made of poly(n-butyl acrylate) (A:B:A mass ratio = 20:60:20, Mw: 65,000, Clarity LA2270)

[0138] Polymer X4: An ABA-type triblock copolymer comprising polymer block A made of poly(methyl methacrylate) and polymer block B made of poly(n-butyl acrylate) (A:B:A mass ratio = 10:80:10, Mw: 107,000, Clarity LA2330)

[0139] Polymer X5: An ABA-type triblock copolymer comprising polymer block A made of poly(methyl methacrylate) and polymer block B made of poly(n-butyl acrylate) (A:B:A mass ratio = 7.5:85:7.5, Mw: 130,000, Clarity LA3320)

[0140] Polymer X6: ABA-type triblock copolymer comprising polymer block A made of poly(methyl methacrylate) and polymer block B made of poly(2-ethylhexyl acrylate / n-butyl acrylate) (A:B:A mass ratio = 7.5:85:7.5, Mw: 60,000, Clarity LK9243)

[0141] The weight-average molecular weight (Mw) of polymers X1 to X6 was measured by the following method: GPC instrument: Waters Co., Ltd. GPC instrument "e2695" Column: Two "Shodex KF-806L" columns connected in series, manufactured by Resonaq Corporation Eluent: Tetrahydrofuran Column Temperature: 40°C Flow rate: 1.0 mL / min Detection method: Suggested refractive index (RI)

[0142] Polymers Y1 to Y3 shown in Table 1 were synthesized by the method described below. A monomer emulsion was prepared by mixing the monomers shown in Table 2 in the amounts (parts by mass) shown in Table 2. Furthermore, an aqueous solution was prepared by dissolving the polymerization initiators (potassium persulfate and ascorbic acid) in the amounts (parts by mass) shown in Table 2 in water (50 parts by mass). Water (150 parts by mass) was placed in a separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel, and the temperature was raised to 80°C. The monomer emulsion and the aqueous solution of the polymerization initiator were continuously supplied to this separable flask over 3 hours while stirring at 80°C to carry out emulsion polymerization and obtain an emulsion. The obtained emulsion was cooled to 25°C. Then, aqueous ammonia (concentration: 25% by mass) and water were added to the emulsion to obtain polymers dispersed in water. The amount of ammonia shown in Table 2 is the amount of ammonia contained in the aqueous ammonia added to the emulsion.

[0143] As the polymerizable surfactant shown in Table 2, polyoxyethylene-1-(allyloxymethyl)alkyl ether sulfate ammonium salt (Daiichi Kogyo Seiyaku Co., Ltd., Aqualon KH-10) was used.

[0144]

[0145] As shown in Table 1, the lithium-ion secondary battery of the example equipped with electrodes containing polymer X as a binder exhibits a smaller change in battery volume compared to the lithium-ion secondary battery of the comparative example equipped with electrodes that do not contain polymer X as a binder. This result suggests that polymer X contained in the electrode binder contributes to suppressing battery swelling.

Claims

1. A binder for use as an electrode component of a non-aqueous secondary battery, comprising polymer X, which includes polymer block A having a glass transition temperature of 25°C or higher, and polymer block B having a glass transition temperature of 0°C or lower.

2. The binder according to claim 1, wherein polymer block A contains structural units derived from alkyl methacrylate, and polymer block B contains structural units derived from alkyl acrylate.

3. The binder according to claim 1, wherein polymer X has a molecular structure in which polymer block A, polymer block B, and polymer block A are arranged in this order.

4. The binder according to claim 1, further comprising polymer Y which is not polymer X.

5. The binder according to claim 4, wherein polymer Y is a monomer polymer containing an ethylenically unsaturated double bond.

6. The binder according to claim 4, wherein the amount of polymer X is 1 to 50 parts by mass per 100 parts by mass of polymer Y.

7. A binder composition comprising the binder according to any one of claims 1 to 6 and an aqueous medium.

8. The binder composition according to claim 7, wherein the particles containing the binder are dispersed in the aqueous medium.

9. An electrode slurry comprising a binder according to any one of claims 1 to 6, an electrode active material, and an aqueous medium.

10. An electrode comprising a binder according to any one of claims 1 to 6 and an electrode active material.

11. A non-aqueous secondary battery comprising the electrode described in claim 10.

Images