Composite particles, binder composition for non-aqueous secondary battery, and non-aqueous secondary battery electrode

Abstract

The composite particles contain a copolymer and a tackifier, wherein: the copolymer has a first structural unit derived from monomer (a1) and a second structural unit derived from monomer (a2); the monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond; and the monomer (a2) is a compound having a carboxy group and only one ethylenically unsaturated bond.

Description

[Technical Field]

[0001] The present invention relates to composite particles, a binder composition for non-aqueous secondary batteries, a slurry for non-aqueous secondary battery electrodes, a non-aqueous secondary battery, and a method for producing composite particles. This application claims priority based on Japanese Patent Application No. 2022-151135, filed on September 22, 2022, the contents of which are incorporated herein by reference. [Background technology]

[0002] Non-aqueous secondary batteries can be made smaller and lighter, and are therefore widely used as power sources for laptop computers, mobile phones, power tools, electronic and communication devices, etc. 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 nonaqueous secondary battery includes a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and an electrolyte. The positive electrode and negative electrode each include a current collector and an electrode active material layer formed on the current collector. The electrode active material layer typically contains a binder that bonds the active materials together and between the active materials and the current collector, thereby fixing the electrode active material layer to the current collector. Conventionally, binders used in non-aqueous secondary batteries are known from Patent Documents 1 and 2.

[0004] Patent Document 1 describes a binder composition for secondary battery electrodes, which contains 100 parts by mass of an aqueous dispersion of at least one polymer selected from the group consisting of a styrene-butadiene copolymer latex and an acrylic emulsion, and 1 to 20 parts by mass of a nonionic surfactant.

[0005] Patent Document 2 describes a binder for lithium ion secondary battery electrodes, which has a glass transition temperature of 30°C or less and is obtained by emulsion polymerization of ethylenically unsaturated monomers containing, as essential components, 15 to 70 mass% of styrene relative to the total amount of ethylenically unsaturated monomers, an ethylenically unsaturated carboxylic acid ester, an ethylenically unsaturated carboxylic acid, and an internal crosslinking agent in the presence of a surfactant.

[0006] Furthermore, Patent Document 3 describes a tire puncture sealant containing an acrylic emulsion, an antifreeze agent, and a tackifier. Patent Document 4 describes an aqueous dispersion type acrylic adhesive tape or sheet for transporting electronic components, which has an adhesive layer made of an acrylic adhesive containing an acrylic emulsion polymer as a main component. Patent Document 4 also describes an acrylic emulsion polymer obtained by emulsion polymerization of an acrylic monomer mixture containing a carboxyl group-containing monomer. Patent Document 4 also discloses that the acrylic adhesive contains a rosin-based or terpene-based tackifier having a softening point of 100°C or higher. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-239070 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-243464 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-224248 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-285221 Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, there has been a strong demand for non-aqueous secondary batteries with higher output, higher capacity, longer life, etc. Binders used in non-aqueous secondary batteries are required to be able to improve the cycle characteristics of non-aqueous secondary batteries having electrodes using the binders.

[0009] The present invention has been made in view of the above circumstances, and aims to provide composite particles that can be used as a binder material capable of forming electrodes that can provide nonaqueous secondary batteries with excellent cycle characteristics, and a method for producing the composite particles.

[0010] Another object of the present invention is to provide a binder composition for a non-aqueous secondary battery, which comprises the composite particle of the present invention and can form an electrode that results in a non-aqueous secondary battery with excellent cycle characteristics; a slurry for a non-aqueous secondary battery electrode; a non-aqueous secondary battery electrode that results in a non-aqueous secondary battery with excellent cycle characteristics; and a non-aqueous secondary battery including the same. [Means for solving the problem]

[0011] The present invention includes the following aspects. A first aspect of the present invention provides the following composite particles. [1] A composite particle comprising a copolymer and a tackifier, The copolymer is a first structural unit derived from the monomer (a1); and a second structural unit derived from the monomer (a2), the monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, The composite particles, wherein the monomer (a2) is a compound having a carboxy group and only one ethylenically unsaturated bond.

[0012] The composite particles of the first aspect of the present invention preferably have the characteristics described in the following items [2] to

[10] . It is also preferable to arbitrarily combine two or more of the characteristics described in the following items [2] to

[10] . [2] The composite particles according to [1], wherein at least a portion of the tackifier is present within a particulate structure consisting of chain molecules of the copolymer. [3] The composite particles according to [1] or [2], wherein the tackifier is at least one selected from the group consisting of hydrogenated petroleum resins and terpene resins. [4] The composite particles according to [3], wherein the tackifier contains a hydrogenated petroleum resin. [5] The composite particles according to [4], wherein the softening point of the hydrogenated petroleum resin is 70°C to 140°C.

[0013] [6] Composite particles according to any one of [1] to [5], wherein the content of the tackifier relative to 100 parts by mass of the monomer components used in producing the copolymer is 0.50 parts by mass or more and 20 parts by mass or less. [7] The composite particle according to any one of [1] to [6], wherein the content of the second structural unit in all structural units of the copolymer is 0.10% by mass or more and 20% by mass or less.

[0014] [8] The copolymer has a third structural unit derived from the monomer (a3), The composite particles according to any one of [1] to [7], wherein the monomer (a3) ​​is a compound having a plurality of independent ethylenically unsaturated bonds. [9] The composite particle according to [8], wherein the content of the third structural unit in all structural units of the copolymer is 0.010% by mass or more and 10% by mass or less.

[0015]

[10] The composite particles according to any one of [1] to [9], which are used as a binder for a non-aqueous secondary battery. A second aspect of the present invention provides the following binder composition for a non-aqueous secondary battery.

[11] A binder composition for a non-aqueous secondary battery, comprising the composite particles according to any one of [1] to [9] and an aqueous medium.

[0016] A third aspect of the present invention provides the following non-aqueous slurry for a secondary battery electrode.

[12] An electrode comprising the composite particles according to any one of [1] to [9], an electrode active material, and an aqueous medium, The aqueous medium is one selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent. A fourth aspect of the present invention provides the following non-aqueous secondary battery electrode.

[13] A non-aqueous secondary battery electrode comprising the composite particles according to any one of [1] to [9]. A fifth aspect of the present invention provides the following nonaqueous secondary battery.

[14] A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode according to

[13] .

[0017] A sixth aspect of the present invention provides the following method for producing composite particles.

[15] A method for producing composite particles, comprising a polymerization step of copolymerizing raw material monomers (a) containing a monomer (a1) and a monomer (a2) in the presence of a tackifier, the monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, The method for producing composite particles, wherein the monomer (a2) is a compound having a carboxy group and only one ethylenically unsaturated bond. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide composite particles that can be used as a binder material for forming electrodes that can provide non-aqueous secondary batteries with excellent cycle characteristics, and a method for producing the same. Furthermore, the present invention can provide a binder composition for non-aqueous secondary batteries and a slurry for non-aqueous secondary battery electrodes that can form electrodes that provide non-aqueous secondary batteries with excellent cycle characteristics. Furthermore, the present invention can provide a non-aqueous secondary battery electrode that can provide a non-aqueous secondary battery with excellent cycle characteristics, and a non-aqueous secondary battery equipped with the same that has excellent cycle characteristics. [Brief explanation of the drawings]

[0019] [Figure 1]FIG. 2 is a schematic diagram illustrating the state of a composition containing a tackifier-containing composite particle and an aqueous medium, obtained by the production method of the present embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating the state of a composition containing other composite particles containing a tackifier and an aqueous medium, which is obtained by the production method of the present embodiment. [Figure 3] FIG. 2 is a comparative schematic diagram illustrating the state of a composition containing copolymer particles, a tackifier positioned apart from the copolymer particles, and an aqueous medium. DETAILED DESCRIPTION OF THE INVENTION

[0020] In order to solve the above problems and realize a binder capable of forming a nonaqueous secondary battery electrode that can produce a nonaqueous secondary battery with excellent cycle characteristics, the present inventors focused on a copolymer obtained by copolymerizing a monomer (a1) consisting of a nonionic compound having only one ethylenically unsaturated bond with a monomer (a2) consisting of a compound having an anionic functional group and having only one ethylenically unsaturated bond, and a tackifier, and conducted extensive research on a binder material containing these.

[0021] As a result, we discovered that composite particles containing a copolymer obtained by copolymerizing monomers including monomer (a1) and monomer (a2) and a tackifier can be used as a binder for nonaqueous secondary batteries. When an electrode is formed using such a binder for nonaqueous secondary batteries, the composite particles present between the electrode active materials and between the electrode active materials and the current collector contain the copolymer and the tackifier. Therefore, the synergistic effect of the copolymer and the tackifier is fully exerted, resulting in an electrode with excellent binding between the electrode active materials and between the electrode active materials and the current collector. As a result, it is believed that a nonaqueous secondary battery and a nonaqueous secondary battery electrode with excellent cycle characteristics can be obtained.

[0022] Furthermore, the present inventors produced an electrode using the above composite particles as a binder for a non-aqueous secondary battery, and confirmed that the non-aqueous secondary battery having this electrode had excellent cycle characteristics, which led to the invention.

[0023] The composite particles, binder composition for non-aqueous secondary batteries, slurry for non-aqueous secondary battery electrodes, non-aqueous secondary batteries, and method for producing composite particles of the present invention are described in detail below. Note that the present invention is not limited to the following embodiments. For example, the present invention allows addition, omission, substitution, and modification of the number, amount, position, ratio, material, configuration, type, order, etc., within the scope of the present invention.

[0024] Here, the following terms used in this specification will be explained. "(Meth)acrylic" is a general term for acrylic and methacrylic. "(Meth)acrylate" is a general term for acrylate and methacrylate. Unless otherwise specified, the term "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability.

[0025] In a polymer using a compound having an ethylenically unsaturated bond, the structural unit derived from the compound having an ethylenically unsaturated bond means a structural unit in which the chemical structure of the portion other than the ethylenically unsaturated bond in the compound having an ethylenically unsaturated bond is the same as the chemical structure of the portion in the polymer other than the portion corresponding to the ethylenically unsaturated bond of the structural unit. The ethylenically unsaturated bond of the compound changes to a single bond when forming a polymer. For example, in a polymer of methyl methacrylate, the structural unit derived from methyl methacrylate is represented by -CH2-C(CH3)(COOCH3)-.

[0026] In the case of a polymer of a compound having an ionic functional group and an ethylenically unsaturated bond, for example, a structural unit having an ionic functional group such as a carboxy group, such as the second structural unit described below, is considered to be a structural unit derived from the same ionic compound, regardless of whether or not a portion of the functional group has been ion-exchanged. For example, a structural unit represented by -CH2-C(CH3)(COONa)- may also be considered to be a structural unit derived from methacrylic acid.

[0027] In addition, for a compound having multiple independent ethylenically unsaturated bonds, one or more ethylenically unsaturated bonds may remain within the structural unit as a structural unit of the polymer of the compound.For example, in the case of a divinylbenzene polymer, the structural unit derived from divinylbenzene may have a structure without an ethylenically unsaturated bond (a form in which both parts corresponding to the two ethylenically unsaturated bonds of divinylbenzene are incorporated into the polymer chain), or may have a structure with one ethylenically unsaturated bond (a form in which only the part corresponding to one ethylenically unsaturated bond is incorporated into the polymer chain).Here, multiple independent ethylenically unsaturated bonds mean multiple ethylenically unsaturated bonds that do not form conjugated dienes with each other.

[0028] Furthermore, after polymerization, when a portion other than the chain structure corresponding to the ethylenically unsaturated bond in the polymer, for example, a functional group such as a carboxy group, no longer corresponds to the chemical structure of the monomer due to a chemical reaction, the structural unit of the polymer is made to be a structural unit derived from a compound having an ethylenically unsaturated bond in the polymer. For example, when vinyl acetate is polymerized and then saponified, the structural unit of the polymer is made to be a structural unit derived from vinyl alcohol, not a structural unit derived from vinyl acetate, based on the chemical structure of the polymer.

[0029] In this embodiment, the term "class" attached to the compound name means a group of compounds that include the compound structure, and also includes the compound having a substituent.

[0030] <1. Composite particle (P)> The composite particles (P) of this embodiment are used, in one form, as binders for non-aqueous secondary batteries. The composite particles (P) of this embodiment include a copolymer and a tackifier. In the composite particles (P) of this embodiment, the chain molecules of the copolymer are presumed to form a particle structure. The shape of the particle structure may be, for example, spherical or nearly spherical, and the molecular weight of the chain molecules may be selected arbitrarily. The composite particles (P) may be emulsion-polymerized particles. The tackifier molecules may be present on either the surface or the interior of the particle structure, or both. It is preferable that at least a portion of the tackifier is present within the particle structure consisting of chain molecules of the copolymer. This is because, for example, compared to when the entire tackifier contained in the composite particles (P) is attached to the outer surface of the particle structure, the presence of at least a portion of the tackifier within the particle structure promotes interaction between the tackifier and the chain molecules, thereby more easily achieving a synergistic effect between the copolymer and the tackifier. As a result, the composite particles (P) can form an electrode with better binding properties between the electrode active materials and between the electrode active material and the current collector.

[0031] (copolymer) The copolymer contained in the composite particle (P) of this embodiment has at least a first structural unit derived from the monomer (a1) shown below and a second structural unit derived from the monomer (a2) shown below. The copolymer contained in the composite particle (P) of this embodiment may contain, in addition to the first structural unit and the second structural unit, a third structural unit derived from a monomer (a3) ​​consisting of a compound having multiple independent ethylenically unsaturated bonds and not corresponding to the monomer (a1) or the monomer (a2), and / or a fourth structural unit derived from another monomer (a4) not corresponding to any of the monomers (a1) to (a3).

[0032] [First structural unit] The first structural unit in the copolymer contained in the composite particle (P) of this embodiment is derived from the monomer (a1). Monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond. That is, monomer (a1) is a compound having neither an anionic functional group nor a cationic functional group. However, silane compounds are not included in monomer (a1). Monomer (a1) may be a single compound or a combination of two or more compounds.

[0033] As the monomer (a1), it is preferable to use at least one of a (meth)acrylic acid ester and an aromatic compound having an ethylenically unsaturated bond, and it is more preferable to use a combination of both compounds. The (meth)acrylic acid ester is more preferably a (meth)acrylic acid alkyl ester. The alkyl group in the (meth)acrylic acid alkyl ester preferably has 1 to 20 carbon atoms. When such a compound is used, a monomer (a1) other than the (meth)acrylic acid alkyl ester and the aromatic compound having an ethylenically unsaturated bond described below may be used in combination.

[0034] Examples of (meth)acrylic acid alkyl esters included in the (meth)acrylic acid esters used in the monomer (a1) 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, stearyl (meth)acrylate, etc. Among these, it is preferable to contain 2-ethylhexyl acrylate, since this results in composite particles (P) that can form an electrode active material layer that has excellent electrolyte resistance.

[0035] Examples of aromatic compounds having an ethylenically unsaturated bond used in the monomer (a1) include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene. When an aromatic vinyl compound is contained as the monomer (a1), it is more preferable that at least one of styrene and α-methylstyrene is contained. It is even more preferable that the monomer (a1) contains styrene, since this has excellent dispersibility in aqueous media, and a nonaqueous secondary battery equipped with an electrode containing the binder for a nonaqueous secondary battery containing the composite particles (P) has better cycle characteristics.

[0036] Examples of the monomer (a1) other than the (meth)acrylic acid alkyl ester and the aromatic compound having an ethylenically unsaturated bond include a compound having an ethylenically unsaturated bond and a polar functional group, an aliphatic hydrocarbon compound having an ethylenically unsaturated bond, and an alicyclic hydrocarbon compound having an ethylenically unsaturated bond.

[0037] The polar functional group in the compound having an ethylenically unsaturated bond and a polar functional group used for the monomer (a1) preferably contains at least one of a hydroxy group and a cyano group, and more preferably contains a hydroxy group. Examples of the compound having an ethylenically unsaturated bond and a polar functional group used in the monomer (a1) include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, (meth)acrylonitrile, etc. It is preferable to contain 2-hydroxyethyl methacrylate because this provides good polymerization stability when producing the composite particles (P).

[0038] [Second structural unit] The second structural unit in the copolymer contained in the composite particle (P) of this embodiment is derived from the monomer (a2). The monomer (a2) is a compound having only one ethylenically unsaturated bond and at least one carboxy group, and may be a single type of compound or a combination of two or more types of compounds. The monomer (a2) may be a compound having two or more carboxy groups in one molecule, that is, the copolymer may contain multiple carboxy groups in one structural unit.

[0039] Examples of the monomer (a2) having a carboxy group include unsaturated monocarboxylic acids such as methacrylic acid, acrylic acid, and crotonic acid; and unsaturated dicarboxylic acids such as itaconic acid and fumaric acid. Among these, it is preferable to use at least one of acrylic acid, methacrylic acid, and itaconic acid as the monomer (a2), since this results in composite particles (P) that can form electrodes with good binding between electrode active materials and between the electrode active material and the current collector.

[0040] At least a portion of the structural units derived from the monomer (a2) may form a salt with a basic substance. Examples of the monomer (a2) that forms a salt include metal salts and ammonium salts of the monomer (a2). Examples of the metal salt include alkali metals such as lithium, sodium, and potassium. Specific examples of the compound include lithium (meth)acrylate, lithium itaconate, dilithium itaconate, sodium (meth)acrylate, sodium itaconate, disodium itaconate, ammonium (meth)acrylate, ammonium itaconate, and diammonium itaconate.

[0041] [Third structural unit] The copolymer contained in the composite particle (P) of this embodiment may have a third structural unit as an optional structural unit. The third structural unit is derived from a monomer (a3). The monomer (a3) ​​is a compound having two or more independent ethylenically unsaturated bonds. The number of ethylenically unsaturated bonds can be selected arbitrarily, for example, 2 to 10, 3 to 8, or 4 to 6. Note that "independent" means that the monomer (a3) ​​does not have a conjugated double bond such as that found in 1,3-butadiene. Therefore, the monomer (a3) ​​is a compound capable of forming a crosslinked structure in radical polymerization with the monomer (a1) and the monomer (a2). The monomer (a3) ​​does not fall under either the monomer (a1) or the monomer (a2). As the monomer (a3), only one compound may be used, or two or more different compounds may be used.

[0042] Examples of the monomer (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. It is preferable to use at least one of divinylbenzene and trimethylolpropane triacrylate as the monomer (a3), because this provides good polymerization stability when producing the composite particles (P), and a nonaqueous secondary battery equipped with an electrode containing a binder for a nonaqueous secondary battery containing the composite particles (P) has lower internal resistance and excellent cycle characteristics.

[0043] [Other monomers (a4)] The other monomer (a4) is a monomer that does not fall under any of the monomers (a1) to (a3). Examples of the other monomer (a4) include, but are not limited to, a compound having only one ethylenically unsaturated bond and having an anionic functional group other than a carboxyl group, such as a sulfo group or a phosphate group, a surfactant having an ethylenically unsaturated bond (hereinafter sometimes referred to as a "polymerizable surfactant"), a compound having an ethylenically unsaturated bond and functioning as a silane coupling agent, etc.

[0044] Examples of 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 in the form of a salt. Among these, it is preferable to use at least one of p-styrenesulfonic acid and p-styrenesulfonic acid salts, and it is more preferable to use p-styrenesulfonic acid salts. It is more preferable to use sodium p-styrenesulfonate because it can provide good polymerization stability when producing composite particles (P).

[0045] As the polymerizable surfactant, which is an example of the other monomer (a4), a compound having an ethylenically unsaturated bond and functioning as a surfactant can be used. Examples of the polymerizable surfactant include compounds represented by the following chemical formulas (1) to (4).

[0046] [ka]

[0047] In formula (1), R 1 is an alkyl group. p is an integer of 10 to 40. R 1 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[0048] [ka]

[0049] In formula (2), R 2 is an alkyl group. q is an integer of 10 to 12. R 2 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms. Examples of the compound represented by formula (4) include polyoxyethylene alkyl ether sulfate (Aqualon KH-10, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.).

[0050] [ka]

[0051] In formula (3), R 3 is an alkyl group. M 1 is NH4 or Na. 3 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[0052] [ka]

[0053] In formula (4), R 4 is an alkyl group. M 2 is NH4 or Na. 4 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[0054] Examples of the other monomer (a4) include compounds having an ethylenically unsaturated bond and functioning as a silane coupling agent, such as vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltriethoxysilane.

[0055] [Content of each structural unit in the copolymer] The content of each structural unit in the copolymer contained in the composite particle (P) of this embodiment is considered to be the same as the content of each monomer in the total amount of monomer components used to produce the composite particle (P).

[0056] (Content of first structural unit among all structural units) The content of the first structural unit in all structural units of the copolymer (in other words, the content of the monomer (a1) in the total amount of the monomer components used in producing the composite particle (P)) is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, and particularly preferably 80% by mass or more. This is because better polymerization stability can be obtained when producing the composite particle (P). The content of the first structural unit in all structural units is preferably 97% by mass or less, more preferably 95% by mass or less, and even more preferably 94% by mass or less. This is because the composite particle (P) can form an electrode with good binding between electrode active materials and between the electrode active material and the current collector.

[0057] Regarding the composition of the monomer (a1), it is preferable to appropriately adjust the type and amount of the compound in order to adjust the glass transition temperature of the composite particles (P) or to adjust the polymerization rate according to the molecular design. Specifically, when the monomer (a1) contains an aromatic compound having an ethylenically unsaturated bond, the content of structural units derived from the aromatic compound having an ethylenically unsaturated bond in all structural units is preferably 36% by mass or more, more preferably 41% by mass or more, and even more preferably 43% by mass or more, because this results in composite particles (P) with excellent dispersibility when a binder composition for a non-aqueous secondary battery containing the composite particles (P) is produced.

[0058] (Content of second structural units in all structural units) The content of the second structural unit in all structural units of the copolymer (in other words, the content of the monomer (a2) in the total amount of the monomer components used in producing the composite particle (P)) is preferably 0.10% by mass or more, more preferably 1.0% by mass or more, even more preferably 3.0% by mass or more, and particularly preferably 4.0% by mass or more. This is because the composite particle (P) can form an electrode with better binding strength between the electrode active materials and between the electrode active material and the current collector. The content of the second structural unit in all structural units is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less. This is because better polymerization stability can be obtained when producing the composite particle (P).

[0059] (Content of third structural units among all structural units) When the copolymer contained in the composite particle (P) of this embodiment contains a third structural unit, the content of the third structural unit in all structural units of the copolymer (in other words, the content of the monomer (a3) ​​in the total amount of the monomer components used to produce the composite particle (P)) is preferably 0.010% by mass or more, more preferably 0.020% by mass or more, and even more preferably 0.030% by mass or more. This is because the effect of the monomer (a3) ​​as an internal crosslinking agent is significantly obtained, deterioration of the copolymer is suppressed, and the composite particle (P) can be used as a binder material to obtain a non-aqueous secondary battery with better cycle characteristics. The content of the third structural unit in all structural units of the copolymer is preferably 10% by mass or less, more preferably 5.0% by mass or less, even more preferably 1.0% by mass or less, and particularly preferably 0.1% by mass or less. This is because gelation of the copolymer can be suppressed.

[0060] (Content of the fourth structural unit among all structural units) When the copolymer contained in the composite particle (P) of this embodiment contains a fourth structural unit derived from another monomer (a4), and the other monomer (a4) is a compound having only one ethylenically unsaturated bond and a sulfo group, the content of the fourth structural unit in all structural units of the copolymer (in other words, the content of the monomer (a4) in the total amount of the monomer components used in producing the composite particle (P)) is preferably 0.10% by mass or more, more preferably 0.20% by mass or more, and even more preferably 0.30% by mass or more. This is because good polymerization stability can be obtained when producing the composite particle (P). The content of the fourth structural unit in all structural units of the copolymer is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.0% by mass or less. This is because the particle size, viscosity, etc. of the composite particle (P) can be appropriately adjusted.

[0061] When the copolymer of this embodiment contains a fourth structural unit derived from another monomer (a4), and the other monomer (a4) is a polymerizable surfactant, the content of the fourth structural unit in all structural units of the copolymer (in other words, the content of the monomer (a4) in the total amount of the monomer components used in producing the composite particles (P)) is preferably 0.10% by mass or more, more preferably 0.20% by mass or more, and even more preferably 0.30% by mass or more. This is because the effect of including the polymerizable surfactant is significant, and good polymerization stability is obtained when producing the composite particles (P). The content of the fourth structural unit in all structural units of the copolymer is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, and even more preferably 1.0% by mass or less. This is because the particle size, viscosity, etc. of the composite particles (P) can be appropriately adjusted.

[0062] (tackifier) The type of tackifier contained in the composite particles (P) of this embodiment is not particularly limited as long as it does not impair the effects of the present invention. The tackifier may be used alone or in combination of two or more. Examples of tackifiers include natural resins such as rosin-based resins and terpene-based resins, and petroleum resins such as hydrogenated petroleum resins and non-hydrogenated petroleum resins. At least one selected from rosin-based resins, terpene-based resins, and hydrogenated petroleum resins is preferred, as it has excellent compatibility with the copolymer in the composite particles of this embodiment, and at least one selected from terpene-based resins and hydrogenated petroleum resins is more preferred.

[0063] Examples of rosin resins include rosin resins such as gum rosin, tall oil rosin, and wood rosin; modified rosin resins such as hydrogenated rosin resin, disproportionated rosin resin, and polymerized rosin resin; and rosin ester resins such as glycerin esters and pentaerythritol esters of these rosin resins and modified rosin resins. The rosin resin may also be in the form of an emulsion obtained by emulsifying these. Examples of the terpene resin include terpene resins containing α-pinene, β-pinene, dipentene, etc. as a main component, aromatic modified terpene resins, hydrogenated terpene resins, terpene phenol resins, etc. The terpene resin may also be in the form of an emulsion obtained by emulsifying these.

[0064] The petroleum resin may be either hydrogenated petroleum resin (hereinafter also referred to as "hydrogenated petroleum resin") or non-hydrogenated petroleum resin. Hydrogenated petroleum resin is preferable because it has good compatibility with copolymers. Examples of petroleum resins include aliphatic (C5) petroleum resins, aromatic (C9) petroleum resins, copolymer (C5 / C9) petroleum resins, dicyclopentadiene petroleum resins, and alicyclic saturated hydrocarbon resins. Hydrogenated petroleum resins are obtained by hydrogenating at least a portion of the unsaturated groups present in these resins. The petroleum resin may also be in the form of an emulsion obtained by emulsifying these. Among these petroleum resins, alicyclic saturated hydrocarbon resins are preferred because they provide composite particles (P) that can form electrodes with better adhesion between electrode active materials and between the electrode active material and the current collector.

[0065] The softening point of the tackifier is not particularly limited. For example, the softening point of the tackifier is preferably 25 to 200°C, more preferably 25 to 175°C, and even more preferably 25 to 150°C. It may be 35 to 130°C, 50 to 100°C, or 60 to 80°C. A softening point of the tackifier of 25°C or higher is preferable because it improves compatibility with the copolymer. A softening point of the tackifier of 200°C or lower results in composite particles (P) that can form electrodes with better binding between electrode active materials and between the electrode active material and the current collector. As a result, nonaqueous secondary batteries equipped with electrodes using this composite particle (P) exhibit better cycle characteristics.

[0066] For example, when the tackifier is a hydrogenated petroleum resin, the softening point of the tackifier is preferably 70 to 140°C, more preferably 80 to 140°C, even more preferably 85 to 135°C, and particularly preferably 90 to 130°C. A softening point of the hydrogenated petroleum resin of 70°C or higher is preferable because it improves compatibility with the copolymer. A softening point of the hydrogenated petroleum resin of 140°C or lower results in composite particles (P) that can form electrodes with better binding strength between electrode active materials and between the electrode active material and the current collector. The softening point of the tackifier is a value measured using a ring and ball softening point measuring apparatus in accordance with JIS K6220-1:2001.

[0067] [Content of tackifier in composite particles (P)] The content of the tackifier relative to the amount of copolymer in the composite particles (P) of this embodiment is considered to be the same as the mass of the tackifier relative to the total mass of the monomer components used in producing the composite particles (P).

[0068] The content of the tackifier is preferably 0.50 to 20 parts by mass, more preferably 0.70 to 18 parts by mass, and even more preferably 1.0 to 15 parts by mass, relative to 100 parts by mass of the monomer components used in producing the copolymer in the composite particles (P) of this embodiment. It may be 1.5 to 10 parts by mass, 2.0 to 8.0 parts by mass, or 3.0 to 6.0 parts by mass. When the content of the tackifier is 0.50 parts by mass or more, the effect of the tackifier contained in the composite particles (P) becomes significant. As a result, the composite particles (P) can form electrodes with better binding between electrode active materials and between the electrode active material and the current collector. When the content of the tackifier is 20 parts by mass or less, the content of the copolymer in the composite particles (P) can be sufficiently ensured, and a nonaqueous secondary battery equipped with an electrode containing a binder for a nonaqueous secondary battery containing the composite particles (P) will have lower internal resistance.

[0069] [Glass transition temperature (Tg) of composite particles (P)] The glass transition temperature (Tg) of the composite particle (P) of the present embodiment is the peak top temperature of a differential scanning calorimetry (DDSC) chart obtained as the temperature derivative of DSC when DSC measurement is performed using a DSC apparatus (EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Corporation) at a temperature rise rate of 10°C / min under a nitrogen gas atmosphere.

[0070] The glass transition temperature (Tg) of the composite particles (P) is preferably −30° C. or higher, more preferably −20° C. or higher, and even more preferably −10° C. or higher, because a nonaqueous secondary battery equipped with an electrode containing a binder for nonaqueous secondary batteries containing the composite particles (P) will have excellent cycle characteristics. The glass transition temperature (Tg) of the composite particles (P) is preferably 100°C or lower, more preferably 50°C or lower, and even more preferably 40°C or lower. This is because the film-forming properties of the composite particles (P) are improved, and a nonaqueous secondary battery equipped with an electrode containing a binder for nonaqueous secondary batteries containing the composite particles (P) has excellent cycle characteristics. The glass transition temperature (Tg) of the composite particles (P) may be, for example, -20°C or higher and 60°C or lower, -5°C or higher and 30°C or lower, 0°C or higher and 25°C or lower, or 5°C or higher and 20°C or lower, as needed.

[0071] [Method for producing composite particles (P)] The composite particles (P) of this embodiment can be produced, for example, by the method shown below. The composite particles (P) can be produced by copolymerizing raw material monomers containing monomer (a1) and monomer (a2), and optionally monomer (a3) ​​consisting of a compound having multiple independent ethylenically unsaturated bonds, and / or other monomer (a4), in the presence of a tackifier (polymerization step). Hereinafter, the monomers (components (a1) to (a4)) used to synthesize the composite particles (P) may be collectively referred to as raw material monomer (a). The raw material monomer (a) may be a mixture containing monomer (a1) and monomer (a2), and optionally further containing monomer (a3) ​​and / or monomer (a4). The method for producing the composite particles (P) may include a step of adding the monomers and / or tackifier to an aqueous medium before the copolymerization step.

[0072] Examples of methods for copolymerizing raw material monomer (a) in the presence of a tackifier include emulsion polymerization, in which raw material monomer (a) is emulsion-polymerized in an aqueous medium (b) containing a tackifier. When producing composite particles (P) by emulsion polymerization, in addition to the tackifier, raw material monomer (a), and aqueous medium (b), components such as a non-polymerizable surfactant (c), a basic substance (d), a radical polymerization initiator (e), and / or a chain transfer agent (f) can be used as needed. A specific example includes a method in which a mixture containing a tackifier, raw material monomer (a), and aqueous medium (b) is prepared, and this mixture and the radical polymerization initiator (e) are continuously fed into a separately prepared aqueous medium (b) to carry out copolymerization.

[0073] [Aqueous medium (b)] The aqueous medium (b) is one selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, isopropyl alcohol, and N-methylpyrrolidone. From the viewpoint of polymerization stability, the aqueous medium (b) is preferably water. As the aqueous medium (b), a mixture of water and a hydrophilic solvent may be used as long as the polymerization stability is not impaired.

[0074] [Non-polymerizable surfactant (c)] When the composite particles (P) are produced by emulsion polymerization, a solution containing a tackifier, an aqueous medium (b), and a raw material monomer (a) may contain a non-polymerizable surfactant (c) and then undergo emulsion polymerization. The non-polymerizable surfactant (c) is a surfactant (c) that does not have a polymerizable unsaturated bond in its chemical structure. The surfactant (c) improves the dispersion stability of the solution during emulsion polymerization and / or the dispersion (emulsion) obtained after polymerization. Preferred surfactants (c) include anionic surfactants and nonionic surfactants.

[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) may be used alone or in combination of two or more.

[0076] [Basic substance (d)] When producing the composite particles (P) by emulsion polymerization, a basic substance (d) may be added to the solution containing the tackifier, aqueous medium (b), and raw material monomer (a) before emulsion polymerization and / or to the dispersion after emulsion polymerization. The basic substance (d) may also be added to the dispersion during emulsion polymerization. By adding the basic substance (d), the acidic components contained in the raw material monomer (a) are neutralized. As a result, the pH of the solution during emulsion polymerization and / or the dispersion after emulsion polymerization is kept within an appropriate range, improving the stability of the solution during emulsion polymerization and / or the dispersion after emulsion polymerization.

[0077] Examples of the basic substance (d) that can be added to the solution before emulsion polymerization and / or the dispersion after emulsion polymerization include ammonia, triethylamine, sodium hydroxide, lithium hydroxide, etc. These basic substances (d) may be used alone or in combination of two or more.

[0078] [Radical polymerization initiator (e)] The radical polymerization initiator (e) used when producing the composite particles (P) by emulsion polymerization is not particularly limited, and known initiators can be used. Examples of the radical polymerization initiator (e) include persulfates such as ammonium persulfate and potassium persulfate; hydrogen peroxide; azo compounds; and organic peroxides such as tert-butyl hydroperoxide, tert-butyl peroxybenzoate, and cumene hydroperoxide. The radical polymerization initiator (e) may be used in the form of an aqueous solution.

[0079] In this embodiment, when the composite particles (P) are produced by emulsion polymerization, redox polymerization may be carried out using a reducing agent such as sodium bisulfite, Rongalite, or ascorbic acid in combination with the radical polymerization initiator (e).

[0080] The amount of radical polymerization initiator (e) added (including a reducing agent when used in combination) is preferably 0.001 parts by mass or more, more preferably 0.002 parts by mass or more, relative to 100 parts by mass of raw material monomer (a). This is because, when producing composite particles (P) by emulsion polymerization, the conversion rate of raw material monomer (a) to composite particles (P) can be increased. The amount of radical polymerization initiator (e) added is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of raw material monomer (a). This is because, the molecular weight of the copolymer contained in the composite particles (P) can be increased, and the swelling rate of a non-aqueous secondary battery electrode containing the composite particles (P) of this embodiment in an electrolyte solution can be reduced. The amount of radical polymerization initiator (e) added may be 0.1 parts by mass or more to 7.0 parts by mass or less, 0.5 parts by mass or more to 3.0 parts by mass or less, or 1.0 parts by mass or more to 2.0 parts by mass or less, but is not limited thereto.

[0081] [Chain transfer agent (f)] The chain transfer agent (f) preferably used when producing the composite particles (P) by emulsion polymerization is used to adjust the molecular weight of the copolymer forming the composite particles (P) obtained by emulsion polymerization. Examples of the chain transfer agent (f) include n-dodecyl mercaptan, tert-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexyl thioglycolate, 2-mercaptoethanol, β-mercaptopropionic acid, methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, and benzyl alcohol.

[0082] [Emulsion polymerization method] Examples of emulsion polymerization methods used in producing the composite particles (P) include a method in which emulsion polymerization is carried out while continuously supplying each component to be used in emulsion polymerization into a reaction vessel. An aqueous medium such as water may be placed in the reaction vessel beforehand. The temperature of the emulsion polymerization is not particularly limited, but is, for example, 30 to 90°C, preferably 50 to 85°C, and more preferably 55 to 80°C. It is preferable to carry out the emulsion polymerization with stirring. It is also preferable to continuously supply the raw material monomer (a), tackifier, and radical polymerization initiator (e) to the solution during emulsion polymerization so that the concentrations of the raw material monomer (a), tackifier, and radical polymerization initiator (e) in the solution during emulsion polymerization are uniform.

[0083] Here, an example of a composition containing the composite particles (P) obtained by the production method of this embodiment and an aqueous medium will be described with reference to the drawings. Fig. 1 is a schematic diagram illustrating the state of a composition containing a composite particle (P) obtained by the production method of this embodiment and an aqueous medium present therearound. That is, the composite particle 10 shown in Fig. 1 is a particle produced using the production method of this embodiment, which includes a polymerization step of copolymerizing raw material monomers (a) containing monomers (a1) and (a2) in the presence of a tackifier 2. The composite particle 10 is dispersed in an aqueous medium.

[0084] The composite particle 10 shown in FIG. 1 contains a copolymer 1 and a tackifier 2. Therefore, when an electrode is formed using a composition containing the composite particle 10 shown in FIG. 1 and an aqueous medium, the synergistic effect of the copolymer 1 and the tackifier 2 contained in the composite particle 10 present between the electrode active materials and the composite particle 10 present between the electrode active materials and the current collector is fully exerted. This results in an electrode with good binding strength between the electrode active materials and between the electrode active materials and the current collector. As a result, a nonaqueous secondary battery and a nonaqueous secondary battery electrode with excellent cycle characteristics can be obtained.

[0085] The copolymer 1 contained in the composite particle 10 shown in FIG. 1 has, as one form conjectured by the inventors, a particulate structure (block structure) 3 composed of randomly coiled polymer chains, i.e., chain molecules, as shown in FIG. 1. In one form conjectured by the inventors, the tackifier 2 has a particulate shape and is integrated with the particulate structure 3 composed of chain molecules. More specifically, the tackifier 2 contained in the composite particle 10 is embedded in the particulate structure 3 composed of chain molecules of the copolymer 1, as shown in FIG. 1. The tackifier 2 present in the particulate structure 3 is formed by the tackifier 2 being surrounded by the chain molecules of the copolymer 1 during the process in which the raw material monomer (a) mixed with the tackifier 2 is converted into the copolymer 1 in the polymerization step described above.

[0086] As shown in Figure 1, the tackifier 2 contained in the composite particle 10 may be entirely present within the particulate structure 3, or a portion may be attached to the outer surface of the particulate structure 3. The content of the tackifier 2 contained in the composite particle 10 and the number of particles made of the tackifier 2 are not particularly limited, and can be changed depending on the size of the composite particle 10, the amount of tackifier 2 used relative to the amount of raw material monomer (a) used in the production of the composite particle 10, etc., and can be determined appropriately depending on the application. The size of the composite particle 10 can also be selected arbitrarily.

[0087] In one embodiment, the composite particle 10 shown in FIG. 1 is an emulsified particle (dispersed particle) containing a copolymer 1, a tackifier 2, and a surfactant 4. Specifically, the composite particle 10 shown in FIG. 1 has a surfactant 4 bonded with a hydrophilic group facing outward to the copolymer 1 forming the outer surface of the particulate structure 3. The surfactant 4 does not correspond to the raw material monomer (a) containing a polymerizable surfactant as another monomer (a4) used in producing the composite particle 10, but is derived from a non-polymerizable surfactant (c).

[0088] The composite particle (P) of this embodiment may be any particle containing a copolymer 1 and a tackifier 2, and may be a composite particle 10 having a surfactant 4 as shown in FIG. 1, or a composite particle 11 having no surfactant as shown in FIG. 2.

[0089] FIG. 2 is a schematic diagram illustrating the state of a composition containing composite particles 11 different from the composite particles 10 obtained by the production method of this embodiment and an aqueous medium surrounding the composite particles 11. The composite particles 11 shown in FIG. 2 are soap-free emulsions that do not contain surfactants and are dispersed in an aqueous medium. A composition containing the surfactant-free composite particles 11 can be produced, for example, by using a soap-free emulsion polymerization method. Specifically, the composition can be produced by using a soap-free emulsion polymerization method in which a surfactant is not used when producing the composite particles 11, but a water-soluble polymer having a functional group such as a carboxy group is used, or a polymerizable surfactant having radical polymerization properties is used as the raw material monomer (a) and the raw material monomer (a) is copolymerized in the presence of a tackifier 2.

[0090] 2 and an aqueous medium, the composite particles 11 present between the electrode active materials and the composite particles 11 present between the electrode active materials and the current collector contain copolymer 1 and tackifier 2, just as in the case of using a composition containing composite particles 10 and an aqueous medium shown in Fig. 1. Therefore, the synergistic effect of copolymer 1 and tackifier 2 is fully exerted, resulting in an electrode with good binding properties between the electrode active materials and between the electrode active material and the current collector.

[0091] In contrast, when an electrode is formed using a binder formed from a composition in which a copolymer produced in the same manner as the composite particle 10 shown in Figure 1, except that the copolymerization of raw material monomer (a) is not carried out in the presence of tackifier 2, and a separately added tackifier 2 are dispersed in an aqueous medium in the presence of surfactant 4, sufficient adhesion between the electrode active materials and between the electrode active materials and the current collector is not obtained, as shown below.

[0092] FIG. 3 is a schematic diagram illustrating the state of a composition containing copolymer particles 20 made of copolymer 1, which were produced in the same manner as composite particle 10 shown in FIG. 1 , except that raw material monomer (a) was copolymerized without tackifier 2, and tackifier 2, which was added separately. Copolymer particles 20 shown in FIG. 3 are emulsified particles containing copolymer 1 and surfactant 4. Tackifier 2 is not contained in the emulsified particles. Tackifier 2 is formed into a separate emulsified particle by bonding with surfactant 42. In the composition shown in FIG. 3, copolymer particles 20 containing copolymer 1 and tackifier 2 are present in an aqueous medium at a distance from each other. This tends to result in the copolymer 1 and tackifier 2 being spaced apart between the electrode active materials forming the electrode and between the electrode active materials and the current collector. As a result, the synergistic effect of copolymer 1 and tackifier 2 is not fully achieved, resulting in an electrode with insufficient adhesion between the electrode active materials and between the electrode active materials and the current collector.

[0093] Furthermore, the composition shown in FIG. 3 contains a surfactant 42 for dispersing tackifier 2 in an aqueous medium, in addition to the surfactant 4 used in producing copolymer 1. Therefore, compared to a composition containing the composite particles of this embodiment, the surfactant content in the composition is higher, increasing the likelihood that the surfactant will remain as an impurity in the electrode. As a result, this may adversely affect the cycle characteristics of a battery equipped with the electrode, potentially causing a decrease in the cycle characteristics of the battery. For this reason, it is preferable not to use surfactant 42 for dispersing tackifier 2. However, from the perspective of the working environment during electrode production, it is preferable to use an aqueous medium as the solvent, and surfactant 42 must be used to disperse tackifier 2 in the aqueous medium. For these reasons, when an electrode is formed using the composition shown in FIG. 3, a non-aqueous secondary battery with excellent cycle characteristics cannot be obtained.

[0094] <2. Non-aqueous secondary battery binders> The binder for a non-aqueous secondary battery of this embodiment contains the composite particles (P) of this embodiment. The electrode binder for a non-aqueous secondary battery may contain other components in addition to the composite particles (P). Specifically, the electrode binder for a non-aqueous secondary battery may contain, for example, a polymer, a surfactant, etc. other than the composite particles (P).

[0095] The binder for nonaqueous secondary batteries is composed of components that remain without volatilizing even when a heating step is performed in the manufacturing method for nonaqueous secondary batteries described below. Specifically, for example, the components that constitute the binder for nonaqueous secondary batteries are the components that remain after weighing out 1 g of the binder composition for nonaqueous secondary batteries containing the composite particles (P), placing it on an aluminum dish with a diameter of 5 cm, placing it in a dryer, and drying it at 1 atmosphere (1013 hPa) and a temperature of 105°C for 1 hour while circulating air in the dryer.

[0096] The content of the composite particles (P) contained in the binder for a non-aqueous secondary battery is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more, because the effect of including the composite particles (P) becomes significant.

[0097] <3. Binder composition for non-aqueous secondary battery> The binder composition for a non-aqueous secondary battery of this embodiment contains the composite particles (P) of this embodiment and an aqueous medium (B). In the binder composition for a non-aqueous secondary battery of this embodiment, the composite particles (P) are preferably dispersed in the aqueous medium (B) in an emulsion state. The binder composition for a non-aqueous secondary battery may contain other components in addition to the composite particles (P) and the aqueous medium (B). Specifically, the binder composition for a non-aqueous secondary battery may contain, for example, the components used in synthesizing the composite particles (P).

[0098] The binder composition for a non-aqueous secondary battery of this embodiment may be a dispersion obtained by producing composite particles (P) by emulsion polymerization. That is, the binder composition for a non-aqueous secondary battery may be an emulsion containing composite particles (P) and an aqueous medium (B). The binder composition for a non-aqueous secondary battery of this embodiment may also be a dispersion obtained by dispersing composite particles (P) obtained by a method other than emulsion polymerization in an aqueous medium (B). In this case, a known method can be used as a method for dispersing the composite particles (P) in the aqueous medium (B).

[0099] [Aqueous medium (B)] The aqueous medium (B) in the non-aqueous secondary battery binder composition of this embodiment is water, a hydrophilic solvent, or a mixture thereof. Examples of the hydrophilic solvent include the same hydrophilic solvents as those exemplified as the aqueous medium (b) used in the synthesis of the composite particles (P). The aqueous medium (B) may be the same as or different from the aqueous medium (b) used in the synthesis of the composite particles (P).

[0100] When the non-aqueous secondary battery binder composition is an emulsion obtained by producing composite particles (P) using an emulsion polymerization method, the aqueous medium (B) may be the aqueous medium (b) used in the synthesis of the composite particles (P). Alternatively, the aqueous medium (B) may be the aqueous medium (b) used in the synthesis of the composite particles (P) to which a new aqueous medium has been added. Alternatively, the aqueous medium (B) may be the aqueous medium obtained by replacing part or all of the aqueous medium (b) contained in the dispersion obtained by producing the composite particles (P) using an emulsion polymerization method with a new aqueous solvent. The new aqueous medium used in this case may have the same composition as the aqueous medium (b) used in the synthesis of the composite particles (P), or it may have a different composition.

[0101] [Non-volatile content of binder composition for non-aqueous secondary battery] The nonvolatile content of the binder composition for a nonaqueous secondary battery of this embodiment is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more. This is to increase the amount of active ingredients contained in the binder composition for a nonaqueous secondary battery. The nonvolatile content of the binder composition for a nonaqueous secondary battery can be adjusted by the content of the aqueous medium (B) contained in the binder composition for a nonaqueous secondary battery. The nonvolatile content of the binder composition for a nonaqueous secondary battery is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less, because this suppresses an increase in viscosity of the binder composition for a nonaqueous secondary battery, making it easier to prepare a slurry for a nonaqueous secondary battery electrode.

[0102] <4. Non-aqueous Slurry for Secondary Battery Electrodes> Next, the non-aqueous secondary battery electrode slurry of this embodiment will be described in detail. The non-aqueous secondary battery electrode slurry contains the composite particles (P) of this embodiment, an electrode active material, and an aqueous medium. The composite particles (P) and electrode active material contained in the non-aqueous secondary battery electrode slurry are preferably dispersed in the aqueous medium. In addition to the composite particles (P), the electrode active material, and the aqueous medium, the non-aqueous secondary battery electrode slurry may also contain a thickener, a conductive additive, the above-mentioned components used in synthesizing the composite particles (P), and the like.

[0103] [Composite particle (P) content] The content of the composite particles (P) in the slurry for a non-aqueous secondary battery electrode is preferably 0.50 parts by mass or more, and more preferably 1.0 part by mass or more, relative to 100 parts by mass of the electrode active material, in order to fully exhibit the effects of including the composite particles (P). The content of the composite particles (P) contained in the slurry for a non-aqueous secondary battery electrode 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, relative to 100 parts by mass of the electrode active material, because this allows the content of the electrode active material contained in the slurry for a non-aqueous secondary battery electrode to be increased.

[0104] [Electrode active material] The electrode active material contained in the slurry for a non-aqueous secondary battery electrode is a material capable of intercalating / deintercalating ions that serve as charge carriers, such as lithium ions. The ions that serve as charge carriers are preferably alkali metal ions, more preferably lithium ions, sodium ions, or potassium ions, and even more preferably lithium ions.

[0105] When the nonaqueous secondary battery electrode produced using the nonaqueous secondary battery electrode slurry is a negative electrode, the electrode active material is a negative electrode active material. The negative electrode active material preferably includes at least one of a carbon material, a silicon-containing material, and a titanium-containing material. Examples of carbon materials used as negative electrode active materials include cokes such as petroleum coke, pitch coke, and coal coke, carbonized organic polymers, and graphites such as artificial graphite and natural graphite. Examples of silicon-containing materials used as negative electrode active materials include silicon alone and silicon compounds such as silicon oxide. Examples of titanium-containing materials used as negative electrode active materials include lithium titanate. These materials used as negative electrode active materials may be used alone or in combination or as a composite.

[0106] The negative electrode active material preferably contains at least one of a carbon material and a silicon-containing material, and more preferably contains a carbon material, because the composite particles (P) contained in the non-aqueous secondary battery electrode slurry have a significant effect of improving the binding between the negative electrode active materials and between the negative electrode active material and the current collector.

[0107] When the nonaqueous secondary battery electrode produced using the nonaqueous secondary battery electrode slurry is a positive electrode, the electrode active material is a positive electrode active material. The positive electrode active material is a material having a more noble standard electrode potential than the negative electrode active material. Specific examples of the positive electrode active material include nickel-containing lithium composite oxides such as Ni-Co-Mn-based lithium composite oxides, Ni-Mn-Al-based lithium composite oxides, and Ni-Co-Al-based lithium composite oxides; lithium cobalt oxide (LiCoO2); spinel-type lithium manganese oxide (LiMn2O4); olivine-type lithium iron phosphate; and chalcogen compounds such as TiS2, MnO2, MoO3, and VO5. These positive electrode active materials may be used alone or in combination.

[0108] [Aqueous medium] The aqueous medium contained in the slurry for a non-aqueous secondary battery electrode of this embodiment is one selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent. Examples of the hydrophilic solvent include the same hydrophilic solvents as those exemplified as the aqueous medium (b) used in the synthesis of the composite particles (P). The aqueous medium contained in the slurry for a non-aqueous secondary battery electrode may be the same as or different from the aqueous medium (b) used in the synthesis of the composite particles (P).

[0109] [Thickener] Examples of thickeners that may be contained in the slurry for a non-aqueous secondary battery electrode include celluloses such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose, and hydroxypropyl cellulose, ammonium salts of celluloses, alkali metal salts of celluloses, polyvinyl alcohol, and polyvinylpyrrolidone. The thickener preferably contains at least one of carboxymethyl cellulose, ammonium salts of carboxymethyl cellulose, and alkali metal salts of carboxymethyl cellulose. This is because the electrode active material in the slurry for a non-aqueous secondary battery electrode becomes more easily dispersed.

[0110] The content of the thickener in the non-aqueous secondary battery electrode slurry is preferably 0.50 parts by mass or more, and more preferably 0.80 parts by mass or more, per 100 parts by mass of the electrode active material. This is because good adhesion is achieved between the electrode active materials contained in the non-aqueous secondary battery electrode prepared using the non-aqueous secondary battery electrode slurry, and between the electrode active material and the current collector. The content of the thickener in the non-aqueous secondary battery electrode slurry is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less, per 100 parts by mass of the electrode active material. This is because good coating properties are achieved with the non-aqueous secondary battery electrode slurry.

[0111] [Conductive additive] Examples of conductive additives that may be contained in the slurry for a non-aqueous secondary battery electrode of this embodiment include carbon black and carbon fiber. Examples of carbon black include furnace black, acetylene black, Denka Black (registered trademark) (manufactured by Denka Company Ltd.), and Ketjen Black (registered trademark) (manufactured by Ketjen Black International Co., Ltd.). Examples of carbon fiber include carbon nanotubes and carbon nanofibers. A preferred example of carbon nanotubes is VGCF (registered trademark, manufactured by Showa Denko K.K.), which is vapor-grown carbon fiber.

[0112] [Method for producing non-aqueous secondary battery electrode slurry] Examples of methods for producing the non-aqueous secondary battery electrode slurry of this embodiment include a method of mixing the composite particles (P) of this embodiment, an electrode active material, an aqueous medium, a thickener that is optionally contained, a conductive additive that is optionally contained, and other components that are optionally contained. Instead of the composite particles (P) of this embodiment, the binder composition of this embodiment may be used to produce the slurry. The mixing order of the components that are the raw materials for the non-aqueous secondary battery electrode slurry is not particularly limited and can be determined appropriately. Methods for mixing the components include methods using a stirring, rotating, shaking, or other type of mixing device.

[0113] <5. Nonaqueous secondary battery electrode> Next, the nonaqueous secondary battery electrode of this embodiment will be described in detail. The electrode of this embodiment contains the composite particles (P) of this embodiment. The electrode of this embodiment includes a current collector and an electrode active material layer formed on the current collector. The shape of the electrode of this embodiment is not particularly limited, and examples thereof include a laminate and a wound body. The area on the current collector where the electrode active material layer is formed is not particularly limited, and the electrode active material layer may be formed on the entire surface of the current collector, or may be formed on only a part of the surface of the current collector. When the current collector is in the shape of a plate, foil, or the like, the electrode active material layer may be formed on both surfaces of the current collector, or on only one surface.

[0114] [Current collector] The current collector is preferably a metal sheet having a thickness of 0.001 mm to 0.5 mm. Examples of metals forming the metal sheet include iron, copper, aluminum, nickel, and stainless steel. When the electrode of this embodiment is a negative electrode of a lithium-ion secondary battery, the current collector is preferably a copper foil.

[0115] [Electrode active material layer] The electrode active material layer contains the composite particles (P) of this embodiment and an electrode active material. The electrode active material layer may contain a conductive additive, a thickener, etc. The electrode active material, the conductive additive, and the thickener can all be the same as those exemplified as components of the slurry for a non-aqueous secondary battery electrode.

[0116] [Method for producing non-aqueous secondary battery electrodes] The electrode of this embodiment can be manufactured, for example, by the method described below. First, the slurry for a non-aqueous secondary battery electrode of this embodiment is applied onto a current collector. Then, the slurry for a non-aqueous secondary battery electrode is dried. This forms an electrode active material layer containing the composite particles (P) on the current collector, forming an electrode sheet. Thereafter, the electrode sheet is cut to an appropriate size as necessary. By performing the above steps, the electrode of this embodiment is obtained.

[0117] The method for applying the non-aqueous secondary battery electrode slurry onto the current collector is not particularly limited, and examples thereof include the reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dipping method, squeeze method, etc. Among these application methods, in consideration of the physical properties such as viscosity of the non-aqueous secondary battery electrode slurry and drying property, it is preferable to use any method selected from the direct roll method, doctor blade method, knife method, and extrusion method, because this allows for the formation of an electrode active material layer with a smooth surface and small thickness variation.

[0118] When the nonaqueous secondary battery electrode slurry is applied to both sides of the current collector, it may be applied to each side sequentially or simultaneously. In addition, the nonaqueous secondary battery electrode slurry may be applied to the current collector continuously or intermittently. The amount of the non-aqueous secondary battery electrode slurry to be applied can be determined appropriately depending on the design capacity of the battery, the composition of the non-aqueous secondary battery electrode slurry, and the like.

[0119] The method for drying the nonaqueous secondary battery electrode slurry applied to the current collector is not particularly limited, and for example, a method selected from hot air, reduced pressure or vacuum environment, (far) infrared rays, and low-temperature air can be used alone or in combination. The drying temperature and drying time when drying the non-aqueous secondary battery electrode slurry can be appropriately adjusted depending on the non-volatile content concentration in the non-aqueous secondary battery electrode slurry, the amount of the slurry applied to the current collector, etc. The drying temperature is preferably 40° C. or higher and 350° C. or lower, and from the viewpoint of productivity, more preferably 60° C. or higher and 100° C. or lower. The drying time is preferably 1 minute or higher and 30 minutes or lower.

[0120] The electrode sheet in which the electrode active material layer is formed on the current collector may be cut to a size and shape appropriate for the electrode. The method for cutting the electrode sheet is not particularly limited, and for example, slitting, laser cutting, wire cutting, a cutter, a Thomson cutter, or the like can be used.

[0121] In this embodiment, the electrode sheet may be pressed as needed before or after cutting the electrode sheet, which allows the electrode active material to be more firmly bound to the current collector and reduces the thickness of the electrode, thereby enabling the nonaqueous secondary battery to be made smaller. The electrode sheet can be pressed by a common method, and it is particularly preferable to use a mold pressing method or a roll pressing method. When using the mold pressing method, the pressing pressure is not particularly limited, but is preferably 0.5 t / cm 2 More than 5t / cm 2It is preferable to do the following: When using the roll press method, the press load is not particularly limited, but is preferably 0.5 t / cm or more and 8 t / cm or less, because this makes it possible to obtain the above-mentioned effects of pressing while suppressing a decrease in the insertion and desorption capacity of charge carriers such as lithium ions into and from the electrode active material.

[0122] <6.Nonaqueous secondary battery> Next, a lithium ion secondary battery will be described as a preferred example of the nonaqueous secondary battery according to this embodiment. Note that the configuration of the nonaqueous secondary battery of the present invention is not limited to the example shown below. The lithium ion secondary battery of this embodiment is configured such that a positive electrode, a negative electrode, an electrolyte, and known components such as a separator that are provided as needed are housed in an exterior body. The shape of the lithium ion secondary battery may be any shape, such as a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, or a flat type.

[0123] [Positive and negative electrodes] In the lithium ion secondary battery of this embodiment, one or both of the positive electrode and the negative electrode are provided with an electrode active material layer of this embodiment containing the composite particles (P) of this embodiment. Of the positive electrode and the negative electrode, it is preferable that at least the negative electrode is provided with an electrode active material layer containing the composite particles (P). In the lithium ion secondary battery of this embodiment, when only one of the positive electrode and negative electrode has an electrode active material layer containing the composite particles (P) of this embodiment, an electrode containing a known binder such as polyvinylidene fluoride is used instead of the composite particles (P) of this embodiment as the electrode that does not contain the composite particles (P) of this embodiment.

[0124] [Electrolyte] The electrolyte solution may be a non-aqueous liquid having ion conductivity. Examples of the electrolyte solution include a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, etc., and the former is preferred because it allows for low production costs and results in a lithium ion secondary battery with low internal resistance.

[0125] As the electrolyte, an alkali metal salt can be used, and can be appropriately selected depending on the type of electrode active material, etc. Examples of the electrolyte include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB 10 Cl 10 , LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, aliphatic lithium carboxylates, etc. Other alkali metal salts can also be used as the electrolyte.

[0126] The organic solvent for dissolving the electrolyte is not particularly limited, but examples thereof include 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); nitrile compounds such as acetonitrile; and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These organic solvents may be used alone or in combination of two or more. Among these, it is preferable to use a combination of linear carbonate solvents as the organic solvent.

[0127] [Exterior body] The exterior body may be made of an aluminum laminate material made of aluminum foil and a resin film, but is not limited to this. [Example]

[0128] The present invention will be specifically described below with reference to examples and comparative examples. The examples shown below are intended to facilitate understanding of the present invention. The present invention is not limited to these examples. In the following examples, a negative electrode for a lithium ion secondary battery was fabricated as an example of a non-aqueous secondary battery electrode of the present invention, and a lithium ion secondary battery was fabricated as an example of a non-aqueous secondary battery. These were compared with a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery of comparative examples to confirm the effects of the present invention. Furthermore, the water used in the following examples and comparative examples is ion-exchanged water unless otherwise specified.

[0129] <1. Production of binder composition for non-aqueous secondary battery> (Examples 1 to 18, Comparative Example 2) A monomer emulsion was prepared by mixing and emulsifying the raw material monomer (a) and tackifier shown in Tables 1 to 7 with 200 parts by mass of water as an aqueous medium (b) in the mass ratios shown in Tables 1 to 7. Next, an aqueous solution was prepared by dissolving each of the radical polymerization initiators (e) shown in Tables 1 to 7 in 50 parts by mass of water in the amounts shown in Tables 1 to 7.

[0130] Into a separable flask equipped with a condenser, a thermometer, a stirrer, and a dropping funnel, 150 parts by mass of water was placed and heated to 75° C. The above monomer emulsion and the above aqueous solution in which the radical polymerization initiator (e) was dissolved were each continuously fed into this separable flask over a period of 3 hours while stirring at 75° C., thereby carrying out emulsion polymerization and obtaining an emulsion.

[0131] The resulting emulsion was cooled to room temperature. Then, 133 parts by mass of water and 25% by mass of aqueous ammonia (17 parts by mass of ammonia, 51 parts by mass of water) in the amounts shown in Tables 1 to 7 were added to the emulsion. In this manner, the nonaqueous secondary battery binder compositions of Examples 1 to 18 and Comparative Example 2 were produced, each consisting of an emulsion in which the dispersed particles of Examples 1 to 18 and Comparative Example 2 were dispersed in an aqueous medium. The dispersed particles (composite particles) of Comparative Example 2 did not contain the monomer (a2).

[0132] (Comparative Example 1) A monomer emulsion was prepared by mixing and emulsifying raw material monomer (a) shown in Table 7 with 200 parts by mass of water as aqueous medium (b) in the mass ratio shown in Table 7. Next, an aqueous solution was prepared by dissolving radical polymerization initiator (e) shown in Table 7 in 50 parts by mass of water in the amount shown in Table 7.

[0133] Into a separable flask equipped with a condenser, a thermometer, a stirrer, and a dropping funnel, 150 parts by mass of water was placed and heated to 75° C. The above monomer emulsion and the above aqueous solution in which the radical polymerization initiator (e) was dissolved were each continuously fed into this separable flask over a period of 3 hours with stirring at 75° C. to carry out emulsion polymerization, thereby obtaining an emulsion.

[0134] The resulting emulsion was cooled to room temperature. Then, 133 parts by mass of water and 25% by mass of aqueous ammonia (as shown in Table 7) were added to the emulsion. This produced a non-aqueous secondary battery binder composition of Comparative Example 1, which consisted of an emulsion in which emulsified particles containing the copolymer of Comparative Example 1 were dispersed in an aqueous medium. The emulsified particles in the emulsion of Comparative Example 1 contained the copolymer but no tackifier.

[0135] (Comparative Example 3 and Comparative Example 4) Emulsions of Comparative Examples 3 and 4 were obtained in the same manner as Comparative Example 1. The emulsified particles in these emulsions contain the copolymer but no tackifier. As will be described later, in Comparative Examples 3 and 4, the tackifier is present separately from the emulsified particles. The resulting emulsion was cooled to room temperature. The tackifier emulsion shown in Table 7 was then added to the emulsion in the amount shown in Table 7, followed by 123 parts by mass of water and 25% by mass of ammonia water in the amount shown in Table 7, and the mixture was stirred for 30 minutes using a homodisper. The amount of emulsion AM-1000-NT added in Table 7 refers to the amount of emulsified particles containing a tackifier in the emulsion.

[0136] As a result, the nonaqueous secondary battery binder compositions of Comparative Example 3 and Comparative Example 4 were produced, each consisting of an emulsion in which emulsified particles containing the copolymer of Comparative Example 3 or Comparative Example 4 and emulsified particles containing a tackifier were independently dispersed in an aqueous medium. Note that no dispersion abnormalities, such as aggregation of the copolymer-containing emulsion particles and the tackifier-containing emulsion particles in the composition, were observed in the binder compositions for nonaqueous secondary batteries of Comparative Examples 3 and 4. That is, in Comparative Examples 3 and 4, composite particles containing the copolymer of the present embodiment and a tackifier were not formed, and the binder compositions for nonaqueous secondary batteries of Comparative Examples 3 and 4 did not contain composite particles containing the copolymer of the present embodiment and a tackifier. This is presumably because, in the nonaqueous secondary battery binder compositions of Comparative Examples 3 and 4, the emulsion particles containing the copolymer and the emulsion particles containing the tackifier in the composition repel each other in terms of charge, thereby maintaining the dispersion of each of the emulsion particles containing the copolymer and the emulsion particles containing the tackifier in the composition.

[0137] [Table 1]

[0138] [Table 2]

[0139] [Table 3]

[0140] [Table 4]

[0141] [Table 5]

[0142] [Table 6]

[0143] [Table 7]

[0144] The polyoxyethylene alkyl ether sulfate salt of the monomer (a4) shown in Tables 1 to 7 (Aqualon KH-10, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) is a polymerizable surfactant. Rongalit SFS in the polymerization initiator (e) is the trade name of Rongalit manufactured by Sumitomo Seika Chemicals Co., Ltd.

[0145] The tackifiers shown in Tables 1 to 7 are as follows. Hydrogenated petroleum resin Alcon M-90 (alicyclic saturated hydrocarbon resin): manufactured by Arakawa Chemical Industries, Ltd., softening point 90°C Alcon M-135 (alicyclic saturated hydrocarbon resin): manufactured by Arakawa Chemical Industries, Ltd., softening point 135°C Alcon P-90 (alicyclic saturated hydrocarbon resin): manufactured by Arakawa Chemical Industries, Ltd., softening point 90°C Alcon P-140 (alicyclic saturated hydrocarbon resin): manufactured by Arakawa Chemical Industries, Ltd., softening point 140°C Emulsion AM-1000-NT (alicyclic saturated hydrocarbon resin): A dispersion (concentration 50%) in which a tackifier similar to Alcon M-90 is dispersed in water using a surfactant in an aqueous medium. The values ​​listed in Table 7 indicate the amount of emulsified particles containing tackifier in the dispersion. Manufactured by Arakawa Chemical Industries, Ltd. Softening point 100°C

[0146] Rosin-based resin Harie Star DS-70L (rosin ester resin): manufactured by Harima Chemical Group Co., Ltd., softening point 70°C Hariestar FK-100 (disproportionated rosin ester resin): manufactured by Harima Chemical Group Co., Ltd., softening point 100°C Terpene Resin YS Resin PX800 (polyterpene resin): manufactured by Yasuhara Chemical Co., Ltd., softening point 180°C YS Resin PX1000 (polyterpene resin): manufactured by Yasuhara Chemical Co., Ltd., softening point 100°C

[0147] The timing of addition shown in Tables 1 to 7 refers to the timing at which the tackifier was used in the production process of the binder composition. "Before polymerization" means that the raw material monomer (a) was copolymerized in the presence of the tackifier. "After polymerization" means that the tackifier was added to an emulsion containing emulsified particles containing a copolymer obtained by copolymerizing the raw material monomer (a).

[0148] The amount of ammonia as the basic substance (d) shown in Tables 1 to 7 is the amount (parts by mass) of ammonia contained in the ammonia water. The amount of water as the aqueous medium (b) shown in Tables 1 to 7 is the total amount (parts by mass) of water contained in the non-aqueous binder composition for a secondary battery.

[0149] <2. Evaluation of Composite Particles and Binder Compositions for Non-Aqueous Secondary Batteries> The glass transition temperature (Tg) of each of the composite particles of Examples 1 to 18 and Comparative Examples 1 to 4 was measured by the method described below. The results are shown in Tables 1 to 7. Furthermore, the nonvolatile content of each of the binder compositions for a nonaqueous secondary battery of Examples 1 to 18 and Comparative Examples 1 to 4 was measured by the method described below. The results are shown in Tables 1 to 7.

[0150] [Glass transition temperature (Tg)] The non-aqueous secondary battery binder composition was applied onto a release PET (polyethylene terephthalate) film and dried at 50° C. for 5 hours to obtain a 2 mm thick film made of composite particles. A square test piece measuring 2 mm in length and 2 mm in width was cut from the obtained film. The test piece was sealed in an aluminum pan, and differential scanning calorimetry (DSC) measurement of the test piece was performed using a differential scanning calorimeter (EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Corporation) in a nitrogen gas atmosphere at a heating rate of 10°C / min. The temperature range of the DSC measurement was -40°C to 200°C. The peak top temperature of the DDSC chart obtained as the temperature derivative of the DSC was then measured, and this temperature was defined as the glass transition temperature Tg (°C) of the composite particles.

[0151] [Non-volatile content] 1 g of the binder composition for a non-aqueous secondary battery was weighed out, placed on an aluminum dish with a diameter of 5 cm, and placed in a dryer. While circulating air in the dryer, the composition was dried at 1 atmosphere (1013 hPa) and a temperature of 105°C for 1 hour, and the mass of the remaining components was measured. The mass ratio (mass%) of the above components remaining after drying relative to the mass (1 g) of the binder composition for a non-aqueous secondary battery before drying was calculated and used as the non-volatile content concentration (mass%).

[0152] <3. Production of non-aqueous secondary batteries> Negative electrodes were produced by the method described below using the binder compositions for nonaqueous secondary batteries of Examples 1 to 18 and Comparative Examples 1 to 4, respectively, and lithium ion secondary batteries, which are the nonaqueous secondary batteries of Examples 1 to 18 and Comparative Examples 1 to 4, were produced using these negative electrodes.

[0153] [Preparation of positive electrode] LiNi as a positive electrode active material 0.6 Mn 0.2 Co 0.2 A mixture was obtained by mixing 94 parts by weight of O2, 3 parts by weight of acetylene black as a conductive additive, and 3 parts by weight of polyvinylidene fluoride as a binder, and 50 parts by weight of N-methylpyrrolidone was added to the mixture and further mixed to obtain a positive electrode slurry.

[0154] A 15 μm thick aluminum foil was prepared as a positive electrode current collector. The positive electrode slurry was applied to both sides of the positive electrode current collector by a direct roll method. The amount of the positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described below would be 125 μm per side. The positive electrode slurry applied to the positive electrode current collector was dried at 120°C for 5 minutes and pressed using a roll press (manufactured by Thank Metals, press load 5 t / cm, roll width 7 cm) to obtain a positive electrode sheet having positive electrode active material layers on both sides of the positive electrode current collector. The obtained positive electrode sheet was cut into a rectangle 50 mm long and 40 mm wide, and a conductive tab was attached to form a positive electrode.

[0155] [Preparation of negative electrode (non-aqueous secondary battery electrode)] 96.9 parts by mass of artificial graphite (G49, manufactured by Jiangxi Zishen Technology Co., Ltd.) as a negative electrode active material, 3.6 parts by mass of any of the binder compositions for non-aqueous secondary batteries produced in Examples 1 to 18 and Comparative Examples 1 to 4 (1.4 parts by mass of non-volatile content (binder polymer)), and 60 parts by mass of a 2% by mass aqueous solution of CMC (carboxymethyl cellulose-sodium salt, manufactured by Nippon Paper Chemicals Co., Ltd., Sunrose (registered trademark) MAC500LC) were mixed, and 16 parts by mass of water was further added and mixed using a planetary centrifugal mixer (ARE-310, manufactured by Thinky Corporation) to obtain a negative electrode slurry (slurry for non-aqueous secondary battery electrodes).

[0156] A copper foil with a thickness of 10 μm was prepared as a negative electrode current collector. The negative electrode slurry was applied to both sides of the negative electrode current collector by a direct roll method. The amount of negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness of the negative electrode active material layer after the roll press treatment described below was 170 μm per side. The negative electrode slurry applied to the negative electrode current collector was dried at 90°C for 10 minutes and pressed using a roll press (manufactured by Thank Metals, press load 8 t / cm, roll width 7 cm) by roll pressing. This resulted in a negative electrode sheet with negative electrode active material layers on both sides of the negative electrode current collector. The resulting negative electrode sheet was cut into a rectangle measuring 52 mm in length and 42 mm in width, and a conductive tab was attached to form a negative electrode.

[0157] [Preparation of non-aqueous secondary battery] A separator (made of polyethylene, 25 μm thick) made of a polyolefin-based porous film was interposed between the positive electrode and the negative electrode, and the positive electrode active material layer and the negative electrode active material layer were laminated so that they faced each other, and then housed in an exterior body (battery pack) made of aluminum laminate material. Then, an electrolyte solution was poured into the exterior body, vacuum impregnation was performed, and the battery was packed with a vacuum heat sealer to obtain a lithium-ion secondary battery. The electrolyte used was a mixture of 99 parts by mass of a solution in which LiPF6 was dissolved at a concentration of 1.0 mol / L in 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, and 1 part by mass of vinylene carbonate.

[0158] <4. Evaluation of non-aqueous secondary batteries> The internal resistance and discharge capacity retention rate after 500 cycles were evaluated by the methods described below for each of the lithium ion secondary batteries of Examples 1 to 18 and Comparative Examples 1 to 4. The results are shown in Tables 1 to 7.

[0159] [Internal resistance (DCR)] The internal resistance (DCR (Ω)) of the lithium-ion secondary battery was measured at 25°C using the following procedure. Specifically, the battery was charged at a constant current of 0.2 C from the rest potential until the voltage reached 3.6 V, and the state of charge was adjusted to 50% of the initial capacity (SOC50%). The battery was then discharged for 60 seconds at current values ​​of 0.2 C, 0.5 C, 1 C, and 2 C. The internal resistance DCR (Ω) at SOC50% was determined from the relationship between these four current values ​​(values ​​over 1 second) and voltage.

[0160] [Discharge capacity retention rate after 500 cycles] Charge and discharge were performed under conditions of 45°C, with one cycle consisting of a series of operations of steps (i) to (iv) shown below. The time-integrated value of the current in steps (i) and (ii) was taken as the charge capacity, and the time-integrated value of the current in step (iv) was taken as the discharge capacity. The discharge capacity at the first cycle and the discharge capacity at the 500th cycle were measured, and the discharge capacity retention rate after 500 cycles was calculated using the following formula. Discharge capacity retention rate (%) = 100 × (discharge capacity at 500th cycle / discharge capacity at 1st cycle)

[0161] (i) Charge at a current of 1C until the voltage reaches 4.2V (constant current (CC) charging). (ii) Charge at a voltage of 4.2 V until the current reaches 0.05 C (constant voltage (CV) charging). (iii) Allow to stand for 30 minutes. (iv) Discharge at a current of 1 C until the voltage reaches 2.75 V (constant current (CC) discharge).

[0162] <5. Evaluation Results> As shown in Tables 1 to 7, it was confirmed that the lithium ion secondary batteries of Examples 1 to 18 all had higher capacity retention rates than the lithium ion secondary batteries of Comparative Examples 1 to 4. This is presumably because the composite particles contained in the negative electrodes of the lithium ion secondary batteries of Examples 1 to 18 contain a copolymer containing structural units derived from the monomers (a1) and (a2) shown in Tables 1 to 6, and a tackifier shown in Tables 1 to 6.

[0163] More specifically, in Comparative Example 1, a negative electrode was produced using a non-aqueous secondary battery binder composition containing no tackifier, in which emulsion particles containing a copolymer were dispersed in an aqueous medium. This is presumably why the binding between the electrode active materials and between the electrode active materials and the current collector was insufficient, resulting in a poor capacity retention rate.

[0164] In Comparative Example 2, the composite particles contained in the negative electrode contained a copolymer not containing a structural unit derived from monomer (a2) and a tackifier. This is presumably because the copolymer did not have an effect of improving the binding between the electrode active materials and between the electrode active materials and the current collector, resulting in a poor capacity retention rate.

[0165] Furthermore, Comparative Example 3 had a poorer capacity retention rate than Example 1, in which a negative electrode was produced using a binder composition for a nonaqueous secondary battery that used the same raw material monomer (a) and contained the same amount of a similar tackifier. Furthermore, Comparative Example 4 had a poorer capacity retention rate than Example 18, in which a negative electrode was produced using a binder composition for a nonaqueous secondary battery that used the same raw material monomer (a) and contained the same amount of a similar tackifier. This is presumably because the binder compositions for nonaqueous secondary batteries used in Comparative Examples 3 and 4 were prepared by adding a tackifier to an emulsion containing emulsified particles containing a copolymer obtained by copolymerizing raw material monomer (a). Therefore, the copolymer and the tackifier were arranged apart between the electrode active materials forming the electrodes and between the electrode active materials and the current collector, resulting in insufficient binding between the electrode active materials and between the electrode active materials and the current collector.

[0166] Furthermore, as shown in Tables 1 to 7, it was confirmed that the lithium ion secondary batteries of Examples 1 to 18 and Comparative Examples 1 to 4 had sufficiently low values ​​for practical use in terms of internal resistance, which is a secondary effect. [Industrial Applicability]

[0167] The present invention provides composite particles that can be used as a binder material to form electrodes that can provide non-aqueous secondary batteries with excellent cycle characteristics. [Explanation of symbols]

[0168] 1...Copolymer 2. Tackifier 3...particulate structure 4, 42...Surfactants 10, 11···Composite particles 20···Co-composite particles

Claims

1. Composite particles for use in a binder for a non-aqueous secondary battery, comprising a copolymer and a tackifier, The copolymer is a first structural unit derived from the monomer (a1); and a second structural unit derived from the monomer (a2), the monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, The composite particles, wherein the monomer (a2) is a compound having a carboxy group and only one ethylenically unsaturated bond.

2. 2. The composite particle according to claim 1, wherein at least a portion of the tackifier is present within a particle structure consisting of chain molecules of the copolymer.

3. The composite particles according to claim 1 , wherein the tackifier is at least one selected from the group consisting of hydrogenated petroleum resins and terpene resins.

4. The composite particle of claim 3 , wherein the tackifier comprises a hydrogenated petroleum resin.

5. The composite particles according to claim 4, wherein the softening point of the hydrogenated petroleum resin is 70°C to 140°C.

6. 2. The composite particle according to claim 1, wherein the content of the tackifier is 0.50 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the monomer components used in producing the copolymer.

7. The composite particle according to claim 1 , wherein the content of the second structural unit in all structural units of the copolymer is 0.10% by mass or more and 20% by mass or less.

8. the copolymer has a third structural unit derived from a monomer (a3), The monomer (a3) ​​is a compound having a plurality of independent ethylenically unsaturated bonds. The composite particle according to claim 1 .

9. The composite particle according to claim 8 , wherein the content of the third structural unit in all structural units of the copolymer is 0.010% by mass or more and 10% by mass or less.

10. A binder composition for a non-aqueous secondary battery, comprising the composite particles according to any one of claims 1 to 9 and an aqueous medium.

11. An electrode comprising the composite particle according to any one of claims 1 to 9, an electrode active material, and an aqueous medium, The aqueous medium is one selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent.

12. A non-aqueous secondary battery electrode comprising the composite particles according to any one of claims 1 to 9.

13. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode described in claim 12.

14. A method for producing composite particles used in a binder for a non-aqueous secondary battery, the method comprising: a polymerization step of copolymerizing raw material monomers (a) including a monomer (a1) and a monomer (a2) in the presence of a tackifier, the monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, The method for producing composite particles, wherein the monomer (a2) is a compound having a carboxy group and only one ethylenically unsaturated bond.

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