Binder composition for non-aqueous secondary batteries, slurry for non-aqueous secondary battery electrodes, non-aqueous secondary battery electrodes, and non-aqueous secondary battery

Abstract

This binder composition for a non-aqueous secondary battery contains a copolymer and an adhesive agent. The copolymer comprises a first structural unit derived from a monomer (a1) and a second structural unit derived from a monomer (a2). Monomer (a1) is a nonionic compound having only one ethylenic unsaturated bond, and monomer (a2) is a compound having a carboxyl group and only one ethylenic unsaturated bond.

Description

[Technical Field]

[0001] The present invention relates to a binder composition for non-aqueous secondary batteries, a slurry for non-aqueous secondary battery electrodes, a non-aqueous secondary battery electrode, and a non-aqueous secondary battery. This application claims priority based on Japanese Patent Application No. 2022-205583, filed in Japan on December 22, 2022, and the contents of that application are incorporated herein by reference. [Background technology]

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

[0003] Non-aqueous secondary batteries include a positive electrode with a metal oxide or the like as the active material, a negative electrode with a carbon material such as graphite as the active material, and an electrolyte. The positive and negative electrodes each comprise a current collector and an electrode active material layer formed on the current collector. The electrode active material layer usually contains a binder that binds the active materials together and between the active materials and the current collector, thereby fixing the electrode active material layer on the current collector. Conventionally, binders used in non-aqueous secondary batteries are known from those described in Patent Documents 1 and 2.

[0004] Patent Document 1 describes a binder composition for secondary battery electrodes containing 100 parts by mass of at least one polymer aqueous dispersion selected from the group consisting of styrene-butadiene copolymer latex and 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 having a glass transition temperature of 30°C or lower, obtained by emulsion polymerization of an ethylenically unsaturated monomer containing 15 to 70% by mass of styrene, an ethylenically unsaturated carboxylic acid ester, an ethylenically unsaturated carboxylic acid, and an internal crosslinking agent as essential components, in the presence of a surfactant.

[0006] Patent Document 3 describes a tire puncture sealing material containing an acrylic emulsion, an antifreeze agent, and a tackifier.

[0007] Patent Document 4 describes a water-dispersible acrylic adhesive tape or sheet for transporting electronic components, which has an adhesive layer made of an acrylic adhesive mainly composed of an acrylic emulsion polymer. Patent Document 4 also describes an acrylic emulsion polymer obtained by emulsion polymerization of an acrylic monomer mixture containing a carboxyl group-containing monomer. Furthermore, Patent Document 4 discloses that the above acrylic adhesive contains a rosin-based or terpene-based tackifier with a softening point of 100°C or higher.

[0008] Patent Document 5 describes a heat-sensitive adhesive label having a pressure-sensitive adhesive layer formed from a pressure-sensitive adhesive which is an acrylic emulsion polymer. Patent Document 5 also discloses that the pressure-sensitive adhesive includes a rosin-based tackifier and / or a petroleum resin-based tackifier. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2014-239070 [Patent Document 2] Japanese Patent Publication No. 2011-243464 [Patent Document 3] Japanese Patent Publication No. 2007-224248 [Patent Document 4] Japanese Patent Publication No. 2008-285221 [Patent Document 5] Japanese Patent Publication No. 2006-82377 [Overview of the project] [Problems that the invention aims to solve]

[0010] In recent years, there has been a strong demand for higher power output, higher capacity, and longer lifespan in non-aqueous secondary batteries. Binders used in non-aqueous secondary batteries are required to improve the cycle characteristics of non-aqueous secondary batteries having electrodes using these binders. However, the disclosures in Patent Documents 1 to 5 have not provided any compositions that satisfy these requirements.

[0011] The present invention has been made in view of the above circumstances, and aims to provide a binder composition for non-aqueous secondary batteries that can form electrodes for non-aqueous secondary batteries with excellent cycle characteristics, a slurry for non-aqueous secondary battery electrodes, a non-aqueous secondary battery electrode that can produce a non-aqueous secondary battery with excellent cycle characteristics, and a non-aqueous secondary battery equipped therewith. [Means for solving the problem]

[0012] To achieve the above objectives, the present invention includes the following embodiments. [1] A copolymer and a tackifier are included, The copolymer is The first structural unit derived from the monomer (a1), It has a second structural unit derived from the monomer (a2), The monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, The monomer (a2) is a compound having a carboxyl group and only one ethylenically unsaturated bond, and is a binder composition for non-aqueous secondary batteries.

[0013] [2] The binder composition for a non-aqueous secondary battery according to [1], wherein the tackifier is at least one selected from hydrogenated petroleum resin and terpene resin. [3] The non-aqueous secondary battery binder composition according to [2], wherein at least one of the tackifiers is the hydrogenated petroleum resin.

[0014] [4] The non-aqueous secondary battery binder composition according to [3], wherein the softening point of the hydrogenated petroleum resin is 70°C to 140°C. [5] The non-aqueous secondary battery binder composition according to any one of [1] to [4], wherein the content of the tackifier with respect to 100 parts by mass of the copolymer is 0.10 parts by mass or more and 50 parts by mass or less.

[0015] [6] The non-aqueous secondary battery binder composition according to any one of [1] to [5], wherein the content of the second structural unit in all the structural units of the copolymer is 0.10% by mass or more and 20% by mass or less. [7] The copolymer has a third structural unit derived from monomer (a3), The non-aqueous secondary battery binder composition according to any one of [1] to [6], wherein the monomer (a3) is a compound having a plurality of independent ethylenically unsaturated bonds.

[0016] [8] The non-aqueous secondary battery binder composition according to [7], wherein the content of the third structural unit in all the structural units of the copolymer is 0.010% by mass or more and 10% by mass or less. [9] The first structural unit derived from the monomer (a1) includes a structural unit derived from an aromatic compound, The non-aqueous secondary battery binder composition according to any one of [1] to [8], wherein the content of the structural unit derived from the aromatic compound in all the structural units of the copolymer is 36% by mass or more.

[0017]

[10] The non-aqueous secondary battery binder composition according to any one of [1] to [9], further containing an aqueous medium.

[11] The non-aqueous secondary battery binder composition according to

[10] , wherein the aqueous medium is one selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent.

[0018]

[12] A binder composition for a non-aqueous secondary battery according to

[10] or

[11] , wherein the copolymer and the tackifier are dispersed in the aqueous medium.

[13] The binder composition for a non-aqueous secondary battery according to any one of [1] to

[12] , wherein the glass transition temperature of the copolymer is -10°C to 40°C.

[0019]

[14] A slurry for a non-aqueous secondary battery electrode, comprising a binder composition for a non-aqueous secondary battery described in any one of items [1] to

[13] , and an electrode active material.

[15] A non-aqueous secondary battery electrode comprising the non-volatile component of the binder composition for non-aqueous secondary batteries described in any one of items [1] to

[13] . A non-aqueous secondary battery comprising the non-aqueous secondary battery electrodes described in

[16]

[15] . [Effects of the Invention]

[0020] According to the present invention, a binder composition for non-aqueous secondary batteries can be provided that can form electrodes for non-aqueous secondary batteries with excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a slurry for non-aqueous secondary battery electrodes that can form electrodes for non-aqueous secondary batteries with excellent cycle characteristics. Furthermore, according to the present invention, it is possible to provide a non-aqueous secondary battery electrode that yields a non-aqueous secondary battery with excellent cycle characteristics, and a non-aqueous secondary battery equipped with the same that also has excellent cycle characteristics. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic cross-sectional view showing an example of a non-aqueous secondary battery electrode manufactured using a binder composition for non-aqueous secondary batteries according to one embodiment of the present invention. [Figure 2] This is a schematic diagram illustrating an example of a binder composition for a non-aqueous secondary battery according to one embodiment of the present invention. [Figure 3] This is a schematic diagram illustrating another example of a binder composition for a non-aqueous secondary battery according to one embodiment of the present invention. [Figure 4] This is a schematic diagram illustrating another example of a binder composition for a non-aqueous secondary battery according to one embodiment of the present invention. [Modes for carrying out the invention]

[0022] The inventors of the present invention have diligently conducted research to solve the above problems and to realize a binder capable of forming a non-aqueous secondary battery electrode that yields a non-aqueous secondary battery with excellent cycle characteristics. As a result, they have obtained the binder composition for non-aqueous secondary batteries, the slurry for non-aqueous secondary battery electrodes, the non-aqueous secondary battery electrode, and the non-aqueous secondary battery of this embodiment.

[0023] Figure 1 is a schematic cross-sectional view showing an example of a non-aqueous secondary battery electrode manufactured using the binder composition for non-aqueous secondary batteries of this embodiment. The non-aqueous secondary battery electrode (hereinafter sometimes referred to as "electrode") 20 shown in Figure 1 includes a current collector 23 made of copper foil or the like, and an electrode active material layer 24 formed on the current collector 23. The electrode active material layer 24 in this embodiment includes an electrode active material 22, a thickener 21, and a binder 25. The binder 25 consists of the non-volatile components of the binder composition for non-aqueous secondary batteries of this embodiment.

[0024] The discharge capacity of a non-aqueous secondary battery equipped with electrodes 20 decreases when the electrode active material layer 24 of the electrodes 20 expands and contracts due to the use of the non-aqueous secondary battery, i.e., the expansion and contraction of the electrode active material 22 during charging and discharging, and when the electrode active material layer 24 peels off from the current collector 23. Furthermore, even if the electrode active material layer 24 does not peel off from the current collector 23, the discharge capacity of a non-aqueous secondary battery decreases when the bonding between the electrode active material 22 and between the electrode active material 22 and the current collector 23 becomes insufficient due to the expansion and contraction of the electrode active material 22. Therefore, it is preferable that the binder 25 is capable of maintaining the bonding between the electrode active materials 22 and between the electrode active materials 22 and the current collector 23 over a long period of time, and that it can form an electrode 20 in which the electrode active material layer 24 is less likely to peel off from the current collector 23.

[0025] Therefore, the present inventors focused on copolymer 1, which is obtained by copolymerizing a monomer (a1) made of a nonionic compound having only one ethylenically unsaturated bond and a monomer (a2) made of a compound having a carboxyl group and only one ethylenically unsaturated bond, as a polymer that makes it easier to obtain an electrode active material layer 24 that is difficult to peel off from a current collector 23 made of copper foil or the like. They then diligently studied binder compositions for non-aqueous secondary batteries containing this copolymer.

[0026] As a result, a binder composition for non-aqueous secondary batteries was discovered, comprising a copolymer 1 obtained by copolymerizing a raw material monomer (a) containing the above-mentioned monomer (a1) and monomer (a2), and a tackifier 2. When electrodes are formed using such a binder composition for non-aqueous secondary batteries of this embodiment, the binder 25 present between the electrode active materials 22 and between the electrode active materials 22 and the current collector 23 contains the copolymer 1 and the tackifier 2. With this configuration, electrodes with good bonding properties between the electrode active materials 22 and between the electrode active materials 22 and the current collector 23 are obtained. As a result, a non-aqueous secondary battery and a non-aqueous secondary battery electrode with excellent cycle characteristics were discovered.

[0027] Furthermore, the present inventors manufactured an electrode 20 using a binder composition for non-aqueous secondary batteries containing the copolymer 1 and the tackifier 2, and confirmed that the non-aqueous secondary battery having this electrode 20 exhibited excellent cycle characteristics, thus conceiving the electrode 20 of this embodiment.

[0028] The following describes in detail the binder composition for aqueous secondary batteries, the slurry for non-aqueous secondary battery electrodes, the non-aqueous secondary battery electrodes, the non-aqueous secondary battery, and the method for producing the binder composition for non-aqueous secondary batteries according to this embodiment. However, the present invention is not limited to the embodiments shown below.

[0029] Herein, we will explain the following terms used in this specification. "(Meth)acrylic" is a general term for acrylic and methacrylic. "(Meth)acrylate" is a general term for acrylate and methacrylate. Unless otherwise specified, "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond that exhibits radical polymerization properties.

[0030] In a polymer using a compound having an ethylenically unsaturated bond, the structural unit derived from the compound having the ethylenically unsaturated bond means a structural unit in which the chemical structure of the portion of the compound other than the ethylenically unsaturated bond is the same as the chemical structure of the portion of the structural unit in the polymer other than the portion corresponding to the ethylenically unsaturated bond. The ethylenically unsaturated bond of the compound changes into 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)-.

[0031] Furthermore, in the case of polymers of compounds having ionic functional groups and ethylenically unsaturated bonds, for example, as shown in the second structural unit described later, structural units having ionic functional groups such as carboxyl groups are considered to be derived from the same ionic compound, regardless of whether or not some of the functional groups are ion-exchanged. For example, the structural unit represented by -CH2-C(CH3)(COONa)- can also be considered to be a structural unit derived from methacrylic acid.

[0032] Furthermore, for compounds having multiple independent ethylenically unsaturated bonds, one or more ethylenically unsaturated bonds may remain within the structural unit of the polymer of the compound. For example, in the case of a polymer of divinylbenzene, the structural unit derived from divinylbenzene may be a structure without ethylenically unsaturated bonds (a form in which both parts corresponding to the two ethylenically unsaturated bonds of divinylbenzene are incorporated into the polymer chain), or it may be a structure having one ethylenically unsaturated bond (a form in which only the part corresponding to one of the ethylenically unsaturated bonds 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.

[0033] Furthermore, if, after polymerization, the parts of the polymer other than the chain structure corresponding to the ethylenically unsaturated bond, such as functional groups like carboxyl groups, no longer correspond to the chemical structure of the monomer due to chemical reactions, then the structural units of the polymer shall be considered to be structural units derived from the compound containing the ethylenically unsaturated bond in the polymer. For example, when vinyl acetate is polymerized and then saponified, the structural units of the polymer shall be considered to be derived from vinyl alcohol, rather than from vinyl acetate, based on the chemical structure of the polymer.

[0034] In this embodiment, the term "class" attached to the compound name refers to a group of compounds that include the compound structure in question, and also includes compounds having substituents.

[0035] <1. Binder composition for non-aqueous secondary batteries> The binder composition for non-aqueous secondary batteries of this embodiment (hereinafter sometimes referred to as "binder composition") comprises a copolymer 1 having a first structural unit and a second structural unit, as described later, and a tackifier 2. The binder composition of this embodiment may contain an aqueous medium, and it is preferable that the copolymer 1 and the tackifier 2 are dispersed in the aqueous medium, as described later. The binder composition of this embodiment may not contain an aqueous medium and may consist of a non-volatile component comprising the copolymer 1 having a first structural unit and a second structural unit, and the tackifier 2.

[0036] The binder composition of this embodiment may contain, along with the copolymer 1 having a first structural unit and a second structural unit, and the tackifier 2, other components. Specifically, the binder composition of this embodiment may contain, for example, a polymer without a first structural unit and / or a second structural unit, a surfactant, or components used in the synthesis of copolymer 1 as other components.

[0037] (Copolymer 1) The copolymer 1 contained in the binder composition 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 1 contained in the binder composition of this embodiment may include, in addition to the first and second structural units, a third structural unit derived from a monomer (a3) ​​consisting of a plurality of independent ethylenically unsaturated bonds that does not correspond to monomer (a1) or monomer (a2), and / or a fourth structural unit derived from another monomer (a4) that does not correspond to any of monomers (a1) to monomer (a3).

[0038] [First structural unit] The first structural unit in copolymer 1 contained in the binder composition of this embodiment is derived from monomer (a1). Monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond. That is, monomer (a1) is a compound that does not have either anionic or cationic functional groups. However, silane compounds are not included in monomer (a1). Monomer (a1) may consist of only one compound or a combination of two or more compounds.

[0039] It is preferable to use at least one of (meth)acrylic acid esters and aromatic compounds having ethylenically unsaturated bonds as monomer (a1), and it is more preferable to use a combination of both compounds. The (meth)acrylic acid ester is more preferably an alkyl (meth)acrylic acid ester. The number of carbon atoms in the alkyl group of the alkyl (meth)acrylic acid ester is preferably 1 to 20. In this case, monomer (a1) other than alkyl (meth)acrylic acid esters and aromatic compounds having ethylenically unsaturated bonds, as described later, may also be used in combination.

[0040] Examples of alkyl (meth)acrylate esters included 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, and stearyl (meth)acrylate. Among these, it is preferable to include 2-ethylhexyl acrylate because it forms a binder composition that can create an electrode active material layer 24 with excellent electrolyte resistance.

[0041] Examples of aromatic compounds having ethylenically unsaturated bonds used in monomer (a1) include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene. When monomer (a1) contains an aromatic vinyl compound, it is more preferable to include at least one of styrene and α-methylstyrene, as this provides excellent dispersibility in aqueous media, and a non-aqueous secondary battery equipped with an electrode 20 manufactured using the binder composition of this embodiment will have superior cycle characteristics; therefore, the inclusion of styrene is even more preferable.

[0042] Examples of monomers (a1) other than (meth)acrylic acid esters and aromatic compounds having ethylenically unsaturated bonds include compounds having ethylenically unsaturated bonds and polar functional groups, aliphatic hydrocarbon compounds having ethylenically unsaturated bonds, and alicyclic hydrocarbon compounds having ethylenically unsaturated bonds.

[0043] In the monomer (a1) and the compound having an ethylenically unsaturated bond and a polar functional group, the polar functional group preferably contains at least one of a hydroxyl group and a cyano group, and more preferably contains a hydroxyl group. Examples of compounds having ethylenically unsaturated bonds and polar functional groups used in monomer (a1) include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and (meth)acrylonitrile. It is preferable to include 2-hydroxyethyl methacrylate because good polymerization stability is obtained when producing copolymer 1.

[0044] [Second structural unit] The second structural unit in copolymer 1 contained in the binder composition of this embodiment is derived from monomer (a2). Monomer (a2) is a compound having exactly one ethylenically unsaturated bond and a carboxyl group. Monomer (a2) may be a single compound or a combination of two or more compounds. As the monomer (a2), a compound having multiple carboxyl groups in one molecule may be used. That is, copolymer 1 may contain multiple carboxyl groups in a single structural unit.

[0045] Examples of monomers (a2) having a carboxyl 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, monomer (a2) is preferably at least one of acrylic acid, methacrylic acid, and itaconic acid, as it forms a binder composition that can form an electrode 20 with good bonding between electrode active materials 22 and between the electrode active materials 22 and the current collector 23.

[0046] At least a portion of the second structural unit derived from monomer (a2) may form a salt with a basic substance. Examples of monomer (a2) that form a salt include metal salts and ammonium salts of monomer (a2). Examples of metals in the metal salts include alkali metals such as lithium, sodium, and potassium. Specific compounds include lithium (meth)acrylate, lithium itaconate, dilithium itaconate, sodium (meth)acrylate, sodium itaconate, disodium itaconate, ammonium (meth)acrylate, ammonium itaconate, and diammonium itaconate.

[0047] [Third structural unit] Copolymer 1 contained in the binder composition of this embodiment may have a third structural unit as an optional structural unit. This third structural unit is derived from monomer (a3). Monomer (a3) ​​is a compound having multiple independent ethylenically unsaturated bonds. "Independent" means that it is not a conjugated double bond like that of 1,3-butadiene. Therefore, monomer (a3) ​​is a compound capable of forming a crosslinked structure in radical polymerization with monomer (a1) and monomer (a2). Monomer (a3) ​​does not correspond to either monomer (a1) or monomer (a2). Monomer (a3) ​​may be just one compound, or two or more different compounds may be used.

[0048] Examples of monomers (a3) ​​include compounds having two ethylenically unsaturated bonds, such as divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate, and compounds having three or more ethylenically unsaturated bonds, such as trimethylolpropane tri(meth)acrylate. It is preferable to use at least one of divinylbenzene and trimethylolpropane triacrylate because monomer (a3) ​​provides good polymerization stability when producing copolymer 1, and a non-aqueous secondary battery equipped with an electrode 20 produced using a binder composition containing copolymer 1 has lower internal resistance and superior cycle characteristics.

[0049] [Other monomers (a4)] Other monomers (a4) are monomers that do not fall under any of monomers (a1) to monomers (a3). Examples of other monomers (a4) include, but are not limited to, compounds having only one ethylenically unsaturated bond and an anionic functional group other than a carboxyl group, such as a sulfo group or a phosphate group; surfactants having an ethylenically unsaturated bond (hereinafter sometimes referred to as "polymerizable surfactants"); and compounds having an ethylenically unsaturated bond and functioning as a silane coupling agent.

[0050] 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 forming a salt. Among these, it is preferable to use at least one of parastyrene sulfonic acid and parastyrene sulfonate, and more preferable to use parastyrene sulfonate. It is even more preferable to use sodium parastyrene sulfonate because good polymerization stability can be obtained when producing copolymer 1.

[0051] As an example of a polymerizable surfactant, which is another monomer (a4), compounds having an ethylenically unsaturated bond and functioning as a surfactant can be used. Examples of polymerizable surfactants include compounds represented by the following chemical formulas (1) to (4).

[0052] [ka]

[0053] In formula (1), R 1 R is an alkyl group. p is an integer between 10 and 40. 1 It is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms.

[0054] [ka]

[0055] In formula (2), R 2 is an alkyl group. q is an integer between 10 and 12. R 2 The C1 is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms. Examples of compounds represented by formula (2) include polyoxyethylene alkyl ether sulfate salts (Aqualon KH-10, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.).

[0056] [ka]

[0057] In formula (3), R 3 M is an alkyl group. 1 R is either NH4 or Na. 3 It is preferably an alkyl group having 10 to 40 carbon atoms, and more preferably a linear, unsubstituted alkyl group having 10 to 40 carbon atoms.

[0058] [ka]

[0059] In formula (4), R 4 is an alkyl group. M 2 is NH4 or Na. R 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.

[0060] Examples of the compound having an ethylenically unsaturated bond and functioning as a silane coupling agent, which is an example of the other monomer (a4), include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltriethoxysilane, and the like.

[0061] [Content ratio of each structural unit in copolymer 1] The content ratio of each structural unit in copolymer 1 contained in the binder composition of the present embodiment is regarded as the same as the content ratio of each monomer in the total amount of monomer components used for producing copolymer 1.

[0062] (Content ratio of the first structural unit in all structural units) The content ratio of the first structural unit in all structural units of copolymer 1 (in other words, the content ratio of monomer (a1) in the total amount of monomer components used for producing copolymer 1) is preferably 60% by mass or more, more preferably 70% by mass or more, still 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 copolymer 1. The content ratio of the first structural unit in all structural units is preferably 97% by mass or less, more preferably 95% by mass or less, and still more preferably 94% by mass or less. This is because it can become a binder composition capable of forming an electrode 20 with good binding properties between electrode active materials 22 and between electrode active material 22 and current collector 23.

[0063] Regarding the composition of monomer (a1), it is preferable to appropriately adjust the type and amount of compound in order to adjust the glass transition temperature of copolymer 1 or to adjust the polymerization rate according to the molecular design. Specifically, when 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 the total 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. This is because when copolymer 1 is dispersed in an aqueous medium to produce a binder composition, copolymer 1 will have excellent dispersibility. The content of structural units derived from the aromatic compound having an ethylenically unsaturated bond in the total structural units is preferably 60% by mass or less.

[0064] (Content of the second structural unit in the total structural units) The content of the second structural unit in the total structural units of copolymer 1 (in other words, the content of monomer (a2) in the total amount of monomer components used in the production of copolymer 1) 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, even more preferably 4.0% by mass or more, and particularly preferably 5.0% by mass or more. This is because the binder composition allows for better bonding between the electrode active materials 22 and between the electrode active materials 22 and the current collector 23 to form an electrode 20. The content of the second structural unit in the total 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 copolymer 1.

[0065] (Content of the third structural unit in all structural units) When the copolymer 1 contained in the binder composition of this embodiment contains a third structural unit, the content of the third structural unit in the total structural units of copolymer 1 (in other words, the content of monomer (a3) ​​in the total amount of monomer components used in the production of copolymer 1) 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 monomer (a3) ​​as an internal crosslinking agent is significantly obtained, the degradation of copolymer 1 is suppressed, and copolymer 1 can be used as a material for a binder composition that yields a non-aqueous secondary battery with superior cycle characteristics. The content of the third structural unit in the total structural units of copolymer 1 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 copolymer 1 can be suppressed.

[0066] (Content of the fourth structural unit in all structural units) In this embodiment, when copolymer 1 contained in the binder composition 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 the total structural units of copolymer 1 (in other words, the content of monomer (a4) in the total amount of monomer components used in the production of copolymer 1) 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 copolymer 1. The content of the fourth structural unit in the total structural units of copolymer 1 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 copolymer 1 can be appropriately adjusted.

[0067] In this embodiment, when copolymer 1 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 the total structural units of copolymer 1 (in other words, the content of monomer (a4) in the total amount of monomer components used in the production of copolymer 1) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.08% by mass or more. This is because the effect of including a polymerizable surfactant becomes significant, and good polymerization stability is obtained when producing copolymer 1. The content of the fourth structural unit in the total structural units of copolymer 1 is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 1.0% by mass or less, and particularly preferably 0.5% by mass. This is because the particle size, viscosity, etc. of copolymer 1 can be appropriately adjusted.

[0068] [Glass transition temperature (Tg) of copolymer 1] The glass transition temperature (Tg) of copolymer 1 contained in the binder composition of this embodiment is the peak top temperature of the DDSC chart obtained as the temperature derivative of the DSC, by performing DSC measurements using a differential scanning calorimetry (DSC) instrument (EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Corporation) at a heating rate of 10°C / min under a nitrogen gas atmosphere.

[0069] The glass transition temperature (Tg) of copolymer 1 is preferably -30°C or higher, and more preferably -10°C or higher. This is because a non-aqueous secondary battery equipped with an electrode 20 manufactured using a binder composition containing copolymer 1 will have excellent cycle characteristics. The glass transition temperature (Tg) of copolymer 1 is preferably 100°C or lower, more preferably 50°C or lower, and even more preferably 40°C or lower. This is because it improves the film-forming properties of the binder composition, resulting in a non-aqueous secondary battery equipped with an electrode 20 manufactured using the binder composition having superior cycle characteristics.

[0070] [Average particle size d50 of emulsion particles containing copolymer 1] In this embodiment, the copolymer 1 contained in the binder composition is preferably in the form of emulsion particles containing copolymer 1 when the binder composition contains an aqueous medium described later. The average particle diameter d50 of the emulsion particles containing copolymer 1 contained in the binder composition of this embodiment is preferably 0.18 μm or more, and more preferably 0.20 μm or more. This is because when the average particle diameter d50 is 0.18 μm or more, an electrode 20 can be formed in which the electrode active material layer 24 is less likely to peel off from the current collector 23.

[0071] The average particle size d50 of the emulsion particles containing copolymer 1 is preferably 1.0 μm or less, more preferably 0.80 μm or less, even more preferably 0.60 μm or less, and particularly preferably 0.50 μm or less. When the average particle size d50 of the emulsion particles containing copolymer 1 is 1.0 μm or less, suitable pressing conditions can be used when pressing the electrode sheet on which the electrode active material layer 24 is formed on the current collector 23 in order to manufacture the electrode 20 using the binder composition. As a result, the electrode active material 24 can be firmly bound to the current collector 23.

[0072] The average particle size d50 of the emulsion particles containing copolymer 1 can be adjusted by known methods. For example, it can be adjusted by the amount of surfactant added when producing copolymer 1 by emulsion polymerization, the selection of raw material monomers, etc. According to emulsion polymerization, a binder composition containing emulsion particles containing copolymer 1 can be easily produced.

[0073] [Method for producing copolymer 1] The copolymer 1 contained in the binder composition of this embodiment can be produced, for example, by the method shown below. Copolymer 1 can be produced by copolymerizing (polymerization step) raw material monomers that include monomer (a1), monomer (a2), and optionally monomer (a3) ​​consisting of a compound having multiple independent ethylenically unsaturated bonds, and / or other monomers (a4). Hereinafter, the monomers (components (a1) to (a4)) used to synthesize copolymer 1 may be collectively referred to as raw material monomer (a).

[0074] One method for copolymerizing the raw material monomer (a) is emulsion polymerization, in which the raw material monomer (a) is emulsion polymerized in an aqueous medium (b). When producing copolymer 1 by emulsion polymerization, in addition to the raw material monomer (a) and the aqueous medium (b), components such as a surfactant (c) that does not polymerize, a basic substance (d), a radical polymerization initiator (e), and a chain transfer agent (f) can be used.

[0075] [Aqueous medium (b)] The aqueous medium (b) is 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 long as polymerization stability is not impaired, a mixture of water and a hydrophilic solvent may be used as the aqueous medium (b).

[0076] [Non-polymerizable surfactants (c)] When producing copolymer 1 by emulsion polymerization, a nonpolymerizable surfactant (c) may be included in the solution containing the aqueous medium (b) and the raw material monomer (a) during emulsion polymerization. A nonpolymerizable surfactant (c) is a surfactant (c) that does not have polymerizable unsaturated bonds 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. It is preferable to use an anionic surfactant or a nonionic surfactant as the surfactant (c).

[0077] 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) described above may be used alone or in combination of two or more types.

[0078] [Basic substances (d)] When producing copolymer 1 by emulsion polymerization, a basic substance (d) may be added to the emulsion polymerization solution containing the aqueous medium (b) and raw material monomer (a), and / or to the dispersion after 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 within an appropriate range, and the stability of the solution during emulsion polymerization and / or the dispersion after emulsion polymerization is improved.

[0079] Examples of basic substances (d) to be added to the emulsion polymerization solution and / or the dispersion after emulsion polymerization include ammonia, triethylamine, sodium hydroxide, and lithium hydroxide. These basic substances (d) may be used individually or in combination of two or more.

[0080] [Radical polymerization initiator (e)] The radical polymerization initiator (e) used when producing copolymer 1 by emulsion polymerization is not particularly limited, and known ones can be used. Examples of radical polymerization initiators (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.

[0081] In this embodiment, when producing copolymer 1 by emulsion polymerization, redox polymerization may be carried out by using a reducing agent such as sodium bisulfite, rongalit, or ascorbic acid in combination with the radical polymerization initiator (e).

[0082] The amount of radical polymerization initiator (e) added (including the reducing agent if used in combination) is preferably 0.001 parts by mass or more, and more preferably 0.002 parts by mass or more, per 100 parts by mass of raw material monomer (a). This is because it is possible to increase the conversion rate of raw material monomer (a) to copolymer 1 when producing copolymer 1 by emulsion polymerization. The amount of radical polymerization initiator (e) added is preferably 10 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of raw material monomer (a). This is because it is possible to increase the molecular weight of copolymer 1 and reduce the swelling rate of the electrode 20 produced using the binder composition of this embodiment in relation to the electrolyte.

[0083] [Chain transfer agent (f)] The chain transfer agent (f) used in the production of copolymer 1 by emulsion polymerization is used to adjust the molecular weight of copolymer 1 obtained by emulsion polymerization. Examples of chain transfer agents (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.

[0084] [Emulsion polymerization method] Examples of emulsion polymerization methods used in producing copolymer 1 include a method in which each component used for emulsion polymerization is continuously supplied into the reaction vessel while emulsion polymerization is carried out. The temperature of emulsion polymerization is not particularly limited, but is preferably 30 to 90°C, preferably 50 to 85°C, and more preferably 55 to 80°C. Emulsion polymerization is preferably carried out while stirring. Furthermore, it is preferable to continuously supply the raw material monomer (a) and radical polymerization initiator (e) to the solution during emulsion polymerization so that the concentrations of the raw material monomer (a) and radical polymerization initiator (e) in the solution during emulsion polymerization become uniform.

[0085] If the binder composition of this embodiment consists of copolymer 1 and tackifier 2 dispersed in an aqueous medium (B) described later, it can be manufactured more easily than, for example, an aqueous medium containing particles in which the tackifier is arranged within the copolymer, or particles in which the tackifier is copolymerized together with the raw material monomer. Furthermore, the binder composition offers greater flexibility in the content of tackifier 2, allowing the content of tackifier 2 to be appropriately changed depending on the application.

[0086] (Adhesion agent) The type of tackifier 2 included in the binder composition of this embodiment is not particularly limited, as long as it does not hinder the effects of the present invention. The tackifier 2 may be used alone or in combination of two or more types. Examples of tackifier 2 include natural resins such as rosin resins and terpene resins; and petroleum resins such as hydrogenated petroleum resins and unhydrogenated petroleum resins. It is preferable that tackifier 2 be at least one selected from rosin resins, terpene resins, and hydrogenated petroleum resins, and more preferably at least one selected from terpene resins and hydrogenated petroleum resins, in order to avoid increasing the internal resistance of the battery manufactured using the binder composition.

[0087] Examples of rosin resins include rosin resins such as gum rosin, tall oil rosin, and wood rosin; modified rosin resins such as hydrogenated rosin resins, disproportionated rosin resins, and polymerized rosin resins; and rosin ester resins such as glycerin esters and pentaerythritol esters of these rosin resins and modified rosin resins. Rosin resins may also be in the form of emulsions obtained by emulsifying them. A specific example of a commercially available rosin resin is Hariester DS-70L (manufactured by Harima Chemicals Group Co., Ltd.), which is in the form of an emulsion.

[0088] Examples of terpene resins include terpene resins mainly composed of α-pinene, β-pinene, dipentene, etc., aromatically modified terpene resins, hydrogenated terpene resins, and terpene phenol resins. Terpene resins may also be in the form of emulsions obtained by emulsifying these. A specific example of a commercially available terpene resin is YS Resin PX800 (manufactured by Yasuhara Chemical Co., Ltd.).

[0089] As the petroleum resin, hydrogenated petroleum resin (hereinafter also referred to as "hydrogenated petroleum resin") may be used, or non-hydrogenated petroleum resin may be used. It is preferable to use hydrogenated petroleum resin because the internal resistance of batteries manufactured using the binder composition is less likely to be high. 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 those in which at least a portion of the unsaturated groups present in these resins have been hydrogenated. 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 form a binder composition that can form electrodes with better bonding between electrode active materials and between electrode active materials and current collectors. Specific examples of commercially available alicyclic saturated hydrocarbon resins include Alcon M-90 (manufactured by Arakawa Chemical Industries, Ltd.) and Alcon M-135 (manufactured by Arakawa Chemical Industries, Ltd.).

[0090] The softening point of the tackifier 2 is not particularly limited. For example, the softening point of the tackifier 2 is preferably 25 to 200°C, more preferably 25 to 175°C, and even more preferably 25 to 150°C. A softening point of 25°C or higher is preferable because it provides better heat resistance and results in a non-aqueous secondary battery with superior cycle characteristics. A softening point of 200°C or lower results in a binder composition that allows for better bonding between electrode active materials and between electrode active materials and current collectors, thereby forming electrodes with better adhesion. As a result, a non-aqueous secondary battery equipped with electrodes using this composition exhibits superior cycle characteristics.

[0091] The softening point of the tackifier 2 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, for example, when the tackifier 2 is a hydrogenated petroleum resin. A softening point of 70°C or higher is preferable because it results in better heat resistance and a non-aqueous secondary battery with superior cycle characteristics. A softening point of 140°C or lower results in a binder composition that can form electrodes with better bonding between electrode active materials and between electrode active materials and current collectors. The softening point of tackifier 2 is the value measured by a ring-type softening point measuring device in accordance with JIS K6220-1:2001.

[0092] [Content of tackifier 2 in the binder composition] In this embodiment, the content of tackifier 2 relative to the amount of copolymer 1 in the binder composition is considered to be the same as the mass of tackifier 2 relative to the total mass of monomer components used in the production of copolymer 1.

[0093] The content of the tackifier 2 is preferably 0.10 parts by mass or more and 50 parts by mass or less, more preferably 0.20 parts by mass or more and 30 parts by mass or less, even more preferably 0.30 parts by mass or more and 15 parts by mass or less, and particularly preferably 1.0 part by mass or more and 8.0 parts by mass or less, based on 100 parts by mass of copolymer 1 (in other words, monomer components used to produce copolymer 1) contained in the binder composition of this embodiment. When the content of the tackifier 2 is 0.10 parts by mass or more, the effect of the binder composition containing the tackifier 2 becomes significant. As a result, the binder composition becomes capable of forming electrodes 20 with better bonding between the electrode active materials 22 and between the electrode active materials 22 and the current collector 23. From the above viewpoint, the content of the tackifier 2 is more preferably 0.20 parts by mass or more, even more preferably 0.30 parts by mass or more, and particularly preferably 1.0 part by mass or more. Furthermore, if the content of the tackifier 2 is 50 parts by mass or less, the content of copolymer 1 in the binder composition can be sufficiently ensured, and the non-aqueous secondary battery equipped with an electrode 20 containing a binder 25 made of the non-volatile components of the binder composition will have lower internal resistance. From the above viewpoint, the content of the tackifier 2 is more preferably 30 parts by mass or less, even more preferably 15 parts by mass or less, and particularly preferably 8.0 parts by mass or less.

[0094] The binder composition of this embodiment, in one form, contains a copolymer 1, a tackifier 2, and an aqueous medium (B). The copolymer 1 and the tackifier 2 may be dispersed in the aqueous medium (B), i.e., a dispersion.

[0095] [Aqueous medium (B)] The aqueous medium (B) is the same as the aqueous medium (b) used in the synthesis of copolymer 1, as described above. The aqueous medium (B) may be the same as the aqueous medium (b) used in the synthesis of copolymer 1, or it may be different.

[0096] If the binder composition of this embodiment contains emulsion particles obtained by producing copolymer 1 using an emulsion polymerization method, the aqueous medium (B) may be the aqueous medium (b) used in the synthesis of copolymer 1. Alternatively, aqueous medium (B) may be obtained by adding a new aqueous medium to the aqueous medium (b) used in the synthesis of copolymer 1. Alternatively, aqueous medium (B) may be obtained by replacing part or all of the aqueous medium (b) contained in the dispersion obtained by producing copolymer 1 by emulsion polymerization with a new aqueous solvent. In this case, the new aqueous medium used may have the same composition as the aqueous medium (b) used in the synthesis of copolymer 1, or it may have a different composition.

[0097] The binder composition of this embodiment may contain known additives as appropriate, as long as they do not impair the effects of the present invention.

[0098] [Non-volatile content concentration of the binder composition] The binder 25 contained in the electrode 20 manufactured using the binder composition of this embodiment consists of components (non-volatile components) that remain without volatilizing even when a heating process is performed in the manufacturing method of a non-aqueous secondary battery described later. Specifically, the components constituting the binder 25 are those that remain after weighing 1 g of the binder composition, placing it on an aluminum dish with a diameter of 5 cm, placing it in a dryer, and drying it for 1 hour at 1 atmosphere (1013 hPa) and a temperature of 105°C while circulating the air inside the dryer.

[0099] The non-volatile content concentration of the binder composition in 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 ensure that the amount of active ingredients contained in the binder composition is sufficiently large. The non-volatile content concentration of the binder composition can be adjusted by the content of the aqueous medium (B) contained in the binder composition. The non-volatile content concentration of the binder composition is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. This is because it suppresses the increase in viscosity of the binder composition, making it easier to prepare a slurry for non-aqueous secondary battery electrodes.

[0100] The total content of copolymer 1 and tackifier in the nonvolatile components of the binder composition of this embodiment is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and still more preferably 98% by mass or more. This is because the effects of the binder composition containing copolymer 1 and tackifier 2 become significant. Furthermore, the total content of copolymer 1 and tackifier in the nonvolatile components of the binder composition of this embodiment may be 100% by mass or less.

[0101] <2. Method for producing binder compositions for non-aqueous secondary batteries> Next, a method for producing the binder composition of this embodiment will be described. One embodiment of the method for producing the binder composition comprises a mixing step of mixing the copolymer 1 and the tackifier 2 described above. Furthermore, it may also include a polymerization step of synthesizing the copolymer 1 described above. The method for producing the binder composition of this embodiment preferably includes a polymerization step of synthesizing the copolymer 1 described above and a mixing step of mixing the obtained copolymer 1 and the tackifier 2 described above.

[0102] In the mixing step of this embodiment, known methods can be used to mix the copolymer 1 and the tackifier 2, and are not particularly limited. For example, methods for mixing the copolymer 1 and the tackifier 2 include using a mixing device such as a stirring type, rotary type, or shaking type.

[0103] When producing a binder composition in which copolymer 1 and tackifier 2 are dispersed in an aqueous medium (B), for example, a method can be used in which a dispersion obtained by producing copolymer 1 by emulsion polymerization is mixed with tackifier 2 and an aqueous medium (B) which may be added as needed, or a method can be used in which copolymer 1 obtained by a method other than emulsion polymerization is mixed with tackifier 2 and an aqueous medium (B).

[0104] When copolymer 1 obtained by a method other than emulsion polymerization is used as copolymer 1, known methods such as using a surfactant can be used to disperse copolymer 1 in an aqueous medium (B). Examples of surfactants include the same surfactants exemplified as nonpolymerizable surfactants (c) that can be used when producing copolymer 1 by emulsion polymerization.

[0105] Furthermore, the method for dispersing the tackifier 2 in the aqueous medium (B) is not particularly limited. The tackifier 2 may be dispersed using a surfactant.

[0106] Here, possible forms of the binder composition of this embodiment will be described with reference to Figures 2, 3, and 4. However, the forms of the binder composition of this embodiment are not limited to the examples described below.

[0107] Figure 2 is a schematic diagram illustrating an example of the binder composition of this embodiment. The binder composition shown in Figure 2 comprises emulsion particles (dispersed particles) 3 containing copolymer 1, a tackifier 2, and an aqueous medium (B). In the binder composition shown in Figure 2, the emulsion particles 3 containing copolymer 1 and the tackifier 2 are dispersed in the aqueous medium (B). The tackifier 2 may or may not have a particulate shape.

[0108] The copolymer 1 shown in Figure 2, as one form conjectured by the inventors, has a particulate structure (bulbous structure) consisting of randomly coiled polymer chains, i.e., chain-like molecules. The emulsion particles 3 containing copolymer 1 shown in Figure 2 are a soap-free emulsion without surfactants and are dispersed in an aqueous medium (B). The emulsion particles 3 containing copolymer 1 can be produced by the emulsion polymerization method described above. The tackifier 2 shown in Figure 2, as one form conjectured by the inventors, may be present in the vicinity of the emulsion particles 3 or in contact with the emulsion particles 3.

[0109] Figure 3 is a schematic diagram illustrating another example of the binder composition of this embodiment. In the binder composition of this embodiment, for example, as shown in Figure 3, emulsion particles containing a tackifier 2 and a surfactant 4 may be present in an aqueous medium (B). The emulsion particles containing the tackifier 2 and the surfactant 4 may be present in the vicinity of the emulsion particles 3, or may be present in contact with the emulsion particles 3.

[0110] The binder composition shown in Figure 3 can be produced by mixing emulsion particles containing tackifier 2 and surfactant 4 with copolymer 1 and an aqueous medium (B). Compared to tackifier 2 alone, the emulsion particles containing tackifier 2 and surfactant 4 are easier to handle and exhibit excellent dispersibility in the aqueous medium (B) due to the repulsion between the emulsion particles.

[0111] Figure 4 is a schematic diagram illustrating another example of the binder composition of this embodiment. In the binder composition of this embodiment, as shown in Figure 4, the emulsion particles 31 may be such that the copolymer 1 is surrounded by a surfactant 41 with its hydrophilic groups facing outward. The surfactant 41 does not correspond to the raw material monomer (a) containing a polymerizable surfactant as another monomer (a4) used in the production of the copolymer 1, but is derived from a non-polymerizable surfactant (c).

[0112] The tackifier 2 shown in Figure 4 may, as one form conjectured by the inventors, be present in the vicinity of the emulsion particles 31, or may be present in contact with the emulsion particles 31 (surfactant 41). Furthermore, if the binder composition shown in Figure 4 contains surfactant 41 that is present in excess and free in the aqueous medium (B) when the emulsion particles 31 are manufactured, the tackifier 2 may exist as emulsion particles containing surfactant 41. In the binder composition shown in Figure 4, the dispersibility of the emulsion particles 31 in the aqueous medium is good, making it easy to handle. Also, because the dispersibility of the emulsion particles 31 is good, the distribution of the binder in the electrode active material layer becomes uniform, resulting in an electrode with better bonding between electrode active materials and between the electrode active material and the current collector.

[0113] When electrodes are formed using the binder composition according to this embodiment, for example, as shown in Figures 2 to 4, a binder containing copolymer 1 and tackifier 2 is considered to exist between the electrode active materials and between the electrode active materials and the current collector. Therefore, when electrodes are formed using the binder composition according to this embodiment, electrodes with good bonding between the electrode active materials and between the electrode active materials and the current collector are obtained. As a result, a non-aqueous secondary battery and a non-aqueous secondary battery electrode with excellent cycle characteristics can be obtained.

[0114] <3. Slurry for non-aqueous secondary battery electrodes> Next, the slurry for non-aqueous secondary battery electrodes of this embodiment will be described in detail. The slurry for non-aqueous secondary battery electrodes comprises a binder composition containing copolymer 1, tackifier 2, and aqueous medium (B), and an electrode active material. Preferably, the electrode active material contained in the slurry for non-aqueous secondary battery electrodes is dispersed in the aqueous medium. In addition to copolymer 1, tackifier 2, electrode active material, and aqueous medium, the slurry for non-aqueous secondary battery electrodes may also contain additives such as thickeners and conductive additives, and the above-mentioned components used in the production of the binder composition.

[0115] [Total content of copolymer 1 and tackifier 2] The total content of copolymer 1 and tackifier 2 in the slurry for non-aqueous secondary battery electrodes is preferably 0.50 parts by mass or more, and more preferably 1.0 part by mass or more, per 100 parts by mass of electrode active material. This is to fully exhibit the effects of including the binder composition of this embodiment. The total content of copolymer 1 and tackifier 2 in the slurry for non-aqueous secondary battery electrodes is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, per 100 parts by mass of electrode active material. This is because it allows for a higher content of electrode active material in the slurry for non-aqueous secondary battery electrodes.

[0116] [Electrode active material] The electrode active material contained in the slurry for non-aqueous secondary battery electrodes is a material that can intercarry and deintercalate charge carrier ions such as lithium ions. The charge carrier ions are preferably alkali metal ions, more preferably lithium ions, sodium ions, and potassium ions, and even more preferably lithium ions.

[0117] When a non-aqueous secondary battery electrode manufactured using a slurry for non-aqueous secondary battery electrodes is the aqueductor, the electrode active material is the aqueductor active material. The aqueductor active material preferably contains at least one of the following: carbon materials, silicon-containing materials, and titanium-containing materials. Examples of carbon materials used as aqueductor active materials include coke such as petroleum coke, pitch coke, and coal coke; carbonized organic polymers; and graphite such as artificial graphite and natural graphite. Examples of silicon-containing materials used as aqueductor active materials include elemental silicon and silicon compounds such as silicon oxide. Examples of titanium-containing materials used as aqueductor active materials include lithium titanate. These materials used as aqueductor active materials may be used individually, or they may be used in mixtures or composites.

[0118] The negative electrode active material preferably contains at least one of carbon materials and silicon-containing materials, and more preferably contains carbon materials. This is because the copolymer 1 and tackifier 2 contained in the slurry for non-aqueous secondary battery electrodes have a significant effect in improving the binding between the negative electrode active materials 22 and between the negative electrode active materials 22 and the current collector 23.

[0119] When a non-aqueous secondary battery electrode manufactured using a slurry for non-aqueous secondary battery electrodes is the positive electrode, the electrode active material is the positive electrode active material. As the positive electrode active material, a material with a higher standard electrode potential than the negative electrode active material is used. Specifically, examples of positive electrode active materials include lithium composite oxides containing nickel, such as Ni-Co-Mn lithium composite oxides, Ni-Mn-Al lithium composite oxides, and Ni-Co-Al lithium composite oxides, as well as chalcogen compounds such as lithium cobalt oxide (LiCoO2), spinel-type lithium manganate (LiMn2O4), olivine-type lithium iron phosphate, TiS2, MnO2, MoO3, and V2O5. These materials used as positive electrode active materials may be used individually or in combination of two or more types.

[0120] [Aqueous medium] The aqueous medium contained in the slurry for the non-aqueous secondary battery electrode of this embodiment is the same as the aqueous medium (b) described for the synthesis of copolymer 1. The aqueous medium may be the same as or different from the aqueous medium (b) used for the synthesis of copolymer 1.

[0121] The aqueous medium contained in the slurry for non-aqueous secondary battery electrodes of this embodiment may be only the aqueous medium (B) contained in the binder composition. Alternatively, a new aqueous medium may be added to the aqueous medium (B) contained in the binder composition. Furthermore, part or all of the aqueous medium (B) contained in the binder composition may be replaced with a new aqueous solvent. The slurry for non-aqueous secondary battery electrodes of this embodiment may also contain additives as appropriate. For example, the following materials are listed below.

[0122] [Thickening agent] Examples of thickeners that may be included in the slurry for non-aqueous secondary battery electrodes include celluloses such as carboxymethylcellulose (CMC), hydroxyethylcellulose, and hydroxypropylcellulose, ammonium salts of celluloses, alkali metal salts of celluloses, polyvinyl alcohol, and polyvinylpyrrolidone. It is preferable that the thickener contains at least one of carboxymethylcellulose, ammonium salts of carboxymethylcellulose, and alkali metal salts of carboxymethylcellulose, as this facilitates the dispersion of the electrode active material in the slurry for non-aqueous secondary battery electrodes.

[0123] The amount of thickener contained in the slurry for non-aqueous secondary battery electrodes 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 electrode active material. This is because it improves the bonding between the electrode active material 22 contained in the non-aqueous secondary battery electrode prepared using the slurry for non-aqueous secondary battery electrodes, and between the electrode active material 22 and the current collector 23. The amount of thickener contained in the slurry for non-aqueous secondary battery electrodes 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 electrode active material. This is because it improves the coating properties of the slurry for non-aqueous secondary battery electrodes.

[0124] [Conductive additive] Examples of conductive additives that may be included in the slurry for non-aqueous secondary battery electrodes of this embodiment include carbon black and carbon fibers. Examples of carbon black include furnace black, acetylene black, Denka Black (registered trademark) (manufactured by Denka Co., Ltd.), and Ketjen Black (registered trademark) (manufactured by Ketjen Black International Co., Ltd.). Examples of carbon fibers include carbon nanotubes and carbon nanofibers. As a carbon nanotube, VGCF (registered trademark, manufactured by Showa Denko K.K.), which is a gas-phase carbon fiber, is a preferred example.

[0125] [Method for manufacturing slurry for non-aqueous secondary battery electrodes] A method for producing the slurry for non-aqueous secondary battery electrodes according to this embodiment includes, for example, mixing a binder composition in which copolymer 1 and tackifier 2 are dispersed in an aqueous medium (B), an electrode active material, a thickener as needed, a conductive additive as needed, and other components as needed. The mixing order of each component, which is the raw material for the slurry for non-aqueous secondary battery electrodes, is not particularly limited and can be determined as appropriate. Methods for mixing each component include using a mixing device such as a stirring type, rotary type, or shaking type.

[0126] <4. Nonaqueous secondary battery electrode> Next, the non-aqueous secondary battery electrode of this embodiment will be described in detail. The electrode 20 of this embodiment contains the non-volatile components of the binder composition of this embodiment. As shown in Figure 1, the electrode 20 of this embodiment comprises a current collector 23 and an electrode active material layer 24 formed on the current collector 23. The shape of the electrode 20 of this embodiment is not particularly limited and can be, for example, a laminate or a wound body. The area in which the electrode active material layer 24 is formed on the current collector 23 is not particularly limited. The electrode active material layer 24 may be formed over the entire surface of the current collector 23, or it may be formed on only a portion of the surface of the current collector 23. If the current collector 23 is in the shape of a plate, foil, etc., the electrode active material layer 24 may be formed on both sides of the current collector 23, or it may be formed on only one side.

[0127] [Current collector] The current collector 23 is preferably a metal sheet with a thickness of 0.001 mm or more and 0.5 mm or less. Examples of metals forming the metal sheet include iron, copper, aluminum, nickel, and stainless steel. When the electrode 20 in this embodiment is the negative electrode of a lithium-ion secondary battery, the current collector 23 is preferably a copper foil.

[0128] [Electrode active material layer] The electrode active material layer 24 contains the binder 25, which is the non-volatile component of the binder composition of this embodiment, and the electrode active material 22. The electrode active material layer 24 may also contain a conductive additive, a thickener 21, etc. The electrode active material 22, conductive additive, and thickener 21 can all be the same as those exemplified as components for a slurry for non-aqueous secondary battery electrodes.

[0129] [Method for manufacturing electrodes of non-aqueous secondary batteries] The electrode 20 of this embodiment can be manufactured, for example, by the method shown below. First, the slurry for non-aqueous secondary battery electrodes of this embodiment is applied to the current collector 23. Next, the slurry for non-aqueous secondary battery electrodes is dried. This forms an electrode active material layer 24 on the current collector 23, which contains the binder 25, a non-volatile component of the binder composition of this embodiment, forming an electrode sheet. After that, the electrode sheet is cut to an appropriate size as needed. By performing the above steps, the electrode 20 of this embodiment is obtained.

[0130] The method for applying the slurry for non-aqueous secondary battery electrodes onto the current collector 23 is not particularly limited, but examples include the reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dip method, and squeeze method. Among these application methods, considering the viscosity and other physical properties and drying properties of the slurry for non-aqueous secondary battery electrodes, it is preferable to use one of the methods selected from the direct roll method, doctor blade method, knife method, or extrusion method. This is because an electrode active material layer 24 with a smooth surface and small variation in thickness can be obtained.

[0131] When applying the slurry for non-aqueous secondary battery electrodes to both sides of the current collector 23, it may be applied sequentially to one side at a time, or to both sides simultaneously. Furthermore, the slurry for non-aqueous secondary battery electrodes may be applied continuously or intermittently to the current collector 23. The amount of slurry applied to the non-aqueous secondary battery electrode can be appropriately determined according to the battery's design capacity and the composition of the slurry.

[0132] The method for drying the slurry for non-aqueous secondary battery electrodes applied to the current collector 23 is not particularly limited, but for example, methods selected from hot air, reduced pressure or vacuum environment, (far) infrared radiation, and low-temperature air can be used individually or in combination. The drying temperature and drying time when drying the slurry for non-aqueous secondary battery electrodes can be appropriately adjusted depending on the concentration of non-volatile components in the slurry, the amount applied to the current collector 23, etc. The drying temperature is preferably 40°C to 350°C, and more preferably 60°C to 100°C from the viewpoint of productivity. The drying time is preferably 1 minute to 30 minutes.

[0133] The electrode sheet, on which the electrode active material layer 24 is formed on the current collector 23, may be cut to a size and shape suitable for the electrode 20. The method of cutting the electrode sheet is not particularly limited, and for example, slitting, laser cutting, wire cutting, cutting machines, die cutting machines, etc., can be used.

[0134] In this embodiment, the electrode sheet may be pressed before or after cutting, if necessary. This allows the electrode active material 22 to be firmly bonded to the current collector 23, and the thickness of the electrode 20 is reduced, thereby enabling miniaturization of the non-aqueous secondary battery. A general method can be used for pressing the electrode sheet. In particular, it is preferable to use a die press method or a roll press method. When using the die pressing method, the press pressure is not particularly limited, but 0.5 t / cm 2 5 t / cm² or more 2 The following is preferable. When using the roll press method, the press load is not particularly limited, but it is preferably 0.5 t / cm or more and 8 t / cm or less. This is because it is 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 the electrode active material 22.

[0135] <5.Nonaqueous secondary battery> Next, a lithium-ion secondary battery will be described as a preferred example of a non-aqueous secondary battery according to this embodiment. Note that the configuration of the non-aqueous secondary battery of the present invention is not limited to the example shown below. The lithium-ion secondary battery of this embodiment has a positive electrode, a negative electrode, an electrolyte, and known components such as separators, which may be provided as needed, housed in an outer casing. The shape of the lithium-ion secondary battery may be any shape, such as coin-shaped, button-shaped, sheet-shaped, cylindrical, prismatic, or flat.

[0136] [Positive electrode / Negative electrode] In this embodiment, the lithium-ion secondary battery comprises an electrode active material layer 24 in which one or both of the positive electrode and the negative electrode contain a binder 25 which is a non-volatile component of the binder composition of this embodiment. In this embodiment, it is preferable that at least the negative electrode of the lithium-ion secondary battery comprises an electrode active material layer 24 which contains a binder 25 which is a non-volatile component of the binder composition.

[0137] In the lithium-ion secondary battery of this embodiment, if only one of the electrodes, the positive electrode or the negative electrode, is equipped with an electrode active material layer 24 containing the non-volatile components of the binder composition of this embodiment, the electrode that does not contain the non-volatile components of the binder composition of this embodiment may be made using a known binder such as polyvinylidene fluoride instead of the binder composition of this embodiment.

[0138] [Electrolyte] As the electrolyte, a non-aqueous liquid with ionic conductivity is used. Examples of electrolytes include solutions in which the electrolyte is dissolved in an organic solvent, and ionic liquids, with the former being preferred. This is because it allows for the production of lithium-ion secondary batteries with low manufacturing costs and low internal resistance.

[0139] Alkali metal salts can be used as electrolytes and can be appropriately selected depending on the type of electrode active material, etc. Examples of electrolytes include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB 10 Cl 10 Examples include LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, and lithium aliphatic carboxylates. Other alkali metal salts can also be used as electrolytes.

[0140] The organic solvent used to dissolve the electrolyte is not particularly limited, but examples 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 individually or in combination of two or more. Among these, it is preferable to use a combination of linear carbonate solvents as the organic solvent.

[0141] [Exterior] As for the exterior, for example, a material formed from aluminum laminate consisting of aluminum foil and resin film can be used as appropriate, but is not limited to this. [Examples]

[0142] The present invention will be described in detail below with reference to examples and comparative examples. The following examples are provided to facilitate understanding of the present invention. The present invention is not limited to these examples. In the following embodiments, 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. The effects of the present invention were confirmed by comparing it with the negative electrode and lithium-ion secondary battery of the comparative example. Furthermore, unless otherwise specified, the water used in the following examples and comparative examples is deionized water.

[0143] <1. Manufacturing of binder compositions for non-aqueous secondary batteries> (Examples 1 to 6) A monomer emulsion was prepared by mixing the raw material monomers (a) shown in Tables 1 and 2 with 200 parts by mass of water as an aqueous medium (b) in the mass ratios shown in Tables 1 and 2, and emulsifying the mixture. Next, aqueous solutions were prepared by dissolving the radical polymerization initiators (e) shown in Tables 1 and 2 in 50 parts by mass of water in the amounts shown in Tables 1 and 2.

[0144] A separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel was filled with 150 parts by mass of water and heated to 75°C. The monomer emulsion and the aqueous solution in which the radical polymerization initiator (e) was dissolved were continuously supplied to this separable flask over 3 hours while stirring at 75°C to carry out emulsion polymerization and obtain an emulsion.

[0145] The resulting emulsion was cooled to room temperature. Then, 132 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 and 2 were added to the emulsion. This yielded an emulsion in which emulsion particles containing copolymer 1 of Examples 1 to 6 were dispersed in water.

[0146] Emulsified particles containing the copolymers of Examples 1 to 6 were dispersed in water to form an emulsion, which was then mixed with the tackifiers shown in Tables 1 and 2 using a homodisperser in the mass ratios shown in Tables 1 and 2 to produce the non-aqueous secondary battery binder compositions of Examples 1 to 6, which contained the copolymers, tackifiers, and water. In the binder compositions for non-aqueous secondary batteries of Examples 1 to 6, no dispersion abnormalities such as aggregation of emulsion particles containing copolymers and tackifiers in the composition were observed, and the dispersion was maintained.

[0147] (Comparative Example 1) In Comparative Example 1, an emulsion in which only emulsion particles containing the copolymer produced in Example 1 were dispersed in water was used as the binder composition for a non-aqueous secondary battery.

[0148] [Table 1]

[0149] [Table 2]

[0150] The monomer (a4) shown in Tables 1 and 2, polyoxyethylene alkyl ether sulfate (Aqualon KH-10, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), is a polymerizable surfactant. In polymerization initiator (e), Longalit SFS is the trade name for Longalit manufactured by Sumitomo Seika Co., Ltd.

[0151] The tackifiers shown in Tables 1 and 2 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℃ • Emulsion AM-1000-NT (alicyclic saturated hydrocarbon resin): A dispersion (50% concentration) prepared by dispersing a tackifier similar to Alcon M-90 in an aqueous medium using a surfactant. The values ​​listed in Table 2 indicate the amount of emulsion particles containing the tackifier in the dispersion. Manufactured by Arakawa Chemical Industries, Ltd., softening point 100°C.

[0152] Rosin-based resin • Emulsion Hallier DS-70L (rosin ester resin); in aqueous media A dispersion (50% concentration) of rosin ester resin is obtained by dispersing it in water using a surfactant. The values ​​listed in Table 2 indicate the amount of emulsion particles containing tackifier in the dispersion. Manufactured by Harima Chemicals Group Co., Ltd., softening point 70°C. Terpene resins • YS Resin PX800 (Polyterpene Resin): Manufactured by Yasuhara Chemical Co., Ltd., softening point 80℃

[0153] The amounts of ammonia as a basic substance (d) shown in Tables 1 and 2 represent the amount of ammonia contained in aqueous ammonia (parts by mass). The amount of water as aqueous medium (b) shown in Tables 1 and 2 represents the total amount of water (parts by mass) contained in the binder composition for non-aqueous secondary batteries.

[0154] <2. Evaluation of copolymer and non-aqueous binder compositions for secondary batteries> The glass transition temperature (Tg) and particle size (d50) of the copolymers in emulsions containing the copolymers of Examples 1 to 6 and Comparative Example 1, dispersed in water, were measured using the methods described below. The results are shown in Tables 1 and 2. Furthermore, the non-volatile content concentration of the binder compositions for non-aqueous secondary batteries of Examples 1 to 6 and Comparative Example 1 was measured using the method described below. The results are shown in Tables 1 and 2.

[0155] [Glass transition temperature (Tg) of copolymers] A 2 mm thick film made of copolymer was obtained by coating an emulsion in which emulsion particles containing copolymer are dispersed in water onto a release PET (polyethylene terephthalate) film and drying it at 50°C for 5 hours. Square test pieces measuring 2 mm in length and 2 mm in width were cut from the obtained film. The test pieces were sealed in an aluminum pan, and differential scanning calorimetry (DSC) measurements were performed on the test pieces under a nitrogen gas atmosphere at a heating rate of 10°C / min using a differential scanning calorimeter (EXSTAR DSC / SS7020, Hitachi High-Tech Science Corporation). The temperature range for 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 measured, and this temperature was defined as the glass transition temperature Tg (°C) of the copolymer.

[0156] [Particle size (d50) of emulsion particles containing copolymer] The particle size (d50) of the copolymer-containing emulsion particles was measured at room temperature using dynamic light scattering (DLS) with a NANOTORAC WAVE II (manufactured by Microtrac-Bell Co., Ltd.) in an emulsion in which copolymer-containing emulsion particles were dispersed in water.

[0157] [Non-volatile content concentration of binder compositions for non-aqueous secondary batteries] A 1g weighout of a binder composition for non-aqueous secondary batteries containing a copolymer, a tackifier, and water was placed on a 5cm diameter aluminum dish and placed in a drying oven. The mixture was dried for 1 hour at 1 atmosphere (1013 hPa) and 105°C while circulating the air inside the oven, and the mass of the remaining components was measured. The mass ratio (mass%) of the components remaining after drying to the mass (1g) of the binder composition for non-aqueous secondary batteries before drying was calculated and expressed as the non-volatile content concentration (mass%).

[0158] <3. Manufacturing of non-aqueous secondary batteries> Using the binder compositions for non-aqueous secondary batteries of Examples 1 to 6 and Comparative Example 1, negative electrodes were prepared by the methods described below, and lithium-ion secondary batteries, which are non-aqueous secondary batteries of Examples 1 to 6 and Comparative Example 1, were prepared using these negative electrodes.

[0159] [Fabrication of the positive electrode] LiNi as a positive electrode active material 0.6 Mn 0.2 Co 0.2A mixture was obtained by mixing 4 parts by mass of O294, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder. 50 parts by mass of N-methylpyrrolidone were added to the mixture and further mixed to obtain a positive electrode slurry.

[0160] A 15 μm thick aluminum foil was prepared as the positive electrode current collector. The positive electrode slurry was applied to both sides of the positive electrode current collector using the direct roll method. The amount of positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described later was 125 μm per side. The positive electrode slurry applied to the positive electrode current collector was dried at 120°C for 5 minutes, and then pressed using a roll press (manufactured by Sankmetal Co., Ltd., press load 5 t / cm, roll width 7 cm) by the roll press method 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 measuring 50 mm in length and 40 mm in width, and conductive tabs were attached to form the positive electrode.

[0161] [Fabrication of negative electrode (non-aqueous secondary battery electrode)] 96.9 parts by mass of artificial graphite (G49, manufactured by Jiangxi Zichen Technology Co., Ltd.) as the negative electrode active material, 3.6 parts by mass (1.4 parts by mass of non-volatile content) of any of the non-aqueous secondary battery binder compositions prepared in Examples 1 to 6 or Comparative Example 1, and 60 parts by mass of a 2% by mass aqueous solution of CMC (carboxymethylcellulose-sodium salt, manufactured by Nippon Paper Chemicals Co., Ltd., Sunrose® MAC500LC) were mixed, and 16 parts by mass of water was added. The mixture was then mixed using a rotation-orbit mixer (ARE-310, manufactured by Thinky Co., Ltd.) to obtain a negative electrode slurry (slurry for non-aqueous secondary battery electrodes).

[0162] A 10 μm thick copper foil was prepared as the negative electrode current collector. The negative electrode slurry was applied to both sides of the negative electrode current collector using the direct roll method. The 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 later 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 then pressed using a roll press (manufactured by Sankmetal Co., Ltd., press load 8 t / cm, roll width 7 cm) by the roll press method. This resulted in obtaining a negative electrode sheet having negative electrode active material layers on both sides of the negative electrode current collector. The obtained negative electrode sheet was cut into a rectangle measuring 52 mm in length and 42 mm in width, and conductive tabs were attached to form the negative electrode.

[0163] [Fabrication of non-aqueous secondary batteries] A separator made of a porous polyolefin film (polyethylene, 25 μm thick) was interposed between the positive and negative electrodes, and the positive electrode active material layer and the negative electrode active material layer were laminated so that they faced each other. These were then housed in an outer casing (battery pack) made of aluminum laminate material. Subsequently, an electrolyte solution was injected into the outer casing, vacuum impregnation was performed, and the battery was packed using a vacuum heat sealer to obtain a lithium-ion secondary battery. As the electrolyte, a mixture was used consisting 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 (VC).

[0164] <4. Evaluation of non-aqueous secondary batteries> The internal resistance and discharge capacity retention rate after 500 cycles were evaluated for the lithium-ion secondary batteries of Examples 1 to 6 and Comparative Example 1, respectively, using the methods described below. The results are shown in Tables 1 and 2.

[0165] [Internal resistance (DCR)] Under conditions of 25°C, the internal resistance (DCR(Ω)) of a lithium-ion secondary battery was measured using the following procedure. Specifically, the battery was charged at a constant current of 0.2C from rest potential until the voltage reached 3.6V, bringing the charge state to 50% of the initial capacity (SOC50%). Subsequently, discharge was performed for 60 seconds at current values ​​of 0.2C, 0.5C, 1C, and 2C. The internal resistance DCR(Ω) at SOC50% was determined from the relationship between these four current values ​​(values ​​per second) and voltage.

[0166] [Discharge capacity retention rate after 500 cycles] Under conditions of 45°C, charging and discharging were performed with each cycle consisting of the following steps (i) to (iv) as one unit. The time integral of the current in steps (i) and (ii) was defined as the charging capacity, and the time integral of the current in step (iv) was defined as the discharging capacity. The discharging capacity after the first cycle and the discharging capacity after 500 cycles were measured, and the discharge capacity retention rate after 500 cycles was calculated using the following formula. Discharge capacity retention rate (%) = 100 × (Discharge capacity at 500 cycles / Discharge capacity at 1 cycle)

[0167] (i) Charge at a current of 1C until the voltage reaches 4.2V (constant current (CC) charging). (ii) Charge at a voltage of 4.2V until the current reaches 0.05C (constant voltage (CV) charging). (iii) Let stand for 30 minutes. (iv) Discharge at a current of 1C until the voltage reaches 2.75V (constant current (CC) discharge).

[0168] <5. Evaluation Results> As shown in Tables 1 and 2, the lithium-ion secondary batteries of Examples 1 to 6 all exhibited higher capacity retention rates compared to the lithium-ion secondary battery of Comparative Example 1. This is presumed to be because the non-volatile components of the non-aqueous secondary battery binder composition contained in the negative electrode of the lithium-ion secondary batteries of Examples 1 to 6 include copolymers containing structural units derived from monomers (a1) and monomers (a2) shown in Tables 1 and 2, and tackifiers shown in Tables 1 and 2.

[0169] More specifically, in Comparative Example 1, the negative electrode was manufactured using a non-aqueous secondary battery binder composition that did not contain a tackifier, in which emulsified particles containing the same copolymer as in Example 1 were dispersed in water. Therefore, it is presumed that in the lithium-ion secondary battery of Comparative Example 1, the bonding between the electrode active materials and between the electrode active materials and the current collector was insufficient, resulting in a poor capacity retention rate.

[0170] Furthermore, the amount of non-aqueous secondary battery binder composition contained in the negative electrodes of Examples 1 to 6 and Comparative Example 1 was small (1.4 parts by mass of non-volatile content). Nevertheless, the cycle characteristics of lithium-ion secondary batteries using the non-aqueous secondary battery binders of Examples 1 to 6 were significantly different from those of Comparative Example 1. From this, it was found that the effects obtained by using the non-aqueous secondary battery binders of Examples 1 to 6 are very remarkable.

[0171] Furthermore, as shown in Tables 1 and 2, it was confirmed that the lithium-ion secondary batteries of Examples 1 to 6 and Comparative Example 1 all exhibited internal resistance values ​​that are sufficiently low for practical use, which is a secondary effect. [Explanation of symbols]

[0172] 1... Copolymer, 2... Tackifier, 3, 31... Emulsified particles containing copolymer 1, 4, 41... Surfactant.

Claims

1. It contains a copolymer and a tackifier, The copolymer is The first structural unit derived from the monomer (a1), It has a second structural unit derived from monomer (a2), The monomer (a1) is a nonionic compound having only one ethylenically unsaturated bond, The monomer (a2) is a compound having a carboxyl group and only one ethylenically unsaturated bond. A binder composition for non-aqueous secondary batteries, wherein the tackifier is at least one selected from rosin resins, terpene resins, hydrogenated petroleum resins, and unhydrogenated petroleum resins.

2. The binder composition for a non-aqueous secondary battery according to claim 1, wherein the tackifier is at least one selected from the hydrogenated petroleum resin and the terpene resin.

3. The binder composition for a non-aqueous secondary battery according to claim 2, wherein at least one of the tackifiers is the hydrogenated petroleum resin.

4. The binder composition for a non-aqueous secondary battery according to claim 3, wherein the softening point of the hydrogenated petroleum resin is 70°C to 140°C.

5. The binder composition for a non-aqueous secondary battery according to claim 1, wherein the content of the tackifier per 100 parts by mass of the copolymer is 0.10 parts by mass or more and 50 parts by mass or less.

6. The binder composition for a non-aqueous secondary battery according to claim 1, wherein the content of the second structural unit in the total structural units of the copolymer is 0.10% by mass or more and 20% by mass or less.

7. The copolymer has a third structural unit derived from monomer (a3), The binder composition for a non-aqueous secondary battery according to claim 1, wherein the monomer (a3) ​​is a compound having a plurality of independent ethylenically unsaturated bonds.

8. The binder composition for a non-aqueous secondary battery according to claim 7, wherein the content of the third structural unit in the total structural units of the copolymer is 0.010% by mass or more and 10% by mass or less.

9. The first structural unit derived from the monomer (a1) includes a structural unit derived from an aromatic compound. The binder composition for a non-aqueous secondary battery according to claim 1, wherein the content of structural units derived from the aromatic compound in the total structural units of the copolymer is 36% by mass or more.

10. The binder composition for non-aqueous secondary batteries according to claim 1, further comprising an aqueous medium.

11. The binder composition for a non-aqueous secondary battery according to claim 10, wherein 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. The binder composition for a non-aqueous secondary battery according to claim 10, wherein the copolymer and the tackifier are dispersed in the aqueous medium.

13. The binder composition for a non-aqueous secondary battery according to claim 1, wherein the glass transition temperature of the copolymer is -10°C to 40°C.

14. A slurry for a non-aqueous secondary battery electrode, comprising a binder composition for a non-aqueous secondary battery according to any one of claims 1 to 13, and an electrode active material.

15. A non-aqueous secondary battery electrode comprising the non-volatile component of the binder composition for non-aqueous secondary batteries described in any one of claims 1 to 13.

16. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode described in claim 15.

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