Copolymer, binder for non-aqueous secondary battery electrode, and slurry for non-aqueous secondary battery electrode

Abstract

Provided are: a copolymer which has less generation of coarse grains and effectively improved peel strength from a current collector of an electrode active material layer, and thus can contribute to a reduction in the internal resistance of a battery and excellent cycle characteristics; a binder for a non-aqueous secondary battery electrode; and a slurry for a non-aqueous secondary battery electrode. A copolymer according to the present invention includes a first structural unit to a third structural unit which are respectively derived from monomers (a1)-(a3). The monomer (a1) is composed of a nonionic compound having an ethylenically unsaturated bond, the monomer (a2) has an ethylenically unsaturated bond and an anionic functional group, and the monomer (a3) has 31st to 33rd structural units represented by formulae (1)-(3). 1.0-30 parts by mass of the second structural unit and 0.010-70 parts by mass of the third structural unit are included with respect to 100 parts by mass of the first structural unit.

Description

[Technical Field]

[0001] The present invention relates to a copolymer, a binder for a non-aqueous secondary battery electrode, and a slurry for a non-aqueous secondary battery electrode. This application claims priority based on Japanese Patent Application No. 2020-184544, filed on November 4, 2020, the contents of which are incorporated herein by reference. [Background technology]

[0002] A nonaqueous secondary battery includes a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and an electrolyte solution. A nonaqueous secondary battery is a secondary battery in which ions move between the positive electrode and the negative electrode to charge and discharge the battery.

[0003] Lithium-ion secondary batteries are a typical example of non-aqueous secondary batteries. Non-aqueous secondary batteries are used as power sources for notebook computers, mobile phones, power tools, and electronic and communication devices due to their compact size and light weight. Recently, they have also been used in electric and hybrid vehicles, with the aim of being environmentally friendly. In this context, there is a strong demand for non-aqueous secondary batteries with higher output, higher capacity, and longer life.

[0004] The binders used in positive and negative electrodes serve to bind the active materials together and to bind the active materials to the current collector. Development of aqueous dispersion binders is underway to improve the capacity of non-aqueous secondary batteries and to protect the working environment. For example, aqueous dispersions of styrene-butadiene rubber (SBR) combined with carboxymethyl cellulose (CMC) as a thickener are known.

[0005] Patent Document 1 describes a method for polymerizing ethylene oxide with an alkylene oxide other than ethylene oxide, an alkyl glycidyl ether, an allyl glycidyl ether, or a combination thereof. It describes that a composition containing a copolymer obtained by polymerization can be used as a binder material in a battery electrode containing electroactive particles.

[0006] Patent Document 2 describes a secondary battery negative electrode having an electrode layer containing a copolymer obtained from a (meth)acrylic acid ester and a vinyl monomer having an acid component, and at least one selected from the group consisting of a polyoxyethylene alkyl ether derivative, a polyoxyethylene-polyoxypropylene condensate, and a polyoxyethylene-polyoxypropylene alkyl ether derivative. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 2012-517519 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-239070 Summary of the Invention [Problem to be solved by the invention]

[0008] However, when the components described in Patent Documents 1 and 2 are used as electrode binders, there is room for improvement in the peel strength of the electrode active material layer from the current collector, and room for reduction in the internal resistance when a battery is fabricated.

[0009] An object of the present invention is to provide a copolymer, a binder for non-aqueous secondary battery electrodes, and a slurry for non-aqueous secondary battery electrodes that can effectively improve the peel strength of an electrode active material layer from a current collector in a non-aqueous secondary battery, thereby contributing to a reduction in the internal resistance of the battery and an improvement in the cycle characteristics. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides the following [1] to

[15] . [1] A polymer of a compound having an ethylenically unsaturated bond, a first structural unit derived from a monomer (a1) and a second structural unit derived from a monomer (a2); and a third structural unit derived from the monomer (a3); or a first structural unit derived from the monomer (a1), a second structural unit derived from the monomer (a2), a third structural unit derived from the monomer (a3), and a fourth structural unit derived from the internal cross-linking agent (a4), the monomer (a1) is a nonionic compound having an ethylenically unsaturated bond, having neither a hydroxy group nor a cyano group, having no polyoxyalkylene structure, and having no multiple independent ethylenically unsaturated bonds; the monomer (a2) is a compound having an ethylenically unsaturated bond and an anionic functional group, and having neither a polyoxyalkylene structure nor a plurality of independent ethylenically unsaturated bonds, The monomer (a3) ​​has a 31st structural unit represented by the following formula (1), a 32nd structural unit represented by the following formula (2), and a 33rd structural unit represented by the following formula (3), The second structural unit is contained in an amount of 1.0 part by mass or more and 30 parts by mass or less relative to 100 parts by mass of the first structural unit, The third structural unit is contained in an amount of 0.010 parts by mass or more and 70 parts by mass or less relative to 100 parts by mass of the first structural unit, a compound in which the content of the fourth structural unit relative to 100 parts by mass of the first structural unit is 0 parts by mass or more and 20 parts by mass or less; The internal cross-linking agent (a4) is a compound that does not correspond to the monomer (a3), has a plurality of independent ethylenically unsaturated bonds, and is capable of forming a cross-linked structure in the radical polymerization of monomers including the monomer (a1), the monomer (a2), and the monomer (a3). A copolymer characterized by: [ka] [ka] (In formula (2), R 1 is an alkyl group having 1 to 6 carbon atoms, which may be branched. [ka] (In formula (3), R 2 is a functional group having an ethylenically unsaturated bond. [2] The monomer (a3) ​​is With respect to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit, The 31 structural unit is contained in an amount of 5.0 mol% or more and 98 mol% or less, The 32nd structural unit is contained in an amount of 0.30 mol% or more and 90 mol% or less, The copolymer according to [1], comprising the 33 structural unit in an amount of 0.30 mol % or more and 10 mol % or less. [3] The copolymer according to [1] or [2], wherein the monomer (a3) ​​has a plurality of independent ethylenically unsaturated bonds in one molecule. [4] In the formula (3), R 2 The copolymer according to any one of [1] to [3], which has at least one selected from the group consisting of a vinyloxy group, an allyloxy group, a (meth)acryloyl group, a (meth)acryloyloxy group, and -OCH2-CH2-CH2=CH2. [5] In the formula (3), R 2 The copolymer according to any one of [1] to [4] is represented by the following formula (4): [ka] (In formula (4), R 21 is an alkylene group having 1 to 5 carbon atoms which may be branched, and R 22 is a functional group selected from the group consisting of a vinyloxy group, an allyloxy group, a (meth)acryloyl group, and a (meth)acryloyloxy group. [6] The copolymer according to any one of [1] to [5], wherein the monomer (a3) ​​has a first block consisting of the 31 structural unit, a second block consisting of the 32 structural unit, and a third block consisting of the 33 structural unit. [7] The copolymer according to any one of [1] to [6], wherein the monomer (a3) ​​contains the 31st structural unit, the 32nd structural unit, and the 33rd structural unit in a total amount of 90 mass% or more of all structural units. [8] The copolymer according to any one of [1] to [7], wherein the monomer (a1) does not have a polar functional group. [9] The copolymer according to any one of [1] to [8], wherein the monomer (a2) is a compound having at least one of a carboxy group and a sulfo group.

[10] The copolymer according to any one of [1] to [9], comprising the first structural unit, the second structural unit, and the third structural unit in a total amount of 80 mass % or more.

[11] The copolymer according to any one of [1] to

[10] , wherein the content of the fourth structural unit relative to 100 parts by mass of the first structural unit is 0.050 parts by mass or more.

[12] A binder composition for a non-aqueous secondary battery electrode, in which the copolymer according to any one of [1] to

[11] is dispersed in an aqueous medium.

[13] A binder for a non-aqueous secondary battery electrode, comprising the copolymer according to any one of [1] to

[11] .

[14] An electrode comprising the binder according to

[13] , an electrode active material, and an aqueous medium; the binder and the electrode active material are dispersed in an aqueous medium, The aqueous medium is a medium selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent.

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

[13] . [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a copolymer, a binder for non-aqueous secondary battery electrodes, and a slurry for non-aqueous secondary battery electrodes that can effectively improve the peel strength of an electrode active material layer from a current collector in a non-aqueous secondary battery, and contribute to reducing the internal resistance of the battery and improving its cycle characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, as embodiments of the present invention, a copolymer, a binder for a non-aqueous secondary battery electrode, a binder composition for a non-aqueous secondary battery electrode, a slurry for a non-aqueous secondary battery electrode, a non-aqueous secondary battery electrode, and a non-aqueous secondary battery will be described.

[0013] "(Meth)acrylic" is a general term for acrylic and methacrylic, and "(meth)acrylate" is a general term for acrylate and methacrylate.

[0014] The "non-volatile content" is the component remaining after weighing 1 g of the composition into a 5 cm diameter aluminum dish and drying it for 1 hour at 105°C with air circulating in a dryer at 1 atmosphere (1013 hPa). The composition may be in the form of a solution, dispersion, or slurry, but is not limited to these. The "non-volatile content concentration" is the mass ratio (mass %) of the non-volatile content after drying under the above conditions to the mass (1 g) of the composition before drying.

[0015] Unless otherwise specified, the term "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond having radical polymerizability.

[0016] In a polymer of a compound having an ethylenically unsaturated bond, a structural unit derived from a compound having an ethylenically unsaturated bond is one in which the chemical structure of the part of the compound other than the ethylenically unsaturated bond is the same as the chemical structure of the part of the polymer other than the part corresponding to the ethylenically unsaturated bond of the structural unit. For example, a structural unit derived from sodium acrylate has the structure -CHCH(COONa)- in the polymer.

[0017] Furthermore, in the case of a compound having multiple independent ethylenically unsaturated bonds, the ethylenically unsaturated bonds may remain as structural units of the polymer. The multiple independent ethylenically unsaturated bonds refer to multiple ethylenically unsaturated bonds that do not form a conjugated diene with each other. For example, the structural unit derived from divinylbenzene may have a structure without an ethylenically unsaturated bond (a form in which portions corresponding to both ethylenically unsaturated bonds are incorporated into the polymer chain), or may have a structure with one ethylenically unsaturated bond (a form in which only a portion corresponding to one of the ethylenically unsaturated bonds is incorporated into the polymer chain).

[0018] Furthermore, when the chemical structure of the monomer does not correspond to the chemical structure of the polymer, such as when a portion other than the chain corresponding to the ethylenically unsaturated bond is chemically reacted after polymerization, the chemical structure after polymerization is used as the basis. For example, when vinyl acetate is polymerized and then saponified, the chemical structure of the polymer is used as the basis, and the structural unit is considered to be derived from vinyl alcohol rather than from vinyl acetate.

[0019] <1. Copolymer (P)> In this embodiment, the copolymer (P) is a copolymer for a non-aqueous secondary battery electrode binder. The copolymer (P) is a polymer of a compound having an ethylenically unsaturated bond. The copolymer (P) has a first structural unit derived from a monomer (a1), a second structural unit derived from a monomer (a2), and a third structural unit derived from a monomer (a3). The copolymer (P) may further have a fourth structural unit derived from an internal crosslinking agent (a4). The copolymer (P) may also contain a structural unit derived from another monomer (a5) that does not fall under any of the monomers (a1), (a2), (a3), and (a4). Details of each monomer and internal crosslinking agent are described below.

[0020] <1-1. Monomer (a1)> The monomer (a1) is a nonionic compound (having neither an anionic functional group nor a cationic functional group) that has an ethylenically unsaturated bond, but does not have a polyoxyalkylene structure, and does not have multiple independent ethylenically unsaturated bonds. The term "having no polyoxyalkylene structure" refers to an alkylene group (-COC) sandwiched between two ether bonds. x It means that there is no bond represented by -OC- (x is an integer of 1 or more).

[0021] The monomer (a1) has neither a hydroxy group nor a cyano group. The monomer (a1) preferably has no polar functional group. The monomer (a1) may contain only one type of compound or two or more types of compounds. The monomer (a1) is preferably at least one of a (meth)acrylic acid ester having no polar functional group and an aromatic vinyl compound, and more preferably contains both. The (meth)acrylic acid ester having no polar functional group more preferably contains a (meth)acrylic acid alkyl ester. The total content of the (meth)acrylic acid alkyl ester and the aromatic vinyl compound in the monomer (a1) is more preferably 80% by mass or more, even more preferably 90% by mass or more, and most preferably 100% by mass.

[0022] Regarding the composition of the monomer (a1), it is preferable to appropriately adjust the preferred compounds and their amounts within the ranges specified in the present invention in order to adjust the glass transition temperature of the copolymer (P) or to adjust the polymerization rate according to the molecular design.

[0023] Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, tert-butyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isobornyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate.

[0024] Here, the aromatic vinyl compound does not contain a (meth)acryloyl group. Examples of the aromatic vinyl compound include styrene, t-butylstyrene, α-methylstyrene, p-methylstyrene, and 1,1-diphenylethylene. When the monomer (a1) contains an aromatic vinyl compound, the monomer (a1) more preferably contains at least one of styrene and α-methylstyrene, and even more preferably contains styrene.

[0025] The monomer (a1) may contain a plurality of ethylenically unsaturated bonds that together form a conjugated diene. Examples of compounds having a plurality of ethylenically unsaturated bonds that together form a conjugated diene include 1,3-butadiene and 1,3-pentadiene.

[0026] [1-2. Monomer (a2)] Monomer (a2) is a compound having an ethylenically unsaturated bond and an anionic functional group. Monomer (a2) does not have a polyoxyalkylene structure or multiple independent ethylenically unsaturated bonds. Examples of the anionic functional group include a carboxy group, a sulfo group, and a phosphate group. Monomer (a2) preferably contains a compound having at least one of a carboxy group and a sulfo group, and more preferably contains a compound having a carboxy group.

[0027] The monomer (a2) may contain only one type of compound, or may contain two or more types of compounds. The monomer (a2) may contain a compound having a plurality of the same type of anionic functional groups in one molecule. That is, the copolymer (P) may contain a plurality of the same type of anionic functional groups in one structural unit. The monomer (a2) may contain a compound having two or more different types of anionic functional groups in one molecule. That is, the copolymer (P) may contain two or more different types of anionic functional groups in one structural unit. Furthermore, the monomer (a2) may contain two or more types of compounds containing different anionic functional groups. That is, the copolymer (P) may contain two or more types of structural units containing different anionic functional groups.

[0028] Examples of the monomer (a2) include unsaturated monocarboxylic acids such as (meth)acrylic acid and crotonic acid, unsaturated dicarboxylic acids such as maleic acid, fumaric acid and itaconic acid, half esters of unsaturated dicarboxylic acids, and p-styrenesulfonic acid. Among these, it is preferable that the monomer (a2) contains at least one of (meth)acrylic acid and itaconic acid.

[0029] At least a portion of the structural units derived from the monomer (a2) may form a salt with a basic substance. Examples of the monomer (a2) that forms a salt include sodium (meth)acrylate and sodium p-styrenesulfonate.

[0030] Monomer (a2) preferably contains at least one of a sulfonic acid having an ethylenically unsaturated bond and a salt thereof, and more preferably contains a sulfonic acid salt having an ethylenically unsaturated bond. The sulfonic acid preferably contains an aromatic vinyl compound having a sulfo group, and more preferably contains para-styrenesulfonic acid. The sulfonic acid salt preferably contains a salt of an aromatic vinyl compound having a sulfo group, more preferably contains para-styrenesulfonate, and even more preferably contains sodium para-styrenesulfonate. This is because the generation of coarse particles in the binder composition can be suppressed.

[0031] [1-3. Monomer (a3)] The monomer (a3) ​​is a compound containing a 31st structural unit represented by the following formula (1), a 32nd structural unit represented by the following formula (2), and a 33rd structural unit represented by the following formula (3). The monomer (a3) ​​preferably has a plurality of ethylenically unsaturated bonds in one molecule. The monomer (a3) ​​may contain only one type of compound, or may contain two or more types of compounds.

[0032] In addition, when describing the constitution of the structural units in the monomer (a3), the terminal structure is not taken into consideration unless otherwise specified. For example, the content of a certain structural unit in the monomer (a3) ​​refers to the content of that structural unit in the structure excluding the terminal structure unless otherwise specified. Furthermore, when the monomer (a3) ​​is said to be composed of a certain structural unit, it may contain a terminal structure in addition to that structural unit. Here, the terminal structure in the monomer (a3) ​​is a structure that is located closer to the molecular terminal than the ether bond closest to the molecular terminal and is not included in any of the structures of the following formulas (1) to (3). Furthermore, the terminal structure does not include the structures shown in the following formulas (1) to (3).

[0033] [ka]

[0034] [ka]

[0035] In equation (2), R 1 R is an alkyl group having 1 to 6 carbon atoms, which may be branched. 1 Preferably, the number of carbon atoms is 4 or less, more preferably 2 or less, and further preferably a methyl group.

[0036] [ka]

[0037] In equation (3), R 2 is a group having an ethylenically unsaturated bond. 2Preferably, the 33rd structural unit has at least one selected from the group consisting of a vinyloxy group (-OCH2=CH2), an allyloxy group (-OCH2-CH2=CH2), a (meth)acryloyl group, a (meth)acryloyloxy group, and -OCH2-CH2-CH2=CH2, more preferably at least one selected from the group consisting of an allyloxy group, a (meth)acryloyl group, and a (meth)acryloyloxy group, and even more preferably an allyloxy group. Preferably, one 33rd structural unit contains one ethylenically unsaturated bond.

[0038] R 2 The structure is preferably represented by the following formula (4).

[0039] [ka]

[0040] In equation (4), R 21 is an alkylene group having 1 to 5 carbon atoms which may be branched, R 22 is any one of a vinyloxy group, an allyloxy group, a (meth)acryloyl group, a (meth)acryloyloxy group, and —OCH 2 —CH 2 —CH 2 ═CH 2 .

[0041] In equation (4), R 21 is preferably an alkylene group having 1 or 2 carbon atoms, and more preferably a methylene group. 22 is more preferably any one of an allyloxy group, a (meth)acryloyl group, and a (meth)acryloyloxy group, and even more preferably an allyloxy group.

[0042] The hydrophilicity of the copolymer (P) can be controlled by adjusting the content of the structural unit No. 31, the structural unit No. 32, and the structural unit No. 33 in the monomer (a3). For example, increasing the content of the structural unit No. 31 in the monomer (a3) ​​improves the hydrophilicity of the copolymer (P), whereas decreasing the content of the structural unit No. 31 reduces the hydrophilicity of the copolymer (P).

[0043] The crystallinity of the monomer (a3) ​​can be adjusted within an appropriate range and the crystallinity of the copolymer (P) can be controlled by adjusting the contents of the structural unit No. 31, the structural unit No. 32, and the structural unit No. 33 in the monomer (a3). For example, increasing the content of the structural unit No. 31 in the monomer (a3) ​​improves the crystallinity of the copolymer (P), while decreasing the content of the structural unit No. 31 decreases the crystallinity of the copolymer (P).

[0044] By adjusting the content of the 33rd structural unit in the monomer (a3), the crosslink density of the copolymer (P) can be adjusted, and the flexibility and strength of the electrode active material layer containing the copolymer (P) as an electrode binder can be controlled. For example, by increasing the content of the 33rd structural unit in the monomer (a3), the crosslink density of the copolymer (P) increases, and the strength of the electrode active material layer can be further improved. On the other hand, by decreasing the content of the 33th structural unit, the crosslink density of the copolymer (P) decreases, and the flexibility of the electrode active material layer can be further improved.

[0045] The relationship between the contents of these structural units contained in the monomer (a3) ​​will be explained below.

[0046] In the monomer (a3), the content of the 31 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 5.0 mol% or more, more preferably 18 mol% or more, and even more preferably 25 mol% or more.

[0047] In the monomer (a3), the content of the 31st structural unit relative to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit is preferably 98 mol % or less, more preferably 97 mol % or less.

[0048] In the monomer (a3), the content of the 32 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 0.30 mol% or more, more preferably 0.50 mol% or more, and even more preferably 0.70 mol% or more.

[0049] In the monomer (a3), the content of the 32 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 90 mol% or less, more preferably 80 mol% or less, and even more preferably 75 mol% or less.

[0050] In the monomer (a3), the content of the 33 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 0.30 mol% or more, more preferably 0.50 mol% or more, and even more preferably 0.70 mol% or more.

[0051] In the monomer (a3), the content of the 33 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 10 mol% or less, more preferably 6.0 mol% or less, and even more preferably 4.5 mol% or less.

[0052] Monomer (a3) ​​may contain a structural unit that does not fall into any of the 31st structural unit, 32nd structural unit, and 33rd structural unit. However, the total content of the 31st structural unit, 32nd structural unit, and 33rd structural unit in all structural units in monomer (a3) ​​is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass, and most preferably 100% by mass. Here, the structural units constituting monomer (a3) ​​do not include terminal structures (defined above). This also applies to monomer (a31) according to the first embodiment and monomer (a32) according to the second embodiment described below.

[0053] The monomer (a3) ​​has the following two preferred forms, which differ in hydrophilicity. These forms will be described below as the monomer (a31) according to the first form and the monomer (a32) according to the second form. The monomer (a32) according to the second form has higher hydrophilicity than the monomer (a31) according to the first form.

[0054] In the monomer (a31) according to the first embodiment, the content of the 31 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 5.0 mol% or more, more preferably 18 mol% or more, and even more preferably 25 mol% or more.

[0055] In the monomer (a31) according to the first embodiment, the content of the 31 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 50 mol% or less, more preferably 40 mol% or less.

[0056] In the monomer (a31) according to the first embodiment, the content of the 32 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 40 mol% or more, more preferably 50 mol% or more, and even more preferably 60 mol% or more.

[0057] In the monomer (a31) according to the first embodiment, the content of the 32 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 90 mol% or less, more preferably 80 mol% or less, and even more preferably 75 mol% or less.

[0058] In the monomer (a31) according to the first embodiment, the content of the 33 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 0.30 mol% or more, more preferably 0.50 mol% or more, and even more preferably 0.70 mol% or more.

[0059] In the monomer (a31) according to the first embodiment, the content of the 33 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 10 mol% or less, more preferably 6.0 mol% or less, and even more preferably 4.5 mol% or less.

[0060] In the monomer (a32) according to the second embodiment, the content of the 31 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more.

[0061] In the monomer (a32) according to the second embodiment, the content of the 31 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 98 mol% or less, more preferably 97 mol% or less.

[0062] In the monomer (a3) ​​according to the second embodiment, the content of the 32 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 0.30 mol% or more, more preferably 0.50 mol% or more, and even more preferably 0.70 mol% or more.

[0063] In the monomer (a32) according to the second embodiment, the content of the 32 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 20 mol% or less, more preferably 15 mol% or less, and even more preferably 10 mol% or less.

[0064] In the monomer (a32) according to the second embodiment, the content of the 33 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 0.30 mol% or more, more preferably 0.50 mol% or more, and even more preferably 0.70 mol% or more.

[0065] In the monomer (a32) according to the second embodiment, the content of the 33 structural unit relative to the total amount of the 31 structural unit, the 32 structural unit, and the 33 structural unit is preferably 10 mol% or less, more preferably 6.0 mol% or less, and even more preferably 4.5 mol% or less.

[0066] Monomer (a3) ​​is preferably a block copolymer having a first block consisting of structural units 31, a second block consisting of structural units 32, and a third block consisting of structural units 33. Monomer (a3) ​​is more preferably a terblock copolymer consisting of a first block, a second block, and a third block (which may contain a terminal structure as defined above). Monomer (a3) ​​is even more preferably a terblock copolymer in which the first block, the second block, and the third block are arranged in that order (i.e., the second block is present between the first block and the third block).

[0067] The preferred range of the weight-average molecular weight of the monomer (a3) ​​varies depending on whether the monomer (a3) ​​is water-soluble or not. When the monomer (a3) ​​is dissolved in a 0.1 M NaNO3 aqueous solution to prepare an aqueous solution containing 0.1 mass % of the monomer (a3), the weight-average molecular weight of the monomer (a3) ​​is a pullulan-equivalent value measured by aqueous GPC under the following conditions:

[0068] [Water-based GPC] GPC equipment: GPC-101 (Showa Denko K.K.) Solvent: 0.1M NaNO3 aqueous solution Sample column: Shodex Column Ohpak SB-806 HQ (8.0 mm I.D. x 300 mm) x 2 Reference column: Shodex Column Ohpak SB-800 RL (8.0mm I.D. x 300mm) x 2 Column temperature: 40℃ Sample concentration: 0.1% by mass Detector: RI-71S (Shimadzu Corporation) Flow rate: 1ml / min Molecular weight standard: pullulan (P-5, P-10, P-20, P-50, P-100, P-200, P-400, P-800, P-1300, P-2500 (Showa Denko K.K.))

[0069] In this case, the weight average molecular weight M of the monomer (a3) w The weight average molecular weight M of the monomer (a3) ​​(as converted to pullulan) is preferably 10,000 or more, more preferably 30,000 or more, and even more preferably 50,000 or more, because this improves the strength of the electrode. w The saturation energy (pullulan equivalent) is preferably 300,000 or less, more preferably 200,000 or less, and even more preferably 120,000 or less. This is because the dispersibility of the solid content in the electrode slurry described below is improved.

[0070] When it is not possible to prepare an aqueous solution containing 0.1% by mass of monomer (a3) ​​by dissolving monomer (a3) ​​in a 0.1 M NaNO3 aqueous solution, the weight average molecular weight of monomer (a3) ​​is a polystyrene-equivalent value measured by solvent-based GPC under the conditions shown below.

[0071] [Solvent-based GPC] GPC equipment: Waters GPC System e2695 Solvent: tetrahydrofuran Column: SHODEX KF-806L x 2, SHODEX KF-G (Showa Denko K.K.) Column temperature: 40°C Column temperature: 40℃ Sample concentration: 0.2% by mass Detector: Waters 2414RI Flow rate: 0.65mL / min Molecular weight standard: polystyrene (Shodex Polystyrene STANDARD SL-105, SM-105 (Showa Denko K.K.))

[0072] In this case, the weight average molecular weight M of the monomer (a3) w The weight average molecular weight M of the monomer (a3) ​​(in terms of polystyrene) is preferably 10,000 or more, more preferably 20,000 or more, and even more preferably 30,000 or more, because this improves the strength of the electrode. w The molecular weight (polystyrene equivalent) is preferably 200,000 or less, more preferably 150,000 or less, and even more preferably 80,000 or less, because this improves the dispersibility of the solid content in the electrode slurry described below.

[0073] [Specific examples of monomer (a3)] The monomer (a3) ​​is preferably, for example, a triblock copolymer represented by the following formula (5).

[0074] [ka]

[0075] In formula (5), n:m:l is preferably 5.0-98:0.30-90:0.30-4.5, n:m:l is preferably 18-97:0.50-80:0.50-6.0, and more preferably n:m:l is 25-97:0.70-75:0.80-4.5. The preferred ranges of the weight average molecular weight are as described above.

[0076] In the first form of the compound represented by formula (5), n:m:l is preferably 5.0-50:40-90:0.30-4.5, more preferably 18-40:50-80:0.50-6, and even more preferably 25-40:60-75:0.80-4.5. When it is impossible to prepare an aqueous solution containing 0.1% by mass of the compound according to the first form by dissolving it in a 0.1 M NaNO3 aqueous solution, the weight-average molecular weight, in terms of polystyrene, is 10,000-200,000, preferably 20,000-150,000, and even more preferably 30,000-80,000.

[0077] A specific example of the first embodiment includes a compound (a3-1) represented by formula (5) in which n:m:l=30:69:1.0 and Mw=50,000.

[0078] The second form of the compound represented by formula (5) is a compound represented by formula (5), in which n:m:l = 70-98:0.30-20:0.30-10, preferably n:m:l = 80-97:0.50-15:0.50-6.0, and more preferably n:m:l = 90-97:0.70-10:0.80-4.5 and Mw = 50,000-80,000. When an aqueous solution containing 0.1% by mass of the compound according to the second form can be prepared by dissolving it in a 0.1 M NaNO3 aqueous solution, the weight-average molecular weight, calculated as pullulan, is 10,000-300,000, preferably 30,000-200,000, and more preferably 50,000-120,000.

[0079] Specific examples of the second form include compound (a3-2) in which n:m:l=93:6.0:1.0 and Mw=80,000, and compound (a3-3) in which n:m:l=96:1.0:3.0 and Mw=80,000 in formula (5).

[0080] [Method for synthesizing monomer (a3)] The method for synthesizing the monomer (a3) ​​is not particularly limited, but it can be obtained, for example, by ring-opening polymerization of an epoxide using an acid catalyst.

[0081] [1-4. Internal crosslinking agent (a4)] The internal cross-linking agent (a4) is a compound that does not fall under the category of the monomer (a3), has multiple independent ethylenically unsaturated bonds, and is capable of forming a cross-linked structure in the radical polymerization of the monomers including the monomers (a1), (a2), and (a3). Examples of such compounds include divinylbenzene, ethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, and 2-hydroxy-3-acryloyloxypropyl methacrylate.

[0082] [1-5. Other Monomers (a5)] The other monomer (a5) does not fall under any of the monomers (a1) to (a4). Examples of the other monomer (a5) include, but are not limited to, a compound having an ethylenically unsaturated bond and a polar functional group, a surfactant having an ethylenically unsaturated bond (hereinafter sometimes referred to as a "polymerizable surfactant"), and a compound having an ethylenically unsaturated bond and functioning as a silane coupling agent.

[0083] The polar functional group preferably contains at least one of a hydroxy group and a cyano group. Examples of monomers having an ethylenically unsaturated bond and a polar functional group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl acrylate, and (meth)acrylonitrile. The copolymer (P) preferably contains a structural unit derived from a compound containing an ethylenically unsaturated bond and a hydroxy group, more preferably a structural unit derived from a (meth)acrylate having a hydroxy group, and even more preferably a structural unit derived from 2-hydroxyethyl (meth)acrylate.

[0084] The polymerizable surfactant is a compound that has an ethylenically unsaturated bond and functions as a surfactant, and examples thereof include compounds represented by the following chemical formulas (6) to (9).

[0085] [ka]

[0086] In formula (6), R 3 is preferably an alkyl group, and p is preferably an integer of 10 to 40. 3 The number of carbon atoms in R is more preferably 10 to 40. 3 is more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[0087] [ka]

[0088] In formula (7), R 4 is preferably an alkyl group, and q is preferably an integer of 10 to 12. 4 The number of carbon atoms in R is more preferably 10 to 40. 4 is more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[0089] [ka]

[0090] In formula (8), R 5 is preferably an alkyl group, and M 1 is preferably NH4 or Na. 5 The number of carbon atoms in R is more preferably 10 to 40. 5 is more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[0091] [ka]

[0092] In formula (9), R 6 is preferably an alkyl group, and M 2 is preferably NH4 or Na. 6The number of carbon atoms in R is more preferably 10 to 40. 6 is more preferably a straight-chain unsubstituted alkyl group having 10 to 40 carbon atoms.

[0093] Examples of compounds that have an ethylenically unsaturated bond and function as a silane coupling agent include vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriethoxysilane, and γ-methacryloxypropyltriethoxysilane.

[0094] [1-6. Content of each structural unit in copolymer (P)] In the copolymer (P), the content of the second structural units derived from the monomer (a2) relative to 100 parts by mass of the first structural units derived from the monomer (a1) is 1.0 part by mass or more, preferably 1.5 parts by mass or more, and more preferably 3.0 parts by mass or more. This is because the mechanical stability of the copolymer (P) is improved. Also, the peel strength of an electrode active material layer containing the copolymer (P) as an electrode binder is improved.

[0095] In the copolymer (P), the content of the second structural units derived from the monomer (a2) relative to 100 parts by mass of the first structural units derived from the monomer (a1) is 30 parts by mass or less, preferably 15 parts by mass or less, and more preferably 7.5 parts by mass or less, in order to suppress gelation of the copolymer (P) and to improve the mechanical stability of the copolymer (P).

[0096] In copolymer (P), the content of the third structural unit derived from monomer (a3) ​​relative to 100 parts by mass of the first structural unit derived from monomer (a1) is 0.010 parts by mass or more, preferably 0.030 parts by mass or more, more preferably 0.15 parts by mass or more, and even more preferably 0.65 parts by mass or more. This is because the peel strength of an electrode active material layer containing copolymer (P) as an electrode binder is improved. Also, this is because the DCR of a battery using an electrode containing copolymer (P) as an electrode binder in an electrode active material layer can be reduced.

[0097] In the copolymer (P), the content of the third structural unit derived from the monomer (a3) ​​relative to 100 parts by mass of the first structural unit derived from the monomer (a1) is 70 parts by mass or less, preferably 40 parts by mass or less, and more preferably 35 parts by mass or less. This is to improve the polymerization stability in radical polymerization and to suppress the generation of coarse particles in the copolymer (P). Also, this is to suppress gelation of the copolymer (P).

[0098] The total mass proportion of the first structural unit, the second structural unit, and the third structural unit in the copolymer (P) is preferably 80 mass% or more, more preferably 85 mass% or more, and even more preferably 90 mass% or more, because increasing the content of these structural units further enhances the effects obtained by the present invention.

[0099] When the copolymer (P) contains a fourth structural unit derived from the internal crosslinking agent (a4), the content of the fourth structural unit derived from the internal crosslinking agent (a4) relative to 100 parts by mass of the first structural unit derived from the monomer (a1) is preferably 0.050 parts by mass or more, more preferably 0.075 parts by mass or more, and even more preferably 0.50 parts by mass or more, because this can suppress deterioration of the copolymer (P) and improve the discharge capacity retention rate of a battery using an electrode containing the copolymer (P) as an electrode binder in the electrode active material layer.

[0100] When the copolymer (P) contains structural units derived from the internal crosslinking agent (a4), the content of the fourth structural units derived from the internal crosslinking agent (a4) relative to 100 parts by mass of the first structural units derived from the monomer (a1) is 20 parts by mass or less, preferably 7.5 parts by mass or less, and more preferably 2.5 parts by mass or less, in order to suppress gelation of the copolymer (P).

[0101] [1-7. Glass transition temperature of copolymer (P)] The glass transition temperature Tg of the copolymer (P) is the peak top temperature of the DSC chart obtained as the temperature derivative of DSC when DSC measurement is performed using an EXSTAR DSC / SS7020 manufactured by Hitachi High-Tech Science Corporation at a heating rate of 10°C / min under a nitrogen gas atmosphere.

[0102] The glass transition temperature Tg of the copolymer (P) is preferably −30° C. or higher, more preferably −10° C. or higher, and even more preferably 0° C. or higher, because this improves the cycle characteristics of a nonaqueous secondary battery using the copolymer (P) as an electrode binder.

[0103] The glass transition temperature Tg of the copolymer (P) is preferably 100°C or lower, more preferably 50°C or lower, and even more preferably 30°C or lower, because this improves the adhesion of the electrode active material layer containing the copolymer (P) as an electrode binder to the current collector foil.

[0104] <2. Method for synthesizing copolymer (P)> The copolymer (P) can be obtained by copolymerizing monomers including the monomers (a1) to (a3). If necessary, an internal crosslinking agent (a4) and other monomers (a5) may also be copolymerized as monomers. Here, the monomers used to synthesize the copolymer (P) are sometimes collectively referred to as monomers (a). Examples of the polymerization method include emulsion polymerization of the monomer (a) in an aqueous medium (b). Examples of other components used in the synthesis of the copolymer (P) by emulsion polymerization include a non-polymerizable surfactant (c), a basic substance (d), a radical polymerization initiator (e), and a chain transfer agent (f). Below, these components necessary for the synthesis of the copolymer (P) or that may be used as needed, as well as the emulsion polymerization method, are described. However, the monomer (a) is not described below as it has been described above.

[0105] [2-1. Aqueous medium (b)] The aqueous medium (b) is water, a hydrophilic solvent, or a mixture thereof. 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 the polymerization stability is not impaired, a medium obtained by adding a hydrophilic solvent to water may also be used as the aqueous medium (b).

[0106] [2-2. Non-polymerizable surfactant (c)] In the emulsion polymerization of the monomer (a), a non-polymerizable surfactant (c) may be used. The surfactant (c) can improve the dispersion stability of the dispersion (emulsion) during and / or after the polymerization. As the surfactant (c), an anionic surfactant or a nonionic surfactant is preferably used.

[0107] Examples of anionic surfactants include alkylbenzene sulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts.

[0108] 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.

[0109] The above surfactants may be used alone or in combination of two or more.

[0110] [2-3. Basic Substances (d)] When the monomer (a) is emulsion polymerized in the aqueous medium (b), a basic substance (d) may be added. By adding the basic substance (d), the acidic components contained in the monomer (a) can be neutralized and the pH can be adjusted. By adjusting the pH, the mechanical stability and chemical stability of the dispersion during and / or after the emulsion polymerization can be improved.

[0111] The pH of the dispersion at 23°C may be adjusted appropriately depending on the specifications of the electrode, the conditions for preparing the slurry described below, etc., and is not limited to a specific value, but is preferably 1.5 to 10, more preferably 6.0 to 9.0, and even more preferably 5.0 to 9.0, in order to prevent the active material from settling in the electrode slurry described below.

[0112] Examples of the basic substance (d) include ammonia, triethylamine, sodium hydroxide, lithium hydroxide, etc. These basic substances (d) may be used singly or in combination of two or more.

[0113] [2-4. Radical Polymerization Initiator (e)] The radical polymerization initiator (e) used during emulsion polymerization is not particularly limited, and known initiators can be used. Examples of radical polymerization initiators include persulfates such as ammonium persulfate and potassium persulfate; hydrogen peroxide; azo compounds; and organic peroxides such as t-butyl hydroperoxide, tert-butyl peroxybenzoate, and cumene hydroperoxide. Among these, persulfates and organic peroxides are preferred. In this embodiment, redox polymerization may be carried out during emulsion polymerization using a radical polymerization initiator in combination with a reducing agent such as sodium bisulfite, Rongalit, or ascorbic acid.

[0114] The amount of radical polymerization initiator added is preferably 0.10 parts by mass or more, and more preferably 0.80 parts by mass or more, per 100 parts by mass of monomer (a). This is because the conversion rate of monomer (a) to copolymer (P) during polymerization can be increased. The amount of radical polymerization initiator added is preferably 3.0 parts by mass or less, and more preferably 2.0 parts by mass or less, per 100 parts by mass of monomer (a). This is because the molecular weight of copolymer (P) can be increased and the swelling rate of the electrode active material layer in the electrolyte can be reduced.

[0115] [2-5. Chain transfer agent (f)] The chain transfer agent (f) is used in emulsion polymerization to adjust the molecular weight of the copolymer (P). Examples of the chain transfer agent (f) include n-dodecyl mercaptan, tert-dodecyl mercaptan, n-butyl mercaptan, 2-ethylhexyl thioglycolate, 2-mercaptoethanol, β-mercaptopropionic acid, methyl alcohol, n-propyl alcohol, isopropyl alcohol, t-butyl alcohol, and benzyl alcohol.

[0116] [2-6. Emulsion polymerization method] Examples of emulsion polymerization methods include a method in which emulsion polymerization is carried out while continuously supplying each component used in emulsion polymerization. The temperature of emulsion polymerization is not particularly limited, but is, for example, 30 to 90°C, preferably 50 to 85°C, and more preferably 55 to 80°C. Emulsion polymerization is preferably carried out with stirring. Furthermore, it is preferable to continuously supply the monomer (a) and the radical polymerization initiator so that they are uniformly mixed in a reaction vessel.

[0117] <3. Non-aqueous secondary battery electrode binders> The non-aqueous secondary battery electrode binder (or non-aqueous secondary battery electrode binder, hereinafter sometimes referred to as "electrode binder") according to this embodiment contains the copolymer (P) described above. The electrode binder may contain other components, such as a polymer other than the copolymer (P), a surfactant, etc.

[0118] Here, the electrode binder consists of the components that remain without volatilizing during the heating process in the battery manufacturing process described below. Specifically, the components that make up the electrode binder are the components that remain after weighing 1 g of a mixture containing the electrode binder into an aluminum dish with a diameter of 5 cm and drying it at 105°C for 1 hour under atmospheric pressure in a dryer with air circulating.

[0119] The content of the copolymer (P) in the electrode binder is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more, in order to increase the contribution of the copolymer (P) to the intended effects of the present invention.

[0120] <4. Binder composition for non-aqueous secondary battery electrodes> The binder composition for a non-aqueous secondary battery electrode of this embodiment (hereinafter sometimes referred to as the binder composition) has a copolymer (P) dispersed in an aqueous medium (B). In addition to these components, the binder composition may contain, for example, the components described above used in synthesizing the copolymer (P). The binder composition may be a dispersion obtained by a method for synthesizing the copolymer (P), a dispersion obtained by dispersing the copolymer (P) obtained by a method other than emulsion polymerization in the aqueous medium (B), or a dispersion obtained by other methods.

[0121] [4-1. Aqueous medium (B)] The aqueous medium (B) is water, a hydrophilic solvent, or a mixture thereof. Examples of hydrophilic solvents are as described in the description of the aqueous medium (b) used in the synthesis of the copolymer (P). The aqueous medium (B) may be the same as or different from the aqueous medium (b) used in the synthesis of the copolymer (P).

[0122] The aqueous medium (B) may be the same aqueous medium (b) used in the synthesis of the copolymer (P), or may be a mixture of the aqueous medium (b) and an aqueous solvent added thereto, or may be a mixture of the aqueous medium (b) and the aqueous medium (b) replaced with a new aqueous solvent after the synthesis of the copolymer (P). The aqueous solvent to be added or replaced may have the same composition as or a different composition from the solvent used in the synthesis of the copolymer (P).

[0123] [4-2. Non-volatile content of binder composition] The nonvolatile content of the binder composition is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, in order to increase the amount of active ingredients contained in the binder composition. The nonvolatile content of the binder composition can be adjusted by the amount of aqueous medium (B).

[0124] The nonvolatile content 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, in order to prevent an increase in the viscosity of the binder composition and to facilitate the preparation of a slurry, which will be described later.

[0125] <5. Non-aqueous Slurry for Secondary Battery Electrodes> Next, the slurry for a non-aqueous secondary battery electrode (hereinafter sometimes referred to as "electrode slurry") will be described in detail. The electrode slurry has a configuration in which the copolymer (P) and an electrode active material are dispersed in an aqueous medium. In addition to these components, the electrode slurry may also contain a thickener, a conductive additive, the above-mentioned components used in synthesizing the copolymer (P), and the like.

[0126] [5-1. Content of copolymer (P)] The content of the copolymer (P) is preferably 0.50 parts by mass or more, and more preferably 1.0 part by mass or more, relative to 100 parts by mass of the electrode active material, in order to fully exhibit the effects of the copolymer (P).

[0127] The content of copolymer (P) is preferably 5.0 parts by mass or less, more preferably 4.0 parts by mass or less, and even more preferably 3.0 parts by mass or less, relative to 100 parts by mass of the electrode active material, in order to increase the content of the electrode active material in the electrode active material layer produced using the electrode slurry.

[0128] [5-2. Electrode active material] The electrode active material is a material capable of intercalating / deintercalating ions that serve as charge carriers, such as lithium ions. The ions that serve as charge carriers are preferably alkali metal ions, more preferably lithium ions, sodium ions, or potassium ions, and even more preferably lithium ions.

[0129] When the electrode is a negative electrode, the electrode active material, i.e., the negative electrode active material, preferably contains at least one of a carbon material, a silicon-containing material, and a titanium-containing material. Examples of carbon materials used as electrode active materials include cokes such as petroleum coke, pitch coke, and coal coke, carbonized organic polymers, and graphites such as artificial graphite and natural graphite. Examples of silicon-containing materials include silicon elemental compounds and silicon oxide. Examples of titanium-containing materials include lithium titanate. These materials may be used alone or in combination.

[0130] The negative electrode active material preferably contains at least one of a carbon material and a silicon-containing material, and more preferably contains a carbon material, because the copolymer (P) has a significant effect of improving the binding between the electrode active materials and between the electrode active material and the current collector.

[0131] When the electrode is a positive electrode, the electrode active material, i.e., the positive electrode active material, is a material with a more noble standard electrode potential than the negative electrode active material. Examples of the positive electrode active material include nickel-containing lithium composite oxides such as Ni-Co-Mn-based lithium composite oxides, Ni-Mn-Al-based lithium composite oxides, and Ni-Co-Al-based lithium composite oxides, as well as chalcogen compounds such as lithium cobalt oxide (LiCoO), spinel-type lithium manganese oxide (LiMnO), olivine-type lithium iron phosphate, TiS, MnO, MoO, and VO. These materials may be used alone or in combination as the positive electrode active material.

[0132] [5-3. Thickeners] Examples of thickeners include celluloses such as carboxymethyl cellulose (CMC), hydroxyethyl cellulose, and hydroxypropyl cellulose, ammonium salts of celluloses, alkali metal salts of celluloses, polyvinyl alcohol, and polyvinylpyrrolidone. The thickener preferably contains at least one of carboxymethyl cellulose, ammonium salts of carboxymethyl cellulose, and alkali metal salts of carboxymethyl cellulose. This is because the electrode active material becomes more easily dispersed in the electrode slurry.

[0133] The content of the thickener in the electrode slurry is preferably 0.50 parts by mass or more, and more preferably 0.80 parts by mass or more, per 100 parts by mass of the electrode active material, in order to improve the binding between the electrode active materials and between the electrode active material and the current collector in the electrode active material layer produced using the electrode slurry.

[0134] The content of the thickener in the electrode slurry is preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, and even more preferably 1.5 parts by mass or less, relative to 100 parts by mass of the electrode active material, in order to improve the coatability of the electrode slurry.

[0135] [5-4. Aqueous medium] The aqueous medium is water, a hydrophilic solvent, or a mixture thereof. Examples of hydrophilic solvents are as described in the description of the aqueous medium (b) in the synthesis of the copolymer (P). The aqueous medium contained in the electrode slurry may be the same as or different from the aqueous medium (B) contained in the binder composition or the aqueous medium (b) used in the synthesis of the copolymer (P).

[0136] [5-5. Conductive additives] As the conductive aid, it is preferable to use carbon black, carbon fiber, etc. Examples of carbon black include furnace black, acetylene black, Denka Black (registered trademark) (manufactured by Denka Company Ltd.), Ketjen Black (registered trademark) (manufactured by Ketjen Black International Co., Ltd.), etc. Examples of carbon fiber include carbon nanotubes and carbon nanofibers, and a preferred example of carbon nanotubes is VGCF (registered trademark, manufactured by Showa Denko K.K.), which is vapor-grown carbon fiber.

[0137] 5-6. Properties of electrode slurry The nonvolatile content of the electrode slurry is preferably 20% by mass or more, more preferably 30% by mass or more, and even more preferably 40% by mass or more. This is because the concentration of the active ingredients in the electrode slurry is high, and a sufficient amount of electrode active material layer can be formed with a small amount of electrode slurry. The nonvolatile content of the electrode slurry can be adjusted by the amount of aqueous medium in the electrode slurry.

[0138] The nonvolatile content of the electrode slurry is preferably 85% by mass or less, more preferably 75% by mass or less, and even more preferably 65% ​​by mass or less, in order to maintain good coatability of the electrode slurry.

[0139] The viscosity of the electrode slurry is preferably 20,000 mPa·s or less, more preferably 10,000 mPa·s or less, and even more preferably 5,000 mPa·s or less. This is because it improves the applicability of the electrode slurry to the current collector and improves electrode productivity. The viscosity of the electrode slurry is greatly affected by the non-volatile content of the electrode slurry and the type and amount of thickener.

[0140] The pH of the electrode slurry at 23°C may be adjusted appropriately depending on the electrode specifications, production conditions, etc., and is not limited, but is preferably 2.0 to 10, more preferably 4.0 to 9.0, and even more preferably 6.0 to 9.0, in order to improve the durability of the battery produced using the electrode slurry.

[0141] 5-7. Manufacturing method of electrode slurry In this embodiment, the electrode slurry can be prepared by mixing a binder composition, an electrode active material, and optionally a thickener, an aqueous medium, an electroconductive additive, and optionally other components, but this is not limiting. The order in which the components are added is not particularly limited and may be determined as appropriate. Examples of mixing methods include using a stirring, rotating, or shaking mixer.

[0142] <6. Nonaqueous secondary battery electrode> The nonaqueous secondary battery electrode (hereinafter sometimes referred to as "electrode") according to this embodiment comprises a current collector and an electrode active material layer formed on the current collector. The electrode may be in the form of, for example, a laminate or a wound body, but is not particularly limited thereto. The area on which the electrode active material layer is formed on the current collector is not particularly limited, and the electrode active material layer may be formed on the entire surface of the current collector, or on a portion of the surface of the current collector. When the current collector is in the form of a plate, foil, or the like, the electrode active material layer may be formed on both surfaces of the current collector, or on only one surface.

[0143] [6-1. Current Collector] The current collector is preferably a metal sheet having a thickness of 0.001 mm to 0.5 mm, and examples of the metal include iron, copper, aluminum, nickel, stainless steel, etc. When the nonaqueous secondary battery electrode is a negative electrode of a lithium ion secondary battery, the current collector is preferably copper foil.

[0144] [6-2. Electrode active material layer] The electrode active material layer according to this embodiment includes an electrode binder and an electrode active material. The electrode active material layer may also include a conductive additive, a thickener, etc. The components listed here are as described above.

[0145] 6-3. Electrode manufacturing method The electrode can be produced, for example, by applying an electrode slurry onto a current collector, drying it to form an electrode active material layer, and then cutting it into an appropriate size.

[0146] The method for applying the electrode slurry onto the current collector is not particularly limited, and examples thereof include the reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dipping method, squeeze method, etc. Among these, in consideration of the physical properties such as viscosity of the electrode slurry and drying property, it is preferable to use the doctor blade method, knife method, or extrusion method, because this allows for obtaining an electrode active material layer with a smooth surface and small variation in thickness.

[0147] The electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. When applying the electrode slurry to both sides of the current collector, the electrode slurry may be applied to each side sequentially, or to both sides simultaneously. The electrode slurry may be applied to the current collector continuously or intermittently. The amount of electrode slurry to be applied can be determined appropriately depending on the design capacity of the battery, the composition of the electrode slurry, and the like. The amount of electrode slurry to be applied depends on the properties of the electrode slurry, but is generally 13 mg / cm. 2 It is preferable that the amount of coating be less than or equal to 10 ...

[0148] An electrode active material layer is formed on the current collector by drying the electrode slurry applied to the current collector. The method for drying the electrode slurry is not particularly limited, but for example, hot air, reduced pressure or vacuum environment, (far) infrared rays, and low-temperature air can be used alone or in combination. The drying temperature and drying time of the electrode slurry can be appropriately adjusted depending on the nonvolatile content concentration in the electrode slurry, the amount applied to the current collector, and the like. The drying temperature is preferably 40°C or higher and 350°C or lower, and from the viewpoint of productivity, more preferably 60°C or higher and 100°C or lower. The drying time is preferably 1 minute or higher and 30 minutes or lower.

[0149] The electrode sheet in which the electrode active material layer is formed on the current collector may be cut to a size and shape appropriate for the electrode. The method for cutting the electrode sheet is not particularly limited, and for example, slitting, laser cutting, wire cutting, a cutter, a Thomson cutter, or the like may be used.

[0150] Before or after cutting the electrode sheet, the electrode sheet may be pressed as needed. This allows the electrode active material to be more firmly attached to the current collector, and further reduces the thickness of the electrode, making it possible to miniaturize the non-aqueous battery. A common pressing method can be used, and it is particularly preferable to use a die pressing method or a roll pressing method. In the case of the die pressing method, the pressing pressure is not particularly limited, but is preferably 0.5 t / cm. 2 More than 5t / cm 2 In the case of the roll press method, the linear pressure is not particularly limited, but is preferably 0.5 t / cm or more and 5 t / cm or less. This is to obtain the above-mentioned effects of pressing while suppressing a decrease in the insertion and desorption capacity of charge carriers such as lithium ions into and from the electrode active material.

[0151] <7. Non-aqueous secondary battery> As a preferred example of the nonaqueous secondary battery according to this embodiment, a lithium ion secondary battery will be described, but the battery configuration is not limited to that described here. The nonaqueous secondary battery according to this embodiment has a positive electrode, a negative electrode, an electrolyte, and, if necessary, components such as a separator housed in an outer casing, and one or both of the positive electrode and the negative electrode use electrodes produced by the above method. In the nonaqueous secondary battery according to this embodiment, at least one of the positive electrode and the negative electrode contains the copolymer (P) in the electrode binder, and it is preferable that at least the negative electrode contains the copolymer (P).

[0152] [7-1. Electrolyte] The electrolyte solution is a non-aqueous liquid having ion conductivity. Examples of the electrolyte solution include a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, etc., but the former is preferred because it allows for low production costs and results in a non-aqueous battery with low internal resistance.

[0153] As the electrolyte, an alkali metal salt can be used, and can be appropriately selected depending on the type of electrode active material, etc. Examples of the electrolyte include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiB 10 Cl 10 , LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, aliphatic lithium carboxylates, etc. Other alkali metal salts can also be used as the electrolyte.

[0154] The organic solvent for dissolving the electrolyte is not particularly limited, but examples thereof include carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); nitrile compounds such as acetonitrile; and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These organic solvents may be used alone or in combination of two or more. Among these, it is preferable to use a combination of linear carbonate solvents. Examples of linear carbonate solvents include diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0155] [7-2. Exterior body] The outer casing may be, for example, a laminate of aluminum foil and a resin film, but is not limited to this. The shape of the battery may be any shape, such as a coin type, button type, sheet type, cylindrical type, square type, or flat type. [Example]

[0156] In the following examples, a negative electrode of a lithium ion secondary battery and a lithium ion secondary battery are fabricated as an example of the configuration of the present invention, and the effects of the present invention are confirmed by comparing the negative electrode of a lithium ion secondary battery and a lithium ion secondary battery according to comparative examples. Note that the present invention is not limited thereto. Note that the water used in the following examples and comparative examples is ion-exchanged water unless otherwise specified.

[0157] <1. Synthesis of Copolymer (P) and Preparation of Binder Composition> In each example and comparative example, the monomer (a), surfactant (c), and chain transfer agent (f) were mixed with water as the aqueous medium (b) in the amounts shown in Tables 1 and 2 to prepare an emulsified monomer emulsion. An 80% by mass aqueous solution of acrylic acid was used, and the amount of acrylic acid shown in the table is the amount of acrylic acid contained in the aqueous solution. The amount of water added here was adjusted so that the total amount, including the amount of water contained in the acrylic acid aqueous solution, was 360 parts by mass.

[0158] Regarding the monomer (a3), the structures of the compounds (a3-1), (a3-2), and (a3-3) in Tables 1 and 2 are as follows:

[0159] Compounds (a3-1), (a3-2), and (a3-3) are all terblock copolymers in which a block consisting of structural unit (10), a block consisting of structural unit (11), and a block consisting of structural unit (12) are arranged in this order. The structures of structural units (10), (11), and (12) are shown below. Compound (a3-1) contains 30 mol% of structural unit (10), 69 mol% of structural unit (11), and 1.0 mol% of structural unit (12), and has a weight-average molecular weight of 50,000 in terms of polystyrene. Compound (a3-2) contains 93 mol% of structural unit (10), 6.0 mol% of structural unit (11), and 1.0 mol% of structural unit (12), and has a weight-average molecular weight of 80,000 in terms of pullulan. Compound (a3-3) contains 96 mol % of structural unit (10), 1.0 mol % of structural unit (11), and 3.0 mol % of structural unit (12), and has a pullulan-equivalent weight-average molecular weight of 80,000.

[0160] [ka]

[0161] [ka]

[0162] [ka]

[0163] A separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel was charged with 169 parts by mass of water and heated to 75°C. The above monomer emulsion and an aqueous solution of 2.2 parts by mass of potassium persulfate as a polymerization initiator (e1) dissolved in 48 parts by mass of water were added dropwise to the separable flask with stirring at 80°C over 4 hours to carry out emulsion polymerization. After the monomer emulsion and the aqueous potassium persulfate solution were added dropwise, the mixture in the separable flask was stirred at 80°C for 60 minutes.

[0164] Next, an aqueous solution prepared by dissolving 0.81 parts by mass of tert-butyl peroxybenzoate (Kayabutyl B, manufactured by Kayaku Akzo Co., Ltd.) and 0.52 parts by mass of ascorbic acid in 8.1 parts by mass of water was added as a polymerization initiator (e2). Next, an aqueous solution prepared by dissolving 2.3 parts by mass of tert-butyl hydroperoxide (Kayabutyl H-70, manufactured by Kayaku Akzo Co., Ltd.) in 15 parts by mass of water as a polymerization initiator (e3), and an aqueous solution prepared by dissolving 2.3 parts by mass of Rongalit in 15 parts by mass of water were added dropwise while stirring for 60 minutes, thereby carrying out polymerization. Thereafter, an aqueous emulsion of copolymer (P) according to the example and an aqueous emulsion of polymer (CP) according to the comparative example were obtained.

[0165] The resulting aqueous emulsion was cooled to room temperature. Then, to neutralize the aqueous emulsion, 19 parts by mass of 25% by mass aqueous ammonia and 155 parts by mass of water were added to a separable flask to obtain a binder composition containing the copolymer (P) according to the example, and a binder composition containing the polymer (CP) according to the example. The amount of ammonia shown in Tables 1 and 2 indicates the amount of ammonia contained in aqueous ammonia.

[0166] The total amount of water used in the synthesis step of copolymer (P) and the synthesis step of polymer (CP) is shown in Tables 1 and 2. The amount of water shown in Tables 1 and 2 includes not only the water added alone but also the water contained in the aqueous acrylic acid solution and the aqueous ammonia, and the water added together with the polymerization initiator, etc.

[0167] <2. Evaluation of Copolymer (P), Polymer (CP) and Binder Composition> The properties and performance of the binder compositions obtained in the examples and comparative examples and the batteries obtained using these binder compositions were evaluated by the following methods. The evaluation results are shown in Tables 1 and 2.

[0168] [2-1. Glass transition temperature Tg of copolymer (P) and polymer (CP)] The binder composition was cast onto a polyethylene sheet, dried at 50° C. for 5 hours, and then vacuum dried at 50° C. for 1 hour under 98 kPa to obtain a film having a thickness of 0.5 mm. The resulting film was cut into 2 mm x 2 mm pieces, sealed in an aluminum pan, and subjected to DSC measurement using an EXSTAR DSC / SS7020 (Hitachi High-Tech Science Corporation) at a heating rate of 10°C / min under a nitrogen gas atmosphere. The peak top temperatures of the DDSC chart obtained as the temperature derivative of the DSC were measured, and these temperatures were taken as the glass transition temperatures Tg (°C) of the copolymer (P) and polymer (CP). The measurement temperature range was -40°C to 200°C.

[0169] [2-2. Non-volatile content] 1 g of the binder composition was weighed into an aluminum dish with a diameter of 5 cm, and dried at 105°C for 1 hour while circulating air in a dryer at 1 atmosphere (1013 hPa), and the mass of the remaining components was measured. The mass ratio (mass%) of the above components remaining after drying to the mass (1 g) of the binder composition before drying was calculated as the non-volatile content concentration.

[0170] [2-3. Coarse particle amount] One liter of the binder composition was sieved through a wire mesh with 300 mesh openings, and then the wire mesh was washed with ion-exchanged water to remove the liquid residue of the binder composition. After washing, the wire mesh was dried at 105°C for 1 hour in a dryer with air circulating at 1 atmosphere (1013 hPa), and the mass of the wire mesh was measured. The difference between the mass of the wire mesh after drying and the mass of the wire mesh alone was calculated as the amount of coarse particles (g / L).

[0171] 3. Evaluation of electrode and battery performance Negative electrodes and lithium ion secondary batteries were fabricated using the binder compositions prepared in each of the Examples and Comparative Examples, and were evaluated.

[0172] [3-1. Battery Construction] [3-1-1. Preparation of positive electrode] LiNi as the positive electrode active material 0.6 Mn 0.2 Co 0.2A positive electrode slurry was prepared by mixing 94 parts by mass of O2, 3 parts by mass of acetylene black as a conductive additive, and 3 parts by mass of polyvinylidene fluoride as a binder, to which 50 parts by mass of N-methylpyrrolidone was added and further mixed.

[0173] The positive electrode slurry was applied to both sides of a 15 μm thick aluminum foil (positive electrode current collector) by a direct roll method. The amount of the positive electrode slurry applied to the positive electrode current collector was adjusted so that the thickness after the roll press treatment described below would be 125 μm per side.

[0174] The positive electrode slurry applied to the positive electrode current collector was dried at 120°C for 5 minutes and pressed with a roll press (manufactured by Thank Metals, press load 5 t, roll width 7 cm) to obtain a positive electrode sheet on which a positive electrode active material layer was formed. The obtained positive electrode sheet was cut into a size of 50 mm x 40 mm, and a conductive tab was attached to prepare a positive electrode.

[0175] [3-1-2. Preparation of negative electrode] A negative electrode slurry was obtained by mixing 100 parts by mass of artificial graphite (G49, manufactured by Jiangxi Zishen Technology Co., Ltd.) as a negative electrode active material, 3.9 parts by mass (1.5 parts by mass as nonvolatile matter) of the binder composition prepared in each example and comparative example, and 62 parts by mass of a 2% by mass aqueous solution of CMC (carboxymethylcellulose-sodium salt, Sunrose (registered trademark) MAC500LC manufactured by Nippon Paper Chemicals Co., Ltd.), and then adding 28 parts by mass of water.

[0176] The negative electrode slurry was applied to both sides of a 10 μm thick copper foil (negative electrode current collector) by a direct roll method. The amount of the negative electrode slurry applied to the negative electrode current collector was adjusted so that the thickness after the roll press treatment described below would be 170 μm per side.

[0177] The negative electrode slurry applied to the negative electrode current collector was dried at 90°C for 10 minutes and pressed using a roll press (manufactured by Thank Metals, press load 8 t, roll width 7 cm) to obtain a negative electrode sheet with a negative electrode active material layer formed on the current collector. The obtained negative electrode sheet was cut into a size of 52 mm x 42 mm, and a conductive tab was attached to prepare a negative electrode.

[0178] [3-1-3. Battery Construction] A separator (25 μm thick, made of polyethylene) consisting of a porous polyolefin film was placed between the positive and negative electrodes, and the positive and negative electrode active material layers were placed facing each other in an aluminum laminate exterior (battery pack). The exterior was filled with an electrolyte solution, vacuum-impregnated, and sealed with a vacuum heat sealer to prepare a lithium-ion secondary battery for evaluation. The electrolyte solution was prepared by mixing 99 parts by weight of a 1.0 mol / L solution of LiPF6 in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 30 / 50 / 20, with 1 part by weight of vinylene carbonate.

[0179] 3-2. Evaluation of electrodes and batteries [3-2-1. Peel strength of negative electrode active material layer (electrode performance)] The peel strength of the negative electrode active material layer to the current collector was measured as follows. The negative electrode sheet after pressing in the above-mentioned negative electrode preparation process was cut into a size of 25 mm × 100 mm to prepare a test piece. The negative electrode active material layer on the test piece was attached to a 50 mm wide, 200 mm long SUS plate using double-sided tape (NITTOTAPE (registered trademark) No. 5, manufactured by Nitto Denko Corporation) so that the center of the test piece and the center of the SUS plate were aligned. The double-sided tape was attached so as to cover the entire area of ​​the test piece.

[0180] After leaving the test specimen and SUS plate in a bonded state for 10 minutes, the negative electrode active material layer was peeled off from one end of the test specimen by 20 mm in the longitudinal direction. The copper foil side of the test specimen was folded back 180°, and this portion (the copper foil side of the test specimen from which the negative electrode active material layer was peeled off) was gripped with the upper chuck of the tester. Furthermore, one end of the SUS plate from which the negative electrode active material layer was peeled was gripped with the lower chuck. In this state, the copper foil was peeled off from the test specimen at a rate of 100±10 mm / min, and a graph of peel length (mm) vs. peel force (mN) was obtained. The average peel force (mN) was calculated for peel lengths of 10 to 45 mm from the graph, and the value obtained by dividing the average peel force by the width of the test specimen (25 mm) was used as the peel strength (mN / mm) of the negative electrode active material layer. In all Examples and Comparative Examples, no peeling occurred between the double-sided tape and the SUS plate or between the double-sided tape and the negative electrode active material layer during the test.

[0181] [3-2-2. Cycle capacity retention rate at high temperatures (battery performance)] The cycle capacity retention rate of the battery at high temperature was determined by repeating the following steps (i) to (iv) in this order at 45° C. Here, one series of steps (i) to (iv) is defined as one cycle. (i) Charge at a current of 1C until the voltage reaches 4.2V (constant current (CC) charging). (ii) Charge at a voltage of 4.2 V until the current reaches 0.05 C (constant voltage (CV) charging). (iii) Leave to stand for 30 minutes. (iv) Discharge at a current of 1 C until the voltage reaches 2.75 V (constant current (CC) discharge).

[0182] The time-integrated value of the current in steps (i) and (ii) is defined as the charge capacity, and the time-integrated value of the current in step (iv) is defined as the discharge capacity. The discharge capacities at the first cycle and the 100th cycle were measured. The cycle capacity retention rate of the battery at high temperature was calculated as 100 × (discharge capacity at the 100th cycle) / (discharge capacity at the first cycle) [%], and is shown in Tables 1 and 2.

[0183] [3-2-3. Internal resistance (DCR)] The battery internal resistance (DCR (Ω)) test was performed at 25°C using the following procedure. The battery was charged at a constant current of 0.2 C from the rest potential to 3.6 V, and the state of charge was adjusted to 50% of the initial capacity (SOC 50%). The battery was then discharged for 60 seconds at current values ​​of 0.2 C, 0.5 C, 1 C, and 2 C. The DCR (Ω) at SOC 50% was determined from the relationship between these four current values ​​(values ​​over 1 second) and voltage. The results are shown in Tables 1 and 2.

[0184] [Table 1]

[0185] [Table 2]

[0186] <4. Evaluation Results> The evaluation results of each Example show that the amount of coarse particles in the binder composition is small in all Examples, and therefore, the copolymer (P) according to these Examples can suppress the generation of coarse particles. In the electrode evaluation, it is found that the electrodes according to all Examples have high peel strength of the negative electrode active material layer. In the battery evaluation, the batteries according to all Examples have low internal resistance and high discharge capacity retention rate (excellent cycle characteristics).

[0187] In Comparative Example 1, a polymer not having a third structural unit derived from monomer (a3) ​​was synthesized. The electrode produced using the polymer according to Comparative Example 1 as an electrode binder had low peel strength of the negative electrode active material layer, and the battery produced using this electrode had high internal resistance.

[0188] In Comparative Example 2, a polymer containing an excess of the third structural unit derived from the monomer (a3) ​​was synthesized, but gelation proceeded, and an electrode and a battery using this polymer as an electrode binder could not be produced.

[0189] In Comparative Example 3, a polymer not containing a second structural unit derived from the monomer (a2) was synthesized. The electrode produced using the polymer according to Comparative Example 3 as an electrode binder had a low peel strength of the negative electrode active material layer.

[0190] In Comparative Example 4, a polymer containing an excess of the second structural unit derived from the monomer (a2) was synthesized, but gelation proceeded, and an electrode and a battery using this polymer as an electrode binder could not be produced.

[0191] In Comparative Example 5, a polymer containing an excess of the fourth structural unit derived from the internal crosslinking agent (a4) was synthesized, but gelation proceeded, and an electrode and a battery using this polymer as an electrode binder could not be produced.

[0192] As can be seen from the above results, copolymer (P) having the configuration according to the present invention can effectively improve the peel strength of the electrode active material layer from the current collector in a nonaqueous secondary battery, thereby contributing to a reduction in the internal resistance of the battery and an improvement in the cycle characteristics.

Claims

1. A polymer of a compound having an ethylenically unsaturated bond, a first structural unit derived from the monomer (a1), a second structural unit derived from the monomer (a2), and a third structural unit derived from the monomer (a3); or a first structural unit derived from the monomer (a1), a second structural unit derived from the monomer (a2), a third structural unit derived from the monomer (a3), and a fourth structural unit derived from the internal cross-linking agent (a4), the monomer (a1) is a nonionic compound that has an ethylenically unsaturated bond, but has neither a hydroxy group nor a cyano group, does not have a polyoxyalkylene structure, and does not have a plurality of independent ethylenically unsaturated bonds, the monomer (a2) is a compound having an ethylenically unsaturated bond and an anionic functional group, and having neither a polyoxyalkylene structure nor a plurality of independent ethylenically unsaturated bonds, The monomer (a3) ​​has a 31st structural unit represented by the following formula (1), a 32nd structural unit represented by the following formula (2), and a 33rd structural unit represented by the following formula (3), The second structural unit is contained in an amount of 1.0 part by mass or more and 30 parts by mass or less relative to 100 parts by mass of the first structural unit, The third structural unit is contained in an amount of 0.010 parts by mass or more and 70 parts by mass or less relative to 100 parts by mass of the first structural unit, a compound in which the content of the fourth structural unit relative to 100 parts by mass of the first structural unit is 0 parts by mass or more and 20 parts by mass or less; The internal cross-linking agent (a4) is a compound that does not correspond to the monomer (a3), has a plurality of independent ethylenically unsaturated bonds, and is capable of forming a cross-linked structure in radical polymerization of monomers including the monomer (a1), the monomer (a2), and the monomer (a3). A copolymer characterized by: 【Chemistry 1】 【Chemistry 2】 (In formula (2), R １ is an alkyl group having 1 to 6 carbon atoms, which may be branched. 【Transformation 3】 (In formula (3), R ２ is a functional group having an ethylenically unsaturated bond.

2. The monomer (a3) ​​is With respect to the total amount of the 31st structural unit, the 32nd structural unit, and the 33rd structural unit, The 31 structural unit is contained in an amount of 5.0 mol% or more and 98 mol% or less, The 32nd structural unit is contained in an amount of 0.30 mol% or more and 90 mol% or less, The copolymer according to claim 1 , comprising the 33 structural unit in an amount of 0.30 mol % or more and 10 mol % or less.

3. The copolymer according to claim 1 or 2, wherein the monomer (a3) ​​has a plurality of independent ethylenically unsaturated bonds in one molecule.

4. In the formula (3), R ２ represents a vinyloxy group, an allyloxy group, a (meth)acryloyl group, a (meth)acryloyloxy group, and —OCH ２ -CH ２ -CH ２ =CH ２ The copolymer according to any one of claims 1 to 3, comprising at least one selected from the group consisting of:

5. In the formula (3), R ２ The copolymer according to any one of claims 1 to 4, wherein the copolymer is represented by the following formula (4): 【Chemistry 4】 (In formula (4), R ２１ is an alkylene group having 1 to 5 carbon atoms which may be branched, and R ２２ is a functional group selected from the group consisting of a vinyloxy group, an allyloxy group, a (meth)acryloyl group, and a (meth)acryloyloxy group.

6. The copolymer according to any one of claims 1 to 5, wherein the monomer (a3) ​​has a first block consisting of the 31 structural unit, a second block consisting of the 32 structural unit, and a third block consisting of the 33 structural unit.

7. The copolymer according to any one of claims 1 to 6, wherein the monomer (a3) ​​contains the 31st structural unit, the 32nd structural unit, and the 33rd structural unit in a total amount of 90 mass% or more of all structural units.

8. The copolymer according to any one of claims 1 to 7, wherein the monomer (a1) does not have a polar functional group.

9. The copolymer according to any one of claims 1 to 8, wherein the monomer (a2) is a compound having at least one of a carboxy group and a sulfo group.

10. The copolymer described in Claim 9, wherein the monomer (a2) is at least one acid selected from the group consisting of (meth)acrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and parastyrenesulfonic acid, or a salt of said acid.

11. The copolymer according to any one of claims 1 to 10, comprising the first structural unit, the second structural unit, and the third structural unit in a total amount of 80 mass% or more.

12. The copolymer according to any one of claims 1 to 11, wherein the content of the fourth structural unit relative to 100 parts by mass of the first structural unit is 0.050 parts by mass or more.

13. A binder composition for a non-aqueous secondary battery electrode, comprising the copolymer according to any one of claims 1 to 12 dispersed in an aqueous medium.

14. A binder for a non-aqueous secondary battery electrode, comprising the copolymer according to any one of claims 1 to 12.

15. An electrode comprising the binder according to claim 14, an electrode active material, and an aqueous medium, the binder and the electrode active material are dispersed in an aqueous medium, The aqueous medium is a medium selected from the group consisting of water, a hydrophilic solvent, and a mixture containing water and a hydrophilic solvent.

16. A non-aqueous secondary battery electrode comprising the binder of claim 14 .

Images