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

Abstract

A binder for a nonaqueous secondary battery electrode, the binder containing a copolymer having 4.0- 75.0 mol% of a structural unit derived from a monomer represented by formula (I) (in formula (I), R 1 is a hydrogen atom or a methyl group, R2 is a hydrogen atom or a hydroxy group, and m and n are 0 or 1) and 25.0-96.0 mol % of a structural unit derived from a monomer represented by formula (II) (R3 is a hydrogen atom, a methyl group or CH2COOX2, and X1 and X2 are a hydrogen atom, an alkali metal or NH4) .

Description

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

[0001] The present invention relates to a binder for non-aqueous secondary battery electrodes, a binder composition for non-aqueous secondary battery electrodes, a slurry for non-aqueous secondary battery electrodes, a non-aqueous secondary battery electrode, and a non-aqueous secondary battery.

[0002] Non-aqueous secondary batteries using non-aqueous electrolytes are superior to secondary batteries using aqueous electrolytes in terms of higher voltage, smaller size, and lighter weight. Therefore, non-aqueous secondary batteries are widely used as power sources for notebook computers, mobile phones, power tools, and electronic and communication devices. Recently, non-aqueous secondary batteries have also been used in electric vehicles and hybrid vehicles from the perspective of environmentally friendly vehicle applications. There is a strong demand for non-aqueous secondary batteries used in automobiles with higher output, higher capacity, and longer life. A representative example of a non-aqueous secondary battery is the lithium-ion secondary battery.

[0003] A non-aqueous secondary battery includes a positive electrode using a metal oxide or the like as an electrode active material, a negative electrode using a carbon material such as graphite as an electrode active material, and a non-aqueous electrolyte solution mainly containing carbonates or a flame-retardant ionic liquid. In a non-aqueous secondary battery, ions move between the positive and negative electrodes to charge and discharge the battery.

[0004] The positive electrode of a non-aqueous secondary battery is obtained by applying a positive electrode slurry containing an electrode active material such as a metal oxide and a binder to the surface of a current collector made of aluminum foil or the like, drying the slurry to form a positive electrode active material layer, and then cutting the slurry to an appropriate size.The negative electrode of a non-aqueous secondary battery is obtained by applying a negative electrode slurry containing an electrode active material such as a carbon material or a siliceous material and a binder to the surface of a current collector made of copper foil or the like, drying the slurry to form a negative electrode active material layer, and then cutting the slurry to an appropriate size.

[0005] The binders contained in the positive and negative electrodes serve to bind the electrode active materials together and between the electrode active materials and the current collector, thereby preventing the electrode active materials from peeling off from the current collector. Known binders include those that use an aqueous solution of carboxymethyl cellulose (CMC) as a thickener in combination with a (meth)acrylic acid ester-based or styrene-butadiene rubber (SBR)-based aqueous dispersion.

[0006] However, because the binder used is CMC, which has low adhesive strength to the electrode active material and the current collector, the binding strength between the electrode active materials and between the electrode active material and the current collector is low. As a result, batteries having positive and negative electrodes using this binder have the problem that the electrode active materials tend to peel off from each other and from the electrode active material and the current collector after repeated charge and discharge, which leads to a decrease in capacity.

[0007] To solve this problem, a method is known in which a polyacrylate-based aqueous solution or a polyacrylamide-based aqueous solution is used as a binder, which does not require a thickener. Patent Document 1 discloses a copolymer for a non-aqueous battery electrode binder, which contains a copolymer of N-vinylacetamide and sodium acrylate (copolymerization ratio: N-vinylacetamide: acrylic acid = 10 / 90 by mass).

[0008] Furthermore, Patent Document 2 discloses an aqueous binder solution for lithium ion batteries containing an acrylamide, sodium acrylate, and acrylonitrile copolymer (copolymerization ratio: acrylamide, sodium acrylate, acrylonitrile=50 / 15 / 35) or an acrylamide, acrylic acid, sodium acrylate, acrylonitrile, and 2-hydroxyethyl acrylate copolymer (copolymerization ratio: acrylamide, acrylic acid, sodium acrylate, acrylonitrile, 2-hydroxyethyl acrylate=37 / 3 / 10 / 15 / 35).

[0009] International Publication No. 2017 / 150200 Patent No. 6888656

[0010] However, non-aqueous secondary battery electrodes having an electrode active material layer formed using a conventional binder for non-aqueous secondary battery electrodes sometimes have an electrode active material layer with insufficient flexibility. If the electrode active material layer of a non-aqueous secondary battery electrode has insufficient flexibility, the yield of the non-aqueous secondary battery during production will be insufficient.

[0011] Furthermore, conventional nonaqueous secondary batteries are required to have an even higher discharge capacity retention rate after charge-discharge cycling. However, nonaqueous secondary batteries equipped with nonaqueous secondary battery electrodes formed using conventional binders for nonaqueous secondary battery electrodes sometimes have insufficient discharge capacity retention rates after charge-discharge cycling. In particular, nonaqueous secondary battery electrodes equipped with an electrode active material layer containing silicon or a silicon compound as the negative electrode active material are prone to swelling of the electrode active material layer during charge-discharge of the nonaqueous secondary battery. This swelling of the electrode active material layer has been problematic because it reduces the discharge capacity retention rate after charge-discharge cycling.

[0012] The present invention has been made in consideration of the above circumstances, and aims to provide a binder for non-aqueous secondary battery electrodes that can be suitably used as a material for non-aqueous secondary battery electrodes, which can produce non-aqueous secondary batteries having an electrode active material layer with good flexibility and a sufficiently high discharge capacity retention rate after charge-discharge cycling. The present invention also aims to provide a binder composition for non-aqueous secondary battery electrodes and a slurry for non-aqueous secondary battery electrodes, which contain the binder for non-aqueous secondary battery electrodes of the present invention. The present invention also aims to provide a non-aqueous secondary battery electrode, which contains the binder for non-aqueous secondary battery electrodes of the present invention, and which can produce non-aqueous secondary batteries having an electrode active material layer with good flexibility and a sufficiently high discharge capacity retention rate after charge-discharge cycling, and a non-aqueous secondary battery including the electrode.

[0013] The present invention includes the following aspects.

[0014] [1] A binder for a non-aqueous secondary battery electrode, comprising a copolymer (P) having a structural unit (a) derived from a monomer (A) represented by the following general formula (I) and a structural unit (b) derived from a monomer (B) represented by the following general formula (II), wherein the content of the structural unit (a) in the copolymer (P) is 4.0 mol % or more and 75.0 mol % or less, and the content of the structural unit (b) in the copolymer (P) is 25.0 mol % or more and 96.0 mol % or less.

[0015] (In formula (I), R １ represents a hydrogen atom or a methyl group. ２ represents a hydrogen atom or a hydroxy group; m and n each independently represent 0 or 1.

[0016] (In formula (II), R ３ is a hydrogen atom, a methyl group, or CH ２ COOX ２ represents. １ and X ２ are each independently a hydrogen atom, an alkali metal, or NH ４ Represents.)

[0017] [2] The binder for a non-aqueous secondary battery electrode according to [1], wherein the copolymer (P) has a structural unit (c) derived from a monomer (C) represented by the following general formula (III), and the content of the structural unit (c) in the copolymer (P) is 0.5 mol % or more and 55.0 mol % or less:

[0018] (In formula (III), R ４ , R ５ each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

[0019] [3] The binder for a non-aqueous secondary battery electrode according to [1] or [2], wherein the monomer (A) contains at least one of N-hydroxyethyl acrylamide and N-methylol acrylamide. [4] The binder for a non-aqueous secondary battery electrode according to any one of [1] to [3], wherein the monomer (B) contains at least one of sodium (meth)acrylate and lithium (meth)acrylate. [5] The binder for a non-aqueous secondary battery electrode according to any one of [2] to [4], wherein the monomer (C) contains at least one of N-vinylformamide and N-vinylacetamide.

[0020] [6] The binder for a non-aqueous secondary battery electrode according to any one of [1] to [5], wherein the weight-average molecular weight of the copolymer (P) is in the range of 300,000 to 5,000,000. [7] The binder for a non-aqueous secondary battery electrode according to any one of [1] to [6], wherein the weight-average molecular weight of the copolymer (P) is in the range of 1,500,000 to 5,000,000.

[0021] [8] The binder for a non-aqueous secondary battery electrode according to [1], wherein the sum of the content of the structural unit (a) and the content of the structural unit (b) in the copolymer (P) is 55.0 mol % or more. [9] The binder for a non-aqueous secondary battery electrode according to any one of [1] to [8], which is used in an electrode active material layer containing an electrode active material containing 5 mass % or more of silicon or a silicon compound.

[0022]

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

[11] A slurry for a non-aqueous secondary battery electrode, comprising the binder for a non-aqueous secondary battery electrode according to any one of [1] to [9], an electrode active material, and an aqueous medium.

[0023]

[12] A non-aqueous secondary battery electrode comprising a current collector and an electrode active material layer formed on the surface of the current collector, wherein the electrode active material layer contains the binder for a non-aqueous secondary battery electrode according to any one of [1] to [9] and an electrode active material.

[13] The non-aqueous secondary battery electrode according to

[12] , wherein the electrode active material contains 5 mass % or more of silicon or a silicon compound.

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

[12] or

[13] .

[0024] The present invention provides a binder for non-aqueous secondary battery electrodes that can be suitably used as a material for non-aqueous secondary battery electrodes having an electrode active material layer with good flexibility and resulting in non-aqueous secondary batteries with a sufficiently high discharge capacity retention rate after charge-discharge cycling, a binder composition for non-aqueous secondary battery electrodes containing the binder, and a slurry for non-aqueous secondary battery electrodes.The present invention also provides a non-aqueous secondary battery electrode that can be used to produce non-aqueous secondary batteries having an electrode active material layer with good flexibility and resulting in non-aqueous secondary batteries with a sufficiently high discharge capacity retention rate after charge-discharge cycling, and a non-aqueous secondary battery including the electrode.

[0025] The binder for a non-aqueous secondary battery electrode, the binder composition for a non-aqueous secondary battery electrode, the slurry for a non-aqueous secondary battery electrode, the non-aqueous secondary battery electrode, and the non-aqueous secondary battery of the present invention will be described in detail below.

[0026] In the nonaqueous secondary battery (hereinafter sometimes referred to as "battery") of this embodiment, ions move between a positive electrode and a negative electrode, which are nonaqueous secondary battery electrodes, during charging and discharging. The positive electrode includes a positive electrode active material, which is an electrode active material. The negative electrode includes a negative electrode active material, which is an electrode active material. These electrode active materials are materials capable of ion intercalation and deintercalation. A preferred example of such a nonaqueous secondary battery is a lithium ion secondary battery.

[0027] In this embodiment, "(meth)acrylic acid" refers to one or both of methacrylic acid and acrylic acid. "(meth)acrylate" refers to one or both of methacrylate and acrylate. "Weight average molecular weight" is a pullulan-equivalent value calculated using gel permeation chromatography (GPC).

[0028] <1. Binder for Non-Aqueous Secondary Battery Electrode> The binder for non-aqueous secondary battery electrodes according to this embodiment (hereinafter sometimes referred to as "electrode binder") contains a copolymer (P). The copolymer (P) contains a structural unit (a) represented by the following general formula (1) and a structural unit (b) represented by the following general formula (2). In addition to the structural unit (a) and the structural unit (b), the copolymer (P) may contain at least one of a structural unit (c) represented by the following general formula (3) and a structural unit (d) different from the structural units (a) to (c).

[0029] (In formula (1), R １ represents a hydrogen atom or a methyl group. ２ represents a hydrogen atom or a hydroxy group. m and n each independently represent 0 or 1. ３ is a hydrogen atom, a methyl group, or CH ２ COOX ２ represents. １ and X ２ are each independently a hydrogen atom, an alkali metal, or NH ４ (In formula (3), R ４ , R ５ each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

[0030] The structural unit (a) and the structural unit (b) contained in the copolymer (P) are repeating units. There is no particular limitation on the arrangement order of the structural unit (a) and the structural unit (b) contained in the copolymer (P). The copolymer (P) may be any of a random copolymer, a block copolymer, and an alternating copolymer containing the structural unit (a) and the structural unit (b). When the copolymer (P) contains not only the structural unit (a) and the structural unit (b) but also at least one of the structural unit (c) and the structural unit (d), there is no particular limitation on the arrangement order of the repeating units, the structural unit (a), the structural unit (b), and at least one of the structural unit (c) and the structural unit (d).

[0031] <1-1. Structural unit (a)> The structural unit (a) represented by general formula (1) is a structural unit derived from a monomer (A) represented by the following general formula (I). The monomer (A) may be only one type of compound, or may be a plurality of types of compounds. The structural unit (a) contributes to improving the flexibility of an electrode active material layer containing an electrode binder containing the copolymer (P), and also contributes to improving the discharge capacity retention rate after charge-discharge cycles in a battery including a nonaqueous secondary battery electrode having this electrode active material layer.

[0032] (In formula (I), R １ represents a hydrogen atom or a methyl group. ２ represents a hydrogen atom or a hydroxy group; m and n each independently represent 0 or 1.

[0033] R in formula (I) １ , R ２ , m and n are R in formula (1) １ , R ２ , m and n are the same as those in formula (I). １ represents a hydrogen atom or a methyl group, and is preferably a hydrogen atom, since this is a material for a nonaqueous secondary battery electrode that can provide a nonaqueous secondary battery with a higher discharge capacity retention rate after charge / discharge cycling.

[0034] In formula (I), m is 0 or 1, and is preferably 0 because it results in a non-aqueous secondary battery electrode with a high solubility parameter (SP value) and better resistance (stability) to the electrolyte solution contained in the battery. When m is 1, R ２ represents a hydrogen atom or a hydroxy group. In formula (I), n is 0 or 1, and preferably 1. This is because the electrode active material layer containing the electrode binder containing the copolymer (P) has better flexibility, and the material becomes a material for a nonaqueous secondary battery electrode that can provide a nonaqueous secondary battery with a higher discharge capacity retention rate after charge-discharge cycles.

[0035] Specific examples of the monomer (A) include the compounds shown below (R １ , R ２ , m, and n are R in formula (I), respectively. １ , R ２ , m, n). N-methylolacrylamide ((N-MAM)R １ : hydrogen atom, m: 0, n: 0), N-hydroxyethyl acrylamide ((HEAA)R １ : hydrogen atom, m: 0, n: 1), N-hydroxypropyl acrylamide (R １ : hydrogen atom, R ２ : hydrogen atom, m: 1, n: 1), N-(2,3-dihydroxypropyl)acrylamide (R １ : hydrogen atom, R ２ : hydroxy group, m: 1, n: 1).

[0036] Among these, it is preferable to contain at least one of N-hydroxyethyl acrylamide and N-methylol acrylamide as the monomer (A). This is because it serves as a material for a nonaqueous secondary battery electrode that can provide a nonaqueous secondary battery with a higher discharge capacity retention rate after charge-discharge cycling. In particular, it is preferable to contain N-hydroxyethyl acrylamide as the monomer (A). This is because it improves the flexibility of an electrode active material layer that includes an electrode binder that contains the copolymer (P), and it serves as a material for a nonaqueous secondary battery electrode that can provide a nonaqueous secondary battery with an even higher discharge capacity retention rate after charge-discharge cycling.

[0037] The reason why a nonaqueous secondary battery electrode having an electrode active material layer containing an electrode binder containing copolymer (P) can provide a battery with a sufficiently high discharge capacity retention rate after charge-discharge cycling when copolymer (P) contains structural unit (a) represented by general formula (1) is not clear, but the inventors speculate that this is due to the following functions being obtained by containing structural unit (a).

[0038] That is, when the electrode binder contains the copolymer (P) containing the structural unit (a) having an amide bond and a hydroxy group, an electrode active material layer having better resistance to the electrolyte contained in the battery can be obtained, compared to, for example, a case in which the electrode binder contains a copolymer containing a structural unit having an ester bond (-C(=O)O-) instead of the structural unit (a). Therefore, the electrode active material layer containing the electrode binder containing the copolymer (P) is less likely to be broken even when subjected to stress accompanying charge and discharge of the battery, and swelling of the electrode accompanying charge and discharge of the battery is suppressed.

[0039] Furthermore, since the copolymer (P) contains the structural unit (a) having an amide bond and a hydroxy group, an electrode active material layer containing an electrode binder containing the copolymer (P) exhibits good binding properties between the electrode active material particles and between the electrode active material particles and the current collector. From these facts, it is presumed that a battery having a nonaqueous secondary battery electrode provided with an electrode active material layer containing an electrode binder containing the copolymer (P) is less susceptible to deterioration due to charge and discharge and has a sufficiently high discharge capacity retention rate after charge and discharge cycles.

[0040] <1-2. Structural unit (b)> The structural unit (b) represented by general formula (2) is a structural unit derived from the monomer (B) represented by the following general formula (II). The monomer (B) may be a single type of compound or a plurality of types of compounds.

[0041] (In formula (II), R ３ is a hydrogen atom, a methyl group, or CH ２ COOX ２ represents. １ and X ２ are each independently a hydrogen atom, an alkali metal, or NH４ Represents.)

[0042] R in formula (II) ３ , X １ and X ２ is R in formula (2). ３ , X １ and X ２ In formula (II), R ３ is a hydrogen atom, a methyl group, or CH ２ COOX ２ R is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom, because it is a material for a nonaqueous secondary battery electrode that can provide a nonaqueous secondary battery with a higher discharge capacity retention rate after charge / discharge cycles. ３ is CH ２ COOX ２ If X ２ is a hydrogen atom, an alkali metal, or NH ４ and an alkali metal or NH ４ This is because it is a material for a non-aqueous secondary battery electrode that can provide a non-aqueous secondary battery with a higher discharge capacity retention rate after charge / discharge cycles. １ is a hydrogen atom, an alkali metal, or NH ４ represents an alkali metal or NH ４ This is because it is a material for a non-aqueous secondary battery electrode that can provide a non-aqueous secondary battery with a higher discharge capacity retention rate after charge / discharge cycles.

[0043] X in formula (II) １ and X ２ When at least one of the above is an alkali metal, examples of the alkali metal include lithium, sodium, and potassium. １ and X ２ Specific examples of preferred monovalent cations corresponding to at least one of X include lithium ion, sodium ion, potassium ion, and ammonium ion. １ and X ２This is because the monomer represented by formula (II) in which at least one of the above is one of these monovalent cations is easily available. Among these monovalent cations, it is preferable to contain at least one of lithium ions and sodium ions, and it is more preferable to contain sodium ions. This is because the copolymer (P) has even better adhesive strength to the electrode active material, and a battery having a nonaqueous secondary battery electrode including an electrode active material layer containing an electrode binder containing this copolymer has a higher discharge capacity retention rate after charge-discharge cycles.

[0044] Specific examples of the monomer (B) include the compounds shown below (R ３ , X １ and X ２ are R in formula (II), respectively. ３ , X １ and X ２ Acrylic acid ((Aa)R ３ : hydrogen atom, X １ : hydrogen atom), methacrylic acid ((MAa)R ３ : methyl group, X １ : hydrogen atom), itaconic acid (R ３ :CH ２ COOX ２ , X １ : hydrogen atom, X ２ : hydrogen atom) and salts thereof (X in formula (II) １ and X ２ At least one of the above is an alkali metal or NH ４ (Compound wherein

[0045] Among these, it is preferable that the monomer (B) contains at least one of an acrylate and a methacrylate, and it is more preferable that the monomer (B) contains at least one of sodium acrylate, lithium acrylate, sodium methacrylate, and lithium methacrylate. This is because it becomes a material for a non-aqueous secondary battery electrode that can obtain a non-aqueous secondary battery with a higher discharge capacity retention rate after charge-discharge cycling. In particular, it is preferable that the monomer (B) contains sodium acrylate. This is because it becomes a material for a non-aqueous secondary battery electrode that can obtain a non-aqueous secondary battery with an even higher discharge capacity retention rate after charge-discharge cycling.

[0046] X in formula (II) １ and X ２ At least one of the above is an alkali metal or NH ４ The monomer (B) represented by the formula (II) is, for example, １ and X ２ In this case, a compound in which at least one of the groups is a hydrogen atom is neutralized with at least one of hydroxide and aqueous ammonia to convert a part of the carboxyl group (—COOH) into a salt. １ and X ２ At least one of the above is an alkali metal or NH ４ When synthesizing the copolymer (P) having the formula (I), for example, the following methods 1 and 2 can be used. Among these, the first method is preferred because it is easy to increase the molecular weight of the copolymer (P) produced.

[0047] In the first method, first, X in formula (II) １ and X ２ A compound in which at least one of X in formula (II) is a hydrogen atom is prepared and neutralized with a known neutralizing agent. １ and X ２ At least one of the above is an alkali metal or NH ４ Then, a compound represented by the formula (II) as the monomer (B) is obtained. １ and X ２ At least one of the above is an alkali metal or NH ４ and a monomer containing the monomer (A) represented by formula (I). This copolymerizes the structural unit (a) represented by formula (1) and the structural unit (b) represented by formula (2), １ and X ２ is at least one of alkali metals, or NH ４ and a structural unit (b) represented by the following formula (1):

[0048] In the second method, the monomer (B) is X in formula (II) １ and X ２The monomers containing the monomer (A) and the monomer (B) are copolymerized with a compound in which at least one of the monomers is a hydrogen atom. The copolymer is then neutralized with a known neutralizing agent. This results in a copolymer of the structural unit (a) represented by formula (1) and the structural unit (b) represented by formula (2), in which X in formula (2) is a １ and X ２ At least one of the above is an alkali metal or NH ４ and a structural unit (b) represented by the following formula (1):

[0049] X in the structural unit (b) represented by general formula (2) １ and X ２ is an alkali metal or NH ４ If X １ and X ２ is the same alkali metal or NH ４ It is preferable that, in the first method described above, X in formula (II) １ and X ２ is a hydrogen atom, or in the second method described above, １ and X ２ By carrying out a step of neutralizing a copolymer obtained by copolymerizing a monomer containing a compound in which X in formula (2) is a hydrogen atom, １ and X ２ is the same alkali metal or NH ４ This is because a copolymer (P) containing the structural unit (b) represented by the formula (1) can be obtained.

[0050] In this embodiment, for example, X in formula (2) is obtained by the first method or the second method described above. １ and X ２ At least one of the above is an alkali metal or NH ４ When a copolymer (P) containing a structural unit (b) represented by the formula: is produced, it is considered that the structural unit (b) derived from the salt of the monomer (B) contained in the copolymer (P) is formed with the structural unit (b) derived from the monomer (B) in an amount equal to the equivalent of the cation contained in the neutralizing agent (the valence of the cation × the number of moles of the cation; the same applies hereinafter).

[0051] In addition, when the cation contained in the neutralizing agent is divalent or more, one cation and the same number of X in the monomer (B) as the valence of the cation are used. １ and X ２ It is considered that at least one of the above is bonded to form a structural unit (b) derived from a salt of the monomer (B).

[0052] Therefore, the equivalent of the cation contained in the neutralizing agent is X in the monomer (B) represented by formula (II) used to produce the copolymer (P). １ and X ２ X contained in a compound in which at least one of １ and X ２ When the number of moles of X in the structural unit (b) derived from the monomer (B) contained in the copolymer (P) obtained after neutralization is larger than the total number of moles of X １ and X ２ are all alkali metals or NH ４ and it is considered that all of the structural units (b) contained in the copolymer (P) are derived from the salt of the monomer (B).

[0053] On the other hand, the equivalent of the cation contained in the neutralizing agent is X in the monomer (B) represented by formula (II) used to produce the copolymer (P). １ and X ２ X contained in a compound in which at least one of １ and X ２ When the number of moles is less than the total number of moles, all of the cations contained in the neutralizing agent are considered to have formed salts of the structural units (b) derived from the monomer (B) contained in the copolymer (P) obtained after neutralization. Accordingly, it is considered that, of the structural units (b) derived from the monomer (B), structural units derived from the salt are formed in an amount equivalent to the amount of the cations contained in the neutralizing agent.

[0054] Specifically, for example, when copolymer (P) is produced by a method in which (meth)acrylic acid is used as monomer (B), a monomer containing (meth)acrylic acid and monomer (A) is copolymerized, and then the copolymer is neutralized using a neutralizing agent, it is considered that structural units (b) derived from a salt of (meth)acrylic acid are formed in the structural units (b) derived from monomer (B) contained in copolymer (P) obtained after neutralization in an amount equal to the equivalent of the cation contained in the neutralizing agent (cation valence × number of moles of cation; the same applies hereinafter).

[0055] The structural unit (b) derived from the monomer (B) is X in the monomer (B) represented by formula (II). １ and X ２ At least one of the above is an alkali metal or NH ４ The copolymer (P) preferably contains 60 mol % or more, more preferably 80 mol % or more, even more preferably 95 mol % or more, and may even contain 100 mol % of the structural unit (b) derived from a compound represented by the formula: The copolymer (P) has even better adhesive strength to an electrode active material, and a battery having a nonaqueous secondary battery electrode including an electrode active material layer containing an electrode binder containing the copolymer exhibits a higher discharge capacity retention rate after charge-discharge cycles.

[0056] The reason why a nonaqueous secondary battery electrode having an electrode active material layer containing an electrode binder containing copolymer (P) can provide a battery with a sufficiently high discharge capacity retention rate after charge-discharge cycling when copolymer (P) contains structural unit (b) represented by general formula (2) is not clear. However, the present inventors speculate that this is due to the following function being obtained by containing structural unit (b).

[0057] That is, (i) when the electrode binder contains the copolymer (P) containing the structural unit (b) having at least one of a carboxy group and a carboxylate, the resistance to the electrolyte contained in the battery is improved compared to, for example, when the electrode binder contains a copolymer containing a structural unit having an ester bond (—C(═O)O—) instead of the structural unit (b). Therefore, an electrode active material layer containing the electrode binder containing the copolymer (P) can suppress swelling of the electrode due to swelling of the electrode binder in contact with the electrolyte.

[0058] Furthermore, (ii) because the copolymer (P) contains the structural unit (b) having at least one of a carboxy group and a carboxylic acid, a non-aqueous secondary battery electrode slurry containing an electrode binder containing the copolymer (P) exhibits good dispersibility of solids such as the electrode active material and the conductive additive. This suppresses solid aggregation, facilitating the formation of an electrode active material layer in which the solids are uniformly dispersed. As a result, a battery having a non-aqueous secondary battery electrode with an electrode active material layer is less likely to experience localized potential bias in the electrode active material layer during charging and discharging, thereby suppressing excess electrolyte decomposition during charging and discharging. Furthermore, (iii) because the copolymer (P) contains the structural unit (b) having at least one of a carboxy group and a carboxylic acid, an electrode active material layer containing an electrode binder containing the copolymer (P) exhibits good adhesion between electrode active material particles and between the electrode active material particles and the current collector.

[0059] It is presumed that, due to the functions provided by the inclusion of these structural units (b) of (i) to (iii), a battery having a nonaqueous secondary battery electrode provided with an electrode active material layer containing an electrode binder including the copolymer (P) is less susceptible to deterioration due to charge and discharge, and has a sufficiently high discharge capacity retention rate after charge and discharge cycles.

[0060] <1-3. Structural unit (c)> The structural unit (c) represented by general formula (3) is a structural unit derived from the monomer (C) represented by the following general formula (III). The monomer (C) may be a single type of compound or a plurality of types of compounds. The structural unit (c) contributes to improving the dispersibility of solid components such as the electrode active material and the conductive additive in a non-aqueous secondary battery electrode slurry containing an electrode binder containing the copolymer (P).

[0061] (In formula (III), R ４ , R ５ each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

[0062] R in formula (III) ４ , R ５ is R in formula (3). ４ , R ５ In formula (III), R ４ , R ５ R each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and is preferably a hydrogen atom or an alkyl group having 1 to 3 carbon atoms. ４ is preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom, because this improves the dispersibility of solid components such as the electrode active material and the conductive additive in a non-aqueous secondary battery electrode slurry containing an electrode binder containing the copolymer (P). ５ is preferably a hydrogen atom or a methyl group, and more preferably a methyl group, because this improves the dispersibility of solid components such as the electrode active material and the conductive additive in a non-aqueous secondary battery electrode slurry containing an electrode binder containing the copolymer (P).

[0063] Specific examples of the monomer (C) include the compounds shown below (R ４ , R ５ are R in formula (III), respectively. ４ , R ５ N-vinylformamide (R ４ : hydrogen atom, R ５ : hydrogen atom), N-vinylacetamide (R ４ : hydrogen atom, R５ Among these, N-vinylacetamide is preferred as the monomer (C) because it provides good dispersibility of solid components such as an electrode active material and a conductive additive in a non-aqueous secondary battery electrode slurry containing an electrode binder containing the copolymer (P).

[0064] <1-4. Structural Unit (d)> The copolymer (P) may contain, in addition to the structural unit (a), the structural unit (b), and the optional structural unit (c), a structural unit (d) different from the structural units (a) to (c), as long as the effects of the present invention are not impaired. The structural unit (d) is a structural unit derived from another monomer (D) that does not fall under any of the monomers (A), (B), and (C). For example, (meth)acrylic acid, itaconic acid, and salts thereof, which are ethylenically unsaturated monomers having a carboxy group, fall under the monomer (B). The monomer (D) may be a single compound or a plurality of compounds.

[0065] The other monomer (D) may be any polymerizable compound that does not fall under any of the monomers (A), (B), and (C), and may include, for example, a hydrophilic ethylenically unsaturated compound and a hydrophobic ethylenically unsaturated compound, and preferably includes a hydrophilic ethylenically unsaturated compound. Examples of the hydrophilic ethylenically unsaturated monomer include compounds having at least one polymerizable ethylenically unsaturated bond and at least one of a polar group such as a hydroxy group, a carboxy group, or a cyano group, and an amide bond.

[0066] Examples of the ethylenically unsaturated monomer having an amide bond include (meth)acrylamide, N-alkyl(meth)acrylamide, N,N-dialkyl(meth)acrylamide, diacetone(meth)acrylamide, dimethylaminoalkyl(meth)acrylamide in which the alkyl group excluding the dimethylamino group has 1 to 5 carbon atoms, (meth)acrylamide-2-methylpropanesulfonic acid, etc. Among these, (meth)acrylamide is preferred as the ethylenically unsaturated monomer having an amide bond, since it can give a copolymer (P) having good resistance to the electrolyte solution contained in the battery.

[0067] Examples of the ethylenically unsaturated monomer having a hydroxy group include 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl acrylate, 1,4-cyclohexanedimethanol monoacrylate, etc. Among these, 2-hydroxyethyl (meth)acrylate is preferred as the ethylenically unsaturated monomer having a hydroxy group, since it improves the flexibility of the electrode active material layer containing the electrode binder containing the copolymer (P).

[0068] Examples of ethylenically unsaturated monomers having a carboxy group include β-carboxyethyl acrylate, maleic acid, fumaric acid, crotonic acid, half esters of unsaturated dicarboxylic acids, etc. Examples of ethylenically unsaturated monomers having a cyano group include (meth)acrylonitrile, etc.

[0069] <1-5. Content of each structural unit in copolymer (P)> Next, the contents of the structural units (a) to (d) contained in copolymer (P) will be described.

[0070] In this embodiment, the content of the structural units derived from each monomer contained in the copolymer (P) can be calculated using the blending amount of each monomer used to produce the copolymer (P). Hereinafter, the content of the structural units derived from each monomer in the copolymer (P) will be explained using the content of each monomer, i.e., the value of mol%, when the total of the monomers from which the structural units in the copolymer (P) are derived is defined as 100 mol%.

[0071] In addition, when a compound other than the monomer, such as a chain transfer agent, is used in polymerizing the copolymer (P), the structural units derived from the compound other than the monomer are also considered to be part of the structure of the copolymer (P). １ and X ２ At least one of the above is an alkali metal or NH ４ When a copolymer (P) containing a structural unit (b) represented by the formula: is produced, it is considered that the structural unit (b) derived from the salt of the monomer (B) contained in the copolymer (P) is formed with the structural unit (b) derived from the monomer (B) in an amount equal to the equivalent of the cation contained in the neutralizing agent (the valence of the cation × the number of moles of the cation; the same applies hereinafter).

[0072] (Content of structural unit (a)) The content of the structural unit (a) in the copolymer (P) is 4.0 mol% or more. This is because the flexibility of an electrode active material layer containing an electrode binder containing the copolymer (P) is improved, and the occurrence of cracks in the electrode active material layer can be suppressed. In addition, this is because a battery having a nonaqueous secondary battery electrode with an electrode active material layer containing the copolymer (P) has a high discharge capacity retention rate after charge / discharge cycling. The content of the structural unit (a) is preferably 15.0 mol% or more, more preferably 35 mol% or more, and even more preferably 40.0 mol% or more, because the above-mentioned effects of including the structural unit (a) are more pronounced.

[0073] The content of the structural unit (a) is 75.0 mol% or less. This is because in a non-aqueous secondary battery electrode slurry containing an electrode binder containing the copolymer (P), the solid contents contained in the electrode active material, conductive additive, electrode binder, etc. are more uniformly present. Furthermore, this is because a battery having a non-aqueous secondary battery electrode comprising an electrode active material layer containing the copolymer (P) exhibits a high discharge capacity retention rate after charge / discharge cycling. For the above reasons, the content of the structural unit (a) is preferably 65.0 mol% or less, more preferably 60.0 mol% or less, and even more preferably 55.0 mol% or less.

[0074] (Content of structural unit (b)) The content of the structural unit (b) in the copolymer (P) is 25.0 mol% or more. This is because, in a slurry for a non-aqueous secondary battery electrode containing an electrode binder containing the copolymer (P), the state of solids contained in the electrode active material, conductive additive, electrode binder, etc. becomes more uniform. Also, this is because a battery having a non-aqueous secondary battery electrode comprising an electrode active material layer containing the copolymer (P) exhibits a high discharge capacity retention rate after charge / discharge cycling. The content of the structural unit (b) is preferably 30.0 mol% or more, more preferably 40.0 mol% or more, and even more preferably 45.0 mol% or more, because the above-mentioned effects of including the structural unit (b) become more pronounced.

[0075] The content of the structural unit (b) is 96.0 mol% or less. This is because the flexibility of the electrode active material layer containing the electrode binder containing the copolymer (P) is improved, and the occurrence of cracks in the electrode active material layer can be suppressed. For the above reasons, the content of the structural unit (b) is preferably 85.0 mol% or less, more preferably 65.0 mol% or less, and even more preferably 60.0 mol% or less.

[0076] (Total Content of Structural Unit (a) and Structural Unit (b)) The sum of the content of the structural unit (a) and the content of the structural unit (b) in the copolymer (P) is preferably 55.0 mol% or more. This is because an electrode binder can be obtained that can form a nonaqueous secondary battery electrode having a more flexible electrode active material layer and providing a battery with a higher discharge capacity retention rate after charge-discharge cycling. In particular, when the above total is 55.0 mol% or more, even if the electrode active material layer contains silicon or a silicon compound, a nonaqueous secondary battery electrode can be formed that has a more flexible electrode active material layer and provides a battery with a sufficiently high discharge capacity retention rate after charge-discharge cycling, which is preferable.

[0077] The sum of the content of the structural unit (a) and the content of the structural unit (b) is more preferably 60.0 mol% or more, and even more preferably 65.0 mol% or more. The sum of the content of the structural unit (a) and the content of the structural unit (b) may be 70.0 mol% or more. The above sum may be 100 mol%. That is, the copolymer (P) may be a binary copolymer consisting only of the structural unit (a) and the structural unit (b). When the structural units contained in the copolymer (P) are only the structural unit (a) and the structural unit (b) (in other words, the above sum is 100 mol%), the copolymer (P) can be easily produced.

[0078] (Content of structural unit (c)) The content of the structural unit (c) in the copolymer (P) is preferably 0.5 mol% or more, more preferably 0.8 mol% or more, and even more preferably 1.0 mol% or more. This is because, in a non-aqueous secondary battery electrode slurry containing an electrode binder containing the copolymer (P), the dispersibility of solid components such as the electrode active material and the conductive additive is improved, and aggregation of the solid components is suppressed, making it easier to form an electrode active material layer in which the solid components are uniformly dispersed.

[0079] The content of the structural unit (c) is preferably 55.0 mol% or less, more preferably 50.0 mol% or less, and even more preferably 45.0 mol% or less, because an electrode active material layer containing an electrode binder containing a copolymer (P) having a content of the structural unit (c) of 55.0 mol% or less has better flexibility and is less susceptible to cracking.

[0080] (Content of structural unit (d)) The content of the structural unit (d) in the copolymer (P) is preferably 40.0 mol% or less, more preferably 35.0 mol% or less, and may be 3.0 mol% or less, or even 0 mol%. When the structural unit (d) is a structural unit derived from an ethylenically unsaturated monomer having an amide bond, particularly (meth)acrylamide, the content of the structural unit (d) is preferably more than 0 mol%, and may be 5.0 mol% or more, or may be 10.0 mol% or more. This is because a copolymer (P) having good resistance to the electrolyte contained in the battery can be obtained.

[0081] When the structural unit (d) is a structural unit derived from an ethylenically unsaturated monomer having an amide bond, particularly (meth)acrylamide, the content of the structural unit (d) is preferably 40.0 mol% or less, more preferably 35.0 mol% or less, and even more preferably 33.0 mol% or less. This is because the copolymer (P) has excellent wettability with respect to electrode active materials and even better adhesive strength to electrode active materials. Furthermore, a battery having a nonaqueous secondary battery electrode equipped with an electrode active material layer containing this copolymer (P) suppresses decomposition of excess electrolyte solution during charging and discharging. When the structural unit (d) is a structural unit derived from an ethylenically unsaturated monomer having an amide bond, particularly (meth)acrylamide, the content of the structural unit (d) may be 0 mol%. In this case, the copolymer (P) has even better wettability with respect to electrode active materials and even better adhesive strength to electrode active materials. In addition, in a battery having a nonaqueous secondary battery electrode provided with an electrode active material layer containing this copolymer (P), decomposition of excess electrolyte solution during charge and discharge is further suppressed.

[0082] <1-6. Weight-average molecular weight of copolymer (P)> The weight-average molecular weight of copolymer (P) is preferably 300,000 or more, more preferably 700,000 or more, and even more preferably 1,000,000 or more. The weight-average molecular weight of copolymer (P) may be 1,500,000 or more, or may be 2,000,000 or more. This is because the electrode active material layer containing the electrode binder containing copolymer (P) has better adhesion between the electrode active materials and between the electrode active material and the current collector. As a result, a battery having a nonaqueous secondary battery electrode with an electrode active material layer containing copolymer (P) has a higher discharge capacity retention rate after charge-discharge cycles.

[0083] The weight-average molecular weight of the copolymer (P) is preferably 5 million or less, more preferably 4 million or less, and even more preferably 3.5 million or less. The weight-average molecular weight of the copolymer (P) may be 3 million or less. This is because the copolymer (P) can be easily produced. In addition, this makes it easy to adjust the viscosity of a slurry for a non-aqueous secondary battery electrode containing an electrode binder containing the copolymer (P), improving the dispersibility of solids such as the electrode active material and the conductive additive and the productivity of the electrode active material layer.

[0084] <1-7. Production method of copolymer (P)> The copolymer (P) is preferably produced by a method of copolymerizing monomers including the monomer (A) and the monomer (B) using a radical polymerization method in an aqueous medium containing a radical polymerization initiator. Examples of the radical polymerization method that can be used include a method in which all of the monomers used to produce the copolymer (P) are charged at once and polymerized, and a method in which the monomers used to produce the copolymer (P) are polymerized while being continuously supplied.

[0085] The content of each monomer in all the monomers used to prepare copolymer (P) is considered to be the content of the structural unit corresponding to that monomer in copolymer (P). For example, the content of monomer (A) in all the monomers used to prepare copolymer (P) is the content of structural unit (a) in the synthesized copolymer (P).

[0086] In this embodiment, for example, by the first method or the second method described above, X in formula (2)１ and / or X ２ is an alkali metal or NH ４ When a copolymer (P) containing a structural unit (b) represented by the formula: is produced, it is considered that the structural unit (b) derived from the salt of the monomer (B) contained in the copolymer (P) is formed with the structural unit (b) derived from the monomer (B) in an amount equal to the equivalent of the cation contained in the neutralizing agent (the valence of the cation × the number of moles of the cation; the same applies hereinafter).

[0087] Therefore, the equivalent of the cation contained in the neutralizing agent is X in the monomer (B) represented by formula (II) used to produce the copolymer (P). １ and X ２ X contained in a compound in which at least one of １ and X ２ When the number of moles of X in the structural unit (b) derived from the monomer (B) contained in the copolymer (P) obtained after neutralization is larger than the total number of moles of X １ and X ２ are all alkali metals or NH ４ and it is considered that all of the structural units (b) contained in the copolymer (P) are derived from the salt of the monomer (B).

[0088] On the other hand, the equivalent of the cation contained in the neutralizing agent is X in the monomer (B) represented by formula (II) used to produce the copolymer (P). １ and X ２ X contained in a compound in which at least one of １ and X ２ When the total number of moles of the cations contained in the neutralizing agent is less than the total number of moles of the cations contained in the neutralizing agent, it is considered that all of the cations contained in the neutralizing agent form salts of the structural units (b) derived from the monomer (B) contained in the copolymer (P) obtained after neutralization. Therefore, it is considered that, of the structural units (b) derived from the monomer (B), structural units derived from the salt are formed in an amount equivalent to the amount of the cations contained in the neutralizing agent.

[0089] When producing the copolymer (P), for example, ammonium persulfate, potassium persulfate, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, azo compounds, etc. can be used as radical polymerization initiators. Examples of azo compounds include 2,2'-azobis(2-methylpropionamidine) dihydrochloride. When producing the copolymer (P) by radical polymerization in an aqueous medium, it is preferable to use a water-soluble compound as the radical polymerization initiator. Furthermore, when polymerizing the copolymer (P), redox polymerization may be performed using a radical polymerization initiator and a reducing agent in combination, as necessary. Examples of reducing agents used in redox polymerization include sodium bisulfite, Rongalite, and ascorbic acid.

[0090] The aqueous medium used in producing the copolymer (P) is preferably water. As long as the polymerization stability of the copolymer (P) is not impaired, a hydrophilic solvent may be added to water. Examples of the hydrophilic solvent to be added to water include methanol, ethanol, and N-methylpyrrolidone.

[0091] The radical polymerization for producing the copolymer (P) is preferably carried out at a temperature of 30 to 90°C.

[0092] During the polymerization for producing the copolymer (P), a chain transfer agent may be used for the purpose of adjusting the molecular weight of the copolymer (P). The chain transfer agent is not particularly limited, but examples thereof include known agents such as thiols such as β-mercaptopropionic acid and octyl thioglycolate, alcohols such as isopropyl alcohol and ethanol, halogenated hydrocarbons such as carbon tetrabromide and carbon tetrachloride, and α-methylstyrene dimer. The amount of these chain transfer agents used is not particularly limited, and known amounts may be used. The amount of the chain transfer agent used is preferably, for example, 10 mol % or less based on the total number of moles of the monomers and compounds used to produce the copolymer (P).

[0093] The electrode binder of this embodiment may contain other components in addition to the copolymer (P). Examples of other components include at least one of a polymer other than the copolymer (P) and a surfactant. When the electrode binder of this embodiment contains other components in addition to the copolymer (P), it can be produced by mixing the copolymer (P) and the other components using a known method.

[0094] Examples of polymers other than the copolymer (P) include water-soluble polymers such as poly(meth)acrylates, poly(meth)acrylamides, carboxymethylcellulose salts, and polyvinyl alcohol, and emulsion-type polymers such as polystyrene-(meth)acrylate copolymers and polystyrene-butadiene copolymers. Examples of surfactants include anionic surfactants such as alkylbenzenesulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts, and nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.

[0095] When the electrode binder of the present embodiment contains other components in addition to the copolymer (P), 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 particularly preferably 98% by mass or more, because the inclusion of the copolymer (P) increases the contribution to the intended effects of the present invention.

[0096] 2. Binder Composition for Non-Aqueous Secondary Battery Electrode The binder composition for non-aqueous secondary battery electrodes (hereinafter also referred to as "electrode binder composition") of this embodiment contains an electrode binder and an aqueous medium.

[0097] The aqueous medium contained in the electrode binder composition contains water. The aqueous medium contained in the electrode binder composition may contain a hydrophilic solvent in addition to water. Examples of hydrophilic solvents include methanol, ethanol, and N-methylpyrrolidone. The water content in the aqueous medium contained in the electrode binder composition is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may be 100% by mass.

[0098] The aqueous medium contained in the electrode binder composition may be, for example, the same as the aqueous medium used in the synthesis of the copolymer (P), or may be the aqueous medium used in the synthesis of the copolymer (P) to which a solvent such as water has been further added. Furthermore, the electrode binder contained in the electrode binder composition of this embodiment may be dissolved or dispersed in the aqueous medium.

[0099] The content of the electrode binder in the electrode binder composition is preferably 30% by mass or less, and more preferably 20% by mass or less. This is because the electrode binder composition is unlikely to have an excessively high viscosity and has an appropriate viscosity. If the electrode binder composition has an appropriate viscosity, when the electrode binder composition is mixed with an electrode active material, etc., described below, to prepare a slurry for a non-aqueous secondary battery electrode, the electrode active material, etc. can be efficiently dispersed.

[0100] The content of the electrode binder in the electrode binder composition is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, and even more preferably 8.0% by mass or more, because when a non-aqueous secondary battery electrode slurry and a non-aqueous secondary battery electrode are produced using the electrode binder composition, the amount of the electrode binder composition used can be reduced.

[0101] The pH of the electrode binder composition is preferably 4.0 or higher, more preferably 5.0 or higher, and even more preferably 6.0 or higher, because when the electrode binder composition is mixed with an electrode active material, etc., described below, to prepare a slurry for a non-aqueous secondary battery electrode, the electrode active material, etc. can be efficiently dispersed.

[0102] The pH of the electrode binder composition is preferably 11 or less, more preferably 10 or less, and even more preferably 9.0 or less. This is because, when the electrode binder composition is mixed with an electrode active material, etc., described below, to prepare a slurry for a non-aqueous secondary battery electrode, the electrode active material, etc. can be efficiently dispersed. The pH of the electrode binder composition is a value measured with a pH meter at a liquid temperature of 23°C.

[0103] The electrode binder composition of this embodiment may contain other components as needed in addition to the electrode binder and the aqueous medium. Examples of other components include a pH adjuster, a surfactant, etc. Examples of pH adjusters include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, and potassium hydroxide, amines such as ethanolamine, triethanolamine, and ethylenediamine, and ammonia.

[0104] Examples of surfactants include anionic surfactants such as alkylbenzenesulfonates, alkyl sulfates, polyoxyethylene alkyl ether sulfates, and fatty acid salts; and nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polycyclic phenyl ethers, polyoxyalkylene alkyl ethers, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.

[0105] The electrode binder composition of this embodiment can be produced by a method of mixing an electrode binder, an aqueous medium, and other components that are contained as necessary.

[0106] 3. Slurry for Non-Aqueous Secondary Battery Electrode The slurry for non-aqueous secondary battery electrodes (hereinafter also referred to as "electrode slurry") of this embodiment contains an electrode binder, an electrode active material, and an aqueous medium. The electrode binder and the electrode active material contained in the electrode slurry of this embodiment may each be dissolved or dispersed in the aqueous medium. The electrode slurry of this embodiment may contain at least one of a conductive aid and a thickener, etc., as necessary. In order to simplify the process of producing the electrode slurry, it is preferable that the electrode slurry does not contain a thickener.

[0107] The method for preparing the electrode slurry is not particularly limited as long as it can uniformly dissolve or disperse the electrode binder and electrode active material in the aqueous medium. The electrode slurry of this embodiment may be produced by mixing the electrode binder composition of this embodiment, the electrode active material, and an aqueous medium that is further added as needed, or by mixing the electrode binder of this embodiment, the electrode active material, and an aqueous medium. Examples of methods for preparing the electrode slurry include a method in which the materials for the electrode slurry are mixed using a mixing device such as a stirring, rotating, or shaking device.

[0108] The nonvolatile content of the electrode slurry can be adjusted by adjusting the amount of aqueous medium contained in the electrode slurry. The nonvolatile content of the electrode slurry includes the copolymer (P) in the electrode binder, the electrode active material, and an optional conductive additive. Unless otherwise specified, the nonvolatile content of the electrode slurry is the ratio of the mass of the components remaining after weighing 1 g of the electrode slurry onto an aluminum dish with a diameter of 5 cm and drying it at 110°C for 5 hours while circulating air in a dryer under atmospheric pressure to the mass before drying.

[0109] The nonvolatile content concentration of the electrode slurry is preferably 30% by mass or more, and more preferably 40% by mass or more. This is because, when the electrode slurry is applied to a current collector and dried to form an electrode active material layer, the energy required for drying can be reduced. The nonvolatile content concentration of the electrode slurry is preferably 70% by mass or less, and more preferably 60% by mass or less. This is because, when the electrode slurry is applied to a current collector and dried to form an electrode active material layer, the electrode slurry has a viscosity that makes it easy to apply.

[0110] <3-1. Electrode Binder Content> The content of the electrode binder in the electrode slurry is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more, relative to the total mass of the electrode binder, the electrode active material, and the conductive assistant contained as needed. This is because, when the electrode slurry is applied to a current collector and dried to form an electrode active material layer, an electrode active material layer can be obtained that has better binding properties between the electrode active material particles and between the electrode active material particles and the current collector.

[0111] The content of the electrode binder in the electrode slurry is preferably 10% by mass or less, more preferably 7.0% by mass or less, and even more preferably 5.0% by mass or less, based on the total mass of the electrode binder, the electrode active material, and the conductive additive contained as needed. This is because by applying the electrode slurry to a current collector and drying it to form an electrode active material layer, a nonaqueous secondary battery electrode that can form a battery with a large charge / discharge capacity and low internal resistance can be obtained.

[0112] <3-2. Electrode Active Material> When the electrode slurry is used to form a negative electrode active material layer, which is an electrode active material layer of a lithium ion secondary battery, the electrode active material may be, for example, the negative electrode active material shown below. Only one type of negative electrode active material may be used, or two or more types may be used.

[0113] Examples of the negative electrode active material include a conductive polymer, a carbon material, lithium titanate, silicon, a silicon compound, etc. Among these negative electrode active materials, it is preferable to use one or more selected from the carbon material, lithium titanate, silicon, and a silicon compound, since this allows a lithium ion secondary battery with a high energy density per volume to be obtained.

[0114] Examples of conductive polymers include polyacetylene and polypyrrole. Examples of carbon materials include cokes such as petroleum coke, pitch coke, and coal coke; and graphites such as artificial graphite and natural graphite. Examples of artificial graphite include SCMG (registered trademark)-XRs (manufactured by Resonac Co., Ltd.). Examples of silicon compounds include silicon oxides, specifically SiO ｘ (0.1≦x≦2.0) and the like.

[0115] The negative electrode active material preferably contains at least one of silicon and a silicon compound, and a carbon material such as graphite. This is because the electrode binder of this embodiment has a more pronounced effect of improving the binding between the negative electrode active materials and between the negative electrode active material and the current collector. In particular, the negative electrode active material preferably contains silicon or a silicon compound, and graphite, and the silicon oxide is SiO. ｘ (0.1≦x≦2.0) and graphite.

[0116] The negative electrode active material contained in the electrode slurry preferably contains 5% by mass or more of silicon or a silicon compound relative to the total amount of the negative electrode active material, more preferably 10% by mass or more, and even more preferably 15% by mass or more. When the negative electrode active material contained in the electrode slurry contains 5% by mass or more of silicon or a silicon compound, a negative electrode active material layer containing 5% by mass or more of silicon or a silicon compound is obtained by applying the electrode slurry to a current collector and drying it. This negative electrode active material layer exhibits good adhesion between the negative electrode active materials and between the negative electrode active material and the current collector. This is because the copolymer (P) contained in the negative electrode active material layer exhibits good adhesion to silicon and silicon compounds. Therefore, in this embodiment, even in a nonaqueous secondary battery electrode including a negative electrode active material layer containing 5% by mass or more of silicon or a silicon compound, swelling of the negative electrode active material layer is unlikely to occur during charging and discharging of the nonaqueous secondary battery, thereby achieving a higher capacity and a high discharge capacity retention rate after charge and discharge cycling.

[0117] The content of silicon or silicon compounds in the negative electrode active material is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 25% by mass or less, based on the total amount of the negative electrode active material, because when the content of silicon or silicon compounds in the negative electrode active material is 50% by mass or less, a lithium ion secondary battery that achieves a high capacity and has an even higher discharge capacity retention rate after charge / discharge cycles may be obtained.

[0118] When the electrode slurry is used to form a positive electrode active material layer, which is an electrode active material layer of a lithium ion secondary battery, the electrode active material may be, for example, the positive electrode active material shown below. Only one type of positive electrode active material may be used, or two or more types may be used.

[0119] The positive electrode active material is, for example, lithium cobalt oxide (LiCoO ２ ), lithium composite oxides containing nickel, spinel-type lithium manganese oxide (LiMn ２ O ４ ), olivine-type lithium iron phosphate, TiS ２ , MnO２ , MoO ３ , V ２ O ５ Examples of the positive electrode active material include chalcogen compounds such as LiNi, LiNiO, and LiNiCoO. Examples of lithium composite oxides containing nickel include Ni-Co-Mn-based lithium composite oxides, Ni-Mn-Al-based lithium composite oxides, and Ni-Co-Al-based lithium composite oxides. Specific examples of the positive electrode active material include LiNi １／３ Mn １／３ Co １／３ O ２ , LiNi ３／５ Mn １／５ Co １／５ O ２ Examples include:

[0120] <3-3. Conductive Aid> The electrode slurry may contain, as a conductive aid, carbon black such as acetylene black, vapor grown carbon fiber, etc. A specific example of vapor grown carbon fiber is VGCF (registered trademark)-H (manufactured by Resonac Inc.).

[0121] <3-4. Aqueous Medium> The aqueous medium contained in the electrode slurry contains water. The aqueous medium contained in the electrode slurry may contain a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, and N-methylpyrrolidone. The water content in the aqueous medium contained in the electrode slurry is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, and may be 100% by mass. The aqueous medium contained in the electrode slurry may be the same as or different from the aqueous medium contained in the electrode binder composition.

[0122] 4. Nonaqueous Secondary Battery Electrode The nonaqueous secondary battery electrode (hereinafter also referred to as "electrode") of this embodiment includes a current collector and an electrode active material layer formed on the surface of the current collector. The electrode active material layer includes the electrode binder of this embodiment and an electrode active material. The shape of the electrode in the battery is not particularly limited. The electrode in the battery may be in the form of a laminate in which layers made of a plurality of electrodes are stacked, or in the form of a wound body in which layers made of strip-shaped electrodes are wound.

[0123] The electrode of this embodiment may be a positive electrode or a negative electrode. Because the electrode of this embodiment includes an electrode active material layer containing the electrode binder of this embodiment, whether it is a positive electrode or a negative electrode, the electrode active materials in the electrode active material layer have good adhesion to each other and to the current collector. Furthermore, the electrode binder in the electrode of this embodiment is less likely to swell when in contact with the electrolyte, so the adhesion of the electrode binder is less likely to decrease. As a result, a non-aqueous secondary battery including the electrode of this embodiment is less likely to experience swelling in the electrode active material layer due to charge and discharge, and has a high discharge capacity retention rate after charge and discharge cycling. Furthermore, because the electrode of this embodiment includes an electrode active material layer containing the electrode binder of this embodiment, the electrode active material layer has good flexibility, resulting in a high yield during the production of non-aqueous secondary batteries.

[0124] The current collectors provided on the electrodes are preferably made of sheet-like metal with a thickness of 0.001 to 0.5 mm. Examples of metals used for the current collectors include iron, copper, aluminum, nickel, and stainless steel. When the nonaqueous secondary battery provided with the electrodes is a lithium-ion secondary battery, it is preferable to use an aluminum-containing current collector for the positive electrode, and it is preferable to use a copper-containing current collector for the negative electrode, although these are not particularly limited.

[0125] The electrode of this embodiment can be manufactured, for example, by a method of applying an electrode slurry onto a current collector and drying it, but is not limited to this method. Examples of methods for applying the electrode slurry onto a current collector 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, the doctor blade method, knife method, and extrusion method are preferred, and application using the doctor blade method is more preferred. This is because it is suitable for various physical properties such as viscosity of the electrode slurry and drying properties, and a coating film with a good surface condition can be obtained.

[0126] 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, it may be applied to one side at a time, or to both sides simultaneously. The electrode slurry may be applied continuously to the entire surface of the current collector, or may be applied intermittently. The amount and application range of the electrode slurry can be appropriately determined depending on the size of the battery, etc. The amount of electrode slurry applied is such that the basis weight of the electrode active material layer after drying is 4 to 20 mg / cm. ２ The amount is preferably 6 to 16 mg / cm ２ It is more preferable that the amount is such that:

[0127] Next, the electrode slurry applied to the current collector is dried. This results in an electrode sheet. The method for drying the applied electrode slurry is not particularly limited, but for example, a method selected from hot air, vacuum, (far) infrared rays, electron beams, microwaves, and low-temperature air can be used alone or in combination. The drying temperature is preferably 40°C or higher and 180°C or lower. The drying time is preferably 1 minute or higher and 30 minutes or lower.

[0128] The electrode sheet may be used as an electrode as is, or may be cut to an appropriate size and shape for use as an electrode. The method for cutting the electrode sheet is not particularly limited, but may be, for example, slitting, laser cutting, wire cutting, a cutter, a Thomson cutter, or the like.

[0129] Before or after cutting the electrode sheet, the electrode sheet may be pressed as needed. This allows the electrode active materials to be more firmly bonded to each other and to the current collector. Pressing also allows the electrode to be thinner, enabling the nonaqueous secondary battery to be even more compact.

[0130] A common method can be used to press the electrode sheet. In particular, it is preferable to use a mold press method or a roll press method as a method for pressing the electrode sheet. The pressure for pressing the electrode sheet is not particularly limited, but it is preferable to set it within a range in which pressing the electrode sheet does not affect the doping / dedoping of lithium ions and the like into the electrode active material. The pressure for pressing the electrode sheet is 0.5 to 5 t / cm ２ It is preferable to set the following.

[0131] 5. Nonaqueous Secondary Battery Next, a lithium ion secondary battery will be described as an example of a nonaqueous secondary battery according to the present embodiment. The lithium ion secondary battery according to the present embodiment includes a positive electrode, a negative electrode, an electrolyte, and optional components such as a separator housed in an exterior case. In the lithium ion secondary battery according to the present embodiment, at least one of the positive electrode and the negative electrode is an electrode according to the present embodiment that includes the electrode binder according to the present embodiment.

[0132] <5-1. Electrolyte> A non-aqueous liquid having ion conductivity is used as the electrolyte. Examples of the electrolyte include a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, etc. It is preferable to use a solution in which an electrolyte is dissolved in an organic solvent as the electrolyte, as this reduces production costs and allows the production of a battery with low internal resistance.

[0133] The electrolyte may be an alkali metal salt, and may be appropriately selected depending on the type of electrode active material. For example, LiClO ４ , LiBF ６ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６, LiSbF ６ , LiB １０ Cl １０ , LiAlCl ４ , LiCl, LiBr, LiB(C ２ H ５ ) ４ , C.F. ３ SO ３ Li, C.H. ３ SO ３ Li, LiCF ３ SO ３ , LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ２ N, lithium aliphatic carboxylates, etc.

[0134] The organic solvent for dissolving the electrolyte is not particularly limited, and examples thereof include carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC), nitrile compounds such as acetonitrile, and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These organic solvents may be used alone or in combination of two or more.

[0135] <5-2. Exterior Body> The exterior body can be made of a known material such as metal, aluminum laminate, etc. The shape of the battery may be any shape, such as coin type, button type, sheet type, cylindrical type, square type, flat type, etc.

[0136] The electrode binder of this embodiment contains a copolymer (P) having a structural unit (a) derived from a monomer (A) represented by general formula (I) and a structural unit (b) derived from a monomer (B) represented by general formula (II). The copolymer (P) contained in the electrode binder of this embodiment has a content of the structural unit (a) of 4.0 mol % or more and 75.0 mol % or less and a content of the structural unit (b) of 25.0 mol % or more and 96.0 mol % or less. Therefore, the electrode binder of this embodiment can be suitably used as a material for a nonaqueous secondary battery electrode, which can provide a nonaqueous secondary battery having an electrode active material layer with good flexibility and a sufficiently high discharge capacity retention rate after charge-discharge cycling.

[0137] The electrode binder composition and electrode slurry of the present embodiment contain the electrode binder of the present embodiment, and therefore can be suitably used as materials for non-aqueous secondary battery electrodes that provide non-aqueous secondary batteries having an electrode active material layer with good flexibility and a sufficiently high discharge capacity retention rate after charge-discharge cycling.

[0138] The nonaqueous secondary battery electrode of this embodiment includes a current collector and an electrode active material layer formed on the surface of the current collector, and the electrode active material layer contains the electrode binder of this embodiment. Therefore, the nonaqueous secondary battery electrode provides a nonaqueous secondary battery with a sufficiently high discharge capacity retention rate after charge-discharge cycling. Furthermore, the nonaqueous secondary battery electrode of this embodiment includes the electrode binder of this embodiment, and therefore has an electrode active material layer with good flexibility. Therefore, nonaqueous secondary batteries including the nonaqueous secondary battery electrode of this embodiment have a good manufacturing yield. Because the nonaqueous secondary battery of this embodiment includes the nonaqueous secondary battery electrode of this embodiment, it can be manufactured with a good manufacturing yield and has a sufficiently high discharge capacity retention rate after charge-discharge cycling.

[0139] The present invention will be described in detail below with reference to examples and comparative examples. The examples shown below are intended to facilitate understanding of the present invention. The present invention is not limited to these examples. Specifically, the following examples will be described using an example of a binder composition for a non-aqueous secondary battery electrode containing the binder for a non-aqueous secondary battery electrode of the present invention, in which a negative electrode binder composition for a lithium ion secondary battery was prepared. However, this binder composition for a non-aqueous secondary battery electrode can also be used as a positive electrode binder composition for a lithium ion secondary battery.

[0140] In the following examples, a negative electrode binder composition for a lithium ion secondary battery was prepared as an example of a binder composition for a non-aqueous secondary battery electrode containing the binder for a non-aqueous secondary battery electrode of the present invention, and a negative electrode slurry, a negative electrode, and a lithium ion secondary battery were prepared using this. The effects of the present invention were confirmed by comparing with a negative electrode binder composition for a lithium ion secondary battery, a negative electrode, and a lithium ion secondary battery according to comparative examples.

[0141] <1. Preparation of Negative Electrode Binder Composition> The monomers (A) to (D) used in the synthesis of the copolymers (P) of Examples 1 to 14 contained in the negative electrode binder compositions and their proportions are shown in Table 1 or Table 2. Furthermore, the monomers (A) to (D) used in the synthesis of the copolymers or polymers of Comparative Examples 1 to 8 contained in the negative electrode binder compositions and their proportions are shown in Table 3. The composition ratio (monomer (A) + monomer (B)) shown in Tables 1 to 3 is the ratio of the total amount of monomer (A) and monomer (B) to the total amount of monomers used in the synthesis. The copolymers (P) of Examples 1 to 14 and the copolymers or polymers of Comparative Examples 1 to 8 were produced in the same manner, except for the types and amounts of monomers and polymerization initiators used in the synthesis.

[0142]

[0143]

[0144]

[0145] The monomers (A) to (D) shown in Tables 1 to 3 are the compounds shown below. When an aqueous solution containing one or more selected from the monomers (A) to (D) is used to synthesize a copolymer or polymer, the amounts of the monomers (A) to (D) used shown in Tables 1 to 3 are the contents of the monomers (A) to (D) themselves in the aqueous solution, and do not include water as the solvent.

[0146] (Monomer (A)) N-hydroxyethyl acrylamide (HEAA) N-methylolacrylamide (N-MAM) (Monomer (B)) Sodium acrylate (AaNa) (28.5% by mass aqueous solution) Sodium methacrylate (MAaNa) (28.5% by mass aqueous solution) Lithium acrylate (AaLi) (28.5% by mass aqueous solution) (Monomer (C)) N-vinylacetamide (NVA) (manufactured by Resonac Inc.) (Other monomers (D)) Acrylamide (AAm) (50.0% by mass aqueous solution) 2-hydroxyethyl acrylate (HEA)

[0147] The details of the radical polymerization initiators used in synthesizing the copolymers (P) of Examples 1 to 14 and the copolymers or polymers of Comparative Examples 1 to 8 are as follows: (Radical polymerization initiator) 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50) (manufactured by Wako Pure Chemical Industries, Ltd.) Ammonium persulfate (manufactured by Wako Pure Chemical Industries, Ltd.)

[0148] <1-1. Preparation of Negative Electrode Binder Compositions of Examples 1 to 10 and 14 and Comparative Examples 1 to 8> A separable flask equipped with a cooling tube, a thermometer, a stirrer, and a dropping funnel was charged with 100 parts by mass of monomers (A) to (D) in total in the proportions shown in Tables 1 to 3, 0.2 parts by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride as a radical polymerization initiator, 0.05 parts by mass of ammonium persulfate, and 567 parts by mass of water at 30°C. The mixture was heated to 80°C, and polymerization was carried out for 4 hours to produce a copolymer or a polymer, thereby obtaining a reaction liquid containing the copolymer or the polymer.

[0149] Water was added to the reaction liquid containing the copolymer or polymer after polymerization to obtain negative electrode binder compositions having a nonvolatile content of 10.0 mass% in Examples 1 to 10 and 14 and Comparative Examples 1 to 8. The amount of water in the negative electrode binder compositions in Examples 1 to 10 and 14 and Comparative Examples 1 to 8 includes the amount of water in the aqueous solutions used as monomers (sodium acrylate, sodium methacrylate, lithium acrylate, acrylamide) when synthesizing the copolymer or polymer.

[0150] <1-2. Preparation of Negative Electrode Binder Composition of Example 11> The negative electrode binder composition of Example 11 was obtained in the same manner as in Example 3, except that the amount of 2,2′-azobis(2-methylpropionamidine) dihydrochloride charged as the radical polymerization initiator was changed to 0.8 parts by mass, and the amount of ammonium persulfate charged was changed to 0.20 parts by mass.

[0151] <1-3. Preparation of Negative Electrode Binder Composition of Example 12> The negative electrode binder composition of Example 12 was obtained in the same manner as in Example 3, except that the amount of 2,2′-azobis(2-methylpropionamidine) dihydrochloride charged as the radical polymerization initiator was changed to 0.4 parts by mass, and the amount of ammonium persulfate charged was changed to 0.10 parts by mass.

[0152] <1-4. Preparation of Negative Electrode Binder Composition of Example 13> The negative electrode binder composition of Example 13 was obtained in the same manner as in Example 3, except that the amount of 2,2′-azobis(2-methylpropionamidine) dihydrochloride charged as the radical polymerization initiator was changed to 0.1 parts by mass and the amount of ammonium persulfate charged was changed to 0.03 parts by mass.

[0153] 2. Weight-Average Molecular Weight of Copolymer or Polymer The weight-average molecular weight of the copolymer or polymer contained in each of the negative electrode binder compositions of Examples 1 to 14 and Comparative Examples 1 to 8 was measured using gel permeation chromatography (GPC) under the following conditions. The results are shown in Tables 1 to 3.

[0154] GPC device: GPC-101 (manufactured by Resonac Co., Ltd.) Solvent: 0.1 M NaNO ３Aqueous solution Sample column: Shodex Column Ohpak SB-806 HQ (8.0 mm I.D. x 300 mm) x 2 (manufactured by Resonac Inc.) Reference column: Shodex Column Ohpak SB-800 RL (8.0 mm I.D. x 300 mm) x 2 (manufactured by Resonac Inc.) Column temperature: 40°C Sample concentration: 0.1 mass% Detector: RI-71S (manufactured by Shimadzu Corporation) Pump: DU-H2000 (manufactured by Shimadzu Corporation) Pressure: 1.3 MPa Flow rate: 1 ml / 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 (manufactured by Resonac Co., Ltd.)

[0155] 3. Preparation of Negative Electrode As the negative electrode active material, 76.8 parts by mass of SCMG (registered trademark)-XRs (manufactured by Resonac Inc.), which is graphite, and 19.2 parts by mass of silicon monoxide (SiO) (manufactured by Sigma-Aldrich) were prepared. In addition, 1 part by mass of VGCF (registered trademark)-H (manufactured by Resonac Inc.) was prepared as a conductive additive.

[0156] Then, the above-mentioned negative electrode active material, the conductive additive, 30 parts by mass of the negative electrode binder composition of any one of Examples 1 to 14 and Comparative Examples 1 to 8 (containing 3 parts by mass of copolymer or polymer and 27 parts by mass of water), and 20 parts by mass of water were mixed to obtain a mixture. The mixing was performed by a method in which the mixture was kneaded for 4 minutes at a rotation speed of 2000 rpm using an agitation mixer (a planetary-type agitation mixer). 53 parts by mass of water was further added to the obtained mixture, and the mixture was further mixed for 4 minutes at a rotation speed of 2000 rpm using the mixer to obtain the negative electrode slurries of Examples 1 to 14 and Comparative Examples 1 to 8.

[0157] The prepared negative electrode slurries of Examples 1 to 14 and Comparative Examples 1 to 8 were applied to one side of a current collector made of copper foil with a thickness of 10 μm so that the weight per unit area after drying was 8 mg / cm ２The negative electrode slurry was applied using a doctor blade method so that the negative electrode slurry was applied. The copper foil to which the negative electrode slurry was applied was dried at 60°C for 10 minutes, and then further dried at 100°C for 5 minutes to form a negative electrode active material layer, thereby producing a negative electrode sheet. Two negative electrode sheet pieces measuring 50 mm in width and 60 mm in length were cut out from the obtained negative electrode sheet. Each cut negative electrode sheet piece was pressed using a mold press at a pressure of 1 t / cm. ２ I pressed it once each.

[0158] One of the two pressed negative electrode sheet pieces was cut into a square measuring 22 mm in length and 22 mm in width, and a conductive tab was attached to form a negative electrode. The other of the two pressed negative electrode sheet pieces was used for the negative electrode evaluation described below.

[0159] 4. Evaluation of Negative Electrode The electrode characteristics of the negative electrodes of Examples 1 to 14 and Comparative Examples 1 to 8 were evaluated by the following method. The results are shown in Tables 1 to 3.

[0160] <4-1. Evaluation of Appearance (Number of Aggregates) of Negative Electrode Active Material Layer> For the pressed negative electrode sheet piece having a width of 50 mm and a length of 60 mm produced in the section <3. Production of Negative Electrode>, the appearance of the entire negative electrode active material layer was visually observed, and the number of aggregates in the negative electrode active material layer was counted.

[0161] <4-2. Evaluation of Flexibility of Negative Electrode Active Material Layer (Winding Test)> The pressed negative electrode sheet piece with a width of 50 mm and a length of 60 mm prepared in the section <4. Preparation of Negative Electrode> was used as a test piece and dried at 80 ° C for 12 hours. Then, using a 50 μm thick tape, one end of the dried test piece in the longitudinal direction was fixed to a stainless steel rod with a diameter of 3 mm, and the other end was fixed to a glass plate. Thereafter, the length direction of the stainless steel rod and the width direction of the test piece were arranged approximately parallel, and the surface of the test piece on the negative electrode active material layer side was wound around the stainless steel rod with the stainless steel rod side (inside). At this time, the wound test piece was wound around the stainless steel rod so that wrinkles and slack did not occur, and the test piece wound around the stainless steel rod and the test piece wound on top of the wound test piece were in close contact. Next, the wound test piece was unwound from the stainless steel rod around which it was wound and spread out flat. Then, the appearance of the entire negative electrode active material layer of the test piece was visually observed, and the number of cracks in the negative electrode active material layer was counted.

[0162] <5. Preparation of Positive Electrode> LiNi as Positive Electrode Active Material １／３ Mn １／３ Co １／３ O ２ 90 parts by mass of the above, 5 parts by mass of acetylene black as a conductive additive, and 5 parts by mass of polyvinylidene fluoride as a positive electrode binder were mixed to obtain a mixture. 100 parts by mass of N-methylpyrrolidone as a solvent was added to the obtained mixture and mixed to obtain a positive electrode slurry (LiNi in the solid content １／３ Mn １／３ Co １／３ O ２ The proportion of was 90% by mass.

[0163] The prepared positive electrode slurry was applied to one side of a current collector made of aluminum foil with a thickness of 20 μm so that the weight per unit area after drying was 22.5 mg / cm ２The positive electrode slurry was applied using a doctor blade method so that the positive electrode active material layer was formed. The aluminum foil to which the positive electrode slurry was applied was dried at 120 ° C. for 5 minutes to form a positive electrode active material layer, thereby producing a positive electrode sheet. The obtained positive electrode sheet was pressed using a roll press to obtain a positive electrode sheet having a positive electrode active material layer with a thickness of 100 μm. The pressed positive electrode sheet was cut into a square measuring 20 mm in length and 20 mm in width, and a conductive tab was attached to form a positive electrode.

[0164] The theoretical capacity of the prepared positive electrode was calculated by multiplying the weight per unit area of ​​the positive electrode slurry after drying (22.5 × 10 －３ g / cm ２ ), the application area of ​​the positive electrode slurry (2.0 cm × 2.0 cm), and LiNi １／３ Mn １／３ Co １／３ O ２ The capacity as a positive electrode active material (160 mAh / g) and the LiNi content in the solid content １／３ Mn １／３ Co １／３ O ２ The theoretical capacity of the positive electrode was calculated using the ratio (0.90) of the positive electrode active material content to the positive electrode active material content in the solid content of the positive electrode slurry. The theoretical capacity of the positive electrode (mAh) = (basis weight of the positive electrode slurry after drying) × (coated area of ​​the positive electrode slurry) × (capacity of the positive electrode active material) × (proportion of the positive electrode active material in the solid content of the positive electrode slurry)

[0165] 6. Preparation of Electrolyte Solution Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 30:50:20 to obtain a mixed solvent. LiPF as an electrode active material was added to the obtained mixed solvent. ６ was added to give a concentration of 1.0 mol / L, vinylene carbonate (VC) was dissolved therein to give concentrations of 1.0 mass % and fluoroethylene carbonate (FEC) to give concentrations of 2.0 mass % to obtain an electrolyte solution.

[0166] 7. Battery Assembly The positive electrode and the negative electrode of any of Examples 1 to 14 and Comparative Examples 1 to 8 were arranged with their active material layers facing each other, via a separator made of a polyolefin porous film, and then housed in an exterior body (battery pack) made of an aluminum laminate material. An electrolyte solution was then injected into the exterior body, and the opening of the exterior body was sealed using a vacuum heat sealer. Through the above steps, laminate-type batteries of Examples 1 to 14 and Comparative Examples 1 to 8 were obtained.

[0167] 8. Evaluation of the Battery The battery characteristics of the batteries of Examples 1 to 14 and Comparative Examples 1 to 8 were evaluated by the following methods. The results are shown in Tables 1 to 3.

[0168] 8-1. Battery Discharge Capacity Retention Rate (100 Cycles) To determine the battery discharge capacity retention rate, a charge-discharge cycle test was performed on the battery at a temperature of 25°C using the following procedure. First, the battery was charged at a current of 1 C until the voltage reached 4.2 V (CC charging). Next, the battery was charged at a voltage of 4.2 V until the current reached 0.05 C (CV charging). After leaving the battery for 30 minutes, the battery was discharged at a current of 1 C until the voltage reached 2.75 V (CC discharging). A series of CC charging, CV charging, and CC discharging operations constituted one cycle, and 100 cycles were performed.

[0169] Next, the sum of the time-integrated values ​​of the current during CC charging and CV charging at the nth cycle was defined as the charge capacity (mAh) at the nth cycle, and the time-integrated value of the current during CC discharging at the nth cycle was defined as the discharge capacity (mAh) at the nth cycle. The discharge capacity retention rate at the 100th cycle of the battery was calculated using the following formula: Discharge capacity retention rate at the 100th cycle (%) = (Discharge capacity at the 100th cycle / Discharge capacity at the 1st cycle) × 100

[0170] 9. Evaluation Results As shown in Tables 1 and 2, the negative electrodes of Examples 1 to 14 had two or less cracks in the negative electrode active material layer and had good flexibility. Moreover, the negative electrodes of Examples 1 to 14 had one or less aggregates in the negative electrode active material layer and had good appearance. Furthermore, the batteries of Examples 1 to 14 had a discharge capacity retention rate of 92% or more at the 100th cycle, confirming that they had good battery characteristics.

[0171] On the other hand, as shown in Table 3, the negative electrode of Comparative Example 1, which contained a polymer obtained by polymerizing only monomer (B) without using monomer (A), had 15 cracks in the negative electrode active material layer and was very poor in flexibility. Furthermore, the negative electrode of Comparative Example 1 had 4 aggregates in the negative electrode active material layer and also had poor appearance. Furthermore, the battery of Comparative Example 1 had a discharge capacity retention rate of 90.1% at the 100th cycle and poor battery characteristics. These results are presumably due to the fact that the polymer contained as a binder in the negative electrode active material layer of Comparative Example 1 did not contain the structural unit (a) derived from monomer (A).

[0172] Furthermore, as shown in Table 3, the negative electrode of Comparative Example 2, which contained a copolymer using monomer (C) instead of monomer (A), had 12 cracks in the negative electrode active material layer, indicating very poor flexibility. Also, as shown in Table 3, the negative electrode of Comparative Example 3, which contained a copolymer using acrylamide, the other monomer (D), instead of monomer (A), had 12 cracks in the negative electrode active material layer, indicating very poor flexibility. Furthermore, the battery of Comparative Example 3 had a discharge capacity retention rate of 91.9% at the 100th cycle, indicating insufficient battery characteristics.

[0173] Furthermore, as shown in Table 3, the negative electrode of Comparative Example 4, which contained a copolymer using hydroxyethyl acrylate, another monomer (D), instead of the monomer (A), had a discharge capacity retention rate of 90.5% at the 100th cycle, and the battery characteristics were insufficient. In Comparative Examples 2 to 4, it is presumed that the copolymer contained as a binder in the negative electrode active material layer did not contain the structural unit (a) derived from the monomer (A), resulting in insufficient negative electrode and battery characteristics.

[0174] Furthermore, as shown in Table 3, the negative electrode of Comparative Example 5, in which the content of monomer (A) used in the synthesis of copolymer (P) was 2 mol %, had 12 cracks in the negative electrode active material layer and was very poor in flexibility. Furthermore, the negative electrode of Comparative Example 5 had 4 aggregates in the negative electrode active material layer and also had poor appearance. Furthermore, the battery of Comparative Example 5 had a discharge capacity retention rate of 91.5% at the 100th cycle and poor battery characteristics. These results are presumably due to the insufficient content of the structural unit (a) derived from monomer (A) in the copolymer contained as a binder in the negative electrode active material layer of Comparative Example 5.

[0175] Furthermore, as shown in Table 3, the battery of Comparative Example 6, in which the content of monomer (A) used in the synthesis of copolymer (P) was 82 mol % and the content of monomer (B) was 18 mol %, had a discharge capacity retention rate of 89.0% at the 100th cycle, and thus had insufficient battery characteristics. This result is presumably due to the fact that in Comparative Example 6, the content of structural unit (a) derived from monomer (A) in the copolymer contained as a binder in the negative electrode active material layer was excessive and the content of structural unit (b) derived from monomer (B) was insufficient.

[0176] Furthermore, as shown in Table 3, the negative electrode of Comparative Example 7, which contained a polymer obtained by polymerizing only the monomer (A) without using the monomer (B), had 6 aggregates in the negative electrode active material layer, and the appearance was unsatisfactory. Furthermore, the battery of Comparative Example 7 had a discharge capacity retention rate of 86.0% at the 100th cycle, and the battery characteristics were also unsatisfactory. These results are presumably due to the fact that the polymer contained as a binder in the negative electrode active material layer of Comparative Example 7 did not contain the structural unit (b) derived from the monomer (B).

[0177] Furthermore, as shown in Table 3, the battery of Comparative Example 8, in which the content of the monomer (A) used in the synthesis of the copolymer (P) was 5 mol % and the content of the monomer (B) was 21 mol %, had a discharge capacity retention rate of 90.5% at the 100th cycle, and the battery characteristics were insufficient. This result is presumably due to the fact that the content of the structural unit (b) derived from the monomer (B) in the copolymer contained as a binder in the negative electrode active material layer in Comparative Example 8 was insufficient.

Claims

1. A binder for a non-aqueous secondary battery electrode, comprising a copolymer (P) having a structural unit (a) derived from a monomer (A) represented by the following general formula (I) and a structural unit (b) derived from a monomer (B) represented by the following general formula (II), wherein the content of the structural unit (a) in the copolymer (P) is 4.0 mol % or more and 75.0 mol % or less, and the content of the structural unit (b) in the copolymer (P) is 25.0 mol % or more and 96.0 mol % or less. (In formula (I), R １ represents a hydrogen atom or a methyl group. ２ represents a hydrogen atom or a hydroxyl group; m and n each independently represent 0 or 1. (In formula (II), R ３ is a hydrogen atom, a methyl group or CH ２ COOX ２ Represents: X １ and X ２ are each independently a hydrogen atom, an alkali metal, or NH ４ Represents.) 2. The binder for a non-aqueous secondary battery electrode according to claim 1, wherein the copolymer (P) has a structural unit (c) derived from a monomer (C) represented by the following general formula (III), and the content of the structural unit (c) in the copolymer (P) is 0.5 mol % or more and 55.0 mol % or less. (In formula (III), R ４ , R ５ each independently represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

3. The binder for a non-aqueous secondary battery electrode according to claim 1 or 2, wherein the monomer (A) contains at least one of N-hydroxyethylacrylamide and N-methylol acrylamide.

4. The binder for a non-aqueous secondary battery electrode according to claim 1 or 2, wherein the monomer (B) contains at least one of sodium (meth)acrylate and lithium (meth)acrylate.

5. The non-aqueous secondary battery electrode binder according to claim 2, wherein the monomer (C) includes at least one of N-vinylformamide and N-vinylacetamide.

6. The binder for a non-aqueous secondary battery electrode according to claim 1 or 2, wherein the weight average molecular weight of the copolymer (P) is in the range of 300,000 or more and 5,000,000 or less.

7. The binder for a non-aqueous secondary battery electrode according to claim 1 or 2, wherein the weight average molecular weight of the copolymer (P) is in the range of 1.5 million to 5 million.

8. The binder for a non-aqueous secondary battery electrode according to claim 1, wherein the sum of the content of the structural unit (a) and the content of the structural unit (b) in the copolymer (P) is 55.0 mol % or more.

9. The binder for a non-aqueous secondary battery electrode according to claim 1 or 2, which is used in an electrode active material layer containing an electrode active material containing 5 mass % or more of silicon or a silicon compound.

10. A binder composition for non-aqueous secondary battery electrodes, comprising the binder for non-aqueous secondary battery electrodes according to claim 1 or 2, and an aqueous medium.

11. A slurry for a non-aqueous secondary battery electrode, comprising the binder for a non-aqueous secondary battery electrode according to claim 1 or 2, an electrode active material, and an aqueous medium.

12. A non-aqueous secondary battery electrode comprising a current collector and an electrode active material layer formed on the surface of the current collector, the electrode active material layer comprising the binder for non-aqueous secondary battery electrodes according to claim 1 or 2, and an electrode active material.

13. The nonaqueous secondary battery electrode according to claim 12, wherein the electrode active material contains 5 mass % or more of silicon or a silicon compound.

14. A non-aqueous secondary battery comprising the non-aqueous secondary battery electrode according to claim 12.

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