JP7782554B2 - Non-aqueous secondary battery electrode binder and non-aqueous secondary battery electrode - Google Patents

Description

The present invention relates to a binder for non-aqueous secondary battery electrodes, a composition thereof, a non-aqueous secondary battery electrode, and a non-aqueous secondary battery.
This application claims priority based on Japanese Patent Application No. 2021-090167, filed on May 28, 2021, the contents of which are incorporated herein by reference.

Secondary batteries that use nonaqueous electrolytes (non-aqueous secondary batteries) are superior to secondary batteries that use aqueous electrolytes in terms of higher voltage, smaller size, and lighter weight. For this reason, non-aqueous secondary batteries are widely used as power sources for laptop computers, mobile phones, power tools, and electronic and communication devices. Recently, non-aqueous batteries have also been used in electric vehicles and hybrid vehicles to promote environmentally friendly vehicles, but there is a strong demand for higher output, higher capacity, and longer life. A typical example of a non-aqueous secondary battery is the lithium-ion secondary battery.

A nonaqueous secondary battery comprises a positive electrode with an active material such as a metal oxide, a negative electrode with a carbon material such as graphite, and a nonaqueous electrolyte solvent primarily composed of carbonates or a flame-retardant ionic liquid. Nonaqueous secondary batteries are secondary batteries in which ions move between the positive and negative electrodes to charge and discharge the battery. Specifically, a positive electrode is obtained by applying a slurry consisting of a metal oxide and a binder to the surface of a positive electrode current collector such as aluminum foil, drying the resulting material, and then cutting it to an appropriate size. A negative electrode is obtained by applying a slurry consisting of a carbon material and a binder to the surface of a negative electrode current collector such as copper foil, drying the resulting material, and then cutting it to an appropriate size. The binder serves to bind the active materials together and to the current collectors in the positive and negative electrodes, preventing the active materials from peeling off from the current collectors.

A well-known binder is a polyvinylidene fluoride (PVDF) binder that uses the organic solvent N-methyl-2-pyrrolidone (NMP) as a solvent. However, this binder has poor adhesion between active materials and between the active materials and the current collector, requiring a large amount of binder for practical use. This has the drawback of reducing the capacity of non-aqueous secondary batteries. Furthermore, because the binder uses NMP, an expensive organic solvent, it has been difficult to reduce manufacturing costs.

As a way to solve these problems, efforts are underway to develop water-dispersed binders. Known examples of water-dispersed binders include using carboxymethyl cellulose (CMC) as a thickener in combination with a (meth)acrylic acid ester-based or styrene-butadiene rubber (SBR)-based water dispersion.

Patent Document 1 discloses a binder composition for lithium-ion battery secondary battery electrodes containing a (meth)acrylic acid ester compound and a polyfunctional thiol compound. Patent Document 2 discloses a binder composition for lithium-ion battery silicon-based negative electrodes containing acrylic acid, a tetrafunctional (meth)acrylate monomer, and an acrylamide.

Patent document 3 discloses a non-aqueous battery electrode binder containing sodium acrylate-N-vinylacetamide copolymer (copolymerization ratio: sodium acrylate/N-vinylacetamide = 10/90 mass ratio).

JP 2014-116265 A JP 2016-181422 A International Publication No. 2017/150200

However, the binder using a multifunctional thiol described in Patent Document 1 requires the use of carboxymethyl cellulose as a thickener, making the slurry preparation process complicated. Furthermore, even this binder does not provide sufficient adhesion between the active materials themselves and between the active material and the current collector. Therefore, when electrodes are produced using a small amount of binder, there is a problem in that some of the active material peels off during the process of cutting the current collector.

The binder using a tetrafunctional acrylate disclosed in Patent Document 2 had the problem that it was not possible to ensure the flexibility of the electrode, and cracks occurred when the electrode was wound, as shown in Comparative Example 5 described below.

The non-aqueous battery electrode binder disclosed in Patent Document 3 had the problem of low electrode flexibility and low discharge capacity retention rate after charge-discharge cycling, as shown in Comparative Example 3 described below.

Therefore, an object of the present invention is to provide a nonaqueous secondary battery electrode binder and a nonaqueous secondary battery electrode binder composition that can significantly improve the discharge capacity retention rate after charge-discharge cycling while improving the flexibility of an electrode active material layer formed on a current collector.
Another object of the present invention is to provide a non-aqueous secondary battery electrode that is highly flexible and has a high discharge capacity retention rate after charge-discharge cycles.
Another object of the present invention is to provide a non-aqueous secondary battery having an electrode that is highly flexible and has a high discharge capacity retention rate after charge/discharge cycles.

In order to solve the above problems, the present invention provides the following [1] to [14].
[1] A non-aqueous secondary battery electrode binder containing a copolymer (P),
The copolymer (P) is
a main chain consisting only of bonds between carbon atoms;
a substituent having an amide bond;
a substituent having a salt of a carboxy group;
A substituent (c) represented by the following general formula (1):
and
the substituent having an amide bond, the substituent having a salt of a carboxy group, and the substituent (c) are each bonded to the main chain,
the amount of amide bonds contained per 1 g of the copolymer (P) is 0.050 mmol/g or more and 5.0 mmol/g or less,
the amount of the salt of the carboxy group contained per 1 g of the copolymer (P) is 5.0 mmol/g or more and 12.0 mmol/g or less;
a non-aqueous secondary battery electrode binder, wherein the amount of the substituent (c) contained per 1 g of the copolymer (P) is 0.15×10 ⁻² mmol/g or more and 8.0×10 ⁻² mmol/g or less.
(In general formula (1), R ³¹ is a hydrocarbon group, m and n each represent the number of corresponding substituents directly bonded to R ³¹ , m is an integer of 0 or more, n is an integer of 1 or more, and m+n≧2.)
[2] The non-aqueous secondary battery electrode binder according to [1], wherein in the general formula (1), R ³¹ is a carbon atom and a hydrogen atom.
[3] The nonaqueous secondary battery electrode binder according to [1] or [2], wherein in the general formula (1), R ³¹ has a plurality of carbon atoms, and all of the bonds between the carbon atoms are single bonds.
[4] The nonaqueous secondary battery electrode binder according to any one of [1] to [3], wherein Mc/(m+n)≦400, where Mc is the formula weight of the substituent (c).
[5] The nonaqueous secondary battery electrode binder according to any one of [1] to [4], wherein the substituent (c) has a structure derived from a polyfunctional thiol compound (C), and the polyfunctional thiol compound (C) has two or more mercapto groups in one molecule.
[6] The nonaqueous secondary battery electrode binder according to any one of [1] to [5], wherein the copolymer (P) further contains 0.50 mass % or more and 20.0 mass % or less of a structural unit (d) represented by the following general formula (2):
(In general formula (2), R ⁴¹ , R ⁴² , and R ⁴⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. R ⁴³ represents an alkyl group having 1 to 6 carbon atoms, and has a larger number of carbon atoms than R ^42. j and k each represent the number of structures in the corresponding parentheses that are bonded in series. j represents an integer of 1 or more, k represents an integer of 0 or more, and j+k≧20.)
[7] The nonaqueous secondary battery electrode binder according to any one of [1] to [6], wherein the copolymer (P) further contains a structural unit (e) represented by the following general formula (3) in an amount of 0.030 mmol/g or more and 1.75 mmol/g or less per 1 g of the copolymer (P):
(In general formula (3), R ⁵¹ represents a hydrogen atom or a methyl group, and R ⁵² represents a substituent having an aromatic ring.)
[8] The nonaqueous secondary battery electrode binder according to any one of [1] to [7], wherein in the copolymer (P), at least a part of the amide bonds is contained as a structural unit (a) represented by the following general formula (4):
(In general formula (4), R ¹¹ and R ¹² each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.)
[9] The nonaqueous secondary battery electrode binder according to any one of [1] to [8], wherein in the copolymer (P), at least a part of the salt of the carboxy group is contained as a structural unit (b) represented by the following general formula (5):
(In general formula (5), ^R2 represents a hydrogen atom or a methyl group, and X represents a cation.)
[10] The nonaqueous secondary battery electrode binder according to any one of [1] to [9], wherein the weight average molecular weight of the copolymer (P) is 700,000 or more and 7,500,000 or less.
[11] A non-aqueous secondary battery electrode binder composition comprising the non-aqueous secondary battery electrode binder according to any one of [1] to [10] 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, wherein the electrode active material layer contains the binder for a non-aqueous secondary battery electrode according to any one of [1] to [10] and an electrode active material.
[13] A battery including a positive electrode, a negative electrode, and an electrolyte solution,
A non-aqueous secondary battery, wherein at least one of the positive electrode and the negative electrode is the non-aqueous secondary battery electrode according to [12].
[14] A method for producing a non-aqueous secondary battery electrode binder, comprising a polymerization step of radically polymerizing a monomer (M) having an ethylenically unsaturated bond in the presence of a polyfunctional thiol compound (C) having two or more mercapto groups in one molecule,
the monomer (M) includes a monomer (A) having an amide bond and a monomer (B) having a salt of a carboxy group,
When the monomer (M), the polyfunctional thiol compound (C), a polymerization initiator, and a chain transfer agent (if used), the chain transfer agent are collectively used as polymerization components, the following can be obtained:
the amount of the monomer (A) contained per 1 g of the polymerization component is 0.050 mmol/g or more and 5.0 mmol/g or less,
the amount of the monomer (B) contained per 1 g of the polymerization component is 5.0 mmol/g or more and 12.0 mmol/g or less,
The method for producing a non-aqueous secondary battery electrode binder, wherein the amount of the polyfunctional thiol compound (C) contained per 1 g of the polymerization component is 0.15×10 ⁻² mmol/g or more and 8.0×10 ⁻² mmol/g or less.

According to the present invention, it is possible to provide a nonaqueous secondary battery electrode binder and a composition thereof that can significantly improve the discharge capacity retention rate after charge-discharge cycling while improving the flexibility of an electrode active material layer formed on a current collector.
Furthermore, the present invention can provide a non-aqueous secondary battery electrode that is highly flexible and has a high discharge capacity retention rate after charge-discharge cycles.
Furthermore, according to the present invention, a non-aqueous secondary battery can be provided that includes an electrode that is highly flexible and has a high discharge capacity retention rate after charge/discharge cycles.

Embodiments of the present invention are described in detail below. In these embodiments, the battery is a secondary battery in which ions move between the positive and negative electrodes during charging and discharging. The positive electrode comprises a positive electrode active material, and the negative electrode comprises a negative electrode active material. These electrode active materials are materials capable of ion insertion and deintercalation (intercalation and deintercalation). A preferred example of a secondary battery with this configuration is a lithium-ion secondary battery.

"(Meth)acrylic acid" refers to either or both of methacrylic acid and acrylic acid. "(Meth)acrylic acid monomer" refers to either or both of methacrylic acid monomer and acrylic acid monomer. "(Meth)acrylate" refers to either or both of methacrylate and acrylate.

"Weight average molecular weight" is a pullulan-equivalent value calculated using gel permeation chromatography (GPC).

"Hydrocarbon group" means a structure consisting only of carbon and hydrogen atoms. However, this does not apply unless otherwise specified, such as when some of the hydrogen atoms have been substituted.

In the following description, if there is no atom at the end of a line indicating a bond in a formula showing a structural unit, it means that the moiety is bonded to another structural unit or terminal structure that forms the polymer.

The salt of a functional group refers to a form in which a partially dissociated ion of the functional group is bonded to a counter ion other than a hydrogen ion or a hydroxide ion. For example, the salt of a carboxy group refers to a form in which COO ⁻ is bonded to a cation other than a hydrogen ion.

<1. Non-aqueous secondary battery electrode binder>
The nonaqueous secondary battery electrode binder (or nonaqueous secondary battery electrode binder, hereinafter sometimes referred to as "electrode binder") according to this embodiment contains the copolymer (P) described below. The electrode binder may contain other components, such as a polymer other than the copolymer (P), a surfactant, etc.

Here, the electrode binder consists of components that remain without volatilizing during the heating process in the battery manufacturing process described below. Specifically, the components that make up the electrode binder are those that remain after weighing 1 g of a mixture containing the electrode binder into an aluminum dish with a diameter of 5 cm and drying it at 110°C for 5 hours under atmospheric pressure in a dryer with air circulating.

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

[1-1. Copolymer (P)]
The copolymer (P) has a main chain consisting only of bonds between carbon atoms, a substituent having an amide bond, a substituent having a salt of a carboxy group, and a substituent (c) represented by the following general formula (1): Preferably, the main chain consists only of single bonds between carbon atoms.

The substituent having an amide bond, the substituent having a carboxyl salt, and the substituent (c) are each bonded to the main chain. The substituent having an amide bond and the substituent having a carboxyl salt are preferably branched from the main chain. The substituent (c) is preferably bonded to the end of the main chain. Multiple main chains may be bonded to one substituent (c). In other words, a single molecule may have a structure in which multiple main chains formed by bonds between carbon atoms are bonded via the substituent (c).

Copolymer (P) preferably further contains at least one of structural unit (d) represented by general formula (2) described below and structural unit (e) represented by general formula (3) described below, and more preferably contains both. Copolymer (P) may also contain structures other than those described above, such as molecular terminal structures.

The weight-average molecular weight of copolymer (P) is preferably 700,000 or more, more preferably 1,000,000 or more, and even more preferably 1,500,000 or more. The weight-average molecular weight of copolymer (P) is preferably 7,500,000 or less, more preferably 5,000,000 or less, and even more preferably 4,000,000 or less.

[1-1-1. Amide bond]
The amount of amide bonds contained per gram of copolymer (P) is 0.050 mmol/g or more, preferably 0.085 mmol/g or more, and more preferably 0.40 mmol/g or more. This is because the dispersibility of the electrode active material, conductive additive, etc. during the preparation of the electrode slurry described below is excellent, and an electrode slurry with good coatability can be prepared. In addition, copolymer (P) improves the electrolyte resistance of the negative electrode active material layer.

The amount of amide bonds contained per gram of copolymer (P) is 5.0 mmol/g or less, preferably 3.0 mmol/g or less, more preferably 1.7 mmol/g or less, and even more preferably 0.90 mmol/g or less. This is to allow copolymer (P) to contain other structures. Furthermore, this is to suppress the occurrence of cracks in electrodes, as described below, and improve electrode productivity.

The amide bond may also be contained in a structural unit having another functional group, such as the structural unit (e) described below.

In copolymer (P), it is preferable that at least a portion of the amide bonds be contained as structural units (a) represented by the following general formula (4). This is because the amount of amide bonds relative to the mass of structural units (a) is large, allowing amide bonds to be efficiently contained in copolymer (P). Of the amide bonds in copolymer (P), the proportion contained in structural units (a) is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more.

In formula (4), R ¹¹ and R ¹² each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

In formula (4), it is more preferable that R ¹¹ and R ¹² each independently represent a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and it is even more preferable that R ¹¹ and R ¹² each independently represent a hydrogen atom or a methyl group.

Particularly preferred specific examples of the combination of R ¹¹ and R ¹² are R ¹¹ :H and R ¹² :H, or R ¹¹ :H and R ¹² :CH ₃ , because the amount of amide bonds relative to the mass is large and the copolymer (P) can contain a large number of amide bonds.

[1-1-2. Salt of Carboxy Group]
The salt of the carboxy group is preferably a salt of ^—COO— with a monovalent cation. The monovalent cation is more preferably an alkali metal ion or an ammonium ion, even more preferably an alkali metal ion, and particularly preferably a lithium ion or a sodium ion.

The amount of carboxyl group salt contained per gram of copolymer (P) is 5.0 mmol/g or more, preferably 6.0 mmol/g or more, and more preferably 7.0 mmol/g or more. This is because copolymer (P) enables the formation of an electrode active material layer with high peel strength from the current collector.

The amount of carboxyl group salt contained per gram of copolymer (P) is 12.0 mmol/g or less, and preferably 9.9 mmol/g or less. This improves the dispersibility of solid components such as the electrode active material and conductive additive during the preparation of electrode slurry, as described below.

The amount of a carboxyl group salt is the amount of ^-COO- bonded to a cation other than a hydrogen ion. For example, if two ^COO- bonds are bonded to one divalent cation, the amount of a carboxyl group salt is two.

In addition, the salt of the carboxy group may be contained together with a structural unit having another functional group, such as the structural unit (e) described below.

In copolymer (P), it is preferable that at least a portion of the carboxyl group salt is contained as structural unit (b) represented by the following general formula (5). This is because the amount of carboxyl group salt relative to the mass is large, allowing the carboxyl group salt to be efficiently contained in copolymer (P). Of the carboxyl group salt in copolymer (P), the proportion contained in structural unit (b) is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more.

In the general formula (5), ^R2 represents a hydrogen atom or a methyl group, and X represents a cation.

In general formula (5), X is preferably a monovalent cation, and even more preferably at least one of lithium ion, sodium ion, potassium ion, and ammonium ion. Among these, it is particularly preferable for X to contain at least one of lithium ion and sodium ion.

The structural unit (b) may be present in the copolymer (P) as two or more structures having different X's in the general formula (5) above. For example, the structural unit (b) may contain two structures: a salt with lithium and a salt with sodium.

[1-1-3. Substituent (c)]
The substituent (c) is represented by the following general formula (1).

In general formula (1), R ³¹ is a hydrocarbon group, m and n each represent the number of corresponding substituents directly bonded to R ³¹ (the number of branches in the structure in parentheses corresponding to m and n), m is an integer of 0 or more, n is an integer of 1 or more, m+n≧2, and R ³² is a hydrogen atom or a methyl group.

The substituent (c) serves to link the main chains together and extend the molecular chain, and if n≧3, it can form a crosslinked structure in the copolymer (P).

In general formula (1), it is preferable that m + n ≥ 3, and more preferably m + n ≥ 4. This is because the electrode active material layer containing copolymer (P) has improved peel strength and toughness from the current collector, and this is because it is believed that at least a portion of the substituents (c) form a crosslinked structure in copolymer (P).

Although not particularly limited, it is preferable that m + n ≦ 6, and more preferably that m + n ≦ 5. It is even more preferable that m + n ≦ 4, and particularly preferable that m + n = 4. This is because the flexibility of the electrode active material layer containing copolymer (P) is improved.

In general formula (1), R ³¹ preferably consists of a carbon atom and a hydrogen atom, and more preferably has a plurality of carbon atoms, ^and all of the bonds between the carbon atoms are single bonds.
In general formula (1), R ³¹ may be a linear hydrocarbon group or a hydrocarbon group having a branched structure. The number of carbon atoms contained in ^{R 31} is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. Furthermore, it is preferable that R ³¹ is not directly bonded to the main chain. In R ³¹ , it is preferable that all bonds between carbon atoms are single bonds. This is to improve the flexibility of the substituent (c) and improve the flexibility of the electrode binder.

In general formula (1), R ³² is preferably a methyl group, because this improves the peel strength of the electrode active material layer containing the copolymer (P).

Where the formula weight of the substituent (c) is Mc, it is preferable that Mc/(m+n) ≦ 400, more preferably Mc/(m+n) ≦ 300, and even more preferably Mc/(m+n) ≦ 200. This is because the substituent (c) has the effect of extending the molecular chain and/or improves the crosslinking density of the copolymer (P), thereby improving the peel strength of the electrode active material layer from the current collector and the toughness of the electrode active material layer.

Substituent (c) is a structural unit derived from a polyfunctional thiol compound (C), and the polyfunctional thiol compound (C) preferably has two or more mercapto groups per molecule. Here, the polyfunctional thiol compound (C) more preferably has three or more mercapto groups per molecule, and even more preferably has four or more mercapto groups per molecule. Details of the polyfunctional thiol compound (C) will be described later in the section on the method for producing copolymer (P).

The amount of the substituent (c) contained per 1 g of the copolymer (P) is 0.15×10 ⁻² mmol/g or more, preferably 0.30×10 ⁻² mmol/g or more, and more preferably 0.65×10 ⁻² mmol/g or more, because in the electrode described below, the strength of the composite layer of the electrode is improved and the discharge capacity retention rate after charge-discharge cycles is improved.

The amount of the substituent (c) contained per 1 g of the copolymer (P) is 8.0 × 10 ^-2 mmol/g or less, preferably 5.5 × 10 ^-2 mmol/g or less, more preferably 4.0 × 10 ^-2 mmol/g or less, and even more preferably 1.4 × 10 ^-2 mmol/g or less. This is to improve the flexibility of the electrode in the electrode described below. Also, this is to improve the cycle characteristics (discharge capacity retention rate) in the nonaqueous secondary battery described below.

[1-1-4. Structural unit (d)]
The structural unit (d) is a structure represented by the following general formula (2).

In general formula (2), R ⁴¹ , R ⁴² , and R ⁴⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. R ⁴³ represents an alkyl group having 1 to 6 carbon atoms, and has a larger number of carbon atoms than R ^42. In this formula, j and k each represent the number of structures in the corresponding parentheses that are bonded in series. j is an integer of 1 or more, k is an integer of 0 or more, and j+k≧20.

In ^general formula (2), R ⁴¹ , R ⁴² , and R ⁴⁴ are preferably each independently a hydrogen atom or an alkyl group having ^{1 to} 3 carbon atoms, more preferably a hydrogen atom or a methyl group, and even more preferably a ^methyl group.

In general formula (2), j is an integer of 1 or greater, k is an integer of 0 or greater, and j + k ≥ 20. This is because when an electrode is prepared using copolymer (P) as a binder for an electrode active material, the flexibility of the electrode is improved and the occurrence of cracks is suppressed. From this perspective, j + k ≥ 30 is preferable, and j + k ≥ 40 is more preferable. Furthermore, j + k ≤ 500 is preferable, j + k ≤ 200 is more preferable, and j + k ≤ 150 is even more preferable. This is because the binding strength of the electrode binder is increased.

In addition, while general formula (2) is limited to the presence of j structural units containing R ⁴² and k structural units containing R ⁴³ , it does not limit the arrangement of these structural units. That is, when k≧1, the polyoxyalkylene chain of general formula (2) may have a block structure in which all or part of the structural units are continuous, a structure in which two structural units are arranged with periodic regularity, such as a structure in which two structural units are arranged alternately, or a structure in which two structural units are arranged randomly. A preferred form of the polyoxyalkylene chain of general formula (2) is a structure in which the structural units are arranged with periodic regularity or a structure in which the structural units are arranged randomly. This is to suppress uneven distribution of each structural unit within the molecular chain forming general formula (2). A more preferred form of the copolymer of general formula (2) is a structure in which the structural units are arranged randomly. This is because polymerization can be performed using a radical polymerization initiator without using a special catalyst, thereby reducing production costs.

In the general formula (2), preferred examples of the combination of R ⁴¹ , R ⁴² , R ⁴³ , R ⁴⁴ , j, and k include the examples in Table 1 below.

The content of structural unit (d) in copolymer (P) is preferably 0.50% by mass or more, more preferably 0.70% by mass or more, and even more preferably 3.5% by mass or more. This is to suppress the occurrence of cracks in the electrodes described below.

The content of structural unit (d) in copolymer (P) is preferably 20.0% by mass or less, more preferably 14.0% by mass or less, and even more preferably 7.0% by mass or less. This is to improve the peel strength of the electrode active material layer. It is also to improve the cycle characteristics (discharge capacity retention rate) in nonaqueous secondary batteries, which will be described later.

[1-1-5. Structural unit (e)]
The structural unit (e) is a structure represented by the following general formula (3).

In general formula (3), ^R51 represents a hydrogen atom or a methyl group, and ^R52 is a substituent having an aromatic ring. ^R52 preferably contains one aromatic ring. ^R52 preferably does not have either an amide bond or a salt of a carboxy group. ^R52 preferably has a benzene ring, and more preferably consists of carbon atoms and hydrogen atoms.

The structural unit (e) is preferably represented by the following general formula (6):

In general formula (6), R ⁵¹ is a hydrogen atom or a methyl group. R ⁵³ is -CH ₂ -, -(CH ₂ CH ₂ O) _h -, or -CH ₂ CH(OH)CH ₂ O-. Here, h is an integer of 1 or more and 5 or less. ^{R 54} is a substituent having an aromatic ring. ^{R 53} is more preferably -CH ₂ - or -CH ₂ CH ₂ O-, and even more preferably -CH ₂ -. It is preferable that R ⁵⁴ contains one aromatic ring. R ⁵⁴ preferably has a benzene ring, and more preferably consists of carbon atoms and hydrogen atoms. It is preferable that R ⁵⁴ does not have either an amide bond or a salt of a carboxy group. It is particularly preferable that R ⁵⁴ is a phenyl group.

The amount of structural unit (e) contained per gram of copolymer (P) is preferably 0.030 mmol/g or more, more preferably 0.045 mmol/g or more, and even more preferably 0.30 mmol/g or more. This is because the occurrence of cracks in the electrode, as described below, is suppressed and electrode productivity is improved.

The amount of structural unit (e) contained per gram of copolymer (P) is preferably 1.75 mmol/g or less, more preferably 1.50 mmol/g or less, and even more preferably 0.90 mmol/g or less. This is to improve the peel strength of the electrode active material layer and suppress swelling of the electrode active material layer in the electrode described below. It is also to improve the cycle characteristics (discharge capacity retention rate) of the nonaqueous secondary battery described below.

[1-1-6. Other structures]
Examples of other structures contained in the copolymer (P) include structures at the molecular chain terminals and structures other than the above-mentioned structures branched from the main chain.

Examples of molecular chain terminal structures include structures derived from polymerization initiators and chain transfer agents. Note that the substituent (c) is not considered a molecular chain terminal structure, even if, for example, n = 1 in general formula (1). The content of terminal structures in copolymer (P) is preferably 10% by mass or less, more preferably 2.0% by mass or less, and even more preferably 1.0% by mass or less. This is to maximize the effect of the above structures in copolymer (P). Note that each chain transfer agent-derived structure is bonded to the molecular chain of copolymer (P) at only one point.

An example of a structure contained in copolymer (P) other than the above structures is a carboxy group. When copolymer (P) contains a carboxy group, the amount of carboxy groups contained per 1 g of copolymer (P) is preferably 0.030 mmol/g or more, and more preferably 1.5 mmol/g or more. The amount of carboxy groups contained per 1 g of copolymer (P) is preferably 5.0 mmol/g or less, and more preferably 3.0 mmol/g or less.

Copolymer (P) may contain a structure that does not fall under any of the following: a main chain formed by bonds between carbon atoms, a substituent (c), an ester bond, an amide bond, a salt of a carboxy group, a structural unit (d), a structural unit (e), or a carboxy group. Its content is preferably 0.50 mmol/g or less, more preferably 0.30 mmol/g or less, and even more preferably 0.10 mmol/g or less. This is to more effectively utilize the effects of the functional groups and structures contained in copolymer (P).

[1-1-7. Examples of suitable structures of copolymer (P)]
An example of a suitable structure of the copolymer (P) is a copolymer having a structural unit (a) represented by general formula (4), a structural unit (b) represented by general formula (5), and a substituent (c) represented by general formula (1). This copolymer may have a structure derived from an initiator and a structure derived from a chain transfer agent at the molecular chain end. The content of each structural unit is determined by the amount of functional groups and structures introduced into the copolymer (P). The amount of functional groups and structures contained in the copolymer (P) is as described above. In this example, the total content of the structural unit (a), the structural unit (b), and the substituent (c) in the copolymer (P) is preferably 97.0% by mass or more, more preferably 98.0% by mass or more, and even more preferably 99.0% by mass or more.

Another example of a suitable structure for copolymer (P) is a copolymer having, in addition to structural unit (a), structural unit (b), and substituent (c), one or both of the structural unit (d) and structural unit (e). This copolymer may have a structure derived from an initiator and a structure derived from a chain transfer agent at the molecular chain end. The content of each structural unit is determined by the amount of functional groups and structures introduced into copolymer (P). The amounts of functional groups and structures contained in copolymer (P) are as described above. In this example, the total content of structural unit (a), structural unit (b), substituent (c), structural unit (d), and structural unit (e) in copolymer (P) is preferably 97.0% by mass or more, more preferably 98.0% by mass or more, and even more preferably 99.0% by mass or more.

1-2. Method for producing copolymer (P)
The method for producing the copolymer (P) is not particularly limited, but preferably involves radical polymerization of a monomer (M) having an ethylenically unsaturated bond in the presence of a polyfunctional thiol compound (C) having two or more mercapto groups per molecule. The polymerization is preferably carried out in an aqueous medium. Examples of polymerization procedures that can be used include a method in which all of the monomers (M) used in the polymerization are charged at once and polymerized, and a method in which the monomers (M) used in the polymerization are polymerized while being continuously supplied. The polymerization temperature is not particularly limited, but is preferably 30°C or higher and 90°C or lower.

As the monomer (M), it is preferable to use a monomer (A) having an amide bond or a monomer (B) having a salt of a carboxy group to simplify the manufacturing process. When synthesizing a copolymer (P) containing structural unit (d), it is preferable to use a monomer (D) represented by general formula (10) described below to simplify the manufacturing process. When synthesizing a copolymer (P) containing structural unit (e), it is preferable to use a monomer (E) represented by general formula (11) described below to simplify the manufacturing process. However, the necessary functional groups may be formed by a post-polymerization reaction or the like without using these monomers.

[1-2-1. Monomer (A)]
The monomer (A) has an ethylenically unsaturated bond and an amide bond. When the monomer (A) has a salt of a carboxy group, the monomer (A) also corresponds to the monomer (B). The monomer (A) preferably has a (meth)acryloyloxy group. This is because the polymerization rate is improved and the productivity of the copolymer (P) is improved. The monomer (A) more preferably has a structure represented by the following general formula (7).

In general formula (7), R ¹¹ and R ¹² have the same structure as those in general formula (4). Particularly preferred examples of the monomer (A) are N-vinylformamide (R ¹¹ : H and R ¹² : H) and N-vinylacetamide (R ¹¹ : H and R ¹² : CH ₃ ). This is because the amount of amide bonds relative to the mass of the monomer (A) is large, and therefore the copolymer (P) can contain a large number of amide bonds.

[1-2-2. Monomer (B)]
The monomer (B) has an ethylenically unsaturated bond and a salt of a carboxy group. When the monomer (B) has an amide bond, the monomer (B) also corresponds to the monomer (A). The monomer (B) preferably has a (meth)acryloyloxy group. This is because the polymerization rate is improved, and the productivity of the copolymer (P) is improved. The monomer (B) more preferably has a structure represented by the following general formula (8).

In general formula (8), ^R2 and X have the same structure as those in general formula (5). As the monomer (B), two or more types of compounds having different X in general formula (8) may be used. For example, two types of compounds, a lithium salt and a sodium salt, may be used as the monomer (B).

[1-2-3. Polyfunctional thiol compound (C)]
The polyfunctional thiol compound (C) has two or more mercapto groups. The polyfunctional thiol compound (C) preferably has a structure represented by the following general formula (9). This is because the polyfunctional thiol compound (C) is inexpensive and easily available, and the reaction rate is improved, thereby improving the productivity of the copolymer (P).

In general formula (9), ^R32 has the same structure as in general formula (1). ^R33 is a hydrocarbon group. f represents the number of corresponding substituents directly bonded to ^R33 (the number of branches in the structure in parentheses). f≧2.

Preferably, f ≧ 3, and more preferably f ≧ 4. This is because a crosslinked structure can be formed in the copolymer (P), improving the peel strength and toughness of the electrode active material layer containing the copolymer (P) relative to the current collector. Although not particularly limited, f ≦ 6 is preferred, f ≦ 5 is more preferred, f ≦ 4 is even more preferred, and f = 4 is most preferred. This is because the flexibility of the electrode active material layer containing the copolymer (P) is improved.

In general formula (9), R ³³ may be a linear hydrocarbon group or a hydrocarbon group having a branched structure. The number of carbon atoms contained in ^{R 33} is preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. Furthermore, R ³³ preferably does not have an ethylenically unsaturated bond. This is to prevent uneven crosslink density and excessive crosslink density.

The thiol equivalent weight (molecular weight per mercapto group) of the polyfunctional thiol compound (C) is preferably 400 or less, more preferably 300 or less, and even more preferably 200 or less. This is because the effect of molecular chain extension by the polyfunctional thiol compound (C) and/or the crosslinking density of the copolymer (P) are improved, thereby improving the peel strength of the electrode active material layer from the current collector and the toughness of the electrode active material layer.

For the same reason, when the polyfunctional thiol compound (C) is a compound represented by formula (9), where MC is the molecular weight of the polyfunctional thiol compound (C), it is preferable that MC/f≦400, more preferably MC/f≦300, and even more preferably MC/f≦200.

Examples of polyfunctional thiol compounds (C) include pentaerythritol tetrakis(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptobutyrate), trimethylolpropane tris(3-mercaptopropionate), tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, 1,4-bis(3-mercaptobutyryloxy)butane, tetraethylene glycol bis(3-mercaptopropionate), and dipentaerythritol hexakis(3-mercaptopropionate). Of these compounds, the monomer (C) more preferably contains pentaerythritol tetrakis(3-mercaptobutyrate), pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptobutyrate), or 1,4-bis(3-mercaptobutyryloxy)butane.

[1-2-4. Monomer (D)]
The monomer (D) is represented by the following general formula (10).

In the general formula (10), R ⁴¹ , R ⁴² , R ⁴³ , R ⁴⁴ , j, and k have the same structure as those in the general formula (2) above.

In general formula (10), k = 0 is more preferred. Examples of the monomer (D) in which k = 0 include polyethylene glycol mono(meth)acrylates, and more specifically, methoxypolyethylene glycol (meth)acrylates (e.g., monomers d1 and d2 in Table 1). An example of methoxypolyethylene glycol methacrylate is VISIOMER (registered trademark) MPEG2005 MA W manufactured by EVONIK INDUSTRIES. In this product, ^R41 = _CH3 , ^R42 = H, ^R44 = _CH3 , j = 45, and k = 0. Another example of methoxypolyethylene glycol methacrylate is VISIOMER® MPEG5005 MA W manufactured by EVONIK INDUSTRIES, in which R ⁴¹ =CH ₃ , R ⁴² =H, R ⁴⁴ =CH ₃ , j=113, k=0.

Another example of monomer (D) where k = 0 is polypropylene glycol mono(meth)acrylate, more specifically, methoxypolypropylene glycol (meth)acrylate, etc.

[1-2-5. Monomer (E)]
The monomer (E) is represented by the following general formula (11).

In the general formula (11), R ⁵¹ and R ⁵² have the same structure as those in the general formula (3).

It is preferable that monomer (E) is represented by the following general formula (12):

In the general formula (12), R ⁵¹ , R ⁵³ and R ⁵⁴ have the same structure as those in the general formula (6) above.

Examples of monomer (E) include benzyl (meth)acrylate, phenoxyethyl (meth)acrylate, phenoxyethylene glycol (meth)acrylate, phenoxydiethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, ethoxylated-o-phenylphenol (meth)acrylate, and 2-hydroxy-3-phenoxypropyl (meth)acrylate. Of these compounds, it is more preferable to use one or both of benzyl (meth)acrylate and phenoxyethyl (meth)acrylate as monomer (E).

[1-2-7. Polymerization initiator]
In the case of radical polymerization, examples of polymerization initiators include, but are not limited to, hydrogen peroxide, t-butyl hydroperoxide, and azo compounds. Examples of azo compounds include 2,2'-azobis(2-methylpropionamidine) dihydrochloride. When polymerization is carried out in water, it is preferable to use a water-soluble polymerization initiator. If necessary, redox polymerization may be carried out by using a radical polymerization initiator in combination with a reducing agent during polymerization. Examples of reducing agents include sodium bisulfite, Rongalite, and ascorbic acid. When an azo compound is used as the polymerization initiator, a component that assists radical generation from the azo compound, such as a persulfate, may be added, but these components do not constitute the copolymer (P). Examples of persulfates include ammonium persulfate and potassium persulfate.

[1-2-8. Aqueous medium]
Although water is preferably used as the aqueous medium, a hydrophilic solvent may be added to water as long as the polymerization stability of the resulting binder copolymer is not impaired. Examples of the hydrophilic solvent to be added to water include methanol, ethanol, and N-methylpyrrolidone.

[1-2-9. Chain transfer agent]
During the polymerization, a chain transfer agent may be used to adjust the molecular weight of the copolymer (P). The chain transfer agent is not particularly limited, but examples thereof include monofunctional 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.

[1-2-10. Content of each component in the polymerizable components]
If the compounds that become part of the structure of the copolymer (P) through a polymerization reaction are considered polymerization components, the polymerization components include each monomer, a chain transfer agent, and a polymerization initiator. The composition of the polymerization components is determined by the amount of functional groups and structures introduced into the copolymer (P). In the case of radical polymerization, unless there is an operation to change a specific functional group, all of the monomers except for the ethylenically unsaturated bond do not react and become structural units of the copolymer (P). Furthermore, in the case of radical polymerization, unless there is an operation to change a specific functional group, all of the polyfunctional thiol compound (C) becomes the substituent (c) of the copolymer (P).

In the synthesis of copolymer (P), there are forms in which neither monomer (D) nor monomer (E) is used, and forms in which one or both of monomer (D) and monomer (E) are used.

The following describes suitable amounts of each monomer and polyfunctional thiol compound (C) used to obtain the copolymer (P) of the present invention, but is not limited to these. Hereinafter, the monomers, polyfunctional thiol compound (C), polymerization initiator, and, if a chain transfer agent is used, the chain transfer agent used in the synthesis of the copolymer (P) are collectively referred to as polymerization components.

The amount of monomer (A) contained per 1 g of polymerization component is preferably 0.050 mmol/g or more, more preferably 0.085 mmol/g or more, and even more preferably 0.40 mmol/g or more. The amount of monomer (A) contained per 1 g of polymerization component is preferably 5.0 mmol/g or less, more preferably 3.0 mmol/g or less, even more preferably 1.7 mmol/g or less, and particularly preferably 0.90 mmol/g or less.

The amount of monomer (B) contained per 1 g of polymerization component is preferably 5.0 mmol/g or more, more preferably 6.0 mmol/g or more, and even more preferably 7.0 mmol/g or more. The amount of monomer (B) contained per 1 g of polymerization component is preferably 12.0 mmol/g or less, and more preferably 9.9 mmol/g or less. Note that when multiple carboxylate ions corresponding to the structure of monomer (B) are bonded to a divalent or higher cation, it is considered that there are as many monomers (B) as there are bonded to the cations.

The amount of the polyfunctional thiol compound (C) contained per 1 g of the polymerization component is 0.15 × 10 ^-2 mmol/g or more, preferably 0.30 × 10 ^-2 mmol/g or more, and more preferably 0.65 × 10 ^-2 mmol/g or more. The amount of the polyfunctional thiol compound (C) contained per 1 g of the polymerization component is 8.0 × 10 ^-2 mmol/g or less, preferably 5.5 × 10 ^-2 mmol/g or less, more preferably 4.0 × 10 ^-2 mmol/g or less, and even more preferably 1.4 × 10 ^-2 mmol/g or less.

The content of monomer (D) in the polymerization components is preferably 0.50% by mass or more, more preferably 0.70% by mass or more, and even more preferably 3.5% by mass or more. The content of monomer (D) in the polymerization components is preferably 20.0% by mass or less, more preferably 14.0% by mass or less, and even more preferably 7.0% by mass or less.

The amount of monomer (E) contained per 1 g of polymerization component is preferably 0.030 mmol/g or more, more preferably 0.045 mmol/g or more, and even more preferably 0.30 mmol/g mass% or more. The amount of monomer (E) contained per 1 g of polymerization component is preferably 1.75 mmol/g or less, preferably 1.50 mmol/g mass% or less, and more preferably 0.90 mmol/g mass% or less.

The content of the chain transfer agent in the polymerization components is not particularly limited, but is preferably 0.10% by mass or more, more preferably 0.25% by mass or more, and even more preferably 0.35% by mass or more. The content of the chain transfer agent in the polymerization components is not particularly limited, but is preferably 10% by mass or less, more preferably 2.0% by mass or less, and even more preferably 0.70% by mass or less.

The amount of chain transfer agent contained per 1 g of polymerization component is preferably 1.0×10 ⁻² mmol/g or more, more preferably 2.0×10 ⁻² mmol/g or more, and even more preferably 3.0×10 ⁻² mmol/g or more. The amount of chain transfer agent contained per 1 g of polymerization component is preferably 20×10 ⁻² mmol/g or less, more preferably 10×10 ⁻² mmol/g or less, and even more preferably 7.0×10 ⁻² mmol/g or less.

The content of the polymerization initiator in the polymerization components is preferably 0.020% by mass or more, more preferably 0.10% by mass or more, and even more preferably 0.15% by mass or more. The content of the polymerization initiator in the polymerization components is preferably 1.0% by mass or less, more preferably 0.50% by mass or less, and even more preferably 0.35% by mass or less. This does not include components such as reducing agents that do not form part of the copolymer (P) structure and that support the function of the polymerization initiator.

The amount of polymerization initiator contained per 1 g of polymerization components is preferably 0.10×10 ⁻² mmol/g or more, more preferably 0.20×10 ⁻² mmol/g or more, and even more preferably 0.50×10 ⁻² mmol/g or more. The amount of polymerization initiator contained per 1 g of polymerization components is preferably 5.0×10 ⁻² mmol/g or less, more preferably 2.0×10 ⁻² mmol/g or less, and even more preferably 1.0×10 ⁻² mmol/g or less. Here, components such as reducing agents that do not form part of the structure of copolymer (P) and that assist the function of the polymerization initiator are not included.

An example of a method for synthesizing copolymer (P) is a configuration in which the total content of the monomer represented by general formula (7) and the monomer represented by general formula (8) in monomer (M) (total monomers) is 90% by mass or more, preferably 95% by mass or more, and even more preferably 100% by mass.

Another example is a configuration in which one or both of monomer (D) and monomer (E) are used. In this example, the total content of the monomer represented by general formula (7), the monomer represented by general formula (8), the monomer represented by general formula (10), and the monomer represented by general formula (11) in monomer (M) (total monomers) is 90% by mass or more, preferably 95% by mass or more, and more preferably 100% by mass.

[1-3. Method for producing non-aqueous secondary battery electrode binder]
The method for producing a non-aqueous secondary battery electrode binder includes a polymerization step of radically polymerizing a monomer (M) having an ethylenically unsaturated bond in the presence of a polyfunctional thiol compound (C) having two or more mercapto groups in one molecule.
The method for producing the nonaqueous secondary battery electrode binder may be the same as the method for producing the copolymer (P), or may include additional steps. The method for producing the copolymer (P) is as described above. Examples of additional steps include a purification step and a mixing step of additives.

<2. Binder composition for non-aqueous secondary battery electrodes>
The nonaqueous secondary battery electrode binder composition (hereinafter sometimes referred to as "electrode binder composition") of this embodiment contains an electrode binder and an aqueous medium. The electrode binder composition may also contain other components such as a pH adjuster and a surfactant, as necessary.

The aqueous medium contained in the electrode binder composition contains water. The aqueous medium contained in the electrode binder composition may also 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 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.

The composition of the aqueous medium contained in the electrode binder composition may be the same as or different from the aqueous medium used in synthesizing the copolymer (P). Furthermore, in the electrode binder composition of this embodiment, the electrode binder may be dissolved or dispersed in the aqueous medium.

The content of copolymer (P) in the electrode binder composition is preferably 30% by mass or less, and more preferably 20% by mass or less. This is to suppress an increase in the viscosity of the electrode binder composition and to efficiently disperse the electrode active material, etc., when the electrode binder composition is mixed with the electrode active material, etc., described below, to prepare an electrode slurry.

The content of copolymer (P) 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. This is because the electrode slurry and electrode can be produced using a smaller amount of electrode binder composition.

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. This is to ensure efficient dispersion of the electrode active material, etc., when mixed with the electrode active material, etc., described below, to prepare an electrode slurry. The pH of the electrode binder composition is preferably 11 or lower, more preferably 10 or lower, and even more preferably 9.0 or lower. This is to ensure efficient dispersion of the electrode active material, etc., when mixed with the electrode active material, etc., described below, to prepare an electrode slurry. Here, the pH is the value measured with a pH meter at a liquid temperature of 23°C.

<3. Non-aqueous secondary battery electrode slurry>
In the non-aqueous secondary battery electrode slurry of this embodiment (hereinafter sometimes referred to as "electrode slurry"), an electrode binder and an electrode active material are dissolved or dispersed in an aqueous medium. The electrode slurry of this embodiment may contain a conductive aid, a thickener, etc. as needed, but it is preferable that the electrode slurry does not contain a thickener in order to simplify the electrode slurry preparation process. The method for preparing the electrode slurry is not particularly limited, and examples include a method in which the necessary components are mixed using a mixing device such as a stirring type, a rotary type, or a shaking type.

The nonvolatile content of the electrode slurry is preferably 30% by mass or more, and more preferably 40% by mass or more. This is to allow a larger amount of electrode active material layer to be formed with a smaller amount of electrode slurry. The nonvolatile content of the electrode slurry is preferably 70% by mass or less, and more preferably 60% by mass or less. The nonvolatile content can be adjusted by the amount of aqueous medium.

Unless otherwise specified, the non-volatile content concentration here refers to the ratio of the mass of the remaining components to the mass before drying when 1 g of the mixture is weighed into an aluminum dish with a diameter of 5 cm and dried at 130°C for 1 hour at atmospheric pressure in a dryer with air circulating.

3-1. Content of copolymer (P) in electrode slurry
The content of copolymer (P) 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 active material (described later), the conductive additive (described later), and the electrode binder. This is because copolymer (P) can ensure the binding between the electrode active materials and between the electrode active material and the current collector. The content of copolymer (P) in the electrode slurry is preferably 10% by mass or less, more preferably 7.0% by mass or less, and even more preferably 4.0% by mass or less, relative to the total mass of the electrode active material, the conductive additive, and the electrode binder. This is because the charge/discharge capacity of the electrode active material layer formed from the electrode slurry can be increased, and the internal resistance when formed into a battery can be reduced.

[3-2. Electrode active material]
The nonaqueous secondary battery is not particularly limited, but in the case of a lithium ion secondary battery, examples of the negative electrode active material include conductive polymers, carbon materials, lithium titanate, silicon, silicon compounds, etc. Examples of conductive polymers include polyacetylene and polypyrrole, etc. Examples of carbon materials include cokes such as petroleum coke, pitch coke, and coal coke; carbides of organic compounds; and graphites such as artificial graphite and natural graphite, etc. Examples of silicon compounds include SiO _x (0.1≦x≦2.0), etc.

Furthermore, a composite material containing Si and graphite (Si/graphite) or the like may be used as the electrode active material. Among these active materials, carbon materials, lithium titanate, silicon, and silicon compounds are preferably used because of their high energy density per volume. Furthermore, carbon materials such as coke, carbides of organic compounds, and graphite, and silicon-containing materials such as SiO _x (0.1≦x≦2.0), Si, and Si/graphite are significantly effective in improving the binding strength of the electrode binder of this embodiment. For example, a specific example of artificial graphite is SCMG (registered trademark)-XRs (manufactured by Showa Denko K.K.). Two or more of the materials listed here may be combined to form the negative electrode active material.

Examples of positive electrode active materials for lithium-ion secondary batteries include lithium cobalt oxide (LiCoO ₂ ), lithium composite oxides containing nickel, spinel-type lithium manganese oxide (LiMn ₂ O ₄ ), olivine-type lithium iron phosphate, and chalcogen compounds such as TiS ₂ , MnO ₂ , MoO ₃ , and V ₂ O _5. The positive electrode active material may contain any of these compounds alone or in combination. Oxides of other alkali metals can also be used. 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 positive electrode active materials include LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and LiNi _3/5 Mn _1/5 Co _1/5 .

[3-3. Conductive additive]
The electrode slurry may contain, as a conductive aid, carbon black, vapor grown carbon fiber, etc. A specific example of vapor grown carbon fiber is VGCF (registered trademark)-H (Showa Denko K.K.).

[3-4. Aqueous medium]
The aqueous medium of the electrode slurry contains water. The aqueous medium of 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 is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. The composition of the aqueous medium of the electrode slurry may be the same as or different from the aqueous medium contained in the electrode binder composition.

<4. Electrode>
The electrode of this embodiment has a current collector and an electrode active material layer formed on the surface of the current collector. The electrode active material layer contains an electrode active material and the electrode binder of this embodiment. The electrode may be in the form of, for example, a laminate or a wound body, but is not particularly limited thereto. The current collector is preferably a metal sheet having a thickness of 0.001 to 0.5 mm. Examples of metals for the current collector include iron, copper, aluminum, nickel, and stainless steel. When the nonaqueous secondary battery is a lithium ion secondary battery, the positive electrode current collector is preferably aluminum, and the negative electrode current collector is preferably copper, but are not particularly limited thereto.

The electrode of this embodiment can be manufactured, for example, by applying electrode slurry to a current collector and drying it, but this method is not limited to this.

Methods for applying the electrode slurry to the current collector include, for example, 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 a doctor blade is more preferred. This is because it is suitable for the physical properties of the electrode slurry, such as viscosity, and drying speed, and produces a coating film with a good surface condition.

The electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. When the electrode slurry is applied 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 or intermittently to the surface of the current collector. The amount and area of application of the electrode slurry can be determined appropriately depending on the size of the battery, etc. The basis weight of the electrode active material layer after drying is preferably 4 to 20 mg/ ^cm2 , and more preferably 6 to 16 mg/ ^cm2 .

An electrode sheet is obtained by drying the electrode slurry applied to the current collector. The drying method is not particularly limited, but for example, 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, and the drying time is preferably 1 minute or higher and 30 minutes or lower.

The electrode sheet may be used as an electrode as is, or may be cut to an appropriate size and shape for the electrode. There are no particular limitations on the method for cutting the electrode sheet, but for example, slitting, laser cutting, wire cutting, cutter, Thomson cutting, etc. can be used.

The electrode sheet may be pressed as needed before or after cutting. This allows the electrode active material to be more firmly attached to the electrode, further thinning the electrode and making the nonaqueous battery more compact. Conventional methods can be used for pressing, with die pressing or roll pressing being particularly preferred. The pressing pressure is not particularly limited, but is preferably set to 0.5 to 5 t/ ^cm² , a range that does not affect the doping/undoping of lithium ions and the like into the electrode active material by pressing.

<5. Battery>
As a preferred example of the battery according to the present embodiment, a lithium ion secondary battery will be described, but the configuration of the battery is not limited to the configuration described below. The lithium ion secondary battery according to the example described here has a positive electrode, a negative electrode, an electrolyte, and, if necessary, components such as a separator housed in an exterior body. At least one of the positive electrode and the negative electrode contains the electrode binder according to the present embodiment.

<5-1. Electrolyte>
The electrolyte solution is a non-aqueous liquid having ion conductivity. Examples of the electrolyte solution include a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, etc., but the former is preferred because it is inexpensive to manufacture and can provide a battery with low internal resistance.

As the electrolyte, an alkali metal salt can be used, and can be appropriately selected depending on the type of electrode active material, etc. Examples of _the electrolyte include _LiClO4 , _LiBF6 , _{LiPF6 , LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiB10Cl10, LiAlCl4 , LiCl , LiBr , LiB ( C2H5)4 , CF3SO3Li , CH3SO3Li , LiCF3SO3 , LiC4F9SO3 , Li} ( _CF3SO2 ) _2N , _and aliphatic lithium carboxylates _. Other alkali metal salts can also be used as the electrolyte.

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

<5-2. Exterior body>
The exterior body can be made of a suitable material such as a metal or an aluminum laminate. The shape of the battery may be any of a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, and the like.

The present invention will be explained in more detail below by showing examples and comparative examples of negative electrode binders, negative electrode slurries, negative electrodes, and lithium ion secondary batteries for lithium ion secondary batteries. However, the present invention is not limited to these examples.

<1. Negative electrode binder>
1-1. Synthesis of copolymer
The compositions of each monomer, polyfunctional thiol compound (C), and chain transfer agent used in Examples 1 to 20 and Comparative Examples 1 to 5 are shown in Tables 2 to 4. Here, each monomer, polyfunctional thiol compound (C), chain transfer agent, and polymerization initiator shown in Tables 2 to 4 are referred to as polymerization components. Details of each raw material compound shown in Tables 2 to 4 are as follows. When a monomer is used as a solution, the amount of monomer used in the table indicates the amount of the monomer itself, not including the solvent.

Note that some of the polymerization initiator, such as nitrogen, is not incorporated into the polymer. However, because the amount of polymerization initiator used is small, in Tables 2 to 4, the content (mass%) of each component in the polymerization components and the number of moles of each component per gram of polymerization components can be taken as the content of the structure corresponding to each component in the resulting copolymer and the number of moles of the structure corresponding to each component per gram of copolymer.

Monomer (A-1): N-vinylacetamide (NVA)
Monomer (B-1): Sodium acrylate (AaNa) (28.5% by mass aqueous solution)
Monomer (B-2): lithium acrylate (AaLi) (28.5% by mass aqueous solution),
Aa: acrylic acid Multifunctional thiol compound (C-1): pentaerythritol tetrakis(3-mercaptobutyrate)
Multifunctional thiol compound (C-2): Trimethylolpropane tris(3-mercaptobutyrate)
Multifunctional thiol compound (C-3): 1,4-bis(3-mercaptobutyryloxy)butane Multifunctional thiol compound (C-4): pentaerythritol tetrakis(3-mercaptopropionate)
Monomer (D-1): 50.0 mass% aqueous solution of methoxypolyethylene glycol methacrylate (VISIOMER (registered trademark) MPEG2005 MA W, manufactured by EVONIK INDUSTRIES) (in general formula (10), R ⁴¹ = CH ₃ , R ⁴² = H, R ⁴⁴ = CH ₃ , j = 45, k = 0, j + k = 45) Monomer (E-1): benzyl acrylate MPA: β-mercaptopropionic acid TMA: tetramethylolmethane tetraacrylate Polymerization initiator: 2,2'-azobis(2-methylpropionamidine) dihydrochloride (V-50, manufactured by Wako Pure Chemical Industries, Ltd.) and ammonium persulfate (manufactured by Wako Pure Chemical Industries, Ltd.)

A separable flask equipped with a condenser, thermometer, stirrer, and dropping funnel was charged with a total of 100 parts by mass of the polymerization components corresponding to each example and comparative example (Tables 2 to 4), 0.050 parts by mass of ammonium persulfate, and 693 parts by mass of water at 30°C. The temperature was raised to 80°C, and polymerization was carried out for 4 hours to synthesize copolymers P1 to CP20 and copolymers CP1 to CP5, respectively.

1-2. Preparation of negative electrode binder composition
Water was added to the reaction solution from which the copolymer was obtained so that the nonvolatile content was 10.0% by mass (the amount of water added was adjusted taking into account the water contained in the monomer (B-1)), and negative electrode binder compositions Q1 to Q20 and CQ1 to CQ5 were prepared. In the following description, when copolymers P1 to P20 are referred to without distinction, they are sometimes referred to as copolymer (P), and when copolymers CP1 to CP5 are referred to without distinction, they are sometimes referred to as copolymer (CP). When negative electrode binder compositions Q1 to Q20 are referred to without distinction, they are sometimes referred to as negative electrode binder composition (Q), and when negative electrode binder compositions CQ1 to CQ5 are referred to without distinction, they are sometimes referred to as negative electrode binder composition (CQ).

[1-3. Weight average molecular weight of copolymer (P)]
The weight average molecular weights of the copolymers (P) and (CP) were measured by gel permeation chromatography (GPC) under the following conditions. The measurement results are shown in Table 4.

GPC device: GPC-101 (Showa Denko K.K.)
Solvent: 0.1 M _NaNO3 aqueous solution Sample column: Shodex Column Ohpak SB-806 HQ (8.0 mm ID x 300 mm) x 2
Reference column: Shodex Column Ohpak SB-800 RL (8.0 mm ID x 300 mm) x 2
Column temperature: 40°C
Sample concentration: 0.1% by mass
Detector: RI-71S (Shimadzu Corporation)
Pump: DU-H2000 (Shimadzu Corporation)
Pressure: 1.3 MPa
Flow rate: 1ml/min
Molecular weight standard: pullulan (P-5, P-10, P-20, P-50, P-100, P-200, P-400, P-800, P-1300, P-2500 (manufactured by Showa Denko K.K.))

<2. Negative electrode slurry>
2-1. Preparation of negative electrode slurry
76.8 parts by mass of SCMG (registered trademark)-XRs (Showa Denko K.K.) graphite, 19.2 parts by mass of silicon monoxide (SiO) (Sigma-Aldrich), 1.0 part by mass of VGCF (registered trademark)-H (Showa Denko K.K.), 30 parts by mass of binder composition (Q) (containing 3.0 parts by mass of copolymer (P) and 27 parts by mass of water), and 20 parts by mass of water were mixed. Mixing was performed by kneading for 4 minutes at 2000 rpm using an agitation mixer (rotation-revolution 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 2000 rpm using the mixer to prepare a negative electrode slurry.

2-2. Appearance evaluation of negative electrode slurry
The appearance of the prepared negative electrode slurry was visually confirmed, and the size of the agglomerates was measured with a micrometer. The presence of agglomerates with a longest dimension of 1 mm or more in 10 g of negative electrode slurry was evaluated as ×, and the absence of agglomerates was evaluated as ○. The evaluation results are shown in Table 5.

<3. Negative electrode＞
3-1. Flexibility of negative electrode active material layer (winding test)
The negative electrode slurry prepared as described above was applied to both sides of a 10 μm-thick copper foil (current collector) using a doctor blade so that the coating weight after drying would be 8 mg/ ^cm² . 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 prepare a negative electrode sheet on which a negative electrode active material layer was formed. This negative electrode sheet was pressed using a mold press at a pressure of 1 t/ ^cm² .

The pressed negative electrode sheet was cut into a piece 50 mm wide and 60 mm long to serve as a test specimen. This test specimen was dried at 80°C for 12 hours. After drying, one widthwise edge of the test specimen was fixed to a 3 mm diameter stainless steel rod with 50 μm thick single-sided adhesive tape (the widthwise edge of the test specimen was parallel to the longitudinal direction of the stainless steel rod). The other widthwise edge of the test specimen was fixed to a glass plate. After wrapping the test specimen around the stainless steel rod, the appearance of the test specimen was visually observed, and the number of cracks in the test specimen was counted.

3-2. Peel strength of negative electrode active material layer from current collector
A pressed negative electrode sheet was prepared in the same manner as in the evaluation of flexibility, except that the negative electrode slurry was applied to both sides of the copper foil so that the weight per unit area after drying would be 8 mg/cm ² .

The entire process was carried out using the pressed negative electrode sheet at 23°C and a relative humidity of 50% by mass. The testing machine used was Tensilon (registered trademark, manufactured by A&D Corporation). The negative electrode sheet was cut into a piece 25 mm wide and 70 mm long to prepare a test piece. The negative electrode active material layer on the test piece was attached to a 50 mm wide and 200 mm long SUS plate using double-sided tape (NITTOTAPE (registered trademark) No. 5, manufactured by Nitto Denko Corporation) so that the center of the test piece coincided with the center of the SUS plate. The double-sided tape was attached to cover the entire area of the test piece. Attachment was performed by moving a 2 kg roller back and forth once over the entire test piece.

After leaving the test specimen and SUS plate bonded together for 10 minutes, the copper foil was peeled off from the negative electrode active material by 20 mm from one end of the specimen in the longitudinal direction, folded back 180°, and the peeled portion of the copper foil was gripped with the upper chuck of the testing machine. The end of the SUS plate from which the copper foil was peeled was then gripped with the lower chuck. In this state, the copper foil was peeled off from the test specimen at a rate of 100±10 mm/min, and a graph of peel length (mm) vs. peel force (mN) was obtained. The average peel force (mN) for peel lengths of 10 to 45 mm was calculated from the graph, and the value obtained by dividing the average peel force by the width of the test specimen (25 mm) was used as the peel strength (mN/mm) of the negative electrode active material layer. In all examples and comparative examples, no peeling occurred between the double-sided tape and the SUS plate, nor between the double-sided tape and the negative electrode active material layer during the test.

4. Lithium-ion secondary battery
4-1. Battery Construction
[Negative electrode]
The pressed negative electrode sheet was cut into a size of 22 mm x 22 mm, and a conductive tab was attached to prepare a negative electrode.

[Positive electrode]
90 parts by mass of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , 5 parts by mass of acetylene black, and 5 parts by mass of polyvinylidene fluoride were mixed, and then 100 parts by mass of N-methylpyrrolidone was mixed to prepare a positive electrode slurry (the proportion of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ in the solid content was 0.90).

The prepared positive electrode slurry was applied to one side of a 20 μm thick aluminum foil (current collector) using a doctor blade method so that the basis weight after drying was 22.5 mg/cm ² (22.5 × 10 ^-3 g/cm ² ). The aluminum foil to which the positive electrode slurry was applied was dried at 120 ° C. for 5 minutes and then pressed with a roll press to produce a positive electrode sheet on which a 100 μm thick positive electrode active material layer was formed. The obtained positive electrode sheet was cut into 20 mm × 20 mm (2.0 cm × 2.0 cm), and a conductive tab was attached to produce a positive electrode.

The theoretical capacity of the produced positive electrode was calculated as follows: basis weight of the positive electrode slurry after drying (22.5 × 10 ⁻³ gg/cm ² ) × application area of the positive electrode slurry (2.0 cm × 2.0 cm) × capacity of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ as a positive electrode active material (160 mAh/g) × proportion of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ in the solid content (0.90), and the calculated value was 13 mAh.

[Electrolyte]
An electrolyte solution was prepared by dissolving _LiPF6 at a concentration of 1.0 mol/L and vinylene carbonate (VC) at a concentration of 1.0 mass% in a mixed solvent prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) in a volume ratio of 30:60:10.

[Battery assembly]
The positive electrode and the negative electrode were arranged with their active material layers facing each other via a separator made of a polyolefin porous film, and the resulting structure was housed in an aluminum laminate exterior (battery pack). An electrolyte solution was poured into the exterior, and the battery was sealed with a vacuum heat sealer to obtain a laminated battery.

4-2. Evaluation of battery cycle characteristics (discharge capacity retention rate)
The cycle characteristics of the batteries prepared in each of the Examples and Comparative Examples were evaluated. The evaluation methods were as follows, and the evaluation results are shown in Table 5.

The battery discharge capacity retention rate (battery charge/discharge cycle test) was measured at 25°C using the following procedure. First, the battery was charged at 1 C until the voltage reached 4.2 V (CC charging), and then charged at 4.2 V until the current reached 0.05 C (CV charging). After leaving the battery for 30 minutes, it was discharged at 1 C until the voltage reached 2.75 V (CC discharging). A series of CC charging, CV charging, and CC discharging operations constitutes one cycle. The sum of the time-integrated values of the current during CC charging and CV charging at the nth cycle is 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 is defined as the discharge capacity (mAh) at the nth cycle. The discharge capacity retention rate of a battery at the nth cycle is the ratio (%) of the discharge capacity at the nth cycle to the discharge capacity at the 1st cycle. In this example and comparative example, the discharge capacity retention rate was evaluated at the 100th cycle.

<5. Evaluation Results>
As can be seen from Table 5, the negative electrode slurries produced in Examples 1 to 20 produced little aggregates. The negative electrodes produced in Examples 1 to 20 produced few cracks in the winding test, indicating high flexibility of the electrode active material layer. The negative electrodes produced in Examples 1 to 20 also had high peel strength of the negative electrode active material layer from the current collector. It can be seen that the lithium ion secondary batteries produced in Examples 1 to 20 had high discharge capacity retention rates during battery use, i.e., excellent cycle characteristics.

In Comparative Example 1, a negative electrode slurry was prepared using copolymer CP1, which does not have an amide bond. The negative electrode slurry prepared in Comparative Example 1 contained agglomerates. The negative electrode slurry prepared in Comparative Example 1 could not be applied evenly to the current collector, and an evaluable negative electrode and battery could not be prepared.

In Comparative Example 2, a negative electrode slurry, a negative electrode, and a lithium-ion secondary battery were prepared using copolymer CP2, which contains an excess of amide bonds. The electrode slurry prepared in Comparative Example 2 contained agglomerates. The negative electrode active material layer of the negative electrode prepared in Comparative Example 2 slid off during a winding test. Furthermore, in Comparative Example 2, the peel strength of the negative electrode active material layer to the current collector was low. The lithium-ion secondary battery prepared in Comparative Example 2 had a low discharge capacity retention rate.

In Comparative Example 3, a negative electrode slurry, a negative electrode, and a lithium-ion secondary battery were prepared using copolymer CP3, which does not have the substituent (c). The negative electrode prepared in Comparative Example 3 had numerous cracks in the negative electrode active material layer after a winding test, indicating low anode flexibility. Furthermore, in Comparative Example 3, the negative electrode active material layer had low peel strength from the current collector. The lithium-ion secondary battery prepared in Comparative Example 3 also had a low discharge capacity retention rate.

In Comparative Example 4, an attempt was made to synthesize copolymer CP4 containing an excess of substituent (c) using a large amount of multifunctional thiol compound (C), but the product gelled and it was not possible to produce a negative electrode slurry that could be evaluated.

In Comparative Example 5, a negative electrode slurry, a negative electrode, and a lithium-ion secondary battery were prepared using copolymer CP5, which does not contain substituent (c) and contains structural units derived from a tetrafunctional acrylate (tetramethylolmethane tetraacrylate). The negative electrode prepared in Comparative Example 5 showed numerous cracks in the negative electrode active material layer after a winding test, indicating low anode flexibility. Furthermore, in Comparative Example 5, the negative electrode active material layer exhibited low peel strength from the current collector. The lithium-ion secondary battery prepared in Comparative Example 5 also exhibited low discharge capacity retention.

Therefore, it was found that by using the binder copolymer of this example as a binder for a non-aqueous battery negative electrode, sufficient binding strength is ensured between the negative electrode active materials in the non-aqueous battery negative electrode and between the negative electrode active material and the current collector, while also imparting flexibility, resulting in good charge-discharge cycle characteristics for the battery.

These binders can also be used as binders for non-aqueous battery positive electrodes, ensuring sufficient binding between the positive electrode active materials and between the positive electrode active materials and the current collector, while producing batteries with good charge-discharge cycle characteristics.

Claims (14)

A non-aqueous secondary battery electrode binder containing a copolymer (P),
The copolymer (P) is
a main chain consisting only of bonds between carbon atoms;
a substituent having an amide bond;
a substituent having a salt of a carboxy group;
A substituent (c) represented by the following general formula (1):
and
the substituent having an amide bond, the substituent having a salt of a carboxy group, and the substituent (c) are each bonded to the main chain,
the amount of amide bonds contained per 1 g of the copolymer (P) is 0.050 mmol/g or more and 5.0 mmol/g or less,
the amount of the salt of the carboxy group contained per 1 g of the copolymer (P) is 5.0 mmol/g or more and 12.0 mmol/g or less;
a non-aqueous secondary battery electrode binder, wherein the amount of the substituent (c) contained per 1 g of the copolymer (P) is 0.15×10 ⁻² mmol/g or more and 8.0×10 ⁻² mmol/g or less.
(In general formula (1), R ³¹ is a hydrocarbon group, m and n each represent the number of corresponding substituents directly bonded to R ³¹ , m is an integer of 0 or more, n is an integer of 1 or more, and m+n≧2.) The non-aqueous secondary battery electrode binder according to claim 1 , wherein in the general formula (1), R ³¹ consists of a carbon atom and a hydrogen atom. The nonaqueous secondary battery electrode binder according to claim 1 or 2, wherein in the general formula (1), R ³¹ has a plurality of carbon atoms, and all of the bonds between the carbon atoms are single bonds. A nonaqueous secondary battery electrode binder according to claim 1 or 2, wherein Mc/(m+n)≦400, where Mc is the formula weight of the substituent (c). A nonaqueous secondary battery electrode binder as described in claim 1 or 2, wherein the substituent (c) has a structure derived from a multifunctional thiol compound (C), and the multifunctional thiol compound (C) has two or more mercapto groups per molecule. 3. The nonaqueous secondary battery electrode binder according to claim 1, wherein the copolymer (P) further contains 0.50 mass % or more and 20.0 mass % or less of a structural unit (d) represented by the following general formula (2):
(In general formula (2), R ⁴¹ , R ⁴² , and R ⁴⁴ each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. R ⁴³ represents an alkyl group having 1 to 6 carbon atoms, and has a larger number of carbon atoms than R ^42. j and k each represent the number of structures in the corresponding parentheses that are bonded in series. j represents an integer of 1 or more, k represents an integer of 0 or more, and j+k≧20.) 3. The nonaqueous secondary battery electrode binder according to claim 1, wherein the copolymer (P) further contains a structural unit (e) represented by the following general formula (3) in an amount of 0.030 mmol/g or more and 1.75 mmol/g or less per 1 g of the copolymer (P):
(In general formula (3), R ⁵¹ represents a hydrogen atom or a methyl group, and R ⁵² represents a substituent having an aromatic ring.) 3. The nonaqueous secondary battery electrode binder according to claim 1, wherein in the copolymer (P), at least a part of the amide bonds is contained as a structural unit (a) represented by the following general formula (4):
(In general formula (4), R ¹¹ and R ¹² each independently represent a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.) 3. The nonaqueous secondary battery electrode binder according to claim 1, wherein in the copolymer (P), at least a portion of the salt of the carboxy group is contained as a structural unit (b) represented by the following general formula (5):
(In general formula (5), ^R2 represents a hydrogen atom or a methyl group, and X represents a cation.) A non-aqueous secondary battery electrode binder as described in claim 1 or 2, characterized in that the weight average molecular weight of the copolymer (P) is 700,000 or more and 7,500,000 or less. A non-aqueous secondary battery electrode binder composition comprising the non-aqueous secondary battery electrode binder according to claim 1 or 2 and an aqueous medium. 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 claim 1 or 2 and an electrode active material. a positive electrode, a negative electrode, and an electrolyte;
13. A non-aqueous secondary battery, wherein at least one of the positive electrode and the negative electrode is the non-aqueous secondary battery electrode according to claim 12. A method for producing a non-aqueous secondary battery electrode binder, comprising a polymerization step of radically polymerizing a monomer (M) having an ethylenically unsaturated bond in the presence of a polyfunctional thiol compound (C) having two or more mercapto groups in one molecule,
the monomer (M) includes a monomer (A) having an amide bond and a monomer (B) having a salt of a carboxy group,
When the monomer (M), the polyfunctional thiol compound (C), a polymerization initiator, and a chain transfer agent (if used), the chain transfer agent are collectively used as polymerization components, the following can be obtained:
the amount of the monomer (A) contained per 1 g of the polymerization component is 0.050 mmol/g or more and 5.0 mmol/g or less,
the amount of the monomer (B) contained per 1 g of the polymerization component is 5.0 mmol/g or more and 12.0 mmol/g or less,
The method for producing a non-aqueous secondary battery electrode binder, wherein the amount of the polyfunctional thiol compound (C) contained per 1 g of the polymerization component is 0.15×10 ⁻² mmol/g or more and 8.0×10 ⁻² mmol/g or less.