Non-aqueous secondary battery electrode binder and non-aqueous secondary battery electrode

Abstract

The present invention provides a non-aqueous secondary battery electrode binder, a composition thereof, and a non-aqueous secondary battery electrode that can significantly improve the discharge capacity retention rate after charge-discharge cycles while improving the flexibility of the electrode active material layer formed on the current collector. The non-aqueous secondary battery electrode binder of the present invention comprises a copolymer (P). The copolymer (P) has a main chain comprising bonds between carbon atoms, a substituent having an amide bond bonded to the main chain, a substituent having a salt of a carboxyl group, and a substituent (c) represented by the following general formula (1). The amount of the amide bond included per 1g of copolymer (P) is 0.050 to 5.0 mmol / g, the amount of the substituent (b1) is 5.0 to 12.0 mmol / g, and the amount of the substituent (c) is 0.15×10⁻² to 8.0×10⁻² mmol / g.

Description

Technology Field

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

[0002] The present application claims priority based on patent application No. 2021-090167 filed in Japan on May 28, 2021, and incorporates the contents thereof herein by reference. Background Technology

[0003] Secondary batteries using non-aqueous electrolytes (non-aqueous secondary batteries) are superior to secondary batteries using aqueous electrolytes in terms of high voltage, miniaturization, and weight reduction. For this reason, non-aqueous secondary batteries are widely used as power sources for notebook personal computers, mobile phones, power tools, and electronic and communication devices. Furthermore, recently, non-aqueous batteries are being used for electric vehicles and hybrid vehicles in the context of environmentally friendly vehicle applications, but there is a strong demand for higher output, higher capacity, and longer lifespan. Lithium-ion secondary batteries can be cited as a representative example of non-aqueous secondary batteries.

[0004] A non-aqueous secondary battery comprises a positive electrode having a metal oxide or the like as an active material, a negative electrode having a carbon material such as graphite as an active material, and a non-aqueous electrolyte solvent centered on carbonates or flame-retardant ionic liquids. A non-aqueous secondary battery is a secondary battery in which charging and discharging of the battery are performed by ions moving between the positive electrode and the negative electrode. Specifically, the positive electrode is obtained by applying a slurry containing a metal oxide and a binder to the surface of a positive electrode current collector, such as aluminum foil, drying it, and then cutting it into a suitable size. The negative electrode is obtained by applying a slurry containing a carbon material and a binder to the surface of a negative electrode current collector, such as copper foil, drying it, and then cutting it into a suitable size. The binder serves to bond the active materials to each other and to the current collector in the positive and negative electrodes, thereby preventing the active material from peeling off from the current collector.

[0005] As a binder, polyvinylidene fluoride (PVDF)-based binders using the organic solvent-based N-methyl-2-pyrrolidone (NMP) are well known. However, this binder exhibits low adhesion between active materials and between the active material and the current collector, requiring a large amount of binder for practical use. Consequently, it has the drawback of reducing the capacity of non-aqueous secondary batteries. Furthermore, since the binder uses NMP, an expensive organic solvent, it has been difficult to control manufacturing costs.

[0006] As a method to solve these problems, the development of water-dispersible binders is underway. As a water-dispersible binder, it is known that (meth)acrylic acid ester-based or styrene-butadiene rubber (SBR)-based water-dispersibles are used in combination with, for example, carboxymethylcellulose (CMC) as a thickener.

[0007] Patent Document 1 discloses a binder composition for a lithium-ion secondary battery electrode comprising a (meth)acrylic acid ester compound and a polyfunctional thiol compound. Additionally, Patent Document 2 discloses a binder composition for a lithium-ion secondary battery silicon-based negative electrode comprising acrylic acid, a tetrafunctional (meth)acrylate monomer, and acrylamide.

[0008] Patent Document 3 discloses a binder for a non-aqueous battery electrode comprising a sodium acrylate-N-vinylacetamide copolymer (copolymer ratio: sodium acrylate / N-vinylacetamide = 10 / 90 mass ratio). Prior art literature

[0009] Japanese Patent Publication No. 2014-116265, Japanese Patent Publication No. 2016-181422, International Publication No. 2017 / 150200 The problem to be solved

[0010] However, the binder using a polyfunctional thiol described in Patent Document 1 requires the combined use of carboxymethylcellulose, a thickening agent, making the slurry preparation process complex. In addition, with this binder, the bonding between active materials and between the active material and the current collector is insufficient, so when an electrode is produced with a small amount of binder, there was a problem in that some of the active material was peeled off during the process of cutting the current collector.

[0011] In the binder using tetrafunctional acrylate disclosed in Patent Document 2, as disclosed in Comparative Example 5 described below, there was a problem in that the flexibility of the electrode could not be secured, and cracks occurred when the electrode was wound.

[0012] In the binder for non-aqueous battery electrodes disclosed in Patent Document 3, as disclosed in Comparative Example 3 described below, there was a problem in that the flexibility of the electrode was low and the discharge capacity retention rate after charge-discharge cycles was low.

[0013] Accordingly, the present invention aims to provide a non-aqueous secondary battery electrode binder and a non-aqueous secondary battery electrode binder composition that can significantly improve the discharge capacity retention rate after charge-discharge cycles while improving the flexibility of the electrode active material layer formed on the current collector.

[0014] In addition, the present invention aims to provide a non-aqueous secondary battery electrode having high flexibility and a high discharge capacity retention rate after charge-discharge cycles.

[0015] In addition, the present invention aims to provide a non-aqueous secondary battery having an electrode that has high flexibility and a high discharge capacity retention rate after charge-discharge cycles. means of solving the problem

[0016] To solve the above problem, the present invention is as follows [1] to

[14] .

[0017] [1] A non-aqueous secondary battery electrode binder comprising a copolymer (P), and

[0018] The above copolymer (P) is,

[0019] A main chain containing only bonds between carbon atoms, and

[0020] A substituent having an amide bond, and

[0021] A substituent having a carboxyl salt, and

[0022] Substituent (c) represented by the following general formula (1)

[0023] having,

[0024] The substituent having the amide bond, the substituent having the salt of the carboxyl group, and the substituent (c) are each bonded to the main chain, and

[0025] The amount of amide bonds contained per 1g of the copolymer (P) is 0.050 mmol / g or more and 5.0 mmol / g or less, and

[0026] The amount of carboxyl group salt contained per 1g of the above copolymer (P) is 5.0 mmol / g or more and 12.0 mmol / g or less, and

[0027] The amount of the substituent (c) contained per 1 g of the copolymer (P) is 0.15 × 10⁻⁶ -2 mmol / g or more 8.0×10 -2 mmol / g or less

[0028] A non-aqueous secondary battery electrode binder characterized by the following.

[0029]

[0030] (In general formula (1), R 31 is a hydrocarbon group, and m and n are, respectively, R 31 Indicates the number of corresponding substituents directly bound to, where m is an integer greater than or equal to 0, n is an integer greater than or equal to 1, and m+n≥2.)

[0031] [2] With the above general formula (1), R 31A non-aqueous secondary battery electrode binder described in [1] containing carbon atoms and hydrogen atoms.

[0032] [3] In the above general formula (1), R 31 A non-aqueous secondary battery electrode binder described in [1] or [2] having multiple carbon atoms, and all bonds between carbon atoms are single bonds.

[0033] [4] A non-aqueous secondary battery electrode binder described in any one of [1] to [3], wherein Mc / (m+n)≤400, where Mc is the food of the substituent (c) above.

[0034] [5] The above substituent (c) is a structure derived from a polyfunctional thiol compound (C), and the polyfunctional thiol compound (C) has two or more mercapto groups in one molecule. It is a non-aqueous secondary battery electrode binder described in any one of [1] to [4].

[0035] [6] The copolymer (P) described above is a non-aqueous secondary battery electrode binder described in any one of [1] to [5], containing 0.50 mass% or more and 20.0 mass% or less of a structural unit (d) represented by the following general formula (2).

[0036]

[0037] (In general formula (2), R 41 , R 42 , R 44 Each is independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. 43 is an alkyl group having 1 to 6 carbon atoms, and R 42 The number of carbon atoms is greater than that. j and k represent the number of structures within the corresponding parentheses that are connected in series, respectively. j is an integer greater than or equal to 1, k is an integer greater than or equal to 0, and j+k≥20.)

[0038] [7] The above copolymer (P) is a non-aqueous secondary battery electrode binder described in any one of [1] to [6], which contains 0.030 mmol / g or more and 1.75 mmol / g or less of a structural unit (e) represented by the following general formula (3) per 1g of the copolymer (P).

[0039]

[0040] (In general formula (3), R 51 represents a hydrogen atom or a methyl group, and R 52 is a substituent having an aromatic ring.)

[0041] [8] A non-aqueous secondary battery electrode binder described in any one of [1] to [7], wherein at least a portion of the amide bonds in the copolymer (P) is included as a structural unit (a) represented by the following general formula (4).

[0042]

[0043] (In general formula (4), R 11 , R 12 Each represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms independently.

[0044] [9] A non-aqueous secondary battery electrode binder described in any one of [1] to [8], wherein in the copolymer (P) above, at least a portion of the salt of the carboxyl group is included as a structural unit (b) represented by the general formula (5) below.

[0045]

[0046] (In general formula (5), R 2 represents a hydrogen atom or a methyl group, and X is a cation.)

[0047]

[10] A non-aqueous secondary battery electrode binder described in any one of [1] to [9], characterized in that the weight average molecular weight of the copolymer (P) is 700,000 or more and 7,500,000 or less.

[0048]

[11] A non-aqueous secondary battery electrode binder composition comprising a non-aqueous secondary battery electrode binder described in any one of [1] to

[10] and an aqueous medium.

[0049]

[12] A current collector and an electrode active material layer formed on the surface of the current collector, and

[0050] The electrode active material layer comprises a non-aqueous secondary battery electrode comprising a binder for a non-aqueous secondary battery electrode and an electrode active material as described in any one of [1] to

[10] .

[0051]

[13] Includes a positive electrode, a negative electrode and an electrolyte, and

[0052] A non-aqueous secondary battery characterized in that at least one of the above positive electrode and the above negative electrode is a non-aqueous secondary battery electrode as described in

[12] .

[0053]

[14] A method for producing a non-aqueous secondary battery electrode binder comprising a polymerization process in which a monomer (M) having an ethylenically unsaturated bond is radically polymerized in the presence of a polyfunctional thiol compound (C) having two or more mercapto groups in one molecule, and

[0054] The above monomer (M) comprises a monomer (A) having an amide bond and a monomer (B) having a salt of a carboxyl group, and

[0055] In cases where the above monomer (M), the above polyfunctional thiol compound (C), the polymerization initiator, and the chain transfer agent are used, the chain transfer agent is also included and referred to as a polymerization component,

[0056] The amount of monomer (A) included per 1g of the polymer component is 0.050 mmol / g or more and 5.0 mmol / g or less, and

[0057] The amount of monomer (B) included per 1g of the polymer component is 5.0 mmol / g or more and 12.0 mmol / g or less, and

[0058] The amount of the polyfunctional thiol compound (C) contained per 1g of the above polymer component is 0.15×10-2 mmol / g or more 8.0×10 -2 mmol / g or less

[0059] A method for manufacturing a non-aqueous secondary battery electrode binder characterized by the following. Effects of the invention

[0060] According to the present invention, a non-aqueous secondary battery electrode binder and its composition can be provided, which can significantly improve the discharge capacity retention rate after a charge-discharge cycle while improving the flexibility of the electrode active material layer formed on the current collector.

[0061] In addition, according to the present invention, a non-aqueous secondary battery electrode with high flexibility and a high discharge capacity retention rate after charge-discharge cycles can be provided.

[0062] In addition, according to the present invention, a non-aqueous secondary battery having an electrode with high flexibility and a high discharge capacity retention rate after charge-discharge cycles can be provided. Specific details for implementing the invention

[0063] Embodiments of the present invention will be described in detail below. In this embodiment, the battery is a secondary battery that involves the movement of ions between a positive electrode and a negative electrode 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 intercaration and deintercalation of ions. A preferred example of a secondary battery with such a configuration is a lithium-ion secondary battery.

[0064] "(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.

[0065] "Weight average molecular weight" is a pullulan equivalent value calculated using gel permeation chromatography (GPC).

[0066] "Hydrocarbon group" refers to a structure containing only carbon atoms and hydrogen atoms. However, it is not limited thereto if there is a special description, such as when some hydrogen atoms are substituted.

[0067] In the following description, regarding the formulas representing structural units, if there is no atom at the end of the line representing the bond, it means that the part is bonded to another structural unit or terminal structure forming the polymer.

[0068] A salt of a functional group refers to a form in which a dissociated ion of a functional group is combined with a counterion other than hydrogen ions and hydroxide ions; for example, a salt of a carboxyl group refers to a form in which COO- is combined with a cation other than a hydrogen ion.

[0069] <1. Non-aqueous secondary battery electrode binder>

[0070] The non-aqueous secondary battery electrode binder according to the present embodiment (or, non-aqueous secondary battery electrode binder; hereinafter referred to as "electrode binder") comprises the copolymer (P) described below. The electrode binder may include other components, and may include, for example, a polymer other than the copolymer (P), a surfactant, etc.

[0071] Here, the electrode binder includes components that remain without volatilizing during a process involving heating in the battery manufacturing process described later. Specifically, the component constituting the electrode binder is the component remaining 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 while circulating air in a dryer under atmospheric pressure.

[0072] The content of the copolymer (P) in the electrode binder is preferably 80 mass% or more, more preferably 90 mass% or more, even more preferably 95 mass% or more, and even more preferably 98 mass% or more. This is to greatly increase the contribution of the copolymer (P) to the effect intended by the present invention.

[0073] [1-1. Copolymer (P)]

[0074] The copolymer (P) has a main chain comprising only bonds between carbon atoms, a substituent having an amide bond, a substituent having a salt of a carboxyl group, and a substituent (c) represented by the following general formula (1). It is preferable that the main chain comprises only single bonds between carbon atoms.

[0075] Substituents having amide bonds, substituents having salts of carboxyl groups, and substituent (c) are each bonded to the main chain. It is preferable that the substituent having amide bonds and the substituent having salts of carboxyl groups are branched from the main chain. It is preferable that substituent (c) be bonded to the end of the main chain. In addition, multiple main chains may be bonded to a single substituent (c). That is, a structure may be formed in which multiple main chains containing bonds between carbon atoms are bonded through substituent (c) within a single molecule.

[0076] The copolymer (P) preferably has at least one of the structural unit (d) represented by the general formula (2) described below and the structural unit (e) represented by the general formula (3) described below, and more preferably has both. The copolymer (P) may have a structure other than the above structures, such as a molecular end structure.

[0077] The weight average molecular weight of the copolymer (P) is preferably 700,000 or more, more preferably 1,000,000 or more, and even more preferably 1,500,000 or more. In addition, the weight average molecular weight of the 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.

[0078] [1-1-1. Amid bond]

[0079] The amount of amide bonds contained per 1g of copolymer (P) is preferably 0.050 mmol / g or more, 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 aid, etc., during the preparation of the electrode slurry described later is excellent, so that an electrode slurry with good coating properties can be prepared. In addition, the electrolyte resistance of the negative electrode active material layer is improved by the copolymer (P).

[0080] The amount of amide bonds contained per 1 g 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 the copolymer (P) to contain other structures. In addition, the occurrence of cracks in the electrode described later is suppressed, thereby improving the productivity of the electrode.

[0081] In addition, the amide bond may be included in all structural units having other functional groups, such as the structural unit (e) described later.

[0082] In the copolymer (P), it is preferable that at least a portion of the amide bonds be included as structural units (a) represented by the following general formula (4). This is because the amount of amide bonds relative to the mass of the structural units (a) is large, allowing the copolymer (P) to efficiently incorporate amide bonds. Among the amide bonds in the copolymer (P), the proportion included in the structural units (a) is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more.

[0083]

[0084] In general formula (4), R 11 , R 12 Each represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms independently.

[0085] In general formula (4), R 11 , R 12 It is more preferable that each is independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R 11 , R 12 It is more preferable that each is independently a hydrogen atom or a methyl group.

[0086] R 11 , R 12 A particularly desirable embodiment as a combination of is R 11 :H also R 12 :H, or R 11 :H also R 12 :CH3. This is because the amount of amide bonds relative to the mass is large, allowing more amide bonds to be included in the copolymer (P).

[0087] [1-1-2. Salts of Carboxyl Groups]

[0088] The salt of the carboxyl group is preferably a salt of -COO- and 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.

[0089] The amount of carboxyl group salt contained per 1 g 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 the copolymer (P) allows for obtaining an electrode active material layer with high peel strength against a current collector.

[0090] The amount of carboxyl group salt contained per 1g of copolymer (P) is preferably 12.0 mmol / g or less and 9.9 mmol / g or less. This is because the dispersibility of solid components such as electrode active materials and conductive aids is further improved during the preparation of the electrode slurry described later.

[0091] In addition, the amount of salt of a carboxyl group is the amount of -COO- bonded to a cation other than a hydrogen ion. For example, if two COO- are bonded to one divalent cation, there are two salts of a carboxyl group.

[0092] In addition, the salt of the carboxyl group may be included in all structural units having other functional groups, such as the structural unit (e) described later.

[0093] In the copolymer (P), it is preferable that at least a portion of the salt of the carboxyl group be included as a structural unit (b) represented by the following general formula (5). This is because the amount of the salt of the carboxyl group relative to the mass is large, allowing the salt of the carboxyl group to be efficiently included in the copolymer (P). Among the salt of the carboxyl group in the copolymer (P), the proportion included in the structural unit (b) is preferably 95 mol% or more, more preferably 98 mol% or more, and even more preferably 99 mol% or more.

[0094]

[0095] In general formula (5), R 2 represents a hydrogen atom or a methyl group, and X is a cation.

[0096] In general formula (5), it is more preferable that X is a monovalent cation, and even more preferable that it is at least one of lithium ions, sodium ions, potassium ions, and ammonium ions. Among these, it is particularly preferable that it contains at least one of lithium ions and sodium ions.

[0097] As a structural unit (b), in the above general formula (5), X may include two or more different types of structures in the copolymer (P). For example, the structural unit (b) may include two types of structures, such as a salt with lithium and a salt with sodium.

[0098] [1-1-3. Substituents (c)]

[0099] Substituent (c) is expressed by the following general formula (1).

[0100]

[0101] In general formula (1), R 31 is a hydrocarbon group, and m and n are, respectively, R 31 Represents the number of corresponding substituents directly bound to (the number of branches of the structure within parentheses corresponding to m and n, respectively), where m is an integer greater than or equal to 0, n is an integer greater than or equal to 1, m+n≥2, and R 32 is a hydrogen atom or a methyl group.

[0102] The substituent (c) has the role of connecting the main chains to extend the molecular chain, and if n≥3, it can form a cross-linked structure in the copolymer (P).

[0103] In general formula (1), it is preferable that m+n≥3, and more preferable that m+n≥4. This is because the peel strength and toughness of the electrode active material layer containing the copolymer (P) against the current collector are improved, and this is because it is thought that at least some of the substituents (c) form a cross-linked structure in the copolymer (P).

[0104] In addition, although not specifically limited, it is preferable that m+n ≤ 6, and more preferable 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 the copolymer (P) is improved.

[0105] In general formula (1), R 31 It is desirable to include silver, carbon atoms, and hydrogen atoms. R 31 It is more desirable that it has multiple carbon atoms and that the bonds between the carbon atoms are all single bonds.

[0106] In general formula (1), R 31 It can be a straight-chain hydrocarbon contribution or a branched-structure hydrocarbon contribution. R 31 The number of carbon atoms included in is preferably 10 or fewer, more preferably 8 or fewer, and even more preferably 6 or fewer. In addition, R 31 It is preferable that the silver is not directly bonded to the main chain. R 31 In this case, it is desirable that all bonds between carbon atoms be single bonds. This is to improve the flexibility of the electrode binder by improving the flexibility of the substituent (c).

[0107] In general formula (1), R 32 It is preferable that it be a methyl group. This is because the peel strength of the electrode active material layer containing the copolymer (P) is improved.

[0108] If the food value of substituent (c) is denoted as Mc, it is preferable that Mc / (m+n) ≤ 400, more preferable that Mc / (m+n) ≤ 300, and even more preferable that Mc / (m+n) ≤ 200. This is because the effect of molecular chain elongation by substituent (c) and / or the crosslinking density of the copolymer (P) is improved, and the peel strength of the electrode active material layer against the current collector and the toughness of the electrode active material layer are improved.

[0109] 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 in one molecule. Here, it is more preferable for the polyfunctional thiol compound (C) to have three or more mercapto groups in one molecule, and even more preferable to have four or more. Details regarding the polyfunctional thiol compound (C) will be described later in the method for preparing the copolymer (P).

[0110] The amount of substituent (c) contained per 1 g of copolymer (P) is 0.15 × 10⁻⁶ -2 mmol / g or more, and 0.30×10 -2 It is desirable that it be mmol / g or higher, and 0.65×10 -2 It is more preferable that the value be mmol / g or higher. This is because, in the electrode described below, the strength of the electrode's composite layer is improved, thereby improving the discharge capacity retention rate after charge-discharge cycles.

[0111] The amount of substituent (c) contained per 1 g of copolymer (P) is 8.0 × 10⁻⁶ -2 mmol / g or less, and 5.5×10 -2 It is desirable that mmol / g or less, and 4.0×10 -2 It is more preferable that it is mmol / g or less, and 1.4×10 -2 It is more desirable that the value be mmol / g or less. This is because it improves the flexibility of the electrode described later. Furthermore, this improves the cycle characteristics (discharge capacity retention rate) of the non-aqueous secondary battery described later.

[0112] [1-1-4. Structural Unit (d)]

[0113] The structural unit (d) is a structure expressed by the following general formula (2).

[0114]

[0115] In general formula (2), R 41 , R 42 , R 44 Each is independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. 43 Silver is an alkyl group having 1 to 6 carbon atoms, and R 42 The number of carbon atoms is greater than that. In this formula, j and k represent the number of structures within the corresponding parentheses that are connected in series, respectively. j is an integer greater than or equal to 1, k is an integer greater than or equal to 0, and j+k≥20.

[0116] In general formula (2), R 41 , R 42 , R 44 Preferably, each is independently a hydrogen atom or an alkyl group having 1 to 3 carbon atoms, and R 41 , R 42 , R 44 It is more preferable that each is independently a hydrogen atom or a methyl group. R 44 It is more preferable that it be a methyl group.

[0117] In general formula (2), j is an integer greater than or equal to 1, k is an integer greater than or equal to 0, and j+k ≥ 20. This is because when an electrode is fabricated using a copolymer (P) as a binder for the electrode active material, the flexibility of the electrode is improved, and the occurrence of cracks is suppressed. From this perspective, it is preferable that j+k ≥ 30, and more preferable that j+k ≥ 40. In addition, it is preferable that j+k ≤ 500, more preferable that j+k ≤ 200, and even more preferable that j+k ≤ 150. This is because the binding strength of the electrode binder is higher.

[0118] Also, in general formula (2), R 42 j structural units including and R 43 Although it is limited that k structural units including [specific structural units] are included, there is no limitation on the arrangement of these structural units. That is, for k≥1, in the polyoxyalkylene chain of general formula (2), each structural unit may have a continuous block structure, either all or part thereof, a structure 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 arranged with periodic regularity or a structure arranged randomly. This is to suppress the skewness of the 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 arranged randomly. This is because it can be polymerized by a radical polymerization initiator without using a special catalyst, thereby reducing manufacturing costs.

[0119] In general formula (2), R 41 , R 42 , R 43 , R 44 Preferable examples of combinations of , j, and k include the examples in Table 1 below.

[0120]

[0121] In the copolymer (P), the content of the structural unit (d) is preferably 0.50 mass% or more, more preferably 0.70 mass% or more, and even more preferably 3.5 mass% or more. This is to suppress the occurrence of cracks in the electrode described later.

[0122] In the copolymer (P), the content of the structural unit (d) is preferably 20.0 mass% or less, more preferably 14.0 mass% or less, and more preferably 7.0 mass% or less. This is to improve the peel strength of the electrode active material layer. In addition, in the non-aqueous secondary battery described later, this is to improve the cycle characteristics (discharge capacity retention rate).

[0123] [1-1-5. Structural Unit (e)]

[0124] The structural unit (e) is a structure expressed by the following general formula (3).

[0125]

[0126] In general formula (3), R 51 represents a hydrogen atom or a methyl group, and R 52 is a substituent having an aromatic ring. R 52 It is preferable that there be only one aromatic ring included in R. 52 It is preferable that it does not have both an amide bond and a carboxyl group salt. R 52 It is preferable that it has a benzene ring, and it is more preferable that it contains carbon atoms and hydrogen atoms.

[0127] The structural unit (e) is preferably expressed by the following general formula (6).

[0128]

[0129] In general formula (6), R 51 is a hydrogen atom or a methyl group. R 53 -CH2- or -(CH2CH2O) h - or -CH2CH(OH)CH2O-. Here, h is an integer between 1 and 5 inclusive. R 54 is a substituent having an aromatic ring. R 53 It is more preferable that it be -CH2- or -CH2CH2O-, and even more preferable that it be -CH2-. R 54It is preferable that there be only one aromatic ring included in R. 54 It is preferable that it has a benzene ring, and more preferable that it includes carbon atoms and hydrogen atoms. R 54 It is preferable that it does not have both an amide bond and a carboxyl group salt. R 54 It is particularly desirable that it be a phenyl group.

[0130] The amount of structural unit (e) contained per 1 g 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 described later is suppressed, thereby improving the productivity of the electrode.

[0131] The amount of structural unit (e) contained per 1 g 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 to suppress the expansion of the electrode active material layer in the electrode described below. In addition, this is to improve the cycle characteristics (discharge capacity retention rate) in the non-aqueous secondary battery described below.

[0132] [1-1-6. Other Structures]

[0133] Other structures included in the copolymer (P) include structures at the ends of molecular chains and structures other than those branched from the main chain.

[0134] Examples of molecular chain end structures include structures derived from polymerization initiators and structures derived from chain transfer agents. In addition, the substituent (c) is not a molecular chain end structure even if n=1 in general formula (1), for example. The content of the end structure in the copolymer (P) is preferably 10 mass% or less, more preferably 2.0 mass% or less, and even more preferably 1.0 mass% or less. This is to increase the effect of the above structure in the copolymer (P). In addition, in a structure derived from a single chain transfer agent, there is only one site of bonding to the molecular chain of the copolymer (P).

[0135] A carboxyl group may be included as a structure other than the above structure included in the copolymer (P). When the copolymer (P) has a carboxyl group, the amount of the carboxyl group included 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 the carboxyl group included per 1 g of copolymer (P) is preferably 5.0 mmol / g or less, and more preferably 3.0 mmol / g or less.

[0136] The copolymer (P) may include a main chain containing bonds between carbon atoms, a substituent (c), an ester bond, an amide bond, a salt of a carboxyl group, a structural unit (d), a structural unit (e), and a structure that does not correspond to any of the carboxyl groups. The content thereof 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 enable a stronger effect from the functional groups and structures included in the copolymer (P).

[0137] [1-1-7. Examples of Suitable Compositions of Copolymer (P)]

[0138] An example of a suitable composition of copolymer (P) may be 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). In this copolymer, the molecular chain ends may have structures derived from an initiator and structures derived from a chain transfer agent, etc. The content of each structural unit is determined according to the amount of functional groups and structures introduced into copolymer (P). The amount of functional groups and structures included in copolymer (P) is as described above. In this example, the total content of structural unit (a), structural unit (b), and substituent (c) in copolymer (P) is preferably 97.0 mass% or more, more preferably 98.0 mass% or more, and even more preferably 99.0 mass% or more.

[0139] Another example of a suitable composition of the copolymer (P) may be a copolymer having one or both of the structural unit (d) and structural unit (e) in addition to the structural unit (a), structural unit (b), and substituent (c). In this copolymer, the molecular chain ends may have structures derived from an initiator and structures derived from a chain transfer agent, etc. The content of each structural unit is determined according to the amount of functional groups and structures introduced into the copolymer (P). The amount of functional groups and structures included in the copolymer (P) is as described above. In this example, the total content of the structural unit (a), structural unit (b), substituent (c), structural unit (d), and structural unit (e) in the copolymer (P) is preferably 97.0 mass% or more, more preferably 98.0 mass% or more, and even more preferably 99.0 mass% or more.

[0140] [1-2. Method for manufacturing copolymer (P)]

[0141] The method for manufacturing the copolymer (P) is not particularly limited, but it is preferable to radically polymerize 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. It is preferable to perform the polymerization in an aqueous medium. As for the polymerization procedure, for example, a method of polymerizing by adding all the monomers (M) to be used for polymerization at once, or a method of polymerizing while continuously supplying the monomers (M) to be used for polymerization, can be applied. The polymerization temperature is not particularly limited, but it is preferable to be 30°C or higher and 90°C or lower.

[0142] As for the monomer (M), it is preferable to use a monomer (A) having an amide bond and a monomer (B) having a salt of a carboxyl group to simplify the manufacturing process. When synthesizing a copolymer (P) containing a structural unit (d), it is preferable to use a monomer (D) represented by the general formula (10) described below to simplify the manufacturing process. When synthesizing a copolymer (P) containing a structural unit (e), it is preferable to use a monomer (E) represented by the general formula (11) described below to simplify the manufacturing process. Additionally, the necessary functional groups may be formed through reactions after polymerization, etc., without using these monomers.

[0143] [1-2-1. Monomer (A)]

[0144] Monomer (A) has ethylenically unsaturated bonds and amide bonds. Additionally, if monomer (A) has a salt of a carboxyl group, this monomer (A) also corresponds to monomer (B). It is preferable for monomer (A) to have (meth)acryloyloxy groups. This is because the polymerization rate is improved, thereby increasing the productivity of the copolymer (P). It is more preferable for monomer (A) to have a structure represented by the following general formula (7).

[0145]

[0146] In general formula (7), R 11 , R 12 is similar to these compositions in the above general formula (4). A particularly preferred embodiment of monomer (A) is N-vinylformamide (R 11 :H also R 12 :H) or N-vinylacetamide (R 11 :H also R 12 :CH3). This is because the amount of amide bonds relative to the mass of monomer (A) is large, allowing more amide bonds to be included in the copolymer (P).

[0147] [1-2-2. Monomer (B)]

[0148] Monomer (B) has an ethylenically unsaturated bond and a salt of a carboxyl group. Additionally, if monomer (B) has an amide bond, this monomer (B) also corresponds to monomer (A). It is preferable for monomer (B) to have a (meth)acryloyloxy group. This is because the polymerization rate is improved and the productivity of the copolymer (P) is improved. It is more preferable for monomer (B) to have a structure represented by the following general formula (8).

[0149]

[0150] In general formula (8), R 2 X and X are similar to the compositions in the above general formula (5). As monomer (B), two or more different compounds of the general formula (8) may be used. For example, as monomer (B), two types of compounds, such as lithium salt and sodium salt, may be used.

[0151] [1-2-3. Polyfunctional thiol compounds (C)]

[0152] The polyfunctional thiol compound (C) has two or more mercapto groups. The polyfunctional thiol compound (C) is preferably of the structure represented by the following general formula (9). This is because it is inexpensive and easily available, and the reaction rate is improved, thereby improving the productivity of the copolymer (P).

[0153]

[0154] In general formula (9), R 32 is the same as the configuration in the above general formula (1). R 33 is a hydrocarbon group. f is, R 33 Indicates the number of corresponding substituents directly bound to (the number of branches of the structure within parentheses). f≥2.

[0155] It is preferable that f ≥ 3, and more preferable that f ≥ 4. This is because a cross-linked structure can be formed in the copolymer (P), and the peel strength and toughness of the electrode active material layer containing the copolymer (P) with respect to the current collector are improved. Additionally, although not particularly limited, it is preferable that f ≤ 6, more preferable that f ≤ 5, even more preferable that f ≤ 4, and most preferable that f ≥ 4. This is because the flexibility of the electrode active material layer containing the copolymer (P) is improved.

[0156] In general formula (9), R 33 It can be a straight-chain hydrocarbon contribution or a branched-structure hydrocarbon contribution. R 33 The number of carbon atoms included in is preferably 10 or fewer, more preferably 8 or fewer, and even more preferably 6 or fewer. In addition, R 33 It is desirable that it does not have ethylenically unsaturated bonds. This is because it suppresses the unevenness of crosslinking density and the excess of crosslinking density.

[0157] The thiol equivalent (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 elongation by the polyfunctional thiol compound (C) and / or the crosslinking density of the copolymer (P) is improved, and the peel strength of the electrode active material layer against the current collector and the toughness of the electrode active material layer are improved.

[0158] For the same reason, when the polyfunctional thiol compound (C) is a compound represented by formula (9), if the molecular weight of the polyfunctional thiol compound (C) is denoted as MC, it is preferable that MC / f ≤ 400, more preferable that MC / f ≤ 300, and even more preferable that MC / f ≤ 200.

[0159] Examples of polyfunctional thiol compounds (C) include, for instance, 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), dipentaerythritol=hexakis(3-mercaptopropionate), etc. Among these compounds, monomer (C) is more preferably composed of pentaerythritol=tetrakis(3-mercaptobutyrate), pentaerythritol=tetrakis(3-mercaptopropionate), trimethylolpropane=tris(3-mercaptobutyrate), and 1,4-bis(3-mercaptobutyryloxy)butane.

[0160] [1-2-4. Monomer (D)]

[0161] The monomer (D) is represented by the following general formula (10).

[0162]

[0163] R in general formula (10) 41 , R42 , R 43 , R 44 , j and k are the same as these configurations in the above general formula (2).

[0164] In general formula (10), it is more preferable that k=0. Examples of monomers (D) for which k=0 include mono(meth)acrylate of polyethylene glycol, and more specifically, methoxypolyethylene glycol(meth)acrylate (e.g., monomers d1 and d2 of Table 1). An example of methoxypolyethylene glycol methacrylate is VISIOMER (registered trademark) MPEG2005 MA W manufactured by EVONIK INDUSTRIES. In this product, R 41 =CH3, R 42 =H, R 44 =CH3, j=45, k=0. Another example of methoxypolyethylene glycol methacrylate is VISIOMER (registered trademark) MPEG5005 MA W manufactured by EVONIK INDUSTRIES, and in this product, R 41 =CH3, R 42 =H, R 44 =CH3, j=113, k=0.

[0165] As another example of a monomer (D) where k=0, polypropylene glycol mono(meth)acrylate can be cited, and more specifically, methoxypolypropylene glycol(meth)acrylate can be cited.

[0166] [1-2-5. Monomer (E)]

[0167] The monomer (E) is represented by the following general formula (11).

[0168]

[0169] R in general formula (11) 51 and R 52 This is similar to the configurations in the above general formula (3).

[0170] The monomer (E) is preferably represented by the following general formula (12).

[0171]

[0172] In general formula (12), R 51 , R 53 and R 54 is the same as these configurations in the above general formula (6).

[0173] Examples of monomers (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, 2-hydroxy-3-phenoxypropyl (meth)acrylate, etc. Among these compounds, it is more preferable to use one or both of benzyl (meth)acrylate and phenoxyethyl (meth)acrylate as monomer (E).

[0174] [1-2-7. Polymerization Initiator]

[0175] In the case of radical polymerization, polymerization initiators may 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. Additionally, if necessary, redox polymerization may be performed by using a radical polymerization initiator and a reducing agent together during polymerization. Examples of reducing agents include sodium bisulfite, rongalite, and asbromic acid. Furthermore, when using an azo compound as a polymerization initiator, components that assist in the generation of radicals from the azo compound, such as persulfates, may be added, but these components do not constitute the copolymer (P). Examples of persulfates include ammonium persulfate and potassium persulfate.

[0176] [1-2-8. Mercury Media]

[0177] While it is preferable to use water as the aqueous medium, a solution prepared by adding a hydrophilic solvent to water may also be used as the aqueous medium, provided that the polymerization stability of the resulting copolymer for the binder is not compromised. Examples of hydrophilic solvents added to water include methanol, ethanol, and N-methylpyrrolidone.

[0178] [1-2-9. Chain Transfer Agent]

[0179] During polymerization, a chain transfer agent may be used to control the molecular weight of the copolymer (P). As a chain transfer agent, examples 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, although they are not particularly limited.

[0180] [1-2-10. Content of each component in the polymerization components]

[0181] If compounds that become part of the structure of a copolymer (P) through a polymerization reaction are called 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 specific functional groups, all monomers become structural units of the copolymer (P) without reacting in parts other than the ethylenically unsaturated bonds. Also, in the case of radical polymerization, unless there is an operation to change specific functional groups, all polyfunctional thiol compounds (C) become substituents (c) of the copolymer (P).

[0182] In the synthesis of the copolymer (P), forms that do not use monomer (D) and monomer (E), or forms that use one or both of monomer (D) and monomer (E) may be cited.

[0183] Hereinafter, suitable amounts of each monomer and polyfunctional thiol compound (C) used to obtain the copolymer (P) according to the present invention will be described, but are not limited thereto. Here, when monomers, polyfunctional thiol compounds (C), polymerization initiators, and chain transfer agents used in the synthesis of the copolymer (P) are used, the chain transfer agent is also collectively referred to as polymerization components.

[0184] The amount of monomer (A) included per 1g of polymer 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) included per 1g of polymer 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.

[0185] The amount of monomer (B) contained per 1g of polymer 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 1g of polymer component is preferably 12.0 mmol / g or less, and more preferably 9.9 mmol / g or less. In addition, if multiple carboxylate ions corresponding to the structure of monomer (B) are bonded to a cation of divalent or higher, it is assumed that there are monomers (B) bonded to the cation.

[0186] The amount of polyfunctional thiol compound (C) contained per 1g of polymer component is 0.15×10⁻⁶ -2 mmol / g or more, and 0.30×10 -2 It is desirable that it be mmol / g or higher, and 0.65×10 -2 It is more preferable that it be mmol / g or more. The amount of polyfunctional thiol compound (C) contained per 1g of polymer component is 8.0×10⁻⁶-2 mmol / g or less, and 5.5×10 -2 It is desirable that mmol / g or less, and 4.0×10 -2 It is more preferable that it is mmol / g or less, and 1.4×10 -2 It is more desirable that it be mmol / g or less.

[0187] The content of monomer (D) in the polymerization component is preferably 0.50 mass% or more, more preferably 0.70 mass% or more, and even more preferably 3.5 mass% or more. The content of monomer (D) in the polymerization component is preferably 20.0 mass% or less, more preferably 14.0 mass% or less, and even more preferably 7.0 mass% or less.

[0188] The amount of monomer (E) included per 1g of polymer 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) included per 1g of polymer 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.

[0189] The content of the chain transfer agent in the polymerization component is not particularly limited, but is preferably 0.10 mass% or more, more preferably 0.25 mass% or more, and even more preferably 0.35 mass% or more. The content of the chain transfer agent in the polymerization component is not particularly limited, but is preferably 10 mass% or less, more preferably 2.0 mass% or less, and even more preferably 0.70 mass% or less.

[0190] The amount of chain transfer agent contained per 1g of polymer component is 1.0×10 -2 It is desirable that it be mmol / g or higher, and 2.0×10 -2It is more desirable that it be mmol / g or higher, and 3.0×10 -2 It is more preferable that it be mmol / g or higher. The amount of chain transfer agent included per 1g of polymer component is 20×10 -2 It is preferable that it be mmol / g or less, and 10×10 -2 It is more preferable that it is mmol / g or less, and 7.0×10 -2 It is more desirable that it be mmol / g or less.

[0191] The content of the polymerization initiator in the polymerization component is preferably 0.020 mass% or more, more preferably 0.10 mass% or more, and even more preferably 0.15 mass% or more. The content of the polymerization initiator in the polymerization component is preferably 1.0 mass% or less, more preferably 0.50 mass% or less, and even more preferably 0.35 mass% or less. Here, components that do not form the structure of the copolymer (P), such as a reducing agent, and assist the function of the polymerization initiator are not included.

[0192] The amount of polymerization initiator contained per 1g of polymerization component is 0.10 × 10⁻⁶ -2 It is desirable that it be mmol / g or higher, and 0.20×10 -2 It is more desirable that it be mmol / g or higher, and 0.50×10 -2 It is more preferable that it be mmol / g or higher. The amount of polymerization initiator included per 1g of polymerization component is 5.0×10 -2 It is desirable that it be mmol / g or less, and 2.0×10 -2 It is more preferable that it is mmol / g or less, and 1.0×10 -2 It is more preferable that the value is mmol / g or less. Here, it does not include components that assist the function of a polymerization initiator, such as reducing agents, and does not form the structure of the copolymer (P).

[0193] As an example of a method for synthesizing a copolymer (P), the total content of the monomer represented by general formula (7) and the monomer represented by general formula (8) in the monomer (M) (total monomer) is 90 mass% or more, preferably 95 mass% or more, and more preferably 100 mass%.

[0194] In addition, as another example, a composition in which one or both of monomer (D) and monomer (E) are used may be given. 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 monomer) is 90 mass% or more, preferably 95 mass% or more, and more preferably 100 mass%.

[0195] [1-3. Method for Manufacturing Non-Aqueous Secondary Battery Electrode Coupling Agent]

[0196] A method for manufacturing a non-aqueous secondary battery electrode binder comprises a polymerization process in which a monomer (M) having an ethylenically unsaturated bond is radically polymerized in the presence of a polyfunctional thiol compound (C) having two or more mercapto groups in one molecule.

[0197] The method for manufacturing a non-aqueous secondary battery electrode binder may be the same as the method for manufacturing the copolymer (P), or additional processes may be added. The method for manufacturing the copolymer (P) is as described above. Additional processes may include, for example, a purification process and an additive mixing process.

[0198] <2. Binder composition for non-aqueous secondary battery electrodes>

[0199] The non-aqueous secondary battery electrode binder composition of the present embodiment (hereinafter, it may also be referred to as the "electrode binder composition") comprises an electrode binder and an aqueous medium. Additionally, the electrode binder composition may include other components, such as a pH adjuster and a surfactant, as needed.

[0200] The aqueous medium included in the electrode binder composition contains water. The aqueous medium included in the electrode binder composition may include a hydrophilic solvent. Examples of hydrophilic solvents include methanol, ethanol, and N-methylpyrrolidone. The water content in the aqueous medium included in the electrode binder composition is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more.

[0201] The composition of the aqueous medium included in the electrode binder composition may be the same as or different from the aqueous medium used for the synthesis of the copolymer (P). In addition, in the electrode binder composition of the present embodiment, the electrode binder may be dissolved or dispersed in the aqueous medium.

[0202] The content of the copolymer (P) in the electrode binder composition is preferably 30 mass% or less, and more preferably 20 mass% or less. This is to suppress the increase in viscosity of the electrode binder composition and to efficiently disperse the electrode active material when mixing with the electrode active material, etc. described later to produce an electrode slurry.

[0203] The content of copolymer (P) in the electrode binder composition is preferably 3.0 mass% or more, more preferably 5.0 mass% or more, and even more preferably 8.0 mass% or more. This is because electrode slurries and electrodes can be produced with less electrode binder composition.

[0204] 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 efficiently disperse the electrode active material, etc. when mixing with the electrode active material, etc. described later to produce 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 efficiently disperse the electrode active material, etc. when mixing with the electrode active material, etc. described later to produce an electrode slurry. Here, pH is a value measured by a pH meter at a liquid temperature of 23°C.

[0205] <3. Non-aqueous secondary battery electrode slurry>

[0206] In the non-aqueous secondary battery electrode slurry of the present embodiment (hereinafter also 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 the present embodiment may include a conductivity aid, a thickener, etc., as needed, but it is preferable not to include a thickener in order to simplify the electrode slurry manufacturing process. The method for preparing the electrode slurry is not particularly limited, but, for example, a method of mixing the necessary components using a mixing device such as a stirring type, a rotary type, or a shaking type may be used.

[0207] The non-volatile content concentration of the electrode slurry is preferably 30 mass% or more, and more preferably 40 mass% or more. This is to form a larger electrode active material layer with a smaller amount of electrode slurry. The non-volatile content concentration of the electrode slurry is preferably 70 mass% or less, and more preferably 60 mass% or less. The non-volatile content concentration can be adjusted by the amount of the aqueous medium.

[0208] The non-volatile content concentration, unless otherwise specified, is the ratio of the mass of the remaining component to the mass before drying, after weighing 1 g of the mixture in an aluminum dish with a diameter of 5 cm and drying it at 130°C for 1 hour while circulating air in a dryer at atmospheric pressure.

[0209] [3-1. Content of copolymer (P) in electrode slurry]

[0210] The content of the copolymer (P) in the electrode slurry is preferably 0.5 mass% or more, more preferably 1.0 mass% or more, and even more preferably 2.0 mass% or more, based on the total mass of the electrode active material (described later), the conductivity aid (described later), and the electrode binder. This is because the copolymer (P) can ensure adhesion between the electrode active materials and between the electrode active material and the current collector. The content of the copolymer (P) in the electrode slurry is preferably 10 mass% or less, more preferably 7.0 mass% or less, and even more preferably 4.0 mass% or less, based on the total mass of the electrode active material, the conductivity aid, and the electrode binder. This is because the charge / discharge capacity of the electrode active material layer formed by the electrode slurry can be increased, and the internal resistance when used as a battery can also be lowered.

[0211] [3-2. Electrode Active Material]

[0212] Non-aqueous secondary batteries are not particularly limited, but in the case of lithium-ion secondary batteries, examples of negative electrode active materials include conductive polymers, carbon materials, lithium titanium dioxide, silicon, silicon compounds, etc. Examples of conductive polymers include polyacetylene and polypyrrole. Examples of carbon materials include coke such as petroleum coke, pitch coke, and coal coke; carbides of organic compounds; and graphite such as artificial graphite and natural graphite. Examples of silicon compounds include SiO₂ x Examples include (0.1≤x≤2.0).

[0213] In addition, composite materials containing Si and graphite (Si / graphite), etc., may be used as electrode active materials. Among these active materials, it is preferable to use carbon materials, lithium titanium dioxide, silicon, and silicon compounds due to their high energy density per unit volume. Furthermore, carbon materials such as coke, carbides of organic compounds, and graphite, and SiO₂ x For silicon-containing materials such as (0.1≤x≤2.0), Si, and Si / graphite, the effect of improving bonding performance by the electrode binder of the present embodiment is significant. For example, as a specific example of artificial graphite, SCMG (registered trademark)-XRs (manufactured by Showa Denko Co., Ltd.) can be cited. In addition, as a negative electrode active material, two or more types of the materials exemplified herein may be combined.

[0214] Examples of positive electrode active materials for lithium-ion secondary batteries include lithium cobaltate (LiCoO2), nickel-containing lithium composite oxides, spinel-type lithium manganate (LiMn2O4), olivine-type lithium iron phosphate, and chalcogen compounds such as TiS2, MnO2, MoO3, and V2O5. The positive electrode active material may contain any one of these compounds alone or may contain multiple types. In addition, oxides of other alkali metals may also be used. Examples of nickel-containing lithium composite oxides 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 O2 or LiNi 3 / 5 Mn 1 / 5 Co 1 / 5 You can lift the back.

[0215] [3-3. Challenge Supplements]

[0216] The electrode slurry may include carbon black, vapor phase carbon fiber, etc. as a conductivity aid. Specific examples of vapor phase carbon fiber include VGCF (registered trademark)-H (Showa Denko Co., Ltd.).

[0217] [3-4. Water-based Media]

[0218] 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 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more. The composition of the aqueous medium of the electrode slurry may be the same as or different from the aqueous medium included in the electrode binder composition.

[0219] <4. Electrode>

[0220] The electrode of the present embodiment comprises a current collector and an electrode active material layer formed on the surface of the current collector. The electrode active material layer comprises an electrode active material and an electrode binder of the present embodiment. Examples of the shape of the electrode include a laminate or a wound body, but are not particularly limited. The current collector is preferably a metal sheet with a thickness of 0.001 to 0.5 mm. Examples of the metal of the current collector include iron, copper, aluminum, nickel, stainless steel, etc. When the non-aqueous secondary battery is a lithium-ion secondary battery, aluminum is preferred as the current collector for the positive electrode and copper as the current collector for the negative electrode, but are not particularly limited.

[0221] The electrode of the present embodiment can be manufactured, for example, by applying an electrode slurry onto a current collector and drying it, but is not limited to this method.

[0222] Examples of methods for applying an 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, immersion method, and squeeze method. Among these, the doctor blade method, knife method, or extrusion method is preferred, and applying using a doctor blade is more preferred. This is because it is suitable for various physical properties such as viscosity and drying properties of the electrode slurry, and allows for obtaining a coating film with a good surface condition.

[0223] The electrode slurry may be applied to only one side of the current collector or 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. Additionally, the electrode slurry may be applied continuously to the surface of the current collector or intermittently. The amount and coverage range of the electrode slurry can be appropriately determined according to the size of the battery, etc. The weight per unit area of ​​the electrode active material layer after drying is preferably 4 to 20 mg / cm², and more preferably 6 to 16 mg / cm².

[0224] An electrode sheet is obtained by drying the electrode slurry coated on 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 may 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.

[0225] The electrode sheet may be used as an electrode as is, but it may be cut to a size or shape suitable for use as an electrode. The method of cutting the electrode sheet is not particularly limited, but, for example, a slit, laser, wire cut, cutter, Thomson, etc. can be used.

[0226] If necessary, the electrode sheet may be pressed before or after cutting. By doing so, the electrode active material is firmly bonded to the electrode, and by making the electrode thinner, the non-aqueous battery can be made more compact. As for the pressing method, general methods can be used, and it is particularly preferable to use a die press method or a roll press method. The pressing pressure is not particularly limited, but it is preferable to set it to 0.5 to 5 t / cm², which is a range that does not affect the doping / dedoping of lithium ions, etc., into the electrode active material by the pressing.

[0227] <5. Battery>

[0228] As a preferred example of the battery according to the present embodiment, a lithium-ion secondary battery is described, but the configuration of the battery is not limited to the configuration described below. In the lithium-ion secondary battery according to the example described herein, components such as a positive electrode, a negative electrode, an electrolyte, and, if necessary, a separator are housed in an outer body. At least one of the positive electrode and the negative electrode includes an electrode binder according to the present embodiment.

[0229] <5-1. Electrolyte>

[0230] As the electrolyte, a non-aqueous liquid with ion conductivity is used. Examples of electrolytes include solutions in which an electrolyte is dissolved in an organic solvent and ionic liquids; however, the former is preferred because it results in a battery with low internal resistance at a lower manufacturing cost.

[0231] Alkali metal salts can be used as electrolytes and can be appropriately selected depending on the type of electrode active material, etc. Examples of electrolytes include LiClO4, LiBF6, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, and LiB 10 Cl 10Examples include LiAlCl4, LiCl, LiBr, LiB(C2H5)4, CF3SO3Li, CH3SO3Li, LiCF3SO3, LiC4F9SO3, Li(CF3SO2)2N, and lithium aliphatic carboxylate. In addition, other alkali metal salts may be used as electrolytes.

[0232] Organic solvents for dissolving electrolytes are 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 individually or in combination of two or more.

[0233] <5-2. Exterior Body>

[0234] As for the outer casing, metal or aluminum laminate materials can be appropriately used. The battery shape may be any shape, such as coin type, button type, sheet type, cylindrical type, prismatic type, or flat type.

[0235] Examples

[0236] The present invention is described in more detail below by presenting examples and comparative examples regarding a negative electrode binder, a negative electrode slurry, a negative electrode, and a lithium-ion secondary battery. Furthermore, the present invention is not limited by these examples.

[0237] <1. Negative Binder>

[0238] [1-1. Synthesis of Copolymers]

[0239] The composition of each monomer, polyfunctional thiol compound (C), and chain transfer agent used in Examples 1 to 20 and Comparative Examples 1 to 5 is 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 is referred to as the polymerization component. The details of each raw material compound shown in Tables 2 to 4 are as follows. When used as a monomer solution, the amount of monomer used in the table represents the amount of the monomer itself excluding the solvent.

[0240] In addition, there are parts of the polymerization initiator that are not introduced into the polymer, such as the nitrogen that is removed. However, since the amount of polymerization initiator used is small, in Tables 2 to 4, the content (mass%) of each component in the polymerization component and the number of moles of each component per 1g of the polymerization component can be expressed 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 1g of the copolymer.

[0241]

[0242]

[0243]

[0244] Monomer (A-1): N-vinylacetamide (NVA)

[0245] Monomer (B-1): Sodium acrylate (AaNa) (28.5 mass% aqueous solution)

[0246] Monomer (B-2): Lithium acrylate (AaLi) (28.5 mass% aqueous solution),

[0247] Aa: Acrylic acid

[0248] Polyfunctional thiol compound (C-1): Pentaerythritol tetrakis(3-mercaptobutyrate)

[0249] Polyfunctional thiol compound (C-2): trimethylolpropanetris(3-mercaptobutyrate)

[0250] Polyfunctional thiol compound (C-3): 1,4-bis(3-mercaptobutyryloxy)butane

[0251] Polyfunctional thiol compound (C-4): Pentaerythritol tetrakis(3-mercaptopropionate)

[0252] Monomer (D-1): Methoxypolyethylene glycol methacrylate (EVONIK INDUSTRIES; VISIOMER (registered trademark) MPEG2005 MA W) (R in general formula (10) 41 =CH3, R 42 =H, R 44 50.0 mass% aqueous solution of =CH3, j=45, k=0, j+k=45)

[0253] Monomer (E-1): Benzyl acrylate

[0254] MPA: β-mercaptopropionic acid

[0255] TMA: Tetramethylolmethanetetraacrylate

[0256] Polymerization initiator: 2,2'-Azobis(2-methylpropionamidine) dihydrochloride (Wako Junyaku Kogyo; V-50) and ammonium persulfate (Wako Junyaku Kogyo)

[0257] In a separable flask assembled with a cooling tube, thermometer, stirrer, and dropping funnel, a total of 100 parts by mass of polymerization components of compositions 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 were added 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.

[0258] [1-2. Preparation of Negative Binder Composition]

[0259] Water was added to the reaction solution in which the copolymer was obtained so that the non-volatile content concentration was 10.0 mass% (the amount of water added was adjusted considering the water contained in monomer (B-1)) to prepare negative coupling compositions Q1 to Q20 and CQ1 to CQ5. In the following description, when copolymers P1 to P20 are mentioned without distinction, they may be referred to as copolymer (P), and when copolymers CP1 to CP5 are mentioned without distinction, they may be referred to as copolymer (CP). When negative coupling compositions Q1 to Q20 are mentioned without distinction, they may be referred to as negative coupling composition (Q), and when negative coupling compositions CQ1 to CQ5 are mentioned without distinction, they may be referred to as negative coupling composition (CQ).

[0260] [1-3. Weight Average Molecular Weight of Copolymer (P)]

[0261] The weight average molecular weight of copolymer (P) and copolymer (CP) was measured using gel permeation chromatography (GPC) under the following conditions, and the measurement results are shown in Table 4.

[0262] GPC Device: GPC-101 (Manufactured by Showa Denko Co., Ltd.)

[0263] Solvent: 0.1M NaNO3 aqueous solution

[0264] Sample Column: Shodex Column Ohpak SB-806 HQ (8.0mm ID x 300mm) × 2

[0265] Reference Column: Shodex Column Ohpak SB-800 RL (8.0mm ID x 300mm) × 2

[0266] Column temperature: 40℃

[0267] Sample concentration: 0.1 mass%

[0268] Detector: RI-71S (Manufactured by Shimazu Seisakusho Co., Ltd.)

[0269] Pump: DU-H2000 (Manufactured by Shimazu Seisakusho, Kabushiki Kaisha)

[0270] Pressure: 1.3MPa

[0271] Flow rate: 1ml / min

[0272] 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 Co., Ltd.))

[0273] <2. Negative Electrode Slurry>

[0274] [2-1. Preparation of Negative Electrode Slurry]

[0275] 76.8 parts by mass of SCMG (registered trademark)-XRs (manufactured by Showa Denko Co., Ltd.) as graphite, 19.2 parts by mass of silicon monoxide (SiO) (manufactured by Sigma-Aldrich), 1.0 part by mass of VGCF (registered trademark)-H (manufactured by Showa Denko Co., Ltd.), 30 parts by mass of a 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 revolutions / min using a stirring mixing device (rotating and revolving stirring mixer). To the obtained mixture, an additional 53 parts by mass of water were added, and the mixture was further mixed for 4 minutes at 2000 revolutions / min in the mixing device to produce a negative electrode slurry.

[0276] [2-2. Evaluation of the Appearance of the Negative Electrode Slurry]

[0277] The appearance of the prepared negative electrode slurry was visually inspected, and the size of the aggregates was measured using a micrometer. × was used to indicate the presence of aggregates with a maximum length of 1 mm or more in 10 g of negative electrode slurry, and ○ was used to indicate the absence of such aggregates. The evaluation results are shown in Table 5.

[0278]

[0279] <3. Pole>

[0280] [3-1. Flexibility of the Negative Electrode Active Layer (Winding Test)]

[0281] The negative electrode slurry prepared as described above was applied to both sides of a copper foil (current collector) with a thickness of 10 μm using a doctor blade so that the weight per unit area after drying was 8 mg / cm². The copper foil coated with the negative electrode slurry was dried at 60°C for 10 minutes, and then dried again at 100°C for 5 minutes to produce a negative electrode sheet with a negative electrode active material layer formed thereon. This negative electrode sheet was pressed using a die press at a press pressure of 1 t / cm².

[0282] Here, a pressed negative electrode sheet was cut into pieces 50 mm wide and 60 mm long to form a test specimen. This test specimen was dried at 80°C for 12 hours. After drying, one side of the test specimen in the width direction was fixed to a stainless steel rod with a diameter of 3 mm using a single-sided adhesive tape 50 μm thick (the width direction of the test specimen and the length direction of the stainless steel rod were parallel). The other side of the test specimen in the width direction was fixed to a glass plate. After winding the test specimen onto this stainless steel rod, the appearance of the test specimen was observed by visual inspection, and the number of cracks in the test specimen was counted.

[0283] [3-2. Peel strength of negative electrode active material layer against current collector]

[0284] A pressed negative electrode sheet was produced in the same manner as the above evaluation of flexibility, except that a negative electrode slurry was applied to both sides of the copper foil so that the weight per unit area after drying was 8 mg / cm².

[0285] Using a negative electrode sheet pressed here, the entire process was carried out in an atmosphere of 23°C and 50 mass% relative humidity. A Tensilon (registered trademark, manufactured by A&D Co., Ltd.) test machine was used. The negative electrode sheet was cut to a width of 25 mm and a length of 70 mm to form a test specimen. The negative electrode active material layer on the test specimen and a SUS plate with a width of 50 mm and a length of 200 mm were bonded using double-sided tape (NITTOTAPE (registered trademark) No. 5, manufactured by Nitto Denko Co., Ltd.) so that the center of the test specimen and the center of the SUS plate aligned. Additionally, the double-sided tape was bonded to cover the entire area of ​​the test specimen. The bonding was performed by passing a 2 kg roller back and forth once over the entire test specimen.

[0286] After leaving the test specimen and the SUS plate bonded together for 10 minutes, the copper foil was peeled from the negative electrode active material by 20 mm in the longitudinal direction from one end of the test specimen, folded 180°, and the peeled portion of the copper foil was gripped by the upper chuck of the test machine. Additionally, one end of the SUS plate from which the copper foil was peeled was gripped by the lower chuck. In this state, the copper foil was peeled from the test specimen at a speed of 100 ± 10 mm / min to obtain a graph of peel length (mm) versus peel force (mN). From the obtained graph, the average value of the peel force (mN) for peel lengths of 10 to 45 mm was calculated, and the value obtained by dividing the average peel force by the width of the test specimen (25 mm) was defined as the peel strength (mN / mm) of the negative electrode active material layer. Furthermore, in any example and comparative example, no peeling occurred between the double-sided tape and the SUS plate or interfacial peeling between the double-sided tape and the negative electrode active material layer during the test.

[0287] <4. Lithium-ion Secondary Battery>

[0288] [4-1. Making a Battery]

[0289] [Buguk]

[0290] The above-mentioned pressed negative electrode sheet was cut into 22 mm × 22 mm pieces, and a conductive tab was installed to produce a negative electrode.

[0291] [Straight Drama]

[0292] LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 90 parts by mass of O2, 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 were mixed to prepare a positive electrode slurry (LiNi in the solid content 1 / 3 Mn 1 / 3 Co 1 / 3 The ratio of O2 is 0.90).

[0293] The prepared positive electrode slurry is applied to one side of a 20㎛ thick aluminum foil (current collector) by the doctor blade method, and after drying, the weight per unit area is 22.5 mg / cm² (22.5 × 10⁻⁶). -3 A positive electrode slurry was applied using a doctor blade to achieve a thickness of g / cm². The aluminum foil coated with the positive electrode slurry was dried at 120°C for 5 minutes, and then pressed by a roll press to produce a positive electrode sheet with a positive electrode active material layer having a thickness of 100㎛. The obtained positive electrode sheet was cut into 20mm × 20mm (2.0cm × 2.0cm) and a conductive tab was installed to produce a positive electrode.

[0294] The theoretical capacity of the fabricated positive electrode is the weight per unit area (22.5 × 10⁻⁶) of the positive electrode slurry after drying. -3 g / cm²) × Coating area of ​​positive electrode slurry (2.0 cm × 2.0 cm) × LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 Capacity of O2 as a positive electrode active material (160mAh / g) × LiNi in the solid content 1 / 3 Mn 1 / 3 Co 1 / 3 It is calculated with an O2 ratio (0.90), and the resulting value is 13mAh.

[0295] [Electrolyte]

[0296] An electrolyte 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 in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and fluoroethylene carbonate (FEC) were mixed in a volume ratio of 30:60:10.

[0297] [Assembly of the Battery]

[0298] The positive and negative electrodes were arranged so that their respective active material layers faced each other through a separator containing a polyolefin porous film, and housed in an aluminum laminate casing (battery pack). An electrolyte was injected into this casing and packed with a vacuum heat sealer to obtain a laminate-type battery.

[0299] [4-2. Evaluation of Battery Cycle Characteristics (Discharge Capacity Retention Rate)]

[0300] The cycle characteristics of each battery fabricated in each example and comparative example were evaluated. The evaluation method is as follows, and the evaluation results are shown in Table 5.

[0301] The measurement of the discharge capacity retention rate of the battery (charge-discharge cycle test of the battery) was performed under conditions of 25°C in the following order. First, the battery was charged with a current of 1C until the voltage reached 4.2V (CC charging), and then charged with a voltage of 4.2V until the current reached 0.05C (CV charging). After leaving it for 30 minutes, it was discharged with a current of 1C until the voltage reached 2.75V (CC discharging). A series of operations including CC charging, CV charging, and CC discharging constitutes one cycle. The sum of the time integrals of the current during the CC charging and CV charging of the nth cycle is defined as the charge capacity of the nth cycle (mAh), and the time integral of the current during the CC discharging of the nth cycle is defined as the discharge capacity of the nth cycle (mAh). The discharge capacity retention rate of the 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 at the 100th cycle was evaluated.

[0302] <5. Evaluation Results>

[0303] As can be seen from Table 5, the negative electrode slurries produced in Examples 1 to 20 have low aggregation. It can be seen that the negative electrodes produced in Examples 1 to 20 have low cracking during the winding test and high flexibility of the electrode active material layer. The negative electrodes produced in Examples 1 to 20 also have high peel strength of the negative electrode active material layer against the current collector. It can be seen that the lithium-ion secondary batteries produced in Examples 1 to 20 have a high discharge capacity retention rate during battery use, that is, excellent cycle characteristics.

[0304] In Comparative Example 1, a negative electrode slurry was prepared using CP1, a copolymer that does not have amide bonds. The negative electrode slurry prepared in Comparative Example 1 contained aggregates. The negative electrode slurry prepared in Comparative Example 1 could not be coated evenly on the current collector, so it was not possible to produce an evaluable negative electrode and battery.

[0305] In Comparative Example 2, a negative electrode slurry, a negative electrode, and a lithium-ion secondary battery were fabricated using a copolymer CP2 containing an excess of amide bonds. The electrode slurry fabricated in Comparative Example 2 contained aggregates. In the negative electrode fabricated in Comparative Example 2, the negative electrode active material layer slipped off during the winding test. Additionally, in Comparative Example 2, the peel strength of the negative electrode active material layer against the current collector was low. The lithium-ion secondary battery fabricated in Comparative Example 2 had a low discharge capacity retention rate.

[0306] In Comparative Example 3, a negative electrode slurry, a negative electrode, and a lithium-ion secondary battery were fabricated using a copolymer CP3 that does not have a substituent (c). In the negative electrode fabricated in Comparative Example 3, it was found that the flexibility of the negative electrode was low, as multiple cracks occurred in the negative electrode active material layer after a winding test. In addition, in Comparative Example 3, the peel strength of the negative electrode active material layer against the current collector was low. The lithium-ion secondary battery fabricated in Comparative Example 3 had a low discharge capacity retention rate.

[0307] In Comparative Example 4, an attempt was made to synthesize a copolymer CP4 containing an excess of substituent (c) using a large amount of a polyfunctional thiol compound (C), but the product gelled and could not produce an evaluable negative electrode slurry.

[0308] In Comparative Example 5, a negative electrode slurry, a negative electrode, and a lithium-ion secondary battery were fabricated using a copolymer CP5 containing structural units derived from tetrafunctional acrylate (tetramethylomethanetetraacrylate) without substituent (c). In the negative electrode fabricated in Comparative Example 5, numerous cracks occurred in the negative electrode active material layer after a winding test, indicating that the flexibility of the negative electrode was low. Additionally, in Comparative Example 5, the peel strength of the negative electrode active material layer against the current collector was low. The lithium-ion secondary battery fabricated in Comparative Example 5 had a low discharge capacity retention rate.

[0309] Therefore, it was found that by using the copolymer for the binder according to the present embodiment as a binder for the negative electrode of a non-aqueous battery, sufficient bonding is secured between the negative electrode active materials and between the negative electrode active materials and the current collector in the negative electrode of the non-aqueous battery, while providing flexibility, resulting in good charge-discharge cycle characteristics as a battery.

[0310] In addition, these binders can also be used as binders for the positive electrode of non-aqueous batteries, and can be used to manufacture batteries with good charge / discharge cycle characteristics while ensuring sufficient bonding between positive electrode active materials and between the positive electrode active materials and the current collector.

Claims

Claim 1 A non-aqueous secondary battery electrode binder comprising a copolymer (P), wherein the copolymer (P) comprises a main chain having only bonds between carbon atoms, a substituent having an amide bond, a substituent having a salt of a carboxyl group, and a substituent (c) represented by the following general formula (1), wherein the substituent having an amide bond, the substituent having a salt of a carboxyl group, and the substituent (c) are each bonded to the main chain, wherein the amount of amide bonds contained per 1g of the copolymer (P) is 0.050 mmol / g or more and 5.0 mmol / g or less, the amount of salt of a carboxyl group contained per 1g of the copolymer (P) is 5.0 mmol / g or more and 12.0 mmol / g or less, and the amount of the substituent (c) contained per 1g of the copolymer (P) is 0.15 × 10⁻⁶ -2 mmol / g or more 8.0×10 -2 A non-aqueous secondary battery electrode binder characterized by being mmol / g or less. (In general formula (1), R 31 is a hydrocarbon group, and m and n are, respectively, R 31 Represents the number of corresponding substituents directly bound to, where m is an integer greater than or equal to 0, n is an integer greater than or equal to 1, m+n≥2, and R 32 is a hydrogen atom or a methyl group.) Claim 2 In claim 1, in the above general formula (1), R 31 A non-aqueous secondary battery electrode binder comprising carbon atoms and hydrogen atoms. Claim 3 In claim 1 or 2, in the above general formula (1), R 31 A non-aqueous secondary battery electrode binder having multiple carbon atoms, wherein the bonds between carbon atoms are all single bonds. Claim 4 A non-aqueous secondary battery electrode binder according to claim 1 or 2, wherein if the food of the substituent (c) is denoted as Mc, then Mc / (m+n)≤400. Claim 5 A non-aqueous secondary battery electrode binder according to claim 1 or 2, wherein the substituent (c) is a structure derived from a polyfunctional thiol compound (C), and the polyfunctional thiol compound (C) has two or more mercapto groups in one molecule. Claim 6 A non-aqueous secondary battery electrode binder according to claim 1 or 2, wherein the copolymer (P) further comprises 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 , R 44 Each is independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. 43 is an alkyl group having 1 to 6 carbon atoms, and R 42 The number of carbon atoms is greater than that. j and k represent the number of structures within the corresponding parentheses that are connected in series, respectively. j is an integer greater than or equal to 1, k is an integer greater than or equal to 0, and j+k≥20.) Claim 7 A non-aqueous secondary battery electrode binder according to claim 1 or 2, wherein the copolymer (P) also 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 is a substituent having an aromatic ring.) Claim 8 A non-aqueous secondary battery electrode binder according to claim 1 or 2, wherein in the copolymer (P), at least a portion of the amide bond is included as a structural unit (a) represented by the following general formula (4). (In general formula (4), R 11 , R 12 Each represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms independently. Claim 9 A non-aqueous secondary battery electrode binder according to claim 1 or 2, wherein in the copolymer (P), at least a portion of the salt of the carboxyl group is included as a structural unit (b) represented by the following general formula (5). (In general formula (5), R 2 represents a hydrogen atom or a methyl group, and X is a cation.) Claim 10 A non-aqueous secondary battery electrode binder according to 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. Claim 11 A non-aqueous secondary battery electrode binder composition comprising a non-aqueous secondary battery electrode binder described in claim 1 or 2 and an aqueous medium. Claim 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 comprises a binder for a non-aqueous secondary battery electrode and an electrode active material as described in claim 1 or 2. Claim 13 A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode is a non-aqueous secondary battery electrode as described in claim 12. Claim 14 A method for preparing a non-aqueous secondary battery electrode binder comprising a polymerization process in which a monomer (M) having an ethylenically unsaturated bond is radically polymerized in the presence of a polyfunctional thiol compound (C) having two or more mercapto groups in one molecule, wherein the monomer (M) comprises a monomer (A) having an amide bond and a monomer (B) having a salt of a carboxyl group, wherein if the monomer (M), the polyfunctional thiol compound (C), a polymerization initiator, and a chain transfer agent are used, the chain transfer agent is also included and referred to as a polymerization component, wherein the amount of the monomer (A) included per 1g of the polymerization component is 0.050 mmol / g or more and 5.0 mmol / g or less, the amount of the monomer (B) included per 1g of the polymerization component is 5.0 mmol / g or more and 12.0 mmol / g or less, and the polyfunctional The amount of thiol compound (C) is 0.15 × 10⁻⁶ -2 mmol / g or more 8.0×10 -2 A method for manufacturing a non-aqueous secondary battery electrode binder characterized by being mmol / g or less.

Images