Electrode binder polymer for non-aqueous secondary battery, electrode binder composition for non-aqueous secondary battery, electrode slurry for non-aqueous secondary battery, electrode for non-aqueous secondary battery, non-aqueous secondary battery, method for producing electrode binder polymer for non-aqueous secondary battery, method for producing electrode binder composition for non-aqueous secondary battery, method for producing electrode slurry for non-aqueous secondary battery, and method for producing electrode for non-aqueous secondary battery

Abstract

The present invention comprises 10-50 mol% of a first structural unit (-CH2CR1(CONR2R3)-), 25-80 mol% of a second structural unit (-CH2CR4(COOX)-), and 1.0-45 mol% of a third structural unit (-CH2CR5(C≡N)-) and has a weight-average molecular weight of not less than 1,500,000.

Description

Electrode binder polymer for non-aqueous secondary batteries, electrode binder composition for non-aqueous secondary batteries, electrode slurry for non-aqueous secondary batteries, electrode for non-aqueous secondary batteries, non-aqueous secondary batteries, method for producing electrode binder polymer for non-aqueous secondary batteries, method for producing electrode binder composition for non-aqueous secondary batteries, method for producing electrode slurry for non-aqueous secondary batteries, and method for producing electrodes for non-aqueous secondary batteries

[0001] The present disclosure relates to an electrode binder polymer for non-aqueous secondary batteries, an electrode binder composition for non-aqueous secondary batteries, an electrode slurry for non-aqueous secondary batteries, an electrode for non-aqueous secondary batteries, a non-aqueous secondary battery, a method for producing an electrode binder polymer for non-aqueous secondary batteries, a method for producing an electrode binder composition for non-aqueous secondary batteries, a method for producing an electrode slurry for non-aqueous secondary batteries, and a method for producing an electrode for non-aqueous secondary batteries.

[0002] Secondary batteries using nonaqueous electrolytes (nonaqueous secondary batteries) are superior to secondary batteries using aqueous electrolytes in terms of higher voltage, smaller size, lighter weight, etc. Therefore, nonaqueous secondary batteries are widely used as power sources for notebook computers, mobile phones, power tools, electronic devices, communication devices, etc. Recently, nonaqueous batteries have also been used in electric vehicles and hybrid vehicles from the perspective of application to environmentally friendly vehicles. In this context, there has been a strong demand for nonaqueous secondary batteries with higher output, higher capacity, longer life, etc.

[0003] A typical example of a non-aqueous secondary battery is a lithium-ion secondary battery. A non-aqueous secondary battery includes a positive electrode using a metal oxide or the like as an active material, a negative electrode using a carbon material such as graphite as an active material, and a non-aqueous electrolyte solvent mainly composed of carbonates or a flame-retardant ionic liquid. A non-aqueous secondary battery is a secondary battery in which charging and discharging are performed by the movement of ions between the positive and negative electrodes. A 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 the resulting product, and then cutting the resulting product to an appropriate size. A 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 the resulting product, and then cutting the resulting product to an appropriate size. The binder serves to bind active materials together and to the current collector, thereby preventing peeling of the active materials from the current collectors in the positive and negative electrodes.

[0004] A well-known binder is a polyvinylidene fluoride (PVDF) binder using the organic solvent N-methylpyrrolidone (NMP) as the solvent. However, when using this binder, there are problems with the binding between active materials and between the active material and the current collector. Therefore, when actually using this binder, a large amount must be used, which has the disadvantage of reducing the capacity of the nonaqueous secondary battery. Furthermore, in this case, NMP, an expensive organic solvent, is used, making it difficult to reduce manufacturing costs.

[0005] To address such problems, for example, Patent Document 1 discloses the use of a copolymer of a monomer mixture containing a monomer having an amide bond, such as N-vinyl acrylamide, and a (meth)acrylate monomer as a copolymer for a binder for a non-aqueous battery electrode.

[0006] Furthermore, Patent Document 2 describes a copolymer of acrylamide, acrylonitrile, and acrylic acid or a salt thereof as a polymer component contained in a secondary battery negative electrode.

[0007] International Publication No. 2017 / 150200 International Publication No. 2021 / 060737

[0008] In non-aqueous secondary batteries, the appearance quality of the electrode is an important factor for fully demonstrating performance, and it is necessary to suppress the occurrence of streaks, aggregates, etc. Furthermore, in non-aqueous secondary batteries, the electrode is immersed in an electrolyte, and even in such an environment, it is necessary to maintain high peel strength of the electrode active material layer. Furthermore, in non-aqueous secondary batteries, it is necessary to use non-aqueous secondary battery electrodes that have excellent appearance and excellent peel strength of the electrode active material layer, and to improve the discharge capacity retention rate during charge-discharge cycles.

[0009] Therefore, the present disclosure aims to provide an electrode binder polymer for nonaqueous secondary batteries that can form electrodes for nonaqueous secondary batteries that have excellent appearance and excellent peel strength of the electrode active material layer, and that can produce nonaqueous secondary batteries with improved discharge capacity retention during charge-discharge cycling. Another object of the present disclosure is to provide an electrode for nonaqueous secondary batteries that has excellent appearance and excellent peel strength of the electrode active material layer. A further object of the present disclosure is to provide a nonaqueous secondary battery that includes an electrode for nonaqueous secondary batteries that has excellent appearance and excellent peel strength of the electrode active material layer, and that has improved discharge capacity retention during charge-discharge cycling. Another object of the present disclosure is to provide an electrode binder composition for nonaqueous secondary batteries and an electrode slurry for nonaqueous secondary batteries that include the electrode binder polymer for nonaqueous secondary batteries. Another object of the present invention is to provide methods for producing the electrode binder polymer for non-aqueous secondary batteries, the electrode binder composition for non-aqueous secondary batteries, the electrode slurry for non-aqueous secondary batteries, and the electrode for non-aqueous secondary batteries.

[0010] The present disclosure includes the following aspects. <1> An electrode binder polymer for a non-aqueous secondary battery, which contains 10 mol % to 50 mol % of a first structural unit represented by the following formula (1), 25 mol % to 80 mol % of a second structural unit represented by the following formula (2), and 1.0 mol % to 45 mol % of a third structural unit represented by the following formula (3), and has a weight average molecular weight of 1,500,000 or more. Formula (1): -CH ２ CR １ (CONR ２ R ３ )- [In formula (1), R１ , R ２ and R ３ are each independently a hydrogen atom or an alkyl group.] Formula (2): -CH ２ CR ４ (COOX)- [In formula (2), R ４ is a hydrogen atom or an alkyl group. COOX is at least one selected from the group consisting of a carboxy group and a salt thereof.] Formula (3): —CH ２ CR ５ (C≡N) - [In formula (3), R ５ is a hydrogen atom, an alkyl group, or an alkoxy group.] <2> The solubility in water at 25°C is 5.0 g / 100 gH ２ <3> The electrode binder polymer for a non-aqueous secondary battery according to <1> or <2>, wherein the total content of the first structural unit, the second structural unit, and the third structural unit is 70 mol % or more. ２ and R ３ <5> The electrode binder polymer for a non-aqueous secondary battery according to any one of <1> to <4>, wherein is a hydrogen atom or an alkyl group having 3 or less carbon atoms. <6> The electrode binder polymer for a non-aqueous secondary battery according to any one of <1> to <5>, which has a glass transition point of 100°C or higher. <7> The electrode binder polymer for a non-aqueous secondary battery according to any one of <1> to <5>, further comprising a fourth structural unit represented by the following formula (4): Formula (4): -CH ２ CR ６ (NR ７ COR ８ ) - [In formula (4), R ６ is a hydrogen atom or an alkyl group. ７ is a hydrogen atom or a hydrocarbon group. ８is a hydrogen atom or a hydrocarbon group.] <7> The electrode binder polymer for non-aqueous secondary batteries according to <6>, containing the fourth structural unit in an amount of 0.30 mol % to 30 mol %. <8> An electrode binder composition for non-aqueous secondary batteries, comprising the electrode binder polymer for non-aqueous secondary batteries according to any one of <1> to <7> and an aqueous medium. <9> The electrode binder composition for non-aqueous secondary batteries according to <8>, in which the electrode binder polymer for non-aqueous secondary batteries is completely dissolved in the aqueous medium at 25°C. <10> An electrode slurry for non-aqueous secondary batteries, comprising the electrode binder polymer for non-aqueous secondary batteries according to any one of <1> to <7>, an electrode active material, and an aqueous medium. <11> An electrode for a non-aqueous secondary battery, comprising: a current collector; and an electrode active material layer provided on at least a partial region of the surface of the current collector, the electrode active material layer comprising an electrode active material and the electrode binder polymer for a non-aqueous secondary battery according to any one of <1> to <7>. <12> A non-aqueous secondary battery comprising the electrode for a non-aqueous secondary battery according to <11>. <13> A method for producing the electrode binder polymer for a non-aqueous secondary battery according to any one of <1> to <7>, comprising radical polymerization in an aqueous medium using (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-ethyl(meth)acrylamide, or N-propyl(meth)acrylamide as the compound from which the first structural unit is derived, at least one selected from the group consisting of (meth)acrylic acid and salts thereof as the compound from which the second structural unit is derived, and (meth)acrylonitrile as the compound from which the third structural unit is derived. <14> A method for producing an electrode binder composition for a non-aqueous secondary battery, comprising mixing the electrode binder polymer for a non-aqueous secondary battery according to any one of <1> to <7> and an aqueous medium. <15> A method for producing an electrode slurry for a non-aqueous secondary battery, comprising mixing the electrode binder polymer for a non-aqueous secondary battery according to any one of <1> to <7>, an electrode active material, and an aqueous medium. <16> A method for producing an electrode for a non-aqueous secondary battery, comprising applying the electrode slurry for a non-aqueous secondary battery according to <10> to at least a part of the surface of a current collector, followed by drying.

[0011] According to the present disclosure, it is possible to provide an electrode binder polymer for non-aqueous secondary batteries that can form electrodes for non-aqueous secondary batteries that have excellent appearance and excellent peel strength of the electrode active material layer and that can produce non-aqueous secondary batteries with improved discharge capacity retention during charge-discharge cycles, an electrode binder composition for non-aqueous secondary batteries that includes the electrode binder polymer for non-aqueous secondary batteries of the present disclosure, an electrode slurry for non-aqueous secondary batteries, an electrode for non-aqueous secondary batteries, and a non-aqueous secondary battery. It is also possible to provide methods for producing the electrode binder polymer for non-aqueous secondary batteries, the electrode binder composition for non-aqueous secondary batteries, the electrode slurry for non-aqueous secondary batteries, and the electrode for non-aqueous secondary batteries.

[0012] The following describes the embodiments in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the components (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit the present disclosure.

[0013] In the present disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in the present disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in the present disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In the present disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component are present in a composition, etc., the content or amount of each component means the total content or amount of the multiple substances present in the composition, etc., unless otherwise specified. In the present disclosure, the term "layer" includes cases where, when the region in which the layer exists is observed, the layer is formed over the entire region, as well as cases where the layer is formed only in a portion of the region.

[0014] In this disclosure, "(meth)acrylic acid" refers to one or both of methacrylic acid and acrylic acid. "(meth)acrylamide" refers to one or both of methacrylamide and acrylamide. "(meth)acrylonitrile" refers to one or both of methacrylonitrile and acrylonitrile. "(meth)acryloyloxy group" refers to one or both of methacryloyloxy group and acryloyloxy group.

[0015] In the present disclosure, the "weight average molecular weight" is a pullulan-equivalent value calculated using gel permeation chromatography (GPC).

[0016] In this disclosure, unless otherwise specified, the term "ethylenically unsaturated bond" refers to an ethylenically unsaturated bond that is radically polymerizable.

[0017] Taking the structural unit A derived from compound X having an ethylenically unsaturated bond B as an example, the chemical structure of the structural unit A contained in the polymer other than the portion corresponding to the ethylenically unsaturated bond B of compound X is the same as the chemical structure of compound X before polymerization other than the ethylenically unsaturated bond B. For example, in a polymer having a structural unit derived from acrylonitrile, the structural unit is "-CH ２ The chemical structure is CH(C≡N)-.

[0018] The compound X from which the structural unit A in the polymer is derived refers to a compound having a structure in which the bond between two carbon atoms bonded to another structural unit is replaced with an ethylenically unsaturated bond. For example, the structural unit "-CH ２ The compound from which "CH(C≡N)-" is derived is acrylonitrile.

[0019] In the present disclosure, when a structural unit having an ionic functional group is subjected to ion exchange after polymerization, the structural unit is referred to based on the structure of the polymer after ion exchange. That is, for example, when a structural unit derived from sodium acrylate is subjected to ion exchange after polymerization, the structural unit in the polymer is referred to as "-CH ２ In this case, this structural unit is referred to as a "structural unit derived from acrylic acid."

[0020] In the present disclosure, the term "salt of a functional group" refers to a form in which a part of the functional group is dissociated and an ion is bonded to a counter ion other than a hydrogen ion or a hydroxide ion. For example, the term "salt of a carboxy group" refers to a salt of a COO － It means a form in which an ion is bonded to a cation other than a hydrogen ion. For example, a sodium salt of a carboxy group means a structure represented by COONa.

[0021] In the present disclosure, "non-volatile content" refers to the components remaining after weighing 1 g of a composition into an aluminum dish with a diameter of 5 cm and drying it at 110°C for 5 hours in a dryer under circulating air at 1 atmosphere (1013 hPa). The composition may be in the form of a solution, dispersion, slurry, or the like, but is not limited to these. Furthermore, in the present disclosure, "non-volatile content concentration" refers to the mass ratio (mass%) of the non-volatile content after drying under the above conditions relative to the mass (1 g) of the composition before drying.

[0022] <1. Electrode Binder Polymer for Non-Aqueous Secondary Battery> The electrode binder polymer for non-aqueous secondary battery according to the present disclosure (hereinafter, sometimes simply referred to as "binder polymer") contains 10 mol % to 50 mol % of a first structural unit represented by the following formula (1), 25 mol % to 80 mol % of a second structural unit represented by the following formula (2), and 1.0 mol % to 45 mol % of a third structural unit represented by the following formula (3), and has a weight average molecular weight of 1.5 million or more. Formula (1): -CH ２ CR １ (CONR ２ R ３ )- [In formula (1), R １ , R ２ and R ３ are each independently a hydrogen atom or an alkyl group.] Formula (2): -CH ２ CR ４ (COOX)- [In formula (2), R ４ is a hydrogen atom or an alkyl group. COOX is at least one selected from the group consisting of a carboxyl group and its salts. That is, X is at least one selected from the group consisting of H and structures corresponding to cations. For example, when COOX is a sodium salt, it is COONa, and when it is an ammonium salt, it is COONH.４ Formula (3): -CH ２ CR ５ (C≡N) - [In formula (3), R ５ is a hydrogen atom, an alkyl group, or an alkoxy group.

[0023] By using the binder polymer having the above-described configuration, it is possible to prepare a non-aqueous secondary battery electrode having an excellent appearance and excellent peel strength of the electrode active material layer, and by using the binder polymer having the above-described configuration, it is possible to prepare a non-aqueous secondary battery having an excellent discharge capacity retention rate and including a non-aqueous secondary battery electrode having an excellent appearance and excellent peel strength of the electrode active material layer.

[0024] [1-1. First structural unit] The first structural unit is represented by the following formula (1): Formula (1): —CH ２ CR １ (CONR ２ R ３ )-

[0025] In the above formula (1), R １ , R ２ and R ３ are each independently a hydrogen atom or an alkyl group. １ , R ２ and R ３ are each independently preferably a hydrogen atom or an alkyl group having 3 or less carbon atoms, more preferably a hydrogen atom or a methyl group. １ and CONR ２ R ３ The steric positional relationship of R is not limited. In other words, the optical isomers in the first structural unit are not distinguished, and any optical isomer may be used. １ , R ２ and R ３ The structures of may be all the same, any two may be the same and the remaining one may be different, or all may be different. ２ and R ３ is preferably a hydrogen atom or an alkyl group having 3 or less carbon atoms, and more preferably a hydrogen atom or a methyl group. １ is a hydrogen atom or a methyl group, and R ２ and R ３is a hydrogen atom, that is, the first structural unit is a structural unit derived from (meth)acrylamide. The content of the structural unit derived from (meth)acrylamide in the first structural unit is preferably 80 mol % or more, particularly preferably 90 mol % or more, and may be 100 mol %.

[0026] Examples of compounds from which the first structural unit is derived include (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-ethyl(meth)acrylamide, N-propyl(meth)acrylamide, N-hexyl(meth)acrylamide, etc. The compound from which the first structural unit is derived is preferably (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-ethyl(meth)acrylamide, or N-propyl(meth)acrylamide, and more preferably (meth)acrylamide.

[0027] The binder polymer of the present disclosure may contain one type of first structural unit alone, or may contain a combination of multiple types of first structural units.

[0028] [1-2. Second structural unit] The second structural unit is represented by the following formula (2): Formula (2): —CH ２ CR ４ (COOX)-

[0029] In the above formula (2), R ４ R is a hydrogen atom or an alkyl group, and is particularly preferably a hydrogen atom or an alkyl group having 3 or less carbon atoms, and more preferably a hydrogen atom or a methyl group. ４ The steric positional relationship between COOX and COOX is not limited. That is, the optical isomers in the second structural unit are not distinguished and any optical isomer may be used.

[0030] In the above formula (2), COOX is at least one selected from the group consisting of a carboxy group (X = H) and a salt thereof. That is, COOX in the second structural unit is at least one selected from the group consisting of a carboxy group and a salt of a carboxy group with a monovalent cation. With respect to COOX in the second structural unit, examples of the salt of a carboxy group with a monovalent cation include a lithium salt of a carboxy group, a sodium salt of a carboxy group, a potassium salt of a carboxy group, and an ammonium salt of a carboxy group.

[0031] In particular, the binder polymer of the present disclosure preferably contains a second structural unit in which COOX in the above formula (2) is a carboxy group, a second structural unit in which COOX in the above formula (2) is a lithium salt of a carboxy group, or a second structural unit in which COOX in the above formula (2) is a sodium salt of a carboxy group. Furthermore, the binder polymer of the present disclosure more preferably contains a second structural unit in which COOX in the above formula (2) is a sodium salt of a carboxy group.

[0032] The binder polymer of the present disclosure may contain one type of second structural unit alone, or may contain a combination of multiple types of second structural units. The binder polymer of the present disclosure may contain a second structural unit in which COOX in the above formula (2) is a carboxy group alone, or a second structural unit in which COOX in the above formula (2) is a salt of a carboxy group alone, or may contain a second structural unit in which COOX in the above formula (2) is a carboxy group and a second structural unit in which COOX in the above formula (2) is a salt of a carboxy group. Furthermore, when the binder polymer of the present disclosure contains a second structural unit in which COOX in the above formula (2) is a salt of a carboxy group, it may contain two or more types of second structural units in which the types of cations constituting the salt of the carboxy group are different.

[0033] In particular, among the second structural units contained in the binder polymer of the present disclosure, the second structural unit in which COOX in the above formula (2) is a sodium salt of a carboxy group (i.e., COONa) is preferably 20 mol% or more, more preferably 40 mol% or more, even more preferably 60 mol% or more, and particularly preferably 80 mol% or more. By setting the second structural unit in which COOX in the above formula (2) is a sodium salt of a carboxy group (i.e., COONa) within this range, the peel strength of the electrode active material layer in an electrode containing the binder polymer is further improved both before and after immersion in an electrolyte solution. Note that the second structural unit contained in the binder polymer of the present disclosure may be configured (i.e., 100 mol%) to consist of the second structural unit in which COOX in the above formula (2) is a sodium salt of a carboxy group.

[0034] The compound from which the second structural unit is derived may be at least one selected from the group consisting of (meth)acrylic acid and its salts. The (meth)acrylic acid salt, which is the compound from which the second structural unit is derived, is preferably a salt of (meth)acrylic acid with a monovalent cation, such as lithium (meth)acrylate, sodium (meth)acrylate, potassium (meth)acrylate, or ammonium (meth)acrylate. In the binder polymer of the present disclosure, it is preferable to use these salts of (meth)acrylic acid with a monovalent cation as the monomer, and it is preferable to use at least one selected from the group consisting of lithium (meth)acrylate, sodium (meth)acrylate, potassium (meth)acrylate, and ammonium (meth)acrylate as the monomer. Among these, it is more preferable to use at least one selected from the group consisting of lithium (meth)acrylate, sodium (meth)acrylate, and ammonium (meth)acrylate as the monomer, and it is most preferable to use sodium acrylate as the monomer. (Meth)acrylates can be obtained, for example, by neutralizing (meth)acrylic acid with hydroxide, aqueous ammonia, or the like. Among these, from the viewpoint of availability, it is preferable to neutralize (meth)acrylic acid with sodium hydroxide.

[0035] [1-3. Third structural unit] The third structural unit is represented by the following formula (3): Formula (3): —CH ２ CR ５ (C≡N)-

[0036] In the above formula (3), R ５ is a hydrogen atom, an alkyl group, or an alkoxy group, preferably a hydrogen atom or a methyl group, and more preferably a hydrogen atom. ５ The alkoxy group in R can be ethoxy. ５ The steric positional relationship between C≡N (nitrile group) is not limited. That is, the optical isomers in the third structural unit are not distinguished, and any optical isomer may be used.

[0037] Examples of compounds from which the third structural unit is derived include (meth)acrylonitrile and 3-ethoxy(meth)acrylonitrile. In particular, the compound from which the third structural unit is derived is preferably (meth)acrylonitrile, and more preferably acrylonitrile. The third structural unit contained in the binder polymer of the present disclosure preferably contains 80 mol % or more, more preferably 90 mol % or more, and may even contain 100 mol % of structural units derived from acrylonitrile.

[0038] [1-4. Content of each structural unit in the binder polymer] The content of the first structural unit in the binder polymer is 10 mol% or more, preferably 20 mol% or more, and more preferably 25 mol% or more. When the content of the first structural unit is within this range, in an electrode containing the binder polymer, the retention rate of the peel strength of the electrode active material layer after immersion in the electrolyte solution relative to before immersion in the electrolyte solution is higher. Furthermore, when the content of the first structural unit is within this range, the occurrence of streaks and aggregates on the electrode surface can be suppressed when an electrode is produced using the binder polymer.

[0039] The content of the first structural unit in the binder polymer is 50 mol % or less, preferably 45 mol % or less, and more preferably 35 mol % or less. When the content of the first structural unit is within this range, in an electrode containing the binder polymer, the retention rate of the peel strength of the electrode active material layer after immersion in the electrolyte solution relative to before immersion in the electrolyte solution is higher.

[0040] Therefore, the content of the first structural unit in the binder polymer of the present disclosure is 10 mol% to 50 mol%, optionally 10 mol% to 45 mol%, optionally 10 mol% to 35 mol%, optionally 20 mol% to 50 mol%, optionally 20 mol% to 45 mol%, optionally 20 mol% to 35 mol%, optionally 25 mol% to 50 mol%, optionally 25 mol% to 45 mol%, or optionally 25 mol% to 35 mol%.

[0041] The content of the second structural unit in the binder polymer is 25 mol % or more, preferably 30 mol % or more, and more preferably 35 mol % or more. When the content of the second structural unit is in this range, the peel strength of the electrode active material layer in an electrode containing the binder polymer is improved both before and after immersion in an electrolyte solution.

[0042] The content of the second structural unit in the binder polymer is 80 mol % or less, preferably 70 mol % or less, more preferably 55 mol % or less, and even more preferably 50 mol % or less. When the content of the second structural unit is in this range, the flexibility of an electrode containing the binder polymer can be increased.

[0043] Therefore, the content of the second structural unit in the binder polymer is 25 mol% to 80 mol%, optionally 25 mol% to 70 mol%, optionally 25 mol% to 55 mol%, optionally 25 mol% to 50 mol%, optionally 30 mol% to 80 mol%, optionally 30 mol% to 70 mol%, optionally 30 mol% to 55 mol%, optionally 30 mol% to 50 mol%, optionally 35 mol% to 80 mol%, optionally 35 mol% to 70 mol%, optionally 35 mol% to 55 mol%, or optionally 35 mol% to 50 mol%.

[0044] The content of the third structural unit in the binder polymer is 1.0 mol% or more, preferably 3.0 mol% or more, more preferably 10 mol% or more, and even more preferably 17.5 mol% or more. When the content of the third structural unit is within this range, the peel strength of the electrode active material layer in an electrode containing the binder polymer is improved both before and after immersion in an electrolyte solution. Furthermore, the content of the third structural unit in the binder polymer may be 25 mol% or more. Even when the content of the third structural unit is within this range, the peel strength of the electrode active material layer in an electrode containing the binder polymer is improved both before and after immersion in an electrolyte solution.

[0045] The content of the third structural unit in the binder polymer is 45 mol% or less, preferably 40 mol% or less, and more preferably 35 mol% or less. When the content of the third structural unit is within this range, in an electrode containing the binder polymer, the peel strength of the electrode active material layer is further improved both before and after immersion in an electrolyte solution. Furthermore, when the content of the third structural unit is within this range, the water solubility of the binder polymer is increased, and separation of the binder polymer during storage can be suppressed. Furthermore, the content of the third structural unit in the binder polymer may be 25 mol% or less. Even when the content of the third structural unit is within this range, the peel strength of the electrode active material layer can be improved both before and after immersion in an electrolyte solution in an electrode containing the binder polymer. Furthermore, even when the content of the third structural unit is within this range, the water solubility of the binder polymer is increased, and separation of the binder polymer during storage can be suppressed.

[0046] Therefore, the content of the third structural unit in the binder polymer is 1.0 mol% to 45 mol%, optionally 1.0 mol% to 45 mol%, optionally 1.0 mol% to 35 mol%, optionally 3.0 mol% to 45 mol%, optionally 3.0 mol% to 45 mol%, optionally 3.0 mol% to 35 mol%, optionally 10 mol% to 45 mol%, optionally 10 mol% to 45 mol%, optionally 10 mol% to 35 mol%, optionally 17.5 mol% to 45 mol%, optionally 17.5 mol% to 45 mol%, optionally 17.5 mol% to 35 mol%, or optionally 25 mol% to 35 mol.

[0047] The total content of the first structural unit, the second structural unit, and the third structural unit in the binder polymer is preferably 70 mol % or more, more preferably 80 mol % or more, more preferably 85 mol % or more, and may be 95 mol % or more, or even 100 mol %. [1-5. Other structural units]

[0048] The binder polymer may also have other structures that do not fall under the first structural unit, the second structural unit, and the third structural unit. Examples of other structural units that do not fall under the first structural unit, the second structural unit, and the third structural unit in the binder polymer of the present disclosure include structural units derived from (meth)acrylates in which the moiety other than the (meth)acryloyloxy group is a hydrocarbon and structural units derived from hydrocarbons having ethylenically unsaturated bonds. The total content of these structural units derived from (meth)acrylates in which the moiety other than the (meth)acryloyloxy group is a hydrocarbon and structural units derived from hydrocarbons having ethylenically unsaturated bonds is preferably 20 mol% or less, more preferably 10 mol% or less, and even more preferably 5.0 mol% or less.

[0049] When the total content of the structural units derived from (meth)acrylates in which the moiety other than the (meth)acryloyloxy group is a hydrocarbon and the structural units derived from hydrocarbons having ethylenically unsaturated bonds is within this range, the solubility of the binder polymer in an aqueous medium, the retention rate of the peel strength of the electrode active material layer after immersion in an electrolyte solution, and the retention rate of the discharge capacity during charge-discharge cycles when formed into a battery can be further improved. Note that the binder polymer of the present disclosure may have a configuration that does not have any of the structural units derived from (meth)acrylates in which the moiety other than the (meth)acryloyloxy group is a hydrocarbon and the structural units derived from hydrocarbons having ethylenically unsaturated bonds.

[0050] Furthermore, the binder polymer of the present disclosure is not particularly limited as the other structural unit, and preferably includes a fourth structural unit represented by the following formula (4): When an electrode including the binder polymer is formed into a battery, the discharge capacity retention rate during charge-discharge cycles can be further improved.

[0051] The fourth structural unit is represented by the following formula (4): Formula (4): —CH ２ CR ６ (NR ７ COR ８ )-

[0052] In the above formula (4), R ６R is a hydrogen atom or an alkyl group, preferably a hydrogen atom or an alkyl group having 3 or less carbon atoms, more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom. ７ R is a hydrogen atom or a hydrocarbon group, preferably a hydrogen atom or an alkyl group, more preferably a hydrogen atom or an alkyl group having 5 or less carbon atoms, even more preferably a hydrogen atom or an alkyl group having 3 or less carbon atoms, and even more preferably a hydrogen atom. ８ R is a hydrogen atom or a hydrocarbon group, more preferably a hydrogen atom or an alkyl group having 5 or less carbon atoms, even more preferably a hydrogen atom or an alkyl group having 3 or less carbon atoms, and even more preferably a methyl group. ６ and NR ７ COR ８ In other words, the optical isomers in the fourth structural unit are not distinguished, and any optical isomer may be used.

[0053] When the binder polymer of the present disclosure has a fourth structural unit, the content of the fourth structural unit in the binder polymer is preferably 0.30 mol% or more, more preferably 0.80 mol% or more, even more preferably 1.0 mol% or more, even more preferably 1.5 mol% or more, and even more preferably 2.0 mol% or more. When the content of the fourth structural unit is within this range, the discharge capacity retention rate during charge / discharge cycles when formed into a battery can be further improved. The content of the fourth structural unit in the binder polymer may be 8 mol% or more, 10 mol% or more, or 15 mol% or more. Even when the content of the fourth structural unit is within this range, the discharge capacity retention rate during charge / discharge cycles when formed into a battery can be further improved.

[0054] The content of the fourth structural unit in the binder polymer is preferably 30 mol% or less, more preferably 20 mol% or less, even more preferably 18 mol% or less, and even more preferably 15 mol% or less. When the content of the fourth structural unit is within this range, the discharge capacity retention rate during charge-discharge cycles when formed into a battery can be further improved. The content of the fourth structural unit in the binder polymer may be 10 mol% or less, or may be 5.0 mol% or more. Even when the content of the fourth structural unit is within this range, the discharge capacity retention rate during charge-discharge cycles when formed into a battery can be further improved.

[0055] That is, the content of the fourth structural unit in the binder polymer may be 0.30 mol% to 30 mol%, 0.80 mol% to 20 mol%, 1.0 mol% to 10 mol%, 1.5 mol% to 5.0 mol%, or 8.0 mol% to 20 mol%.

[0056] Examples of compounds from which the fourth structural unit is derived include N-vinylformamide and N-vinylacetamide. In particular, N-vinylacetamide is preferred as the compound from which the fourth structural unit is derived. When the binder polymer of the present disclosure has a fourth structural unit, the content of the N-vinylformamide-derived structural unit and the N-vinylacetamide-derived structural unit in the fourth structural unit contained in the binder polymer of the present disclosure is preferably 80 mol% or more, more preferably 90 mol% or more, and may even be 100 mol%. Furthermore, when the binder polymer of the present disclosure has a fourth structural unit, the content of the N-vinylacetamide-derived structural unit in the fourth structural unit contained in the binder polymer of the present disclosure is preferably 80 mol% or more, more preferably 90 mol% or more, and may even be 100 mol%.

[0057] [1-6. Molecular Weight of Binder Polymer] The weight-average molecular weight of the binder polymer of the present disclosure is 1.5 million or more, more preferably 2 million or more, even more preferably 2.3 million or more, and may be 3 million or more. When the weight-average molecular weight of the binder polymer of the present disclosure is within this range, the peel strength of the electrode active material layer in an electrode containing the binder polymer is further improved both before and after immersion in an electrolyte. Furthermore, when the weight-average molecular weight of the binder polymer of the present disclosure is within this range, the discharge capacity retention rate during charge-discharge cycles in a non-aqueous secondary battery using an electrode containing the binder polymer is further improved. These effects are particularly pronounced in a binder polymer containing 10 mol% to 50 mol% of the first structural unit represented by formula (1), 25 mol% to 80 mol% of the second structural unit represented by formula (2), and 1.0 mol% to 45 mol% of the third structural unit represented by formula (3).

[0058] The weight-average molecular weight of the binder polymer is preferably 10 million or less, more preferably 6 million or less, even more preferably 4 million or less, and may be 3 million or less. By setting the weight-average molecular weight of the binder polymer within this range, an increase in viscosity of a liquid composition containing the binder polymer, such as an electrode binder composition or electrode slurry described below, can be suppressed, and components such as the electrode active material contained in the liquid composition can be sufficiently dispersed.

[0059] That is, the weight average molecular weight of the binder polymer may be 1.5 million to 10 million, 1.5 million to 6 million, 1.5 million to 4 million, 1.5 million to 3 million, 2 million to 10 million, 2 million to 6 million, 2 million to 4 million, 2 million to 3 million, 2.3 million to 10 million, 2.3 million to 6 million, 2.3 million to 4 million, 2.3 million to 3 million, 3 million to 10 million, 3 million to 6 million, or 3 million to 4 million. The weight average molecular weight of the binder polymer may also be 4 million to 6 million.

[0060] [1-7. Glass Transition Point of Binder Polymer] The glass transition point Tg of the binder polymer of the present disclosure is calculated using the Fox formula based on the glass transition point when each structural unit contained in the binder polymer is treated as a homopolymer. A specific method for calculating the glass transition point Tg of the binder polymer is to calculate it using the following formula (1) from the glass transition point Tgi of the homopolymer of each structural unit Mi (i = 1, 2, 3, etc., i.e., the first structural unit to the third structural unit, etc.) and the mass fraction Xi of the structural unit Mi in the binder polymer (ΣXi (total structural units) = 1). In formula (1), Tg and Tgi are both calculated as absolute temperature (K) values. 1 / Tg=Σ(Xi / Tgi) (1) When the binder polymer has a structural unit other than the first structural unit, the second structural unit, and the third structural unit (for example, a fourth structural unit), the glass transition temperature Tg of the binder polymer can also be calculated for this other structural unit by substituting the glass transition temperature Tgi of the homopolymer and the mass fraction Xi in the binder polymer into the above formula (1).

[0061] The glass transition temperature Tg of the binder polymer is preferably 100°C (373K) or higher, more preferably 130°C (403K) or higher, even more preferably 150°C (423K) or higher, and may be 200°C (573K) or higher. The glass transition temperature Tg of the binder polymer may be 300°C (673K) or lower, or may be 250°C or lower.

[0062] The glass transition temperature Tg of the binder polymer may be 100°C to 300°C, 130°C to 300°C, 150°C to 300°C, 200°C to 300°C, 100°C to 250°C, 130°C to 250°C, 150°C to 250°C, or 200°C to 250°C.

[0063] [1-8. Solubility of Binder Polymer] The binder polymer of the present disclosure can be dissolved in an aqueous medium. Examples of the aqueous medium include water and solvents containing water. The water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 95% by mass or more, or even 100% by mass. The aqueous medium may contain a hydrophilic solvent other than water. The hydrophilic solvent is not particularly limited, and examples thereof include methanol, ethanol, and N-methylpyrrolidone.

[0064] The binder polymer of the present disclosure has a solubility in water at 25°C of 5.0 g / 100 gH ２ It is preferable that the viscosity is 8.0 g / 100 gH or more. ２ More preferably, it is 11 g / 100 gH or more. ２ More preferably, it is 20 g / 100 gH or more. ２ More preferably, it is 25 g / 100 gH or more. ２ It is more preferable that the solubility in water at 25°C of the binder polymer of the present disclosure is in this range, so that an electrode for a non-aqueous secondary battery can be easily produced from a slurry in which the binder polymer is dissolved in an aqueous medium.

[0065] <2. Method for Producing Binder Polymer> The synthesis of the binder polymer of the present disclosure is not particularly limited, and is preferably carried out by radical polymerization in an aqueous medium. More specifically, a method in which all of the monomers used in the polymerization are charged at once and polymerized, or a method in which the monomers used in the polymerization are polymerized while being continuously supplied, can be applied. For example, according to the method in the examples described below, all of the monomers used in the synthesis of the binder polymer are converted into structural units of the binder polymer. The temperature at which the radical polymerization is carried out is not particularly limited, and is preferably 30°C to 90°C.

[0066] In the case of radical polymerization, ammonium persulfate, sodium persulfate, hydrogen peroxide, t-butyl hydroperoxide, azo compounds, and the like can be used as polymerization initiators, but are not limited to these. Examples of azo compounds include 2,2'-azobis(2-methylpropionamidine) dihydrochloride. When polymerization is carried out in an aqueous medium, it is preferable to use a water-soluble polymerization initiator. Furthermore, if necessary, redox polymerization may be carried out by using a radical polymerization initiator in combination with a reducing agent during polymerization. Examples of reducing agents include sodium bisulfite, Rongalite, and ascorbic acid.

[0067] The aqueous medium preferably contains water. The water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 95% by mass or more, or even 100% by mass. The aqueous medium may contain a hydrophilic solvent other than water. The hydrophilic solvent is not particularly limited, and examples thereof include methanol, ethanol, and N-methylpyrrolidone.

[0068] 3. Electrode Binder Composition for Non-Aqueous Secondary Battery The electrode binder composition for a non-aqueous secondary battery according to the present disclosure (hereinafter sometimes referred to as the "electrode binder composition") contains the binder polymer described above, an aqueous medium, and the like. The electrode binder composition may also contain other components such as a pH adjuster and a surfactant, as necessary. The electrode binder composition may contain one type of binder polymer according to the present disclosure alone, or may contain two or more types of binder polymers according to the present disclosure. The electrode binder composition is obtained by mixing the binder polymer described above with an aqueous medium. It is preferable that the binder polymer in the electrode binder composition is completely dissolved in the aqueous medium at 25°C. When the electrode binder composition contains two or more types of binder polymers, it is preferable that these two or more types of binder polymers are completely dissolved in the aqueous medium at 25°C.

[0069] Here, "the binder polymer is completely soluble in the aqueous medium at 25°C" means that the binder polymer is dissolved in the aqueous medium to a range equal to or less than the solubility of the binder polymer in the aqueous medium at 25°C. When the electrode binder composition contains two or more types of binder polymers, this means that each binder polymer is dissolved in the aqueous medium to a range equal to or less than its respective solubility. Therefore, even if a saturated solution of the binder polymer precipitates partly due to a decrease in temperature, or even if some of the two or more types of binder polymers precipitate due to a decrease in temperature, the binder polymer is still considered to be completely dissolved in the aqueous medium.

[0070] The aqueous medium contained in the electrode binder composition preferably contains water. The water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 95% by mass or more, or even 100% by mass. The aqueous medium may contain a hydrophilic solvent other than water. The hydrophilic solvent is not particularly limited, and examples thereof include methanol, ethanol, and N-methylpyrrolidone.

[0071] The aqueous medium contained in the electrode binder composition may be the same as or different from the aqueous medium used in the synthesis of the binder polymer.

[0072] The content of the binder polymer in the electrode binder composition is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less. When the content of the binder polymer in the electrode binder composition is within this range, an increase in the viscosity of the electrode binder composition is suppressed, and when the electrode binder composition is mixed with an electrode active material and the like described below to prepare an electrode slurry, the electrode active material and the like can be efficiently dispersed.

[0073] The content of the binder polymer in the electrode binder composition is preferably 3.0% by mass or more, more preferably 5.0% by mass or more, and even more preferably 8.0% by mass or more. When the content of the binder polymer in the electrode binder composition is within this range, the amount of volatile matter can be suppressed, and an electrode slurry and an electrode can be produced from a smaller amount of the electrode binder composition.

[0074] 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. When the electrode binder composition has a pH within this range, when the electrode binder composition is mixed with an electrode active material, etc., described below, to prepare an electrode slurry, the electrode active material, etc. can be efficiently dispersed. The pH of the electrode binder composition is preferably 10 or lower, more preferably 9.0 or lower, and even more preferably 8.0 or lower. When the electrode binder composition has a pH within this range, when the electrode binder composition is mixed with an electrode active material, etc., described below, to prepare an electrode slurry, the electrode active material, etc. can be efficiently dispersed. Here, the pH is a value measured with a pH meter at a liquid temperature of 23°C.

[0075] That is, the pH of the electrode binder composition may be 4.0 to 10.0, 5.0 to 9.0, or 6.0 to 8.0.

[0076] 4. Electrode Slurry for Non-Aqueous Secondary Battery The electrode slurry for a non-aqueous secondary battery (hereinafter sometimes referred to as "electrode slurry") of the present disclosure contains the above-described binder polymer, an electrode active material, and an aqueous medium. The electrode slurry is obtained by mixing the above-described binder polymer, the electrode active material, and the aqueous medium. It is preferable that the binder polymer in the electrode slurry is completely dissolved in the aqueous medium.

[0077] Here, the binder polymer being completely dissolved in the aqueous medium has the same meaning as that explained in the section <3. Electrode binder composition for non-aqueous secondary battery>.

[0078] The electrode slurry may contain a conductive aid, a thickener, etc. as needed, but it is preferable that it does not contain a thickener in order to simplify the electrode slurry preparation process. The method for producing the electrode slurry is not particularly limited, and examples include methods of mixing the necessary components using a mixing device such as a stirring type, a rotary type, or a shaking type.

[0079] The electrode active material is not particularly limited, and when the nonaqueous secondary battery is a lithium ion secondary battery, examples of the negative electrode active material include conductive polymers, carbon materials, lithium titanate, silicon, silicon compounds, etc. Examples of conductive polymers include polyacetylene and polypyrrole. Examples of carbon materials include cokes such as petroleum coke, pitch coke, and coal coke; carbides of organic compounds, carbon fiber, and carbon blacks such as acetylene black; and graphites such as artificial graphite and natural graphite. Examples of silicon compounds include SiO ｘ (0.1≦x≦2.0), etc. Specific examples of artificial graphite include SCMG-XRs (manufactured by Resonac Co., Ltd.). Two or more of the materials listed here may be combined to form the negative electrode active material. Furthermore, a composite material containing Si and graphite (Si / graphite) may also be used as the negative electrode active material.

[0080] Among these negative electrode active materials, carbon materials, lithium titanate, silicon, silicon compounds, etc. are preferably used because of their high energy density per volume. Also, as the negative electrode active material, carbon materials such as coke, carbides of organic compounds, graphite, SiO ｘ (0.1≦x≦2.0), it is preferable to use a silicon-containing material such as Si or Si / graphite. When such a silicon-containing material is used, the binder polymer of the present disclosure has a significant effect of improving the binding property.

[0081] On the other hand, an example of a positive electrode active material for a lithium ion secondary battery is lithium cobalt oxide (LiCoO ２ ); lithium composite oxides containing nickel; spinel-type lithium manganese oxide (LiMn ２ O ４ ); olivine-type lithium iron phosphate; TiS ２ , MnO ２, MoO ３ , V ２ O ５ Examples of the positive electrode active material include chalcogen compounds such as LiNi, LiNi-Co-Mn, Ni-Mn-Al, and Ni-Co-Al. The positive electrode active material may contain any one of these compounds alone or a combination of these compounds. Oxides of other alkali metals can also be used. Examples of lithium composite oxides containing nickel include Ni-Co-Mn-based lithium composite oxides, Ni-Mn-Al-based lithium composite oxides, and Ni-Co-Al-based lithium composite oxides. Specific examples of the positive electrode active material include LiNi １／３ Mn １／３ Co １／３ O ２ , LiNi ３／５ Mn １／５ Co １／５ O ２ etc.

[0082] The aqueous medium contained in the electrode slurry preferably contains water. The water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, and may be 95% by mass or more, or even 100% by mass. The aqueous medium may contain a hydrophilic solvent other than water. The hydrophilic solvent is not particularly limited, and examples thereof include methanol, ethanol, and N-methylpyrrolidone.

[0083] The aqueous medium contained in the electrode slurry may be the same as the aqueous medium contained in the electrode binder composition or the same as the aqueous medium used in synthesizing the binder polymer. The aqueous medium contained in the electrode slurry may be different from the aqueous medium contained in the electrode binder composition and the aqueous medium used in synthesizing the binder polymer.

[0084] Examples of the conductive additive contained in the electrode slurry include carbon black, vapor grown carbon fiber, etc. A specific example of vapor grown carbon fiber is VGCF-H (Resonac Corporation).

[0085] The nonvolatile content concentration of the electrode slurry is preferably 30% by mass or more, more preferably 40% by mass or more. By setting the nonvolatile content concentration of the electrode slurry within this range, a larger number of electrode active material layers can be formed with a smaller amount of electrode slurry. Furthermore, the nonvolatile content concentration of the electrode slurry is preferably 70% by mass or less, more preferably 60% by mass or less. That is, the nonvolatile content concentration of the electrode slurry may be 30% by mass to 70% by mass, or may be 40% by mass to 60% by mass. The nonvolatile content concentration of the electrode slurry can be adjusted by the amount of aqueous medium used.

[0086] The content of the binder polymer in the electrode slurry is preferably 0.50% by mass or more, more preferably 1.0% by mass or more, and even more preferably 2.0% by mass or more, and can be, for example, 3.0% by mass, relative to the total mass of the electrode active material, the conductive assistant, and the binder polymer. By setting the content of the binder polymer in the electrode slurry within this range, the binder polymer can improve the binding strength between the electrode active materials and between the electrode active material and the current collector.

[0087] The content of the binder polymer in the electrode slurry is preferably 7.0 mass % or less, more preferably 5.0 mass % or less, and even more preferably 4.0 mass % or less, based on the total mass of the electrode active material, the conductive additive, and the binder polymer. By setting the content of the binder polymer in the electrode slurry within this range, the charge / discharge capacity of the electrode active material layer formed from the electrode slurry can be increased, and the internal resistance when formed into a battery can be reduced.

[0088] Therefore, the content of the binder polymer in the electrode slurry may be 0.50% by mass to 7.0% by mass, 1.0% by mass to 5.0% by mass, or 2.0% by mass to 4.0% by mass, relative to the total mass of the electrode active material, the conductive assistant, and the binder polymer.

[0089] 5. Electrode for Non-Aqueous Secondary Battery The electrode for a non-aqueous secondary battery (hereinafter sometimes referred to as "electrode") of the present disclosure comprises a current collector and an electrode active material layer provided on at least a partial region of the surface of the current collector. The electrode active material layer contains an electrode active material and the above-mentioned binder polymer. The shape of the electrode includes, but is not limited to, a laminate, a wound body, etc. The current collector is not particularly limited, and is preferably a sheet-like metal with a thickness of 0.001 mm to 0.5 mm. Examples of metals include iron, copper, aluminum, nickel, and stainless steel. When the non-aqueous secondary battery is a lithium-ion secondary battery, aluminum is preferably used as the material for the positive electrode current collector, and copper is preferably used as the material for the negative electrode current collector.

[0090] The electrode of the present disclosure can be produced by a method in which the above-described electrode slurry is applied to at least a portion of the surface of a current collector, preferably the entire surface, and then dried, but the method is not limited to this.

[0091] Examples of methods for applying the electrode slurry onto the current collector include the reverse roll method, direct roll method, doctor blade method, knife method, extrusion method, curtain method, gravure method, bar method, dipping method, and squeeze method. Among these, it is preferable to apply the electrode slurry onto the current collector by the doctor blade method, knife method, or extrusion method, and it is more preferable to apply the electrode slurry onto the current collector using a doctor blade. This is because these methods are suitable for the physical properties such as viscosity of the electrode slurry and drying property, and can obtain a coating film with a good surface condition.

[0092] The electrode slurry may be applied to only one side of the current collector, or may be applied to both sides. When the electrode slurry is applied to both sides of the current collector, it may be applied to each side sequentially, or both sides may be applied at once. The electrode slurry may be applied to the current collector continuously or intermittently. The amount of electrode slurry to be applied can be determined appropriately depending on the design capacity of the battery, the composition of the electrode slurry, etc. The amount of electrode active material layer to be applied after drying (the amount to be applied per side when applied to both sides) is 4 mg / cm. ２ ~20 mg / cm ２ and preferably 6 mg / cm２ ~16 mg / cm ２ It is more preferable that:

[0093] The electrode active material layer is formed on the current collector by drying the electrode slurry applied to the current collector. The method for drying the electrode slurry is not particularly limited, and hot air, reduced pressure or vacuum environment, (far) infrared rays, electron beams, microwaves, or low-temperature air can be used alone or in combination. The drying temperature is preferably 40°C to 180°C, and the drying time is preferably 1 minute to 30 minutes.

[0094] The electrode sheet may be used as an electrode as is, or may be cut to a size and shape appropriate for an electrode. The method for cutting the electrode sheet is not particularly limited, and slitting, laser cutting, wire cutting, a cutter, a Thomson cutter, or the like may be used.

[0095] Before or after cutting the electrode sheet, the electrode sheet may be pressed as necessary. Pressing the electrode sheet allows the electrode active material to be more firmly bonded to the electrode, and further enables the electrode to be made thinner, thereby making it possible to compact the non-aqueous battery. As a pressing method, a general method can be used, and in particular, a mold pressing method or a roll pressing method is preferably used. The pressing pressure is not particularly limited, and is preferably 0.5 t / cm, which is within a range that does not affect the doping and dedoping of lithium ions and the like into and from the electrode active material by pressing. ２ ~5t / cm ２ It is preferable to set the following.

[0096] 6. Nonaqueous Secondary Battery The nonaqueous secondary battery of the present disclosure includes the nonaqueous secondary battery electrode of the present disclosure. The nonaqueous secondary battery of the present disclosure is a secondary battery in which ions move between a positive electrode and a negative electrode during charging and discharging. The nonaqueous secondary battery of the present disclosure includes a positive electrode active material in the positive electrode and a negative electrode active material in the negative electrode. These positive electrode active materials and negative electrode active materials are materials capable of ion intercalation and deintercalation. An example of the nonaqueous secondary battery of the present disclosure is a lithium ion secondary battery.

[0097] A lithium-ion secondary battery will be described as one embodiment of the nonaqueous secondary battery of the present disclosure, but the configuration of the nonaqueous secondary battery is not limited to the configuration described below. The lithium-ion secondary battery described as this embodiment has a configuration in which components such as a positive electrode, a negative electrode, an electrolyte, and, if necessary, a separator, are housed in an exterior body. In the lithium-ion secondary battery of this embodiment, at least one of the positive electrode and the negative electrode contains the binder polymer described above.

[0098] The electrolyte solution is a non-aqueous liquid having ion conductivity. Examples of the electrolyte solution include a solution in which an electrolyte is dissolved in an organic solvent, an ionic liquid, etc., but a solution in which an electrolyte is dissolved in an organic solvent is preferred because it has low production costs and can produce a battery with low internal resistance.

[0099] The electrolyte can be an alkali metal salt, and can be appropriately selected depending on the type of electrode active material, etc. The electrolyte can be LiClO ４ , LiBF ６ , LiPF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ , LiSbF ６ , LiB １０ Cl １０ , LiAlCl ４ , LiCl, LiBr, LiB(C ２ H ５ ) ４ , C.F. ３ SO ３ Li, C.H. ３ SO ３ Li, LiCF ３ SO ３ , LiC ４ F ９ SO ３ , Li(CF ３ SO ２ ) ２ Examples of the electrolyte include lithium N and aliphatic carboxylate. Other alkali metal salts can also be used as the electrolyte.

[0100] The organic solvent for dissolving the electrolyte is not particularly limited, and examples thereof include carbonate ester compounds such as ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC); nitrile compounds such as acetonitrile; and carboxylic acid esters such as ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate. These organic solvents may be used alone or in combination of two or more.

[0101] The exterior can be made of a metal, an aluminum laminate, etc. The shape of the battery may be any of coin type, button type, sheet type, cylindrical type, square type, flat type, etc.

[0102] Hereinafter, one example of an embodiment of the present disclosure will be specifically described using examples, but the embodiment is not limited to these examples. The examples and comparative examples shown below are examples of fabricating a negative electrode binder for a lithium ion secondary battery, a negative electrode slurry, a negative electrode, and a lithium ion secondary battery.

[0103] <1. Preparation of Negative Electrode Binder Composition (Electrode Binder Composition)> In each of Examples 1 to 9 and Comparative Examples 1 to 7, a separable flask equipped with a condenser, a thermometer, a stirrer, and a dropping funnel was charged with a total of 100 parts by mass of monomers in the proportions shown in Table 1 (when the monomers were used as a solution, the amount of monomer used in the table indicates the amount of the monomer itself, not including the solvent), 0.2 parts by mass of 2,2'-azobis(2-methylpropionamidine) dihydrochloride as a radical polymerization initiator, 0.05 parts by mass of ammonium persulfate, and 567 parts by mass of water at 30°C. The mixture was heated to 80°C, and polymerization was carried out for 4 hours to produce a copolymer or polymer, thereby obtaining a reaction liquid containing the copolymer or polymer. In Comparative Example 6, the monomers were used in the same composition ratio as in Example 2, and a reaction solution containing a copolymer or a polymer was obtained in the same manner as in Example 2, except that 0.6 parts by mass of 2,2′-azobis(2-methylpropionamidine) dihydrochloride and 0.15 parts by mass of ammonium persulfate were used as radical polymerization initiators.

[0104] In Table 1, "monomer (A)" is a compound from which the first structural unit is derived. "monomer (B)" is a compound from which the second structural unit is derived. "monomer (C)" is a compound from which the third structural unit is derived. "monomer (D)" is a compound from which the fourth structural unit is derived.

[0105] Water was added to the reaction liquid containing the copolymer or polymer after polymerization to obtain negative electrode binder compositions of Examples 1 to 9 and Comparative Examples 1 to 7 having a nonvolatile content of 10.0 mass %.

[0106]

[0107] The abbreviations of the monomers listed in Table 1 are as follows: AAm: acrylamide AaNa: sodium acrylate AaLi: lithium acrylate AN: acrylonitrile MN: methacrylonitrile NVA: N-vinylacetamide

[0108] <2. Various Measurements of Negative Electrode Binder Composition> The binder polymer and the negative electrode binder composition were subjected to the following measurements. The measurement results are shown in Table 1.

[0109] 2-1. Weight-average molecular weight of binder polymer The weight-average molecular weight of the binder polymer was measured using gel permeation chromatography (GPC) under the following conditions.

[0110] GPC device: GPC-101 (manufactured by Resonac Co., Ltd.) Solvent: 0.1 M NaNO ３ Aqueous solution Sample column: Shodex Column Ohpak SB-806 HQ (8.0 mm I.D. x 300 mm) x 2 Reference column: Shodex Column Ohpak SB-800 RL (8.0 mm I.D. x 300 mm) x 2 Column temperature: 40°C Sample concentration: 0.1 mass% Detector: RI-71S (Shimadzu Corporation) Pump: DU-H2000 (Shimadzu Corporation) Pressure: 1.3 MPa Flow rate: 1 ml / min Molecular weight standard: Pullulan (P-5, P-10, P-20, P-50, P-100, P-200, P-400, P-800, P-1300, P-2500 (Resonac Corporation))

[0111] 2-2. pH of Negative Electrode Binder Composition The pH of the negative electrode binder composition was measured at a liquid temperature of 23° C. using a pH meter (manufactured by DKK-TOA).

[0112] [2-3. Solubility of Binder Polymer in Water] The solubility of the negative electrode binder composition in water was evaluated as follows. That is, the negative electrode binder composition was dried at 110° C. for 5 hours to remove moisture, and then the negative electrode binder composition was subjected to a 25 g / 100 g H ２ O or 11g / 100gH ２ Ion-exchanged water was added to the dried product so that the concentration was 0, and the mixture was stirred at 25°C for 24 hours. At 25°C, it was visually confirmed whether the appearance became cloudy or whether a precipitate occurred.

[0113] <3. Preparation of Negative Electrode Slurry (Electrode Slurry)> 76.8 parts by mass of SCMG-XRs (manufactured by Resonac Co., Ltd.) as graphite, 19.2 parts by mass of silicon monoxide (SiO) (manufactured by Sigma-Aldrich), 1 part by mass of VGCF-H (manufactured by Resonac Co., Ltd.), 30 parts by mass of a negative electrode binder composition (containing 3 parts by mass of copolymer and 27 parts by mass of water), and 20 parts by mass of water were mixed. Mixing was performed by kneading for 4 minutes at 2000 rpm using an agitation mixer (rotation-revolution agitation mixer). 53 parts by mass of water was further added to the obtained mixture, and the mixture was further kneaded for 4 minutes at 2000 rpm using the mixer to prepare a negative electrode slurry.

[0114] <4. Battery Fabrication> [4-1. Fabrication of Negative Electrode] The prepared negative electrode slurry was applied to one side of a 10 μm thick copper foil (current collector) so that the weight per unit area after drying was 8 mg / cm. ２ The negative electrode slurry was applied using a doctor blade so that the negative electrode slurry was uniformly dispersed. The copper foil coated with the negative electrode slurry was dried at 60°C for 10 minutes and then further dried at 110°C for 5 minutes to produce a negative electrode sheet on which a negative electrode active material layer was formed. This negative electrode sheet was pressed using a roll press at a pressure of 10 ton. The pressed negative electrode sheet was cut into a size of 52 mm x 42 mm, and a conductive tab was attached to produce a negative electrode.

[0115] [4-2. Preparation of Positive Electrode] LiNi was used as the positive electrode active material. ３／５ Mn １／５ Co １／５ O ２ 90 parts by mass of cellulose acetate, 5 parts by mass of acetylene black, and 5 parts by mass of polyvinylidene fluoride were mixed, and then 100 parts by mass of N-methylpyrrolidone was mixed to prepare a positive electrode slurry (LiNi in the solid content ３／５ Mn １／５ Co １／５ O ２ The mass ratio is 0.90).

[0116] The prepared positive electrode slurry was applied to one side of an aluminum foil (current collector) having a thickness of 15 μm by a doctor blade method so that the weight per unit area after drying was 27 mg / cm ２The positive electrode slurry was applied using a doctor blade so that the thickness of the aluminum foil coated with the positive electrode slurry was 100 μm. The aluminum foil was then dried at 120° C. for 5 minutes and pressed with a roll press to prepare a positive electrode sheet on which a positive electrode active material layer having a thickness of 100 μm was formed. The obtained positive electrode sheet was cut into a size of 50 mm × 40 mm (5.0 cm × 4.0 cm), and a conductive tab was attached to prepare a positive electrode.

[0117] A mixed solvent was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DMC) in a volume ratio of 30:50:20. ６ to a concentration of 1.0 mol / L, and then vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were dissolved therein to a concentration of 1.0 mass% and 2.0 mass%, respectively, to prepare an electrolyte solution. In the following description, unless otherwise specified, the term "electrolyte solution" refers to the electrolyte solution prepared here.

[0118] The positive electrode and the negative electrode were arranged with their active material layers facing each other via a separator made of a polyolefin porous film, and the resulting assembly was housed in an aluminum laminate exterior (battery pack). An electrolyte solution was poured into the exterior, and the battery was sealed with a vacuum heat sealer to obtain a laminated battery.

[0119] 5. Evaluation of Negative Electrode and Battery The negative electrode and battery of each example and comparative example were evaluated. The evaluation method was as follows, and the evaluation results are shown in Table 2.

[0120] [5-1. Appearance of Negative Electrode] The fabricated negative electrodes were visually inspected to count the number of coating streaks and aggregates caused by poor leveling during the slurry coating. The aggregates were presumably caused by poor dispersion of the negative electrode active material and conductive additive in the slurry.

[0121] [5-2. Peel strength of negative electrode active material layer] The peel strength of the negative electrode active material layer from the current collector was measured as follows. The negative electrode sheet before pressing in the above-mentioned negative electrode production process was cut into a size of 25 mm x 100 mm to prepare a test piece. Two test pieces were prepared for each Example and Comparative Example. For one of the two test pieces, the peel strength of the negative electrode active material layer was measured as it was before immersion in the electrolyte solution. For the other test piece, the peel strength of the negative electrode active material layer was measured after immersion in the electrolyte solution.

[0122] The electrolyte immersion was carried out by immersing the test piece in the electrolyte in a sealed container, storing it at 45°C for 72 hours, then removing it, immersing it in ethyl methyl carbonate (EMC) for 1 minute, and then drying it at 23°C and 50% RH for 2 hours.

[0123] The peel strength of the negative electrode active material layer was measured as follows. First, the negative electrode active material layer on the test piece was attached to a stainless steel (SUS) plate 50 mm wide and 200 mm long using double-sided tape (NITTO TAPE No. 5, manufactured by Nitto Denko Corporation) so that the center of the test piece and the center of the SUS plate coincided. The double-sided tape was attached so as to cover the entire area of ​​the test piece.

[0124] Next, the test piece and the SUS plate were left in a bonded state for 10 minutes, and then the negative electrode active material layer was peeled off 20 mm from one end of the test piece in the longitudinal direction, and the copper foil side of the test piece was folded back 180°. The folded back portion (the copper foil side of the test piece from which the negative electrode active material layer was peeled off) was gripped with the upper chuck of the tester. Furthermore, one end of the SUS plate from which the negative electrode active material layer was peeled off was gripped with the lower chuck of the same tester. In this state, the copper foil was peeled off from the test piece at a rate of 100±10 mm / min, and a graph of peel length (mm) vs. peel force (mN) was obtained. In the graph obtained, the average peel force (mN) at peel lengths of 10 mm to 45 mm was calculated, and the value obtained by dividing the average peel force by the width of the test piece (25 mm) was taken as the peel strength (mN / mm) of the negative electrode active material layer. In all of the Examples and Comparative Examples, peeling did not occur between the double-sided tape and the SUS plate, and interfacial peeling did not occur between the double-sided tape and the negative electrode active material layer during the test.

[0125] 5-3. Battery Characteristics Using the laminated type batteries fabricated in each Example and Comparative Example, the battery characteristics were evaluated by calculating the discharge capacity retention rate in charge / discharge cycles.

[0126] First, under the condition of 25°C, charge and discharge were performed, with one cycle consisting of a series of operations of the following steps (i) to (iv). The time-integrated value of the current in steps (i) and (ii) was taken as the charge capacity, and the time-integrated value of the current in step (iv) was taken as the discharge capacity. Then, the discharge capacity at the first cycle and the discharge capacity at the 100th cycle were measured, and the discharge capacity retention rate after 100 cycles was calculated using the following formula: (Formula): Discharge capacity retention rate after 100 cycles (%) = 100 × (discharge capacity at the 100th cycle / discharge capacity at the first cycle)

[0127] (i) Charge at a current of 0.5 C until the voltage reaches 4.2 V (constant current (CC) charging). (ii) Charge at a voltage of 4.2 V until the current reaches 0.05 C (constant voltage (CV) charging). (iii) Leave to stand for 30 minutes. (iv) Discharge at a current of 0.5 C until the voltage reaches 2.75 V (constant current (CC) discharging).

[0128] 5-4. Test Results Table 2 shows the results of the evaluation of the peel strength of the negative electrode active material layer, the battery characteristics, and the appearance of the negative electrode.

[0129]

[0130] <Evaluation Results> As shown in Table 2, in Examples 1 to 9, electrodes having excellent negative electrode appearance and excellent peel strength of the negative electrode active material layer were produced compared to Comparative Examples 1 to 7. Furthermore, in Examples 1 to 9, batteries having excellent discharge capacity retention and including electrodes having excellent negative electrode appearance and excellent peel strength of the negative electrode active material layer were produced. That is, by using a binder polymer containing 10 mol% to 50 mol% of the first structural unit represented by formula (1), 25 mol% to 80 mol% of the second structural unit represented by formula (2), and 1.0 mol% to 45 mol% of the third structural unit represented by formula (3), and having a weight-average molecular weight of 1.5 million or more, it was possible to produce electrodes having excellent appearance and high peel strength of the electrode active material layer even after immersion in an electrolyte solution. It was also shown that it was possible to produce nonaqueous secondary batteries having excellent discharge capacity retention and including electrodes having excellent appearance and excellent peel strength of the electrode active material layer.

[0131] The disclosure of Japanese Patent Application No. 2023-223505 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards mentioned herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A non-aqueous secondary battery electrode binder polymer containing 10 mol% to 50 mol% of a first structural unit represented by the following formula (1), 25 mol% to 80 mol% of a second structural unit represented by the following formula (2), and 1.0 mol% to 45 mol% of a third structural unit represented by the following formula (3), and having a weight average molecular weight of 1,500,000 or more. Formula (1): -CH ２ CR １ (CONR ２ R ３ ) - [In formula (1), R １ , R ２ and R ３ are each independently a hydrogen atom or an alkyl group.] Formula (2): -CH ２ CR ４ (COOX) - [In formula (2), R ４ is a hydrogen atom or an alkyl group. COOX is at least one selected from the group consisting of a carboxy group and its salts.] Formula (3): -CH ２ CR ５ (C≡N) - [In formula (3), R ５ is a hydrogen atom, an alkyl group or an alkoxy group.] 2. The electrode binder polymer for non-aqueous secondary batteries according to claim 1, having a solubility in water at 25 °C of 5.0 g / 100 g H ２ 2O or more.

3. The total content of the first structural unit, the second structural unit, and the third structural unit is 70 mol% or more. The electrode binder polymer for a non-aqueous secondary battery according to claim 1.

4. R ２ and R ３ is a hydrogen atom or an alkyl group having 3 or less carbon atoms, the non-aqueous secondary battery electrode binder polymer according to claim 1.

5. The glass transition point is 100 °C or higher. The electrode binder polymer for a non-aqueous secondary battery according to claim 1.

6. The electrode binder polymer for a non-aqueous secondary battery according to claim 1, further comprising a fourth structural unit represented by the following formula (4). Formula (4): -CH ２ CR ６ (NR ７ COR ８ ) - [In formula (4), R ６ is a hydrogen atom or an alkyl group. R ７ is a hydrogen atom or a hydrocarbon group. R ８ is a hydrogen atom or a hydrocarbon group.] 7. The fourth structural unit is contained in an amount of 0.30 mol% to 30 mol%. The electrode binder polymer for a non-aqueous secondary battery according to claim 6.

8. An electrode binder composition for a non-aqueous secondary battery, comprising the electrode binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 7 and an aqueous medium.

9. The electrode binder polymer for a non-aqueous secondary battery is completely dissolved in the aqueous medium at 25 °C. The electrode binder composition for a non-aqueous secondary battery according to claim 8.

10. An electrode slurry for a non-aqueous secondary battery, comprising the electrode binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 7, an electrode active material, and an aqueous medium.

11. A current collector, and an electrode active material layer provided on at least a part of the surface of the current collector and containing an electrode active material and the electrode binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 7. An electrode for a non-aqueous secondary battery.

12. A non-aqueous secondary battery comprising the electrode for a non-aqueous secondary battery according to claim 11.

13. A method for producing an electrode binder polymer for a non-aqueous secondary battery, which is the method according to any one of claims 1 to 7, using (meth)acrylamide, N,N-dimethyl(meth)acrylamide, N,N-diethyl(meth)acrylamide, N-ethyl(meth)acrylamide, or N-propyl(meth)acrylamide as a compound derived from the first structural unit, at least one selected from the group consisting of (meth)acrylic acid and its salts as a compound derived from the second structural unit, and (meth)acrylonitrile as a compound derived from the third structural unit, and performing radical polymerization in an aqueous medium. A method for producing an electrode binder polymer for a non-aqueous secondary battery.

14. A method for producing an electrode binder composition for a non-aqueous secondary battery, which comprises mixing the electrode binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 7 and an aqueous medium.

15. A method for manufacturing an electrode slurry for a non-aqueous secondary battery, comprising mixing the electrode binder polymer for a non-aqueous secondary battery according to any one of claims 1 to 7, an electrode active material, and an aqueous medium.

16. A method for manufacturing an electrode for a non-aqueous secondary battery, comprising applying the electrode slurry for a non-aqueous secondary battery according to claim 10 to at least a part of the surface of a current collector and drying it.