Electrode mixture, electrode, and battery

Abstract

To provide an electrode mixture that contains a carbon-coated electrode active material and a vinylidene fluoride copolymer having a carboxy group, and that is easy to handle.SOLUTION: An electrode mixture includes a vinylidene fluoride copolymer having a constituent unit derived from vinylidene fluoride and a constituent unit derived from a vinyl compound having a carboxy group, and an electrode active material coated with carbon, and when a slurry for viscosity measurement is prepared by mixing the vinylidene fluoride copolymer, the electrode active material, carbon nanotubes, polyvinylpyrrolidone, and N-methylpyrrolidone in a predetermined ratio, the slurry for viscosity measurement has a predetermined slurry viscosity.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrode mixture, an electrode, and a battery. [Background technology]

[0002] To form a mixture layer of an electrode of a non-aqueous electrolyte secondary battery, an electrode mixture containing a binder (binding agent) and an active material is usually used. A vinylidene fluoride polymer is typically used as the binder (binding agent). High adhesiveness is required for the binder, as it serves to adhere the active material to the current collector. For example, Patent Document 1 describes introducing a functional group such as a carboxyl group into a fluorine-based resin to improve adhesion to the current collector and solubility in a solvent. Patent Document 2 describes a binder composition containing a copolymer (vinylidene fluoride copolymer) of vinylidene fluoride and a compound with a specific structure, and describes that the vinylidene fluoride copolymer exhibits high adhesiveness to the current collector.

[0003] On the other hand, in order to reduce the cost of batteries, the use of lithium iron phosphate (LFP) as a positive electrode active material is being considered, and the use of lithium iron manganese phosphate (LFMP) as a next-generation material is also being considered. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 6-172452 [Patent Document 2] Patent No. 5797206 Summary of the Invention [Problem to be solved by the invention]

[0005] In order to improve adhesion to a current collector or the like, it is conceivable to use the vinylidene fluoride copolymer described in Patent Document 1 or Patent Document 2 as an electrode binder in an electrode mixture (slurry) containing the above-mentioned lithium iron phosphate (LFP) or lithium iron manganese phosphate (LFMP). However, when LFP or LFMP is mixed with a vinylidene fluoride copolymer that has high adhesive strength to a current collector, the carbon coating present on the surface of the LFP or LFMP and the vinylidene fluoride copolymer having a carboxy group interact with each other, making it very difficult to produce an electrode (mixture layer).

[0006] The present invention has been made in view of the above-mentioned problems. An object of the present invention is to provide an electrode mixture that contains a carbon-coated electrode active material and a vinylidene fluoride copolymer having a carboxy group, and that is easy to handle. Another object of the present invention is to provide an electrode and a battery obtained using the electrode mixture. [Means for solving the problem]

[0007] [1] The present invention provides an electrode mixture comprising a vinylidene fluoride copolymer having a structural unit derived from vinylidene fluoride and a structural unit derived from a vinyl compound having a carboxy group, and an electrode active material coated with carbon, wherein the vinylidene fluoride copolymer, the electrode active material, and a carbon-coated electrode active material having a BET specific surface area of ​​220 to 280 m 2 The present invention provides an electrode mixture, wherein when a slurry for viscosity measurement is prepared by mixing carbon nanotubes having a viscosity of 7 to 11 nm, polyvinylpyrrolidone, and N-methylpyrrolidone in a mass ratio of 1.3:52.5:1.1:0.1:45.0, the slurry for viscosity measurement satisfies the following requirements (A) and (B): Requirement (A): At 25°C, a shear rate of 40 s using an E-type viscometer -1 The slurry viscosity V measured 30 seconds after the start of stirring 40 is between 1000 mPa·s and 10000 mPa·s Requirement (B): At 25°C, a shear rate of 1 s using an E-type viscometer -1 The slurry viscosity V1 measured 120 seconds after the start of stirring and the slurry viscosity V40 But V1 / V 40 ≦15 [2] The present invention provides the slurry viscosity V of the viscosity measurement slurry. 40 is 1000 mPa·s or more and 10000 mPa·s or less, and the slurry viscosity V1 and the slurry viscosity V 40 is V1 / V 40 The electrode mixture according to [1] satisfies the condition of ≦12. [3] The present invention provides an electrode mixture according to [1] or [2], wherein the weight-average molecular weight Mwa of the vinylidene fluoride copolymer is 50,000 or more, and when the vinylidene fluoride copolymer is modified with a labeling substance consisting of 1-bromomethylpyrene to determine the weight-average molecular weight Mwc of a carboxyl group-containing vinylidene fluoride copolymer that absorbs light at a wavelength of 345 nm, the Mwc is less than 0.90 relative to the Mwa. [4] The present invention provides an electrode mixture according to any one of [1] to [3], wherein the amount of carbon coating on the electrode active material is 0.5% by mass or more and 3.0% by mass or less with respect to the mass of the electrode active material. [5] The present invention provides the electrode mixture according to any one of [1] to [4], wherein the vinyl compound is a compound represented by the following general formula (1): [ka] (In general formula (1), R 1 , R 2 , R 3 each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 5 carbon atoms, and X represents a hydroxy group or -Y-COOH (wherein Y represents a divalent atomic group containing either an oxygen atom or a nitrogen atom, having 1 to 10 atoms in the main chain, and having a molecular weight of 500 or less)

[0008] [6] An electrode is provided, which contains the solid content of the electrode mixture according to any one of the above [1] to [5]. [7] A battery is provided, comprising the electrode described in [6] above. [Effects of the Invention]

[0009] According to the present invention, there is provided an electrode mixture that is easy to handle and that contains a carbon-coated electrode active material and a vinylidene fluoride copolymer having a carboxy group. Further, there are also provided an electrode and a battery obtained using the electrode mixture. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1. Electrode mixture The electrode mixture of the present invention is a composition containing a vinylidene fluoride copolymer having structural units derived from vinylidene fluoride and structural units derived from a vinyl compound having a carboxy group, and a carbon-coated electrode active material (hereinafter also simply referred to as "active material"). The electrode mixture may further contain a conductive aid, a solvent, other additives, etc. When the electrode mixture contains a solvent, the vinylidene fluoride copolymer may be dissolved in the solvent or may be dispersed in the solvent. The electrode mixture is usually in the form of a slurry, but is not limited to this.

[0011] As mentioned above, when an electrode mixture (slurry) is prepared by mixing a vinylidene fluoride copolymer having carboxyl groups with a carbon-coated active material (e.g., LFP or LFMP), it is difficult to form an electrode (mixture layer). Generally, LFP, LFMP, and other active materials have small particle sizes and are coated with carbon, resulting in a large surface area and the presence of many functional groups, such as OH groups, on the surface. Therefore, these functional groups are likely to interact with the carboxyl groups of the vinylidene fluoride copolymer. Therefore, when a typical vinylidene fluoride copolymer is used, a strong network originating from the active material is formed within the electrode mixture, making it difficult to form a mixture layer.

[0012] In contrast, the vinylidene fluoride copolymer and electrode active material contained in the electrode mixture of the present invention satisfy the following requirements (A) and (B) when a slurry for viscosity measurement is prepared by mixing the vinylidene fluoride copolymer, the electrode active material, specific carbon nanotubes (CNTs), polyvinylpyrrolidone (PVP), and N-methylpyrrolidone (NMP) in a predetermined ratio. The specific composition of the slurry for viscosity measurement will be described later. Requirement (A): At 25°C, a shear rate of 40 s using an E-type viscometer -1 The slurry viscosity V measured 30 seconds after the start of stirring 40 is between 1000 mPa·s and 10000 mPa·s Requirement (B): At 25°C, a shear rate of 1 s using an E-type viscometer -1 The slurry viscosity V1 measured 120 seconds after the start of stirring and the above-mentioned slurry viscosity V 40 But V1 / V 40 ≦15

[0013] According to the inventors' intensive studies, it has become clear that when the above-mentioned viscosity measurement slurry is prepared, an electrode mixture using a vinylidene fluoride copolymer and an electrode active material that satisfy the above-mentioned requirement (B) is very easy to handle and enables the preparation of a desired mixture layer, even though the vinylidene fluoride copolymer has a carboxy group and the electrode active material is coated with carbon.

[0014] Furthermore, when the viscosity measurement slurry contains a vinylidene fluoride copolymer and an active material that satisfies the above-mentioned requirement (A), the electrode mixture is less likely to have uneven thickness after the mixture layer is formed. In other words, it has also been revealed that the mixture layer has good formability. There are no particular limitations on the method for adjusting the viscosity measurement slurry to satisfy requirements (A) and (B). Examples include adjusting the amount of carboxyl group-containing structural units in the vinylidene fluoride copolymer, adjusting the amount of carboxyl group-containing polymer (the carboxyl group-containing copolymer described below), and adjusting the molecular weight of the carboxyl group-containing copolymer. Below, the vinylidene fluoride copolymer, its physical properties, active material, and other components that may be contained in the electrode mixture of the present invention are described in detail.

[0015] (Vinylidene fluoride copolymer) As described above, the vinylidene fluoride copolymer is a copolymer obtained by copolymerizing vinylidene fluoride with a vinyl compound having a carboxy group, and optionally with other compounds. The vinylidene fluoride copolymer is an aggregate of many polymers. The vinylidene fluoride copolymer (aggregate of many polymers) preferably includes a polymer containing structural units derived from vinylidene fluoride and structural units derived from a vinyl compound having a carboxy group (also referred to herein as a "carboxy group-containing vinylidene fluoride copolymer" or a "carboxy group-containing copolymer"), and a polymer mainly composed of structural units derived from vinylidene fluoride and not containing structural units derived from a vinyl compound. In this specification, unless otherwise specified, the term "vinylidene fluoride copolymer" refers to the entire aggregate of many polymers (such as a carboxy group-containing copolymer or a collection of polymers mainly composed of structural units derived from vinylidene fluoride).

[0016] The amount of vinylidene fluoride-derived structural units in the vinylidene fluoride copolymer is preferably 90.00 mol% or more, and more preferably 95.00 mol% or more and 99.98 mol% or less, relative to 100.00 mol% of all structural units in the vinylidene fluoride copolymer. When the amount of vinylidene fluoride-derived structural units is 90.0 mol% or more, physical properties specific to vinylidene fluoride are more likely to be obtained.

[0017] On the other hand, the amount of the constituent units derived from a vinyl compound having a carboxy group in the vinylidene fluoride copolymer is preferably 0.01 mol% or more and 0.80 mol% or less, more preferably 0.02 mol% or more and 0.50 mol% or less, relative to 100.0 mol% of all constituent units of the vinylidene fluoride copolymer. If the amount of the constituent units derived from the vinyl compound is 0.01 mol% or more, when an electrode is formed using the electrode mixture, the adhesion of the vinylidene fluoride copolymer to the current collector is likely to be further improved. On the other hand, if the amount of the constituent units derived from the vinyl compound is 0.80 mol% or less, the slurry viscosity V1 (hereinafter also referred to as "initial viscosity") of the slurry for viscosity measurement is more likely to fall within the desired range. The amount of the constituent units derived from the vinyl compound is determined by neutralization titration or 1 It can be determined from H-NMR spectrum, etc.

[0018] Here, the structure of the vinyl compound is not particularly limited, and it may be a compound having a vinyl group polymerizable with vinylidene fluoride and a carboxy group. The number of carboxy groups contained in the vinyl compound may be one or two or more. In this specification, an acid anhydride structure composed of two carboxy groups is also considered to be a type of carboxy group. The vinylidene fluoride copolymer may contain only one type of structural unit derived from the vinyl compound, or may contain two or more types. Examples of preferred vinyl compounds include compounds represented by the following general formula (1): [ka] In general formula (1), R 1 , R 2 , R 3each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 5 carbon atoms. Examples of the alkyl group having 1 to 5 carbon atoms include linear or branched alkyl groups, specific examples of which include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, a sec-butyl group, an isobutyl group, a t-butyl group, and a pentyl group. Among these, a methyl group, an ethyl group, or a butyl group is preferred from the viewpoint of availability and the like. In particular, from the viewpoint of less steric hindrance during polymerization with vinylidene fluoride, R 1 , R 2 , and R 3 are each independently a hydrogen atom or a methyl group.

[0019] In the general formula (1), X is a hydroxy group or a group represented by -Y-COOH, where Y represents a divalent atomic group containing either an oxygen atom or a nitrogen atom, having a main chain with 1 to 10 atoms, and having a molecular weight of 500 or less.

[0020] The atomic group (Y) may be linear, branched, or cyclic, or may be a combination thereof. Among these, the atomic group (Y) is preferably linear or branched, from the viewpoint of less occurrence of steric hindrance during polymerization with vinylidene fluoride.

[0021] The number of atoms in the main chain of the atomic group (Y) may be from 1 to 10, and preferably from 2 to 8. In this specification, the main chain of the atomic group (Y) refers to the longest chain among the chains connecting the carbonyl group in general formula (1) and the carboxy group of -Y-COOH.

[0022] Here, the atomic group (Y) contains either one or both of an oxygen atom and a nitrogen atom (hereinafter, these are also collectively referred to as "heteroatoms"). The number of heteroatoms in the atomic group (Y) is preferably 1 to 10, more preferably 1 to 5. When the atomic group (Y) contains two or more heteroatoms, these may be the same type of atom or different types of atoms. The heteroatom may be contained in any structure (functional group) and may be located at any position within the atomic group (Y). Examples of structures (functional groups) containing these heteroatoms include an ether bond, an ester bond, a carbonyl group, a carboxy group, an amide group, and a hydroxy group. Among these, an ether bond, an ester group, a carbonyl group, a carboxy group, an amide group, and a hydroxy group are preferred.

[0023] The structure of the atomic group (Y) is not particularly limited, and can be, for example, a structure in which a hydrocarbon group such as an alkylene group or an alkyl group is bonded to the above-mentioned heteroatom-containing structure (functional group). The molecular weight of the atomic group (Y) is sufficient as long as it is 500 or less, and is preferably 30 to 200 from the viewpoint of polymerization reactivity.

[0024] Specific examples of the compound represented by the general formula (1) include (meth)acrylic acid, (meth)acryloyloxyethyl succinate, (meth)acryloyloxypropyl succinate, 2-carboxyethyl (meth)acrylate, 2-carboxymethyl (meth)acrylate, (meth)acryloyloxyethyl phthalate, and (meth)acrylamide-based compounds such as N-carboxyethyl (meth)acrylamide. In this specification, (meth)acrylic represents methacrylic, acrylic, or a mixture thereof; (meth)acrylate represents methacrylate, acrylate, or a mixture thereof; and (meth)acryloyl represents methacryloyl, acryloyl, or a mixture thereof.

[0025] The compound represented by the above general formula (1) is more preferably acrylic acid, acryloyloxyethyl succinate, acryloyloxypropyl succinate, 2-carboxyethyl acrylate, or 2-carboxymethyl acrylate, from the viewpoints of availability and reactivity with vinylidene fluoride.

[0026] However, the vinyl compound is not limited to the compound represented by general formula (1). Examples of vinyl compounds other than the compound represented by general formula (1) include unsaturated dibasic acids such as maleic acid, fumaric acid, and itaconic acid; unsaturated dibasic acid anhydrides such as maleic anhydride and itaconic anhydride; and unsaturated dibasic acid monoesters such as monomethyl fumarate, monoethyl fumarate, monomethyl maleate, monoethyl maleate, monomethyl citraconic acid, monoethyl citraconic acid, monomethyl phthalate, monoethyl phthalate, monomethyl itaconate, and monoethyl itaconate.

[0027] Furthermore, the vinylidene fluoride copolymer may partially contain structural units derived from compounds (other compounds) other than vinylidene fluoride and the above vinyl compounds having a carboxy group, as long as the purpose and effects of the present invention are not impaired. The vinylidene fluoride copolymer may contain only one type of structural unit derived from the other compounds, or may contain two or more types. However, the total amount of structural units derived from the other compounds relative to 100.0 mol% of all structural units of the vinylidene fluoride copolymer is preferably 10.0 mol% or less, more preferably 5.0 mol% or less. These amounts are 19 F-NMR spectrum and 1 It is identified by H-NMR spectroscopy, neutralization titration, etc.

[0028] Examples of other compounds include fluorine-based vinyl compounds having a vinyl group and a fluorine atom or a fluorine-containing alkyl group in one molecule. Examples of fluorine-based vinyl compounds include vinyl fluoride, trifluoroethylene, tetrafluoroethylene, chlorotrifluoroethylene, hexafluoropropylene, and perfluoroalkyl vinyl ethers such as perfluoromethyl vinyl ether. Examples of other compounds also include compounds having a vinyl group but not containing fluorine. Examples of such compounds include unsaturated hydrocarbon compounds such as ethylene and propylene.

[0029] Here, the weight-average molecular weight Mwa of the vinylidene fluoride copolymer is not particularly limited, but is preferably 50,000 or more, more preferably 200,000 to 4,000,000, and even more preferably 250,000 to 3,000,000. When the weight-average molecular weight Mwa of the vinylidene fluoride copolymer is within this range, the viscosity measurement slurry more easily satisfies the above-mentioned requirements (A) and (B), and thus the heat resistance and strength of the electrode (electrode mixture layer) obtained using the electrode mixture are more likely to be improved. In this specification, the weight-average molecular weight Mwa of the vinylidene fluoride copolymer is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). In GPC, N,N-dimethylacetamide is used as the eluent, and the value is determined using a refractive index (RI) detector.

[0030] Here, among the vinylidene fluoride copolymers, the weight average molecular weight Mwc of the carboxy group-containing copolymer is preferably 10,000 or more, more preferably 25,000 or more and 4,700,000 or less, even more preferably 50,000 or more and 3,800,000 or less, and particularly preferably 63,000 or more and 2,800,000 or less.

[0031] Furthermore, the value of the weight-average molecular weight Mwc to the weight-average molecular weight Mwa of the vinylidene fluoride copolymer, i.e., Mwc / Mwa, is preferably less than 0.9, more preferably 0.25 or more but less than 0.90, and even more preferably 0.25 or more but less than 0.85. When this ratio is less than 0.90, the slurry for viscosity measurement is more likely to satisfy the above-mentioned requirements (A) and (B).

[0032] In this specification, the weight-average molecular weight Mwc of the carboxyl group-containing copolymer is a value measured as follows. A labeling substance (1-bromomethylpyrene) for labeling the carboxyl groups and potassium carbonate are mixed with a vinylidene fluoride copolymer to esterify the carboxyl groups. This results in a vinylidene fluoride copolymer modified with pyrene. Gel permeation chromatography (GPC) is then performed using N,N-dimethylacetamide as the eluent. The weight-average molecular weight Mwc is a polystyrene-equivalent value measured using an ultraviolet-visible (UV-visible) detector (detection wavelength: 345 nm). The pyrene structure has a characteristic absorption in the ultraviolet-visible region, strongly absorbing light at a wavelength of 345 nm. Therefore, the weight-average molecular weight Mwc of the carboxyl group-containing copolymer can be determined by esterifying the carboxyl groups with 1-bromomethylpyrene.

[0033] The inherent viscosity of the vinylidene fluoride copolymer is preferably 0.5 dL / g or more and 6.0 dL / g or less, more preferably 0.5 dL / g or more and 5.0 dL / g or less, and even more preferably 0.8 dL / g or more and 4.5 dL / g or less. When the inherent viscosity is 0.5 dL / g or more, the adhesive strength of the vinylidene fluoride copolymer to the active material and the current collector tends to be increased. On the other hand, when the inherent viscosity is 5.0 dL / g or less, the initial viscosity when measuring the viscosity of the electrode mixture does not become too high, and workability is particularly good. The inherent viscosity (η i) indicates logarithmic viscosity. First, 80 mg of vinylidene fluoride copolymer is dissolved in 20 ml of N,N-dimethylformamide, and the viscosity is measured using an Ubbelohde viscometer in a thermostatic bath at 30°C. Then, the viscosity is calculated from the obtained value based on the following formula. η i =(1 / C)·ln(η / η0) In the above formula, η is the viscosity of the solution, η0 is the viscosity of the solvent N,N-dimethylformamide alone, and C is the concentration of vinylidene fluoride copolymer in the solution, ie, 0.4 g / dl.

[0034] The amount of vinylidene fluoride copolymer contained in the solid content of the electrode mixture (components excluding components that volatilize during mixture layer formation) is preferably 0.2 to 20% by mass, more preferably 0.2 to 10% by mass, and even more preferably 0.2 to 5% by mass. When the amount of vinylidene fluoride copolymer is within this range, a mixture layer with high strength is likely to be obtained.

[0035] The vinylidene fluoride copolymer can be prepared by copolymerizing vinylidene fluoride, the vinyl compound, and, if necessary, other compounds. Examples of the copolymerization method include suspension polymerization, emulsion polymerization, solution polymerization, etc., but suspension polymerization is preferred from the viewpoint of reducing impurities.

[0036] In suspension polymerization using water as a dispersion medium, a suspending agent such as methyl cellulose, propoxylated methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyethylene oxide, or gelatin is added in an amount of 0.005 to 1.0 part by mass, preferably 0.01 to 0.4 part by mass, per 100 parts by mass of all monomers used in the copolymerization (vinylidene fluoride, vinyl compounds having carboxy groups, and other monomers).

[0037] Examples of polymerization initiators that can be used include diisopropyl peroxydicarbonate, di-normal propyl peroxydicarbonate, di-normal heptafluoropropyl peroxydicarbonate, isobutyryl peroxide, di(chlorofluoroacyl)peroxide, di(perfluoroacyl)peroxide, and t-butyl peroxypivalate. The amount used is 0.05 to 10 parts by mass, and preferably 0.15 to 5 parts by mass, relative to 100 parts by mass of all monomers used in copolymerization (vinylidene fluoride, a vinyl compound having a carboxy group, and other monomers as needed).

[0038] It is also possible to adjust the degree of polymerization of the resulting vinylidene fluoride copolymer by adding a chain transfer agent such as ethyl acetate, methyl acetate, diethyl carbonate, acetone, ethanol, n-propanol, acetaldehyde, propylaldehyde, ethyl propionate, carbon tetrachloride, etc. When a chain transfer agent is used, the amount used is usually 0.01 to 5 parts by mass, preferably 0.01 to 3 parts by mass, based on 100 parts by mass of all monomers used in the copolymerization (vinylidene fluoride, vinyl compound having a carboxy group, and any other monomers).

[0039] The amount of all monomers (vinylidene fluoride, vinyl compound having a carboxy group, and other monomers) used in copolymerization is usually 1:1 to 1:10, preferably 1:2 to 1:5, in terms of the mass ratio of all monomers to water.

[0040] The polymerization temperature T is the 10-hour half-life temperature T of the polymerization initiator. 10 It is usually selected according to T 10 -25℃≦T≦T 10 +25°C. For example, the T 10are 54.6°C and 40.5°C, respectively (see NOF Corporation product catalog). Therefore, in polymerizations using t-butyl peroxypivalate and diisopropyl peroxydicarbonate as polymerization initiators, the polymerization temperature T is appropriately selected within the ranges of 29.6°C≦T≦79.6°C and 15.5°C≦T≦65.5°C, respectively. The polymerization time is not particularly limited, but considering productivity and the like, it is preferably 100 hours or less. The polymerization is usually carried out under increased pressure, preferably 2.0 to 10.0 MPa-G.

[0041] Here, methods for adjusting the weight-average molecular weight Mwc of the carboxyl group-containing copolymer to a desired range include, for example, the following two methods. However, the methods are not limited to these. The first method is a method in which vinylidene fluoride (or other compounds) and the entire amount of the vinyl compound having a carboxyl group are mixed together and then polymerization is initiated. The second method is a method in which vinylidene fluoride (or other compounds) is polymerized to a certain extent, and then the entire amount of the vinyl compound having a carboxyl group is added to the reaction system in a short period of time and further polymerization is carried out. An example of adding the vinyl compound having a carboxyl group in a short period of time includes setting the addition rate of the vinyl compound having a carboxyl group to 0.2 parts by mass / hour or more when the total monomers used in the copolymerization is 100 parts by mass. This allows the weight-average molecular weight Mwc to be adjusted to a desired range. The weight-average molecular weight Mwa of the vinylidene fluoride copolymer can be adjusted by the amount of polymerization initiator, the amount of chain transfer agent, the polymerization temperature, etc.

[0042] (active material) The active material contained in the electrode mixture of the present invention is preferably a compound coated with carbon, with the carbon coating amount being 0.5% by mass or more and 3.0% by mass or less relative to the mass of the active material. The carbon coating amount is determined by separating the active material from the vinylidene fluoride copolymer, dissolving the separated active material in aqua regia by heating, suction filtering through a membrane filter, and calculating the acid-insoluble content (carbon amount) from the amount remaining on the filter. The carbon coating amount is preferably 0.5% by mass or more and 2.7% by mass or less, more preferably 0.5% by mass or more and 2.5% by mass or less.

[0043] Here, the type of active material is not particularly limited as long as the above-mentioned carbon coating amount is satisfied, but generally, the surface of positive electrode active materials such as LiFePO4 (LFP) and LiFeMnPO4 (LFMP) is often carbon-coated to reduce particle resistance, making it easier to satisfy the above-mentioned coverage rate. When such a carbon-coated active material is used, it may be difficult to apply the electrode mixture, but by setting the slurry viscosity within the above-mentioned range, the electrode mixture becomes easier to handle and the desired electrode can be easily formed.

[0044] Furthermore, the above-mentioned LFP and LFMP have a relatively small average particle size. When the average particle size of the active material in the electrode mixture is small, it is usually difficult to apply the electrode mixture. However, by setting the slurry viscosity within the above-mentioned range, it becomes easier to form a desired electrode. In this specification, the average particle size of the active material refers to the particle size cumulative fraction 50% (Dv50) in a volume-based particle size cumulative diagram specified in accordance with JISK 1474. The average particle size (Dv50) is preferably 15 μm or less, and more preferably 0.1 μm or more and 15 μm or less. However, the average particle size of the active material is not limited to this range.

[0045] The amount of active material contained in the electrode mixture is appropriately selected depending on the application of the electrode mixture, etc., but is preferably 50% by mass or more and 99.9% by mass or less of the total amount of solids in the electrode mixture. When the amount of active material is within this range, for example, sufficient charge / discharge capacity is obtained, and battery performance is likely to be good.

[0046] (Conductive additive) The electrode mixture may further contain a conductive aid. The conductive aid contained in the electrode mixture is not particularly limited as long as it is a compound that can further increase the conductivity between the active materials or between the active material and the current collector. Examples of the conductive aid include acetylene black, ketjen black, carbon black, graphite powder, carbon nanofibers, carbon nanotubes, and carbon fibers. Among these, it is preferable to contain at least one or both of carbon black and carbon nanotubes from the viewpoint of improving conductivity.

[0047] The amount of the conductive additive contained in the electrode mixture is appropriately selected depending on the type of the conductive additive, etc. From the viewpoint of improving both the conductivity and the dispersibility of the conductive additive, the amount is preferably 0.1% by mass to 15% by mass or less, more preferably 0.1% by mass to 7% by mass, and even more preferably 0.1% by mass to 5% by mass, relative to the total amount of solids in the electrode mixture.

[0048] (solvent) The electrode mixture may contain a solvent. The solvent may be a nonaqueous solvent or water. The nonaqueous solvent may also be a polar solvent. Examples of polar solvents include amide compounds such as N,N-dimethylformamide, N,N-dimethylacetamide, and N-methylpyrrolidone; alcohol compounds such as methanol, ethanol, isopropyl alcohol, 2-ethyl-1-hexanol, 1-nonanol, lauryl alcohol, and tripropylene glycol; amine compounds such as o-toluidine, m-toluidine, and p-toluidine; imide compounds such as 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide; lactone compounds such as γ-butyrolactone and δ-butyrolactone; sulfoxide / sulfone compounds such as dimethyl sulfoxide and sulfolane; ether compounds such as tetrahydrofuran, diethyl ether, 1,4-dioxane, and diethylene glycol dimethyl ether; and ketone compounds such as acetone, 2-butanone, methyl isobutyl ketone, and cyclohexanone. The electrode mixture may contain only one of the above solvents, or may contain two or more of them. Among these, N-methylpyrrolidone is particularly preferred from the viewpoint that the above-mentioned slurry viscosity can be easily satisfied.

[0049] The total amount of solvent in the electrode mixture is not particularly limited as long as it satisfies the above-mentioned slurry viscosity, but is usually preferably 10 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the above-mentioned active material.

[0050] (Other ingredients) The electrode mixture may further contain a dispersant, an adhesive aid, a thickener, etc., and known compounds can be used for these. Examples of the dispersant include polyvinylpyrrolidone, methyl cellulose, methoxylated methyl cellulose, propoxylated methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyethylene oxide, polypropylene oxide, gelatin, etc. Examples of the adhesive aid include poly(meth)acrylic acid, metal poly(meth)acrylates such as sodium poly(meth)acrylate, and carboxymethyl cellulose. The amount of these is not particularly limited as long as it does not impair the object and effect of the present invention, but is preferably 15 mass% or less based on the total solid content of the electrode mixture.

[0051] The electrode mixture may further contain additives such as phosphorus compounds, sulfur compounds, nitrogen compounds such as amine compounds and ammonium compounds, organic acids, organic esters, various silane-based, titanium-based, and aluminum-based coupling agents, and resins such as vinylidene fluoride polymers other than the vinylidene fluoride copolymers described above, polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), and polyacrylonitrile (PAN). These additives are not particularly limited as long as they do not impair the objectives and effects of the present invention, but the amount is preferably 15% by mass or less of the total solid content of the electrode mixture.

[0052] (Physical properties of electrode mixture) The vinylidene fluoride copolymer and active material contained in the electrode mixture of the present invention are a vinylidene fluoride copolymer, an electrode active material, and a polymer having a BET specific surface area of ​​220 to 280 m 2When a viscosity measurement slurry is prepared by mixing carbon nanotubes having a viscosity of 1.3 / g and a tube diameter of 7 to 11 nm with polyvinylpyrrolidone and N-methylpyrrolidone in a mass ratio of 1.3:52.5:1.1:0.1:45.0, the viscosity measurement slurry satisfies the above-mentioned requirements (A) and (B). Here, the tube diameter of the carbon nanotubes used to prepare the viscosity measurement slurry is the average value obtained by observing the cross sections of 10 or more carbon nanotubes using an electron microscope such as a SEM or TEM and measuring the diameter from the observed image. The BET specific surface area and tube diameter of carbon nanotubes vary, but even commercially available carbon nanotubes typically have a certain range. Therefore, it is difficult to fix them to a specific value. Furthermore, if carbon nanotubes whose BET specific surface area and tube diameter fall within the specified range are used, the values ​​are unlikely to deviate significantly, and therefore, in the opinion of the inventors, there is no problem.

[0053] As described above, the viscosity measurement slurry was measured at 25°C using an E-type viscometer at a shear rate of 40 s -1 The slurry viscosity V measured 30 seconds after the start of stirring 40 The viscosity of the slurry is 1000 mPa·s or more and 10000 mPa·s or less (requirement (A)). 40 The viscosity measurement slurry was measured using an E-type viscometer at 25°C for 60 seconds, and then at a shear rate of 40 s -1 The value was read 30 seconds after rotating the rotor. 40 From the viewpoint of ease of handling during molding of the mixture layer, the viscosity is preferably 1000 mPa·s or more and 5000 mPa·s or less, and more preferably 1000 mPa·s or more and 4000 mPa·s or less.

[0054] The viscosity measurement slurry was measured at 25°C using an E-type viscometer at a shear rate of 1 s -1 When the slurry viscosity measured 120 seconds after the start of stirring is V1, the slurry viscosity V1 and the slurry viscosity V 40 But V1 / V 40 ≦15 (Requirement (B)), but V1 / V 40is preferably 2 or more and 12 or less, more preferably 3 or more and 11 or less. The slurry viscosity V1 is measured by measuring the viscosity of the slurry for viscosity measurement at a shear rate of 1 s after keeping the slurry at 25°C for 60 seconds using an E-type viscometer. -1 The slurry viscosity V1 is measured 120 seconds after the rotor starts rotating at a speed of 1000 kJ / s. The slurry viscosity V1 is preferably 2000 mPa·s or more and 60000 mPa·s or less, and more preferably 5000 mPa·s or more and 30000 mPa·s or less. When the slurry viscosity V1 is in this range, the handleability of the electrode mixture tends to be further improved.

[0055] The slurry viscosity of the actual electrode mixture is not particularly limited, but it is preferable that the above requirements be satisfied when the slurry viscosity is specified using an actual electrode mixture in the same manner as the slurry for viscosity measurement.

[0056] (Method for preparing electrode mixture) The electrode mixture may be prepared by mixing all of the components at once, or by first mixing some of the components and then mixing the remaining components.

[0057] 2.Electrode The electrode mixture described above can be used to form a mixture layer of an electrode of various nonaqueous electrolyte secondary batteries. The electrode of a nonaqueous electrolyte secondary battery includes, for example, a current collector and a mixture layer disposed on the current collector. The electrode mixture described above can be used to form the mixture layer.

[0058] Current collector The current collector is a terminal for extracting electricity. The material of the current collector is not particularly limited, and metal foil or metal mesh of aluminum, copper, iron, stainless steel, steel, nickel, titanium, etc. can be used. Alternatively, the current collector may have a layer containing carbon black or the like formed on the surface of another medium, or may have the above-mentioned metal foil or metal mesh applied thereto.

[0059] Mixture layer The mixture layer is a layer formed by applying the electrode mixture described above onto a current collector and solidifying it. That is, the mixture layer contains at least the vinylidene fluoride compound and the active material described above. The mixture layer may be formed on only one surface of the current collector, or may be disposed on both surfaces.

[0060] The mixture layer contains at least the components contained in the electrode mixture described above, i.e., the vinylidene fluoride copolymer and the active material, and further contains various additives such as a conductive aid, a dispersant, an adhesive aid, a thickener, etc. as needed, which are the same as those described for the electrode mixture.

[0061] The thickness of the mixture layer is not particularly limited, but in one example, it is preferably 1 μm or more and 300 μm or less. The weight of the mixture layer formed on one surface of the current collector is not particularly limited, and can be any weight, but in one example, it is 50 g / m 2 More than 500g / m 2 Preferably less than 100 g / m 2 More than 300g / m 2 The following is more preferred:

[0062] The mixture layer can be formed by carrying out a step of applying the electrode mixture onto a current collector and a step of solidifying the applied mixture.

[0063] The method for applying the electrode mixture is not particularly limited, and methods such as a doctor blade method, a reverse roll method, a comma bar method, a gravure method, an air knife method, a die coating method, and a dip coating method can be used.

[0064] After application of the electrode mixture, the mixture is heated at a desired temperature to dry the solvent. In one example, the drying temperature is preferably 60°C or higher and 200°C or lower, and more preferably 80°C or higher and 150°C or lower. Heating may be performed multiple times at different temperatures. The solvent in the mixture may be dried under atmospheric pressure, pressure, or reduced pressure, or may be dried in an environment of air, nitrogen, argon, or the like. After drying, a heat treatment may be further performed.

[0065] After the electrode mixture is applied and dried, a pressing process may be further performed. The pressing process can improve the electrode density. In one example, the pressing pressure is preferably 1 kPa or more and 10 GPa or less.

[0066] 3.Battery The above-mentioned electrode mixture can be used for electrodes of various non-aqueous electrolyte secondary batteries, as described above, and may also be used to form other layers of non-aqueous electrolyte secondary batteries. [Example]

[0067] Specific examples of the present invention will be described below together with comparative examples, but the present invention is not limited to these.

[0068] 1.Methods for measuring and evaluating various physical properties The methods for measuring the inherent viscosity of the vinylidene fluoride copolymer, the weight-average molecular weight Mwa of the vinylidene fluoride copolymer, and the weight-average molecular weight Mwc of the carboxyl group-containing copolymer are shown below. The methods for measuring the average particle size (Dv50) of the electrode active material and the carbon coating amount are also shown below. Furthermore, the vinylidene fluoride copolymer and active material used in the examples were used to prepare predetermined slurries for viscosity measurement, and the viscosities of the slurries (V1 and V 40 The measurement method for ) is shown below.

[0069] (1) Inherent viscosity of vinylidene fluoride copolymer The inherent viscosity of the vinylidene fluoride copolymer was measured as follows. First, 80 mg of vinylidene fluoride copolymer was dissolved in 20 ml of N,N-dimethylformamide, and the viscosity was measured using an Ubbelohde viscometer in a thermostatic bath at 30°C. Then, from the obtained value, the inherent viscosity (η i ) was calculated. η i =(1 / C)·ln(η / η0) In the above formula, η is the viscosity of the solution, η0 is the viscosity of the solvent N,N-dimethylformamide alone, and C is the concentration of vinylidene fluoride copolymer in the solution, i.e., 0.4 g / dl.

[0070] (2) Weight average molecular weight Mwa of vinylidene fluoride copolymer The weight-average molecular weight Mwa of the vinylidene fluoride copolymer prepared in each Example and Comparative Example was measured using a differential refractometer (RI). Specifically, GPC (gel permeation chromatography) was performed under the following conditions, and Mwa was determined using a differential refractive index detector. Separation column: Shodex KD-807, KD-806M Detector: JASCO RI-4030 (differential refractive index detector) Eluent: 10 mM LiBr-N,N-dimethylacetamide (DMAc) solution Eluent flow rate: 0.5 mL / min Column temperature: 40℃ Standard polymer for calibration curve: TSK standard POLY(STYRENE) (standard polystyrene) (manufactured by Tosoh Corporation)

[0071] (3) Weight average molecular weight Mwc of carboxyl group-containing copolymer To 10 mg of DMAc, 10 mg of vinylidene fluoride copolymer prepared in each Example and Comparative Example, 2 mg of 1-bromomethylpyrene, and 2 mg of potassium carbonate were added, and the mixture was dissolved and reacted while stirring in a thermostatic shaking bath at 50°C, and the potassium carbonate was removed using a 0.45 μm filter. As a result, the carboxy group of the carboxy group-containing copolymer in the vinylidene fluoride copolymer was labeled with 1-bromomethylpyrene.

[0072] The weight-average molecular weight of the carboxyl group-containing copolymer (a polymer that absorbs light at a wavelength of 345 nm) contained in the vinylidene fluoride copolymer labeled with 1-bromomethylpyrene was determined using the following UV-vis detector. The measurement conditions were the same as for Mwa above, except for the detector. The detection wavelength was 345 nm, and the weight-average molecular weight Mwc of the carboxyl group-containing copolymer was determined.

[0073] (4) Measurement of the average particle diameter Dv50 of the electrode mixture 0.1 g of dispersant (cationic surfactant "SN Wet 366" (manufactured by San Nopco) was added to 0.01 g of active material, and the dispersant was allowed to soak into the sample. Next, 20 mL of pure water was added, and the sample was dispersed in an ultrasonic cleaner for approximately 5 minutes. After that, the particle size distribution in the particle size range of 0.1 to 1000 μm was determined using a particle size distribution measuring device (manufactured by Microtrac: MT3300EXII). The dispersion medium was pure water, and the refractive index of the dispersion medium was 1.333. From the obtained particle size distribution, the particle size at which the cumulative frequency was 50% on a volume basis was calculated, and Dv50 was calculated.

[0074] (5) Method for determining the amount of carbon coating on the electrode mixture 500 mg of active material was weighed into a beaker, 40 mL of water and aqua regia (3 mL of nitric acid + 9 mL of hydrochloric acid) were added, and the mixture was heated and dissolved. The mixture was then suction filtered through a membrane filter, and the acid-insoluble matter (amount of carbon coating) was calculated from the remaining amount.

[0075] (6) Slurry viscosity of electrode mixture Slurries for viscosity measurement were prepared as follows using the combinations of vinylidene fluoride copolymers and active materials used in the Examples and Comparative Examples. Vinylidene fluoride copolymer, active material, and BET specific surface area of ​​220 to 280 m 2 Carbon nanotubes having a mass of 1.3:52.5:1.1:0.1:45.0 were mixed with polyvinylpyrrolidone and N-methylpyrrolidone in a weight ratio of 1.3:52.5:1.1:0.1:45.0. The viscosity of the prepared viscosity measurement slurry was measured. The viscosity measurement slurry was placed in an E-type viscometer (RE-215 type viscometer manufactured by Toki Sangyo Co., Ltd., rotor 3° × R14) immediately after preparation. After keeping the temperature at 25°C for 60 seconds, the viscosity measurement slurry was heated at a shear rate of 1 s -1 The rotor was rotated at 120 seconds, and the viscosity measured 120 seconds after the start of rotor rotation was determined as the slurry viscosity V1. Furthermore, after a 60-second incubation period at 25°C in the above-mentioned device, the sample was subjected to a shear rate of 40 s -1 The rotor is rotated at , and the viscosity 30 seconds after the rotor starts rotating is the slurry viscosity V40 was identified as. Furthermore, at a specified shear rate of 1 s -1 The viscosity of the slurry is V1 and the shear rate is 40 s -1 Slurry viscosity V 40 The viscosity ratio (V1 / V 40 ) was identified.

[0076] 2. Material Preparation The following materials were prepared as electrode mixtures in the Examples and Comparative Examples.

[0077] (1)Active material ·LFP-A: Carbon coverage: 1.0%, average particle diameter Dv50: 2μm) ·LFP-B: Carbon coverage: 1.4%, average particle diameter Dv50: 4μm) ·LFP-C: Carbon coverage: 2.1%, average particle diameter Dv50: 10μm) LFMP: carbon coating amount: 2.0%, average particle size Dv50: 1 μm) LCO (lithium cobalt oxide): carbon coating amount: 0.0%, average particle size Dv50: 2 μm

[0078] (2) Vinylidene fluoride copolymer VDF / APS-1: Prepared in Synthesis Example 1 below VDF / APS-2: Prepared using Synthesis Example 2 below VDF / AA-1: Prepared in Synthesis Example 3 below VDF / AA-2: Prepared in Synthesis Example 4 below

[0079] <Synthesis Example 1> A 2-liter autoclave was charged with 1240 g of ion-exchanged water as a dispersion medium, 0.4 g of Metolose SM-100 (Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspension agent, 2.0 g of acryloyloxypropyl succinic acid (APS), 1.40 g of a 50% by mass diisopropyl peroxydicarbonate-HFE-347pc-f solution as a polymerization initiator, 0.8 g of ethyl acetate as a chain transfer agent, and 400 g of vinylidene fluoride, and the temperature was raised to 45°C over 2 hours. While maintaining the temperature at 45°C, the reaction was continued until the pressure in the system decreased to 1.5 MPa. After the polymerization was completed, the polymer slurry was heat-treated at 95°C for 60 minutes, dehydrated, washed with water, and then dried at 80°C for 20 hours to obtain a powder of vinylidene fluoride copolymer (VDF / APS-1), which is a copolymer of vinylidene fluoride (VDF) and acryloyloxypropyl succinic acid (APS). The inherent viscosity, weight-average molecular weight Mwa, and weight-average molecular weight Mwc of the carboxyl group-containing copolymer of the vinylidene fluoride copolymer are shown in Table 1 below.

[0080] <Synthesis Example 2> A 2-liter autoclave was charged with 1054.5 g of ion-exchanged water as a dispersion medium, 0.23 g of Metrolose SM-100 (Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspension agent, 0.07 g of APS, 3.50 g of a 50 wt% diisopropyl peroxydicarbonate-HFE-347pc-f solution as a polymerization initiator, and 400 g of vinylidene fluoride. The mixture was heated to 26°C over 55 minutes. While maintaining the temperature at 26°C, 2 hours after the start of the temperature increase, 0.86 g of a 5 wt% aqueous APS solution (solute equivalent) was added over 4.3 hours. After the pressure had dropped 0.2 MPaG from the pressure at the end of the temperature increase, the mixture was heated to 55°C over 40 minutes. The reaction was continued while maintaining the temperature at 55°C until the pressure in the system decreased to 1.3 MPaG. The resulting polymer slurry was treated in the same manner as in Synthesis Example 1 to obtain a powder of vinylidene fluoride copolymer (VDF / APS-2), which is a copolymer of vinylidene fluoride (VDF) and acryloyloxypropyl succinic acid (APS). The inherent viscosity, weight-average molecular weight Mwa, and weight-average molecular weight Mwc of the carboxyl group-containing copolymer of the vinylidene fluoride copolymer are shown in Table 1 below.

[0081] <Synthesis Example 3> A 2-liter autoclave was charged with 1056 g of ion-exchanged water as a dispersion medium, 0.44 g of Metrolose SM-100 (Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspension agent, 9.37 g of acrylic acid (AA), 5.28 g of a 50% by mass concentration tertiary butyl peroxypivalate-HFE-347pc-f solution as a polymerization initiator, 0.44 g of ethyl acetate as a chain transfer agent, and 440 g of vinylidene fluoride, and the temperature was raised to 52°C over 110 minutes. While maintaining the temperature at 52°C, the reaction was continued until the pressure in the system decreased to 4.7 MPaG. The resulting polymer slurry was treated in the same manner as in Synthesis Example 1 to obtain a powder of vinylidene fluoride copolymer (VDF / AA-1), which is a copolymer of vinylidene fluoride (VDF) and acrylic acid (AA). The inherent viscosity, weight-average molecular weight Mwa, and weight-average molecular weight Mwc of the carboxyl group-containing copolymer of the vinylidene fluoride copolymer are shown in Table 1 below.

[0082] <Synthesis Example 4> A 2-liter autoclave was charged with 1056 g of ion-exchanged water as a dispersion medium, 0.44 g of Metolose SM-100 (Shin-Etsu Chemical Co., Ltd.) as a cellulose-based suspension agent, 0.22 g of acrylic acid (AA), 3.08 g of a 50% by weight solution of tertiary butyl peroxypivalate-HFE-347pc-f as a polymerization initiator, 0.44 g of isododecane as a chain transfer agent, and 440 g of vinylidene fluoride, and the mixture was heated to 52 °C over 110 minutes. While maintaining the temperature at 52 °C, 3.74 g of a 1% by weight aqueous AA solution (solute equivalent) was added to maintain the pressure immediately after the temperature increase. The reaction was continued until the pressure in the system decreased to 7.18 MPaG. The resulting polymer slurry was treated in the same manner as in Synthesis Example 1 to obtain a powder of vinylidene fluoride copolymer (VDF / AA-2), which is a copolymer of vinylidene fluoride (VDF) and acrylic acid (AA). The inherent viscosity, weight-average molecular weight Mwa, and weight-average molecular weight Mwc of the carboxyl group-containing copolymer of the vinylidene fluoride copolymer are shown in Table 1 below.

[0083] (3) Physical properties of vinylidene fluoride copolymer The physical properties of the vinylidene fluoride copolymer are shown below. [Table 1]

[0084] 3. Preparation of Electrode Mixture Each electrode mixture was prepared by the following method.

[0085] Example 1 LFP-A was used as the electrode active material, VDF / APS-1 was used as the vinylidene fluoride copolymer (binder), and a carbon nanotube (CNT) NMP dispersion was used as the conductive additive. These were then mixed using a planetary centrifugal mixer, Thinky Corporation's Awatori Rentaro ARE310, to prepare an electrode mixture. The mass ratio of the electrode active material, conductive additive, and binder in the resulting electrode mixture was 100:2:2.5, and the solids concentration was 55.0 mass%.

[0086] (Examples 2 to 5, Comparative Examples 1 to 5, and Reference Examples 1 and 2) As shown in Table 2, electrode mixtures were prepared in the same manner as in Example 1 above, except that the type of electrode active material, the type of vinylidene fluoride copolymer, and the solid content concentration in Example 4 and Comparative Example 4 were changed to 52%.

[0087] (evaluation) The electrode mixtures prepared in the above Examples and Comparative Examples were evaluated for their handling properties, fluidity, and thickness unevenness after forming the mixture layer.

[0088] (1) Liquidity assessment The flowability of the electrode mixture was evaluated according to the following criteria. ○: When the container containing the electrode mixture was tilted by 20°, the electrode mixture flowed. ×: When the container containing the electrode mixture was tilted at 20°, the electrode mixture did not flow, but when tilted at 45° or more, it flowed immediately.

[0089] (2) Uneven electrode thickness The mixture layer was applied to an aluminum current collector foil to a thickness of 300 μm, and then dried at 110° C. for 5 minutes and then at 130° C. for 2.5 minutes to form the electrode. The unevenness in electrode thickness after forming was measured with a thickness meter and evaluated according to the following criteria. ◯: Electrode thickness unevenness after coating and drying was 3 μm or less ×: Unevenness in electrode thickness after coating and drying was more than 3 μm

[0090] (result) [Table 2]

[0091] As shown in Table 2 above, when an electrode mixture was prepared using an active material not coated with carbon and a vinylidene fluoride copolymer having a carboxy group, no problems arose in the handling of the electrode mixture (Reference Examples 1 and 2). On the other hand, when an active material having a carbon coating amount of 0.5% by mass or more and 3% by mass or less was combined with a vinylidene fluoride copolymer having a carboxy group, the slurry viscosity V of the viscosity measurement slurry was 40 In the case of the combination of vinylidene fluoride copolymer and active material where the viscosity was more than 10,000 mPa·s (Comparative Example 2), the electrode thickness after the mixture layer was formed was significantly uneven. 40 Ratio of V1 / V 40 In the combination of the vinylidene fluoride copolymer and the active material where the viscosity V exceeds 15, the fluidity of the electrode mixture deteriorated and the handling was poor (Comparative Examples 1 to 5). 40 is 1000 or more and 10000 mPa·s or less, and the slurry viscosity V1 and the slurry viscosity V 40 Ratio of V1 / V 40 In the combination of the vinylidene fluoride copolymer and the active material where the σ is 15 or less, the fluidity of the electrode mixture was observed, the thickness unevenness of the electrode mixture layer was small, and the handling was very good (Examples 1 to 5). [Industrial Applicability]

[0092] According to the present invention, there is provided an electrode mixture that is easy to handle and that contains a carbon-coated electrode active material and a vinylidene fluoride copolymer having a carboxy group. The electrode mixture is very useful in the field of manufacturing various batteries.

Claims

1. a vinylidene fluoride copolymer having a structural unit derived from vinylidene fluoride and a structural unit derived from a vinyl compound having a carboxy group; a carbon-coated electrode active material; An electrode mixture comprising: The vinylidene fluoride copolymer, the electrode active material, and a BET specific surface area of ​​220 to 280 m ２ When a slurry for viscosity measurement was prepared by mixing carbon nanotubes having a viscosity of 7 to 11 nm, polyvinylpyrrolidone, and N-methylpyrrolidone in a mass ratio of 1.3:52.5:1.1:0.1:45.0, The electrode mixture, wherein the slurry for viscosity measurement satisfies the following requirements (A) and (B): Requirement (A): At 25°C, a shear rate of 40 s using an E-type viscometer －１ The slurry viscosity V measured 30 seconds after the start of stirring ４０ is 1000 mPa·s or more and 10000 mPa·s or less Requirement (B): At 25°C, a shear rate of 1 s using an E-type viscometer －１ The slurry viscosity V measured 120 seconds after the start of stirring １ and the slurry viscosity V ４０ But, V １ / V ４０ ≦15

2. The slurry viscosity V of the viscosity measurement slurry ４０ is 1000 mPa s or more and 10000 mPa s or less, The slurry viscosity V of the viscosity measurement slurry １ and the slurry viscosity V ４０ V １ / V ４０ ≦12, The electrode mixture according to claim 1 .

3. The weight average molecular weight M of the vinylidene fluoride copolymer is 50,000 or more, When the vinylidene fluoride copolymer is modified with a labeling substance consisting of 1-bromomethylpyrene and the weight average molecular weight Mwc of the carboxy group-containing vinylidene fluoride copolymer that absorbs light at a wavelength of 345 nm is specified, The Mwc is less than 0.90 relative to the Mwa. The electrode mixture according to claim 1 .

4. The amount of carbon coating on the electrode active material is 0.5% by mass or more and 3.0% by mass or less with respect to the mass of the electrode active material. The electrode mixture according to claim 1 .

5. The vinyl compound is a compound represented by the following general formula (1): The electrode mixture according to claim 1 . 【Chemical 1】 (In general formula (1), R １ , R ２ , R ３ each independently represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 5 carbon atoms, X represents a hydroxy group or -Y-COOH (Y represents a divalent atomic group containing either an oxygen atom or a nitrogen atom, having 1 to 10 atoms in the main chain, and having a molecular weight of 500 or less).

6. An electrode comprising the solid content of the electrode mixture according to any one of claims 1 to 5.

7. A battery comprising the electrode of claim 6.

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