Binder, electrode mixture, electrode, and battery

Abstract

The purpose of the present invention is to provide a binder which, even when mixed with an active material having a high nickel ratio and the like to prepare an electrode mixture, is unlikely to result in thickening or gelation in the electrode mixture. A binder that solves the above problem comprises a vinylidene fluoride-based polymer that includes a structural unit derived from vinylidene fluoride, wherein the vinylidene fluoride-based polymer exhibits an adsorption rate of not more than 16% with respect to a lithium metal oxide a that has a water content of not more than 500 ppm, a pH of 10.9, an average particle size D50 of 12 μm, and a specific surface area of 0.38m2 / g, LiNi0.78Co0.19Al0.03, as determined by a specific method.

Description

Binders, electrode mixtures, electrodes, and batteries

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

[0002] Vinylidene fluoride homopolymers and vinylidene fluoride-based polymers obtained by copolymerizing vinylidene fluoride with other monomers are widely used as binders for lithium-ion secondary batteries. Lithium-ion secondary batteries are used for a variety of purposes, and there is a strong demand for higher capacity. One method for increasing the capacity of lithium-ion secondary batteries is to use a ternary positive electrode active material with a high nickel ratio.

[0003] However, positive electrode active materials with a high nickel content often contain a large amount of base. Therefore, when an electrode mixture slurry containing a known vinylidene fluoride polymer and the positive electrode active material is prepared, the electrode mixture slurry tends to thicken and gel. Therefore, there is a need to suppress the thickening and gelling of the electrode mixture slurry.

[0004] For example, Patent Document 1 describes the addition of a dispersion resin having a polycyclic aromatic hydrocarbon group and a polymerization inhibitor in addition to a positive electrode active material and a polyvinylidene fluoride polymer.

[0005] Japanese Patent Application Laid-Open No. 2017-228412

[0006] However, even when other dispersion resins, polymerization inhibitors, and the like are added as in Patent Document 1, it is difficult to sufficiently suppress thickening and gelation of the electrode mixture slurry. Therefore, it has been desired to provide a binder that is less likely to cause thickening and gelation when made into an electrode mixture slurry, and an electrode mixture (electrode mixture slurry) containing such a binder.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a binder that is less likely to cause thickening or gelation of an electrode mixture slurry even when mixed with an active material having a high nickel ratio, as well as an electrode mixture, an electrode, and a battery that contain the binder.

[0008] [1] The present invention provides a binder containing a vinylidene fluoride polymer containing a structural unit derived from vinylidene fluoride, the vinylidene fluoride polymer being identified by the following method: ０．７８ Co ０．１９ Al ０．０３ , specific surface area 0.38m ２The binder has an adsorption rate of 16% or less for lithium metal oxide a having a molecular weight of 10 ... (3) The pre-adsorption sample is subjected to gel permeation measurement to identify the peak area A derived from the vinylidene fluoride polymer (a 10 mmol / L lithium bromide-containing N,N-dimethylacetamide solution is used as the mobile phase for the gel permeation measurement). (4) In an environment with a dew point of -30°C or less, the lithium metal oxide a, the vinylidene fluoride polymer solution, and N-methylpyrrolidone are mixed in a mass ratio of 100:25:6.8, and then kneaded using a planetary centrifugal mixer to prepare a slurry. (5) The slurry is stored for 7 days at a dew point of -30°C or less and at 21°C. (6) In an environment with a dew point of −30° C. or lower, the slurry is kneaded again using a planetary centrifugal mixer, and then the slurry is diluted with a 10 mmol / L lithium bromide-containing N,N-dimethylacetamide solution to obtain a diluted slurry having a vinylidene fluoride polymer concentration of 0.1% by mass, where the total of the vinylidene fluoride polymer and the solvent (N-methylpyrrolidone and the lithium bromide-containing N,N-dimethylacetamide solution) in the obtained diluted slurry is taken as 100% by mass. (7) In an environment with a dew point of −30° C. or lower, the lithium metal oxide a is removed from the diluted slurry by centrifugation to obtain a post-adsorption sample. (8) The post-adsorption sample is subjected to gel permeation measurement to identify the peak area B derived from the vinylidene fluoride polymer. (9) The adsorption rate is calculated from the peak area A and the peak area B according to the following formula: Adsorption rate = (peak area A - peak area B) / (peak area A) × 100

[0009] [2] The present invention provides the binder according to [1], wherein the amount of the vinylidene fluoride-derived structural units relative to the amount of all structural units of the vinylidene fluoride polymer is 90 mol % or more.

[0010] [3] The present invention provides an electrode mixture containing the binder according to the above [1] or [2] and an active material. [4] The present invention provides an electrode mixture containing the binder according to the above [1] or [2] and an active material. １－ａ Ni ｘ Co ｙ M ｚ O ２ (M represents Mn or Al, and a, x, y, and z respectively satisfy −0.5≦a≦0.5, 0.45<x<1, 0<y<1, 0<z<1, and x+y+z=1).

[0011] [5] The present invention provides an electrode comprising the solid content of the binder according to the above [1] or [2] and an active material.

[0012] [6] The present invention provides a battery comprising the electrode according to the above [5].

[0013] The binder of the present invention is unlikely to cause thickening or gelling of the electrode mixture even when mixed with an active material having a high nickel ratio, and therefore, the binder can provide a highly stable and high-quality electrode mixture (electrode mixture slurry), electrode, and battery.

[0014] 1. Binder The binder of the present invention may contain a specific vinylidene fluoride polymer, and may contain other components together with the vinylidene fluoride polymer, as necessary. Examples of other components include additives, solvents, etc.

[0015] The vinylidene fluoride polymer contained in the binder of the present invention is LiNi, which is specified by the following method. ０．７８ Co ０．１９ Al ０．０３ , specific surface area 0.38m ２The adsorption rate for lithium metal oxide a having a molecular weight of 1.01g / g, an average particle diameter D50 of 12 μm, a pH of 10.9, and a water content of 500 ppm or less is 16% or less, preferably 13% or less, more preferably 12% or less, and even more preferably 10% or less. The lithium metal oxide a may be a commercially available product (e.g., 503LP manufactured by JFE Mineral Co., Ltd.) or may be one prepared by a known method.

[0016] (Method for Determining Adsorption Rate) (1) In an environment with a dew point of −30°C or lower, a vinylidene fluoride polymer and N-methylpyrrolidone are mixed to prepare a vinylidene fluoride polymer solution having a vinylidene fluoride polymer concentration of 6% by mass. (2) In an environment with a dew point of −30°C or lower, the vinylidene fluoride polymer solution prepared in (1) is diluted with a 10 mmol / L N,N-dimethylacetamide solution containing lithium bromide to obtain a pre-adsorption sample having a 0.1% by mass vinylidene fluoride polymer concentration. (3) The pre-adsorption sample prepared in (2) is subjected to gel permeation measurement to determine the peak area A derived from the vinylidene fluoride polymer. In this case, a 10 mmol / L N,N-dimethylacetamide solution containing lithium bromide is used as the mobile phase for the gel permeation measurement. (4) In an environment with a dew point of −30° C. or less, the lithium metal oxide a, the vinylidene fluoride polymer solution prepared in (1), and N-methylpyrrolidone are mixed in a mass ratio of 100:25:6.8, and then kneaded using a planetary centrifugal mixer to prepare a slurry. (5) The slurry prepared in (4) is stored for 7 days at a dew point of −30° C. or less and 21° C. (6) In an environment with a dew point of −30° C. or less, the slurry stored in (5) is kneaded again, and then the slurry is diluted with a 10 mmol / L N,N-dimethylacetamide solution containing lithium bromide to obtain a diluted slurry having a vinylidene fluoride polymer concentration of 0.1% by mass, where the total of the vinylidene fluoride polymer and the solvent (N-methylpyrrolidone and the lithium bromide-containing N,N-dimethylacetamide solution) in the obtained diluted slurry is taken as 100% by mass. (7) In an environment with a dew point of -30°C or less, the lithium metal oxide a is removed by centrifugation from the diluted slurry prepared in (6) to obtain a post-adsorption sample. (8) The post-adsorption sample prepared in (7) is subjected to gel permeation measurement to identify the peak area B derived from the vinylidene fluoride polymer. (9) The adsorption rate is calculated from the peak area A obtained in (3) and the peak area B obtained in (8) based on the following formula: Adsorption rate = (peak area A - peak area B) / (peak area A) × 100

[0017] As described above, when a binder containing a conventional vinylidene fluoride polymer is used and an active material containing a large amount of base is prepared as an electrode mixture (electrode mixture slurry), the electrode mixture tends to thicken and gel. According to the inventors' intensive studies, it has been found that the base contained in the active material induces a dehydrofluorination reaction of the vinylidene fluoride polymer. Then, the polyene-(CH═CF) generated in the vinylidene fluoride polymer is dehydrofluorinated. ｎ The vinylidene fluoride polymer interacts with the active material, causing the vinylidene fluoride polymer to adsorb to the active material. The adsorption of the vinylidene fluoride polymer to multiple active materials creates a crosslinked structure between the multiple active materials via the adsorbed vinylidene fluoride polymer. When the density of the crosslinked structure (crosslink density) increases, a network connecting multiple active materials is formed, which causes thickening and gelation. In contrast, even when the vinylidene fluoride polymer contained in the binder of the present invention is mixed with an active material containing a large amount of base to prepare an electrode mixture (electrode mixture slurry), the electrode mixture is less likely to thicken or gel. This is because the adsorption rate of the vinylidene fluoride polymer in the binder to the metal oxide a is 16% or less. Because the vinylidene fluoride polymer in the binder has low adsorption properties for the active materials, crosslinked structures via the vinylidene fluoride polymer are less likely to form between multiple active materials when the binder and active materials are mixed. Furthermore, even if a crosslinked structure is partially formed, it is thought that the crosslink density is unlikely to increase, and therefore thickening or gelation is unlikely to occur.

[0018] In the above method for determining the adsorption rate, the above metal oxide a (LiNi ０．８ Co ０．１ Al ０．１ O ２ , LiNi ０．７８ Co ０．１９ Al ０．０３ O ２ ) to determine the adsorption rate.

[0019] The lithium metal oxide a has a specific surface area of ​​0.38 m ２ / g, average particle diameter D ５０The pH here is the value measured by adding 49 g of ultrapure water to 1 g of lithium metal oxide a, stirring for 10 minutes, and then measuring the pH of the water, and represents the amount of base contained in the lithium metal oxide a. In addition, in this specification, the average particle diameter D ５０ Unless otherwise specified, the values ​​are measured by the following method: 50 mg of lithium metal oxide a is added to 20 mL of water containing a nonionic surfactant, and the mixture is dispersed by ultrasonic treatment to prepare a sample. The sample is measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3000II manufactured by Microtrac-Bell), and the particle size at which the cumulative frequency is 50% on a number basis is determined as the average particle size D ５０ In this case, the analysis is performed assuming that the refractive index of lithium metal oxide a is 1.71. The specific surface area of ​​lithium metal oxide a can be measured by a general BET flow method using a mixed gas of 20% nitrogen and 80% helium.

[0020] The lithium metal oxide a contains a relatively large amount of base due to its high nickel ratio. Therefore, if the adsorption rate of the vinylidene fluoride polymer to such lithium metal oxide a is 16% or less, it is clear that thickening and gelling of the electrode mixture (electrode mixture slurry) is unlikely to occur even when the vinylidene fluoride polymer is combined with another positive electrode active material. In other words, the binder of the present invention is unlikely to cause thickening and gelling of the electrode mixture (electrode mixture slurry) even when the electrode mixture (electrode mixture slurry) is prepared by combining the binder with an electrode active material other than the lithium metal oxide a (NCA).

[0021] In addition, to control the moisture content in the slurry when determining the adsorption rate, the lithium metal oxide a, vinylidene fluoride polymer, and N-methylpyrrolidone are all used with a moisture content of 500 ppm or less. The moisture content can be measured by coulometric titration using a general Karl Fischer moisture meter. Furthermore, as described above, the methods (1) to (7) for determining the adsorption rate in this application must be performed in an environment with a dew point of −30°C or less.

[0022] A 10 mmol / L N,N-dimethylacetamide solution containing lithium bromide is used as the mobile phase for gel permeation chromatography (GPC) measurements to determine the adsorption rate. A detector capable of detecting the weight concentration of vinylidene fluoride polymer in the measurement sample is used. Examples of detectors include a differential refractometer detector and an evaporative light scattering detector, but it is preferable to use a differential refractometer detector.

[0023] Furthermore, the method of kneading the slurry in determining the adsorption rate can be a method using commercially available devices such as a rotation / revolution mixer, a planetary disper, or a homodisper, but as mentioned above, it is preferable to use a rotation / revolution mixer. During kneading, heat generation is suppressed so that the surface temperature of the slurry is 40° C. or less. Means for suppressing heat generation during kneading of the slurry include adjusting the kneading time and number of times, and allowing the slurry to cool between kneadings.

[0024] Here, the vinylidene fluoride polymer contained in the binder of the present invention is not particularly limited in structure as long as it contains at least a structural unit derived from vinylidene fluoride and satisfies the above-mentioned adsorption rate. However, the amount of the structural units derived from vinylidene fluoride relative to the amount of all structural units of the vinylidene fluoride polymer is preferably 90.0 mol% or more, more preferably 93.0 mol% to 99.8 mol%, even more preferably 96.0 mol% to 99.7 mol%, and particularly preferably 99.3 mol% to 99.7 mol%. When the amount of the structural units derived from vinylidene fluoride is 90.0 mol% or more, physical properties specific to vinylidene fluoride are easily obtained. On the other hand, the vinylidene fluoride copolymer may be a copolymer of vinylidene fluoride and one or more other monomers. The above-mentioned adsorption rate can be adjusted by the type of monomer copolymerized with vinylidene fluoride. The method for making the adsorption rate of a vinylidene fluoride polymer 16% or less is not particularly limited, and examples include using, as the monomer, one containing at least one atom selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms (hereinafter also simply referred to as "halogen atoms other than fluorine"); increasing the content of the monomer; increasing the random ratio (described below) of structural units derived from the monomer; increasing the amount of halogen atoms other than fluorine in the vinylidene fluoride polymer; decreasing the molecular weight of the vinylidene fluoride polymer, etc. These methods make it easier for the adsorption rate to fall within the desired range.

[0025] Examples of monomers that can easily increase the content or random ratio of monomer-derived structural units contained in the vinylidene fluoride polymer include monomers having a (meth)acrylate structure, a (meth)acrylamide structure, or a vinyl ester structure; and monomers having an unsaturated dibasic acid monoester structure, such as a fumaric acid monoester structure, a maleic acid monoester structure, a citraconic acid monoester structure, or an itaconic acid monoester structure.

[0026] An example of a vinylidene fluoride polymer satisfying the above adsorption rate includes a vinylidene fluoride polymer containing a structural unit derived from vinylidene fluoride and a structural unit derived from a compound represented by the general formula (1) described below (hereinafter also referred to as "compound (1)") and / or a structural unit derived from a compound represented by the general formula (2) described below (hereinafter also referred to as "compound (2)"). The vinylidene fluoride polymer may contain only one of the structural units derived from compound (1) and the structural units derived from compound (2), or may contain both. Furthermore, the vinylidene fluoride polymer may partially contain structural units derived from compounds other than these (hereinafter also referred to as "other compounds"), as long as the purpose and effects of the present invention are not impaired. The vinylidene fluoride polymer will be described in detail below, but the vinylidene fluoride polymer contained in the binder of the present invention is not limited to vinylidene fluoride polymers having the above structure.

[0027] In vinylidene fluoride polymers containing structural units derived from compound (1) and / or compound (2), the amount of structural units derived from vinylidene fluoride is preferably 90.0 mol% or more and 99.8 mol% or less, more preferably 93.0 mol% or more and 99.8 mol% or less, still more preferably 96.0 mol% or more and 99.7 mol% or less, and particularly preferably 99.3 mol% or more and 99.7 mol% or less, relative to the amount of all structural units of the vinylidene fluoride polymer. When the amount of structural units derived from vinylidene fluoride is 90.0 mol% or more, physical properties specific to vinylidene fluoride are easily obtained. On the other hand, when the amount of structural units derived from vinylidene fluoride is 99.8 mol% or less, it indicates that the amount of structural units derived from compound (1) and / or structural units derived from compound (2), described below, is sufficiently large. As a result, the adsorption rate is more likely to fall within the desired range. The amount of vinylidene fluoride-derived structural units in the vinylidene fluoride polymer is, for example, １９ It can be identified by F-NMR analysis, etc.

[0028] The structure of compound (1) is shown below. In general formula (1), R １ , R ２ , and R ３each independently represents a hydrogen 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.

[0029] On the other hand, X in the above general formula (1) represents an atomic group containing at least one heteroatom selected from the group consisting of oxygen, sulfur, nitrogen, and phosphorus atoms, and at least one atom selected from the group consisting of chlorine, bromine, and iodine atoms (hereinafter also simply referred to as "halogen atom other than fluorine"). The number of atoms in the main chain of the atomic group is 1 to 20, and the molecular weight of the atomic group is 552 or less.

[0030] The atomic group (X) may be linear, branched, or cyclic, or may be a combination thereof. Among these, the atomic group (X) is preferably linear or branched, from the viewpoint of less occurrence of steric hindrance during polymerization with vinylidene fluoride.

[0031] The number of atoms in the main chain of the atomic group (X) may be 1 or more and 20 or less, preferably 1 or more and 15 or less, and more preferably 1 or more and 10 or less. In this specification, the main chain of the atomic group (X) refers to the longest chain that is bonded to the carbonyl group in general formula (1). Furthermore, the number of atoms in the main chain refers to the number of carbon atoms and hetero atoms that constitute the main chain, and does not include the number of hydrogen atoms and halogen atoms other than fluorine that are bonded thereto. Furthermore, hydrogen atoms and halogen atoms other than fluorine that are bonded to the terminal carbon atoms or hetero atoms of the main chain are not counted in the number of atoms in the main chain.

[0032] The atomic group (X) may contain at least one heteroatom selected from an oxygen atom, a sulfur atom, a nitrogen atom, and a phosphorus atom. The number of heteroatoms is preferably 1 to 10, more preferably 1 to 7. When the atomic group (X) contains two or more heteroatoms, these may be the same type of atom or different types of atoms. The heteroatoms may constitute any structure (functional group). Furthermore, they may be present at any position within the atomic group (X). Examples of structures (functional groups) containing these heteroatoms include an ether bond, an ester group, a carbonyl group, a carboxy group, an amide group, a hydroxy group, a sulfide bond, a sulfonyl group, a thiol group, an amino group, a nitrile group, a nitro group, a phosphoryl group, and the like. Among these, an ether bond, an ester group, a carbonyl group, a carboxy group, an amide group, and a hydroxy group are preferred because of their excellent reactivity with vinylidene fluoride during polymerization of the vinylidene fluoride polymer.

[0033] The atomic group (X) contains at least one atom (a halogen atom other than fluorine) selected from a chlorine atom, a bromine atom, and an iodine atom. The number of halogen atoms other than fluorine contained in the atomic group (X) may be one or more, preferably 1 to 5, and more preferably 1 to 3. When the atomic group (X) contains two or more halogen atoms other than fluorine, these may be the same type of atom or different types of atoms. The bonding position of the halogen atoms other than fluorine in the atomic group (X) is not particularly limited. Among the halogen atoms other than fluorine, a chlorine atom is particularly preferred from the viewpoint of the stability of compound (1) during the polymerization process of a vinylidene fluoride polymer.

[0034] The structure of the atomic group (X) is not particularly limited, and may be, for example, a structure in which a hydrocarbon group such as an alkylene group or an alkyl group, the structure (functional group) containing a heteroatom, and a halogen atom other than fluorine are bonded. The molecular weight of the atomic group (X) may be 552 or less, preferably 50 to 352, and more preferably 50 to 252.

[0035] Specific examples of the compound (1) include 3-chloro-1-methacryloyloxypropyl 2-succinic acid, 3-chloro-1-acryloyloxypropyl 2-succinic acid, 1-chloro-2-(meth)acryloyloxypropyl 3-succinic acid, 1-(meth)acryloyloxy-3-chloropropyl succinate, 1-(meth)acryloyloxypropyl 2-(1-chloro)succinic acid, 1-(meth)acryloyloxypropyl 2-(2-chloro)succinic acid, 1-(meth)acryloyloxypropyl 2-(1-bromo)succinic acid, 1-(meth)acryloyloxypropyl Propyl 2-(2-bromo)succinate, 1-(meth)acryloyloxypropyl 2-(1,2-dichloro)maleate, 1-(meth)acryloyloxypropyl 2-(1-bromo)maleate, 1-(meth)acryloyloxypropyl 2-(2-bromo)maleate, (meth)acryloyloxyethyl(1-chloro)succinate, (meth)acryloyloxyethyl(2-chloro)succinate, (meth)acryloyloxyethyl(1-bromo)succinate, (meth)acryloyloxyethyl(2-bromo)succinate, (meth)acryloyloxyethyl(1, 2-dichloro)maleic acid, (meth)acryloyloxyethyl (1-bromo)maleic acid, (meth)acryloyloxyethyl (2-bromo)maleic acid, (meth)acryloyloxyethyl (4-chloro)phthalic acid, (meth)acryloyloxyethyl (tetrachloro)phthalic acid, 2-chloroethyl acrylate (CLEA), 2-chloroethyl methacrylate, 2,2,2-trichloroethyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 2-chloro-3-hydroxypropyl (meth)acrylate, (meth)acrylic acid 3-chloro-hydroxypropyl (meth)acrylate, chloromethyl (meth)acrylate, 3-chloro-2-butene (meth)acrylate, 2-(2-chloropropionyl)ethyl (meth)acrylate, 6-chlorohexyl (meth)acrylate, 4-chloro-3-methylphenyl (meth)acrylate, (N-chloro)2,2,6,6-tetramethyl-4-piperidyl (meth)acrylate, 2-bromoethyl (meth)allylate, 2-(2-bromopropionyl)ethyl (meth)acrylate, 2-(2-bromoisobutyryloxy)ethyl (meth)acrylate, and the like.In this specification, (meth)acrylic refers to methacrylic, acrylic, or a mixture thereof, (meth)acrylate refers to methacrylate, acrylate, or a mixture thereof, and (meth)acryloyl refers to methacryloyl, acryloyl, or a mixture thereof.

[0036] The compound (1) is preferably a compound represented by the following general formula (1a) (hereinafter also referred to as "compound (1a)"), in that it satisfies the above adsorption rate and has excellent reactivity with vinylidene fluoride in polymerization. R in the general formula (1a) １ , R ２ , and R ３ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and these are the same as R １ , R ２ , and R ３ is the same as:

[0037] Also, X １ represents an atomic group containing at least one atom (a halogen atom other than fluorine) selected from a chlorine atom, a bromine atom, and an iodine atom, having a main chain with 1 to 19 atoms and a molecular weight of 536 or less.

[0038] Atomic group (X １ The atomic group (X) can have a structure in which a hydrocarbon group such as an alkylene group or an alkyl group is bonded to a halogen atom other than fluorine. １ ) may further contain a structure (functional group) containing a heteroatom. The structure (functional group) containing a heteroatom is the same as the structure (functional group) containing a heteroatom contained in the atomic group (X) of the compound (1). １ The number of atoms in the main chain of the atomic group (X) may be 1 or more and 19 or less, preferably 1 or more and 14 or less, and more preferably 1 or more and 9 or less. １The main chain of the general formula (1a) refers to the longest chain that includes atoms bonded to the -C(=O)O- group. Furthermore, the number of atoms in the main chain refers to the number of carbon atoms and heteroatoms that constitute the main chain, and does not include the number of hydrogen atoms or halogen atoms other than fluorine bonded thereto. Furthermore, hydrogen atoms and halogen atoms other than fluorine bonded to the terminal carbon atoms or heteroatoms of the main chain are not counted in the number of atoms in the main chain. Furthermore, the atomic group (X １ The molecular weight of the copolymer (B) may be 536 or less, preferably 50 or more and 336 or less, and more preferably 50 or more and 236 or less.

[0039] Specific examples of compound (1a) include 3-chloro-1-methacryloyloxypropyl 2-succinic acid, 3-chloro-1-acryloyloxypropyl 2-succinic acid, 1-chloro-2-(meth)acryloyloxypropyl 3-succinic acid, 1-(meth)acryloyloxy-3-chloropropyl succinate, 1-(meth)acryloyloxypropyl 2-(1-chloro)succinic acid, 1-(meth)acryloyloxypropyl 2-(2-chloro)succinic acid, 1-(meth)acryloyloxypropyl 2-(1-bromo)succinic acid, 1-(meth)acryloyloxypropyl 2-(2-bromo)succinic acid, 1-(meth)acryloyloxypropyl 2-(1,2-dichloro)maleate, 1-(meth)acryloyloxypropyl 2-(1-bromo)maleate, 1-(meth)acryloyloxypropyl 2-(2-bromo)maleate, (meth)acryloyloxyethyl(1-chloro)succinate, (meth)acryloyloxyethyl(2-chloro)succinate, (meth)acryloyloxyethyl(1-bromo)succinate, (meth)acryloyloxyethyl(2-bromo)succinate, (meth)acryloyloxyethyl(1,2- (dichloro)maleic acid, (meth)acryloyloxyethyl (1-bromo)maleic acid, (meth)acryloyloxyethyl (2-bromo)maleic acid, (meth)acryloyloxyethyl (4-chloro)phthalate, (meth)acryloyloxyethyl (tetrachloro)phthalate, 2-chloroethyl acrylate (CLEA), 2-chloroethyl methacrylate, 2,2,2-trichloroethyl (meth)acrylate, 3-chloro-2-hydroxypropyl (meth)acrylate, 2-chloro-3-hydroxypropyl (meth)acrylate, (meth)acrylic acid Examples include 3-chlorohydroxypropyl, chloromethyl (meth)acrylate, 3-chloro-2-butene (meth)acrylate, 2-(2-chloropropionyl)ethyl (meth)acrylate, 6-chlorohexyl (meth)acrylate, 4-chloro-3-methylphenyl (meth)acrylate, (N-chloro)2,2,6,6-tetramethyl-4-piperidyl (meth)acrylate, 2-bromoethyl (meth)allylate, 2-(2-bromopropionyl)ethyl (meth)acrylate, and 2-(2-bromoisobutyryloxy)ethyl (meth)acrylate.

[0040] The structure of compound (2) is shown below. In general formula (2), R ４ , R ５ , and R ６ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. １ , R ２ , and R ３ From the viewpoint that steric hindrance is unlikely to occur during polymerization with vinylidene fluoride, R ４ , R ５ , and R ６ are preferably each independently a hydrogen atom or a methyl group.

[0041] On the other hand, Z in general formula (1) represents an atomic group containing at least one atom (a halogen atom other than fluorine) selected from a chlorine atom, a bromine atom, and an iodine atom, having 1 or more and 20 or less atoms in the main chain, and having a molecular weight of 564 or less.

[0042] The atomic group (Z) may be linear, branched, or cyclic, or may be a combination thereof. Among these, the atomic group (Z) is preferably linear or branched, from the viewpoint of less occurrence of steric hindrance during polymerization with vinylidene fluoride.

[0043] The number of atoms in the main chain of the atomic group (Z) may be 1 or more and 20 or less, preferably 1 or more and 15 or less, and more preferably 1 or more and 10 or less. In this specification, the main chain of the atomic group (Z) refers to the longest chain that is bonded to the ether bond in general formula (2). Furthermore, the number of atoms in the main chain refers to the number of carbon atoms and hetero atoms that constitute the main chain, and does not include the number of hydrogen atoms and halogen atoms other than fluorine that are bonded thereto. Furthermore, hydrogen atoms and detached halogen atoms bonded to the carbon atoms or hetero atoms at the terminals of the main chain are not counted in the number of atoms in the main chain.

[0044] The atomic group (Z) contains at least one atom (a halogen atom other than fluorine) selected from a chlorine atom, a bromine atom, and an iodine atom. The number of halogen atoms other than fluorine contained in the atomic group (Z) may be one or more, preferably 1 to 5, and more preferably 1 to 3. When the atomic group (Z) contains two or more halogen atoms other than fluorine, these may be the same type of atoms or different types of atoms. The bonding position of the halogen atoms other than fluorine in the atomic group (Z) is not particularly limited. Among halogen atoms other than fluorine, a chlorine atom is particularly preferred from the viewpoint of stability in the polymerization process of a vinylidene fluoride polymer.

[0045] The structure of the atomic group (Z) is not particularly limited, and may be, for example, a structure in which a hydrocarbon group such as an alkylene group or an alkyl group is bonded to a halogen atom other than fluorine. Furthermore, the atomic group (Z) may further contain a structure (functional group) containing a heteroatom. The structure (functional group) containing a heteroatom is the same as the structure (functional group) containing a heteroatom contained in the atomic group (X) of the compound (1). Here, the molecular weight of the atomic group (Z) may be 564 or less, preferably 50 or more and 364 or less, and more preferably 50 or more and 264 or less.

[0046] Specific examples of compound (2) include vinyl chloroacetate (VCAc), vinyl dichloroacetate, vinyl trichloroacetate, vinyl 3-chloropropionate, 1-chloroethyl vinyl ether, 2-chloroethyl vinyl ether, 3-chloropropyl vinyl ether, 4-chlorophenyl vinyl ether, 2-chlorophenyl vinyl ether, 6-chlorohexyl vinyl ether, 8-chlorooctyl vinyl ether, 2-bromoethyl vinyl ether, 4-bromophenyl vinyl ether, 1,2-dichloroethyl vinyl ether, and the like.

[0047] In addition, it is preferable that the compound (2) is a compound represented by the following general formula (2a) (hereinafter also referred to as “compound (2a)”), in that it satisfies the above adsorption rate and has excellent reactivity with vinylidene fluoride in polymerization. R in the general formula (2a) ４ , R ５ , and R６ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms, and these are the same as R ４ , R ５ , and R ６ is the same as:

[0048] Also, X １ represents an atomic group, and its structure is the same as that of the atomic group (X １ ) is the same as

[0049] Specific examples of the compound (2a) include vinyl chloroacetate (VCAc), vinyl dichloroacetate, vinyl trichloroacetate, vinyl 3-chloropropionate, and the like.

[0050] The numbers of atoms in the main chains of 2-chloroethyl acrylate (CLEA) and vinyl chloroacetate (VCAc) used in the examples described below are as follows:

[0051] CLEA corresponds to the compound represented by formula (1) and the compound represented by formula (1a). When the compound represented by formula (1) is a CLEA, the atomic group of X is —OCH ２ CH ２ The number of atoms in the main chain of the atomic group does not include the oxygen atom constituting the carbonyl group, the hydrogen atom constituting the methylene group, the hydrogen atom constituting the hydroxyl group, Cl which is a leaving halogen atom, and the methylene group in the side chain. That is, the main chain skeleton part of the atomic group is -O-C-C-, and the number of atoms is 3. Similarly, when the compound represented by formula (1a) is a CLEA, X １ The main chain of the atomic group represented by the formula has two atoms.

[0052] VCAc corresponds to the compound represented by formula (2) and the compound represented by formula (2a). When the compound represented by formula (2) is VCAc, the main chain of the atomic group represented by Z has two atoms, and when the compound represented by formula (2a) is VCAc, X １ The main chain of the atomic group represented by the formula has one atom.

[0053] In the vinylidene fluoride polymer containing the structural units derived from the compound (1) or (2), the total amount of the structural units derived from the compound (1) and the structural units derived from the compound (2) is preferably 10.0 mol or less, more preferably 0.2 mol% or more and 7.0 mol% or less, more preferably 0.3 mol% or more and 4.0 mol% or less, and particularly preferably 0.3 mol% or more and 0.7 mol% or less, relative to the total amount of the structural units derived from the vinylidene fluoride, the structural units derived from the compound (1), and the structural units derived from the compound (2). When the total amount of the structural units derived from the compound (1) and the structural units derived from the compound (2) is 0.2 mol% or more, the adsorption rate tends to fall within the desired range. On the other hand, when the total amount of the structural units derived from the compound (1) and the structural units derived from the compound (2) is 10.0 mol% or less, the physical properties specific to vinylidene fluoride are easily obtained.

[0054] The vinylidene fluoride polymer containing structural units derived from the compound (1) or compound (2) may partially contain structural units derived from compounds other than vinylidene fluoride, compound (1), and compound (2) (other compounds) to the extent that the adsorption rate can be within the desired range. The vinylidene fluoride polymer 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 all structural units of the vinylidene fluoride polymer is preferably 10.0 mol% or less, more preferably 5.0 mol% or less.

[0055] Examples of other compounds include fluorine-based vinyl compounds having a fluorine atom or a fluorine-containing alkyl group in addition to a vinyl 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 thereof include unsaturated hydrocarbon compounds such as ethylene and propylene; (meth)acrylic acid; 2-carboxyethyl (meth)acrylate; (meth)acryloyloxyethyl succinate; (meth)acryloyloxypropyl succinate; (meth)acryloyloxyethyl phthalate; 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 citraconate, monoethyl citraconate, monomethyl phthalate, monoethyl phthalate, monomethyl itaconate, and monoethyl itaconate.

[0056] Here, the vinylidene fluoride polymer containing the structural units derived from the compound (1) or compound (2) may be a copolymer of vinylidene fluoride, the compound (1) and / or the compound (2), and, if necessary, other compounds. The vinylidene fluoride polymer may be a block copolymer or a random copolymer, but is more preferably a random copolymer. In particular, the random ratio of the structural units derived from the compound (1) and the structural units derived from the compound (2) is preferably 0.5% or more and 100% or less, and more preferably 1.0% or more and 100% or less. The random ratio represents the degree to which the structural units derived from the compound (1) and the structural units derived from the compound (2) are randomly contained in the polymer chain of the vinylidene fluoride polymer, １９ F-NMR and １The random ratio is a value determined from the results of H-NMR measurement by the method described below. A high random ratio indicates that structural units derived from compound (1) and structural units derived from compound (2) are dispersed and arranged in the vinylidene fluoride polymer. As a result, when the random ratio is 0.5% or more, the adsorption ratio tends to decrease, and thickening and gelation of the electrode mixture are more likely to be suppressed.

[0057] In this specification, the random ratio of a vinylidene fluoride polymer can be determined by dividing the total number [mol %] of sequences containing a structural unit derived from compound (1) and sequences containing a structural unit derived from compound (2) in the vinylidene fluoride polymer by the total number [mol %] of structural units derived from compound (1) and structural units derived from compound (2) in the vinylidene fluoride polymer (random ratio [%] = (total number [mol %] of sequences containing a structural unit derived from compound (1) and sequences containing a structural unit derived from compound (2)) / (total number [mol %] of structural units derived from compound (1) and structural units derived from compound (2)) × 100). Here, the sequences containing structural units derived from compound (1) and the sequences containing structural units derived from compound (2) refer to structures in which one or more structural units derived from compound (1) are consecutive, which are present in isolation in a polymer chain, structures in which one or more structural units derived from compound (2) are consecutive, or structures containing one or more structural units derived from compound (1) and one or more structural units derived from compound (2), but which do not contain structural units derived from vinylidene fluoride between them. In other words, a high random rate means that the total number of sequences containing structural units derived from compound (1) and the total number of sequences containing structural units derived from compound (2) are large. The total number of sequences containing structural units derived from compound (1) and the total number of sequences containing structural units derived from compound (2) are: １９ The total number of structural units derived from compound (1) and structural units derived from compound (2) can be determined from the F-NMR spectrum. １ It can be determined from the H-NMR spectrum.

[0058] Here, the amount of halogen atoms other than fluorine contained in the vinylidene fluoride polymer is preferably 28 μmol / g or more and 1550 μmol / g or less, more preferably 28 μmol / g or more and 1100 μmol / g or less, and even more preferably 28 μmol / g or more and 650 μmol / g or less. The amount of halogen atoms other than fluorine can be measured, for example, by combustion ion chromatography as shown below. First, an absorption solution consisting of 30 mL of pure water and 50 μL of hydrogen peroxide is placed in a combustion flask, and a filter paper containing 10 mg of vinylidene fluoride polymer is burned in the basket of the combustion flask. After shaking the flask well, the absorption solution is made up to 50 mL with pure water, and ion chromatogram measurement is performed to determine the sum (A) of the peak areas of halogen atoms other than fluorine captured in the absorption solution. Similarly, the peak area (B) of halogen atoms other than fluorine obtained when only the filter paper is burned and measured is used as a blank, and the peak area difference (A - B) is determined. The amount of halogen atoms other than fluorine in the vinylidene fluoride polymer is calculated from the difference in peak area between a calibration curve obtained from measurements of standard samples of each halogen atom other than fluorine and (A-B). When the amount of halogen atoms other than fluorine in the vinylidene fluoride polymer is within the range, the adsorption rate is more likely to be reduced. The amount of halogen atoms other than fluorine can be adjusted to a desired range by adjusting the number of halogen atoms other than fluorine in the structures of compound (1) and compound (2) in the vinylidene fluoride polymer, or the amount of structural units derived therefrom.

[0059] Regardless of the structure of the vinylidene fluoride polymer contained in the binder, the melting point thereof is preferably 150°C or higher and 180°C or lower, more preferably 160°C or higher and 175°C or lower, and particularly preferably 165°C or higher and 175°C or lower. When the vinylidene fluoride polymer has a melting point of 150°C or higher, when the vinylidene fluoride polymer is used in an electrode mixture (electrode mixture slurry), the polymer is less likely to swell with an electrolyte, and the resulting battery tends to have good performance. On the other hand, when the melting point is 180°C or lower, the flexibility of the formed electrode tends to be good. The melting point of the vinylidene fluoride polymer can be determined by calorimetry using a differential scanning calorimeter (DSC).

[0060] The weight-average molecular weight of the vinylidene fluoride polymer contained in the binder is preferably 100,000 or more and 5,000,000 or less, more preferably 200,000 or more and 4,000,000 or less, even more preferably 200,000 or more and 3,000,000 or less, and particularly preferably 200,000 or more and 2,000,000 or less. The weight-average molecular weight is a polystyrene-equivalent value measured by gel permeation chromatography (GPC). When the weight-average molecular weight of the vinylidene fluoride polymer is within the above range, the vinylidene fluoride polymer is easily dissolved in a solvent. In measuring the weight-average molecular weight, the type of mobile phase for GPC is not limited as long as the weight-average molecular weight of the vinylidene fluoride polymer can be appropriately measured.

[0061] The inherent viscosity of the vinylidene fluoride polymer is preferably 0.5 dL / g or more and 8.0 dL / g or less, more preferably 1.0 dL / g or more and 5.0 dL / g or less, and most preferably 1.0 dL / g or more and 4.0 dL / g or less. If the inherent viscosity is 0.5 dL / g or more, when the vinylidene fluoride polymer is mixed with an active material or a current collector, the adhesive strength between these and the polymer is likely to be increased. On the other hand, if the inherent viscosity is 5.0 dL / g or less, the viscosity of the slurry does not become too high when an electrode mixture (electrode mixture slurry) is prepared, and workability is likely to be excellent. Inherent viscosity (η ｉ ) indicates logarithmic viscosity. First, 80 mg of vinylidene fluoride polymer 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 / η ０ In the above formula, η is the viscosity of the solution, η ０ is the viscosity of the solvent N,N-dimethylformamide alone, and C is the concentration of the vinylidene fluoride polymer in the solution, ie, 0.4 g / dl.

[0062] Regardless of the structure of the vinylidene fluoride polymer contained in the binder, it can be prepared by polymerizing vinylidene fluoride and, if necessary, other monomers (for example, the above-mentioned compound (1) or the above-mentioned compound (2)) by a known method. Examples of the polymerization method include suspension polymerization, emulsion polymerization, solution polymerization, etc., but suspension polymerization is preferred from the viewpoint that impurities are likely to be reduced.

[0063] In suspension polymerization using water as a dispersion medium, a suspending agent such as methyl cellulose, methoxylated methyl cellulose, propoxylated methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyethylene oxide, gelatin, etc. 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, compound (1), and / or compound (2), and other compounds copolymerized as necessary).

[0064] 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, preferably 0.15 to 5 parts by mass, based on 100 parts by mass of all monomers used in the copolymerization (vinylidene fluoride, compound (1) and / or compound (2), and other monomers copolymerized as needed).

[0065] It is also possible to adjust the degree of polymerization of the resulting vinylidene fluoride polymer 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, per 100 parts by mass of all monomers used in the copolymerization (vinylidene fluoride, compound (1) and / or compound (2), and other monomers copolymerized as necessary).

[0066] The amount of all monomers (vinylidene fluoride, compound (1) and / or compound (2), and other monomers copolymerized as necessary) used in the copolymerization is generally 1:1 to 1:10, preferably 1:2 to 1:5, in terms of the mass ratio of all monomers to water. The polymerization temperature T is the 10-hour half-life temperature T １０ is selected appropriately depending on the １０ -25℃≦T≦T １０ +25°C. For example, the T １０ are 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 is preferably 100 hours or less in consideration of productivity and the like. The polymerization is usually carried out under increased pressure, preferably 2.0 to 10.0 MPa-G.

[0067] By carrying out aqueous suspension polymerization under the above conditions, vinylidene fluoride, compound (1) and / or compound (2), and other monomers used as needed can be easily polymerized, and the vinylidene fluoride polymer of the present invention can be obtained.

[0068] The form of the binder is not particularly limited, and may be powder or liquid. The binder may be composed of the vinylidene fluoride polymer alone, or may contain a solvent, be dissolved in a solvent, or be dispersed in a solvent, as necessary.

[0069] The solvent may be a non-aqueous solvent or water. The non-aqueous solvent may also be a polar solvent (polar solvent). Examples of the polar solvent 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 binder may contain only one of the above solvents, or may contain two or more of them.

[0070] The amount of the solvent in the binder is preferably 50 parts by mass or more and 10,000 parts by mass or less, and more preferably 100 parts by mass or more and 5,000 parts by mass or less, relative to 100 parts by mass of the vinylidene fluoride polymer. When the amount of the solvent in the binder is within this range, the vinylidene fluoride polymer can be uniformly dispersed or dissolved in the solvent.

[0071] The binder may further contain various additives such as other resins such as acrylic resins, fillers such as inorganic fillers, dispersants, emulsifiers, etc., within the scope of not impairing the objects and effects of the present invention.

[0072] 2. Electrode Mixture The above-described binder and an active material (positive electrode active material or negative electrode active material) can be mixed to prepare an electrode mix for producing an electrode of a non-aqueous electrolyte secondary battery. The electrode mix may further contain a conductive aid, a solvent, other additives, etc.

[0073] The amount of binder-derived solids (particularly vinylidene fluoride polymer) relative to the total amount of binder-derived solids (total amount excluding components that volatilize during curing), the active material, and the conductive additive is preferably 0.2 mass% or more and 20 mass% or less, more preferably 0.2 mass% or more and 10 mass% or less, and even more preferably 0.2 mass% or more and 7 mass% or less.

[0074] Furthermore, even when the vinylidene fluoride polymer contained in the binder is mixed with an active material containing a large amount of base to prepare an electrode mixture (electrode mixture slurry), the electrode mixture is less likely to thicken or gel. Therefore, various active materials can be used as the active material for the electrode mixture. The active material is not particularly limited, and any known active material for a negative electrode (negative electrode active material) or active material for a positive electrode (positive electrode active material) can be used.

[0075] Examples of negative electrode active materials include carbon materials such as artificial graphite, natural graphite, non-graphitizable carbon, easily graphitizable carbon, activated carbon, or phenolic resin and pitch that have been fired and carbonized; metal and alloy materials such as Cu, Li, Mg, B, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr, and Y; and GeO, GeO ２ , SnO, SnO ２ , PbO, PbO ２ The negative electrode active material may be a material in which a coating is applied to the surface of the above-mentioned carbon material, metal / alloy material, metal oxide, etc. The negative electrode active material may be a commercially available product.

[0076] On the other hand, examples of the positive electrode active material include lithium-based positive electrode active materials containing lithium. Examples of the lithium-based positive electrode active material include LiCoO ２ , LiNi ｘ Co １－ｘ O ２ (0<x≦1) ２(M is one or more transition metals such as Co, Ni, Fe, Mn, Cr, and V, and Y is a chalcogen element such as O or S); ２ O ４ composite metal oxides having a spinel structure such as LiMaPO ４ (wherein Ma is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr); Li ２ MnO ３ -LiMbO ２ Lithium-excess solid solution represented by (Mb=Mn, Co, Ni); lithium titanate (Li ４ Ti ５ O １２ ); titanium oxide (TiO ２ ); Li ｓ Ni ｔ Co ｕ Al ｖ O ２ (0.9<s<1.3, 0.9<t+u+v<1.1); Li １－ａ Ni ｘ Co ｙ M ｚ O ２ (M represents Mn or Al, and a, x, y, and z satisfy −0.5≦a≦0.5, 0<x<1, 0<y<1, 0<z<1, and x+y+z=1, respectively). １－ａ Ni ｘ Co ｙ M ｚ O ２(M represents Mn or Al, and a, x, y, and z respectively satisfy the following conditions: -0.5≦a≦0.5, 0.45<x<1, 0<y<1, 0<z<1, and x+y+z=1) (lithium metal oxide b) is preferred. In the above formula, x is preferably 0.45<x<1, more preferably 0.75<x<1, y is preferably 0<y<0.35, more preferably 0<y<0.20, and z is preferably 0<z<0.20, more preferably 0<z<0.05. Even when the binder described above is mixed with such lithium metal oxide b to prepare an electrode mixture (electrode mixture slurry), the electrode mixture is less likely to thicken or gel, and a high-quality electrode mixture can be obtained. The positive electrode active material may be a compound having a surface coating applied thereto. Furthermore, the positive electrode active material may be a commercially available product.

[0077] 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 50.0 mass % to 99.9 mass % of the total amount of the solid content derived from the binder, the active material, and the conductive additive. When the amount of active material is within this range, for example, sufficient charge / discharge capacity can be obtained, and battery performance tends to be good.

[0078] The conductive additive 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 additive include acetylene black, ketjen black, carbon black, graphite powder, carbon nanofiber, carbon nanotube, and carbon fiber.

[0079] 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, based on the total amount of the solid content derived from the binder, the active material, and the conductive additive.

[0080] The electrode mixture may contain a solvent different from the solvent that the binder may contain, and the solvent can be selected from the solvents that the binder may contain.

[0081] The total amount of solvent in the electrode mixture (including the amount of non-aqueous solvent in the binder) is not particularly limited, but is usually preferably 10 parts by mass or more and 150 parts by mass or less per 100 parts by mass of the active material.

[0082] 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 salts of poly(meth)acrylic acid such as sodium poly(meth)acrylate, carboxymethyl cellulose, etc. The amount of these is not particularly limited as long as it does not impair the purpose and effects of the present invention, but is preferably 15% by mass or less based on the total amount of the solid content derived from the binder and the active material.

[0083] 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, vinylidene fluoride polymers other than the above-mentioned vinylidene fluoride polymers, polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), and other resins. These are not particularly limited as long as they do not impair the objects and effects of the present invention, but are preferably 15 mass% or less based on the total amount of the solid content derived from the binder and the active material.

[0084] 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.

[0085] The viscosity of the electrode mixture (electrode mixture slurry) is not particularly limited as long as it can prevent dripping, uneven coating, and delayed drying after coating when the electrode mixture is applied to form a mixture layer, and provides good workability and applicability when preparing the mixture layer. The viscosity is a value measured at 21°C using a Brookfield viscometer, rotating the spindle at 12 rpm with the Brookfield viscometer, and is the value measured 2 minutes after the start of spindle rotation.

[0086] 3. Electrode The above-described electrode mixture can be used to form a mixture layer of an electrode of various non-aqueous electrolyte secondary batteries. An electrode of a non-aqueous electrolyte secondary battery includes, for example, a current collector and a mixture layer disposed on the current collector. The above-described electrode mixture can be used to form the mixture layer.

[0087] 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.

[0088] 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 solid content of the binder described above (e.g., a vinylidene fluoride compound) and an active material. The mixture layer may be formed on only one surface of the current collector, or may be disposed on both surfaces.

[0089] The mixture layer contains at least the components contained in the above-mentioned electrode mixture (electrode mixture slurry), i.e., the solid content derived from the binder (vinylidene fluoride polymer) and the active material, and further contains various additives such as a conductive aid, a dispersant, an adhesive aid, a thickener, etc. as needed. These are the same as those described for the electrode mixture.

[0090] Here, the thickness of the mixture layer is not particularly limited, but in one example, it is preferably 1 μm or more and 1000 μm or less. The weight per unit area of ​​the mixture layer formed on one surface of the current collector is not particularly limited, and can be any weight per unit area. In one example, it is 50 g / m ２More than 1000g / m ２ Preferably, 100 g / m or less ２ More than 500g / m ２ The following is more preferred:

[0091] 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.

[0092] 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.

[0093] After application of the electrode mixture, the mixture is heated at an arbitrary temperature to dry the solvent. In one example, the drying temperature is preferably 60°C or higher and 500°C or lower, and more preferably 80°C or higher and 200°C or lower. Heating may be performed multiple times at different temperatures, or drying may be performed in an environment such as air, nitrogen, or argon. The solvent in the mixture may be dried under atmospheric pressure, pressure, or reduced pressure. After drying, a further heat treatment may be performed.

[0094] 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.

[0095] 4. Batteries The binders and electrode mixtures described above can be used in electrodes of various non-aqueous electrolyte secondary batteries, and may also be used to form other layers of non-aqueous electrolyte secondary batteries.

[0096] Specific examples of the present invention will be described below together with comparative examples, but the present invention is not limited to these.

[0097] (Methods for measuring and evaluating physical properties) In the examples and comparative examples described later, the inherent viscosity of the vinylidene fluoride polymer, the amount of halogen atoms other than fluorine, the comonomer content, the random ratio, the adsorption rate to NCA (lithium metal oxide a), and the viscosity of the electrode mixture slurry (immediately after preparation and after 3 days) were determined by the following methods.

[0098] Inherent Viscosity The inherent viscosity of a vinylidene fluoride polymer was measured as follows. First, 80 mg of a vinylidene fluoride polymer 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. ｉ =(1 / C)・ln(η / η ０ In the above formula, η is the viscosity of the solution, η ０ is the viscosity of the solvent N,N-dimethylformamide alone, and C is the concentration of the vinylidene fluoride polymer in the solution, ie, 0.4 g / dl.

[0099] Amount of halogen atoms other than fluorine An absorption solution consisting of 30 mL of pure water and 50 μL of hydrogen peroxide was placed in a combustion flask, and a filter paper containing 10 mg of vinylidene fluoride polymer was burned in the basket of the combustion flask. After shaking the flask well, the absorption solution was made up to 50 mL with pure water, and ion chromatogram measurement was performed to determine the peak area (A) attributable to halogen atoms other than fluorine dissolved in the absorption solution. Similarly, the peak area (B) measured by burning only the filter paper was used as a blank, and the peak area difference (A - B) was determined. The amount of halogen atoms other than fluorine in the vinylidene fluoride polymer was calculated from the peak area difference (A - B) and a calibration curve obtained from measurements of diluted solutions of the standard stock solution for each halogen atom other than fluorine.

[0100] Comonomer Content The proportion of constituent units (monomers) derived from monomers other than vinylidene fluoride (herein, compound (1) and / or compound (2), hereinafter also collectively referred to as "comonomers") among the constituent units (monomers) of a vinylidene fluoride polymer (comonomer content) was measured as follows. Using a nuclear magnetic resonance spectrometer (NMR, JEOL, JNM-ECZ600R / S1, frequency 600 MHz), dimethyl sulfoxide-d ６ of vinylidene fluoride polymer dissolved in １ H-NMR was measured. １The comonomer content was calculated from the H-NMR spectrum according to the following formula (1): Comonomer content (mol %)=(D) / (D+C)×100 (Formula 1) where (D) is the number of comonomers calculated from the integrated intensity of the peaks attributable to the comonomers, and (C) is the number of vinylidene fluorides calculated from the integrated intensity of the peaks attributable to vinylidene fluoride.

[0101] ・Random ratio The random ratio of vinylidene fluoride polymers is １ H-NMR and １９ Specifically, the compound was identified by F-NMR using a nuclear magnetic resonance spectrometer (JEOL, JNM-ECZ600R / S1, frequency 600 MHz). ６ of vinylidene fluoride polymer dissolved in １ H-NMR and １９ F-NMR was measured. １ The comonomer content was determined from the H-NMR spectrum. １９ In the spectrum obtained by F-NMR, when the peak derived from the normal bond of vinylidene fluoride polymer is set as the reference peak (-91.6 ppm), the CF derived from VDF adjacent to a monomer (comonomer) other than vinylidene fluoride is ２ is observed as a peak around -94 ppm. The integrated intensity of this peak around -94 ppm is expressed as follows in equation (2): １９ The number of sequences (mol %) containing structural units derived from the comonomer was calculated by dividing the result by the integral of all peaks obtained by F-NMR and then dividing by 2. Number of sequences (mol %) containing structural units derived from the comonomer = (integral intensity of the peak near -94 ppm) / (integral value of all peaks) / 2 × 100 (Equation 2) The calculated number of sequences (mol %) containing structural units derived from the comonomer (compound (1) and compound (2)) was then divided by the comonomer content (mol %) as shown in the following equation (3) and further multiplied by 100 to obtain the random ratio. Random ratio (%) = number of sequences (mol %) containing structural units derived from the comonomer / comonomer content (mol %) × 100 (Equation 3)

[0102] Method for Determining Adsorption Rate The adsorption rate of vinylidene fluoride polymers in the binders prepared in the Examples and Comparative Examples to NCA was determined according to the following procedures (1) to (9). The results are shown in Table 1. 503LP (LiNi) manufactured by JFE Mineral Co., Ltd. was used as NCA. ０．７８ Co ０．１９ Al ０．０３ , specific surface area 0.38m ２ / g, average particle diameter D ５０ The average particle diameter D of the NCA was 12 μm and pH 10.9. ５０ was measured using the laser diffraction / scattering particle size distribution analyzer under the conditions described above. The NCA, vinylidene fluoride polymer, and N-methylpyrrolidone (hereinafter referred to as NMP) all had a moisture content of 500 ppm or less. The following steps (1) to (7) were carried out in an environment with a dew point of -30°C or less.

[0103] (1) Each vinylidene fluoride polymer was mixed with N-methylpyrrolidone to prepare a vinylidene fluoride polymer solution having a vinylidene fluoride polymer concentration of 6% by mass. (2) The vinylidene fluoride polymer solution prepared in (1) was diluted with a 10 mmol / L N,N-dimethylacetamide solution containing lithium bromide so that the vinylidene fluoride polymer concentration was 0.1% by mass. The diluted liquid was used as a pre-adsorption sample. (3) The pre-adsorption sample prepared in (2) was subjected to GPC measurement using a 10 mmol / L N,N-dimethylacetamide solution containing lithium bromide as the mobile phase, and the peak area A derived from the vinylidene fluoride polymer was determined using a JASCO RI-4030 detector. (4) NCA, the vinylidene fluoride polymer solution prepared in (1), and N-methylpyrrolidone were mixed in a mass ratio of 100:25:6.8. The mixture was then kneaded using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro Model: ARE-310) to prepare a slurry. The kneading was carried out in multiple batches so that the surface temperature of the slurry immediately after kneading was 40°C or less, and the slurry was allowed to cool between each batch until the surface temperature reached 25°C or less. (5) The slurry prepared in (4) was stored at 21°C for 7 days. (6) After storage at 21°C, the slurry was again kneaded in the above-mentioned centrifugal / revolving mixer at a revolution speed of 2000 rpm and a rotation speed of 800 rpm for 1 minute, and then diluted with a 10 mmol / L lithium bromide-containing N,N-dimethylacetamide solution to obtain a diluted slurry having a vinylidene fluoride polymer concentration of 0.1% by mass, where the total of the vinylidene fluoride polymer and the solvent (N-methylpyrrolidone and lithium bromide-containing N,N-dimethylacetamide solution) in the obtained diluted slurry was taken as 100% by mass. (7) NCA was removed from the diluted slurry prepared in (6) by centrifugation to prepare a post-adsorption sample. (8) The post-adsorption sample prepared in (7) was subjected to GPC measurement, and the peak area B derived from the vinylidene fluoride polymer was determined. (9) The adsorption rate was calculated from the peak area A determined in (3) and the peak area B determined in (8) based on the following formula: Adsorption rate = (peak area A - peak area B) / (peak area A) x 100

[0104] Slurry Viscosity The slurry viscosity of the electrode mixtures prepared in the Examples and Comparative Examples was measured immediately after production of the electrode mixture and three days (72 hours) after production. Specifically, the viscosity of the electrode mixture immediately after production was measured as follows. Using a Brookfield viscometer (manufactured by Toki Sangyo Co., Ltd., TVB-10M, spindle No. M4), the viscosity measured two minutes after the start of rotation at 21°C and 12 rpm was taken as the slurry viscosity. The electrode mixture was stored for three days (72 hours) in an atmosphere with a dew point temperature of -30°C or lower. The storage temperature was 21°C when the active material was NCA, and 30°C when the active material was NCM, as described below. The slurry viscosity was then determined in the same manner as above.

[0105] Example 1 Polymerization was carried out by the following method to obtain a vinylidene fluoride copolymer as a powder. A 2-L autoclave was charged with 1,140 g of ion-exchanged water as a dispersion medium, 0.4 g of a cellulose-based suspending agent (Metolose SM-100, manufactured by Shin-Etsu Chemical Co., Ltd.), 0.2 g of 2-chloroethyl acrylate (CLEA), 1.3 g of a polymerization initiator (a 50% by mass solution of tert-butyl peroxypivalate-HFE-347pc-f) (hereinafter also referred to as PB-PV), 1.3 g of a chain transfer agent (ethyl acetate), and 380 g of vinylidene fluoride (hereinafter also referred to as "VDF"), and the temperature was raised to 55°C over 120 hours. While maintaining the temperature at 55°C, 2.1 g (solute equivalent) of a 3 mass% CLEA solution (solvent: water / methanol, mass ratio 1:1) was added from 2.7 hours after the start of temperature increase until the end of polymerization. After the end of polymerization, the vinylidene fluoride polymer was dehydrated, washed with water, and heat-treated at 95°C for 60 minutes. Thereafter, it was dehydrated, washed with water, and further dried at 80°C for 12 hours. In this way, a vinylidene fluoride polymer powder was obtained. Hereinafter, the obtained vinylidene fluoride polymer powder was used as a binder. CLEA is a compound represented by the following structure.

[0106] [Preparation of electrode mixture a] LiNi was used as the electrode active material. ０．７８ Co ０．１９ Al ０．０３ (JFE Mineral Co., Ltd. 503LP, specific surface area 0.38 m２ / g, average particle size D50 = 12 μm, pH 10.9) (hereinafter referred to as NCA) was used. Carbon black (Denka Black manufactured by Denka Corporation) was used as a conductive additive. A Thinky Mixer Model ARE-310 was used for the kneading. The kneading speed was a revolution speed of 2000 rpm and a rotation speed of 800 rpm. All operations were carried out in an environment with a controlled temperature of 21°C and a dew point of -30°C. First, the above-mentioned binder (vinylidene fluoride polymer) was dissolved in N-methylpyrrolidone (NMP) to prepare a liquid binder. The concentration of the vinylidene fluoride polymer in the binder was 6% by mass. Next, the carbon black and binder were mixed, and primary kneading was performed for 1 minute. Next, NCA and NMP were added, and the mixture was kneaded in multiple batches while adjusting the kneading time so that the heat generated by kneading would be 40°C or less, to obtain an electrode mixture (electrode mixture slurry). Between each kneading, the electrode mixture was allowed to cool until the surface temperature reached 25°C or less, and then NMP was added as needed. The weight ratio of NCA, carbon black, and vinylidene fluoride polymer in the obtained electrode mixture was 100:1.5:1.5, and the solids concentration was 73% by mass.

[0107] Example 2 A vinylidene fluoride polymer was prepared in the same manner as in Example 2, except that the polymerization conditions were changed as shown in Table 1, and an electrode mixture a was also prepared.

[0108] (Example 3) A vinylidene fluoride polymer was prepared in the same manner as in Example 1, except that CLEA was changed to vinyl chloroacetate (VCAc) and the polymerization conditions were changed as shown in Table 1. VCAc is a compound represented by the following structure. Then, using the vinylidene fluoride polymer, an electrode mixture a was prepared in the same manner as in Example 1. Furthermore, an electrode mixture b was prepared by the following procedure.

[0109] [Preparation of electrode mixture b] Instead of NCA, LiNi ０．８６ Co ０．１０ Mn ０．０４ O ２、 (Specific surface area 0.43m ２ / g, average particle diameter D５０ An electrode mixture b was prepared in the same manner as the electrode mixture a, except that an NCM (N=10 μm) was used.

[0110] Comparative Example 1 A powder of vinylidene fluoride homopolymer was obtained in the same manner as in Example 1, except that CLEA was not used, the initiator was changed from PB-PV to a 50% by mass diisopropyl peroxydicarbonate-HFE-347pc-f solution (hereinafter also referred to as IPP), and the polymerization conditions were changed as shown in Table 1. Then, using the vinylidene fluoride homopolymer, electrode mixtures a and b were prepared in the same manner as in Example 3 above.

[0111] Comparative Example 2 A vinylidene fluoride polymer was prepared in the same manner as in Example 1, except that the polymerization conditions were changed as shown in Table 1, and an electrode mixture a was also prepared.

[0112]

[0113] As shown in the above table, when a binder containing a vinylidene fluoride polymer with an adsorption rate of 19% or a vinylidene fluoride polymer with an adsorption rate of 22% was used, gelation progressed and the slurry viscosity became unmeasurable 3 days after the preparation of the electrode mixture, regardless of the presence or absence of a comonomer or the type of active material (Comparative Example 1 and Comparative Example 2).

[0114] In contrast, when a vinylidene fluoride polymer with an adsorption rate of 16% or less was used as a binder, gelation did not occur regardless of the type of active material, and the slurry viscosity was within a range that did not pose any problems in use (Examples 1 to 3).

[0115] This application claims priority from Japanese Patent Application No. 2024-028986, filed February 28, 2024. The entire contents of the specification of that application are incorporated herein by reference.

[0116] According to the present invention, there is provided a binder that causes little deterioration or thickening of an electrode mixture even when the electrode mixture is prepared by mixing the binder with an active material containing a large amount of base, etc. The binder is very useful in the field of manufacturing various batteries.

Claims

1. A binder containing a vinylidene fluoride polymer containing a structural unit derived from vinylidene fluoride, wherein the vinylidene fluoride polymer is LiNi, which is specified by the following method: ０．７８ Co ０．１９ Al ０．０３ , specific surface area 0.38m ２ A binder having an adsorption rate of 16% or less for lithium metal oxide a having a water content of 500 ppm or less, an average particle diameter D50 of 12 μm, a pH of 10.9, and a water content of 500 ppm or less. (Method for determining adsorption rate) (1) In an environment with a dew point of −30° C. or less, the vinylidene fluoride polymer and N-methylpyrrolidone having a water content of 500 ppm or less are mixed to prepare a vinylidene fluoride polymer solution having a vinylidene fluoride polymer concentration of 6 mass %. (2) In an environment with a dew point of −30° C. or less, the vinylidene fluoride polymer solution is diluted with a 10 mmol / L N,N-dimethylacetamide solution containing lithium bromide to obtain a pre-adsorption sample having a vinylidene fluoride polymer concentration of 0.1 mass %. (3) The pre-adsorption sample is subjected to gel permeation measurement to identify the peak area A derived from the vinylidene fluoride polymer (a 10 mmol / L lithium bromide-containing N,N-dimethylacetamide solution is used as the mobile phase for the gel permeation measurement). (4) In an environment with a dew point of -30°C or less, the lithium metal oxide a, the vinylidene fluoride polymer solution, and N-methylpyrrolidone are mixed in a mass ratio of 100:25:6.8, and then kneaded using a planetary centrifugal mixer to prepare a slurry. (5) The slurry is stored for 7 days at a dew point of -30°C or less and at 21°C. (6) In an environment with a dew point of −30° C. or lower, the slurry is kneaded again using a planetary centrifugal mixer, and then the slurry is diluted with a 10 mmol / L lithium bromide-containing N,N-dimethylacetamide solution to obtain a diluted slurry having a vinylidene fluoride polymer concentration of 0.1% by mass, where the total of the vinylidene fluoride polymer and the solvent (N-methylpyrrolidone and the lithium bromide-containing N,N-dimethylacetamide solution) in the obtained diluted slurry is taken as 100% by mass. (7) In an environment with a dew point of −30° C. or lower, the lithium metal oxide a is removed from the diluted slurry by centrifugation to obtain a post-adsorption sample. (8) The post-adsorption sample is subjected to gel permeation measurement to identify the peak area B derived from the vinylidene fluoride polymer. (9) The adsorption rate is calculated from the peak area A and the peak area B according to the following formula: Adsorption rate = (peak area A - peak area B) / (peak area A) × 100 2. The binder according to claim 1, wherein the amount of said vinylidene fluoride-derived structural units relative to the total amount of structural units of said vinylidene fluoride polymer is 90 mol % or more.

3. An electrode mixture comprising the binder according to claim 1 or 2 and an active material.

4. The active material is Li １－ａ Ni ｘ Co ｙ M ｚ O ２ (M represents Mn or Al, and a, x, y, and z respectively satisfy −0.5≦a≦0.5, 0.45<x<1, 0<y<1, 0<z<1, and x+y+z=1).

5. An electrode comprising the solid content of the binder according to claim 1 or 2 and an active material.

6. A battery comprising the electrode according to claim 5.

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