Vinylidene fluoride polymer, binder, electrode mixture, electrode, and battery

Abstract

The purpose is to provide a binder for a nonaqueous electrolyte secondary battery that is unlikely to cause thickening or gelation of an electrode mixture even when mixed with an active material or the like containing many bases and that is stable over an extended period of time. A binder for a nonaqueous secondary battery that solves the problem contains a structural unit derived from vinylidene fluoride, the IR absorbance ratio calculated by a specific formula from an absorption spectrum measured by Fourier transform infrared spectroscopy is 0.1-16, and the total content of chlorine atoms, bromine atoms, and iodine atoms is 28-1550 μmol / g.

Description

Vinylidene fluoride polymer, binder, electrode mixture, electrode, and battery

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

[0002] Homopolymers of vinylidene fluoride 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 positive electrode active material with a high nickel ratio (see, for example, Patent Document 1).

[0003] Special Publication No. 2020-537315

[0004] However, active materials with a high nickel content often contain a large amount of base, and when an electrode mixture (slurry) is prepared using such an active material with a high nickel content and a conventional vinylidene fluoride polymer, the electrode mixture tends to thicken and gel.

[0005] In order to suppress thickening and gelation of the electrode mixture, it has been proposed to add an organic acid to the electrode mixture to neutralize the base contained in the active material. However, depending on the type of organic acid, the organic acid may remain in the electrode and affect battery performance. Therefore, there is a need to prevent thickening and gelation of the electrode mixture without adding an additive for suppressing the base, and there is a need to provide a vinylidene fluoride polymer that is less likely to cause thickening and gelation of the electrode mixture.

[0006] The present invention has been made in view of the above-mentioned problems, and aims to provide a vinylidene fluoride polymer that is unlikely to cause thickening or gelation of an electrode mixture (slurry) even when mixed with an active material having a high nickel content, as well as a binder, an electrode mixture, an electrode, and a battery that contain the same.

[0007] [1] The present invention provides a vinylidene fluoride polymer that contains structural units derived from vinylidene fluoride, has an IR absorbance ratio calculated from an absorption spectrum measured by Fourier transform infrared spectroscopy using the following formula of 0.1 or more and 16 or less, and has a total content of chlorine atoms, bromine atoms, and iodine atoms of 28 μmol / g or more and 1550 μmol / g or less. Ｃ＝Ｏ / A Ｃ－Ｈ (In the formula, A Ｃ＝Ｏ represents the absorbance of the peak due to C═O stretching, and A Ｃ－Ｈ represents the absorbance of the peak due to C-H stretching)

[0008] [2] The present invention provides the vinylidene fluoride polymer according to [1], which has an inherent viscosity of 0.5 dl / g or more and 5.0 dl / g or less.

[0009] [3] The present invention provides the vinylidene fluoride polymer according to [1] or [2], further comprising structural units derived from a compound other than vinylidene fluoride, wherein the structural units derived from the compound other than vinylidene fluoride have a random ratio of 0.5% or more within the polymer chain. [4] The present invention provides the vinylidene fluoride polymer according to any one of [1] to [3], further comprising structural units derived from a compound other than vinylidene fluoride, wherein the compound other than vinylidene fluoride contains at least one atom selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom, and a carboxy group.

[0010] [5] The present invention provides a binder containing the vinylidene fluoride polymer according to any one of [1] to [4]. [6] The present invention provides an electrode mixture containing the vinylidene fluoride polymer according to any one of [1] to [4] and an active material. [7] 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). [8] The present invention provides an electrode comprising the vinylidene fluoride polymer according to any one of [1] to [4] and an active material. [9] The present invention provides a battery comprising the electrode according to [8].

[0011] The vinylidene fluoride polymer of the present invention is unlikely to thicken or gel when mixed with an active material having a high nickel content to prepare an electrode mixture (slurry). Therefore, the vinylidene fluoride polymer can provide a binder, electrode mixture, electrode, and battery that are highly stable and high quality.

[0012] 1. Vinylidene fluoride polymer The vinylidene fluoride polymer of the present invention relates to a polymer containing structural units derived from vinylidene fluoride. The vinylidene fluoride polymer preferably contains structural units derived primarily from vinylidene fluoride. Specifically, the vinylidene fluoride polymer preferably contains 90.0 mol% to 99.9 mol% of structural units derived from vinylidene fluoride, more preferably 93.0 mol% to 99.8 mol%, and particularly preferably 96.0 mol% to 99.7 mol%, of all structural units in 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 more likely to be obtained. On the other hand, when the amount of structural units derived from vinylidene fluoride is 99.9 mol% or less, this indicates that the amount of structural units derived from compounds other than vinylidene fluoride contained in the vinylidene fluoride polymer is sufficiently large. This makes it easier for the IR absorbance ratio (described later) to be 0.1 or more, and for the amount of atoms selected from the group consisting of chlorine atoms, bromine atoms, and iodine atoms (hereinafter, these atoms are also collectively referred to as "eliminated halogen atoms") to be 28 μmol / g or more. １９ It can be identified by F-NMR analysis, etc.

[0013] The vinylidene fluoride polymer of the present invention has an IR absorbance ratio calculated from the absorption spectrum measured by Fourier infrared spectroscopy (FT-IR) using the following formula: IR absorbance ratio = A Ｃ＝Ｏ / A Ｃ－Ｈ Here, A Ｃ＝Ｏ is the absorbance of the peak due to C═O stretching, and A Ｃ－Ｈ is the absorbance of the peak due to C-H stretching. The IR absorbance ratio is preferably 0.1 or more and 12.0 or less, more preferably 0.1 or more and 6.5 or less, even more preferably 0.1 or more and 3.0 or less, and particularly preferably 0.1 or more and 1.0 or less. In the FT-IR absorption spectrum of the vinylidene fluoride polymer of the present invention, A Ｃ－Ｈ The wave number is 3023 cm －１ This absorbance mainly represents the amount of structural units derived from vinylidene fluoride. Ｃ＝Ｏ Wave number 1650-1800 cm －１ The IR absorbance ratio is the absorbance of the peak derived from the C=O stretching present in the range, and this absorbance represents the amount of structural units derived from compounds other than vinylidene fluoride that have a carbonyl group (C=O). Since the vinylidene fluoride polymer of the present invention has the IR absorbance ratio of 0.1 or more, the carbonyl group contained in the vinylidene fluoride polymer undergoes a reaction such as hydrolysis with the base contained in the active material, consuming a large amount of base and thereby suppressing thickening and gelation of the electrode mixture. Meanwhile, since the vinylidene fluoride polymer of the present invention has the IR absorbance ratio of 16.0 or less, it also fully possesses the physical properties unique to vinylidene fluoride. Therefore, the vinylidene fluoride polymer is extremely useful as a material for electrode mixtures, etc.

[0014] Here, the FT-IR measurement can be carried out by the following procedure. First, 30 mg of vinylidene fluoride polymer is heat-pressed at 200°C to prepare a film having a thickness of 0.05 to 0.3 mm. The film is measured with a transmission infrared spectrophotometer to obtain an FT-IR spectrum. From the obtained FT-IR spectrum, the IR absorbance ratio is calculated using the above-mentioned formula. Furthermore, when multiple peaks derived from C=O are observed in the obtained absorption spectrum, the peak intensity of the highest peak is used as A. Ｃ＝Ｏ The IR absorbance ratio can be adjusted to a desired range by adjusting the copolymerization ratio of vinylidene fluoride to a compound other than vinylidene fluoride or the number of carbonyl groups contained in the compound other than vinylidene fluoride.

[0015] Furthermore, the total amount of detached halogen atoms (chlorine atoms, bromine atoms, and iodine atoms) contained in the vinylidene fluoride polymer of the present invention is 28 μmol / g or more and 1550 μmol / g or less. This total content is preferably 28 μmol / g or more and 1100 μmol / g or less, and more preferably 28 μmol / g or more and 650 μmol / g or less. When the amount of detached halogen atoms in the vinylidene fluoride polymer is within this range, as will be described in detail later, even when the vinylidene fluoride polymer is mixed with an active material containing a large amount of base to prepare an electrode mixture (slurry), the electrode mixture is less likely to thicken or gel. The amount of detached halogen atoms 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 chromatography is performed to determine the sum (A) of the peak areas of each released halogen atom captured in the absorption solution. Similarly, the peak area (B) of each released halogen atom obtained when only the filter paper is burned and measured is used as the blank, and the peak area difference (A-B) is determined. The content of released halogen atoms in the vinylidene fluoride polymer is calculated from the peak area difference (A-B) and a calibration curve obtained from the measurement of a standard sample of each released halogen atom. The amount of released halogen atoms can be adjusted to a desired range by adjusting the number of released halogen atoms contained in the compound copolymerizable with vinylidene fluoride, the content of the compound containing released halogen atoms in the vinylidene fluoride polymer, or the like.

[0016] Here, in the vinylidene fluoride polymer, the detached halogen atom may be bonded to the main chain of the vinylidene fluoride polymer, but is more preferably bonded to a side chain. When the detached halogen atom is bonded to the main chain of the vinylidene fluoride polymer, the site where the detached halogen atom has been detached, as described below, may reduce the stability of the adjacent vinylidene fluoride structural unit of the main chain. On the other hand, when the detached halogen atom is bonded to a side chain, the site where the detached halogen atom has been detached is distant from the vinylidene fluoride structural unit of the main chain, making it less likely to reduce the stability of the vinylidene fluoride structural unit of the main chain.

[0017] Here, vinylidene fluoride-chlorotrifluoroethylene copolymers are generally known as examples of vinylidene fluoride polymers in which the detached halogen atoms are bonded to the main chain. ６ Dissolve in １９ When measured by F-NMR, peaks due to chlorotrifluoroethylene structural units appear at -102 to -110 ppm and -116 to -121 ppm, relative to the peak due to normal bonds in vinylidene fluoride polymers (-91.6 ppm). By this method, it is possible to identify the position of the eliminated halogen atom in a vinylidene fluoride polymer.

[0018] The structure of the vinylidene fluoride polymer of the present invention is not particularly limited, but the following vinylidene fluoride polymer is an example of a vinylidene fluoride polymer that satisfies the above-mentioned IR absorbance ratio and amount of eliminated halogen atoms. The vinylidene fluoride polymer contains a structural unit derived from vinylidene fluoride, and a structural unit derived from a compound represented by general formula (1) (hereinafter also referred to as "compound (1)") and / or a structural unit derived from a compound represented by general formula (2) (hereinafter also referred to as "compound (2)"). However, the vinylidene fluoride polymer of the present invention is not limited to the vinylidene fluoride polymer described below.

[0019] The structure of compound (1) is shown below. In general formula (1), R １ , R ２ , and R３ each independently represents a hydrogen atom or an alkyl group which may have a substituent having from 1 to 5 carbon atoms. Examples of the alkyl group having from 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. Examples of the substituent that may be bonded to the alkyl group include a fluorine atom, an ether bond, a hydroxy group, a sulfide bond, a sulfonyl group, a thiol group, an amino group, a nitrile group, a nitro group, and a phosphoryl group.

[0020] Meanwhile, X in the 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 the detached halogen atom, the number of atoms in the main chain of the atomic group being 1 to 20, and the molecular weight thereof being 552 or less.

[0021] 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.

[0022] The number of atoms in the main chain of the atomic group (X) may be 1 or more and 20 or less, and preferably 1 or more and 15 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 bonded thereto or detached halogen atoms. In addition, hydrogen atoms and detached halogen atoms bonded to carbon atoms and hetero atoms present at the terminals of the main chain are not counted in the number of atoms in the main chain.

[0023] Furthermore, the atomic group (X) may contain at least one heteroatom selected from oxygen, sulfur, nitrogen, and phosphorus atoms. 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 form any structure (functional group). They may also be located at any position within the atomic group (X). Examples of structures (functional groups) containing these heteroatoms include ether bonds, ester groups, carbonyl groups, carboxy groups, amide groups, hydroxy groups, sulfide bonds, sulfonyl groups, thiol groups, amino groups, nitrile groups, nitro groups, and phosphoryl groups. Among these, ether bonds, ester groups, carbonyl groups, carboxy groups, amide groups, and hydroxy groups are preferred from the viewpoint of high stability and easy enhancement of affinity and adhesion between vinylidene fluoride polymers and active materials, etc.

[0024] The atomic group (X) contains at least one detached halogen atom selected from a chlorine atom, a bromine atom, and an iodine atom. The number of detached halogen atoms contained in the atomic group (X) may be one or two or more, as long as it satisfies the above-mentioned amount of detached halogen atoms. The amount of detached halogen atoms in the atomic group (X) is preferably 1 to 5, more preferably 1 to 3. When the atomic group (X) contains two or more detached halogen atoms, these atoms may be the same type or different types. The bonding position of the detached halogen atoms within the atomic group (X) is not particularly limited. Among the detached halogen atoms, a chlorine atom is particularly preferred because it provides an excellent balance between detachability in the electrode mixture and stability during the polymerization process of the vinylidene fluoride polymer.

[0025] 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, a structure (functional group) containing the heteroatom, and a detached halogen atom are bonded. The molecular weight of the atomic group (X) may be 552 or less, and preferably 50 to 352.

[0026] Specific examples of the compound (1) include 3-chloro-1-methacryloyloxypropyl 2-succinic acid (MACPS), 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 ... Acryloyloxypropyl 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)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, Examples of such acrylates include 3-chlorohydroxypropyl (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, and 2-(2-bromoisobutyryloxy)ethyl (meth)acrylate.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.

[0027] The compound (1) is preferably a compound represented by the following general formula (1a) (hereinafter also referred to as "compound (1a)"), since it 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 optionally having a substituent, and these are the same as R １ , R ２ , and R ３ is the same as:

[0028] Also, X １ represents an atomic group containing at least one detached halogen atom 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.

[0029] 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 detached halogen atom. １ The type and number of the detached halogen atoms contained in the atomic group (X) are the same as those in the atomic group (X) of the compound (1). 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, and preferably 1 or more and 14 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 make up the main chain, and does not include the number of hydrogen atoms bonded thereto or detached halogen atoms. Furthermore, hydrogen atoms and detached halogen atoms 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 may be 536 or less, and preferably 50 or more and 336 or less.

[0030] Specific examples of compound (1a) include 3-chloro-1-methacryloyloxypropyl 2-succinic acid (MACPS), 3-chloro-1-acryloyloxypropyl 2-succinic acid, 1-chloro-2-(meth)acryloyloxypropyl 3-succinic acid, 1-(meth)acryloyloxy-3-chloro-propyl 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)maleic acid, 1-(meth)acryloyloxypropyl 2-(1-bromo)maleic acid, 1-(meth)acryloyloxypropyl 2-(2-bromo)maleic acid, (meth)acryloyloxyethyl(1-chloro)succinic acid, (meth)acryloyloxyethyl(2-chloro)succinic acid, (meth)acryloyloxyethyl(1-bromo) Succinic acid, (meth)acryloyloxyethyl (2-bromo)succinic acid, (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, (meth)acrylic acid 2,2 , 2-trichloroethyl, 3-chloro-2-hydroxypropyl (meth)acrylate, 2-chloro-3-hydroxypropyl (meth)acrylate, 3-chloro-hydroxypropyl (meth)acrylate, 2-(2-chloropropionyl)ethyl (meth)acrylate, (N-chloro)2,2,6,6-tetramethyl-4-piperidyl (meth)acrylate, 2-(2-bromopropionyl)ethyl (meth)acrylate, 2-(2-bromoisobutyloxy)ethyl (meth)acrylate, and the like.

[0031] It is more preferable that the compound (1) is a compound represented by the following general formula (1b) (hereinafter also referred to as “compound (1b)”), from the viewpoint of more easily satisfying the above-mentioned IR absorbance ratio. R in the general formula (1b) １ , R ２ , and R ３ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms and optionally having a substituent, and these are the same as R １ , R ２ , and R ３ is the same as:

[0032] In addition, X in general formula (1b) ２ represents an atomic group containing at least one atom (a detached halogen atom) selected from a chlorine atom, a bromine atom, and an iodine atom, having 1 or more and 17 or less atoms in the main chain, and having a molecular weight of 491 or less.

[0033] The atomic group (X ２ The structure of the compound (X) has the same structure as the atomic group (X) in the general formula (1a) except that it has a carboxyl group at the terminal. １ ) and the atomic group (X ２ ) can have a structure in which a hydrocarbon group such as an alkylene group or an alkyl group is bonded to a detached halogen atom, and optionally a structure (functional group) containing a heteroatom. ２ The number of atoms in the main chain of the atomic group (X) may be 1 or more and 17 or less, and preferably 1 or more and 12 or less. ２ The main chain of the general formula (1b) refers to the longest chain connecting the -C(=O)O- group and the terminal COOH group. Furthermore, the number of atoms in the main chain refers to the number of carbon atoms and heteroatoms that make up the main chain, and does not include the number of hydrogen atoms bonded thereto or detached halogen atoms. Furthermore, the atomic group (X ２ The molecular weight of the copolymer may be 491 or less, and is preferably 50 or more and 291 or less.

[0034] Specific examples of compound (1b) include 3-chloro-1-methacryloyloxypropyl 2-succinic acid (MACPS), 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)maleic acid, 1-(meth)acryloyloxypropyl 2-(1,2-dichloro)maleic acid, 1-(meth)acryloyloxypropyl 2-(1,2-dichloro)maleic acid, 1-(meth)acryloyloxypropyl 2-(1-chloro ...1-bromo)succinic acid, 1-(meth)acryloyloxypropyl 2-(2-bromo)succinic acid, 1-(meth)acryloyloxypropyl 2-(1,2 Examples of acryloyloxyethyl esters include (meth)acryloyloxyethyl 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)maleate, (meth)acryloyloxyethyl(1-bromo)maleate, (meth)acryloyloxyethyl(2-bromo)maleate, (meth)acryloyloxyethyl(4-chloro)phthalate, and (meth)acryloyloxyethyl(tetrachloro)phthalate.

[0035] 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 and optionally having a substituent. 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.

[0036] On the other hand, Z in general formula (1) represents an atomic group that contains a carbonyl group and at least one atom (a detached halogen atom) selected from a chlorine atom, a bromine atom, and an iodine atom, has 1 or more and 20 or less atoms in the main chain, and has a molecular weight of 564 or less.

[0037] The atomic group (Z) may be linear, branched, or cyclic, or may be a combination thereof. Among these, the atomic group is preferably linear or branched, from the viewpoint of less steric hindrance during polymerization with vinylidene fluoride. The position of the carbonyl group is not particularly limited, and may be, for example, adjacent to the ether bond in general formula (2) or distant from the ether bond. The carbonyl group may form a ketone structure or an aldehyde structure, or may form a carboxy group, within the atomic group (Z).

[0038] The number of atoms in the main chain of the atomic group (Z) may be 1 or more and 20 or less, and preferably 1 or more and 15 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 detached halogen atoms that are bonded thereto. In addition, 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.

[0039] The atomic group (Z) contains at least one detached halogen atom selected from a chlorine atom, a bromine atom, and an iodine atom. The number of detached halogen atoms 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 detached halogen atoms, these may be the same type of atom or different types of atoms. The bonding position of the detached halogen atoms within the atomic group (Z) is not particularly limited. Among the detached halogen atoms, a chlorine atom is particularly preferred because it provides an excellent balance between detachability in the electrode mixture and stability during the polymerization process of the vinylidene fluoride polymer.

[0040] 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 carbonyl group and a detached halogen atom. The atomic group (Z) may further contain a structure (functional group) containing a heteroatom. The heteroatom-containing structure (functional group) is the same as the heteroatom-containing structure (functional group) contained in the atomic group (X) of the compound (1). The molecular weight of the atomic group (Z) may be 564 or less, and preferably 50 or more and 364 or less.

[0041] Specific examples of the compound (2) include vinyl chloroacetate (VCAc), vinyl dichloroacetate, vinyl trichloroacetate, vinyl 3-chloropropionate, and the like.

[0042] Furthermore, it is more preferable that the compound (2) is a compound represented by the following general formula (2a) (hereinafter also referred to as "compound (2a)") from the viewpoint of reactivity with vinylidene fluoride, etc. R in the general formula (2a) ４ , R ５ , and R ６ are each independently a hydrogen atom or an alkyl group having 1 to 5 carbon atoms and optionally having a substituent, and these are the same as R ４ , R ５ , and R ６ It is the same as X １ represents an atomic group, and its structure is the same as that of the atomic group (X １ ) is the same as

[0043] Specific examples of the compound (2a) include vinyl chloroacetate (VCAc), vinyl dichloroacetate, vinyl trichloroacetate, vinyl 3-chloropropionate, and the like.

[0044] The numbers of atoms in the main chains of 3-chloro-1-methacryloyloxypropyl 2-succinate (MACPS), 2-chloroethyl acrylate (CLEA), and vinyl chloroacetate (VCAc) used in the examples described below are as follows:

[0045] MACPS corresponds to the compound represented by formula (1), the compound represented by formula (1a), and the compound represented by formula (1b). When the compound represented by formula (1) is MACPS, the atomic group of X is —OCH ２ CH (CH ２ Cl)O-(CO)-CH 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-CC-O-C-C-C-C-O-, and the number of atoms is 9. Similarly, when the compound represented by formula (1a) is MACPS, X １ The main chain of the atomic group represented by the formula (1b) has 8 atoms, and when the compound represented by the formula (1b) is MACPS, X ２ The main chain of the atomic group represented by the formula has six atoms.

[0046] 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 main chain of the atomic group represented by X has 3 atoms, and 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.

[0047] 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 has one atom.

[0048] In the vinylidene fluoride polymer of the present invention, the total amount of the structural units derived from compound (1) and the structural units derived from compound (2) is preferably 0.01 mol% or more and 10.0 mol% or less, more preferably 0.02 mol% or more and 7 mol% or less, and even more preferably 0.03 mol% or more and 4 mol% or less, relative to the total amount of the structural units derived from vinylidene fluoride, the structural units derived from compound (1), and the structural units derived from compound (1). When the total amount of the structural units derived from compound (1) and the structural units derived from compound (2) is 0.01 mol% or more, the above-mentioned IR absorbance ratio and the amount of released halogen atoms are likely to be satisfied. On the other hand, when the total amount of the structural units derived from compound (1) and the structural units derived from compound (2) is 10 mol% or less, the physical properties specific to vinylidene fluoride are likely to be obtained.

[0049] The vinylidene fluoride polymer may partially contain structural units derived from compounds (other compounds) other than vinylidene fluoride, compound (1), and compound (2) within a range that does not impair the objects and effects of the present invention. 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 mol % or less, more preferably 5 mol % or less.

[0050] 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.

[0051] Here, the vinylidene fluoride polymer may be a copolymer of vinylidene fluoride, the above-mentioned compound (1) and / or 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 in the polymer chain of the structural units derived from compound (1) and the structural units derived from 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 compound (1) and the structural units derived from 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. A random ratio of 0.5% or more indicates that structures having eliminated halogen atoms (X in the above-mentioned general formula (1) and Z in the general formula (2)) are likely to be uniformly arranged in the vinylidene fluoride polymer structure. As a result, thickening and gelation of the electrode mixture are more likely to be suppressed.

[0052] 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 the 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, in vinylidene fluoride polymers with the same content of compound (1), a high random ratio 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) present in the polymer chain is large. Furthermore, 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) present in the polymer chain is 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. １It can be determined from the H-NMR spectrum.

[0053] The melting point of the vinylidene fluoride polymer is preferably 150°C or higher and 180°C or lower, more preferably 160°C or higher and 175°C or lower, and most 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 as an electrode mixture, the polymer is less likely to swell with an electrolyte, and the performance of the resulting battery is likely to be good. On the other hand, when the melting point is 180°C or lower, the flexibility of the formed electrode is likely to be good. The melting point of the vinylidene fluoride polymer can be determined by calorimetry using a differential scanning calorimeter (DSC).

[0054] The weight-average molecular weight of the vinylidene fluoride polymer is preferably 100,000 or more and 5,000,000 or less, more preferably 200,000 or more and 4,000,000 or less, and even more preferably 200,000 or more and 3,000,000 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 soluble in a solvent.

[0055] 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 0.5 dL / g or more and 5.0 dL / g or less, even more preferably 1.0 dL / g or more and 5.0 dL / g or less, and particularly preferably 1.0 dL / g or more and 4.0 dL / g or less. When the inherent viscosity is 0.5 dL / g or more, the adhesive strength when the vinylidene fluoride polymer is mixed with an active material or a current collector tends to be increased. On the other hand, when the inherent viscosity is 5.0 dL / g or less, the viscosity of the slurry does not become too high when an electrode mixture (slurry) is prepared, and workability is particularly good. 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 / η０ 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.

[0056] The vinylidene fluoride polymer can be prepared by copolymerizing vinylidene fluoride, the compound (1) and / or the compound (2), and, if necessary, other compounds, by a known method. Examples of the copolymerization method include suspension polymerization, emulsion polymerization, solution polymerization, etc., but suspension polymerization is preferred from the viewpoint that impurities tend to be reduced.

[0057] 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 monomers copolymerized as necessary).

[0058] 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).

[0059] 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).

[0060] 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 of the polymerization initiator. 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.

[0061] By carrying out aqueous suspension polymerization under the above conditions, vinylidene fluoride and, if necessary, other copolymerizable monomers can be easily copolymerized, thereby obtaining the vinylidene fluoride polymer of the present invention. Note that, although the above explanation has been given taking as an example the copolymerization with compound (1) or compound (2), the same applies to the copolymerization of vinylidene fluoride with other monomers.

[0062] As described above, when a known vinylidene fluoride polymer is mixed with an active material containing a large amount of nickel to prepare an electrode mixture (slurry), there is a problem that the electrode mixture tends to thicken and gel. In contrast, the vinylidene fluoride polymer of the present invention is less likely to thicken or gel when mixed with an active material containing a large amount of nickel. The reason for this is not clear, but is thought to be as follows. In the case of known vinylidene fluoride polymers, a base derived from the active material reacts with the vinylidene fluoride polymer, causing a dehydrofluorination reaction in the vinylidene fluoride polymer. The polyene -(CH=CF) generated as a result ｎ The - interacts with the active material to form crosslinks, and the crosslink density increases, causing the electrode mixture to thicken and eventually gel. In contrast, as described above, the vinylidene fluoride polymer of the present invention contains a specific amount of detached halogen atoms. When an electrode mixture containing a vinylidene fluoride polymer and an active material is prepared, the detached halogen atoms are easily detached from the vinylidene fluoride polymer. As a result, it is believed that the detached halogen atoms suppress the interaction between the polyene and the active material, thereby suppressing thickening and gelation of the electrode mixture. Furthermore, as described above, the vinylidene fluoride polymer of the present invention has a carbonyl group. The carbonyl group undergoes a reaction such as hydrolysis with a base derived from the active material, consuming the base. As a result, it is believed that the dehydrofluorination reaction of the vinylidene fluoride polymer is suppressed, and thickening and gelation of the electrode mixture are suppressed.

[0063] Furthermore, since the vinylidene fluoride polymer itself contains a detached halogen atom, there is no need to add a separate compound to suppress the interaction between the polyene and the active material. Therefore, the vinylidene fluoride polymer of the present invention can more reliably suppress the interaction between the polyene and the active material. Furthermore, the vinylidene fluoride polymer does not require the separate addition of compounds that may affect the battery or its electrodes to the electrode mixture (slurry). Therefore, the vinylidene fluoride polymer is very useful as a material for electrode mixtures for lithium ion secondary batteries. However, the use of the vinylidene fluoride polymer of the present invention is not limited to this.

[0064] 2. Binder The present invention provides a binder containing the vinylidene fluoride polymer. The form of the binder is not particularly limited, and the binder may be in powder or liquid form. The binder may be composed solely of the vinylidene fluoride polymer, or, if necessary, may contain a solvent, or may be dissolved in a solvent or dispersed in a solvent.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 3. 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 mixture for producing an electrode of a non-aqueous electrolyte secondary battery. The electrode mixture may further contain a conductive aid, a solvent, other additives, etc.

[0069] The amount of the binder-derived solid content (vinylidene fluoride polymer) relative to the total amount of the binder-derived solid content (total amount excluding volatile components), 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.

[0070] Furthermore, the vinylidene fluoride polymer contained in the binder is unlikely to cause thickening or gelation of the electrode mixture even when mixed with an active material containing a large amount of base. Therefore, various 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.

[0071] 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.

[0072] 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, Ti, 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 x, y, and z satisfy −0.5≦a≦0.5, 0<x<1, 0<y<1, 0<z<1, and x+y+z=1), etc. 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.

[0073] 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 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] The total amount of solvent in the electrode mixture (including the amount of 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] The viscosity of the electrode mixture is not particularly limited as long as it can prevent dripping, uneven coating, and delayed drying after coating when applying the electrode mixture to form a mixture layer, and provides good workability and applicability when preparing the mixture layer. The viscosity is a value measured at 25°C using an E-type viscometer, and is measured at a shear rate of 2 s after an incubation period of 60 seconds at 25°C using an E-type viscometer. －１ The rotor is rotated at 1000 kJ / min, and the value is measured 60 seconds after the rotor starts rotating.

[0082] 4. Electrode The above-described electrode mixture can be used to form a mixture layer of an electrode of various nonaqueous electrolyte secondary batteries. An electrode of a nonaqueous 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.

[0083] 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.

[0084] 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.

[0085] The mixture layer contains at least the components contained in the electrode mixture described above, i.e., the solid content derived from the binder (vinylidene fluoride polymer) and the active material, and may further contain 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.

[0086] 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:

[0087] 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.

[0088] 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.

[0089] 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. The solvent in the mixture may be dried under atmospheric pressure, pressure, or reduced pressure, or may be dried in an environment such as air, nitrogen, or argon. After drying, a heat treatment may be further performed.

[0090] 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.

[0091] 5. Batteries As described above, 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.

[0092] Specific examples of the present invention will be described below together with comparative examples, but the present invention is not limited to these.

[0093] (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 eliminated halogen atoms, the IR absorbance ratio, the comonomer content, the random ratio, the slurry viscosity of the electrode mixture, and the peel strength of the electrode mixture layer were measured by the following methods.

[0094] 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.

[0095] Amount of Eliminated Halogen Atoms An absorption solution consisting of 30 mL of pure water and 50 μL of hydrogen peroxide was placed in a combustion flask, and filter paper containing 10 mg of vinylidene fluoride polymer was combusted 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 chromatography was performed to determine the peak area (A) of the eliminated halogen atoms 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 content of eliminated halogen atoms in the vinylidene fluoride polymer was calculated from the peak area difference (A - B) and the calibration curve obtained from measurements of diluted solutions of each standard stock solution of eliminated halogen atoms.

[0096] IR absorbance ratio An absorption spectrum was prepared by Fourier transform infrared spectroscopy under the following conditions. <Measurement conditions> 30 mg of a vinylidene fluoride polymer was heat-pressed at 200°C to produce three pressed films with a thickness of 0.1 mm. Each of the three obtained pressed films was measured using a transmission infrared spectrophotometer (Infrared Spectrophotometer 4100 Type A manufactured by JASCO Corporation) to obtain an FT-IR spectrum. The average value calculated from the FT-IR spectrum of each of the three pressed films using the following formula was taken as the IR absorbance ratio. IR absorbance ratio = A Ｃ＝Ｏ / A Ｃ－Ｈ (In the formula, A Ｃ＝Ｏ represents the absorbance of the peak due to C═O stretching, and A Ｃ－Ｈrepresents the absorbance of the peak due to C-H stretching)

[0097] Comonomer Content The proportion of constituent units (monomers) derived from monomers other than vinylidene fluoride (herein, compound (1) or compound (2), hereinafter also collectively referred to as "comonomer") 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. １ The 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.

[0098] ・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): １９The number (mol %) of sequences containing structural units derived from the comonomer present in the polymer chain 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)

[0099] Slurry viscosity The slurry viscosity of the electrode mixture prepared in the examples and comparative examples was measured immediately after the production of the electrode mixture and after 7 days (168 hours) had elapsed since the production. Specifically, the viscosity of the electrode mixture was measured immediately after the electrode mixture was produced. The electrode mixture was placed in an E-type viscometer (RE-215 type viscometer manufactured by Toki Sangyo Co., Ltd., rotor 3° x R14) immediately after preparation. After a 60-second incubation period at 25°C in the device, the electrode mixture was slurried at a shear rate of 2 s －１ The rotor was rotated at 100°C, and the viscosity measured 60 seconds after the start of rotor rotation was determined as the slurry viscosity. The electrode mixture was stored for 7 days (168 hours) in an atmosphere at 21°C and a dew point temperature of -30°C or lower. The electrode mixture was then kneaded for 1 minute using a Thinky Corporation Awatori Rentaro Model ARE-310 at an orbital rotation speed of 2000 rpm and a rotation speed of 800 rpm, and then placed in an E-type viscometer (Toki Sangyo Co., Ltd. RE-215 viscometer, rotor 3° x R14). The slurry viscosity was then determined in the same manner as above. The viscosity change (slurry viscosity after storage) / (slurry viscosity immediately after production) was calculated from the determined slurry viscosity immediately after production and the slurry viscosity after storage.

[0100] Peel strength: The electrode mixtures prepared in the examples and comparative examples were applied to aluminum foil with a thickness of 15 μm using a bar coater and dried at 110° C. for 30 minutes, resulting in a coating weight of 300 g / cm ２A single-sided coated electrode was obtained. The resulting single-sided coated electrode was cut into a length of 70 mm and a width of 20 mm, and the peel strength between the aluminum foil and the mixture layer was evaluated. Specifically, the top surface of the formed mixture layer was bonded to a thick plastic plate (made of acrylic resin, 5 mm thick), and a 90° peel test was performed at a head speed of 10 mm / min using a tensile tester (single column material testing machine STB-1225S manufactured by Orientec Co., Ltd.) in accordance with JIS K6854-1. The measurement environment was a controlled temperature of 25°C and a dew point of -20°C.

[0101] Example 1 Preparation of vinylidene fluoride polymer Polymerization was carried out by the following method to obtain a vinylidene fluoride polymer as a powder. A 2-liter 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 3-chloro-1-methacryloyloxypropyl 2-succinate (MACPS), 2.5 g of a polymerization initiator (a 50% by mass solution of tert-butyl peroxypivalate-HFE-347pc-f) (hereinafter also referred to as PB-PV), 0.3 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, 3.4 g (in terms of solute) of a 5% by mass MACPS solution (solvent: water / methanol, mass ratio 1:1) was added from 2.5 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. It was then dehydrated, washed with water, and further dried at 80°C for 12 hours. This yielded a vinylidene fluoride polymer powder. Hereinafter, the obtained vinylidene fluoride polymer powder was used as a binder. MACPS is a compound represented by the following structure:

[0102] [Preparation of electrode mixture] A nickel-cobalt-aluminum ternary lithium-based composite metal oxide (Ni content 78%, Co content 19%, Al content 3%, specific surface area 0.38 m measured by BET flow method using a mixed gas of 20% nitrogen and 80% helium) was used as an electrode active material. ２ / g, average particle diameter D measured by the following method５０ The average particle diameter of the NCA was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3000II manufactured by Microtrac Bell Co., Ltd.), and the particle diameter at which the cumulative frequency reached 50% on a number basis was defined as the average particle diameter D ５０ The analysis was performed assuming the refractive index of NCA to be 1.71. 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 performed in an environment with a controlled temperature of 21°C and a dew point of -30°C. First, the vinylidene fluoride polymer described above 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 subjected to primary kneading for 1 minute. Next, NCA and NMP were added and secondary kneading was performed for 1 minute. Thereafter, kneading was performed while adjusting the kneading time so that the surface temperature of the electrode mixture during kneading would be 40°C or less, thereby obtaining an 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. In the obtained electrode mixture, the weight ratio of NCA, carbon black, and vinylidene fluoride polymer was 100:1:1, and the solid content concentration was 77% by mass.

[0103] [Production of Electrode] The obtained electrode mixture was applied to a current collector (aluminum foil having a thickness of 15 μm) using a bar coater. The resultant was dried in a thermostatic chamber under a nitrogen atmosphere at 110° C. for 30 minutes to obtain a dry mixture coating weight of 300 g / m. ２ The electrodes were fabricated.

[0104] (Example 2) A vinylidene fluoride polymer powder was obtained in the same manner as in Example 1, except that MACPS was replaced with 2-chloroethyl acrylate (CLEA) and the polymerization conditions were changed as shown in Table 1. CLEA is a compound represented by the following structure. Then, using the vinylidene fluoride polymer, an electrode mixture and an electrode were produced in the same manner as in Example 1 above.

[0105] (Example 3) A vinylidene fluoride polymer powder was obtained in the same manner as in Example 2, except that the polymerization conditions were changed as shown in Table 1. Then, using the vinylidene fluoride polymer, an electrode mixture and an electrode were produced in the same manner as in Example 1 above.

[0106] (Example 4) A vinylidene fluoride polymer powder was obtained in the same manner as in Example 1, except that MACPS was replaced with 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 and an electrode were produced in the same manner as in Example 1 above.

[0107] Comparative Example 1 A powder of vinylidene fluoride homopolymer was obtained in the same manner as in Example 1, except that MACPS and MACPS solution were not used, the initiator was changed from PB-PV to a 50 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, an electrode mixture and an electrode were produced in the same manner as in Example 1 above.

[0108]

[0109] As shown in the table above, when an electrode mixture slurry was prepared by mixing vinylidene fluoride homopolymer and an active material, the viscosity increased by 6.8 times after 7 days (Comparative Example 1). It is believed that the electrode mixture using vinylidene fluoride homopolymer experienced a significant increase in viscosity. The chlorine content when the vinylidene fluoride homopolymer was used is believed to be chlorine derived from impurities.

[0110] In contrast, when a vinylidene fluoride polymer having an IR absorbance ratio measured by FT-IR of 0.1 to 16.0 and a total content of eliminated halogen atoms of 28 μmol / g to 1550 μmol / g was used, even when an electrode mixture was prepared with an active material (NCA) containing a large amount of nickel, the change in viscosity after 7 days (viscosity after 7 days of storage / viscosity immediately after production) was 3.1 times or less, that is, less than half of that when a vinylidene fluoride homopolymer was used (Examples 1 to 4).

[0111] This application claims priority from Japanese Patent Application No. 2024-028992, filed February 28, 2024, the entire contents of which are incorporated herein by reference.

[0112] According to the present invention, there is provided a vinylidene fluoride polymer that is resistant to thickening and gelling of an electrode mixture (slurry) even when mixed with an active material containing a large amount of base, etc. The vinylidene fluoride polymer is very useful in the field of manufacturing various batteries.

Claims

1. A vinylidene fluoride polymer containing structural units derived from vinylidene fluoride, having an IR absorbance ratio calculated from an absorption spectrum measured by Fourier transform infrared spectroscopy using the following formula of 0.1 or more and 16 or less, and having a total content of chlorine atoms, bromine atoms, and iodine atoms of 28 μmol / g or more and 1550 μmol / g or less. IR absorbance ratio = A Ｃ＝Ｏ / A Ｃ－Ｈ (In the formula, A Ｃ＝Ｏ represents the absorbance of the peak due to C═O stretching, and A Ｃ－Ｈ represents the absorbance of the peak due to C-H stretching) 2. The vinylidene fluoride polymer according to claim 1, having an inherent viscosity of 0.5 dl / g or more and 5.0 dl / g or less.

3. The vinylidene fluoride polymer according to claim 1, further comprising structural units derived from a compound other than vinylidene fluoride, wherein the randomness of the structural units derived from a compound other than vinylidene fluoride within the polymer chain is 0.5% or more.

4. The vinylidene fluoride polymer according to claim 1, further comprising a structural unit derived from a compound other than vinylidene fluoride, wherein the compound other than vinylidene fluoride contains at least one atom selected from the group consisting of a chlorine atom, a bromine atom, and an iodine atom, and a carboxy group.

5. A binder comprising the vinylidene fluoride polymer according to any one of claims 1 to 4.

6. An electrode mixture comprising the vinylidene fluoride polymer according to any one of claims 1 to 4 and an active material.

7. 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).

8. An electrode comprising the vinylidene fluoride polymer according to any one of claims 1 to 4 and an active material.

9. A battery comprising the electrode according to claim 8.

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