Electrode mixture, secondary battery and composition

Abstract

Provided is an electrode mixture which contains an electrode active substance, an organic solvent, a binder and an additive. The binder contains a fluorine-containing copolymer that contains vinylidene fluoride units and fluorinated monomer units (excluding vinylidene fluoride units). The additive is a polymer material having a repeating unit represented by -[CH2-CHR]- (in this repeating unit, R is a chain-like or cyclic amido group, a nitrile group or an alkyl group having 1-4 carbon atoms, with at least one hydrogen atom in said alkyl group being substituted with a chain-like or cyclic amido group or a nitrile group). The content of the binder is 0.1-1.6 parts by mass relative to 100 parts by mass of the electrode active substance. The content of the additive is 0.001-0.2 parts by mass relative to 100 parts by mass of the electrode active substance.

Description

[Technical Field]

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

[0002] Non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries are used in small, portable electrical and electronic devices such as notebook computers, mobile phones, smartphones, tablet computers, and ultrabooks, due to their high voltage, high energy density, low self-discharge, low memory effect, and the ability to be made extremely lightweight. Furthermore, they are increasingly being put into practical use as a wide range of power sources, including on-board power sources for driving automobiles and large-scale stationary power sources.

[0003] As an electrode mixture for forming an electrode included in such a non-aqueous electrolyte secondary battery, for example, Patent Document 1 discloses an electrode mixture characterized by including a binder composition, a solvent, and an electrode active material, wherein the binder composition includes a vinylidene fluoride polymer and a polymer additive, the vinylidene fluoride polymer includes a vinylidene fluoride copolymer including a structural unit derived from vinylidene fluoride and a structural unit derived from chlorotrifluoroethylene, and the polymer additive includes a repeating unit as follows: -[CH2-CHR]- The electrode mixture is characterized by being a polymer material having the formula: (In the above repeating unit, R represents a linear or cyclic amide group, a nitrile group, a hydroxy group, an ester-containing group, or an alkyl group having 1 to 4 carbon atoms, in which at least one hydrogen atom of the alkyl group has been substituted with a linear or cyclic amide group, a nitrile group, or a hydroxy group.)

[0004] Patent Document 2 describes a positive electrode for a lithium secondary battery, which is produced by a process comprising the steps of: using polyvinylpyrrolidone as a dispersant; dispersing carbon black as a conductive additive in a solvent using a high-pressure jet mill to prepare a carbon black-containing dispersion; mixing the obtained carbon black-containing dispersion with at least a positive electrode active material containing lithium to prepare a paint for forming a positive electrode coating film; applying the obtained paint for forming a positive electrode coating film to a current collector; and drying the paint. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2019 / 167322 [Patent Document 2] Japanese Patent Application Laid-Open No. 2004-281096 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present disclosure is to provide an electrode mixture that is capable of forming an electrode mixture layer that is less likely to increase in viscosity and that has excellent adhesion to a current collector and flexibility, and that can form a secondary battery with sufficient load characteristics. [Means for solving the problem]

[0007] According to the present disclosure, an electrode active material is provided which contains an electrode active material, an organic solvent, a binder, and an additive, the binder contains a fluorine-containing copolymer containing a vinylidene fluoride unit and a fluorinated monomer unit (excluding the vinylidene fluoride unit), and the additive contains a repeating unit as follows: -[CH2-CHR]- (In the above repeating unit, R represents a linear or cyclic amide group, a nitrile group, or an alkyl group having 1 to 4 carbon atoms, where at least one hydrogen atom of the alkyl group is substituted with a linear or cyclic amide group or a nitrile group.) The content of the binder is 0.1 to 1.6 parts by mass relative to 100 parts by mass of the electrode active material, and the content of the additive is 0.001 to 0.2 parts by mass relative to 100 parts by mass of the electrode active material.

[0008] In the electrode mixture of the present disclosure, the fluorinated monomer unit of the fluorine-containing copolymer is preferably at least one selected from the group consisting of a tetrafluoroethylene unit, a chlorotrifluoroethylene unit, a fluoroalkyl vinyl ether unit and a hexafluoropropylene unit. In the electrode mixture of the present disclosure, the content of the vinylidene fluoride units in the fluorine-containing copolymer is preferably 50.0 to 99.0 mol % based on the total monomer units. In the electrode mixture of the present disclosure, the additive is preferably at least one selected from the group consisting of polyvinylpyrrolidone and polyacrylonitrile, and more preferably polyvinylpyrrolidone. In the electrode mixture of the present disclosure, the additive preferably has a number average molecular weight of 10,000 to 500,000. In the electrode mixture of the present disclosure, the electrode active material is preferably at least one selected from the group consisting of lithium-containing transition metal composite oxides and lithium-containing transition metal phosphate compounds.

[0009] The present disclosure also provides an electrode including a current collector and an electrode mixture layer formed from the electrode mixture and provided on one or both surfaces of the current collector.

[0010] The present disclosure also provides a secondary battery including the above electrode.

[0011] Further, according to the present disclosure, there is provided a fluorine-containing copolymer containing vinylidene fluoride units and tetrafluoroethylene units, and a fluorine-containing copolymer containing, as an additive, the following repeating unit: -[CH2-CHR]- (In the above repeating unit, R represents a linear or cyclic amide group, a nitrile group, or an alkyl group having 1 to 4 carbon atoms, and at least one hydrogen atom of the alkyl group is substituted with a linear or cyclic amide group or a nitrile group.)

[0012] In the composition of the present disclosure, the content of the vinylidene fluoride units in the fluorine-containing copolymer is preferably 50.0 to 99.0 mol % based on the total monomer units. In the composition of the present disclosure, the mass ratio (a / b) of the fluorine-containing copolymer (a) to the additive (b) is preferably 1 / 99 to 99 / 1. The composition of the present disclosure preferably further contains an organic solvent. [Effects of the Invention]

[0013] According to the present disclosure, it is possible to provide an electrode mixture that can form an electrode mixture layer that is less likely to increase in viscosity and that has excellent adhesion to a current collector and flexibility, and that can form a secondary battery with sufficient load characteristics. DETAILED DESCRIPTION OF THE INVENTION

[0014] Specific embodiments of the present disclosure will be described in detail below, but the present disclosure is not limited to the following embodiments.

[0015] The electrode mixture of the present disclosure contains an electrode active material, an organic solvent, a binder, and an additive.

[0016] <Electrode active material> The electrode active material contained in the electrode mixture of the present disclosure may be a positive electrode active material or a negative electrode active material. There are no particular limitations on the positive electrode active material as long as it is capable of electrochemically absorbing and releasing lithium ions. However, lithium composite oxides are preferred, and lithium transition metal composite oxides are more preferred, as they can increase the capacity of the secondary battery. Lithium-containing transition metal phosphate compounds are also preferred as the positive electrode active material. It is also preferred that the positive electrode active material be a substance containing lithium and at least one transition metal, such as a lithium transition metal composite oxide or a lithium-containing transition metal phosphate compound.

[0017] The transition metal of the lithium transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. Specific examples of the lithium transition metal composite oxide include lithium-cobalt composite oxides such as LiCoO2, lithium-nickel composite oxides such as LiNiO2, lithium-manganese composite oxides such as LiMnO2, LiMn2O4, and Li2MnO3, and those in which some of the transition metal atoms that make up the main components of these lithium transition metal composite oxides have been substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, and Si. Examples of the substituted oxides include lithium-nickel-manganese composite oxide, lithium-nickel-cobalt-aluminum composite oxide, lithium-nickel-cobalt-manganese composite oxide, lithium-manganese-aluminum composite oxide, and lithium-titanium composite oxide. More specifically, LiNi 0.5 Mn 0.5 O2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2, LiMn 1.8 Al0.2 O4, LiMn 1.5 Ni 0.5 O4, Li4Ti5O 12 , LiNi 0.82 Co 0.15 Al 0.03 Examples include O2.

[0018] The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc., and specific examples of the lithium-containing transition metal phosphate compound include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7, cobalt phosphates such as LiCoPO4, and lithium transition metal phosphate compounds in which a portion of the transition metal atoms that constitute the main components of these lithium transition metal phosphate compounds has been substituted with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, and Si.

[0019] The positive electrode active material is preferably at least one selected from the group consisting of lithium-cobalt composite oxide, lithium-nickel composite oxide, lithium-manganese composite oxide, iron phosphates, lithium-nickel-manganese composite oxide, lithium-nickel-cobalt-manganese composite oxide, and lithium-nickel-cobalt-aluminum composite oxide, and more preferably at least one selected from the group consisting of lithium-cobalt composite oxide, lithium-nickel composite oxide, lithium-manganese composite oxide, lithium-nickel-manganese composite oxide, lithium-nickel-cobalt-manganese composite oxide, and lithium-nickel-cobalt-aluminum composite oxide, because this allows the formation of an electrode mixture layer that has even better adhesion to the current collector. The positive electrode active material is LiCoO2, LiNiO2, LiMn2O4, LiFePO4, LiNi 0.33 Mn 0.33 Co 0.33 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.82 Co 0.15 Al 0.03 O2, LiNi0.6 Mn 0.2 Co 0.2 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2 and LiNi 0.90 Mn 0.05 Co 0.05 At least one selected from the group consisting of O2 is preferred.

[0020] As the lithium-containing transition metal composite oxide, lithium-nickel composite oxides are particularly preferred, and are represented by the general formula (1): General formula (1): Li y Ni 1-x M x O2 (In the formula, x is 0.01≦x≦0.5, y is 0.9≦y≦1.2, and M represents a metal atom (excluding Li and Ni).) More preferred is a lithium-nickel composite oxide represented by the formula: In this way, lithium-containing transition metal oxides containing a large amount of Ni are useful for increasing the capacity of secondary batteries. Furthermore, even when the electrode mixture of the present disclosure contains a lithium-containing transition metal oxide containing a large amount of Ni as the electrode active material, the viscosity does not easily increase and the electrode mixture has excellent coatability.

[0021] In general formula (1), x is a coefficient that satisfies 0.01≦x≦0.5, and is preferably 0.05≦x≦0.4, and more preferably 0.10≦x≦0.3, since this allows a secondary battery with an even higher capacity to be obtained.

[0022] In general formula (1), examples of the metal atom of M include V, Ti, Cr, Mn, Fe, Co, Cu, Al, Zn, Mg, Ga, Zr, Si, etc. Preferred metal atoms of M are transition metals such as V, Ti, Cr, Mn, Fe, Co, and Cu, or combinations of the above transition metals with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mg, Ga, Zr, and Si.

[0023] The lithium-nickel composite oxide represented by the general formula (1) is LiNi 0.80Co 0.15 Al 0.05 O2, LiNi 0.82 Co 0.15 Al 0.03 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.8 Mn 0.1 Co 0.1 O2 and LiNi 0.90 Mn 0.05 Co 0.05 At least one selected from the group consisting of LiNi 0.82 Co 0.15 Al 0.03 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2 and LiNi 0.8 Mn 0.1 Co 0.1 At least one selected from the group consisting of O2 is more preferred.

[0024] The lithium-nickel composite oxide represented by general formula (1) may be used in combination with a different positive electrode active material. Specific examples of the different positive electrode active material include LiCoO 2、 LiMnO2, LiMn2O4, Li2MnO 3、 LiMn 1.8 Al 0.2 O 4、 Li4Ti5O 12、 LiFePO4, Li3Fe2(PO4)3, LiFeP2O 7、 LiCoPO4, Li 1.2 Fe 0.4 Mn 0.4 O2, LiNiO2, etc.

[0025] Furthermore, a substance having a different composition from the substance constituting the main positive electrode active material may be attached to the surface of the positive electrode active material. Examples of the surface-attached substance include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide, sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate, and carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.

[0026] These surface-attaching substances can be attached to the surface of the positive electrode active material by, for example, a method of dissolving or suspending the surface-attaching substance precursor in a solvent, adding the substance to the positive electrode active material by impregnation, and drying the solvent; a method of dissolving or suspending the surface-attaching substance precursor in a solvent, adding the substance to the positive electrode active material by impregnation, and then reacting the substance by heating or the like; a method of adding the substance to the positive electrode active material precursor and simultaneously baking the substance; or the like.

[0027] The amount of the surface-attached substance is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more by mass relative to the positive electrode active material, and is preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less by mass relative to the positive electrode active material. The surface-attached substance can suppress the oxidation reaction of the nonaqueous electrolyte on the surface of the positive electrode active material and improve the battery life, but if the amount of attachment is too small, the effect will not be fully exerted, and if it is too large, the movement of lithium ions into and out of the positive electrode active material will be hindered, which may increase the resistance.

[0028] The particle shape of the positive electrode active material may be a block, polyhedron, sphere, ellipsoid, plate, needle, column, or the like, as conventionally used. However, a spherical or ellipsoidal secondary particle is preferred, in which primary particles aggregate to form secondary particles. Typically, electrochemical devices experience stress-induced expansion and contraction of the active material in the electrode during charging and discharging, which can lead to deterioration such as destruction of the active material and disconnection of the conductive path. Therefore, a material in which primary particles aggregate to form secondary particles is preferred over a single-particle active material consisting of only primary particles, as this relieves the stress of expansion and contraction and prevents deterioration. Furthermore, spherical or ellipsoidal particles are preferred over plate-like equiaxially oriented particles because they are less oriented during electrode molding, resulting in less expansion and contraction of the electrode during charging and discharging, and are also more easily mixed uniformly with the conductive additive when preparing the electrode.

[0029] The tap density of the positive electrode active material is typically 1.3 g / cm 3 or more, preferably 1.5 g / cm 3 More preferably, 1.6 g / cm 3 or more, most preferably 1.7 g / cm 3 That's all. If the tap density of the positive electrode active material is below the above lower limit, the amount of dispersion medium required when forming the positive electrode mixture layer increases, and the amounts of conductive additive and binder required also increase, which may restrict the filling rate of the positive electrode active material in the positive electrode mixture layer and restrict the battery capacity. By using a metal composite oxide powder with a high tap density, a high-density positive electrode mixture layer can be formed. Generally, the higher the tap density, the more preferable it is, and there is no particular upper limit. However, if it is too high, the diffusion of lithium ions in the positive electrode mixture layer using the nonaqueous electrolyte as a medium becomes rate-determining, which may lead to a decrease in load characteristics. Therefore, the tap density is usually set to 2.5 g / cm. 3 or less, preferably 2.4 g / cm 3 The following is the result.

[0030] The tap density of the positive electrode active material is measured by passing it through a sieve with a mesh size of 300 μm and measuring it in 20 cm 3After dropping the sample into the tapping cell to fill the cell volume, tapping is performed 1000 times with a stroke length of 10 mm using a powder density measuring device (for example, Tap Denser manufactured by Seishin Enterprise Co., Ltd.), and the density calculated from the volume and weight of the sample at that time is defined as the tap density.

[0031] The median particle diameter d50 of the positive electrode active material (the secondary particle diameter when primary particles aggregate to form secondary particles) is typically 0.1 μm or larger, preferably 0.5 μm or larger, more preferably 1 μm or larger, and most preferably 3 μm or larger, and typically 20 μm or smaller, preferably 18 μm or smaller, more preferably 16 μm or smaller, and most preferably 15 μm or smaller. Below the lower limit, high bulk density products may not be obtained. Above the upper limit, lithium diffusion within the particles takes longer, resulting in reduced battery performance and problems such as streaking during battery positive electrode preparation, i.e., when the active material, conductive additive, binder, etc. are slurried with a solvent and applied as a thin film. Mixing two or more positive electrode active materials with different median diameters d50 can further improve the packing properties during positive electrode preparation.

[0032] The median diameter d50 in this disclosure is measured using a known laser diffraction / scattering particle size distribution analyzer. When using a HORIBA LA-920 as the particle size distribution analyzer, the measurement is performed using a 0.1% by mass aqueous solution of sodium hexametaphosphate as the dispersion medium, and after ultrasonic dispersion for 5 minutes, the measurement is performed with a refractive index set to 1.24.

[0033] When primary particles aggregate to form secondary particles, the average primary particle diameter of the positive electrode active material is typically 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.08 μm or more, and most preferably 0.1 μm or more, and typically 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and most preferably 0.6 μm or less. If the diameter exceeds the upper limit, it becomes difficult to form spherical secondary particles, adversely affecting powder packing, and the specific surface area is significantly reduced, potentially resulting in a decrease in battery performance, such as output characteristics. Conversely, if the diameter is below the lower limit, problems such as poor charge / discharge reversibility due to underdeveloped crystals may occur. The primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, the diameter is determined by taking a 10,000x magnification photograph of 50 primary particles and averaging the longest intercepts of a horizontal line at the left and right boundaries of the primary particles.

[0034] The BET specific surface area of ​​the positive electrode active material is 0.2 m 2 / g or more, preferably 0.3m 2 / g or more, more preferably 0.4m 2 / g or more, 4.0m 2 / g or less, preferably 2.5m 2 / g or less, more preferably 1.5m 2 If the BET specific surface area is smaller than this range, the battery performance is likely to decrease, whereas if it is larger, it becomes difficult to increase the tap density, which may easily cause problems with the coating properties when forming the positive electrode mixture layer.

[0035] The BET specific surface area is defined as the value measured by a surface area meter (for example, an automatic surface area measuring device manufactured by Okura Riken) using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3, after which the sample is pre-dried at 150°C for 30 minutes under a nitrogen flow, by the nitrogen adsorption BET single-point method using a gas flow method.

[0036] The positive electrode active material is produced by a method generally used for producing inorganic compounds. In particular, various methods can be considered for producing spherical or oval-spherical active materials, such as a method of dissolving or pulverizing and dispersing transition metal raw materials such as transition metal nitrates and sulfates, and if necessary, raw materials of other elements, in a solvent such as water, adjusting the pH while stirring to produce and recover spherical precursors, which are then dried as needed, and then adding a Li source such as LiOH, Li2CO3, or LiNO3, and calcining at a high temperature to obtain an active material; a method of dissolving or pulverizing transition metal raw materials such as transition metal nitrates, sulfates, hydroxides, or oxides, and if necessary, raw materials of other elements, in a solvent such as water, Examples of such methods include dispersing a precursor in the form of a sphere or ellipsoid, drying and molding it using a spray dryer or the like to form a spherical or ellipsoidal precursor, adding a Li source such as LiOH, Li2CO3, or LiNO3 to the precursor, and firing it at a high temperature to obtain an active material; and dissolving or pulverizing and dispersing a transition metal raw material such as a transition metal nitrate, sulfate, hydroxide, or oxide, a Li source such as LiOH, Li2CO3, or LiNO3, and, if necessary, raw materials of other elements, in a solvent such as water, drying and molding it using a spray dryer or the like to form a spherical or ellipsoidal precursor, and firing this at a high temperature to obtain an active material.

[0037] In the present disclosure, one type of positive electrode active material powder may be used alone, or two or more types having different compositions or different powder properties may be used in any combination and ratio.

[0038] The negative electrode active material is not particularly limited as long as it can electrochemically absorb and release lithium ions, and examples thereof include carbonaceous materials, metal oxides such as tin oxide and silicon oxide, metal composite oxides, lithium alone, lithium alloys such as lithium-aluminum alloys, and metals capable of forming alloys with lithium, such as Sn and Si. These may be used alone or in any combination and ratio of two or more. Of these, carbonaceous materials or lithium composite oxides are preferably used from the standpoint of safety.

[0039] The metal composite oxide is not particularly limited as long as it is capable of absorbing and releasing lithium, but it is preferable that the metal composite oxide contains titanium and / or lithium as a constituent component from the viewpoint of high current density charge / discharge characteristics.

[0040] As the metal composite oxide, a lithium-containing transition metal composite oxide is preferable. For example, in addition to the lithium-nickel composite oxide represented by the above-mentioned general formula (1), a Li-based composite oxide having a spinel structure is also preferable. 4+x Ti5O 12 (0≦x≦3) and Li with ramsteride structure 2+y Examples include lithium titanates such as Ti3O7 (0≦y≦3).

[0041] Carbonaceous materials include: (1) Natural graphite, (2) Artificial carbonaceous materials and artificial graphitic materials; carbonaceous materials {for example, natural graphite, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or oxidized versions of these pitches, needle coke, pitch coke, and partially graphitized carbon materials, furnace black, acetylene black, pitch-based carbon fiber, and other organic pyrolysis products; carbonizable organic materials (for example, coal tar pitch ranging from soft pitch to hard pitch, coal-based heavy oils such as carbonized liquefied oil, atmospheric residue, straight-run heavy oils such as vacuum residue, cracked petroleum heavy oils such as ethylene tar produced as a by-product during the thermal decomposition of crude oil, naphtha, etc.); aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene; N-ring compounds such as phenazine and acridine; S-ring compounds such as thiophene and bithiophene; biphenyls; terphenyls; carbonaceous materials obtained by heat-treating the following at least once in the range of 400 to 3200°C: (polyphenylenes such as phenylene, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized products of these, nitrogen-containing organic polymers such as polyacrylonitrile and polypyrrole, sulfur-containing organic polymers such as polythiophene and polystyrene, natural polymers such as cellulose, lignin, mannan, polygalacturonic acid, chitosan, and polysaccharides represented by saccharose, thermoplastic resins such as polyphenylene sulfide and polyphenylene oxide, and thermosetting resins such as furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin), and carbonized products thereof, or solutions of carbonizable organic substances dissolved in low-molecular organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane, and carbonized products thereof; (3) A carbonaceous material in which the negative electrode mixture layer is made of at least two or more carbonaceous materials having different crystallinities and / or has an interface where the carbonaceous materials having different crystallinities are in contact with each other; (4) A carbonaceous material in which the negative electrode mixture layer is made of at least two or more kinds of carbonaceous materials having different orientations and / or has an interface where the carbonaceous materials having different orientations are in contact with each other; The material selected from the above is preferable because it has a good balance between initial irreversible capacity and high current density charge / discharge characteristics.

[0042] The content of the electrode active material (positive electrode active material or negative electrode active material) is preferably 40 mass % or more in the electrode mixture in order to increase the capacity of the resulting electrode.

[0043] The content of the electrode active material in the positive electrode mixture of the present disclosure is preferably 96.0 to 99.0 mass %, more preferably 96.5 to 98.9 mass %, and even more preferably 97.0 to 98.8 mass %, relative to the mass of the positive electrode mixture.

[0044] <Conductive additive> The electrode mixture of the present disclosure preferably further contains a conductive auxiliary agent, such as carbon blacks (e.g., acetylene black, ketjen black, etc.), carbon materials (e.g., graphite), carbon fibers, carbon nanotubes, and carbon nanohorns.

[0045] The content of the conductive auxiliary in the positive electrode mixture of the present disclosure is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and even more preferably 0.1 to 2 parts by mass, relative to 100 parts by mass of the positive electrode active material.

[0046] <Organic solvents> The electrode mixture of the present disclosure further contains an organic solvent. Examples of the organic solvent include nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and dimethylformamide; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, and methyl isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; ether solvents such as tetrahydrofuran and dioxane; β-alkoxypropionamides such as β-methoxy-N,N-dimethylpropionamide, β-n-butoxy-N,N-dimethylpropionamide, and β-n-hexyloxy-N,N-dimethylpropionamide; and low-boiling general-purpose organic solvents such as mixed solvents thereof. Among these, the solvent is preferably at least one selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and β-alkoxypropionamides, and more preferably at least one selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylacetamide, because of its excellent coating properties.

[0047] <Binder> The binder contained in the electrode mixture of the present disclosure contains a fluorine-containing copolymer containing vinylidene fluoride units (VdF units) and fluorinated monomer units (excluding VdF units). Because the electrode mixture of the present disclosure contains a fluorine-containing copolymer containing VdF units and fluorinated monomer units as a binder, it can form an electrode mixture layer that adheres sufficiently to the current collector, and has excellent coatability with little increase in viscosity, allowing the electrode mixture layer to be easily formed and improving the flexibility of the electrode mixture layer.

[0048] Examples of fluorinated monomers (excluding VdF) include tetrafluoroethylene (TFE), vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene, and trans-1,3,3,3-tetrafluoropropene. Among these, at least one selected from the group consisting of TFE, CTFE, HFP, fluoroalkyl vinyl ether, and 2,3,3,3-tetrafluoropropene is preferred, as this can further suppress an increase in the viscosity of the electrode mixture and can form an electrode mixture layer that is more excellent in adhesion to the current collector and flexibility. At least one selected from the group consisting of TFE, CTFE, fluoroalkyl vinyl ether, and HFP is more preferred, and at least one selected from the group consisting of TFE and HFP is even more preferred, with TFE being particularly preferred.

[0049] The fluoroalkyl vinyl ether (FAVE) is preferably a fluoroalkyl vinyl ether having a fluoroalkyl group having 1 to 5 carbon atoms, and more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether).

[0050] The fluorinated monomer units (except for the VdF units) may or may not have a polar group.

[0051] The content of VdF units in the fluorine-containing copolymer is preferably 50.0 to 99.0 mol%, more preferably 57.0 mol% or more, even more preferably 60.0 mol% or more, particularly preferably 63.0 mol% or more, more preferably 97.0 mol% or less, even more preferably 95.0 mol% or less, particularly preferably 90.0 mol% or less, and most preferably 85.0 mol% or less, based on the total monomer units, because this can further suppress an increase in the viscosity of the electrode mixture and enable the formation of an electrode mixture layer that is more excellent in adhesion to the current collector and flexibility.

[0052] The content of fluorinated monomer units (excluding VdF units) in the fluorine-containing copolymer is preferably 1.0 mol% or more, more preferably 3.0 mol% or more, even more preferably 5.0 mol% or more, particularly preferably 10.0 mol% or more, most preferably 15.0 mol% or more, and preferably 50.0 mol% or less, more preferably 43.0 mol% or less, even more preferably 40.0 mol% or less, particularly preferably 37.0 mol% or less, based on all monomer units.

[0053] In the present disclosure, the composition of the fluorine-containing copolymer is, for example, 19 It can be measured by F-NMR measurement.

[0054] The fluorine-containing copolymer may further contain a non-fluorinated monomer unit. Examples of the non-fluorinated monomer include a non-fluorinated monomer having no polar group, such as ethylene or propylene, and a non-fluorinated monomer having a polar group (hereinafter sometimes referred to as a polar group-containing monomer).

[0055] When a non-fluorinated monomer having a polar group is used, the polar group is introduced into the fluorine-containing copolymer, thereby achieving even better adhesion between the electrode mixture layer and the current collector. The polar group that the fluorine-containing copolymer may have is preferably at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, a hydroxy group, a sulfonic acid group, a sulfate group, a phosphate group, an amino group, an amide group, and an alkoxy group, more preferably at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, and a hydroxy group, and even more preferably a carbonyl group-containing group. The hydroxy group does not include a hydroxy group that constitutes a part of the carbonyl group-containing group. The amino group is a monovalent functional group obtained by removing hydrogen from ammonia, a primary amine, or a secondary amine.

[0056] The carbonyl group-containing group is a functional group having a carbonyl group (-C(=O)-). The carbonyl group-containing group is preferably a group represented by the general formula -COOR (R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) or a carboxylic acid anhydride group. The number of carbon atoms in the alkyl group or hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of the group represented by the general formula -COOR include -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, and -COOC2H5. When the group represented by the general formula -COOR is -COOH or contains -COOH, the -COOH may be a carboxylate such as a metal carboxylate or an ammonium carboxylate.

[0057] The carbonyl group-containing group may also be a group represented by the general formula: -X-COOR (X is an atomic group having a main chain composed of 2 to 15 atoms, and the molecular weight of the atomic group is preferably 350 or less; R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group). The alkyl group and the hydroxyalkyl group preferably have 1 to 16 carbon atoms, more preferably 1 to 6, and even more preferably 1 to 3 carbon atoms.

[0058] The amide group is preferably a group represented by the general formula: -CO-NRR' (R and R' independently represent a hydrogen atom or a substituted or unsubstituted alkyl group), or a bond represented by the general formula: -CO-NR"- (R" represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group).

[0059] Examples of the polar group-containing monomer include hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropyl acrylate; alkylidene malonic acid esters such as dimethyl methylidene malonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; (meth)acryloyloxyalkyl dicarboxylic acid esters such as acryloyloxyethyl succinate, acryloyloxypropyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, and methacryloyloxyethyl phthalate; monoesters of unsaturated dibasic acids such as maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, and citraconic acid monoethyl ester; and compounds represented by the general formula (2): [ka] (In the formula, R 1 ~R 3 R independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. 4 represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. 1 represents an inorganic cation and / or an organic cation.

[0060] The polar group-containing monomer unit that the fluorine-containing copolymer can contain is preferably a unit based on the monomer (2) represented by the general formula (2).

[0061] In general formula (2), Y1 represents an inorganic cation and / or an organic cation. Examples of inorganic cations include cations such as H, Li, Na, K, Mg, Ca, Al, and Fe. Examples of organic cations include NH4, NHR, and the like. 5 , NH2R 5 2. NHR 5 3.NR 5 4(R 5 and each independently represent an alkyl group having 1 to 4 carbon atoms. 1 As the cation, H, Li, Na, K, Mg, Ca, Al, and NH4 are preferred, H, Li, Na, K, Mg, Al, and NH4 are more preferred, H, Li, Al, and NH4 are still more preferred, and H is particularly preferred. For convenience, the symbols and valences of specific examples of inorganic cations and organic cations are omitted.

[0062] In general formula (2), R 1 ~R 3 R independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. The hydrocarbon group is a monovalent hydrocarbon group. The hydrocarbon group preferably has 4 or less carbon atoms. Examples of the hydrocarbon group include alkyl groups, alkenyl groups, alkynyl groups, etc. having the above carbon numbers, with a methyl group or an ethyl group being preferred. 1 and R 2 are preferably independently a hydrogen atom, a methyl group, or an ethyl group, and R 3 is preferably a hydrogen atom or a methyl group.

[0063] In general formula (2), R 4 represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. The hydrocarbon group is a divalent hydrocarbon group. The hydrocarbon group preferably has 4 or less carbon atoms. Examples of the hydrocarbon group include alkylene groups and alkenylene groups having the above carbon numbers, and among these, at least one selected from the group consisting of a methylene group, an ethylene group, an ethylidene group, a propylidene group, and an isopropylidene group is preferred, with a methylene group being more preferred.

[0064] Monomer (2) is preferably at least one selected from the group consisting of (meth)acrylic acid and salts thereof, vinylacetic acid (3-butenoic acid) and salts thereof, 3-pentenoic acid and salts thereof, 4-pentenoic acid and salts thereof, 3-hexenoic acid and salts thereof, 4-heptenoic acid and salts thereof, and 5-hexenoic acid and salts thereof, and more preferably at least one selected from the group consisting of 3-butenoic acid and salts thereof, and 4-pentenoic acid and salts thereof.

[0065] The content of the polar group-containing monomer units in the fluorine-containing copolymer is preferably 0.05 to 2.0 mol %, more preferably 0.10 mol % or more, even more preferably 0.25 mol % or more, particularly preferably 0.40 mol % or more, and more preferably 1.5 mol % or less, based on all monomer units.

[0066] In the present disclosure, the content of polar group-containing monomer units in the fluorine-containing copolymer can be measured, for example, when the polar group is an acid group such as a carboxylic acid, by acid-base titration of the acid group.

[0067] Examples of the fluorine-containing copolymer include VdF / TFE copolymer, VdF / HFP copolymer, VdF / TFE / HFP copolymer, VdF / 2,3,3,3-tetrafluoropropene copolymer, VdF / TFE / 2,3,3,3-tetrafluoropropene copolymer, VdF / TFE / (meth)acrylic acid copolymer, VdF / HFP / (meth)acrylic acid copolymer, VdF / CTFE copolymer, VdF / TFE / 4-pentenoic acid copolymer, VdF / TFE / 3-butenoic acid copolymer, VdF / TFE / HFP / (meth)acrylic acid copolymer, VdF / CTFE copolymer, VdF / TFE / 4-pentenoic acid copolymer, VdF / TFE / 3-butenoic acid copolymer, VdF / TFE / HFP / (meth)acrylic acid copolymer, V Examples of the copolymer include VdF / TFE / HFP / 4-pentenoic acid copolymer, VdF / TFE / HFP / 3-butenoic acid copolymer, VdF / TFE / 2-carboxyethyl acrylate copolymer, VdF / TFE / HFP / 2-carboxyethyl acrylate copolymer, VdF / TFE / acryloyloxyethyl succinic acid copolymer, VdF / TFE / HFP / acryloyloxyethyl succinic acid copolymer / VdF / FAVE copolymer, VdF / FAVE / (meth)acrylic acid copolymer, and VdF / FAVE / 2-carboxyethyl acrylate copolymer.

[0068] The fluorine-containing copolymer is preferably a fluorine-containing copolymer consisting only of VdF units, TFE units and any non-fluorinated monomer units.

[0069] When the fluorine-containing copolymer contains VdF units and TFE units, the molar ratio of VdF units to TFE units (VdF units / TFE units) is preferably 50 / 50 to 99 / 1, more preferably 57 / 43 to 97 / 3, still more preferably 60 / 40 to 95 / 5, particularly preferably 63 / 37 to 90 / 10, and most preferably 63 / 37 to 85 / 15.

[0070] The weight average molecular weight (polystyrene equivalent) of the fluorine-containing copolymer is preferably 50,000 to 3,000,000, more preferably 80,000 or more, even more preferably 100,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, particularly preferably 2,000,000 or less. The weight average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0071] The number average molecular weight (polystyrene equivalent) of the fluorine-containing copolymer is preferably 20,000 to 1,500,000, more preferably 40,000 or more, even more preferably 70,000 or more, particularly preferably 140,000 or more, more preferably 1,400,000 or less, even more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less. The number average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0072] The melting point of the fluorine-containing copolymer is preferably 100 to 170° C., more preferably 110 to 165° C., and even more preferably 120 to 163° C. The melting point is determined using a differential scanning calorimetry (DSC) device as the temperature at the maximum on the heat of fusion curve obtained by increasing the temperature from 30° C. to 220° C. at a rate of 10° C. / min, then decreasing the temperature to 30° C. at 10° C. / min, and again increasing the temperature to 220° C. at a rate of 10° C. / min.

[0073] The fluorine-containing copolymer preferably has an elongation at break of 100% or more, more preferably 200% or more, and even more preferably 300% or more.

[0074] The elongation at break can be measured by the following method. A fluorocopolymer solution obtained by dissolving a fluorocopolymer in N-methyl-2-pyrrolidone (NMP) to a concentration of 10 to 20% by mass is cast onto a glass plate, dried at 100°C for 12 hours, and further dried under vacuum at 100°C for 12 hours to obtain a film with a thickness of 50 to 100 μm. This film is punched into a dumbbell shape, and the elongation at break at 25°C is measured using an autograph.

[0075] The fluorine-containing copolymer preferably has a storage modulus at 30°C of 1100 MPa or less and a storage modulus at 60°C of 500 MPa or less. The storage modulus of the fluorine-containing copolymer at 30°C is more preferably 800 MPa or less, and further preferably 600 MPa or less. The storage modulus of the fluorine-containing copolymer at 60°C is more preferably 350 MPa or less. The storage modulus of the fluorine-containing copolymer at 30°C is preferably 100 MPa or more, more preferably 150 MPa or more, and even more preferably 200 MPa or more. The storage modulus of the fluorine-containing copolymer at 60°C is preferably 50 MPa or more, more preferably 80 MPa or more, and even more preferably 130 MPa or more.

[0076] The storage modulus is the measured value at 30°C and 60°C for a sample with a length of 30 mm, width of 5 mm, and thickness of 50 to 100 μm, measured using a dynamic viscoelasticity measurement device DVA220 manufactured by IT Measurement & Control Co., Ltd. under the following conditions: tensile mode, grip width 20 mm, measurement temperature -30°C to 160°C, heating rate 2°C / min, and frequency 1 Hz.

[0077] A measurement sample can be prepared, for example, by dissolving a fluorinated copolymer in N-methyl-2-pyrrolidone (NMP) to a concentration of 10 to 20 mass%, casting the resulting fluorinated copolymer solution onto a glass plate, drying it at 100°C for 12 hours, and further drying it under vacuum at 100°C for 12 hours, and cutting the resulting film having a thickness of 50 to 100 μm into a length of 30 mm and a width of 5 mm.

[0078] The fluorocopolymer preferably has a weight increase rate of 250% by mass or less, more preferably 200% by mass or less, after immersion in an electrolyte solution at 60° C. for one week. The weight increase rate of the fluorocopolymer after immersion in an electrolyte solution at 60° C. for one week is further preferably 180% by mass or less, particularly preferably 160% by mass or less, and may be 105% by mass or more.

[0079] The weight gain rate can be determined by the following method. A 200 μm thick film of the fluorine-containing copolymer is produced by casting an NMP solution (8% by mass) on a glass petri dish and vacuum drying it for 12 hours at 100°C. The obtained film is punched out to a size of 6 mmΦ and placed in a sample bottle containing an electrolyte (a solution of LiPF6 dissolved at a concentration of 1 M in a solvent of ethylene carbonate / ethyl methyl carbonate at a volume ratio of 3 / 7), and left to stand at 60°C for one week, after which the weight gain is determined.

[0080] The binder contained in the electrode mixture of the present disclosure preferably further contains polyvinylidene fluoride (PVdF). By using a fluorine-containing copolymer and PVdF as the binder, an increase in the viscosity of the electrode mixture can be further suppressed, and an electrode mixture layer having even better adhesion to the current collector and flexibility can be formed.

[0081] Polyvinylidene fluoride (PVdF) is a polymer containing units based on vinylidene fluoride (VdF) (hereinafter referred to as VdF units), and may be a VdF homopolymer consisting of only VdF units, or a polymer containing VdF units and units based on a monomer copolymerizable with VdF.

[0082] In the above PVdF, the monomer copolymerizable with VdF is preferably a monomer other than tetrafluoroethylene (TFE), that is, PVdF preferably does not contain a TFE unit.

[0083] In the above-mentioned PVdF, examples of the monomer copolymerizable with VdF include fluorinated monomers and non-fluorinated monomers, with fluorinated monomers being preferred. Examples of the above-mentioned fluorinated monomers include vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene, and trans-1,3,3,3-tetrafluoropropene. Examples of the above-mentioned non-fluorinated monomers include ethylene and propylene.

[0084] In the above-mentioned PVdF, the monomer copolymerizable with VdF is preferably at least one fluorinated monomer selected from the group consisting of CTFE, fluoroalkyl vinyl ether, HFP, and 2,3,3,3-tetrafluoropropene, and more preferably at least one fluorinated monomer selected from the group consisting of CTFE, HFP, and fluoroalkyl vinyl ether.

[0085] In PVdF, the content of monomer units copolymerizable with VdF is preferably 0 to 5.0 mol%, more preferably 0 to 3.0 mol%, and even more preferably 0 to 1.0 mol%, based on the total monomer units. In PVdF, the content of fluorinated monomer units copolymerizable with VdF is preferably less than 5.0 mol%, more preferably less than 3.0 mol%, and even more preferably less than 1.0 mol%, based on the total monomer units.

[0086] The content of VdF units in PVdF, based on all monomer units, is preferably 95.0 mol% or more, more preferably 97.0 mol% or more, and even more preferably 99.0 mol% or more. The content of VdF units in PVdF, based on all monomer units, is preferably more than 95.0 mol%, more preferably more than 97.0 mol%, and even more preferably more than 99.0 mol%.

[0087] The content of VdF units in PVdF is preferably 95.0 to 99.999 mol%, more preferably 97.0 mol% or more, even more preferably 98.5 mol% or more, more preferably 99.99 mol% or less, and even more preferably 99.90 mol% or less, based on all monomer units.

[0088] In the present disclosure, the composition of PVdF is, for example, 19 It can be measured by F-NMR measurement.

[0089] The PVdF may have a polar group. By using a fluorine-containing copolymer and PVdF having a polar group as a binder, an electrode mixture layer having even better flexibility and adhesion to the current collector can be formed.

[0090] The polar group is not particularly limited as long as it is a polar functional group. However, since this can further improve the adhesion of the electrode mixture layer to the current collector, at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, a hydroxy group, a sulfonic acid group, a sulfate group, a phosphate group, an amino group, an amide group, and an alkoxy group is preferred, at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, and a hydroxy group is more preferred, and a carbonyl group-containing group is even more preferred. The hydroxy group does not include a hydroxy group that constitutes a part of the carbonyl group-containing group. The amino group is a monovalent functional group obtained by removing hydrogen from ammonia, a primary amine, or a secondary amine.

[0091] The carbonyl group-containing group is a functional group having a carbonyl group (-C(=O)-). The carbonyl group-containing group is preferably a group represented by the general formula -COOR (R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) or a carboxylic acid anhydride group, and more preferably a group represented by the general formula -COOR, because these groups can further improve the adhesion of the electrode mixture layer to the current collector. The number of carbon atoms in the alkyl group or hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of the group represented by the general formula -COOR include -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, and -COOC2H5. When the group represented by the general formula -COOR is -COOH or contains -COOH, the -COOH may be a carboxylate such as a metal carboxylate or an ammonium carboxylate.

[0092] The carbonyl group-containing group may also be a group represented by the general formula: -X-COOR (X is an atomic group having a main chain composed of 2 to 15 atoms, and the molecular weight of the atomic group is preferably 350 or less; R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group). The alkyl group and the hydroxyalkyl group preferably have 1 to 16 carbon atoms, more preferably 1 to 6, and even more preferably 1 to 3 carbon atoms.

[0093] The amide group is preferably a group represented by the general formula: -CO-NRR' (R and R' independently represent a hydrogen atom or a substituted or unsubstituted alkyl group), or a bond represented by the general formula: -CO-NR"- (R" represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group).

[0094] The polar group can be introduced into PVdF by polymerizing VdF with a monomer having the polar group (hereinafter referred to as a polar group-containing monomer), or by reacting PVdF with a compound having the polar group. From the viewpoint of productivity, however, it is preferable to polymerize VdF with the polar group-containing monomer.

[0095] Polymerization of VdF and the polar group-containing monomer yields PVdF containing VdF units and polar group-containing monomer units. That is, PVdF preferably contains the polar group-containing monomer units, since this can further improve the adhesion of the electrode mixture layer to the current collector. The content of the polar group-containing monomer units is preferably 0.001 to 5.0 mol %, more preferably 0.01 to 3.0 mol %, and even more preferably 0.10 to 1.5 mol %, based on the total monomer units.

[0096] In the present disclosure, the content of polar group-containing monomer units in PVdF can be measured by acid-base titration of the acid group, for example, when the polar group is an acid group such as a carboxylic acid.

[0097] Examples of the polar group-containing monomer include hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropyl acrylate; unsaturated monobasic acids such as (meth)acrylic acid, crotonic acid, vinylacetic acid (3-butenoic acid), 3-pentenoic acid, 4-pentenoic acid, 3-hexenoic acid, and 4-heptenoic acid; unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid, and citraconic anhydride; alkylidene malonic acid esters such as dimethyl methylidene malonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; Examples thereof include carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; (meth)acryloyloxyalkyl dicarboxylic acid esters such as acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, acryloyloxypropyl succinate, and methacryloyloxyethyl phthalate; and monoesters of unsaturated dibasic acids such as maleic acid monomethyl ester, maleic acid monoethyl ester, citraconic acid monomethyl ester, and citraconic acid monoethyl ester.

[0098] When the polar group is introduced into PVdF by reacting PVdF with a compound having the polar group, the compound having the polar group can be the polar group-containing monomer, or a silane-based coupling agent or titanate-based coupling agent having a group reactive with PVdF and a hydrolyzable group. The hydrolyzable group is preferably an alkoxy group. When a coupling agent is used, it can be added to PVdF by reacting it with PVdF dissolved or swollen in a solvent.

[0099] PVdF can also be obtained by partially dehydrofluorinating PVdF with a base and then reacting the partially dehydrofluorinated PVdF with an oxidizing agent, such as hydrogen peroxide, hypochlorite, palladium halide, chromium halide, alkali metal permanganate, peroxy compounds, alkyl peroxides, and alkyl persulfates.

[0100] The weight-average molecular weight (polystyrene equivalent) of PVdF is preferably 50,000 to 3,000,000, more preferably 80,000 or more, even more preferably 100,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, and particularly preferably 2,000,000 or less, because this can further suppress an increase in the viscosity of the electrode mixture and further enable the formation of an electrode mixture layer with superior adhesion to the current collector and flexibility. The weight-average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent. The weight-average molecular weight of PVdF may be 1,000,000 or more, or even 1,500,000 or more, because this can further suppress an increase in the viscosity of the electrode mixture and further enable the formation of an electrode mixture layer with superior adhesion to the current collector and flexibility.

[0101] The number average molecular weight (polystyrene equivalent) of PVdF can further suppress an increase in the viscosity of the electrode mixture and can form an electrode mixture layer with even better adhesion to the current collector and flexibility, so it is preferably 20,000 to 1,500,000, more preferably 40,000 or more, even more preferably 70,000 or more, particularly preferably 140,000 or more, more preferably 1,400,000 or less, even more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less. The number average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0102] The melting point of PVdF is preferably 100 to 240° C. The melting point can be determined as the temperature corresponding to the maximum value on the heat of fusion curve when the temperature is increased at a rate of 10° C. / min using a differential scanning calorimetry (DSC) device.

[0103] PVdF can be produced by a conventionally known method, for example, by appropriately mixing VdF, the polar group-containing monomer, and additives such as a polymerization initiator, and carrying out solution polymerization or suspension polymerization.

[0104] The storage modulus of PVdF at 30°C is preferably 2000 MPa or less, more preferably 1800 MPa or less. The storage modulus of PVdF at 60°C is preferably 1500 MPa or less, more preferably 1300 MPa or less. The storage modulus of PVdF at 30°C is preferably 1000 MPa or more, more preferably 1100 MPa or more. The storage modulus of PVdF at 60°C is preferably 600 MPa or more, and more preferably 700 MPa or more. The storage modulus of PVdF can be measured by the same method as that for the storage modulus of a fluorinated copolymer.

[0105] The mass ratio of PVdF to the fluorine-containing copolymer in the binder (PVdF / fluorine-containing copolymer) is preferably 99 / 1 to 1 / 99, more preferably 97 / 3 to 10 / 90, even more preferably 95 / 5 to 40 / 60, and most preferably 90 / 10 to 50 / 50, because this can further suppress an increase in the viscosity of the electrode mixture and enable the formation of an electrode mixture layer that is even more excellent in adhesion to the current collector and flexibility.

[0106] The binder may contain other polymers in addition to PVdF and the fluorine-containing copolymer, such as polymethacrylate, polymethyl methacrylate, polyimide, polyamide-imide, polycarbonate, styrene rubber, and butadiene rubber.

[0107] The content of the fluorine-containing copolymer in the binder is preferably 1% by mass or more, more preferably 3% by mass or more, even more preferably 5% by mass or more, particularly preferably 10% by mass or more, and most preferably 15% by mass or more, and may be 100% by mass or less, relative to the mass of the binder, because this can further suppress an increase in the viscosity of the electrode mixture and enable the formation of an electrode mixture layer that is more excellent in adhesion to the current collector and flexibility.

[0108] The content of the binder in the electrode mixture is preferably 0.1 to 1.6 parts by mass, more preferably 0.3 to 1.6 parts by mass, even more preferably 0.5 to 1.6 parts by mass, particularly preferably 0.8 to 1.5 parts by mass, and most preferably 1.0 to 1.5 parts by mass, relative to 100 parts by mass of the electrode active material, because this can further suppress an increase in the viscosity of the electrode mixture and enable the formation of an electrode mixture layer that is even more excellent in adhesion to the current collector and flexibility.

[0109] (additives) The electrode mixture of the present disclosure contains, as an additive, the following repeating unit: -[CH2-CHR]- (In the above repeating unit, R represents a linear or cyclic amide group, a nitrile group, or an alkyl group having 1 to 4 carbon atoms, in which at least one hydrogen atom of the alkyl group is substituted with a linear or cyclic amide group or a nitrile group.) The electrode mixture of the present disclosure contains an additive, and therefore has excellent flexibility and can form an electrode mixture layer that adheres sufficiently to the current collector. In addition, the electrode mixture is resistant to an increase in viscosity and has excellent coatability, so that the electrode mixture layer can be easily formed.

[0110] As the additive, at least one selected from the group consisting of polyvinylpyrrolidone and polyacrylonitrile is preferred, and polyvinylpyrrolidone is more preferred, because it can further suppress an increase in the viscosity of the electrode mixture and can form an electrode mixture layer that has even better adhesion to the current collector and flexibility.

[0111] The number-average molecular weight of the additive is preferably 10,000 to 500,000, more preferably 20,000 or more, even more preferably 30,000 or more, more preferably 400,000 or less, and even more preferably 300,000 or less, because this can further suppress an increase in the viscosity of the electrode mixture and further enable the formation of an electrode mixture layer that is more excellent in adhesion to the current collector and flexibility. In the present disclosure, the number-average molecular weight of the additive can be measured by gel permeation chromatography (GPC).

[0112] The polyvinylpyrrolidone is not particularly limited as long as it is a polymer of N-vinyl-2-pyrrolidone, and may be a polymer consisting of N-vinyl-2-pyrrolidone alone or a copolymer of N-vinyl-2-pyrrolidone and another monomer. However, a polymer consisting of N-vinyl-2-pyrrolidone alone or a copolymer of N-vinyl-2-pyrrolidone and a non-fluorinated monomer is preferred, and a polymer consisting of N-vinyl-2-pyrrolidone alone is more preferred.

[0113] The number average molecular weight of polyvinylpyrrolidone is preferably 10,000 to 500,000, more preferably 20,000 or more, even more preferably 30,000 or more, more preferably 400,000 or less, even more preferably 300,000 or less.

[0114] The polyacrylonitrile is not particularly limited as long as it is a polymer of acrylonitrile, and may be a polymer consisting of only acrylonitrile or a copolymer of acrylonitrile and other monomers, but a polymer consisting of only N-vinyl-2-pyrrolidone or a copolymer of N-vinyl-2-pyrrolidone and a non-fluorinated monomer is preferred, and a polymer consisting of only N-vinyl-2-pyrrolidone is more preferred. Examples of non-fluorinated monomers include (meth)acrylic acid.

[0115] The number average molecular weight of polyacrylonitrile is preferably 100,000 to 350,000, more preferably 130,000 or more, more preferably 250,000 or less, and even more preferably 220,000 or less.

[0116] The content of the additive in the electrode mixture is preferably 0.001 to 0.2 parts by mass, more preferably 0.01 part by mass or more, even more preferably 0.02 part by mass or more, more preferably 0.15 part by mass or less, and even more preferably 0.11 part by mass or less, relative to 100 parts by mass of the electrode active material, because this can further suppress an increase in the viscosity of the electrode mixture and further enable the formation of an electrode mixture layer that is more excellent in adhesion to the current collector and flexibility.

[0117] In the electrode mixture of the present disclosure, the mass ratio of the fluorine-containing copolymer (referred to as "fluorine-containing copolymer (a)") to the additive (referred to as "additive (b)") (fluorine-containing copolymer (a) / additive (b)) is preferably 1 / 99 to 99 / 1, more preferably 20 / 80 or more, even more preferably 40 / 60 or more, particularly preferably 60 / 40 or more, more preferably 98 / 2 or less, and even more preferably 90 / 10 or less.

[0118] The contents of the electrode active material, binder, and additive in the electrode mixture of the present disclosure are determined taking into consideration the applicability to a current collector, the formability of a thin film after drying, etc. The total content of the electrode active material, binder, and additive in the electrode mixture is preferably 50 to 90 mass%, more preferably 60 to 85 mass%, and even more preferably 70 to 80 mass%. The electrode mixture of the present disclosure is less likely to increase in viscosity even when it contains high concentrations of the electrode active material, binder, and additive.

[0119] The electrode mixture of the present disclosure can be prepared by mixing an electrode active material, an organic solvent, a binder, an additive, and, if necessary, other components. The order in which the components are mixed is not particularly limited. For example, the binder, the additive, and the organic solvent may be mixed together, and then the electrode active material and other components may be mixed. Alternatively, a composite material of the binder and the electrode active material may be obtained by, for example, spraying a binder solution or dispersion onto the electrode active material and drying the mixture, and then the obtained composite material may be mixed with the organic solvent, the additive, and other components.

[0120] In order to enable quick dissolution in an organic solvent, it is desirable that the binder be used with a small particle size of 1000 μm or less, particularly 50 to 350 μm on average.

[0121] <Composition> The present disclosure relates to a fluorine-containing copolymer containing vinylidene fluoride units and tetrafluoroethylene units, and a fluorine-containing copolymer containing, as an additive, the following repeating unit: -[CH2-CHR]- The present invention also relates to a composition containing a polymer material having the repeating unit (wherein R represents a linear or cyclic amide group, a nitrile group, or an alkyl group having 1 to 4 carbon atoms, and at least one hydrogen atom of the alkyl group is substituted with a linear or cyclic amide group or a nitrile group).

[0122] The composition of the present disclosure has the above-described configuration, and therefore, when used as a material for forming an electrode mixture, it is possible to easily produce an electrode mixture that is resistant to an increase in viscosity, and it is also possible to form an electrode mixture layer that has excellent adhesion to a current collector and flexibility, and it is possible to easily produce an electrode mixture that can form a secondary battery with sufficient load characteristics.

[0123] The fluorine-containing copolymer contained in the composition of the present disclosure can have the same constitution as the fluorine-containing copolymer contained in the electrode mixture of the present disclosure, except that it contains VdF units and TFE units as essential monomer units. Furthermore, the additive contained in the composition of the present disclosure can have the same constitution as the additive contained in the electrode mixture of the present disclosure.

[0124] In the composition of the present disclosure, the mass ratio of the fluorine-containing copolymer (referred to as "fluorine-containing copolymer (a)") to the additive (referred to as "additive (b)") (fluorine-containing copolymer (a) / additive (b)) is preferably 1 / 99 to 99 / 1, more preferably 20 / 80 or more, even more preferably 40 / 60 or more, particularly preferably 60 / 40 or more, more preferably 98 / 2 or less, and even more preferably 90 / 10 or less.

[0125] It is also preferable that the composition of the present disclosure further contains polyvinylidene fluoride (PVdF). The PVdF contained in the composition of the present disclosure may have the same composition as the PVdF contained in the electrode mixture of the present disclosure.

[0126] The mass ratio of PVdF to the fluorine-containing copolymer in the composition of the present disclosure (PVdF / fluorine-containing copolymer) is preferably 99 / 1 to 1 / 99, more preferably 97 / 3 to 10 / 90, even more preferably 95 / 5 to 40 / 60, and most preferably 90 / 10 to 50 / 50, because when used as a material for forming an electrode mixture, it is possible to easily produce an electrode mixture that is less likely to increase in viscosity and that is capable of forming an electrode mixture layer that is more excellent in adhesion to and flexibility than the current collector.

[0127] It is also preferable that the composition of the present disclosure further contains an organic solvent. The organic solvent contained in the composition of the present disclosure may have the same configuration as the organic solvent contained in the electrode mixture of the present disclosure.

[0128] The contents of the fluorine-containing copolymer and additives in the composition of the present disclosure are preferably 0.5 to 50% by mass, more preferably 1.0 to 30% by mass, because they can be easily mixed with the electrode active material and good homogeneity can be ensured when used to prepare an electrode mixture. Furthermore, the contents of the fluorine-containing copolymer, PVdF, and additives in the composition of the present disclosure are preferably 0.5 to 50% by mass, more preferably 1.0 to 30% by mass, because they can be easily mixed with the electrode active material and good homogeneity can be ensured.

[0129] The composition of the present disclosure can be suitably used as a material for producing an electrode mixture. The present disclosure also relates to an electrode mixture obtained using the above composition.

[0130] The composition of the present disclosure may be a composition for a secondary battery. In the present disclosure, the composition for a secondary battery includes compositions used in the positive electrode, negative electrode, and separator of the secondary battery.

[0131] The electrode mixture and composition of the present disclosure can be suitably used as materials for forming secondary batteries. The electrode mixture and composition of the present disclosure are resistant to viscosity increases and can form an electrode mixture layer that has excellent adhesion and flexibility to the current collector, allowing for the formation of a secondary battery with sufficient load characteristics. Therefore, they are suitable as electrode mixtures and compositions for use in electrodes of secondary batteries. The secondary battery to which the electrode mixture and composition of the present disclosure can be applied includes a positive electrode in which a positive electrode mixture is supported on a positive electrode current collector, a negative electrode in which a negative electrode mixture is supported on a negative electrode current collector, and an electrolyte.

[0132] The electrode mixture of the present disclosure may be an electrode mixture for a secondary battery or an electrode mixture for a lithium-ion secondary battery. The electrode mixture of the present disclosure may be a positive electrode mixture used in preparing a positive electrode or a negative electrode mixture used in preparing a negative electrode, but is preferably a positive electrode mixture. The electrode mixture layer formed from the electrode mixture of the present disclosure may be a positive electrode mixture layer or a negative electrode mixture layer.

[0133] <Electrode> The electrode of the present disclosure includes a current collector and an electrode mixture layer. The electrode mixture layer is formed using the electrode mixture of the present disclosure and may be provided on one or both sides of the current collector.

[0134] The electrode of the present disclosure includes an electrode mixture layer formed using the electrode mixture of the present disclosure, and therefore has excellent flexibility, sufficient adhesion between the current collector and the electrode mixture layer, and can form a secondary battery with excellent battery characteristics.

[0135] The density of the electrode mixture layer is preferably 2.0 to 5.0 g / cm 3 and more preferably 2.5 to 5.0 g / cm 3 is.

[0136] The density of the electrode mixture layer can be calculated from the mass and volume of the electrode mixture layer.

[0137] The thickness of the electrode mixture layer is preferably 20 μm or more, more preferably 45 μm or more, even more preferably 55 μm or more, particularly preferably 60 μm or more, and preferably 170 μm or less, more preferably 150 μm or less, because even better battery characteristics can be obtained. The thickness of the electrode mixture layer may also be 85 μm or less, or may be less than 69 μm.

[0138] The thickness of the electrode mixture layer can be measured with a micrometer. In the present disclosure, the thickness of the electrode mixture layer is the thickness per side when the electrode mixture layer is provided on both sides of the current collector.

[0139] Examples of the current collector provided in the electrode of the present disclosure include metal foils or metal meshes made of iron, stainless steel, copper, aluminum, nickel, titanium, etc., and among these, aluminum foil is preferred.

[0140] The electrode of the present disclosure can be suitably produced by a production method in which the electrode mixture of the present disclosure is applied to a current collector. After the electrode mixture is applied, the coating may be dried and the resulting dried coating may be pressed.

[0141] The amount of electrode mixture applied to the current collector is preferably 15 mg / cm 2 More preferably, it is 17.5 mg / cm or more. 2 or more, preferably 60 mg / cm 2 or less, more preferably 50 mg / cm 2 The application amount of the electrode mixture is the dry weight of the electrode mixture per unit area.

[0142] <Secondary battery> The present disclosure also provides a secondary battery including the above electrode.

[0143] The secondary battery of the present disclosure includes an electrode formed using the electrode mixture of the present disclosure, and therefore exhibits sufficient load characteristics and excellent battery properties.

[0144] The secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and one or both of the positive electrode and the negative electrode are preferably the above-described electrodes. Also, the secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode is preferably the above-described electrode.

[0145] The non-aqueous electrolyte is not particularly limited, and one or more of known solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, etc. Any of the conventionally known electrolytes can be used, such as LiClO4, LiAsF6, LiPF6, LiBF4, LiCl, LiBr, CH3SO3Li, CF3SO3Li, and cesium carbonate.

[0146] The electrode of the present disclosure has excellent flexibility, the current collector and the electrode mixture layer are in sufficient contact with each other, and a secondary battery having excellent battery characteristics can be formed, and therefore the electrode can be suitably used as an electrode for a wound-type secondary battery.

[0147] The electrode of the present disclosure is useful for nonaqueous electrolyte secondary batteries, not only for the lithium ion secondary batteries using the liquid electrolyte described above, but also for polymer electrolyte lithium secondary batteries, and is also useful for electric double layer capacitors.

[0148] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims. [Example]

[0149] Next, embodiments of the present disclosure will be described with reference to experimental examples and fabrication examples, but the present disclosure is not limited to these experimental examples and fabrication examples.

[0150] (Polymerization Example 1) Into a 4-liter autoclave were placed 1340 g of pure water, 0.75 g of methylcellulose, 1280 g of perfluorocyclobutane (C318), and 218 g of a mixed gas having a VdF / TFE molar ratio of 94.3 / 5.7 (mol%). After adjusting the temperature to 37°C, 0.699 g of di-secondary butyl peroxydicarbonate, 6 g of methanol, and 0.88 g of ethyl acetate were added, and 384 g of a mixed gas having a VdF / TFE molar ratio of 85 / 15 (mol%) was added so that the tank pressure remained constant at 1.4 MPaG. 11 hours after the start of the reaction, the tank was depressurized to obtain a fluorine-containing copolymer (A-1).

[0151] (Polymerization Example 2) A 2-L autoclave was charged with 0.6 kg of purified water and 0.6 g of methylcellulose. After thorough nitrogen substitution, 0.57 kg of 1,1,1,3,3-pentafluorobutane was added and the system was maintained at 37°C. A mixed gas with a TFE / VdF molar ratio of 7 / 93 was added, and the vessel pressure was adjusted to 1.5 MPa. 0.17 g of 4-pentenoic acid and 0.5 g of a 50% by mass methanol solution of di-n-propyl peroxydicarbonate were added to initiate polymerization. A mixed gas with a TFE / VdF molar ratio of 15 / 85 was supplied to maintain the vessel pressure, and 70 g of the mixed gas was added by the end of the reaction. 4-pentenoic acid was continuously added in accordance with the supply of the mixed gas, and 0.43 g was added by the end of the reaction. After the addition of 70 g of the mixed gas was completed, the gas in the vessel was released and the reaction was terminated. The reaction product was washed with water and dried to obtain fluorocopolymer (A-2).

[0152] The physical properties of the fluorine-containing copolymers and PVdF ((A-1) to (A-6)) and additives ((B-1) to (B-4)) used in the experimental examples and comparative examples are shown below.

[0153] Fluorine-containing copolymer (A-1) VdF / TFE=83.3 / 16.7 (mol %) Solution viscosity: 847mPa·s Weight average molecular weight: 1160000 Fluorine-containing copolymer (A-2) VdF / TFE / 4-pentenoic acid=81.63 / 17.92 / 0.45 (mol %) Solution viscosity: 393mPa·s Weight average molecular weight: 8200000 PVdF(A-3) VdF=100 (mol%) Solution viscosity: 2400mPa·s Weight average molecular weight: 1800000 Fluorine-containing copolymer (A-4) VdF / HFP=95.0 / 5.0 (mol %) Solution viscosity: 269mPa·s Weight average molecular weight: 730000 Fluorine-containing copolymer (A-5) VdF / CTFE=98 / 2 (mol%) Solution viscosity: 433mPa·s Weight average molecular weight; 850000 PVdF(A-6) VdF / acrylic acid=99 / 1 (mol%) Solution viscosity: 800mPa·s Weight average molecular weight; 1100000

[0154] Additive (B-1) Polyvinylpyrrolidone (K30) (Tokyo Chemical Industry Co., Ltd.) Number average molecular weight: 40000 Additive (B-2) Polyvinylpyrrolidone (K90) (Tokyo Chemical Industry Co., Ltd.) Number average molecular weight: 360000 Additive (B-3) Polyacrylonitrile (Sigma-Aldrich) Number average molecular weight: 150000 Additive (B-4) Polyvinyl alcohol (manufactured by Denka) Degree of polymerization: 2000 Saponification degree: 98.5-99.4%

[0155] (Experimental Example 1) A positive electrode mixture (slurry) was prepared by the following method. 0.8 Mn 0.1 Co0.1 100 parts by mass of O2), 1.54 parts by mass of the conductive additive acetylene black (AB), 0.23 parts by mass of fluorine-containing copolymer (A-1), 0.90 parts by mass of PVdF (A-3), and 0.05 parts by mass of additive (B-1) were weighed out. The fluorine-containing copolymer (A-1), PVdF (A-3), and additive (B-1) were dissolved in N-methyl-2-pyrrolidone (NMP) to a total concentration of 6% by mass. Then, predetermined amounts of the positive electrode active material and conductive additive were added to this solution and thoroughly mixed with a stirrer to ensure good homogeneity. The total solids concentration of the positive electrode active material, conductive additive, fluorine-containing copolymer, PVdF, and additive relative to the total mass of the slurry was adjusted to 80% by mass.

[0156] (Experimental Example 2) NMC622 (LiNi) was used as the positive electrode active material. 0.6 Mn 0.2 Co 0.2 A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that O2) was used.

[0157] (Experimental Example 3) A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that LCO (LiCoO) was used as the positive electrode active material and the total solid content concentration of the positive electrode active material, conductive additive, fluorine-containing copolymer, PVdF, and additives was adjusted to 79 mass% relative to the total mass of the slurry.

[0158] (Experimental Example 4) A positive electrode mixture (slurry) was prepared using the following method. 100 parts by mass of positive electrode active material (LFP (LiFePO4)), 20.41 parts by mass of a 5% by mass NMP dispersion of carbon nanotubes (CNTs), 0.20 parts by mass of fluorine-containing copolymer (A-1), 0.82 parts by mass of PVdF (A-3), and 0.10 parts by mass of additive (B-1) were weighed out. The fluorine-containing copolymer (A-1), PVdF (A-3), and additive (B-1) were dissolved in N-methyl-2-pyrrolidone (NMP) to a total concentration of 5.5% by mass. Then, a predetermined amount of positive electrode active material and CNT dispersion were added to this solution and thoroughly mixed with a stirrer to ensure good homogeneity. The total solids concentration of the positive electrode active material, conductive additive, fluorine-containing copolymer, PVdF, and additives relative to the total mass of the slurry was adjusted to 65% by mass.

[0159] (Experimental Example 5) A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that additive (B-2) was used as the additive and the total solid content concentration of the positive electrode active material, conductive additive, fluorine-containing copolymer, PVdF, and additives was adjusted to 78 mass% relative to the total mass of the slurry.

[0160] (Experimental Example 6) A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that 0.23 parts by mass of the fluorine-containing copolymer (A-4) and 0.90 parts by mass of PVdF (A-3) were used as the fluorine-containing copolymer and the PVdF, respectively.

[0161] (Experimental Example 7) A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that LCO (LiCoO) was used as the positive electrode active material, 0.23 parts by mass of fluorine-containing copolymer (A-1) was used as the fluorine-containing copolymer, and 0.90 parts by mass of PVdF (A-6) was used as the PVdF.

[0162] (Experimental Example 8) A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that LCO (LiCoO) was used as the positive electrode active material, 0.23 parts by mass of fluorine-containing copolymer (A-2) was used as the fluorine-containing copolymer, and 0.90 parts by mass of PVdF (A-3) was used as the PVdF.

[0163] (Experimental Example 9) A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that 0.05 parts by mass of additive (B-3) was used as the additive.

[0164] (Experimental Example 10) A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that 1.13 parts by mass of the fluorocopolymer (A-5) was used as the fluorocopolymer and PVdF was not used.

[0165] (Experimental Example 11) NMC622 (LiNi) was used as the positive electrode active material. 0.6 Mn 0.2 Co 0.2 A positive electrode mixture was prepared in the same manner as in Experimental Example 9, except that O2) was used.

[0166] (Comparative Example 1) A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that no fluorine-containing copolymer was used, 1.13 parts by mass of PVdF (A-3) was used as PVdF, and the total solid content concentration of the positive electrode active material, conductive additive, PVdF, and additives was adjusted to 78% by mass relative to the total mass of the slurry.

[0167] (Comparative Example 2) A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that no additives were used and the total solid concentration of the positive electrode active material, conductive additive, fluorine-containing copolymer and PVdF was adjusted to 76 mass% relative to the total mass of the slurry.

[0168] (Comparative Example 3) A positive electrode mixture was prepared in the same manner as in Experimental Example 4, except that no additive was used.

[0169] Comparative Example 4 A positive electrode mixture was prepared in the same manner as in Experimental Example 1, except that 0.05 parts by mass of additive (B-4) was used as the additive, and the total solid content concentration of the positive electrode active material, conductive additive, fluorine-containing copolymer, PVdF, and additives was adjusted to 76% by mass relative to the total mass of the slurry.

[0170] (Comparative Example 5) NMC622 (LiNi) was used as the positive electrode active material. 0.6 Mn 0.2 Co 0.2 A positive electrode mixture was prepared in the same manner as in Comparative Example 1, except that O2) was used.

[0171] (Comparative Example 6) NMC622 (LiNi) was used as the positive electrode active material. 0.6 Mn 0.2 Co 0.2 A positive electrode mixture was prepared in the same manner as in Comparative Example 2, except that O2) was used.

[0172] (Preparation of positive electrode) The positive electrode mixtures prepared in Experimental Examples 1 to 11 and Comparative Examples 1 to 6 were applied to one side of a positive electrode current collector (aluminum foil with a thickness of 20 μm) in an amount of 22.5 mg / cm 2 After completely volatilizing the NMP, the cathode was pressed using a roll press at a pressure of 10 tons to produce a cathode including a cathode mixture layer and a cathode current collector. The density of the cathode mixture layer was 2.75 g / cc.

[0173] (Preparation of negative electrode) The negative electrode mixture slurry was prepared by mixing artificial graphite powder as the negative electrode active material, an aqueous dispersion of sodium carboxymethylcellulose as the thickener (concentration of sodium carboxymethylcellulose: 1% by mass), and an aqueous dispersion of styrene-butadiene rubber as the binder (concentration of styrene-butadiene rubber: 50% by mass) in an aqueous solvent at a solids ratio of 97.6 / 1.2 / 1.2 (mass%). The mixture was uniformly applied to a 20 μm thick copper foil, dried, and then compressed using a press to form a negative electrode.

[0174] (Preparation of Electrolyte) LiPF6 was dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC = 30:70 (v / v)), and then 1 mass% of vinylene carbonate (VC) was added. Here, the LiPF6, EC, EMC, and VC used were battery-grade products manufactured by Kishida Chemical Industry.

[0175] (Production Example 1) The positive electrode mixture prepared in Experimental Example 2 was applied to one side of a positive electrode current collector (aluminum foil with a thickness of 20 μm) in an amount of 20.0 mg / cm 2 After the NMP was completely evaporated, the mixture was pressed using a roll press to prepare a positive electrode. The prepared positive electrode, the negative electrode produced as described above, and a polyethylene separator were laminated in this order: negative electrode, separator, positive electrode, to prepare a battery element. This battery element was inserted into a bag made of a laminated film in which both sides of an aluminum sheet (40 μm thick) were coated with a resin layer, with the positive and negative terminals protruding, and then the above-mentioned electrolyte solution was injected into each bag, followed by vacuum sealing to produce a sheet-shaped lithium ion secondary battery.

[0176] (Production Example 2) A lithium ion secondary battery was produced in the same manner as in Production Example 1, except that the positive electrode mixture produced in Experimental Example 11 was used.

[0177] (Production Example 3) A lithium ion secondary battery was produced in the same manner as in Production Example 1, except that the positive electrode mixture produced in Comparative Example 5 was used.

[0178] (Production Example 4) A lithium ion secondary battery was produced in the same manner as in Production Example 1, except that the positive electrode mixture produced in Comparative Example 6 was used.

[0179] The viscosity change rate, peel strength between the positive electrode mixture layer of the positive electrode and the positive electrode current collector, and flexibility were measured for the positive electrode mixtures obtained in Experimental Examples 1 to 10 and Comparative Examples 1 to 4. Furthermore, the load characteristics of the lithium ion secondary batteries obtained in Preparation Examples 1 to 4 were measured.

[0180] The measurement method is as follows.

[0181] (polymer composition) The contents of TFE units, HFP units, and CTFE units in the fluorocopolymer and PVdF were analyzed using an NMR analyzer (Agilent Technologies, VNS400MHz). 19 It was determined by methods such as F-NMR measurement.

[0182] (4-pentenoic acid content) The content of 4-pentenoic acid units in the fluorine-containing copolymer is determined by esterifying the carboxyl groups of the 4-pentenoic acid units to convert them into ester groups, and then 1 The esterified fluorocopolymer was analyzed using H-NMR to measure the content. Specifically, 400 mg of the fluorocopolymer, 10 mg of trimethylsilyldiazomethane, and 3 mg of methanol were reacted at 25°C for 12 hours, and the resulting polymer was washed with methanol and vacuum-dried at 70°C for 24 hours. 1 The dried polymer was analyzed using H-NMR. 1 It was determined from the H-NMR spectrum at 3.7 ppm.

[0183] (acrylic acid content) The acrylic acid unit content in PVdF was measured by acid-base titration of the carboxyl group. Specifically, approximately 0.5 g of PVdF was dissolved in acetone at 70-80°C. 5 ml of water was added dropwise under vigorous stirring to avoid solidification of the PVdF. At a neutral transition of approximately -270 mV, titration with a 0.1 N NaOH aqueous solution was performed until complete neutralization of the acidity. From the measurement results, the amount of acrylic acid unit content in 1 g of PVdF was determined, and the acrylic acid unit content was calculated.

[0184] (solution viscosity) An NMP solution (5% by mass) of a fluorocopolymer or PVdF was prepared. The viscosity of the NMP solution was measured 10 minutes after the start of measurement using a Brookfield viscometer (TV-10M, manufactured by Toki Sangyo Co., Ltd.) at 25°C, rotor No. M4, and a rotation speed of 6 rpm.

[0185] (Weight average molecular weight) Measurement was performed by gel permeation chromatography (GPC). Calculations were made using data measured using Tosoh AS-8010, CO-8020, and columns (three GMHHR-H columns connected in series) and Shimadzu RID-10A, with dimethylformamide (DMF) as the solvent at a flow rate of 1.0 ml / min (reference: polystyrene).

[0186] (Viscosity change rate of positive electrode mixture) Using a Brookfield viscometer (TV-10M, manufactured by Toki Sangyo Co., Ltd.), the viscosity of the positive electrode mixture was measured 10 minutes after the start of measurement under conditions of 25°C, rotor No. M4, and a rotation speed of 6 rpm. The viscosity change rate (Xn) was calculated using the following formula from the viscosity (η0) of the positive electrode mixture measured immediately after preparation and the viscosity (ηn) 5 days after preparation of the mixture. Xn=ηn / η0×100[%]

[0187] (Density of the positive electrode mixture layer) The density of the positive electrode mixture layer was calculated from the area, film thickness and weight of the positive electrode mixture layer measured.

[0188] (Peel strength between positive electrode mixture layer of positive electrode and positive electrode current collector) A 1.2 cm x 7.0 cm test piece was prepared by cutting out the positive electrode. The positive electrode mixture layer side of the test piece was fixed to a movable jig with double-sided tape, and then the tape was applied to the surface of the positive electrode current collector. The stress (N / cm) when the tape was pulled at a 90-degree angle at a speed of 100 mm / min was measured using an autograph. A 50 N load cell was used for the autograph.

[0189] (Positive electrode flexibility) The positive electrode obtained by pressing using a roll press was cut out to prepare 2 cm × 10 cm test pieces, which were then wrapped around round rods with diameters of 3.5 mm, 3 mm, and 2.5 mm, and the positive electrode mixture layer was visually inspected and evaluated according to the following criteria. ◯: No cracks were observed. Δ: Cracks were observed, but no breakage of the positive electrode mixture layer or the positive electrode current collector was observed. ×: The positive electrode mixture layer and the positive electrode current collector were broken. *Complies with JIS-K5600-5-1 bending resistance (cylindrical mandrel method)

[0190] (2C / 0.2C load characteristic measurement) The lithium-ion secondary battery fabricated above was sandwiched between plates and pressurized, and then subjected to constant-current / constant-voltage charging (hereafter referred to as CC / CV charging) at a current equivalent to 1 C up to 4.2 V (0.1 C cutoff). It was then discharged at a constant current equivalent to 0.2 C down to 3 V, and this was taken as the 0.2 C discharge capacity. Here, 1 C represents the current value required to discharge the battery's reference capacity in 1 hour; for example, 0.2 C represents 1 / 5 of that current value. After CC / CV charging under the same conditions as above, the battery was discharged at a constant current equivalent to 2 C down to 3 V, and this was taken as the 2 C discharge capacity. The ratio of the 2 C discharge capacity to the 0.2 C discharge capacity was calculated, and this was taken as the 2 C / 0.2 C load characteristic (%). (2C discharge capacity)÷(0.2C discharge capacity)×100=2C / 0.2C load characteristics (%)

[0191] The evaluation results are shown in Tables 1 and 2.

[0192] [Table 1]

[0193] [Table 2]

Claims

1. Contains an electrode active material, an organic solvent, a binder, and an additive, the binder contains a fluorine-containing copolymer containing vinylidene fluoride units and fluorinated monomer units (excluding vinylidene fluoride units), and polyvinylidene fluoride; the content of the vinylidene fluoride units in the fluorine-containing copolymer is 50.0 to 95.0 mol % based on all monomer units, and the content of the fluorinated monomer units in the fluorine-containing copolymer is 5.0 to 50.0 mol % based on all monomer units, The content of vinylidene fluoride units in the polyvinylidene fluoride is more than 99.0 mol% based on all monomer units, a mass ratio of the polyvinylidene fluoride to the fluorine-containing copolymer (polyvinylidene fluoride / fluorine-containing copolymer) of 90 / 10 to 50 / 50; The additive comprises the following repeating unit: -[CH ２ -CHR]- (In the above repeating unit, R represents a linear or cyclic amide group, a nitrile group, or an alkyl group having 1 to 4 carbon atoms, and at least one hydrogen atom of the alkyl group is substituted with a linear or cyclic amide group or a nitrile group.) The content of the binder is 0.1 to 1.6 parts by mass relative to 100 parts by mass of the electrode active material, The content of the additive is 0.001 to 0.2 parts by mass relative to 100 parts by mass of the electrode active material. Electrode mixture.

2. 2. The electrode mixture according to claim 1, wherein the fluorinated monomer unit is at least one selected from the group consisting of a tetrafluoroethylene unit, a chlorotrifluoroethylene unit, a fluoroalkyl vinyl ether unit, and a hexafluoropropylene unit.

3. 3. The electrode mixture according to claim 1, wherein the additive is at least one selected from the group consisting of polyvinylpyrrolidone and polyacrylonitrile.

4. 4. The electrode mixture according to claim 1, wherein the additive is polyvinylpyrrolidone.

5. 5. The electrode mixture according to claim 1, wherein the electrode active material is at least one selected from the group consisting of lithium-containing transition metal composite oxides and lithium-containing transition metal phosphate compounds.

6. 6. The electrode mixture according to any one of claims 1 to 5, wherein the content of said vinylidene fluoride units in said fluorine-containing copolymer is 50.0 to 85.0 mol % based on all monomer units, and the content of said fluorinated monomer units in said fluorine-containing copolymer is 15.0 to 50.0 mol % based on all monomer units.

7. An electrode comprising: a current collector; and an electrode mixture layer formed on one or both surfaces of the current collector using the electrode mixture according to any one of claims 1 to 6.

8. A secondary battery comprising the electrode according to claim 7.

9. Fluorine-containing copolymers containing vinylidene fluoride units and tetrafluoroethylene units, polyvinylidene fluoride, and The additive may contain the following repeating units: -[CH ２ -CHR]- (In the above repeating unit, R represents a linear or cyclic amide group, a nitrile group, or an alkyl group having 1 to 4 carbon atoms, and at least one hydrogen atom of the alkyl group is substituted with a linear or cyclic amide group or a nitrile group.) Contains the content of said vinylidene fluoride units in said fluorine-containing copolymer is 50.0 to 95.0 mol % based on all monomer units, and the content of said tetrafluoroethylene units in said fluorine-containing copolymer is 5.0 to 50.0 mol % based on all monomer units, The content of vinylidene fluoride units in the polyvinylidene fluoride is more than 99.0 mol% based on all monomer units, A composition in which the mass ratio of the polyvinylidene fluoride to the fluorine-containing copolymer (polyvinylidene fluoride / fluorine-containing copolymer) is 90 / 10 to 50 / 50.

10. The composition according to claim 9, wherein the content of said vinylidene fluoride units in said fluorine-containing copolymer is 50.0 to 85.0 mol % based on all monomer units, and the content of said tetrafluoroethylene units in said fluorine-containing copolymer is 15.0 to 50.0 mol % based on all monomer units.

11. The composition according to claim 9 or 10, wherein the mass ratio (a / b) of said fluorine-containing copolymer (a) to said additive (b) is 1 / 99 to 99 / 1.

12. The composition according to any one of claims 9 to 11, further comprising an organic solvent.

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