Electrode mixture, secondary battery, and composition

Abstract

Provided is an electrode mixture containing an electrode active material, an organic solvent, a binder, and an additive, the binder including a fluorine-containing copolymer containing a vinylidene fluoride unit and a fluorinated monomer unit (excluding the vinylidene fluoride unit), the additive being a polymer material having the following repeating unit: -[CH2-CHR]- (in the repeating unit, R represents a chain or cyclic amide group, a nitrile group, or a substituent which is an alkyl group having 1 to 4 carbon atoms and in which at least one hydrogen atom of the alkyl group is replaced with a chain or cyclic amide group or a nitrile group), the content of the binder being 0.1 to 1.6 parts by mass per 100 parts by mass of the electrode active material, and the content of the additive being 0.001 to 0.2 parts by mass per 100 parts by mass of the electrode active material.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrode mixture, a secondary battery, and a composition. BACKGROUND

[0002] A lithium ion secondary battery or the like nonaqueous electrolyte secondary battery is used in small and portable electrical and electronic devices such as notebook personal computers, mobile phones, smartphones, tablet computers, ultrabooks, and the like due to reasons such as high voltage, high energy density, low self-discharge, low memory effect, and the like, and further, as a power source for driving a vehicle-mounted power source or a stationary large power source or the like used widely in automotive applications and the like, practical use is being made.

[0003] As an electrode mixture for forming an electrode possessed by such a nonaqueous electrolyte secondary battery, for example, in Patent Literature 1, an electrode mixture is described which is characterized by comprising a binder composition, a solvent, and an electrode active material, characterized in that the binder composition comprises a vinylidene fluoride polymer and a polymer additive, the vinylidene fluoride polymer comprises a vinylidene fluoride copolymer comprising a structural unit derived from vinylidene fluoride and a structural unit derived from chlorotrifluoroethylene, and the polymer additive is a polymer material having the following repeating unit,

[0004] - [CH2-CHR] -.

[0005] (In the above repeating unit, R represents a chain or cyclic amide group, a nitrile group, a hydroxyl group, an ester-containing group, or a substituent which is an alkyl group having 1 to 4 carbon atoms and in which at least one hydrogen atom of the alkyl group is substituted with a chain or cyclic amide group, a nitrile group, or a hydroxyl group.)

[0006] Further, in Patent Literature 2, a positive electrode for a lithium secondary battery is described which is characterized in that it is manufactured by the following process, that is, a carbon black dispersion liquid containing carbon black is prepared by using polyvinylpyrrolidone as a dispersant and dispersing the carbon black as a conductive aid in a solvent using a high-pressure jet-type grinder, and a positive electrode coating film forming paint is prepared by mixing at least the positive electrode active material containing lithium with the carbon black dispersion liquid thus obtained, the positive electrode coating film forming paint thus obtained is applied to a current collector and dried.

[0007] PRIOR ART DOCUMENTS

[0008] PATENT LITERATURE

[0009] Patent Literature 1: International Publication No. 2019 / 167322

[0010] Patent Literature 2: Japanese Patent Application Publication No. 2004-281096 SUMMARY

[0011] Problem to be Solved by the Invention

[0012] An object of the present application is to provide an electrode mixture which is less likely to increase in viscosity and which is capable of forming an electrode mixture layer excellent in adhesion to a current collector and in softness and capable of forming a secondary battery having sufficient load characteristics.

[0013] Means for Solving the Problem

[0014] According to the present application, there is provided an electrode mixture which contains an electrode active material, an organic solvent, a binder, and an additive, the binder including a fluorine-containing copolymer containing a vinylidene fluoride unit and a fluorinated monomer unit (which does not include the vinylidene fluoride unit), the additive being a polymer material having the following repeating unit:

[0015] -[CH2-CHR]-

[0016] (in the above repeating unit, R represents a chain or cyclic amide group, a nitrile group, or a substituent which is an alkyl group having 1 to 4 carbon atoms and in which at least one hydrogen atom of the alkyl group is replaced with a chain or cyclic amide group or a nitrile group), the content of the binder being 0.1 parts by mass to 1.6 parts by mass with respect to 100 parts by mass of the electrode active material, and the content of the additive being 0.001 parts by mass to 0.2 parts by mass with respect to 100 parts by mass of the electrode active material.

[0017] In the electrode mixture of the present application, the fluorinated monomer unit of the fluorine-containing copolymer is preferably at least one selected from the group consisting of a tetrafluoroethylene unit, a trifluorochloroethylene unit, a fluoroalkyl vinyl ether unit, and a hexafluoropropylene unit.

[0018] In the electrode mixture of the present application, the content of the vinylidene fluoride unit of the fluorine-containing copolymer is preferably 50.0 mol% to 99.0 mol% with respect to the total monomer units.

[0019] In the electrode mixture of the present application, the additive is preferably at least one selected from the group consisting of polyvinylpyrrolidone and polyacrylonitrile, and more preferably polyvinylpyrrolidone.

[0020] In the electrode mixture of the present application, the number average molecular weight of the additive is preferably 10,000 to 500,000.

[0021] In the electrode mixture of the present application, the electrode active material is preferably at least one selected from the group consisting of a lithium-containing transition metal complex oxide and a lithium-containing transition metal phosphoric compound.

[0022] Further, according to the present application, there is provided an electrode which has a current collector and an electrode mixture layer provided on one or both sides of the current collector and formed from the above electrode mixture.

[0023] Further, according to the present application, there is provided a secondary battery including the electrode described above.

[0024] Further, according to the present application, there is provided a composition including:

[0025] a fluorine-containing copolymer including a vinylidene fluoride unit and a tetrafluoroethylene unit; and

[0026] a polymer material as an additive, the polymer material having the following repeating unit,

[0027] -[CH2-CHR]-

[0028] (in the above repeating unit, R represents a chain or cyclic amide group, a nitrile group, or a substituent in which an alkyl group having 1 to 4 carbon atoms is substituted with a chain or cyclic amide group or a nitrile group, and at least one hydrogen atom of the alkyl group is substituted with the chain or cyclic amide group or the nitrile group.)

[0029] In the composition of the present application, the content of the above vinylidene fluoride unit of the above fluorine-containing copolymer is preferably 50.0 mol% to 99.0 mol% with respect to the total monomer units.

[0030] In the composition of the present application, the mass ratio (a / b) of the above fluorine-containing copolymer (a) to the above additive (b) is preferably 1 / 99 to 99 / 1.

[0031] The composition of the present application preferably further includes an organic solvent.

[0032] Effects of the Invention

[0033] According to the present application, it is possible to provide an electrode mixture which is less likely to increase in viscosity, and which can form an electrode mixture layer excellent in adhesion to a current collector and in softness, and can form a secondary battery having sufficient load characteristics. DETAILED DESCRIPTION

[0034] Hereinafter, a specific embodiment of the present application will be described in detail, but the present application is not limited to the following embodiment.

[0035] The electrode mixture of the present application includes an electrode active material, an organic solvent, a binder, and an additive.

[0036] <Electrode Active Material>

[0037] The electrode active material contained in the electrode mixture of the present application can be either a positive electrode active material or a negative electrode active material. As the positive electrode active material, there is no particular limitation as long as it can electrochemically occlude and release lithium ions, and from the viewpoint of improving the capacity of the secondary battery, a lithium complex oxide is preferred, and a lithium transition metal complex oxide is more preferred. As the positive electrode active material, a lithium-containing transition metal phosphoric compound is also preferred. The positive electrode active material is also preferably a substance containing lithium and at least one transition metal, such as a lithium transition metal complex oxide, a lithium-containing transition metal phosphoric compound, and the like.

[0038] As the transition metal of the lithium transition metal complex oxide, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, and the like are preferred, and as specific examples of the lithium transition metal complex oxide, lithium-cobalt complex oxides such as LiCoO2; lithium-nickel complex oxides such as LiNiO2; lithium-manganese complex oxides such as LiMnO2, LiMn2O4, Li2MnO3; and substances obtained by substituting a part of the transition metal atoms that are the main component of these lithium transition metal complex oxides with other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Si, and the like can be given. As the substances obtained by the above substitution, lithium-nickel-manganese complex oxides, lithium-nickel-cobalt-aluminum complex oxides, lithium-nickel-cobalt-manganese complex oxides, lithium-manganese-aluminum complex oxides, lithium-titanium complex oxides, and the like can be given, and 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 Al 0.2 O4, LiMn 1.5 Ni 0.5 O4, Li4Ti5O 12 , LiNi 0.82 Co 0.15 Al 0.03 O2, and the like.

[0039] As the transition metal of the lithium-containing transition metal phosphoric compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc. are preferable, and as specific examples of the lithium-containing transition metal phosphoric compound, for example, lithium iron phosphate such as LiFePO4, Li3Fe2(PO4)3, LiFeP2O7, etc.; lithium cobalt phosphate such as LiCoPO4; a substance obtained by substituting a part of the transition metal atoms as the main body of these lithium transition metal phosphoric compounds with Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc. other metal, etc. can be mentioned.

[0040] As the positive electrode active material, at least one selected from the group consisting of lithium-cobalt composite oxides, lithium-nickel composite oxides, lithium-manganese composite oxides, iron phosphate, lithium-nickel-manganese composite oxides, lithium-nickel-cobalt-manganese composite oxides, and lithium-nickel-cobalt-aluminum composite oxides is preferable, and at least one selected from the group consisting of lithium-cobalt composite oxides, lithium-nickel composite oxides, lithium-manganese composite oxides, lithium-nickel-manganese composite oxides, lithium-nickel-cobalt-manganese composite oxides, and lithium-nickel-cobalt-aluminum composite oxides is more preferable in order to form an electrode mixture layer having more excellent adhesion to the current collector.

[0041] In addition, as the positive electrode active material, at least one selected from the group consisting of 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, 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 O2.

[0042] As the lithium-containing transition metal composite oxide, lithium-nickel system composite oxides are preferable, and more preferable are those represented by general formula (1):

[0043] General formula (1): Li y Ni 1-x M x O2

[0044] (wherein x is 0.01≤x≤0.5, y is 0.9≤y≤1.2, and M represents a metal atom (excluding Ni).) A lithium-nickel composite oxide represented by the formula. The lithium-containing transition metal oxide containing a large amount of Ni is thus advantageous for high capacity of the secondary battery. In addition, the electrode mixture of the present application is excellent in coatability, even when the lithium-containing transition metal oxide containing a large amount of Ni is included as the electrode active material.

[0045] In the general formula (1), x is a coefficient satisfying 0.01≤x≤0.5; from the viewpoint of further obtaining a high-capacity secondary battery, it is preferably 0.05≤x≤0.4, and more preferably 0.10≤x≤0.3.

[0046] In the general formula (1), as the metal atom of M, V, Ti, Cr, Mn, Fe, Co, Cu, Al, Zn, Mg, Ga, Zr, Si, and the like can be given. As the metal atom of M, a transition metal such as V, Ti, Cr, Mn, Fe, Co, Cu, and the like; or a combination of the above-mentioned transition metal and other metals such as Al, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mg, Ga, Zr, Si, and the like is preferable.

[0047] As the lithium-nickel composite oxide represented by the general formula (1), at least one selected from the group consisting of LiNi 0.80 Co 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 O2 is more preferable, and 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 O2 is more preferable.

[0048] The lithium-nickel-based complex oxide represented by General Formula (1) and a positive electrode active material different therefrom can be used in combination. As the different positive electrode active material, LiCoO2, LiMnO2, LiMn2O4, Li2MnO3, LiMnO4, Li4Ti5O12, LiFePO4, Li3Fe2(PO4)3, LiFeP2O7, LiCoPO4, LiFeO2, LiNiO2, etc. can be specifically mentioned. 1.8 Al 0.2 O4, Li4Ti5O 12 12, LiFePO4, Li3Fe2(PO4)3, LiFeP2O7, LiCoPO4, Li 1.2 Fe 0.4 Mn 0.4 O2, LiNiO2, etc. can be specifically mentioned.

[0049] In addition, a substance different from the substance constituting the positive electrode active material as the main body can be attached to the surface of these positive electrode active materials, and the positive electrode active material thus obtained can be used. As the surface-attached substance, oxides such as alumina, silica, titania, zirconia, magnesia, calcia, boria, antimony oxide, bismuth oxide, etc.; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, etc.; carbonates such as lithium carbonate, calcium carbonate, magnesium carbonate, etc. can be mentioned.

[0050] These surface-attached substances can be attached to the surface of the positive electrode active material, for example, by a method of dissolving or suspending in a solvent, impregnating and adding to the positive electrode active material, and drying; a method of dissolving or suspending a surface-attached substance precursor in a solvent, impregnating and adding to the positive electrode active material, and then reacting by heating or the like; a method of adding to the positive electrode active material precursor and simultaneously performing firing; etc.

[0051] As the amount of the surface-attached substance, relative to the positive electrode active material, it is preferable that the lower limit be 0.1 ppm or more, more preferably 1 ppm or more, and further preferably 10 ppm or more, and the upper limit be 20% or less, more preferably 10% or less, and further preferably 5% or less, in terms of mass. By using the surface-attached substance, the oxidation reaction of the nonaqueous electrolyte solution at the surface of the positive electrode active material can be suppressed, and the battery life can be improved; however, in the case where the attached amount is too small, the effect thereof cannot be sufficiently exhibited, and in the case where the attached amount is too large, the lithium ion can be hindered from coming in and out, and thus the resistance can increase.

[0052] The shape of the positive electrode active material particles is preferably a secondary particle formed by agglomeration of primary particles, among the shapes such as block, polyhedron, sphere, ellipsoidal sphere, plate, needle, and column, which have been used conventionally, with the secondary particle being spherical or ellipsoidal. In general, in an electrochemical device, the active material in the electrode swells and shrinks with charge and discharge, and thus deterioration such as breakage of the active material or disconnection of the conductive path due to stress is likely to occur. Therefore, the active material formed by agglomeration of primary particles into secondary particles is preferable because it can moderate the stress of swelling and shrinking and prevent deterioration, compared to a single particle active material that is only primary particles. In addition, in the case of spherical or ellipsoidal particles, orientation during molding of the electrode is less than in the case of plate-like particles that are axially oriented, and thus swelling and shrinking of the electrode during charge and discharge is less, and the conductive aid is easily mixed uniformly during production of the electrode, and thus spherical or ellipsoidal particles are preferable.

[0053] The tap density of the positive electrode active material is generally 1.3 g / cm 3 Preferably, it is 1.5 g / cm 3 Further preferably, it is 1.6 g / cm 3 Most preferably, it is 1.7 g / cm 3 If the tap density of the positive electrode active material is less than the lower limit described above, the amount of dispersion medium required during formation of the positive electrode mixture layer increases, and the amount of conductive aid or binder required also increases, and sometimes the packing rate of the positive electrode active material in the positive electrode mixture layer is limited, and the capacity of the battery is limited. By using a metal complex oxide powder having a high tap density, a positive electrode mixture layer having a high density can be formed. The tap density is generally greater, and there is no particular upper limit, but if it is too great, the diffusion of lithium ions in the positive electrode mixture layer, which uses a nonaqueous electrolyte as the medium, becomes the rate-determining step, and sometimes the load characteristics are easily reduced, and thus it is generally 2.5 g / cm 3 Preferably, it is 2.4 g / cm 3 Further preferably, it is 2.3 g / cm

[0054] The tap density of the positive electrode active material is measured by passing the sample through a sieve having a mesh size of 300 μm, dropping the sample into a 20 cm 3 tapping cell, filling the cell volume, and then using a powder density tester (for example, Tap Denser manufactured by Seishin Enterprise Co., Ltd.) to perform oscillation with a stroke of 10 mm for 1000 times, and calculating the density from the volume at that time and the weight of the sample. This density is defined as the tap density.

[0055] The median diameter d50 of the particles of the positive electrode active material (in the case of secondary particles formed by agglomeration of primary particles) is usually 0.1 μm or more, preferably 0.5 μm or more, more preferably 1 μm or more, and most preferably 3 μm or more; and is usually 20 μm or less, preferably 18 μm or less, more preferably 16 μm or less, and most preferably 15 μm or less. If less than the lower limit, a high bulk density product can not be obtained; and if more than the upper limit, diffusion of lithium within the particles takes time, thus causing a decrease in battery performance, or problems such as streaks can occur when the positive electrode is produced by forming a slurry of the active material and a conductive aid, a binder, etc. using a solvent and coating in a thin film shape. Here, by mixing two or more positive electrode active materials having different median diameters d50, the filling property at the time of production of the positive electrode can be further improved.

[0056] Note that the median diameter d50 in the present application is measured using a publicly known laser diffraction / scattering type particle size distribution measuring device. When LA-920 manufactured by HORIBA Ltd. is used as the particle size distribution meter, a 0.1 mass% aqueous solution of sodium hexametaphosphate is used as the dispersion medium used at the time of measurement, and the measurement refractive index is set to 1.24 after 5 minutes of ultrasonic dispersion to perform the measurement.

[0057] In the case of secondary particles formed by agglomeration of primary particles, the average primary particle diameter of the positive electrode active material is usually 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 is usually 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and most preferably 0.6 μm or less. If more than the upper limit, it is difficult to form spherical secondary particles, the powder filling property is adversely affected, or the specific surface area is greatly reduced, thus the possibility that the battery performance such as output characteristics will decrease sometimes becomes large. In contrast, if less than the lower limit, problems such as poor reversibility in charge and discharge due to poor crystallization sometimes occur. Note that the primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification of 10,000 times, the longest value of the cut surface produced by the left and right intersection lines of the primary particles with respect to a straight line in the horizontal direction is found for 50 arbitrary primary particles, and the average value is taken to find the primary particle diameter.

[0058] The BET specific surface area of the positive electrode active material is 0.2 m 2 / g or more, preferably 0.3 m 2 / g or more, and more preferably 0.4 m 2 / g or more; and is 4.0 m 2 / g or less, preferably 2.5 m 2 / g or less, and more preferably 1.5 m2 If the BET specific surface area is less than this range, the battery performance tends to decrease, and if the BET specific surface area is greater than this range, the tap density is difficult to increase, and the coating property at the time of formation of the positive electrode mixture layer tends to sometimes cause problems.

[0059] The BET specific surface area is defined as follows: using a surface area meter (for example, a full-automatic surface area measuring device manufactured by Shinto Scientific Co., Ltd.), the sample is pre-dried at 150°C for 30 minutes under nitrogen flow, and then the BET one-point method by nitrogen adsorption based on the gas flow method is performed using nitrogen-helium mixed gas adjusted to a relative pressure value of 0.3 of nitrogen to atmospheric pressure, and the obtained value is defined as the BET specific surface area.

[0060] As the method for producing the positive electrode active material, a common method used as a method for producing an inorganic compound is used. In particular, various methods are considered for producing a spherical or ellipsoidal active material, and for example, the following methods can be given: a method in which a transition metal raw material such as a transition metal nitrate, a sulfate, or the like, and a raw material of another element if necessary are dissolved or dispersed by pulverization in a solvent such as water, the pH is adjusted under stirring, a spherical precursor is produced and recovered, and the precursor is dried as necessary, and then a Li source such as LiOH, Li2CO3, LiNO3, or the like is added and fired at a high temperature to obtain an active material; a method in which a transition metal raw material such as a transition metal nitrate, a sulfate, a hydroxide, an oxide, or the like, and a raw material of another element if necessary are dissolved or dispersed by pulverization in a solvent such as water, and dried and formed by a spray dryer or the like to produce a spherical or ellipsoidal precursor, and a Li source such as LiOH, Li2CO3, LiNO3, or the like is added to the precursor and fired at a high temperature to obtain an active material; and a method in which a transition metal raw material such as a transition metal nitrate, a sulfate, a hydroxide, an oxide, or the like, and a Li source such as LiOH, Li2CO3, LiNO3, or the like, and a raw material of another element if necessary are dissolved or dispersed by pulverization in a solvent such as water, and dried and formed by a spray dryer or the like to produce a spherical or ellipsoidal precursor, and the precursor is fired at a high temperature to obtain an active material; and the like.

[0061] Note that in the present application, the positive electrode active material powder can be used alone, or two or more kinds of positive electrode active material powders having different compositions or different powder properties can be used in combination and at an arbitrary ratio.

[0062] As the negative active material, there is no particular restriction as long as it can electrochemically occlude and release lithium ions, and carbonaceous materials, metal oxides such as tin oxide or silicon oxide, metal complex oxides, lithium alloys such as lithium simple substance or lithium-aluminum alloy, metals that can form alloys with lithium such as Sn or Si, and the like can be given. They can be used singly with one kind, or two or more kinds can be used in any combination and proportion. Among them, from the aspect of safety, it is preferable to use carbonaceous materials or lithium complex oxides.

[0063] As the metal complex oxide, there is no particular restriction as long as it can occlude and release lithium, and from the aspect of high current density charge-discharge characteristics, it is preferable to contain titanium and / or lithium as a constituent component.

[0064] As the metal complex oxide, it is preferable to be a lithium-containing transition metal complex oxide, and for example, in addition to lithium-nickel complex oxides represented by the above general formula (1), Li 4+x Ti5O 12 (0≤x≤3), Li 2+y Ti3O7(0≤y≤3), and the like lithium titanate.

[0065] As the carbonaceous material, for the reason that the balance of initial irreversible capacity and high current density charge-discharge characteristics is good, it is preferable to be selected from the following substances:

[0066] (1) natural graphite;

[0067] (2) Artificial carbonaceous substances and artificial graphitic substances; carbonaceous materials obtained by subjecting carbonaceous substances {for example, natural graphite, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or a substance obtained by oxidizing these pitches, needle coke, pitch coke, and carbon materials obtained by partially graphitizing these, furnace black, acetylene black, pitch-based carbon fibers, and the like organic matter, organic matter capable of carbonization (for example, coal tar pitch from soft pitch to hard pitch, or coal-based heavy oil such as dry distillation liquid oil, atmospheric residue, vacuum residue, straight-run heavy oil, crude oil, naphtha, decomposition-based petroleum heavy oil such as ethylene tar generated as a byproduct upon thermal decomposition, and aromatic hydrocarbons such as cymene, decacyclene, anthracene, and phenanthrene, N ring compounds such as phenazine and acridine, S ring compounds such as thiophene and bithiophene, polyphenyls such as biphenyl and terphenyl, polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized products of these substances, polyacrylonitrile containing nitrogen, polypyrrole, and other organic polymers, polythiophene containing sulfur, polystyrene, natural polymers such as cellulose, lignin, mannans, polygalacturonic acid, chitosan, and sucrose, thermoplastic resins such as polyphenylene sulfide and polyphenylene ether, furfuryl alcohol resin, phenol-formaldehyde resin, imide resin, and the like) and their carbonized products, or a solution obtained by dissolving organic matter capable of carbonization in a low-molecular organic solvent such as benzene, toluene, xylene, quinoline, n-hexane, and the like, and their carbonized products} in a range of 400°C to 3200°C by heat treatment one or more times;

[0068] (3) Carbonaceous materials in which the negative electrode mixture layer is composed of at least two or more carbonaceous substances having different crystallinities and / or having an interface at which carbonaceous substances having different crystallinities are in contact;

[0069] (4) Carbonaceous materials in which the negative electrode mixture layer is composed of at least two or more carbonaceous substances having different orientations and / or having an interface at which carbonaceous substances having different orientations are in contact.

[0070] In order to increase the capacity of the resulting electrode, the content of the electrode active material (positive electrode active material or negative electrode active material) in the electrode mixture is preferably 40% by mass or more.

[0071] The content of the electrode active material in the positive electrode mixture of the present application is preferably 96.0% to 99.0% by mass, more preferably 96.5% to 98.9% by mass, and further preferably 97.0% to 98.8% by mass, relative to the mass of the positive electrode mixture.

[0072] <Conductive aid>

[0073] The electrode mixture of the present application also preferably contains a conductive aid. As the conductive aid, for example, carbon black such as acetylene black and Ketjen black, carbon materials such as graphite, carbon fibers, carbon nanotubes, and carbon nanohorns can be given.

[0074] The content of the conductive aid in the positive electrode mixture of the present application is preferably 0.01 to 5 parts by mass, more preferably 0.05 to 3 parts by mass, and further preferably 0.1 to 2 parts by mass, relative to 100 parts by mass of the positive electrode active material.

[0075] <Organic solvent>

[0076] The electrode mixture of the present application also contains an organic solvent. As the organic solvent, there can be mentioned, for example, nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide, and the like; ketone-based solvents such as acetone, methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone, and the like; ester-based solvents such as ethyl acetate, butyl acetate, and the like; ether-based solvents such as tetrahydrofuran, dioxane, and the like; β-alkyloxypropionamides such as β-methoxy-N,N-dimethylpropionamide, β-n-butyloxy-N,N-dimethylpropionamide, β-n-hexyloxy-N,N-dimethylpropionamide, and the like; and low-boiling general-purpose organic solvents such as mixed solvents thereof. Among these, as the solvent, 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-alkyloxypropionamides is preferred from the viewpoint of excellent coatability, and at least one selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylacetamide is more preferred.

[0077] <Binder>

[0078] The binder contained in the electrode mixture of the present application contains a fluorine-containing copolymer containing a vinylidene fluoride unit (VdF unit) and a fluorinated monomer unit (but not including the VdF unit). The electrode mixture of the present application contains a fluorine-containing copolymer as a binder, and the fluorine-containing copolymer contains a VdF unit and a fluorinated monomer unit, and thus an electrode mixture layer that is sufficiently adhered to a current collector can be formed, and the coatability is excellent because the viscosity does not easily increase, and thus the electrode mixture layer can be easily formed, and the softness of the electrode mixture layer can be improved.

[0079] As the fluorinated monomer (excluding VdF), for example, tetrafluoroethylene (TFE), fluoroethylene, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene, and trans-1,3,3,3-tetrafluoropropene can be given. Among them, from the viewpoint of further suppressing the increase in the viscosity of the electrode mixture, and further from the viewpoint of being able to form an electrode mixture layer that is more excellent in adhesion to the current collector and in softness, at least one selected from the group consisting of TFE, CTFE, HFP, fluoroalkyl vinyl ether, and 2,3,3,3-tetrafluoropropene is preferred, at least one selected from the group consisting of TFE, CTFE, fluoroalkyl vinyl ether, and HFP is more preferred, at least one selected from the group consisting of TFE and HFP is further preferred, and TFE is particularly preferred.

[0080] As the fluoroalkyl vinyl ether (FAVE), a fluoroalkyl vinyl ether having a fluoroalkyl group having 1 to 5 carbon atoms is preferred, and at least one selected from the group consisting of perfluoro(methyl vinyl ether), perfluoro(ethyl vinyl ether), and perfluoro(propyl vinyl ether) is more preferred.

[0081] The fluorinated monomer unit (excluding the VdF unit) can have a polar group or can not have a polar group.

[0082] The content of the VdF unit of the fluorine-containing copolymer is preferably 50.0 mol% to 99.0 mol%, more preferably 57.0 mol% or more, further preferably 60.0 mol% or more, and particularly preferably 63.0 mol% or more, and more preferably 97.0 mol% or less, further preferably 95.0 mol% or less, particularly preferably 90.0 mol% or less, and most preferably 85.0 mol% or less, with respect to the total monomer units, from the viewpoint of further suppressing the increase in the viscosity of the electrode mixture, and further from the viewpoint of being able to form an electrode mixture layer that is more excellent in adhesion to the current collector and in softness.

[0083] The content of the fluorinated monomer unit (excluding the VdF unit) of the fluorine-containing copolymer is preferably 1.0 mol% or more, more preferably 3.0 mol% or more, further preferably 5.0 mol% or more, particularly preferably 10.0 mol% or more, and most preferably 15.0 mol% or more, and preferably 50.0 mol% or less, more preferably 43.0 mol% or less, further preferably 40.0 mol% or less, and particularly preferably 37.0 mol% or less, with respect to the total monomer units.

[0084] In the present application, the composition of the fluorine-containing copolymer can be determined, for example, by 19 F-NMR measurement.

[0085] The fluorine-containing copolymer can also contain non-fluorinated monomer units. As the above non-fluorinated monomer, mention can be made of non-fluorinated monomers having no polar group such as ethylene, propylene, and the like, non-fluorinated monomers having a polar group (hereinafter sometimes referred to as a polar group-containing monomer), and the like.

[0086] When a non-fluorinated monomer having a polar group is used as the non-fluorinated monomer, a polar group is introduced into the fluorine-containing copolymer, whereby more excellent adhesion of the electrode mixture layer to the current collector can be obtained. As the polar group which the fluorine-containing copolymer can have, at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, a hydroxyl group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid 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 hydroxyl group is more preferred, and a carbonyl group-containing group is further preferred. The above hydroxyl group does not include a hydroxyl group which forms a part of the above carbonyl group-containing group. In addition, the above amino group is a monovalent functional group after removal of hydrogen from ammonia, a primary amine, or a secondary amine.

[0087] The above carbonyl group-containing group refers to a functional group having a carbonyl group (-C(=0)-). As the above carbonyl group-containing group, a group represented by the general formula: -COOR (R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) or a carboxylic anhydride group is preferred. As the number of carbon atoms of the alkyl group and the hydroxyalkyl group, 1 to 16 is preferred, 1 to 6 is more preferred, and 1 to 3 is further preferred. As the group represented by the general formula: -COOR, -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, -COOC2H5, and the like can be specifically mentioned. In the case where the group represented by the general formula: -COOR is -COOH or includes -COOH, -COOH can be a carboxylate such as a carboxylic acid metal salt, a carboxylic acid ammonium salt, and the like.

[0088] In addition, as the above carbonyl group-containing group, a group represented by the general formula: -X-COOR (X is a chain of atoms consisting of 2 to 15 atoms in number, and the molecular weight of the chain of atoms is preferably 350 or less. R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) is preferred. As the number of carbon atoms of the alkyl group and the hydroxyalkyl group, 1 to 16 is preferred, 1 to 6 is more preferred, and 1 to 3 is further preferred.

[0089] As the above amide group, 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.) is preferred.

[0090] As the above-mentioned monomer containing a polar group, mention can be made of hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and the like (hydroxyalkyl (meth) acrylate); dimethyl methylene malonate, and the like (alkylidene malonate); vinyl carboxymethyl ether, vinyl carboxyethyl ether, and the like (vinyl carboxyalkyl ether); 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, and the like (carboxyalkyl (meth) acrylate); acryloyloxyethyl succinate, acryloyloxypropyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, methacryloyloxyethyl phthalate, and the like ( (meth) acryloyloxyalkyl dicarboxylate) ; monomethyl maleate, monoethyl maleate, monomethyl citraconate, monoethyl citraconate, and the like (monoester of an unsaturated dibasic acid) ; a monomer (2) represented by General Formula (2) :

[0091] [Chemical Formula 1]

[0092]

[0093] (In the formula, R 1 ~R 3 independently represent a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. R 4 represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. Y 1 represents an inorganic cation and / or an organic cation.) represented by the monomer (2) represented by General Formula (2) ; and the like.

[0094] As the above-mentioned monomer containing a polar group which can be contained in the fluorine-containing copolymer, a unit based on the monomer (2) represented by General Formula (2) is preferable.

[0095] In General Formula (2), Y 1 represents an inorganic cation and / or an organic cation. As the inorganic cation, mention can be made of H, Li, Na, K, Mg, Ca, Al, Fe, and the like. As the organic cation, mention can be made of NH4, NH3R 5 , NH2R 5 2, NHR 5 3, NR 5 4 (R 5 independently represents an alkyl group having 1 to 4 carbon atoms), and the like. As Y 1 , H, Li, Na, K, Mg, Ca, Al, NH4are preferable, H, Li, Na, K, Mg, Al, NH4are more preferable, H, Li, Al, NH4are further preferable, and H is particularly preferable. Note that, for convenience, the notation of the specific examples of the inorganic cation and the organic cation is omitted from the valence number.

[0096] In General Formula (2), R 1 ~R 3independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. The above hydrocarbon group is a monovalent hydrocarbon group. The number of carbon atoms of the above hydrocarbon group is preferably 4 or less. As the above hydrocarbon group, an alkyl group, an alkenyl group, an alkynyl group, or the like having the above number of carbon atoms can be given, and a methyl group or an ethyl group is preferred. R 1 and R 2 independently preferably represents a hydrogen atom, a methyl group, or an ethyl group, and R 3 preferably represents a hydrogen atom or a methyl group.

[0097] In General Formula (2), R 4 represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. The above hydrocarbon group is a divalent hydrocarbon group. The number of carbon atoms of the above hydrocarbon group is preferably 4 or less. As the above hydrocarbon group, an alkylene group, an alkenylene group, or the like having the above number of carbon atoms can be given, and 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, and a methylene group is more preferred.

[0098] As the monomer (2), at least one selected from the group consisting of a (meth)acrylic acid and a salt thereof, a vinylacetic acid (3-butenoic acid) and a salt thereof, a 3-pentenoic acid and a salt thereof, a 4-pentenoic acid and a salt thereof, a 3-hexenoic acid and a salt thereof, a 4-hexenoic acid and a salt thereof, and a 5-hexenoic acid and a salt thereof is preferred, and at least one selected from the group consisting of a 3-butenoic acid and a salt thereof and a 4-pentenoic acid and a salt thereof is more preferred.

[0099] The content of the above monomer unit containing a polar group in the fluorine-containing copolymer is preferably 0.05 to 2.0 mol%, more preferably 0.10 mol% or more, further preferably 0.25 mol% or more, and particularly preferably 0.40 mol% or more, and more preferably 1.5 mol% or less, with respect to the total monomer units.

[0100] In the present application, the content of the monomer unit containing a polar group in the fluorine-containing copolymer can be measured by acid-base titration of the acid group in the case where the polar group is an acid group such as a carboxylic acid.

[0101] As the fluorine-containing copolymer, for example, 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 / 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, VdF / FAVE / 2-carboxyethyl acrylate copolymer, and the like can be given.

[0102] As the fluorine-containing copolymer, a fluorine-containing copolymer composed of only VdF units, TFE units, and optional non-fluorinated monomer units is preferred.

[0103] When the fluorine-containing copolymer contains VdF units and TFE units, the molar ratio of the VdF units to the TFE units (VdF units / TFE units) is preferably from 50 / 50 to 99 / 1, more preferably from 57 / 43 to 97 / 3, further preferably from 60 / 40 to 95 / 5, particularly preferably from 63 / 37 to 90 / 10, most preferably from 63 / 37 to 85 / 15.

[0104] The weight average molecular weight (polystyrene conversion) of the fluorine-containing copolymer is preferably from 50000 to 3000000, more preferably 80000 or more, further preferably 100000 or more, particularly preferably 200000 or more; more preferably 2400000 or less, further preferably 2200000 or less, particularly preferably 2000000 or less. The above weight average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0105] The number average molecular weight (polystyrene conversion) of the fluorine-containing copolymer is preferably from 20000 to 1500000, more preferably 40000 or more, further preferably 70000 or more, particularly preferably 140000 or more; more preferably 1400000 or less, further preferably 1200000 or less, particularly preferably 1100000 or less. The above number average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0106] The melting point of the fluorine-containing copolymer is preferably 100°C to 170°C, more preferably 110°C to 165°C, and further preferably 120°C to 163°C. The melting point is obtained as follows: using a differential scanning calorimeter (DSC) device, the temperature is raised from 30°C to 220°C at a rate of 10°C / minute, then lowered to 30°C at a rate of 10°C / minute, and again raised to 220°C at a rate of 10°C / minute, and the temperature corresponding to the maximum value of the heat of fusion curve at this time is obtained.

[0107] The elongation at break of the fluorine-containing copolymer is preferably 100% or more. The elongation at break is more preferably 200% or more, and further preferably 300% or more.

[0108] The elongation at break can be measured as follows. That is, the fluorine-containing copolymer is dissolved in N-methyl-2-pyrrolidone (NMP) at a concentration of 10 mass% to 20 mass% to obtain a fluorine-containing copolymer solution, the fluorine-containing copolymer solution is cast onto a glass plate, dried at 100°C for 12 hours, and further dried at 100°C under vacuum for 12 hours to obtain a film having a thickness of 50 μm to 100 μm. The film is punched into a dumbbell shape, and the elongation at break at 25°C is measured using an autograph.

[0109] The storage modulus of the fluorine-containing copolymer at 30°C is preferably 1100 MPa or less, and the storage modulus at 60°C is preferably 500 MPa or less.

[0110] 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.

[0111] The storage modulus of the fluorine-containing copolymer at 60°C is more preferably 350 MPa or less.

[0112] The storage modulus of the fluorine-containing copolymer at 30°C is preferably 100 MPa or more, more preferably 150 MPa or more, and further preferably 200 MPa or more.

[0113] The storage modulus of the fluorine-containing copolymer at 60°C is preferably 50 MPa or more, more preferably 80 MPa or more, and further preferably 130 MPa or more.

[0114] The storage modulus is a measured value obtained as follows: for a sample having a length of 30 mm, a width of 5 mm, and a thickness of 50 to 100 μm, the value at 30°C and 60°C is measured by dynamic viscoelasticity measurement using a dynamic viscoelasticity measuring device DVA220 manufactured by IT Keisokuseigyo Co., Ltd. under conditions of a tensile mode, a clamping width of 20 mm, a measurement temperature of -30°C to 160°C, a temperature increase rate of 2°C / min, and a frequency of 1 Hz.

[0115] The measurement sample can be produced as follows: for example, a fluorine-containing copolymer is dissolved in N-methyl-2-pyrrolidone (NMP) at a concentration of 10 to 20 mass% to obtain a fluorine-containing copolymer solution, the fluorine-containing copolymer solution is cast onto a glass plate, dried at 100°C for 12 hours, and further dried at 100°C under vacuum for 12 hours, and the obtained film having a thickness of 50 to 100 μm is cut into a length of 30 mm and a width of 5 mm, whereby the measurement sample can be produced.

[0116] The weight increase rate of the fluorine-containing copolymer after immersion in the electrolyte at 60°C for 1 week is preferably 250 mass% or less, more preferably 200 mass% or less. The weight increase rate of the fluorine-containing copolymer after immersion in the electrolyte at 60°C for 1 week is further preferably 180 mass% or less, particularly preferably 160 mass% or less, and can also be 105 mass% or more.

[0117] The above weight increase rate can be obtained by the following method.

[0118] An NMP solution (8 mass%) of the fluorine-containing copolymer was cast onto a glass dish, vacuum-dried at 100°C for 12 hours, whereby a fluorine-containing copolymer film having a thickness of 200 μm was produced. The obtained film was punched into a size of 6 mm Φ, and placed in a sample bottle containing an electrolyte (a solution obtained by dissolving LiPF6 at a concentration of 1 M in a solvent of ethylene carbonate / methyl ethyl carbonate at a ratio of 3 / 7 (by volume)), and the weight increase rate was obtained after standing at 60°C for 1 week.

[0119] The binder contained in the electrode mixture of the present application preferably further contains polyvinylidene fluoride (PVdF). By using the fluorine-containing copolymer and PVdF as the binder, the viscosity increase of the electrode mixture can be further suppressed, and an electrode mixture layer having more excellent adhesion to the current collector and softness can be formed.

[0120] Polyvinylidene fluoride (PVdF) is a polymer containing a unit based on vinylidene fluoride (VdF) (hereinafter referred to as a VdF unit), and can be either a VdF homopolymer composed only of the VdF unit, or a polymer containing the VdF unit and a unit based on a monomer copolymerizable with VdF.

[0121] Among the above PVdF, as the monomer copolymerizable with VdF, a monomer other than tetrafluoroethylene (TFE) is preferable. That is, PVdF preferably does not contain a TFE unit.

[0122] Among the above PVdF, as the monomer copolymerizable with VdF, a fluorinated monomer, a non-fluorinated monomer, or the like can be mentioned, and a fluorinated monomer is preferable. As the above fluorinated monomer, vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, or the like can be mentioned. As the above non-fluorinated monomer, ethylene, propylene, or the like can be mentioned.

[0123] Among the above PVdF, as the monomer copolymerizable with VdF, at least one fluorinated monomer selected from the group consisting of CTFE, fluoroalkyl vinyl ether, HFP, and 2,3,3,3-tetrafluoropropene is preferable, and at least one fluorinated monomer selected from the group consisting of CTFE, HFP, and fluoroalkyl vinyl ether is more preferable.

[0124] In the PVdF, the content of the monomer unit copolymerizable with VdF is preferably 0 to 5.0 mol%, more preferably 0 to 3.0 mol%, and further preferably 0 to 1.0 mol% with respect to the total monomer units. In the PVdF, the content of the fluorinated monomer unit copolymerizable with VdF is preferably less than 5.0 mol%, more preferably less than 3.0 mol%, and further preferably less than 1.0 mol% with respect to the total monomer units.

[0125] The content of the VdF unit of the PVdF is preferably 95.0 mol% or more, more preferably 97.0 mol% or more, and further preferably 99.0 mol% or more with respect to the total monomer units. In addition, the content of the VdF unit of the PVdF is preferably more than 95.0 mol%, more preferably more than 97.0 mol%, and further preferably more than 99.0 mol% with respect to the total monomer units.

[0126] In addition, the content of the VdF unit of the PVdF is preferably 95.0 mol% to 99.999 mol%, more preferably 97.0 mol% or more, and further preferably 98.5 mol% or more, more preferably 99.99 mol% or less, and further preferably 99.90 mol% or less with respect to the total monomer units.

[0127] In the present application, the composition of the PVdF can be determined, for example, by 19 F-NMR measurement.

[0128] The PVdF described above can also have a polar group. By using a fluorine-containing copolymer and a PVdF having a polar group as the binder, an electrode mixture layer that is more excellent in flexibility and adhesion to the current collector can be formed.

[0129] As the polar group described above, there is no particular limitation as long as it is a functional group having polarity, and since it can make the adhesion of the electrode mixture layer to the current collector more excellent, it is preferably at least one selected from the group consisting of a group having a carbonyl group, an epoxy group, a hydroxyl group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group, an amino group, an amide group, and an alkoxy group, more preferably at least one selected from the group consisting of a group having a carbonyl group, an epoxy group, and a hydroxyl group, and further preferably a group having a carbonyl group. The hydroxyl group described above does not include a hydroxyl group that is a part of the group having a carbonyl group described above. In addition, the amino group is a monovalent functional group after removing hydrogen from ammonia, a primary amine, or a secondary amine.

[0130] The group having a carbonyl group described above refers to a functional group having a carbonyl group (-C(=O)-). As the group having a carbonyl group described above, since it can make the adhesion of the electrode mixture layer to the current collector more excellent, it 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 anhydride group, and more preferably a group represented by the general formula: -COOR. As the number of carbon atoms of the alkyl group and the hydroxyalkyl group, it is preferably 1 to 16, more preferably 1 to 6, and further preferably 1 to 3. As the group represented by the general formula: -COOR, specific examples include -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, -COOC2H5, and the like. In the case where the group represented by the general formula: -COOR is -COOH or includes -COOH, -COOH can be a carboxylate such as a carboxylate metal salt, a carboxylate ammonium salt, or the like.

[0131] In addition, as the group having a carbonyl group described above, a group represented by the general formula: -X-COOR (X is a group consisting of 2 to 15 atoms in the main chain, and the molecular weight of the group is preferably 350 or less. R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) is preferable. As the number of carbon atoms of the alkyl group and the hydroxyalkyl group, it is preferably 1 to 16, more preferably 1 to 6, and further preferably 1 to 3.

[0132] As the amide group described above, 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.) is preferable.

[0133] The above-mentioned polar group can be introduced into the PVdF by polymerizing the VdF with the above-mentioned monomer having a polar group (hereinafter referred to as a polar group-containing monomer), or by reacting the PVdF with the above-mentioned compound having a polar group, but from the viewpoint of productivity, it is preferable to polymerize the VdF with the above-mentioned polar group-containing monomer.

[0134] When the VdF and the above-mentioned polar group-containing monomer are polymerized, a PVdF containing VdF units and polar group-containing monomer units can be obtained. That is, since the adhesion of the electrode mixture layer to the current collector can be made more excellent, the PVdF preferably contains the above-mentioned polar group-containing monomer units. The content of the above-mentioned polar group-containing monomer units is preferably 0.001 to 5.0 mole%, more preferably 0.01 to 3.0 mole%, and further preferably 0.10 to 1.5 mole%, relative to the total monomer units.

[0135] In the present application, the content of the polar group-containing monomer units in the PVdF can be measured by acid-base titration of the acid group in the case where the polar group is an acid group such as a carboxylic acid group.

[0136] As the above-mentioned polar group-containing monomer, there can be mentioned hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and the like (hydroxyalkyl (meth) acrylate) ; (meth) acrylic acid, crotonic acid, vinyl acetic acid (3-butenoic acid), 3-pentenoic acid, 4-pentenoic acid, 3-hexenoic acid, 4-heptenoic acid, and the like (unsaturated monobasic acid) ; maleic acid, maleic anhydride, citraconic acid, citraconic anhydride, and the like (unsaturated dibasic acid) ; dimethyl methylene malonate, and the like (alkylidene malonate) ; vinyl carboxymethyl ether, vinyl carboxyethyl ether, and the like (vinyl carboxyalkyl ether) ; 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate, and the like (carboxyalkyl (meth) acrylate) ; acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, acryloyloxypropyl succinate, methacryloyloxyethyl phthalate, and the like ( (meth) acryloyloxyalkyl dicarboxylate) ; monomethyl maleate, monoethyl maleate, monomethyl citraconate, monoethyl citraconate, and the like (monoester of unsaturated dibasic acid) ; and the like.

[0137] In the case where the PVdF is reacted with the above-mentioned compound having a polar group to introduce the above-mentioned polar group into the PVdF, as the above-mentioned compound having a polar group, the above-mentioned polar group-containing monomer, or a silane-based coupling agent or a titanate-based coupling agent having a group reactive with the PVdF and a hydrolyzable group can be used. As the above-mentioned hydrolyzable group, an alkoxy group is preferable. In the case where a coupling agent is used, it is added to the PVdF by reaction with the PVdF dissolved or swelled in a solvent.

[0138] As the PVdF, PVdF obtained by partially dehydrofluorinating PVdF with a base and further reacting the partially dehydrofluorinated PVdF with an oxidizing agent can also be used. As the oxidizing agent, hydrogen peroxide, hypochlorite, palladium halide, chromium halide, alkali metal permanganate, peroxide, alkyl peroxide, alkyl persulfate, and the like can be given.

[0139] Since the viscosity increase of the electrode mixture can be further suppressed, and furthermore, an electrode mixture layer having more excellent adhesion to the current collector and softness can be formed, the weight average molecular weight (polystyrene conversion) of the PVdF is preferably 50,000 to 3,000,000, more preferably 80,000 or more, further preferably 100,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, further 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 N,N-dimethylformamide as a solvent. In addition, since the viscosity increase of the electrode mixture can be further suppressed, and furthermore, an electrode mixture layer having more excellent adhesion to the current collector and softness can be formed, the weight average molecular weight of the PVdF can be 1,000,000 or more, or 1,500,000 or more.

[0140] Since the viscosity increase of the electrode mixture can be further suppressed, and furthermore, an electrode mixture layer having more excellent adhesion to the current collector and softness can be formed, the number average molecular weight (polystyrene conversion) of the PVdF is preferably 20,000 to 1,500,000, more preferably 40,000 or more, further preferably 70,000 or more, particularly preferably 140,000 or more, more preferably 1,400,000 or less, further preferably 1,200,000 or less, 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.

[0141] The melting point of the PVdF is preferably 100°C to 240°C. The melting point can be obtained as follows: using a differential scanning calorimetry (DSC) device, the temperature is increased at a rate of 10°C / minute, and the temperature corresponding to the maximum value of the heat of fusion curve at this time is obtained.

[0142] The PVdF can be produced by a publicly known method: for example, solution polymerization, suspension polymerization, or the like, by appropriately mixing VdF and the above-described monomer containing a polar group, a polymerization initiator, and the like.

[0143] The storage modulus of the PVdF at 30°C is preferably 2,000 MPa or less, more preferably 1,800 MPa or less.

[0144] The storage modulus of the PVdF at 60°C is preferably 1500 MPa or less, more preferably 1300 MPa or less.

[0145] The storage modulus of the PVdF at 30°C is preferably 1000 MPa or more, more preferably 1100 MPa or more.

[0146] The storage modulus of the PVdF at 60°C is preferably 600 MPa or more, more preferably 700 MPa or more.

[0147] The storage modulus of the PVdF can be measured by the same method as that of the fluorine-containing copolymer.

[0148] Since the viscosity increase of the electrode mixture can be further suppressed, and furthermore, an electrode mixture layer having more excellent adhesion and softness to the current collector can be formed, the mass ratio of the PVdF to the fluorine-containing copolymer (PVdF / fluorine-containing copolymer) in the binder is preferably 99 / 1 to 1 / 99, more preferably 97 / 3 to 10 / 90, further preferably 95 / 5 to 40 / 60, and most preferably 90 / 10 to 50 / 50.

[0149] The binder can contain other polymers in addition to the PVdF and the fluorine-containing copolymer. As the other polymers, polymethacrylate, polymethyl methacrylate, polyimide, polyamide-imide, polycarbonate, styrene rubber, butadiene rubber, and the like can be given.

[0150] Since the viscosity increase of the electrode mixture can be further suppressed, and furthermore, an electrode mixture layer having more excellent adhesion and softness to the current collector can be formed, the content of the fluorine-containing copolymer in the binder is preferably 1% by mass or more, more preferably 3% by mass or more, further preferably 5% by mass or more, particularly preferably 10% by mass or more, and most preferably 15% by mass or more, relative to the mass of the binder; and can be 100% by mass or less.

[0151] Since the viscosity increase of the electrode mixture can be further suppressed, and furthermore, an electrode mixture layer having more excellent adhesion and softness to the current collector can be formed, the content of the binder in the electrode mixture is preferably 0.1 parts by mass to 1.6 parts by mass, more preferably 0.3 parts by mass to 1.6 parts by mass, further preferably 0.5 parts by mass to 1.6 parts by mass, particularly preferably 0.8 parts by mass to 1.5 parts by mass, and most preferably 1.0 parts by mass to 1.5 parts by mass, relative to 100 parts by mass of the electrode active material; and can be 1.0 parts by mass or less.

[0152] (Additives)

[0153] In the electrode mixture of the present application, as the additive, a polymer material having the following repeating unit is contained,

[0154] -[CH2-CHR]-

[0155] (in the above repeating unit, R represents a chain or cyclic amido group, a nitrile group, or a substituent in which at least one hydrogen atom of an alkyl group having 1 to 4 carbon atoms is substituted with a chain or cyclic amido group or a nitrile group.) The electrode mixture of the present application contains an additive, and thus can form an electrode mixture layer that is excellent in flexibility and sufficiently adhered to a current collector, and is excellent in coatability because the viscosity does not easily increase, and thus can easily form an electrode mixture layer.

[0156] Since the viscosity increase of the electrode mixture can be further suppressed, and thus an electrode mixture layer that is more excellent in adhesion to a current collector and flexibility can be formed, as the additive, at least one selected from the group consisting of polyvinylpyrrolidone and polyacrylonitrile is preferred, and polyvinylpyrrolidone is more preferred.

[0157] Since the viscosity increase of the electrode mixture can be further suppressed, and thus an electrode mixture layer that is more excellent in adhesion to a current collector and flexibility can be formed, as the number average molecular weight of the additive, 10,000 to 500,000 is preferred, 20,000 or more is more preferred, 30,000 or more is further preferred, 400,000 or less is more preferred, and 300,000 or less is further preferred. In the present application, the number average molecular weight of the additive can be measured by gel permeation chromatography (GPC).

[0158] As the polyvinylpyrrolidone, a polymer of N-vinyl-2-pyrrolidone is acceptable without particular limitation, and can be a polymer composed only of N-vinyl-2-pyrrolidone, or a copolymer of N-vinyl-2-pyrrolidone and another monomer, and is preferably a polymer composed only of N-vinyl-2-pyrrolidone or a copolymer of N-vinyl-2-pyrrolidone and a non-fluorinated monomer, and is more preferably a polymer composed only of N-vinyl-2-pyrrolidone.

[0159] As the number average molecular weight of the polyvinylpyrrolidone, 10,000 to 500,000 is preferred, 20,000 or more is more preferred, 30,000 or more is further preferred, 400,000 or less is more preferred, and 300,000 or less is further preferred.

[0160] As the polyacrylonitrile, there is no particular limitation as long as it is a polymer of acrylonitrile, and it can be a polymer consisting only of acrylonitrile or a copolymer of acrylonitrile and another monomer, and it is preferably a polymer consisting only of N-vinyl-2-pyrrolidone or a copolymer of N-vinyl-2-pyrrolidone and a non-fluorinated monomer, and it is more preferably a polymer consisting only of N-vinyl-2-pyrrolidone. As the non-fluorinated monomer, (meth)acrylic acid and the like can be given.

[0161] As the number average molecular weight of the polyacrylonitrile, it is preferably 100,000 to 350,000, more preferably 130,000 or more, and more preferably 250,000 or less, and further preferably 220,000 or less.

[0162] Since the viscosity of the electrode mixture can be further inhibited from increasing, and furthermore, an electrode mixture layer having more excellent adhesion to the current collector and softness can be formed, as the content of the additive in the electrode mixture, it is preferably 0.001 parts by mass to 0.2 parts by mass, more preferably 0.01 parts by mass or more, and further preferably 0.02 parts by mass or more, and more preferably 0.15 parts by mass or less, and further preferably 0.11 parts by mass or less, with respect to 100 parts by mass of the electrode active material.

[0163] In the electrode mixture of the present application, as the mass ratio of the fluorine-containing copolymer (denoted as "fluorine-containing copolymer (a)") to the additive (denoted as "additive (b)") (fluorine-containing copolymer (a) / additive (b)), it is preferably 1 / 99 to 99 / 1, more preferably 20 / 80 or more, and further preferably 40 / 60 or more, and particularly preferably 60 / 40 or more, and more preferably 98 / 2 or less, and further preferably 90 / 10 or less.

[0164] The contents of the electrode active material, the binder, and the additive in the electrode mixture of the present application are determined in consideration of the coatability to the current collector, the film formation property after drying, and the like. The total content of the electrode active material, the binder, and the additive in the electrode mixture is preferably 50 mass% to 90 mass%, more preferably 60 mass% to 85 mass%, and further preferably 70 mass% to 80 mass%. The electrode mixture of the present application does not easily increase in viscosity even when the electrode active material, the binder, and the additive are contained at a high concentration.

[0165] The electrode mixture of the present application can be prepared by mixing the electrode active material, the organic solvent, the binder, the additive, and other components as necessary. At this time, the order of mixing the components is not particularly limited. For example, the electrode active material and other components can be mixed after mixing the binder, the additive, and the organic solvent. Alternatively, for example, a composite of the binder and the electrode active material can be obtained by spraying a solution or dispersion of the binder to the electrode active material and drying, and the obtained composite can be mixed with the organic solvent, the additive, and other components.

[0166] In order to enable rapid dissolution in the organic solvent, the binder is preferably used in a small particle size of 1000 μm or less, particularly 50 μm to 350 μm in average particle diameter.

[0167] <Composition>

[0168] The present application also relates to a composition containing:

[0169] a fluorine-containing copolymer containing a vinylidene fluoride unit and a tetrafluoroethylene unit; and

[0170] a polymer material having a repeating unit of

[0171] -[CH2-CHR]-

[0172] (in the above repeating unit, R represents a chain or cyclic amido group, a nitrile group, or a substituent which is an alkyl group having 1 to 4 carbon atoms and in which at least one hydrogen atom of the alkyl group is replaced with a chain or cyclic amido group or a nitrile group.)

[0173] The composition of the present application has the above-described configuration, and thus, in the case of being used as a material for forming an electrode mixture, an electrode mixture in which the viscosity is less likely to increase can be easily manufactured, and an electrode mixture layer excellent in adhesion to a current collector and in softness can be formed, and an electrode mixture which can form a secondary battery having sufficient load characteristics can be easily manufactured.

[0174] The fluorine-containing copolymer contained in the composition of the present application can have the same configuration as the fluorine-containing copolymer contained in the electrode mixture of the present application, except that the VdF unit and the TFE unit are contained as necessary monomer units. In addition, the additive contained in the composition of the present application can have the same configuration as the additive contained in the electrode mixture of the present application.

[0175] The mass ratio of the fluorine-containing copolymer (denoted as "fluorine-containing copolymer (a)") to the additive (denoted as "additive (b)") in the composition of the present application (fluorine-containing copolymer (a) / additive (b)) is preferably 1 / 99 to 99 / 1, more preferably 20 / 80 or more, further preferably 40 / 60 or more, particularly preferably 60 / 40 or more, and more preferably 98 / 2 or less, further preferably 90 / 10 or less.

[0176] The composition of the present application preferably also contains polyvinylidene fluoride (PVdF). The PVdF contained in the composition of the present application can have the same composition as the PVdF contained in the electrode mixture of the present application.

[0177] The mass ratio of the PVdF to the fluorine-containing copolymer in the composition of the present application (PVdF / fluorine-containing copolymer) is preferably 99 / 1 to 1 / 99, more preferably 97 / 3 to 10 / 90, further preferably 95 / 5 to 40 / 60, and most preferably 90 / 10 to 50 / 50, when used as a material for forming an electrode mixture, because it is possible to easily produce an electrode mixture whose viscosity is less likely to increase, and it is possible to easily produce an electrode mixture layer that has superior adhesion to a current collector and superior softness.

[0178] The composition of the present application preferably also contains an organic solvent. The organic solvent contained in the composition of the present application can have the same composition as the organic solvent contained in the electrode mixture of the present application.

[0179] The content of the fluorine-containing copolymer and the additive in the composition of the present application is preferably 0.5 mass% to 50 mass%, and more preferably 1.0 mass% to 30 mass%, when used for the production of an electrode mixture, because it is possible to easily mix with an electrode active material and reliably achieve good homogeneity.

[0180] The composition of the present application can be suitably used as a material for producing an electrode mixture. The present application also relates to an electrode mixture obtained using the above composition.

[0181] The composition of the present application can be a secondary battery composition. In the present application, the secondary battery composition includes a composition used in the positive electrode, the negative electrode, and the separator of a secondary battery.

[0182] The electrode mixture and the composition of the present application are suitably used as a material for forming a secondary battery. The electrode mixture and the composition of the present application are not liable to increase in viscosity, and can form an electrode mixture layer excellent in adhesion to a current collector and in flexibility, and can form a secondary battery having sufficient load characteristics, and thus are suitable as an electrode mixture and a composition used for an electrode of a secondary battery. A secondary battery to which the electrode mixture and the composition of the present application are applied is provided with: a positive electrode in which a positive electrode mixture is held on a positive electrode current collector; a negative electrode in which a negative electrode mixture is held on a negative electrode current collector; and an electrolyte.

[0183] The electrode mixture of the present application can be an electrode mixture for a secondary battery, or an electrode mixture for a lithium ion secondary battery. In addition, the electrode mixture of the present application can be a positive electrode mixture for producing a positive electrode, or a negative electrode mixture for producing a negative electrode, and is preferably a positive electrode mixture. The electrode mixture layer formed from the electrode mixture of the present application can be a positive electrode mixture layer, or a negative electrode mixture layer.

[0184] <electrode>

[0185] The electrode of the present application is provided with a current collector and an electrode mixture layer. The electrode mixture layer is formed using the electrode mixture of the present application, and can be provided on one surface of the current collector, or on both surfaces.

[0186] The electrode of the present application is provided with an electrode mixture layer formed using the electrode mixture of the present application, and thus is excellent in flexibility, the current collector is sufficiently adhered to the electrode mixture layer, and a secondary battery excellent in battery characteristics can be formed.

[0187] The density of the electrode mixture layer is preferably 2.0 g / cm 3 ~ 5.0 g / cm 3 , more preferably 2.5 g / cm 3 ~ 5.0 g / cm 3 .

[0188] The density of the electrode mixture layer can be calculated from the mass and the volume of the electrode mixture layer.

[0189] The thickness of the electrode mixture layer is preferably 20 μm or more, more preferably 45 μm or more, further preferably 55 μm or more, and particularly preferably 60 μm or more, from the viewpoint of obtaining higher battery characteristics, and is preferably 170 μm or less, more preferably 150 μm or less. In addition, the thickness of the electrode mixture layer can be 85 μm or less, or less than 69 μm.

[0190] The thickness of the electrode mixture layer can be measured by a micrometer. In the case where the electrode mixture layer is provided on both surfaces of the current collector, the thickness of the electrode mixture layer in the present application is the thickness of each surface.

[0191] As the current collector of the electrode of the present application, a metal foil or a metal mesh of, for example, iron, stainless steel, copper, aluminum, nickel, titanium, or the like can be mentioned, with an aluminum foil being preferred.

[0192] The electrode of the present application can be suitably manufactured by a manufacturing method of coating the electrode mixture of the present application on a current collector. After the electrode mixture is coated, the coated film can be further dried and pressed.

[0193] As the coating amount of the electrode mixture on the current collector, 15 mg / cm 2 More preferably, 17.5 mg / cm 2 More preferably, 17.5 mg / cm 2 More preferably, 17.5 mg / cm 2 More preferably, 17.5 mg / cm The coating amount of the electrode mixture is the dried weight of the electrode mixture per unit area.

[0194] <Secondary battery>

[0195] Further, according to the present application, a secondary battery provided with the above electrode is provided.

[0196] The secondary battery of the present application is provided with an electrode formed using the electrode mixture of the present application, and thus exhibits sufficient load characteristics and excellent battery characteristics.

[0197] The secondary battery of the present application is provided with a positive electrode, a negative electrode, and a nonaqueous electrolyte, and preferably one or both of the positive electrode and the negative electrode is the above electrode. Further, the secondary battery of the present application is provided with a positive electrode, a negative electrode, and a nonaqueous electrolyte, and preferably the positive electrode is the above electrode.

[0198] The nonaqueous electrolyte is not particularly limited, and one or two or more kinds of publicly known solvents such as propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate can be used. As the electrolyte, a publicly known electrolyte can be used, and LiClO4, LiAsF6, LiPF6, LiBF4, LiCl, LiBr, CH3SO3Li, CF3SO3Li, cesium carbonate, or the like can be used.

[0199] The electrode of the present application is excellent in flexibility, the current collector and the electrode mixture layer are sufficiently adhered to each other, and a secondary battery excellent in battery characteristics can be formed, and thus can be appropriately used as an electrode for a wound-type secondary battery. Further, the secondary battery of the present application can be a wound-type secondary battery.

[0200] The electrode of the present application is useful not only in a lithium ion secondary battery using the above-described liquid electrolyte, but also in a polymer electrolyte lithium secondary battery. In addition, it is also useful as a double layer capacitor.

[0201] The above-described embodiments are described, but it is understood that various modifications in form or details can be made without departing from the spirit and scope of the claims.

[0202] Examples

[0203] Next, the embodiments of the present application will be described with reference to experimental examples and production examples, but the present application is not limited to the experimental examples and production examples.

[0204] (Polymerization Example 1)

[0205] Into a 4-liter autoclave having a content volume of 4 liters, 1340 g of pure water, 0.75 g of methyl cellulose, 1280 g of perfluorocyclobutane (C318), and 218 g of a mixed gas of VdF / TFE at a molar ratio of 94.3 / 5.7 (mole %) were charged, and the temperature was adjusted to 37°C. Then, 0.699 g of di-sec-butyl peroxydicarbonate, 6 g of methanol, and 0.88 g of ethyl acetate were added, and 384 g of a mixed gas of VdF / TFE at a molar ratio of 85 / 15 (mole %) was added, and the tank pressure was maintained at 1.4 MPaG. After 11 hours from the start of the reaction, the pressure in the tank was reduced, and a fluorine-containing copolymer (A-1) was obtained.

[0206] (Polymerization Example 2)

[0207] Into a 2-liter autoclave having a content volume of 2 liters, 0.6 kg of pure water and 0.6 g of methyl cellulose were charged, and nitrogen substitution was performed, and then 0.57 kg of 1,1,1,3,3-pentafluorobutane was charged, and the system was maintained at 37°C. A mixed gas of TFE / VdF = 7 / 93 (molar ratio) was charged, and the pressure in the tank was adjusted to 1.5 MPa. Then, 0.17 g of 4-pentenoic acid and 0.5 g of a 50 mass % methanol solution of di-n-propyl peroxydicarbonate were added, and the polymerization was initiated. In order to maintain the pressure in the tank, a mixed gas of TFE / VdF = 15 / 85 (molar ratio) was supplied, and 70 g of the mixed gas was added until the end of the reaction. In correspondence with the supply of the mixed gas, 4-pentenoic acid was continuously added, and 0.43 g was added until the end of the reaction. After the addition of 70 g of the mixed gas was completed, the gas in the tank was released, and the reaction was terminated. The reaction product was washed with water and dried, and a fluorine-containing copolymer (A-2) was obtained.

[0208] The physical properties of the fluorine-containing copolymers and PVdF ((A-1) to (A-6)) and the additives ((B-1) to (B-4)) used in the experimental examples and comparative examples are shown.

[0209] Fluorine-containing copolymer (A-1)

[0210] VdF / TFE = 83.3 / 16.7 (mol%)

[0211] Solution viscosity: 847 mPa-s

[0212] Weight average molecular weight: 1160000

[0213] Fluorine-containing copolymer (A-2)

[0214] VdF / TFE / 4-pentenoic acid = 81.63 / 17.92 / 0.45 (mol%)

[0215] Solution viscosity: 393 mPa-s

[0216] Weight average molecular weight: 8200000

[0217] PVdF (A-3)

[0218] VdF = 100 (mol%)

[0219] Solution viscosity: 2400 mPa-s

[0220] Weight average molecular weight: 1800000

[0221] Fluorine-containing copolymer (A-4)

[0222] VdF / HFP = 95.0 / 5.0 (mol%)

[0223] Solution viscosity: 269 mPa-s

[0224] Weight average molecular weight: 730000

[0225] Fluorine-containing copolymer (A-5)

[0226] VdF / CTFE = 98 / 2 (mol%)

[0227] Solution viscosity: 433 mPa-s

[0228] Weight average molecular weight; 850000

[0229] PVdF (A-6)

[0230] VdF / acrylic acid = 99 / 1 (mol%)

[0231] Solution viscosity: 800 mPa-s

[0232] Weight average molecular weight; 1100000

[0233] Additive (B-1)

[0234] Polyvinylpyrrolidone (K30) (manufactured by Tokyo Chemical Industry Co., Ltd.) Number average molecular weight: 40,000

[0235] Additive (B-2)

[0236] Polyvinylpyrrolidone (K90) (manufactured by Tokyo Chemical Industry Co., Ltd.) Number average molecular weight: 360,000

[0237] Additive (B-3)

[0238] Polyacrylonitrile (manufactured by Sigma-Aldrich Co.)

[0239] Number average molecular weight: 150,000

[0240] Additive (B-4)

[0241] Polyvinyl alcohol (manufactured by Denka Co.)

[0242] Degree of polymerization: 2,000

[0243] Degree of saponification: 98.5 to 99.4%

[0244] (Experimental Example 1)

[0245] A positive electrode mixture (slurry) was produced by the following method. 100 parts by mass of a positive electrode active material (NMC811 (LiNi 0.8 Mn 0.1 Co 0.1 O2), 1.54 parts by mass of a conductive aid acetylene black (AB), 0.23 parts by mass of the fluorine-containing copolymer (A-1), 0.90 parts by mass of PVdF (A-3), and 0.05 parts by mass of the additive (B-1) were weighed. After the fluorine-containing copolymer (A-1), the PVdF (A-3), and the additive (B-1) were dissolved in N-methyl-2-pyrrolidone (NMP) so that the total concentration of these was 6% by mass, the prescribed amounts of the positive electrode active material and the conductive aid were added to the solution, and these were mixed well using a stirrer, and good homogeneity was ensured. The total solid content concentration of the positive electrode active material, the conductive aid, the fluorine-containing copolymer, the PVdF, and the additive was adjusted to 80% by mass with respect to the total mass of the slurry.

[0246] (Experimental Example 2)

[0247] NMC622 (LiNi 0.6 Mn 0.2 Co 0.2 O2) was used as the positive electrode active material, and otherwise, a positive electrode mixture was produced in the same manner as in Experimental Example 1.

[0248] (Experimental Example 3)

[0249] Using LCO (LiCoO2) as the positive electrode active material, the total solid content concentration of the positive electrode active material, conductive additive, fluorinated copolymer, PVdF and additives was adjusted to 79% by mass relative to the total mass of the slurry. Otherwise, the positive electrode mixture was prepared in the same manner as in Experimental Example 1.

[0250] (Experimental Example 4)

[0251] The positive electrode mixture (slurry) was prepared using the following method: 100 parts by weight of the positive electrode active material (LFP(LiFePO4)), 20.41 parts by weight of 5% by weight NMP dispersion of carbon nanotubes (CNTs), 0.20 parts by weight of fluorinated copolymer (A-1), 0.82 parts by weight of PVdF (A-3), and 0.10 parts by weight of additive (B-1) were weighed. The fluorinated 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 weight. The specified amounts of the positive electrode active material and CNT dispersion were then added to this solution, and the mixture was thoroughly mixed using a stirrer to ensure good homogeneity. The total solid content concentration of the positive electrode active material, conductive additive, fluorinated copolymer, PVdF, and additive was adjusted to 65% by weight relative to the total mass of the slurry.

[0252] (Experimental Example 5)

[0253] Using additive (B-2) as an additive, the total solid content concentration of the positive electrode active material, conductive additive, fluorinated copolymer, PVdF and additive was adjusted to 78% by mass relative to the total mass of the slurry. Otherwise, the positive electrode mixture was prepared in the same manner as in Experimental Example 1.

[0254] (Experimental Example 6)

[0255] The positive electrode was prepared in the same manner as in Experimental Example 1, using 0.23 parts by mass of fluorinated copolymer (A-4) as the fluorinated copolymer and 0.90 parts by mass of PVdF (A-3) as the PVdF.

[0256] (Experiment Example 7)

[0257] LCO (LiCoO2) was used as the positive electrode active material, 0.23 parts by mass of fluorinated copolymer (A-1) was used as the fluorinated copolymer, and 0.90 parts by mass of PVdF (A-6) was used as the PVdF. Otherwise, the positive electrode mixture was prepared in the same manner as in Experimental Example 1.

[0258] (Experimental Example 8)

[0259] An electrode mixture was produced in the same manner as in Experimental Example 1, except that LCO (LiCoO2) was used as the positive electrode active material, 0.23 parts by mass of the 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.

[0260] (Experimental Example 9)

[0261] An electrode mixture was produced in the same manner as in Experimental Example 1, except that 0.05 parts by mass of the additive (B-3) was used as the additive.

[0262] (Experimental Example 10)

[0263] An electrode mixture was produced in the same manner as in Experimental Example 1, except that 1.13 parts by mass of the fluorine-containing copolymer (A-5) was used as the fluorine-containing copolymer and no PVdF was used.

[0264] (Experimental Example 11)

[0265] An electrode mixture was produced in the same manner as in Experimental Example 9, except that NMC622 (LiNi 0.6 Mn 0.2 Co 0.2 O2) was used as the positive electrode active material.

[0266] (Comparative Example 1)

[0267] An electrode mixture was produced 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 the PVdF, and the total solid content concentration of the positive electrode active material, the conductive aid, the PVdF, and the additive was adjusted to 78% by mass with respect to the total mass of the slurry.

[0268] (Comparative Example 2)

[0269] An electrode mixture was produced in the same manner as in Experimental Example 1, except that no additive was used and the total solid content concentration of the positive electrode active material, the conductive aid, the fluorine-containing copolymer, and the PVdF was adjusted to 76% by mass with respect to the total mass of the slurry.

[0270] (Comparative Example 3)

[0271] An electrode mixture was produced in the same manner as in Experimental Example 4, except that no additive was used.

[0272] (Comparative Example 4)

[0273] An electrode mixture was produced in the same manner as in Experimental Example 1, except that 0.05 parts by mass of the additive (B-4) was used as the additive and the total solid content concentration of the positive electrode active material, the conductive aid, the fluorine-containing copolymer, the PVdF, and the additive was adjusted to 76% by mass with respect to the total mass of the slurry.

[0274] (Comparative Example 5)

[0275] NMC622 (LiNi 0.6 Mn 0.2 Co 0.2 O2) was used as the positive electrode active material, and otherwise, the positive electrode mixture was produced in the same manner as in Comparative Example 1.

[0276] (Comparative Example 6)

[0277] NMC622 (LiNi 0.6 Mn 0.2 Co 0.2 O2) was used as the positive electrode active material, and otherwise, the positive electrode mixture was produced in the same manner as in Comparative Example 2.

[0278] (Production of Positive Electrode)

[0279] The positive electrode mixture produced in Experimental Examples 1 to 11 and Comparative Examples 1 to 6 was uniformly applied to one side of a positive electrode current collector (aluminum foil having a thickness of 20 μm) so that the application amount was 22.5 mg / cm 2 After NMP was completely volatilized, pressing was performed using a roll press machine with a pressure of 10 t, whereby a positive electrode having a positive electrode mixture layer and a positive electrode current collector was produced. The density of the positive electrode mixture layer was 2.75 g / cc.

[0280] (Production of Negative Electrode)

[0281] An artificial graphite powder was used as the negative electrode active material, an aqueous dispersion of carboxymethyl cellulose sodium (concentration of carboxymethyl cellulose sodium: 1 mass%) was used as the thickening agent, and an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50 mass%) was used as the adhesive, and the solid content ratio of the active material, the thickening agent, and the adhesive was 97.6 / 1.2 / 1.2 (mass%) to prepare a negative electrode mixture slurry in a slurry state. After uniform application and drying on a copper foil having a thickness of 20 μm, compression was performed using a press machine, whereby a negative electrode was produced.

[0282] (Preparation of Electrolyte)

[0283] After LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) (EC: EMC = 30:70 (v / v)) at a concentration of 1 mol / L, 1 mass% of vinylene carbonate (VC) was added, and the electrolyte thus obtained was used. Here, LiPF6, EC, EMC, and VC were battery-grade products manufactured by KISHIDA Chemical Industry.

[0284] (Production Example 1)

[0285] The positive electrode mixture prepared in Experimental Example 2 was uniformly applied to one side of a positive electrode current collector (aluminum foil having a thickness of 20 μm) so that the application amount was 20.0 mg / cm2. 2 After NMP was completely volatilized, the positive electrode was prepared by pressing using a roll press.

[0286] The positive electrode prepared, the negative electrode prepared as described above, and a polyethylene separator were stacked in the order of negative electrode, separator, and positive electrode to prepare a battery element.

[0287] After the terminals of the positive electrode and the negative electrode were protrudingly provided, the battery element was inserted into a pouch made of a laminated film obtained by covering both sides of an aluminum sheet (having a thickness of 40 μm) with a resin layer, and the above-described electrolyte solution was injected into the pouch, and vacuum packaging was performed to prepare a sheet-shaped lithium ion secondary battery.

[0288] (Production Example 2)

[0289] A lithium ion secondary battery was prepared in the same manner as in Production Example 1, except that the positive electrode mixture prepared in Experimental Example 11 was used.

[0290] (Production Example 3)

[0291] A lithium ion secondary battery was prepared in the same manner as in Production Example 1, except that the positive electrode mixture prepared in Comparative Example 5 was used.

[0292] (Production Example 4)

[0293] A lithium ion secondary battery was prepared in the same manner as in Production Example 1, except that the positive electrode mixture prepared in Comparative Example 6 was used.

[0294] The positive electrode mixtures obtained in Experimental Examples 1 to 10 and Comparative Examples 1 to 4 were subjected to measurement of the rate of change in viscosity, the peeling strength between the positive electrode mixture layer and the positive electrode current collector of the positive electrode, and the flexibility of the positive electrode. Further, the load characteristics of the lithium ion secondary batteries obtained in Production Examples 1 to 4 were measured.

[0295] The measurement method was as follows.

[0296] (Polymer composition)

[0297] The contents of TFE units, HFP units, and CTFE units in the fluorine-containing copolymer and PVdF were determined by1H-NMR analysis using an NMR analyzer (manufactured by Agilent Technologies, Inc., VNS 400 MHz). 19 The contents were determined by1H-NMR analysis.

[0298] (4-pentenoic acid content)

[0299] The content of 4-pentenoic acid units in the fluorine-containing copolymer was determined as follows: after conversion to ester groups by esterification of the carboxyl groups of the 4-pentenoic acid units, the content of 4-pentenoic acid units was determined using 1 H-NMR was performed on the esterified fluorine-containing copolymer, whereby the determination was performed. Specifically, 400 mg of the fluorine-containing copolymer, 10 mg of trimethylsilyldiazomethane, and 3 mg of methanol were allowed to react at 25°C for 12 hours, the resulting polymer was washed with methanol, and after vacuum drying at 70°C for 24 hours, H-NMR was performed using 1 H-NMR was performed on the dried polymer, and the content of 4-pentenoic acid units was determined from the spectrum at 3.7 ppm of H-NMR. 1 The content of 4-pentenoic acid units was determined from the spectrum at 3.7 ppm of H-NMR.

[0300] (Acrylic acid content)

[0301] The content of acrylic acid units in PVdF was determined by acid-base titration of the carboxyl groups. Specifically, about 0.5 g of PVdF was dissolved in acetone at a temperature of 70°C to 80°C. While stirring vigorously, 5 ml of water was added dropwise to avoid coagulation of the PVdF. In a neutral shift of about -270 mV, titration was performed using an aqueous NaOH solution having a concentration of 0.1 N until the acidity was completely neutralized. From the determination results, the mass of the acrylic acid units contained in 1 g of PVdF was determined, and the content of the acrylic acid units was calculated.

[0302] (Solution viscosity)

[0303] An NMP solution (5 mass%) of the fluorine-containing copolymer or PVdF was prepared. Using a B-type viscometer (manufactured by Toyo Seiki Co., Ltd., TV-10M), the viscosity of the NMP solution after 10 minutes from the start of the determination was determined at 25°C, rotor No. M4, and a rotation speed of 6 rpm.

[0304] (Weight average molecular weight)

[0305] The determination was performed by gel permeation chromatography (GPC). Using AS-8010, CO-8020, and a column (3 GMHHR-H connected in series) manufactured by Tosoh Corporation and RID-10A manufactured by Shimadzu Corporation, dimethylformamide (DMF) was flowed at a flow rate of 1.0 ml / minute as a solvent, and the weight average molecular weight was calculated from the determined data (reference: polystyrene).

[0306] (Viscosity change rate of positive electrode mixture)

[0307] The viscosity of the positive electrode mixture was measured 10 minutes after the start of measurement at 25°C, using a B-type viscometer (manufactured by Tokimec, Inc., TV-10M), with rotor No. M4 and a rotation speed of 6 rpm. The viscosity change rate (Xn) was calculated from the viscosity of the positive electrode mixture immediately after measurement (η0) and the viscosity after 5 days from the preparation of the mixture (ηn) using the following equation.

[0308] Xn = ηn / η0 x 100 [%]

[0309] (Density of the positive electrode mixture layer)

[0310] The area, film thickness, and weight of the positive electrode mixture layer were measured, and the density of the positive electrode mixture layer was calculated from these values.

[0311] (Adhesion strength between the positive electrode mixture layer and the positive electrode current collector of the positive electrode)

[0312] A test piece of 1.2 cm x 7.0 cm was prepared by cutting the positive electrode. The positive electrode mixture layer side of the test piece was fixed to a movable jig with double-sided tape, and the tape was attached to the surface of the positive electrode current collector. The stress (N / cm) at the time when the tape was stretched to 90 degrees at a speed of 100 mm / min was measured with a universal testing machine. The load cell of the universal testing machine was 50 N.

[0313] (Softness of the positive electrode)

[0314] The positive electrode was cut from the positive electrode obtained by pressing with a roll press, and a test piece of 2 cm x 10 cm was prepared. The test piece was wound around a round bar of each size having a diameter of 3.5 mm, 3 mm, and 2.5 mm, and the positive electrode mixture layer was visually confirmed, and evaluated according to the following criteria.

[0315] O: No cracks were observed.

[0316] Δ: Cracks were observed, but no breakage of the positive electrode mixture layer and the positive electrode current collector was observed.

[0317] X: The positive electrode mixture layer and the positive electrode current collector were broken.

[0318] ※Based on JIS-K5600-5-1 Flexibility (cylindrical mandrel method)

[0319] (2C / 0.2C load characteristics)

[0320] In a state where the above-mentioned fabricated lithium ion secondary battery was held with a board and was subjected to pressurization, constant current-constant voltage charging (hereinafter referred to as CC / CV charging) was performed at a current equivalent to 1C (0.1C cut-off) to 4.2V, and then constant current discharging was performed at a current equivalent to 0.2C to 3V, which was taken as the 0.2C discharging capacity. Here, 1C indicates a current value at which the reference capacity of the battery is discharged in 1 hour, and 0.2C indicates a current value which is 1 / 5 of the current value, for example. After CC / CV charging was performed again under the same conditions as above, constant current discharging was performed at a current equivalent to 2C to 3V, which was taken as the 2C discharging capacity. The proportion of the 2C discharging capacity to the 0.2C discharging capacity was calculated, which was taken as the 2C / 0.2C load characteristic (%).

[0321] (2C discharging capacity) ÷ (0C discharging capacity) x 100 = 2C / 0C load characteristic (%)

[0322] The evaluation results are shown in Tables 1 and 2.

[0323] [Table 1]

[0324]

[0325] [Table 2]

[0326] Table 2

[0327]

Claims

1. An electrode mixture comprising an electrode active substance, an organic solvent, a binder, and additives. The adhesive comprises a fluorinated copolymer containing vinylidene fluoride units and fluorinated monomer units, and polyvinylidene fluoride, wherein, The fluorinated monomer unit does not include the vinylidene fluoride unit. The content of the vinylidene fluoride unit in the fluorinated copolymer is 50.0 mol% to 99.0 mol% relative to all monomer units. The polyvinylidene fluoride (PVDF) contains more than 99.0 mol% PVDF units relative to all monomer units. The mass ratio of the fluorinated copolymer to the additive is 60 / 40 to 99 / 1. The additive is a polymer material having the following repeating units, -[CH2-CHR]- In the repeating unit, R represents a chain or cyclic amide group, a nitrile group, or a substituent that is an alkyl group having 1 to 4 carbon atoms, wherein at least one hydrogen atom of the alkyl group is replaced by a chain or cyclic amide group or a nitrile group. The content of the binder is 0.1 to 1.6 parts by weight relative to 100 parts by weight 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.

2. The electrode mixture as described in claim 1, wherein, The fluorinated monomer unit is selected from at least one of the group consisting of tetrafluoroethylene unit, trifluorochloroethylene unit, fluoroalkyl vinyl ether unit and hexafluoropropylene unit.

3. The electrode mixture as described in claim 1 or 2, wherein, The additive is selected from at least one of the groups consisting of polyvinylpyrrolidone and polyacrylonitrile.

4. The electrode mixture as described in claim 1 or 2, wherein, The additive is polyvinylpyrrolidone.

5. The electrode mixture as described in claim 1 or 2, wherein, The electrode active material is selected from at least one of the groups consisting of lithium-containing transition metal complex oxides and lithium-containing transition metal phosphate compounds.

6. An electrode comprising a current collector and an electrode mixture layer disposed on one or both sides of the current collector, and formed of the electrode mixture according to any one of claims 1 to 5.

7. A secondary battery comprising the electrode as described in claim 6.

8. A composition comprising: A fluorinated copolymer containing vinylidene fluoride units and tetrafluoroethylene units; Polyvinylidene fluoride; and The polymer material used as an additive has the following repeating units. -[CH2-CHR]- In the repeating unit, R represents a chain or cyclic amide group, a nitrile group, or a substituent that is an alkyl group having 1 to 4 carbon atoms, wherein at least one hydrogen atom of the alkyl group is replaced by a chain or cyclic amide group or a nitrile group. The content of the vinylidene fluoride unit in the fluorinated copolymer is 50.0 mol% to 99.0 mol% relative to all monomer units. The polyvinylidene fluoride (PVDF) contains more than 99.0 mol% PVDF units relative to all monomer units. The mass ratio of the fluorinated copolymer to the additive is 60 / 40 to 99 / 1.

9. The composition of claim 8, further comprising an organic solvent.

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