Carbon nanotube dispersion composition and use thereof

Abstract

To provide: a carbon nanotube dispersion composition having high conductivity and good fluidity and storage stability; electrode mixture slurry based on the carbon nanotube dispersion composition; an electrode film; and a nonaqueous electrolyte secondary battery employing them which has excellent rate characteristics and cycle characteristics.SOLUTION: The present invention provides a carbon nanotube dispersion composition containing carbon nanotubes having an average outer diameter of 3 nm or less, a polymer component, and a solvent. The polymer component contains as a main component a polyvinylidene fluoride resin optionally having substituents. In the carbon nanotube dispersion composition, the particle size D90 at the volume accumulation of 90% in the particle size distribution measured by the laser diffraction method is greater than or equal to 2.0 μm and less than 20.0 μm, and the pH is 7.5 or higher.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a carbon nanotube dispersion composition. More specifically, the present invention relates to a carbon nanotube dispersion composition, a composite slurry containing the carbon nanotube dispersion composition and an active material, an electrode film formed from the composite slurry, and a nonaqueous electrolyte secondary battery including the electrode film. [Background technology]

[0002] With the spread of electric vehicles and the miniaturization, weight reduction, and high performance of portable devices, secondary batteries with high energy density and higher capacity are required. Under such a background, non-aqueous electrolyte secondary batteries using non-aqueous electrolytes, particularly lithium ion secondary batteries, are being used in many devices because of their characteristics of high energy density and high voltage.

[0003] The capacity of a lithium-ion secondary battery depends heavily on the main materials, the positive and negative electrode active materials, and various materials for use in these electrode active materials have been actively researched. However, the charge capacity when using electrode active materials in practical use has reached a level close to the theoretical value, and the improvement of electrode active materials is close to its limit. Therefore, since the charge capacity can be simply increased by increasing the filling amount of the electrode active material in the electrode film, attempts have been made to reduce the amount of conductive material and binder resin added, which do not directly contribute to the charge capacity.

[0004] Generally, fine carbon materials are used as conductive materials, and carbon nanotubes have been used more and more in recent years. In particular, there are high expectations for single-walled carbon nanotubes, which have the smallest outer diameter, in order to reduce the amount of conductive material added to the minimum without worsening the electrode resistance. However, single-walled carbon nanotubes have very strong cohesive forces and are difficult to use, so various studies are being conducted.

[0005] For example, Patent Documents 1 to 3 propose a method of providing a nonaqueous electrolyte secondary battery with good characteristics by finely dispersing carbon nanotubes in advance using various dispersants and then producing an electrode composite slurry. Patent Document 4 describes an electrode including a carbon nanotube structure in which 2 to 5,000 single-walled carbon nanotube units are bonded to each other, and a battery including the electrode. Patent Documents 1 to 3 aim to provide a nonaqueous electrolyte secondary battery with good characteristics by defibrating carbon nanotubes to form a fine conductive network developed in the electrode, and Patent Document 4 aims to provide a nonaqueous electrolyte secondary battery with good characteristics by dispersing single-walled carbon nanotubes as bundled structures to form a thick and long conductive network. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 7107413 [Patent Document 2] Patent No. 7109632 [Patent Document 3] JP 2022-063234 A [Patent Document 4] Special table 2021-517352 publication Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Documents 1 to 3, a dispersant is used as an essential component, and a dispersion composition having good fluidity and storage stability even at a high concentration can be obtained. Since the specific surface area is larger, ideally a conductive network can be efficiently formed, and therefore a dispersion composition using carbon nanotubes with an average outer diameter of 3 nm or less has been studied. However, according to the study by the present inventor, in the case of carbon nanotubes with an average outer diameter of 3 nm or less, when defibrating them with a sufficient amount of a dispersant with high dispersing ability, the carbon nanotubes are cut as they are defibrated and become shorter than their original length, which increases the contact resistance and, as a result, may deteriorate the resistance of the electrode.

[0008] On the other hand, in Patent Document 4, single-walled carbon nanotubes are mixed with polyvinylidene fluoride resin without using a dispersant with high dispersing ability, and it is presumed that the original length of the carbon nanotubes is appropriately maintained, but there are problems with storage stability, such as a low carbon nanotube concentration, high viscosity and poor fluidity, and the carbon nanotubes aggregate and settle during storage, causing phase separation. In addition, a dispersion composition with a low carbon nanotube concentration has problems such as a low degree of design freedom when mixing materials such as active materials, and high transportation costs per non-volatile content. Furthermore, poor fluidity makes it difficult to remove from a tank during transportation or storage, and poor storage stability may shorten the expiration date or deteriorate the stability of quality.

[0009] Therefore, there is a demand for stable dispersion of carbon nanotubes with small average outer diameters at high concentrations, and in particular, there is an urgent need to disperse mainly single-walled carbon nanotubes in bundle-like structures at high concentrations to obtain a dispersion composition with excellent fluidity and storage stability.

[0010] In other words, the problem that the present invention aims to solve is to provide a carbon nanotube dispersion composition that has high conductivity and good fluidity and storage stability, and to provide a non-aqueous electrolyte secondary battery that has excellent rate characteristics and cycle characteristics by using an electrode composite slurry and an electrode film that use the carbon nanotube dispersion composition. [Means for solving the problem]

[0011] The inventors of the present invention have investigated the relationship between the dispersion state of carbon nanotubes and the rate characteristics, and have found that maintaining the state of a bundle structure of carbon nanotubes with an average outer diameter of 3 nm or less and dispersing them without shortening the fiber length leads to a reduction in contact resistance and is effective in improving the rate characteristics and cycle characteristics. 90 It has been found that by controlling the particle size to be 2.0 μm or more and less than 20.0 μm and the pH to be 7.5 or more, the storage stability and fluidity are dramatically improved and the settling of the carbon nanotubes can be suppressed.

[0012] More specifically, the carbon nanotube dispersion composition includes carbon nanotubes having an average outer diameter of 3 nm or less, a polymer component, and a solvent, the polymer component includes a polyvinylidene fluoride resin which may have a substituent as a main component, and the carbon nanotube dispersion composition has a particle diameter D at a cumulative volume of 90% of a particle size distribution measured by a laser diffraction method. 90 By ensuring that the particle size is 2.0 μm or more and less than 20.0 μm and the pH is 7.5 or more, a dispersion composition excellent in storage stability and flowability can be provided, and a good conductive network can be formed in the electrode.

[0013] That is, the present invention includes the following embodiments, but the embodiments of the present invention are not limited to the following. <1> A carbon nanotube dispersion composition comprising carbon nanotubes having an average outer diameter of 3 nm or less, a polymer component, and a solvent, the polymer component contains, as a main component, a polyvinylidene fluoride resin which may have a substituent; The carbon nanotube dispersion composition has a particle size D at 90% cumulative volume of the particle size distribution measured by a laser diffraction method. 90 is 2.0 μm or more and less than 20.0 μm, and pH is 7.5 or more; Carbon nanotube dispersion composition. <2> The content of the polyvinylidene fluoride resin which may have a substituent is 30 parts by mass or more and 270 parts by mass or less with respect to 100 parts by mass of the carbon nanotubes having an average outer diameter of 3 nm or less. <1> The carbon nanotube dispersion composition described above. <3> Further containing a basic compound, The content of the basic compound is 0.01% by mass or more and 0.2% by mass or less based on the mass of the dispersion composition. <1> or <2> The carbon nanotube dispersion composition described above. <4> The total content of the carbon nanotubes having an average outer diameter of 3 nm or less and the polymer component is 80 mass% or more based on the total mass of the non-volatile components of the dispersion composition. <1> ~ <3> The carbon nanotube dispersion composition according to any one of the above. <5> The content of the polyvinylidene fluoride resin which may have a substituent is 87 mass% or more based on the mass of the polymer component. <1> ~ <4> The carbon nanotube dispersion composition according to any one of the above. <6> <1> ~ <5> A composite slurry comprising any one of the carbon nanotube dispersion compositions and an active material. <7> <6> An electrode film formed from the composite slurry described above. <8> A non-aqueous electrolyte secondary battery including a positive electrode and a negative electrode, At least one of the positive electrode and the negative electrode is <7> A non-aqueous electrolyte secondary battery comprising the electrode film described above. Effect of the Invention

[0014] According to an embodiment of the present invention, a carbon nanotube dispersion composition having high electrical conductivity and good storage stability is provided, and a composite slurry using the carbon nanotube dispersion composition makes it possible to provide a nonaqueous electrolyte secondary battery having excellent rate characteristics and cycle characteristics. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a photograph (30,000x) of the positive electrode 10 observed by a scanning electron microscope. [Diagram 2]FIG. 2 is a photograph (30,000 times) of the comparative positive electrode 6 observed with a scanning electron microscope. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The dispersion composition, the composite slurry, and the nonaqueous electrolyte secondary battery according to the embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments, and the present invention also includes embodiments that are implemented within the scope of the present invention.

[0017] In this specification, carbon nanotubes may be referred to as "CNTs," carbon nanotube dispersion compositions may be referred to as "dispersion compositions" or "CNT dispersion compositions," and polyvinylidene fluoride resins which may have substituent groups may be referred to as "polyvinylidene fluoride resins" or "PVdF."

[0018] <Carbon nanotube dispersion composition> The carbon nanotube dispersion composition of the present embodiment contains carbon nanotubes having an average outer diameter of 3 nm or less, a polymer component, and a solvent, and has a particle size D at 90% cumulative volume of the particle size distribution measured by a laser diffraction method. 90 The particle size is 2.0 μm or more and less than 20.0 μm and the pH is 7.5 or more, and the polymer component contains, as a main component, a polyvinylidene fluoride resin which may have a substituent.

[0019] The dispersion composition of the present invention does not contain an active material. In this specification, when the dispersion composition contains an active material, it is defined as a composite slurry.

[0020] That is, the dispersion composition of the embodiment of the present invention means a state before the active material is added. In this respect, the dispersion composition is distinguished from a composite slurry containing an active material. That is, the dispersion composition does not substantially contain an active material. This is a concept excluding a state in which an active material is intentionally added to the dispersion composition, and the active material may be 1 mass % or less, 0.5 mass % or less, or 0.1 mass % or less, or may be 0 mass %, based on the total mass of the dispersion composition. The active material will be described later.

[0021] The dispersion composition can be suitably used for electrodes for non-aqueous electrolyte secondary batteries. However, it is not limited to the use of non-aqueous electrolyte secondary batteries, and can also be used for storage devices other than non-aqueous electrolyte secondary batteries, such as electrodes for electric double layer capacitors, electrodes for non-aqueous electrolyte capacitors, etc., or antistatic materials such as IC trays for plastic or rubber products and molded bodies of electronic component materials, electronic components, transparent electrodes (ITO films) substitutes, electromagnetic wave shields, etc.

[0022] <Carbon nanotubes> The carbon nanotubes of this embodiment have an average outer diameter of 3 nm or less, preferably 1 nm or more and 3 nm or less, and more preferably 1 nm or more and 2 nm or less. When the average outer diameter of the carbon nanotubes is in the above range, the specific surface area is increased, and therefore a conductive network can be efficiently formed. The average outer diameter of the carbon nanotubes can be calculated by observing the morphology of the carbon nanotubes using a transmission electron microscope (manufactured by JEOL Ltd.), measuring the lengths of the minor axes of 100 tubes, and averaging the measured values.

[0023] In addition, the carbon nanotubes of this embodiment preferably include single-walled carbon nanotubes, and may be a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes. Single-walled carbon nanotubes alone are more preferable. Single-walled carbon nanotubes are preferable because they have a small average outer diameter and a large specific surface area, allowing a conductive network to be efficiently formed. Single-walled carbon nanotubes may be produced in combination with multi-walled carbon nanotubes during synthesis. It is preferable that single-walled carbon nanotubes are the main component of carbon nanotubes. Single-walled carbon nanotubes have a structure in which one layer of graphite is wrapped around them, and multi-walled carbon nanotubes have a structure in which two or three or more layers of graphite are wrapped around them. The main component refers to the component with the highest content.

[0024] The BET specific surface area of ​​the carbon nanotube of this embodiment is 550 m 2 / g or more 1200m 2 / g or less, and 2 / g or more 1200m 2 / g or less is more preferable, and 2 / g or more 1200m 2 / g or less is more preferable, and 2 / g or more 1200m 2 When the BET specific surface area of ​​the carbon nanotubes is within the above range, the carbon nanotubes tend to be entangled evenly with the electrode active material, and therefore a conductive network can be efficiently formed.

[0025] The carbon nanotube of this embodiment has a Raman spectrum of 1560 to 1600 cm -1 The maximum peak intensity in the range of 1310 to 1350 cm is G. -1 When the maximum peak intensity within this range is D, the G / D ratio is preferably 5 to 100, more preferably 10 to 90, and even more preferably 20 to 80. When the G / D ratio of the carbon nanotubes is within the above range, the crystallinity is high and good electrical conductivity is easily obtained.

[0026] The volume resistivity of the carbon nanotube of this embodiment is 1.0×10 -3 Ω cm or more 3.0×10 -2 It is preferable that the resistance is Ω·cm or less, and 1.0×10 -3 Ω cm or more 1.0×10 -2 It is more preferable that the resistivity is Ω·cm or less. The volume resistivity of the carbon nanotubes can be measured using a powder resistivity measuring device (Mitsubishi Chemical Analytech Co., Ltd.: Loresta GP Powder Resistivity Measuring System MCP-PD-51). When the volume resistivity of the carbon nanotubes is in the above range, the electron transfer resistance between the carbon nanotubes and the active material can be reduced.

[0027] The carbon purity of the carbon nanotubes of this embodiment is represented by the content (%) of carbon atoms in the carbon nanotubes. The carbon purity is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, relative to 100% by mass of the carbon nanotubes. When the carbon purity of the carbon nanotubes is within the above range, problems such as short circuits caused by the formation of dendrites due to impurities such as metal catalysts can be prevented.

[0028] The amount of metal contained in the carbon nanotube of this embodiment is preferably less than 20% by mass, more preferably less than 10% by mass, and even more preferably less than 5% by mass, based on 100% by mass of the carbon nanotube. Examples of metals contained in the carbon nanotube include metals and metal oxides used as catalysts when synthesizing the carbon nanotube, and metal powders mixed in due to wear of the equipment. Specific examples include metals such as cobalt, nickel, aluminum, magnesium, silica, manganese, and molybdenum, alloys of these metals, metal oxides, and composite oxides of these metals.

[0029] The carbon nanotube of this embodiment may be a surface-treated carbon nanotube. The carbon nanotube may also be a carbon nanotube derivative to which a functional group such as a carboxyl group has been added. Carbon nanotubes that encapsulate substances such as organic compounds and metal atoms may also be used.

[0030] The carbon nanotubes of this embodiment may be pulverized carbon nanotubes. The pulverization is performed by using a pulverizer containing pulverization media such as beads and steel balls to pulverize the carbon nanotubes without the presence of a liquid substance, and is also called dry pulverization. The pulverization is performed by utilizing the pulverization force or destructive force caused by the collision between pulverization media. The pulverization mainly has the effect of reducing the size of the secondary particles of the carbon nanotubes, and can improve the dispersibility of the carbon nanotubes. As a dry pulverization device, a known method such as a dry attritor, ball mill, vibration mill, or bead mill can be used, and the pulverization time can be set arbitrarily depending on the device.

[0031] The carbon nanotubes of this embodiment may be produced by any method, including, but not limited to, laser ablation, arc discharge, thermal CVD, plasma CVD, and combustion.

[0032] <Polymer component> The polymer component of the present embodiment contains a polyvinylidene fluoride resin, which may have a substituent, as a main component. For the purpose of assisting dispersion, a polymer component other than the polyvinylidene fluoride resin may be contained. In this specification, the term "polymer" refers to a molecule having a weight average molecular weight of 1,000 or more, and the term "main component" refers to a component having the highest content.

[0033] The content of the polyvinylidene fluoride resin in the polymer component is preferably 87% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the total amount of the polymer component. By setting the content in the above range, the particle size D 90 Since the increase in contact resistance caused by the decrease in the capacitance can be suppressed and the resistance of the electrode can be improved, the rate characteristics can be improved.

[0034] As the polymer component other than the polyvinylidene fluoride resin, any conventionally known surfactant or polymer dispersant can be used without any particular limitation. When the dispersion composition of the present invention contains a polymer component other than polyvinylidene fluoride resin, the content of the polymer component other than polyvinylidene fluoride resin is preferably 13 mass% or less, more preferably 10 mass% or less, even more preferably 5 mass% or less, based on the total amount of the polymer components, and most preferably none.

[0035] [Polyvinylidene fluoride resin which may have a substituent] Examples of polyvinylidene fluoride resins include homopolymers of polyvinylidene fluoride, copolymers of vinylidene fluoride with hexafluoropropylene, tetrafluoroethylene, etc., and the like, with copolymers being preferred. Unlike the dispersants described in Patent Documents 1 to 3, polyvinylidene fluoride resins do not have the dispersing ability to disperse carbon nanotubes at a high concentration, for example, down to individual tubes, but by containing polyvinylidene fluoride resin and setting the pH to 7.5 or higher, the state of the bundled structure of carbon nanotubes can be maintained and the carbon nanotubes can be dispersed without shortening the fiber length.

[0036] In addition, the polyvinylidene fluoride resin preferably has a substituent. The substituent is not particularly limited, but is preferably a substituent with low elimination ability, and more preferably an acidic functional group such as a carboxyl group. When the polyvinylidene fluoride resin has an acidic functional group, it is ionized or polarized, and the effect of dispersion stabilization due to electrostatic repulsion can be obtained.

[0037] When the polyvinylidene fluoride resin is a copolymer or has a substituent, the concerted de-HF reaction caused by the basic compound is stopped due to the presence of some heterogeneous bonds, which makes it possible to suppress an increase in viscosity and gelation, which is preferable.

[0038] Examples of commercially available polyvinylidene fluoride resins having no substituents (i.e., homopolymers) include KF Polymer series (W#7300, W#7200, W#1700, W#1300, W#1100, L#7305, L#7208, L#1710, L#1320, L#1120) manufactured by Kureha Corporation, and Solef series (6008, 6010, 6012, 1015, 6020, 9007, 460, 41308) manufactured by Solvay.

[0039] Commercially available products of polyvinylidene fluoride resins, which are copolymers, include, for example, the Solef series "21216, 11010, 21510, 31508, 60512" manufactured by Solvay.

[0040] Commercially available substituted polyvinylidene fluoride resins include, for example, KF Polymer Series "W#9700, W#9300, W#9100" manufactured by Kureha Corporation, and Solef Series "5130" manufactured by Solvay.

[0041] For the purpose of binding when forming an electrode film, the polyvinylidene fluoride resin may be further added after the dispersion composition is produced or when the composite slurry is produced. The composite slurry will be described in detail later.

[0042] <Solvent> The dispersion composition of the present embodiment contains a solvent. The solvent is not particularly limited, but is preferably a solvent capable of dissolving polyvinylidene fluoride resin. In this specification, "capable of dissolving polyvinylidene fluoride resin" means that when 0.5 g of polyvinylidene fluoride resin is dissolved in 100 g of a solvent at 25°C, no insoluble matter can be visually confirmed and the solution is clear and transparent.

[0043] In one embodiment, the solvent preferably includes any one of high dielectric constant solvents or a mixed solvent of two or more of them. In addition, the high dielectric constant solvent may be used by mixing one or more other solvents. In this specification, the "high dielectric constant solvent" is preferably a solvent having a relative dielectric constant value described in the Solvent Handbook of 25 to 60 at 20°C, more preferably 25 to 50. By using a solvent having a dielectric constant in the above range, the polyvinylidene fluoride resin can be stably dissolved, and in particular, when a basic compound is contained, the storage stability and flowability of the dispersion composition can be improved by polarization of the solvent.

[0044] Examples of high dielectric constant solvents that can be used include amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclics (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxides (dimethyl sulfoxide, etc.), sulfones (hexamethylphosphorotriamide, sulfolane, etc.), lower ketones (acetone, methyl ethyl ketone, etc.), carbonates (diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate), and others, such as tetrahydrofuran and acetonitrile. The solvent preferably contains an amide-based organic solvent, and more preferably contains at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0045] In one embodiment, the solvent preferably does not substantially contain water. Polyvinylidene fluoride resins tend to have low solubility in water. In addition, when the solvent contains water, hydrogen fluoride may be eliminated to form conjugated double bonds in the main chain, causing gelation, or hydrogen fluoride may corrode other materials or devices. In addition, the adsorption of polyvinylidene fluoride resin to carbon nanotubes may decrease, making it difficult for carbon nanotubes to exist stably in the solvent. "Substantially free" means that water is not intentionally added beyond the amount contained by moisture absorption or the like. The content of water based on the total mass of the solvent is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less.

[0046] <Basic compounds> In one embodiment, the dispersion composition preferably contains a basic compound. When the dispersion composition contains a basic compound, the strong polarization of the polyvinylidene fluoride resin and the basic compound interact with each other, and the fluidity and storage stability of the dispersion composition can be further improved. The basic compound to be added can be at least one selected from the group consisting of inorganic bases, inorganic metal salts, organic bases, and organic base salts.

[0047] Examples of inorganic bases and inorganic metal salts include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, borates of alkali metals or alkaline earth metals; and ammonium hydroxide, etc. Among these, hydroxides or alkoxides of alkali metals, which are strong bases, are preferred because they easily interact with polyvinylidene fluoride resin.

[0048] Examples of the hydroxides of alkali metals include lithium hydroxide, sodium hydroxide, and hydroxide. Examples of the hydroxide of an alkaline earth metal include calcium hydroxide and magnesium hydroxide. Among these, it is more preferable to use at least one selected from the group consisting of lithium hydroxide, sodium hydroxide, and potassium hydroxide. The metal contained in the inorganic base may be a transition metal.

[0049] Examples of the alkoxide of an alkali metal include lithium methoxide, lithium ethoxide, lithium-n-butoxide, lithium-t-butoxide, potassium methoxide, potassium ethoxide, potassium-n-butoxide, potassium-t-butoxide, sodium methoxide, sodium ethoxide, sodium-n-butoxide, and sodium-t-butoxide. The number of carbon atoms of the alkoxide may be 5 or more. In particular, sodium-t-butoxide is preferable.

[0050] Examples of the alkoxide of an alkaline earth metal include magnesium methoxide, magnesium ethoxide, magnesium n-butoxide, magnesium t-butoxide, etc. The number of carbon atoms of the alkoxide may be 5 or more.

[0051] Among these, lithium hydroxide, sodium hydroxide, potassium hydroxide, lithium carbonate, sodium carbonate, lithium t-butoxide, potassium t-butoxide, and sodium t-butoxide are more preferred, sodium hydroxide and sodium t-butoxide are even more preferred, and sodium hydroxide is the most preferred. The metal contained in the inorganic base and inorganic metal salt of the present invention may be a transition metal.

[0052] Examples of the organic base include primary, secondary and tertiary amine compounds having 1 to 40 carbon atoms which may have a substituent (eg, alkylamines, amino alcohols, etc.), organic hydroxides, and organic metal salts.

[0053] When a basic compound is contained, the content of the basic compound is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, based on the mass of the dispersion composition, and is preferably 0.2% by mass or less, more preferably 0.15% by mass or less, and even more preferably 0.10% by mass or less. When the content of the basic compound is equal to or higher than the lower limit, the effect of storage stability tends to be easily obtained. When the content of the basic compound is equal to or lower than the upper limit, the gelation of the polyvinylidene fluoride resin is suppressed, and further, the corrosion of the dispersion device and / or the inside of the battery can be prevented, which is preferable.

[0054] <Method of producing dispersion composition> Hereinafter, as an example of a method for producing a dispersion composition, a method for dispersing carbon nanotubes in a solvent will be described. The dispersion composition is preferably produced, for example, by dispersing carbon nanotubes, polyvinylidene fluoride resin which may have a substituent, and a solvent, finely dispersing them using a dispersing device. The dispersion process can be a multi-stage process of two or more steps, with the timing of adding the materials being arbitrarily adjusted.

[0055] In addition, when a basic compound is contained, the timing of adding the basic compound is not particularly limited, but it is preferable to add the basic compound after dispersing the mixture of the solvent, the polyvinylidene fluoride resin, and the carbon nanotubes, which makes it easier to obtain a dispersion composition with excellent storage stability and flowability. That is, the method includes a step of producing a carbon nanotube dispersion containing carbon nanotubes, a polymer component, and a solvent, and then mixing the carbon nanotube dispersion with a basic compound, and the particle size D at 90% cumulative volume of the particle size distribution measured by a laser diffraction method is 90 Carbon nanotubes having a diameter of 2.0 μm or more and less than 20.0 μm and a pH of 7.5 or more. A method for producing a carbon nanotube dispersion composition is preferably used, in which the carbon nanotube dispersion composition is a carbon nanotube dispersion composition.

[0056] Examples of the dispersion device include a kneader, a two-roll mill, a three-roll mill, a planetary mixer, a ball mill, a horizontal sand mill, a vertical sand mill, an annular bead mill, an attritor, a high shear mixer, a high pressure homogenizer, and an ultrasonic homogenizer. Among them, in order to finely disperse the CNT in the dispersion composition and obtain suitable dispersibility, it is preferable to use a high shear mixer, a high pressure homogenizer, an ultrasonic homogenizer, or a combination of these. In particular, from the viewpoint of promoting the wetting of the CNT and dissolving coarse particles, it is preferable to use a high shear mixer in the initial dispersion step, and then to use a high pressure homogenizer from the viewpoint of dispersing the CNT while maintaining its aspect ratio. The pressure when using the high pressure homogenizer is preferably 50 to 150 MPa, more preferably 70 to 150 MPa.

[0057] Dispersion methods using a dispersing device include batch dispersion, pass dispersion, circulation dispersion, etc., and any of these methods may be used, or two or more methods may be combined. Batch dispersion is a method in which dispersion is performed using only the dispersing device body without using piping or the like. It is easy to handle, so it is preferable for small-scale production. Pass dispersion is a dispersion method in which the dispersing device body is equipped with a tank that supplies the dispersion liquid (a mixture containing dispersoid and dispersion medium, which is a precursor of the dispersion composition) through piping, and a tank that receives the dispersion liquid, and the dispersion liquid is passed through the dispersing device body. In addition, circulation dispersion is a method in which the dispersion liquid that has passed through the dispersing device body is returned to the tank that supplies the dispersion liquid, and dispersion is performed while circulating. In either case, the longer the processing time, the more the dispersion progresses, so it is sufficient to repeat the pass or circulation until the desired dispersion state is reached, and the processing amount can be increased by changing the size of the tank or the processing time. Pass dispersion is preferable in that it is easier to make the dispersion state uniform than circulation dispersion. Circulation dispersion is preferable in that the work and manufacturing equipment are simpler than pass dispersion. In the dispersion step, the disintegration of aggregated particles, the loosening, wetting, stabilization, etc. of the conductive material proceed sequentially or simultaneously, and the final dispersion state differs depending on how the steps proceed. Therefore, it is preferable to manage the dispersion state in each dispersion step by using various evaluation methods.

[0058] The pH of the dispersion composition of the present invention is 7.5 or more. The pH of the dispersion composition is more preferably 7.7 or more, and most preferably 8.0 or more. Also, it is preferably 13.0 or less, more preferably 12.0 or less, and most preferably 11.0 or less. If the pH exceeds the above-mentioned preferred upper limit, problems such as corrosion of various raw materials and exterior materials in the battery, or gelation of polyvinylidene fluoride resin will occur. Also, if the pH is below the above-mentioned lower limit, it is difficult to obtain the effect of storage stability.

[0059] The "pH" of the dispersion composition in this specification is the value of the pH of a "pH measurement sample" obtained by diluting the dispersion composition with water, measured using a general pH meter. The pH measurement sample is adjusted by adding water so that the mass of the nonvolatile content of the pH measurement sample is 40 parts by mass when the mass of the nonvolatile content of the dispersion composition is 100 parts by mass. For example, if the dispersion composition has a nonvolatile content concentration of 2% by mass, water may be added so that the nonvolatile content concentration of the dispersion composition is 0.8% by mass, and the measurement can be performed by the method described in the Examples.

[0060] The following factors are thought to be the reasons why storage stability improves when the pH is adjusted to a specified value. For example, when a basic compound is added, proton abstraction from the polyvinylidene fluoride resin and fluoride ion elimination occur in a concerted manner (de-HF reaction), resulting in the formation of polyacetylene moieties in some areas. It is believed that by including polyacetylene moieties in some of the polyvinylidene fluoride resin, the adsorptive power can be increased through π-π interactions with the π conjugation on the carbon nanotube surface. In addition, since some C-F bonds remain unreacted, the highly electronegative fluorine atoms cause electrostatic repulsion between negative charges, improving not only dispersibility. It is believed that a dispersion composition having excellent storage stability can be obtained.

[0061] The particle size D at 90% cumulative volume of the dispersion composition of this embodiment measured by a laser diffraction method 90is preferably 2.0 μm or more, more preferably 2.2 μm or more, even more preferably 2.4 μm or more, and most preferably 2.5 μm or more. Also, it is preferably 20.0 μm or less, more preferably 15.0 μm or less, and most preferably 10.0 μm or less. 90 By keeping the above range, it is possible to advantageously obtain a dispersion composition in which the conductive material is reduced in fine fractures while maintaining the number of carbon nanotubes contained in the bundles at a certain level or higher. If the above upper limit is exceeded, many carbon nanotubes are present in an aggregated state, reducing the number of bundles, while if the above lower limit is exceeded, many conductive materials are produced that are finely cut, making it difficult to form an efficient conductive network.

[0062] Particle size D 90 As a method for keeping the value within the above range, there can be mentioned a method in which a polyvinylidene fluoride resin containing no or a trace amount of a dispersant having high dispersing ability is used, and the dispersion strength and time are adjusted. In addition, particle size D 90 can be measured by using a dispersion liquid that has been subjected to ultrasonic operation as a pretreatment, and using a general laser diffraction measuring device. If pretreatment is not performed, the measured values ​​may vary, making accurate evaluation difficult. More specifically, it can be measured by the method described in the Examples. In this specification, the particle diameter D at 90% of the cumulative 90 "D 90 " may be written as ".

[0063] The viscosity of the dispersion composition of this embodiment, measured at 25° C. and 12 rpm with a Brookfield viscometer, is preferably 8,000 mPa·s or more and less than 11,000 mPa·s, more preferably 6,000 mPa·s or more and less than 8,000 mPa·s, and even more preferably less than 6,000 mPa·s. When the viscosity of the dispersion composition is within the above range, it can be easily handled.

[0064] In the dispersion composition of the present embodiment, the content of carbon nanotubes having an average outer diameter of 3 nm or less is preferably 0.4 mass% or more, more preferably 0.5 mass% or more, even more preferably 0.8 mass% or more, and most preferably 1.1 mass% or more, based on 100 mass% of the dispersion composition. Also, it is preferably 3.0 mass% or less, preferably 2.0 mass% or less, more preferably 1.6 mass% or less, and even more preferably 1.3 mass% or less.

[0065] In the dispersion composition of this embodiment, the content of polyvinylidene fluoride resin is preferably 30 parts by mass or more, more preferably 70 parts by mass or more, per 100 parts by mass of carbon nanotubes having an average outer diameter of 3 nm or less. Also, it is preferably 270 parts by mass or less, more preferably 200 parts by mass or less, and even more preferably 150 parts by mass or less. If it exceeds the upper limit, the viscosity of the dispersion composition increases with an increase in polyvinylidene fluoride resin not adsorbed to the carbon nanotubes, and handling properties may be impaired. Also, if it is below the lower limit, a suitable dispersion state of the carbon nanotubes cannot be obtained, the fluidity of the dispersion composition may decrease, and storage stability may be reduced. Furthermore, by having an appropriate amount of polymer component, the particle size D90 of the carbon nanotubes is prevented from becoming smaller due to cutting, which would otherwise cause an increase in contact resistance. This improves the resistance of the electrodes, resulting in more excellent rate characteristics.

[0066] In the dispersion composition of the present embodiment, the total mass of the carbon nanotubes having an average outer diameter of 3 nm or less and the polyvinylidene fluoride resin which may have a substituent is the non-volatile matter in the dispersion composition. The total mass of the emitting components may be 100% by mass or less, preferably 80% by mass or more, more preferably 82.5% by mass or more, and even more preferably 85% by mass or more. By setting the content within the above range, the carbon nanotubes having an average outer diameter of 3 nm or less, the polyvinylidene fluoride resin which may have a substituent, and the basic compound can interact uniformly, so that a dispersion composition which is more well dispersed can be obtained.

[0067] <Composition slurry> The composite slurry of the present embodiment can be obtained by adding an active material to the dispersion composition, and can be used for electrodes of non-aqueous electrolyte secondary batteries. The composite slurry may further include a polyvinylidene fluoride resin or / and other polymer components that may have a substituent added to the dispersion composition for the purpose of better binding the active material, etc. In this specification, the polyvinylidene fluoride resin or / and other polymer components that may have a substituent added to the dispersion composition for the purpose of better binding the active material, etc. may be referred to as a "binder resin". In addition, if necessary, other optional components may be appropriately included for the purpose of wetting, surface activity, pH adjustment, wetting promotion, leveling, conductivity assistance, etc., within a range that does not impede the purpose of the present invention. The optional components can be added at any timing, such as before preparing the composite slurry, during mixing, after mixing, or a combination thereof. The active material may be a positive electrode active material or a negative electrode active material. In this specification, the positive electrode active material and the negative electrode active material may be simply referred to as "active material". An active material is a material that is the basis of a battery reaction. The active materials are divided into positive electrode active materials and negative electrode active materials based on the electromotive force. A positive electrode active material can be used to prepare a positive electrode mixture slurry, and a negative electrode active material can be used to prepare a negative electrode mixture slurry. The composite slurry is preferably in a slurry form to improve uniformity and processability.

[0068] The binder resin added for the purpose of further binding the active material and the like is not particularly limited as long as it is a polymer component that is usually used as a binder resin for batteries, and can be appropriately selected according to the purpose. The above-mentioned polyvinylidene fluoride resin that may have a substituent may be used, and other polymer components such as polymers or copolymers having ethylene, propylene, vinyl chloride, vinyl acetate, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, styrene, etc. as constituent components; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins; elastomers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene, etc. may also be used. In addition, modified bodies, mixtures, and copolymers of these resins may be used, and one type may be used alone, or two or more types may be used in combination.

[0069] The content of CNT in the composite slurry is preferably 0.01 parts by mass or more, more preferably 0.03 parts by mass or more, and even more preferably 0.05 parts by mass or more, relative to 100 parts by mass of the active material. Also, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. If it exceeds the upper limit, the amount of the active material filled in the electrode may decrease, resulting in a decrease in the capacity of the battery. Also, if it falls below the lower limit, the conductivity of the electrode and the battery may be insufficient.

[0070] The content of the polymer component in the composite slurry is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, relative to 100 parts by mass of the active material. By setting it within the above range, the adhesion of the conductive film can be further improved. Also, it is preferably 20 parts by mass or less, more preferably 10 parts by mass or less. By setting it within the above range, the active material concentration of the conductive film can be increased, and a higher capacity can be achieved.

[0071] <Cathode active material> The positive electrode active material is not particularly limited. For example, for non-aqueous electrolyte secondary battery applications, metal compounds such as metal oxides and metal sulfides that can reversibly dope or intercalate lithium ions can be used. For example, lithium manganese composite oxides (such as Li x Mn2O4 or Li x MnO2), lithium nickel composite oxides (such as Li x NiO2), lithium cobalt composite oxides (Li x CoO2), lithium nickel cobalt composite oxides (such as Li x Ni 1-y Co y O2), lithium manganese cobalt composite oxides (such as Li x Mn y Co 1-y O2), lithium nickel manganese cobalt composite oxides (such as Li x Ni y Co z Mn 1-y-z O2), spinel-type lithium manganese nickel composite oxides (such as Li x Mn 2-y Ni y O4), etc., composite oxide powders of lithium and transition metals, lithium phosphate oxide powders having an olivine structure (such as Li x FePO4, Li x Fe 1-y Mn y PO4, Li x CoPO4, etc.), transition metal oxide powders such as manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxides (such as V2O5, V6O 13 ), titanium oxide, etc., transition metal sulfide powders such as iron sulfate (Fe2(SO4)3), TiS2, and FeS, etc. However, x, y, and z are numbers, where 0 < x < 1, 0 < y < 1, 0 < z < 1, and 0 < y + z < 1. These positive electrode active materials can also be used alone or in combination of two or more.

[0072] <Negative electrode active material> The negative electrode active material is not particularly limited. For example, it can be metallic Li capable of reversibly doping or intercalating lithium ions, or its alloy, tin alloy, silicon alloy negative electrode, Li x TiO2, Li x Fe2O3, Li x Fe3O4, Li x Metal oxide systems such as WO2, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials can be used. However, x is a number and 0 < x < 1. These negative electrode active materials can be used alone or in combination of two or more. In particular, when using a silicon alloy negative electrode, although the theoretical capacity is large, the volume expansion is extremely large. Therefore, it is preferably used in combination with artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials, etc.

[0073] <Method for manufacturing composite material slurry> In the method for preparing the composite material slurry, when adding a binder resin to the dispersion composition, the order of adding the binder resin and the active material is not particularly limited. For example, a method of adding a binder resin to the dispersion composition and then adding the active material; a method of adding the active material to the dispersion composition and then adding the binder resin; a method of adding the binder resin and the active material to the dispersion composition all at once, etc. can be mentioned. Also, the binder resin may be dissolved in advance before adding. As a method for preparing the composite material slurry, a method of adding a binder resin to the dispersion composition and then further adding the active material and performing a stirring treatment is preferable. The stirring device used for stirring is not particularly limited. For the stirring device, a disperser, a homogenizer, etc. can be used.

[0074] The non-volatile content in the composite material slurry is preferably 30% by mass or more, more preferably 40% by mass or more, based on the mass of the composite material slurry (assuming the mass of the composite material slurry is 100% by mass). Also, it is preferably 90% by mass or less, more preferably 85% by mass or less.

[0075] ≪Nonaqueous electrolyte secondary battery≫ A non-aqueous electrolyte secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode, and an electrolyte, and at least one selected from the group consisting of the positive electrode and the negative electrode has an electrode film formed from the composite slurry according to this embodiment. The positive electrode and the negative electrode may further include a current collector. When one of the electrode films of the positive electrode or the negative electrode is an electrode film using the dispersion composition according to this embodiment, the electrode film of the other electrode is not particularly limited, and may be any of the conventionally known It may be an electrode film.

[0076] The structure of the nonaqueous electrolyte secondary battery of one embodiment is not particularly limited, but typically includes a positive electrode, a negative electrode, an electrolyte, and a separator that is provided as needed, and may have various shapes depending on the purpose of use, such as a paper type, a cylindrical type, a button type, or a laminated type.

[0077] <Positive or negative electrode> The positive electrode or negative electrode has an electrode film formed from a composite slurry using the dispersion composition of this embodiment, and a current collector. The electrode film can be formed, for example, by applying the dispersion composition onto a current collector and drying it. The electrode film formed using the positive electrode composite slurry can be used as a positive electrode. The electrode film formed using the negative electrode composite slurry can be used as a negative electrode. In this specification, the film formed using the dispersion composition containing an active material may be referred to as an "electrode composite layer".

[0078] The material and shape of the current collector used to form the electrode film are not particularly limited, and can be appropriately selected from those suitable for various nonaqueous electrolyte secondary batteries. Examples of the material of the current collector include conductive metals or alloys such as aluminum, copper, nickel, titanium, and stainless steel. In addition, as for the shape, a flat foil is generally used, but a current collector with a roughened surface, a perforated foil current collector, and a mesh current collector can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0079] The method of applying the dispersion composition onto the current collector is not particularly limited, and any known method can be used.Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic painting.The drying method includes, but is not limited to, drying by leaving it to dry, or drying using a blower dryer, a hot air dryer, an infrared heater, or a far infrared heater.

[0080] After coating, rolling treatment may be performed using a lithographic press, a calendar roll, etc. The thickness of the formed film is, for example, from 1 μm to 500 μm, and preferably from 10 μm to 300 μm.

[0081] A film formed using the dispersion composition can also be used as an underlayer for the electrode mixture layer in order to improve the adhesion between the electrode mixture layer and the current collector or to improve the conductivity of the electrode film.

[0082] <Electrolytes> As the electrolyte, various conventionally known electrolytes capable of moving ions can be used. For example, those containing lithium salts such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (wherein Ph is a phenyl group) can be used, but are not limited thereto. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0083] The non-aqueous solvent is not particularly limited, and examples thereof include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; Examples of the solvent include glymes such as sietan, esters such as methyl formate, methyl acetate, and methyl propionate, sulfoxides such as dimethyl sulfoxide and sulfolane, and nitriles such as acetonitrile. These solvents may be used alone or in combination of two or more.

[0084] The non-aqueous electrolyte secondary battery preferably has a separator. Examples of the separator include, but are not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics obtained by subjecting these to hydrophilic treatment. EXAMPLES

[0085] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not deviate from the gist of the invention. In addition, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass". The evaluation results of the examples and comparative examples were evaluated as follows: C for feasible range, B for better range, A for particularly excellent range, and D for the rest.

[0086] In the examples and comparative examples, polyvinylidene fluoride resins which may have the following substituents were used. W#7300: KF Polymer W#7300 (Kureha, polyvinylidene fluoride resin, homopolymer) W#7200: KF Polymer W#7200 (Kureha, polyvinylidene fluoride resin, homopolymer) W#1300: KF Polymer W#1300 (Kureha, polyvinylidene fluoride resin, homopolymer) W#1100: KF Polymer W#1100 (Kureha, polyvinylidene fluoride resin, homopolymer) · W#9300: KF Polymer W#9300 (Kureha, polyvinylidene fluoride resin, copolymer) W#9700: KF Polymer W#9700 (Kureha, polyvinylidene fluoride resin with substituents) W#9100: KF Polymer W#9100 (Kureha, polyvinylidene fluoride resin with substituents) S-6010: Solef6010 (Solvay, polyvinylidene fluoride resin, homopolymer) S-6020: Solef6020 (Solvay, polyvinylidene fluoride resin, homopolymer) S-5130: Solef5130 (Solvay, polyvinylidene fluoride resin with substituents)

[0087] In the examples and comparative examples, the following carbon nanotubes were used. TNSR: Single-wall carbon nanotube (Timesnano, average outer diameter 1.5 nm, carbon purity 95%, specific surface area 610 m 2 / g) TNSAR: Single-wall carbon nanotube (Timesnano, average outer diameter 1.5 nm, carbon purity 95%, specific surface area 950 m 2 / g) TUBALL: Single-wall carbon nanotube (OCSiAl, average outer diameter 1.6 nm, carbon purity 99%, specific surface area 980 m 2 / g) TUBALL: Single-wall carbon nanotube (OCSiAl, average outer diameter 1.8 nm, carbon purity 80%, specific surface area 520 m 2 / g)

[0088] <Preparation of Dispersion Composition> (Example 1-1) According to the materials and compositions shown in Table 1, a dispersion composition was prepared as follows. First, NMP was taken in a stainless steel container. Next, a standard round hole type head was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), and polyvinylidene fluoride resin was added while stirring at a speed of 3,000 rpm, and then stirred for 1 hour to dissolve the polyvinylidene fluoride resin. Next, CNT was added while stirring with a high shear mixer, and batch dispersion was performed at a speed of 6,000 rpm for 1 hour. Next, the liquid to be dispersed was supplied from the stainless steel container through a pipe to a high pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine), and a circulation type dispersion treatment was performed according to the number of passes shown in Table 1. The dispersion treatment was performed using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Next, the liquid to be dispersed was supplied from the high pressure homogenizer through a pipe to a stainless steel container, and a basic compound was added while stirring at a speed of 3,500 rpm with a high shear mixer. Stirring was performed for 30 minutes to obtain a dispersion composition 1. At this time, the carbon nanotube content based on Dispersion Composition 1 was 1.0 mass%, the polymer component was 1.0 mass% (the polyvinylidene fluoride resin content based on the polymer component was 100 mass%), the basic compound content was 0.04 mass%, and the solvent was 97.96 mass%. The total content of the carbon nanotubes and the polymer component was 98 mass% based on the total mass of the non-volatile components of Dispersion Composition 1.

[0089] (Examples 1-2 to 1-30) Except for changing the materials, composition, and number of passes as shown in Table 1, the same procedures as in Example 1-1 were carried out to obtain each of Dispersion Compositions 2 to 30.

[0090] (Examples 1-31 to 1-37) According to the materials and compositions shown in Table 1, the dispersion compositions were prepared as follows. First, NMP was placed in a stainless steel container. Next, a high shear mixer (L5M-A, manufactured by SILVERSON) was fitted with a standard round hole head, and polyvinylidene fluoride resin and other polymeric components were added while stirring at a speed of 3,000 rpm, and then the mixture was stirred for 1 hour to dissolve the polyvinylidene fluoride resin and other polymeric components. Then, in the same manner as in the working process of the dispersion composition of Example 1-1, a circulation type dispersion treatment was performed with a high pressure homogenizer to obtain each of the dispersion compositions 31 to 37.

[0091] (Comparative Examples 1-1 to 1-3) Comparative dispersion compositions 1 to 3 were obtained in the same manner as in Example 1-1, except that the materials, compositions, and number of passes were changed according to those shown in Table 1.

[0092] (Comparative Examples 1-4) Comparative dispersion composition 4 was obtained in the same manner as in Example 1-31, except that the materials and compositions were changed according to those shown in Table 1.

[0093] (Comparative Examples 1-5) According to the materials and compositions shown in Table 1, a dispersion composition was prepared as follows. First, NMP was placed in a stainless steel container. Next, a standard round hole head was attached to a high shear mixer (L5M-A, manufactured by Silverson), and the polymer component and basic compound were added while stirring at a speed of 3,000 rpm, and then the mixture was stirred for 1 hour to dissolve the polymer component and basic compound. Next, CNT was added while stirring with the high shear mixer, and batch dispersion was performed at a speed of 6,000 rpm for 1 hour. Next, the liquid to be dispersed was supplied from the stainless steel container through a pipe to a high pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine), and a circulation dispersion process was performed according to the number of passes shown in Table 1. The dispersion process was performed using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Next, the liquid to be dispersed was supplied from the high pressure homogenizer through a pipe to a stainless steel container, and the mixture was dispersed while stirring with a disperser. The entire amount of polyvinylidene fluoride resin was dissolved to obtain a comparative dispersion composition 5.

[0094] The basic compounds listed in Table 1 are as follows: NaOH: Sodium hydroxide (Tokyo Chemical Industry Co., Ltd., purity >98.0%, granular) LiOH: Lithium hydroxide (Tokyo Chemical Industry Co., Ltd., purity >98.0%) KOH: Potassium hydroxide (Tokyo Chemical Industry Co., Ltd., purity >86.0%) ·Na2CO3: Sodium carbonate (Tokyo Chemical Industry Co., Ltd., purity >99.0%) C2H5NH2: 2-aminoethanol (Tokyo Chemical Industry Co., Ltd., purity >99.0%)

[0095] The other polymer components (dispersants) listed in Table 1 are as follows: H-NBR1: Therban(R)3406 (ARLANXEO, hydrogenated acrylonitrile-butadiene rubber) H-NBR2: Therban(R)AT 3404 (made by ARLANXEO, hydrogenated a Crylonitrile-butadiene rubber) ·H-NBR3: Zetpole 2000L (manufactured by Zeon Corporation, hydrogenated acrylonitrile-butadiene rubber) PVP: Polyvinylpyrrolidone K-15 (ISP) PVA: Kuraray Poval 3-86SD (Kuraray, modified polyvinyl alcohol)

[0096] [Table 1]

[0097] <Measurement and evaluation of physical properties of dispersion composition> (D of the dispersion composition 90 (Method of measuring particle size) D 90was measured using a particle size distribution analyzer (Partical LA-960V2, manufactured by HORIBA). The operating conditions for circulation / ultrasonics were: circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 1, stirring mode: continuous. During air removal, ultrasonic operation was performed with ultrasonic intensity 7 and ultrasonic time 5 seconds. The refractive index of water was 1.333, and that of the carbon material was 1.92. The measurement sample was diluted so that the transmittance of the red laser diode was 70-90%, and ultrasonic operation was performed under the conditions of ultrasonic intensity: 7 and ultrasonic time: 1 minute, and the particle size standard was volume. The values ​​in Table 1 are particle size D 90 is within the following range. 1: Less than 2.0μm 2: 2.0μm or more and less than 2.3μm 3: 2.3μm or more and less than 2.5μm 4: 2.5μm or more and less than 10.0μm 5: 10.0μm or more and less than 15.0μm 6: 15.0μm or more and less than 20.0μm 7:20.0μm or more

[0098] (Method for measuring pH of dispersion composition) The pH measurement sample was adjusted by adding water dropwise while stirring the dispersion composition with a disperser so that the non-volatile content of the pH measurement sample was 40 parts when the mass of the non-volatile content of the dispersion composition was 100 parts. Measurements were performed at 25°C using a benchtop pH meter (Seven Compact S200 Expert Pro, manufactured by Mettler Toledo). The values ​​in Table 1 indicate the pH ranges listed below. Less than 1:7.5 2:7.5 or more and less than 7.7 3:7.7 or more and less than 8.0 4:8.0 or more and less than 11.0 5: 11.0 or more and less than 12.0 6: 12.0 to 13.0 7:13.0 or better

[0099] (Method of measuring viscosity of dispersion composition) The viscosity of the dispersion composition was measured using a Brookfield viscometer ("BL" manufactured by Toki Sangyo Co., Ltd.) at a temperature of 25°C, immediately after thorough stirring with a spatula, at a rotor speed of 12 rpm. The viscosity measured at 12 rpm was taken as the initial viscosity. From the viewpoint of fluidity, the lower the initial viscosity, the better, and evaluation criteria A to C indicate good handling. Initial Viscosity Evaluation Criteria A: Less than 6,000 mPa·s B: 6,000 mPa s or more and less than 8,000 mPa s C: 8,000 mPa s or more and less than 11,000 mPa s D: 11,000mPa·s or more

[0100] (Method for Evaluating Storage Stability of Dispersion Composition) The storage stability was evaluated by determining whether or not phase separation occurred after the dispersion composition was left to stand and stored at 40°C. The determination method is as follows. 1.5g to 2.0g of the supernatant of the dispersion composition was placed in an aluminum dish with a diameter of 7.5 cm and a height of 1 cm, and dried in an electric oven at 120°C ± 5°C for 1 hour. Thereafter, the weight of the solid content was measured, and if it was reduced by 0.10% or more from the theoretical solid content, it was determined that phase separation had occurred. Storage stability evaluation criteria A: No phase separation occurred even after one month. B: Phase separation occurred after 1 week. C: Phase separation occurred after 3 days. D: Phase separation occurred after 1 day.

[0101] [Table 2]

[0102] <Preparation of positive electrode mixture slurry and positive electrode> According to the combination and composition ratio shown in Table 3, a positive electrode mixture slurry and a positive electrode were prepared as follows. Capacity: 150 cm 3The dispersion composition, the positive electrode active material, and NMP were added to the plastic container, and the mixture was stirred at 2,000 rpm for 150 seconds using a centrifugal mixer (Thinky's Awatori Rentaro, ARE-310) to obtain a positive electrode mixture slurry. The non-volatile content of the positive electrode mixture slurry was 78 mass%.

[0103] The positive electrode mixture slurry was applied onto an aluminum foil having a thickness of 20 μm using an applicator, and then dried in an electric oven at 120°C ± 5°C for 25 minutes to prepare an electrode film. The electrode film was rolled using a roll press (3 ton hydraulic roll press manufactured by Sun Metals) to obtain positive electrodes (positive electrodes 1 to 32, comparative positive electrodes 1 to 3). The weight per unit area of ​​the electrode mixture layer was 20 mg / cm. 2 The density of the electrode mixture layer after rolling was 3.2 g / cc.

[0104] In the examples and comparative examples, the following positive electrode active materials were used. NMC1: S800 (LiNi 0.8 Mn 0.1 Co 0.1 O2, made by Kinwa)

[0105] <Evaluation of the positive electrode> Scanning electron microscope photographs (30,000x magnification) of the obtained positive electrode are shown in Figures 1 and 2. Figure 1 is a photograph of Example 2-10 (positive electrode 10), and Figure 2 is a photograph (30,000x magnification) of Comparative Example 2-6 (comparative positive electrode 6). As a result, in Figure 2, the carbon nanotubes are defibrated one by one and placed on the positive electrode active material. However, it can be seen in Figure 1 that the bundle structure is maintained. It is believed that the fiber length of the bundle structure is longer than that of a single carbon nanotube, which reduces the contact resistance between the carbon nanotubes.

[0106] (Method for evaluating the conductivity of the positive electrode) This was carried out in the same manner as in paragraph 0172 of Patent No. 7107413. Conductivity Evaluation Criteria A: Less than 5Ω cm B: 5 Ω·cm or more and less than 10 Ω·cm C: 10 Ω·cm or more and less than 20 Ω·cm D: 20Ω cm or more

[0107] (Method for evaluating adhesion of positive electrode) This was carried out in the same manner as in paragraph 0173 of Patent No. 7107413. Adhesion Evaluation Criteria A:1.0N / cm or more B: 0.8N / cm or more and less than 1.0N / cm C: 0.5N / cm or more and less than 0.8N / cm D: Less than 0.5N / cm

[0108] [Table 3]

[0109] <Preparation and evaluation of non-aqueous electrolyte secondary batteries> (Preparation of standard negative electrode) 0.5% by mass of acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka), 1% by mass of MAC500LC (carboxymethylcellulose sodium salt, Sunrose special type MAC500L, manufactured by Nippon Paper Industries Co., Ltd., non-volatile content 100%), and 98.4% by mass of water were added to a 150-mL plastic container, and the mixture was mixed in a centrifugal mixer (Thinky The mixture was stirred at 2,000 rpm for 30 seconds using a rotating / revolving mixer (Thinky's Awatori Rentaro, ARE-310). Furthermore, 97% by mass of artificial graphite (CGB-20, Nippon Graphite Industries) was added as an active material, and the mixture was stirred at 2,000 rpm for 150 seconds using a rotating / revolving mixer (Thinky's Awatori Rentaro, ARE-310). Next, 3.1% by mass of SBR (styrene butadiene rubber, TRD2001, non-volatile content 48%, JSR) was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a rotating / revolving mixer (Thinky's Awatori Rentaro, ARE-310) to obtain a standard negative electrode composite slurry. The non-volatile content of the standard negative electrode composite slurry was 50% by mass.

[0110] The above-mentioned standard negative electrode composite slurry was applied to a 20 μm-thick copper foil current collector using an applicator, and then dried in an electric oven at 80°C ± 5°C for 25 minutes to obtain an electrode with a coating weight per unit area of ​​10 mg / cm. 2 Further, a rolling process was performed using a roll press (Thank Metals, 3 t hydraulic roll press) to adjust the density of the electrode mixture layer to 1.6 g / cm. 3 A standard negative electrode was prepared.

[0111] (Preparation of non-aqueous electrolyte secondary battery) The positive and negative electrodes shown in Table 4 were punched out to 50 mm x 45 mm and 45 mm x 40 mm, respectively, and the punched positive and negative electrodes and the separator (porous polypropylene film) inserted between them were inserted into an aluminum laminate bag and dried in an electric oven at 70°C for 1 hour. Then, in a glove box filled with argon gas, 2 mL of electrolyte (a mixed solvent of ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1 was prepared, and vinylene carbonate was further added at 1 mass% to 100 mass% as an additive, followed by dissolving LiPF6 at a concentration of 1M) was injected, and the aluminum laminate was sealed to prepare nonaqueous electrolyte secondary batteries.

[0112] (Method for evaluating rate characteristics of non-aqueous electrolyte secondary battery) This was carried out in the same manner as in paragraph 0178 of Patent No. 7107413. Rate characteristics Evaluation criteria A: 90% or more B: 85% or more but less than 90% C: 80% or more but less than 85% D: Less than 80%

[0113] (Method for Evaluating Cycle Characteristics of Non-Aqueous Electrolyte Secondary Battery) This was carried out in the same manner as in paragraph 0179 of Patent No. 7107413. Cycle characteristics evaluation criteria A: 90% or more B: 80% or more but less than 90% C: 70% or more but less than 80% D: Less than 70%

[0114] [Table 4]

[0115] The overall evaluation shown in Table 4 is the evaluation value obtained by adding up the number of evaluations A for initial viscosity, storage stability, electrical conductivity, adhesion, rate characteristics, and cycle characteristics, and a higher value indicates a better performance.

[0116] As shown in the table, the carbon nanotube dispersion composition of the present invention has high conductivity and good fluidity and storage stability, and it has been confirmed that an electrode composite slurry and an electrode film using the carbon nanotube dispersion composition can be used to obtain a nonaqueous electrolyte secondary battery with excellent rate characteristics and cycle characteristics. In contrast, the comparative examples had poor initial viscosity, storage stability, electrical conductivity, adhesion, rate characteristics, and size. Furthermore, it has not been possible to achieve both the storage stability of the dispersion composition and the rate characteristics and cycle characteristics when used in a non-aqueous electrolyte secondary battery.

Claims

1. A carbon nanotube dispersion composition comprising carbon nanotubes having an average outer diameter of 3 nm or less, a polymer component, and a solvent, the polymer component contains, as a main component, a polyvinylidene fluoride resin which may have a substituent; the carbon nanotubes are bundle-shaped structures, The carbon nanotube dispersion composition has a pH of 7.5 or more. Carbon nanotube dispersion composition.

2. 2. The carbon nanotube dispersion composition according to claim 1, wherein the content of the polyvinylidene fluoride resin which may have a substituent is 30 parts by mass or more and 270 parts by mass or less per 100 parts by mass of the carbon nanotubes having an average outer diameter of 3 nm or less.

3. 2. The carbon nanotube dispersion composition according to claim 1, wherein the total content of the carbon nanotubes having an average outer diameter of 3 nm or less and the polymer component is 80 mass % or more based on the total mass of the non-volatile components of the dispersion composition.

4. further containing a basic compound, 2. The carbon nanotube dispersion composition according to claim 1, wherein the content of the basic compound is 0.01% by mass or more and 0.2% by mass or less, based on the mass of the dispersion composition.

5. 2. The carbon nanotube dispersion composition according to claim 1, wherein the content of the polyvinylidene fluoride resin which may have a substituent is 87 mass % or more based on the mass of the polymer component.

6. A composite slurry comprising the carbon nanotube dispersion composition according to any one of claims 1 to 5 and an active material.

7. An electrode film formed from the composite slurry according to claim 6.

8. A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode, A non-aqueous electrolyte secondary battery, wherein at least one of the positive electrode and the negative electrode has the electrode film according to claim 7.

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