JP2021095314A - Carbon nanotube, carbon nanotube dispersion and their uses - Google Patents

Abstract

To provide a carbon nanotube, a carbon nanotube dispersion, a carbon nanotube resin composition and a mixed slurry having high dispersibility in order to obtain an electrode film having high adhesion and conductivity, and more specifically to provide a non-aqueous electrolyte secondary battery having excellent rate characteristics and cycle characteristics.SOLUTION: A carbon nanotube satisfies the following (1) to (6): (1) an average outer diameter is 5-25 nm; (2) a BET specific surface area is 150-400 m2/g; (3) a fiber length is 0.5-5.0 μm; (4) in Raman spectra, a G/D ratio is 0.7 to 2.0, where G is the maximum peak intensity in the range of 1,560 to 1,600 cm-1 and D is the maximum peak intensity in the range of 1,310 to 1,350 cm-1; (5) a volume resistivity is 1.0 x 10-2 to 1.5×10-2 Ω-cm; and (6) a true density is 1.7 to 2.1 g/cc.SELECTED DRAWING: None

Description

The present invention relates to carbon nanotubes. More specifically, it is formed of a carbon nanotube, a carbon nanotube dispersion liquid, a resin composition containing a carbon nanotube dispersion liquid and a resin, a mixture slurry containing a carbon nanotube dispersion liquid, a resin and an active material, and forming a film thereof. The present invention relates to a non-aqueous electrolyte secondary battery comprising an electrode film, an electrode film and an electrolyte.

With the widespread use of electric vehicles, the reduction in size and weight of mobile devices, and the increase in performance, secondary batteries having a high energy density and the capacity of the secondary batteries are required to be increased. Against this background, non-aqueous electrolyte secondary batteries that use non-aqueous electrolytes, especially lithium-ion secondary batteries, have come to be used in many devices due to their characteristics of high energy density and high voltage.

As the negative electrode material used for these lithium ion secondary batteries, a carbon material typified by graphite having a low potential close to that of lithium (Li) and a large charge / discharge capacity per unit mass is used. However, these electrode materials are used to the point where the charge / discharge capacity per mass is close to the theoretical value, and the energy density per mass as a battery is approaching the limit. Therefore, in order to increase the utilization rate as an electrode, attempts are being made to reduce conductive auxiliaries and binders that do not contribute to the discharge capacity.

As the conductive auxiliary agent, carbon black, Ketjen black, fullerene, graphene, fine carbon material and the like are used. In particular, carbon nanotubes, which are a type of fine carbon fibers, are often used. For example, by adding carbon nanotubes to graphite or silicon negative electrodes, the electrode resistance is reduced, and the electrode strength and expansion / contraction properties are improved, thereby improving the cycle life of the lithium secondary battery. (See, for example, Patent Documents 1, 2 and 3) Further, studies have been conducted to reduce the electrode resistance by adding carbon nanotubes to the positive electrode. Among them (see, for example, Patent Documents 4 and 5), multi-walled carbon nanotubes having an outer diameter of 10 nm to several tens of nm are relatively inexpensive and are expected to be put into practical use.

When carbon nanotubes having a small average outer diameter are used, a conductive network can be efficiently formed with a small amount, and the amount of conductive auxiliary material contained in the positive electrode and the negative electrode of the lithium ion secondary battery can be reduced. Further, it is known that the same effect is obtained when carbon nanotubes having a large fiber length are used. (For example, see Patent Document 6) However, carbon nanotubes having these characteristics have strong cohesive force and are difficult to disperse.

Therefore, carbon nanotubes having excellent dispersibility have been produced by various methods. For example, Patent Document 7 proposes that carbon nanotubes having a small average outer diameter and good dispersibility can be obtained by producing multi-walled carbon nanotubes using cobalt hydroxide as a catalyst. However, since a large amount of catalyst is used to obtain carbon nanotubes having a small diameter, the produced carbon nanotubes contain a large amount of insulating material, and there is a problem that the volume resistivity of the carbon nanotubes is high. Further, in Patent Document 8, the catalyst contained in the carbon nanotubes is removed by introducing chlorine gas into the carbon nanotubes under a high temperature condition of 0.1% or less and performing a purification treatment to remove the catalyst and dispersibility. It has been proposed that carbon nanotubes having excellent conductivity can be obtained. However, there is a problem that the volume resistivity of the carbon nanotubes is increased by performing the purification treatment for a long time in order to make the high-density carbon nanotubes have a purity of 99.9% or more.

Further, in Patent Document 9, carbon nanotubes having a median diameter D50 value of 0.1 to 8 μm when dispersed by an ultrasonic homogenizer are produced and used as a dispersion liquid to obtain a carbon nanotube dispersion liquid having excellent dispersion stability. It is proposed to be. However, there is a problem that the BET specific surface area of carbon nanotubes is 100 m ² / g or less, the outer diameter of carbon nanotubes is as large as 25 to 26 nm, and the electrode resistance is high. Then, in Patent Document 10, carbon nanotubes having a bulk density of 0.01 to 0.05 g / cc, a small powder resistivity, and a large fiber length are produced and used as a dispersion liquid to obtain dispersibility and conductivity. It has been proposed that a carbon nanotube dispersion liquid having excellent properties can be obtained, but it is necessary to add a large amount of carbon nanotubes in order to obtain an electrode film having good conductivity. Therefore, it has been an important issue for expanding applications to obtain carbon nanotubes that can reduce electrode resistance with a small amount of addition and can contribute to improvement of rate characteristics and cycle characteristics of lithium ion secondary batteries.

Japanese Unexamined Patent Publication No. 4-155776 Japanese Unexamined Patent Publication No. 4-237971 Japanese Unexamined Patent Publication No. 2004-178922 Japanese Unexamined Patent Publication No. 2011-070908 Japanese Unexamined Patent Publication No. 2014-19619 Japanese Unexamined Patent Publication No. 2012-221672 Japanese Patent No. 6380588 Japanese Patent No. 6586197 International Publication No. 2016/024525 Special Table 2018-534747

The problem to be solved by the present invention is to provide a carbon nanotube, a carbon nanotube dispersion liquid, a carbon nanotube resin composition, and a mixture slurry having high dispersibility in order to obtain an electrode film having high adhesion and conductivity. is there. More specifically, it is to provide a non-aqueous electrolyte secondary battery having excellent rate characteristics and cycle characteristics.

As a result of diligent studies to solve the above problems, the present inventors have obtained an electrode film having excellent conductivity and adhesion by using carbon nanotubes satisfying predetermined physical properties, excellent rate characteristics and excellent rate characteristics. It has been found that a non-aqueous electrolyte secondary battery having cycle characteristics can be obtained. The inventors have come to the present invention based on such a discovery.

That is, the present invention relates to carbon nanotubes, which are characterized by satisfying the following (1) to (6).
(1) The average outer diameter is 5 to 25 nm (2) The BET specific surface area is 150 to 400 m ² / g (3) The fiber length is 0.5 to 5.0 μm (4) ) in the Raman spectra a maximum peak intensity in the range of 1560~1600cm ^-1 G, the G / D ratio maximum peak intensity upon the D in the range of 1310~1350cm ^-1, 0.7~2 .0 (5) Volume resistivity is 1.0 x 10 ^{-2 to} 1.5 x 10 ^-2 Ω · cm (6) True density is 1.7 to 2.1 g / cc Being

The present invention also relates to the carbon nanotubes having a half-value width of 2 to 6 °.

The present invention also relates to the carbon nanotubes, which are characterized by having a carbon purity of 95% or more.

The carbon nanotube according to the present invention is characterized in that the angle of repose is 40 to 70 °.

The present invention also relates to a carbon nanotube dispersion liquid containing the carbon nanotubes, a solvent, and a dispersant.

The present invention also relates to the carbon nanotube dispersion liquid, which comprises 20 to 100 parts by mass of a dispersant with respect to 100 parts by mass of carbon nanotubes.

Further, the present invention is a dispersion liquid containing carbon nanotubes of 0.5 parts by mass or more and 3.0 parts by mass or less in 100 parts by mass of the carbon nanotube dispersion liquid, and the rotor rotation speed of the B-type viscometer at 25 ° C. is 60 rpm. The present invention relates to the carbon nanotube dispersion liquid, wherein the viscosity measured in 1 is 10 mPa · s or more and less than 2000 mPa · s.

The present invention also relates to the carbon nanotube dispersion liquid, wherein the solvent contains water.

The present invention also relates to a carbon nanotube resin composition containing the carbon nanotube dispersion liquid and a binder.

The present invention also relates to the carbon nanotube resin composition, wherein the binder contains at least one selected from the group consisting of carboxymethyl cellulose, styrene-butaene rubber and polyacrylic acid.

The present invention also relates to a mixture slurry characterized by containing the carbon nanotube resin composition and an active material.

The present invention also relates to an electrode film formed by forming the mixture slurry in the form of a film.

Further, the present invention is a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode contains the electrode film. Regarding secondary batteries.

By using the carbon nanotubes of the present invention, a resin composition, a mixture slurry, and an electrode film having excellent conductivity and adhesion can be obtained. In addition, a non-aqueous electrolyte secondary battery having excellent rate characteristics and cycle characteristics can be obtained. Therefore, the carbon nanotubes of the present invention can be used in various application fields where high conductivity, adhesion, and durability are required.

Hereinafter, the carbon nanotube, the carbon nanotube dispersion liquid, the resin composition, the mixture slurry, the electrode film formed by forming the mixture slurry, and the non-aqueous electrolyte secondary battery of the present invention will be described in detail.

(1) Carbon Nanotube The carbon nanotube of the present embodiment has a shape in which flat graphite is wound in a cylindrical shape. The carbon nanotubes may be a mixture of single-walled carbon nanotubes and multi-walled carbon nanotubes. Single-walled carbon nanotubes have a structure in which one layer of graphite is wound. Multi-walled carbon nanotubes have a structure in which two or three or more layers of graphite are wound. Further, the side wall of the carbon nanotube does not have to have a graphite structure. For example, a carbon nanotube having a side wall having an amorphous structure can be used as the carbon nanotube.

The carbon nanotubes of the present embodiment preferably have 3 or more and 30 or less carbon nanotube layers, more preferably 3 or more and 20 or less layers, and more preferably 3 or more and 10 or less layers. preferable.

The shape of the carbon nanotubes of this embodiment is not limited. Examples of such a shape include various shapes including a needle shape, a cylindrical tube shape, a fish bone shape (fishbone or cup laminated type), and a coil shape. Further, it may be a plate-shaped or platelet-shaped secondary agglomerate obtained by dry-treating cylindrical tube-shaped carbon nanotubes using beads, and has a thread-like shape in which carbon nanotubes are randomly entangled. It may be a secondary agglomerate of No. 1 or a bundle-shaped secondary agglomerate having orientation, and a bundle-shaped secondary agglomerate having orientation is more preferable. The carbon nanotubes may have a single shape or a combination of two or more shapes.

The form of the carbon nanotubes of the present embodiment includes, but is not limited to, for example, graphite whisker, firamentas carbon, graphite fiber, ultrafine carbon tube, carbon tube, carbon fibril, carbon microtube and carbon nanofiber. .. The carbon nanotubes may have a single form thereof or a combination of two or more kinds thereof.

The average outer diameter of the carbon nanotubes of the present embodiment is 5 to 25 nm, more preferably 5 to 20 nm, and even more preferably 7 to 18 nm.

The standard deviation of the outer diameter of the carbon nanotubes of the present embodiment is preferably 1 to 5 nm, more preferably 1 to 4 nm.

The outer diameter and the average outer diameter of the carbon nanotubes of the present embodiment are obtained as follows. First, carbon nanotubes are observed and imaged with a transmission electron microscope. Next, in the observation photograph, any 300 carbon nanotubes are selected and the outer diameter of each is measured. Next, the average outer diameter (nm) of the carbon nanotube is calculated as the number average of the outer diameters.

BET specific surface area of the carbon nanotubes of the present embodiment is 150 to 400 m ² / g, more preferably those which are 180~350m ² / g, more preferably those which are 180~300m ² / g.

The fiber length of the carbon nanotubes of the present embodiment is 0.5 to 5.0 μm, more preferably 0.8 to 4.0 μm, and even more preferably 0.8 μm to 3.0 μm.

Carbon nanotubes are evaluated by the G / D ratio (peak ratio of G-band to D-band). The G / D ratio of the carbon nanotubes of the present embodiment can be determined by Raman spectroscopy. The carbon nanotube of the present embodiment is G / D when the maximum peak intensity in the range of ^{1560 to 1600 cm -1} is G and the maximum peak intensity in the range ^{of 131 to 1350 cm -1 is D in the Raman spectrum.} The ratio is 0.7 to 2.0, more preferably 0.7 to 1.5.

There are various laser wavelengths used in Raman spectroscopy, but 532 nm and 632 nm are used here. ^{The Raman shift seen near 1590 cm -1} in the Raman spectrum is called the G band derived from ^{graphite, and the Raman shift seen near 1350 cm -1} is called the D band derived from defects in amorphous carbon or graphite. The higher the G / D ratio, the higher the degree of graphitization.

The volume resistivity of the carbon nanotubes of the present embodiment is 1.0 × 10 ^{-2 to} 1.5 × 10 ^-2 Ω · cm, and 1.0 × 10 ^{-2 to} 1.4 × 10 ^-2 Ω · cm. It is more preferable that it is 1.0 × 10 ^{-2 to} 1.2 × 10 ^-2 Ω · cm. The volume resistivity of carbon nanotubes can be measured using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd .: Lorester GP powder resistivity measuring system MCP-PD-51)).

The true density of the carbon nanotubes of the present embodiment is 1.7 to 2.1 g / cc, more preferably 1.7 to 2.0 g / cc, and preferably 1.7 to 1.9 g / cc. More preferred. The true density of carbon nanotubes can be measured using a dry automatic density meter (Acupic 1330 manufactured by Shimadzu Corporation).

The carbon nanotube of the present embodiment preferably has a peak at a diffraction angle of 2θ = 25 ° ± 2 ° when powder X-ray diffraction analysis is performed, and the half-value width of the peak is preferably 2 ° to 6 °. It is more preferably 2 ° to 4 °, and even more preferably 2 ° to 3 °.

The carbon purity of the carbon nanotubes of the present embodiment is represented by the content (%) of carbon atoms in the carbon nanotubes. The carbon purity is preferably 90% by mass or more, more preferably 95% by mass or more, still more preferably 98% by mass or more, based on 100% by mass of carbon nanotubes.

The amount of metal contained in the carbon nanotubes of the present embodiment is preferably less than 10% by mass, more preferably less than 5% by mass, still more preferably less than 2% by mass, based on 100% by mass of the carbon nanotubes. Examples of the metal contained in the carbon nanotube include a metal and a metal oxide used as a catalyst in synthesizing the carbon nanotube. Specific examples thereof include metals such as cobalt, nickel, aluminum, magnesium, silica, manganese and molybdenum, metal oxides and composite oxides thereof.

The water contact angle of the carbon nanotubes of the present embodiment is preferably 120 ° or less, more preferably 90 ° or less, and even more preferably 70 ° or less. The water contact angle of the carbon nanotubes can be calculated by the sessile drop method after applying pressure to the carbon nanotubes to prepare a carbon nanotube substrate having a density of 1.0 g / cc. The contact angle of water of carbon nanotubes can be measured using, for example, an automatic contact angle meter (DM-501Hi manufactured by Kyowa Surface Science Co., Ltd.).

The bulk density of the carbon nanotubes of the present embodiment is preferably 0.005 to 0.1 g / cc, and more preferably 0.01 to 0.06 g / cc. The bulk density of carbon nanotubes can be measured by JIS-K-5101 using a bulk density measuring device (JIS bulk density measuring device manufactured by Tsutsui Rikagaku Kikai Co., Ltd.).

The angle of repose of the carbon nanotubes of the present embodiment is preferably 40 to 90 °, more preferably 45 to 85 °, and even more preferably 45 to 70 °. The angle of repose can be measured by the injection method. The injection method is a method of measuring by depositing powder on a table with a disk-shaped upper surface, which is not easily affected by the material of the table, and the angle between the conical powder and the horizontal plane is a protractor. Etc. can be used for measurement. It is also possible to measure the angle of repose using a commercially available measuring machine.

The carbon nanotubes of the present embodiment may be carbon nanotubes that have been surface-treated. Further, the carbon nanotube may be a carbon nanotube derivative to which a functional group typified by a carboxyl group is imparted. Further, carbon nanotubes containing a substance typified by an organic compound, a metal atom, or fullerene can also be used.

The carbon nanotubes of the present embodiment may be carbon nanotubes produced by any method. Carbon nanotubes can generally be produced by a laser ablation method, an arc discharge method, a thermal CVD method, a plasma CVD method, and a combustion method, but are not limited thereto. For example, carbon nanotubes can be produced by contact-reacting a carbon source with a catalyst at 500 to 1000 ° C. in an atmosphere having an oxygen concentration of 1% by volume or less. The carbon source may be at least one of hydrocarbons and alcohols.

As the raw material gas that is the carbon source of the carbon nanotubes, any conventionally known raw material gas can be used. For example, hydrocarbons typified by methane, ethylene, propane, butane and acetylene, carbon monoxide, and alcohol can be used as the raw material gas containing carbon, but the gas is not limited thereto. In particular, from the viewpoint of ease of use, it is desirable to use at least one of hydrocarbon and alcohol as a raw material gas.

As a method for purifying carbon nanotubes of the present embodiment, various conventionally known methods can be used. For example, acid treatment, graphitization treatment and chlorination treatment can be mentioned.

The acid used for acid treatment of the carbon nanotube of the present embodiment may be any acid that can dissolve the metal and metal oxide contained in the carbon nanotube, but an inorganic acid or a carboxylic acid is preferable, and among the inorganic acids, it is preferable. , Hydrochloric acid, sulfuric acid and nitric acid are particularly preferred.

The acid treatment of the carbon nanotubes of the present embodiment is preferably carried out in a liquid phase, and it is more preferable to disperse and / or mix the carbon nanotubes in the liquid phase. It is preferable that the carbon nanotubes after the acid treatment are washed with water and dried.

The graphitization treatment of the carbon nanotubes of the present embodiment can be carried out by heating the carbon nanotubes at 1500 ° C. to 3500 ° C. in an inert atmosphere having an oxygen concentration of 0.1% or less.

The chlorination treatment of the carbon nanotubes of the present embodiment can be carried out by introducing chlorine gas in an inert atmosphere having an oxygen concentration of 0.1% or less and heating the carbon nanotubes (A) at 800 ° C. to 2000 ° C. it can.

(2) Dispersant The dispersant of the present embodiment is not particularly limited as long as the carbon nanotubes can be dispersed and stabilized, and a surfactant and a resin-type dispersant can be used. Surfactants are mainly classified into anionic, cationic, nonionic and amphoteric. Appropriately suitable types of dispersants can be used in suitable blending amounts according to the properties required for dispersion of carbon nanotubes.

When selecting an anionic surfactant, the type thereof is not particularly limited. Specifically, fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkylaryl sulfonates, alkylnaphthalene sulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, alkyl phosphates, polyoxy Examples thereof include ethylene alkyl ether sulfate, polyoxyethylene alkylaryl ether sulfate, naphthalene sulfonic acid formalin condensate, polyoxyethylene alkyl phosphate sulfonate, glycerol volate fatty acid ester, and polyoxyethylene glycerol fatty acid ester. Not limited to. Further, specific examples thereof include sodium dodecylbenzene sulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate, and sodium salt of β-naphthalene sulfonic acid formalin condensate. , Not limited to these.

Further, as the cationic surfactant, there are alkylamine salts and quaternary ammonium salts. Specifically, stearylamine acetate, trimethyl palm ammonium chloride, trimethyl beef ammonium chloride, dimethyldiolyl ammonium chloride, methyloleyl diethanol chloride, tetramethylammonium chloride, laurylpyridinium chloride, laurylpyridinium bromide, laurylpyridinium disulfate, cetylpyridinium bromide. , 4-Alkylmercaptopyridine, poly (vinylpyridine) -dodecyl bromide and dodecyl benzyl triethylammonium chloride, but are not limited thereto. Further, the amphoteric surfactant includes, but is not limited to, aminocarboxylic acid salt.

Further, examples of the nonionic surfactant include, but are not limited to, polyoxyethylene alkyl ether, polyoxyalkylene derivative, polyoxyethylene phenyl ether, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester and alkyl allyl ether. Specific examples thereof include, but are not limited to, polyoxyethylene lauryl ether, sorbitan fatty acid ester and polyoxyethylene octylphenyl ether.

The surfactant selected is not limited to a single surfactant. Therefore, it is possible to use two or more kinds of surfactants in combination. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. At that time, the blending amount is preferably a suitable blending amount for each surfactant component. As the combination, a combination of an anionic surfactant and a nonionic surfactant is preferable. The anionic surfactant is preferably a polycarboxylic acid salt. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

Specific examples of the resin-type dispersant include cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, and hydroxypropyl methyl cellulose. , Carboxymethyl cellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone and the like. In particular, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, and polyvinylpyrrolidone are preferable.

As the carboxymethyl cellulose, a salt such as a sodium salt of carboxymethyl cellulose in which the hydroxy group of carboxymethyl cellulose is replaced with a sodium carboxymethyl group can also be used.

Further, in addition to the dispersant of the present embodiment, an inorganic base and a metal-free salt may be contained. The inorganic base and the inorganic metal salt are preferably compounds having at least one of an alkali metal and an alkaline earth metal. Specifically, the alkali metal and the alkaline earth metal are chloride, hydroxide, and carbonic acid. Examples thereof include salts, nitrates, sulfates, phosphates, tungstates, vanadium salts, molybdates, niobates, borates and the like. Among these, alkali metals, chlorides of alkaline earth metals, hydroxides, and carbonates are preferable in terms of easily supplying cations. Examples of the alkali metal hydroxide include lithium hydroxide, sodium hydroxide, potassium hydroxide and the like. Examples of the hydroxide of the alkaline earth metal include calcium hydroxide and magnesium hydroxide. Examples of the alkali metal carbonate include lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate and the like. Examples of carbonates of alkaline earth metals include calcium carbonate and magnesium carbonate. Among these, lithium hydroxide, sodium hydroxide, lithium carbonate and sodium carbonate are more preferable.

(3) Solvent The solvent of the present embodiment is not particularly limited as long as the carbon nanotubes can be dispersed, but is a mixed solvent consisting of one or more of water and / or a water-soluble organic solvent. It is preferable, and it is more preferable to contain water. When water is contained, it is preferably 95 parts by mass or more, and more preferably 98 parts by mass or more with respect to 100 parts by mass of the solvent.

Water-soluble organic solvents include alcohol-based solvents (methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, etc.) and polyhydric alcohol-based solvents (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene). Glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc., polyhydric alcohol ethers (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene) Glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl Ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amine-based (ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine , Ethylenediamine, diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone, etc.) (NEP), N, N-dimethylformamide, N, N-dimethylacetamide, N, N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic system (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2) -Imidazolidinone, γ-butyrolactone, etc.), Sulfoxide-based (dimethylsulfoxide, etc.), Sulfon-based (hexamethylphosphorotriamide, sulfolane, etc.), Lower ketone-based (acetone, methylethylketone, etc.), Others, tetrahydrofuran, urea, aceto Nitrile and the like can be used.

(4) Carbon Nanotube Dispersion Liquid The carbon nanotube dispersion liquid of the present embodiment contains carbon nanotubes, a dispersant, and a solvent.

The fiber length of the carbon nanotubes in the carbon nanotube dispersion liquid of the present embodiment is preferably 0.8 to 3.5 μm, more preferably 0.8 to 2.5 μm.

The cumulative particle size D50 of the carbon nanotube dispersion liquid of the present embodiment is preferably 400 to 4000 nm, more preferably 1000 to 3000 nm. The cumulative particle size D50 of the carbon nanotube dispersion can be measured using a particle size distribution meter (Nanotrac UPA, model UPA-EX, manufactured by Microtrac Bell Co., Ltd.).

In order to obtain the carbon nanotube dispersion liquid of the present embodiment, it is preferable to carry out a treatment of dispersing the carbon nanotubes in a solvent. The disperser used to perform such processing is not particularly limited.

As the disperser, a disperser usually used for pigment dispersion or the like can be used. For example, mixers such as disposables, homomixers, planetary mixers, homogenizers (BRANSON Advanced Digital Sonifer (registered trademark), MODEL 450DA, M-Technique "Clearmix", PRIMIX "Fillmix", etc., silver. Son's "Abramix" etc.), paint conditioner (Red Devil), colloid mill (PUC's "PUC colloid mill", IKA's "colloid mill MK"), cone mill (IKA's "corn mill") MKO ", etc.), ball mill, sand mill ("Dyno mill "manufactured by Simmal Enterprises, etc.), attritor, pearl mill (" DCP mill "manufactured by Eirich, etc.), media type disperser such as coball mill, wet jet mill (Genus) Medialess dispersers such as "Genus PY" manufactured by Sugino Machine Limited, "Nanomizer" manufactured by Nanomizer, "Claire SS-5" manufactured by M-Technique, and "MICROS" manufactured by Nara Machinery Co., Ltd. Other examples include, but are not limited to, roll mills and the like.

The solid content of the carbon nanotube dispersion liquid of the present embodiment is preferably 0.2 to 20 parts by mass, preferably 0.5 to 10 parts by mass, and 1 to 3 parts by mass with respect to 100 parts by mass of the carbon nanotube dispersion liquid. The portion is more preferable.

The amount of the dispersant in the carbon nanotube dispersion liquid of the present embodiment is preferably 20 to 100 parts by mass, more preferably 20 to 80 parts by mass, and 20 to 80 parts by mass with respect to 100 parts by mass of carbon nanotubes. It is more preferable to use 50 parts by mass.

The pH of the carbon nanotube dispersion liquid of the present embodiment is preferably 6 to 12, more preferably 7 to 12, further preferably 8 to 12, and particularly preferably 9 to 12. The pH of the carbon nanotube dispersion can be measured using a pH meter (pH METER F-52, manufactured by HORIBA, Ltd.).

The carbon nanotube dispersion liquid of the present embodiment contains 0.5 parts by mass or more and 3.0 parts by mass or less of carbon nanotubes in 100 parts by mass of the carbon nanotube dispersion liquid, and the viscosity is 25 ° C. using a B-type viscometer. The viscosity measured at 60 rpm is preferably 10 mPa · s or more and less than 10000 mPa · s, and more preferably 10 mPa · s or more and less than 2000 mPa · s.

(5) Binder A binder is a resin for binding substances such as carbon nanotubes.

Examples of the binder of the present embodiment include ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, and the like. Polymers or copolymers containing vinylpyrrolidone, etc. as constituent units; polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicon resin, fluororesin Cellulosic resins such as carboxymethyl cellulose; rubbers such as styrene butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene. Further, modified products and mixtures of these resins and copolymers may be used. Of these, carboxymethyl cellulose, styrene-butadiene rubber, and polyacrylic acid are preferable.

The type and amount ratio of the binder are appropriately selected according to the properties of coexisting substances such as carbon nanotubes and active materials. For example, regarding the amount of carboxymethyl cellulose used, when the mass of the active material is 100 parts by mass, the ratio of carboxymethyl cellulose is preferably 0.5 to 3.0 parts by mass, and 1.0 to 2.0 parts by mass. More preferred.

The viscosity of carboxymethyl cellulose as a binder when a 1% aqueous solution is prepared is preferably 500 to 6000 mPa · s, and more preferably 1000 to 3000 mPa · s. The viscosity of the 1% aqueous solution of carboxymethyl cellulose can be measured under the condition of 25 ° C. at a rotor rotation speed of a B-type viscometer rotor of 60 rpm.

The degree of etherification of carboxymethyl cellulose as a binder is preferably 0.6 to 1.5, and more preferably 0.8 to 1.2.

As the styrene-butadiene rubber, if it is an oil droplet emulsion in water, one generally used as a binder for electrodes can be used. Regarding the amount of styrene-butadiene rubber used, when the mass of the active material is 100 parts by mass, the proportion of styrene-butadiene rubber is preferably 0.5 to 3.0 parts by mass, and 1.0 to 2.0 parts by mass. More preferred.

Regarding the amount of polyacrylic acid used, when the mass of the active material is 100 parts by mass, the proportion of polyacrylic acid is preferably 1 to 25 parts by mass, and more preferably 5 to 20 parts by mass.

(5) Carbon Nanotube Resin Composition The carbon nanotube resin composition of the present embodiment contains carbon nanotubes, a dispersant, a solvent, and a binder.

In order to obtain the carbon nanotube resin composition of the present embodiment, it is preferable to mix and homogenize the carbon nanotube dispersion liquid and the binder. As the mixing method, various conventionally known methods can be used. The carbon nanotube resin composition can be produced by using the dispersion device described in the carbon nanotube dispersion liquid.

(6) Mixture Slurry The mixture slurry of the present embodiment contains carbon nanotubes, a dispersant, a solvent, a binder, and an active material.
<Active material>
The active material of the present embodiment is a material that is the basis of a battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material according to the electromotive force.

The positive electrode active material is not particularly limited, but a metal oxide capable of doping or intercalating lithium ions, a metal compound such as a metal sulfide, a conductive polymer, or the like can be used. Examples thereof include oxides of transition metals such as Fe, Co, Ni and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specifically, transition metal oxide powders such as MnO, V ₂ O ₅ , V ₆ O ₁₃ , TiO ₂ , layered lithium nickel oxide, lithium cobalt oxide, lithium manganate, lithium manganate having a spinel structure, etc. Examples thereof include a composite oxide powder of lithium and a transition metal, a lithium iron phosphate-based material which is a phosphoric acid compound having an olivine structure, and a transition metal sulfide powder such as _{TiS 2 and FeS.} Further, a conductive polymer such as polyaniline, polyacetylene, polypyrrole, or polythiophene can also be used. Further, the above-mentioned inorganic compounds and organic compounds may be mixed and used.

The negative electrode active material is not particularly limited as long as it can be doped with or intercalated with lithium ions. For example, metal Li, alloys such as tin alloy, silicon alloy, lead alloy, etc., Li _X Fe ₂ O ₃ , Li _X Fe ₃ O ₄ , Li _X WO ₂ (x is a number of 0 <x <1). ), Metal oxides such as lithium titanate, lithium vanadium, lithium siliconate, conductive polymers such as polyacetylene and poly-p-phenylene, and amorphous carbonaceous materials such as soft carbon and hard carbon. Examples thereof include artificial graphite such as highly graphitized carbon material, carbon powder such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon material, vapor-grown carbon fiber, and carbon-based material such as carbon fiber. These negative electrode active materials may be used alone or in combination of two or more.

As the negative electrode active material of the present embodiment, a silicon-based negative electrode active material which is a negative electrode active material containing silicon such as a silicon alloy or lithium siliconate is preferable.

Examples of the silicon-based negative electrode active material include so-called metallurgical grade silicon produced by reducing silicon dioxide with carbon, industrial grade silicon obtained by reducing impurities by acid treatment or unidirectional solidification of metallurgical grade silicon, and silicon. High-purity silicon produced from silane obtained by reaction and having different crystal states such as single crystal, polycrystalline, and amorphous, and industrial grade silicon are highly purified by sputtering method or EB vapor deposition (electron beam vapor deposition) method. At the same time, silicon whose crystal state and precipitation state are adjusted can be mentioned.

Further, silicon oxide which is a compound of silicon and oxygen, various alloys of silicon and various alloys, and a silicon compound in which the crystal state thereof is adjusted by a quenching method or the like can be mentioned. Of these, a silicon-based negative electrode active material having a structure in which silicon nanoparticles are dispersed in silicon oxide, the outside of which is coated with a carbon film, is preferable.

The negative electrode active material of the present embodiment is, in addition to the silicon negative negative active material, an amorphous carbon material such as soft carbon or hard carbon, artificial graphite such as high graphitized carbon material, or carbon powder such as natural graphite. It is preferable to use. Among them, it is preferable to use carbonaceous powder such as artificial graphite or natural graphite.

When the amount of the silicon-based negative electrode active material is 100 parts by mass of a carbonaceous powder such as artificial graphite or natural graphite, it is preferably 3 to 50 parts by mass, and more preferably 5 to 25 parts by mass.

BET specific surface area of the active material of the present embodiment is preferably a 0.1 to 10 m ² / g, more preferably a 0.2~5m ² / g, yet those 0.3~3m ² / g preferable.

The average particle size of the active material of the present embodiment is preferably in the range of 0.5 to 50 μm.
It is more preferably 2 to 20 μm. The average particle size of the active material as used herein is an average value of the particle size of the active material measured with an electron microscope.

(7) Method for Producing Mixture Slurry The mixture slurry of the present embodiment can be produced by various conventionally known methods. For example, a method of adding an active material to a carbon nanotube resin composition to prepare the composition, and a method of adding an active material to a carbon nanotube dispersion liquid and then adding a binder to prepare the carbon nanotube resin composition can be mentioned.

In order to obtain the mixture slurry of the present embodiment, it is preferable to add an active material to the carbon nanotube resin composition and then disperse it. The disperser used to perform such processing is not particularly limited. As the mixture slurry, the mixture slurry can be obtained by using the dispersion device described in the carbon nanotube dispersion liquid.

The amount of the active material in the mixture slurry of the present embodiment is preferably 20 to 85 parts by mass, more preferably 30 to 75 parts by mass, and 40 to 70 parts by mass with respect to 100 parts by mass of the mixture slurry. It is more preferably parts by mass.

The amount of carbon nanotubes in the mixture slurry of the present embodiment is preferably 0.01 to 10 parts by mass and preferably 0.02 to 5 parts by mass with respect to 100 parts by mass of the active material. It is preferably 03 to 1 part by mass.

The amount of the binder in the mixture slurry of the present embodiment is preferably 0.5 to 30 parts by mass, more preferably 1 to 25 parts by mass, and 2 to 20 parts by mass with respect to 100 parts by mass of the active material. It is particularly preferable that it is by mass.

The solid content of the mixture slurry of the present embodiment is preferably 30 to 90% by mass, more preferably 30 to 80% by mass, and 40 to 75% by mass with respect to 100% by mass of the mixture slurry. It is preferably mass%.

(8) Electrode film The electrode film of the present embodiment is formed by forming a mixture slurry in the form of a film. For example, it is a coating film in which an electrode mixture layer is formed by applying and drying a mixture slurry on a current collector.

The material and shape of the current collector used for the electrode film of the present embodiment are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, examples of the material of the current collector include metals and alloys such as aluminum, copper, nickel, titanium, and stainless steel. As the shape, a foil on a flat plate is generally used, but a roughened surface, a perforated foil, or a mesh-shaped current collector can also be used.

The method of applying the mixture slurry on the current collector is not particularly limited, and a known method can be used. Specific examples include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method, an electrostatic coating method, and the like, and drying. As the method, a neglected drying, a blower dryer, a warm air dryer, an infrared heater, a far infrared heater and the like can be used, but the method is not particularly limited thereto.

Further, after coating, a rolling process such as a lithographic press or a calendar roll may be performed. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

(8) Non-aqueous electrolyte secondary battery The non-aqueous electrolyte secondary battery of the present embodiment includes a positive electrode, a negative electrode, and an electrolyte.

As the positive electrode, a current collector obtained by applying and drying a mixture slurry containing a positive electrode active material to prepare an electrode film can be used.

As the negative electrode, a mixture slurry containing the negative electrode active material on the current collector is coated and dried to prepare an electrode film.

As the electrolyte, various conventionally known electrolytes in which ions can move can be used. For example, LiBF ₄ , LiClO ₄ , LiPF ₆ , _{LiAsF 6} , LiSbF ₆ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , Li (CF ₃ SO ₂ ) ₃ C, LiI , LiBr, LiCl, LiAlCl, LiHF ₂ , LiSCN, or LiBPh ₄ (where Ph is a phenyl group) and the like, but are not limited to those containing a sodium salt or a calcium salt. Can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

The non-aqueous solvent is not particularly limited, and is, for example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethylmethyl carbonate, and diethyl carbonate; γ-butyrolactone, γ-valerolactone, and γ. Solvents such as −octanoic lactone; tetrahydrofuran, 2-methyl tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1, Glymes such as 2-dibutoxyetane; esters such as methylformate, methylacetate, and methylpropionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. Each of these solvents may be used alone, or two or more kinds may be mixed and used.

The non-aqueous electrolyte secondary battery of the present embodiment preferably contains a separator. Examples of the separator include, but are not limited to, polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and those obtained by subjecting them to a hydrophilic treatment.

The structure of the non-aqueous electrolyte secondary battery of the present embodiment is not particularly limited, but is usually composed of a positive electrode and a negative electrode, and a separator provided as needed, and includes a paper type, a cylindrical type, a button type, a laminated type, and the like. It can have various shapes according to the purpose of use.

Hereinafter, the present invention will be described in more detail with reference to examples. The present invention is not limited to the following examples as long as the gist of the present invention is not exceeded. In the examples, "carbon nanotubes" may be abbreviated as "CNT". Unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass".

<Measurement method of physical properties>
The physical characteristics of the CNTs used in each of the examples and comparative examples described later were measured by the following methods.

<Average outer diameter of CNT>
Using an electronic balance (manufactured by Sartorius, MSA225S100DI), weigh 0.2 g of CNT into a 450 mL SM sample bottle (manufactured by Sansho Co., Ltd.), add 200 mL of toluene, and add an ultrasonic homogenizer (Advanced Digital Sonyer) (registered). A CNT dispersion liquid was prepared by performing a dispersion treatment under ice cooling for 5 minutes at an amplitude of 50% using (trademark), MODEL 450DA, manufactured by BRANSON. Then, the CNT dispersion was appropriately diluted, dropped in the form of a collodion film in the form of several μL, dried at room temperature, and then observed using a direct transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.). Observation is performed at a magnification of 50,000 times, multiple photographs containing 10 or more CNTs in the field of view are taken, the outer diameters of 300 arbitrarily extracted CNTs are measured, and the average value is the average outer diameter of CNTs (the average outer diameter of CNTs). nm).

<BET specific surface area of CNT>
After weighing 0.03 g of CNTs using an electronic balance (MSA225S100DI manufactured by Sartorius), the CNTs were dried at 110 ° C. for 15 minutes while degassing. ^{Then, the BET specific surface area (m 2} / g) of CNT was measured using a fully automatic specific surface area measuring device (HM-model 1208 manufactured by MOUNTECH).

<Fiber length of CNT>
Using an electronic balance (manufactured by Sartorius, MSA225S100DI), weigh 0.2 g of CNT into a 450 mL SM sample bottle (manufactured by Sansho Co., Ltd.), add 200 mL of toluene, and add an ultrasonic homogenizer (Advanced Digital Sonyer) (registered). A sample for measuring the fiber length of CNT was prepared by subjecting it to dispersion treatment under ice cooling for 5 minutes at an amplitude of 50% using (trademark), MODEL 450DA, manufactured by BRANSON. Then, several μL of a sample for measuring the fiber length of CNT was dropped onto the mica substrate, and then dried in an oven at 80 ° C. to prepare a substrate for measuring the fiber length of CNT. After that, the substrate for measuring the fiber length of CNT was platinum sputtered and observed using SEM. For observation, take multiple photographs containing 10 or more CNTs in the field of view at a magnification of 5000 times or 20,000 times according to the fiber length of CNTs, and measure the fiber lengths of 100 CNTs arbitrarily extracted. The average value was taken as the average fiber length (μm) of CNT.

<G / D ratio of CNT>
A CNT was installed in a Raman microscope (XploRA, manufactured by HORIBA, Ltd.), and measurement was performed using a laser wavelength of 532 nm. The measurement conditions were an capture time of 60 seconds, an integration frequency of 2 times, a dimming filter of 10%, an objective lens magnification of 20 times, a confocus hole of 500, a slit width of 100 μm, and a measurement wavelength of 100 to 3000 cm ^-1 . The CNTs for measurement were separated on a slide glass and flattened using a spatula. Among the obtained peaks, the maximum peak intensity is G in the range of 1560 to 1600 cm ^{-1 in the spectrum, the maximum peak intensity is D in the range of 131 to 1350 cm -1} , and the G / D ratio is G / of CNT. It was set to D ratio.

<Volume resistivity of CNT>
Using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd .: Lorester GP powder resistivity measuring system MCP-PD-51), the sample mass was 1.2 g, and the probe unit for powder (four probes). -Measure the volume resistivity [Ω · cm] of conductive powder under various pressurization with the applied voltage limiter set to 90 V with a ring electrode, electrode spacing 5.0 mm, electrode radius 1.0 mm, sample radius 12.5 mm). did. The value of the volume resistivity of CNT at a density of 1 g / cm ^{3 was evaluated.}

<True density of CNT>
The true density of CNTs was measured using a dry automatic density meter (Acupic 1330 manufactured by Shimadzu Corporation). The true density was measured using helium gas under the condition of 25 ° C.

<Half price range of CNT>
A CNT was placed in the central recess of an aluminum sample plate (outer diameter φ46 mm, thickness 3 mm, sample portion φ26.5 mm, thickness 2 mm) and flattened using a slide glass. Then, a medicine wrapping paper was placed on the surface on which the sample was placed, and a load of 1 ton was applied to the surface on which the aluminum high sheet packing was placed to flatten the surface. Then, the medicine wrapping paper and the aluminum high sheet packing were removed to obtain a sample for powder X-ray diffraction analysis of CNT. Then, a sample for powder X-ray diffraction analysis of CNT was placed in an X-ray diffractometer (Ultima2100, manufactured by Rigaku Co., Ltd.) and operated from 15 ° to 35 ° for analysis. Sampling is performed every 0.02 °, and the scan speed is 2 ° / min. And said. The voltage was 40 kV, the current was 40 mA, and the X-ray source was CuKα ray. The plots appearing at the diffraction angle 2θ = 25 ° ± 2 ° obtained at this time were simply moved averaged at 11 points, and the half-value width of the peak was defined as the half-value width of CNT. The baseline was a line connecting the plots of 2θ = 16 ° and 2θ = 34 °.

<Carbon purity of CNT>
The CNT was acid-decomposed using a microwave sample pretreatment device (ETHOS1 manufactured by Milestone General Co., Ltd.) to extract the metal contained in the CNT. Then, analysis was performed using a multi-type ICP emission spectrophotometer (720-ES, manufactured by Agilent), and the amount of metal contained in the extract was calculated. The carbon purity of CNT was calculated as follows.
(Equation 1) Carbon purity (%) = ((mass of CNT-mass of metal in CNT) ÷ mass of CNT) × 100%

<Bulk density and angle of repose of CNT>
The bulk density of CNT was measured with JIS-K-5101 using a bulk density measuring device (JIS bulk density measuring instrument manufactured by Tsutsui Rikagaku Kikai Co., Ltd.). First, the mass of the receiver was weighed, then the bulk density measuring device was leveled, the funnel was attached to the funnel stand, the sieve was placed on the funnel, and the receiver was placed on the receiver stand. Then, the CNT was placed on the sieve using a spatula, the CNT was lightly wiped evenly over the entire surface of the sieve with a brush, and the sample passed through the sieve was received by the receiver. This work was repeated until the CNTs were piled up on the receiver. The angle formed by the conical powder deposited in a heap and the horizontal plane was measured using a protractor and used as the angle of repose of CNT. After that, the mountain part was scraped off with a spatula, and the receiver containing the sample was weighed. The bulk density of CNTs was calculated by subtracting the receiver mass from the receiver mass containing CNTs and then dividing by the receiver capacity.

<pH measurement of CNT dispersion liquid>
The CNT dispersion was allowed to stand in a constant temperature bath at 25 ° C. for 1 hour or more, and then the CNT dispersion was sufficiently stirred, and then measured using a pH meter (pH METER F-52, manufactured by HORIBA, Ltd.). ..

<Viscosity of CNT dispersion liquid>
The CNT dispersion was allowed to stand in a constant temperature bath at 25 ° C. for 1 hour or more, and then the CNT dispersion was sufficiently stirred, and then immediately performed at a B-type viscometer rotor rotation speed of 60 rpm. The rotor used for the measurement was No. 1 when the viscosity value was less than 100 mPa · s. If 1 is 100 or more and less than 500 mPa · s, No. If 2 is 500 or more and less than 2000 mPa · s, No. If 3 is 2000 or more and less than 10000 mPa · s, No. The ones of 4 were used respectively.

<length of CNT Fibers in CNT Dispersion> The CNT dispersions prepared in Examples and Comparative Examples described later are diluted with the solvent used to prepare the CNT dispersion so that the CNT concentration is 0.01% by mass. After dropping several μL onto the mica substrate, the substrate was dried in an electric oven at 120 ° C. to prepare a substrate for observing the length of CNT fibers. Then, the surface of the prepared substrate for observing the CNT fiber length was sputtered with platinum. After that, it was observed using SEM. For observation, take multiple photographs containing 10 or more CNTs in the field of view at a magnification of 5000 times or 20,000 times according to the fiber length of CNTs, and measure the fiber lengths of 100 CNTs arbitrarily extracted. The average value was taken as the average fiber length (μm) of CNT.

<Volume resistivity of electrode film for negative electrode>
The negative electrode mixture slurry is applied onto a copper foil using an applicator so that the amount of the electrode per unit is 8 mg / cm ^2, and then in an electric oven at 120 ° C. ± 5 ° C. for 25 minutes. The coating was dried. Then, the surface resistivity (Ω / □) of the coating film after drying was measured using Lorester GP and MCP-T610 manufactured by Mitsubishi Chemical Analytech Co., Ltd. After the measurement, the thickness of the electrode mixture layer formed on the copper foil was multiplied to obtain the volume resistivity (Ω · cm) of the electrode film for the negative electrode. The thickness of the electrode mixture layer is determined by subtracting the thickness of the copper foil from the average value measured at three points in the electrode film using a film thickness meter (DIGIMICRO MH-15M manufactured by NIKON). The volume resistivity (Ω · cm) was used.

<Peeling strength of electrode film for negative electrode>
The negative electrode mixture slurry is applied onto a copper foil using an applicator so that the amount of the electrode per unit is 8 mg / cm ^2, and then in an electric oven at 120 ° C. ± 5 ° C. for 25 minutes. The coating was dried. Then, two pieces were cut into a rectangle of 90 mm × 20 mm with the coating direction as the major axis. A desktop tensile tester (Strograph E3 manufactured by Toyo Seiki Seisakusho Co., Ltd.) was used to measure the peel strength, and the peel strength was evaluated by a 180-degree peel test method. Specifically, a 100 mm × 30 mm size double-sided tape (No. 5000NS, manufactured by Nitoms Co., Ltd.) was attached onto a stainless steel plate, and the produced battery electrode mixture layer was brought into close contact with the other surface of the double-sided tape. Peeling was performed while pulling from the bottom to the top at a constant speed (50 mm / min), and the average value of stress at this time was taken as the peel strength.

<Preparation of standard positive electrode>
The standard positive electrodes used in Examples and Comparative Examples described later were prepared by the following methods.

First, 93 parts by mass of positive electrode active material (BASF Toda Battery Materials GK, HED (registered trademark) NCM-111 1100), 4 parts by mass of acetylene black (Denka Co., Ltd., Denka Black (registered trademark) HS100), PVDF (Kureha KF Polymer W # 1300, manufactured by Kureha Battery Materialal's Japan Co., Ltd.) ^{After adding 3} parts by mass to a plastic container having a capacity of 150 cm3, the mixture was mixed using a spatula until the powder became uniform. Then, 20.5 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer (Awatori Rentaro manufactured by Shinky Co., Ltd., ARE-310). Then, the mixture in the plastic container was mixed using a spatula until it became uniform, and the mixture was stirred at 2000 rpm for 30 seconds using the rotation / revolution mixer. After that, 14.6 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using the rotation / revolution mixer. Finally, using a high-speed stirrer, the mixture was stirred at 3000 rpm for 10 minutes to obtain a mixture slurry for a positive electrode. Then, the mixture slurry for the positive electrode is applied on an aluminum foil having a thickness of 20 μm as a current collector using an applicator, and then dried in an electric oven at 120 ° C. ± 5 ° C. for 25 minutes per unit area of the electrode. The amount of the grain was adjusted to ^{20 mg / cm 2.} Further, rolling processing was performed by a roll press (3t hydraulic roll press manufactured by Thunk Metal Co., Ltd.) to prepare a standard positive electrode having ^{a density of the mixture layer of 3.1 g / cm 3.}

<Evaluation of rate characteristics of lithium-ion secondary battery>
A laminated lithium-ion secondary battery was installed in a constant temperature room at 25 ° C., and charge / discharge measurement was performed using a charge / discharge device (SM-8 manufactured by Hokuto Denko Co., Ltd.). After performing constant current constant voltage charging (cutoff current 1.1mA (0.02C)) at a charging end voltage of 4.2V at a charging current of 11mA (0.2C), the discharge current is 11mA (0.2C). , Constant current discharge was performed with a discharge end voltage of 2.5 V. After repeating this operation three times, constant current constant voltage charging (cutoff current (1.1mA 0.02C)) is performed at a charging end voltage of 4.2V at a charging current of 11mA (0.2C), and the discharge current is 0. Constant current discharge was performed at 2C and 3C until the discharge end voltage reached 2.5 V, and the discharge capacity was determined for each. The rate characteristic can be expressed by the following equation 2 which is the ratio of the 0.2C discharge capacity to the 3C discharge capacity.
(Equation 2) Rate characteristics = 3C discharge capacity / 3rd 0.2C discharge capacity x 100 (%)

<Evaluation of cycle characteristics of lithium-ion secondary batteries>
A laminated lithium-ion secondary battery was installed in a constant temperature room at 25 ° C., and charge / discharge measurement was performed using a charge / discharge device (SM-8 manufactured by Hokuto Denko Co., Ltd.). After performing constant current constant voltage charging (cutoff current 1.38mA (0.025C)) at a charging end voltage of 4.2V at a charging current of 55mA (1C), the discharge end voltage is applied at a discharge current of 55mA (1C). A constant current discharge was performed at 2.5 V. This operation was repeated 200 times. 1C was defined as a current value for discharging the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be expressed by the following equation 3 which is the ratio of the 3rd 1C discharge capacity to the 200th 1C discharge capacity at 25 ° C.
(Equation 3) Cycle characteristics = 3rd 1C discharge capacity / 200th 1C discharge capacity x 100 (%)

<Production example of catalyst for CNT synthesis>
The catalysts for CNT synthesis used in each of the examples and comparative examples described later were prepared by the following methods.

<Catalyst for CNT synthesis (A)>
After weighing 1000 parts by mass of magnesium acetate tetrahydrate in a heat-resistant container and drying it at an atmospheric temperature of 170 ± 5 ° C. for 6 hours using an electric oven, a crusher (Sample Mill KIIW-I type, Co., Ltd.) A 1 mm screen was attached using (manufactured by Dalton Corporation) and pulverized to obtain a dried magnesium acetate pulverized product. 45.8 parts of dried and pulverized magnesium acetate product, 7 parts of ammonium molybdate tetrahydrate, _{1.0 part of silicon oxide (SiO 2} , manufactured by Aerosil Japan Co., Ltd .: AEROSIL® 200), steel beads (bead diameter 2. 200 parts (0 mmφ) were charged into an SM sample bottle (manufactured by Sansho Co., Ltd.), and pulverized and mixed for 30 minutes using a paint conditioner manufactured by Red Devil. Then, using a stainless sieve, the pulverized and mixed powder and steel beads (bead diameter 2.0 mmφ) were separated to obtain a catalyst carrier for CNT synthesis. Then, 30 parts by mass of cobalt (II) hydroxide was weighed in a heat-resistant container and dried at an atmospheric temperature of 170 ± 5 ° C. for 2 hours to obtain a cobalt composition containing _{CoHO 2.} After that, 54.9 parts by mass of the catalyst carrier for CNT synthesis and 29 parts by mass of the cobalt composition were charged into a crusher (Wonder Crusher WC-3, manufactured by Osaka Chemical Co., Ltd.), a standard lid was attached, and the SPEED dial was set to 2. Was pulverized and mixed for 30 seconds to obtain a catalyst precursor for CNT synthesis. The catalyst precursor for CNT synthesis is transferred to a heat-resistant container, fired in a muffle furnace (FO510, manufactured by Yamato Kagaku Co., Ltd.) for 30 minutes in an air atmosphere at 450 ± 5 ° C., and then pulverized in a mortar. A catalyst for CNT synthesis (A) was obtained.

<Catalyst for CNT synthesis (B)>
A CNT synthesis catalyst (B) was obtained in the same manner as the CNT synthesis catalyst (A) except that the amount of ammonium molybdate tetrahydrate added was changed from 7 parts to 11.2 parts.

<Catalyst for CNT synthesis (C)>
A CNT synthesis catalyst (C) was obtained in the same manner as the CNT synthesis catalyst (A) except that the amount of ammonium molybdate tetrahydrate added was changed from 7 parts to 16.8 parts.

<Catalyst for CNT synthesis (D)>
A CNT synthesis catalyst (D) was obtained in the same manner as the CNT synthesis catalyst (A) except that the amount of ammonium molybdate tetrahydrate added was changed from 7 parts to 0 parts.

<Catalyst for CNT synthesis (E)>
A CNT synthesis catalyst (E) was obtained in the same manner as the CNT synthesis catalyst (A) except that 160 parts of cobalt acetate tetrahydrate was used instead of 60 parts of cobalt hydroxide.

(Example 1) Synthesis of CNT (A1) 1.0 g of the catalyst for CNT synthesis (A) was sprayed on the central portion of a horizontal reaction tube having an internal volume of 10 L, which can be pressurized and heated by an external heater. A quartz glass bakeware was installed. Exhaust was performed while injecting nitrogen gas, the air in the reaction tube was replaced with nitrogen gas, and the atmosphere in the horizontal reaction tube was adjusted to an oxygen concentration of 1% by volume or less. Then, it was heated by an external heater until the center temperature in the horizontal reaction tube reached 680 ° C. After reaching 680 ° C., ethylene gas was introduced into the reaction tube at a flow rate of 2 L / min as a carbon source, and the contact reaction was carried out for 1 hour. After completion of the reaction, the gas in the reaction tube was replaced with nitrogen gas, the gas in the reaction tube was replaced with nitrogen gas, the temperature of the reaction tube was cooled to 100 ° C. or lower, and the mixture was taken out to obtain a CNT composition.
Then, 10 g of the CNT composition was weighed in a carbon heat-resistant container, and the carbon heat-resistant container containing the CNT composition was installed in the furnace. After that, the inside of the furnace was evacuated to 1 Torr (133 Pa) or less, and the carbon heater was further energized to raise the temperature inside the furnace to 1000 ° C. Next, argon gas was introduced into the furnace to adjust the pressure in the furnace to 70 Torr (9.33 kPa), and then 1 L of argon gas per minute was introduced into the furnace. After that, chlorine gas was introduced in addition to argon gas to adjust the pressure in the furnace to 90 Torr (11.99 kPa), and after the pressure reached that pressure, 0.3 L of chlorine gas per minute was introduced into the furnace. Introduced. In the same state, after holding for 1 hour, the energization was stopped, the introduction of argon gas and chlorine gas was stopped, and vacuum cooling was performed. Finally, vacuum cooling was performed at a pressure of 1 Torr (133 Pa) or less for 12 hours, and after confirming that the inside of the furnace was cooled to room temperature, nitrogen gas was introduced into the furnace until it reached atmospheric pressure, and heat resistance was achieved. The container was taken out to obtain CNT (A1).

(Examples 2 to 5) CNTs (B1) to (E1)
CNTs (B1) to (E1) were obtained by the same method as in Example 1 except that the CNT synthesis catalyst (A) was changed to the CNT synthesis catalysts (B) to (E).

(Example 6) CNT (C2)
CNT (C2) was obtained by the same method as in Example 1 except that the temperature inside the furnace before introducing chlorine gas into the furnace was changed from 1000 ° C. to 1500 ° C.

(Example 7) CNT (C3)
CNT (C3) was obtained by the same method as in Example 1 except that the temperature inside the furnace before introducing chlorine gas into the furnace was changed from 1000 ° C. to 1800 ° C.

(Example 8) CNT (C4)
The CNT (C4) was obtained by the same method as in Example 1 except that the catalyst for CNT synthesis (A) was changed to the catalyst for CNT synthesis (C) and the contact reaction time was changed from 1 hour to 2 hours. ..

(Example 9) CNT (C5)
The CNT (C5) was obtained by the same method as in Example 1 except that the catalyst for CNT synthesis (A) was changed to the catalyst for CNT synthesis (C) and the contact reaction time was changed from 1 hour to 3 hours. ..

(Example 10) Synthesis of CNT (D2) 1.0 g of the catalyst (D) for CNT synthesis was sprayed on the central portion of a horizontal reaction tube having an internal volume of 10 L, which can be pressurized and heated by an external heater. A quartz glass bakeware was installed. Exhaust was performed while injecting nitrogen gas, the air in the reaction tube was replaced with nitrogen gas, and the atmosphere in the horizontal reaction tube was adjusted to an oxygen concentration of 1% by volume or less. Then, it was heated by an external heater until the center temperature in the horizontal reaction tube reached 680 ° C. After reaching 680 ° C., ethylene gas was introduced into the reaction tube at a flow rate of 2 L / min as a carbon source, and the contact reaction was carried out for 1 hour. After completion of the reaction, the gas in the reaction tube was replaced with nitrogen gas, the gas in the reaction tube was replaced with nitrogen gas, and the temperature of the reaction tube was cooled to 100 ° C. or lower and taken out to obtain CNT (D2). ..

(Comparative Example 1) Synthesis of CNT (A2) 10 g of the CNT composition obtained in Example 1 was weighed in a heat-resistant container made of carbon, and the heat-resistant container containing the CNT composition was installed in the furnace. After that, nitrogen gas was introduced into the furnace to discharge the air in the furnace while maintaining the positive pressure. After the oxygen concentration in the furnace became 0.1% or less, the temperature in the furnace was raised to 2900 ° C. over 30 hours, and then the temperature was maintained at 2900 ° C. for 3 hours. Then, the heating in the furnace was stopped and the sample was cooled to obtain CNT (A2).

(Comparative Examples 2 to 5) CNT (F) to (I)
Carbon nanotubes (VGCF-H, manufactured by Showa Denko) are CNT (F), multi-walled carbon nanotubes (NC7000, manufactured by Nanosil) are CNT (G), and single-walled carbon nanotubes (TUBALL, manufactured by OCSiAl) are CNT (H). , Multi-walled carbon nanotubes (Flotube 9000, manufactured by Canon) were designated as CNT (I).

(Comparative Example 6) CNT (J)
A catalyst for CNT synthesis was prepared by the method described in paragraph [0121] of Japanese Patent No. 6380588, and CNT (J) was obtained by the method described in paragraph [0124].

Table 1 shows the evaluation results of CNTs (A1) to (J). Since CNT (H) could not be screened, bulk density and angle of repose could not be measured.

Table 2 shows the dispersants used in Examples and Comparative Examples.

(Example 11)
Add 98.45 parts of ion-exchanged water, 0.5 part of dispersant (A), and 0.05 part of defoamer (Surfinol 104E manufactured by Nisshin Kagaku Kogyo Co., Ltd.) to a stainless steel container until it becomes uniform with a disper. Stirred. Then, while stirring with a disper, one part of CNT (A1) was added, and the mixture was further stirred with a disper until uniform. After that, a high-pressure homogenizer (manufactured by Sugino Machine Limited, Starburst 10) was used for dispersion treatment. A single nozzle chamber was used for the dispersion treatment, and a 5-pass treatment was performed at a nozzle diameter of 0.17 mm and a pressure of 100 MPa to obtain a CNT dispersion liquid (A1a).

(Examples 12 to 26), (Comparative Examples 7 to 12)
CNT was added by the same method as in Example 11 except that the CNT type, CNT addition amount, dispersant type, dispersant addition amount, defoamer addition amount, ion-exchanged water addition amount, and number of passes shown in Table 3 were changed. Dispersions (B1a) to (Ja) were obtained. The nozzle of the CNT dispersion liquid (Ha) was blocked during dispersion with a high-pressure homogenizer, and the dispersion treatment could not be performed.

Table 4 shows the evaluation results of the CNT dispersions prepared in Examples 11 to 26 and Comparative Examples 7 to 12. The viscosity of the CNT dispersion is evaluated as +++ (excellent) for those with less than 500 mPa · s, ++ (good) for those with 500 or more and less than 2000 mPa · s, and + (possible) for those with 2000 or more and less than 10000 mPa · s. For s or more, sedimentation or separation was defined as − (defective). The evaluation of the CNT fiber length in the CNT dispersion liquid is +++ (excellent) for those with 1.5 μm or more, ++ (good) for those with 1.2 μm or more and less than 1.5 μm, and those with 0.8 μm or more and less than 1.2 μm. Was + (possible), and those less than 0.8 μm were − (impossible).

(Example 27)
7.5 parts by mass of CNT dispersion liquid (A1a), 2% by mass of CMC (manufactured by Daicel FineChem Co., Ltd., # 1190) dissolved in a plastic container with a capacity of 150 cm ^{3 12.5 parts by mass, ion-exchanged water 4.9} Weighed by mass. Then, using a rotation / revolution mixer (Awatori Rentaro manufactured by Shinky Co., Ltd., ARE-310), the mixture was stirred at 2000 rpm for 30 seconds to obtain a CNT resin composition (A1a). After that, 2.4 parts by mass of silicon monoxide (SILICON MONOOXIDE, SiO 1.3C 5 μm manufactured by Osaka Titanium Technology Co., Ltd.) was added, and a rotation / revolution mixer (Awatori Rentaro manufactured by Shinky Co., Ltd., ARE-310) was added. Using, the mixture was stirred at 2000 rpm for 30 seconds. Furthermore, 21.9 parts by mass of artificial graphite (CGB-20 manufactured by Nippon Graphite Industry Co., Ltd.) was added, and using a rotation / revolution mixer (Awatori Rentaro manufactured by Shinky Co., Ltd., ARE-310), 2000 rpm for 30 seconds. Stirred. After that, 0.78 parts by mass of styrene-butadiene emulsion (TRD2001 manufactured by JSR Corporation) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotation / revolution mixer (Awatori Rentaro manufactured by Shinky Co., Ltd., ARE-310). , Negative mixture slurry (A1a) was obtained.

(Examples 28 to 42), (Comparative Examples 13 to 17)
By the same method as in Example 27, the CNT dispersion liquid shown in Table 5 was changed, and the amount of the CNT dispersion liquid added was adjusted so that the CNT in 100 parts by mass of the mixture slurry was 0.3 parts by mass. , Negative mixture slurries (B1a) to (Ja) were obtained.

(Example 43)
The negative electrode mixture slurry (A1a) is applied onto a copper foil using an applicator so that the grain size per unit of the electrode is 8 mg / cm ^2, and then at 120 ° C. ± 5 ° C. in an electric oven. The coating film was dried for 25 minutes to obtain an electrode film (A1a).

(Examples 44 to 58), (Comparative Examples 18 to 22)
Electrode films (B1a) to (Ja) were obtained by the same method as in Example 43 except that the slurry was changed to the negative electrode mixture slurry shown in Table 6.

Table 7 shows the evaluation results of the mixture slurries prepared in Examples 43 to 58 and Comparative Examples 18 to 22. For conductivity evaluation, the volume resistivity (Ω · cm) of the electrode film is +++ (excellent) when it is less than 0.15, ++ (good) when it is 0.15 or more and less than 0.2, and + when it is 0.2 or more and less than 0.3. (Yes), 0.3 or more was set to- (No). Adhesion evaluation is as follows: Peeling strength (N / cm) of 0.5 or more is +++ (excellent), 0.4 or more and less than 0.5 is ++ (good), 0.3 or more and less than 0.4 is + (possible), Less than 0.3 was defined as- (impossible).

(Example 59)
The electrode film (A1a) was rolled by a roll press (3t hydraulic roll press manufactured by Thunk Metal Co., Ltd.) to prepare a negative electrode having ^{a mixture layer density of 1.6 g / cm 3.}

(Examples 60 to 74), (Comparative Examples 23 to 27)
A negative electrode was prepared in the same manner as in Example 59 except that the electrode film was changed to the electrode film shown in Table 8.

(Example 75)
The negative electrode (A1a) and the standard positive electrode are punched into 50 mm × 45 mm and 45 mm × 40 mm, respectively, and the separator (porous polypropylene film) inserted between them is inserted into an aluminum laminate bag at 60 ° C. in an electric oven. It was dried for 1 hour. Then, in a glove box filled with argon gas, an electrolytic solution (a mixed solvent in which ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate were mixed at a ratio of 3: 5: 2 (volume ratio) was prepared, and further used as an additive. , VC (vinylene carbonate) and FEC (fluoroethylene carbonate) were added by 1 part by mass with respect to 100 parts by mass of the mixed solvent, and then 2 mL of a non-aqueous electrolyte solution in which _{LiPF 6 was dissolved at a concentration of 1 M) was injected.} , The aluminum laminate was sealed to prepare a laminated lithium ion secondary battery (A1a).

(Examples 76 to 90), (Comparative Examples 28 to 32)
Laminated lithium ion secondary batteries (B1a) to (Ja) were produced by the same method except that the negative electrode was changed to the negative electrode shown in Table 9.

Table 10 shows the evaluation results of the laminated lithium ion secondary batteries produced in Examples 75 to 90 and Comparative Examples 28 to 32. The rate characteristics are +++ (excellent) for those with a rate characteristic of 80% or more, ++ (good) for those with a rate characteristic of 70% or more and less than 80%, + (possible) for those with a rate characteristic of 60% or more and less than 70%, and less than 60%. The thing was set to- (impossible). As for the cycle characteristics, 90% or more of the cycle characteristics was +++ (excellent), 85% or more and less than 90% was ++ (good), 80% or more and less than 85% was + (possible), and less than 80% was- (impossible). ..

In the above embodiment, the outer diameter is 5 to 25 nm, the BET specific surface area is 150 to 400 m ² / g, the fiber length of CNT is 0.5 to 5.0 μm, and the G / D ratio is 0.8. Carbon nanotubes having a volume resistivity of 1.0 × 10 ^{-2 to} 1.5 × 10 ^-2 Ω · cm and a true density of 1.7 to 2.1 g / cc were used. .. In the examples, a lithium ion secondary battery having excellent rate characteristics and cycle characteristics as compared with the comparative example was obtained. Therefore, it has been clarified that the present invention can provide a lithium ion secondary battery having high capacity, high output and high durability, which cannot be realized by conventional carbon nanotubes.

Although the invention of the present application has been described above with reference to the embodiments, the invention of the present application is not limited to the above. Various changes that can be understood by those skilled in the art can be made within the scope of the invention in the configuration and details of the invention of the present application.

Claims (13)

A carbon nanotube characterized by satisfying the following (1) to (6).
(1) The average outer diameter is 5 to 25 nm (2) The BET specific surface area is 150 to 400 m ² / g (3) The fiber length is 0.5 to 5.0 μm (4) ) in the Raman spectra a maximum peak intensity in the range of 1560~1600cm ^-1 G, the G / D ratio maximum peak intensity upon the D in the range of 1310~1350cm ^-1, 0.7~2 .0 (5) Volume resistivity is 1.0 x 10 ^{-2 to} 1.5 x 10 ^-2 Ω · cm (6) True density is 1.7 to 2.1 g / cc Being The carbon nanotube according to claim 1, wherein the half-value width is 2 to 6 °. The carbon nanotube according to claim 1 or 2, wherein the carbon purity is 95% or more. The carbon nanotube according to any one of claims 1 to 3, wherein the angle of repose is 40 to 70 °. A carbon nanotube dispersion liquid containing the carbon nanotube according to any one of claims 1 to 4, a solvent, and a dispersant. The carbon nanotube dispersion liquid according to claim 5, wherein the dispersant is contained in an amount of 20 to 100 parts by mass with respect to 100 parts by mass of the carbon nanotubes. A dispersion containing 0.5 parts by mass or more and 3.0 parts by mass or less of carbon nanotubes in 100 parts by mass of the carbon nanotube dispersion liquid, and the viscosity measured at a rotor rotation speed of a B-type viscometer at 25 ° C. is 60 rpm. The carbon nanotube dispersion liquid according to claim 5 or 6, characterized in that it is 10 mPa · s or more and less than 2000 mPa · s. The carbon nanotube dispersion liquid according to any one of claims 5 to 7, wherein the solvent contains water. A carbon nanotube resin composition comprising the carbon nanotube dispersion liquid according to any one of claims 5 to 8 and a binder. The carbon nanotube resin composition according to claim 9, wherein the binder contains at least one selected from the group consisting of carboxymethyl cellulose, styrene-butaene rubber, and polyacrylic acid. A mixture slurry comprising the carbon nanotube resin composition according to claim 10 and an active material. An electrode film formed by forming the mixture slurry according to claim 11 in the form of a film. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode includes the electrode film according to claim 12. battery.