Dispersion of carbon nanotubes, coating liquid composition for electrodes using the same, electrodes, and lithium ion secondary batteries

Abstract

To provide a dispersion of carbon nanotubes having excellent dispersibility in an organic solvent.SOLUTION: A dispersion according to an embodiment is obtained by dispersing carbon nanotubes in an organic solvent with a polyimide including an aromatic diamine compound represented by general formula (1) as a polymerization component. In formula (1), R1-R8 are selected from the group consisting of a hydrogen atom, a fluorine atom, a saturated aliphatic group, a saturated alicyclic group, and an aromatic group, and at least one of R1-R8 is an aromatic group.SELECTED DRAWING: None

Description

Technical Field

[0001] Embodiments of the present invention relate to a dispersion obtained by dispersing carbon nanotubes in an organic solvent, an electrode coating liquid composition containing the dispersion, an electrode using the electrode coating liquid composition, and a lithium ion secondary battery including the electrode.

Background Art

[0002] Carbon nanotubes are cylindrical carbons having a diameter on the nanometer scale and have properties such as conductivity, heat conductivity, and mechanical strength. While having such excellent properties, carbon nanotubes have strong aggregation due to van der Waals forces and are difficult to uniformly disperse in an organic solvent.

[0003] In order to improve the dispersibility of carbon nanotubes, Patent Document 1 proposes using a polyamic acid in which at least a part of the diamine component is a unit containing a benzimidazole structure as a dispersant for dispersing carbon nanotubes in a polar organic solvent, and it is also described that the polyamic acid is imidized to be converted into a heat-resistant polyimide.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An embodiment of the present invention aims to provide a dispersion of carbon nanotubes having excellent dispersibility in an organic solvent.

Means for Solving the Problems

[0006] The present invention includes the following embodiments. [1] A dispersion obtained by dispersing carbon nanotubes in an organic solvent with a polyimide containing an aromatic diamine compound represented by the following general formula (1) as a polymerization component. [Chemical formula] (In general formula (1), R 1 ~R 8 are each independently selected from the group consisting of a hydrogen atom, a fluorine atom, a substituted or unsubstituted saturated aliphatic group, a substituted or unsubstituted saturated alicyclic group, and a substituted or unsubstituted aromatic group, and at least one of R 1 ~R 8 is a substituted or unsubstituted aromatic group.) [2] The dispersion according to [1], wherein the aromatic diamine compound contains a compound represented by the following formula (2). [Chemical formula] [3] The dispersion according to [1] or [2], wherein the carbon nanotubes are single-walled carbon nanotubes. [4] The dispersion according to any one of [1] to [3], wherein the organic solvent contains N-methyl-2-pyrrolidone. [5] A coating liquid composition for an electrode containing the dispersion according to any one of [1] to [4]. [6] The coating liquid composition for an electrode according to [5], further containing a silicon-based negative electrode active material. [7] An electrode comprising a layer composed of the solid content of the coating liquid composition for an electrode according to [5] or [6]. [8] A lithium ion secondary battery comprising the electrode according to [7]. [Advantages of the Invention]

[0007] According to an embodiment of the present invention, the dispersibility of carbon nanotubes in an organic solvent can be improved. [Modes for Carrying Out the Invention]

[0008] The dispersion according to this embodiment is a dispersion obtained by dispersing carbon nanotubes in an organic solvent with polyimide, and contains (A) carbon nanotubes, (B) polyimide, and (C) an organic solvent.

[0009] [(A) Carbon nanotubes] Carbon nanotubes are substances in which a six-membered ring network (graphene sheet) composed of carbon is formed into a single-layer or multi-layer coaxial tubular shape. Examples of carbon nanotubes include single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT). Among multi-layers, those with particularly two layers are called double-walled carbon nanotubes (DWCNT), and any one or a combination of two or more of these can be used. Preferably, single-walled carbon nanotubes are used as the carbon nanotubes.

[0010] The manufacturing method of carbon nanotubes is not particularly limited, and can be obtained by various known manufacturing methods such as pyrolysis using a catalyst, arc discharge method, laser evaporation method, and CVD methods such as HiPco method and CoMoCAT method.

[0011] The average diameter of the carbon nanotubes is not particularly limited, and may be 0.5 to 100 nm, or may be 1 to 50 nm. The average length of the carbon nanotubes is not particularly limited, and may be, for example, 50 nm to 10 mm, or may be 500 nm to 100 μm. The aspect ratio of the carbon nanotubes (that is, the ratio of the average length to the average diameter) is not particularly limited, and may be, for example, 10 or more, or may be 100 or more.

[0012] The average diameter and average length of the carbon nanotubes can be determined by measuring the dimensions of 50 randomly selected carbon nanotubes in an atomic force microscope image and taking the arithmetic mean. For lengths on the order of mm that cannot be measured by an atomic force microscope, they can be measured using an image taken by a microscope.

[0013] [(B) Polyimide] Polyimide is a general term for polymers containing imide bonds in repeating units. In this embodiment, a polyimide containing an aromatic diamine compound represented by the following general formula (1) is used as a polymerization component. Here, the polymerization component means a monomer constituting the polyimide. [Chemical formula]

[0014] In general formula (1), R 1 ~R 8 are each independently selected from the group consisting of a hydrogen atom, a fluorine atom, a substituted or unsubstituted saturated aliphatic group, a substituted or unsubstituted saturated alicyclic group, and a substituted or unsubstituted aromatic group, and at least one of R 1 ~R 8 is a substituted or unsubstituted aromatic group. Preferably, one or two of R 1 ~R 8 are substituted or unsubstituted aromatic groups.

[0015] In general formula (1), the saturated aliphatic group is a monovalent saturated aliphatic group, which may be linear or branched. As the saturated aliphatic group, an alkyl group is preferred, but an alkoxy group or an alkylamino group that binds to the main skeleton via an oxygen atom or a nitrogen atom may also be used. The saturated aliphatic group is preferably unsubstituted, but may have a substituent. Examples of the substituent include halogen groups such as a fluoro group and a chloro group, an amino group, a nitro group, a hydroxyl group, a cyano group, a carboxyl group, a sulfonic acid group, etc., and one or more of these substituents may be included.

[0016] The number of carbon atoms in the saturated aliphatic group, preferably an alkyl group, is preferably from 1 to 10, more preferably from 1 to 3. Here, the number of carbon atoms means the number of carbon atoms including the substituent when the substituent contains a carbon atom. Specific examples of the saturated aliphatic group having 1 to 10 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, tert-butyl group, n-pentyl group, sec-pentyl group, n-hexyl group, n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, fluoromethyl group, difluoromethyl group, trifluoromethyl group, chloromethyl group, dichloromethyl group, trichloromethyl group, bromomethyl group, dibromomethyl group, tribromomethyl group, fluoroethyl group, difluoroethyl group, trifluoroethyl group, chloroethyl group, dichloroethyl group, trichloroethyl group, bromoethyl group, dibromoethyl group, tribromoethyl group, hydroxymethyl group, hydroxyethyl group, hydroxylpropyl group, methoxy group, ethoxy group, n-propoxy group, n-butoxy group, n-pentyloxy group, sec-pentyloxy group, n-hexyloxy group, n-heptyloxy group, n-octyloxy group, n-nonyloxy group, n-decyloxy group, trifluoromethoxy group, methylamino group, dimethylamino group, trimethylamino group, ethylamino group, propylamino group, etc. Among these, it is preferable to use a methyl group, an ethyl group, a methoxy group, an ethoxy group, and a trifluoromethyl group from the viewpoints of steric hindrance and the like.

[0017] In the general formula (1), the saturated alicyclic group is a monovalent saturated alicyclic group, and may have an aliphatic group as long as it has a non-aromatic carbon ring. As the saturated alicyclic group, a cycloalkyl group is preferable, but a cycloalkyloxy group or a cycloalkylamino group bonded to the main skeleton via an oxygen atom or a nitrogen atom may also be used. The saturated alicyclic group is preferably unsubstituted, but may have a substituent. Examples of the substituent include an alkyl group, a halogen group such as a fluoro group or a chloro group, an amino group, a nitro group, a hydroxyl group, a cyano group, a carboxyl group, a sulfonic acid group, etc., and one or more of these substituents may be included.

[0018] The carbon number of the saturated alicyclic group, preferably a cycloalkyl group, is preferably 3 to 10. The carbon number referred to here is the number of carbon atoms including substituents when the substituent contains a carbon atom. Specific examples of the saturated alicyclic group having 3 to 10 carbon atoms include a cyclopropyl group, a cyclobutyl group, a cyclopentyl group, a cyclohexyl group, a cycloheptyl group, a cyclohexyloxy group and the like.

[0019] In the general formula (1), the aromatic group is a monovalent aromatic group, and it is preferable that the aromatic ring is directly bonded to the main skeleton, but it may be bonded to the main skeleton via an alkylene group, an oxygen atom or a nitrogen atom. The aromatic group includes a heteroaromatic group such as a pyrrole group. The aromatic group is preferably unsubstituted, but may have a substituent. Examples of the substituent include an alkyl group, an alkoxy group, a halogen group such as a fluoro group and a chloro group, an amino group, a nitro group, a hydroxyl group, a cyano group, a carboxyl group, a sulfonic acid group and the like, and one or more of these substituents may be included.

[0020] The number of carbon atoms in the aromatic group is preferably 5 to 20, more preferably 6 to 10. Here, when the substituent contains a carbon atom, the number of carbon atoms includes the substituent. The aromatic ring contained in the aromatic group is preferably a five-membered ring or more. Specific examples of the aromatic group having 5 to 20 carbon atoms include phenyl group, tolyl group, dimethylphenyl group, ethylphenyl group, diethylphenyl group, propylphenyl group, butylphenyl group, fluorophenyl group, pentafluorophenyl group, chlorophenyl group, bromophenyl group, methoxyphenyl group, dimethoxyphenyl group, ethoxyphenyl group, diethoxyphenyl group, benzyl group, methoxybenzyl group, dimethoxybenzyl group, ethoxybenzyl group, diethoxybenzyl group, aminophenyl group, aminobenzyl group, nitrophenyl group, nitrobenzyl group, cyanophenyl group, cyanobenzyl group, phenethyl group, phenylpropyl group, phenoxy group, benzyloxy group, phenylamino group, diphenylamino group, biphenyl group, naphthyl group, phenylnaphthyl group, anthryl group, anthrylphenyl group, phenylanthryl group, phenanthryl group, phenanthrylphenyl group, phenylphenanthryl group, pyrenyl group, phenylpyrenyl group, fluorenyl group, phenylfluorenyl group, naphthylethyl group, naphthylpropyl group, anthracenylethyl group, phenanthrylethyl group, etc. Specific examples thereof also include heteroaromatic groups such as pyrrole group, imidazole group, thiazole group, oxazole group, furan group, thiophene group, triazole group, pyrazole group, isoxazole group, isothiazole group, pyridine group, pyrimidine group, benzofuran group, benzothiophene group, quinoline group, isoquinoline group, indolyl group, benzothiazolyl group, carbazolyl group. Among these aromatic groups, from the viewpoints of easy availability of starting materials and synthesis cost, phenyl group, phenoxy group, benzyl group and benzyloxy group are preferred.

[0021] In the above general formula (1), one or two of R 5 ~R 8 are preferably a substituted or unsubstituted aromatic group, more preferably at least R 5 or R 7is a substituted or unsubstituted aromatic group. By having an aromatic group at such a position, the steric hindrance of the aromatic diamine compound can be suppressed, and the polymerization reaction with an acid anhydride or the like can proceed favorably.

[0022] In a preferred embodiment, R in the general formula (1) 5 ~R 8 One or two of them are substituted or unsubstituted aromatic groups, and R other than the aromatic group 1 ~R 8 is selected from the group consisting of a hydrogen atom, a fluorine atom, a substituted or unsubstituted saturated aliphatic group, and a substituted or unsubstituted saturated alicyclic group. Specifically, as the aromatic diamine compound represented by the general formula (1), a compound represented by the following formula (2) can be mentioned as a preferred example (in the formula (1), R 7 is an aromatic group, and R 7 other than R 1 ~R 6 and R 8 are hydrogen atoms).

Chemical formula

[0023] In this embodiment, (B) polyimide is a reaction product of a diamine (BX) containing an aromatic diamine compound of the general formula (1) (hereinafter simply referred to as "aromatic diamine (BX1)") and an acid anhydride (BY), and contains the diamine (BX) and the acid anhydride (BY) as polymerization components.

[0024] As the diamine (BX), the aromatic diamine (BX1) alone may be used, or other diamines may be used in combination. Other diamines are not particularly limited, and examples include aromatic diamines (excluding aromatic diamine (BX1)), alicyclic diamines, and aliphatic diamines. Among these, aromatic diamines are preferred.

[0025] Examples of the aromatic diamine other than the aromatic diamine (BX1) include a carboxy group-free aromatic diamine (BX2) and a carboxy group-containing aromatic diamine (BX3). Either one of the carboxy group-free aromatic diamine (BX2) and the carboxy group-containing aromatic diamine (BX3) may be used in combination with the aromatic diamine (BX1), or both may be used in combination.

[0026] Specific examples of the carboxy group-free aromatic diamine (BX2) include bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), diamino diphenyl sulfones such as 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, and 3,7-diamino-dimethyldibenzothiophene 5,5-dioxide, diamino diphenyl propanes such as 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 2,2-bis(4-aminophenyl)propane, and 2,2-bis(3-methyl-4-aminophenyl)propane, diamino diphenoxy benzenes such as 1,3-bis(3-aminophenoxy)benzene (APB-N), 1,3-bis(4-aminophenoxy)benzene (TPE-R), and 1,4-bis(4-aminophenoxy)benzene, diamino benzenes such as m-phenylenediamine, p-phenylenediamine, 2,4-diaminotoluene, 2,4-diamino-3,5-diethyltoluene, and 2,6-diamino-3,5-diethyltoluene, diamino indanes such as 5-amino-1,3,3-trimethyl-1-(4-aminophenyl)indane and 6-amino-1,3,3-trimethyl-1-(4-aminophenyl)indane, diamino biphenyls such as 4,4'-diamino-2,2'-dimethyl-1,1'-biphenyl, 4,4'-diamino-3,3'-dimethyl-1,1'-biphenyl, and 2,2'-bis(trifluoromethyl)benzidine, diamino diphenyl ethers such as 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether, diamino diphenyl sulfides such as 4,4'-diaminodiphenyl sulfide, diamino diphenyl esters such as 4-aminophenyl-4-aminobenzoate, diamino fluorenes such as 4,4'-(9-fluorenylidene)dianiline and 9,9'-bis(3-methyl-4-aminophenyl)fluorene, diamino diphenyl hexafluoropropanes such as 4,4'-(hexafluoroisopropylidene)dianiline, 2,2-bis(3-amino-4-methylphenyl)hexafluoropropane, and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, α,α-bis[4-(4-aminophenoxy)phenyl]-1,3-diisopropylbenzene, α,Diaminodiisopropylbenzenes such as α-bis[4-(4-aminophenoxy)phenyl]-1,4-diisopropylbenzene, 3,3'-diamino-4,4'-dihydroxy-1,1'-biphenyl, 4,4'-diamino-3,3'-dihydroxy-1,1'-biphenyl, 2,2-bis(3-amino-4-hydroxyphenyl)propane, 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane, 1,3-bis(3-hydroxy-4-aminophenoxy)benzene, 2,2-bis(3-hydroxy-4-aminophenyl)benzene, and hydroxy group-containing diamines such as 3,3'-diamino-4,4'-dihydroxydiphenylsulfone. These can be used alone or in combination of two or more. Among these, as the carboxy group-free aromatic diamine (BX2), it is preferable to use diaminodiphenylsulfones such as bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), and / or diaminodiphenylpropanes such as 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP).

[0027] Specific examples of the carboxy group-containing aromatic diamine (BX3) include 5,5'-methylenebis(2-aminobenzoic acid) (MBAA), 4,4'-methylenebis(2-aminobenzoic acid), 1,2-bis(4-amino-3-carboxyphenyl)ethane, 1,2-bis(3-amino-4-carboxyphenyl)ethane, 3,3'-dicarboxybiphenyl-4,4'-diamine, 4,4'-dicarboxybiphenyl-3,3'-diamine, bis(4-amino-3,5-dicarboxyphenyl)methane, 1,2-bis(4-amino-3,5-dicarboxyphenyl)ethane, 3,3',5,5'-tetracarboxybiphenyl-4,4'-diamine, 1,3-bis(4-amino-2-carboxyphenoxy)benzene, 3,5-bis(4-aminophenoxy)benzoic acid, 5-amino-2-(aminophenoxy)benzoic acid, 3,5-diaminobenzoic acid, and the like. These can be used alone or in combination of two or more. Among these, as the carboxy group-containing aromatic diamine (BX3), it is preferable to use at least one selected from the group consisting of 5,5'-methylenebis(2-aminobenzoic acid) (MBAA), 1,2-bis(4-amino-3-carboxyphenyl)ethane, and 3,3'-dicarboxybiphenyl-4,4'-diamine.

[0028] The amount of the aromatic diamine (BX1) contained in the diamine (BX) is not particularly limited, and the aromatic diamine (BX1) may be 10 to 100 mol% with respect to 100 mol% of the diamine (BX), preferably 20 to 80 mol%, and more preferably 30 to 70 mol%.

[0029] The diamine (BX) as a polymerization component may contain an aromatic diamine (BX1) and a carboxy group-free aromatic diamine (BX2). In that case, with respect to 100 mol% of the diamine (BX), it is preferable that the aromatic diamine (BX1) is 20 to 80 mol% and the carboxy group-free aromatic diamine (BX2) is 20 to 80 mol%, and more preferably the aromatic diamine (BX1) is 30 to 70 mol% and the carboxy group-free aromatic diamine (BX2) is 30 to 70 mol%.

[0030] The diamine (BX) as a polymerization component may contain an aromatic diamine (BX1), a carboxyl group-free aromatic diamine (BX2), and a carboxyl group-containing aromatic diamine (BX3). In that case, based on 100 mol% of the diamine (BX), it is preferable that the aromatic diamine (BX1) is 10 to 60 mol%, the carboxyl group-free aromatic diamine (BX2) is 10 to 60 mol%, and the carboxyl group-containing aromatic diamine (BX3) is 10 to 60 mol%. More preferably, the aromatic diamine (BX1) is 20 to 40 mol%, the carboxyl group-free aromatic diamine (BX2) is 20 to 40 mol%, and the carboxyl group-containing aromatic diamine (BX3) is 20 to 40 mol%.

[0031] When using the aromatic diamine (BX1) and the carboxyl group-free aromatic diamine (BX2) in combination as the diamine (BX), the molar ratio BX1 / BX2 of the two is preferably 1 / 3 to 3 / 1, more preferably 1 / 2 to 2 / 1, and even more preferably 2 / 3 to 3 / 2.

[0032] The acid anhydride (BY) as a polymerization component is not particularly limited, and an aromatic acid anhydride, an alicyclic acid anhydride, or an aliphatic acid anhydride can be used. Any one of these may be used, or two or more thereof may be used in combination. Preferably, the acid anhydride (BY) contains an aromatic acid anhydride.

[0033] As the aromatic acid anhydride, an aromatic tetracarboxylic dianhydride can be used. Specific examples thereof include 4,4'-oxydiphthalic anhydride (ODPA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, pyrromellitic dianhydride, 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 2,2',3,3'-benzophenonetetracarboxylic dianhydride, 2,2-bis[3-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride, 1,2,5,5-benzenetetracarboxylic dianhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, methylene-4,4'-diphthalic anhydride, 1,3-bis[2-(3,4-dicarboxyphenyl)-2-propyl]benzene dianhydride, bis[3-(3,4-dicarboxyphenoxy)phenyl]methane dianhydride, difluoromethylene-4,4'-diphthalic anhydride, 3,3',4,4'-diphenylsulfonetetracarboxylic dianhydride, bis(3,4-dicarboxyphenyl) ether dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 9,9-bis(3,4-dicarboxyphenyl)fluorene dianhydride, 4,4'-[4,4'-(propane-2,2-diyl)diphenoxy]diphthalic anhydride, and the like. Any one of these or a combination of two or more thereof can be used.

[0034] As the alicyclic acid anhydride, an alicyclic tetracarboxylic dianhydride can be used. Specific examples thereof include norbornane-2-spiro-α-cyclopentanone-α'-spiro-2''-norbornane-5,5'',6,6''-tetracarboxylic dianhydride (CpODA), bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BTA), 1,2,4,5-cyclohexanetetracarboxylic dianhydride, 1,1'-bicyclohexane-3,3',4,4'-tetracarboxylic dianhydride, methylene-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, oxy-4,4'-bis(cyclohexane-1,2-dicarboxylic acid) dianhydride, and the like. These can be used alone or in combination of two or more thereof.

[0035] As the aliphatic acid anhydride, an aliphatic tetracarboxylic dianhydride can be used. Specific examples thereof include 1,2,3,4-butanetetracarboxylic dianhydride and the like.

[0036] Among the above, as the acid anhydride (BY), it is preferable to use at least one selected from the group consisting of 4,4'-oxydiphthalic dianhydride (ODPA), 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), and 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA).

[0037] In one embodiment, (B) the polyimide may contain, as polymerization components, an aromatic diamine (BX1), a carboxyl group-free aromatic diamine (BX2), and an aromatic acid anhydride. In another embodiment, (B) the polyimide may contain, as polymerization components, an aromatic diamine (BX1), a carboxyl group-free aromatic diamine (BX2), a carboxyl group-containing aromatic diamine (BX3), and an aromatic acid anhydride.

[0038] The number average molecular weight (Mn) of the (B) polyimide, which is a reaction product of a diamine (BX) containing an aromatic diamine (BX1) and an acid anhydride (BY), is not particularly limited, and may be, for example, 20,000 to 150,000, or may be 30,000 to 100,000. Here, the number average molecular weight is a polystyrene conversion value based on a calibration curve prepared using standard polystyrene by a gel permeation chromatography (GPC) apparatus. For example, as the measurement conditions of GPC, the column: two Shodex OH pak SB-806M (8.0 mmφ×300 mm) manufactured by Showa Denko KK, mobile phase: N,N-dimethylformamide containing 50 mmol / L lithium bromide, flow rate: 0.5 mL / min, column temperature: 50 °C, injection volume: 100 μL, sample concentration: 0.1 mass% can be used.

[0039] (B) The method for synthesizing the polyimide is not particularly limited, and it can be synthesized by a known method. Specifically, (B) the polyimide can be obtained by reacting a diamine (BX) and an acid anhydride (BY) to obtain a polyamic acid, and then performing a cyclodehydration reaction to convert it into a polyimide.

[0040] The mixing ratio of the diamine (BX) and the acid anhydride (BY) is not particularly limited, but the molar ratio BX / BY of the diamine (BX) to the acid anhydride (BY) is preferably 50 / 100 to 150 / 100, and more preferably 90 / 100 to 110 / 100.

[0041] The reaction between diamine (BX) and acid anhydride (BY) may be carried out in an organic solvent. The organic solvent is not particularly limited as long as it does not react with diamine (BX) and acid anhydride (BY) and can dissolve the reaction product of diamine (BX) and acid anhydride (BY). Specific examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide (DMF), N,N-diethylformamide, N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, 1,3-dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO), γ-butyrolactone, and the like. These can be used alone or in combination of two or more.

[0042] The imidization reaction (cyclization dehydration reaction) may be a chemical imidization or a thermal imidization. An imidization catalyst may be used during the cyclization dehydration reaction. For example, trimethylamine, triethylamine, propylamine, aniline, benzylamine, toluidine, pyridine, picoline, quinoline, isoquinoline, etc. can be used. Further, if necessary, an azeotropic dehydrating agent such as toluene, xylene, ethylcyclohexane, or an acid catalyst such as acetic anhydride, propionic anhydride, butyric anhydride, benzoic anhydride, etc. may be used. Also, a sealing agent such as benzoic acid, phthalic anhydride, hydrogenated phthalic anhydride, etc. may be used for the reaction between diamine and acid anhydride.

[0043] [(C) Organic solvent] The (C) organic solvent contained in the dispersion according to this embodiment may be the organic solvent used during the synthesis reaction of the above polyimide, or may be an organic solvent different from that used during the synthesis reaction. Preferably, it contains the organic solvent used during the synthesis reaction.

[0044] (C) Specific examples of the organic solvent include polar organic solvents such as N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide (DMF), N,N-diethylformamide, N,N-dimethylacetamide (DMAc), N,N-diethylacetamide, 1,3-dimethyl-2-imidazolidinone (DMI), dimethyl sulfoxide (DMSO), γ-butyrolactone, etc. Any one or a combination of two or more of these can be used. Among these, as the (C) organic solvent, an amide-based solvent composed of amides is preferable, and more preferably N-methyl-2-pyrrolidone is used.

[0045] In one embodiment, the (C) organic solvent may be N-methyl-2-pyrrolidone alone, or N-methyl-2-pyrrolidone and other organic solvents may be used in combination. It is preferable that 50% by mass or more of the (C) organic solvent is N-methyl-2-pyrrolidone, and more preferably 80% by mass or more (i.e., 80 - 100% by mass) is N-methyl-2-pyrrolidone.

[0046] [Dispersion] The dispersion according to this embodiment is a dispersion liquid obtained by dispersing (A) carbon nanotubes in (C) an organic solvent with (B) polyimide, and (B) polyimide has a function as a dispersant for dispersing (A) carbon nanotubes in (C) an organic solvent.

[0047] In the dispersion according to this embodiment, the content of (A) carbon nanotubes is not particularly limited, and may be, for example, 0.05 - 2.0% by mass or 0.2 - 1.0% by mass with respect to 100% by mass of the dispersion.

[0048] The content of (B) polyimide in the dispersion is not particularly limited as long as (A) carbon nanotubes can be dispersed in (C) an organic solvent. The content of (B) polyimide is preferably, for example, 0.5 - 10.0% by mass with respect to 100% by mass of the dispersion, and more preferably 1.0 - 4.0% by mass.

[0049] The content of the organic solvent (C) in the dispersion is not particularly limited, and may be, for example, 88.0 to 99.4% by mass, or 95.0 to 98.8% by mass, based on 100% by mass of the dispersion.

[0050] The method for producing the dispersion is not particularly limited as long as the carbon nanotubes are dispersed in the organic solvent. For example, carbon nanotubes and polyimide may be added to the organic solvent for dispersion treatment. Alternatively, after adding carbon nanotubes to the organic solvent for dispersion treatment, polyimide may be added for further dispersion treatment. In that case, as the polyimide, a polyimide solution synthesized in the organic solvent may be used.

[0051] The method for the dispersion treatment for dispersing the carbon nanotubes is not particularly limited, and examples include stirring treatment and ultrasonic treatment. Examples of the stirring treatment include high-speed stirring such as a homomixer or a homogenizer, media mills such as a bead mill, a sand mill, and a planetary mill, and planetary rotation stirring. Examples of the ultrasonic treatment include treatment using a bath-type or probe-type sonicator.

[0052] The dispersion according to the present embodiment may contain an additive in addition to (A) carbon nanotubes, (B) polyimide, and (C) organic solvent. Examples of the additive include a weathering agent, an antibacterial agent, an antifungal agent, a pigment, a rust preventive agent, a dye, a film-forming aid, a silane coupling agent, an antiblocking agent, a viscosity modifier, a leveling agent, an antifoaming agent, a dispersion stabilizer, a light stabilizer, an antioxidant, an ultraviolet absorber, an inorganic filler, an organic filler, a plasticizer, a lubricant, an antistatic agent, etc.

[0053] [Coating Liquid Composition for Electrode] In one embodiment, the above dispersion is used as a coating liquid for an electrode. That is, the coating liquid composition for an electrode according to one embodiment contains the dispersion according to the above embodiment.

[0054] The electrode coating liquid composition is used, for example, to form an active material layer on a current collector in an electrode including the current collector and the active material layer formed thereon. In that case, the electrode coating liquid composition may contain an electrode active material and a conductive agent together with the dispersion containing the above-mentioned (A) carbon nanotube, (B) polyimide, and (C) organic solvent.

[0055] As one of the causes of the decrease in discharge capacity with the progress of charge-discharge cycles at the negative electrode of a lithium-ion battery, loss of contact between active material particles due to expansion and contraction of the electrode active material is cited. (A) Carbon nanotubes play a role in securing a conductive path connecting the active materials with lost contact. (B) Polyimide contained in the dispersion functions as a dispersant for dispersing (A) carbon nanotubes in the dispersion, and in the electrode coating liquid composition, it functions as a binder for fixing the electrode active materials to each other or the electrode active materials and the conductive agent to the current collector. According to this embodiment, as described above, (B) polyimide is excellent in the dispersibility of (A) carbon nanotubes and also excellent in adhesion and durability, so that the number of conductive paths in the cycle test can be significantly increased, and therefore, it leads to an improvement in the performance of a battery including an electrode produced using the electrode coating liquid composition.

[0056] The electrode coating liquid composition is preferably used for the electrodes of a lithium-ion secondary battery, and more preferably used for its negative electrode. Therefore, the electrode active material contained in the electrode coating liquid composition is preferably a negative electrode active material.

[0057] Examples of the negative electrode active material include silicon-based negative electrode active materials, metallic lithium, metal oxides, graphite, etc., and any one or a combination of two or more of these can be used.

[0058] In one embodiment, the negative electrode active material preferably contains a silicon-based negative electrode active material. The silicon-based negative electrode active material contains silicon (atoms) and is a material capable of electrochemically occluding and releasing lithium ions. Examples of the silicon-based negative electrode active material include particles of elemental silicon and particles of a silicon compound. Examples of the silicon compound include an alloy of at least one metal selected from the group consisting of tin, nickel, iron, copper, silver, cobalt, manganese, and zinc and silicon, and a compound of at least one selected from the group consisting of boron, nitrogen, oxygen, and carbon and silicon. Specific examples of the silicon-based negative electrode active material include SiO, SiO2, SiB4, Mg2Si, Ni2Si, CoSi2, NiSi2, Cu5Si, FeSi2, MnSi2, ZnSi2, SiC, Si3N4, and Si2N2O.

[0059] Examples of the conductive agent contained in the coating liquid composition for an electrode include carbon black (such as acetylene black, ketjen black, furnace black, etc.), graphite, carbon fiber, carbon flake, metal fiber, and foil, etc. Any one of these or a combination of two or more thereof can be used. Among these, carbon black is preferable, and acetylene black is more preferable.

[0060] The content of (A) carbon nanotubes in the solid content of the coating liquid composition for an electrode is not particularly limited, and may be, for example, 0.01 to 1.0% by mass or 0.05 to 0.5% by mass. The content of (B) polyimide in the solid content of the coating liquid composition for an electrode is not particularly limited, and may be, for example, 0.5 to 30% by mass or 3 to 20% by mass. The content of (C) organic solvent in the coating liquid composition for an electrode is not particularly limited, and may be, for example, 20 to 80% by mass or 40 to 70% by mass. The content of the electrode active material in the solid content of the coating liquid composition for an electrode is not particularly limited, and may be, for example, 65 to 99% by mass or 75 to 95% by mass. The content of the conductive agent in the solid content of the coating liquid composition for an electrode is not particularly limited, and may be, for example, 0.1 to 25% by mass or 1 to 20% by mass.

[0061] In addition to the above components, the electrode coating liquid composition may further contain additives such as weathering agents, antibacterial agents, antifungal agents, pigments, rust preventives, dyes, film-forming aids, silane coupling agents, anti-blocking agents, viscosity modifiers, leveling agents, defoaming agents, dispersion stabilizers, light stabilizers, antioxidants, ultraviolet absorbers, inorganic fillers, organic fillers, plasticizers, lubricants, antistatic agents, etc.

[0062] [Electrode] The electrode according to the embodiment includes a layer composed of the solid content of the above electrode coating liquid composition. In one embodiment, the electrode may include a current collector and an active material layer (preferably a negative electrode active material layer) formed on the current collector. In that case, the active material layer is a layer composed of the solid content of the above electrode coating liquid composition. Therefore, the active material layer may contain (A) carbon nanotubes, (B) polyimide, an electrode active material (preferably a negative electrode active material), and a conductive agent.

[0063] The active material layer can be formed, for example, by coating the electrode coating liquid composition on the current collector and drying it. The thickness of the active material layer is not particularly limited, and may be, for example, 15 to 150 μm.

[0064] The current collector is not particularly limited as long as it is an electronic conductor that does not have an adverse effect on the constructed battery. For example, as the current collector, in addition to copper, stainless steel, nickel, aluminum, titanium, fired carbon, conductive polymers, conductive glass, Al-Cd alloys, etc., for the purpose of improving adhesion, conductivity, and oxidation resistance, those obtained by treating the surface of copper, etc. with carbon, nickel, titanium, silver, etc. can be used. Regarding the shape of the current collector, in addition to foil shape, film shape, sheet shape, net shape, punched or expanded materials, molded bodies such as lattices, porous bodies, and foams are also used.

[0065] [Lithium-ion secondary battery] The lithium-ion secondary battery according to the embodiment includes the above electrode, and preferably includes the above electrode as a negative electrode. Specifically, the lithium-ion secondary battery includes a negative electrode, a positive electrode, a separator disposed between the negative electrode and the positive electrode, and an electrolyte, and an electrode prepared using the above electrode coating liquid composition is used for the negative electrode. Known configurations can be adopted for the positive electrode, separator, and electrolyte, and they are not particularly limited.

[0066] As one embodiment, the lithium-ion secondary battery may include a laminate in which a negative electrode and a positive electrode are alternately laminated via a separator, a container that houses the laminate, and an electrolyte such as a non-aqueous electrolyte injected into the container. As the non-aqueous electrolyte, for example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in an organic solvent can be used to configure the lithium-ion secondary battery.

Examples

[0067] Hereinafter, a more detailed description will be given based on examples and comparative examples, but the present invention is not limited thereto.

[0068] The chemical formulas of the diamine and acid anhydride used in the examples are shown below. (Diamine)

Chemical formula

Chemical formula

Chemical formula

Chemical formula

Chemical formula

[0069] (Acid anhydride)

Chemical formula

[0070] Details of the carbon nanotubes used in the examples are as follows. · Carbon nanotubes: Single-walled carbon nanotubes (SWCNT). Carbon purity > 99%, average diameter = 1.6 nm. "TUBALL BATT" manufactured by OCSiAL

[0071] The synthesis methods of polyimides - 1 to 5 are as follows. (Synthesis Example 1: Polyimide - 1) 43.25 g (100 mmol) of bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), an aromatic diamine compound represented by the above formula, 30.43 g (100 mmol) of (2-phenyl-4-aminophenyl)-4-aminobenzoate (PHBAAB), an aromatic diamine compound represented by the above formula, 62.04 g (200 mmol) of 4,4'-oxydiphthalic anhydride (ODPA) represented by the above formula, 868 g of N-methyl-2-pyrrolidone, 4.0 g (50 mmol) of pyridine, and 87 g of toluene were charged into a 2000 ml separable flask equipped with a nitrogen inlet tube and a stirrer, and reacted at 180°C for 6 hours while removing toluene out of the system under a nitrogen atmosphere to obtain a 15% by mass polyimide solution.

[0072] (Synthesis Example 2: Polyimide - 2) Into a 2000 ml separable flask equipped with a nitrogen inlet tube and a stirring device, 28.83 g (67 mmol) of bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), which is an aromatic diamine compound represented by the above formula, 20.29 g (67 mmol) of (2-phenyl-4-aminophenyl)-4-aminobenzoate (PHBAAB), which is an aromatic diamine compound represented by the above formula, 19.09 g (67 mmol) of 5,5'-methylenebis(2-aminobenzoic acid) (MBAA), which is an aromatic diamine compound represented by the above formula, 29.42 g (100 mmol) of diphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA), which is represented by the above formula, 31.02 g (100 mmol) of 4,4'-oxydiphthalic anhydride (ODPA), which is represented by the above formula, 868 g of N-methyl-2-pyrrolidone, 4.0 g (50 mmol) of pyridine and 87 g of toluene were charged, and the mixture was reacted at 180 °C for 6 hours while removing toluene outside the system during the reaction under a nitrogen atmosphere to obtain a 15% by mass polyimide solution.

[0073] (Synthesis Example 3: Polyimide-3) Into a 2000 ml separable flask equipped with a nitrogen inlet tube and a stirring device, 86.50 g (200 mmol) of bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), which is an aromatic diamine compound represented by the above formula, 29.42 g (100 mmol) of diphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA), which is represented by the above formula, 31.02 g (100 mmol) of 4,4'-oxydiphthalic anhydride (ODPA), which is represented by the above formula, 868 g of N-methyl-2-pyrrolidone, 4.0 g (50 mmol) of pyridine and 87 g of toluene were charged, and the mixture was reacted at 180 °C for 6 hours while removing toluene outside the system during the reaction under a nitrogen atmosphere to obtain a 15% by mass polyimide solution.

[0074] (Synthesis Example 4: Polyimide-4) Into a 2000 ml separable flask equipped with a nitrogen inlet tube and a stirring device, 41.05 g (100 mmol) of 2,2'-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), an aromatic diamine compound represented by the above formula, 29.23 g (100 mmol) of 1,3-bis(3-aminophenoxy)benzene (APB-N), an aromatic diamine compound represented by the above formula, 32.22 g (100 mmol) of 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), an aromatic diamine compound represented by the above formula, 31.02 g (100 mmol) of 4,4'-oxydiphthalic anhydride (ODPA), 868 g of N-methyl-2-pyrrolidone, 4.0 g (50 mmol) of pyridine and 87 g of toluene were added, and the mixture was reacted at 180 °C for 6 hours while removing toluene outside the system during the reaction under a nitrogen atmosphere to obtain a 15% by mass polyimide solution.

[0075] (Synthesis Example 5: Polyimide-5) Into a 2000 ml separable flask equipped with a nitrogen inlet tube and a stirring device, 86.50 g (200 mmol) of bis[4-(4-aminophenoxy)phenyl]sulfone (BAPS), an aromatic diamine compound represented by the above formula, 76.88 g (200 mmol) of 2'-oxodispiro[bicylco[2.2.1]heptane-2,1'-cyclopentane-3',2''-bicylco[2.2.1]heptane]-5,6:5'',6''-tetracarboxylic dianhydride (CpODA), an aromatic diamine compound represented by the above formula, 868 g of N-methyl-2-pyrrolidone, 4.0 g (50 mmol) of pyridine and 87 g of toluene were added, and the mixture was reacted at 180 °C for 10 hours while removing toluene outside the system during the reaction under a nitrogen atmosphere to obtain a 15% by mass polyimide solution.

[0076] (Dispersion evaluation method) The dispersion of carbon nanotubes in Examples and Comparative Examples was evaluated using pulsed NMR. As the apparatus, "Spin Track TD-NMR Spectrometer" manufactured by RESONANCE SYSTEMS was used, and the observed nucleus was 1With the resonance frequency at 14 MHz and the measurement unit temperature-controlled at 30 °C, the relaxation time of the solvent molecules in the dispersion was measured.

[0077] In pulsed NMR, the affinity between the particles and the solvent can be evaluated by measuring the relaxation time of the solvent molecules in the dispersion. Relaxation refers to the process by which the energy once absorbed decays. The relaxation time of the free liquid (bulk liquid) not in contact with the particle surface is long. On the other hand, the relaxation time of the liquid in contact with the particle surface is short. Therefore, the shorter the relaxation time, the larger the surface area of the carbon nanotubes in contact with the solvent, and the higher the dispersibility of the carbon nanotubes. The R2sp value is a value normalized by the relaxation time of the solvent and is calculated by the following formula. The larger the R2sp, the more solvent can be constrained at the particle interface, which means the larger the surface area of the carbon nanotubes, that is, the higher the dispersibility of the carbon nanotubes. R2sp value = Rav ÷ Rb - 1 In the formula, Rav: average relaxation constant (reciprocal of the relaxation time of the sample), Rb: relaxation constant of bulk water molecules (reciprocal of the relaxation time of blank water).

[0078] (Test Example 1: Examples 1 - 3 and Comparative Examples 1 - 3) In Examples 1 - 3, to the disperser "Stirring and Defoaming Device Kakuhunter SK400TR" manufactured by Shashin Kagaku Co., Ltd., polyimide - 1 obtained in Synthesis Example 1, carbon nanotubes, and N - methyl - 2 - pyrrolidone were added such that the concentration of polyimide - 1 in the whole mixture was 2% by mass and the concentration of carbon nanotubes was 0.4% by mass (total weight of the mixture 80 g), and a rough mixing process was carried out under the conditions (revolution speed, rotation speed, and treatment time) shown in Table 1 below, and then a dispersion process was carried out to obtain a dispersion of carbon nanotubes. Specifically, in the rough mixing process, the revolution speed = 300 rpm, the rotation speed = 300 rpm, and the time = 15 minutes, and in the dispersion process, the revolution speed = 1400 rpm, the rotation speed = 2000 rpm, and the time was set to 10 minutes (Example 1), 35 minutes (Example 2), and 60 minutes (Example 3).

[0079] In Comparative Examples 1 to 3, instead of Polyimide-1, Polyimide-5 obtained in Synthesis Example 5 was used, and in other respects, in the same manner as in Examples 1 to 3, a dispersion of carbon nanotubes was obtained.

[0080]

Table 1

[0081] When the dispersibility of the carbon nanotubes in the obtained dispersions of Examples 1 to 3 and Comparative Examples 1 to 3 was evaluated, as shown in Table 1, in Examples 1 to 3, compared with Comparative Examples 1 to 3, the relaxation time was small and R2sp was large. Therefore, the dispersibility of the carbon nanotubes was significantly improved.

[0082] (Test Example 2: Examples 4, 5 and Comparative Examples 4 to 6) In Example 4, to the disperser “Stirring and Defoaming Device Kakuhunter SK400TR” manufactured by Shashin Kagaku Co., Ltd., Polyimide-1 obtained in Synthesis Example 1, carbon nanotubes and N-methyl-2-pyrrolidone were added so that the concentration of Polyimide-1 in the whole mixture was 2% by mass and the concentration of carbon nanotubes was 0.4% by mass (total weight of the mixture: 80 g). After performing a rough mixing treatment at a revolution speed = 300 rpm, a rotation speed = 300 rpm, and a time = 15 minutes, a dispersion treatment was performed at a revolution speed = 1400 rpm, a rotation speed = 2000 rpm, and a time = 35 minutes to obtain a dispersion of carbon nanotubes.

[0083] Instead of Polyimide-1, in Example 5, Polyimide-2 obtained in Synthesis Example 2 was used, in Comparative Example 4, Polyimide-3 obtained in Synthesis Example 3 was used, in Comparative Example 5, Polyimide-4 obtained in Synthesis Example 4 was used, and in Comparative Example 6, Polyimide-5 obtained in Synthesis Example 5 was used. In other respects, in the same manner as in Example 4, dispersions of carbon nanotubes were obtained respectively.

[0084]

Table 2

[0085] The dispersibility of the carbon nanotubes in the obtained dispersions of Example 4 and 5 and Comparative Examples 4 to 6 was evaluated. As shown in Table 2, in Examples 4 and 5, the relaxation time was shorter and R2sp was larger than those in Comparative Examples 4 to 6. Therefore, the dispersibility of the carbon nanotubes was significantly improved.

[0086] In addition, various numerical ranges described in the specification can be arbitrarily combined with their upper and lower limit values, and all such combinations are described in this specification as preferred numerical ranges. Also, the description of the numerical range "X to Y" means X or more and Y or less.

[0087] As described above, some embodiments of the present invention have been described. However, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and their omissions, replacements, changes, etc. are included in the scope and gist of the invention, and are also included in the invention described in the claims and its equivalent scope.

Claims

1. A dispersion obtained by dispersing carbon nanotubes in an organic solvent with a polyimide containing an aromatic diamine compound represented by the following general formula (1) as a polymerization component. 【Chemical 1】 In general formula (1), R １ ~R ８ are each independently selected from the group consisting of a hydrogen atom, a fluorine atom, a substituted or unsubstituted saturated aliphatic group, a substituted or unsubstituted saturated alicyclic group, and a substituted or unsubstituted aromatic group, and at least one of R １ ~R ８ is a substituted or unsubstituted aromatic group. Dispersion.

2. The dispersion according to Claim 1, wherein the aromatic diamine compound contains a compound represented by the following formula (2). 【Chemical Formula 2】 The dispersion according to Claim 1.

3. The dispersion according to Claim 1 or 2, wherein the carbon nanotubes are single-walled carbon nanotubes.

4. The dispersion according to any one of Claims 1 to 3, wherein the organic solvent contains N-methyl-2-pyrrolidone.

5. An electrode coating liquid composition containing the dispersion according to any one of Claims 1 to 4.

6. The electrode coating liquid composition according to Claim 5, further containing a silicon-based negative electrode active material.

7. An electrode comprising a layer composed of the solid content of the electrode coating liquid composition according to Claim 5 or 6.

8. A lithium ion secondary battery comprising the electrode according to Claim 7.

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