Carbonaceous material dispersion and method for producing same

Abstract

To provide a carbonaceous material dispersion in which a carbonaceous material is dispersed in high concentration and homogeneously, which can be easily applied, and which can stably exhibit very excellent electrical characteristics when used as a conductive auxiliary for lithium ion secondary batteries.SOLUTION: There is provided a carbonaceous material dispersion in which a carbonaceous material is dispersed in a nonaqueous solvent consisting of a nitrogen-containing heterocyclic amide compound having a solvent purity of 99.9% or more. The carbonaceous material dispersion has a carbonaceous material concentration of 15 to 30 mass% relative to the total mass, an amine component concentration in the dispersion excluding a predetermined amine compound to be added as necessary that is less than 3×10-6 by mass, and a water concentration in the dispersion that is less than 1×10-3.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a carbonaceous material dispersion and a method for producing the same. More specifically, the present invention relates to a carbonaceous material dispersion that is suitably used as a conductive additive in forming an electrode layer in the field of batteries, particularly in the production of lithium ion secondary batteries, and a method for producing the same. [Background technology]

[0002] In recent years, high-capacity, high-power lithium-ion secondary batteries have been widely used in many fields, including electronic devices such as portable personal computers, smartphones, and mobile phones, as well as in the automotive field, including electric vehicles and hybrid vehicles. Further development in these fields requires improved performance of lithium-ion secondary batteries and more efficient production processes.

[0003] Electrodes used in lithium-ion secondary batteries are generally produced by applying an electrode slurry to a current collector, drying it, and then compressing it with a press. The electrode slurry is prepared by mixing an electrode active material, a conductive additive, a binder, etc. in a solvent.

[0004] In order to efficiently prepare such electrode slurries, it has been proposed to use a carbonaceous material dispersion in which a carbonaceous material serving as a conductive aid is dispersed in advance in a solvent (for example, Patent Documents 1 to 3). When an electrode slurry is prepared using a carbonaceous material dispersion, the carbonaceous material dispersion and the electrode active material can be easily mixed, and an electrode with good conductivity in which the carbonaceous material is uniformly dispersed can be obtained.

[0005] For example, in the positive electrode of a lithium ion secondary battery, lithium transition metal composite oxides such as lithium cobalt oxide and lithium manganese oxide are used as the positive electrode active material, but these oxides themselves have poor electronic conductivity, i.e., electrical conductivity. Therefore, in order to impart electrical conductivity to the lithium transition metal composite oxides, carbonaceous materials such as carbon black, graphite, carbon nanotubes, and carbon nanofibers are added to the electrode as conductive additives.

[0006] Regarding the properties required for a carbonaceous material dispersion, for example, Patent Document 4 describes that the dispersion state of a carbonaceous material such as carbon black in the carbonaceous material dispersion mixed with a positive electrode agent paste affects battery performance.

[0007] The carbonaceous material dispersion liquid should have a low viscosity to make it easier to mix when it is made into a paste and kneaded into the positive electrode active material. Furthermore, a low viscosity carbonaceous material dispersion liquid is also desirable when pre-processing, such as filtering, to remove impurities, to prevent contamination of the battery material with other metal particles. On the other hand, since the solvent must be dried in the final step of electrode production, a small amount of solvent is desirable.

[0008] To make a paste for the positive electrode, the positive electrode active material and conductive additive must be mixed evenly and dispersed in a way that maintains the conductive additive's conductivity. Furthermore, binder components such as polyvinylidene fluoride (PVdF) are dissolved in the paste for bonding to metal foil. A non-aqueous solvent, such as N-methyl-2-pyrrolidone (NMP), is used as the solvent.

[0009] Conventionally, in order to achieve the above-described low viscosity in a carbonaceous material dispersion, an amine-based compound, which is a volatile pH adjuster, has been added. However, even when such an amine-based compound is added, the properties of the carbonaceous material dispersion are not stable, and the viscosity does not remain constant.

[0010] Patent Document 5 proposes a technique for dissolving polyvinylidene fluoride in a solvent containing a nitrogen-containing heterocyclic amide compound, such as 2-pyrrolidone or N-methyl-2-pyrrolidone, and applying the resulting resin solution to the surface of a substrate, such as a metal plate or a resin molded body, to form a coating that imparts water resistance and weather resistance to the substrate. However, the technique suggests that the resin solution is discolored by trace impurities contained in the nitrogen-containing heterocyclic amide compound solvent, resulting in a coating formed using the solution that is discolored. For example, when a resin container containing the coating is used as a transport container for precision components such as LEDs or ICs, the presence of impurities in the coating can cause malfunctions in electronic devices and automotive parts incorporating these precision components. To solve this problem, the technique proposes using a nitrogen-containing heterocyclic amide compound that has been (i) previously contacted with a solid acidic substance, or (ii) recovered by distillation after contact with an acidic substance. The technique also reports that, while these discoloring impurities cannot be removed by simply distilling the nitrogen-containing heterocyclic amide compound, the discoloration problem is resolved by using a compound treated by the above method. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-30777 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-46188 [Patent Document 3] JP 2018-45820 A [Patent Document 4] International Publication WO2014 / 042266 [Patent Document 5] Japanese Patent Application Publication No. 10-310795 Summary of the Invention [Problem to be solved by the invention]

[0012] As described above, conventional carbonaceous material dispersions have been required to have stable performance, to have the carbonaceous material dispersed uniformly at a high concentration, and to be easily coatable, but none of them have had properties that are sufficiently satisfactory for practical use.

[0013] Therefore, an object of the present invention is to provide an improved carbonaceous material dispersion. Another object of the present invention is to provide a carbonaceous material dispersion that is suitable as a conductive additive dispersion for lithium-ion secondary batteries, and a method for producing the same. A further object of the present invention is to provide a carbonaceous material dispersion in which a carbonaceous material is uniformly dispersed at a high concentration and that can be easily applied, and a method for producing the same. A further object of the present invention is to provide a carbonaceous material dispersion that can stably exhibit very excellent electrical properties when used as a conductive additive for lithium-ion secondary batteries, and a method for producing the same. [Means for solving the problem]

[0014] The present inventors have conducted extensive research into producing a carbonaceous material dispersion liquid that solves the above-mentioned problems, and as a result have found that nitrogen-containing heterocyclic amide compounds such as N-methyl-2-pyrrolidone often contain amine components as impurities, and that when an electrode for a lithium ion secondary battery is formed using the carbonaceous material dispersion liquid, the amine components as impurities can cause the viscosity to vary from lot to lot, resulting in adverse effects such as coating problems.

[0015] As mentioned above, electrode pastes contain binder components such as polyvinylidene fluoride (PVdF) for bonding to metal foils. Nitrogen-containing heterocyclic amide compounds such as N-methyl-2-pyrrolidone are solvents capable of dissolving binder components such as PVdF. However, because PVdF is a fluorine-based resin, some of the amine components contained as impurities in nitrogen-containing heterocyclic amide compounds are thought to cause dehydrofluorination reactions with basic substances in the presence of moisture. In fact, we found that the more strongly amine components affect PVdF, the more likely they are to cause coloration and a greater change in the UV absorption spectrum. Using this UV absorption spectrum as an indicator, our research also revealed that the degree of influence on PVdF varies depending on the type of amine.

[0016] In light of these points, the present inventors have discovered that, when producing a carbonaceous material dispersion, by controlling the amine component concentration and water concentration in a nitrogen-containing heterocyclic amide compound such as N-methyl-2-pyrrolidone used as a non-aqueous solvent so that they are not more than predetermined levels, and by preparing a carbonaceous material dispersion using a non-aqueous solvent that satisfies these predetermined conditions, the carbonaceous material dispersion will have a low viscosity even when the carbonaceous material concentration is as high as 15 to 30 mass %, and that even when the obtained carbonaceous material dispersion is used to produce an electrode slurry for a lithium ion secondary battery, for example, the viscosity of the slurry will be constant for each lot, and an electrode that stably exhibits very excellent electrical properties can be formed, thereby arriving at the present invention.

[0017] In the present invention, a specific amine compound, which is a volatile pH adjuster, is added as needed to achieve low viscosity. This specific amine compound has little effect on the binder, such as polyvinylidene fluoride resin, and is highly effective in dispersing carbonaceous materials. By eliminating unspecified amine compounds contained as impurities in nitrogen-containing heterocyclic amide compounds, such as N-methyl-2-pyrrolidone, which are non-aqueous solvents, and then adding this specific amine compound, the electrode slurry is further mixed with the positive electrode active material and binder in a stable state, thereby successfully preserving the inherent functionality of the binder. As a result, the amine component concentration is always controlled when the positive electrode paste is finally produced, thereby reducing viscosity variation from lot to lot and dramatically reducing production problems.

[0018] That is, the present invention, which solves the above-mentioned problems, provides a method for producing a carbonaceous material dispersion in which a carbonaceous material is dispersed in a non-aqueous solvent comprising a nitrogen-containing heterocyclic amide compound having a solvent purity of 99.9% or more, the method comprising: The concentration of the amine component in the non-aqueous solvent is 3×10 mass fraction -6 and an amine control concentration confirmation process to confirm that the concentration is less than The water concentration in the non-aqueous solvent is 5×10 mass fraction -4 A moisture control concentration confirmation process to confirm that the moisture content is less than This is a method for producing a carbonaceous material dispersion, characterized by comprising a dispersion step of adding a carbonaceous material to a non-aqueous solvent that satisfies the conditions in the amine control concentration confirmation step and the water control concentration confirmation step, stirring and mixing the carbonaceous material so that the concentration of the carbonaceous material relative to the total mass is 15 to 30 mass%.

[0019] In one embodiment of the method for producing a carbonaceous material dispersion according to the present invention, a method for producing a carbonaceous material dispersion in which the nitrogen-containing heterocyclic amide compound is a 2-pyrrolidone is provided.

[0020] In one embodiment of the method for producing a carbonaceous material dispersion according to the present invention, the nitrogen-containing heterocyclic amide compound is N-methyl-2-pyrrolidone.

[0021] In one embodiment of the method for producing a carbonaceous material dispersion according to the present invention, a method for producing a carbonaceous material dispersion is provided, characterized in that a resin-based dispersant is added as a dispersant.

[0022] One embodiment of the method for producing a carbonaceous material dispersion liquid according to the present invention is a method for producing a carbonaceous material dispersion liquid, characterized in that a predetermined amine compound is added as a dispersant.

[0023] In one embodiment of the method for producing a carbonaceous material dispersion according to the present invention, the carbonaceous material is carbon black.

[0024] In one embodiment of the method for producing a carbonaceous material dispersion according to the present invention, the dispersion treatment is carried out so that when the dispersion is measured with a laser diffraction particle size distribution analyzer, two or more particle size peaks are formed.

[0025] The present invention for solving the above-mentioned problems also provides a carbonaceous material dispersion obtained by the above-mentioned method for producing a carbonaceous material dispersion, wherein the carbonaceous material concentration relative to the total mass is 15 to 30 mass %, and the amine component concentration in the dispersion excluding a predetermined amine compound added as needed is 3×10 mass fraction. -6 When the water concentration in the dispersion is less than 1×10 -3 The carbonaceous material dispersion is characterized in that the carbonaceous material dispersion is less than

[0026] One embodiment of the carbonaceous material dispersion according to the present invention is a carbonaceous material dispersion in which the carbonaceous material is carbon black and the nitrogen-containing heterocyclic amide compound is N-methyl-2-pyrrolidone.

[0027] One embodiment of the carbonaceous material dispersion according to the present invention is a carbonaceous material dispersion characterized in that the viscosity is 50 to 500 mPa·s.

[0028] One embodiment of the carbonaceous material dispersion according to the present invention is a carbonaceous material dispersion in which two or more particle size peaks are formed when measured with a laser diffraction particle size distribution analyzer.

[0029] One embodiment of the carbonaceous material dispersion according to the present invention shows a carbonaceous material dispersion in which, when measured with a laser diffraction particle size distribution analyzer, two or more particle size peaks are formed, and the height ratio (P1:P2) of at least two main peaks P1 and P2 among these peaks is 1:0.7 to 0.7:1. [Effects of the Invention]

[0030] According to the present invention, it is possible to obtain a carbonaceous material dispersion that is highly dispersed at a low solvent content, has a low viscosity, and is capable of exhibiting good electrical properties. [Brief explanation of the drawings]

[0031] [Figure 1] 1 is a graph showing a particle size distribution in one embodiment of a carbonaceous material dispersion according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] The present invention will be described in more detail below based on specific embodiments.

[0033] <Method of manufacturing carbonaceous material dispersion> A method for producing a carbonaceous material dispersion liquid according to the present invention is a method for producing a carbonaceous material dispersion liquid in which a carbonaceous material is dispersed in a non-aqueous solvent comprising a nitrogen-containing heterocyclic amide compound having a solvent purity of 99.9% or more, The concentration of the amine component in the non-aqueous solvent is 3×10 mass fraction -6 and an amine control concentration confirmation process to confirm that the concentration is less than The water concentration in the non-aqueous solvent is 5×10 mass fraction -4 A moisture control concentration confirmation process to confirm that the moisture content is less than The method is characterized by comprising a dispersion step of adding a carbonaceous material to a non-aqueous solvent that satisfies the conditions in the amine control concentration confirmation step and the water control concentration confirmation step, stirring and mixing the carbonaceous material so that the concentration of the carbonaceous material relative to the total mass is 15 to 30 mass %.

[0034] (Nitrogen-containing heterocyclic amide compounds) The nitrogen-containing heterocyclic amide compound used in the present invention includes, for example, a compound represented by the general formula (I):

[0035] [ka]

[0036] [In the formula, R 1 and R 2 are each independently hydrogen or an alkyl group having 1 to 4 carbon atoms. Examples of suitable 2-pyrrolidones include those represented by the following formula:

[0037] Specific examples of 2-pyrrolidones include 2-pyrrolidone, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone, N-butyl-2-pyrrolidone, 5-methyl-2-pyrrolidone, 5-ethyl-2-pyrrolidone, and 5-propyl-2-pyrrolidone, which may be used alone or in combination. Among these 2-pyrrolidones, N-methyl-2-pyrrolidone is particularly preferred.

[0038] The nitrogen-containing heterocyclic amide compound, particularly N-methyl-2-pyrrolidone, used in the present invention is not particularly limited in terms of its synthesis method and supply route, and may be one that has been obtained through any synthesis method or supply route, but it is basically desirable that the compound is one that is unlikely to be contaminated with amine components and moisture as impurities.

[0039] For example, N-methyl-2-pyrrolidone is produced by the synthesis method shown below, but is not particularly limited thereto, and if necessary, it can be used after being subjected to a purification treatment such as adsorption or distillation (newly produced product).

[0040] Examples of methods for producing N-methyl-2-pyrrolidone (NMP) include a method in which γ-butyrolactone (GBL) and methylamine are reacted in a shaft-type reaction column at 200 to 350°C and approximately 10 MPa (Ullmann's Encyclopedia of Industrial Chemistry, 5th Ed., Vol. A22, pp. 458-459); γ-Butyrolactam (γ-2-pyrrolidone, γ-BL) is produced from GBL by complete reaction with liquid ammonia at 270° C. and about 120 bar, for example in a cascade of three stirred reactors (selectivity: 94 mol%), and NMP is formed in the same manner with methylamine (Winnacker, Kuechler “Chemische Technologie”, 4th edition, 1982, Vol. 6, p. 99, lines 5-9); For example, as described in JP-A-10-158238, a method of reacting γ-BL with excess monomethylamine (MMA) in the presence of water at 250 to 300°C to form NMP; A method for producing NMP by reacting γ-BL with excess MMA, as described in JP-A-1-190667; A method for synthesizing NMP by heating γ-BL or its open-chain derivative with dimethylamine (DMA) and / or trimethylamine (TMA) at 200°C or higher, as described in JP-A-7-218751; A method for producing N-alkylated lactams by reacting the corresponding lactone with a secondary amine in the presence of water to give the corresponding N,N-dialkyl-omega-hydroxycarboxamide as an intermediate, as described in JP 1-186864 (note that Example 1 of this patent publication reports that NMP is obtained in 60% yield by the reaction of γ-BL with aqueous DMA, and that the methylamide of γ-hydroxybutyric acid is additionally formed. A further Example of this publication also reports a 60% yield of NMP by the corresponding reaction of γ-BL with DMA); A method for producing N-alkylated lactams by reacting the corresponding lactone with a tertiary amine or a tertiary or quaternary ammonium compound in the presence of water and removing the corresponding alcohol, as described in JP-A-1-186863 (note that, according to Example 1 of this patent, NMP is obtained in 8% yield by the reaction of γ-BL with aqueous TMA, and large amounts of by-products, such as methylamide of γ-hydroxybutyric acid, 2-pyrrolidone, and γ-hydroxybutyric acid, are formed); A method for synthesizing NMP by reacting GBL and MeNH2 together in the presence of water, as described in JP-B-4-47021420; A method for synthesizing NMP by reacting GBL with MeNH2 at 220-290°C and ≥6 MPa, as described in Chem. Abstracts 124:145893 (CN-A-1104635) (NMP can be obtained in 97% yield by batchwise reacting a mixture of GBL, 30% aqueous MeNH2, and water in a ratio of 1:1.4:5.6 at 280°C and 6 MPa); A process for the continuous production of NMP by reacting GBL with MMA in three successive reaction steps in the liquid phase, as described in International Patent Publication WO 99 / 52867, wherein the first step is operated at a temperature of 150-220°C, the second step at a temperature of 220-270°C, and the third step at a temperature of 250-310°C, the pressure in all three steps being 30-90 ATE (30.4 and 91.2 bar), preferably 40-60 ATE (40.5 and 60.8 bar), and the molar ratio of GBL to MMA being 1:1.05 to 1:1.4; A method for producing GBL by reacting 1 part with 2 parts of MMA and 2 to 4 parts of water (molar ratio of 1:5.5:9.6 to 19.1) at 200 to 300°C, particularly 230 to 300°C (for 2 hours), as described in Chem. Abstract 82:13994; As described in Chem. Abstract 87:5802, the reaction of GBL with MMA and water was carried out in a 1:1.4:4 mixture (molar ratio = 1:3.9:19.1) at 250 °C and 45-50 kg / cm 2 How to do it in; Purification of NMP by treatment with alkali metal hydroxides in aqueous solution followed by distillation, as shown in U.S. Pat. No. 2,964,535; As disclosed in JP-A-2006-503793, a method for continuously producing NMP by reacting GBL and MMA in a liquid phase is disclosed, in which GBL and MMA are used in a molar ratio of 1:1.08 to 1:2, and the reaction is carried out at a temperature of 320 to 380°C and an absolute pressure of 70 to 120 bar; Non-limiting examples include:

[0041] Alternatively, any recycled product obtained through a distillation and purification process from wastewater of N-methyl-2-pyrrolidone used in, for example, a lithium ion secondary battery manufacturing process, a coating process in which a polyvinylidene fluoride resin solution is applied to the surface of a substrate such as a metal plate or a resin molded body, or any other process, can also be used.

[0042] Among these, recycled products obtained from effluent from a lithium-ion secondary battery production process are particularly preferred because both the amine component concentration and the water concentration can be easily and satisfactorily controlled. In particular, recycled products obtained from effluent from a production process, such as a lithium-ion secondary battery production process, using a carbonaceous material dispersion produced by the production method of the present invention are most desirable. That is, a preferred embodiment is one in which a recycled product obtained from effluent from a production process using a carbonaceous material dispersion produced by the production method of the present invention is subjected to the production method of the present invention again.

[0043] The nitrogen-containing heterocyclic amide compound used as the non-aqueous solvent in the present invention is expected to contain impurities mainly consisting of amine compounds and water, as described below, but it is also desirable that other components are contained as little as possible, and in this sense, the purity is at least 99.9% or more, more preferably 99.95% or more. This purity is measured using a Karl Fischer moisture meter and gas chromatography.

[0044] (carbonaceous material) The carbonaceous material used is not particularly limited as long as it is conductive and can be in a powdery or granular form. Examples include carbon black (CB), carbon nanotubes (CNT), carbon nanofibers (CNF), graphene, fullerene, natural graphite, artificial graphite, non-graphitizable carbon, cokes, graphites, etc., which can be used alone or in combination of two or more. CB is particularly preferred. Examples of CB include furnace black, ketjen black, channel black, acetylene black, thermal black, etc., and any of these can be used. Among these, acetylene black is preferred because its manufacturing process inherently results in a low metal content.

[0045] As the carbon black, it is possible to use carbon black that has undergone a conventional oxidation treatment, graphitized carbon black, etc. Oxidation treatment of carbon black involves treating the carbon black at high temperatures in air or secondary treatment with nitric acid, nitrogen dioxide, ozone, etc., to directly introduce (covalently bond) oxygen-containing polar functional groups such as phenol groups, quinone groups, carboxyl groups, and carbonyl groups onto the carbon black surface, thereby improving the dispersibility of the carbon black.

[0046] The carbonaceous material can also be subjected to a dry magnetic separation treatment to remove metal impurities prior to production of a carbonaceous material dispersion, as necessary, and / or can be subjected to a wet magnetic separation treatment after being dispersed in a non-aqueous solvent to form a carbonaceous material dispersion.

[0047] Here, in this specification, the "particulate" form of the carbonaceous material as a raw material to be dispersed in a non-aqueous solvent is not limited as long as it is at least dispersible in the non-aqueous solvent as described above. Furthermore, the shape is not particularly limited, and is not limited to a roughly spherical shape, but may include an elliptical shape, a flaky shape, a needle-like or short fiber-like shape, an amorphous shape, etc.

[0048] As explained on the Carbon Black Association website (https: / / carbonblack.biz / index.html), the smallest unit of carbon black that cannot be decomposed is the aggregate (primary agglomerate), and a part of it (domain) is commonly referred to as a particle. This particle can be considered to fall under the definition of the smallest unit of nanomaterials, but it is merely a part of the aggregate. Aggregates form agglomerates (secondary agglomerates) through physical forces such as van der Waals forces. Furthermore, in order to prevent scattering and improve handling, carbon black products are almost always transported and sold in the form of processed particles called beads, which have been compressed or granulated.

[0049] For example, it may include primary aggregates having an average particle size of about 10 to 100 nm, secondary aggregates formed by aggregation of such primary aggregates to form particles having an average particle size of about 0.1 to 100 μm, or particles that have been processed to have an average particle size of about 500 to 5000 μm by compression or granulation in consideration of ease of handling. From the viewpoint of carbon black conductivity, conductive carbon fine particles are preferably aggregates in which primary particles are connected to some extent to form a chain-like or cluster-like structure. The connection of the primary particles in the aggregate is also called structure, and the degree of such structure can be determined by particle size distribution measurement (dynamic light scattering or laser diffraction / light scattering) or observation with an electron microscope (either scanning or transmission type). Such a structure can efficiently form conductive paths between positive electrode active material particles. Therefore, excellent conductivity can be imparted to the positive electrode active material layer with a smaller amount of the material used.

[0050] (Amine control concentration confirmation process and water control concentration confirmation process) In the production method according to the present invention, first, an amine control concentration confirmation step and a water control concentration confirmation step are carried out to confirm the amine component concentration and water concentration of the non-aqueous solvent to be used with a purity of 99.9% or higher.

[0051] The amine control concentration confirmation step and the water control concentration confirmation step can be performed for each lot of non-aqueous solvent used, or in a continuous production plant, can be performed at regular or arbitrary intervals on non-aqueous solvent samples taken, for example, through a sampling pipeline.

[0052] The amine control concentration verification step and the water control concentration verification step can be separate steps or can be performed simultaneously.

[0053] The step of confirming the amine control concentration is usually carried out using ion chromatography. This can be carried out by a method in which all peaks of amine species that are expected to be mixed in advance are quantified using a calibration curve, or by an internal standard method, standard addition method, or the like. This allows the concentration of the amine component in the non-aqueous solvent to be determined as a mass fraction of 3 × 10 -6 More preferably, it should be less than 2×10 -6 less than 1×10 -6 Here, the reason for providing such an amine control concentration is that the amine component concentration in the non-aqueous solvent is determined to be less than a mass fraction of 3×10 -6 If the concentration is above this range, the carbonaceous material dispersion may become unstable. Furthermore, when a binder component as described below is blended into the prepared carbonaceous material dispersion, the viscosity may vary from lot to lot, resulting in a decrease in workability. Note that, although not particularly limited, some of the unspecified amine species contained as impurities in the non-aqueous solvent may contain, for example, ethylenediamine, cyclohexylamine, dipropylamine, 2-ethylpiperidine, morpholine, etc., which are likely to have an effect on the viscosity and other properties of the carbonaceous material dispersion as described above. However, when the concentration of the amine component in the non-aqueous solvent as described above is 3×10 mass fraction or more, -6 By controlling the concentration so that it is less than 100%, the desired improvement effect can be achieved even if amines that are thought to have such a high impact are contained as impurities. As will be described later, when a specified amine compound is added as a dispersant in preparing a carbonaceous material dispersion, the amine component concentration referred to here, i.e., the amine control concentration, does not include the concentration of the specified amine compound, but refers to the total amount of other amine components (if the non-aqueous solvent used originally contained the same compound as the specified amine compound as an impurity, the total amount of the amount added later as a dispersant and the amount originally present as an impurity is to be excluded from the calculation of the amine control concentration).

[0054] The moisture control concentration confirmation step can be carried out using, for example, a Karl Fischer moisture concentration meter, a near-infrared absorbance trace moisture concentration meter, a refractive index concentration meter, or the like. Alternatively, it can be carried out with higher accuracy by gas chromatography using an ionic liquid column. This allows the moisture concentration in the non-aqueous solvent to be confirmed as a mass fraction of 5 × 10 -4 Less than 2×10 -4 less than 1×10 -4 It is checked whether the water content satisfies the standard that the water content is less than 100%. The reason for providing such a water control concentration is that, in the carbonaceous material dispersion according to the present invention, the solvent (in the sense of including water) in the dispersion is usually ultimately removed when a product is manufactured using the carbonaceous material dispersion. Therefore, an increase in the water content in the solvent increases the risk of defects occurring in the product manufacturing process. Furthermore, when a binder component as described below is blended into the prepared carbonaceous material dispersion, the presence of water in the non-aqueous solvent may have a significant effect on the viscosity variation in the blend as described above.

[0055] If the non-aqueous solvent to be used is determined to meet the criteria in both the amine control concentration confirmation step and the water control concentration confirmation step, the process proceeds to the dispersion step in which the carbonaceous material is dispersed in this non-aqueous solvent.

[0056] On the other hand, if it is determined that the non-aqueous solvent does not meet the criteria in either the amine control concentration confirmation step or the water control concentration confirmation step, the non-aqueous solvent will not be used as is in the dispersion treatment.

[0057] The non-aqueous solvent is purified by, for example, (1) distillation, (2) contact with an acidic substance such as mineral acids such as sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, and the like; water-soluble inorganic acids such as isopolyacids, heteropolyphosphoric acids, tungstosilicic acid, molybdosilicic acid, and the like; water-insoluble inorganic solid acids such as zeolite, alumina, silica-alumina, silica-magnesium oxide, and silica-zirconium oxide, and the like; acid-pretreated activated carbon; water-insoluble acidic cation exchange resins such as strongly acidic cation exchange resins; or organic carboxylic acids such as acetic acid, propionic acid, butyric acid, succinic acid, lactic acid, malic acid, and oxalic acid, or (3) contact with an acidic substance followed by distillation, and then the solvent is again subjected to the amine control concentration confirmation step and the water control concentration confirmation step.

[0058] Of course, it is also possible to use a different non-aqueous solvent in the amine control concentration confirmation step and the water control concentration confirmation step without using the non-aqueous solvent.

[0059] (Dispersion process) If the non-aqueous solvent is determined to meet the standards in both the amine control concentration confirmation step and the water control concentration confirmation step, a carbonaceous material is added to this non-aqueous solvent and dispersed by stirring and mixing to prepare a carbonaceous material dispersion in which the carbonaceous material concentration relative to the total mass of the dispersion is 15 to 30 mass%. The concentration of the carbonaceous material relative to the total mass of the dispersion is more preferably 16 to 28 mass%, and particularly preferably 18 to 25 mass%. If the concentration of the carbonaceous material is lower than the above, the energy required to remove the solvent during product production increases, and the costs of transporting the dispersion and the solvent increase. On the other hand, if the concentration of the carbonaceous material is higher than the above, it becomes difficult to obtain sufficient fluidity, and handling becomes difficult.

[0060] The dispersing device is not particularly limited, and dispersing machines that are normally used for dispersing pigments, etc., can be used. For example, mixers such as Disper, Homomixer, and Planetary Mixer, homogenizers (M-Technique's "Clearmix", PRIMIX's "Filmix", Silverson's "Abramix", etc.), paint conditioners (Red Devil), colloid mills (PUC's "PUC Colloid Mill", IKA's "Colloid Mill MK"), cone mills (IKA's "Cone Mill MKO", etc.), ball mills, sand mills (Shinmaru), etc. Examples of dispersing machines include, but are not limited to, media-type dispersers such as Enterprises' "Dynomill," attritors, pearl mills (Eirich's "DCP mill," etc.), and Coball mills; wet jet mills (Genus' "Genus PY," Sugino Machine's "Starburst," Nanomizer's "Nanomizer," etc.); media-less dispersers such as M-Technique's "Claire SS-5" and Nara Kikai's "MICROS," and other roll mills.

[0061] Preferably, the carbonaceous material is finally prepared by dispersing the carbonaceous material in a media mill, particularly a media mill using beads with an average particle size of 0.05 to 2 mm. More preferably, the carbonaceous material is prepared by carrying out a dispersion treatment using a shear-type disperser as described in detail below prior to the dispersion treatment using the media mill, and then carrying out a dispersion treatment using the media mill.

[0062] If the particle size of the beads used in the media mill is too small, the carbonaceous material, such as primary aggregates of carbon black, may be broken into small pieces, and excessive energy may be required for the dispersion process. Furthermore, handling becomes difficult, so the average particle size of the beads is preferably 0.05 mm or more, and more preferably 0.5 mm or more. On the other hand, if the beads are too large, the number of beads per unit volume decreases, reducing dispersion efficiency, resulting in insufficient grinding of the carbonaceous material and the presence of carbonaceous material particles with a large aspect ratio, which may prevent the liquid properties required for paints and coatings from being achieved. For this reason, the average diameter of the beads is preferably 2 mm or less, and more preferably 1.5 mm or less.

[0063] The material of the beads used as dispersion media in a media mill is not particularly limited, and examples include alumina, zirconia, steel, chromium steel, and glass. However, among these, it is preferable to use zirconia beads, taking into consideration the risk of contamination of the product and the magnitude of kinetic energy resulting from the specific gravity.

[0064] The shape of the beads is not particularly limited, but spherical shapes are generally used.

[0065] The structure of the media mill is not particularly limited, and various known media mills can be used, including various known attritors, sand mills, and bead mills.

[0066] The filling ratio of the beads in the vessel can be determined depending on the vessel, stirring mechanism, structure, etc., and is not particularly limited. However, if the ratio is too low, there is a risk that the carbonaceous material will not be sufficiently crushed or cut. On the other hand, if the ratio is too high, a large driving force will be required for rotation, and there is a risk that wear of the beads will increase contamination of the medium to be processed. For this reason, it is desirable that the filling ratio of the beads be, for example, approximately 70 to 85 volume % of the effective volume of the vessel.

[0067] Furthermore, operating conditions such as treatment time, shaft rotation speed, vessel internal pressure, and motor load are influenced by the blending amount of the carbonaceous material and the properties of the resin to be dispersed, particularly the viscosity and compatibility with the carbonaceous material, and may be set appropriately depending on the purpose.

[0068] Prior to the dispersion treatment using such a media mill, a preliminary dispersion treatment can be carried out using other stirring devices, for example, shear type stirrers such as a disper or homomixer.

[0069] By carrying out the dispersion treatment in this manner, a dispersion liquid having a viscosity of about 50 to 500 mPa·s, more preferably 100 to 400 mPa·s, and even more preferably 150 to 300 mPa·s is prepared.

[0070] Furthermore, when preparing a carbonaceous material dispersion in this manner, it is desirable to carry out a dispersion treatment so that the carbonaceous material in the resulting dispersion has two or more particle size peaks when measured with a laser diffraction particle size distribution analyzer, as shown in Figure 1. By forming two or more particle size peaks in this manner, good dispersibility and flowability are exhibited while the aggregate structure of the carbon black or the like is favorably maintained to a certain extent, and good conductive properties can be exhibited when an electrode is formed, for example.

[0071] In particular, it is desirable that primary particles or primary aggregates of carbon black or the like and secondary aggregates are both present in sufficient proportions, and that when measured with a laser diffraction particle size distribution analyzer, two or more particle size peaks are formed, and the height ratio (P1:P2) of at least two of these peaks, the main peaks P1 and P2, is 1:0.7 to 0.7:1.

[0072] (dispersant) When preparing the carbonaceous material dispersion of the present invention as described above, in order to obtain the high fluidity described above, it is preferable to add a resin-based dispersant and / or a predetermined amine compound as a dispersant. It is particularly preferable to add both a resin-based dispersant and a predetermined amine compound.

[0073] Examples of resin-based dispersants include polyvinyl alcohols, methyl cellulose, ethyl cellulose, hydroxypropyl methyl celluloses, polyvinyl acetals, polyvinyl pyrrolidones, etc., of which polyvinyl alcohol, methyl cellulose, etc. are particularly preferred. The amount of the resin-based dispersant added is about 0.01 to 5% by mass, more preferably 0.05 to 3% by mass, and even more preferably 0.1 to 2% by mass, based on the total amount of the dispersion.

[0074] Examples of the predetermined amine compound include tertiary amines, secondary amines, primary amines, cyclic amines, alkanolamines or amino alcohols, which are compounds having an amino group and a hydroxy group in an alkane skeleton, as well as other amines such as diglycolamine, tris(hydroxymethyl)aminomethane (THAM), and morpholine. While not particularly limited, 2-methylaminoethanol, 2-amino-1-butanol, 4-ethylamino-1-butanol, triethylamine, 2-amino-2-ethyl-1,3-propanediol (AEPD), 2-amino-2-methyl-1-propanol (AMP), and THAM are particularly preferred. The amount of the predetermined amine compound added is 0.01 to 5%, more preferably 0.05 to 3%, and even more preferably 0.1 to 2% of the total amount of the dispersion.

[0075] (binder) The carbonaceous material dispersion of the present invention can further contain a binder. Alternatively, when the carbonaceous material dispersion of the present invention is used to prepare, for example, a slurry for an electrode, such a binder can be used in combination.

[0076] Examples of binders that can be used include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, and vinyl pyrrolidone as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, and fluororesins; rubbers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified resins, mixtures, and copolymers of these resins are also acceptable. For lithium-ion secondary battery applications, polymeric compounds containing fluorine atoms in the molecule, such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene, are particularly preferred.

[0077] The weight-average molecular weight of these resins used as binders is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,000,000, and particularly preferably 200,000 to 1,000,000. A small molecular weight may result in a decrease in the resistance and adhesion of the binder. A large molecular weight may improve the resistance and adhesion of the binder, but may increase the viscosity of the binder itself, reducing workability, and may act as a flocculant, causing significant aggregation of dispersed particles.

[0078] In view of the industrial applicability envisaged by the present invention, the binder preferably contains a polymer compound having a fluorine atom, is preferably a polymer compound having a fluorine atom, is more preferably a vinylidene fluoride copolymer, and is particularly preferably polyvinylidene fluoride.

[0079] <Carbonaceous material dispersion> The carbonaceous material dispersion according to the present invention is a carbonaceous material dispersion characterized by being obtained by the method for producing a carbonaceous material dispersion according to the present invention as described above, and wherein the carbonaceous material concentration relative to the total mass is 15 to 30 mass %, and the amine component concentration in the dispersion, excluding a predetermined amine compound added as needed, is a mass fraction of 3×10 -6 When the water concentration in the dispersion is less than 1×10 -3 The carbonaceous material dispersion is characterized in that the carbonaceous material dispersion is less than

[0080] The amine component concentration of the carbonaceous material dispersion was set to a mass fraction of 3 × 10, which was the same as the amine control concentration in the manufacturing method. -6 More preferably, it should be less than 2×10 -6 less than 1×10 -6 It is desirable that it be less than this.

[0081] On the other hand, the water concentration of the carbonaceous material dispersion is 1 × 10 mass fraction. -3 less than 5 × 10 -4 less than 2 × 10 -4 The moisture control concentration in the manufacturing process is less than 5 x 10 mass fraction. -4 Less than 2×10 -4 less than 1×10 -4 While the moisture concentration of the carbonaceous material dispersion liquid as a product is within a slightly higher, permissible range, this is because even if the moisture concentration of the non-aqueous solvent used in production is controlled within the above-mentioned range, the product may absorb moisture from the air during the production process or during subsequent storage, resulting in an increase in moisture content. However, even if the moisture content in the product increases slightly from the moisture control concentration at the time of production, this does not pose any particular problem in terms of product properties. Conversely, the moisture control concentration at the time of production is set low in advance, anticipating that the product properties will not be affected even if the product absorbs moisture from the air and the moisture concentration increases.

[0082] As described above in the description of the production method, a desirable embodiment of the carbonaceous material dispersion according to the present invention is one in which the carbonaceous material is carbon black and the nitrogen-containing heterocyclic amide compound is N-methyl-2-pyrrolidone. Similarly, as described above, a desirable embodiment is one in which, when measured with a laser diffraction particle size distribution analyzer, two or more particle size peaks are formed, and further, the height ratio (P1:P2) of at least the two main peaks P1 and P2 among these peaks is 1:0.7 to 0.7:1.

[0083] Furthermore, although there are no particular limitations on the carbonaceous material dispersion liquid according to the present invention, it is desirable that the viscosity thereof is 50 to 500 mPa·s, more preferably 100 to 400 mPa·s, and even more preferably 150 to 300 mPa·s.

[0084] (Applications of carbonaceous material dispersions) The carbonaceous material dispersion of the present invention can be prepared as an electrode paste by further adding the binder as described above and the following electrode active material. In particular, it is preferable to use the carbonaceous material dispersion containing the dispersant, carbon black as the carbonaceous material, and N-methyl-2-pyrrolidone as the non-aqueous solvent as an electrode paste by adding the binder and the electrode active material.

[0085] (electrode active material) The positive electrode active material for a lithium ion secondary battery is not particularly limited, but metal compounds such as metal oxides and metal sulfides that can be doped or intercalated with lithium ions, and conductive polymers can be used. Examples include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfides. Specific examples include MnO, VO, and VO. 13Examples of suitable materials include transition metal oxide powders such as TiO2, composite oxide powders of lithium and transition metals such as layered lithium nickel oxide, lithium cobalt oxide, lithium manganate, and spinel-structured lithium manganate, lithium iron phosphate-based materials that are phosphate compounds with an olivine structure, and transition metal sulfide powders such as TiS2 and FeS. Conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can also be used. Mixtures of the above inorganic and organic compounds may also be used.

[0086] The negative electrode active material for a lithium ion secondary battery is not particularly limited as long as it can dope or intercalate lithium ions. For example, metallic Li, its alloys such as tin alloys, silicon alloys, and lead alloys, Li X Fe2O3, Li X Fe3O4, Li X Examples of the negative electrode active material include metal oxides such as WO2, lithium titanate, lithium vanadate, and lithium silicate, conductive polymers such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-baked carbon materials, vapor-grown carbon fiber, and carbon fiber. These negative electrode active materials can be used alone or in combination.

[0087] These electrode active materials preferably have an average particle size in the range of 0.05 to 100 μm, more preferably 0.1 to 50 μm. The average particle size of the electrode active material referred to in this specification is the average value of particle sizes measured with an electron microscope.

[0088] This electrode paste can be produced by mixing the carbonaceous material dispersion, a binder, and an electrode active material. The order of addition of the components is not limited, and examples of the method include a method of mixing all of the components at once, a method of adding the remaining components to a carbonaceous material dispersion prepared in advance by the above-mentioned method and mixing them, and a method of adding a binder to a carbonaceous material dispersion prepared in advance by the above-mentioned method and kneading them, and then adding the electrode active material to the kneaded mixture and mixing them.

[0089] As an apparatus for producing this electrode paste, the same apparatus as that used for producing the carbonaceous material dispersion liquid of the present invention described above can be used. [Example]

[0090] The present invention will be described in detail below based on examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention. In these examples, parts represent parts by mass and % represents % by mass. Carbon black (sometimes abbreviated as "CB"), dispersants, binders, etc. used in the examples and comparative examples are shown below.

[0091] <Carbon black> Denka Black Granules (manufactured by Denka): acetylene black, specific surface area 69m 2 / g.

[0092] <Non-aqueous solvent> The following non-aqueous solvents were used: ·N-methyl-2-pyrrolidone (NMP). Various NMP non-aqueous solvents were prepared, each with the following composition: NMP-A: A distilled and purified product produced by Nippon Refine Co., Ltd. from wastewater from the lithium-ion secondary battery manufacturing process. NMP-B: A new liquid NMP available on the market. NMP-C1: A mixture of 16.67 parts by mass of the above NMP-B and 483.33 parts by mass of the above NMP-A. NMP-C2: A mixture of 50.00 parts by mass of the above NMP-B and 450.00 parts by mass of the above NMP-A. NMP-AW1: A comparative product in which 0.01% purified water has been added to the above NMP-A. NMP-AW2: A comparative product in which 0.05% purified water has been added to the above NMP-A. NMP-AW3: A comparative product in which 0.10% purified water has been added to the above NMP-A. NMP-AA1: Add 2-ethylpiperidine to the above NMP-A at a mass fraction of 3 × 10 -6 It is added so that NMP-AA2: Add morpholine to the above NMP-A at a mass fraction of 3 x 10 -6 It is added so that NMP-AA3: Triethylamine was added to the above NMP-A at a mass fraction of 3 × 10 -6 It is added so that

[0093] <Dispersant> Polyvinyl alcohol 500 (Kanto Chemical): Degree of polymerization 500, degree of saponification 86.5-89.0%, hereafter abbreviated as PVA.

[0094] <Prescribed amine compound> · AEPD: 2-amino-2-ethyl-1,3-propanediol.

[0095] <Binder> KF Polymer W9100 (Kureha Corporation): Polyvinylidene fluoride (PVDF), weight-average molecular weight approximately 280,000. Hereinafter abbreviated as W9100.

[0096] <Evaluation of carbonaceous material dispersion> The carbonaceous material dispersions obtained in Examples 1 to 14 and Comparative Examples 1 to 9 were evaluated by measuring the initial viscosity value and the rate of change in viscosity. The evaluation methods were as follows.

[0097] <Initial viscosity value and viscosity change rate> The dispersion stability, which is an issue in the present invention, can be evaluated from the rate of change in viscosity over time of the resulting carbonaceous material dispersion. The rate of change in viscosity was evaluated by the rate of change in the viscosity measurement value after standing and storing at 25°C for 10 days, 17 days, or 30 days, based on the viscosity measurement value (initial viscosity value) after dispersion. The smaller the change, the better the stability. The viscosity value was measured immediately after thoroughly stirring the dispersion composition with a spatula at a temperature of 25°C and a B-type viscometer rotor rotation speed of 60 rpm using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., "BL"). The rotor used for the measurement was No. 20 when the viscosity value was less than 100 mPa·s, No. 21 when it was 100 mPa·s or more and less than 500 mPa·s, No. 22 when it was 500 mPa·s or more and less than 2000 mPa·s, and No. 23 when it was 2000 mPa·s or more and less than 10000 mPa·s, respectively.

[0098] <Concentration of amine component, moisture, and impurity concentration in NMP> [Preliminary Test 1] The amine component concentration (mass fraction), moisture (mass fraction), and solvent purity of various NMPs as the above-mentioned non-aqueous solvents were measured by ion chromatography, Karl Fischer moisture concentration meter, and gas chromatography, respectively. As a result, the following analytical values were shown respectively. NMP-A: Amine component concentration 0.05×10 -6 , Moisture 3×10 -5 , Solvent purity 99.95% NMP-C1: Amine component concentration 1.0×10 -6 , Moisture 3×10 -5 [[ID=​​​​​​​​​​​​​​​​​, Solvent purity 99.95% NMP-AW3: Amine component concentration 0.05 x 10 -6 , water 1 x 10 -3 , Solvent purity 99.94% NMP-B: Amine component concentration 3.0 x 10 -5 , water 3 x 10 -5 , Solvent purity 99.95% NMP-AA1: Amine component (2-ethylpiperidine) concentration 3.0 x 10 -6 , water 3 x 10 -5 , Solvent purity 99.95% NMP-AA2: Amine component (morpholine) concentration 3.0 x 10 -6 , water 3 x 10 -5 , Solvent purity 99.95% NMP-AA3: Amine component (triethylamine) concentration 3.0 x 10 -6 , water 3 x 10 -5 , Solvent purity 99.95% It should be noted that all the compounds except for NMP-A, NMP-C1, and NMP-AW1 were outside the allowable range of the specified amine control concentration and water control concentration according to the present invention.

[0099] <Preparation of Carbonaceous Material Dispersion> [Example 1] A glass bottle was charged with 77.5 parts of NMP-A (as N-methyl-2-pyrrolidone), 1 part of PVA (as a dispersant), and 0.5 parts of AEPD (as a specified amine). After thorough mixing and dissolving or dispersing, 21 parts of granular carbon black was added and dispersed in a bead mill using zirconia beads as a medium until the viscosity reached 250 mPa·s or less. Carbonaceous Material Dispersion D-1 was obtained. The initial viscosity of Carbonaceous Material Dispersion D-1 was 174 mPa·s. Furthermore, as shown in Figure 1, particle size peaks measured using a laser diffraction particle size analyzer were present at 1.01 μm and 0.25 μm, with a peak ratio of 1.0:0.9. After standing at 25°C for 10 days, the viscosity of the dispersion was 166 mPa·s, a viscosity change of 5%. After standing for 17 days, the viscosity of the dispersion was 160 mPa·s, a viscosity change of 8%. After standing for 30 days, the viscosity of the dispersion was 161 mPa·s, a viscosity change of 8%.

[0100] [Example 2] Carbonaceous material dispersion D-C1 was obtained in the same manner as above, except that NMP-C1 was used instead of NMP-A as N-methyl-2-pyrrolidone. The initial viscosity of the prepared dispersion was 212 mPa s, and the viscosity of the dispersion after standing at 25°C for 30 days was 192 mPa s, a viscosity change rate of 9%.

[0101] [Comparative Example 1] Carbonaceous material dispersion D-C2 was obtained in the same manner as above, except that NMP-C2 was used instead of NMP-A as N-methyl-2-pyrrolidone. The initial viscosity of the prepared dispersion was 217 mPa s, and the viscosity of the dispersion after standing at 25°C for 30 days was 183 mPa s, a viscosity change rate of 16%.

[0102] Comparative Example 2 Carbonaceous material dispersion DB was obtained in the same manner as above, except that NMP-B was used instead of NMP-A as N-methyl-2-pyrrolidone. The initial viscosity of the prepared dispersion was 211 mPa s, and the viscosity of the dispersion after standing at 25°C for 30 days was 180 mPa s, a viscosity change rate of 15%.

[0103] [Example 3] Carbonaceous material dispersion D-AW1 was obtained in the same manner, except that NMP-AW1 was used instead of NMP-A as N-methyl-2-pyrrolidone. The initial viscosity of the prepared dispersion was 210 mPa s. After standing at 25°C for 10 days, the viscosity of the dispersion was 191 mPa s, and the viscosity change rate was 10%.

[0104] Comparative Example 3 Carbonaceous material dispersion D-AW2 was obtained in the same manner, except that NMP-AW2 was used instead of NMP-A as N-methyl-2-pyrrolidone. The initial viscosity of the prepared dispersion was 220 mPa s. After standing at 25°C for 10 days, the viscosity of the dispersion was 183 mPa s, and the viscosity change rate was 16%.

[0105] Comparative Example 4 Carbonaceous material dispersion D-AW3 was obtained in the same manner, except that NMP-AW3 was used instead of NMP-A as N-methyl-2-pyrrolidone. The initial viscosity of the prepared dispersion was 223 mPa s. After standing at 25°C for 10 days, the viscosity of the dispersion was 183 mPa s, a viscosity change rate of 18%.

[0106] [Reference example 1] Carbonaceous material dispersion D-AA1 was obtained in the same manner, except that NMP-AA1 was used instead of NMP-A as N-methyl-2-pyrrolidone. The initial viscosity of the prepared dispersion was 190 mPa s. After standing at 25°C for 17 days, the viscosity of the dispersion was 158 mPa s, and the viscosity change rate was 17%.

[0107] [Reference example 2] Carbonaceous material dispersion D-AA2 was obtained in the same manner, except that NMP-AA2 was used instead of NMP-A as N-methyl-2-pyrrolidone. The initial viscosity of the prepared dispersion was 205 mPa s. After standing at 25°C for 17 days, the viscosity of the dispersion was 175 mPa s, and the viscosity change rate was 15%.

[0108] [Reference example 3] Carbonaceous material dispersion D-AA3 was obtained in the same manner, except that NMP-AA3 was used instead of NMP-A as N-methyl-2-pyrrolidone. The initial viscosity of the prepared dispersion was 207 mPa s. After standing at 25°C for 17 days, the viscosity of the dispersion was 179 mPa s, a viscosity change rate of 14%.

[0109] [Example 4] To 24.5 parts of the carbonaceous material dispersion liquid prepared in Example 1, 70.5 parts of the same NMP-A as in Example 1 and 5 parts of binder W9100 were added, and the mixture was thoroughly mixed and dispersed with a stirrer at 60°C for 1 hour to prepare a coating paste. The initial viscosity of the prepared coating paste was 155 mPa s, and the viscosity of the paste after standing at 45°C for 7 days was 599 mPa s, suggesting sufficient workability during coating and appropriate subsequent curing properties.

[0110] [Example 5] To 24.5 parts of the carbonaceous material dispersion liquid prepared in Example 2, 70.5 parts of the same NMP-C1 as in Example 2 and 5 parts of binder W9100 were added, and the mixture was thoroughly mixed and dispersed using a stirrer at 60°C for 1 hour to prepare a coating paste. The initial viscosity of the prepared coating paste was 165 mPa s, and after allowing to stand at 45°C for 7 days, the viscosity of the paste was 550 mPa s, suggesting sufficient workability during coating and appropriate subsequent curing properties.

[0111] Comparative Example 6 To 24.5 parts of the carbonaceous material dispersion liquid prepared in Comparative Example 1, 70.5 parts of the same NMP-C2 as in Comparative Example 1 and 5 parts of binder W9100 were added, and the mixture was thoroughly mixed and dispersed with a stirrer at 60°C for 1 hour to prepare a coating paste. The initial viscosity of the prepared coating paste was 135 mPa s, and after allowing to stand at 45°C for 7 days, the viscosity of the paste was 403 mPa s, indicating sufficient workability during coating, but suggesting that the subsequent curing properties were significantly lower than in Example 4.

[0112] Comparative Example 7 To 24.5 parts of the carbonaceous material dispersion liquid prepared in Comparative Example 2, 70.5 parts of the same NMP-B as in Comparative Example 2 and 5 parts of binder W9100 were added, and the mixture was thoroughly mixed and dispersed with a stirrer at 60°C for 1 hour to prepare a coating paste. The initial viscosity of the prepared coating paste was 128 mPa s, and after allowing to stand at 45°C for 7 days, the viscosity of the paste was 402 mPa s, indicating sufficient workability during coating, but suggesting that the subsequent curing properties would be significantly lower than in Example 4.

[0113] [Reference example 4] To 24.5 parts of the carbonaceous material dispersion liquid prepared in Reference Example 1, 70.5 parts of NMP-AA1, the same as in Reference Example 1, and 5 parts of binder W9100 were added, and the mixture was thoroughly mixed and dispersed with a stirrer at 60°C for 1 hour to prepare a coating paste. The initial viscosity of the prepared coating paste was 140 mPa s, and after allowing to stand at 45°C for 7 days, the viscosity of the paste was 356 mPa s, suggesting that the paste did not have sufficient workability during coating and that its subsequent curing properties were significantly inferior to those of Example 4.

[0114] [Reference example 5] To 24.5 parts of the carbonaceous material dispersion liquid prepared in Reference Example 2, 70.5 parts of the same NMP-AA2 as in Reference Example 2 and 5 parts of binder W9100 were added, and the mixture was thoroughly mixed and dispersed with a stirrer at 60°C for 1 hour to prepare a coating paste. The initial viscosity of the prepared coating paste was 136 mPa s, and after allowing to stand at 45°C for 7 days, the viscosity of the paste was 320 mPa s, suggesting that the paste did not have sufficient workability during coating and that its subsequent curing properties were significantly inferior to those of Example 4.

[0115] [Reference example 6] To 24.5 parts of the carbonaceous material dispersion liquid prepared in Reference Example 3, 70.5 parts of the same NMP-AA3 as in Reference Example 3 and 5 parts of binder W9100 were added, and the mixture was thoroughly mixed and dispersed with a stirrer at 60°C for 1 hour to prepare a coating paste. The initial viscosity of the prepared coating paste was 131 mPa s, and after allowing to stand at 45°C for 7 days, the viscosity of the paste was 316 mPa s, suggesting that the paste did not have sufficient workability during coating and that its subsequent curing properties were significantly inferior to those of Example 4.

Claims

1. A carbonaceous material dispersion liquid in which a carbonaceous material is dispersed in a non-aqueous solvent comprising a nitrogen-containing heterocyclic amide compound having a solvent purity of 99.9% or more, wherein the concentration of the carbonaceous material relative to the total mass is 15 to 30 mass%, and the concentration of amine components in the dispersion liquid excluding a predetermined amine compound comprising at least one selected from the group consisting of added tertiary amines, secondary amines, primary amines, cyclic amines, alkanolamines or amino alcohols which are compounds having an amino group and a hydroxy group in an alkane skeleton, diglycolamine, tris(hydroxymethyl)aminomethane, and morpholine is 3×10 mass fraction. －６ The water concentration in the dispersion is less than 1×10 －３ a carbonaceous material dispersion, wherein the carbonaceous material dispersion is less than 100%.

2. A carbonaceous material dispersion in which a carbonaceous material is dispersed in a non-aqueous solvent comprising a nitrogen-containing heterocyclic amide compound having a solvent purity of 99.9% or more, an amine control concentration confirmation step of measuring the amine component concentration in the non-aqueous solvent using ion chromatography to confirm whether the amine component concentration satisfies the standard of less than 3×10 −6 in mass fraction; 2. The carbonaceous material dispersion according to claim 1, which is obtained by a water control concentration confirmation step of measuring the water concentration in the non-aqueous solvent with a Karl Fischer water concentration meter, a near-infrared absorbance trace water concentration meter, a refractive index densitometer, or gas chromatography using an ionic liquid column to confirm whether the water concentration satisfies the standard of less than 5 × 10 −4 in mass fraction, and a dispersion step of adding a carbonaceous material to a non-aqueous solvent that satisfies the conditions in the amine control concentration confirmation step and the water control concentration confirmation step, and stirring and mixing the mixture so that the carbonaceous material concentration relative to the total mass is 15 to 30 mass %.

3. 2. The carbonaceous material dispersion according to claim 1, wherein the nitrogen-containing heterocyclic amide compound is a 2-pyrrolidone.

4. The carbonaceous material dispersion according to claim 1, wherein the nitrogen-containing heterocyclic amide compound is N-methyl-2-pyrrolidone.

5. The carbonaceous material dispersion according to any one of claims 1 to 4, wherein a resin-based dispersant is blended as a dispersant.

6. The carbonaceous material dispersion according to any one of claims 1 to 5, characterized in that a predetermined amine compound consisting of at least one member selected from the group consisting of 2-methylaminoethanol, 2-amino-1-butanol, 4-ethylamino-1-butanol, triethylamine, 2-amino-2-ethyl-1,3-propanediol, 2-amino-2-methyl-1-propanol, and tris(hydroxymethyl)aminomethane is blended as a dispersant.

7. 7. The carbonaceous material dispersion according to claim 1, wherein the carbonaceous material is carbon black.

8. 8. The carbonaceous material dispersion according to claim 1, wherein the carbonaceous material is carbon black, and the nitrogen-containing heterocyclic amide compound is N-methyl-2-pyrrolidone.

9. 9. The carbonaceous material dispersion according to claim 1, wherein the viscosity is 50 to 500 mPa·s.

10. The carbonaceous material dispersion according to any one of claims 1 to 9, wherein when measured with a laser diffraction particle size distribution meter, two or more particle size peaks are formed.

11. 11. The carbonaceous material dispersion according to claim 1, wherein, when measured with a laser diffraction particle size distribution meter, two or more particle size peaks are formed, and the height ratio (P1:P2) of at least two main peaks P1 and P2 among these peaks is 1:0.7 to 0.7:1.

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