Composition for secondary battery electrode, method for producing electrically conductive material dispersion liquid, electrode film, secondary battery, and vehicle

Abstract

A conductive material dispersion liquid, a method for producing the same, a secondary battery electrode composition using the same, an electrode film, a secondary battery, and a vehicle, the conductive material dispersion liquid containing a conductive material, carboxymethyl cellulose or a salt thereof, and water, the conductive material including at least one selected from the group consisting of carbon nanotubes and carbon black, the conductive material dispersion liquid having a weight average molecular weight of the carboxymethyl cellulose or the salt thereof of 10,000 to 150,000, an etherification degree of 0.5 to 0.9, and a product of complex elastic modulus (Pa) and phase angle (°) of the conductive material dispersion liquid of 100 or more and 1,500 or less. The present application provides a conductive material dispersion liquid having high concentration and high dispersibility and a secondary battery electrode composition, which obtain an electrode film having high conductivity.

Description

Technical Field

[0001] This invention relates to a conductive material dispersion and its manufacturing method, as well as compositions for secondary battery electrodes, electrode films, secondary batteries, and vehicles using the same. Background Technology

[0002] The capacity of lithium-ion secondary batteries largely depends on the positive and negative electrode active materials, which are the main materials. Therefore, various materials have been actively researched. However, the charging capacity of practically applied active materials has reached near-theoretical levels, with improvements approaching their limits. Therefore, increasing the amount of active material in the battery can simply increase the capacity. Thus, the following attempt was made: reducing the amount of conductive materials or binders added, which do not directly contribute to capacity. Conductive materials form conductive pathways within the battery, connecting the active material particles and preventing the interruption of these pathways due to the expansion and contraction of the active materials. To maintain performance with minimal addition, it is effective to use conductive material dispersions to form efficient conductive networks (Patent Document 1).

[0003] Carbon black, Ketjen black, graphene, and micro-carbon materials are used as conductive materials. If carbon nanotubes, a type of micro-carbon fiber, are used, especially those with small outer diameters and large specific surface areas, a conductive network can be efficiently formed with a small amount of carbon, reducing the amount of conductive material contained in the positive and negative electrodes of lithium-ion secondary batteries. For example, by adding carbon nanotubes to graphite or silicon negative electrodes, the electrode resistance can be reduced, the battery load resistance improved, the electrode strength increased, or the electrode expansion and contraction improved, thereby increasing the cycle life of lithium-ion secondary batteries (Patent Documents 2, 3, and 4). Compared to graphite, silicon-based active materials have a larger theoretical capacity and can contribute to high battery capacity, but they also exhibit significant volume changes during charging and discharging. Therefore, attempts have been made to improve cycle life by combining silicon with graphite after micronization and the formation of a thin carbon film on the particle surface.

[0004] In anodes using graphite and silicon-based active materials, the selection of a binder presents a significant challenge. Styrene-butadiene rubber (SBR), used in graphite-only systems, exhibits significantly deteriorated properties in systems using graphite and silicon-based active materials. While SBR is designed to bind active material particles with rubber particles and bring the active material into contact with the electrolyte, the adhesion is weak when SBR is used alone when combined with silicon-based anode active materials that expand and contract more than graphite, leading to bond failure during the initial charge-discharge cycle. Therefore, a method has been implemented whereby a binder such as polyacrylic acid or polyacrylate, uniformly dispersed or dissolved in water, is used in conjunction with SBR. This binder extensively covers the surface of the active material, and the resin layer on this surface bonds the active materials together (Patent Document 5). However, using low molecular weight polyacrylic acid or polyacrylate as a binder fails to achieve satisfactory cycle characteristics (Patent Document 6 and Non-Patent Document 1).

[0005] In the positive electrode, research has also been conducted on reducing electrode resistance by adding carbon nanotubes (Patent Documents 7 and 8). Most positive electrode active materials are unstable relative to water, but lithium iron phosphate, for example, is relatively stable, so water can be used as a dispersion medium in the manufacture of electrodes for secondary batteries. Furthermore, lithium iron phosphate is particularly poor in conductivity, so it is generally used to form a thin carbon film. Because lithium iron phosphate has high lithium diffusion resistance in solid form, methods are known to improve the resistance of the electrode film by using it in particulate form.

[0006] Furthermore, from the perspective of reducing environmental impact or cutting costs, the demand for conductive material dispersions using water as the dispersion medium is increasing. However, carbon nanotubes are highly hydrophobic, making them difficult to disperse in water, and various attempts have been reported. For example, Patent Document 9 discloses a dispersion of a carbon nanotube-containing composition, which includes carboxymethyl cellulose or its salt with a weight average molecular weight of 0.5 million or more and 60,000 or less as determined by gel permeation chromatography, and an aqueous solvent. Patent Document 10 discloses a dispersion of a carbon nanotube-containing composition, which includes a dispersant and a dispersion medium, wherein the dispersant includes carboxymethyl cellulose or its salt with a degree of etherification of 0.4 or more and less than 0.7. Patent Document 11 describes a method for improving conductivity by dispersing carbon nanotubes with an outer diameter of 50 nm or more and 110 nm or less together with sodium carboxymethyl cellulose in water for use as an electrode in a secondary battery.

[0007] Furthermore, Patent Document 12 proposes a conductive material dispersion using carboxymethyl cellulose with an average degree of polymerization of 500 or more and 2500 or less. However, in order to form a viscous material suitable for coating, a bead mill is used for dispersion, which has the problem of reducing the structure of the conductive material. Patent Document 13 proposes a material containing a specific surface area of ​​25 m².2 / g or more and 300m 2 A conductive material dispersion containing less than 1 g of carbon black is required, but a large amount of dispersant is needed to produce a conductive material dispersion with excellent dispersion stability. Patent Document 14 proposes an aqueous conductive material dispersion using ethyl cellulose as a dispersant, but it is difficult to achieve a high concentration of conductive material in the dispersion in order to produce a conductive material dispersion with excellent dispersibility.

[0008] Generally, the smaller the outer diameter of carbon nanotubes, the larger their specific surface area, resulting in poorer wettability to water and making it difficult to obtain high-concentration and well-dispersed solutions. However, since carbon nanotubes with smaller outer diameters and higher specific surface areas are more likely to form efficient conductive networks, obtaining well-dispersed solutions of carbon nanotubes with small outer diameters and high specific surface areas is of paramount importance. Furthermore, low-concentration dispersions of carbon nanotubes lead to problems such as reduced design freedom when formulating active substances or binders, and increased delivery costs per unit of solid carbon nanotube component. Therefore, there is also a demand for high-concentration dispersions of carbon nanotubes or carbon black with small outer diameters and high specific surface areas.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: Japanese Patent Application Publication No. 2005-162877

[0012] Patent Document 2: Japanese Patent Application Publication No. 4-155776

[0013] Patent Document 3: Japanese Patent Application Publication No. 4-237971

[0014] Patent Document 4: Japanese Patent Application Publication No. 2004-178922

[0015] Patent Document 5: Japanese Patent Application Publication No. 2013-229163

[0016] Patent Document 6: U.S. Patent No. 8034485

[0017] Patent Document 7: Japanese Patent Application Publication No. 2011-70908

[0018] Patent Document 8: Japanese Patent Application Publication No. 2005-162877

[0019] Patent Document 9: Japanese Patent Publication No. 2014-002885

[0020] Patent Document 10: Japanese Patent Application Publication No. 2016-204203

[0021] Patent Document 11: Japanese Patent Application Publication No. 2016-028109

[0022] Patent Document 12: Japanese Patent Application Publication No. 2017-10822

[0023] Patent Document 13: Japanese Patent Application Publication No. 2017-84682

[0024] Patent Document 14: Japanese Patent Application Publication No. 2011-70908

[0025] Non-patent literature

[0026] Non-patent literature 1: Journal of Electrochem. Soc., 2008, 155, A812-A816 Summary of the Invention

[0027] The problem that the invention aims to solve

[0028] For example, the dispersions of carbon nanotube-containing compositions described in Patent Documents 9 and 10 cannot contain more than a few percent by mass of carbon nanotubes. Furthermore, the dispersion described in Patent Document 11 exhibits insufficient dispersibility when dispersing carbon nanotubes with small outer diameters and high specific surface areas. Consequently, high-concentration carbon nanotube dispersions are prone to agglomeration and precipitation during storage, thus raising concerns about storage stability. While using a high molecular weight dispersant to increase the viscosity of the carbon nanotube dispersion is effective in preventing sedimentation, it also presents problems such as reduced coatability and easy gelation. Additionally, in the method for manufacturing a negative electrode for a secondary battery described in Patent Document 5, the method of adding dissolved polyacrylic acid to the composition for the secondary battery electrode and performing a coating treatment on the surface of a silicon-based active material is recommended. However, even with this method, when using carbon nanotubes as the conductive material, uneven distribution of polyacrylic acid can still occur.

[0029] Furthermore, according to the results of the research conducted by the inventors, it is known that silicon-based active materials with a carbon film formed on their surface after micronization, as well as active materials such as lithium iron phosphate, are difficult to achieve a high concentration and good dispersion in water as a dispersion medium for the same reasons as the carbon nanotubes. Therefore, it goes without saying that various active materials, especially when combined with carbon nanotubes, are difficult to achieve a particularly good dispersion, and consequently, it is difficult to obtain a secondary battery with excellent rate and cycle characteristics.

[0030] The problem to be solved by the present invention is to provide a high-concentration and highly dispersible conductive material dispersion and a composition for secondary battery electrodes in order to obtain an electrode film with high conductivity. More specifically, it provides a secondary battery with excellent rate characteristics and cycle characteristics.

[0031] Therefore, the objective of embodiments of the present invention is to provide a conductive material dispersion with high concentration and high dispersibility, and a method for manufacturing the same. Furthermore, another objective of embodiments of the present invention is to provide a composition for a secondary battery electrode. Moreover, another objective of embodiments of the present invention is to provide an electrode film that improves the output and cycle life of a secondary battery, and a secondary battery having high output and good cycle life. Furthermore, another objective of embodiments of the present invention is to provide a vehicle including a secondary battery.

[0032] Technical means to solve the problem

[0033] According to the results of the researchers' efforts, by dispersing carboxymethyl cellulose or its salt having a specific weight average molecular weight and degree of etherification, and at least one of the group consisting of carbon nanotubes and carbon black as conductive materials, and dispersing them such that the product of the complex elastic modulus X (Pa) and the phase angle Y (°) (X×Y) is 100 or more and 1,500 or less, carbon nanotubes and / or carbon black can be well dispersed in water, and a good conductive network can be maintained with a small amount of addition. This improves the rate characteristics and cycle life of secondary batteries.

[0034] The following illustrates one example of an embodiment of the present invention.

[0035] The present invention relates to a conductive material dispersion containing a conductive material, carboxymethyl cellulose or a salt thereof, and water. The conductive material comprises at least one selected from the group consisting of carbon nanotubes and carbon black. In the conductive material dispersion, the weight average molecular weight of carboxymethyl cellulose or a salt thereof is 10,000 to 150,000, the degree of etherification is 0.5 to 0.9, and the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) of the conductive material dispersion is 100 or more and 1,500 or less.

[0036] Another embodiment of the present invention relates to the conductive material dispersion, wherein the carboxymethyl cellulose or its salt has a weight average molecular weight of 10,000 to 100,000.

[0037] Another embodiment of the present invention relates to a conductive material dispersion containing carbon nanotubes, carboxymethyl cellulose or its salt, and water. In the conductive material dispersion, the weight average molecular weight of carboxymethyl cellulose or its salt is 10,000 to 100,000, the degree of etherification is 0.5 to 0.9, and the product (X×Y) of the complex elastic modulus X (Pa) and the phase angle Y (°) of the conductive material dispersion is 100 or more and 1,500 or less.

[0038] Another embodiment of the present invention relates to the conductive material dispersion, wherein the amount of acidic groups in the carbon nanotubes is 0.1 μmol / m 2 ~0.8 μmol / m 2 .

[0039] Another embodiment of the present invention relates to the conductive material dispersion, wherein the amount of acidic groups of carbon nanotubes is 40 μmol / g to 500 μmol / g.

[0040] Another embodiment of the present invention relates to the conductive material dispersion, wherein the complex elastic modulus is less than 50 Pa and the phase angle is greater than 15°.

[0041] Another embodiment of the present invention relates to the conductive material dispersion, wherein the carbon nanotubes include a first carbon nanotube with an average outer diameter of 0.5 nm or more and less than 5 nm, and a second carbon nanotube with an average outer diameter of 5 nm or more and less than 20 nm, wherein the mass ratio of the first carbon nanotube to the second carbon nanotube is 1:10 to 1:100.

[0042] Another embodiment of the present invention relates to the conductive material dispersion, which further comprises polyacrylic acid.

[0043] Another embodiment of the present invention relates to the conductive material dispersion, wherein the median particle size of the conductive material dispersion is 0.5 μm or more and 2.0 μm or less.

[0044] Another embodiment of the present invention relates to the conductive material dispersion, wherein the thixotropic index (TI) of the conductive material dispersion is 2.0 to 5.0.

[0045] Another embodiment of the present invention relates to the conductive material dispersion, wherein the gloss of the coating film of the conductive material dispersion is 5 to 120, measured with respect to an incident angle of 60°.

[0046] Another embodiment of the present invention relates to the conductive material dispersion, wherein the pH of the conductive material dispersion is 7.0 to 10.5.

[0047] Another embodiment of the present invention relates to a composition for a secondary battery electrode comprising the aforementioned conductive material dispersion.

[0048] Another embodiment of the present invention relates to an electrode film comprising a coating film of the aforementioned composition for secondary battery electrodes.

[0049] Another embodiment of the present invention relates to a secondary battery comprising the aforementioned electrode membrane.

[0050] Another embodiment of the present invention relates to a method for manufacturing the conductive material dispersion by sequentially performing the steps (1) and (2) described below.

[0051] (1) A process of dispersing particles at a pressure of 60 MPa to 120 MPa using a high-pressure homogenizer to achieve a median particle size of less than 4.0 μm.

[0052] (2) Dispersion using a bead mill until the phase angle is above 40°.

[0053] Another embodiment of the invention relates to a vehicle that includes the aforementioned secondary battery.

[0054] The effects of the invention

[0055] According to embodiments of the present invention, a high-concentration and highly dispersible conductive material dispersion and its manufacturing method, as well as a composition for secondary battery electrodes, can be provided. Furthermore, according to embodiments of the present invention, an electrode film that improves the output and cycle life of a secondary battery, and a secondary battery having high output and good cycle life, can be provided. Additionally, according to embodiments of the present invention, a vehicle including a secondary battery can be provided. Detailed Implementation

[0056] The following provides a detailed description of carbon nanotubes, carbon black, carboxymethyl cellulose and its salts, carbon nanotube and carbon black dispersions, compositions for secondary battery electrodes, electrode films, secondary batteries, and vehicles, as described in embodiments of the present invention. The present invention is not limited to the embodiments described below, and also includes embodiments implemented without altering the spirit of the invention.

[0057] In this specification, carbon nanotubes are sometimes referred to as "CNT". Carboxymethyl cellulose is sometimes referred to as "CMC". In addition, in this specification, conductive material dispersions are sometimes simply referred to as "dispersions".

[0058] <Conductive material dispersion>

[0059] The conductive material dispersion contains at least one of the group consisting of CNTs and carbon black, CMC or a salt thereof, and water.

[0060] Carbon nanotubes

[0061] Carbon nanotubes (CNTs) that can be used as conductive materials are formed by winding planar graphite into a cylindrical shape. They include single-layer CNTs or multi-layer CNTs, or a mixture of both. Single-layer CNTs have a structure with one layer of graphite wound around them. Multi-layer CNTs have a structure with two or more layers of graphite wound around them. Furthermore, the sidewalls of CNTs may not be graphite. Additionally, CNTs that include, for example, sidewalls with an amorphous structure are also included in the CNTs described in this specification.

[0062] The shape of CNTs is not limited. Examples of possible shapes include needle-like, cylindrical, fishbone-like (or cup-like), platelet-like, and coil-like. In this embodiment, the shape of the CNT is preferably needle-like or cylindrical. CNTs can be a single shape or a combination of two or more shapes.

[0063] Examples of CNT forms include: graphite whiskers, filamentous carbon, graphite fibers, ultrafine carbon nanotubes, carbon nanotubes, carbon protofibrils, carbon microtubes, and carbon nanofibers. CNTs can have these forms individually or in combination of two or more forms.

[0064] The acidity of CNTs can be determined by back titration based on the adsorption amount of hexylamine. Using the surface area of ​​CNTs calculated using the Brunauer-Emmett-Teller (BET) method as a benchmark, the preferred acidity of CNTs determined from the adsorption amount of hexylamine is 0.1 μmol / m². 2 The above, more preferably 0.2 μmol / m 2 That's all. Additionally, 0.8 μmol / m is preferred. 2 The following is more preferably 0.7 μmol / m 2 Based on the mass of CNTs, the amount of acidic groups in CNTs, determined from the adsorption amount of hexylamine, is preferably 40 μmol / g or more, more preferably 50 μmol / g or more, and even more preferably 120 μmol / g or more. Furthermore, it is preferably 500 μmol / g or less, more preferably 250 μmol / g or less, and even more preferably 220 μmol / g or less. By setting the amount of acidic groups in CNTs within the aforementioned range, the affinity balance between CMC and water, the dispersion medium, is improved, resulting in a well-dispersed conductive material dispersion. Furthermore, the conductive material dispersion containing CNTs is also referred to as a CNT dispersion.

[0065] The outer diameter of CNTs is preferably 0.5 nm or more, more preferably 1 nm or more, and even more preferably 5 nm or more. Furthermore, it is preferably 30 nm or less, more preferably 20 nm or less, and even more preferably 13 nm or less. Regarding the average outer diameter, the CNTs can first be observed and photographed using a transmission electron microscope. Then, from the photographs, any 300 CNTs are selected, the outer diameter of each CNT is measured, and the average diameter is calculated.

[0066] When using two or more CNTs with different average outer diameters, the average outer diameter of the first CNT is preferably 0.5 nm or more, more preferably 1 nm or more. It is also preferable to have an average outer diameter of less than 5 nm. The average outer diameter of the second CNT is preferably 5 nm or more and 30 nm or less, more preferably 5 nm or more and 20 nm or less. The average outer diameter of the CNT can be calculated by observing the morphology of the CNT using a transmission electron microscope (manufactured by Nippon Electron Co., Ltd.) and measuring the length of the minor axis, based on the average value of the number of CNTs.

[0067] When using two or more CNTs with different average outer diameters, the mass ratio of the first CNT to the second CNT is preferably 1:10 to 1:100, more preferably 1:10 to 1:50.

[0068] CNTs with small outer diameters can conduct electricity between active materials that are far apart in the electrode layer. In addition, they can easily follow the expansion and contraction of active materials during charging and discharging, so they are preferred. On the other hand, CNTs with large outer diameters can conduct electricity between active materials that are close together and have a high probability of contact with active materials, so they are preferred.

[0069] The preferred specific surface area of ​​CNTs is 100 m². 2 / g or more, preferably 150 m 2 / g or more, and preferably 200 m 2 / g or more. Additionally, 1200 m is preferred. 2 / g or less, more preferably 1000 m 2 / g or less. The specific surface area of ​​CNTs was calculated using the BET method based on nitrogen adsorption determination.

[0070] The carbon purity of CNTs is expressed by the percentage (mass%) of carbon atoms in the CNTs. For 100% CNTs, a carbon purity of 80% by mass or more is preferred, more preferably 90% by mass or more, further preferably 95% by mass or more, and particularly preferably 98% by mass or more. By setting the carbon purity within this range, adverse conditions such as short circuits caused by dendrite formation from impurities can be prevented.

[0071] In the conductive material dispersion, the CNT content is preferably 0.2% by mass or more, more preferably 0.4% by mass or more, and even more preferably 1% by mass or more. Furthermore, it is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. By setting it within the aforementioned range, sedimentation and gelation are not caused, allowing the CNTs to exist well and stably. Additionally, the CNT content is preferably appropriately adjusted based on the specific surface area of ​​the CNTs, their affinity for the dispersion medium, and the dispersing ability of the dispersant, to obtain a carbon nanotube dispersion with appropriate flowability or viscosity.

[0072] [Carbon Black]

[0073] Examples of carbon black include acetylene black, furnace black, hollow carbon black, channel black, thermal cracking black, and Ketjen black. Furthermore, carbon black can be neutral, acidic, or alkaline, and can also be oxidized or graphitized.

[0074] The average primary particle size of carbon black is in the same range as that of carbon black used in general dispersions or coatings, preferably 0.01 μm to 1 μm, particularly preferably 0.01 μm to 0.2 μm, and even more preferably 0.01 μm to 0.1 μm. The average primary particle size referred to here is the arithmetic mean particle size measured using an electron microscope; this property value is generally used to describe the physical properties of carbon black.

[0075] Other known physical properties of carbon black include BET specific surface area and pH. BET specific surface area refers to the specific surface area measured by nitrogen adsorption using the BET method (hereinafter referred to as specific surface area). This specific surface area corresponds to the surface area of ​​the carbon black; the larger the specific surface area, the more dispersant is required. pH varies depending on the functional groups on the carbon black surface or the presence of impurities.

[0076] The preferred BET specific surface area for carbon black is 20 m². 2 / g~1500 m 2 / g, more preferably 30 m 2 / g~1000m 2 / g, preferably 100 m 2 / g~300 m 2 / g.

[0077] Carboxymethyl cellulose or its salts

[0078] Carboxymethyl cellulose (CMC) or its salts are anionic water-soluble polymers obtained from cellulose as a raw material. The weight-average molecular weight of CMC is preferably 10,000 or more. Furthermore, it is preferably 150,000 or less, more preferably 100,000 or less, more preferably 70,000 or less, more preferably 60,000 or less, and particularly preferably 30,000 or less. By setting the weight-average molecular weight within this range, the balance of intermolecular forces between CMC and CNTs and carbon black, and between CMC and water, is improved, allowing for good dispersion and maintenance. Furthermore, the degree of etherification of CMC is preferably 0.5 or more, more preferably 0.6 or more. Furthermore, it is preferably 0.9 or less, more preferably 0.8 or less. By setting the degree of etherification within this range, appropriate affinity can be achieved for water, CNTs, and carbon black. Furthermore, in the case of secondary batteries, adverse conditions such as the dispersant dissolving in the electrolyte within the battery, leading to an increase in electrolyte viscosity, can be prevented.

[0079] There are no particular limitations on the manufacturing method of CMC or its salts; they can be manufactured using general methods for manufacturing CMC or its salts. CMC or its salts are manufactured by: after a mercerizing reaction in which alkali reacts with cellulose, an etherifying agent is added to the obtained alkali cellulose to carry out an etherification reaction. For example, it can be manufactured by: after a mercerizing reaction using a mixed solvent containing water and an organic solvent, adding monochloroacetic acid to carry out an etherification reaction; then, neutralizing excess alkali with acid; and finally, removing the mixed solvent, washing, drying, and pulverizing. By extending the reaction time of the mercerizing reaction, the molecular weight of the cellulose raw material can be reduced.

[0080] The weight-average molecular weight of CMC, converted from pullulan, is preferably 10,000 or more, more preferably 15,000 or more. It is also preferably 100,000 or less, more preferably 60,000 or less, and even more preferably 30,000 or less. Having a suitable weight-average molecular weight improves the adsorption of CNTs and carbon black, further enhancing the stability of the dispersion. Furthermore, within the aforementioned range, the tendency for increased hygroscopicity and a decrease in film strength can be suppressed. Additionally, through hydrogen bonding in the aqueous solution, the tendency for increased viscosity and decreased discharge and storage stability of CNTs and carbon black can be suppressed. Furthermore, when using a disperser such as a nozzle-type high-pressure homogenizer where the dispersed liquid passes through a narrow flow path, the difficulty of transporting the liquid into the narrow flow path and the resulting decrease in dispersion efficiency can be suppressed.

[0081] Since commercially available CMCs mostly have molecular weights higher than the preferred range, they can be reduced in molecular weight through hydrolysis in an acidic aqueous solution before use. The weight-average molecular weight of the hydrolyzed CMC is preferably greater than 60,000 and less than 500,000. If the weight-average molecular weight is less than 500,000, the time-consuming hydrolysis reaction and the generation of large amounts of CMC oxidation decomposition products can be suppressed, thus facilitating purification. If the hydrolysis reaction in the acidic aqueous solution is carried out under heating and pressure, the reaction occurs in a short time. The molecular weight of the CMC can be controlled by adjusting the reaction time, temperature, and pH. Furthermore, the reaction can be stopped by cooling and neutralizing with an alkali to a pH of 7 or higher. Commonly available acids and alkalis can be used.

[0082] Based on the mass of CNTs and carbon black, the content of CMC or its salts is preferably 10% by mass or more, more preferably 20% by mass or more. Furthermore, it is preferably 100% by mass or less, more preferably 60% by mass or less, and even more preferably 40% by mass or less. By setting it within this range, CNTs and carbon black can be present well and stably without compromising conductivity when used as electrodes for secondary batteries. Additionally, from the viewpoint of coating processability and storage stability, CMC with a higher molecular weight than the CMC used in dispersion can also be added. When adding high molecular weight CMC, it is preferable to add it after manufacturing the CNT dispersion or at the final stage of the dispersion process. If added from the initial stage of dispersion, it may cause adverse conditions such as excessively high viscosity of the dispersion medium leading to reduced stirring efficiency, or changes in the adsorption equilibrium of CNTs leading to reduced dispersibility.

[0083] [Dispersion medium]

[0084] The dispersion medium is water, and may contain any water-soluble solvent. Examples of water-soluble solvents include: ethanol, propanol, butanol, methyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, N-methyl-2-pyrrolidone (NMP), etc.

[0085] [Other ingredients]

[0086] The conductive material dispersion can be appropriately formulated with dispersants, wetting agents, defoamers, surfactants, pH adjusters, wetting and penetrating agents, antioxidants, preservatives, mildew inhibitors, leveling agents, and other additives, or water-soluble dispersion media, conductive materials other than CNTs and carbon black, and polymeric components other than CMC, as needed and within the scope not affecting the purpose of the embodiments of the present invention. These can be added at any time, before, during, or after the dispersion is prepared. As a conductive material other than CNTs and carbon black, for example, one or more carbon materials such as graphite can be used. Polyacrylic acid is preferably used as a pH adjuster. Polyacrylic acid of any degree of polymerization can be used, and it can also be used as a copolymer with any monomer. It can be manufactured using generally known synthetic methods, or commercially available products can be used.

[0087] There is no particular limitation on the molecular weight of the polyacrylic acid that functions as a pH adjuster, but the weight average molecular weight is preferably 5,000 to 100,000, and more preferably 10,000 to 50,000.

[0088] Polyacrylic acid used as a pH adjuster is preferably unneutralized polyacrylic acid. When polyacrylic acid undergoes carboxyl group neutralization, it experiences counterionic condensation, resulting in a significant increase in the viscosity of the aqueous solution. This increase in viscosity deteriorates the processability of the conductive material dispersion, and even after drying, trace amounts of moisture remain, potentially affecting the performance of the secondary battery.

[0089] The pH of the conductive material dispersion is preferably 7.0 or higher and 10.5 or lower, more preferably 9.0 or higher and 10.5 or lower. When the pH is within this range, the tendency of the conductive material dispersion to gel can be suppressed. Furthermore, it can suppress corrosion of various raw materials and outer packaging materials within the battery, as well as gelation of adhesives. The pH can be measured using a general pH meter.

[0090] The dispersibility of conductive materials such as CNTs and carbon black in conductive material dispersions can be evaluated using the complex elastic modulus and phase angle obtained from dynamic viscoelasticity measurements. The complex elastic modulus represents the hardness of the conductive material dispersion; better dispersibility and lower viscosity result in a smaller complex elastic modulus. However, in cases where the carbon nanotube fiber length is large, or the carbon black structure length is large, even when the conductive material is uniformly and stably dispersed in the medium, the complex elastic modulus can sometimes be high due to the inherent structural viscosity of the conductive material. Furthermore, the phase angle refers to the phase shift of the stress wave when the strain applied to the conductive material dispersion is considered a sine wave, indicating the ease of flow of the dispersion. For a purely elastic body, it becomes a sine wave with the same phase as the applied strain, thus the phase angle is 0°. On the other hand, for a purely viscous body, it becomes a stress wave with a 90° phase shift. In typical viscoelasticity tests, the phase angle of a sample is a sine wave with a phase angle greater than 0° and less than 90°. If the conductive material in the dispersion is well dispersed, the phase angle is close to 90° of a pure viscous body. However, similar to the complex elastic modulus, when the conductive material itself has structural viscosity, even when the conductive material is uniformly and stably dispersed in the medium, the phase angle can sometimes be a low value.

[0091] The complex elastic modulus of the conductive material dispersion is preferably 50 Pa or less, more preferably less than 20 Pa, even more preferably 10 Pa or less, and further preferably 5 Pa or less. The complex elastic modulus of the conductive material dispersion is preferably 0.01 Pa or more, more preferably 0.05 Pa or more, and further preferably 0.1 Pa or more. The phase angle of the conductive material dispersion is preferably 5° or more, more preferably 19° or more, further preferably 30° or more, and particularly preferably 45° or more. The phase angle of the conductive material dispersion is preferably 90° or less, more preferably 85° or less, and further preferably 80° or less. The complex elastic modulus and phase angle can be determined using the methods described in the examples.

[0092] The complex elastic modulus and phase angle of the conductive material dispersion are determined by the dispersibility of CNTs and carbon black in the dispersion, as well as the entanglement of CNTs, carbon black, CMC, and other resin components, or the influence of their intermolecular forces. Therefore, if the complex elastic modulus X (Pa) and phase angle Y (°) are set within the preferred range, and their product (X×Y) is 100 or more and 1,500 or less, a conductive material dispersion with excellent dispersion stability can be obtained, thereby forming an excellent conductive network, and thus obtaining an electrode film with very good conductivity. In addition, although CMC with a weight average molecular weight of 10,000 to 150,000 and a degree of etherification of 0.5 to 0.9 has low viscoelasticity, if the product (X×Y) of the complex elastic modulus X (Pa) and phase angle Y (°) when the conductive material dispersion is prepared is 100 or more and 1,500 or less, it is considered to act as a thickener or binder for use in electrode compositions of secondary batteries, thereby improving electrode strength and battery performance. Furthermore, it is even more preferable to have a complex elastic modulus of 50 Pa or less and a phase angle of 15° or more. It is not enough for the conductive material dispersion to simply have low viscosity (apparently) and good dispersibility; it is particularly effective to combine conventional indicators such as complex elastic modulus, phase angle, and viscosity to determine the dispersion state.

[0093] The dispersibility of CNTs in the conductive material dispersion can also be evaluated by the median particle size (μm) determined using a laser diffraction / scattering particle size analyzer. Based on the particle size distribution of scattered light, the particle size of the CNT aggregates can be estimated from the median particle size (μm) determined by the laser diffraction / scattering particle size analyzer. The median particle size (μm) is preferably 0.5 μm or more and 5.0 μm or less, more preferably 0.5 μm or more and 2.0 μm or less. By setting it within this range, a CNT dispersion with appropriate dispersion can be obtained. If the value is below this range, aggregated CNTs exist; conversely, if the value is above this range, a large number of finely cleaved CNTs are generated, making it difficult to efficiently form a conductive network. The median particle size can be determined using the method described in the examples.

[0094] The dispersibility of CNTs in conductive material dispersions can also be evaluated using gloss, measured at 60° (i.e., the intensity of reflected light at 60° relative to the angle of incidence), obtained by coating a smooth glass substrate and sintering and drying it. For example, 1 mL of CNT dispersion is dropped onto a smooth glass substrate, coated at 2 cm / s using a No. 7 rod coater, sintered in a 140°C hot air oven for 10 minutes, and then cooled to obtain a coating. Using a gloss meter (BYK Gardner micro-gross 60°), three points are randomly selected on the coating surface (excluding the ends), and measurements are taken once at each point. The average value is taken as the gloss at 60°. Regarding the incident light on the coating, better dispersion results in a smoother coating surface, and therefore higher gloss. Conversely, the worse the dispersibility, the more light scattering occurs due to the unevenness of the coating surface, resulting in lower gloss. The gloss at 60° can be measured using the method described in the examples. The gloss is preferably 5 or higher, more preferably 50 or higher, even more preferably 60 or higher, and particularly preferably 70 or higher. Furthermore, it is preferably 120 or lower, even more preferably 110 or lower. By setting it within the aforementioned range, a CNT dispersion with a suitable dispersion state can be obtained. If it is below the range, aggregated CNTs exist; if it is above the range, a large number of finely cleaved CNTs are generated, making it difficult to efficiently form a conductive network.

[0095] The thixotropic index (TI) of the conductive material dispersion can be calculated by dividing the viscosity (mPa·s) measured at 60 rpm using a type B viscometer by the viscosity (mPa·s) at 6 rpm. The TI value is preferably 2.0 or higher and 5.0 or lower. A higher TI value indicates greater structural viscosity caused by the entanglement of CNTs, carbon black, CMC, and other resin components, or their intermolecular forces; a lower TI value indicates less structural viscosity. By setting the TI value within the aforementioned range, the entanglement of CNTs, carbon black, CMC, and other resin components can be suppressed, while allowing their intermolecular forces to function appropriately.

[0096] The fiber length of carbon nanotubes in the conductive material dispersion is preferably 0.3 μm to 5 μm, more preferably 0.5 μm to 3.5 μm.

[0097] (Dispersion method)

[0098] The conductive material dispersion is preferably manufactured by finely dispersing, for example, CNT, carbon black, CMC or their salts, and water using a dispersion device. Furthermore, the dispersion process can be performed in multiple stages, with the timing of material addition adjusted as needed.

[0099] Examples of dispersion devices include: kneaders, two-roll mills, three-roll mills, planetary mixers, ball mills, horizontal sand mills, vertical sand mills, ring bead mills, grinding mills, high-shear mixers, high-pressure homogenizers, and ultrasonic homogenizers. In particular, from the viewpoint of promoting the wetting of CNTs and carbon black and breaking down coarse particles, a high-shear mixer is most preferably used in the initial dispersion process. Furthermore, from the viewpoint of dispersing while maintaining the fiber length of CNTs or the structure of carbon black, a high-pressure homogenizer is most preferably used. Additionally, after dispersing using a high-pressure homogenizer to achieve a median particle size of 4.0 μm or less, further dispersing using a bead mill to a phase angle of 40° or more can achieve uniform dispersion while maintaining fiber length. The pressure when using a high-pressure homogenizer is preferably 60 MPa to 150 MPa, more preferably 60 MPa to 120 MPa.

[0100] Dispersion methods using dispersion devices include batch dispersion, through-flow dispersion, and circulating dispersion, and can be any one of these methods or a combination of two or more. Batch dispersion is a method that disperses the liquid without piping, relying solely on the main body of the dispersion device. It is preferred for small-scale production due to its simplicity. Through-flow dispersion includes a tank supplying the liquid to be dispersed to the main body of the dispersion device via piping, and a receiving tank for the liquid, allowing the liquid to pass through the main body of the dispersion device. Circulating dispersion refers to a method where the liquid being dispersed, after passing through the main body of the dispersion device, is returned to the supply tank, allowing dispersion to continue while circulating. In all these methods, dispersion progresses with longer processing time; therefore, the through-flow or circulating process can be repeated until the target dispersion state is achieved. Furthermore, the throughput can be increased by changing the tank size or processing time. Through-flow dispersion is preferred for its ease of achieving a uniform dispersion state compared to circulating dispersion. Circulating dispersion is preferred for its simplicity in operation and manufacturing equipment compared to through-flow dispersion. In the dispersion process, the crushing of aggregated particles, decomposition of CNTs, wetting, and stabilization are carried out sequentially or simultaneously. The resulting dispersion state varies depending on the method of execution. Therefore, it is preferable to manage the dispersion state in each dispersion process by using various evaluation methods. For example, the methods described in the embodiments can be used for management.

[0101] <Composition for Secondary Battery Electrodes>

[0102] The composition for secondary battery electrodes comprises at least the conductive material dispersion, and may include a binder resin, and may further mix any other components. The composition for secondary battery electrodes comprises water, and may also optionally include a water-soluble solvent exemplified as a dispersion medium.

[0103] [Adhesive Resin]

[0104] When the composition for secondary battery electrodes also includes a binder resin, there are no particular restrictions as long as it is a substance commonly used as a binder resin in coatings, and it can be selected appropriately according to the purpose. In addition, the binder resin used in the composition for secondary battery electrodes can be a resin that can bind active materials, CNTs, carbon black, other conductive materials, etc., and can also be a CMC with a molecular weight, degree of etherification, etc., that is different from the CMC contained in the conductive material dispersion. Examples of binder resins used in compositions for secondary battery electrodes include: polymers or copolymers comprising ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylate, methacrylic acid, methacrylate, acrylonitrile, styrene, vinylbutyral, vinyl acetal, and vinylpyrrolidone 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 fluoropolymers; cellulose resins; elastomers such as styrene-butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified forms or mixtures of these resins, and copolymers, may also be used. Among these, when used as a binder resin for the positive electrode, polymers or copolymers containing fluorine atoms within the molecule are preferred from a durability point of view, such as polyvinylidene fluoride, polyvinylidene fluoride, and tetrafluoroethylene. In addition, when using an adhesive resin as a negative electrode, CMC with good adhesion (of which the molecular weight, degree of etherification, etc. are different from those of the CMC contained in the conductive material dispersion), styrene-butadiene rubber, polyacrylic acid, etc. are preferred.

[0105] In the non-volatile components of the composition for secondary battery electrodes, the content of the binder resin used in the composition for secondary battery electrodes is preferably 0.5% to 30% by mass, more preferably 0.5% to 25% by mass.

[0106] The electrode composition for secondary batteries may contain either a positive electrode active material or a negative electrode active material. In this specification, the positive and negative electrode active materials are sometimes simply referred to as "active materials." An active material is a material that forms the basis of the battery reaction. Active materials are classified into positive electrode active materials and negative electrode active materials according to their electromotive force. In this specification, the electrode composition for secondary batteries containing either a positive or negative electrode active material is sometimes referred to as a "positive electrode composite material composition," a "negative electrode composite material composition," or simply a "composite material composition," respectively. To improve uniformity and processability, the composite material composition is preferably in slurry form. The composite material composition contains at least a conductive material dispersion and an active material, and may also contain a binder resin.

[0107] [Positive electrode active material]

[0108] There are no particular limitations on the positive electrode active material. For example, in secondary battery applications, it can be a metal compound such as a metal oxide or metal sulfide that can reversibly dope or intercalate lithium ions. Examples include lithium manganese composite oxides (e.g., Li). x Mn2O4 or Li x MnO2), lithium-nickel composite oxides (e.g., Li) x NiO2), lithium cobalt composite oxide (Li x CoO2), lithium nickel cobalt composite oxides (e.g., Li) x Ni 1-y Co y O2), lithium manganese cobalt composite oxides (e.g., Li) x Mn y Co 1-y O2), lithium nickel manganese cobalt composite oxides (e.g., Li) x Ni y Co z Mn 1-y-z O2), spinel-type lithium manganese nickel composite oxides (e.g., Li) x Mn 2-y Ni y Lithium-transition metal composite oxide powders such as O4, and lithium phosphorus oxide powders with olivine structure (e.g., Li) x FePO4, Li x Fe 1- y Mn y PO4, Li x CoPO4, manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxide (e.g., V2O5, V6O) 13 The active materials include transition metal oxide powders such as titanium dioxide, ferric sulfate (Fe2(SO4)3), TiS2, and transition metal sulfide powders such as FeS. Here, x, y, and z represent quantities, where 0 < x < 1, 0 < y < 1, 0 < z < 1, and 0 < y + z < 1. One or a combination of these positive electrode active materials can be used.

[0109] [Negative Electrode Active Material]

[0110] There are no particular limitations on the negative electrode active material. For example, metallic Li, or its alloys, tin alloys, silicon alloys, or Li can be used as negative electrodes that can reversibly dope or intercalate lithium ions. x TiO2, Li x Fe2O3, Li x Fe3O4, Li xMetal oxides such as WO2; conductive polymers such as polyacetylene and poly(p-phenylene); artificial graphite or carbonaceous powders such as highly graphitized carbon materials, or natural graphite; and resin-calcined carbon materials. Here, x represents the quantity, 0 < x < 1. These negative electrode active materials can be used individually or in combination. Especially when using silicon alloy negative electrodes, the theoretical capacity is large; however, the volume expansion is extremely large. Therefore, it is preferable to use them in combination with artificial graphite or carbonaceous powders such as highly graphitized carbon materials, or resin-calcined carbon materials.

[0111] Based on the mass of the active material (with the mass of the active material set as 100% by mass), the content of the conductive material in the composite material composition is preferably 0.01% by mass or more, more preferably 0.02% by mass or more, and even more preferably 0.03% by mass or more. Furthermore, it is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0112] Based on the mass of the active substance (with the mass of the active substance set as 100% by mass), the content of the dispersant in the composite material composition is preferably 0.01% by mass or more, more preferably 0.02% by mass or more. Furthermore, it is preferably 10% by mass or less, more preferably 5% by mass or less.

[0113] When the composite composition contains a binder resin, the content of the binder resin in the composite composition is preferably 0.5% by mass or more, based on the mass of the active substance (where the mass of the active substance is set to 100% by mass). Furthermore, it is preferably 30% by mass or less, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0114] Based on the mass of the composite material composition (with the mass of the composite material composition set as 100% by mass), the amount of solid components in the composite material composition is preferably 30% by mass or more, more preferably 40% by mass or more. Furthermore, it is preferably 90% by mass or less, more preferably 80% by mass or less.

[0115] Composite material compositions can be manufactured using various methods known in the art. Examples include: methods involving adding an active substance to a conductive material dispersion; methods involving adding an active substance to a conductive material dispersion followed by adding a binder resin; and methods involving adding an active substance to a conductive material dispersion followed by adding a binder resin. A preferred method for manufacturing composite material compositions is to add a binder resin to a conductive material dispersion, then further add an active substance and disperse it. The dispersion apparatus used for dispersion is not particularly limited. The dispersion apparatus listed in the description of the conductive material dispersion can be used to obtain the composite material composition. Therefore, another method for manufacturing composite material compositions is to add an electrode active substance to the conductive material dispersion without adding a binder resin and disperse it.

[0116] <Electrode film>

[0117] The electrode film includes at least one selected from the group consisting of films formed using a conductive material dispersion and films formed using a secondary battery electrode composition. The electrode film may also include a current collector. The electrode film, for example, can be obtained by coating a secondary battery electrode composition onto a current collector and then drying it, including both the current collector and the film. An electrode film formed using a positive electrode composite composition can be used as a positive electrode. An electrode film formed using a negative electrode composite composition can be used as a negative electrode. In this specification, a film formed using a secondary battery electrode composition containing an active material is sometimes referred to as an "electrode composite layer."

[0118] There are no particular limitations on the material and shape of the current collector used to form the electrode film; materials and shapes suitable for various secondary batteries can be selected. Examples of materials for the current collector include conductive metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. Regarding shape, planar foils are generally used, but current collectors with roughened surfaces, perforated foil-shaped current collectors, and mesh-like current collectors can also be used. The thickness of the current collector is preferably around 0.5 μm to 30 μm.

[0119] There are no particular limitations on the method of coating a conductive material dispersion or a composition for secondary battery electrodes onto a current collector, and known methods can be used. Specifically, examples include: mold coating, dip coating, roller coating, blade coating, spray coating, gravure coating, screen printing, or electrostatic coating. As for drying methods, examples include: drying by placement, or drying using a blower dryer, a warm air dryer, an infrared heater, or a far-infrared heater, but these are not particularly limited to these methods.

[0120] After coating, the film can be calendered using a flatbed press, calendering roller, or similar equipment. The resulting film has a thickness of, for example, 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0121] To improve the adhesion between the electrode composite layer and the current collector, or to improve the conductivity of the electrode film, a film formed using a conductive material dispersion or a composition for secondary battery electrodes can also be used as the base layer of the electrode composite layer.

[0122] Secondary batteries

[0123] A secondary battery includes a positive electrode, a negative electrode, and an electrolyte, and at least one selected from the group consisting of positive and negative electrodes includes an electrode membrane.

[0124] As the electrolyte, various conventionally known electrolytes capable of ion mobility can be used. Examples include lithium salt-containing electrolytes such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (where Ph is phenyl), but these are not limited to. The electrolyte is preferably used as an electrolyte solution after being dissolved in a non-aqueous solvent.

[0125] As non-aqueous solvents, there are no particular limitations. Examples include: carbonates such as ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octyl lactone; ethylene glycol dimethyl ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxacyclopentane, 4-methyl-1,3-dioxacyclopentane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents can be used individually or in mixtures of two or more.

[0126] A secondary battery containing a non-aqueous electrolyte in a non-aqueous solvent (a non-aqueous electrolyte secondary battery) preferably includes a separator. Examples of separators include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics that have undergone hydrophilic treatment, but are not particularly limited to these.

[0127] There are no particular limitations on the structure of non-aqueous electrolyte secondary batteries. They typically include a positive electrode and a negative electrode, as well as a separator as needed. They can be made into various shapes, such as paper type, cylindrical type, button type, and stacked type, depending on the intended use.

[0128] <Vehicles>

[0129] The vehicle includes a secondary battery. Secondary batteries can be used, for example, as a power source for vehicles such as cars, buses, trucks, and trams, and can be incorporated into hybrid vehicles, electric vehicles, etc.

[0130] This invention is related to the subject matter of Japanese Patent Application No. 2020-078026 filed on April 27, 2020 and Japanese Patent Application No. 2020-205488 filed on December 11, 2020, the entire disclosure of which is incorporated herein by reference.

[0131] Example

[0132] The following examples illustrate the invention in more detail. The invention is not limited to these examples as long as it does not depart from its spirit. Furthermore, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0133] (Method for determining weight-average molecular weight (Mw))

[0134] The weight-average molecular weight (Mw) of the manufactured sodium carboxymethyl cellulose was determined by gel permeation chromatography (GPC) equipped with a refractive index (RI) detector under the following conditions. Molecular weight is a conversion value from pachymenopausal polysaccharides.

[0135] Test sample: 0.1% by mass aqueous solution

[0136] Device: HLC-8320GPC (manufactured by Tosoh)

[0137] Eluent: 0.1M NaCl aqueous solution

[0138] Column: TSK gel, SuperMultipore PW-M (manufactured by Tosoh)

[0139] Flow rate: 1.0 mL / min

[0140] Temperature: 25℃

[0141] Injection volume: 100 μl

[0142] (Method for determining the degree of etherification)

[0143] 0.6 g of sodium carboxymethyl cellulose was dried at 105 °C for 4 hours. The dried product was accurately weighed, wrapped in filter paper, and ashed in a magnetic crucible. The ashed product was transferred to a 500 ml beaker, and 250 ml of water and 35 ml of a 0.05 mol / L sulfuric acid aqueous solution were added. The mixture was boiled for 30 minutes. After cooling, the excess acid was back-titrated with a 0.1 mol / L potassium hydroxide aqueous solution. Phenolphthalein was used as an indicator. The degree of etherification was calculated using the results from Equation 1.

[0144] (Degree of etherification) = 162 × A / (10000 - 80A) (Equation 1)

[0145] A = (af - bf1) / weight of dried product (g)

[0146] A: The amount (ml) of 0.05 mol / L sulfuric acid aqueous solution consumed by the combination of 1 g of sample with the alkali.

[0147] a: Volume (ml) of 0.05 mol / L sulfuric acid aqueous solution used.

[0148] f: Titration rate of 0.05 mol / L sulfuric acid aqueous solution

[0149] b: Titration volume (ml) of 0.1 mol / L potassium hydroxide aqueous solution

[0150] f1: Titration rate of 0.1 mol / L potassium hydroxide aqueous solution

[0151] (Preparation of sodium carboxymethyl cellulose)

[0152] (Manufacturing Example 1)

[0153] Ten parts by weight of a low-density slurry, pulverized using a household mixer, were placed in the vessel of a planetary mixer (HIVIS DISPER MIX 3D-2, manufactured by Primix). Then, 90 parts by weight of a 15% by weight sodium hydroxide / IPA (isopropanol) / water solution (IPA:water mass ratio of 80:20) were added to the vessel, and the mixture was stirred at 40°C for 150 minutes to induce mercerization, yielding alkali cellulose. Next, 10 parts by weight of monochloroacetic acid were dissolved in 6 parts by weight of the sodium hydroxide / IPA / water solution. After adjusting the temperature to 25°C, the alkali cellulose was added over 60 minutes while maintaining the temperature at 35°C. The temperature was then increased to 80°C over 30 minutes, and an etherification reaction was carried out at 80°C for 50 minutes. Finally, the mixture was neutralized with 50% by weight acetic acid to a pH of 7.0.

[0154] The solid components of the neutralized product were separated using a Büchner funnel. The funnel was then washed with a 70% (w / w) methanol aqueous solution to remove byproducts such as sodium chloride, sodium glycolate, and sodium acetate. The product was transferred to a stainless steel square container and dried in a hot air oven at 90°C for 4 hours. After pulverization, sodium carboxymethyl cellulose (CMC1) was obtained. The weight-average molecular weight and degree of etherification of the obtained sodium carboxymethyl cellulose are shown in Table 1.

[0155] (Manufacturing Example 2, Manufacturing Example 3)

[0156] Except for changing the reaction times of the mercerizing and etherification processes to those recorded in Table 1, sodium carboxymethyl cellulose (CMC2, CMC3) was obtained in the same manner as in Manufacturing Example 1. The weight average molecular weight and degree of etherification of the obtained sodium carboxymethyl cellulose are shown in Table 1.

[0157] [Table 1]

[0158]

[0159] (Method for determining the acidity of CNTs)

[0160] The acidic basis of CNTs was calculated by back titration to determine the adsorption capacity of hexylamine as follows: 0.2 g of CNTs were collected in a glass bottle (M-70, manufactured by Kashiwagawa Glass), and 30 ml of hexylamine / NMP solution (0.02 mol / L) was added. The glass bottle was irradiated with ultrasound (frequency 28 Hz) for 1 hour, and coarse particles were removed using a 25 μm nylon mesh. Then, the mixture was centrifuged at 10,000 rpm for 10 minutes using a small centrifuge (MCF-1350, manufactured by LMS), and the supernatant was collected and filtered using a membrane filter (0.22 μm pore size). The filtrate was recovered. 10 ml of the obtained filtrate was collected and diluted with 40 ml of deionized water to prepare the titrant. Additionally, 10 ml of the CNTs and 10 ml of the untreated hexylamine / NMP solution (0.02 mol / L) were diluted with 40 ml of deionized water to prepare a standard titrant. A separate potentiometric titration apparatus (AT-710S, manufactured by Kyoto Electronics Industry) was used to titrate the titrant and the standard titrant separately with a 0.1 mol / L HCl / ethanol solution. The amount of hexylamine adsorbed on CNTs ([hexylamine adsorption amount] (μmol)) was calculated from the difference in titration amount at the isoelectric point.

[0161] 10 ml of the titrant was collected from 30 ml of hexylamine / NMP solution. The mass of CNTs was 0.2 g. Therefore, the value of [hexylamine adsorption capacity] multiplied by 3 and divided by 0.2 is the [hexylamine adsorption capacity] per unit weight of conductive material (μmol / g). This value is further divided by the specific surface area of ​​CNTs to obtain the "hexylamine adsorption capacity" per unit surface area of ​​CNTs (μmol / m²). 2 ).

[0162] (Method for determining the specific surface area of ​​conductive materials)

[0163] Using an electronic balance (Sartorius, MSA225S100DI), 0.03 g of conductive material was weighed and then dried at 110°C for 15 minutes while degassing. Then, the specific surface area (m²) of the conductive material was measured using a fully automated specific surface area measuring device (Mountech, HM-model 1208). 2 / g).

[0164] (Method for determining the G / D ratio of conductive materials)

[0165] A conductive material was placed in a Raman microscope (XploRA, manufactured by Horiba Manufacturing Co., Ltd.), and measurements were performed using a 532 nm laser wavelength. The measurement conditions were set as follows: 60-second acquisition time, 2 repetitions, 10% neutral density filter, 20x objective lens magnification, 500mm confocal aperture, 100 μm slit width, and 100 cm⁻¹ measurement wavelength. -1 ~3000cm -1 The conductive material used for the measurement was spread onto a glass slide and flattened using a spatula. Within the obtained peak, the spectrum at 1560 cm⁻¹... -1 ~1600 cm -1 The maximum peak intensity is set to G within the range, and it is at 1310 cm⁻¹ in the spectrum. -1 ~1350 cm -1 Within the range, the maximum peak intensity is set as D, and the G / D ratio of the conductive material is measured.

[0166] (Methods for determining dispersed particle size)

[0167] The particle size distribution was determined using a grinding gauge with a maximum groove depth of 300 μm, based on the judgment method of Japanese Industrial Standards (JIS) K5600-2-5.

[0168] (Methods for measuring gloss)

[0169] The samples used for gloss measurement were obtained as follows: 1 mL of conductive material dispersion was dropped onto a smooth glass substrate, coated at 2 cm / s using a No. 7 bar coater, sintered in a hot air oven at 140°C for 10 minutes, and then allowed to cool. The coated area was set to approximately 10 cm × 10 cm. Using a gloss meter (BYK Gardner Micro-Gross 60°), three points were randomly selected on the coated surface excluding the ends, and each measurement was performed once. The average value was set as the gloss at 60°.

[0170] (Method for determining the median particle size of conductive material dispersions)

[0171] Median particle size was determined using a particle size distribution measuring device (Partical LA-960V2, manufactured by Horiba). The operating conditions for the circulating / ultrasonic test were set as follows: circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 1, stirring mode: continuous. Additionally, ultrasonic testing was performed in the exhaust gas at an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds. The refractive index of water was set to 1.333, and the refractive index of carbon materials was set to 1.92. Measurements were performed after diluting the test sample until the transmittance of the red laser diode was 60%–80%, and the particle size was determined based on volume.

[0172] (Method for determining the viscosity of conductive material dispersions)

[0173] The viscosity of the conductive material dispersion was measured using a Type B viscometer ("BL" manufactured by Toki Sangyo). The dispersion was thoroughly stirred with a scraper at 25°C, and the measurement was immediately taken at a rotor speed of 6 rpm, followed by a measurement at 60 rpm. Lower viscosity indicates better dispersibility, while higher viscosity indicates poorer dispersibility. Significant separation or sedimentation of the resulting dispersion was considered poor dispersibility. The viscosity index (TI) was calculated by dividing the viscosity (mPa·s) at 60 rpm by the viscosity (mPa·s) at 6 rpm. For the conductive material dispersion, viscosity less than 500 mPa·s is excellent, 500 mPa·s or more but less than 2,000 mPa·s is good, 2,000 mPa·s or more but less than 10,000 mPa·s is poor, and 10,000 mPa·s or more, with sedimentation or separation, is extremely poor.

[0174] (Determination of complex elastic modulus and phase angle of conductive material dispersion)

[0175] The complex elastic modulus X and phase angle Y of the conductive material dispersion were evaluated using a rheometer (RheoStress 1 rotary rheometer manufactured by Thermo Fisher Scientific) with a diameter of 35 mm and a 2° cone, at 25°C and a frequency of 1 Hz, within a strain rate range of 0.01% to 5%. A smaller complex elastic modulus indicates better dispersibility, while a larger one indicates poorer dispersibility. Similarly, a larger phase angle indicates better dispersibility, while a smaller one indicates poorer dispersibility. The product of the obtained complex elastic modulus X (Pa) and the phase angle Y (°) (X×Y) was then calculated.

[0176] (Method for pH determination of conductive material dispersion)

[0177] The pH of the conductive material dispersion was measured at 25°C using a benchtop pH meter (SevenCompact S220 Expert Pro, manufactured by Mettler-Toledo).

[0178] (Stability evaluation method for conductive material dispersions)

[0179] The evaluation of storage stability involves measuring the viscosity of the dispersion after it has been stored at 50°C for 7 days. The method used is the same as that used for initial viscosity measurement.

[0180] Judgment Criteria

[0181] A: Same as the initial stage (excellent)

[0182] B: Viscosity changed slightly (Good)

[0183] C: Viscosity increased but did not gel (acceptable)

[0184] E: Gel formation (extremely poor)

[0185] (Preparation of conductive material dispersion)

[0186] The abbreviations used in the following description are as follows.

[0187] • 10B: JENOTUBE 10B (manufactured by JEIO, multilayer CNT, outer diameter 7 nm~12 nm, average outer diameter 8.8 nm, specific surface area 230 m²) 2 / g, acidic base content 0.67 μmol / m 2 , 154 μmol / g, G / D ratio 0.80)

[0188] • 6A: JENOTUBE 6A (manufactured by JEIO, multilayer CNT, outer diameter 5 nm~7 nm, average outer diameter 6.9 nm, specific surface area 700 m²) 2 / g, acidic base content 0.27 μmol / m 2 , 190 μmol / g, G / D ratio 0.80)

[0189] ·TUBALL1: Single-walled carbon nanotubes (manufactured by OCSiAl, outer diameter 1.3 nm–2.3 nm, average outer diameter 1.8 nm, purity 80%, specific surface area 490 m²) 2 / g, acidic base content 0.38 μmol / m 2 , 186 μmol / g, G / D ratio 39.1)

[0190] ·TUBALL2: Single-walled carbon nanotubes (manufactured by OCSiAl, outer diameter 1.2 nm–2.0 nm, average outer diameter 1.5 nm, purity 93%, specific surface area 975 m²) 2 / g, acidic base content 0.21 μmol / m 2 , 205 μmol / g, G / D ratio 41.7)

[0191] • TNSR: Single-walled carbon nanotubes (manufactured by Timesnano, outer diameter 1.0 nm–2.0 nm, average outer diameter 1.6 nm, specific surface area 610 m²). 2 / g, acidic base content 0.79 μmol / m 2 , 480 μmol / g, G / D ratio 27.8)

[0192] TNSAR: Single-walled carbon nanotubes (manufactured by Timesnano, outer diameter 1.0 nm–2.0 nm, average outer diameter 1.3 nm, specific surface area 950 m²). 2 / g, acidic base content 0.31 μmol / m 2 , 290 μmol / g, G / D ratio 36.4)

[0193] EC-300J: Ketjen Black (manufactured by Lion Specialty Chemicals), average primary particle size 40 nm, specific surface area 800 m². 2 / g, acidic base content 0.27 μmol / m 2 219 μmol / g

[0194] • HS-100: DENKA Black HS-100 (manufactured by Denka, Nippon Electric Machinery Co., Ltd., acetylene black, average primary particle size 48 nm, specific surface area 39 m²) 2 / g, acidic base content 0.21 μmol / m 2 205 μmol / g

[0195] • LITX200: LITX (registered trademark) 200 (manufactured by Cabot, furnace black, specific surface area 130m²) 2 / g)

[0196] • LITXHP: LITX (registered trademark) HP (manufactured by Cabot, furnace black, specific surface area 100m²) 2 / g)

[0197] FX-35: Denka Black (manufactured by Denka Corporation, Japan; acetylene black; specific surface area 133 m²) 2 / g)

[0198] • APP-84: Sodium carboxymethyl cellulose, manufactured by Nippon Paper, Sunrose A APP-84

[0199] • F01MC: Sodium carboxymethyl cellulose, manufactured by Nippon Paper, Sunrose F F01MC

[0200] • F04HC: Sodium carboxymethyl cellulose, manufactured by Nippon Paper, Sunrose F F04MC

[0201] • A02SH: Sodium carboxymethyl cellulose, manufactured by Nippon Paper, Sunrose.

[0202] • F10LC: Sodium carboxymethyl cellulose, manufactured by Nippon Paper, Sunrose F F10LC

[0203] • F10MC: Sodium carboxymethyl cellulose, manufactured by Nippon Paper, Sunrose F10MC

[0204] • F30MC: Sodium carboxymethyl cellulose, manufactured by Nippon Paper, Sunrose F F30MC

[0205] • MAC500LC: Sodium carboxymethyl cellulose, manufactured by Nippon Paper, Sunrose Special Type MAC500LC

[0206] Cellogen 5A: Sodium carboxymethyl cellulose, manufactured by First Industrial Pharmaceuticals.

[0207] Cellogen 6A: Sodium carboxymethyl cellulose, manufactured by First Industrial Pharmaceuticals.

[0208] PAA: Polyacrylic acid, manufactured by Wako Pure Chemical Industries, with an average molecular weight of 25,000.

[0209] • AC-10P: Polyacrylic acid, manufactured by Dong-A Synthetic, average molecular weight 9,000

[0210] • AC-10LP: Polyacrylic acid, manufactured by Dong-A Synthetic, average molecular weight 50,000

[0211] HL415: Polyacrylic acid, manufactured by Nippon Catalyst Co., Ltd., Aqualic, average molecular weight 10,000, NV 45%.

[0212] (Example 1-A1)

[0213] 93.7 parts by weight of ion-exchanged water were added to a stainless steel container, and 1.25 parts by weight of APP-84 (CMC) were added and dissolved while stirring using a dispersant. Then, 2.0 parts by weight of 10B (CNT) were added while stirring using a dispersant. A square-hole high-shear screen was installed on a high-shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was homogenized at 8,600 rpm. Batch dispersion was performed using a grinder until the particle size reached below 250 μm. At this point, the particle size confirmed by the grinder was 180 μm. Subsequently, the dispersed liquid was supplied from the stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINOMACHINE) via piping for circulating dispersion. The dispersion was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Dispersion was carried out until the viscosity of the dispersed liquid, measured at 60 rpm using a Type B viscometer (manufactured by TOKISANGYO, model: BL), reached below 3,000 mPa·s. Then, while stirring with a disperser, 0.5 parts by weight of 10B were added to a stainless steel container, and the mixture was again dispersed using a high-pressure homogenizer. This process of circulating dispersion using a high-pressure homogenizer until the viscosity reached below 3,000 mPa·s was repeated, with 10B added to the stainless steel container while stirring with a disperser. This process was repeated a total of 6 times (the total amount of 10B added was 5.0 parts by weight). Next, a through-flow dispersion process was performed 10 times using a high-pressure homogenizer to obtain a conductive material dispersion containing 5.0 parts by weight of CNTs (CNT dispersion A1).

[0214] (Example 1-A2, Example 1-A3)

[0215] Except for changing the number of dispersion cycles to 20 and 30 times respectively, conductive material dispersions (CNT dispersion A2 and CNT dispersion A3) were obtained in the same manner as in Example 1-A1.

[0216] (Examples 1-A4 to Example 1-A12, Example 1-A17 to Example 1-A20)

[0217] Except for changing the materials, composition ratios, and number of dispersions as shown in Table 3, conductive material dispersions (CNT dispersions A4 to A20) were obtained in the same manner as in Examples 1-1A.

[0218] (Comparative Examples 1-a1 to 1-a14)

[0219] Except for changing the materials, composition ratios, and number of dispersions as shown in Table 4, conductive material dispersions (CNT dispersions a1 to a14) were obtained in the same manner as in Examples 1-1A.

[0220] (Example 1-A13)

[0221] The conductive material dispersion (CNT dispersion A3) obtained in Example 1-A3 was placed in a stainless steel container. While stirring with a disperser, PAA was added to bring the total amount to 0.004 parts by mass, thereby obtaining a conductive material dispersion (CNT dispersion A13) containing 5.0 parts by mass of CNTs. The pH of CNT dispersion A13 was 7.5.

[0222] (Example 1-A14)

[0223] Except for changing PAA to AC-10P, a conductive material dispersion (conductive material dispersion A14) was obtained using the same method as in Examples 1-A13. The pH of CNT dispersion A14 was 7.1.

[0224] (Example 1-A15)

[0225] Except for changing PAA to AC-10LP, a conductive material dispersion (CNT dispersion A15) was obtained using the same method as in Examples 1-A13. The pH of CNT dispersion A15 was 7.0.

[0226] (Example 1-A16)

[0227] Except for changing PAA to HL415, a conductive material dispersion (CNT dispersion A16) was obtained using the same method as in Examples 1-A13. The pH of CNT dispersion A16 was 7.5.

[0228] (Example 1-A21)

[0229] 98.05 parts by weight of ion-exchanged water were added to a stainless steel container, and 0.45 parts by weight of APP-084 (CMC) were added while stirring using a disperser to dissolve it. Then, 0.115 parts by weight of TNSR (CNT) and 1.385 parts by weight of 10B (CNT) were added while stirring using a disperser. A square-hole high-shear screen was installed on a high-shear mixer (L5M-A, manufactured by SILVERSON), and the mixture was homogenized at 8,600 rpm. Batch dispersion was performed using a grinding mill until the particle size reached below 250 μm. Subsequently, the dispersion was supplied from the stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINO MACHINE) via piping for 20 pass-through dispersion treatments. The dispersion process was carried out using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain a conductive material dispersion (CNT dispersion A2) containing 1.5 parts by mass of CNTs. The mass ratio of TSRN to 10B CNTs was 1:12.

[0230] (Example 1-A22)

[0231] Except for changing the amount of ion-exchanged water added from 98.05 parts by mass to 96.75 parts by mass, the amount of APP-084 added from 0.45 parts by mass to 0.75 parts by mass, the amount of 10B added from 1.385 parts by mass to 2.4 parts by mass, and the amount of TNSR added from 0.115 parts by mass to 0.1 parts by mass, a conductive material dispersion (CNT dispersion A22) containing 2.5 parts by mass of CNTs was obtained using the same method as in Example 1-A21. The mass ratio of TNSR to 10B CNTs was 1:24.

[0232] (Example 1-A23)

[0233] 98.64 parts by weight of ion-exchanged water were added to a stainless steel container, and 0.56 parts by weight of APP-084 (CMC) were added while stirring with a disperser to dissolve it. Then, 0.062 parts by weight of TNSR (CNT) and 0.738 parts by weight of 6A (CNT) were added while stirring with a disperser. The mixture was then homogenized using a high-shear mixer (L5M-A, manufactured by SILVERSON) with a square-hole high-shear screen installed, and dispersed in batches at 8,600 rpm until the particle size reached below 250 μm using a grinding mill. Subsequently, the dispersion was supplied from the stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINO MACHINE) via piping for 20 pass-through dispersion treatments. The dispersion process was carried out using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain a conductive material dispersion (CNT dispersion A23) containing 1.0 part by mass of CNTs. The mass ratio of TSRN to 6A CNTs was 1:12.

[0234] (Example 1-A24)

[0235] Except for changing the amount of ion-exchanged water added from 98.64 parts by mass to 98.3 parts by mass, the amount of APP-084 added from 0.56 parts by mass to 0.70 parts by mass, the amount of 6A added from 0.738 parts by mass to 0.96 parts by mass, and the amount of TNSR added from 0.062 parts by mass to 0.04 parts by mass, a conductive material dispersion (CNT dispersion A24) containing 2.5 parts by mass of CNTs was obtained using the same method as in Examples 1-A23. The mass ratio of TNSR to 6A CNTs was 1:24.

[0236] (Example 1-A25)

[0237] Except for changing the amount of ion-exchanged water added from 98.64 parts by mass to 98.13 parts by mass, the amount of APP-084 added from 0.56 parts by mass to 0.77 parts by mass, the amount of 6A added from 0.738 parts by mass to 1.08 parts by mass, and the amount of TNSR added from 0.062 parts by mass to 0.02 parts by mass, a conductive material dispersion (CNT dispersion A25) containing 1.1 parts by mass of CNTs was obtained using the same method as in Examples 1-A23. The mass ratio of TNSR to 6A CNTs was 1:48.

[0238] (Comparative Example 1-a15)

[0239] The conductive material dispersion (CNT dispersion A3) obtained in Example 1-A3 was placed in a stainless steel container. While stirring with a disperser, PAA was added to achieve a concentration of 0.04 parts by weight based on the mass of CNTs, resulting in a conductive material dispersion (CNT dispersion a15) containing 5.0 parts by weight of CNTs. The pH of CNT dispersion a15 was 5.5.

[0240] (Comparative Examples 1-a16 to 1-a17)

[0241] Except for changing the materials, composition ratios, and number of dispersions as shown in Table 4, dispersions (CB dispersion a1 to CB dispersion a2) were obtained in the same manner as in Examples 1-1A.

[0242] (Examples 1-B1 to Example 1-B3)

[0243] 80 parts by weight of the conductive material dispersions (CNT dispersions A1 to A3) obtained in Examples 1-A1 to 1-A3 were placed in a glass bottle (M-140, manufactured by Kashiwagawa Glass) and 140 parts by weight of zirconia beads (bead diameter 1.0 mmφ) were added. After dispersion treatment for 2 hours using a paint conditioner manufactured by Red Devil, the zirconia beads were separated to obtain conductive material dispersions (CNT dispersions B1 to B3).

[0244] (Example 1-B4)

[0245] Take 80 parts by weight of the conductive material dispersion (CNT dispersion A3) obtained in Example 1-A3 into a glass bottle (M-140, manufactured by Kashiwagawa Glass), and add 0.012 parts by weight of MAC500LC and 140 parts by weight of zirconia beads (bead diameter 1.0 mmφ). After dispersing for 5 hours using a paint conditioner manufactured by Red Devil, separate the zirconia beads to obtain the conductive material dispersion (conductive material dispersion B4).

[0246] (Examples 1-C1 to Example 1-C3)

[0247] The conductive material dispersions (CNT dispersions A1 to A3) obtained in Examples 1-A1 to 1-A3 were placed in a stainless steel container and diluted with ion-exchanged water while being stirred using a disperser to obtain conductive material dispersions (CNT dispersions C1 to CNT dispersions C3) containing 2.0 parts by mass of CNTs.

[0248] (Examples 1-D1 to Example 1-D3)

[0249] 2.0 parts by weight of 10B (CNT), 0.5 parts by weight of CMC as shown in Table 3, 97.6 parts by weight of ion-exchanged water, and 140 parts by weight of zirconia beads (bead diameter 0.5 mmφ) were placed in a glass bottle (M-140, manufactured by Kashiwagawa Glass). After dispersion treatment for 4 hours using a paint conditioner manufactured by RedDevil, the zirconia beads were separated to obtain conductive material dispersions (CNT dispersions D1 to D3).

[0250] (Example 1-D4)

[0251] Add 97.6 parts by weight of ion-exchanged water to a stainless steel container and dissolve it by adding 0.4 parts by weight of F10LC (CMC) while stirring with a disperser. Then, add 1.5 parts by weight of 10B (CNT) while stirring with a disperser. Install a square-hole high-shear screen on a high-shear mixer (L5M-A, manufactured by SILVERSON) and homogenize the mixture at 8,600 rpm. Batch dispersion is performed using a grinding meter until the particle size reaches below 250 μm. Dispersion was carried out until the viscosity of the dispersed liquid reached 3,000 mPa·s or less at 60 rpm as measured by a Type B viscometer (manufactured by TOKI SANGYO, model: BL). While stirring with a disperser, 0.5 parts by weight of 10B were added to a stainless steel container. The dispersion was carried out 10 times using a high-pressure homogenizer to obtain a conductive material dispersion containing 2.0 parts by weight of CNT (CNT dispersion D4).

[0252] (Example 1-E1)

[0253] 83.5 parts by weight of ion-exchanged water were added to a stainless steel container, and 1.5 parts by weight of APP-84 (CMC) were added while stirring using a disperser to dissolve it. Then, 10 parts by weight of LITX200 (furnace black) were added while stirring using a disperser. A square-hole high-shear screen was installed on a high-shear mixer (L5M-A, manufactured by SILVERSON) and the mixture was homogenized at 8,600 rpm. Batch dispersion was performed using a grinding mill until the particle size reached below 250 μm. Subsequently, the dispersed liquid was supplied from the stainless steel container to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SUGINO MACHINE) via piping for circulating dispersion. The dispersion was performed using a single-nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Dispersion was carried out until the viscosity of the dispersed liquid, measured at 60 rpm using a Type B viscometer (manufactured by TOKI SANGYO, model: BL), reached below 1,000 mPa·s. Then, while stirring with a disperser, 1 part by weight of LITX200 was added to a stainless steel container, and the mixture was again dispersed using a high-pressure homogenizer. This process of circulating dispersion using a high-pressure homogenizer until the viscosity reached below 1,000 mPa·s was repeated, with LITX200 added to the stainless steel container while stirring with a disperser. This process was repeated a total of 5 times (the total amount of LITX200 added was 15 parts by weight). Next, a through-flow dispersion process was performed three times using a high-pressure homogenizer to obtain a conductive material dispersion (CB dispersion E1) containing 15 parts by weight of LITX200.

[0254] (Example 1-E2 to Example 1-E3)

[0255] Except for changing to the conductive material shown in Table 3, conductive material dispersions (CB dispersion E2 to CB dispersion E3) were obtained in the same manner as in Examples 1-E1.

[0256] (Comparative Examples 1-d1 to 1-d3)

[0257] Except for changing to the materials shown in Table 4, conductive material dispersions (CNT dispersions d1 to d3) were obtained in the same manner as in Examples 1-D1.

[0258] Furthermore, the weight-average molecular weight and degree of etherification of carboxymethyl cellulose or its salts used in the examples and comparative examples are shown in Table 2. The weight-average molecular weight and degree of etherification were calculated using the same determination method as in the manufacturing examples.

[0259] [Table 2]

[0260]

[0261] [Table 3]

[0262]

[0263]

[0264] [Table 4]

[0265]

[0266] (Negative electrode composite material composition and negative electrode fabrication)

[0267] The abbreviations used in the following description are as follows.

[0268] • Silicon: Silicon monoxide (manufactured by Osaka Titanium Technology Co., Ltd., silicon monoxide (SiO 1.3C 5 μm, 100% non-volatile component)

[0269] • Artificial graphite: CGB-20 (manufactured by Japan Graphite Industry, 100% non-volatile components)

[0270] • MAC500LC: Sodium carboxymethyl cellulose, Sunrose Special MAC500LC (manufactured by Nippon Paper, 100% non-volatile components)

[0271] •SBR: Styrene-butadiene rubber TRD2001 (manufactured by JSR, 48% non-volatile components)

[0272] (Example 2-A1)

[0273] In a capacity of 150 cm 3 CNT dispersion (CNT dispersion A1), MAC500LC (CMC), and water were added to a plastic container and stirred at 2,000 rpm for 30 seconds using a spin-revolution mixer (Thinky's defoaming stirrer Taro, ARE-310). Then, artificial graphite and silicon were added as negative electrode active materials, and stirred at 2,000 rpm for 150 seconds using the spin-revolution mixer. Subsequently, SBR was added, and stirred at 2,000 rpm for 30 seconds using the spin-revolution mixer to obtain the negative electrode composite composition. The non-volatile component of the negative electrode composite composition was set to 48% by mass. The ratio of non-volatile components of artificial graphite:silicon:CNT:CMC (MAC500LC):SBR in the non-volatile component of the negative electrode composite composition was set to 87:10:0.5:1:1.5.

[0274] The obtained negative electrode composite material composition was coated onto a 20 μm thick copper foil using a coating applicator, and then the coating was dried in an electric oven at 120℃±5℃ for 25 minutes to prepare the electrode film. The electrode film was then calendered using a roll forming machine (manufactured by THANK-METAL, a 3t hydraulic roll forming machine) to obtain the negative electrode (negative electrode A1). Furthermore, the unit area weight of the composite material layer was 10 mg / cm². 2 The density of the composite layer after calendering is 1.6 g / cc.

[0275] (Examples 2-A2 to 2-A25, Examples 2-B1 to 2-B4, Examples 2-C1 to 2-C3, Examples 2-D1 to 2-D4, Examples 2-E1 to 2-E3, Comparative Examples 2-a1 to 2-a17, Comparative Examples 2-d1 to 2-d3)

[0276] Except for changing the CNT dispersion to the CNT dispersions shown in Table 5 (CNT dispersion A2 to CNT dispersion A25, CNT dispersion B1 to CNT dispersion B4, CNT dispersion C1 to CNT dispersion C3, CNT dispersion D1 to CNT dispersion D4, CB dispersion E1 to CB dispersion E3, CNT dispersion a1 to CNT dispersion a15, CB dispersion a1, CB dispersion a2, CNT dispersion d1 to CNT dispersion d3), negative electrodes A2 to A25, B1 to B3, C1 to C3, D1 to D4, E1 to E3, and a1 to a17 and d1 to d3 were obtained using the same method as in Example 2-A1.

[0277] (Methods for evaluating the conductivity of the negative electrode)

[0278] For the obtained negative electrode, the surface resistivity of the composite layer was measured using a LORESTA GP, MCP-T610 manufactured by Mitsubishi Chemical Analytech. After measurement, the volume resistivity (Ω·cm) of the negative electrode is obtained by multiplying the composite layer thickness. Regarding the composite layer thickness, a film thickness gauge (Nikon MH-15M) was used to measure three points on the electrode. The average value obtained was subtracted from the copper foil thickness to obtain the volume resistivity (Ω·cm) of the negative electrode.

[0279] Judgment Criteria

[0280] A: Less than 0.3 Ω·cm (Excellent)

[0281] B: Above 0.3 Ω·cm and less than 0.5 Ω·cm (Good)

[0282] D: Above 0.5 Ω·cm (Defective)

[0283] (Method for evaluating the tightness of the negative electrode)

[0284] The obtained negative electrode was cut into two 90 mm × 20 mm rectangles with the coating direction as the major axis. Peel strength was measured using a benchtop tensile testing machine (Toyo Seiki Co., Ltd., STROGRAPH E3) and evaluated using the 180-degree peel test method. Specifically, a 100 mm × 30 mm double-sided adhesive tape (No. 5000NS, Nitoms) was adhered to a stainless steel plate, ensuring the composite layer side of the negative electrode was in close contact with the other side of the tape, thus creating a test specimen. The test specimen was then vertically fixed with the shorter sides of the rectangle aligned vertically. The copper foil was stretched from bottom to top at a fixed speed (50 mm / min) while being peeled. The average stress at this point was taken as the peel strength.

[0285] Judgment Criteria

[0286] A: Above 0.5 N / cm (Excellent)

[0287] B: Above 0.1 N / cm and less than 0.5 N / cm (Good)

[0288] D: Less than 0.1 N / cm (Poor)

[0289] [Table 5]

[0290]

[0291] The negative electrode of the conductive material dispersion using the described embodiment exhibits good conductivity and adhesion. This is believed to be because the dispersant can function effectively by satisfying the structural requirements of the described embodiment. Furthermore, it is believed that the carbon layer of the finely coated silicon-based active material used in the examples is similar to the surface state of CNTs with a specific range of acidic groups in the described embodiment, and since the silicon-based active material carries a negative surface charge in water, it exhibits particularly excellent interaction with the CNT dispersion, resulting in a good material distribution even in a dry electrode film.

[0292] (Composite material composition for positive electrode and fabrication of positive electrode)

[0293] The abbreviations used in the following description are as follows.

[0294] • LFP: Lithium iron phosphate HED (trademark) LFP-400 (manufactured by BASF, 100% non-volatile components)

[0295] • PTFE: Polytetrafluoroethylene POLYFLON PTFE D-210C (manufactured by Daikin, 60% non-volatile components)

[0296] • MAC500LC: Sodium carboxymethyl cellulose, Sunrose Special MAC500LC (manufactured by Nippon Paper, 100% non-volatile components)

[0297] (Example 3-A1)

[0298] In a capacity of 150 cm 3 Conductive material dispersion (conductive material dispersion A1), MAC500LC, and water were added to a plastic container. The mixture was then stirred at 2,000 rpm for 30 seconds using a spin-revolution mixer (Thinky's ARE-310 defoaming stirrer). Next, LFP was added as the positive electrode active material, and the mixture was stirred at 2,000 rpm for 150 seconds using the same mixer. Subsequently, PTFE was added, and the mixture was stirred at 2,000 rpm for 30 seconds using the same mixer to obtain a positive electrode composite composition. The non-volatile component of the positive electrode composite composition was set to 75% by mass. The ratio of non-volatile components of LFP: conductive material: PTFE: MAC500LC in the composite material composition for positive electrodes is set to 97:0.5:1:1.5.

[0299] The positive electrode composite material composition was coated onto a 20 μm thick aluminum foil using a coating apparatus and then dried in an electric oven at 120℃±5℃ for 25 minutes to prepare the electrode film. The electrode film was then calendered using a roll press (manufactured by THANK-METAL, a 3t hydraulic roll press) to obtain the positive electrode (positive electrode A1). Furthermore, the unit area weight of the composite material layer was 20 mg / cm². 2 The density of the composite layer after calendering is 2.1 g / cc.

[0300] (Examples 3-A2 to 3-A25, Examples 3-B1 to 3-B4, Examples 3-C1 to 3-C3, Examples 3-D1 to 3-D4, Examples 3-E1 to 3-E3, Comparative Examples 3-a1 to 3-a17, Comparative Examples 3-d1 to 3-d3)

[0301] Except for changing the CNT dispersions to the CNT dispersions shown in Table 6 (CNT dispersions A2 to A25, B1 to B4, C1 to C3, D1 to D4, E1 to E3, a1 to a15, a1, a2, d1 to d3), positive electrodes A2 to A25, B1 to B3, C1 to C3, D1 to D4, a1 to a17, and d1 to d3 were obtained using the same method as in Example 3-A1.

[0302] (Methods for evaluating the conductivity of the positive electrode)

[0303] In addition to using aluminum foil instead of copper foil, the conductivity of the obtained positive electrode was evaluated using the same method as that used for the negative electrode.

[0304] Judgment Criteria

[0305] A: Less than 10 Ω·cm (Excellent)

[0306] B: Above 10 Ω·cm and less than 20 Ω·cm (Good)

[0307] D: Above 20 Ω·cm (Poor)

[0308] (Methods for evaluating the tightness of the positive electrode)

[0309] In addition to using aluminum foil instead of copper foil, the adhesion of the obtained positive electrode was evaluated using the same method as that used for the negative electrode.

[0310] Judgment Criteria

[0311] A: 1 N / cm or higher (Excellent)

[0312] B: Above 0.5 N / cm and less than 1 N / cm (Good)

[0313] D: Less than 0.5 N / cm (Poor)

[0314] [Table 6]

[0315]

[0316] The positive electrode using the conductive material dispersion of the described embodiment exhibits good conductivity and adhesion. This is believed to be because, similar to the negative electrode, the dispersant can function effectively by satisfying the structural requirements of the described embodiment. Furthermore, similar to the case of silicon-based active materials, the carbon layer of the finely carbon-coated lithium iron phosphate used in the examples is similar to the surface state of CNTs with a specific range of acidic base content in the described embodiment. Moreover, lithium iron phosphate carries a negative surface charge in water, resulting in a particularly excellent interaction with the CNT dispersion, and a good material distribution is formed in the dry electrode film.

[0317] (Making a standard positive electrode)

[0318] In a 150 ml plastic container, add 92 parts by weight of LFP (HED LFP-400, manufactured by BASF, 100% non-volatile content) as the positive electrode active material, 4 parts by weight of DENKA BLACK (DENKA HS-100, manufactured by DENKA, 100% non-volatile content), and 1.6 parts by weight of MAC500LC (sodium carboxymethyl cellulose, Sunrose Special Type MAC500L, manufactured by Nippon Paper, 100% non-volatile content). Mix using a scraper until the powder becomes uniform. Then, add 25 parts by weight of water and stir at 2,000 rpm for 30 seconds using a rotary mixer (Thinky ARE-310 defoaming stirrer). Next, the mixture in the plastic container was mixed with a scraper until homogeneous. 4 parts by weight of PTFE (manufactured by Daikin, 60% by weight of non-volatile components) were added using a spin-revolution mixer, and the mixture was stirred at 2,000 rpm for 30 seconds. Then, 11.2 parts by weight of water were added, and the mixture was stirred at 2,000 rpm for 30 seconds using a spin-revolution mixer. Finally, the mixture was stirred at 3,000 rpm for 10 minutes using a high-speed mixer to obtain a standard positive electrode composite composition. The non-volatile component of the standard positive electrode composite composition was set to 79% by weight.

[0319] After applying the standard positive electrode composite material composition to a 20 μm thick aluminum foil as a current collector using a coating applicator, the electrode is dried in an electric oven at 120℃±5℃ for 25 minutes to adjust the weight per unit area of ​​the electrode to 20 mg / cm². 2 Furthermore, the composite layer was calendered using a roll forming machine (manufactured by THANK-METAL, a 3t hydraulic roll forming machine) to achieve a density of 2.1 g / cm³. 3 The standard positive electrode.

[0320] (Making a standard negative electrode)

[0321] In a 150 ml plastic container, add 0.5 parts by weight of acetylene black (DENKA BLACK (registered trademark) HS-100, manufactured by DENKA), 1 part by weight of MAC500LC (Sunrose special type MAC500L sodium carboxymethyl cellulose, manufactured by Nippon Paper, 100% non-volatile components), and 98.4 parts by weight of water. Then, using a rotary mixer (Thinky defoaming stirrer Taro, ARE-310), stir at 2,000 rpm for 30 seconds. Next, add 87 parts by weight of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries) and 10 parts by weight of silicon as active materials, and stir at 2,000 rpm for 150 seconds using the same rotary mixer. Next, 3.1 parts by weight of SBR (TRD2001, manufactured by JSR) were added, and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation-revolution mixer (Thinky's defoaming stirrer Taro, ARE-310) to obtain a standard negative electrode composite composition. The non-volatile component of the standard negative electrode composite composition was set to 50% by weight.

[0322] After applying the standard negative electrode composite material composition to a 20 μm thick copper foil as a current collector using a coating applicator, the electrode is dried in an electric oven at 80℃±5℃ for 25 minutes to adjust the weight per unit area of ​​the electrode to 10 mg / cm². 2 Furthermore, the composite layer was calendered using a roll forming machine (manufactured by THANK-METAL, a 3t hydraulic roll forming machine) to achieve a density of 1.6 g / cm³. 3 The standard negative electrode.

[0323] (Examples 4-A1 to 4-A25, Examples 4-B1 to 4-B4, Examples 4-C1 to 4-C3, Examples 4-D1 to 4-D4, Examples 4-E1 to 4-E3, Comparative Examples 4-a1 to 4-a17, Comparative Examples 4-d1 to 4-d3)

[0324] (Examples 5-A1 to 5-A25, Examples 5-B1 to 5-B4, Examples 5-C1 to 5-C3, Examples 5-D1 to 5-D4, Examples 5-E1 to 5-E3, Comparative Examples 5-a1 to 5-a17, Comparative Examples 5-d1 to 5-d3)

[0325] (Making a secondary battery)

[0326] Using the negative and positive electrodes listed in Tables 7 and 8, respectively, the electrodes were cut into 50 mm × 45 mm and 45 mm × 40 mm pieces. The separator (porous polypropylene membrane) to be inserted between them was then inserted into an aluminum laminated bag and dried in an electric oven at 70°C for 1 hour. Subsequently, 2 mL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1, and then adding 1 part by mass of ethylene carbonate to 100 parts by mass, and dissolving LiPF6 at a concentration of 1 M) was injected into an argon-filled glove box. The aluminum laminated bag was then sealed to fabricate secondary batteries.

[0327] (Evaluation method for rate characteristics of secondary batteries)

[0328] The obtained secondary battery was placed in a constant temperature chamber at 25°C and charge / discharge measurements were performed using a charge / discharge device (manufactured by Beidou Electric, SM-8). Constant current and constant voltage charging (cutoff current 1 mA (0.02 C)) was performed at a charging current of 10 mA (0.2 C) and a charging termination voltage of 4.3 V. Then, constant current discharge was performed at a discharging current of 10 mA (0.2 C) and a discharging termination voltage of 3 V. This operation was repeated three times. Then, constant current and constant voltage charging (cutoff current 1 mA (0.02 C)) was performed at a charging current of 10 mA (0.2 C) and a charging termination voltage of 4.3 V, followed by constant current discharge at discharging currents of 0.2 C and 3 C until the discharging termination voltage of 3.0 V was reached. The discharge capacity was calculated for each. The rate characteristic can be expressed by the ratio of the 0.2 C discharge capacity to the 3 C discharge capacity, as shown in Equation 1 below.

[0329] (Equation 1) Rate characteristic = 3 C discharge capacity / 0.2 C discharge capacity of the third discharge × 100 (%)

[0330] Judgment Criteria

[0331] A: Over 80% (Excellent)

[0332] B: 60% or higher but less than 80% (Good)

[0333] D: Less than 60% (Poor)

[0334] (Evaluation method for cycle characteristics of secondary batteries)

[0335] The obtained secondary battery was placed in a constant temperature chamber at 25°C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Beidou Electric, SM-8). After constant current and constant voltage charging (cutoff current 2.5 mA (0.05 C)) at a charging current of 25 mA (0.5 C) and a charging termination voltage of 4.3 V, constant current discharging was performed at a discharging current of 25 mA (0.5 C) and a discharging termination voltage of 3 V. This operation was repeated 200 times. The cycle characteristics can be expressed by the ratio of the 0.5 C discharge capacity of the third cycle at 25°C to the 0.5 C discharge capacity of the 200th cycle, as shown in Equation 2 below.

[0336] (Equation 2) Cyclic characteristic = 0.5 C discharge capacity at the third cycle / 0.5 C discharge capacity at the 200th cycle × 100 (%)

[0337] Judgment Criteria

[0338] A: 85% or higher (Excellent)

[0339] B: Above 80% but less than 85% (Good)

[0340] D: Less than 80% (Poor)

[0341] [Table 7]

[0342]

[0343] [Table 8]

[0344]

[0345] In the embodiments using the conductive material dispersion of the described embodiment, a non-aqueous electrolyte secondary battery with superior cycle characteristics compared to the comparative example was obtained. Therefore, it is clear that the embodiments can provide a non-aqueous electrolyte secondary battery with cycle characteristics that are difficult to achieve with conventional conductive material dispersions.

Claims

1. A composition for a secondary battery electrode, comprising a conductive material dispersion, said conductive material dispersion containing a conductive material, carboxymethyl cellulose or a salt thereof, and water, said conductive material comprising carbon nanotubes, wherein the conductive material dispersion contains... The carboxymethyl cellulose or its salt has a weight average molecular weight of 10,000 to 150,000 and a degree of etherification of 0.5 to 0.

9. At 25°C and 1 Hz, within a strain rate range of 0.01% to 5%, the product of the complex elastic modulus and the phase angle of the obtained conductive material dispersion is greater than 100 and less than 1,500. The complex elastic modulus is above 0.1 Pa and below 50 Pa. The phase angle is greater than 5° and less than 80°. In the conductive material dispersion, the content of carbon nanotubes is above 0.4% by mass and below 30% by mass. Based on the mass of carbon nanotubes, the content of carboxymethyl cellulose or its salt is more than 10% by mass and less than 100% by mass.

2. The composition for a secondary battery electrode according to claim 1, wherein, The carboxymethyl cellulose or its salts have a weight-average molecular weight of 10,000 to 100,000.

3. A composition for a secondary battery electrode, comprising a conductive material dispersion, said conductive material dispersion containing carbon nanotubes, carboxymethyl cellulose or a salt thereof, and water, wherein the conductive material dispersion contains... The carboxymethyl cellulose or its salt has a weight average molecular weight of 10,000 to 100,000 and a degree of etherification of 0.5 to 0.

9. At 25°C and 1 Hz, within a strain rate range of 0.01% to 5%, the product of the complex elastic modulus and the phase angle of the obtained conductive material dispersion is greater than 100 and less than 1,500. The complex elastic modulus is above 0.1 Pa and below 50 Pa. The phase angle is greater than 5° and less than 80°. In the conductive material dispersion, the content of the carbon nanotubes is 0.4% by mass or more and 5.0% by mass or less. Based on the mass of carbon nanotubes, the content of carboxymethyl cellulose or its salt is more than 10% by mass and less than 100% by mass.

4. The composition for a secondary battery electrode according to claim 3, wherein, The amount of acidic groups of the carbon nanotubes is 0.1 μmol / m 2 ~ 0.8 μmol / m 2 .

5. The composition for a secondary battery electrode according to claim 3 or 4, wherein, The amount of acidic groups in the carbon nanotubes is 40 μmol / g to 500 μmol / g.

6. The composition for a secondary battery electrode according to claim 1 or 3, wherein, The phase angle is above 15° and below 80°.

7. The composition for a secondary battery electrode according to claim 3 or 4, wherein, The carbon nanotubes include a first carbon nanotube with an average outer diameter of 0.5 nm or more and less than 5 nm, and a second carbon nanotube with an average outer diameter of 5 nm or more and less than 20 nm, wherein the mass ratio of the first carbon nanotube to the second carbon nanotube is 1:10 to 1:

100.

8. The composition for a secondary battery electrode according to claim 3 or 4 further comprises polyacrylic acid.

9. The composition for a secondary battery electrode according to claim 1 or 3, wherein, The median particle size of the conductive material dispersion is above 0.5 μm and below 2.0 μm.

10. The composition for a secondary battery electrode according to claim 1 or 3, wherein, The thixotropic index of the conductive material dispersion is 2.0 to 5.

0.

11. The composition for a secondary battery electrode according to claim 1 or 3, wherein, In the coating film of the conductive material dispersion, the gloss level, measured with respect to an incident angle of 60°, is 5 to 120.

12. The composition for a secondary battery electrode according to claim 1 or 3, wherein, The pH of the conductive material dispersion is 7.0 to 10.

5.

13. The composition for a secondary battery electrode according to claim 1 or 3, wherein, The complex elastic modulus is above 3.2 Pa and below 50 Pa.

14. An electrode film comprising a coating film of the composition for a secondary battery electrode as described in any one of claims 1 to 13.

15. A secondary battery comprising the electrode membrane as described in claim 14.

16. A method for manufacturing a conductive material dispersion, comprising manufacturing a conductive material dispersion contained in a composition for a secondary battery electrode as described in any one of claims 3 to 13, wherein the method comprises performing the following steps (1) and (2) sequentially. (1) A process of dispersing particles at a pressure of 60 MPa to 120 MPa using a high-pressure homogenizer to achieve a median particle size of less than 4.0 μm; (2) Use a bead mill to disperse until the phase angle is above 40°.

17. A vehicle comprising the secondary battery as claimed in claim 15.

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