Carbon material dispersion, electrode slurry, electrode, and method for producing secondary battery

Abstract

The present invention is capable of providing: a method for producing a carbon material dispersion that contains a small amount of metal magnetic foreign matter in the carbon material dispersion and that exhibits excellent temporal stability; and, additionally, a secondary battery using said carbon material dispersion and having good cycle characteristics. The present disclosure relates to a method for producing a carbon material dispersion containing a carbon material, a dispersant, and a solvent, the method comprising the following steps (1) to (3). [Step (1)] A step for obtaining a carbon material pre-dispersion (X1) having a sliding angle of less than 70° with respect to a metal substrate and a cumulative particle diameter D50 of 20 μm or greater. [Step (2)] A step for obtaining a carbon material pre-dispersion (X2) by removing metal magnetic foreign matter by magnetic separation treatment simultaneously with and / or after the production of the carbon material pre-dispersion (X1). [Step (3)] A step for producing a carbon material dispersion by dispersing the carbon material pre-dispersion (X2).

Description

Carbon material dispersion, electrode slurry, electrode, and method for manufacturing secondary battery

[0001] Embodiments of the present disclosure relate to methods for producing a carbon material dispersion, an electrode slurry, an electrode, and a secondary battery.

[0002] Lithium ion secondary batteries are widely used as batteries for electric vehicles, portable devices, etc. As the performance of electric vehicles and portable devices improves, demands for lithium ion secondary batteries with high capacity, high output, and small size and light weight are increasing year by year.

[0003] Because the capacity of lithium-ion secondary batteries is highly dependent on the cathode and anode active materials, which are the main components of the electrodes, various materials for these active materials have been actively researched. However, the charge capacity of practical active materials has reached a level close to the theoretical value, and improvement is near its limit. Therefore, since the charge capacity can be simply increased by increasing the loading of the active material in the electrode film, attempts have been made to reduce or eliminate the amount of conductive additives and binder resins that do not directly contribute to the charge capacity.

[0004] Conductive additives play a key role in forming conductive paths within electrodes, and are therefore required to be resistant to breakage due to the expansion and contraction of the electrode film. To maintain conductive paths with a small amount of conductive additive, it is desirable to use carbon materials with a large specific surface area, such as ketjen black, carbon nanotubes, graphene, and fullerenes. However, these carbon materials contain metallic catalysts during synthesis and magnetic metal particles derived from the manufacturing process, which can lead to voltage drop problems. These magnetic metal particles dissolve within secondary batteries, precipitate in the form of dendrites, and can break through the separator, causing internal short circuits. Furthermore, electrode films containing carbon materials with a high content of magnetic metal particles are prone to deterioration of the electrolyte and active materials during high-temperature charging and discharging of secondary batteries, resulting in poor high-temperature cycle performance.

[0005] Therefore, Patent Document 1 proposes a method for removing particulate metal components containing at least one metal selected from the group consisting of Fe, Ni, and Cr from a slurry composition in which carbon black particles have been dispersed, using a magnet with a magnet cover having a Vickers hardness of 10 GPa or more but less than 25 GPa as a particulate metal removal step. Furthermore, carbon nanotubes in particular often contain residual metallic magnetic impurities derived from the metal catalyst used during synthesis, making them more susceptible to voltage drop problems. Therefore, Patent Document 2 proposes a method for crushing carbon nanotubes containing metallic magnetic impurities such as iron, cobalt, and nickel, and removing the metallic magnetic impurities from the carbon nanotubes using an electromagnet. Patent Document 3 proposes a method for removing particulate metals contained in a binder composition. Patent Document 4 proposes a method for removing metallic magnetic impurities, which are ferromagnetic impurities, from a medium liquid containing carbon nanotubes defibrated in a shear module in a carbon nanotube manufacturing method. Patent Document 5 proposes that by using a copolymer containing a nitrile group-containing monomer unit as a dispersant and specifying the pH of the dispersion, carbon fibers with strong cohesive power can be well dispersed in a solvent, and the degree of dispersion of the conductive dispersion can be increased, thereby obtaining a dispersion that is easy to handle even if it contains a high concentration of carbon fibers, and making it possible to improve the efficiency of removing metal foreign matter, which is an inhibitor of the conductive network.

[0006] Japanese Patent Application Laid-Open No. 2015-191756 Japanese Patent Application Laid-Open No. 2010-174418 Republished No. 2010-032784 Japanese Patent Application Laid-Open No. 2021-065846 Japanese Patent No. 6962428

[0007] However, conventional methods such as those described in Patent Documents 1 to 5 have limitations in reducing the content of metallic magnetic foreign matter in the carbon material dispersion, and the current situation is that the stability over time of the carbon material dispersion and the characteristics of a secondary battery when made into the carbon material dispersion have not been sufficiently improved.

[0008] For example, when removing metallic magnetic contaminants from carbon materials themselves using methods such as magnetic separation or filtering, it is difficult to remove metallic magnetic contaminants that have been incorporated into the carbon material. On the other hand, when removing metallic magnetic contaminants from carbon material dispersions, although it is possible to expose metallic magnetic contaminants incorporated into the carbon material through a dispersion process, it is necessary to prepare the carbon material dispersion with a low viscosity in order to efficiently remove the metal using magnetic separation or filtering. However, dispersion not only fines the carbon material but also the metallic magnetic contaminants, which may reduce the efficiency of metallic magnetic contaminant removal. Therefore, there is room for improvement in maximizing the efficiency of metallic magnetic contaminant removal from carbon material dispersions. In the technology disclosed in Patent Document 5, a copolymer, an organic solvent, and a conductive material are subjected to a batch dispersion process, followed by a pass dispersion process, and after sufficient dispersion, magnetic separation is performed using a magnetic separation filter. In this technology, the conductive material in the dispersion fed to the magnetic separation filter has already been finely processed, so the metallic contaminants are also finely divided, making removal by the magnetic separation filter difficult.

[0009] Therefore, an object of an embodiment of the present disclosure is to provide a method for producing a carbon material dispersion that has a low content of metallic magnetic contaminants and excellent stability over time. Furthermore, an object is to provide a secondary battery using the same that has good cycle characteristics. In particular, an object is to provide a carbon nanotube dispersion that has a lower content of metallic magnetic contaminants than conventional carbon nanotube dispersions, even when using carbon nanotubes, which often contain residual metallic magnetic contaminants derived from the metal catalyst used in their synthesis.

[0010] According to the inventors' intensive study, it is found that the sliding angle is less than 70° and the cumulative particle diameter D ５０It has been found that by removing the metallic magnetic foreign matter simultaneously with and / or after the production of a carbon material pre-dispersion liquid having a particle size of 20 μm or more, the metallic magnetic foreign matter can be efficiently recovered, and the amount of metallic magnetic foreign matter in the carbon material dispersion liquid can be reduced more than conventionally. Furthermore, it has been found that this improves the stability over time of the carbon material dispersion liquid after dispersion. As a result, embodiments of the present disclosure can provide a carbon material dispersion liquid having a low content of metallic magnetic foreign matter and good stability over time, and can provide a secondary battery with good cycle characteristics.

[0011] That is, the present disclosure includes the following embodiments. The embodiments of the present disclosure are not limited to the following. [1] A method for producing a carbon material dispersion containing a carbon material, a dispersant, and a solvent, comprising all of the following steps (1) to (3): [Step (1)] Dispersing a carbon material having a sliding angle with respect to a metal substrate of less than 70° and a cumulative particle diameter D ５０ [Step (2)] A step of removing metallic magnetic foreign matter by magnetic separation treatment simultaneously with and / or after the production of the carbon material pre-dispersion liquid (X1) to obtain a carbon material pre-dispersion liquid (X2). [Step (3)] A step of dispersing the carbon material pre-dispersion liquid (X2) to produce a carbon material dispersion liquid. [2] A method for producing a carbon material dispersion liquid according to [1], wherein the solvent is a non-aqueous solvent. [3] A method for producing a carbon material dispersion liquid according to [1] or [2], further comprising a step of removing metallic magnetic foreign matter simultaneously with and / or after the dispersion of the carbon material pre-dispersion liquid (X2). [4] A method for producing an electrode slurry, comprising mixing an active material with the carbon material dispersion liquid produced by the method according to any one of [1] to [3]. [5] A method for producing an electrode, comprising a step of applying the electrode slurry produced by the method according to [4] to a current collector to form an electrode film. [6] A method for producing a secondary battery, comprising a step of applying the electrode slurry produced by the method according to [4] to a current collector to form an electrode film.

[0012] According to the embodiment of the present disclosure, it is possible to provide a carbon material dispersion liquid that has a low content of metallic magnetic foreign matter and has good stability over time. Furthermore, by using this, it is possible to provide a secondary battery with good cycle characteristics.

[0013] Hereinafter, the carbon material dispersion, electrode slurry, electrode, and secondary battery according to the embodiments of the present disclosure, as well as the manufacturing methods thereof, will be described in detail, but the present disclosure is not limited thereto. Note that the numerical values ​​specified in this specification are values ​​determined by the methods disclosed in the embodiments or examples.

[0014] In addition, in this specification, a numerical range specified using "to" includes the numerical values ​​written before and after "to" as the lower and upper limit ranges. In this specification, "carbon nanotubes" may be referred to as "CNT," "N-methyl-2-pyrrolidone" as "NMP," "carbon material pre-dispersion liquid (X1)" as "pre-dispersion liquid (X1)," "carbon material pre-dispersion liquid (X2)" as "pre-dispersion liquid (X2)," and "carbon material dispersion liquid" as "dispersion liquid." In addition, "carbon material pre-dispersion liquid (X1)" and "carbon material pre-dispersion liquid (X2)" may be collectively referred to as "carbon material pre-dispersion liquid." The "step of removing metallic magnetic foreign matter by magnetic separation treatment" is also simply referred to as the "magnetic separation step." Unless otherwise noted, the various components appearing in this specification may be used independently, either alone or in combination of two or more.

[0015] <Method for Producing Carbon Material Dispersion> One embodiment of the present disclosure is a method for producing a carbon material dispersion containing a carbon material, a dispersant, and a solvent, the method comprising all of the following steps (1) to (3): [Step (1)] Dispersing a carbon material having a sliding angle with respect to a metal substrate of less than 70° and a cumulative particle diameter D ５０ [Step (2)] A step of removing metallic magnetic foreign matters by magnetic separation treatment simultaneously with and / or after the production of the carbon material pre-dispersion (X1) to obtain a carbon material pre-dispersion (X2). [Step (3)] A step of dispersing the carbon material pre-dispersion (X2) to produce a carbon material dispersion.

[0016] The method for producing a carbon material dispersion according to the present embodiment makes it possible to produce a carbon material dispersion having a lower metallic magnetic contaminant content than conventional carbon material dispersions and excellent stability over time. Furthermore, the use of the carbon material dispersion makes it possible to produce a secondary battery having excellent cycle characteristics. In particular, even when using carbon nanotubes, which often contain residual metallic magnetic contaminants derived from the metal catalyst used in their synthesis, a carbon nanotube dispersion can be produced in which the metallic magnetic contaminant content is reduced compared to conventional carbon material dispersions.

[0017] The step (3) preferably further comprises a step of removing metallic magnetic foreign matter simultaneously with and / or after the dispersion of the carbon material pre-dispersion liquid (X2).

[0018] A method for producing a carbon material dispersion liquid comprising steps (1) to (3) will be described. [Step (1)] In step (1), a carbon material having a sliding angle with respect to a metal substrate of less than 70° and a cumulative particle diameter D ５０ This is a step of obtaining a carbon material pre-dispersion liquid (X1) having a sliding angle with respect to the metal substrate of less than 70° and a cumulative particle diameter D ５０ When the particle size is 20 μm or more, the metallic magnetic foreign matter particles contained in the carbon material pre-dispersion liquid (X1) can be efficiently reduced by the magnetic separation step in step (2), and a carbon material dispersion liquid having a low content of metallic magnetic foreign matter and excellent stability over time can be obtained.

[0019] The smaller the sliding angle, the better the droplet sliding property (water sliding property). The sliding angle of the carbon material pre-dispersion (X1) of this embodiment is less than 70°. It is preferably 60° or less, more preferably 50° or less, and even more preferably 40° or less. It is also preferably 1° or more. When the sliding angle is less than 70°, adhesion to the magnetic separator surface is weak, and the carbon material pre-dispersion (X1) is less likely to adhere to the magnetic separator during magnetic separation treatment, improving the efficiency of removing metal magnetic foreign matter by magnetic separation treatment. When the sliding angle is 70° or more, adhesion to the magnetic separator surface is strong, and the carbon material pre-dispersion (X1) adheres to the magnetic separator during magnetic separation treatment. Therefore, a thickness equivalent to the amount of the adhered carbon material pre-dispersion (X1) is produced, and the magnetic force decreases in proportion to the square of the distance, thereby reducing the efficiency of removing metal magnetic foreign matter by magnetic separation treatment. The sliding angle can be adjusted by adjusting the specific surface area of ​​the carbon material, the amount of functional groups on the surface, the type and composition of the dispersant, the type of solvent, the dispersion conditions (time, strength, etc.), and the like.

[0020] The metal substrate used for measuring the sliding angle is not particularly limited, but is preferably made of the material of the magnet that comes into contact with the carbon material pre-dispersion liquid (X1). Examples include SUS316L, SUS304, and SUS430. Specifically, the sliding angle can be measured by the method described in the [Examples] section, for example.

[0021] Cumulative particle diameter D of carbon material pre-dispersion liquid (X1) ５０ is 20 μm or more, preferably 30 μm or more, more preferably 40 μm or more, and is preferably 300 μm or less, more preferably 250 μm or less. ５０ If the cumulative particle diameter D is less than 20 μm, the carbon material pre-dispersion liquid (X1) becomes highly viscous, which causes a decrease in the magnetic separation efficiency. In addition, as the carbon material pre-dispersion liquid (X1) disperses, the dispersion of the metallic magnetic foreign matter also progresses, and the magnetic separation efficiency may decrease as the metallic magnetic foreign matter becomes finer. ５０ If the cumulative particle diameter D is larger than 300 μm, the metallic magnetic foreign matter contained in the carbon material may not be sufficiently revealed and may not be removed by the magnetic separation step. ５０is determined from a volume-based particle size distribution curve measured by a laser diffraction / scattering particle size distribution measurement method, and specifically, can be measured by the method described in the section [Examples], for example.

[0022] The carbon material pre-dispersion (X1) can be produced, for example, by mixing, kneading, or dispersing a mixture containing a carbon material, a dispersant, a solvent, and optional components as described below using a known mixer or the like. For example, the solvent and dispersant may be mixed and then the carbon material may be added, or the carbon material and dispersant may be kneaded and then the solids content of the carbon material pre-dispersion (X1) may be adjusted. The carbon material pre-dispersion (X1) may be in a state where the dispersion treatment is less advanced than that of the final carbon material dispersion. If the carbon material pre-dispersion (X1) is excessively dispersed, the viscosity of the dispersion may increase due to the finer carbon material, potentially increasing the sliding angle. Furthermore, if the carbon material pre-dispersion (X1) is excessively dispersed, the carbon material may become more finely divided, which may make it more likely to adhere to the magnetic separator surface. Furthermore, if the carbon material pre-dispersion (X1) is excessively dispersed, metallic magnetic foreign matter may also become finer, making it difficult to remove with a magnetic separator without a stronger magnetic force. For example, in a state where a mass of metallic magnetic foreign matter is coated with a carbon material, or in a state where a plurality of metallic magnetic foreign matter is dispersed and contained in an aggregate of a carbon material, if the particle diameter is large, the magnetic properties of the metallic magnetic foreign matter are high and it is easy to remove by a magnetic separation treatment. However, if these states are refined by an excessive dispersion treatment, the magnetic properties of the refined individual particles become weak, and it may become difficult to remove by a magnetic separation treatment even with a strong magnetic force. In this embodiment, the sliding angle and cumulative particle diameter D of the carbon material pre-dispersion (X1) are used as indicators of the dispersion treatment for providing the carbon material pre-dispersion (X1). ５０ can be used.

[0023] As an apparatus for producing the carbon material pre-dispersion liquid (X1), a mixer, kneader, disperser, or the like that is commonly used for pigment dispersion, etc. can be used. Specifically, the sliding angle and cumulative particle diameter D of the carbon material pre-dispersion liquid (X1) can be determined by ５０It is preferable to use a disperser that can easily control the viscosity so that it falls within the desired range. Examples of suitable dispersers include mixers such as a Disper, a Homomixer, and a Planetary Mixer, as well as MODEL 450DA, "Clearmix" manufactured by M Technique, "Filmix" manufactured by PRIMIX, and "Abramix" manufactured by Silverson. The dispersion treatment to provide the carbon material pre-dispersion (X1) may be carried out by batch dispersion since excessive dispersion is not required. By carrying out batch dispersion using such a disperser and then carrying out magnetic separation treatment in step (2), it is possible to more efficiently remove metallic magnetic foreign matter from the carbon material pre-dispersion (X1).

[0024] [Step (2)] Step (2) is a magnetic separation step in which metallic magnetic foreign matter is removed by magnetic separation simultaneously with and / or after the production of the carbon material pre-dispersion (X1) to obtain a carbon material pre-dispersion (X2). In this specification, the carbon material pre-dispersion that has been magnetically separated is referred to as the carbon material pre-dispersion (X2). This step of removing metallic magnetic foreign matter by magnetic separation may be performed either simultaneously with and / or after the production of the carbon material pre-dispersion (X1). That is, steps (1) and (2) may be performed simultaneously, or the carbon material pre-dispersion (X1) obtained in step (1) may be used to perform the magnetic separation in step (2). Note that when steps (1) and (2) are performed simultaneously, the carbon material pre-dispersion (X2) and the carbon material pre-dispersion (X1) correspond to the same thing.

[0025] Therefore, the method for producing the carbon material pre-dispersion (X2) is to: (i) produce a carbon material pre-dispersion having a sliding angle with respect to the metal substrate of less than 70° and a cumulative particle diameter D ５０ (ii) a method of obtaining a carbon material pre-dispersion (X2) having a sliding angle of less than 70° with respect to a metal substrate and a cumulative particle diameter D ５０In this embodiment, the carbon material pre-dispersion (X2) during the magnetic separation treatment has a sliding angle with respect to the metal substrate of less than 70° and a cumulative particle diameter D ５０ It is important that the particle size is 20 μm or more, which makes it possible to efficiently reduce the metallic magnetic foreign particles contained in the carbon material pre-dispersion. Therefore, the carbon material dispersion obtained has a low content of metallic magnetic foreign particles and is a carbon material dispersion having excellent stability over time. In addition, it is preferable that the carbon material pre-dispersion (X2) obtained by the magnetic separation treatment is not subjected to excessive dispersion treatment during the magnetic separation treatment. For example, the sliding angle and cumulative particle diameter D of the carbon material pre-dispersion (X2) ５０ may be approximately the same as those of the carbon material pre-dispersion liquid (X1), and more preferably within a range of plus or minus 20%, 10%, or 5% of those of the carbon material pre-dispersion liquid (X1).

[0026] In this embodiment, the term "metallic magnetic foreign matter" refers to a substance that exists in the form of particles in the carbon material pre-dispersion liquid or the carbon material dispersion liquid, and does not include a substance that exists in the form of dissolved metal ions. Examples of the metal of the metallic magnetic foreign matter include Fe, Co, and Cr.

[0027] The method for removing metallic magnetic contaminants by magnetic separation is not particularly limited as long as it is a method that removes metallic magnetic contaminants using magnetic force, and various magnetic separators, etc., can be used. A method using an electromagnet is preferred as a method for removing metallic magnetic contaminants using magnetic force. The use of an electromagnet is preferred because it allows an appropriate magnetic force to be set by controlling the current flowing through the electromagnet, thereby enabling efficient removal of magnetic components. Furthermore, since the magnetic force can be reduced to nearly zero by setting the current to zero, it is easier to remove adsorbed magnetic components than with a permanent magnet, and therefore is also easier to maintain. Examples of magnetic separation methods using an electromagnet include a method of passing the carbon material pre-dispersion (X2) through a filter equipped with an electromagnet, a method of stirring the carbon material pre-dispersion (X2) with a stirring member equipped with an electromagnet, and a method of installing a magnetic separation member equipped with an electromagnet in a dispersion container, flow path, etc. of the carbon material pre-dispersion (X2).

[0028] Specifically, for example, CS-150HHH, CS-250HHH, CS-300HHH manufactured by Nippon Magnetics Co., Ltd., DVF-50-6, DVF-50-9, DVF-50-12 manufactured by Nippon Eriez Magnetics Co., Ltd., EMF-100S, EMF-150S, EMF-250S, EMF-300S manufactured by Taiho Magnetic Co., Ltd., and the like can be used.

[0029] The magnetic flux density of the electromagnet is preferably 5,000 to 30,000 gauss, more preferably 12,000 to 30,000 gauss, and even more preferably 14,000 to 30,000 gauss. Use of an electromagnet within the above range is preferable because it not only makes it possible to remove metallic magnetic foreign matter contained in raw materials such as carbon materials, but also makes it possible to remove metallic magnetic foreign matter generated during the manufacturing process.

[0030] The flow rate of the carbon material pre-dispersion liquid (X1) when it comes into contact with the electromagnet is preferably 1 L / min or more and 200 L / min or less, and more preferably 50 L / min or more and 150 L / min or less.

[0031] The carbon material pre-dispersion liquid (X1) is preferably passed through the electromagnet three or more times. If the number of passes is too small, there is a possibility that metallic magnetic foreign matter may not be sufficiently removed. When the carbon material pre-dispersion liquid (X1) is passed through the electromagnet in a circulating manner, it is preferable to pass the electromagnet a greater number of times in consideration of the uniformity in the tank used in the production process.

[0032] The amount of metallic magnetic foreign matter in the carbon material pre-dispersion (X2) after the magnetic separation treatment is preferably as small as possible, and the content in 30 kg of the pre-dispersion (X2) determined under the following condition (I) is preferably less than 100 mg, more preferably less than 40 mg, and even more preferably less than 10 mg. ５０By subjecting a carbon material pre-dispersion (X1) having a particle size of 20 μm or more to magnetic separation treatment, the amount of metallic magnetic foreign matter contained can be significantly reduced compared to conventional methods. As a result, the content of metallic magnetic foreign matter in the carbon material dispersion can also be reduced, resulting in a secondary battery with excellent battery characteristics. <Condition (I)> 30 kg of the carbon material pre-dispersion is passed through an electromagnet (magnetic flux density 16,000 gauss) five times and washed with an amide-based polar solvent, and the obtained metallic magnetic foreign matter is deposited on a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metallic foreign matter particles on the filter is measured.

[0033] The content of metallic magnetic foreign matter can be measured specifically by, for example, the method described in the Examples.

[0034] [Step (3)] Step (3) is a step of dispersing the carbon material pre-dispersion (X2) to produce a carbon material dispersion. Note that step (3) preferably further comprises a step of removing metallic magnetic foreign matter simultaneously with and / or after dispersing the carbon material pre-dispersion (X2).

[0035] The carbon material dispersion has a cumulative particle diameter D ５０ The cumulative particle diameter D is preferably less than 20 μm, more preferably 10 μm or less, and even more preferably 5 μm or less. Also, it is preferably 0.1 μm or more. ５０ If the cumulative particle diameter D is within this range, not only the characteristics when formed into a secondary battery are excellent, but also the stability over time can be improved. ５０ If the cumulative particle diameter D is large, the particles tend to settle, and the stability over time may be deteriorated. ５０ If the cumulative particle diameter D is too small, the particles are unstable, and the particles tend to aggregate and settle, which may result in poor stability over time. ５０ is determined from a volume-based particle size distribution curve measured by a laser diffraction / scattering particle size distribution measurement method, and specifically, can be measured by the method described in the section [Examples], for example.

[0036] The carbon material dispersion may be subjected to a sufficient dispersion treatment in order to obtain sufficient stability over time by micronizing the carbon material and improving the dispersibility of the particles. For example, in the case of a long carbon material such as carbon nanotubes, a dispersion treatment using a dispersion medium or a dispersion treatment using shear force may be used to break down aggregates and reduce the particle size while maintaining the shape of the carbon material. The dispersing machine that can be used to produce the carbon material dispersion is not particularly limited, and examples thereof include media-type dispersing machines such as a paint conditioner (manufactured by Red Devil), colloid mills (PUC Colloid Mill manufactured by PUC, Colloid Mill MK manufactured by IKA), cone mills (Cone Mill MKO manufactured by IKA, etc.), ball mills, sand mills (Dyno Mill manufactured by Shinmaru Enterprises, etc.), attritors, pearl mills (DCP Mill manufactured by Eirich, etc.), and bead mills (Star Mill manufactured by Ashizawa Finetech Co., Ltd., etc.), high-pressure homogenizers (Genus PY manufactured by Genus, Star Burst manufactured by Sugino Machine, Nanomizer manufactured by Nanomizer, etc.), media-less dispersing machines such as M Technique's Claire SS-5 and Nara Kikai's MICROS, and other roll mills. From the viewpoint of dispersion efficiency, it is recommended to carry out the dispersion process using these dispersing machines until the carbon material dispersion becomes uniform. The distributed processing may be a pass-type distributed processing or a circulating-type distributed processing.

[0037] The production of the carbon material dispersion also preferably includes a step of removing metallic magnetic contaminants using the magnetic force of a magnet or the like. The same method as described in step (2) can be used as a method for removing metallic magnetic contaminants by magnetic separation. Furthermore, the carbon material dispersion can be further improved in removing metallic magnetic contaminants by incorporating a filtering step. On the other hand, the particle size of the carbon material pre-dispersion (X2) is larger than that of the carbon material dispersion, and the carbon material pre-dispersion (X2) clogs the filter, making it difficult to incorporate the carbon material pre-dispersion (X2).

[0038] The filter may be a surface filter such as a membrane filter or a depth filter, but a depth filter is more preferred. Because metal magnetic foreign matter is not spherical and is often oriented, the use of a depth filter makes it possible to efficiently remove the metal magnetic foreign matter from the carbon material dispersion.

[0039] Unlike surface filters (which capture particulate matter in fluids primarily on the filter surface), depth filters capture particulate matter in fluids primarily within the filter media, and are characterized by high particle retention and resistance to clogging. Using a depth filter makes it possible to more selectively remove metallic magnetic foreign matter from carbon material dispersions.

[0040] As the depth filter, for example, a nonwoven fabric depth cartridge NT-T series manufactured by 3M™ PP, Profile II manufactured by Nippon Pall Co., Ltd., or Slope Pure manufactured by Loki Co., Ltd. can be used.

[0041] The filtration accuracy of the filter is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less. If a filter with a small pore size is used for the purpose of increasing the efficiency of removing metallic magnetic foreign matter from a carbon material dispersion, the efficiency of removing metallic magnetic foreign matter may decrease due to clogging of the carbon material, etc. By using a filter with a filtration accuracy in the above range, metallic foreign matter can be efficiently removed, and a carbon material dispersion with a low content of metallic foreign matter can be obtained.

[0042] A low content of metallic magnetic foreign matter suppresses thickening of the carbon material dispersion over time, resulting in good stability over time. On the other hand, a high content of metallic magnetic foreign matter may cause the dispersant in the carbon material dispersion to adsorb to the metallic magnetic foreign matter, disrupting the dispersion of the carbon material and resulting in thickening over time. Furthermore, if a secondary battery contains a large amount of metallic magnetic foreign matter, the metallic magnetic foreign matter may dissolve at the positive electrode during charge / discharge cycles and precipitate at the negative electrode, penetrating the separator and causing partial contact between the negative electrode and the positive electrode, potentially leading to voltage failure. This may also result in Li ion inhibition. Furthermore, if the amount of metallic magnetic foreign matter is large, it may come into contact with the positive electrode, causing a short circuit. Therefore, the smaller the amount of metallic magnetic foreign matter in the carbon material dispersion, the better. The content per 30 kg of carbon material dispersion determined under the following condition (II) is preferably less than 100 mg, more preferably less than 40 mg, and even more preferably less than 10 mg. <Condition (II)> 30 kg of a carbon material dispersion is passed through an electromagnet (magnetic flux density: 16,000 gauss) five times, washed with an amide-based polar solvent, and the obtained metallic magnetic foreign matter is deposited on a filter with a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metallic foreign matter particles on the filter is measured.

[0043] The content of metallic magnetic foreign matter can be measured specifically by, for example, the method described in the Examples.

[0044] <Carbon Material Pre-Dispersion and Carbon Material Dispersion> The carbon material pre-dispersion and carbon material dispersion of the present embodiment contain at least a carbon material, a dispersant, and a solvent.

[0045] The carbon material pre-dispersion (X1) has a sliding angle of less than 70° and a cumulative particle diameter D ５０ The carbon material pre-dispersion (X2) is obtained by removing metallic magnetic foreign matters by magnetic separation treatment simultaneously with and / or after the production of the carbon material pre-dispersion (X1). Specifically, a carbon material, a dispersant, and a solvent are mixed, and further dispersed as necessary, to obtain a carbon material pre-dispersion (X1) having a sliding angle of less than 70° and a cumulative particle diameter D ５０A carbon material pre-dispersion (X1) having a particle size of 20 μm or more can be obtained. By removing the metallic magnetic foreign matter in the carbon material pre-dispersion by magnetic separation simultaneously with and / or after the production of this carbon material pre-dispersion (X1) to obtain a carbon material pre-dispersion (X2), it is possible to reduce the content of the metallic magnetic foreign matter in the dispersion without excessively miniaturizing the carbon material and the metallic magnetic foreign matter, and also to achieve stability over time of the carbon material dispersion. The magnetic separation process can also be used to reduce the sliding angle and cumulative particle size D ５０ Since the sliding angle is almost unchanged, the carbon material pre-dispersion liquid (X2) also has a sliding angle of less than 70° and a cumulative particle diameter D ５０ is 20 μm or more.

[0046] The carbon material dispersion of the present embodiment is obtained by dispersing the carbon material pre-dispersion (X2). Preferably, the carbon material dispersion is obtained by further removing metallic magnetic foreign matter simultaneously with and / or after the dispersion of the carbon material pre-dispersion (X2).

[0047] Cumulative particle diameter D of carbon material dispersion ５０ is preferably 5 μm or less, more preferably 3 μm or less, and even more preferably 2 μm or less. Also, it is preferably 0.5 μm or more, and even more preferably 1 μm or more. ５０ When the value is in the above range, metallic magnetic foreign matter contained in the carbon material can be easily removed by magnetic separation treatment, and a carbon material dispersion composition having a low metallic magnetic foreign matter content and good stability over time can be easily obtained.

[0048] The carbon material dispersion refers to a state before the active material is added. In this respect, the carbon material dispersion is distinguished from an electrode slurry containing an active material. That is, the carbon material dispersion is one that does not substantially contain an active material. This concept excludes a state in which an active material is intentionally added to the carbon material dispersion, and the active material may be present in an amount of 1 mass % or less, 0.5 mass % or less, or 0.1 mass % or less, relative to the total mass of the carbon material dispersion. The active material will be described later.

[0049] (Carbon Material) The carbon material in this embodiment is not particularly limited. Examples of conductive carbon materials include graphite, carbon black, and fibrous carbon materials such as carbon nanotubes, carbon nanofibers, and carbon fibers, which can be used alone or in combination. The carbon material plays a role in forming a conductive path within the electrode. From the viewpoint of being less susceptible to breakage due to the expansion and contraction of the electrode film, it is preferable to include a fibrous carbon material, and more preferably a fibrous carbon material. From the viewpoints of conductivity, availability, and cost, the use of carbon black and / or carbon nanotubes is preferred. Furthermore, from the viewpoints of reducing raw material costs and efficiently forming a conductive network, two or more types of the same type of carbon material with different physical properties may be used in combination. Examples of carbon materials with different physical properties include two types of carbon nanotubes with different average outer diameters or average fiber diameters, or two types of carbon black with different specific surface areas.

[0050] Carbon materials may contain metallic magnetic contaminants during the manufacturing process of the carbon material. It is difficult to remove all of these metallic magnetic contaminants from the carbon material. In particular, carbon nanotubes may contain metallic magnetic contaminants derived from raw materials such as metal catalysts. Carbon nanotubes can be dispersed to reveal the metallic magnetic contaminants contained therein, but the metallic magnetic contaminants are also micronized at the same time as the carbon nanotubes are cut by micronization, making it difficult to extract the metallic magnetic contaminants from the dispersion. However, the method for manufacturing a carbon material dispersion composition of this embodiment can produce a carbon material having a sliding angle with respect to a metal substrate of less than 70° and a cumulative particle diameter D ５０ By performing the magnetic separation process using a carbon material pre-dispersion liquid having a particle size of 20 μm or more, it is possible to efficiently remove metallic magnetic contaminants derived from the carbon material. Therefore, according to the method for producing a carbon material dispersion liquid of this embodiment, even when using carbon nanotubes on which metallic magnetic contaminants derived from the metal catalyst used in synthesis often remain, the content of metallic magnetic contaminants can be reduced more than in the past.

[0051] The carbon purity of a carbon material is expressed as the content (% by mass) of carbon atoms in the carbon material. The higher the carbon purity, the better, and it is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more, relative to 100% by mass of the carbon material. By keeping the carbon purity within the above range, problems such as short circuits caused by the formation of dendrites by impurities can be prevented.

[0052] [Carbon Black] Carbon black is a fine particle primarily composed of carbon. It is produced by incomplete combustion of oil or gas, controlling various properties. Carbon black has a secondary structure (aggregate) in which primary particles are linked together like beads, and a tertiary structure (agglomerate) in which the secondary structures further aggregate. These secondary and tertiary structures are collectively referred to as the "structure." Although primary particles appear spherical when observed under an electron microscope, the primary particles are not chemically independent. Instead, they are chemically bonded to adjacent primary particles within the aggregate to form the secondary structure. Meanwhile, the secondary structures are chemically independent and aggregate through intermolecular forces to form the tertiary structure. Therefore, the conductivity within the secondary structures is higher than the conductivity between the secondary structures, including the contact resistance. Therefore, deagglomerating the tertiary structure while maintaining the structure of the secondary structures as much as possible is effective in obtaining electrodes with excellent conductivity. In this specification, the secondary structure may be simply referred to as the "structure."

[0053] The carbon black used in this embodiment may be any of various commercially available carbon blacks, such as acetylene black, furnace black, hollow carbon black, channel black, thermal black, ketjen black, etc. Carbon black that has undergone a conventional oxidation treatment or graphitization treatment may also be used.

[0054] Oxidation treatment of carbon black is a treatment in which oxygen-containing polar functional groups such as phenol groups, quinone groups, carboxyl groups, and carbonyl groups are directly introduced (covalently bonded) to the surface of the carbon black by treating the carbon black at high temperatures in air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, or the like. This treatment is commonly carried out to improve the dispersibility of carbon black.

[0055] Examples of commercially available carbon black include Super P-Li (manufactured by TIMCAL Corporation), Ketjen Black EC-300J, EC-600JD (manufactured by Lion Corporation), Denka Black, Denka Black Li-400, FX-35 (manufactured by Denka Company, acetylene black), and the like. Examples of graphite include artificial graphite and natural graphite such as flake graphite, lump graphite, and amorphous graphite, but are not limited to these, and two or more types may be used in combination.

[0056] The average primary particle diameter of carbon black is preferably 10 nm to 1 μm, particularly preferably 20 nm to 200 nm, and more preferably 25 nm to 100 nm. The average primary particle diameter of carbon black can be calculated by first observing and photographing the carbon black using a transmission electron microscope, randomly selecting 100 spherical-like carbon black primary particles from the photograph, and measuring the outer diameter of each.

[0057] The BET specific surface area of ​​carbon black is 10 m ２ / g or more 1500m ２ / g or less, and ２ / g or more 1000m ２ / g or less is more preferable, and 100m ２ / g or more 850m ２ / g or less is even more preferable. When the BET specific surface area is within the above range, an efficient conductive network can be formed with a small amount of carbon black, allowing the amount of conductive material in the electrode to be reduced. This increases the degree of freedom in battery design, such as by increasing the amount of active material or binder resin. Furthermore, when preparing an electrode slurry, the active material and carbon black are more likely to be combined, making it easier to obtain an electrode film having a homogeneous conductive network in which the active material surface is coated with carbon black, thereby suppressing the electrolyte decomposition reaction at the interface between the electrolyte and the active material and improving the cycle characteristics of the battery. The BET specific surface area can be measured by the BET method described in JIS Z 8830.

[0058] [Carbon Nanotubes] Carbon nanotubes have a structure in which planar graphite is rolled up into a cylindrical shape. Carbon nanotubes preferably include multi-walled carbon nanotubes, and may include multi-walled carbon nanotubes and single-walled carbon nanotubes. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are rolled up. Single-walled carbon nanotubes have a structure in which one layer of graphite is rolled up. The sidewalls of carbon nanotubes do not have to have a graphite structure. For example, carbon nanotubes with sidewalls having an amorphous structure can also be used as the carbon material.

[0059] The average outer diameter of the carbon nanotubes is preferably 1 nm or more and 25 nm or less, more preferably 3 nm or more and 20 nm or less, and even more preferably 4 nm or more and 15 nm or less. When the average outer diameter is within the above range, a good conductive network is easily formed within the electrode, and the active material inside the secondary battery is uniformly utilized during charge and discharge, thereby suppressing deterioration of the active material and further improving the cycle characteristics of the secondary battery.

[0060] The G / D ratio (peak ratio of G-band to D-band) of carbon nanotubes is 1560 cm in the Raman spectrum when used in an amide-based polar solvent. －１ ~1600cm －１ The maximum peak intensity within the range of G, 1310 cm －１ ~1350cm－１ When the maximum peak intensity within the range is defined as D, the G / D ratio is preferably 0.5 to 10, more preferably 0.7 to 4.5. When used in a solvent containing 50% or more water, the peak intensity at 1560 cm in the Raman spectrum is －１ ~1600cm －１ The maximum peak intensity within the range of G, 1310 cm －１ ~1350cm －１ When the maximum peak intensity within this range is defined as D, the G / D ratio is preferably 5 to 100, and more preferably 10 to 50. When the G / D ratio of the carbon nanotubes is within the above range, it is believed that the contact resistance between the carbon nanotubes is reduced, making it easier to obtain good conductivity. It is also believed that this is because the amount of functional groups on the multi-walled carbon nanotube surface is appropriate, which results in good affinity with the solvent and better dispersibility.

[0061] The BET specific surface area of ​​carbon nanotubes is 100 m ２ / g or more 1500m ２ / g or less, and ２ / g or more 1000m ２ / g or less is more preferable, and 200m ２ / g or more 800m ２ / g or less is even more preferable. When the BET specific surface area is within the above range, an efficient conductive network can be formed with a small amount, and the amount of conductive material in the electrode can be reduced. This increases the degree of freedom in battery design, such as by increasing the amount of active material or binder resin. Furthermore, when preparing the composite slurry, the active material and carbon nanotubes are more likely to be combined, making it easier to obtain an electrode film having a homogeneous conductive network in which the active material surface is coated with carbon nanotubes, thereby suppressing the electrolyte decomposition reaction at the interface between the electrolyte and the active material and improving the cycle characteristics of the battery. The BET specific surface area can be measured by the BET method described in JIS Z 8830.

[0062] The carbon purity of carbon nanotubes can be adjusted by purification treatment. Various conventionally known methods can be used to purify carbon nanotubes. Examples include acid treatment, graphitization treatment, and chlorination treatment.

[0063] The acid used in acid-treating carbon nanotubes may be any acid capable of dissolving the metals and metal oxides contained in the carbon nanotubes, and is preferably, for example, an inorganic acid or a carboxylic acid. Among inorganic acids, hydrochloric acid, sulfuric acid, and nitric acid are particularly preferred. The acid-treatment of carbon nanotubes is preferably carried out in a liquid phase, and more preferably, the carbon nanotubes are dispersed and / or mixed in the liquid phase. After the acid treatment, the carbon nanotubes are preferably washed with water and dried.

[0064] The graphitization treatment of the carbon nanotubes is not particularly limited, but can be carried out by heating the carbon nanotubes at 1500° C. to 3500° C. in an inert atmosphere with an oxygen concentration of 0.1% or less.

[0065] The chlorination treatment of carbon nanotubes is not particularly limited, but can be carried out, for example, by introducing chlorine gas into an inert atmosphere with an oxygen concentration of 0.1% or less and heating the carbon nanotubes at 800°C to 2000°C.

[0066] The carbon nanotubes may be surface- or terminal-modified with functional groups or alkyl groups, or may be doped with alkali metals or halogens. For example, they may be functionalized with carboxyl groups, sulfo groups, or hydroxyl groups by heating in an acid. It is preferable to use carbon nanotubes that do not have acidic functional groups such as carboxyl groups or sulfo groups, as this allows the resulting carbon nanotube dispersion to have both good stability and fluidity.

[0067] (Dispersant) The dispersant of the present embodiment is not particularly limited as long as it can stabilize the dispersion of the carbon material in the dispersion liquid, and surfactants, resin-type dispersants, etc. can be used. Surfactants are mainly classified into anionic, cationic, nonionic, and amphoteric. Depending on the properties required for dispersing the carbon material, a suitable type of dispersant can be used in a suitable amount.

[0068] When an anionic surfactant is selected, its type is not particularly limited. Specific examples include, but are not limited to, fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkylaryl sulfonates, alkylnaphthalenesulfonates, dialkylsulfonates, dialkylsulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylaryl ether sulfates, naphthalenesulfonate-formalin condensates, polyoxyethylene alkyl phosphate sulfonates, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters. Specific examples include, but are not limited to, sodium dodecylbenzenesulfonate, sodium laurate sulfate, polyoxyethylene lauryl ether sodium sulfate, polyoxyethylene nonylphenyl ether sulfate, and the sodium salt of β-naphthalenesulfonate-formalin condensates.

[0069] Cationic surfactants include alkylamine salts and quaternary ammonium salts. Specific examples include, but are not limited to, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkylmercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyl triethyl ammonium chloride. Amphoteric surfactants include, but are not limited to, aminocarboxylic acid salts.

[0070] Nonionic surfactants include, but are not limited to, polyoxyethylene alkyl ethers, polyoxyalkylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers, and more specifically, include, but are not limited to, polyoxyethylene lauryl ethers, sorbitan fatty acid esters, and polyoxyethylene octylphenyl ethers.

[0071] The surfactant to be selected is not limited to a single surfactant. Therefore, it is also possible to use a combination of two or more surfactants. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. In this case, it is preferable to blend an appropriate amount for each surfactant component. A combination of an anionic surfactant and a nonionic surfactant is preferred. The anionic surfactant is preferably a polycarboxylate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0072] Specific examples of resin-type dispersants include fluorine-based resins, cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethylhydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, carboxymethyl cellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, hydrogenated nitrile butadiene rubber, and polyacrylonitrile polymers. Fluorine-based resins, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, hydrogenated nitrile butadiene rubber, and polyacrylonitrile polymers are particularly preferred. The molecular weight of the resin-type dispersant is preferably 10,000 to 300,000 from the viewpoint of achieving both stability over time of the carbon material and the efficiency of removing metallic magnetic foreign matter by magnetic separation treatment.

[0073] From the viewpoint of oxidation resistance, the dispersant is preferably hydrogenated nitrile butadiene rubber or polyacrylonitrile polymer.

[0074] From the viewpoint of the stability over time of the carbon material, the content of the dispersant is preferably 10 to 300 parts by mass, more preferably 10 to 100 parts by mass, relative to 100 parts by mass of the carbon material. By setting the content within this range, the dispersed state of the carbon material can be kept stable, and the stability over time can be further improved.

[0075] In addition to the dispersant, it is preferable to add an amine compound or an inorganic base. As the amine compound, a primary amine (primary amine), a secondary amine (secondary amine), or a tertiary amine (tertiary amine) is used, and ammonia or a quaternary ammonium compound is not included. As the amine compound, in addition to monoamine, amine compounds such as diamine, triamine, and tetramine having multiple amino groups in the molecule can be used. Specific examples of inorganic bases include, but are not limited to, aliphatic primary amines such as methylamine, ethylamine, butylamine, and octylamine, aliphatic secondary amines such as dimethylamine, diethylamine, and dibutylamine, aliphatic tertiary amines such as trimethylamine, triethylamine, and dimethyloctylamine, amino acids such as alanine, methionine, proline, serine, asparagine, glutamine, lysine, arginine, histidine, aspartic acid, glutamic acid, and cysteine, alkanolamines such as dimethylaminoethanol, monoethanolamine, diethanolamine, methylethanolamine, and triethanolamine, and alicyclic nitrogen-containing heterocyclic compounds such as hexamethylenetetramine, morpholine, and piperidine. Examples of inorganic bases include alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, alkali metal phosphates, and alkaline earth metal phosphates.

[0076] When an amine compound or an inorganic base is used, the content thereof is preferably 0.1 parts by mass or more and 10 parts by mass or less, more preferably 0.5 parts by mass or more and 6 parts by mass or less, and more preferably 1 part by mass or more and 3 parts by mass or less, relative to 100 parts by mass of the dispersant. This improves the wettability of the carbon material to the solvent, thereby further improving dispersibility. When carbon nanotubes are used as the carbon material, dispersibility is significantly improved.

[0077] (Solvent) The solvent of the present embodiment is not limited as long as it can disperse the carbon material, and water or an organic solvent such as an amide-based organic solvent can be used.

[0078] Since aqueous solvents can corrode magnets, weakening the magnetic force of the magnet and generating metallic magnetic contaminants, the use of an amide organic solvent can reduce the amount of metallic magnetic contaminants in the carbon material dispersion. When using an aqueous solvent, corrosion can be prevented by coating or plating the magnet with Teflon (registered trademark) or epoxy, and the amount of metallic magnetic contaminants in the carbon material dispersion can be reduced.

[0079] Examples of the amide organic solvent include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc. In particular, it is preferable to use at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0080] When an organic solvent is used as the solvent in this embodiment, it is preferable that the organic solvent contains substantially no water, from the viewpoint of suppressing thickening of the carbon material. Specifically, the water content is preferably 100 to 3000 ppm, more preferably 200 to 1500 ppm, and more preferably 200 to 1000 ppm, based on the carbon material dispersion liquid. If a large amount of water is contained, there is a risk of thickening or gelling of the carbon material dispersion liquid or an electrode slurry using the same. By setting the water content within the above range, the dispersed state of the carbon material can be maintained well, and thickening can be suppressed even when the carbon material dispersion liquid is stored for a long period of time, which is preferable.

[0081] (Other Optional Components) The carbon material pre-dispersion and the carbon material dispersion may contain, as needed, other additives such as a wetting agent, a pH adjuster, a wetting and penetrating agent, a leveling agent, a binder resin described below, other conductive materials, and the like, as long as the additives do not impair the object of the present invention. These additives may be added at any timing, such as before preparing the mixed solution, during or after mixing, or when preparing the carbon material pre-dispersion or the carbon material dispersion.

[0082] <<Production of Electrode Slurry>> The electrode slurry can be produced by mixing an active material with the carbon material dispersion liquid of this embodiment. The active material may be either a positive electrode active material or a negative electrode active material. Furthermore, a binder resin, other conductive materials, or a solvent may be further included, and optional components may be further mixed. In this specification, the positive electrode active material and the negative electrode active material may be simply referred to as "active material." The active material is a material that serves as the basis for a battery reaction. Active materials are classified into positive electrode active materials and negative electrode active materials based on electromotive force. The electrode slurry may also be referred to as "composite slurry" or "electrode composite slurry," and electrode slurries containing a positive electrode active material or a negative electrode active material may be referred to as "positive electrode slurry" and "negative electrode slurry," respectively. The electrode slurry is preferably in a slurry form to improve uniformity and processability.

[0083] (Positive Electrode Active Material) The positive electrode active material is not particularly limited. For example, for secondary battery applications, metal compounds such as metal oxides and metal sulfides that can reversibly dope or intercalate lithium ions can be used. For example, lithium manganese composite oxides (e.g., Li ｘ Mn ２ O ４ or LixMnO ２ ), lithium nickel composite oxide (e.g., Li ｘ NiO ２ ), lithium cobalt composite oxide (Li ｘ CoO ２ ), lithium nickel cobalt composite oxide (e.g., Li ｘ Ni １－ｙ Co ｙ O ２ ), lithium manganese cobalt composite oxide (e.g., Li ｘ Mn ｙ Co １－ｙ O ２ ), lithium nickel manganese cobalt composite oxide (e.g., Li ｘ Ni ｙ Co ｚ Mn １－ｙ－ｚ O ２ ), spinel-type lithium manganese nickel composite oxide (e.g., Li ｘ Mn ２－ｙ Niｙ O ４ ), lithium phosphate powder having an olivine structure (e.g., Li ｘ FePO ４ , Li ｘ Fe １－ｙ Mn ｙ P.O. ４ , Li ｘ CoPO ４ etc.), manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxide (e.g., V ２ O ５ , V ６ O １３ ), transition metal oxide powder such as titanium oxide, iron sulfate (Fe ２ (SO ４ ) ３ ), TiS ２ Examples include transition metal sulfide powders such as FeS. Here, x, y, and z are numbers, and 0<x<1, 0<y<1, 0<z<1, and 0<y+z<1. These positive electrode active materials can be used singly or in combination. Among these active materials, active materials containing Ni and / or Mn (especially when the total amount of Ni and / or Mn in the transition metals is 50 mol% or more) tend to become highly basic due to the elution of raw material-derived components or metal ions. This can easily cause binder gelation or deterioration of the dispersion state, making the problem of the present invention particularly pronounced. Therefore, this embodiment is particularly effective for batteries containing active materials containing Ni and / or Mn.

[0084] (Negative Electrode Active Material) The negative electrode active material is not particularly limited, but examples thereof include metal Li, or its alloy, tin alloy, silicon alloy negative electrode, Li Ｘ TiO ２ , Li Ｘ Fe ２ O ３ , Li Ｘ Fe ３ O ４ , Li Ｘ WO ２Examples of materials that can be used include metal oxides such as those listed above, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, and resin-baked carbon materials. Here, x is a number, 0<x<1. These negative electrode active materials can be used alone or in combination. In particular, when a silicon alloy negative electrode is used, the theoretical capacity is large but the volume expansion is extremely large. Therefore, it is preferable to use it in combination with artificial graphite such as highly graphitized carbon materials, carbonaceous powders such as natural graphite, resin-baked carbon materials, or the like.

[0085] The content of the carbon material in the electrode slurry is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.10 parts by mass or more, per 100 parts by mass of the active material. It is also preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and even more preferably 3 parts by mass or less. If the content exceeds the above range, the amount of active material filled in the electrode may decrease, resulting in a decrease in the capacity of the battery. If the content is below the above range, the conductivity of the electrode and the battery may be insufficient.

[0086] The content of the dispersant in the electrode slurry is preferably 0.01 parts by mass or more, more preferably 0.02 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the active material.

[0087] (Binder Resin) When the electrode slurry further contains a binder resin, there are no particular limitations as long as it is typically used as a binder resin for paints and the like, and it can be appropriately selected depending on the purpose. The binder resin used in the electrode slurry is a resin that can bond materials such as active materials and conductive materials. Examples of binder resins used in the electrode slurry include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid esters, methacrylic acid, methacrylic acid esters, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, and fluororesins; cellulose resins; elastomers such as styrene butadiene rubber and fluororubber; and conductive resins such as polyaniline and polyacetylene. Modified products, mixtures, and copolymers of these resins are also acceptable. Among these, when used as a binder resin for a positive electrode, it is preferable to use, for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc. as a binder resin in terms of durability, and when used as a binder resin for a negative electrode, it is preferable to use, for example, CMC, styrene butadiene rubber, polyacrylic acid, etc., which have good adhesion.

[0088] When the electrode slurry contains a binder resin, the content of the binder resin in the electrode slurry is preferably 0.5 parts by mass or more, and more preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less, per 100 parts by mass of the active material.

[0089] The solid content of the electrode slurry is preferably 30% by mass or more, more preferably 40% by mass or more, based on the mass of the electrode slurry (the mass of the electrode slurry being 100% by mass), and is preferably 90% by mass or less, more preferably 80% by mass or less.

[0090] The electrode slurry can be prepared by various conventionally known methods. Examples include a method of adding an active material to a carbon material dispersion; a method of adding an active material to a carbon material dispersion and then adding a binder resin; and a method of adding a binder resin to a carbon material dispersion and then adding an active material. The dispersion device used for dispersion is not particularly limited, and the electrode slurry can be obtained using the dispersion means mentioned in the description of the carbon material dispersion. Therefore, the electrode slurry can be prepared by adding and dispersing an electrode active material to a carbon material dispersion without adding a binder resin.

[0091] <<Production of Electrode>> The electrode is obtained by forming an electrode film using the carbon material dispersion liquid or the electrode slurry. The electrode is preferably produced by applying the electrode slurry to a current collector to form an electrode film, and may be a positive electrode or a negative electrode.

[0092] The electrode has, for example, a current collector and an electrode film obtained by applying an electrode slurry onto the current collector and drying it. An electrode formed using the electrode slurry for a positive electrode can be used as a positive electrode. An electrode formed using the electrode slurry for a negative electrode can be used as a negative electrode. In this specification, an electrode film formed using an electrode slurry containing an active material may be referred to as an "electrode mixture layer."

[0093] The material and shape of the current collector used to form the electrode are not particularly limited, and can be appropriately selected from those suitable for various secondary batteries. Examples of current collector materials include conductive metals or alloys such as aluminum, copper, nickel, titanium, and stainless steel. Furthermore, while flat foils are generally used, current collectors with roughened surfaces, perforated foil current collectors, and mesh current collectors can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0094] The method for applying the carbon material dispersion or electrode slurry to the current collector is not particularly limited, and any known method can be used. Specific examples include die coating, dip coating, roll coating, doctor coating, knife coating, spray coating, gravure coating, screen printing, and electrostatic painting. Examples of drying methods include, but are not limited to, leaving the coating to dry, or drying using a blower dryer, warm air dryer, infrared heater, far-infrared heater, or the like.

[0095] After coating, the coating may be rolled using a lithographic press, a calender roll, etc. The thickness of the formed film is, for example, from 1 μm to 500 μm, and preferably from 10 μm to 300 μm.

[0096] A film formed using a carbon material dispersion or an electrode slurry can also be used as an underlayer for an electrode in order to improve the adhesion between the electrode film and a current collector or to improve the conductivity of the electrode film.

[0097] <<Manufacturing of Secondary Battery>> The secondary battery includes a step of forming an electrode film using the carbon material dispersion or the electrode slurry. The secondary battery preferably includes a step of forming an electrode film by applying the electrode slurry to a current collector. The secondary battery includes, for example, a positive electrode, a negative electrode, and an electrolyte, and at least one of the positive electrode and the negative electrode may be an electrode obtained by the manufacturing method of this embodiment.

[0098] As the electrolyte, various known materials in which ions can move can be used. For example, LiBF ４ , LiClO ４ , LiPF ６ , LiAsF ６ , LiSbF ６ , LiCF ３ SO ３ , Li(CF ３ SO ２ ) ２ N, LiC ４ F ９ SO ３ , Li(CF ３ SO ２) ３ C, LiI, LiBr, LiCl, LiAlCl, LiHF ２ , LiSCN, or LiBPh ４ (wherein Ph is a phenyl group) and the like. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0099] The non-aqueous solvent is not particularly limited, but examples thereof include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 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 may be used alone or in combination of two or more.

[0100] The secondary battery preferably has a separator. Examples of the separator include, but are not limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics obtained by subjecting these to hydrophilic treatment.

[0101] The structure of the secondary battery of the present embodiment is not particularly limited, but typically includes a positive electrode, a negative electrode, and a separator that is provided as needed, and can be in various shapes depending on the purpose of use, such as a paper type, a cylindrical type, a button type, or a laminated type.

[0102] The present invention will be described in more detail below with reference to examples. The present invention is not limited to the following examples as long as it does not depart from the gist of the invention. Unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0103] The materials used in the examples and comparative examples are shown below. <Carbon materials> Carbon material 1: Carbon nanotubes (manufactured by JEIO, JENOTUBE10B) Carbon material 2: Carbon nanotubes (manufactured by JEIO, JENOTUBE6A) Carbon material 7: Carbon nanotubes (manufactured by OCSiAl, TUBALL 01RW03) Carbon material 9: Ketjenblack (manufactured by Lion Specialty Chemical, Ketjenblack EC300J) Carbon material 10: Carbon nanotubes (manufactured by Cnano, FT2020) <Dispersants> Dispersant 1: Hydrogenated nitrile butadiene rubber (manufactured by ARLANXEO, Therban(R) 3406) Dispersant 2: Hydrogenated nitrile butadiene rubber (manufactured by ARLANXEO, Therban(R) 3404) Dispersant 3: Liquid hydrogenated nitrile butadiene rubber (Zanna <Additives> Additive 1 NaOH; sodium hydroxide (Tosoh Corporation, granular caustic soda "Tosoh Pearl") Additive 2 2-aminoethanol (Fujifilm Wako Pure Chemical Industries, Ltd., Wako Grade 1) <Additives> Additive 3 NaOH; sodium hydroxide (Tosoh Corporation, granular caustic soda "Tosoh Pearl") Additive 4 2-aminoethanol (Fujifilm Wako Pure Chemical Industries, Ltd., Wako Grade 1) <Additives> Additive 5 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 6 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 7 2-aminoethanol (Tosoh Corporation, granular caustic soda "Tosoh Pearl") <Additives> Additive 8 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 9 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 10 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 11 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 12 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 13 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 14 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 15 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 16 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 17 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Additive 18 2-aminoethanol (Tosoh Corporation, Wako Grade 1) <Additives> Add

[0104] <Preparation of Carbon Material 3> 10 kg of carbon material 1 was weighed into a 120 L heat-resistant container, and the heat-resistant container containing carbon material 1 was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was discharged while maintaining positive pressure. After the oxygen concentration in the furnace reached 0.1% or less, the furnace was heated to 1600°C over 30 hours. While maintaining the furnace temperature at 1600°C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Nitrogen gas was then introduced at 50 L / min, and the furnace was cooled while maintaining positive pressure, to obtain carbon material 3.

[0105] <Preparation of Carbon Material 4> 10 kg of carbon material 2 was weighed into a 120 L heat-resistant container, and the heat-resistant container containing carbon material 2 was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was discharged while maintaining positive pressure. After the oxygen concentration in the furnace became 0.1% or less, the furnace was heated to 1600°C over 30 hours. While maintaining the furnace temperature at 1600°C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Nitrogen gas was then introduced at 50 L / min, and the mixture was cooled while maintaining positive pressure, to obtain carbon material 4.

[0106] <Preparation of Carbon Material 5> Carbon material 1 was milled in a dynamic mill (manufactured by Nippon Coke and Engineering Co., Ltd.) with zirconia beads having a diameter of 8 mm as milling media, and the mill was operated under conditions of feeding at 10.0 kg / h and a peripheral speed of 5.0 m / s, thereby obtaining carbon material 5.

[0107] <Preparation of Carbon Material 6> Carbon material 4 was milled in a dynamic mill (manufactured by Nippon Coke & Co., Ltd.) using zirconia beads with a diameter of 8 mm as milling media, and was fed at an operating condition of 10.0 kg / h and a peripheral speed of 5.0 m / s, thereby obtaining carbon material 6.

[0108] <Preparation of Carbon Material 8> 3 kg of carbon material 7 was weighed into a 120 L heat-resistant container, and the heat-resistant container containing carbon material 7 was placed in a furnace. Nitrogen gas was then introduced into the furnace, and the air in the furnace was discharged while maintaining positive pressure. After the oxygen concentration in the furnace reached 0.1% or less, the furnace was heated to 1600°C over 30 hours. While maintaining the furnace temperature at 1600°C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Nitrogen gas was then introduced at 50 L / min, and the mixture was cooled while maintaining positive pressure, to obtain carbon material 8.

[0109] <<Methods for Measuring and Evaluating Physical Properties>> The methods for measuring and evaluating the physical properties of the carbon material, carbon material pre-dispersion, carbon material dispersion, electrode, and secondary battery used in each of the examples and comparative examples described below are as follows.

[0110] <Average outer diameter of carbon nanotubes> Using an electronic balance (MSA225S100DI, manufactured by Sartorius), 0.2 g of carbon nanotubes was weighed into a 450 mL SM sample bottle (manufactured by Sanshosha Co., Ltd.), 200 mL of toluene was added, and the mixture was dispersed under ice cooling at an amplitude of 30% for 5 minutes using an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, manufactured by BRANSON) to prepare a carbon nanotube dispersion. Thereafter, the carbon nanotube dispersion was appropriately diluted, dropped onto a collodion film, dried at room temperature, and then directly observed using a transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.). The observation was performed at a magnification of 50,000 times, and multiple photographs were taken of each containing 10 or more carbon nanotubes within the field of view. The outer diameters of 300 randomly selected carbon nanotubes were measured, and the average value was taken as the average outer diameter (nm) of the carbon nanotubes. When the carbon nanotubes formed bundle-like aggregates, they were observed at a magnification of 1,000,000 times using a transmission electron microscope (JEOL, JEM2800) and similar measurements were made to determine the average outer diameter of the carbon nanotubes.

[0111] <Primary Particle Diameter of Carbon Black> The primary particle diameter of carbon black was determined by observing at least 30 or more (e.g., 30 to 100) primary particles in a photograph taken with an electron microscope (either a scanning or transmission electron microscope can be used, and a transmission electron microscope is preferred), and using the arithmetic average value of the particle diameters obtained.

[0112] <BET Specific Surface Area of ​​Carbon Material> 0.03 g of a carbon material was weighed using an electronic balance (MSA225S100DI, manufactured by Sartorius), and then dried for 15 minutes while degassing at 110° C. Thereafter, the BET specific surface area of ​​the carbon material was measured using a fully automatic specific surface area measuring device (HM-model 1208, manufactured by MOUNTECH).

[0113] <Carbon Purity of Carbon Material> The carbon material was subjected to acid decomposition using a microwave sample pretreatment device (ETHOS1, manufactured by Milestone General) to extract the metals contained in the carbon material. Then, analysis was performed using a multi-type ICP optical emission spectrometer (720-ES, manufactured by Agilent) to calculate the amount of metals (total amount of iron, cobalt, nickel, copper, and chromium) contained in the extract. The carbon purity of the carbon material was calculated as follows: Carbon purity (%) of carbon material = ((mass of carbon material - amount of metal) ÷ ​​mass of carbon material) × 100

[0114]

[0115]

[0116] <Sliding Angle of Carbon Material Pre-Dispersion> A sample plate made of SUS316L as a metal substrate was fixed horizontally to a contact angle meter (DM-501) manufactured by Kyowa Interface Science Co., Ltd., and 10 μL of the carbon material pre-dispersion as a test liquid was dropped onto the horizontally placed sample plate to form a water droplet. The sample plate was then tilted little by little, and the angle of the sample plate at which the water droplet started to roll was measured. The smaller the angle, the better the water droplet sliding property (water slide property).

[0117] <Cumulative particle diameter D of carbon material pre-dispersion liquid and carbon material dispersion liquid ５０ Measurement > Cumulative particle diameter D by particle size distribution ５０The measurements were performed using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd.; Partical LA-960V2). The laser wavelength of this analyzer was 650 nm, and the detectors included one ring-shaped 64-segment silicon photodiode, five 4-channel array detectors, and three silicon photodetectors. The measurement unit also used a synthetic quartz flow cell (sample cell). First, NMP, the same solvent as the dispersion, was introduced into a sample bath containing the sample cell, and circulation / ultrasonic cleaning was performed. The operating modes were circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 7, and stirring mode: continuous. Next, ultrasonic operation was performed at ultrasonic intensity: 7 and ultrasonic time: 5 seconds to remove air, and then a blank (background) measurement was performed. The particle size was measured by volume, the particle refractive index was set to 1.920-0.522i (carbon material), and the solvent refractive index was set to 1.468 (NMP). The dispersion was added dropwise so that the laser light transmittance during measurement was 60%±1%, and the sample was prepared. The operation mode during measurement was set to circulation speed: 3, stirring speed: 7, and stirring mode: continuous.

[0118] <Measurement of the amount of metallic magnetic foreign matter in the carbon material pre-dispersion> 30 kg of the carbon material pre-dispersion was passed through an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., magnetic flux density 16,000 Gauss) five times via a diaphragm pump. Thereafter, N-methyl-2-pyrrolidone (NMP) was passed through an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., magnetic flux density 16,000 Gauss), and the carbon material pre-dispersion in the diaphragm pump and the electromagnet was extrusion-washed until substantially no solid content remained. Further thereafter, the power supply to the electromagnet was turned off, and after confirming that the magnetic force of the filter had disappeared, the NMP was passed through the electromagnet to obtain 10 kg of NMP containing metallic magnetic foreign matter. The resulting mixture was then transferred to a 2 L plastic container containing 1 kg of NMP containing the metal magnetic contaminants. After ultrasonic treatment for 5 minutes at 300 W output and 28 kHz frequency using an ultrasonic cleaner (manufactured by Aiwa Medical Industries, Inc.), a bar magnet with a magnetic flux density of 12,000 gauss was attached to the outside of the plastic container to capture the metal magnetic contaminants, and NMP was then poured through. The entire amount of the captured metal magnetic contaminants was then collected using a filter bell on a pre-weighed mesh (weight: W1, diameter: 47 mm, mesh size: 5 μm) using ethanol. The mesh on which the metal magnetic contaminants had accumulated was then removed, and the mesh was dried at 60°C for 20 minutes using a hot air oven. This process was then repeated for all 10 kg of the recovered NMP containing the metal magnetic contaminants. The weight of the dried mesh (W2) was measured, and the weight (W1) minus the pre-weighed weight was used to determine the amount of metal magnetic contaminants (W0). The smaller the amount of metallic magnetic foreign matter (W0), the more desirable it is. The amount of metallic magnetic foreign matter (W0) is A: less than 10 mg, B: 10 mg or more but less than 40 mg, C: 40 mg or more but less than 100 mg, and D: 100 mg or more.

[0119] <Evaluation of the amount of metallic magnetic foreign matter in carbon material dispersion> The amount of metallic magnetic foreign matter (W0) in the carbon material dispersion was determined in the same manner as in measuring the amount of metallic magnetic foreign matter in the carbon material pre-dispersion, except that the carbon material pre-dispersion was changed to a carbon material dispersion. The smaller the amount of metallic magnetic foreign matter (W0), the more desirable it was, and the metallic magnetic foreign matter amount (W0) was rated as follows: ⊚ (excellent), 10 mg or more but less than 40 mg: ◯ (good), 40 mg or more but less than 100 mg: Δ (passable), and 100 mg or more: × (unacceptable).

[0120] <Evaluation of Temporal Stability of Carbon Material Dispersion> The viscosity value was measured using a Brookfield viscometer ("BL" manufactured by Toki Sangyo Co., Ltd.) by leaving the measurement sample in a thermostatic chamber at 25°C for at least one hour, and then measuring the viscosity at a rotor rotation speed of 100 rpm. The types of rotors used for the measurement were No. 1 when the viscosity value was less than 100 mPa·s, No. 2 when the viscosity value was 100 or more and less than 500 mPa·s, No. 3 when the viscosity value was 500 or more and less than 2,000 mPa·s, and No. 4 when the viscosity value was 2,000 or more and less than 10,000 mPa·s. The lower the viscosity, the better the dispersibility, and the higher the viscosity, the worse the dispersibility. The temporal stability of the carbon material dispersion was evaluated using the following equation 1. (Formula 1) Temporal stability = (initial viscosity) / (viscosity after storage in a constant temperature bath at 40°C for 3 days) × 100 (%) The temporal stability evaluation was rated as follows: ⊚: 60% or more (excellent), ○: 50% or more and less than 60% (good), △: 40% or more and less than 50% (passable), ×: less than 40% (unacceptable).

[0121] <Evaluation of Cycle Characteristics of Lithium-Ion Secondary Battery> After leaving the laminated cell secondary batteries manufactured in the Examples and Comparative Examples stationary for 24 hours, they were charged and discharged at a charge / discharge rate of 4.25 V and 0.1 C, and the initial capacity was measured. The laminated cell lithium-ion secondary batteries were placed in a thermostatic chamber at 60°C, and charge / discharge measurements were performed using a charge / discharge device (SM-8, manufactured by Hokuto Denko Corporation). Constant-current, constant-voltage charging (cutoff current 1.25 mA (0.025 C)) was performed at a charge current of 50 mA (1 C) with a charge cutoff voltage of 4.2 V, followed by constant-current discharging at a discharge current of 50 mA (1 C) with a discharge cutoff voltage of 2.5 V. This operation was repeated 100 times. 1 C was defined as the current value required to discharge the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be expressed as the ratio of the initial capacity to the 100th 1 C discharge capacity, using the following equation 2: (Formula 2) Cycle characteristic = (100th 1C discharge capacity) / (initial capacity) × 100 (%) The cycle characteristic was evaluated as follows: ⊚ (excellent) when the cycle characteristic was 80% or more, ○ (good) when it was 70% or more and less than 80%, △ (fair) when it was 60% or more and less than 70%, and × (poor) when it was less than 60%.

[0122] Example A-1 [Step (1)] 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of Dispersant 1 were added to a stainless steel container, and the mixture was stirred at 80°C using a disperser to completely dissolve Dispersant 1, thereby preparing an 8% solution of Dispersant 1. Thereafter, 85.75 parts of N-methyl-2-pyrrolidone (NMP) and 11.25 parts of the 8% solution of Dispersant 1 (0.90 parts of Dispersant 1 added) were added to the stainless steel container, and the mixture was stirred with a disperser until uniform. Three parts of Carbon Material 1 were then weighed out and added while stirring with a disperser. A fine emulsion screen was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was performed at a speed of 9000 rpm until the mixture became uniform and the dispersion particle size measured with a grind gauge reached 200 μm or less, thereby obtaining a pre-dispersion (X1-1). The sliding angle of the pre-dispersion (X1-1) was 67°, and the cumulative particle diameter D ５０ was 43 μm.

[0123] [Step (2)] The obtained pre-dispersion (X1-1) was passed through an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16,000 gauss) three times to obtain a pre-dispersion (X2-1).

[0124] [Step (3)] The pre-dispersion liquid (X2-1) was transferred to a stainless steel container, and a circulation dispersion treatment was carried out with a residence time of 10 minutes using a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises) filled with zirconia beads having a diameter of 1.0 mm. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping, and a 20-pass dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Thereafter, the dispersion liquid was supplied to an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., magnetic flux density 16,000 Gauss), and a three-pass treatment was carried out to obtain a carbon material dispersion liquid 1.

[0125] Examples A-2 to A-20, 29 to 31 Carbon material pre-dispersions (X1-2 to 19, 22 to 24) were produced in the same manner as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additives were changed as shown in Tables 2-1 to 2-3. Subsequently, carbon material pre-dispersions (X2-2 to 20, 23 to 25) and carbon material dispersions 2 to 20, 29 to 31 were obtained.

[0126] (Example A-21) [Step 1 and Step 2] 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of Dispersant 1 were added to a stainless steel container and stirred at 80°C using a disperser to completely dissolve Dispersant 1, thereby preparing an 8% solution of Dispersant 1. Thereafter, 87.23 parts of N-methyl-2-pyrrolidone (NMP), 11.25 parts of the 8% solution of Dispersant 1 (0.9 parts of Dispersant 1 added), and 0.02 parts of NaOH were added to the stainless steel container and stirred with a disperser until uniform, after which 1.5 parts of Carbon Material 4 was taken and added while stirring with a disperser to obtain a carbon pre-dispersion. Subsequently, a fine emulsion screen was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), two bar magnets with a magnetic flux density of 17,000 gauss were installed in the outlet piping of the high shear mixer, and batch dispersion was carried out at a speed of 9,000 rpm until the entire mixture became uniform and the dispersion particle size was 200 μm or less as measured by a grind gauge. Magnetic separation was carried out simultaneously with the production of the carbon material pre-dispersion (X1-20), thereby obtaining a carbon material pre-dispersion (X2-21). That is, the carbon material pre-dispersion (X2-21) corresponds to the carbon material pre-dispersion (X1-20), and has a sliding angle of 53° and a cumulative particle diameter D ５０ was 50 μm.

[0127] [Step 3] Subsequently, the carbon material pre-dispersion liquid (X2-21) was transferred to a stainless steel container, and a circulation dispersion treatment was carried out with a residence time of 10 minutes using a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises) filled with zirconia beads having a diameter of 1.0 mm. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping, and a 20-pass dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Thereafter, the dispersion liquid was supplied to an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16,000 Gauss), and a three-pass treatment was carried out to obtain carbon material dispersion liquid 27.

[0128] (Example A-22) A carbon pre-dispersion (X1-21) was produced in the same manner as in Example A-21, except that the magnetic separation conditions, carbon material, dispersant, and additives were changed as shown in Table 2, and subsequently a carbon material pre-dispersion (X2-22) and a carbon material dispersion 28 were obtained. That is, the carbon material pre-dispersion (X2-22) corresponds to the carbon material pre-dispersion (X1-21), and has a sliding angle of 55° and a cumulative particle diameter D ５０ was 45 μm.

[0129] Example A-23 [Step (1)], [Step (2)] A carbon material pre-dispersion (X2-11) was produced in the same manner as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additives were changed to those shown in Table 2.

[0130] [Step (3)] The carbon material pre-dispersion liquid (X2-11) was sent to a stainless steel container, and the dispersion liquid was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping, and a 20-pass dispersion treatment was performed. The dispersion treatment was performed using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Thereafter, the dispersion liquid was supplied to an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., magnetic flux density 16,000 Gauss), and a 3-pass treatment was performed, to obtain carbon material dispersion liquid 23.

[0131] (Examples A-24 to A-26) A carbon material pre-dispersion (X1) was produced, and then a carbon material pre-dispersion (X2) and carbon material dispersions 24 to 26 were obtained in the same manner as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additives were changed as shown in Table 2. For carbon material dispersions 24 to 26, magnetic separation treatment was not carried out simultaneously with or after dispersion of the carbon material dispersion.

[0132] Example A-27 [Step (1)], [Step (2)] A carbon material pre-dispersion liquid (X2-11) was obtained in the same manner as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additives were changed as shown in Table 2.

[0133] [Step 3] Subsequently, the carbon material pre-dispersion liquid (X2-11) was pumped into a stainless steel container, and a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises) filled with zirconia beads having a diameter of 1.0 mm was used to carry out a circulation dispersion treatment with a residence time of 10 minutes. Next, the carbon material pre-dispersion liquid was pumped into the stainless steel container, and the dispersion liquid was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping. Two bar magnets with a magnetic flux density of 17,000 gauss were installed in the outlet piping of the homogenizer, and a 20-pass dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa, to obtain carbon material dispersion liquid 27.

[0134] Example A-28 Carbon material dispersion 28 was obtained in the same manner as in Example A-27, except that the carbon material pre-dispersion shown in Table 2 was changed to carbon material pre-dispersion (X2-12).

[0135] (Comparative Example A-1) [Step (1)] A carbon material pre-dispersion (X1-1) was obtained in the same manner as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additives were changed as shown in Table 2. The sliding angle of the pre-dispersion (X1-1) was 67°, and the cumulative particle diameter D ５０ was 43 μm.

[0136] [Step (3)] Subsequently, the carbon material pre-dispersion liquid (X1-1) was transferred to a stainless steel container, and a circulation dispersion treatment was carried out with a residence time of 10 minutes using a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises) filled with zirconia beads having a diameter of 1.0 mm. Subsequently, the liquid to be dispersed was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping, and a 20-pass dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa, to obtain a comparative carbon material dispersion liquid 1. The comparative carbon material dispersion liquid 1 was not subjected to the magnetic separation treatment of step (2).

[0137] (Comparative Example A-2) [Step (1)] 94.6 parts of N-methyl-2-pyrrolidone (NMP) and 5.0 parts of an 8% solution of Dispersant 1 (0.4 parts of Dispersant 1 added) were added to a stainless steel container and stirred until uniform. Thereafter, 0.4 parts of Carbon Material 7 was weighed out and added while stirring with a Dispersant. A fine emulsion screen was attached to a high shear mixer (L5M-A, manufactured by SILVERSON) and batch-dispersed at a speed of 9000 rpm until the entire mixture became uniform and the dispersion particle size measured by a grind gauge was 200 μm or less. The contents of the stainless steel container were then transferred to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping, and the dispersion liquid was supplied to the high-pressure homogenizer. A three-pass dispersion treatment was performed to obtain a pre-dispersion liquid (X'1-1). The sliding angle of the pre-dispersion (X'1-1) is 80°, and the cumulative particle diameter D ５０ was 11 μm.

[0138] [Step (2)] Thereafter, the mixture was passed through an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., magnetic flux density 16,000 gauss) three times to prepare a carbon material pre-dispersion liquid (X'2-1).

[0139] Subsequently, the carbon material pre-dispersion liquid (X'2-1) was sent to a stainless steel container, and the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine Ltd.) via piping, and a 20-pass dispersion treatment was performed to obtain a comparative carbon material dispersion liquid 2. The dispersion treatment was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0140] (Comparative Example A-3) [Step (1)] A carbon material pre-dispersion liquid (X1-1) was obtained in the same manner as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additives were changed as shown in Table 2.

[0141] [Step (3)] Subsequently, the carbon material pre-dispersion liquid (X1-1) was sent to a stainless steel container, and the dispersion liquid was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping, whereupon a 10-pass dispersion treatment was carried out. The dispersion treatment was carried out using a single nozzle chamber, with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Thereafter, the dispersion liquid was supplied to an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., magnetic flux density 16,000 gauss), whereupon a 3-pass treatment was carried out, whereupon a comparative carbon material dispersion liquid 3 was obtained. The comparative carbon material dispersion liquid 3 was not subjected to the magnetic separation treatment of step (2).

[0142]

[0143]

[0144]

[0145] In Table 2-3 above, in Examples A-24 to A-26, the magnetic separation treatment in step (3) was not performed. In Comparative Example A-1, the magnetic separation treatment in step (2) and the magnetic separation treatment in step (3) were not performed. In Comparative Example A-2, the sliding angle and cumulative particle diameter D of the pre-dispersion (X1) provided for the magnetic treatment in step (2) were ５０ did not satisfy the expected range, and furthermore, the magnetic separation treatment of step (3) was not carried out. In Comparative Example A-3, the magnetic separation treatment of step (2) was not carried out.

[0146] From the results in Table 2, it can be seen that the sliding angle is less than 70° and the cumulative particle diameter D ５０It was confirmed that the magnetic separation efficiency was high and the metallic magnetic contaminants were reduced by producing a carbon material pre-dispersion liquid having a particle diameter of 20 μm or more and removing the metallic magnetic contaminants simultaneously with and / or after the production. Furthermore, the carbon material dispersion liquid obtained in the example had excellent stability over time. On the other hand, when the magnetic separation treatment was performed, the sliding angle was less than 70° and the cumulative particle diameter D ５０ When the pre-dispersion liquid was one in which the particle size was not 20 μm or more, the reduction in the metallic magnetic foreign matter was insufficient. This is presumably because the carbon material pre-dispersion liquid (X1) had a strong adhesive property to the magnetic separator, and the carbon material pre-dispersion liquid (X1) adhered to the magnetic separator, weakening the magnetic force.

[0147] The results of Examples A-24 to A-26 show that by performing steps (1) and (2), it is possible to reduce the content of metallic magnetic foreign matter in the carbon material dispersion, even if the magnetic separation treatment in step (3) is not necessary. Comparative Examples A-1 and A-3 show that the content of metallic magnetic foreign matter in the carbon material dispersion increases when step (2) is not performed. Comparative Example A-2 shows that the cumulative particle diameter D of the pre-dispersion (X1) is increased before the magnetic separation treatment in step (2). ５０ It can be seen that when the dispersion treatment is carried out until the particle size reaches 11 μm, the metallic magnetic foreign matter is also miniaturized, and therefore the efficiency of removing the metallic magnetic foreign matter in the magnetic separation treatment in step (2) decreases, and the content of the metallic magnetic foreign matter in the carbon material dispersion liquid increases.

[0148] (Example B-1) <Preparation of electrode slurry 1> Capacity 150 cm ３ Into a plastic container, 18.8 parts by mass of an NMP solution in which 8% by mass of PVDF (polyvinylidene fluoride, Solvay, Solef #5130) was dissolved, and 5.8 parts by mass of NMP were weighed. Thereafter, 13.3 parts by mass of the carbon material dispersion 1 whose stability had been evaluated was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Awatori Rentaro, ARE-310). Further, 98.1 parts by mass of a positive electrode active material (BASF Toda Battery Materials, LLC, HED (registered trademark) NCM-111 1100) was added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a planetary centrifugal mixer (Awatori Rentaro, ARE-310) to obtain electrode slurry 1.

[0149] <Preparation of Electrode 1> Electrode slurry 1 was applied to the electrode using an applicator so that the weight per unit area of ​​the electrode was 20 mg / cm ２ After that, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode 1. Electrode 1 was then rolled using a roll press (Thank Metal, 3 ton hydraulic roll press) to obtain a positive electrode (electrode 1). The weight per unit area of ​​the composite layer was 20 mg / cm. ２ The density of the composite layer after rolling was 3.1 g / cc.

[0150] <Preparation of Standard Negative Electrode Composite Slurry> Denka Black Li-400 (manufactured by Denka Co., Ltd.), CMC#1190 (manufactured by Daicel FineChem Co., Ltd.), and water were added to a 150 mL plastic container, and then the mixture was stirred at 2,000 rpm for 30 seconds using a centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310). Furthermore, artificial graphite CGB-20 (manufactured by Nippon Graphite Industries Co., Ltd.) was added as the negative electrode active material, and the mixture was stirred at 2,000 rpm for 150 seconds using a centrifugal mixer. Subsequently, SBR (styrene butadiene rubber, TRD2001 (manufactured by JSR Corporation, solid content 48%)) was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a centrifugal mixer to obtain a standard negative electrode composite slurry. The solid content of the standard negative electrode composite slurry was 48% by mass. The solid content ratio of the negative electrode active material:conductive material:CMC:SBR in the standard negative electrode mixture slurry was 97:0.5:1:1.5.

[0151] <Preparation of Standard Negative Electrode> The negative electrode composite slurry was applied to a copper foil having a thickness of 20 μm, which served as a current collector, using an applicator, and then dried in an electric oven at 80° C.±5° C. for 25 minutes to obtain an electrode with a coating weight per unit area of ​​10 mg / cm. ２ Further, a rolling treatment was carried out using a roll press (a 3-ton hydraulic roll press manufactured by Thank Metal Co., Ltd.) to adjust the density of the negative electrode mixture layer to 1.5 g / cm. ３ A negative electrode having the following structure was fabricated.

[0152] <Preparation of Secondary Battery 1> Electrode 1 was punched out to 45 mm x 40 mm, and the standard negative electrode was punched out to 50 mm x 45 mm. The separator (porous polypropylene film) to be inserted between them was placed in an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. Thereafter, in a glove box filled with argon gas, an electrolyte solution (a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1) was prepared, and 2 parts by mass of VC (vinylene carbonate) was added as an additive to 100 parts by mass of the mixed solvent. LiPF ６ After that, 2 mL of a non-aqueous electrolyte solution in which 1M of ammonium hydroxide was dissolved was poured into the aluminum laminated bag, and the bag was sealed to prepare a secondary battery 1.

[0153] (Example B-2 to Example B-28), (Comparative Example B-1 to Comparative Example B-3) Electrodes 2 to 28, comparative electrodes 1 to 3, secondary batteries 2 to 28, and comparative secondary batteries 1 to 3 were produced by the same method as in the production of the laminate-type lithium ion secondary battery (secondary battery 1), except that the carbon material dispersion liquid listed in Table 3 was changed.

[0154]

[0155] As shown in Table 3, a carbon material pre-dispersion (X1) having a sliding angle of less than 70° and a cumulative particle diameter D50 of 20 μm or more was produced, and metallic magnetic foreign matter was removed simultaneously with and / or after the production. A battery equipped with an electrode using the obtained carbon material dispersion had good cycle characteristics.

[0156] On the other hand, Comparative Example A-1, which does not include a step of removing metallic magnetic foreign matter, and Comparative Example A-2, which has a sliding angle of less than 70° and a cumulative particle diameter D ５０ The batteries using the carbon material dispersion liquid of Comparative Example A-2, which was produced using a carbon material pre-dispersion liquid whose particle size did not satisfy 20 μm or more, and the carbon material dispersion liquid of Comparative Example A-3, which was produced by subjecting only the carbon material dispersion liquid to magnetic separation treatment without subjecting the carbon material pre-dispersion liquid to magnetic separation treatment, both had poor cycle characteristics.

[0157] <Preparation of Standard Positive Electrode> First, 93 parts by mass of a positive electrode active material (HED (registered trademark) NCM-111 1100, manufactured by BASF Toda Battery Materials LLC), 4 parts by mass of acetylene black (Denka Black (registered trademark) HS100, manufactured by Denka Co., Ltd.), and 3 parts by mass of polyvinylidene fluoride (PVDF) (Kureha KF Polymer W#1300, manufactured by Kureha Battery Materials Japan Co., Ltd.) were mixed in a 150 cm ３ After adding the mixture to a plastic container, the powder was mixed using a spatula until it was uniform. Then, 20.5 parts by mass of N-methyl-2-pyrrolidone (NMP) was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation, ARE-310). The mixture in the plastic container was then mixed using a spatula until it was uniform, and the mixture was stirred at 2000 rpm for 30 seconds using the planetary centrifugal mixer. Further, 14.6 parts by mass of NMP was added, and the mixture was stirred at 2000 rpm for 30 seconds using the planetary centrifugal mixer. Finally, the mixture was stirred at 3000 rpm for 10 minutes using a high-speed stirrer to obtain a positive electrode composite slurry. Thereafter, the positive electrode composite slurry was applied to a 20 μm thick aluminum foil as a current collector using an applicator, and then dried in an electric oven at 120° C.±5° C. for 25 minutes to obtain an electrode with a coating weight per unit area of ​​20 mg / cm. ２ Further, a rolling treatment was carried out using a roll press (3 t hydraulic roll press manufactured by Thank Metal Co., Ltd.) to adjust the density of the composite layer to 3.1 g / cm ３ A standard positive electrode was fabricated.

[0158] (Examples B-29 to B-31) <Preparation of electrode 29> Capacity 150 cm ３Into a plastic container, 10.0 parts by mass of carbon material dispersion 29, 12.5 parts by mass of an aqueous solution containing 2% by mass of CMC (#1190, manufactured by Daicel FineChem Co., Ltd.), and 7.0 parts by mass of ion-exchanged water were weighed. The mixture was then stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310) to obtain a carbon nanotube-dispersed resin composition (carbon nanotube-dispersed resin composition W1). Then, 2.4 parts by mass of silicon monoxide (SILICON MONOOXIDE, SiO 1.3C 5 μm, manufactured by Osaka Titanium Technology Co., Ltd.) was added, and the mixture was stirred at 2000 rpm for 30 seconds using the planetary centrifugal mixer. Further, 21.9 parts by mass of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries Co., Ltd.) was added, and the mixture was stirred for 30 seconds at 2000 rpm using the rotation / revolution mixer. Thereafter, 0.78 parts by mass of styrene butadiene emulsion (TRD2001, manufactured by JSR Corporation) was added, and the mixture was stirred for 30 seconds at 2000 rpm using the rotation / revolution mixer to obtain electrode slurry 29.

[0159] Next, the electrode slurry 29 is applied to the electrode using an applicator so that the amount of the electrode slurry per unit area is 8 mg / cm ２ After that, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film. Thereafter, the electrode film was subjected to a rolling treatment using a roll press to obtain a composite layer having a density of 1.6 g / cm. ３ A negative electrode (electrode 29) having the following structure was fabricated.

[0160] <Preparation of Electrodes 30 and 31> As shown in Table 4, electrode slurries 30 and 31 and electrodes 30 and 31 were obtained in the same manner as in preparation of electrode 29, except that carbon material dispersions 30 and 31 were used instead of carbon material dispersion 29.

[0161] <Preparation of Secondary Battery 29> The electrode 29 was punched out to 50 mm x 45 mm, and the standard positive electrode was punched out to 45 mm x 40 mm. The separator (porous polypropylene film) to be inserted between them was inserted into an aluminum laminate bag, and dried in an electric oven at 60°C for 1 hour. Thereafter, in a glove box filled with argon gas, an electrolyte (a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 3:5:2) was prepared, and further, 1 part by mass of VC (vinylene carbonate) and 1 part by mass of FEC (fluoroethylene carbonate) were added as additives to 100 parts by mass of the mixed solvent, and LiPF ６ After 2 mL of a non-aqueous electrolyte solution in which 1M of ethylenediaminetetraacetic acid was dissolved was poured into the aluminum laminated bag, the bag was sealed to prepare a secondary battery 29 .

[0162] <Fabrication of Secondary Batteries 30 and 31> Secondary batteries 30 and 31 were fabricated in the same manner as secondary battery 29, except that the negative electrode shown in Table 4 was changed.

[0163] (Example B-32) <Preparation of electrode 32> Capacity 150 cm ３ 5.0 parts by mass of carbon material dispersion 20, 12.5 parts by mass of an aqueous solution containing 2% by mass of CMC (#1190, manufactured by Daicel FineChem Co., Ltd.), and 12.0 parts by mass of ion-exchanged water were weighed into a plastic container. The mixture was then stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro, ARE-310) to obtain a carbon nanotube-dispersed resin composition (carbon nanotube-dispersed resin composition W1). 2.4 parts by mass of silicon monoxide (SILICON MONOOXIDE, SiO 1.3C 5 μm, manufactured by Osaka Titanium Technology Co., Ltd.) were then added, and the mixture was stirred at 2000 rpm for 30 seconds using the planetary centrifugal mixer. Further, 21.9 parts by mass of artificial graphite (CGB-20, manufactured by Nippon Graphite Industries Co., Ltd.) was added, and the mixture was stirred for 30 seconds at 2000 rpm using the rotation / revolution mixer. Thereafter, 0.78 parts by mass of styrene butadiene emulsion (TRD2001, manufactured by JSR Corporation) was added, and the mixture was stirred for 30 seconds at 2000 rpm using the rotation / revolution mixer to obtain electrode slurry 32.

[0164] Next, the electrode slurry 32 is applied to the electrode using an applicator so that the weight per unit area of ​​the electrode is 8 mg / cm ２ After that, the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode film. Thereafter, the electrode film was subjected to a rolling treatment using a roll press to obtain a composite layer having a density of 1.6 g / cm. ３ A negative electrode (electrode 32) having the following structure was fabricated.

[0165] <Fabrication of Secondary Battery 32> Secondary battery 32 was fabricated in the same manner as secondary battery 29, except that the electrodes shown in Table 4 were changed.

[0166]

[0167] As shown in Table 4, a carbon material pre-dispersion (X1) having a sliding angle of less than 70° and a cumulative particle diameter D50 of 20 μm or more was produced, and metallic magnetic foreign matter was removed simultaneously with and / or after the production. A battery equipped with an electrode using the obtained carbon material dispersion had good cycle characteristics.

[0168] As a result, a secondary battery including an electrode film produced using the carbon material dispersion produced by the production method of this embodiment has excellent cycle characteristics, and therefore, lithium ion secondary batteries can be widely used as batteries for vehicles such as electric vehicles, stationary power sources, large electronic devices such as large servers, and small electronic devices such as personal computers, mobile phones, tablet terminals, etc. In particular, it can be seen that by installing the secondary battery according to this embodiment in a vehicle, a vehicle with high safety and improved fuel efficiency can be obtained.

[0169] Although the present invention has been described with reference to the above-mentioned embodiments, the present invention is not limited to the above-mentioned embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

Claims

1. A method for producing a carbon material dispersion liquid containing a carbon material, a dispersant, and a solvent, comprising the following steps (1) to (3): [Step (1)] Dispersing a carbon material having a sliding angle with respect to a metal substrate of less than 70° and a cumulative particle diameter D ５０ [Step (2)] A step of obtaining a carbon material pre-dispersion liquid (X1) having a particle size of 20 μm or more. [Step (3)] A step of removing metallic magnetic foreign matter by magnetic separation treatment simultaneously with and / or after the production of the carbon material pre-dispersion liquid (X1) to obtain a carbon material pre-dispersion liquid (X2).

2. The method for producing a carbon material dispersion liquid according to claim 1, wherein the solvent is a non-aqueous solvent.

3. The method for producing a carbon material dispersion liquid according to claim 1, further comprising a step of removing metallic magnetic foreign matter simultaneously with and / or after dispersion of the carbon material pre-dispersion liquid (X2) in the step (3).

4. A method for producing an electrode slurry, which comprises mixing an active material with the carbon material dispersion produced by the method according to any one of claims 1 to 3.

5. A method for manufacturing an electrode, comprising a step of applying the electrode slurry produced by the method according to claim 4 to a current collector to form an electrode film.

6. A method for producing a secondary battery, comprising a step of applying the electrode slurry produced by the method according to claim 4 to a current collector to form an electrode film.

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