Method for manufacturing carbon material dispersion, electrode slurry, electrode, and secondary battery

Abstract

To provide a method for manufacturing a carbon material dispersion having a small content of metallic magnetic foreign matter in the carbon material dispersion and excellent stability over time, and provide a secondary battery having good cycle characteristics using the carbon material dispersion.SOLUTION: The problem is solved by a method for manufacturing carbon material dispersion comprising a carbon material, a dispersant, and a solvent, the method comprising all of the following steps (1) to (3). [Step (1)] a step of obtaining a carbon material pre-dispersion (X1) having a sliding angle with respect to a metal substrate of less than 70° and a cumulative particle diameter D50 of 20 μm or more. [Step (2)] a step of obtaining a carbon material pre-dispersion (X2) by removing metallic magnetic foreign matter by magnetic sorting at the same time and / or after manufacturing the carbon material pre-dispersion (X1). [Step (3)] a step of dispersing the carbon material pre-dispersion (X2) and manufacturing a carbon material dispersion.SELECTED DRAWING: None

Description

[Technical field]

[0001] An embodiment of the present invention relates to a method for producing a carbon material dispersion, an electrode slurry, an electrode, and a secondary battery. [Background technology]

[0002] Lithium ion secondary batteries are widely used as batteries for electric vehicles, portable devices, etc. As electric vehicles and portable devices become more powerful, there is an increasing demand year by year for lithium ion secondary batteries with higher capacity, higher output, and smaller size and lighter weight.

[0003] The capacity of a lithium-ion secondary battery depends heavily on the positive and negative electrode active materials, which are the main materials of the electrodes, and various materials for use in these active materials have been actively researched. However, the charge capacity when using active materials in practical use has reached a level close to the theoretical value, and improvement is close to the limit. Therefore, since the charge capacity can be simply increased by increasing the filling amount of the active material in the electrode film, attempts have been made to reduce or eliminate the amount of conductive additives and binder resins, which do not directly contribute to the charge capacity.

[0004] The conductive assistant plays a role in forming a conductive path inside the electrode, and is required to be difficult to break due to the expansion and contraction of the electrode film. In order to maintain the conductive path with a small amount of conductive assistant, it is desirable to use a carbon material with a large specific surface area, such as Ketjen black, carbon nanotubes, graphene, fullerene, etc. However, these carbon materials contain metal catalysts during synthesis and metallic magnetic foreign matter derived from the manufacturing process, which causes a problem of voltage drop failure. The metallic magnetic foreign matter dissolves inside the secondary battery, precipitates in the form of dendrites, breaks through the separator, and may cause an internal short circuit. Furthermore, in an electrode film containing a carbon material with a high content of metallic magnetic foreign matter, the electrolyte and active material are easily deteriorated due to high-temperature charging and discharging of the secondary battery, and the deterioration of high-temperature cycle characteristics becomes a problem.

[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 in a slurry composition that has been subjected to a dispersion treatment of carbon black particles, using a magnet with a magnet cover having a Vickers hardness of 10 GPa or more and less than 25 GPa as a particulate metal removal step. In particular, carbon nanotubes often contain residual metallic magnetic contaminants derived from the metal catalyst used in the synthesis, making them more susceptible to voltage drop problems. Therefore, Patent Document 2 considers a method of crushing carbon nanotubes containing metallic magnetic contaminants such as iron, cobalt, and nickel, and removing the metallic magnetic contaminants from the carbon nanotubes using an electromagnet. Patent Document 3 proposes a method for removing particulate metal contained in a binder composition. Patent Document 4 proposes a method for removing metallic magnetic foreign matter, which is a ferromagnetic impurity, from a medium liquid containing carbon nanotubes defibrated in a shear module in a carbon nanotube manufacturing method. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-191756 A [Patent Document 2] JP 2010-174418 A [Patent Document 3] Re-table No. 2010-032784 [Patent Document 4] Patent Publication No. 2021-065846 Summary of the Invention [Problem to be solved by the invention]

[0007] However, conventional methods such as those described in Patent Documents 1 to 4 have limitations in reducing the content of metallic magnetic foreign matter in the carbon material dispersion liquid, and the current situation is that the temporal stability of the carbon material dispersion liquid and the characteristics of a secondary battery when used as the dispersion liquid have not been sufficiently improved.

[0008] For example, when removing metallic magnetic foreign matter from the carbon material itself by a method such as magnetic separation or filtering, it is difficult to remove metallic magnetic foreign matter that has been incorporated inside the carbon material. On the other hand, when removing metallic magnetic foreign matter from a carbon material dispersion, it is possible to make the metallic magnetic foreign matter that has been incorporated inside the carbon material visible by a dispersion process, but in order to efficiently remove the metal by magnetic separation or filtering, it is necessary to prepare the carbon material dispersion to have a low viscosity. However, since not only the carbon material but also the metallic magnetic foreign matter is finely divided during dispersion, there is a risk that the efficiency of removing the metallic magnetic foreign matter will decrease. Therefore, there is room for improvement in order to maximize the efficiency of removing the metallic magnetic foreign matter in the carbon material dispersion.

[0009] Therefore, an object of the present invention is to provide a method for producing a carbon material dispersion having a low content of metallic magnetic foreign matter and excellent stability over time, and further to provide a secondary battery using the same having good cycle characteristics. In particular, the objective is to provide a carbon nanotube dispersion liquid in which the content of metallic magnetic foreign matter is reduced compared to conventional methods, even when using carbon nanotubes, which often contain residual metallic magnetic foreign matter derived from the metal catalyst used during synthesis. [Means for solving the problem]

[0010] According to the inventors' intensive study, the sliding angle is less than 70° and the cumulative particle diameter D 50 It 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 before. It has also been found that this improves the temporal stability of the dispersed carbon material dispersion liquid. As a result, the present invention can provide a carbon material dispersion liquid that contains a small amount of metallic magnetic foreign matter and has good stability over time, and can provide a secondary battery with good cycle characteristics.

[0011] That is, the present invention includes the following embodiments, but the embodiments of the present invention are not limited to the following. [1] The method comprises all of the following steps (1) to (3): A method for producing a carbon material dispersion containing a carbon material, a dispersant, and a solvent. [Process (1)] The sliding angle on the metal substrate is less than 70° and the cumulative particle diameter D 50 A step of obtaining a carbon material pre-dispersion liquid (X1) having a particle size of 20 μm or more [Process (2)] A process for 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). [Process (3)] A process of dispersing the carbon material pre-dispersion liquid (X2) to produce a carbon material dispersion liquid. [2] The 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 according to [1] or [2], further comprising a step of removing metallic magnetic foreign matter simultaneously with and / or after dispersion of the carbon material pre-dispersion (X2). [4] A method for producing an electrode slurry, comprising mixing an active material with the carbon material dispersion 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. Effect of the Invention

[0012] According to the embodiment of the present invention, it is possible to provide a carbon material dispersion liquid having a low content of metallic magnetic foreign matter and good stability over time. Furthermore, by using the same, it is possible to provide a secondary battery having good cycle characteristics. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0014] In addition, in this specification, a numerical range specified using "to" is intended to include the numerical values ​​before and after "to" as the lower and upper limit values ​​of the range. 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 "process of removing metallic magnetic foreign matter by magnetic separation processing" is also simply referred to as the "magnetic separation process." Unless otherwise noted, the various components appearing in this specification may be used independently as a single type or as a mixture of two or more types.

[0015] <Method for producing carbon material dispersion> One embodiment of the present invention is a method for producing a carbon material dispersion liquid containing a carbon material, a dispersant, and a solvent, the method comprising all of the following steps (1) to (3). [Process (1)] The sliding angle on the metal substrate is less than 70° and the cumulative particle diameter D 50 A step of obtaining a carbon material pre-dispersion liquid (X1) having a particle size of 20 μm or more [Process (2)] A process for 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). [Process (3)] A process of dispersing the carbon material pre-dispersion liquid (X2) to produce a carbon material dispersion liquid.

[0016] According to the method for producing a carbon material dispersion of the present invention, it is possible to obtain a carbon material dispersion having a lower content of metallic magnetic foreign matter than conventional carbon material dispersions and excellent stability over time. Furthermore, by using the carbon material dispersion, a secondary battery having excellent cycle characteristics can be obtained. In particular, even when using carbon nanotubes, which often contain residual metallic magnetic foreign matter derived from the metal catalyst used during synthesis, it is possible to produce a carbon nanotube dispersion liquid with a reduced content of metallic magnetic foreign matter compared to conventional methods.

[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, which includes steps (1) to (3), will be described. [Process (1)] In step (1), the sliding angle with respect to the metal substrate is less than 70° and the cumulative particle diameter D 50 This is a step of obtaining a carbon material pre-dispersion liquid (X1) having a particle size of 20 μm or more. The sliding angle on the metal substrate is less than 70° and the 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 the carbon material dispersion liquid can have a low content of metallic magnetic foreign matter and excellent stability over time.

[0019] The smaller the sliding angle, the better the droplet sliding property (water sliding property), and the sliding angle of the carbon material pre-dispersion liquid (X1) of the present invention is less than 70°. It is preferably 60° or less, more preferably 50° or less, and further preferably 40° or less. Also, it is preferably 1° or more. A sliding angle of less than 70° provides good wettability to the magnetic separation filter surface, and the carbon material pre-dispersion liquid (X1) is less likely to adhere to the magnetic separator during magnetic separation, improving the efficiency of removing magnetic metal foreign matter by magnetic separation. If the sliding angle is 70° or more, wettability to the magnetic separation filter surface is poor, and the carbon material pre-dispersion liquid (X1) adheres to the magnetic separator during magnetic separation. This results in a thickness equivalent to the amount of the adhered carbon material pre-dispersion liquid (X1), and the magnetic force decreases in proportion to the square of the distance, reducing the efficiency of removing magnetic metal foreign matter by magnetic separation. 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 in 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), such as SUS316L, SUS304, or 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, and more preferably 40 μm or more, and is preferably 300 μm or less, and more preferably 250 μm or less. Cumulative particle size D 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, so the magnetic separation efficiency may decrease as the metallic magnetic foreign matter becomes finer. On the other hand, 50If the diameter is larger than 300 μm, there is a risk that metallic magnetic foreign matter contained in the carbon material will not be sufficiently revealed and will not be removed by the magnetic separation step. Cumulative particle size D 50 is determined from a volume-based particle size distribution curve measured by a laser diffraction / scattering particle size distribution measurement method, and specifically, it can be measured, for example, by the method described in the [Examples] section.

[0022] The carbon material pre-dispersion liquid (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 required, using a known mixer, etc. For example, the solvent and the dispersant may be mixed and then the carbon material may be added, or the carbon material and the dispersant may be kneaded and then the solid content of the carbon material pre-dispersion liquid (X1) may be adjusted.

[0023] As an apparatus for producing the carbon material pre-dispersion liquid (X1), a mixer, kneader, disperser, or the like that is usually used for dispersing pigments, etc., can be used. For example, mixers such as a Disper, a Homomixer, a Planetary Mixer, MODEL 450DA, M - Silver, such as Technique's "Clearmix" and PRIMIX's "Filmix" Examples include "Abramix" manufactured by Son Co., Ltd.

[0024] [Process (2)] Step (2) is a magnetic separation step in which metallic magnetic foreign matter is removed 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). In this specification, the carbon material pre-dispersion liquid that has been subjected to the magnetic separation treatment is referred to as carbon material pre-dispersion liquid (X2). The step of removing the metallic magnetic foreign matter by magnetic separation treatment may be carried out either simultaneously with and / or after the production of the carbon material pre-dispersion liquid (X1). That is, the step (1) and the step (2) may be carried out simultaneously, or the magnetic separation treatment in the step (2) may be carried out using the carbon material pre-dispersion liquid (X1) obtained in the step (1). When the step (1) and the step (2) are carried out simultaneously, the carbon material pre-dispersion liquid (X2) and the carbon material pre-dispersion liquid (X1) correspond to the same thing.

[0025] Therefore, the method for producing the carbon material pre-dispersion liquid (X2) is as follows: (i) The sliding angle with respect to the metal substrate is less than 70° and the cumulative particle diameter D 50 a carbon material pre-dispersion liquid (X1) having a particle size of 20 μm or more, and then removing metallic magnetic foreign matter from the carbon material pre-dispersion liquid (X1) by magnetic separation treatment to obtain a carbon material pre-dispersion liquid (X2); (ii) removing metallic magnetic foreign matter from a carbon material pre-dispersion liquid containing a carbon material, a dispersant, and a solvent by magnetic separation processing, and dispersing the carbon material pre-dispersion liquid to a metal substrate such that the sliding angle with respect to the metal substrate is less than 70° and the cumulative particle diameter D 50 A method for obtaining a carbon material pre-dispersion liquid (X2) having a particle size of 20 μm or more, etc. In the present invention, the carbon material pre-dispersion liquid used in 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 liquid. Therefore, the obtained carbon material dispersion liquid has a low content of metallic magnetic foreign particles and has excellent stability over time.

[0026] In the present invention, the 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 foreign matter by magnetic separation is not particularly limited as long as it is a method for removing metallic magnetic foreign matter by magnetic force, and various magnetic separators and the like can be used. As a method for removing by magnetic force, a method using an electromagnet is preferable. When an electromagnet is used, an appropriate magnetic force can be set by controlling the current flowing through the electromagnet, and magnetic components can be efficiently removed, which is preferable. In addition, since the magnetic force can be made close to 0 by setting the current to 0, it is easier to remove the attracted magnetic components compared to a permanent magnet, and therefore maintenance is also excellent.

[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 gauss or more and 30,000 gauss or less, and more preferably 12,000 gauss or more and 30,000 gauss or less. By using an electromagnet in the above range, not only can metallic magnetic foreign matter contained in raw materials such as carbon materials be removed, but also metallic magnetic foreign matter generated during the manufacturing process can be removed, which is preferable.

[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 to 200 L / min, more preferably 50 L / min to 150 L / min.

[0031] The carbon material pre-dispersion liquid (X1) is preferably passed through the electromagnet three or more times. If the number of passes is small, there is a possibility that metallic magnetic foreign matter cannot be sufficiently removed. When passing through the electromagnet in a circulating manner, it is preferable to pass through the electromagnet a larger number of times in consideration of the uniformity in the tank used in the manufacturing 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. In the present invention, the sliding angle with respect to the metal substrate is less than 70° and the cumulative particle diameter D 50 By carrying out magnetic separation treatment on the carbon material pre-dispersion liquid (X1) having a particle size of 20 μm or more, the amount of contained metallic magnetic foreign matter can be significantly reduced compared to the conventional method. This makes it possible to reduce the content of metallic magnetic foreign matter in the carbon material dispersion liquid, and to obtain a secondary battery with excellent battery characteristics. <Condition (I)> 30 kg of the carbon material pre-dispersion liquid is passed through an electromagnet (magnetic flux density 16,000 gauss) five times and washed with an amide-based polar solvent. The resulting metallic magnetic foreign matter is deposited on a filter with a disk diameter of 47 mm and 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 specifically measured, for example, by the method described in the Examples.

[0034] [Process (3)] The step (3) is a step of dispersing the carbon material pre-dispersion liquid (X2) to produce a carbon material dispersion liquid. It is preferable to further include a step of removing metallic magnetic foreign matter simultaneously with and / or after dispersion of the carbon material pre-dispersion liquid (X2).

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

[0036] 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 paint conditioners (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 Coball mills; high-pressure homogenizers (Genus PY manufactured by Genus, Starburst 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.

[0037] Similarly to the production of the carbon material pre-dispersion liquid (X2), the production of the carbon material dispersion liquid also preferably includes a step of removing metallic magnetic foreign matter by the magnetic force of a magnet or the like. The method for removing the metallic magnetic foreign matter by magnetic separation treatment can be the same as the method described in step (2). Furthermore, the carbon material dispersion can remove more metallic magnetic foreign matter by incorporating a filtering process using a filter. 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 filter becomes clogged, making it difficult to incorporate.

[0038] The filter may be a surface filter such as a membrane filter or a depth filter, but a depth filter is more preferable. Since the metallic magnetic foreign matter is not spherical and has orientation, the metallic magnetic foreign matter in the carbon material dispersion can be efficiently removed by using a depth filter.

[0039] Unlike surface filters (filters that capture particulate matter in fluids mainly on the filter surface), depth filters capture particulate matter in fluids mainly inside the filter media, and are characterized by high particle retention and low clogging. By using a depth filter, metallic magnetic foreign matter in carbon material dispersions can be more selectively removed.

[0040] As the depth filter, for example, 3M(TM) PP nonwoven fabric depth cartridge NT-T series, Nippon Pall Corporation's Profile II, and Loki Corporation's Slope Pure 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 the 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, and the stability over time can be improved. On the other hand, if the content of metallic magnetic foreign matter is high, the dispersant in the carbon material dispersion may be adsorbed to the metallic magnetic foreign matter, causing the dispersion of the carbon material to collapse, and the viscosity may increase over time. In addition, if a secondary battery contains a large amount of metallic magnetic foreign matter, the metallic magnetic foreign matter may dissolve in the positive electrode during the charge / discharge cycle, and precipitate in the negative electrode, penetrating the separator and causing parts of the negative and positive electrodes to come into contact, which may lead to voltage failure. Li-ion inhibition may also occur. Furthermore, if there is a large amount of metallic magnetic foreign matter, it may come into contact with the positive electrode and cause a short circuit. Therefore, the amount of metallic magnetic foreign matter in the carbon material dispersion is preferably as small as possible, and the content in 30 kg of the 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 the carbon material dispersion is passed through an electromagnet (magnetic flux density 16,000 gauss) five times and washed with an amide-based polar solvent. The resulting metallic magnetic foreign matter is deposited on a filter with a disk diameter of 47 mm and 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 specifically measured, for example, by the method described in the Examples.

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

[0045] The carbon material pre-dispersion liquid (X1) has a sliding angle of less than 70° and a cumulative particle diameter D 50 The carbon material pre-dispersion liquid (X2) is obtained by removing metallic magnetic foreign matter by a magnetic separation process simultaneously with and / or after the production of the carbon material pre-dispersion liquid (X1). Specifically, a carbon material, a dispersant, and a solvent are mixed and further dispersed as necessary to obtain a particle 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 treatment 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 finely dividing the carbon material and the metallic magnetic foreign matter, and also to achieve the stability over time of the carbon material dispersion. In addition, the sliding angle and cumulative particle diameter D 50 Since the sliding angle of the carbon material pre-dispersion liquid (X2) is almost the same, the sliding angle of the carbon material pre-dispersion liquid (X2) is less than 70° and the cumulative particle diameter D 50 is 20 μm or more.

[0046] The carbon material dispersion of the embodiment of the present invention is obtained by dispersing the carbon material pre-dispersion (X2). Preferably, the carbon material dispersion is one from which metallic magnetic foreign matter has been removed simultaneously with and / or after dispersion of the carbon material pre-dispersion (X2).

[0047] Cumulative particle size 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 amount of the magnetic metal particles contained in the carbon material is within the above range, the magnetic metal particles contained in the carbon material can be easily removed by magnetic separation treatment, and a carbon material dispersion composition having a low content of the magnetic metal particles and good stability over time can be easily obtained.

[0048] The carbon material dispersion means 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 does not substantially contain an active material. This is a concept excluding a state in which an active material is intentionally added to the carbon material dispersion, and the active material may be 1 mass % or less, 0.5 mass % or less, or 0.1 mass % or less, or may be 0 mass %, based on the total mass of the carbon material dispersion. The active material will be described later.

[0049] (Carbon materials) The carbon material in the present invention is not particularly limited. Examples of carbon materials having electrical conductivity 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 inside the electrode, and from the viewpoint of being required to be less likely to be cut 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 electrical conductivity, ease of availability, and cost, it is preferable to use carbon black and / or carbon nanotubes. In addition, 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 having different physical properties may be used in combination. Examples of carbon materials having different physical properties of the same type include two types of carbon nanotubes having different average outer diameters or average fiber diameters, or two types of carbon black having different specific surface areas.

[0050] Carbon materials may contain metallic magnetic foreign matter during the manufacturing process. It is difficult to completely remove these metallic magnetic foreign matters from carbon materials. Carbon nanotubes, in particular, may contain metallic magnetic foreign matters derived from raw materials such as metal catalysts. The metallic magnetic foreign matters contained in carbon nanotubes can be made visible by dispersing them, but When the nanotubes are broken down into smaller pieces, the metallic magnetic foreign matter is also broken down into smaller pieces, making it difficult to extract the metallic magnetic foreign matter from the dispersion liquid. However, in the method for producing the carbon material dispersion composition of the present invention, the sliding angle with respect to the metal substrate is less than 70° and the cumulative particle diameter D 50 By carrying out the magnetic separation process using a carbon material pre-dispersion liquid having a particle size of 20 μm or more, metallic magnetic foreign matter derived from the carbon material can be efficiently removed. Therefore, according to the method for producing a carbon material dispersion of the present invention, even when using carbon nanotubes which often contain residual metallic magnetic foreign matter derived from the metal catalyst used during synthesis, the content of metallic magnetic foreign matter can be reduced more than in the past.

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

[0052] [Carbon black] Carbon black is a fine particle whose main component is carbon, and is produced by controlling various properties by incomplete combustion of oil or gas. 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 are further aggregated. The secondary and tertiary structures are collectively called structure. When primary particles are observed under an electron microscope, they appear spherical, but the primary particles are not independent in terms of chemical structure, but are linked to adjacent primary particles in the aggregate by chemical bonds to form a secondary structure. On the other hand, the secondary structures are each independent in terms of chemical structure, and are aggregated by intermolecular forces to form a tertiary structure. Therefore, the conductivity inside the secondary structure is higher than the conductivity between the secondary structures, including the contact resistance, and it can be said that deaggregating the tertiary structure while maintaining the structure of the secondary structure as much as possible is effective in obtaining an electrode with excellent conductivity. In this specification, the secondary structure may be simply called "structure".

[0053] As the carbon black used in the present invention, various types of commercially available carbon black can be used, such as acetylene black, furnace black, hollow carbon black, channel black, thermal black, ketjen black, etc. In addition, carbon black that has been subjected to a commonly used oxidation treatment and carbon black that has been subjected to a graphitization treatment can also be used.

[0054] Oxidation treatment of carbon black is a process 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 carbon black surface by treating the carbon black at high temperatures in air or by secondary treatment with nitric acid, nitrogen dioxide, ozone, etc., and is commonly carried out to improve the dispersibility of carbon black.

[0055] Examples of commercially available carbon black include SuperP-Li (manufactured by TIMCAL), 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 earthy graphite, but are not limited to these, and two or more types may be used in combination.

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

[0057] The BET specific surface area of ​​carbon black is 10m 2 / g or more 1500m 2 / g or less, and 2 / g or more 1000m 2 / g or less is more preferable, and 2 / g or more 850m 2 / g or less is 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 increasing the amount of active material and binder resin. Furthermore, when preparing an electrode slurry, the active material and carbon black are easily 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. The 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 the 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 to 25 nm, more preferably 3 nm to 20 nm, and even more preferably 4 nm to 15 nm. When the average outer diameter is within the above range, a good conductive network is easily formed in the electrode, and the active material inside the secondary battery is used uniformly during charging and discharging, so that deterioration of the active material is suppressed and the cycle characteristics of the secondary battery are further improved.

[0060] The G / D ratio (peak ratio of the G-band to the D-band) of carbon nanotubes is 1560 cm -1 ~1600cm -1The maximum peak intensity in the range of G, 1310 cm -1 ~1350cm -1 When the maximum peak intensity within this range is D, the G / D ratio is preferably 0.5 to 10, and more preferably 0.7 to 4.5. 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 small, and good electrical conductivity is easily obtained. It is also believed that the amount of functional groups on the multi-walled carbon nanotube surface is appropriate, and the affinity with the solvent is good, resulting in better dispersibility.

[0061] The BET specific surface area of ​​carbon nanotubes is 100m 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 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 increasing the amount of active material and binder resin. Furthermore, when preparing the composite slurry, the active material and the carbon nanotubes are easily 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, and the electrolyte decomposition reaction at the interface between the electrolyte and the active material can be suppressed, thereby 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. As a method for purifying carbon nanotubes, various conventionally known methods can be used. For example, acid treatment, graphitization treatment, and chlorination treatment can be mentioned.

[0063] The acid used for the acid treatment of carbon nanotubes may be any acid capable of dissolving the metal and metal oxide contained in the carbon nanotubes, and for example, inorganic acids and carboxylic acids are preferred, and 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 the carbon nanotubes is not particularly limited, but can be carried out, for example, by introducing chlorine gas in 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 modified on the surface or ends 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 and sulfo groups, since this allows the resulting carbon nanotube dispersion to have both good stability and flowability.

[0067] (Dispersant) The dispersant of the present embodiment is not particularly limited as long as it can disperse and stabilize 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 characteristics required for dispersing the carbon material, a suitable type of dispersant can be used in a suitable amount.

[0068] When selecting an anionic surfactant, 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, naphthalenesulfonic acid formalin condensates, polyoxyethylene alkyl phosphate sulfonates, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters.Furthermore, specific examples include, but are not limited to, sodium dodecylbenzenesulfonate, sodium lauric acid sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate, and sodium salt of β-naphthalenesulfonic acid formalin condensates.

[0069] Cationic surfactants include alkylamine salts and quaternary ammonium salts, specifically stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl beef tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, and lauryl pyridinium disulfide. Examples of amphoteric surfactants include, but are not limited to, amino carboxylates, cetylpyridinium bromide, 4-alkylmercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride.

[0070] Examples of 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.Specific examples 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 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 use a suitable amount for each surfactant component. As a combination, a combination of an anionic surfactant and a nonionic surfactant is preferable. The anionic surfactant is preferably a polycarboxylate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

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

[0073] From the viewpoint of oxidation resistance, the dispersant is preferably a hydrogenated nitrile butadiene rubber or a 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 the above range, the dispersed state of the carbon material can be stably maintained, and the stability over time can be 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. In addition to monoamines, amine compounds such as diamines, triamines, and tetramines having multiple amino groups in the molecule can be used. Specifically, for example, 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, and dimethylaminoethanol can be used. Examples of inorganic bases include, but are not limited to, alkanolamines such as 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 using an amine compound or an inorganic base, the content 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 and further improves the dispersibility. When carbon nanotubes are used as the carbon material, the dispersibility is significantly improved.

[0077] (solvent) The solvent in this 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, weaken the magnetic force of the magnet, and generate metallic magnetic foreign matter, the use of an amide-based organic solvent can reduce the amount of metallic magnetic foreign matter contained in the carbon material dispersion.

[0079] Examples of the amide-based 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 include 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 of the present embodiment, it is preferable that the organic solvent does not substantially contain 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 the electrode slurry using the same. By setting the content of water within the above range, the dispersion 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 ingredients) The carbon material pre-dispersion liquid and the carbon material dispersion liquid may contain, as necessary, a wetting agent, a pH adjuster, a wetting penetrant, a leveling agent, or other additives, a binder resin described below, other conductive materials, and the like, as appropriate within a range that does not impair the object of the present invention. These additives may be added at any timing, such as before preparing the mixed liquid, during or after mixing, or when preparing the carbon material pre-dispersion liquid or the carbon material dispersion liquid.

[0082] <Production of electrode slurry> The electrode slurry can be produced by mixing an active material with the carbon material dispersion liquid of the present invention. The active material may be either a positive electrode active material or a negative electrode active material, and may further contain a binder resin, other conductive materials, or a solvent, or may further contain any other optional components. In this specification, the positive electrode active material and the negative electrode active material may be simply referred to as "active material". An active material is a material that is the basis of a battery reaction. Active materials are divided into positive electrode active materials and negative electrode active materials based on electromotive force. An electrode slurry may be called a "composite material slurry" or an "electrode composite material slurry", and an electrode slurry containing a positive electrode active material or a negative electrode active material may be called a "positive electrode slurry" or a "negative electrode slurry", respectively. The electrode slurry is preferably in a slurry form to improve uniformity and processability.

[0083] (Cathode 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 capable of reversibly doping or intercalating lithium ions can be used. For example, lithium manganese composite oxides (e.g., Li x Mn2O4 or LixMnO2), lithium nickel composite oxides (e.g. Li x NiO2), lithium cobalt complex oxide (Li x CoO2), lithium nickel cobalt complex oxide (e.g. Li x Ni 1-y Co y O2), lithium manganese cobalt complex oxide (e.g. Li x Mn y Co 1-y O2), lithium nickel manganese cobalt composite oxide (e.g. Li x Ni y Co z Mn 1-y-z O2), spinel-type lithium manganese nickel composite oxide (e.g. Li x Mn 2-y Ni y O4), lithium phosphate powder with an olivine structure (e.g. Li x FePO4, Li x Fe 1-y Mny PO4, Li x such as CoPO4), manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxides (e.g., V2O5, V6O 13 ), titanium oxide and other transition metal oxide powders, iron sulfate (Fe2(SO4)3), TiS2, and FeS and other transition metal sulfide powders, etc. However, x, y, and z are numbers, where 0 < x < 1, 0 < y < 1, 0 < z < 1, and 0 < y + z < 1. These cathode active materials can also be used alone or in combination of two or more. Among these active materials, in particular, active materials containing Ni and / or Mn (especially when the total amount of Ni and / or Mn in the transition metal is 50 mol% or more) tend to become highly basic due to the elution of components derived from the raw materials or metal ions, and the gelation of the binder and the deterioration of the dispersion state are likely to occur due to this effect, so the problems of the present invention may become prominent. Therefore, the present invention is particularly effective in the case of a battery containing an active material containing Ni and / or Mn.

[0084] (Anode active material) The anode active material is not particularly limited. For example, it can be metal Li that can reversibly dope or intercalate lithium ions, or its alloy, tin alloy, silicon alloy anode, Li X TiO2, Li X Fe2O3, Li X Fe3O4, Li X Metal oxide systems such as WO2, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials can be used. However, x is a number, where 0 < x < 1. These anode active materials can also be used alone or in combination of two or more. In particular, when using a silicon alloy anode, although the theoretical capacity is large, the volume expansion is extremely large, so it is preferably used in combination with artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, and resin-fired carbon materials, etc.

[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, relative to 100 parts by mass of the active material. Also, it is 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 it exceeds the above range, the amount of the active material filled in the electrode may decrease, resulting in a decrease in the capacity of the battery. Also, if it 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 is 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 is no particular restriction as long as it is normally used as a binder resin for paints and the like, and it can be appropriately selected according to the purpose. In addition, the binder resin used in the electrode slurry is a resin that can bond between materials such as active materials and conductive materials. Examples of the binder resin 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 constituent units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluororesins; cellulose resins; elastomers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene, etc. In addition, modified bodies, mixtures, and copolymers of these resins may be used. 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 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 relative to 100 parts by mass of the active material, and is 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.

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

[0090] The electrode slurry can be prepared by various conventional methods. For example, a method of preparing the electrode slurry by adding an active material to a carbon material dispersion liquid; a method of preparing the electrode slurry by adding an active material to a carbon material dispersion liquid and then adding a binder resin; a method of preparing the electrode slurry by adding a binder resin to a carbon material dispersion liquid and then adding an active material, etc. The dispersion device used for dispersion is not particularly limited, and the electrode slurry can be obtained by using the dispersion means mentioned in the description of the carbon material dispersion liquid. Therefore, as a method of preparing the electrode slurry, a process of adding and dispersing an electrode active material without adding a binder resin to the carbon material dispersion liquid may be performed.

[0091] <Electrode manufacturing> 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 the material of the current collector include conductive metals or alloys such as aluminum, copper, nickel, titanium, and stainless steel. In addition, the shape of the current collector is generally a flat foil, but a current collector with a roughened surface and a perforated foil are also available. A current collector having a thickness of about 0.5 to 30 μm can also be used.

[0094] The method for applying the carbon material dispersion or electrode slurry onto 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.The drying method includes, but is not limited to, drying by leaving it to dry, or drying using a blower dryer, a hot air dryer, an infrared heater, a far infrared heater, or the like.

[0095] After coating, rolling treatment may be performed using a lithographic press, a calendar 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 of an electrode in order to improve the adhesion between the electrode film and a current collector or to improve the electrical conductivity of the electrode film.

[0097] <Secondary battery manufacturing> The secondary battery includes a step of forming an electrode film using the carbon material dispersion liquid 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 the present invention.

[0098] As the electrolyte, various conventionally known electrolytes capable of moving ions can be used. For example, those containing lithium salts such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, or LiBPh4 (wherein Ph is a phenyl group) can be used, but are not limited thereto. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0099] Examples of non-aqueous solvents include, but are not limited to, 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 is generally a battery having a positive electrode, a negative electrode, and a separator that is provided as necessary. The battery may be of any type, such as a paper type, a cylindrical type, a button type, or a laminated type. The shape may vary depending on the purpose. EXAMPLES

[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 present invention. In addition, 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 nanotube (JEIO, JENOTUBE10B) Carbon material 2 Carbon nanotubes (JEIO, JENOTUBE6A) Carbon material 7 Carbon nanotube (OCSiAl, TUBALL 01RW03) Carbon material 9 Ketjen black (Lion Specialty Chemical, Ketjen black EC300J) <Dispersant> Dispersant 1 Hydrogenated nitrile butadiene rubber (ARLANXEO, Therban(R)3406) Dispersant 2 Hydrogenated nitrile butadiene rubber (ARLANXEO, Therban(R)3404) Dispersant 3: Liquid hydrogenated nitrile butadiene rubber (Zannan Scitech, ZN35050L3) Dispersant 4 Polyacrylonitrile (Sigma Aldrich, polyacrylonitrile Mw150000) Dispersant 5 Polyvinyl butyral (Sekisui Chemical Co., Ltd., BL-10) Dispersant 6 Polyvinylidene fluoride (Solvey, Solef#5130) Dispersant 7: Polyvinyl alcohol (Kuraray Co., Ltd., Kuraray Poval 3-80) <Additives> Additive 1 NaOH; sodium hydroxide (Tosoh Corporation, granular caustic soda "Tosoh Pearl") Additive 2 2-aminoethanol (Fujifilm Wako Pure Chemical Industries, Wako Grade 1)

[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 became 0.1% or less, it was heated to 1600°C over 30 hours. While maintaining the temperature in the furnace 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 to cool the material while maintaining positive pressure, and carbon material 3 was obtained.

[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, it was heated to 1600°C over 30 hours. While maintaining the temperature in the furnace 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 to cool the material while maintaining positive pressure, and carbon material 4 was obtained.

[0106] <Preparation of carbon material 5> Carbon material 1 was fed into a Dynamic Mill (manufactured by Nippon Coke & Co., Ltd.) with zirconia beads having a diameter of 8 mm as a grinding medium under operating conditions of 10.0 kg / h supply and a peripheral speed of 5.0 m / s, and carbon material 5 was obtained.

[0107] <Preparation of carbon material 6> Carbon material 4 was fed into a Dynamic Mill (manufactured by Nippon Coke & Co., Ltd.) using zirconia beads with a diameter of 8 mm as a grinding medium under operating conditions of 10.0 kg / h supply and a peripheral speed of 5.0 m / s, and carbon material 6 was obtained.

[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 became 0.1% or less, it was heated to 1600°C over 30 hours. While maintaining the temperature in the furnace 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 to cool the material while maintaining positive pressure, and carbon material 8 was obtained.

[0109] <Physical property measurement and evaluation method> The physical properties of the carbon material, the carbon material pre-dispersion, the carbon material dispersion, the electrodes, and the secondary batteries used in the examples and comparative examples described later were measured and evaluated as follows.

[0110] <Average outer diameter of carbon nanotubes> 0.2 g of carbon nanotubes were weighed into a 450 mL SM sample bottle (manufactured by Sanshosha Co., Ltd.) using an electronic balance (manufactured by Sartorius, MSA225S100DI), 200 mL of toluene was added, and the mixture was homogenized using an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, BR A carbon nanotube dispersion was prepared by dispersing the carbon nanotube under ice cooling at an amplitude of 30% for 5 minutes using a microcentrifuge (manufactured by ANSON Co., Ltd.). The carbon nanotube dispersion was then appropriately diluted, several μL of the carbon nanotube dispersion was dropped onto a collodion film, and the film was dried at room temperature. The film was 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 in which 10 or more carbon nanotubes were included 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.

[0111] <Primary particle size 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 an electron microscope (either scanning or transmission type can be used, preferably a transmission electron microscope) photograph, and the arithmetic average value of the particle diameters obtained was used.

[0112] <BET specific surface area of ​​carbon material> The carbon material was weighed out in an amount of 0.03 g using an electronic balance (MSA225S100DI, manufactured by Sartorius), and then dried for 15 minutes at 110° C. while degassing. The BET specific surface area of ​​the carbon material was then measured using a fully automatic specific surface area measuring device (HM-model1208, manufactured by MOUNTECH).

[0113] <Carbon purity of carbon materials> The carbon material was decomposed with acid using a microwave sample pretreatment device (Milestone General, ETHOS1) to extract the metals contained in the carbon material. After that, analysis was performed using a multi-type ICP emission spectrometer (Agilent, 720-ES) 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) x 100

[0114] [Table 1-1]

[0115] [Table 1-2]

[0116] <Sliding angle of carbon material pre-dispersion liquid> A sample plate 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 liquid, which was the test liquid, was dropped onto the horizontally placed sample plate to form a water droplet.Then, the sample plate was gradually tilted, and the angle of the sample plate when the water droplet started to roll was measured.The smaller the angle, the better the water droplet sliding property (water sliding).

[0117] <Cumulative particle size D of carbon material pre-dispersion and carbon material dispersion 50 Measurement> Cumulative particle size D due to particle size distribution 50 The measurement was performed using a laser diffraction / scattering type particle size distribution analyzer (HORIBA, Ltd. Partical LA-960V2). The laser light wavelength of this measurement device is 650 nm, and the detectors are one ring-shaped 64-segment silicon photodiode, five 4-channel array detectors, and three silicon photodetectors. The measurement section uses a flow-type cell (sample cell) made of synthetic quartz. First, NMP, which is the same solvent as the dispersion liquid, was put into a sample bath containing a sample cell, and circulation / ultrasonic cleaning was performed. The operation modes were circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 7, and stirring mode: continuous. Next, in order to remove air, ultrasonic operation was performed at ultrasonic intensity: 7 and ultrasonic time: 5 seconds, and then a blank (background) measurement was performed. The particle size standard was set to 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 liquid was dropped so that the laser light transmittance during measurement was 60% ± 1%, and sample adjustment was performed. The operation modes during measurement were circulation speed: 3, stirring speed: 7, and stirring mode: continuous, and the measurement was performed.

[0118] <Measurement of the amount of metallic magnetic foreign matter in carbon material pre-dispersion liquid> 30 kg of the carbon material pre-dispersion liquid was passed through an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) five times via a diaphragm pump. Then, N-methyl-2-pyrrolidone (NMP) was passed through an electromagnet (manufactured by Taiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) to measure the temperature of the diaphragm pump and the electromagnet. The carbon material pre-dispersion liquid was extrusion washed until it was substantially free of solids, and then the power source of 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. Then, the metal magnetic foreign matter was transferred to a 2L poly container of 1kg of NMP, and ultrasonic treatment was performed for 5 minutes using an ultrasonic treatment machine (manufactured by Aiwa Medical Industry, ultrasonic cleaner) at an output of 300W and a frequency of 28kHz. A bar magnet with a magnetic flux density of 12000 Gauss was then fixed to the outside of the poly container to collect the metal magnetic foreign matter, and NMP was poured. The collected metal magnetic foreign matter was then collected using a filter bell and a mesh (weight: W1, diameter: 47mm, mesh size: 5μm) whose weight had been measured in advance was used to collect the entire amount using ethanol. The mesh on which the metal magnetic foreign matter had accumulated was then removed, and the mesh was dried at 60°C for 20 minutes using a hot air oven. This process was performed for all 10kg of NMP containing the collected metal magnetic foreign matter, and the weight (W2) of the dried mesh was measured, and the weight (W1) measured in advance was subtracted to obtain the amount of metal magnetic foreign matter (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 the measurement of the amount of metallic magnetic foreign matter in the carbon material pre-dispersion liquid, except that the carbon material pre-dispersion liquid was changed to the carbon material dispersion liquid. The smaller the amount of metallic magnetic foreign matter (W0), the more desirable it is. The metallic magnetic foreign matter amount (W0) was determined as follows: less than 10 mg: ◎ (excellent), 10 mg or more but less than 40 mg: ◯ (good), 40 mg or more but less than 100 mg: △ (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 rotating the Brookfield viscometer rotor at a speed of 100 rpm. The types of rotors used in the measurements were No. 1 when the viscosity value was less than 100 mPa·s, No. 2 when it was 100 or more and less than 500 mPa·s, No. 3 when it was 500 or more and less than 2,000 mPa·s, and No. 4 when it 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 stability over time of the carbon material dispersion was evaluated using the following formula 1. (Formula 1) Stability over time = (initial viscosity) / (viscosity after storage in a thermostatic chamber at 40°C for 3 days) x 100 (%) The stability over time was evaluated as follows: ◎: 60% or more (excellent), ○: 50% or more but less than 60% (good), △: 40% or more but less than 50% (passable), ×: less than 40% (unacceptable).

[0121] <Evaluation of cycle characteristics of lithium-ion secondary batteries> After the laminated cell secondary battery manufactured in the examples and comparative examples was left to stand for 24 hours, it was charged and discharged at a charge and discharge rate of 4.25V and 0.1C, and the initial capacity was measured. The laminated cell lithium ion secondary battery was placed in a thermostatic chamber at 60°C, and charge and discharge measurements were performed using a charge and discharge device (Hokuto Denko Corporation, SM-8). After constant current and constant voltage charging (cutoff current 1.25mA (0.025C)) was performed with a charge current of 50mA (1C) and a charge end voltage of 4.2V, constant current discharging was performed with a discharge current of 50mA (1C) and a discharge end voltage of 2.5V. This operation was repeated 100 times. 1C was the current value at which the theoretical capacity of the positive electrode was discharged in 1 hour. The cycle characteristics can be expressed by the ratio of the initial capacity to the 100th 1C discharge capacity at 60°C, as shown in the following formula 2. (Formula 2) Cycle characteristics = (100th 1C discharge capacity) / (initial capacity) x 100(%) The cycle characteristics were evaluated as follows: 80% or more was rated as excellent, 70% or more but less than 80% was rated as good, 60% or more but less than 70% was rated as fair, and less than 60% was rated as poor.

[0122] (Example A-1) [Process (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. Then, 85.75 parts of N-methyl-2-pyrrolidone (NMP) and 11.25 parts of an 8% solution of dispersant 1 (0.90 parts of dispersant 1 added) were added to a stainless steel container and stirred with a disperser until uniform. Then, 3 parts of carbon material 1 were weighed out and added while stirring with a disperser, and a fine emulsion screen was attached to a high shear mixer (L5M-A, Silverson), and batch dispersion was performed at a speed of 9000 rpm until the entire mixture became uniform and the dispersion particle size was 200 μm or less using a grind gauge, obtaining a pre-dispersion (X1-1). The sliding angle of the pre-dispersion liquid (X1-1) is 67°, and the cumulative particle diameter D 50 was 43 μm.

[0123] [Process (2)] The obtained pre-dispersion liquid (X1-1) was passed through an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., magnetic flux density 16000 Gauss) three times to obtain a pre-dispersion liquid (X2-1).

[0124] [Process (3)] The pre-dispersion liquid (X2-1) was sent to a stainless steel container, and a circulation type dispersion treatment was carried out for 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. Next, 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) via piping, and a 20-pass dispersion process was carried out. The dispersion process was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Thereafter, the liquid to be dispersed was supplied to an electromagnet (EMF-100S, manufactured by Taiho Magnetic Co., Ltd., magnetic flux density 16000 Gauss) and a three-pass treatment was carried out, whereby a carbon material dispersion liquid 1 was obtained.

[0125] (Examples A-2 to A-20) Carbon material pre-dispersions (X1-2 to 20) 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 Table 2, and then carbon material pre-dispersions (X2-2 to 20) and carbon material dispersions 2 to 20 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 the mixture was stirred at 80° C. using a disperser to completely dissolve Dispersant 1, thereby preparing an 8% solution of Dispersant 1. Then, 87.23 parts of N-methyl-2-pyrrolidone (NMP), 11.25 parts of an 8% solution of dispersant 1 (0.9 parts of dispersant 1 added), and 0.02 parts of NaOH were added to a stainless steel container and stirred with a disperser until homogenous. Then, 1.5 parts of carbon material 4 were added while stirring with a disperser to obtain a carbon pre-dispersion. Next, 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 performed 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 performed simultaneously with the production of a carbon material pre-dispersion liquid (X1-20), and a carbon material pre-dispersion liquid (X2-21) was obtained. That is, the carbon material pre-dispersion liquid (X2-21) is The sliding angle is 53° and the cumulative particle diameter D 50 was 50 μm.

[0127] [Process 3] Next, the carbon material pre-dispersion liquid (X2-21) was sent to the stainless steel container, and a circulation type dispersion treatment was performed for 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. Next, 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) via piping, and a 20-pass dispersion process was carried out. The dispersion process was carried out using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Thereafter, the liquid to be dispersed was supplied to an electromagnet (manufactured by Taiho Magnetics, EMF-100S, magnetic flux density 16000 Gauss) and a three-pass treatment was carried out, whereby a carbon material dispersion liquid 27 was obtained.

[0128] (Example A-22) A carbon pre-dispersion liquid (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 then a carbon material pre-dispersion liquid (X2-22) and a carbon material dispersion liquid 28 were produced. That is, the carbon material pre-dispersion liquid (X2-22) corresponds to the carbon material pre-dispersion liquid (X1-21), the sliding angle is 55°, and the cumulative particle diameter D 50 was 45 μm.

[0129] (Example A-23) [Process (1)], [Process (2)] A carbon material pre-dispersion liquid (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 as shown in Table 2.

[0130] [Process (3)] The carbon material pre-dispersion liquid (X2-11) was pumped into 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) via piping, and a 20-pass dispersion process was performed. The dispersion process was performed using a single nozzle chamber with a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Thereafter, the liquid to be dispersed was supplied to an electromagnet (manufactured by Taiho Magnetics, EMF-100S, magnetic flux density 16000 Gauss), and a three-pass treatment was carried out to obtain a carbon material dispersion liquid 23.

[0131] (Examples A-24 to A-26) A carbon material pre-dispersion liquid (X1) was 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 Table 2, and then a carbon material pre-dispersion liquid (X2) and carbon material dispersion liquids 24 to 26 were produced. In the carbon material dispersions 24 to 26, magnetic separation was not carried out simultaneously with or after dispersion of the carbon material dispersions.

[0132] (Example A-27) [Process (1)], [Process (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] [Process 3] Next, the carbon material pre-dispersion liquid (X2-11) was sent to the stainless steel container, and a circulation type dispersion treatment was performed for 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. Next, the carbon material pre-dispersion liquid was sent to the stainless steel container, and the mixture was passed through a piping to a high-pressure homogenizer. The liquid to be dispersed was supplied to a homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine), and 20-pass dispersion treatment was carried out with two bar magnets with a magnetic flux density of 17,000 gauss installed at the outlet piping of the homogenizer. 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 the carbon material pre-dispersion (X2-12).

[0135] (Comparative example A-1) [Process (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. The sliding angle of the pre-dispersion liquid (X1-1) is 67°, and the cumulative particle diameter D 50 was 43 μm.

[0136] [Process (3)] Next, the carbon material pre-dispersion liquid (X1-1) was sent to a stainless steel container, and a circulation type dispersion treatment was performed for 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. Next, 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 1 was not subjected to the magnetic separation treatment in the step (2).

[0137] (Comparative example A-2) [Process (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 the mixture was stirred with a disperser until homogenous. Then, 0.4 parts of carbon material 7 was 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 entire mixture became uniform and the dispersion particle size was 200 μm or less as measured by a grind gauge. The contents of the stainless steel container were then pumped and the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a three-pass dispersion process was performed to obtain a pre-dispersion liquid (X'1-1). The sliding angle of the pre-dispersion liquid (X'1-1) is 80°, and the cumulative particle diameter D 50 was 11 μm.

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

[0139] Next, the above 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) via piping, and a 20-pass dispersion process was performed to obtain a comparative carbon material dispersion liquid 2. The dispersion process 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) [Process (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] [Process (3)] Next, the carbon material pre-dispersion liquid (X1-1) was sent to the stainless steel container, and the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Lab HJP-17007, manufactured by Sugino Machine) via piping, and a 10-pass dispersion process was performed. The dispersion process 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 16000 Gauss) and a three-pass treatment was carried out to obtain a comparative carbon material dispersion liquid 3. The comparative carbon material dispersion 3 was not subjected to the magnetic separation treatment in the step (2).

[0142] [Table 2-1]

[0143] [Table 2-2]

[0144] [Table 2-3]

[0145] From the results in Table 2, the sliding angle is less than 70° and the cumulative particle diameter D 50 It was confirmed that the magnetic separation efficiency was high and the amount of metallic magnetic foreign matter was reduced by producing a carbon material pre-dispersion liquid having a particle size of 20 μm or more and removing the metallic magnetic foreign matter 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 performing magnetic separation, the sliding angle is less than 70° and the cumulative particle diameter D 50 When the pre-dispersion liquid was not 20 μm or more, the reduction of metallic magnetic foreign matter was insufficient. This is presumably because the carbon material pre-dispersion liquid (X1) had poor wettability with the magnetic separator, so the carbon material pre-dispersion liquid (X1) adhered to the magnetic separator, weakening the magnetic force.

[0146] (Example B-1) <Preparation of electrode slurry 1> Capacity 150cm 3 Into a plastic container, 18.8 parts by mass of an NMP solution in which 8% by mass of PVDF (polyvinylidene fluoride, Solvey, Solef#5130) was dissolved, and 5.8 parts by mass of NMP were weighed out. Then, 13.3 parts by mass of the carbon material dispersion 1 whose stability was evaluated was added, and the mixture was stirred at 2000 rpm for 30 seconds using a planetary centrifugal mixer (Awatori Rentaro, ARE-310). After that, a positive electrode active material (BASF Toda Battery Materials, 98.1 parts by mass of HED (registered trademark) NCM-111 1100, manufactured by Arzu LLC, was added and stirred at 2000 rpm for 2.5 minutes using a planetary centrifugal mixer (Awatori Rentaro, ARE-310) to obtain electrode slurry 1.

[0147] <Preparation of electrode 1> Electrode slurry 1 was applied to the electrode using an applicator so that the amount of electrode coating per unit area was 20 mg / cm 2 After coating on an aluminum foil so that the coating was as follows: the coating was dried in an electric oven at 120°C ± 5°C for 25 minutes to obtain an electrode 1. The electrode 1 was then rolled using a roll press (3t hydraulic roll press, manufactured by Sun Metals) to obtain a positive electrode (positive 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.

[0148] <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 plastic container with a capacity of 150 mL, and then the mixture was stirred for 30 seconds at 2,000 rpm using a rotation and revolution mixer (Thinky Corporation's Awatori Rentaro, ARE-310). Furthermore, artificial graphite CGB-20 (manufactured by Nippon Graphite Industries Co., Ltd.) was added as a negative electrode active material, and the mixture was stirred for 150 seconds at 2,000 rpm using a rotation and revolution mixer. SBR (styrene butadiene rubber, TRD2001 (manufactured by JSR Corporation, solid content 48%) was then added, and the mixture was stirred for 30 seconds at 2,000 rpm using a rotation and revolution 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.

[0149] <Preparation of standard negative electrode> The negative electrode composite slurry was applied to a 20 μm-thick copper foil current collector using an applicator, and then dried in an electric oven at 80°C ± 5°C for 25 minutes to obtain a coating weight per unit area of ​​the electrode of 10 mg / cm. 2 Further, a rolling process was performed using a roll press (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 Thus, a negative electrode having the above structure was fabricated.

[0150] <Preparation of secondary battery 1> The 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 inserted into an aluminum laminate bag, and dried in an electric oven at 60°C for 1 hour. After that, in a glove box filled with argon gas, 2 mL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a ratio of 1:1:1 (volume ratio) and adding 2 parts by mass of VC (vinylene carbonate) as an additive to 100 parts by mass of the mixed solvent, and then dissolving LiPF6 at a concentration of 1M) was injected, and the aluminum laminate was sealed to prepare secondary battery 1.

[0151] (Examples B-2 to B-28), (Comparative Examples B-1 to B-3) Secondary batteries 2 to 28 and comparative secondary batteries 1 to 3 were produced in the same manner as in the production of the laminated lithium ion secondary battery (secondary battery 1), except that the carbon material dispersion liquid shown in Table 3 was changed.

[0152] [Table 3]

[0153] As shown in Table 3, when the sliding angle is less than 70° and the cumulative particle diameter D 50 A carbon material pre-dispersion liquid (X1) having a particle size 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 liquid had good cycle characteristics.

[0154] On the other hand, in Comparative Example A-1, which does not include a process for removing metallic magnetic foreign matter, the sliding angle is less than 70° and the cumulative particle diameter is 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 that did not satisfy the particle size requirement of 20 μm or more, and the carbon material dispersion liquid of Comparative Example A-3, in which the magnetic separation treatment was not performed on the carbon material pre-dispersion liquid and only the carbon material dispersion liquid was subjected to the magnetic separation treatment, both had poor cycle characteristics.

[0155] As a result, a vehicle having the secondary battery of the present invention has high charge / discharge performance and is highly resistant to high-temperature cycles. It is clear that due to its excellent characteristics, a vehicle with high safety and improved fuel efficiency can be obtained.

[0156] Although the present invention has been described with reference to the above-mentioned embodiment, the present invention is not limited to the above. 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. The method comprises all of the following steps (1) to (3): A method for producing a carbon material dispersion containing a carbon material, a dispersant, and a solvent. [Step (1)] The sliding angle with respect to the metal substrate is less than 70° and the cumulative particle diameter D ５０ A step of obtaining a carbon material pre-dispersion liquid (X1) having a particle size of 20 μm or more. [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. 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 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 (X2).

4. A method for producing an electrode slurry, comprising 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 producing 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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