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] Embodiments of the present invention relate to a carbon material dispersion, an electrode slurry, an electrode, and a method for manufacturing a secondary battery.

Background Art

[0002] Lithium-ion secondary batteries are widely used as batteries for electric vehicles, portable devices, and the like. With the improvement of performance of electric vehicles, portable devices, and the like, the requirements for lithium-ion secondary batteries, such as high capacity, high output, and small size and light weight, have been increasing year by year.

[0003] Since the capacity of a lithium-ion secondary battery largely depends on the positive electrode active material and the negative electrode active material which are the main materials of the electrode, various materials for use in these active materials have been actively studied. However, when using the active materials that have been put into practical use, the charge capacity has reached a level close to the theoretical value, and the improvement is approaching the limit. Therefore, if the filling amount of the active material in the electrode film increases, the charge capacity can be simply increased. Therefore, attempts have been made to reduce the addition amount of conductive aids and binder resins that do not directly contribute to the charge capacity.

[0004] The conductive aid plays a role of forming a conductive path inside the electrode, and it is required that the conductive aid is not easily cut due to the expansion and contraction of the electrode film. In order to maintain the conductive path with a small amount of conductive aid, it is desirable to use a carbon material having a large specific surface area, such as Ketjen black, carbon nanotube, graphene, fullerene, etc. However, these carbon materials contain metal catalysts during synthesis and metal magnetic foreign substances derived from the manufacturing process, and there is a problem of voltage drop failure due to this. The metal magnetic foreign substances dissolve inside the secondary battery, precipitate in a dendrite shape, may break through the separator, and may cause internal short circuit. Furthermore, in an electrode film containing a carbon material with a large content of metal magnetic foreign substances, deterioration of the electrolyte and the active material is likely to occur due to high-temperature charge and discharge of the secondary battery, and deterioration of the high-temperature cycle characteristics becomes a problem.

[0005] Therefore, in Patent Document 1, a particulate metal component containing at least one metal selected from the group consisting of Fe, Ni, and Cr in a slurry composition in which carbon black particles are dispersion-treated is removed as a particulate metal removal step by a magnet having a Vickers hardness of 10 GPa or more and less than 25 GPa. In particular, carbon nanotubes often have metal magnetic foreign substances derived from the metal catalyst used in the synthesis remaining, and the problem of voltage drop failure is more likely to occur. Therefore, in Patent Document 2, a method of crushing carbon nanotubes containing metal magnetic foreign substances such as iron, cobalt, and nickel and removing the metal magnetic foreign substances of the carbon nanotubes using an electromagnet has been studied. Patent Document 3 proposes a method for removing particulate metals contained in a binder composition. Patent Document 4 proposes a method for removing metal magnetic foreign substances, which are ferromagnetic impurities in a medium liquid containing carbon nanotubes defibrated by a shear modulus, in a method for producing carbon nanotubes.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, in the conventional methods such as those described in Patent Documents 1 to 4, there is a limit to reducing the content of metal magnetic foreign substances in the carbon material dispersion, and at present, the stability over time of the carbon material dispersion and the characteristics of the secondary battery have not been sufficiently improved.

[0008] For example, when removing metal magnetic foreign substances from the carbon material itself by methods such as magnetic separation or filters, it is difficult to remove the metal magnetic foreign substances incorporated inside the carbon material. On the other hand, when removing metal magnetic foreign substances from the carbon material dispersion, it is possible to make the metal magnetic foreign substances incorporated inside the carbon material apparent by the dispersion process. However, in order to efficiently remove the metal with magnetic separation or filters, etc., it is necessary to prepare the carbon material dispersion to have a low viscosity. However, due to dispersion, not only the carbon material but also the metal magnetic foreign substances are refined, so there is a risk that the removal efficiency of the metal magnetic foreign substances will decrease. Therefore, there was room for improvement to maximize the reduction efficiency of the metal magnetic foreign substances 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 metal magnetic foreign substances and excellent stability over time. Furthermore, it is an object of the present invention to provide a secondary battery having good cycle characteristics using the same. In particular, even in the case of using carbon nanotubes, where metal magnetic foreign substances derived from the metal catalyst used during synthesis often remain, an object is to provide a carbon nanotube dispersion with a lower content of metal magnetic foreign substances than before.

Means for Solving the Problems

[0010] According to intensive studies by the present inventors, a carbon material pre-dispersion having a slip angle of less than 70° and a cumulative particle diameter D 50 of 20 μm or more, by removing metal magnetic foreign substances simultaneously with and / or after its production, it was found that the metal magnetic foreign substances can be efficiently recovered and the amount of metal magnetic foreign substances in the carbon material dispersion can be reduced compared to the conventional method. Furthermore, it was found that this improves the stability over time of the carbon material dispersion after dispersion. Accordingly, the present invention can provide a carbon material dispersion liquid with a low content of metal magnetic foreign substances and good stability over time, and can also provide a secondary battery with good cycle characteristics.

[0011] That is, the present invention includes the following embodiments. The embodiments of the present invention are not limited to the following. [1] A method for producing a carbon material dispersion liquid comprising all of the following steps (1) to (3). A method for producing a carbon material dispersion liquid containing a carbon material, a dispersant, and a solvent. [Step (1)] A step of obtaining a carbon material pre-dispersion liquid (X1) having a slip angle with respect to a metal substrate of less than 70° and a cumulative particle diameter D 50 of 20 μm or more. [Step (2)] A step of removing metal magnetic foreign substances 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 [1], wherein the solvent is a non-aqueous solvent. [3] The method for producing a carbon material dispersion liquid according to [1] or [2], further comprising a step of removing metal magnetic foreign substances simultaneously with and / or after the dispersion of the carbon material pre-dispersion liquid (X2). [4] A method for producing an electrode slurry, in which an active material is mixed with the carbon material dispersion liquid produced by the method according to any one of [1] to [3]. [5] A method for producing an electrode, comprising a step of coating the electrode slurry produced by the method according to [4] on a current collector to form an electrode film. [6] A method for producing a secondary battery, comprising a step of coating the electrode slurry produced by the method according to [4] on a current collector to form an electrode film. [Advantages of the Invention]

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

Embodiments for Carrying Out the Invention

[0013] Hereinafter, the carbon material dispersion liquid, electrode slurry, electrode, and secondary battery of the present invention, as well as their manufacturing methods, will be described in detail, but are 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, the numerical range specified using "~" shall include the numerical values described before and after "~" as the range of the lower limit value and the upper limit value. In this specification, "carbon nanotube" may be denoted 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". Also, "carbon material pre-dispersion liquid (X1)" and "carbon material pre-dispersion liquid (X2)" may be collectively referred to as "carbon material pre-dispersion liquid". The step of "removing metallic magnetic foreign substances by magnetic separation treatment" is also simply referred to as the "magnetic separation step". Unless otherwise noted, each of the various components appearing in this specification may be used alone or in combination of two or more.

[0015] ≪Manufacturing Method of Carbon Material Dispersion Liquid≫ One embodiment of the present invention is characterized by comprising all of the following steps (1) to (3) in a method for manufacturing a carbon material dispersion liquid containing a carbon material, a dispersant, and a solvent. [Step (1)] A step of obtaining a carbon material pre-dispersion liquid (X1) having a sliding angle with respect to a metal substrate of less than 70° and a cumulative particle diameter D 50 of 20 μm or more [Step (2)] Step of removing metal magnetic foreign substances from the carbon material pre-dispersion (X1) by magnetic separation treatment during and / or after the production of the carbon material pre-dispersion (X1) to obtain the carbon material pre-dispersion (X2) [Step (3)] Step of dispersing the carbon material pre-dispersion (X2) to produce a carbon material dispersion

[0016] By 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 metal magnetic foreign substances in the carbon material dispersion than before and excellent stability over time. Furthermore, by using the carbon material dispersion, it is possible to obtain a secondary battery having excellent cycle characteristics. Among them, even in the case of using carbon nanotubes, in which metal magnetic foreign substances derived from metal catalysts used in synthesis often remain, it is possible to obtain a carbon nanotube dispersion having a lower content of metal magnetic foreign substances than before.

[0017] Note that step (3) preferably includes a step of further removing metal magnetic foreign substances during and / or after the dispersion of the carbon material pre-dispersion (X2).

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

[0019] The smaller the sliding angle, the better the droplet sliding property (water sliding property). The sliding angle of the carbon material pre-dispersion (X1) of the present invention is less than 70°. Preferably it is 60° or less, more preferably 50° or less, still more preferably 40° or less. Also, preferably it is 1° or more. Since the sliding angle is less than 70°, the wettability with respect to the surface of the magnetic separation filter is good. When performing the magnetic separation treatment, the carbon material pre-dispersion (X1) is less likely to adhere to the magnetic separator, and the metal magnetic foreign matter removal efficiency by the magnetic separation treatment is improved. When the sliding angle is 70° or more, the wettability with respect to the surface of the magnetic separation filter deteriorates, and when performing the magnetic separation treatment, the carbon material pre-dispersion (X1) adheres to the magnetic separator. Therefore, the thickness of the adhered carbon material pre-dispersion (X1) appears, and since the magnetic force decreases by the square of the distance, the metal magnetic foreign matter removal efficiency by the magnetic separation treatment decreases. The sliding angle can be adjusted by adjusting the specific surface area of the carbon material, the amount of surface functional groups, the type and composition of the dispersant, the type of solvent, the dispersion conditions (time, intensity, etc.), and the like.

[0020] The metal substrate used in the measurement of the sliding angle is not particularly limited, but it is preferably the material of the magnet in contact with the carbon material pre-dispersion (X1). For example, SUS316L, SUS430, etc. can be mentioned. Specifically, the sliding angle can be measured by, for example, the method described in the section of [Examples].

[0021] The cumulative particle size D of the carbon material pre-dispersion (X1) 50 is 20 μm or more. Preferably it is 30 μm or more, more preferably 40 μm or more. Also, preferably it is 300 μm or less, more preferably 250 μm or less. The cumulative particle size D 50 If it is less than 20 μm, the carbon material pre-dispersion (X1) becomes highly viscous, which causes a decrease in magnetic separation efficiency. Also, since the dispersion of metal magnetic foreign matters progresses as the carbon material pre-dispersion (X1) is dispersed, there is a risk that the magnetic separation efficiency will decrease as the metal magnetic foreign matters become finer. On the other hand, the cumulative particle size D 50When it is larger than 300 μm, there is a risk that the metallic magnetic foreign matter encapsulated in the carbon material may not be sufficiently manifested and removed by the magnetic separation process. Cumulative particle size D 50 is determined from the volume-based particle size distribution curve measured by the laser diffraction / scattering particle size distribution measurement method. Specifically, for example, it can be measured by the method described in the section of [Examples].

[0022] The production of the carbon material pre-dispersion (X1) can be carried out, 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 or the like. For example, the solvent and the dispersant may be mixed first, and then the carbon material may be added, or after kneading the carbon material and the dispersant, the solid content of the carbon material pre-dispersion (X1) may be adjusted.

[0023] As the apparatus for producing the carbon material pre-dispersion (X1), a mixer, kneader, or disperser commonly used for pigment dispersion or the like can be used. For example, mixers such as a disper, a homomixer, and a planetary mixer, "Clear Mix" manufactured by M & TEC Co., Ltd., "Film Mix" manufactured by PRIMIX Corporation, "Abramic Mix" manufactured by Silver · Son Co., Ltd., etc. can be mentioned.

[0024] [Step (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 (X1) to obtain a carbon material pre-dispersion (X2). In this specification, the carbon material pre-dispersion subjected to magnetic separation treatment is referred to as the carbon material pre-dispersion (X2). The step of removing this metallic magnetic foreign matter by magnetic separation treatment may be either simultaneously with and / or after the production of the carbon material pre-dispersion (X1). That is, Step (1) and Step (2) may be carried out simultaneously, or the magnetic separation treatment of Step (2) may be carried out using the carbon material pre-dispersion (X1) obtained in Step (1). In addition, when steps (1) and (2) are carried out simultaneously, the carbon material pre-dispersion liquid (X2) corresponds to the same one as the carbon material pre-dispersion liquid (X1).

[0025] Therefore, as a method for producing the carbon material pre-dispersion liquid (X2), (i) Obtaining a carbon material pre-dispersion liquid (X1) having a slip angle with respect to the metal substrate of less than 70° and a cumulative particle diameter D 50 of 20 μm or more, and then removing the metal magnetic foreign substances in the carbon material pre-dispersion liquid (X1) by magnetic separation treatment to obtain the carbon material pre-dispersion liquid (X2); (ii) Removing the metal magnetic foreign substances in the carbon material pre-dispersion liquid containing a carbon material, a dispersant, and a solvent by magnetic separation treatment to obtain a carbon material pre-dispersion liquid (X2) having a slip angle with respect to the metal substrate of less than 70° and a cumulative particle diameter D 50 of 20 μm or more; and the like can be mentioned. In the present invention, in this way, it is important that the carbon material pre-dispersion liquid during magnetic separation treatment has a slip angle with respect to the metal substrate of less than 70° and a cumulative particle diameter D 50 of 20 μm or more. Thereby, it becomes possible to efficiently reduce the metal magnetic foreign substance particles contained in the carbon material pre-dispersion liquid. Therefore, the content of the metal magnetic foreign substances in the obtained carbon material dispersion liquid is small, and a carbon material dispersion liquid excellent in stability over time is obtained.

[0026] In the present invention, the metal magnetic foreign substances refer to those present in a particulate state in the carbon material pre-dispersion liquid or the carbon material dispersion liquid, and do not include those present in a dissolved state as metal ions. Further, examples of the metal of the metal magnetic foreign substances include Fe, Co, and Cr.

[0027] As a method for removing metallic magnetic foreign substances by magnetic separation treatment, there is no particular limitation as long as it is a method for removing metallic magnetic foreign substances 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 using an electromagnet, an appropriate magnetic force can be set by controlling the current flowing through the electromagnet, and it is preferable because magnetic components can be efficiently removed. In addition, since the magnetic force can be made close to 0 by setting the current to 0, compared with a permanent magnet, it is easier to remove the adsorbed magnetic components, and the maintainability 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 Eliz Magnetics Co., Ltd., EMF-100S, EMF-150S, EMF-250S, EMF-300S manufactured by Daiho Magnetic Co., Ltd. etc. can be used.

[0029] The magnetic flux density of the electromagnet is preferably 5000 Gauss or more and 30000 Gauss or less, and more preferably 12000 Gauss or more and 30000 Gauss or less. By using an electromagnet within the above range, not only can metallic magnetic foreign substances contained in raw materials such as carbon materials be removed, but also metallic magnetic foreign substances generated in the manufacturing process can be removed, which is preferable.

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

[0031] The number of times the carbon material pre-dispersion liquid (X1) passes through the electromagnet is preferably 3 times or more. When the number of passes is small, there is a possibility that metallic magnetic foreign substances cannot be sufficiently removed. When passing through the electromagnet in a circulating manner, considering the uniformity in the tank used in the manufacturing process, it is preferable to pass through more times.

[0032] The amount of metallic magnetic foreign matter in the carbon material pre-dispersion (X2) after 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, by performing a magnetic separation treatment on the carbon material pre-dispersion (X1) having a slip angle with respect to the metal substrate of less than 70° and a cumulative particle diameter D 50 of 20 μm or more, the contained metallic magnetic foreign matter can be significantly reduced as compared with the prior art. Thereby, the content of the metallic magnetic foreign matter contained in the carbon material dispersion can also be reduced, and a secondary battery excellent in battery characteristics can be obtained. <Condition (I)> The metal foreign matter particles in 30 kg of the carbon material pre-dispersion are passed through an electromagnet (magnetic flux density: 16,000 gauss) five times, washed with an amide-based polar solvent, and the obtained metallic magnetic foreign matter is deposited on a filter having a disk diameter of 47 mm and a mesh size of 5 μm, and the weight of the metal foreign matter particles on the filter is measured.

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

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

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

[0036] The disperser that can be used to produce the carbon material dispersion is not particularly limited, and examples include paint conditioners (manufactured by Red Devil), colloid mills (such as "PUC colloid mill" manufactured by PUC and "Colloid mill MK" manufactured by IKA), cone mills (such as "Cone mill MKO" manufactured by IKA), ball mills, sand mills (such as "Dynomill" manufactured by Shinmaru Enterprises), attritors, pearl mills (such as "DCP mill" manufactured by Ehrig), media-type dispersers such as coball mills, high-pressure homogenizers (such as "Genius PY" manufactured by Genius, " Starburst" manufactured by Sugino Machine, "Nanomizer" manufactured by Nanomizer), media-less dispersers such as "Clear SS-5" manufactured by M Techniq and "MICROS" manufactured by Nara Machinery, and other roll mills.

[0037] In the production of the carbon material dispersion as well, similar to the production of the carbon material pre-dispersion (X2), it is preferable to include a step of removing metal magnetic foreign substances by magnetic force such as a magnet. As a method of removing metal magnetic foreign substances by magnetic separation treatment, the same method as the method described in step (2) can be used. Furthermore, the carbon material dispersion can remove more metal magnetic foreign substances by incorporating a filtration step using a filter. On the other hand, the particle size of the carbon material pre-dispersion (X2) is larger compared to the carbon material dispersion, and it is difficult to incorporate it because it clogs the filter.

[0038] As the filter, it may be a surface filter such as a membrane filter or a depth filter, but a depth filter is more preferable. Since many metal magnetic foreign substances are not spherical but have orientation, using a depth filter can efficiently remove metal magnetic foreign substances in the carbon material dispersion.

[0039] Unlike a surface filter (a filter that mainly captures particulate matter in a fluid on the filter surface), a depth filter is a filter that mainly captures particulate matter in a fluid inside the filter medium, and has the characteristics of high particle retention performance and being less likely to clog. By using a depth filter, metal magnetic foreign substances in the carbon material dispersion can be removed more selectively.

[0040] As the depth filter, for example, 3M(TM) PP non-woven fabric depth cartridge NT-T series, Profile II manufactured by Nippon Paul Co., Ltd., and Slope Pure manufactured by Loki Co., Ltd. can be used.

[0041] The filtration accuracy of the filter is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less. When a filter with a small filter pore diameter is used for the purpose of increasing the removal efficiency of metal magnetic foreign substances in the carbon material dispersion, the removal efficiency of metal magnetic foreign substances may decrease due to clogging of the carbon material or the like. By using a filter with a filtration accuracy within the above range, metal foreign substances can be removed efficiently, and a carbon material dispersion with a low metal foreign substance content can be obtained.

[0042] Since the content of metal magnetic foreign substances is small, the thickening over time of the carbon material dispersion can be suppressed, and the stability over time can be made good. On the other hand, if the content of metal magnetic foreign substances is large, the dispersant in the carbon material dispersion may adsorb to the metal magnetic foreign substances, resulting in the breakdown of the dispersion of the carbon material and the possibility of thickening over time. In addition, if a secondary battery contains a large amount of metal magnetic foreign matter, the metal magnetic foreign matter dissolves at the positive electrode during the charge-discharge cycle, precipitates at the negative electrode, penetrates the separator, and a part of the negative electrode comes into contact with the positive electrode, which may lead to voltage failure. Also, inhibition of Li ions may occur. Furthermore, when the amount of metal magnetic foreign matter is large, it may touch the positive electrode and cause a short circuit. Therefore, the amount of metal magnetic foreign matter in the carbon material dispersion is preferably as small as possible. The content in 30 kg of the carbon material dispersion obtained 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)> Pass the metal foreign particles in 30 kg of the carbon material dispersion through an electromagnet (magnetic flux density: 16,000 gauss) five times, wash with an amide-based polar solvent, deposit the obtained metal magnetic foreign matter on a filter with a disk diameter of 47 mm and a mesh opening of 5 μm, and measure the weight of the metal foreign particles on the filter.

[0043] Specifically, the content of the metal magnetic foreign matter can be measured, for example, by the method described in the examples.

[0044] <Carbon material pre-dispersion liquid, and carbon material dispersion liquid> The carbon material pre-dispersion liquid and the carbon material dispersion liquid of 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 slip angle of less than 70° and a cumulative particle diameter D 50 of 20 μm or more. Also, the carbon material pre-dispersion liquid (X2) is obtained by removing metal magnetic foreign matter by magnetic separation treatment 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. The slip angle is less than 70° and the cumulative particle diameter D 50It can be a carbon material pre-dispersion (X1) with a particle size of 20 μm or more. Then, simultaneously with and / or after the production of this carbon material pre-dispersion (X1), metal magnetic foreign substances in the carbon material pre-dispersion are removed by magnetic separation treatment to obtain a carbon material pre-dispersion (X2). This enables not only the reduction of the content of metal magnetic foreign substances in the dispersion without excessive refinement of the carbon material and the metal magnetic foreign substances, but also the compatibility of the temporal stability of the carbon material dispersion. Note that due to the fact that the angle of repose and the cumulative particle size D 50 remain almost unchanged through the magnetic separation process, the carbon material pre-dispersion (X2) also has an angle of repose of less than 70° and a cumulative particle size D 50 of 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, it is a carbon material dispersion from which metal magnetic foreign substances have been further removed simultaneously with and / or after the dispersion of the carbon material pre-dispersion (X2).

[0047] Note that the carbon material dispersion refers to the state before the addition of the active material. In this regard, the carbon material dispersion is distinguished from the electrode slurry containing the active material. That is, the carbon material dispersion does not substantially contain the active material. This is a concept excluding the state where the active material is intentionally added to the carbon material dispersion. For the total mass of the carbon material dispersion, 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%. The active material will be described later.

[0048] (Carbon material) The carbon material in the present invention is not particularly limited. Examples of the conductive carbon material include graphite, carbon black, or fibrous carbon materials such as carbon nanotubes, carbon nanofibers, or carbon fibers, which can be used alone or in combination of two or more. The carbon material plays a role of forming a conductive path inside the electrode, and from the viewpoint that it is required to be less likely to be cut due to the expansion and contraction of the electrode film, it preferably contains a fibrous carbon material, and more preferably is a fibrous carbon material. From the viewpoints of conductivity, ease of availability, and cost, the use of carbon black and / or carbon nanotubes is preferred. Also, from the viewpoints of reducing raw material costs and forming an efficient conductive network, two or more types of carbon materials with different physical properties of the same kind may be used in combination. Examples of carbon materials of the same kind with different physical properties include two types of carbon nanotubes with different average outer diameters or average fiber diameters, or two types of carbon black with different specific surface areas, etc.

[0049] The carbon material may contain metal magnetic foreign substances during the manufacturing process of the carbon material. It is difficult to completely remove all of these metal magnetic foreign substances from the carbon material. Among them, carbon nanotubes may contain metal magnetic foreign substances derived from raw materials such as metal catalysts. Carbon nanotubes can make the contained metal magnetic foreign substances become apparent by dispersion, but at the same time as the carbon nanotubes are cut due to miniaturization, the metal magnetic foreign substances are also miniaturized, making it difficult to extract the metal magnetic foreign substances from the dispersion liquid. However, the method for producing the carbon material dispersion composition of the present invention can efficiently remove metal magnetic foreign substances derived from the carbon material by performing magnetic separation using a carbon material pre-dispersion liquid having a sliding angle with respect to the metal substrate of less than 70° and a cumulative particle diameter D of 20 μm or more. 50 Therefore, according to the method for producing the carbon material dispersion of the present invention, even when using carbon nanotubes in which metal magnetic foreign substances derived from the metal catalyst used during synthesis often remain, the content of metal magnetic foreign substances can be reduced compared to the prior art.

[0050] The carbon purity of the carbon material is represented by the content rate (mass %) of carbon atoms in the carbon material. The higher the carbon purity, the more preferable it is. For 100% by mass of the carbon material, 90% by mass or more is preferable, 95% by mass or more is more preferable, 98% by mass or more is still more preferable, and 99% by mass or more is particularly preferable. By setting the carbon purity within the above range, problems such as the formation of dendrites due to impurities and short circuits can be prevented.

[0051] [Carbon black] Carbon black is fine particles mainly composed of carbon, and is manufactured by controlling various properties by incompletely burning oil or gas. Carbon black has a secondary structure (aggregate) in which primary particles are connected in a bead-like manner, and a tertiary structure (agglomerate) in which the secondary structures are further aggregated. The secondary structure and the tertiary structure are collectively referred to as a structure. When observing the primary particles with an electron microscope or the like, they appear spherical, but the primary particles are not chemically independent individuals, but are connected by chemical bonds with adjacent primary particles within the aggregate to form a secondary structure. On the other hand, the secondary structures are chemically independent individuals, and aggregate by intermolecular forces to form a tertiary structure. Therefore, it can be said that the conductivity inside the secondary structure is higher than the conductivity between the secondary structures including the contact resistance, and it is effective to obtain an electrode with excellent conductivity by de-aggregating the tertiary structure while maintaining the structure of the secondary structure as much as possible. In this specification, the secondary structure may sometimes be simply referred to as "structure".

[0052] As the carbon black used in the present invention, various commercially available acetylene black, furnace black, hollow carbon black, channel black, thermal black, ketjen black, etc. can be used. Further, oxidized carbon black or graphitized carbon black that is usually performed can also be used.

[0053] The oxidation treatment of carbon black is a treatment that directly introduces (covalently bonds) oxygen-containing polar functional groups such as phenolic groups, quinone groups, carboxyl groups, and carbonyl groups onto the carbon black surface by subjecting carbon black to high-temperature treatment in air or secondarily treating it with nitric acid, nitrogen dioxide, ozone, etc. It is generally carried out to improve the dispersibility of carbon black.

[0054] Examples of commercially available carbon blacks include SuperP-Li (manufactured by TIMCAL), Ketjenblack EC-300J, EC-600JD (manufactured by Lion), Denka Black, Denka Black Li-400, FX-35 (manufactured by Denka, acetylene black), etc. Examples of graphite include natural graphite such as artificial graphite, flake graphite, massive graphite, and earthy graphite, but are not limited thereto, and two or more types may be used in combination.

[0055] The average primary particle diameter of carbon black is preferably 10 nm to 1 μm, particularly preferably 20 nm to 200 nm, and even more preferably 25 nm to 100 nm. The average primary particle diameter of carbon black can be calculated by first observing and imaging carbon black with a transmission electron microscope, and in the observation photograph, selecting any 100 spherical-like carbon black primary particles and measuring their respective outer diameters.

[0056] The BET specific surface area of carbon black is preferably 10 m 2 / g or more and 1500 m 2 / g or less, more preferably 40 m 2 / g or more and 1000 m 2 / g or less, and even more preferably 100 m 2 / g or more and 850 m 2It is more preferable that it is below / g. When the BET specific surface area is within the above range, a small amount of efficient conductive network can be formed, and the amount of conductive material in the electrode can be reduced. Thereby, the degree of freedom in battery design such as increasing the amount of active material and binder resin is increased. Furthermore, when preparing the electrode slurry, since the composite of the active material and carbon black easily proceeds, an electrode film having a homogeneous conductive network in which the surface of the active material is covered with carbon black is easily obtained, and the electrolyte decomposition reaction at the interface between the electrolyte and the active material is suppressed, and the cycle characteristics of the battery can be improved. The BET specific surface area can be measured by the BET method described in JIS Z 8833.

[0057] [Carbon nanotube] Carbon nanotubes have a structure in which planar graphite is wound in a cylindrical shape. Carbon nanotubes preferably include multi-walled carbon nanotubes, and may include multi-walled carbon nanotubes and single-walled carbon nanotubes. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are wound. Single-walled carbon nanotubes have a structure in which one layer of graphite is wound. The side wall of the carbon nanotube does not have to be a graphite structure. For example, carbon nanotubes having side walls with an amorphous structure can also be used as the carbon material.

[0058] The average outer diameter of the carbon nanotubes is preferably 1 nm or more and 25 nm or less, more preferably 3 nm or more and 20 nm or less, and even more preferably 4 nm or more and 15 nm or less. When the average outer diameter is within the above range, a good conductive network is easily formed in the electrode, and during charge and discharge, the active material inside the secondary battery is uniformly utilized, so that the deterioration of the active material is suppressed and the cycle characteristics of the secondary battery are further improved.

[0059] The G / D ratio (peak ratio of G-band and D-band) of the carbon nanotubes is 1560 cm in the Raman spectrum -1 ~1600 cm -1Let the maximum peak intensity within the range be G, and within the range of 1310 cm -1 ~1350 cm -1 When the maximum peak intensity within the range is D, the G / D ratio is preferably 0.5 to 10, more preferably 0.7 to 4.5. When the G / D ratio of the carbon nanotubes is within the above range, it is considered that the contact resistance between the carbon nanotubes becomes small and good conductivity is easily obtained. Also, it is presumed that the amount of functional groups on the surface of the multi-walled carbon nanotubes is appropriate, the affinity with the solvent is good, and the dispersibility becomes better.

[0060] The BET specific surface area of the carbon nanotubes is preferably 100 m 2 / g or more and 1500 m 2 / g or less, more preferably 150 m 2 / g or more and 1000 m 2 / g or less, even more preferably 200 m 2 / g or more and 800 m 2 / g or less. 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. Thereby, the degree of freedom in battery design such as increasing the amount of active material and binder resin is increased. Furthermore, during the preparation of the composite slurry, the composite of the active material and the carbon nanotubes proceeds more easily, so that an electrode film having a homogeneous conductive network in which the surface of the active material is coated with carbon nanotubes can be easily obtained, 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 8833.

[0061] The carbon purity of the carbon nanotubes can be adjusted by purification treatment. As the purification treatment method of the carbon nanotubes, various conventionally known methods can be used. For example, acid treatment, graphitization treatment, and chlorination treatment can be mentioned.

[0062] As the acid used for acid-treating carbon nanotubes, any acid capable of dissolving the metals and metal oxides contained in the carbon nanotubes may be used. For example, inorganic acids and carboxylic acids are preferable, and among the inorganic acids, hydrochloric acid, sulfuric acid, and nitric acid are particularly preferable. The acid treatment of carbon nanotubes is preferably carried out in a liquid phase, and it is more preferable to disperse and / or mix the carbon nanotubes in the liquid phase. The carbon nanotubes after acid treatment are preferably washed with water and dried.

[0063] The graphitization treatment of 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.

[0064] The chlorination treatment of carbon nanotubes is not particularly limited, but for example, it can be carried out by introducing chlorine gas and heating the carbon nanotubes at 800°C to 2000°C in an inert atmosphere with an oxygen concentration of 0.1% or less.

[0065] The surface or ends of the carbon nanotubes may be modified with functional groups or alkyl groups, or may be doped with alkali metals or halogens. For example, by heating in an acid, it may be functionalized with carboxyl groups, sulfonic groups, or hydroxyl groups. Since it is possible to achieve both good stability and fluidity of the resulting carbon nanotube dispersion, it is preferable to use carbon nanotubes that do not have acidic functional groups such as carboxyl groups and sulfonic groups.

[0066] (Dispersant) The dispersant of this 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 types. Appropriate types of dispersants can be used in appropriate blending amounts according to the characteristics required for the dispersion of the carbon material.

[0067] When selecting an anionic surfactant, its type is not particularly limited. Specifically, fatty acid salts, polysulfonate salts, polycarboxylate salts, alkyl sulfate esters, alkylaryl sulfonate salts, alkylnaphthalene sulfonate salts, dialkyl sulfonate salts, dialkyl sulfosuccinate salts, alkyl phosphate salts, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylaryl ether sulfates, naphthalene sulfonic acid formalin condensates, polyoxyethylene alkyl phosphate sulfonate salts, glycerol borate fatty acid esters, and polyoxyethylene glycerol fatty acid esters can be mentioned, but are not limited thereto. Further specifically, sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate ester salts, and sodium salts of β-naphthalene sulfonic acid formalin condensates can be mentioned, but are not limited thereto.

[0068] Also, examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Specifically, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyl oleyl diethanol chloride, tetramethyl ammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkyl mercapto pyridine, poly(vinyl pyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride can be mentioned, but are not limited thereto. Also, examples of amphoteric surfactants include aminocarboxylate salts, but are not limited thereto. ーte, cetyl pyridinium bromide, 4-alkyl mercapto pyridine, poly(vinyl pyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride can be mentioned, but are not limited thereto. Also, examples of amphoteric surfactants include aminocarboxylate salts, but are not limited thereto.

[0069] 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. Specifically, examples include, but are not limited to, polyoxyethylene lauryl ether, sorbitan fatty acid ester, and polyoxyethylene octyl phenyl ether.

[0070] The surfactant to be selected is not limited to a single surfactant. Therefore, it is also possible to use a combination of two or more surfactants. For example, a combination of an anionic surfactant and a nonionic surfactant, or a combination of a cationic surfactant and a nonionic surfactant can be used. The blending amount at that time is preferably a suitable blending amount for each surfactant component. As the 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.

[0071] Specific examples of the resin-type dispersant include fluororesins, cellulose derivatives (such as 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-based polymers, and the like. In particular, fluororesins, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, hydrogenated nitrile butadiene rubber, and polyacrylonitrile-based polymers are preferred. From the perspective of achieving both the temporal stability of the carbon material and the removal efficiency of metal magnetic foreign substances by magnetic separation treatment, the molecular weight of the resin-type dispersant is preferably from 10,000 to 300,000.

[0072] From the perspective of oxidation resistance, hydrogenated nitrile butadiene rubber and polyacrylonitrile-based polymers are preferred as the dispersant.

[0073] From the perspective of the temporal stability of the carbon material, the content of the dispersant is preferably from 10 to 300 parts by mass, more preferably from 10 to 100 parts by mass, based on 100 parts by mass of the carbon material. By setting the content within the above range, the dispersion state of the carbon material can be stably maintained, and the temporal stability can also be improved.

[0074] In addition to the dispersant, it is preferable to add an amine compound or an inorganic base. As the amine compound, primary amines, secondary amines, and tertiary amines are used, excluding ammonia and quaternary ammonium compounds. As the amine-based compound, in addition to monoamines, amine-based compounds such as diamines, triamines, and tetraamines having a plurality of 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, alkanolamines such as dimethylaminoethanol, monoethanolamine, diethanolamine, methylethanolamine, and triethanolamine, alicyclic nitrogen-containing heterocyclic compounds such as hexamethylenetetramine, morpholine, and piperidine, etc. can be mentioned, but it is not limited thereto. As the inorganic base, hydroxides of alkali metals, hydroxides of alkaline earth metals, carbonates of alkali metals, carbonates of alkaline earth metals, phosphates of alkali metals, phosphates of alkaline earth metals, etc. can be mentioned. Examples include, but are not limited to, alkanolamines such as dimethylaminoethanol, monoethanolamine, diethanolamine, methylethanolamine, and triethanolamine, alicyclic nitrogen-containing heterocyclic compounds such as hexamethylenetetramine, morpholine, and piperidine. As the inorganic base, hydroxides of alkali metals, hydroxides of alkaline earth metals, carbonates of alkali metals, carbonates of alkaline earth metals, phosphates of alkali metals, phosphates of alkaline earth metals, etc. can be mentioned.

[0075] When using an amine compound or an inorganic base, its content is preferably 0.1 part by mass or more and 10 parts by mass or less, more preferably 0.5 part by mass or more and 6 parts by mass or less, and even more preferably 1 part by mass or more and 3 parts by mass or less with respect to 100 parts by mass of the dispersant. Thereby, the wettability of the carbon material is improved, and the dispersibility can be further improved. When using carbon nanotubes as the carbon material, the dispersibility is remarkably improved.

[0076] (Solvent) The solvent of this embodiment is not limited as long as it can disperse the carbon material, but water or an organic solvent such as an amide-based organic solvent can be used.

[0077] Since an aqueous solvent may corrode a magnet, causing weakening of the magnetic force of the magnet and generation of metallic magnetic foreign matter, using an amide-based organic solvent can reduce the content of metallic magnetic foreign matter in the carbon material dispersion.

[0078] 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, and the like. In particular, it is preferably included at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0079] When using an organic solvent as the solvent of the present embodiment, from the viewpoint of suppressing thickening of the carbon material, it is preferably substantially free of moisture. Specifically, the moisture is preferably 100 to 3000 ppm, more preferably 200 to 1500 ppm, and preferably 1000 ppm or less based on the carbon material dispersion. If a large amount of moisture is contained, there is a risk of thickening or gelling of the carbon material dispersion or the electrode slurry using the same. By setting the water content within the above range, the dispersion state of the carbon material can be kept good, and thickening can be suppressed even when the carbon material dispersion is stored for a long time, which is preferable.

[0080] (Other optional components) The carbon material pre-dispersion and the carbon material dispersion can be appropriately blended with wetting agents, pH adjusters, wetting and penetrating agents, leveling agents, and other additives, binder resins described later, other conductive materials, etc., within a range not inhibiting the object of the present invention, and can be added at any timing such as before preparation of the mixed solution, during mixing, after mixing, or during preparation of the carbon material pre-dispersion or the carbon material dispersion.

[0081] ≪Manufacture of electrode slurry≫ The electrode slurry can be manufactured by mixing an active material with the carbon material dispersion of the present invention. The active material may be either a positive electrode active material or a negative electrode active material. Further, it may further contain a binder resin, other conductive materials, and a solvent, and may further be mixed with any components. In this specification, the positive electrode active material and the negative electrode active material may sometimes be simply referred to as "active material". The active material is a material that serves as the basis for the battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material from the electromotive force. The electrode slurry may also be referred to as a "composite slurry" or an "electrode composite slurry" ", and the electrode slurry containing the positive electrode active material or the negative electrode active material may sometimes be referred to as "positive electrode slurry" and "negative electrode slurry", respectively. The electrode slurry is preferably in a slurry state in order to improve uniformity and processability.

[0082] (Positive electrode active material) The positive electrode active material is not particularly limited. For example, for secondary battery applications, metal compounds such as metal oxides and metal sulfides capable of reversibly doping or intercalating lithium ions can be used. For example, lithium manganese composite oxides (such as Li x Mn2O4 or LixMnO2), lithium nickel composite oxides (such as Li x NiO2), lithium cobalt composite oxides (Li x CoO2), lithium nickel cobalt composite oxides (such as Li x Ni 1-y Co y O2), lithium manganese cobalt composite oxides (such as Li x Mn y Co 1-y O2), lithium nickel manganese cobalt composite oxides (such as Li x Ni y Co z Mn 1-y-z O2), spinel-type lithium manganese nickel composite oxides (such as Li x Mn 2-y Ni y O4), etc., composite oxide powders of lithium and transition metals, lithium phosphate oxide powders having an olivine structure (such as Li x FePO4, Li x Fe1-y Mn y PO4, Li x CoPO4, etc.), manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxides (e.g., V2O5, V6O 13 ), etc.), transition metal oxide powders such as titanium oxide, iron sulfate (Fe2(SO4)3), transition metal sulfide powders such as TiS2 and FeS, 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 elution of components derived from raw materials or metal ions, and as a result, gelation of the binder and deterioration of the dispersion state are likely to occur, 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.

[0083] (Anode active material) The anode active material is not particularly limited. For example, metal Li capable of reversibly doping or intercalating 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, 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, resin-fired carbon materials, etc.

[0084] The content of the carbon material in the electrode slurry is preferably 0.01 part by mass or more, more preferably 0.05 part by mass or more, and still more preferably 0.10 part by mass or more with respect 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 still more preferably 3 parts by mass or less. If it exceeds the above range, the filling amount of the active material in the electrode may decrease, leading to a reduction in the battery capacity. Also, if it is below the above range, the conductivity of the electrode and the battery may be insufficient.

[0085] The content of the dispersant in the electrode slurry is preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more with respect 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.

[0086] (Binder resin) When the electrode slurry further contains a binder resin, there is usually no particular limitation as long as it is a binder resin such as a paint, and it can be appropriately selected according to the purpose. The binder resin used in the electrode slurry is a resin that can bind substances such as active materials and conductive materials. The binder resin used in the electrode slurry is, for example, a polymer or copolymer containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinyl pyrrolidone, etc. as constituent units; polyurethane resin, polyester resin, phenol resin, epoxy resin, phenoxy resin, urea resin, melamine resin, alkyd resin, acrylic resin, formaldehyde resin, silicone resin, fluororesin; cellulose resin; elastomers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene, etc. Also, modified products, mixtures, and copolymers of these resins may be used. Among these, when used as the binder resin for the positive electrode, it is preferable to use, for example, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylene, etc. as the binder resin from the perspective of resistance. Also, when used as the binder resin for the negative electrode, CMC, styrene-butadiene rubber, polyacrylic acid, etc. with good adhesion are preferable.

[0087] 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 with respect to 100 parts by mass of the active material. Also, it 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.

[0088] The solid content of the electrode slurry is preferably 30% by mass or more, more preferably 40% by mass or more, based on the mass of the electrode slurry (assuming the mass of the electrode slurry is 100% by mass). Also, it is preferably 90% by mass or less, more preferably 80% by mass or less.

[0089] The electrode slurry can be prepared by various conventionally known methods. For example, a method of preparing by adding an active material to a carbon material dispersion; a method of preparing by adding a binder resin after adding the active material to the carbon material dispersion; a method of preparing by adding the active material after adding the binder resin to the carbon material dispersion, and the like. The dispersion device used for dispersion is not particularly limited, and the electrode slurry can be obtained by using the dispersion means described in the description of the carbon material dispersion. Therefore, as a method of preparing the electrode slurry, a process of adding an electrode active material and dispersing it may be performed without adding a binder resin to the carbon material dispersion.

[0090] ≪Manufacture of electrode≫ The electrode is obtained by forming an electrode film using the carbon material dispersion or the electrode slurry. The electrode is preferably manufactured by coating the electrode slurry on a current collector to form an electrode film, and it may be a positive electrode or a negative electrode.

[0091] The electrode has, for example, a current collector and an electrode film obtained by coating and drying the electrode slurry on the current collector. An electrode formed using a positive electrode slurry can be used as a positive electrode. An electrode formed using a negative electrode slurry 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 composite layer".

[0092] The material and shape of the current collector used for forming the electrode are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. Examples of the material of the current collector include conductive metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. Also, as the shape, generally a flat foil is used, but a current collector with a roughened surface, a perforated foil-shaped current collector, or a mesh-shaped current collector can also be used. The thickness of the current collector is preferably about 0.5 to 30 μm.

[0093] As a method of coating a carbon material dispersion or an electrode slurry on a current collector, there is no particular limitation, and known methods can be used. Specifically, a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method, an electrostatic coating method, etc. can be mentioned. As drying methods, air drying, or drying using a blowing dryer, a hot air dryer, an infrared heater, a far-infrared heater, etc. can be mentioned, but it is not particularly limited to these.

[0094] After coating, a rolling treatment may be performed using a lithographic press, a calendar roll, etc. The thickness of the formed film is, for example, 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0095] The film formed using the carbon material dispersion or the electrode slurry can also be used as an underlayer of the electrode in order to improve the adhesion between the electrode film and the current collector or to improve the conductivity of the electrode film.

[0096] ≪Manufacture of secondary battery≫ The secondary battery includes a step of forming an electrode film using the carbon material dispersion or the electrode slurry. The secondary battery preferably includes a step of forming an electrode film by coating the electrode slurry on 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.

[0097] As the electrolyte, various conventionally known ones in which ions can move 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 (where Ph is a phenyl group) can be mentioned, but it is not limited to these. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0098] The non-aqueous solvent is not particularly limited. For example, 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.

[0099] The secondary battery preferably has a separator. Examples of the separator include, but are not particularly limited to, polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics subjected to hydrophilic treatment thereof.

[0100] The structure of the secondary battery of this embodiment is not particularly limited, but usually includes a positive electrode and a negative electrode, and a separator provided as necessary, and can have various shapes such as a paper type, a cylindrical type, a button type, a laminated type, etc., according to the purpose of use. It can be made into various shapes according to the purpose of use.

Examples

[0101] Examples are given below to more specifically explain the present invention. The present invention is not limited to the following examples as long as the gist thereof is not exceeded. Unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass".

[0102] The materials used in the examples and comparative examples are shown below. <Carbon material> · Carbon material 1: Carbon nanotubes (manufactured by JEIO, JENOTUBE10B) · Carbon material 2: Carbon nanotubes (manufactured by JEIO, JENOTUBE6A) · Carbon material 7: Carbon nanotubes (manufactured by OCSiAl, TUBALL 01RW03); Carbon material 9: Ketjen black (manufactured by Lion Specialty Chemicals, Ketjen black EC300J) <Dispersant> · Dispersant 1: Hydrogenated nitrile butadiene rubber (manufactured by ARLANXEO, Therban(R)3406) · Dispersant 2: Hydrogenated nitrile butadiene rubber (manufactured by ARLANXEO, Therban(R)3404) · Dispersant 3: Liquid hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, ZN35050L3) · Dispersant 4: Polyacrylonitrile (manufactured by Sigma Aldrich, Polyacrylonitrile Mw150000) · Dispersant 5: Polyvinyl butyral (manufactured by Sekisui Chemical Co., Ltd., BL-10) · Dispersant 6: Polyvinylidene fluoride (manufactured by Solvey, Solef#5130) · Dispersant 7: Polyvinyl alcohol (manufactured by Kuraray Co., Ltd., Kuraray Poval 3-80) <Additive> · Additive 1: NaOH; Sodium hydroxide · Additive 2: 2-Aminoethanol (manufactured by Fujifilm Wako Pure Chemical Corporation, Wako 1st grade)

[0103] <Preparation of carbon material 3> Weighed 10 kg of carbon material 1 into a 120 L heat-resistant container, and placed the heat-resistant container containing carbon material 1 into the furnace. Then, introduced nitrogen gas into the furnace and discharged the air in the furnace while maintaining a positive pressure. After the oxygen concentration in the furnace reached 0.1% or less, heated it to 1600 °C over 30 hours. While maintaining the furnace temperature at 1600 °C, introduced chlorine gas at a rate of 50 L / min for 50 hours. Then, introduced nitrogen gas at 50 L / min and cooled it while maintaining a positive pressure to obtain carbon material 3.

[0104] <Production of Carbon Material 4> Weighed 10 kg of carbon material 2 into a 120 L heat-resistant container, and placed the heat-resistant container containing carbon material 2 into the furnace. Then, introduced nitrogen gas into the furnace and discharged the air in the furnace while maintaining a positive pressure. After the oxygen concentration in the furnace reached 0.1% or less, it was heated to 1600 °C over 30 hours. While maintaining the furnace temperature at 1600 °C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Then, nitrogen gas was introduced at 50 L / min and cooled while maintaining a positive pressure to obtain carbon material 4.

[0105] <Production of Carbon Material 5> Carbon material 1 was charged into a dynamic mill (manufactured by Nippon Coke & Engineering Co., Ltd.) with zirconia beads having a diameter of 8 mm as a grinding medium, supplied at an operating condition of 10.0 kg / h, and processed at a peripheral speed of 5.0 m / s to obtain carbon material 5.

[0106] <Production of Carbon Material 6> Carbon material 4 was charged into a dynamic mill (manufactured by Nippon Coke & Engineering Co., Ltd.) with zirconia beads having a diameter of 8 mm as a grinding medium, supplied at an operating condition of 10.0 kg / h, and processed at a peripheral speed of 5.0 m / s to obtain carbon material 6.

[0107] <Production of Carbon Material 8> Weighed 3 kg of carbon material 7 into a 120 L heat-resistant container, and placed the heat-resistant container containing carbon material 7 into the furnace. Then, introduced nitrogen gas into the furnace and discharged the air in the furnace while maintaining a positive pressure. After the oxygen concentration in the furnace reached 0.1% or less, it was heated to 1600 °C over 30 hours. While maintaining the furnace temperature at 1600 °C, chlorine gas was introduced at a rate of 50 L / min for 50 hours. Then, nitrogen gas was introduced at 50 L / min and cooled while maintaining a positive pressure to obtain carbon material 8.

[0108] ≪Physical Property Measurement and Evaluation Method≫ The physical property measurement and evaluation methods for the carbon materials, carbon material pre-dispersion liquids, carbon material dispersion liquids, electrodes, and secondary batteries used in the following examples and comparative examples are as follows.

[0109] <Average Outer Diameter of Carbon Nanotubes> Using an electronic balance (MSA225S100DI, manufactured by Sartorius), 0.2 g of carbon nanotubes was weighed into a 450 mL SM sample bottle (manufactured by Sansho Co., Ltd.). Then, 200 mL of toluene was added, and using an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, BR manufactured by ANSON), a dispersion treatment was carried out under ice-cooling for 5 minutes at an amplitude of 30% to prepare a carbon nanotube dispersion. Thereafter, the carbon nanotube dispersion was appropriately diluted, and several μL was dropped in the form of a collodion film and dried at room temperature. Then, it was directly observed using a transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.). The observation was carried out at a magnification of 50,000 times, and multiple photos containing 10 or more carbon nanotubes in the field of view were taken. The outer diameters of 300 arbitrarily extracted carbon nanotubes were measured, and the average value was taken as the average outer diameter (nm) of the carbon nanotubes.

[0110] <Primary Particle Size of Carbon Black> For the primary particle size of carbon black, at least 30 or more (for example, 30 to 100) primary particles were observed from an electron microscope (either a scanning type or a transmission type can be used. Preferably a transmission electron microscope) photograph, and the arithmetic average value of the obtained particle sizes was adopted.

[0111] <BET Specific Surface Area of Carbon Material> Using an electronic balance (MSA225S100DI, manufactured by Sartorius), 0.03 g of the carbon material was weighed, and then dried while degassing at 110 °C for 15 minutes. Thereafter, using a fully automatic specific surface area measuring device (HM-model1208, manufactured by MOUNTECH), the BET specific surface area of the carbon material was measured.

[0112] <Carbon Purity of Carbon Material> The carbon material was acid-digested using a microwave sample pretreatment apparatus (ETHOS1, manufactured by Milestone General) to extract the metals contained in the carbon material. Subsequently, analysis was performed using a multi-type ICP emission spectrometer (720-ES, manufactured by Agilent), and the amount of metals (total amount of iron, cobalt, nickel, copper, nickel, and chromium) contained in the extract was calculated. The carbon purity of the carbon material was calculated as follows. Carbon purity (%) of carbon material = ((carbon material mass - metal amount) ÷ carbon material mass) × 100

[0113]

Table 1-1

[0114]

Table 1-2

[0115] <Sliding angle of carbon material pre-dispersion liquid> A sample plate of SUS316L was horizontally fixed to a contact angle meter (DM-501, manufactured by Kyowa Interface Science Co., Ltd.) as a metal substrate. 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 inclined, and the angle of the sample plate when the water droplet began to roll was measured. The smaller the angle, the better the water droplet slipperiness (hydrophobicity).

[0116] <Cumulative particle size D of carbon material pre-dispersion liquid and carbon material dispersion liquid> 50 Measurement Measurement of cumulative particle size D by particle size distribution 50 was performed using a laser diffraction / scattering particle size distribution measuring device (Partical LA-960V2, manufactured by Horiba, Ltd.). The laser light wavelength of this measuring device is 650 nm, and it is equipped with one ring-shaped 64-segment silicon photodiode, five 4-channel array detectors, and three silicon photodetectors as detectors. In addition, the measuring section uses a flow cell (sample cell) made of synthetic quartz. First, NMP, which is the same solvent as the dispersion liquid, was introduced into the sample bath containing the sample cell, and circulation / ultrasonic cleaning was performed. As the operating mode, the circulation rate was set to 3, the ultrasonic intensity to 7, the ultrasonic time to 1 minute, the stirring rate to 7, and the stirring mode to continuous. Subsequently, for air evacuation, after performing ultrasonic operation at an ultrasonic intensity of 7 and an ultrasonic time of 5 seconds, a blank (background) measurement was carried out. The particle size standard was set as volume, the particle refractive index was 1.920 - 0.522i (carbon material), and the solvent refractive index was 1.468 (NMP). The dispersion liquid was dropped to adjust the sample so that the laser light transmittance during measurement would be 60% ± 1%. The operating mode during measurement was set with a circulation rate of 3, a stirring rate of 7, and a stirring mode of continuous for the measurement.

[0117] <Measurement of the amount of metallic magnetic foreign substances in the carbon material pre-dispersion liquid> 30 kg of the carbon material pre-dispersion liquid was passed through an electromagnet (manufactured by Dabo Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 gauss) 5 times via a diaphragm pump. Subsequently, N-methyl-2-pyrrolidone (NMP) was passed through the electromagnet (manufactured by Dabo Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 gauss), and the The carbon material pre-dispersion liquid was extrusion-washed until the solid content was substantially eliminated. After that, the power supply of the electromagnet was turned off, and after confirming that the magnetic force of the filter had disappeared, NMP was passed through the electromagnet to obtain 10 kg of NMP containing metallic magnetic foreign substances. Subsequently, it was transferred to a plastic container containing 1 kg of NMP and 2 L of NMP, and ultrasonic treatment was performed for 5 minutes under the conditions of an output of 300 W and a frequency of 28 kHz using an ultrasonic processor (manufactured by Awa Medical Industry Co., Ltd., ultrasonic cleaner). After that, a bar magnet with a magnetic flux density of 12,000 gauss was fixed outside the plastic container to collect the ferromagnetic foreign matter, and the NMP was drained. Subsequently, the collected ferromagnetic foreign matter was recovered in its entirety using a filtering bell with a mesh (weight: W1, diameter: 47 mm, aperture: 5 μm) that had been weighed in advance using ethanol. After that, the mesh on which the ferromagnetic foreign matter had accumulated was removed, and the mesh was dried in a hot air oven at 60 °C for 20 minutes. After performing this process for all 10 kg of NMP containing the recovered ferromagnetic foreign matter, the weight (W2) of the dried mesh was measured, and the value obtained by subtracting the previously measured weight (W1) was defined as the amount of ferromagnetic foreign matter (W0). The smaller the amount of ferromagnetic foreign matter (W0), the more desirable it is. The amount of ferromagnetic foreign matter (W0) is less than 10 mg: A, 10 mg or more and less than 40 mg: B, 40 mg or more and less than 100 mg: C, 100 mg or more: D.

[0118] <Evaluation of the Amount of Ferromagnetic Foreign Matter in the Carbon Material Dispersion> The amount of ferromagnetic foreign matter (W0) in the carbon material dispersion was determined in the same manner as the measurement of the amount of ferromagnetic foreign matter in the carbon material pre-dispersion, except that the carbon material pre-dispersion was changed to the carbon material dispersion. The smaller the amount of ferromagnetic foreign matter (W0), the more desirable it is. The amount of ferromagnetic foreign matter (W0) is less than 10 mg: ◎ (excellent), 10 mg or more and less than 40 mg: ○ (good), 40 mg or more and less than 100 mg: △ (fair), 100 mg or more: × (poor).

[0119] <Evaluation of the Aging Stability of the Carbon Material Dispersion> The viscosity value was measured using a B-type viscometer (manufactured by Toki Sangyo Co., Ltd., "BL"). After leaving the measurement sample in a thermostatic bath at 25°C for 1 hour or more, the measurement was performed at a rotor rotation speed of 100 rpm of the B-type viscometer. The type of rotor used for the measurement was 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 temporal stability of the carbon material dispersion was evaluated by the following formula 1. (Formula 1) Temporal stability = (Initial viscosity) / (Viscosity after storage in a thermostatic bath at 40°C for 3 days) × 100 (%) For the evaluation of temporal stability, ◎: 60% or more (excellent), 〇: 50% or more and less than 60% (good), △: 40% or more and less than 50% (acceptable), ×: less than 40% were regarded as × (unacceptable).

[0120] <Evaluation of cycle characteristics of lithium-ion secondary battery> After leaving the secondary batteries of the laminate-type cells manufactured in the examples and comparative examples to stand for 24 hours, charging and discharging operations were performed at a charge-discharge rate of 4.25 V and 0.1C, and the initial capacity was measured. The lithium-ion secondary batteries of the laminate-type cells were placed in a thermostatic chamber at 60°C, and charge-discharge measurements were performed using a charge-discharge device (manufactured by Hokuto Denko Corporation, SM-8). After performing constant current-constant voltage charging (cutoff current 1.25 mA (0.025C)) at a charging current of 50 mA (1C) and a charging termination voltage of 4.2 V, constant current discharging was performed at a discharging current of 50 mA (1C) and a discharging termination voltage of 2.5 V. This operation was repeated 200 times. 1C was defined as the current value for discharging the theoretical capacity of the positive electrode in 1 hour. The cycle characteristics can be represented 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) × 100 (%) For the evaluation of cycle characteristics, when the cycle characteristics were 80% or more, it was rated as ◎ (excellent), when it was 70% or more and less than 80%, it was rated as 〇 (good), when it was 60% or more and less than 70%, it was rated as △ (acceptable), and when it was less than 60%, it was rated as × (poor).

[0121] (Example A-1) [Step (1)] Into a stainless steel container, 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of Dispersant 1 were added, and stirred using a disper at 80 °C until Dispersant 1 was completely dissolved to prepare an 8% solution of Dispersant 1. Subsequently, 85.75 parts of N-methyl-2-pyrrolidone (NMP) and 11.25 parts of the 8% solution of Dispersant 1 (the added amount of Dispersant 1 was 0.90 parts) were added to the stainless steel container and stirred with a disper until uniform. Then, 3 parts of Carbon Material 1 were weighed and added while stirring with a disper. A fine emulsifier screen was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), and batch dispersion was carried out at a speed of 9000 rpm until the whole became uniform and the dispersion particle size became 200 μm or less as measured by a grind gauge to obtain a pre-dispersion liquid (X1-1). The slip angle of the pre-dispersion liquid (X1-1) was 67°, and the cumulative particle size D 50 was 43 μm.

[0122] [Step (2)] The obtained pre-dispersion liquid (X1-1) was passed through an electromagnet (manufactured by Daibao Magnetic Co., EMF-100S, magnetic flux density 16000 gauss) three times to obtain a pre-dispersion liquid (X2-1).

[0123] [Step (3)] The pre-dispersion liquid (X2-1) was fed into a stainless steel container, and a circulation type dispersion treatment with a residence time of 10 minutes was performed using a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises Co., Ltd.) filled with zirconia beads having a diameter of 1.0 mmφ. Subsequently, from the stainless steel container, the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Labo HJP-17007, manufactured by Sugino Machine) through a pipe, and a 20-pass type dispersion treatment was performed. The dispersion treatment was carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Subsequently, the dispersion liquid was supplied to an electromagnet (manufactured by Dabo Magnetic Co., EMF-100S, magnetic flux density 16000 Gauss), and a three-pass treatment was performed to obtain Carbon Material Dispersion Liquid 1.

[0124] (Examples A-2 to A-20) Carbon material pre-dispersion liquids (X1-2 to 20) were produced by the same method as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additive shown in Table 2 were changed. Subsequently, carbon material pre-dispersion liquids (X2-2 to 20) and carbon material dispersion liquids 2 to 20 were obtained.

[0125] (Example A-21) [Steps 1 and 2] In a stainless steel container, 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of Dispersant 1 were added, and stirred at 80 °C using a disper to completely dissolve Dispersant 1 to prepare an 8% solution of Dispersant 1. Subsequently, 87.23 parts of N-methyl-2-pyrrolidone (NMP), 11.25 parts of the 8% solution of Dispersant 1 (addition amount of Dispersant 1: 0.9 part), and 0.02 part of NaOH were added to the stainless steel container, and stirred with a disper until uniform. Then, 1.5 parts of Carbon Material 4 were taken and added while stirring with a disper to obtain a carbon pre-dispersion liquid. Subsequently, a fine emulsifier screen was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), two bar magnets with a magnetic flux density of 17000 Gauss were installed in the outlet pipe of the high shear mixer, and batch dispersion was performed at a speed of 9000 rpm until the whole became uniform and the dispersion particle size became 200 μm or less as measured by a grind gauge. Magnetic separation treatment was performed simultaneously with the production of the carbon material pre-dispersion liquid (X1-20) to obtain the carbon material pre-dispersion liquid (X2-21). That is, the carbon material pre-dispersion liquid (X2-21) corresponds to the carbon material pre-dispersion liquid (X1-20), and the angle of repose is 53°, and the cumulative particle diameter D is 50 μm. 50

[0126] [Step 3] ​Subsequently, the carbon material pre-dispersion (X2-21) was fed into a stainless steel container, and a circulation type dispersion treatment with a residence time of 10 minutes was performed using a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises Co., Ltd.) filled with zirconia beads having a diameter of 1.0 mmφ. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Labo HJP-17007, manufactured by Sugino Machine) via a pipe, and a 20-pass type dispersion treatment was performed. The dispersion treatment was carried out using a single nozzle chamber at 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 Daiho Magnetic Co., Ltd., magnetic flux density 16000 gauss), and a 3-pass type treatment was performed to obtain a carbon material dispersion liquid 27.

[0127] (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 additive shown in Table 2 were changed. Subsequently, a carbon material pre-dispersion liquid (X2-22) and a carbon material dispersion liquid 28 were obtained. That is, the carbon material pre-dispersion liquid (X2-22) corresponds to the carbon material pre-dispersion liquid (X1-21), and the slip angle was 55°, and the cumulative particle diameter D 50 was 45 μm.

[0128] (Example A-23) [Step (1)], [Step (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 additive shown in Table 2 were changed.

[0129] [Step (3)] The carbon material pre-dispersion liquid (X2-11) was fed into a stainless steel container, and the dispersion liquid was supplied to a high-pressure homogenizer (Starburst Labo HJP-17007, manufactured by Sugino Machine) via a pipe, and a 20-pass type dispersion treatment was performed. The dispersion treatment was carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Subsequently, the dispersion liquid was supplied to an electromagnetic magnet (manufactured by Dabao Magnetic Co., EMF-100S, magnetic flux density 16000 Gauss), and a three-pass type treatment was performed to obtain a carbon material dispersion liquid 23.

[0130] (Examples A-24 to A-26) A carbon material pre-dispersion liquid (X1) was produced by the same method as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additive shown in Table 2 were changed. Subsequently, a carbon material pre-dispersion liquid (X2), and carbon material dispersion liquids 24 to 26 were obtained. In the carbon material dispersion liquids 24 to 26, magnetic separation treatment was not performed simultaneously with or after the dispersion of the carbon material dispersion liquid.

[0131] (Example A-27) [Step (1)], [Step (2)] A carbon material pre-dispersion liquid (X2-11) was obtained by the same method as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additive shown in Table 2 were changed.

[0132] [Step 3] Subsequently, the carbon material pre-dispersion liquid (X2-11) was fed into a stainless steel container, and a circulation type dispersion treatment with a residence time of 10 minutes was performed using a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises Co., Ltd.) filled with zirconia beads having a diameter of 1.0 mmφ. Next, the carbon material pre-dispersion liquid was fed into the stainless steel container, and the dispersion liquid was supplied to a high-pressure homogenizer (Starburst Labo HJP-17007, manufactured by Sugino Machine). With two bar magnets having a magnetic flux density of 17000 Gauss installed in the outlet pipe of the homogenizer, a 20-pass type dispersion treatment was performed. The dispersion treatment was performed using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain a carbon material dispersion liquid 27.

[0133] (Example A-28) A carbon material dispersion liquid 28 was obtained by the same method as in Example A-27, except that the carbon material pre-dispersion liquid shown in Table 2 was changed to a carbon material pre-dispersion liquid (X2-12).

[0134] (Comparative Example A-1) [Step (1)] A carbon material pre-dispersion (X1-1) was obtained in the same manner as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additive shown in Table 2 were changed. The slip angle of the pre-dispersion (X1-1) was 67°, and the cumulative particle diameter D 50 was 43 μm.

[0135] [Step (3)] Subsequently, the carbon material pre-dispersion (X1-1) was fed into a stainless steel container, and a circulation-type dispersion treatment with a residence time of 10 minutes was performed using a bead mill (Dyno Mill MULTI LAB, manufactured by Shinmaru Enterprises Co., Ltd.) filled with zirconia beads having a diameter of 1.0 mmφ. Subsequently, the dispersion liquid was supplied from the stainless steel container to a high-pressure homogenizer (Starburst Labo HJP-17007, manufactured by Sugino Machine) via a pipe, and a 20-pass type dispersion treatment was performed. The dispersion treatment was performed using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa to obtain Comparative Carbon Material Dispersion Liquid 1. Comparative Carbon Material Dispersion Liquid 1 does not perform the magnetic separation treatment in Step (2).

[0136] (Comparative Example A-2) [Step (1)] 94.6 parts of N-methyl-2-pyrrolidone (NMP) and 5.0 parts of an 8% solution of Dispersant 1 (0.4 part of Dispersant 1 added) were added to a stainless steel container and stirred with a disper until uniform. Thereafter, 0.4 part of Carbon Material 7 was weighed and added while stirring with a disper. A fine emulsifier screen was attached to a high shear mixer (L5M-A, manufactured by SILVERSON), and batch-type dispersion was performed at a speed of 9000 rpm until the whole became uniform and the dispersion particle size became 200 μm or less as measured by a grind gauge. Then, the content of the above stainless steel container was fed, and the dispersion liquid was supplied to a high-pressure homogenizer (Starburst Labo HJP-17007, manufactured by Sugino Machine) via a pipe, and a 3-pass type dispersion treatment was performed to obtain a pre-dispersion (X'1-1). The slip angle of the pre-dispersion liquid (X’1-1) was 80°, and the cumulative particle size D 50 was 11 μm.

[0137] [Step (2)] Subsequently, an electromagnet (manufactured by Dabo Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 gauss) was passed through three times to prepare a carbon material pre-dispersion liquid (X’2-1).

[0138] Subsequently, the above carbon material pre-dispersion liquid (X’2-1) was fed into a stainless steel container, and the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Turbo HJP-17007, manufactured by Sugino Machine) via a pipe, and a 20-pass dispersion treatment was performed to obtain Comparative Carbon Material Dispersion Liquid 2. The dispersion treatment was performed using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0139] (Comparative Example A-3) [Step (1)] A carbon material pre-dispersion liquid (X1-1) was obtained in the same manner as in Example A-1, except that the magnetic separation conditions, carbon material, dispersant, and additive shown in Table 2 were changed.

[0140] [Step (3)] Subsequently, the carbon material pre-dispersion liquid (X1-1) was fed into a stainless steel container, and the liquid to be dispersed was supplied to a high-pressure homogenizer (Starburst Turbo HJP-17007, manufactured by Sugino Machine) via a pipe, and a 10-pass dispersion treatment was performed. The dispersion treatment was performed using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa. Subsequently, the liquid to be dispersed was supplied to an electromagnet (manufactured by Dabo Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 gauss), and a 3-pass treatment was performed to obtain Comparative Carbon Material Dispersion Liquid 3. Comparative Carbon Material Dispersion Liquid 3 did not undergo the magnetic separation treatment in Step (2).

[0141]

Table 2-1

[0142]

Table 2-2

[0143]

Table 2-3

[0144] From the results in Table 2, a carbon material pre-dispersion liquid with a sliding angle of less than 70° and a cumulative particle size D 50 of 20 μm or more was produced, and by removing metallic magnetic foreign substances simultaneously with and / or after the production, it was confirmed that the magnetic separation efficiency was high and the metallic magnetic foreign substances could be reduced. Furthermore, the carbon material dispersion liquid of the obtained example was excellent in stability over time. On the other hand, when performing the magnetic separation treatment, if the pre-dispersion liquid does not satisfy a sliding angle of less than 70° and a cumulative particle size D 50 of 20 μm or more, the reduction of metallic magnetic foreign substances was insufficient. This is presumably because the wettability of the carbon material pre-dispersion liquid (X1) with respect to the magnetic separator was poor, so the carbon material pre-dispersion liquid (X1) adhered to the magnetic separator and the magnetic force weakened.

[0145] (Example B-1) (Preparation of Electrode Slurry 1) In a plastic container with a volume of 150 cm 3 , 18.8 parts by mass of an NMP solution in which 8% by mass of PVDF (polyvinylidene fluoride, manufactured by Solvey, Solef#5130) was dissolved and 5.8 parts by mass of NMP were weighed. Then, 13.3 parts by mass of the carbon material dispersion liquid 1 with evaluated stability was added, and using a rotation-revolution mixer (Avatorem, ARE-310), it was stirred at 2000 rpm for 30 seconds. Furthermore, thereafter, 98.1 parts by mass of a positive electrode active material (manufactured by BASF Toda Battery Materials Co., Ltd., HED (registered trademark) NCM-111 1100) was added, and using a rotation-revolution mixer (Avatorem, ARE-310), it was stirred at 2000 rpm for 2.5 minutes to obtain Electrode Slurry 1.

[0146] (Preparation of Electrode 1) ​Electrode slurry 1 was applied to the electrode using an applicator so that the amount of electrode 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.

[0147] <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.

[0148] <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.

[0149] <Preparation of secondary battery 1> The electrode 1 was punched out to 45 mm × 40 mm, the standard negative electrode was punched out to 50 mm × 45 mm, and the separator (porous polypropylene film) inserted therebetween was inserted into an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. Thereafter, in a glove box filled with argon gas, an electrolytic solution (a mixed solvent prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate at a ratio of 1:1:1 (volume ratio), and further, as an additive, 2 parts by mass of VC (vinylene carbonate) was added to 100 parts by mass of the mixed solvent, and then LiPF6 was dissolved at a concentration of 1 M to prepare a non-aqueous electrolytic solution) was injected in an amount of 2 mL, and then the aluminum laminate was sealed to fabricate a secondary battery 1.

[0150] (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 fabricated in the same manner as the fabrication of the laminate-type lithium ion secondary battery (secondary battery 1), except that the carbon material dispersion liquid listed in Table 3 was changed.

[0151]

Table 3

[0152] As shown in Table 3, a carbon material pre-dispersion liquid (X1) having a sliding angle of less than 70° and a cumulative particle diameter D 50 of 20 μm or more was fabricated, and metal magnetic foreign matters were removed simultaneously with and / or after the fabrication. A battery equipped with an electrode using the obtained carbon material dispersion liquid had good cycle characteristics.

[0153] On the other hand, Comparative Example A-1 not having a step of removing metal magnetic foreign matters, a carbon material dispersion liquid Comparative Example A-2 fabricated using a carbon material pre-dispersion liquid not satisfying a sliding angle of less than 70° and a cumulative particle diameter D 50 of 20 μm or more, and a battery using the carbon material dispersion liquid of Comparative Example A-3 in which magnetic separation treatment was not performed on the carbon material pre-dispersion liquid and only magnetic separation treatment was performed on the carbon material dispersion liquid all had poor cycle characteristics.

[0154] As a result, a vehicle having the secondary battery of the present invention has high charge and discharge performance and excellent high-temperature cycle characteristics, so it can be seen that a vehicle with high safety and improved fuel efficiency can be obtained.

[0155] The present invention has been described with reference to the above embodiments, but the present invention is not limited thereto. 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

Claim 1 A method for producing a carbon material dispersion liquid comprising all of the following steps (1) to (3): A method for producing a carbon material dispersion liquid containing a carbon material, a dispersant, and a solvent. [Step (1)] A step of obtaining a carbon material pre-dispersion liquid (X1) having a sliding angle with respect to a metal substrate of less than 70° and a cumulative particle diameter D ５０ of 20 μm or more [Step (2)] A step of removing metal magnetic foreign substances 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 Claim 2 The method for producing a carbon material dispersion liquid according to Claim 1, wherein the solvent is a non-aqueous solvent. Claim 3 The method for producing a carbon material dispersion liquid according to Claim 1, further comprising a step of removing metal magnetic foreign substances simultaneously with and / or after the dispersion of the carbon material pre-dispersion liquid (X2). Claim 4 A method for producing an electrode slurry, wherein an active material is mixed with the carbon material dispersion liquid produced by the method according to any one of Claims 1 to 3. Claim 5 A method for producing an electrode, comprising a step of coating the electrode slurry produced by the method according to Claim 4 on a current collector to form an electrode film. Claim 6 A method for producing a secondary battery, comprising a step of coating the electrode slurry produced by the method according to Claim 4 on a current collector to form an electrode film.

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