Carbon material dispersion composition, mixture slurry, electrode film, secondary battery, and vehicle

Abstract

To provide a carbon material dispersion composition capable of providing excellent battery performance.SOLUTION: A carbon material dispersion composition comprises a carbon material, a dispersant, and a liquid medium, satisfying the following (1) to (3): (1) The number of metal foreign particles of 20 μm or more determined by the following condition 1 is 100 or less. (2) The cumulative particle diameter D90 of dispersed particles in the carbon material dispersion composition by laser diffraction / scattering method is 0.5 to 5 μm. (3) The maximum flow rate in a pressure filtration test at 0.06 MPa pressure using a membrane filter with a diameter of 47 mm and mesh opening of 5 μm is 0.00375 to 0.0375 m / s.<Condition 1>The carbon material dispersion composition is filtered through a filter with a mesh opening of 15 μm to obtain X-ray transmission distribution of the filter after filtration, and the size and number of metal foreign particles are measured from the X-ray transmission distribution based on the X-ray permeability of the material.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a carbon material dispersion composition, a composite slurry, an electrode film, a secondary battery, and a vehicle.

Background Art

[0002] With the popularization of electric vehicles and the miniaturization, light weight, and high performance of portable devices, there is a demand for secondary batteries having a high energy density, and further, an increase in the capacity of such secondary batteries. Under such circumstances, non-aqueous electrolyte secondary batteries using non-aqueous electrolytes, particularly lithium ion secondary batteries, have come to be used in many devices due to their characteristics of high energy density and high voltage.

[0003] As negative electrode materials used in these lithium ion secondary batteries, carbon materials typified by graphite, which have a low potential close to lithium (Li) and a large charge-discharge capacity per unit mass, are used. However, these electrode materials are used up to a point where the charge-discharge capacity per mass is close to the theoretical value, and the energy density per mass of the battery is approaching its limit. Therefore, in order to increase the utilization rate of the electrode, studies are underway to reduce conductive aids and binders that do not contribute to the discharge capacity.

[0004] The conductive aid plays a role of forming a conductive path inside the electrode, and it is required that it is not easily cut by the expansion and contraction of the electrode film. In order to maintain the conductive path with a small amount of conductive aid, it is effective to use a carbon material having a large specific surface area, particularly carbon nanotubes, which are a type of nanocarbon. However, although batteries using carbon materials have excellent output characteristics, metal foreign substances derived from metal catalysts used in the synthesis of carbon materials often remain, and there has been a problem of voltage drop failure.

[0005] In addition, the metal foreign particles contained in the carbon material dispersion composition may dissolve inside the secondary battery, precipitate in a dendrite shape, pierce through the separator, and cause internal short circuits. Furthermore, if the content of metal foreign particles is high, the electrolytic solution and the active material are likely to deteriorate due to high-temperature charge and discharge of the secondary battery, and the deterioration of the high-temperature cycle characteristics becomes a problem. Therefore, it is required to reduce the amount of metal foreign particles contained in the carbon material dispersion composition.

[0006] Therefore, in Patent Document 1, a method of crushing carbon nanotubes containing metal foreign particles such as iron, cobalt, and nickel and removing the metal foreign particles of the carbon nanotubes using an electromagnet has been studied.

[0007] In Patent Documents 2 and 3, a technique for removing metal foreign particles of carbon nanotubes by dispersing the carbon nanotubes, crushing them, and then attaching the metal foreign particles to a magnet is disclosed.

[0008] In addition, in Patent Document 4, a method of removing metal foreign particles is proposed by circulating a dispersion containing a conductive assistant through a primary filter multiple times in a circulation system and then arranging at least two filters in series and passing them through once.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0010] However, the conventional methods such as those described in Patent Documents 1 to 4 have limitations in reducing the metal content in the carbon material dispersion composition. In response to the demand for high performance and miniaturization of secondary batteries, the adverse effects of contamination of electrode films of secondary batteries with foreign metal particles may become more serious. Furthermore, there is a risk of problems such as an increase in viscosity due to the inhibition of dispersion stability by foreign metal particles, and insufficient characteristics when used as a secondary battery.

[0011] Therefore, one of the problems to be solved by the present invention is to provide a carbon material dispersion composition capable of providing excellent battery performance, a composite slurry containing the same, and an electrode film using the same. More specifically, it is to provide a secondary battery having excellent rate characteristics and high-temperature cycle characteristics, and a vehicle having the secondary battery, which is highly safe and has improved fuel efficiency. [Means for solving the problem]

[0012] The present inventor has conducted intensive research to solve the above problems. The present inventor has found that a carbon material dispersion composition containing a carbon material, a dispersant, and a liquid medium, having 100 or less metal foreign particles of 20 μm or more as determined under condition 1 described below, and having a specified cumulative particle diameter D90 of the dispersed particles and a maximum flow rate in a pressure filtration test, can suppress internal short circuiting in a secondary battery and can also provide dispersion stability of the carbon material dispersion composition. In addition, the inventor has found that a highly reliable electrode film can be obtained by using such a carbon material dispersion composition. Furthermore, the inventor has found that a secondary battery obtained by using this composition is suppressed from causing an internal short circuit and has excellent reliability. Based on such findings, the present inventor has come up with the present invention.

[0013] That is, the present invention includes the following embodiments, but the embodiments of the present invention are not limited to the following. [1] A carbon material dispersion composition comprising a carbon material, a dispersant, and a liquid medium, the carbon material dispersion composition satisfying the following (1) to (3): (1) The number of metallic foreign particles having a size of 20 μm or more, as determined by the following condition 1, is 100 or less. (2) The cumulative particle size D90 of the dispersed particles of the carbon material dispersion composition by the laser diffraction / scattering method is 0.5 to 5 μm. (3) The maximum flow rate is 0.00375 to 0.0375 m / s by the pressure filtration test at a pressure of 0.06 MPa using a membrane filter with a diameter of 47 mm and an opening of 5 μm. <Condition 1> Filter the carbon material dispersion composition with a filter having an opening of 15 μm to obtain the X-ray transmission distribution of the filter after filtration, and measure the size and number of metal foreign particles from the X-ray transmission distribution based on the X-ray permeability of the substance.

[0014] [2] The carbon material dispersion composition according to [1] above, wherein the total content of iron, cobalt, nickel, chromium, molybdenum, and copper is 100 ppm or less. [3] A composite material slurry containing the carbon material dispersion composition according to [1] or [2] above and an active material. [4] An electrode film formed from the composite material slurry according to [3] above. [5] A secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode has the electrode film according to [4] above. [6] A vehicle equipped with the secondary battery according to [5] above.

Advantages of the Invention

[0015] According to one embodiment of the present invention, it is possible to provide a carbon material dispersion composition capable of providing excellent battery performance, a composite material slurry containing the same, and an electrode film using the same. Furthermore, it is possible to provide a secondary battery having excellent reliability, and by having this secondary battery, it is possible to provide a vehicle with high safety and improved fuel efficiency. As a result, it can be suitably used even in vehicle applications such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles, which require high reliability, high capacity, high output, and high durability for the secondary battery to be mounted.

Embodiments for Carrying Out the Invention

[0016] Hereinafter, a carbon material dispersion composition, a composite material slurry, an electrode film, and a secondary battery according to some embodiments of the present invention will be described in detail, but the present invention is not limited thereto. In the present disclosure, the numerical values specified are values obtained by the methods disclosed in the embodiments or examples.

[0017] In the present disclosure, 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 the present disclosure, carbon nanotubes may be denoted as "CNT", and N-methyl-2-pyrrolidone may be denoted as "NMP". In the present disclosure, the carbon material dispersion composition may sometimes be referred to as the "dispersion composition". In the present disclosure, the metal foreign matter particles do not relate to the size and shape, and include fine metal powders and the like, and do not mean those existing in a dissolved state as metal ions. Unless otherwise noted, each of the various components appearing in the present disclosure may be used alone or in combination of two or more.

[0018] In the present disclosure, the carbon material dispersion composition means the state before the active material is added. In this regard, the carbon material dispersion composition is distinguished from the composite material slurry containing the active material. That is, the carbon material dispersion composition substantially does not contain the active material. This is a concept excluding the state where the active material is intentionally added to the carbon material dispersion composition. With respect to the total mass of the carbon material dispersion composition, the active material may be 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, or may be 0% by mass. The active material will be described later.

[0019] <<Carbon Material Dispersion Composition>> One embodiment of the carbon material dispersion composition is a carbon material dispersion composition containing a carbon material, a dispersant, and a liquid medium, and satisfies the following (1) to (3). (1) The number of metal foreign matter particles of 20 μm or more obtained by the following Condition 1 is 100 particles / kg or less. (2) The cumulative particle size D90 of the dispersed particle size of the carbon material dispersion composition by the laser diffraction / scattering method is 0.5 to 5 μm. (3) The maximum flow rate is 0.00375 to 0.0375 m / s by the pressure filtration test using a membrane filter with a diameter of 47 mm and an opening of 5 μm at a pressure of 0.06 MPa. <Condition 1> Filter the carbon material dispersion composition with a filter having an opening of 15 μm to obtain the X-ray transmission distribution of the filter after filtration, and measure the size and number of metal foreign particles from the X-ray transmission distribution based on the X-ray permeability of the substance.

[0020] By using this carbon material dispersion composition, internal short circuit of the secondary battery can be prevented. Hereinafter, the requirements specified by the above (1) to (3) are also referred to as requirement (1) to requirement (3), respectively.

[0021] In a secondary battery, an electrolyte is interposed between a pair of electrodes, and a separator is disposed between the pair of electrodes to prevent short circuit between the electrodes. From the viewpoints of battery performance and miniaturization of the battery, thinning of the electrodes and the separator is required. By thinning, the electrode material is more precisely controlled, and reduction of metal foreign substances that may be contained in the electrode material is also an important issue. Conventionally, the amount of metal contained in the entire electrode material has been analyzed by ICP (inductively coupled plasma) analysis. However, for more precise control, control of metal particles having a size that can cause short circuit between the electrodes is desired. For example, when metal particles with a large particle size are mixed into the electrode material, the metal particles may protrude from the surface of the electrode film in the electrode film, break through the separator, and further contact the electrode film of the counter electrode to cause an internal short circuit. Even if the frequency of such large particle size metal particles contained in the carbon material dispersion composition is very low, it can become apparent in the final product secondary battery.

[0022] According to requirement (1), by having the number of metal foreign particles of 20 μm or more obtained according to condition 1 be 100 particles / Kg or less, internal short circuit in the secondary battery can be prevented.

[0023] According to Requirement (2), since the cumulative particle diameter D90 of the dispersed particles in the carbon material dispersion composition by the laser diffraction / scattering method is in the range of 0.5 to 5 μm, internal short circuits in secondary batteries can be further prevented. According to Requirement (2), the inclusion of particles and aggregates of carbon materials having a certain size in the carbon material dispersion composition is allowed. Also, the number of metal foreign matter particles is reduced in the range of the cumulative particle diameter D90 or more compared to Requirement (1). Therefore, the particles in the range of the cumulative particle diameter D90 or more have a higher proportion of carbon materials and the like other than metal and are relatively soft materials. Even if metal foreign matter particles of 20 μm or more are included within the range of Requirement (1), since carbon materials and the like having a relatively large size can be included within the range of Requirement (2), the metal foreign matter particles can be coated with carbon materials and the like in the electrode film, and the exposure of the metal surface from the surface of the electrode film can be suppressed. As a result, even if metal foreign matter particles are included in the range of the cumulative particle diameter D90 or more, short circuits between the electrodes can be prevented by the carbon materials and the like in the same range.

[0024] According to Requirement (3), the maximum flow rate is 0.00375 to 0.0375 m / s by a pressure filtration test using a membrane filter with a diameter of 47 mm and an aperture of 5 μm at a pressure of 0.06 MPa. Hereinafter, this requirement will also be referred to as the "maximum flow rate by the pressure filtration test". According to this Requirement (3), the dispersion stability of the carbon material dispersion composition can be obtained. In particular, sedimentation of the solid content over time can be suppressed. When dispersed particles with a cumulative particle diameter D90 or more are included within the range of Requirement (2), sedimentation of the solid content may occur in the carbon material dispersion composition. By satisfying Requirement (3), sedimentation is suppressed, and even if sedimentation occurs, redispersibility can be provided. Also, when the carbon material dispersion composition is passed through the filter again to redisperse it in the case of sedimentation, since the pressure loss is small, the redispersion treatment can be performed efficiently.

[0025] In order to satisfy requirement (1), it is preferable to subject the carbon material dispersion composition to mechanical treatments such as filtration treatment and magnetic separation treatment. In this case, by satisfying requirement (3), more efficient mechanical treatment becomes possible, and it becomes possible to provide a carbon material dispersion composition that satisfies requirement (1). Furthermore, after the carbon material dispersion composition is provided as a product, in foreign matter detection such as filtration treatment as a product inspection, the detection efficiency can be improved. Also, for the same reason, requirement (3) is useful even when filtering treatment or the like is performed on the carbon material dispersion composition to finally remove foreign matter in the process of using the product.

[0026] In the synthesis of carbon materials, metal catalysts are used depending on the manufacturing method. Metals derived from the metal catalyst may remain in the carbon material, and furthermore, the metal catalyst may be encapsulated. Metals derived from the metal catalyst encapsulated in the carbon material, wear debris that may be included when dispersing the carbon material, etc. can be included as metal foreign particles in the carbon material dispersion composition. These metals can be refined during the dispersion treatment in the manufacturing process of the carbon material dispersion composition. However, large particle diameter metal foreign particles that still remain after the dispersion treatment, metal foreign particles mixed in from the manufacturing equipment after the dispersion treatment, etc. can be mixed into the carbon material dispersion composition.

[0027] Metal foreign particles may include wear debris due to wear of the inner wall of the disperser, piping, etc. used in the dispersion process of the carbon material, and in some cases, dispersion media, stirring blades, etc. Wear debris derived from a part of piping and tanks containing SUS304, SUS316, etc. used for the disperser, piping, etc. changes its crystal structure due to an external stress applied to SUS304, SUS316, etc. and becomes metal foreign particles with magnetism. However, since the magnetism is weak, it is difficult to remove. Metal foreign particles with weak magnetism may be mixed into the carbon material dispersion composition without being completely removed by magnetic separation treatment.

[0028] As a method for producing a carbon material dispersion composition satisfying requirements (1), (2), and (3), it can be controlled by reducing the introduction of metal foreign substances derived from raw materials as much as possible, removing metal foreign substances derived from dispersion equipment and the dispersion process during the process, filtering the dispersed carbon material dispersion composition, etc. Further, the content of metal foreign substance particles can be further reduced by magnetic separation treatment using a magnet with a narrow gap between magnetic poles such as an electromagnet. Since metal foreign substance particles often have orientation, it is preferable to pass them through a magnet or a filter multiple times. These processes may be appropriately combined and controlled to satisfy requirements (1), (2), and (3).

[0029] The carbon material dispersion composition satisfies the following requirement (1). (1) The number of metal foreign substance particles of 20 μm or more determined by the following condition 1 is 100 or less. <Condition 1> Filter the carbon material dispersion with a filter having an opening of 15 μm to obtain the X-ray transmission distribution of the filter after filtration, and measure the size and number of metal foreign substance particles from the X-ray transmission distribution based on the X-ray transmissibility of the substance.

[0030] The number of metal foreign substance particles of 20 μm or more determined by this condition 1 is preferably 100 or less, and more preferably 80 or less, 60 or less, 40 or less, or 20 or less from the viewpoint of preventing the occurrence of internal short circuits. This number may be 20 or less, 15 or less, 10 or less, or 8 or less because mechanical dispersion treatment can be efficiently performed in the carbon material dispersion composition. For example, this number may be 0 to 100, 1 to 80, 2 to 60, 3 to 40, or 5 to 20.

[0031] The measurement method for requirement (1) is specifically as follows. First, pass 1 kg of the carbon material dispersion composition through a mesh filter with a mesh opening of 15 μm, collect the residue filtered by the filter together with the filter, and dry the collected filter at 60 °C until there is no further mass change. For the dried filter, obtain the X-ray transmission distribution using an X-ray transmission device. From the X-ray transmission distribution, count the number of detected particles of 20 μm or more using analysis software. As the X-ray transmission device, "Cheetah EVO" (manufactured by Comet Technology Japan Co., Ltd.) can be used. The measurement conditions of the X-ray transmission device are a tube voltage of 60 kV and a tube current of 40 μA. As the analysis software, Winroof can be used. Specifically, it can be measured according to the method of the examples.

[0032] In the measurement method for requirement (1), based on the X-ray permeability of the substance, it is determined whether it is a metal from the threshold of the image density of the X-ray transmission distribution. The threshold of the image density is determined by pre-evaluating the X-ray permeability and image density of the metal and carbon nanotubes. The particle size is the value obtained by measuring the major axis of the shape of the particles determined to be metal from the image of the X-ray transmission distribution.

[0033] The carbon material dispersion composition satisfies the following requirement (2). (2) The cumulative particle size D90 of the dispersed particle size of the carbon material dispersion composition by the laser diffraction / scattering method is 0.5 to 5 μm.

[0034] The carbon material dispersion composition preferably has a cumulative particle size D90 of 0.5 to 5 μm. More preferably, it is 0.8 to 4 μm, and even more preferably, it is 1 to 2 μm. If the cumulative particle size D90 is within this range, short circuit can be prevented when a secondary battery is formed. Furthermore, the dispersion stability over time can be made more excellent. If the cumulative particle size D90 is large, the particles are likely to settle, and the stability over time may deteriorate. Also, if the cumulative particle size D90 is too small, the particles are unstable, the particles aggregate with each other, and are likely to settle, so the stability over time may deteriorate. Although it is difficult to distinguish whether the dispersed particles in the range where D90 is 5 μm or more are metal foreign matter particles or carbon material particles, in one embodiment, the size and number of metal foreign matter particles can be evaluated using the X-ray transmission distribution.

[0035] The cumulative particle size D90 is determined from the volume-based particle size distribution curve measured by the laser diffraction / scattering particle size distribution measurement method. Specifically, it can be measured according to the method of the examples.

[0036] The carbon material dispersion composition satisfies the following requirement (3). (3) The maximum flow rate is 0.00375 to 0.0375 m / s by a pressure filtration test at a pressure of 0.06 MPa using a membrane filter with a diameter of 47 mm and an opening of 5 μm.

[0037] Within the above range, the dispersion stability of the carbon material contained in the carbon material dispersion composition is appropriate. It is considered that the carbon material dispersion composition satisfying requirement (3) within the above range has an appropriate composition ratio and dispersion process of the carbon material, dispersant, and liquid medium, and good dispersion stability. Furthermore, it is easy to remove metal foreign matter particles using a filter, electromagnet, etc. In the case where the dispersibility of the carbon material dispersion composition decreases, sedimentation occurs and re-dispersion treatment is performed, or in the case where metal foreign matter particles are detected in the carbon material dispersion composition during product inspection and re-metal removal treatment is performed, etc., the carbon material dispersion composition is designed to be easily subjected to a filter, electromagnet, etc.

[0038] The measuring method of Requirement (3) is specifically as follows. A tank equipped with a mesh filter with a diameter of 47 mm and an aperture of 5 μm is filled with the carbon material dispersion composition, and while applying a pressure of 0.06 MPa, the mass of the carbon material dispersion composition discharged at each time is measured. Assuming the density of the carbon material dispersion composition is 1 g / cm 3 ³, the maximum flow rate is calculated from the time-dependent mass of the discharged carbon material dispersion composition. The volume of the carbon material dispersion composition contained in the tank is preferably 100 g to 200 g. Specifically, it can be measured according to the method of the examples.

[0039] According to Requirements (1), (2) and (3), the number of metal foreign particle with a size that affects the short circuit of the secondary battery is limited, and while preventing the short circuit of the secondary battery, the dispersion stability of the carbon material dispersion composition can be improved. On the other hand, when it is subjected to the dispersion treatment in a state including metal foreign particles contained in the raw material of the carbon material, metal foreign particles mixed in from the manufacturing process, etc., these metal foreign particles can be refined. The refined metal foreign particles are difficult to be removed from the carbon material dispersion composition even through magnetic separation treatment and filter treatment, and may cause an increase in the total metal amount in the final product. Therefore, it is preferable to remove large-sized metal foreign particles from the pre-dispersion composition of the carbon material before, during, or in a combination of these, the dispersion treatment. The removal method may be magnetic separation treatment, filter treatment, or a combination thereof. Thereby, a carbon material dispersion composition with a lower total metal amount can be provided.

[0040] The total content of iron, cobalt, nickel, chromium, molybdenum and copper in the carbon material dispersion composition is preferably as small as possible, and is preferably 100 ppm or less by mass ratio. More preferably, it is 50 ppm or less, and even more preferably, it is 10 ppm or less. When the number of metal foreign particles of 20 μm or more obtained by Condition 1 is 100 or less and the total content of iron, cobalt, nickel, chromium, molybdenum and copper is within the above range, the voltage failure of the secondary battery can be more suppressed.

[0041] The contents of iron, cobalt, nickel, chromium, and molybdenum are each preferably 10 ppm or less, more preferably 5 ppm or less, and even more preferably 1 ppm or less. Further, the copper content is preferably 5 ppm or less, more preferably 1 ppm or less, and even more preferably 0.1 ppm or less.

[0042] Iron, cobalt, nickel, and molybdenum are used as catalyst raw materials in the production of carbon nanotubes. Since carbon nanotubes are produced in a reducing atmosphere, the above-mentioned iron, cobalt, nickel, and molybdenum exist in the form of pure metals encapsulated in the carbon nanotubes. Because of their low oxidation potential, they dissolve in the electrolyte and precipitate on the negative electrode surface, which may lead to voltage problems and capacity reduction in secondary batteries. Also, iron, nickel, and chromium may come from the wear powder of tanks and stirrers for producing the carbon material dispersion composition, and copper may be mixed in from motors of dispersion equipment, etc. Among these, copper has a low oxidation-reduction potential, dissolves in the electrolyte, and precipitates dendritically on the negative electrode surface, which may lead to voltage problems in secondary batteries. As described above, these metals are preferably removed before or during the dispersion treatment. If these metals remain after the dispersion treatment with large particle sizes, they may be removed by filtration, magnetic separation treatment, etc.

[0043] The amounts of these metal elements can be measured, for example, by ICP emission spectrometry. Specifically, they can be measured according to the method of the examples.

[0044] The content rate of the carbon material contained in the carbon material dispersion composition is preferably 1% by mass or more and 10% by mass or less (with the mass of the carbon material dispersion composition being 100% by mass), more preferably 2% by mass or more and 8% by mass or less, and even more preferably 3% by mass or more and 6% by mass or less, based on the mass of the carbon material dispersion composition.

[0045] The content of the dispersant is preferably 5 parts by mass or more and 200 parts by mass or less, more preferably 10 parts by mass or more and 100 parts by mass or less, and even more preferably 20 parts by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the carbon material. When the amount of the dispersant is within the above range, the dispersion stability of the carbon material in the carbon material dispersion composition tends to be good. Also, the peel strength of the electrode for the secondary battery becomes good.

[0046] The content rate of the liquid medium is preferably 90% by mass to 99% by mass, more preferably 92% by mass to 98% by mass based on the carbon material dispersion composition (100% by mass). When it is within the above range, a carbon material dispersion composition excellent in fluidity and dispersion stability is likely to be obtained. By using a carbon material dispersion composition excellent in fluidity and dispersion stability, it is easy to remove metal foreign matters, an electrode film having stable conductivity can be obtained, and the quality of the secondary battery is likely to be stable.

[0047] When an organic solvent is used as the liquid medium in the carbon material dispersion composition, it is preferably substantially free of moisture from the viewpoint of suppressing thickening of the carbon material. The carbon material dispersion composition preferably has a moisture content of 10 ppm or more and 3000 ppm or less, more preferably 100 ppm or more and 1500 ppm or less, and even more preferably 200 ppm or more and 1000 ppm or less. When the moisture content of the carbon material dispersion composition is within the above range, gelation of the composite slurry described later is suppressed, and a composite slurry and an electrode film of stable quality are likely to be obtained. When the moisture content exceeds the above range, the metal encapsulated in the carbon material may dissolve during the dispersion treatment, making it difficult to remove metal foreign matters in the manufacturing process. The carbon material dispersion composition may contain an organic solvent and be substantially free of moisture.

[0048] <Carbon material> The carbon material in this embodiment is not particularly limited. Examples of the conductive carbon material include graphite, carbon black; or fibrous carbon materials such as carbon nanotubes and carbon nanofibers. These may be used alone or in combination of two or more. Examples of graphite include artificial graphite, flaky graphite, massive graphite; natural graphite such as earthy graphite. The carbon material plays a role of forming a conductive path inside the electrode, and from the viewpoint that it is not easily cut due to the expansion and contraction of the electrode film, it is preferably included a fibrous carbon material, and more preferably 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 of the same kind with different physical properties may be used in combination. Examples of carbon materials of the same kind with different physical properties include, for example, 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.

[0049] 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 mass% of the carbon material, 90 mass% or more is preferable, 95 mass% or more is more preferable, 98 mass% or more is still more preferable, and 99 mass% or more is particularly preferable. By setting the carbon purity within the above range, problems such as dendrite formation and short circuit caused by impurities such as metals can be prevented.

[0050] <Carbon black> Carbon black is fine particles mainly composed of carbon and is manufactured by controlling various properties through the incomplete combustion of 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 secondary structures are further aggregated. The secondary and tertiary structures are collectively referred to as the structure. When observing primary particles with an electron microscope or the like, they appear spherical, but primary particles are not chemically independent individuals. They are connected by chemical bonds to adjacent primary particles within the aggregate to form a secondary structure. On the other hand, 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 secondary structures including contact resistance, and it is effective to obtain an electrode with excellent conductivity by deaggregating the tertiary structure while maintaining the structure of the secondary structure as much as possible. Note that the secondary structure may sometimes be simply referred to as "structure".

[0051] As carbon black, various types such as acetylene black, furnace black, hollow carbon black, channel black, thermal black, and ketjen black can be used. Also, commonly used oxidized carbon black or graphitized carbon black can be used.

[0052] The oxidation treatment of carbon black is a treatment in which carbon black is heat-treated in air or secondarily treated with nitric acid, nitrogen dioxide, ozone, etc., to directly introduce (covalently bond) oxygen-containing polar functional groups such as phenolic groups, quinone groups, carboxyl groups, and carbonyl groups onto the carbon black surface. It is generally carried out to improve the dispersibility of carbon black.

[0053] Examples of commercially available carbon blacks include, but are not limited to, 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. Two or more of these may be combined and used.

[0054] The average primary particle diameter of the 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 the carbon black can be calculated by first observing and imaging the carbon black with a transmission electron microscope, and then selecting any 100 spherical carbon black primary particles in the observation photograph and measuring their respective outer diameters.

[0055] The BET specific surface area of the 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 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. As a result, 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, the composite of the active material and the carbon black tends to proceed, so it is easy to obtain an electrode film having a homogeneous conductive network in which the surface of the active material is covered with carbon black, 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.

[0056] <Carbon Nanotube> Carbon nanotubes have a structure in which planar graphite is wound into a cylindrical shape, including single-walled carbon nanotubes and multi-walled carbon nanotubes, and these may be mixed. Among them, it is preferable to include multi-walled carbon nanotubes. Multi-walled carbon nanotubes have a structure in which two or more layers of graphite are wound, and single-walled carbon nanotubes have a structure in which one layer of graphite is wound. The side wall of the carbon nanotube does not necessarily have to be a graphite structure. For example, carbon nanotubes having side walls with an amorphous structure can also be used as carbon materials.

[0057] 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, it is easy to form a good conductive network in the electrode, and during charge and discharge, the active material inside the secondary battery is uniformly utilized, so the deterioration of the active material is suppressed and the cycle characteristics of the secondary battery are further improved.

[0058] The BET specific surface area of the carbon nanotubes is 2 100 m 2 / g or more and 1000 m 2 / g or less, more preferably 170 m 2 / g or more and 600 m 2 / g or less, and even more preferably 200 m 2 / g or more and 500 m / 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 easily, so that an electrode film having a homogeneous conductive network in which the surface of the active material is coated with the carbon nanotubes can be 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.

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

[0060] The volume resistivity of the carbon nanotube is preferably 1.0×10 -2 Ω·cm to 3.0×10 -2 Ω·cm, and more preferably 1.0×10 -2 Ω·cm to 2.0×10 -2 Ω·cm. The volume resistivity of the carbon nanotube can be measured using a powder resistivity measuring device (manufactured by Mitsubishi Chemical Analytech Co., Ltd.: Loresta GP Powder Resistivity Measuring System MCP-PD-51). When the volume resistivity is within the above range, the conductivity of the electrode film becomes good, and a secondary battery having excellent rate characteristics and cycle characteristics can be obtained.

[0061] The carbon nanotube is preferably one from which metal foreign particles have been removed by using an electromagnet and magnetic force. For example, it is preferable to set an electromagnet in the pulverization process or filling process of the carbon nanotube and pass the carbon nanotube through it to remove the metal foreign particles.

[0062] The higher the carbon purity of the carbon nanotubes, the more preferable it is. Preferably, it is 98.0% by mass or more, more preferably 99.5% by mass or more, still more preferably 99.8% by mass or more, and particularly preferably 99.9% by mass or more in 100% by mass of the carbon nanotubes. That is, the lower the content rate of metal foreign particles, the more preferable it is. Preferably, it is 2.0% by mass or less, more preferably 0.5% by mass or less, still more preferably 0.2% by mass or less, and particularly preferably 0.1% by mass or less in 100% by mass of the carbon nanotubes. By using carbon nanotubes produced by a production method that does not use a metal catalyst as a core, or carbon nanotubes obtained by a conventional purification treatment method such as acid treatment, the content rate of metal foreign particles can be made 2.0% by mass or less with respect to 100% by mass of the carbon nanotubes, the content of metal foreign particles contained in the carbon material dispersion composition can be reduced, and various characteristics of the secondary battery can be improved. The carbon purity of the carbon nanotubes can be measured by an ICP emission spectroscopic analyzer. Specifically, it can be measured according to the method in the examples.

[0063] <Dispersant> The dispersant 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. A suitable type of dispersant can be used in a suitable blending amount according to the characteristics required for the dispersion of the carbon material.

[0064] 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 salt, and sodium salt of β-naphthalene sulfonic acid formalin condensate can be mentioned, but are not limited thereto.

[0065] Also, as cationic surfactants, there are alkylamine salts and quaternary ammonium salts. Specifically, stearylamine acetate, trimethyl coconut ammonium chloride, trimethyl tallow ammonium chloride, dimethyldioleyl ammonium chloride, methyloleyl diethanol chloride, tetramethylammonium chloride, lauryl pyridinium chloride, lauryl pyridinium bromide, lauryl pyridinium disulfate, cetyl pyridinium bromide, 4-alkyl mercaptopyridine, poly(vinyl pyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride can be mentioned, but are not limited thereto. Also, as amphoteric surfactants, aminocarboxylate salts can be mentioned, but are not limited thereto.

[0066] 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.

[0067] 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 preferred. The anionic surfactant is preferably a polycarboxylate. The nonionic surfactant is preferably polyoxyethylene phenyl ether.

[0068] 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. Particularly preferred are fluororesins, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, hydrogenated nitrile butadiene rubber, and polyacrylonitrile-based polymers. From the viewpoint of achieving both the temporal stability of the carbon material and the efficiency of removing metal magnetic foreign substances by magnetic separation treatment, the molecular weight of the resin-type dispersant is preferably from 10,000 to 300,000.

[0069] From the viewpoint of oxidation resistance, hydrogenated nitrile butadiene rubber and polyacrylonitrile-based polymers are preferred as the dispersant.

[0070] 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, and ammonia and quaternary ammonium compounds are not included. In addition to monoamines, amine compounds having a plurality of amino groups in the molecule, such as diamines, triamines, and tetraamines, can be used as the amine-based compound. 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, and alicyclic nitrogen-containing heterocyclic compounds such as hexamethylenetetramine, morpholine, and piperidine can be mentioned, but are not limited thereto. Examples of the inorganic base include hydroxides of alkali metals, hydroxides of alkaline earth metals, carbonates of alkali metals, carbonates of alkaline earth metals, phosphates of alkali metals, and phosphates of alkaline earth metals.

[0071] 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 still 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.

[0072] <Liquid medium> The liquid medium is not limited as long as it can disperse the carbon material, and may be water or an organic solvent. Examples of the organic solvent may include amide-based organic solvents, alcohol-based organic solvents, etc. Examples of the alcohol-based organic solvents may include ethanol, propanol, butanol, methyl cellosolve, butyl cellosolve, propylene glycol monomethyl ether, etc.

[0073] Since the aqueous solvent may corrode the magnet, weaken the magnetic force of the magnet, and generate metal magnetic foreign substances, by using an amide-based organic solvent, the content of metal magnetic foreign substances in the carbon material dispersion can be reduced.

[0074] Examples of the amide-based organic solvents may include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc. In particular, it is preferably included at least one selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0075] <Optional component> The carbon material dispersion composition may optionally contain other additives such as alkali metal hydroxides, wetting agents, pH adjusters, wetting and penetrating agents, leveling agents, etc., and optional components such as other conductive materials other than carbon nanotubes, as long as the object of the present invention is not impaired. The optional components can be added at any timing, such as before the preparation of the carbon material dispersion composition, during mixing, after mixing, or a combination thereof.

[0076] Examples of the alkali metal hydroxides may include lithium hydroxide, sodium hydroxide, potassium hydroxide, etc. When using an alkali metal hydroxide, its content is preferably 0.5 parts by mass or more and 4 parts by mass or less, more preferably 1 part by mass or more and 3 parts by mass or less, and even more preferably 1.5 parts by mass or more and 2.5 parts by mass or less, based on 100 parts by mass of the dispersant. When an alkali metal hydroxide is used, the wettability of the carbon nanotubes is improved, and the dispersibility is further improved. In addition, since the dispersion proceeds to the target viscosity in a short time, there are few defects in the carbon nanotubes, and it is easy to obtain an electrode film and a secondary battery with good conductivity.

[0077] <Method for producing carbon material dispersion composition> The carbon material dispersion composition of the present embodiment is obtained by dispersing a mixture containing a carbon material, a dispersant, and a liquid medium with a disperser. The production method is not particularly limited, but it preferably includes a step of applying a shear stress to the carbon material to crush the carbon material, and a step of removing magnetic foreign substances for removing metal foreign particles in the carbon material dispersion composition, such as a magnetic separation step, a filtration step using a filter, and a centrifugation step. As these metal foreign particle removal steps, at least one of a magnetic separation step and a filtration step is preferable. The metal foreign particle removal step may be at any timing, such as before, during, or after the dispersion of the carbon material dispersion composition. It is preferable to remove the metal foreign particles before they are refined by the dispersion step, and it is preferable to include a metal foreign particle removal step before and / or during the dispersion of the carbon material dispersion composition.

[0078] Note that a method for producing a carbon material dispersion composition including the following steps (1) to (3) is preferable. Step (1) Crushing step: A step of applying a shear force to the carbon material to crush the carbon material. Step (2) Magnetic separation step: A step of removing metal foreign particles using an electromagnet. Step (3) Filtration step: A step of filtering using a filter.

[0079] The order of step (1), step (2), and step (3) is not particularly limited, and the metal foreign matter removal steps of step (2) and step (3) may be before, simultaneous with, or a combination of these before and after step (1). Preferably, each step is provided in the order of step (1), step (2), and step (3), or step (1) and step (2) are performed simultaneously, and then the step of step (3) is provided.

[0080] Thereby, in step (1) the crushing step, the metal foreign matter particles encapsulated in the carbon material are exposed, and then or simultaneously in step (2) the magnetic separation step, the magnetic metal foreign matter particles can be removed by bringing them into contact with a magnet. Subsequently, in step (3) the filtration step, metal foreign matter particles with weak magnetism (such as those with a large particle size but weak magnetism, or those with a particle size that is too small and has a low magnetic attachment area and cannot be caught by the magnet and flow away with the liquid) that cannot be completely removed by the magnet can be removed.

[0081] [Step of crushing carbon material] In the step of applying a shearing force to the carbon material to crush the carbon material, the carbon material can be subjected to a crushing treatment by a dispersion device or the like in a dry and / or wet manner.

[0082] The dispersion device used for crushing the carbon material is not particularly limited. As the dispersing device, a disperser commonly used for pigment dispersion or the like can be used. For example, mixers such as a disper, a homomixer, a planetary mixer, homogenizers (Advanced Digital Sonifer (registered trademark), MODEL 450DA manufactured by BRANSON, "Claremix" manufactured by M. TECHNIQUE, "Filmix" manufactured by PRIMIX, "Abramix" manufactured by SILVERSON, etc.), paint cons ( "Colloid Mill MK" manufactured by IKA), media type dispersers such as a cone mill ("Cone Mill MKO" manufactured by IKA, a disshoner (manufactured by Red Devil), "PUC Colloid Mill" manufactured by PUC), a ball mill, a sand mill ("Dynomill" manufactured by Shinmaru Enterprises, etc.), an attritor, a pearl mill ("DCP Mill" manufactured by Ehrlich, etc.), a coball mill, high-pressure homogenizers ("Genius PY" manufactured by Genius, "Starburst" manufactured by Sugino Machine, "Nanomizer" manufactured by Nanomizer, etc.), media-less dispersers such as "Clare SS-5" manufactured by M. TECHNIQUE, "MICROS" manufactured by Nara Machinery, and other roll mills, etc. can be mentioned, but it is not limited to these.

[0083] Since it is desirable that the mixing of wear powder during the crushing process is less, a media-less disperser is preferred. The rotor and stator of the dispersing device are preferably made of ceramics. When using a bead mill in wet dispersion, the dispersion medium is also preferably made of ceramics. When using a bead mill as a wet dispersing device, it is preferably used after applying shear stress to the carbon material in advance using a media-less disperser to crush the carbon material before the dispersion treatment by the bead mill. This is because when the bead mill is operated at a high circumferential speed for a low-viscosity dispersion material in which the crushing of the carbon material has not progressed, the beads are likely to wear. Also, when using a high-pressure homogenizer as the dispersing device, if there is wear powder of beads during the dispersion process, there is a risk of nozzle clogging or valve breakage of the high-pressure homogenizer.

[0084] In order to obtain the size and number of metal foreign particles required under Condition 1, it is preferable to use a carbon material dispersion composition obtained by crushing the carbon material and then removing the metal foreign particles by a filter or magnetic force.

[0085] [Step of removing metal foreign particles] The method for removing metal foreign particles is not particularly limited, and examples include a filtration step of filtering by a filter and a magnetic separation step such as a magnetic separation treatment using an electromagnet. It is preferable to include a filtration step and a magnetic separation step. This is because the magnetic separation step can remove metal foreign particles in the carbon material grown with a metal catalyst as a nucleus, and the filtration step can recover metal foreign particles that cannot be removed by a magnet. Furthermore, it is more preferable to perform a magnetic separation step after the filtration step. By performing the filtration step at the end before shipping the CNT dispersion composition, metal foreign particles from pipes and the like can also be removed. As a result, by reducing the metal foreign particles, the characteristics as a battery can be made even more excellent.

[0086] (Magnetic separation step) As a method for removing metal foreign particles using magnetic force by the magnetic separation step, various conventionally known methods can be used. For example, a method of setting an electromagnet during the manufacturing process of the carbon material dispersion composition and passing the carbon material dispersion composition through it to remove metal foreign particles is preferable.

[0087] The magnetic flux density of the electromagnet is preferably 5000 Gauss or more and 20000 Gauss or less, and more preferably 10000 Gauss or more and 20000 Gauss or less. By using an electromagnet within the above range, not only metal foreign particles contained in the carbon material but also metal foreign particles mixed in during the manufacturing process can be removed.

[0088] 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 Elyz Magnetics Co., Ltd., EMF-100S, EMF-150S, EMF-250S, EMF-300S manufactured by Dabo Magnetic Co., Ltd. etc. can be used.

[0089] When the carbon material dispersion composition contacts the electromagnet, the flow rate is preferably 1 L / min or more and 300 L / min or less, and more preferably 30 L / min or more and 100 L / min or less.

[0090] The number of times the carbon material dispersion composition passes through the electromagnet is preferably 3 times or more. If the number of passes is small, there is a possibility that metal foreign particles cannot be 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.

[0091] (Filtration step) As a filter for filtering metal foreign particles, it may be a surface filter such as a membrane filter or a depth filter, but a depth filter is more preferable. Since metal foreign particles are not spherical and many have orientation, by using a depth filter, the metal foreign particles in the carbon material dispersion composition can be efficiently removed.

[0092] Different from 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, the metal foreign particles in the carbon material dispersion composition can be removed more selectively.

[0093] As a depth filter, for example, 3M(TM) PP non-woven depth cartridge NT-T series can be used.

[0094] The filtration accuracy of the filter is preferably 5 μm or more and 50 μm or less, more preferably 10 μm or more and 40 μm or less. When a filter with a small pore diameter is used for the purpose of increasing the removal efficiency of metal foreign particles in the carbon material dispersion composition, the removal efficiency of metal foreign particles 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 efficiently removed, and a carbon material dispersion composition with few metal foreign particles can be obtained.

[0095] Even if the filtration treatment is performed with a filter having a filtration accuracy of 5 μm, the metal foreign particles may have orientation due to their shape being needle-like or the like, and it is impossible to completely remove the metal foreign particles, which will remain in the carbon material dispersion composition. Therefore, it is important to appropriately control the composition and viscosity of the carbon material dispersion composition, the dispersion process, or the method of the metal foreign substance removal process, etc., to reduce the size and number of metal foreign particles required under Condition 1.

[0096] <<Composite Material Slurry>> The composite material slurry of this embodiment contains at least a carbon material dispersion composition and an active material. That is, it preferably contains at least a carbon material, a dispersant, a liquid medium, and an active material, and a binder resin.

[0097] The binder resin is a resin used to bind between substances. There is no particular limitation on the binder resin. For example, polymers or copolymers containing units such as fluororesin, 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.; Polyurethane resins, polyester resins, phenol resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, rubbers such as butadiene rubber; Conductive resin compounds such as polyaniline and polyacetylene, fluororesin; Cellulose resins such as carboxymethyl cellulose; Rubbers such as butadiene rubber; Conductive resins such as polyaniline and polyacetylene. Among these, from the viewpoint of electrochemical oxidation-reduction resistance, it is preferable to use a fluororesin as the binder resin.

[0098] As the fluororesin of this embodiment, for example, polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene are preferable.

[0099] The weight average molecular weight of the fluororesin is preferably 10,000 or more and 2,000,000 or less, more preferably 100,000 or more and 1,000,000 or less, and particularly preferably 200,000 or more and 1,000,000 or less.

[0100] The active material is a material that serves as the basis of the battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material based on the electromotive force. In the present disclosure, the positive electrode active material and the negative electrode active material may be simply referred to as the "active material". The active material is a material that serves as the basis of the battery reaction. The active material is divided into a positive electrode active material and a negative electrode active material based on the electromotive force.

[0101] The positive electrode active material is not particularly limited, but metal compounds such as metal oxides and metal sulfides capable of doping or intercalating lithium ions, and conductive polymers can be used. For example, oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, inorganic compounds such as transition metal sulfides, etc. are included. Specifically, transition metal oxide powders such as MnO, V2O5, V6O 13 , TiO2, etc., composite oxide powders of lithium and transition metals such as layered lithium nickelate, lithium cobaltate, lithium manganate, spinel-structured lithium manganate, lithium iron phosphate-based materials which are olivine-structured phosphate compounds, transition metal sulfide powders such as TiS2 and FeS, etc. are included. Also, conductive polymers such as polyaniline, polyacetylene, polypyrrole, and polythiophene can be used. Further, the above inorganic compounds and organic compounds may be mixed and used.

[0102] The positive electrode active material is preferably a composite oxide with lithium containing transition metals such as Al, Fe, Co, Ni, and Mn, more preferably a composite oxide with lithium containing any of Al, Co, Ni, and Mn, and particularly preferably a composite oxide with lithium containing Ni and / or Mn. When these active materials are used, particularly good effects can be obtained on the battery characteristics.

[0103] The negative electrode active material is not particularly limited as long as it can be doped or intercalated with lithium ions. For example, metal Li, alloy systems such as tin alloys, silicon alloys, and lead alloys that are its alloys, metal oxide systems such as LiXFe2O3, LiXFe3O4, LiXWO2 (x is a number where 0 < x < 1), lithium titanate, lithium vanadate, lithium silicate, conductive polymer systems such as polyacetylene and poly-p-phenylene, amorphous carbonaceous materials such as soft carbon and hard carbon, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, carbon black, mesophase carbon black, resin-fired carbon materials, gas-phase grown carbon fibers, carbon fibers, and other carbon-based materials. These negative electrode active materials can also be used alone or in combination of two or more.

[0104] The BET specific surface area of the active material is preferably 0.1 m 2 / g or more and 10 m 2 / g or less, more preferably 0.2 m 2 / g or more and 5 m 2 / g or less, and even more preferably 0.3 m 2 / g or more and 3 m 2 / g or less.

[0105] The average particle size of the active material is preferably in the range of 0.05 μm to 100 μm, and more preferably in the range of 0.1 μm to 50 μm. The average particle size of the active material referred to in the present disclosure is the average value of the particle sizes measured by an electron microscope for the active material.

[0106] To obtain the composite material slurry of the present embodiment, it is preferable to perform a dispersion treatment after adding an active material to the carbon material dispersion composition. The dispersion device used for performing such treatment is not particularly limited. The composite material slurry can be obtained using the dispersion device described for the carbon material dispersion composition above.

[0107] The content of the active material in the composite material slurry is preferably 20% by mass to 85% by mass, and particularly preferably 40% by mass to 85% by mass, based on 100% by mass of the composite material slurry.

[0108] The content of the carbon material in the composite material slurry is preferably 0.05 part by mass to 10 parts by mass, more preferably 0.1 part by mass to 5 parts by mass, and particularly preferably 0.1 part by mass to 3 parts by mass, based on 100 parts by mass of the active material.

[0109] The content of the binder resin in the composite material slurry is preferably 0.5 part by mass to 20 parts by mass, more preferably 1 part by mass to 10 parts by mass, and particularly preferably 1 part by mass to 5 parts by mass, based on 100 parts by mass of the active material.

[0110] The solid content concentration of the composite material slurry is preferably 30% by mass to 90% by mass, and preferably 40% by mass to 85% by mass, based on 100% by mass of the composite material slurry.

[0111] The water content in the composite material slurry is preferably 500 ppm or less, more preferably 300 ppm or less, and particularly preferably 100 ppm or less.

[0112] <<Electrode>> According to this embodiment, an electrode film formed from a composite material slurry is provided. Further, according to this embodiment, an electrode including a current collector and an electrode film formed from a composite material slurry is provided. The details of the composite material slurry are as described above. The electrode film is a coating film of the composite material slurry. For example, the electrode film is a coating film in which an electrode composite material layer is formed by coating and drying the composite material slurry on the current collector.

[0113] The material and shape of the current collector used in the electrode of this embodiment are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, examples of the material of the current collector include metals and alloys such as aluminum, copper, nickel, titanium, or stainless steel. Further, as the shape, generally a foil on a flat plate is used, but those with a roughened surface, perforated foil-like ones, and mesh-shaped current collectors can also be used.

[0114] There is no particular limitation on the method of coating the composite material slurry on the current collector to form the electrode film, and known methods can be used. Specifically, examples include the die coating method, dip coating method, roll coating method, doctor coating method, knife coating method, spray coating method, gravure coating method, screen printing method, or electrostatic coating method, etc. As the drying method, air drying, hot air dryer, warm air dryer, infrared heater, far-infrared heater, etc. can be used, but it is not particularly limited to these.

[0115] Further, a rolling process may be performed by a flat plate press, a calendar roll, etc. after coating. The thickness of the electrode composite material layer is generally 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0116] According to one embodiment, in order to meet the requirement of thinning the electrode film, when the thickness of the electrode film is 100 μm or less, 50 μm or less, or 20 μm or less, it is possible to exhibit a function of preventing the incorporation of metal foreign particles with a large particle size into the electrode film. For the same reason, it is particularly useful when the thickness of the separator disposed between the electrodes is 100 μm or less, 50 μm or less, or 20 μm or less. For example, it can be applied to a secondary battery in which the thickness of the electrode film is 10 to 20 μm and the thickness of the separator is 10 to 20 μm.

[0117] <<Secondary Battery>> According to this embodiment, there is provided a secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode has an electrode film according to the above-described embodiment. The carbon material dispersion composition of this embodiment is excellent in rate characteristics in order to form a good conductive network in the secondary battery electrode, and since the active material is uniformly utilized during charge and discharge, the deterioration of the active material is less likely to progress. Furthermore, overcharge and overdischarge during charge and discharge are suppressed. Further, since there are few metal foreign substances derived from the carbon material dispersion composition, deterioration of battery characteristics due to electrolyte decomposition or metal precipitation is less likely to occur, and the high-temperature cycle characteristics are excellent.

[0118] As the positive electrode, one obtained by coating and drying a composite material slurry containing a positive electrode active material on a current collector to form an electrode film can be used.

[0119] As the negative electrode, one obtained by coating and drying a composite material slurry containing a negative electrode active material on a current collector to form an electrode film can be used.

[0120] As the electrolyte, various conventionally known substances 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 thereto, and those containing sodium salts can also be used. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolytic solution.

[0121] 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 can be mentioned. These solvents may be used alone or in combination of two or more.

[0122] The secondary battery of this embodiment preferably includes a separator. Examples of the separator include, but are not particularly limited to, polyethylene non-woven fabric, polypropylene non-woven fabric, polyamide non-woven fabric, and those obtained by subjecting these to hydrophilic treatment.

[0123] The structure of the secondary battery of this embodiment is not particularly limited, but it is usually composed of a positive electrode and a negative electrode, and a separator provided as necessary, and can have various shapes according to the purpose of use, such as a paper type, a cylindrical type, a button type, a laminated type, etc.

[0124] The application of the secondary battery of this embodiment is not particularly limited. Specifically, it can be used as a power source for consumer devices such as mobile phones, notebook computers, digital cameras, etc., as an emergency power source for hospitals, factories, buildings, etc., and for vehicles such as hybrid vehicles, plug-in hybrid vehicles, electric vehicles, assist bicycles, railway vehicles, etc. The secondary battery is, for example, one that recovers the regenerative energy of the vehicle's power.

[0125] Among them, since it is a secondary battery having high charge and discharge performance and excellent cycle characteristics, it can be suitably used for vehicles, and a vehicle with high safety and expected fuel consumption improvement can be obtained. Furthermore, excellent effects can also be exhibited in the case of vehicle applications where charge and discharge at a large current are desired.

[0126] The mounting position of the secondary battery in the vehicle of this embodiment is not particularly limited. For example, when mounting the secondary battery in an automobile, the secondary battery can be mounted in the engine room of the vehicle, behind the vehicle body, or under the seat.

Examples

[0127] Examples will be given below to explain the present invention more specifically. The present invention is not limited to the following examples as long as it does not exceed the gist thereof. Unless otherwise specified, "parts" represents "parts by mass" and "%" represents "% by mass". In addition, the compounding amounts in the table are in parts by mass, and except for the solvent, they are values in terms of non-volatile content. Note that the blanks in the table indicate that they are not compounded. In addition, carbon nanotubes are also denoted as "CNT", N-methyl-2-pyrrolidone is also denoted as NMP, and the carbon material dispersion composition is also denoted as the dispersion composition.

[0128] The materials used in the examples and comparative examples are shown below. · Hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, ZN35052, Mooney viscosity 20, weight average molecular weight 110,000, alkylene structural unit 66% by mass, content of nitrile group-containing structural unit 34% by mass) was used as the dispersant (A) below. · Carbon nanotubes (manufactured by JEIO, JENOTUBE10B) Hereinafter, they were designated as carbon nanotubes (A1). · Carbon nanotubes (manufactured by JEIO, JENOTUBE6A) Hereinafter, they were designated as carbon nanotubes (B1).

[0129] <Preparation of carbon nanotubes (C1)> Weighed 1 kg of carbon nanotubes (A1) into a 100 L glass container, added 50 kg of 20% hydrochloric acid (manufactured by Fujifilm Wako Pure Chemical Corporation), and then stirred well using a stirrer under the condition of 25°C. Then, it was sufficiently diluted with ion-exchanged water and vacuum filtered using a membrane filter. After repeating the dilution and filtration operations, the CNTs were transferred to a PTFE vat and then dried at 80°C using an oven to obtain carbon nanotubes (C1).

[0130] <Preparation of carbon nanotubes (E1)> Weighed 10 kg of carbon nanotubes (A1) into a 120 L heat-resistant container, and placed the heat-resistant container containing carbon nanotubes into the furnace. Then, nitrogen gas was introduced into the furnace to discharge 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 1800°C over 30 hours. While maintaining the furnace temperature at 1800°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 nanotubes (E1).

[0131] <Preparation of carbon nanotubes (E2)> The carbon nanotubes (E1) were passed through an electromagnet (CG-150HHH manufactured by Nippon Magnetics Co., Ltd.) three times to remove magnetic foreign substances in the raw material, and carbon nanotubes (E2) were obtained. An electromagnetic separator with a screen opening of 10 mm was used.

[0132] <Preparation of carbon nanotubes (E3)> Carbon nanotubes (E1) were 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, processed at a peripheral speed of 5.0 m / s, then passed through an electromagnet (CG-150HHH manufactured by Nippon Magnetics Co., Ltd.) three times to remove magnetic foreign substances in the raw material, and carbon nanotubes (E3) were obtained. An electromagnet with a screen opening of 10 mm was used.

[0133] <Production of Carbon Nanotubes (H1)> 10 kg of carbon nanotubes (B1) were weighed into a heat-resistant container of 120 L, and the heat-resistant container containing the carbon nanotubes was installed in the furnace. Then, nitrogen gas was introduced into the furnace to discharge 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 1800 °C over 30 hours. While maintaining the furnace temperature at 1800 °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. After that, the carbon nanotubes were taken out, and the carbon nanotubes were 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, processed at a peripheral speed of 5.0 m / s, then passed through an electromagnet (CG-150HHH manufactured by Nippon Magnetics Co., Ltd.) three times to remove metal foreign particles in the raw material, and carbon nanotubes (H1) were obtained. An electromagnet with a screen opening of 10 mm was used.

[0134] Table 1 shows the physical properties of the carbon nanotubes used in the examples and comparative examples.

[0135]

Table 1

[0136] <Measurement of Weight-Average Molecular Weight of Dispersant> The weight average molecular weight (Mw) of the dispersant was measured by gel permeation chromatography (GPC) equipped with an RI detector. Using HLC-8320GPC (manufactured by Tosoh Corporation) as the apparatus, three separation columns were connected in series. As the packing materials, "TSK-GEL SUPER AW-4000", "AW-3000", and "AW-2500" manufactured by Tosoh Corporation were used in order. The oven temperature was 40 °C, and a solution of 30 mM triethylamine and 10 mM LiBr in N,N-dimethylformamide was used as the eluent. The measurement was carried out at a flow rate of 0.6 mL / min. The measurement sample was adjusted to a concentration of 1% using a solvent composed of the above eluent and 20 microliters were injected. The weight average molecular weight is a polystyrene conversion value.

[0137] <Fabrication of Standard Negative Electrode> To a plastic container with a volume of 150 ml, 0.5 part by mass of acetylene black (Denka Black (registered trademark) HS-100, manufactured by Denka), 1 part by mass of MAC500LC (sodium carboxymethyl cellulose salt, Sanroze special type MAC500L, manufactured by Nippon Paper Industries Co., Ltd., non-volatile content 100%), and 98.4 parts by mass of water were added. Then, using a rotating and revolving mixer (Sinkei, Awaotorikentaro, ARE-310), it was stirred at 2000 rpm for 30 seconds. Further, 92 parts by mass of artificial graphite (manufactured by Nippon Graphite Industry Co., Ltd., CGB-20) and 5 parts by mass of silicon (manufactured by Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE SiO 1.3C 5μm, non-volatile content 100%) were added as active materials and stirred at 3000 rpm for 10 minutes using a high-speed stirrer. Subsequently, 3.1 parts by mass of SBR (TRD2001, manufactured by JSR Corporation) was added and stirred at 2000 rpm for 30 seconds using the above rotating and revolving mixer so that the coating weight per unit area of the negative electrode became 8 mg / cm 2 After coating on a copper foil so as to obtain, and then the negative electrode composite material slurry was obtained in an electric oven. Then, using an applicator, the coating weight per unit area of the electrode was 8 mg / cm 2After coating on the copper foil so as to obtain the following, the coating film was dried in an electric oven at 120 °C ± 5 °C for 25 minutes. Further, rolling treatment was performed using a roll press (manufactured by Sanku Metal Co., Ltd., 3t hydraulic roll press), and the density of the composite material layer was 1.6 g / cm 3 A standard negative electrode having the following was produced.

[0138] <<Physical Property Measurement and Evaluation Methods>> The physical property measurement and evaluation methods for the carbon nanotubes, carbon material dispersion composition, electrode film, and secondary battery used in each of the following Examples and Comparative Examples are as follows.

[0139] <Outer Diameter of Carbon Nanotubes> Using an electronic balance (manufactured by Sartorius, MSA225S100DI), 0.2 g of carbon nanotubes was weighed into a 450 mL SM sample bottle (manufactured by Sansho Co., Ltd.). 200 mL of toluene was added, and using an ultrasonic homogenizer (Advanced Digital Sonifer (registered trademark), MODEL 450DA, manufactured by BRANSON), dispersion treatment was performed under ice cooling at an amplitude of 30% for 5 minutes to prepare a carbon nanotube dispersion. Thereafter, the carbon nanotube dispersion was appropriately diluted, several μL was dropped in the form of a collodion film, and after drying at room temperature, observation was performed using a transmission electron microscope (H-7650, manufactured by Hitachi, Ltd.). Observation was performed at a magnification of 50,000 times, and a plurality of photographs containing 10 or more carbon nanotubes in the visual field were taken, and the average outer diameter of 300 arbitrarily extracted carbon nanotubes was measured, and the average value was taken as the outer diameter (nm) of the carbon nanotubes.

[0140] <BET Specific Surface Area of Carbon Nanotubes> Using an electronic balance (manufactured by Sartorius, MSA225S100DI), 0.03 g of carbon nanotubes was weighed, and then dried while degassing at 110 °C for 15 minutes. Thereafter, using a fully automatic specific surface area measuring device (manufactured by MOUNTECH, HM-model1208), the BET specific surface area of the carbon nanotubes was measured.

[0141] <G / D Ratio of Carbon Nanotubes> Carbon nanotubes were placed on a Raman microscope (XploRA, manufactured by Horiba, Ltd.) and measured using a laser wavelength of 532 nm. The measurement conditions were an integration time of 60 seconds, an integration count of 2 times, a neutral density filter of 10%, an objective lens magnification of 20 times, a confocal hole of 500, a slit width of 100 μm, and a measurement wavelength range of 100 cm -1 ~3000 cm -1 The carbon nanotubes for measurement were separated on a slide glass and flattened using a spatula. Among the obtained peaks, the maximum peak intensity in the spectrum within the range of 1560 cm -1 ~1600 cm -1 was defined as G, and the maximum peak intensity in the range of 1310 cm -1 ~1350 cm -1 was defined as D. The ratio of G / D was defined as the G / D ratio of the carbon nanotubes.

[0142] <Carbon Purity of Carbon Nanotubes> The carbon nanotubes were acid-decomposed using a microwave sample pretreatment apparatus (ETHOS1 manufactured by Milestone General) to extract the metals contained in the carbon nanotubes. Then, analysis was performed using a multi-type ICP emission spectrometer (720-ES manufactured by Agilent) to calculate the amount of metals (total amount of iron, cobalt, nickel, copper, nickel, molybdenum) contained in the extract. The carbon purity of the carbon nanotubes was calculated as follows. Carbon purity of carbon nanotubes (%) = ((carbon nanotube mass - metal mass) ÷ carbon nanotube mass) × 100

[0143] <Amount of Metal Elements in Carbon Material Dispersion Composition> The carbon material dispersion composition was dried using a hot air oven, and then acid decomposition was performed using a microwave sample pretreatment apparatus (ETHOS1 manufactured by Milestone General) to extract the metals contained in the carbon nanotubes. Thereafter, analysis was performed using a multi-type ICP emission spectrometer (720-ES manufactured by Agilent), and the amount of metal elements (total content of iron, cobalt, nickel, chromium, molybdenum, and copper) contained in the extract was calculated.

[0144] <Number and Size of Metal Foreign Matter Particles in Carbon Material Dispersion Composition> 1 kg of the carbon material dispersion composition was passed through a mesh filter with an opening of 15 μm, and the residue filtered by the filter was collected together with the filter. The collected filter was dried at 60 °C until there was no change in mass. The dried filter was used with an X-ray transmission device “CheetahEVO” (manufactured by Comet Technology Japan) to obtain an X-ray transmission distribution at a tube voltage of 60 kV and a tube current of 40 μA. From the X-ray transmission distribution, the number of particles of 20 μm or more detected was counted using analysis software Winroof.

[0145] In this measurement, based on the X-ray transmissibility of the substance, it is determined whether it is a metal from the threshold value of the image density of the X-ray transmission distribution. The threshold value of the image density is determined by previously evaluating the X-ray transmissibility and image density of the metal and carbon nanotubes. The size of the particle is a numerical value obtained by measuring the major axis of the shape of the particle determined to be a metal from the X-ray transmission distribution image.

[0146] <Measurement of Cumulative Particle Size D90 of Carbon Material Dispersion Composition> The measurement of the cumulative particle size D90 by the particle size distribution was performed using a laser diffraction / scattering type particle size distribution measuring device (Partical LA-960V2 manufactured by Horiba, Ltd.). The laser light wavelength of this measuring device is 650 nm, and as detectors, it is equipped with one ring-shaped 64-segment silicon photodiode, five 4ch array detectors, and three silicon photodetectors. Also, the measurement unit uses a flow cell (sample cell) made of synthetic quartz. First, NMP, which is the same solvent as the carbon material dispersion composition, was put into a sample bath containing a sample cell, and circulation / ultrasonic cleaning was performed. The operation modes were circulation speed: 3, ultrasonic intensity: 7, ultrasonic time 1 minute, stirring speed: 7, and stirring mode: continuous. Next, in order to remove air, ultrasonic operation was performed at ultrasonic intensity: 7 and ultrasonic time 5 seconds, and then a blank (background) measurement was performed. The particle size standard was volume, the particle refractive index was set to 1.920-0.522i (carbon material), and the solvent refractive index was set to 1.468 (NMP). The carbon material dispersion composition was dropped so that the laser light transmittance during measurement was 60% ± 1%, and sample adjustment was performed. The operation modes during measurement were circulation speed: 3, stirring speed: 7, and stirring mode: continuous, and the measurement was performed.

[0147] <Pressure filtration test of carbon material dispersion composition> The pressure filtration test of the carbon material dispersion liquid was carried out as follows. 100g to 200g of the carbon material dispersion composition was filled into a stainless steel holder with a tank (KST-47 type, manufactured by ADVANTEC) equipped with a polyester mesh filter with a diameter of 47 mm and a mesh size of 5 μm, and the mass of the carbon material dispersion composition discharged per hour was measured while applying a pressure of 0.06 MPa. The density of the carbon material dispersion composition was set to 1 g / cm 3 The maximum flow velocity was calculated from the change in weight of the discharged carbon material dispersion composition over time.

[0148] <Short circuit test evaluation method> A total of 10 laminated lithium ion secondary batteries (secondary batteries) were fabricated and charged at a constant current of 1.0 C with a charge cut-off voltage of 4.3 V using a charge / discharge device (Hokuto Denko, SM-8) at 25°C. If a short circuit occurs, charging to 4.3 V is not possible, so cells that could not be charged to 4.3 V even after 2 hours from the start of charging were considered to be short-circuited, and the number of cells that experienced internal short circuits was counted out of the 10 cells. In the short circuit test, the fewer the number of short-circuited cells, the better the short circuit prevention effect. A: All 10 cells are not shorted and can be fully charged. B: Of the 10 cells, 8 to 9 cells do not short-circuit and can be fully charged. Among 10 cells, 6 or more and 7 or less cells are not short-circuited and can be fully charged. Among 10 cells, 5 or more cells are short-circuited and cannot be charged.

[0149] (Example 1-1) 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of dispersant (A) were added to a stainless steel container, stirred at 80 °C using a disper until the dispersant (A) was completely dissolved, passed through a nylon mesh with an opening of 48 μm, and then an 8% solution of dispersant (A) was prepared through a high magnetic force mag filter (manufactured by Aisin, surface magnetic flux density 17000 gauss). Subsequently, 89.5 parts of N-methyl-2-pyrrolidone (NMP) and 7.5 parts of an 8% solution of dispersant (A) were added to a stainless steel container and stirred with a disper until uniform. Then, 3 parts of carbon nanotubes (E1) were taken 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. After that, a carbon nanotube preliminary dispersion (E1) was prepared through a high magnetic force mag filter (manufactured by Aisin, surface magnetic flux density 17000 gauss). Further, the carbon nanotube preliminary dispersion was fed, and a circulating dispersion treatment with a residence time of 15 minutes (bead filling rate 80%, peripheral speed 12 m / s) was carried out using a bead mill (manufactured by Ashizawa Fine Tech Co., Ltd., Mugen Flow (registered trademark)) filled with zirconia beads having a diameter of 1.0 mm φ. Subsequently, the dispersion liquid was supplied to a high-pressure homogenizer (manufactured by Sugino Machine, Starburst Turbo), and a 15-pass dispersion treatment was carried out. 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. After that, the dispersion liquid was supplied to an electromagnet (manufactured by Daiho Magnetic Co., Ltd., EMF-100S, magnetic flux density 16000 gauss, spatial volume 1.7 L, diameter: 10 cm, thickness 1.3 cm, equipped with 31 grid screens), and a 3-pass treatment was carried out. Then, it was passed through depth filters (manufactured by 3M, PP non-woven fabric depth cartridge NT-T series, filtration accuracy 20 μm) installed in series, and Carbon Material Dispersion Composition 1 was prepared.

[0150] (Examples 1-2 to 1-13), (Comparative Examples 1-1 to 1-2) Except for changing the dispersion conditions and carbon nanotubes shown in Table 2, Dispersion Compositions 1-1 to 1-13 and Comparative Dispersion Compositions 1-1 to 1-2 were obtained in the same manner as in Example 1-1. The depth filters in the examples and comparative examples used 3M-made PP non-woven fabric depth cartridge NT-T series. Comparative Example 1-2 could not filter with a filter having a filtration accuracy of 20 μm and could not be prepared.

[0151]

Table 2

[0152] Table 3 shows the evaluation results of the dispersion compositions prepared in (Examples 1-1 to 1-13) and (Comparative Examples 1-1 to 1-2).

[0153]

Table 3

[0154] (Example 2-1) 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 a carbon material dispersion composition (dispersion composition 1) was added, and using a rotation / revolution mixer (Avatore Rentaro, ARE-310), it was stirred at 2000 rpm for 30 seconds. Subsequently, 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 (Avatore Rentaro, ARE-310), it was stirred at 2000 rpm for 2.5 minutes to obtain a composite material slurry (composite material slurry 1).

[0155] Subsequently, the composite material slurry (composite material slurry 1) was applied onto an aluminum foil using an applicator so that the basis weight per unit of the electrode was 20 mg / cm 2 , and then the coating film was dried in an electric oven at 120 °C ± 5 °C for 25 minutes to obtain an electrode film (electrode film 1). Then, the electrode film (electrode film 1) was subjected to rolling treatment using a roll press (manufactured by Sanku Metal, 3t hydraulic roll press) to obtain a positive electrode (positive electrode 1). Note that the basis weight per unit of the composite material layer was 20 mg / cm 2 , and the density of the composite material layer after the rolling treatment was 3.1 g / cc.

[0156] (Examples 2-2 to 2-13), (Comparative Example 2-1) As shown in Table 4, except that Dispersion Composition 2 to Comparative Dispersion Composition 1 were used instead of Dispersion Composition 1, Composite Material Slurry 2 to Comparative Composite Material Slurry 1, Electrode Film 2 to Comparative Electrode Film 1, and Positive Electrode 2 to Comparative Positive Electrode 1 were obtained in the same manner as in Example 2-1. In Comparative Example 1-2, Comparative Dispersion Composition 2 could not be filtered through a filter with a filtration accuracy of 20 μm and could not be prepared, so it could not be evaluated after the preparation of the composite material slurry.

[0157] Table 4 shows the details of the electrode films prepared in Examples 2-1 to 2-13 and Comparative Example 2-1. Note that all the electrode films in the examples had good conductivity and adhesion.

[0158]

Table 4

[0159] (Example 3-1) The positive electrode (Positive Electrode 1) and the standard negative electrode were each punched out to 45 mm × 40 mm and 50 mm × 45 mm, and the separator (porous polypropylene film) inserted between them was inserted into an aluminum laminate bag and dried in an electric oven at 60°C for 1 hour. Then, 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 in a ratio of 1:1:1 (volume ratio), and further, as an additive, VC (vinylene carbonate) was added in an amount of 2 parts by mass per 100 parts by mass of the mixed solvent, and then LiPF6 was dissolved at a concentration of 1 M) was injected in an amount of 2 mL, and then the aluminum laminate was sealed to fabricate a laminated lithium-ion secondary battery (Secondary Battery 1).

[0160] (Examples 3-2 to 3-13), (Comparative Example 3-1) Except for changing to the positive electrodes shown in Table 5, laminated lithium-ion secondary batteries (Secondary Battery 2) to (Comparative Secondary Battery 1) were fabricated in the same manner as the fabrication of the laminated lithium-ion secondary battery (Secondary Battery 1).

[0161] Table 5 shows the evaluation results of the secondary batteries prepared in Examples 3-1 to 3-13 and Comparative Example 3-1. Note that all of the secondary batteries in the examples had good rate characteristics and high-temperature cycle characteristics.

[0162]

Table 5

[0163] According to each example, a carbon material dispersion composition can be obtained that includes carbon nanotubes, a dispersant, and a liquid medium, has 100 or fewer metal foreign particles with a size of 20 μm or more, and has a cumulative particle diameter D90 and a maximum flow rate in a pressure filtration test within a predetermined range. In each example, it was clarified that the occurrence of short circuits in the secondary battery can be suppressed, and a lithium-ion secondary battery with high reliability that is difficult to achieve with conventional carbon material dispersion compositions can be provided. A vehicle having the lithium-ion secondary battery of this embodiment has high charge and discharge performance and excellent high-temperature cycle characteristics, so a vehicle with high safety and improved fuel efficiency can be obtained.

[0164] As described above, the present invention has been described with reference to the embodiments, but the present invention is not limited to the above. Various changes 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 invention.

Claims

1. A carbon material dispersion composition comprising a carbon material, a dispersant, and a liquid medium, which satisfies the following (1) to (3). (1) The number of metal foreign particles having a size of 20 μm or more determined by the following Condition 1 is 100 or less. (2) The cumulative particle size D90 of the dispersed particle size of the carbon material dispersion composition by the laser diffraction / scattering method is 0.5 to 5 μm. (3) The maximum flow rate is 0.00375 to 0.0375 m / s by a pressure filtration test at a pressure of 0.06 MPa using a membrane filter having a diameter of 47 mm and an opening of 5 μm. <Condition 1> Filter the carbon material dispersion composition through a filter with an opening of 15 μm to obtain the X-ray transmission distribution of the filter after filtration, and measure the size and number of metal foreign particles from the X-ray transmission distribution based on the X-ray transmissibility of the substance.

2. The carbon material dispersion composition according to Claim 1, wherein the total content of iron, cobalt, nickel, chromium, molybdenum, and copper is 100 ppm or less.

3. A composite material slurry comprising the carbon material dispersion composition according to Claim 1 or 2 and an active material.

4. An electrode film formed from the composite material slurry according to Claim 3.

5. A secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive electrode and the negative electrode has the electrode film according to Claim 4.

6. A vehicle equipped with the secondary battery according to Claim 5.

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