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

Abstract

The present invention can provide: a method for producing a carbon material dispersion liquid having a low content of metal magnetic foreign matter in the carbon material dispersion liquid and excellent stability over time; and a secondary battery having good cycle characteristics using the carbon material dispersion liquid. The present disclosure pertains to a method for producing a carbon material dispersion containing a carbon material, a dispersant, and a solvent, the method comprising the following steps (1)-(3). [Step (1)] A step for obtaining a carbon material pre-dispersion (X1) having a sliding angle with respect to a metal substrate of less than 70 DEG and a cumulative particle diameter (D50) of 20 [mu] m or more; [step (2)] a step for obtaining a carbon material pre-dispersion (X2) by removing metal magnetic foreign matter by magnetic separation treatment while and / or after the production of the carbon material pre-dispersion (X1); [step (3)] A step for producing a carbon material dispersion by dispersing the carbon material pre-dispersion (X2).

Description

Technical Field

[0001] The embodiments disclosed herein relate to methods for manufacturing carbon material dispersions, electrode slurries, electrodes, and secondary batteries. Background Technology

[0002] Lithium-ion rechargeable batteries are widely used in electric vehicles and portable devices. As electric vehicles and portable devices become more high-performance, the requirements for high capacity, high output, and small and lightweight lithium-ion rechargeable batteries are increasing year by year.

[0003] The capacity of lithium-ion secondary batteries largely depends on the positive and negative electrode active materials, which serve as the main electrode materials. Therefore, various materials for these active materials are being actively researched. However, the charging capacity using practically applicable active materials has reached near-theoretical levels, and improvements are approaching their limits. Therefore, increasing the amount of active material within the electrode film can directly increase the charging capacity. Consequently, efforts have been made to reduce or eliminate the amount of conductive additives and binder resins, which do not directly contribute to the charging capacity.

[0004] Conductive additives play a crucial role in forming conductive pathways within the electrode, and must be resistant to disruption due to the expansion and contraction of the electrode film. To maintain these pathways with minimal additives, carbon materials with large specific surface areas, such as Ketjenblack, carbon nanotubes, graphene, and fullerenes, are preferred. However, these carbon materials contain metal catalysts from synthesis and metallic magnetic foreign matter from the manufacturing process, leading to voltage drop issues. These metallic magnetic foreign matter can sometimes dissolve inside the secondary battery, precipitating as dendrites and breaching the separator, becoming a primary cause of internal short circuits. Furthermore, in electrode films made of carbon materials with high levels of metallic magnetic foreign matter, the high-temperature charging and discharging of the secondary battery easily leads to the degradation of the electrolyte and active materials, gradually resulting in poor high-temperature cycling performance.

[0005] Therefore, in Patent Document 1, as a process for removing particulate metal, a method is proposed to remove particulate metal components containing at least one metal selected from the group consisting of Fe, Ni and Cr from a slurry composition that has undergone carbon black particle dispersion treatment by using a magnet with a magnetic shield having a Vickers hardness of 10 GPa or more and less than 25 GPa.

[0006] Furthermore, carbon nanotubes often contain residual metallic magnetic foreign matter from the metal catalysts used in their synthesis, which can easily cause problems with voltage drop. Therefore, Patent Document 2 investigated a method for pulverizing carbon nanotubes containing metallic magnetic foreign matter such as iron, cobalt, and nickel, and then removing the metallic magnetic foreign matter from the carbon nanotubes using an electromagnet.

[0007] Patent document 3 discloses a method for removing particulate metal contained in an adhesive composition.

[0008] Patent document 4 proposes a method for removing impurities, namely metallic magnetic foreign objects, from a medium liquid containing carbon nanotubes after they have been de-fibrated using a shearing module during the manufacturing process of carbon nanotubes.

[0009] Patent document 5 proposes to use a copolymer containing nitrile monomer units as a dispersant to specify the pH of the dispersion, thereby enabling the cohesive carbon fibers to be well dispersed in the solvent, improving the dispersion degree of the conductive dispersion. Thus, even with a high concentration of carbon fibers, a dispersion with excellent operability can be obtained, and the removal efficiency of metal foreign matter, which is an obstacle to the conductive network, can be improved.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 2015-191756

[0013] Patent Document 2: Japanese Patent Application Publication No. 2010-174418

[0014] Patent Document 3: Japanese Re-evaluation No. 2010-032784

[0015] Patent Document 4: Japanese Patent Application Publication No. 2021-065846

[0016] Patent Document 5: Japanese Patent No. 6962428 Summary of the Invention

[0017] The problem that the invention aims to solve

[0018] However, in existing methods such as those in Patent Documents 1-5, there is a limit to reducing the content of metallic magnetic foreign matter in carbon material dispersions, and the stability of carbon material dispersions over time and their properties when used to make secondary batteries cannot be sufficiently improved.

[0019] For example, when removing metallic magnetic foreign matter from the carbon material itself using methods such as magnetic separation and filtration, it is difficult to remove metallic magnetic foreign matter that has penetrated into the interior of the carbon material. On the other hand, when removing metallic magnetic foreign matter from a carbon material dispersion, it is possible to make the metallic magnetic foreign matter that has entered into the interior of the carbon material through the dispersion process visible, but in order to efficiently remove the metal through magnetic separation and filtration, the carbon material dispersion needs to be prepared to have a low viscosity. However, with dispersion, not only the carbon material becomes finer, but the metallic magnetic foreign matter also becomes finer, so the removal efficiency of the metallic magnetic foreign matter may decrease. Therefore, there is room for improvement in maximizing the removal efficiency of metallic magnetic foreign matter in the carbon material dispersion. In the technology disclosed in Patent Document 5, the copolymer, organic solvent, and conductive material are subjected to intermittent dispersion treatment, followed by through-type dispersion treatment, and after sufficient dispersion treatment, magnetic separation treatment is performed using a magnetic separator. In this technology, the conductive material of the dispersion supplied to the magnetic separator has already been finely processed, so the metallic foreign matter is also finely processed, making it difficult to remove using the magnetic separator.

[0020] Therefore, the objective of this disclosure is to provide a method for manufacturing a carbon material dispersion with low content of metallic magnetic foreign matter and excellent stability over time. Furthermore, the objective of this disclosure is to provide a secondary battery using this carbon material dispersion with good cycle characteristics.

[0021] In particular, the present disclosure aims to provide a carbon nanotube dispersion that reduces the content of metallic magnetic foreign matter even when using carbon nanotubes that mostly contain residual metallic magnetic foreign matter from the metal catalyst used in the synthesis.

[0022] Methods for solving problems

[0023] The inventors conducted in-depth research and discovered that by removing metallic magnetic foreign matter during and / or after the manufacture of the carbon material pre-dispersion liquid, the metallic magnetic foreign matter can be effectively recovered. Compared with previous methods, this reduces the amount of metallic magnetic foreign matter in the carbon material dispersion liquid. Specifically, the slip angle of this carbon material pre-dispersion liquid is less than 70° and the cumulative particle size D... 50 The particle size is above 20 μm. This further indicates that the dispersion of carbon materials exhibits improved stability over time.

[0024] Therefore, the embodiments of this disclosure can provide a carbon material dispersion with low content of metallic magnetic foreign matter and good stability over time, and can provide a secondary battery with good cycle characteristics.

[0025] That is, this disclosure includes the following embodiments. The embodiments of this disclosure are not limited to the following.

[0026] [1] A method for manufacturing a carbon material dispersion, wherein the carbon material dispersion comprises carbon material, dispersant and solvent, and the method for manufacturing the carbon material dispersion comprises all of the following steps (1) to (3).

[0027] [Process (1)]

[0028] A drop angle of less than 70° relative to the metal substrate and a cumulative particle size D were obtained. 50 The process is for a carbon material pre-dispersion liquid (X1) with a particle size of 20 μm or larger;

[0029] [Process (2)]

[0030] The process of removing metallic magnetic foreign matter by magnetic separation during and / or after the manufacture of carbon material predispersed liquid (X1) to obtain carbon material predispersed liquid (X2).

[0031] [Process (3)]

[0032] The process of dispersing a carbon material pre-dispersion liquid (X2) to manufacture a carbon material dispersion liquid.

[0033] [2] The method for manufacturing carbon material dispersion according to [1], wherein the solvent is a non-aqueous solvent.

[0034] [3] The method for manufacturing carbon material dispersion according to [1] or [2] includes a step of further removing metallic magnetic foreign matter during and / or after the dispersion of carbon material pre-dispersion liquid (X2).

[0035] [4] A method for manufacturing an electrode paste, wherein an active substance is mixed in a carbon material dispersion manufactured by any one of the methods described in [1] to [3].

[0036] [5] A method for manufacturing an electrode, comprising a step of coating an electrode paste manufactured by the method described in [4] onto a current collector to form an electrode film.

[0037] [6] A method for manufacturing a secondary battery, comprising a step of coating an electrode slurry manufactured by the method described in [4] onto a current collector to form an electrode film.

[0038] Invention Effects

[0039] According to embodiments of this disclosure, a carbon material dispersion with low content of metallic magnetic foreign matter and good stability over time can be provided. Furthermore, by using this carbon material dispersion, a secondary battery with good cycle characteristics can be provided. Detailed Implementation

[0040] The following provides a detailed description of the carbon material dispersion, electrode slurry, electrode, and secondary battery according to embodiments of the present disclosure, as well as methods for manufacturing them, but is not intended to limit the scope of the description to these embodiments. Furthermore, the numerical values ​​defined in this specification are values ​​obtained through the methods disclosed in the embodiments or examples.

[0041] Furthermore, in this specification, the numerical range defined by "~" includes the values ​​before and after "~" as the lower and upper limits.

[0042] In this specification, "carbon nanotubes" are sometimes referred to as "CNT", "N-methyl-2-pyrrolidone" as "NMP", "carbon material pre-dispersion (X1)" as "pre-dispersion (X1)", "carbon material pre-dispersion (X2)" as "pre-dispersion (X2)", and "carbon material dispersion" as "dispersion". Additionally, "carbon material pre-dispersion (X1)" and "carbon material pre-dispersion (X2)" are sometimes collectively referred to as "carbon material pre-dispersion".

[0043] The process of removing magnetic foreign objects from metals through magnetic separation is also referred to as the "magnetic separation process".

[0044] Unless otherwise specified, each ingredient mentioned in this instruction manual may be used independently or in combination with two or more other ingredients.

[0045] Method for manufacturing carbon material dispersions

[0046] One embodiment of this disclosure is characterized in that the method for manufacturing a carbon material dispersion comprising carbon material, a dispersant and a solvent includes all of the following steps (1) to (3).

[0047] [Process (1)]

[0048] A drop angle of less than 70° relative to the metal substrate and a cumulative particle size D were obtained. 50 The process is for a carbon material pre-dispersion liquid (X1) with a particle size of 20 μm or larger;

[0049] [Process (2)]

[0050] The process of removing metallic magnetic foreign matter by magnetic separation during and / or after the manufacture of carbon material predispersed liquid (X1) to obtain carbon material predispersed liquid (X2).

[0051] [Process (3)]

[0052] The process of dispersing a carbon material pre-dispersion liquid (X2) to manufacture a carbon material dispersion liquid.

[0053] The carbon material dispersion manufacturing method of this embodiment can produce a carbon material dispersion with lower content of metallic magnetic foreign matter and excellent stability over time compared to conventional methods. Furthermore, by using this carbon material dispersion, a secondary battery with excellent cycle characteristics can be manufactured.

[0054] In particular, even when using carbon nanotubes that contain mostly metallic magnetic foreign matter from the metal catalyst used in synthesis, it is possible to produce carbon nanotube dispersions with a reduced content of metallic magnetic foreign matter compared to the past.

[0055] It should be noted that step (3) preferably includes a step of removing metallic magnetic foreign matter during and / or after the dispersion of the carbon material pre-dispersion liquid (X2).

[0056] The manufacturing method of carbon material dispersion with steps (1) to (3) is described.

[0057] [Process (1)]

[0058] Step (1) is to obtain a drop angle of less than 70° relative to the metal substrate and a cumulative particle size D. 50 The process is a pre-dispersion liquid (X1) of carbon materials with a particle size of 20 μm or larger.

[0059] By making the slip angle relative to the metal substrate less than 70° and the cumulative particle size D 50 With a particle size of 20 μm or larger, the magnetic separation process in step (2) can effectively reduce the metallic magnetic foreign particles contained in the carbon material pre-dispersion liquid (X1), and can produce a carbon material dispersion with low content of metallic magnetic foreign particles and excellent stability over time.

[0060] The smaller the drop angle, the better the droplet slippage (hydrophobicity). The carbon material pre-dispersion liquid (X1) of this embodiment has a drop angle of less than 70°. Preferably, it is 60° or less, more preferably 50° or less, and even more preferably 40° or less. In addition, it is preferably 1° or more.

[0061] With a slip angle less than 70°, the adhesion to the magnetic separator surface is weak, making it difficult for the carbon material pre-dispersion liquid (X1) to adhere to the separator during magnetic separation, thus improving the removal efficiency of metallic magnetic foreign matter based on magnetic separation. If the slip angle is greater than 70°, the adhesion to the magnetic separator surface is strong, and the carbon material pre-dispersion liquid (X1) will adhere to the separator during magnetic separation. Therefore, a thickness corresponding to the adhered carbon material pre-dispersion liquid (X1) will form, and the magnetic force decreases with the square of the distance, thus reducing the removal efficiency of metallic magnetic foreign matter based on magnetic separation.

[0062] The slip angle can be adjusted by modifying the specific surface area of ​​the carbon material, the amount of functional groups on the surface, the type and composition of the dispersant, the type of solvent, and the dispersion conditions (time, intensity, etc.).

[0063] There are no particular restrictions on the metal substrate used when measuring the slip angle, but it is preferable to use a magnet material that is in contact with the carbon material pre-dispersion liquid (X1). Examples include SUS 316L, SUS 304, and SUS 430.

[0064] Specifically, the slip angle can be measured, for example, by the method described in the [Example] section.

[0065] The cumulative particle size D of the carbon material pre-dispersion (X1) 50 The micrometer size is 20 μm or more. Preferably, it is 30 μm or more, more preferably 40 μm or more. Furthermore, it is preferably 300 μm or less, more preferably 250 μm or less.

[0066] Cumulative particle size D 50 When the particle size is less than 20 μm, the carbon material pre-dispersion liquid (X1) becomes highly viscous, contributing to the decrease in magnetic separation efficiency. Furthermore, as the carbon material pre-dispersion liquid (X1) disperses, the metallic magnetic foreign matter also disperses; therefore, the finer the metallic magnetic foreign matter, the more likely the magnetic separation efficiency will decrease. On the other hand, at a cumulative particle size D... 50 In the case of particles larger than 300 μm, metallic magnetic foreign matter encapsulated in carbon materials is not fully exposed and may not be able to be removed by magnetic separation.

[0067] Cumulative particle size D 50 The particle size distribution curve of the volume reference is determined by laser diffraction / scattering particle size distribution measurement method, specifically, for example, by the method described in the [Example] item.

[0068] The carbon material pre-dispersion (X1) can be manufactured, for example, by mixing, kneading, or dispersing a mixture comprising carbon material, dispersant, solvent, and any other desired components, as described below, using a known mixer. For example, the carbon material can be added after mixing the solvent and dispersant, or the carbon material and dispersant can be kneaded and adjusted to the desired solid composition of the carbon material pre-dispersion (X1). The carbon material pre-dispersion (X1) can be in a state where it has not undergone dispersion treatment compared to the carbon material dispersion of the final product. When the carbon material pre-dispersion (X1) is over-dispersed, the viscosity of the dispersion increases due to the micronization of the carbon material, and the slip angle may become larger. Furthermore, if the carbon material pre-dispersion (X1) is over-dispersed, the carbon material becomes micronized, and therefore may easily condense on the surface of the magnetic separator. Additionally, if the carbon material pre-dispersion (X1) is over-dispersed, metallic magnetic foreign matter will also be micronized, and may be difficult to remove with a magnetic separator unless a stronger magnetic force is used. For example, when a mass of metallic magnetic foreign matter is coated with carbon material, or when multiple metallic magnetic foreign matter is dispersed within a carbon material aggregate, the magnetic properties of the foreign matter are high when the particle size is large, making it easy to remove by magnetic separation. However, if these states are refined through over-dispersion, the magnetic properties of each refined particle become weaker, making it difficult to remove them by magnetic separation even with strong magnetic force. In this embodiment, the slip angle and cumulative particle size D of the carbon material pre-dispersion (X1) can be used as indicators for the dispersion treatment of the carbon material pre-dispersion (X1). 50 .

[0069] As the apparatus for manufacturing the carbon material predispersant (X1), a mixer, kneader, or disperser commonly used in pigment dispersion and the like can be used. Specifically, an apparatus that easily adjusts the slip angle and cumulative particle size D of the carbon material predispersant (X1) can be used. 50 Dispersants controlled within the desired range. Examples include dispersers, homogenizers, planetary mixers, MODEL 450DA, M-Technique's "CLEARMIX", PRIMIX's "FILMIX", Silverson's "Abramix", etc. The dispersion process for providing the carbon material pre-dispersion liquid (X1) does not require excessive dispersion, so it can be carried out by intermittent dispersion. By using these dispersers for intermittent dispersion, followed by magnetic separation in step (2), metallic magnetic foreign matter can be removed more effectively from the carbon material pre-dispersion liquid (X1).

[0070] [Process (2)]

[0071] Step (2) is a magnetic separation process in which the predispersed carbon material liquid (X1) is produced simultaneously and / or after the production of the predispersed carbon material liquid (X1) and the metal magnetic foreign matter is removed by magnetic separation to obtain the predispersed carbon material liquid (X2).

[0072] In this specification, the carbon material predispersed solution treated by magnetic separation is referred to as carbon material predispersed solution (X2).

[0073] The process of removing the metallic magnetic foreign matter by magnetic separation can be carried out during and / or after the manufacture of the carbon material pre-dispersion liquid (X1).

[0074] That is, process (1) and process (2) can be carried out simultaneously, or the carbon material pre-dispersion liquid (X1) obtained by process (1) can be used for magnetic separation treatment in process (2).

[0075] It should be noted that when processes (1) and (2) are performed simultaneously, the carbon material pre-dispersion liquid (X2) and the carbon material pre-dispersion liquid (X1) are equivalent to the same substance.

[0076] Therefore, the following methods can be cited as methods for manufacturing carbon material predispersants (X2):

[0077] (i) Obtaining a slip angle of less than 70° relative to the metal substrate and a cumulative particle size D 50 A method is used to obtain carbon material predispersion liquid (X2) by removing metallic magnetic foreign matter from carbon material predispersion liquid (X1) with a carbon material predispersion liquid (X1) of 20 μm or larger through magnetic separation.

[0078] (ii) Removing metallic magnetic foreign matter from the carbon material pre-dispersion containing carbon material, dispersant, and solvent by magnetic separation to obtain a slip angle relative to the metal substrate of less than 70° and a cumulative particle size D. 50 Methods for preparing carbon material predispersants (X2) with a particle size greater than 20 μm, etc.

[0079] In this embodiment, it is important that the slip angle of the carbon material pre-dispersion liquid relative to the metal substrate during magnetic separation is less than 70° and the cumulative particle size D is [missing information]. 50 With a particle size of 20 μm or larger, the amount of metallic magnetic foreign particles contained in the carbon material predispersant can be effectively reduced. Therefore, the resulting carbon material dispersion exhibits low content of metallic magnetic foreign particles and excellent long-term stability. Furthermore, the carbon material predispersant (X2) obtained for magnetic separation is preferably not subjected to excessive dispersion treatment during the magnetic separation process. For example, the drop angle and cumulative particle size D of the carbon material predispersant (X2) are... 50 The slip angle and cumulative particle size D of the carbon material pre-dispersion liquid (X1) can be respectively compared. 50For the same degree, the slip angle and cumulative particle size D relative to the carbon material pre-dispersion (X1) 50 A range of ±20%, 10%, or 5% is better.

[0080] In this embodiment, metallic magnetic foreign matter refers to substances existing in the form of particles in a carbon material pre-dispersion liquid or carbon material dispersion liquid, excluding substances that exist in the form of dissolved metal ions. Furthermore, examples of metals that can be considered metallic magnetic foreign matter include Fe, Co, and Cr.

[0081] As a method for removing metallic magnetic foreign matter by magnetic separation, there is no particular limitation as long as the method involves removing metallic magnetic foreign matter by magnetic force, and various magnetic separators can be used. As a method of removal by magnetic force, the use of an electromagnet is preferred. If an electromagnet is used, the appropriate magnetic force can be set by controlling the current flowing in the electromagnet, and magnetic components can be effectively removed, thus making it preferred. Furthermore, by making the current zero, the magnetic force can be made close to zero, therefore, compared to a permanent magnet, the removal of adsorbed magnetic components becomes easier, and thus maintenance is excellent. Examples of magnetic separation methods using electromagnets include passing a carbon material pre-dispersion liquid (X2) through a filter equipped with an electromagnet, stirring the carbon material pre-dispersion liquid (X2) using a stirring member equipped with an electromagnet, and installing a magnetic separation member equipped with an electromagnet in a dispersion container or flow path of the carbon material pre-dispersion liquid (X2).

[0082] Specifically, for example, you can use CS-150HHH, CS-250HHH, CS-300HHH manufactured by Japan Magnetics Co., Ltd., DVF-50-6, DVF-50-9, DVF-50-12 manufactured by Japan Eriez Magnetics Co., Ltd., and EMF-100S, EMF-150S, EMF-250S, EMF-300S manufactured by Daihwa Magnet Co., Ltd.

[0083] The magnetic flux density of the electromagnet is preferably 5000 Gauss or more and 30000 Gauss or less, more preferably 12000 Gauss or more and 30000 Gauss or less, and even more preferably 14000 Gauss or more and 30000 Gauss or less. By using an electromagnet within the above range, not only can metallic magnetic impurities contained in raw materials such as carbon materials be removed, but also metallic magnetic impurities generated during the manufacturing process can be removed, therefore it is preferred.

[0084] The flow rate of the carbon material predispersed liquid (X1) when in contact with the electromagnet is preferably 1 L / min or more and 200 L / min or less, more preferably 50 L / min or more and 150 L / min or less.

[0085] The carbon material pre-dispersion liquid (X1) is preferably passed through the electromagnet at least three times. If the number of passes is too low, it may not be sufficient to remove metallic magnetic foreign matter. When the electromagnet is passed through in a cyclic manner, it is preferable to pass it through more times to ensure uniformity within the container used in the manufacturing process.

[0086] The less metallic magnetic foreign matter in the carbon material predispersed solution (X2) after magnetic separation, the better. The content of the predispersed solution (X2) in 30 kg under the following conditions (I) is preferably less than 100 mg, more preferably less than 40 mg, and even more preferably less than 10 mg.

[0087] In this embodiment, by using a slip angle of less than 70° relative to the metal substrate and a cumulative particle size D... 50 Magnetic separation of carbon material pre-dispersion liquid (X1) with a particle size of 20 μm or larger can significantly reduce the amount of metallic magnetic foreign matter contained therein compared to the past.

[0088] This also reduces the content of metallic magnetic foreign matter in carbon material dispersions, resulting in secondary batteries with excellent battery characteristics.

[0089] <Condition (I)>

[0090] 30 kg of carbon material pre-dispersion liquid was passed through an electromagnet (magnetic flux density 16000 Gauss) 5 times, and then washed with an amide-based polar solvent. The resulting metallic magnetic foreign matter was deposited on a filter with a disc diameter of 47 mm and a mesh size of 5 μm. The weight of the metallic foreign matter particles on the filter was measured.

[0091] Specifically, the content of metallic magnetic foreign matter can be determined, for example, by the method described in the examples.

[0092] [Process (3)]

[0093] Step (3) is to disperse the above-mentioned carbon material pre-dispersion liquid (X2) to manufacture carbon material dispersion liquid.

[0094] In addition, in step (3), it is preferable to further include a step of removing metallic magnetic foreign matter while and / or after the carbon material pre-dispersion liquid (X2) is being dispersed.

[0095] The preferred cumulative particle size D of carbon material dispersion 50 Less than 20 μm. More preferably 10 μm or less, and even more preferably 5 μm or less. Additionally, preferably 0.1 μm or more.

[0096] If the cumulative particle size D 50 Within this range, not only are the properties excellent when used to manufacture secondary batteries, but the stability over time is also superior. Cumulative particle size D 50When the particle size is large, the particles tend to settle easily, and their stability may deteriorate over time. Additionally, if the cumulative particle size D... 50 If the particle size is too small, the particles will be unstable, clump together, and easily settle, thus potentially leading to decreased stability over time.

[0097] Cumulative particle size D 50 The particle size distribution curve of the volume reference is determined by laser diffraction / scattering particle size distribution measurement method, specifically, for example, by the method described in the [Example] item.

[0098] From the perspective of miniaturizing carbon materials, improving particle dispersibility, and achieving sufficient long-term stability, carbon material dispersions can undergo thorough dispersion treatment. For example, in elongated carbon materials such as carbon nanotubes, in order to maintain the shape of the carbon material while making the aggregates loose and smaller in particle size, dispersion treatment using a dispersion medium or dispersion treatment using shear force can be used. There are no particular limitations on the type of disperser that can be used to manufacture carbon material dispersions. Examples include paint conditioners (manufactured by Red Devil), colloid mills (PUC colloid mill, IKA MK colloid mill), conical mills (IKA MKO conical mill, etc.), ball mills, sand mills (Shinmaru Enterprises DynoMill, etc.), grinding mills, bead mills (Eirich DCP Mill, etc.), bead mills (Ashizawa Finetech Star Mill, etc.), high-pressure homogenizers (Genus PY, Sugino Machine Star Burst, Nanozer), M-Technique CLEAR SS-5, Nara Machinery MICROS, etc., media-free dispersers, and roller mills. From the perspective of dispersion efficiency, these dispersers can be used to disperse the carbon material until the dispersion becomes homogeneous. The dispersion process can be either a through-process dispersion or a circulating dispersion.

[0099] In the manufacture of carbon material dispersions, it is also preferable to have a process that uses the magnetic force of magnets or the like to remove metallic magnetic foreign matter.

[0100] As a method for removing metallic magnetic foreign matter by magnetic separation, the same method as described in step (2) can be used.

[0101] Furthermore, the carbon material dispersion can be filtered using a filter to remove metallic magnetic impurities. On the other hand, the carbon material pre-dispersion (X2) has a larger particle size than the carbon material dispersion, which can clog the filter and makes it difficult to add.

[0102] As a filter, it can be a surface filter like a membrane filter, or a depth filter, with a depth filter being more preferred. Since metallic magnetic foreign matter is not spherical and mostly oriented, a depth filter can effectively remove metallic magnetic foreign matter from a carbon material dispersion.

[0103] Depth filters differ from surface filters (filters that primarily capture particulate matter in the fluid on the filter surface). Depth filters primarily capture particulate matter within the filter media, offering high particle retention and resistance to clogging. By using depth filters, metallic magnetic impurities in carbon material dispersions can be removed more selectively.

[0104] As a depth filter, for example, 3M(TM) PP nonwoven fabric Depth Cartridge NT-T series, Pall's Profile II, and ROKI's SLOPE PURE can be used.

[0105] 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 using a filter with a small pore size to improve the removal efficiency of metallic magnetic impurities in a carbon material dispersion, the removal efficiency may decrease due to clogging of the carbon material. By using a filter with a filtration accuracy within the above-mentioned range, metallic impurities can be removed efficiently, resulting in a carbon material dispersion with a low content of metallic impurities.

[0106] By minimizing the content of metallic magnetic impurities, the thickening of the carbon material dispersion over time can be suppressed, resulting in good stability over time. On the other hand, when the content of metallic magnetic impurities is high, the dispersant in the carbon material dispersion is adsorbed onto the metallic magnetic impurities, thereby disrupting the dispersion of the carbon material and potentially causing thickening over time.

[0107] Furthermore, if the secondary battery contains a large amount of metallic magnetic foreign matter, during charge-discharge cycles, this foreign matter will dissolve at the positive electrode and precipitate at the negative electrode. Part of the negative and positive electrodes may then penetrate the separator and come into contact, potentially leading to poor voltage. Additionally, Li ion obstruction may sometimes occur. Moreover, in cases with a high amount of metallic magnetic foreign matter, it may sometimes come into contact with the positive electrode, causing a short circuit.

[0108] Therefore, the less metallic magnetic foreign matter in the carbon material dispersion, the better. Under the following conditions (II), the content in 30 kg of carbon material dispersion is preferably less than 100 mg, more preferably less than 40 mg, and even more preferably less than 10 mg.

[0109] <Condition (II)>

[0110] 30 kg of carbon material dispersion was passed through an electromagnet (magnetic flux density 16000 Gauss) 5 times, and then washed with an amide-based polar solvent. The resulting metallic magnetic foreign matter was deposited on a filter with a disc diameter of 47 mm and a mesh size of 5 μm. The weight of the metallic foreign matter particles on the filter was measured.

[0111] Specifically, the content of metallic magnetic foreign matter can be determined, for example, by the method described in the examples.

[0112] <Carbon Material Predispersant and Carbon Material Dispersion>

[0113] The carbon material predispersant and carbon material dispersion of this embodiment contain at least carbon material, dispersant and solvent.

[0114] The carbon material pre-dispersion (X1) has a slip angle of less than 70° and a cumulative particle size D 50 The size is 20 μm or larger. In addition, the carbon material predispersant (X2) is obtained by removing metallic magnetic foreign matter by magnetic separation during and / or after the manufacture of the carbon material predispersant (X1).

[0115] Specifically, carbon materials, dispersants, and solvents can be mixed and further dispersed as needed to produce a drop angle of less than 70° and a cumulative particle size D. 50 A carbon material predispersant (X1) with a particle size of 20 μm or larger is prepared. Furthermore, during and / or after the manufacture of the carbon material predispersant (X1), metallic magnetic foreign matter in the carbon material predispersant is removed by magnetic separation to prepare a carbon material predispersant (X2). In this way, the carbon material and metallic magnetic foreign matter are not excessively miniaturized, which not only reduces the content of metallic magnetic foreign matter in the dispersion, but also takes into account the long-term stability of the carbon material dispersion.

[0116] In addition, through the magnetic separation process, the slip angle and the cumulative particle size D 50 The change is almost constant, therefore the carbon material pre-dispersion (X2) also has a slip angle of less than 70° and a cumulative particle size D 50 It is above 20μm.

[0117] The carbon material dispersion of this embodiment is obtained by dispersing a carbon material pre-dispersion (X2).

[0118] Preferably, the carbon material dispersion is obtained by removing metallic magnetic foreign matter during and / or after dispersion of the carbon material pre-dispersion liquid (X2).

[0119] Cumulative particle size D of carbon material dispersion 50 Preferably, the particle size is 5 μm or less, more preferably 3 μm or less, and even more preferably 2 μm or less. Additionally, it is preferably 0.5 μm or more, and even more preferably 1 μm or more. The cumulative particle size D of the carbon material dispersion... 50When the content is within the above range, it is easy to remove the metallic magnetic foreign matter contained in the carbon material by magnetic separation, and it is easy to obtain a carbon material dispersion composition with low content of metallic magnetic foreign matter and good stability over time.

[0120] Furthermore, carbon material dispersion refers to the state before the addition of active material. In this respect, carbon material dispersion is distinguished from electrode slurry containing active material. That is, carbon material dispersion substantially does not contain active material. This concept excludes the state in which active material is intentionally added to the carbon material dispersion; the active material content relative to the total mass of the carbon material dispersion can be less than 1%, 0.5%, or 0.1% by mass, or even 0% by mass. Regarding active material, it will be discussed later.

[0121] (Carbon materials)

[0122] The carbon material used in this embodiment is not particularly limited. As a conductive carbon material, graphite, carbon black, or carbon nanotubes, carbon nanofibers, or carbon fibers, either alone or in combination, can be used. The carbon material serves to form a conductive pathway within the electrode. From the viewpoint of minimizing the risk of interruption due to the expansion and contraction of the electrode film, fibrous carbon materials are preferred, and more preferably fibrous carbon materials. Considering conductivity, ease of acquisition, and cost, carbon black and / or carbon nanotubes are preferred. Furthermore, from the viewpoint of reducing raw material costs and effectively forming a conductive network, two or more materials of the same type but with different physical properties can be used in combination. Examples of materials of the same type but with different physical properties include two types of carbon nanotubes with different average outer diameters or average fiber diameters, or two types of carbon black with different specific surface areas.

[0123] Carbon materials sometimes contain metallic magnetic foreign matter during the manufacturing process. It is difficult to completely remove this metallic magnetic foreign matter from the carbon material. In particular, carbon nanotubes sometimes contain metallic magnetic foreign matter derived from raw materials such as metal catalysts. While dispersing carbon nanotubes can make the contained metallic magnetic foreign matter visible, the process of miniaturizing and cutting the carbon nanotubes also miniaturizes the metallic magnetic foreign matter, making it difficult to extract from the dispersion.

[0124] However, the method for manufacturing the carbon material dispersion composition in this embodiment uses a slip angle of less than 70° relative to the metal substrate and a cumulative particle size D 50 Magnetic separation of pre-dispersed carbon materials with a particle size greater than 20 μm can efficiently remove metallic magnetic foreign matter from carbon materials.

[0125] Therefore, according to the method for manufacturing carbon material dispersion of this embodiment, even when using carbon nanotubes that mostly contain metallic magnetic foreign matter from the metal catalyst used in synthesis, the content of metallic magnetic foreign matter can be reduced compared to the past.

[0126] The carbon purity of a carbon material is expressed as the percentage (by mass%) of carbon atoms in the carbon material. Higher carbon purity is preferred; preferably, it is 90% by mass or more, more preferably 95% by mass or more, even more preferably 98% by mass or more, and particularly preferably 99% by mass or more, relative to 100% by mass of the carbon material. By setting the carbon purity within the above range, it is possible to prevent adverse conditions such as short circuits caused by dendrites formed from impurities.

[0127] [Carbon black]

[0128] Carbon black is manufactured by controlling various properties through the incomplete combustion of oil and gas, primarily composed of carbon microparticles. Carbon black possesses a secondary structure (aggregate) formed by primary particles linked together in a bead-like pattern, and a tertiary structure (cluster) formed by further aggregation of these secondary structures. Both secondary and tertiary structures are collectively referred to as the "structure." When observed with an electron microscope, primary particles appear spherical, but these particles are not chemically independent entities; rather, they are connected to adjacent primary particles within the aggregate through chemical bonds, forming the secondary structure. On the other hand, secondary structures are chemically independent entities that aggregate through intermolecular forces to form the tertiary structure. Therefore, it can be said that the conductivity within a secondary structure is higher than the conductivity between secondary structures containing contact resistance. Deaggregating the tertiary structure while preserving the secondary structure as much as possible is effective for obtaining electrodes with excellent conductivity. In this specification, the secondary structure is sometimes simply referred to as the "structure."

[0129] The carbon black used in this embodiment can be various commercially available carbon blacks such as acetylene black, furnace black, hollow carbon black, channel black, thermal cracking black, and Ketjen black. Alternatively, carbon black that has undergone conventional oxidation treatment or graphitization treatment can also be used.

[0130] Oxidation treatment of carbon black involves subjecting it to high-temperature treatment in air or secondary treatment with nitric acid, nitrogen dioxide, ozone, etc., thereby directly introducing (covalently bonding) oxygen-containing polar functional groups such as phenolic, quinone, carboxyl, and carbonyl groups onto the surface of the carbon black. This process is usually carried out to improve the dispersibility of carbon black.

[0131] Commercially available carbon blacks include, for example, SuperP-Li (manufactured by TIMCAL), Ketjen Black EC-300J, EC-600JD (manufactured by Lion), DENKA BLACK, DENKA BLACK Li-400, and FX-35 (manufactured by DENKA, acetylene black). Graphite types include, for example, artificial graphite, flake graphite, block graphite, and natural graphite, but are not limited to these; two or more types can be used in combination.

[0132] The average primary particle size of carbon black is preferably 10 nm to 1 μm, particularly preferably 20 nm to 200 nm, and even more preferably 25 nm to 100 nm.

[0133] The average primary particle size of carbon black can be calculated as follows: First, observe and photograph the carbon black using a transmission electron microscope. Select any 100 spherical primary carbon black particles from the photographs and measure their outer diameters. The average primary particle size of carbon black can then be calculated.

[0134] The preferred BET specific surface area for carbon black is 10 m². 2 / g or more and 1500m 2 / g or less, preferably 40m 2 / g or more and 1000m 2 / g or less, more preferably 100m 2 / g or more and 850m 2 / g or less. When the BET specific surface area is within the above range, an effective conductive network can be formed with a small amount, reducing the amount of conductive material in the electrode. This increases the freedom of battery design in terms of increasing the amount of active material, binder resin, etc. Furthermore, during the preparation of the electrode slurry, the composite of the active material and carbon black is easily achieved, thus easily obtaining an electrode film with a homogeneous conductive network coated with carbon black on the surface of the active material. This suppresses electrolyte decomposition reactions at the interface between the electrolyte and the active material, improving the battery's cycle characteristics.

[0135] BET specific surface area can be determined by the BET method as described in JIS Z 8830.

[0136] Carbon nanotubes

[0137] Carbon nanotubes have a structure in which planar graphite is wound into a cylindrical shape. Preferably, the carbon nanotubes comprise multilayer carbon nanotubes, but they can also comprise both multilayer and single-layer carbon nanotubes. Multilayer carbon nanotubes have a structure consisting of two or more layers of wound graphite. Single-layer carbon nanotubes have a structure consisting of a single layer of wound graphite. The sidewalls of the carbon nanotubes do not necessarily have to be graphite. For example, carbon nanotubes with amorphous sidewalls can also be used as the carbon material.

[0138] The average outer diameter of the carbon nanotubes is preferably 1 nm or more and 25 nm or less, more preferably 3 nm or more and 20 nm or less, and even more preferably 4 nm or more and 15 nm or less. When the average outer diameter is within the above range, a good conductive network can be easily formed in the electrode. During charging and discharging, the active material inside the secondary battery is utilized homogeneously, thus suppressing the degradation of the active material and further improving the cycle characteristics of the secondary battery.

[0139] Regarding the G / D ratio (the ratio of G-band to D-band peaks) of carbon nanotubes, in the case of using amide-based polar solvents, the peak value at 1560 cm⁻¹ in the Raman spectrum is... -1 ~1600cm -1 The maximum peak intensity within the range is set as G, and 1310 cm⁻¹ is used. -1 ~1350cm -1 When the maximum peak intensity within the range is set to D, the G / D ratio is preferably 0.5 to 10, more preferably 0.7 to 4.5. Furthermore, when using a solvent containing 50% or more water, the 1560 cm⁻¹ Raman spectrum is... -1 ~1600cm -1 The maximum peak intensity within the range is set as G, and 1310 cm⁻¹ is used. -1 ~1350cm -1 When the maximum peak intensity within the range is set to D, the G / D ratio is preferably 5 to 100, and more preferably 10 to 50.

[0140] When the G / D ratio of carbon nanotubes is within the above-mentioned range, it is believed that the contact resistance between carbon nanotubes decreases, making it easier to obtain good electrical conductivity. Furthermore, it is speculated that this is because the amount of functional groups on the surface of multilayer carbon nanotubes is appropriate, resulting in good affinity with solvents and improved dispersibility.

[0141] The preferred BET specific surface area of ​​carbon nanotubes is 100 m². 2 / g or more and 1500m 2 / g or less, more preferably 150m 2 / g or more and 1000m 2 / g or less, more preferably 200m 2 / g or more and 800m 2 / g or less. When the BET specific surface area is within the above range, an effective conductive network can be formed with a small amount of material, reducing the amount of conductive material in the electrode. This increases the freedom of battery design in terms of increasing the amount of active material, binder resin, etc. Furthermore, during the preparation of the slurry, the composite of the active material and carbon nanotubes is easily achieved, thus easily obtaining an electrode film with a homogeneous conductive network of carbon nanotubes coated on the surface of the active material. This suppresses electrolyte decomposition reactions at the interface between the electrolyte and the active material, improving the cycle characteristics of the battery.

[0142] BET specific surface area can be determined by the BET method as described in JIS Z 8830.

[0143] The carbon purity of carbon nanotubes can be adjusted through purification processes. Various methods known in the art can be used as purification methods for carbon nanotubes. Examples include acid treatment, graphitization, and chlorination.

[0144] The acid used for acid treatment of carbon nanotubes can be any acid capable of dissolving the metals and metal oxides contained in the carbon nanotubes. Inorganic acids and carboxylic acids are preferred, with hydrochloric acid, sulfuric acid, and nitric acid being particularly preferred among the inorganic acids. The acid treatment of carbon nanotubes is preferably carried out in a liquid phase, and more preferably, the carbon nanotubes are dispersed and / or mixed in a liquid phase. After acid treatment, the carbon nanotubes are preferably washed with water and dried.

[0145] There are no particular limitations on the graphitization of carbon nanotubes. It can be carried out by heating carbon nanotubes at 1500℃ to 3500℃ in an inactive atmosphere with an oxygen concentration of less than 0.1%.

[0146] There are no particular limitations on the chlorination treatment of carbon nanotubes. For example, chlorine gas can be introduced into the carbon nanotubes in an inactive atmosphere with an oxygen concentration of less than 0.1%, and the carbon nanotubes can be heated at 800℃ to 2000℃.

[0147] The surface or ends of carbon nanotubes can be modified with functional groups or alkyl groups, and can also be doped with alkali metals or halogens. For example, functionalization can be achieved by heating in acid with carboxyl, sulfonyl, or hydroxyl groups. From the perspective of achieving both good stability and flowability of the obtained carbon nanotube dispersion, it is preferable to use carbon nanotubes without acidic functional groups such as carboxyl and sulfonyl groups.

[0148] (Dispersant)

[0149] In this embodiment, the dispersant is not particularly limited as long as it can stabilize the carbon material in the dispersion; surfactants, resin-based dispersants, etc., can be used. Surfactants are mainly classified as anionic, cationic, nonionic, and amphoteric. Depending on the required characteristics for the dispersion of the carbon material, an appropriate type of dispersant can be used in a suitable proportion.

[0150] When choosing anionic surfactants, the type is not particularly limited. Specifically, examples include: fatty acid salts, polysulfonates, polycarboxylates, alkyl sulfates, alkyl aryl sulfonates, alkyl naphthalene sulfonates, dialkyl sulfonates, dialkyl sulfosuccinates, alkyl phosphates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyl aryl ether sulfates, naphthalene sulfonic acid formaldehyde condensates, polyoxyethylene alkyl phosphate sulfonates, glyceryl borate fatty acid esters, and polyoxyethylene glyceryl fatty acid esters, but are not limited to these. Further, specifically, examples include sodium dodecylbenzenesulfonate, sodium lauryl sulfate, sodium polyoxyethylene lauryl ether sulfate, polyoxyethylene nonylphenyl ether sulfate, and sodium salts of β-naphthalene sulfonic acid formaldehyde condensates, but are not limited to these.

[0151] In addition, alkylamine salts and quaternary ammonium salts are examples of cationic surfactants. Specifically, examples include stearamine acetate, trimethylcocoylammonium chloride, trimethyltallowylammonium chloride, dimethyl dioleylammonium chloride, methyl oleyl diethanol chloride, tetramethylammonium chloride, laurylpyridinium chloride, laurylpyridinium bromide, laurylpyridinium disulfide, hexadecylpyridinium bromide, 4-alkylmercaptopyridine, poly(vinylpyridine)-dodecyl bromide, and dodecylbenzyltriethylammonium chloride, but these are not limited to. Additionally, aminocarboxylate salts are examples of amphoteric surfactants, but these are not limited to.

[0152] In addition, examples of nonionic surfactants include polyoxyethylene alkyl ethers, polyoxyethylene derivatives, polyoxyethylene phenyl ethers, sorbitan fatty acid esters, polyoxyethylene sorbitan fatty acid esters, and alkyl allyl ethers, but are not limited to these. Specifically, examples include polyoxyethylene lauryl ether, sorbitan fatty acid esters, and polyoxyethylene octylphenyl ether, but are not limited to these.

[0153] The surfactant selected is not limited to a single surfactant. Therefore, two or more surfactants can be used in combination. For example, a combination of anionic and nonionic surfactants, or a combination of cationic and nonionic surfactants, can be used. In this case, the amount of surfactant used is preferably appropriate relative to each surfactant component. As a combination, a combination of anionic and nonionic surfactants is preferred. The anionic surfactant is preferably a polycarboxylate. The nonionic surfactant is preferably a polyoxyethylene phenyl ether.

[0154] In addition, resin-type dispersants can specifically include fluorinated resins, cellulose derivatives (cellulose acetate, cellulose acetate butyrate, cellulose butyrate, cyanoethyl cellulose, ethyl hydroxyethyl cellulose, nitrocellulose, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, etc.), polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, hydrogenated nitrile rubber, and polyacrylonitrile polymers. Fluorinated resins, methyl cellulose, ethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinylpyrrolidone, hydrogenated nitrile rubber, and polyacrylonitrile polymers are particularly preferred. From the viewpoint of balancing the long-term stability of carbon materials and the efficiency of removing metallic magnetic foreign matter based on magnetic separation, the molecular weight of the resin-type dispersant is preferably between 10,000 and 300,000.

[0155] From the perspective of antioxidant properties, hydrogenated nitrile butadiene rubber and polyacrylonitrile polymers are preferred dispersants.

[0156] From the viewpoint of the long-term stability of carbon materials, the content of the dispersant is preferably 10 to 300 parts by mass relative to 100 parts by mass of carbon materials, and more preferably 10 to 100 parts by mass. By setting it within the above range, the dispersion state of the carbon materials can be stably maintained, and the long-term stability can also be better.

[0157] In addition to dispersants, amine compounds and inorganic bases are preferably added. As amine compounds, primary amines, secondary amines, and tertiary amines are used, excluding ammonia and quaternary ammonium compounds. Besides monoamines, amine compounds such as diamines, triamines, and tetraamines with multiple amino groups within their molecules can also be used. Specifically, examples include: 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, but these are not limited to these. Examples of inorganic bases 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.

[0158] When using amine compounds or inorganic bases, their content relative to 100 parts by mass of the dispersant is preferably 0.1 parts by mass or more and 10 parts by mass or less, more preferably 0.5 parts by mass or more and 6 parts by mass or less, and even more preferably 1 part by mass or more and 3 parts by mass or less. This improves the wettability of the carbon material to the solvent, further enhancing dispersibility. When carbon nanotubes are used as the carbon material, dispersibility is significantly improved.

[0159] (solvent)

[0160] The solvent used in this embodiment is not limited as long as it can disperse the carbon material; water or organic solvents such as amide-based organic solvents can be used.

[0161] Aqueous solvents can sometimes corrode magnets, weakening their magnetic strength and introducing metallic magnetic impurities. Therefore, using amide-based organic solvents can reduce the content of metallic magnetic impurities in carbon material dispersions. When using aqueous solvents, applying Teflon (registered trademark), epoxy coating, or plating to the magnets can prevent corrosion and reduce the content of metallic magnetic impurities in the carbon material dispersion.

[0162] Examples of amide-based organic solvents include N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, and N-methylcaprolactam. Particularly preferred solvents include at least one solvent selected from the group consisting of N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone.

[0163] When using an organic solvent as the solvent in this embodiment, it is preferable to have a substantially water-free content, from the viewpoint of suppressing thickening of the carbon material. Specifically, as a reference for the carbon material dispersion, the water content is preferably 100 to 3000 ppm, more preferably 200 to 1500 ppm, and most preferably 200 to 1000 ppm. If a large amount of water is present, the carbon material dispersion or the electrode slurry using it may thicken or gel. By setting the water content within the above range, the dispersion state of the carbon material can be well maintained, and thickening can be suppressed even when the carbon material dispersion is stored for a long time, which is therefore preferable.

[0164] (Other arbitrary ingredients)

[0165] The carbon material pre-dispersion and carbon material dispersion can be appropriately combined with wetting agents, pH adjusters, wetting and penetrating agents, leveling agents and other additives, adhesive resins described later, other conductive materials, etc., within the scope that does not hinder the purpose of the present invention. They can be added at any time, such as before the preparation of the mixture, during the mixing, after the mixing, or during the preparation of the carbon material pre-dispersion or carbon material dispersion.

[0166] Manufacturing of Electrode Paste

[0167] Electrode slurry can be manufactured by mixing active substances into the carbon material dispersion of this embodiment.

[0168] The active material can be either a positive electrode active material or a negative electrode active material. Additionally, it may further contain binder resin, other conductive materials, solvents, and may further mix any other components.

[0169] In this specification, the positive electrode active material and the negative electrode active material are sometimes referred to simply as "active material". Active material refers to the material that forms the basis of the battery reaction. Active materials are classified into positive electrode active materials and negative electrode active materials according to their electromotive force. Electrode slurry is sometimes also called "mixed slurry" or "electrode mixed slurry", and sometimes electrode slurries containing positive electrode active materials or negative electrode active materials are referred to as "positive electrode slurry" and "negative electrode slurry", respectively. To improve uniformity and processability, the electrode slurry is preferably in slurry form.

[0170] (Positive electrode active material)

[0171] The positive electrode active material is not particularly limited; for example, for secondary battery applications, metal compounds such as metal oxides and metal sulfides that can reversibly dope or intercalate lithium ions can be used. Examples include lithium manganese composite oxides (e.g., Li). x Mn₂O₄ or LixMnO₂), lithium-nickel composite oxides (e.g., Li₂O₄ or LixMnO₂), and lithium-nickel composite oxides (e.g., Li₂O₄). x NiO2), lithium cobalt composite oxide (Li x CoO2), lithium nickel cobalt composite oxides (e.g., Li) x Ni 1-y Co y O2), lithium manganese cobalt composite oxides (e.g., Li) x Mn y Co 1-y O2), lithium nickel manganese cobalt composite oxides (e.g., Li) x Ni y Co z Mn 1-y-z O2), spinel-type lithium manganese nickel composite oxides (e.g., Li) x Mn 2-y Ni y Lithium-transition metal composite oxide powders such as O4, and lithium phosphorus oxide powders with olivine structure (e.g., Li) x FePO4, Li x Fe 1-y Mn y PO4, Li x CoPO4, manganese oxide, iron oxide, copper oxide, nickel oxide, vanadium oxide (e.g., V2O5, V6O)13 ) Transition metal oxide powders such as titanium oxide, iron(III) sulfate (Fe2(SO4)3), transition metal sulfide powders such as TiS2 and FeS, etc. Among them, x, y, and z are numbers, 0 < x < 1, 0 < y < 1, 0 < z < 1, 0 < y + z < 1. These positive electrode active materials can also be used alone or in combination of multiple kinds. Among these active materials, especially active materials containing Ni and / or Mn (especially further when the total amount of Ni and / or Mn in the transition metal is 50 mol% or more), due to the elution of components or metal ions from the raw materials, there is a tendency for the alkalinity to increase, and due to this influence, gelation of the binder and deterioration of the dispersion state are likely to occur, so sometimes the problems of the present invention appear significantly. Therefore, in the case of a battery containing an active material containing Ni and / or Mn, this embodiment is particularly effective.

[0172] (Negative electrode active material)

[0173] The negative electrode active material is not particularly limited. For example, metallic Li that can reversibly dope or intercalate lithium ions, or its alloy, tin alloy, silicon alloy negative electrode, Li X TiO2, Li X Fe2O3, Li X Fe3O4, Li X Metal oxide systems such as WO2, conductive polymers such as polyacetylene and polyphenylene, artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, resin-fired carbon materials. Among them, x is a number, 0 < x < 1. These negative electrode active materials can also be used alone or in combination of multiple kinds. Especially in the case of using a silicon alloy negative electrode, the theoretical capacity is large, but the volume expansion is extremely large, so it is preferably used in combination with artificial graphite such as highly graphitized carbon materials, or carbonaceous powders such as natural graphite, resin-fired carbon materials, etc.

[0174] The content of the carbon material in the electrode paste is preferably 0.01 part by mass or more, more preferably 0.05 part by mass or more, and further preferably 0.10 part by mass or more with respect to 100 parts by mass of the active material. In addition, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and further preferably 3 parts by mass or less. If it is higher than the above range, sometimes the filling amount of the active material in the electrode decreases, resulting in a low capacity of the battery. In addition, when it is lower than the above range, sometimes the conductivity of the electrode and the battery becomes insufficient.

[0175] The content of the dispersant in the electrode paste is preferably 0.01 part by mass or more, more preferably 0.02 part by mass or more with respect to 100 parts by mass of the active material. In addition, it is preferably 10 parts by mass or less, more preferably 5 parts by mass or less.

[0176] (Binder resin)<0******

[0177] When the electrode paste also contains a binder resin, there are no particular restrictions as long as the substance is commonly used as a binder resin in coatings or similar materials; it can be selected appropriately depending on the purpose. Furthermore, the binder resin used in the electrode paste is a resin capable of binding active substances, conductive materials, and other substances together. Examples of binder resins used in electrode pastes include: polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylates, methacrylic acid, methacrylates, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinylpyrrolidone, etc., as structural units; polyurethane resins, polyester resins, phenolic resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, fluoropolymers; cellulose resins; elastomers such as styrene-butadiene rubber and fluororubber; conductive resins such as polyaniline and polyacetylene. Modified forms, mixtures, and copolymers of these resins are also possible. When using a binder resin as the positive electrode, materials such as polyvinylidene fluoride, polyvinyl fluoride, and tetrafluoroethylene are preferred for durability. When using a binder resin as the negative electrode, materials with good adhesion such as CMC, styrene-butadiene rubber, and polyacrylic acid are preferred.

[0178] When the electrode slurry contains a binder resin, the content of the binder resin in the electrode slurry is preferably 0.5 parts by mass or more relative to 100 parts by mass of the active material. Furthermore, it is preferably 30 parts by mass or less, more preferably 25 parts by mass or less, and even more preferably 20 parts by mass or less.

[0179] The solid content of the electrode paste, based on the mass of the electrode paste (with the mass of the electrode paste set to 100% by mass), is preferably 30% by mass or more, more preferably 40% by mass or more. Furthermore, it is preferably 90% by mass or less, more preferably 80% by mass or less.

[0180] Electrode slurries can be prepared using various methods known in the art. Examples include methods involving adding an active substance to a carbon material dispersion; methods involving adding an active substance to a carbon material dispersion followed by the addition of a binder resin; and methods involving adding an active substance to a carbon material dispersion followed by the addition of a binder resin. The dispersion apparatus used is not particularly limited, and the dispersion methods listed in the description of the carbon material dispersion can be used to obtain the electrode slurry. Therefore, as a method for preparing an electrode slurry, it is possible to omit the binder resin from the carbon material dispersion and instead perform a process of adding an electrode active substance and dispersing it.

[0181] Electrode Manufacturing

[0182] The electrode is obtained by forming an electrode film using the aforementioned carbon material dispersion or electrode slurry. Preferably, the electrode is manufactured by coating an electrode slurry onto a current collector to form an electrode film, and it can be either a positive or negative electrode.

[0183] An electrode may have, for example, a current collector and an electrode film obtained by coating the current collector with an electrode paste and drying it. An electrode formed using a positive electrode paste may be used as a positive electrode. An electrode formed using a negative electrode paste may be used as a negative electrode. In this specification, an electrode film formed using an electrode paste containing an active substance is sometimes referred to as an "electrode mixture layer".

[0184] The material and shape of the current collector used in the formation of the above electrodes are not particularly limited, and a current collector suitable for various secondary batteries can be appropriately selected. Examples of materials for the current collector include conductive metals or alloys such as aluminum, copper, nickel, titanium, or stainless steel. Regarding the shape, a planar foil is generally used, but current collectors with roughened surfaces, perforated foil-shaped current collectors, and mesh-shaped current collectors can also be used. The thickness of the current collector is preferably around 0.5 to 30 μm.

[0185] There are no particular limitations on the method of coating the current collector with a carbon material dispersion or electrode slurry, and known methods can be used. Specifically, examples include mold coating, dip coating, roller coating, scraper coating, blade coating, spray coating, gravure coating, screen printing, or electrostatic coating. As for drying methods, examples include drying by placing or using a blower dryer, hot air dryer, infrared heater, far-infrared heater, etc., but these are not particularly limited.

[0186] After coating, the film can be rolled using a flatbed press, rolling rolls, or similar equipment. The resulting film has a thickness of, for example, 1 μm or more and 500 μm or less, preferably 10 μm or more and 300 μm or less.

[0187] To improve the adhesion between the electrode film and the current collector or to improve the conductivity of the electrode film, films formed using carbon material dispersions or electrode slurries can also be used as the base layer of the electrode.

[0188] Manufacturing Secondary Batteries

[0189] The secondary battery includes a step of forming an electrode film using the aforementioned carbon material dispersion or electrode slurry. Preferably, the secondary battery includes a step of coating an electrode slurry onto a current collector to form an electrode film. The secondary battery may include, for example, a positive electrode, a negative electrode, and an electrolyte, wherein at least one of the positive and negative electrodes may be an electrode obtained by the manufacturing method of this embodiment.

[0190] As the electrolyte, various conventionally known electrolytes capable of ion mobility can be used. Examples include, but are not limited to, substances 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 phenyl). The electrolyte is preferably dissolved in a non-aqueous solvent for use as the electrolyte solution.

[0191] As a non-aqueous solvent, there are no particular limitations. Examples include carbonates such as ethylene carbonate, propylene carbonate, butyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octyl lactone; glycol dimethyl ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methyl formate, methyl acetate, and methyl propionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents can be used individually or in combination.

[0192] The secondary battery preferably has a separator. Examples of separators include polyethylene nonwoven fabric, polypropylene nonwoven fabric, polyamide nonwoven fabric, and nonwoven fabrics that have undergone hydrophilic treatment, but are not particularly limited to these.

[0193] The structure of the secondary battery in this embodiment is not particularly limited. It usually has a positive electrode and a negative electrode, as well as a separator as needed. It can be made into various shapes such as paper type, cylindrical type, button type, and stacked type, depending on the purpose of use.

[0194] Example

[0195] The following examples illustrate the present invention in further detail. The present invention is not limited to the following examples unless it departs from its spirit. Furthermore, unless otherwise specified, "parts" refers to "parts by mass" and "%" refers to "% by mass".

[0196] The materials used in the examples and comparative examples are shown below.

[0197] <Carbon Materials>

[0198] • Carbon Material 1: Carbon Nanotubes (manufactured by JEIO, JENOTUBE10B)

[0199] • Carbon material 2: Carbon nanotubes (manufactured by JEIO, JENOTUBE6A)

[0200] • Carbon Material 7: Carbon Nanotubes (made of OCSiAl, TUBALL 01RW03)

[0201] • Carbon material 9 Ketjen Black (manufactured by Lion Specialty Chemical, Ketjen Black EC 300J)

[0202] • Carbon materials 10 Carbon nanotubes (Cnano made, FT 2020)

[0203] <Dispersant>

[0204] • Dispersant 1: Hydrogenated nitrile butadiene rubber (ARLANXEO, Therban(R)3406)

[0205] • Dispersant 2: Hydrogenated nitrile butadiene rubber (manufactured by ARLANXEO, Therban(R)3404)

[0206] • Dispersant 3: Liquid hydrogenated nitrile butadiene rubber (manufactured by Zannan Scitech, ZN 35050 L3)

[0207] • Dispersant 4: Polyacrylonitrile (manufactured by Sigma Aldrich, polyacrylonitrile Mw 150000)

[0208] • Dispersant 5: Polyvinyl butyral (manufactured by Sekisui Chemicals Co., Ltd., BL-10)

[0209] • Dispersant 6: Polyvinylidene fluoride (Solvay, Solef #5130)

[0210] • Dispersant 7: Polyvinyl alcohol (manufactured by Kuraray, Kuraray POVAL 3-80)

[0211] • Dispersant 8: Carboxymethyl cellulose (manufactured by Nippon Paper Corporation, APP-84)

[0212] <Additives>

[0213] Additive 1 NaOH: Sodium hydroxide (Tosoh Pearl granular caustic soda manufactured by Tosoh Corporation)

[0214] Additive 2: 2-Aminoethanol (manufactured by Fujifilm and Wako Pure Chemical Industries, Wako Grade 1)

[0215] <The Making of Carbon Material 3>

[0216] 10 kg of carbon material 1 was weighed into a 120 L heat-resistant container and placed inside a furnace. Nitrogen gas was then introduced into the furnace, and air was vented while maintaining positive pressure. After the oxygen concentration in the furnace reached below 0.1%, the furnace was heated to 1600°C for 30 hours. Chlorine gas was then introduced at a rate of 50 L / min for 50 hours while maintaining the furnace temperature at 1600°C. Then, nitrogen gas was introduced at a rate of 50 L / min, and the furnace was cooled under positive pressure to obtain carbon material 3.

[0217] <The Making of Carbon-4 Materials>

[0218] 10 kg of carbon material 2 was weighed into a 120 L heat-resistant container and placed inside a furnace. Nitrogen gas was then introduced into the furnace, and air was vented while maintaining positive pressure. After the oxygen concentration in the furnace reached below 0.1%, the furnace was heated to 1600°C for 30 hours. Chlorine gas was then introduced at a rate of 50 L / min for 50 hours while maintaining the furnace temperature at 1600°C. Then, nitrogen gas was introduced at a rate of 50 L / min, and the furnace was cooled under positive pressure to obtain carbon material 4.

[0219] <Making of Carbon Material 5>

[0220] For carbon material 1, zirconia beads with a diameter of 8 mm were fed into a dynamic grinding mill (manufactured by Nippon Kogyo Kogyo) as the grinding medium, and the mill was processed at a circumferential speed of 5.0 m / s under operating conditions of 10.0 kg / h to obtain carbon material 5.

[0221] <The Production of Carbon-6 Material>

[0222] For carbon material 4, 8mm diameter zirconium oxide beads were fed into a dynamic grinding mill (manufactured by Nippon Kogyo Kogyo) as the grinding medium, and the mill was processed at a circumferential speed of 5.0m / s under operating conditions of 10.0kg / h to obtain carbon material 6.

[0223] <The Making of Carbon-8 Materials>

[0224] 3 kg of carbon material 7 was weighed into a 120 L heat-resistant container and placed inside a furnace. Nitrogen gas was then introduced into the furnace, and air was vented while maintaining positive pressure. Once the oxygen concentration in the furnace reached below 0.1%, the furnace was heated to 1600°C for 30 hours. Chlorine gas was then introduced at a rate of 50 L / min for 50 hours while maintaining the furnace temperature at 1600°C. Finally, nitrogen gas was introduced at a rate of 50 L / min, and the furnace was cooled under positive pressure to obtain carbon material 8.

[0225] Methods for Determination and Evaluation of Physical Properties

[0226] The methods for measuring and evaluating the physical properties of the carbon materials, carbon material pre-dispersions, carbon material dispersions, electrodes, and secondary batteries used in the embodiments and comparative examples described below are as follows.

[0227] <Average outer diameter of carbon nanotubes>

[0228] For carbon nanotubes, 0.2 g of carbon nanotubes were weighed into a 450 mL SM sample vial (Mitsu Ltd.) using an electronic balance (Sartorius MSA225S100DI). 200 mL of toluene was added, and the nanotubes were dispersed using an ultrasonic homogenizer (Advanced Digital Sonifer MODEL 450DA, BRANSON Ltd.) at 30% amplitude under ice-cooling for 5 minutes to prepare a carbon nanotube dispersion. The dispersion was then appropriately diluted, and several μL were added dropwise in the form of a collodion film. After drying at room temperature, the nanotubes were observed directly using a transmission electron microscope (H-7650, Hitachi, Ltd.). Observation involved taking multiple photographs containing 10 or more carbon nanotubes within the field of view at 50,000x magnification. The outer diameter of 300 randomly extracted carbon nanotubes was measured, and the average value was taken as the average outer diameter (nm) of the carbon nanotubes. When carbon nanotubes form bundle-like aggregates, they are observed at 1 millionx magnification using a transmission electron microscope (JEM 2800, manufactured by NEC Corporation) and the same measurements are taken as the average outer diameter of the carbon nanotubes.

[0229] <Primary particle size of carbon black>

[0230] The primary particle size of carbon black is obtained by observing at least 30 (e.g., 30 to 100) primary particles through an electron microscope (either scanning or transmission electron microscope can be used, with transmission electron microscope preferred).

[0231] <BET specific surface area of ​​carbon materials>

[0232] After weighing 0.03 g of carbon material using an electronic balance (Sartorius MSA225S100DI), it was dried at 110°C for 15 minutes while being degassed. Then, the BET specific surface area of ​​the carbon material was measured using a fully automated specific surface area measuring device (MOUNTECH HM-model1208).

[0233] <Carbon purity of carbon materials>

[0234] The carbon material was acid-decomposed using a microwave sample pretreatment device (Milestone General, ETHOS1) to extract the metals contained within it. Then, a multi-channel ICP-ELISA analyzer (Agilent 720-ES) was used to analyze the extract and calculate the total amount of metals (iron, cobalt, nickel, copper, and chromium). The carbon purity of the carbon material was calculated as follows.

[0235] Carbon purity (%) of carbon materials = ((mass of carbon materials - metal content) ÷ mass of carbon materials) × 100

[0236] [Table 1-1]

[0237]

[0238] [Table 1-2]

[0239]

[0240] <Slip angle of carbon material predispersion>

[0241] A SUS 316 L sample plate, serving as a metal substrate, was horizontally fixed to a contact angle meter (DM-501) manufactured by Kyowa Interface Science Co., Ltd. 10 μL of a carbon material pre-dispersion liquid, used as the test solution, was dropped onto the horizontally placed sample plate to form a water droplet. The sample plate was then tilted slightly, and the angle of the sample plate at which the water droplet began to roll was measured. The smaller the angle, the better the water droplet's slippage (hydrophobicity).

[0242] The cumulative particle size D of carbon material predispersant and carbon material dispersion 50 Measurement >

[0243] Cumulative particle size D based on particle size distribution 50 The particle size distribution was measured using a laser diffraction / scattering particle size distribution measuring device (manufactured by Horiba Manufacturing Co., Ltd.; Partical LA-960 V2). This measuring device uses a laser wavelength of 650 nm and employs one annular 64-segment silicon photodiode, five 4-channel array detectors, and three silicon photodetectors as detectors. Furthermore, the measuring section utilizes a flow-through sample cell (sample cell) made of synthetic quartz.

[0244] First, NMP, the same solvent as the dispersion, was added to a sample bath containing the sample cell, and a circulating / ultrasonic cleaning process was performed. The operating mode was set as follows: circulation speed: 3, ultrasonic intensity: 7, ultrasonic time: 1 minute, stirring speed: 7, stirring mode: continuous. Next, to remove air, ultrasonic cleaning was performed at ultrasonic intensity: 7 and ultrasonic time: 5 seconds, followed by a blank (background) measurement. The particle size was set to volume, the particle refractive index was set to 1.920–0.522i (carbon material), and the solvent refractive index was set to 1.468 (NMP). The dispersion was added dropwise at a laser transmittance of 60% ± 1% during measurement to prepare the sample. The measurement was performed with a circulation speed of 3, stirring speed: 7, and stirring mode: continuous.

[0245] <Determination of the amount of metallic magnetic foreign matter in carbon material predispersants>

[0246] 30 kg of carbon material pre-dispersion liquid was passed through an electromagnet (manufactured by Daibo Magnet Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) five times via a diaphragm pump. Then, N-methyl-2-pyrrolidone (NMP) was passed through the electromagnet (manufactured by Daibo Magnet Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) to expel and wash the carbon material pre-dispersion liquid from the diaphragm pump and electromagnet until substantially no solid components remained. Afterward, the power to the electromagnet was disconnected, and after confirming that the magnetic force of the filter had disappeared, NMP was passed through the electromagnet to obtain 10 kg of NMP containing metallic magnetic foreign matter.

[0247] Next, 1 kg of NMP containing metallic magnetic foreign matter was transferred to a 2L plastic container and ultrasonically treated for 5 minutes using an ultrasonic cleaner (Aiwa Medical Industrial Co., Ltd.) at an output power of 300W and a frequency of 28kHz. Then, a rod magnet with a magnetic flux density of 12000 Gauss was fixed to the outside of the plastic container to trap the metallic magnetic foreign matter, allowing the NMP to flow. The trapped metallic magnetic foreign matter was then filtered using ethanol to recover all the pre-weighed sieve (weight: W1, diameter: 47mm, mesh size: 5μm). The sieve containing the accumulated metallic magnetic foreign matter was then removed and dried in a hot air oven at 60°C for 20 minutes. After performing this process on 10 kg of NMP containing the recovered metallic magnetic foreign matter, the weight of the dried sieve (W2) was measured, and the value obtained by subtracting the pre-weighed weight (W1) was taken as the amount of metallic magnetic foreign matter (W0).

[0248] The lower the amount of metallic magnetic foreign matter (W0), the better. A is less than 10mg of metallic magnetic foreign matter (W0), B is more than 10mg but less than 40mg, C is more than 40mg but less than 100mg, and D is more than 100mg.

[0249] Evaluation of the amount of metallic magnetic foreign matter in carbon material dispersions

[0250] Except for changing the carbon material predispersant to a carbon material dispersion, the amount of metallic magnetic foreign matter (W0) in the carbon material dispersion was determined using the same method as for determining the amount of metallic magnetic foreign matter in the carbon material predispersant.

[0251] The lower the amount of metallic magnetic foreign matter (W0), the better. A metallic magnetic foreign matter (W0) of less than 10 mg is ◎ (excellent), 10 mg or more but less than 40 mg is 〇 (good), 40 mg or more but less than 100 mg is △ (acceptable), and more than 100 mg is × (unacceptable).

[0252] <Evaluation of the long-term stability of carbon material dispersions>

[0253] Viscosity was measured using a Type B viscometer (manufactured by Toki Sangyo Co., Ltd., "BL"). The sample was allowed to stand in a constant temperature bath at 25°C for at least one hour, and then the measurement was performed with the Type B viscometer rotor rotating at 100 rpm. The rotor used for the measurement was No. 1 for viscosities less than 100 mPa·s, No. 2 for viscosities between 100 and 500 mPa·s, No. 3 for viscosities between 500 and 2,000 mPa·s, and No. 4 for viscosities between 2,000 and 10,000 mPa·s. Lower viscosity indicates better dispersibility, while higher viscosity indicates poorer dispersibility. The long-term stability of the carbon material dispersion was evaluated using the following formula 1.

[0254] (Equation 1)

[0255] Stability over time = (Initial viscosity) / (Viscosity after 3 days of storage in a constant temperature bath at 40℃) × 100%

[0256] In the evaluation of stability over time, ◎ indicates 60% or more (excellent), 〇 indicates 50% or more but less than 60% (good), △ indicates 40% or more but less than 50% (acceptable), and × indicates less than 40% and is rated × (unacceptable).

[0257] <Cycle Characteristics Evaluation of Lithium-ion Secondary Batteries>

[0258] After the secondary batteries of the laminated batteries manufactured in the examples and comparative examples were left to stand for 24 hours, they were charged and discharged at a rate of 4.25V and 0.1C to determine the initial capacity. The lithium-ion secondary batteries of the laminated batteries were placed in a constant temperature chamber at 60°C and charged and discharged using a charge-discharge apparatus (SM-8, manufactured by Beidou Electric Co., Ltd.). Constant current and constant voltage charging was performed with a charging current of 50mA (1C) and a charging termination voltage of 4.2V (cutoff current 1.25mA (0.025C)), followed by constant current discharging with a discharging current of 50mA (1C) and a discharging termination voltage of 2.5V. This operation was repeated 100 times. 1C is the current value at which the theoretical capacity of the positive electrode is discharged in 1 hour. The cycle characteristics can be expressed as the ratio of the initial capacity to the 1C discharge capacity of the 100th cycle, as shown in Equation 2 below.

[0259] (Equation 2)

[0260] Cyclic characteristics = (1C discharge capacity at 100th cycle) / (initial capacity) × 100%

[0261] In the evaluation of cycling characteristics, a cycling characteristic of 80% or more is ◎ (excellent), 70% or more but less than 80% is ○ (good), 60% or more but less than 70% is △ (acceptable), and less than 60% is × (poor).

[0262] (Example A-1)

[0263] [Process (1)]

[0264] Add 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of dispersant 1 to a stainless steel container, and stir using a disperser at 80°C to completely dissolve dispersant 1, thus preparing an 8% solution of dispersant 1.

[0265] Then, add 85.75 parts of N-methyl-2-pyrrolidone (NMP) and 11.25 parts of an 8% solution of dispersant 1 (0.90 parts of dispersant 1 added) to a stainless steel container, and stir with a disperser until homogeneous. Then, weigh 3 parts of carbon material 1 and add it while stirring with a disperser. Install a precision emulsifying sieve on a high-shear mixer (L5M-A, manufactured by SILVERSON) and disperse intermittently at a speed of 9000 rpm until the whole mixture becomes homogeneous and the dispersed particle size obtained by the particle size analyzer reaches below 200 μm, to obtain a pre-dispersion (X1-1).

[0266] The pre-dispersion (X1-1) has a slip angle of 67° and a cumulative particle size D. 50 It is 43μm.

[0267] [Process (2)]

[0268] The obtained pre-dispersion liquid (X1-1) was passed through an electromagnet (manufactured by Daibo Magnet Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) 3 times to obtain the pre-dispersion liquid (X2-1).

[0269] [Process (3)]

[0270] The pre-dispersed liquid (X2-1) was fed into a stainless steel container and dispersed in a circulating manner with a residence time of 10 minutes using a bead mill (DYNO-MILL MULTI LAB, Shinmaru Enterprises) filled with zirconia beads with a diameter of 1.0 mmφ.

[0271] Next, the dispersion liquid is supplied from the stainless steel container to the high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping, and a 20-pass dispersion process is performed. The dispersion process is carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0272] Then, the dispersed liquid is supplied to the electromagnet (manufactured by Daibo Magnet Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) and subjected to three through-processing steps to obtain carbon material dispersion 1.

[0273] (Examples A-2 to A-20, 29 to 31)

[0274] Except for changing the magnetic separation conditions, carbon materials, dispersants, and additives as shown in Tables 2-1 to 2-3, carbon material pre-dispersions (X1-2 to 19, 22 to 24) were manufactured using the same method as in Example A-1, and then carbon material pre-dispersions (X2-2 to 20, 23 to 25) and carbon material dispersions 2 to 20, 29 to 31 were obtained.

[0275] (Example A-21)

[0276] [Process 1 and Process 2]

[0277] Add 92 parts of N-methyl-2-pyrrolidone (NMP) and 8 parts of dispersant 1 to a stainless steel container, and stir using a disperser at 80°C to completely dissolve dispersant 1, thus preparing an 8% solution of dispersant 1.

[0278] Then, add 87.23 parts of N-methyl-2-pyrrolidone (NMP), 11.25 parts of 8% solution of dispersant 1 (0.9 parts of dispersant 1 added), and 0.02 parts of NaOH to a stainless steel container, and stir with a disperser until uniform. Then, take 1.5 parts of carbon material 4 and add it while stirring with a disperser to obtain a carbon pre-dispersion.

[0279] Next, a precision emulsifying screen was installed on a high-shear mixer (L5M-A, manufactured by SILVERSON). Two rod magnets with a magnetic flux density of 17,000 Gauss were installed on the outlet pipe of the high-shear mixer. The mixture was intermittently dispersed at a speed of 9,000 rpm until it became uniform and the dispersed particle size obtained by the grinding particle size analyzer reached less than 200 μm. Magnetic separation was performed at the same time as the carbon material predispersant liquid (X1-20) to obtain the carbon material predispersant liquid (X2-21).

[0280] That is, the carbon material predispersant (X2-21) corresponds to the carbon material predispersant (X1-20), with a slip angle of 53° and a cumulative particle size D. 50 It is 50μm.

[0281] [Process 3]

[0282] Next, a carbon material pre-dispersion liquid (X2-21) is fed into a stainless steel container and dispersed in a circulating manner for 10 minutes using a bead mill (DYNO-MILL MULTI LAB, Shinmaru Enterprises) filled with zirconia beads with a diameter of 1.0 mmφ.

[0283] Next, the dispersion liquid is supplied from the stainless steel container to the high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping, and a 20-pass dispersion process is performed. The dispersion process is carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0284] Then, the dispersed liquid was supplied to the electromagnet (manufactured by Daibo Magnet Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) and subjected to three through-processing steps to obtain carbon material dispersion 27.

[0285] (Example A-22)

[0286] Except for changing the magnetic separation conditions, carbon material, dispersant, and additives as shown in Table 2, carbon predispersants (X1-21) were manufactured using the same method as in Example A-21, followed by carbon material predispersants (X2-22) and carbon material dispersions 28.

[0287] That is, the carbon material predispersant (X2-22) corresponds to the carbon material predispersant (X1-21), with a slip angle of 55° and a cumulative particle size D. 50 It is 45μm.

[0288] (Example A-23)

[0289] [Process (1)], [Process (2)]

[0290] Except for changing the magnetic separation conditions, carbon material, dispersant, and additives as shown in Table 2, a carbon material pre-dispersion liquid (X2-11) was prepared by the same method as in Example A-1.

[0291] [Process (3)]

[0292] A pre-dispersed carbon material solution (X2-11) is fed into a stainless steel container and then supplied via piping to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by Sugino Machine Co., Ltd.) for 20 pass-through dispersion treatments. The dispersion treatment is carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0293] Then, the dispersed liquid is supplied to the electromagnet (manufactured by Daibo Magnet Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) and subjected to three through-processing steps to obtain carbon material dispersion 23.

[0294] (Examples A-24~A-26)

[0295] Except for changing the magnetic separation conditions, carbon material, dispersant, and additives as shown in Table 2, carbon material predispersant (X1) was prepared by the same method as in Example A-1, and then carbon material predispersant (X2) and carbon material dispersion 24-26 were obtained.

[0296] In carbon material dispersions 24-26, magnetic separation is not performed during or after dispersion.

[0297] (Example A-27)

[0298] [Process (1)][Process (2)]

[0299] Except for changing the magnetic separation conditions, carbon material, dispersant, and additives as shown in Table 2, a carbon material pre-dispersion liquid (X2-11) was obtained by the same method as in Example A-1.

[0300] [Process 3]

[0301] Next, a carbon material pre-dispersion liquid (X2-11) was fed into a stainless steel container and subjected to a circulating dispersion process with a residence time of 10 minutes using a bead mill (DYNO-MILL MULTI LAB, Shinmaru Enterprises) filled with zirconia beads with a diameter of 1.0 mm. Then, the carbon material pre-dispersion liquid was fed into the stainless steel container and supplied to a high-pressure homogenizer (Star Burst Labo HJP-17007, Sugino Machine Co., Ltd.) via piping. With two rod magnets with a magnetic flux density of 17,000 Gauss installed on the outlet piping of the homogenizer, a 20-pass dispersion process was performed. The dispersion process was carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa, yielding a carbon material dispersion 27.

[0302] (Example A-28)

[0303] Except for changing the carbon material predispersant shown in Table 2 to a carbon material predispersant (X2-12), carbon material dispersion 28 was obtained by the same method as in Example A-27.

[0304] (Comparative Example A-1)

[0305] [Process (1)]

[0306] Except for changing the magnetic separation conditions, carbon material, dispersant, and additives as shown in Table 2, a carbon material pre-dispersion liquid (X1-1) was obtained by the same method as in Example A-1.

[0307] The pre-dispersion (X1-1) has a slip angle of 67° and a cumulative particle size D. 50 It is 43μm.

[0308] [Process (3)]

[0309] Next, the carbon material pre-dispersion liquid (X1-1) is fed into a stainless steel container and dispersed in a circulating manner for 10 minutes using a bead mill (DYNO-MILL MULTI LAB, Shinmaru Enterprises) filled with zirconia beads with a diameter of 1.0 mmφ.

[0310] Next, the dispersion liquid was supplied from the stainless steel container to the high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping, and a pass-through dispersion process was performed 20 times. The dispersion process was carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa, resulting in a comparative carbon material dispersion 1.

[0311] The carbon material dispersion 1 was not subjected to the magnetic separation treatment of step (2).

[0312] (Comparative Example A-2)

[0313] [Process (1)]

[0314] Add 94.6 parts of N-methyl-2-pyrrolidone (NMP) and 5.0 parts of 8% solution of dispersant 1 (0.4 parts of dispersant 1) to a stainless steel container, and stir with a disperser until homogeneous.

[0315] Then, 0.4 parts of carbon material 7 were weighed and added while stirring with a disperser. A precision emulsifying sieve was installed on a high-shear mixer (L5M-A, manufactured by SILVERSON) and the mixture was intermittently dispersed at a speed of 9000 rpm until the mixture became homogeneous and the particle size obtained by the grinding particle size analyzer reached less than 200 μm. Then, the contents of the stainless steel container were transported and the dispersed liquid was supplied to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by SuginoMachine Co., Ltd.) through a pipe. The mixture was subjected to three through-type dispersion processes to obtain a pre-dispersion liquid (X'1-1).

[0316] The pre-dispersion (X'1-1) has a slip angle of 80° and a cumulative particle size D. 50 It is 11μm.

[0317] [Process (2)]

[0318] Then, the electromagnet (manufactured by Daibo Magnet Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) was passed through 3 times to prepare a carbon material pre-dispersion liquid (X'2-1).

[0319] Next, the pre-dispersed carbon material liquid (X'2-1) was transported to a stainless steel container, and then supplied to a high-pressure homogenizer (Star Burst Labo HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping for 20 pass-through dispersion treatments to obtain comparative carbon material dispersion 2. 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.

[0320] (Comparative Example A-3)

[0321] [Process (1)]

[0322] Except for changing the magnetic separation conditions, carbon material, dispersant, and additives as shown in Table 2, a carbon material pre-dispersion liquid (X1-1) was obtained by the same method as in Example A-1.

[0323] [Process (3)]

[0324] Next, a pre-dispersed carbon material solution (X1-1) is fed into a stainless steel container, and the solution to be dispersed is supplied to a high-pressure homogenizer (StarBurst Labo HJP-17007, manufactured by Sugino Machine Co., Ltd.) via piping for 10 pass-through dispersion processes. The dispersion process is carried out using a single nozzle chamber at a nozzle diameter of 0.25 mm and a pressure of 100 MPa.

[0325] Then, the dispersed liquid was supplied to the electromagnet (manufactured by Daibo Magnet Co., Ltd., EMF-100S, magnetic flux density 16000 Gauss) and subjected to three through-processing steps to obtain the comparative carbon material dispersion 3.

[0326] The carbon material dispersion 3 was not subjected to the magnetic separation treatment of step (2).

[0327] [Table 2-1]

[0328]

[0329] [Table 2-2]

[0330]

[0331] [Table 2-3]

[0332]

[0333] In Tables 2-3 above, in Examples A-24-A-26, the magnetic separation process (3) was not performed. In Comparative Example A-1, neither the magnetic separation process (2) nor the magnetic separation process (3) was performed. In Comparative Example A-2, the slip angle and cumulative particle size D of the pre-dispersion liquid (X1) provided in the magnetic separation process (2) were... 50 The desired range was not met, and the magnetic separation process (3) was not performed. In Comparative Example A-3, the magnetic separation process (2) was not performed.

[0334] The results in Table 2 confirm that by manufacturing particles with a drop angle of less than 70° and a cumulative particle size D... 50 The carbon material pre-dispersion liquid, with a particle size of 20 μm or larger, removes metallic magnetic impurities during and / or after its manufacture, resulting in high magnetic separation efficiency and reduced metallic magnetic impurities. Furthermore, the carbon material dispersion liquid obtained in the examples exhibits excellent stability over time.

[0335] On the other hand, during magnetic separation, if the drop angle is less than 70° and the cumulative particle size D... 50If the pre-dispersion liquid does not meet the requirement of being larger than 20 μm, it will result in insufficient reduction of metallic magnetic foreign matter. It is speculated that this is because the carbon material pre-dispersion liquid (X1) has strong adhesion to the magnetic separator, thus the magnetic force is weakened when the carbon material pre-dispersion liquid (X1) adheres to the magnetic separator.

[0336] As can be seen from the results of Examples A-24 to A-26, by performing steps (1) and (2), the content of metallic magnetic foreign matter in the carbon material dispersion can be reduced even without the magnetic separation treatment in step (3). As can be seen from Comparative Examples A-1 and A-3, the content of metallic magnetic foreign matter in the carbon material dispersion increases when step (2) is not performed. As can be seen from Comparative Example A-2, before performing the magnetic separation treatment in step (2), dispersion treatment is performed until the cumulative particle size D of the pre-dispersion liquid (X1) reaches a certain value. 50 When it becomes 11μm, the metallic magnetic foreign matter is also miniaturized. Therefore, the removal efficiency of metallic magnetic foreign matter in the magnetic separation process in step (2) is reduced, and the content of metallic magnetic foreign matter in the carbon material dispersion increases.

[0337] (Example B-1)

[0338] <Preparation of Electrode Paste 1>

[0339] 150cm capacity 3 In a plastic container, 18.8 parts by mass of NMP solution containing 8% PVDF (polyvinylidene fluoride, Solvay, Solef #5130) and 5.8 parts by mass of NMP were dissolved. Then, 13.3 parts by mass of carbon material dispersion 1, which had undergone stability evaluation, were added, and the mixture was stirred at 2000 rpm for 30 seconds using a rotary mixer (defoaming Rentaro, ARE-310). Next, 98.1 parts by mass of positive electrode active material (BASF Toda Battery Materials Contractors, HED (registered trademark) NCM-1111100) were added, and the mixture was stirred at 2000 rpm for 2.5 minutes using a rotary mixer (defoaming Rentaro, ARE-310) to obtain electrode slurry 1.

[0340] <Fabrication of Electrode 1>

[0341] Using a dressing applicator, the electrode paste 1 is applied at a weight of 20 mg / cm² per unit area of ​​the electrode. 2 After being coated onto aluminum foil, the coating was dried in an electric oven at 120℃±5℃ for 25 minutes to obtain electrode 1. Then, electrode 1 was subjected to rolling processing using a roller press (Thank Metal, 3t hydraulic roller press) to obtain the positive electrode (electrode 1). Additionally, the weight per unit area of ​​the mixture layer was 20 mg / cm³. 2 The density of the compound layer after rolling is 3.1 g / cc.

[0342] <Preparation of Standard Negative Electrode Slurry>

[0343] DENKA BLACK Li-400 (manufactured by DENKA Corporation), CMC#1190 (manufactured by Daicel FineChem Corporation), and water were added to a 150 mL plastic container. The mixture was stirred at 2,000 rpm for 30 seconds using a rotary mixer (THINKY Corporation, ARE-310, defoaming mixer). Next, artificial graphite CGB-20 (manufactured by Nippon Graphite Industries, Ltd.) was added as the negative electrode active material, and the mixture was stirred at 2,000 rpm for 150 seconds using a rotary mixer. Then, SBR (styrene-butadiene rubber, TRD 2001 (manufactured by JSR Corporation, 48% solids)) was added, and the mixture was stirred at 2,000 rpm for 30 seconds using a rotary mixer to obtain a standard negative electrode slurry. The standard negative electrode slurry had a solids content of 48% by mass. The solid component ratio of negative electrode active material, conductive material, CMC, and SBR in the standard negative electrode slurry is set to 97:0.5:1:1.5.

[0344] <Making a Standard Negative Electrode>

[0345] After applying the negative electrode slurry to a 20μm thick copper foil to form the current collector using a coating applicator, it is dried in an electric oven at 80℃±5℃ for 25 minutes, adjusting the weight per unit area of ​​the electrode to 10mg / cm². 2 Further rolling was performed using a roller press (Thank Metal, 3t hydraulic roller press) to produce a negative electrode binder layer with a density of 1.5 g / cm³. 3 The negative electrode.

[0346] <Making a Secondary Battery 1>

[0347] Electrode 1 was punched to a size of 45mm × 40mm, and the standard negative electrode was punched to a size of 50mm × 45mm. A separator (porous polypropylene membrane) was inserted between them into an aluminum laminated bag and dried in an electric oven at 60°C for 1 hour. Then, in an argon-filled glove box, 2 mL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a 1:1:1 (volume ratio) mixture, and further adding 2 parts by mass of VC (ethylene carbonate) as an additive to 100 parts by mass of the mixture to dissolve LiPF6 at a concentration of 1M) was injected. The aluminum laminated bag was then sealed to produce secondary battery 1.

[0348] (Examples B-2 to B-28), (Comparative Examples B-1 to B-3)

[0349] Except for the carbon material dispersion described in Table 3, electrodes 2 to 28, comparison electrodes 1 to 3, secondary cells 2 to 28, and comparison secondary cells 1 to 3 are manufactured using the same method as that used in manufacturing laminated lithium-ion secondary batteries (secondary cells 1).

[0350] [Table 3]

[0351]

[0352] As shown in Table 3, a carbon material pre-dispersion (X1) with a slip angle of less than 70° and a cumulative particle size D50 of more than 20 μm was manufactured. During and / or after manufacturing, metallic magnetic foreign matter was removed. The battery with an electrode using the obtained carbon material dispersion exhibited good cycle characteristics.

[0353] On the other hand, batteries using carbon material dispersions from the following comparative examples exhibit poor cycle characteristics: Comparative Example A-1, which lacks a process for removing metallic magnetic foreign matter, and those using dispersions that do not meet the requirement of a slip angle less than 70° and a cumulative particle size D. 50 Comparative Example A-2, which was manufactured as a carbon material predispersant with a particle size of 20 μm or larger, and Comparative Example A-3, which was manufactured by magnetic separation of the carbon material dispersion without using the carbon material predispersant.

[0354] <Making a Standard Positive Electrode>

[0355] First, 93 parts by weight of the positive electrode active material (manufactured by BASF Toda Battery Materials Contract Co., Ltd., HED (registered trademark) NCM-1111100), 4 parts by weight of acetylene black (manufactured by DENKA Corporation, DENKA BLACK (registered trademark) HS100), and 3 parts by weight of polyvinylidene fluoride (PVDF) (manufactured by KUREHA Battery Materials Japan Co., Ltd., KUREHA KF Polymer W#1300) are added to a capacity of 150cm³. 3After adding the powder to a plastic container, mix with a spatula until the powder becomes uniform. Then, add 20.5 parts by weight of N-methyl-2-pyrrolidone (NMP) and stir at 2000 rpm for 30 seconds using a rotary mixer (THINKY Corporation, Defoaming Rentarō, ARE-310). Next, mix the mixture in the plastic container with a spatula until uniform, and stir at 2000 rpm for 30 seconds using the same rotary mixer. Then, add 14.6 parts by weight of NMP and stir at 2000 rpm for 30 seconds using the same rotary mixer. Finally, stir at 3000 rpm for 10 minutes using a high-speed mixer to obtain a positive electrode slurry. Then, use a coating tool to coat the positive electrode slurry onto a 20 μm thick aluminum foil to form the current collector, and dry in an electric oven at 120℃±5℃ for 25 minutes, adjusting the weight per unit area of ​​the electrode to 20 mg / cm². 2 Further rolling was performed using a roller press (Thank Metal, 3t hydraulic roller press) to produce an alloy layer with a density of 3.1 g / cm³. 3 The standard positive electrode.

[0356] (Examples B-29~31)

[0357] <Fabrication of Electrode 29>

[0358] 150cm capacity 3 In a plastic container, 10.0 parts by weight of carbon material dispersion, 29 parts by weight of an aqueous solution containing 2% CMC (Daicel FineChem Co., Ltd., #1190), and 7.0 parts by weight of deionized water were weighed out. Then, using a rotary mixer (THINKY Co., Ltd., Defoaming Rentarō, ARE-310), the mixture was stirred at 2000 rpm for 30 seconds to obtain a carbon nanotube dispersion resin composition (carbon nanotube dispersion resin composition W1). Next, 2.4 parts by weight of silica (Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5μm) were added, and the mixture was stirred at 2000 rpm for 30 seconds using the same rotary mixer. Finally, 21.9 parts by weight of artificial graphite (Japan Graphite Industry Co., Ltd., CGB-20) were added, and the mixture was stirred at 2000 rpm for 30 seconds using the same rotary mixer. Then, 0.78 parts by weight of styrene-butadiene emulsion (manufactured by JSR Corporation, TRD 2001) were added, and the mixture was stirred at 2000 rpm for 30 seconds using the above-mentioned rotary mixer to obtain electrode slurry 29.

[0359] Next, the electrode paste 29 was applied using a dressing applicator at a weight of 8 mg / cm² per unit area of ​​the electrode. 2After being coated onto copper foil, the coating was dried in an electric oven at 120℃±5℃ for 25 minutes to obtain the electrode film. Then, the electrode film was subjected to a rolling process using a roller press to produce an alloy layer with a density of 1.6 g / cm³. 3 The negative electrode (electrode 29).

[0360] <Fabrication of Electrodes 30 and 31>

[0361] As shown in Table 4, carbon material dispersions 30 and 31 are used instead of carbon material dispersion 29. Otherwise, electrode slurries 30 and 31, and electrodes 30 and 31 are obtained by the same method as the preparation of electrode 29.

[0362] <Making a Second-hand Battery 29>

[0363] Electrode 29 was punched to a size of 50mm × 45mm, and the standard positive electrode was punched to a size of 45mm × 40mm. A separator (porous polypropylene membrane) was inserted between them into an aluminum laminated bag and dried in an electric oven at 60°C for 1 hour. Then, in an argon-filled glove box, 2 mL of electrolyte (a non-aqueous electrolyte prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a 3:5:2 (volume ratio) ratio to form a mixed solvent, and further as an additive, 1 part by mass of VC (ethylene carbonate) and FEC (fluoroethylene carbonate) were added to each 100 parts by mass of the mixed solvent to dissolve LiPF6 at a concentration of 1M) was added. The aluminum laminated bag was then sealed to produce secondary battery 29.

[0364] <Making of Secondary Batteries 30 and 31>

[0365] Except for changing the negative electrode as described in Table 4, secondary batteries 30 and 31 are manufactured using the same method as secondary battery 29.

[0366] (Example B-32)

[0367] <Fabrication of Electrode 32>

[0368] 150cm capacity 3In a plastic container, 5.0 parts by weight of a carbon material dispersion, 20 parts by weight of an aqueous solution containing 2% CMC (Daicel FineChem Co., Ltd., #1190), and 12.0 parts by weight of deionized water were weighed. Then, using a rotary mixer (THINKY Co., Ltd., Defoaming Rentarō, ARE-310), the mixture was stirred at 2000 rpm for 30 seconds to obtain a carbon nanotube dispersion resin composition (carbon nanotube dispersion resin composition W1). Next, 2.4 parts by weight of silica (Osaka Titanium Technology Co., Ltd., SILICON MONOOXIDE, SiO 1.3C 5μm) were added, and the mixture was stirred at 2000 rpm for 30 seconds using the same rotary mixer. Further, 21.9 parts by weight of artificial graphite (Japan Graphite Industry Co., Ltd., CGB-20) were added, and the mixture was stirred at 2000 rpm for 30 seconds using the same rotary mixer. Then, 0.78 parts by weight of styrene-butadiene emulsion (manufactured by JSR Corporation, TRD 2001) were added, and the mixture was stirred at 2000 rpm for 30 seconds using the above-mentioned rotary mixer to obtain electrode slurry 32.

[0369] Next, the electrode paste 32 was applied using a dressing applicator at a weight of 8 mg / cm² per unit area of ​​the electrode. 2 After being coated onto copper foil, the coating was dried in an electric oven at 120℃±5℃ for 25 minutes to obtain the electrode film. Then, the electrode film was subjected to a rolling process using a roller press to produce an alloy layer with a density of 1.6 g / cm³. 3 The negative electrode (electrode 32).

[0370] <Making a Second-hand Battery 32>

[0371] Except for the electrodes described in Table 4, the secondary battery 32 is manufactured using the same method as the secondary battery 29.

[0372] [Table 4]

[0373]

[0374] As shown in Table 4, a carbon material pre-dispersion (X1) with a slip angle of less than 70° and a cumulative particle size D50 of more than 20 μm was manufactured. During and / or after manufacturing, metallic magnetic foreign matter was removed. The battery with an electrode using the obtained carbon material dispersion exhibited good cycle characteristics.

[0375] Therefore, the secondary battery equipped with an electrode film made using a carbon material dispersion manufactured by the manufacturing method of this embodiment exhibits excellent cycle characteristics. Thus, the lithium-ion secondary battery can be widely used as a battery in vehicles such as electric vehicles, stationary power supplies, large electronic devices such as large servers, and small electronic devices such as personal computers, mobile phones, and tablet terminals. In particular, it is known that by equipping a vehicle with the secondary battery of this embodiment, a vehicle with high safety and improved fuel economy can be obtained.

[0376] The present invention has been described with reference to the above embodiments, but the present invention is not limited thereto. Various modifications that can be understood by those skilled in the art can be made to the structure and details of the present invention within the scope of the present invention.

Claims

1. A method for manufacturing a carbon material dispersion, wherein the carbon material dispersion comprises carbon material, a dispersant, and a solvent. The method for manufacturing the carbon material dispersion comprises the following steps (1) to (3): [Process (1)] A drop angle of less than 70° relative to the metal substrate and a cumulative particle size D were obtained. 50 The process is for a carbon material pre-dispersion liquid (X1) with a particle size of 20 μm or larger; [Process (2)] The process of removing metallic magnetic foreign matter by magnetic separation during and / or after the manufacture of carbon material predispersed liquid (X1) to obtain carbon material predispersed liquid (X2). [Process (3)] The process of dispersing a carbon material pre-dispersion liquid (X2) to manufacture a carbon material dispersion liquid.

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

3. The method for manufacturing the carbon material dispersion according to claim 1, wherein, In the process (3), there is a further step of removing metallic magnetic foreign matter while dispersing the carbon material pre-dispersion liquid (X2) and / or after dispersion.

4. A method for manufacturing an electrode paste, comprising mixing an active substance in a carbon material dispersion manufactured by any one of claims 1 to 3.

5. A method for manufacturing an electrode, comprising the step of coating an electrode paste manufactured by the method of claim 4 onto a current collector to form an electrode film.

6. A method for manufacturing a secondary battery, comprising a step of coating an electrode slurry manufactured by the method of claim 4 onto a current collector to form an electrode film.

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