Method for manufacturing negative electrode material for lithium-ion secondary battery, and method for manufacturing lithium-ion secondary battery

Abstract

In the present invention, a method for manufacturing a negative electrode material for a lithium-ion secondary battery comprises: (a) a step of obtaining a mixture that includes a graphitizable aggregate and a graphitizable binder; (b) a step of molding the mixture to obtain a molded article; (c) a step of graphitizing the molded article to obtain a graphitized article; and (d) a step of pulverizing the graphitized article to obtain a pulverized article, wherein the binder includes an aqueous binder that contains a macromolecular compound that has water solubility or water absorbency.

Description

Method for producing negative electrode material for lithium ion secondary battery and method for producing lithium ion secondary battery

[0001] The present disclosure relates to a method for producing a negative electrode material for a lithium ion secondary battery and a method for producing a lithium ion secondary battery.

[0002] Lithium-ion secondary batteries have a higher energy density than other secondary batteries such as nickel-cadmium batteries, nickel-metal hydride batteries, and lead-acid batteries, and are therefore widely used as power sources for portable electrical appliances such as laptops and mobile phones. In addition to relatively small electrical appliances, lithium-ion secondary batteries are also expected to be used in electric vehicles, power storage devices, and other applications.

[0003] Graphite is widely used as a material for the negative electrode of a lithium-ion secondary battery (negative electrode material). For example, Patent Document 1 describes a method for producing a graphite-based negative electrode material, in which a carbon material, a binder, and the like are mixed and pulverized to obtain a mixture, the pulverized product is molded using a mold and graphitized, and the graphitized product is further pulverized.

[0004] International Publication No. 2015 / 147012

[0005] Demand for lithium-ion secondary batteries for electrical appliances, electric vehicles, power storage devices, etc. is increasing, and this has led to a need to improve the production efficiency of negative electrode materials for lithium-ion secondary batteries.

[0006] From the viewpoint of the production efficiency of a negative electrode material for a lithium ion secondary battery, the present inventors have been studying a method for producing a negative electrode material for a lithium ion secondary battery by molding a mixture containing a graphitizable aggregate and a graphitizable binder, graphitizing the molded product to obtain a graphitized product, and further pulverizing the graphitized product to obtain a pulverized product.

[0007] In the method for producing the negative electrode material for lithium ion secondary batteries described above, it is desirable to improve the strength of the molded product from the viewpoint of improving the handleability of the molded product (for example, the handleability in graphitization treatment, etc.). Furthermore, from the viewpoint of ease of production of the negative electrode material for lithium ion secondary batteries, it is desirable that the graphitized product can be easily pulverized when it is graphitized.

[0008] In view of the above circumstances, an object of the present disclosure is to provide a method for producing a negative electrode material for a lithium ion secondary battery, which is capable of producing a molded product having excellent strength and easily pulverizing a graphitized material, and a method for producing a lithium ion secondary battery including the method for producing this negative electrode material.

[0009] Specific means for solving the above problems include the following embodiments. <1> A method for producing a negative electrode material for a lithium ion secondary battery, comprising: (a) a step of obtaining a mixture containing a graphitizable aggregate and a graphitizable binder; (b) a step of molding the mixture to obtain a molded product; (c) a step of graphitizing the molded product to obtain a graphitized product; and (d) a step of pulverizing the graphitized product to obtain a pulverized product, wherein the binder comprises an aqueous binder containing a water-soluble or water-absorbent polymer compound. <2> In the step of obtaining a molded product, the mixture is molded to obtain a powder having a density of 1.25 g / cm ３ <3> A method for producing a negative electrode material for a lithium ion secondary battery according to <1>, which comprises the steps of: (a) obtaining a mixture containing a graphitizable aggregate and a graphitizable binder; and (b) molding the mixture to obtain a molded product having a density of 1.25 g / cm. ３ (c) graphitizing the molded product to obtain a molded product having a density of 1.20 g / cm ３ (d) pulverizing the graphitized material to obtain a pulverized material. <4> A method for producing a negative electrode material for a lithium ion secondary battery, comprising: (a) obtaining a mixture containing a graphitizable aggregate and a graphitizable binder; (b) molding the mixture by extrusion molding to obtain a molded product; and (c) graphitizing the molded product to obtain a pulverized material having a density of 1.50 g / cm. ３(d) a step of obtaining a graphitized material, and (e) a step of pulverizing the graphitized material to obtain a pulverized material. <5> A method for producing a negative electrode material for a lithium ion secondary battery according to <3> or <4>, wherein the binder comprises an aqueous binder containing a water-soluble or water-absorbent polymer compound. <6> A method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1>, <2>, and <5>, wherein the water-soluble or water-absorbent polymer compound comprises at least one selected from the group consisting of starch, amylose, amylopectin, polyacrylic acid, carboxymethyl cellulose, polyvinyl alcohol, and a water-soluble protein. <7> A method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1>, <2>, <5>, and <6>, wherein the water content in the mixture is 10% by mass to 50% by mass with respect to the total amount of the mixture. <8> The method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1> to <7>, wherein a content of the binder in the mixture is 3% by mass to 30% by mass with respect to the total amount of the mixture. <9> The method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1> to <8>, wherein the aggregate contains calcined coke. <10> The method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1> to <9>, wherein the aggregate contains unheat-treated raw coke. <11> A method for producing a lithium ion secondary battery, comprising: producing a negative electrode material for a lithium ion secondary battery by the method for producing a negative electrode material for a lithium ion secondary battery according to any one of <1> to <10>; and fabricating a negative electrode using the negative electrode material for a lithium ion secondary battery.

[0010] According to the present disclosure, it is possible to provide a method for producing a negative electrode material for a lithium ion secondary battery, which is capable of producing a molded product with excellent strength and easily pulverizing a graphitized material, and a method for producing a lithium ion secondary battery including the method for producing this negative electrode material.

[0011] Modes for carrying out the present invention are described in detail below. However, the present invention is not limited to the following embodiments. In the following embodiments, components (including elementary steps, etc.) are not essential unless otherwise specified or considered to be clearly essential in principle. The same applies to numerical values ​​and their ranges, and do not limit the present invention. In this disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes as long as the purpose of the process is achieved. In this disclosure, numerical ranges indicated using "to" include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. In numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced with a value shown in the examples. In this disclosure, each component may contain multiple corresponding substances. When a composition contains multiple substances corresponding to each component, the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, multiple types of particles corresponding to each component may be contained. When a composition contains multiple types of particles corresponding to each component, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In the present disclosure, the term "layer" includes cases where, when observing the region where the layer exists, the layer is formed over the entire region, as well as cases where the layer is formed only in a part of the region.

[0012] <Method for Manufacturing Negative Electrode Material for Lithium-Ion Secondary Battery> [First Embodiment] A method for manufacturing a negative electrode material for a lithium-ion secondary battery (hereinafter also simply referred to as a negative electrode material) according to a first embodiment of the present disclosure includes: (a) obtaining a mixture containing a graphitizable aggregate and a graphitizable binder; (b) molding the mixture to obtain a molded product; (c) graphitizing the molded product to obtain a graphitized product; and (d) pulverizing the graphitized product to obtain a pulverized product, wherein the binder includes an aqueous binder containing a water-soluble or water-absorbent polymer compound. Note that the steps of the above method may be performed consecutively or discontinuously. The steps of the above method may be performed in the same location or in different locations.

[0013] In the production method of this embodiment, an aqueous binder containing a water-soluble or water-absorbent polymer compound is used. This improves the strength of the molded product, thereby improving the handleability in subsequent graphitization treatments and the like. When the strength of the molded product is improved, the graphitized product generally tends to become difficult to pulverize after the graphitization treatment. However, in the production method of this embodiment, the use of the above-mentioned aqueous binder improves the strength of the molded product and makes it easy to pulverize the graphitized product.

[0014] The reason why the manufacturing method of the present embodiment enables the graphitized material to be easily pulverized while improving the strength of the molded product is presumed to be as follows: Note that the present disclosure is not limited to the following presumption.

[0015] In the manufacturing method of this embodiment, an aqueous binder containing a water-soluble or water-absorbent polymer compound is used, and the aggregate is incorporated into the binder swollen with water. This makes the surface of the graphitizable aggregate slippery during molding of the mixture, promoting alignment of the mixture and reducing voids. As a result, the density and strength of the molded product tend to be improved. Furthermore, the water not incorporated into the binder fills the gaps between the aggregates, resulting in liquid crosslinking, and thus improving the strength of the molded product.

[0016] In the manufacturing method of this embodiment, the molded product is heat-treated by heating as necessary, and then graphitized to obtain a graphitized product. By using an aqueous binder, water volatilizes during the heat treatment, graphitization, etc. Therefore, the molded product has a high density before the heat treatment, graphitization, etc., but the density of the graphitized product after graphitization is reduced. Therefore, the graphitized product can be easily pulverized.

[0017] Furthermore, the manufacturing method of this embodiment allows the graphitized material to be easily pulverized, and as a result, a pulverized material with a small specific surface area is easily obtained. By using a negative electrode material containing a pulverized material with a small specific surface area in the production of a lithium ion secondary battery, the contact area of ​​the negative electrode material with the electrolyte can be reduced. This suppresses the decomposition reaction of the electrolyte, extending the battery life and, as a result, the cycle characteristics of the lithium ion secondary battery tend to be excellent.

[0018] Conventionally, when raw coke is used, problems arise in that molding is difficult and the strength of the molded product is low, and it has been necessary to improve the moldability, strength of the molded product, etc. by subjecting the raw coke to heat treatment or the like. On the other hand, in the production method of this embodiment, even when raw coke is used without heat treatment, molded products with excellent moldability and high strength can be obtained. Therefore, as the graphitizable aggregate, heat-treated raw coke (calcined coke) may be used to form the molded product, or raw coke that has not been heat-treated may be used to form the molded product.

[0019] In the manufacturing method of this embodiment, since the molded product has excellent strength, there is no need to pack the mixture into a graphitization crucible or the like when graphitizing. In other words, there is no need to use a graphitization crucible or the like, and graphitization can be performed by placing only the molded product in a graphitization furnace. Therefore, compared to using a graphitization crucible or the like, the manufacturing efficiency of the negative electrode material for lithium-ion secondary batteries tends to be superior.

[0020] Typically, increasing the amount of graphitizable binder can increase the strength of the molded product. However, if the amount of graphitizable binder is excessive, the density of the graphitized product tends to be high and the graphitized product tends to be difficult to pulverize, which tends to decrease the battery characteristics, such as the initial charge / discharge efficiency of the negative electrode material. In this embodiment, it is possible to increase the strength of the molded product without increasing the amount of graphitizable binder, and it is also possible to prevent a decrease in battery characteristics due to excessive use of binder. Furthermore, by reducing the amount of binder, it becomes easier to apply a hard carbon-derived coating to the surface of the pulverized product, which tends to improve the input characteristics of the lithium-ion secondary battery.

[0021] In step (a), a mixture containing a graphitizable aggregate and a graphitizable binder is obtained. The graphitizable binder includes an aqueous binder containing a water-soluble or water-absorbent polymer compound. The method for obtaining the mixture is not particularly limited, and can be performed using a kneader or the like. The mixing may be performed at room temperature or with heating. When an aqueous binder is used, pitch, tar, etc. are not used as the graphitizable binder, or the amount of pitch, tar, etc. used can be reduced. Therefore, there is no need to perform the mixing at a temperature at which the graphitizable binder softens, and treatments such as heating can be omitted.

[0022] The time for mixing the graphitizable aggregate and the graphitizable binder by kneading or the like is not particularly limited, and may be, for example, 10 seconds to 30 minutes, 30 seconds to 20 minutes, or 1 minute to 15 minutes. As the mixing time increases, the density and strength of the molded product tend to improve.

[0023] The graphitizable aggregate is not particularly limited as long as it can be graphitized by a graphitization treatment. Specific examples include cokes such as fluid coke, needle coke, and mosaic coke. Among these, needle coke is preferably used because it can suppress an increase in the density of the graphitized product produced, thereby making it easy to pulverize the graphitized product. The graphitizable aggregate is preferably particulate. The mixture may contain only one type of graphitizable aggregate or two or more types of graphitizable aggregate.

[0024] When coke is used as the graphitizable aggregate, the coke may contain calcined coke in order to improve the strength of the molded product. Note that, in the manufacturing method of the embodiment, raw coke that has not been heat-treated may be used to form the molded product because the strength of the molded product is excellent.

[0025] When the graphitizable aggregate is particulate, the average particle size of the graphitizable aggregate is, for example, preferably 5 μm to 40 μm, more preferably 8 μm to 30 μm, and even more preferably 8 μm to 25 μm. The average particle size is, for example, the volume average particle size (D50) measured by the laser diffraction / scattering method described below. The volume average particle size (D50) is the particle size at 50% cumulative when a volume cumulative distribution curve is drawn from the small diameter side in the particle size distribution.

[0026] The standard deviation of the particle size distribution of the graphitizable aggregate is, for example, preferably 0.25 or less, more preferably 0.20 or less, even more preferably 0.18 or less, and particularly preferably 0.16 or less. By having the standard deviation of the particle size distribution of the aggregate be 0.20 or less, the particle size variation of the aggregate can be reduced, and the particle size variation of the resulting pulverized material can also be suppressed. By using a negative electrode material containing pulverized material with small particle size variation in the production of a lithium ion secondary battery, the resistance distribution within the negative electrode can be made uniform. As a result, the rapid charging performance of the lithium ion secondary battery tends to be improved. Furthermore, by reducing the particle size variation of the aggregate, the binder function can be suitably ensured even when the content or amount of the graphitizable binder is reduced. The standard deviation of the particle size distribution is, for example, a value (volume basis) measured by the laser diffraction / scattering method described below. The lower limit of the standard deviation of the particle size distribution of the graphitizable aggregate is not particularly limited, and may be, for example, 0.05 or more, or 0.10 or more.

[0027] Methods for adjusting the average particle size of the graphitizable aggregate and the standard deviation of the particle size distribution of the graphitizable aggregate to fall within the above-mentioned ranges include sieve classification, air classification, wet classification, and the like.

[0028] The graphitizable binder is not particularly limited as long as it includes an aqueous binder containing a water-soluble or water-absorbent polymer compound and can be graphitized by a graphitization treatment. Examples of aqueous binders include compositions containing a water-soluble or water-absorbent polymer compound and water. The graphitizable binder may contain one type of water-soluble or water-absorbent polymer compound, or may contain two or more types of water-soluble or water-absorbent polymer compounds.

[0029] The adhesive strength of the aqueous binder is preferably 0.2 N or more from the viewpoint of suppressing cracking of the molded body, and preferably 0.4 N or more from the viewpoint of obtaining a molded body with superior strength. The adhesive strength of the aqueous binder is measured as follows. First, 25 g of binder and 100 g of water are mixed and mixed for 1 hour using a roller mixer to prepare a sample. 20 g to 30 g of the sample is filled into a 20 mm diameter mold, and the sample is pressed 10 mm at a descending speed of 60 mm / min using a small benchtop testing machine EZ-S manufactured by Shimadzu Corporation, and then a tensile test is performed at an ascending speed of 600 mm / min to determine the adhesive strength. As the binder concentration increases, the adhesive strength of the aqueous binder tends to increase. By maintaining the binder concentration below a certain level and ensuring moisture, the binder's function can be fully exerted and the binding strength tends to be maintained.

[0030] The graphitizable binder may contain components other than the water-based binder, and may contain binders such as coal-based, petroleum-based, artificial pitch and tar, thermoplastic resin, and thermosetting resin.

[0031] The water-soluble or water-absorbent polymer compound is not particularly limited, and may include, for example, at least one selected from the group consisting of starch, amylose, amylopectin, polyacrylic acid, carboxymethyl cellulose, polyvinyl alcohol, and water-soluble protein.

[0032] The content of the aqueous binder in the graphitizable binder is preferably 50% by mass to 100% by mass, more preferably 70% by mass to 100% by mass, and even more preferably 90% by mass to 100% by mass, based on the total amount of the binder. In the present disclosure, the aqueous binder refers to a composition of water, a water-soluble or water-absorbent polymer compound that functions as a binder, and a water-soluble or water-absorbent monomer component that is included as needed.

[0033] From the viewpoint of formability and strength of the molded product, the water content in the mixture is preferably 10% by mass to 50% by mass, more preferably 12% by mass to 40% by mass, and even more preferably 15% by mass to 35% by mass, relative to the total amount of the mixture.

[0034] From the viewpoint of formability and strength of a molded product, the content of the water-soluble or water-absorbent polymer compound in the binder is preferably 10% by mass to 70% by mass, more preferably 15% by mass to 60% by mass, and even more preferably 15% by mass to 50% by mass, relative to the total amount of the binder.

[0035] From the viewpoint of formability and strength of a molded product, the content of the water-soluble or water-absorbent polymer compound in the mixture is preferably 3% by mass to 30% by mass, more preferably 4% by mass to 25% by mass, and even more preferably 5% by mass to 20% by mass, relative to the total amount of the mixture.

[0036] From the viewpoint of formability and strength of the molded product, the water content in the aqueous binder is preferably 30% by mass to 90% by mass, more preferably 40% by mass to 85% by mass, and even more preferably 50% by mass to 85% by mass, relative to the total amount of the binder.

[0037] The mixture may or may not contain components other than the graphitizable aggregate or the graphitizable binder (hereinafter also referred to as "other components"), such as aromatic compounds, graphite, dispersants, graphitization catalysts, etc.

[0038] The aromatic compound is not particularly limited as long as it is a compound having an aromatic ring. The aromatic compound may be a compound having an aromatic ring and having a molecular weight of 500 or less, or may be a compound having a molecular weight of 300 or less. Examples of the aromatic compound include naphthalene, methylnaphthalenes such as 1-methylnaphthalene and 2-methylnaphthalene, acenaphthene, biphenyl, fluorene, benzopyrene, benzanthracene, dibenzanthracene, diphenylene oxide, quinoline, and isoquinoline. The aromatic compound contained in the mixture may be one type only, or two or more types.

[0039] Among these, methylnaphthalene and naphthalene are preferred as the aromatic compound from the viewpoint of moldability when forming a molded product.

[0040] When the mixture contains an aromatic compound, the amount thereof is not particularly limited. The content of the aromatic compound in the mixture is preferably 1 mass % or less, more preferably 0.5 mass % or less, and even more preferably 0 mass %, based on the total amount of the mixture.

[0041] The mixture may contain graphite. Examples of graphite include natural graphite and artificial graphite. The graphite is preferably in particulate form. The mixture may contain only one type of graphite or two or more types of graphite.

[0042] From the viewpoint of facilitating dispersion of the components in the mixture in step (b), the mixture preferably contains a dispersant. By including a dispersant in the mixture, the particle size variation of the pulverized material obtained by pulverizing the graphitized material can be suppressed, making it easier to obtain pulverized material with a uniform particle size. As a result, the rapid charging performance of the lithium-ion secondary battery tends to be improved. Furthermore, the inclusion of a dispersant in the mixture leads to a reduction in the amount of graphitizable binder, which is expected to improve battery characteristics such as the initial charge / discharge efficiency of the negative electrode material.

[0043] The type of dispersant is not particularly limited. Specific examples include hydrocarbons such as liquid paraffin, paraffin wax, and polyethylene wax; fatty acids such as stearic acid, oleic acid, erucic acid, and 12-hydroxystearic acid; fatty acid metal salts such as zinc stearate, lead stearate, aluminum stearate, calcium stearate, and magnesium stearate; fatty acid amides such as stearic acid amide, oleic acid amide, erucic acid amide, methylene bisstearic acid amide, and ethylene bisstearic acid amide; fatty acid esters such as stearic acid monoglyceride, stearyl stearate, and hydrogenated oil; and higher alcohols such as stearyl alcohol. Among these, fatty acids are preferred, and stearic acid is more preferred, because they do not affect the performance of the negative electrode material, are easy to handle because they are solid at room temperature, disappear in the process up to the graphitization treatment, and are inexpensive.

[0044] When the mixture contains a dispersant, the amount thereof is not particularly limited. For example, the content of the dispersant relative to the total mass of the mixture may be 0.1% by mass to 20% by mass, 0.5% by mass to 10% by mass, or 0.5% by mass to 5% by mass.

[0045] From the viewpoint of promoting graphitization of the graphitizable aggregate or binder, the mixture preferably contains a graphitization catalyst. The type of graphitization catalyst is not particularly limited. Specific examples include substances having graphitization catalytic activity such as silicon, iron, nickel, titanium, and boron, as well as carbides of these substances, oxides of these substances, and nitrides of these substances.

[0046] When the mixture contains a graphitization catalyst, the amount thereof is not particularly limited. For example, the content of the graphitization catalyst relative to the total mass of the mixture may be 0.1% by mass to 50% by mass, 0.5% by mass to 40% by mass, or 0.5% by mass to 30% by mass.

[0047] In step (b), the mixture obtained in step (a) is molded to obtain a molded product. Preferably, the mixture is molded into a predetermined shape by a uniaxial press or the like. By molding the mixture in this manner, it is possible to increase the amount of the mixture packed into a graphitization furnace when graphitizing the mixture, thereby improving productivity and improving the effect of the graphitization catalyst.

[0048] In step (b), the method for molding the mixture is not particularly limited, and examples thereof include a molding method in which the mixture is placed in a container such as a metal mold and pressurized in a uniaxial direction, a vibration molding method in which the mixture is placed in a container such as a metal mold, a weight is placed on top, and vibration and impact are applied to the metal frame to mold the mixture, and an extrusion molding method in which the mixture is extruded from a nozzle or the like using a horizontal press to mold the mixture.

[0049] In step (b), it is preferable to extrude the mixture to obtain a molded product. Molding the mixture by extrusion molding provides excellent production efficiency for the molded product, and also improves the density of the molded product, thereby improving handleability. When extrusion molding is usually performed, the density of the molded product increases, which in turn increases the density of the graphitized product, making it difficult to pulverize the graphitized product. However, in this embodiment, moisture volatilizes during heat treatment, graphitization, and the like, so the density of the graphitized product decreases, making it easy to pulverize the graphitized product, even when extrusion molding is employed.

[0050] In step (b), the density of the molded product obtained is not particularly limited, and may be, for example, 0.90 g / cm ３ or more, and 0.95 g / cm ３ or more, and 1.00 g / cm ３ or more, 1.25 g / cm ３ or more, 1.30 g / cm ３ or more, 1.30 g / cm ３ The density of the resulting molded article may be greater than 1.70 g / cm ３ or less, 1.60 g / cm ３ or less, 1.55 g / cm ３ In the manufacturing method of this embodiment, since an aqueous binder is used, when the density of the molded product is relatively low (for example, 1.25 g / cm ３ The use of an aqueous binder tends to improve the strength of the molded product even when the density of the molded product is relatively high (for example, 1.25 g / cm or less), because water evaporates during heat treatment, graphitization, etc. ３Even in the above cases, the density of the graphitized material tends to decrease. As a result, the graphitized material can be easily pulverized, and pulverized material with a small specific surface area tends to be obtained. By using a negative electrode material containing pulverized material with a small specific surface area in the production of a lithium ion secondary battery, the contact area of ​​the negative electrode material with the electrolyte can be reduced. As a result, the decomposition reaction of the electrolyte can be suppressed, the battery life can be extended, and a lithium ion secondary battery with excellent cycle characteristics tends to be produced.

[0051] The molded product obtained in step (b) is preferably subjected to a heat treatment before being graphitized in step (c). By performing the heat treatment, organic components contained in the mixture that do not contribute to graphitization are removed, and gas generation and the like during the graphitization treatment tend to be suppressed.

[0052] The temperature of the heat treatment is not particularly limited, but is preferably lower than the temperature of the heat treatment for graphitization in step (c), and may be, for example, in the range of 500°C to 1000°C.

[0053] In step (c), the molded product obtained in step (b) is graphitized. The method for graphitizing the molded product is not particularly limited as long as the conditions are such that the graphitizable component contained in the mixture can be graphitized. For example, a method of heat treating the mixture in an atmosphere in which the mixture is unlikely to be oxidized can be used. The atmosphere in which the mixture is unlikely to be oxidized is not particularly limited, and examples thereof include an inert atmosphere such as nitrogen or argon, and a vacuum.

[0054] The temperature of the heat treatment for graphitization may be, for example, 1500°C or higher, 2000°C or higher, 2500°C or higher, or 2800°C or higher. The upper limit of the heat treatment temperature is not particularly limited, and may be, for example, 3200°C or lower. When the heat treatment temperature is 1500°C or higher, crystal changes tend to occur, making graphitization more likely to proceed. When the heat treatment temperature is 2000°C or higher, the development of graphite crystals tends to be better. On the other hand, when the heat treatment temperature for graphitization is 3200°C or lower, sublimation of a portion of the graphite tends to be suppressed.

[0055] In the step (c), the density of the graphitized product obtained is not particularly limited, and from the viewpoint of the handleability of the graphitized product, it is, for example, 0.80 g / cm ３ or more, and 0.85 g / cm ３ or more, and 0.90 g / cm ３ The density of the graphitized material obtained may be 1.50 g / cm or more from the viewpoint of ease of pulverization of the graphitized material. ３ or less, 1.30 g / cm ３ or less, 1.20 g / cm ３ or less, 1.15 g / cm ３ or less, 1.12 g / cm ３ or less, 1.10 g / cm ３ It may be the following:

[0056] In step (d), the graphitized material obtained in step (c) is pulverized to obtain a pulverized product. The pulverization method is not particularly limited, and can be performed by a known method using a jet mill, a vibration mill, a pin mill, a hammer mill, or the like. The particle size of the pulverized product may be adjusted to a desired size. The method for adjusting the particle size is not particularly limited, and examples thereof include a method using the above-mentioned pulverization device and a method using a sieve.

[0057] If necessary, the pulverized material obtained in step (d) may be subjected to steps such as (e) a step of disposing low-crystalline carbon on at least a portion of the surface of the pulverized material, and (f) a step of mixing the pulverized material with other negative electrode active materials.

[0058] In step (e), low-crystalline carbon can be disposed on at least a portion of the surface of the pulverized material by, for example, mixing the pulverized material with a substance (such as a resin) that can be converted to low-crystalline carbon by heat treatment, followed by heat treatment. When low-crystalline carbon is disposed on at least a portion of the surface of the pulverized material, the input / output characteristics, such as rapid charge / discharge characteristics, of a lithium-ion secondary battery using the pulverized material as a negative electrode material may be improved.

[0059] The method for mixing the pulverized material with other negative electrode active materials in step (f) is not particularly limited. By mixing the pulverized material with other negative electrode active materials, the desired characteristics of the lithium ion secondary battery may be improved compared to when only the pulverized material is used as the negative electrode active material. Examples of other negative electrode active materials include, but are not limited to, graphite particles such as natural graphite and artificial graphite, and particles containing elements capable of absorbing and desorbing lithium ions. Examples of elements capable of absorbing and desorbing lithium ions include, but are not limited to, Si, Sn, Ge, and In.

[0060] The pulverized product obtained in step (f) may contain particles in which a plurality of flat graphite particles are aggregated or bonded together, or may contain particles in which a plurality of flat graphite particles are aggregated or bonded together so that the main surfaces of the graphite particles are non-parallel to each other (hereinafter also referred to as secondary graphite particles).

[0061] When the pulverized material is in the form of graphite secondary particles, the phenomenon in which the particles of the negative electrode material are oriented along the direction of the current collector when pressed to densify the negative electrode is suppressed, and there tends to be sufficient pathways for lithium ions to enter and exit the negative electrode material.

[0062] Furthermore, by containing particles in which a plurality of flat graphite particles are aggregated or bonded together, the voids present between the plurality of flat graphite particles reduce the effect of the pressure applied during pressing on the individual graphite particles, which tends to suppress the destruction of graphite particles, the generation of cracks, etc.

[0063] In the present disclosure, the term "flat graphite particles" refers to non-spherical graphite particles having an anisotropic shape. Examples of flat graphite particles include graphite particles having a scaly, flake, or partially lumpy shape.

[0064] The flat graphite particles preferably have an aspect ratio, expressed as A / B, where A is the length in the major axis direction and B is the length in the minor axis direction, of, for example, 1.2 to 20, and more preferably 1.3 to 10. When the aspect ratio is 1.2 or more, the contact area between particles increases, tending to further improve conductivity. When the aspect ratio is 20 or less, input / output characteristics such as rapid charge / discharge characteristics of the lithium ion secondary battery tend to further improve.

[0065] The aspect ratio is determined by observing graphite particles under a microscope, randomly selecting 100 graphite particles, measuring the A / B ratio for each, and then calculating the arithmetic mean of these measurements. In observing the aspect ratio, the length A in the major axis direction and the length B in the minor axis direction are measured as follows. That is, in a projected image of a graphite particle observed under a microscope, two parallel tangents circumscribing the periphery of the graphite particle, tangent lines a1 and a2, which have the greatest distance between them, are selected, and the distance between these tangent lines a1 and a2 is defined as the length A in the major axis direction. Two parallel tangents circumscribing the periphery of the graphite particle, tangent lines b1 and b2, which have the smallest distance between them, are selected, and the distance between these tangent lines b1 and b2 is defined as the length B in the minor axis direction.

[0066] In the present disclosure, the phrase "main surfaces are non-parallel" of graphite secondary particles means that the surfaces (main surfaces) of the plurality of flat graphite particles with the largest cross-sectional areas are not aligned in a fixed direction. Whether the main surfaces of the plurality of flat graphite particles are non-parallel to each other can be confirmed by microscopic observation. When the plurality of flat graphite particles are aggregated or bonded together with their main surfaces non-parallel to each other, the orientation of the main surfaces of the flat graphite particles in the negative electrode is suppressed, expansion of the negative electrode during charging is suppressed, and the cycle characteristics of the lithium-ion secondary battery tend to be further improved. Note that the graphite secondary particles may partially include a structure in which the plurality of flat graphite particles are aggregated or bonded together with their respective main surfaces parallel to each other.

[0067] In the present disclosure, the phrase "a state in which a plurality of flat graphite particles are aggregated or bonded" refers to a state in which two or more flat graphite particles are aggregated or bonded. "Bonded" refers to a state in which the particles are chemically bonded to each other directly or via a carbon substance. "Aggregated" refers to a state in which the particles are not chemically bonded to each other but maintain the shape of an aggregate due to their shape or the like. The flat graphite particles may be aggregated or bonded via a carbon substance. Examples of carbon substances include graphitized products of graphitizable binders. From the viewpoint of mechanical strength, it is preferable that two or more flat graphite particles are bonded via a carbon substance. Whether the flat graphite particles are aggregated or bonded can be confirmed, for example, by observation using a scanning electron microscope.

[0068] From the viewpoint of ease of aggregation or bonding, the average particle size of the flat graphite particles is, for example, preferably 1 μm to 50 μm, more preferably 1 μm to 25 μm, and even more preferably 1 μm to 15 μm. Examples of a method for measuring the average particle size of the flat graphite particles include a method using a scanning electron microscope, and the average particle size of the flat graphite particles is, for example, the arithmetic mean value of the particle sizes of 100 flat graphite particles.

[0069] The flat graphite particles and the raw material thereof are not particularly limited, and examples thereof include artificial graphite, scaly natural graphite, scaly natural graphite, coke, resin, tar, pitch, etc. Among these, graphite obtained from artificial graphite, natural graphite, or coke tends to be soft particles with high crystallinity, which makes it easier to increase the density of the negative electrode.

[0070] The negative electrode material may contain spherical graphite particles. When the negative electrode material contains spherical graphite particles, the spherical graphite particles themselves have a high density, so that the pressing pressure required to obtain a desired electrode density tends to be reduced.

[0071] Examples of spherical graphite particles include spherical artificial graphite and spherical natural graphite. From the viewpoint of increasing the density of the negative electrode, the spherical graphite particles are preferably high-density graphite particles. Specifically, spherical natural graphite that has been subjected to a particle spheroidization treatment to enable a high tap density is preferred. Furthermore, a negative electrode material layer containing spherical natural graphite has excellent peel strength and tends to be less likely to peel off from the current collector even when pressed with a strong force.

[0072] When the negative electrode material contains spherical graphite particles, it may contain both the above-mentioned flat graphite particles and spherical graphite particles. When the negative electrode material contains the above-mentioned flat graphite particles and spherical graphite particles, the ratio between the two is not particularly limited and can be set depending on the desired electrode density, pressure conditions during pressing, desired battery characteristics, etc.

[0073] When the negative electrode material contains flat graphite particles and spherical graphite particles, the negative electrode material may be in a state where flat graphite particles and spherical graphite particles are mixed, or in a state where flat graphite particles and spherical graphite particles are bonded together (hereinafter also referred to as composite particles), etc. Examples of composite particles include particles in which flat graphite particles and spherical graphite particles are bonded together via an organic carbide.

[0074] The composite particles can be produced, for example, by using a mixture containing flat graphite particles or raw materials thereof and spherical graphite particles in the step (a).

[0075] The average particle size of the negative electrode material produced by the above method is not particularly limited. For example, it is preferably 5 μm to 40 μm, more preferably 10 μm to 30 μm, and even more preferably 10 μm to 25 μm. The average particle size may be measured, for example, by a scanning electron microscope in the same manner as the average particle size of the flat graphite particles described above, or it may be the volume average particle size (D50) measured by a laser diffraction / scattering method.

[0076] Examples of methods for measuring the average particle size when an electrode (negative electrode) is manufactured using a negative electrode material include a method in which a sample electrode is prepared, embedded in epoxy resin, mirror-polished, and the electrode cross section is observed with a scanning electron microscope (e.g., Keyence Corporation, "VE-7800"); and a method in which an electrode cross section is prepared using an ion milling device (e.g., Hitachi High-Technologies Corporation, "E-3500") and measured with a scanning electron microscope (e.g., Keyence Corporation, "VE-7800"). In this case, the average particle size is the median value of particle sizes of 100 particles arbitrarily selected from the observed particles.

[0077] The sample electrode can be produced, for example, by preparing a dispersion by adding water to a mixture of 98 parts by mass of a negative electrode material, 1 part by mass of styrene-butadiene resin as a binder, and 1 part by mass of carboxymethyl cellulose as a thickener as solid content, coating the dispersion onto a 10 μm-thick copper foil to a thickness of about 70 μm (when coated), and then drying at 105° C. for 1 hour.

[0078] The orientation of the negative electrode material when made into a negative electrode (when a pressing step is involved in the production of the negative electrode, the negative electrode after pressing) may be 40 or less, 20 or less, or 15 or less. The aforementioned orientation may be 10 or more. The orientation of the negative electrode material is an index that indicates the degree of orientation of the particles of the negative electrode material contained in the negative electrode. A low orientation means that the particles of the negative electrode material are oriented in random directions. In other words, this means that the pressure applied during pressing prevents the graphite particles from orienting along the surface of the current collector.

[0079] In the present disclosure, the orientation of the negative electrode is determined by measuring the surface of the sample electrode using an X-ray diffraction device that uses CuKα radiation as an X-ray source. Specifically, the X-ray diffraction pattern of the surface of the sample electrode is measured, and the orientation is determined from the intensities of the carbon (004) plane diffraction peak detected at a diffraction angle 2θ of approximately 53° to 56° and the carbon (110) plane diffraction peak detected at a diffraction angle 2θ of approximately 70° to 80° using the following formula (1): (004) plane diffraction peak intensity / (110) plane diffraction peak intensity Formula (1)

[0080] The specific surface area of ​​the negative electrode material is set to 3.0 m from the viewpoint of cycle characteristics and storage characteristics. ２ / g or less, and ２ / g or less, and more preferably 0.5m ２ / g to 2.5m ２ / g, and more preferably 0.7m ２ / g to 2.0m ２ The specific surface area of ​​the negative electrode material may be calculated by the BET method using a specific surface area / pore distribution measuring device (e.g., Flowsorb III 2310, Shimadzu Corporation) and a mixed gas of nitrogen and helium (nitrogen:helium=3:7), measuring nitrogen adsorption at liquid nitrogen temperature (77 K) by a single-point method at a relative pressure of 0.3.

[0081] [Second embodiment] A method for producing a negative electrode material according to a second embodiment of the present disclosure includes: (a) obtaining a mixture containing a graphitizable aggregate and a graphitizable binder; and (b) molding the mixture to obtain a negative electrode material having a density of 1.25 g / cm. ３ (c) graphitizing the molded product to obtain a molded product having a density of 1.20 g / cm ３ and (d) a step of pulverizing the graphitized product to obtain a pulverized product. In the present disclosure, the necessary and preferred configurations in each embodiment may be combined as appropriate. Preferred conditions for steps (b) and (c) other than the density of the molded product and the density of the graphitized product are the same as the preferred conditions for steps (b) and (c) in the first embodiment described above.

[0082] In the manufacturing method of this embodiment, the density of the molded product obtained in step (b) is 1.25 g / cm ３ By satisfying the above, the strength of the molded product is improved, and therefore the handling properties in the subsequent graphitization treatment and the like are also improved. ３ By satisfying the above condition, the graphitized material can be easily pulverized.

[0083] Furthermore, the manufacturing method of this embodiment allows the graphitized material to be easily pulverized, and as a result, a pulverized material with a small specific surface area is easily obtained. By using a negative electrode material containing a pulverized material with a small specific surface area in the production of a lithium ion secondary battery, the contact area of ​​the negative electrode material with the electrolyte can be reduced. This suppresses the decomposition reaction of the electrolyte, extending the battery life and, as a result, the cycle characteristics of the lithium ion secondary battery tend to be excellent.

[0084] In the production method of this embodiment, the method for molding the mixture in step (b) is not particularly limited. Examples include the aforementioned molding method, vibration molding method, and extrusion molding method. From the viewpoint of reducing the density of the graphitized product, molding method or vibration molding method is preferred.

[0085] In the production method of this embodiment, from the viewpoint of suitably reducing the density of the graphitized product obtained in step (c), the graphitizable binder may include an aqueous binder containing a water-soluble or water-absorbent polymer compound. The preferred form of the aqueous binder is the same as that of the first embodiment.

[0086] In step (b), the density of the resulting molded product is 1.25 g / cm ３ or more, and 1.30 g / cm ３ or more, 1.30 g / cm ３ The density of the resulting molded article may be greater than 1.70 g / cm ３ or less, 1.60 g / cm ３ or less, 1.55 g / cm ３ It may be the following:

[0087] In step (c), the density of the graphitized product obtained is 1.20 g / cm ３ or less, and 1.12 g / cm ３ or less, 1.10 g / cm ３ The density of the graphitized material obtained may be 0.80 g / cm or less. ３ or more, and 0.85 g / cm ３ or more, and 0.90 g / cm ３ It may be more than that.

[0088] [Third embodiment] A method for producing a negative electrode material according to a third embodiment of the present disclosure includes: (a) obtaining a mixture containing a graphitizable aggregate and a graphitizable binder; (b) forming the mixture by extrusion molding to obtain a molded product; and (c) graphitizing the molded product to obtain a negative electrode material having a density of 1.50 g / cm. ３ and (d) a step of pulverizing the graphitized product to obtain a pulverized product. In the present disclosure, the necessary and preferred configurations in each embodiment may be combined as appropriate. Preferred conditions for steps (b) and (c) other than the molding method for the molded product and the density of the graphitized product are the same as the preferred conditions for steps (b) and (c) in the first embodiment described above.

[0089] In the manufacturing method of this embodiment, the strength of the molded product is improved by obtaining the molded product by extrusion molding in step (b). Therefore, the handleability in the subsequent graphitization treatment and the like is also improved. The density of the graphitized product obtained in step (c) is 1.50 g / cm ３ By satisfying the above condition, the graphitized material can be pulverized relatively easily.

[0090] In the production method of this embodiment, from the viewpoint of suitably reducing the density of the graphitized product obtained in step (c), the graphitizable binder may include an aqueous binder containing a water-soluble or water-absorbent polymer compound. The preferred form of the aqueous binder is the same as that of the first embodiment.

[0091] In step (b), the density of the resulting molded product is 1.25 g / cm ３ or more, 1.30 g / cm ３ or more, 1.30 g / cm ３ The density of the resulting molded article may be greater than 1.70 g / cm ３ or less, 1.60 g / cm ３ or less, 1.55 g / cm ３ It may be the following:

[0092] In step (c), the density of the graphitized product obtained is 1.50 g / cm ３ or less, and 1.30 g / cm３ or less, 1.20 g / cm ３ or less, 1.15 g / cm ３ or less, 1.12 g / cm ３ or less, 1.10 g / cm ３ The density of the graphitized material obtained may be 0.80 g / cm or less. ３ or more, and 0.85 g / cm ３ or more, and 0.90 g / cm ３ It may be more than that.

[0093] In the production method of this embodiment, unheat-treated raw coke may be used to form the molded product because the molded product has excellent strength. Furthermore, by using unheat-treated raw coke, it is possible to suitably reduce the density of the graphitized product obtained in step (c), making it easier to pulverize the graphitized product.

[0094] <Method for manufacturing lithium ion secondary battery> A method for manufacturing a lithium ion secondary battery according to the present disclosure includes a step of manufacturing a negative electrode material by the above-described method for manufacturing a negative electrode material, and a step of fabricating a negative electrode using the negative electrode material.

[0095] The method for producing a negative electrode using the negative electrode material is not particularly limited, and examples thereof include a method in which a negative electrode material layer is formed on a current collector using a composition containing the negative electrode material, a binder, and a solvent, and then heat treatment, pressing treatment, or the like is performed as necessary.

[0096] The binder contained in the composition is not particularly limited. Examples include styrene-butadiene rubber, polymeric compounds having an ethylenically unsaturated carboxylic acid ester (methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, hydroxyethyl (meth)acrylate, etc.) as a polymerization component, polymeric compounds having an ethylenically unsaturated carboxylic acid (acrylic acid, methacrylic acid, itaconic acid, fumaric acid, maleic acid, etc.) as a polymerization component, and polymeric compounds such as polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyimide, and polyamideimide. In the present disclosure, (meth)acrylate refers to either or both of methacrylate and acrylate.

[0097] The solvent contained in the composition is not particularly limited, and specifically, organic solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and γ-butyrolactone, and water may be used.

[0098] The composition may contain a thickener to adjust the viscosity, if necessary, such as carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid and its salts, oxidized starch, phosphated starch, casein, etc.

[0099] The composition may contain a conductive additive, if necessary. Examples of the conductive additive include carbon black, graphite, acetylene black, conductive oxides, and conductive nitrides.

[0100] The material and shape of the current collector used to prepare the negative electrode are not particularly limited. For example, materials such as strip-shaped foil, perforated foil, and mesh made of metal or alloy such as aluminum, copper, nickel, titanium, and stainless steel can be used. Porous materials such as porous metal (foamed metal) and carbon paper can also be used.

[0101] The method for forming a negative electrode material layer on a current collector using the composition is not particularly limited, and can be any known method such as metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade coating, gravure coating, screen printing, etc. When the negative electrode material layer and the current collector are integrated, they can be integrated by any known method such as rolling, pressing, or a combination thereof.

[0102] After the negative electrode material layer is formed on the current collector, it may be subjected to a heat treatment (drying). The heat treatment removes the solvent contained in the negative electrode material layer, hardens the binder, and increases the strength, improving the adhesion between particles and between the particles and the current collector. The heat treatment may be performed in an inert atmosphere such as helium, argon, or nitrogen, or in a vacuum atmosphere, to prevent oxidation of the current collector during the treatment.

[0103] After the negative electrode material layer is formed on the current collector, a press treatment may be performed. By performing the press treatment, the electrode density of the negative electrode can be adjusted. The electrode density of the negative electrode is not particularly limited, but is preferably 1.5 g / cm. ３ ~1.9 g / cm ３ 1.6 g / cm ３ ~1.8g / cm ３ The higher the electrode density, the more the volumetric capacity of the negative electrode is improved, the more the adhesion of the negative electrode material layer to the current collector is improved, and the more the cycle characteristics tend to improve. It is preferable to perform the pressing treatment before the heat treatment.

[0104] The lithium ion secondary battery produced by the above method may include a negative electrode produced by the above method, a positive electrode, and an electrolyte. The lithium ion secondary battery may have a configuration in which, for example, the negative electrode and the positive electrode are arranged to face each other with a separator interposed therebetween, and an electrolytic solution containing the electrolyte is injected.

[0105] The positive electrode may be prepared by forming a positive electrode layer on the surface of a current collector in the same manner as the negative electrode. The current collector may be a strip-shaped foil, a perforated foil, a strip-shaped mesh, or the like, made of a metal or alloy such as aluminum, titanium, or stainless steel.

[0106] The positive electrode material contained in the positive electrode layer is not particularly limited. For example, metal compounds, metal oxides, metal sulfides, and conductive polymer materials capable of doping or intercalating lithium ions can be used. Furthermore, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), lithium manganese oxide (LiMnO ２ ), and their double oxides (LiCo ｘ Ni ｙ Mn ｚ O ２ , x+y+z=1, 0<x, 0<y; LiNi ２－ｘ Mn ｘ O ４ , 0<x≦2), lithium manganese spinel (LiMn ２ O ４ ), lithium vanadium compounds, V ２ O ５ , V ６ O １３ , V.O. ２ , MnO ２ , TiO ２ , MoV ２ O ８ , TiS ２ , V ２ S ５ , V.S. ２ , MoS ２ , MoS ３ , Cr ３ O ８ , Cr ２ O ５ , olivine-type LiMPO ４ (M: Co, Ni, Mn, Fe), conductive polymers such as polyacetylene, polyaniline, polypyrrole, polythiophene, and polyacene, and porous carbon can be used alone or in combination of two or more. Among these, lithium nickel oxide (LiNiO ２ ) and its double oxide (LiCo ｘ Ni ｙ Mn ｚ O ２ , x+y+z=1, 0<x, 0<y; LiNi ２－ｘ Mn ｘ O ４, 0<x≦2) are suitable as positive electrode materials due to their high capacity.

[0107] Examples of the separator include nonwoven fabrics, cloths, microporous films, and combinations thereof, each of which is primarily made of a polyolefin such as polyethylene or polypropylene. If the lithium ion secondary battery has a structure in which the positive electrode and the negative electrode do not come into contact with each other, there is no need to use a separator.

[0108] The electrolyte is LiClO ４ , LiPF ６ , LiAsF ６ , LiBF ４ , LiSO ３ CF ３ A so-called organic electrolyte solution can be used in which a lithium salt such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, fluoroethylene carbonate, cyclopentanone, sulfolane, 3-methyl sulfolane, 2,4-dimethyl sulfolane, 3-methyl-1,3-oxazolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, etc. is dissolved in a non-aqueous solvent, either alone or as a mixture of two or more components. In particular, an electrolyte solution containing fluoroethylene carbonate tends to form a stable SEI (solid electrolyte interface) on the surface of the negative electrode material, which is suitable because it significantly improves cycle characteristics.

[0109] The form of the lithium ion secondary battery is not particularly limited, and examples thereof include a paper-type battery, a button-type battery, a coin-type battery, a laminated battery, a cylindrical battery, a prismatic battery, etc. The negative electrode material for lithium ion secondary batteries can be applied to all electrochemical devices other than lithium ion secondary batteries, such as hybrid capacitors, which use the insertion and desorption of lithium ions as a charge and discharge mechanism.

[0110] The above embodiment will be described in more detail below based on examples, but the above embodiment is not limited to the following examples.

[0111] Example 1 (Formation of Molded Product) Unheat-treated raw needle coke with an average particle size of 11 μm and a standard deviation of particle size distribution of 0.25 was used as the aggregate, and the following materials were also used as raw materials. The average particle sizes of the aggregate and negative electrode material, and the standard deviation of the aggregate particle size distribution were measured using a particle size distribution analyzer (Shimadzu Corporation, SALD-3000) that utilizes laser diffraction and scattering. The standard deviation of the aggregate particle size distribution is the standard deviation defined on a logarithmic scale. The raw materials shown below were mixed without heating in the proportions and conditions shown in Table 1 to prepare a mixture. The resulting mixture was then molded at room temperature using a uniaxial press to obtain a molded product measuring 10 mm x 10 mm x 50 mm. Aggregate: Raw needle coke with an average particle size of 11 μm and a standard deviation of particle size distribution of 0.25 Binder: Starch (10 parts by mass relative to 100 parts by mass of coke) Water (33.2 parts by mass relative to 100 parts by mass of needle coke)

[0112] The molded product was then heat-treated in a nitrogen atmosphere at 800°C to 850°C for 8 hours to obtain a fired product. The fired product was then graphitized at 2600°C to 3100°C for 30 hours to obtain a graphitized product. The graphitized product was pulverized to obtain the graphite powder of Example 1 (anode material for lithium-ion secondary batteries).

[0113] The density (g / cm) of the molded product obtained in the above step ３ ), density of the fired product (g / cm ３ ) and the density of the graphite (g / cm ３ ) are shown in Table 1.

[0114] (Evaluation of bending test force) The bending test force (N) of the molded product was measured as follows. Specifically, a mixture having the composition shown in Table 1 was molded at room temperature to obtain a molded product of 10 mm x 10 mm x 50 mm. The density (g / cm) of the obtained molded product was ３The bending test force (N) required for fracture was measured using the molded product and an autograph manufactured by Shimadzu Corporation at a test speed of 10 mm / min and a support distance of 7 mm. The results are shown in Table 1.

[0115] (Evaluation of Moldability) Three molded articles were produced in the same manner as in Example 1. Of the three molded articles produced, the number of molded articles that had chips of 1 mm or more when carried was evaluated. A number of 0 means that none of the molded articles produced had such chips, and a number of 3 means that all of the molded articles produced had such chips. The results are shown in Table 1.

[0116] (Evaluation of large-scale moldability) The mixture obtained was molded at room temperature to obtain a large-scale molded product of 150 mm × 300 mm × 100 mm. The large-scale moldable product obtained was evaluated as being large-scale moldable if it could be lifted with both hands without large cracks, large chips, etc., and was evaluated as being large-scale moldable if large cracks, large chips, etc. occurred when trying to lift the product with both hands, or if it could not be lifted with both hands.

[0117] (Calculation of residual carbon ratio) The residual carbon ratio was calculated based on the following formula. When starch was used as the binder, the mass of carbon derived from the binder was set to 20 mass% of the charged amount, and when tar pitch was used as the binder, the mass of carbon derived from the binder was set to 50 mass% of the charged amount. Residual carbon ratio (%) = [mass of carbon derived from binder / (mass of carbon derived from binder+mass of carbon derived from coke)] × 100

[0118] [Examples 2 to 8] (Formation of Molded Product) The raw needle coke used in Example 1 was heat-treated in a nitrogen atmosphere at 800°C to 850°C for 8 hours to produce calcined needle coke, which was used in Examples 2 to 8. Furthermore, the following materials were used as raw materials. The raw materials shown below were mixed without heating in the proportions and conditions shown in Table 1 to prepare mixtures. Next, the resulting mixtures were used to obtain graphite powders (negative electrode materials for lithium ion secondary batteries) of Examples 2 to 8 by the same procedure as in Example 1. The densities (g / cm) of the resulting molded products were ３), density of the fired product (g / cm ３ ) and the density of the graphite (g / cm ３ ) are shown in Table 1. Aggregate: Needle coke with an average particle size of 10 μm and a standard deviation of particle size distribution of 0.24 Binder: Starch (amount shown in Table 1) Water (amount shown in Table 1)

[0119] [Example 9] A graphite powder (negative electrode material for lithium ion secondary batteries) of Example 9 was obtained in the same manner as in Example 1, except that the amount of water in Example 1 was changed to the amount shown in Table 1. The density (g / cm) of the obtained molded product was ３ ), density of the fired product (g / cm ３ ) and the density of the graphite (g / cm ３ ) are shown in Table 1.

[0120] [Examples 10 and 11] Graphite powders (negative electrode materials for lithium ion secondary batteries) of Examples 10 and 11 were obtained in the same manner as in Example 1, except that the amount of water in Example 1 was changed to the amount shown in Table 1, the kneading time was changed to the time shown in Table 1, and the molding method was changed to extrusion molding. The densities (g / cm) of the obtained molded products were ３ ), density of the fired product (g / cm ３ ) and the density of the graphite (g / cm ３ ) are shown in Table 1.

[0121] The molded products obtained in Examples 2 to 11 were evaluated in the same manner as in Example 1. The results are shown in Table 1. "-" in the table means that no data was available.

[0122] [Comparative Example 1] (Formation of Molded Product) Unheat-treated raw needle coke having an average particle size of 11 μm and a standard deviation of particle size distribution of 0.25 was used as the aggregate, and the following materials were further used as raw materials. The following raw materials were mixed while heating at 140° C. in the blending ratio and conditions shown in Table 2 to prepare a mixture. Next, the obtained mixture was used in the same manner as in Example 1 to obtain graphite powder (negative electrode material for lithium ion secondary batteries) of Comparative Example 1. The density (g / cm) of the obtained molded product was ３ ), density of the fired product (g / cm ３ ) and the density of the graphite (g / cm ３) are shown in Table 2. Aggregate: Raw needle coke with an average particle size of 11 μm and a standard deviation of particle size distribution of 0.25 Binder: Tar pitch (10 parts by mass relative to 100 parts by mass of coke) Aromatic compound: Methylnaphthalene-containing additive (total content of aromatic compounds: 77% by mass or more, 3 parts by mass relative to 100 parts by mass of coke)

[0123] The molded product obtained in Comparative Example 1 was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0124] [Comparative Examples 2 and 3] (Formation of Molded Product) In Comparative Examples 2 and 3, calcined needle coke was used as the aggregate as in Examples 2 to 8. Furthermore, the raw materials shown below were mixed under heating at 140°C in the blending ratios and conditions shown in Table 2 to prepare a mixture. Next, the graphite powders (negative electrode materials for lithium ion secondary batteries) of Comparative Examples 2 and 3 were obtained using the obtained mixture in the same manner as in Comparative Example 1. The density (g / cm) of the obtained molded product was ３ ), density of the fired product (g / cm ３ ) and the density of the graphite (g / cm ３ ) are shown in Table 2. Aggregate: Needle coke with an average particle size of 10 μm and a standard deviation of particle size distribution of 0.24 Binder: Tar pitch (10 parts by mass relative to 100 parts by mass of coke) Aromatic compound: Methylnaphthalene-containing additive (total content of aromatic compounds: 77% by mass or more, 3 parts by mass or 7 parts by mass relative to 100 parts by mass of coke)

[0125] [Comparative Example 4] A graphite powder (anode material for lithium ion secondary batteries) of Comparative Example 4 was obtained in the same manner as in Comparative Example 2, except that no aromatic compound was used, the amount of tar pitch was changed to the amount shown in Table 2, and the molding method was changed to extrusion molding. The density (g / cm) of the obtained molded product was ３ ), density of the fired product (g / cm ３ ) and the density of the graphite (g / cm ３ ) are shown in Table 2.

[0126] The molded products obtained in Comparative Examples 2 to 4 were evaluated in the same manner as in Example 1. The results are shown in Table 2. "-" in the table means that no data was available.

[0127]

[0128]

[0129] In Examples 1 to 9, the molded articles tended to have superior bending test force (N) and the density of the graphitized material also tended to be lower than in Comparative Examples 1 to 3. Furthermore, in Examples 1 to 9, chipping of the molded articles was suppressed and large-scale molding was possible. Furthermore, in Examples 10 and 11, which employed extrusion molding, the density of the graphitized material tended to be lower than in Comparative Example 4. Furthermore, in Examples 10 and 11, large-scale molding was possible.

[0130] All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. (a) obtaining a mixture comprising a graphitizable aggregate and a graphitizable binder; (b) forming the mixture into a molded product; (c) graphitizing the molded product to obtain a graphitized product; (d) pulverizing the graphitized material to obtain a pulverized material; The method for producing a negative electrode material for a lithium ion secondary battery, wherein the binder comprises an aqueous binder containing a polymer compound having water solubility or water absorption.

2. In the step of obtaining the molded product, the mixture is molded to have a density of 1.25 g / cm ３ The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1, which obtains a molded product having the above properties.

3. (a) obtaining a mixture comprising a graphitizable aggregate and a graphitizable binder; (b) molding the mixture to obtain a molded product having a density of 1.25 g / cm ３ A step of obtaining the above molded product; (c) graphitizing the molded product to have a density of 1.20 g / cm ３ Obtaining a graphitized product, (d) pulverizing the graphitized material to obtain a pulverized material.

4. (a) obtaining a mixture comprising a graphitizable aggregate and a graphitizable binder; (b) forming the mixture by extrusion to obtain a molded product; (c) graphitizing the molded product to have a density of 1.50 g / cm ３ Obtaining a graphitized product, (d) pulverizing the graphitized material to obtain a pulverized material.

5. 5. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 3, wherein the binder comprises an aqueous binder containing a water-soluble or water-absorbent polymer compound.

6. 3. The method for producing a negative electrode material for a lithium ion secondary battery according to claim 1, wherein the water-soluble or water-absorbent polymer compound comprises at least one selected from the group consisting of starch, amylose, amylopectin, polyacrylic acid, carboxymethyl cellulose, polyvinyl alcohol, and water-soluble protein.

7. The method for producing a negative electrode material for lithium ion secondary batteries according to claim 1 or 2, wherein the water content in the mixture is 10% by mass to 50% by mass with respect to the total amount of the mixture.

8. The method for producing a negative electrode material for lithium ion secondary batteries according to any one of claims 1 to 4, wherein the content of the binder in the mixture is 3% by mass to 30% by mass with respect to the total amount of the mixture.

9. The method for producing a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the aggregate contains calcined coke.

10. The method for producing a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the aggregate contains unheat-treated raw coke.

11. A method for producing a lithium ion secondary battery, comprising: a step of producing a negative electrode material for a lithium ion secondary battery by the method for producing a negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 4; and a step of producing a negative electrode using the negative electrode material for a lithium ion secondary battery.