Carbon materials, methods for manufacturing carbon materials, methods for manufacturing spherical carbon materials, methods for manufacturing composite carbon materials, and methods for manufacturing secondary batteries.

Abstract

The carbon material of this invention comprises natural graphite and satisfies the following formulas (1) and (2). y≧0.23x+3.1 (1) z≧0.43 (2) (x is the d50 (μm) of the carbon material, y is the d90 / d10 of the carbon material, and z is the tap density (g / cm3))

Description

[Technical Field]

[0001] This invention relates to a carbon material, a method for manufacturing the carbon material, a method for manufacturing spherical carbon material, a method for manufacturing composite carbon material, and a method for manufacturing a secondary battery comprising the composite carbon material. [Previous Technology]

[0002] In recent years, with the miniaturization of electronic devices, the demand for high-capacity secondary batteries is increasing. In particular, lithium-ion secondary batteries, with their higher energy density and superior high-current charge-discharge characteristics compared to nickel-cadmium or nickel-metal hydride batteries, have attracted considerable attention. Previously, the increase in capacity of lithium-ion secondary batteries was extensively studied. In recent years, the demand for higher performance of lithium-ion secondary batteries has become increasingly stringent. Therefore, for lithium-ion secondary batteries, there is a requirement to achieve higher capacity, higher input-output ratios, and longer lifespan.

[0003] Regarding lithium-ion secondary batteries, it is known that carbon materials such as graphite are used as active materials for the negative electrode. It is known that when graphite with a high degree of graphitization is used as the active material for the negative electrode in lithium-ion secondary batteries, a capacity close to the theoretical lithium uptake capacity of graphite (372 mAh / g) can be obtained, and the cost and durability are also excellent. Therefore, graphite with a high degree of graphitization is preferred as the active material for the negative electrode.

[0004] If the active material layer containing the negative electrode material is made denser in order to achieve high capacity, problems such as increased irreversible charge and discharge capacity during the initial cycle, decreased high current charge and discharge characteristics, and decreased cycle characteristics will occur due to material damage and deformation.

[0005] To solve the above problems, for example, Patent Document 1 discloses a technique for manufacturing spherical natural graphite by performing mechanical energy treatment on flake-shaped natural graphite. Patent Document 2 discloses a method for obtaining spherical graphite particles with smooth particle surfaces by adding a resin binder to raw graphite particles for spheroidization treatment. Patent Document 3 discloses a method for obtaining spherical graphite particles with excellent spheroidization efficiency by performing spheroidization treatment on flake-shaped, scaly, or blocky carbon materials.

[0006] Patent Document 1: Japanese Patent Application Publication No. 2000-340232; Patent Document 2: Japanese Patent Application Publication No. 2014-114197; Patent Document 3: Japanese Patent Application Publication No. 2017-126425

[0007] According to the research of the present inventors, when using spherical graphite particles that have undergone the above-mentioned spheroidization treatment as disclosed in Patent Documents 1 to 3, the problem of battery swelling sometimes occurs. Therefore, in order to improve the safety of secondary batteries, further improvements are necessary. [Summary of the Invention]

[0008] The purpose of this invention is to provide a carbon material that can improve the problem of battery swelling.

[0009] The inventors discovered that by using a carbon material, battery swelling can be reduced, thus completing the present invention. The carbon material contains natural graphite, and the relationship between the volume-based average particle size (d50) of the carbon material measured by laser diffraction and the ratio (d90 / d10) of the particle size of 90% of the cumulative portion from the small particle side to the particle size of 10% of the cumulative portion satisfies a specific formula, and the tap density is above a specific value.

[0010] The reasons for the aforementioned effects of the carbon material of the present invention are as follows: By spherizing the carbon material of the present invention, smaller particles are placed in the interparticle spaces formed by larger particles, thereby creating dense particles. The spherical carbon material densified in this way ensures a conductive path, thus reducing battery swelling.

[0011] The main idea of ​​the present invention is as follows. [1] A carbon material comprising natural graphite and satisfying the following formulas (1) and (2). y≧0.23x+3.1 (1) z≧0.43 (2) (x is the d50 (μm) of the carbon material, y is the d90 / d10 of the carbon material, and z is the tap density (g / cm3)) [2] The carbon material described in [1] has a d50 of 3.0 μm or more. [3] The carbon material described in [1] or [2] has a d50 of 20.0 μm or less. [4] The carbon material described in any one of [1] to [3] has an SA of 20.0 m2 / g or less. [5] The carbon material described in any one of [1] to [4] is selected from the shape of flakes, scales and blocks. [6] The carbon material described in any one of [1] to [5] has an average thickness of 3 μm or less. [7] The carbon material described in any one of [1] to [6] has a d002 value of 0.340 nm or less. (The d002 value is the interlayer distance of the lattice plane (002 plane) determined by X-ray diffraction using the vibratory method.) [8] The carbon material described in any one of [1] to [7] is used as a negative electrode material for a secondary battery. [9] A method for manufacturing a spherical carbon material includes a step of spherizing the carbon material described in any one of [1] to [8].

[10] The method for manufacturing a spherical carbon material described in [9], wherein the spherical carbon material is used as a negative electrode material for a secondary battery.

[11] A method for manufacturing a composite carbon material, comprising a step of combining a spherical carbon material obtained by the manufacturing method described in [9] or

[10] with a carbonaceous precursor.

[12] A method for manufacturing a carbon material as described in any one of claims [1] to [8], comprising a step of pulverizing the raw carbon material.

[13] A method for manufacturing a secondary battery comprising a positive electrode, a negative electrode and an electrolyte, comprising a step of forming a negative electrode active material layer comprising the composite carbon material obtained by the manufacturing method of the composite carbon material described in

[11] on a current collector to obtain a negative electrode. [Effects of the Invention]

[0012] The spherical carbon material manufactured using the carbon material of the present invention can suppress the swelling of the secondary battery.

Implementation Method

[0014] Hereinafter, the contents of the present invention will be described in detail. The following description of the constituent elements of the invention is an example (representative example) of one embodiment of the present invention, and the present invention is not limited to these embodiments as long as it does not depart from its spirit.

[0015] <Carbon Material> One embodiment of the present invention is a carbon material containing natural graphite, which satisfies the following formulas (1) and (2), and is preferably used as a negative electrode material for secondary batteries. y≧0.23x+3.1 (1) z≧0.43 (2) (x is the d50 (μm) of the carbon material, y is the d90 / d10 of the carbon material, and z is the tap density (g / cm3))

[0016] In this specification, the average particle size (d50) of various volume references, the particle size (d10) corresponding to 10% of the particle size measured according to the volume reference from the small particle side, and the particle size (d90) corresponding to 90% of the particle size measured according to the volume reference from the small particle side are values ​​calculated based on the particle size distribution of the volume reference measured by laser diffraction.

[0017] In this specification, the various tap densities are calculated by using a powder testing machine to fill a cylindrical tap cell with a diameter of 5 cm and a volume of 100 cm3, and then subjecting it to 500 taps with a stroke length of 18 mm. The density is then calculated from the volume and mass of the sample at that time.

[0018] The spherical carbon material manufactured using carbon material containing natural graphite and satisfying the above formulas (1) and (2) can suppress the swelling of the secondary battery for the reasons described above.

[0019] From the viewpoint of suppressing battery swelling in secondary batteries, the carbon material satisfying the above formula (1) is preferably satisfied by the following formula (1A), and more preferably by the following formula (1B). y≧0.23x+3.3 (1A) 0.23x+6.5≧y≧0.23x+3.5 (1B)

[0020] Carbon materials satisfying the above formulas (1) and (2) can be obtained by the following method: shredding scaly particles with a d50 of 100 μm and utilizing the fine powder produced during shredding without grading. As a shredding process, cyclic shredding by repeatedly applying impact force, shear force or grinding force in a shredder shows a tendency to effectively produce fine powder and easily increase the size of d90 / d10 relative to d50.

[0021] Carbon materials are typically graphite. Graphite is readily available commercially and theoretically has a charge-discharge capacitance of up to 372 mAh / g. Therefore, compared with the use of other carbon materials, the improvement in charge-discharge characteristics at high current densities is greater, making it superior.

[0022] The graphite is preferably of low impurity content and can be used after undergoing various known purification treatments as needed. Examples of graphite types include natural graphite and artificial graphite. In this invention, in terms of good charge-discharge characteristics at high capacity and high current density, a material containing at least natural graphite is used. Carbon materials can be used alone or in combination of two or more. In order to effectively obtain the aforementioned effects produced by using natural graphite, the proportion of natural graphite in the carbon material is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 95 to 100% by mass of the carbon material.

[0023] (Physical properties of carbon material) • Particle size d50 of carbon material The volume-based average particle size (d50) of the carbon material in this embodiment is generally 20.0 μm or less, preferably 16.0 μm or less, more preferably 14.0 μm or less, further preferably 12.0 μm or less, especially preferably 11.0 μm or less, and generally 3.0 μm or more, preferably 5.0 μm or more, more preferably 7.0 μm or more, further preferably 8.0 μm or more, especially preferably 10.0 μm or more.

[0024] When d50 is below the upper limit mentioned above, there is a tendency for streaks to be less likely to occur during the slurry coating process when manufacturing electrodes, and for improved high-speed charge-discharge characteristics or low-temperature input-output characteristics. When d50 is above the lower limit mentioned above, there is a tendency to easily prevent irreversible capacity increase and initial battery capacity loss.

[0025] ·Particle size d10 of carbon material The particle size (d10) of the carbon material measured according to the volume basis, corresponding to 10% of the smallest particles, is generally 1.0 μm or more, preferably 1.5 μm or more, more preferably 2.0 μm or more, even more preferably 2.5 μm or more, and even more preferably 3.0 μm or more. It is generally 12.0 μm or less, preferably 10.0 μm or less, even more preferably 8.0 μm or less, even more preferably 6.0 μm or less, and even more preferably 4.0 μm or less.

[0026] When d10 is within the above range, the tendency of particles to aggregate will not be too strong, which can avoid adverse situations such as the increase of slurry viscosity, the decrease of electrode strength in the secondary battery, and the decrease of initial charge and discharge efficiency. When d10 is within the above range, it can also avoid the tendency of high current density charge and discharge characteristics to decrease and output characteristics to decrease.

[0027] ·Particle size d90 of carbon material The particle size (d90) of the carbon material in this embodiment, which corresponds to 90% of the particle size from the small particle side as measured according to the volume basis, is generally 50.0 μm or less, preferably 40.0 μm or less, more preferably 35.0 μm or less, further preferably 30.0 μm or less, even more preferably 25.0 μm or less, and generally 9.0 μm or more, preferably 13.0 μm or more, more preferably 15.0 μm or more, even more preferably 18.0 μm or more, and even more preferably 20.0 μm or more.

[0028] When d90 is within the above range, the following trends are observed: it can avoid the decrease in electrode strength and initial charge / discharge efficiency in secondary batteries, as well as the occurrence of streaks and other defects in the coating process, the decrease in high current density charge / discharge characteristics, and the decrease in output characteristics.

[0029] ·d90 / d10 of carbon material In this embodiment, the ratio (d90 / d10) of the particle size corresponding to 90% of the particle size from the small particle side and the particle size corresponding to 10% of the particle size from the small particle side, as measured according to the volume basis, is generally 5.6 or more, preferably 5.9 or more, more preferably 6.2 or more, and generally 20 or less, preferably 10 or less, more preferably 7 or less.

[0030] When d90 / d10 is within the above range, the swelling resistance is excellent.

[0031] · Tap density of carbon material The tap density of the carbon material in this embodiment is generally 0.43 g / cm3 or more, preferably 0.44 g / cm3 or more, more preferably 0.45 g / cm3 or more, and even more preferably 0.46 g / cm3 or more, and is generally 0.80 g / cm3 or less, preferably 0.70 g / cm3 or less, more preferably 0.60 g / cm3 or less, and even more preferably 0.55 g / cm3 or less.

[0032] When the tap density is within the above range, spheroidization is carried out with high efficiency, and there is a tendency to increase the tap density of the spherical carbon material obtained after spheroidization treatment.

[0033] ·Specific surface area (hereinafter sometimes referred to as "SA") of carbon material measured by BET (Brunauer-Emmett-Teller) method The specific surface area (SA) of carbon material of this embodiment measured by BET method is generally 20.0 m2 / g or less, preferably 18.0 m2 / g or less, more preferably 16.0 m2 / g or less, further preferably 14.0 m2 / g or less, especially preferably 12.0 m2 / g or less, and generally 3.0 m2 / g or more, preferably 4.5 m2 / g or more, more preferably 6.0 m2 / g or more, further preferably 7.5 m2 / g or more, especially preferably 8.5 m2 / g or more.

[0034] When the specific surface area is within the above range, spherical carbon materials with high sphericity efficiency, high tap density, and high SA can be obtained. As a result, there are more lithium-ion insertion and extraction sites, thus there is a trend to obtain spherical carbon materials with excellent low-temperature input-output characteristics.

[0035] In this specification, the various specific surface areas (SA) are values ​​measured by the BET method using nitrogen adsorption.

[0036] · Shape of carbon material The shape of carbon material particles in this embodiment is not particularly limited, as long as it satisfies the above formulas (1) and (2). It is preferred to be scaly, scaly, or blocky, and more preferably scaly. When it is the above shape, the particle contact area is larger, which can increase the number of particle contacts, thus ensuring the conductive path when making the electrode.

[0037] ·Average thickness of carbon material particles The average thickness of carbon material particles in this embodiment is generally 3 μm or less, preferably 2 μm or less, more preferably 1 μm or less, and generally 0.01 μm or more, preferably 0.05 μm or more, more preferably 0.1 μm or more.

[0038] When the average thickness of the carbon material particles is within the above-mentioned range, fine powder is easily generated during the spheroidization process. The generated fine powder can be carried in while spheroidization is carried out efficiently, thus enabling the production of dense spherical carbon materials with high tap density. As a result, there is a tendency to obtain spherical carbon materials that ensure conductive paths and suppress electrodeposition and reduce swelling.

[0039] In this specification, the average thickness of various particles is obtained by observing the particle profile using a scanning electron microscope (SEM), randomly selecting 30 particles, measuring the particle thickness equivalent to the length of the vertical direction relative to the plane direction, removing 5 particles from the large value side and 5 particles from the small value side, and calculating the average thickness of the remaining 20 particles.

[0040] When the planar orientation of the particles is not determined, the particle cross-section can be observed using a scanning electron microscope (SEM) after the particles are aligned. The plane of a particle is defined as the surface with the largest area enclosed by the particle's outline when observing the particle from multiple directions. Furthermore, in the case of scaly or flake-like carbon materials, the basal surface is used as the plane.

[0041] · The d002 value (X-ray parameter) of the carbon material: The d002 value (interlayer distance) of the lattice plane (002 plane) of the carbon material of this embodiment, obtained by X-ray diffraction using the vibratory method, is preferably 0.330 nm or more, more preferably 0.332 nm or more, and even more preferably 0.334 nm or more, and preferably 0.340 nm or less, more preferably 0.339 nm or less, and even more preferably 0.338 nm or less. When the d002 value is within the above range, the crystallinity of the carbon material is moderately improved, and the increase in irreversible capacity tends to be reduced.

[0042] In this specification, the various d002 values ​​are obtained by X-ray diffraction using the vibration method.

[0043] ·Raman R value of carbon material The Raman R value of carbon material in this embodiment is generally 0.05 or above, preferably 0.08 or above, more preferably 0.10 or above, and generally 0.50 or below, preferably 0.40 or below, more preferably 0.30 or below.

[0044] In this specification, the various Raman R values ​​are obtained by measuring the intensity IA of the peak PA near 1580 cm⁻¹ and the intensity IB of the peak PB near 1360 cm⁻¹ in the Raman spectrum obtained by Raman spectroscopy, and calculating their intensity ratio (IB / IA). "Near 1580 cm⁻¹" refers to the range of 1580 to 1620 cm⁻¹. "Near 1360 cm⁻¹" refers to the range of 1350 to 1370 cm⁻¹.

[0045] The Raman R value is an indicator of the crystallinity near the surface of carbon particles (from the particle surface to 100 Å). A larger Raman R value indicates lower crystallinity or a more disordered crystal structure. When the Raman R value is within the above range, a structure with a moderately lower crystallinity is obtained on the carbon material surface, facilitating lithium ion insertion and extraction. Therefore, it is considered to obtain good input-output characteristics. Raman spectroscopy can be performed using a Raman spectrometer. Specifically, the sample is filled by allowing the target particles to fall naturally into the measurement cell. Argon ion laser light is irradiated into the measurement cell while the measurement cell is rotated in a plane perpendicular to the laser light, and the measurement is performed simultaneously.

[0046] <Method for manufacturing carbon material> As a method for manufacturing carbon material that satisfies the above-mentioned superior characteristics, for example, a method of crushing carbon material (also called raw carbon material) as raw material can be cited.

[0047] · Carbon material as raw material Examples of carbon materials as raw materials include natural graphite, artificial graphite, etc. In terms of suppressing electrode bulging or good process compatibility, at least natural graphite is used in this invention.

[0048] Natural graphite is classified according to its properties into flake graphite, crystalline graphite, vein graphite, and amorphous graphite (refer to the graphite section in "Powder and Granulation Process Technology Integration" (Academia Sinica, Inc., 1974) and "HANDBOOK OF CARBON, GRAPHITE, DIAMOND AND FULLERENES" (Noyes Publications)). Crystalline and vein graphite have the highest degree of graphitization, at 100%, followed by flake graphite at 99.9%. In this embodiment, graphitization with a higher degree is preferred. As natural graphite, it is preferable to have fewer impurities among the aforementioned types. Natural graphite can be used after undergoing various known purification treatments as needed.

[0049] Natural graphite is found in Madagascar, China, Brazil, Ukraine, Canada, etc. Flake graphite is found in Sri Lanka, etc. Amorphous graphite is mainly found in the Korean Peninsula, China, Mexico, etc.

[0050] Artificial graphite can be obtained by graphitizing a raw material containing a large amount of easily graphitizable carbon in a temperature range of 2500°C to 3200°C. During calcination, silicon-containing compounds or boron-containing compounds can also be used as graphitization catalysts.

[0051] As easily graphitized carbon, examples include: coal tar pitch, dry distillation liquefied oil and other coal-based heavy oils; straight-run heavy oils such as atmospheric pressure residue oil and vacuum pressure residue oil; cracked heavy oils such as ethylene tar, a byproduct of thermal cracking of crude oil and naphtha; petroleum-based asphalt; aromatic hydrocarbons such as ethylene naphthalene, decacycloene, anthracene; nitrogen-containing cyclic compounds such as phenazine and acridine; sulfur-containing cyclic compounds such as thiophene; aliphatic cyclic compounds such as adamantane; polyphenylene such as biphenyl and biphenylene oxide; polyethylene esters such as polyvinyl chloride, polyvinyl acetate, and polyvinyl butyral; thermoplastic polymers such as polyvinyl alcohol.

[0052] As described above, in order to obtain carbon materials with high capacity and good charge and discharge characteristics at high current density, the raw carbon material is preferably composed of more than 80% by mass of natural graphite, more preferably more than 90% by mass, and even more preferably 95 to 100% by mass.

[0053] • Grinding Process Regarding the apparatus used for grinding, since it is necessary to reduce the particle size of the carbon powder, a pulverizer is preferable. In particular, in terms of improving filling properties and increasing tap density by making the pulverized particles more spherical, it is preferable to grind using not only impact force but also shear force or grinding force. Furthermore, cyclic grinding by repeatedly applying impact force, shear force or grinding force within the pulverizer is preferable because it produces fine powder, increases tap density, and increases the d90 / d10 to d50 ratio.

[0054] Examples of pulverizers include: mechanical pulverizers, airflow pulverizers, and cyclone pulverizers. Specifically, examples include: ball mills, vibratory mills, pin mills, stirred mills, jet mills, cyclone mills, turbine pulverizers, and KRYPTRON mills. In particular, for increasing the d90 / d10 relative to d50, a cyclone pulverizer is preferred.

[0055] When processing raw carbon materials using the above-described apparatus, the circumferential speed of the rotating rotor is typically 30 m / s or more, preferably 75 m / s or more, more preferably 100 m / s or more, even more preferably 110 m / s or more, particularly preferably 120 m / s or more, and most preferably 200 m / s or less. When the circumferential speed of the rotor is within the above-described range, suitable spherical carbon materials can be obtained from the obtained carbon materials, which is therefore preferable.

[0056] The crushing process is preferably carried out by circulating or retaining the raw carbon material within the device. When the material is circulated or retained within the device, the flow velocity of the exhaust fan used to discharge from the crusher is typically 10 m / s or more, preferably 20 m / s or more, more preferably 25 m / s or more, and typically 100 m / s or less, preferably 80 m / s or less, more preferably 60 m / s or less. When the flow velocity of the exhaust fan is within the above range, both the size of d90 / d10 relative to d50 and productivity can be considered.

[0057] The pulverization process can be carried out, for example, in an atmospheric environment, an oxidizing atmosphere, or an inert gas atmosphere such as carbon dioxide, nitrogen, or argon. Since the oxidation of the carbon material surface creates micropores, thereby increasing the SA (sulfuric acid), it is preferable to carry out the process in an atmospheric environment or an oxidizing atmosphere.

[0058] ·Grading treatment In order to satisfy the above formulas (1) and (2), it is preferable not to perform grading treatment on the carbon material.

[0059] High-purity treatment can also be performed when manufacturing the carbon material of this embodiment. As a method for high-purity treatment of the carbon material, an example is acid treatment using an acidic solution containing nitric acid or hydrochloric acid. This method is preferable because it removes impurities such as metals, metal compounds, and inorganic compounds from the carbon material without introducing sulfates, which may become highly reactive sulfur sources, into the system.

[0060] The above-mentioned acid treatment can use any acid containing nitric acid and / or hydrochloric acid. Other acids may also be used, for example, an acid composed of appropriate mixtures of inorganic acids such as bromic acid, hydrofluoric acid, boric acid, and iodic acid, or organic acids such as citric acid, formic acid, acetic acid, oxalic acid, trichloroacetic acid, and trifluoroacetic acid. The acids used for acid treatment are preferably concentrated hydrofluoric acid, concentrated nitric acid, or concentrated hydrochloric acid, and more preferably concentrated nitric acid or concentrated hydrochloric acid. In this embodiment, sulfuric acid may also be used to treat the carbon material, but it should be used in a quantity and concentration that does not impair the effects and physical properties of this embodiment.

[0061] When using multiple acids, a combination of hydrofluoric acid, nitric acid, and hydrochloric acid is preferred as it can efficiently remove the aforementioned impurities. When using multiple acids, the mixing ratio of the mixed acids is typically at least 10% by mass or more, preferably 20% by mass or more, and even more preferably 25% by mass or more. The upper limit refers to the value when all acids are mixed in equal amounts (expressed as 100% by mass per type of acid).

[0062] Acid treatment is carried out, for example, by immersing the carbon material in an acidic solution as described above.

[0063] The amount of acidic solution used for impregnation, in terms of the ratio (mass ratio) of carbon material to acidic solution, is typically 100:10 or more, preferably 100:20 or more, even more preferably 100:30 or more, and typically 100:1000 or less, preferably 100:500 or less, even more preferably 100:300 or less. When the amount of acidic solution used is 100:10 or more, there is a tendency to remove the aforementioned impurities efficiently. When the amount of acidic solution used is 100:1000 or less, the amount of carbon material that can be washed in one go increases, thus achieving both increased productivity and reduced costs.

[0064] The impregnation time is typically 0.5 to 48 hours, preferably 1 to 40 hours, more preferably 2 to 30 hours, and even more preferably 3 to 24 hours. When the impregnation time is below the upper limit mentioned above, both increased productivity and reduced costs can be achieved. When the impregnation time is above the lower limit mentioned above, there is a tendency to remove the aforementioned impurities more efficiently.

[0065] The immersion temperature is typically above 25°C, preferably above 40°C, more preferably above 50°C, and even more preferably above 60°C. When using an aqueous acid, the theoretical upper limit of the immersion temperature is the boiling point of water, i.e., 100°C. When the immersion temperature is within the above range, there is a tendency to efficiently remove the aforementioned impurities.

[0066] To remove residual acid components from the acid treatment and raise the pH value from weakly acidic to neutral, it is preferable to wash the acid-treated carbon material with water. If the pH value of the acid-treated carbon material is typically 3 or higher, preferably 3.5 or higher, more preferably 4 or higher, and even more preferably 4.5 or higher, then water washing can be omitted. If the pH value of the acid-treated carbon material does not reach the above-mentioned upper limit, it is preferable to wash with water as needed. From the viewpoint of improving washing efficiency and preventing impurities from being mixed in, it is preferable to use ion-exchanged water or distilled water for washing.

[0067] The ion content of the rinse water, i.e., its resistivity at 25°C, is typically 0.1 MΩ·cm or higher, preferably 1 MΩ·cm or higher, and even more preferably 10 MΩ·cm or higher. The theoretical upper limit of the resistivity of the rinse water is 18.24 MΩ·cm. A resistivity of the rinse water above the above lower limit indicates a lower ion content in the water, which is preferable from the viewpoint of suppressing impurities and improving rinsing efficiency.

[0068] Water washing can be carried out, for example, by mixing the treated carbon material with water.

[0069] The mixing ratio (mass ratio) of the treated carbon material and water in the water washing process is generally 100:10 or more, preferably 100:30 or more, more preferably 100:50 or more, and even more preferably 100:100 or more. It is generally 100:1000 or less, preferably 100:700 or less, even more preferably 100:500 or less, and even more preferably 100:400 or less. When the mixing ratio of the treated carbon material and water is 100:1000 or less, there is a tendency to improve production efficiency. When the mixing ratio of the treated carbon material and water is 100:10 or more, there is a tendency to achieve excellent reduction in residual impurities and acid components.

[0070] The stirring temperature (temperature of the washing water) is usually above 25°C, preferably above 40°C, more preferably above 50°C, and even more preferably above 60°C. The upper limit of the stirring temperature is the boiling point of water, i.e., 100°C. When the stirring temperature is above the above lower limit, there is a tendency for excellent reduction in residual impurities and acid components.

[0071] The stirring time is typically 0.5 to 48 hours, preferably 1 to 40 hours, more preferably 2 to 30 hours, and even more preferably 3 to 24 hours. When the stirring time is below the upper limit mentioned above, there is a tendency to increase production efficiency. When the stirring time is above the lower limit mentioned above, there is a tendency to achieve excellent reduction in residual impurities and acid components.

[0072] In the case of batch washing, from the viewpoint of removing impurities and acidic components, it is preferable to repeatedly perform the stirring-filtration process in the wash water. The washing process can also be repeated in a manner where the pH value of the carbon material is typically 3 or higher, preferably 3.5 or higher, more preferably 4 or higher, and even more preferably 4.5 or higher. The washing process is typically performed once or more, preferably twice or more, and more preferably three times or more.

[0073] The hydrogen ion concentration in the wastewater obtained after acid treatment and, if necessary, further water washing of the carbon material is typically below 200 ppm, preferably below 100 ppm, more preferably below 50 ppm, and even more preferably below 30 ppm, and typically above 1 ppm, preferably above 2 ppm, even more preferably above 3 ppm, and even more preferably above 4 ppm. When the hydrogen ion concentration in the wastewater is below the above-mentioned upper limit, there is a tendency for acid components to be removed and the decrease in pH value to be suppressed. When the hydrogen ion concentration in the wastewater is above the above-mentioned lower limit, there is a tendency to shorten the treatment time, thereby improving productivity.

[0074] • Heat treatment of carbon material: When manufacturing the carbon material of this embodiment, heat treatment can be performed to adjust the unstable carbon content or crystallinity of the carbon material. When the above-described pulverization process is performed, there is a situation where the unstable carbon content on the surface of the carbon material particles increases excessively. Therefore, by performing heat treatment, the unstable carbon content can be appropriately reduced.

[0075] In this case, the temperature conditions during heat treatment can be set according to the target degree of crystallinity, typically above 300°C, preferably above 500°C, more preferably above 700°C, and even more preferably above 800°C, and typically below 2000°C, preferably below 1500°C, and more preferably below 1200°C. When the above temperature conditions are met, the crystallinity of the carbon particle surface can be appropriately improved.

[0076] When the carbon material used as the raw material has low crystallinity, in order to increase the discharge capacitance, the low crystallinity carbon material can be graphitized by heat treatment to improve its crystallinity. In this case, the temperature conditions during heat treatment can be set according to the target degree of crystallinity, typically above 600°C, preferably above 900°C, more preferably above 1600°C, and even more preferably above 2500°C, and typically below 3200°C, preferably below 3100°C. Under the above temperature conditions, the crystallinity of the carbon material particle surface can be improved.

[0077] The crystallization on the surface of carbon particles is sometimes disordered, and this disorder is particularly pronounced when the above-mentioned crushing process is performed. Therefore, heat treatment can repair the disordered crystallization on the surface of carbon particles. When performing heat treatment, the temperature conditions are maintained within the above-mentioned range for a period of 10 seconds or more, and usually for 72 hours or less.

[0078] The heat treatment is carried out in an inert gas atmosphere such as nitrogen, or in a non-oxidizing atmosphere formed by the gas generated from the raw carbon material. Examples of heat treatment equipment that can be used include: shuttle furnaces, tunnel furnaces, electric furnaces, Redhammer furnaces, rotary kilns, direct-fired furnaces, Ashison furnaces, resistance heating furnaces, induction heating furnaces, etc.

[0079] <Method for manufacturing spherical carbon material> One embodiment of the present invention is a method for manufacturing spherical carbon material, which involves spherizing the carbon material as one embodiment of the present invention to obtain spherical carbon material (hereinafter sometimes referred to as "spherical carbon material of this embodiment").

[0080] · Circularity of Spherical Carbon Material The spherical carbon material in this embodiment typically has a circularity of 0.85 or higher, and preferably 0.90 or higher. Circularity is determined by measuring the particle size distribution based on the equivalent diameter of a circle using a flow particle image analysis device, and calculating the average circularity. Circularity is defined by the following formula (3), where a circularity of 1 represents a theoretically true sphere. [Circularity] = [Circumference of an equivalent circle with the same area as the particle projection shape] / [Actual circumference of the particle projection shape] (3)

[0081] In the determination of roundness, deionized water was used as the dispersion medium, and polyoxyethylene (20) monolaurate was used as the surfactant. The equivalent diameter refers to the diameter of a circle (equivalent circle) with the same projected area as the captured particle image. Roundness is the ratio obtained by dividing the circumference of the equivalent circle by the circumference of the captured particle projection image. The roundness of particles with equivalent diameters ranging from 3 μm to 40 μm was averaged and taken as the roundness.

[0082] Spheroidization Processing: Spheroidization processing can be performed using known methods. For example, a method using a device that repeatedly applies mechanical actions such as compression, friction, and shearing forces, primarily impact forces, to the particles and also includes particle interactions, can be cited. Specifically, a device having a rotor with multiple blades inside the housing, which, by rotating at high speed, applies mechanical actions such as impact compression, friction, and shearing forces to the carbon material introduced inside, thereby performing surface treatment. Furthermore, a device having a mechanism that repeatedly applies mechanical actions by circulating the carbon material particles is also preferred.

[0083] Specific devices may include, for example: a hybridization system (manufactured by Nara Machine Works Co., Ltd.), KRYPTRON, KRYPTRON Orb (manufactured by EARTHTECHNICA Co., Ltd.), a CF mill (manufactured by Ube Industries Co., Ltd.), a mechanical fusion system, NOBILTA, FACULTY (manufactured by Hosokawa Micron Co., Ltd.), Theta Composer (manufactured by Tokusu Works Co., Ltd.), COMPOSI (manufactured by NIPPON COKE & ENGINEERING), etc. Among these, the hybridization system manufactured by Nara Machine Works Co., Ltd. is preferred.

[0084] When using the above-described apparatus for spheroidization, the circumferential speed of the rotating rotor is typically 30–100 m / s, preferably 40–100 m / s, and even more preferably 50–100 m / s. Spheroidization can be performed simply by passing carbon material through the apparatus, but it is preferable to circulate or retain the carbon material within the apparatus for at least 30 seconds, and even more preferably to circulate or retain it within the apparatus for at least 1 minute.

[0085] ·Spheroidization treatment with granulating agent can also be carried out in the presence of granulating agent. By using granulating agent, the adhesion between carbon materials is increased, and spherical carbon materials with carbon materials more firmly attached can be produced.

[0086] The granulating agent used in this embodiment may not contain an organic solvent, or, if it does contain an organic solvent, preferably at least one of the organic solvents does not have an ignition point, or if it does have an ignition point, the ignition point is 5°C or higher. Therefore, when granulating the carbon material in subsequent steps, the risk of ignition, fire, and explosion caused by impact or heat from organic compounds can be prevented, enabling stable and efficient manufacturing. In this specification, the ignition point can be determined using known methods.

[0087] Examples of granulating agents include: coal tar, petroleum-based heavy oil, liquid paraffin and other paraffinic oils, olefinic oils, naphthenic oils, aromatic oils and other synthetic oils; plant-based oils, animal-based aliphatic oils, esters, higher alcohols and other natural oils; resin adhesive solutions obtained by dissolving resin adhesives in organic solvents with an ignition point of 5°C or higher, preferably 21°C or higher, and other organic compounds; water and other aqueous solvents; mixtures of the above.

[0088] Examples of organic solvents with an ignition point above 5°C include: alkylbenzenes such as xylene, isopropylbenzene, ethylbenzene, and propylbenzene; alkylnaphthalenes such as methylnaphthalene, ethylnaphthalene, and propylnaphthalene; aromatic hydrocarbons such as allylbenzene and allylnaphthalene, including styrene; aliphatic hydrocarbons such as octane, nonane, and decane; ketones such as methyl isobutyl ketone, diisobutyl ketone, and cyclohexanone; esters such as propyl acetate, butyl acetate, isobutyl acetate, and amyl acetate; alcohols such as methanol, ethanol, propanol, butanol, isopropanol, isobutanol, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and glycerol; and ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, and diethylene glycol. Diol derivatives such as monobutyl ether, triethylene glycol monobutyl ether, tetraethylene glycol monobutyl ether, propylene glycol methyl ether, propylene glycol methyl ether acetate, methoxymethylbutanol, methoxybutyl acetate, diethylene glycol dimethyl ether, dipropylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, triethylene glycol dimethyl ether, tripropylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and ethylene glycol monophenyl ether; ethers such as 1,4-dimethyl ether; nitrogen-containing compounds such as dimethylformamide, pyridine, 2-pyrrolidone, and N-methyl-2-pyrrolidone; sulfur-containing compounds such as dimethyl sulfoxide; halogen-containing compounds such as dichloromethane, chloroform, carbon tetrachloride, dichloroethane, trichloroethane, and chlorobenzene; and mixtures thereof. For example, it does not contain organic solvents with low ignition points such as toluene. These organic solvents can be used alone as granulating agents.

[0089] Examples of resin adhesives include: cellulose-based resin adhesives such as ethyl cellulose, methyl cellulose, and their salts; acrylic-based resin adhesives such as polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, polyacrylic acid, and their salts; methacrylic-based resin adhesives such as polymethyl methacrylate, polyethyl methacrylate, and polybutyl methacrylate; and phenolic resin adhesives.

[0090] As a granulating agent, coal tar, petroleum-based heavy oil, liquid paraffin and other paraffin oils, alcohols and aromatic oils are better because they can produce spherical carbon materials with higher sphericity and less fine powder.

[0091] As a granulating agent, it is preferable to have the properties of being able to remove [something] efficiently and not adversely affecting battery characteristics such as capacitance, output characteristics, storage, and cycle characteristics. Specifically, it is advisable to select one in which the mass reduction when heated to 700°C in an inert gas atmosphere is typically 50% or more, preferably 80% or more, more preferably 95% or more, further preferably 99% or more, and even more preferably 99.9% or more.

[0092] Examples of methods for mixing carbon material and granulating agent include: mixing carbon material and granulating agent using a mixer or kneader; and mixing carbon material with a granulating agent obtained by dissolving an organic compound in a low-viscosity diluent (organic solvent) and then removing the diluent (organic solvent). Alternatively, a method can be described that simultaneously performs the following two steps: adding granulating agent and carbon material to a granulation apparatus and mixing the carbon material and granulating agent during the spheroidization process; and performing the spheroidization process.

[0093] The amount of granulating agent added relative to 100 parts by weight of carbon material is typically 0.1 parts by weight or more, preferably 1 part by weight or more, more preferably 3 parts by weight or more, further preferably 6 parts by weight or more, especially 10 parts by weight or more, and typically less than 1000 parts by weight, preferably less than 100 parts by weight, more preferably less than 80 parts by weight, further preferably less than 50 parts by weight, and especially preferably less than 20 parts by weight. When the amount of granulating agent added is within the above range, not only is the adhesion between particles improved and the roundness improved, but problems such as decreased productivity due to carbon material adhering to the equipment are also less likely to occur.

[0094] When a granulating agent is used in the manufacture of the spherical carbon material of this embodiment, a step of removing the granulating agent may be included. Examples of methods for removing the granulating agent include: washing with a solvent, and removing the granulating agent by volatilization and decomposition through heat treatment.

[0095] When the granulating agent is volatilized, decomposed, or removed by heat treatment, the heat treatment temperature is generally 60°C or higher, preferably 100°C or higher, more preferably 200°C or higher, even more preferably 300°C or higher, and especially preferably 500°C, and generally below 1500°C, preferably below 1000°C, and even more preferably below 800°C. When the heat treatment temperature is within the above range, the granulating agent can be sufficiently volatilized, decomposed, and removed, thereby improving productivity.

[0096] The heat treatment time is typically 0.5 to 48 hours, preferably 1 to 40 hours, more preferably 2 to 30 hours, and even more preferably 3 to 24 hours. When the heat treatment time is within the above range, the granulating agent can be fully volatilized, decomposed, and removed, thereby improving productivity.

[0097] Examples of suitable atmospheres for heat treatment include atmospheric atmospheres (active gas atmospheres) and inert gas atmospheres such as nitrogen or argon. When heat treatment is performed at 200–300°C, there are no particular restrictions on the atmosphere. However, when heat treatment is performed at temperatures above 300°C, from the viewpoint of preventing graphite surface oxidation, an inert gas atmosphere such as nitrogen or argon is preferred.

[0098] The pressurization process preferably includes a step of pressurizing the spherical carbon material after obtaining it. Examples of methods for pressurizing the spherical carbon material include isotropic pressurization using hydrostatic pressure with water as the pressurizing medium, and isotropic pressurization using gas pressure with gas as the pressurizing medium. Alternatively, the process may involve filling the spherical carbon material into a mold and pressurizing it in a fixed direction using a uniaxial press.

[0099] The pressure of the pressurizing medium in the above-mentioned pressurization treatment is typically 50–4000 kgf / cm², preferably 300–3500 kgf / cm², and even more preferably 500–3000 kgf / cm². When the pressure of the pressurizing medium is above the lower limit mentioned above, the pore volume can be set to a smaller range. When the pressure of the pressurizing medium is below the upper limit mentioned above, there is a tendency to easily suppress the increase in specific surface area.

[0100] <Method for Manufacturing Composite Carbon Material> One embodiment of the present invention is a method for manufacturing composite carbon material, in which the spherical carbon material obtained by the method for manufacturing spherical carbon material according to one embodiment of the present invention is combined with a carbonaceous precursor to obtain composite carbon material.

[0101] The composite carbon material formed by combining spherical carbon material and carbonaceous material in this embodiment can suppress side reactions with electrolyte, improve high-speed charge and discharge performance, and suppress battery swelling of secondary battery.

[0102] The carbonaceous material used here is preferably one with lower crystallinity than the carbon material used in one embodiment of the present invention.

[0103] Examples of methods for obtaining composite carbon materials include: mixing the spherical carbon material of this embodiment with a carbonaceous precursor, and vapor depositing the carbonaceous precursor onto the spherical carbon material of this embodiment. Preferably, methods include mixing the spherical carbon material of this embodiment with a carbonaceous precursor and heating under a non-oxidizing atmosphere (referred to as the mixing method in this embodiment), and vapor depositing the carbonaceous precursor onto the spherical carbon material of this embodiment under an inert gas atmosphere (referred to as the vapor phase method in this embodiment).

[0104] · In the mixing method, it is preferable to mix the spherical carbon material of this embodiment with an organic compound that serves as a carbonaceous precursor and heat it under a non-oxidizing atmosphere.

[0105] Examples of organic compounds that serve as precursors to carbonaceous substances include: soft or hard coal tar pitch, coal tar, coal liquefaction oil, and other carbonaceous heavy oils; crude oil atmospheric or vacuum distillation residues and other petroleum-based heavy oils; cracked heavy oils that are byproducts of ethylene production from naphtha cracking; and petroleum-based pitch, etc.

[0106] Organic compounds derived from resins as precursors of carbonaceous materials include, for example: thermosetting resins such as phenolic resins, polyacrylonitrile, and polyimide; thermoplastic resins such as polyvinyl chloride, polyvinylidene chloride, and polyvinyl alcohol; and natural polymers such as cellulose, starch, and polysaccharides.

[0107] Examples of coal-based feedstock oils include: coal tar pitch, impregnated pitch, shaped pitch, coal liquefaction oil, and other coal-based heavy oils manufactured from coal; and purified coal tar pitch obtained by removing insoluble components from coal tar pitch. Coal-based feedstock oils contain various plate-shaped aromatic hydrocarbons such as dibenzo[a]benzo[b] ...

[0108] Examples of petroleum-based feedstocks include: distillation residue of heavy oil, naphtha cracking residue, and contact cracking heavy oil. Examples also include ethylene tar pitch, FCC (fluid catalytic cracking) decanter, and Ashland asphalt obtained by heat treatment of cracked heavy oil. Petroleum-based feedstocks contain plate-shaped aromatic hydrocarbons formed by multiple benzene rings, but also contain multiple linear paraffinic hydrocarbons, and further include plate-shaped aromatic hydrocarbons formed by multiple benzene rings, often with side chains such as methyl groups, or where some benzene rings are replaced by cyclohexane rings. Therefore, when increasing the temperature during the calcination process to increase fluidity and allow the surfaces of the plate-shaped aromatic hydrocarbons to overlap, the presence of numerous linear paraffins on these surfaces tends to hinder this overlap. Furthermore, aromatic hydrocarbons with side chains such as methyl groups bonded to their plate-shaped surfaces tend to hinder the recombination of these aromatic hydrocarbons. Cyclohexane rings also tend to hinder the recombination of aromatic hydrocarbons, and the thermal cracking of the cyclohexane ring into side chains such as methyl groups further hinders this recombination. Therefore, petroleum-based feedstocks tend to exhibit a lower degree of crystallization progress compared to coal-based feedstocks. Therefore, petroleum-based feedstocks are preferred as organic compounds used in this embodiment as precursors for carbonaceous materials.

[0109] Specifically, in terms of obtaining an amorphous phase with a smaller degree of crystallization, the preferred carbonaceous precursors are petroleum-based heavy oil produced during petroleum purification and asphalt obtained by heat treatment of heavy oil.

[0110] Furthermore, the organic compound used as a carbonaceous precursor in this embodiment may also be formed by adding petroleum-based feedstock, resin-derived organic compounds, and other solvents to coal-based feedstock.

[0111] Typically, these coal-based feedstock oils contain light oil components. Therefore, in order to extract useful components and improve productivity, it is preferable to perform distillation to purify the oil before use.

[0112] The residual carbon content of the organic compound used as a carbonaceous precursor is generally 1% or more, preferably 10% or more, more preferably 20% or more, and even more preferably 30% or more, and is generally 99% or less, preferably 90% or less, even more preferably 80% or less, and even more preferably 70% or less. When the residual carbon content is within the above range, the carbonaceous precursor can diffuse and penetrate uniformly into the surface and micropores of the spherical carbon material, tending to improve input and output characteristics. The residual carbon content is determined according to the method of JIS 2270.

[0113] The carbonaceous precursor can be diluted by adding solvents, etc. By adding solvents, the viscosity of the carbonaceous precursor can be reduced, and the carbonaceous precursor tends to diffuse and penetrate more evenly into the surface and micropores of the spherical carbon material.

[0114] As a method for mixing the spherical carbon material and the carbonaceous precursor of this embodiment, for example, a method can be described by using a mixer or kneader to mix the spherical carbon material and the carbonaceous precursor to obtain a mixture in which the carbonaceous precursor is attached to the spherical carbon material. If necessary, the spherical carbon material, the carbonaceous precursor, and solvents, etc., can be mixed under heating.

[0115] ·The vapor phase method is an example of the CVD (Chemical Vapor Deposition) method, which involves uniformly depositing a vapor phase coating raw material compound, which is a carbon precursor, onto the spherical carbon material of this embodiment under an inert gas atmosphere.

[0116] Examples of gas-phase coating raw material compounds include gaseous compounds that can be decomposed by heat or plasma to form a carbonaceous film on the surface of spherical carbon materials. Examples of gaseous compounds include: unsaturated aliphatic hydrocarbons such as ethylene, acetylene, and propylene; saturated aliphatic hydrocarbons such as methane, ethane, and propane; and aromatic hydrocarbons such as benzene, toluene, and naphthalene. Only one of these gaseous compounds may be used, or a mixture of two or more gases may be prepared for use.

[0117] The temperature, pressure, time, etc. of the CVD process can be appropriately selected according to the type of coating material used or the amount of carbonaceous material to be coated.

[0118] Other treatments: After the carbonaceous material is compounded into the spherical carbon material of this embodiment by the above-described mixing method or gas-phase method, crushing and / or pulverizing treatments can be performed. Furthermore, other steps or control conditions not described above can be added as long as the effect of this embodiment is not impaired.

[0119] · The carbon content in the composite carbon material The carbon content in the composite carbon material of this embodiment is generally 0.01% by mass or more in 100% by mass of the composite carbon material, preferably 0.1% by mass or more, more preferably 1.0% by mass or more, and generally 20.0% by mass or less, preferably 15.0% by mass or less, more preferably 12.0% by mass or less.

[0120] When the carbonaceous content in the composite carbon material is below the upper limit mentioned above, the following trend is observed: when calendering is performed under sufficiently high pressure to achieve high capacity in a secondary battery, the composite carbon material is less prone to material damage, and the irreversible capacity increase during initial charging and discharging can be suppressed, thus suppressing the initial efficiency decrease. When the carbonaceous content in the composite carbon material is above the lower limit mentioned above, there is a tendency to easily obtain the effect of carbonaceous material.

[0121] The carbonaceous content in the composite carbon material is calculated using the mass of the material before and after calcination, as shown in the following formula (4). In this case, the mass change of the spherical carbon material before and after calcination is ignored in the calculation. Carbonaceous content (mass%) = {(w2 - w1) / w2} × 100 (4) (w1 is the mass of the spherical carbon material (kg), w2 is the mass of the composite carbon material (kg))

[0122] (Physical properties of composite carbon material) • Particle size d50 of composite carbon material The volume-based average particle size (d50) of the composite carbon material obtained in this embodiment is generally 50.0 μm or less, preferably 40.0 μm or less, more preferably 25.0 μm or less, and generally 5.0 μm or more, preferably 8.0 μm or more, more preferably 10.0 μm or more.

[0123] When d50 is below the upper limit mentioned above, there is a tendency for streaks to be less likely to occur during the slurry coating process when manufacturing electrodes, and for high-speed charge-discharge characteristics or low-temperature input-output characteristics to be improved. When d50 is above the lower limit mentioned above, there is a tendency to easily prevent irreversible capacity increase and initial battery capacity loss.

[0124] ·Particle size d10 of composite carbon material The particle size (d10) of the composite carbon material obtained in this embodiment, which is the cumulative 10% of the particle size from the small particle side as measured according to the volume basis, is generally 3.0 μm or more, preferably 4.0 μm or more, more preferably 5.0 μm or more, and generally 30.0 μm or less, preferably 20.0 μm or less, more preferably 15.0 μm or less.

[0125] When d10 is within the above range, the tendency of particles to aggregate will not become too strong, which can avoid adverse conditions such as the increase in slurry viscosity, as well as the decrease in electrode strength and initial charge-discharge efficiency in the secondary battery. In addition, it can also avoid the tendency of high current density charge-discharge characteristics to decrease and output characteristics to decrease.

[0126] ·Particle size d90 of composite carbon material The particle size (d90) of the composite carbon material obtained in this embodiment, which is the cumulative 90% of the particle size from the small particle side as measured according to the volume basis, is generally 70.0 μm or less, preferably 50.0 μm or less, more preferably 40.0 μm or less, and generally 10.0 μm or more, preferably 15.0 μm or more, more preferably 20.0 μm or more.

[0127] When d90 is within the above range, the following trends are observed: it can avoid the decrease in electrode strength and initial charge / discharge efficiency in secondary batteries, as well as the occurrence of streaks and other defects in the coating process, the decrease in high current density charge / discharge characteristics, and the decrease in output characteristics.

[0128] ·d90 / d10 of composite carbon material In this embodiment, the ratio (d90 / d10) of the particle size corresponding to 90% of the particle size from the small particle side and the particle size corresponding to 10% of the particle size from the small particle side, as measured according to the volume basis, is generally 1.5 or more, preferably 2.0 or more, more preferably 2.5 or more, and even more preferably 3.0 or more, and is generally 5.0 or less, preferably 4.5 or less, more preferably 4.0 or less, and even more preferably 3.5 or less.

[0129] When d90 / d10 is within the above range, the swelling resistance is excellent.

[0130] · Tap density of composite carbon material The tap density of the composite carbon material obtained in this embodiment is generally 0.50 g / cm3 or more, preferably 0.80 g / cm3 or more, more preferably 1.00 g / cm3 or more, and generally 2.00 g / cm3 or less, preferably 1.60 g / cm3 or less, more preferably 1.40 g / cm3 or less.

[0131] When the tap density is within the above range, the high-speed charge and discharge characteristics and productivity are good.

[0132] ·Specific surface area (SA) of composite carbon material measured by BET method The specific surface area (SA) of the composite carbon material obtained in this embodiment by BET method is generally 10.0 m2 / g or less, preferably 5.0 m2 / g or less, more preferably 3.0 m2 / g or less, and generally 0.1 m2 / g or more, preferably 0.5 m2 / g or more, more preferably 1.0 m2 / g or more.

[0133] When the specific surface area is within the above range, the high-speed charge and discharge characteristics and productivity are good.

[0134] · Circularity of Composite Carbon Material The circularity of the composite carbon material obtained in this embodiment is generally 0.85 or higher, and preferably 0.90 or higher.

[0135] <Method for Manufacturing a Secondary Battery> One embodiment of the present invention is a method for manufacturing a secondary battery comprising a positive electrode, a negative electrode and an electrolyte, which includes the step of forming a negative electrode active material layer comprising a composite carbon material obtained by the method for manufacturing a composite carbon material according to one embodiment of the present invention on a current collector to obtain a negative electrode.

[0136] (Negative electrode active material layer) The negative electrode active material layer can be mixed with carbon materials different from composite carbon materials to improve the alignment of the electrode plate, the permeability of the electrolyte, the conductive path, etc., and improve the cycle characteristics and electrode plate swelling, etc.

[0137] Examples of carbon materials that differ from composite carbon materials include: natural graphite, artificial graphite, amorphous carbon, and carbon materials containing metal particles or metal compounds. These carbon materials can be used alone or in combination of two or more.

[0138] As for natural graphite, examples include high-purity natural graphite. High-purity treatment typically refers to the process of dissolving and removing ash or metals contained in low-purity natural graphite by treating it in acids such as hydrochloric acid, sulfuric acid, nitric acid, or hydrofluoric acid, or by combining multiple acid treatment steps. Usually, water washing is performed after the acid treatment step to remove the acid components used. Alternatively, ash or metals can be removed by evaporating them at high temperatures above 2000°C instead of acid treatment. Ash or metals can also be removed by treating the graphite in a halogen gas atmosphere such as chlorine during high-temperature heat treatment. These methods can be used in any combination.

[0139] The volume-based average particle size (d50) of natural graphite is typically 5 μm or more, preferably 8 μm or more, more preferably 10 μm or more, and typically 60 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the volume-based average particle size is within this range, the high-speed charge-discharge characteristics and productivity are good.

[0140] The specific surface area (SA) of natural graphite, measured by the BET method, is typically 1 m² / g or more, preferably 2 m² / g or more, and typically 30 m² / g or less, preferably 15 m² / g or less. If the specific surface area is within this range, the high-speed charge-discharge characteristics and productivity are good.

[0141] The tap density of natural graphite is typically 0.4 g / cm³ or higher, preferably 0.6 g / cm³ or higher, more preferably 0.8 g / cm³ or higher, and typically 1.3 g / cm³ or lower, preferably 1.2 g / cm³ or lower, more preferably 1.1 g / cm³ or lower. If the tap density is within this range, the high-speed charge / discharge characteristics and productivity are good.

[0142] Examples of artificial graphite include: particles obtained by calcining and graphitizing a single graphite precursor particle while maintaining it in a powder state; and granulated particles obtained by shaping multiple graphite precursor particles, calcining and graphitizing them, and then crushing them.

[0143] The volume-based average particle size (d50) of artificial graphite is typically 5 μm or more, preferably 10 μm or more, and typically 60 μm or less, preferably 40 μm, and even more preferably 30 μm or less. If the volume-based average particle size is within this range, it provides good suppression of electrode bulging or good productivity.

[0144] The specific surface area (SA) of the artificial graphite, measured by the BET method, is typically 0.5 m² / g or more, preferably 1.0 m² / g or more, and typically 8 m² / g or less, preferably 6 m² / g or less, and even more preferably 4 m² / g or less. If the specific surface area is within this range, it provides good suppression of electrode bulging or good productivity.

[0145] The tap density of artificial graphite is typically 0.6 g / cm³ or higher, preferably 0.7 g / cm³, more preferably 0.8 g / cm³, and typically 1.5 g / cm³ or lower, preferably 1.4 g / cm³ or lower, more preferably 1.3 g / cm³ or lower. If the tap density is within this range, it provides good suppression of electrode bulging or good productivity.

[0146] Amorphous carbon can be, for example, particles formed by calcining a bulk mesophase, or particles formed by calcining an easily graphitizable organic compound after non-melting treatment.

[0147] The volume-based average particle size (d50) of amorphous carbon is typically 5 μm or more, preferably 12 μm or more, and typically 60 μm or less, preferably 40 μm or less. If the volume-based average particle size is within this range, the high-speed charge-discharge characteristics and productivity are good.

[0148] The specific surface area (SA) of amorphous carbon, measured by the BET method, is typically 1 m² / g or more, preferably 2 m² / g or more, more preferably 2.5 m² / g or more, and typically 8 m² / g or less, preferably 6 m² / g or less, more preferably 4 m² / g or less. If the specific surface area is within this range, the high-speed charge-discharge characteristics and productivity are good.

[0149] The tap density of amorphous carbon is typically 0.6 g / cm³ or higher, preferably 0.7 g / cm³ or higher, more preferably 0.8 g / cm³ or higher, and typically 1.3 g / cm³ or lower, preferably 1.2 g / cm³ or lower, more preferably 1.1 g / cm³ or lower. If the tap density is within this range, the high-speed charge-discharge characteristics and productivity are good.

[0150] As a carbon material containing metal particles or metal compounds, examples include materials formed by combining metals or their compounds selected from the group consisting of Fe, Co, Sb, Bi, Pb, Ni, Ag, Si, Sn, Al, Zr, Cr, P, S, V, Mn, Nb, Mo, Cu, Zn, Ge, In, and Ti with graphite. Alloys containing two or more metals may also be used. Among these, metals or their compounds selected from the group consisting of Si, Sn, As, Sb, Al, Zn, and W are preferred, and Si and SiOx are even more preferred. SiOx is obtained from silicon dioxide (SiO2) and metallic silicon (Si). The value of x is generally 0 < x < 2, preferably 0.2 or more, more preferably 0.4 or more, further preferably 0.6 or more, and preferably 1.8 or less, more preferably 1.6 or less, and even more preferably 1.4 or less. If x is within this range, the capacity is higher, while the irreversible capacity generated by lithium-oxygen bonding is reduced.

[0151] The volume-based average particle size (d50) of the metal particles is typically 0.005 μm or more, preferably 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.03 μm or more, and is typically 10 μm or less, preferably 9 μm or less, and more preferably 8 μm or less. If the volume-based average particle size is within this range, the volume expansion accompanying charge and discharge can be reduced, the charge and discharge capacitance can be maintained, and good cycle characteristics can be obtained.

[0152] The specific surface area (SA) of the metal particles, as measured by the BET method, is typically 0.5 m² / g or higher, preferably 1 m² / g or higher, and typically 120 m² / g or lower, preferably 100 m² / g or lower. If the specific surface area is within this range, the charge / discharge efficiency and discharge capacity of the secondary battery are higher, and lithium can be moved in and out faster during high-speed charge / discharge, exhibiting excellent rate characteristics.

[0153] The negative electrode active material layer preferably contains an adhesive. Examples of adhesives include those with intramolecular olefinic unsaturated bonds. Specifically, examples include styrene-butadiene rubber, styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, and ethylene-propylene-diene copolymers. By using an adhesive with intramolecular olefinic unsaturated bonds, the swelling and wetting of the negative electrode active material layer to the electrolyte can be reduced. Among these, styrene-butadiene rubber is preferred in terms of ease of acquisition.

[0154] The negative electrode active material layer of this embodiment is formed by dispersing composite carbon material and binder in a dispersion medium to form a slurry and then coating it onto a current collector. Examples of dispersion media include organic solvents such as alcohols and water. A conductive agent may be added to the slurry. Examples of conductive agents include carbon black such as acetylene black, Ketjen black, and furnace black, as well as fine powders formed from Cu, Ni, or alloys thereof.

[0155] As a current collector, examples include: rolled copper foil, electrolytic copper foil, stainless steel foil, and other metal thin films. The thickness of the current collector is preferably 4 μm or more, more preferably 6 μm or more, and preferably 30 μm or less, more preferably 20 μm or less.

[0156] The drying temperature after coating the slurry onto the current collector is preferably 60°C or higher, more preferably 80°C or higher, and more preferably 200°C or lower, and more preferably 195°C or lower. The drying atmosphere after coating the slurry onto the current collector is preferably air or an inert gas atmosphere.

[0157] The thickness of the negative electrode active material layer is preferably 5 μm or more, more preferably 20 μm or more, further preferably 30 μm or more, and preferably 200 μm or less, more preferably 100 μm or less, and further preferably 75 μm or less. If the thickness of the negative electrode active material layer is within the above range, it has excellent practicality as a negative electrode and can obtain the function of absorbing and releasing sufficient lithium for high-density current values.

[0158] (Positive electrode active material layer) The positive electrode is formed by forming a positive electrode active material layer containing positive electrode active material and binder on the current collector.

[0159] Examples of positive electrode active materials include metal chalcogenide compounds that can absorb and release alkali metal cations such as lithium ions during charging and discharging. Examples of metal chalcogenide compounds include: transition metal oxides such as vanadium oxide, molybdenum oxide, manganese oxide, chromium oxide, titanium oxide, and tungsten oxide; transition metal sulfides such as vanadium sulfide, molybdenum sulfide, titanium sulfide, and CuS; phosphorus-sulfur compounds of transition metals such as NiPS3 and FePS3; selenium compounds of transition metals such as VSe2 and NbSe3; composite oxides of transition metals such as Fe0.25V0.75S2 and Na0.1CrS2; and composite sulfides of transition metals such as LiCoS2 and LiNiS2.

[0160] Among these, V2O5, V5O13, VO2, Cr2O5, MnO2, TiO2, MoV2O8, LiCoO2, LiNiO2, LiMn2O4, TiS2, V2S5, Cr0.25V0.75S2, Cr0.5V0.5S2, and more preferably LiCoO2, LiNiO2, and LiMn2O4, wherein a portion of these transition metals is replaced by other metals in a lithium transition metal composite oxide. These positive electrode active materials can be used alone or in combination.

[0161] Examples of adhesives used to bind the positive electrode active material include inorganic compounds such as silicates and water glass; and resins without unsaturated bonds such as Teflon (registered trademark) and polyvinylidene fluoride. Among these, resins without unsaturated bonds are preferred in terms of suppressing decomposition during oxidation reactions. The weight average molecular weight of resins without unsaturated bonds is typically 10,000 or more, preferably 100,000 or more, and typically 3 million or less, preferably 1 million or less.

[0162] The positive electrode active material layer may also contain a conductive agent to improve the conductivity of the electrode. Examples of conductive agents include: acetylene black, carbon black, graphite and other carbon powders; metal fibers, powders and foils.

[0163] The positive electrode is formed by using the same method as the negative electrode, by using a dispersion medium to slurry the positive electrode active material or binder, coating it onto the current collector and drying it.

[0164] For example, the current collectors used as positive electrodes are aluminum, nickel, and stainless steel (SUS).

[0165] (Electrolyte) The electrolyte is preferably a non-aqueous electrolyte, such as a non-aqueous electrolyte obtained by dissolving lithium salt in a non-aqueous solvent, or a non-aqueous electrolyte obtained by forming a gel, rubber, or solid sheet from an organic polymer compound.

[0166] Examples of non-aqueous solvents used as non-aqueous electrolytes include: chain carbonates such as diethyl carbonate, dimethyl carbonate, and methyl ethyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, and butyl carbonate; chain ethers such as 1,2-dimethoxyethane; cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, cyclobutane, and 1,3-dioxolane; chain esters such as methyl formate, methyl acetate, and methyl propionate; and cyclic esters such as γ-butyrolactone and γ-valerolactone.

[0167] These non-aqueous solvents may be used alone or in combination of two or more. In the case of mixed solvents, it is preferable to use a combination of mixed solvents containing cyclic carbonates and chain carbonates. In terms of exhibiting high ionic conductivity at low temperatures and improving low-temperature non-rechargeable properties, it is preferable that the cyclic carbonates are a mixture of ethylene carbonate and propylene carbonate.

[0168] Lithium salts used as non-aqueous electrolytes include, for example, inorganic lithium salts such as halides like LiCl and LiBr, perhalates like LiClO4, LiBrO4, and LiClO4, and inorganic fluoride salts like LiPF6, LiBF4, and LiAsF6; and fluorinated organic lithium salts such as perfluoroalkyl sulfonates like LiCF3SO3 and LiC4F9SO3, and perfluoroalkyl sulfonium salts like lithium trifluorosulfonium imide ((CF3SO2)2NLi). Among these, LiClO4, LiPF6, and LiBF4 are preferred.

[0169] Lithium salts can be used alone or in combination of two or more. The concentration of lithium salts in non-aqueous electrolytes is usually above 0.5 mol / L and usually below 2.0 mol / L.

[0170] Organic polymers used to form non-aqueous electrolytes into gel-like, rubber-like, or solid sheet-like forms include, for example: polyether polymers such as polyethylene oxide and polypropylene oxide; cross-linked polymers of polyether polymers; vinyl alcohol polymers such as polyvinyl alcohol and polyvinyl butyral; insolubles of vinyl alcohol polymers; polyepoxychlorohydrin; polyphosphazene; polysiloxane; vinyl pyrrolidone, polyvinyl carbonate, polyacrylonitrile, etc.; and polymer copolymers such as poly(ω-methoxyloxyethylene methacrylate), poly(ω-methoxyloxyethylene methacrylate-copolymer-methyl methacrylate), and poly(hexafluoropropylene-vinylidene fluoride).

[0171] The electrolyte may further include a film-forming agent. Examples of film-forming agents include: carbonate compounds such as vinylene carbonate, vinyl ethyl carbonate, and methyl phenyl carbonate; sulfurized olefins such as ethylene sulfide and propylene sulfide; sulfonyl lactone compounds such as 1,3-propane sulfonyl lactone and 1,4-butane sulfonyl lactone; and acid anhydrides such as maleic anhydride and succinic anhydride.

[0172] The electrolyte may further include diphenyl ether, cyclohexylbenzene and other anti-overcharging agents.

[0173] (Separator) A porous separator, such as a porous membrane or non-woven fabric, is typically placed between the positive and negative electrodes to prevent short circuits between them. In this case, the electrolyte is impregnated within the porous separator. Examples of materials used as separators include: polyolefins such as polyethylene and polypropylene; polyether ether. Polyolefins are preferred.

[0174] (Secondary Battery) The form of the secondary battery in this embodiment is not particularly limited. Examples include: a cylindrical type with a spiral sheet electrode and separator; a cylindrical type with an inside-out structure formed by combining a pellet electrode and separator; and a coin type formed by stacking pellet electrodes and separators. By housing batteries of these forms in a packaging shell, they can be made into any shape such as coin-shaped, cylindrical, or square for use.

[0175] There are no particular restrictions on the order of assembling the secondary battery of this embodiment, as long as it is assembled in an appropriate order according to the structure of the battery. For example, the following method can be used: place the negative electrode on the packaging shell, place the electrolyte and separator on the negative electrode, and then place the positive electrode in a manner opposite to the negative electrode, and then caulk together with the gasket and sealing plate to form a battery.

[0176] When a negative electrode is made by forming the negative electrode active material layer as described above, there are no particular restrictions on the method or the selection of other materials. Furthermore, when a secondary battery is made using this negative electrode, there are no particular restrictions on the method or the selection of necessary components in the battery structure, such as the positive electrode and the electrolyte.

[0177] A secondary battery using a spherical carbon material containing natural graphite and satisfying formulas (1) and (2) of this embodiment as a negative electrode material can suppress battery swelling for the reasons described above. Therefore, the negative electrode material using the carbon material of this embodiment can be appropriately used in secondary batteries, such as lithium-ion secondary batteries. [Example]

[0178] Next, the specific features of the present invention will be described in more detail by way of examples. The present invention is not limited to these examples.

[0179] <d50, d90, d10> Based on the particle size distribution of the volume reference measured by laser diffraction, the d50, d90, and d10 of the carbon materials obtained in Examples 1-6 and Comparative Examples 1-4, and the composite carbon materials obtained in Examples 7-9 and Comparative Examples 5-6 were calculated. Specifically, 0.01 g of carbon material or composite carbon material was suspended in approximately 150 mL of a 0.1% (v / v) aqueous solution of polyoxyethylene (20) sorbitan monolaurate (Tween 20 (registered trademark)) as a surfactant. This sample was introduced into a laser diffraction / scattering particle size distribution measuring device (HORIBA's "LA-920"), and the sample was irradiated with ultrasound at intensity 4 for 1 minute. Based on the particle size distribution of the volume reference measured by the above measuring device, the d50, d90, and d10 of the volume reference were calculated.

[0180] <Specific Surface Area (SA) Measured by BET Method> The specific surface area (SA) of the carbon materials obtained in Examples 1-6 and Comparative Examples 1-4, and the composite carbon materials obtained in Examples 7-9 and Comparative Examples 5-6, measured by BET method, was determined using a specific surface area measuring device (GEMINI 2360 manufactured by Shimadzu Corporation). The sample was pre-dried at 350°C for 15 minutes under nitrogen flow, and then cooled to liquid nitrogen temperature. The measurement was performed using the nitrogen adsorption BET 6-point method under the condition that the relative pressure of nitrogen to atmospheric pressure was 0.05-0.31.

[0181] <Tap Density> Using a powder testing machine (“PT-S” manufactured by Hosokawa Micron), the carbon materials obtained in Examples 1-6 and Comparative Examples 1-4, and the composite carbon materials obtained in Examples 7-9 and Comparative Examples 5-6, were passed through a sieve with a mesh size of 1.7 mm and dropped into a cylindrical tapping container with a diameter of 5 cm and a volume of 100 cm3, filling the container completely. Then, 500 vibrations with a stroke length of 18 mm were performed, and the density was calculated from the volume and mass of the sample at that time as the tap density.

[0182] <d002> The carbon materials obtained in Examples 1-6 and Comparative Examples 1-4 were used to determine d002 by X-ray diffraction using the vibratory method. Specifically, a sample was prepared by mixing approximately 15% by mass of X-ray standard high-purity silicon powder with the carbon material. CuKα rays monochromated by a graphite monochromator were used as the radiation source. The wide-angle X-ray diffraction curve was determined by the reflection diffraction method, and the surface spacing (d002) was calculated using the vibratory method.

[0183] <Average Particle Thickness> The average particle thickness of the carbon materials obtained in Examples 1-6 and Comparative Examples 1-4 was calculated by observing particle cross-sections using a scanning electron microscope (SEM). Specifically, for the particle cross-section images observed using a scanning electron microscope (SEM), 30 particles were randomly selected, and their length in the vertical direction relative to the plane (base plane) was measured. After removing 5 particles from the larger side and 5 particles from the smaller side, the average thickness of the remaining 20 particles was calculated as the average particle thickness. Furthermore, the term "average thickness <1 μm" means that the average thickness is less than 1 μm but greater than or equal to 0.01 μm.

[0184] <Circularity> The circularity of the carbon materials obtained in Examples 1-6 and Comparative Examples 1-4, and the composite carbon materials obtained in Examples 7-9 and Comparative Examples 5-6, was determined by the following method: using a flow particle image analysis device, the particle size distribution based on the equivalent diameter of the circle was measured, and the average circularity was calculated. Circularity is defined by the following formula (3). [Circularity] = [Circumference of the equivalent circle with the same area as the particle projection shape] / [Actual circumference of the particle projection shape] (3) In the determination of circularity, ion-exchanged water was used as the dispersion medium, and polyoxyethylene (20) monolaurate was used as the surfactant. The equivalent diameter of the circle refers to the diameter of the circle (equivalent circle) with the same projection area as the captured particle image, and the circularity refers to the ratio obtained by dividing the circumference of the equivalent circle by the circumference of the captured particle projection image. The average of the measured sphericity of particles with an equivalent diameter of 3 μm to 40 μm is taken as the sphericity.

[0185] <Swelling> To the composite carbon material obtained in Examples 7-9 and Comparative Examples 5-6, 60.60±0.12 g (equivalent to 0.6 g in terms of solid content) of a 1% sodium carboxymethyl cellulose aqueous solution and 1.237±0.012 g (equivalent to 0.6 g in terms of solid content) of a styrene-butadiene rubber aqueous dispersion with a weight average molecular weight of 270,000 were added. The mixture was stirred for 5 minutes using a Hybrid Mixer manufactured by Keyence and then degassed for 30 seconds to obtain a slurry. Using a small die-coating machine, the slurry was coated onto a 10 μm thick copper foil (serving as the current collector) to a width of 5 cm, with a solid content of 10.00 ± 0.2 mg / cm². The coating was then rolled using a 25 cm diameter roller to adjust the density of the negative electrode active material layer to 1.50 ± 0.03 g / cm³, resulting in a negative electrode sheet (the thickness of which is H). The obtained negative electrode sheet, NMC (nickel / manganese / cobalt) positive electrode sheet, and polyethylene separator were stacked in the order of negative electrode, separator, and positive electrode. The battery elements obtained in this manner were coated with an aluminum laminate, and an electrolyte was injected, formed by dissolving LiPF6 at 1 mol / L in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio = 3:7). The mixture was then vacuum-sealed to manufacture a sheet-like non-aqueous secondary battery.

[0186] The manufactured, uncharged battery was restrained at 25°C under a restraint pressure of 80 kPa and placed on a horizontal surface. A laser displacement meter (Keyence Corporation's "CL-3000") was used to irradiate the upper surface of the restraint fixture, and the thickness change of the battery during charging and discharging was measured. The battery underwent two initial charge-discharge cycles at a voltage range of 4.1 V to 3.0 V and a current of 0.1 C (the current value of the rated capacity of the discharge capacitor at a 1-hour rate is set as 1 C), and then two more initial charge-discharge cycles at a voltage range of 4.2 V to 3.0 V and a current of 0.2 C. Following the initial charge-discharge, 25 charge-discharge cycles were repeatedly performed at a voltage range of 4.2 V to 3.0 V and a current of 0.5 C, and the thickness change of the battery during the cycles was measured. Let the thickness change under the discharge state after the initial charge and discharge be d(0), and let the thickness change under the discharge state after 25 cycles be d(25). Use the following formula (5) to calculate the battery swelling δ. δ(%)=[d(25)-d(0)] / H×100 (5) (H is the thickness of the negative electrode sheet before liquid injection after rolling)

[0187] (Example 1) In a dry cyclone pulverizer equipped with pulverizing blades and an airflow classification mechanism inside the pulverizing chamber, flake-shaped natural graphite with d50 = 100 μm, thickness < 10 μm, d002 = 0.336 nm, and Raman value = 0.17 was introduced. Under atmospheric conditions, the graphite was circulated and pulverized through collisions, shearing, and grinding between particles, between particles and the pulverizing blades, and between particles and the inner wall of the pulverizing chamber. The pulverized powder was recovered using a filter bag without removing the fine powder, thus obtaining flake-shaped carbon material. The physical properties of the obtained carbon material are shown in Table 1.

[0188] (Example 2) Except that the flow rate of the exhaust fan of the dry cyclone pulverizer was set to 44 m / s, carbon material was obtained in the same manner as in Example 1. The physical properties of the obtained carbon material are shown in Table 1.

[0189] (Example 3) Except that the flow rate of the exhaust fan of the dry cyclone pulverizer was set to 40 m / s, carbon material was obtained in the same manner as in Example 1. The physical properties of the obtained carbon material are shown in Table 1.

[0190] (Example 4) Except that the flow rate of the exhaust fan of the dry cyclone pulverizer was set to 35 m / s, carbon material was obtained in the same manner as in Example 1. The physical properties of the obtained carbon material are shown in Table 1.

[0191] (Example 5) Except that the flow rate of the exhaust fan of the dry cyclone pulverizer was set to 31 m / s, carbon material was obtained in the same manner as in Example 1. The physical properties of the obtained carbon material are shown in Table 1.

[0192] (Example 6) Except that the flow rate of the exhaust fan of the dry cyclone pulverizer was set to 26 m / s, carbon material was obtained in the same manner as in Example 1. The physical properties of the obtained carbon material are shown in Table 1.

[0193] (Comparative Example 1) In a dry cyclone pulverizer equipped with pulverizing blades and an airflow classification mechanism inside the pulverizing chamber, flake-like natural graphite with d50 = 100 μm, thickness < 10 μm, d002 = 0.336 nm, and Raman value = 0.17 was fed in with the pulverizing blades rotating at a circumferential speed of 115 m / s and the exhaust fan speed at the pulverizer outlet adjusted to 36 m / s. Under atmospheric conditions, the graphite was circulated and pulverized through collisions, shearing, and grinding between particles, between particles and the pulverizing blades, and between particles and the inner wall of the pulverizing chamber. The pulverized powder was then collected using a cyclone dust collector to classify the fine powder, thereby obtaining carbon material. The physical properties of the obtained carbon material are shown in Table 1.

[0194] (Comparative Example 2) Except that the flow rate of the exhaust fan of the dry cyclone pulverizer was set to 34 m / s, carbon material was obtained in the same manner as in Comparative Example 1. The physical properties of the obtained carbon material are shown in Table 1.

[0195] (Comparative Example 3) UF8 manufactured by AMG Mining was used as a carbon material. The properties of the carbon material used are shown in Table 1.

[0196] (Comparative Example 4) Carbon material was obtained by pulverizing flake-like natural graphite with d50 = 100 μm, thickness < 10 μm, d002 = 3.36 Å, and Raman value = 0.17 using a collision plate jet mill. The physical properties of the obtained carbon material are shown in Table 1.

[0197] (Example 7) 12 parts by mass of liquid oil were mixed with 100 parts by mass of the carbon material obtained in Example 3 as a granulating agent, and then sphericalized. The liquid oil used as a granulating agent was removed by heat treatment to obtain spherical carbon material. The obtained spherical carbon material was filled into a rubber container and sealed. After isotropic pressure treatment, the obtained molded article was crushed and graded. The obtained powder was mixed with asphalt as a carbon precursor. The asphalt had an ash content of 0.02% by mass, a metal impurity content of 20 ppm by mass, and a quinoline insoluble content of 1% by mass. After the furnace pressure was reduced to below 10 Torr, it was restored to atmospheric pressure using nitrogen. Nitrogen was further circulated to ensure that the oxygen concentration in the furnace did not reach 100 ppm. The furnace was then heated at 700°C for 1 hour in an inert gas environment, and then heated at 1000°C for 1 hour. By crushing and classifying the obtained calcined material, a composite carbon material containing amorphous carbonaceous material on the surface of spherical carbon material was obtained. Based on the calcination yield, the mass ratio of spherical carbon material to amorphous carbonaceous material in the obtained composite carbon material was confirmed to be 1:0.08 (the carbonaceous material content in the composite carbon material is 7.4% by mass). The physical properties of the obtained composite carbon material are shown in Table 2.

[0198] (Example 8) Except that the carbon material was the same as that obtained in Example 4, a composite carbon material was obtained by the same method as in Example 7. The physical properties of the obtained composite carbon material are shown in Table 2.

[0199] (Example 9) Except that the carbon material was the same as that obtained in Example 5, a composite carbon material was obtained using the same method as in Example 7. The physical properties of the obtained composite carbon material are shown in Table 2.

[0200] (Comparative Example 5) Except that the carbon material was the same as that obtained in Comparative Example 1, a composite carbon material was obtained using the same method as in Example 7. The physical properties of the obtained composite carbon material are shown in Table 2.

[0201] (Comparative Example 6) Except that the carbon material was the same as that obtained in Comparative Example 2, a composite carbon material was obtained using the same method as in Example 7. The physical properties of the obtained composite carbon material are shown in Table 2.

[0202] (Comparative Example 7) Except that the carbon material was the same as that obtained in Comparative Example 4, the same method as in Example 7 was used to attempt sphericalization, but due to the low tap density, spherical carbon material could not be obtained.

[0203] [Table 1] d50 [μm] d90 [μm] d10 [μm] d90 / d10 [-] y 0.23x + 3.1 SA [m 2 / g] Tap density [g / cm³] 3 ] d 002 [nm] Average thickness [μm] Circularity [-] Example 1 13.4 31.7 4.4 7.2 7.2 6.2 8.3 0.49 0.336 <1 0.87 Example 2 11.5 25.0 3.9 6.4 6.4 5.7 9.0 0.48 0.336 <1 0.87 Example 3 10.9 23.5 3.7 6.4 6.3 5.6 9.6 0.48 0.336 <1 0.87 Example 4 10.6 24.1 3.5 6.9 6.8 5.5 10.4 0.46 0.336 <1 0.87 Actual example 5 10.1 22.4 3.4 6.6 6.6 5.4 10.8 0.47 0.336 <1 0.87 Actual example 6 8.8 18.5 3.1 6.0 5.9 5.1 12.2 0.45 0.336 <1 0.87 Comparative Example 1 11.6 23.2 4.2 5.5 5.5 5.8 9.7 0.51 0.336 <1 0.87 Comparative Example 2 11.0 21.7 4.0 5.4 5.4 5.6 10.4 0.50 0.336 <1 0.87 Comparative Example 3 8.2 14.9 3.2 4.7 4.7 5.0 12.5 0.40 0.336 <1 0.88 Comparative Example 4 5.7 10.9 2.6 4.2 4.2 4.4 13.9 0.29 0.336 <1 0.87

[0204] [Table 2] Types of carbon materials spheroidization d50 [μm] d90 [μm] d10 [μm] d90 / d10 [-] SA [m 2 / g] Tap density [g / cm 3 ] Circularity [-] bloating [%] Example 7 Example 3 Can 16.7 29.7 9.6 3.1 1.6 1.22 0.91 3.8 Example 8 Example 4 Can 16.5 29.6 9.4 3.1 1.8 1.22 0.91 3.5 Actual example 9 Actual example 5 Possible 15.7 29.0 9.0 3.2 2.0 1.22 0.91 4.0 Comparative Example 5 Comparative Example 1 Possible 16.7 29.1 9.9 2.9 1.9 1.24 0.91 5.1 Comparative Example 6 Comparative Example 2 Possible 16.1 27.8 9.6 2.9 1.9 1.23 0.91 4.9 Comparative Example 7 Comparative Example 4 No - - - - - - - -

[0205] As can be seen from Tables 1 and 2, the composite carbon materials of Examples 7 to 9, obtained by using carbon materials containing natural graphite and satisfying the above formulas (1) and (2), can suppress battery swelling. On the other hand, the composite carbon materials of Comparative Examples 5 and 6, obtained by using carbon materials that do not satisfy the above formula (1), cannot suppress battery swelling. It is believed that the reason is that in the carbon materials of this embodiment, by placing smaller particles in the interparticle gaps formed by larger particles, dense particles can be created. By densifying in this way, a conductive path is ensured, and therefore battery swelling can be suppressed. Comparative Example 7 is an example of using carbon materials with a lower tap density, but because of the lower tap density, spherical carbon materials cannot be manufactured.

[0206] The present invention has been described in detail using specific forms, and it will be apparent to those skilled in the art that various modifications can be made without departing from the intent and scope of the invention. This application is based on Japanese Patent Application 2021-148060, filed on September 10, 2021, the entire contents of which are incorporated herein by reference. [Industrial Applicability]

[0207] Using a carbon material containing natural graphite and satisfying the above formulas (1) and (2) as a raw material in a secondary battery for use as a negative electrode material can suppress battery swelling. Therefore, the carbon material of this embodiment can be preferably used as a negative electrode material for secondary batteries, such as lithium-ion secondary batteries. [Simplified Explanation of the Diagram]

[0013] Figure 1 is a graph showing the relationship between x (d50) and y (d90 / d10) of the carbon material recorded in Table 1.

Claims

1. A carbon material comprising natural graphite and satisfying the following formulas (1) and (2): y≧0.23x+3.1 (1) z≧0.43 (2) (x is the d50 (μm) of the carbon material, y is the d90 / d10 of the carbon material, and z is the tap density (g / cm3)).

2. For carbon materials as requested in item 1, the d50 is 3.0 μm or larger.

3. For carbon materials as requested in item 1 or 2, the d50 is less than 20.0 μm.

4. For carbon materials as requested in item 1 or 2, the SA is less than 20.0 m2 / g.

5. The carbon material as requested in item 1 or 2, wherein the shape of the carbon material is selected from scaly, scaly, and blocky.

6. The carbon material as requested in item 1 or 2 has an average thickness of less than 3 μm.

7. For carbon materials as requested in item 1 or 2, the d002 value is less than 0.340 nm (the d002 value is the interlayer distance of the lattice plane (002 plane) determined by X-ray diffraction using the optical vibration method).

8. The carbon material as described in claim 1 or 2 is used as the negative electrode material for a secondary battery.

9. A method for manufacturing a spherical carbon material, comprising the step of spheroidizing the carbon material as claimed in any one of claims 1 to 8.

10. The method for manufacturing spherical carbon material as claimed in claim 9, wherein the spherical carbon material is used as a negative electrode material for a secondary battery.

11. A method for manufacturing a composite carbon material, comprising the step of combining a spherical carbon material obtained by the manufacturing method of claim 9 or 10 with a carbonaceous precursor.

12. A method for manufacturing carbon material as claimed in any one of claims 1 to 8, comprising the step of crushing raw carbon material.

13. A method for manufacturing a secondary battery, comprising a positive electrode, a negative electrode and an electrolyte, and including the step of forming a negative electrode active material layer on a current collector comprising a composite carbon material obtained by the method for manufacturing composite carbon material as claimed in claim 11, thereby obtaining a negative electrode.

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