Carbon material, negative electrode, secondary battery, and methods for production thereof

Abstract

The present invention relates to a carbon material coated with an amorphous carbonaceous substance, the carbon material having an absorbance parameter of 1-12 as obtained by using a specific measurement method on a slurry of the carbon material having a solid content concentration of 58%, the slurry obtained by mixing the carbon material and a 1.5 mass% aqueous solution of a carboxymethylcellulose Na salt.

Description

Carbon material, negative electrode, secondary battery, and method for manufacturing the same.

[0001] This invention relates to carbon materials, negative electrodes, secondary batteries, and methods for manufacturing the same.

[0002] In recent years, with the miniaturization of electronic devices, the demand for high-capacity rechargeable batteries has been increasing. In particular, rechargeable batteries with higher energy density and superior charge / discharge characteristics compared to nickel-cadmium batteries and nickel-metal hydride batteries, especially lithium-ion rechargeable batteries, are attracting attention. Lithium-ion rechargeable batteries consist of positive and negative electrodes that can absorb and release lithium ions, as well as LiPF (Lithium-ion Photovoltaic Filter). ６ ya LiBF ４ Non-aqueous lithium secondary batteries, consisting of a non-aqueous electrolyte containing dissolved lithium salts, have been developed and put into practical use.

[0003] While improving the performance of lithium-ion secondary batteries has been widely studied, there has been a growing demand for even higher performance in recent years. Regarding the negative electrode of lithium-ion secondary batteries, for example, Patent Document 1 discloses that certain battery characteristics can be improved by using an active material with controlled properties of spheroidized graphite as the negative electrode.

[0004] International Publication No. 2016 / 006617

[0005] However, it was found that simply controlling the physical properties of the active material, spheroidized graphite itself, as described in Patent Document 1, is insufficient; rather, controlling the physical properties of the slurry containing the active material is necessary to achieve both curvature and powder resistance.

[0006] Therefore, the present invention aims to provide a carbon material that achieves both a curve ratio and powder resistance, and a method for manufacturing the same. It also aims to provide a negative electrode using such a carbon material, a method for manufacturing the same, and a secondary battery and a method for manufacturing the same.

[0007] The inventors of the present invention have conducted extensive research to solve the above problems and have found that by setting the value of an absorbance parameter, calculated using a predetermined method with absorbance measured using a spectrophotometer, to a specific range, it is possible to produce a carbon material with low curvature and low powder resistance, thereby completing the present invention. In other words, the gist of the present invention is as follows.

[0008] Embodiment 1 of the present invention is a carbon material coated with an amorphous carbonaceous material, wherein the absorbance parameter obtained by the following measurement method for a slurry with a solid content of 58% of the carbon material, obtained by mixing the carbon material with a 1.5% by mass aqueous solution of carboxymethylcellulose sodium salt, is between 1 and 12. <Measurement Method> The slurry is diluted 10 times by mass using deionized water and placed in a 2 mL centrifugation container, and centrifuged at 12,000 rpm for 30 minutes. The supernatant after centrifugation is diluted 5 times by volume using deionized water, and the absorbance of the supernatant of the diluted solution is measured using a spectrophotometer. The average value of the absorbance at each wavelength of 400 nm, 500 nm, 600 nm, and 700 nm is multiplied by 5 to determine the absorbance parameter.

[0009] Aspect 2 of the present invention is a carbon material having a BET specific surface area of ​​1 to 5 m². ２ The carbon material is as described in Embodiment 1, and is / g.

[0010] A third aspect of the present invention is the carbon material according to aspect 1 or aspect 2, wherein the circularity of the carbon material is 0.91 or greater.

[0011] Aspect 4 of the present invention is the volume-based average particle size d of the carbon material. ５０ The carbon material is according to any one of embodiments 1 to 3, wherein the thickness is 5 to 17 μm.

[0012] Aspect 5 of the present invention is the volume-based average particle size d of the carbon material. ５０ The volume-based average particle size d is 5 to 17 μm. ５０ The carbon material according to any one of embodiments 1 to 4, wherein the ratio of the content (mass%) of the amorphous carbonaceous material in the carbon material to (μm) is 0.35 to 2.0.

[0013] Aspect 6 of the present invention is a carbon material according to any one of aspects 1 to 5, wherein the cumulative pore volume of 1000 nm or less is 0.1 to 0.5 mL / g.

[0014] Embodiment 7 of the present invention is a negative electrode comprising the carbon material described in any one of Embodiments 1 to 6.

[0015] Embodiment 8 of the present invention is a non-aqueous secondary battery comprising a positive electrode, a negative electrode, and an electrolyte capable of intercalating and releasing lithium ions, wherein the negative electrode comprises a carbon material described in any one of Embodiments 1 to 6.

[0016] Embodiment 9 of the present invention relates to a specific surface area of ​​1 to 5 m². ２ A method for producing a carbon material having a density of / g and a circularity of 0.91 or higher, comprising crushing a mixture containing heated graphite and an amorphous carbonaceous material precursor at a peripheral speed of 30 to 120 m / s.

[0017] Aspect 10 of the present invention is a method for producing a carbon material having an integrated pore volume of 0.1 to 0.5 mL / g of 1000 nm or less, comprising crushing a mixture containing heated graphite and an amorphous carbonaceous material precursor at a peripheral speed of 30 to 120 m / s.

[0018] Aspect 11 of the present invention is a method for producing a carbon material according to aspect 9 or aspect 10, wherein the heating temperature is 1200°C or higher.

[0019] Embodiment 12 of the present invention is a method for manufacturing a negative electrode, comprising the step of applying a carbon material described in any one of Embodiments 1 to 6 onto a current collector.

[0020] Aspect 13 of the present invention is a method for manufacturing a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is obtained by the manufacturing method described in Aspect 12.

[0021] The carbon material according to the present invention easily achieves both powder resistance and curvature when used as a negative electrode. Furthermore, the method for manufacturing the carbon material according to the present invention can produce the carbon material described above. Moreover, the negative electrode and secondary battery according to the present invention contain the above-described excellent carbon material as a negative electrode active material, and such a negative electrode and secondary battery can be obtained by the method for manufacturing the negative electrode and secondary battery according to this embodiment.

[0022] The present invention will be described in detail below, but the present invention is not limited to the embodiments described below and can be implemented with various modifications within the scope of its gist. In this specification, when the expression "~" is used, it shall be used to include the numerical value or physical property value before and after it. In addition, the upper and lower limits of the numerical ranges disclosed in the specification can be arbitrarily combined. Mass% and weight%, and mass ppm and weight ppm are synonymous.

[0023] 《Carbon Material》 The carbon material according to this embodiment is a carbon material coated with an amorphous carbonaceous material, and the absorbance parameter obtained by the following measurement method for a slurry of the carbon material and a 1.5% by mass aqueous solution of carboxymethylcellulose sodium salt, with a solid content concentration of 58% of the carbon material, is 1 to 12.

[0024] The carbon material according to this embodiment has an absorbance parameter of 1 to 12. Here, from the viewpoint of reducing the curvature ratio, the absorbance parameter is preferably 1 or higher, more preferably 2 or higher, and even more preferably 3 or higher. Furthermore, from the viewpoint of balancing with powder resistance, the absorbance parameter is 12 or lower, preferably 9 or lower, more preferably 6.5 or lower, even more preferably 6 or lower, and especially preferably 5.5 or lower.

[0025] In the negative electrode slurry used in lithium-ion secondary batteries, carbon such as graphite is generally used as the active material, so chipping or cracking of the active material can be evaluated using the absorbance parameter of the slurry.

[0026] According to this embodiment, chipping or cracking of the carbon material that serves as the active material is stably suppressed, so that the absorbance parameter of the electrode paste can be stably kept below a desired value. The chipping or cracking of the carbon material can be controlled by mixing with amorphous carbonaceous material and by the disintegration strength after heating, as described later. Furthermore, the disintegration strength can be controlled by the stirring rotation speed, the diameter of the stirring blades, the size of the stirring tank, etc.

[0027] The following describes a measurement method for determining absorbance parameters using the above slurry. <Measurement Method> The slurry is diluted 10 times by mass using deionized water and placed in a 2 mL centrifugation container. The slurry is then centrifuged at 12,000 rpm for 30 minutes. The supernatant after centrifugation is diluted 5 times by volume using deionized water, and the absorbance of the supernatant of the diluted solution is measured using a spectrophotometer. The average value of the absorbance at each wavelength of 400 nm, 500 nm, 600 nm, and 700 nm is multiplied by 5 to determine the absorbance parameter.

[0028] To explain the above measurement method in more detail, first, carbon material, carboxymethylcellulose sodium salt as a thickener, and ionized water as a dispersion medium are prepared as materials for preparing the slurry. Specifically, first, the carbon material and a 1.5% CMC aqueous solution are mixed so that the solid content concentration of the carbon material is 64%. Next, ion-exchanged water is added to adjust the slurry so that the final solid content concentration is 58%.

[0029] The slurry obtained by the above method is diluted 10 times by mass with deionized water. This is placed in a 2 mL centrifuge container and centrifuged at 12,000 rpm for 30 minutes. The supernatant after centrifugation is collected and diluted 5 times by volume with deionized water. The absorbance of the supernatant of this diluted solution is measured using a spectrophotometer. The absorbance at each wavelength of 400 nm, 500 nm, 600 nm, and 700 nm is determined, and the average value of these values ​​multiplied by 5 is taken as the absorbance parameter.

[0030] The volume-based average particle size of the carbon material according to this embodiment is preferably 5 to 17 μm or less. Here, from the viewpoint of obtaining good input / output characteristics, the volume-based average particle size is preferably 16.5 μm or less, more preferably 16 μm or less, still more preferably 14 μm or less, particularly preferably 12 μm or less, especially preferably 10 μm or less, and most preferably 9 μm or less. Further, from the viewpoint of suppressing an excessive reaction with the electrolyte and realizing suitable initial efficiency, the volume-based average particle size is preferably 2 μm or more, more preferably 3 μm or more, still more preferably 4 μm or more, and even more preferably 5 μm or more. The volume-based average particle size of the carbon material can be adjusted, for example, by pulverization, classification, or the like.

[0031] In this specification, the volume-based average particle size refers to the volume-based median diameter d ５０ measured by a laser diffraction / scattering particle size distribution measuring device, and specifically, it is a value measured by the following method.

[0032] <Volume-based average particle size d ５０ > Suspend 0.01 g of the carbon material in 10 mL of a 0.2 mass% aqueous solution of polyoxyethylene sorbitan monolaurate (manufactured by Kishida Chemical Co., Ltd., Tween 20), which is a surfactant, and introduce it into a laser diffraction / scattering particle size distribution measuring device (LA-920, manufactured by Horiba, Ltd.). Then, after irradiating with ultrasonic waves of 28 kHz at an output of 60 W for 1 minute, obtain the volume-based particle size distribution using the above measuring device. The volume-based median diameter obtained from the particle size distribution is defined as the volume-based average particle size d ５０ of the carbon material.

[0033] The true density of the carbon material according to this embodiment is preferably 2.25 g / cm ３ or less, and more preferably 2.10 g / cm ３ to 2.25 g / cm ３ . Here, from the viewpoint of suppressing an increase in irreversible capacity as a negative electrode material and obtaining good initial efficiency and long-term storage recovery rate, the true density is preferably 2.25 g / cm ３ or less, more preferably 2.24 g / cm ３ or less, and still more preferably 2.23 g / cm ３ or less. Further, from the same viewpoint, the true density is 2.10 g / cm３ The above is preferable, and 2.15 g / cm³ ３ The above is more preferable, specifically 2.20 g / cm³. ３ The above is even more preferable. The true density of the carbon material can be adjusted by the content of amorphous carbonaceous material, the heating temperature during carbon material production, etc., as described later.

[0034] In this specification, true density refers to the value measured by the liquid-phase displacement method (pycnometer method) using butanol, and specifically, the value measured by the method described below.

[0035] <True Density> The true density of the carbon material is measured by the liquid-phase displacement method (pycnometer method) using butanol. The true density is measured five times, and the average value is taken as the true density of the carbon material.

[0036] The Raman R value of the carbon material according to this embodiment is preferably 0.50 or less, more preferably 0.01 to 0.50, and even more preferably 0.20 to 0.50. Here, from the viewpoint of suppressing an increase in irreversible capacity as a negative electrode material and obtaining good initial efficiency and long-term storage recovery rate, and from the viewpoint of suppressing excessive reaction with the electrolyte and preventing a decrease in charge / discharge efficiency and an increase in gas generation, the above Raman R value is preferably 0.50 or less, more preferably 0.49 or less, and even more preferably 0.48 or less. Furthermore, from the viewpoint of avoiding a decrease in charge / discharge resistance characteristics as crystals become less likely to orient in a planar orientation when the density is increased, the above Raman R value is preferably 0.01 or more, more preferably 0.10 or more, and even more preferably 0.20 or more. The Raman R value of the carbon material can be adjusted by the content of amorphous carbonaceous material and the heating temperature during carbon material manufacturing, as described later.

[0037] Here, the Raman R value is a value expressed by the following formula: Raman R value = (1360 cm⁻¹ in Raman spectral analysis) －１ Nearby Peak P Ｂ Strength I Ｂ ) / (1580 cm in Raman spectral analysis) －１ Nearby Peak P Ａ Strength I Ａ ) In the above formula, "1580 cm －１ "Nearby" means 1580 cm －１ ~1620cm －１It refers to the range of "1360 cm". －１ "Nearby" means 1350 cm －１ ~1370cm －１ It refers to the range.

[0038] Here, 1580cm －１ Nearby Peak P Ａ This is one of the peaks characteristic of graphite, a peak called the G-band that originates from the carbon planar structure, and is located at 1360 cm⁻¹. －１ Nearby Peak P Ｂ This refers to a peak called the D-band, which is caused by structural disorder or the introduction of defects. By using the Raman R value derived from these peaks, it is possible to evaluate the crystallinity and defect rate of carbon materials.

[0039] Raman spectra are obtained by measurement using a Raman spectrometer. Specifically, micro-Raman spectra are obtained for each of 100 carbon particles, and then the Raman R value is determined by averaging the 100 Raman spectra. The measurement conditions are as follows: Laser wavelength: 532 nm Laser power on sample: 0.1 mW or less Objective lens: NA 0.50 Spectral resolution: 1.82 cm －１ / pixel Measurement range: 623cm －１ ~3526cm －１

[0040] The DBP oil absorption amount of the carbon material according to this embodiment is preferably 47 mL / 100 mg or less, more preferably 20 mL / 100 g to 47 mL / 100 mg. Here, from the viewpoint of suppressing streaking when forming the electrode plate, the DBP oil absorption amount is preferably 47 mL / 100 mg or less, more preferably 46 mL / 100 mg or less, and even more preferably 45 mL / 100 mg or less. Furthermore, from the viewpoint of avoiding a decrease in the reaction surface due to the presence of suitable voids within the particles, the DBP oil absorption amount is preferably 20 mL / 100 mg or more, more preferably 30 mL / 100 mg or more, and even more preferably 35 mL / 100 mg or more. The DBP oil absorption amount can be adjusted by the particle size, tap density, amorphous carbonaceous material content, etc. of the carbon material. In this specification, DBP oil absorption amount refers to butyl oil absorption amount when phthalate is used, and is a value measured in accordance with ISO 4546, and more specifically, is a value measured by the method described below.

[0041] <DBP Oil Absorption Amount> The DBP oil absorption amount of the carbon material is measured in accordance with ISO 4546:1993. Specifically, 30 g of carbon material is placed in an oil absorption measuring device (manufactured by Asahi Research Institute Co., Ltd., S410D), and the measurement is taken under conditions of a dropping rate of 4 mL / min and a rotation speed of 200 rpm.

[0042] The total pore volume of the carbon material according to this embodiment is preferably 0.58 mL / g or less, and more preferably 0.35 mL / g to 0.58 mL / g. Here, from the viewpoint of the dispersibility of the thickener and binder used when forming the electrode plate, the total pore volume is preferably 0.58 mL / g or less, more preferably 0.57 mL / g or less, and even more preferably 0.56 mL / g or less. Also, from the same viewpoint, the total pore volume is preferably 0.35 mL / g or more, more preferably 0.4 mL / g or more, and even more preferably 0.45 mL / g or more. The total pore volume can be adjusted by the particle size of the carbon material and the content of amorphous carbonaceous material. Note that the total pore volume in this specification is a value measured using a mercury porosimeter by the mercury intrusion method, and more specifically, it is a value measured by the method described below.

[0043] <Total pore volume, integrated pore volume below 3000 nm, integrated pore volume below 1000 nm> Carbon material weighed to approximately 0.2 g is sealed in the powder cell of a mercury porosimeter (Micromeritex, Autopore 9520), and pre-treatment is performed by degassing at 25°C under vacuum (below 50 μmHg) for 10 minutes. Next, the pressure is reduced to 4 psia (approximately 28 kPa) and mercury is introduced into the powder cell. The pressure is then increased in steps from 4 psia (approximately 28 kPa) to 40000 psia (approximately 280 MPa), and then decreased to 25 psia (approximately 170 kPa). The number of steps during the pressure increase is set to 80 or more, and after an equilibrium time of 10 seconds at each step, the amount of mercury injected is measured. The pore distribution is calculated from the mercury injection curve obtained above using Washburn's equation. For the calculation, the surface tension (γ) of mercury is assumed to be 485 dyne / cm, and the contact angle (ψ) is assumed to be 140°. From the obtained results, the total pore volume, the integrated pore volume below 3000 nm, and the integrated pore volume below 1000 nm are determined.

[0044] In this embodiment, the cumulative pore volume of the carbon material below 3000 nm is preferably 0.3 mL / g or more, and more preferably 0.3 mL / g to 0.55 mL / g. Here, from the viewpoint of obtaining good input / output characteristics, the cumulative pore volume is preferably 0.3 mL / g or more, more preferably 0.35 mL / g or more, and even more preferably 0.4 mL / g or more. Furthermore, from the viewpoint of suppressing excessive reaction with the electrolyte and obtaining good initial efficiency, the cumulative pore volume is preferably 0.55 mL / g or less, more preferably 0.53 mL / g or less, and even more preferably 0.5 mL / g or less. The cumulative pore volume below 3000 nm is affected by the amount of intraparticle voids and interparticle voids. The cumulative pore volume below 3000 nm can be adjusted by the structure and particle size of the carbon material, the manufacturing method, and the content of amorphous carbonaceous material. Note that the cumulative pore volume below 3000 nm in this specification is a value measured by the same method as the total pore volume described above.

[0045] In this embodiment, the cumulative pore volume of the carbon material with a diameter of 1000 nm or less is preferably 0.1 mL / g or more, and more preferably 0.1 mL / g to 0.5 mL / g. Here, from the viewpoint of avoiding a decrease in reaction area, the cumulative pore volume is preferably 0.1 mL / g or more, more preferably 0.11 mL / g or more, and even more preferably 0.12 mL / g or more. Furthermore, from the viewpoint of suppressing excessive reaction with the electrolyte, the cumulative pore volume is preferably 0.5 mL / g or less, more preferably 0.4 mL / g or less, and even more preferably 0.3 mL / g or less. The cumulative pore volume with a diameter of 1000 nm or less refers to the amount of void space within the particle.

[0046] The cumulative pore volume of 1000 nm or less can be adjusted by the method of manufacturing the carbon material. For example, it can be adjusted by known methods such as a method of sphericalizing flake graphite without a grinding process, or a method of forming a folded structure as described in International Publication No. 2015 / 080203. In this specification, the cumulative pore volume of 1000 nm or less is a value measured by the same method as the total pore volume described above.

[0047] In this embodiment, the cumulative pore volume of the carbon material in the 10 nm to 50 nm range is preferably 0.01 mL / g or less, and more preferably 0.001 mL / g to 0.01 mL / g. Here, from the viewpoint of suppressing excessive reaction with the electrolyte, the cumulative pore volume is preferably 0.01 mL / g or less, more preferably 0.009 mL / g or less, and even more preferably 0.008 mL / g or less. Also, from the viewpoint of avoiding a decrease in reaction area, the cumulative pore volume is preferably 0.001 mL / g or more, more preferably 0.002 mL / g or more, and even more preferably 0.003 mL / g or more. The cumulative pore volume in the 10 nm to 50 nm range can be adjusted by the particle size of the carbon material and the content of amorphous carbonaceous material. Note that the cumulative pore volume in the 10 nm to 50 nm range in this specification is a value measured by BJH method analysis with an adsorption isotherm in nitrogen adsorption / desorption measurement, and more specifically, it is a value measured by the method described below.

[0048] <Integrated pore volume from 10 nm to 50 nm> After heat-treating the carbon material under reduced pressure at 100°C for 3 hours, an adsorption isotherm is obtained using nitrogen as the adsorbing gas at liquid nitrogen temperature using a gas adsorption measurement device (Autosorb 3B, manufactured by Quantachrome). Using the obtained adsorption isotherm, assuming the mesopores are cylindrical, the mesopore volume and mesopore surface area for each pore size are determined by BJH method analysis. From the obtained results, the integrated pore volume from 10 nm to 50 nm is determined.

[0049] The carbon material according to this embodiment preferably satisfies one or more of the following conditions: total pore volume of 0.58 mL / g or less, cumulative pore volume of 3000 nm or less of 0.3 mL / g or more, cumulative pore volume of 1000 nm or less of 0.1 mL / g or more, and cumulative pore volume of 10 nm to 50 nm of 0.01 mL / g or less. It is more preferably satisfied with two or more conditions, even more preferably with three or more conditions, and particularly preferably with all four conditions.

[0050] Furthermore, the carbon material according to this embodiment more preferably satisfies one or more of the following conditions: total pore volume of 0.35 mL / g to 0.58 mL / g, cumulative pore volume of 3000 nm or less of 0.3 mL / g to 0.55 mL / g, cumulative pore volume of 1000 nm or less of 0.1 mL / g to 0.5 mL / g, and cumulative pore volume of 10 nm to 50 nm of 0.001 mL / g to 0.01 mL / g. It is even more preferably satisfied with two or more conditions, even more preferably satisfied with three or more conditions, and particularly preferably satisfied with all four conditions.

[0051] The specific surface area (BET specific surface area) of the carbon material according to this embodiment is 1 to 5 m². ２ A value of less than or equal to / g is also preferable. Here, from the viewpoint of avoiding a decrease in the reaction area, the above specific surface area is 1 m². ２ Preferably 2m / g or more. ２ More preferably 2.5 m ２ More preferably 3m / g or more. ２ A value of 3.5 m or more is particularly preferred. ２ A value of 13 m² or more is particularly preferred. Furthermore, from the viewpoint of suppressing excessive reaction with the electrolyte, the specific surface area is 13 m². ２ Preferably less than / g, and 10m ２ / g or less is more preferable, 8m ２ It is even more preferable to be less than / g, and 5m ２ Preferably less than / g, and 4.5m ２ It is more preferable to have less than or equal to 4.35 m ２ A value of less than or equal to / g is even more preferable. The above specific surface area can be adjusted by the particle size of the carbon material and the content of amorphous carbonaceous material. In this specification, the specific surface area is the value measured by the nitrogen adsorption BET single-point method using the gas flow method, which is one of the BET methods for nitrogen adsorption and desorption measurement, and more specifically, the value measured by the method described in the examples described later.

[0052] The tap density of the carbon material according to this embodiment is 0.70 g / cm³. ３ ~1.40 g / cm ３ This is preferable. Here, the tap density is 0.70 g / cm³, which can suppress process defects such as scribing during electrode plate manufacturing, and improves high-speed charge / discharge characteristics due to increased density of the negative electrode sheet resulting from improved filling properties and a more uniform shape of the voids between particles. ３ The above is preferable, and 0.80 g / cm³ ３ The above is more preferable, 0.90 g / cm³ ３ The above is even more preferable. Furthermore, from the viewpoint of electrode plate pressability, high-speed charge / discharge characteristics, and low-temperature input / output characteristics, which are achieved by providing appropriate spaces on the surface and inside of the particles, the above tap density is 1.40 g / cm³. ３ The following is preferable: 1.30 g / cm³ ３ The following is more preferable: 1.20 g / cm³ ３ The following is even more preferable. Note that in this specification, the tap density is determined using a powder density meter with a diameter of 1.6 cm and a volume of 20 cm³. ３ This is the density value calculated from the volume and mass of the sample when a cylindrical tap cell is filled to the brim with the sample and then tapped under the conditions of a stroke length of 10 mm and 1000 taps.

[0053] In this embodiment, the circularity of the carbon material is preferably 0.91 or higher, and more preferably 0.91 to 0.99. Here, the curvature of lithium ion diffusion is reduced, the movement of the electrolyte into the voids between particles becomes smoother, and the rapid charge-discharge characteristics are excellent, so the above circularity is more preferably 0.92 or higher, and even more preferably 0.93 or higher. Furthermore, the above circularity is preferably 0.99 or lower, more preferably 0.98 or lower, and even more preferably 0.97 or lower, as this ensures good contact between the carbon materials and provides excellent cycle characteristics. In this specification, circularity is a value expressed as {(perimeter of an equivalent circle with the same area as the particle projection shape) / (actual perimeter of the particle projection shape)}, obtained by measuring the particle size distribution of the equivalent circle diameter by flow-type particle image analysis, and the average value of the circularity of particles with an equivalent circle diameter in the range of 1.5 μm to 40 μm from images taken of at least 1000 carbon material particles is taken as the circularity.

[0054] The carbon dioxide adsorption amount of the carbon material according to this embodiment is preferably 0.01 mL / g to 0.13 mL / g. Here, from the viewpoint of avoiding a decrease in reaction area, the carbon dioxide adsorption amount is preferably 0.01 mL / g or more, and more preferably 0.02 mL / g or more. Furthermore, from the viewpoint of suppressing excessive reaction with the electrolyte, the carbon dioxide adsorption amount is preferably 0.13 mL / g or less, more preferably 0.12 mL / g or less, even more preferably 0.11 mL / g or less, and particularly preferably 0.10 mL / g or less. In this specification, the carbon dioxide adsorption amount is measured using a gas adsorption amount measuring device on a sample dried at 350°C under reduced pressure for 2 hours, with carbon dioxide as the adsorbed gas, and measured at a relative pressure of 1.0°C. －７ This is the adsorption amount value within the measurement range of ~0.03.

[0055] The carbon material according to this embodiment preferably contains amorphous carbonaceous material, more preferably contains graphite and amorphous carbonaceous material, and even more preferably contains natural graphite and amorphous carbonaceous material.

[0056] Details of graphite and amorphous carbonaceous materials will be described later, but the volume-based average particle size d of carbon materials ５０ Let x be x (μm) and y be the content of amorphous carbonaceous material in the carbon material (mass%). Then, the volume-based average particle size d is expressed as y / x. ５０The ratio of amorphous carbonaceous material content to the total material is preferably 0.35 to 2.0. Here, from the viewpoint of curvature, the above ratio is preferably 0.45 or higher, more preferably 0.55 or higher, even more preferably 0.65 or higher, especially preferably 0.75 or higher, and particularly preferably 0.8 or higher. Furthermore, from the viewpoint of balancing curvature and powder resistance, the above ratio is preferably 2.0 or lower, more preferably 1.7 or lower, even more preferably 1.5 or lower, especially preferably 1.2 or lower, particularly preferably 1.0 or lower, and most preferably 0.9 or lower.

[0057] The content of the above amorphous carbonaceous material is preferably 4% to 15% by mass. Here, the content is preferably 4% or more by mass, more preferably 4.5% or more by mass, even more preferably 5% or more by mass, even more preferably 6% by mass, especially preferably 7% by mass, and also preferably 15% or less by mass, more preferably 12% or less by mass, and even more preferably 9% or less by mass.

[0058] 《Method for Manufacturing Carbon Material》 The method for manufacturing the carbon material according to this embodiment includes the following steps in order. From the viewpoint of improving lithium ion diffusion, the carbon material has a specific surface area of ​​1 to 5 m². ２ It is preferable that the volume per gram and the circularity are 0.91 or higher. Furthermore, from the viewpoint of controlling the reactivity with the electrolyte, it is preferable that the carbon material has an integrated pore volume of 0.1 to 0.5 mL / g or less at 1000 nm. (i) A step of mixing natural graphite with an amorphous carbonaceous precursor; (ii) A step of heating the mixture obtained in step (i); (iii) A step of crushing the mixture after heating in step (ii) at a peripheral speed of 30 to 120 m / sec.

[0059] The method for manufacturing the carbon material described above under "Carbon Material" is not particularly limited as long as absorbance parameters within the desired range can be obtained, but one embodiment is that it can be obtained by the manufacturing method described above. Furthermore, the preferred embodiment of the carbon material obtained by the method for manufacturing the carbon material according to this embodiment is the same as the preferred embodiment described above under "Carbon Material".

[0060] <Step (i)> In step (i) of the carbon material manufacturing method according to this embodiment, natural graphite and amorphous carbonaceous precursor are mixed. The natural graphite has a volume-based average particle size d５０ It is preferable to use particles with a size of 5 to 17 μm or less.

[0061] • Natural Graphite The natural graphite in this embodiment is not particularly limited and includes, for example, earthy graphite, scaly graphite, and flake graphite. Among these, scaly graphite and flake graphite are preferred from the viewpoint of having a high degree of graphitization and low impurity content, and flake graphite is more preferred.

[0062] Furthermore, spheroidized natural graphite is particularly preferred from the viewpoint of particle packing and charge / discharge load characteristics, by forming suitable dense pores inside the carbon material. Spheroidized natural graphite is particularly preferred if the above-mentioned flake graphite has been spheroidized. Here, spheroidized natural graphite means natural graphite with a circularity of 0.70 or higher. If the natural graphite in this embodiment is spheroidized natural graphite, its circularity should be 0.70 or higher, but 0.80 or higher is preferred, 0.88 or higher is more preferred, 0.90 or higher is even more preferred, 0.91 or higher is even more preferred, and 0.92 or higher is particularly preferred. The upper limit of the circularity is not particularly limited and may be 1.

[0063] Volume-based average particle size d of natural graphite in this embodiment ５０ The particle size is preferably 9 μm or less, and more preferably 2 μm to 9 μm. Here, the volume-based average particle size d of the obtained carbon material is ５０ From the perspective of reducing the size and suppressing process-related inconveniences such as scribing at the electrode plate formation stage, the above volume-based average particle size d ５０ The particle size is preferably 9 μm or less, more preferably 8.8 μm or less, and even more preferably 8.6 μm or less. Furthermore, from the viewpoint of not making the specific surface area too large and suppressing activity in the electrolyte, the above volume-based average particle size d ５０ The particle size is preferably 2 μm or larger, more preferably 3 μm or larger, and even more preferably 4 μm or larger.

[0064] The true density of natural graphite in this embodiment is 2.20 g / cm³. ３ ~2.26 g / cm³ ３ This is preferable. Here, the theoretical value of the true density of graphite is 2.26 g / cm³. ３ Therefore, the true density is 2.26 g / cm³. ３The following applies. Furthermore, in order to suppress the irreversible increase in capacity of the resulting carbon material used as a negative electrode material and to obtain good initial efficiency and long-term storage recovery rate, the true density is 2.20 g / cm³. ３ The above is preferable, and 2.22 g / cm³ ３ The above is more preferable, specifically 2.24 g / cm³. ３ The above is even more preferable.

[0065] In this embodiment, the Raman R value of natural graphite is typically 0.1 to 0.9. Here, from the viewpoint of preventing the crystallinity of the particle surface from becoming too high and making it difficult for crystals to orient in a direction parallel to the negative electrode plate when the density is increased, thereby avoiding a decrease in load characteristics, the above Raman R value is typically 0.1 or higher, preferably 0.15 or higher, and more preferably 0.2 or higher. Furthermore, from the viewpoint of preventing the crystallinity of the particle surface from becoming too disordered and suppressing reactivity with the electrolyte, thereby avoiding a decrease in charge / discharge efficiency and an increase in gas generation, the above Raman R value is typically 0.9 or lower, preferably 0.7 or lower, and more preferably 0.5 or lower.

[0066] In this embodiment, the natural graphite has a particle size d that corresponds to 90% of the cumulative total from the smallest particle on a volume basis. ９０ The particle size d is preferably 15 μm or less, and more preferably 9 μm to 15 μm. Here, from the viewpoint of suppressing streaking when forming the electrode plate, the particle size d ９０ The particle size d is preferably 15 μm or less, more preferably 14 μm or less, and even more preferably 13 μm or less. Furthermore, from the viewpoint of suppressing a decrease in electrode plate strength, the particle size d ９０ The particle size is preferably 9 μm or larger, more preferably 10 μm or larger, and even more preferably 11 μm or larger.

[0067] In this embodiment, the natural graphite has a particle size d that corresponds to a cumulative 10% from the smallest particle on a volume basis. １０ The particle size d is preferably 6 μm or less, and more preferably 1 μm to 6 μm. Here, from the viewpoint of suppressing striating when forming the electrode plate, the particle size d １０ The particle size d is preferably 6 μm or less, more preferably 5.7 μm or less, and even more preferably 5.4 μm or less. Furthermore, from the viewpoint of suppressing particle aggregation and ensuring good slurry stability and electrode plate strength, the particle size d is as described above. １０ The particle size is preferably 1 μm or larger, more preferably 2 μm or larger, and even more preferably 3 μm or larger.

[0068] In this embodiment, the DBP oil absorption amount of natural graphite is preferably 40 mL / 100 g to 70 mL / 100 mg. Here, from the viewpoint of suppressing streaking during electrode formation, the DBP oil absorption amount is preferably 70 mL / 100 mg or less, more preferably 66 mL / 100 mg or less, and even more preferably 63 mL / 100 mg or less. Furthermore, from the viewpoint of avoiding a decrease in the reaction surface due to the presence of suitable voids within the particles, the DBP oil absorption amount is preferably 40 mL / 100 mg or more, more preferably 45 mL / 100 mg or more, and even more preferably 50 mL / 100 mg or more.

[0069] In this embodiment, the total pore volume of the natural graphite is preferably 0.1 mL / g to 1.5 mL / g. Here, from the viewpoint of the dispersion effect of the thickener and binder during electrode formation, the total pore volume is preferably 0.1 mL / g or more, more preferably 0.2 mL / g or more, and even more preferably 0.3 mL / g or more. Also, from the same viewpoint, the total pore volume is preferably 1.5 mL / g or less, more preferably 1.2 mL / g or less, and even more preferably 1.0 mL / g or less.

[0070] In this embodiment, the cumulative pore volume of the natural graphite at 3000 nm or less is preferably 0.1 mL / g to 1.0 mL / g. Here, from the viewpoint of obtaining good input / output characteristics, the cumulative pore volume is preferably 0.1 mL / g or more, more preferably 0.2 mL / g or more, and even more preferably 0.3 mL / g or more. Furthermore, from the viewpoint of suppressing excessive reaction with the electrolyte and obtaining good initial efficiency, the cumulative pore volume is preferably 1.0 mL / g or less, more preferably 0.9 mL / g or less, and even more preferably 0.8 mL / g or less.

[0071] In this embodiment, the cumulative pore volume of the natural graphite with a diameter of 1000 nm or less is more preferably 0.05 mL / g to 0.5 mL / g. Here, from the viewpoint of avoiding a decrease in reaction area, the cumulative pore volume is preferably 0.05 mL / g or more, more preferably 0.1 mL / g or more, and even more preferably 0.12 mL / g or more. Furthermore, from the viewpoint of suppressing excessive reaction with the electrolyte, the cumulative pore volume is preferably 0.5 mL / g or less, more preferably 0.3 mL / g or less, and even more preferably 0.2 mL / g or less.

[0072] In the present embodiment, the cumulative pore volume of natural graphite of 10 nm to 50 nm is more preferably 0.001 mL / g to 0.1 mL / g. Here, from the viewpoint of suppressing an excessive reaction with the electrolyte, the cumulative pore volume is preferably 0.1 mL / g or less, more preferably 0.07 mL / g or less, and even more preferably 0.05 mL / g or less. Further, from the viewpoint of avoiding a decrease in the reaction area, the cumulative pore volume is preferably 0.001 mL / g or more, more preferably 0.01 mL / g or more, and even more preferably 0.015 mL / g or more.

[0073] The specific surface area of natural graphite in the present embodiment is usually 0.3 m ２ / g to 30 m ２ / g. Here, from the viewpoint of ensuring sufficient sites for Li to enter and exit and obtaining good high-rate charge-discharge characteristics and output characteristics, the specific surface area is usually 0.3 m ２ / g or more, preferably 0.5 m ２ / g or more, more preferably 1 m ２ / g or more, even more preferably 2 m ２ / g or more, and particularly preferably 5 m ２ / g or more. Further, from the viewpoint of moderately suppressing the activity of the active material with respect to the electrolyte, suppressing an increase in the initial irreversible capacity, and manufacturing a high-capacity battery, the specific surface area is usually 30 m ２ / g or less, preferably 20 m ２ / g or less, and more preferably 15 m ２ / g or less.

[0074] The tap density of natural graphite in the present embodiment is usually 0.1 g / cm ３ to 1.3 g / cm ３ . Here, from the viewpoint of obtaining good high-rate charge-discharge characteristics, the tap density is usually at least 0.1 g / cm ３ , preferably at least 0.15 g / cm ３ , more preferably at least 0.2 g / cm ３ , and even more preferably at least 0.3 g / cm ３ . Further, from the viewpoint of suppressing an increase in the carbon density inside the particles and suppressing a decrease in the rolling property, and thus facilitating the formation of a high-density negative electrode sheet, the tap density is usually 1.3 g / cm３ The following is the value: 1.2 g / cm³ ３ The following is preferable: 1.1 g / cm³ ３ The following are preferable.

[0075] The natural graphite used in this embodiment may be commercially available or manufactured. Alternatively, commercially available graphite may be used after appropriate processing. Examples of such processing include particle size adjustment, spheroidization, and pressure treatment.

[0076] The method for adjusting the particle size of natural graphite is not particularly limited, and conventionally known methods can be used, such as crushing and classification.

[0077] The method for spheroidizing natural graphite is not particularly limited, and conventional methods can be used. A granulating agent may be mixed in before the spheroidizing process, and the granulating agent may be removed after the spheroidizing process.

[0078] The method for spheroidizing natural graphite in this embodiment is not particularly limited, and conventionally known methods can be employed. For example, a method of spheroidizing natural graphite by applying mechanical energy is preferred because it allows for easy control of the particle shape. Examples of mechanical energy include impact, compression, friction, and shear force. These mechanical energies may be used individually or in combination of two or more. The method of spheroidizing natural graphite by applying mechanical energy can be carried out by using a device that applies mechanical energy.

[0079] Amorphous carbonaceous precursor In the method for producing carbon material according to this embodiment, the amorphous carbonaceous precursor mixed with natural graphite can be one of the conventionally known precursors. Examples include tar, pitch, aromatic hydrocarbons such as naphthalene and anthracene, and thermoplastic resins such as phenolic resins and polyvinyl alcohol resins. These precursors may be used individually or in combination of two or more.

[0080] Among these amorphous carbonaceous precursors, tar, pitch, and aromatic hydrocarbons are preferred because their carbon structure develops easily and they can be used for coating in small amounts, with dehydrated tar being more preferred among the tars. The residual carbon content of the amorphous carbonaceous precursor is preferably 10% by mass or more, and more preferably 20% by mass or more.

[0081] In this embodiment, the ash content in the amorphous carbonaceous precursor is preferably 0.00001% by mass to 1% by mass. Here, the above content is preferably 0.00001% by mass or more. Furthermore, the above content is preferably 1% by mass or less, more preferably 0.5% by mass or less, and even more preferably 0.1% by mass or less.

[0082] In this embodiment, the content of metal impurities in the amorphous carbonaceous precursor is preferably 0.1 ppm by mass to 1000 ppm by mass. Here, the above content is preferably 0.1 ppm by mass or more. Furthermore, the above content is preferably 1000 ppm by mass or less, more preferably 500 ppm by mass or less, and even more preferably 100 ppm by mass or less. In this specification, the metal impurity content means the value obtained by dividing the total content of Fe, Al, Si, and Ca in the amorphous carbonaceous precursor by the residual carbon content.

[0083] In this embodiment, the Qi (quinoline-insoluble content) in the amorphous carbonaceous precursor is preferably 5% by mass or less, and more preferably 3% by mass or less.

[0084] • Mixing: The mixing of natural graphite and amorphous carbonaceous precursor in this embodiment can be carried out by conventionally known methods. For example, methods include mixing natural graphite and amorphous carbonaceous precursor using a mixer or kneader, or adding natural graphite to a solution in which amorphous carbonaceous precursor is dissolved and then removing the solvent. Among these methods, the method of mixing natural graphite and amorphous carbonaceous precursor using a mixer or kneader is preferred from the viewpoint of uniform mixing in a short time.

[0085] The mixing ratio of natural graphite to amorphous carbonaceous precursor is adjusted so that the amorphous carbonaceous content in the resulting carbon material is between 4% and 15% by mass. The amount of amorphous carbonaceous precursor mixed with natural graphite can be calculated from the residual carbon content of the amorphous carbonaceous precursor.

[0086] <Step (ii)> In step (ii) of the carbon material manufacturing method according to this embodiment, the mixture obtained in step (i) is heated. The heating is preferably carried out until the Raman R value of the obtained carbon material is 0.50 or less. The Raman R value can be adjusted by the temperature, time, atmosphere, content of amorphous carbonaceous material, etc. during heating.

[0087] The heating temperature is preferably 1200°C or higher, and more preferably 1200°C to 1500°C. Here, from the viewpoint of developing the crystal structure to the minimum extent, the above temperature is preferably 1200°C or higher, more preferably 1230°C or higher, and even more preferably 1250°C or higher. Furthermore, from the viewpoint of preventing the crystal structure from reaching the same level as that of graphite, the above temperature is preferably 1500°C or lower, more preferably 1450°C or lower, and even more preferably 1400°C or lower.

[0088] The heating time is preferably between 0.1 hours and 1000 hours. Here, from the viewpoint of suppressing uneven heating, the above time is preferably 0.1 hours or more, more preferably 0.5 hours or more, and even more preferably 1 hour or more. Also, from the viewpoint of productivity, the above time is preferably 1000 hours or less, more preferably 750 hours or less, and even more preferably 500 hours or less.

[0089] The heating atmosphere is preferably a non-oxidizing atmosphere, with an oxygen concentration of 1% by volume or less, more preferably 0.1% by volume or less, even more preferably 0.01% by volume or less, and the lower the better. Furthermore, from the viewpoint of suppressing oxidation, a nitrogen atmosphere, argon atmosphere, or carbon dioxide atmosphere is more preferable for heating, with a nitrogen atmosphere being even more preferable. A mixed gas atmosphere containing two or more selected from nitrogen, argon, and carbon dioxide is also acceptable.

[0090] As a result of the heating described above, the amorphous carbonaceous precursor in the mixture is amorphously carbonized and becomes amorphous carbonaceous material.

[0091] The content of amorphous carbonaceous material in the carbon material after heating is preferably 4% to 15% by mass. Here, from the viewpoint of achieving a more uniform coating state and good charge acceptance, the above content is preferably 4% by mass or more, more preferably 4.5% by mass or more, and even more preferably 5% by mass or more. Furthermore, from the viewpoint of obtaining good rolling properties when forming the electrode plate, the above content is preferably 15% by mass or less, more preferably 12% by mass or less, and even more preferably 9% by mass or less. The content of amorphous carbonaceous material in the carbon material can be determined by the following formula (1). That is, it is determined by the mixing ratio of graphite and amorphous carbonaceous material and the firing yield after firing. Content of amorphous carbonaceous material (%) = ([Mass of sample after firing - Mass of graphite] / [Mass of sample after firing]) × 100 (1)

[0092] If the above mixing ratio and firing yield are unknown, the content of amorphous carbonaceous material is estimated using the difference in true density between graphite and amorphous carbonaceous material. Specifically, the crystallinity of graphite in the carbon material is confirmed by the d002 value, and if the d002 value is 3.357 Å or less (high crystallinity), the content of amorphous carbonaceous material is estimated using the following formula (2): Amorphous carbonaceous material content (%) = 596.72 - 264.02 × true density (2)

[0093] <Step (iii)> After step (ii), the material is crushed and further pulverized as necessary. The peripheral speed in the above pulverization is 30 to 120 m / sec. From the viewpoint of controlling the absorbance parameter, the peripheral speed is 30 m / sec or more, preferably 35 m / sec or more, more preferably 40 m / sec or more, even more preferably 50 m / sec or more, especially preferably 55 m / sec or more, particularly preferably 60 m / sec or more, and most preferably 65 m / sec or more. Also, from the viewpoint of efficiency, the peripheral speed is preferably 120 m / sec or less, more preferably 110 m / sec or less, even more preferably 105 m / sec or less, even more preferably 100 m / sec or less, especially preferably 95 m / sec or less, particularly preferably 90 m / sec or less, and most preferably 85 m / sec or less.

[0094] After the crushing process described above, further classification may be performed as needed to determine the volume-based average particle size d of the carbon material. ５０ You may set it to the desired range.

[0095] 《Negative Electrode and Method for Manufacturing the Same》 The negative electrode according to this embodiment includes the carbon material described in the section above. Specifically, the negative electrode according to this embodiment includes a current collector and a negative electrode active material layer formed on the current collector, and the negative electrode active material layer includes the carbon material described in the section above. In the negative electrode or the negative electrode active material layer, this carbon material has the effect of a negative electrode active material. Preferred embodiments of the carbon material are the same as preferred embodiments described in the section above.

[0096] In other words, the method for manufacturing the negative electrode according to this embodiment includes the step of applying the carbon material onto the current collector.

[0097] The method of applying the carbon material to the current collector is not particularly limited, but for example, from the viewpoint of being inexpensive and having excellent productivity, a slurry in which the carbon material is mixed with an optional component such as a binder resin is applied to the current collector and dried.

[0098] In addition to binder resins, other optional components include thickeners and conductive additives. Examples of conductive additives include carbon black, carbon nanotubes, and artificial graphite.

[0099] Organic solvents such as alcohol or water can be used as the dispersion medium for forming the slurry.

[0100] Conventional current collectors can be used, but examples include thin metal films such as copper foil and stainless steel foil. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0101] After the drying process described above, it is preferable to increase the density of the negative electrode active material layer formed on the current collector by applying pressure, thereby increasing the battery capacity per unit volume.

[0102] The density of the negative electrode active material layer varies depending on the application, but for example, in applications where capacity is important, it is 1.00 g / cm³. ３ ~1.90 g / cm ３ This is preferable. Here, from the viewpoint of ensuring battery capacity per unit volume, the density is 1.00 g / cm³. ３ The above is preferable, specifically 1.05 g / cm³. ３The above is more preferable. Furthermore, from the viewpoint of suppressing a decrease in rate characteristics, the above density is 1.90 g / cm³. ３ The following is preferable: 1.80 g / cm³ ３ The following are preferable.

[0103] The specific capacity of the negative electrode active material varies depending on the application, but for example, 300 to 600 mAh / g is preferred. Here, from the viewpoint of battery capacity, the specific capacity is preferably 300 mAh / g or more, more preferably 320 mAh / g or more, and even more preferably 350 mAh / g or more. Furthermore, from the viewpoint of durability, the specific capacity is preferably 600 mAh / g or less, more preferably 550 mAh / g or less, and even more preferably 500 mAh / g or less.

[0104] 《Secondary Battery and Method for Manufacturing the Same》 The secondary battery according to this embodiment includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode and the negative electrode are capable of intercalating and releasing lithium ions. In particular, the negative electrode is the one described in the section on "Negative Electrode," that is, it includes the carbon material described in the section on "Carbon Material," and more specifically, it includes the carbon material described in the section on "Carbon Material" as the negative electrode active material.

[0105] In other words, the method for manufacturing a secondary battery according to this embodiment is a method for manufacturing a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is obtained by the manufacturing method described above for the "negative electrode".

[0106] The positive electrode only needs to be capable of intercalating and releasing lithium ions, and conventionally known types can be used. Specifically, a positive electrode active material layer containing a positive electrode active material and a binder can be formed on a current collector.

[0107] The electrolyte can be any material that conducts lithium ions, and conventionally known electrolytes can be used. For example, a non-aqueous electrolyte obtained by dissolving a lithium salt in a non-aqueous solvent, or a non-aqueous electrolyte that has been gelled, rubberized, or made into a solid sheet by an organic polymer compound, etc.

[0108] The secondary battery according to this embodiment further includes a separator to prevent short circuits between electrodes when the electrolyte is liquid. Conventional known separators can be used, such as porous membranes or nonwoven fabrics. The method for manufacturing the negative electrode includes the step of coating the carbon material onto the current collector.

[0109] <Applications> By using the carbon material according to this embodiment as the negative electrode active material of a secondary battery, good initial efficiency and long-term storage recovery rate can be achieved without increasing irreversible capacity. For this reason, the carbon material according to this embodiment can be suitably used as the negative electrode active material of a secondary battery, more suitably used as the negative electrode active material of a non-aqueous secondary battery, and particularly suitably used as the negative electrode active material of a lithium-ion secondary battery.

[0110] The present invention will be described in more detail below using examples, but the present invention is not limited to the following examples without departing from its essence.

[0111] <Measurement and Evaluation> <Specific Surface Area> Using a specific surface area measuring device (Macsorb HM-1210, manufactured by Mountec Co., Ltd.), the carbon material was pre-dried under reduced pressure at 350°C for 15 minutes under nitrogen flow, and then cooled to liquid nitrogen temperature. Then, using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure was 0.3, the specific surface area of ​​the carbon material was measured by the nitrogen adsorption BET single-point method using the gas flow method. The results are shown in Table 1 as "Specific Surface Area (m²)". ２ It is shown as / g).

[0112] <Absorbance Parameters> Slurries for measuring absorbance were prepared according to the following procedure. Carbon material obtained in each example, carboxymethylcellulose sodium salt as a thickener, and ion-exchanged water as a dispersion medium were prepared. Specifically, first, the carbon material and a 1.5% CMC aqueous solution were mixed so that the solid content concentration of the carbon material was 64%. Next, ion-exchanged water was added to adjust the final solid content concentration of the slurry to 58%. The slurry obtained by the above method was diluted 10 times by mass using ion-exchanged water. This was placed in a 2 mL centrifuge container and centrifuged at 12,000 rpm for 30 minutes. The supernatant after centrifugation was collected and diluted 5 times by volume using ion exchange. The absorbance of the supernatant of this diluted solution was measured using a spectrophotometer. Specifically, the absorbance at wavelengths of 400 nm, 500 nm, 600 nm, and 700 nm was measured, and the average value of these measurements multiplied by 5 was obtained as the absorbance parameter. The results are shown in Table 1 under "Absorbance Parameters".

[0113] <Test Example; Carbon Material> <Example 1> The carbon material raw material was spheroidized so that the pore volume reached a predetermined value. Spheroidized natural graphite and dehydrated tar, which is an amorphous carbonaceous material precursor, were blended so that the amorphous carbonaceous material content in the resulting carbon material was 6.5% by mass, and mixed using a mixer. The resulting mixture was subjected to a heat treatment at 1300°C for 2 hours in an inert gas environment where nitrogen was circulated to reduce the oxygen concentration in the furnace to 0.01% by volume or less. The resulting calcined material was crushed and classified at a peripheral speed of 88 m / s to obtain carbon material. Note that the volume-based flat particle size d of the carbon material was ５０ The particle size was 7.3 μm, the amorphous carbonaceous material content was 6.5% by mass, and the circularity was 0.93.

[0114] <Example 2> A carbon material was obtained in the same manner as in Example 1, except that the amount of dehydrated tar, which is an amorphous carbonaceous precursor, was changed, and the calcined material obtained by heat treatment was crushed and classified at a peripheral speed of 71 m / s. The volume-based flat particle size d of the carbon material was ５０ The pore size was 7.9 μm, the amorphous carbonaceous material content was 6.5% by mass, the circularity was 0.93, and the cumulative pore volume below 1000 nm was 0.12.

[0115] <Example 3> A carbon material was obtained in the same manner as in Example 1, except that the amount of dehydrated tar, which is an amorphous carbonaceous precursor, was changed, and the calcined material obtained by heat treatment was crushed and classified at a peripheral speed of 69 m / sec. The volume-based flat particle size d of the carbon material was ５０ The particle size was 7.8 μm, the amorphous carbonaceous material content was 6.5% by mass, and the circularity was 0.93.

[0116] <Example 4> Spheroidized natural graphite, prepared by spheroidizing flake-like natural graphite, was filled into a rubber container, sealed, and subjected to isotropic pressure treatment at 200 MPa to control the powder properties. The resulting molded product was crushed and classified. The obtained spheroidized graphite powder was mixed with tar adjusted to an amorphous carbon precursor with an ash content of <0.01%, a metal impurity content of 60 ppm, and Qi <0.1%. The furnace pressure was then reduced to 10 torr or less, restored to atmospheric pressure with nitrogen, and then nitrogen was circulated to reduce the oxygen concentration in the furnace to <100 ppm, followed by heat treatment at 1300°C. The resulting calcined product was crushed and classified to obtain a carbon material. Note that the volume-based flat particle size d of the carbon material is... ５０ The particle size was 11.4 μm, the amorphous carbonaceous material content was 6.5% by mass, and the circularity was 0.91.

[0117] <Comparative Example 1> Volume-based average particle size (d ５０ ) 100 μm flaky natural graphite is crushed, and the volume-based average particle size (d ５０ Graphite with a particle size of 11 μm was obtained. 100 parts by mass of the obtained graphite and 12 parts by mass of granulator were mixed, then subjected to a spheroidizing treatment, and the granulator was removed by further heat treatment to obtain spheroidized graphite. The obtained spheroidized graphite was filled into a rubber container, the rubber container was sealed, and subjected to isotropic pressurization treatment, followed by crushing and classification to obtain spheroidized graphite powder. The obtained spheroidized graphite powder was mixed with pitch (ash content 0.02 mass%, metal impurity content 20 mass ppm, Qi 1 mass%) as an amorphous carbonaceous material precursor, the furnace pressure was reduced to 10 torr or less, and then restored to atmospheric pressure with nitrogen. Furthermore, nitrogen was circulated to reduce the oxygen concentration in the furnace to 0.01 volume% or less, and heat treatment was performed at 1300°C in an inert gas. The obtained calcined product was crushed and classified to obtain carbon material. Note that the volume-based flat particle size d of the carbon material ５０The pore size was 17.2 μm, the amorphous carbonaceous material content was 7.5% by mass, the circularity was 0.90, and the cumulative pore volume below 1000 nm was 0.12.

[0118] 《Test Example; Secondary Battery》 The carbon material obtained in each example was used as the negative electrode active material to prepare an electrode plate. Specifically, 50.00 ± 0.02 g of the carbon material obtained in Examples 1 to 4 or Comparative Example 1 was mixed with 50.00 ± 0.02 g (0.50 g in terms of solid content) of a 1% by mass aqueous solution of carboxymethylcellulose sodium salt and 1.00 ± 0.05 g (0.50 g in terms of solid content) of styrene-butadiene rubber aqueous dispersion with a weight-average molecular weight of 270,000. The mixture was stirred for 5 minutes in a hybrid mixer (manufactured by Keyence Corporation) and degassed for 30 seconds to obtain a slurry. The obtained slurry was placed on a 10 μm thick copper foil, which served as the current collector, with a dry negative electrode material content of 10.00 ± 0.20 mg / cm². ２ To ensure adhesion, the material was applied in a 10 cm wide strip using a die coater. After drying, it was cut into 5 cm wide strips and roll-pressed using a 20 cm diameter roller. The roll-pressed strips had an active material layer density of 1.20 ± 0.03 g / cm³. ３ The process was adjusted to achieve the desired result, and a negative electrode sheet was obtained.

[0119] Two discs were prepared by punching out the obtained negative electrode sheet into a 12.5 mm diameter disc shape, and they were arranged so that the active material layers faced each other. Between the opposing negative electrode sheets, LiPF was placed in a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio 30:70). ６ A 2016 coin-type battery was fabricated by placing a separator (made of porous polyethylene film) impregnated with an electrolyte solution containing 1 mol / L of dissolved benzene into the separator.

[0120] 《Evaluation: Curvature》 2016 coin-type batteries obtained using the carbon materials of Examples 1 to 4 or Comparative Example 1 were left standing at 25°C for 24 hours, and then impedance response analysis was performed. The impedance response analysis was performed using an impedance analyzer (Solartron Corporation) under the conditions of a frequency of 20 kHz to 10 mHz and a voltage amplitude of 10 mV. The ion resistance R of the active material layer of the negative electrode sheet was determined using the intersection of the 45° straight line in the high-frequency region and the vertical line in the low-frequency region on the Cole-Cole plot. ｉｏｎ The following was obtained. Let S be the area of ​​the negative electrode sheet, L be the thickness of the active material layer of the negative electrode sheet, σ be the conductivity of the electrolyte, and ε be the porosity of the active material layer. The curve ratio was calculated from the following formula (5): Curve ratio = R ｉｏｎ × (ε / 2 × L) × (σ × S) (5) The result is shown in Table 1 as "Curve ratio".

[0121] 《Evaluation: Powder Resistance》 The powder density of the carbon material in Examples 1 to 5 or Comparative Example 1 was determined using a powder resistance measuring device (Mitsubishi Chemical Analytec's powder resistance measuring system MCP-PD51, Lorestar-GP4 terminal type, and MCP-T600) with a cross-sectional area of ​​3.14 cm². ２ 3.0 g of carbon material was placed in a cylindrical container for measuring powder resistance, and pressure was gradually applied to increase the powder density. The powder density was measured when the powder density reached 1.40 g / cc. More specifically, the following was done: First, the apparatus was calibrated. When calibrating the load, the load was first set to 0 kgf / 3.14 cm when the bottom of the cylindrical container into which the negative electrode material is placed and the push rod inserted into the container from above to apply pressure to the negative electrode material were not in contact. ２ This was confirmed. Next, the thickness gauge was calibrated. A hydraulic pump was used to bring the cylindrical container and the push rod closer together, and the load was 20 kgf / 3.14 cm. ２At this point, zero-point correction was performed so that the thickness gauge reading was 0.00 mm. After the correction was completed, 3.0 g of carbon material was placed in a cylindrical container with a diameter of 2 cm, and the height of the carbon material was adjusted so that the load was applied uniformly. Using a hydraulic pump, the base was raised and a push rod was inserted into the cylindrical container. Pressure was applied while checking the thickness gauge, and the density of the powder was gradually increased. The powder density was measured when the powder density reached 1.40 g / cc. To reduce measurement variability, measurements were performed at least twice, and if there was variability, three measurements were performed, and the average of the two closest values ​​was used. The results are shown in Table 1 as "Powder Resistance (Ωcm)". Note that, with Comparative Example 1 set to 100, the overall evaluation of the example in which both the curvature ratio and the relative value of powder resistance are 70 or less is judged as "A" (extremely good), and all others are judged as "B" (good).

[0122]

[0123] From the above results, the carbon materials of Examples 1 to 4 had their absorbance parameters adjusted under predetermined conditions. The absorbance parameters were reduced by improving the active material. When such an active material was used as the negative electrode material, excellent powder resistance and negative electrode curvature were obtained. The above results were particularly remarkable in Examples 2 and 3, which achieved both powder resistance and negative electrode curvature.

[0124] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.

[0125] The carbon material according to this embodiment can be used as the negative electrode active material of a secondary battery to achieve good initial efficiency and long-term storage recovery rate without increasing irreversible capacity. Therefore, it can be suitably used as the negative electrode active material of a secondary battery, more suitably used as the negative electrode active material of a non-aqueous secondary battery, and particularly suitably used as the negative electrode active material of a non-aqueous lithium-ion secondary battery.

Claims

1. A carbon material coated with amorphous carbonaceous material, wherein the absorbance parameter obtained by the following measurement method for a slurry with a solid content of 58% of the carbon material, obtained by mixing the carbon material with a 1.5% by mass aqueous solution of carboxymethylcellulose sodium salt, is between 1 and 12. <Measurement Method> The slurry is diluted 10 times by mass using deionized water and placed in a 2 mL centrifugation container, and centrifuged at 12,000 rpm for 30 minutes. The supernatant after centrifugation is diluted 5 times by volume using deionized water, and the absorbance of the supernatant of the diluted solution is measured using a spectrophotometer. The average value of the absorbance at each wavelength of 400 nm, 500 nm, 600 nm, and 700 nm is multiplied by 5 to determine the absorbance parameter.

2. The BET specific surface area of ​​the carbon material is 1 to 5 m². ２ The carbon material according to claim 1, wherein the value is / g.

3. The carbon material according to claim 1, wherein the circularity of the carbon material is 0.91 or greater.

4. Volume-based average particle size d of the carbon material ５０ The carbon material according to claim 1, wherein the thickness is 5 to 17 μm.

5. Volume-based average particle size d of the carbon material ５０ The volume-based average particle size d is 5 to 17 μm. ５０ The carbon material according to claim 1, wherein the ratio of the content (mass%) of the amorphous carbonaceous material in the carbon material to (μm) is 0.35 or more and 2.0 or less.

6. The carbon material according to claim 1, wherein the cumulative pore volume of 1000 nm or less is 0.1 to 0.5 mL / g.

7. A negative electrode comprising the carbon material described in any one of claims 1 to 6.

8. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and an electrolyte capable of intercalating and releasing lithium ions, wherein the negative electrode comprises the carbon material described in any one of claims 1 to 6.

9. Specific surface area 1-5m ２ A method for producing a carbon material having a density of / g and a circularity of 0.91 or higher, comprising crushing a mixture containing heated graphite and an amorphous carbonaceous material precursor at a peripheral speed of 30 to 120 m / s.

10. A method for producing a carbon material having an integrated pore volume of 0.1 to 0.5 mL / g of 1000 nm or less, comprising crushing a mixture containing heated graphite and an amorphous carbonaceous precursor at a peripheral speed of 30 to 120 m / s.

11. The method for producing a carbon material according to claim 9 or 10, wherein the heating temperature is 1200°C or higher.

12. A method for manufacturing a negative electrode, comprising the step of applying a carbon material according to any one of claims 1 to 6 onto a current collector.

13. A method for manufacturing a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode is obtained by the manufacturing method described in claim 12.

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