TW202034569A - Composite carbon particles, method for producing same, and lithium ion secondary battery - Google Patents

Abstract

The present invention provides composite carbon particles, each of which comprises a carbon particle (A) and a carbonaceous cover layer (B) that covers the surface of the carbon particle (A), and which is configured such that the carbonaceous cover layer (B) is composed of single-walled graphene or multi-walled graphene having a thickness of from 0.1 nm to 30.0 nm (inclusive). The R value of the particles is preferably 0.10-0.40; and the variation coefficient of the R value is preferably 0.30 or less. The composite carbon particles according to the present invention enable the achievement of a lithium ion secondary battery which is excellent in terms of low-temperature charge and discharge rate characteristics, high-temperature storage characteristics and high-temperature cycle characteristics, while having low internal resistance and high coulombic efficiency.

Description

Composite carbon particles, manufacturing method thereof and lithium ion secondary battery

The present invention relates to composite carbon particles, a method of manufacturing the same, a negative electrode active material containing the aforementioned particles, a negative electrode containing the negative electrode active material, and a lithium ion secondary battery using the negative electrode.

Lithium ion secondary batteries are used as power sources for portable electronic devices. Lithium-ion batteries initially had many issues such as insufficient battery capacity and short charge-discharge cycle life. Now, this problem has been overcome. The use of lithium-ion secondary batteries started with weak electrical machines such as mobile phones, notebook computers, and digital cameras, and is also widely used in power tools, electric bicycles and other strong electrical machines that require electricity. Furthermore, lithium ion secondary batteries are particularly expected to be used as power sources for automobiles, and research and development such as electrode materials and battery structures are extremely prosperous.

Lithium-ion secondary batteries used as power sources for automobiles require excellent low-temperature charge-discharge rate characteristics, high-temperature storage characteristics, and high-temperature cycle characteristics, as well as low internal resistance and high coulombic efficiency. Various techniques have been adopted for various issues.

A carbon material is used as the negative electrode active material of the lithium ion secondary battery. In addition, it has been proposed to form a coating layer on the surface in order to repair surface defects of the carbon material or to impart characteristics different from the carbon material used as the core material.

In Patent Document 1, it is described that the work uses petroleum-based pitch as a covering material to form composite carbon particles with an amorphous carbon layer on the surface.

Patent Document 2 describes composite carbon particles in which a thermally decomposed carbon layer is formed on the surface by CVD treatment.

Patent Document 3 describes a work of composite carbon particles in which graphene is used as a covering material to adhere graphene on the surface.

Patent Document 4 describes carbon composite silicon in which graphene sheets are adhered to the surface of silicon.

Patent Document 5 describes a method for producing a graphene shell with a graphene film as a shell structure.

Non-Patent Document 1 describes multilayer graphene, and Non-Patent Document 2 describes two-layer graphene. [Prior Technical Literature] [Patent Literature]

[Patent Document 1] Japanese Patent No. 4531174 [Patent Document 2] Japanese Patent No. 5898628 (European Patent No. 2650955) [Patent Document 3] International Publication No. WO2017/168982 [Patent Document 4] JP 2013-60355 A (US Patent No. 9815691) [Patent Document 5] Japanese Patent No. 5749418 (European Patent No. 0973698) [Non-Patent Literature]

[Non-Patent Document 1] Production and Technology, Vol. 66 No. 3 (2014) 88-91 [Non-Patent Document 2] Science, 313(2006)951

[The problem to be solved by the invention]

The conventional technology of using pitch to form a coating layer can produce composite carbon particles in which an amorphous carbon layer is formed on the surface of the carbon particles. However, the high-temperature characteristics of the amorphous carbon layer are insufficient, and it is difficult to uniformly control the thickness of the amorphous carbon layer. Therefore, the electron conductivity is uneven, the internal resistance is high, and the rate characteristics are insufficient.

When a carbon coating layer is formed by CVD, it is difficult to form a thin and uniform layer of a core material with large concavities and convexities such as carbon particles. To form a uniform layer, the coating layer must be thickened or a buffer layer formed inside. As a result, high-temperature cycle characteristics or high-temperature storage characteristics are insufficient.

The graphene coating technique described in Patent Document 3 uses amorphous carbon for the consolidation of the core material and graphene, and the high-temperature characteristics are insufficient.

The technique for coating graphene described in Patent Document 4 uses an electrophoresis method to adhere the coating layer, and the graphene layer cannot be formed on the surface of the carbon particles.

The graphene shell in which a graphene film is used as a shell described in Patent Document 5 uses a catalyst metal inside, and the carbon particle surface cannot be covered with a graphene layer.

The subject of the present invention is to provide composite carbon particles for lithium ion secondary batteries with excellent low-temperature charge and discharge rate characteristics, high-temperature storage characteristics, and high-temperature cycle characteristics, low internal resistance, and high coulombic efficiency. [Means for problem solving]

The present invention is constituted by the following. [1] A composite carbon particle characterized by comprising carbon particles (A) and a carbon coating layer (B) covering the surface thereof, wherein the carbon coating layer (B) is a single-layer graphene of 0.1 nm to 30.0 nm Or multilayer graphene. [2] The compound according to item 1 carbon particles, obtained by the R value of Raman spectrum of micro-Raman spectroscopy (vicinity of 1350 cm ^-1 peak intensity (ID) 1580cm ^-1 vicinity of the peak intensity (IG) and the ratio (ID/IG)) The coefficient of variation is 0.30 or less. [3] The composite carbon particles of the preceding paragraph 1 or the preceding paragraph 2 have an R value measured by Raman spectroscopy from 0.10 to 0.40. [4] In the composite carbon particles of any one of the preceding paragraphs 1 to 3, the average interplanar spacing d002 of the (002) plane measured by the X-ray diffraction method is 0.3354 nm or more and 0.3370 nm or less. [5] As for the composite carbon particles of any one of items 1 to 4, the 50% particle size (D50) of the cumulative particle size distribution based on the volume basis of the laser diffraction method is 1.0 μm or more and 30.0 μm or less, and the compactness of 400 times is 0.30g/cm ³ or more and 1.50g/cm ³ or less. [6] The composite carbon particles according to any one of 1 to 5 above, wherein the BET specific surface area is 1.0 m ² /g or more and 10.0 m ² /g or less. [7] The composite carbon particles according to any one of 1 to 6 above, wherein the carbon particles (A) are graphite particles. [8] The composite carbon particles according to any one of 1 to 7 above, wherein (BET specific surface area of composite carbon particles)/(BET specific surface area of carbon particles (A)) is 0.30 or more and 0.90 or less. [9] The composite carbon particles according to any one of 1 to 8 above, wherein (Raman R value of composite carbon particles)/(Raman R value of carbon particles (A)) is 1.50 or more and 10.00 or less. [10] A negative electrode active material characterized by comprising the composite carbon particles of any one of 1 to 9 above. [11] A negative electrode characterized by comprising the negative electrode active material of item 11 and a current collector. [12} A lithium ion secondary battery characterized by using the negative electrode of the preceding paragraph 11. [13] An all-solid-state lithium ion secondary battery characterized by using the negative electrode of item 11 above. [14] A method for producing composite carbon particles, characterized in that the carbon particles (A) and a carboxylic acid compound each having at least one carboxyl group and a hydroxyl group are combined with the total mass of the carbon particles (A) and the carboxylic acid compound. The carbon particles (A) are mixed so that the content is 80.0% by mass or more and 99.9% by mass or less, and the carboxylic acid compound is 0.1% by mass or more and 20.0% by mass or less, and the obtained mixture is heat-treated. [15] A method for producing composite carbon particles, characterized in that the carbon particles (A) and a carboxylic acid compound having two or more carboxyl groups are combined into carbon particles (A) and the carboxylic acid compound. A) The mixture is mixed so that it is 80.0% by mass or more and 99.9% by mass or less, the carboxylic acid compound is 0.1% by mass or more and 20.0% by mass or less, and the resulting mixture is heat-treated. [16] A method for producing composite carbon particles, characterized in that carbon particles (A) are combined with a carboxylic acid compound having at least one carboxyl group and a hydroxyl group, and a carboxylic acid compound having two or more carboxyl groups to match the carbon particles The total mass of (A) and the carboxylic acid compound is such that the carbon particles (A) are 80.0% by mass or more and 99.90% by mass or less, and the carboxylic acid compound is 0.1% by mass or more and 20.0% by mass or less. [Effects of Invention]

According to the present invention, the surface of the carbon particles is formed with a thin and uniform carbon coating layer, which can provide composite carbon particles with excellent low-temperature charge and discharge rate characteristics, high-temperature storage characteristics, and high-temperature cycle characteristics, low internal resistance, and high coulombic efficiency.

Hereinafter, the implementation mode of the present invention will be described in detail.

[1] Composite carbon particles The composite carbon particles of one embodiment of the present invention comprise carbon particles (A) and a carbon coating layer (B) covering the surface of the carbon particles. The carbon coating layer is single-layer graphene or multilayer graphene (hereinafter referred to as graphite Olefin layer). The carbon particles (A) are not particularly limited, and graphite particles, soft carbon, hard carbon, and other carbon particles, graphene, etc. can be used, and composite materials of such composite metals, metal oxides, and alloys can also be used. Examples of the metal include silicon, tin, and zinc, and examples of the metal oxide include these oxides. The shape of the particles is not limited, and examples include spherical, massive, scaly, fibrous, etc., but particles are preferred. Specific examples of fibrous ones include nanowires, vapor-grown carbon fibers, carbon nanotubes, and the like. Among these, graphite particles are particularly preferred. Graphite particles have high crystallinity, so they are excellent in discharge capacity, high temperature cycle characteristics, and high temperature storage characteristics. The carbon particles (A) also include those whose surface is partially or entirely coated with amorphous carbon. Among graphite particles, artificial graphite particles are also preferred, and artificial graphite particles with a solid structure are even better. When the interior has a solid structure, even if repeated expansion and contraction is caused by charging and discharging, there is almost no delamination in the particles, and the high temperature cycle characteristics and high temperature storage characteristics are excellent. The graphene-based carbon particles contained in the carbon coating layer (B) are honeycomb-like continuous two-dimensional flake-like substances, and have superior electrical conductivity, chemical stability, and higher mechanical strength than amorphous carbon. By covering the surface of the carbon particles with graphene, the volume change of the carbon particles can be suppressed, the conductivity can be improved, and a negative electrode material for lithium ion secondary batteries having excellent durability and charge-discharge characteristics can be obtained. Graphene is preferably formed as a graphene layer along the surface of the carbon particles (A), and more preferably formed along the surface of the carbon particles (A) as a graphene layer on substantially all or part of the surface. The surface coverage of A) is almost completely formed as a graphene layer and it is better. In addition, it is better to directly cover the surface of the carbon particles (A) with a single-layer graphene or a multilayer graphene layer. In addition, graphene composed of one layer is referred to as single-layer graphene, graphene composed of two or more layers is referred to as multilayer graphene, and graphene also includes graphene oxide. Graphene with a thickness of more than 30 nm is graphite (graphite), and is excluded from the graphene layer forming the carbon coating layer (B).

The thickness of the carbon coating layer (B) is 0.1 nm or more. The 0.1nm system corresponds to the thickness of a single layer of graphene. From the viewpoint of having conductivity, chemical stability, and mechanical strength above a certain level, the thickness of the carbon coating layer (B) is preferably 1.0 nm or more, and more preferably 2.0 nm or more. The thickness of the carbon coating layer (B) is 30.0 nm or less. When the thickness of the carbon coating layer (B) is 30.0 nm or less, the formation of the excessive carbon coating layer (B) can be suppressed, and the high temperature storage properties or high temperature cycle characteristics can be maintained well. From the same viewpoint, it is preferably 20.0 nm or less, more preferably 10.0 nm or less, and most preferably 5.0 nm or less.

The thickness of the carbon coating layer (B) was measured by observation with a transmission electron microscope (TEM). From the viewpoint of measurement accuracy, the measurement point is preferably 30 points or more, and more preferably 60 points or more. The average value is the thickness of the carbon coating layer (B). Specifically, it can be measured by the method described in the examples.

The R value of the composite carbon particles of an embodiment of the present invention is preferably 0.10 or more. When the R value is 0.10 or more, the conductive resistance of the surface of the composite carbon particles decreases, and a lithium ion secondary battery with good low-temperature charge and discharge characteristics can be obtained. From the same viewpoint, the R value is more preferably 0.15 or more, and most preferably 0.20 or more. The R value of the composite carbon particles is preferably 0.40 or less. When the R value is 0.40 or less, the crystallinity of the surface will not be too low, so that good high-temperature storage and high-temperature cycle characteristics can be maintained. From the same viewpoint, the R value is preferably 0.35 or less, and more preferably 0.30 or less. R value, based mean intensity peak strength was measured in accordance with Raman spectroscopy is observed in the vicinity of 1350cm ^-1 (ID) and close to the peak intensity 1580cm ^-1 (IG) the ratio (ID / IG). The R value can be used to evaluate the surface state of the composite carbon particles. It shows that the smaller the R value, the higher the crystallinity of the surface of the composite carbon particles.

The coefficient of variation of the R value (ID/IG) of the composite carbon particles of an embodiment of the present invention is preferably 0.30 or less. When the coefficient of variation of the R value is 0.30 or less, the dispersion of the coating state is small, the effect of lowering resistance is large, and the high-temperature cycle characteristics and low-temperature rate characteristics are improved. From the same viewpoint, the coefficient of variation is preferably 0.25 or less, and more preferably 0.20 or less. The coefficient of variation of the R value is obtained by measuring the R value at multiple points by Raman microscopy, and dividing the standard deviation value by the average value of the R value. By obtaining the coefficient of variation, the dispersion of the coating state can be evaluated. The greater the coefficient of variation of the display, the lower the uniformity of the R value, and the greater the dispersion of the coating state. Micro-Raman spectroscopy uses a micro-laser Raman spectrometer with high spatial resolution to determine the R value of multiple points on the same sample. From the viewpoint of measurement accuracy, 50 points or more is preferable, and 100 points or more is more preferable. Typically, after each round of measurement, the laser irradiation position is removed and the measurement is performed so that the position is different for each round. When the spatial resolution is too low (that is, when the irradiation position overlaps too much), the dispersion between particles is difficult to reflect in the R value, and there are occasions where the accuracy of the evaluation result is low.

In the composite carbon particles of an embodiment of the present invention, (Raman R value of composite carbon particles)/(Raman R value of carbon particles (A)) is preferably 1.50 or more. When the aforementioned ratio is 1.50 or more, a carbon coating layer is formed on the surface of the carbon particles (A), the effect of lowering the resistance is large, and the low-temperature rate characteristic is improved. From the same viewpoint, the aforementioned ratio is more preferably 1.80 or more, and 2.10 or more is most preferable. On the other hand, (Raman R value of composite carbon particles)/(Raman R value of carbon particles (A)) is preferably 10.00 or less. When the aforementioned ratio is 10.00 or less, the formation of an excessive carbon coating layer (B) can be suppressed, thereby maintaining good high-temperature storage properties or high-temperature cycle characteristics. From the same viewpoint, the aforementioned ratio is more preferably 6.00 or less, and most preferably 4.00 or less.

The average interplanar spacing d002 of the (002) plane measured by the X-ray diffraction method of the composite carbon particles of one embodiment of the present invention is 0.3354 nm or more. This is the theoretical lower limit of graphite. d002 is below 0.3370nm. When d002 is 0.3370nm or less, the discharge capacitance becomes larger, and a battery that meets the energy density required by a large battery can be obtained. From the same viewpoint, d002 is preferably 0.3367 nm or less, and more preferably 0.3364 nm or less.

Preferably, the 50% particle size (D50) of the composite carbon particles in an embodiment of the present invention is 1.0 μm or more. When D50 is 1.0 μm or more, aggregation of particles is suppressed, and slurry for electrode coating can be easily produced. From the same viewpoint, D50 is more preferably 3.0 μm or more, and most preferably 5.0 μm or more. D50 is preferably 50.0 μm or less. When D50 is 50.0μm or less, the conductive resistance of the electrode will decrease and the rate characteristic will improve. From the same viewpoint, it is more preferably 30.0 μm or less, and most preferably 10.0 μm or less. In this specification, "50% particle size (D50)" means the particle size of the cumulative 50% particle size distribution on a volume basis calculated by the laser diffraction/scattering method.

The 400-back knock compactness of the composite carbon particles of one embodiment of the present invention is preferably 0.30 g/cm ³ or more. If the tap density is 0.30 g/cm ³ or more, the electrode density reached during pressing can be sufficiently increased, and a battery with high energy density can be obtained. From the same viewpoint, it is more preferable that the knock tightness is 0.40 g/cm ³ or more, and 0.50 g/cm ³ or more is the most preferable. The tightness of 400 times knocking is better than 1.50g/cm ³ . When the knock tightness is 1.50g/cm ³ or less, the contact density between the materials in the electrode can be sufficiently improved, and a battery with high input and output characteristics can be obtained. From the same viewpoint, it is more preferable that the knock tightness is 1.20 g/cm ³ or less, and 0.90 g/cm ³ or less is the most preferable.

The BET specific surface area of the composite carbon particles of one embodiment of the present invention is preferably 0.1 m ² /g or more. If the BET specific surface area is 0.1 m ² /g or more, it can be charged and discharged at high speed. From the same viewpoint, BET specific surface area is more preferably 1.0m ² / g or more, 3.0m ² / g or more optimal. The BET specific surface area is preferably 10.0 m ² /g or less. If it is 10.0 m ² /g or less, aggregation is suppressed, making it easy to prepare slurry, and side reactions when forming a battery are suppressed, and the coulombic efficiency, high-temperature storage properties, or high-temperature cycle characteristics are excellent. From the same viewpoint, is 8.0m ² / g or less good, 5.0m ² / g or less more preferably.

The d002, D50, and 400 knockback tightness and BET specific surface area described in this specification were measured by the method described in the examples.

[2] Manufacturing method of composite carbon particles An embodiment of the method for producing composite carbon particles of the present invention includes: a mixing step of mixing carbon particles with a carboxylic acid compound to obtain a mixture, and heat treatment of the mixture obtained in the mixing step at 500°C to 2000°C Heat treatment step.

[2-1] Mixing steps In the mixing step, the carbon particles (A) and the carboxylic acid compound are mixed to obtain a mixture.

The carboxylic acid compound used in one embodiment of the present invention is a compound containing two or more carboxyl groups in one molecule (abbreviated as "polycarboxylic acid compound"). In addition, it contains more than one carboxyl group and one hydroxyl group in one molecule. The compound (abbreviated as "hydroxy carboxylic acid compound"). Examples of such polycarboxylic acid compounds include succinic acid (melting point 185°C), glutaric acid (melting point 95°C), maleic acid (melting point 131°C), and phthalic acid (melting point 210°C). ), oxalic acid (melting point 161℃), malonic acid (melting point 135℃). Examples of hydroxycarboxylic acids include malic acid (melting point 130°C), citric acid (melting point 153°C), tartaric acid (melting point 168°C (L body), melting point 151°C (meso type), melting point 206°C) Racemate)), gallic acid (melting point 250°C), salicylic acid (melting point 159°C). By using such a carboxylic acid compound, in the heat treatment step described later, a denser network structure is formed through intermolecular dehydration, and the carboxylic acid compound can cover the carbon particles in a wider range and thinly and strongly. Among them, compounds containing more than two carboxyl groups and more than one hydroxyl group in one molecule are more preferred, and malic acid (melting point 130°C), citric acid (melting point 153°C), and tartaric acid (melting point 168°C (L body)) are particularly preferred. The carboxylic acid compound may contain one type or two or more types. That is, two or more kinds of polycarboxylic acid compounds may be used, or two or more kinds of hydroxycarboxylic acid compounds may be used, or a polycarboxylic acid compound and a hydroxycarboxylic acid compound may be used in combination. In addition, the aforementioned carboxylic acid compound may be used in combination with a compound containing one carboxyl group in one molecule.

The melting point of the carboxylic acid compound is preferably 300°C or less. When the melting point is within this range, the thermal decomposition of the carboxylic acid compound is small and the covering effect is improved. From the same viewpoint, the melting point is preferably 250°C or lower, and more preferably 200°C or lower. The melting point of the carboxylic acid compound is preferably 90°C or higher. With the melting point in this range, the handling of the carboxylic acid compound is easy and the yield after the mixing treatment is also high. From the same viewpoint, the melting point is preferably 110°C or higher, more preferably 130°C or higher.

The mixture obtained in the mixing step may contain materials other than carbon particles and carboxylic acid compounds, but the mixture is preferably composed of carbon particles and carboxylic acid compounds. The carboxylic acid compound is preferably used in powder form. The mixing method is preferably dry mixing, and commercially available mixers and mixers can be used. As specific examples, mixers such as ribbon mixers, V-type mixers, W-type mixers, single-blade mixers, and Nauta mixers can be cited.

The blending amount of the carbon particles (A) and the carboxylic acid compound is 80.0% by mass to 99.9% by mass for the total mass of the carbon particles (A) and the carboxylic acid compound, and the carboxylic acid compound is 0.1% by mass. The above 20.0 mass% or less is preferable. The reason for setting the blending amount of the carboxylic acid compound to be 0.1% by mass or more is that the carbon particles are sufficiently covered with the carboxylic acid compound. From this viewpoint, the amount of the carboxylic acid compound is preferably 0.5% by mass or more, and more preferably 1.0% by mass or more. The reason for setting the compounding amount of the carboxylic acid compound to be 20.0% by mass or less is to suppress the formation of an excessive carbon coating layer (B), thereby maintaining good high-temperature storage properties or high-temperature cycle characteristics. From this viewpoint, the amount of the carboxylic acid compound is preferably 15.0% by mass or less, and more preferably 10.0% by mass or less.

[2-2] Heat treatment steps The step of heat-treating the aforementioned mixture can be performed using heat-treating devices such as rotary kilns, roller kilns, and electric tubular furnaces. Through the heat treatment step, composite carbon particles whose surfaces are covered by the carbon coating layer (B) can be obtained.

In order to fully carry out carbonization, suppress hydrogen or oxygen residue, and improve battery characteristics, the heat treatment temperature in the heat treatment step is preferably 500°C or higher, more preferably 700°C or higher, and most preferably 900°C or higher. In addition, in order to suppress graphitization and maintain good charge and discharge rate characteristics, the heat treatment temperature is preferably 2000°C or less, more preferably 1500°C or less, and most preferably 1200°C or less. The treatment time is sufficient to allow the carbonization to proceed sufficiently, and is not particularly limited, but it is preferably at least 10 minutes, preferably at least 30 minutes, and more preferably at least 50 minutes.

The heat treatment step is preferably performed under an inert gas atmosphere. As the inert gas used in the inert gas atmosphere, argon, nitrogen and the like can be mentioned.

(BET specific surface area of composite carbon particles)/(BET specific surface area of carbon particles (A)) is preferably 0.90 or less. When the aforementioned ratio is 0.90 or less, the surface of the carbon particles (A) will be sufficiently covered and the effect of lowering the resistance will be great, and the charge and discharge characteristics will be improved. From the same viewpoint, the aforementioned ratio is more preferably 0.80 or less, and most preferably 0.70 or less. The aforementioned ratio is preferably 0.30 or more. When the aforementioned ratio is 0.30 or more, the coating amount will not be excessive, and the cycle characteristics and high-temperature storage characteristics can be maintained well. From the same viewpoint, the aforementioned ratio is more preferably 0.50 or more, and most preferably 0.60 or more.

[3] The negative electrode active material of lithium ion secondary battery The negative electrode active material of the lithium ion secondary battery of one embodiment of the present invention is composed of the aforementioned composite carbon particles.

The negative electrode active material is composed of the aforementioned composite carbon particles, or further contains another carbon material or a conductivity imparting agent. When other carbon materials or conductivity-imparting agents are included, the spherical natural graphite or artificial graphite may be used in an amount of 0.01 to 200 parts by weight, preferably 0.01 to 100 parts by weight, relative to 100 parts by weight of the composite carbon particles. By mixing and using other graphite materials, it is possible to create a negative electrode active material that also has the excellent characteristics of other graphite materials while maintaining the excellent characteristics of the composite carbon particles. Such a negative electrode active material can be obtained by mixing composite carbon particles and other carbon materials. When mixing, the mixing material can be appropriately selected and the mixing amount can be determined according to the required battery characteristics.

In addition, carbon fiber may be blended with the negative electrode active material. The blending amount is preferably 0.01-20 parts by mass, and more preferably 0.5-5 parts by mass relative to 100 parts by mass of the aforementioned negative electrode active material.

Examples of carbon fibers include organic carbon fibers such as PAN-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, and vapor-grown carbon fibers. Among these, vapor-grown carbon fibers with high crystallinity and high thermal conductivity are particularly preferred. When the carbon fiber is bonded to the surface of the composite carbon particles, the vapor-grown carbon fiber is particularly preferred.

As a device for mixing composite carbon particles with other materials, commercially available mixers and mixers can be used. As specific examples, mixers such as ribbon mixers, V-type mixers, W-type mixers, single-blade mixers, and Nauta mixers can be cited.

[4] Paste for electrodes An embodiment of the electrode paste of the present invention is composed of the aforementioned negative electrode active material, a binder, and a solvent. The electrode paste can be obtained by kneading the negative electrode active material and the binder. For mixing, you can use a ribbon mixer, screw kneader, Spartan Luzer (high-speed mixing mixer), Lödige mixer (high-performance powder/fluid mixer), Planetary mixer (planetary wheel mixer), and universal mixing Machine and other devices. The electrode paste can be formed into flakes, granules, etc.

Examples of the binder used in the electrode paste include fluorine-based polymers such as polyvinylidene fluoride and polytetrafluoroethylene, and rubber-based materials such as SBR (styrene butadiene rubber).

The amount of the binder used is preferably 1-30 parts by mass, more preferably 1-10 parts by mass relative to 100 parts by mass of the negative electrode active material.

As a solvent used in kneading, it is suitable for various binders. For example, toluene and N-methylpyrrolidone are used in the case of fluoropolymers; water is used in the case of SBR; others include dimethylformamide and isopropyl. Alcohol etc. When water is used as the binder of the solvent, for example, it is best to use a thickening agent such as carboxymethyl cellulose (CMC). The amount of solvent and thickener is adjusted in such a way that the electrode paste becomes easy to be applied to the current collector.

[5] Negative electrode for lithium ion secondary battery The negative electrode for a lithium ion secondary battery in an embodiment of the present invention is composed of a current collector and a negative electrode active material on the current collector. The negative electrode is obtained by coating the aforementioned electrode paste on a current collector, drying and press-forming it.

Examples of the current collector include foils and meshes such as aluminum, nickel, copper, and stainless steel. The coating thickness of the paste is preferably 50-200μm. The coating method of the paste is not particularly limited, and, for example, a method of forming by roll pressing or the like after coating with a doctor blade or rod coater or the like can be mentioned.

As the press molding method, a molding method such as roll press and squeeze press may be mentioned. The pressure during press molding is preferably 1×10 ³ to 3×10 ³ kg/cm ² .

[6] Lithium ion secondary battery Lithium ion secondary batteries have a structure in which the positive and negative electrodes are immersed in an electrolyte or electrolyte. The lithium ion secondary battery of one embodiment of the present invention is constructed by using the aforementioned negative electrode as the negative electrode.

For the positive electrode of lithium ion secondary batteries, as the positive electrode active material, lithium-containing transition metal oxides are usually used; use mainly containing at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo and W One type of transition metal element and lithium oxide, and a compound with a molar ratio of lithium to transition metal element of 0.3 to 2.2 is preferred; use a compound that mainly contains at least one selected from V, Cr, Mn, Fe, Co and Ni An oxide of one transition metal element and lithium, and a compound having a molar ratio of lithium to transition metal of 0.3 to 2.2 is more preferable. In addition, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, etc. may be contained within a range of less than 30 mol% of the transition metal that is mainly present. Among the aforementioned positive electrode active materials, it is preferable to use Li _x MO ₂ (at least one of M-based Co, Ni, Fe, and Mn, x=0.02 to 1.2) in the general formula, or Li _y N ₂ O ₄ ( The N system contains at least one of the spinel structure materials represented by Mn.y=0.02~2).

In the lithium ion secondary battery, a separator is provided between the positive electrode and the negative electrode. Examples of the separator include non-woven fabrics, cloths, microporous films, or a combination of these, which have polyolefins such as polyethylene and polypropylene as a main component.

As the electrolyte and electrolyte constituting the lithium ion secondary battery of the preferred embodiment of the present invention, well-known organic electrolytes, inorganic solid electrolytes, and polymer solid electrolytes can be used, but from the viewpoint of electrical conductivity, organic electrolysis Liquid is better.

[7] All solid lithium ion secondary battery The all-solid lithium ion secondary battery has a structure in which the positive electrode and the negative electrode are in contact with the solid electrolyte layer. FIG. 9 is a schematic diagram of an example of the configuration of the all-solid-state lithium ion secondary battery 1 of this embodiment. The all-solid lithium ion secondary battery 1 includes a positive electrode layer 11, a solid electrolyte layer 12, and a negative electrode layer 13.

The positive electrode 11 has a positive electrode current collector 111 and a positive electrode mixture layer 112. The positive electrode current collector 111 is connected with a positive electrode lead 111a for transferring and receiving electric charges from an external circuit. The positive electrode current collector 111 is preferably a metal foil, and aluminum foil is preferably used as the metal foil.

The positive electrode mixture layer 112 contains a positive electrode active material, and may further contain a solid electrolyte, a conductive assistant, a binder, and the like. As the positive electrode active material, LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Mn _1/3 Co _1/3 O ₂ and other rock salt layered active materials, LiMn ₂ O ₄ and other spinels can be used Stone-type active materials, olivine-type active materials such as LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCuPO ₄ , and sulfide active materials such as Li ₂ S. In addition, these active materials can also be coated with LTO (Lithium Tin Oxide) or carbon.

As the solid electrolyte that may be included in the positive electrode mixture layer 112, the materials exemplified for the solid electrolyte layer 12 described later may be used, but a material different from the material included in the solid electrolyte layer 12 may be used. The content of the solid electrolyte in the positive electrode mixture layer 112 is preferably 50 parts by mass or more based on 100 parts by mass of the positive electrode active material, preferably 70 parts by mass or more, and more preferably 80 parts by mass or more. The content of the solid electrolyte in the positive electrode mixture layer 112 is preferably 200 parts by mass or less based on 100 parts by mass of the positive electrode active material, preferably 150 parts by mass or less, and more preferably 125 parts by mass or less.

As the conductive auxiliary agent, it is preferable to use a particulate carbonaceous conductive auxiliary agent or a fibrous carbonaceous conductive auxiliary agent. As the particulate carbonaceous conductive auxiliary agent, Denka Black ^® (manufactured by Denka Company Limited), Ketjenblack ^® (manufactured by Lion Corporation), graphite powder SFG series (manufactured by TIMCAL Ltd.), graphite Particulate carbon such as alkene. As a fibrous carbon conductive aid, vapor-grown carbon fiber (VGCF ^® , VGCF ^® -H (manufactured by SHOWA DENKO KK)), carbon nanotube, carbon nanohorn, etc. Because of its excellent cycle characteristics, vapor-grown carbon fiber "VGCF ^® -H" (manufactured by SHOWA DENKO KK) is the best. The content of the conductive auxiliary agent of the positive electrode mixture layer 112 is preferably 0.1 parts by mass or more, preferably 0.3 parts by mass or more based on 100 parts by mass of the positive electrode active material. The content of the conductive auxiliary agent of the positive electrode mixture layer 112 is preferably 5 parts by mass or less, preferably 3 parts by mass or less based on 100 parts by mass of the positive electrode active material.

As the binding agent, for example, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene oxide, polyvinyl acetate, polymethacrylate, polyacrylate, polyacrylonitrile, polyvinyl alcohol, benzene can be cited. Ethylene-butadiene rubber, carboxymethyl cellulose, etc.

In the positive electrode mixture layer 112, the content of the binder to 100 parts by mass of the positive electrode active material is preferably 1 part by mass or more and 10 parts by mass or less, preferably 1 part by mass or more and 7 parts by mass or less.

The solid electrolyte layer 12 is interposed between the positive electrode layer 11 and the negative electrode layer 13 and serves as a medium for lithium ions to move between the positive electrode layer 11 and the negative electrode layer 13. The solid electrolyte layer 12 preferably contains at least one selected from the group consisting of a sulfide solid electrolyte and an oxide solid electrolyte, and preferably contains a sulfide solid electrolyte.

Examples of the sulfide solid electrolyte include sulfide glass, sulfide glass ceramics, Thio-LISICON type sulfide, and the like. More specifically, examples thereof include _{Li 2 SP 2 S 5, Li} 2 SP 2 S 5 -LiI, Li 2 SP 2 S 5 -LiCl, Li 2 SP 2 S 5 -LiBr, Li 2 SP 2 S 5 - Li ₂ O, Li ₂ SP ₂ S ₅ -Li ₂ O-LiI, Li ₂ S-SiS ₂ , Li ₂ S-SiS ₂ -LiI, Li ₂ S-SiS ₂ -LiBr, Li ₂ S-SiS ₂ -LiCl , Li ₂ S-SiS ₂ -B ₂ S ₃ -LiI, Li ₂ S-SiS ₂ -P ₂ S ₅ -LiI, Li ₂ SB ₂ S ₃ , Li ₂ SP ₂ S ₅ -Z _m S _n (where m and n are positive numbers, and Z represents any of Ge, Zn, and Ga), Li ₂ S-GeS ₂ , Li ₂ S-SiS ₂ -Li ₃ PO ₄ , Li ₂ S-SiS ₂ -Li _x MO _y (Where x and y are positive numbers, M represents any of P, Si, Ge, B, Al, Ga, In), Li ₁₀ GeP ₂ S ₁₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , 30Li ₂ S ･26B ₂ S ₃ ･44LiI, 63Li ₂ S･36SiS ₂ ･1Li ₃ PO ₄ , 57Li ₂ S･38SiS ₂ ･5Li ₄ SiO ₄ , 70Li ₂ S･30P ₂ S ₅ , 50LiS ₂ ･50GeS ₂ , Li ₇ P ₃ S ₁₁ , Li _3.25 P _0.95 S ₄ , Li ₃ PS ₄ , Li ₂ S･P ₂ S ₃ ･P ₂ S ₅ and so on. The sulfide solid electrolyte material may be amorphous, crystalline, or glass ceramic.

Examples of the oxide solid electrolyte include perovskite, garnet, and LISICON type oxides. More specifically, for example, La _0.51 Li _0.34 TiO _2.94 , Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , Li ₇ La ₃ Zr ₂ O ₁₂ , 50Li ₄ SiO ₄ ･50Li ₃ BO ₃ , Li _2.9 PO _3.3 N _0.46 (LIPON), Li _3.6 Si _0.6 P _0.4 O ₄ , Li _1.07 Al _0.69 Ti _1.46 (PO ₄ ) ₃ , Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ and so on. The oxide solid electrolyte material may be amorphous, crystalline, or glass ceramic.

The negative electrode layer 13 has a negative electrode current collector 131 and a negative electrode mixture layer 132. The negative electrode current collector 131 is connected to a negative electrode lead 131a for transferring and receiving electric charges from an external circuit. The negative electrode current collector 131 is preferably a metal foil, and as the metal foil, stainless steel foil, copper foil, or aluminum foil is preferably used. The surface of the current collector can be coated with carbon or the like.

The negative electrode mixture layer 132 contains a negative electrode active material, and may also contain a solid electrolyte, a binder, a conductive assistant, and the like. As the negative electrode active material, the aforementioned composite carbon particles can be used.

As the solid electrolyte that may be included in the negative electrode mixture layer 132, the materials listed for the solid electrolyte layer 12 can be used, but a material different from the solid electrolyte contained in the solid electrolyte layer 12 or the solid electrolyte contained in the positive electrode mixture layer is used. It can be. The content of the solid electrolyte in the negative electrode mixture layer 132 is preferably 50 parts by mass or more based on 100 parts by mass of the negative electrode active material, preferably 70 parts by mass or more, and more preferably 80 parts by mass or more. The solid electrolyte content of the negative electrode mixture layer 132 is preferably 200 parts by mass or less based on 100 parts by mass of the negative electrode active material, preferably 150 parts by mass or less, and more preferably 125 parts by mass or less.

As the conductive auxiliary agent that may be included in the negative electrode mixture layer 132, the conductive auxiliary agent mentioned in the description of the positive electrode mixture layer 112 can be used, but a material different from the conductive auxiliary agent contained in the positive electrode mixture layer 112 may be used. The content of the conductive auxiliary agent of the negative electrode mixture layer 132 is preferably 0.1 parts by mass or more, preferably 0.3 parts by mass or more based on 100 parts by mass of the negative electrode active material. The content of the conductive auxiliary agent in the negative electrode mixture layer 132 is preferably 5 parts by mass or less, preferably 3 parts by mass or less based on 100 parts by mass of the negative electrode active material.

As the binder, for example, the materials mentioned in the description of the positive electrode mixture layer 112 can be used, but it is not limited thereto. In the negative electrode mixture layer 132, the content of the binder to 100 parts by mass of the negative electrode active material is preferably 0.3 parts by mass or more and 10 parts by mass or less, and more preferably 0.5 parts by mass and 5 parts by mass or less.

In addition, the selection of components necessary for the configuration of the battery other than the foregoing is not limited in any way. [Example]

Hereinafter, embodiments of the present invention will be described in detail. In addition, these are only examples for explanation and do not limit the present invention. The evaluation method of the carbon particles, the production method of the battery, the measurement method of the battery characteristics, and the raw materials used in each example of the Examples and Comparative Examples are as follows.

[1] Evaluation of carbon particles [1-1]50% particle size (D50) As a particle size measuring device, a Mastersizer 2000 manufactured by Malvern (Mastersizer is a registered trademark) was used, a 5 mg sample was put into a container, and 10 g of water containing 0.04% by mass of a surfactant was added to perform ultrasonic treatment for 5 minutes, followed by measurement.

[1-2] Knock tightness As a tap density measuring device, Autotap manufactured by Quantachrome was used. A 50 g sample was placed in a 250 mL glass compression cylinder, and the volume after 400 taps was measured to calculate the density. This is a measurement method based on ASTM B527 and JIS K5101-12-2, and the drop height of the automatic tapping is 5mm.

[1-3] BET specific surface area As a BET specific surface area measuring device, NOVA2200e manufactured by Quantachrome was used, 3 g of the sample was placed in a sample cell (9 mm×135 mm), and it was dried under vacuum at 300°C for 1 hour, and then measured. N _{2 is} used as the gas for measuring the BET specific surface area.

[1-4] Surface interval d002 Fill the glass sample plate (sample plate window 18×20mm, depth 0.2mm) with a mixture of composite carbon particles and standard silicon particles (manufactured by NIST) at a mass ratio of 9 to 1 and proceed under the following conditions了定。 The determination. XRD device: SmartLab (registered trademark) manufactured by Rigaku Corporation X-ray species: Cu-Kα line Kβ line removal method: Ni filter X-line output: 45kV, 200mA Measuring range: 24.0～30.0deg. Scanning speed: 2.0deg./min. For the obtained waveform, apply the Gakushin method to find the value of the surface interval d002.

[1-5] The coefficient of variation of the R value and the R value was measured with an excitation wavelength of 532.36 nm using NRS-5100 manufactured by JASCO Corporation as a microlaser Raman spectrometer. The ratio of the peak intensity near 1350cm ^-1 in the Raman spectrum of (ID) to the vicinity of the peak intensity 1580cm ^-1 (IG) of the R value (ID / IG). The composite carbon particles were imaged by laser Raman spectroscopy in the following areas. Measuring point: 22×28 measuring step width: 0.32μm Measuring area: 7.0×9.0μm In the previous measurement, 100 points were randomly selected from the area equivalent to carbon particles, and the standard deviation of the obtained R value was divided by the average value of the R value The value is used as the coefficient of variation. In addition, the average value of the R value is regarded as the R value of the composite carbon particles.

[1-6] The state and thickness of the carbon coating layer (B) observed by a transmission electron microscope (TEM) The composite carbon particles were dispersed in ethanol and recovered in a microgrid mesh, and the measurement was performed under the following conditions. Transmission electron microscope device: Hitachi H-9500 Accelerating voltage: 300kV Observation magnification: 30,000 times The state of the carbon coating layer (B) was observed from the measurement. Next, one carbon particle was arbitrarily selected, the coating layer on the surface of the carbon particle was observed at the aforementioned magnification of 5, and the thickness of the coating layer at two locations per one field of view was measured. The thickness of the covering layer everywhere is the average value of the covering layer length of 10 nm. This measurement is performed on three arbitrarily selected carbon particles to obtain a total of 30 data points, and the average is used as the thickness of the coating layer. In addition, the FFT (Fast Fourier Transform) pattern is evaluated to determine the layer structure of the graphene layer, the amorphous carbon layer, and the like.

[2] Preparation of battery [2-1] Preparation of electrode paste 96.5 g of carbon particles obtained in each of the Examples and Comparative Examples described later, carbon black (manufactured by TIMCAL Ltd., C65) 0.5 g, 1.5 g of carboxymethyl cellulose (CMC) as a thickener and 8-12 g of water are added to adjust the viscosity, 1.5 g of aqueous binder (manufactured by SHOWA DENKO KK, Polysol ^® ) dispersed in fine particles are added and stirred/mixed, Prepare a slurry-like dispersion with sufficient fluidity to make electrode paste.

[2-2] Preparation of negative electrode 1 The electrode paste was coated with a doctor blade to a thickness of 150 μm on high-purity copper foil, and vacuum dried at 70°C for 12 hours. After being punched with a press so that the coated portion became 4.2×4.2 cm ² , it was sandwiched by a supersteel pressing plate, and pressed so that the electrode density became 1.3 g/cm ³ to produce a negative electrode 1. The thickness of the active material layer after pressing was 65 μm.

[2-3] Production of negative electrode 2 After punching the copper foil coated with the aforementioned electrode paste into a 16mmφ round shape, it was pressed in the same way as negative electrode 1 so that the electrode density became 1.3g/cm ³ to produce a negative electrode 2. The thickness of the active material layer after pressing was 65 μm.

[2-4] The positive electrode is made of 95 g of LiFe ₂ PO ₄ (D50: 7μm), 1.2 g of carbon black (manufactured by TIMCAL Ltd., C65) as a conductive aid, and vapor-grown carbon fiber (manufactured by SHOWA DENKO KK, VGCF ^® -H) 0.3 g, 3.5 g of polyvinylidene fluoride (PVdF) as a consolidation material, and N-methyl-rolidone while stirring/mixing as appropriate to prepare a positive electrode slurry. This positive electrode slurry was coated on an aluminum foil having a thickness of 20 μm with a roller coater so that the thickness was uniform, and after drying, it was rolled and pressed so that the coated portion became 4.2×4.2 cm ² to obtain a positive electrode. The thickness of the active material layer after pressing was 65 μm.

[2-5] Electrolyte is produced in a mixed solution of 3 parts by mass of EC (ethylene carbonate), 2 parts by mass of DMC (dimethyl carbonate), and 5 parts by mass of EMC (ethyl methyl carbonate) as electrolyte Dissolve 1.2 mol/liter LiPF ₆ and add 1 part by mass of VC (ethylene carbonate) as an additive to prepare an electrolyte.

[2-6] Battery assembly (Two-pole battery) Using an ultrasonic welding machine, a nickel sheet was welded and fixed to the copper foil portion of the negative electrode 1, and an aluminum sheet was welded and fixed to the aluminum foil portion of the positive electrode. The negative electrode 1 and the positive electrode were laminated facing each other through a polypropylene thin film microporous film, and the aluminum laminate film was used to encapsulate the electrolyte. After the electrolyte was injected, the opening was sealed by heat fusion to produce a two-electrode battery.

(Opposite lithium battery (half battery)) In a polypropylene screw-type battery with a lid (with an inner diameter of about 18mm), a separator (polypropylene microporous film (Celgard 2400)) is inserted between the negative electrode 2 and a metal lithium foil punched to 16mmφ. Laminate, add electrolyte and use a caulking machine to fill the gaps to produce a counter-electrode lithium battery.

[3] Evaluation of battery [3-1] Determination of Coulomb efficiency in the first return The test was conducted in a thermostat set at 25°C using a counter electrode lithium battery. From resting potential to 0.005V, constant current charging is performed at 0.02mA. Next, 0.005V was converted to constant voltage charging, and the total of constant current charging and constant voltage charging was charged for 40 hours, and the initial charging capacity (a) was measured. The upper limit voltage is 1.5V and constant current discharge is performed at 0.2mA, and the initial discharge capacitance (b) is measured. The initial discharge capacitance (b)/the initial charge capacitance (a) is the value expressed as a percentage, that is, 100×(b)/(a) is the initial return Coulomb efficiency.

[3-2] Measurement of reference capacitance Using a two-pole battery, the test was performed in a thermostat set at 25°C. The upper limit voltage is 4V and 0.2C (the current value of the fully charged battery is set to 1C within 1 hour, the same below). After the battery is charged with a constant current, the cut-off current value is 0.85mA and 4V for constant voltage charging. After that, the lower limit voltage is 2V and 0.2C for constant current discharge. Repeat the foregoing operations 4 times, and set the fourth discharge capacitance as the reference capacitance (c) of the two-pole battery.

[3-3] Measurement of high temperature cycle characteristics Using a two-pole battery, the test was carried out in a thermostat set at 55°C. The charging system starts from the resting potential with an upper limit voltage of 4V and constant current charging at a constant current value of 85mA (equivalent to 5C), followed by a cut-off current value of 0.34mA and constant voltage charging at 4V. After that, the lower limit voltage is 2V and constant current discharge is performed at 85mA. According to the aforementioned conditions, 500 cycles of charge and discharge were repeated to measure the high temperature cycle discharge capacity (d). According to the aforementioned conditions, the measured high-temperature cyclic discharge capacitance (d)/reference capacitance (c) of the two-pole battery is expressed as a percentage, that is, 100×(d)/(c) as the high-temperature cyclic capacitance maintenance rate.

[3-4] Measurement of internal resistance (DC-IR) The test was carried out in a thermostat set at 25°C. From the fully charged state to 50% of the fully charged capacitor, discharge at a constant current of 0.1C. After a 30-minute break, the internal resistance (DC-IR) (e) of the two-electrode battery is obtained from the voltage drop after the 17 mA discharge for 5 seconds according to Ohm's law (R=ΔV/0.017).

[3-5] High temperature storage and measurement test of recovery characteristics: Using a two-pole battery, both charging and discharging are tested in a thermostat set at 25°C. The upper limit voltage is 4V and the battery is charged with a constant current of 0.2C, and the cut-off current value is 0.34mA, and the battery is charged with a constant voltage of 4V. After the charged battery is allowed to stand for 4 weeks in a thermostat set at 60°C, discharge at a constant current of 0.2C with a lower limit voltage of 2V, and measure the discharge capacity. Set this discharge capacitor as the high-temperature storage capacitor (f). The high-temperature storage capacitor (f) is the value expressed as a percentage of the reference capacitor (c) of the two-pole battery, that is, 100×(f)/(c) as the value of the high-temperature retention characteristic.

After measuring the storage capacitance, the upper limit voltage is 4V and the battery is charged with a constant current of 0.2C, and the cut-off current value is 0.34mA, and the battery is charged with a constant voltage of 4V. After that, the lower limit voltage is 2V and 0.2C for constant current discharge, and the discharge capacitance is measured. Set this discharge capacitor as the high temperature recovery capacitor (g). The value expressed as a percentage of the high temperature recovery capacitance (g) to the reference capacitance (c) of the two-pole battery, that is, 100×(g)/(c) is used as the value of the high temperature recovery characteristic.

[3-6] Low temperature charge and discharge rate measurement Use a two-pole battery to test. In a thermostat set at 25°C, the upper limit voltage is 4V and the battery is charged with a constant current of 0.2C, and the cut-off current value is 0.34mA, and the battery is charged with a constant voltage of 4V. Discharge the charged battery at a constant current with a lower limit voltage of 2V and 1C in a thermostat set at -20°C, and measure the discharge capacity. Set this discharge capacitor as a low-temperature discharge capacitor (h). The low-temperature discharge capacitance (h) is expressed as a percentage of the reference capacitance (c) of the two-pole battery, that is, 100×(h)/(c) is used as the value of the low-temperature discharge rate characteristic.

After the low-temperature discharge capacitance is measured, the temperature in the thermostat is returned to 25°C, and the lower limit voltage is 2V and 0.2C for constant current discharge. In a thermostat set at -20°C, the upper limit voltage is 4V and the battery is charged with a constant current of 1C, and the cut-off current value is 0.34mA, charged with a constant voltage of 4V, and the charging capacitance is measured. Set this charging capacitor as a low-temperature charging capacitor (i). The low-temperature charging capacitor (i) is the value expressed as a percentage of the reference capacitor (c) of the two-pole battery, that is, 100×(i)/(c) as the value of the low-temperature charging rate characteristic.

[4] Raw carbon particles (A): Artificial graphite (manufactured by SHOWA DENKO KK, SCMG ^® ), 50% particle size (D50): 6.0 μm, BET specific surface area: 5.9 m ² /g. Raw materials for carbon coating: the materials shown in Table 1 and Table 2.

Examples 1-24, Comparative Examples 1-23: In each embodiment and each comparative example, the raw materials and ratios shown in Table 1 and Table 2 were put into a V-type mixer (VM-10, manufactured by DULTON CO., LTD.), and dry mixing was performed at room temperature for 10 minutes. This mixture was heat-treated in an electric tubular furnace at the temperature shown in Table 1 and Table 2 in a nitrogen atmosphere for 1 hour to obtain composite carbon particles or carbon particles. In addition, in Table 1 and Table 2, if the column of the heat treatment step is "None", it means that the heat treatment step has not been performed. Various physical properties of the obtained carbon particles were measured. In addition, the obtained carbon particles were used to fabricate batteries and evaluated. The results are shown in Tables 1 to 4. TEM photographs of the carbon particles obtained in Examples 1, 5 and Comparative Examples 3 and 13 are shown in Figs. 1 to 4, respectively. The R value imaging results of the carbon particles obtained in Example 5 and Comparative Examples 1 and 3 are shown in Figs. 5-7, respectively. R-value imaging systems without shades indicate less dispersion of R-value (smaller coefficient of variation).

Comparative examples 24～26: Nitrogen containing 0.05g/L of benzene was introduced into the flow reactor at 1L/mim, and the carbon particles (A) were treated by chemical vapor deposition (CVD) in a flowing state at 900°C for the time shown in Table 2. ). The amount of benzene used for CVD treatment is 1 to 5 mass%. With respect to the obtained carbon particles, various physical properties were measured in the same manner as in the examples, and a battery was produced. The results are shown in Table 2 and Table 4. The R value imaging result of the carbon particles obtained in Comparative Example 26 is shown in FIG. 8.

It can be seen from the table and the figure that the composite carbon particles of the examples have a thin and uniform graphene layer formed on the surface of the carbon particles, and the results of each battery evaluation are all improved. On the other hand, composite carbon particles with an amorphous carbon layer formed on the surface of carbon particles have lower DC-IR, first-return Coulomb efficiency, and improved low-temperature rate characteristics compared to carbon particles without a carbon layer formed on the surface. However, the battery characteristics at high temperatures deteriorated (Comparative Examples 3 to 5, Comparative Examples 12 to 17). In addition, the coefficient of variation of the R value is large, so the coating is not uniform, and the covering effect is not sufficiently obtained. In addition, if the amount of the carboxylic acid compound used is too small, the coating layer will not be formed, and almost no effect will be seen in all battery characteristics (Comparative Examples 6, 8, and 10). If the amount of carboxylic acid compound is too large, the low DC-IR and low temperature rate characteristics will be improved, but d002 will increase and knock tightness will be low, and the R value and BET will increase excessively, resulting in low initial Coulombic efficiency and low battery characteristics at high temperatures. (Comparative Examples 7, 9, 11). In the case of coating by CVD treatment, it is difficult to control the graphene layer to be thin for particles with large unevenness such as carbon particles. In order to reduce the variation coefficient of the R value to 0.20 or less, the graphene layer becomes excessively thick. As a result of the excessive increase in the value, the battery characteristics at high temperatures are lowered (Comparative Examples 24 to 26, Fig. 8).

1: Lithium ion secondary battery 11: positive layer 12: Solid electrolyte layer 13: negative electrode layer 111: positive current collector 112: Positive electrode mixture layer 111a: positive lead 131: negative current collector 131a: negative lead 132: negative electrode mixture layer

[Fig. 1] It is a transmission electron micrograph of the composite carbon particles produced in Example 1. [Fig. [Fig. 2] It is a transmission electron micrograph of the composite carbon particles produced in Example 5. [Fig. [Fig. 3] A transmission electron micrograph of composite carbon particles produced in Comparative Example 3. [Fig. [Fig. 4] It is a transmission electron micrograph of composite carbon particles produced in Comparative Example 13. [Fig. [Fig. 5] It is the imaging result of the R value of the composite carbon particles manufactured in Example 5. [Fig. [Fig. 6] It is the result of R value imaging of carbon particles manufactured in Comparative Example 1. [Fig. [Fig. 7] It is the result of R value imaging of composite carbon particles manufactured in Comparative Example 3. [Fig. [Fig. 8] This is the result of R value imaging of composite carbon particles manufactured in Comparative Example 26. Fig. 9 is a schematic diagram of an example of the configuration of an all-solid-state lithium ion secondary battery 1 related to an embodiment of the present invention.

Claims (16)

A composite carbon particle characterized by comprising carbon particles (A) and a carbon coating layer (B) covering the surface thereof, wherein the carbon coating layer (B) is a single-layer graphene or multi-layer graphite with a thickness of 0.1 nm to 30.0 nm Ene. The particles of the composite carbon requested item 1, wherein the R value of Raman spectrum of the obtained micro-Raman spectroscopy (peak intensity in the vicinity of 1350 cm ^-1 (ID) 1580cm ^-1 vicinity of the peak intensity (IG) and the ratio ( The coefficient of variation of ID/IG)) is 0.30 or less. The composite carbon particle of claim 1, wherein the R value measured by Raman spectroscopy is 0.10 or more and 0.40 or less. The composite carbon particle of claim 1, wherein the average interplanar spacing d002 of the (002) plane measured by X-ray diffraction method is 0.3354 nm or more and 0.3370 nm or less. For example, the composite carbon particles of claim 1, in which the 50% particle size (D50) of the cumulative particle size distribution based on the volume basis of the laser diffraction method is 1.0 μm or more and 30.0 μm or less, and the compactness of 400 times is 0.30 g/cm ³ or more 1.50g/cm ³ or less. The composite carbon particles of claim 1, wherein the BET specific surface area is 1.0 m ² /g or more and 10.0 m ² /g or less. The composite carbon particles of claim 1, wherein the aforementioned carbon particles (A) are graphite particles. The composite carbon particles of claim 1, wherein (BET specific surface area of composite carbon particles)/(BET specific surface area of carbon particles (A)) is 0.30 or more and 0.90 or less. Such as the composite carbon particles of claim 1, wherein (Raman R value of composite carbon particles)/(Raman R value of carbon particles (A)) is 1.50 or more and 10.00 or less. A negative electrode active material characterized by comprising composite carbon particles according to any one of claims 1-9. A negative electrode characterized by comprising the negative electrode active material of claim 10 and a current collector. A lithium ion secondary battery characterized by using the negative electrode of Claim 11. An all-solid-state lithium ion secondary battery characterized by using the negative electrode of claim 11. A method for producing composite carbon particles, characterized in that carbon particles (A) and a carboxylic acid compound each having one or more carboxyl groups and hydroxyl groups are used to form carbon particles (A) and the carboxylic acid compound in total mass ( A) The mixture is mixed so that it is 80.0% by mass or more and 99.9% by mass or less, the carboxylic acid compound is 0.1% by mass or more and 20.0% by mass or less, and the resulting mixture is heat-treated. A method for producing composite carbon particles, which is characterized in that carbon particles (A) and a carboxylic acid compound having two or more carboxyl groups are combined into carbon particles (A) based on the total mass of the carbon particles (A) and the carboxylic acid compound 80.0% by mass or more and 99.9% by mass or less, and the carboxylic acid compound is mixed so that it is 0.1% by mass or more and 20.0% by mass or less, and the resulting mixture is heat-treated. A method for producing composite carbon particles, which is characterized in that carbon particles (A) are combined with a carboxylic acid compound having at least one carboxyl group and a hydroxyl group, and a carboxylic acid compound having two or more carboxyl groups. The total mass with the carboxylic acid compound is mixed so that the carbon particles (A) are 80.0% by mass to 99.90% by mass, and the carboxylic acid compound is 0.1% by mass to 20.0% by mass, and the resulting mixture is heat-treated.

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