Carbon material, conductive additive, dispersion, electrode mixture layer forming composition, secondary battery, and method for manufacturing carbon material

Abstract

This invention provides a carbon material containing carbon fibers and exhibiting excellent dispersibility. [Solution] A carbon material containing carbon fibers having a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of fiber thickness, with an average fiber diameter greater than 100 nm and 170 nm or less, and an average fiber length of 1 μm to 4.5 μm.

Description

[Technical Field]

[0001] This disclosure relates to carbon materials, conductive additives, dispersions, compositions for forming electrode mixture layers, secondary batteries, and methods for producing carbon materials. [Background technology]

[0002] Rechargeable batteries, with their small size, light weight, and high voltage characteristics, are widely used in electronic devices such as notebook PCs, mobile phones, smartphones, and tablet PCs. In recent years, due to environmental concerns, rechargeable batteries such as lithium-ion batteries have become popular in electric vehicles (EVs) that run solely on batteries, and hybrid electric vehicles (HEVs) that combine gasoline engines and batteries.

[0003] A composite carbon fiber has been proposed in which multilayer carbon nanotubes are homogeneously dispersed between graphitized carbon nanofibers and near the surface of the graphitized carbon nanofibers as a conductivity imparting agent to the electrodes of secondary batteries (for example, Patent Document 1). This composite carbon fiber disperses easily in a matrix such as resin without leaving aggregates and has an excellent effect in reducing resistance. When this composite carbon fiber is included as a conductivity imparting agent in the electrodes of a secondary battery, battery characteristics such as capacity retention rate are improved. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Patent No. 5497109 [Overview of the project] [Problems that the invention aims to solve]

[0005] When preparing a slurry for coating the electrodes of a lithium-ion battery using carbon fibers as a conductive additive, it is desirable to obtain a uniform slurry free of aggregates. However, unlike the composite carbon fibers described in Patent Document 1, when ordinary carbon fibers are used, the carbon fibers tend to entangle with each other and form aggregates. From the viewpoint of suppressing these issues, it is desirable to improve the dispersibility of the carbon fibers.

[0006] This disclosure is made in view of the above circumstances and aims to provide a carbon material containing carbon fibers and having excellent dispersibility, as well as a conductive additive, dispersion, electrode mixture layer forming composition, and secondary battery containing the carbon material. Furthermore, this disclosure aims to provide a method for producing carbon materials that include carbon fibers and have excellent dispersibility. [Means for solving the problem]

[0007] The specific means for achieving the aforementioned objectives are as follows: <1> A carbon material containing carbon fibers having a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of fiber thickness, with an average fiber diameter greater than 100 nm and 170 nm or less, and an average fiber length of 1 μm to 4.5 μm. <2> The average fiber diameter of the carbon fibers is 120 nm to 165 nm. <1> The carbon material described above. <3> The average fiber length of the carbon fibers is 2 μm to 4.5 μm. <1> or <2> The carbon material described above. <4> Compression density: 0.6 g / cm³ 3 The compression resistivity is 0.0345 Ω·cm or less. <1> ~ <3> A carbon material as described in any one of the following. <5> BET specific surface area is 14.0 m² 2 / g or more <1> ~ <4> A carbon material as described in any one of the following. <6> The packing bulk density is 0.085 g / cm³. 3 The following is <1> ~ <5> A carbon material as described in any one of the following. <7> <1> ~ <6> A conductive additive containing any one of the carbon materials described in one of the following. <8> <1> ~ <6> A dispersion containing any one of the carbon materials described in one of the following. <9> <1> ~ <6> A composition for forming an electrode mixture layer, comprising any one of the carbon materials described in one of the following. <10> A positive electrode comprising a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector, and a negative electrode comprising a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector, At least one of the positive electrode mixture layer and the negative electrode mixture layer <1> ~ <6> A secondary battery containing a carbon material as described in any one of the following. <11> A method for producing a carbon material, comprising introducing a raw material liquid containing a carbon source and a catalyst source into a reaction tube with an inner diameter of 400 mm or more using a carrier gas, and heating the components introduced into the reaction tube. <12> The wall temperature in the central part of the reaction tube in the direction of flow of the raw material liquid is 1250°C or higher. <11> A method for producing the carbon material described above. [Effects of the Invention]

[0008] According to this disclosure, it is possible to provide a carbon material containing carbon fibers and exhibiting excellent dispersibility, as well as a conductive additive, dispersion, electrode mixture layer forming composition, and secondary battery containing the carbon material. Furthermore, this disclosure provides a method for producing carbon materials that include carbon fibers and have excellent dispersibility. [Brief explanation of the drawing]

[0009] [Figure 1] This is a diagram showing a longitudinal cross-section of a cell used for measuring powder resistance. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure are described in detail below. However, this disclosure is not limited to the embodiments described below. In the embodiments described below, the components (including elemental steps, etc.) are not essential unless otherwise specified. The same applies to numerical values ​​and their ranges, and do not limit this disclosure.

[0011] In this disclosure, the term "process" includes not only processes that are independent of other processes, but also processes that cannot be clearly distinguished from other processes, provided that the purpose of such process is achieved. In this disclosure, the numerical range indicated using "~" includes the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples. In this disclosure, each component may contain multiple types of the corresponding substance. If multiple types of the substance corresponding to each component are present in the composition, the content or amount of each component means the total content or amount of the multiple types of substances present in the composition, unless otherwise specified. In this disclosure, each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified. In this disclosure, the terms “layer” or “film” include cases where, when the region in which the layer or film exists is observed, it is formed not only over the entire region but also over only a portion of the region. In this disclosure, the term "lamination" refers to stacking layers, and two or more layers may be bonded together or detachable.

[0012] <Carbon materials> The carbon material of this disclosure has a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of the fiber thickness, and contains carbon fibers with an average fiber diameter greater than 100 nm and 170 nm or less, and an average fiber length of 1 μm to 4.5 μm. The carbon material of this disclosure has excellent dispersibility, and a dispersed state can be easily obtained in compositions such as compositions for forming electrode mixture layers. This is because entanglement and aggregation of carbon fibers are suppressed. As a result, the carbon material of this disclosure can be used in applications where dispersibility is required, and can be suitably used, for example, as a conductive additive. The carbon material disclosed herein exhibits excellent dispersibility, and the finer carbon fibers result in an increased number of carbon fibers per unit mass compared to conventional materials. This facilitates the formation of a uniform and sufficient conductive network within the electrode, thereby improving the rate characteristics and cycle characteristics of secondary batteries.

[0013] From the viewpoint of producing a secondary battery with good carbon material dispersibility and excellent cycle and rate characteristics, the average fiber diameter of the carbon fibers is preferably greater than 100 nm and 170 nm or less, more preferably between 120 nm and 165 nm, and even more preferably between 130 nm and 150 nm.

[0014] The average fiber diameter of carbon fibers can be determined from the arithmetic mean of the diameters of 200 fibers randomly observed by SEM of the electrodes. The diameter of a single fiber can be determined by measuring the width of one randomly selected point on the fiber, excluding both ends, as seen in the SEM image. Here, fiber width refers to the dimension of the fiber in the direction perpendicular to the longitudinal direction.

[0015] From the viewpoint of producing a secondary battery with good carbon material dispersibility and excellent cycle and rate characteristics, the average fiber length of the carbon fibers is preferably 2 μm to 4.5 μm, more preferably 2.5 μm to 4.0 μm, and even more preferably 3.0 μm to 3.5 μm.

[0016] The average fiber length of the carbon fiber can be measured as follows. The carbon material is dispersed in a dispersion medium, and the material spread on, for example, an aluminum foil is observed by SEM after drying. The lengths of 200 randomly selected fibers along the fiber axis are measured, and the average fiber length can be measured by taking the arithmetic mean. The carbon material obtained by washing the electrode with a solvent and removing the binder and the like may be taken out, and the average fiber length of the carbon fiber may be determined using the taken-out carbon material.

[0017] In the carbon material of the present disclosure, the compaction resistivity at a compression density of 0.6 g / cm 3 is preferably 0.0345 Ω·cm or less. By the compaction resistivity being 0.0345 Ω·cm or less, a decrease in the conductivity of the carbon material is suppressed, and it tends to contribute to an improvement in battery characteristics. In the carbon material of the present disclosure, the aforementioned compaction resistivity may be 0.0200 Ω·cm to 0.0345 Ω·cm, may be 0.0230 Ω·cm to 0.0340 Ω·cm, or may be 0.0250 Ω·cm to 0.0300 Ω·cm. The measurement of the compaction resistivity of the carbon material at a compression density of 0.6 g / cm 3 can be performed by the method described in the examples below.

[0018] In the carbon material of the present disclosure, the BET specific surface area is preferably 14.0 m 2 / g or more. The BET specific surface area may be 14.0 m 2 / g to 19.0 m 2 / g, may be 14.5 m 2 / g to 17.5 m 2 / g, or may be 15.0 m 2 / g to 17.0 m 2 / g. The BET specific surface area of the carbon material is calculated by the BET multipoint method from the adsorption isotherm data at three points near a relative pressure of 0.1, near 0.2, and near 0.3.

[0019] In the carbon material of the present disclosure, the packed bulk density is preferably 0.0850 g / cm 3 or less. The packed bulk density is 0.0500 g / cm3 ~0.0850 g / cm³ 3 It may also be 0.0600 g / cm³ 3 ~0.0830 g / cm³ 3 It may be 0.0700 g / cm³ 3 ~0.0820 g / cm³ 3 That's fine. The bulk density of the carbon material can be measured by the method described in the examples below.

[0020] The C0 of the carbon material is preferably 0.6782 nm or less, and from the viewpoint of battery characteristics, it is preferably 0.6760 nm to 0.6780 nm, more preferably 0.6764 nm to 0.6776 nm, and even more preferably 0.6766 nm to 0.6772 nm. The C0 of a carbon material refers to the lattice constant C0 in the c-axis direction of graphite, determined by X-ray diffraction of the carbon material, specifically by the JSPS method. C0 is the average interplanar spacing d of the (002) planes of graphite. 002 It is twice the value of the previous one.

[0021] From the viewpoint of suppressing performance degradation of secondary batteries, the moisture content of the carbon material is preferably less than 0.0500% by mass, more preferably 0.0450% by mass or less, and even more preferably 0.0400% by mass or less. The lower limit of the moisture content of the carbon material is not particularly limited; for example, it may be 0% by mass or 0.01% by mass or more. The water content can be measured by Karl Fischer titration.

[0022] The carbon material of this disclosure may be used as a conductive additive, or in the preparation of dispersions, electrode mixture layer forming compositions, etc.

[0023] The carbon material of this disclosure may be used in the form of a dispersion in a solvent or the like. The dispersion may contain other components such as a positive electrode active material, a negative electrode active material, a binder, and additives.

[0024] The carbon material of this disclosure may be used in the preparation of a composition for forming an electrode mixture layer (composition for forming an electrode mixture layer). Examples of compositions for forming electrode mixture layers include compositions for forming a positive electrode mixture layer and compositions for forming a negative electrode mixture layer. The composition for forming the positive electrode mixture layer comprises a positive electrode active material and the carbon material of this disclosure, and may further optionally contain carbon black, a binder, a solvent, etc. The negative electrode mixture layer forming composition comprises a negative electrode active material and the carbon material of this disclosure, and may further optionally contain a conductive additive, binder, solvent, etc.

[0025] <Secondary battery> The secondary battery of the present disclosure comprises a positive electrode having a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector, and a negative electrode having a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector, wherein at least one of the positive electrode mixture layer and the negative electrode mixture layer contains the carbon material of the present disclosure.

[0026] The secondary battery may take the form of a structure in which multiple positive and negative electrodes are stacked in the thickness direction within an outer casing, a laminated secondary battery, or a wound secondary battery. As an example of a wound secondary battery, it may be a cylindrical secondary battery in which an electrode pair and electrolyte obtained by winding a laminate in which positive and negative electrodes are stacked with a separator in between are sealed inside a cylindrical outer casing, or a cylindrical secondary battery in which a cell obtained by winding a laminate in which positive and negative electrodes are stacked with a solid electrolyte in between is sealed inside a cylindrical outer casing.

[0027] A secondary battery may be a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a separator in between, and an electrolyte are housed in an outer casing, or it may be a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a solid electrolyte in between is housed in an outer casing.

[0028] The types of secondary batteries are not particularly limited, and include lithium-based secondary batteries, sodium-based secondary batteries, potassium-based secondary batteries, magnesium-based secondary batteries, and aluminum-based secondary batteries. Among these, lithium-based secondary batteries, which can achieve high voltage and high energy density, and sodium-based secondary batteries, which can be cost-effective, are preferred. Examples of lithium-based secondary batteries include lithium-ion secondary batteries and lithium-based secondary batteries in which the negative electrode is metallic lithium (including, for example, lithium-sulfur batteries and lithium-air batteries). These include liquid electrolyte batteries and solid electrolyte batteries that contain at least one of the following: electrolyte, polymer electrolyte, polymer gel electrolyte, or solid electrolyte. Furthermore, for secondary batteries other than lithium-based secondary batteries, the positive electrode active material, negative electrode active material, electrolyte, etc., are not limited and can take various forms, similar to the lithium-based secondary batteries mentioned above. The following describes an example of a lithium-ion secondary battery, but the present invention is not limited to this example.

[0029] [Positive electrode] The secondary battery of this disclosure comprises a positive electrode having a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector.

[0030] The material of the positive electrode current collector is not particularly limited as long as it does not oxidize and dissolve at high potential and is electrically conductive; it can be selected from aluminum, nickel, titanium, stainless steel, etc. The state of the positive electrode current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. As an example, aluminum foil is used as the positive electrode current collector.

[0031] The positive electrode mixture layer may contain the carbon material of this disclosure. For example, a positive electrode mixture layer is formed on a positive electrode current collector by coating it with a positive electrode active material and the carbon material of this disclosure, and optionally further containing carbon black, a binder, a solvent, etc., using a composition for forming a positive electrode mixture layer (a type of composition for forming an electrode mixture layer), drying the coated slurry, and then pressing it.

[0032] The thickness of the positive electrode mixture layer may be 30 μm or more, 50 μm to 70 μm, or 70 μm to 100 μm, from the viewpoint of energy density and safety.

[0033] The density of the positive electrode mixture layer is 2.0 g / cm³, from the viewpoint of energy density and safety. 3 It may be greater than or equal to 3.0 g / cm³. 3 It may be greater than or equal to 3.0 g / cm³. 3 ~4.0g / cm 3 That's fine.

[0034] The basis weight of the positive electrode mixture layer is 10.0 mg / cm³, considering energy density and safety. 2 It may be greater than or equal to 10.0 mg / cm³. 2 ~30.0 mg / cm³ 2 That's fine.

[0035] The average electrode area per sheet (average positive electrode area and average negative electrode area) is 20 cm². 2 ~10,000cm 2 It may also be 300cm 2 ~10,000cm 2 That's fine.

[0036] (Cathode active material) The positive electrode mixture layer contains a positive electrode active material. The positive electrode active material can be appropriately selected depending on the type of secondary battery, and examples include compounds containing at least one of lithium, sodium, potassium, magnesium, and aluminum. Examples of positive electrode active materials include nickel-containing oxides and phosphates having an olivine-type structure. When the secondary battery is a lithium-based secondary battery, the positive electrode active material is LiNi x Mn y Co z Al w O2 (x, y, z, w≧0, x+y+z+w=1), LiMPO4 (M is one or more selected from Fe, Co, Mn and Ni), LiMn a Ni b Examples include O4 (a, b ≥ 0, a + b = 2), etc.

[0037] The positive electrode active material is LiNi x Mn y Co z Al w It is preferable that the mixture contains O2 (x, y, z, w≧0, x+y+z+w=1) or LiMPO4 (where M is one or more selected from Fe, Co, Mn, and Ni).

[0038] LiRing x Mn y Co z Al w For O2(x, y, z, w≧0, x+y+z+w=1), it is preferable that the nickel content is relatively high, for example, x≧0.5 or higher, and Li(Ni x Mn y Co z It is more preferable that O2(x≧0.5, y≦0.3, z≦0.3, x+y+z=1). Li(Ni x Mn y Co z As a positive electrode active material represented by O2 (x≧0.5, y≦0.3, z≦0.3, x+y+z=1), for example, Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, Li(Ni 0.7 Mn 0.2 Co 0.1 )O2, Li(Ni 0.7 Mn 0.1 Co 0.2 )O2, Li(Ni 0.6 Mn 0.2 Co 0.2 )O2, Li(Ni 0.5 Mn 0.3 Co 0.2 )O2 and Li(Ni 0.5 Mn 0.2 Co 0.3 )O2 is one example.

[0039] Examples of positive electrode active materials represented as LiMPO4 (where M is one or more selected from Fe, Co, Mn, and Ni) include LiFePO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn0.7 PO4, LiCoPO4 and LiCo 0.5 Mn 0.5 PO4 is one example.

[0040] In the positive electrode mixture layer, the content of the positive electrode active material is preferably 90.0% by mass or more, more preferably 93.0% by mass or more, and even more preferably 95.0% by mass or more, from the viewpoint of positive electrode capacity.

[0041] In the positive electrode mixture layer, the content of the positive electrode active material is preferably 98.0% by mass or less, more preferably 97.0% by mass or less, and even more preferably 96.5% by mass or less, from the viewpoint of ensuring the amount of other components.

[0042] The positive electrode mixture layer may contain the carbon material of this disclosure. When the positive electrode mixture layer contains the above-mentioned carbon material, the content of the above-mentioned carbon material in the positive electrode mixture layer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0043] In the positive electrode mixture layer, the content of the carbon material is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less.

[0044] The cathode mixture layer may contain carbon materials other than the carbon material of this disclosure (other carbon materials). Examples of other carbon materials include carbon fibers that do not meet the average fiber diameter or average fiber length requirements of the carbon fibers contained in the carbon material of this disclosure, composite carbon fibers, carbon nanotubes such as single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), and carbon nanofibers. The cathode mixture layer may, for example, contain carbon nanotubes and carbon black as described below, together with the carbon material of this disclosure.

[0045] (Carbon Black) The positive electrode mixture layer may further contain carbon black. Carbon black is used as a conductive additive in secondary batteries. Examples of carbon black include Denka Black (registered trademark, manufactured by Denka Co., Ltd.), C-NERGY (registered trademark) Super C45, C65 (manufactured by Imerys Graphite & Carbon), and Ketjen Black (manufactured by Ketjen Black International).

[0046] The primary particle size of carbon black may be between 10 nm and 100 nm. Here, "primary particle" refers to the portion corresponding to one particle contained within a group of particles called an aggregate. When the primary particle size of carbon black is within this range, it tends to disperse uniformly on the surface of the active material. From the viewpoint of improving dispersibility, the primary particle size of carbon black is preferably between 20 nm and 80 nm, and more preferably between 30 nm and 70 nm.

[0047] The primary particle size of carbon black can be determined by randomly selecting 100 primary carbon black particles from SEM images of the electrode and cross-sectional SEM images, and then taking the arithmetic mean of the maximum particle length measured using image recognition software.

[0048] When the positive electrode mixture layer contains carbon black, the carbon black content is preferably 0.2% by mass or more, more preferably 0.6% by mass or more, and even more preferably 1.0% by mass or more, from the viewpoint of obtaining excellent cycle characteristics and rate characteristics.

[0049] In the positive electrode mixture layer, the carbon black content is preferably 6.0% by mass or less, more preferably 4.0% by mass or less, and even more preferably 2.0% by mass or less, from the viewpoint of ensuring the capacity of the positive electrode.

[0050] (binder) The positive electrode mixture layer may contain a binder. Suitable binders include those commonly used in positive electrode mixture layers for lithium-ion secondary batteries. Examples of binders include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE).

[0051] If the positive electrode mixture layer contains a binder, the binder content is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2.0% by mass or more, from the viewpoint of obtaining the function of a binder.

[0052] In the positive electrode mixture layer, the binder content is preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably 4.0% by mass or less, from the viewpoint of suppressing an increase in the resistance of the positive electrode.

[0053] (Other ingredients) In addition to the above, the positive electrode mixture layer may contain other components such as dispersants and additives. For example, it may contain various dispersants for dispersing the positive electrode active material, and agents for surface modification of the positive electrode active material.

[0054] [Negative electrode] The secondary battery comprises a negative electrode which includes a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector.

[0055] The material of the negative electrode current collector is not particularly limited as long as it is an electronically conductive material, and can be selected from copper, nickel, titanium, stainless steel, etc. The state of the negative electrode current collector is not particularly limited and can be selected from foil, perforated foil, mesh, etc. As an example, copper foil is used as the negative electrode current collector.

[0056] The negative electrode mixture layer may contain the carbon material of this disclosure. For example, a composition for a negative electrode binder layer (a kind of composition for forming an electrode binder layer) containing a negative electrode active material and the carbon material of the present disclosure, and further containing a conductive assistant, a binder, a solvent, etc. as needed, is applied onto the negative electrode current collector, the applied slurry is dried, and then pressed to form a negative electrode binder layer on the negative electrode current collector.

[0057] From the viewpoints of energy density and safety, the thickness of the negative electrode binder layer may be 30 μm or more, may be 50 μm to 100 μm, or may be 100 μm to 150 μm.

[0058] From the viewpoints of energy density and safety, the density of the negative electrode binder layer may be 1.3 g / cm 3 or more, and may be 1.5 g / cm 3 to 2.0 g / cm 3 and may be suitable.

[0059] From the viewpoints of energy density and safety, the basis weight of the negative electrode binder layer may be 5.0 mg / cm 2 or more, and may be 10 mg / cm 2 to 20 mg / cm 2 and may be suitable.

[0060] (Negative electrode active material) The negative electrode binder layer contains a negative electrode active material. Examples of the negative electrode active material include Si, SiO x (0 < x ≤ 2), soft carbon, hard carbon, graphite, a composite of silicon and carbon, Li4Ti5O 12 , metallic Li, InO x (0 < x ≤ 1.5), AlO x (0 < x ≤ 1.5), AgO x (0 < x ≤ 0.5), CdO x (0 < x ≤ 1), SbO x (0 < x ≤ 1.5), BiO x (0 < x ≤ 1.5), ZnO x (0 < x ≤ 1), etc. Among them, it is preferable that the negative electrode active material contains graphite. Also, at least a part of the surface of the negative electrode active material may be coated with amorphous carbon.

[0061] In the negative electrode mixture layer, the content of the negative electrode active material is preferably 90.0% by mass or more, more preferably 93.0% by mass or more, and even more preferably 95.0% by mass or more.

[0062] In the negative electrode mixture layer, the content of the negative electrode active material is preferably 98.0% by mass or less, more preferably 97.0% by mass or less, and even more preferably 96.5% by mass or less, from the viewpoint of ensuring the amount of other components.

[0063] The negative electrode mixture layer may contain the carbon material of this disclosure. When the negative electrode mixture layer contains the above-mentioned carbon material, the content of the above-mentioned carbon material in the negative electrode mixture layer is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more.

[0064] In the negative electrode mixture layer, the content of the carbon material is preferably 3.0% by mass or less, more preferably 2.5% by mass or less, and even more preferably 2.0% by mass or less.

[0065] (Conductive additive) The negative electrode mixture layer may contain a conductive additive. Examples of conductive additives include carbon-containing materials such as carbon black and graphene.

[0066] If the negative electrode mixture layer contains a conductive additive, the content of the conductive additive may be 0.1% by mass to 3.0% by mass. The conductive additive that may be included in the negative electrode mixture layer may be one type or two or more types.

[0067] (binder) The negative electrode mixture layer may contain a binder. Examples of binders include PVdF, PTFE, etc., as with the positive electrode mixture layer, as well as styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PAA), etc.

[0068] If the negative electrode mixture layer contains a binder, the binder content is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2.0% by mass or more, from the viewpoint of obtaining the function of a binder.

[0069] In the negative electrode mixture layer, the binder content is preferably 5.0% by mass or less, more preferably 4.5% by mass or less, and even more preferably 4.0% by mass or less, from the viewpoint of suppressing an increase in the resistance of the negative electrode.

[0070] (Other ingredients) In addition to the above, the negative electrode mixture layer may contain other components such as dispersants and additives. For example, it may contain various dispersants for dispersing the negative electrode active material, and agents for surface modification of the negative electrode active material.

[0071] (Exterior materials) The outer casing material for housing the positive and negative electrodes is not limited as long as it can accommodate the positive and negative electrodes, and optionally a separator and electrolyte, or a solid electrolyte. Examples of outer casing materials include commercially available battery packs, 18650 type cylindrical cells, and those packaged in aluminum foil, and the outer casing material can be freely designed and used.

[0072] (Separator) A secondary battery may include a separator between the positive and negative electrodes. The separator can be freely selected from those commonly used in secondary batteries, such as microporous films made of polyethylene or polypropylene. Separators containing particles such as SiO2 or Al2O3 as fillers, or separators with these particles attached to the surface, can also be used.

[0073] (electrolyte) The secondary battery may contain an electrolyte. There are no particular restrictions on the electrolyte, and any electrolyte that can be used in a typical secondary battery can be suitably used. For example, an organic solvent in which a lithium salt is dissolved in a concentration of 0.5 mol / L to 2.0 mol / L can be used.

[0074] Examples of lithium salts include LiPF6, LiBF4, LiClO4, LiAsF6, and LiFSI.

[0075] Examples of organic solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and propylene carbonate (PC). Organic solvents listed here and others may be appropriately selected and mixed. Examples of electrolyte additives include vinylene carbonate (VC), propane sultone (PS), and fluoroethylene carbonate (FEC). When additives are used, the additive content is preferably 0.01% to 20% by mass, more preferably 0.1% to 10% by mass, and even more preferably 0.5% to 5% by mass, based on 100% by mass of the organic solvent.

[0076] (Ionic liquid) Ionic liquids may be used as electrolytes, or ionic liquids may be used in combination with the aforementioned organic solvents. The ionic liquid is not particularly limited, and examples include combinations of cations such as imidazolium cations, pyrrolidinium cations, piperinidium cations, and ammonium cations with anions such as bis(trifluoromethane)sulfonamide anions.

[0077] (solid electrolyte) A solid electrolyte may be used as the electrolyte. When a solid electrolyte is used, a separator is not required, and a battery (for example, an all-solid-state lithium-ion secondary battery) can be formed in which the positive electrode and negative electrode are sandwiched between solid electrolytes.

[0078] Examples of solid electrolytes include polymer electrolytes and inorganic solid electrolytes. Polymer electrolytes are not particularly limited, and examples include polymers such as polyethylene oxide impregnated with the above-mentioned lithium salt. Inorganic solid electrolytes are not particularly limited, and examples include Li 13 Ti 1.7 Al 0.3 Examples include (PO4)3 and Li2S-P2S5.

[0079] The secondary battery of this disclosure can be used as a power source for electronic devices such as smartphones, tablet PCs, and personal digital assistants; as a power source for electric motors such as power tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; and for storing electricity obtained from fuel cells, solar power generation, wind power generation, etc.

[0080] <Method for manufacturing carbon materials> The present disclosure's method for producing a carbon material includes introducing a raw material liquid containing a carbon source and a catalyst source into a reaction tube with an inner diameter of 400 mm or more using a carrier gas, and heating the components introduced into the reaction tube. The present disclosure's method for producing a carbon material is a floating catalyst method. In the floating catalyst method, a hollow tube is generally formed starting from the catalyst source in the initial stages of the reaction, and carbon fibers grow in the longitudinal direction. Growth in the longitudinal direction continues until catalytic activity is lost, such as when the surface of the catalyst particles is covered with carbon. Once growth in the longitudinal direction is complete, pyrolysis carbon is deposited on the surface of the hollow tube, and growth in the thickness direction of the fibers progresses, forming a structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction.

[0081] In this disclosure, the structure in which tubular carbon hexagonal mesh surfaces are stacked in the thickness direction refers to a structure in which multiple tubular structures formed by winding carbon hexagonal mesh surfaces are stacked along the thickness direction (also referred to as a specific structure). A specific structure can be confirmed, for example, by observing a carbon material with a transmission electron microscope (TEM) as follows: Observe an image in which the longitudinal direction of the carbon fiber can be confirmed (hereinafter also referred to as a "TEM longitudinal image") and an image in which the cross-section can be confirmed when the carbon fiber is cut in a direction intersecting the longitudinal direction (hereinafter also referred to as a "TEM cross-sectional image"). If, in the TEM longitudinal image, multiple lines along the longitudinal direction exist inside the carbon fiber, and in the TEM cross-sectional image, multiple closed curves with different maximum diameters exist, and the closed curves are arranged sequentially towards the inside as the maximum diameter decreases, then it can be confirmed that the carbon fiber has a specific structure. Furthermore, by observing diffraction lines similar to those of graphite particles for the (002), (100), (101), (110), or (112) planes using X-ray diffraction (XRD), the structure in which carbon hexagonal mesh surfaces are stacked can be confirmed. The structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction may be a structure in which multiple cylindrical carbon hexagonal mesh surfaces of different diameters are arranged so as to have concentric cross-sections (for example, like a concentric multi-tube), and the central axes (lines connecting the centers of each cross-section of a given tube) of multiple cylindrical carbon hexagonal mesh surfaces of different diameters do not all have to be aligned, and only some of the central axes may be aligned. The shape of the cross-section of the tube is not limited to a perfect circle, but may be an ellipse, a polygon, etc., and a part of the outer circumference may be a perfect circle, ellipse, other curve, polygon, or a combination thereof (the above "closed curve" refers to such a shape. In these cases, the "central axis" is the line connecting the centroids of each cross-section). The structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction may be a structure in which the central axes of multiple cylindrical carbon hexagonal mesh surfaces with different maximum cross-sectional widths (for example, elliptical or polygonal cross-sections) are all arranged to coincide, or the central axes may not all be aligned, or only some of the central axes may be aligned.

[0082] In the manufacturing method of the present disclosure, the carbon material of the present disclosure can be obtained by introducing the raw material liquid into a reaction tube with an inner diameter of 400 mm or more and heating it inside the reaction tube. This is presumed to be because increasing the inner diameter of the reaction tube suppresses the growth of carbon fibers, making it easier to obtain relatively short and thin carbon fibers.

[0083] The carbon source can be any raw material used in the suspended catalyst method, such as decahydronaphthalene (decalin), toluene, benzene, hexane, cyclohexane, xylene, ethylbenzene, cyclohexane, and ethylcyclohexane.

[0084] The catalyst source can be any catalyst used in the suspension catalyst method, such as ferrocene or sulfur compounds. A combination of ferrocene and sulfur compounds may also be used as the catalyst source. The amount of catalyst source in the raw material liquid may be 1% to 10% by mass, or 2% to 5% by mass.

[0085] Any gas that can be introduced into the reaction tube from the raw material liquid can be used as the carrier gas, such as hydrogen. Alternatively, the raw material liquid may be gasified and then introduced into the reaction tube as the carrier gas.

[0086] The ratio of the raw material liquid flow rate (g / min) to the hydrogen flow rate (NL / min) may be 0.30 to 1.00 g / NL or 0.40 to 0.80 g / NL, from the viewpoint of making it easier to obtain carbon fibers having an average fiber diameter and average fiber length within a desired range. Increasing the raw material liquid flow rate and thus increasing the ratio makes it easier for carbon coating to occur on the catalyst source surface, suppressing length growth, and thus making it easier to obtain carbon fibers with a large average fiber diameter and a small average fiber length. Increasing the hydrogen flow rate and thus decreasing the ratio makes it harder for carbon coating to occur on the catalyst source surface, promoting length growth, and thus making it easier to obtain carbon fibers with a small average fiber diameter and a large average fiber length.

[0087] The heating temperature when heating the raw material liquid introduced into the reaction tube is not particularly limited, and may be, for example, 1000°C or higher. In particular, from the viewpoint of making it easier to obtain carbon fibers having an average fiber diameter and average fiber length within a desired range, the wall temperature in the central part of the reaction tube in the direction of raw material liquid flow is preferably 1250°C or higher, and more preferably 1250°C to 1350°C.

[0088] To improve the crystallinity of the carbon material obtained by the floating catalyst method, heat treatment may be performed at 800-1500°C under an inert gas atmosphere such as argon, followed by graphitization treatment at 2000-3000°C. Graphitization treatment simultaneously removes the catalyst metal by evaporation, enabling high-purity carbon material production. The heat treatment may be performed at 800°C to 1500°C, preferably 900°C to 1300°C, under an inert gas atmosphere such as argon. Furthermore, the temperature for the graphitization treatment is preferably 2500°C to 3000°C, and more preferably 2600°C to 3000°C. [Examples]

[0089] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0090] (Manufacturing Example 1) A reactor was prepared consisting of a cylindrical reaction tube with an inner diameter of 500 mm and a length of 2000 mm, and a heater. A two-fluid mixing nozzle for supplying raw materials was placed at the top of the reaction tube. Ferrocene and sulfur were dissolved in benzene to prepare a starting material solution (3.5% by mass of ferrocene and 0.08% by mass of sulfur in the starting material solution). The prepared starting material solution and hydrogen were supplied at a flow rate corresponding to the inner diameter of the reaction tube and sprayed into the reaction tube from a two-fluid mixing nozzle. The ratio of the starting material solution flow rate to the hydrogen flow rate at this time was 0.54 to 0.71 g / NL. A carbon material containing carbon fibers was obtained by passing a sprayed raw material liquid through a reaction tube whose temperature (temperature of the wall inside the reaction tube) was adjusted to 1230-1290°C. At this time, the temperature of the furnace wall in the middle section of the reaction tube was 1270°C.

[0091] (Manufacturing example 2) A reactor was prepared consisting of a cylindrical reaction tube with an inner diameter of 590 mm and a length of 2000 mm, and a heater. A two-fluid mixing nozzle for supplying raw materials was placed at the top of the reaction tube. The raw material liquid and hydrogen, prepared in the same manner as in Production Example 1, were supplied at a flow rate corresponding to the inner diameter of the reaction tube and sprayed into the reaction tube from a two-fluid mixing nozzle. The ratio of the raw material liquid flow rate to the hydrogen flow rate at this time was 0.54 to 0.71 g / NL. A carbon material containing carbon fibers was obtained by passing a sprayed raw material liquid through a reaction tube whose temperature (temperature of the wall inside the reaction tube) was adjusted to 1230-1290°C. At this time, the temperature of the furnace wall in the middle section of the reaction tube was 1290°C.

[0092] (Manufacturing Example 3) A reactor was prepared consisting of a cylindrical reaction tube with an inner diameter of 370 mm and a length of 2000 mm, and a heater. A two-fluid mixing nozzle for supplying raw materials was placed at the top of the reaction tube. The raw material liquid and hydrogen, prepared in the same manner as in Production Example 1, were supplied at a flow rate corresponding to the inner diameter of the reaction tube and sprayed into the reaction tube from a two-fluid mixing nozzle. The ratio of the raw material liquid flow rate to the hydrogen flow rate at this time was 0.54 to 0.71 g / NL. A carbon material containing carbon fibers was obtained by passing a sprayed raw material liquid through a reaction tube whose temperature (temperature of the wall inside the reaction tube) was adjusted to 1230-1290°C. At this time, the temperature of the furnace wall in the middle section of the reaction tube was 1230°C.

[0093] (Transmission electron microscope (TEM) observation) The carbon fibers contained in each carbon material obtained in Production Examples 1-3 were dispersed in ethanol, scooped up with a microgrid, and dried to obtain the samples. TEM observation of the samples was performed. In the carbon materials obtained in Manufacturing Examples 1-3, it was confirmed that the carbon fibers contained in each material had a structure in which tubular carbon hexagonal mesh surfaces were stacked in the direction of the fiber thickness, as described below. First, the carbon materials were observed using TEM-EDX to obtain images showing the longitudinal direction of the carbon fibers (hereinafter also referred to as "TEM longitudinal image") and images showing the cross-section when the carbon fibers were cut in a direction intersecting the longitudinal direction (hereinafter also referred to as "TEM cross-sectional image"). In the TEM longitudinal image, it was confirmed that there were multiple lines along the longitudinal direction inside the carbon fibers, and in the TEM cross-sectional image, it was confirmed that there were multiple closed curves with different maximum diameters arranged concentrically. Thus, the structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of the fiber thickness in the carbon fibers was confirmed. Device name: JEM-ARM200F (manufactured by JEOL Ltd.)

[0094] (Average fiber length and average fiber diameter) The average fiber length (μm) and average fiber diameter (nm) of the carbon fibers contained in each carbon material obtained in Production Examples 1 to 3 were measured. Carbon material was dispersed in ethanol and spread onto aluminum foil. After drying, the carbon fibers were photographed panoramically at 4000x magnification using a scanning electron microscope to prepare a field of view that allowed measurement of both ends of the carbon fibers. The lengths of 200 randomly selected carbon fibers were measured, and the average length was determined from these measurements. Carbon material was dispersed in ethanol and spread onto aluminum foil. After drying, the diameters of 200 randomly selected carbon fibers were measured using a scanning electron microscope at 20,000x magnification, and the average of these measurements was defined as the average fiber diameter. The measurement results are shown in Table 1.

[0095] (BET specific surface area) A NOVA4200e (manufactured by Quantachrome Instruments) was used as the measuring device, and the total surface area of ​​the sample was measured in a sample cell (9 mm x 135 mm) of 2 m². 2 ~5m 2 The sample was placed in the container as shown, dried at 300°C under vacuum conditions for 1 hour, and then the sample weight was measured. Nitrogen was used as the gas for measurement. The BET specific surface area of the carbon material was calculated by the BET multi-point method from the adsorption isotherm data at three points near relative pressures of 0.1, 0.2, and 0.3.

[0096] (C0) Using a sample horizontal multi-purpose X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation), in accordance with the Gakushin method (the latest Carbon Material Experimental Techniques (Analysis and Analysis Edition), edited by the Carbon Materials Society), the measurement of C0 of the carbon material was carried out using silicon powder as an internal standard.

[0097] (Apparent bulk density) 1.000 g of the powder was weighed and placed in a graduated cylinder. It was vibrated for 30 seconds with a test tube mixer. Intensity ON1 was selected. The surface of the powder was leveled, and the scale of the graduated cylinder was read. The bulk density of the powder was calculated from the obtained volume and mass. Test tube mixer: Model number 'Touch Mixer MT31' (manufactured by Yamato Scientific Co., Ltd.)

[0098] (Consolidation resistivity, load-compression density curve) The measuring jig shown in Fig. 1 was used. Cell 4 was made of resin, and the inside had a bottom area of (1×4) cm 2 , and a depth of 10 cm. It had a copper electrode 3 for passing an electric current through the object to be measured 5, and a voltage measurement terminal 1 between the electrodes 3. A certain amount of sample was put into cell 4, and a force was applied to the compression rod 2 from above to compress the sample. A current of 0.1 A was passed through the sample, and when the bulk density reached 0.6 g / cm 3 , the voltage between 2.0 cm of the two voltage measurement terminals 1 inserted from the bottom of the container was read, and the resistivity ρ was calculated from the following formula. ρ=(E / 0.1)×S / 2 In the formula, R is the resistivity [Ω·cm], S is the cross-sectional area (depth × width) in the direction where the current flows in the sample = d×1 [cm 2 , and E is the voltage between the terminals [V]. In this example, the resistivity when compressed to a bulk density of 0.6 g / cm 3 was defined as the consolidation resistivity.

[0099] (Moisture content) The measurement was performed using the Karl Fischer titration method.

[0100] [Table 1]

[0101] In manufacturing examples 1 and 2, carbon materials were synthesized using reaction tubes with larger inner diameters than those used in manufacturing example 3, which enabled the production of fibers with smaller average fiber length and average fiber diameter. Microscopic observation of the carbon materials obtained in manufacturing examples 1 and 2 revealed that entanglement and aggregation were suppressed.

[0102] Next, evaluation batteries were fabricated using the carbon materials from Manufacturing Example 1 and Manufacturing Example 2, and charge-discharge cycle tests were performed.

[0103] (Manufacturing of positive electrode sheets) NMC811(Li(Ni)) is used as the positive electrode active material. 0.8 Mn 0.1 Co 0.1 An NMP solution (solid content concentration 7.3% by mass) was prepared containing 96.5 parts by mass of O2 (manufactured by Amoy Tungsten Co., Ltd.), 1.0 part by mass of carbon black (C-NERGY® Super C65, manufactured by Imerys Graphite & Carbon, primary particle size: 33 nm) as a conductive additive, 0.5 parts by mass of vapor-phase carbon fiber VGCF®-H (manufactured by Resonac Co., Ltd.), and 2.0 parts by mass of PVDF as a binder, and mixed in a kneader. For comparison, we also prepared a sample using only carbon black as a conductive additive. Subsequently, the mixture was kneaded in a kneader while adding NMP as needed to prepare a slurry with adjusted viscosity. The slurry was coated onto a 20 μm thick aluminum foil using a roll coater and dried to obtain a positive electrode sheet. After vacuum drying, the basis weight of the positive electrode mixture layer was reduced to 11.2 mg / cm² by roll pressing. 2 , density 3.2 g / cm³ 3 I adjusted it to that.

[0104] (Manufacturing of negative electrode sheets) Carboxymethylcellulose (CMC, CMC1380, manufactured by Daicel) was prepared as a binder. Specifically, the white powder of CMC was dissolved in purified water to obtain an aqueous solution with a solid content of 2% by mass. Carbon black (C-NERGY® Super C45, manufactured by Imerys Graphite & Carbon) was used as a conductive additive. As the negative electrode active material, graphite 1(D) V50 (50% particle size in the volume-based cumulative particle size distribution. Measured with a laser diffraction particle size analyzer): 14.4 μm, specific surface area: 1.7 m² 2 / g), and graphite 2(D V50 :5.7μm, specific surface area:3.2m 2 A mixture with a mass ratio of 7:3 ( / g) was used. As an aqueous binder, a dispersion of Polysol® LB150 (manufactured by Resonaq Corporation) fine particles was prepared. 96.5 parts by mass of negative electrode active material, 1.3 parts by mass of conductive additive, 1.5 parts by mass of CMC solids, and 1.5 parts by mass of aqueous binder were weighed out and mixed in a kneader to obtain a slurry for the negative electrode. The aforementioned negative electrode slurry was coated onto a 20 μm thick copper foil using a roll coater. After drying, it was further vacuum-dried to obtain a negative electrode sheet. The negative electrode sheet was roll-pressed at a pressure of 300 MPa to obtain a density of 1.4 g / cm³ of the negative electrode mixture layer. 3 I adjusted it to that. The discharge rate per unit weight of active material was evaluated in a half-cell with a counter electrode of lithium, and the capacity (Q) of the positive electrode sheet was determined. C Capacity (Q) of the negative electrode sheet relative to ) A The capacity of the negative electrode sheet was finely adjusted so that the ratio of ) was 1.2.

[0105] (Preparation of evaluation batteries) The following operations were performed inside a glove box maintained in a dry argon gas atmosphere with a dew point of -80°C or lower. The above negative electrode sheet and positive electrode sheet are punched out to form an area of ​​20 cm². 2A negative electrode and a positive electrode were obtained. An Al tab was attached to the Al foil of the positive electrode, and a Ni tab was attached to the Cu foil of the negative electrode. A polypropylene microporous film was sandwiched between the negative electrode and the positive electrode, and the assembly was packed into an aluminum laminate. Then, an electrolyte was injected into it. After that, the opening of the aluminum laminate was sealed by heat fusion to create a battery for evaluation. The electrolyte used was a solution prepared by dissolving 1% by mass of vinylene carbonate (VC), 30% by mass of fluoroethylene carbonate (FEC), and LiPF6 at a concentration of 1 mol / L in a solvent mixture of ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate in a volume ratio of 3:5:2.

[0106] (Charge-discharge cycle test) The battery underwent five charge-discharge cycles at a current of 0.2C (aging process). Next, a charge-discharge cycle test was performed using the following method. Charging was performed in CC (Constant Current) mode with an upper voltage limit of 4.2V and a current value of 1C, and in CV (Constant Voltage) mode with a cutoff current of 0.05C. The discharge was performed in CC mode with a lower voltage limit of 2.8V and a current value of 1C. This charge-discharge operation was repeated 200 times. The discharge rate retention rate after 200 cycles was defined and calculated using the following formula. (200-cycle discharge capacity retention rate (%)) = [(Discharge capacity at 200 cycles) / (Initial discharge capacity)] × 100

[0107] Table 2 shows the results of charge-discharge cycle tests using the carbon material from Manufacturing Example 1 or Manufacturing Example 2, and the results of charge-discharge cycle tests using only carbon black as a conductive additive without the carbon material (comparative example).

[0108] [Table 2]

[0109] As can be seen from the results in Table 2, it was confirmed that the cycle characteristics were improved by using the carbon material from Manufacturing Example 1 or Manufacturing Example 2.

Claims

1. A carbon material containing carbon fibers having a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of fiber thickness, with an average fiber diameter greater than 100 nm and 170 nm or less, and an average fiber length of 1 μm to 4.5 μm.

2. The carbon material according to claim 1, wherein the average fiber diameter of the carbon fibers is 120 nm to 165 nm.

3. The carbon material according to claim 1, wherein the average fiber length of the carbon fibers is 2 μm to 4.5 μm.

4. Compression density: 0.6 g / cm³ ３ The carbon material according to claim 1, wherein the compaction resistivity in is 0.0345 Ω·cm or less.

5. The BET specific surface area is 14.0 m². ２ The carbon material according to claim 1, wherein the amount is 1 / g or more.

6. The packing bulk density is 0.085 g / cm³. ３ The carbon material according to claim 1, wherein the carbon material is as follows:

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

8. A dispersion comprising the carbon material according to any one of claims 1 to 6.

9. A composition for forming an electrode mixture layer, comprising the carbon material described in any one of claims 1 to 6.

10. A positive electrode comprising a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector, and a negative electrode comprising a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector, A secondary battery comprising at least one of the positive electrode mixture layer and the negative electrode mixture layer, wherein the carbon material is as described in any one of claims 1 to 6.

11. A method for producing a carbon material, comprising introducing a raw material liquid containing a carbon source and a catalyst source into a reaction tube with an inner diameter of 400 mm or more using a carrier gas, and heating the components introduced into the reaction tube.

12. The method for producing a carbon material according to claim 11, wherein the wall temperature in the central part of the reaction tube in the flow direction of the raw material liquid is 1250°C or higher.

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