Carbon material, conductive aid, dispersion, composition for forming an electrode binder layer, secondary battery, and method for producing a carbon material

Abstract

Provided is a carbon material containing carbon fibers and having excellent dispersibility. 【Solution means】A carbon material containing carbon fibers having a structure in which tubular carbon hexagonal net surfaces are laminated in the fiber thickness direction, with an average fiber diameter greater than 100 nm and less than or equal to 170 nm, and an average fiber length of 1 μm to 4.5 μm.

Description

Technical Field

[0001] The present disclosure relates to a carbon material, a conductive assistant, a dispersion liquid, a composition for forming an electrode binder layer, a secondary battery, and a method for manufacturing a carbon material.

Background Art

[0002] Secondary batteries take advantage of the characteristics of being small, lightweight, and having a high voltage, and are widely used in electronic devices such as notebook PCs, mobile phones, smartphones, and tablet PCs. In recent years, against the backdrop of environmental issues, secondary batteries such as lithium-based secondary batteries have become popular in electric vehicles (EVs) that run solely on batteries and hybrid electric vehicles (HEVs) that combine a gasoline engine and a battery.

[0003] As a conductivity-imparting agent for the electrodes of secondary batteries, composite carbon fibers in which multi-walled carbon nanotubes are homogeneously dispersed between graphitized carbon nanofibers and near the surface of the graphitized carbon nanofibers have been proposed (for example, Patent Document 1). The composite carbon fibers can be easily dispersed in a matrix such as a resin without leaving aggregates, and have an excellent effect of reducing resistance. When the composite carbon fibers are contained as a conductivity-imparting agent in the electrodes of secondary batteries, battery characteristics such as the capacity retention rate are improved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

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

[0006] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a carbon material containing carbon fibers and having excellent dispersibility, and a conductive additive, a dispersion, a composition for forming an electrode mixture layer, and a secondary battery containing the carbon material. Another object of the present disclosure is to provide a method for producing a carbon material capable of producing a carbon material containing carbon fibers and having excellent dispersibility.

Means for Solving the Problems

[0007] Specific means for achieving the above object are as follows. <1> A carbon material containing carbon fibers having a structure in which cylindrical carbon hexagonal net surfaces are laminated in the fiber thickness direction, an average fiber diameter of more 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 <1>, wherein the average fiber diameter of the carbon fibers is 120 nm to 165 nm. <3> The carbon material according to <1> or <2>, wherein the average fiber length of the carbon fibers is 2 μm to 4.5 μm. <4> The carbon material according to any one of <1> to <3>, wherein the compaction resistivity at a compression density of 0.6 g / cm 3 is 0.0345 Ω·cm or less. <5> The carbon material according to any one of <1> to <4>, wherein the BET specific surface area is 14.0 m 2 / g or more. <6> The carbon material according to any one of <1> to <5>, wherein the packed bulk density is 0.085 g / cm 3 or less. <7> A conductive additive containing the carbon material according to any one of <1> to <6>. <8> A dispersion liquid containing the carbon material according to any one of <1> to <6>. <9> A composition for forming an electrode binder layer containing the carbon material according to any one of <1> to <6>. <10> A positive electrode including a positive electrode current collector and a positive electrode binder layer disposed on the positive electrode current collector and containing a positive electrode active material, and a negative electrode including a negative electrode current collector and a negative electrode binder layer disposed on the negative electrode current collector and containing a negative electrode active material. A secondary battery in which at least one of the positive electrode binder layer and the negative electrode binder layer contains the carbon material according to any one of <1> to <6>. <11> A method for producing a carbon material, including introducing a raw material liquid containing a carbon source and a catalyst source into a reaction tube having 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 <11>, wherein the wall surface temperature at the center in the flow direction of the raw material liquid in the reaction tube is 1250 °C or higher.

Advantages of the Invention

[0008] According to the present disclosure, it is possible to provide a carbon material containing carbon fibers and having excellent dispersibility, and a conductive auxiliary agent, a dispersion liquid, a composition for forming an electrode binder layer, and a secondary battery containing the carbon material. Further, according to the present disclosure, it is possible to provide a method for producing a carbon material capable of producing a carbon material containing carbon fibers and having excellent dispersibility.

Brief Description of the Drawings

[0009]

Figure 1

Modes for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following embodiments, the constituent elements (including element steps, etc.) are not essential unless otherwise specified. The same applies to numerical values and their ranges, which do not limit the present disclosure.

[0011] In the present disclosure, the term "step" includes not only a step independent of other steps, but also the step even if it cannot be clearly distinguished from other steps as long as the purpose of the step is achieved. In the numerical range indicated by using "~" in the present disclosure, the numerical values described before and after "~" are included as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Further, in the numerical ranges described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, each component may contain a plurality of corresponding substances. When there are a plurality of substances corresponding to each component in the composition, the content rate or content of each component means the total content rate or content of the plurality of substances present in the composition, unless otherwise specified. In the present disclosure, the particles corresponding to each component may contain a plurality of types. When there are a plurality of types of particles corresponding to each component in the composition, the particle diameter of each component means a value for the mixture of the plurality of types of particles present in the composition, unless otherwise specified. In the present disclosure, the term "layer" or "film" includes not only the case where it is formed over the entire region when observing the region where the layer or film exists, but also the case where it is formed only in a part of the region. In the present disclosure, the term "lamination" indicates stacking layers, and two or more layers may be bonded, and two or more layers may be detachable.

[0012] <Carbon material> The carbon material of the present disclosure has a structure in which tubular carbon hexagonal net planes are laminated in the thickness direction of the fiber, and includes carbon fibers having an average fiber diameter of more than 100 nm and 170 nm or less, and an average fiber length of 1 μm to 4.5 μm. The carbon material of the present disclosure has excellent dispersibility and can easily obtain a dispersed state in a composition such as a composition for forming an electrode binder layer. This is because entanglement, aggregation, etc. of the carbon fibers are suppressed. Thereby, the carbon material of the present disclosure can be used for applications that require dispersibility, and for example, it can be suitably used as a conductive auxiliary agent or the like. The carbon material of the present disclosure has excellent dispersibility, and further, since the carbon fibers are thinner, the number of carbon fibers per unit mass increases compared to the conventional case. As a result, it becomes easier to form a uniform and sufficient conductive network in the electrode, so that the rate characteristics and cycle characteristics of the secondary battery are likely to be improved.

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

[0014] The average fiber diameter of the carbon fibers can be obtained from the arithmetic mean of the diameters of 200 fibers randomly observed by SEM of the electrode. The diameter of one fiber can be obtained by measuring the width of one randomly selected location excluding both ends of the fiber shown in the SEM photograph. Here, the width of the fiber refers to the dimension of the fiber in the direction perpendicular to the longitudinal direction.

[0015] From the viewpoint of producing a secondary battery having excellent cycle characteristics and rate characteristics as well as the dispersibility of the carbon material, 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 carbon fibers can be measured as follows. The carbon material is dispersed in a dispersion medium, spread on aluminum foil or the like, and after drying, SEM observation is performed. 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 electrodes can be washed with a solvent, the carbon material with the binder and the like removed, and the average fiber length of the carbon fibers can be determined using the removed 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 / cm 3 may also be, 0.0600 g / cm 3 ~0.0830 g / cm 3 may also be, 0.0700 g / cm 3 ~0.0820 g / cm 3 may also be acceptable. The bulk density of the carbon material can be measured by the method described in the examples below.

[0020] 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. C0 of the carbon material means the lattice constant C0 in the c-axis direction of graphite obtained by the X-ray diffraction method of the carbon material, specifically, the Kagakushin method. C0 is twice the value of the average interplanar spacing d of the (002) plane of graphite. 002 of the numerical value.

[0021] 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 from the viewpoint of suppressing the performance degradation of the secondary battery. The lower limit of the moisture content of the carbon material is not particularly limited, and for example, it may be 0% by mass, or may be 0.01% by mass or more. The moisture content can be measured by the Karl Fischer titration method.

[0022] The carbon material of the present disclosure may be used as a conductive assistant or the like, and may also be used for the preparation of a dispersion, a composition for forming an electrode binder layer, or the like.

[0023] The carbon material of the present disclosure may also be used in the form of a dispersion dispersed 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 an additive.

[0024] The carbon material of the present disclosure may be used for preparing a composition for forming an electrode binder layer (composition for forming an electrode binder layer). Examples of the composition for forming an electrode binder layer include a composition for forming a positive electrode binder layer for forming a positive electrode binder layer, a composition for forming a negative electrode binder layer for forming a negative electrode binder layer, and the like. The composition for forming a positive electrode binder layer contains a positive electrode active material and the carbon material of the present disclosure, and may further contain carbon black, a binder, a solvent, etc. as necessary. The composition for forming a negative electrode binder layer contains a negative electrode active material and the carbon material of the present disclosure, and may further contain a conductive aid, a binder, a solvent, etc. as necessary.

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

[0026] As the form of the secondary battery, a structure in which a plurality of positive and negative electrodes housed in an exterior material are laminated in the thickness direction may be used, a laminated secondary battery may be used, or a wound secondary battery may be used. As the wound secondary battery, for example, a cylindrical secondary battery in which an electrode pair obtained by winding a laminate formed by laminating a positive electrode and a negative electrode via a separator and an electrolytic solution are enclosed in a cylindrical exterior body may be used, or alternatively, a cylindrical secondary battery in which a cell obtained by winding a laminate formed by laminating a positive electrode and a negative electrode via a solid electrolyte is enclosed in a cylindrical exterior body may be used.

[0027] The secondary battery may be a battery in which a laminate formed by laminating a positive electrode and a negative electrode via a separator and an electrolytic solution are housed in an exterior material, or a battery in which a laminate formed by laminating a positive electrode and a negative electrode via a solid electrolyte is housed in an exterior material.

[0028] The type of the secondary battery is not particularly limited, and examples include lithium-based secondary batteries, sodium-based secondary batteries, potassium-based secondary batteries, magnesium-based secondary batteries, aluminum-based secondary batteries, and the like. Among them, lithium-based secondary batteries capable of achieving high voltage and high energy density and sodium-based secondary batteries capable of cost reduction are preferable. Examples of the lithium-based secondary battery include lithium-ion secondary batteries and lithium secondary batteries in which the negative electrode is metallic lithium (including, for example, lithium-sulfur batteries and lithium-air batteries), and examples thereof include liquid electrolyte type batteries and solid electrolyte type batteries including at least one of electrolytes, polymer electrolytes, polymer gel electrolytes, and solid electrolytes. Also, for secondary batteries other than lithium-based secondary batteries, similar to the aforementioned lithium-based secondary batteries, the positive electrode active material, negative electrode active material, electrolyte, etc. are not limited and can take various forms. Hereinafter, as an example, an example of a lithium-based secondary battery will be described, but the present invention is not limited thereto.

[0029] [Positive Electrode] The secondary battery of the present disclosure includes a positive electrode including a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector and containing a positive electrode active material.

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

[0031] The positive electrode mixture layer may contain the carbon material of the present disclosure. For example, a composition for forming a positive electrode mixture layer (a kind of composition for forming an electrode mixture layer) containing a positive electrode active material and the carbon material of the present disclosure, and further containing carbon black, a binder, a solvent, etc. as necessary is applied on the positive electrode current collector, the applied slurry is dried, and then pressed to form a positive electrode mixture layer on the positive electrode current collector.

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

[0033] The density of the positive electrode active material layer may be 2.0 g / cm 3 or more, may be 3.0 g / cm 3 or more, and may be 3.0 g / cm 3 to 4.0 g / cm 3 from the viewpoints of energy density and safety.

[0034] The areal weight of the positive electrode active material layer may be 10.0 mg / cm 2 or more, may be 10.0 mg / cm 2 to 30.0 mg / cm 2 from the viewpoints of energy density and safety.

[0035] The average electrode area (average positive electrode area and average negative electrode area) per sheet may be 20 cm 2 to 10000 cm 2 or may be 300 cm 2 to 10000 cm 2 from the viewpoints of energy density and safety.

[0036] (Positive electrode active material) The positive electrode active material layer contains a positive electrode active material. The positive electrode active material can be appropriately selected according to the type of the secondary battery. For example, compounds containing at least one of lithium, sodium, potassium, magnesium, and aluminum can be mentioned. Examples of the positive electrode active material include oxides containing nickel, phosphates having an olivine-type structure, etc. When the secondary battery is a lithium-based secondary battery, examples of the positive electrode active material include 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 O4 (a, b ≥ 0, a + b = 2), etc.

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

[0038] LiNi x Mn y Co z Al w As for O2 (where x, y, z, w ≧ 0 and x + y + z + w = 1), it is preferable that the proportion of nickel is relatively high, for example, x ≧ 0.5 or more. Li(Ni x Mn y Co z )O2 (where x ≧ 0.5, y ≦ 0.3, z ≦ 0.3, and x + y + z = 1) is more preferable. As the positive electrode active material represented by Li(Ni x Mn y Co z )O2 (where x ≧ 0.5, y ≦ 0.3, z ≦ 0.3, and 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 can be mentioned.

[0039] As the positive electrode active material represented by LiMPO4 (where M is one or more selected from Fe, Co, Mn, and Ni), for example, LiFePO4, LiFe 0.5 Mn 0.5 PO4, LiFe 0.3 Mn0.7 PO4, LiCoPO4, and LiCo 0.5 Mn 0.5 PO4 may be mentioned.

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

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

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

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

[0044] The positive electrode mixture layer may contain a carbon material other than the carbon material of the present disclosure (other carbon materials). Examples of other carbon materials include carbon fibers that do not satisfy the conditions of the average fiber diameter or average fiber length of the carbon fibers contained in the carbon material of the present disclosure, composite carbon fibers, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), and carbon nanofibers. The positive electrode mixture layer may contain, for example, carbon nanotubes and carbon black described later together with the carbon material of the present disclosure.

[0045] (Carbon black) The positive electrode active material layer may further contain carbon black. Carbon black is used as a conductive aid for the secondary battery. 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 diameter of the carbon black may be 10 nm to 100 nm. Here, the primary particle refers to a portion corresponding to one particle contained in a plurality of particles called aggregates. If the primary particle diameter of the carbon black is within this range, it tends to be uniformly dispersed on the surface of the active material. From the viewpoint of improving dispersibility, the primary particle diameter of the carbon black is preferably 20 nm to 80 nm, and more preferably 30 nm to 70 nm.

[0047] The primary particle diameter of the carbon black can be obtained by randomly selecting 100 primary particles of carbon black from the SEM photograph of the electrode and the cross-sectional SEM photograph, and calculating the arithmetic mean of the measurement results of the maximum length of the particles by image recognition software.

[0048] When the positive electrode active material layer contains carbon black, the content of carbon black 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 active material layer, the content of carbon black 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 active material layer may contain a binder. As the binder, a binder used for a positive electrode active material layer of a normal lithium ion secondary battery can be preferably used. Examples of the binder include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE).

[0051] When the positive electrode active material layer contains a binder, the content of the binder is preferably 1.0% by mass or more, more preferably 1.5% by mass or more, and still more preferably 2.0% by mass or more from the viewpoint of obtaining the function as a binder.

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

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

[0054] [Negative electrode] The secondary battery includes a negative electrode including a negative electrode current collector and a negative electrode active material layer 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 a material having electron conductivity, and can be selected from copper, nickel, titanium, stainless steel, and the like. The state of the negative electrode current collector is not particularly limited, and can be selected from foil, perforated foil, mesh, and the like. As an example, a copper foil is used as the negative electrode current collector.

[0056] The negative electrode active material layer may contain the carbon material of the present 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 required, 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 or more.

[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 or more.

[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. Further, at least a part of the surface of the negative electrode active material may be coated with amorphous carbon.

[0061] In the negative electrode binder 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 binder layer, from the viewpoint of ensuring the amount of other components, 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.

[0063] The negative electrode binder layer may contain the carbon material of the present disclosure. When the negative electrode binder layer contains the above carbon material, in the negative electrode binder layer, the content of the above carbon material 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 binder layer, the content of the above 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 aid) The negative electrode binder layer may contain a conductive aid. Examples of the conductive aid include carbon-containing materials such as carbon black and graphene.

[0066] When the negative electrode binder layer contains a conductive aid, the content of the conductive aid may be 0.1% by mass to 3.0% by mass. The conductive aid that can be contained in the negative electrode binder layer may be one type or two or more types.

[0067] (Binder) The negative electrode binder layer may contain a binder. As examples of the binder, in addition to using PVdF, PTFE, etc. in the same manner as the positive electrode binder layer, styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), etc. can also be used.

[0068] When the negative electrode mixture layer contains a binder, the content of the binder 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 as a binder.

[0069] In the negative electrode mixture layer, the content of the binder 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 components) In addition to the above, the negative electrode mixture layer may contain other components such as a dispersant and an additive. For example, it may contain various dispersants for dispersing the negative electrode active material, agents for surface-modifying the negative electrode active material, and the like.

[0071] (Outer packaging material) The outer packaging material for housing the positive electrode and the negative electrode is not limited as long as it can house the positive electrode and the negative electrode, and optionally a separator and an electrolytic solution, or a solid electrolyte, etc. Examples of the outer packaging material include a commercially available battery pack, a cylindrical cell of the 18650 type, a form packed with an aluminum packaging material, etc., and the outer packaging material can be freely designed and used.

[0072] (Separator) The secondary battery may be provided with a separator between the positive electrode and the negative electrode. The separator can be freely selected from those that can be used in a general secondary battery, and examples thereof include a microporous film made of polyethylene or polypropylene. Separators in which particles such as SiO2 and Al2O3 are mixed as fillers, and separators having these particles adhered to the surface can also be used.

[0073] (Electrolytic solution) The secondary battery may contain an electrolyte solution. There is no particular limitation on the electrolyte solution, and an electrolyte solution that can be used in a normal secondary battery can be preferably used. For example, an organic solvent in which a lithium salt of 0.5 mol / L to 2.0 mol / L is dissolved can be used.

[0074] Examples of the lithium salt include LiPF6, LiBF4, LiClO4, LiAsF6, LiFSI, etc.

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

[0076] (Ionic liquid) An ionic liquid may be used as the electrolyte, or the ionic liquid may be used in combination with the aforementioned organic solvent. The ionic liquid is not particularly limited, and examples thereof include combinations of cations such as imidazolium cation, pyrrolidinium cation, piperidinium cation, ammonium cation, etc. and anions such as bis(trifluoromethane)sulfonamide anion.

[0077] (Solid electrolyte) A solid electrolyte may be used as the electrolyte. When using a solid electrolyte, a separator becomes unnecessary, and a battery in a form in which a positive electrode and a negative electrode are sandwiched by the solid electrolyte (for example, an all-solid-state lithium-ion secondary battery) can be formed.

[0078] Examples of the solid electrolyte include polymer electrolytes and inorganic solid electrolytes. The polymer electrolyte is not particularly limited, and examples thereof include a polymer such as polyethylene oxide impregnated with the above lithium salt. The inorganic solid electrolyte is not particularly limited, and examples thereof include Li 13 Ti 1.7 Al 0.3 (PO4)3, Li2S-P2S5, and the like.

[0079] The secondary battery of the present disclosure can be used as a power source for electronic devices such as smartphones, tablet PCs, and portable information terminals; a power source for electric motors such as power tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; and the storage of electric power obtained by fuel cells, solar power generation, wind power generation, and the like.

[0080] <Method for manufacturing carbon material> The method for manufacturing a carbon material of the present disclosure includes introducing a raw material liquid containing a carbon source and a catalyst source into a reaction tube having an inner diameter of 400 mm or more using a carrier gas, and heating the components introduced into the reaction tube. The method for manufacturing a carbon material of the present disclosure is a manufacturing method by a floating catalyst method. In the floating catalyst method, generally, a hollow tube is formed starting from the catalyst source at the initial stage of the reaction, and growth in the length direction of the carbon fiber occurs. The growth in the length direction continues until the catalytic activity is lost, for example, when the surface of the catalyst particles is covered with carbon. When the growth in the length direction ends, pyrolytic carbon is deposited on the surface of the hollow tube, and growth in the thickness direction of the fiber proceeds, forming a structure in which cylindrical carbon hexagonal net planes are laminated in the thickness direction.

[0081] In the present disclosure, the structure in which cylindrical carbon hexagonal net planes are stacked in the thickness direction refers to a structure in which structures formed by winding carbon hexagonal net planes into a cylindrical shape are stacked in the thickness direction (also referred to as a specific structure). The 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 a carbon fiber can be confirmed (hereinafter also referred to as a "TEM longitudinal image") and an image in which a 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"). Then, in the TEM longitudinal image, when there are a plurality of lines along the longitudinal direction inside the carbon fiber, and in the TEM cross-sectional image, there are a plurality of closed curves with different maximum diameters, and the closed curves are arranged in order on the inner side as the maximum diameter decreases, it can be confirmed that the carbon fiber has a specific structure. Also, in X-ray diffraction (XRD), by confirming diffraction lines similar to those of graphite particles for planes of (002), (100), (101), (110), or (112), a structure in which carbon hexagonal net planes are stacked can be confirmed. The structure in which cylindrical carbon hexagonal net planes are stacked in the thickness direction may be a structure in which a plurality of cylindrical carbon hexagonal net planes with different diameters are arranged in a concentric circular cross section (such as a concentric multi-tube), and for a plurality of cylindrical carbon hexagonal net planes with different diameters, the central axes (lines connecting the centers of each of the cross sections of a cylinder) may not all be aligned, or only a part of the central axes may be aligned. The shape of the cross section of the cylinder is not limited to a perfect circle, and may be an elliptical shape, a polygonal shape, etc., and a part of the outer periphery may be a perfect circle, an ellipse, other curves, a polygonal shape, or a combination thereof (the above-mentioned "closed curve" refers to such a shape. Also, in these cases, the "central axis" is a line connecting the centroids of each of the cross sections). The structure in which cylindrical carbon hexagonal net planes are stacked in the thickness direction may be a structure in which the central axes of a plurality of cylindrical (for example, the cross section is an elliptical shape, a polygonal shape) carbon hexagonal net planes with different maximum widths of the cross section are all aligned, or the central axes may not all be aligned, or only a part of the central axes may be aligned.

[0082] In the manufacturing method of the present disclosure, a raw material liquid is introduced into a reaction tube having an inner diameter of 400 mm or more, and the carbon material of the present disclosure described above can be obtained by heating the raw material liquid in the reaction tube. For this reason, it is presumed that by increasing the inner diameter of the reaction tube, the growth of carbon fibers is suppressed, and relatively short and thin carbon fibers can be easily obtained.

[0083] As the carbon source, any raw material used in the floating catalyst method may be used. For example, decahydronaphthalene (decalin), toluene, benzene, hexane, cyclohexane, xylene, ethylbenzene, cyclohexane, and ethylcyclohexane can be mentioned.

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

[0085] As the carrier gas, any gas that can introduce the raw material liquid into the reaction tube may be used, such as hydrogen. Alternatively, the gasified raw material liquid may be introduced into the reaction tube by 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 may be 0.40 to 0.80 g / NL from the viewpoint of easily obtaining carbon fibers having an average fiber diameter and an average fiber length within a desired range. By increasing the raw material liquid flow rate and increasing the above ratio, carbon coating on the surface of the catalyst source is likely to occur, and length growth is suppressed, so that carbon fibers having a large average fiber diameter and a small average fiber length can be easily obtained. By increasing the hydrogen flow rate and decreasing the above ratio, carbon coating on the surface of the catalyst source is less likely to occur, and length growth is promoted, so that carbon fibers having a small average fiber diameter and a large average fiber length can be easily obtained.

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

[0088] For the carbon material obtained by the floating catalyst method, for the purpose of increasing the crystallinity, heat treatment may be performed at 800 to 1500°C in an inert gas atmosphere such as argon, and then graphitization treatment may be performed at 2000 to 3000°C. The graphitization treatment can simultaneously evaporate and remove the catalyst metal, enabling the high-purity of the carbon material. Heat treatment may be performed at 800°C to 1500°C, preferably 900°C to 1300°C, in an inert gas atmosphere such as argon. Also, the temperature for performing the graphitization treatment is preferably 2500°C to 3000°C, and more preferably 2600°C to 3000°C.

Examples

[0089] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples.

[0090] (Production Example 1) A reactor composed of a cylindrical reaction tube with an inner diameter of 500 mm and a length of 2000 mm and a heater was prepared. A two-fluid mixing nozzle for supplying raw materials was arranged at the upper part of the reaction tube. Ferrocene and sulfur were dissolved in benzene to prepare a raw material liquid (ferrocene 3.5% by mass, sulfur 0.08% by mass in the raw material liquid). The prepared raw material liquid and hydrogen were supplied at a flow rate corresponding to the inner diameter of the reaction tube and sprayed into the reaction tube from the 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. By passing the raw material liquid sprayed into the reaction tube whose temperature (the temperature of the wall surface inside the reaction tube) was adjusted to 1230 to 1290°C, a carbon material containing carbon fibers was obtained. At this time, the temperature of the furnace wall in the middle stage of the reaction tube was 1270°C.

[0091] (Production Example 2) A reactor composed of a cylindrical reaction tube with an inner diameter of 590 mm and a length of 2000 mm and a heater was prepared. A two-fluid mixing nozzle for supplying raw materials was arranged at the upper part 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 the 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. By passing the raw material liquid sprayed into the reaction tube whose temperature (the temperature of the inner wall surface of the reaction tube) was adjusted to 1230 to 1290 °C, a carbon material containing carbon fibers was obtained. At this time, the temperature of the furnace wall in the middle stage of the reaction tube was 1290 °C.

[0092] (Production Example 3) A reactor composed of a cylindrical reaction tube with an inner diameter of 370 mm and a length of 2000 mm and a heater was prepared. A two-fluid mixing nozzle for supplying raw materials was arranged at the upper part 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 the 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. By passing the raw material liquid sprayed into the reaction tube whose temperature (the temperature of the inner wall surface of the reaction tube) was adjusted to 1230 to 1290 °C, a carbon material containing carbon fibers was obtained. At this time, the temperature of the furnace wall in the middle stage 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 to 3 were dispersed in ethanol, and the sample was scooped up with a microgrid and dried. The TEM observation of the sample was performed. It was confirmed as follows that all the carbon fibers contained in each of the carbon materials obtained in Production Examples 1 to 3 had a structure in which cylindrical carbon hexagonal net planes were laminated in the fiber thickness direction. First, the carbon material was observed by TEM-EDX, and an image in which the longitudinal direction of the carbon fiber could be confirmed (hereinafter also referred to as a "TEM longitudinal image") and an image in which a cross section could be confirmed when the carbon fiber was cut in a direction intersecting the longitudinal direction (hereinafter also referred to as a "TEM cross-sectional image") were observed. Then, in the TEM longitudinal image, it was confirmed that a plurality of lines along the longitudinal direction existed inside the carbon fiber, and in the TEM cross-sectional image, a plurality of closed curves with different maximum diameters existed concentrically. From the above, a structure in which cylindrical carbon hexagonal net planes in the carbon fiber were laminated in the fiber thickness direction was confirmed. Apparatus name: JEM-ARM200F (manufactured by JEOL Ltd.)

[0094] (Average fiber length and average fiber diameter) For the carbon fibers contained in each of the carbon materials obtained in Production Examples 1 to 3, the average fiber length (μm) and the average fiber diameter (nm) were measured. The carbon material was dispersed in ethanol, and the one developed on an aluminum foil was dried and then the carbon fibers were panoramically photographed at 4000 times with a scanning electron microscope, and a field of view in which both ends of the carbon fibers could be measured was prepared. The lengths of 200 randomly selected carbon fibers were measured, and the average of them was defined as the average fiber length. The carbon material was dispersed in ethanol, and the one developed on an aluminum foil was dried and then the diameters of 200 randomly selected carbon fibers were measured at 20000 times with a scanning electron microscope, and the average of them was defined as the average fiber diameter. The measurement results are shown in Table 1.

[0095] (BET specific surface area) Using NOVA4200e (manufactured by Quantachrome Instruments) as the measuring device, the sample was put into a sample cell (9 mm × 135 mm) so that the total surface area of the sample was 2 m 2 ~5 m 2 Then, after drying at 300 °C under vacuum conditions for 1 hour, the sample weight was measured and the measurement was carried out. Nitrogen was used as the gas for measurement. The BET specific surface area of the carbon material was calculated by the BET multipoint 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] (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 was equipped with 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 placed in 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 in the direction in which the current flows in the sample (depth × width)=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) It was measured by the Karl Fischer titration method.

[0100]

Table 1

[0101] In Production Examples 1 and 2, by synthesizing the carbon material using a reaction tube with a larger inner diameter than that in Production Example 3, it was possible to produce fibers with a small average fiber length and average fiber diameter. When the carbon materials obtained in Production Examples 1 and 2 were observed with a microscope, entanglement, aggregation, etc. were suppressed.

[0102] Next, evaluation batteries were fabricated using the carbon materials of Production Example 1 and Production Example 2, and charge-discharge cycle tests were conducted.

[0103] (Manufacture of positive electrode sheet) As the positive electrode active material, 96.5 parts by mass of NMC811 (Li(Ni 0.8 Mn 0.1 Co 0.1 )O2, manufactured by Amoytungsten Co., Ltd.), 1.0 part by mass of carbon black (C-NERGY (registered trademark) Super C65, manufactured by Imerys Graphite & Carbon, primary particle diameter: 33 nm) as a conductive assistant, 0.5 part by mass of vapor-grown carbon fiber VGCF (registered trademark)-H (manufactured by Resonac Co., Ltd.), and 2.0 parts by mass of PVDF as a binder were included in an NMP solution (solid content concentration: 7.3% by mass), and they were mixed with a kneader. Also, for comparison, a sample using only carbon black as a conductive assistant was prepared. Thereafter, while appropriately adding NMP, it was mixed with a kneader to prepare a slurry with adjusted viscosity. The slurry was coated on an aluminum foil with a thickness of 20 μm using a roll coater and dried to obtain a positive electrode sheet. After vacuum drying this, the basis weight of the positive electrode mixture layer was adjusted to 11.2 mg / cm 2 , and the density was adjusted to 3.2 g / cm 3 .

[0104] (Manufacture of Negative Electrode Sheet) Carboxymethyl cellulose (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 (registered trademark) Super C45, manufactured by Imerys Graphite & Carbon) was used as a conductive assistant. As the negative electrode active material, graphite 1 (D V50 (50% particle size in the cumulative particle size distribution based on volume. Measured with a laser diffraction particle size distribution analyzer): 14.4 μm, specific surface area: 1.7 m 2 / g), and a mixture of graphite 2 (D V50 : 5.7 μm, specific surface area: 3.2 m 2 / g) with a mass ratio of 7:3 was used. As an aqueous binder, a dispersion of fine particles of Polyzol (registered trademark) LB150 (manufactured by Resonac Co., Ltd.) was prepared. 96.5 parts by mass of the negative electrode active material, 1.3 parts by mass of the conductive assistant, 1.5 parts by mass of the CMC solid content, and 1.5 parts by mass of the aqueous binder were weighed, and these were mixed with a kneader to obtain a slurry for the negative electrode. The slurry for the negative electrode was coated on a copper foil with a thickness of 20 μm using a roll coater. After drying, it was further dried in vacuo to obtain a negative electrode sheet. The negative electrode sheet was roll-pressed at a pressure of 300 MPa to adjust the density of the negative electrode mixture layer to 1.4 g / cm 3 . The discharge capacity per unit weight of the active material was evaluated in a half cell of the counter electrode Li, and the capacity of the negative electrode sheet was finely adjusted so that the ratio of the capacity (Q C ) of the negative electrode sheet to the capacity (Q A ) of the positive electrode sheet was 1.2.

[0105] (Fabrication of Evaluation Battery) The following operations were carried out in 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 were punched out to an area of 20 cm 2A negative electrode plate and a positive electrode plate were obtained. An Al tab was attached to the Al foil of the positive electrode plate, and an Ni tab was attached to the Cu foil of the negative electrode plate. A microporous film made of polypropylene was sandwiched between the negative electrode plate and the positive electrode plate, and in that state, it was packed in an aluminum laminate. Then, an electrolytic solution was injected into it. Thereafter, the mouth of the aluminum laminate was sealed by heat fusion to fabricate a battery for evaluation. As the electrolytic solution, vinylene carbonate (VC) was 1% by mass, fluoroethylene carbonate (FEC) was 30% by mass, and LiPF6 was dissolved at a concentration of 1 mol / L in a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed at a volume ratio of 3:5:2.

[0106] (Charge-discharge cycle test) Charging and discharging were repeated 5 times at a current value of 0.2C (aging treatment). Next, a charge-discharge cycle test was conducted in the following manner. Charging was performed in CC (constant current) mode with an upper limit voltage of 4.2V and a current value of 1C and CV (constant voltage) mode with a cut-off current of 0.05C. Discharging was performed in CC mode with a lower limit voltage of 2.8V and a current value of 1C. This charge-discharge operation cycle was repeated 200 times. The 200-cycle discharge capacity retention rate was defined and calculated by 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 the charge-discharge cycle test when using the carbon material of Production Example 1 or Production Example 2, and the results of the charge-discharge cycle test when using only carbon black as a conductive assistant without using 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 of Production Example 1 or Production Example 2.

Claims

1. A carbon material comprising carbon fibers having a structure in which cylindrical carbon hexagonal net surfaces are laminated in the fiber thickness direction, an average fiber diameter greater than 100 nm and not more than 170 nm, and an average fiber length of 4.0 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. Compression density of 0.6 g / cm ３ The carbon material according to claim 1, wherein the consolidation resistivity at [compression density of 0.6 g / cm] is 0.0345 Ω·cm or less.

4. The carbon material according to claim 1, having a BET specific surface area of 14.0 m ２ / g or more.

5. The bulk density of the filling is 0.085 g / cm ３ The carbon material according to claim 1, wherein the bulk density of the filling is 0.085 g / cm or less.

6. A conductive auxiliary agent comprising the carbon material according to any one of claims 1 to 5.

7. A dispersion liquid comprising the carbon material according to any one of claims 1 to 5.

8. A composition for forming an electrode binder layer comprising the carbon material according to any one of claims 1 to 5.

9. A positive electrode comprising a positive electrode current collector and a positive electrode binder layer including 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 binder layer including a negative electrode active material disposed on the negative electrode current collector, A secondary battery, wherein at least one of the positive electrode binder layer and the negative electrode binder layer contains the carbon material according to any one of claims 1 to 5.

10. 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 having an inner diameter of 400 mm or more using a carrier gas, and heating the components introduced into the reaction tube, wherein the carbon source is decahydronaphthalene (decalin), toluene, benzene, hexane, cyclohexane, xylene, ethylbenzene, cyclohexane or ethylcyclohexane, the catalyst source is at least one of ferrocene and a sulfur compound, the carrier gas is hydrogen, the ratio of the raw material liquid flow rate (g / min) to the hydrogen flow rate (NL / min) is 0.30 to 1.00 g / NL, and the temperature of the reaction tube is adjusted to 1230°C to 1290°C, and the carbon material has a structure in which cylindrical carbon hexagonal net surfaces are laminated in the fiber thickness direction, an average fiber diameter greater than 100 nm and not more than 170 nm, and an average fiber length of 4.0 μm to 4.5 μm.

11. The method for producing a carbon material according to claim 10, wherein the wall temperature at the central part in the flow direction of the raw material liquid in the reaction tube is 1250°C or higher.

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