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

Abstract

Provided is a carbon material containing carbon fibers having a structure in which cylindrical carbon hexagonal net surfaces are laminated in the fiber thickness direction, and having an average fiber diameter superior to 100 nm and inferior or equal to 170 nm, and an average fiber length of 1 μm to 4.5 μm.

Description

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

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

[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.

[0004] Patent No. 5497109

[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 has been 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 a carbon material that contains carbon fibers and has excellent dispersibility.

[0007] The specific means for achieving the above objectives are as follows: <1> A carbon material comprising 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 <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> Compression density of 0.6 g / cm³ ３ A carbon material according to any one of <1> to <3>, wherein the compaction resistivity in <5> is 0.0345 Ω·cm or less. ２ A carbon material described in any one of <1> to <4>, having a packing bulk density of 0.085 g / cm³. ３ A carbon material according to any one of the following <1> to <5>. <7> A conductive additive comprising the carbon material according to any one of <1> to <6>. <8> A dispersion comprising the carbon material according to any one of <1> to <6>. <9> A composition for forming an electrode mixture layer comprising the carbon material according to any one of <1> to <6>. <10> A secondary battery comprising a positive electrode having a positive electrode current collector and a positive electrode mixture layer comprising 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 comprising 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 comprises the carbon material according to any one of <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 <11>, wherein 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.

[0008] This disclosure provides 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 a carbon material that contains carbon fibers and exhibits excellent dispersibility.

[0009] This is a diagram showing a longitudinal cross-section of a cell used for measuring powder resistance.

[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 the process is achieved. In this disclosure, numerical ranges indicated using "~" include the numbers before and after "~" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit of one numerical range may be replaced by the upper or lower limit of another numerical range described in stages. Also, in numerical ranges described in this disclosure, the upper or lower limit of that numerical range may be replaced by 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 means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified. In this disclosure, the terms “layer” or “film” include cases where, when observed, the layer or film is formed over the entire region in which it exists, as well as cases where it is formed over only a portion of the region in which it exists. In this disclosure, the term “laminated” refers to stacking layers, and two or more layers may be bonded together or detachable.

[0012] <Carbon Material> The carbon material of this disclosure has a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of fiber thickness, and includes carbon fibers having 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 electrode mixture layer forming compositions. 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 of this disclosure has excellent dispersibility, and furthermore, because the carbon fibers are thinner, the number of carbon fibers per unit mass increases compared to conventional materials. As a result, it is easier to form a uniform and sufficient conductive network in the electrode, and thus the rate characteristics and cycle characteristics of secondary batteries are easily improved.

[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 perpendicular to its 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 carbon fibers can be measured as follows: Carbon material is dispersed in a dispersion medium, spread on aluminum foil or the like, and after drying, observed by SEM. The length along the fiber axis of 200 randomly selected fibers is measured, and the average fiber length is determined by taking the arithmetic mean. Alternatively, the electrode may be washed with a solvent to remove binders and other contaminants, and the average fiber length of the carbon fibers may be determined using the removed carbon material.

[0017] Fiber length and diameter will be measured only for specimens that are clearly carbon fibers. Carbon fibers selected will be those whose ends are included within a single field of view. Even if a fiber is curved, it will be measured if it can be confirmed as a single fiber. Specimens that are not clearly a single fiber due to overlapping or branching, specimens in contact with each other (e.g., those that are fixed or aggregated), specimens with a fiber length of less than 1 μm along the fiber axis, and specimens that cannot be determined to be carbon fibers will be excluded.

[0018] The carbon material of this disclosure has a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of fiber thickness, and includes carbon fibers having 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, but may also include carbon materials other than the carbon fibers. In the carbon material of this disclosure, the proportion of carbon fibers is preferably 10% or more, more preferably 30% or more, even more preferably 50% or more, even more preferably 70% or more, and most preferably 90% or more, when the total carbon material is considered as 100% or more in an image of the carbon material by SEM or TEM. The proportion of carbon fibers is not particularly limited as long as it is 100% or less, for example it may be 99% or less, or 95% or less. In this disclosure, "carbon fiber" preferably refers to a carbon material having an aspect ratio of 5 or more. The aspect ratio can be determined by the ratio of length to diameter (length / diameter). For any measurement target, a center line (also called the fiber axis) is defined, and the length along the fiber axis is defined as the length in terms of aspect ratio. The center line can be provided by image analysis software such as ImageJ.

[0019] The method for determining the proportion of carbon fibers is not particularly limited. For example, one method involves dispersing a carbon material in a dispersion medium such as ethanol, spreading it onto aluminum foil and drying it, then observing it with a SEM at an appropriate magnification and counting the number of carbon fibers and the number of other carbon atoms. Another method involves dispersing a carbon material in a dispersion medium such as ethanol, scooping it up with a microgrid and drying it, then observing it with a TEM and counting the number of carbon fibers, carbon fibers having structures other than those mentioned above, and the number of other carbon atoms such as particulate carbon.

[0020] The carbon material disclosed herein has a compressive density of 0.6 g / cm³. ３The consolidation specific resistance in [the relevant situation] is preferably 0.0345 Ω·cm or less. By the consolidation specific resistance being 0.0345 Ω·cm or less, the decrease in the conductivity of the carbon material is suppressed, and it tends to contribute to the improvement of battery characteristics. In the carbon material of the present disclosure, the aforementioned consolidation specific resistance 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 consolidation specific resistance of the carbon material can be carried out by the method described in the examples below. ３ The measurement of the consolidation specific resistance in [the relevant situation] can be carried out by the method described in the examples below.

[0021] 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 relative pressures of 0.1, 0.2, and 0.3.

[0022] In the carbon material of the present disclosure, the tapped bulk density is preferably 0.0850 g / cm ３ or less. The tapped bulk density may be 0.0500 g / cm ３ to 0.0850 g / cm ３ , may be 0.0600 g / cm ３ to 0.0830 g / cm ３ , or may be 0.0700 g / cm ３ to 0.0820 g / cm ３ . The measurement of the tapped bulk density of the carbon material can be carried out by the method described in the examples below.

[0023] The C of the carbon material ０The wavelength is preferably 0.6782 nm or less, preferably 0.6760 nm to 0.6780 nm from the viewpoint of battery characteristics, more preferably 0.6764 nm to 0.6776 nm, and even more preferably 0.6766 nm to 0.6772 nm. ０ This refers to the c-axis lattice constant C of graphite, which was determined by X-ray diffraction of carbon materials, specifically by the Japan Society for the Promotion of Science (JSPS) method. ０ This means C ０ The average interplanar spacing d of the (002) planes of graphite is ００２ It is twice that number.

[0024] From the viewpoint of suppressing performance degradation of secondary batteries, the moisture content of the carbon material is preferably less than 0.0500 mass%, more preferably 0.0450 mass% or less, and even more preferably 0.0400 mass% or less. The lower limit of the moisture content of the carbon material is not particularly limited; for example, it may be 0 mass%, or 0.01 mass% or more. The moisture content can be measured by Karl Fischer titration.

[0025] 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.

[0026] 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.

[0027] The carbon material of this disclosure may be used in the preparation of compositions for forming electrode mixture layers (compositions for forming electrode mixture layers). 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 a 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 composition for forming a negative electrode mixture layer comprises a negative electrode active material and the carbon material of this disclosure, and may further optionally contain a conductive additive, a binder, a solvent, etc.

[0028] <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.

[0029] 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.

[0030] 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.

[0031] 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, aluminum-based secondary batteries, etc. Among these, lithium-based secondary batteries that can achieve high voltage and high energy density and sodium-based secondary batteries that 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 (for example, lithium-sulfur batteries and lithium-air batteries are also included), and include liquid electrolyte type batteries and solid electrolyte type batteries that contain at least one of the following: electrolyte, polymer electrolyte, polymer gel electrolyte, solid electrolyte, etc. 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-based secondary battery, but the present invention is not limited thereto.

[0032] [Positive electrode] The secondary battery of this disclosure comprises 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.

[0033] 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, and 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.

[0034] 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 composition for forming a positive electrode mixture layer (a type of composition for forming an electrode mixture layer) which contains a positive electrode active material and the carbon material of this disclosure, and optionally carbon black, a binder, a solvent, etc., drying the coated slurry, and then pressing it.

[0035] 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.

[0036] 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 ~4.0 g / cm ３ That's fine.

[0037] The basis weight of the positive electrode mixture layer is 10.0 mg / cm³, from the viewpoint of energy density and safety. ２ It may be greater than or equal to 10.0 mg / cm³. ２ ~30.0mg / cm ２ That's fine.

[0038] The average electrode area per sheet (average positive electrode area and average negative electrode area) is 20 cm². ２ ~10,000 cm ２ It may also be 300 cm ２ ~10,000 cm２ That's fine.

[0039] (Positive Electrode 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 O ２ (x, y, z, w≧0, x+y+z+w=1), LiMPO ４ (M is one or more selected from Fe, Co, Mn, and Ni), LiMn ａ Ni ｂ O ４ Examples include (a, b ≥ 0, a + b = 2).

[0040] The positive electrode active material is LiNi ｘ Mn ｙ Co ｚ Al ｗ O ２ (x, y, z, w≧0, x+y+z+w=1) or LiMPO ４ (It is preferable that M contains one or more selected from Fe, Co, Mn, and Ni.)

[0041] LiNi ｘ Mn ｙ Co ｚ Al ｗ O ２ (x, y, z, w≧0, x+y+z+w=1) preferably has a relatively high nickel content, for example, x≧0.5 or more, Li(Ni ｘ Mn ｙ Co ｚ ) O ２ It is more preferable that (x ≥ 0.5, y ≤ 0.3, z ≤ 0.3, x + y + z = 1). Li(Ni ｘ Mn ｙ Co ｚ ) O ２Examples of the positive electrode active material represented by (x ≥ 0.5, y ≤ 0.3, z ≤ 0.3, x + y + z = 1) include, for example, Li(Ni ０．８ Mn ０．１ Co ０．１ )O ２ 、Li(Ni ０．７ Mn ０．２ Co ０．１ )O ２ 、Li(Ni ０．７ Mn ０．１ Co ０．２ )O ２ 、Li(Ni ０．６ Mn ０．２ Co ０．２ )O ２ 、Li(Ni ０．５ Mn ０．３ Co ０．２ )O ２ and Li(Ni ０．５ Mn ０．２ Co ０．３ )O ２ .

[0042] Examples of the positive electrode active material represented by LiMPO ４ (M is one or more selected from Fe, Co, Mn and Ni) include, for example, LiFePO ４ , LiFe ０．５ Mn ０．５ PO ４ , LiFe ０．３ Mn ０．７ PO ４ , LiCoPO ４ and LiCo ０．５ Mn ０．５ PO ４ .

[0043] In the positive electrode binder layer, from the viewpoint of the positive electrode capacity, the content rate of the positive electrode active material is preferably 90.0% by mass or more, more preferably 93.0% by mass or more, and further preferably 95.0% by mass or more.

[0044] In the positive electrode binder layer, from the viewpoint of ensuring the amount of other components, the content rate of the positive electrode active material is preferably 98.0% by mass or less, more preferably 97.0% by mass or less, and further preferably 96.5% by mass or less.

[0045] The positive electrode mixture layer may contain the carbon material of this disclosure. When the positive electrode mixture layer contains the carbon material, the content of the 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.

[0046] 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.

[0047] 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.

[0048] (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).

[0049] The primary particle size of the 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 the 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 the carbon black is preferably between 20 nm and 80 nm, and more preferably between 30 nm and 70 nm.

[0050] 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.

[0051] 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.

[0052] 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.

[0053] (Binder) The positive electrode mixture layer may contain a binder. Suitable binders are those commonly used in positive electrode mixture layers for lithium-ion secondary batteries. Examples of binders include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE).

[0054] 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.

[0055] 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.

[0056] (Other components) 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.

[0057] [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.

[0058] 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.

[0059] The negative electrode mixture layer may contain the carbon material of this disclosure. For example, a negative electrode mixture layer is formed on a negative electrode current collector by coating it with a negative electrode active material and the carbon material of this disclosure, and further optionally containing a conductive additive, binder, solvent, etc., a composition for a negative electrode mixture layer (a type of composition for forming an electrode mixture layer), drying the coated slurry, and then pressing it.

[0060] The thickness of the negative electrode mixture layer may be 30 μm or more, 50 μm to 100 μm, or 100 μm to 150 μm, from the viewpoint of energy density and safety.

[0061] The density of the negative electrode mixture layer is 1.3 g / cm³, from the viewpoint of energy density and safety. ３ It may be greater than or equal to 1.5 g / cm³. ３ ~2.0 g / cm ３ That's fine.

[0062] The basis weight of the negative electrode mixture layer is 5.0 mg / cm³, considering energy density and safety. ２ It may be greater than or equal to 10 mg / cm³. ２ ~20 mg / cm³ ２ That's fine.

[0063] (Negative electrode active material) The negative electrode mixture layer contains a negative electrode active material. The negative electrode active material is Si, SiO ｘ (0 < x ≤ 2), soft carbon, hard carbon, graphite, silicon-carbon composite, Li ４ Ti ５ O １２ , metal Li, InO ｘ (0<x≦1.5), AlO ｘ (0<x≦1.5), AgOｘ (0<x≦0.5), CdO ｘ (0<x≦1), SbO ｘ (0<x≦1.5), BiO ｘ (0<x≦1.5), ZnO ｘ Examples include oxides such as (0 < x ≤ 1). Among these, the negative electrode active material preferably contains graphite. Furthermore, at least a portion of the surface of the negative electrode active material may be coated with amorphous carbon.

[0064] 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.

[0065] 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.

[0066] The negative electrode mixture layer may contain the carbon material of this disclosure. When the negative electrode mixture layer contains the carbon material, the content of the 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.

[0067] 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.

[0068] (Conductive additive) The negative electrode mixture layer may contain a conductive additive. Examples of conductive additives include carbon black, graphene, and other carbon-containing materials.

[0069] 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 contained in the negative electrode mixture layer may be one type or two or more types.

[0070] (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.

[0071] 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.

[0072] 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.

[0073] (Other components) 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.

[0074] (Outer packaging) The outer packaging 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, etc. Examples of outer packaging include commercially available battery packs, 18650 type cylindrical cells, and those packaged in aluminum foil, and the outer packaging can be freely designed and used.

[0075] (Separator) A secondary battery may be equipped with a separator between the positive and negative electrodes. The separator can be freely selected from those commonly used in secondary batteries, such as a microporous film made of polyethylene or polypropylene. SiO ２ Al ２ O ３ Separators containing particles such as these as fillers, or separators with these particles attached to the surface, can also be used.

[0076] (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 normal secondary battery can be suitably used. For example, an organic solvent in which a lithium salt is dissolved in an amount of 0.5 mol / L to 2.0 mol / L can be used.

[0077] LiPF is an example of a lithium salt. ６ LiBF ４ LiClO ４ LiAsF ６ Examples include LiFSI.

[0078] 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.

[0079] (Ionic Liquids) Ionic liquids may be used as electrolytes, or they may be used in combination with the aforementioned organic solvents. The ionic liquids are 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.

[0080] (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 in which the positive electrode and negative electrode are sandwiched between solid electrolytes (for example, an all-solid-state lithium-ion secondary battery) can be formed.

[0081] 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 (PO ４ ) ３ Li ２ S-P ２ S ５ These are some examples.

[0082] 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.

[0083] <Method for Manufacturing Carbon Materials> The method for manufacturing carbon materials according to this disclosure 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 method for manufacturing carbon materials according to this disclosure is a suspension catalyst method. In the suspension 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. When growth in the longitudinal direction is completed, pyrolysis carbon is deposited on the surface of the hollow tube, and growth in the thickness direction of the fibers proceeds, forming a structure in which cylindrical carbon hexagonal mesh surfaces are stacked in the thickness direction.

[0084] 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, an ellipse, another curve, a 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 aligned, or the central axes may not all be aligned, or only some of the central axes may be aligned.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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.

[0089] 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.

[0090] 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.

[0091] To improve the crystallinity of the carbon material obtained by the floating catalyst method, a heat treatment may be performed at 800 to 1500°C under an inert gas atmosphere such as argon, followed by a graphitization treatment at 2000 to 3000°C. The graphitization treatment can simultaneously evaporate and remove the catalyst metal, enabling the carbon material to be purified to a high degree. The heat treatment may be performed at 800 to 1500°C, preferably 900 to 1300°C, under an inert gas atmosphere such as argon. Furthermore, the temperature for the graphitization treatment is preferably 2500 to 3000°C, and more preferably 2600 to 3000°C.

[0092] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0093] (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 raw material solution (3.5% by mass of ferrocene and 0.08% by mass of sulfur in the raw material solution). The prepared raw 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 the two-fluid mixing nozzle. At this time, the ratio of the raw material solution flow rate to the hydrogen flow rate was 0.54 to 0.71 g / NL. A carbon material containing carbon fibers was obtained by passing the sprayed raw material solution through the reaction tube, whose temperature (temperature of the wall surface inside the reaction tube) was adjusted to 1230 to 1290°C. At this time, the temperature of the furnace wall in the middle of the reaction tube was 1270°C. The carbon material produced by this operation is sometimes called "generated carbon material". The obtained generated carbon material was set in a calcination furnace (inner diameter 120 mm). The carbon material was heated to 1000°C under an argon atmosphere to remove any tar adhering to it. After calcination, the carbon material obtained in this operation is sometimes called "calcined carbon material." The obtained calcined carbon material was placed in a high-frequency heating furnace (inner diameter 120 mm). The calcined carbon material was graphitized by heating to 2800°C under an argon atmosphere. The carbon material obtained in this operation is sometimes called "graphitized carbon material." After the graphitization treatment, the recovered graphitized carbon material was pulverized using a jet mill type pulverizer to obtain the carbon material for Production Example 1.

[0094] (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 Manufacturing 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. At this time, the ratio of the raw material liquid flow rate to the hydrogen flow rate was 0.54 to 0.71 g / NL. A carbon material containing carbon fibers was obtained by passing the sprayed raw material liquid through the reaction tube, whose temperature (temperature of the wall surface inside the reaction tube) was adjusted to 1230 to 1290°C. At this time, the temperature of the furnace wall in the middle section of the reaction tube was 1290°C. The carbon material was obtained by calcination, graphitization, and pulverization in the same manner as in Manufacturing Example 1.

[0095] (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 Manufacturing 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. At this time, the ratio of the raw material liquid flow rate to the hydrogen flow rate was 0.54 to 0.71 g / NL. A carbon material containing carbon fibers was obtained by passing the sprayed raw material liquid through the reaction tube, whose temperature (temperature of the wall surface inside the reaction tube) was adjusted to 1230 to 1290°C. At this time, the temperature of the furnace wall in the middle section of the reaction tube was 1230°C. The carbon material was obtained by calcination, graphitization, and pulverization in the same manner as in Manufacturing Example 1.

[0096] (Transmission Electron Microscope (TEM) Observation) The carbon fibers contained in each carbon material obtained in Production Examples 1 to 3 were dispersed in ethanol, scooped up with a microgrid, and dried to obtain samples. TEM observation was performed on the samples. It was confirmed that the carbon fibers contained in each carbon material obtained in Production Examples 1 to 3 all have a structure in which tubular carbon hexagonal mesh surfaces are stacked in the direction of the fiber thickness, as described below. First, the carbon material was observed using TEM-EDX to obtain an image showing the longitudinal direction of the carbon fiber (hereinafter also referred to as the "TEM longitudinal image") and an image showing the cross-section when the carbon fiber is cut in a direction intersecting the longitudinal direction (hereinafter also referred to as the "TEM cross-sectional image"). It was confirmed that in the TEM longitudinal image, there are multiple lines along the longitudinal direction inside the carbon fiber, and in the TEM cross-sectional image, there are 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 fiber was confirmed. Device name: JEM-ARM200F (manufactured by JEOL Ltd.)

[0097] (Average Fiber Length and Average Fiber Diameter) The average fiber length (μm) and average fiber diameter (nm) were measured for the carbon fibers contained in each carbon material obtained in Production Examples 1 to 3. The carbon material was dispersed in ethanol, spread on aluminum foil, and 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 of these lengths was taken as the average fiber length. The carbon material was dispersed in ethanol, spread on aluminum foil, and after drying, the diameters of 200 randomly selected carbon fibers were measured at 20000x magnification using a scanning electron microscope, and the average of these diameters was taken as the average fiber diameter. Carbon fibers with a length along the fiber axis (fiber length) of less than 1 μm were excluded from the solids for which the average fiber length was to be determined. In addition, solids that were not clearly a single fiber due to overlapping or branching, solids that were in contact with each other (e.g., solids that were fixed or aggregated), and solids that could not be identified as carbon fibers were also excluded from the measurement. The measurement results are shown in Table 1.

[0098] (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) to 2 m². ２ ~5m ２ The sample was placed in the container, 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 using the BET multipoint method from adsorption isotherm data at three points near relative pressures of approximately 0.1, 0.2, and 0.3.

[0099] (C ０ Using a horizontal sample type multi-purpose X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation), and following the JSPS method (Latest Experimental Techniques for Carbon Materials (Analysis and Analysis), edited by the Carbon Materials Society), silicon powder was used as the internal standard for carbon materials C ０ Measurements were taken.

[0100] (Bulk Density) 1,000 g of powder was weighed and placed in a graduated cylinder. It was vibrated in a test tube mixer for 30 seconds. The intensity was set to ON1. The surface of the powder was leveled, and the scale on 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.)

[0101] (Consolidation resistivity, load-compression density curve) The measurement jig shown in Figure 1 was used. Cell 4 is made of resin, and its interior has a bottom area of ​​(1 × 4) cm². ２ The depth was 10 cm. A copper electrode 3 for passing an electric current through the object to be measured 5 and a voltage measuring terminal 1 between the electrodes 3 were provided. A certain amount of sample was placed in the cell 4, and 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 the bulk density was 0.6 g / cm³. ３ At that point, the voltage between the two voltage measuring terminals 1 inserted from the bottom of the container at a distance of 2.0 cm was read, and the resistivity ρ was calculated from the following formula: ρ = (E / 0.1) × S / 2, where R is the resistivity [Ω・cm], and S is the cross-sectional area (depth × width) in the direction of current flow in the sample = d × 1 [cm]. ２ ], where E is the terminal voltage [V]. In this example, the bulk density is 0.6 g / cm³. ３ The resistivity when compressed was defined as the compaction resistivity.

[0102] (Moisture content) Measured by Karl Fischer titration.

[0103]

[0104] In Production Examples 1 and 2, carbon materials were synthesized using reaction tubes with larger inner diameters than those used in Production 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 Production Examples 1 and 2 revealed that entanglement and aggregation were suppressed.

[0105] Next, evaluation batteries were fabricated using the carbon materials from Manufacturing Example 1 and Manufacturing Example 2, and charge-discharge cycle tests were performed.

[0106] (Manufacturing of positive electrode sheets) NMC811 (Li(Ni) as positive electrode active material ０．８ Mn ０．１ Co０．１ ) O ２ An NMP solution (solid content 7.3% by mass) was prepared containing 96.5 parts by mass of (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, a solution using only carbon black as a conductive additive was also prepared. Subsequently, a slurry was prepared by mixing in a kneader while adding NMP as appropriate to adjust the 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.

[0107] (Manufacturing of negative electrode sheet) 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. Graphite 1 (D) was used as the negative electrode active material. 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 ２A mixture with a mass ratio of 7:3 ( / g) was used. As an aqueous binder, a dispersion of fine particles of Polysol® LB150 (manufactured by Resonac Co., Ltd.) 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 and mixed in a kneader to obtain a negative electrode slurry. The negative electrode slurry was coated onto a copper foil with a thickness of 20 μm 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 The adjustment was made to evaluate the discharge rate per unit weight of active material in a half-cell with a counter electrode of Li, and the capacity (Q) of the positive electrode sheet was determined. C Capacity of the negative electrode sheet (Q) A The capacity of the negative electrode sheet was finely adjusted so that the ratio of ) was 1.2.

[0108] (Preparation of evaluation batteries) The following operations were performed in a glove box maintained in a dry argon gas atmosphere with a dew point of -80°C or lower. The negative electrode sheet and positive electrode sheet were punched out to form an area of ​​20 cm². ２ A 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 in 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 consisted of a solvent in which ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate were mixed in a volume ratio of 3:5:2, with 1% by mass of vinylene carbonate (VC), 30% by mass of fluoroethylene carbonate (FEC), and LiPF ６ A solution prepared by dissolving [the substance] at a concentration of 1 mol / L was used.

[0109] (Charge-Discharge Cycle Test) The battery was charged and discharged five times at a current of 0.2C (aging treatment). 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 of 1C, and in CV (Constant Voltage) mode with a cutoff current of 0.05C. Discharging was performed in CC mode with a lower voltage limit of 2.8V and a current of 1C. This charge-discharge operation was repeated 200 times. The 200-cycle discharge capacity retention rate was defined and calculated using the following formula: (200-cycle discharge capacity retention rate (%)) = [(Discharge capacity at 200 cycles) / (Initial discharge capacity)] × 100

[0110] 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).

[0111]

[0112] 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.

[0113] The disclosure of Japanese Patent Application No. 2024-195466 is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

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. 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 secondary battery comprising: 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 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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