Carbon nanotube composite and carbon nanotube composite assembled wire

Abstract

This carbon nanotube composite comprises carbon nanotubes and core-shell type nanoparticles attached to the carbon nanotubes, wherein: each of the core-shell type nanoparticles includes a core formed from iron, and a shell having iron and sulfur covering the core; and the percentage of the number of sulfur atoms relative to the total number of iron atoms and sulfur atoms in the core-shell type nanoparticles is 6%-45%.

Description

Carbon nanotube composite and carbon nanotube composite wire

[0001] The present disclosure relates to a carbon nanotube composite and a carbon nanotube composite assembly wire. This application claims priority to Japanese Patent Application No. 2024-054384, filed March 28, 2024. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] In recent years, development of lithium-sulfur batteries has been progressing, which have a theoretical energy density approximately two to three times higher than that of current lithium-ion batteries.

[0003] The carbon nanotube composite of the present disclosure comprises a carbon nanotube and a core-shell nanoparticle attached to the carbon nanotube, the core-shell nanoparticle including a core made of iron and a shell containing iron and sulfur that covers the core, and the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticle is 6% or more and 45% or less.

[0004] Fig. 1 is a diagram for explaining a conventional method for producing carbon nanotubes. Fig. 2 is a diagram for explaining a method for producing a carbon nanotube composite according to embodiment 1. Fig. 3 is a transmission electron microscope image of the carbon nanotube composite obtained in sample 5.

[0005] [Problem to be Solved by the Present Disclosure] In lithium-sulfur batteries, sulfur is used in the positive electrode, but sulfur and its compounds have low electrical conductivity and cannot be used as an electrode material as is. Therefore, there is a need for a material that contains sulfur and has good electrical conductivity.

[0006] Therefore, an object of the present disclosure is to provide a material that contains sulfur and has good electrical conductivity.

[0007] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a carbon nanotube composite that is a material that contains sulfur and has good electrical conductivity.

[0008] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) A carbon nanotube composite of the present disclosure is a carbon nanotube composite comprising a carbon nanotube and a core-shell nanoparticle attached to the carbon nanotube, the core-shell nanoparticle including a core made of iron and a shell containing iron and sulfur that covers the core, and the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticle is 6% or more and 45% or less.

[0009] According to the present disclosure, it is possible to provide a carbon nanotube composite that is a material that contains sulfur and has good electrical conductivity.

[0010] When the percentage of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles is 6% or more, the sulfur content of the carbon nanotube composite increases, and when the carbon nanotube composite is applied to the positive electrode of a lithium-sulfur battery, this contributes to further improving the theoretical energy density of the lithium-sulfur battery.When the percentage is less than 6%, there is insufficient sulfur relative to lithium during the charge and discharge process of the lithium-sulfur battery, making it impossible to obtain sufficient energy density.

[0011] When the percentage of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles is 45% or less, the conductivity of iron can be maintained. Therefore, when the carbon nanotube composite is applied to the positive electrode of a lithium-sulfur battery, the electrochemical reaction between sulfur and lithium can be promoted during the charge and discharge process of the lithium-sulfur battery.

[0012] (2) In the above (1), the particle diameter of the core-shell nanoparticles may be 2 nm or more and 50 nm or less. If the particle diameter of the core-shell nanoparticles exceeds 50 nm, they will not contribute as a catalyst for synthesizing carbon nanotubes, and the production efficiency of carbon nanotubes will be significantly reduced, making it impossible to obtain good electrical conductivity, and their function as a conductive aid for carbon nanotubes will be impaired.

[0013] (3) In the above (1) or (2), the carbon nanotube composite may have a carbon content of 50% by mass or more and 95% by mass or less. When the carbon content is 50% by mass or more, the electrical conductivity of the carbon nanotube composite is improved. When the carbon content is 50% by mass or more and the percentage of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles is 6% or more, the theoretical energy density of a lithium-sulfur battery is further improved when the carbon nanotube composite is used in the positive electrode of the lithium-sulfur battery.

[0014] (4) A carbon nanotube composite assembly wire according to the present disclosure is a carbon nanotube composite assembly wire including a plurality of the carbon nanotube composites according to any one of (1) to (3) above.

[0015] According to the present disclosure, it is possible to provide a carbon nanotube composite assembly wire that contains sulfur and has good electrical conductivity.

[0016] (5) In the above (4), the carbon nanotube composite assembly wire may have a carbon content of 50% by mass or more and 95% by mass or less. When the carbon content is 50% by mass or more, the electrical conductivity of the carbon nanotube composite assembly wire is improved. When the carbon content is 50% by mass or more and the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles is 6% or more, when the carbon nanotube composite assembly wire is used in the positive electrode of a lithium-sulfur battery, the theoretical energy density of the lithium-sulfur battery is further improved.

[0017] [Details of the Embodiments of the Present Disclosure] Specific examples of the carbon nanotube composite and carbon nanotube composite assembly wire of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference symbols represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been changed as appropriate for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0018] In this specification, the notation in the format "A to B" means greater than or equal to A and less than or equal to B. When no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0019] In the present disclosure, when one or more numerical values ​​are listed as the lower limit and the upper limit of a numerical range, the combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit is also considered to be disclosed.

[0020] [Embodiment 1: Carbon Nanotube Composite] A carbon nanotube composite according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a carbon nanotube composite comprising a carbon nanotube and a core-shell nanoparticle attached to the carbon nanotube, the core-shell nanoparticle including a core made of iron and a shell covering the core, the shell containing iron and sulfur, and the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticle is 6% or more and 45% or less.

[0021] Since the carbon nanotube composite of the first embodiment includes carbon nanotubes having excellent electrical conductivity, the carbon nanotube composite can also have good electrical conductivity.

[0022] The carbon nanotube composite of the first embodiment includes core-shell nanoparticles attached to carbon nanotubes, and the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles is 6% to 45%. Since the core-shell nanoparticles contain sulfur, they can be used as positive electrodes in lithium-sulfur batteries.

[0023] <Structure of Carbon Nanotube Composite> The carbon nanotube composite of embodiment 1 comprises a carbon nanotube and core-shell nanoparticles attached to the carbon nanotube. The attachment position and form of the core-shell nanoparticles are not particularly limited as long as they are attached to the carbon nanotube. The core-shell nanoparticles may be attached to the ends of the carbon nanotube, or to regions other than the ends of the carbon nanotube. At least a portion of the core-shell nanoparticles may be embedded inside the carbon nanotube. The number of core-shell nanoparticles attached to one carbon nanotube composite may be one or more. The attachment of core-shell nanoparticles to the carbon nanotube composite can be confirmed by observing the carbon nanotube composite with a transmission electron microscope at 100,000 to 1,500,000 magnifications.

[0024] <Carbon Nanotubes> Carbon nanotubes (hereinafter also referred to as "CNTs") may be CNTs of known structures. For example, they may be single-walled CNTs in which only one carbon layer (graphene) is cylindrical, double-walled CNTs or multi-walled CNTs in which multiple carbon layers are stacked in a cylindrical shape, or cup-stacked CNTs in which graphene is stacked in the shape of a paper cup with a bottom.

[0025] The shape of the CNT is not particularly limited, and it may be either closed or open at the end. One or both ends of the CNT may have a cone made of conical graphene.

[0026] The length of the CNTs can be appropriately selected depending on the application. The length of the CNTs may be 1 μm or more and 600 mm or less, 10 μm or more and 600 mm or less, or 100 μm or more and 600 mm or less. The length of the CNTs is measured by observation with a scanning electron microscope.

[0027] The diameter of the CNTs may be 0.6 nm or more and 20 nm or less, 0.7 nm or more and 10 nm or less, or 0.8 nm or more and 5 nm or less.

[0028] In this disclosure, the diameter of a carbon nanotube refers to the average outer diameter of a single CNT. The average outer diameter of a CNT is obtained by directly observing the cross section of a CNT at any two points using a transmission electron microscope, measuring the outer diameter, which is the distance between the two most distant points on the circumference of the CNT, and calculating the average of the obtained outer diameters. If the CNT includes a cone portion at one or both ends, the diameter is measured at a location excluding the cone portion.

[0029] <Core-shell nanoparticles> Core-shell nanoparticles include a core made of iron and a shell containing iron and sulfur that covers the core. The core-shell nanoparticles are derived from the catalyst and auxiliary catalyst used in the production of CNT composites. The catalyst is ferrocene (Fe(C ５ H ５ ) ２ ) as a co-catalyst. ２ ), sulfur (S ８ ) are listed.

[0030] The core may contain inevitable impurities, such as iron carbide, in addition to iron, as long as the effects of the present disclosure are not impaired.

[0031] The shell may contain inevitable impurities, such as iron carbide, in addition to iron and sulfur, as long as the effects of the present disclosure are not impaired.

[0032] In the core-shell nanoparticles, the entire surface of the core may be covered with the shell, but a portion of the surface of the core may not be covered with the shell as long as the effects of the present disclosure are not impaired.

[0033] The core-shell nanoparticles may be composed of a core made of iron and a shell containing iron and sulfur that covers the core. The core-shell nanoparticles may contain carbon and oxygen in addition to the core and shell, as long as the effects of the present disclosure are not impaired.

[0034] The fact that the core-shell nanoparticles contain a core made of iron and a shell containing iron and sulfur that covers the core is confirmed by an energy dispersive X-ray spectroscopy (EDX) device or an electron energy loss spectroscopy (EELS) device attached to a transmission electron microscope (TEM).

[0035] The percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles (hereinafter also referred to as the "sulfur content of the core-shell nanoparticles") is 6% or more and 45% or less, or may be 10% or more and 40% or less, or may be 20% or more and 35% or less.

[0036] In the present disclosure, the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in a core-shell nanoparticle is measured as follows: A carbon nanotube composite is measured for characteristic X-rays derived from iron (Fe-Kα rays) and characteristic X-rays derived from sulfur (S-Kα rays) using an energy dispersive X-ray spectrometer attached to a scanning electron microscope (SEM), and the atomic ratio of sulfur to iron is calculated from the signal intensities and a correction factor.

[0037] When a carbon nanotube composite contains multiple core-shell nanoparticles, the above measurement is performed on each of all of the core-shell nanoparticles. In the present disclosure, the sulfur content of the core-shell nanoparticles being 6% or more and 45% or less means that the sulfur content of each of the multiple core-shell nanoparticles contained in a carbon nanotube composite is within the range of 6% or more and 45% or less. The same applies to other numerical ranges.

[0038] The particle size of the core-shell nanoparticles may be 2 nm or more and 50 nm or less, 4 nm or more and 25 nm or less, or 6 nm or more and 10 nm or less.

[0039] In the present disclosure, the particle size of core-shell nanoparticles is measured as follows. First, carbon nanotube composites are added to ethanol and dispersed by ultrasonic irradiation. This dispersion is dropped onto a dedicated grid and dried. Then, the dispersion is observed at a magnification of 100,000 to 1,500,000 using a transmission electron microscope (TEM). Next, in this TEM image, the outer diameter, which is the distance between the two most distant points on the periphery of each core-shell nanoparticle, is measured. This outer diameter corresponds to the particle size of the core-shell nanoparticle.

[0040] When one carbon nanotube composite contains multiple core-shell nanoparticles, the above measurement is performed for each of all of the core-shell nanoparticles. In the present disclosure, the particle size of the core-shell nanoparticles being 2 nm or more and 50 nm or less means that the particle size of each of the multiple core-shell nanoparticles contained in one carbon nanotube composite is within the range of 2 nm or more and 50 nm or less. The same applies to other numerical ranges.

[0041] The particle size of the core may be 1 nm or more and 48 nm or less, 2 nm or more and 23 nm or less, or 3 nm or more and 8 nm or less.

[0042] The thickness of the shell may be 0.5 nm or more and 12 nm or less, 1 nm or more and 6 nm or less, or 1.5 nm or more and 3 nm or less.

[0043] In the present disclosure, the method for measuring the particle size of the core and the average thickness of the shell is as follows. First, core-shell nanoparticles are observed at a magnification of 100,000 to 1,500,000 times using a transmission electron microscope (TEM). Then, in the same field of view, an electron energy loss spectroscopy (EELS) device attached to the TEM is used to measure two-dimensional mapping images of signals derived from Fe-Fe bonds (core region) and Fe-S bonds (shell region). The outer diameter, which is the distance between the two most distant points on the periphery of the region corresponding to the core portion, is measured. This outer diameter corresponds to the particle size of the core. The shell thickness is calculated based on the difference between the particle size of the core-shell nanoparticles and the particle size of the core.

[0044] <Coarse Particles> The carbon nanotube composite may not contain coarse particles having a particle size of more than 50 nm. The coarse particles may be formed by the catalyst ferrocene (Fe(C ５ H ５ ) ２ ) decomposes into iron particles during the production of the carbon nanotube composite, resulting in coarse iron particles. These coarse particles do not contribute to the synthesis of CNTs and affect the electrical conductivity characteristics of the CNTs. If the carbon nanotube composite does not contain these coarse particles, the CNTs can maintain their inherent electrical conductivity.

[0045] The absence of coarse particles in the carbon nanotube composite can be confirmed by observing the carbon nanotube composite with a TEM. The composition of the coarse particles is measured with an energy dispersive X-ray diffractometer (TEM-EDX) attached to the TEM.

[0046] <Carbon Content of Carbon Nanotube Composite> The carbon content of the carbon nanotube composite may be 50% by mass or more and 95% by mass or less, 55% by mass or more and 90% by mass or less, or 60% by mass or more and 85% by mass or less.

[0047] The carbon content of the carbon nanotube composite is measured by thermogravimetric analysis. The specific measurement method is as follows: Approximately 1 to 5 mg of a sample of the carbon nanotube composite is weighed and immersed in dry air (N ２ :O ２ While flowing a mixture of 200 mL / min of ethanol (distilled water, ethanol = 8:2), the sample is heated from 30°C to 1000°C at a temperature increase rate of 3°C / min, and the change in weight of the sample is measured. The carbon components in the sample are burned in the range of 300 to 900°C and released as gases such as carbon dioxide, resulting in a decrease in weight. The sample is further heated to 1000°C, and the weight of the sample remaining after the carbon components have been completely burned corresponds to the content of catalyst particles contained therein before combustion. Therefore, the carbon content can be calculated by measuring the content of catalyst particles.

[0048] <Method for Manufacturing Carbon Nanotube Composite> First, a conventional method for manufacturing a carbon nanotube composite will be described to deepen understanding of the method for manufacturing a carbon nanotube composite of embodiment 1. Conventional carbon nanotube composites are manufactured by a gas flow method using, for example, a carbon nanotube composite manufacturing apparatus 10 shown in FIG.

[0049] The carbon nanotube composite production apparatus 10 is arranged on one side of a first end 12c of the quartz tube 12, and includes a quartz tube 12 and a carbon source gas (methane, ethylene, acetone, etc.), a catalyst (ferrocene), and a co-catalyst (thiophene, sulfur (S ８ The apparatus may include a spray 13 for supplying a catalyst raw material-containing liquid containing the catalyst raw material, such as hydroxyapatite, and hydrogen gas as a carrier gas, and an electric furnace 11 for heating the quartz tube 12 .

[0050] The electric furnace 11 heats the quartz tube 12 so that the inside of the quartz tube 12 reaches a CNT synthesis temperature (approximately 1200 to 1500°C). The components contained in the carbon source gas and catalyst raw material-containing liquid supplied to the inside of the quartz tube 12 are heated and thermally decomposed. The thermal decomposition temperature of ferrocene is approximately 400 to 500°C, the thermal decomposition temperature of thiophene is approximately 750 to 850°C, and the thermal decomposition temperature of the carbon source is approximately 800 to 1050°C.

[0051] The temperature of the inner region of the first end 12c of the quartz tube 12 (hereinafter also referred to as the "radiant heat receiving region") is approximately 400 to 900°C due to the radiant heat of the electric furnace 11. In the radiant heat receiving region 12e, iron particles formed by thermal decomposition of ferrocene and thiophene or sulfur (S ８ ) is decomposed to form sulfur (S ２ ) to form core-shell nanoparticles having a core made of iron, which is an iron particle, and a shell containing iron and sulfur that covers the core.

[0052] An internal region of the quartz tube 12 facing the electric furnace downstream of the radiant heat receiving region 12e (hereinafter also referred to as the "electric furnace heating region") is at a CNT synthesis temperature of approximately 1200 to 1500°C. Carbon formed by decomposition of the carbon source is supplied to the core-shell nanoparticles that have been transported to the electric furnace heating region 12f by the flow of the carrier gas, and carbon nanotubes grow from the core-shell nanoparticles, forming carbon nanotube composites.

[0053] In conventional carbon nanotube manufacturing methods, the quartz tube 12 is heated to a carbon nanotube synthesis temperature of approximately 1200 to 1500°C. Therefore, the length of the radiant heat receiving region 12e, which has a temperature sufficient for forming core-shell nanoparticles, along the longitudinal direction of the quartz tube 12 is very short, even shorter than the length of the electric furnace heating region 12f along the longitudinal direction. In the gas flow method, a gas containing a carbon source gas and a catalyst raw material-containing liquid (hereinafter also referred to as "raw material-containing gas") passes from the first end 12c to the second end 12d without stagnation. Therefore, the time it takes for the raw material-containing gas to pass through the radiant heat receiving region 12e is very short (much shorter than one second), resulting in insufficient time for the formation of core-shell nanoparticles. As a result, the catalyst and auxiliary catalyst remain intact along with the core-shell nanoparticles, or coarse iron particles are formed. Furthermore, even when core-shell nanoparticles were formed, the iron particles were excessively coated with sulfur, so that the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles was 46% or more in the conventional carbon nanotube manufacturing method. Therefore, the conventional carbon nanotube manufacturing method did not form core-shell nanoparticles that included a core made of iron and a shell having iron and sulfur covering the core, and in which the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles was 6% or more and 45% or less.

[0054] The present inventors have created a new manufacturing method, focusing particularly on the process of forming core-shell nanoparticles, in order to obtain the carbon nanotube composite of Embodiment 1. The manufacturing method of the carbon nanotube composite of Embodiment 1 will be described below. The carbon nanotube composite of Embodiment 1 is manufactured by a gas flow method using, for example, a carbon nanotube composite manufacturing apparatus 10 shown in FIG.

[0055] The carbon nanotube composite production apparatus 10 is arranged on one side of a first end 12c of the quartz tube 12, and includes a quartz tube 12 and a carbon source gas (methane, ethylene, acetone, etc.), a catalyst (ferrocene), and a co-catalyst (thiophene, sulfur (S ８ The apparatus may include a spray 13 that supplies a catalyst raw material-containing liquid containing the catalyst raw material, such as HCl, and hydrogen gas as a carrier gas, and a first electric furnace 11 a and a second electric furnace 11 b that heat the quartz tube 12 .

[0056] The first region 12a, which is the internal region of the quartz tube 12 on the first end 12c side facing the first electric furnace 11a, is heated by the first electric furnace 11a to a temperature of approximately 800 to 1000°C, at which core-shell nanoparticles can be formed. The second region 12b, which is the internal region of the quartz tube 12 on the second end 12d side facing the second electric furnace 11b, is heated by the second electric furnace 11b to a temperature of approximately 1200 to 1500°C, at which carbon nanotubes can be synthesized.

[0057] In the carbon nanotube composite production apparatus 10, the length of the first region 12a along the longitudinal direction of the quartz tube 12 is sufficiently longer than the length of the radiant heat receiving region 12e along the longitudinal direction of the quartz tube 12, which corresponds to the first region 12a in conventional carbon nanotube composite production apparatuses. Therefore, in the carbon nanotube composite production apparatus 10, the time it takes for the gas containing the carbon source gas and the catalyst raw material-containing liquid to pass through the first region 12a is long (e.g., 1 second or more), ensuring sufficient time for the formation of core-shell nanoparticles. Therefore, the carbon nanotube composite production apparatus 10 can form core-shell nanoparticles that include an iron core and a shell containing iron and sulfur covering the core, in which the percentage of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles is 6% or more and 45% or less. Furthermore, the catalyst and auxiliary catalyst are prevented from remaining as they are, and coarse iron particles are prevented from being formed.

[0058] The ratio of the length of the first region 12a to the length of the second region 12b along the longitudinal direction of the quartz tube 12 may be, for example, first region 12a:second region 12b=1:1 to 1:10.

[0059] The length of the first region 12a along the longitudinal direction of the quartz tube 12 may be, for example, 100 to 1000 mm. The length of the second region 12b along the longitudinal direction of the quartz tube 12 may be, for example, 300 to 1000 mm.

[0060] The total flow rate of the carrier gas and the raw material-containing gas in the first region 12a may be, for example, 0.4 to 10 cm / sec, and the total flow rate of the carrier gas and the raw material-containing gas in the second region 12b may be, for example, 0.4 to 10 cm / sec.

[0061] The second region 12b of the quartz tube 12 is at a CNT synthesis temperature of approximately 1200 to 1500° C. Carbon formed by decomposition of the carbon source is supplied to the core-shell nanoparticles that have been transported to the second region 12b by the flow of the raw material-containing gas, and carbon nanotubes grow from the core-shell nanoparticles, thereby forming the carbon nanotube composite of the first embodiment.

[0062] [Embodiment 2: Carbon nanotube composite assembled wire] A carbon nanotube composite assembled wire according to an embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") is a carbon nanotube composite assembled wire including a plurality of the carbon nanotube composites of Embodiment 1.

[0063] The carbon nanotube composite assembled wire of the second embodiment includes carbon nanotubes having excellent electrical conductivity, and therefore the carbon nanotube composite assembled wire can also have good electrical conductivity.

[0064] The carbon nanotube composite assembly wire of the second embodiment includes core-shell nanoparticles attached to carbon nanotubes, and the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles is 6% or more and 45% or less. Because the core-shell nanoparticles contain sulfur, they can be used in the positive electrode of a lithium-sulfur battery.

[0065] The carbon nanotube composite assembly wire of Embodiment 2 may be composed of a plurality of the carbon nanotube composites of Embodiment 1. The carbon nanotube composite assembly wire of Embodiment 2 may also include a plurality of the carbon nanotube composites of Embodiment 1 and carbon nanotubes to which no core-shell nanoparticles are attached. The carbon nanotube composite assembly wire of Embodiment 2 may also include components other than the carbon nanotube composites and carbon nanotubes, as long as the effects of the present disclosure are not impaired. Examples of other components include fullerene, graphene, amorphous carbon, and polymers used as binders for electrodes.

[0066] The shape of the carbon nanotube composite assembled wire of the second embodiment is not particularly limited and can be appropriately set depending on the application. The shape of the carbon nanotube composite assembled wire can be, for example, a thread shape in which a plurality of carbon nanotube composites are aligned in the longitudinal direction and assembled.

[0067] The length of the carbon nanotube composite assembly wire of embodiment 1 is not particularly limited and can be set appropriately depending on the application. The length of the CNT composite assembly wire may be, for example, 100 μm or more and 100 m or less, 1000 μm or more and 100 m or less, or 10 cm or more and 100 m or less. The length of the CNT composite assembly wire is measured by observation with a scanning electron microscope, an optical microscope, or visual observation.

[0068] The diameter of the carbon nanotube composite assembled wire of embodiment 1 is not particularly limited and can be set appropriately depending on the application. The diameter of the CNT composite assembled wire may be, for example, 0.1 μm or more and 100 μm or less, or 1 μm or more and 100 μm or less. The diameter of the CNT composite assembled wire is smaller than the length of the CNT composite assembled wire. In other words, the length direction of the CNT composite assembled wire corresponds to the longitudinal direction.

[0069] In the present disclosure, the diameter of a carbon nanotube composite assembly wire refers to the average outer diameter of a single carbon nanotube composite assembly wire. The average outer diameter of a single carbon nanotube composite assembly wire is measured as follows: A cross section of a single carbon nanotube composite assembly wire at any two points is observed using a transmission electron microscope or a scanning electron microscope, and the outer diameter, which is the distance between the two most distant points on the circumference of the carbon nanotube composite assembly wire at the cross section, is measured. The average value of the outer diameters at the two points is calculated. This average value corresponds to the diameter of the carbon nanotube composite assembly wire.

[0070] In the carbon nanotube composite assembled wire, the core-shell nanoparticles may be present dispersed in the longitudinal direction of the CNT composite assembled wire. Here, "the core-shell nanoparticles being dispersed in the longitudinal direction of the CNT composite assembled wire" means that the core-shell nanoparticles are not unevenly distributed in the longitudinal direction of the CNT composite assembled wire. This allows the core-shell nanoparticles to have no effect on the electrical conductivity characteristics of the CNTs, and the CNT composite assembled wire can be elongated while maintaining the electrical conductivity that the CNTs inherently possess.

[0071] Whether the core-shell nanoparticles contained in the CNT composite assembly wire are dispersed in the longitudinal direction of the CNT composite assembly wire can be confirmed by EDX, which can be used for simultaneous measurements with an electron microscope such as an SEM or a TEM, or electron energy loss spectrometry (EELS).

[0072] The carbon content of the carbon nanotube composite assembly wire may be 50% by mass or more and 95% by mass or less, 55% by mass or more and 90% by mass or less, or 60% by mass or more and 85% by mass or less.

[0073] The carbon content of the carbon nanotube composite assembly wire is measured by thermogravimetric analysis, the specific method of which is as described in the first embodiment.

[0074] <Method for Manufacturing Carbon Nanotube Composite Assembly Wire> The carbon nanotube composite assembly wire of the second embodiment can be manufactured by assembling a plurality of carbon nanotube composites of the first embodiment while aligning them in the longitudinal direction.

[0075] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0076] <Apparatus 1> Carbon nanotube composites were produced using a carbon nanotube composite production apparatus having the structure shown in Fig. 2 as apparatus 1. The quartz tube 12 had an inner diameter of 46 mm and a length of 1200 mm. The first electric furnace 11a had a length of 500 mm, and the second electric furnace 11b had a length of 500 mm.

[0077] <Apparatus 2> A carbon nanotube composite was produced using the carbon nanotube composite production apparatus having the structure shown in Fig. 1 as apparatus 2. The quartz tube 12 had an inner diameter of 46 mm and a length of 1200 mm. The electric furnace 11 had a length of 1000 mm.

[0078] <Preparation of Carbon Nanotube Composites> Carbon nanotube composites of Samples 1 to 9 were prepared using Apparatus 1. Carbon nanotube composites of Samples 1-1 to 1-3 were prepared using Apparatus 2. The specific production methods are as follows.

[0079] Ferrocene and thiophene were dissolved in toluene to prepare a catalyst raw material-containing solution. The ferrocene content of the catalyst raw material-containing solution was 4 mass%. For each sample, the thiophene content of the catalyst raw material solution was adjusted so that the atomic ratio of iron to sulfur in the catalyst raw material solution was the ratio shown in the "Fe:S" column of "Catalyst Raw Material-Containing Solution" in Table 1.

[0080] In each of Apparatus 1 and Apparatus 2, the temperature inside the electric furnace was increased while hydrogen gas with a hydrogen gas concentration of 100% by volume was supplied from the spray 13 into the internal space of the quartz tube at a flow rate of 7 L / min (flow velocity of 7 cm / sec). For each sample using Apparatus 1, the temperature of the first region 12a inside the quartz tube 12 facing the first electric furnace 11a and the temperature of the second region 12b inside the quartz tube 12 facing the second electric furnace 11b are shown in the "Temperature" column of "First Region" and the "Temperature" column of "Second Region" in Table 1, respectively. For each sample using Apparatus 2, the temperature inside the entire quartz tube 12 was set to 1400°C.

[0081] Next, while hydrogen gas was flowing, ethylene gas was supplied from the spray 13 to the internal space of the quartz tube at a flow rate of 50 mL / min (flow rate 0.05 cm / sec) and the catalyst raw material-containing liquid was supplied at a flow rate of 0.1 mL / min (flow rate 0.02 cm / sec) for 5 minutes. The total flow rate of the gas containing hydrogen gas, ethylene gas, and catalyst raw material-containing liquid was 7.07 cm / sec.

[0082] Thereafter, the carbon nanotube composite formed in the quartz tube was collected.

[0083]

[0084] [Evaluation of carbon nanotube composite]

[0085] <Observation with a Transmission Electron Microscope> The carbon nanotube composites of each sample were observed at 200,000 magnifications using a transmission electron microscope. Carbon nanotubes and particles attached to the carbon nanotubes were confirmed in all samples. A transmission electron microscope image of the carbon nanotube composite obtained in Sample 5 is shown in Figure 3.

[0086] <Measurement of Core-Shell Nanoparticles> For each sample of carbon nanotube composite, the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles was measured. The specific measurement method is as described in embodiment 1. The results are shown in the "S / (Fe+S)" column of "Core-Shell Nanoparticles" in Table 2. For example, the description "40-45%" for sample 1 indicates that the sulfur content of each of the multiple core-shell nanoparticles contained in one carbon nanotube composite was within the range of 40-45% (i.e., the minimum value was 40% and the maximum value was 45%).

[0087] The particle size of the core-shell nanoparticles in each sample of carbon nanotube composite was measured. The specific measurement method is as described in embodiment 1. The results are shown in the "Particle size" column of "Core-shell nanoparticles" in Table 2. For example, the description "3 to 40 nm" for sample 1 indicates that the particle size of each of the multiple core-shell nanoparticles contained in one carbon nanotube composite was within the range of 3 to 40 nm (i.e., the minimum value was 3 nm and the maximum value was 40 nm).

[0088] <Carbon Nanotube Measurement> The length and diameter of the carbon nanotubes in the carbon nanotube composites of each sample were measured. The specific measurement method is as described in embodiment 1. The results are shown in the "Length" and "Diameter" columns of "CNT" in Table 2. For example, the description of the length of sample 1 as "1 to 100 μm" indicates that multiple carbon nanotube composites were produced for each sample, and that the length of each of the carbon nanotubes contained in each carbon nanotube composite was within the range of 1 to 100 μm (i.e., the minimum value was 1 μm and the maximum value was 100 μm). The same applies to the diameter.

[0089] <Measurement of Carbon Content of Carbon Nanotube Composite> The carbon content of each sample of carbon nanotube composite was measured. The specific measurement method is as described in Embodiment 1. The results are shown in the "Carbon Content" column of "CNT Composite" in Table 2.

[0090] <Presence or absence of coarse particles> For each sample, multiple carbon nanotube composites were observed at 200,000 magnification using a transmission electron microscope. No coarse particles with a particle size of more than 50 nm were observed in Samples 1 to 9. For Samples 1-1 to 1-3, it was confirmed that coarse particles with a particle size of more than 50 nm were attached to some of the carbon nanotube composites.

[0091] <Observation of Carbon Nanotube Composite Assembly Wire> In each sample, a carbon nanotube composite assembly wire in which a plurality of carbon nanotube composites were assembled was also produced. The carbon content of the carbon nanotube composite assembly wires of Samples 1 to 9 was the same as the carbon content of the carbon nanotube composite. Furthermore, in the carbon nanotube composite assembly wires of Samples 1 to 9, it was confirmed that the core-shell nanoparticles were dispersed in the longitudinal direction of the CNT composite assembly wire.

[0092]

[0093] The carbon nanotube composites and carbon nanotube composite assembly wires of Samples 1 to 9 correspond to examples, in that the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles is 25% or more and 45% or less.

[0094] In the carbon nanotube composites and carbon nanotube composite assembly wires of Samples 1-1 to 1-3, the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticles is 46% or more, and corresponds to a comparative example.

[0095] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0096] 1 Carbon nanotube, 2 Core-shell nanoparticle, 3 Carbon nanotube composite assembly wire, 10 Carbon nanotube composite manufacturing apparatus, 11 Electric furnace, 11a First electric furnace, 11b Second electric furnace, 12 Quartz tube, 12a First region, 12b Second region, 12c First end, 12d Second end, 12e Radiant heat receiving region, 12f Electric furnace heating region, 13 Spray.

Claims

1. A carbon nanotube composite comprising a carbon nanotube and a core-shell nanoparticle attached to the carbon nanotube, wherein the core-shell nanoparticle comprises a core made of iron and a shell containing iron and sulfur covering the core, and the percentage of the number of sulfur atoms relative to the total number of iron and sulfur atoms in the core-shell nanoparticle is 6% or more and 45% or less.

2. The carbon nanotube composite according to claim 1, wherein the particle diameter of the core-shell nanoparticles is 2 nm or more and 50 nm or less.

3. The carbon nanotube composite according to claim 1 or 2, wherein the carbon content of the carbon nanotube composite is 50% by mass or more and 95% by mass or less.

4. A carbon nanotube composite assembly wire comprising a plurality of carbon nanotube composites according to any one of claims 1 to 3.

5. The carbon nanotube composite assembly wire according to claim 4, wherein the carbon content of the carbon nanotube composite assembly wire is 50% by mass or more and 95% by mass or less.

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