Multilayer carbon nanotube assembly, multilayer carbon nanotube dispersion liquid, conductive material, electrode, secondary battery, planar assembly, filter, electromagnetic wave shield, and pellicle for extreme ultraviolet rays

Abstract

Provided are: a multilayer carbon nanotube assembly having high conductivity and good dispersibility in a dispersion medium; a multilayer carbon nanotube dispersion liquid; a conductive material; an electrode; a secondary battery; a planar assembly; a filter; an electromagnetic wave shield; and a pellicle for extreme ultraviolet rays.　Provided are: a multilayer carbon nanotube assembly comprising multilayered carbon nanotubes having a maximum length of 1000-30000 μm and Fe atoms, wherein the content ratio of Fe atoms to the total mass of the assembly is 0.5% by mass or more and less than 10% by mass; a multilayer carbon nanotube dispersion liquid; a conductive material; an electrode; a secondary battery; a planar assembly; a filter; an electromagnetic wave shield; and a pellicle for extreme ultraviolet rays.

Description

Multi-walled carbon nanotube aggregates, multi-walled carbon nanotube dispersions, conductive materials, electrodes, secondary batteries, planar aggregates, filters, electromagnetic wave shields, and pellicles for extreme ultraviolet rays

[0001] The present disclosure relates to a multi-walled carbon nanotube aggregate, a multi-walled carbon nanotube dispersion, a conductive material, an electrode, a secondary battery, a planar aggregate, a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet rays.

[0002] Carbon nanotubes have excellent mechanical and electronic properties and are expected to be used in a variety of applications. Known carbon nanotubes (hereinafter sometimes referred to as "CNTs") include single-walled carbon nanotubes (hereinafter sometimes referred to as "SWCNTs") and multi-walled carbon nanotubes (hereinafter sometimes referred to as "MWCNTs"), which are several micrometers to several tens of micrometers in length. SWCNTs are seamless cylindrical tubes formed from a single layer of graphene and have a high specific surface area, which allows for the expected high electrical conductivity. As a result, they have attracted attention as conductive additives. Meanwhile, MWCNTs are composed of multiple overlapping concentric cylindrical tubes. Some MWCNTs have as many as several tens of layers. Because the diameter of the cylindrical tubes of MWCNTs is larger and the specific surface area is smaller than that of SWCNTs, MWCNTs are somewhat easier to handle than SWCNTs, but there is a problem in that it is difficult to achieve the same high electrical conductivity as SWCNTs. Furthermore, CNTs with lengths of several μm to several tens of μm are in powder form and are primarily composed of carbonaceous matter, making them fundamentally difficult to handle, and the dispersibility of CNTs in dispersion media is an issue.

[0003] In recent years, attention has been focused on longer CNTs, specifically long fiber MWCNTs with lengths measured in the order of several millimeters. Although long fiber MWCNTs have a low specific surface area, they are expected to have higher electrical conductivity than short MWCNTs due to their long length. They are also easier to handle than powdered CNTs. While long fiber MWCNTs have traditionally been difficult to manufacture, recent developments in production technology have led to expectations that they will become more readily available.

[0004] For example, a method has been proposed in which a plurality of CNTs are aligned in the longitudinal direction and collected to obtain a long CNT-assembled wire or a CNT-assembled wire bundle (see, for example, Patent Document 1). According to the technology described in Patent Document 1, it is stated that the length of the CNT-assembled wire can be made 10 cm or more.

[0005] International Publication No. 2020 / 138379

[0006] The CNT aggregate obtained by the technique described in Patent Document 1 includes an aggregate of long fibers formed by oriented CNT fibers. Patent Document 1 does not pay attention to the dispersibility in a dispersion medium, which is important for the application of CNTs.

[0007] An object of one embodiment of the present disclosure is to provide a multi-walled carbon nanotube aggregate having high electrical conductivity and good dispersibility in a dispersion medium, a conductive material, an electrode, a secondary battery, and a planar aggregate, each of which includes the multi-walled carbon nanotube aggregate.An object of another embodiment of the present disclosure is to provide a multi-walled carbon nanotube dispersion containing a multi-walled carbon nanotube aggregate having high electrical conductivity.An object of yet another embodiment of the present disclosure is to provide a planar aggregate containing multi-walled carbon nanotube powder, and a filter, an electromagnetic wave shield, and a pellicle for extreme ultraviolet radiation, each of which uses the planar aggregate.

[0008] <1> An aggregate of multi-walled carbon nanotubes comprising multi-walled carbon nanotubes having a maximum length of 1000 μm to 30000 μm and Fe atoms, wherein a content ratio of Fe atoms to the total mass of the aggregate is 0.5 mass% or more and less than 10 mass%. <2> The aggregate of multi-walled carbon nanotubes according to <1>, which is a conductive assistant. <3> A multi-walled carbon nanotube dispersion comprising the aggregate of multi-walled carbon nanotubes according to <1> or <2> and a dispersion medium. <4> A conductive material comprising the aggregate of multi-walled carbon nanotubes according to <1> or <2>. <5> The multi-walled carbon nanotube dispersion according to <3>, which is an ink composition for forming a negative electrode of a lithium battery. <6> An electrode comprising an electrode active material and the conductive material according to <4>. <7> A secondary battery comprising the electrode according to <6>. <8> A composition comprising the aggregate of multi-walled carbon nanotubes according to <1> or <2>, and at least one selected from the group consisting of resin, ceramics, and concrete. <9> An aggregate of multi-walled carbon nanotubes comprising multi-walled carbon nanotubes having a tensile strength of 10 MPa to 100 MPa and Fe atoms, wherein the content ratio of Fe atoms to the total mass of the aggregate is 0.5 mass% or more and less than 10 mass%. <10> The aggregate of multi-walled carbon nanotubes according to <9>, which is a conductive assistant. <11> A multi-walled carbon nanotube dispersion comprising the aggregate of multi-walled carbon nanotubes according to <9> or <10>, and a dispersion medium. <12> A conductive material comprising the aggregate of multi-walled carbon nanotubes according to <9> or <10>. <13> The multi-walled carbon nanotube dispersion according to <11>, which is an ink composition for forming a negative electrode of a lithium battery. <14> An electrode comprising an electrode active material and the conductive material according to <12>. <15> A secondary battery comprising the electrode according to <14>. <16> A composition comprising the aggregate of multi-walled carbon nanotubes according to <9> or <10>, and at least one selected from the group consisting of resin, ceramics, and concrete. <17> A composition comprising: an aggregate of multi-walled carbon nanotubes, the aggregate containing multi-walled carbon nanotubes and Fe atoms, wherein the content ratio of Fe atoms relative to the total mass of the aggregate is 0.5 mass% or more and less than 10 mass%, and at least one selected from the group consisting of a dispersion medium, a resin, a ceramic, and a concrete.<18> A multi-walled carbon nanotube dispersion comprising multi-walled carbon nanotubes having a tensile strength of 10 MPa to 100 MPa and a dispersion medium. <19> A planar assembly comprising the aggregate of multi-walled carbon nanotubes according to <1>, <2>, <9> or <10>. <20> A filter using the planar assembly according to <19>. <21> An electromagnetic wave shield using the planar assembly according to <19>. <22> A pellicle for extreme ultraviolet radiation using the planar assembly according to <19>.

[0009] According to one embodiment of the present disclosure, it is possible to provide a multi-walled carbon nanotube aggregate having high conductivity and good dispersibility in a dispersion medium, a conductive material containing the multi-walled carbon nanotube aggregate, an electrode, a secondary battery, and a planar aggregate. According to another embodiment of the present disclosure, it is possible to provide a multi-walled carbon nanotube dispersion containing a multi-walled carbon nanotube aggregate having high conductivity. According to yet another embodiment of the present disclosure, it is possible to provide a planar aggregate containing multi-walled carbon nanotube powder, and a filter, an electromagnetic wave shield, and an extreme ultraviolet pellicle using the planar aggregate.

[0010] 1 is a scanning electron microscope photograph showing one embodiment of a multi-walled carbon nanotube aggregate of the present disclosure.

[0011] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in the present disclosure, the upper or lower limit value described in a certain numerical range may be replaced with a value shown in the Examples. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, when there are multiple substances corresponding to each component, the amount of each component means the total amount of the multiple substances unless otherwise specified. In this specification, the term "process" does not only refer to an independent process, but also includes a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0012] <Multi-walled carbon nanotube aggregate: First embodiment> The multi-walled carbon nanotube aggregate of the present disclosure is an aggregate of multi-walled carbon nanotubes comprising multi-walled carbon nanotubes having a maximum length of 1000 μm to 30000 μm and Fe atoms, wherein the content ratio of Fe atoms to the total mass of the aggregate is 0.5 mass% or more and less than 10 mass%. The multi-walled carbon nanotube aggregate of the present disclosure can take the form of a sheet, a fiber, or the like. Here, a sheet-like aggregate means that an aggregate of multi-walled carbon nanotubes has a sheet-like form. Furthermore, a fibrous aggregate means that the multi-walled carbon nanotubes have a thread-like form. The fibrous aggregate may contain multi-walled carbon nanotubes in the form of a monofilament (single fiber), or may contain them in the form of a multi-filament, i.e., a thread in which a plurality of multi-walled carbon nanotube fibers are twisted together.

[0013] [Multi-walled Carbon Nanotubes] The multi-walled carbon nanotube aggregate of the present disclosure (hereinafter, sometimes simply referred to as the "aggregate of the present disclosure") includes multi-walled carbon nanotubes having a maximum length of 1000 μm to 30,000 μm. Hereinafter, "multi-walled carbon nanotubes having a maximum length of 1000 μm to 30,000 μm" may be abbreviated as "ULMWCNT." ULMWCNTs have a maximum length of 1000 μm to 30,000 μm, are longer than general-purpose MWCNTs, and can take the form of fibers. Herein, the term "fiber" is generally used to refer to a structure in which one dimension is larger than the other two dimensions. The fibers may be thread-like fibers with a circular cross section, ribbon-like fibers with a rectangular cross section, hollow, or have other shapes. From the viewpoint of increasing the electrical conductivity of the aggregate of the present disclosure, the ULMWCNT preferably has a circular cross section and is preferably hollow.

[0014] By taking on a fibrous shape, ULMWCNTs have the property of easily entangling with each other. The aggregate of the present disclosure preferably includes at least one ULMWCNT, and is an aggregate including a plurality of ULMWCNTs, from the viewpoint that the MWCNTs are likely to entangle with each other and form a more stable aggregate. Hereinafter, an aggregate including ULMWCNTs may be abbreviated as a "ULMWCNT aggregate." The aggregate of the present disclosure may also be an aggregate having a three-dimensional structure in which the ULMWCNTs are entangled with each other. FIG. 1 is a scanning electron microscope (SEM) photograph showing one embodiment of the aggregate of the present disclosure. The SEM photograph shown in FIG. 1 shows that multiple fibrous ULMWCNTs are entangled to form a sheet-like aggregate. In this way, the entangled state of the ULMWCNTs in the aggregate of the present disclosure can be confirmed by SEM observation.

[0015] The length of ULMWCNT can be measured by focusing on a single ULMWCNT and observing multiple SEM photographs taken at adjacent viewing angles. Here, "length" refers to the length of the ULMWCNT in the longitudinal direction, and the maximum value of the measured lengths is referred to as the "maximum length." When observing the SEM photograph as described above, if a single ULMWCNT with a maximum length in the range of 1,000 μm to 30,000 μm is observed within the viewing angle of the SEM photograph, it can be confirmed that the observed aggregate is the aggregate of the present disclosure.

[0016] As described above, it is preferable that a plurality of ULMWCNTs having a maximum length measured in the range of 1,000 μm to 30,000 μm are present within the viewing angle of the SEM photograph. Focusing on 100 MWCNTs included in the viewing angle of the SEM photograph using the above method, the maximum length of each is measured, and from the viewpoint of further improving the stability of the aggregate due to entanglement of ULMWCNTs, it is preferable that 10% or more, in terms of number, of the observed MWCNTs have a maximum length in the range of 1,000 μm to 30,000 μm, more preferably 20% or more, even more preferably 30% or more, and particularly preferably 50% or more.

[0017] The diameter of a ULMWCNT can be measured by observing an SEM photograph or a transmission electron microscope (TEM) photograph. Here, the diameter refers to the length in the direction perpendicular to the longitudinal direction of the ULMWCNT. The diameter is measured at 10 different locations on a single ULMWCNT, and the average value is taken as the diameter of that ULMWCNT.

[0018] The length of the ULMWCNT contained in the aggregate of the present disclosure is in the range of 1,000 μm to 30,000 μm, preferably in the range of 1,050 μm to 25,000 μm, more preferably in the range of 1,100 μm to 20,000 μm, even more preferably in the range of 1,200 μm to 18,000 μm, and particularly preferably in the range of 1,300 μm to 15,000 μm. The diameter of the ULMWCNT contained in the aggregate of the present disclosure is preferably 1 nm to 100 nm, more preferably 2 nm to 80 nm, even more preferably 3 nm to 50 nm, and particularly preferably 5 nm to 30 nm.

[0019] The length / diameter ratio of the ULMWCNT, or the so-called aspect ratio, is preferably 1,000 or more, more preferably 3,000 or more, even more preferably 5,000 or more, and particularly preferably 10,000 or more. The aspect ratio can be calculated from the ratio of the maximum length to the diameter of a single ULMWCNT. From the viewpoint of measurement accuracy, it is preferable to use the average value of the measurements of 20 or more ULMWCNTs.

[0020] From the viewpoint of dispersibility, the specific gravity of the ULMWCNT aggregate is preferably in the range of 1.5 to 2.5, more preferably in the range of 1.7 to 2.4, and even more preferably in the range of 1.8 to 2.2. The specific gravity of the ULMWCNT aggregate can be measured by the method described in JIS Z8807-2012 "Method for measuring density and specific gravity of solids."

[0021] The purity of the ULMWCNT aggregate as MWCNT can be measured by thermogravimetric analysis. For example, a thermogravimetric (TG) curve and a differential thermal analysis (DTA) curve of the ULMWCNT aggregate are obtained using a thermal analyzer (Shimadzu Corporation, DTG-60). The largest exothermic peak in the DTA curve, which has a peak top near 650°C to 750°C, is considered to be the combustion of MWCNT, and any other exothermic peaks are considered to be the combustion of substances other than MWCNT. The purity of the MWCNT is determined from the weight loss rate of the TG curve. From the viewpoint of the electrical conductivity of the resulting aggregate, the purity of the ULMWCNT aggregate is preferably 50% by mass or more, more preferably 65% ​​by mass or more, even more preferably 80% by mass or more, and particularly preferably 95% by mass or more.

[0022] ULMWCNT may contain 0.01% to 50% by mass of Fe atoms derived from the iron catalyst used during production. ULMWCNT may contain Fe atoms, for example, adsorbed on the surface of the ULMWCNT or incorporated into the fibrous ULMWCNT formed during production. The resulting fibrous ULMWCNT is preferably flexible and strong. Furthermore, the electrical conductivity of the ULMWCNT itself is 5000 Ω. －１ ・m －１ It is preferable that the resistance is 10,000Ω or more. －１ ・m －１ The electrical conductivity of the ULMWCNT itself is usually 1,000,000 Ω or more. －１ ・m －１ The following is the result.

[0023] There are no particular limitations on the method for producing the ULMWCNT contained in the aggregate of the present disclosure. Examples of methods that can be used for producing the ULMWCNT of the present disclosure include conventionally known chemical vapor deposition (CVD) methods and methods in which a gaseous reactant containing a carbon source is reacted in the presence of a catalyst.

[0024] The MWCNTs of the present disclosure can be produced, for example, by referring to the production method described in JP 2016-102047 A. An example of the production method for MWCNTs of the present disclosure will be described below. However, the production method for MWCNTs of the present disclosure is not limited to the following example.

[0025] An example of a method for producing ULMWCNT in the present disclosure is the method described in JP 2016-102047 A, i.e., a production method (hereinafter also referred to as "Production Method X") comprising the steps of passing gaseous reactants containing one or more carbon sources through a reactor, reacting the one or more gaseous reactants in a reaction zone of the reactor in the presence of a catalyst to form product particles containing carbon, aggregating the product particles into agglomerates, and applying force to the agglomerates to continuously move the agglomerates out of the reaction zone. Production Method X makes it possible to obtain MWCNTs containing ULMWCNT in the form of fibrous agglomerates or other agglomerate forms that are easy to handle.

[0026] In production method X, the force applied to the product particles may be a mechanical force. When the agglomerates include fibrous CNTs, the mechanical force applied to the product particles may be applied by a rotating spindle around which the agglomerates including the fibrous CNTs are wound. In this manner, the fibrous CNTs may be collected as an aggregate on the spindle, or after rotating around the spindle one or more times, the spindle may be continuously unwound and the fibrous CNT aggregates may be accumulated elsewhere.

[0027] The spindle is preferably oriented with its axis perpendicular or parallel to the direction of flow of the gaseous reagent(s), although the spindle axis may be oriented at other orientations, for example, a spindle with its axis oriented at an angle of 25° to the direction of gas flow may also be suitable for applying mechanical forces to the product particles.

[0028] The spindle can rotate about two axes, for example, two perpendicular axes. In particular, the spindle can rotate about axes perpendicular and parallel to the direction of flow of the gaseous reactants. Such a spindle can pull and twist the aggregates containing fibrous CNTs so that the twist number and length can be controlled.

[0029] The spindle may be made of a metal, ceramic, or resin material. The spindle may have a suitable shape depending on the properties of the material and the intended use of the ULMWCNT aggregate. The spindle may be used as a mold for producing a carbon product by a spin coating method, for example. The preferred shape of the spindle is a rod or box shape.

[0030] Fibrous MWCNTs are deposited on a spindle or elsewhere, and the coating thickness and orientation can be controlled by controlling the reaction time and conditions, or by the conditions under which an electric or other field is applied to the carbon product. The coating thickness and orientation of the carbon product can be controlled, for example, by gas flow forces.

[0031] The spindle rotation speed is preferably between 0.01 rpm (revolutions per minute; hereinafter the same) and 10,000 rpm, and more preferably between 0.1 rpm and 100 rpm. The spinning speed, i.e., the rotation speed of the spindle, may be adjusted so that the material is collected at the same rate as it is produced. The rotation speed may also control the thickness of the fibrous ULMWCNT aggregate. In a preferred embodiment, as the spindle rotates, the fibrous ULMWCNT aggregate is processed in the axial direction of the spindle. This processing means that the fibrous ULMWCNT is evenly wrapped around the spindle, rather than being stacked in only one position on the spindle. The formation of an aggregate by the accumulation of fibrous ULMWCNT may also be achieved by other means used in fiber technology.

[0032] The aggregates of fibrous ULMWCNT may be collected, for example, on the reactor wall by a substrate placed in the reactor. The substrate may be a fixed substrate or a rotating guide used to apply a strong and uniform force to the ULMWCNT as it is collected. Suitable substrate configurations for fiber technology include a substrate consisting of two guides positioned perpendicular to each other.

[0033] In manufacturing method X, the mechanical force applied to the product particles may be a force applied by an accelerating gas flow. The accelerating gas flow may be generated by passing the product particles through a reactor having a narrow diameter or through a capillary tube downstream of the reaction zone. A vacuum may be applied to the product particles.

[0034] Other forces that can be applied to the product particles include electrostatic forces, suitably applied by a charged plate. Electrostatic forces require that the product particles be charged. The use of a charged plate allows the MWCNTs to form entangled mats on the charged plate.

[0035] Other forces applied to the product particles may also be magnetic forces or photon pressure applied by a light source.

[0036] Instead of a gaseous reactant containing a carbon source, the CNT source may be injected in the form of a liquid containing a carbon source. When a liquid is used as the CNT source, it can be injected through a single inlet or multiple inlets, for example, in a showerhead configuration.

[0037] Preferably, the gaseous reactant or reactants are reacted at a temperature between 500° C. and 1600° C., more preferably between 1000° C. and 1500° C. or 1600° C. (especially between 1000° C. and 1500° C.). A temperature gradient is preferably maintained within the reactor, with the reaction zone being maintained at a higher temperature than the product zone of the reactor.

[0038] The gaseous reactants may be mixed with one or more gases that act as diluents. The gaseous reactants may also be mixed with gases that play a supporting role in the reaction, but do not play a direct role in the reaction. For example, a gas may be used as a diluent to react with the amorphous carbon by-product, thereby keeping reactive sites on the catalyst available for nanotube production.

[0039] Examples of gases that can be used as diluents include argon or other inert gases, hydrogen, nitrogen, ammonia, carbon dioxide, and helium. Among these, hydrogen is particularly preferred as a gas that can be used as a diluent. The flow rate of the gas used as a diluent is preferably 2000 mL (milliliters) / min or less, and more preferably 400 mL / min to 800 mL / min.

[0040] The gas pressure of the gaseous reactants and any diluents is preferably between 0.1 bar and 50 bar, more preferably between 0.5 bar and 5 bar, and even more preferably between 1 bar and 2 bar. If there is a gas effluent from the furnace, the effluent gas can be recycled with or without cleaning.

[0041] By monitoring the agglomerated product and modifying the reaction conditions according to the information obtained, the composition of the product can be controlled. For example, the product can be monitored by online Raman spectroscopy. For carbon nanotubes, data can be obtained indicating the single-walled or multi-walled nature of the nanotubes, their diameter, and their crystallinity. The product can also be monitored by online conductivity measurements, gas analysis, monitoring the opacity of the reaction zone, and / or monitoring the winding force. The reaction conditions can be modified by an operator or automatically.

[0042] When the agglomerate is removed from the reactor, it is preferable to prevent air from entering the reactor. When the diluent gas contains hydrogen, preventing air from entering the reactor is particularly important, for example, from the viewpoint of preventing an explosive mixture of hydrogen and air from forming in the reactor.

[0043] The product particles in the above production method include ULMWCNTs. Depending on the production conditions, they may also contain single-walled carbon nanotubes in addition to multi-walled carbon nanotubes. Fibrous ULMWCNTs may also be produced by chemical vapor deposition, in which a gaseous reactant, a carbon source, is reacted in the presence of a catalyst.

[0044] Examples of carbon-containing compounds suitable as carbon sources include carbon monoxide, carbon dioxide, aromatic hydrocarbons (e.g., benzene, toluene, xylene, cumene, ethylbenzene, naphthalene, or mesitylene), non-aromatic hydrocarbons (e.g., methane, ethane, propane, butane, pentane, hexane, cyclohexane, ethylene, propylene, or acetylene), and oxygen-containing hydrocarbons (e.g., formaldehyde, acetaldehyde, acetone, methanol, ethanol, diethyl ether, polyethylene glycol, 1-propanol, ethyl formate, and hydrocarbons containing mixtures of two or more thereof). Preferred carbon-containing compounds are carbon monoxide, methane, ethylene, or acetylene.

[0045] Preferably, the carbon source contains oxygen. Ethanol is a particularly preferred carbon source. Oxygen can be introduced into the reactor by other methods, such as by using a diluent gas or a carbon source containing water.

[0046] The gaseous reactant, which is a carbon source, is preferably injected into the reactor at a rate of 0.01 mL / min to 10 mL / min, more preferably 0.08 mL / min to 0.25 mL / min.

[0047] The catalyst is preferably a transition metal, particularly a Group VIB transition metal such as chromium (Cr), molybdenum (Mo), tungsten (W), or a Group VIIIB transition metal. Specifically, the catalyst may be, for example, iron (Fe), cobalt (Co), nickel (Ni), ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), platinum (Pt), or manganese (Mn), or a mixture thereof. Metals from the lanthanide and actinide series (e.g., yttrium (Y)) may also be used as catalysts. Fe, Ni, Co, Mo, and mixtures thereof, such as a 50 / 50 mixture of Ni and Co, a mixture of Fe and Ni, or a mixture of Fe and Mo, are more preferred. Any of these transition metals, alone or in combination with any of the other transition metals listed, may serve as a catalyst for CNT growth. It is particularly preferred that the catalyst is a mixture of two or more of the metals listed.

[0048] The catalyst is preferably formed by decomposition of a precursor. The precursor is preferably a thermally, photo-, or plasma-decomposable compound of one or more of the above metals, such as a carbonyl or cyclopentadienyl organometallic compound. Ferrocene, iron pentacarbonyl, nickelocene, and cobaltocene are particularly preferred precursors. Suitably, at least 0.01% by weight of the precursor is contained in the carbon source, and preferably 0.2% to 2.5% by weight of the precursor is contained in the carbon source. In one embodiment, 0.23% to 2.3% by weight of the precursor is contained in the carbon source. The catalyst may be supported on a carrier. Preferred carriers include silica and magnesium oxide.

[0049] The carbon source is preferably reacted in the presence of a promoter. Suitable promoters include one or more of sulfur, phosphorus, molybdenum, and organic compounds of these elements. Thiophene is one of the preferred promoters. Suitably, up to 10% by weight (10% by weight or less) of the promoter is contained in the carbon source. Preferably, 0.2% to 6% by weight of the promoter is contained in the carbon source. When a high or low concentration of thiophene is used as the promoter, MWCNTs are formed. For example, MWCNTs are successfully formed using ethanol containing 0% by weight or 1.5% to 4.0% by weight of thiophene and 1.0% to 10.0% by weight (particularly 2.3% by weight) of ferrocene, with an injection rate of 5.0 mL / hour to 30.0 mL / hour (particularly 7.5 mL / hour), a hydrogen flow rate of 400 mL / min to 800 mL / min, and a synthesis temperature of 1100°C to 1180°C.

[0050] According to production method X, fibrous CNTs having a length of at least 500 μm, for example, at least 1 mm, can be obtained. The fibrous CNTs can take the form of threads or mats. The length of the fibrous CNTs can be controlled, for example, by the winding capacity of the spindle used to produce the fibrous CNTs.

[0051] Production method X preferably includes the steps of reacting a carbon source in a reaction zone of a reactor to produce CNTs, and aggregating the CNTs into aggregates by applying force to the CNTs. According to this production method, a fibrous CNT aggregate can be easily produced.

[0052] Another embodiment may include producing ULMWCNTs in a reaction zone by the above method, agglomerating the ULMWCNTs to form the aggregate, and continuously withdrawing the aggregate from near the reaction zone. Another embodiment may include producing ULMWCNTs in a reaction zone, continuously electrostatically withdrawing the ULMWCNTs from the reaction zone, and recovering the ULMWCNTs as the aggregate.

[0053] The above manufacturing method X is an example, and the manufacturing method of MWCNTs including ULMWCNTs is not limited to the above.

[0054] [Fe Atoms] The aggregate of the present disclosure contains Fe atoms, and the Fe atom content ratio relative to the total mass of the aggregate is 0.5% by mass or more and less than 10% by mass. ULMWCNT contain carbon and are expected to be electrically conductive. However, when ULMWCNT are produced in the presence of a catalyst containing metal atoms such as Fe, there is a concern that Fe atoms derived from the catalyst will be contained in the ULMWCNT, resulting in a decrease in electrical conductivity. Therefore, conventionally, after production of ULMWCNT, the ULMWCNT is washed with acid to remove Fe atoms and other metal atoms. However, according to the studies of the present inventors, when ULMWCNT having a maximum length of 1,000 μm to 30,000 μm are included, the maximum length of the CNT is within the above range, and the Fe atom content ratio relative to the total mass of the aggregate is 0.5% by mass or more and less than 10% by mass, thereby maintaining the electrical conductivity of the aggregate and further improving dispersibility in a dispersion medium.

[0055] The content ratio of Fe atoms relative to the total mass of the aggregate of the present disclosure is 0.5 mass% or more and less than 10 mass%, preferably more than 1.0 mass% and less than 10 mass%, more preferably 1.2 mass% to 9.5 mass%, even more preferably 1.5 mass% to 9 mass%, particularly preferably 2 mass% to 8 mass%, and especially preferably 3 mass% to 7 mass%.

[0056] The content ratio of Fe atoms relative to the total mass of the aggregate can be measured, for example, by the following method. The aggregate of the present disclosure is completely dissolved in an acid such as hydrochloric acid or nitric acid. In order to completely dissolve the aggregate of the present disclosure in acid, pretreatment such as dry ashing, wet ashing, or melting treatment may be performed. The content ratio of Fe atoms can be measured by performing inductively coupled plasma atomic emission spectroscopy (ICP-AES) or inductively coupled plasma mass spectrometry (ICP-MS) on a solution in which the aggregate of the present disclosure is completely dissolved in acid. ICP-MS is preferably used because it allows for more sensitive measurements.

[0057] As described above, ULMWCNT may contain 0.01% by mass to 50% by mass of Fe atoms derived from the iron catalyst used during production. ULMWCNT may contain Fe atoms, for example, adsorbed on the surface of the ULMWCNT or incorporated into the fibrous ULMWCNT formed during production. That is, in the present disclosure, the Fe atoms contained in the aggregate may include Fe atoms derived from the catalyst used in the production of multi-walled carbon nanotubes. In the aggregate of the present disclosure, taking into account the content of catalyst-derived Fe atoms contained in the ULMWCNT, it is preferable to adjust the Fe atom content ratio to the total mass of the aggregate to the desired value within a range of 0.5% by mass or more and less than 10% by mass. It goes without saying that if the content ratio of catalyst-derived Fe atoms to the total mass of the aggregate is the desired content ratio, no particular measures for adjusting the Fe atom content ratio are required.

[0058] When the content ratio of Fe atoms relative to the total mass of the aggregate is 10% by mass or more, the content ratio of Fe atoms relative to the total mass of the aggregate can be adjusted to less than 10% by mass by using a known method, for example, washing the aggregate with water, acid, or an acid aqueous solution (e.g., a 1% by mass to 37% by mass aqueous solution of hydrochloric acid, particularly a 35% by mass aqueous solution) to wash and remove some of the Fe atoms. When the content ratio of Fe atoms relative to the total mass of the aggregate is less than 0.5% by mass, the content ratio of Fe atoms relative to the total mass of the aggregate can be adjusted to 0.5% by mass or more by immersing the aggregate in a 1% by mass to 46% by mass (particularly about 5% by mass) aqueous solution of iron nitrate or a 1% by mass to 47% by mass (particularly about 40% by mass) aqueous solution of iron chloride as a source of Fe atoms, thereby adsorbing Fe atoms onto the surface of the fibrous ULMWCNT.

[0059] The mechanism of action related to the improvement of conductivity and dispersibility in the aggregate of the present disclosure is not clear, but is thought to be as follows. However, the following speculation is not intended to limit the interpretation of the aggregate of the present disclosure, but is explained as an example. When known short-length CNTs contain Fe atoms, the presence of the Fe atoms narrows the contact points between them, making it difficult to connect conductive paths, resulting in a problem of reduced conductivity.

[0060] The ULMWCNTs contained in the aggregates of the present disclosure have a maximum length in the range of 1,000 μm to 30,000 μm, which increases the contact areas between them and makes them more susceptible to aggregation. Here, when an appropriate amount of Fe atoms are attached to the surface of the ULMWCNT, the Fe atoms contained in the aggregate moderately inhibit contact between multiple ULMWCNTs, thereby suppressing aggregation and improving dispersibility. Suppressing aggregation of ULMWCNTs generally reduces electrical conductivity. However, since the ULMWCNTs contained in the aggregates of the present disclosure have a maximum length in the range of 1,000 μm to 30,000 μm, a sufficient contact area is ensured even when aggregation is suppressed by the presence of Fe atoms, which is thought to achieve both improved dispersibility and good electrical conductivity. In ULMWCNTs with an Fe atom content of 10% by mass or more, the presence of the Fe atoms narrows the contact points between the ULMWCNTs, making it difficult to connect conductive paths and reducing conductivity. Furthermore, in ULMWCNTs with an Fe atom content of less than 0.5% by mass, the presence of the Fe atoms does not function to suppress aggregation, and the contact points widen, resulting in good conductivity but reduced dispersibility.

[0061] When the content of Fe atoms relative to the total mass of the aggregate of the present disclosure is within the above range, the specific gravity of the ULMWCNT aggregate increases slightly due to the presence of Fe atoms. For example, if the content ratio of Fe atoms in the aggregate is 5 mass%, the specific gravity is approximately 2.2. When the aggregate of the present disclosure is used as a conductive additive (described below), the specific gravity of graphite, which is the carbon material in the electrode, is 2.2, and the specific gravity of Ketjen black is 2.7. Therefore, by increasing the specific gravity of the aggregate due to Fe atoms, the difference in specific gravity with the carbon material is reduced, resulting in the additional effect of improving dispersibility in the carbon material. The method for measuring the specific gravity of the aggregate is as described in the section on multi-walled carbon nanotubes.

[0062] <Multi-walled carbon nanotube aggregate: Second embodiment> A second embodiment of the multi-walled carbon nanotube aggregate of the present disclosure includes multi-walled carbon nanotubes having a tensile strength of 10 MPa to 100 MPa and Fe atoms, and the content ratio of Fe atoms to the total mass of the aggregate is 0.5 mass% or more and less than 10 mass%.

[0063] A second embodiment of the multi-walled carbon nanotube aggregate of the present disclosure is an aggregate of multi-walled carbon nanotubes including multi-walled carbon nanotubes having a tensile strength of 10 MPa to 100 MPa and Fe atoms, wherein the content ratio of Fe atoms to the total mass of the aggregate is 0.5 mass% or more and less than 10 mass%.

[0064] In the present disclosure, "tensile strength" is measured with reference to the tensile test described in the ISO 527-1 standard. The tensile strength of the multi-walled carbon nanotubes according to the second embodiment of the present disclosure refers to a value measured in a tensile state such as a sheet or fiber. When the aggregate of multi-walled carbon nanotubes is in a sheet form, a measurement sample is cut from the sheet-like aggregate to a size of 75 mm x 10 mm, which is fixed to the grip of a tensile testing machine (Shimadzu Corporation, Autograph AGS-X series), and a tensile test is performed at a speed of 1 mm / min. The breaking strength at which the measurement sample breaks is defined as the tensile strength. When the multi-walled carbon nanotubes are in a filament form, a measurement sample is cut from a fibrous multi-walled carbon nanotube to a length of 500 mm, which is fixed to the grip of a tensile testing machine (Shimadzu Corporation, Autograph AGS-X series), and a tensile test is performed at a speed of 1 mm / min using a thin-wire grip (Shimadzu Corporation), and the breaking strength at which the measurement sample breaks is defined as the tensile strength. When the sheet-like measurement sample does not satisfy the above-mentioned size, or when the thread-like measurement sample does not satisfy the above-mentioned length, the measurement sample is used as is to measure the tensile strength.

[0065] The tensile strength of the multi-walled carbon nanotubes according to the present disclosure is preferably 10 MPa or more and 100 MPa or less, more preferably 30 MPa or more and 85 MPa or less, and even more preferably 50 MPa or more and 70 MPa or less. When the tensile strength of the multi-walled carbon nanotubes is 50 MPa or more, the maximum length of the multi-walled carbon nanotubes is sufficient, making it easier to ensure the electrical conductivity of the multi-walled carbon nanotubes. When the tensile strength of the multi-walled carbon nanotubes is 70 MPa or less, less force is required when pulverizing the sheet-like or fibrous multi-walled carbon nanotubes as needed, making it easier to perform the pulverization process, which is a post-processing step that is performed as needed.

[0066] The multi-walled carbon nanotubes having a tensile strength of 10 MPa to 100 MPa according to the present disclosure can be crushed as needed by, for example, freeze crushing. The freeze crushing method is a processing method in which, whether the aggregate of multi-walled carbon nanotubes is in the form of a sheet or fiber, the aggregate is rapidly cooled with liquid nitrogen to eliminate the elasticity of the multi-walled carbon nanotubes and facilitate crushing. Alternatively, crushing may be performed by a known crushing method such as a ball mill.

[0067] The aggregate of multi-walled carbon nanotubes contains Fe atoms, and the content ratio of Fe atoms to the total mass of the aggregate is 0.5 mass% or more and less than 10 mass%. In a second embodiment of the aggregate of the present disclosure, the content ratio of Fe atoms to the total mass is 0.5 mass% or more and less than 10 mass%, preferably more than 1.0 mass% and less than 10 mass%, more preferably 1.2 mass% to 9.5 mass%, even more preferably 1.5 mass% to 9 mass%, particularly preferably 2 mass% to 8 mass%, and especially preferably 3 mass% to 7 mass%. Unless otherwise specified, "aggregate of the present disclosure" refers to the aggregate of the first embodiment of the present disclosure.

[0068] <Method for manufacturing aggregate according to the present disclosure> The aggregate according to the present disclosure can be obtained by adjusting the Fe atom content ratio relative to the total mass of an aggregate containing ULMWCNT obtained by the manufacturing method described above to a range of 0.5 mass% or more and less than 10 mass%. The method for adjusting the Fe atom content ratio is as described above. First, the Fe atom content ratio attributable to the reaction catalyst in the aggregate containing ULMWCNT is measured, and then the Fe atom content ratio can be adjusted by removing or further adsorbing the Fe atoms in consideration of the content ratio. If the Fe atom content ratio in the aggregate containing ULMWCNT is within the target value range, there is no need to particularly adjust the Fe atom content ratio.

[0069] <Physical Properties of the Assembly of the Present Disclosure> 1. Rsp Value The assembly of the present disclosure preferably has an Rsp value with respect to the dispersion medium of 300 to 10,000, more preferably 500 to 7,000, even more preferably 1,000 to 5,000, and particularly preferably 3,500 to 4,500. The Rsp value is a measure of affinity with respect to the dispersion medium and can be measured by pulsed nuclear magnetic resonance (pulse NMR) method. Pulse NMR method allows measurement without diluting the dispersion liquid and does not approximate the shape of the dispersoid to a sphere, making it suitable for measuring the affinity of a dispersion such as the assembly of the present disclosure with respect to the dispersion medium. When the Rsp value of the assembly of the present disclosure with respect to the dispersion medium is within an appropriate range, it can be determined that the dispersibility of the assembly of the present disclosure with respect to the dispersion medium is good. The Rsp value is determined by measuring the relaxation time T ２ｓ and the relaxation time T measured by putting only the dispersion medium in the test tube. ２ｂ By comparing the above, it can be calculated using the following formula: Rsp = (T ２ｂ / T ２ｓ )-1

[0070] 2. Viscosity As described above, the aggregate of the present disclosure has a high affinity for the dispersion medium, and therefore the viscosity of the dispersion tends to be low. When the viscosity of the dispersion is in an appropriate range, it can be determined that the dispersibility of the aggregate of the present disclosure in the dispersion medium is good. When the shear rate of the dispersion is 1 s －１The viscosity at this time is preferably 0.1 Pa·s to 4.8 Pa·s, more preferably 0.5 Pa·s to 4.5 Pa·s, and even more preferably 1.0 Pa·s to 4.2 Pa·s. －１ The viscosity at each shear rate is preferably 0.001 Pa·s to 0.11 Pa·s, more preferably 0.005 Pa·s to 0.1 Pa·s, and even more preferably 0.01 Pa·s to 0.09 Pa·s. The viscosity at each shear rate can be obtained by rheometer measurement. For example, the shear rate dependency of viscosity can be evaluated using a viscoelasticity measuring device (MCR302, manufactured by Anton Paar) under the following measurement conditions. Measurement jig: cone plate Measurement mode: rotational mode Shear rate: 0.01 s －１ ~1000s －１ Temperature: 25°C From the obtained data, the viscosity at the following shear rate is read: Shear rate = 1 s －１ Shear rate = 100s －１

[0071] 3. Electrical Conductivity The aggregate of the present disclosure has good electrical conductivity because its main component is carbon. The electrical conductivity of the aggregate of the present disclosure can be determined from its volume resistivity. When the volume resistivity measured under the following conditions is lower than a predetermined value, the polymer of the present disclosure can be determined to have good electrical conductivity. The electrical conductivity of the aggregate of the present disclosure calculated from the volume resistivity is 1.5 × 10 －２ It is preferably Ω cm or less, and 1.0 × 10 －５ Ω・cm~1.2×10 －２ More preferably, it is 5.0×10 －５ Ω・cm~1.0×10 －２ More preferably, it is 1.0×10 －４ Ω・cm~9.9×10 －３ It is particularly preferable that the resistivity is Ω·cm.

[0072] The volume resistivity of the aggregate of the present disclosure is measured by a four-probe method at 25°C using a resistivity meter. A Loresta apparatus can be used as the resistivity meter. Specifically, using a Loresta apparatus (product names: powder resistivity measurement system MCP-PD51, low resistivity meter Loresta-GP, low resistance probe for powder MCP-PD511 (constant current application type four-probe method), all manufactured by Nitto Seiko Analytech Co., Ltd.), the multi-walled carbon nanotube aggregate is introduced into a powder resistivity measurement probe unit, and pressed at 5 kN using the attached hydraulic pump. After the target load is reached, the volume resistivity (Ω cm) is measured. If pulverization of the aggregate is necessary to measure the volume resistivity of the aggregate of the present disclosure, for example, a freeze-pulverization method can be used, as described above. Alternatively, pulverization may be performed using a known pulverization method such as a ball mill.

[0073] The volume resistivity of the aggregate of the present disclosure can also be calculated from the surface resistance value measured by the following method. The surface resistance value of the ULMWCNT aggregate is measured using a resistivity test by the four-probe method in accordance with JIS K 7149-1994, using a Loresta EP MCP-T360 (manufactured by Dia Instruments Co., Ltd.). The volume resistivity is calculated by multiplying the surface resistance value obtained by the four-probe method by the film thickness of the aggregate. The conductivity of the aggregate is calculated from the obtained volume resistivity. The film thickness of the aggregate of the present disclosure can be measured using a thickness gauge with two circular horizontal plates in accordance with ISO Method A, a thickness measurement method in JIS L 1913-2010 "General Nonwoven Fabric Testing Methods."

[0074] [Conductive Aid] As described above, the aggregate of the present disclosure has good electrical conductivity. Therefore, the aggregate of the present disclosure can be used as a conductive aid (preferably, a conductive aid for a negative electrode). A conductive aid coexists with a conductive material, such as a positive electrode active material or a negative electrode active material, and functions to further improve the conductivity of the conductive material. Because the aggregate of the present disclosure contains ULMWCNT, the aggregate of the present disclosure can be used as a conductive aid in addition to known conductive aids such as graphite and Ketjen Black for an active material serving as a conductive material. As described above, the aggregate of the present disclosure contains Fe atoms at a predetermined content ratio. Therefore, the specific gravity of the aggregate of the present disclosure tends to be slightly higher than that of an aggregate of ULMWCNT, which generally has a specific gravity in the range of 1.8 to 2.0. For example, when the content ratio of Fe atoms in the aggregate is 5 mass %, the specific gravity of the aggregate is about 2.2, which is smaller than the difference in specific gravity between the aggregate and graphite (specific gravity 2.2) and Ketjen black (specific gravity 2.7), which are carbonaceous materials used as conductive additives. In addition to the inherent dispersibility in the dispersion medium that the aggregate of the present disclosure has, the aggregate also has better dispersibility in the carbonaceous material used in combination.

[0075] An example of use as a conductive additive is, for example, when manufacturing a positive electrode of a battery, a positive electrode active material, the conductive additive which is the aggregate of the present disclosure, and a binder are mixed in a predetermined mass ratio, a solvent is added to the mixture to prepare a slurry, which is applied to a current collector for the positive electrode, dried, and stretched to produce a positive electrode.

[0076] Another example of the use as a conductive additive is, for example, when manufacturing a negative electrode of a battery, a negative electrode active material, the conductive additive which is the aggregate of the present disclosure, and a binder are mixed in a predetermined mass ratio, a solvent is added to the mixture to prepare a slurry, which is applied to a current collector for the negative electrode, dried, and stretched to produce a negative electrode.

[0077] Although the combination of the carbon material as the conductive material and the conductive additive that is the aggregate of the present disclosure has been described above, the use of the conductive additive of the present disclosure is not limited to the above.

[0078] When the assembly of the present disclosure is used as a conductive assistant, the content ratio can be any ratio relative to the total mass of the solid content of the material including the conductive material and the conductive assistant.

[0079] The assembly of the present disclosure may also be used as a conductive material. The conductive material of the present disclosure includes the above-described assembly of the present disclosure. The conductive material can be used as an electrode material, specifically, as a negative electrode active material or a positive electrode active material, in a battery, for example, a lithium ion battery.

[0080] <Multi-walled carbon nanotube dispersion> The aggregate of the present disclosure has good dispersibility and can therefore be suitably used as a dispersion. The multi-walled carbon nanotube dispersion of the present disclosure contains the aggregate of the present disclosure described above and a dispersion medium. Another multi-walled carbon nanotube dispersion of the present disclosure contains multi-walled carbon nanotubes having a tensile strength of 10 MPa to 100 MPa and a dispersion medium. These multi-walled carbon nanotube dispersions may be simply referred to as the dispersions of the present disclosure.

[0081] [Dispersion Medium] The dispersion medium that may be contained in the dispersion liquid of the present disclosure will be described.

[0082] The dispersion medium preferably contains water, and more preferably contains water as a main component. "Containing water as a main component" means that the proportion of water in the dispersion medium is more than 50% by mass. The proportion of water in the dispersion medium is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, and may be, for example, 100% by mass. The water is not particularly limited, but is preferably distilled water, ion-exchanged water, pure water, etc., in terms of having few impurities.

[0083] The dispersion medium may be a mixture of water and a hydrophilic solvent. Examples of the hydrophilic solvent include carbonate compounds such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and butylene carbonate; ether compounds such as tetrahydrofuran; ketone compounds such as acetone; lower alcohol compounds such as methanol and ethanol; and solvents such as acetonitrile. When the dispersion medium contains a hydrophilic solvent, the proportion of the hydrophilic solvent in the dispersion medium is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0084] The dispersion of the present disclosure may further contain other components that can be used in the dispersion in addition to the aggregate and dispersion medium of the present disclosure. Examples of other components include dispersants, antifoaming agents, antistatic agents, CNTs other than the ULMWCNTs of the present disclosure, and carbon materials other than CNTs. The dispersion may also contain trace amounts of impurity components, so-called unavoidable impurities.

[0085] [Dispersant] The dispersion of the present disclosure may contain a dispersant for the purpose of further improving the dispersibility and dispersion stability of the aggregate of the present disclosure. The dispersant is not particularly limited, and examples thereof include various surfactants. The dispersant also includes polymer compounds such as resins. The dispersant is preferably a surfactant. The surfactant may be an ionic surfactant or a nonionic surfactant, and is not particularly limited. The surfactant may be used alone or in combination of two or more types.

[0086] Examples of ionic surfactants include anionic surfactants, cationic surfactants, and amphoteric surfactants. Examples of anionic surfactants include aromatic sulfonic acid surfactants such as alkylbenzene sulfonates (e.g., dodecylbenzene sulfonate) and dodecylphenyl ether sulfonate; ether sulfate surfactants; phosphate surfactants; and carboxylic acid surfactants. Examples of cationic surfactants include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkylbetaine surfactants and amine oxide surfactants. Examples of ionic surfactants include ionic surfactants having an aromatic ring (so-called aromatic ionic surfactants), and more preferably aromatic sulfonic acid surfactants such as alkylbenzene sulfonates and dodecylphenyl ether sulfonates. Aromatic ionic surfactants tend to have excellent dispersibility, dispersion stability, and high concentration of multi-walled carbon nanotube aggregates.

[0087] Examples of nonionic surfactants include sugar ester surfactants such as sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters; fatty acid ester surfactants such as polyoxyethylene resin acid esters and polyoxyethylene fatty acid diethyl esters; ether surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkyl phenyl ethers, and polyoxyethylene-polypropylene glycols; and aromatic nonionic surfactants such as polyoxyalkylene octyl phenyl ether, polyoxyalkylene nonyl phenyl ether, polyoxyalkyl dibutyl phenyl ether, polyoxyalkyl styryl phenyl ether, polyoxyalkyl benzyl phenyl ether, polyoxyalkyl bisphenyl ether, polyoxyalkyl cumyl phenyl ether, and polyoxyalkylene phenyl ether. As nonionic surfactants, ionic surfactants having an aromatic ring (so-called aromatic nonionic surfactants) are preferred, polyoxyalkylene phenyl ether is more preferred, and polyoxyethylene phenyl ether is even more preferred. Aromatic nonionic surfactants tend to be excellent in dispersibility, dispersion stability, and concentration of multi-walled carbon nanotube aggregates.

[0088] Other dispersants that are excellent in dispersibility, dispersion stability, and concentration of multi-walled carbon nanotube aggregates include DEMOL (registered trademark: the same applies hereinafter) N, DEMOL RN, and DEMOL T (manufactured by Kao Corporation), which are sodium salts of β-naphthalenesulfonic acid formalin condensates; Brij S 100 (manufactured by Sigma-Aldrich), which are polyoxyethylene stearyl ethers; polyvinylpyrrolidone K30 (manufactured by, for example, Fujifilm Wako Pure Chemical Industries, Ltd.); carboxymethylcellulose (CMC) (manufactured by, for example, Daicel Miraize Co., Ltd.); sodium deoxycholate (manufactured by, for example, Fujifilm Wako Pure Chemical Industries, Ltd.); and SOLSPERSE ＴＭ W100, SOLSPERSE ＴＭ W150 (manufactured by Lubrizol Japan, Inc.) etc. CMC is particularly preferred from the viewpoint of excellent dispersibility, dispersion stabilization ability and high concentration of the aggregate of multi-walled carbon nanotubes.

[0089] When the dispersion liquid of the present disclosure contains a dispersant, the amount of the dispersant used is not particularly limited and can be set appropriately depending on the type of dispersant, the amount of the aggregate of multi-walled carbon nanotubes, the amount of the dispersion medium, and the like.

[0090] [Method for Producing Dispersion] The method for producing the dispersion of the present disclosure is not particularly limited. The dispersion of the present disclosure can be produced by dispersing the aggregate of the present disclosure in a dispersion medium. That is, the dispersion according to the present disclosure can be produced by a method including a step of dispersing the aggregate of multi-walled carbon nanotubes according to the present disclosure in a dispersion medium (also referred to as a "dispersion step"). The dispersion medium that can be used in the dispersion step is as described above.

[0091] The dispersion method is not particularly limited. Examples of the dispersion method include methods using dispersion devices such as a stirrer, homogenizer, colloid mill, flow jet mixer, dissolver, paint conditioner, Manton emulsifier, jet mill, and ultrasonic device. Examples of the dispersion method include methods using known pulverization means, such as ball milling (e.g., ball mill, vibration ball mill, planetary ball mill, bead mill, etc.), sand milling, colloid milling, jet milling, roller milling, vertical or horizontal agitator mill, attritor, colloid mill, three-roll mill, pearl mill, super mill, impeller, disperser, KD mill, dynatron, and pressure kneader. As a dispersion method, a method using a jet mill is preferred, and a method using a wet jet mill is more preferred. A wet jet mill is a dispersion device that pressure-feeds a mixture in a solvent as a high-speed flow from a nozzle arranged in a sealed pressure-resistant container. In a wet jet mill, aggregates of multi-walled carbon nanotubes are dispersed by collisions between countercurrent flows in a pressure-resistant container, collisions with the container wall, turbulence caused by high-speed flow, shear flow, etc. As the wet jet mill, an ultra-high pressure homogenizer (model number: NAGS20, NAGS100, NAGS200, NAGS1000, etc.) manufactured by Joko Co., Ltd. can be suitably used. However, the wet jet mill is not limited to this. When the ultra-high pressure homogenizer is used as the dispersing device, the processing pressure for dispersion is preferably 10 MPa to 250 MPa.

[0092] The method for producing a dispersion according to the present disclosure may include a step of drying the aggregate according to the present disclosure (also referred to as a "drying step") before the dispersion step. If moisture adheres to the multi-walled carbon nanotubes, the multi-walled carbon nanotubes tend to adhere to each other due to the surface tension of the water, which may result in a decrease in dispersibility. Therefore, by performing a drying step on the aggregate before the dispersion step, moisture adhered to the surfaces of the ULMWCNTs contained in the aggregate is removed, suppressing adhesion between the ULMWCNTs due to moisture adhesion, and further improving the dispersibility of the aggregate according to the present disclosure in the dispersion medium. The drying method is not particularly limited. Examples of drying methods include heat drying, vacuum drying, and heat vacuum drying. Heat vacuum drying is preferred as the drying method. The drying temperature is not particularly limited, and is preferably, for example, 40°C to 100°C. The drying time is not particularly limited, and can be set appropriately depending on the drying temperature, the degree of moisture adhesion to the aggregate according to the present disclosure, and the like.

[0093] [Applications of Dispersion] The dispersion of the present disclosure has good dispersibility of the aggregate of the present disclosure in a dispersion medium and excellent conductivity, and therefore can be used in a variety of applications. Examples of applications for the dispersion include conductive inks, antistatic agents, conductive materials for forming circuit patterns, materials for transparent electrodes, and water-soluble polymer fillers, and it is preferable to use it as a conductive ink. Among conductive inks, the dispersion of the present disclosure is preferably applied to an ink composition for forming a lithium battery anode. By using the dispersion of the present disclosure as an ink composition for forming a lithium battery anode, a lithium battery anode with good conductivity can be easily produced.

[0094] When the dispersion liquid of the present disclosure is applied to a conductive ink, the dispersion liquid can be produced in the same manner as the dispersion liquid of the present disclosure, except that the dispersion liquid further contains a viscosity modifier, an antioxidant, etc., which are components of the conductive ink.

[0095] One application of the assembly of the present disclosure is an electrode and a secondary battery containing the assembly of the present disclosure as a conductive additive. An electrode containing the conductive additive according to the present disclosure is excellent in forming a conductive path within the electrode. Therefore, a secondary battery containing the electrode has excellent cycle characteristics. The electrode may contain the conductive additive according to the present disclosure described above. The conductive additive contained in the electrode is the same as the conductive additive according to the present disclosure, and therefore, a description of the conductive additive will be omitted below. The electrode may be at least one of a positive electrode and a negative electrode. The electrode may include an electrode active material layer. The electrode may include a current collector and an electrode active material layer disposed on the current collector.

[0096] The current collector is not particularly limited as long as it does not induce chemical changes in the battery and is conductive. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, baked carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector.

[0097] The electrode active material layer may contain an electrode active material, which is preferably electrode active material particles.

[0098] When the electrode is a positive electrode, the electrode active material particles are not particularly limited and may include a positive electrode active material that is commonly used as an electrode material for a positive electrode. Specifically, the positive electrode active material may be, for example, lithium cobalt oxide (LiCoO ２ ), lithium nickel oxide (LiNiO ２ ), compounds substituted with one or more transition metals; LiFe ３ O ４ Lithium iron oxides such as those with the chemical formula Li １＋ｃ１ Mn ２－ｃ１ O ４ (0≦c1≦0.33), LiMnO ３ , LiMn ２ O ３ , LiMnO ２ Lithium manganese oxides such as lithium copper oxide (Li ２ CuO２ ); LiV ３ O ８ , V ２ O ５ , Cu ２ V ２ O ７ Vanadium oxides such as LiNi １－ｃ２ M ｃ２ O ２ (wherein M is at least one selected from the group consisting of Co, Mn, Al, Cu, Fe, Mg, B, and Ga, and satisfies 0.01≦c2≦0.66); Ni-site lithium nickel oxide represented by the chemical formula LiMn ２－ｃ３ M ｃ３ O ２ (wherein M is at least one selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ta, and satisfies 0.01≦c3≦0.1) or Li ２ Mn ３ MO ８ (wherein M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn ２ O ４ etc.

[0099] When the electrode is a negative electrode, the electrode active material is not particularly limited and may include a negative electrode active material commonly used for negative electrode materials. Specifically, the negative electrode active material may include graphite-based active material particles or silicon-based active material particles. The graphite-based active material particles may be one or more selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesocarbon microbeads. The use of artificial graphite can improve rate characteristics.

[0100] The silicon-based active material particles may be one or more selected from the group consisting of Si, SiOx (0<x<2), a Si-C composite, and a Si-Y alloy (wherein Y is an element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, Group 13 elements, Group 14 elements, rare earth elements, and combinations thereof). The use of silicon-based active material particles can increase the capacity of the battery.

[0101] The electrode active material layer may further contain a binder. The binder is not particularly limited and may contain binders commonly used in electrode materials. Examples of binders include at least one polymer selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber, and polyacrylic acid, as well as polymers in which the hydrogen atoms of these polymers have been substituted with Li, Na, Ca, or the like.

[0102] <Secondary Battery> The secondary battery may be configured to include a negative electrode, a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode is preferably an electrode according to the present disclosure, and the negative electrode is preferably an electrode according to the present disclosure.

[0103] The separator separates the negative electrode and positive electrode and provides a path for lithium ions to move. There are no particular limitations on the separator, as long as it is typically used as a separator in secondary batteries. The separator preferably has low resistance to ion migration of the electrolyte and excellent electrolyte humidification capacity. Specific examples of separators include porous polymer films. The porous polymer film may be, for example, a porous polymer film made from a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer, or a laminate structure comprising two or more layers of these films. The separator may also be a conventional porous nonwoven fabric, such as a nonwoven fabric made from high-melting-point glass fiber or polyethylene terephthalate fiber. To ensure heat resistance or mechanical strength, the separator may also be coated with a ceramic component or a polymeric substance. The separator may optionally have a single-layer or multi-layer structure.

[0104] Examples of the electrolyte include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in producing lithium ion secondary batteries.

[0105] Specifically, the electrolyte may contain a non-aqueous organic solvent and a metal salt. Examples of the non-aqueous organic solvent include aprotic organic solvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl propionate, and ethyl propionate.

[0106] Among carbonate organic solvents, cyclic carbonates such as ethylene carbonate and propylene carbonate are preferred as non-aqueous organic solvents because they are highly viscous organic solvents with high dielectric constants and good dissociation of lithium salts. It is more preferred to use a non-aqueous organic solvent in which such cyclic carbonates are mixed with linear carbonates with low viscosity and low dielectric constants, such as dimethyl carbonate and diethyl carbonate, in an appropriate ratio, since this allows the production of electrolytes with high electrical conductivity.

[0107] The metal salt may be a lithium salt. The lithium salt is a substance that is easily dissolved in a non-aqueous electrolyte solution. The anion portion of the lithium salt may be, for example, F － , Cl － , I － , NO ３ － , N (CN) ２ － , B.F. ４ － , ClO ４ － , P.F. ６ － , (CF ３ ) ２ PF ４ － , (CF３ ) ３ PF ３ － , (CF ３ ) ４ PF ２ － , (CF ３ ) ５ PF － , (CF ３ ) ６ P － , C.F. ３ SO ３ － , C.F. ３ CF ２ SO ３ － , (CF ３ SO ２ ) ２ N － , (FSO ２ ) ２ N － , C.F. ３ CF ２ (CF ３ ) ２ CO － , (CF ３ SO ２ ) ２ CH － , (SF ５ ) ３ C － , (CF ３ SO ２ ) ３ C － , C.F. ３ (CF ２ ) ７ SO ３ － , C.F. ３ CO ２ － , C.H. ３ CO ２ － , SCN － , and (CF ３ CF ２ SO ２ ) ２ N － One or more selected from the group consisting of:

[0108] In addition to the non-aqueous organic solvent and metal salt, which are the constituent components of the electrolyte, the electrolyte may further contain one or more additives such as a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dye, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving the life characteristics of the battery, suppressing a decrease in battery capacity, improving the discharge capacity of the battery, etc.

[0109] The above-described secondary battery can be configured into a battery module including the secondary battery as a unit cell, and a battery pack including the battery module. The battery module and the battery pack can be used as a power source for a medium- to large-sized device selected from the group consisting of an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.

[0110] <Composition> [Resin, Ceramics, Concrete, etc.] A composition according to the present disclosure is a composition comprising the aggregate according to the present disclosure and at least one selected from the group consisting of resin, ceramic, and concrete. Another composition according to the present disclosure is a composition comprising a multi-walled carbon nanotube aggregate containing multi-walled carbon nanotubes and Fe atoms, wherein the Fe atom content relative to the total mass of the aggregate is 0.5 mass% or more and less than 10 mass%, and at least one selected from the group consisting of a dispersion medium, resin, ceramic, and concrete. Examples of resins include thermoplastic resins and thermosetting resins, and preferred examples include olefin-based resins, polycarbonate-based resins, polyester-based resins, polyamide-based resins, thermoplastic polyurethane resins, polysulfone-based resins, and silicone resins. Examples of ceramics include crystalline ceramics and amorphous ceramics. Examples of concrete include Portland cement concrete. The composition according to the present disclosure may further contain other components such as water and organic solvents. In the composition according to the present disclosure, when the content of the aggregate according to the present disclosure is taken as 100 parts by mass, the content of at least one component selected from the group consisting of resin, ceramic, and concrete is typically 10 to 1,000,000 parts by mass, preferably 100 to 100,000 parts by mass, and more preferably 1,000 to 40,000 parts by mass. Furthermore, when other components are included, the content is preferably 1 to 10,000 parts by mass, and more preferably 10 to 1,000 parts by mass. In the composition according to the present disclosure, the aggregate according to the present disclosure, resin, ceramic, concrete, and other components may each be included singly or in combination of two or more types.

[0111] [Method for Producing Composition] The composition according to the present disclosure can be produced, for example, by mixing the aggregate according to the present disclosure with resin, ceramics, or pre-hardened concrete. The resin may be in the form of powder, pellets, solution, or dispersion. The ceramics may be in the form of powder, precursor solution, or dispersion. The composition according to the present disclosure can also be produced, for example, by dispersing the aggregate according to the present disclosure in a resin solution, a ceramic precursor or dispersion, or pre-hardened concrete, followed by molding.

[0112] [Uses of the Composition] When the composition according to the present disclosure contains a resin or ceramic, it is useful as, for example, a structural material, a conductive material, a heat management material, or an antistatic material. When the composition according to the present disclosure contains concrete, it is useful as a lightweight, durable building material or an electricity storage device (impregnated with an electrolyte as needed).

[0113] <Planar aggregate> The planar aggregate of the present disclosure includes the aggregate of multi-walled carbon nanotubes of the present disclosure. The content of the aggregate of multi-walled carbon nanotubes of the present disclosure contained in the planar aggregate of the present disclosure is usually 1 mass % or more with respect to the total mass of the planar aggregate. The planar aggregate of the present disclosure may include other components such as aggregates of carbon nanotubes having a maximum length of less than 1000 μm, particularly aggregates of multi-walled carbon nanotubes having a maximum length of less than 1000 μm.

[0114] [Method for Producing Planar Assembly] The method for producing the planar assembly according to the present disclosure is not particularly limited. The planar assembly according to the present disclosure can be produced, for example, as a nonwoven fabric-like planar assembly by dispersing the aggregate of multi-walled carbon nanotubes according to the present disclosure, or the aggregate of multi-walled carbon nanotubes according to the present disclosure and other components such as aggregates of multi-walled carbon nanotubes having a maximum length of less than 1000 μm, particularly aggregates of multi-walled carbon nanotubes having a maximum length of less than 1000 μm, in water or other fluid, and filtering once or twice or more times.

[0115] Some embodiments of the planar assembly of the present disclosure include, for example, a film.

[0116] The planar assemblies of the present disclosure are useful, for example, in filters, electromagnetic shields, and extreme ultraviolet (EUV) pellicles.

[0117] The aggregates and dispersions containing the aggregates of the present disclosure will be described in more detail below with reference to examples. The aggregates and dispersions of the present disclosure are not limited to the following examples as long as they are within the scope of the present disclosure. Unless otherwise specified, "%" means "% by mass."

[0118] Example 1 1. Production of Sheet-Like ULMWCNT Aggregate 1 Sheet-like ULMWCNT Aggregate 1 was produced by a floating catalyst method (CVD method) that directly interacts with the self-assembly of CNT bundles in the gas phase. First, ferrocene as a metal catalyst precursor containing Fe atoms and thiophene as a promoter were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled at 400°C to 700°C. A mixture of nitrogen and argon was used as the carrier gas. The flow rate of the carrier gas was 30,000 sccm (standard cubic centimeters per minute). By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor was produced as a particulate metal catalyst. The region where the metal catalyst was produced is referred to as the first temperature zone.

[0119] Next, methane, a carbon source, was released into the carrier gas stream. The metal catalyst and the carbon source were fed into a second temperature zone downstream of the first temperature zone, which was temperature-controlled at 1400°C. The second temperature zone was maintained at a temperature sufficient to produce carbon nanotube aggregates.

[0120] In the second temperature zone, an electric field was generated in the temperature-controlled flow reactor, thereby generating ULMWCNT aggregates. The aggregates were continuously discharged through the outlet of the flow reactor, which was temperature-controlled at 100°C to 500°C, and a sheet-like ULMWCNT aggregate was collected by continuous discharge. The obtained sheet-like ULMWCNT aggregate contained ULMWCNT and MWCNT. The obtained sheet-like ULMWCNT aggregate was washed with deionized water for 10 seconds to adjust the content ratio of Fe atoms, and sheet-like ULMWCNT aggregate 1 was obtained.

[0121] 2. Preparation of Dispersion 1 The following materials were mixed and pre-dispersed by processing for 1 hour with an Ace Homogenizer manufactured by Nippon Seiki Co., Ltd. to obtain pre-dispersion 1. Note that the sheet-like ULMWCNT aggregate 1 was cut into small pieces of about 1 cm x 1 cm with scissors before mixing so that the sheet-like ULMWCNT aggregate 1 would not become entangled with the blades of the homogenizer. (Dispersion composition) - Sheet-like ULMWCNT aggregate 1 obtained above 1.1 g - CARBOXYMETHYL CELLULOSE SODIUM SALT HIGH VISCOSITY (manufactured by MP Biomedicals) 1.65 g - Pure water 547.2 g Using an ultra-high pressure homogenizer (model number: NAGS100) manufactured by Joko Co., Ltd. as a wet jet mill, the pre-dispersion 1 was main-dispersed to obtain dispersion 1. Nozzle diameter: 0.22 mm Pressure: 85 MPa Number of times: 8 Method: Circulation method

[0122] 3. Evaluation 3-1. Content ratio of ULMWCNT with a maximum length of 1000 μm to 30000 μm First, when observing 100 MWCNTs in a plurality of adjacent SEM photographs (magnification: 5000x) of the sheet-like ULMWCNT aggregate 1 of Example 1 obtained above, the content ratio of ULMWCNT with a maximum length of 1000 μm to 30000 μm was 75%, and the maximum value of the maximum length of the 100 observed MWCNTs was 3500 μm.

[0123] 3-2. Content ratio of Fe atoms to the total mass of the aggregate Using an inductively coupled plasma mass spectrometry (ICP-MS) device (NexION 2000C, manufactured by PerkinElmer), the content ratio of Fe atoms contained in the sheet-like ULMWCNT aggregate 1 of Example 1 was measured. As a result of low-temperature ashing / acid dissolution of the sheet-like ULMWCNT aggregate 1 as a pretreatment and measurement with the above device, the content ratio of Fe atoms to the total mass of the aggregate in the sheet-like ULMWCNT aggregate 1 of Example 1 was 5.6 mass%.

[0124] 3-3. Rsp value The dispersion 1 obtained by dispersing the sheet-like ULMWCNT aggregate 1 of Example 1 by the above method was placed in a sample tube, and the relaxation time T ２ｓ In addition, pure water was placed in the sample tube, and the relaxation time T ２ｂ The Rsp value was calculated using the following formula: Rsp = (T ２ｂ / T ２ｓ )-1 The results are shown in Table 1.

[0125] The viscosity of Dispersion 1 was measured using a rheometer. Using a viscoelasticity measuring device (MCR302, manufactured by Anton Paar), the shear rate dependency of viscosity was evaluated under the following conditions: Measurement jig: cone plate Measurement mode: rotation mode Shear rate: 0.01 s －１ ~1000s －１ Temperature: 25°C From the obtained data, the viscosity was read at the following shear rates: Shear rate = 1 s －１ Shear rate = 100s －１ The results are shown in Table 1.

[0126] 3-5. Volume Resistivity The sheet-like ULMWCNT aggregate 1 of Example 1 was pulverized using a freeze-pulverization method. Using a Loresta device (product name: powder resistivity measurement system MCP-PD51, low resistivity meter Loresta-GP, low resistance probe for powder MCP-PD511 (constant current application type 4-probe method), all manufactured by Nitto Seiko Analytech Co., Ltd.), the pulverized sheet-like ULMWCNT aggregate 1 was introduced into a powder resistivity measurement probe unit, and pressed at 5 kN using an attached hydraulic pump, and after the target load was reached, the volume resistivity (Ω cm) was measured. As a result, the volume resistivity was 9.2 × 10 at 5 kN. －３ The value was Ω·cm.

[0127] 3-6. Tensile strength A measurement sample was obtained by cutting out the sheet-like ULMWCNT aggregate 1 of Example 1 to a size of 5 mm x 100 mm, and the sample was fixed to the grip of a tensile testing device (Shimadzu Corporation, Autograph AG-IS) and subjected to a tensile test at a speed of 1 mm / min. As a result, the tensile strength was 11.3 MPa.

[0128] (Example 2) 1. Production of fibrous ULMWCNT aggregate 2

[0129] Like the sheet-like ULMWCNT aggregate 1, the fibrous ULMWCNT aggregate 2 was also produced by the floating catalyst method (CVD method), which directly interacts with the self-assembly of CNT bundles in the gas phase. First, ferrocene as a metal catalyst precursor containing Fe atoms and thiophene as a promoter were introduced into a continuous flow of carrier gas in a once-through reactor whose temperature was controlled at 400°C to 700°C. A mixture of nitrogen and argon was used as the carrier gas. The flow rate of the carrier gas was 30,000 sccm. By maintaining the temperature in the once-through reactor within the above range, the metal catalyst precursor was produced as a particulate metal catalyst. The region where the metal catalyst was produced is referred to as the first temperature zone.

[0130] Next, methane, a carbon source, was released into the carrier gas stream. The metal catalyst and the carbon source were fed into a second temperature zone downstream of the first temperature zone, which was temperature-controlled at 1400°C. The second temperature zone was maintained at a temperature sufficient to produce carbon nanotube aggregates.

[0131] In the second temperature zone, an electric field was generated in the temperature-controlled flow reactor, thereby generating fibrous ULMWCNT aggregates. The aggregates were continuously discharged as carbon nanotube aggregates through an outlet of the flow reactor, which was temperature-controlled at 100°C to 500°C, and a fibrous ULMWCNT aggregate was collected by continuous discharge. The obtained fibrous ULMWCNT aggregate contained ULMWCNT and MWCNT. The obtained fibrous ULMWCNT aggregate was washed with deionized water for 10 seconds to adjust the content ratio of Fe atoms, and a fibrous ULMWCNT aggregate 2 was obtained.

[0132] 2. Preparation of Dispersion 2 Using the obtained fibrous ULMWCNT aggregate 2, dispersion 2 was obtained in the same manner as in Example 1. However, the fibrous ULMWCNT aggregate 2 was cut with scissors to a length of about 1 cm before mixing so that the fibrous ULMWCNT aggregate 2 would not become entangled with the blades of the homogenizer.

[0133] 3. Evaluation In measuring the tensile strength, the fibrous ULMWCNT aggregate 2 of Example 2 was cut to a length of 100 mm, fixed to the gripping portion of a tensile testing device (Shimadzu Corporation, Autograph AG-IS), and a tensile test was performed at a speed of 1 mm / min using a thin-wire grip (Shimadzu Corporation). Except for this, evaluation was performed in the same manner as in Example 1 for the fibrous ULMWCNT aggregate 2 and dispersion 2 of Example 2. The results are shown in Table 1.

[0134] (Comparative Example 1) 1. Production of Sheet-like ULMWCNT Aggregate 3 The sheet-like ULMWCNT aggregate collected in Example 1 was immersed in a polytetrafluoroethylene (PTFE) tray containing hydrochloric acid (special grade reagent, manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) for 24 hours. Thereafter, the sheet-like ULMWCNT aggregate was taken out of the tray and washed with deionized water until the pH of the washing water reached 7, thereby obtaining a sheet-like ULMWCNT aggregate 3.

[0135] 2. Preparation of Dispersion 3 Dispersion 3 was obtained in the same manner as in Example 1 using the sheet-like ULMWCNT aggregate 3 obtained in Comparative Example 1.

[0136] 3. Evaluation The sheet-like ULMWCNT aggregate 3 and dispersion liquid 3 of Comparative Example 1 were evaluated in the same manner as in Example 1. The results are shown in Table 1. The results are shown in Table 1.

[0137] (Comparative Example 2) 1. Preparation of powdered MWCNT aggregate 1 As the powdered MWCNT aggregate 1, "multi-walled carbon nanotubes" (catalog number: FT7000, manufactured by C-nano Co., Ltd.) was prepared.

[0138] 2. Preparation of Dispersion 4 Dispersion 4 was obtained in the same manner as in Example 1 using the powdered MWCNT1 of Comparative Example 2.

[0139] 3. Evaluation In measuring the tensile strength, the dispersion 4 was poured onto a 22 mm × 75 mm × 3 mm slide-type silicon plate (Dosaka EM Co., Ltd., #08-1044), heated to 100°C and dried to prepare a measurement sample, which was then fixed to the gripping portion of a tensile testing device (Shimadzu Corporation, Autograph AG-IS) and subjected to a tensile test at a speed of 1 mm / min. Except for this, evaluation was performed in the same manner as in Example 1 on the powdered MWCNT aggregate 1 of Comparative Example 2 and the dispersion 4. The results are shown in Table 1.

[0140] (Comparative Example 3) 1. Preparation of powdered MWCNT aggregate 2 As the powdered MWCNT aggregate 2, "multi-walled carbon nanotubes" (catalog number: FT6120, manufactured by C-nano Co., Ltd.) was prepared.

[0141] 2. Preparation of Dispersion Liquid 5 Using the powdered MWCNT aggregate 2 of Comparative Example 3, dispersion liquid 5 was obtained in the same manner as in Example 1.

[0142] 3. Evaluation In measuring the tensile strength, the dispersion 5 was poured onto a 22 mm × 75 mm × 3 mm slide glass type silicon plate (Dosaka EM Co., Ltd., #08-1044), heated to 100°C and dried to prepare a measurement sample, which was fixed to the gripping portion of a tensile testing device (Shimadzu Corporation, Autograph AG-IS) and subjected to a tensile test at a speed of 1 mm / min. Except for this, evaluation was performed in the same manner as in Example 1 on the powdered MWCNT aggregate 2 of Comparative Example 3 and the dispersion 5. The results are shown in Table 1.

[0143] (Comparative Example 4) 1. Preparation of Powdered SWCNT Aggregate 1 As the powdered SWCNT aggregate 1, "single-walled carbon nanotubes" (catalog number: TUBALL, manufactured by OCSiAl) were prepared.

[0144] 2. Preparation of Dispersion Liquid 6 Dispersion liquid 6 (trade name: TUBALL) was prepared as a dispersion liquid of powdered SWCNT aggregate 1 of Comparative Example 4. ＴＭ BATT H ２ The CNT concentration was adjusted to 0.2 mass %.

[0145] 3. Evaluation In measuring the tensile strength, dispersion 6 was poured onto a 22 mm x 75 mm x 3 mm slide glass type silicon plate (Dosaka EM Co., Ltd., #08-1044), heated to 100°C and dried to prepare a measurement sample, which was then fixed to the gripping portion of a tensile testing device (Shimadzu Corporation, Autograph AG-IS) and subjected to a tensile test at a speed of 1 mm / min. Except for this, evaluation was performed in the same manner as in Example 1 on the powdered SWCNT aggregate 1 of Comparative Example 4 and dispersion 6. The results are shown in Table 1.

[0146]

[0147] As shown in Table 1, the sheet-like ULMWCNT aggregate 1 (Example 1) and the fibrous ULMWCNT aggregate 2 (Example 2) of the examples are ULMWCNT aggregates that have the property of easily entangling with each other, and therefore have high conductivity, and since the content ratio of Fe atoms is 0.5 mass% or more and less than 10 mass%, the Rsp value of the obtained dispersion was high, affinity with the dispersion medium was good, and viscosity showed a value that does not pose a practical problem. From this, it can be seen that the aggregates of the examples have high conductivity and good dispersibility in the dispersion medium.

[0148] On the other hand, the sheet-like ULMWCNT aggregate 3 (Comparative Example 1) of the comparative example, in which the content ratio of Fe atoms is less than 0.5 mass%, is a ULMWCNT aggregate that has the property of easily entangled with one another, and therefore has high conductivity. However, since the contact between multiple ULMWCNTs is not adequately inhibited by the Fe atoms and aggregation is not suppressed, the Rsp value of the obtained dispersion is low, there is a problem with affinity to the dispersion medium, and the viscosity, particularly at a shear rate of 100 s －１ It can be seen that the value of is high and at a level that is problematic in practical use. Therefore, it can be seen that the dispersibility in the dispersion medium is inferior to the aggregates of the Examples. It can be seen that the powdered MWCNT aggregate 1 (Comparative Example 2) and powdered MWCNT aggregate 2 (Comparative Example 3) of the comparative examples have a short maximum length and poor entanglement properties, and therefore low conductivity. Furthermore, because the entanglement properties are poor, aggregation of MWCNTs is unlikely to occur, and regardless of the content ratio of Fe atoms, the Rsp value of the obtained dispersion is low, there is a problem with affinity with the dispersion medium, and the viscosity is low, which is at a level that is problematic in practical use. It can be seen that the powdered SWCNT aggregate 1 (Comparative Example 4) of the comparative example is SWCNT, and therefore has high conductivity compared to MWCNT. However, SWCNTs tend to aggregate more strongly than MWCNTs, and even if the Fe atom content is increased to 10.0 mass% or more, SWCNT aggregation is not suppressed. As a result, the Rsp value of the resulting dispersion is low, there are problems with its affinity with the dispersion medium, and the viscosity value is high, which is at a level that is problematic for practical use.

Claims

1. A multi-walled carbon nanotube aggregate comprising: multi-walled carbon nanotubes having a maximum length of 1,000 μm to 30,000 μm; and Fe atoms, the content of the Fe atoms being 0.5 mass % or more and less than 10 mass % relative to the total mass of the aggregate.

2. The aggregate of multi-walled carbon nanotubes according to claim 1, which is a conductive assistant.

3. A multi-walled carbon nanotube dispersion liquid comprising the multi-walled carbon nanotube aggregate according to claim 1 or 2 and a dispersion medium.

4. A conductive material comprising the multi-walled carbon nanotube aggregate according to claim 1 or 2.

5. The multi-walled carbon nanotube dispersion according to claim 3, which is an ink composition for forming a negative electrode of a lithium battery.

6. An electrode comprising an electrode active material and the conductive material according to claim 4.

7. A secondary battery comprising the electrode according to claim 6.

8. A composition comprising the aggregate of multi-walled carbon nanotubes according to claim 1 or 2, and at least one material selected from the group consisting of resin, ceramics and concrete.

9. A multi-walled carbon nanotube aggregate comprising: multi-walled carbon nanotubes having a tensile strength of 10 MPa to 100 MPa; and Fe atoms, the Fe atom content being 0.5 mass% or more and less than 10 mass% relative to the total mass of the aggregate.

10. The aggregate of multi-walled carbon nanotubes according to claim 9, which is a conductive assistant.

11. A multi-walled carbon nanotube dispersion liquid comprising the multi-walled carbon nanotube aggregate according to claim 9 or 10 and a dispersion medium.

12. A conductive material comprising the multi-walled carbon nanotube aggregate according to claim 9 or 10.

13. The multi-walled carbon nanotube dispersion according to claim 11, which is an ink composition for forming a negative electrode of a lithium battery.

14. An electrode comprising an electrode active material and the conductive material of claim 12.

15. A secondary battery comprising the electrode according to claim 14.

16. A composition comprising the aggregate of multi-walled carbon nanotubes according to claim 9 or 10, and at least one material selected from the group consisting of resin, ceramics, and concrete.

17. A composition comprising a multi-walled carbon nanotube aggregate, the multi-walled carbon nanotube aggregate containing multi-walled carbon nanotubes and Fe atoms, wherein the Fe atom content relative to the total mass of the aggregate is 0.5 mass% or more and less than 10 mass%, and at least one material selected from the group consisting of a dispersion medium, a resin, a ceramic, and a concrete.

18. A multi-walled carbon nanotube dispersion comprising multi-walled carbon nanotubes having a tensile strength of 10 MPa to 100 MPa and a dispersion medium.

19. A planar aggregate comprising the multi-walled carbon nanotube aggregate according to claim 1, claim 2, claim 9 or claim 10.

20. A filter using the planar assembly according to claim 19.

21. An electromagnetic wave shield using the planar assembly according to claim 19.

22. A pellicle for extreme ultraviolet rays using the planar assembly according to claim 19.

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