JP5663855B2 - Conductive composite and negative electrode for lithium ion battery. - Google Patents

Description

  The present invention relates to a conductive composite containing fine particles, a conductivity imparting agent, and a dispersant. More specifically, the present invention relates to a conductive composite containing fine particles, a conductivity imparting agent, and a dispersant, and a negative electrode for a lithium ion battery containing the same.

  With the development of communication systems, electronic devices such as notebook computers and mobile phones are becoming more portable and cordless, and their performance is improving year by year. Along with the improvement in performance of such mobile electronic devices, high integration is required in the supply of power sources that satisfy the high power consumption of those electronic devices and the mounting of electronic information materials.

  As an electric power source for electronic devices, improvement of high energy density, high output, etc. is strongly desired. Lithium ion batteries have been developed as batteries that satisfy these requirements and have been widely used since the 1990s. However, with the recent improvement in performance of mobile electronic devices, demands for the charge / discharge capacity and charge / discharge cycle characteristics of lithium ion batteries have become stronger.

In order to improve these characteristics, it has been studied from various aspects such as battery constituent materials such as electrode active materials and electrolytes and battery structure design, and representative examples thereof include a conductivity imparting agent that is an electrode material. .
Since it is necessary to charge and discharge a large amount of current in order to increase the capacity of a lithium ion battery, a negative electrode material having a low electrical resistance of the electrode, that is, a high conductivity is required.

  Patent Document 1 discloses a conductive composite of particles including a double-walled carbon nanotube dispersion and a conductive material. However, when a single particle is simply added to a carbon nanotube dispersion, a non-uniform conductive composite having a structure in which carbon nanotubes adhere to particle aggregates may be obtained. Moreover, the dispersing agent which has disperse | distributed carbon nanotube may be redistributed on the particle | grain surface, and may cause aggregation of a carbon nanotube. Therefore, even when a double-walled carbon nanotube dispersion is used, the double-walled carbon nanotubes may aggregate and localize without covering the particle surface, and the conductivity inherent to the double-walled carbon nanotubes in the composite may be present. It may not be expressed. In addition, if the content of carbon nanotubes, which is a conductivity-imparting agent, is too high, the various properties of the particles are impaired, so the composition ratio of the particles to the carbon nanotubes is also important in order to effectively bring out the properties as a composite material. is there.

  In addition, in high integration, connection terminals with fine pitches can be connected by an anisotropic conductive material that performs connection by interposing conductive particles between the electrodes. Until now, metal fine particles such as gold and silver have been used for such conductive particles, but these have higher specific gravity than binder resin, and they settle or disperse uniformly in the conductive paste. However, there is a drawback that the connection is not reliable. In order to eliminate the above drawbacks, there is a strong demand for a conductive material having conductive particles having a specific gravity smaller than that of metal fine particles and high conductivity.

  In order to meet such demands, a conductive composite of insulating particles such as organic polymers and a conductivity imparting agent has been developed. In Patent Document 2, single-walled carbon nanotubes and two-layered carbon nanotubes are formed on the surface of organic polymer particles. Conductive particles having a conductive fiber layer such as single-walled carbon nanotubes are disclosed. Usually, micro-order and nano-order substances have the property of agglomerating, but the dispersibility of the conductive fiber layer on the surface of these particles is not particularly mentioned, and there is also a process of dispersing conductive fibers when preparing conductive particles. Since it does not exist, it is considered that the conductive fibers are present on the particle surface in an entangled and aggregated state. In such a state, the conductivity of the conductive fibers cannot be sufficiently exhibited.

JP 2009-149516 A JP 2006-54066 A

  This invention is made | formed in view of the above situations, and it aims at providing the electroconductive composite_body | complex which the electroconductivity imparting agent disperse | distributed with the dispersing agent coat | covers the surface of microparticles | fine-particles. Another object of the present invention is to provide a negative electrode for a lithium ion battery using the conductive composite.

That is, this invention consists of the following structures.
[1] A conductive composite containing fine particles containing at least one selected from carbon, silicon and tin having an average particle size of 1000 μm or less, a conductivity imparting agent and a dispersant, and satisfying the following conditions:
(1) The carbon nanotube aggregate in which the conductivity-imparting agent contains carbon nanotubes.
(2) When the carbon nanotube aggregate is observed with a transmission electron microscope, the outer diameter of 50 or more of the 100 is 1 to 6 nm.
(3) The conductivity imparting agent dispersed by the dispersant coats the surface of the fine particles.
(4) The conductivity imparting agent in the conductive composite is 0.1 to 20% by weight.
[2] The conductive composite according to [1], wherein the proportion of the double-walled carbon nanotubes contained in the carbon nanotube aggregate is 50% or more.
[3] The volume resistivity of the carbon nanotube aggregate is 1 × 10 ⁻⁵ Ω · cm to 1 × 10 ⁻² Ω · cm, according to any one of [1] or [2] Conductive composite.
[4] Any one of [1] to [3], wherein the height ratio (G / D ratio) of the G band and the D band according to Raman spectroscopic analysis at a wavelength of 532 nm of the aggregate of carbon nanotubes is 30 or more The conductive composite according to 1.
[5] The conductive composite according to any one of [1] to [4], wherein the aggregate of carbon nanotubes is previously oxidized.
[6] The conductive composite as described in [5], wherein the oxidation treatment is a firing treatment within a range of the combustion temperature peak of the carbon nanotube aggregate ± 50 ° C.
[7] A negative electrode for a lithium ion battery, comprising the conductive composite according to any one of [1] to [6].

  According to the present invention, a conductive composite having high conductivity can be provided by coating the surface of particles with a conductivity imparting agent dispersed by a dispersant. In addition, by dispersing the conductivity-imparting agent in the conductive composite, the addition amount of the conductivity-imparting agent can be suppressed to a small amount, and the conductivity imparted sufficient conductivity without impairing various characteristics of the fine particles. A complex can be provided. Furthermore, a highly conductive negative electrode for a lithium ion battery can be provided by using the conductive composite of the present invention.

FIG. 1 shows a state in which the catalyst exists uniformly in the cross section of the reaction tube. FIG. 2 is a schematic view of the fluidized bed apparatus used in Production Example 1. FIG. 3 is a high-resolution transmission electron micrograph of the carbon nanotubes obtained in Production Example 1. FIG. 4 is a Raman spectroscopic analysis chart of the carbon nanotubes obtained in Production Example 1. FIG. 5 is a scanning photomicrograph of the conductive composite obtained in Example 1. 6 is a scanning micrograph of the conductive composite obtained in Example 2. FIG. FIG. 7 is a scanning micrograph of the conductive composite obtained in Comparative Example 1.

The conductive composite of the present invention contains fine particles of 1000 μm or less, a conductivity imparting agent and a dispersant, and satisfies the following conditions:
(1) The carbon nanotube aggregate in which the conductivity-imparting agent contains carbon nanotubes.
(2) When the carbon nanotube aggregate is observed with a transmission electron microscope, the outer diameter of 50 or more of the 100 is 1 to 6 nm.
(3) The conductivity imparting agent dispersed by the dispersant coats the surface of the fine particles.
(4) The conductivity imparting agent in the conductive composite is 0.1 to 20% by weight.

[Conductivity imparting agent]
As the conductivity-imparting agent, an aggregate of carbon nanotubes including thin carbon nanotubes having an outer diameter of 1 to 6 nm of 50 or more out of 100 when observed with a transmission electron microscope can be used. Since the aggregate of carbon nanotubes has a small diameter, the linearity is good and the carbon nanotubes are not easily entangled with each other. A carbon nanotube with a large diameter has a structure in which a tube is crushed and bent, and it is difficult to disperse because it is easy to have a complex entangled structure. In general, the larger the diameter of a carbon nanotube, the easier it is to form a carbon nanotube with a lot of defects in the bent part or the graphite layer. Since such a carbon nanotube does not easily interact with the dispersant, the dispersibility and dispersion stability tend to decrease. is there. Therefore, thin carbon nanotubes are superior in dispersibility and electrical conductivity than multi-walled carbon nanotubes and vapor grown carbon fibers. In particular, a double-walled carbon nanotube with a small diameter is preferable because it is more rigid than a single-walled carbon nanotube. Furthermore, the aggregate of carbon nanotubes comprising double-walled carbon nanotubes is superior in durability to single-walled carbon nanotubes having the same degree of conductivity, and has a graphite structure even when dispersed by applying external force such as ultrasonic waves. Since there are relatively few defects, it is preferable as a conductivity imparting agent. In addition to the double-walled carbon nanotubes, the conductivity-imparting agent may contain carbon-based materials such as single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon nanofibers, carbon nanohorns, carbon nanocoils, graphite, and carbon black.

  The outer diameter of the carbon nanotube aggregate is preferably 1 to 6 nm. In the present invention, when the carbon nanotube aggregate measured by the above method is observed with a transmission electron microscope, the outer diameter of 50 or more of 100 is 1 to 6 nm. As the diameter of the carbon nanotube becomes thinner, the linearity increases, the contact resistance caused by the entanglement of the carbon nanotubes can be suppressed, and the conductivity tends to be higher. More preferably, the number is 1 to 5 nm. Particularly preferably, the number is from 1 to 3 nm. The measurement of the outer diameter of the carbon nanotube is performed as follows. The carbon nanotube aggregate is observed with a transmission electron microscope at a magnification at which the number of layers can be seen, printed on A4 size paper so that the 10 nm scale is 3 cm or more, and has a viewing area of 10 in a 75 nm square field of view. The outer diameter is measured and evaluated for 100 carbon nanotubes arbitrarily extracted from a field of view in which at least% is a carbon nanotube aggregate. When 100 lines cannot be measured in one field of view, measurement is performed from a plurality of fields until 100 lines are obtained. At this time, one carbon nanotube is counted as one if a part of the carbon nanotube is visible in the field of view, and both ends are not necessarily visible. In addition, even if it is recognized as two in the field of view, it may be connected outside the field of view and become one, but in that case, it is counted as two.

  The surface of the fine particles in the conductive composite of the present invention is coated with a conductivity imparting agent dispersed by a dispersant. When the conductivity-imparting agent is present in an aggregated state, the electric resistance is biased in the composite, and in some cases, the conductivity of the composite as a whole is reduced. On the other hand, if the conductivity-imparting agent is present in a dispersed state in the composite and covers the surface of the fine particles, there will be no bias in electrical resistance in the composite, and there will be no adverse effect of lowering the conductivity. . Dispersion here refers to a mixture of bundles of various thicknesses from one to the other, even if the carbon nanotubes in the aggregate of carbon nanotubes are loosened one by one or several are gathered together to form a bundle. Even if it is present, it is expressed as being dispersed if it is evenly dispersed in the composite. Further, it is not necessary that the particle surface is completely covered, and it is sufficient that the particle surface is covered to such an extent that a conductive path can be formed between the particles. For example, it may be a degree covered with a conductivity imparting agent in a mesh shape.

  The method of coating the surface of the fine particles with the conductivity-imparting agent is performed as follows. A dispersion in which fine particles are dispersed in a dispersant and a dispersion medium and a dispersion in which a conductivity imparting agent is dispersed in a dispersant and a dispersion medium are respectively prepared, and each dispersion is mixed to thereby disperse the conductivity imparting agent. A conductive composite in which the particle surface is uniformly coated can be obtained. At this time, when either the fine particles or the conductivity-imparting agent is mixed in a powder form instead of as a dispersion, or when the fine particles and the conductivity-imparting agent are dry-mixed, the dry mixture is mixed with the dispersant and the dispersion medium. In the case of preparing a dispersion by adding from the above, fine particles or conductivity imparting agent is not dispersed, and a non-uniform conductive composite having a structure in which the conductivity imparting agent is attached to the fine particle aggregate can be obtained, It is considered that a conductive composite having a structure in which the conductivity-imparting agent aggregate and the fine particle aggregate are localized is obtained. Therefore, in order to obtain the conductive composite of the present invention, it is preferable to prepare a dispersion of fine particles or a conductive composite and to mix the dispersion.

  The surface state of the particles coated with the conductivity-imparting agent can be observed using a scanning microscope (SEM). Regarding the coating of the particles with the conductivity-imparting agent, 20% or more of the surface area of the portion shown in the image of one particle among the 50 arbitrarily selected particles observable from the SEM image is the conductivity-imparting agent. It is preferable that the number of invisible particles is 30 or more, more preferably 40 or more. More preferably, the conductive composite is composed of 40 or more particles in which 25% or more of the surface area of the portion of the image of one particle is invisible by the conductivity-imparting agent. As a method for calculating the surface area in which the particles are coated with the conductivity-imparting agent, for example, there is a method for quantitatively calculating an SEM image using image processing software. In addition, when the analysis of the SEM image by image processing software is difficult, the preferable coating form can be evaluated by the coating state of the conductivity imparting agent on the particle surface of the SEM image. SEM is used to observe the conductivity-imparting agent on the particle surface, and is printed on A4 size paper so that the 1 μm scale is 4.5 cm or more. The conductivity-imparting agent on the particle surface uniformly distributes the particle surface. It is preferable that the coating is performed and the conductivity imparting agent is arranged so that a current flows. The state in which the particle surface is uniformly coated as described above does not require that the entire surface of the particle is covered with the conductivity-imparting agent, and the conductivity-imparting agent is observed with the same probability at any location on the particle surface. For example, the conductivity-imparting agent may be arranged in a mesh form on the particle surface. More preferably, the carbon nanotubes are not present alone, but are in the form of covering the particle surface in contact with other carbon nanotubes, and it is preferable that 30 or more of such particles are present. More preferably, the number is 40 or more.

  The addition amount of the conductivity-imparting agent in the conductive composite of the present invention is 0.1 to 20% by weight. If the addition amount is less than 0.1 wt%, the conductivity imparting effect to the composite by the conductivity imparting agent is insufficient, and if the addition amount exceeds 20 wt%, the conductivity imparting effect is sufficient, Various properties of the fine particles are impaired. Therefore, the addition amount of the conductivity-imparting agent is preferably 0.1 to 20% by weight, and more preferably 0.1 to 10% by weight.

  When the aggregate of carbon nanotubes is observed with a transmission electron microscope, it is preferable that 50 or more of 100 carbon nanotubes are double-walled carbon nanotubes. More preferably, 60 or more of 100 carbon nanotubes are double-walled carbon nanotubes. The carbon nanotube is observed as follows. The carbon nanotube aggregate is observed with a transmission electron microscope at a magnification at which the number of layers can be seen, printed on A4 size paper so that the 10 nm scale is 3 cm or more, and has a viewing area of 10 in a 75 nm square field of view. Evaluation is made on 100 carbon nanotubes arbitrarily extracted from the field of view in which at least% is an aggregate of carbon nanotubes. When 100 lines cannot be measured in one field of view, measurement is performed from a plurality of fields until 100 lines are obtained. At this time, one carbon nanotube is counted as one if a part of the carbon nanotube is visible in the field of view, and both ends are not necessarily visible. In addition, even if it is recognized as two in the field of view, it may be connected outside the field of view and become one, but in that case, it is counted as two.

The volume resistivity of the carbon nanotube aggregate is preferably 1 × 10 ⁻⁵ Ω · cm to 1 × 10 ⁻² Ω · cm, and the lower the volume resistivity of the carbon nanotube aggregate, the more conductive the composite is. Since the imparting effect is high, it is more preferably 1 × 10 ⁻⁴ Ω · cm to 1 × 10 ⁻² Ω · cm.

  The volume resistivity can be calculated by preparing a carbon nanotube film as follows, measuring the surface resistance value of the film by the four-terminal method, and then multiplying the surface resistance value by the film thickness of the carbon nanotube film. The surface resistance value can be measured by, for example, Loresta EP MCP-T360 (manufactured by Dia Instruments Co., Ltd.) using a 4-terminal 4-probe method according to JISK7149. When measuring high resistance, it can be measured using Hiresta UP MCP-HT450 (manufactured by Dia Instruments, 10V, 10 seconds).

  Carbon nanotubes (20 mg) are mixed with N-methylpyrrolidone (16 mL), an ultrasonic homogenizer is irradiated with ultrasonic waves at an output of 20 W for 20 minutes, mixed with ethanol (10 mL), and a filter with an inner diameter of 35 mmφ is obtained. However, instead of collecting the filtered material at this point, the filtered material and the filter used for filtering can be dried at 60 ° C. for 2 hours. The produced carbon nanotube film can be measured by peeling it from the filter paper with tweezers, etc. If it cannot be peeled off, measure the total thickness of the filter and carbon nanotube film together, and then subtract the thickness of the filter alone from the whole. You may do it. The filter for filtration used for filtration can use a membrane filter (OMINIPOREMBRANE FILTERS, FILTER TYPE: 1.0 μm JA, 47 mmφ). In addition, the diameter of the filter may be 1.0 μm or less as long as the filtrate can pass through, but it must be made of a material that does not dissolve in NMP and ethanol, and preferably a filter made of fluororesin (PTFE) is used. It is preferable to do this.

The quality of the carbon nanotube aggregate can be evaluated by the Raman spectroscopic analysis method. Although there are various laser wavelengths used in the Raman spectroscopic analysis method, 532 nm is used here. The Raman shift observed in the vicinity of 1590 cm ⁻¹ in the Raman spectrum is called a graphite-derived G band, and the Raman shift observed in the vicinity of 1350 cm ⁻¹ is called a D band derived from defects in amorphous carbon or graphite. The height ratio between the G band and the D band is expressed as a G / D ratio. A carbon nanotube aggregate having a higher G / D ratio has a higher degree of graphitization and higher quality. The higher the Raman G / D ratio is, the better, but if it is 30 or more, it can be said to be a high-quality carbon nanotube aggregate. The higher the Raman G / D ratio, the better. However, the upper limit of the G / D ratio is substantially about 200 at most. The G / D ratio is preferably 40 or more and 200 or less, more preferably 50 or more and 150 or less. In addition, solid Raman spectroscopy such as carbon nanotubes may vary depending on sampling. Therefore, it is preferable to perform Raman spectroscopic analysis at three different locations. The Raman G / D ratio is preferably expressed by taking its arithmetic average.

  The carbon nanotube aggregate is preferably subjected to an oxidation treatment before being used as a conductivity-imparting agent. Examples of the oxidation treatment include baking treatment in the gas phase, and the temperature of the oxidation treatment in the gas phase is preferably 300 to 1000 ° C, more preferably 400 to 900 ° C. Since the oxidation temperature of the carbon nanotube aggregate in the gas phase is affected by the atmospheric gas, the particularly preferable temperature varies depending on the atmosphere. The carbon nanotubes contained mainly differ depending on whether they are single-walled or multi-walled. Specifically, for example, when contacting with oxygen, it is preferably performed at 400 to 900 ° C. Particularly, in the case of a carbon nanotube aggregate mainly composed of two or more multi-walled carbon nanotubes, it is preferable to perform a firing treatment in the range of the combustion peak temperature of the carbon nanotube aggregate ± 50 ° C. in the atmosphere. By performing the calcination treatment in the range of the combustion peak temperature ± 50 ° C., it is possible to remove impurities in the produced carbon nanotube aggregate. Thereby, it is possible to improve the purity of the multi-walled carbon nanotubes such as two-layers. At this time, even if the firing treatment is performed at a combustion peak temperature of less than −50 ° C., the single-walled carbon nanotubes having low impurities and heat resistance are difficult to be fired. It is difficult to improve. Further, even if the firing treatment is performed at a combustion peak temperature + 50 ° C. or higher, all of the produced carbon nanotube aggregates are fired and disappear. Therefore, it is preferable to fire near the combustion peak temperature of the carbon nanotube aggregate. More preferably, it is the range of the combustion peak temperature ± 30 ° C. When a mixed gas such as oxygen and an inert gas is used as the gas phase, it is preferable that the oxidation treatment is performed at a relatively low temperature when the oxygen concentration is high and at a relatively high temperature when the oxygen concentration is low.

  The combustion peak temperature of the carbon nanotube aggregate can be measured by thermal analysis of the carbon nanotube aggregate in the atmosphere. About 10 mg of sample is placed in a differential thermal analyzer (for example, DTG-60 manufactured by Shimadzu Corporation) and heated from room temperature to 900 ° C. at a temperature increase rate of 10 ° C./min in the air. It is possible to determine the exothermic peak temperature.

  The case where the single-walled carbon nanotube is mainly used is also the same as above, but the condition is selected so that the target single-walled carbon nanotube does not disappear and impurities can be removed.

  The reaction conditions can be adjusted by increasing the firing time when the firing temperature is low, and shortening the firing time when the firing temperature is high. This is preferable in that the effect of the invention is more remarkably exhibited. Therefore, the firing time is not particularly limited as long as the carbon nanotube of the present invention is obtained. The firing time is preferably 5 minutes to 24 hours, more preferably 10 minutes to 12 hours, and even more preferably 30 minutes to 5 hours. Firing is preferably performed in the air, but may be performed in an oxygen / inert gas with a controlled oxygen concentration. The oxygen concentration at this time is not particularly limited. Oxygen may be appropriately set in the range of 0.1% to 100%. As the inert gas, helium, nitrogen, argon or the like is used.

  The oxidation treatment can also be performed by a method in which oxygen or a mixed gas containing oxygen is intermittently brought into contact with the carbon nanotubes to perform the firing treatment. When firing is performed by intermittently contacting oxygen or a mixed gas containing oxygen, the treatment can be performed at a relatively high temperature. This is because, since oxygen or a mixed gas containing oxygen is intermittently flowed, even if oxidation occurs, the reaction stops immediately when oxygen is consumed. When the baking treatment is performed in the air, the temperature range is preferably about 500 to 1200 ° C, more preferably about 600 to 950 ° C. As described above, the temperature is about 500 to 1200 ° C. during the production of carbon nanotubes. Therefore, when the firing process is performed immediately after the production of the carbon nanotube, it is preferable to perform such an intermittent firing process.

  The method for producing a carbon nanotube aggregate is not limited as long as the carbon nanotube aggregate defined in the present invention is obtained. For example, the carbon nanotube aggregate is produced as follows.

  In the vertical fluidized bed reactor, a fluidized bed made of powdered catalyst with iron supported on magnesia is formed on the entire horizontal cross-sectional direction of the reactor, and methane is circulated in the vertical direction in the reactor. After the carbon nanotube aggregate is produced by contacting with the catalyst at 500 to 1200 ° C., the resulting carbon nanotube aggregate is obtained by oxidation treatment. That is, a carbon nanotube aggregate that can be used particularly preferably in the present invention can be obtained by sufficiently oxidizing the carbon nanotube aggregate containing carbon nanotubes obtained by the above-described carbon nanotube synthesis method in the gas phase. .

  By supporting iron, which is a catalyst, on magnesia, which is a carrier, it is easy to control the particle size of iron, and sintering does not easily occur at high temperatures even when iron is present at a high density. Therefore, a high quality carbon tube can be efficiently synthesized in large quantities. Furthermore, since magnesia dissolves in an acidic aqueous solution, both the magnesia and iron can be removed simply by treating with an acidic aqueous solution, so that the purification process can be simplified.

As magnesia, a commercially available product may be used, or a synthesized product may be used. As a preferable production method of magnesia, magnesium metal is heated in air, magnesium hydroxide is heated to 850 ° C. or higher, and magnesium carbonate 3MgCO ₃ .Mg (OH) ₂ .3H ₂ O is heated to 950 ° C. or higher. There are methods.

  Among magnesias, light magnesia is preferable. Light magnesia is magnesia with a small bulk density, specifically 0.20 g / mL or less is preferable, and 0.05 to 0.16 g / mL is preferable from the viewpoint of fluidity of the catalyst. . Bulk density is the mass of powder per unit bulk volume. The bulk density measurement method is shown below. The bulk density of the powder may be affected by the temperature and humidity at the time of measurement. The bulk density referred to here is a value measured at a temperature of 20 ± 10 ° C. and a humidity of 60 ± 10%. For the measurement, a 50 mL graduated cylinder is used as a measurement container, and the powder is added so as to occupy a predetermined volume while tapping the bottom of the graduated cylinder. When measuring the bulk density, 10 mL of powder is added. However, if there is a shortage of measurable samples, the amount is as close to 10 mL as possible. Then, after dropping the bottom of the graduated cylinder from the height of 1 cm on the floor 20 times, the change rate of the volume value occupied by the powder is within ± 0.2 mL (± 2% when there are few samples). Is confirmed, and the stuffing operation is terminated. If there is a visual change in the volume value that exceeds ± 0.2 mL (± 2%), add the powder while tapping the bottom of the graduated cylinder, and drop the graduated cylinder from the height of 1 cm on the floor again. This is repeated 20 times, and it is confirmed that there is no change exceeding ± 0.2 mL (± 2%) in the volume value occupied by the powder, and the operation is finished. The determination of the weight of a certain amount of powder packed by the above method is repeated three times, and the value obtained by dividing the average weight by the volume occupied by the powder (= weight (g) / volume (mL)) is the bulk density of the powder. To do.

  The iron supported on the carrier is not always in a zero-valent state. Although it can be estimated that the metal is in a zero-valent state during the reaction, it may be a compound containing iron or an iron species. For example, organic salts or inorganic salts such as iron formate, iron acetate, iron trifluoroacetate, iron iron citrate, iron nitrate, iron sulfate, and iron halide, complex salts such as ethylenediaminetetraacetic acid complex and acetylacetonate complex, etc. Used. Iron is preferably fine particles. The particle diameter of the fine particles is preferably 0.5 to 10 nm. When iron is a fine particle, a carbon nanotube with a small outer diameter is likely to be generated.

  The method for supporting iron on magnesia is not particularly limited. For example, magnesia is impregnated in a non-aqueous solution (for example, ethanol solution) or an aqueous solution in which an iron salt to be supported is dissolved, sufficiently dispersed and mixed by stirring or ultrasonic irradiation, and then dried (impregnation method). Furthermore, iron may be supported on magnesia by heating at a high temperature (300 to 1000 ° C.) in a gas selected from air, oxygen, nitrogen, hydrogen, an inert gas, and a mixed gas thereof or in a vacuum.

  The larger the amount of iron supported, the higher the yield of carbon nanotubes. However, if the amount is too large, the particle diameter of iron increases, and the resulting carbon nanotubes become thicker. When the amount of iron supported is small, the particle size of the supported iron becomes small and carbon nanotubes with a thin outer diameter can be obtained, but the yield tends to be low. The optimum iron loading varies depending on the pore volume, outer surface area, and loading method of magnesia, but it is preferable to load 0.1 to 20% by weight of iron with respect to magnesia, particularly 0.2 to 10% by weight. It is preferable that

  The vertical fluidized bed reactor is a reactor installed so that methane flows in the vertical direction (hereinafter sometimes referred to as “longitudinal direction”). Methane flows in the direction from one end of the reactor toward the other end and passes through the catalyst layer. As the reactor, for example, a reactor having a tube shape can be preferably used. In the above, the vertical direction includes a direction having a slight inclination angle with respect to the vertical direction (for example, 90 ° ± 15 °, preferably 90 ° ± 10 ° with respect to the horizontal plane). The vertical direction is preferable. Note that the methane supply section and the discharge section do not necessarily have to be end portions of the reactor, and methane may flow in the above-described direction and pass through the catalyst layer in the flow process.

  In the vertical fluidized bed reactor, the catalyst is present on the entire surface in the horizontal cross-section direction of the reactor, and a fluidized bed is formed during the reaction. By doing in this way, a catalyst and methane can be made to contact effectively. In the case of a horizontal reactor, in order to effectively bring the catalyst into contact with methane, in order to make it exist in the entire cross section of the reactor in a direction perpendicular to the flow of methane, the catalyst is viewed from the left and right due to gravity It is necessary to pinch. However, in the case of the carbon nanotube aggregate formation reaction, the carbon nanotube aggregate is generated on the catalyst as the reaction proceeds, and the volume of the catalyst is increased. Therefore, the method of sandwiching the catalyst from the left and right is not preferable. Moreover, it is difficult to form a fluidized bed in a horizontal type. In the present invention, the reactor is set to a vertical type, a stage through which gas can permeate is installed in the reactor, and the catalyst is placed on the reactor, so that the catalyst can be evenly distributed in the cross-sectional direction of the reactor without sandwiching the catalyst from both sides. A catalyst can be present, and a fluidized bed can also be formed when methane is passed in the vertical direction. The state in which the catalyst is present on the entire surface in the horizontal sectional direction of the vertical fluidized bed reactor refers to a state in which the catalyst spreads throughout the horizontal sectional direction and the platform at the bottom of the catalyst cannot be seen. As a preferable embodiment in such a state, for example, there are the following modes.

  A. A stage (ceramic filter or the like) on which a gas permeable catalyst is placed in the reactor, and the catalyst is filled therewith to a predetermined thickness. The upper and lower sides of the catalyst layer may be slightly uneven (FIG. 1 (a)). FIG. 1A is a conceptual diagram showing a state in which a stand 2 on which a catalyst is placed is installed in a reactor 1 and a catalyst 3 is present on the entire horizontal cross-sectional direction of the reactor.

  B. An object (filler) other than the catalyst and the catalyst are mixed and filled on the table on which the catalyst similar to A is placed. The catalyst layer is preferably uniform, but the upper and lower sides may be somewhat uneven (FIG. 1 (b)). FIG. 1 (b) is a conceptual diagram showing a state in which a platform 2 on which a catalyst is placed is installed in the reactor 1, and a mixture 4 of an object other than the catalyst and the catalyst exists on the entire cross-sectional direction of the reactor. It is.

  C. The catalyst is dropped from the upper part of the reactor by spraying or the like, and the catalyst powder is uniformly present in the horizontal cross-sectional direction of the reactor through the gas (FIG. 1 (c)). FIG. 1C is a conceptual diagram showing a catalyst state in which the catalyst 5 sprayed from the upper part of the reactor 1 spreads over the entire horizontal cross-sectional direction of the reactor. As an example of the vertical fluidized bed reactor, there are a mode in which the catalyst as described above C is dropped from the upper part of the reactor by spraying or a mode in which a catalyst generally called a boiling bed type flows (a method according to the above A and B). Can be mentioned. Examples of the fixed bed type include the above-described aspects A and B.

  In the fluidized bed type, continuous synthesis is possible by continuously supplying the catalyst and continuously taking out the aggregate containing the catalyst and the aggregate of carbon nanotubes after the reaction. It can be obtained and is preferable. In the present invention, magnesia is used as a catalyst carrier, but magnesia has very good fluidity due to its particle characteristics (specific gravity, bulk density, surface charge, etc.), and in particular, a carbon nanotube aggregate is synthesized in a fluidized bed reactor. Suitable for doing. When a magnesia support is used as a catalyst, when carbon nanotube aggregates are synthesized in a fluidized bed type, long carbon nanotubes are likely to be generated because the fluidized state is good. The long carbon nanotubes defined here are carbon nanotubes having an average length of 1 μm or more. Since fluidity is good in fluidized bed type reaction, carbon nanotube synthesis reaction is performed uniformly so that the raw material methane and catalyst are in uniform and efficient contact, and catalyst covering by impurities such as amorphous carbon is suppressed, and catalytic activity Becomes longer.

  In contrast to a vertical reactor, a horizontal reactor has a laterally (horizontal) reactor in which a catalyst placed on a quartz plate is placed, and methane passes over the catalyst. It refers to a reaction device in a mode of contacting and reacting. In this case, carbon nanotubes are generated on the catalyst surface, but hardly react because methane does not reach the inside of the catalyst. On the other hand, in the vertical reactor, the raw material methane can be brought into contact with the entire catalyst, so that a large amount of carbon nanotube aggregates can be efficiently synthesized.

  The reactor is preferably heat resistant and is preferably made of a heat resistant material such as quartz or alumina.

  By passing methane from the lower part or the upper part of the catalyst layer installed in the reactor, contacting with the catalyst, and reacting, a carbon nanotube aggregate is generated.

  The temperature at which the catalyst and methane are brought into contact is preferably 600 to 950 ° C, more preferably 700 ° C to 900 ° C. When the temperature is lower than 600 ° C., the yield of the carbon nanotube aggregate is deteriorated. On the other hand, when the temperature is higher than 950 ° C., there are restrictions on the material of the reactor to be used, and joining of the carbon nanotubes starts, making it difficult to control the shape of the carbon nanotubes. The reactor may be brought to the reaction temperature while contacting methane with the catalyst, or after the pretreatment with heat is completed, the reactor may be brought to the reaction temperature and then the supply of methane may be started.

  Prior to the reaction for generating the carbon nanotube aggregate, the catalyst may be pretreated with heat. The pretreatment time by heat is not particularly limited. However, if it is too long, metal agglomeration occurs on magnesia, and carbon nanotubes with a large outer diameter may be formed accordingly, and therefore, it is preferably within 120 minutes. The temperature of the pretreatment may be equal to or lower than the reaction temperature as long as the catalytic activity is exhibited, or may be equal to or higher than the reaction temperature. By performing the pretreatment with heat, the catalyst may be brought into a more active state.

  The heat pretreatment and the reaction for generating the carbon nanotube aggregate are preferably performed under reduced pressure or atmospheric pressure.

  When the contact between the catalyst and methane is performed under reduced pressure, the reaction system can be decompressed with a vacuum pump or the like. Moreover, when reacting at atmospheric pressure, you may make it contact with a catalyst as a mixed gas which mixed methane and dilution gas.

  The diluent gas is not particularly limited, but a gas other than oxygen gas is preferably used. Oxygen is not usually used because it may explode, but it may be used if it is outside the explosion range. Nitrogen, argon, hydrogen, helium, etc. are preferably used as the dilution gas. These gases are effective for controlling the linear velocity and concentration of methane and as a carrier gas. Hydrogen is preferable because it is effective in activating the catalytic metal. Nitrogen and argon are particularly preferable.

[Fine particles]
In the present invention, the fine particle is not limited to a spherical shape but may be indefinite, and a particle having an average particle diameter of 1000 μm or less is preferably exemplified. The average particle diameter in the present invention refers to the median diameter, and the median diameter is 0.1 to 1000 μm, more preferably 0.1 to 100 μm. When the particle size exceeds this range, for example, when a conductive composite using this particle is formed into an electrode in a negative electrode material for a lithium ion battery, the gap between the particles is large when formed into a molded body using the particle. It becomes too much, and it becomes difficult to form a conductive path between particles by the conductivity imparting agent, and the conductivity imparting effect to the conductive composite may be lowered. On the other hand, if the particle size is less than this range, the total surface area of the particles becomes too large, causing aggregation of the particles, or insufficient conductivity imparting agent, making it difficult to uniformly coat the particle surface. If the median diameter is 0.1 to 1000 μm, a conductive path between the particles can be formed, and a sufficient conductivity imparting effect can be obtained. The median diameter in the present invention indicates a median diameter measured by a laser diffraction particle size distribution analyzer based on the so-called Mie scattering / diffraction theory. Specifically, when the particle size distribution between the particle size and the solid particle amount is obtained, it means a particle size (so-called 50% particle size) at which the integrated solid particle amount is 50% with respect to the total solid particle amount. .

  As the fine particles used in the present invention, inorganic compound particles, thermoplastic resin particles, or particles combining them can be used.

  Examples of inorganic compounds constituting the inorganic compound particles include silica such as metal oxides (fine powder silica (anhydride), white carbon (hydrate)), alumina, titania, zirconia, titanium oxide, iron oxide, strontium oxide, cerium oxide. Zinc oxide), metal hydroxide (such as aluminum hydroxide), metal salt (sulfate, carbonate such as calcium carbonate; phosphate such as calcium phosphate and titanium phosphate; mica, calcium silicate, bentonite, zeolite, Silicates such as barley stone, talc and montmorillonite; tungstates such as calcium tungstate; titanates such as barium titanate, potassium titanate and aluminum titanate), metal nitrides (silicon nitride, boron nitride, Aluminum nitride, titanium nitride, etc.), metal carbide (carbonization) Iodine, boron carbide, titanium carbide, tungsten carbide, etc.), metal borides (titanium boride, zirconium boride, etc.), metals (gold, platinum, palladium, etc.), carbon (carbon black, graphite, fullerene, carbon nanotubes, etc.) And the like. The inorganic particles may be in the form of powder or may be in the form of fibers (for example, glass fibers, carbon fibers, metal fibers, whiskers, etc.). Inorganic particles are ferromagnetic materials such as ferromagnetic metals (powder) such as iron, cobalt, nickel; ferromagnetic alloys (powder) such as magnetite and ferrite; ferromagnetic metal oxides (powder) such as magnetic iron oxide, etc. It may be. These inorganic particles can be used alone or in combination of two or more. In particular, inorganic compound particles containing carbon, silicon, or tin as constituent elements are preferable. These particles are preferably used as a negative electrode active material for lithium ion batteries, and among them, graphite fine particles are more preferable because they are inorganic compound particles most used as a negative electrode active material for lithium ion batteries.

  The thermoplastic resin constituting the thermoplastic resin particles includes polyethylene resin, polypropylene resin, polymethylpentene resin, cyclic olefin resin, acrylonitrile / butadiene / styrene resin (ABS resin), acrylonitrile / styrene resin (AS resin), and cellulose acetate. Cellulosic resins such as polyester resin, polyamide resin, polycarbonate resin, polyphenylene ether resin, polyarylate resin, polysulfone resin, polyphenylene sulfide resin, polyether ether ketone resin, polyether sulfide resin, polyether sulfone resin, styrene resin And vinyl resins such as acrylic resins, polyacetal resins, polyimide resins, and polyetherimide resins. These polymers may be used alone or in combination of two or more. Among these polymers, polyamide resin, polycarbonate resin, acrylonitrile / butadiene / styrene resin (ABS resin), polyester resin, polyphenylene sulfide resin, polyethersulfone resin and the like are preferable because of excellent heat resistance and toughness. Of these, a polyamide resin is particularly preferable. It is considered that the conductive composite obtained by coating these resin particles with a conductivity imparting agent can be suitably used as an anisotropic conductive material. More preferred are melt-moldable resin particles. Since these particles are elastic, the electrode or the particles are not damaged, and further, a sufficient contact area is provided for heat compression deformation, and the connection reliability is high.

  Examples of the polyamide resin include an aliphatic polyamide polymer, an alicyclic polyamide polymer, an aromatic polyamide polymer, and the like. Usually, an aliphatic polyamide polymer is used. These polyamide polymers can be used alone or in combination of two or more.

  Examples of the aliphatic polyamide polymer include aliphatic diamine components (C4-10 alkylenediamine such as tetramethylenediamine and hexamethylenediamine) and aliphatic dicarboxylic acid components (C4 such as adipic acid, sebacic acid and dodecanedioic acid). -20 Condensates with alkylene dicarboxylic acid etc. (for example, polyamide 46, polyamide 66, polyamide 610, polyamide 612, polyamide 1010, polyamide 1012, polyamide 1212 etc.), carbon such as lactam (ε-caprolactam, ω-laurolactam) 4-20 lactam or the like) or aminocarboxylic acid (4-20 carbon carboxylic acid such as ω-aminoundecanoic acid) alone or a copolymer (for example, polyamide 6, polyamide 11, polyamide 12, etc.), these Polyamide Examples thereof include copolyamides having components copolymerized (for example, polyamide 6/11, polyamide 6/12, polyamide 66/11, polyamide 66/12, etc.).

  An amorphous polyamide resin can be used as the polyamide resin. Isophthalic acid, terephthalic acid, metaxylylenediamine, 1,3-bisaminomethylcyclohexane, isophoronediamine, 2,2,4- or 2,4,4-trimethylhexamethylenediamine, 4,4'-diaminodicyclohexylmethane, It is preferable that at least one component selected from 4,4′-diamino-3,3′-dimethyldicyclohexylmethane and 4,4′-diaminodicyclohexylpropane is used as a constituent component. These can be synthesized according to the required properties, or those commercially available as transparent nylon (the amorphous polyamide resin of the present invention is generally called transparent nylon) can be used. Commercially available products include 'Grillamide (registered trademark)' TR55 (manufactured by Mzavelke), 'Grillamide (registered trademark)' TR70LX (manufactured by Mzavelke), 'Grillamide (registered trademark)' TR90 (manufactured by Mzavelke), 'TROGAMID ( Registered trademark) 'CX7323 (manufactured by Degussa). These polymers may be used in combination.

The thermoplastic resin particles may be commercial products or preparations, and the production method thereof is not particularly limited. Examples of commercially available products include 'SP-500 (registered trademark)' (manufactured by Toray Industries, Inc.), and the production method includes the following methods.
(1) The polymer is crystallized by heating and melting and cooling.
(2) The polymer is dissolved in a solvent, and the solvent is volatilized to be removed and precipitated.
(3) The polymer is dissolved in a solvent, sprayed in a mist and dried (spray drying method).
(4) The polymer is dissolved in a solvent, and the solution is poured into a solvent that does not dissolve the polymer in the form of a mist to cause precipitation (spray reprecipitation method).
(5) A polymer solution obtained by dissolving a polymer in a solvent is added to and mixed with a poor solvent of the polymer and a solvent incompatible with the solvent of the polymer, and stirred strongly to obtain an emulsified and dispersed state. The solvent in the dispersion is removed and the polymer is removed. At this time, the thermosetting resin can also be dissolved in the same solvent as the polymer and added.
(6) The polymer is dissolved in a solvent, and the solution is emulsified by gradually adding a dispersion medium that is insoluble or hardly soluble in the solution while stirring the solution. Then, after removing a solvent, it collects as a core microparticle.
(7) Grind using a mechanical grinder using a ball mill, jet mill or the like.
(8) The polymerization monomer is polymerized into particles using a polymerization method such as emulsion polymerization, non-aqueous dispersion polymerization, seed emulsion polymerization, and suspension polymerization.

[Dispersant]
As the dispersant, a surfactant, various polymer materials, and the like can be used. The dispersant is useful for improving the dispersibility and dispersion stabilization ability of the aggregate of carbon nanotubes or fine particles. Surfactants are classified into ionic surfactants and nonionic surfactants. In the present invention, any surfactant can be used. Examples of the surfactant include the following surfactants. Such surfactants can be used alone or in admixture of two or more.

  The ionic surfactant is classified into a cationic surfactant, an amphoteric surfactant and an anionic surfactant. Examples of the cationic surfactant include alkylamine salts and quaternary ammonium salts. Examples of amphoteric surfactants include alkylbetaine surfactants and amine oxide surfactants. Examples of anionic surfactants include alkylbenzene sulfonates such as dodecylbenzene sulfonic acid, aromatic sulfonic acid surfactants such as dodecyl phenyl ether sulfonate, monosoap anionic surfactants, ether sulfate-based interfaces Examples thereof include an activator, a phosphate surfactant, and a carboxylic acid surfactant. Among them, those containing an aromatic ring, that is, aromatic ionic surfactants are preferable because they are excellent in dispersibility, dispersion stability, and high concentration, and in particular, aromatics such as alkylbenzene sulfonate and dodecyl phenyl ether sulfonate. Group ionic surfactants are preferred.

  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 , Polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, ether surfactants such as polyoxyethylene / polypropylene glycol, polyoxyalkylene octyl phenyl ether, polyoxyalkylene nonyl phenyl ether, polyoxyalkyl dibutyl phenyl ether, poly Oxyalkyl styryl phenyl ether, polyoxyalkyl benzyl phenyl ether, polyoxyalkyl bisphenyl ether, polyoxyalkyl alkyl Aromatic anionic surfactants such as phenyl ether and the like. In the above, the alkyl may be an alkyl selected from C1-20. Among them, a nonionic surfactant is preferable because of its excellent dispersibility, dispersion stability, and high concentration, and polyoxyethylene phenyl ether which is an aromatic nonionic surfactant is particularly preferable.

  Examples of various polymer materials include water-soluble polymers such as polyvinyl alcohol, polyvinyl pyrrolidone, polystyrene sulfonate ammonium salt, polystyrene sulfonate sodium salt, carboxymethyl cellulose and its salts (sodium salt, ammonium salt, etc.), methyl cellulose, hydroxyethyl cellulose, and the like. Sugar polymers such as amylose, cycloamylose and chitosan. In addition, conductive polymers such as polythiophene, polyethylenedioxythiophene, polyisothianaphthene, polyaniline, polypyrrole, polyacetylene, and derivatives thereof can also be used. In particular, the use of water-soluble polymers such as carboxymethyl cellulose and its salts (sodium salt, ammonium salt, etc.), polystyrene sulfonate ammonium salt, polystyrene sulfonate sodium salt, etc. effectively demonstrates the conductive properties of the carbon nanotube aggregate. This is preferable.

  The dispersion medium of the carbon nanotube aggregate or the fine particles is not particularly limited. An aqueous solvent may be sufficient and a non-aqueous solvent may be sufficient. Non-aqueous solvents include hydrocarbons (toluene, xylene, etc.), chlorine-containing hydrocarbons (methylene chloride, chloroform, chlorobenzene, etc.), ethers (dioxane, tetrahydrofuran, methyl cellosolve, etc.), ether alcohols (ethoxyethanol, methoxy) Ethoxyethanol, etc.), esters (methyl acetate, ethyl acetate, etc.), ketones (cyclohexanone, methyl ethyl ketone, etc.), alcohols (ethanol, isopropanol, phenol, etc.), lower carboxylic acids (acetic acid, etc.), amines (triethylamine, triethylamine, etc.) Methanolamine, etc.), nitrogen-containing polar solvents (N, N-dimethylformamide, nitromethane, N-methylpyrrolidone, etc.), sulfur compounds (dimethyl sulfoxide, etc.) and the like can be used.

  Among these, the dispersion medium is preferably a dispersion medium containing water, alcohol, toluene, acetone, ether, and a solvent obtained by combining them. When an aqueous solvent is required and when a binder is used as will be described later, and the binder is an inorganic polymer binder, polar solvents such as water, alcohols and amines are used. Moreover, when using a liquid thing at normal temperature as a binder so that it may mention later, itself can also be used as a dispersion medium.

  The preferable blending ratio of each component in the dispersion liquid in which the carbon nanotube aggregates or fine particles are dispersed in the dispersant and the dispersion medium is as follows. The concentration of carbon nanotube aggregates or fine particles in the dispersion is preferably independently 0.01% by weight or more and 20% by weight or less, more preferably 0.01 to 10% by weight.

  The content of the dispersing agent in the dispersion when preparing the carbon nanotube aggregate or the fine particle dispersion is not particularly limited, but is preferably 0.01 to 50% by weight, more preferably 0. 01 to 30% by weight. The mixing ratio of the dispersant and the carbon nanotube aggregate or the dispersant and the fine particle is not particularly limited, but is preferably 0.1 to 20 by weight ratio of the dispersant / carbon nanotube aggregate or the dispersant / fine particle. Preferably it is 0.3-10. In addition, since the aggregate of carbon nanotubes is excellent in dispersibility, it is possible to once prepare a dispersion having a concentration higher than the desired carbon nanotube content and dilute it with a solvent to use it at a desired concentration.

  The carbon nanotube aggregates or fine particles can be used as a dispersion by being dispersed in a dispersion medium or a dispersant. When a carbon nanotube aggregate or fine particles are dispersed in a liquid dispersion medium, it may be called a dispersion. There is no restriction | limiting in particular in the adjustment method of a carbon nanotube dispersion or a fine particle dispersion. For example, when the dispersion medium is a solvent, carbon nanotube aggregates or fine particles, a dispersant and a solvent are mixed with a known mixing and dispersing machine (for example, a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, an attritor, a resolver, a paint shaker, etc.) And can be mixed to produce a dispersion.

[Method for producing conductive composite]
The conductive composite of the present invention is produced as follows. A carbon nanotube dispersion liquid in which a dispersion medium and a dispersant are added and dispersed in the aggregate of carbon nanotubes and a fine particle dispersion liquid in which a dispersion medium and a dispersant are added and dispersed in the fine particles are mixed. Mixing here can be performed using a well-known apparatus. For example, devices such as a magnetic stirrer, homomixer, ribbon mixer, ball mill, bead mill, sand mill, roll mill, homogenizer, attritor, resolver, paint shaker can be used. Next, the conductive composite can be obtained by removing the dispersion medium in the mixed solution. The method for removing the dispersion medium is not particularly limited, and examples thereof include distillation, freeze drying, and the like. However, since the aggregate of carbon nanotubes in the conductive composite may be aggregated by heating, freeze drying is preferable.

[Usage]
The conductive composite of the present invention thus obtained has excellent conductivity per conductive agent-coated fine particles, and therefore has excellent conductivity per weight, and can be used for various applications such as anisotropic conductive materials. However, when inorganic fine particles are used, it can be preferably used for a negative electrode for a lithium ion battery.

[Anode for lithium ion batteries]
The conductive composite of the present invention can be used as a negative electrode material for a lithium ion battery by adding a binder. There is no restriction | limiting in particular as a binder, It can select from a conventionally well-known material suitably as a binder of the negative electrode for lithium ion batteries, and can use it. Examples of such a binder include fluorine such as styrene butadiene copolymer rubber (SBR), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, and the like. A high molecular polymer etc. can be mentioned preferably. The content of the binder in the negative electrode material is in the range of 1 to 10% by weight with respect to 100% by weight of the negative electrode material for lithium ion batteries, from the viewpoint of improving conductivity and sufficiently exhibiting the binding force as the binder. Preferably there is.

[Method for producing negative electrode for lithium ion battery]
The manufacturing method of the negative electrode for lithium ion batteries of this invention consists of the process of preparing the negative electrode material for lithium ion batteries, and the process of apply | coating the said negative electrode material to a collector. The step of preparing a negative electrode material for a lithium ion battery is a step of mixing a conductive composite, a solution or dispersion containing a binder, and a solvent. The dispersion at the time of preparing the conductive composite is adjusted to a desired concentration. The conductive composite may be mixed by concentration. There are no particular restrictions on the solvent (including the “dispersion medium”) used in preparing the solution containing the binder, and one or more of the solvents conventionally used for forming electrodes in lithium batteries can be selected. can do. Examples of such a solvent include N-methyl-2-pyrrolidone (NMP), methyl ethyl ketone, dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, and tetrahydrofuran. In particular, when PVDF is used as the binder, it is preferable to use N-methyl-2-pyrrolidone as the solvent.

  In addition to the above solvents, other solvents can be added to impart fluidity. As such solvents, the above can be used, and water can also be used. it can.

  On the other hand, when SBR is used as a binder, a solution containing SBR can be prepared using N-methyl-2-pyrrolidone or water as a solvent. When water is used as a solvent, in order to impart viscosity to the resulting slurry, before adding the aqueous dispersion of SBR to the kneading machine, the aqueous thickener solution is added to the kneading machine, and the conductive composite It is preferable to mix with.

  As the thickener, for example, polyethylene glycols, celluloses, polyacrylamides, poly N-vinyl amides, poly N-vinyl pyrrolidones and the like can be used. Among these, celluloses such as polyethylene glycols and carboxymethylcellulose are preferable, and carboxymethylcellulose having a high affinity for SBR is particularly preferable. Carboxymethyl cellulose includes a sodium salt type and an ammonium salt type, and any of them may be used.

  Mixing here can be performed using a well-known apparatus. For example, apparatuses such as a homomixer, a ribbon mixer, a ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, an attritor, a resolver, and a paint shaker can be used.

  As a solution containing a binder, for example, when using a PVDF solution or SBR solution containing N-methyl-2-pyrrolidone as a solvent, the conductive composite by the mixer, the PVDF solution or SBR solution, and optionally A negative electrode material made of a slurry is prepared by mixing with a solvent (preferably NMP).

  On the other hand, as a solution containing a binder, for example, when an SBR aqueous dispersion using water as a solvent is used, first, the above-described mixer is used to first mix the conductive composite and the above-described thickener aqueous solution. A negative electrode material made of a slurry is prepared by kneading this mixture, an aqueous SBR dispersion, and optionally water of a solvent.

  The applying step is a step of applying the negative electrode material obtained through the preparation step of the negative electrode material for a lithium ion battery onto the current collector.

  As the current collector, conventionally known materials such as aluminum, nickel, titanium and alloys thereof, stainless steel, platinum, and carbon sheets can be used. There is no particular limitation on the method of applying the electrode forming material onto these current collectors, and a conventionally known method such as a method of applying using a doctor blade or a bar coater can be employed. The electrode sheet obtained by coating in this manner is dried by a known method, and then molded to have a desired thickness and density by a known method such as a roll press or a pressure press. A negative electrode for a lithium ion battery is obtained.

  EXAMPLES Hereinafter, the present invention will be specifically described by way of examples. However, the following examples are given for illustrative purposes and should not be used in any way as a limited interpretation of the present invention. .

  In the examples, various physical properties were evaluated by the following methods.

(Assessment of carbon nanotube aggregate)
[Thermal analysis]
About 1 mg of the sample was placed in a differential thermal analyzer (DTG-60 manufactured by Shimadzu Corporation), and the temperature was increased from room temperature to 900 ° C. at a temperature increase rate of 10 ° C./min. The combustion peak temperature due to heat generation was read from the DTA curve at that time.

[Raman spectroscopy]
A powder sample was placed in a resonance Raman spectrometer (INF-300 manufactured by Horiba Joban Yvon), and measurement was performed using a laser wavelength of 532 nm. When measuring the G / D ratio, analysis was performed on three different locations of the sample, and the arithmetic average was obtained.

[High-resolution transmission electron micrograph]
1 mg of the carbon nanotube aggregate was placed in 1 mL of ethanol, and dispersion treatment was performed using an ultrasonic bath for about 15 minutes. A few drops of the dispersed sample were dropped on the grid and dried. The grid thus coated with the sample was placed in a transmission electron microscope (JEM-2100 manufactured by JEOL Ltd.) and measured. The measurement magnification is 50,000 times to 500,000 times. The acceleration voltage is 120 kV.

(Evaluation of conductive composite)
[Powder resistance measurement]
The powder resistance of the conductive composite was measured using a powder resistance measurement unit (MCP-PD51 manufactured by Dia Instruments). The measurement cell has a cylindrical shape with a diameter of 10 mm and a height of 50 mm, and 1 g of the conductive composite is put into this cell, and pressure is applied from above using a compression rod to compress the powder. At this time, an electric current was passed through the powder while measuring the pressure and volume, and the resistance value was measured with a Loresta EP MCP-T360 (manufactured by Dia Instruments Co., Ltd.) using the 4-terminal 4-probe method of JIS K7149. It was measured. In addition, since powder resistance changes with densities, the evaluation compares with the value of a fixed density for every fine particle seed | species. For example, in the case of graphite particles, the density is compared at a value of 2.1 g / cm ³ .

(Evaluation of negative electrode for lithium battery)
[Volume resistance measurement]
The volume resistance value of the negative electrode for a lithium ion battery can be calculated by multiplying the surface resistance value by the thickness of the negative electrode after measuring the surface resistance value by the four-terminal method, and the electrode density is 1100 g / cm ³ . Compare by value. The surface resistance value was measured by Loresta EP MCP-T360 (manufactured by Dia Instruments Co., Ltd.) using a four-terminal four-probe method according to JIS K7149.

(Production Example 1) Preparation of aggregate of carbon nanotubes (Support of catalyst metal salt on magnesia)
2.46 g of ammonium iron citrate (Wako Pure Chemical Industries, Ltd.) was dissolved in 500 mL of methanol (Kanto Chemical Co., Ltd.). To this solution, 100 g of magnesia (manufactured by Iwatani Chemical Industry Co., Ltd.) was added and stirred at room temperature for 60 minutes, and then methanol was removed under reduced pressure conditions at a water bath temperature of 40 ° C. to 60 ° C. using an evaporator. Then, it dried for 2 hours with a 120 degreeC dryer, and obtained the solid catalyst by which the catalyst metal salt was carry | supported by the magnesia powder. At this time, the bulk density of the catalyst was 0.58 g / mL.

(Synthesis of double-walled carbon nanotube)
Carbon nanotubes were synthesized in the vertical reactor shown in FIG.

  The reactor 100 is a cylindrical quartz tube having an inner diameter of 75 mm and a length of 1700 mm. A quartz sintered plate 101 is provided at the center, an inert gas and raw material gas supply line 104 at the lower part of the quartz tube, a waste gas line 105 at the upper part, a sealed catalyst feeder 102 and a catalyst charging line 103. It has. In addition, a heater 106 is provided that surrounds the circumference of the reactor so that the reactor can be maintained at an arbitrary temperature. The heater 106 is provided with an inspection port 107 so that the flow state in the apparatus can be confirmed.

  132 g of the catalyst was taken, and the catalyst was set on the quartz sintered plate 101 through the catalyst charging line 103. Subsequently, supply of nitrogen gas from the source gas supply line 104 was started at 10.0 L / min. After the inside of the reactor was placed in a nitrogen gas atmosphere, the temperature was heated to 850 ° C. (temperature rising time 30 minutes).

After reaching 850 ° C., the temperature was maintained, the nitrogen flow rate of the raw material gas supply line 104 was increased to 16.5 L / min, and fluidization of the solid catalyst on the quartz sintered plate was started. After confirming fluidization from the heating furnace inspection port 107, methane was further fed to the reactor at 0.78 L / min (methane concentration 4.5 vol%, methane linear velocity 6.5 cm / sec). After supplying the mixed gas for 60 minutes, the flow was switched to a flow of only nitrogen gas to complete the synthesis. At this time, the contact time between methane and the catalyst was 1.69 × 10 ⁻¹ g · min / mL.

  The heating was stopped and the mixture was allowed to stand at room temperature, and the composition containing the catalyst and the carbon nanotube aggregate was taken out from the reactor. The obtained carbon nanotube aggregate was subjected to the following steps.

  The obtained carbon nanotube aggregate was subjected to thermal analysis by the method described above. The combustion peak temperature was 480 ° C.

(Baking and refining of carbon nanotube aggregates)
30 g of the carbon nanotube aggregate was placed in a magnetic dish (150φ), placed in a muffle furnace (FP41, manufactured by Yamato Kagaku Co., Ltd.) heated to 450 ° C. in the atmosphere, and held for 3 hours, and then allowed to cool naturally. Then, in order to remove a catalyst from said carbon nanotube, the refinement | purification process was performed as follows. Carbon nanotubes were added to a 6N hydrochloric acid aqueous solution and stirred in a water bath at 80 ° C. for 1 hour. Filtration was performed using a filter having a pore size of 1 μm to obtain a recovered product. This operation was repeated two more times, and finally, after washing several times with water, the filtrate was dried in an oven at 120 ° C. overnight to remove magnesia and catalytic metal, and the carbon nanotubes could be purified.

(Thermal analysis of carbon nanotube aggregates)
The obtained carbon nanotube aggregate was subjected to thermal analysis. The combustion peak temperature was 664 ° C. Moreover, it turned out that the weight reduction amount from 200 degreeC to 400 degreeC is 5% of the weight reduction from 200 degreeC to 900 degreeC.

(High-resolution transmission electron microscope analysis of carbon nanotube aggregates)
When the aggregate of carbon nanotubes obtained as described above was observed with a high-resolution transmission electron microscope, as shown in FIG. 3, the carbon nanotubes were composed of clean graphite layers, and the number of the carbon nanotubes was two. Was observed. Two-layer carbon nanotubes occupied 80% or more (85) of 100 carbon nanotubes. The number of carbon nanotubes in three or more layers was 10% or less (seven). Of the 100 carbon nanotubes, 97 had an outer diameter of 1 to 3 nm.

(Resonance Raman spectroscopic analysis of carbon nanotube aggregates)
The aggregate of carbon nanotubes obtained as described above was subjected to Raman spectroscopic measurement. As a result, as shown in FIG. 4, in the Raman spectroscopic analysis at a wavelength of 532 nm, it was found that the G / D ratio was 53, which is a high-quality double-walled carbon nanotube having a high degree of graphitization.

(Measurement of volume resistivity of carbon nanotube aggregate)
20 mg of the carbon nanotube aggregate obtained as described above was mixed with 16 mL of N-methylpyrrolidone, subjected to ultrasonic irradiation at 20 W for 20 minutes using an ultrasonic homogenizer, then mixed with 10 mL of ethanol, and a filter with an inner diameter of 35 mmφ was added. Then, the filtered product and the filter used for filtration were dried in a dryer at 60 ° C. for 2 hours. When the membrane filter with the carbon nanotube film was removed, the membrane thickness was measured together with the membrane filter, and the membrane thickness of the membrane filter was subtracted, the thickness of the carbon nanotube film was 65 μm. As the membrane filter, OMINIPOREMBRANE FILTERS, FILTER TYPE: 1.0 μm JA, 47 mmφ was used. The obtained carbon nanotube film was measured by a Loresta EP MCP-T360 (manufactured by Dia Instruments Co., Ltd.) using a four-terminal four-probe method according to JIS K7149, and it was 0.249Ω / □. Therefore, the volume resistivity is 1.62 × 10 ⁻³ Ω · cm.

( Reference Example 1 ) Preparation of double-layer CNT conductive composite (nylon 12 particles)
Weigh 20 mg of the carbon nanotube aggregate obtained in Production Example 1 and 2000 mg of an aqueous carboxymethyl cellulose solution (manufactured by Aldrich, 1% by weight) into a 50 mL container, add 11.31 mL of distilled water, and output an ultrasonic homogenizer of 25 W, 20 Dispersion treatment was carried out under ice-cooling for a minute to prepare a carbon nanotube dispersion. Aggregates could not be visually confirmed in the prepared liquid, and the carbon nanotube aggregates were well dispersed.

  Also, weigh 950 mg of nylon 12 particles (SP-500, average particle size 4 μm, manufactured by Toray Industries, Inc.) and 1000 mg of carboxymethylcellulose aqueous solution (manufactured by Aldrich, 1% by weight) into a 50 mL container, and 4.72 mL of distilled water. And stirred with a magnetic stirrer for 30 minutes. One drop of the adjusted liquid was collected on a slide glass, and the preparation sandwiched between the cover glasses was observed with an optical microscope and found to be well dispersed.

A carbon nanotube dispersion was added to this nylon 12 particle dispersion, and further stirred for 30 minutes with a magnetic stirrer, and the resulting mixture was freeze-dried to obtain a conductive composite. The results of measuring the powder resistance of this conductive composite are shown in Table 1, and the SEM image is shown in FIG.

( Reference Example 2) Preparation of single-walled CNT conductive composite (nylon 12 particles)
In Example 1, a conductive composite was prepared in the same manner as in Reference Example 1 except that single-walled carbon nanotubes (manufactured by Meijo Nanocarbon Co., Ltd.) were used instead of the carbon nanotube aggregates, and the powder resistance was measured. The results are shown in Table 1, and the SEM image is shown in FIG.

The physical properties of the single-walled carbon nanotubes used at this time were measured by the method described above. As a result, the Raman G / D ratio by 532 nm light was 43, the volume resistivity was 1.15 × 10 ⁻² Ω · cm, The ratio of layered CNTs was 68 out of 100, the ratio of double-walled CNTs was 30 out of 100, 97 of 100 CNTs with an outer diameter of 1 to 6 nm, and 83 of 100 CNTs of 1 to 3 nm. It was.

(Example 1) two-layer CNT conductive preparing double polymer (silica gel particles)
In Reference Example 1 , a conductive composite was prepared in the same manner as in Reference Example 1 except that silica gel particles (manufactured by Kanto Chemical Co., Inc., silica gel 60N, average particle size 50 μm) were used instead of nylon 12 particles. The results of measuring the powder resistance are shown in Table 1.

(Example 2 ) Preparation of single-walled CNT conductive composite (silica gel particles)
In Example 1 , a conductive composite was prepared and powder resistance was measured in the same manner as in Example 1 except that single-walled carbon nanotubes (manufactured by Meijo Nanocarbon Co., Ltd.) were used instead of the carbon nanotube aggregates. The results are shown in Table 1.

(Example 3) bilayer CNT conductive preparing double polymer (graphite particles)
In Reference Example 1 , a conductive composite was prepared in the same manner as in Reference Example 1 except that graphite particles (manufactured by Nippon Graphite Industries Co., Ltd., CGB-20, average particle size 20 μm) were used instead of nylon 12 particles. The results of measuring the powder resistance are shown in Table 1.

(Example 4 ) Preparation of negative electrode for lithium ion battery (graphite particles)
The conductive composite prepared in Example 3 was transferred to a homomixer, 64.98 mg of SBR aqueous dispersion (manufactured by JSR Corporation, TRD2001, solid concentration 48.6 wt%), and 912. 74 mg was added and kneaded at 10,000 rpm for 30 minutes to prepare a negative electrode material. The obtained negative electrode material was applied onto an aluminum foil using a doctor blade, and dried for 30 minutes with a dryer (120 ° C.). Table 2 shows the results of measuring the volume resistance after drying and preparing a negative electrode sample by pressing with a press molding machine.

Comparative Example 1 Multilayer CNT composite (nylon 12 particles)
In Reference Example 1 , except that multi-walled carbon nanotubes (manufactured by CNT Corporation) were used instead of the carbon nanotube aggregate, a conductive composite was prepared in the same manner as in Reference Example 1, and the results of measuring the powder resistance are shown in Table 1. FIG. 7 shows an SEM image. The physical properties of the multi-walled carbon nanotubes used at this time were measured by the above-described method. As a result, the Raman G / D ratio by light of 532 nm was 1.3, and the ratio of two-walled CNTs was 1 or less out of 100. The number of 1 to 6 nm CNTs was 1 or less out of 100.

(Comparative Example 2) Vapor grown carbon fiber composite (nylon 12 particles)
In Reference Example 1 , a conductive composite was prepared in the same manner as in Reference Example 1 except that vapor-grown carbon fiber (VGCF manufactured by Showa Denko KK) was used instead of the carbon nanotube aggregate. The results of measuring are shown in Table 1. In addition, the carbon fibers having a diameter of 6 nm or less in the carbon fibers used at this time were 1 or less in 100 fibers.

Comparative Example 3 Multilayer CNT composite (silica gel particles)
In Example 1 , except that multi-walled carbon nanotubes (manufactured by CNT Corporation) were used instead of the carbon nanotube aggregate, a conductive composite was prepared in the same manner as in Example 1, and the results of measuring the powder resistance are shown in Table 1. Shown in

(Comparative Example 4) Vapor grown carbon fiber CNT composite (silica gel particles)
In Example 1 , a conductive composite was prepared in the same manner as in Example 1 except that vapor-grown carbon fiber (VGCF manufactured by Showa Denko KK) was used instead of the carbon nanotube aggregate. The results of measuring are shown in Table 1.

(Comparative Example 5) Graphite particles only In Example 3 , except that graphite particles were used instead of the carbon nanotube aggregate, a conductive composite was prepared in the same manner as in Example 3 and the powder resistance was measured. Table 1 shows.

Comparative Example 6 Multilayer CNT composite (graphite particles)
In Example 3 , a conductive composite was prepared in the same manner as in Example 3 except that multi-walled carbon nanotubes (manufactured by CNT Corporation) were used instead of the carbon nanotube aggregate, and the results of measuring the powder resistance are shown in Table 1. Shown in

(Comparative Example 7) Vapor grown carbon fiber composite (graphite particles)
In Example 3 , a conductive composite was prepared in the same manner as in Example 3 except that vapor grown carbon fiber (VGCF manufactured by Showa Denko KK) was used instead of the carbon nanotube aggregate, and powder resistance The results of measuring are shown in Table 1.

(Comparative Example 8) Preparation of additive-free negative electrode for lithium ion battery (graphite particles)
In Example 4 , a negative electrode for a lithium ion battery was prepared in the same manner as in Example 2 except that the conductive composite prepared in Comparative Example 5 was used instead of the conductive composite prepared in Example 3. The results of measuring the resistance are shown in Table 2.

  The conductive composite obtained in the present invention can be used for electronic parts such as negative electrode materials for lithium ion batteries and anisotropic conductive materials, toner for electrophotography, aircraft parts, and the like.

DESCRIPTION OF SYMBOLS 1 Reactor 2 Stand which puts catalyst 3 Catalyst 4 Mixture of objects and catalyst other than catalyst 5 Catalyst 100 Reactor 101 Quartz sintered plate 102 Sealed catalyst feeder 103 Catalyst input line 104 Raw gas supply line 105 Waste gas line 106 Heating 107 Inspection port 108 Catalyst

Claims (7)

A conductive composite containing fine particles containing at least one selected from carbon, silicon and tin having an average particle size of 1000 μm or less, a conductivity-imparting agent and a dispersant, and satisfying the following conditions:
(1) The carbon nanotube aggregate in which the conductivity-imparting agent contains carbon nanotubes.
(2) When the carbon nanotube aggregate is observed with a transmission electron microscope, the outer diameter of 50 or more of the 100 is 1 to 6 nm.
(3) The conductivity imparting agent dispersed by the dispersant coats the surface of the fine particles.
(4) The conductivity imparting agent in the conductive composite is 0.1 to 20% by weight.   The conductive composite according to claim 1, wherein the proportion of the double-walled carbon nanotubes contained in the aggregate of carbon nanotubes is 50% or more. 3. The conductive composite according to claim 1, wherein the volume resistivity of the aggregate of carbon nanotubes is 1 × 10 ⁻⁵ Ω · cm to 1 × 10 ⁻² Ω · cm. .   The electrical conductivity according to any one of claims 1 to 3, wherein a height ratio (G / D ratio) of the G band and the D band by a Raman spectroscopic analysis at a wavelength of 532 nm of the aggregate of carbon nanotubes is 30 or more. Complex. The conductive composite according to any one of claims 1 to 4, wherein the aggregate of carbon nanotubes has been previously oxidized.   6. The conductive composite according to claim 5, wherein the oxidation treatment is performed by firing within a range of the combustion temperature peak of the carbon nanotube aggregate ± 50 ° C.   A negative electrode for a lithium ion battery, comprising the conductive composite according to any one of claims 1 to 6.

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