JP7163645B2 - Carbon nanotube electrode, electricity storage device using the same, and method for producing carbon nanotube composite - Google Patents

Description

TECHNICAL FIELD The present invention relates to a carbon nanotube electrode, an electricity storage device using the same, and a method for producing a carbon nanotube composite.

Carbon nanotubes are being studied for their use in various technical fields due to their unique properties not found in conventional materials such as graphite and diamond. For example, the use of carbon nanotubes as an electrode material for electric storage devices is under study.

Patent Literature 1 and Patent Literature 2 disclose an electrode material (negative electrode material) having a coating layer made of amorphous carbon made of amorphous carbon on the surface of a multi-walled carbon nanotube. Non-Patent Document 1 discloses an electrode material having a layer of carbon with low crystallinity on the surface of a multi-walled carbon nanotube.

Japanese Patent Application Laid-Open No. 2004-303613 JP 2014-231446 A

“In Situ Transmission Electron Microscopy Study of Electrochemical Sodiation and Potassiation of Carbon Nanofibers” Nanoletter 2014, 14, 3445-3452

However, since amorphous carbon has a limited number of sites into which lithium ions can be inserted (because of its low energy density per unit volume), there is a limit to improvement in negative electrode capacity. Since the technique of Non-Patent Document 1 synthesizes multi-walled carbon nanotubes by a gas-phase flow method, multi-walled carbon nanotubes cannot be grown directly on a substrate. Therefore, in the technique of Non-Patent Document 1, a binder is required for the configuration of the electrodes, so the resistance increases accordingly. Moreover, the negative electrode capacity per unit weight is reduced.

The present invention has been made to address the above-mentioned problems. That is, one of the objects of the present invention is to provide a carbon nanotube electrode capable of improving the negative electrode capacity (hereinafter sometimes referred to as "the carbon nanotube electrode of the present invention") and an electricity storage device using the same (hereinafter , may be referred to as the “electricity storage device of the present invention”) and a method for producing a carbon nanotube composite (hereinafter sometimes referred to as “the method for producing the carbon nanotube composite of the present invention”). That's what it is.

In order to solve the above problems,
The carbon nanotube electrode of the present invention is
a conductive substrate made of a conductive metal having conductivity;
multi-walled carbon nanotubes grown from seed catalyst particles provided on a conductive substrate;
including
The multi-walled carbon nanotube is
a main body including a plurality of concentrically arranged tubular graphene sheets extending along the axial direction of the multi-walled carbon nanotube;
A surface layer portion that includes a plurality of graphene sheets having physical properties different from those of the tubular graphene sheet that overlaps the outside of the main portion, and that has more carbon ring-deficient portions, which are portions in which the carbon rings of the graphene sheets are lacking, compared to the main portion. When,
including.

In one aspect of the carbon nanotube electrode of the present invention,
The electron diffraction image of the surface layer portion includes a diffraction spot due to the carbon 002 surface that is elongated compared to the shape of the diffraction spot due to the carbon 002 surface in the electron diffraction image of the main portion.

In one aspect of the carbon nanotube electrode of the present invention,
The thickness of the surface layer portion is 2.5 times or more the thickness of the main portion.

The electricity storage device of the present invention is
a positive electrode;
a negative electrode made of a carbon nanotube electrode;
an electrolyte;
including
The carbon nanotube electrode is
a conductive substrate made of a conductive metal having conductivity;
multi-walled carbon nanotubes grown from seed catalyst particles provided on a conductive substrate;
including
The multi-walled carbon nanotube is
a main body including a plurality of concentrically arranged tubular graphene sheets extending along the axial direction of the multi-walled carbon nanotube;
A surface layer portion that includes a plurality of graphene sheets having physical properties different from those of the tubular graphene sheet that overlaps the outside of the main portion, and that has more carbon ring-deficient portions, which are portions in which the carbon rings of the graphene sheets are lacking, compared to the main portion. When,
including.

The method for producing the carbon nanotube composite of the present invention comprises
a laminate forming step of forming a catalyst layer composed of seed catalyst particles for forming multi-walled carbon nanotubes on a conductive base material composed of a conductive metal having electrical conductivity;
a carbon nanotube layer forming step of forming the multi-walled carbon nanotubes on the catalyst layer;
has
The carbon nanotube layer forming step includes
The laminate is placed in a chamber, and when the temperature of the laminate in the chamber is within a first temperature range selected from a temperature range of 450° C. or higher and 550° C. or lower, the gas flow rate of the carbon source gas is reduced to the first temperature range. 1 After introducing into the chamber at a predetermined gas flow rate, with the gas flow rate of the carbon source gas set to the first predetermined gas flow rate, up to a multi-walled carbon nanotube synthesis temperature range selected from the range of 800 ° C. or higher and 850 ° C. or lower. a precursor forming step including a precursor growing step of forming a precursor that serves as a starting point for growth of the multi-walled carbon nanotubes on a portion of the surface of the seed catalyst particles by raising the temperature;
After the precursor forming step, when the temperature of the laminate is within the multi-walled carbon nanotube synthesis temperature range, the gas flow rate of the carbon raw material gas is set to a second predetermined gas flow rate, and the precursor is used as a starting point. a carbon nanotube growth step for growing multi-walled carbon nanotubes, wherein the second predetermined gas flow rate is 1.8 times or more and 15.0 times or less the first predetermined gas flow rate;
including.

In one aspect of the method for producing the carbon nanotube composite of the present invention,
The precursor forming step includes
The method further includes, before the precursor growing step, a step of heating seed catalyst particles for maintaining the temperature of the layered body in the chamber within the first temperature range by heating the layered body.

According to the present invention, the negative electrode capacity can be improved.

FIG. 1 is a plan view showing a configuration example of a carbon nanotube electrode according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view along line I-I' of FIG. FIG. 3 is a schematic diagram and a TEM image for explaining the structure of multi-walled carbon nanotubes. FIG. 4 is a graph and a schematic diagram showing a temperature profile and a gas flow rate profile for explaining the method for producing a carbon nanotube composite according to an embodiment of the invention. 5 is a graph showing the temperature profile and gas flow rate profile of Example 1. FIG. 6 is a graph showing the temperature profile and gas flow rate profile of Comparative Example 2. FIG. FIG. 7 is a photograph showing an SEM image and a TEM image when observing the formation state of the multi-walled carbon nanotube of Example 1. FIG. FIG. 8 is a photograph showing an SEM image and a TEM image when observing the formation state of the multi-walled carbon nanotube of Example 2. FIG. 9 is a photograph showing an SEM image and a TEM image when observing the formation state of the multi-walled carbon nanotube of Comparative Example 1. FIG. FIG. 10 is a photograph showing SEM and TEM images when observing the state of formation of multi-walled carbon nanotubes of Comparative Example 2. FIG. FIG. 11 is a TEM image for observing the formation state of the multi-walled carbon nanotube of Example 1 and the multi-walled carbon nanotube of Comparative Example 1, and an FFT image (electron diffraction image) obtained by inverse Fourier transforming the TEM image. FIG. 12 is a graph plotting the measurement results (CNT length) of Examples and Comparative Examples on the coordinates of the vertical axis: CNT length and the horizontal axis: first gas introduction temperature tg1. FIG. 13 is a graph plotting the measurement results (CNT length) of the example and the comparative example on the coordinates of the vertical axis: CNT length and the horizontal axis: first predetermined gas flow rate M1. FIG. 14 is a graph plotting the measurement results (CNT amount) of Examples and Comparative Examples on the coordinates of the vertical axis: CNT amount and the horizontal axis: multilayer CNT synthesis temperature tg2. FIG. 15 is a graph plotting the measurement results (CNT length) of Examples and Comparative Examples on the coordinates of the vertical axis: CNT amount and the horizontal axis: second predetermined gas flow rate M2. FIG. 16 is a graph plotting the measurement results (capacity) of the example and the comparative example on the coordinates of the vertical axis: capacity and the horizontal axis: the second predetermined gas flow rate M2.

A carbon nanotube composite according to an embodiment of the present invention will be described below with reference to the drawings. In addition, in all the drawings of the embodiment, the same reference numerals are given to the same or corresponding parts.

The carbon nanotube composite according to the embodiment of the present invention can be suitably used, for example, as an electrode (eg, negative electrode, etc.) of an electric storage device (eg, lithium ion capacitor, lithium ion secondary battery, etc.). An electrode composed of a carbon nanotube composite is also called a “carbon nanotube electrode”.

<Structure of carbon nanotube electrode>
1 and 2 show configuration examples in which a carbon nanotube composite is applied to an electrode. As shown in FIG. 1, the electrode 10 has a terminal portion 10a and an electrode portion 10b. The terminal portion 10a is composed of an exposed portion where the conductive base material 11 is exposed without the carbon nanotube layer 14 (hereinafter referred to as "CNT layer 14") formed thereon, and extracts current to the outside. is established for

The electrode portion 10b has, for example, a rectangular planar shape and is made of a carbon nanotube composite. As shown in FIG. 2, the carbon nanotube composite constituting the electrode portion 10b has a catalyst layer 13 and a CNT layer 14 on one main surface and the other main surface of the conductive substrate 11, respectively. Although illustration is omitted, the carbon nanotube composite may have the catalyst layer 13 and the CNT layer 14 only on one main surface of the conductive substrate 11 .

(Conductive substrate)
The conductive base material 11 is made of a conductive metal having conductivity, and is, for example, a foil-shaped conductive metal (conductive metal foil). As the conductive metal, it is preferable to use, for example, copper (Cu) suitable for an electrode (current collector) of a lithium ion capacitor.

(catalyst layer)
The catalyst layer 13 is composed of a seed catalyst for forming carbon nanotubes, for example, a material capable of catalyzing the formation of carbon nanotubes (eg, transition metal particles, etc.) supported on the conductive substrate 11. consists of Materials constituting the catalyst layer 13 include, for example, Fe-based seed catalyst particles such as iron (Fe) or iron-titanium alloy (FeTi) particles, and seed catalyst particles such as cobalt (Co) particles and nickel (Ni) particles. can be used.

As the seed catalyst particles, typically, particles having a primary particle size of nanosize (nanoparticles) can be used. A nanosize typically means a size of several nanometers or more and several tens of nanometers or less. Materials with nano-sized dimensions are referred to with the prefix "nano", eg, nanoparticles. The average particle size of the primary particles of the seed catalyst particles is preferably 20 nm or less from the viewpoint of better growth of carbon nanotubes.

The CNT layer 14 is composed of multi-walled carbon nanotubes 24 formed on the catalyst layer 13 . Specifically, as shown in FIG. 3, the CNT layer 14 is multi-walled carbon nanotubes 24 having orientation grown from seed catalyst particles 23 (catalyst layer 13) supported on the conductive substrate 11. It is configured.

The multi-walled carbon nanotube 24 includes a main body portion 24a and a surface layer portion 24b overlapping the outside of the main body portion 24a. The main body 24a has a configuration in which a plurality of tubular graphene sheets with high crystallinity (black portions in the TEM image shown in block R1) are concentrically arranged (stacked).

The surface layer portion 24b is arranged (overlapped) on the outside of the main body portion 24a so as to cover the main body portion 24a. The surface layer portion 24b is composed of a plurality of graphene sheets having physical properties different from those of the tubular graphene sheets forming the main portion 24a. The surface layer portion 24b includes more carbon ring-lacking portions (also referred to as “carbocyclic ring-lacking portions”) in which the carbon rings (one or more carbon rings) of the graphene sheet are missing compared to the main portion 24a. .

A graphene sheet is a layer (single layer) composed of carbon atoms containing at least graphene. Graphene is a layer of carbon atoms arranged in a hexagonal lattice (a layer of six-membered carbon rings (a layer with a thickness of one atom)). The graphene sheet may contain at least one of carbon atoms arranged pentagonally (5-membered carbon ring) and carbon atoms arranged heptagonally (7-membered carbon ring). Furthermore, the graphene sheet may contain a missing portion of a carbocyclic ring in which the carbocyclic ring is missing.

The plurality of graphene sheets that constitute the surface layer portion 24b are, for example, a plurality of small piece-like graphene sheets (for example, graphene sheets in which a tube-like graphene sheet including a missing portion of a carbon ring and divided into a large number of tube-like graphene sheets) are laminated. At least one of a laminated body (hereinafter also referred to as a “flaky graphene sheet laminated body”) and a tubular graphene sheet containing more missing portions of carbon rings than the graphene sheet of the main portion 24a. It is an aggregate. In addition, it is considered that the tube-shaped graphene sheet that constitutes the main body 24a has substantially no missing portions of the carbon rings, or, if present, there are very few missing portions of the carbon rings.

Note that the difference between the main body portion 24a and the surface layer portion 24b can be confirmed by the difference in appearance by TEM observation and by the FFT image (electron diffraction image) obtained by inverse Fourier transforming the TEM image (Fig. 11).

That is, in the TEM image of the main body portion 24a shown in the block R1, a plurality of graphene sheets (black portions) extend along the direction indicated by the arrow G1 (the axial direction of the multi-walled carbon nanotube). ) and in the direction indicated by the arrow G2 (radial direction).

On the other hand, in the TEM image of the surface layer portion 24b, a plurality of intermittent graphene sheets (black portions) are superimposed on the outside of the main portion 24a. A plurality of intermittently present graphene sheets (black portions) may extend along the direction indicated by the arrow G1 (axial direction), but may extend not along the direction indicated by the arrow G1 (axial direction). There are many. Therefore, it is conceivable that the orientation of the plurality of graphene sheets (black portion) is lower than that of the plurality of graphene sheets of the main portion 24a.

In addition, many of the white portions (white portions not along the axial direction) that divide the graphene sheets are considered to be portions lacking carbon rings in the graphene sheets. Therefore, it can be said that the surface layer portion 24b tends to have more missing portions of the carbon rings than the main portion 24a. Furthermore, it is considered that the white portions (white portions not along the axial direction) that divide a plurality of graphene sheets include gaps between small piece-like graphene sheets. Note that the white portion extending in the direction indicated by the arrow G1 is considered to be the portion (interlayer of the graphene sheet) between the carbocyclic plane (002 plane of carbon) and the (002 plane of carbon) of the graphene sheet. .

In the FFT image of the plurality of graphene sheets forming the surface layer portion 24b, the diffraction spots S1a and S1b (see Example 1 of FIG. 11) due to the 002 plane of carbon are the carbon of the plurality of graphene sheets forming the main portion 24a. The diffraction spots S2a and S2b and S3a and S3b (see Comparative Example 1 in FIG. 11) by the 002 plane of .

Note that the FFT image of the plurality of graphene sheets forming the surface layer portion 24b is not a halo pattern that appears in the amorphous state. In other words, the plurality of graphene sheets forming the surface layer portion 24b are considered to have higher crystallinity than amorphous carbon and lower crystallinity than the plurality of graphene sheets forming the main portion 24a.

Since the surface layer portion 24b can occlude lithium ions from the missing portions of the carbon rings, the lithium ions easily enter between the layers of the graphene sheets forming the surface layer portion 24b. On the other hand, in the main body portion 24a, the entrance between the layers of the graphene sheets constituting the main body portion 24a is mainly the end portion in the axial direction, so it is difficult for lithium ions to enter between the layers of the graphene sheets. . Therefore, it is considered that the surface layer portion 24b can increase the number of lithium ion absorption sites compared to the main portion 24a. Thereby, the negative electrode capacity can be improved.

Furthermore, it is considered that the plurality of graphene sheets that constitute the surface layer portion 24b have a structure with lower orientation than the main portion 24a, so that the number of lithium ion absorption sites can be increased compared to the main portion 24a. Thereby, the negative electrode capacity can be further improved.

Further, it is considered that the gaps between the small piece-like graphene sheets included in the surface layer portion 24b can also serve as lithium ion absorption sites. Thereby, the negative electrode capacity can be further improved.

The thickness of the surface layer portion 24b is preferably 2.5 times or more the thickness of the main portion 24a from the viewpoint of further improving the capacity. More preferably, it is 5 times or more and 13 times or less. The thickness of the surface layer portion 24b is the thickness along the radial direction perpendicular to the axial direction (the direction indicated by the arrow G1) of the main portion 24a (multiwalled carbon nanotube).

<Overview of method for producing carbon nanotube composite>
Next, the outline of the method for producing the carbon nanotube composite (electrode portion 10b) according to the embodiment of the present invention described above will be described. The carbon nanotube composite described above is produced, for example, as follows. That is, first, the conductive base material 11 is prepared.

Next, the catalyst layer 13 is formed on each of the one main surface and the other main surface of the conductive substrate 11 by forming the catalyst layer 13 on each of the one main surface and the other main surface of the conductive substrate 11. A formed laminate is obtained.

Next, a carbon nanotube layer forming step (hereinafter referred to as a “CNT layer forming step”) for forming multi-walled carbon nanotubes 24 on the catalyst layer 13 of this laminate by a chemical vapor deposition (CVD) method. ). Thereby, the carbon nanotube composite (electrode portion 10b) shown in FIGS. 1 and 2 can be obtained.

Although the details will be described later, this CNT layer forming step includes a precursor forming step of forming a precursor that serves as a starting point for the growth of the multi-walled carbon nanotubes 24 on a part of the surface of the seed catalyst particle 23, and a step of forming the precursor. As a starting point, it is roughly divided into a multi-walled carbon nanotube growth step (hereinafter referred to as a “multi-walled CNT growth step”) for growing the multi-walled carbon nanotubes 24 .

(Precursor forming step)
The precursor forming process is roughly divided into a heating process of the seed catalyst particles 23 and a precursor growing process.

(Heating step of seed catalyst particles)
The step of heating the seed catalyst particles 23 is a step of maintaining the temperature of the laminate within the first temperature range for a predetermined time. By heating the seed catalyst particles 23 within the first temperature range, the seed catalyst particles 23 are activated (increased in reactivity) and the aggregation of the seed catalyst particles 23 is promoted to some extent, thereby increasing the size of the seed catalyst particles 23. The height is increased to a size suitable for growing multi-walled carbon nanotubes 24 .

As long as the temperature is within the first temperature range, the temperature is not limited to being kept constant at the predetermined holding temperature, and the temperature may be raised or lowered from the predetermined holding temperature. At least one of maintaining the temperature, raising the temperature, and lowering the temperature may be performed one or more times.

The first temperature range is a temperature range selected from 450° C. or higher and 550° C. or lower. If the lower limit of the first temperature range is lower than 450° C., the reactivity of the catalyst will be low, and the growth of the precursor will be reduced, thereby reducing the growth of the multi-walled carbon nanotubes 24 . If the upper limit of the first temperature range is higher than 550° C., the seed catalyst particles 23 are excessively agglomerated, which reduces the growth of the precursor, thereby reducing the growth of the multi-walled carbon nanotubes 24 . end up

(Precursor growth step)
The precursor growth step is a step of forming a precursor that serves as a starting point for growth of the multi-walled carbon nanotubes 24 on part of the surface of the seed catalyst particle 23 . Here, the precursor refers to a substance in a stage prior to synthesizing the multi-walled carbon nanotubes 24, or a substance in the initial stage of synthesizing the multi-walled carbon nanotubes 24 (this material may be used even if the surface layer portion 24b is not formed). good.)

In the precursor growth step, the laminate is heat-treated in an atmosphere containing the carbon source gas, and when the temperature of the laminate is within the first temperature range, the gas flow rate of the carbon source gas is set to the first predetermined gas flow rate. . Then, while heating (raising the temperature) from the first temperature range to the multi-walled carbon nanotube synthesis temperature range (hereinafter referred to as “multi-walled CNT synthesis temperature range”), the gas flow rate of the carbon source gas is changed to the first predetermined gas to flow rate. As a result, a precursor that serves as a starting point for the growth of the multi-walled carbon nanotubes 24 is formed on part of the surface of the seed catalyst particle 23 .

The first predetermined gas flow rate is an amount (smaller than the second predetermined gas flow rate, which will be described later) that can form a suitable (required) precursor for the growth of the multi-walled carbon nanotubes 24 . Specifically, the first predetermined gas flow rate is 1/15 times (≈0.067 times) or more and 1/1.8 times (≈0.56 times) or less than the second predetermined gas flow rate. It is preferable (in other words, the second predetermined gas flow rate is preferably 1.8 times or more and 15.0 times or less of the first predetermined gas flow rate).

If the first predetermined gas flow rate is less than 1/15 times the second predetermined gas flow rate (in other words, if the second predetermined gas flow rate is greater than 15.0 times the first predetermined gas flow rate), the carbon source gas is less. As a result, there is a possibility that the growth of the multi-walled carbon nanotubes 24 will decrease due to the decrease in the growth of the precursor.

When the first predetermined gas flow rate is more than 1/1.8 times the second predetermined gas flow rate (in other words, when the second predetermined gas flow rate is less than 15.0 times the first predetermined gas flow rate), the initial temperature rise ( For example, at 600° C. or lower), excessive decomposition of the carbon raw material gas may cause excessive amorphous carbon (soot) to deposit on the surfaces of the seed catalyst particles 23 . As a result, there is a possibility that the growth of the multi-walled carbon nanotubes 24 will decrease due to the decrease in the growth of the precursor.

That is, the rate of diffusion (diffusion coefficient) of the seed catalyst particles 23 into the inside tends to be higher as the temperature is higher and lower as the temperature is lower. Therefore, in a temperature range lower than the carbon nanotube synthesis temperature (600° C.), carbon becomes difficult to diffuse into the seed catalyst particles 23 , and excessive carbon tends to deposit on the surfaces of the seed catalyst particles 23 .

Therefore, if the carbon raw material gas is introduced into the chamber at a relatively large gas flow rate within a temperature range lower than the carbon nanotube synthesis temperature, the following problem occurs.

That is, excessive carbon (soot) deposits on the surfaces of the seed catalyst particles 23, and the surfaces of the seed catalyst particles 23 are covered with thick amorphous carbon. In such a state, the carbon raw material gas cannot contact the surfaces of the seed catalyst particles 23, thereby deactivating the catalyst, and as a result, the growth of carbon nanotubes is remarkably lowered. For this reason, it becomes impossible to form a suitable precursor for growing the multi-walled carbon nanotubes 24 (furthermore, the multi-walled carbon nanotubes 24 that grow starting from this).

A typical first predetermined gas flow rate of the carbon raw material gas is, for example, 0.2 SLM or more and 0.5 SLM or less.

(Multilayer CNT growth process)
The multi-walled CNT growth step is a step of growing multi-walled carbon nanotubes 24 starting from the precursor.

In the multilayer CNT growth step, when the temperature of the laminate reaches the multilayer CNT synthesis temperature range, the gas flow rate of the carbon source gas is changed from the first predetermined gas flow rate to the second predetermined gas flow rate. Then, when the temperature of the laminate is within the multilayer CNT synthesis temperature range, the gas flow rate of the carbon raw material gas is set to the second predetermined gas flow rate. As a result, multi-walled carbon nanotubes 24 are grown starting from the precursor.

As long as it is within the multi-layer CNT synthesis temperature range, it is not limited to being held constant at the predetermined holding temperature, and the temperature may be raised or lowered from the predetermined holding temperature, and after raising or lowering the temperature, At least one of holding at a constant temperature, raising the temperature, and lowering the temperature may be performed one or more times.

The multilayer CNT synthesis temperature range is a temperature range selected from 800° C. or higher and 850° C. or lower. If the lower limit of the temperature range for synthesizing multi-walled CNTs is lower than 800° C., the reactivity of the multi-walled carbon nanotubes 24 growth reaction is lowered, and the growth of the multi-walled carbon nanotubes 24 is lowered.

If the upper limit of the multilayer CNT synthesis temperature range is higher than 850° C., excessive decomposition of the carbon source gas causes excessive amorphous carbon (soot) to deposit on the surfaces of the seed catalyst particles 23 . As a result, the growth of the precursor is lowered, and the growth of the multi-walled carbon nanotubes 24 is lowered.

The second predetermined gas flow rate is preferably 1.8 to 15.0 times the first predetermined gas flow rate. If the second predetermined gas flow rate is less than 1.8 times the first predetermined gas flow rate, there is a possibility that the growth of the multi-walled carbon nanotubes 24 will deteriorate due to the insufficient amount of the carbon raw material gas.

If the second predetermined gas flow rate is more than 15.0 times the first predetermined gas flow rate, excessive decomposition of the carbon raw material gas causes excessive amorphous carbon (soot) to deposit on the surfaces of the seed catalyst particles 23. There is a possibility that the growth properties of the multi-walled carbon nanotubes 24 may deteriorate due to the storage.

A typical second predetermined gas flow rate is, for example, 0.9 SLM or more and 3.0 SLM or less.

<Detailed description of the method for producing a carbon nanotube composite>
Details of each step of the method for producing a carbon nanotube composite will be described below. An example using a copper foil as the conductive base material 11 will be described below.

(Catalyst layer forming step)
First, for example, a copper foil having a portion (convex portion) extending from a part of one side of a rectangle is prepared as the conductive base material 11 . Next, a catalyst layer 13 is formed by supporting seed catalyst particles 23 for forming multi-walled carbon nanotubes on the copper foil (conductive substrate 11) by, for example, a dip coating method.

Specifically, first, a catalyst mixture containing seed catalyst particles 23 is prepared. Next, using a dip coater (dip coating device), the copper foil is immersed in the catalyst mixed solution, and then the copper foil is pulled up from the catalyst mixed solution at a constant speed. As a result, a laminate in which the seed catalyst particles 23 are supported on the copper foil and the seed catalyst particles 23 are supported on each of the one main surface and the other main surface of the copper foil is obtained.

(CNT layer forming step)
Next, the layered product is put into a chamber of a CVD apparatus (CVD furnace), and the layered product put into the chamber is subjected to a CVD method (for example, a thermal CVD method, etc.) to form a multilayer on the surface of the catalyst layer 13. A carbon nanotube 24 is produced. That is, the multi-walled carbon nanotubes 24 are generated on the surface of the catalyst layer 13 by placing the laminate in a chamber, introducing a carbon source gas into the chamber, and heating the laminate to the temperature for synthesizing multi-walled CNTs.

As shown in FIG. 4, the CNT layer forming process is roughly divided into a precursor forming process and a multilayer CNT growing process. A CNT layer 14 is formed on the layer 13 .

(Precursor forming step)
(Heating step of seed catalyst particles))
First, the layered product is put into, for example, a chamber of a CVD apparatus. Next, a carrier gas (inert gas such as nitrogen gas) is introduced into the chamber, and the atmosphere in the chamber is heated under an inert gas atmosphere such as a nitrogen gas atmosphere, thereby increasing the temperature of the laminate (surface temperature) is raised from room temperature to the first gas introduction temperature tg1. Then, the first gas introduction temperature tg1 is maintained for a predetermined time. The first gas introduction temperature tg1 is a temperature selected from 450° C. or higher and 550° C. or lower (for example, tg1=500° C.).

(Precursor growth step)
After holding for a predetermined time, a carrier gas and a reaction gas (a carbon source gas such as a hydrocarbon gas such as an acetylene (C ₂ H ₂ ) gas) are introduced into the chamber. The temperature of the laminate at this time is the first gas introduction temperature tg1. At this time, the carbon raw material gas is introduced so that the gas flow rate becomes the first predetermined gas flow rate M1 (for example, M1=0.3 SLM).

Simultaneously with the introduction of the carbon source gas, the atmosphere in the chamber is heated to change the temperature (surface temperature) of the laminate from the first gas introduction temperature tg1 to the multi-walled carbon nanotube synthesis temperature tg2 (hereinafter referred to as "multi-walled CNT synthesis temperature tg2"). Continue to raise the temperature until the The multilayer CNT synthesis temperature tg2 is a temperature selected from 800° C. or higher and 850° C. or lower (for example, tg2=850° C.).

In this case, until the temperature of the laminate rises from the first gas introduction temperature tg1 (for example, tg1=500° C.) to the multilayer CNT synthesis temperature tg2 (for example, tg2=850° C.), the carbon source gas The gas flow rate becomes the first predetermined gas flow rate M1.

At the initial stage of temperature rise, the carbon source gas supplied into the chamber is thermally decomposed within the chamber. Carbon is generated in the gas phase or by decomposition of the carbon source gas on the surfaces of the seed catalyst particles 23 . The generated carbon diffuses into the seed catalyst particles 23 supported on the surface of the copper foil and forms a solid solution. When the concentration of carbon dissolved in the seed catalyst particles 23 rises to a predetermined concentration (limit concentration of solid solution of carbon in the seed catalyst particles 23) or higher, the growth of carbon nanotubes (multi-walled carbon nanotubes) from the seed catalyst particles 23 A carbon structure (precursor) that serves as the starting point of the is deposited.

This carbon structure (precursor) is a substantially hemispherical carbon structure generated in the initial stage of carbon nanotube growth, and has, for example, a substantially hemispherical cap structure containing six- and five-membered rings of carbon. It is a carbon structure. The seed catalyst particles 23 having the “carbon structures (precursors) serving as starting points for the growth of carbon nanotubes” formed on their surfaces are suppressed from agglomerating due to heating. Therefore, when the temperature of the laminate is raised from the first gas introduction temperature tg1 to the multilayer CNT synthesis temperature tg2, aggregation of the seed catalyst particles 23 is suppressed, thereby suppressing a decrease in growth of carbon nanotubes. .

That is, when the temperature of the laminate is raised from the first gas introduction temperature tg1 to the multi-layered CNT synthesis temperature tg2, when the temperature reaches the synthesis temperature (for example, 600° C. or higher) at which the carbon nanotubes are synthesized, the carbon nanotubes are formed. When the introduction of the carbon source gas required for growth is started, the following problem arises.

That is, since the seed catalyst particles 23 aggregate in a temperature range lower than the carbon nanotube synthesis temperature and become too coarse, the growth of the carbon nanotubes is hindered. In general, it is known that when the seed catalyst particles 23 aggregate and become too coarse, the growth of carbon nanotubes deteriorates. , the aggregation of the seed catalyst particles 23 is suppressed.). Therefore, when the carbon raw material gas required for the growth of carbon nanotubes is introduced for the first time when the synthesis temperature (for example, 600° C.) at which carbon nanotubes are synthesized is reached, the growth of the carbon nanotubes is hindered by aggregation of the seed catalyst particles 23 . end up

On the other hand, in the precursor growth step, the temperature range from the first gas introduction temperature tg1 to the carbon nanotube synthesis temperature (600° C.) in which the aggregation of the seed catalyst particles 23 is further promoted, the “carbon nanotube (multi-layer A carbon structure (precursor) that serves as a starting point for the growth of carbon nanotubes) is formed on the surface of the seed catalyst particle 23 . This suppresses aggregation of the seed catalyst particles 23 that occurs when the temperature is raised to the carbon nanotube synthesis temperature, and suppresses a decrease in growth of the carbon nanotubes.

In the precursor growth step, the gas flow rate of the carbon source gas when the temperature of the laminate rises from the first gas introduction temperature tg1 (first temperature range) to the multilayer CNT synthesis temperature tg2 (multilayer CNT synthesis temperature range) is , the first predetermined gas flow rate M1. As a result, a "carbon structure (precursor) that serves as a starting point for the growth of carbon nanotubes" can be formed. Note that the surface layer portion 24b is not formed at the time of this precursor.

After forming the precursor, by growing multi-walled carbon nanotubes from the precursor at a second predetermined gas flow rate, multi-walled carbon nanotubes including the surface layer portion 24b can be obtained (the surface layer portion 24b can be formed).

(Multiwalled carbon nanotube (CNT) growth process)
When the temperature of the laminate reaches the multilayer CNT synthesis temperature tg2, a carrier gas and a reaction gas (carbon raw material gas) are introduced into the chamber, and the gas flow rate of the carbon raw material gas is set to a second predetermined gas flow rate M2 (for example, M2 = 3.0 SLM). Then, the temperature of the laminate is held at the multilayer CNT synthesis temperature tg2 for a predetermined time.

Multi-walled carbon nanotubes 24 grow from the seed catalyst particles 23 starting from the precursor formed on the surface of the seed catalyst particles 23 . As a result, the multi-walled carbon nanotubes 24 grown from the catalyst layer 13 are formed (that is, the CNT layer 14 is formed on the catalyst layer 13). The surface layer portion 24b is formed mainly by the reaction of the carbon source gas on the surface of the main portion 24a grown from the seed catalyst particles 23. Growth is also possible.

According to the carbon nanotube electrode according to the embodiment of the present invention described above, the surface layer portion 24b is provided with superior lithium ion absorption characteristics compared to the main portion 24a. Furthermore, by growing the multi-walled carbon nanotubes 24 from the seed catalyst particles 23 supported on the conductive substrate 11, the CNT layer 14 having relatively excellent adhesion to the conductive substrate 11 can be obtained. This makes it possible to obtain an electrode (carbon nanotube electrode body) that does not use (contain) a binder for adhering the active material to the conductive substrate 11 (current collector). As a result, the negative electrode capacity can be improved.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited only to these examples.

<Example 1>
The carbon nanotubes of Example 1 were formed by forming a catalyst layer 13 (Fe seed catalyst particles)/CNT layer 14 in a rectangular shape on one main surface of a copper foil (20 μm thick) cut into a rectangular planar shape. A composite was produced.

First, a laminate having a catalyst layer formed on a copper foil was obtained by performing the following "catalyst layer forming step".

(Catalyst layer forming step)
A catalyst layer was formed by carrying Fe (iron) seed catalyst particles (average particle size: 5 nm) on each of one main surface and the other main surface of the copper foil. First, the copper foil was immersed in the coating liquid using a dip coater. A coating liquid was prepared by dispersing Fe seed catalyst particles in heptane. Next, the copper foil was pulled up from the coating liquid. As a result, a laminate was obtained in which a catalyst layer (thickness: 20 nm) composed of the Fe-type catalyst supported on the surface of the copper foil was formed. That is, a laminate was obtained in which the Fe-type catalyst particles were carried on the surface of the copper foil.

(CNT layer forming step)
(Precursor forming step)
(Heating step of seed catalyst particles)
Next, after setting this laminate at a predetermined position in the chamber of the CVD apparatus, the chamber was covered and evacuated to 10 Pa. Next, 5 SLM of nitrogen gas was introduced as a carrier gas into the chamber of the CVD apparatus, and the pressure was adjusted to 90 kPa.

Thereafter, as shown in FIG. 5, the atmosphere in the chamber is heated from room temperature (RT) until the temperature (surface temperature) of the laminate reaches 500° C. (the first gas introduction temperature tg1), thereby lowering the temperature of the laminate. The temperature was raised at a constant heating rate. After that, the same temperature (500° C.) was held for 600 seconds.

(Precursor growth step)
After that, acetylene gas (C ₂ H ₂ gas) and carrier gas (nitrogen gas) were introduced into the chamber at a gas flow rate of C ₂ H ₂ gas: carrier gas = 0.3 SLM (first predetermined gas flow rate M1): 5 SLM. introduced. Simultaneously with the introduction of the gas, the atmosphere in the chamber was heated from 500°C (first gas introduction temperature tg1) at a constant heating rate for 500 seconds until the temperature of the laminate reached 850°C (multilayer CNT synthesis temperature tg2). was heated to raise the temperature. As a result, a multi-walled carbon nanotube precursor was formed on the surface of the seed catalyst particles.

(Multilayer CNT growth process)
After that, when the temperature of the laminated body reached 850° C. (multilayer CNT synthesis temperature tg2), acetylene gas (C ₂ H ₂ gas) and carrier gas (nitrogen gas) were mixed with C ₂ H ₂ gas:carrier gas=3. 0 SLM (second predetermined gas flow rate M2): introduced into the chamber at a gas flow rate of 17 SLM.

Thereafter, the same temperature (850° C.) was maintained for 2500 seconds to form multi-walled carbon nanotubes on the surface of the copper foil of the laminate. As described above, a carbon nanotube composite of Example 1 was produced.

<Example 2>
A carbon nanotube composite of Example 2 was produced in the same manner as in Example 1, except that the second predetermined gas flow rate M2 of the acetylene gas in the multilayer CNT growth step was changed to 0.9 SLM.

<Comparative Example 1>
A carbon nanotube composite of Comparative Example 1 was produced in the same manner as in Example 1, except that the second predetermined gas flow rate M2 of the acetylene gas in the multilayer CNT growth step was changed to 0.3 SLM.

<Comparative Example 2>
A carbon nanotube composite of Comparative Example 2 was produced in the same manner as in Example 1, except that the catalyst layer forming step and the CNT layer forming step were changed as follows.

(Catalyst layer forming step)
In the same manner as in Example 1, except that Fe (iron) seed catalyst particles (average particle size 25 nm) were used instead of Fe (iron) seed catalyst particles (average particle size 5 nm). A laminate carrying the Fe seed catalyst particles was obtained.

(CNT layer forming step)
After the laminate was set at a predetermined position in the chamber of the CVD apparatus, the chamber was covered and evacuated to 10 Pa. Next, 5 SLM of nitrogen gas was introduced as a carrier gas into the chamber of the CVD apparatus, and the pressure was adjusted to 90 kPa.

Thereafter, as shown in FIG. 6, the temperature of the laminate was raised by heating the atmosphere in the chamber until the temperature (surface temperature) of the laminate reached 850° C. from room temperature at a constant heating rate. .

(CNT growth process)
After that, when the temperature of the laminate reached 850° C., acetylene gas (C ₂ H ₂ gas) and carrier gas (nitrogen gas) were added at that temperature, C ₂ H ₂ gas:carrier gas=0.3 SLM:17 SLM. was introduced into the chamber at a gas flow rate of

Thereafter, the same temperature (850) was maintained for 2500 seconds to form multi-walled carbon nanotubes on the surface of the copper foil of the laminate. As described above, a carbon nanotube composite of Comparative Example 2 was produced.

<Comparative Example 3>
A carbon nanotube composite of Comparative Example 3 was produced in the same manner as in Comparative Example 2, except that the flow rate of the acetylene gas introduced when the temperature of the laminate reached 850 ° C. in the CNT growth process was changed to 3.0 SLM. made.

(evaluation)
(Observation of state of carbon nanotube formation)
For the carbon nanotubes of each of the carbon nanotube composites of Examples 1 to 2 and Comparative Examples 1 to 3, the state of formation of the carbon nanotubes was observed using a SEM (Scanning Electron Microscope) and a TEM (Transmission Electron Microscope). . SEM images and TEM images at that time are shown in FIGS.

Furthermore, FFT images (electron diffraction images) were obtained by subjecting the TEM images of Example 1 and Comparative Example 1 to inverse Fourier transform, and diffraction spots due to the carbon 002 plane were confirmed. FFT images of Example 1 and Comparative Example 1 are shown in FIG.

As shown in FIGS. 7 to 10, according to the TEM images of Examples 1 and 2, a portion (R11) corresponding to the main portion 24a and a portion (R11) corresponding to the surface layer portion 24b are included in the region R11 and the region R12. A difference in appearance from the portion (R12) was confirmed. That is, the formation of the surface layer portion 24b different from the main portion 24a was confirmed. On the other hand, in Comparative Examples 1 and 2, formation of the surface layer portion 24b could not be confirmed.

As shown in FIG. 11, in the FFT image of Example 1, the shape of the diffraction spots S2a and S2b and S3a and S3b of Comparative Example 1, which can be regarded as corresponding to the main body portion 24a of Example 1, is elongated. Diffraction spots S1a and S1b were confirmed. That is, a difference in physical properties between the main body portion 24a and the surface layer portion 24b was confirmed.

(Measurement of CNT amount (mg/cm ² ))
The mass (mg/cm ² ) of multi-walled carbon nanotubes (multi-walled carbon nanotubes in the comparative example) per unit area of the CNT layer 14 formed on the copper foil was measured as the CNT amount (mg/cm ² ).

(Measurement of CNT height, measurement of CNT diameter, thickness of each main part and surface layer, and measurement of thickness magnification)
Based on the SEM image or TEM image, the CNT height, CNT diameter, thickness of the main portion and surface layer portion, and thickness magnification were measured. The thickness ratio is the thickness of the surface layer portion relative to the thickness of the main portion (that is, thickness ratio = thickness of surface portion/thickness of main portion).

(capacitance measurement)
A coin cell was produced using the produced carbon nanotube composite (that is, the negative electrode). The produced carbon nanotube composite was used as a negative electrode, and metallic lithium was used as a counter electrode.

A disc-shaped working electrode and a counter electrode (electrode area: 1.77 cm ² ) sandwiching a disc-shaped polyethylene separator (porous film) was placed in a SUS disc-shaped battery case (CR2032 type coin cell case). inserted into the Next, 1 mL of the electrolytic solution was injected into the battery case, the laminate was immersed in the electrolytic solution, and the battery case was sealed to prepare a coin cell.

A coin cell was charged at a temperature of 25° C. with a charging voltage of 3.8 V and a charging current of 1 mA, and then discharged with a discharging current of 1 mA to measure the discharge capacity. The capacity (negative electrode capacity) (mAh/g) was determined by dividing the measured discharge capacity by the mass of the multi-walled carbon nanotubes contained in the carbon nanotube composite.

Table 1 shows the manufacturing processes of Examples and Comparative Examples, and Table 2 shows the evaluation results. In Comparative Example 3, it was confirmed visually that CNTs were sparsely scattered because the seed catalyst particles aggregated and the amount of acetylene gas supplied was too large. That is, the growth of carbon nanotubes was poor, and it was determined that the evaluation was not possible.

<Examples 3-1 to 3-4 and Comparative Examples 3-1 to 3-2>
As described below, Examples 3-1 to 3-4 and Comparative Examples 3-1 to 3-2 were produced by changing the first gas introduction temperature tg1 to various temperatures.

<Example 3-1>
A carbon nanotube composite of Example 3-1 was produced in the same manner as in Example 1.

<Example 3-2>
A carbon nanotube composite of Example 3-2 was produced in the same manner as in Example 3-1, except that the first gas introduction temperature tg1 in the precursor forming step was changed to 450°C.

<Example 3-3>
A carbon nanotube composite of Example 3-3 was produced in the same manner as in Example 3-1, except that the first gas introduction temperature tg1 in the precursor forming step was changed to 470°C.

<Example 3-4>
A carbon nanotube composite of Example 3-4 was produced in the same manner as in Example 3-1, except that the first gas introduction temperature tg1 in the precursor forming step was changed to 550°C.

<Comparative Example 3-1>
A carbon nanotube composite of Example 3-2 was produced in the same manner as in Example 3-1, except that the first gas introduction temperature tg1 in the precursor forming step was changed to 400°C.

<Comparative Example 3-2>
A carbon nanotube composite of Example 3-2 was produced in the same manner as in Example 3-2, except that the first gas introduction temperature tg1 in the precursor forming step was changed to 600°C.

(evaluation)
(Measurement of CNT length)
The length of the CNTs (precursor) grown from the seed catalyst particles at the time when the precursor forming step was completed was measured as the CNT length. CNT length was obtained from the SEM image.

The production processes of Examples 3-1 to 3-4 and Comparative Examples 3-1 to 3-2 are shown in Table 3, and the measurement results of the CNT length of each Example and each Comparative Example are shown in FIG. .

As shown in FIG. 12, according to Examples 3-1 to 3-4, precursors suitable for growing multi-walled carbon nanotubes could be produced. In contrast, according to Comparative Examples 3-1 and 3-2, it was not possible to grow a suitable precursor for growing multi-walled carbon nanotubes. From the above, it has been confirmed that the first gas introduction temperature tg1 is preferably in the range of 450° C. or more and 550° C. or less.

<Examples 4-1 to 4-4, Comparative Examples 4-1 to 4-2>
As described below, Examples 4-1 to 4-4 and Comparative Examples 4-1 to 4-2 were produced by varying the flow rate of acetylene introduced at the first gas introduction temperature tg1.

<Example 4-1>
A carbon nanotube composite of Example 4-1 was produced in the same manner as in Example 1.

<Example 4-2>
A carbon nanotube composite of Example 4-2 was produced in the same manner as in Example 4-1, except that the first predetermined gas flow rate M1 of the acetylene gas in the precursor forming step was changed to 0.2 SLM.

<Example 4-3>
A carbon nanotube composite of Example 4-3 was produced in the same manner as in Example 4-1, except that the first predetermined gas flow rate M1 of the acetylene gas in the precursor forming step was changed to 0.4 SLM.

<Example 4-4>
A carbon nanotube composite of Example 4-4 was produced in the same manner as in Example 4-1, except that the first predetermined gas flow rate M1 of the acetylene gas in the precursor forming step was changed to 0.5 SLM.

<Comparative Example 4-1>
A carbon nanotube composite of Comparative Example 4-1 was produced in the same manner as in Example 4-1, except that the first predetermined gas flow rate M1 of the acetylene gas in the precursor forming step was changed to 0.1 SLM.

(evaluation)
(Measurement of CNT length of precursor)
The length of the CNTs (precursor) grown from the seed catalyst particles at the time when the precursor forming step was completed was measured as the CNT length. CNT length was obtained from the SEM image.

Table 4 shows the production processes of Examples 4-1 to 4-4 and Comparative Example 4-1, and FIG. 13 shows the measurement results of the CNT length of each Example and each Comparative Example.

As shown in FIG. 13, according to Examples 4-1 to 4-4, precursors suitable for growing multi-walled carbon nanotubes could be produced. In contrast, according to Comparative Example 4-1, it was not possible to grow a suitable precursor for growing multi-walled carbon nanotubes. From the above, it has been confirmed that the first predetermined gas flow rate M1 is preferably in the range of 0.2 SLM or more and 0.5 SLM or less.

<Examples 5-1 to 5-2, Comparative Example 5-1>
As described below, carbon nanotube composites of Examples 5-1 to 5-2 and Comparative Example 5-1 were produced by varying the multilayer CNT synthesis temperature tg2.

<Example 5-1>
A carbon nanotube composite of Example 5-1 was produced in the same manner as in Example 1.

<Example 5-2>
A carbon nanotube composite of Example 5-2 was produced in the same manner as in Example 5-1, except that the multi-walled CNT synthesis temperature tg2 in the multi-walled CNT growth step was changed to 800°C.

<Comparative Example 5-1>
A carbon nanotube composite of Comparative Example 5-1 was produced in the same manner as in Example 5-1, except that the multi-walled CNT synthesis temperature tg2 in the multi-walled CNT growth step was changed to 770°C.

(evaluation)
(Measurement of CNT amount (mg/cm ² ))
The amount of CNT (mg/cm ² ) was measured in the same manner as in Example 1.

The production processes of Examples 5-1 to 5-2 and Comparative Example 5-1 are shown in Table 5, and the measurement results of the CNT basis weight of each Example and Comparative Example are shown in FIG.

As shown in FIG. 14, according to Examples 5-1 and 5-2, it was confirmed that the growth of multi-walled carbon nanotubes was good. On the other hand, according to Comparative Example 5-1, it was confirmed that the multi-walled carbon nanotube growth was low. From the above, it has been confirmed that the multilayer CNT synthesis temperature tg2 is preferably in the range of 800° C. or higher and 850° C. or lower.

<Examples 6-1 to 6-2, Comparative Example 6-1>
As will be described below, carbon nanotube composites of Examples 6-1 to 6-2 and Comparative Example 6-1 were produced by varying the second predetermined gas flow rate M2 of the acetylene gas in the multilayer CNT growth process. did.

<Example 6-1>
A carbon nanotube composite of Example 6-1 was produced in the same manner as in Example 1.

<Example 6-2>
A carbon nanotube composite of Example 6-2 was produced in the same manner as in Example 6-1, except that the second predetermined gas flow rate M2 of the acetylene gas in the multilayer CNT growth step was changed to 0.9 SLM.

<Example 6-3>
A carbon nanotube composite of Example 6-3 was produced in the same manner as in Example 6-1, except that the second predetermined gas flow rate M2 of the acetylene gas in the multilayer CNT growth process was changed to 2.5 SLM.

<Comparative Example 6-1>
A carbon nanotube composite of Comparative Example 6-1 was produced in the same manner as in Example 6-1, except that the second predetermined gas flow rate M2 of the acetylene gas in the multilayer CNT growth step was changed to 0.3 SLM.

(evaluation)
(Measurement of CNT amount (mg/cm ² ))
The amount of CNT (mg/cm ² ) was measured in the same manner as in Example 1.

(capacitance measurement)
The capacity was measured in the same manner as in Example 1-1.

The production processes of Examples 6-1 to 6-3 and Comparative Example 6-1 are shown in Table 6, and the measurement results of the CNT basis weight of each Example and Comparative Example are shown in FIG. FIG. 16 shows the measurement results of the capacitance of .

As shown in FIGS. 15 and 16, according to Examples 6-1 to 6-3, it was confirmed that the growth of multi-walled carbon nanotubes was good. On the other hand, according to Comparative Example 6-1, it was confirmed that the growth of multi-walled carbon nanotubes was low. From the above, it has been confirmed that the second predetermined gas flow rate M2 of the acetylene gas is preferably in the range of 0.9 SLM or more and 3.0 SLM or less. In addition to this, considering the preferable range of the first predetermined gas flow rate M1 (range of 0.2 SLM or more and 0.5 SLM or less) confirmed by Examples 4-1 to 4-4 described above, the amount of acetylene gas It was confirmed that the second predetermined gas flow rate M2 is preferably 1.8 times (=0.9SLM/0.5SLM) or more and 15 times (=3.0SLM/0.2SLM) or less than the first predetermined gas flow rate M1. .

<Modification>
Although the embodiments and examples of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments and examples, and various modifications are possible based on the technical concept of the present invention. is.

For example, the configurations, methods, steps, shapes, materials, numerical values, etc., given in the above-described embodiments and examples are merely examples, and different configurations, methods, steps, shapes, materials, numerical values, etc., may be used if necessary. may be used.

Also, the configurations, methods, steps, shapes, materials, numerical values, etc. of the above-described embodiments and examples can be combined with each other without departing from the gist of the present invention.

You may use the carbon nanotube electrode mentioned above for the electrode (for example, negative electrode) of an electrical storage device. The electricity storage device may be, for example, a lithium ion capacitor, a lithium ion secondary battery, a dual carbon battery, or other electricity storage devices.

DESCRIPTION OF SYMBOLS 10... Electrode 10a... Electrode part 10b... Terminal part 11... Conductive base material 13... Catalyst layer 14... CNT (carbon nanotube) layer 23... Seed catalyst particle 24... Multi-walled carbon nanotube 24a... Main body Part, 24b... Surface layer part

Claims (6)

a conductive substrate made of a conductive metal having conductivity;
multi-walled carbon nanotubes grown from seed catalyst particles provided on a conductive substrate;
including
The multi-walled carbon nanotube is
a main body including a plurality of concentrically arranged tubular graphene sheets extending along the axial direction of the multi-walled carbon nanotube;
A surface layer portion that includes a plurality of graphene sheets having physical properties different from those of the tubular graphene sheet that overlaps the outside of the main portion, and that has more carbon ring-deficient portions, which are portions in which the carbon rings of the graphene sheets are lacking, compared to the main portion. When,
including,
carbon nanotube electrode. The carbon nanotube electrode of claim 1 ,
The carbon nanotube electrode, wherein the electron diffraction image of the surface layer portion includes a diffraction spot due to the carbon 002 surface that is elongated compared to the shape of the diffraction spot due to the carbon 002 surface in the electron diffraction image of the main portion. In the carbon nanotube electrode according to claim 1 or claim 2,
The thickness of the surface layer is 2.5 times or more the thickness of the main body,
carbon nanotube electrode. a positive electrode;
a negative electrode made of a carbon nanotube electrode;
an electrolyte;
including
The carbon nanotube electrode is
a conductive substrate made of a conductive metal having conductivity;
multi-walled carbon nanotubes grown from seed catalyst particles provided on a conductive substrate;
including
The multi-walled carbon nanotube is
a main body including a plurality of concentrically arranged tubular graphene sheets extending along the axial direction of the multi-walled carbon nanotube;
A surface layer portion that includes a plurality of graphene sheets having physical properties different from those of the tubular graphene sheet that overlaps the outside of the main portion, and that has more carbon ring-deficient portions, which are portions in which the carbon rings of the graphene sheets are lacking, compared to the main portion. When,
including,
storage device. a laminate forming step of forming a catalyst layer composed of seed catalyst particles for forming multi-walled carbon nanotubes on a conductive base material composed of a conductive metal having electrical conductivity;
a carbon nanotube layer forming step of forming the multi-walled carbon nanotubes on the catalyst layer;
has
The carbon nanotube layer forming step includes
The laminate is placed in a chamber, and when the temperature of the laminate in the chamber is within a first temperature range selected from the temperature range of 450° C. or higher and 550° C. or lower, the gas flow rate of the carbon source gas is reduced to the first temperature range. 1 After introducing into the chamber at a predetermined gas flow rate, with the gas flow rate of the carbon raw material gas set to the first predetermined gas flow rate, up to a multi-walled carbon nanotube synthesis temperature range selected from the range of 800 ° C. or higher and 850 ° C. or lower. a precursor forming step including a precursor growing step of forming a precursor that serves as a starting point for growth of the multi-walled carbon nanotubes on a portion of the surface of the seed catalyst particles by raising the temperature;
After the precursor forming step, when the temperature of the laminate is within the multi-walled carbon nanotube synthesis temperature range, the gas flow rate of the carbon raw material gas is set to a second predetermined gas flow rate, and the precursor is used as a starting point. a carbon nanotube growth step for growing multi-walled carbon nanotubes, wherein the second predetermined gas flow rate is 1.8 times or more and 15.0 times or less the first predetermined gas flow rate;
including,
A method for producing a carbon nanotube composite. In the method for producing a carbon nanotube composite according to claim 5,
The precursor formation step includes
Further comprising a seed catalyst particle heating step of maintaining the temperature of the laminate in the chamber within the first temperature range by heating the laminate before the precursor growth step,
A method for producing a carbon nanotube composite.

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