JP2017174789A - Electrode for battery, biofuel cell and manufacturing method of electrode for battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrode for a battery capable of enhancing the output furthermore, and to provide a biofuel cell and a manufacturing method of the electrode for the battery.SOLUTION: An electrode for a battery includes a base material containing multiple carbon fiber bundles, and a conductive mesh structure 18 adhering to the surface and interior of the base material, and containing an aggregation of carbon nanotube foils 20. The conductive mesh structure 18 formed in the base material interconnects the carbon fibers 16 contained in a carbon fiber bundle 14, and connects the carbon fibers contained in one carbon fiber bundle with the carbon fibers contained in the other carbon fiber bundle.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a battery electrode, a biofuel cell, and a method for producing a battery electrode.

  In recent years, biofuel cells have attracted attention as fuel cells using enzymes as catalysts instead of metal catalysts such as platinum. In biofuel cells, oxidoreductases are used to oxidize fuel and reduce oxygen to convert chemical energy into electrical energy.

  In such a biofuel cell, various improvements have been made to improve the output.

  For example, Patent Document 1 discloses an enzyme electrode in which carbon fine particles such as carbon nanotubes are fixed to a conductive base material together with an enzyme and a metal oxide to increase the efficiency of the enzyme reaction.

JP 2012-28181 A

  Since carbon fine particles are conductive materials having a large specific surface area, they are useful as electrode materials. The greater the amount of fine carbon particles fixed to the substrate, the higher the performance of the electrode. By using an electrode on which a larger amount of carbon fine particles are fixed, a battery with improved output can be obtained.

  However, when the carbon fine particles are attached to the substrate surface, the carbon fine particles are easily detached when the amount of the carbon fine particles attached increases. In this case, the surroundings may be contaminated by the desorbed carbon fine particles. On the other hand, when carbon fine particles are adhered to the base material so as not to desorb, the amount of carbon fine particles attached is not sufficient for improving the performance.

  In order to further improve the output of the biofuel cell, there is a need for a battery electrode in which a larger amount of carbon fine particles are effectively adhered to a substrate.

  Then, an object of this invention is to provide the manufacturing method of the electrode for batteries which can improve an output more, a biofuel cell, and the electrode for batteries.

  The battery electrode of the present invention includes a base material including a plurality of carbon fiber bundles, and a conductive network structure that is attached to the surface and the inside of the base material and includes an aggregate of thin pieces of carbon nanotubes. The conductive network structure formed inside the material connects the carbon fibers between the carbon fibers contained in the carbon fiber bundle, and the carbon fiber contained in one carbon fiber bundle and the other carbon fiber. It is characterized by connecting the carbon fibers contained in the bundle.

  The biofuel cell of the present invention is characterized by using the aforementioned battery electrode.

  The method for producing a battery electrode according to the present invention includes a step of preparing a carbon nanotube dispersion, and using the carbon nanotube dispersion, a conductive network structure including an aggregate of carbon nanotube flakes is formed on a surface of a substrate and The carbon nanotube flakes are formed by freeze-drying the carbon nanotube dispersion.

  In the battery electrode of the present invention, the conductive network structure is attached to the surface and inside of the substrate. Since the conductive network structure includes an aggregate of thin pieces of carbon nanotubes, the amount of carbon nanotubes contained in the battery electrode is larger than when the carbon nanotubes are attached to the substrate in a single state. In addition, since the conductive network structure has a large surface area, the surface area of the battery electrode efficiently increases when the conductive network structure adheres to the surface of the substrate.

  Further, since the battery electrode has a sufficient conductive path formed on the base material by such a conductive network structure, the output of the battery can be further improved when used for a battery.

  The biofuel cell of the present invention uses a battery electrode with a sufficient conductive path, so that it can generate electric energy more efficiently than the conventional one, and the surface area of the battery electrode is large. The current density can be increased more and the output of the battery can be further improved.

  In the method for producing a battery electrode according to the present invention, the carbon nanotube dispersion is freeze-dried to form the carbon nanotube flakes. In the manufacturing method of the present invention, since the carbon nanotube flakes are formed on the surface and inside of the base material, or the carbon nanotube flakes are permeated into the base material, the electrode for battery having the conductive network structure attached to the base material Can be manufactured.

It is a schematic diagram which expands and shows a part of battery electrode which concerns on this embodiment. It is a schematic diagram which shows the structure of a carbon fiber bundle. It is a CCD microscope image which image | photographed the electroconductive network structure. FIG. 4A is a scanning electron microscope (SEM) image of a conductive mesh structure, FIG. 4A is an overall image, and FIG. 4B is an enlarged image of a region X1 in FIG. 4A. It is a schematic diagram explaining the state of the some carbon fiber contained in a carbon fiber bundle. It is a SEM image which shows the carbon fiber connected by the electroconductive network structure. It is a SEM image which shows a block-like CNT flake (bulk body). It is a schematic diagram of a block-like CNT flake (bulk body). It is a schematic diagram which expands and shows a part of battery electrode which concerns on other embodiment. 3 is a graph comparing current-potential curves of the battery electrode of Example 1 and the battery electrode of Comparative Example 1. FIG. It is a graph which shows the electric current-potential curve of the battery electrode of Examples 2-10. It is a graph which shows the time change of the reduction current value of the electrode for batteries of Examples 2-10. It is the graph which compared the electric current-potential curve of the battery electrode of Example 9, and the battery electrode of the comparative example 1. It is the graph which compared the CNT adhesion amount dependence of the battery electrode of an Example and the battery electrode of a comparative example. It is a SEM image of the surface of the carbon fiber in the base material contained in the battery electrode of Example 5, FIG. 15A is an overall image, and FIG. 15B is an enlarged image. 4 is a SEM image of the surface of carbon fibers in a base material included in the battery electrode of Comparative Example 1. It is a SEM image of the surface of the carbon fiber in the base material contained in the battery electrode of Comparative Example 4. 6 is a SEM image of a cross section of a base material included in the battery electrode of Example 5. 4 is a SEM image of a cross section of a base material included in the battery electrode of Comparative Example 1.

(1) Biofuel cell of this embodiment The biofuel cell according to this embodiment uses a battery electrode of this embodiment described later as at least one of an anode electrode and a cathode electrode. The biofuel cell according to the present embodiment can use a configuration of a known biofuel cell except for this point.

  For example, the biofuel cell of this embodiment has a configuration in which an anode electrode and a cathode electrode are arranged in an electrolyte solution. The electrolyte includes a fuel that is oxidized to release electrons, an oxidoreductase, and, if necessary, an electron transfer mediator. The oxidoreductase oxidizes fuel at the anode electrode and reduces oxygen and the like at the cathode electrode. The electron transfer mediator mediates the transfer of electrons between the enzyme and the electrode.

  As the fuel, all reducing substances that can be used as an energy source by living organisms such as sugar, alcohol, organic acid, amine, hydrogen and inorganic compounds can be used.

  More specifically, as fuel, alcohols such as methanol, ethanol, propanol, glycerin and polyvinyl alcohol, sugars such as glucose, fructose and sorbose, aldehydes such as formaldehyde and acetaldehyde, and mixtures thereof can be used. .

  As the oxidoreductase, an enzyme capable of oxidizing the above fuel and reducing oxygen can be selected and used according to the fuel used.

  Examples of oxidoreductases include laccase, ascorbate oxidase, bilirubin oxidase (BOD), glucose dehydrogenase (GDH), alcohol dehydrogenase (ADH), aldehyde dehydrogenase, glucose oxidase (GOD), alcohol oxidase (AOD), and aldehyde oxidase. Can be used.

  Only one type of oxidoreductase may be used alone, or two or more types may be used in combination.

  Electron transfer mediators include, for example, metal complexes having metal elements such as Os, Fe, Ru, Co, Cu, Ni, V, Mo, Cr, Mn, Pt, and W, quinones, benzoquinones, anthraquinones, and naphthoquinones. And heterocyclic compounds such as quinogens such as viologen, methyl viologen and benzyl viologen. The electron transfer mediator is selected according to the oxidoreductase used.

(2) Configuration of Battery Electrode of this Embodiment As shown in FIG. 1, the battery electrode 10 includes a base material 12 including a plurality of carbon fiber bundles 14.

  In the present embodiment, the base material 12 is a plain woven fabric (carbon fiber cloth) in which the carbon fiber bundle 14 is a warp yarn 14a and a weft yarn 14b. The substrate 12 may be subjected to water repellent treatment with a fluororesin such as Teflon (registered trademark). The carbon fiber bundle 14 includes a plurality of carbon fibers 16 as shown in FIG.

  On one surface of the substrate 12, a conductive network structure 18 as shown in the CCD microscope image of FIG. 3 is formed. The CCD microscope image in FIG. 3 is an observation of the conductive network structure 18 redispersed in ethanol. The conductive network structure 18 is attached to the surface of the carbon fiber 16 included in the carbon fiber bundle 14 on the one surface of the substrate 12. The conductive network structure 18 is not limited to a single structure that covers one surface of the substrate 12. The conductive network structure 18 may include a plurality of structures having a size of about 5 μm □ to 600 μm □.

  The conductive network structure 18 includes an aggregate of thin pieces 20 of carbon nanotubes (hereinafter referred to as CNT). In the present embodiment, the conductive network structure 18 is composed of an aggregate of CNT flakes 20 (see FIGS. 4A and 4B). The CNT flakes 20 are flakes in which a plurality of CNTs are directly connected to each other and stacked in a plurality of layers. The CNT flakes 20 have a thickness of about several nm to several tens of nm. The plurality of CNT slices 20 are three-dimensionally joined to form a network, and the conductive network structure 18 is formed. The CNT flakes 20 may be coupled to other CNT flakes 20 via CNTs. In the conductive network structure 18, open bubbles having a size of about 1 to 100 μm are present.

  Direct connection means that the CNTs are not covered with a dispersant, a surfactant, an adhesive, etc., but are entangled with each other, and an inclusion such as an adhesive, a dispersant, a surfactant, etc. Indicates that the connection is made without going through. Direct connection includes physical connection (simple contact) and chemical connection.

  In the battery electrode 10, the conductive network structure 18 is attached to the inside of the base material 12. The inside of the base material 12 refers to a portion not exposed to the outside of the base material 12 and includes the inside of the carbon fiber bundle 14. As shown in FIG. 5, inside the carbon fiber bundle 14, a conductive network structure 18 having a gap 24 between the CNT thin pieces 20 connects the carbon fibers 16.

  The conductive network structure 18 is directly fixed to the surface of the carbon fiber 16. The conductive network structure 18 is fixed to the surface of the carbon fiber 16 by the CNT flakes 20 or CNT (not shown) included in the conductive network structure 18 being directly fixed to the surface of the carbon fiber 16. ing. There are no adhesives, dispersants, surfactants, etc. between the carbon fibers 16 and the CNT flakes 20 and between the carbon fibers 16 and the CNTs.

  Although not shown, the conductive network structure 18 also connects the carbon fibers 16 to each other on the surface of the carbon fiber bundle 14. Also in this case, the CNT flakes 20 or CNTs are directly fixed to the surface of the carbon fiber 16. In a portion where two carbon fiber bundles 14 (warp yarn 14a and weft yarn 14b) are in contact, a plurality of CNT slices 20 form a conductive network structure 18, and carbon contained in one carbon fiber bundle 14 (for example, warp yarn 14a). The fiber 16 and the carbon fiber 16 contained in the other carbon fiber bundle 14 (for example, the weft 14b) can be connected.

  An SEM image of the carbon fiber 16 connected by the conductive network structure 18 is shown in FIG. A gap 24 exists between the two carbon fibers 16, and the carbon fibers 16 are connected to each other by a conductive network structure 18 made of an aggregate of the CNT thin pieces 20. The CNT flakes 20 in the conductive network structure 18 are directly fixed to the surface of the carbon fiber 16. Although not shown in FIG. 6, open bubbles of a predetermined size exist in the conductive network structure 18. It is confirmed that the CNT 19 is attached to a part of the surface of the carbon fiber 16.

  The fixation means the bonding by the van der Waals force between the CNTs contained in the conductive network structure 18 and the carbon fibers 16 and the chemistry via the functional groups of the CNTs contained in the conductive network structure 18 and the carbon fibers 16. Including typical bonds. As will be described later, the functional group is formed on the surface of the carbon fiber 16 or the surface of the CNT included in the conductive network structure 18.

  In the present embodiment, the surface of the carbon fiber 16 is oxidized. A functional group such as a hydroxy group and a carboxy group is formed on a part of the surface of the carbon fiber 16.

  The surface of the CNT included in the conductive network structure 18 is similarly oxidized, and has functional groups such as a hydroxy group and a carboxy group on the surface. The functional group on the CNT surface contributes to the delivery of electrons when the battery electrode 10 is used as a battery electrode.

  As a result, electrons are transferred more smoothly. As a result, in the battery using the battery electrode 10 as an electrode, electric energy can be generated efficiently, and the output of the battery is improved. When the battery electrode 10 is used as an electrode of a biofuel cell, such a biofuel cell in which electrons are transferred between the conductive network structure 18 and the electron transfer mediator via a functional group. In this case, the delivery of electrons becomes smoother and the output of the battery is further improved.

  As described above, the battery electrode 10 of the present embodiment includes the conductive network structure 18 attached to the substrate 12. The conductive network structure 18 is composed of an aggregate of a plurality of CNT slices 20. The total amount of CNT contained in the conductive network structure 18 is preferably a ratio of 0.01 wt% or more and 10 wt% or less with respect to the base material 12. When it is less than 0.01 wt%, the presence frequency of CNTs is low, and it is difficult to connect carbon fibers. On the other hand, if it exceeds 10 wt%, the thixotropy is too high and the affinity with the carbon fiber cloth deteriorates, making it difficult to form a composite. When the CNT is within the above range, the output of the battery can be increased without impairing the function of the substrate 12. The total amount of CNT contained in the battery electrode 10 is more preferably 0.1 wt% or more and 10 wt% or less with respect to the base material 12, and most preferably 3 wt% or more and 10 wt% or less.

  The CNT flakes 20 are only required to form a network on one surface and inside of the base material 12 to form the conductive network structure 18, and the distribution state of the CNT flakes 20 in the thickness direction of the base material 12 is particularly Not specified. The conductive network structure 18 may be formed on the other surface in addition to the one surface of the substrate 12.

  In addition, unless the function of the base material 12 and the conductive network structure 18 is limited, the battery electrode 10 includes the CNT flakes 20 including CNTs bonded to the carbon fibers 16 via an adhesive, a dispersant, or the like. May be.

(3) Manufacturing method of battery electrode of this embodiment Subsequently, the manufacturing method of the battery electrode 10 is demonstrated. The method for manufacturing the battery electrode 10 includes (3-1) a step of preparing a CNT dispersion, and (3-2) a step of attaching a conductive network structure made of an aggregate of CNT flakes to a substrate. . The CNT flakes are formed by lyophilizing the CNT dispersion. Hereinafter, each step will be described.

(3-1) Step of Preparing CNT Dispersion The CNT dispersion can be prepared by, for example, preparing CNTs and dispersing the obtained CNTs in a dispersion solvent.

(3-1-1) Production of CNT CNT can be produced using a thermal CVD method as described in, for example, Japanese Patent Application Laid-Open No. 2007-126311. In this case, first, a catalyst film made of aluminum and iron is formed on a silicon substrate, and the catalyst film is heat-treated to form catalyst particles on the surface of the catalyst film. Next, CNT can be produced by bringing hydrocarbon gas into contact with the catalyst particles in a heated atmosphere and growing the CNTs from the catalyst particles.

  The CNTs thus produced are linearly oriented in the direction perpendicular to the substrate surface on the substrate and have a high aspect ratio of several hundred to several thousand. The CNT is used by cutting it from the substrate. When the cut CNT contains catalyst residues such as catalyst particles and fragments thereof, it is desirable to remove the catalyst residues by performing an appropriate treatment. The catalyst residue can be removed by annealing the produced CNT at a high temperature in an inert gas. Or you may remove a catalyst residue by immersing CNT in the mixed acid of nitric acid and a sulfuric acid, or the hydrogen peroxide solution and the sulfuric acid persulfate of a sulfuric acid, and performing an acid treatment. The ratio of nitric acid and sulfuric acid in the mixed acid can be arbitrarily determined. The ratio of the hydrogen peroxide solution and sulfuric acid in the sulfuric acid / hydrogen peroxide can also be determined arbitrarily. When the CNT is subjected to an acid treatment, the surface of the CNT is oxidized.

  CNTs are preferably produced by a method that can be obtained without containing impurities (such as catalyst residues) other than CNTs as much as possible. CNT can also be produced by other methods such as an arc discharge method and a laser evaporation method. When the produced CNT contains impurities, it is desirable to remove the impurities in the same manner as the catalyst residue.

  The CNT is preferably multi-layered. Moreover, it is preferable that CNT is 0.1 micrometer or more and 50 micrometers or less in length. When the length of the CNT is 0.1 μm or more, the CNTs are entangled and directly connected. Further, when the length of the CNT is 50 μm or less, it becomes easy to disperse evenly. On the other hand, if the length of the CNT is less than 0.1 μm, the CNTs are less likely to be entangled with each other. Further, CNTs tend to aggregate when the length exceeds 50 μm.

  The CNT preferably has a diameter of 30 nm or less. If the diameter of the CNT is 30 nm or less, the CNT flakes 20 can be easily deformed, so that the conductive network structure 18 can be easily formed by forming the CNT flakes 20. On the other hand, if the diameter of the CNT is more than 30 nm, the CNT flakes 20 are difficult to form because the flexibility is poor and deformation is difficult.

  The diameter of CNT is more preferably 20 nm or less. The diameter of CNT is taken as the average diameter calculated | required from the image image | photographed with the transmission electron microscope (TEM: Transmission Electron Microscope). The image can be taken by taking a part of the CNT from the CNT dispersion before lyophilization.

(3-1-2) Dispersion of CNT First, the CNT produced by the above method is oxidized in an oxygen atmosphere at a predetermined temperature. The catalyst and metal are removed by oxidation, and a functional group such as a hydroxy group or a carboxy group is formed on a part of the surface of the CNT. CNT can be oxidized by ozone treatment. CNTs can also be oxidized by immersing them in a mixed acid of nitric acid and sulfuric acid, or in a hydrogen peroxide solution and sulfuric acid persulfate. The ratio of nitric acid and sulfuric acid in the mixed acid can be arbitrarily determined. The ratio of the hydrogen peroxide solution and sulfuric acid in the sulfuric acid / hydrogen peroxide can also be determined arbitrarily.

  As described above, when the catalyst residue is removed by acid treatment in CNT production, the surface of the CNT is oxidized. Since a functional group such as a hydroxy group or a carboxy group has already been formed on a part of the surface of the CNT by oxidation, the oxidation here is not necessarily performed.

  The CNT having a surface oxidized is added to a dispersion solvent so as to have a predetermined concentration, and is uniformly dispersed to obtain a CNT dispersion. If the CNT concentration in the CNT dispersion is too low, it becomes difficult to form the CNT flakes 20 and obtain the conductive network structure 18. It is desirable that the concentration of CNT in the CNT dispersion is at least about 500 ppm. Even if a CNT dispersion having an excessively high concentration of CNTs is used, a remarkable effect is not obtained. It is sufficient that the CNT concentration in the CNT dispersion is about 10,000 ppm at the maximum. The concentration of CNT in the CNT dispersion can be set to 1000 ppm, for example.

  In order to uniformly disperse CNTs, a homogenizer, high-pressure shear, an ultrasonic disperser, or the like can be used. The CNT dispersion liquid is dispersed in the dispersion solvent in a state where the CNTs are physically separated and are not entangled one by one. The ratio of aggregates in which two or more CNTs aggregate is 10% or less of the entire CNTs. The proportion of CNT aggregates can be determined by measuring the number of CNTs and the number of aggregates from a TEM image.

  In addition to being able to disperse CNTs therein, the dispersion solvent is required to be frozen by contact with a cryogenic refrigerant and to be removed by drying. Examples of the dispersion solvent include water, alcohols (ethanol, methanol, isopropyl alcohol, etc.), organic solvents (toluene, acetone, tetrahydrofuran (THF), methyl ethyl ketone (MEK), hexane, normal hexane, ethyl ether, xylene, methyl acetate. , Ethyl acetate, etc.) can be used. The CNT dispersion liquid may contain a dispersant, a surfactant, an adhesive and the like as long as the functions of the base material 12 and the CNT are not limited.

  In preparing the CNT dispersion, it is not always necessary to produce CNTs. When a CNT having the above-described conditions is obtained, a CNT dispersion can be prepared by dispersing in a predetermined dispersion solvent. When the CNT dispersion itself can be obtained, the CNT dispersion can be prepared without producing CNT or dispersing CNT in the dispersion solvent.

(3-2) A process of attaching a conductive network structure composed of an aggregate of CNT flakes to a base material After pre-treating the base material 12, it is composed of an aggregate of CNT flakes 20 using a CNT dispersion. A conductive network structure is attached to the substrate 12.

(3-2-1) Pretreatment of base material As the base material 12, a carbon fiber cloth cut into a predetermined size is prepared. The carbon fiber cloth can be a plain woven fabric having a carbon fiber bundle 14 including a plurality of carbon fibers 16 as warps 14a and wefts 14b. The carbon fiber cloth may be subjected to water repellency treatment with Teflon. Examples of the substrate 12 that can be used include carbon cloth (EC-CC1-0601T) manufactured by Toyo Technica.

  The base material 12 is heated to a predetermined temperature in an oxygen atmosphere to oxidize the surface of the carbon fibers 16 constituting the carbon fiber bundle 14. The substrate 12 is heated. Thereby, the catalyst and the metal are removed, and a functional group such as a hydroxy group or a carboxy group is formed on a part of the surface of the carbon fiber 16. The surface of the carbon fiber 16 can be oxidized by ozone treatment. Alternatively, for example, the surface of the carbon fiber 16 may be oxidized by immersing the base material 12 in a mixed acid of nitric acid and sulfuric acid. The ratio of nitric acid and sulfuric acid in the mixed acid can be arbitrarily determined.

  In this way, a functional group such as a hydroxy group or a carboxy group is formed on a part of the surface of the carbon fiber 16, and the substrate 12 is pretreated.

(3-2-2) Adhesion of Conductive Network Structure to Substrate Conductive network structure 18 allows CNT dispersion prepared as described above to permeate base material 12 after pretreatment and freeze. The CNT flakes 20 can be formed on the surface and inside of the substrate 12 by drying, and can be adhered to the substrate 12 (first adhesion method). Alternatively, the conductive network structure 18 can be attached to the base material 12 by infiltrating the CNT flake dispersion into the base material 12 after the pretreatment (second attachment method). The CNT flake dispersion is a dispersion containing the CNT flakes 20 and can be prepared by freeze-drying the CNT dispersion. For the freeze-drying of the CNT dispersion liquid, for example, a method described in JP-A-2015-101531 can be referred to. The first and second adhesion methods will be described below.

<First adhesion method>
First, the CNT dispersion prepared as described above is allowed to permeate the substrate 12 after pretreatment. The CNT dispersion liquid is required to permeate the inside of the carbon fiber bundle 14 constituting the substrate 12, specifically, between the carbon fibers 16. The base material 12 can be immersed in the CNT dispersion liquid to allow the CNT dispersion liquid to penetrate into the carbon fiber bundle 14. The CNT dispersion may be dropped on the surface of the base material 12 placed on a water-repellent resin sheet so as to penetrate into the carbon fiber bundle 14. As the water-repellent resin sheet, for example, a polytetrafluoroethylene (PTFE) sheet can be used.

  The base material 12 infiltrated with the CNT dispersion is rapidly cooled to freeze the CNT dispersion. For example, the base material 12 infiltrated with the CNT dispersion liquid is accommodated in a predetermined container, the whole container is immersed in a cryogenic refrigerant, and the CNT dispersion liquid infiltrated into the base material 12 is frozen. For example, liquid nitrogen or dry ice can be used as the cryogenic refrigerant. The dispersion solvent in the CNT dispersion liquid is rapidly frozen and frozen on the surface and inside of the carbon fiber bundle 14 constituting the base material 12, and a large number of frozen ice blocks are generated throughout the base material 12.

  On the surface and inside of the carbon fiber bundle 14, the CNT in the CNT dispersion is pushed out of the frozen ice block. A plurality of CNTs are directly connected to each other and laminated in a plurality of layers to form a flake. Thus, a plurality of CNT flakes 20 are formed on the surface and inside of the carbon fiber bundle 14. The thickness of the CNT flakes 20 is about several nm to several tens of nm. Since the carbon fiber bundle 14 in which the CNT dispersion is frozen contains a plurality of carbon fibers 16, the gap between the carbon fibers 16 is filled with frozen ice blocks and CNT flakes 20. CNT that did not contribute to the formation of the CNT flakes 20 may remain as it is.

  Next, drying under reduced pressure is performed to remove frozen ice blocks. The reduced-pressure drying can be achieved, for example, by placing the base material 12 in a vacuum dryer for a predetermined time. The frozen ice block is removed, and the plurality of CNT slices 20 are three-dimensionally joined to form a network, and the conductive network structure 18 is formed. The conductive network structure 18 may contain open cells of about 1 to 100 μm. If CNT remains, this CNT is also taken into the conductive network structure 18. The CNT flakes 20 or CNTs are directly fixed to the carbon fibers 16, and the conductive network structure 18 adheres to the inside of the substrate 12.

  The conductive network structure 18 connects the carbon fibers 16 inside the carbon fiber bundle 14. Further, the conductive network structure 18 can connect the carbon fibers 16 to each other even between the carbon fiber bundles 14. The portion from which the frozen ice block has been removed becomes a gap 24 of the conductive network structure 18. The size of the gap 24 is about 10 to 500 nm.

  When the dispersion solvent in the CNT dispersion liquid that has permeated the substrate 12 is frozen, the CNT flakes 20 are also formed on the surface of the substrate 12 together with a large number of frozen ice blocks. By removing the frozen ice block, the conductive network structure 18 also adheres to the surface of the substrate 12.

  Thus, in the first adhesion method, the conductive network structure 18 is formed on the surface and inside of the substrate 12 by freeze-drying the CNT dispersion that has permeated the substrate 12.

<Second adhesion method>
First, the CNT dispersion prepared as described above is accommodated in a predetermined container, and the container is immersed in a cryogenic refrigerant such as liquid nitrogen to freeze the CNT dispersion. By freezing the CNT dispersion, the dispersion solvent becomes frozen ice blocks, and the CNTs are pushed out of the frozen ice blocks. The CNT flakes 20 are formed in a lump shape by the pushed CNTs. The size of the massive CNT flakes 20 (hereinafter also referred to as a bulk body) is about several to several hundred μm. As described above, the CNT flakes 20 are formed by a plurality of CNTs being directly connected to each other and stacked in a plurality of layers.

  FIG. 7 shows an SEM image of the massive CNT flake 20 (bulk body 200). A large number of CNT flakes 20 gather at a high density to form a bulk body 200. The bulk body 200 is schematically shown in FIG. In the bulk body 200, a gap 240 exists between the CNT slices 20. Due to the presence of the gap 240, mechanical energy can be applied in a later step and the individual CNT flakes 20 can be separated.

  A dispersion solvent is added, and mechanical energy is applied to the massive CNT flakes 20 (bulk body 200) to separate them into individual CNT flakes 20. The CNT flakes 20 are flakes having a minimum size that does not become any smaller. Such a CNT flake 20 can be obtained by applying mechanical energy equal to or greater than the stress expected to be received when the battery is fabricated to the bulk body 200 in the dispersion solvent. Examples of the dispersion solvent include alcohols (ethanol, methanol, isopropyl alcohol, etc.), water, organic solvents (toluene, acetone, THF, MEK, hexane, normal hexane, ethyl ether, xylene, methyl acetate, ethyl acetate, etc.) and the like. Can be used. Examples of mechanical energy include ultrasonic waves and homogenizers. For example, by applying ultrasonic waves of about 100 to 1200 W for about 1 to 30 minutes to 10 to 100 ml of the dispersion solvent containing the bulk body 200, a CNT flake dispersion containing the target CNT flakes 20 is obtained.

  The conductive network structure 18 can be adhered to the surface and the inside of the base material 12 by infiltrating the CNT flake dispersion into the base material 12 after the pretreatment. The CNT flake dispersion is required to penetrate into the inside of the carbon fiber bundle 14 constituting the base material 12, specifically, between the carbon fibers 16. The base material 12 can be immersed in the CNT flake dispersion to allow the CNT flake dispersion to penetrate into the carbon fiber bundle 14. The CNT flake dispersion can be dropped on the surface of the base material 12 placed on a water-repellent resin sheet to penetrate into the carbon fiber bundle 14.

  Next, the dispersion solvent is removed from the base material 12 infiltrated with the CNT flake dispersion. The dispersion solvent can be removed from the substrate 12 by a general method. The dispersion solvent is removed, and the plurality of CNT slices 20 are three-dimensionally joined to form a network, and the conductive network structure 18 is formed. When the CNT flakes 20 are directly fixed to the carbon fibers 16, the conductive network structure 18 adheres to the inside of the base material 12.

  The conductive network structure 18 connects the carbon fibers 16 inside and on the surface of the carbon fiber bundle 14. Thus, a conductive network structure 18 including a plurality of CNT slices 20 is formed on the surface and inside of the substrate 12.

  The battery electrode 10 of this embodiment is formed by forming the CNT flakes 20 from the CNT dispersion by an arbitrary method using lyophilization, and attaching the conductive network structure 18 to the surface and inside of the substrate 12. Can be manufactured.

(4) Evaluation of Battery Electrode The manufactured battery electrode 10 can be evaluated for performance by measuring the reduction current value by the following method, for example.

  First, an enzyme (for example, BOD) is adsorbed on the liquid phase side surface of the battery electrode, and a water-repellent resin sheet (for example, PTFE sheet) is disposed on the gas phase side rear surface to prepare a sample electrode.

  Using a counter electrode (for example, a platinum electrode) and a reference electrode (Ag-AgCl electrode), an enzyme is reduced in an electrolytic solution, and the reduction current value of the battery electrode is measured. As the electrolytic solution, for example, a citrate buffer solution (1.5 mol / L) having a pH of 5 can be used. The cell temperature is 40 ° C., for example, and measurement is performed in an oxygen atmosphere.

(5) Action and Effect In the battery electrode 10 of the present embodiment, the conductive network structure 18 made of an aggregate of the CNT thin pieces 20 is attached to the surface and the inside of the substrate 12. The conductive network structure 18 inside the base material 12 enters the carbon fiber bundle 14 constituting the base material 12 and connects the carbon fibers 16 included in the carbon fiber bundle 14. Further, the conductive network structure 18 also connects the carbon fibers 16 between the carbon fiber bundles 14.

  The CNT flakes 20 are formed by freeze-drying the CNT dispersion before or after the CNT dispersion penetrates the substrate 12. As a result, the conductive network structure 18 can be attached to the surface and the inside of the substrate 12. Since the conductive network structure 18 made of an aggregate of the CNT flakes 20 is attached to the base material 12, there is a great possibility that the surface of the base material 12 is covered with the CNT layer or the base material 12 is clogged. small.

  In the battery electrode 10, since the conductive network structure 18 is also attached to the inside of the base material 12, the amount of CNT attached can be increased as compared with the case where CNT is attached only to the surface of the base material. I was able to. Since the CNT forms the conductive network structure 18 and connects the carbon fibers 16 inside the base material 12, the possibility that the CNT is detached from the base material 12 is small. The battery electrode 10 has a larger amount of CNT effectively attached to the substrate 12.

  Since the CNTs adhere to the surface of the base material 12 as the conductive network structure 18, when the battery electrode 10 is used as an electrode of a biofuel cell, the circulation of the electrolyte, oxidoreductase, etc. is promoted. In addition, since the amount of enzyme that can be taken into the electrode is improved by increasing the surface area, the output of the battery is further improved.

  The conductive network structure 18 that connects the carbon fibers 16 forms a conductive path inside the carbon fiber bundle 14. Since the conductive network structure 18 connects the carbon fibers 16 in the carbon fiber bundle 14, a conductive path is formed inside the carbon fiber bundle 14. As the conductive network structure 18 adheres to the carbon fibers 16 on the surface of the carbon fiber bundle 14, a conductive path is also formed on the surface of the carbon fiber bundle 14. Since the plurality of carbon fiber bundles 14 constitute the base material 12 of the battery electrode 10, the conductive path caused by the conductive network structure 18 exists throughout the base material 12. Thereby, when the battery electrode 10 is used for a battery, the output of the battery can be further improved.

  The surface area of the battery electrode 10 is increased by the conductive network structure 18 adhering to one surface of the substrate 12. Since the conductive network structure 18 has a network shape, the rate of increase in the surface area is larger than when the CNTs are attached to the substrate. Such an increase in surface area also contributes to an improvement in battery output.

  The biofuel cell of this embodiment is configured using the battery electrode 10 of this embodiment. In the biofuel cell, since the conductive network structure 18 exists on the surface and inside of the base material 12, the conductive path is sufficiently formed, so that electric energy can be generated more efficiently than before. Moreover, since the surface area of the battery electrode 10 is large, the current density can be increased as compared with the conventional case, and the output of the battery can be further improved.

(6) Configuration of Battery Electrode of Other Embodiments The base material 12 is not limited to a woven fabric as long as it includes a plurality of carbon fiber bundles 14. The battery electrode 10 </ b> A can also be configured using a nonwoven fabric including a plurality of carbon fiber bundles 14 as shown in FIG. 9 as the base material 22. In the battery electrode 10A, a conductive mesh structure 18 made of an aggregate of CNT thin pieces 20 is attached to the carbon fiber bundle 14 on the surface of the base material 22 as shown in FIG. Although not shown, the conductive network structure 18 is attached to the carbon fiber bundle 14 even inside the base material 22.

  As in the case of the battery electrode 10 shown in FIG. 1, the carbon fiber bundle 14 includes a plurality of carbon fibers (not shown). The carbon fibers contained in the carbon fiber bundle 14 are connected by the conductive network structure 18 as described above.

  The base material 22 is bonded to a part such as a part where a plurality of carbon fiber bundles 14 intersecting each other, a part where adjacent carbon fiber bundles 14 contact each other, and a mesh formed by the plurality of carbon fiber bundles 14. An adhesive portion (not shown) made of an agent may be formed. In this case, the carbon fiber bundles 14 are bonded together by the bonding portion.

  For example, the bonding portion is formed by carbonizing a resin material such as a fluororesin. When the bonded portion is carbonized, it exhibits conductivity. In this case, the base material 22 has higher conductivity as compared with the case where the bonding portion is formed of an insulator such as a resin.

  In the battery electrode 10 </ b> A, since the carbon fibers contained in the carbon fiber bundle 14 are connected by the conductive network structure 18, a conductive path is formed inside the carbon fiber bundle 14. The nonwoven fabric used as the base material 22 has a larger gap between the carbon fiber bundles 14 than a woven fabric in which the carbon fiber bundles 14 are woven as warps 14a and wefts 14b. In the nonwoven fabric, the conductive network structure 18 is densely formed by the gaps between the carbon fiber bundles 14. Even between the carbon fiber bundles 14, the carbon fibers are connected by the conductive network structure 18.

  The extending direction of the carbon fiber bundle 14 included in the woven fabric is only two directions of the vertical direction and the horizontal direction, whereas the carbon fiber bundle 14 included in the nonwoven fabric extends in an arbitrary direction. The carbon fiber bundle 14 constituting the base material 22 extends in an arbitrary direction, so that the conductive path is more efficiently formed in the base material 22.

  It is expected that the battery electrode 10 </ b> A using the nonwoven fabric as the base material 22 is more effective than the battery electrode 10.

(7) Example The battery electrode of Example 1 was produced according to the procedure shown in the above "(3) Method for producing battery electrode of this embodiment". As the CNTs, multi-walled carbon nanotubes grown on a silicon substrate to a diameter of 10 to 15 nm and a length of 100 μm or more by the above-described thermal CVD method were used.

The CNTs cut from the substrate were immersed in a mixed acid of nitric acid and sulfuric acid, and then filtered and dried to remove catalyst residues. The ratio of nitric acid and sulfuric acid in the mixed acid can be arbitrarily determined. The surface of CNT is oxidized by being immersed in a mixed acid. Since a functional group such as a hydroxy group or a carboxy group is formed on a part of the surface of the CNT, it is not necessary to separately oxidize the CNT. CNT was dispersed in water at a concentration of 3000 ppm to prepare a CNT dispersion.
Using the prepared CNT dispersion, a conductive network structure was adhered to the base material by the above <second adhesion method>.

  As the substrate, Toyo Technica carbon cloth (model number: EC-CC1-060T) was cut into a size of 50 × 50 mm and used. The base material used here is a water-repellent base material that has been subjected to Teflon treatment. The substrate was pretreated by heating in a sealed container (containing 1 cc of oxygen in a volume of 1000 cc) at 500 ° C. for 10 minutes and acid cleaning. By acid cleaning, metal removal and surface group introduction are achieved.

  The CNT dispersion was immersed in liquid nitrogen together with the container, and the CNT dispersion was frozen to produce a massive CNT flake (bulk body). The weight of the bulk body was about 0.01 g. The bulk body was accommodated in 100 g of ethanol, and an ultrasonic wave of about 100 W was applied for about 10 minutes. As a result, the bulk body was separated into CNT flakes having a thickness of about 20 to 30 nm, and a CNT flake dispersion was obtained.

  The CNT flake dispersion was dropped on the pretreated substrate, and the CNT flake dispersion was infiltrated into the substrate. The substrate infiltrated with the CNT flake dispersion was vacuum-dried to remove ethanol, thereby attaching a conductive network structure to the surface and inside of the substrate. Thus, the battery electrode of Example 1 was obtained. In the battery electrode of Example 1, the amount of CNT attached was about 3 wt%. Note that the CNT adhesion amount is a ratio of the total amount of CNTs to the base material. The amount of CNT attached can be determined based on the difference in the weight of the substrate before and after CNT attachment.

  In addition, the same CNT and base material were used, and a single CNT was adhered to the base material to produce a battery electrode of Comparative Example 1. CNT was dropped on the base material as a CNT dispersion liquid dispersed in ethanol at a concentration of 1000 ppm and allowed to permeate the base material. By volatilizing and removing the ethanol in the CNT dispersion liquid that had permeated the base material, CNTs were attached to the surface and inside of the base material. The battery electrode of Comparative Example 1 obtained in this way had a CNT adhesion amount of 9 wt%.

In FIG. 10, the current-potential curve of the battery electrode of Example 1 is compared with the current-potential curve of the battery electrode of Comparative Example 1. In FIG. 10, the horizontal axis indicates the potential (V), and the vertical axis indicates the current value (mAcm ⁻² ). Curve a is the result of the battery electrode of Example 1, and curve b is the result of the battery electrode of Comparative Example 1. The reduction current value was measured by the method shown in “(4) Evaluation of battery electrode” using a saturated potassium chloride aqueous solution as an electrolytic solution.

In the battery electrode of Comparative Example 1, the reduction current value rises quickly, but the reduction current value remains at −15 mAcm ⁻² (curve b). On the other hand, the battery electrode of Example 1 has a reduction current value of −22 mAcm ⁻² (curve a). Incidentally, the reduction current value of a similar base material not containing CNTs was about −0.001 mAcm ⁻² .

  In the battery electrode of Comparative Example 1, 9 wt% of CNT alone is attached to the substrate, whereas the amount of CNT attached to the battery electrode of Example 1 is smaller than that of Comparative Example 1. Nevertheless, the battery electrode of Example 1 shows a reduction current value higher than that of Comparative Example 1. As described above, in the battery electrode of Example 1, the conductive network structure composed of an aggregate of CNT flakes is attached to the base material. It is presumed that the CNT flakes can ensure the conduction more reliably and the gas permeability is improved, which is a cause of the improvement of the reduction current value.

  In FIG. 11, the electric current-potential curve of the battery electrode of Examples 2-10 is shown. The battery electrodes of Examples 2 to 10 were produced in the same manner as in the case of the battery electrode of Example 1 except that the CNT adhesion amount was changed. The CNT adhesion amount is 2 wt% in Examples 2 to 4, 4 wt% in Examples 5 to 7, and 6 wt% in Examples 8 to 10. The CNT adhesion amount was adjusted by changing the amount of the CNT flake dispersion dropped onto the substrate. Also in the battery electrodes of Examples 2 to 10, like the battery electrode of Example 1, what is attached to the base material is a conductive network structure made of an aggregate of CNT flakes.

  FIG. 12 shows the change over time in the reduction current value for the battery electrodes of Examples 2-10. When the CNT adhesion amount is 2 wt% (Examples 2 to 4), the reduction current value is almost constant up to 60 seconds. When the CNT adhesion amount is 4 wt% (Examples 5 to 7), the time during which the reduction current value is kept constant is shortened, and the reduction current value is gradually decreased. The same tendency appears more conspicuously when the CNT adhesion amount is 6 wt% (Examples 8 to 10). This is presumed to be caused by the fact that the water produced by the oxidation / reduction at the electrode remains and the function of the conductive network structure in the substrate is lowered.

In FIG. 13, the current-potential curves of the battery electrode of Example 9 and the battery electrode of Comparative Example 1 are compared and shown. In FIG. 13, the horizontal axis indicates the potential (V), and the vertical axis indicates the current value (mAcm ⁻² ). The reduction current value was measured by the method shown in “(4) Evaluation of battery electrode” using a saturated potassium chloride aqueous solution as an electrolytic solution.

  Although the battery electrode of Example 9 has a CNT adhesion amount of 6 wt% and 2/3 of Comparative Example 1 (9 wt%), the reduction current value is more than twice that of the battery electrode of Comparative Example 1 Has improved. Similar to the battery electrode of Example 1, in the battery electrode of Example 9, it is presumed that the conduction is more reliably ensured by the CNT flakes and the gas permeability is improved and the reduction current value is improved. . Furthermore, in the battery electrode of Example 9, since the amount of CNT attached was larger than that of Example 1, it can be seen that the reduction current value was further improved by the effect of CNT.

  FIG. 14 shows the relationship between the amount of CNT attached to the battery electrode and the current value. A curve c in FIG. 14 shows the average value of the values after 15 seconds of the battery electrodes of Examples 2, 3, and 4 shown in FIG. The average value of the values and the values after 15 seconds of the battery electrodes of Examples 8, 9, and 10 are plotted and obtained based on the plots. A curve d is obtained by measuring the current values of the battery electrodes of Comparative Examples 1 to 4 and plotting the values after 15 seconds and based on the plots. The battery electrodes of Comparative Examples 2 to 4 were produced in the same manner as Comparative Example 1 except that the CNT adhesion amount was changed to 1 wt%, 2 wt%, and 4 wt%. Therefore, the battery electrodes of Comparative Examples 2 to 4 are also CNT alone attached to the base material, like the battery electrode of Comparative Example 1.

As shown by the curves c and d in FIG. 14, the current value of the battery electrode increases as the amount of CNT attached increases. The current value of the battery electrode of the comparative example tends to increase until the CNT adhesion amount is about 4 w%, but is constant at about −15 mAcm ⁻² even if the CNT adhesion amount further increases (curve d). . The current value of the battery electrode of the example increases more rapidly than in the comparative example, and is about −33 mAcm ⁻² when the CNT adhesion amount is 6 wt% (curve c). This result shows that by attaching the conductive network structure to the base material, a high reduction current value that cannot be achieved by attaching CNT alone is obtained.

  In the battery electrode of the example, a conductive network structure made of an aggregate of CNT flakes is attached to a substrate. Since there are appropriate voids in the conductive network structure, a gas permeation path in the battery electrode is ensured even if the amount of CNT adhesion increases. Since the battery electrode of an Example is excellent in gas permeability, when the electroconductive network structure adheres to a base material, it is estimated that the high electric current value was able to be obtained.

  The conductive network structure attached to the substrate can be confirmed by an SEM image. The SEM image which image | photographed the surface of the carbon fiber in the base material contained in the battery electrode of Example 5 is shown in FIGS. 15A and 15B. FIG. 15B is an enlarged image of the region X1 in FIG. 15A. A conductive network structure 18 made of an aggregate of CNT flakes 20 is attached to the surface of the carbon fiber, and irregularities are generated on the surface of the carbon fiber. Due to the presence of irregularities on the surface of the carbon fiber, the surface area of the battery electrode increases. Appropriate voids are formed inside the battery electrode due to surface irregularities. As a result, it was speculated that the gas permeation path was ensured as one of the reasons why the reduction current values of the battery electrodes of Examples 5 to 7 were increased.

  FIG. 16 is an SEM image obtained by photographing the surface of the carbon fiber included in the battery electrode of Comparative Example 1. In the case of the battery electrode of Comparative Example 1, a large amount of CNT 19 is adhered to the surface of the carbon fiber to form a CNT layer 190. Unlike the conductive network structure 18 shown in FIG. 15B, the CNT layer 190 does not form irregularities on the surface of the carbon fiber. Since the carbon fiber is covered with such a CNT layer 190, the battery electrode of Comparative Example 1 cannot obtain the effect due to the unevenness of the surface. Covering the surface of the carbon fiber with the CNT layer 190 also causes clogging of the substrate.

  FIG. 17 is an SEM image obtained by photographing the surface of the carbon fiber included in the battery electrode of Comparative Example 4. Similarly to the case of Comparative Example 1, it is shown that the carbon fiber is covered with the CNT layer 190 also in the battery electrode of Comparative Example 4. In the battery electrode of Comparative Example 4, the CNT adhesion amount is 4 wt%, which is less than that of the battery electrode of Comparative Example 1 (9 wt%). For this reason, CNT contained in the CNT layer 190 to be formed is smaller than that in the case of Comparative Example 1. Still, due to the fact that the CNTs alone adhere to the substrate, the surface of the carbon fiber is covered with the CNT layer 190 also in the battery electrode of Comparative Example 4.

  Since the density of the contained CNT is lower than the battery electrode of the comparative example, the battery electrode of the example has more voids inside. This can be confirmed from the SEM image of the cross section. FIG. 18 shows an SEM image obtained by photographing the cross section of the base material contained in the battery electrode of Example 5, and FIG. 19 shows an SEM image obtained by photographing the cross section of the base material contained in the battery electrode of Comparative Example 1. . White dots in these figures represent CNTs.

  In FIG. 18, about 25 CNTs were observed in the region Y1 (1 μm square). In the case of FIG. 19, CNTs twice or more as large as the region Y1 in FIG. 18 were observed in the region Y2 (1 μm □). Since the battery electrode of Comparative Example 1 has a high CNT density, it can be seen that there are few internal voids.

  In the battery electrode of the example, the conductive network structure composed of the aggregate of CNT flakes adheres to the base material, so that an appropriate gap can be secured inside the electrode. Since the conductive network structure adheres to the base material, both a sufficient conductive path and a sufficient gas permeation path are compatible, and thus a battery electrode with improved output is obtained.

(8) Modifications The present invention is not limited to the embodiment described above, and various modifications can be made within the scope of the gist of the present invention.

  In the above embodiment, the case where the electron transfer mediator and the oxidoreductase are present in the electrolytic solution has been described. However, the present invention is not limited to this, and the electron transfer mediator and the oxidoreductase are fixed to the battery electrode 10. It may be.

  The battery electrode 10 of the present invention can be used as an electrode of a battery other than a biofuel cell, for example, a fuel cell or a lithium ion secondary battery.

  The conductive network structure 18 may be fixed to the surface of the substrate 12 using a binding member. Examples of the binding member include PTFE emulsion. By electrically fixing the conductive network structure 18 to the carbon fiber 16, the conductive network structure 18 is reinforced by the binding member in the battery electrode of the modification. Since the conductive network structure 18 is more firmly fixed to the carbon fiber 16, when used in a battery, a decrease in battery output and a short circuit between the electrodes due to the peeling of the conductive network structure 18 can be suppressed. The durability of can be improved.

  In the said embodiment, although the electroconductive network structure 18 shall consist of the aggregate | assembly of the CNT thin piece 20, the electroconductive network structure 18 in the battery electrode of this invention is not limited to this. As long as the function of the conductive network structure 18 is not hindered, graphene, carbon black, or the like may be included in the conductive network structure 18. For example, by impregnating the base material 12 with a CNT flake dispersion containing graphene or carbon black, a battery electrode in which the conductive network structure 18 containing graphene or carbon black is attached to the base material 12 can be obtained. it can.

DESCRIPTION OF SYMBOLS 10 Battery electrode 12 Base material 14 Carbon fiber bundle 16 Carbon fiber 18 Conductive network structure 20 Carbon nanotube (CNT) flake

Claims (10)

A substrate including a plurality of carbon fiber bundles;
A conductive network structure attached to the surface and the inside of the base material, and including an aggregate of flakes of carbon nanotubes;
The conductive network structure formed inside the base material connects the carbon fibers between carbon fibers contained in the carbon fiber bundle, and the carbon fibers contained in one carbon fiber bundle and the other. A battery electrode characterized by connecting carbon fibers contained in a carbon fiber bundle.   The battery electrode according to claim 1, wherein the carbon nanotube has at least one of a hydroxy group and a carboxy group on a surface thereof.   The battery electrode according to claim 1 or 2, wherein a surface of the carbon fiber is oxidized.   The battery electrode according to claim 1, wherein the base material is a woven fabric.   The battery electrode according to any one of claims 1 to 3, wherein the substrate is a nonwoven fabric.   A biofuel cell using the battery electrode according to claim 1. Preparing a carbon nanotube dispersion,
Using the carbon nanotube dispersion, and attaching a conductive network structure including an aggregate of thin pieces of carbon nanotubes to the surface and inside of the substrate,
The method for producing a battery electrode, wherein the carbon nanotube flakes are formed by freeze-drying the carbon nanotube dispersion.   The method for producing a battery electrode according to claim 7, wherein the concentration of the carbon nanotubes in the carbon nanotube dispersion is 500 to 10,000 ppm.   9. The method for producing a battery electrode according to claim 7, wherein the carbon nanotube dispersion liquid is infiltrated into the base material before the carbon nanotube dispersion liquid is freeze-dried. 9. The battery according to claim 7 or 8, wherein the carbon nanotube dispersion is freeze-dried to form the carbon nanotube flakes, and then the dispersion containing the carbon nanotube flakes is infiltrated into the substrate. Electrode manufacturing method.

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