Graphite-coated carbon fiber

Abstract

A graphite-coated carbon fiber according to the present invention has: a carbon fiber skeleton; graphite particles that cover the surface of the carbon fiber skeleton; and a carbonaceous binder that binds the graphite particles to the carbon fiber skeleton, wherein the graphite particles cover 50 area% or more of the surface of the carbon fiber skeleton when subjected to image observation with a scanning electron microscope.

Description

Graphite-coated carbon fiber

[0001] This invention relates to graphite-coated carbon fibers.

[0002] In recent years, various carbon materials have been widely used in fields such as electronic components. Carbon materials are valued for their electrical properties and physical properties such as mechanical strength, and various forms have been proposed.

[0003] Patent Document 1 discloses a metal-coated spherical glassy carbon. This metal-coated spherical glassy carbon is characterized in that the surface of spherical glassy carbon with an average particle size of 0.5 to 1000 μm is coated with graphite, and its outer surface is further coated with metal.

[0004] Patent Document 2 discloses a method for producing highly graphitizable fibers by coating a carbon fiber substrate with an easily graphitizable layer using a chemical vapor deposition method with infrared heating, and then heat-treating it at a temperature of 2800°C or higher. This method is characterized in that the formation of the easily graphitizable layer and the heat treatment are carried out under a pressurized atmosphere.

[0005] Patent Document 3 discloses a carbonaceous fibrous structure having a fibrous carbon skeleton and a carbonaceous binding portion coating the fibrous carbon skeleton, having interconnected pores, and having a porosity of 50 to 85% as measured by the mercury intrusion method.

[0006] JP 11-157816 JP 2-210060 JP 2024-31548

[0007] The present invention aims to provide a novel carbon fiber having higher electrical conductivity.

[0008] The present inventors, after diligent study, found that the above problems could be solved by the following means, and thus completed the present invention. That is, the present invention is as follows: <Aspect 1> A graphite-coated carbon fiber having a carbon fiber skeleton, graphite particles covering the surface of the carbon fiber skeleton, and a carbonaceous binder bonding the graphite particles to the carbon fiber skeleton, wherein when observed with a scanning electron microscope, the graphite particles cover 50% or more of the surface area of ​​the carbon fiber skeleton. <Aspect 2> The graphite-coated carbon fiber according to Aspect 1, wherein when observed with a scanning electron microscope, the graphite particles cover 70% or more of the surface area of ​​the carbon fiber skeleton. <Aspect 3> A graphite-coated carbon fiber structure having the graphite-coated carbon fiber according to Aspect 1 or 2, and a carbonaceous binder bonding the graphite-coated carbon fibers to each other. <Aspect 4> The graphite-coated carbon fiber structure according to Aspect 3, having a porosity of 30 to 90%. <Aspect 5> A battery component comprising a graphite-coated carbon fiber structure according to Aspect 3 or 4. <Aspect 6> A method for producing graphite-coated carbon fibers according to Aspect 1 or 2, comprising: providing a resin dispersion in which graphite particles are mixed and dispersed in a liquid resin; impregnating a porous carbon fiber precursor with the resin dispersion; removing a portion of the resin dispersion from the carbon fiber precursor impregnated with the resin dispersion; and heat-treating the carbon fiber precursor, the graphite particles, and the liquid resin in a non-oxidizing atmosphere to carbonize the carbon fiber precursor and the liquid resin. <Aspect 7> A method for producing a graphite-coated carbon fiber structure according to aspect 3 or 4, comprising: providing a resin dispersion in which graphite particles are mixed and dispersed in a liquid resin; impregnating a porous fibrous carbon skeleton precursor with the resin dispersion; removing a portion of the resin dispersion from the fibrous carbon skeleton precursor impregnated with the resin dispersion; and heat-treating the fibrous carbon skeleton precursor, the graphite particles, and the liquid resin in a non-oxidizing atmosphere to carbonize the fibrous carbon skeleton precursor and the liquid resin.

[0009] According to the present invention, it is possible to provide a novel carbon fiber having higher electrical conductivity.

[0010] Figure 1 is a magnified image of the carbon fiber structure of Example 1 obtained by scanning electron microscope (SEM). Figure 2 is a magnified image of the carbon fiber structure of Comparative Example 1 obtained by scanning electron microscope (SEM). Figure 3 is a magnified image of the carbon fiber structure of Comparative Example 2 obtained by scanning electron microscope (SEM). Figure 4 is a magnified image of the carbon fiber structure of Comparative Example 3 obtained by scanning electron microscope (SEM). Figure 5 is a magnified image of the carbon fiber structure of Comparative Example 4 obtained by scanning electron microscope (SEM).

[0011] 《Graphite-Coated Carbon Fiber》 The graphite-coated carbon fiber of the present invention comprises a carbon fiber skeleton, graphite particles covering the surface of the carbon fiber skeleton, and a carbonaceous binder binding the graphite particles to the carbon fiber skeleton, and when observed with a scanning electron microscope, the graphite particles cover 50% or more of the surface area of ​​the carbon fiber skeleton.

[0012] The graphite-coated carbon fiber with the above configuration can achieve good electrical conductivity because the surface of the carbon fiber skeleton is coated with graphite particles.

[0013] The graphite-coated carbon fibers of the present invention, when observed using a scanning electron microscope, show that graphite particles cover 50% or more of the surface area of ​​the carbon fiber skeleton. The graphite particles can cover 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, or 85% or more, or 90% or more of the surface area of ​​the carbon fiber skeleton.

[0014] The average fiber diameter of the graphite-coated carbon fibers may be, for example, 2 μm or more and 40 μm or less. This average fiber diameter may be 2 μm or more, 5 μm or more, 7 μm or more, or 10 μm or more, and may also be 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 17 μm or less, 15 μm or less, or 13 μm or less.

[0015] In this specification, the average fiber diameter can be obtained by image analysis using a scanning electron microscope.

[0016] In particular, the graphite-coated carbon fiber of the present invention can be obtained by a method that includes heat-treating a carbon fiber precursor, graphite particles, and a liquid resin in a non-oxidizing atmosphere to carbonize the carbon fiber precursor and the liquid resin, as described in relation to the method for producing graphite-coated carbon fiber. Therefore, the graphite-coated carbon fiber of the present invention may not contain any resin components.

[0017] Furthermore, the graphite-coated carbon fiber of the present invention may not contain metallic components such as elemental metals or metallic compounds.

[0018] The following describes each component of the present invention.

[0019] <Carbon Fiber Backbone> The graphite-coated carbon fiber of the present invention has a carbon fiber backbone.

[0020] The carbon fiber skeleton may be composed of amorphous carbon. The carbon fiber skeleton can be obtained, for example, by carbonizing a carbon fiber precursor under a non-oxidizing atmosphere. Details of the carbon fiber precursor will be discussed in relation to the method for producing graphite-coated carbon fibers.

[0021] <Graphite particles> Graphite particles cover the surface of the carbon fiber skeleton. The graphite particles and the carbon fiber skeleton are bonded together via a carbonaceous binder.

[0022] Examples of graphite particles that can be used include expanded graphite powder, flaky graphite, spheroidal graphite, lump graphite, flake graphite, graphene, graphene oxide, and graphitized carbon fiber powder.

[0023] The volume-average particle size of the graphite particles may be 0.1 μm or more and 10.0 μm or less. The volume-average diameter may be 0.3 μm or more, 0.5 μm or more, 0.7 μm or more, 1.0 μm or more, 1.5 μm or more, 2.0 μm or more, 2.5 μm or more, 3.0 μm or more, or 3.5 μm or more, and may also be 10.0 μm or less, 9.0 μm or less, 8.0 μm or less, 7.0 μm or less, 6.0 μm or less, 5.0 μm or less, or 4.5 μm or less.

[0024] In this invention, the "volume-average particle size" (Mv) can be obtained by using a laser diffraction particle size distribution analyzer (for example, the MT-3000 manufactured by Microtrac-Bell) to obtain a weighted average value obtained by the product of the frequency of each particle size and the volume of each particle calculated using that particle size, and then dividing that average value by the average volume.

[0025] The graphite particle content may be 5% by mass or more and 45% by mass or less, relative to the mass of the graphite particle-coated carbon fiber. This content may be 5% by mass or more, 10% by mass or more, 15% by mass or more, or 18% by mass or more, and may also be 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, or 25% by mass or less.

[0026] <Carbonaceous Binder> The carbonaceous binder binds graphite particles to the carbon fiber backbone.

[0027] Carbonaceous binders can be obtained, for example, by carbonizing a liquid resin in a non-oxidizing atmosphere. Details of the liquid resin will be discussed in relation to the method for producing graphite-coated carbon fibers.

[0028] The graphite-coated carbon fibers of the present invention can be manufactured by any method, but can be manufactured in particular by the method of the present invention described below.

[0029] 《Graphite-Coated Carbon Fiber Structure》 The graphite-coated carbon fiber structure of the present invention comprises the above-mentioned graphite-coated carbon fibers and a carbonaceous binder that joins the graphite-coated carbon fibers together.

[0030] The graphite-coated carbon fiber structure of the present invention may have interconnected pores.

[0031] The bulk density of the graphite-coated carbon fiber structure of the present invention is 0.9 g / cm³. ３ Below, 0.8g / cm ３ Below, 0.7g / cm ３ Below, 0.6g / cm ３ Below, 0.5g / cm ３ The following, or 0.4 g / cm³ ３ It can be less than or equal to 0.2 g / cm³. ３ Above, or 0.3 g / cm³ ３It can be as described above. Here, the bulk density can be calculated from the volume and mass of the outer shape of the graphite-coated carbon fiber structure.

[0032] The porosity of the graphite-coated carbon fiber structure of the present invention can be 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, or 75% or more, and can also be 90% or less, 85% or less, or 80% or less.

[0033] The porosity can be calculated as follows using the true density and the bulk density. Porosity (%) = (1 - bulk density (g / cm ３ ) / true density (g / cm ３ )) × 100

[0034] Here, the true density can be calculated by the weighted average of the densities of each material weighted by the content rate.

[0035] In the graphite-coated carbon fiber structure of the present invention, the graphite-coated carbon fibers may constitute a fibrous carbon skeleton. The fibrous carbon skeleton is a carbonaceous skeleton having a fibrous outer shape. This fibrous carbon skeleton may be a carbon skeleton derived from a woven fabric, or may be a carbon skeleton derived from a non-woven fabric, that is, a carbide of a non-woven fabric. In particular, it is preferable from the viewpoint of gas permeability that the fibrous carbon skeleton is a carbon skeleton derived from a non-woven fabric, that is, the carbonaceous fiber structure of the present invention is a carbon non-woven fabric.

[0036] It is preferable from the viewpoint of forming the skeleton that the fibrous carbon skeleton is composed of long fibers. Here, in the present invention, "long fiber" means a fiber having a length sufficient to extend to both ends in the plane direction of one carbon non-woven fabric, for example, a fiber of 5 cm or more, 10 cm or more, 15 cm or more, or 20 cm or more.

[0037] When the graphite-coated carbon fiber structure of the present invention is observed by an image using a scanning electron microscope, the graphite particles can cover 50 area% or more of the surface of the fibrous carbon skeleton. The graphite particles can cover 50 area% or more, 55 area% or more, 60 area% or more, 65 area% or more, 70 area% or more, 75 area% or more, 80 area% or more, or 85 area% or more, or 90 area% or more of the surface of the carbon fiber skeleton.

[0038] <Carbonaceous Binder> The carbonaceous binder joins the graphite-coated carbon fibers to each other.

[0039] The carbonaceous binder can be obtained, for example, by carbonizing a liquid resin in a non-oxidizing atmosphere.

[0040] The graphite-coated carbon fiber structure of the present invention can be manufactured by any method, but can be particularly manufactured by the method of the present invention shown below.

[0041] <Battery Member> The battery member of the present invention is composed of the above graphite-coated carbon fiber structure. The battery member composed of the above graphite-coated carbon fiber structure is useful in terms of its porosity and high conductivity due to the graphite particles covering the surface.

[0042] Examples of the battery member of the present invention include a current collector, particularly a negative electrode current collector, and a gas permeable membrane filter.

[0043] <Filter> The filter of the present invention is composed of the above graphite-coated carbon fiber structure. The filter composed of the above graphite-coated carbon fiber structure is useful because the unevenness of the surface due to the graphite particles covering the surface of the carbon fiber skeleton can be expected to improve the adsorption characteristics and suppress the detachment of the captured substances.

[0044] <Method for Manufacturing Graphite-Coated Carbon Fibers> The method of the present invention for manufacturing graphite-coated carbon fibers includes providing a resin dispersion in which graphite particles are mixed and dispersed in a liquid resin, impregnating a porous carbon fiber precursor with the resin dispersion, removing a part of the resin dispersion from the carbon fiber precursor impregnated with the resin dispersion, and heat-treating the carbon fiber precursor, the graphite particles, and the liquid resin in a non-oxidizing atmosphere to carbonize the carbon fiber precursor and the liquid resin.

[0045] The method of the present invention may further include curing the liquid resin after removing a part of the resin dispersion. In this case, the cured liquid resin is carbonized by heat treatment.

[0046] <Provision of Resin Dispersion> A resin dispersion can be provided by mixing and dispersing graphite particles in a liquid resin.

[0047] Mixing and dispersion may be carried out by known methods, for example, by stirring using a high-speed emulsifier and disperser.

[0048] Examples of liquid resins that can be used include thermosetting resins such as furan resins, phenolic resins, epoxy resins, furan-phenolic resins, phenol-modified furan cocondensates, melamine resins, urea resins, and furan-urea resins.

[0049] From the viewpoint of adequately coating the fibrous carbon skeleton obtained after carbonization, it is preferable that the residual carbon content of the liquid resin be 20% or more, 25% or more, 30% or more, 35% or more, 40% or more, or 45% or more. This residual carbon content may be 70% or less, 65% or less, 69% or less, or 55% or less.

[0050] For information on graphite particles, please refer to the description of graphite-coated carbon fibers.

[0051] <Impregnation with resin dispersion> Impregnation with resin dispersion is a process in which a resin dispersion, which is a mixture of graphite particles and a porous carbon fiber precursor, is impregnated with the resin dispersion.

[0052] Carbon fiber precursors are composed of porous fibers. Such fibers can include cellulose-derived fibers, such as synthetic fibers like rayon, and natural fibers like cotton, hemp, and cotton.

[0053] Porous fibers, due to their porous structure, allow liquid resin to penetrate into the fiber's interior during the impregnation process, while simultaneously trapping graphite on the fiber's surface. By carbonizing this, the fiber itself can be composed of amorphous carbon, while the surface can be uniformly coated with graphite.

[0054] From the viewpoint of maintaining its shape after carbonization, it is preferable that the carbon fiber precursor is composed of synthetic fibers, particularly rayon.

[0055] The average fiber diameter of the carbon fiber precursor may be, for example, 2 μm or more and 40 μm or less. This average fiber diameter may be 2 μm or more, 5 μm or more, 7 μm or more, or 10 μm or more, and may also be 40 μm or less, 35 μm or less, 30 μm or less, 25 μm or less, 20 μm or less, 17 μm or less, 15 μm or less, or 13 μm or less.

[0056] From the viewpoint of maintaining shape after carbonization, it is preferable that the carbon residue rate of porous fibers be 15% or more, 17% or more, 20% or more, 22% or more, or 25% or more. This carbon residue rate may be 40% or less, 35% or less, or 30% or less. Here, in relation to the present invention, "carbon residue rate" is a value measured as follows.

[0057] Using a thermobalance, the temperature is raised from room temperature to 900°C at a rate of 20°C / min in a nitrogen atmosphere. The mass after firing is taken as the temperature at 850°C, and the residual carbon percentage (mass%) is calculated using the following formula: Residual carbon percentage (%) = (Mass after firing (850°C) / Mass before firing) × 100

[0058] <Removal of Resin Dispersion> Removal of the resin dispersion is a step in which a portion of the resin dispersion is removed from the carbon fiber precursor impregnated with the resin dispersion. The amount of resin dispersion to be removed can be adjusted according to the density of the carbon nonwoven fabric to be obtained. This step may be carried out by compression or by suction.

[0059] In removing the resin dispersion, it is preferable that the amount of the resin dispersion be 70% by mass or less, 68% by mass or less, or 60% by mass or less, relative to the total mass of the carbon fiber precursor and the resin dispersion, and that it be 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, or 55% by mass or more, from the viewpoint of making the content of the carbonaceous binder after carbonization the value mentioned above with respect to the carbonaceous binder.

[0060] <Heat Treatment> Carbonization is a process of heat-treating the carbon fiber precursor, graphite particles, and liquid resin in a non-oxidizing atmosphere to carbonize the carbon fiber precursor and the liquid resin.

[0061] The non-oxidizing atmosphere may be an atmosphere of inert gas flow such as nitrogen or argon, or 0.1 Pa or less, 10 －２ Pa or less, 10 －３ Pa or less, 10 －４ Pa or less, 10 －５ Pa or less, 10 －６ Pa or less, or 10 －７ Pa is less than or equal to 10 －８ A vacuum of Pa or higher is also acceptable.

[0062] The heat treatment can be carried out by raising the temperature to a predetermined maximum temperature. The maximum temperature may be 500°C or higher, 600°C or higher, 700°C or higher, 800°C or higher, 900°C or higher, or 950°C or higher, and is particularly preferable to be 800°C or higher for applications where electrical conductivity is important. This maximum temperature may be 2500°C or lower, 2400°C or lower, 2300°C or lower, 2200°C or lower, 2100°C or lower, 2000°C or lower, 1900°C or lower, 1800°C or lower, 1700°C or lower, 1600°C or lower, 1500°C or lower, 1400°C or lower, 1300°C or lower, 1200°C or lower, or 1100°C or lower.

[0063] The time for which the maximum temperature is maintained may be 30 minutes or more, 1 hour or more, 2 hours or more, or 3 hours or more, and may also be 72 hours or less, 70 hours or less, 60 hours or less, 50 hours or less, 40 hours or less, 30 hours or less, 20 hours or less, 10 hours or less, 8 hours or less, 5 hours or less, or 4 hours or less.

[0064] 《Method for Manufacturing Graphite-Coated Carbon Fiber Structures》 The present invention provides a method for manufacturing graphite-coated carbon fiber structures, comprising: providing a resin dispersion in which graphite particles are mixed and dispersed in a liquid resin; impregnating a porous fibrous carbon skeleton precursor with the resin dispersion; removing a portion of the resin dispersion from the fibrous carbon skeleton precursor impregnated with the resin dispersion; and heat-treating the fibrous carbon skeleton precursor, the graphite particles, and the liquid resin in a non-oxidizing atmosphere to carbonize the fibrous carbon skeleton precursor and the liquid resin.

[0065] The method of the present invention may further include curing the liquid resin after removing a portion of the resin dispersion. In this case, the cured liquid resin is carbonized by heat treatment.

[0066] <Provision of Resin Dispersion> For information on the provision of resin dispersion, please refer to the description of the method for manufacturing graphite-coated carbon fibers.

[0067] <Impregnation of resin dispersion> Impregnation of the resin dispersion is carried out by impregnating a porous fibrous carbon skeleton precursor with the resin dispersion.

[0068] Here, as the porous fibrous carbon skeleton precursor, for example, a nonwoven fabric formed from cellulose-derived fibers, particularly long fibers, as mentioned as the carbon fiber precursor, can be used. This nonwoven fabric may be obtained, for example, by the spunbond method.

[0069] <Removal of Resin Dispersion> Removal of the resin dispersion is a step in which a portion of the resin dispersion is removed from the fibrous carbon skeleton precursor impregnated with the resin dispersion. The amount of resin dispersion to be removed can be adjusted according to the density of the graphite-coated carbon fiber structure to be obtained. This step may be carried out by compression or by suction.

[0070] In removing the resin dispersion, it is preferable that the amount of the resin dispersion be 70% by mass or less, 68% by mass or less, or 60% by mass or less, relative to the total mass of the fibrous carbon skeleton precursor and the resin dispersion, and that it be 10% by mass or more, 15% by mass or more, 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, or 55% by mass or more, from the viewpoint of making the content of the carbonaceous binder after carbonization a value mentioned with respect to the carbonaceous binder.

[0071] <Curing and Heat Treatment of Liquid Resins> For curing and heat treatment of liquid resins, refer to the description of the method for manufacturing graphite-coated carbon fibers.

[0072] The present invention will be specifically described by examples and comparative examples, but the present invention is not limited thereto.

[0073] <Example 1> 85 parts of furan resin (carbon residue rate: 35%) as a liquid resin and 15 parts of graphite (flaky graphite, average particle size 4 μm) were thoroughly stirred using a high-speed emulsifier and disperser (Primix Co., Ltd. Homomixer MARK II 2.5 type) to obtain a resin dispersion. This resin dispersion was impregnated into a porous rayon nonwoven fabric (carbon residue rate: 27%) formed by the spunbond method. Next, the amount of impregnated resin was adjusted by removing the resin dispersion by liquid absorption so that the mass ratio of rayon to resin dispersion was as shown in the table. Then, the nonwoven fabric and liquid resin were carbonized by heat treatment at a temperature of 1000°C under an inert atmosphere to produce the carbon fiber structure of Example 1.

[0074] <Example 2> The carbon fiber structure of Example 2 was prepared in the same manner as in Example 1, except that the type and amount of resin dispersion were changed as shown in Table 1.

[0075] <Comparative Example 1> A rayon nonwoven fabric, which is a porous long-fiber material formed by the spunbond method, was carbonized by heat treatment at a temperature of 1000°C in an inert atmosphere without impregnation with resin, thereby producing the carbon fiber structure of Comparative Example 1.

[0076] <Comparative Example 2> A carbon fiber structure of Comparative Example 2 was prepared in the same manner as in Example 1, except that only furan resin was used as the impregnation resin, i.e., graphite was not included.

[0077] <Comparative Example 3> A carbon fiber structure of Comparative Example 3 was prepared in the same manner as in Example 2, except that a nonwoven fabric of flame-resistant acrylic fiber (carbon residue rate: 50%) that is not porous was used as the fibrous carbon skeleton precursor, and the amount of resin dispersion added was changed as shown in Table 1.

[0078] <Comparative Example 4> A carbon fiber structure of Comparative Example 4 was prepared in the same manner as in Example 2, except that the carbon fiber structure of Comparative Example 1 was used instead of rayon nonwoven fabric, and the amount of resin dispersion added was changed as shown in Table 1.

[0079] <Evaluation> <Visual Observation> The visual appearance of the carbon fiber structures of Example 1 and Comparative Examples 1-4 was observed under magnification using a scanning electron microscope (SEM).

[0080] <True Density> The true density of the obtained carbon fiber structure was calculated using the following values: Density of amorphous carbon: 1.5 g / cm³ ３ Density of graphite: 2.2 g / cm³ ３

[0081] <Bulk Density> The bulk density was calculated from the volume and mass of the obtained carbon fiber structures.

[0082] <Porosity> The porosity of the obtained carbon fiber structures was calculated from their bulk density and true density.

[0083] <Resistance> The fabricated carbonaceous porous material was sandwiched between gold-plated plate electrodes, and a pressure of 1 MPa was applied. Next, a current of 1 A was applied to these plate electrodes, and the resistance of the fabricated carbonaceous porous material was measured from the resistance obtained by measuring the voltage between the electrodes.

[0084] <Physical Strength> The state of the fabricated carbonaceous porous material after handling was evaluated sensorily. A: Did not collapse during handling. B: Collapsed during handling.

[0085] The configurations and evaluation results of the examples and comparative examples are shown in Table 1 and Figures 1 to 5. Regarding the magnified observation images shown in Figures 1 to 5, Figures 1(a), 2(a), 3(a), 4(a), and 5(a) each show 50x magnification, Figures 1(b), 2(b), 3(b), 4(b), and 5(b) each show 1,000x magnification, and Figure 1(c) shows 3,000x magnification.

[0086]

[0087] From Figure 1, it can be seen that in the carbon fiber structure of Example 1, graphite particles cover almost the entire carbon fiber skeleton. Furthermore, it can be seen that the carbon fiber structure of Example 1 achieves lower resistance than the comparative example. Although an enlarged image of Example 2 is not available, the same points as for Example 1 can be mentioned.

[0088] Furthermore, Figures 4 and 5 can be seen to confirm that the carbon fiber structures of Comparative Examples 3 and 4 have almost no graphite particles on the surface of the carbon fiber skeleton. From this, it can be understood that even if a liquid resin containing mixed and dispersed graphite particles is impregnated into non-cellulose-derived fibers, such as those used in Comparative Example 3, and into carbon fiber structures, such as those used in Comparative Example 4, the surface of the carbon fiber skeleton cannot be coated with graphite.

Claims

1. A graphite-coated carbon fiber having a carbon fiber skeleton, graphite particles covering the surface of the carbon fiber skeleton, and a carbonaceous binder binding the graphite particles to the carbon fiber skeleton, wherein, when observed with a scanning electron microscope, the graphite particles cover 50% or more of the surface area of ​​the carbon fiber skeleton.

2. The graphite-coated carbon fiber according to claim 1, wherein, when observed using a scanning electron microscope, the graphite particles cover 70% or more of the surface area of ​​the carbon fiber skeleton.

3. A graphite-coated carbon fiber structure comprising graphite-coated carbon fibers according to claim 1 or 2, and a carbonaceous binder that joins the graphite-coated carbon fibers together.

4. The graphite-coated carbon fiber structure according to claim 3, wherein the porosity is 30 to 90%.

5. A battery component comprising a graphite-coated carbon fiber structure according to claim 3 or 4.

6. A method for producing graphite-coated carbon fibers according to claim 1 or 2, comprising: providing a resin dispersion in which graphite particles are mixed and dispersed in a liquid resin; impregnating a porous carbon fiber precursor with the resin dispersion; removing a portion of the resin dispersion from the carbon fiber precursor impregnated with the resin dispersion; and heat-treating the carbon fiber precursor, the graphite particles, and the liquid resin in a non-oxidizing atmosphere to carbonize the carbon fiber precursor and the liquid resin.

7. A method for producing a graphite-coated carbon fiber structure according to claim 3 or 4, comprising: providing a resin dispersion in which graphite particles are mixed and dispersed in a liquid resin; impregnating a porous fibrous carbon skeleton precursor with the resin dispersion; removing a portion of the resin dispersion from the fibrous carbon skeleton precursor impregnated with the resin dispersion; and heat-treating the fibrous carbon skeleton precursor, the graphite particles, and the liquid resin in a non-oxidizing atmosphere to carbonize the fibrous carbon skeleton precursor and the liquid resin.

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