WO2019124596A1 - Composite electrode for redox flow battery and manufacturing method therefor - Google Patents

Abstract

A composite electrode according to the present invention has advantages in that it is possible to simplify manufacturing processes and reduce process costs by inserting an electrode into a bipolar plate included in a battery cell, to improve lamination stability by reducing the volume of the cell, and to prevent corrosion of the electrode by removing a contact between the electrode and an electrolyte. In addition, as the bipolar plate is manufactured by heating under specific conditions in a fixed state, it is possible to quickly and stably manufacture the composite electrode by generating a crack due to an expansion of the bipolar plate. Further, it is possible to reduce contact resistance and increase output by integrally forming the bipolar plate and the electrode.

Description

Composite electrode for redox flow cell and manufacturing method thereof

The present invention relates to a composite electrode for a redox flow cell and a method of manufacturing the same. More particularly, the present invention relates to a composite electrode for a redox flow battery, which comprises a bipolar plate to which a battery cell is inserted, Electrode integrated type composite electrode in which electrodes are formed by inserting a certain region and a manufacturing method thereof.

Recently, renewable energy such as solar energy or wind energy is attracting attention as a method to suppress greenhouse gas emission, which is a major cause of global warming. However, renewable energy is heavily influenced by location conditions and natural conditions. Moreover, since the output fluctuation is significant, the energy can not be continuously supplied uniformly. Therefore, in order to use the renewable energy for home or commercial use, a system that stores energy when the output is high and stored energy when the output is low is introduced and used.

As such an energy storage system, a large-capacity secondary battery is used. For example, a large-capacity secondary battery storage system is introduced into a large-scale solar power generation and wind power generation complex. The secondary battery for the large-capacity power storage includes a lead storage battery, a sodium sulfide (NaS) battery, and a redox flow battery (RFB).

Redox flow cells are capable of operating at room temperature and are capable of independently designing their capacity and output, and therefore many studies have been made with large capacity secondary batteries.

The redox flow battery is a secondary battery which can charge and discharge electric energy by forming a stack by arranging a membrane, an electrode and a bipolar plate in a series similar to a fuel cell, battery. In the redox flow battery, the anode electrolyte and the cathode electrolyte supplied from the anode and cathode electrolyte storage tanks are circulated on both sides of the separator, and the ion exchange is performed. In this process, electrons move to charge and discharge. Such a redox flow battery is known to be the most suitable for an ESS (Energy storage system) because it can be manufactured as a medium to large-sized system of kW to MW class, as compared with a conventional secondary battery.

The redox flow cell consists of porous electrodes (positive electrode and negative electrode), bipolar plate, and frame laminated on both sides of an ion exchange membrane (separator), and the bipolar plate is a plate separating each cell of the stack , Conductivity is required in order to minimize the internal resistance of the battery, and water tightness is required so that the electrolytic solution does not leak to the adjacent cells and can be surely blocked.

Conventional redox flow cells use various materials such as frames and electrodes that can support the bipolar plate when stacking the stack, which increases the volume of the whole stack and the stacking process time. Since a large number of bipolar plates, frames, and electrodes are required to be stacked thereon, a large amount of expensive materials are used, which is disadvantageous in that the cost is increased and the bonding is maintained. In addition, the bipolar plate should have good in-plane conductivity as well as thickness direction conductivity, which can improve the performance of the battery.

[Prior Art Literature]

Korean Patent Publication No. 10-2017-0115848 (Oct. 18, 2017)

SUMMARY OF THE INVENTION The present invention has been conceived to solve the problems described above, and it is an object of the present invention to simplify the manufacturing process and reduce the process cost by inserting electrodes into the bipolar plate included in the battery cell, And a composite electrode for a redox flow cell, which can prevent contact between an electrode and an electrolyte and prevent corrosion of the electrode.

Another object of the present invention is to provide a method for manufacturing the composite electrode, wherein the bipolar plate is heated under specific conditions in a fixed state to generate cracks due to the expansion of the bipolar plate, so that a composite electrode can be manufactured quickly and stably .

The present invention relates to a composite electrode for a redox flow battery and a method of manufacturing the same.

According to an aspect of the present invention, there is provided a bipolar plate including a carbon material, the bipolar plate having an insertion groove formed by recessing one side of the bipolar plate; And an electrode inserted in the insertion groove of the bipolar plate, the electrode being inserted to expose a certain portion from the bipolar plate.

In the present invention, the bipolar plate includes 70 to 95% by weight of a carbon material and 5 to 30% by weight of a polymer resin. The carbon material may be carbon fiber, carbon black, graphene, graphite, carbon paper, acetylene black, Wherein the polymer resin is selected from the group consisting of polyolefin, polyamide, polystyrene, polyvinyl chloride, polyurethane, polyester, poly Acryl, epoxy, phenol, urea, melamine, and unsaturated polyester.

In another aspect of the present invention,

A) preparing a composition for producing a bipolar plate from a composition comprising a carbonaceous material;

B) forming an electrolytic solution flow path through the bipolar plate in a direction of stacking the bipolar plate;

C) a pressing step of pressing both side ends of the bipolar plate with a fixing member whose positional displacement is limited, and pressing the electrolyte flow path so as to cover the fixing member;

D) forming an insertion groove by heating a central portion of the bipolar plate to form an insertion groove by cracking of the bipolar plate; And

E) inserting an electrode into the insertion groove so as to expose a predetermined portion;

And more particularly, to a method for producing a composite electrode for a redox flow battery.

In the present invention, the composition comprises 70 to 95% by weight of a carbon material and 5 to 30% by weight of a polymer resin, wherein when the polymer resin is a thermoplastic resin, the step C) proceeds after curing of the thermoplastic resin , And when the polymer resin is a thermosetting resin, the step (D) is characterized in that the curing degree of the thermosetting resin proceeds in the B-stage or the B-stage.

In the present invention, the heating temperature in step D) is 500 to 1500 ° C. and the heating time is 1 to 15 seconds.

The composite electrode according to the present invention can simplify the manufacturing process and reduce the manufacturing cost by inserting the electrode into the bipolar plate included in the battery cell. It is possible to reduce the volume of the cell to improve the stability of the lamination and to eliminate contact between the electrode and the electrolyte It has an advantage that corrosion of the electrode can be prevented.

In addition, the bipolar plate is fixed and heated under specific conditions to produce a crack due to the expansion of the bipolar plate. Thus, the composite electrode can be manufactured quickly and stably. By forming the bipolar plate and the electrode as one body, The efficiency can be increased.

1 is a perspective view of a composite electrode of the present invention.

2 shows a cross section of the composite electrode of the present invention.

FIGS. 3 to 7 illustrate a manufacturing process of a composite electrode according to the present invention.

8 is a conceptual diagram showing an example of a component including a cell of a redox flow cell including a composite electrode manufactured according to the present invention.

Hereinafter, a composite electrode for a redox flow battery according to the present invention and a method for manufacturing the same will be described in detail with reference to specific examples. The following specific embodiments are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention.

Therefore, the present invention is not limited to the embodiments shown below, but may be embodied in other forms. The embodiments shown below are only for clarifying the spirit of the present invention, and the present invention is not limited thereto.

Here, unless otherwise defined, technical terms and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. In the following description, the gist of the present invention is unnecessarily blurred And a description of the known function and configuration will be omitted.

In addition, the following drawings are provided by way of example so that those skilled in the art can fully understand the spirit of the present invention. Therefore, the present invention is not limited to the following drawings, but may be embodied in other forms, and the drawings presented below may be exaggerated in order to clarify the spirit of the present invention. Also, throughout the specification, like reference numerals designate like elements.

Also, the singular forms as used in the specification and the appended claims are intended to include the plural forms as well, unless the context clearly indicates otherwise.

In describing the components of the present invention, terms such as first, second, A, B, (a), and (b) may be used. These terms are intended to distinguish the constituent elements from other constituent elements, and the terms do not limit the nature, order or order of the constituent elements. When a component is described as being "connected", "coupled", or "connected" to another component, the component may be directly connected to or connected to the other component, It should be understood that an element may be "connected," "coupled," or "connected."

The term 'battery cell' in the present invention is a minimum unit in which charging and discharging occurs through an electrolytic solution, and includes a separator, separator, etc., in which ion exchange occurs.

In the present invention, the term " stack " means that a plurality of battery cells are stacked or configured.

The term " bipolar plate " in the present invention refers to a plate for separating each cell of a stack. The bipolar plate includes at least one of a separator, an anode, and a cathode. The bipolar plate includes a channel for transporting an electrolyte, And minimizes it.

The lamination direction in the present invention means the direction of the dotted line passing through the center of each constitution in the process of manufacturing the composite electrode shown in FIG. At this time, the stacking direction means both one end direction and the other end direction of the dotted line.

The inventor of the present invention uses various materials such as a frame and an electrode that can support the bipolar plate when stacking the stack, which is a disadvantage of the redox flow battery, so that the volume of the entire stack and the time for the stacking process are increased, Since the bipolar plate, frame, and electrode must be stacked, it is necessary to simplify the manufacturing process by inserting the electrode inside the bipolar plate included in the battery cell, It is possible to reduce the cost, increase the lamination stability by reducing the volume of the cell, eliminate the contact between the electrode and the electrolyte, prevent the corrosion of the electrode, and find a method for manufacturing the composite electrode quickly and stably. It was completed.

1 and 2, the composite electrode 100 for a redox flow battery according to the present invention includes a bipolar plate 110 having an insertion groove 111 formed therein with one side indented therein, And an electrode 120 inserted into the bipolar plate such that a certain portion thereof is exposed from the bipolar plate.

The bipolar plate according to the present invention will be described in more detail,

A) preparing a composition for producing a bipolar plate from a composition comprising a carbonaceous material;

B) forming an electrolytic solution flow path through the bipolar plate in a direction of stacking the bipolar plate;

C) a pressing step of pressing both side ends of the bipolar plate with a fixing member whose positional displacement is limited, and pressing the electrolyte flow path so as to cover the fixing member;

D) forming an insertion groove by heating a central portion of the bipolar plate to form an insertion groove by cracking of the bipolar plate; And

E) inserting an electrode into the insertion groove so as to expose a predetermined portion;

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In the present invention, the carbon material is a main component of the bipolar plate, and is required to have high conductivity for minimizing the internal resistance of the battery, high miscibility with the polymer resin, and high dispersibility.

Examples of the carbon material in the present invention include carbon fibers, carbon black, graphene, graphite, carbon paper, acetylene black, activated carbon, fullerene, carbon nanotubes, carbon nanowires, carbon nanohorns, Any one or a plurality of these may be used in combination. It is more preferable to use carbon fiber or graphite in consideration of compatibility with a polymer resin and dispersibility.

The carbon material does not limit the particle size, but is preferably 10 nm to 900 탆, more preferably 1 to 100 탆. If the particle size is less than 10 nm, it may be difficult to disperse in the resin because of the volume per particle, and if the particle size exceeds 900 μm, the uniformity of dispersion may be lowered.

In the present invention, it is preferable that the carbon material includes 70 to 95 wt% of 100 wt% of the bipolar plate composition. If the amount is less than the above range, the polymer resin in the bipolar plate may be present in an excessive amount, resulting in an increase in battery resistance and a decrease in energy efficiency. If the amount exceeds 95 wt%, the mechanical properties of the bipolar plate may deteriorate.

In the present invention, the polymer resin is a kind of adhesive for dispersing and fixing the particles of the carbon material, and it is desirable that a high level of acid resistance is required because the electrolyte is in direct contact with the polymer, and the compatibility and dispersibility with the carbon material are high.

In the present invention, the polymer resin is not limited in its kind as long as it satisfies the above-mentioned characteristics, and is preferably a polyolefin such as polyethylene, polypropylene, ethylene vinyl acetate, or a polyolefin such as polyamide, polystyrene, polyvinyl chloride, polyurethane, Thermoplastic resins such as polyacryl; Or thermosetting resins such as epoxy, phenol, urea, melamine and unsaturated polyester. One or a mixture of these may be used.

In the present invention, the polymer resin is preferably added in an amount of 5 to 30% by weight based on 100% by weight of the entire bipolar plate composition. If the amount is less than the above range, the adhesion property of the carbon material may be reduced or voids may be formed on the surface and inside of the bipolar plate. If the amount is exceeded, the amount of resin may be excessively present, .

Further, the bipolar plate according to the present invention may further include a conductive filler as needed in the preparation of the composition.

The conductive filler is used to further increase the electrical characteristics of the bipolar plate, and it is preferable to use metal particles having high miscibility and dispersibility with the carbon material or the polymer resin.

Examples of the conductive filler include copper, aluminum, titanium, gold, platinum, iron, silver, silicon, tin, bismuth, magnesium, zinc, indium, germanium, lead and the like And one or a mixture of these may be used.

The conductive filler may have a particle size the same as or similar to that of the carbon material, and the addition amount thereof is not limited. However, the addition of 0.01 to 1 part by weight of the conductive filler in 100 parts by weight of the total bipolar plate composition results in dispersion characteristics and electrical conductivity Can be satisfied.

The bipolar plate composition according to the present invention may further contain additives such as an organic solvent, a curing agent and a dispersing agent in consideration of curability, ease of sheet production, and viscosity control. In this case, the addition amount of the additives is not limited to the present invention. Specifically, it is preferable that the total amount of the additives is 10 to 100 parts by weight in 100 parts by weight of the entire bipolar plate composition.

The manufacturing method of the bipolar plate according to the present invention is not limited. Specifically, the composition can be prepared by mixing the composition as described above, pouring the composition into a mold having a desired size and thermo-pressing it. In this case, the temperature and the pressure to be applied are not limited. Specifically, the pressure and the pressure may be adjusted while the temperature is lower than the deterioration temperature in consideration of the characteristics of the polymer resin. In particular, in the case of a thermosetting resin, since it can be cured at a low temperature, it can be easily produced by applying a certain amount of pressure.

The bipolar plate produced in accordance with the present invention is not limited in size and shape. However, if the thickness is too thin, it may cause breakage in the process of forming the insertion groove. Therefore, it is preferable that the thickness is equal to or more than a certain thickness. In consideration of the volume of the whole battery cell and the thickness of the inserted electrode, Mm. ≪ / RTI >

Next, the electrolyte flow path forming step for forming the electrolyte flow path through the bipolar plate in the stacking direction of the completed bipolar plate is performed (step B).

1 and 2, the anode electrolyte or the cathode electrolyte may be transferred to the space formed by the flow path frame and the gasket through the bipolar plate or may be transferred to the electrolyte tank from the space. And may be provided on one side of the bipolar plate.

More specifically, the electrolyte flow path 112 serves as an inlet through which the anode or cathode electrolyte flows into the space formed by the flow path frame or the gasket, and a discharge port discharged from the flow path frame or gasket to the electrolyte tank , The bipolar plate may have a rectangular shape as shown in Fig. 1, and may be formed to overlap with diagonal lines connecting the respective vertexes, for example. In this case, the bipolar plate has a rectangular shape as described above. However, the position of the electrolyte flow path can be freely changed according to the shape of the bipolar plate, and the present invention is not limited thereto.

Next, the both ends of the bipolar plate as described above are pressed by the fixing member 500 whose positional displacement is limited as shown in FIG. 4 (C)).

The step C) is for forming an insertion hole by inducing internal cracks due to thermal deformation of the bipolar plate. The fixing member 500 having a limited positional displacement, for example, a jig, When heat is applied to a certain portion of the bipolar plate, the bipolar plate thermally expands, but since the both ends are fixed by the jig, expansion may continue and cracks may occur in a certain region of the bipolar plate as shown in FIG. .

The carbon material is relatively low in layer strength, but has a high thermal conductivity, so that when it is expanded by heat, it cracks from the central portion and extends in the longitudinal direction rather than the vertical direction.

It is preferable that when the bipolar plate is pressed by the holding member, the electrolyte flow path is pressed so that the holding member covers the bipolar plate. If the fixing member does not cover the electrolyte flow path when a certain region of the bipolar plate is heated by heating a certain region of the bipolar plate in the next step, the electrolyte flow path is deformed at the time of thermal deformation of the bipolar plate, It can be.

After fixing the bipolar plate as described above, a predetermined region of the bipolar plate may be heated to induce cracks in the bipolar plate to form the electrode insertion groove 111 (step D).

In the present invention, the heating conditions, particularly the heating temperature and the heating time, of the bipolar plate are preferably set in consideration of the dissolution, deformation and deterioration temperature of the composition of the bipolar plate, in particular, the polymer resin.

In the present invention, the heating temperature of the bipolar plate can be controlled according to the size and speed of the bipolar plate, but it is preferably 500 to 1,500 ° C, more preferably 800 to 900 ° C, more preferably 1 to 15 seconds, Preferably 3 to 7 seconds. It is preferable that the insertion groove according to the thermal expansion of the bipolar plate can be uniformly formed while preventing the dissolution, deformation and deterioration of the polymer resin in the above range.

In the present invention, the bipolar plate heating apparatus can be used without limitation as long as the heating temperature and the heating time can be easily controlled and the size thereof is small so as not to inconvenience in the heating process. For example, a butane flame generator may be used, and various heating means may be used.

Also, the step (D) may control the heating time according to the polymer condition of the bipolar plate. For example, when the polymer resin is a thermoplastic resin, it may be heated after the bipolar plate is completely cured. However, in the case of a thermosetting resin, after the bipolar plate is completely cured, it has a three-dimensional net structure, However, if the three-dimensional net structure is destroyed, the bipolar plate may not be restored. Therefore, if cracks due to thermal deformation are generated after complete curing, breakage of the bipolar plate may occur due to cracks. .

More specifically, when the polymer resin is a thermosetting resin, the step D) preferably proceeds in the B-stage or the B-stage of the curing process of the thermosetting resin.

Next, as shown in FIGS. 5 and 6, when the insertion groove 111 is formed in the bipolar plate, the electrode insertion step may be performed in which the electrode 120 is inserted into the insertion groove formed in the bipolar plate, (E) step).

The electrode may be divided into an anode and a cathode according to the position in the battery cell. When the anode and the cathode are divided into the anode and the cathode as described above, the anode and the cathode may have different thicknesses, porosity distributions, porosities, specific surface areas, Can be taken differently from each other.

The electrode is not limited to a material having conductivity as long as it is used as a redox flow battery or an electrode of a secondary battery in the art. For example, carbon materials such as graphite, graphene and carbon fibers, metals such as copper, silver, gold, platinum and aluminum, and metal oxides of the above metals may be mentioned. The carbon material may be mixed with a metal or a metal oxide May be used.

The electrodes according to the present invention are not limited in size or shape. However, since the electrode is to be inserted into the insertion groove of the bipolar plate in a predetermined area, it is preferable that the size, shape and thickness of the electrode are smoothly inserted into the insertion groove. In particular, it is preferable that the thickness is smaller than the thickness of the bipolar plate, and it is preferably 2 mm or less, more preferably 0.05 to 2 mm in consideration of the volume of the whole battery cells and the width and depth of the insertion grooves.

The electrode is preferably pushed into the insertion groove as shown in FIGS. 1 and 2, and a portion of the electrode is exposed from the bipolar plate so that the electrode can be electrically connected to the outside.

When the electrode is inserted into the insertion groove as described above, the bipolar plate is cooled and contracted as shown in FIG. 7, whereby the expanded bipolar plate can be restored to its original state and completed. At this time, the cooling condition of the bipolar plate differs depending on the kind of the resin included in the bipolar plate composition, the addition amount, the presence or absence of other additives, and the present invention is not limited thereto.

In addition, the composite electrode may be exposed to the electrode by sealing the insertion groove after inserting the electrode into the bipolar plate, if necessary. At this time, the method of sealing the insertion groove is not limited to the present invention, but preferably, the bipolar plate composition can be poured into the insertion groove and cured.

The present invention may further include a battery cell including the composite electrode and the composite electrode manufactured as described above, and a redox flow cell including the same.

8, the battery cell includes the composite electrodes 100a and 100b, the gaskets 200a, 200b, 200c, and 200d, the flow path frames 300a and 300b, and the separation membrane 400 And may further include a fixed frame (not shown) for pressing the cell and an electrolyte flow path (not shown).

Assuming that the composite electrode 100a located at the uppermost one of the composite electrodes of the battery cell is an anode and the composite electrode 100b located at the lower end thereof is a cathode, the anode electrolyte flows from the anode electrolyte flow channel (not shown) Side flow path frame through the inlet-side flow path of the anode-side flow path frame 300a, and then flows into the anode-side electrolyte flow path (not shown) through the outflow-side flow path. Here, the inlet-side flow path and the outlet-side flow path are formed at the opposite corner of one side of the flow path frame 300a in Fig.

The negative electrode electrolytic solution flows into the negative electrode side flow path frame from the negative electrode electrolyte flow path (not shown) through the inflow-side flow path of the negative electrode side flow path frame 300b, and then the negative electrode electrolyte flowed into the negative electrode side flow path frame, And flows out to the negative electrode electrolyte flow path (not shown) through the outflow-side flow path. Here, the inflow-side flow path and the outflow-side flow path are formed at the opposite edge of one side of the flow path frame 300b in Fig.

8, the outflow-side flow path and the inflow-side flow path of the positive-electrode-side flow path frame 300a are staggered so as not to face the outflow-side flow path and the inflow-side flow path of the negative electrode side flow path frame 300b. However, And it is of course possible to form various channels because the separator 400 can not mix the positive and negative electrode electrolytic solutions.

The separator is ion-exchanged between the anode electrolyte and the cathode electrolyte while circulating the anode electrolyte in contact with the one surface of the separator, and contacting the cathode electrolyte with the other electrolyte. The separation membrane is ion-exchangeable, and charging / discharging proceeds.

Electrons generated through ion exchange as described above may be charged and discharged while being moved through the composite electrode 100. As shown in FIGS. 1 and 2, the composite electrode includes a metal electrode and a bipolar plate (separator) surrounding a part of the metal electrode. The bipolar plate is a kind of conductor, And transferred to the electrode.

As described above, the positive electrode electrolytic solution circulates along the positive electrode electrolyte flow path, the negative electrode electrolyte circulates along the negative electrode electrolyte flow path, and the respective electrolytic solution introduced into the inside flows through the ion exchange membrane 400, Charging and discharging may occur due to the reduction reaction.

In the redox flow cell according to the present invention, since the electrode is inserted into the bipolar plate, it is not necessary to form a trough, which is a flow path of the electrolytic solution, to the electrode, and through which a buffer for preventing corrosion of the tread by the electrolyte (O-ring), and the like. Therefore, a step may be formed between the buffer and the bipolar plate as a result of simplification of the process, and a general redox flow cell having a buffer in the other electrode of the electrode. However, in the redox flow battery having the composite electrode according to the present invention, There is no disadvantage. Since the electrode is inserted into the bipolar plate, the electrolyte is not directly contacted with the electrode, so that corrosion due to the pre-nucleus solution can be prevented, and the volume of the battery cell can be drastically reduced by integrating the bipolar plate and the electrode.

As described above, the approximate connection structure of the redox flow cell according to the present invention has been described. However, those skilled in the art will appreciate that various modifications and changes may be made without departing from the spirit and scope of the present invention as set forth in the following claims It will be understood that the invention may be variously modified and changed.

Claims (10)

1. A bipolar plate including a carbon material, the bipolar plate having an insertion groove formed by recessing one side of the bipolar plate; And

   An electrode inserted into the insertion groove of the bipolar plate such that a certain portion is exposed from the bipolar plate;

   Wherein the composite electrode has a thickness of less than or equal to 100 nm.
2. The method according to claim 1,

   Wherein the bipolar plate comprises 70 to 95% by weight of a carbon material and 5 to 30% by weight of a polymer resin.
3. 3. The method of claim 2,

   The carbon material may include one or more selected from carbon fiber, carbon black, graphene, graphite, carbon paper, acetylene black, activated carbon, fullerene, carbon nanotubes, carbon nanowires, Wherein the redox-flowable battery is a composite electrode.
4. 3. The method of claim 2,

   Wherein the polymer resin comprises one or more selected from polyolefin, polyamide, polystyrene, polyvinyl chloride, polyurethane, polyester, polyacrylic, epoxy, phenol, urea, melamine and unsaturated polyester Composite electrode for battery.
5. A) preparing a composition for producing a bipolar plate from a composition comprising a carbonaceous material;

   B) forming an electrolytic solution flow path through the bipolar plate in a direction of stacking the bipolar plate;

   C) a pressing step of pressing both side ends of the bipolar plate with a fixing member whose positional displacement is limited, and pressing the electrolyte flow path so as to cover the fixing member;

   D) forming an insertion groove by heating a central portion of the bipolar plate to form an insertion groove by cracking of the bipolar plate; And

   E) inserting an electrode into the insertion groove so as to expose a predetermined portion;

   Wherein the composite electrode has a thickness of 100 nm or less.
6. 6. The method of claim 5,

   Wherein the composition comprises 70 to 95% by weight of the carbon material and 5 to 30% by weight of the polymer resin.
7. The method according to claim 6,

   Wherein when the polymer resin is a thermoplastic resin, the step (D) proceeds after curing of the thermoplastic resin.
8. The method according to claim 6,

   Wherein when the polymer resin is a thermosetting resin, the curing degree of the thermosetting resin proceeds in a B-stage or a B-stage in the step (D).
9. 6. The method of claim 5,

   Wherein the heating temperature in the step (D) is 500 to 1500 ° C.
10. 6. The method of claim 5,

    Wherein the heating time in the step (D) is 1 to 15 seconds.

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