KR20240022152A - Manufacturing method of conductive material for secondary battery and conductive material prepared therefrom - Google Patents

Abstract

An expanded graphene manufacturing step of forming graphene oxide (GO) from graphite and heat-treating it to produce expanded graphene with a diameter of several μm; And a conductive material manufacturing step of manufacturing a conductive material in powder form by hybridizing the expanded graphene prepared in the expanded graphene manufacturing step and carbon nanotubes; A method for manufacturing a conductive material for a secondary battery comprising a conductive material, a conductive material manufactured therefrom, and a secondary battery containing the same are provided.

Description

Method for manufacturing conductive materials for secondary batteries and conductive materials manufactured therefrom {MANUFACTURING METHOD OF CONDUCTIVE MATERIAL FOR SECONDARY BATTERY AND CONDUCTIVE MATERIAL PREPARED THEREFROM}

The present invention relates to a method for manufacturing a conductive material for secondary batteries and a conductive material manufactured therefrom, and more specifically, to a conductive material in which graphene flakes and carbon nanotubes are hybridized.

Secondary batteries (e.g., lithium-ion secondary batteries) are attracting attention as a main energy source for various miniaturized and lightweight electronic devices, hybrid vehicles, and electric vehicles due to their high output and high energy characteristics.

A secondary battery consists of a positive electrode and a negative electrode mainly composed of an electrode active material, a binder, and a conductive material, and a separator and electrolyte solution interposed between the positive electrode and the negative electrode.

In the case of the negative electrode, graphite-based materials (natural graphite, artificial graphite) have been used as negative electrode active materials, but they have limitations in low electric capacity, and attempts to use silicon-based materials as a material to overcome these limitations are continuing.

This silicon-based anode active material can secure a theoretical electric capacity (4200 mAh/g) that is about 10 times that of the graphite-based material mentioned above, but silicon undergoes volume expansion and contraction of more than 400% during the charging and discharging process. . This large change in the volume of silicon ultimately caused a decrease in cell durability.

Accordingly, research is being conducted from various angles to alleviate volume changes during the charging and discharging process of secondary batteries by combining silicon with various materials. As part of this research, Republic of Korea Patent Publication No. 10-1613518 (“Carbon-silicon composite electrode material and manufacturing method thereof”, application date: 2014.08.25., registration date: 2016.04.12.), Republic of Korea Patent Publication No. 10 -1898110 (“Active material for lithium secondary battery containing activated carbon-silicon composite and manufacturing method thereof”, application date: 2016.08.31., registration date: 2018.09.06.), etc. have been presented.

Meanwhile, in the case of the negative electrode, the carbon-based material contained in the negative electrode active material itself has high conductivity, so it can serve as a conductive material in parallel. However, as charging/discharging progresses, the negative electrode active material reacts with lithium ions and the electron conduction path becomes unstable. In some cases, a separate conductive material must be included to supplement this. Although these conductive materials are used in electrodes only in small amounts, they play a very important role in improving the performance of secondary batteries.

The current mass-produced conductive material is Super-P (carbon black), and recently, MWCNT (multi-wall CNT), a carbon nanotube (CNT), is being used. And, graphene has been proposed as a research and development material.

At this time, carbon nanotubes have a tube shape with a diameter of several nm in which six carbon atoms are rolled up in a hexagonal shape, and have excellent electrical and mechanical properties, thermal stability, and adsorption and transport characteristics, so they can be used as other cathode materials, especially silicon-based cathodes. When added as a conductive material to a secondary battery to which an active material is applied, a large volume change of silicon can be prevented during charging/discharging, thereby improving the capacity and lifespan characteristics of a secondary battery to which a silicon-based anode active material is applied.

Additionally, graphene is evaluated as a suitable material for forming the negative electrode of secondary batteries due to its excellent electrical properties, charge mobility, and specific surface area.

Recently, attempts have been made to hybridize these two materials to realize the synergistic effect of the properties of the two carbon materials and apply them to transparent electrodes, semiconductors, secondary batteries, etc.

As one of these attempts, the present invention proposes a technology that hybridizes graphene and carbon nanotubes to produce a conductive material that can improve the performance of secondary batteries containing silicon-based anode active materials, while securing price competitiveness from a commercialization perspective. I want to do it.

The present invention is intended to solve the above-described problems, and its purpose is to provide a method for manufacturing a conductive material for secondary batteries that can secure price competitiveness while improving the performance of secondary batteries containing a silicon-based anode active material, and a conductive material manufactured therefrom. there is.

To achieve this purpose, a method of manufacturing a conductive material for secondary batteries according to an embodiment of the present invention involves forming graphene oxide (GO) from graphite and heat-treating it to form expanded graphene with a diameter of several μm. Expanded graphene manufacturing step of manufacturing pins; And a conductive material manufacturing step of manufacturing a conductive material in powder form by hybridizing the expanded graphene prepared in the expanded graphene manufacturing step and carbon nanotubes; may include.

At this time, the carbon nanotube may be a thin multi wall carbon nanotube (TMWCNT).

In addition, the expanded graphene manufacturing step includes a chemical treatment step of chemically treating the graphite by adding it to a mixed solution containing a strong acid and an oxidizing agent so that the graphite is oxidized and forms oxidized graphite; In the chemical treatment step, the graphite oxide suspension, which is a chemically treated product, is placed in an ultrasonic disperser, and the graphite oxide with an increased interlayer distance is partially exfoliated as layer separation occurs, and is stirred for 2 to 5 hours to form graphene oxide. An ultrasonic treatment step of applying ultrasonic waves; A filtering-neutralization step of filtering the graphene oxide treated in the ultrasonic treatment step by vacuum filtration and neutralizing it by pouring distilled water until it becomes neutral; A drying step of drying the graphene obtained through the filtering-neutralization step at a temperature of 60 ℃ to 100 ℃ for more than 12 hours; and a heat treatment step of heat treating the graphene dried in the drying step for 0.5 to 2 hours to form expanded graphene. It includes, and the expanded graphene has a diameter of 5 μm or less and may be multilayer graphene having at least two or more layers.

Here, the oxidizing agent may include at least one of potassium dichromate, chromic acid, nitric acid, and hydrogen peroxide.

At this time, in the chemical treatment step, sodium chlorate and nitric acid are mixed in the mixed solution at a ratio of 1:3.5, and the graphite can be added to the mixed solution having a capacity 38 to 40 times that of the graphite.

In addition, in the heat treatment step, the graphene may be heat treated at a temperature of 250 ° C to 300 ° C in an air atmosphere.

In addition, the conductive material manufacturing step is to crush the expanded graphene and the carbon nanotubes formed through the heat treatment step to reduce the size, and to ensure that the graphene flakes and carbon nanotubes formed by layer separation from the expanded graphene are uniform. A hybrid step of applying physical force to disperse and hybridize; and a conducting material obtaining step of drying the graphene flakes and carbon nanotubes hybridized in the hybrid step at a temperature of 60° C. to 100° C. for more than 12 hours to obtain a conductive material in powder form; may include.

Here, in the hybrid step, the expanded graphene and carbon nanotubes are pulverized through a basket mill to reduce the size, and the graphene flakes and carbon nanotubes formed by layer separation from the expanded graphene are dispersed. A milling step of milling the carbon nanotubes using beads so that the carbon nanotubes are bonded to the graphene flakes by mutual attraction; and A homogenization step of homogenizing the graphene flakes and carbon nanotubes milled in the milling step through a high pressure homogenizer so that they are uniformly dispersed; may include.

At this time, the milling step may be performed for 1 to 3 hours at a speed of 2500 to 3500 rpm.

Additionally, the homogenization step may be repeated three or more times at a pressure of 800 bar or higher.

Meanwhile, the conductive material can be manufactured using the method for manufacturing the conductive material for secondary batteries described above.

In addition, a negative electrode containing a conductive material manufactured through the above-described method of manufacturing a conductive material for a secondary battery and a secondary battery including the negative electrode can be provided.

As described above, according to the present invention, the following effects are achieved.

First, in order to increase conductivity when mixed with activated carbon, uniform graphene flakes of less than 5 μm, which are smaller than activated carbon, are manufactured, but by forming them with multilayer graphene, the costs associated with the process can be reduced.

Second, it is necessary to manufacture conductive materials by hybridizing graphene flake, which is a multi-layer graphene that can be manufactured at a lower cost than high-crystal single-layer graphene, and high-crystal TMWCNT, which is cheaper than SMWCNT among carbon nanotubes and has higher electrical conductivity than MWCNT. While reducing the cost, the conductive material manufactured from this can have excellent electrical properties as carbon nanotubes uniformly dispersed between graphene flake layers and on the surface constitute an electron transfer path.

Third, in order to overcome the difficulty of exfoliation, which is a disadvantage of expanded graphene, the equipment advantages of the basket mill and high-pressure homogenizer are utilized to simultaneously apply physical force to expanded graphene (or graphene flakes) and carbon nanotubes to control size and By performing dispersion, price competitiveness can be secured by implementing a low-cost process for manufacturing a highly conductive powder in which the two materials are hybridized.

Fourth, the conductive material, which is a hybrid of graphene flakes and carbon nanotubes, can even supplement the role of the negative electrode active material, improving the capacity and lifespan characteristics of secondary batteries using it.

Fifth, when applied to a secondary battery using a silicon-based negative active material, it can control volume changes during charging/discharging and provide excellent electrical conductivity and stability.

Figure 1 is a flowchart showing a method of manufacturing a conductive material for a secondary battery according to an embodiment of the present invention.
Figure 2 is a flowchart showing the expanded graphene manufacturing step in the manufacturing method of a conductive material for secondary batteries according to an embodiment of the present invention.
Figure 3 is a scanning electron microscope showing (a) graphite and (b) expanded graphene produced through the expanded graphene manufacturing steps illustrated in Figure 2, and (c) expanded graphene illustrated in Figure 3 (b). (SEM) This is a photo.
Figure 4 is a scanning electron microscope (SEM) photograph of the expanded graphene finally manufactured according to the ultrasonic dispersion time (3H, 5H) of the ultrasonic treatment step among the expanded graphene manufacturing steps illustrated in Figure 2, (a) is a case where the ultrasonic dispersion time is 3 hours, and (b) is a case where the ultrasonic dispersion time is 5 hours.
Figure 5 is a flowchart showing the manufacturing step of a conductive material in the method of manufacturing a conductive material for a secondary battery according to an embodiment of the present invention.
Figure 6 is a schematic diagram schematically showing the pulverization and dispersion process of the basket mill used in the milling step in the manufacturing step of the conductive material illustrated in Figure 5.
Figure 7 is a scan measuring (a) expanded graphene, (b) TMWCNT, and (c) graphene flakes that have undergone the milling and homogenization steps introduced into the basket mill in the milling step of the conductive material manufacturing step illustrated in Figure 4. This is an electron microscope (SEM) photo.
Figure 8 is a scanning electron microscope (SEM) photograph measuring graphene flakes and TMWCNTs that were primarily hybridized through a basket mill in the milling step.
Figure 9 is a scanning electron microscope measuring a conductive material in which (a) graphene flakes and TMWCNTs are finally hybridized by being put into a high-pressure homogenizer in the homogenization step of the conductive material manufacturing step illustrated in Figure 5, and (b) a comparative example thereof (b) SEM) This is a photo.
Figure 10 is a graph showing the powder conductivity measurement results of the conductive material shown in Figure 9(a).

Preferred embodiments of the present invention will be described in more detail with reference to the attached drawings, but technical parts that are already well-known will be omitted or compressed for brevity of explanation.

Figure 1 is a flowchart showing a method of manufacturing a conductive material for a secondary battery according to an embodiment of the present invention.

Referring to Figure 1, a method of manufacturing a conductive material for a secondary battery according to an embodiment of the present invention may include the following steps.

1. Expanded graphene manufacturing step <S100>

The expanded graphene manufacturing step (S100) is a step of forming graphene oxide (GO) from graphite and heat-treating it to manufacture expanded graphene with a diameter of several μm.

Below, the expanded graphene manufacturing step (S100) will be described in more detail.

Figure 2 is a flowchart showing the expanded graphene manufacturing step in the manufacturing method of a conductive material for secondary batteries according to an embodiment of the present invention, and Figure 3 is a flow chart showing (a) graphite (Mag = 10K) and expanded graphene illustrated in Figure 2. (b) expanded graphene (Mag = 5K) and (c) produced through the manufacturing step are scanning electron microscope (SEM) photographs enlarged (Mag = 10K) of the expanded graphene illustrated in Figure 3 (b), Figure 4 is a scanning electron microscope (SEM) photograph of the expanded graphene finally manufactured according to the ultrasonic dispersion time (3H, 5H) of the ultrasonic treatment step among the expanded graphene manufacturing steps illustrated in Figure 2, (a) is the case where the ultrasonic dispersion time is 3 hours (Mag=1K, 10K, 50K), and (b) is the case where the ultrasonic dispersion time is 5 hours (Mag=10K, 50K).

Referring to Figures 2 to 4, the expanded graphene manufacturing step (S100) may include the following steps.

1-1. Chemical treatment step <S110>

The chemical treatment step (S110) is a chemical treatment step in which graphite is added to a mixed solution containing a strong acid and an oxidizing agent so that the graphite is oxidized and forms graphite oxide. In other words, oxidized graphite is produced by oxidizing graphite with a strong acid and an oxidizing agent.

At this time, the mixed solution contains sodium chlorate (98%) and fuming nitric acid (93%) in a ratio of 1:3.5, and graphite is added to the mixed solution with a capacity 38 to 40 times that of graphite. More specifically, in the chemical treatment step (S110), the graphite:mixture may have a ratio of 1:38 to 40, and more preferably, may have a ratio of 1:38.5.

1-2. Sonication step <S120>

In the ultrasonic treatment step (S120), the graphite oxide suspension, which is a chemically treated product in the chemical treatment step (S100), is placed in an ultrasonic disperser, and the graphite oxide with an increased interlayer distance is partially exfoliated as layer separation occurs, forming graphite oxide. This is the step of applying ultrasound for 2 to 5 hours to form. For example, an ultrasonic disperser may be a sonication water bath that can disperse ultrasonic waves in a specific frequency band for a certain period of time.

To explain more specifically, the graphite oxide suspension is placed in a beaker and then the beaker is placed in an ultrasonic disperser. The oxidizing agent weakens the interaction force of the carbon structure, that is, weakens the force between layers, causing the gap between layers to widen, and acidic substances penetrate into this weakened interlayer bond. At this time, some of the expanded graphite oxide layers are peeled off through ultrasonic treatment, and the number of graphite layers can be primarily reduced.

For reference, after chemical treatment of graphite, in addition to the ultrasonic dispersion method proposed by the present invention, the size can be reduced through a ball mill process. However, due to the nature of expanded graphite that expands through chemical treatment, that is, acid treatment, there is impact on the particles during ball milling. When applied, it does not split, but absorbs shock due to its expanded structure, so it returns to an appearance similar to graphite before expansion. Accordingly, the size reduction effect cannot be expected, and there is a problem in that the distance between carbon layers increased from the acid treatment process is reduced again.

In addition, in the ultrasonic treatment step (S120), the process of dispersing the graphite oxide suspension by applying ultrasonic waves may be carried out for 2 to 5 hours. Referring to FIG. 4, even if it is carried out for at least 3 hours, the chemical treatment of graphite (e.g., It was confirmed that there was no problem with expansion by acid treatment) and thermal expansion by the heat treatment step to be described later. Accordingly, it may be desirable to perform the ultrasonic dispersion process for at least 3 hours.

For reference, Figure 4(a) is an SEM photograph showing graphite (e.g., expanded graphene) thermally expanded through a heat treatment step to be described later after ultrasonic dispersion for 3 hours after acid treatment in the chemical treatment step, at different magnifications. , Figure 4(b) is the SEM time showing graphite (e.g., expanded graphene) thermally expanded through a heat treatment step after ultrasonic dispersion for 5 hours after acid treatment at different magnifications.

1-3. Filtering-neutralization step<S130>

This is a step in which the graphene oxide treated in the ultrasonic treatment step 120 is filtered using reduced pressure filtration, and distilled water is poured until it becomes neutral.

To be more specific, in the case of filtering, a filtration device set and an aspirator are used. Graphene oxide is placed in a flask or funnel provided in the filtration device set, and then vacuum filtration is performed. do. At this time, neutralization can be performed by pouring distilled water (DI water) into the flask containing graphene oxide until neutrality appears using a pH test paper.

That is, the filtering-neutralization step (S130) is a step of cleaning and obtaining the expanded graphene oxide.

1-4. Drying step<S140>

The drying step (S140) is a step of drying the graphene obtained through the filtering-neutralization step (130) at a temperature of 60°C to 100°C for more than 12 hours.

To be more specific, the drying step (S140) was set to the optimal conditions for drying the solvent (e.g., water), using a vacuum oven at a temperature of 60°C to 100°C, more preferably 80°C, at least 12°C. Allow time to dry.

1-5. Heat treatment step <S150>

The heat treatment step (S150) is a step of heat treating the graphene dried in the drying step (S140) for 0.5 to 2 hours to form expanded graphene expanded by heat.

Here, the heat treatment step (S150) is performed at a temperature of 250°C to 300°C in an air atmosphere so that the layers are separated and expanded by the blowout pressure generated when the nitric acid molecules inserted between the graphene layers are released, and the oxygen functional group is removed. The graphene is heat treated within 2 hours.

At this time, the heat treatment step (S150) is a heat treatment process for removing the oxygen functional group of the graphene dried in the drying step (S140) and expanding the graphite, so there is no need to proceed for a long time.

To explain this in more detail, the oxygen functional group of graphene obtained and dried through the above-described series of processes can be removed at a heat treatment temperature of 270 ° C to 295 ° C. In addition, at a heat treatment temperature of 200 ℃ or higher, the interlayer compounds of the obtained and dried graphene are decomposed and gas is generated. The nitric acid molecules inserted between the dried graphene layers are released all at once by the heat treatment, and the resulting blowout pressure causes interlayer separation. It occurs and expands, and during this process, some of the dried graphene is exfoliated. Accordingly, in the heat treatment step (S150) in the method for manufacturing a conductive material for secondary batteries proposed by the present invention, it may be preferable to place graphene in a device for heat treatment and then perform the heat treatment at a temperature of 300 ° C. for 1 hour.

The expanded graphene finally manufactured through the heat treatment step (S150) has a diameter of 2 μm or less and may be multilayer graphene having at least two or more layers.

For reference, carbon-based materials (e.g., activated carbon) have been proposed as a representative material that is manufactured as a negative electrode active material by combining with silicon. At this time, in order to increase conductivity when mixed with activated carbon, the conductive material needs to be manufactured smaller than the size of the activated carbon. If the conductive material has a diameter exceeding 5 μm, the resistance of the cathode manufactured including it increases.

Accordingly, the present invention manufactures expanded graphene of less than 5 μm by chemically treating graphite less than 5 μm and then heat treatment expansion, but forms it into multi-layer graphene rather than single-layer graphene, which is a technology for producing conventional high-crystalline graphene. Compared to others, the process is simplified and the costs associated with manufacturing expanded graphene can be reduced.

At this time, even if the finally manufactured expanded graphene is formed of multi-layer graphene as illustrated in Figure 3(b), its conductivity is low as it is proposed to have a homogeneously hybridized structure with highly crystalline carbon nanotubes (TMWCNT), which will be described later. Since it can be improved, it is also possible to secure conduction characteristics.

2. Conductive material manufacturing step <S200>

The conductive material manufacturing step (S200) is a step of manufacturing a conductive material in powder form by hybridizing the expanded graphene prepared in the expanded graphene manufacturing step (S100) with carbon nanotubes. For example, the hybrid ratio of expanded graphene and carbon nanotubes may be 1:1, but is not limited to this and may be set in various ways.

At this time, it is preferable that the carbon nanotube is TMWCNT (Thin multi wall carbon nanotube). For reference, TMWCNT refers to a carbon nanotube with more walls than SWCNT (single wall carbon nanotube) and fewer walls than MWCNT (multi wall carbon nanotube). That is, TMWCNT may be a multi-walled carbon nanotube having 3 to 7 walls.

For example, TMWCNT has a diameter of 4 nm to 9 nm, a length of 10 μm to 200 μm, a specific surface area of 400 m ² /g to 700 m ² /g, and a purity of >98.5 wt.%. It may be a subject matter.

Below, the conductive material manufacturing step (S200) will be described in more detail.

Figure 5 is a flow chart showing the conductive material manufacturing step in the manufacturing method of the conductive material for secondary batteries according to an embodiment of the present invention, and Figure 6 is a schematic diagram schematically showing the pulverization and dispersion process of the basket mill used in the milling step, Figure 7 shows (a) expanded graphene (Mag = 50K), (b) TMWCNT (Mag = 1K), and (c) milling and homogenization steps added to the basket mill in the milling step of the conductive material manufacturing step illustrated in Figure 4. This is a scanning electron microscope (SEM) photograph measuring graphene flakes (Mag = 10K), and Figure 8 is a scanning electron microscope (SEM) photograph measuring graphene flakes and TMWCNTs that were primarily hybridized through a basket mill in the milling stage. SEM) photo (Mag = 5K), and Figure 9 is a conductive material (Mag = 10K) in which (a) graphene flakes and TMWCNT are finally hybridized by being put into a high-pressure homogenizer in the homogenization step of the conductive material manufacturing step illustrated in Figure 5. ) and its (b) comparative example (Mag=30K) are scanning electron microscope (SEM) photographs, and Figure 10 is a graph showing the powder conductivity measurement results of the conductive material shown in Figure 9(a).

5 to 10, the conductive material manufacturing step (S200) may include the following steps.

2-1. Hybrid stage (S210)

In the hybrid step (S210), the expanded graphene and carbon nanotubes formed through the heat treatment step (S150) are pulverized to reduce the size, but the graphene flakes and carbon nanotubes formed by layer separation from the expanded graphene exert an attractive force on each other. This is the step of applying physical force so that the expanded graphene and carbon nanotubes are uniformly dispersed and hybridized.

Here, the hybrid step (S210) may include a milling step (S211) and a homogenization step (S212).

In the milling step (S211), the expanded graphene and carbon nanotubes are pulverized through a basket mill to reduce the size, but the layers are separated from the expanded graphene and the formed graphene flakes and carbon nanotubes are dispersed and interact with each other. This is the step of milling using beads so that the carbon nanotubes are bonded to the graphene flakes by attractive force.

The basket mill is a machine that mills and disperses the sample using beads inside the basket, which is excellent for dispersing the sample. Referring to Figure 6, it has a pin-type stirring bar in a basket-shaped chamber that maintains a fine gap (gap 200 μm), so the internal The two samples can be pulverized and dispersed using the energy generated by stirring the beads. As the sample inside the vessel circulates through the rotation of the stirring rod, layer separation of the expanded graphene may occur due to the force of hitting the beads, that is, balls.

In other words, the basket mill pulverizes the expanded graphene to reduce its size, and ensures that the two reduced-sized sample graphene flakes and the released TMWCNTs are properly dispersed. In this process, the graphene flake and the unlocked TMWCNT meet and attract force, and as illustrated in Figure 8, the two samples can be primarily hybridized.

Here, the milling step (S211) may be performed for 1 to 3 hours at a speed of 2500 to 3500 rpm. More specifically, it is preferably performed for 2 hours at a speed of 3000 rpm. At this time, in the method of manufacturing a conductive material according to an embodiment of the present invention, the mass of the ball (or bead) used in the milling step in which graphene flakes and carbon nanotubes are primarily hybridized from the basket mill is 660 g, and its size is 660 g. It was 1 mm.

For reference, when the speed conditions were changed to 2500 rpm, 3000 rpm, 3500 rpm, and 4000 rpm in the milling step (S211) and a test was performed for each condition, the size of expanded graphene and carbon nanotubes was reduced at 3000 rpm. It was confirmed that the two samples were sufficient for primary hybridization.

The homogenization step (S212) is a step of homogenizing the graphene flakes and carbon nanotubes milled in the milling step (S211) using a high pressure homogenizer so that they are uniformly dispersed.

More specifically, in the homogenization step (S212), the two samples that were primarily hybridized in the milling step (S211), i.e., graphene flakes and carbon nanotubes, are subjected to high pressure through a narrow gap (gap 100 nm) of a high-pressure homogenizer. As it exits, additional layer separation of the graphene flake occurs, even dispersion of the graphene flake and TMWCNT is performed, and the graphene flake and carbon nanotube can be secondaryly hybridized. In other words, through the high-pressure homogenizer, layer peeling of the graphene flakes occurs, and at the same time, the carbon nanotubes are released into a loose form and the carbon nanotubes can be effectively dispersed.

At this time, the homogenization step (S212) may be repeated (pass) three or more times under a pressure of 800 bar or more.

For reference, in the homogenization step (S212), when tests were performed for 1 pass, 3 pass, and 5 pass conditions based on pressure conditions of 1000 bar, the graphene flakes and carbon nanotubes were evenly dispersed under the 3 pass condition, and ultimately hybridized. It was confirmed that it was sufficient.

2-2. Conductive material acquisition step (S220)

The step of obtaining a conductive material (S220) is a step of obtaining a conductive material in powder form by drying the graphene flakes and carbon nanotubes hybridized in the hybrid step (S210) at a temperature of 60 ℃ to 100 ℃ for more than 12 hours.

To be more specific, the drying step (S140) is performed using a vacuum oven at a temperature of 60°C to 100°C, more preferably 80°C, for at least 12 hours.

The conductive material in powder form manufactured through the above-described process has a uniform size of graphene flake, as illustrated in Figure 9 (a), and the carbon nanotubes in a loose form are uniformly adsorbed on the surface of the graphene flake. You can confirm that it exists. For reference, it can be seen that Figure 9(a) shows superior dispersibility of carbon nanotubes compared to Figure 9(b), which is a comparative example. At this time, the comparative example is the result of omitting the chemical treatment step (S110), heat treatment step (S150), and milling step (S211) of the manufacturing method of the conductive material for secondary batteries proposed by the present invention.

As described above, in a conductive material having a structure in which graphene flakes and carbon nanotubes are uniformly dispersed, carbon nanotubes act as a bridge between graphene flakes and affect the movement path of electrons, thereby affecting the flow of graphene flakes. Contact resistance can be reduced, and thus the electrical conductivity of the conductive material can be further increased.

This can be confirmed from the powder conductivity measurement results illustrated in Figure 10.

Referring to Figure 10, when measuring powder conductivity, pressure was applied to the sample to measure the conductivity. In the entire range of applied pressure, the conductivity of the final hybridized conductive material sample (chemically treated graphite + TMWCNT) was compared to the graphene flake sample (chemically treated). It was measured to be higher than the conductivity of graphite). From this, it was confirmed that conductivity was improved by carbon nanotubes providing a path between graphite.

At this time, the method for manufacturing a conductive material for secondary batteries proposed by the present invention utilizes the equipment advantages of a basket mill and a high-pressure homogenizer to overcome the difficulty of exfoliation, which is a disadvantage of expanded graphene, and by utilizing such equipment, a low-cost process can be achieved. The process was able to be implemented. In addition, the present invention can have excellent electrical properties by hybridizing multi-layer graphene, graphene flake, and high-crystalline TMWCNT, so it can provide a conductive material with significantly improved electrical properties and price competitiveness.

Meanwhile, the conductive material produced by the conductive material manufacturing method proposed by the present invention can be combined with an electrode active material and a binder and used as a negative electrode material for a secondary battery. In addition, of course, a secondary battery can be manufactured consisting of a cathode containing a conductive material produced by the method of manufacturing a conductive material according to an embodiment of the present invention, as well as a positive electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution.

As described above, the specific description of the present invention has been made by way of examples with reference to the accompanying drawings, but since the above-described embodiments are only explained by referring to preferred examples of the present invention, the present invention is limited to the above-described embodiments. It should not be understood as being possible, and the scope of rights of the present invention should be understood in terms of the claims described later and their equivalent concepts.

Claims (13)

An expanded graphene manufacturing step of forming graphene oxide (GO) from graphite and heat-treating it to produce expanded graphene with a diameter of several μm; and
A conducting material manufacturing step of manufacturing a conductive material in powder form by hybridizing the expanded graphene prepared in the expanded graphene manufacturing step and carbon nanotubes; Characterized by including
Method for manufacturing conductive materials for secondary batteries.
According to paragraph 1,
The carbon nanotube is characterized in that it is a TMWCNT (Thin multi wall carbon nanotube).
Method for manufacturing conductive materials for secondary batteries.
According to paragraph 2,
The expanded graphene manufacturing step is,
A chemical treatment step of chemically treating the graphite by adding it to a mixed solution containing a strong acid and an oxidizing agent so that the graphite is oxidized and forms oxidized graphite;
In the chemical treatment step, the chemically treated graphite oxide suspension is placed in an ultrasonic disperser, and the oxide graphite with an increased interlayer distance is partially exfoliated as layer separation occurs for 2 to 5 hours to form graphene oxide. An ultrasonic treatment step of applying ultrasonic waves;
A filtering-neutralization step of filtering the graphene oxide treated in the ultrasonic treatment step by vacuum filtration and neutralizing it by pouring distilled water until it becomes neutral;
A drying step of drying the graphene obtained through the filtering-neutralization step at a temperature of 60 ℃ to 100 ℃ for more than 12 hours; and
A heat treatment step of heat treating the graphene dried in the drying step for 0.5 to 2 hours to form expanded graphene; Includes,
The expanded graphene has a diameter of 5 μm or less and is characterized in that it is multilayer graphene having at least two layers or more.
Method for manufacturing conductive materials for secondary batteries.
According to paragraph 3,
The oxidizing agent is characterized in that it contains at least one of potassium dichromate, chromic acid, nitric acid, and hydrogen peroxide.
Method for manufacturing conductive materials for secondary batteries.
According to paragraph 3,
In the chemical treatment step, the mixed solution is mixed with sodium chlorate and nitric acid in a ratio of 1:3.5, and the graphite is added to the mixed solution having a capacity of 38 to 40 times that of the graphite.
Method for manufacturing conductive materials for secondary batteries.
According to paragraph 3,
The heat treatment step is characterized in that the graphene is heat-treated at a temperature of 250 ℃ to 300 ℃ in an air atmosphere.
Method for manufacturing conductive materials for secondary batteries.
According to paragraph 3,
The conductive material manufacturing step is,
Grinding the expanded graphene and the carbon nanotubes formed through the heat treatment step to reduce the size, but applying physical force so that the graphene flakes and carbon nanotubes formed by layer separation from the expanded graphene are uniformly dispersed and hybridized. hybrid stage; and
A conductive material obtaining step of drying the graphene flakes and carbon nanotubes hybridized in the hybridization step at a temperature of 60° C. to 100° C. for more than 12 hours to obtain a conductive material in powder form; Characterized by including
Method for manufacturing conductive materials for secondary batteries.
In clause 7,
The hybrid step is,
The expanded graphene and carbon nanotubes are pulverized through a basket mill to reduce the size, but the graphene flakes and carbon nanotubes formed by layer separation from the expanded graphene are dispersed by the attractive force acting on each other. A milling step of milling the carbon nanotubes using a bead so that they are bonded to the graphene flakes; and
A homogenization step of homogenizing the graphene flakes and carbon nanotubes milled in the milling step through a high pressure homogenizer so that they are uniformly dispersed; Characterized by including
Method for manufacturing conductive materials for secondary batteries.
According to clause 8,
The milling step is performed for 1 to 3 hours at a speed of 2500 to 3500 rpm.
Method for manufacturing conductive materials for secondary batteries.
According to clause 8,
The homogenization step is characterized in that it is repeated (pass) three or more times at a pressure of 800 bar or more.
Method for manufacturing conductive materials for secondary batteries.
A conductive material manufactured by the method for manufacturing a conductive material for secondary batteries according to claims 1 to 10.
A cathode containing the conductive material according to claim 11.
A secondary battery comprising the cathode according to claim 12.