KR102661213B1 - Method for preparing a core-shell structured composite coated with graphene on the surface of hydrophobic particles using a kneading method, and a core-shell structured composite prepared therefrom - Google Patents

Abstract

The present invention relates to a method for manufacturing a core-shell composite in which graphene is coated on the surface of hydrophobic particles using a kneading method, and a core-shell composite manufactured therefrom.
The present invention includes the steps of mixing hydrophobic particles and alcohol to prepare an active material paste; Preparing a spray solution by mixing an active material paste and an aqueous solvent-based hydrophilic graphene; The technical gist includes the step of spray-drying the spray solution to produce a core-shell composite in which hydrophilic graphene is coated on the surface of the hydrophobic particles.

Description

Method for manufacturing a core-shell composite coated with graphene on the surface of hydrophobic particles using a kneading method, and a core-shell composite manufactured therefrom KNEADING METHOD, AND A CORE-SHELL STRUCTURED COMPOSITE PREPARED THEREFROM}

The present invention relates to a method for manufacturing a core-shell composite in which graphene is coated on the surface of hydrophobic particles using a kneading method, and a core-shell composite manufactured therefrom.

In secondary batteries, electrode materials are differentiated depending on the field of application, and cell performance is deteriorated due to side reactions such as surface characteristics and size diversity of electrode materials, active materials, conductive materials, and binders. For example, in the case of silicon-based high-capacity anode materials, a change in the crystal structure occurs when lithium ions are absorbed and stored, resulting in a volume change of approximately 400% or more. The continued volume change causes the structure of the silicon to break down, so the initial Because efficiency and cycle characteristics decrease, technology that improves the reversibility of secondary batteries while maintaining high capacity is essential.

To this end, a method of coating active materials with carbon using thermal chemical vapor deposition is mainly used to improve performance such as structural stability, surface stabilization, impregnation with electrolyte, and reduction of resistance in interface reactions. However, in the case of carbon coating, a metal catalyst cannot be introduced to the surface of the active material, so it has the disadvantage of reduced crystallinity and difficulty controlling the thickness of the carbon layer.

Since it is impossible to introduce a high-capacity active material into a secondary battery electrode without coating a carbon layer on the surface, a carbon layer with many defects is mostly used by growing it on the surface of the active material. In addition, most active materials, such as carbon-coated metals and metal oxides, graphite, carbon nanotubes, carbon black, graphene, soft carbon, hard carbon, and sulfur composites, have carbon on their surfaces to improve electrochemical properties. The process of applying a material that has excellent electrical conductivity and does not cause side reactions with the electrolyte is important.

In 'Method for manufacturing graphene-carbon nanotube composite (Publication number: 10-2021-0128176)', graphene obtained by reducing graphene oxide and acid-treated carbon nanotubes are dispersed in a solvent and spray-dried to produce graphene-carbon nanotubes. A method for manufacturing a carbon nanotube composite is disclosed. In addition, in 'Method for manufacturing a crumpled graphene-carbon nanotube composite, a graphene-carbon nanotube composite manufactured thereby, and a supercapacitor containing the same (10-1744122)', acid-treated carbon nanotubes, graphene oxide, and A method of producing a graphene-carbon nanotube composite is disclosed by spray drying and heat treating a colloidal mixed solution mixed with a solvent.

However, the surface of the carbon material used as an active material is hydrophobic and difficult to disperse in aqueous solvents, so it is also difficult to disperse in aqueous solutions such as graphene oxide or reduced graphene oxide. Alternatively, when mixed with reduced graphene oxide, a phase separation phenomenon easily occurs, which ultimately leads to a decrease in electrode efficiency. Therefore, research to solve this problem is urgently needed.

Domestic Open Patent Publication No. 10-2021-0128176, published on October 26, 2021. Domestic Patent Publication No. 10-1744122, registered on May 31, 2017.

The present invention was invented to solve the above problems, a method for manufacturing a core-shell composite coated with graphene on the surface of hydrophobic particles using a kneading method to prevent layer separation, and a core-shell composite manufactured therefrom. The technical solution is to provide .

In order to solve the above technical problem, the present invention includes the steps of mixing hydrophobic particles and alcohol to prepare an active material paste; Preparing a spray solution by mixing the active material paste and hydrophilic graphene based on an aqueous solvent; And spray-drying the spray solution to prepare a core-shell composite in which the hydrophilic graphene is coated on the surface of the hydrophobic particle. Graphene is coated on the surface of the hydrophobic particle using a kneading method. A method for manufacturing a core-shell composite is provided.

In the present invention, the hydrophobic particle is one selected from the group consisting of natural graphite, artificial graphite, carbon nanotubes, carbon black, carbon-coated metal, carbon-coated metal oxide, graphene, soft carbon, and hard carbon. It is characterized by the above.

In the present invention, the hydrophilic graphene is characterized in that it is a graphene solution formed by dispersing graphene oxide or reduced graphene oxide in an aqueous solvent containing water (H ₂ O).

In the present invention, the graphene solution is characterized in that it is a graphene oxide dispersion solution formed by oxidizing graphite and then dispersing and exfoliating graphene oxide through cation-pi interaction.

In the present invention, the graphene solution is formed by oxidizing graphite and then dispersing and exfoliating graphene oxide to form a graphene oxide dispersion solution through cation-pi interaction, and adding a reducing agent to the graphene oxide dispersion solution. It is characterized in that it is a dispersion solution of reduced graphene oxide material reduced by adding .

In the present invention, the spray solution is characterized as a solute-solvent based solution dissolved by mutual attraction due to intermolecular polar forces and hydrogen bonds between the alcohol and the aqueous solvent.

In order to solve the above other technical problems, the present invention includes hydrophobic particles produced by the above method and disposed as a core; and hydrophilic graphene coated on the outside of the hydrophobic particles and disposed as a shell.

In the present invention, the hydrophobic particle is one selected from the group consisting of natural graphite, artificial graphite, carbon nanotubes, carbon black, carbon-coated metal, carbon-coated metal oxide, graphene, soft carbon, and hard carbon. It is characterized by the above.

In the present invention, the hydrophilic graphene is characterized in that it is graphene oxide or a reduced graphene oxide product.

According to the present invention as a means of solving the above problem, the active material dough is manufactured using a kneading method of mixing particles with a hydrophobic surface and alcohol, thereby wetting the surface of the hydrophobic particles with alcohol to produce graphene oxide or graphene oxide. After being dispersed with the reduced product, it is possible to mass-produce a core-shell structured composite powder in which hydrophobic particles are arranged as the core and graphene oxide or graphene oxide reduced product is arranged as the shell through spray drying in a simpler process.

Accordingly, the high-performance composite active material composed of the core-shell composite of the present invention can suppress side reactions that may form at the interface with the electrolyte and increase electrical conductivity, so it is used for secondary batteries that require electrochemical properties of high capacity, long life, and high stability. When applied to electrodes, it has the effect of improving performance.

1 is a flowchart showing a method of manufacturing a core-shell composite according to the present invention.
Figure 2 is a photograph showing a comparison of layer separation depending on whether ethanol was kneaded into graphite in Example 1 and Comparative Example 1.
Figure 3a is an SEM photograph showing the active material-reduced graphene oxide composite powder according to Example 1, and Figure 3b is an SEM photograph showing an enlarged view of Figure 3a.
Figure 4a is an SEM photograph showing a mixed powder of graphite and reduced graphene oxide, and Figure 4b is an SEM photograph showing an enlarged view of Figure 4a.
Figure 5 is an SEM photograph showing pure graphite, a hydrophobic active material.
Figure 6a is a photograph of the water contact angle of the active material-reduced graphene oxide composite powder according to Example 1, Figure 6b is a photograph of the water contact angle of the mixed powder of graphite and reduced graphene oxide, and Figure 6c is a photograph of the water contact angle of pure graphite. .
FIG. 7A is a graph showing thermogravimetric analysis, FIG. 7B is a graph showing the differential curve of the curve obtained by thermogravimetric analysis for FIG. 7A, and FIG. 7C is an enlarged graph showing area A of FIG. 7A.

Hereinafter, the present invention will be described in detail.

The present invention relates to a method of manufacturing a core-shell composite coated with graphene on the surface of hydrophobic particles using a kneading method. The method of manufacturing a core-shell composite is a flowchart of the method of manufacturing a core-shell composite according to the present invention. As shown in Figure 1, a step of preparing an active material paste by mixing particles with a hydrophobic surface and alcohol (S10), a step of preparing a spray solution by mixing the active material paste and hydrophilic graphene (S20), and spraying It includes a step (S30) of spray-drying the solution to produce a core-shell composite in which graphene is coated on the surface of the hydrophobic particles.

According to the above-described manufacturing method, first, an active material paste is prepared by mixing particles with a hydrophobic surface and alcohol (S10).

Before explaining, particles with a hydrophobic surface become the core of the active material, and the surface is hydrophobic, making it difficult to disperse in an aqueous solvent such as water, which has hydrophilic properties. This is because graphene is not easily dispersed in an aqueous dispersed solution. When complexed with hydrophilic graphene, phase separation occurs.

To solve this problem, in this step, the active material is kneaded using a kneading method of mixing an alcohol-based solvent so that particles with a hydrophobic surface can be homogeneously mixed with at least one of graphene oxide and graphene oxide reduced product in a hydrophilic solvent. manufactures.

The surface of the active material dough, which is manufactured through a kneading method by mixing alcohol, has wetting properties, and when it is homogeneously dispersed with graphene oxide or reduced graphene oxide and then spray-dried, graphene oxide is added to hydrophobic particles. It can be manufactured as a powder in the form of a composite core-shell structure coated with graphene from pin or reduced graphene oxide.

The hydrophobic particles may be one or more selected from the group consisting of carbon-coated metal, carbon-coated metal oxide, natural graphite, artificial graphite, carbon nanotubes, carbon black, soft carbon, hard carbon, and graphene, and are used for secondary batteries. It refers to particles with a hydrophobic surface that can be used as an active material.

Among them, graphite has a layered structure in which carbon hexagonal network planes are arranged in parallel, and can be divided into natural graphite and artificial graphite depending on their crystallinity. The hydrophobicity of graphite is due to insufficient wettability of the graphite surface by water. This may result in the creation of unstable by-products. In this case, there is a problem in which undispersed graphite particles aggregate when graphene oxide or reduced graphene oxide is coated, so coating hydrophobic particles is important.

The alcohol used in the kneading method may be any one or more alcohol-based solvents among methanol, ethanol, propanol, isopropyl alcohol, butyl alcohol, and isobutyl alcohol. It is not limited to the above types, and is kneaded with hydrophobic active material particles to form a hydrophobic active material. Any alcohol-based solvent that can provide wettability to the surface of particles can be used in a variety of ways.

Hydrophobic particles and alcohol may be mixed at a weight ratio of 1:1 to 5. If the alcohol is mixed in less than 1 weight ratio compared to 1 weight ratio of the hydrophobic particles, it does not provide sufficient wettability to the surface of the hydrophobic particles, making it difficult to uniformly coat the hydrophilic graphene, which ultimately makes it impossible to manufacture a stable core-shell composite. There is. On the other hand, if the alcohol is mixed in a weight ratio exceeding 5, it is difficult to maintain the shape of the hydrophobic particles, so there is a problem in that they are not easily formed into a core-shell complex.

Kneading the hydrophobic particles and alcohol can be carried out for 5 to 20 minutes. If you knead for less than 5 minutes, it is not enough time to disperse the hydrophobic particles and provide wettability to the surface. If you knead for more than 20 minutes, you will not see any better kneading efficiency compared to kneading for less than 20 minutes, so it is not necessary to knead for more than 20 minutes. So there is no need to knead it.

Next, a spray solution is prepared by mixing the active material paste and hydrophilic graphene (S20).

Hydrophilic graphene is a graphene solution formed by dispersing graphene oxide or reduced graphene oxide in an aqueous solvent containing water (H ₂ O), and is composed of water-dispersed graphene oxide or reduced graphene oxide. By being uniformly applied to the surface of particles having a hydrophobic surface, the performance of the active material can be improved.

In other words, the graphene solution is a graphene oxide dispersion solution formed by oxidizing graphite and then dispersing and exfoliating graphene oxide through cation-pi interaction, or an oxidation solution obtained by reducing the graphene oxide dispersion solution by adding a reducing agent. It may be made of a graphene reduced water dispersion solution. When a graphene oxide dispersion solution is used as a graphene solution, the graphene oxide is reduced through a process such as heat treatment to form a core-shell complex before spray-drying the spray solution or by spray-drying it, ultimately leading to active material oxidation. It is possible to manufacture a core-shell composite of reduced graphene material.

In a solution in which at least one of graphene oxide and reduced graphene oxide is dispersed in aqueous water, in the case of a polar-polar solution such as alcohol kneaded with the water in which the graphene was dispersed and hydrophobic particles, the solubility parameter , δ), the dispersibility of hydrophobic active materials and water-dispersed graphene can be improved by introducing a solute-solvent solubility method using mutual attraction between molecules due to polar force and hydrogen bonding.

Solubility parameters are not particularly limited and may follow known methods. For example, it can be calculated or obtained by the intermolecular dispersion force, intermolecular polarity force, and intermolecular hydrogen bond component according to HSP (Hansen solubility parameter). In other words, the solubility parameter can predict the behavior of the spray solution and the suitability of water and alcohol from the relationship between the alcohol kneaded with the hydrophobic particles and the water in which the graphene was dispersed. Assuming that solubility is closely related to the cohesion of the solvent, The solubility parameter is expressed only by the cohesive energy density.

Finally, the spray solution is spray-dried to prepare a core-shell composite in which graphene is coated on the surface of the hydrophobic particles (S30).

By spray drying a spray solution containing particles with a hydrophobic surface and graphene oxide or reduced graphene oxide, the particles with a hydrophobic surface are arranged as a core during spray drying, and among the graphene oxide and reduced graphene oxide It is possible to form a powder in the form of a core-shell composite in which one or more graphene is arranged as a shell.

In the synthesized core-shell composite powder, the average contact angle range of the reduced graphene oxide material with respect to the surface of the hydrophobic particle may be 10 to 20°, and there is no need to control the contact angle to be less than 10°, and the contact angle may be greater than 20°. This means that the wettability of the hydrophobic particles is not good, so there is a problem in that a coating film of reduced graphene oxide material is not formed uniformly on the surface of the hydrophobic particles.

The core-shell composite in powder form synthesized in this way is a high-performance composite active material formed by applying one or more graphene oxide or reduced graphene oxide to particles with a hydrophobic surface. It imparts electrical conductivity to the high-performance composite active material and , surface stabilization can be achieved while improving impregnation characteristics with electrolyte solution. Accordingly, it is possible to increase the electrochemical characteristics of secondary battery electrodes by suppressing side reactions formed at the interface between the high-performance composite active material and the electrolyte and improving conductivity.

Hereinafter, embodiments of the present invention will be described in more detail as follows. However, the following examples are merely illustrative to aid understanding of the present invention and are not intended to limit the scope of the present invention.

<Example 1>

1-1. Preparation of graphite paste

10 g of ethanol was added to 5 g of pure graphite (99.98% purity, manufactured by POSCO), a hydrophobic active material, and mixed well with a spatula. At this time, it was kneaded for 10 minutes to allow ethanol to sufficiently permeate into the graphite, which has hydrophobic surface properties.

1-2. Preparation of graphene oxide dispersion solution

10 g of pure graphite (purity 99.9995%, -200 mesh, manufactured by Alfar Aesar), 350 ml of fuming nitric acid, and 74 g of sodium chloride oxide (NaClO ₄ ) were sequentially mixed at room temperature in 37 g portions. After stirring the mixture for 48 hours, graphene oxide was prepared through neutralization, washing, filtration, cleaning, and drying. The graphene oxide produced through the above process was treated with a homogenizer at 15,000 rpm for 1 hour in distilled water (pH 10) containing KOH dissolved at a concentration of 300 mg/l to create a uniform graphene oxide dispersion solution. Then, in order to apply cation-pi interaction, the reaction time of the graphene oxide dispersion solution was maintained at room temperature for more than 1 hour, and then freeze-dried for more than 10 hours to prepare graphene oxide in powder form. A graphene oxide dispersion solution with a concentration of 300 mg/L was prepared using distilled water as a solvent for dispersing graphene oxide in powder form.

1-3. Production of active material-reduced graphene oxide composite powder

The graphite dough prepared in Example 1-1 was added to 50 ml (0.5 wt%) of the graphene oxide dispersion solution prepared in Example 1-2 and treated with a mechanical stirrer at 1,000 rpm for 20 minutes to form a graphite-graphene oxide composite. After preparing the spray solution, the mixed solution was spray dried to prepare an active material-graphene oxide composite anode material powder. The powder was heated at 17°C/min and heat treated at 1,000°C for 1 hour to prepare active material-reduced graphene oxide powder.

<Example 2>

2-1. Preparation of graphite paste

10 g of ethanol was added to 5 g of pure graphite (99.98% purity, manufactured by POSCO), a hydrophobic active material, and mixed well with a spatula. At this time, it was kneaded for 10 minutes to allow ethanol to sufficiently permeate into the graphite, which has hydrophobic surface characteristics.

2-2. Preparation of reduced graphene oxide dispersion solution

10 g of pure graphite (purity 99.9995%, -200 mesh, manufactured by Alfar Aesar), 350 ml of fuming nitric acid, and 74 g of sodium chloride oxide (NaClO ₄ ) were mixed sequentially in 37 g portions at room temperature. After stirring the mixture for 48 hours, graphene oxide was prepared through neutralization, washing, filtration, cleaning, and drying. The graphene oxide produced through the above process was treated with a homogenizer at 15,000 rpm for 1 hour in distilled water (pH 10) containing KOH dissolved at a concentration of 300 mg/l to create a uniform graphene oxide dispersion solution. Then, in order to apply cation-pi interaction, the reaction time of the graphene oxide dispersion solution was maintained at room temperature for more than 1 hour, and then freeze-dried for more than 10 hours to prepare graphene oxide in powder form. Distilled water was used as a solvent to disperse graphene oxide in powder form, and 170 ㎕ of HI acid was added to the graphene oxide dispersion solution with a concentration of 300 mg/l and stirred at 400 rpm for 16 hours to reduce the graphene oxide dispersed in high concentration. A dispersion solution of pin-reduced water was prepared. At this time, the size of the reduced graphene oxide was 5 to 10㎛.

2-3. Production of active material-reduced graphene oxide composite powder

The graphite dough prepared in Example 2-1 was added to 50 ml (0.5 wt%) of the reduced graphene oxide dispersion solution prepared in Example 2-2 and treated with a mechanical stirrer at 1,000 rpm for 20 minutes to produce graphite-graphite oxide. A pin-reduced product composite spray solution was prepared. The mixed solution was spray dried to prepare active material-reduced graphene oxide composite powder.

<Comparative Example 1>

In Comparative Example 1, graphite dough was not prepared by adding ethanol to graphite and kneading it as in Examples 1 and 2. That is, 5 g of pure graphite (purity 99.98%, manufactured by POSCO), a hydrophobic active material, was added to 50 ml (0.5 wt%) of the graphene oxide dispersion solution, treated with a mechanical stirrer at 1,000 rpm for 20 minutes, and the graphite-graphene oxide reduced product complex was sprayed. A solution was made. The mixed solution was spray dried to prepare an active material-reduced graphene oxide composite powder.

<Test Example 1>

In this test example, the active material-graphene oxide reduced material composite powder prepared in Example 1, graphite powder, and the graphene oxide reduced material dispersion solution prepared in Example 2 were mixed with spray-dried graphene oxide reduced material powder. The shapes of powder and pure graphite were analyzed.

In relation to this, FIG. 2 is a photograph showing a comparison of layer separation depending on whether graphite was kneaded with ethanol in Example 1 and Comparative Example 1. As shown in Figure 2, in Example 1, it was confirmed that wettability was provided to the graphite surface through a kneading method of mixing ethanol with graphite, so that layer separation was not created and uniform mixing was achieved, whereas in Comparative Example 1, pure graphite was used. It was confirmed that layer separation occurred because wettability was not provided to the graphite surface as it was not kneaded using ethanol. It can be seen that when layer separation occurs as in Comparative Example 1, pure graphite and reduced graphene oxide are not homogeneously mixed.

Figure 3a is an SEM photograph of the active material-reduced graphene oxide composite powder according to Example 1 measured at 10.0 kV and enlarged at 5,000 times, and Figure 3b shows Figure 3a enlarged, measured at 10.0 kV. This is enlarged at 10,000 magnification and shown as an SEM photo. Referring to FIGS. 3A and 3B, it can be seen that the reduced graphene oxide material is stably coated on the surface of the particle-shaped graphite.

For comparison with FIG. 3, the form of the mixed powder was confirmed by mixing graphite powder and graphene oxide reduced material powder spray-dried with the graphene oxide reduced material dispersion solution prepared in Example 2 (graphite powder and graphene oxide The weight of the reduced product powder was equal to that in Example 1.) In relation to this, Figure 4a is an SEM photograph showing a mixed powder of graphite and reduced graphene oxide measured at 10.0kV and magnified at 5,000 times, and Figure 4b is an enlarged view of Figure 4a, measured at 10.0kV and magnified at 10,000 times. This is shown in SEM photos. Referring to Figures 4a and 4b, it is confirmed that the reduced graphene oxide material that was not coated on the surface of the graphite powder exists in a state separated from the graphite powder, and in Figure 4b, reduced graphene oxide is present on the surface of the graphite powder (G). It was confirmed that water (rGO) was not coated with a uniform film and stuck to the surface of the graphite powder (G) in a lumped state. In addition, Figure 5 shows an SEM photograph of pure graphite, a hydrophobic active material, measured at 10.0 kV and magnified at 10,000 magnification. Referring to Figure 5, the form of pure graphite without external coating is confirmed. In this way, unlike in FIGS. 4 and 5, referring to FIG. 3 showing the active material-reduced graphene oxide material composite powder of Example 1, wettability is provided on the surface of the hydrophobic particles, resulting in a composite in which the coating of the reduced graphene oxide material is stable. formation can be confirmed.

<Test Example 2>

In this test example, the active material-graphene oxide reduced material composite powder prepared in Example 1, graphite powder, and the graphene oxide reduced material dispersion solution prepared in Example 2 were mixed with spray-dried graphene oxide reduced material powder. The water contact angle of powder and pure graphite was compared and analyzed.

In relation to this, the normal contact angle is the angle between the liquid-gas interface and the liquid-solid interface measured from the inside of the liquid, and can be used to check whether the surface coating is good. The average contact angle of a liquid on a solid surface can be predicted to the degree of surface coating. There will be.

The contact angle was measured using a contact angle meter (Phoenix 300, Surface & Electro-Optics Co.). For this purpose, a powder sample was placed on a glass substrate with a groove of 2 × 2 cm in width and 2 mm in depth, and adjusted to the height of the glass substrate. After filling it flat, it was placed in a contact angle meter and measured after adding a drop of water through a syringe.

Figure 6a shows a photograph of the water contact angle of the active material-reduced graphene oxide composite powder according to Example 1, Figure 6b shows a photograph of the water contact angle of the mixed powder of graphite and reduced graphene oxide, and Figure 6c shows a photograph of the water contact angle of pure graphite. This is a picture of the water contact angle.

In order for reduced graphene oxide to be uniformly coated on the hydrophobic particle surface, it is important to lower the average contact angle of the spray solution with respect to the hydrophobic particle surface. Referring to FIG. 6a, there is a difference between the surface of the hydrophobic active material particle and the spray solution in contact with this surface. It was confirmed that the formed contact angle was lowered. The alcohol kneaded with the hydrophobic active material particles is polar, and the aqueous solvent that makes up the hydrophilic graphene is also polar, and the solubility of alcohol and water increases due to mutual attraction due to polarity and hydrogen bonding between polar molecules and forms on the surface of hydrophobic particles. By lowering the average contact angle of the spray solution, a thin and uniform hydrophilic graphene coating film is formed on the surface of the hydrophobic active material particles.

Unlike Figures 6b (contact angle: 102.28°) and Figure 6c (contact angle: 120.64°), the contact angle of the active material-reduced graphene oxide composite powder of Example 1 with respect to the surface of the glass substrate as shown in Figure 6a is 13.83°. , it can be confirmed that the average contact angle range is 10 to 20°, and in this range, the contact area between the active material and the electrolyte can be maximized as the reduced graphene oxide material is uniformly coated on the hydrophobic particles.

<Test Example 3>

In this test example, the active material-graphene oxide reduced material composite powder (G@rGO) prepared in Example 1, graphite powder, and graphene oxide reduced material dispersion solution prepared in Example 2 were spray dried. Thermogravimetric analysis (TGA) was performed on mixed powder (G/rGO), which was simply mixed powder, and pure graphite (G). However, in the case of G/rGO, the weight of the active material and reduced graphene oxide in Example 1 was set to be the same in order to obtain accurate thermogravimetric analysis results.

In relation to this, thermogravimetric analysis was measured using a thermogravimetric analyzer (TA Instruments, TGA Q50). For this purpose, each sample was prepared in a dried powder state, about 10 mg was placed in a ceramic pan, and the sample was heated from room temperature to 100°C. After removing the moisture inside, it was cooled to 40°C and the weight change was measured at 10°C/min from 40°C to 900°C.

The results of thermogravimetric analysis are shown graphically in FIG. 7A, FIG. 7B is a graphical representation of the differential curve of the curve obtained by thermogravimetric analysis for FIG. 7A, and FIG. 7C is an enlarged view of area A of FIG. 7A. .

FIG. 7B is a graph obtained by differentiating FIG. 7A and showing the derivative thermogravimetric curve of the thermogravimetric curve obtained by the thermogravimetric analysis of FIG. 7A. This differential curve is converted from data measured by thermogravimetric analysis. It can be obtained by doing so, where the According to FIG. 7b, the peak occurs at the temperature at which weight loss begins to occur, and the maximum value is shown at the point where the weight loss rate according to temperature is maximum, so it is possible to easily determine the change in weight loss rate according to temperature.

Referring to FIG. 7C, which is an enlarged portion of part A of FIG. 7A, it can be seen whether there is a step in the curve depending on the presence or absence of reduced graphene oxide. In the case of pure graphite (G), the weight decreases without a step in the curve around 700°C. occurs, and in the case of the active material-reduced graphene oxide material composite powder (G@rGO) according to Example 1 of the present invention, the reduced graphene oxide material is coated on the surface of the active material, which is relatively lower than the graphite (G) itself. Thermal decomposition occurs at temperature.

In the case of Example 1 (G@rGO), the reduced graphene oxide material was well bonded to the surface of the active material, so there was no step in the decomposition temperature graph line, showing thermal stability. However, the graphite powder and the reduced graphene oxide powder were simply mixed together. In the case of mixed mixed powder (G/rGO), the graphene oxide reduced product, the oxide functional group contained in the graphene oxide reduced product, and the graphite are not thermally decomposed at the same time but are thermally decomposed separately over time, Example 1 Unlike in , it can be seen that more steps appear, such as part a of Figure 7c.

From these thermogravimetric analysis results, the graphite powder and the graphene oxide reduced product powder were simply mixed, resulting in different thermal decomposition temperatures for the oxide functional groups of the graphite, graphene oxide reduced product, and graphene oxide reduced product. It can be seen that the powder (G/rGO) is not coated with reduced graphene oxide material on the surface of graphite, and in Example 1, reduced graphene oxide material binds to the surface of the active material compared to the simple mixed powder of graphite and reduced graphene oxide material. It can be seen that this is done well, forming a single complex and thermally decomposing.

In summary, the present invention is a core coated with hydrophilic graphene on the surface of the hydrophobic particles by spray-drying a spray solution that mixes active material kneading through a kneading method of mixing hydrophobic particles with alcohol and hydrophilic graphene based on an aqueous solvent. There is a feature that allows a shell complex to be obtained.

That is, a spray solution in which graphene oxide or reduced graphene oxide dispersion solution and homogeneous dispersion are obtained through a kneading method using alcohol on the surface of the hydrophobic active material particles, and then spray-dried to form a core-shell mixture of the hydrophobic active material and hydrophilic graphene. It is meaningful that the problems of essential carbon coating can be solved by applying the structured high-performance composite active material to the electrode.

Therefore, the high-performance composite active material composed of the core-shell composite of the present invention can suppress side reactions that may form at the interface with the electrolyte and increase electrical conductivity through this, and thus requires electrochemical characteristics of high capacity, long life, and high stability. It is expected that it can be applied to electrodes for secondary batteries to improve performance.

The above description is merely an illustrative explanation of the technical idea of the present invention, and those skilled in the art will be able to make various modifications and variations without departing from the essential characteristics of the present invention. Accordingly, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention, but are for explanation, and the scope of the technical idea of the present invention is not limited by these examples. The scope of protection of the present invention should be interpreted in accordance with the scope of the patent claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of rights of the present invention.

Claims (9)

Preparing an active material paste by mixing hydrophobic particles and alcohol;
Preparing a spray solution by mixing the active material paste and a hydrophilic graphene solution; and
Spray-drying the spray solution to prepare a core-shell composite in which the hydrophilic graphene is coated on the surface of the hydrophobic particles,
The hydrophilic graphene solution is a graphene solution formed by dispersing graphene oxide or reduced graphene oxide in an aqueous solvent containing water (H ₂ O),
The spray solution is a solute-solvent based solution dissolved by the intermolecular polar force of the alcohol and the aqueous solvent and the mutual attraction due to hydrogen bonding,
The core-shell composite is characterized in that the average contact angle of the hydrophilic graphene coated on the surface of the hydrophobic particle is 10 to 20°.
Method for manufacturing a core-shell composite in which hydrophilic graphene is coated on the surface of hydrophobic particles using a kneading method. According to paragraph 1,
The hydrophobic particles are,
Characterized by at least one selected from the group consisting of natural graphite, artificial graphite, carbon nanotubes, carbon black, carbon-coated metal, carbon-coated metal oxide, graphene, soft carbon, and hard carbon, using a kneading method. Method for manufacturing core-shell composite. delete According to paragraph 1,
The graphene solution is,
A method of manufacturing a core-shell composite using a kneading method, characterized in that the graphene oxide dispersion solution is formed by oxidizing graphite and then dispersing and exfoliating graphene oxide through cation-pi interaction. According to paragraph 1,
The graphene solution is,
Graphene oxide, which is formed by oxidizing graphite, then dispersing and exfoliating, forms a graphene oxide dispersion solution through cation-pi interaction, and a reducing agent is added to the graphene oxide dispersion solution to reduce the graphene oxide dispersion. A method of manufacturing a core-shell composite using a kneading method, characterized in that it is a solution. delete Manufactured by the method of any one of paragraphs 1, 2, 4, and 5,
Hydrophobic particles disposed as a core; and
A core-shell composite using a kneading method, characterized in that it is formed including; hydrophilic graphene coated on the outside of the hydrophobic particles and disposed as a shell. delete delete