KR102163165B1 - Method for preparing graphene-activated carbon composite and graphene-activated carbon composite prepared by the same - Google Patents

Abstract

Preparing graphene oxide; Dispersing activated carbon and graphene oxide in a solvent to prepare a spray solution; Spraying the spray solution into droplets; And applying heat to the droplets to prepare a graphene-activated carbon composite including activated carbon coated with a graphene layer. A method of preparing a graphene-activated carbon composite is provided.

Description

Method for producing a graphene-activated carbon composite, and graphene-activated carbon composite produced thereby TECHNICAL FIELD [METHOD FOR PREPARING GRAPHENE-ACTIVATED CARBON COMPOSITE AND GRAPHENE-ACTIVATED CARBON COMPOSITE PREPARED BY THE SAME}

The present invention relates to a new method for producing a graphene-activated carbon composite and a graphene-activated carbon composite produced thereby. More specifically, it relates to a method for producing a graphene-activated carbon composite with reduced surface resistance and a graphene-activated carbon composite produced thereby.

Recently, due to the depletion of fossil fuels, interest in renewable energies such as wind power, tidal power and solar power that is sustainable and free of environmental pollution is increasing. Since the generation time and the amount of electric power generated by such new and renewable energy are not constant and generate a large amount instantaneously, research on energy storage devices for efficiently storing such energy is being focused. Among them, supercapacitors and secondary batteries are emerging as alternatives to solve this problem.

Supercapacitors (electric double layer capacitors, EDLC) can store and take out large-capacity energy quickly, have higher output density than secondary batteries, can be used semi-permanently, and have stable characteristics because they do not use chemical reactions. It can be applied as a device such as a mobile phone, a hybrid vehicle, a large-capacity power assistant and storage device, and is attracting great attention as a storage device such as solar power, wind power, and hydrogen fuel cells, which are eco-friendly and renewable energy. In general, such a supercapacitor has an electrolyte solution, an electrode, and a separator made of a porous material that is positioned between the two electrodes to insulate and prevent short circuits while only conducting ions, and other components such as a gasket and a metal cap. In order to manufacture a supercapacitor electrode, a porous carbon material (activated carbon (AC), carbon fiber (CF), carbon nanofiber (CNF), carbon nanotube (CNT), graphene, etc.)) capable of storing electric charges is mainly used as an active material. An electrode is manufactured by mixing such an active material, a binder, and a conductive material. Most of the active materials currently applied to mass-produced supercapacitors use activated carbon having a low price and a high specific surface area. However, since activated carbon is manufactured based on amorphous carbon, the electrical conductivity value is low, so a material such as a conductive material must be used when manufacturing an electrode. When the amount of the conductive material is increased, the amount of the electrode active material is relatively small, resulting in a decrease in capacity and long-term reliability. There is a falling problem.

Lithium secondary batteries are being studied a lot for application as a power source for electric vehicles. Currently, graphite is used as an anode active material for lithium secondary batteries for automobiles, and it has a high discharge voltage of 3.6V, so the energy density of lithium secondary batteries is high, and its excellent reversibility guarantees high lifespan characteristics of the secondary battery, making it the most widely used. . However, graphite has a problem in that energy input/output characteristics are inferior, and in particular, low-temperature output characteristics are insufficient. In addition, when charging and discharging, a change in the volume of graphite occurs by about 10%, which adversely affects the bonding force between the current collector and the mixture layer, thereby deteriorating the lifespan of the battery. In order to solve this problem, some non-graphitizable carbon with micropores has been proposed and used. Non-graphitizable carbon has a structure in which lithium ions are stored and released in a number of pores. There is little volume expansion during charging and discharging of lithium ions, so the lifespan of the battery is very excellent, and lithium ions are absorbed through micropores in all directions of the particles. It is known to be excellent in output characteristics as it can be stored and released. However, there is a disadvantage in that the initial efficiency is low and the amount of lithium that is irreversibly consumed is large. This irreversibility is caused by the decomposition reaction of the electrolyte on the surface of the electrode during charging, and the formation of SEI (Solid electrolyte interphase), which is a surface film, and lithium stored in the carbon particles during charging is released during discharge. It may be due to the failure to do so. Of these, the former is more problematic, and the formation of a surface film is known as a major irreversible cause.

Accordingly, there is a need to develop a material for a composite electrode active material that can exhibit excellent electrical conductivity and electrode capacity when used in an electrode without changing the properties of the basic active material as a material of the composite electrode active material.

Republic of Korea Patent Publication 10-1591264

In embodiments of the present invention, it is intended to provide a method of preparing a graphene-activated carbon composite.

In other embodiments of the present invention, it is intended to provide a graphene-activated carbon composite prepared through the method of preparing the graphene-activated carbon composite.

In still other embodiments of the present invention, a supercapacitor and a lithium ion battery including the graphene-activated carbon composite are provided.

In exemplary embodiments of the present invention, as a graphene-activated carbon composite, a graphene-activated carbon composite including an activated carbon as a core and a graphene layer as a shell, a supercapacitor including the same, an electrical device such as a lithium ion battery Provides.

In other exemplary embodiments of the present invention, the steps of preparing graphene oxide; Dispersing activated carbon and the graphene oxide in a solvent to prepare a spray solution; Spraying the spray solution into droplets; And it provides a method for producing a graphene-activated carbon composite comprising; and applying heat to the droplets to prepare a graphene-activated carbon composite including activated carbon coated with a graphene layer.

The graphene-activated carbon composite according to exemplary embodiments of the present invention is manufactured by a droplet spraying process, and may exhibit an equivalent to high specific surface area value compared to a general activated carbon while exhibiting excellent electrical performance. Accordingly, it can be widely used as an active material for various electrodes.

In addition, the graphene-activated carbon composite is manufactured through a droplet spraying process, which is a mass-produced process. Accordingly, it is possible to easily prepare a graphene-activated carbon composite.

1 is a flow chart showing a method of manufacturing a graphene-activated carbon composite according to an embodiment of the present invention.
2A and 2B are differential scanning microscopy (SEM) photographs of graphene-activated carbon composites (FIG. 2A) and activated carbon (FIG. 2B) according to an embodiment of the present invention, respectively.
3 is a graph of the powder resistance of the graphene-activated carbon composite according to an embodiment of the present invention, and it can be seen that the resistance reduction characteristics are shown.
4A and 4B are graphs showing electrical properties of graphene-activated carbon composites and activated carbon according to an embodiment of the present invention, and FIG. 4A is a graph showing the characteristics of current capacity according to current density, and FIG. 4B is It is a graph showing the change in retention capacity.
5 is a graph showing the charging and discharging results of a lithium secondary battery prepared to include a graphene-activated carbon composite and activated carbon, respectively, according to an embodiment of the present invention.
6A and 6B are graphs showing 100 cycle characteristics and (6a), capacity preservation rate and Coulomb efficiency (6b) of a lithium secondary battery each prepared to include a graphene-activated carbon composite and activated carbon according to an embodiment of the present invention.
7 is a graph showing a discharge capacity according to a current density of a lithium secondary battery prepared to include a graphene-activated carbon composite according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The embodiments of the present invention disclosed in the text are exemplified for purposes of explanation only, and the embodiments of the present invention may be implemented in various forms and should not be construed as being limited to the embodiments described in the text. .

The present invention is not intended to limit the present invention to a specific disclosed form, as various changes can be added and various forms may be added, and all changes, equivalents or substitutes included in the spirit and scope of the present invention It should be understood to include.

Hereinafter, the present invention will be described in more detail through examples. These examples are for illustrative purposes only, and it will be apparent to those of ordinary skill in the art that the scope of the present invention is not construed as being limited by these examples.

Graphene -Method for producing activated carbon composite

In exemplary embodiments of the present invention, a method of preparing a graphene-activated carbon composite is provided. According to the above manufacturing method, a graphene-activated carbon composite having a reduced electrical resistance value can be prepared in a simpler and simpler method.

1 is a flow chart showing a method of manufacturing the graphene-activated carbon composite. Hereinafter, each step will be described in detail with reference to FIG. 1.

First, to prepare graphene oxide (S10).

In an exemplary embodiment, the graphene oxide may be prepared through a Coater-Taylor flow reactor.

In one embodiment, the graphene oxide may be prepared through a Hummers method or a modified Hummers method.

Thereafter, activated carbon and the graphene oxide are dispersed in a solvent to prepare a spray solution (S20).

In an exemplary embodiment, biomass-based activated carbon and phenol-based activated carbon may be used as the activated carbon.

In an exemplary embodiment, the activated carbon may have a size (average diameter) in the range of 10 to 100 μm. When the size of the activated carbon is less than 10 μm, it is difficult to expect a high specific surface area value due to coating of too many graphene oxide layers, and when it exceeds 100 μm, it is difficult to prepare a dispersion, and application of the spray drying method may be limited.

In one embodiment, the solvent may include at least one selected from the group consisting of water or organic solvents (such as ethanol and acetone).

Meanwhile, in the solvent, the graphene oxide and activated carbon may be mixed in a weight ratio of 1:1 to 1:10. When the mixing ratio of graphene oxide and activated carbon is less than 1:1, the ratio of graphene and activated carbon is not complexed, and the ratio that exists alone is high, and the number of graphene coating layers is too large to decrease the specific surface area characteristics, and graphene oxide and activated carbon When the mixing ratio of is more than 1:10, graphene may not sufficiently cover the surface of the activated carbon, and thus the effect of improving electrical conductivity may be insufficient.

Meanwhile, in order to improve the dispersibility of the graphene oxide, a dispersant or the like may be additionally used.

Then, the spray solution is sprayed into droplets (S30).

In an exemplary embodiment, the droplet spraying process may be performed under temperature conditions in the range of 100 to 300 °C. When the temperature of the droplet spraying process is less than 100°C, the solvent does not evaporate sufficiently, so that the spray drying effect may be insufficient, and when it exceeds 300°C, it may be difficult to manufacture a graphene/activated carbon composite due to too rapid evaporation of the solvent. .

In an exemplary embodiment, the droplet spraying process may be performed at a spray pressure of 49 to 245 kPa, and a supply rate of the dispersion may be supplied at 150 to 1700 ml/hr. When the spray pressure of the droplet spraying process is less than 49 kPa, dried powder may not be formed, and when it exceeds 245 kPa, it may be difficult to form a graphene layer on the surface of the activated carbon.

In an exemplary embodiment, when the supply rate of the dispersion is less than 150 ml/hr, it may be difficult to form a spherical complex, and when it exceeds 1700 ml/hr, it may be difficult to obtain a dried powder form.

Thereafter, heat is applied to the droplet to prepare a graphene-activated carbon composite including activated carbon coated with a graphene layer (S40).

Specifically, a graphene-activated carbon composite including activated carbon coated with a graphene layer is prepared by applying heat to the droplet in a nitrogen atmosphere.

In an exemplary embodiment, the heating process may be performed within the range of 800 to 2000° C. by heating at a heating rate of 5 to 20° C. per minute. When the temperature of the heating condition is less than 800°C, the reduction of graphene may not be sufficient, and when it exceeds 2000°C, the structure of the activated carbon may collapse.

In an exemplary embodiment, the heating process may be performed for 50 minutes to 640 minutes. If the execution time of the heating process is less than 50 minutes, reduction of graphene may not be sufficient, and if it exceeds 640 minutes, the structure of the activated carbon may collapse.

Meanwhile, the heating process may be performed in a nitrogen atmosphere, and accordingly, the graphene oxide layer surrounding the activated carbon core may be reduced.

Alternatively, the graphene oxide layer may be reduced by using a reducing agent such as hydrazine during the heating process.

Accordingly, a graphene-activated carbon composite including an activated carbon as a core and a graphene layer as a shell may be prepared.

Graphene -Activated carbon complex

In another embodiment of the present invention, a graphene-activated carbon composite including activated carbon as a core and a graphene layer as a shell is provided as a graphene-activated carbon composite. That is, the graphene-activated carbon composite of the present invention may have a structure in which a graphene layer surrounds the activated carbon, and graphene connects adjacent activated carbon molecules. Accordingly, the graphene-activated carbon composite may exhibit excellent specific surface area characteristics of the activated carbon while exhibiting improved electrical characteristics compared to the activated carbon.

In an exemplary embodiment, in the graphene-activated carbon composite, the weight ratio of the activated carbon and the graphene layer may be 2:1 to 5:1. If the mixing ratio of reduced graphene and activated carbon is less than 2:1, the effect of improving the electrical conductivity of the graphene-activated carbon composite may be insufficient, and when the mixing ratio of the reduced graphene and activated carbon exceeds 5:1, the specific surface area It may be difficult to use as an electrode active material by causing a decrease in the.

In an exemplary embodiment, the activated carbon may be biomass-based activated carbon or phenol-based activated carbon, and may have a size ranging from 10 to 100 μm. When the size of the activated carbon is less than 10 μm, it is difficult to expect a coating effect of graphene oxide, and when the size of the activated carbon exceeds 100 μm, it is difficult to prepare a dispersion, which may limit application of the spray drying process.

In an exemplary embodiment, the graphene layer may be coated to have a thickness in the range of 1 nm to 200 nm. When the graphene layer is coated with a thickness of less than 1 nm, the effect of improving electrical conductivity may be insufficient, and when it exceeds 20 nm, the properties of activated carbon may be deteriorated. However, the present invention is not limited to the embodiments.

Meanwhile, the specific surface area of the graphene-activated carbon composite is within the range of 1000 to 2500 (m ² /g), the graphene-activated carbon composite includes a plurality of pores, and the average diameter of the pores is within the range of 1.00 to 2.00 nm. There may be. As such, the graphene-activated carbon composite may exhibit an equivalent or increased specific surface area value compared to the existing activated carbon, and thus exhibit excellent properties when used as an active material for various electrodes. However, the present invention is not limited to the embodiments.

In addition, the graphene-activated carbon composite may exhibit electrical conductivity in the range of 1.55 to 10 S/cm, which is a remarkably improved value compared to the existing activated carbon (0.67 S/cm, 1.29 MPa). However, the present invention is not limited to the embodiments.

As such, it exhibits excellent electrical conductivity, and can be widely used in electronic devices such as supercapacitors and lithium ion batteries.

[Example]

The embodiments of the present invention described above should not be construed as limiting the technical idea of the present invention. The protection scope of the present invention is limited only by the matters described in the claims, and those of ordinary skill in the technical field of the present invention can improve and change the technical idea of the present invention in various forms. Therefore, such improvements and changes will fall within the scope of the present invention as long as it is apparent to those of ordinary skill in the art.

Example One: Graphene -Production of activated carbon composite ( Graphene Oxide : Mixing ratio of activated carbon 1:1)

Graphene oxide was prepared using a Couette-Taylor flow reactor and dispersed in water together with activated carbon (YP17D) to prepare a spray solution. At this time, the mixing ratio of graphene oxide and activated carbon was spray-dried at a ratio of 1:1 to 1:10. On the other hand, in order to disperse the spray solution, magnetic stirring and ultrasonic treatment were performed.

Thereafter, a droplet spray drying process was performed under hot air conditions between 100 and 300° C. to prepare droplets including activated carbon coated with graphene oxide.

Thereafter, the graphene-activator composite including an activated carbon core coated with graphene as a shell was prepared by heating to 800 to 2000°C at a heating rate of 5°C per minute in a nitrogen atmosphere.

Comparative example One

As a comparative example, general activated carbon (YP17D) was used.

Experimental example One: Graphene -Structure and characterization of activated carbon composites

2A and 2B are differential scanning microscopy (SEM) photographs of a graphene-activated carbon composite (FIG. 2A) and activated carbon (FIG. 2B) according to an embodiment of the present invention, respectively. Referring to FIG. 2A, in the case of graphene-activated carbon, it can be seen that the graphene layer is well wrapped around the activated carbon core, which is a result contrasted with FIG. 2B.

Meanwhile, the specific surface area of the graphene-activated carbon composite was analyzed through nitrogen adsorption and desorption experiments, and the total pore volume and average pore size were measured, and are shown in Table 1 below.

BET specific surface area
(m ² /g) Total pore volume
(cm ³ /g) Average pore diameter
(nm) Graphene-Activated Carbon Complex 1,539 0.74 1.94 Activated carbon 1,519 0.71 1.87

Looking at Table 1, it was confirmed that the surface area of the graphene-activated carbon composite was similar to that of the activated carbon even after the composite was combined, and it was confirmed that the BET specific surface area value was slightly higher.

Meanwhile, in order to confirm the resistance reduction characteristics of the graphene-activated carbon composite (Example 1) and the activated carbon (Comparative Example 1), the powder resistance was measured and the results are shown in FIG. 3. Specifically, powder resistance was measured at a pressure of 1 to 52 Mpa based on a 0.5 g sample. As a result, the activated carbon exhibited a resistance of 3.54 to 0.201 Ωcm, whereas the prepared graphene-activated carbon composite exhibited resistance of 0.645 to 0.08 Ωcm, and it was confirmed that the resistance was reduced by 82 to 60%.

This is believed to be due to the presence of graphene having excellent electrical conductivity on the surface of the activated carbon core, thereby reducing resistance as well as reducing resistance by connecting graphene between adjacent activated carbons.

Experimental example 3: Supercapacitor behavior analysis

After selecting the graphene-activated carbon composite according to Example 1 and the activated carbon according to Comparative Example 1 as active materials, respectively, an electrode material was prepared in a ratio of 90:10 of the active material and the binder for electrochemical property evaluation. The prepared electrode was evaluated by preparing two electrodes with a diameter of 1.5 cm and assembling a 2032 coin cell type. At this time, TEABF ₄ in 1.5 M PC was used as the electrolyte, and the charging/discharging current density was evaluated by applying 1 to 30 mAcm ^{- 2} based on a voltage of 2.5 V, and the results are shown in FIGS. 4A and 4B.

4A and 4B, the supercapacitor including the graphene-activated carbon composite according to Example 1 is at 1 mAcm ^-2 111 Fg ^-1 , 30 mAcm ^-2 the 46 Fg ^- supercapacitor (1 mAcm which showed a capacitance of weight ^1, which comprises the activated carbon of Comparative Example 1 ^{- 2:} 99 Fg ^-1 / 30 mAcm ^{- 2} : 20 Fg ^-1 ) compared to 112 ~ 230% increased value was confirmed.

Experimental example 4: Lithium secondary battery Cathode behavior analysis

After selecting the graphene-activated carbon composite according to Example 1 and the activated carbon according to Comparative Example 1 as a negative active material, respectively, Super-P was used as a conductive material and polyacrylic acid was used as a binder. The composition of the electrode was mixed with 80 wt% of a negative electrode active material, 10 wt% of a conductive material, and 10 wt% of a binder. A coin cell composed of the prepared negative electrode and LiPF ₆ 1:1 vol% ethylene carbonate (EC)/dimethyl carbonate (DMC) liquid electrolyte was prepared, and a charge/discharge experiment was performed on the coin cell using a charge/discharge device. Charge/discharge capacity, cycle characteristics, and rate-limiting characteristics as negative electrodes of the prepared lithium secondary battery were investigated.

Charging and discharging was performed in a voltage range of 0.005 to 2.0 V with a current of 35 mA/g (0.1C).

Thereafter, the charging/discharging results of the lithium secondary battery, cycle characteristics, capacity retention rate, coulomb efficiency, and rate-limiting characteristics are shown in FIGS. 5, 6a, 6b and 7 respectively. As shown in FIG. 5, the lithium secondary battery manufactured using the graphene-activated carbon composite and the lithium secondary battery manufactured using the activated carbon each exhibit negative electrode initial capacities of 434 mAh/g and 422 mAh/g, respectively, and charge/discharge. Comparing the post-Coulomb efficiency, it is shown that 31.8% when using activated carbon and 39.5% when using graphene-activated carbon composite.

Meanwhile, FIG. 6 shows the life characteristics, capacity retention rate, and Coulomb efficiency of the lithium secondary battery. Referring to FIGS. 6A and 6B, the case of using the graphene-activated carbon composite is higher than that of the case of using activated carbon even in the result of charging and discharging 100 times. Was maintained, and it was confirmed that more excellent cycle characteristics, capacity retention rate, and Coulomb efficiency were shown.

On the other hand, Figure 7 is to compare the discharge characteristics according to the current density of the graphene-activated carbon composite according to Example 1 and the lithium ion battery electrode prepared using the activated carbon according to Comparative Example 1, using a charge and discharge cycle After carrying out a 5 cycle charge/discharge experiment under current density conditions of 0.1, 0.2, 0.5, 1, 2, 5 C (1C=350 mA/g) of current, 0.2 C was measured again to check the capacity retention rate. Shows the experimental results.

Referring to FIG. 7, when a lithium ion battery negative electrode was manufactured using the graphene-activated carbon composite according to Example 1, the capacity characteristics and capacity retention rate were obtained by using the activated carbon according to Comparative Example 1 at various discharge currents. It can be seen that it was significantly improved compared to the case of manufacturing. It is believed that this is because the graphene layer surrounds the activated carbon core, thereby reducing the specific resistance of the electrode surface of the lithium ion battery, thereby inducing an effective electrochemical reaction during charging and discharging of the battery. That is, in the electrode including the graphene-activated carbon composite, graphene shortens the lithium diffusion path and maintains electrical conductivity, so it is determined that the electrochemical properties are improved.

Claims (11)

delete delete delete delete delete As a method for preparing a graphene-activated carbon composite,
Preparing graphene oxide;
Dispersing activated carbon and the graphene oxide in a solvent to prepare a spray solution;
Spraying the spray solution into droplets; And
Including; applying heat to the droplet to prepare a graphene-activated carbon composite comprising activated carbon coated with a graphene layer;
The graphene-activated carbon composite includes activated carbon as a core, a graphene layer as a shell, and has a structure in which graphene is connected between adjacent activated carbons, and has a spherical shape, a method of manufacturing a graphene-activated carbon composite.
The method of claim 6,
In the spray solution, the activated carbon and graphene oxide are contained in a weight ratio of 1:1 to 1:10, graphene-activated carbon composite manufacturing method.
The method of claim 6,
The droplet spraying step is performed at a spray pressure of 49 to 245 kPa and a supply rate of 150 to 1700 ml/hr of the dispersion under temperature conditions in the range of 100 to 300°C, graphene-activated carbon composite manufacturing method.
The method of claim 6,
The step of applying heat to the droplets is carried out for 50 minutes to 640 minutes in the range of 800 to 2000 ℃ by heating at a heating rate of 5 ~ 20 ℃ per minute, a method for producing a graphene-activated carbon composite.
delete delete

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