KR20140072269A - Metal or Metal oxide/Graphene self-assembly Nanocomposite of Three-dimensional structure and Method of preparing the same - Google Patents

Abstract

The present invention relates to a metal or metal oxide/graphene nanocomposite with a three-dimensional structure and a method for preparing the same. The present invention improves electrical conductivity, charge and discharge characteristics, and life characteristics when compared to existing batteries by effectively controlling the lamination layer and aggregation of graphene by uniformly combining uniform-sized metal or metal oxide with the surface of the graphene. Moreover, the method for preparing a metal or metal oxide/graphene nanocomposite with a three-dimensional structure without an additional post-treatment in a reactive container has time and economic advantages.

Description

TECHNICAL FIELD The present invention relates to a metal or metal oxide / graphene nanocomposite having a three-dimensional structure and a method for manufacturing the same.

The present invention relates to a metal or metal oxide / graphene nanocomposite having a three-dimensional structure and a manufacturing method thereof.

Graphene is a two-dimensional nanosheet monolayer carbon structure in which the sp ² carbon atoms form a hexagonal honeycomb lattice. In 2004, Geim scientists in the United Kingdom, Reports of graphene have persisted since graphene separation. Graphene is a new material with remarkable surface area relative to volume, excellent electron conduction properties and physical and chemical stability.

In particular, graphene can act as an efficient template for depositing nano-sized transition metal oxides due to its high specific surface area, excellent electrical conductivity and physical and chemical stability. It can be used as an energy storage material (Lithium ion secondary battery, hydrogen storage fuel cell, ultra-high-capacity capacitor electrode), gas sensor, microcomputer for medical engineering, and high-performance complex.

However, in the case of graphene, due to the van der Waals action between the graphene layers due to the sp ² carbon bond at the surface, the graphene layer is not easily peeled off in solution and is not a single layer graphene but mostly thicker graphene graphene (multilayer graphene), and even if it is peeled off, it has a property of restacking again. Aggregated or re-deposited graphene results in reduced specific surface area and electrical conductivity. Therefore, when a composite material with a transition metal oxide is synthesized by using graphene as a precursor in a solution, the high specific surface area of the single-layer graphene can not be utilized and it is difficult to form a uniform composite structure. It is a factor that hinders utilization.

On the other hand, graphite oxide is a material in which a variety of oxygen functional groups are introduced on the surface of a graphene layer forming a graphite layer structure by a strong oxidizing treatment. When a large amount of graphene is synthesized through a chemical reduction method or a thermal peeling method It is a substance used as a precursor. Unlike graphene, unlike graphene, various oxygen functions on the surface can easily disperse into single layer graphite oxide or graphene oxide when applied to other solutions after ultrasonic treatment. . Therefore, when a composite material of a transition metal oxide is synthesized by using graphene oxide uniformly dispersed in a solution as a precursor, graphene oxide can serve as a template for uniformly depositing nano-sized transition metal oxide . However, since various oxygen functional groups on the surface of graphene oxide introduced through oxidation treatment are generated by partially breaking sp ² bonds of graphene, there is a problem that electric conductivity is lowered. Therefore, in order to utilize the excellent electrical conductivity of graphene when the graphene oxide is combined with a nano-sized transition metal oxide, a composite material with a nano-sized transition metal oxide is formed and then a reducing agent is used or a high temperature heat treatment There is a problem that the post-treatment for restoring the sp ² bond of the graphene is necessary to remove oxygen functional groups on the surface of the graphen oxide again.

To date, the process for preparing metal or metal oxide / graphene composites has been limited by the addition of a conductive material as a solution to reattachment and agglomeration of graphene and an additional post-treatment to reduce the graphite oxide to graphene There is a disadvantage in terms of time and economy, and the effect of restraining layer and flocculation phenomenon is also unsatisfactory.

Accordingly, the present invention provides a metal or metal oxide / graphene nanocomposite having a three-dimensional structure that effectively controls the re-layering and aggregation of graphene by uniformly bonding metal or metal oxide, which is a nanoparticle of uniform size, ≪ / RTI >

It is also intended to provide a production method capable of synthesizing a metal or metal oxide / graphene nanocomposite having a three-dimensional structure, which is a final product, in one reaction vessel without addition of a conductive material and additional post-treatment.

In addition, the energy storage materials (lithium secondary battery, hydrogen storage fuel cell, ultra-high capacity capacitor electrode), gas sensor, and fine parts for medical use of various devices including the metal or metal oxide / graphene nanocomposite having the three- ≪ / RTI >

Graphene has the characteristics of low mass density, high electrical conductivity, and high specific surface area, and exhibits its properties when present independently. That is, when a single graphene is applied to an actual electrode or the like to be applied to a specific application, the characteristic inherent to the graphene is lost. This is because when a number of graphenes concentrate at a specific position, a van der Waals force is generated between them and interacts with each other by this force, so that re-layering or agglomeration occurs between the graphen sheets. Since the graphene does not exist as a single sheet in the electrode due to the rewetting layer and the agglomeration, the electrical conductivity and the high specific surface area characteristic are lost, and the performance difference between the electrode and the porous carbon material using the graphene I'm not getting out.

Accordingly, the present invention relates to a method and apparatus for uniformly bonding a uniform nano-sized metal or metal oxide to the surface of graphene, thereby increasing the specific surface area of graphene and preventing re-layering and agglomeration, Dimensional structure of metal or metal oxide / graphene nanocomposite. The metal or metal oxide / graphene nanocomposite having the three-dimensional structure is uniformly bonded to the graphene surface with uniformly sized metal or metal oxide nanoparticles on the other side. Therefore, conductivity is improved without adding a conductive material, The charge / discharge characteristics (charge / discharge capacity and charging / discharging rate) of the electrode can be improved. Since graphene acts as a physical buffer for the transition metal and its oxide, which are large in volume change due to the conversion reaction during charging and discharging, The lifetime characteristics can be increased.

The metal or metal oxide / graphene nanocomposite of the three-dimensional structure is obtained by (a) mixing a graphite oxide solution with a salt of a metal or a metal oxide to form a metal or metal oxide / graphite oxide complex; And (b) adding a reducing agent to the mixed solution and stirring to synthesize a metal or metal oxide / graphene nanocomposite having a three-dimensional structure.

Step (a) is to select the type of metal or metal oxide to be formed on the graphene and to mix the corresponding metal or metal oxide salt with the graphite oxide solution. This step forms a metal or metal oxide / graphite oxide complex. For example, when a ruthenium salt is put into an aqueous solution of graphite oxide, a ruthenium ion (Ru ^{2 +} ) reacts with a functional group on the surface of graphite oxide to cause a ruthenium ion (Ru ^{2 +} ) to become ruthenium oxide (RuO ₂ ) / Graphite oxide complex is formed.

The graphite oxide solution used in step (a) is formed by mixing one kind of solvent selected from the group consisting of distilled water, ethanol and ethylene glycol with graphite oxide, and the kind of solvent used is not particularly limited. The mixing method of the graphite oxide solution and the salt of the metal or the metal oxide is not limited, and it is only necessary to uniformly disperse the graphite oxide in the solvent using simple stirring or ultrasonic waves.

The graphite oxide may be in a powder form and the graphite oxide may be prepared by a method commonly used in the art such as Brodie method, Staudenmaier method or Hummer's method .

In addition, the content of graphite oxide in the graphite oxide solution can be appropriately adjusted according to requirements such as the dispersion in the graphite oxide solution and the density of the graphene structure. In one embodiment, the amount of graphite oxide in the graphite oxide solution may be from 1 to 10 parts by weight, for example, from 2 to 6 parts by weight, based on 100 parts by weight of the solvent. The content range is a range in which the density of the produced graphene structure is excessively low to prevent the energy density per volume from being lowered and at the same time the degree of dispersion of the graphite oxide can be increased.

On the other hand, the metal or metal oxide salt to be mixed with the graphite oxide solution may be a metal or a kind of metal oxide to be laminated on the graphene depending on the end use of the metal or metal oxide / graphene nanocomposite according to the present invention Can be determined. The metal forming the salt of the metal or metal oxide may be a transition metal, and preferably tin, ruthenium, iron, gold, silver, palladium, titanium, and manganese. The salt of the metal or metal oxide may be in the form of an acid addition salt, such as a hydrochloride, a bromate, a sulfate, a phosphate, a nitrate, a carbonate, or a borate salt.

When a salt of a metal or a metal oxide is added to a solution in which graphite oxide is uniformly dispersed, a salt of a metal or a metal oxide easily precipitates as a metal or a metal oxide in a solvent and bonds with the graphite oxide surface.

The step (b) is a step of reducing a graphite oxide to a graphene (Graphene or Reduced Graphene Oxide) by adding a reducing agent to the solution containing the metal or the metal oxide / graphite oxide complex obtained through the step (a). Reducing the graphite oxide to water (H ₂ O) by reducing the functional groups present on the surface of the graphite oxide such as carboxyl group (-COOH), formyl group (-CHO) and carbonyl group (-CO-) Thereby forming a three-dimensional hydrogel. In the above process, the sp ² bond is restored between the carbon atoms of the graphene, and the three-dimensional structure having pores is formed while forming the π-π bond according to the restoration of the sp ² bond.

The kind of the reducing agent used for reduction of the graphite oxide in the step (b) is not particularly limited. The reducing agent may be a conventionally used reducing agent, and any reducing agent capable of reducing the functional group on the surface of graphite to water can be used. Examples of the reducing agent include ascorbic acid (C ₆ H ₈ O ₆ ), sodium sulfide (Na ₂ S), hydrogen iodide (HI), sodium hydrogensulfite (NaHSO ₃ ), sodium sulfate (Na ₂ SO ₃ ), sodium bisulfate ₄ ), sodium borohydride (NaBH ₄ ), hydrazine (N ₂ H ₄ ).

The content of the reducing agent is not particularly limited, and it may be sufficient to induce sufficient reduction while remaining the residual reducing agent at the same time. The reducing agent may be used in an amount of 200 to 2,000 parts by weight, for example, 300 to 800 parts by weight, based on 100 parts by weight of the graphite oxide.

The particle size of the metal / metal oxide formed on the graphene surface may be 1 to 10 nm in particle size.

The manufacturing method may further include a step (c) of washing and drying the metal or metal oxide / graphene nanocomposite having the three-dimensional structure synthesized in the step (b).

The cleaning may be carried out by addition of a surplus metal or a salt of a metal oxide, a surplus metal or a metal oxide / graphite oxide, a surplus reducing agent or the like in a mixed solution that may remain in the synthesized three-dimensional metal or metal oxide / graphene nanocomposite This can be repeated to remove the compound, until the material is removed. As the cleaning solution, a conventional solvent can be used. For example, deionized water, ethanol, acetone, methanol, propanol, etc. can be used. The use of organic solvents is preferred for removal of organic materials.

Conventional drying methods such as general drying, oven drying, freeze drying and the like may be used for the drying. For example, drying may be carried out at ambient temperature to 70 ° C.

The present invention also provides a three-dimensional structure metal or metal oxide / graphene nanocomposite produced according to the above-described production method.

Since the metal / metal oxide / graphene nanocomposite having the three-dimensional structure obtained according to the above manufacturing method is bonded to the graphene surface of the metal / metal oxide, it is possible to take advantage of graphene's inherent advantage by controlling the re- In addition, since the metal / metal oxide is uniformly bonded to the surface of the graphene, the composite has a high specific surface area, exhibits excellent electrical conductivity without addition of an additional conductive material, suppresses the volume expansion of the electrode upon charge and discharge , Thereby exhibiting excellent high-rate characteristics and excellent lifetime characteristics.

In addition, due to the three-dimensional structure, it is possible to manufacture an electrode without a binder in the manufacture of an electrode and to facilitate the movement between the electrode material and the electrolyte, thereby improving capacity characteristics and improving output characteristics.

The present invention also provides a negative electrode made of a metal or a metal oxide / graphene nanocomposite having a three-dimensional structure, a negative electrode made of the negative electrode material, and a lithium secondary battery including the negative electrode.

The present invention has an advantage in a manufacturing method capable of forming a three-dimensional metal or metal oxide / graphene nanocomposite in a one-step process, and also has the advantage that uniformly sized nanoparticles of metal or metal oxide are uniformly Thereby effectively controlling the re-layering and agglomeration of the graphene, thereby improving electrical conductivity and lifetime characteristics compared with conventional batteries without adding additional conductive material.

FIG. 1 is a photograph of RuO ₂ / graphene nanocomposite having a three-dimensional structure.
2 is an FETEM of a RuO ₂ / graphene nanocomposite having a three-dimensional structure.
3 is a photograph of a SnO ₂ / graphene nanocomposite having a three-dimensional structure.
4 is an FETEM of a three-dimensional structure SnO ₂ / graphene nanocomposite.
5 is XRD of a three-dimensional structure SnO ₂ / graphene nanocomposite.
6 is a SEM of a three-dimensional structure SnO ₂ / graphene nanocomposite.
7 is SEM-EDAX of a three-dimensional structure SnO ₂ / graphene nanocomposite.
8 is XPS of graphene (a) and SnO ₂ / graphene nanocomposite (b) having a three-dimensional structure.
9 is a graph showing the capacity of an active material per unit weight of an electrode obtained by evaluating charge / discharge capacity characteristics of an electrode including a SnO ₂ / graphene nanocomposite having a three-dimensional structure.
10 is a graph showing excellent lifetime characteristics of a battery including a three-dimensional structure SnO ₂ / graphene nanocomposite.

Advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described in detail below. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

Fabrication of RuO ₂ / graphene nanocomposite with three-dimensional structure

4 mg of the graphite oxide powder prepared by the Hummer's method was added to 100 ml of distilled water and the graphite oxide was uniformly dispersed in the distilled water by treating with ultrasonic waves. 0.02 mg of ruthenium trichloride (RuCl ₃ ) was added to the graphite oxide aqueous solution, followed by stirring for 12 hours. Subsequently, 4 mg of sodium hydrogen sulfite (NaHSO ₃ ) was added as a reducing agent to the mixed solution, and the mixture was stirred for 10 minutes to synthesize a three-dimensional ruthenium oxide / graphene nanocomposite. The synthesized ruthenium oxide / graphene nanocomposite was sequentially washed with acetone, ethanol and distilled water in this order, and washed repeatedly until the impurities were completely removed. The prepared three-dimensional RuO ₂ / graphene composite was dried at 70 ° C for 12 hours.

FIG. 1 is a photograph of a three-dimensional ruthenium oxide / graphene nanocomposite prepared according to Example 1, and it can be confirmed that a three-dimensional structure is formed.

Field Emission Transmission Electron Micsroscope (FETEM) was used to observe the surface of the three-dimensional ruthenium oxide / graphene nanocomposite. FIG. 2 is a photograph of an FETEM of a three-dimensional ruthenium oxide / graphene nanocomposite fabricated according to Example 1, wherein ruthenium oxide is uniformly formed on graphene in the form of nanoparticles having a particle size of about 1 to 10 nm , It can be confirmed that all the shapes are spherical. That is, according to the method of the present invention, the transition metal oxide can be uniformly formed on the graphene surface in the form of nano-sized particles.

Fabrication of SnO ₂ / graphene nanocomposite with three-dimensional structure

4 mg of the graphite oxide powder prepared by the Hummer's method was added to 100 ml of distilled water and the graphite oxide was uniformly dispersed in the distilled water by ultrasonic treatment. 0.01 mg of tin chloride (SnCl ₂ ) was added to the graphite oxide aqueous solution and stirred for 12 hours. Subsequently, 4 mg of sodium hydrogen sulfite (NaHSO ₃ ) was added to the mixed solution as a reducing agent, and the mixture was stirred for 10 minutes. Acetone, ethanol and distilled water in that order, and washed repeatedly until the impurities were completely removed. The prepared three-dimensional SnO ₂ / graphene composite was dried at 70 ° C for 12 hours.

FIG. 3 is a photograph of a tin oxide / graphene nanocomposite having a three-dimensional structure according to Example 2, which shows that a three-dimensional structure was formed.

Field Emission Transmission Electron Micsroscope (FETEM) was used to observe the surface of the three-dimensional ruthenium oxide / graphene nanocomposite. FIG. 4 is an FETEM image of a three-dimensional tin oxide / graphene nanocomposite fabricated according to Example 2, wherein tin oxide is uniformly formed on graphene in the form of nanoparticles having a particle size of about 1 to 10 nm , It can be confirmed that all of the shapes are spherical. That is, according to the method of the present invention, the transition metal oxide can be uniformly formed on the graphene surface in the form of nano-sized particles.

XRD analysis was performed to analyze the components of the nanocomposite. FIG. 5 is an XRD graph of a tin oxide / graphene nanocomposite having a three-dimensional structure prepared according to Example 2, wherein tin oxide is present.

FIG. 6 is a SEM photograph of a three-dimensional tin oxide / graphene nanocomposite prepared according to Example 2, which shows that a tin oxide / graphene complex having a three-dimensional structure pore is formed.

FIG. 7 is a SEM-EDAX analysis result of a tin oxide / graphene nanocomposite having a three-dimensional structure according to Example 2. As a result, tin oxide was formed on the surface of a graphene having a three-dimensional structure.

8 is a graph showing X-ray photoelectron spectroscopy (XPS) analysis of a tin oxide / graphene nanocomposite having a three-dimensional structure according to Example 2. FIG. 8A is a graphite oxide, Tin oxide / graphene complex. 284.5 eV from the C-C orbitals and 287.6 eV from the C-O functional groups on the surface. In the case of the tin oxide / graphene complex of the three-dimensional structure, the conductivity is improved by increasing the C-C peak.

In (b), it is possible to confirm the formation of SnO ₂ particles. Sn, 3d, 4s, 4p and 4d are derived from SnO ₂ .

Experimental Example 1

 Checking charge / discharge capacity

The electrochemical characteristics of the three-dimensional tin oxide / graphene nanocomposite prepared according to Example 2 were analyzed. The charge / discharge capacity of the electrode was evaluated in a half-cell using a three-dimensional tin oxide / graphene nanocomposite as a lithium ion battery cathode material. 5 parts by weight of PVDF was mixed with 95 parts by weight of a three-dimensional structure tin oxide / graphene composite and added to NMP (N-methyl-2-pyrrolidone) to prepare an electrode slurry. To 3 mg were coated and dried to prepare an electrode. Lithium metal was used as a reference electrode and a counter electrode, and 1M LiPF ₆ in EC / DMC (1/1) was used as an electrolyte. The voltage range was 0.1 ~ 3 V and the charge / discharge rate was changed from 0.1 A / g to 4 A / g. 9 is a graph showing the capacity of the metal or metal oxide / graphene nanocomposite per unit weight of the electrode. When the charge / discharge rate is 0.1 A / g, the charge / discharge capacity is 600 mAh / g or more, It can be seen that when the discharge speed is 4 A / g, the charge / discharge capacity has a value of 200 mAh / g or more. This indicates that the SnO ₂ lithium secondary battery anode has a very excellent charge / discharge capacity as compared to the charge / discharge rate of 2 A / g and the charge / discharge capacity of 200 mAh / g or less.

Experimental Example 2

Check volume expansion effect (life)

The tin oxide / graphene nanocomposite of the three-dimensional structure prepared according to Example 2 was used as a negative electrode material of a lithium ion battery, and then the volume expansion inhibition effect (lifetime) of the electrode was evaluated in a half-cell . The electrode was manufactured in the same manner as in Experimental Example 1 above. FIG. 10 is a graph showing lifetime characteristics of a three-dimensional tin oxide / graphene nanocomposite fabricated according to the present invention. The charge / discharge capacity was maintained at 60 cycles or more. This is because the graphene structure physically buffered tin oxide, which is a material that has a large volume change due to the conversion reaction during charging and discharging. The conventional SnO ₂ (Life span) of lithium secondary battery cathodes.

Claims (15)

(a) mixing a graphite oxide solution with a salt of a metal or a metal oxide to form a metal or metal oxide / graphite oxide complex; And (b) adding a reducing agent to the mixed solution and stirring to synthesize a three-dimensional metal or metal oxide / graphene nanocomposite.
The method according to claim 1,
Wherein the graphite oxide solution is formed by mixing one solvent selected from the group consisting of distilled water, ethanol and ethylene glycol, and graphite oxide, and a method for producing the metal or metal oxide / graphene nanocomposite having a three-dimensional structure.
3. The method of claim 2,
Wherein the graphite oxide is mixed in an amount of 1 to 10 parts by weight based on 100 parts by weight of the solvent.
The method according to claim 1,
Wherein the metal or metal oxide is composed of a transition metal or an oxide thereof, wherein the metal or metal oxide is a transition metal or an oxide thereof.
5. The method of claim 4,
Wherein the transition metal is at least one selected from the group consisting of tin, ruthenium, iron, gold, silver, palladium, titanium and manganese.
The method according to claim 1,
Wherein the salt of the metal or the metal oxide is in the form of an acid addition salt of a hydrochloride, a bromate, a sulfate, a phosphate, a nitrate, a carbonate or a borate salt.
The method according to claim 1,
The reducing agent ascorbic acid _{(C 6 H 8 O 6)} , sodium sulfide (Na ₂ S), hydrogen iodide (HI), sodium bisulfite (NaHSO _3), sodium sulfate (Na ₂ SO _3), sodium bisulfate (NaHSO ₄₎ , Sodium borohydride (NaBH ₄ ), and hydrazine (N ₂ H ₄ ). The method for producing the metal or metal oxide / graphene nanocomposite according to claim 1,
The method according to claim 1,
(C) washing and drying the metal or metal oxide / graphene nanocomposite having the three-dimensional structure synthesized in the step (b), and drying the metal or metal oxide / graphene nanocomposite Gt;
A three-dimensional structure metal or metal oxide / graphene nanocomposite prepared according to the method of claim 1
10. The method of claim 9,
The metal or metal oxide / graphene nanocomposite having a three-dimensional structure in which the metal or metal oxide has a particle diameter of 1 nm or more and 10 nm or less. A negative electrode material comprising a metal or metal oxide / graphene nanocomposite having a three-dimensional structure according to claim 9.
An anode made of a cathode material according to claim 11.
A lithium secondary battery comprising a negative electrode according to claim 12.
14. The method of claim 13,
And a charge / discharge capacity of 200 mAh / g or more when the charge / discharge speed is 4 A / g.
14. The method of claim 13,
And has a lifetime characteristic capable of maintaining the charge / discharge capacity at 100 cycles or more.

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