KR20180010693A - 3 dimensional composite including metal oxide material and porous grapheme - Google Patents

Abstract

The present invention relates to a composite with a three-dimensional structure including metal oxide and porous graphene and a negative electrode active material including the composite with a three-dimensional structure. The composite with a three-dimensional structure according to the present invention can be manufactured through a single process, thereby reducing manufacturing costs and simplifying a process. When the composite with a three-dimensional structure is used as a negative electrode active material, a sodium secondary battery excellent in chemical characteristics by improving reversibility and charging/discharging capacity can be provided.

Description

TECHNICAL FIELD [0001] The present invention relates to a three-dimensional composite structure containing metal oxides and porous graphenes,

The present invention relates to a composite of a three-dimensional structure including a metal oxide and a porous graphene, and a negative active material including the composite of the three-dimensional structure.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. Electrochemical devices have attracted the greatest attention in this respect. Among them, the development of rechargeable secondary batteries has become a focus of attention. In recent years, in order to improve charge / discharge capacity, And research and development on the design of the battery is under way.

Li-ion batteries are one of the main technologies in R & D and commercialization. However, when the battery market is rapidly expanded due to limited lithium resources and regional localization, Is expected. In addition, lithium-ion batteries use a combustible organic electrolyte as an electrolyte. Therefore, there is a risk of stability and leakage of liquid, and there is a risk of ignition as the temperature rises due to the increase of the discharge speed due to the limit of energy density. Therefore, there is a need for a new secondary battery technology having high stability, high capacity, long service life and low price for use in electric vehicles and energy storage systems.

Na-ion batteries are being studied as one of the secondary batteries that can replace lithium-ion batteries, and in Japan, research is being actively conducted as "post-Li-ion batteries". Sodium is about 33 times lower in price than lithium, the standard electrode potential is about 0.3 V, the ion volume is about 2.4 times, the atomic weight is about 3.3 times higher, and the theoretical capacity is about 3.2 times lower. Therefore, the sodium secondary battery has excellent competitiveness in terms of material water ac- curacy and manufacturing cost by using sodium abundant on the earth, and has a merit that a large capacity battery can be made simple structure compared to a lithium ion battery.

However, since the sodium ion size and weight are larger than lithium, it is difficult to move the ions between the electrodes, which is a weak point as an electric storage device. Therefore, the development of sodium ion batteries is important to choose the chemical reaction of the battery that reacts well with sodium at the atomic level. NaTi ₂ (PO ₄ ) _{3, which} is used as a negative electrode active material of conventional sodium electrode, has a low electric conductivity, which causes an inefficient supply of electrons and thus acts as a factor to deteriorate the efficiency of the electrode. Therefore, it is urgently required to develop a technique for increasing the electric conductivity of the negative electrode active material.

On the other hand, graphene is attracting attention as a material that will become the basis of future industry due to its inherent physical properties that are superior to existing carbon materials such as high electric conductivity and high specific surface area. In addition, graphene nanocomposite is far superior to existing materials due to its excellent physical properties, and has become a future material to replace existing materials in various fields such as catalysts, electronic materials, energy materials, and biomedical materials. Thus, many research groups around the world are keen on securing graphene-based nanocomposite synthesis technology that demonstrates superior performance.

Therefore, it is urgently required to develop a negative electrode active material having a reversible capacity and charge / discharge capacity, which is a combination of NaTi ₂ (PO ₄ ) ₃ and graphene, and a secondary battery including the same.

Korean Patent Publication No. 10-2015-0143372.

An object of the present invention is to provide a negative active material having excellent reversibility, charge / discharge capacity, and a secondary battery including the negative active material.

In order to solve the above-mentioned problems, the present invention provides a process for producing a phosphorous compound of M1-M2-P-O based phosphorus (M1 is an alkali metal and M2 is a transition metal); And graphene, wherein the composite forms a three-dimensional structure having a BET specific surface area in the range of 10 to 500 m < 2 > / g.

The present invention also provides an anode active material comprising the composite of the three-dimensional structure.

The composite of the three-dimensional structure according to the present invention can be manufactured through a single process, thereby reducing the manufacturing cost and simplifying the process. When the composite having the three-dimensional structure is used as the negative electrode active material, the reversibility and the charge- It is possible to provide a sodium secondary battery having excellent chemical properties

1 is a field-emission transmission electron microscope (FE-SEM) photograph of a composite of a three-dimensional structure according to Example 1. Fig.
2 is a FIB-HRTEM photograph of a composite of a three-dimensional structure according to Example 1. Fig.
Fig. 3 shows Raman spectrum results of a three-dimensional structure complex according to Example 1. Fig.
FIG. 4 is an EDX photograph showing that each element exists in the composite of the three-dimensional structure.
5 is a graph of an X-ray photoelectron spectroscopy (XPS) analysis result of a composite of a three-dimensional structure according to Example 1. Fig.
6 is a graph showing the BET specific surface area of the composite according to Embodiment 1 (A) and Comparative Example 1 (B).
7 is a graph showing the pore volume fraction (dV / dD) of the composite according to Example 1 (A) and Comparative Example 1 (B), with reference to FIG.
8 is a cyclic voltage-current curve of the half-cell according to the third embodiment.
9 is a graph showing the results of charging and discharging tests of the half-cell according to the third embodiment.
10 is a result of life characteristics of the half-cell according to the third embodiment.
11 is a graph showing a change in the specific capacity according to the charge / discharge speed of the half-cell according to the third embodiment.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a composite of a three-dimensional structure and a negative electrode active material containing the same.

The complex of the three-dimensional structure according to the present invention is an M1-M2-P-O phosphorus oxide (M1 is an alkali metal and M2 is a transition metal); And graphenes, wherein said composite forms a three-dimensional structure having a BET specific surface area in the range of 10 to 500 m < 2 > / g.

Specifically, the composite of the three-dimensional structure according to the present invention may have a structure in which M1-M2-P-O phosphorus oxide particles are dispersed on the graphene surface. The three-dimensional structure means a structure in which grains having M1-M2-P-O phosphorus oxide particles dispersed therein are granulated to form a three-dimensional shape.

The BET specific surface area of the composite of the three-dimensional structure may be in the range of 20 to 400 m 2 / g, 30 to 300 m 2 / g, 40 to 200 m 2 / g, or 50 to 100 m 2 / g. The composite of the three-dimensional structure according to the present invention is M1-M2-P-O phosphorus oxide; And graphenes. Therefore, it is possible to satisfy the specific surface area in the above range, thereby increasing the contact area of the electrolyte, thereby realizing excellent electrical conductivity and ionic conductivity when used as a negative electrode active material.

Further, the pore volume fraction of the composite of the three-dimensional structure (dV / dD) is 0.04 cm ³ g ^-1 nm ^{- 1} or more, 0.045 to ^{0.2 cm 3 g -1 nm -1,} 0.048 to 0.15 cm ³ g ^-1 nm may be a range of ^{1 - 1,} from 0.05 to 0.1 cm ³ g ^-1 nm ^-1 or 0.52 to 0.6 cm ³ g ^-1 nm. The pore average diameter of the complex of the three-dimensional structure may be in the range of 0.5 to 10 nm, 1 to 9 nm, 1.2 to 8.5 nm, 1.5 to 7.5 nm, or 1.8 to 5 nm. The complex of the three-dimensional structure according to the present invention is a M1-M2-PO phosphorus oxide; And graphenes, it is possible to satisfy the above-described range of pore volume fraction and average pore diameter, thereby facilitating the movement of the electrolyte, thereby easily achieving excellent charge-discharge capacity and reversibility of the secondary battery .

In the M1-M2-PO phosphorus oxide (M1 is an alkali metal and M2 is a transition metal) of the present invention, M1 is at least one alkali metal selected from the group consisting of Na, Li, K, Rb, . Specifically, M1 may include Na. M2 is selected from the group consisting of Ti, V, Sc, Cr, Mn, Fe, Co, Ni and Cu in the M1-M2-PO phosphorus oxide (M1 is an alkali metal and M2 is a transition metal) And may include one or more transition metals. Specifically, M2 may include Ti.

As one example, M1-M2-PO-based phosphate in the present invention (M1 is an alkali metal, M2 is a transition metal Im) is _{NaTi 2 (PO 4) 3,} Li 3 V 2 (PO 4) 3, and LiFePO ₄ , and more specifically may be NaTi ₂ (PO ₄ ) _{3 having} a nasicon structure.

The complex of the three-dimensional structure according to the present invention may be in the form of a spherical particle having an average particle diameter in the range of 1 to 10 mu m. Specifically, the average particle size of the composite of the three-dimensional structure may be in the range of 1.5 to 9 占 퐉, 1.8 to 8 占 퐉, 2 to 7.5 占 퐉, or 2.5 to 5 占 퐉. The complex of the three-dimensional structure according to the present invention can increase the area of the reaction system by having an average particle size within the above range. Also, the composite of the three-dimensional structure according to the present invention may include graphene, thereby improving the charge / discharge capacity and discharge sustaining rate of the sodium secondary battery by providing an anode active material having improved electrochemical properties due to an increase in C-C bond. For example, when the charge / discharge speed of the sodium secondary battery is 0.1C, the charge / discharge capacity may be about 133 mAh / g. In addition, even when the charge / discharge speed is 50 C, the charge / discharge capacity of 85 mAh / g or more can be obtained.

The complex of the three-dimensional structure according to the present invention may also be in the form of spherical particles. The spherical particle shape is easy to have a high specific surface area, and thus the area of contact with the electrolyte is widened, thereby providing a negative electrode active material having significantly improved electrochemical characteristics.

In the present invention, at least one of the M1-M2-PO phosphorus oxide (M1 is an alkali metal and M2 is a transition metal) and graphene is at least one selected from the group consisting of nitrogen, phosphorus, sulfur and boron It may be doped. Specifically, the graphenes according to the present invention may be in a nitrogen doped form, and the doping may be doped during thermal reduction of graphene oxide during the manufacturing process.

The graphene according to the present invention may be a porous structure having a plurality of holes. Here, the average diameter of the holes may be in the range of 0.5 to 10 nm, and specifically, the average diameter of the holes may be in the range of 1 to 9 nm, 1.2 to 8.5 nm, 1.5 to 7.5 nm, or 1.8 to 5 nm. The composite of the three-dimensional structure according to the present invention includes graphene formed with a plurality of holes in the above range, so that the surface area of the composite of the three-dimensional structure can be easily increased. Accordingly, the electrical conductivity and the ionic conductivity are improved by the increase of the contact area of the electrolyte, and the charge / discharge capacity and reversibility of the sodium secondary battery can be improved.

As an example, the graphene according to the present invention may have a structure comprising a first graphene layer and an nth graphene layer, where n may be two or more. Specifically, the graphene according to the present invention may be formed by stacking graphene having a plurality of holes in a range of 2 to 50 layers, 3 to 40 layers, 5 to 30 layers or 7 to 20 layers.

Further, nano-sized carbonaceous components may be dispersed in at least one of interfaces between the first graphene layer and the nth graphene layer. Specifically, the carbonaceous component may include at least one member selected from the group consisting of graphite, carbon fiber, graphite, carbon black, and carbon nanotube. In the present invention, the carbonaceous component may be carbon nanotubes. The structure of the graphene may be a structure in which a carbonaceous component is dispersed between each graphene layer, and prevents the graphene from being re-deposited due to the carbonaceous component, so that the movement of the electrolyte through the graphene hole is smooth .

The carbonaceous component in the present invention may be a nano-sized carbonaceous component having a diameter in the range of 0.5 to 20 nm. The nano-sized carbonaceous component may be dispersed between graphene and graphene to prevent re-deposition of a single layer of graphene. In this case, when the carbonaceous component is a carbon nanotube, the diameter may be a diameter of a cross section perpendicular to the longitudinal direction of the carbon nanotube.

In this case, the surface charge of graphene may have a negative charge, and the surface charge of the carbonaceous component may have a negative charge. As described above, since the graphene and carbon nanotubes according to the present invention have different charges, It can be easily dispersed among the graphene layers to prevent the carbon nanotubes from aggregating and to further facilitate bonding of the graphene and the carbon nanotubes.

As one example, the carbonaceous component according to the present invention may be doped with any one or more of nitrogen, phosphorus, sulfur and boron, and may be doped with nitrogen in particular.

The present invention provides a method for producing a composite of the above three-dimensional structure.

In the method for producing a three-dimensional composite according to the present invention, the first step is to prepare a precursor dispersion solution in which graphene and Na-Ti-P-O nanoparticles are uniformly mixed. Herein, the precursor dispersion solution containing graphene nanomaterial and Na-Ti-P-O nanoparticles comprises (a) graphene oxide synthesized from commercial graphene or graphite, (b) Na-Ti-P-O nanoparticles; And a first solvent that uniformly disperses them.

In the present invention, graphene can be produced by using commercially available graphene without limitation or by chemical reduction using a reducing agent of graphene oxide, or by using thermal exfoliation and reduction It is possible.

As one example of preparing the graphene oxide, a commercially available graphite is supported on a high concentration H ₂ SO ₄ solution at room temperature and sufficiently stirred, and then the graphite-supported solution is cooled to a low temperature of 0 ° C. or lower Next, KMnO ₄ is slowly added, and then the temperature of the mixed solution containing KMnO ₄ is maintained at 35 ° C, and a predetermined amount of H ₂ O ₂ is added. When such an oxidation process is carried out, the solution carrying the graphite changes its color from the initial black to the light brown solution. Then, the graphite oxide can be synthesized by sufficiently washing the powder obtained after washing with distilled water and ethanol several times using a centrifuge, in an oven.

In the present invention, graphene oxide in an oxidized form of graphene is in the form of flakes of a single atomic layer, and they are formed by various kinds of oxygen functional groups such as an epoxy group, a carboxyl group, a carbonyl group and a hydroxyl group It is hydrophilic due to functional groups. Therefore, it is possible to exhibit excellent dispersibility in a hydrophilic solvent even without introduction of a surfactant.

The NaTi ₂ (PO ₄ ) ₃ nanoparticles usable in the present invention are not particularly limited as long as they are nanoparticles composed of NaTi ₂ (PO ₄ ) ₃ components, and those conventionally known in the art can be used. The average diameter of the NaTi ₂ (PO ₄ ) ₃ nanoparticles may be 10 to 500 nm, preferably 50 to 150 nm.

The first solvent that can be used in the present invention is not particularly limited as long as it is capable of dispersing graphene or graphene oxide and Na-Ti-PO nanoparticles and can be applied to a spraying process. Preferably, A hydrophilic solvent can be used. Non-limiting examples of the first solvent that can be used include water, methanol, ethanol, acetone solution, or a mixture of at least one thereof.

In the present invention, in order to uniformly disperse the graphene or graphene oxide and Na-Ti-P-O nanoparticles in the first solvent, a general dispersion method such as ultrasonic waves may be used. For example, the ultrasonic treatment may be performed at a power of about 150 to 900 W for about 5 to 60 minutes, but is not limited thereto.

In the precursor dispersion solution prepared in the first step, the compounding ratio (by weight) of the graphene carbon material (graphene or graphene oxide) and Na-Ti-PO nanoparticles was Which has an important influence on the environment. If the weight ratio of Na-Ti-P-O in the precursor dispersion solution is too high, the amount of graphene required to form microstructure becomes relatively small, which makes it difficult to form uniform Na-Ti-P-O / graphene microparticles. Therefore, in order to produce uniform Na-Ti-P-O / graphene microparticles, the blending ratio of the Na-Ti-P-O nanoparticles and the graphene carbon material in the precursor dispersion solution is about 90:10.

In the present invention, the weight ratio of each of Na-Ti-P-O and graphene contained in the finally prepared Na-Ti-P-O / graphene microparticles can be controlled by controlling the compounding ratio of the dispersion solution. By controlling the weight ratio of each material contained in the Na-Ti-P-O / graphene microparticles, it is possible to control the electrochemical performance expressed by the electrode.

The second step is a step of spraying a precursor solution containing graphene or graphene oxide. In the second step, a precursor dispersion solution (spray solution) in which graphene or graphene oxide and Na-Ti-PO nanoparticles are uniformly dispersed, Into the spraying apparatus and spraying the sprayed droplets. Examples of the atomizing apparatus include an ultrasonic atomizing apparatus, a first-flow atomizing apparatus, a twin-screw air nozzle atomizing apparatus, an ultrasonic nozzle atomizing apparatus, a disk type droplet generating apparatus, and the like , But is not limited thereto.

In particular, an ultrasonic atomizing apparatus is preferable for ultrafine powder synthesis of several to several tens micron size (탆) for use in displays and capacitors. The ultrasonic atomizing apparatus can freely form micrometer-unit droplets having a uniform size distribution from the precursor dispersion solution through ultrasonic vibration. When the precursor dispersion solution is sprayed through the spray device described above, the spray solution forms micro-sized spherical droplets, and Na-Ti-PO / graphene microparticles are formed inside the spherical droplets Graphene oxide or graphene oxide and Na-Ti-PO particles are uniformly dispersed in the first solvent. In the present invention, it is possible to produce Na-Ti-PO / graphene microparticles of a size that can be used as an anode material for a secondary battery of excellent performance. The size of the droplets formed in the above- It is preferable to adjust the size to be larger than the fin microparticles. This is because the solution contained in the droplet is evaporated in the step of assembling and drying the graphene grains, so that only the graphene and Na-Ti-PO nanoparticles contained in the droplet are started to be assembled, Is formed. Accordingly, the average diameter of the droplets according to the present invention may range from 1 to 500 mu m, preferably from 10 to 100 mu m.

Finally, the Na-Ti-PO / graphene microparticle precursor was heat-treated at 800 ° C for 10 hours in an inert atmosphere (Ar) to finally form a complex of NaTi ₂ (PO ₄ ) ₃ / Can be manufactured.

The composite of the three-dimensional structure synthesized in the present invention has a structure in which graphene is efficiently assembled into a three-dimensional spherical microparticle form and the NaTi ₂ (PO ₄ ) ₃ nanoparticles in the assembled microparticles are supported . Due to such structural characteristics, it is possible to dramatically increase the capacity, high rate and lifetime characteristics of the negative electrode active material, and it can be applied to a variety of devices such as a sodium secondary battery, a display, and a sensor technology. It can contribute to development. In addition, it can be applied to various fields such as energy storage materials such as super capacitors, catalyst applications, electronic materials, optical materials, biomaterials, heat storage materials, automobile parts, solar thermal materials, toners and inks.

Furthermore, the present invention provides an anode active material comprising the composite of the three-dimensional structure. The present invention also provides a sodium secondary battery comprising the negative electrode active material according to the present invention. The sodium secondary battery may include a cathode, an anode, an electrolyte, and a current collector. For example, an electrode having 2 to 3 mg of a negative electrode active material coated on a copper current collector; A reference electrode and a counter electrode using sodium metal; And an electrolyte comprising an organic solvent and a sodium salt.

Hereinafter, the present invention will be described in more detail with reference to the following Examples. However, the scope of the present invention is not limited by the following Examples.

Manufacturing example  One: Graphite Oxide  Produce

(H ₂ SO ₄ ) and potassium permanganate (KMnO ₄ ) and stirred at room temperature for 2 hours or more. When the color of the solution turns yellow, hydrogen peroxide (H ₂ O ₂ ) Was added to complete the reaction. After completion, centrifugation was carried out, followed by drying to obtain a fine powdery graphite oxide.

Example  One

[Step 1] Preparation of graphene-containing precursor dispersion solution (spray solution)

The commercially available graphite (product name: Graphite, manufactured by Sigma Aldrich) was supported on a high concentration of H ₂ SO ₄ solution at room temperature and sufficiently stirred, then the graphite-impregnated solution was cooled to a low temperature of 0 ° C. or lower , KMnO ₄ was slowly added to the solution, and the temperature of the mixed solution containing KMnO ₄ was maintained at 35 ° C, and a predetermined amount of H ₂ O ₂ was added. When such an oxidation process is carried out, the solution carrying the graphite changes its color from the initial black to the light brown solution. Subsequently, the resultant was washed five times with distilled water and ethanol using a centrifuge, and the obtained powder was sufficiently dried in an oven to synthesize graphene. The thus-prepared graphene and Na-Ti-PO nanoparticles were dispersed in 100 mL of a first solvent (1: 1 ratio of water and ethanol) at a mixing ratio of 90:10, and the mixture was subjected to a power of about 500 W for about 30 minutes To prepare a precursor dispersion solution (spray solution) in which Na-Ti-PO / graphene microparticles were uniformly dispersed.

[Step 2] Spraying of the graphene-containing precursor dispersion solution

The precursor dispersion solution was sprayed using an ultrasonic atomizer to spray droplets of the graphene-containing precursor dispersion solution prepared in Step 1. The atomized spray solution forms micro-sized spherical droplets. Inside the spherical droplets, graphene and Na-Ti-PO particles to form Na-Ti-PO / Are uniformly dispersed in the solvent. At this time, the average diameter of droplets was about 50 탆.

Finally, heat treatment of the Na-Ti-PO / graphene precursor (droplet) in an inert (Ar) atmosphere at 800 ° C for 10 hours finally yielded a complex of three-dimensional structure of NaTi ₂ (PO ₄ ) ₃ / . At this time, the average particle size of the composite of the prepared three-dimensional structure was about 3 탆.

1 is a field-emission transmission electron microscope (FE-SEM) photograph of a composite of a three-dimensional structure produced according to Example 1. Referring to FIG. 1, spherical particles having an average particle diameter of about 3 μm can be identified, and it can be seen that many pores are formed.

FIG. 2 is a FIB-HRTEM image of the composite of the three-dimensional structure according to Example 1. As a result, it can be confirmed that the interplanar spacing of NaTi ₂ (PO ₄ ) ₃ is well formed by 0.366 nm.

Fig. 3 shows Raman spectrum results of a three-dimensional structure complex according to Example 1. Fig. Here, A can confirm the peak of NaTi ₂ (PO ₄ ) ₃ and graphene as a result of Example 1, confirming that NaTi ₂ (PO ₄ ) ₃ and graphene are present. On the other hand, B could not confirm the peak of graphene as a result of Raman spectrum of NaTi ₂ (PO ₄ ) ₃ . C is the peak of graphene.

FIG. 4 is an EDX photograph showing that each element exists in the composite of the three-dimensional structure.

FIG. 5 is a graph showing an X-ray photoelectron spectroscopy (XPS) analysis result of a composite having a three-dimensional structure according to Example 1. FIG. Referring to FIG. 5, C-C orbitals at 284.6 eV, C-O, C = O and O-C = O functional groups on the surface can be identified at 286.1 eV, 287.0 eV and 288.4 eV. In addition, in the case of the composite of the three-dimensional structure prepared in Example 1, it can be confirmed that the C-C peak is increased, which means that the electrochemical characteristics are improved.

Example  2

In the same manner as in Example 1 except that 0.1 g of commercially available carbon nanotubes (manufactured by JC Co., Ltd., product name: CNT M95) was further added to 0.1 g of the graphite oxide powder in Production Example 1 A complex of three dimensional structure was prepared. At this time, the average particle diameter of the composite of the prepared three-dimensional structure was about 2.5 占 퐉.

Example  3

90 parts by weight of the composite of the three-dimensional structure prepared in Example 1 and 10 parts by weight of polyvinylidene fluoride (PVDF) were mixed with a binder, and N-methyl-2-pyrrolidone -2-pyrrolidone, NMP) to prepare an electrode slurry. The electrode slurry was coated with 2 ~ 3 mg of copper on the collector and dried to prepare an electrode. Sodium perchlorate (NaClO ₄ ) dissolved in a mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) at a ratio of 1: 1 was used as a reference electrode and a counter electrode. halfcell) was prepared.

Comparative Example  One

An anode active material was prepared in the same manner as in Example 1 except that NaTi ₂ (PO ₄ ) ₃ alone was used without adding graphite oxide powder. The average particle size of the prepared negative electrode active material was about 110 nm.

Experimental Example  1: Specific surface area  Measure

To determine the BET specific surface area of the composite according to Example 1 and Comparative Example 1, N ₂ adsorption isotherms were measured. The results are shown in Fig. 6, the specific surface area of Example 1 (A) is about 61.4 m ² / g, and the specific surface area of Comparative Example 1 (B) is about 21.8 m ² / g. It was found that the specific surface area of the composite of Example 1 was significantly improved as compared with Comparative Example 1.

Experimental Example  2: Pore volume fraction  And average porosity diameter  Measure

The pore volume fraction and average pore diameter of the composite according to Example 1 and Comparative Example 1 were measured. 7, the pore volume fraction (dV / dD) of the composite of the three-dimensional structure according to Example 1 (A) is about 0.055 cm ³ g ^-1 nm ^-1 and the average pore diameter is about 4.5 nm. < / RTI > On the contrary, the pore volume fraction of Comparative Example 1 (B) is about 0.38 cm ³ g ^-1 nm ^-1 . As a result, it was found that the pore volume fraction of the composite of the three-dimensional structure obtained by complexing NaTi ₂ (PO ₄ ) ₃ with graphene was improved as compared with Comparative Example 1 containing no graphene.

Experimental Example  3: Reversibility evaluation

The reversibility was evaluated with Bio-logic VSP-300 using the cyclic voltammetry method to evaluate the reversibility of the reversed paper according to Example 3 above. The results are shown in FIG. 8, and the cyclic voltammetric curve shown in FIG. 8 shows that the redox peak was well observed. Therefore, when the complex of the three-dimensional structure according to the present invention is used as the negative electrode active material, it shows good reversibility in the oxidation-reduction reaction. Therefore, the three-dimensional structure complex according to the present invention is useful for the anode and the cathode of the sodium secondary battery. .

Experimental Example  4: Charging and discharging  Capacity assessment

Charge-discharge experiments were conducted using potentiostat / galvanostat (VMP2, Princeton Applied Research) to evaluate the charge / discharge capacities of the semiconductors prepared in Example 3 above. At this time, the voltage range was set to 1.5 to 3.0 V, and the charging / discharging rate was varied from 0.1 C to 50 C, and the results are shown in FIG. 9 is a graph showing the capacity of an electrode including a composite of a three-dimensional structure manufactured in Example 1 per unit weight of an electrode as a negative electrode active material. When the charge / discharge speed is 0.1 C, the charge / discharge capacity is about 133 mAh / g, which is a very good charge / discharge capacity. Furthermore, it was confirmed that the charge / discharge capacity was excellent because the charge / discharge capacity value was about 85 mAh / g even under the severe condition that the charge / discharge speed was 50 C.

In addition, an experiment was performed in which the electrode was repeatedly charged and discharged 200 times at a rate of 10 C, and the results are shown in FIG. FIG. 10 is a graph showing the discharge sustaining rate of an electrode. As shown in FIG. 10, it can be seen that an excellent discharge sustaining rate of 95% of the initial discharge capacity can be confirmed at a rate of 10 C even after 200 cycles.

FIG. 11 is a graph showing the change of the specific capacity according to the charging / discharging speed. Referring to FIG. 10, when the charging / discharging rate is in the range of 0.1 to 20 C, the charging / discharging capacity is higher than 120 mAh / g, It can be confirmed that the charge / discharge capacity recovery performance is excellent when the speed is changed to 50 C and then 0.1 C is applied.

Therefore, it was confirmed that the negative electrode active material including the composite of the three-dimensional structure according to the present invention can provide a sodium secondary battery having excellent electrochemical performance by significantly improving the charge / discharge capacity of the sodium secondary battery.

Claims (13)

M1-M2-PO phosphorous acid (M1 is an alkali metal and M2 is a transition metal); And
Forming a composite comprising graphene,
Wherein said composite forms a three-dimensional structure having a BET specific surface area in the range of 10 to 500 m < 2 > / g.
The method according to claim 1,
Wherein M1 comprises at least one alkali metal selected from the group consisting of Na, Li, K, Rb, Cs and Fr.
The method according to claim 1,
M2 is at least one transition metal selected from the group consisting of Ti, V, Sc, Cr, Mn, Fe, Co, Ni and Cu.
The method according to claim 1,
(Wherein M1 is an alkali metal, M2 is a transition metal Im) M1-M2-PO-based phosphate is _{NaTi 2 (PO 4) 3,} Li 3 V 2 (PO 4) 3, and 1 is selected from the group consisting of LiFePO ₄ Or more of the three-dimensional structure.
The method according to claim 1,
Wherein the complex of the three-dimensional structure has an average particle diameter in the range of 1 to 10 mu m.
The method according to claim 1,
Wherein the complex of the three-dimensional structure is in the form of spherical particles.
The method according to claim 1,
At least one of M1-M2-PO phosphorus (M1 is an alkali metal and M2 is a transition metal) and graphene is doped with at least one selected from the group consisting of nitrogen, phosphorus, sulfur and boron A composite of three-dimensional structures characterized.
The method according to claim 1,
Wherein the graphene is a porous structure having a plurality of holes formed therein.
9. The method of claim 8,
Wherein the average diameter of the holes is in the range of 0.5 to 10 nm.
The method according to claim 1,
The graphene includes a first graphene layer and a nth graphene layer,
and n is 2 or more.
11. The method of claim 10,
Wherein the nano-sized carbonaceous component is dispersed in at least one of interfaces between the first graphene layer and the nth graphene layer.
12. The method of claim 11,
Wherein the carbonaceous component comprises at least one member selected from the group consisting of graphite, carbon fiber, graphite, carbon black and carbon nanotube.
12. An anode active material comprising a composite of a three-dimensional structure according to any one of claims 1 to 12.

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