WO2015026110A1 - Method for preparing graphite-titanium oxide composite - Google Patents

Abstract

The present invention relates to a method for preparing a graphite-titanium oxide composite. The method for preparing a graphite-titanium oxide composite, according to the present invention, comprises the steps of: (S1) modifying the surface of graphite with benzyl alcohol or a cellulose-based material using a sol-gel technique; (S2) dispersing the graphite of which the surface is modified with benzyl alcohol or the cellulose-based material in a solvent, adding a titanium precursor, and then mixing same; and (S3) treating the mixture obtained from the step S2 with heat and growing a titanium-based oxide on the surface of the graphite. According to the method for preparing the graphite-titanium oxide in the present invention, by uniformly coating the surface of the graphite with titanium-based oxide, formation of a solid electrolyte interphase (SEI) film due to electrolyte decomposition, which occurs during charging and discharging, can be stabilized, thereby delaying collapsing of the structure of the graphite, and securing stable charge and discharge characteristics, which in turn enables securing of excellent life characteristics. Also, insertion of polar solvent molecules of the electrolyte other than lithium-ions on the graphite surface can be reduced thereby allowing improvement of rate control characteristics.

Description

Method for producing graphite-titanium oxide composite

The present invention relates to a method for producing a graphite-titanium oxide composite, and more particularly, to a method for producing a graphite-titanium oxide composite that can improve charge and discharge characteristics and rate-rate characteristics through a simple process.

Secondary batteries have been used to portable electronic devices, hybrid vehicles (HEV), and the like, and their use is expected to be extended to energy storage devices of electric vehicles (EVs) and power generation systems.

However, higher energy density, power density and stability are required to be used in such a large-scale device, and various studies are being conducted to satisfy this.

The carbon-based active material commercialized as a negative electrode active material of the existing secondary battery has a problem of high initial irreversible capacity and low thermal stability despite the reasonable price and excellent life characteristics, and improvement of this is essential.

In order to improve the thermal stability of the carbon-based active material, it is possible to improve the metal oxides such as aluminum oxide and zirconium oxide by coating the graphite surface.

Among them, titanium oxide is a material that does not generate stress during insertion and desorption of lithium. It is considered to have very good structural and thermal stability during charge and discharge.

Accordingly, the present inventors uniformly coat titanium-based oxides to improve the electrochemical properties of graphite, and improve the thermal and structural stability of the graphite, as well as the electrochemical life characteristics and rate-rate characteristics.

[Preceding technical literature]

[Patent Documents]

(Patent Document 1) Domestic Publication No. 10-1999-0044404

(Patent Document 2) Domestic Registered Patent No. 10-2007-0040853

In order to solve the problems of the prior art as described above, the present invention is a graphite-titanium oxide composite that can improve the thermal and structural stability of graphite and improve the electrochemical life characteristics and rate characteristics by uniformly coating the titanium oxide It is an object of the present invention to provide a method for producing the same.

Another object of the present invention is to provide a graphite-titanium oxide composite prepared by the above production method and a negative electrode active material of a lithium secondary battery comprising the same, and a lithium secondary battery comprising the same.

In order to achieve the above object, the present invention, the surface-modified graphite to benzyl alcohol or cellulose-based material using a sol-gel (S1); Dispersing the surface-modified graphite in the benzyl alcohol or the cellulose-based material in a solvent, and adding and adding a titanium precursor (S2); And heat treating the mixture obtained in the step S2 to grow a titanium oxide on the graphite surface (S3).

The solvent may be ethanol and distilled water or a mixture of ethanol and hydrogen peroxide.

NH ₄ OH or HNO ₃ may be added to the distilled water.

The weight ratio of ethanol and distilled water in the ethanol and distilled water mixture is preferably 5: 1 to 100: 1.

The weight ratio of ethanol and hydrogen peroxide in the ethanol and hydrogen peroxide mixture is preferably 5: 1 to 100: 1.

Preferably, 5 to 40 parts by weight of the titanium precursor is added to 100 parts by weight of the graphite in the step S2.

As the titanium precursor, titanium butoxide or titanium isopropoxide may be used.

The heat treatment is preferably performed for 2 to 5 hours at a temperature of 600 to 800 ℃ in Ar atmosphere.

After the step S2 may further comprise the step of hydrothermally synthesized by mixing the lithium precursor to the mixture obtained in the step S2.

The hydrothermal synthesis is preferably performed for 10 to 12 hours at a temperature of 80 to 180 ℃.

The amount of the lithium precursor added is preferably 10 to 80 parts by weight based on 100 parts by weight of graphite.

Lithium precursor, lithium acetate dihydrate and lithium nitrate may be used as the lithium precursor.

The present invention also provides a graphite-titanium oxide composite prepared according to the above production method.

The present invention also provides a negative electrode active material of a secondary battery including the graphite-titanium oxide composite.

The present invention also provides a secondary battery comprising the negative electrode active material.

According to the method of manufacturing the graphite-titanium oxide composite of the present invention, by uniformly coating the titanium oxide on the graphite surface to stabilize the formation of SEI film (Solid electrolyte interphase) by the decomposition of the electrolyte generated during charging and discharging to collapse the structure of the graphite Delay and through this, it is possible to secure a stable charge and discharge characteristics and thereby excellent life characteristics.

In addition, it is also possible to improve the rate characteristic by reducing the insertion of polar solvent molecules of the electrolyte in addition to lithium ions on the graphite surface.

In addition, it is expected to easily commercialize by producing a graphite-titanium oxide composite through a simple process.

1 is an X-ray diffraction graph of graphite and the graphite-lithium titanium oxide composite of Example 1. FIG.

2 is an X-ray diffraction analysis graph of graphite and the graphite-titanium oxide composite of Example 2. FIG.

3 is a scanning electron micrograph of graphite.

4 is a scanning electron micrograph of a graphite-lithium titanium oxide composite (titanium precursor: 10%).

5 is a scanning electron micrograph of a graphite-lithium titanium oxide composite (titanium precursor: 20%).

FIG. 6 is a scanning electron micrograph of a graphite-titanium oxide composite (titanium precursor: 10%).

7 is a scanning electron micrograph of a graphite-titanium oxide composite (titanium precursor: 20%).

8 is a graph showing discharge capacity and efficiency of graphite and graphite-lithium titanium oxide composite of Example 1. FIG.

9 is a graph showing discharge capacity and efficiency of graphite and graphite-titanium oxide composite of Example 2. FIG.

10 is a graph showing the measurement results of charge and discharge rate characteristic of graphite.

11 is a graph showing the measurement results of charge and discharge rate characteristic of graphite-lithium titanium oxide composite (titanium precursor: 10%).

12 is a graph showing measurement results of charge / discharge rate characteristic of graphite-lithium titanium oxide composite (titanium precursor: 20%).

FIG. 13 is a graph showing measurement results of charge and discharge rate characteristic of a graphite-titanium oxide composite (titanium precursor: 10%).

14 is a graph showing measurement results of charge and discharge rate characteristic of a graphite-titanium oxide composite (titanium precursor: 20%).

15 is a photograph of TiO ₂ hydrolyzed in the state of lowering pH by adding HNO ₃ to distilled water.

FIG. 16 is a photograph of TiO ₂ hydrolyzed in a state of increasing pH by adding NH ₄ OH to distilled water.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail. In the following description of the present invention, detailed descriptions of related well-known configurations or functions may be omitted.

The terms or words used in the specification and claims are not to be construed as being limited to conventional or dictionary meanings, but should be construed as meanings and concepts corresponding to the technical matters of the present invention.

The embodiments described in the specification and the configuration shown in the drawings are preferred embodiments of the present invention, and do not represent all of the technical idea of the present invention, various equivalents and modifications that can replace them at the time of the present application are There may be.

The present invention is a method for producing a graphite-titanium oxide composite by uniformly coating the titanium oxide through heat treatment after distributing the titanium precursor on the graphite surface through the sol-gel (hydro-gel) method and hydrothermal (hydrothermal) It is about.

The graphite-titanium oxide composite manufacturing method of the present invention comprises the steps of dispersing graphite in benzyl alcohol or cellulose-based material and then filtering the surface to modify the graphite to benzyl alcohol or cellulose-based material (S1); Dispersing the graphite surface-modified with benzyl alcohol or a cellulose-based material in a solvent, adding a titanium precursor, and then mixing (S2); And growing a titanium oxide on the graphite surface by heat-treating the mixture obtained in the step S2 (S4).

Hereinafter, the method for preparing the graphite-titanium oxide composite of the present invention will be described in detail step by step.

First, graphite is dispersed in benzyl alcohol or a cellulose-based material, which is a hydrophilic surfactant, and then filtered to surface-modify the graphite with benzyl alcohol or a cellulose-based material (S1).

Benzyl alcohol and cellulosic materials modify the graphite surface hydrophilicly so that the nucleation of titanium oxide is well formed on the hydrophobic graphite surface. This allows the titanium oxide to be uniformly coated on the graphite surface.

Here, benzyl alcohol has a benzene ring structure, the benzene ring structure has a sp2 hybrid structure. Since this structure is planar, the base surface of graphite and van der Waals attraction can be bonded, and the -OH group opposite to the benzene ring can form a covalent bond with Ti.

When dispersing graphite in the benzyl alcohol or cellulose-based material, graphite is preferably added in an amount of 1 to 10 parts by weight based on 100 parts by weight of benzyl alcohol or cellulose-based material. However, the present invention is not limited thereto.

If the amount of graphite exceeds the upper limit of the above range, the dispersibility is not good and uniform surface modification is not possible. If the amount is less than the lower limit, the uniform surface modification is not possible due to excessive benzyl alcohol and cellulose-based materials. Not desirable

Next, the graphite surface-modified with benzyl alcohol or cellulose-based material is dispersed in a solvent and mixed after adding a titanium precursor (S2).

The solvent may be a mixture of ethanol and distilled water or a mixture of ethanol and hydrogen peroxide.

In the mixed solution of ethanol and distilled water, the weight ratio of ethanol and distilled water is preferably 5: 1 to 100: 1. However, the present invention is not limited thereto.

When the weight ratio of ethanol in the mixture of ethanol and distilled water exceeds the upper limit of the range, there is a problem that the hydrolysis time of titanium is long or complete hydrolysis does not occur. It is not preferable because there is a problem that does not occur uniform coating.

The weight ratio of the ethanol and hydrogen peroxide is preferably 5: 1 to 100: 1. However, the present invention is not limited thereto.

When the weight ratio of ethanol in the mixture of ethanol and hydrogen peroxide exceeds the upper limit of the range, there is a problem that the hydrolysis time of titanium is long or complete hydrolysis does not occur. It is not preferable because there is a problem that does not occur uniform coating.

Here, NH ₄ OH or HNO ₃ may be added to the distilled water. NH ₄ OH or HNO ₃ added to the distilled water can control the pH of the reactant to more easily control the formation and thickness of the TiO 2 coating layer on the graphite surface (see FIGS. 15 and 16).

In addition, the amount of the titanium precursor added to 100 parts by weight of graphite in the step S2 is preferably 5 to 40 parts by weight. However, the present invention is not limited thereto.

If the addition amount of the titanium precursor exceeds the upper limit of the range there is a problem that the uncoated titanium residue is generated, if the lower limit of the range may cause the uncoated portion on the surface of the graphite particles may occur It is not desirable to have.

In addition, the titanium precursor may be used alone or in combination, for example, titanium butoxide, titanium isopropoxide and the like.

Next, by heating the mixture obtained in the step S2 to grow a titanium oxide on the graphite surface (S3).

The heat treatment is preferably performed for 2 to 5 hours at a temperature of 600 to 800 ℃ in Ar atmosphere.

If the heat treatment temperature exceeds the upper limit of the above range, there is a problem that agglomeration of particles occurs. If the heat treatment temperature is lower than the lower limit, there is a problem that the crystallinity of the titanium oxide is low, which is not preferable.

 In addition, when the heat treatment time exceeds the upper limit of the above range, there is a problem that agglomeration occurs, and when the heat treatment time is lower than the lower limit, there is a problem that the crystallinity of the titanium oxide is low, which is not preferable.

Through the above process, it is possible to prepare a graphite-titanium oxide composite in which a titanium-based oxide is uniformly coated on the graphite surface.

According to the method of manufacturing the graphite-titanium oxide composite of the present invention, by uniformly coating the titanium oxide on the graphite surface to stabilize the formation of SEI film (Solid electrolyte interphase) by the decomposition of the electrolyte generated during charging and discharging to collapse the structure of the graphite Can be delayed.

Through this, it is possible to secure stable charge and discharge characteristics and thereby excellent life characteristics.

In addition, it is also possible to improve the rate characteristic by reducing the insertion of polar solvent molecules of the electrolyte in addition to lithium ions on the graphite surface.

In addition, the graphite-titanium oxide composite manufacturing method of the present invention may further comprise a step of hydrothermally synthesized by mixing a lithium precursor to the mixture obtained in the step S2 after the step S2.

Hydrothermal synthesis by addition of a lithium precursor can produce a graphite-lithium titanium oxide composite having further improved electrochemical life and rate-limiting properties.

The hydrothermal synthesis is preferably performed for 10 to 12 hours at a temperature of 80 to 180 ℃.

If the temperature of the hydrothermal synthesis exceeds the upper limit of the above range, there is a problem in that the titanium is separated from the graphite, and if it falls below the lower limit of the above range, there is a problem that the lithium precursor does not combine with the titanium is not preferable.

 In addition, when the time of hydrothermal synthesis exceeds the upper limit of the above range, the particle may be deformed. When the hydrothermal synthesis time is lower than the lower limit of the above range, the lithium precursor is undesirably bound with titanium.

Here, the amount of the lithium precursor added is preferably 10 to 80 parts by weight relative to 100 parts by weight of graphite. However, the present invention is not limited thereto.

When the amount of the lithium precursor added exceeds the upper limit of the range, there is a problem in that a phase that is excessive lithium appears. When the lithium precursor is less than the lower limit, two phases appear, such as lithium titanium oxide and titanium oxide, to show lithium titanium oxide. It is not desirable because there is a problem that cannot be obtained everyday.

On the other hand, the lithium precursor, for example, lithium hydroxide, lithium acetate dihydrate and lithium nitrate may be used alone or in combination.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and it will be apparent to those skilled in the art that various changes and modifications can be made within the scope and spirit of the present invention. It is natural that such variations and modifications fall within the scope of the appended claims.

Example 1 Preparation of Graphite-Lithium Titanium Oxide (Li ₄ Ti ₅ O ₁₂ ) Composite

First, graphite is dispersed in benzyl alcohol and then filtered to obtain graphite having a surface treatment. Thereafter, the mixture was added to ethanol and distilled water, and then uniformly dispersed. Titanium precursor was added, stirred, and hydrolyzed.

Then, the graphite-titanium oxide powder and the lithium hydroxide monohydrate solution prepared above were put in a Teflon container and hydrothermally synthesized at 80 ° C. for 10 hours.

The mixture prepared through hydrothermal synthesis was heat treated at 600 ° C. for 2 hours in an Ar atmosphere to complete a graphite-lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) composite.

Example 2 Preparation of Graphite Titanium Oxide (TiO ₂ ) Composite

In the method of manufacturing the graphite-lithium titanium oxide (Li ₄ Ti ₅ O ₁₂ ) composite of Example 1 to prepare a graphite titanium oxide (TiO ₂ ) composite by heat treatment immediately without proceeding the hydrothermal synthesis step by adding a lithium precursor It was.

Experimental Example X-ray Diffraction Analysis

In order to analyze the structure of the graphite- (lithium) titanium oxide composites prepared in Examples 1 and 2, X-ray diffraction analysis with graphite particles as a control is shown in FIGS. 1 and 2.

As can be seen in Figures 1 and 2, a characteristic peak of graphite appeared, and the graphite- (lithium) titanium-based oxide composite of the present invention was also characteristic at an angle of 2 theta (θ) such as graphite. Peaks appeared. In addition, as the titanium precursor ratio increases, the peaks corresponding to Li ₄ Ti ₅ O ₁₂ and TiO ₂ appeared.

From the above results, it can be seen that the graphite- (lithium) titanium oxide composite of the present invention has the same crystal structure as graphite.

Experimental Example Scanning Electron Microscope

Scanning electron microscope analysis was performed to analyze the images of the graphite- (lithium) titanium oxide composites prepared in Examples 1 and 2, and are shown in FIGS. 3 to 7.

As can be seen in Figures 3-7, it was confirmed that the surface of the graphite is uniformly coated with (lithium) titanium oxide, and as the proportion of the precursor increases, the nuclear growth of (lithium) titanium oxide is developed on the surface. It is consistent with the result of X-ray diffraction analysis.

Comparative Example Analysis of Charge and Discharge Curve and Coulomb Efficiency

The half-cells prepared by using the graphite- (lithium) titanium-based oxide composites prepared in Examples 1 and 2 as negative electrode active materials were charged and discharged at 0.01 C to 1.5 V at C / 10, respectively. The measurement results are shown in FIGS. 8 and 9. In addition, charge and discharge were performed at C / 10, C / 5, C / 2, 1C, and 2C at 0.01V to 3V, and the measurement results of the charge and discharge characteristics are shown in FIGS. 10 to 14. As can be seen in Figures 8 and 9, the graphite shows a low capacity close to 230 mAh / g at the first discharge, but the graphite- (lithium) titanium-based oxide composite prepared in the preparation example than the graphite at the first discharge It can be seen that the capacity is maintained as it shows a high capacity and then repeatedly charge and discharge.

As can be seen in Figures 10 to 14, in the case of graphite, the capacity (capacity) is significantly reduced as it increases from C / 10 to 2C, whereas the graphite- (lithium) titanium oxide composite of the present invention has a charge and discharge rate The decrease in capacity with increasing decreases with respect to graphite.

From the above results, the graphite- (lithium) titanium-based oxide composite of the present invention has improved electrochemical properties by the SEI film formed more stably than the control graphite.

Claims (15)

Surface modifying graphite with benzyl alcohol or a cellulose-based material by using a sol-gel method (S1); Dispersing the surface-modified graphite in the benzyl alcohol or the cellulose-based material in a solvent, and adding and adding a titanium precursor (S2); And Heat treating the mixture obtained in the step S2 to grow a titanium oxide on the graphite surface (S3); a method of manufacturing a graphite-titanium oxide composite, comprising: a. The method of claim 1, The solvent is a method for producing a graphite-titanium oxide composite, characterized in that the mixture of ethanol and distilled water or ethanol and hydrogen peroxide. The method of claim 2, Method for producing a graphite-titanium oxide composite, characterized in that NH ₄ OH or HNO ₃ is added to the distilled water. The method of claim 2, Method for producing a graphite-titanium oxide composite, characterized in that the weight ratio of ethanol and distilled water in the mixture of ethanol and distilled water is 5: 1 to 100: 1. The method of claim 2, Method for producing a graphite-titanium oxide composite, characterized in that the weight ratio of ethanol and hydrogen peroxide in the ethanol and hydrogen peroxide mixed solution is 5: 1 to 100: 1. The method of claim 1, Method of producing a graphite-titanium oxide composite, characterized in that 5 to 40 parts by weight of the titanium precursor is added to 100 parts by weight of graphite in the step S2. The method of claim 1, The titanium precursor is a titanium-butoxide or titanium isopropoxide, characterized in that the manufacturing method of graphite-titanium oxide composite. The method of claim 1, The heat treatment is a method for producing a graphite-titanium oxide composite, characterized in that for 2 to 5 hours at a temperature of 600 to 800 ℃ in an Ar atmosphere. The method of claim 1, Method of producing a graphite-titanium oxide composite further comprising the step of hydrothermally synthesized by mixing the lithium precursor to the mixture obtained in the step S2 after the step S2. The method of claim 9, The hydrothermal synthesis is a method for producing a graphite-titanium oxide composite, characterized in that carried out for 10 to 12 hours at a temperature of 80 to 180 ℃. The method of claim 9, The amount of the lithium precursor added is 10 to 80 parts by weight based on 100 parts by weight of graphite, the method for producing a graphite-titanium oxide composite. The method of claim 9, The lithium precursor is a lithium hydroxide, lithium acetate dihydrate and lithium nitrate manufacturing method of the graphite-titanium oxide composite. Graphite-titanium oxide composite prepared according to the method of claim 1 to claim 12. A negative active material of a secondary battery comprising the graphite-titanium oxide composite of claim 13. A secondary battery comprising the anode active material of claim 14.

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