KR20040058635A - Negative active material for lithium secondary battery and method of preparing same - Google Patents

Abstract

PURPOSE: Provided is an effective and easy preparation method of a negative electrode active material in which nano-sized metal particles in an amorphous form is present, by mixing the nano-sized metal particles with carbon material in an efficient and convenient manner. CONSTITUTION: The preparation method of a negative electrode active material comprises: preparing a positive electrode for arc discharge by filling a hollow carbon rod(2) with a metal powder(1); carrying out arc discharge with the positive electrode for arc discharge and a negative electrode that is a carbon rod to accumulate the nano-sized amorphous metal and nano-sized graphite particles from the positive electrode to the negative electrode; and recovering the metal and graphite particles from the surface of the negative electrode.

Description

Negative active material for lithium secondary battery and manufacturing method thereof {NEGATIVE ACTIVE MATERIAL FOR LITHIUM SECONDARY BATTERY AND METHOD OF PREPARING SAME}

[Industrial use]

The present invention relates to a negative electrode active material for a lithium secondary battery and a method for manufacturing the same, and more particularly, to a negative electrode active material for a lithium secondary battery in which a metal has a nano size and is present in an amorphous state, and a method for manufacturing the same.

[Prior art]

At present, the theoretical charge and discharge capacity of graphite, which is mainly used as a negative electrode active material of a lithium secondary battery, is only 372 mAh / g, which is not suitable for next generation mobile communication devices, notebook computers, and electric vehicles. Therefore, in order to apply a lithium secondary battery in this field, a new negative electrode active material having a high capacity is required. Known as such a material is a composite of lithium and alloyable metal powder (about 1 μm in diameter) and a carbon material. When the material is used as a negative electrode active material, the discharge capacity of the negative electrode can be increased beyond the theoretical discharge capacity of graphite. Can be.

However, during charging and discharging, in the process of forming an alloy with Li, an excessive volume expansion and contraction is repeated, resulting in a problem that the metal is broken. As a result, the deterioration of characteristics becomes worse as the number of charge and discharge cycles increases. Life is shortened.

In order to suppress this problem, first, the size of the metal particles should be very small, such as nano size, and second, the metal should be in an amorphous state. Therefore, many studies have been conducted to reduce the particle size of the metal powder by mixing the metal powder and the carbon material by a ball milling method, but it is not possible to obtain nano metal particles having a size of 100 nm or less. Rather, it was very difficult to exist in an amorphous state.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing a negative electrode active material for a lithium secondary battery, which can effectively and easily mix metal particles in a nano-sized amorphous state with a carbon material.

Another object of the present invention to provide a negative electrode active material for a lithium secondary battery prepared by the above manufacturing method.

1 is a view schematically showing a metal-filled carbon rod structure used in the arc discharge of the present invention.

FIG. 2 is a left side view of the carbon rod shown in FIG. 1. FIG.

Figure 3 is a SEM photograph of the negative electrode active material for a lithium secondary battery prepared according to an embodiment of the present invention.

Figure 4 is an EDS mapping picture of the negative electrode active material for a lithium secondary battery prepared according to an embodiment of the present invention.

5 is a graph showing the Raman spectral intensity of the negative active material for a lithium secondary battery of the present invention.

6 is a graph showing X-ray diffraction peaks of the negative active material for a lithium secondary battery of the present invention.

7 is a graph showing the initial charge and discharge capacity of the lithium half battery prepared using the negative electrode active material of Example 1 of the present invention and the lithium half battery prepared using the negative electrode active material of Comparative Example.

In order to achieve the above object, the present invention is to fill the carbon powder with a central hole of the metal powder to prepare an anode for arc discharge; Arc-discharging using the arc discharge anode and the carbon rod cathode to move the nano-sized amorphous metal and the nano-sized graphite particles from the anode to the cathode to be stacked on the cathode surface; The negative electrode active material for lithium secondary batteries including the process of obtaining a metal and graphite particle from the said negative electrode surface is manufactured.

The invention also provides amorphous metal nanoparticles prepared by the above method; And it provides a negative electrode active material for a lithium secondary battery containing carbon.

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

The present invention relates to a negative electrode active material to which a metal is added in order to increase the theoretical charge / discharge capacity of graphite which is generally used as a negative electrode active material of a lithium secondary battery. In the negative electrode active material, the metal has a particle size of nano size and is in an amorphous state, so that the metal may be broken due to excessive volume expansion and contraction in the process of forming an alloy with lithium. In the present invention, for this purpose, an arc discharge process has been introduced.

In the method for producing the negative electrode active material of the present invention, first, as shown in Fig. 1, a hole is formed in the carbon rod 2 for arc discharge, and then the metal powder 1 is filled in the hole to manufacture an anode for arc discharge. The left side view of the arc discharge carbon rod shown in FIG. 1 is shown in FIG. 2, and as can be seen from FIG. 2, the manufactured arc discharge anode is filled with metal powder 1 in the center of the carbon rod 2.

As the metal, any metal capable of alloying with lithium may be used, and representative examples include Al, Mg, Sn, Si, Sb, Ge, Pb, Ag, Au, Zn, In, Cd, Bi, Pt, Pd, Ca At least one of, B, Te, P, S, Se or As can be used.

Another carbon rod is prepared and used as the cathode for arc discharge. The carbon rods used as the positive electrode and the negative electrode use carbon rods having different diameters, and the carbon rods used as the positive electrode have a diameter of about 6 to 8 mm, and the carbon rods used as the negative electrode have a diameter of about 10 to 12 mm. Use it. The hole formed in the anode is preferably about 3 to 4mm in diameter.

As the carbon rods, it is preferable to use graphite rods having excellent conductivity.

The arc discharge is performed by applying a voltage of DC 20 to 30 V under a pressure of 100 to 500 torr while maintaining a constant distance between the anode and the cathode for arc discharge. When the arc discharge starts, the distance between the two electrodes is kept constant, in order to keep the arc constant. Usually, the distance between the electrodes is kept within 1 mm, the current value at this time is 50 to 100 A. In response to such arc discharge, metal particles are melted and quenched in the process of being discharged from the anode by a very high temperature (~ 5000K) arc plasma and accumulating on the surface of the cathode maintained by the cooling water. It is transformed into amorphous nanoparticles. At this time, carbon particles are also released from the carbon rods, and nano-size carbon particles are also accumulated on the negative electrode surface. The metal particles emitted from the anode are in an amorphous form, the size of which has a nano size of 30 to 50 nm, and the carbon particles also have a nano size.

Metal and carbon particles accumulated on the surface of the negative electrode are collected and used as a negative electrode active material for a lithium secondary battery.

The above-described manufacturing method of the present invention can produce two or more kinds of nanoparticles at the same time, and has a great effect in the production of a composite of a carbon material and a low affinity metal. In particular, it is possible to solve the micronization and amorphousization of metals, which are considered to be a conventional difficulty, in a single process. In addition, this method has a high application value in the field of composite synthesis of carbon and metal particles, such as a negative electrode material of a lithium secondary battery, and has the advantage of designing a desired capacity by controlling the content of metal particles.

The negative electrode active material for a lithium secondary battery manufactured by the above-described method is a carbon-metal composite in which nano metal particles having a size of 50 nm or less are uniformly distributed in a carbon material. Since the temperature is higher than the melting point of the metal, the metal nanoparticles are formed in the amorphous state because they have a quenching effect of rapidly decreasing the temperature when they are accumulated in the cathode which is kept at a low temperature state by the cooling water.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only one preferred embodiment of the present invention and the present invention is not limited to the following examples.

(Example 1)

A graphite rod having a diameter of about 6 mm was drilled to have a diameter of about 3 mm, and a Si powder was filled in the hole to prepare an anode for arc discharge. A graphite rod having a diameter of about 10 mm was prepared and used as an anode for arc discharge. After arranging the positive electrode and the negative electrode at intervals of about 1 mm, arc discharge was performed by applying a DC voltage of 30 V under 300 torr pressure. As a result of arc discharge, Si and graphite powder accumulated on the said negative electrode surface were collected, and it was set as the negative electrode active material for lithium secondary batteries.

A SEM photograph of the negative electrode active material prepared by the method of Example 1 is shown in FIG. 3. As shown in FIG. 3, it can be seen that the negative active material of Example 1 is composed of nanoparticles having a diameter of about 50 nm.

In addition, EDS (electron dispersion spectroscope) mapping of the negative electrode active material is shown in FIG. 4. In FIG. 4, since the bright visible part is a part in which Si is present, it can be seen that the Si nanoparticles are uniformly distributed in the negative electrode active material prepared from FIG. 4. The component ratio was determined from the EDS results, and the resulting negative active material contained 75%, 20%, and 5% of C, Si, and O, respectively. Among them, O was exposed to air before the EDS measurement after the experiment. It is thought to be.

Raman spectral intensity graph of the negative electrode active material of Example 1 is shown in Figure 5 and X-ray diffraction peak intensity graph in Figure 6, respectively. Referring to FIG. Raman spectral intensity graph of Figure 5, the peak G- (~1600cm ^-1), D- peak (~1300cm ^-1) in addition to a strong Si peak (~500cm ^-1) indicated by the carbon-SiC weak peaks were observed . In addition, the Si peak did not appear in the X-ray diffraction peak intensity graph of FIG. 6. Raman peaks of the crystalline and the amorphous Si are each appear at 490cm ^-1 and 520cm ^-1, in the present embodiment, because a peak is observed at 500 cm ^-1, the produced Si can be seen that near to the amorphous form. Accordingly, it can be seen from the results of FIGS. 5 and 6 that Si is present in the prepared anode active material, and that Si is in an amorphous form.

In addition, a lithium half battery was manufactured by a conventional method using the negative electrode active material of Example 1, and the produced battery was charged and discharged at 0.2C, and the initial charge and discharge capacity is shown in FIG. 7. 7 shows a charge and discharge capacity of a battery manufactured using a negative electrode active material prepared by ball milling Si and graphite powder as a comparative example. As shown in FIG. 7, the initial charge and discharge capacities of Example 1 and Comparative Examples were 676/527 mAh / g and 594/455 mAh / g, respectively. Thus, the negative electrode active material of Example 1 exhibited a high charge and discharge capacity. It can be seen that a battery can be provided.

The production method of the present invention can effectively produce an anode active material in which amorphous metal particles are present in nano size.

Claims (10)

Filling a carbon rod with a center hole into a metal powder to prepare an anode for arc discharge; Arc-discharging using the arc discharge anode and the carbon rod cathode to move the nano-sized amorphous metal and the nano-sized graphite particles from the anode to the cathode to be stacked on the cathode surface; Obtaining metal and graphite particles from the cathode surface The manufacturing method of the negative electrode active material for lithium secondary batteries containing a process. The method of claim 1, wherein the metal is a metal capable of reacting with lithium. The method of claim 2, wherein the metal is Al, Mg, Sn, Si, Sb, Ge, Pb, Ag, Au, Zn, In, Cd, Bi, Pt, Pd, Ca, B, Te, P, S, Se And As is selected from the group consisting of a method for producing a negative electrode active material for a lithium secondary battery. The method of claim 1, wherein the arc discharge is applied under a DC voltage of 20 to 30 V, and is performed under a pressure of 100 to 500 torr. The method of claim 1, wherein the nano-sized metal particles have a size of 30 to 50 nm. The method of claim 1, wherein the carbon rod is formed of crystalline carbon or amorphous carbon. Amorphous metal nanoparticles; And A negative electrode active material for lithium secondary battery containing carbon. The method of claim 7, wherein the metal is Al, Mg, Sn, Si, Sb, Ge, Pb, Ag, Au, Zn, In, Cd, Bi, Pt, Pd, Ca, B, Te, P, S, Se And as negative electrode active material for a lithium secondary battery selected from the group consisting of. The negative active material of claim 7, wherein the carbon is crystalline carbon or amorphous carbon. The negative active material of claim 7, wherein the metal particles have a size of 30 to 50 nm.