KR20160053029A - Preparing method of anode active materials for Li-ion secondary battery - Google Patents

Abstract

The present invention provides a method for preparing negative electrode active materials for a lithium-ion secondary battery, the method comprising the steps of: placing a titanium oxide in a furnace, and removing air inside the furnace by introducing nitrogen gas into the furnace (first step); coating surfaces of particles of the titanium oxide with carbon by introducing hydrocarbon gas into the furnace and heating the furnace (second step); and acquiring negative electrode active materials composed of titanium oxide cores and carbon shells by cooling the furnace (third step). Therefore, electric conductivity can be considerably increased by applying carbon having high conductivity and including a titanium oxide having low electric conductivity due to characteristics of a semiconductor; negative electrode active materials having low corrosivity can be manufactured even when a carbon-based material having considerably high corrosivity is included; and per-volume capacity is improved and thus energy density is increased because a conductive agent is not required for manufacturing of a shell for a lithium-ion battery.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for preparing an anode active material for a lithium ion battery,

The present invention relates to an electrode active material for a lithium ion battery, and more particularly, to a method for manufacturing a negative electrode active material having a core-shell structure.

A lithium secondary battery is an energy storage device in which lithium moves from a cathode to an anode during a discharge process and lithium ions move from an anode to a cathode during charging to store electric energy in the battery. Compared to other cells, the degree of self-discharge with a high energy density is small, and it is used in various projects. Components of the lithium secondary battery can be divided into an anode, a cathode, an electrolyte, and a separator. In the early lithium secondary battery, lithium metal was used as an anode active material. However, lithium metal was replaced with a carbon-based material such as graphite due to repeated safety of charging and discharging. The carbonaceous anode active material has a similar electrochemical reaction potential with lithium metal and is widely used in the development of anode active materials because of the ability to continuously charge the battery due to a small change in crystal structure during the continuous removal of lithium ions .

Carbon-based materials are widely used as an anode active material. However, when graphite is used, there is a problem that the cycle is rapidly lowered due to corrosion.

In order to solve such a problem, Korean Patent Laid-Open Publication No. 2012-0139631 discloses an electrode active material comprising a core layer which is a metal or a metalloid and an amorphous carbon layer which is coated on the surface of the core layer. Oxide is a material having a semiconducting property and is not high in electric conductivity. For this reason, it has a low lithium diffusion coefficient in discharge process, and there is a tendency that the lifetime of the battery is reduced, thereby increasing the electric conductivity and increasing the energy density. This increased new anode active material is still needed.

An object of the present invention is to provide an anode active material which overcomes the fact that a carbon-based material is extremely vulnerable to corrosiveness by increasing the electrical conductivity of a composite containing titanium oxide, which is frequently used as a conventional anode active material.

In order to accomplish the above object, the present invention provides a method of manufacturing a semiconductor device, comprising: (a) a step of disposing titanium oxide in a furnace and introducing nitrogen gas to remove air in the furnace; Adding hydrocarbon gas to the furnace and heating it to coat carbon on the surface of titanium oxide particles (second step); And cooling the furnace to obtain a negative electrode active material composed of a titanium oxide core and a carbon shell (third step).

The nitrogen gas may be introduced for 15 to 20 minutes.

The hydrocarbon gas may be any one selected from the group consisting of methane, ethane, and propane.

In the second step, the hydrocarbon gas may be introduced at a flow rate of 100 to 200 mL / min and heated at 800 to 850 DEG C for 3 to 4 hours.

According to another aspect of the present invention, there is provided a negative electrode comprising a negative active material prepared by the above method.

According to the method for manufacturing an anode active material according to the present invention, it is possible to increase the electrical conductivity by covering the carbon having high electrical conductivity while containing titanium oxide having low electrical conductivity due to the semiconductor property, It is possible to manufacture a negative electrode active material having low corrosion resistance. Since a conductive material is not required in manufacturing a cell for a lithium ion battery, the capacity per volume is increased and the energy density is increased.

1 is a schematic view of a titanium oxide-carbon composite produced by a method of manufacturing an anode active material according to an embodiment of the present invention.
FIG. 2 is a scanning electron microscope image of a titanium oxide-carbon composite produced by the method of manufacturing an anode active material according to an embodiment of the present invention.
FIG. 3 is a field emission transmission electron microscope image of a negative electrode active material prepared according to the method of manufacturing an anode active material according to an embodiment of the present invention.
4 is a graph showing charge / discharge data of a negative electrode active material manufactured according to the method of manufacturing a negative active material according to an embodiment of the present invention.
FIG. 5 is a graph comparing energy densities per unit volume of a negative electrode prepared by the method of manufacturing an anode active material according to an embodiment of the present invention.

The present inventors have been studying an anode active material used in a lithium ion battery. When titanium oxide is reacted in an atmosphere of methane gas as an active material, carbon is coated on the titanium powder to increase the electric conductivity. Therefore, The present inventors have completed the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings.

In the present invention, the titanium oxide is disposed in a furnace and nitrogen gas is introduced to remove air in the furnace (first step); Adding hydrocarbon gas to the furnace and heating it to coat carbon on the surface of titanium oxide particles (second step); And cooling the furnace to obtain a negative electrode active material composed of a titanium oxide core and a carbon shell (third step).

The titanium oxide is preferably titanium dioxide (TiO ₂ ). Titanium dioxide can be used as an active material in the production of the negative electrode active material, and can be structurally and chemically stable.

The nitrogen gas may be introduced for 15 to 20 minutes.

The nitrogen gas does not react with the titanium oxide as an inert gas, and can remove all the air from the tube in the furnace in which the titanium oxide is disposed.

When the time for injecting the nitrogen gas is less than 15 minutes, the air in the tube can not be completely removed. If the time is longer than 20 minutes, since the air is completely removed, unnecessary nitrogen gas is supplied to the reactor, Problems may arise.

In the second step, the hydrocarbon gas may be introduced at a flow rate of 100 to 200 mL / min and heated at 800 to 850 DEG C for 3 to 4 hours.

The hydrocarbon gas may be any one selected from the group consisting of methane, ethane, and propane.

The methane may coat carbon on the surface of the titanium oxide and the carbon may have a high electrical conductivity and may serve as a conductive agent without containing a conductive agent to increase the energy density when the anode active material is manufactured.

When the hydrocarbon gas is supplied at a flow rate of less than 100 mL / min, carbon may not be sufficiently supplied to the titanium oxide particles. When the flow rate exceeds 200 mL / min, unnecessary methane gas is supplied to increase the efficiency Can fall.

It can be confirmed that a carbon layer is formed on the titanium oxide surface when the hydrocarbon gas is introduced in the second step and heated at 800 to 850 ° C for 3 to 4 hours. If the conditions are different, A different carbon layer can be formed.

In the second step, the carbon layer is formed even when heated at 700 ° C or more for 1 hour or more. However, the carbon layer formed under the above conditions does not satisfy the optimum effect of the present invention in electrical conductivity and electrochemical evaluation results.

According to another aspect of the present invention, there is provided a negative electrode comprising a negative active material prepared by the above method.

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 to the following examples.

Example 1 Production of Titanium Oxide-Carbon Composite

1, nanoparticle complex

0.2 g of titanium dioxide (TiO ₂ , Degussa, P-25) was placed in a quartz boat and placed in a furnace tube. Nitrogen gas (N ₂ ), which is an inert gas, was supplied for 15 minutes to remove air in the tube. After the methane (CH ₄₎ while the gas flow rate to the flow rate of 200 mL / min, and heated to a furnace for 3 hours at 800 ℃. The heated furnace was cooled to room temperature and the titanium oxide-carbon composite thus prepared was obtained.

2. Manufacture of Li-ion battery

To make a lithium ion battery, a polyvinylidene fluoride (PVDF) was added to the titanium oxide-carbon composite, and N-methylpyrrolidione (NMP) was added to adjust the viscosity. Then, the mixture was evenly mixed with stirring, and coated on a copper foil having a thickness of 18 탆. The cathode was cut into 1.3272 cm wide and dried in an oven at 110 ° C for one day to prepare a cathode for a lithium ion battery (hereinafter, 'f-titanium oxide @ carbon').

Lithium foil (FMC Co.) was used as a counter electrode, and a mixture of ethylene carbonate (EC) and di-methyl carbonate (DMC) in a volume ratio of 1: 1 M lithium fluorophosphate (LiPF _6, Techno Semichem Co.) was dissolved and used.

≪ Comparative Example 1 > Preparation of a lithium ion battery containing a conductive agent

First, a negative electrode active material containing a conductive agent was prepared for electrochemical evaluation and analysis of a titanium oxide-carbon composite. First, 70 wt% of titanium dioxide (TiO ₂ ) is used as the active material, 10 wt% of carbon black (Ketjan Black) is used as the conductive material, and 20 wt% of polyvinylidene fluoride (PVDF) Respectively. The mixture was prepared by adding N-methyl-pyrrolidone (NMP) to prepare slurry.

The mixture was stirred again, coated on a copper foil of 18 μm, cut to a size of 1.3273 cm 2, and then dried in an oven at 110 ° C. to prepare a negative electrode for a lithium ion battery (hereinafter referred to as "C- ). The cell assembly proceeded in a glove box filled with a high concentration of argon gas and a lithium foil (FMC Co.) was used as a counter electrode. Examples of the electrolyte include ethylene carbonate (EC) and dimethyl carbonate (di-methyl carbonate (DMC)) dissolved in 1.1 M lithium fluoride phosphate (LiPF ₆ ) in a solvent mixed at a volume ratio of 1: 1.

≪ Experimental Example > Properties of titanium oxide-carbon composite

1. Form of titanium oxide-carbon composite

1 is a schematic view of a titanium oxide-carbon composite produced by a method of manufacturing an anode active material according to an embodiment of the present invention.

Fig. 1 (a) shows a case where a conductor is added, and Fig. 1 (b) shows a case where carbon is coated on a surface by introducing hydrocarbon gas into titanium oxide and heating the same.

It can be seen that the amount of the titanium oxide-carbon composite, which is the negative electrode active material, can be greatly increased when the conductive agent is not added under the influence of a bulky conductive agent in a limited cell environment, .

FIG. 2 is a scanning electron microscope (SEM, JEOL-6701F) image of a titanium oxide-carbon composite prepared by a method for producing an anode active material according to an embodiment of the present invention.

Figure 2 (a) shows a cross section of a typical copper foil with an average thickness of 17.93 [mu] m. FIG. 2 (b) is a cross-sectional view of a negative electrode active material prepared by the negative active material manufacturing method according to an embodiment of the present invention, and FIG. 2 (c) is an image of a cross section of a negative active material prepared by adding a conductive agent.

Referring to the drawing, the thickness of a typical copper foil was the thinnest, the thickness of the negative active material of f-titanium oxide @ carbon increased to 31.45 μm, and the thickness of the negative active material of c-titanium oxide @ carbon was 36.75 Lt; / RTI > The applied volume of the cell was calculated as the width of the cell (1.3272 cm ² ) × the thickness of the active material, the calculated volume of the active material was 0.00001795 cm ³ for f-titanium oxide @ carbon and the case of c-titanium oxide @ has been identified as 0.00002497 cm ³ showed that the volume of the negative electrode active material comprising the titanium oxide f- @ carbon decreased 39.1%.

FIG. 3 is a field emission transmission electron microscope (FE-TEM, Philips Tecnai F20) image of a negative electrode active material prepared according to the method of manufacturing an anode active material according to an embodiment of the present invention.

Referring to the drawing, after a negative active material containing f-titanium oxide @ carbon diluted with ethanol was dropped on a copper grid, the scale was observed at 200 kV. As a result, a scale having a thickness of 5 nm was observed, Lt; / RTI >

2. Electrochemical analysis

Charging and discharging tests were carried out using a negative electrode comprising the f-titanium oxide @ carbon and c-titanium oxide @ carbon prepared in Example 1 and Comparative Example 2 as a sample. The test was performed in the range of 1 to 3 V (V vs. Li / Li +).

4 is a graph showing charge / discharge data of a negative electrode active material manufactured according to the method of manufacturing a negative active material according to an embodiment of the present invention.

When the charge / discharge cycle is 100 mA / g, the flat region around 1.4 V appearing in the first cycle of each sample is the portion where lithium ion intercalation occurs on the rutile of titanium oxide. Referring to FIG. 4 (c), current values of 50 mA / g, 100 mA / g, 200 mA / g and 500 mA / g are applied to compare the capacities of high current values. In the case of the negative electrode active material containing f-titanium oxide @ carbon, it can be seen that the charge / discharge capacity is good even at a high current value. This is because the carbon shell surrounding the titanium oxide particles serves as a more effective conducting agent Respectively.

FIG. 5 is a graph comparing energy densities per unit volume of a negative electrode prepared by the method of manufacturing an anode active material according to an embodiment of the present invention.

Referring to FIG. 5A, capacity per weight is shown in FIG. 5A, and capacity per volume is shown in cycle in FIG. 5B. Comparing the capacities at 50 cycles, the capacity per weight was 1.2 times higher and the capacity per volume was 1.67 times higher. This means that it is capable of exhibiting high capacity with small volume in the application of volume-limited lithium ion batteries and also has a high energy density.

As described above, the present invention can produce a lithium ion battery having an excellent charge / discharge capacity by increasing the electric conductivity without containing a conductive agent for increasing the electric conductivity of the negative electrode active material. In particular, by introducing methane gas into the titanium oxide, confirming the optimum heating temperature and reaction time conditions at which the carbon contained in the methane gas can be coated on the surface of the titanium oxide particles, the negative electrode active material is prepared, The negative electrode exhibited a higher charge / discharge capacity than the negative electrode active material containing the conventional conductive material, and exhibited a higher energy density. Thus, the present invention was completed.

While the invention has been described with reference to a limited number of embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

Claims (5)

Placing titanium oxide in a furnace and introducing nitrogen gas to remove air in the furnace (first step);
Adding hydrocarbon gas to the furnace and heating it to coat carbon on the surface of titanium oxide particles (second step); And
And cooling the furnace to obtain a negative electrode active material composed of a titanium oxide core and a carbon shell (third step). The method of claim 1, wherein the nitrogen gas is introduced for 15 to 20 minutes. The method of claim 1, wherein the hydrocarbon gas is any one selected from the group consisting of methane, ethane, and propane. The method of claim 1, wherein the hydrocarbon gas is introduced at a flow rate of 100 to 200 mL / min in the second step and heated at 800 to 850 ° C for 3 to 4 hours. An anode comprising a negative electrode active material produced by the method of any one of claims 1 to 4.

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