KR101680459B1 - Method of manufacturing silicon oxifluoride as an anode material for lithium secondary batteries using solid state reaction and an anode and a lithium secondary battery comprising the anode - Google Patents

Abstract

The present invention relates to a method for producing a fluorine-treated silicon oxide which can be used as an anode active material of a lithium secondary battery through a simple heat treatment.
The method according to the present invention is characterized in that a precursor mixture comprising silicon or silicon oxide and an organic compound comprising fluorine is heated to produce a fluorinated silicon oxide of the formula:
[Chemical Formula]
SiOxFy (where 0x2, 0y2)

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon oxyfluoride for a negative electrode active material of a lithium secondary battery using a solid-phase reaction, a negative electrode, and a lithium secondary battery including the negative electrode, AND A LITHIUM SECONDARY BATTERY COMPRISING THE ANODE}

The present invention relates to a process for producing a silicon oxyfluoride which can be used as an anode active material of a lithium secondary battery, and more particularly, to a process for producing a silicon oxyfluoride which can be used as an anode active material of a lithium secondary battery by a solid- And a method for manufacturing the same.

In order to miniaturize and improve the performance of portable devices, and the need for secondary batteries in electric vehicles and large-capacity energy storage industries, the demand for improvement in performance of lithium secondary batteries is increasing.

Since the anode material is an important factor for determining the capacity characteristics of a lithium ion battery, studies are currently being conducted to develop a high capacity anode material that exceeds the capacity limit of carbon-based anode materials currently commercialized.

Especially, materials such as Si, Ge, and Sn, which correspond to quaternary semiconductor materials, are attracting attention as a new anode material because they have a high theoretical capacity. Silicon has a high capacity of 4,200 mAh / g, Has been attracting attention as a next-generation material to replace cathode materials.

However, in the case of silicon, the amount of lithium per silicon is up to 4.4, resulting in a high capacity as an alloy, which causes a volume change of more than about 300%. This volume change causes a problem that the active material silicon breaks as the charge and discharge continue, which leads to a decrease in the battery capacity.

On the other hand, silicon suboxide (SiO _x ), which is an active material, has an advantage in that the capacity reduction problem due to shrinkage due to volume change is less than that of conventional Si and Sn. The advantages of such an oxide-based cathode material have already been studied a lot, and representative examples thereof include transition metal oxide or SnO ₂ .

Specifically, when silicon oxide, which is an active material, is also reacted with lithium, lithium silicate (Li _x SiO _y ), lithium oxide (Li ₂ O), and the like are formed. Thereby effectively preventing the capacity reduction due to the volume expansion. In addition, SiO _x , which exists in a metastable state, has a low activation energy and is advantageous in alloying / dealloying with Li.

Non-Patent Document 1 reports that the cycle characteristics and the maximum capacity are determined according to the oxygen ratio in the silicon oxynitride. It has a capacity of 750 mAh / g for SiO _1.1 and an initial reversible capacity of 93% for the 25th cycle, 1700 mAh / g for Si _0.8 and 40% for the 25th cycle. That is, as the oxygen ratio decreases, the capacity increases but the cycle characteristics deteriorate.

Non-Patent Document 2 reports that Si / SiO _x core-shell type nanocomposite exhibits excellent performance, and the results of this study indicate that silicon oxide is an excellent material for accommodating high volume changes occurring during charging / discharging Explain that.

However, if lithium silicate (Li _x SiO _y ), lithium oxide (Li ₂ O), or the like, which is an inactive material, is formed in the first cycle, lithium is consumed in addition to the electrochemical reaction to cause irreversibility. This problem is understood as a trade-off relationship between irreversibility and lifetime characteristics depending on the content of oxygen. In addition, low electrical conductivity is one of the disadvantages of silicon oxides.

Non-Patent Documents 3 and 4 propose a method of forming a compound of a silicon oxide and a conductive material or depositing a carbon thin film on the surface in order to solve this problem.

Despite these improvements, further improvements in physical properties are still required for use of silicon oxide as an anode material.

1. J. Yang, Y. Takeda, N. Imanishi, C. Capiglia, J. Y. Xie, O. Yamanoto, Solid State Ionics 152 (2002) 125. 2. J. Wang, H. Zhao, J. He, C. Wang, J. Wang, J. Power Sources 196 (2011) 4811. 3. Y.-S. Hu, R. Demir-Cakan, M.-M. The titter, J.-O. Mller, R. Schlgl, M. Antonietti, J. Maier, Angew. Chem. 47 (2008) 1645. 4. T. Zhang, J. Gao, H.P. Zhang, L.C. Yang, Y.P. Wu, H.Q. Wu, Electrochem. Commun. 9 (2007) 886.

An object of the present invention is to provide a method capable of mass-synthesizing fluorine-bonded silicon oxides, which can be used as an anode material for a lithium secondary battery, at low cost by using a conventional commercialized device.

Another object of the present invention is to provide a negative electrode capable of solving a cycle irreversibility, which is a problem of a conventional silicon-based negative electrode, and a lithium secondary battery having the negative electrode.

According to an aspect of the present invention, there is provided a method of manufacturing a silicon oxide comprising a silicon precursor and a fluorine-containing organic compound by heating a precursor mixture comprising a silicon precursor and an organic compound containing fluorine, And a manufacturing method thereof.

[Chemical Formula]

SiO _x F _y (where 0 <x? 2, 0 <y? 2)

The silicon precursor, may be at least one selected from Si, SiO and SiO _2.

Carbon may be produced during the production of the fluorine-containing silicon oxide.

The fluorine-containing organic compound may be contained in the precursor mixture in an amount of 10 to 200% based on the weight of the silicon precursor.

The fluorine-containing organic compound may be polytetrafluoroethylene (PTFE) or polyfluorinated vinylidene (PVDF).

The heating temperature of the precursor mixture may be 500 to 800 ° C.

During the heat treatment, the fluorine-containing organic compound may exist in a form separated from the silicon precursor.

According to another aspect of the present invention, there is provided a lithium secondary battery comprising: a negative electrode for a lithium secondary battery comprising silicon oxide, a binder and a conductive powder synthesized by the above-described method; a negative electrode for the lithium secondary battery; Thereby providing a secondary battery.

The method of synthesizing silicon oxides according to the present invention is a method of synthesizing silicon oxy-oxide by incorporating a fluorine-containing organic compound into a precursor and then subjecting the silicon oxide fluoride (SiO _x F _y , 0 &lt; It is possible to mass-produce silicon oxide at low cost.

Further, according to the present invention, a negative electrode to which silicon oxide containing fluorine is applied has excellent cycle characteristics.

1 is an XRD pattern of SiO _x F _y prepared according to Example 1 of the present invention.
2 is an XRD pattern of SiO _x F _y prepared according to Example 2 of the present invention.
3 is an XRD pattern of SiO _x F _y prepared according to Example 3 of the present invention.
4 is a graph showing the results of evaluating the electrochemical behavior of a cathode using SiO _x F _y prepared according to Example 3 of the present invention.

Hereinafter, the present invention will be described in detail with reference to the preferred embodiments of the present invention with reference to the accompanying drawings.

It should also be understood that the terms or words used in the present specification and claims should not be construed in a conventional and dictionary sense and that the inventors may properly define the concept of the term to best describe its invention And should be construed in accordance with the principles and meanings and concepts consistent with the technical idea of the present invention. Therefore, the embodiments described in the present specification and the configurations shown in the drawings are merely preferred embodiments of the present invention and do not represent all the technical ideas of the present invention, so that various equivalents And the scope of the present invention is not limited to the following embodiments.

In the case of silicon, when heat treatment is performed to cause fluorination, fluorine is liable to simple bonding rather than chemical bonding. This simple combination disappears naturally over time. In addition, if the temperature rises above a certain temperature, it tends to become stable silicon dioxide (SiO ₂ ) in the air. Therefore, it is very difficult to synthesize silicon oxides having an amount of oxygen (SiO _x , x = 1) excellent in capacity and cycle characteristics and to simultaneously fluorinate them.

As a result of research and development to solve such problems, the inventors of the present invention have found that, in synthesizing a silicon oxide such as a fluorine-treated silicon oxide (SiO _x F _y ), a fluorine source and a reducing atmosphere An organic compound or an ammonium compound containing fluorine is used. By adjusting the ratio of the fluorine organic compound or the ammonium compound, it is possible to control the ratio of silicon to silicon oxide, which has a significant effect on the capacity, and to realize fluorine-oxygen-silicon chemical bonding by fluorination.

The fluorine-treated silicon oxide synthesis method according to the present invention is characterized in that a fluorine compound of the following formula is prepared by heating a silicon precursor and a precursor comprising an organic compound containing fluorine.

[Chemical Formula]

SiO _x F _y (where 0 <x? 2, 0 <y? 2)

The silicon precursor provides a silicon component to the composition of the formula and may be any material capable of synthesizing the formula material through heating or oxidation. Examples of the precursor include Si, SiO, SiO ₂ , Si (C ₂ H ₅ ) ₄ , Si (OC ₂ H ₅ ) _4, and the like can be used singly or in the form of a mixture.

The fluorine-containing organic compound is a compound containing carbon and hydrogen. Any compound that is easily decomposed at a solid-phase reaction temperature to provide fluorine while remaining decomposed without being involved in the synthesis reaction can be used have. For example, polytetrafluoroethylene (PTFE), polyfluorinated vinylidene (PVDF), or the like can be used.

The addition amount of the organic compound plays an important role in the production of the silicon oxide. The amount of the organic compound added is preferably in the range of 10 to 200% by weight based on the amount of the silicon precursor added. When the amount of the organic compound is less than 10% by weight, The amount is too small to achieve chemical bonding, and if it exceeds 200% by weight, the manufacturing cost becomes high. For sufficient fluorination, the addition amount of the organic compound is preferably 100 to 200%.

The precursor may be prepared by a pretreatment process including a mixing process of a raw material, a drying process, and a pelletizing process.

In the mixing process of the raw materials, a silicon precursor and a fluorine-containing organic compound may be added to a solvent such as acetone and then mixed using a ball mill. The time of the ball mill is preferably from 1 hour to 24 hours. When the time is less than 1 hour, the ball mill is not sufficient for dissolving, crushing or mixing the precursor. If the time exceeds 24 hours, the mixing effect is saturated, This is economically disadvantageous.

The drying step is a step of removing the solvent by heating the mixed precursor through a mixing process to a predetermined temperature. In the drying process, it is preferable to use a device such as a hot plate to heat the mixture containing the solvent to 50 to 100 ° C. If the drying time is less than 50 ° C, the drying time becomes too long, This is because a phase can be formed.

The pelletization process is performed so that gas components decomposed in a subsequent synthesis process can be easily discharged and synthesis is facilitated, and a known pelletization apparatus is used to make pellets.

The heating temperature for the solid-phase reaction is preferably 500 to 800 ° C. If the temperature is lower than 500 ° C, the synthesis is difficult to occur. If the temperature exceeds 800 ° C, silicon dioxide (SiO ₂ ) Considering that it is difficult to synthesize a substance having a good electrochemical characteristic because it is difficult to remove, the heating temperature for solid phase reaction is more preferably 600 to 800 ° C.

The heating time of the solid-phase reaction is preferably 1 to 2 hours. If the heating time is less than 1 hour, the synthesis reaction is not sufficient. If the heating time is more than 2 hours, it is economically disadvantageous.

[Example 1]

In Example 1 of the present invention, SiO _x F _y was synthesized in the following manner.

First, as a precursor for the solid-phase reaction, PTFE (product of Sigma-Aldrich Co., particle size about 1 μm) was prepared as follows together with SiO (product of Sigma Aldrich Co., purity of 99% or more) and the following.

SiO + 100 wt% PTFE

(Here, the addition amount of PTFE is 100% of the weight of SiO)

The thus prepared precursor was put in an acetone solvent, followed by ball milling for about 24 hours to dissolve the PTFE, and the agglomerated powder in the precursor was disintegrated to prepare a uniformly mixed mixture. Zirconia balls having diameters of 3.5 mm and 10 mm were used for the ball milling.

After mixing the powders through ball milling, the mixture was dried in air at a temperature of 80 ° C using a hot plate, and the dried mixture was pelletized using a disc mold.

The thus prepared pellets were placed in an alumina crucible and heated to 700 DEG C under an argon gas atmosphere (0.5 mL flow rate per minute). At this time, the heating rate was 3.8 占 폚 / min and the heating time at 700 占 폚 was 1 hour so that the solid phase reaction was caused. After heating, it was allowed to cool naturally at room temperature.

The powder obtained through the above method was analyzed using XRD, and Fig. 1 shows the result. As shown in FIG. 1, the powder obtained according to Example 1 of the present invention exhibited an XRD pattern of silicon oxide and silicon.

[Example 2]

In Example 2 of the present invention, SiO _x F _y was synthesized _{by the} following method.

First, as a precursor for the solid-phase reaction, PTFE (product of Sigma-Aldrich Co., particle size about 1 μm) was prepared as follows together with SiO (product of Sigma Aldrich Co., purity of 99% or more) and the following.

SiO 2 + 200 wt% PTFE

(Here, the addition amount of PTFE is 200% of the weight of SiO)

The subsequent synthesis step was carried out in the same manner as in Example 1 to synthesize SiO _x F _y . That is, the synthesis was carried out in the same manner as in Example 1, except that the amount of PTFE added was 100% by weight more than in Example 1.

Fig. 2 shows XRD analysis results of the material synthesized according to Example 2. Fig. 2, the material synthesized according to Example 2 also exhibited an XRD pattern of silicon oxide and silicon. However, the ratio of silicon to silicon oxide varies depending on the amount of PTFE.

[Example 3]

In Example 3 of the present invention, SiO _x F _y was synthesized _{by the} following method.

First, as a precursor for the solid-phase reaction, PTFE (Sigma Aldrich, about 1 탆 in particle diameter) was used as a fluorine source together with SiO (product of Sigma Aldrich Co., purity of 99% or more) as follows.

SiO 2 + 200 wt% PTFE

(Here, the addition amount of PTFE is 200% of the weight of SiO)

The thus prepared precursor was put in an acetone solvent, followed by ball milling for about 24 hours to dissolve the PTFE, and the agglomerated powder in the precursor was disintegrated to prepare a uniformly mixed mixture. Zirconia balls having diameters of 3.5 mm and 10 mm were used for the ball milling.

After mixing the powders through ball milling, the mixture was dried in air at a temperature of 80 ° C using a hot plate, and the dried mixture was pelletized using a disc mold. Unlike Examples 1 and 2, 100% by weight of PTFE was ball milled together with silicon oxide, and the remaining 100% by weight of PTFE produced pellets made only of pure PTFE without ball milling.

The two pellets thus prepared were placed in an alumina crucible and heated to 700 under an argon gas atmosphere (0.5 mL flow rate per minute). At this time, the heating rate was 3.8 占 폚 / min and the heating time at 700 占 폚 was 1 hour so that the solid phase reaction was caused. After heating, it was allowed to cool naturally at room temperature.

Fig. 3 shows the XRD analysis results of the material synthesized according to Example 3. Fig. From Fig. 3, the material synthesized according to Example 3 also showed an XRD pattern of silicon oxide and silicon.

Charging / discharging characteristics evaluation result

4 shows the results of evaluating charge and discharge characteristics of SiO _x F _y prepared according to Example 3 of the present invention.

In order to evaluate the electrochemical behavior, an electrode was formed using SiO _x F _y prepared according to Example 3 of the present invention to conduct an electrochemical test.

80 wt% of the active material SiO _x F _y prepared in Example 3 of the present invention and 15 wt% of super P as a carbon powder were put into a mortar and mixed well for 20 to 30 minutes. The mixed powder is added to 5% by weight of liquid PVdF and mixed for 6 hours by stirring. At this time, 5 ~ 10 mL of NMP is added to adjust the viscosity of the mixed liquid material. Sterilize for 6 hours and add the mixed material to the homogenizer or the mixer and mix for 10 minutes.

The mixed material is applied onto a Cu foil and slurry cast using a doctor blade. After sufficiently dried in an oven at 80 ° C, heat treatment is carried out in a 120 ° C vacuum oven for 12 to 24 hours. After the heat treatment, the electrode was moved to the glove box without air exposure and then punched out with a 9 mm punch to form a 1 to 3 mg cathode.

The cell was assembled using the thus prepared negative electrode. In the cell assembly, the wellcos 2400 was cut to about 13 mm. The electrolyte was 1M LiPF ₆ in an EC / DMC (1: 1 weight ratio) organic solvent, Lithium metal was used as the electrode.

The electrochemical behavior of the thus prepared cell was measured at room temperature. The measurement equipment was a maccor series 4000, and the measurement was started from charging 0.01V to 2.5V and the current was measured by applying a C / 10 rate scale.

4 is a graph showing the results of evaluating the electrochemical behavior of a cathode using SiO _x F _y prepared according to Example 3 of the present invention.

As shown in FIG. 4, the battery using the active material according to Example 3 of the present invention showed a performance of about 1700 mAh / g for the first discharge.

Claims (9)

A method for producing a silicon oxide for a cathode material for a lithium secondary battery, the method comprising: heating a precursor mixture containing a silicon precursor and an organic compound containing fluorine to synthesize silicon oxide containing fluorine of the following formula:
[Chemical Formula]
SiO _x F _y (where 0 <x? 2, 0 <y? 2) The method according to claim 1,
Wherein the silicon precursor is at least one selected from Si, SiO, and SiO ₂ . The method according to claim 1,
Wherein carbon is produced during the production of the silicon oxide. The method according to claim 1,
Wherein the fluorine-containing organic compound is added in an amount of 10% to 200% of the weight of the silicon precursor. The method according to claim 1,
Wherein the fluorine-containing organic compound is polytetrafluoroethylene (PTFE) or polyfluorinated vinylidene (PVDF). 2. The method of claim 1, wherein the fluorine-containing organic compound is polytetrafluoroethylene (PTFE) or polyfluorinated vinylidene (PVDF). The method according to claim 1,
Wherein the precursor mixture has a heating temperature of 500 to 800 占 폚. The method according to claim 1,
Wherein the fluorine-containing organic compound is present in a form separated from the silicon precursor during the heat treatment. 8. An anode for a lithium secondary battery comprising a silicon oxide produced by the method according to any one of claims 1 to 7, a binder and a conductive powder. A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to claim 8, an electrolyte, and a positive electrode.

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