KR101399042B1 - Method for manufacturing silicon-graphene based complex composite in use of anode material for secondary battery - Google Patents

Abstract

A silicone-graphene composite material that can be used as an anode material for a secondary battery is disclosed. The present invention relates to a method for producing a silicon-graphite composite material, comprising: a first step of mixing a silicon chloride and a glycol as a dihydric alcohol to form a porous material; A second step of forming a silicon oxide represented by the general formula SiOx wherein the content (x) of oxygen is in the range of 0 < x < 2 by subjecting the porous material to heat treatment in an inert gas atmosphere; A third step of forming a composite powder of Si-SiOx by mixing and solid-reacting the silicon oxide and the metal silicon formed in the second step; And a fourth step of mixing the Si-SiOx composite powder and the graphene powder formed in the third step, followed by heat treatment in an inert gas atmosphere.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a high-capacity silicon-graphite composite material for a negative electrode of a secondary battery,

The present invention relates to a negative electrode active material for improving the energy density and lifetime of a lithium secondary battery which requires a high output and a high voltage, and more particularly, to a negative electrode active material for improving the energy storage characteristics and lifetime of a mid- And a manufacturing technique thereof.

The negative electrode active material of the lithium ion battery is mainly composed of carbonaceous materials such as graphite, coke and meso carbon because these carbonaceous materials are close to the standard electrode potential of the lithium metal , Energy density per volume and weight is high, and stability and closest to the conditions necessary for high-speed charge and discharge.

However, since these carbonaceous materials are excellent in stability and reversibility, there is a limit in terms of capacity. Therefore, in order to be used in medium and large sized vehicles, such as electric vehicles, energy storage systems, Therefore, it is a reality that a new anode active material is required for realizing such a middle- or large-sized secondary battery.

Meanwhile, materials capable of increasing the capacity four times or more by using nano silicon (Si) and tin (Sn) have been under development. However, since the volume of the negative electrode active material after the charge / discharge cycle is increased, It is a reality that is not applied. In addition, materials such as carbon nanotubes, carbon nanofibers, carbon nanowires, etc., to which nanotechnology is applied are not commercially applicable to use as an active material of a lithium secondary battery alone due to their high price .

Graphene, the last carbon-free molecule developed recently among carbon materials, has superior electrical conductivity than graphite, has a large surface area of 2600 m2 / g or more, and is chemically stable. Therefore, But it is a reality that it can not be applied at a high price for a single use.

The present invention relates to a negative electrode active material for a lithium secondary battery used in an electric vehicle, an energy storage system, etc., and a silicon-graphite composite material as a high capacity negative electrode active material for replacing a conventional graphite negative electrode material. .

Another object of the present invention is to provide a negative electrode material for a secondary battery having a high capacity and a method of manufacturing a silicon-graphite composite material containing silicon oxide having an oxygen content of less than 2, Graphene composite material which is easy to control the size of the particles to nano-size.

The method of manufacturing a silicon-grafin composite material according to the present invention includes a first step of mixing a silicon chloride and a glycol as a dihydric alcohol to form a porous material; A second step of forming a silicon oxide represented by the general formula SiOx wherein the content (x) of oxygen is in the range of 0 < x < 2 by subjecting the porous material to heat treatment in an inert gas atmosphere; A third step of forming a composite powder of Si-SiOx by mixing and solid-reacting the silicon oxide and the metal silicon formed in the second step; And a fourth step of mixing the Si-SiOx composite powder and the graphene powder formed in the third step, followed by heat treatment in an inert gas atmosphere.

In the first step, the content of the silicon chloride is preferably 10 parts by weight or more and 90 parts by weight or less based on 100 parts by weight of the total mixture of the silicon chloride and the glycol. The silicon chloride may be at least one selected from the group consisting of silicon tetrachloride and dialkyldichlorosilane. In addition, the glycol may be at least one selected from the group consisting of ethylene glycol, propylene glycol, and pinacol.

It is preferable that the heat treatment in the second step is performed at a temperature of 600 ° C or more and 900 ° C or less.

In the third step, the content of the silicon oxide is preferably 2 parts by weight or more and 98 parts by weight or less based on 100 parts by weight of the mixed powder of the silicon oxide and the metal silicon.

In the fourth step, the content of the graphene powder is preferably 0.1 part by weight or more and 10 parts by weight or less based on 100 parts by weight of the total weight of the Si-SiOx composite powder and the graphene.

It is preferable that the heat treatment in the fourth step is performed at a temperature of 200 ° C or more and 600 ° C or less.

The silicon-grit composite for a cathode material of a secondary battery according to the present invention is a silicon oxide powder represented by the general formula SiOx in which the content (x) of oxygen is in the range of 0 < x < Metal silicon powder; And graphene powder. Here, the silicon oxide powder and the metal silicon powder are solid-reacted with each other to form a Si-SiOx composite powder. The Si-SiOx composite powder and the graphene powder thus formed are homogeneously mixed and then heat-treated to form a silicon- .

In particular, the content of the silicon oxide powder is preferably 2 parts by weight or more and 98 parts by weight or less based on 100 parts by weight of the total weight of the silicon oxide powder and the metal silicon powder, -SiOx composite powder and the graphene in an amount of 0.1 part by weight or more and 10 parts by weight or less based on 100 parts by weight of the total weight of the graphene-SiOx composite powder and the graphene.

The silicon-graphene composite material according to the present invention may be composed of metal silicon, silicon oxide having less than 2 oxygen atoms and graphene. Such a silicone-graphene composite material is particularly advantageous as an anode material of a lithium secondary battery Can be used.

In the case of using the silicon-graphene composite material containing metal silicon, silicon oxide having less than 2 oxygen atoms and graphene as the anode material of the secondary battery by the method according to the present invention, the volume expansion of the silicon oxide is suppressed and the electrical conductivity And the metal silicon promotes the reaction with oxygen to suppress the irreversibility. At the same time, the silicon oxide having the oxygen number less than 2 accelerates the reaction of the negative electrode active material with lithium, thereby achieving the long life and high capacity of the lithium secondary battery .

Further, according to the process for producing a silicon-based composite material according to the present invention, the particle size can be easily controlled and the irreversibility of the negative electrode material can be suppressed in manufacturing the negative electrode material used in the middle- or large-sized secondary battery and the high- It is very effective in producing a high-capacity powder that can dramatically improve energy storage characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a process flow chart for explaining a method of manufacturing a silicon-graphite composite according to the present invention. FIG.
FIG. 2 is an exemplary view for explaining the detailed structure of a silicon-graphene composite according to the present invention.
3 is an electron micrograph of the silicon-graphene composite material produced by the present invention.
4 shows the results of the electrochemical property evaluation of the silicon-grafin composite material produced by the present invention.

Hereinafter, preferred embodiments of a silicon-grafix based composite material and a method of manufacturing the same according to the present invention will be described in detail with reference to the accompanying drawings.

First, the silicon-graphite composite according to the present invention comprises a silicon oxide powder represented by a general formula SiOx having an oxygen content (x) in the range of 0 < x < 2, A metal silicon powder for forming a composite powder, and a graphene powder mixed uniformly with the Si-SiOx composite powder and then heat-treated and combined with the Si-SiOx composite powder. Particularly, the content (x) of oxygen in the silicon oxide is more preferably in the range of 0.1? X? 1.9.

The silicon-based composite material according to the present invention can be produced by the following method. That is, the method for producing a silicon-based composite material according to the present invention comprises the steps of: forming a porous material by mixing silicon chloride and glycol as a first step; and heat-treating the porous material in an inert gas atmosphere as a second step Forming a silicon oxide represented by the general formula SiOx in which the content (x) of oxygen is in the range of 0 < x <2; and, as a third step, mixing the silicon oxide and the metal silicon formed in the second step, Forming a Si-SiOx composite powder by mixing the Si-SiOx composite powder and the graphene powder; and, as a fourth step, uniformly mixing the Si-SiOx composite powder and the graphene powder formed in the third step, followed by heat treatment.

In the above-described method, first, a silicon oxide having an oxygen content of less than 2 is prepared, powdered and mixed with the bulk metallic silicon powder and solid-phase reacted to form a Si-SiOx composite powder. By this solid phase reaction, a composite powder in which the silicon oxide powder and the metal silicon powder are mutually bonded can be obtained. Then, the Si-SiOx composite powder thus obtained is uniformly mixed again with the use of a dispersion solvent, and then heat-treated in an inert gas atmosphere to obtain a silicon-graphene composite in which the Si-SiOx composite powder and the graphene are physically bonded Obtain the composite material.

Hereinafter, the method for producing the above-described silicon-graphene composite will be described in more detail.

[Preparation of Porous Material]

First, to produce a porous material as an initial material for the formation of silicon oxide (SiOx; 0 < x < 2) with an oxygen content of less than 2, 2, which is a dihydric alcohol. Examples of the silicon chloride having a purity of 90% or more include silicon tetrachloride (silicon tetrachloride), dialkyldichlorosilane (RRSiCl2; Diacyldichlorosilane] and the like can be used. As the glycol, all alcohols represented by R (OH) 2, for example, ethylene glycol, propylene glycol, pinacol and the like can be used. Silicon chloride and glycols are rapidly mixed to produce a porous material. In the mixing sequence, a large amount of a porous material in the form of a sponge can be produced by rapid reaction when silicon chloride is added to the glycol. Conversely, glycol may be added to the silicon chloride, in which case the porous material and the sol-state liquid material may be formed together. In the reaction of silicon chloride with glycol, the reaction rate can be controlled within a chemical weight ratio, and can be adjusted to have a reaction time of 1 minute to 60 minutes in consideration of rapid mixing time and weight ratio in real time mixing.

On the other hand, the mixing ratio of silicon chloride and glycol is adjusted so as to be in the range of 0.1: 0.9 to 0.9: 0.1 in order to produce HCl through hydrogen reaction of chlorine and glycol in the silicon chloride so that the silicon oxide can be produced easily. do. Here, when the weight ratio of the silicon chloride to 100 parts by weight of the entire mixture of silicon chloride and glycol is less than 10 parts by weight, the oxidation reaction in the silicon can not be performed smoothly and silicon oxide can not be formed. If the weight ratio of the silicon chloride to the whole mixture exceeds 90 parts by weight, the chlorine reaction in the glycol explosively increases and the silicon oxide can be dissolved.

[Heat treatment of porous material]

The porous material produced by the above-described method is subjected to heat treatment to produce silicon oxide having an oxygen content of less than 2. More specifically, the produced porous material is heat-treated in an inert gas atmosphere using a mixed gas of hydrogen, nitrogen, argon, or a mixture of these three gases. For example, the produced porous material is heat-treated at 600 ° C to 900 ° C for 15 minutes to 6 hours in a vertical, horizontal, or heat treatment furnace including a conveyor belt. During the heat treatment, the chlorine gas is evaporated by the reaction of chlorine in the silicon chloride with carbon in the glycol, and by the reaction of the silicon cluster in the silicon chloride with oxygen in the glycol, a silicon oxide having an oxygen number less than 2 is produced. Here, the inert gas atmosphere is maintained because an oxidizing atmosphere for forming a silicon oxide having less than 2 oxygen atoms is not formed when an oxidizing gas or a reducing gas is included.

On the other hand, when the heat treatment temperature is less than 600 ° C, the reaction rate of chlorine and hydrogen is lowered, so that chlorine gas is not removed smoothly, and silicon oxide is not easily formed. On the other hand, if the temperature exceeds 900 ° C., the particle size of the generated silicon oxide may grow and eventually the activity of the secondary battery may deteriorate. Also, due to the explosive generation of chlorine gas, An oxide having a valence of 2 or more can be produced. If the heat treatment temperature is less than 15 minutes, formation of silicon oxide is not easy, and if it exceeds 6 hours, particle growth problem may occur. During the cooling after the heat treatment, it is preferable to perform air cooling or slow cooling to 20 ° C or less per minute because excessive quenching may cause problems of degradation of electrochemical characteristics due to grain size growth.

[Powder Collection and Control of Particle Size]

The silicon oxide prepared by the above-mentioned method is composed of a bulk material as a porous material. The bulk of the bulk state is a state in which nanoparticles are aggregated and must be formed in powder form for application to a secondary cell and control of particle size. For this purpose, it is desirable to control the particle size of the bulk silicon oxide mass produced through the ball mill. In the case of a ball mill, it is preferable to control the rotation speed to 300 rpm or less and the ball mill time to 12 hours or less since the electrochemical characteristics may deteriorate when the particle size is extremely fine.

[Solid phase reaction of silicon oxide and bulk metal silicon]

Next, the silicon oxide (i. E., Silicon monoxide) prepared above is mixed with the bulk silicon metal. The metal silicon in the bulk state is preferably a metal silicon powder having an average particle diameter of 10 nm or more and 200 mu m or less, for example. The thus-prepared silicon oxide powder and metal silicon powder were charged into alumina pores and then charged at 150 rpm for 2 hours using an Attritor, Planatery, Spex, Ball Miller, Mixer ), Etc., and subjected to a solid-phase reaction at room temperature to produce a composite powder of silicon oxide and metal silicon. By such a solid-phase reaction, a composite powder body in which a silicon oxide powder and a metal silicon powder are physically bonded to each other can be formed.

In the solid-phase reaction, the weight ratio of silicon oxide to metal silicon is limited to a range of 2: 98 to 98: 2, the rotation speed is set to 50 rpm to 2,000 rpm, and the solid phase reaction time is limited to 30 minutes to 6 hours . Particularly, when the content of silicon oxide is less than 2 parts by weight based on 100 parts by weight of the mixed powder of silicon oxide and metal silicon, silicon oxide is not distributed in the metal silicon powder base, and the capacity increasing effect can not be obtained. If the content of the silicon oxide exceeds 98 parts by weight, the reaction between the bulk metal silicon and oxygen does not progress smoothly, and irreversibility can not be suppressed. Particularly, the weight ratio of silicon oxide (SiOx; 0 <x <2) to metal silicon is more preferably 30:70.

On the other hand, when the rotational speed is less than 50 rpm, composite powdering does not occur, so that bulk metallic silicon and silicon oxide are separated and a composite powder can not be formed. When the rotation speed exceeds 2,000 rpm, the nano-scale of the composite powder occurs, and irreversible inhibition effect due to the reaction of bulk silicon metal and oxygen can not be obtained. Further, if the solid phase reaction time is less than 30 minutes, the composite powder does not occur. If the reaction time is more than 6 hours, the powder particles are refined in spite of the low rotational speed, so that oxidation of the composite powder proceeds rapidly. On the other hand, the bulk metallic silicon does not react with oxygen, so it can be mixed in the air, preferably in an inert atmosphere.

[Mixing and heat treatment of Si-SiOx composite powder and graphene]

Next, graphene is mixed with the composite powder of Si-SiOx (0 < x < 2) prepared as described above. For example, a solution prepared by dispersing graphene powder in ethylene glycol at a concentration of 1 mg / mL may be prepared, and then the solution and the Si-SiOx composite powder prepared above may be mixed and mixed at 50 rpm for 30 minutes.

When the powders are mixed, the dispersion concentration is preferably 0.1 to 10 mg / mL. If the dispersion concentration is less than 0.1 mg / mL, it is difficult to sufficiently disperse the graphene particles as the dispersion concentration decreases. When the dispersion concentration exceeds 10 mg / mL The excessive dispersion of graphene is not achieved due to the addition of excessive graphene. If the rotation speed is less than 10 rpm, the added graphene can not be easily penetrated into the entire mixed powder, so that the dispersion can not be smoothly performed. If the rotation speed exceeds 1000 rpm The size of the finally formed composite powder itself may be reduced, so that the reaction between the composite powder and lithium may be reduced and the capacity may be reduced. If the mixing time is less than 10 minutes, the reactivity of the mixed Si-SiOx composite powders and graphene is lowered. When the mixing time exceeds 2 hours, the time The capacity may be lowered due to the refinement of Si-SiOx composite powders.

The mixing ratio (graphene: Si-SiOx composite powder) of the graphene powder and the composite powder of Si-SiOx (0 <x <2) is preferably 0.1: 99 or more and 10: 99 &lt; / RTI &gt; If the content of the graphene powder is less than 0.1 part by weight based on 100 parts by weight of the combined weight of the composite powder of Si-SiOx and the graphene powder, the graphene powder is not dispersed in the Si-SiOx composite powder, It is difficult to expect an increase in surface area. If the content of the graphene powder exceeds 10 parts by weight based on 100 parts by weight of the total weight of the composite powder of Si-SiOx and the graphene powder, the reaction between SiOx and lithium is not smooth due to excessive graphene dispersion, Can be degraded.

Next, the mixed powder of the prepared Si-SiOx composite powder and the graphene powder is heat-treated in an inert gas atmosphere at a temperature range of 200 ° C to 600 ° C for 1 to 4 hours to obtain a final silicon-graphene composite material . At this time, argon (Ar), nitrogen, hydrogen, or a mixed gas of these three gases may be preferably used as the inert gas. The heat treatment temperature in the heat treatment step is preferably in the range of 200 ° C or higher and 600 ° C or lower, more preferably 2 hours at 400 ° C. Through such heat treatment, the dispersant used for uniform mixing and dispersion of powders is removed during the heat treatment, and finally a silicon-graphene composite material in which Si-SiOx composite powder and graphene are physically bonded to each other can be obtained .

FIG. 1 shows a schematic view of a silicon-graphene composite material produced according to the above-described manufacturing method. That is, the composite powder 30 formed by solid-phase reaction of the metal silicon 10 and the silicon oxide (SiOx; 0 <x <2) powder 20 and the sheet-like graphene powder 40 are mixed and heat- Whereby the silicon-graphene composite material 50 can be obtained. 2, the packed powder 40 is rearranged between the voids of the Si-SiOx composite powder 30 so that the graphene 40 is a Si-SiOx composite It is possible to reduce the volume expansion of SiOx that can be increased by the insertion of lithium (Li) ions, and also the Si metal in the Si-SiOx composite powder to oxidize through the reaction with oxygen Can be controlled. Further, the voids between the Si-SiOx composite powder 30 and the graphene 40 function as a buffer space during charging and discharging. Since the silicon-graphite composite having such a structure can utilize the excellent electrical conductivity of graphene, it can contribute to obtain excellent lithium secondary battery characteristics compared with the conventional nano silicon or silicon oxide.

On the other hand, referring to the electron micrograph of the silicon-graphene composite material according to the present invention shown in FIG. 3, silicon oxide (SiOx) powder is dispersed in the composite powder state on the surface of the metal silicon of the bulk, , And that the sheet-like graphene is stably dispersed between the composite powders.

4 shows the electrochemical property evaluation results of the silicon-graphene composite material produced by this embodiment. As shown in FIG. 4, it can be seen that the silicon-graphite composite according to the present invention exhibits excellent electrode characteristics as compared with the conventional negative electrode material. Particularly, it can be confirmed that the silicone-graphene composite material according to the present invention maintains excellent irreversible characteristics and long life. This is because the electrical conductivity of the added graphene is improved and the bulk silicon is reacted with oxygen Not only suppressing irreversible phase but also the complexed silicon oxide promotes the reaction with lithium and becomes structurally and chemically stable. Due to these properties, irreversible and short life problems, which are problems of conventional silicon based anode materials, can be solved. Particularly, the manufacturing method according to the present invention does not require the carbon-based coating process as in the conventional graphite material, and thus, the process cost can be reduced.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, 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 invention. It is therefore to be understood that the embodiments of the invention described herein are to be considered in all respects as illustrative and not restrictive, and the scope of the invention is indicated by the appended claims rather than by the foregoing description, Should be interpreted as being included in.

Claims (12)

A first step of mixing a silicon chloride and a glycol as a dihydric alcohol to form a porous material;
A second step of forming a silicon oxide represented by the general formula SiOx wherein the content (x) of oxygen is in the range of 0 < x < 2 by subjecting the porous material to heat treatment in an inert gas atmosphere;
A third step of forming a composite powder of Si-SiOx by mixing and solid-reacting the silicon oxide and the metal silicon formed in the second step; And
And a fourth step of mixing the Si-SiOx composite powder and the graphene powder formed in the third step, followed by heat treatment in an inert gas atmosphere.
The method according to claim 1,
In the first step, the content of the silicon chloride is 10 parts by weight or more and 90 parts by weight or less based on 100 parts by weight of the total mixture of the silicon chloride and the glycol. &Lt; / RTI &gt;
The method according to claim 1,
Wherein the silicon chloride is at least one selected from the group consisting of silicon tetrachloride and dialkyldichlorosilane. 2. The method of claim 1, wherein the silicon chloride is at least one selected from the group consisting of silicon tetrachloride and dialkyldichlorosilane.
The method according to claim 1,
Wherein the glycol is at least one selected from the group consisting of ethylene glycol, propylene glycol, and pinacol.
The method according to claim 1,
Wherein the heat treatment is performed at a temperature of 600 ° C or more and 900 ° C or less in the second step.
The method according to claim 1,
In the third step, the content of the silicon oxide is 2 parts by weight or more and 98 parts by weight or less based on 100 parts by weight of the mixed powder of the silicon oxide and the metal silicon. A method of manufacturing a composite material.
The method according to claim 1,
In the fourth step, the content of the graphene powder is 0.1 part by weight or more and 10 parts by weight or less based on 100 parts by weight of the total weight of the Si-SiOx composite powder and the graphene. - Manufacturing method of graphene composite.
The method according to claim 1,
Wherein the heat treatment is performed at a temperature of 200 ° C or more and 600 ° C or less in the fourth step.
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