KR101937020B1 - Synthesis method of silicon composite and anodes for li-ion battery and li-ion battery having the same - Google Patents

Abstract

The present invention relates to a synthesis method of a silicon composite, a lithium secondary battery including a cathode and a cathode.
One embodiment of the present invention is directed to a method of preparing a precursor composition comprising the steps of: (a) providing a precursor mixture comprising a silicon precursor and a metal compound; and (b) heating the precursor mixture to form Si, SiO _{x y} Si _z O wherein Me = Li or Na is an alkali metal or an alkaline earth metal, 0 < y? 2, 0 < z? 2.

Description

TECHNICAL FIELD The present invention relates to a lithium secondary battery including a negative electrode and a negative electrode, a method for synthesizing a silicon composite including a nanosilicon for a lithium secondary battery anode material using a metal compound, a lithium secondary battery including a negative electrode and a negative electrode, }

The present invention relates to a method of synthesizing a silicon composite material including a nanosilicon for a lithium secondary battery anode material using a metal compound, a lithium secondary battery including the anode and the cathode, and more particularly, A method of synthesizing a silicon composite which uses a metal compound to produce a silicon composite containing a used nano silicon and a silicon oxide through a simple heat treatment, and a lithium secondary battery including a cathode and a cathode.

The demand for high capacity lithium secondary batteries is increasing as the demand for products that require large amounts of energy such as electric vehicles as well as portable devices increases. The negative electrode material is one of the main factors for determining the capacity characteristics of the lithium secondary battery, and studies are being conducted to solve the capacitive limitations of the conventional carbonaceous negative electrode materials. Among them, silicon (Si), germanium (Ge), tin (Sn) and the like have attracted attention because they have a high charge / discharge capacity through an alloying reaction with lithium.

In particular, silicon is the next-generation material to be spotlighted because its theoretical capacity is the highest at about 4200 mAh / g. However, due to the change in the volume caused by the large amount of lithium, the electrodes were destroyed, and the side reaction was promoted, thus limiting the lifetime characteristics. In order to solve the problem of the volume expansion of silicon, a technique using silicon oxide (SiOx) which can suppress the volume change is considered.

For example, in Non-Patent Document 1, a material containing silicon capable of mitigating the volume change by performing heat treatment at a high temperature of 1200 ° C for several hours is synthesized to maintain a capacity of 1000 mAh / g up to 50 cycles .

However, the process of performing the heat treatment at such a high temperature not only increases the manufacturing cost itself, but also causes a problem that the process is complicated because a particle growth is easily generated and a post-treatment process including a grinding process is performed.

Yoon Hwa, Cheol-Min Park, Hun-Joon Sohn, Journal of Power Sources, 222 (2013), 129-134

An object of the present invention is to provide a method for synthesizing a composite material containing nanosilicon, which can be used as an anode material for a lithium secondary battery, at a low temperature for a short time.

Another object of the present invention is to provide a negative electrode capable of solving a volume expansion which is a problem of a conventional silicon-based negative electrode and improving a low life characteristic, and a lithium secondary battery having the negative electrode.

(A) preparing a precursor mixture comprising a silicon precursor and a metal compound; (b) heating the precursor mixture to form a precursor mixture comprising Si, SiO _x (0 < x & And Me _y Si _z O wherein Me = Li or Na is an alkali metal or an alkaline earth metal, 0 < y? 2, 0 &lt; z? 2, To provide a method for synthesizing a silicon composite.

The method for synthesizing a silicon composite material comprising a nanosilicon and a silicon oxide according to the present invention can achieve synthesis at a low temperature in a short time by using a metal compound as a raw material, thereby simplifying the process and reducing manufacturing cost .

In addition, the silicon composite including the nano silicon and the silicon oxide of the present invention can suppress the volume expansion during the operation of the lithium battery, thereby exhibiting the long life characteristics of the cathode for the lithium secondary battery.

1 is an XRD result of a silicon composite synthesized according to Example 1. Fig.
2 shows XRD results of a silicon composite synthesized according to Example 2. Fig.
3 shows the XRD results of the materials synthesized according to the comparative examples.
FIG. 4 shows the results of evaluating the charge-discharge characteristics of the negative electrode using the silicon composite prepared according to Example 1 and silicon oxide (Sigma Aldrich) as an active material.

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.

In addition, terms and words used in the present specification and claims should not be construed in a conventional and dictionary sense, and inventors may appropriately define the concept of a term in order to describe its invention in the best possible way It should be construed as meaning and concept 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 are not intended to represent all of 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.

As described above, in the case of silicon oxide, a heat treatment at a high temperature is required to form nanosilicon, and a grinding process is necessary to solve the grain growth problem that occurs in this case. For this reason, there is a problem of complexity and high cost of the process for forming nanosilicon.

In order to solve these problems, the inventors of the present invention have studied about lowering the process temperature in synthesizing a composite material including a silicon precursor and a silicon precursor, and found that when a metal compound is used, And the present invention has been accomplished.

In addition, in the present invention, it is possible to control the production amount of nanosilicon and metal silicon oxide, which affects lifetime and capacity, by controlling the ratio of the metal compound to be added.

A method of synthesizing a silicon composite comprising nanosilicon according to the present invention comprises:

(a) providing a precursor mixture comprising a silicon precursor and a metal compound;

(b) heating the precursor mixture to form a mixture of Si, SiO _x (0 < x? 2), and Me _y Si _z O wherein an alkali metal or alkaline earth metal comprising Me = Li or Na, 2, 0 < z < 2).

The silicon precursor provides a silicon component to the composite, and can be used without particular limitation as long as it can provide silicon to the silicon composite through heating or oxidation. For example, Si, SiO, SiO ₂ , Si (OC ₂ H ₅ ) ₄ , Si (C ₂ H ₅ ) _4, etc. may be used singly or in a mixture of two or more kinds.

The metal compound is a material capable of forming nanosilicon at a low temperature, and is preferably a material containing an alkali metal or an alkaline earth metal including Li or Na, and examples thereof include lithium hydroxide, lithium oxide, A material including at least one of lithium carbonate, sodium hydroxide, and sodium carbonate may be used.

In addition, the mixing ratio between the metal compound and the silicon precursor greatly affects the physical properties of the composite, and the metal compound may be added in the range of about 0.03 to about 10 times the weight of the silicon precursor.

If the addition amount of the metal compound is less than about 0.03 times the addition amount of the silicon precursor, it is insufficient to induce the formation of nanosilicon. If the addition amount of the metal compound exceeds about 10 times the addition amount of the silicon precursor, a large amount of metal silicon oxide is formed, The capacity of the ion battery can be reduced.

The precursor mixture can be prepared through a pretreatment process including a raw material mixing process, a drying process, and a pelletizing process.

In the mixing process of the raw materials, the entire silicon precursor and the metal compound may be added to a solvent such as acetone, and then mixed using a ball mill. Here, the ball mill can be performed for about 1 hour to about 24 hours. If the ball milling time is less than about 1 hour, dissolution, crushing or mixing of the precursor is insufficient, and if the ball milling time is longer than about 24 hours, the mixing effect is saturated, which is economically disadvantageous due to prolongation of the processing time.

On the other hand, in the mixing step, a method of improving the electron conductivity of silicon oxide is used, including a method of forming a silicon oxide film, which includes pitch, polyacrylonitrile (PAN), polydodamine, saccharose, carbon nanofiber (CNF) The carbon additive may be further mixed into the precursor mixture. Here, the carbon additive can be used for the coating of silicon oxide.

The drying process of the raw material is a process of removing the solvent by heating the mixed precursor mixture through a mixing process to a specific temperature. In the drying process, the mixture containing the solvent can be heated to a process temperature of 50 ° C to 150 ° C using equipment such as a hot plate. If the process temperature is less than 50 ° C, the drying time becomes longer. If the process temperature exceeds 150 ° C, the material reacts to form an unintended phase.

The pelletization process of the raw material is intended to increase the contact area between the precursors in a subsequent synthesis process to facilitate synthesis, and a known pelletization apparatus can be used to make pellets.

Next, in the step of synthesizing the silicon oxide by heating the precursor mixture, the synthesis process can be performed according to the heating conditions using the solid phase reaction.

Wherein the heating conditions can be set to heat the precursor mixture at a temperature of 500 ° C to 1000 ° C for 5 minutes to 5 hours in an inert atmosphere of argon (Ar) or nitrogen (N 2).

The heating temperature for the solid-phase reaction is preferably 500 ° C to 1000 ° C. When the temperature is lower than 500 ° C, nanosilicon is hardly formed, and when the temperature exceeds 1000 ° C, rapid growth of silicon crystals occurs to synthesize a material having improved electrochemical characteristics It can be difficult. More preferably, the heating temperature is 700 ° C to 900 ° C.

The heating time of the solid phase reaction is preferably from 5 minutes to 5 hours. If the heating time is less than 5 minutes, the silicon crystal is not sufficient to form, and if it exceeds 5 hours, excessive growth of the silicon crystal may occur.

The method of synthesizing a silicon compound including nano silicon according to the present invention can be carried out at a low temperature in a short time using a metal compound, so that it can be mass-produced at low cost. In addition, the silicon composite containing nano-silicon can suppress the volume expansion and thus exhibit the long life characteristics of the cathode for a lithium secondary battery.

[Example 1]

In Example 1 of the present invention, a silicon composite containing nanosilicon was synthesized by the following method.

First, lithium hydroxide monohydrate (manufactured by Sikuma Aldrich) as a metal compound together with SiO (product of Sigma Aldrich Co., purity of 99% or more) was prepared as a precursor mixture for the solid-phase reaction at the following mixing ratios.

SiO (90.5 wt%) + lithium hydroxide monohydrate (9.5 wt%)

The precursor was mixed with an ethanol solvent using zirconia balls of 3, 5, and 10 mm for about 24 hours.

After mixing, the mixture was dried in air at a temperature of 100 DEG 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 800 DEG C under an argon gas atmosphere (flow rate of 1.0 mL per minute). At this time, the solid-phase reaction was allowed to take place at a heating rate of 4.0 ° C / min and a heating time of 10 minutes. After heating, it was allowed to cool naturally at room temperature. The powders synthesized through the above method were analyzed using XRD, and Fig. 1 shows the results.

1, in the case of the powder obtained according to Example 1 of the present invention, amorphous silicon oxide (part appearing in wave form at the XRD peak), crystalline silicon (part indicated by Si in the XRD peak), crystalline Of lithium silicon oxide (the portion indicated by the metal oxide in the XRD peak) is formed.

[Example 2]

In Example 2 of the present invention, silicon oxide containing nanosilicon was synthesized by the following method.

First, lithium hydroxide monohydrate (manufactured by Sikuma Aldrich) as a metal compound together with SiO (product of Sigma-Aldrich Co., purity of 99% or more) was prepared as a precursor mixture for solid-phase reaction at the following mixing ratio.

SiO (65 wt%) + lithium hydroxide monohydrate (35 wt%)

The precursor mixture was mixed with an ethanol solvent using zirconia balls of 3, 5, and 10 mm for about 24 hours.

After mixing, the mixture was dried in air at a temperature of 100 DEG 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 800 DEG C under an argon gas atmosphere (flow rate of 1.0 mL per minute). At this time, the heating rate was 4.0 占 폚 / min and the heating time was 10 minutes so that a solid-phase reaction was caused. After heating, it was allowed to cool naturally at room temperature.

The powders synthesized by the above method were analyzed using XRD, and Fig. 2 shows the results.

2, the powder obtained according to Example 2 of the present invention can also be obtained by mixing amorphous silicon oxide (a portion represented by a wave form at an XRD peak), crystalline silicon (a portion indicated by Si at an XRD peak) It can be seen that a composite containing lithium silicon oxide (the portion indicated by the metal oxide in the XRD peak) is formed.

[Comparative Example]

For comparison with Examples 1 and 2 of the present invention, a silicon compound not containing a metal compound was synthesized by the following method.

As a precursor for the solid-phase reaction, SiO (product of Sigma-Aldrich, purity of 99% or more) was prepared.

The precursor was dispersed with an ethanol solvent using zirconia balls of 3, 5, and 10 mm for about 24 hours.

After dispersion, the powder was dried in air at a temperature of 100 캜 using a hot plate, and the dried mixture was pelletized using a disk mold.

The thus prepared pellets were placed in an alumina crucible and heated to 800 DEG C under an argon gas atmosphere (flow rate of 1.0 mL per minute). At this time, the heating rate was 4.0 占 폚 / min and the heating time was 10 minutes so that a solid-phase reaction was caused. After heating, it was allowed to cool naturally at room temperature.

The powders synthesized by the above method were analyzed using XRD, and Fig. 3 shows the results.

As can be seen in FIG. 3, the powder obtained according to the comparative example exhibited an XRD pattern of amorphous silicon oxide. That is, as compared with Examples 1 and 2, silicon and metal silicon were not produced.

[Evaluation results of charging / discharging characteristics]

FIG. 4 shows the results of comparing the charge and discharge characteristics of a silicon oxide material prepared according to Example 1 of the present invention and a material prepared in the same manner without adding lithium hydroxide monohydrate (Comparative Example).

In order to evaluate the electrochemical behavior, an electrode was made using the material manufactured according to the alias name of Example 1 and an electrochemical test was conducted.

70 wt% of the material prepared according to Example 1 of the present invention and 20 wt% of Super P as a carbon powder were put in a mortar and mixed for 15 to 20 minutes. Mixed powder and 10% by weight of PAA are added to 3 ml of distilled water and mixed by stirrer for 6 hours.

The mixed liquid mixture is applied onto a copper foil and slurry cast using a doctor blade. After drying for 2 hours or more in an oven at 80 ° C, it is dried in a vacuum oven at 120 ° C for 12 hours. And the electrode was punched with a diameter of 8 mm.

Celgard 2400 was used as a separator together with the above-mentioned electrode and punched to a diameter of 13 mm. The electrolyte was EC / DEC (weight ratio 1: 1) containing 1M LiPF6. Then, a lithium metal was punched as a counter electrode into a diameter of 10 mm, and a battery was manufactured.

The battery manufactured by the above method was measured at room temperature using a Maccor series 4000 and measured at a C / 20 rate in the range of 0.01 to 2.0V. At this time, C rate was calculated based on 1400 mAh / g.

As can be seen from FIG. 4, in the case of the material according to the embodiment of the present invention, since the discharge capacity is maintained up to 20 cycles, the discharge capacity tends to gradually decrease in the case of the comparative example. It is found that the characteristics of the material are superior.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. In addition, it is a matter of course that various modifications and variations are possible without departing from the scope of the technical idea of the present invention by anyone having ordinary skill in the art.

Claims (11)

(a) preparing a precursor mixture comprising SiO and a metal compound; and
(b) heating the precursor mixture to form crystalline Si, amorphous SiO _x (0 <x? 2), and crystalline Me _y Si _z O, where Me = alkali metal or alkaline earth metal, 0 <y? z < / = 2). &lt; / RTI &gt;
The method according to claim 1,
The step (a)
(a-1) a mixing step of mixing the SiO and the metal compound into a solvent and then mixing them using a ball mill,
(a-2) a drying step of heating the mixed precursor mixture through the mixing step to remove the solvent, and
(a-3) a pelletizing step of forming the precursor mixture into pellets.
3. The method of claim 2,
In the step (a-1), the metal compound is added in an amount of 0.03 to 10 times the weight of the SiO and mixed.
3. The method of claim 2,
In the step (a-1), in order to improve the electron conductivity of the silicon oxide, a pitch, a polyacrylonitrile (PAN), a polydopamine, a saccharose, a carbon nanofiber (CNF) And further adding a carbon additive containing a carbon precursor.
The method according to claim 1,
In the step (b)
Heating the precursor mixture in an inert atmosphere at a temperature of 500 ° C to 1000 ° C for 5 minutes to 5 hours.
The method according to claim 1,
In the step (b)
Heating the precursor mixture in an inert atmosphere at a temperature of 700 ° C to 900 ° C for 5 minutes to 5 hours.
The method according to claim 6,
Wherein the inert atmosphere is an argon gas atmosphere, a nitrogen gas atmosphere, or a mixed gas atmosphere thereof.
delete The method according to claim 1,
Wherein the metal compound comprises at least one of lithium hydroxide, lithium oxide, lithium carbonate, sodium hydroxide, and sodium carbonate.
A negative electrode for a lithium secondary battery comprising a silicon composite formed by the method of any one of claims 1 to 7 and a binder and a conductive powder.
11. A lithium secondary battery comprising the negative electrode for a lithium secondary battery according to claim 10.

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