KR102679255B1 - Method for Manufacturing Silicon Mixture and Silicon Mixture Prepared by the Same - Google Patents

Abstract

The present invention relates to a method for producing a silicon mixture comprising the step of (A) mixing silicon dioxide with a lithium-based molten salt containing lithium metal, and to a silicon mixture prepared according to the above-described method for producing a silicon mixture. .

Description

Method for manufacturing silicon mixture and silicon mixture prepared thereby {Method for Manufacturing Silicon Mixture and Silicon Mixture Prepared by the Same}

The present invention relates to a method for producing a silicone mixture and a silicone mixture prepared thereby.

Recently, as the demand for lithium secondary batteries has increased, interest in developing technology for anode materials, which are a component of batteries, is also increasing. Conventionally, materials commonly used as cathode materials include graphite. However, graphite has a low reversible capacity of about 372 mAh/g, so research on alternative materials with high reversible capacity has been actively conducted.

Silicon (Si), one of the most actively researched materials, has a high reversible capacity of 4,200 mAh/g and a high volume of 9,786 mAh/cm. In addition, silicon has the advantage of being easy to obtain, cheap, and environmentally friendly. However, silicon (Si) has a large volume change (approximately 400%) during charging and discharging, which reduces its durability, and the silicon compound formed at the solid-electrolyte interface interferes with the alloy/de-alloy process. .

To overcome these shortcomings, silicon (Si), which has better performance, was developed as a nanostructure, but silicon (Si), which has structures such as nanowires and nanotubes, is not economical as the manufacturing process becomes complicated, and toxic chemicals are used. Because it requires the use of , there is a problem that production is difficult even at a large-scale industrial level.

For simpler and more environmentally friendly manufacturing of silicon, an electrochemical manufacturing method using molten salt as an electrolyte has received attention. For example, there is a method of immersing SiO ₂ in CaCl ₂ molten salt at 850 ℃ and then using it as an anode to supply electrons to reduce it to silicon (Si). However, when SiO ₂ is used as a raw material, silicon ( It is difficult to completely and uniformly reduce SiO 2 to Si), and when SiO ₂ is manufactured and used as a porous pellet, a pretreatment process that requires sintering at over 900 ℃ after compressing SiO ₂ powder is required, making the process complicated and uneconomical. There is a problem that has not been resolved. Alternatively, a method has been developed to dissolve SiO ₃ ^2- in molten salt and then supply electrons to reduce it to silicon (Si), but there is a problem of low yield.

Research on silicon compounds is continuing to solve the various problems described above and to make them suitable for use as electrode (e.g., anode) materials for lithium secondary batteries.

The present invention is intended to solve the above problems, using a lithium-based molten salt (LiCl molten salt) with a lower melting point than the conventional CaCl ₂ molten salt, and using lithium metal as a reducing agent to produce silicon dioxide (LiCl molten salt) without the supply of electrical energy. The aim is to provide a silicon mixture that can be manufactured only through spontaneous chemical reaction of SiO ₂ ).

One embodiment of the present invention provides a method for producing a silicon mixture, comprising the step of (A) mixing silicon dioxide with a lithium-based molten salt containing lithium metal.

Another embodiment of the present invention provides a silicone mixture prepared according to the above-described method for producing a silicone mixture.

The method for producing a silicon mixture of the present invention is to perform a reduction reaction of silicon dioxide without an additional process (e.g., electrolytic reduction process, etc.) simply by mixing silicon dioxide (SiO ₂ ) with a lithium-based molten salt containing lithium metal. This has the effect of easily obtaining a silicon mixture suitable as an electrode material for a lithium secondary battery by simply raising the reaction temperature to a temperature higher than the melting point of lithium-based molten salt (for example, LiCl molten salt).

In addition, the composition of the silicon mixture can be adjusted by adjusting the content of lithium metal or the ratio of silicon dioxide (SiO ₂ ) and lithium metal, which has the effect of providing the necessary product easily with a simple operation.

1 is a diagram showing a photograph of a graphite reactor and a silicon mixture prepared in a graphite reactor according to an embodiment of the present invention.
Figure 2 is a diagram showing an SEM photograph of silicon dioxide (SiO2) before reaction used in one embodiment of the present invention.
Figure 3 is a diagram showing the results of SEM analysis of the silicone mixtures of Examples 1 to 3 according to Experimental Example 1 of the present invention.
Figure 4 is a diagram showing the results of SEM analysis of the silicone mixtures of Comparative Examples 1 to 3 according to Experimental Example 1 of the present invention.
Figure 5 is a diagram showing the results of XRD analysis of the silicon mixture of Example 1 according to Experimental Example 1 of the present invention.
Figure 6 is a diagram showing the results of XRD analysis of the silicon mixture of Example 2 according to Experimental Example 1 of the present invention.
Figure 7 is a diagram showing the results of XRD analysis of the silicon mixture of Example 3 according to Experimental Example 1 of the present invention.
Figure 8 is a diagram showing the results of XRD analysis of the silicon mixture of Comparative Example 1 according to Experimental Example 1 of the present invention.
Figure 9 is a diagram showing the results of XRD analysis of the silicon mixture of Comparative Example 2 according to Experimental Example 1 of the present invention.
Figure 10 is a diagram showing the results of XRD analysis of the silicon mixture of Comparative Example 3 according to Experimental Example 1 of the present invention.
Figure 11 is a graph showing the charge/discharge capacity and charge/discharge efficiency of the silicon mixture of Example 1 and Comparative Example 3 according to Experimental Example 2 of the present invention.

The present invention is subject to various changes and may have various embodiments, and specific embodiments will be illustrated in the drawings and described in detail in the detailed description. However, this is not intended to limit the present invention to specific embodiments, and should be understood to include all changes, equivalents, and substitutes included in the spirit and technical scope of the present invention.

The terminology used herein is only used to describe specific embodiments and is not intended to limit the invention. Singular expressions include plural expressions unless the context clearly dictates otherwise.

Therefore, the configuration shown in the embodiment described in this specification is only a preferred embodiment of the present invention, and does not represent the entire technical idea of the present invention, so various equivalents can be substituted for them at the time of filing the present application. There may be variations.

Hereinafter, the present invention will be described in detail.

The present invention provides a method for producing a silicone mixture.

The method for producing the silicon mixture may include the step of (A) mixing silicon dioxide with a lithium-based molten salt containing lithium metal.

Through the reaction of step (A), silicon (Si) is essential and at least one selected from the group consisting of lithium silicate (Li ₂ SiO ₃ ) and lithium disilicate (Li ₂ Si ₂ O ₅ ) is optionally added. It may be to manufacture a silicone mixture containing.

Specifically, the silicon mixture may include silicon (Si), lithium silicate (Li ₂ SiO ₃ ), and lithium disilicate (Li ₂ Si ₂ O ₅ ).

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The lithium silicate (Li ₂ SiO ₃ ) and/or lithium disilicate (Li ₂ Si ₂ O ₅ ) may be formed in the process of reducing silicon dioxide to silicon (Si) in step (A).

Silicon (Si) included in the silicon mixture in step (A) may be obtained by reducing the silicon dioxide. That is, in the present invention, silicon can be obtained from silicon dioxide by simply mixing silicon dioxide with lithium-based molten salt using lithium metal as a reducing agent as described above, without supplying electrical energy, which is a conventional method.

In particular, in step (A), the step of reacting silicon dioxide with lithium-based molten salt may be performed spontaneously (i.e., without additional processes) under the relevant process conditions.

Meanwhile, the electrolytic reduction process for producing silicon requires a process of containing the reactant, silicon dioxide (SiO ₂ ), using a porous ceramic basket or stainless mesh basket to use it as an electrode. However, porous ceramics are not widely used because they have a problem of being damaged in molten salt due to their low mechanical strength, and as the electrolytic reduction process occurs in the lithium-based molten salt system, silicon dioxide (SiO ₂ ) is converted into a needle-like structure, etc. Because there is a problem with the mixture leaking out of the basket, the electrolytic reduction process is not suitable for obtaining silicon in high yield from lithium-based molten salt (especially LiCl molten salt-based).

Therefore, the method for producing a silicon mixture according to the present invention using lithium metal as a reducing agent in a lithium-based molten salt does not use an electrochemical reaction by passing a current to an electrode as in the conventional electrolytic reduction process, but rather requires the electrolytic reduction process as described above. The reaction may be carried out spontaneously simply by heating (that is, without the supply of electrical energy). Accordingly, there is no need for a separate electrochemical process to supply electrical energy or a device for this, so there is an advantage in being able to provide high-purity silicon without the need for complicated procedures and without the use of various chemicals.

In addition, according to the method for producing a silicon mixture of the present invention, the product produced is completely contained in the reactor without the need to contain silicon dioxide (SiO ₂ ) like in the electrolytic reduction process, so leakage of unnecessary product can be eliminated, and a simple product can be produced. The desired silicon mixture can be obtained in high yield just by the separation process (process).

Hereinafter, the method for producing the silicone mixture of the present invention will be sequentially described.

Step (A) may include adding lithium-based molten salt and lithium metal into the reactor and then heating to a temperature higher than the melting point of the lithium-based molten salt.

The lithium-based molten salt may include LiCl molten salt, and accordingly, step (A) may include heating to a temperature of 605°C or higher, which is the melting point of the LiCl molten salt, preferably 650°C or higher. Therefore, step (A) may be performed at 605°C or higher, specifically 650°C or higher.

The reactor may be made of graphite to minimize the safety of the reactor and the influence of reactants even at high temperatures (over 600°C) as described above. That is, the reactor may include a graphite reactor, and specifically may include a graphite crucible, but is not limited thereto.

The silicon mixture may further include graphite. As described above, as a reactor made of graphite is used, the final silicon mixture may further contain carbon. This is a natural phenomenon that occurs due to the intercalation characteristics of lithium metal.

In particular, when used as a negative electrode of a lithium secondary battery, battery efficiency is improved when the negative electrode material contains carbon in an appropriate ratio. Therefore, when the silicon mixture of the present invention further contains carbon (graphite), it can be used as a negative electrode in a lithium secondary battery. It becomes more advantageous to apply it to the cathode.

In the step (A), the lithium metal may be mixed in an amount of 1 to 5 parts by weight based on 100 parts by weight of the lithium-based molten salt, specifically, 1 to 3 parts by weight, or 1 to 1.5 parts by weight. It could be.

When the content of lithium metal satisfies the above range, the reduction reaction of silicon dioxide can be efficiently performed to efficiently form the desired silicon mixture.

In step (A), mixing silicon dioxide (SiO ₂ ) into a lithium-based molten salt containing lithium metal may include a method of immersing silicon dioxide (SiO ₂ ) into the lithium-based molten salt.

At this time, the mixing weight ratio of the silicon dioxide (SiO ₂ ) and the lithium metal may be 1:0.5 or more and less than 1:4, specifically 1:0.5 to 1:3, 1:1 to 1:3, or 1:0.5. It may be 1:1.5 or more, 1:1 or more and less than 1:1.5, or 1:1.5 or more and less than 1:4, or 1:1.5 to 1:3.

When the mixing weight ratio of silicon dioxide (SiO ₂ ) and lithium metal satisfies the above range, the desired silicon mixture can be efficiently formed.

In addition, within the range of the content of the lithium metal and the mixing weight ratio of the silicon dioxide (SiO ₂ ) and the lithium metal, as the content of the lithium metal increases compared to silicon dioxide (SiO ₂ ), the silicon mixture that is the final product increases. The proportion of lithium silicide can be increased, and in addition, the reaction time to form the silicon mixture can be shortened.

For example, when the mixing weight ratio of the silicon dioxide (SiO ₂ ) and the lithium metal is 1:0.5 or more and less than 1:1.15, the silicon mixture contains lithium silicate (Li ₂ SiO ₃ ) and lithium disilicate (Li) rather than Si. ₂ Si ₂ O ₅ ) may be included in greater amounts, and when the mixed weight ratio of the silicon dioxide (SiO ₂ ) and the lithium metal is 1:1.15 or more and less than 1:4, the silicon mixture contains Si as lithium silicate ( It may be included in greater amounts than Li ₂ SiO ₃ ) and lithium disilicate (Li ₂ Si ₂ O ₅ ).

That is, in step (A), as described above, a lithium-based molten salt containing lithium metal is first added to the reactor, heated to a temperature of 650 ° C. or higher, and then silicon dioxide (SiO ₂ ) is immersed in the lithium-based molten salt. It may include steps.

At this time, step (A) may include mixing silicon dioxide (SiO ₂ ) with the lithium-based molten salt and reacting the mixture for 1 to 12 hours. Specifically, it may be 1 to 7 hours.

In particular, in order to manufacture the silicon mixture of the present invention in a short time, the average particle diameter (D ₅₀ ) of the silicon dioxide (SiO ₂ ) may be 0.2 to 45 ㎛.

The average particle diameter (D ₅₀ ) of the silicon dioxide may be measured using a laser diffraction method or a scanning electron microscope (SEM), which are commonly used to measure the particle diameter, but is not limited thereto.

Subsequently, the method for producing a silicone mixture of the present invention may further include (B) cooling the product obtained in step (A).

As described above, when the lithium-based molten salt is heated to a temperature higher than the melting point and then mixed with silicon dioxide (SiO ₂ ), a reduction reaction occurs spontaneously within the reactor to generate a silicon mixture.

The product obtained in step (A) may include a silicon mixture present in a lithium-based molten salt.

That is, the step of cooling the product obtained in step (A) in step (B) may be cooling the silicon mixture present in the lithium-based molten salt contained in the reactor.

Among the products obtained in step (A) remaining in the reactor after step (B), the lithium-based molten salt may exist in a crystal form as shown in Figure 2, and the silicon mixture may exist in a solid state at the bottom ( see Figure 2).

In addition, the method for producing a silicon mixture of the present invention may further include the step (C) of separating the lithium-based molten salt from the product obtained in step (A).

Step (C) may include dissolving the product obtained in step (A) in water.

Specifically, after step (A), it may include dissolving the product cooled through step (B) in water.

As described above, the cooled product contains a lithium-based molten salt and a silicon mixture, and the desired product, the silicon mixture, can be separated from the lithium-based molten salt simply by dissolving it in water (deionized water). .

Additionally, the method for producing the silicon mixture may include the step of reusing the lithium-based molten salt dissolved in water and separated from the silicon mixture as described above in step (A). Step (C) may further include removing moisture from the lithium-based molten salt through distillation.

At this time, distillation can be used without limitation as long as it is a method that can generally vaporize water into steam.

As a result, the silicon mixture can be obtained in high yield simply by dissolving it in water, without the final process of washing the silicon product with an acidic solution in the electrolytic reduction process.

Below, the present invention will be described in more detail with reference to preferred embodiments.

However, these examples are for illustrating the present invention in more detail, and the scope of the present invention is not limited thereto.

<Example 1>

After adding 0.3 g of lithium metal and 20 g of LiCl molten salt to the graphite crucible, it was placed in a heating furnace and heated to 650°C.

Next, 0.2 g of silicon dioxide (SiO ₂ ) was immersed and reacted for 1 hour.

Afterwards, the graphite crucible was removed from the heating furnace and cooled at room temperature, and the material in the graphite crucible was dissolved in water and dried to obtain a silicon mixture.

<Example 2>

A silicon mixture was prepared in the same manner as in Example 1, except that 0.2 g of silicon dioxide was immersed and then reacted for 7 hours instead of 1 hour.

<Example 3>

A silicon mixture was prepared in the same manner as in Example 1, except that 0.2 g of lithium metal was used instead of 0.3 g of lithium metal, and the reaction was conducted for 12 hours instead of 1 hour.

<Comparative Example 1>

In Example 1, instead of 0.3 g of lithium metal and 20 g of LiCl molten salt, only 20 g of LiCl molten salt was used, and instead of 0.2 g of silicon dioxide (SiO ₂ ), 0.1 g of silicon dioxide (SiO ₂ ) was immersed, and immersed for 1 hour. A silicone mixture was prepared in the same manner as Example 1, except that the reaction was performed for 2 hours instead of the reaction.

<Comparative Example 2>

In Comparative Example 1, a silicone mixture was prepared in the same manner as Comparative Example 1, except that the reaction was performed for 7 hours instead of 2 hours.

<Comparative Example 3>

In Example 1, 0.4 g of lithium metal was used instead of 0.3 g of lithium metal, 0.1 g of silicon dioxide (SiO ₂ ) was immersed instead of 0.2 g of silicon dioxide (SiO ₂ ), and the reaction was performed for 7 hours instead of 1 hour. Except, a silicone mixture was prepared in the same manner as in Example 1.

<Experimental Example 1> - Confirmation of structure and composition of silicone mixture

SEM photographs of the microstructure of the silicon mixtures of Examples 1 to 3 and Comparative Examples 1 to 3 were measured, and the results are shown in Figures 3 and 4.

In addition, to confirm the composition of the silicone mixture of Examples 1 to 3, the XRD test results are shown in Figures 5 to 7, and to confirm the composition of the silicone mixture of Comparative Examples 1 to 3, the XRD test results are shown in Figures 8 to 10 indicated.

<Experimental Example 2> - Evaluation of charge/discharge capacity and efficiency

With respect to the silicon mixture of Example 1 and Comparative Example 3, when used in the negative electrode of an actual lithium secondary battery, the results of measuring the charge/discharge capacity and initial charge/discharge efficiency (coulombic efficiency) are shown in Table 1 and Figure 11 below. (evaluation conditions are as follows).

Electrode: Silicone mixture: Super P:PAA/CMC = 6:2:2

Electrolyte: EC/DEC (3/7) w/ 10wt% of FEC & 1.3 M LiPF ₆

Precycle: 0.05C

(PAA: polyacrylic acid, CMC: carboxymethyl cellulose, EC: ethylene carbonate, DEC: diethyl carbonate, FEC: fluorinated ethylene carbonate)

division Furtherance charging capacity
(charge capacity)(mAh/g) discharge capacity
(discharge capacity)(mAh/g) Initial charge/discharge efficiency
(initial coulombic efficiency)(%) Example 1 Si/graphite 531 749 70.9 Comparative Example 3 Si/graphite 275 643 42.8

Claims (14)

(A) comprising mixing silicon dioxide with a lithium-based molten salt containing lithium metal,
The lithium metal is included in an amount of 1 to 5 parts by weight based on 100 parts by weight of the lithium-based molten salt,
A method of producing a silicon mixture, wherein the mixing weight ratio of the silicon dioxide and the lithium metal is 1:1 or more and less than 1:4. In claim 1,
The silicon mixture essentially includes silicon (Si),
A method for producing a silicon mixture, which optionally includes at least one selected from the group consisting of lithium silicate (Li ₂ SiO ₃ ) and lithium disilicate (Li ₂ Si ₂ O ₅ ). In claim 2,
A method of producing a silicon mixture, wherein the silicon is obtained by reducing the silicon dioxide. delete delete In claim 2,
A method of producing a silicon mixture, wherein the silicon mixture further includes graphite. In claim 1,
A method of producing a silicon mixture, wherein the lithium-based molten salt includes LiCl molten salt. In claim 1,
The method of producing a silicone mixture, wherein step (A) is performed at 650 ° C. or higher. In claim 1,
A method for producing a silicon mixture, wherein in step (A), silicon dioxide is mixed with the lithium-based molten salt and then reacted for 1 to 12 hours. In claim 1,
(B) A method for producing a silicone mixture, further comprising cooling the product obtained in step (A). In claim 1,
(C) A method for producing a silicon mixture, further comprising the step of separating the lithium-based molten salt from the product obtained in step (A). In claim 11,
The step (C) includes dissolving the product obtained in the step (A) in water. In claim 11,
A method for producing a silicon mixture, comprising the step of reusing the separated lithium-based molten salt in step (A). A silicone mixture prepared according to the method for producing a silicone mixture of any one of claims 1 to 3 and claims 6 to 13.