KR20220118575A - Mass producing method of Lithium sulfide - Google Patents

Abstract

The present invention relates to a method for mass production of high-purity lithium sulfide which comprises the step of a) injecting lithium hydroxide (LiOH) and lithium oxide (Li_2O) into a first reactor and mechanically milling the same to prepare a micronized powder mixture; b) transferring the micronized powder mixture to a second reactor and making the same a first reaction with hydrogen sulfide gas at high temperature and high pressure to prepare a first reactant; and c) transferring the first reactant to a third reactor and making the same a second reaction with hydrogen sulfide gas at high temperature and high pressure to prepare lithium sulfide having a purity of 99.9 % or more.

Description

Mass producing method of high purity lithium sulfide {Mass producing method of Lithium sulfide}

The present invention relates to a method for mass production of high purity lithium sulfide.

The lithium-sulfur secondary battery has a theoretical energy density of 2,800 Wh/kg (1675 mAh/g), which is very high compared to the lithium secondary battery currently commercially available. It is attracting attention as an environmentally friendly material.

In such a lithium-sulfur secondary battery, lithium metal used as a negative electrode is dissociated from lithium metal during the charging/discharging process of the battery and then re-precipitated. There is a problem of causing a short circuit in the battery, which is a factor that lowers the stability of the battery, so it is pointed out as a major limitation in the commercialization of lithium-sulfur secondary batteries.

In addition, in order to activate sulfur in a lithium-sulfur secondary battery, a composite with carbon must be made. In this case, the sublimation temperature of sulfur is too low (~ 115° C.), so an ampoule must always be used. Moreover, even if such an ampoule is used, the degree of adsorption with carbon is very low, so that the loading density of sulfur can be obtained at an appropriate level only by repeating the same process several times, resulting in high process costs.

In order to fundamentally solve the problem of the lithium-sulfur secondary battery, a method of using lithium sulfide (Li ₂ S) instead of sulfur as a positive electrode has been proposed.

When lithium sulfide is used as the positive electrode, lithium metal does not have to be used as the negative electrode, and the filling rate of the positive electrode can be adjusted to a desired degree due to the high melting temperature (~1,000° C.), so that the battery can be implemented with an easier process.

In addition, because of the high melting temperature, various types of post-treatment processes can be performed at high temperatures, and there is an advantage in that the activity of lithium sulfide can be maximized through the post-treatment process.

In addition, in terms of capacity, lithium sulfide, a new cathode material for lithium-sulfur secondary batteries, has a high theoretical capacity (~1,166 mAh/g) comparable to that of sulfur (~ 1,672 mAh/g).

On the other hand, one of the conventional synthesis methods for lithium sulfide is a method using a reaction between lithium hydroxide (LiOH) and hydrogen sulfide as a gaseous sulfur source. A method for producing lithium sulfide in a dry method was proposed by setting the heating temperature to 130 to 445° C. during the reaction of lithium hydroxide and hydrogen sulfide in an inert gas atmosphere.

However, in the dry lithium sulfide manufacturing method as described above, lithium hydroxide has high hygroscopicity, so it is easy to agglomerate, making it difficult to handle a large amount, and it is not easy to micronize the obtained lithium sulfide, and it is difficult to mass-produce lithium sulfide. there is

Japanese Patent Application Laid-Open No. Hei 09-278423 (October 28, 1997)

In order to solve the above problems, an object of the present invention is to provide a method for mass production of lithium sulfide that can be mass-produced and can obtain lithium sulfide with high purity and an average particle size of several microns.

However, the above purpose is illustrative, and the technical spirit of the present invention is not limited thereto.

In one aspect of the present invention for achieving the above object, a) lithium hydroxide (LiOH) and lithium oxide (Li ₂ O) are introduced into a first reactor, and mechanical milling is performed to prepare a pulverized powder mixture; b) transferring the pulverized powder mixture to a second reactor, performing a first high-temperature and high-pressure reaction with hydrogen sulfide gas to prepare a first reactant, and removing impurities; and c) transferring the first reactant to a third reactor, and performing a second high-temperature and high-pressure reaction with hydrogen sulfide gas to produce lithium sulfide; it relates to a mass production method of high-purity lithium sulfide comprising:

In one aspect, the average particle size of the pulverized powder mixture may be 0.1 to 5 ㎛.

In one aspect, the molar ratio of lithium hydroxide to lithium oxide may be 1:0.1 to 1.2.

In the above aspect, the first high-temperature and high-pressure reaction and the second high-temperature and high-pressure reaction may be performed independently of each other at 80 to 500°C.

In one aspect, the average particle size of the lithium sulfide prepared through the manufacturing method may be 10 ㎛ or less.

In one aspect, the purity of the lithium sulfide prepared through the manufacturing method may be 99.9% or more.

The mass production method of high purity lithium sulfide according to the present invention mixes lithium oxide (Li ₂ O) with low hygroscopicity with lithium hydroxide (LiOH), mechanically mills them to pulverize them, and reacts with hydrogen sulfide gas, By lowering the hygroscopicity, the size of the finally obtained lithium sulfide can be reduced to a level of several microns, and when this is applied to a lithium-sulfur secondary battery, there is an advantage that excellent battery performance can be realized.

In addition, by reducing the size of the powder mixture through the mechanical milling treatment process, the disadvantage of lithium oxide with low reactivity with hydrogen sulfide can be compensated so that the finally obtained lithium sulfide has high purity, and when reacting with hydrogen sulfide, the After the high-temperature and high-pressure reaction, the reactor is moved to carry out the second high-temperature and high-pressure reaction, so that the remaining moisture that has not been removed is completely removed, so that more than 99.9% of high purity lithium sulfide can be produced.

Furthermore, there is an advantage in that the hygroscopicity problem caused by lithium hydroxide is improved and mass production is possible.

1 schematically shows each process of a method for mass production of lithium sulfide according to an example of the present invention.
2 is a scanning electron microscope (SEM) image of a powder mixture subjected to mechanical milling according to Examples 1 to 4 (scale bar; 20 μm).
3 is an SEM image of lithium sulfide synthesized according to Examples 1 to 4 (scale bar; 20 μm).
4 is an SEM image of lithium sulfide synthesized according to Comparative Example 2 (scale bar; 50 μm).
5 is an X-ray diffraction (XRD) analysis result of lithium sulfide synthesized according to Examples 1 to 4;
6 is an XRD analysis result of lithium sulfide synthesized according to Comparative Examples 2 and 3.

Hereinafter, a method for mass production of high purity lithium sulfide according to the present invention will be described in detail. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Accordingly, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be exaggerated to clarify the spirit of the present invention. At this time, if there is no other definition in the technical terms and scientific terms used, it has the meaning commonly understood by those of ordinary skill in the art to which this invention belongs, and the gist of the present invention in the following description and accompanying drawings Descriptions of known functions and configurations that may be unnecessarily obscure will be omitted.

One aspect of the present invention comprises the steps of: a) adding lithium hydroxide (LiOH) and lithium oxide (Li ₂ O) to a first reactor, and performing mechanical milling to prepare a pulverized powder mixture; b) transferring the pulverized powder mixture to a second reactor and performing a first high-temperature and high-pressure reaction with hydrogen sulfide gas to prepare a first reactant; and c) transferring the first reactant to a third reactor and performing a second high-temperature and high-pressure reaction with hydrogen sulfide gas to produce lithium sulfide.

As described above, in the method for mass production of high purity lithium sulfide according to the present invention, lithium oxide (Li ₂ O) with low hygroscopicity is mixed with lithium hydroxide (LiOH), and these are milled mechanically to be pulverized and then reacted with hydrogen sulfide gas. Accordingly, the size of the finally obtained lithium sulfide can be reduced to a level of several microns by lowering the hygroscopicity, and when applied to a lithium-sulfur secondary battery, excellent battery performance can be realized.

In addition, by reducing the size of the powder mixture through the mechanical milling treatment process, the disadvantage of lithium oxide with low reactivity with hydrogen sulfide can be compensated so that the finally obtained lithium sulfide has high purity, and when reacting with hydrogen sulfide, the After the high-temperature and high-pressure reaction, the reactor is moved to carry out the second high-temperature and high-pressure reaction, so that the remaining moisture that has not been removed is completely removed, so that more than 99.9% of high purity lithium sulfide can be produced.

Furthermore, there is an advantage in that the hygroscopicity problem caused by lithium hydroxide is improved and mass production is possible.

Hereinafter, each step of the method for mass production of high purity lithium sulfide according to an example of the present invention will be described in more detail.

First, a) lithium hydroxide (LiOH) and lithium oxide (Li ₂ O) are introduced into the first reactor, and a mechanical milling treatment is performed to prepare a pulverized powder mixture.

Lithium hydroxide has high hygroscopicity and is easy to aggregate with each other. Accordingly, when producing lithium sulfide as shown in Scheme 1 below, it is difficult to obtain lithium sulfide micronized to a level of several microns, and there is a problem in that mass production is rather difficult.

Scheme 1: 2LiOH + H ₂ S → Li ₂ S + 2H ₂ O

Accordingly, during repeated research on a method for synthesizing high purity lithium sulfide in large quantities while supplementing the problem of high hygroscopicity of lithium hydroxide, when lithium oxide with low hygroscopicity is mixed with lithium hydroxide, the above problem is solved The present invention was completed by finding that it can be solved.

However, the lithium oxide has low hygroscopicity and has the advantage that it can supplement the high hygroscopicity of lithium hydroxide, but the reaction with hydrogen sulfide is very slow or the reaction is difficult to progress to the inside of the particles after the reaction has progressed to some extent on the surface. , as shown in Scheme 2 below, it is very important to mechanically mill the powder mixture made of lithium hydroxide and lithium oxide to perform mechanical alloying and pulverization. If the milling treatment is not performed sufficiently, it is difficult for lithium oxide to completely react with hydrogen sulfide, so that the purity of lithium sulfide may be reduced.

Scheme 2: LiOH + Li ₂ O → Li ₃ O ₂ H

As a specific example, the mechanical milling treatment may be performed for 30 to 150 minutes, preferably 40 to 100 minutes, and more preferably 50 to 80 minutes. When the mechanical milling treatment is performed for less than 30 minutes, the powder mixture is not sufficiently pulverized, so unreacted lithium oxide may remain in excess, and when the mechanical milling treatment is performed for more than 150 minutes, the powder mixture is no longer pulverized, resulting in energy and Only time can be wasted.

However, the time for the mechanical milling treatment may vary depending on the performance of the machine. Preferably, the mechanical milling treatment time is adjusted according to the average particle size of the pulverized powder mixture after the milling treatment.

As a specific example, the average particle size of the pulverized powder mixture may be 0.1 to 5 μm, more preferably 0.1 to 3 μm, and even more preferably 0.1 to 1.5 μm. In this range, the lithium sulfide finally obtained may have high purity and a size of several microns. Specifically, the average particle size of lithium sulfide prepared by reacting a pulverized powder mixture satisfying the above range with hydrogen sulfide gas may be 10 μm or less, more preferably 0.1 to 5 μm, even more preferably 0.5 to 2 μm, and The purity of lithium sulfide may be 99.9% or more, more preferably 99.93% or more, even more preferably 99.95% or more. In this case, the upper limit of the purity may be 100, and in reality, it may be 99.999%.

Meanwhile, the mechanical milling process may be performed using a planetary mill, a ball mill, a vibration mill, a jet mill, or an attrition mill. Specifically, the mechanical milling treatment may be performed at 0 to 150° C., but the temperature range is not particularly limited, and may be performed in an inert atmosphere such as argon (Ar) or nitrogen (N ₂ ). The ball used in the mechanical milling process has a sphere shape with a diameter of 1 to 50 mm, and may be made of a material such as stainless steel, ceramic, alumina or zirconium, and the weight ratio of the ball: lithium hydroxide and lithium oxide is 1 to 10: 1, but is not necessarily limited thereto.

In addition, in one embodiment of the present invention, the molar ratio of lithium hydroxide: lithium oxide may be 1: 0.5 to 1.2, more preferably 1: 0.8 to 1.2, even more preferably 1: 0.9 to 1.1, most preferably 1 : May be 1. In such a range, it is possible to sufficiently compensate for the high hygroscopicity of lithium hydroxide to produce a finely divided powder mixture, and then to synthesize high-purity lithium sulfide. On the other hand, when lithium oxide is added in an amount less than 0.5 mole times compared to lithium hydroxide, sufficient hygroscopicity improvement is not achieved, so the particle size of the powder mixture may not be sufficiently small even after the same mechanical milling treatment, and lithium oxide is added in more than 1.2 mole times compared to lithium hydroxide Even if the average particle diameter of the powder mixture is sufficiently small when the powder mixture is used, unreacted lithium oxide remains as shown in FIGS.

Thereafter, a step of preparing lithium sulfide (Li ₂ S) by reacting the pulverized powder mixture with hydrogen sulfide gas may be performed, and may be represented by the following Reaction Scheme 3.

Scheme 3: 2Li ₃ O ₂ H + 3H ₂ S → 3Li ₂ S + 4H ₂ O

More specifically, the reaction with the hydrogen sulfide gas comprises the steps of: b) transferring the pulverized powder mixture to a second reactor, and reacting the pulverized powder mixture with the hydrogen sulfide gas at a first high temperature and high pressure to prepare a first reactant; and c) transferring the first reactant to a third reactor and performing a second high-temperature and high-pressure reaction with hydrogen sulfide gas to produce lithium sulfide with a purity of 99.9% or more.

As described above, by mechanically milling lithium hydroxide and lithium oxide and reacting with hydrogen sulfide gas, the high hygroscopicity of lithium hydroxide and the low reactivity of lithium oxide are supplemented to synthesize lithium sulfide having high purity and a size of several microns. After the first high-temperature and high-pressure reaction, the reactor is moved to the second high-temperature and high-pressure reaction, so the remaining moisture that could not be removed is completely removed, so that it is possible to produce lithium sulfide with a purity of 99.9% or more. Mass production of lithium sulfide may also be possible.

As a specific example, the first high-temperature and high-pressure reaction and the second high-temperature and high-pressure reaction may be independently performed at 80 to 500° C., and more preferably at 120 to 200° C. Li ₃ O ₂ H reacts well with hydrogen sulfide gas in this range, so that lithium sulfide can be well synthesized.

In addition, the first high-temperature and high-pressure reaction and the second high-temperature and high-pressure reaction may be independently performed at 1 to 5 atm, and more preferably at 1 to 3 atm. Li ₃ O ₂ H reacts well with hydrogen sulfide gas in this range, so that lithium sulfide can be well synthesized.

The reaction time is sufficient as long as all of the pulverized powder mixture can be converted into lithium sulfide, for example, it may be carried out for 1 hour to 20 hours, but is not necessarily limited thereto.

In this case, steps b) and c) may be independently performed in an inert atmosphere such as argon (Ar) or nitrogen (N ₂ ).

Hereinafter, a method for mass production of high purity lithium sulfide according to the present invention will be described in more detail through examples. However, the following examples are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Also, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention. In addition, the unit of additives not specifically described in the specification may be weight %.

[Example 1]

After adding LiOH and Li ₂ O in a molar ratio of 50:50 to the first reactor, mechanical milling was performed for 15 minutes to prepare a powder mixture having an average particle size of 16.4 μm.

After transferring the pulverized powder mixture to the second reactor, while injecting a mixed gas of hydrogen sulfide and argon at a flow rate of 10 ℓ/h (hydrogen sulfide: argon = 95: 5 volume ratio), 160 ° C. and 2 atm for 5 hours reacted while After the formation of the first reactant, moisture and other impurities are removed, the first reactant is transferred to the third reactor, and hydrogen sulfide gas (hydrogen sulfide: 100%) is again injected at a flow rate of 10 ℓ/h, at 160° C. and 2 atm. and reacted for 5 hours to prepare lithium sulfide (Li ₂ S).

[Example 2]

Lithium sulfide (Li ₂ S) was prepared in the same manner as in Example 1 except that the milling time was 30 minutes and a powder mixture having an average particle size of 9.4 μm was prepared.

[Example 3]

Lithium sulfide (Li ₂ S) was prepared in the same manner as in Example 1 except that a powder mixture having an average particle size of 3.6 μm was prepared by using a milling time of 45 minutes.

[Example 4]

Lithium sulfide (Li ₂ S) was prepared in the same manner as in Example 1 except that the milling time was 60 minutes and a powder mixture having an average particle size of 1.3 μm was prepared.

[Comparative Example 1]

Lithium sulfide ₍ Li ₂ S) was prepared.

[Comparative Example 2]

Lithium sulfide (Li ₂ S) was prepared in the same manner as in Example 1 except that LiOH was not milled and reacted with hydrogen sulfide gas in a raw powder state.

[Comparative Example 3]

Lithium sulfide (Li ₂ S) was prepared in the same manner as in Example 1 except that Li ₂ O was reacted with hydrogen sulfide gas in a raw powder state without milling treatment.

[Comparative Example 4]

Lithium sulfide (Li ₂ S) was prepared in the same manner as in Example 4 except that only LiOH was used.

[Comparative Example 5]

Lithium sulfide (Li ₂ S) was prepared in the same manner as in Example 4 except that only Li ₂ O was used.

Raw material molar ratio milling time
(minute) powder mixture
Average particle size (㎛) Li ₂ S
Average particle size (㎛) note LiOH Li ₂ O Example 1 50 50 15 16.4 4.7 Example 2 50 50 30 9.4 2.6 Example 3 50 50 45 3.6 1.5 Example 4 50 50 60 1.3 0.8 Comparative Example 1 50 50 - LiOH >100,
Li ₂ O 33 45 Comparative Example 2 100 - - >100 64 Comparative Example 3 - 100 - 33 - Only the particle surface reacts Comparative Example 4 100 - 60 >100 79 Comparative Example 5 - 100 60 1.0 - Only the particle surface reacts

[Characteristic evaluation]

1) Particle size analysis:

The average particle sizes of the powder mixtures of Examples 1 to 4 and Comparative Examples 1 to 5 and lithium sulfide were analyzed using a laser particle size analyzer, and are shown in Table 1 above.

Referring to Table 1, in the case of mechanical milling of lithium hydroxide and lithium oxide, it can be seen that the average particle size of the powder mixture, Li ₃ O ₂ H, decreases as the milling time increases. It was confirmed that the average particle size of Li ₃ O ₂ H was reduced to 5 μm or less when performing.

On the other hand, in Comparative Examples 1, 2, and 3, the average particle size of the two powder mixtures was very large at the level of several tens of microns as the raw material was used without mechanical milling, and in particular, in the case of Comparative Example 3, as shown in FIG. It was confirmed that the reaction proceeded only on the surface of the lithium oxide, and most of the lithium oxide remained. In Comparative Example 4, lithium hydroxide having high hygroscopicity showed a tendency to agglomerate more as the mechanical milling treatment was performed. There was a problem in that the reaction did not proceed and only occurred on the surface of the particle, leaving lithium oxide.

In addition, a scanning electron microscope (SEM) was measured for the powder mixture of Examples 1 to 4 and lithium sulfide prepared according to Examples 1 to 4 and Comparative Example 2, and the results are shown in FIGS. 1 to 3 .

1 is an SEM image of the powder mixture of Examples 1 to 4, and it was confirmed that, as in the particle size analysis, the average particle size of the powder mixture gradually decreased as the milling time increased, as can be seen from the following XRD analysis. , it was found that the smaller the average particle size of the powder mixture, the better it reacted with hydrogen sulfide gas, and the content of impurities gradually decreased.

2 and 3 are SEM images of lithium sulfide prepared according to Examples 1 to 4 and Comparative Example 2, which is also the same as the particle size analysis. Accordingly, it was confirmed that the particle size gradually decreased. In particular, in the case of lithium sulfide prepared in Example 4, the average particle size was ultra-fine to 0.8 μm. On the other hand, as for the lithium sulfide prepared in Comparative Example 2, only non-milled LiOH was used, so that a large-sized lithium sulfide having an average particle size of 64 μm was prepared.

2) X-ray diffraction analysis (XRD):

XRD was analyzed for lithium sulfide prepared according to Examples 1 to 4 and Comparative Examples 2 to 3, and the results are shown in FIGS. 4 and 5 .

Referring to FIG. 4 , as the milling time increased, the content of impurities gradually decreased, and in the case of Example 4, which was milled for 60 minutes, it was found that lithium sulfide was manufactured with high purity without impurities.

In particular, even in the results of analyzing the lithium sulfide of Example 4 by inductively coupled plasma spectroscopy (ICP-OES), the three analysis samples showed purity of 99.994%, 99.970%, and 99.987%, respectively, with an average of 99.98% or higher. It was confirmed that high-purity lithium sulfide could be produced by showing the purity. At this time, the purity of lithium sulfide (Li ₂ S) was calculated through the order method, specifically, it was calculated as 100- (sum of weight % of analyte elements detected through ICP-OES analysis), and the analyte element was Ca, Si, Sb, Al, As, B, Ba, Be, Bi, Cd, Ce, Co, Cr, Cu, Fe, Ga, Ge, Hf, In, K, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Rb, Sc, Se, Sn, Ta, Ti, Tl, V, W, Zn and Zr.

On the other hand, referring to FIG. 5 , in Comparative Example 2 using only LiOH, lithium sulfide was prepared without impurities, whereas in Comparative Example 3 using only Li ₂ O, Li ₂ O was still remaining at a high content, and Li ₂ S and LiOH was detected in small amounts. In addition, even in the case of Comparative Example 5 (not shown), there was a problem in that Li ₂ O was not completely reacted and remained in a high content. It is judged that the reaction is very slow or that the reaction is difficult to proceed to the inside of the particle after the reaction has progressed to some extent on the surface.

Although the present invention has been described through the specific matters and limited examples as described above, these are only provided to help a more general understanding of the present invention, and the present invention is not limited to the above examples, and the present invention pertains to Various modifications and variations are possible from these descriptions by those of ordinary skill in the art.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and not only the claims to be described later, but also all those with equivalent or equivalent modifications to the claims will be said to belong to the scope of the spirit of the present invention. .

Claims (6)

a) preparing a pulverized powder mixture by introducing lithium hydroxide (LiOH) and lithium oxide (Li ₂ O) into a first reactor, and performing mechanical milling;
b) transferring the pulverized powder mixture to a second reactor and performing a first high-temperature and high-pressure reaction with hydrogen sulfide gas to prepare a first reactant; and
c) preparing lithium sulfide by transferring the first reactant to a third reactor and reacting with hydrogen sulfide gas at a second high temperature and pressure;
A method for mass production of high-purity lithium sulfide, comprising:
The method of claim 1,
The average particle size of the pulverized powder mixture is 0.1 to 5 ㎛, mass production method of high purity lithium sulfide.
The method of claim 1,
The molar ratio of lithium hydroxide: lithium oxide is 1: 0.1 to 1.2, mass production method of high purity lithium sulfide.
The method of claim 1,
The first high-temperature and high-pressure reaction and the second high-temperature and high-pressure reaction are each independently performed at 80 to 500° C., a method for mass production of high-purity lithium sulfide.
The method of claim 1,
An average particle size of the lithium sulfide prepared through the above production method is 10 μm or less, a method for mass production of high purity lithium sulfide.
The method of claim 1,
The purity of the lithium sulfide manufactured through the above manufacturing method is 99.9% or more, a mass production method of high purity lithium sulfide.

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