Lithium sulfide powder and manufacturing method thereof

Abstract

The lithium sulfide powder according to the present invention comprises 2 wt % or less of Li2O 2 on the basis of the total 100 wt% thereof, wherein the lithium sulfide powder has an oxygen content of 1 wt% or less and a carbon content of 0.15 wt% or less.

Description

Lithium sulfide powder and method for producing the same

[0001] The present invention relates to lithium sulfide powder and a method for producing the same.

[0002] The next-generation battery field is expected to focus on technological development aimed at improving the performance of currently commercialized lithium-ion batteries, targeting electric vehicles, and on developing all-solid-state batteries with enhanced performance, safety, and large-capacity applications. Among these, there is growing demand for technological development in all-solid-state batteries, which offer advantages such as safety, high energy density based on a bipolar structure, high output, and temperature stability.

[0003] Among the solid electrolytes used in all-solid-state batteries, sulfide-based electrolyte materials offer advantages in ionic conductivity and cell performance. Lithium sulfide (Li2S), the primary material for these sulfide-based electrolytes, is a key component of solid electrolytes. However, the high difficulty of manufacturing technology hinders high-quality, high-purity, and mass production.

[0004] Typically, lithium sulfide is produced by thermal reduction using a carbon-containing powder source, such as coke or artificial graphite, and a lithium and sulfur-containing source, such as lithium sulfate. Typically, this thermally reduced lithium sulfide is often mixed with a reducing agent, carbon powder. To improve its quality, the lithium sulfide undergoes an extraction process using an organic solvent, such as ethanol. This is followed by a drying process to remove the organic solvent.

[0005] At this time, heat treatment is performed to remove residual solvents such as ethanol from the manufactured lithium sulfide dried product. However, if ethanol and the resulting decomposition gas are not discharged smoothly during the heat treatment, surface soot is generated due to carbonization.

[0006] To suppress this, a large amount of argon gas is injected during the heat treatment process, but there is a problem that the process cost increases when a large amount of argon gas is used.

[0007] Therefore, there is a need to develop a method for manufacturing lithium sulfide powder that can lower the process cost while suppressing the carbonization phenomenon.

[0008] The present invention aims to provide lithium sulfide powder having excellent whiteness and a low content of impurities.

[0009] The present invention aims to provide a method for manufacturing lithium sulfide powder, which can reduce the cost of the manufacturing process of lithium sulfide powder by reducing the amount of argon gas used while suppressing the carbonization phenomenon, and can reduce impurities.

[0010] The present invention provides a lithium sulfide powder comprising 2 wt% or less of Li2O with respect to a total of 100 wt%, wherein the oxygen content in the lithium sulfide powder is 1 wt% or less and the carbon content in the lithium sulfide powder is 0.15 wt% or less.

[0011] In addition, the present invention provides a method for producing lithium sulfide powder, comprising the steps of: preparing a lithium sulfide precursor powder containing 60 wt% or less of ethanol with respect to a total of 100 wt%; and subjecting the lithium sulfide precursor powder to a reduced pressure heat treatment.

[0012] Lithium sulfide according to the present invention has the advantages of excellent whiteness due to less surface soot and a low content of impurities.

[0013] Furthermore, the method for manufacturing lithium sulfide powder according to the present invention has the advantage of reducing process costs by suppressing carbonization and eliminating the use of argon gas. Furthermore, it has the advantage of easily manufacturing lithium sulfide with excellent whiteness and low impurity content.

[0014] Figure 1 is a diagram showing lithium sulfide powder manufactured according to examples and comparative examples.

[0015] Figure 2 is a diagram showing XRD peaks of lithium sulfide powder manufactured according to examples and comparative examples.

[0016] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention. The present invention is defined solely by the scope of the claims set forth below.

[0017] In the present invention, when it is said that a member is located “on” another member, this includes not only cases where a member is in direct contact with another member, but also cases where another member is interposed between the two members.

[0018] When a part of the present invention is said to "include" a certain component, this does not mean that other components are excluded, but rather that other components may be included, unless otherwise specifically stated.

[0019]

[0020] <Lithium sulfide powder>

[0021] One aspect of the present invention relates to a lithium sulfide powder comprising 2 wt% or less of Li2O with respect to a total of 100 wt%, wherein the oxygen content in the lithium sulfide powder is 1 wt% or less and the carbon content in the lithium sulfide powder is 0.15 wt% or less.

[0022] The lithium sulfide powder according to the present invention has the advantage of having a very low content of impurities such as Li2O and, in particular, a low carbon content.

[0023]

[0024] In another embodiment of the present invention, the Li2O may be included in an amount of 1.5 wt% or less, specifically 1.0 wt% or less, and more specifically 0.8 wt% or less, based on 100 wt% of the total lithium sulfide powder.

[0025] When the above Li2O is included within the above range, it is preferable because it can provide excellent performance when applied as a solid electrolyte.

[0026]

[0027] The above lithium sulfide powder may not contain impurities composed of other lithium compounds, such as LiOH, Li2SO4, Li2CO3, etc., other than the above Li2O.

[0028]

[0029] In another embodiment of the present invention, the oxygen content in the lithium sulfide powder may be 0.85 wt% or less, more specifically 0.45 wt% or less.

[0030] The lithium sulfide powder according to the present invention has the advantage of being useful as a solid electrolyte because the content of oxygen in the lithium sulfide powder is low.

[0031]

[0032] In another embodiment of the present invention, the carbon content in the lithium sulfide powder may be 0.12 wt% or less, specifically 0.11 wt% or less.

[0033] The lithium sulfide powder according to the present invention is preferable because, during the manufacturing process, the phenomenon of carbonization of ethanol remaining in the lithium sulfide precursor powder and the resulting decomposition gas is suppressed, so that the carbon content is very low and the whiteness is excellent.

[0034]

[0035] The lithium sulfide powder according to the present invention has a low content of impurities and excellent whiteness, and thus has the advantage of being usefully applied as a sulfide-based solid electrolyte for next-generation secondary batteries and as a battery material such as a lithium-sulfur battery.

[0036]

[0037] <Method for producing lithium sulfide powder>

[0038] Another aspect of the present invention relates to a method for producing lithium sulfide powder, comprising the steps of: preparing a lithium sulfide precursor powder containing 60 wt% or less of ethanol with respect to a total of 100 wt%; and subjecting the lithium sulfide precursor powder to a reduced pressure heat treatment.

[0039] The method for manufacturing lithium sulfide powder according to the present invention includes a step of subjecting the lithium sulfide precursor powder to a reduced pressure heat treatment, thereby enabling rapid discharge of by-product gases generated during the heat treatment process, thereby suppressing carbonization. In addition, there is an advantage in that the amount of argon gas used can be reduced.

[0040]

[0041] A method for producing lithium sulfide powder according to the present invention includes the step of preparing a lithium sulfide precursor powder containing 60 wt% or less of ethanol with respect to a total of 100 wt%.

[0042] The lithium sulfide precursor powder containing the above ethanol can be obtained by mixing the above pulverized carbon-based material with lithium sulfate powder or an aqueous solution, then thermally reducing the mixture to obtain a thermally reduced product, extracting the mixture, and drying the mixture, but is not limited thereto. In this case, during the process of obtaining the thermally reduced product, a solvent (antisolvent) may be further added to prepare a slurry, and then thermally reducing the mixture to obtain the thermally reduced product, but is not limited thereto.

[0043] Specifically, the ethanol may be a component derived from a solvent used in the process of obtaining the lithium sulfide precursor powder, specifically, a solvent used in the process of extracting the thermally reduced product.

[0044] In short, the method for producing lithium sulfide powder according to the present invention removes the remaining solvent by subjecting lithium sulfide precursor powder to reduced pressure heat treatment.

[0045]

[0046] In another embodiment of the present invention, in the step of preparing the lithium sulfide precursor powder, the molar ratio of S / Li in the lithium sulfide precursor powder may be 0.46 to 0.49, preferably 0.47 to 0.48.

[0047] When the molar ratio of S / Li in the lithium sulfide precursor powder satisfies the above range, it is preferable because it has the advantage of being able to reduce the oxygen weight and carbon content of the lithium sulfide powder produced.

[0048]

[0049] A method for producing lithium sulfide powder according to the present invention includes a step of subjecting the lithium sulfide precursor powder to reduced pressure heat treatment.

[0050] Since the present invention includes a step of subjecting the lithium sulfide precursor powder to reduced pressure heat treatment, there is an advantage in that a lithium sulfide powder having a low content of impurities can be manufactured by suppressing the carbonization phenomenon without using argon gas, which has been used in the past.

[0051]

[0052] In another embodiment of the present invention, the step of heat treating the lithium sulfide precursor powder under reduced pressure may be performed at a pressure of 10 to 25 mbar, preferably at a pressure of 13 to 23 mbar.

[0053] When the step of heat treating the lithium sulfide powder under reduced pressure is performed under the above pressure, it is preferable that the phenomenon of the unit cost of the equipment increasing and the economic feasibility of the manufacturing process being lowered can be suppressed, while the advantage of reduced pressure, i.e., the reduction in the unit cost of the process due to non-use of argon gas, can be realized.

[0054] Without wishing to be limited by theory, the dried lithium sulfide is heat-treated to remove residual solvents such as ethanol, yielding the final purified white lithium sulfide powder. However, if ethanol and its resulting decomposition gases are not smoothly discharged during the heat treatment, surface soot may occur due to carbonization.

[0055] Therefore, in the past, in order to suppress surface soot caused by the above-mentioned carbonization phenomenon, a large amount of argon gas had to be injected during the heat treatment process, but the method for manufacturing lithium sulfide powder according to the present invention has the advantage of not having to use the above-mentioned argon gas because it uses reduced pressure heat treatment.

[0056]

[0057] In another embodiment of the present invention, the step of heat-treating the lithium sulfide precursor powder under reduced pressure may be a step of removing the ethanol contained in the lithium sulfide precursor powder.

[0058]

[0059] The step of performing a reduced pressure heat treatment on lithium sulfide powder according to the present invention does not use argon gas.

[0060]

[0061] In another embodiment of the present invention, the step of subjecting the lithium sulfide precursor powder to a reduced pressure heat treatment may include a step of subjecting the lithium sulfide precursor powder to a first reduced pressure heat treatment at a temperature of 50 to 200°C; and a step of subjecting the lithium sulfide precursor powder subjected to the first reduced pressure heat treatment to a second reduced pressure heat treatment at 700 to 1,000°C.

[0062] When the step of heat treating the above lithium sulfide precursor powder under reduced pressure is performed in two steps as described above, there is an advantage in that the carbonization phenomenon caused by ethanol and organic decomposition products derived from ethanol is suppressed as much as possible, thereby obtaining lithium sulfide powder with a low content of impurities, which is preferable.

[0063] The above first pressure-reducing heat treatment step can be performed to remove residual ethanol and organic decomposition products derived from ethanol as much as possible at a relatively low temperature.

[0064] The first reduced pressure heat treatment may be preferably performed at a temperature of 100 to 200°C, more preferably at a temperature of 100 to 150°C, for 2 to 5 hours, but is not limited thereto. However, when the first reduced pressure heat treatment is performed within the above range, the removal rate of the ethanol and organic decomposition products derived from the ethanol is excellent while minimizing the reduced pressure heat treatment time, which is preferable.

[0065]

[0066] The second reduced pressure heat treatment step may be performed to increase the crystallinity of the first reduced pressure heat treatment material and to prevent substances caused by a very small amount of residual ethanol from being generated as impurities such as LiOH or Li2CO3.

[0067] The above second reduced pressure heat treatment may be preferably performed at a temperature of 700 to 900°C, more preferably at a temperature of 800 to 900°C, for 1 to 3 hours, but is not limited thereto.

[0068] When the second reduced pressure heat treatment is performed within the above range, it is preferable to produce lithium sulfide with low impurities and high crystallinity while minimizing the reduced pressure heat treatment time.

[0069]

[0070] The above first reduced pressure heat treatment and the above second reduced pressure heat treatment may be performed as a continuous process. Specifically, the second reduced pressure heat treatment may be performed as a continuous process within the furnace in which the first reduced pressure heat treatment was performed, but is not limited thereto.

[0071]

[0072] The method for producing lithium sulfide powder according to the present invention has the advantage of easily producing lithium sulfide with high purity through a step of reduced pressure heat treatment even when there is a certain difference in the raw material of lithium sulfide powder.

[0073]

[0074] Hereinafter, preferred embodiments and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention, and the present invention is not limited to the following examples.

[0075]

[0076] Manufacturing example

[0077] 5.1 kg of graphite and 1.7 kg of lithium sulfate monohydrate were evenly mixed, and then heated to 200°C at a rate of 5°C per minute in an inert gas (Ar) atmosphere. The mixture was maintained at 200°C for 3 hours to remove any water present in the mixture. Subsequently, the temperature was raised to 900°C at a rate of 5°C per minute, and thermal reduction treatment was performed at the same temperature for 2 hours. This resulted in the reduction of lithium sulfate to lithium sulfide, which was then mixed with graphite.

[0078] Afterwards, the obtained mixture was naturally cooled in an inert gas atmosphere and stored in a glove box. Then, it was divided into small portions and used in all examples and comparative experiments.

[0079] In an inert gas atmosphere, 0.7 kg of thermal reduction product and 3 g of solid sulfur powder were placed in a 20-L filtration reactor containing 5 L of ethanol and stirred sufficiently. The amount of sulfur powder introduced here is a process parameter that controls the S / Li molar ratio of the lithium sulfide precursor powder obtained in the subsequent drying step. After stopping stirring and filtering the mixed slurry, the graphite that is insoluble in ethanol remains wet at the top of the filtration reactor, and the remainder is obtained as a solution in a 20-L glass flask located below the filtration reactor. At this time, the color of the solution was transparent yellow.

[0080] Afterwards, the prepared filtrate was transferred to a 10 L round-bottom flask, which was then mounted on a rotary evaporator, and the solution was evaporated and concentrated using a vacuum pump to proceed with the drying process. The vacuum pressure was initially 350 mbar and then lowered to 100 mbar within 30 minutes, and drying was performed for 2 or 3 hours. The ethanol content in the dried precursor powder varied depending on the drying time. During drying, the temperature was maintained at 60°C in an external constant-temperature water bath to obtain the dried lithium sulfide precursor powder.

[0081]

[0082] Examples 1 and 2

[0083] Lithium sulfide precursor powders manufactured according to the manufacturing examples were subjected to reduced pressure heat treatment under the conditions shown in Table 1 to obtain lithium sulfide powders. Specifically, the heat treatment was performed in two stages. In order to remove residual ethanol and organic decomposition products derived from ethanol, the first reduced pressure heat treatment was performed at 100°C and 150°C for 5 hours (Example 1) and 2 hours (Example 2), respectively, and finally, the second reduced pressure heat treatment was performed at 800°C for 2 hours to obtain lithium sulfide powders. The heat treatment temperature increase rate was 5°C / min.

[0084]

[0085] Comparative Examples 1 and 2

[0086] To investigate the influence of the S / Li molar ratio of the precursor powder, lithium sulfide powder was obtained by the following method. The manufacturing process of obtaining lithium sulfide powder from thermal reduction of lithium sulfate was performed in the same manner as described in the above manufacturing examples and examples. However, in the step of extracting lithium sulfide in a solution phase by adding the thermal reduction product and solid sulfur powder to ethanol, the amounts of sulfur powder added were changed to 2 g and 3 g, respectively.

[0087]

[0088] Experimental example

[0089] The analysis results of the lithium sulfide precursor powder manufactured according to the manufacturing example and the lithium sulfide powder manufactured according to the examples and comparative examples are shown in Table 1 below.

[0090] At this time, the ethanol content was measured using a TA instruments SDT Q600 thermogravimetric analyzer (TGA), and the S / Li molar ratio of the lithium sulfide precursor powder was measured using a SpectroArcos inductively coupled plasma optical emission spectrometer (ICP-OES) from Spectro Ametek. In the case of the optical emission analysis method, in order to accurately measure the amount of the corresponding element in the precursor powder, the powder was pretreated with a hydrogen peroxide solution in an aqueous state, and then the analysis was performed.

[0091] The crystal phase of the manufactured lithium sulfide powder was analyzed using an X-ray diffractometer equipped with a D / MAX 2500 from Rigaku, and the impurity content ratio was measured through this. The oxygen and carbon contents were measured using an elemental analyzer from Leco, and the results are shown in Table 1 below. At this time, H% in the impurity content ratio is a value expressed as a relative ratio of the intensity of the main diffraction peak line of Li2O to 100% of the intensity of the main diffraction peak line of Li2S in XRD analysis.

[0092] In addition, it was reported that the oxygen content in lithium sulfide was all derived from the Li2O crystal phase observed in the XRD analysis results, and the weight % of Li2O was calculated based on the molar concept.

[0093]

[0094] In addition, a photograph of the manufactured lithium sulfide powder is shown in Fig. 1, and the XRD analysis results of each powder are shown in Fig. 2.

[0095]

[0096] Lithium sulfide precursor powder heat treatment conditions Lithium sulfide powder (Li2S) analysis S / Li molar ratio (mol / mol) Ethanol content (wt%) 1st temperature (℃) 2nd temperature (℃) Reduced pressure condition (mbar) Impurity content ratio Powder color Oxygen content (wt%) Carbon content (wt%) Li2O (H%) Li2O (wt%) Example 10.47560100800130.40.8 White 0.410.12 Example 20.47746150800231.41.5 White or light gray 0.820.11 Comparative example 10.45863150800233.54.5 White or light gray 2.40.10 Comparative example 20.49261150800130.30.6 Dark Gray 0.331.5

[0097]

[0098] Referring to Table 1, Figures 1 and 2 above, the lithium sulfide powder manufactured according to the example has the advantage of having a very low content of impurities and excellent whiteness.

[0099]

[0100] The present invention is not limited to the above-described embodiments, but can be manufactured in a variety of different forms. Those skilled in the art will appreciate that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive.

Claims

1. For 100% of the total weight, In lithium sulfide powder containing Li2O 2 wt% or less, The oxygen content in the above lithium sulfide powder is 1 wt% or less, The carbon content in the lithium sulfide powder is 0.15 wt% or less, Lithium sulfide powder.

2. In paragraph 1, Lithium sulfide powder wherein the above Li2O is contained in an amount of 1.5 wt% or less with respect to 100 wt% of the total lithium sulfide powder.

3. In paragraph 1, Lithium sulfide powder having an oxygen content of 0.85 wt% or less in the lithium sulfide powder.

4. In paragraph 1, Lithium sulfide powder having a carbon content of 0.12 wt% or less in the lithium sulfide powder.

5. A step of preparing a lithium sulfide precursor powder containing 60 wt% or less of ethanol with respect to the total 100 wt%; and A step of heat treating the lithium sulfide precursor powder under reduced pressure; A method for producing lithium sulfide powder comprising:

6. In paragraph 5, The step of heat-treating the lithium sulfide precursor powder under reduced pressure; A step of first reducing pressure heat treatment of the above lithium sulfide precursor powder at a temperature of 50 to 200°C; and A step of performing a second reduced pressure heat treatment on the lithium sulfide precursor powder subjected to the first reduced pressure heat treatment at 700 to 1,000°C; A method for producing lithium sulfide powder comprising:

7. In paragraph 5, A method for producing lithium sulfide powder, wherein the step of subjecting the lithium sulfide precursor powder to reduced pressure heat treatment is performed at a pressure of 10 to 25 mbar.

8. In paragraph 7, A method for producing lithium sulfide powder, wherein the step of subjecting the lithium sulfide precursor powder to reduced pressure heat treatment is performed at a pressure of 13 to 23 mbar.

9. In paragraph 5, A method for producing lithium sulfide powder, wherein the step of heat-treating the lithium sulfide precursor powder under reduced pressure is a step of removing the ethanol contained in the lithium sulfide powder.

10. In paragraph 6, A method for producing lithium sulfide powder, wherein the first reduced pressure heat treatment is performed at a temperature of 100 to 150°C.

11. In paragraph 6, A method for producing lithium sulfide powder, wherein the second reduced pressure heat treatment is performed at a temperature of 700 to 900°C.

12. In paragraph 6, A method for producing lithium sulfide powder, wherein the first reduced pressure heat treatment is performed for 2 to 5 hours.

13. In paragraph 6, A method for producing lithium sulfide powder, wherein the second reduced pressure heat treatment is performed for 1 to 3 hours.

14. In paragraph 5, A method for producing lithium sulfide powder, wherein in the step of preparing the lithium sulfide precursor powder, the molar ratio of S / Li in the lithium sulfide precursor powder is 0.46 to 0.49.

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