Preparation method of high-purity lithium sulfide

Abstract

The invention provides a preparation method of high-purity lithium sulfide, which comprises the following steps: (1) under the protection of inert atmosphere, mixing and dispersing silicon sulfide and lithium fluoride, transferring into a reactor, heating the material in the reactor to a certain temperature under the inert atmosphere, and keeping the temperature for a certain time for reaction to obtain a lithium sulfide crude product and silicon fluoride gas; and (2) dissolving the lithium sulfide crude product in an organic solvent, filtering to remove insoluble impurities, concentrating, and drying to obtain the high-purity lithium sulfide. The preparation method is simple and efficient, and the prepared lithium sulfide is high in purity.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of compound preparation, and in particular to a preparation method of high-purity lithium sulfide. BACKGROUND

[0002] With the acceleration of global energy structure transformation, the demand for high-energy density and low-cost energy storage systems for electric vehicles, smart grids and portable electronic devices is growing exponentially. Traditional batteries have been difficult to meet market demand, and there is an urgent need to develop a battery technology with high energy density, high safety and low cost. All-solid-state metal lithium batteries and lithium-sulfur batteries have become one of the most potential next-generation energy storage technologies due to their ultra-high energy density. The core raw material lithium sulfide plays a key role in determining the energy density, cycle life and reaction kinetics of lithium-sulfur batteries.

[0003] Lithium sulfide (Li2S) as a positive active material for lithium-sulfur batteries and a precursor for sulfide solid-state electrolytes is one of the most important basic raw materials for solid-state lithium-ion batteries. The purity of industrial-grade Li2S is usually above 99.5%, while battery-grade products usually need to be further purified to above 99.9% to meet the requirements of electrochemical performance.

[0004] Current preparation methods of lithium sulfide are mostly in the laboratory research and development stage, and the industrialization progress is slow. There are problems such as low purity of the prepared product, the need for further purification, high cost, and complex process. CN112607712A discloses a preparation method of lithium sulfide by direct reaction of sulfur and metal lithium. However, this preparation method has problems of residual polysulfide and high cost of metal lithium. CN118289714A discloses a method for preparing high-purity lithium sulfide. The method is to mix lithium fluoride and chlorosilicon compound, then dissolve in a first organic solvent, then pass in hydrogen sulfide gas, heat to react to obtain lithium sulfide, fluorosilicon compound gas and hydrogen chloride gas, then wash and filter with a second organic solvent, and finally dry under reduced pressure to obtain lithium sulfide product. This method produces a large amount of acidic and corrosive gas, which requires high equipment requirements. In addition, hydrogen sulfide gas is used as raw material, which is a highly toxic gas that can cause death in a short time at a concentration of 10 ppm. Therefore, the industrialization of this process has a large safety problem.

[0005] Therefore, it is urgent to develop a green, safe and low-cost production process to prepare high-purity lithium sulfide to meet the demand for battery-grade lithium sulfide. SUMMARY

[0006] To solve the problems in the background art, the present application provides a preparation method of high-purity lithium sulfide, which is simple and efficient, and the prepared lithium sulfide has high purity. The technical solution of the present application to solve the above technical problems is as follows: A method for preparing high-purity lithium sulfide, comprising the following steps: (1) mixing and dispersing silicon sulfide and lithium fluoride under the protection of inert atmosphere, transferring to a reactor, heating the materials in the reactor to a certain temperature under inert atmosphere for a certain time to react, obtaining crude lithium sulfide and silicon fluoride gas; (2) dissolving the crude lithium sulfide in an organic solvent, removing insoluble impurities by filtration, concentrating and drying to obtain high-purity lithium sulfide.

[0007] According to the above scheme, the molar ratio of silicon sulfide to lithium fluoride is 1:2.4-1:8.

[0008] According to the above scheme, the molar ratio of silicon sulfide to lithium fluoride is 1:4-1:6.

[0009] According to the above scheme, the dispersion method is any one of ball milling, mechanical fusion, dry grinding or gas phase dispersion.

[0010] According to the above scheme, the temperature in step (1) is 150-900℃, and the time is 1.6-24h.

[0011] Preferably, the temperature of the reaction is 400-800℃, and the time is 12-18h.

[0012] According to the above scheme, the reaction in step (1) is carried out under negative pressure.

[0013] According to the above scheme, the pressure of the reaction is -0.1-0MPa, preferably -0.098MPa--0.080MPa.

[0014] According to the above scheme, the organic solvent in step (2) is selected from one or a combination of several of alcohol solvents, ether solvents or amide solvents.

[0015] The organic solvent is selected from one or a combination of several of alcohol solvents such as methanol, ethanol, isopropanol, ether solvents such as dimethyl ether, diethyl ether, ethylene glycol monomethyl ether, ethylene glycol dimethyl ether, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, or amide solvents such as dimethylformamide, dimethylacetamide, N-methylpyrrolidone.

[0016] According to the above scheme, the mass concentration of the crude lithium sulfide in the organic solvent is 5%-25%.

[0017] According to the above scheme, the precision of the filter used to remove insoluble impurities in step (2) is 0.01-20μm.

[0018] According to the above scheme, the drying temperature in step (2) is 50-120℃, preferably 80-120℃.

[0019] According to the above scheme, the drying pressure in step (2) is -0.1-1.0 MPa, preferably -0.1--0.08 MPa or 0-0.5 MPa.

[0020] The present application utilizes the natural affinity of silicon and fluorine, mixes and disperses silicon sulfide and lithium fluoride, and then heats to form lithium sulfide crude and volatile silicon tetrafluoride gas, and the reaction equation is: SiS2+ 4LiF → 2Li2S + SiF4↑ Lithium sulfide is dissolved in an organic solvent, while the remaining silicon sulfide and lithium fluoride in the reaction system are insoluble in most organic solvents. By taking advantage of the solubility difference of lithium sulfide, raw silicon sulfide and lithium fluoride in organic solvents and the volatility of silicon fluoride, high-purity lithium sulfide can be obtained by dissolving, filtering, concentrating and drying after the reaction.

[0021] The present application has the following advantages: 1) The present application uses silicon disulfide and lithium fluoride as raw materials, utilizes the strong affinity of fluorine and silicon for directional reaction to form lithium sulfide and by-product silicon tetrafluoride. On the one hand, the raw materials are widely available, stable in nature and low in price. On the other hand, the reaction efficiency is high, the side reaction is less, and the purity of the lithium sulfide crude obtained by direct reaction is above 95%. On the other hand, the by-product is a volatile gas, easy to separate, and is an important chemical raw material with certain economic value.

[0022] 2) After the raw materials are heated and reacted, high-purity lithium sulfide can be obtained by dissolving in an organic solvent, filtering, concentrating and drying. The separation and purification is simple, the purification efficiency is high, and the purity of the obtained lithium sulfide is above 99.95%, meeting the requirements of battery-grade lithium sulfide purity.

[0023] 3) The preparation process of the present application is simple, the production cost is low, the requirement for equipment is low, and it is suitable for mass production. DETAILED DESCRIPTION

[0024] The principles and features of the present application are described below in conjunction with specific embodiments, and the examples are used to explain the present application and are not intended to limit the scope of the present application.

[0025] A method for preparing high-purity lithium sulfide is provided in the present application, which utilizes the natural affinity of silicon and fluorine, mixes and disperses silicon sulfide and lithium fluoride, and then heats to form lithium sulfide crude and volatile silicon tetrafluoride gas, and the reaction equation is: SiS2+ 4LiF → 2Li2S + SiF4↑ Lithium sulfide is dissolved in organic solvents, while the remaining silicon sulfide and lithium fluoride in the reaction system are insoluble in most organic solvents. By taking advantage of the difference in solubility of lithium sulfide, raw material silicon sulfide and lithium fluoride in organic solvents and the volatility of silicon fluoride, high-purity lithium sulfide can be obtained by dissolving, filtering, concentrating and drying after the reaction. The following is a specific example.

[0026] Example 1 In a nitrogen atmosphere glove box, 129.7g of lithium fluoride (5 moles) and 92.21g of silicon disulfide (1 mole) were weighed into a ball mill jar, sealed, and mixed and dispersed at a speed of 800 rpm for 2 hours. The mixed sample was transferred to a muffle furnace under a nitrogen atmosphere, heated to 500°C at a rate of 10°C / min under -0.090 MPa, and reacted for 15h to obtain crude lithium sulfide.

[0027] The crude lithium sulfide obtained by the above reaction was dissolved in ethylene glycol dimethyl ether to prepare a 15% lithium sulfide / ethylene glycol dimethyl ether solution by mass fraction. The solution was filtered through a precision filter with a pore size of 0.05um and concentrated under reduced pressure to obtain wet lithium sulfide. The wet lithium sulfide was transferred to a muffle furnace under a nitrogen atmosphere, dried at 120°C under -0.09 MPa for 8h to obtain high-purity lithium sulfide with a purity of 99.95%.

[0028] Example 2 In a nitrogen atmosphere glove box, 103.76g of lithium fluoride (4 moles) and 92.21g of silicon disulfide (1 mole) were weighed into a high-speed mechanical mixer and mixed and dispersed for 2 hours. The mixed sample was transferred to a muffle furnace under a nitrogen atmosphere, heated to 400°C at a rate of 10°C / min under -0.080 MPa, and reacted for 17h to obtain crude lithium sulfide.

[0029] The crude lithium sulfide obtained by the above reaction was dissolved in dimethyl ether to prepare an 18% lithium sulfide / dimethyl ether solution by mass fraction. The solution was filtered through a precision filter with a pore size of 1.00um and concentrated under reduced pressure to obtain wet lithium sulfide. The wet lithium sulfide was transferred to a muffle furnace under a nitrogen atmosphere, dried at 100°C under 0.2MPa for 10h to obtain high-purity lithium sulfide with a purity of 99.98%.

[0030] Example 3 In a nitrogen atmosphere glove box, 155.64g of lithium fluoride (6 moles) and 92.21g of silicon disulfide (1 mole) were weighed into a nitrogen stream mill and mixed and dispersed at high speed for 2 hours. The mixed sample was transferred to a muffle furnace under a nitrogen atmosphere, heated to 600°C at a rate of 10°C / min under -0.095 MPa, and reacted for 12h to obtain crude lithium sulfide.

[0031] The lithium sulfide crude product obtained from the above reaction was dissolved in N-methyl pyrrolidone to form a 25% by mass lithium sulfide / N-methyl pyrrolidone solution. The solution was filtered through a precision filter with a pore size of 0.01 um and concentrated under reduced pressure to obtain lithium sulfide wet product. The lithium sulfide wet product was transferred to a muffle furnace under a nitrogen atmosphere, dried at 90°C under -0.05 MPa for 8 h to obtain high-purity lithium sulfide with a purity of 99.96%.

[0032] Example 4 In a nitrogen atmosphere glove box, 207.52 g of lithium fluoride (8 moles) and 92.21 g of silicon disulfide (1 mole) were mixed and dispersed in a high-speed shearing disperser for 4 h. The mixed sample was transferred to a muffle furnace under a nitrogen atmosphere, heated to 550°C at a rate of 10°C / min under -0.080 MPa, and reacted at high temperature for 15 h to obtain lithium sulfide crude product.

[0033] The lithium sulfide crude product obtained from the above reaction was dissolved in dimethylacetamide to form a 20% by mass lithium sulfide / dimethylacetamide solution. The solution was filtered through a precision filter with a pore size of 0.1 um and concentrated under reduced pressure to obtain lithium sulfide wet product. The lithium sulfide wet product was transferred to a muffle furnace under a nitrogen atmosphere, dried at 80°C under -0.1 MPa for 12 h to obtain high-purity lithium sulfide with a purity of 99.95%.

[0034] Example 5 In a nitrogen atmosphere glove box, 62.26 g of lithium fluoride (2.4 moles) and 92.21 g of silicon disulfide (1 mole) were mixed and dispersed in a ball mill tank, sealed, and mixed and dispersed at a speed of 800 rpm for 2 h. The mixed sample was transferred to a muffle furnace under a nitrogen atmosphere, heated to 800°C at a rate of 10°C / min under -0.090 MPa, and reacted at high temperature for 14 h to obtain lithium sulfide crude product.

[0035] The lithium sulfide crude product obtained from the above reaction was dissolved in isopropyl alcohol to form a 10% by mass lithium sulfide / isopropyl alcohol solution. The solution was filtered through a precision filter with a pore size of 20 um and concentrated under reduced pressure to obtain lithium sulfide wet product. The lithium sulfide wet product was transferred to a muffle furnace under a nitrogen atmosphere, dried at 110°C under -0.5 MPa for 9 h to obtain high-purity lithium sulfide with a purity of 99.97%.

[0036] Comparative Example 1 Comparative Example 1 and Example 1 differ only in the reaction temperature of silicon sulfide and lithium fluoride.

[0037] In a nitrogen atmosphere glove box, 129.7 g of lithium fluoride (5 moles) and 92.21 g of silicon disulfide (1 mole) were mixed and dispersed in a ball mill tank, sealed, and mixed and dispersed at a speed of 800 rpm for 2 h. The mixed sample was transferred to a muffle furnace under a nitrogen atmosphere, heated to 950°C at a rate of 10°C / min under -0.090 MPa, and reacted at high temperature for 15 h to obtain lithium sulfide crude product.

[0038] The lithium sulfide crude product obtained by the above reaction was dissolved in ethylene glycol dimethyl ether to prepare a lithium sulfide / ethylene glycol dimethyl ether solution with a mass fraction of 15%. The solution was filtered through a precision filter with a pore size of 0.05 um, and then concentrated under reduced pressure to obtain lithium sulfide wet product. The lithium sulfide wet product was transferred to a muffle furnace under a nitrogen atmosphere, dried at -0.09 MPa and 120℃ for 8h to obtain lithium sulfide with a purity of 98.20%.

[0039] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is only that the precision of the filter used to filter the lithium sulfide solution is different.

[0040] In a nitrogen atmosphere glove box, 129.7g of lithium fluoride (5 moles) and 92.21g of silicon disulfide (1 mole) were weighed into a ball mill jar, sealed, and mixed and dispersed at a speed of 800 rpm for 2 hours. The mixed sample was transferred to a muffle furnace under a nitrogen atmosphere, heated to 500℃ at a rate of 10℃ / min under -0.09 MPa, and reacted at 500℃ for 15h to obtain lithium sulfide crude product.

[0041] The lithium sulfide crude product obtained by the above reaction was dissolved in ethylene glycol dimethyl ether to prepare a lithium sulfide / ethylene glycol dimethyl ether solution with a mass fraction of 15%. The solution was filtered through a precision filter with a pore size of 50um, and then concentrated under reduced pressure to obtain lithium sulfide wet product. The lithium sulfide wet product was transferred to a muffle furnace under a nitrogen atmosphere, dried at -0.09 MPa and 120℃ for 8h to obtain lithium sulfide with a purity of 97.20%.

[0042] The purity of the lithium sulfide crude product obtained by the preparation method of Example 1-5, Comparative Example 1 and 2, the purity of high-purity lithium sulfide, and the yield were determined, and the results are shown in Table 1.

[0043] Table 1

[0044] As can be seen from Example 1 and Comparative Example 1, the reaction temperature of lithium fluoride and silicon sulfide has a great influence on the purity of the finally obtained lithium sulfide. If the temperature is too high, by-products such as lithium polysulfide will be generated and will be difficult to remove, and the generated lithium sulfide will be partially decomposed. As can be seen from Example 1 and Comparative Example 1, the precision of the filter also has a great influence on the purity of the prepared lithium sulfide. The precision of the filter needs to be within the range of 0.01-20um.

[0045] The purity of the lithium sulfide crude product obtained by the method of the present application can reach more than 95.00%, indicating that the reaction has fewer side reactions. Further controlling the filtration precision to be below 20um can obtain lithium sulfide products with a purity of more than 99.90% to meet the requirements of electronic grade.

[0046] The above merely describes preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing high-purity lithium sulfide, characterized in that: The steps include: (1) Under the protection of an inert atmosphere, silicon sulfide and lithium fluoride are mixed and dispersed, and then transferred to a reactor. The materials in the reactor are heated to a certain temperature under an inert atmosphere and kept warm for a certain time to react to obtain crude lithium sulfide and silicon fluoride gas; (2) Dissolve the crude lithium sulfide in an organic solvent, filter to remove insoluble impurities, concentrate and dry to obtain high-purity lithium sulfide.

2. The method for preparing high-purity lithium sulfide according to claim 1, characterized in that: The molar ratio of silicon sulfide to lithium fluoride is 1:2.4~1:

8.

3. The method for preparing high-purity lithium sulfide according to claim 2, characterized in that: The molar ratio of silicon sulfide to lithium fluoride is 1:4~1:

6.

4. The method for preparing high-purity lithium sulfide according to claim 1, characterized in that: The reaction temperature in step (1) is 150-900°C and the reaction time is 1.6-24h.

5. The method for preparing high-purity lithium sulfide according to claim 4, characterized in that: The reaction temperature in step (1) is 400-800°C and the reaction time is 12-18 hours.

6. The method for preparing high-purity lithium sulfide according to claim 1, characterized in that: The reaction in step (1) is carried out under negative pressure.

7. The method for preparing high-purity lithium sulfide according to claim 6, characterized in that: The reaction pressure in step (1) is -0.098 MPa to -0.080 MPa.

8. The method for preparing high-purity lithium sulfide according to claim 1, characterized in that: The organic solvent in step (2) is selected from one or a combination of alcohol solvents, ether solvents or amide solvents.

9. The method for preparing high-purity lithium sulfide according to claim 1, characterized in that: The filter used to filter out insoluble impurities in step (2) has an accuracy of 0.01 to 20 μm.

10. The method for preparing high-purity lithium sulfide according to claim 1, characterized in that: The temperature for drying lithium sulfide in step (2) is 50-120°C.

Images