A method for preparing lithium sulfide based on double decomposition reaction

Abstract

The present invention provides a method for preparing battery-grade lithium sulfide through a metathesis reaction. The method uses lithium chloride as a lithium source compound and anhydrous sodium sulfide as a sulfur source compound. The lithium source compound and the sulfur source compound are dissolved in a mixed solvent of anhydrous ethanol and acetonitrile, and subjected to a metathesis reaction to obtain battery-grade lithium sulfide. By changing the feeding method to batch addition of the sulfur source compound solution, the efficiency of the metathesis reaction can be further improved. The purity of the lithium sulfide crystals obtained by the method meets the requirements for battery-grade applications. The method also significantly improves reaction efficiency and product yield, facilitating further industrial production.

Description

Technical field:

[0001] The present invention relates to the technical field of battery materials, and more particularly to a method for preparing lithium sulfide based on a double decomposition reaction. Background technology:

[0002] According to research from an authoritative organization in the electric vehicle and related industry chains, global sales of new energy vehicles will exceed 14.653 million units in 2023, a year-on-year increase of 35.4%. China will lead the way with sales of 9.495 million units. Solid-state lithium-ion batteries, a promising candidate for next-generation battery technology, offer new hope for the development of new energy electric vehicles.

[0003] Solid-state electrolytes (SEs) are core components for high-performance all-solid-state lithium batteries (ASSLBs). Their ionic conductivity and electronic insulation properties are crucial. Currently, research on SE materials focuses on four main categories: organic polymer SEs, oxide SEs, halide SEs, and sulfide SEs. Lithium sulfide (Li2S) is a key raw material for sulfide SEs. Therefore, exploring low-cost, high-purity Li2S synthesis technologies is a crucial step toward the commercialization of sulfide SEs and ASSLBs.

[0004] Currently, the methods for synthesizing lithium sulfide can be divided into the following categories according to the lithium source: lithium metal method, organic lithium salt method, and inorganic lithium salt method. Representative of the inorganic lithium salt method are the double decomposition reaction method and Li2SO4 reduction method. Among them, the double decomposition reaction is a green, safe, and efficient method for synthesizing Li2S. Li2S is obtained by double decomposing relatively inexpensive lithium chloride and sodium sulfide in anhydrous ethanol. The reaction equation is as follows:

[0005] Na2S+2LiCl→Li2S+2NaCl↓

[0006] The Kipps free energy of this reaction is less than zero, allowing it to proceed spontaneously at room temperature. Furthermore, the NaCl produced by this reaction has a low solubility in anhydrous ethanol, allowing the reaction to proceed rapidly. After filtering out the NaCl, an ethanol solution of Li2S is obtained.

[0007] Patent CN112551491A discloses a method for preparing lithium sulfide. First, under an inert atmosphere, a lithium source compound and a sulfur source compound are weighed and their respective alcoholic solutions are prepared. The alcoholic solution of the lithium source compound is then added to the alcoholic solution of the sulfur source compound. After magnetic stirring, the fully reacted product is centrifuged and the supernatant is collected. The supernatant is then transferred to a tube furnace for heating and crystallization to obtain a crude lithium sulfide product. The crude lithium sulfide product is then washed with N-methylpyrrolidone or acetone and centrifuged to collect a solid product. The solid product is then washed with n-hexane and centrifuged, and dried to obtain lithium sulfide. This method can produce lithium sulfide through a double decomposition reaction, but the overall purity is insufficient and the reaction efficiency is poor.

[0008] Therefore, there is an urgent need for a method for preparing battery-grade lithium sulfide through a metathesis reaction that can further improve purity and yield. Summary of the invention:

[0009] The present invention provides a new method for preparing battery-grade lithium sulfide by double decomposition reaction, so as to solve the practical problem of low purity and low yield of lithium sulfide prepared by double decomposition reaction method in the prior art.

[0010] To achieve the above purpose, the technical ideas adopted by the present invention are as follows:

[0011] Lithium sulfide is prepared by utilizing the principle of double decomposition reaction between sulfur source compounds and lithium source compounds. By improving the method of adding reaction raw materials and the selection of solvents, the efficiency of the double decomposition reaction is further improved, thereby increasing the yield of lithium sulfide.

[0012] The technical solution of the present invention comprises the following steps:

[0013] (1) Under the protection of inert gas, a lithium source compound and a sulfur source compound are respectively dissolved in a solvent to prepare a solution; the sulfur source compound solution is added to the lithium source compound solution in batches, and magnetic stirring is performed to obtain a suspension;

[0014] (2) centrifuging the suspension under an inert atmosphere and collecting the supernatant;

[0015] (3) transferring the supernatant to a reactor, introducing an inert atmosphere for protection, heating, evaporating, and crystallizing to obtain a crude lithium sulfide product;

[0016] (4) under inert atmosphere, washing the crude lithium sulfide product with N-methylpyrrolidone or acetone, centrifuging, and collecting the solid product;

[0017] (5) Under the protection of an inert atmosphere, the solid product is washed with n-hexane, centrifuged, and vacuum-dried to obtain lithium sulfide.

[0018] The inert atmosphere is nitrogen or argon, and the reaction furnace is a tubular furnace or a muffle furnace.

[0019] Wherein, the lithium source compound in step (1) is lithium chloride, the sulfur source compound is anhydrous sodium sulfide; the solvent is a mixed solvent of anhydrous ethanol and acetonitrile, wherein the volume ratio of anhydrous ethanol to acetonitrile is (6-10):1.

[0020] Preferably, the overall molar ratio of the sulfur source compound to the lithium source compound is (0.7-0.9):2. The molar ratio of the sulfur source compound to the lithium source compound added for the first time is (0.5-0.6):2; the remaining sulfur source compound is added after 4-6 hours of reaction, and the stirring time after addition is continued for 2-8 hours.

[0021] Wherein, in step (1), the rotation speed of the magnetic stirring is 500-800 rpm.

[0022] Wherein, in step (3), the heating conditions are preheating at 50-80°C for 3-8h, then heating to 200-500°C, and continuing heating for 6-24h.

[0023] In steps (2), (4) and (5), the centrifugal speed is 4000-10000 rpm and the time is 5-30 min.

[0024] In the present invention, by adding the sulfur source compound in batches, the lithium source compound is effectively maintained in excess in the reaction system. This design not only fully consumes the sulfur source compound, but also, due to the high chloride ion concentration in the system, facilitates the precipitation of the generated NaCl, further promoting the reaction.

[0025] Secondly, the present invention optimizes the solvent system, replacing the single anhydrous ethanol with a mixed solvent of anhydrous ethanol and acetonitrile. This improvement significantly reduces the solubility of NaCl in the solvent while not affecting the solubility of the lithium source compound and the sulfur source compound in the solvent, thereby further promoting the reaction. Compared with the prior art, the present invention has the following beneficial effects:

[0026] By adding the sulfur source compound in batches, the lithium source compound is consistently present in a high proportion during the initial and intermediate stages of the reaction, thereby fully consuming the sulfur source compound and improving reaction efficiency. The use of a mixed solvent of anhydrous ethanol and acetonitrile significantly reduces the solubility of NaCl while maintaining the solubility of the reactants, further facilitating the reaction. Through these technological improvements, the present invention significantly increases the efficiency of lithium sulfide synthesis, providing a more efficient and economical solution for industrial production. Specific implementation method:

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the technical solutions of the present invention are further described below through specific embodiments. Those skilled in the art should know that the embodiments are only for helping to understand the technical content and technical effects of the present invention and should not be regarded as limiting the present invention.

[0028] Example 1

[0029] (1) In a nitrogen atmosphere glove box, anhydrous sodium sulfide and lithium chloride were weighed according to the overall molar ratio of 0.8:2. Weigh 19.5g and 11.7g of sodium sulfide (molar ratio 5:3), add 2L and 1L of a mixed solvent of anhydrous ethanol / acetonitrile (volume ratio 9:1), respectively, and stir magnetically at a speed of 600rpm for 30min. Weigh 42.4g of lithium chloride, add 1.5L of a mixed solvent of anhydrous ethanol / acetonitrile (volume ratio 9:1), stir magnetically at a speed of 600rpm for 20min. Add the solution containing 19.5g of sodium sulfide to the lithium chloride solution, stir continuously for 4h at a speed of 600rpm, then add the solution containing 11.7g of sodium sulfide to the reaction again, and react again for 4h to obtain a suspension.

[0030] (2) After the reaction is complete, the suspension is transferred to a centrifuge tube and centrifuged under nitrogen atmosphere. The centrifuge speed is set to 8000 rpm for 15 min.

[0031] (3) Under nitrogen atmosphere, the supernatant was transferred to a porcelain boat with a pipette, and then transferred to a nitrogen-protected tubular furnace. The mixture was preheated at 70°C for 4 h, and then heated to 300°C at a rate of 5°C / min. The mixture was heated for 8 h to allow the lithium sulfide to fully crystallize, thereby obtaining a crude lithium sulfide product containing a small amount of lithium chloride.

[0032] (4) Under nitrogen atmosphere, the crude product was washed with N-methylpyrrolidone, and then centrifuged at a speed of 8000 rpm for 15 min to collect the solid product.

[0033] (5) The solid product was washed with n-hexane and centrifuged under a nitrogen atmosphere at 8000 rpm for 10 min, repeated twice, and finally dried under vacuum to obtain the lithium sulfide product. The obtained lithium sulfide product was weighed and found to be 17.6 g, with a yield of 95.6%.

[0034] Example 2

[0035] (1) In a nitrogen atmosphere glove box, according to the molar ratio of anhydrous sodium sulfide and lithium chloride of 0.8:2, 23.4g and 7.8g of sodium sulfide (molar ratio 6:2) were weighed respectively, and 2.4L and 0.8L of a mixed solvent of anhydrous ethanol / acetonitrile (volume ratio 7:1) were added respectively, and magnetic stirring was performed, magnetic stirring was performed at a speed of 500rpm, and the stirring time was 30min. Weigh 42.4g of lithium chloride, add 1.2L of a mixed solvent of anhydrous ethanol / acetonitrile (volume ratio 7:1), magnetic stirring was performed, and the speed was 500rpm, and the stirring time was 30min. The solution containing 23.4g of sodium sulfide was added to the lithium chloride solution, and the mixture was stirred for 6h at a speed of 500rpm. Then, the solution containing 7.8g of sodium sulfide was added to the reaction again, and the reaction was continued for 4h to obtain a suspension.

[0036] (2) After the reaction is complete, the suspension is transferred to a centrifuge tube and centrifuged under nitrogen atmosphere. The centrifuge speed is set to 6000 rpm for 20 min.

[0037] (3) Under nitrogen atmosphere, the supernatant was transferred to a porcelain boat with a pipette, and then transferred to a nitrogen-protected tubular furnace. After preheating at 60°C for 4 h, the temperature was increased to 250°C at a rate of 5°C / min and continued to be heated for 12 h to fully crystallize the lithium sulfide to obtain a crude lithium sulfide product containing a small amount of lithium chloride.

[0038] (4) Under nitrogen atmosphere, the crude product was washed with N-methylpyrrolidone and then centrifuged at a speed of 8000 rpm for 10 min to collect the solid product.

[0039] (5) The solid product was washed with n-hexane and centrifuged under an argon atmosphere at 8000 rpm for 10 min, repeated twice, and finally dried under vacuum to obtain the lithium sulfide product. The obtained lithium sulfide product was weighed and found to be 17.4 g, with a yield of 94.5%.

[0040] Comparative Example 1

[0041] The preparation method is the same as that in Example 1, except that some steps in step (1) are changed as follows: 31.2 g of sodium sulfide is dissolved in 3 L of anhydrous ethanol / acetonitrile (volume ratio 9:1) solvent to prepare a sodium sulfide solution, the sodium sulfide solution is added to the lithium chloride solution, and the reaction is continued with stirring for 8 hours to obtain a suspension.

[0042] The obtained lithium sulfide product was weighed to 15.8 g, with a yield of 85.8%.

[0043] Comparative Example 2

[0044] The preparation method is the same as that of Example 1, except that the anhydrous ethanol / acetonitrile (volume ratio 9:1) solvent in step (1) is replaced with anhydrous ethanol.

[0045] The obtained lithium sulfide product was weighed to 16.1 g, with a yield of 87.5%.

[0046] The purity of the lithium sulfide prepared in Examples 1-2 was tested, and the purity of the prepared lithium sulfide crystals reached 99.99%, meeting the requirements of battery-grade lithium sulfide, and the actual yield reached more than 94%, greatly saving costs.

[0047] Comparing Example 1 with Comparative Example 1, since sodium sulfide is added twice, the lithium source compound is ensured to be in a higher proportion in the early and middle stages of the reaction, so that the sulfur source compound in the reaction system can be fully consumed, and the yield of lithium sulfide is greatly improved.

[0048] From Example 1 and Comparative Example 2, replacing anhydrous ethanol with a mixture of anhydrous ethanol / acetonitrile further reduces the solubility of NaCl in the solvent without affecting the solubility of the lithium source compound and the sulfur source compound therein, thereby promoting further reaction and significantly improving the yield of lithium sulfide.

[0049] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing battery-grade lithium sulfide based on a metathesis reaction, characterized in that: The steps include: (1) Under the protection of inert gas, a lithium source compound and a sulfur source compound are respectively dissolved in a solvent to prepare a solution; the sulfur source compound solution is added to the lithium source compound solution in batches, and magnetic stirring is performed to obtain a suspension; wherein the lithium source compound is lithium chloride, and the sulfur source compound is anhydrous sodium sulfide; the solvent is a mixed solvent of anhydrous ethanol and acetonitrile, wherein the volume ratio of anhydrous ethanol to acetonitrile is (6-10):1; (2) Under the protection of an inert atmosphere, centrifuge the suspension and collect the supernatant; (3) transferring the supernatant to a reactor, introducing an inert atmosphere for protection, heating, evaporating, and crystallizing to obtain a crude lithium sulfide product; (4) Under inert atmosphere, washing the crude lithium sulfide product with N-methylpyrrolidone or acetone, centrifuging, and collecting the solid product; (5) Under the protection of an inert atmosphere, the solid product is washed with n-hexane, centrifuged, and vacuum-dried to obtain lithium sulfide.

2. The method according to claim 1, characterized in that The inert atmosphere is nitrogen or argon, and the reaction furnace is a tubular furnace or a muffle furnace.

3. The method according to claim 1, characterized in that The overall molar ratio of the sulfur source compound to the lithium source compound is (0.7-0.9):

2.

4. The method according to claim 3, wherein: The molar ratio of the first added sulfur source compound to the lithium source compound is (0.5-0.6):2; the remaining sulfur source compounds are added after the reaction for 4-6 hours, and the stirring time after addition is continued for 2-8 hours.

5. The method according to claim 1, wherein In step (1), the rotation speed of the magnetic stirring is 500-800 rpm.

6. The method according to claim 1, characterized in that In step (3), the heating conditions are preheating at 50-80°C for 3-8h, then heating to 200-500°C, and continuing heating for 6-24h.

7. The method according to claim 1, characterized in that In steps (2), (4) and (5), the centrifugal speed is 4000-10000 rpm and the time is 5-30 min.