Method for preparing lithium sulfide based on liquid phase extraction

Abstract

The invention discloses a method for preparing lithium sulfide based on liquid phase extraction. The method comprises the following steps: S1, mixing and stirring lithium salt and ionic liquid to obtain turbid liquid; s2, introducing hydrogen sulfide gas into the turbid liquid for reaction to generate turbid liquid of lithium sulfide; and S3, adding an alcohol solution into the turbid liquid generating the lithium sulfide as an extracting agent, and extracting and separating to obtain the lithium sulfide. The reaction is promoted by removing the generated water in situ in the reaction by adopting the ionic liquid, and the product is separated from the ionic liquid by dissolving the product with the extracting agent after the reaction is completed, so that the method has the advantages of quick reaction and easiness in large-scale preparation.

Description

Technical Field

[0001] This invention belongs to the technical field of secondary batteries, specifically relating to a method for preparing lithium sulfide based on liquid phase extraction. Background Technology

[0002] With the continued expansion of the electric vehicle market, the requirements for the safety performance and energy density of its core energy storage device—lithium-ion batteries—are further increasing. All-solid-state lithium-ion batteries have received widespread attention from academia and industry due to their significant safety performance and high energy density advantages. Among them, sulfide solid electrolytes have become the most promising solid electrolytes for industrialization due to their high room-temperature ionic conductivity and wide electrochemical window. However, lithium sulfide, as one of the key raw materials for synthesizing sulfide solid electrolytes, is difficult to prepare and purify, becoming a key technology limiting the large-scale application of solid electrolytes.

[0003] Currently, the main methods for preparing high-purity lithium sulfide include (1) carbothermal reduction method (representative patents are CN119461260A, CN118833782A, CN115947313A): difficult to remove impurities, high energy consumption in high-temperature processes, and high cost; (2) solid-phase ball milling method (representative patents are CN120081395A, CN120004221A): high equipment requirements, not conducive to large-scale preparation and low product purity.

[0004] Therefore, in order to achieve large-scale preparation of high-purity lithium sulfide materials, how to propose a low-cost method suitable for industrial preparation is an urgent problem to be solved. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing lithium sulfide based on liquid phase extraction. This method promotes the reaction by using an ionic liquid to remove water generated in situ during the reaction, and separates the product from the ionic liquid by using an extractant to dissolve the product after the reaction. This method has the advantages of rapid reaction and ease of large-scale preparation.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A method for preparing lithium sulfide based on liquid phase extraction, the method comprising: S1. Mix and stir lithium salt and ionic liquid to obtain a suspension; S2. Hydrogen sulfide gas is passed into a suspension to react and generate a suspension of lithium sulfide. S3. Add an alcohol solution as an extractant to the suspension that produces lithium sulfide, and extract and separate to obtain lithium sulfide.

[0007] The technical concept of this invention lies in addressing the issue that the reaction between inorganic lithium salts and high-purity hydrogen sulfide produces water as a byproduct, which then reacts with the product lithium sulfide, preventing the reaction from proceeding or resulting in an impure product. This invention proposes a solvent extraction method to remove the water generated during the reaction, allowing the reaction to continue uninterrupted. Specifically, the ionic liquid used in this invention is immiscible with the alcohol-based extractant. The ionic liquid continuously absorbs water during the reaction, enabling the reaction to occur. After the reaction is complete, the product is dissolved using the extractant, separating the product from the ionic liquid to obtain pure lithium sulfide. This invention cleverly utilizes the strong hygroscopic property of ionic liquids to enable the reaction to proceed rapidly and in large quantities, yielding high-purity lithium sulfide.

[0008] In S1, the lithium salt is lithium carbonate and / or lithium hydroxide.

[0009] In S1, the ionic liquid is selected from one or more of 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate, or 1-ethyl-3-methylimidazolium tetrafluoroborate.

[0010] In S1, the mixing speed is set to 100-10000 rpm, the mixing temperature is between 30℃ and 100℃, and the mixing time is 5-48h.

[0011] In S2, the flow rate of hydrogen sulfide gas introduced is 0.2-4 NI / min.

[0012] In step S2, an inert gas is first introduced into the suspension in step S1, followed by hydrogen sulfide gas. Further, the inert gas is selected from one or more of nitrogen, argon, or helium.

[0013] In S3, the alcohol solution is selected from one or more of methanol, ethanol, ethylene glycol or butanol.

[0014] Furthermore, in S3, after adding the extractant and stirring, stratification occurs: lithium sulfide is obtained by collecting the upper liquid and drying it; or lithium sulfide can be obtained directly by solid-liquid separation.

[0015] Furthermore, the drying temperature is 80-300℃, and the drying time is 1-36 hours.

[0016] The method provided by the present invention further includes: S4, collecting the remaining lower layer solution, drying it at 100-300°C to remove moisture and recover the ionic liquid, and then using it again in step S1.

[0017] In S4, the methods for removing moisture include thermal evaporation and vacuum evaporation at atmospheric pressure, such as rotary evaporation, tube furnace, oven or muffle furnace, as well as one or more of the following methods: reaction of lithium metal powder or bulk with moisture, and water absorption by molecular sieves.

[0018] The present invention also provides lithium sulfide obtained according to the above preparation method. The purity of the lithium sulfide is at least 99.90%.

[0019] Compared with the prior art, the present invention has the following superior effects: 1. The method provided by this invention has simple operation steps; compared with other methods, this method only requires two steps: aeration reaction and product separation, which greatly improves production efficiency; 2. The method provided by this invention innovatively uses ionic liquids in the lithium sulfide preparation process to remove water in situ during the reaction, and the ionic liquids can be recycled, which greatly reduces costs; 3. The method provided by this invention does not require high temperature and high pressure during the reaction process, thus reducing energy consumption and environmental pollution; 4. The method provided by this invention has high reaction efficiency, achieving a raw material utilization rate of over 90%, and is easy to scale up for production. Attached Figure Description

[0020] Figure 1 This is an X-ray diffraction pattern of lithium sulfide prepared in Example 1 of this invention. Detailed Implementation

[0021] The technical solution of the present invention is further illustrated below through specific embodiments. These specific embodiments do not represent a limitation on the scope of protection of the present invention.

[0022] Example 1 S1. Weigh 50 ml of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid and place it in a three-necked flask. Add 5 g of lithium hydroxide powder, set the magnetic stirrer speed to 700 rpm / min, and stir for 15 min, maintaining the temperature at 30℃. Simultaneously, start introducing argon gas to purge moisture and air from the apparatus.

[0023] S2. Subsequently, hydrogen sulfide gas was introduced at a flow rate of 0.5 NI / min, and the reaction was continued for 20 minutes until the lithium hydroxide was completely reacted, forming a suspension of lithium sulfide. The reaction equation is as follows: 2LiOH + H₂S → Li₂S + 2H₂O; S3. Add 100 ml of anhydrous ethanol and start stirring to extract Li2S from the suspension. After two hours, the suspension becomes a clear liquid with upper and lower layers, where the upper layer is an ethanol solution of lithium sulfide and the lower layer is an ionic liquid.

[0024] S4. Transfer the upper liquid to an Erlenmeyer flask and dry it in a vacuum oven at 120 °C for 12 hours to obtain lithium sulfide powder.

[0025] S5. Transfer the lower layer liquid to an Erlenmeyer flask, set the heating platform to 120°C to remove moisture, and then apply the dried 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid back to step S1.

[0026] The lithium sulfide prepared in this embodiment has a purity of 99.98% and a lithium hydroxide conversion rate of 95%.

[0027] As shown in Table 1, the C / S content in this embodiment was detected using a carbon-sulfur analyzer. As shown in Table 2, the content of major metallic impurity elements in this embodiment was tested by ICP full elemental scanning, showing that it has the characteristics of low impurity element content and no carbonization.

[0028] Table 1. Carbon and sulfur elemental analysis results of lithium sulfide prepared in Example 1 .

[0029] Table 2. ICP elemental impurity analysis results of lithium sulfide prepared in Example 1 .

[0030] Example 2 S1. Weigh 50 ml of 1-ethyl-3-methylimidazolium chloride ionic liquid and place it in a three-necked flask. Add 5 g of lithium hydroxide powder, set the magnetic stirrer speed to 1000 rpm / min, and stir for 15 min, maintaining the temperature at 30℃. Simultaneously, start introducing argon gas to purge moisture and air from the apparatus. S2. Subsequently, hydrogen sulfide gas was introduced at a flow rate of 0.5 NI / min, and the reaction was continued for 30 minutes until the lithium hydroxide was completely reacted, forming a suspension of lithium sulfide. The reaction equation is as follows: 2LiOH + 2H₂S → Li₂S + 2H₂O; S3. Add 100 ml of anhydrous ethanol and start stirring to extract Li2S from the suspension. After two hours, the suspension becomes a clear liquid with upper and lower layers, where the upper layer is an ethanol solution of lithium sulfide and the lower layer is an ionic liquid. S4. Transfer the upper liquid to a conical flask and place it in a vacuum oven to dry. Set the drying temperature to 100 °C and dry for 12 hours to obtain lithium sulfide powder. S5. Transfer the lower layer liquid to an Erlenmeyer flask, set the heating platform to 120°C to remove moisture, and then apply the dried 1-ethyl-3-methylimidazolium chloride ionic liquid back to step S1.

[0031] The lithium sulfide prepared in this embodiment has a purity of 99.95% and a lithium hydroxide conversion rate of 90%.

[0032] Example 3 S1. Weigh 50 ml of the 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid recovered in Example 1 and place it in a three-necked flask. Add 5 g of lithium carbonate powder, set the magnetic stirrer speed to 1500 rpm / min, and stir for 30 min, maintaining the temperature at 30°C. Simultaneously, start introducing argon gas to purge moisture and air from the apparatus. S2. Subsequently, hydrogen sulfide gas was introduced at a flow rate of 0.5 NI / min, and the reaction was continued for 60 min until the lithium carbonate was completely reacted, forming a suspension of lithium sulfide. The reaction equation is as follows: Li2CO3 + H2S → Li2S + H2O + CO2; S3. Add 100ml of anhydrous ethanol and start stirring to extract Li2S from the suspension. After two hours, the suspension becomes a clear liquid with upper and lower layers, where the upper layer is an ethanol solution of lithium sulfide and the lower layer is an ionic liquid. S4. Transfer the upper liquid to a conical flask and place it in a vacuum oven to dry. Set the drying temperature to 120 °C and dry for 12 hours to obtain lithium sulfide powder. S5. Transfer the lower layer liquid to an Erlenmeyer flask, set the heating platform to 120°C to remove moisture, and then apply the dried 1-ethyl-3-methylimidazolium acetate ionic liquid back to step S1.

[0033] The lithium sulfide prepared in this embodiment has a purity of 99.93% and a lithium carbonate conversion rate of 92%.

[0034] Example 4 S1. Weigh 50 ml of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid and place it in a three-necked flask. Add 5 g of lithium hydroxide powder, set the magnetic stirrer speed to 700 rpm / min, and stir for 15 min, maintaining the temperature at 30℃. Simultaneously, start introducing argon gas to purge moisture and air from the apparatus.

[0035] S2. Subsequently, hydrogen sulfide gas was introduced at a flow rate of 0.5 NI / min, and the reaction was continued for 20 minutes until the lithium hydroxide was completely reacted, forming a suspension of lithium sulfide. The reaction equation is as follows: 2LiOH + H₂S → Li₂S + 2H₂O; S3. Add 100 ml of anhydrous butanol and start stirring to extract Li2S from the suspension. After two hours, the suspension becomes a clear liquid with upper and lower layers, where the upper layer is an ethanol solution of lithium sulfide and the lower layer is an ionic liquid.

[0036] S4. Transfer the upper liquid to an Erlenmeyer flask and dry it in a vacuum oven at 120 °C for 12 hours to obtain lithium sulfide powder.

[0037] S5. Transfer the lower layer liquid to an Erlenmeyer flask, set the heating platform to 120°C to remove moisture, and then apply the dried 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid back to step S1.

[0038] The lithium sulfide prepared in this embodiment has a purity of 99.9% and a lithium hydroxide conversion rate of 91%.

[0039] Comparative Example 1 S1. Weigh 50 ml of dimethylformamide and place it in a three-necked flask. Add 5 g of lithium hydroxide powder. Set the magnetic stirrer speed to 700 rpm / min and stir for 15 min, maintaining the temperature at 30℃. Simultaneously, start introducing argon gas to purge moisture and air from the apparatus.

[0040] S2. Subsequently, hydrogen sulfide gas was introduced at a flow rate of 0.5 NI / min, and the reaction was continued for 20 minutes until the lithium hydroxide was completely reacted, forming a suspension of lithium sulfide. The reaction equation is as follows: 2LiOH + H₂S → Li₂S + 2H₂O; S3. Solid-liquid separation was performed by vacuum filtration to obtain crude lithium sulfide powder. 100 ml of tetrahydrofuran was added, and Li2S was stirred and washed for half an hour. Then, solid-liquid separation was performed again by vacuum filtration. This washing process was repeated 5 times to obtain crude lithium sulfide powder with dimethylformamide removed.

[0041] S4. The obtained crude lithium sulfide is placed in a vacuum oven and dried at a temperature of 40°C for 12 hours to obtain lithium sulfide powder.

[0042] The lithium sulfide prepared in this comparative example has a purity of 94.53% and a lithium hydroxide conversion rate of 70%.

[0043] The comparison results of the purity, raw material conversion rate and carbon content of lithium sulfide prepared in Examples 1-4 and Comparative Example 1 are shown in Table 3. It can be seen that the method provided by the present invention can achieve a lithium salt conversion rate of over 90%, and the purity of the prepared lithium sulfide is over 99.90%, with the characteristics of low impurity elements and no carbonization.

[0044] Table 3 Comparison of purity and raw material conversion rate between Examples 1-4 and Comparative Example 1

Claims

1. A method for producing lithium sulfide based on liquid phase extraction, characterized by, The method comprises: S1, mixing and stirring lithium salt and ionic liquid to obtain a suspension; S2, passing hydrogen sulfide gas into the suspension to generate a lithium sulfide suspension; S3, adding an alcohol solution as an extractant to the lithium sulfide suspension to obtain lithium sulfide by extraction and separation.

2. The method for producing lithium sulfide based on liquid phase extraction according to claim 1, characterized by, In S1, the lithium salt is lithium carbonate or / and lithium hydroxide.

3. The method for producing lithium sulfide based on liquid phase extraction according to claim 1, characterized by, In S1, the ionic liquid is selected from one or more of 1-ethyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium acetate or 1-ethyl-3-methylimidazolium tetrafluoroborate.

4. The method for producing lithium sulfide based on liquid phase extraction according to claim 1, characterized by, In S2, inert gas is first passed into the suspension in S1, and then hydrogen sulfide gas is passed.

5. The method for producing lithium sulfide based on liquid phase extraction according to claim 4, characterized by, The inert gas is selected from one or more of nitrogen, argon or helium.

6. The method for producing lithium sulfide based on liquid phase extraction according to claim 1, characterized by, In S3, the alcohol solution is selected from one or more of methanol, ethanol, ethylene glycol or butanol.

7. The method for producing lithium sulfide based on liquid phase extraction according to claim 1, characterized by, In S3, after adding the extractant, stirring causes the layers to separate: by collecting the upper liquid, drying to obtain lithium sulfide; or directly performing solid-liquid separation to obtain lithium sulfide.

8. The method for producing lithium sulfide based on liquid phase extraction according to claim 7, characterized by, The drying temperature is 80-300℃, and the drying time is 1-36h.

9. The method for producing lithium sulfide based on liquid phase extraction according to claim 7, characterized by, The method comprises: collecting the remaining lower solution, removing water by drying at 100-300℃ to recover the ionic liquid, and using it again in S1.

10. Lithium sulfide obtained by the preparation method according to any one of claims 1-9.

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