Lithium sulfide, its preparation method and application

Abstract

This invention discloses a lithium sulfide, its preparation method, and its applications. The invention employs a unique mixed solvent system, pre-adding an appropriate amount of water to the reaction system. Utilizing the stability of the xylene-water azeotropic system, a stable reaction environment is achieved under closed, pressurized conditions to synthesize lithium sulfide. Existing technologies rely on the formation of an azeotrope between the water generated in the reaction and the organic solvent to remove moisture. However, the rate of water formation varies with the reaction progress, leading to fluctuations in the water / organic solvent ratio within the system, which in turn affects the azeotropic temperature and pressure. This invention pre-adds sufficient water, ensuring that the system remains within a stable azeotropic composition range throughout the reaction. Pressure and temperature do not require dynamic adjustment, resulting in better process reproducibility. The stable azeotropic reaction environment promotes sufficient contact between reactants and product crystallization. Experiments have shown that the lithium sulfide prepared by this invention can achieve a purity of over 99.9%.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to a lithium sulfide, its preparation method, and its application. Background Technology

[0002] Lithium sulfide (Li₂S), as the cathode material and core raw material of sulfide solid electrolytes in lithium-sulfur batteries, has its purity and cost directly affecting the development of next-generation high-energy-density batteries and all-solid-state batteries. Existing methods for preparing lithium sulfide mainly include carbothermal reduction, liquid-phase metathesis, and high-temperature, high-pressure synthesis.

[0003] Carbothermic reduction methods (such as CN112678780B), while using readily available raw materials, typically require high temperatures (>675℃), and the products are often grayish in color due to residual carbon. Liquid-phase metathesis methods (such as CN112551491B and CN114455549B) offer milder conditions, but often use anhydrous sodium sulfide and specific lithium salts (such as lithium chloride and lithium nitrate) in alcohols or polar organic solvents, resulting in complex product separation steps and requiring large amounts of organic solvents, which is not environmentally friendly. Furthermore, existing routes that directly use hydrogen sulfide gas (such as CN116354315B) often have high equipment requirements and pose safety risks. While methods using metallic lithium for direct synthesis (such as CN117163922B) offer high purity, the raw material costs are expensive.

[0004] In the aforementioned lithium sulfide preparation methods, water in the reaction system is generally considered to lead to increased side reactions and reduced reaction efficiency. Therefore, existing technologies typically involve rigorous dehydration treatment of the raw materials and solvents. Some technologies employ the method of forming an azeotrope with water using organic solvents to continuously remove the water generated during the reaction from the system, thereby maintaining a low water content.

[0005] However, these methods often have problems such as harsh process conditions, high production costs, or solvent safety hazards. Therefore, developing a method for preparing high-purity lithium sulfide with mild reaction conditions, moderate raw material costs, green and safe processes is still of great practical significance. Summary of the Invention

[0006] This invention addresses the technical bias in existing technologies where the presence of water in the reaction system leads to higher levels of impurities in the reaction products. It provides a lithium sulfide, its preparation method, and its applications. This invention actively adds water to the reaction system, utilizing the stability of the xylene-water azeotropic system to achieve a stable reaction environment under closed and pressurized conditions, resulting in high reaction stability and product purity.

[0007] One of the technical solutions of this invention is to provide a method for preparing lithium sulfide, wherein xylene, water, and lithium hydroxide are mixed evenly and hydrogen gas is introduced, followed by hydrogen sulfide gas, and the reaction is carried out at 140℃~180℃ and 0.2~0.5 MPa pressure for 2~10 hours. After the reaction is completed, lithium sulfide is obtained by centrifugation, washing, and drying; wherein the volume ratio of xylene to water is 1:1 to 5:1. Preferably, the reaction time is 4~6 hours.

[0008] This invention employs a unique mixed solvent system: in the lithium sulfide synthesis step, a mixed solvent of xylene and water is added beforehand, and the reaction is carried out under pressure and moderate temperature conditions. The invention pre-adds a specific proportion of water, ensuring that the reaction system is near the xylene-water azeotropic composition from the initial stage. Under closed pressurized conditions, this azeotropic system maintains a constant azeotropic state at the reaction temperature, allowing for stable reaction without the need for additional temperature and pressure adjustments.

[0009] Furthermore, the method for preparing the hydrogen sulfide gas is as follows: using methylnaphthalene as the reaction medium, liquid sulfur is reacted at a temperature of 200℃~250℃ to generate hydrogen sulfide.

[0010] Furthermore, the washing method involves washing with an inert organic solvent, wherein the inert organic solvent is at least one of n-hexane and toluene.

[0011] Furthermore, the drying method is vacuum drying.

[0012] Furthermore, the reaction temperature is 150℃~170℃, and the pressure is 0.25~0.4 MPa.

[0013] Preferably, the reaction temperature is 160°C and the pressure is 0.3 MPa.

[0014] The second technical solution of the present invention is to provide lithium sulfide prepared by the above-described method. The lithium sulfide prepared by the present invention has a purity of not less than 99.5%.

[0015] The third technical solution of the present invention is to provide the application of the above-mentioned lithium sulfide.

[0016] The advantages of this invention are: This invention employs a unique mixed solvent system. An appropriate amount of water is pre-added to the reaction system, leveraging the stability of the xylene-water azeotropic system to achieve a stable reaction environment for lithium sulfide synthesis under closed, pressurized conditions. Existing technologies rely on the water generated in the reaction forming an azeotrope with the organic solvent to remove moisture. However, the water formation rate varies with the reaction progress, leading to fluctuations in the water / organic solvent ratio within the system, which in turn affects the azeotropic temperature and pressure. This invention pre-adds sufficient water, ensuring the system remains within a stable azeotropic composition range throughout the reaction. Pressure and temperature do not require dynamic adjustment, resulting in better process reproducibility. The stable azeotropic reaction environment promotes sufficient contact between reactants and product crystallization. Experiments have shown that the lithium sulfide prepared by this invention can achieve a purity of over 99.9%. Attached Figure Description

[0017] Figure 1 The image shows the X-ray diffraction (XRD) pattern of the lithium sulfide product prepared in Example 1 of this invention. Detailed Implementation

[0018] The following examples are provided to further illustrate the present invention and are intended to explain the invention, not to limit its scope. Unless otherwise specified, all figures are expressed in parts by weight and weight percentages.

[0019] Unless otherwise specified, the raw materials used in this invention are all conventional commercially available products; unless otherwise specified, the methods used in this invention are all conventional methods in the field.

[0020] The embodiments of the present invention will be further described below with reference to several examples.

[0021] It should be understood that the described embodiments are merely some, not all, of the embodiments in this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without inventive effort are within the scope of protection of this application.

[0022] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0023] Example 1 Synthesis of hydrogen sulfide In a reactor equipped with a stirrer, a reflux condenser, and a gas outlet, 500 mL of methylnaphthalene solvent was added, and the temperature was raised to 220°C. Liquid elemental sulfur (99.9% purity) was slowly added under stirring, with a sulfur to methylnaphthalene mass ratio of 1:2. The sulfur reacted with methylnaphthalene to produce hydrogen sulfide gas. The generated hydrogen sulfide gas was condensed and demisted before being directly introduced into the next reactor step.

[0024] Synthesis of lithium sulfide In a high-pressure reactor, add 300 mL of xylene and 100 mL of deionized water (xylene:water = 3:1), and then add lithium hydroxide (LiOH·H₂O, 0.2 mol). Seal the reactor and purge the air inside three times with an inert gas (such as argon). Then, introduce hydrogen gas until the pressure reaches 0.2 MPa, raise the temperature to 160°C, and then introduce hydrogen sulfide gas generated in step 1 until the total pressure inside the reactor reaches 0.3 MPa (gauge pressure). Maintain the temperature and pressure under these conditions for 5 hours. During the reaction, continuously introduce a small amount of hydrogen sulfide to maintain the pressure.

[0025] After the reaction was complete, the mixture was allowed to cool naturally to room temperature, and the residual gas in the reactor was slowly released. The reactor was then opened, and the reaction mixture was filtered to obtain a white crude solid. The crude solid was washed three times with n-hexane and then dried under vacuum at 80°C for 6 hours to obtain a white lithium sulfide powder. Its XRD pattern is shown below. Figure 1 As shown.

[0026] Testing showed that the lithium sulfide prepared in this embodiment had a purity of 99.95%, and the content of major metal impurities (Na, K, Fe, etc.) was all below 80 ppm.

[0027] Example 2 Synthesis of hydrogen sulfide In a reactor equipped with a stirrer, a reflux condenser, and a gas outlet, 500 mL of methylnaphthalene solvent was added, and the temperature was raised to 220°C. Liquid elemental sulfur (99.9% purity) was slowly added under stirring, with a sulfur to methylnaphthalene mass ratio of 1:2. The sulfur reacted with methylnaphthalene to produce hydrogen sulfide gas. The generated hydrogen sulfide gas was condensed and demisted before being directly introduced into the next reactor step.

[0028] Synthesis of lithium sulfide In a high-pressure reactor, add 200 mL of xylene and 200 mL of deionized water (xylene:water = 1:1), and then add lithium hydroxide (LiOH·H₂O, 0.2 mol). Seal the reactor and purge the air inside three times with an inert gas (such as argon). Then, introduce hydrogen gas until the pressure reaches 0.2 MPa, raise the temperature to 160°C, and then introduce hydrogen sulfide gas generated in step 1 until the total pressure inside the reactor reaches 0.3 MPa (gauge pressure). Maintain the temperature and pressure under these conditions for 5 hours. During the reaction, continuously introduce a small amount of hydrogen sulfide to maintain the pressure.

[0029] After the reaction was complete, the mixture was allowed to cool naturally to room temperature, and the remaining gas in the reactor was slowly released. The reactor was then opened, and the reaction mixture was filtered to obtain a white crude solid. The crude solid was washed three times with n-hexane and then dried under vacuum at 80°C for 6 hours to obtain a white lithium sulfide powder.

[0030] The purity of the obtained lithium sulfide product was 99.91%.

[0031] Example 3 Synthesis of hydrogen sulfide In a reactor equipped with a stirrer, a reflux condenser, and a gas outlet, 500 mL of methylnaphthalene solvent was added, and the temperature was raised to 220°C. Liquid elemental sulfur (99.9% purity) was slowly added under stirring, with a sulfur to methylnaphthalene mass ratio of 1:2. The sulfur reacted with methylnaphthalene to produce hydrogen sulfide gas. The generated hydrogen sulfide gas was condensed and demisted before being directly introduced into the next reactor step.

[0032] Synthesis of lithium sulfide In a high-pressure reactor, add 500 mL of xylene and 100 mL of deionized water (xylene:water = 5:1), and then add lithium hydroxide (LiOH·H₂O, 0.2 mol). Seal the reactor and purge the air inside three times with an inert gas (such as argon). Then, introduce hydrogen gas until the pressure reaches 0.2 MPa, raise the temperature to 160°C, and then introduce hydrogen sulfide gas generated in step 1 until the total pressure inside the reactor reaches 0.3 MPa (gauge pressure). Maintain this temperature and pressure for 5 hours. During the reaction, continuously introduce a small amount of hydrogen sulfide to maintain the pressure.

[0033] After the reaction was complete, the mixture was allowed to cool naturally to room temperature, and the remaining gas in the reactor was slowly released. The reactor was then opened, and the reaction mixture was filtered to obtain a white crude solid. The crude solid was washed three times with n-hexane and then dried under vacuum at 80°C for 6 hours to obtain a white lithium sulfide powder.

[0034] The purity of the obtained lithium sulfide product was 99.74%.

[0035] Comparative Example 1 Synthesis of hydrogen sulfide In a reactor equipped with a stirrer, a reflux condenser, and a gas outlet, 500 mL of methylnaphthalene solvent was added, and the temperature was raised to 220°C. Liquid elemental sulfur (99.9% purity) was slowly added under stirring, with a sulfur to methylnaphthalene mass ratio of 1:2. The sulfur reacted with methylnaphthalene to produce hydrogen sulfide gas. The generated hydrogen sulfide gas was condensed and demisted before being directly introduced into the next reactor step.

[0036] Synthesis of lithium sulfide In a high-pressure reactor, add 300 mL of xylene and 100 mL of deionized water (xylene:water = 3:1), and then add lithium hydroxide (LiOH·H₂O, 0.2 mol). Seal the reactor and purge the air inside three times with an inert gas (such as argon). Raise the temperature to 160°C and introduce hydrogen sulfide gas generated in step 1 until the total pressure inside the reactor reaches 0.3 MPa (gauge pressure). Maintain this temperature and pressure for 5 hours. During the reaction, continuously introduce a small amount of hydrogen sulfide to maintain the pressure.

[0037] After the reaction was complete, the mixture was allowed to cool naturally to room temperature, and the remaining gas in the reactor was slowly released. The reactor was then opened, and the reaction mixture was filtered to obtain a white crude solid. The crude solid was washed three times with n-hexane and then dried under vacuum at 80°C for 6 hours to obtain a white lithium sulfide powder.

[0038] The resulting lithium sulfide product had a purity of 95.20% and a slightly yellow color.

[0039] Comparative Example 2 Synthesis of hydrogen sulfide In a reactor equipped with a stirrer, a reflux condenser, and a gas outlet, 500 mL of methylnaphthalene solvent was added, and the temperature was raised to 220°C. Liquid elemental sulfur (99.9% purity) was slowly added under stirring, with a sulfur to methylnaphthalene mass ratio of 1:2. The sulfur reacted with methylnaphthalene to produce hydrogen sulfide gas. The generated hydrogen sulfide gas was condensed and demisted before being directly introduced into the next reactor step.

[0040] Synthesis of lithium sulfide In a high-pressure reactor, add 300 mL of xylene and 0.2 mol of lithium hydroxide (LiOH·H₂O). Seal the reactor and purge the air inside three times with an inert gas (such as argon). Then, introduce hydrogen gas until the pressure reaches 0.2 MPa, raise the temperature to 160°C, and then introduce hydrogen sulfide gas generated in step 1 until the total pressure inside the reactor reaches 0.3 MPa (gauge pressure). Maintain this temperature and pressure for 5 hours. During the reaction, continuously introduce a small amount of hydrogen sulfide to maintain the pressure.

[0041] After the reaction was complete, the mixture was allowed to cool naturally to room temperature, and the remaining gas in the reactor was slowly released. The reactor was then opened, and the reaction mixture was filtered to obtain a white crude solid. The crude solid was washed three times with n-hexane and then dried under vacuum at 80°C for 6 hours to obtain a white lithium sulfide powder.

[0042] During the reaction, it was observed that due to the lack of pre-added water to form a stable azeotropic system with xylene, the pressure and temperature inside the reactor fluctuated slightly (pressure fluctuation range ±0.05 MPa, temperature fluctuation range ±5℃).

[0043] The purity of the obtained lithium sulfide was 94.51%.

[0044] The content of metal impurities was detected by inductively coupled plasma optical emission spectroscopy (ICP-OES), and the purity of lithium sulfide was calculated by differential method.

[0045] Table 1. Performance Comparison of Examples and Comparative Examples The results of the above embodiments and comparative examples demonstrate that the present invention successfully achieved the stable preparation of high-purity lithium sulfide through a pre-actively added azeotropic solvent system combined with hydrogen pressurized reaction conditions. Compared with the comparative examples, the lithium sulfide prepared by the embodiments of the present invention has higher purity and better reproducibility, exhibiting significant technical advantages.

[0046] The above embodiments describe in detail the structure, features, and effects of the present invention. The above description is only a preferred embodiment of the present invention. Any changes made in accordance with the concept of the present invention, or equivalent embodiments modified to have equivalent changes, shall still fall within the scope of protection of the present invention if they do not exceed the scope covered by the specification.

Claims

1. A method for preparing lithium sulfide, characterized in that, Xylene, water, and lithium hydroxide are mixed evenly and hydrogen gas is introduced. Then hydrogen sulfide gas is introduced and the mixture is reacted at 140℃~180℃ and 0.2~0.5 MPa pressure for 2~10 hours. After the reaction is completed, lithium sulfide is obtained by centrifugation, washing, and drying. The volume ratio of xylene to water is 1:1 to 5:

1.

2. The method according to claim 1, characterized in that, The method for preparing the hydrogen sulfide gas is as follows: using methylnaphthalene as the reaction medium, liquid sulfur is reacted at a temperature of 200℃~250℃ to generate hydrogen sulfide.

3. The method according to claim 1, characterized in that, The washing method involves washing with an inert organic solvent, wherein the inert organic solvent is at least one of n-hexane and toluene.

4. The method according to claim 1, characterized in that, The drying method is vacuum drying.

5. The method according to claim 1, characterized in that, The reaction temperature is 150℃~170℃, and the pressure is 0.25~0.4MPa.

6. The method according to claim 1, characterized in that, The reaction temperature was 160℃ and the pressure was 0.3 MPa.

7. The method according to claim 1, characterized in that, The reaction time is 4 to 6 hours.

8. A lithium sulfide prepared by the method of claim 1.

9. An application of lithium sulfide as described in claim 8.

Images