Method for preparing lithium sulfide

Abstract

The invention relates to a method for preparing lithium sulfide, which comprises the following steps: respectively dissolving a sulfur source compound and a lithium source compound in alcohol under the protection of inert atmosphere, and then mixing the two alcohol solutions for double decomposition reaction to generate a lithium sulfide suspension; and then carrying out evaporative crystallization, supercritical fluid washing, centrifugal separation and freeze drying treatment to obtain a lithium sulfide product. The purity of the lithium sulfide prepared through the method can reach 99.9% or above, the lithium sulfide can be used as a positive electrode material of a lithium-sulfur battery or a raw material of a sulfide solid electrolyte in an all-solid-state battery, and the method is low in energy consumption, conforms to the concept of green chemistry and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation and purification of lithium sulfide, and in particular, relates to a method for preparing lithium sulfide, and high-purity lithium sulfide obtained by the method. Background Art

[0002] With the growing demand for energy storage technology in modern society, lithium-ion batteries have become the core of portable electronic devices, electric vehicles, and renewable energy storage systems. However, lithium-ion batteries face the challenges of specific energy approaching the theoretical limit and insufficient safety, so it is necessary to develop a new generation of energy storage batteries with higher performance. In this context, lithium-sulfur batteries and all-solid-state batteries have become research hotspots in the field of energy storage due to their high theoretical specific energy and excellent safety. As the core raw material of the positive electrode material of lithium-sulfur batteries and the sulfide electrolyte of all-solid-state batteries, lithium sulfide (Li2S) occupies an important position in energy storage materials due to its high theoretical capacity (1166mAh / g) and excellent electrochemical properties.

[0003] At present, the preparation methods of lithium sulfide mainly include: solid phase ball milling, liquid phase reaction, high temperature / high pressure and carbon thermal reduction. Among them, the solid phase ball milling process is simple but the reaction is not sufficient; the liquid phase reaction process is relatively complex and involves flammable and explosive solvents; the high temperature / high pressure method has high energy consumption and strict equipment requirements; the carbon thermal reduction method produces a large amount of greenhouse gases, which does not meet environmental protection requirements.

[0004] CN112551491B discloses a method for preparing lithium sulfide, which is achieved by performing a double decomposition reaction of a lithium source and a sulfur source under an inert atmosphere, combined with multi-step washing and vacuum drying technology. However, this method relies on detergents (such as N-methylpyrrolidone and n-hexane), so solvent recovery is difficult and increases the environmental burden.

[0005] The existing methods have high preparation costs, insufficient purity of the obtained lithium sulfide, and are often accompanied by problems such as high energy consumption or environmental pollution, which seriously restrict the commercial application of lithium-sulfur batteries and all-solid-state batteries.

[0006] The present invention provides a method for preparing lithium sulfide, wherein a sulfur source compound and a lithium source compound are dissolved in alcohol respectively under the protection of an inert atmosphere, and double decomposition reaction is performed to generate a lithium sulfide suspension, and then a high-purity lithium sulfide product is obtained by evaporation crystallization, supercritical fluid washing, centrifugal separation and freeze drying. The method of the present invention is efficient, environmentally friendly and easy to industrialize. Summary of the invention

[0007] The present invention aims to provide a new method for preparing lithium sulfide, which can produce high-purity lithium sulfide, and the method is environmentally friendly, has low production cost, and is suitable for industrial production. The purpose of the present invention is achieved by the following technical solution:

[0008] A method for preparing lithium sulfide, characterized in that the method comprises the following steps:

[0009] (1) Under the protection of an inert atmosphere, a sulfur source compound and a lithium source compound are respectively dissolved in alcohol to form a solution, and then the sulfur source compound solution is added to the lithium source compound solution to form a uniform reaction solution, wherein the molar ratio of the sulfur source compound to the lithium source compound is 1:1-1:4;

[0010] (2) subjecting the reaction solution to a double decomposition reaction under microwave heating conditions to generate a lithium sulfide suspension;

[0011] (3) Under the protection of an inert atmosphere, the lithium sulfide suspension is evaporated and crystallized with the assistance of ultrasound to obtain a crude lithium sulfide product;

[0012] (4) washing the crude lithium sulfide product with carbon dioxide supercritical fluid to remove impurities, and recovering the solid product by centrifugal separation;

[0013] (5) Under the protection of an inert atmosphere, the obtained solid product is freeze-dried to obtain high-purity lithium sulfide.

[0014] In step (1), the sulfur source compound can be selected from one or more of sodium thiosulfate, sodium sulfide, and potassium sulfide.

[0015] The lithium source compound may be selected from one or more of lithium nitrate, lithium chloride, lithium sulfate, and lithium hydroxide.

[0016] The alcohol is one or more of ethanol, n-propanol, isopropanol, n-butanol or isobutanol.

[0017] In step (2), the microwave heating frequency is 2450 MHz, the power range is 300 to 800 W, and the heating temperature is controlled between 40° C. and 80° C.

[0018] In step (3), the ultrasonic frequency of the ultrasonic-assisted evaporation crystallization is 20 to 40 kHz, the processing time is 30 to 60 minutes, and the solvent evaporation rate is controlled to be above 90% during the crystallization process.

[0019] In step (5), the freeze-drying temperature ranges from -10°C to -60°C, and the drying time ranges from 1 to 24 hours.

[0020] In each step of the method according to the present invention, the gas used in the inert atmosphere is nitrogen or argon, and the purity of the nitrogen or argon gas is not less than 99.99%.

[0021] The present invention further relates to high-purity lithium sulfide obtained by the method according to the present invention. The purity of the lithium sulfide prepared by the method according to the present invention can reach above 99.9%.

[0022] Compared with the prior art methods, the method according to the present invention has the following advantages:

[0023] The raw materials used in the method of the present invention are low-priced and the production cost is economical; the reaction time is short and the reaction conditions are low temperature, which significantly reduces energy consumption; the obtained high-purity lithium sulfide can be well used as the positive electrode material of lithium-sulfur batteries or the raw material of sulfide solid electrolyte in all-solid-state batteries; the use of carbon dioxide supercritical fluid cleaning and freeze-drying process reduces the impact of traditional solvents on the environment, eliminates greenhouse gas emissions, avoids the use of high temperature / high pressure and toxic solvents, and is suitable for large-scale industrial production. Specifically, 1. Compared with the solid phase ball milling method, the liquid phase double decomposition reaction step in the method of the present invention ensures sufficient reaction and the purity of the generated lithium sulfide is high; the mixed alcohol solution and microwave heating increase the reaction rate, shorten the preparation time, and avoid the introduction of impurities by mechanical ball milling, thereby improving the reproducibility of the product. 2. Compared with the liquid phase reaction method, the method of the present invention uses carbon dioxide supercritical fluid as a detergent to replace traditional organic solvents, avoids the problem of flammable and explosive solvents, and conforms to the concept of green chemistry; ultrasonic assisted technology improves the crystallization efficiency, further improves the product purity, reduces solvent loss and processing costs, and makes the production process more environmentally friendly and economical. 3. Compared with the high temperature / high pressure method, the method of the present invention adopts microwave heating and inert atmosphere protection, and the reaction temperature can be as low as 200-300°C, avoiding the harsh conditions of high temperature and high pressure, and no high pressure container is required. The reaction conditions are mild, the process equipment is simple, and the energy consumption and equipment cost are significantly reduced, which is suitable for large-scale industrial applications. 4. Compared with the carbon thermal reduction method, the method of the present invention replaces high temperature reduction with liquid phase reaction, avoids the production of carbon dioxide, and reduces the impact on the environment; no high temperature treatment step is required, which significantly reduces energy consumption; freeze drying is used to retain the crystal integrity of lithium sulfide and improve its performance in the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a flow chart of the method for preparing lithium sulfide according to the present invention.

[0025] Figure 2 This is a scanning electron microscope (SEM) image of the lithium sulfide prepared in Example 1 of the present invention.

[0026] Figure 3 This is the X-ray diffraction (XRD) spectrum of the lithium sulfide prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with specific embodiments. The embodiments are merely illustrative and do not constitute any limitation to the present invention. Various modifications may be made within the technical concept of the present invention. According to the teachings of the present invention, all changes or modifications obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Embodiment 1:

[0029] Sodium sulfide (0.1 mol) and lithium chloride (0.3 mol) were dissolved in a mixed solution of ethanol and n-butanol in a volume ratio of 2:1 to obtain an alcohol solution of sodium sulfide and lithium chloride. The two alcohol solutions were mixed, heated with a 300W microwave, and subjected to a double decomposition reaction at 50°C for 15 minutes. The suspension generated by the reaction was subjected to ultrasonic assisted crystallization (40kHz frequency, 45 minutes) to evaporate the solvent, and then washed with supercritical CO2, and the solid product was recovered by centrifugation. The recovered product was freeze-dried at -40°C for 16 hours to obtain a lithium sulfide product with a purity of 99.90%.

[0030] Embodiment 2:

[0031] Under nitrogen protection, 0.1mol sodium thiosulfate and 0.1mol lithium nitrate are dissolved in a 1:1 mixed solution of ethanol and isopropanol to obtain an alcohol solution of sodium thiosulfate and lithium nitrate. The two alcohol solutions are mixed, and a double decomposition reaction is carried out at 60°C for 30 minutes by microwave heating at a frequency of 2450MHz and a power of 500W to generate a lithium sulfide suspension. After the reaction is completed, ultrasonic assisted crystallization (30kHz frequency, 30 minutes) is used to evaporate and remove the solvent to obtain a crude lithium sulfide product. The solid product is recovered by washing and removing impurities with a carbon dioxide supercritical fluid, and centrifugation is performed to recover the solid product. The recovered product is freeze-dried at -50°C for 12 hours to obtain a lithium sulfide product with a purity of 99.95%.

[0032] Embodiment 3:

[0033] Potassium sulfide (0.05 mol) and lithium sulfate (0.05 mol) were dissolved in isopropanol solution to obtain alcohol solutions of potassium sulfide and lithium sulfate. The two alcohol solutions were mixed and heated to 70°C for reaction for 20 minutes at 2450MHz and 800W microwave power. The resulting suspension was evaporated with the assistance of ultrasound (35kHz frequency, 30 minutes), and the residual solid was cleaned by carbon dioxide supercritical fluid, and the solid product was recovered by centrifugation. The recovered product was freeze-dried (-60°C, 24 hours) to obtain a lithium sulfide product with a purity of 99.90%.

[0034] Embodiment 4:

[0035] Sodium thiosulfate (0.2 mol) and lithium hydroxide (0.2 mol) were dissolved in a mixed solution of ethanol and n-propanol in a ratio of 1:1, respectively, to obtain an alcohol solution of sodium thiosulfate and lithium hydroxide. The two alcohol solutions were mixed and subjected to double decomposition reaction, the microwave heating power was 400 W, the reaction temperature was controlled at 60 ° C, and the time was 20 minutes. After the reaction, normal temperature ultrasonic assisted crystallization (20 kHz frequency, 60 minutes) was directly carried out. The crude product was washed with CO2 supercritical fluid, and the solid product was recovered by centrifugation. The recovered product was freeze-dried (-50 ° C, 12 hours) to obtain a lithium sulfide product with a purity of 99.92%.

[0036] Embodiment 5:

[0037] Under the protection of an inert atmosphere, sodium sulfide (0.5 mol) and lithium nitrate (1 mol) were dissolved in a mixed solution of ethanol and isobutanol (volume ratio of 3:1) to obtain an alcohol solution of sodium sulfide and lithium nitrate. The two alcohol solutions were mixed, heated by microwave (frequency 2450 MHz, power 600 W), and reacted at 60 ° C for 40 minutes. The resulting suspension was treated with ultrasonic assistance (40 kHz frequency, 50 minutes), and impurities were removed by carbon dioxide supercritical fluid washing, and solid products were recovered by centrifugation. The recovered product was freeze-dried (-45 ° C, 20 hours) to obtain a lithium sulfide product with a purity of 99.90%.

Claims

1. A method for preparing lithium sulfide, characterized in that: The method comprises the following steps: (1) Under the protection of an inert atmosphere, a sulfur source compound and a lithium source compound are respectively dissolved in alcohol to form a solution, and then the sulfur source compound solution is added to the lithium source compound solution to form a uniform reaction solution, wherein the molar ratio of the sulfur source compound to the lithium source compound is 1:1-1:4; (2) subjecting the reaction solution to a double decomposition reaction under microwave heating conditions to generate a lithium sulfide suspension; (3) Under the protection of an inert atmosphere, the lithium sulfide suspension is evaporated and crystallized with the assistance of ultrasound to obtain a crude lithium sulfide product; (4) washing the crude lithium sulfide product with carbon dioxide supercritical fluid to remove impurities, and recovering the solid product by centrifugal separation; (5) Under the protection of an inert atmosphere, freeze-dry the obtained solid product to obtain lithium sulfide.

2. The method according to claim 1, characterized in that: In step (1), the sulfur source compound is selected from one or more of sodium thiosulfate, sodium sulfide and potassium sulfide.

3. The method according to claim 1, characterized in that: In step (1), the lithium source compound is selected from one or more of lithium nitrate, lithium chloride, lithium sulfate and lithium hydroxide.

4. The method according to claim 1, characterized in that: In step (1), the alcohol is one or more of ethanol, n-propanol, isopropanol, n-butanol or isobutanol.

5. The method according to claim 1, characterized in that: In step (2), the microwave heating frequency is 2450 MHz, the power range is 300 to 800 W, and the heating temperature is controlled at 40° C. to 80° C.

6. The method according to claim 1, characterized in that: In step (3), the ultrasonic frequency of the ultrasonic-assisted evaporation crystallization is 20 to 40 kHz, the processing time is 30 to 60 minutes, and the solvent evaporation rate is controlled to be above 90% during the crystallization process.

7. The method according to claim 1, characterized in that: In step (5), the freeze-drying temperature ranges from -10°C to -60°C, and the drying time ranges from 1 to 24 hours.

8. Lithium sulfide obtained according to the method of any one of the preceding claims 1-7.

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