Method for preparing high-purity and fine-particle-size lithium sulfide based on carbon thermal reduction

Abstract

The invention provides a method for preparing high-purity and fine-particle-size lithium sulfide based on carbon thermal reduction. The method comprises the following steps: weighing lithium sulfate monohydrate, an insoluble inorganic carbon source and cysteine in a set proportion to form a raw material mixture; mixing the raw material mixture with water according to a set solid-to-liquid ratio, performing ultrasonic dispersion to obtain homogeneous dispersion liquid, and enabling the dispersion liquid to pass through a nitrogen circulating spray dryer to obtain uniform and dry precursor powder; in a vacuum environment, carrying out segmented calcination to obtain a crude product lithium sulfide; and in a dry and anhydrous environment, washing the crude product lithium sulfide for multiple times by using absolute ethyl alcohol according to a set liquid-solid ratio to obtain an alcoholic solution containing lithium sulfide, and then obtaining lithium sulfide fine powder through a nitrogen circulating spray dryer. The invention solves the problems of side reaction, low purity, large product particles, uncontrollable particle size and the like of lithium sulfide prepared by a carbon thermal reduction method in the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of lithium sulfide preparation, and in particular to a method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction. Background Art

[0002] With the profound transformation of the global energy structure towards clean and low-carbon, and the widespread implementation of the sustainable development strategy, the exploration of efficient, safe and environmentally friendly energy storage technology has become a key driving force for the vigorous development of the new energy industry. In this context, solid-state batteries, with their energy density, cycle life and safety performance far higher than traditional liquid batteries, have shown broad market prospects in the fields of electric vehicles, smart grid construction and portable electronic devices. Among the many candidate materials for solid electrolytes, sulfides have become the key materials for building high-performance all-solid-state batteries due to their excellent ion conductivity. As the core raw material of sulfur-based solid electrolytes and lithium-sulfur battery composite positive electrodes, the purity and quality of lithium sulfide (Li2S) directly affect the overall efficiency of the entire battery system. Lithium sulfide can effectively inhibit the growth of dendrites due to its good interface stability, which is crucial to preventing battery short circuits and improving the stability and safety of batteries during cycling. Therefore, how to prepare high-purity lithium sulfide efficiently and at low cost has become an important issue to be solved.

[0003] At present, the preparation methods of lithium sulfide are mainly divided into liquid phase reaction method and solid phase reaction method. The liquid phase reaction method can be divided into suspension type, solution type and mixed type, etc., using solvent to dissolve or disperse the raw materials to form a precursor, and finally obtain lithium sulfide by removing the solvent and performing heat treatment. However, the liquid phase reaction method has significant defects, such as the volatilization of the solvent leading to environmental pollution, and the difficulty of recycling is also relatively large, which limits its large-scale application. The solid phase reaction method mainly includes high temperature solid phase method, ball milling method, magnesium thermal reduction method and carbon thermal reduction method. The high temperature solid phase method usually mixes sulfur powder with lithium powder or lithium compound in a certain proportion, and reacts at high temperature to generate lithium sulfide. The lithium sulfide particles generated by this method are large, resulting in poor electrochemical performance and short cycle life. The ball milling method involves mixing elemental lithium with elemental sulfur, or mixing lithium compounds with reducing agents, and then performing carbonization reaction after ball milling. The operation is relatively simple and suitable for small-scale preparation, but it also faces problems such as high raw material cost, long reaction time and low synthesis conversion rate, which limits its wide application. The magnesium thermal reduction method uses magnesium powder and lithium sulfate to undergo an oxidation-reduction reaction to generate lithium sulfide. Although it has a high reaction efficiency in theory, it has an extremely high instantaneous reaction temperature and an explosion risk, so it has a large safety hazard in practical applications. The carbon thermal reduction method uses abundant and readily available carbon materials as a reducing agent to directly react with lithium compounds such as lithium sulfate under high temperature conditions to prepare lithium sulfide. With its significant advantages such as abundant raw material resources, significant cost-effectiveness, simple and fast process and short cycle, it occupies an important position in the commercial production of lithium sulfide.

[0004] However, the carbon thermal reduction method in the prior art has problems such as the occurrence of side reactions, low purity, large product particles and uncontrollable particle size. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing high-purity, fine-particle lithium sulfide based on carbon thermal reduction, aiming to solve the problems of side reactions, low purity, large product particles and uncontrollable particle size in the preparation of lithium sulfide by carbon thermal reduction in the prior art.

[0006] An object of the present invention is to provide a method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction, the method comprising:

[0007] Weighing lithium sulfate monohydrate, an insoluble inorganic carbon source and cysteine ​​in a set ratio to form a raw material mixture;

[0008] The raw material mixture is mixed with water according to a set solid-liquid ratio and then ultrasonically dispersed into a homogeneous dispersion, and the dispersion is passed through a nitrogen circulation spray dryer to obtain a uniform and dry precursor powder;

[0009] Under a vacuum environment, the precursor powder is placed in a tubular furnace, heated to a first preset temperature at a first preset heating rate and kept warm for a first preset time to perform a thermal decomposition treatment, then heated to a second preset temperature at a second preset heating rate and kept warm for a second preset time in a nitrogen atmosphere to perform a carbonization reduction reaction, and finally heated to a third preset temperature at a third preset heating rate and kept warm for a third preset time in a H2S atmosphere to obtain a crude lithium sulfide;

[0010] In a dry and anhydrous environment, the crude lithium sulfide is washed several times with anhydrous ethanol at a set liquid-to-solid ratio to obtain an alcohol solution containing lithium sulfide, and then the lithium sulfide fine powder is obtained by a nitrogen circulation spray dryer.

[0011] Furthermore, in the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbon thermal reduction, lithium sulfate monohydrate and insoluble inorganic carbon source are weighed according to a molar ratio of 1:2.0 to 2.5, and the amount of cysteine ​​added is 4 to 12 wt% of the total mass of lithium sulfate monohydrate and insoluble inorganic carbon source.

[0012] Furthermore, in the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbon thermal reduction, in the step of passing the dispersion through a nitrogen circulation spray dryer to obtain a uniform and dry precursor powder, the inlet temperature of the nitrogen circulation spray dryer is 160°C-200°C, the outlet temperature is 110°C-150°C, and the atomization frequency is 300r / min-500r / min.

[0013] Furthermore, in the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbon thermal reduction, the first preset heating rate is no more than 2-4°C / min, the first preset temperature is 150°C-230°C, and the first preset time is 1h-2h.

[0014] Furthermore, in the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbon thermal reduction, the second preset heating rate is not greater than 5°C / min, the second preset temperature is 630°C-760°C, and the second preset time is 4h-7h.

[0015] Furthermore, in the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbon thermal reduction, the third preset heating rate is not greater than 5°C / min, the third preset temperature is 690°C-850°C, and the third preset time is 2h.

[0016] Furthermore, in the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbon thermal reduction, the weighed sample is dispersed into a homogeneous dispersion by dissolving it in pure water at a solid-to-liquid ratio of 1:10 under ultrasonication for 30 minutes.

[0017] Furthermore, in the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction, the ratio of crude lithium sulfide to anhydrous ethanol is 5 to 10:1.

[0018] Furthermore, in the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbon thermal reduction, in the step of obtaining lithium sulfide fine powder through a nitrogen circulation spray dryer after obtaining an alcohol solution containing lithium sulfide, the inlet temperature of the nitrogen circulation spray dryer is 100-150°C, the outlet temperature is 75-105°C, and the atomization frequency is 300-500r / min.

[0019] Another object of the present invention is to provide a lithium sulfide prepared by the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction.

[0020] Compared with the prior art: The embodiment of the present invention introduces a nitrogen circulation spray drying method to achieve effective control of particle size: Since the crystal particle size prepared by the traditional evaporation crystallization or cooling crystallization method is often large and difficult to control, under the premise of ensuring high purity of lithium sulfide, the parameters of the nitrogen circulation spray dryer can be adjusted to achieve effective control of the particle size of lithium sulfide powder, and the contact between lithium sulfate and carbon source and cysteine ​​can be significantly enhanced by preparing the precursor by spray drying, so that the reactants are evenly mixed. Using an insoluble carbon source as a reducing agent, inorganic insoluble carbon sources have higher thermal stability, more efficient reducing ability, less impurity introduction, and less environmental impact compared to organic soluble carbon sources. The stability, purity and uniformity of the reaction are improved, while reducing the negative impact on the environment. Sulfur is supplemented twice during the staged calcination process: the precursor powder undergoes ammonia sulfide decomposition at an initial lower temperature, which can inhibit the formation of lithium oxide by-products, improve the conversion rate of lithium sulfide, and shorten the reaction time. Then, the introduction of H2S can make up for the loss of sulfur during the sintering process, avoiding the reduction of material purity and crystallinity due to the lack of sulfur under high temperature conditions, and finally obtaining lithium sulfide with high purity and uniform particle size. This solves the problem in the prior art that the heat treatment method of ultra-thin high-silicon steel made by the rapid solidification method affects the performance of the strip. DETAILED DESCRIPTION

[0021] Figure 1 This is a flow chart of a method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction according to one embodiment of the present invention; DETAILED DESCRIPTION

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0024] In addition, the term "and / or" as used herein includes any and all combinations of one or more related listed items. In the detailed description and claims, a list of items connected by the term "one of" may mean any of the listed items. For example, if items A and B are listed, the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements. In the detailed description and claims, a list of items connected by the terms "at least one of", "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" or "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" or "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0025] In view of the problems of the existing lithium sulfide prepared by carbothermal reduction method, such as side reactions, low purity, large product particles and uncontrollable particle size, the present invention proposes a method for preparing high-purity and fine-particle lithium sulfide based on carbothermal reduction. Please refer to Figure 1 , wherein the method comprises:

[0026] Step S10, weighing lithium sulfate monohydrate, an insoluble inorganic carbon source and cysteine ​​in a set ratio to form a raw material mixture.

[0027] Among them, a certain amount of lithium sulfate monohydrate (purity ≥ 99.9%), insoluble inorganic carbon source (preferably activated carbon powder, multi-walled carbon nanotubes, graphene, carbon microspheres, biomass carbon (carbon material fired with biomass as raw material), etc.), and cysteine ​​(purity ≥ 99%) are accurately weighed. The lithium sulfate monohydrate and the insoluble inorganic carbon source used are weighed according to a molar ratio of 1:2.0 to 2.5, and the amount of cysteine ​​added is 4 to 12wt% of the total mass of the lithium sulfate monohydrate and the insoluble inorganic carbon source. The insoluble inorganic carbon source and lithium sulfate are weighed according to Li2SO4+2C=Li2S+2CO2 to avoid excessive carbon powder that may cause side reactions.

[0028] Step 11, mixing the raw material mixture with water according to a set solid-liquid ratio and then ultrasonically dispersing it into a homogeneous dispersion, and passing the dispersion through a nitrogen circulation spray dryer to obtain a uniform and dry precursor powder.

[0029] The weighed sample was dissolved in pure water at a solid-liquid ratio of 1:10 and dispersed into a homogeneous dispersion by ultrasonication for 30 minutes. The nitrogen circulation spray dryer was set with an inlet temperature of 160-200°C, an outlet temperature of 110-150°C, and an atomization frequency of 300-500r / min, and the dispersion was passed through the nitrogen circulation spray dryer to obtain a uniform and dry precursor powder.

[0030] Step S12, under a vacuum environment, placing the precursor powder in a tubular furnace, heating it to a first preset temperature at a first preset heating rate and keeping it warm for a first preset time to perform thermal decomposition treatment, then under a nitrogen atmosphere, heating it to a second preset temperature at a second preset heating rate and keeping it warm for a second preset time to perform a carbonization reduction reaction, and finally under a H2S atmosphere, heating it to a third preset temperature at a third preset heating rate and keeping it warm for a third preset time to obtain crude lithium sulfide.

[0031] Among them, first, under a vacuum environment, the precursor prepared in step 2 is placed in a tubular furnace, heated to 150-230°C (preferably 190°C-210°C) at a heating rate of no more than 2-4°C / min and kept warm for 1-2h for thermal decomposition treatment, so that cysteine ​​decomposes to produce H2S, and initially prevents the generation of lithium oxide. Subsequently, under a nitrogen atmosphere, at a heating rate of no more than 5°C / min, it is heated to 630-760°C (preferably 690°C-760°C) and kept warm for 4-7h for carbonization reduction reaction. After completion, in order to ensure sufficient reaction, under the introduction of H2S atmosphere, at a heating rate of no more than 5°C / min, it is heated to 690-850°C (preferably 800°C-820°C) and kept warm for 2h to react with the lithium oxide byproduct generated by the carbonization reduction reaction: Li2O+H2S=Li2S, remove excess byproduct Li2O, and obtain crude lithium sulfide after calcination.

[0032] Step S13, in a dry and water-free environment, using anhydrous ethanol with a set liquid-to-solid ratio to wash the crude lithium sulfide for multiple times to obtain an alcohol solution containing lithium sulfide, and then passing the solution through a nitrogen circulation spray dryer to obtain lithium sulfide fine powder.

[0033] Among them, based on the characteristic that the solubility of lithium sulfide in alcohol is much higher than that of impurities, alcohol substances are used for purification. In a dry and water-free environment (glove box), anhydrous ethanol is used at a liquid-to-solid ratio of 5 to 10:1 to wash the crude lithium sulfide obtained in step three several times, and unreacted lithium sulfate, carbon powder and lithium oxide are filtered out, which can be returned to the preparation of precursor powder for use, thereby improving the utilization rate of raw materials. The nitrogen circulation spray dryer is set with an inlet temperature of 100-150°C, an outlet temperature of 75-105°C, and an atomization frequency of 300-500r / min. The alcohol solution containing lithium sulfide is passed through a nitrogen circulation spray dryer to obtain a high-purity lithium sulfide fine powder with uniform particle size and dryness.

[0034] On the other hand, the present invention also provides a lithium sulfide, which is prepared by the above-mentioned method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction.

[0035] In order to facilitate understanding of the present invention, several embodiments of the present invention are provided below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thorough and comprehensive.

[0036] Example 1

[0037] 1) Weigh 31.99g lithium sulfate monohydrate, 6.0g activated carbon powder, and 1.52g cysteine ​​in a beaker.

[0038] 2) Add 400 mL of pure water and disperse the raw materials into a homogeneous dispersion by ultrasonication for 30 min. Set the nitrogen circulation spray dryer with an inlet temperature of 160°C, an outlet temperature of 110°C, and an atomization frequency of 300 r / min, and pass the dispersion through the nitrogen circulation spray dryer to obtain a uniform and dry precursor powder.

[0039] 3) Under vacuum, the precursor prepared in step 2) is placed in a tubular furnace, heated to 150°C at a heating rate of no more than 4°C / min and kept warm for 2 hours for thermal decomposition treatment, so that cysteine ​​decomposes to produce H2S, and initially prevents the formation of lithium oxide. Subsequently, in a nitrogen atmosphere, the carbonization reduction reaction is carried out at a heating rate of no more than 5°C / min and heated to 630°C for 4 hours. After completion, in order to ensure sufficient reaction, in an H2S atmosphere, the temperature is increased at a rate of no more than 5°C / min, and heated to 690°C and kept warm for 2 hours to remove excess by-product Li2O, and crude lithium sulfide is obtained after calcination.

[0040] 4) In a dry and anhydrous glove box, the crude lithium sulfide obtained in step 3) is washed several times with anhydrous ethanol at a liquid-to-solid ratio of 5:1, and unreacted lithium sulfate, carbon source, lithium oxide, etc. are filtered out, and returned to step 2) for use. The nitrogen circulating spray dryer is set with an inlet air temperature of 100°C, an outlet air temperature of 75°C, and an atomization frequency of 300r / min. The alcohol solution containing lithium sulfide is passed through the nitrogen circulating spray dryer to obtain a high-purity lithium sulfide powder with uniform texture and dryness.

[0041] Example 2

[0042] 1) Weigh 15.995g lithium sulfate monohydrate, 3.0g graphene, and 1.52g cysteine ​​in a beaker

[0043] 1) Weigh 41.985g lithium sulfate monohydrate, 9.0g multi-walled carbon nanotubes, and 3.06g cysteine ​​in a beaker.

[0044] 2) Add 550 mL of pure water and disperse the raw materials into a homogeneous dispersion by ultrasonication for 30 min. Set the nitrogen circulation spray dryer with an inlet temperature of 170°C, an outlet temperature of 120°C, and an atomization frequency of 300 r / min, and pass the dispersion through the nitrogen circulation spray dryer to obtain a uniform and dry precursor powder.

[0045] 3) Under vacuum, the precursor prepared in step 2) is placed in a tubular furnace, heated to 170°C at a heating rate of no more than 3°C / min and kept warm for 2 hours for thermal decomposition treatment, so that cysteine ​​decomposes to produce H2S, and initially prevents the formation of lithium oxide. Subsequently, in a nitrogen atmosphere, the carbonization reduction reaction is carried out at a heating rate of no more than 5°C / min and heated to 660°C for 5 hours. After completion, in order to ensure sufficient reaction, in an H2S atmosphere, the temperature is increased at a rate of no more than 5°C / min, heated to 730°C and kept warm for 2 hours to remove excess by-product Li2O, and crude lithium sulfide is obtained after calcination.

[0046] 4) In a dry and anhydrous glove box, the crude lithium sulfide obtained in step 3) is washed several times with anhydrous ethanol at a liquid-to-solid ratio of 7:1, and unreacted lithium sulfate, carbon source, lithium oxide, etc. are filtered out, and returned to step 2) for use. The nitrogen circulating spray dryer is set with an inlet air temperature of 115°C, an outlet air temperature of 85°C, and an atomization frequency of 400r / min. The alcohol solution containing lithium sulfide is passed through the nitrogen circulating spray dryer to obtain a high-purity lithium sulfide powder with uniform texture and dryness.

[0047] Example 3

[0048] 1) Weigh 15.995g lithium sulfate monohydrate, 3.0g graphene, and 1.52g cysteine ​​in a beaker

[0049] 2) Add 200 mL of pure water and disperse the raw materials into a homogeneous dispersion by ultrasonication for 30 min. Set the nitrogen circulation spray dryer with an inlet temperature of 180°C, an outlet temperature of 130°C, and an atomization frequency of 400 r / min, and pass the dispersion through the nitrogen circulation spray dryer to obtain a uniform and dry precursor powder.

[0050] 3) Under vacuum, the precursor prepared in step 2) is placed in a tubular furnace, heated to 190°C at a heating rate of no more than 2°C / min and kept warm for 1h for thermal decomposition treatment, so that cysteine ​​decomposes to produce H2S, and initially prevents the formation of lithium oxide. Subsequently, in a nitrogen atmosphere, the carbonization reduction reaction is carried out at a heating rate of no more than 5°C / min and heated to 690°C for 6h. After completion, in order to ensure sufficient reaction, in an H2S atmosphere, the temperature is increased at a rate of no more than 5°C / min, heated to 780°C and kept warm for 2h to remove excess by-product Li2O, and crude lithium sulfide is obtained after calcination.

[0051] 4) In a dry and anhydrous glove box, the crude lithium sulfide obtained in step 3) is washed several times with anhydrous ethanol at a liquid-to-solid ratio of 8:1, and unreacted lithium sulfate, carbon source, lithium oxide, etc. are filtered out, and returned to step 2) for use. The nitrogen circulating spray dryer is set with an inlet air temperature of 130°C, an outlet air temperature of 95°C, and an atomization frequency of 400r / min. The alcohol solution containing lithium sulfide is passed through the nitrogen circulating spray dryer to obtain a high-purity lithium sulfide powder with uniform texture and dryness.

[0052] Example 4

[0053] 1) Weigh 23.99 g lithium sulfate monohydrate, 4.5 g carbon microspheres, and 2.85 g cysteine ​​into a beaker.

[0054] 2) Add 310 mL of pure water and disperse the raw materials into a homogeneous dispersion by ultrasonication for 30 min. Set the nitrogen circulation spray dryer with an inlet temperature of 190°C, an outlet temperature of 140°C, and an atomization frequency of 400 r / min, and pass the dispersion through the nitrogen circulation spray dryer to obtain a uniform and dry precursor powder.

[0055] 3) Under vacuum, the precursor prepared in step 2) is placed in a tubular furnace, heated to 210°C at a heating rate of no more than 3°C / min and kept warm for 1 hour for thermal decomposition treatment, so that cysteine ​​decomposes to produce H2S, and initially prevents the formation of lithium oxide. Subsequently, in a nitrogen atmosphere, the carbonization reduction reaction is carried out at a heating rate of no more than 5°C / min and heated to 720°C for 7 hours. After completion, in order to ensure sufficient reaction, in an H2S atmosphere, the temperature is increased at a rate of no more than 5°C / min, heated to 820°C and kept warm for 2 hours to remove excess by-product Li2O, and crude lithium sulfide is obtained after calcination.

[0056] 4) In a dry and anhydrous glove box, the crude lithium sulfide obtained in step 3) is washed several times with anhydrous ethanol at a liquid-to-solid ratio of 9:1, and unreacted lithium sulfate, carbon source, lithium oxide, etc. are filtered out, and returned to step 2) for use. The nitrogen circulating spray dryer is set with an inlet air temperature of 140°C, an outlet air temperature of 105°C, and an atomization frequency of 500r / min. The alcohol solution containing lithium sulfide is passed through the nitrogen circulating spray dryer to obtain a high-purity lithium sulfide powder with uniform texture and dryness.

[0057] Example 5

[0058] 1) Weigh 35.985 g of lithium sulfate monohydrate, 6.75 g of biochar, and 5.13 g of cysteine ​​into a beaker.

[0059] 2) Add 480 mL of pure water and disperse the raw materials into a homogeneous dispersion by ultrasonication for 30 min. Set the nitrogen circulation spray dryer with an inlet temperature of 200°C, an outlet temperature of 150°C, and an atomization frequency of 500 r / min, and pass the dispersion through the nitrogen circulation spray dryer to obtain a uniform and dry precursor powder.

[0060] 3) Under vacuum, the precursor prepared in step 2) is placed in a tubular furnace, heated to 230°C at a heating rate of no more than 2°C / min and kept warm for 1 hour for thermal decomposition treatment, so that cysteine ​​decomposes to produce H2S, and initially prevents the formation of lithium oxide. Subsequently, in a nitrogen atmosphere, the carbonization reduction reaction is carried out at a heating rate of no more than 5°C / min, heated to 760°C and kept warm for 7 hours. After completion, in order to ensure sufficient reaction, in an H2S atmosphere, the temperature is increased at a rate of no more than 5°C / min, heated to 850°C and kept warm for 2 hours to remove excess by-product Li2O, and crude lithium sulfide is obtained after calcination.

[0061] 4) In a dry and anhydrous glove box, the crude lithium sulfide obtained in step 3) is washed several times with anhydrous ethanol at a liquid-to-solid ratio of 10:1, and unreacted lithium sulfate, carbon source, lithium oxide, etc. are filtered out, and returned to step 2) for use. The nitrogen circulating spray dryer is set with an inlet air temperature of 150°C, an outlet air temperature of 115°C, and an atomization frequency of 500r / min. The alcohol solution containing lithium sulfide is passed through the nitrogen circulating spray dryer to obtain a high-purity lithium sulfide powder with uniform texture and dryness.

[0062] Please refer to the following Table 1, which shows the performance parameters of the lithium sulfide prepared in the above Examples 1-4 of the present invention.

[0063] Table 1

[0064]

[0065] It can be clearly seen that the present application introduces a nitrogen circulation spray drying method to achieve effective control of particle size: since the particle size of crystals prepared by traditional evaporation crystallization or cooling crystallization methods is often large and difficult to control, under the premise of ensuring high purity of lithium sulfide, by adjusting parameters such as the centrifugal atomization frequency of the nitrogen circulation spray dryer, the particle size of lithium sulfide powder can be effectively controlled, and its D(50) can reach 22μm-35μm;

[0066] The precursor is prepared by spray drying: spray drying can significantly enhance the contact between lithium sulfate, carbon source and cysteine, so that the reactants are mixed evenly;

[0067] Using insoluble carbon sources as reducing agents: Compared with organic soluble carbon sources, inorganic insoluble carbon sources have higher thermal stability, more efficient reducing ability, less impurity introduction, and less environmental impact. This improves the stability, purity, and uniformity of the reaction while reducing negative impacts on the environment.

[0068] Sulfur is added twice during the staged calcination process: the precursor powder in step 3 undergoes ammonia sulfide decomposition at an initial low temperature, which can inhibit the formation of lithium oxide byproducts, increase the conversion rate of lithium sulfide, and shorten the reaction time. Then, the introduction of H2S can replenish the sulfur loss during the sintering process, avoiding the reduction of material purity and crystallinity due to insufficient sulfur under high temperature conditions. The final lithium sulfide purity can reach more than 99%;

[0069] The utilization rate of raw materials is improved through full utilization: in step 4, the raw materials that have not been completely reacted are filtered and recycled to the precursor preparation stage, so that the comprehensive utilization rate of raw materials is improved and the production cost is reduced.

[0070] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction, characterized in that: The method comprises: Weighing lithium sulfate monohydrate, an insoluble inorganic carbon source and cysteine ​​in a set ratio to form a raw material mixture; The raw material mixture is mixed with water according to a set solid-liquid ratio and then ultrasonically dispersed into a homogeneous dispersion, and the dispersion is passed through a nitrogen circulation spray dryer to obtain a uniform and dry precursor powder; Under a vacuum environment, the precursor powder is placed in a tubular furnace, heated to a first preset temperature at a first preset heating rate and kept warm for a first preset time to perform a thermal decomposition treatment, then heated to a second preset temperature at a second preset heating rate and kept warm for a second preset time in a nitrogen atmosphere to perform a carbonization reduction reaction, and finally heated to a third preset temperature at a third preset heating rate and kept warm for a third preset time in a H2S atmosphere to obtain a crude lithium sulfide; In a dry and anhydrous environment, the crude lithium sulfide is washed several times with anhydrous ethanol at a set liquid-to-solid ratio to obtain an alcohol solution containing lithium sulfide, and then the lithium sulfide fine powder is obtained by a nitrogen circulation spray dryer.

2. The method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction according to claim 1, characterized in that: Lithium sulfate monohydrate and insoluble inorganic carbon source are weighed in a molar ratio of 1:2.0-2.5, and the amount of cysteine ​​added is 4-12wt% of the total mass of lithium sulfate monohydrate and insoluble inorganic carbon source.

3. The method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction according to claim 1, characterized in that: In the step of passing the dispersion through a nitrogen circulation spray dryer to obtain a uniform and dry precursor powder, the inlet air temperature of the nitrogen circulation spray dryer is 160°C-200°C, the outlet air temperature is 110°C-150°C, and the atomization frequency is 300r / min-500r / min.

4. The method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction according to claim 1, characterized in that: The first preset heating rate is no more than 2-4°C / min, the first preset temperature is 150°C-230°C, and the first preset time is 1h-2h.

5. The method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction according to claim 1, characterized in that: The second preset heating rate is no more than 5°C / min, the second preset temperature is 630°C-760°C, and the second preset time is 4h-7h.

6. The method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction according to claim 1, characterized in that: The third preset heating rate is no more than 5°C / min, the third preset temperature is 690°C-850°C, and the third preset time is 2h.

7. The method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction according to claim 1, characterized in that: The weighed sample was dissolved in pure water at a solid-to-liquid ratio of 1:10 and dispersed into a homogeneous dispersion by ultrasonication for 30 min.

8. The method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction according to claim 1, characterized in that: The ratio of crude lithium sulfide to anhydrous ethanol is 5 to 10:

1.

9. The method for preparing high-purity, fine-particle lithium sulfide based on carbothermal reduction according to claim 1, characterized in that: In the step of obtaining lithium sulfide fine powder through a nitrogen circulation spray dryer after obtaining the alcohol solution containing lithium sulfide, the nitrogen circulation spray dryer has an air inlet temperature of 100-150°C, an air outlet temperature of 75-105°C, and an atomization frequency of 300-500r / min.

10. A lithium sulfide, characterized in that: The lithium sulfide is prepared by the method for preparing high-purity and fine-particle lithium sulfide based on carbothermal reduction as described in any one of claims 1 to 9.

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