Method for preparing high-purity lithium sulfide from lithium carbonate

Abstract

The invention provides a method for preparing high-purity lithium sulfide from lithium carbonate, and belongs to the technical field of lithium material preparation, and the method comprises the following steps: heating a ball-milled mixture of industrial-grade lithium carbonate and an alumina additive to 750-900 DEG C, and carrying out heat preservation and calcination to generate lithium oxide; performing hydrolysis reaction on lithium oxide in hot water, and filtering to obtain a high-purity lithium hydroxide solution; mixing the lithium hydroxide solution with the sulfur-containing protein, and performing spray drying to obtain a mixed precursor; calcining the mixed precursor at a low temperature of 210-340 DEG C in an inert atmosphere; and heating to 550-660 DEG C, calcining at a high temperature, introducing hydrogen sulfide gas, reacting lithium hydroxide to generate lithium sulfide, and cooling to obtain the high-purity lithium sulfide. The invention provides the method for preparing the high-purity lithium sulfide, the purity, the production efficiency and the raw material utilization rate of the lithium sulfide are remarkably improved, and the technical defects of low purity, incomplete raw material reaction, non-uniform precursor mixing, complicated process, difficulty in large-scale production and the like in the traditional lithium sulfide preparation method are overcome.

Description

Technical Field

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

[0002] Against the backdrop of the global acceleration of the transition to renewable energy, new energy technologies have developed rapidly. Solid-state batteries have become a hot material in research and industry due to their superior safety performance, high energy density and long cycle life. Among them, lithium sulfide (Li2S), as one of the ideal solid electrolyte materials, has attracted much research attention due to its good performance. Unlike traditional liquid batteries, solid electrolytes greatly reduce the risk of thermal runaway and combustion, significantly improving the safety performance of batteries. In addition, solid-state batteries can provide higher energy density, meeting the ever-increasing demand for electric vehicles for mileage. In terms of cycle life, liquid electrolytes in traditional batteries are prone to cause the formation of lithium dendrites, resulting in internal short circuits in the battery, while solid electrolytes can effectively inhibit this phenomenon, significantly extending the battery life and improving its stability. At the same time, the solid electrolyte in solid-state batteries has higher mechanical stability and can maintain structural integrity under higher voltages and more demanding working environments, further broadening its application in various scenarios. However, to give full play to the advantages of solid-state batteries and realize their wide application, the key lies in the ability to efficiently and scalably prepare lithium sulfide, making it an important material for promoting the commercialization of high-performance solid-state batteries in the future.

[0003] In order to meet the demand for lithium sulfide in industry and scientific research, a variety of preparation methods have been developed, including direct synthesis, solvent, mechanical and high-temperature solid-phase sintering. The direct synthesis method directly heats metallic lithium and sulfur powder to 650°C to 700°C in a controlled inert gas environment to react to generate lithium sulfide. This method has few reaction pathways and can directly generate lithium sulfide, but the ratio of reactants and the temperature of the reaction environment need to be precisely controlled, which increases the complexity of the process. The solvent method dissolves sulfur and lithium precursors in an organic solvent and then heats at a lower temperature to promote the formation of lithium sulfide. Compared with the direct synthesis method, the solvent method can be carried out at a lower temperature and can better control the generated morphology, but its disadvantage is its dependence on organic solvents, which not only increases costs, but also may bring environmental and health risks. The mechanical method mixes and grinds sulfur and lithium source materials (such as lithium metal or lithium salts) in a high-energy ball mill. This method does not rely on high temperature or organic solvents, is environmentally friendly and cost-effective, but the long ball milling process may cause equipment wear and energy consumption. The high-temperature solid-phase sintering method directly mixes the sulfide and lithium source in powder form and then heat treats them at high temperature to form lithium sulfide. Its simplified production process and low environmental impact make it very suitable for large-scale production. In addition, this method does not involve toxic chemicals or complex post-processing steps, which further reduces production costs and reduces environmental impact. Therefore, the cost-effectiveness and environmental friendliness of the high-temperature solid-phase sintering method make it an extremely attractive lithium sulfide production technology.

[0004] However, the traditional high-temperature solid-phase sintering method still has many problems in practical applications. First, high temperature conditions can easily lead to the loss of raw materials, thus affecting the yield of the final product. Secondly, during the high-temperature sintering process, uneven mixing of raw materials will lead to incomplete reaction, resulting in unreacted impurities remaining in the lithium sulfide, affecting the final battery performance. In addition, the traditional method failed to effectively control the atmosphere during the high-temperature sintering stage, resulting in the difficulty in timely discharge of the generated moisture, further reducing the purity of the lithium sulfide. These problems not only reduce the overall quality of the product, but also limit its competitiveness in high-end applications. Therefore, there is an urgent need to develop a more efficient new technology to overcome the limitations of the existing high-temperature sintering method, improve the yield and purity of lithium sulfide and other properties, promote the application of lithium sulfide in the field of solid-state batteries, and provide important technical references for the preparation of other high-performance materials. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a method for preparing high-purity lithium sulfide from lithium carbonate, aiming to solve at least one technical problem in the background technology.

[0006] The present invention is achieved in that:

[0007] A method for preparing high-purity lithium sulfide from lithium carbonate, the method comprising the following steps:

[0008] The ball-milled mixture of industrial-grade lithium carbonate and alumina additive is heated to 750°C to 900°C for calcination, and the lithium carbonate is thermally decomposed and decarbonized to generate lithium oxide;

[0009] Lithium oxide is hydrolyzed in hot water, and filtered after the reaction to obtain a high-purity lithium hydroxide solution;

[0010] The lithium hydroxide solution and the sulfur-containing protein are mixed in a preset ratio and then spray-dried to obtain a mixed precursor;

[0011] The mixed precursor is calcined in stages under an inert atmosphere, first at a low temperature of 210°C to 340°C; then the temperature is raised to 550°C to 660°C for high temperature calcination, and hydrogen sulfide gas is introduced at a preset flow rate, lithium hydroxide reacts to generate lithium sulfide, and high-purity lithium sulfide is obtained after cooling.

[0012] Furthermore, during the staged calcination, hydrogen sulfide ventilation and vacuuming are performed alternately, specifically: every 10 to 40 minutes of hydrogen sulfide gas ventilation is alternately followed by 5 to 15 minutes of vacuuming to discharge water vapor generated during calcination.

[0013] Furthermore, in the staged calcination, the low-temperature calcination time is 90 min to 150 min, and the high-temperature calcination time is 120 min to 210 min.

[0014] Furthermore, during the staged calcination, the flow rate of the hydrogen sulfide gas is 0.2 to 0.7 L / min.

[0015] Furthermore, the mass ratio of the industrial-grade lithium carbonate to the aluminum oxide is 1:0.5-1.3, the ball milling time is 30 min-180 min, the ball milling speed is 400 r / min-900 r / min, and the two are evenly mixed;

[0016] Furthermore, the calcination time of the mixture of industrial-grade lithium carbonate and alumina is 60 min to 180 min.

[0017] Furthermore, in the hydrolysis reaction, the hot water is pure water at 45°C to 75°C; the liquid-to-solid ratio of lithium oxide to hot water is 30 to 60; and the reaction time is 30 min to 60 min.

[0018] Furthermore, the molar ratio of the lithium hydroxide solution to the sulfur-containing protein is 1:0.08-0.18; in the spray drying, the air inlet temperature is set to 150°C-200°C, the feed rate is set to 10mL / min-20mL / min, and the atomization frequency is set to 320r / min-500r / min.

[0019] Furthermore, the sulfur-containing protein is selected from cysteine ​​and / or methionine.

[0020] Furthermore, a vacuum environment is maintained during the cooling process after the high-temperature calcination.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention provides a method for preparing high-purity lithium sulfide, which solves the technical defects of low purity, incomplete raw material reaction, uneven precursor mixing, complex process and difficulty in scale-up in the traditional lithium sulfide preparation method. The present invention significantly improves the purity, production efficiency and raw material utilization rate of lithium sulfide by calcining in stages during the sintering process, supplementing the gas sulfur source and extracting the water alternately, and spray drying the sulfur-containing protein and lithium material.

[0023] 2. The present invention reduces the decarbonization temperature of lithium carbonate by introducing an auxiliary agent. By introducing alumina, the original decarbonization temperature of lithium carbonate can be reduced by about 300°C, which greatly reduces energy consumption and is environmentally friendly. In addition, the present invention has a lower purity requirement for lithium carbonate, which can reduce production costs to a certain extent.

[0024] 3. The present invention prepares the precursor by using a spray drying method, which can significantly enhance the contact between lithium hydroxide and sulfur-containing protein, so that the reactants are mixed evenly, which is beneficial to the high-temperature sintering reaction in the next stage.

[0025] 4. The present invention improves the utilization rate of raw materials by fully utilizing them, and by filtering the raw materials that have not been completely reacted and recycling them to the raw material pretreatment link, the comprehensive utilization rate of raw materials is improved and the production cost is reduced.

[0026] 5. The present invention does not require purification and effectively improves the purity of lithium sulfide. By intermittently removing the water generated by the reaction of lithium hydroxide and hydrogen sulfide to prevent the water from reacting with lithium sulfide, the purity of the final lithium sulfide product is improved.

[0027] 6. The present invention allows the raw materials to fully react during the staged calcination process, combines sulfur-containing protein with hydrogen sulfide as a comprehensive sulfur source, and the sulfur-containing protein can initially react with lithium hydroxide, and then the introduction of H2S can replenish the possible loss of sulfur during the sintering process, so that the lithium hydroxide is converted into lithium sulfide to the greatest extent, thereby improving the conversion rate of lithium sulfide.

[0028] 7. The present invention significantly improves the purity, production efficiency and raw material utilization of lithium sulfide by means of staged calcination, alternating sulfur source supplementation and water extraction, and spray drying process during the sintering process. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific implementation cases described herein are only used to explain the present invention and are not used to limit the present invention.

[0031] like Figure 1 As shown, a method for preparing high-purity lithium sulfide from lithium carbonate comprises the following steps:

[0032] S1. Thermal decomposition and decarbonization of industrial-grade lithium carbonate to generate lithium oxide

[0033] Industrial-grade lithium carbonate and alumina are ball-milled at a ratio of 1:0.5-1.3, with a ball-milling time of 30 min-180 min and a ball-milling speed of 400 r / min-900 r / min to ensure uniform mixing; alumina, as an auxiliary agent, can lower the melting point of lithium carbonate and promote its decomposition; the mixture is then heated to 750°C-900°C and calcined at high temperature for 60 min-180 min to decarbonize the lithium carbonate and decompose it into lithium oxide.

[0034] S2, lithium oxide hydrolyzes lithium hydroxide solution;

[0035] The lithium oxide generated in S1 is added into pure water at 45°C to 75°C, mixed and stirred, and hydrolyzed to generate lithium hydroxide; the amount of water added is 30 to 60 times the mass of the lithium oxide, and the reaction time is 30 to 60 minutes; after the hydrolysis reaction is completed, the solid recovered by filtration is residual aluminum oxide and lithium carbonate (with extremely low solubility) which can be reused in step S1, and the obtained liquid is a pure lithium hydroxide solution.

[0036] S3, mixing the lithium hydroxide solution and the sulfur-containing protein and then spray drying to obtain a mixed precursor;

[0037] The lithium hydroxide prepared by S2 is uniformly mixed with sulfur-containing protein (mainly cysteine ​​or methionine or a mixture of the two); the mixing ratio is based on a molar ratio of lithium oxide to protein of 1:0.08-0.18; then, the mixture is spray-dried, and the inlet air temperature is set at 150°C-200°C, the feed rate is 10mL / min-20mL / min, and the atomization frequency is 320r / min-500r / min, so as to form a uniform mixed precursor powder.

[0038] S4, staged calcination to obtain lithium sulfide

[0039] The stepwise calcination is carried out under an inert atmosphere (such as nitrogen or argon), specifically:

[0040] First, the mixed precursor is calcined at a low temperature of 210°C to 340°C for 90min to 150min. In a vacuum thermal environment, part of cysteine ​​and / or methionine reacts with a small amount of water in the mixed precursor to generate hydrogen sulfide, which then reacts preliminarily with lithium hydroxide;

[0041] Then continue to heat to 550°C to 660°C for high-temperature calcination for 120min to 210min, and introduce hydrogen sulfide gas at a flow rate of 0.2L / min to 0.7L / min to ensure that the lithium hydroxide is fully reacted to form lithium sulfide; at the same time, every 10min to 40min of hydrogen sulfide gas introduction, alternately perform vacuuming operation for 5min to 15min, so as to timely discharge the moisture generated during the reaction process to prevent the residual moisture from affecting the purity of the lithium sulfide;

[0042] After calcination is completed, the reaction system is naturally cooled to room temperature; a vacuum environment is maintained during the cooling process to prevent product oxidation; finally, a high-purity lithium sulfide product is collected.

[0043] In the prior art, the preparation of lithium sulfide by high-temperature solid-phase sintering has great application prospects, but the high-temperature solid-phase sintering method faces many challenges, including low purity, incomplete raw material reaction, uneven precursor mixing, and complex process and difficulty in scale. The present invention first significantly reduces the decarburization temperature of lithium carbonate by adding alumina as an auxiliary agent, thereby reducing energy consumption. Secondly, a uniform mixed precursor is prepared by spray drying, which improves the contact between lithium hydroxide and the sulfur source, thereby improving the uniformity and completeness of the reaction. In addition, the present invention introduces a staged calcination technology during the calcination process, and ensures the full reaction of lithium hydroxide and hydrogen sulfide by maintaining an inert atmosphere, supplementing a sulfur source, and alternately extracting water at different stages. At the same time, the water generated by the reaction is discharged in time, which significantly improves the purity of lithium sulfide. Moreover, by filtering and recovering the raw materials that have not been completely reacted, the comprehensive utilization rate of the raw materials is improved. The production cost is further reduced, and the feasibility of industrial-scale production is enhanced. These technical innovations solve the core problems in the prior art and provide a more efficient and economical method for producing high-purity lithium sulfide.

[0044] Example 1

[0045] A method for preparing high-purity lithium sulfide from lithium carbonate, comprising the following steps:

[0046] 1) Weigh 37.5 g of industrial grade lithium carbonate (98.5%), mix with 25.73 g of (99%) alumina, ball mill for 30 min at 400 r / min, then heat the mixture to 750° C., calcine at high temperature for 60 min, and the decarbonization thermal decomposition product is lithium oxide;

[0047] 2) The generated lithium oxide was mixed with 400 mL of 45° C. pure water and stirred for 30 min. After the reaction was completed, a pure lithium hydroxide solution was obtained by filtration, and 4.36 g of cysteine ​​was added to fully disperse the solution. The spray dryer was set to have an inlet air temperature of 150° C., a feed rate of 10 mL / min, and an atomization frequency of 320 r / min. The dispersed solution was spray dried to obtain a mixed precursor powder.

[0048] 3) In an inert atmosphere, the mixture was heated to 210°C at a heating rate of 2°C / min for 90 minutes. In a vacuum high temperature environment, cysteine ​​reacted with a small amount of water in the mixed precursor powder to generate hydrogen sulfide, which initially reacted with lithium hydroxide. The temperature was then raised to 550°C at a rate of 5°C / min for high temperature calcination for 120 minutes. At this time, in order to ensure that the lithium hydroxide was fully reacted, hydrogen sulfide gas was introduced again at a flow rate of 0.2L / min to react with lithium hydroxide to generate lithium sulfide. At the same time, the hydrogen sulfide gas was passed through for 10 minutes and vacuum operation was performed for 5 minutes to discharge the water generated during the reaction.

[0049] 4) After the calcination is completed, the reaction system is naturally cooled to room temperature. During the cooling process, the vacuum operation is maintained to obtain high-purity lithium sulfide with uniform texture and dryness, and the purity is 96.8%.

[0050] Example 2

[0051] A method for preparing high-purity lithium sulfide from lithium carbonate, the steps are as follows:

[0052] 1) Weigh 28.13 g of industrial grade lithium carbonate (98.5%), mix with 27.02 g of (99%) alumina, ball mill for 60 min at 500 r / min, then heat the mixture to 780°C, calcine at high temperature for 90 min, and the decarbonization thermal decomposition product is lithium oxide;

[0053] 2) Mix the generated lithium oxide with 450 mL of 50° C. pure water and stir for 40 min; after the reaction is completed, filter to obtain a pure lithium hydroxide solution, and add 4.01 g of cysteine ​​to fully disperse; set the spray dryer inlet temperature to 160° C., the feed rate to 12 mL / min, and the atomization frequency to 360 r / min, spray dry the dispersed solution, and collect the material to obtain a mixed precursor powder;

[0054] 3) In an inert atmosphere, heating to 240°C at a heating rate of 2°C / min for 100 min; in a vacuum high temperature environment, cysteine ​​reacts with a small amount of water in the mixed precursor powder to generate hydrogen sulfide, which initially reacts with lithium hydroxide; then the temperature is raised to 575°C at 5°C / min for high temperature calcination for 135 min; at this time, in order to ensure that the lithium hydroxide is fully reacted, hydrogen sulfide gas is introduced again at a flow rate of 0.3L / min to react with lithium hydroxide to generate lithium sulfide; at the same time, the hydrogen sulfide gas is passed through for 20 min each time and vacuum operation is performed for 8 min to discharge the moisture generated during the reaction;

[0055] 4) After the calcination is completed, the reaction system is naturally cooled to room temperature; the vacuum operation is maintained during the cooling process to obtain high-purity lithium sulfide with a uniform texture and dryness, and the purity is 97.3%.

[0056] Example 3

[0057] A method for preparing high-purity lithium sulfide from lithium carbonate, comprising the following steps:

[0058] 1) Weigh 45.00 g of industrial grade lithium carbonate (98.5%), mix with 44.02 g of (99%) alumina, ball mill for 90 min at 600 r / min, then heat the mixture to 810° C., calcine at high temperature for 120 min, and the decarbonization thermal decomposition product is lithium oxide;

[0059] 2) Mix the generated lithium oxide with 720 mL of 55° C. pure water and stir for 50 min; after the reaction is completed, filter to obtain a pure lithium hydroxide solution, and add 10.74 g of methionine to fully disperse; set the spray dryer inlet temperature to 170° C., the feed rate to 14 mL / min, and the atomization frequency to 400 r / min, spray dry the dispersed solution, and collect the material to obtain a mixed precursor powder;

[0060] 3) In an inert atmosphere, heating to 265°C at a heating rate of 2°C / min for 110 min; in a vacuum high temperature environment, methionine reacts with a small amount of water in the mixed precursor powder to generate hydrogen sulfide, which initially reacts with lithium hydroxide; then the temperature is raised to 590°C at 5°C / min for high temperature calcination for 150 min; at this time, in order to ensure that the lithium hydroxide is fully reacted, hydrogen sulfide gas is introduced again at a flow rate of 0.4L / min to react with lithium hydroxide to generate lithium sulfide; at the same time, the hydrogen sulfide gas is passed through for 25 min each time and vacuum operation is performed for 10 min to discharge the moisture generated during the reaction;

[0061] 4) After the calcination is completed, the reaction system is naturally cooled to room temperature; the vacuum operation is maintained during the cooling process to obtain high-purity lithium sulfide with a uniform texture and dryness, and the purity is 97.9%.

[0062] Example 4

[0063] A method for preparing high-purity lithium sulfide from lithium carbonate, comprising the following steps:

[0064] 1) Weigh 30.00 g of industrial grade lithium carbonate (98.5%), mix with 40.76 g of (99%) alumina, ball mill for 120 min at 750 r / min, then heat the mixture to 840° C., calcine at high temperature for 150 min, and the decarbonization thermal decomposition product is lithium oxide;

[0065] 2) Mix the generated lithium oxide with 600 mL of 60° C. pure water and stir for 50 min; after the reaction is completed, filter to obtain a pure lithium hydroxide solution, and add 8.36 g of methionine to fully disperse; set the spray dryer inlet temperature to 180° C., the feed rate to 16 mL / min, and the atomization frequency to 430 r / min, spray dry the dispersed solution, and collect the material to obtain a mixed precursor powder;

[0066] 3) In an inert atmosphere, heating to 280°C at a heating rate of 2°C / min for 130 min; in a vacuum high temperature environment, methionine reacts with a small amount of water in the mixed precursor powder to generate hydrogen sulfide, which initially reacts with lithium hydroxide; then the temperature is raised to 615°C at 5°C / min for high temperature calcination for 170 min; at this time, in order to ensure that the lithium hydroxide is fully reacted, hydrogen sulfide gas is introduced again at a flow rate of 0.5L / min to react with lithium hydroxide to generate lithium sulfide; at the same time, the hydrogen sulfide gas is passed through for 30 min each time and vacuum operation is performed for 12 min alternately to discharge the moisture generated during the reaction;

[0067] 4) After the calcination is completed, the reaction system is naturally cooled to room temperature; the vacuum operation is maintained during the cooling process to obtain high-purity lithium sulfide with a uniform texture and dryness, and the purity is 98.5%.

[0068] Example 5

[0069] A method for preparing high-purity lithium sulfide from lithium carbonate, comprising the following steps:

[0070] 1) Weigh 22.50 g of industrial grade lithium carbonate (98.5%), mix with 33.63 g of (99%) alumina, ball mill for 150 min at 800 r / min, then heat the mixture to 870°C, calcine at high temperature for 160 min, and the decarbonization thermal decomposition product is lithium oxide;

[0071] 2) Mix the generated lithium oxide with 450 mL of 70° C. pure water and stir for 55 min; after the reaction is completed, filter to obtain a pure lithium hydroxide solution, and add 2.91 g of cysteine ​​and 3.58 g of methionine until fully dispersed; set the spray dryer inlet temperature to 200° C., the feed rate to 18 mL / min, and the atomization frequency to 450 r / min, spray dry the dispersed solution, and collect the material to obtain a mixed precursor powder;

[0072] 3) In an inert atmosphere, heating to 310°C at a heating rate of 2°C / min for 140 min; in a vacuum high temperature environment, cysteine ​​and methionine react with a small amount of water in the mixed precursor powder to generate hydrogen sulfide, which initially reacts with lithium hydroxide; then the temperature is raised to 640°C at 5°C / min for high temperature calcination for 190 min; at this time, in order to ensure that the lithium hydroxide is fully reacted, hydrogen sulfide gas is introduced again at a flow rate of 0.6L / min to react with lithium hydroxide to generate lithium sulfide; at the same time, the hydrogen sulfide gas is passed through for 40 min each time and vacuum operation is performed for 13 min alternately to discharge the moisture generated during the reaction;

[0073] 4) After the calcination is completed, the reaction system is naturally cooled to room temperature; the vacuum operation is maintained during the cooling process to obtain high-purity lithium sulfide with a uniform texture and dryness, and the purity is 98.9%.

[0074] Example 6

[0075] A method for preparing high-purity lithium sulfide from lithium carbonate, the steps are as follows:

[0076] 1) Weigh 56.25 g of industrial grade lithium carbonate (98.5%), mix with 87.89 g of (99%) alumina, ball mill for 180 min at 900 r / min, then heat the mixture to 900° C., calcine at high temperature for 180 min, and the decarbonization thermal decomposition product is lithium oxide;

[0077] 2) The generated lithium oxide was mixed with 1350 mL of 75° C. pure water and stirred for 60 min; after the reaction was completed, the pure lithium hydroxide solution was filtered, and 8.18 g of cysteine ​​and 10.07 g of methionine were added until fully dispersed, and the spray dryer inlet temperature was set to 200° C., the feed rate was 20 mL / min, and the atomization frequency was 500 r / min. The dispersed solution was spray dried and the mixed precursor powder was obtained;

[0078] 3) In an inert atmosphere, heating to 340°C at a heating rate of 2°C / min for 150 min; in a vacuum high temperature environment, cysteine ​​and methionine react with a small amount of water in the mixed precursor powder to generate hydrogen sulfide, which initially reacts with lithium hydroxide; then the temperature is raised to 660°C at 5°C / min for high temperature calcination for 210 min; at this time, in order to ensure that the lithium hydroxide is fully reacted, hydrogen sulfide gas is introduced again at a flow rate of 0.7L / min to react with lithium hydroxide to generate lithium sulfide; at the same time, the hydrogen sulfide gas is passed through for 40 min and the vacuum operation is alternately performed for 15 min to discharge the moisture generated during the reaction;

[0079] 4) After the calcination is completed, the reaction system is naturally cooled to room temperature; the vacuum operation is maintained during the cooling process to obtain high-purity lithium sulfide with a uniform and dry texture and a purity of 99.3%.

[0080] Comparative Example 1

[0081] Comparative Example 1 is a method for preparing high-purity lithium sulfide from lithium carbonate, which differs from Example 6 only in that low-temperature calcination is deleted in step 3).

[0082] Step 3) in this comparative example 1 is specifically as follows: under an inert atmosphere, the temperature is raised to 660° C. at a rate of 5° C. / min for high-temperature calcination for 210 min; at this time, in order to ensure that the lithium hydroxide is fully reacted, hydrogen sulfide gas is introduced again at a flow rate of 0.7 L / min to react with the lithium hydroxide to generate lithium sulfide; at the same time, the hydrogen sulfide gas is passed through for 40 min each time, and a vacuum operation is alternately performed for 15 min to discharge the moisture generated during the reaction.

[0083] The other steps and reaction parameters are the same as those in Example 6.

[0084] Comparative Example 2

[0085] Comparative Example 2 is a method for preparing high-purity lithium sulfide from lithium carbonate, which differs from Example 6 only in that the drainage operation during the high-temperature calcination process is deleted in step 3).

[0086] Step 3) in this comparative example 2 is specifically as follows: in an inert atmosphere, heating to 340°C at a heating rate of 2°C / min for 150 min; in a vacuum high temperature environment, cysteine ​​and methionine react with a small amount of water in the mixed precursor powder to generate hydrogen sulfide, which initially reacts with lithium hydroxide; then the temperature is raised to 660°C at 5°C / min for high temperature calcination for 210 min; at this time, in order to ensure that the lithium hydroxide is fully reacted, hydrogen sulfide gas is introduced again at a flow rate of 0.7L / min to react with lithium hydroxide to generate lithium sulfide.

[0087] The other steps and reaction parameters are the same as those in Example 6.

[0088] Comparative Example 3

[0089] Comparative Example 3 is a method for preparing high-purity lithium sulfide from lithium carbonate, and the only difference between it and Example 6 is that in step 2), the spray drying to prepare the mixed precursor powder is replaced by conventional heating and refining to prepare the powder.

[0090] Step 2) in this comparative example 3 is specifically as follows: mixing the generated lithium oxide with 1350 mL of 75° C. pure water and stirring for 60 min; after the reaction is completed, filtering to obtain a pure lithium hydroxide solution, adding 8.18 g of cysteine ​​and 10.07 g of methionine until fully dispersed, heating to above 100° C. until the water is basically removed, concentrating it into a solid, and grinding it into a powder.

[0091] The other steps and reaction parameters are the same as those in Example 6.

[0092] Comparative Example 4

[0093] Comparative Example 4 is a method for preparing high-purity lithium sulfide from lithium carbonate, which differs from Example 6 only in that sulfur-containing protein is deleted as a sulfur source in step 2).

[0094] Step 2) in this comparative example 4 is specifically as follows: mixing the generated lithium oxide with 1350 mL of 75° C. pure water and stirring for 60 min; after the reaction is completed, filtering to obtain a pure lithium hydroxide solution, setting the spray dryer inlet temperature to 200° C., the feed rate to 20 mL / min, and the atomization frequency to 500 r / min, spray drying the lithium hydroxide solution, and collecting the material to obtain a mixed precursor powder.

[0095] Accordingly, step 3) in this comparative example 4 is adjusted as follows: in an inert atmosphere, hydrogen sulfide gas is introduced at a flow rate of 0.7 L / min, and the mixture is first heated to 340°C at a heating rate of 2°C / min for 150 min; then the temperature is raised to 660°C at a rate of 5°C / min for high-temperature calcination for 210 min; at the same time, the hydrogen sulfide gas is passed for 40 min and vacuum operation is performed alternately for 15 min to discharge the moisture generated during the reaction.

[0096] The other steps and reaction parameters are the same as those in Example 6.

[0097] The mass of the solid lithium products (lithium oxide, lithium sulfide) obtained in each step of Examples 1 to 6 and Comparative Examples 1 to 4 was measured, and the molar conversion rate of lithium sulfide was calculated. At the same time, the purity of the product lithium sulfide was measured based on ICP. The results are shown in Table 1. Conversion rate of lithium sulfide Among them, m1 is the mass of lithium sulfide, p1 is the measured purity of lithium sulfide, Mr1 is the relative molecular mass of lithium sulfide 45.88; m0 is the mass of lithium carbonate, p0 is the purity of lithium carbonate (98.5%), and Mr0 is the relative molecular mass of lithium carbonate 73.88.

[0098] Table 1

[0099]

[0100] It can be seen from the data in Table 1 that Examples 1 to 6 of the present invention overcome the limitations of the existing high-temperature sintering method and improve the yield and purity of lithium sulfide.

[0101] Compared with Example 6, Comparative Example 1 deleted the low-temperature calcination step, and the yield and purity of lithium sulfide were reduced. The reason is that the early low-temperature calcination provides mild heat treatment conditions, decomposes the sulfur-containing protein in the precursor, produces hydrogen sulfide, provides sufficient sulfur source for subsequent reactions, and reacts preliminarily with lithium hydroxide to improve the yield and purity of lithium sulfide; in addition, the low-temperature calcination effectively utilizes the sulfur element in the precursor, thereby reducing the introduction of part of hydrogen sulfide, further reducing the production cost;

[0102] Compared with Example 6, Comparative Example 2 deleted the drainage operation during the high-temperature calcination process, and the yield and purity of lithium sulfide were reduced. The reason is that: the drainage process was reduced during the high-temperature calcination stage, and the water vapor generated condensed into water at the lower temperature at both ends of the tube cavity, reacting with the generated lithium sulfide, and at the same time causing the material to agglomerate and affect the full progress of the reaction. Both of these will reduce the yield and purity of lithium sulfide;

[0103] Comparative Example 3 Compared with Example 6, the mixed precursor powder adopts conventional heating to remove water, and the yield and purity of lithium sulfide are reduced. The reason is that the precursor particles obtained by conventional heating to remove water are large and uneven, which affects the efficiency of the later high-temperature solid-phase reaction;

[0104] Compared with Example 6, in Comparative Example 4, sulfur-containing protein is deleted as a sulfur source, and the yield and purity of lithium sulfide are reduced. The reason is that: in the early stage when there is no sulfur-containing protein as a sulfur source, lithium hydroxide and the introduced hydrogen sulfide gas may not react fully, and the hydrogen sulfide gas produced by the decomposition of the sulfur-containing protein can be used as a protective gas for the early reaction, so that the generated lithium sulfide will not react with contact with air; at the same time, the amount of hydrogen sulfide gas used can be reduced to reduce costs.

[0105] 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 lithium sulfide from lithium carbonate, characterized in that: The method comprises the following steps: The ball-milled mixture of industrial-grade lithium carbonate and alumina additive is heated to 750°C to 900°C for calcination, and the lithium carbonate is thermally decomposed and decarbonized to generate lithium oxide; Lithium oxide is hydrolyzed in hot water, and filtered after the reaction to obtain a high-purity lithium hydroxide solution; The lithium hydroxide solution and the sulfur-containing protein are mixed in a preset ratio and then spray-dried to obtain a mixed precursor; The mixed precursor is calcined in stages under an inert atmosphere, first at a low temperature of 210°C to 340°C; then the temperature is raised to 550°C to 660°C for high temperature calcination, and hydrogen sulfide gas is introduced at a preset flow rate, lithium hydroxide reacts to generate lithium sulfide, and high-purity lithium sulfide is obtained after cooling.

2. The method for preparing high-purity lithium sulfide from lithium carbonate according to claim 1, characterized in that: In the staged calcination, hydrogen sulfide ventilation and vacuuming are performed alternately, specifically: every 10-40 minutes of hydrogen sulfide gas ventilation is alternately followed by 5-15 minutes of vacuuming operation to discharge water vapor generated during calcination.

3. The method for preparing high-purity lithium sulfide from lithium carbonate according to claim 1 or 2, characterized in that: In the staged calcination, the low-temperature calcination time is 90 min to 150 min, and the high-temperature calcination time is 120 min to 210 min.

4. The method for preparing high-purity lithium sulfide from lithium carbonate according to claim 1 or 2, characterized in that: During the staged calcination, the flow rate of hydrogen sulfide gas is 0.2 to 0.7 L / min.

5. The method for preparing high-purity lithium sulfide from lithium carbonate according to claim 1, characterized in that: The mass ratio of the industrial-grade lithium carbonate to alumina is 1:0.5-1.3, the ball milling time is 30 min-180 min, the ball milling speed is 400 r / min-900 r / min, and the two are uniformly mixed.

6. The method for preparing high-purity lithium sulfide from lithium carbonate according to claim 1 or 5, characterized in that: The calcination time of the mixture of industrial-grade lithium carbonate and aluminum oxide is 60 minutes to 180 minutes.

7. The method for preparing high-purity lithium sulfide from lithium carbonate according to claim 1, characterized in that: In the hydrolysis reaction, the hot water is pure water at 45° C. to 75° C.; the liquid-to-solid ratio of lithium oxide to hot water is 30 to 60; and the reaction time is 30 to 60 minutes.

8. The method for preparing high-purity lithium sulfide from lithium carbonate according to claim 1, characterized in that: The molar ratio of the lithium hydroxide solution to the sulfur-containing protein is 1:0.08-0.18; in the spray drying, the air inlet temperature is set to 150°C-200°C, the feed rate is set to 10mL / min-20mL / min, and the atomization frequency is set to 320r / min-500r / min.

9. The method for preparing high-purity lithium sulfide from lithium carbonate according to claim 1 or 8, characterized in that: The sulfur-containing protein is selected from cysteine ​​and / or methionine.

10. The method for preparing high-purity lithium sulfide from lithium carbonate according to claim 1, characterized in that: The vacuum environment is maintained during the cooling process after the high-temperature calcination.

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