High-purity lithium sulfide and preparation method thereof

Abstract

The invention provides high-purity lithium sulfide and a preparation method thereof.The preparation method comprises the steps that a lithium source and sulfur powder are mixed and then subjected to first ball milling in the mixed atmosphere of hydrogen and inert gas, and the temperature of first ball milling is 200-300 DEG C; switching the ball milling atmosphere into a mixed gas of hydrogen, inert gas and ammonia gas, continuously heating to 350-450 DEG C, and carrying out second ball milling; and switching the ball milling atmosphere into gas containing hydrogen sulfide, heating to 600-900 DEG C, and carrying out third ball milling to obtain the high-purity lithium sulfide. According to the preparation method provided by the invention, high-purity lithium sulfide can be prepared, the purity of the prepared lithium sulfide is up to 99.9% or above or even up to 99.99%, the content of metal impurities and carbon is low, the reaction controllability is good, the safety is good, the required raw materials are relatively low in price, and the preparation method is suitable for large-scale production.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of battery material synthesis, and particularly relates to high-purity lithium sulfide and a preparation method thereof. BACKGROUND

[0002] With the acceleration of global energy transformation and the promotion of smart grid construction, the commercialization process of solid-state batteries in large-scale energy storage, electric vehicles and other fields has significantly accelerated, giving rise to an explosive demand for high-performance lithium sulfide materials. Lithium sulfide (Li2S) as a core functional material of the electrolyte system of solid-state batteries, its purity, particle size distribution and interface compatibility directly determine the ion conduction efficiency and battery cycle stability of sulfide solid electrolyte. In recent years, sulfide-based solid-state batteries are considered as a key technology direction to break through the performance bottleneck of traditional lithium-ion batteries due to their high energy density (> 500 Wh / kg) and intrinsic safety, and the controllable preparation of high-quality lithium sulfide is the core cornerstone of the industrialization of this technology.

[0003] Currently, the mainstream preparation process of lithium sulfide includes ball milling method, solution double decomposition method and thermal decomposition method, etc. Among them, the ball milling method promotes the solid phase reaction of lithium source and sulfur source through high-energy ball milling, although the process is simple, but it is limited by the solid-state diffusion kinetics, and long-time ball milling is needed to achieve high conversion rate, and the product is easy to introduce ball milling medium pollution, leading to excessive metal ion residues. The solution double decomposition method relies on polar organic solvents as reaction medium, although it can realize the synthesis of nanoscale lithium sulfide, but the solvent recovery cost is high, and the large-scale use of flammable and explosive solvents has major safety hazards, which is difficult to meet the environmental protection requirements of industrial production. The thermal decomposition method prepares pure phase Li2S through high-temperature decomposition of lithium sulfide precursor, but it faces technical difficulties such as complex preparation process of precursor, narrow pyrolysis temperature window, and easy agglomeration of product into blocks, resulting in poor consistency of batch performance, which is difficult to meet the strict standards of battery-grade materials. SUMMARY

[0004] The present application aims to solve the above-mentioned problems of the prior art, and the purpose is to provide high-purity lithium sulfide and a preparation method thereof.

[0005] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows: The present application aims to break through the technical limitations of the existing lithium sulfide preparation process, which is complex and has low product purity, and create a new process for preparing carbon-composite lithium sulfide with low impurities, high efficiency and simple operation. The existing technology has multiple drawbacks: the traditional ball milling method is limited by the solid-solid reaction mechanism, the contact area of the materials is insufficient, which causes slow reaction progress and poor conversion efficiency, and impurities such as lithium polysulfide are left in the product, making subsequent purification difficult; the organic purification process requires a large amount of organic solvent, which is flammable, explosive and volatile, threatening production safety and causing environmental pollution; in practical applications, the carbon-composite method is difficult to accurately control the ratio of reaction raw materials, resulting in significant fluctuations in product quality. The carbon content of the metathesis reaction is high, and the product quality needs to be balanced between carbon content and conversion rate. The carbon thermal reduction method introduces impurities such as high sodium and high chlorine, and there are still many residues after purification.

[0006] Specifically, in a first aspect, a method for preparing high-purity lithium sulfide is provided, comprising: mixing a lithium source with sulfur powder, and then performing first ball milling in a mixed gas atmosphere of hydrogen and inert gas, the temperature of the first ball milling being 200-300℃; switching the ball milling gas atmosphere to a mixed gas of hydrogen, inert gas and ammonia, and continuing to heat to 350-450℃ to perform second ball milling; switching the ball milling gas atmosphere to a gas containing hydrogen sulfide, heating to 600-900℃ to perform third ball milling, and obtaining high-purity lithium sulfide.

[0007] Further, the purity of the lithium source is 99.5% or higher, preferably 99.9% or higher, further preferably 99.95% or higher, and more preferably 99.99% or higher; the lithium source is at least one of anhydrous lithium hydroxide, lithium oxide, and lithium hydroxide containing crystal water.

[0008] Further, the purity of the sulfur powder is 99.99% or higher.

[0009] Further, the purity of the high-purity lithium sulfide is 99.9% or higher; preferably, the total amount of metal impurity elements in the high-purity lithium sulfide is not higher than 70ppm, more preferably not higher than 50ppm, and further preferably not higher than 30ppm.

[0010] Further, the molar ratio of lithium in the lithium source to sulfur in the sulfur powder is 2:1.2-1.5; the ratio of the molar amount of lithium in the lithium source to the total molar amount of hydrogen in the first ball milling and the second ball milling is not higher than 1:4.

[0011] Further, the rotation speed of the first ball milling is 200-400rpm; the duration of the first ball milling is 20-60min; in the mixed gas atmosphere of hydrogen and inert gas, the volume fraction of hydrogen is 40-80%.

[0012] Further, the rotation speed of the second ball mill is 200-400 rpm; the time length of the second ball mill is 2-4 h; in the mixed gas of hydrogen, inert gas and ammonia, the volume fraction of hydrogen is 40-80%, and the volume fraction of ammonia is 5-20%.

[0013] Further, the rotation speed of the third ball mill is 200-400 rpm; the time length of the third ball mill is 15-30 min; in the hydrogen sulfide-containing gas, the volume fraction of hydrogen sulfide gas is 10-30%; the hydrogen sulfide-containing gas is a mixed gas of hydrogen sulfide and inert gas.

[0014] Further, the preparation method of the anhydrous lithium hydroxide comprises: (1) dissolving industrial-grade lithium hydroxide hydrate in water, and performing precision filtration to obtain a lithium hydroxide solution; (2) introducing the lithium hydroxide solution into an evaporation system with an oxygen content of not more than 5 ppm, and evaporating and concentrating at 75-90°C; and performing centrifugal separation on the obtained evaporation and concentration liquid to obtain crude lithium hydroxide; (3) taking the crude lithium hydroxide as a raw material, repeating the process of "preparing the crude lithium hydroxide into a crude lithium hydroxide solution - step (2)" at least once, and then preparing the obtained lithium hydroxide into a solution and performing spray drying to obtain high-purity anhydrous lithium hydroxide.

[0015] Further, in step (3), after the lithium hydroxide is prepared into a solution, hydroxyethylidene diphosphonic acid and ethylenediaminetetraacetic acid are further added to the solution, and after reaction, filtration is performed, and then the filtrate is subjected to spray drying.

[0016] Further, in step (3), the ratio of the total molar amount of Ca ions and magnesium ions in the solution to the molar amount of hydroxyethylidene diphosphonic acid and ethylenediaminetetraacetic acid is 1:0.6-0.9:0.3-0.5.

[0017] Further, in step (3), the solid-liquid ratio when the lithium hydroxide is prepared into a solution is 1:5-10.

[0018] Further, in step (3), the reaction temperature is 70-110°C, and preferably 80-95°C.

[0019] Further, the filtration and spray drying are performed in an inert atmosphere or a nitrogen atmosphere.

[0020] Further, in step (2), the evaporation system is an MVR evaporator; and the concentration ratio of the evaporation and concentration is 6-12:1.

[0021] Further, in step (1), the mass ratio of the industrial-grade lithium hydroxide hydrate to water is 1:10-20.

[0022] Further, in step (3), when the crude lithium hydroxide is prepared into a crude lithium hydroxide solution, the solid-liquid ratio is 1:10-20.

[0023] Further, in step (3), the process of "preparing the crude lithium hydroxide into a crude lithium hydroxide solution-step (2)" is repeated 1-3 times.

[0024] In a second aspect, the high-purity lithium sulfide is prepared by the preparation method of the first aspect.

[0025] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects: Currently, the main lithium sulfide preparation processes are double decomposition reaction and carbon thermal reduction method, and more than 80% of enterprises use one of the two processes. Other methods, such as metal thermal reduction method, lithium sulfide combination method, etc., have been gradually eliminated due to high cost, complex technical process, etc. The two mainstream processes also have unavoidable defects in the manufacture of high-purity products. For example, the carbon content of lithium sulfide prepared by double decomposition reaction is high, and the product quality needs to be balanced between carbon content and conversion rate; the carbon thermal reduction method will introduce high sodium and high chlorine and other impurity elements that are difficult to accept in the back end. To solve these problems, additional purification steps must be added, and the purified lithium sulfide still contains 0.3-0.6% of carbon content and more than 40 ppm of sodium ion / chlorine ion content. The preparation method provided by the present application can prepare high-purity lithium sulfide, and the prepared lithium sulfide has a purity of 99.9% or even 99.99%, low metal impurity and carbon content, good controllability and safety of the reaction, low price of the required raw materials, and is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0027] Figure 1 XRD pattern of lithium sulfide prepared in Example 1. DETAILED DESCRIPTION

[0028] Some embodiments provide a preparation method of high-purity lithium sulfide, comprising: After mixing the lithium source with the sulfur powder, first ball milling is performed in a mixed gas atmosphere of hydrogen and inert gas, and the temperature of the first ball milling is 200-300°C. Switching the ball milling atmosphere to a mixed gas of hydrogen, inert gas and ammonia, continuing to heat to 350-450℃, and performing a second ball milling; Switching the ball milling atmosphere to a gas containing hydrogen sulfide, heating to 600-900℃, and performing a third ball milling to obtain high-purity lithium sulfide.

[0029] In the above preparation method, the temperature of the first ball milling is 200-300℃, such as 200℃, 220℃, 240℃, 260℃, 280℃, 300℃, etc.

[0030] In the above preparation method, the temperature of the second ball milling is 350-450℃, such as 350℃, 370℃, 390℃, 410℃, 430℃, 450℃, etc.

[0031] In the above preparation method, the temperature of the third ball milling is 600-900℃, such as 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, etc.

[0032] In some preferred embodiments, the lithium source is a high-purity lithium source, the purity of the lithium source is 99.5% or higher, preferably 99.9% or higher, further preferably 99.95% or higher, and more preferably 99.99% or higher; the lithium source is at least one of anhydrous lithium hydroxide, lithium oxide, lithium hydroxide containing crystal water (such as lithium hydroxide monohydrate), and preferably a lithium source without crystal water is used.

[0033] In the above preparation method, the ball milling can be performed using a high-temperature ball mill. The first ball milling, the second ball milling and the third ball milling use a normal ball-to-material ratio, such as a ball-to-material ratio of 5-10:1. The grinding balls can be stable grinding balls, such as zirconia grinding balls.

[0034] In the above preparation method, before the first ball milling, the material and the grinding balls are first transferred into a high-temperature ball mill pot, sealed, vacuumed to below 1 Pa, then slowly introduced with hydrogen-argon mixed gas to normal pressure, and then heated and ball milled while continuously introducing the hydrogen-argon mixed gas, and the pot is not sealed again during the subsequent ball milling.

[0035] In some preferred embodiments, the sulfur powder is a high-purity sulfur powder with a purity of 99.99% or higher.

[0036] In some preferred embodiments, the high-purity lithium sulfide has a purity of 99.9% or higher.

[0037] In some preferred embodiments, the high-purity lithium sulfide has a total amount of metal impurity elements of not higher than 70 ppm, preferably not higher than 50 ppm, further preferably not higher than 40 ppm, and more preferably not higher than 30 ppm, not higher than 25 ppm, or not higher than 20 ppm.

[0038] In some preferred embodiments, the molar ratio of lithium in the lithium source to sulfur in the sulfur powder is 2:1.2-1.5, such as 2:1.2, 2:1.3, 2:1.4, 2:1.5, etc.

[0039] In some preferred embodiments, the ratio of the molar amount of lithium in the lithium source to the total molar amount of hydrogen in the first ball milling and the second ball milling is not higher than 1:4, such as 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, etc. It is worth mentioning that the first ball milling and the second ball milling need to ensure that there is sufficient hydrogen in the system during the reaction process, such as the average flow difference of hydrogen introduced during the first ball milling and the second ball milling is not more than 20%, so as to improve the controllability of the process.

[0040] In some preferred embodiments, the rotation speed of the first ball milling is 200-400 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, etc.

[0041] In some preferred embodiments, the duration of the first ball milling is 20-60 min, such as 20 min, 30 min, 40 min, 50 min, 60 min, etc.

[0042] In some preferred embodiments, in the mixed gas atmosphere of hydrogen and inert gas, the volume fraction of hydrogen is 40-80%, such as 40%, 50%, 60%, 70%, 80%, etc. Preferably, the purity of hydrogen is above 99.99%.

[0043] In some preferred embodiments, the rotation speed of the second ball milling is 200-400 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, etc.

[0044] In some preferred embodiments, the duration of the second ball milling is 2-4 h, such as 2 h, 2.5 h, 3 h, 3.5 h, 4 h, etc.

[0045] In some preferred embodiments, in the mixed gas of hydrogen, inert gas and ammonia, the volume fraction of hydrogen is 40-80%, such as 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc., and the volume fraction of ammonia is 5-20%, such as 5%, 10%, 15%, 20%, etc. Preferably, the purity of hydrogen is above 99.99%.

[0046] In some preferred embodiments, the rotation speed of the third ball milling is 200-400 rpm, such as 200 rpm, 250 rpm, 300 rpm, 350 rpm, 400 rpm, etc.

[0047] In some preferred embodiments, the third ball milling is performed for 15-30 minutes, such as 15 minutes, 20 minutes, 25 minutes, 30 minutes, etc.

[0048] In some preferred embodiments, the hydrogen sulfide-containing gas has a volume fraction of hydrogen sulfide gas of 10-30%, such as 10%, 15%, 20%, 25%, 30%, etc. The hydrogen sulfide-containing gas is preferably a mixture of hydrogen sulfide and an inert gas.

[0049] It is worth mentioning that the inert gas is a noble gas such as argon, helium, etc., and does not include nitrogen.

[0050] In some preferred embodiments, the method for preparing anhydrous lithium hydroxide comprises: (1) dissolving industrial-grade hydrated lithium hydroxide in water, and performing precision filtration to obtain a lithium hydroxide solution; (2) introducing the lithium hydroxide solution into an evaporation system with an oxygen content of not more than 5 ppm, and performing evaporation concentration at 75-90°C (such as 75°C, 80°C, 85°C, 90°C, etc.), and performing centrifugal separation on the obtained evaporation concentrated solution to obtain crude lithium hydroxide; (3) using the crude lithium hydroxide as a raw material, repeating the process of "preparing a crude lithium hydroxide solution from crude lithium hydroxide - step (2)" at least once, preparing a solution from the obtained lithium hydroxide, and performing spray drying to obtain high-purity anhydrous lithium hydroxide.

[0051] In the above preparation method, in step (1), the precision filtration can use a filter membrane with a pore size commonly used in the art, such as a pore size of 0.2-0.5 μm.

[0052] In the above preparation method, in step (1), the industrial-grade hydrated lithium hydroxide can be industrial-grade monohydrate lithium hydroxide with a purity of ≥95%.

[0053] In the above preparation method, in step (1), when the industrial-grade hydrated lithium hydroxide is dissolved in water, the dissolution can be performed under conventional conditions, such as stirring and dissolving at 80-90°C, and the stirring speed can be a conventional speed, such as 200-400 rpm.

[0054] In some preferred embodiments, in step (3), after the obtained lithium hydroxide is prepared into a solution, the method further comprises adding hydroxyethylidene diphosphonic acid and ethylenediaminetetraacetic acid to the solution, filtering after reaction, and then performing spray drying on the filtrate.

[0055] In some preferred embodiments, the ratio of the total molar amount of Ca ions and Mg ions in the solution to the molar amount of hydroxyethylidene diphosphonic acid, ethylenediaminetetraacetic acid is 1:0.6-0.9:0.3-0.5, such as 1:0.6:0.3, 1:0.7:0.3, 1:0.8:0.3, 1:0.9:0.3, 1:0.6:0.35, 1:0.7:0.35, 1:0.8:0.35, 1:0.9:0.35, 1:0.6:0.4, 1:0.7:0.4, 1:0.8:0.4, 1:0.9:0.4, 1:0.6:0.45, 1:0.7:0.45, 1:0.8:0.45, 1:0.9:0.45, 1:0.6:0.5, 1:0.7:0.5, 1:0.8:0.5, 1:0.9:0.5, and the like.

[0056] In some preferred embodiments, the solid-liquid ratio of the lithium hydroxide when formulated into a solution is 1:5-10, such as 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, and the like.

[0057] In some preferred embodiments, the temperature of the reaction is 70-110°C, such as 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, and further preferably 80-95°C.

[0058] In some preferred embodiments, the filtration and spray drying are performed under an inert atmosphere or a nitrogen atmosphere. The filtration can be a plate-and-frame filtration. The spray drying uses a conventional temperature, such as an inlet temperature of 250-350°C.

[0059] In some preferred embodiments, in step (2), the evaporation system is an MVR evaporator; and the concentration ratio of the evaporation concentration is 6-12:1, such as 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, and the like.

[0060] In step (2), the specific operation of introducing the lithium hydroxide solution into the evaporation system with an oxygen content of not higher than 5 ppm can be: vacuumizing the MVR evaporation bin to below 10 Pa, introducing high-purity inert gas (purity ≥ 99.999%, such as argon) for replacement multiple times, ensuring that the oxygen content in the MVR evaporation bin is <5 ppm, and then introducing the lithium hydroxide solution into the evaporation bin.

[0061] In step (2), the centrifugal separation can be performed at a conventional rotation speed, such as 2000-4000 rpm, for example, 2000 rpm, 2200 rpm, 2500 rpm, 2800 rpm, 3000 rpm, 3200 rpm, 3500 rpm, 3800 rpm, 4000 rpm, etc. The centrifugal process maintains a slight positive pressure in the system to prevent air backflow. The concentrated solution can be transferred to the centrifuge through a heat preservation conduit.

[0062] In some preferred embodiments, in step (1), the mass ratio of the industrial-grade lithium hydroxide monohydrate to water is 1:10-20, for example, 1:10, 1:12, 1:15, 1:18, 1:20, etc.

[0063] In some preferred embodiments, in step (3), when the crude lithium hydroxide is prepared into a crude lithium hydroxide solution, the solid-liquid ratio is 1:10-20, for example, 1:10, 1:12, 1:15, 1:18, 1:20, etc.

[0064] In some preferred embodiments, in step (3), the process of "preparing crude lithium hydroxide into a crude lithium hydroxide solution-step (2)" is repeated 1-3 times.

[0065] In some embodiments, the high-purity lithium sulfide prepared by the above preparation method is also provided.

[0066] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the accompanying drawings and preferred embodiments. However, the scope of protection of the present application is not limited to the following specific embodiments.

[0067] Unless otherwise defined, all the professional terms used herein have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present application.

[0068] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0069] Example 1 Step 1: Dissolve 100 g of industrial-grade lithium hydroxide monohydrate in 1 L of deionized water. Turn on the mechanical stirrer and set the rotation speed to 200 rpm. Control the temperature at 80°C. Continue stirring for 30 minutes until the solute is completely dissolved and the solution is basically clear. Use a filter membrane with a pore size of 0.5 μm to precisely filter the solution to remove water-insoluble substances and collect the completely clear solution. Evacuate the MVR evaporation tank to below 10 Pa, and replace it with high-purity argon (purity ≥ 99.999%) for 3 times.

[0070] Step two: The clear solution obtained in step one was pumped into an evaporation tank and concentrated to 1 / 6 of the original volume at 75°C. The concentrated solution was transferred to a centrifuge through a heat preservation conduit and centrifuged at a speed of 2000 rpm for 15 min to obtain the first crude lithium hydroxide. The entire process was kept under a slight positive pressure to prevent air from flowing back.

[0071] Step three: The first crude lithium hydroxide was dissolved in deionized water at a solid-liquid ratio of 1:10, and then treated once again in the same way as before to obtain the second crude lithium hydroxide. The second crude lithium hydroxide was dissolved in deionized water at a solid-liquid ratio of 1:5, and the concentration of calcium and magnesium ions in the solution was detected after dissolution. Hydroxyethylidene diphosphonic acid (HEDP) and ethylenediaminetetraacetic acid (EDTA) were added in a molar ratio of 1:0.8:0.4, and a stable chelate was formed after stirring at 80°C for 10 min. The filtered solution was obtained by removing the chelate through plate and frame filtration. The filtered solution was spray dried at a flow rate of 0.5 L / min, an atomization frequency of 500 Hz, and an inlet temperature of 250°C. The entire filtration and spray drying process was carried out in an inert gas environment to obtain high-purity anhydrous lithium hydroxide.

[0072] Step four: Anhydrous lithium hydroxide and high-purity sulfur powder were added to a high-temperature ball mill tank in a molar ratio of 2:1.2, and 5 mm zirconia balls were loaded (ball-to-material ratio 5:1). After sealing, the tank was evacuated to below 1 Pa, and hydrogen-argon mixed gas (hydrogen volume fraction 40%, purity ≥99.99%) was introduced to normal pressure. The hydrogen-argon mixed gas was continuously introduced after the tank was unsealed. The tank was ball milled at a speed of 200 rpm, and the temperature was programmed to rise to 200°C and maintained for 0.5 h. Then, hydrogen, argon, and ammonia mixed gas (hydrogen volume fraction 40%, ammonia volume fraction 10%, purity ≥99.99%) was introduced, and the temperature was programmed to rise to 350°C and maintained for 4 h. The total amount of hydrogen introduced in this step was 4 times the molar amount of lithium hydroxide.

[0073] Step five: The temperature in the furnace cavity was increased to 600°C, and the ball milling reaction was carried out at a speed of 200 rpm for 15 min. During this period, 10% hydrogen sulfide gas was continuously introduced into the reaction tank. The grinding balls and reaction powder products were separated by opening the filter port, and high-purity lithium sulfide products were collected. The XRD pattern of the obtained lithium sulfide is shown in Figure 1 , and it can be seen from Figure 1 that pure lithium sulfide was synthesized, and no impurity phase was observed.

[0074] Example 2 Step 1: Take 100g of industrial grade lithium hydroxide monohydrate and dissolve it in 1.5L of deionized water. Turn on the mechanical stirrer and set the speed to 300 rpm. Control the temperature at 85°C. Continue stirring for 30 minutes until the solute is completely dissolved and the solution is clear. Use a filter membrane with a pore size of 1 μm to filter the solution and remove water-insoluble substances. Collect the completely clear solution.

[0075] Step 2: Vacuum the MVR evaporation tank to below 10 Pa and replace it with high-purity argon gas (purity ≥ 99.999%) for 3 times. Pump the clear solution obtained in step 1 into the evaporation tank and evaporate and concentrate it to 1 / 10 of the original volume at 85°C. Transfer the concentrated solution to a centrifuge through a heat preservation conduit and centrifuge at 3000 rpm for 15 min to separate the first crude lithium hydroxide. Maintain the system at a slight positive pressure throughout the process to prevent air from flowing back.

[0076] Step 3: Dissolve the first crude lithium hydroxide in deionized water at a solid-liquid ratio of 1:15, and then process it again in the same way as before to obtain the second crude lithium hydroxide. Dissolve the second crude lithium hydroxide in deionized water at a solid-liquid ratio of 1:5. After dissolving, detect the concentration of calcium and magnesium ions in the solution. Add hydroxyethylidene diphosphonic acid (HEDP) and ethylenediaminetetraacetic acid (EDTA) at a molar ratio of 1:0.8:0.4. Stir at 80°C for 20 min to form a stable chelate, then remove the chelate by plate and frame filtration to obtain the filtered solution. Spray dry the filtered solution at a flow rate of 1 L / min, atomization frequency of 600 Hz, and inlet temperature of 300°C. The entire filtration and spray drying process is carried out in an inert gas environment to obtain high-purity anhydrous lithium hydroxide.

[0077] Step 4: Add anhydrous lithium hydroxide and high-purity sulfur powder to a high-temperature ball mill tank at a molar ratio of 2:1.4. Fill with 10mm zirconia balls (ball-to-material ratio 5-10:1). After sealing, vacuum to below 1 Pa and then replace with hydrogen-argon mixed gas (hydrogen volume fraction 50%, purity ≥ 99.99%) to normal pressure. Ball mill at 300 rpm while programming the temperature to 250°C for 0.5h. Then slowly introduce hydrogen, argon, and ammonia mixed gas (hydrogen volume fraction 50%, ammonia volume fraction 10%, purity ≥ 99.99%) while programming the temperature to 400°C for 3h. The total amount of hydrogen introduced is 7 times the molar amount of lithium hydroxide.

[0078] Step 5: Increase the temperature in the furnace cavity to 800°C and ball mill at 300 rpm for 15 min. During this period, continuously introduce 20% hydrogen sulfide gas into the reaction tank. Open the filter port to separate the grinding balls and reaction powder product. Collect the high-purity lithium sulfide product.

[0079] Example 3 Step one: Take 100g of industrial grade lithium hydroxide monohydrate and dissolve it in 2L of deionized water. Turn on the mechanical stirrer and set the speed to 400 rpm. Control the temperature at 90°C. Continue stirring for 30 minutes until the solute is completely dissolved and the solution is basically clear. Use a filter membrane with a pore size of 0.2μm to filter the solution to remove water-insoluble substances and collect the completely clear solution.

[0080] Step two: Vacuum the MVR evaporation tank to below 10 Pa and replace it with high-purity argon gas (purity ≥ 99.999%) for 3 times. Pump the clear solution obtained in step one into the evaporation tank and evaporate and concentrate to 1 / 12 of the original volume at 90°C. Transfer the concentrated solution to a centrifuge through a heat preservation conduit and centrifuge at a speed of 4000 rpm for 15 min to separate and obtain the first crude lithium hydroxide.

[0081] Step three: Dissolve the first crude lithium hydroxide in deionized water at a solid-liquid ratio of 1:20, and then process it twice with the same process as before to obtain the second crude lithium hydroxide. Dissolve the second crude lithium hydroxide in deionized water at a solid-liquid ratio of 1:5, and then detect the concentration of calcium and magnesium ions in the solution. Add hydroxyethylidene diphosphonic acid (HEDP) and ethylenediaminetetraacetic acid (EDTA) at a molar ratio of 1:0.8:0.4, stir at 80°C for 30 min to form a stable chelate, and then remove the chelate by plate and frame filtration to obtain a filtered solution. Spray dry the filtered solution at a flow rate of 2 L / min, an atomization frequency of 800 Hz, and an inlet temperature of 350°C. The entire filtration and spray drying process is carried out in an inert gas environment to obtain high-purity anhydrous lithium hydroxide.

[0082] Step four: Add anhydrous lithium hydroxide and high-purity sulfur powder to a high-temperature ball mill tank at a molar ratio of 2:1.5, and fill it with 20mm zirconia balls (ball-to-material ratio 10:1). After sealing, vacuum to below 1 Pa, and then introduce hydrogen-argon mixed gas (hydrogen volume fraction 80%, purity ≥ 99.99%) to normal pressure and continuously introduce it. Mill at a speed of 400 rpm while programming the temperature to rise to 300°C and maintain for 0.5h. Then introduce hydrogen, argon and ammonia mixed gas (hydrogen volume fraction 80%, ammonia volume fraction 10%, purity ≥ 99.99%) while programming the temperature to rise to 450°C and maintain for 4h. The total amount of hydrogen introduced is 10 times the molar amount of lithium hydroxide.

[0083] Step five: Increase the temperature in the furnace cavity to 900°C and mill at a speed of 400 rpm for 15 min. During this period, continuously introduce 30% hydrogen sulfide gas into the reaction tank. Open the filter port to separate the grinding balls and the reaction powder product, and collect the high-purity lithium sulfide product.

[0084] Example 4 This example is based on the preparation of high-purity lithium sulfide by gas-phase neutralization method, and the difference from Example 1 is only that steps one to three are omitted, and a certain battery-grade anhydrous lithium hydroxide on the market is directly used as a raw material to perform steps four to five.

[0085] Example 5 This example is based on the preparation of high-purity lithium sulfide by gas-phase neutralization method, and the difference from Example 1 is only that the step of adding hydroxyethylidene diphosphonic acid (HEDP) and ethylenediaminetetraacetic acid (EDTA) for reaction in step three is omitted.

[0086] Comparative Example 1 This comparative example is based on the preparation of high-purity lithium sulfide by gas-phase neutralization method, and the difference from Example 1 is only that step three is omitted, and the primary crude lithium hydroxide obtained in step two is directly used as a raw material for step four.

[0087] Comparative Example 2 This comparative example is based on the preparation of high-purity lithium sulfide by gas-phase neutralization method, and the difference from Example 1 is only that the reaction device for steps four and five is replaced by a tube furnace.

[0088] Comparative Example 3 This comparative example is based on the preparation of high-purity lithium sulfide by gas-phase neutralization method, and the difference from Example 1 is only that step five is omitted, and the material in step four is taken as the final product.

[0089] Comparative Example 4 This comparative example differs from Example 1 only in step four, specifically, step four includes: anhydrous lithium hydroxide and high-purity sulfur powder are added to a high-temperature ball mill tank at a molar ratio of 2:1.2, and 5 mm zirconia balls are loaded (ball-to-material ratio 5:1). After sealing, vacuum is drawn to below 1 Pa, hydrogen-argon mixed gas (hydrogen volume fraction 40%, purity ≥99.99%) is introduced to normal pressure, and then continuous introduction of hydrogen, argon and ammonia mixed gas (hydrogen volume fraction 40%, ammonia volume fraction 10%, purity ≥99.99%) is continued. Ball milling is performed at a speed of 200 rpm, while the temperature is programmed to rise to 350°C and maintained for 4h. The total amount of hydrogen introduced is 4 times the molar amount of lithium hydroxide.

[0090] Comparative Example 5 This comparative example differs from Example 1 only in step four, specifically, step four includes: anhydrous lithium hydroxide and high-purity sulfur powder are added to a high-temperature ball mill tank at a molar ratio of 2:1.2, and 5 mm zirconia balls are loaded (ball-to-material ratio 5:1). After sealing, vacuum is drawn to below 1 Pa, hydrogen-argon mixed gas (hydrogen volume fraction 40%, purity ≥99.99%) is introduced to normal pressure, and then continuous introduction of hydrogen, argon and ammonia mixed gas (hydrogen volume fraction 40%, ammonia volume fraction 10%, purity ≥99.99%) is continued. Ball milling is performed at a speed of 200 rpm, while the temperature is programmed to rise to 350°C and maintained for 4h. The total amount of hydrogen introduced is 4 times the molar amount of lithium hydroxide.

[0091] The purity of the un-carbon-complexed micro-powder grade lithium sulfide of Example 1 to Example 5, Comparative Example 1 to Comparative Example 5 was tested, and the mass of sulfur in the powder was calculated by a carbon-sulfur analyzer, and the formula was as follows: Purity = mass of sulfur element ratio x 45.947 / 32.065 x 100% In addition, the carbon content and the content of main metal impurities of the products obtained in Example 1 to 5 and Comparative Example 1 to 5 were tested by potential titration, carbon-sulfur analyzer and ICP, and all the results were shown in Table 1.

[0092] Table 1 As can be seen from the above, the lithium sulfide prepared by lithium hydroxide and hydrogen sulfide by the segmented method in the embodiments of the present application has the characteristics of high whiteness, high purity, low impurity elements and low carbonization degree, and the purity meets ≥ 99.9%, and the content of metal impurities is not higher than 70 ppm, and the content of metal impurities in the lithium sulfide prepared in Example 1 to 3 is not higher than 10 ppm, and the purity far exceeds the current industry level.

[0093] As can be seen from Comparative Example 1 and Example 4, compared with the lithium hydroxide refined by vacuum for many times, the conventional battery grade lithium hydroxide on the market has a higher impurity content, which will directly bring impurities into the lithium sulfide product, resulting in a comprehensive impurity content of more than 50 ppm.

[0094] As can be seen from Comparative Example 1 and Example 5, Example 5 only does not perform the step of adding hydroxyethylidene diphosphonic acid (HEDP) and ethylenediaminetetraacetic acid (EDTA) to react in step three, and the content of calcium and magnesium as impurity elements increases to 21.87 ppm and 18.75 ppm, which shows that the organic solvent can form a chelate with calcium and magnesium elements to effectively remove Ca and Mg impurities, and thus greatly reduce the content of impurity metal elements in high-purity lithium sulfide.

[0095] As can be seen from Comparative Example 1 and Comparative Example 1, the use of the material centrifuged directly without spray drying will cause the conversion rate to be low and the purity to decrease. It is analyzed and speculated that this is because the lithium hydroxide centrifuged out is not only combined with water, but also contains a large amount of free water, and the particle size of the material is large. In addition, a large amount of water evaporates rapidly at the initial stage of reaction roasting, which further promotes the agglomeration of the raw materials, and hinders the contact between hydrogen sulfide and lithium hydroxide in the subsequent reaction, so that the reaction is incomplete.

[0096] As can be seen from Comparative Example 1 and Comparative Example 2, the product purity of Comparative Example 2 is greatly reduced because the high-temperature ball mill is not used but the tube furnace is used for reaction.

[0097] Comparative Example 1 and Comparative Example 3 can be known, Comparative Example 3 omits step five, the carbon content increases significantly and the whiteness is only 69.8, after analysis, it is speculated that lithium carbonate and trace residual sulfur are still present in the product.

[0098] Comparative Example 1 and Comparative Example 4 can be known, Comparative Example 4 only does not add ammonia gas in the atmosphere in step four, which leads to a slight decrease in purity, which is mainly due to the fact that ammonia gas can react with hydrogen sulfide to generate ammonium sulfide and sodium hydrosulfide two intermediate substances, reducing the acidity in the atmosphere, thereby inhibiting the reaction of a small amount of oxygen impurities in the gas with lithium hydroxide to generate lithium oxide at high temperature; in addition, ammonia gas can also act as a catalyst, thereby achieving the effect of improving the purity of the final product.

[0099] Comparative Example 1 and Comparative Example 5 can be known, Comparative Example 5 omits the low-temperature calcination and ball milling process, which leads to a slight decrease in purity. After analysis, this may be because the low-temperature calcination process is a slow reaction, which generates a layer of lithium sulfide product shell on the surface of the powder, preventing the subsequent reaction from sticking and caking due to too fast reaction speed, thereby increasing the conversion rate.

[0100] The above only describes the preferred embodiments of the present application, and it should be noted that for ordinary skilled persons in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A method for preparing high-purity lithium sulfide, characterized in that: include: After mixing the lithium source and the sulfur powder, performing a first ball milling in a mixed atmosphere of hydrogen and an inert gas, wherein the temperature of the first ball milling is 200-300° C.; The ball milling atmosphere was switched to a mixture of hydrogen, inert gas and ammonia, and the temperature was continued to rise to 350-450°C for the second ball milling. The ball milling atmosphere is switched to a gas containing hydrogen sulfide, the temperature is raised to 600-900°C, and the third ball milling is performed to obtain high-purity lithium sulfide.

2. The method for preparing high-purity lithium sulfide according to claim 1, wherein The purity of the lithium source is 99.5% or more, preferably 99.9% or more, more preferably 99.95% or more, and more preferably 99.99% or more; the lithium source is at least one of anhydrous lithium hydroxide, lithium oxide, and lithium hydroxide containing crystal water; The purity of the sulfur powder is above 99.99%; The purity of the high-purity lithium sulfide is above 99.9%. Preferably, the total amount of metallic impurity elements in the high-purity lithium sulfide is not higher than 70 ppm, more preferably not higher than 50 ppm, and even more preferably not higher than 30 ppm.

3. The method for preparing high-purity lithium sulfide according to claim 1, wherein The molar ratio of lithium in the lithium source to sulfur in the sulfur powder is 2:1.2-1.5; the ratio of the molar amount of lithium in the lithium source to the total molar amount of hydrogen in the first ball mill and the second ball mill is not higher than 1:

4.

4. The method for preparing high-purity lithium sulfide according to claim 1, wherein The rotation speed of the first ball mill is 200-400 rpm; the duration of the first ball mill is 20-60 min; the volume fraction of hydrogen in the mixed atmosphere of hydrogen and inert gas is 40-80%; The rotation speed of the second ball mill is 200-400 rpm; the duration of the second ball mill is 2-4 hours; in the mixed gas of hydrogen, inert gas and ammonia, the volume fraction of hydrogen is 40-80%, and the volume fraction of ammonia is 5-20%.

5. The method for preparing high-purity lithium sulfide according to claim 1, wherein The rotation speed of the third ball mill is 200-400 rpm; the duration of the third ball mill is 15-30 min; the volume fraction of hydrogen sulfide gas in the hydrogen sulfide-containing gas is 10-30%; the hydrogen sulfide-containing gas is a mixture of hydrogen sulfide and inert gas.

6. The method for preparing high-purity lithium sulfide according to claim 2, wherein: The preparation method of the anhydrous lithium hydroxide comprises: (1) Dissolving industrial-grade hydrated lithium hydroxide in water and filtering the solution to obtain a lithium hydroxide solution; (2) introducing the lithium hydroxide solution into an evaporation system with an oxygen content of no more than 5 ppm, evaporating and concentrating at 75-90° C., and centrifuging the obtained evaporated concentrate to obtain crude lithium hydroxide; (3) Using crude lithium hydroxide as a raw material, repeating the process of "preparing the crude lithium hydroxide into a crude lithium hydroxide solution - step (2)" at least once, then preparing the obtained lithium hydroxide into a solution, and spray drying it to obtain high-purity anhydrous lithium hydroxide.

7. The method for preparing high-purity lithium sulfide according to claim 6, wherein: In step (3), after the obtained lithium hydroxide is prepared into a solution, hydroxyethylidene diphosphonic acid and ethylenediamine tetraacetic acid are added to the solution, the solution is filtered after reaction, and the filtrate is spray-dried; Preferably, in step (3), the ratio of the total molar amount of Ca ions and magnesium ions in the solution to the molar amount of hydroxyethylidene diphosphonic acid and ethylenediamine tetraacetic acid is 1:0.6-0.9:0.3-0.5; Preferably, in step (3), the solid-to-liquid ratio of the lithium hydroxide when the solution is prepared is 1:5-10; Preferably, in step (3), the reaction temperature is 70-110°C, preferably 80-95°C; Preferably, the filtering and spray drying are performed under an inert atmosphere or a nitrogen atmosphere.

8. The method for preparing high-purity lithium sulfide according to claim 6, wherein: In step (2), the evaporation system is an MVR evaporator; the concentration ratio of the evaporation concentration is 6~12:

1.

9. The method for preparing high-purity lithium sulfide according to claim 6, wherein: In step (1), the mass ratio of the industrial-grade hydrated lithium hydroxide to water is 1:10-20; In step (3), when the crude lithium hydroxide is prepared into a crude lithium hydroxide solution, the solid-liquid ratio is 1:10-20; In step (3), the process of "preparing the crude lithium hydroxide into a crude lithium hydroxide solution - step (2)" is repeated 1 to 3 times.

10. High-purity lithium sulfide, characterized in that The method is as described in any one of claims 1 to 9.

Images