Large-scale preparation method of lithium sulfide

Abstract

The invention discloses a large-scale preparation method of lithium sulfide, and belongs to the technical field of preparation of battery materials. Lithium sulfate monohydrate is adopted as a reaction raw material and is subjected to dehydration and purification treatment to obtain anhydrous lithium sulfate, and the anhydrous lithium sulfate is calcined in hydrogen and carbon dioxide mixed gas without introducing other impurities; the method has the advantages that safety under high-temperature calcination reaction can be guaranteed, the produced lithium sulfide crude product is dissolved by the methanol / isopropanol mixed solution to directly generate lithium sulfide crystals, redundant impurities can be removed by calcining the generated lithium sulfide crystals, no other by-products are generated in the reaction process, and the purity of lithium sulfide is guaranteed. According to the Li2S preparation method developed by increasing the purification step and exploring the reaction conditions and the impurity removal mode, low-cost, high-purity and large-scale preparation of Li2S can be realized.

Description

Technical Field

[0001] The invention relates to the technical field of battery material preparation, and in particular to a large-scale preparation method of lithium sulfide. Background Art

[0002] With the vigorous development of new energy vehicles, researchers have gradually deepened their research on power battery technology and found that traditional liquid power batteries have problems such as safety and low-temperature failure. All-solid-state batteries replace the electrolyte in liquid batteries with solid electrolytes, which can greatly improve the safety and low-temperature performance of the battery. Among the many types of solid electrolytes, sulfide solid electrolytes have attracted much attention for their excellent ionic conductivity. However, their high price has hindered their further development. One of the reasons for the high price of sulfide solid electrolytes is the high price of the synthetic raw material lithium sulfide. Lithium sulfide has poor air stability and will quickly react with water and deteriorate when exposed to air. Therefore, the entire process of synthesizing lithium sulfide is carried out in an argon glove box, which increases the cost of synthesizing lithium sulfide.

[0003] At present, the relevant reports on the synthesis method of lithium sulfide mainly include: lithium / sulfur dry method, lithium / sulfur wet method, double decomposition reaction method, magnesium thermal reduction reaction method, hydrogen thermal reduction reaction method and carbon thermal reduction reaction method. The hydrogen thermal reduction reaction method is a method for cleanly and sustainably synthesizing lithium sulfide (Li2S) by reducing lithium sulfate (Li2S04) with hydrogen. However, the purity of lithium sulfide obtained by simply calcining Li2S04 available on the market is not high and cannot meet the battery grade standard. In addition, the cost of the preparation process is relatively high, which is not conducive to large-scale preparation and hinders the further development of sulfide solid electrolytes. Summary of the invention

[0004] In view of the above-mentioned prior art, the object of the present invention is to provide a large-scale preparation method of lithium sulfide.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] In a first aspect, the present invention provides a method for preparing high-purity lithium sulfide on a large scale, comprising the following steps:

[0007] (1) calcining lithium sulfate monohydrate in an air atmosphere for the first time, cooling and pulverizing to obtain anhydrous lithium sulfate fine powder;

[0008] (2) introducing anhydrous lithium sulfate fine powder into a hydrogen-containing inert mixed gas for a second calcination, and crushing to obtain a crude lithium sulfide product;

[0009] (3) under the protection of an inert atmosphere, dissolving the crude lithium sulfide product with a mixed solution of methanol / isopropanol, filtering, drying and crystallizing the filtrate to obtain lithium sulfide crystals;

[0010] (4) Under the protection of a hydrogen-containing inert mixed gas, the lithium sulfide crystals are calcined for a third time to obtain high-purity lithium sulfide.

[0011] In step (3), the volume ratio of methanol to isopropanol in the methanol / isopropanol mixed solution is 5:2.

[0012] The methanol and isopropanol are both industrial grade organic solvents with a content of 99.9%.

[0013] In step (3), the mass volume ratio of the crude lithium sulfide product to the mixed solution of methanol / isopropanol is 1:

[0014] (40-45).

[0015] Preferably, in step (3), the mass volume ratio of the crude lithium sulfide to the mixed solution of methanol / isopropanol is 1:40.

[0016] In step (2) and step (4), the hydrogen-containing inert mixed gas is one or more of a hydrogen-carbon dioxide mixed gas, a hydrogen-argon mixed gas, a hydrogen-nitrogen mixed gas, and a hydrogen-helium mixed gas.

[0017] The hydrogen-containing inert mixed gas is a hydrogen-carbon dioxide mixed gas, and the volume ratio of hydrogen to carbon dioxide in the hydrogen-carbon dioxide mixed gas is 2:1.

[0018] Preferably, in step (1), the temperature of the first calcination is 300-400° C., and the calcination time is 3-5 h.

[0019] Preferably, in step (2), the temperature of the second calcination is 600-800° C., and the calcination time is 18-24 hours.

[0020] In step (4), the temperature of the third calcination is 400-600° C., and the calcination time is 2-4 hours.

[0021] Beneficial effects of the present invention:

[0022] 1. The present invention uses lithium sulfate monohydrate as a reaction raw material, dehydrates and purifies lithium sulfate monohydrate to obtain anhydrous lithium sulfate, which is calcined in a hydrogen and carbon dioxide mixed gas without introducing other impurities, and can also ensure the safety under high-temperature calcination reaction. The produced lithium sulfide crude product is dissolved in a methanol / isopropanol mixed solution to directly generate lithium sulfide crystals, and the generated lithium sulfide crystals can be calcined to remove excess impurities. No other by-products are generated during the reaction process, and the purity of lithium sulfide is guaranteed. The present invention increases the purification step, explores the reaction conditions and the impurity removal method to develop the Li2S preparation method, which can achieve low-cost, high-purity, and large-scale preparation of Li2S.

[0023] 2. The volume ratio of methanol to isopropanol in the methanol / isopropanol mixed solution used in the present invention is 5:2, the dissolution reaction conditions are mild, the content of precipitated lithium sulfide crystals is higher, the solubility of the mixed solution is more suitable for precipitating lithium sulfide, and the yield of prepared lithium sulfide is increased. In addition, the used methanol / isopropanol mixed solution can be recovered by distillation and recycled for the preparation of the next batch of lithium sulfide crystals, which is environmentally friendly and suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Process flow chart for large-scale preparation of high-purity lithium sulfide.

[0025] Figure 2 This is the XRD pattern of the high-purity lithium sulfide synthesized in Example 1 (wrapped with polyimide tape during testing).

[0026] Figure 3 This is the XRD pattern of the high-purity lithium sulfide synthesized in Comparative Example 1 (wrapped with polyimide tape during testing).

[0027] Figure 4 This is the XRD pattern of the high-purity lithium sulfide synthesized in Comparative Example 2 (wrapped with polyimide tape during testing). DETAILED DESCRIPTION

[0028] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0029] The following detailed description is for illustrative purposes only and is intended to provide further explanation of the present application, rather than to limit the scope of the present invention.

[0030] As described in the background technology, in view of the problems of low purity and high cost of synthesizing lithium sulfide by reducing lithium sulfate with hydrogen, the present invention provides a large-scale preparation method of lithium sulfide, comprising the following steps:

[0031] (1) In an air atmosphere, lithium sulfate monohydrate is calcined for the first time, and then pulverized to obtain anhydrous lithium sulfate fine powder after cooling, the calcination temperature is 300-400° C., and the calcination time is 3-5 h;

[0032] (2) placing anhydrous lithium sulfate fine powder in a fluidized bed reactor, introducing a hydrogen-containing inert mixed gas for a second calcination, the calcination temperature is 600-800° C., the calcination time is 18-24 hours, and the crude lithium sulfide product is obtained after crushing;

[0033] (3) under the protection of an inert atmosphere, dissolving the crude lithium sulfide product with a mixed solution of methanol / isopropanol, filtering, drying and crystallizing the filtrate to obtain lithium sulfide crystals;

[0034] (4) The lithium sulfide crystals are subjected to a third calcination to remove impurities under the protection of a hydrogen-containing inert mixed gas, the calcination temperature is 400-600° C., and the calcination time is 2-4 hours to obtain high-purity lithium sulfide.

[0035] The reaction that occurs during the first calcination of the present invention is: Anhydrous lithium sulfate was obtained; the reaction that occurred during the second calcination was The crude lithium sulfide was obtained; the reaction occurred during the third calcination was The Li2S2 by-product is removed to obtain high-purity lithium sulfide.

[0036] The invention adopts three calcinations and one alcohol-dissolving purification to obtain high-purity lithium sulfide. The raw material lithium sulfate monohydrate is cheap, the purification process is simple to operate, no other by-products are generated, and the equipment requirements are low. The mixed solution of methanol / isopropanol can be recycled and reused, which is environmentally friendly. The lithium sulfide yield reaches 92%, and is suitable for large-scale production.

[0037] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, the technical solution of the present application will be described in detail below in conjunction with specific embodiments.

[0038] The raw materials used in the examples of the present invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0039] Example 1: Preparation of lithium sulfide

[0040] (1) Weigh 1280 g of lithium sulfate monohydrate powder, calcine it at 300° C. in an air atmosphere, maintain the heating rate at 5° C. / min, and keep it at this temperature for 5 h. After cooling, grind it into powder to obtain anhydrous lithium sulfate fine powder.

[0041] (2) In a drying room, the anhydrous lithium sulfate fine powder obtained in step (1) is placed in a fluidized bed reactor, and calcined at 600° C. under the protection of a hydrogen and carbon dioxide mixed gas (hydrogen and carbon dioxide volume ratio is 2:1), with the heating rate maintained at 5° C. / min, and calcined for 24 hours after reaching 600° C. After the temperature drops naturally, a crude lithium sulfide product is obtained.

[0042] (3) In a drying room, the crude lithium sulfide obtained in step (2) is ground and dissolved in a mixed solution of methanol / isopropanol (the volume ratio of methanol to isopropanol is 5:2) at a mass volume ratio of 1:40 to precipitate lithium sulfide crystals, and residual impurities such as lithium sulfate are filtered out, and the methanol / isopropanol mixed solution from which lithium sulfide is precipitated is dried in a spray dryer into which nitrogen is introduced to obtain dry lithium sulfide crystals.

[0043] (4) In a drying room, the lithium sulfide crystals obtained in step (3) were placed in a tubular furnace and calcined at 400° C. under the protection of a hydrogen and carbon dioxide mixture (hydrogen and carbon dioxide in a volume ratio of 2:1) to remove Li2S2. The heating rate was 5° C. / min. After reaching 400° C., the mixture was calcined for 4 h. After the temperature was naturally cooled, 422.96 g of lithium sulfide was obtained.

[0044] After use, the methanol / isopropanol mixed solution can be evaporated and recovered for the next lithium sulfide crystal preparation.

[0045] Example 2: Preparation of lithium sulfide

[0046] (1) Weigh 1280 g of lithium sulfate monohydrate powder, calcine it at 400° C. in an air atmosphere, maintain the heating rate at 5° C. / min, and keep it at this temperature for 3 h. After cooling, grind it into powder to obtain anhydrous lithium sulfate fine powder.

[0047] (2) In a drying room, the anhydrous lithium sulfate fine powder obtained in step (1) is placed in a fluidized bed reactor, and calcined at 800° C. under the protection of a hydrogen and carbon dioxide mixed gas (hydrogen and carbon dioxide volume ratio is 2:1), with the heating rate maintained at 5° C. / min, and calcined for 18 hours after reaching 800° C. After the temperature drops naturally, a crude lithium sulfide product is obtained.

[0048] (3) In a drying room, the crude lithium sulfide obtained in step (2) is ground and dissolved in a mixed solution of methanol / isopropanol (the volume ratio of methanol to isopropanol is 5:2) at a mass volume ratio of 1:40 to precipitate lithium sulfide crystals, and residual impurities such as lithium sulfate are filtered out. The methanol / isopropanol mixed solution from which lithium sulfide is precipitated is dried in a spray dryer into which argon gas is introduced to obtain dry lithium sulfide crystals.

[0049] (4) In a drying room, the lithium sulfide crystals obtained in step (3) are placed in a tubular furnace and calcined at 600° C. under the protection of a hydrogen and carbon dioxide mixture (hydrogen and carbon dioxide in a volume ratio of 2:1) to remove Li2S2. The heating rate is 5° C. / min. After reaching 600° C., the mixture is calcined for 2 h. After the temperature is naturally cooled, 420.18 g of lithium sulfide is obtained.

[0050] Comparative Example 1: Preparation of lithium sulfide

[0051] The difference between Comparative Example 1 and Example 1 is that the crude lithium sulfide is ground and dissolved in a methanol solution to precipitate lithium sulfide crystals, as follows:

[0052] (1) Weigh 1280 g of lithium sulfate monohydrate powder, calcine it at 300° C. in an air atmosphere, maintain the heating rate at 5° C. / min, and keep it at this temperature for 5 h. After cooling, grind it into powder to obtain anhydrous lithium sulfate fine powder.

[0053] (2) In a drying room, the anhydrous lithium sulfate fine powder obtained in step (1) is placed in a fluidized bed reactor, and calcined at 600° C. under the protection of a hydrogen and carbon dioxide mixed gas (hydrogen and carbon dioxide volume ratio is 2:1), with the heating rate maintained at 5° C. / min, and calcined for 24 hours after reaching 600° C. After the temperature drops naturally, a crude lithium sulfide product is obtained.

[0054] (3) In a drying room, the crude lithium sulfide obtained in step (2) is ground and dissolved in a methanol solution at a mass volume ratio of 1:40 to precipitate lithium sulfide crystals, and residual impurities such as lithium sulfate are filtered out, and the methanol solution from which the precipitated lithium sulfide is dried in a spray dryer into which nitrogen is introduced to obtain dry lithium sulfide crystals.

[0055] (4) In a drying room, the lithium sulfide crystals obtained in step (3) are placed in a tubular furnace and calcined at 400° C. under the protection of a hydrogen and carbon dioxide mixture (hydrogen and carbon dioxide in a volume ratio of 2:1) to remove Li2S2. The heating rate is 5° C. / min. After reaching 400° C., the mixture is calcined for 4 hours. After the temperature is naturally lowered, 399.97 g of lithium sulfide is obtained.

[0056] Comparative Example 2: Preparation of lithium sulfide

[0057] The difference between Comparative Example 1 and Example 1 is that the crude lithium sulfide is ground and dissolved in an isopropanol solution to precipitate lithium sulfide crystals. The specific operation steps are as follows:

[0058] (1) Weigh 1280 g of lithium sulfate monohydrate powder, calcine it at 300° C. in an air atmosphere, maintain the heating rate at 5° C. / min, and keep it at this temperature for 5 h. After cooling, grind it into powder to obtain anhydrous lithium sulfate fine powder.

[0059] (2) In a drying room, the anhydrous lithium sulfate fine powder obtained in step (1) is placed in a fluidized bed reactor, and calcined at 600° C. under the protection of a hydrogen and carbon dioxide mixed gas (hydrogen and carbon dioxide volume ratio is 2:1), with the heating rate maintained at 5° C. / min, and calcined for 24 hours after reaching 600° C. After the temperature drops naturally, a crude lithium sulfide product is obtained.

[0060] (3) In a drying room, the crude lithium sulfide obtained in step (2) is ground and dissolved in an isopropanol solution at a mass volume ratio of 1:40 to precipitate lithium sulfide crystals, and residual impurities such as lithium sulfate are filtered out. The isopropanol solution of the precipitated lithium sulfide is dried in a spray dryer into which nitrogen is introduced to obtain dry lithium sulfide crystals.

[0061] (4) In a drying room, the lithium sulfide crystals obtained in step (3) are placed in a tubular furnace and calcined at 400° C. under the protection of a hydrogen and carbon dioxide mixture (hydrogen and carbon dioxide in a volume ratio of 2:1) to remove Li2S2. The heating rate is 5° C. / min. After reaching 400° C., the mixture is calcined for 4 hours. After the temperature is naturally lowered, 409.17 g of lithium sulfide is obtained.

[0062] Test Example 1: Lithium sulfide content and purity detection

[0063] The preparation method of synthesizing lithium sulfide using the existing hydrogen reduction method using lithium sulfate as a reaction raw material is used as a control, and the operation steps are as follows:

[0064] (1) Weigh 1280 g of commercially available lithium sulfate, calcine it at 600° C. for 24 h under inert gas protection, and allow the temperature to cool naturally to obtain crude lithium sulfide.

[0065] (2) In a drying room, the crude lithium sulfide obtained in step (1) is ground and dissolved in an anhydrous ethanol solution at a mass volume ratio of 1:40 to precipitate lithium sulfide crystals, residual impurities such as lithium sulfate are filtered out, and the anhydrous ethanol solution from which lithium sulfide is precipitated is dried in a spray dryer into which nitrogen is introduced to obtain dry lithium sulfide crystals.

[0066] (3) In a drying room, the lithium sulfide crystals obtained in step (2) were placed in a tubular furnace and calcined at 400° C. for 4 h under the protection of inert gas to obtain 390.78 g of lithium sulfide by reduction.

[0067] After the lithium sulfide prepared in Example 1, Comparative Example 1, Comparative Example 2 and the control group was collected, the main content of the prepared lithium sulfide was measured using the ICP-OES method to obtain the concentration of lithium sulfide. Since the lithium element in the product comes from the raw material, the ratio of the mass of lithium in the product to the mass of lithium in the raw material reflects the yield of the prepared lithium sulfide. The measurement results are shown in Table 1:

[0068] Table 1:

[0069] Grouping Lithium sulfide content (g) Lithium sulfide yield (%) Lithium sulfide concentration (%) Example 1 Group 422.96g 92％ 99.8 Comparative Example 1 399.97g 87％ 98.7 Comparative Example 2 409.17g 89％ 98.9 Control group 390.78g 85％ 98.2

[0070] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing lithium sulfide on a large scale, characterized in that: The following steps are involved: (1) calcining lithium sulfate monohydrate in an air atmosphere for the first time, cooling and pulverizing to obtain anhydrous lithium sulfate fine powder; (2) introducing anhydrous lithium sulfate fine powder into a hydrogen-containing inert mixed gas for a second calcination, and crushing to obtain a crude lithium sulfide product; (3) under the protection of an inert atmosphere, dissolving the crude lithium sulfide product with a mixed solution of methanol / isopropanol, filtering, drying and crystallizing the filtrate to obtain lithium sulfide crystals; (4) Under the protection of a hydrogen-containing inert mixed gas, the lithium sulfide crystals are calcined for a third time to obtain high-purity lithium sulfide.

2. The preparation method according to claim 1, characterized in that: In step (3), the volume ratio of methanol to isopropanol in the methanol / isopropanol mixed solution is 5:

2.

3. The preparation method according to claim 1, characterized in that: In step (3), the mass volume ratio of the crude lithium sulfide to the mixed solution of methanol / isopropanol is 1:(40-45).

4. The preparation method according to claim 1, characterized in that: In step (2) and step (4), the hydrogen-containing inert mixed gas is one or more of a hydrogen-carbon dioxide mixed gas, a hydrogen-argon mixed gas, a hydrogen-nitrogen mixed gas, and a hydrogen-helium mixed gas.

5. The preparation method according to claim 4, characterized in that: The hydrogen-containing inert mixed gas is a hydrogen-carbon dioxide mixed gas, and the volume ratio of hydrogen to carbon dioxide in the hydrogen-carbon dioxide mixed gas is 2:

1.

6. The preparation method according to claim 1, characterized in that: In step (1), the temperature of the first calcination is 300-400° C., and the calcination time is 3-5 hours.

7. The preparation method according to claim 1, characterized in that: In step (2), the temperature of the second calcination is 600-800° C., and the calcination time is 18-24 hours.

8. The preparation method according to claim 1, characterized in that: In step (4), the temperature of the third calcination is 400-600° C., and the calcination time is 2-4 hours.

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