Ev-grade high-purity lithium sulfide and preparation method therefor

Abstract

The present invention relates to the technical field of lithium battery materials, and relates to EV-grade high-purity lithium sulfide and a preparation method therefor. The preparation method for the EV-grade high-purity lithium sulfide comprises: A, uniformly mixing and grinding a lithium source and a sulfur source to obtain a mixture; B, primary reaction: mixing the mixture with hydrazine hydrate in an inert atmosphere, and reacting to obtain an intermediate slurry; C, secondary reaction: carrying out secondary reaction on the intermediate slurry in an inert atmosphere, and drying to obtain crude lithium sulfide; and D, calcining the crude lithium sulfide, and carrying out ball milling to obtain EV-grade high-purity lithium sulfide. According to the method of the present invention, the purity is 99.9% or above, the whiteness is 80 or above, D50 is smaller than or equal to 15 μm, and the method involves simple technological operation, has high safety, low energy consumption, low device requirements and low production costs, and is suitable for industrial production.

Description

EV-grade high-purity lithium sulfide and its preparation method

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims the benefit of and priority to Chinese patent application No. CN 202311216612X filed on September 20, 2023, and is incorporated herein by reference in its entirety for all other purposes. Technical Field

[0003] The present invention relates to EV-grade high-purity lithium sulfide and a preparation method thereof, belonging to the technical field of lithium battery materials. Background Art

[0004] In recent years, with the rapid development of new energy electric vehicles (EVs), the short battery life, long charging times, and poor safety of traditional liquid lithium-ion batteries have gradually become apparent, hindering the further development of the EV market. High-energy-density battery systems, such as lithium-sulfur batteries, lithium-oxygen batteries, and all-solid-state batteries, are expected to address the battery technology challenges facing EVs and are attracting considerable attention. Among them, all-solid-state batteries, with their high energy density, wide operating temperature range, excellent safety, and long cycle life, have attracted significant market attention and hold the greatest commercial potential. Sulfide solid electrolytes, as key components of all-solid-state batteries, have become the most promising technology due to their high ionic conductivity, ease of processing, and excellent electrochemical stability. Lithium sulfide (Li2S), a key precursor material for the synthesis of sulfide solid electrolytes, is extremely sensitive to water and air, limiting its production and storage, making it difficult to commercialize. This, in turn, makes lithium sulfide extremely expensive, hindering the development of sulfide solid-state batteries.

[0005] Patent CN112678781A synthesizes a lithium sulfide intermediate using lithium hydroxide monohydrate as a lithium source, sulfur powder as a sulfur source, and hydrazine hydrate as a reducing agent. The resulting intermediate product is then dehydrated and dried to produce a high-purity lithium sulfide product. The process is simple, highly operable, and energy-efficient. The raw material and equipment requirements are low, batch production is stable, and no toxic gases or secondary pollution are generated, meeting the requirements for safe operation and commercialization of lithium sulfide. However, the purity of the dried lithium sulfide product is relatively low, reaching only 97.88% at most. Furthermore, its whiteness is also relatively low. Whiteness describes the degree of whiteness of an object's surface, expressed as a percentage of white content. Factors affecting lithium sulfide's whiteness primarily include impurities, particle size, and particle size distribution. Higher purity and smaller particle size increase the whiteness of the lithium sulfide. Therefore, improving the product's whiteness further improves the purity and particle size of the lithium sulfide. Purity and particle size are important indicators for lithium sulfide applications in downstream sulfide solid electrolytes.

[0006] Summary of the Invention

[0007] The purpose of the present invention is to provide a new method for preparing EV-grade high-purity lithium sulfide.

[0008] To achieve the first object of the present invention, the method for preparing EV-grade high-purity lithium sulfide comprises:

[0009] A. Mixing the lithium source and the sulfur source and grinding them uniformly to obtain a mixture;

[0010] B. Primary reaction: mixing the mixture with hydrazine hydrate under an inert atmosphere and reacting to obtain an intermediate slurry;

[0011] C. Secondary reaction: subjecting the intermediate slurry to a secondary reaction under an inert atmosphere and drying to obtain crude lithium sulfide;

[0012] D. calcining and ball-milling the crude lithium sulfide to obtain EV-grade high-purity lithium sulfide.

[0013] The inert atmosphere described in the present invention refers to a gas atmosphere that does not react with the reaction system.

[0014] In a specific embodiment, the lithium source in step A is at least one of lithium hydroxide monohydrate, lithium sulfite or lithium thiosulfate, and the sulfur source is at least one of sulfur powder, lithium sulfite or lithium thiosulfate.

[0015] In a specific embodiment, the lithium source and the sulfur source are added in step A at a molar ratio of Li2O:S=1:1-2.

[0016] In a specific embodiment, the amount of hydrazine hydrate added in step B is Li2O:N2H2·H2O molar ratio = 1:2-4; preferably, the hydrazine hydrate is added in three batches, with an interval of 0.5-1h between each addition.

[0017] In a specific embodiment, the mixing and reacting in step B includes stirring at 30-70° C. for 1-5 hours; the stirring speed is preferably 100-200 r / min.

[0018] In a specific embodiment, step C adopts staged heating, with the first stage at 100-150° C. for 2-4 hours, and the second stage at 200-400° C. for 4-6 hours.

[0019] In a specific embodiment, the calcination temperature in step D is 450-600° C., and the calcination time is 2-6 hours.

[0020] In one embodiment, the calcination in step D is carried out by microwave calcination;

[0021] The frequency of microwaves generated during the microwave calcination is preferably 2.45 GHz.

[0022] In a specific embodiment, the ball milling in step D is to ball mill the calcined lithium sulfide at a rotation speed of 100 to 500 r / min for 5 to 10 hours.

[0023] In a specific embodiment, the inert gas in step B and step C is argon or nitrogen; the calcination in step D is carried out under a nitrogen protective atmosphere, and the ball milling is carried out under closed conditions under inert atmosphere protection.

[0024] A second object of the present invention is to provide an EV-grade high-purity lithium sulfide.

[0025] To achieve the second purpose of the present invention, the EV-grade high-purity lithium sulfide is prepared using the above-mentioned method for preparing EV-grade high-purity lithium sulfide. The purity of the EV-grade high-purity lithium sulfide is above 99.9%, the whiteness is above 80, and D50≤15μm.

[0026] In a specific embodiment, the EV-grade high-purity lithium sulfide has a purity of 99.95% or higher and a whiteness of 82.5 or higher. Beneficial effects:

[0027] The present invention provides a method for preparing EV-grade high-purity lithium sulfide. The method comprises the following steps: grinding and mixing lithium hydroxide monohydrate and sulfur powder to ensure uniform mixing and contact of the raw materials; performing an oxidation-reduction reaction in the presence of a reducing agent, hydrazine hydrate, to obtain a lithium sulfide intermediate slurry; performing a secondary reaction and drying by heating to obtain a crude lithium sulfide product; and then calcining and ball milling to improve the whiteness of the product, to finally obtain an EV-grade lithium sulfide product having a main content of more than 99.9%, a whiteness (blue light whiteness) of more than 80, and D50 ≤ 15 μm.

[0028] The lithium sulfide prepared by this method has simple process operation, high safety, low energy consumption, low equipment requirements, low production cost, and is suitable for industrial production. DETAILED DESCRIPTION

[0029] To achieve the first object of the present invention, the method for preparing EV-grade high-purity lithium sulfide comprises:

[0030] The preparation method of EV-grade high-purity lithium sulfide includes:

[0031] A. Mixing the lithium source and the sulfur source and grinding them uniformly to obtain a mixture;

[0032] B. Primary reaction: mixing the mixture with hydrazine hydrate under an inert atmosphere and reacting to obtain an intermediate slurry;

[0033] C. Secondary reaction: subjecting the intermediate slurry to a secondary reaction and drying under an inert atmosphere to obtain crude lithium sulfide;

[0034] D. calcining and ball-milling the crude lithium sulfide to obtain EV-grade high-purity lithium sulfide.

[0035] The reaction principle in step B and step C is:

[0036] 4LiOH·H2O+2S+N2H4·H2O=2Li2S+N2+9H2O.

[0037] Step B is a single reaction. The mixed raw materials are transferred to a reaction device protected by inert gas, and then hydrazine hydrate is added and stirred to obtain a lithium sulfide intermediate slurry. The initial reaction is accompanied by the generation of a large number of bubbles. The addition rate of hydrazine hydrate is related to the amount of reactants. If the amount of reactants is large and hydrazine hydrate is added too quickly, a violent reaction will generate a large number of bubbles, causing the reaction materials to overflow. Hydrazine hydrate needs to be added in batches. The addition rate is mainly controlled according to the reaction degree of the reactants. Preferably, hydrazine hydrate is added in three batches, with an interval of 0.5 to 1 hour between each addition.

[0038] In a specific embodiment, the lithium source in step A is at least one of lithium hydroxide monohydrate, lithium sulfite or lithium thiosulfate, and the sulfur source is at least one of sulfur powder, lithium sulfite or lithium thiosulfate.

[0039] In a specific embodiment, the lithium source in step A is lithium hydroxide monohydrate, and the sulfur source is sulfur powder.

[0040] Lithium hydroxide monohydrate and sulfur powder are ground and mixed to ensure uniform mixing and contact of the raw materials. In the presence of the reducing agent hydrazine hydrate, an oxidation-reduction reaction occurs to obtain a lithium sulfide intermediate slurry. A secondary reaction and drying are carried out by heating to obtain a crude lithium sulfide product, which is then calcined and ball-milled to improve the whiteness of the product, ultimately obtaining a lithium sulfide product.

[0041] In a specific embodiment, the lithium source and the sulfur source are added in step A at a molar ratio of Li2O:S=1:1-2.

[0042] The molar ratio of the present invention is the ratio of the amount of substances. Lithium is calculated as Li2O, which is the sum of the molar amounts of Li2O in all raw materials, and S is the sum of the molar amounts of sulfur in all raw materials.

[0043] In a specific embodiment, the amount of hydrazine hydrate added in step B is Li2O:N2H2·H2O molar ratio = 1:2-4; preferably, the hydrazine hydrate is added in three batches, with an interval of 0.5-1h between each addition.

[0044] In a specific embodiment, the mixing and reacting in step B includes stirring at 30-70° C. for 1-5 hours; the stirring speed is preferably 100-200 r / min.

[0045] In a specific embodiment, step C adopts staged heating, with the first stage at 100-150° C. for 2-4 hours, and the second stage at 200-400° C. for 4-6 hours.

[0046] Step C involves a secondary reaction and drying process, wherein the lithium sulfide intermediate slurry is transferred to a reaction vessel protected by an inert gas atmosphere and heated for further reaction and drying. The heating is performed in stages to obtain a crude lithium sulfide product. The staged heating process is employed to prevent excessively high heating temperatures, which could lead to bumping during liquid evaporation and slurry overflow, and excessively low temperatures, which could result in incomplete reaction and reduced product quality.

[0047] In a specific embodiment, the calcination temperature in step D is 450-600° C., and the calcination time is 2-6 hours.

[0048] In one embodiment, the calcination in step D is carried out by microwave calcination;

[0049] The frequency of microwaves generated during the microwave calcination is preferably 2.45 GHz.

[0050] Microwave calcination, based on the penetrating properties of microwaves and the targeted absorption effect of high-dielectric-loss dielectrics, causes polar molecules to orient and align in the electromagnetic field. This high-speed orientation intensifies molecular motion and collisions, leading to an increase in system temperature. Heating impurities in crude lithium sulfide, such as sulfur, polysulfides, and residual hydrazine hydrate, rapidly reaches their boiling point, thereby removing impurities and enhancing whiteness. Furthermore, the high-frequency directional rotation of polar molecules under microwaves increases effective collisions between molecules, dispersing impurities such as sulfur encapsulated within the lithium sulfide molecules. Compared to traditional calcination methods, microwave calcination offers milder conditions, faster and more uniform heating, higher efficiency, and easier control.

[0051] In a specific embodiment, the ball milling in step D is to ball mill the calcined lithium sulfide at a rotation speed of 100 to 500 r / min for 5 to 10 hours.

[0052] In a specific embodiment, the inert gas in step B and step C is argon or nitrogen; the calcination in step D is carried out under a nitrogen protective atmosphere, and the ball milling is carried out under closed conditions under inert atmosphere protection.

[0053] To achieve the second purpose of the present invention, the EV-grade high-purity lithium sulfide is prepared using the above-mentioned method for preparing EV-grade high-purity lithium sulfide. The purity of the EV-grade high-purity lithium sulfide is above 99.9%, the whiteness is above 80, and D50≤15μm.

[0054] In a specific embodiment, the purity of the EV-grade high-purity lithium sulfide is above 99.95%, and the whiteness is above 82.5.

[0055] The specific embodiments of the present invention are further described below in conjunction with examples, but the present invention is not limited to the scope of the examples.

[0056] Example 1

[0057] Lithium hydroxide monohydrate, sulfur powder, and hydrazine hydrate were prepared in a molar ratio of Li₂O:S:N₂H₄·H₂O = 1:1:3 and mixed in a grinder. The ground materials were placed in an argon-protected reactor, and hydrazine hydrate was added in batches. The mixture was reacted at a stirring speed of 100 rpm and a temperature of 30°C for 1 hour. The lithium sulfide intermediate slurry was transferred to an argon-protected reactor. The reaction was initially carried out at 100°C for 2 hours, followed by drying at 300°C for 4 hours to obtain crude lithium sulfide. The crude lithium sulfide was then transferred to a microwave calciner and calcined at 450°C for 2 hours under a nitrogen atmosphere to obtain high-whiteness lithium sulfide. The calcined lithium sulfide was placed in a sealed ball mill and ball-milled at 100 rpm for 5 hours at room temperature to obtain the lithium sulfide product, Li₂S-1. The purity, whiteness, and particle size of the resulting product are shown in Table 1.

[0058] Example 2

[0059] Lithium hydroxide monohydrate, sulfur powder, and hydrazine hydrate were prepared in a molar ratio of Li2O:S:N2H4·H2O = 1:2:3.5 and mixed in a grinder. The ground materials were placed in an argon-protected reactor, and hydrazine hydrate was added in batches. The mixture was reacted at a stirring speed of 150 r / min and a temperature of 30°C for 3 hours. The lithium sulfide intermediate slurry was transferred to an argon-protected reactor. The reaction was initially carried out at 120°C for 3 hours, followed by drying at 350°C for 5 hours to obtain crude lithium sulfide. The crude lithium sulfide was then transferred to a microwave calciner and calcined at 500°C for 4 hours under a nitrogen atmosphere to obtain high-whiteness lithium sulfide. The calcined lithium sulfide was placed in a sealed ball mill and ball-milled at 300 r / min at room temperature for 8 hours to obtain the lithium sulfide product, Li2S-2. The purity, whiteness, particle size and other parameters of the obtained product are shown in Table 1.

[0060] Example 3

[0061] Lithium hydroxide monohydrate, sulfur powder, and hydrazine hydrate were prepared in a molar ratio of Li2O:S:N2H4·H2O = 1:2:4 and mixed and ground in a grinder. The ground materials were placed in an argon-protected reactor, and hydrazine hydrate was added in batches. The mixture was reacted at a stirring speed of 200 r / min and a temperature of 30°C for 5 hours. The lithium sulfide intermediate slurry was transferred to an argon-protected reactor. The reaction was initially carried out at 150°C for 4 hours, followed by drying at 400°C for 6 hours to obtain a crude lithium sulfide product. The crude lithium sulfide product was then transferred to a microwave calciner and calcined at 600°C for 6 hours under a nitrogen atmosphere to obtain high-whiteness lithium sulfide. The calcined lithium sulfide was placed in a sealed ball mill and ball-milled at 500 r / min at room temperature for 10 hours to obtain the lithium sulfide product, Li2S-3. The purity, whiteness, particle size and other parameters of the obtained product are shown in Table 1.

[0062] Comparative Example 1

[0063] This comparative example provides a method for preparing lithium sulfide. The method is similar to that of Example 3, differing only in that the lithium sulfide product is obtained directly after Step C, without subsequent calcination and ball milling steps. The lithium sulfide obtained in this comparative example has low purity and whiteness due to the presence of small amounts of impurities such as sulfur powder, polysulfides, and hydrazine hydrate remaining in the dried product. Parameters such as the purity, whiteness, and particle size of the resulting product are shown in Table 1.

[0064] Table 1 Purity, whiteness and particle size of products in Examples and Comparative Examples

Claims

1. A method for preparing EV-grade high-purity lithium sulfide, characterized in that: The method comprises: A. Mixing and grinding the lithium source and the sulfur source to obtain a mixture; B. Primary reaction: mixing the mixture with hydrazine hydrate under an inert atmosphere and reacting to obtain an intermediate slurry; C. Secondary reaction: The intermediate slurry is subjected to secondary reaction under an inert atmosphere and dried to obtain a crude lithium sulfide product. Step C adopts staged heating, with the first stage at 100-150° C. for 2-4 hours and the second stage at 200-400° C. for 4-6 hours; D. Calcine and ball-mill the crude lithium sulfide to obtain EV-grade high-purity lithium sulfide. The calcination method in step D is microwave calcination. The calcination temperature in step D is 450-600° C. and the calcination time is 2-6 hours.

2. The method for preparing EV-grade high-purity lithium sulfide according to claim 1, characterized in that: In step A, the lithium source is at least one of lithium hydroxide monohydrate, lithium sulfite or lithium thiosulfate, and the sulfur source is at least one of sulfur powder, lithium sulfite or lithium thiosulfate.

3. The method for preparing EV-grade high-purity lithium sulfide according to claim 1 or 2, characterized in that: The lithium source and the sulfur source in step A are added at a molar ratio of Li2O:S=1:1-2.

4. The method for preparing EV-grade high-purity lithium sulfide according to claim 1 or 2, characterized in that: The amount of hydrazine hydrate added in step B is according to the molar ratio of Li2O:N2H2·H2O=1:2-4.

5. The method for preparing EV-grade high-purity lithium sulfide according to claim 1 or 2, characterized in that: The hydrazine hydrate is added in three batches, with an interval of 0.5 to 1 hour between each addition.

6. The method for preparing EV-grade high-purity lithium sulfide according to claim 1 or 2, characterized in that: The mixing and reaction in step B includes stirring at 30-70° C. for 1-5 hours.

7. The method for preparing EV-grade high-purity lithium sulfide according to claim 6, characterized in that: The stirring speed is 100-200 r / min.

8. The method for preparing EV-grade high-purity lithium sulfide according to claim 1, characterized in that: The frequency of microwaves generated during the microwave calcination is 2.45 GHz.

9. The method for preparing EV-grade high-purity lithium sulfide according to claim 1 or 2, characterized in that: The ball milling in step D is to ball mill the calcined lithium sulfide at a rotation speed of 100 to 500 r / min for 5 to 10 hours.

10. The method for preparing EV-grade high-purity lithium sulfide according to claim 1 or 2, characterized in that: The inert gas in step B and step C is argon or nitrogen; the calcination in step D is carried out under a nitrogen protective atmosphere, and the ball milling is carried out under a closed condition under inert atmosphere protection. 11.EV grade high purity lithium sulfide, characterized in that: The EV-grade high-purity lithium sulfide is prepared by the preparation method of the EV-grade high-purity lithium sulfide described in claim 9. The mass purity of the EV-grade high-purity lithium sulfide is above 99.9%, the whiteness is above 80, and D50≤15μm.

12. The EV-grade high-purity lithium sulfide according to claim 11, characterized in that: The mass purity of the EV-grade high-purity lithium sulfide is above 99.95%, and the whiteness is above 82.5.

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