Preparation method for EV-grade high-purity lithium sulfide

Abstract

To provide a preparation method for EV-grade high-purity lithium sulfide characterized by simple process operation, high safety, low energy consumption, low equipment requirements, and low production cost, and therefore, is suitable for industrial production, and provide the EV-grade high-purity lithium sulfide.SOLUTION: A preparation method for EV-grade high-purity lithium sulfide includes: 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: performing secondary reaction on the intermediate slurry in the inert atmosphere and drying to obtain a crude lithium sulfide product; and D. calcining and ball milling the crude lithium sulfide product to obtain the EV-grade high-purity lithium sulfide. The purity of the EV-grade high-purity lithium sulfide prepared by the method according to the present invention is above 99.9%, the whiteness thereof is above 80, and D50≤15 μm.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to EV-grade high-purity lithium sulfide and a method for preparing the same, and belongs to the technical field of lithium-ion battery materials.

Background Art

[0002] In recent years, with the rapid development of EV vehicles, problems of conventional liquid lithium-ion batteries, such as short driving range, long charging time, and low safety, have gradually become apparent, hindering the further development of the EV vehicle market. High-energy density batteries such as lithium-sulfur batteries, lithium-oxygen batteries, and all-solid-state batteries are expected to solve the technical problems related to EV vehicle batteries. Among them, all-solid-state batteries have attracted attention from the market because they have characteristics such as high energy density, wide operating temperature range, high safety, and long cycle life, and are the most promising battery with the highest possibility of practical application. Sulfide solid electrolytes have become the most promising technical means as the main components of all-solid-state batteries due to their high ionic conductivity, easy processing characteristics, and good electrochemical stability. Lithium sulfide (Li2S) is an important precursor material for synthesizing sulfide solid electrolytes, but it is very sensitive to water and air, so there are many restrictions on manufacturing and storage. As a result, industrial production is difficult and very expensive, limiting the development of sulfide all-solid-state batteries.

[0003] In Patent Document 1, lithium hydroxide monohydrate is used as the lithium source, sulfur powder as the sulfur source, and hydrazine hydrate as the reducing agent to synthesize and prepare a lithium sulfide intermediate. The obtained intermediate product is further dehydrated and dried to obtain high-purity lithium sulfide. The process is simple, highly operable, has low energy consumption, does not have strict requirements for the equipment due to the raw materials, has stable mass production, does not generate toxic gases, and has no secondary pollution, so it can meet the requirements such as safe operation and practical application of lithium sulfide. However, the purity of the dried lithium sulfide is low and can only reach 97.88% at most. Also, the whiteness is low. Whiteness represents the degree of whiteness of the surface of an object and is expressed as the content rate of whiteness. The main factors affecting the whiteness of lithium sulfide include mainly impurities, particle size, particle size distribution, etc. The smaller the particle size as the purity increases, the higher the whiteness of lithium sulfide. Therefore, to improve its whiteness, the requirements for the purity and particle size of lithium sulfide become strict. On the other hand, purity and particle size are important indicators of lithium sulfide used in the downstream sulfide solid electrolyte.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a new method for preparing EV-grade high-purity lithium sulfide.

Means for Solving the Problems

[0006] To achieve the first object of the present invention, the above-mentioned method for preparing EV-grade high-purity lithium sulfide is as follows: A. Uniformly mix and pulverize a lithium source and a sulfur source to obtain a mixed material, B. Primary reaction: Mix the mixed material with hydrazine hydrate in an inert atmosphere and react to obtain an intermediate slurry. C. Secondary reaction: Subject the intermediate slurry to a secondary reaction and drying in an inert atmosphere to obtain a crude product of lithium sulfide. D. The procedure includes firing and ball milling the crude product of lithium sulfide to obtain EV-grade high-purity lithium sulfide. The inert atmosphere in the present invention refers to a gas atmosphere that does not react with the reaction system.

[0007] In one embodiment, the lithium source in procedure 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.

[0008] In one embodiment, the lithium source and the sulfur source in procedure A are added in a molar ratio of Li2O:S of 1:1 to 2.

[0009] In one embodiment, the hydrazine hydrate in procedure B is added in a molar ratio of Li2O:N2H2·H2O of 1:2 to 4, and preferably, the hydrazine hydrate is added in three portions at intervals of 0.5 to 1 h.

[0010] In one embodiment, the mixing and reaction in procedure B include stirring at 30 to 70°C for 1 to 5 h, and preferably, the rotation speed of the stirring is 100 to 200 r / min.

[0011] In one embodiment, procedure C employs a stepwise temperature increase, handling at 100 to 150°C for 2 to 4 h in the first stage and at 200 to 400°C for 4 to 6 h in the second stage.

[0012] In one embodiment, the firing temperature in procedure D is 450 to 600°C, and the firing time is 2 to 6 h.

[0013] In one embodiment, the firing method in procedure D is microwave firing. Preferably, the frequency of the microwave generated by the microwave firing is 2.45 GHz.

[0014] In one embodiment, the ball milling in procedure D is to ball mill the fired lithium sulfide at a rotation speed of 100 to 500 r / min for 5 to 10 h.

[0015] In one embodiment, the inert gas in procedures B and C is argon or nitrogen, the firing in procedure D is carried out under a nitrogen protection atmosphere, and the ball milling is carried out under sealed conditions protected by an inert atmosphere.

[0016] The second object of the present invention is to provide EV-grade high-purity lithium sulfide.

[0017] To achieve the second object of the present invention, the EV-grade high-purity lithium sulfide is prepared by the above-described method for preparing EV-grade high-purity lithium sulfide, and the purity of the EV-grade high-purity lithium sulfide is 99.9% or more, the whiteness is 80 or more, D 50 ≦15 μm.

[0018] In one embodiment, the EV-grade high-purity lithium sulfide has a purity of 99.95% or more and a whiteness of 82.5 or more.

Advantages of the Invention

[0019] The present invention provides a method for preparing EV-grade high-purity lithium sulfide, in which lithium hydroxide monohydrate and sulfur powder are pulverized and mixed to ensure uniform mixing and contact of the raw materials, and a redox reaction occurs in the presence of hydrazine hydrate as a reducing agent to obtain an intermediate slurry of lithium sulfide, and then a secondary reaction and drying are carried out by heating to obtain a crude product of lithium sulfide. Next, firing and ball milling are carried out to improve the whiteness of the product, and finally, an EV-grade lithium sulfide with a main component content of 99.9% or more, a whiteness (blue light whiteness) of 80 or more, and D 50 ≦15 μm is obtained. 。

[0020] The lithium sulfide prepared by this method is suitable for industrial production because the process is simple, safe, consumes less energy, has less stringent requirements for equipment, and has low production costs.

Embodiments for Carrying Out the Invention

[0021] To achieve the first object of the present invention, a method for preparing EV-grade high-purity lithium sulfide is A method for preparing EV-grade high-purity lithium sulfide is A. Uniformly mix a lithium source and a sulfur source, pulverize them to obtain a mixed material, B. Primary reaction: Mix the mixed material with hydrazine hydrate in an inert atmosphere and react to obtain an intermediate slurry, C. Secondary reaction: Perform a secondary reaction and drying on the intermediate slurry in an inert atmosphere to obtain a crude product of lithium sulfide, D. The procedure includes firing and ball milling the crude product of lithium sulfide to obtain EV-grade high-purity lithium sulfide.

[0022] The reaction principles of procedures B and C are as follows. 4LiOH·H2O + 2S + N2H4·H2O = 2Li2S + N2 + 9H2O

[0023] Procedure B is a primary reaction in which the mixed raw materials are transferred to a reaction device protected by an inert gas, hydrazine hydrate is added and stirred to obtain an intermediate slurry of lithium sulfide. A large number of bubbles are generated during the reaction, and the addition rate of hydrazine hydrate varies depending on the amount of reactants. If the amount of reactants is large and the addition of hydrazine hydrate is too fast, a large amount of bubbles will be generated due to the violent reaction, and the reactants will overflow. Therefore, it is necessary to add hydrazine hydrate in several portions, and the addition rate is mainly controlled according to the reactivity of the reactants. However, it is preferable to add hydrazine hydrate in three portions at intervals of 0.5 to 1 h.

[0024] In one embodiment, the lithium source in procedure 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.

[0025] In one embodiment, the lithium source in procedure A is lithium hydroxide monohydrate, and the sulfur source is sulfur powder.

[0026] Lithium hydroxide monohydrate and sulfur powder are pulverized and mixed to ensure uniform mixing and contact of the raw materials. An oxidation-reduction reaction occurs in the presence of hydrazine hydrate as a reducing agent to obtain an intermediate slurry of lithium sulfide. Secondary reaction and drying are carried out by heating to obtain a crude product of lithium sulfide. Next, calcination and ball milling are carried out to improve the whiteness of the product, and finally lithium sulfide is obtained.

[0027] In one embodiment, the lithium source and the sulfur source in procedure A are added in a molar ratio of Li2O:S of 1:1 to 2.

[0028] Note that the molar ratio in the present invention is the ratio of the amount of substance. Among them, lithium is calculated as Li2O, which is the total molar amount of Li2O in all raw materials, and S is also the total molar amount of sulfur in all raw materials.

[0029] In one embodiment, the hydrazine hydrate in procedure B is added in a molar ratio of Li2O:N2H2·H2O of 1:2 to 4, and preferably, the hydrazine hydrate is added in three portions at intervals of 0.5 to 1 h.

[0030] In one embodiment, the mixing and reaction in procedure B include stirring at 30 to 70 °C for 1 to 5 h, and preferably, the stirring speed is 100 to 200 r / min.

[0031] In one embodiment, procedure C employs a stepwise temperature increase, handling at 100 to 150 °C for 2 to 4 h in the first step and at 200 to 400 °C for 4 to 6 h in the second step.

[0032] Procedure C is secondary reaction and drying. The intermediate slurry of lithium sulfide is transferred to a reaction vessel protected by an inert gas, and further reaction and drying are carried out by stepwise heating to obtain a crude lithium sulfide product. In the present invention, stepwise heating is adopted to prevent the heating temperature from being too high, which may cause bumping or overflow of the slurry during the liquid evaporation process, or the temperature from being too low, resulting in insufficient reaction and deterioration of the product quality.

[0033] In one embodiment, the firing temperature in Procedure D is 450 - 600 °C, and the firing time is 2 - 6 h.

[0034] In one embodiment, the firing method in Procedure D is microwave firing. Preferably, the frequency of the microwave generated by the microwave firing is 2.45 GHz.

[0035] Microwave firing is based on the microwave permeability and the target absorption effect of the high-dielectric-loss medium. Microwaves cause polar molecules to rotate and orient as electromagnetic field dipoles, and the rapid direction change and orientation of the molecules intensify the molecular motion and collision, leading to an increase in the system temperature. Regarding the impurities in the crude lithium sulfide product such as sulfur, polysulfides, and residual hydrazine hydrate, heating can quickly reach the boiling point of the impurities, achieving the effect of impurity removal and whitening. Also, under the action of microwaves, the high-frequency directional rotation of polar molecules increases the effective collision between molecules, and sulfur and other impurities encapsulated inside the lithium sulfide molecules can be dispersed. Compared with the conventional firing method, microwave firing has mild conditions, a fast and uniform heating rate, high efficiency, and easy control.

[0036] In one embodiment, the ball milling in Procedure D is to ball mill the fired lithium sulfide at a rotation speed of 100 - 500 r / min for 5 - 10 h.

[0037] In one embodiment, the inert gas in procedures B and C is argon or nitrogen, the firing in procedure D is carried out under a nitrogen protection atmosphere, and the ball milling is carried out under sealed conditions protected by an inert atmosphere.

[0038] To achieve the second object of the present invention, the EV-grade high-purity lithium sulfide is prepared by the above-described method for preparing EV-grade high-purity lithium sulfide, and the purity of the EV-grade high-purity lithium sulfide is 99.9% or more, the whiteness is 80 or more, and D 50 ≦15 μm.

[0039] In one embodiment, the EV-grade high-purity lithium sulfide has a purity of 99.95% or more and a whiteness of 82.5 or more.

[0040] Hereinafter, specific embodiments of the present invention will be further described in conjunction with examples, but the present invention is not limited to the scope of the described examples.

Examples

[0041] <Example 1> Take lithium hydroxide monohydrate, sulfur powder, and hydrazine hydrate so that the molar ratio is Li2O:S:N2H4·H2O = 1:1:3. Put lithium hydroxide monohydrate and sulfur powder into a pulverizer, mix and pulverize them. Put the pulverized raw materials into a reaction apparatus protected by argon, add hydrazine hydrate in several portions, and react at a stirring rotation speed of 100 r / min and a temperature of 30 °C for 1 h. Transfer the intermediate slurry of lithium sulfide to a reaction vessel protected by argon, react at 100 °C for 2 h in the first stage, and then raise the temperature and dry at 300 °C for 4 h to obtain a crude lithium sulfide product. Next, transfer the crude lithium sulfide product to a microwave firing furnace and fire at 450 °C for 2 h under an atmosphere protected by nitrogen to obtain lithium sulfide with high whiteness. Put the fired lithium sulfide into a sealed ball milling tank and ball mill at a rotation speed of 100 r / min at room temperature for 5 h to obtain a lithium sulfide product Li2S-1. The purity, whiteness, particle size, etc. of the obtained product are shown in Table 1.

[0042] <Example 2> Take lithium hydroxide monohydrate, sulfur powder, and hydrazine hydrate so that the molar ratio is Li2O:S:N2H4·H2O = 1:2:3.5. Put lithium hydroxide monohydrate and sulfur powder into a pulverizer, mix and pulverize them. Put the pulverized raw materials into a reaction apparatus protected by argon, add hydrazine hydrate in several portions, and react at a stirring rotation speed of 150 r / min and a temperature of 30 °C for 3 h. Transfer the intermediate slurry of lithium sulfide to a reaction vessel protected by argon, react at 120 °C for 3 h in the first stage, then raise the temperature and dry at 350 °C for 5 h to obtain a crude lithium sulfide product. Next, transfer the crude lithium sulfide product to a microwave firing furnace and fire it at 500 °C for 4 h in an atmosphere protected by nitrogen to obtain lithium sulfide with high whiteness. Put the fired lithium sulfide into a sealed ball milling tank and ball mill it at a rotation speed of 300 r / min at room temperature for 8 h to obtain a lithium sulfide product Li2S-2. The purity, whiteness, particle size, etc. of the obtained product are shown in Table 1.

[0043] <Example 3> Take lithium hydroxide monohydrate, sulfur powder, and hydrazine hydrate so that the molar ratio is Li2O:S:N2H4·H2O = 1:2:4. Put lithium hydroxide monohydrate and sulfur powder into a pulverizer, mix and pulverize them. Put the pulverized raw materials into a reaction apparatus protected by argon, add hydrazine hydrate in several portions, and react at a stirring rotation speed of 200 r / min and a temperature of 30 °C for 5 h. Transfer the intermediate slurry of lithium sulfide to a reaction vessel protected by argon, react at 150 °C for 4 h in the first stage, then raise the temperature and dry at 400 °C for 6 h to obtain a crude lithium sulfide product. Next, transfer the crude lithium sulfide product to a microwave firing furnace and fire it at 600 °C for 6 h in an atmosphere protected by nitrogen to obtain lithium sulfide with high whiteness. Put the fired lithium sulfide into a sealed ball milling tank and ball mill it at a rotation speed of 500 r / min at room temperature for 10 h to obtain a lithium sulfide product Li2S-3. The purity, whiteness, particle size, etc. of the obtained product are shown in Table 1.

[0044] <Comparative Example 1> This comparative example provides a method for preparing lithium sulfide. This method is not significantly different from the method of Example 3, and the only difference is that the lithium sulfide product is obtained immediately after Procedure C without subsequent firing and ball milling. The lithium sulfide obtained in this comparative example has a low purity and a low whiteness because a small amount of impurities such as sulfur powder, polysulfide, and hydrazine hydrate remain after drying. Table 1 shows the purity, whiteness, particle size, etc. of the obtained product.

[0045]

Table 1

[0046] (Cross-reference to related applications) This application claims the rights and priority of Chinese Patent Application CN202311216612X filed on September 20, 2023, and is incorporated herein by reference in its entirety for all purposes.

Claims

1. A. Uniformly mix a lithium source and a sulfur source, and pulverize them to obtain a mixed material, B. Primary reaction: Step B of mixing the mixed material with hydrazine hydrate in an inert atmosphere and reacting to obtain an intermediate slurry, C. Secondary reaction: Perform a secondary reaction and drying on the intermediate slurry in an inert atmosphere to obtain a crude product of lithium sulfide, adopting a stepwise temperature increase, handling at 100 - 150 °C for 2 - 4 h in the first stage, and handling at 200 - 400 °C for 4 - 6 h in the second stage, Step C, D. Bake and ball-mill the crude product of lithium sulfide to obtain EV-grade high-purity lithium sulfide, wherein the baking is microwave baking, the baking temperature is 450 - 600 °C, and the baking time is 2 - 6 h, and a method for preparing EV-grade high-purity lithium sulfide, characterized by comprising Step D.

2. 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, the method for preparing EV-grade high-purity lithium sulfide according to Claim 1.

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

4. The hydrazine hydrate in Step B is added in a molar ratio of Li₂O:N₂H₂·H₂O of 1:2 - 4, the method for preparing EV-grade high-purity lithium sulfide according to Claim 1 or 2.

5. The hydrazine hydrate is added in three portions at intervals of 0.5 - 1 h, the method for preparing EV-grade high-purity lithium sulfide according to Claim 1 or 2.

6. The mixing and reaction in Step B include stirring at 30 - 70 °C for 1 - 5 h, the method for preparing EV-grade high-purity lithium sulfide according to Claim 1 or 2.

7. The rotation speed of the stirring is 100 - 200 r / min, the method for preparing EV-grade high-purity lithium sulfide according to Claim 6.

8. The frequency of the microwave generated by the microwave baking is 2.45 GHz, the method for preparing EV-grade high-purity lithium sulfide according to Claim 1.

9. The ball milling in procedure D is characterized in that the fired lithium sulfide is ball milled at a rotation speed of 100 to 500 r / min for 5 to 10 h, and it is the method for preparing EV-grade high-purity lithium sulfide according to claim 1 or 2.

10. The inert gas in procedures B and C is argon or nitrogen, the firing in procedure D is carried out under a nitrogen protection atmosphere, and the ball milling is carried out under sealed conditions protected by an inert atmosphere, and it is the method for preparing EV-grade high-purity lithium sulfide according to claim 1 or 2.

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