Ev-grade high-purity lithium sulfide and preparation method for the same

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 its preparation method, which belongs to the technical field of lithium ion battery materials. [Background technology]

[0002] In recent years, with the rapid development of EV vehicles, the problems of traditional 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 and are the batteries with the highest potential for practical application because of their characteristics of high energy density, wide operating temperature range, high safety, and long cycle life. 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-to-process properties, 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 limitations in its production and storage, which results in difficult industrial production and very expensive, limiting the development of sulfide all-solid-state batteries.

[0003] In Patent Document 1, lithium hydroxide monohydrate is used as a lithium source, sulfur powder as a sulfur source, and hydrazine hydrate as a reducing agent to synthesize and prepare a lithium sulfide intermediate, and the obtained intermediate product is further dehydrated and dried to obtain high-purity lithium sulfide. The process is simple, has high operability, low energy consumption, is not strict on the equipment due to the raw materials, is stable in mass production, does not generate toxic gas, and does not cause secondary pollution, so that it can meet the requirements of safe operation and practical use of lithium sulfide. However, the purity of the dried lithium sulfide is low, and can only reach a maximum of 97.88%. It also has a low whiteness. Whiteness represents the degree of whiteness of the surface of an object and is expressed as the whiteness content. Factors that affect the whiteness of lithium sulfide include mainly impurities, particle size, particle size distribution, etc., and the higher the purity, the smaller the particle size, and the higher the whiteness of lithium sulfide. Therefore, in order to improve its whiteness, the requirements for the purity and particle size of lithium sulfide become stricter. On the other hand, purity and particle size are important indicators of the lithium sulfide used in downstream sulfide solid electrolytes. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] China Patent Application Publication No. 112678781 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention aims to provide a new method for preparing EV grade high purity lithium sulfide. [Means for solving the problem]

[0006] In order to achieve the first object of the present invention, the above-mentioned method for preparing EV grade high purity lithium sulfide includes: A. The lithium source and the sulfur source are uniformly mixed and crushed to obtain a mixed material; B. Primary reaction: The mixed material is mixed with hydrazine hydrate under an inert atmosphere and reacted to obtain an intermediate slurry; C. Secondary reaction: The intermediate slurry is subjected to a secondary reaction and dried under an inert atmosphere to obtain a crude product of lithium sulfide. D. The crude lithium sulfide is calcined and ball milled to obtain EV grade high purity lithium sulfide. In the present invention, the inert atmosphere refers to a gas atmosphere that does not react with the reaction system.

[0007] In one 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.

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

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

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

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

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

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

[0014] In one 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.

[0015] In one embodiment, the inert gas in steps B and C is argon or nitrogen, the calcination in step D is carried out under a nitrogen protective atmosphere, and said ball milling is carried out under sealed conditions protected by an inert atmosphere.

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

[0017] In order to achieve the second object of the present invention, the EV grade high purity lithium sulfide is prepared by the above-mentioned 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.

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

[0019] The present invention provides a method for preparing EV grade high purity lithium sulfide, which is prepared by grinding and mixing lithium hydroxide monohydrate and sulfur powder to ensure uniform mixing and contact of the raw materials, and then an oxidation-reduction reaction occurs in the presence of the reducing agent hydrazine hydrate to obtain an intermediate slurry of lithium sulfide, which is then heated for a secondary reaction and dried to obtain a crude product of lithium sulfide, which is then calcined and ball milled to improve the whiteness of the product, and finally the main component content is 99.9% or more, the whiteness (blue light whiteness) is 80 or more, and the D 50 Obtain EV grade lithium sulfide ≦15μm.

[0020] The lithium sulfide prepared by this method is suitable for industrial production due to its simple process, high safety, low energy consumption, low requirements on equipment, and low production cost. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] In order to achieve the first object of the present invention, the method for preparing EV grade high purity lithium sulfide includes: The preparation method of EV grade high purity lithium sulfide is as follows: A. The lithium source and the sulfur source are uniformly mixed and crushed to obtain a mixed material; B. Primary reaction: The mixed material is mixed with hydrazine hydrate under an inert atmosphere and reacted to obtain an intermediate slurry; C. Secondary reaction: The intermediate slurry is subjected to a secondary reaction and dried under an inert atmosphere to obtain a crude product of lithium sulfide. D. The crude lithium sulfide product is calcined and ball milled to obtain EV grade high purity lithium sulfide.

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

[0023] Step B is the primary reaction in which the mixed raw materials are transferred to a reactor protected by inert gas, hydrazine hydrate is added and stirred to obtain an intermediate slurry of lithium sulfide. The reaction generates a large number of bubbles, and the addition speed of hydrazine hydrate varies depending on the amount of reactants. If the amount of reactants is large and hydrazine hydrate is added too quickly, 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 speed is mainly controlled according to the reactivity of the reactants, but 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 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.

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

[0026] Lithium hydroxide monohydrate and sulfur powder are ground and mixed to ensure uniform mixing and contact of the raw materials, and an oxidation-reduction reaction occurs in the presence of hydrazine hydrate as a reducing agent to obtain an intermediate slurry of lithium sulfide, which is then heated for a secondary reaction and dried to obtain a crude lithium sulfide product, which is then calcined and ball milled 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 step A are added in a molar ratio of Li2O:S of 1:1-2.

[0028] In the present invention, the molar ratio is a ratio of amounts of substances. Among them, lithium is calculated as Li2O, and is the total molar amount of Li2O in all raw materials, and S is the total molar amount of sulfur in all raw materials.

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

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

[0031] In one embodiment, procedure C employs a stepwise temperature increase, with a first stage at 100-150° C. for 2-4 h and a second stage at 200-400° C. for 4-6 h.

[0032] Step C is the secondary reaction and drying, in which the lithium sulfide intermediate slurry is transferred to a reaction vessel protected by inert gas, and further reacted and dried by stepwise heating to obtain a lithium sulfide crude product. The present invention adopts stepwise heating to prevent the heating temperature from being too high, which would cause bumping and overflowing of the slurry during the liquid evaporation process, or the temperature from being too low, which would cause insufficient reaction and poor product quality.

[0033] In one embodiment, the firing temperature in step D is 450 to 600° C., and the firing time is 2 to 6 hours.

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

[0035] Microwave calcination is based on the permeability of microwaves and the target absorption effect of high dielectric loss media, and microwaves cause polar molecules to rotate and orient with the electromagnetic field dipoles, and the rapid reorientation and orientation intensify the motion and collision of molecules, leading to the rise of the system temperature. For impurities in lithium sulfide crude products such as sulfur, polysulfides, and residual hydrazine hydrate, the boiling point of the impurities can be quickly reached by heating, realizing the effect of impurity removal and whitening. In addition, the high-frequency directional rotation of polar molecules under the action of microwaves can increase the effective collision between molecules, which can disperse the sulfur and other impurities wrapped inside the lithium sulfide molecules. Compared with traditional calcination methods, microwave calcination has milder conditions, faster and more uniform heating rate, higher efficiency, and easier control.

[0036] In one 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.

[0037] In one embodiment, the inert gas in steps B and C is argon or nitrogen, the calcination in step D is carried out under a nitrogen protective atmosphere, and said ball milling is carried out under sealed conditions protected by an inert atmosphere.

[0038] In order to achieve the second object of the present invention, the EV grade high purity lithium sulfide is prepared by the above-mentioned 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 greater and a whiteness index of 82.5 or greater.

[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> Lithium hydroxide monohydrate, sulfur powder, and hydrazine hydrate are taken so that the molar ratio is Li2O:S:N2H4·H2O=1:1:3. Lithium hydroxide monohydrate and sulfur powder are mixed and crushed in a crusher. The crushed raw materials are placed in a reactor protected by argon, and hydrazine hydrate is added in several batches. The stirring speed is 100 r / min and the temperature is 30°C for 1 h. The intermediate slurry of lithium sulfide is transferred to a reaction vessel protected by argon, and in the first stage, the reaction is carried out at 100°C for 2 h, and then the temperature is raised to 300°C and dried for 4 h to obtain lithium sulfide crude product. Next, the lithium sulfide crude product is transferred to a microwave calcination furnace and calcined at 450°C for 2 h under a nitrogen atmosphere to obtain lithium sulfide with high whiteness. The calcined lithium sulfide is placed in a sealed ball milling tank and ball milled at room temperature at a rotation speed of 100 r / min for 5 h to obtain the lithium sulfide product Li2S-1. The purity, whiteness, particle size, etc. of the obtained product are shown in Table 1.

[0042] <Example 2> Lithium hydroxide monohydrate, sulfur powder, and hydrazine hydrate are taken in a molar ratio of Li2O:S:N2H4·H2O=1:2:3.5, and lithium hydroxide monohydrate and sulfur powder are mixed and crushed in a crusher. The crushed raw materials are placed in a reactor protected by argon, and hydrazine hydrate is added in several batches, and the mixture is reacted at a stirring speed of 150 r / min and a temperature of 30°C for 3 hours. The intermediate slurry of lithium sulfide is transferred to a reaction vessel protected by argon, and in the first stage, the mixture is reacted at 120°C for 3 hours, and then the temperature is raised to 350°C and dried for 5 hours to obtain a crude lithium sulfide product. Next, the crude lithium sulfide product is transferred to a microwave calcination furnace and calcined at 500°C for 4 hours under a nitrogen atmosphere to obtain lithium sulfide with high whiteness. The calcined lithium sulfide is placed in a sealed ball milling tank and ball milled at room temperature at a rotation speed of 300 r / min for 8 hours to obtain the lithium sulfide product Li2S-2. The purity, whiteness, particle size, etc. of the obtained product are shown in Table 1.

[0043] <Example 3> Lithium hydroxide monohydrate, sulfur powder, and hydrazine hydrate are taken so that the molar ratio is Li2O:S:N2H4·H2O=1:2:4. Lithium hydroxide monohydrate and sulfur powder are mixed and crushed in a crusher. The crushed raw materials are placed in a reactor protected by argon, and hydrazine hydrate is added in several batches. The stirring speed is 200 r / min and the temperature is 30°C for 5 h. The intermediate slurry of lithium sulfide is transferred to a reaction vessel protected by argon, and in the first stage, the reaction is carried out at 150°C for 4 h, and then the temperature is raised and dried at 400°C for 6 h to obtain lithium sulfide crude product. Next, the lithium sulfide crude product is transferred to a microwave calcination furnace and calcined at 600°C for 6 h under a nitrogen atmosphere to obtain lithium sulfide with high whiteness. The calcined lithium sulfide is placed in a sealed ball milling tank and ball milled at room temperature for 10 hours at a rotation speed of 500 r / min to obtain the 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 very different from that of Example 3, with the only difference being that the lithium sulfide product is obtained immediately after procedure C, without subsequent calcination and ball milling. The lithium sulfide obtained in this comparative example has low purity and low whiteness, due to the presence of small amounts of impurities such as sulfur powder, polysulfides, and hydrazine hydrate remaining after drying. The purity, whiteness, particle size, etc. of the obtained product are shown in Table 1.

[0045] [Table 1]

[0046] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of and priority to Chinese patent application CN202311216612X, filed on September 20, 2023, which is incorporated in its entirety by reference and for all other purposes.

Claims

1. A. A lithium source and a sulfur source are uniformly mixed and pulverized to obtain a mixed material; B. Primary reaction: Step B, mixing and reacting the mixed materials with hydrazine hydrate under an inert atmosphere to obtain an intermediate slurry; C. Secondary reaction: the intermediate slurry is subjected to secondary reaction and drying under an inert atmosphere to obtain a crude product of lithium sulfide, and a stepwise temperature increase is adopted, the first step is handled at 100-150°C for 2-4h, and the second step is handled at 200-400°C for 4-6h; D. A method for preparing EV grade high purity lithium sulfide, comprising calcining a crude product of lithium sulfide and ball milling it to obtain EV grade high purity lithium sulfide, the calcination being microwave calcination, the calcination temperature being 450 to 600°C, and the calcination time being 2 to 6 hours.

2. 2. The method for preparing EV grade high purity lithium sulfide according to claim 1, wherein 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.

3. The lithium and sulfur sources in procedure A are Li ２ The method for preparing EV grade high purity lithium sulfide according to claim 1 or 2, characterized in that O:S is added in a molar ratio of 1:1 to 2.

4. The hydrazine hydrate in step B is Li ２ O:N ２ H ２ ・H ２ The method for preparing EV grade high purity lithium sulfide according to claim 1 or 2, characterized in that O is added in a molar ratio of 1:2 to 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 portions at intervals of 0.5 to 1 h.

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 to 70 ° C. for 1 to 5 h.

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

8. 2. The method for preparing EV grade high purity lithium sulfide according to claim 1, wherein the frequency of the microwave generated by the microwave firing 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 ball milling the calcined lithium sulfide at a rotation speed of 100 to 500 r / min for 5 to 10 hours.

10. 3. The method for preparing EV grade high purity lithium sulfide according to claim 1 or 2, characterized in that the inert gas in steps B and 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 sealed condition protected by an inert atmosphere.

11. The EV grade high purity lithium sulfide is prepared by the method for preparing EV grade high purity lithium sulfide according to claim 9, and the EV grade high purity lithium sulfide has a purity of 99.9% or more, a whiteness of 80 or more, and a D ５０ EV grade high purity lithium sulfide having a particle size of ≦15 μm.

12. The EV grade high purity lithium sulfide according to claim 11, characterized in that the EV grade high purity lithium sulfide has a purity of 99.95% or more and a whiteness of 82.5 or more.

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