Lithium sulfide and a method of producing lithium sulfide

Abstract

The application belongs to the technical field of chemical materials, and specifically discloses a method for preparing lithium sulfide, which comprises the following steps: mixing and reacting lithium salt and ammonium sulfide to obtain lithium sulfide; wherein the lithium salt comprises at least one of lithium hexafluorophosphate, lithium difluorophosphate and lithium tetrafluoroborate. In the method for preparing lithium sulfide, the lithium salt and the ammonium sulfide can be fully reacted under mild conditions, the reaction time is short, the reaction yield is high, and the obtained lithium sulfide has high purity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of chemical materials, and particularly relates to lithium sulfide and a preparation method thereof. BACKGROUND

[0002] At present, the preparation conditions of lithium sulfide with less impurity content, high purity and high yield are harsh, which is not conducive to mass production. For example, in the related art, anhydrous sodium sulfide and lithium iodide are used as reactants, the reactants need to be pretreated for a long time first, then the pretreated sodium sulfide and lithium iodide are reacted at 120 DEG C for 12 hours according to a molar ratio of 0.4:2, then washed with an organic solvent, then the byproduct is separated out by using a tetrahydrofuran solution, and finally the lithium sulfide product is dried, etc. This method is time-consuming and laborious. For another example, in the related art, lithium hydride and elemental sulfur are mixed to obtain lithium sulfide by mechanical ball milling, the reaction is violent, the heat generated is difficult to control, and the lithium sulfide prepared has low purity. It can be seen that the preparation method in the related art is time-consuming and laborious, and the lithium sulfide obtained has low purity, which is not conducive to industrial mass production. It is of great significance to develop a mild preparation method of lithium sulfide suitable for mass production. SUMMARY

[0003] The present application aims to at least partly solve one of the technical problems in the related art. To this end, the present application provides a method for preparing lithium sulfide with mild reaction conditions, short reaction time, high reaction yield or high product purity, and lithium sulfide prepared by the method.

[0004] The first aspect of the present application provides a method for preparing lithium sulfide, comprising: mixing and reacting a lithium salt and ammonium sulfide to obtain lithium sulfide; wherein the lithium salt comprises at least one of lithium hexafluorophosphate, lithium difluorophosphate and lithium tetrafluoroborate.

[0005] The preparation method of the first aspect of the present application at least has the following beneficial effects: mild reaction conditions, short reaction time, high reaction yield (such as a yield of 98% or more) and high product purity.

[0006] In addition, the preparation method according to the above embodiments of the present application can also have the following additional technical features:

[0007] In some embodiments, the lithium salt and ammonium sulfide are reacted in an organic solvent, and the organic solvent comprises at least one of an ester solvent and an ether solvent. The reaction is carried out in an ether or ester organic solvent, on the one hand, the ether or ester solvent has good solubility for the lithium salt and ammonium sulfide, which helps the reactants to be fully dispersed in the reaction system, improves the reaction rate, and makes the reaction more complete, while the solvent consumption is less; on the other hand, the chemical stability of the ester and ether solvent is high, and it is not easy to have side reactions with the lithium salt and ammonium sulfide, thereby improving the purity of the product.

[0008] In some embodiments, the ester organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, ethyl acetate and methyl acetate; the ether solvent includes at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, methyl tert-butyl ether and diethyl ether. The above organic solvents have excellent dissolving performance, stable chemical properties, are less likely to cause side reactions with raw materials, and are relatively safe.

[0009] In some embodiments, the mass ratio of the lithium salt and the organic solvent is 1:3-1:20, specifically 1:4-1:8. In this way, the lithium salt is completely dissolved in the organic solvent, and the organic solvent is not wasted.

[0010] In some embodiments, the reaction of the lithium salt and the ammonium sulfide satisfies at least one of the following conditions:

[0011] The reaction temperature is 15°C-70°C, specifically 40°C-50°C;

[0012] The reaction time is 2h-6h, specifically 3h-4h;

[0013] The reaction atmosphere is an inert atmosphere.

[0014] In this way, the reaction can proceed smoothly, the reaction efficiency is improved, there are fewer side reactions, and time is not wasted.

[0015] In some embodiments, the molar ratio of the lithium salt and the ammonium sulfide is 2:1-2.1:1. In this way, the reaction can be more complete, and the reaction rate can be improved.

[0016] In some embodiments, after the mixing reaction of the lithium salt and the ammonium sulfide is completed, at least one of the following post-processing steps is further included:

[0017] After the mixing reaction of the lithium salt and the ammonium sulfide, a mixed solution containing lithium sulfide is obtained, the mixed solution is subjected to solid-liquid separation, and a lithium sulfide crude product is obtained;

[0018] The lithium sulfide crude product is dried at 50°C-120°C and -0.095Mpa for 1h-5h to obtain a dried lithium sulfide crude product;

[0019] The dried lithium sulfide crude product is calcined at 400°C-800°C and -0.095Mpa for 1h-5h.

[0020] After the above post-processing steps, the filtrate and impurities generated in the side reaction are removed, and the purity of the lithium sulfide is improved.

[0021] In some embodiments, the yield of the lithium sulfide is ≥98%. This facilitates industrial mass production.

[0022] The second aspect of the present application provides the lithium sulfide prepared by the method for preparing lithium sulfide described above. The lithium sulfide has high purity and few impurities, and can be used to prepare a sulfide electrolyte, thereby improving the ionic conductivity and interface stability of the electrolyte, and thus improving the electrochemical performance and safety performance of the battery.

[0023] In some embodiments, the lithium sulfide has a purity of ≥ 99.95%.

[0024] The present application has at least the following beneficial effects:

[0025] 1. In the present application, the lithium salt (at least one of lithium hexafluorophosphate, lithium difluorophosphate and lithium tetrafluoroborate) is reacted with ammonium sulfide in an ether or ester organic solvent to obtain lithium sulfide, which is a homogeneous reaction with mild reaction conditions and high conversion rate of lithium salt.

[0026] 2. The lithium salt used in the present application is one of the commonly used battery raw materials, and has high quality. The lithium sulfide product generated by the lithium salt has few impurities and high quality.

[0027] 3. In the present application, an ester or ether solvent is used as a solvent. The solubility of lithium salt in the ester or ether solvent is high, the solvent consumption is low, and the reaction efficiency is high. Compared with an alcohol solvent, the lithium salt will not decompose to produce a large amount of impurities, thereby resulting in low product yield and purity.

[0028] 4. In the method of the present application, the generated lithium sulfide is insoluble in the ester or ether solvent, and the lithium sulfide product can be obtained directly by filtration after the reaction is completed. The separation and purification are simple, and the product has high quality.

[0029] 5. The by-products of the present application are ammonium hexafluorophosphate, ammonium difluorophosphate and ammonium tetrafluoroborate, which can be recycled as an electrolyte or used as a raw material for synthesizing an electrolyte. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 FIG. 1 is an XRD spectrum of lithium sulfide prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0031] The embodiments of the present application are described in detail below, which are intended to explain the present application and cannot be understood as a limitation of the present application.

[0032] The present application is based on the following findings and recognitions of the inventor:

[0033] The inventors find that the current preparation conditions of lithium sulfide with low impurity content, high purity and high yield are harsh, which is not conducive to mass production. For example, in the related art, anhydrous sodium sulfide and lithium iodide are used as reactants, the reactants are pretreated for a long time, then the pretreated sodium sulfide and lithium iodide are reacted at a molar ratio of 0.4:2 at 120℃ for 12h, then washed with an organic solvent, then the byproduct is separated by a tetrahydrofuran solution, and finally the lithium sulfide product is dried, etc. This method is time-consuming and laborious. For another example, in the related art, lithium hydride and elemental sulfur are mixed and mechanically ball milled to obtain lithium sulfide, the reaction is violent, the heat generated is difficult to control, and the prepared lithium sulfide has low purity. It can be seen that the preparation method in the related art is time-consuming and laborious, and the prepared lithium sulfide has low purity, which is not conducive to industrial mass production.

[0034] To this end, the inventors of the present application have conducted in-depth exploration on the preparation method of lithium sulfide. On the one hand, in order to realize large-scale production, the reaction conditions of the synthesis route should avoid routes that require high temperature and high pressure conditions, etc. which are energy-consuming and difficult to control the reaction. On the other hand, the lithium salt and sulfur salt involved in the reaction should have appropriate reactivity, neither too high to cause violent reaction and difficult to operate, nor too low to require harsh conditions. Therefore, the inventors have developed a method for preparing lithium sulfide, which uses lithium salt and sulfur salt with high quality to react under mild conditions to prepare lithium sulfide with high purity.

[0035] The first aspect of the present application provides a method for preparing lithium sulfide, comprising:

[0036] mixing and reacting the lithium salt with ammonium sulfide to obtain lithium sulfide;

[0037] The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate and lithium tetrafluoroborate.

[0038] The reaction equation is as follows:

[0039]

[0040] X can be at least one of PF6 - , PO2F2 - , BF4 - .

[0041] In the present application, lithium salt and ammonium sulfide are subjected to metathesis reaction to prepare lithium sulfide. Compared with other reaction routes, the principle is simple, the reaction condition is mild, the reaction rate is fast, and the product yield is high. The lithium salt in the above reaction is lithium salt such as lithium hexafluorophosphate, lithium difluorophosphate and lithium tetrafluoroborate, which has good chemical stability and is not easy to decompose at normal temperature and pressure, and is suitable for large-scale transportation, storage and other industrial applications. Similarly, ammonium sulfide is widely used as a sulfur source in the chemical industry, and is relatively easy to obtain. Ammonium sulfide is stable at room temperature and is easy to store and transport. Moreover, the reaction activity between the two is high, and it is easy to react to generate lithium sulfide. The raw materials are easy to obtain, the reaction condition is mild, and the product yield is high. The by-products are ammonium hexafluorophosphate, ammonium difluorophosphate and ammonium tetrafluoroborate, which can be recycled as electrolyte or used as raw materials for synthesizing electrolyte.

[0042] Further, lithium salt such as lithium hexafluorophosphate, lithium difluorophosphate and lithium tetrafluoroborate is also a common raw material for batteries at present. Battery-grade lithium hexafluorophosphate, lithium difluorophosphate and lithium tetrafluoroborate have certain guarantee for the quality of the product in the production process. The lithium salt has high quality, less impurities, high purity and stable chemical properties. Therefore, the battery-grade lithium salt can be used in the method for preparing lithium sulfide of the present application, thereby directly reducing the introduction of impurities in the reaction, which helps to improve the purity of the product. At the same time, the source of such lithium salt is relatively extensive.

[0043] In some embodiments, the lithium salt and ammonium sulfide are reacted in an organic solvent, and the organic solvent includes at least one of an ester solvent and an ether solvent. The metathesis reaction of lithium salt and ammonium sulfide in an organic solvent system to prepare lithium sulfide has good solubility of lithium salt and ammonium sulfide, which helps to fully disperse the reactants in the reaction system, increases the contact area between the reactants, improves the reaction rate, and makes the reaction more complete.

[0044] Specifically, the types of commonly used organic solvents include alcohol, ester, ether and the like. The inventors found that when alcohol solvent is used to dissolve lithium salt, the alcohol solvent contains hydroxyl group, which has high activity and is easy to react with some groups in lithium salt, resulting in decomposition of lithium salt and generation of a large amount of impurities, thereby reducing the product yield and purity. For example, lithium hexafluorophosphate LiPF6 and alcohol solvent ROH can react as follows: LiPF6+ROH=LiPF5(OR)+HF, and LiPF5(OR) can further decompose to generate HF, PF5, POF3, ROPOF2 and other impurities; the generated HF itself can catalyze the subsequent alcoholysis reaction, thereby forming a vicious cycle.

[0045] The ester or ether solvent is more stable in chemical properties than the alcohol solvent, is less likely to react with the lithium salt, can ensure the stability of the reaction system, has better solubility, and thus can save the solvent usage and reduce the cost, and has a wider application range. In addition, the generated lithium sulfide is insoluble in the ester or ether solvent, and the subsequent separation and purification steps are relatively simple.

[0046] In some embodiments, the ester organic solvent includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, ethyl acetate, or methyl acetate. In some embodiments, the ether solvent includes at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, methyl tert-butyl ether, or diethyl ether. In this way, the chemical properties are more stable, the solubility is better, and the reaction with the lithium salt is less likely to occur, so that the stability of the reaction system can be further ensured, and the subsequent separation and purification steps are easier.

[0047] In some embodiments, the mass ratio of the lithium salt to the organic solvent is 1:3 to 1:20, and specifically, can be 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19, 1:20, etc. In some embodiments, the mass ratio of the lithium salt to the organic solvent is 1:4 to 1:8. In this way, the lithium salt can be completely dissolved in the organic solvent, and the waste of the organic solvent can be avoided.

[0048] In some embodiments, the temperature for reacting the lithium salt and the ammonium sulfide is 15°C to 70°C, and specifically, can be 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, etc. In some embodiments, the temperature for reacting the lithium salt and the ammonium sulfide can be 40°C to 50°C. In the above temperature conditions, the reaction efficiency can be further improved, the conditions are mild, the side reactions are less, the requirement for the equipment is lower, and the industrial production is easy to realize. The problems of low reaction rate caused by too low temperature or high requirement for the equipment caused by too high temperature can be basically avoided.

[0049] In some embodiments, the time for reacting the lithium salt and the ammonium sulfide is 2h to 6h, and specifically, can be 2h, 3h, 4h, 5h, 6h, etc. In some embodiments, the time for reacting the lithium salt and the ammonium sulfide can be 3h to 4h. In the above reaction time, the reaction can be basically ensured to be complete, the reaction efficiency is high, and the time waste and the cost are low.

[0050] In some embodiments, the atmosphere in which the lithium salt and the ammonium sulfide react can be an inert atmosphere. In some embodiments, the inert atmosphere includes at least one of nitrogen and argon. In this way, the reaction can be ensured to proceed smoothly, reducing the occurrence of side reactions, and improving the purity and yield of the product.

[0051] In some embodiments, the molar ratio of the lithium salt to the ammonium sulfide is 2:1 to 2.1:1, and specifically can be 2:1, 2.01:1, 2.02:1, 2.03:1, 2.04:1, 2.05:1, 2.06:1, 2.07:1, 2.08:1, 2.09:1, 2.1:1, etc. In this way, the reaction rate can be further improved, and the reaction can be made more complete.

[0052] In some embodiments, after the lithium salt and the ammonium sulfide are mixed and the reaction is complete, at least one of the following steps is further included:

[0053] After the lithium salt and the ammonium sulfide are mixed and reacted, a mixed solution containing lithium sulfide is obtained, and the mixed solution is subjected to solid-liquid separation to obtain a lithium sulfide crude product;

[0054] The lithium sulfide crude product is dried at 50°C to 120°C and -0.095 MPa for 1h to 5h to obtain a dried lithium sulfide crude product;

[0055] The dried lithium sulfide crude product is calcined at 400°C to 800°C and -0.095 MPa for 1h to 5h.

[0056] Specifically, after the lithium salt and the ammonium sulfide are reacted in the organic solvent, a mixed solution containing lithium sulfide is directly obtained, and a lithium sulfide precipitate can be obtained by solid-liquid separation. The specific filtration method can be selected according to actual needs, for example, including but not limited to suction filtration, etc.

[0057] It can be understood that the lithium sulfide crude precipitate obtained by direct solid-liquid separation generally contains residual organic solvent, moisture, and impurities, etc., and the residual organic solvent, moisture, and volatile impurities can be removed by drying. In some embodiments, the drying temperature can be specifically 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, etc.; the drying pressure can be specifically -0.095 MPa, etc.; and the drying time can be specifically 1h, 2h, 3h, 4h, 5h, etc. Under the above conditions, the lithium sulfide can reach a higher purity.

[0058] It can be understood that some non-volatile impurities can also exist in the filtered and dried dry lithium sulfide, and therefore can be further removed by calcination, and at the same time, high-temperature calcination can make the crystal structure of lithium sulfide more perfect. Specifically, the calcination temperature can be 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, etc.; the calcination pressure can be specifically 0.095 MPa, etc.; and the calcination time can be specifically 1 h, 2 h, 3 h, 4 h, 5 h, etc. Thus, the structure of lithium sulfide can be further improved to be more perfect and have a higher purity.

[0059] In some embodiments, the yield of lithium sulfide prepared by the method of the present application is ≥98%, and can be 98%, 98.5%, 99.0%, 99.5%, 100%, etc. Thus, the method can achieve industrial production.

[0060] The second aspect of the present application proposes the lithium sulfide prepared by the method described above. The lithium sulfide has a high purity and few impurities, and can be used to prepare a sulfide electrolyte, which can improve the ionic conductivity and interface stability of the electrolyte, thereby improving the electrochemical performance and safety performance of the battery.

[0061] In some embodiments, the purity of the lithium sulfide is ≥99.95%. Specifically, it can be 99.95%, 99.96%, 99.97%, 99.98%, 99.99%, 100%, etc. Thus, the lithium sulfide used to prepare a sulfide electrolyte and applied in a full solid-state battery can effectively improve the electrochemical performance and safety performance of the battery.

[0062] The embodiments of the present application are described in detail below.

[0063] Embodiment 1

[0064] 1. Argon was introduced into a dry reaction kettle to sweep and maintain an argon atmosphere, 311.42 g of lithium hexafluorophosphate, 68.14 g of ammonium sulfide, and 1245.68 g of methyl ethyl carbonate were added, stirring was started, and the temperature was raised to 40°C for 3 h;

[0065] 2. After the reaction was completed, the filter cake was obtained by filtration, and the filter cake was washed with methyl ethyl carbonate. The washed filter cake was dried at a vacuum degree of -0.095 MPa and a temperature of 80°C for 3 h to obtain crude lithium sulfide;

[0066] 3. The crude lithium sulfide was calcined at a vacuum degree of -0.095 MPa and a temperature of 600°C for 3 h to obtain lithium sulfide.

[0067] Embodiments 2-42

[0068] The same as the method of embodiment 1, and the specific parameters are different, as shown in Table 1.

[0069] Example 43

[0070] 1, dry reactor was purged with argon to maintain anhydrous atmosphere, 311.42 g of lithium hexafluorophosphate, 68.14 g of ammonium sulfide and 1245.68 g of ethanol were added, stirring was started, and the temperature was raised to 40°C for 3 h;

[0071] 2, after the reaction was completed, the filter cake was obtained by filtration, the filter cake was washed with methyl ethyl carbonate, and the washed filter cake was dried at a vacuum degree of -0.095 MPa and a temperature of 80°C for 3 h to obtain the crude lithium sulfide;

[0072] 3, the crude lithium sulfide was calcined at a vacuum degree of -0.095 MPa and a temperature of 600°C for 3 h to obtain lithium sulfide.

[0073] Comparative Example 1

[0074] 1, dry reactor was purged with argon to maintain anhydrous atmosphere, 86.90 g of lithium chloride, 68.14 g of ammonium sulfide and 1245.68 g of methyl ethyl carbonate were added, stirring was started, and the temperature was raised to 40°C for 3 h;

[0075] 2, after the reaction was completed, the filter cake was obtained by filtration, the filter cake was washed with methyl ethyl carbonate, and the washed filter cake was dried at a vacuum degree of -0.095 MPa and a temperature of 80°C for 3 h to obtain the crude lithium sulfide;

[0076] 3, the crude lithium sulfide was calcined at a vacuum degree of -0.095 MPa and a temperature of 600°C for 3 h to obtain lithium sulfide.

[0077] Performance detection:

[0078] 1, lithium sulfide structure test: the structure of the product was tested by X-ray diffraction, and the XRD spectrum of the lithium sulfide prepared in Example 1 is shown in Figure 1 .

[0079] 2, yield: the yield was calculated based on the final lithium sulfide product, i.e. the mass of the calcined lithium sulfide was measured, and the mass ratio of the lithium sulfide to the theoretical yield of lithium sulfide (calculated based on the amount of raw materials and the reaction equation) was calculated, i.e. the yield.

[0080] 3, purity: the content of metal ions (Na, K, Ca, Fe, Mg, Al, Cr, Pb, Ni, Co) was detected by inductively coupled plasma atomic emission spectrometer (ICP), and the purity of the product was calculated by the difference method. - / BF4 - / PO2F2 - .

[0081]

[0082] From the above test data, compared with Comparative Example 1, the lithium sulfide obtained by mixing and reacting at least one of lithium hexafluorophosphate, lithium difluorophosphate and lithium tetrafluoroborate with ammonium sulfide in the application can fully react under mild conditions, the reaction time is short and the reaction yield is high, and the purity of the obtained lithium sulfide is high.

[0083] Specifically, as can be seen from Examples 1-9, the purity and yield of the prepared lithium sulfide do not change significantly by selecting different lithium salts and organic solvents, which indicates that the types of lithium salts and organic solvents used in the application can ensure the smooth preparation of lithium sulfide, and high purity and yield can be achieved.

[0084] As can be seen from Examples 1, 10-16, when the mass ratio of lithium salt to organic solvent is 1:3~1:20, the purity and yield of lithium sulfide are higher, and when the mass ratio of lithium salt to organic solvent is 1:4~1:8, the purity and yield of lithium sulfide are better.

[0085] As can be seen from Examples 1, 17-23, when the reaction temperature is 15℃~70℃, the purity and yield of lithium sulfide are higher, and when the reaction temperature is 40℃~50℃, the purity and yield of lithium sulfide are better.

[0086] As can be seen from Examples 1, 24-27, when the reaction time is 2h~6h, the purity and yield of lithium sulfide are higher, and when the reaction time is 3h~4h, the purity and yield of lithium sulfide are better.

[0087] As can be seen from Examples 1, 28-30, when the molar ratio of lithium salt to ammonium sulfide is 2:1~2.1:1, the purity and yield of lithium sulfide are higher.

[0088] As can be seen from Examples 1, 31-36, when the drying temperature is 50℃~120℃ and the drying time is 1h~5h, the purity and yield of lithium sulfide are higher.

[0089] As can be seen from Examples 1, 37-43, when the calcination temperature is 400℃~800℃ and the calcination time is 1h~5h, the purity and yield of lithium sulfide are higher.

[0090] In the description of the specification, the description using the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" etc. means that the particular feature, structure, material or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. Descriptive expressions of the above terms in the specification do not necessarily refer to the same embodiment or example. Also, the particular feature, structure, material or characteristic described can be combined in any suitable manner in one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

[0091] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method of producing lithium sulfide, characterized by, The method comprises the following steps: mixing and reacting lithium salt and ammonium sulfide to obtain lithium sulfide; the lithium salt and the ammonium sulfide are reacted in an organic solvent, and the organic solvent comprises at least one of an ester solvent and an ether solvent; wherein the lithium salt comprises at least one of lithium hexafluorophosphate, lithium difluorophosphate and lithium tetrafluoroborate.

2. The method of claim 1, wherein, The ester solvent comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, ethylene carbonate, ethyl acetate and methyl acetate; and / or the ether solvent comprises at least one of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, methyl tert-butyl ether and diethyl ether.

3. The method of claim 1, wherein, The mass ratio of the lithium salt to the organic solvent is 1:3-1:

20.

4. The method of claim 3, wherein, The mass ratio of the lithium salt to the organic solvent is 1:4-1:

8.

5. The method of claim 1, wherein, The mixing and reacting of the lithium salt and the ammonium sulfide satisfy at least one of the following conditions: the reaction temperature is 15-70℃; the reaction time is 2-6h; the reaction atmosphere is inert atmosphere.

6. The method of claim 5, wherein, The mixing and reacting of the lithium salt and the ammonium sulfide satisfy at least one of the following conditions: the reaction temperature is 40-50℃; the reaction time is 3-4h.

7. The method of claim 1, wherein, The molar ratio of the lithium salt to the ammonium sulfide is 2:1-2.1:

1.

8. The method of claim 1, wherein, After the mixing and reacting of the lithium salt and the ammonium sulfide is completed, at least one of the following steps is further included: After the mixing and reacting of the lithium salt and the ammonium sulfide, a mixed solution containing lithium sulfide is obtained, and the mixed solution is subjected to solid-liquid separation to obtain lithium sulfide crude product; the lithium sulfide crude product is dried at 50-120℃ and-0.095Mpa for 1-5h to obtain dried lithium sulfide crude product; the dried lithium sulfide crude product is calcined at 400-800℃ and-0.095Mpa for 1-5h.

9. The method of any one of claims 1-8, wherein, The yield of the lithium sulfide is greater than or equal to 98%.

10. Lithium sulfide characterized in that, The lithium sulfide is prepared according to any one of the methods of claims 1-9.

11. The lithium sulfide according to claim 10, characterized in that, The purity of the lithium sulfide is greater than or equal to 99.95%.

Images