Preparation method of lithium sulfide and lithium sulfide

Abstract

The invention relates to a preparation method of lithium sulfide and lithium sulfide.In the preparation method, hexamethyldisilazane and alkalescent lithium salt serve as raw materials and react in an organic solvent to prepare the lithium sulfide, and the pKa range of the alkalescent lithium salt is 4.5-5.5. The lithium sulfide is prepared by taking hexamethyldisilazane and alkalescent lithium salt with the pKa value of 4.5-5.5 as raw materials and reacting in an organic solvent, and the preparation method of the lithium sulfide, which is simple, efficient, low in cost and high in purity, can be realized.

Description

Technical Field

[0001] The present application relates to the technical field of battery materials, and in particular to a preparation method of lithium sulfide and lithium sulfide. Background Art

[0002] Lithium sulfide (Li2S), an important inorganic compound, has broad application prospects in batteries, electronic materials, and other fields. Currently, there are five main methods for preparing lithium sulfide.

[0003] Method 1: Direct reaction method. This involves direct mixing of metallic lithium and elemental sulfur. Although this method has low raw material costs, it is subject to harsh reaction conditions, requiring a high temperature and high pressure environment. Furthermore, byproducts are easily produced during the reaction, making it difficult to guarantee purity.

[0004] Method 2: Liquid Phase Method: Lithium / lithium compounds and sulfur / sulfur compounds are mixed and reacted in a solvent medium. Although the reaction is relatively mild, the organic solvent is flammable, explosive, and volatile, causing serious environmental pollution and a complex purification process.

[0005] Method 3: High temperature and high pressure method. Although the process is simple, it requires high equipment, the reaction conditions are difficult to control, and there are safety risks.

[0006] Method 4: Ball milling. The preparation of lithium sulfide through mechanical ball milling is a simple and environmentally friendly process, but it involves high raw material costs (e.g., using lithium hydride), long reaction times, low conversion rates, and the presence of impurities such as lithium polysulfide in the product, making it difficult to purify.

[0007] Method 5: Carbon composite method. This method uses the strong reducing property of carbon to synthesize lithium sulfide / carbon composite materials. Although it solves some problems, the product quality is unstable and the controllability of the composite material morphology is poor.

[0008] The lithium sulfide prepared by the above five methods has many defects, which limits the large-scale application of lithium sulfide.

[0009] There are also some improved methods in the existing art, such as the reaction of carbon monoxide with anhydrous lithium sulfate to produce lithium sulfide. Although this method avoids the use of hydrogen sulfide, the reaction conditions are still relatively harsh and the raw material costs are high. Another example is the production of high-purity lithium sulfide through a specific process. Although the purity is high, the process is complex and difficult to scale up industrially. Summary of the Invention

[0010] The embodiments of the present application provide a method for preparing lithium sulfide and lithium sulfide, aiming to overcome the defects of the prior art and realize a simple, efficient, low-cost, and high-purity method for preparing lithium sulfide.

[0011] In order to achieve the above-mentioned object, according to the first aspect of the present application, a method for preparing lithium sulfide is provided, in which hexamethyldisilathane and a weakly basic lithium salt are used as raw materials to react in an organic solvent to prepare lithium sulfide, wherein the pKa range of the weakly basic lithium salt is 4.5~5.5.

[0012] In some embodiments of the present application, the weakly alkaline lithium salt is selected from one of lithium acetate, lithium butyrate, lithium isobutyrate, lithium levulinate and lithium propionate.

[0013] In some embodiments of the present application, the organic solvent is selected from at least one of tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.

[0014] In some embodiments of the present application, the organic solvent includes a first solvent and a second solvent, the first solvent is selected from at least one of tetrahydrofuran and 2-methyltetrahydrofuran, and the second solvent is selected from at least one of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.

[0015] In some embodiments of the present application, the first solvent is tetrahydrofuran, and the second solvent is ethylene glycol dimethyl ether; or the first solvent is 2-methyltetrahydrofuran, and the second solvent is diethylene glycol dimethyl ether.

[0016] In some embodiments of the present application, the mass ratio of the first solvent to the second solvent is (2:1) to (4:1).

[0017] In some embodiments of the present application, the reaction of hexamethyldisilathioane with the weakly alkaline lithium salt includes a first-stage reaction and a second-stage reaction. The temperature of the first-stage reaction is -20°C to 0°C, and the temperature of the second-stage reaction is 20°C to 25°C.

[0018] In some embodiments of the present application, the molar ratio of the hexamethyldisilathione to the weakly basic lithium salt is greater than 2:1 and less than or equal to 2:1.3.

[0019] In some embodiments of the present application, the method for preparing lithium sulfide comprises the following steps: At room temperature, in an inert gas atmosphere, the weakly alkaline lithium salt and the organic solvent are mixed to obtain a mixed solution, and the mixture is stirred and cooled to -20°C to 0°C; Adding hexamethyldisilathioethane to the mixed solution, and performing a first-stage reaction at a reaction temperature of -20°C to 0°C; Conducting the second stage reaction at a reaction temperature of 20°C to 25°C, and obtaining crude lithium sulfide after the reaction is completed; and The crude lithium sulfide product is dried and calcined to obtain lithium sulfide.

[0020] In some embodiments of the present application, the reaction time of the first stage reaction is 2 h to 4 h, and the reaction time of the second stage reaction is 2 h to 5 h.

[0021] In some embodiments of the present application, in the step of drying and calcining the crude lithium sulfide to obtain lithium sulfide, the drying conditions are as follows: drying temperature is 50°C~100°C, drying vacuum is -0.08 Mpa~-0.1Mpa, and drying time is 1 h~3 h.

[0022] In some embodiments of the present application, in the step of drying and calcining the crude lithium sulfide to obtain lithium sulfide, the calcination conditions are as follows: calcination temperature is 400° C. to 800° C., and calcination time is 1 h to 5 h.

[0023] According to a second aspect of the present application, there is provided a lithium sulfide, which is prepared by any of the preparation methods described above.

[0024] Other features and advantages of the present application will be described in detail in the subsequent detailed description.

[0025] Beneficial effects: In the preparation method of lithium sulfide of the embodiment of the present application, hexamethyldisilathione is used as a sulfur source and a weakly alkaline lithium salt with a pKa value of 4.5 to 5.5 is used as a lithium source. Compared with traditional lithium salts (such as lithium hydroxide and lithium chloride), the weakly alkaline lithium salt with a pKa value of 4.5 to 5.5 can avoid excessive hydrolysis of lithium sulfide due to the formation of byproducts such as water during the reaction of hexamethyldisilathione and the weakly alkaline lithium salt in the present application, and can also avoid the formation of colloidal byproducts, thereby improving the low purity problem existing in the traditional lithium sulfide synthesis route. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application are described clearly and completely below. It is understood that the described embodiments are only some of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments of the present application without creative work are within the scope of protection of the present application.

[0027] The lithium salt used in traditional lithium sulfide synthesis is usually lithium hydroxide or lithium chloride. In the process of synthesizing lithium sulfide using lithium hydroxide as a lithium source, the OH produced by the ionization of lithium hydroxide is - It will lead to the generation of water, which will cause the hydrolysis of lithium sulfide, thereby reducing the purity of lithium sulfide. In addition, in the process of synthesizing lithium sulfide using lithium chloride as a lithium source, the Li +Colloidal aggregates are easily generated to form colloidal by-products, which also reduce the purity of lithium sulfide.

[0028] In response to the above-mentioned problems existing in the above-mentioned prior art, an embodiment of the present application provides a method for preparing lithium sulfide. In this preparation method, hexamethyldisilathioane and a weakly basic lithium salt are used as raw materials to react in an organic solvent to prepare lithium sulfide, wherein the pKa of the weakly basic lithium salt is 4.5~5.5.

[0029] In the preparation method of lithium sulfide of the embodiment of the present application, hexamethyldisilathione is used as a sulfur source and a weakly alkaline lithium salt with a pKa value of 4.5 to 5.5 is used as a lithium source. Compared with traditional lithium salts (such as lithium hydroxide and lithium chloride), the weakly alkaline lithium salt with a pKa value of 4.5 to 5.5 can avoid excessive hydrolysis of lithium sulfide due to the formation of byproducts such as water during the reaction of hexamethyldisilathione and the weakly alkaline lithium salt in the present application, and can also avoid the formation of colloidal byproducts, thereby improving the low purity problem existing in the traditional lithium sulfide synthesis route.

[0030] In this application, pKa represents the ability of an acid to dissociate hydrogen ions. pKa is the negative logarithm of the acid's dissociation constant (Ka). The pKa value is closely related to the strength of the acid. A smaller pKa value corresponds to a larger Ka value, indicating that the acid dissociates hydrogen ions more readily in water and is more acidic. Conversely, a larger pKa value corresponds to a smaller Ka value, indicating a weaker acid.

[0031] In some embodiments of the present application, a weakly alkaline lithium salt with a pKa of 4.5-5.0 is used as the lithium source.

[0032] In some embodiments of the present application, the weakly alkaline lithium salt is selected from one of lithium acetate, lithium butyrate, lithium isobutyrate, lithium levulinate, and lithium propionate. Among them, the pKa value of lithium acetate is approximately 4.76, the pKa value of lithium butyrate is approximately 4.83, the pKa value of lithium isobutyrate is approximately 4.86, the pKa value of lithium levulinate is approximately 4.5, and the pKa value of lithium propionate is approximately 4.88. Using the above lithium salts to synthesize lithium sulfide can further avoid the formation of by-products, thereby further improving the purity of lithium sulfide.

[0033] In some embodiments of the present application, the weakly alkaline lithium salt is selected from lithium acetate or lithium propionate. When lithium acetate or lithium propionate is used as the lithium source, during the synthesis of lithium sulfide, lithium acetate or lithium propionate can directionally cleave the S-Si bond, avoiding the formation of byproducts, thereby improving product purity. Furthermore, the use of lithium acetate or lithium propionate can make the synthesis of lithium sulfide milder and easier to operate.

[0034] In some embodiments of the present application, taking lithium acetate as an example, the reaction process of hexamethyldisilathioethane and lithium acetate to generate lithium sulfide is as follows: Among them, the by-product It can be removed by distillation under reduced pressure during the reaction.

[0035] In some embodiments of the present application, the molar ratio of the hexamethyldisilathione to the weakly basic lithium salt is 2:1.

[0036] In some embodiments of the present application, the molar ratio of hexamethyldisilathione to the weakly basic lithium salt is greater than 2:1 and less than or equal to 2:1.3. A slight excess of hexamethyldisilathione can increase the reaction rate and conversion rate. Furthermore, after the reaction, excess hexamethyldisilathione can be removed by vacuum distillation without affecting the purity of the lithium sulfide. In some specific embodiments, the molar ratio of hexamethyldisilathione to the weakly basic lithium salt can be 2:1.1, 2:1.2, or 2:1.3.

[0037] In some embodiments of the present application, the organic solvent is selected from at least one of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF, Me represents methyl), ethylene glycol dimethyl ether (DME) and diethylene glycol dimethyl ether (DEGDME). The above solvents can stabilize the intermediates produced during the synthesis of lithium sulfide, thereby inhibiting the occurrence of side reactions. Specifically, in the synthesis of lithium sulfide, taking lithium acetate as an example of a lithium source, when hexamethyldisilathane reacts with lithium acetate, the intermediates Me3Si-SLi and Me3Si-OAc generated are prone to further condensation or decomposition, and the lone pair electrons of polar solvents (such as THF) react with Li + Coordination to form a stable solvation shell (such as [Li(THF)4] + ), to prevent Li + With siloxane anions (Me3Si-O - ) directly combine to form a colloid. Ether solvents (such as DME) form weak hydrogen bonds (CH···O) with silane groups (Me3Si-) through their oxygen atoms, inhibiting the self-condensation reaction of Me3Si-OAc, thereby further reducing the probability of by-product formation and further improving the purity of lithium sulfide.

[0038] In some embodiments of the present application, the organic solvent includes a first solvent and a second solvent, the first solvent being selected from at least one of tetrahydrofuran and 2-methyltetrahydrofuran, and the second solvent being selected from at least one of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether. In the embodiments of the present application, a mixed solvent of the first and second solvents is used. The combined use of the first and second solvents can further stabilize intermediates produced during the lithium sulfide synthesis process, thereby further suppressing the occurrence of side reactions during the lithium sulfide synthesis process.

[0039] In some embodiments of the present application, the organic solvent is selected from tetrahydrofuran and ethylene glycol dimethyl ether, or 2-methyltetrahydrofuran and diethylene glycol dimethyl ether. When the organic solvent is selected from either of the above two combinations, the synergistic effect of the lithium salt selection and the above combination can greatly reduce the probability of by-product formation, thereby further improving the purity of lithium sulfide.

[0040] For example, when the weakly basic lithium salt is lithium acetate, the first solvent is THF, and the second solvent is DME, the mechanism of action of the mixed solvent in the embodiment of the present application is as follows: During the reaction of hexamethyldisilathioethane with lithium acetate, the intermediates Me3Si-SLi and Me3Si-OAc generated by the reaction are prone to condensation or decomposition, which may produce ions such as Li + and Me3Si-O - , silane group (Me3Si-). The lone pair electrons of THF in the reaction system will react with Li + Coordination to form a stable solvation shell (such as [Li(THF)4] + ), to prevent Li + With Me3Si-O - Furthermore, DME forms weak hydrogen bonds (CH···O) with silane groups (Me3Si-) through oxygen atoms, thereby inhibiting the self-condensation reaction of Me3Si-OAc.

[0041] In some embodiments of the present application, the mass ratio of the first solvent to the second solvent is: (2:1) to (4:1), for example, it can be 2:1, 2.5:1, 3:1, 3.5:1, or 4:1. It is understood that if the first solvent accounts for a large proportion, due to the high dielectric constant of the first solvent, excessive polarization will lead to the occurrence of side reactions; if the second solvent accounts for a large proportion, due to the low dielectric constant of the second solvent, the chemical reaction rate during the lithium sulfide synthesis process will be reduced. Therefore, by setting the mass ratio of the first solvent to the second solvent within the above range, the chemical reaction rate during the lithium sulfide synthesis process can be increased while avoiding the occurrence of side reactions.

[0042] In some embodiments of the present application, in the preparation method of lithium sulfide, the reaction of hexamethyldisilathioane and a weakly alkaline lithium salt includes a first-stage reaction and a second-stage reaction, the temperature of the first-stage reaction is -20°C to 0°C, and the temperature of the second-stage reaction is 20°C to 25°C.

[0043] It is understood that the S-Si bond (bond energy 310 kJ / mol) in hexamethyldisilathione will randomly break at high temperatures (above room temperature) or under strong alkaline conditions, generating siloxane and forming a colloidal polymer. In this application, taking the reaction of hexamethyldisilathione with lithium acetate as an example, in the above embodiment, by dividing the synthesis of lithium sulfide into two reaction stages, in the first stage reaction, at a low temperature environment of -20°C to 0°C, the breaking rate constant (k) of the S-Si bond in hexamethyldisilathione will be reduced by 10 compared to the reaction at a high temperature (above room temperature) or under strong alkaline conditions. 3 times, thereby avoiding excessive breakage of the S-Si bond and ensuring controlled breakage of the S-Si bond. Furthermore, the intermediates generated during the reaction (e.g., Me3Si-OAc) are prone to polymerization at high temperatures. In this embodiment, since the first-stage reaction is carried out in a low-temperature environment of -20°C to 0°C, the polymerization of the intermediates can be suppressed, reducing the formation of by-products and further improving the purity of the lithium sulfide. Furthermore, in the second-stage reaction, the room temperature environment of 20°C to 25°C promotes the growth of lithium sulfide crystals, facilitating the formation of lithium sulfide with a well-formed crystal structure, thereby obtaining lithium sulfide with a good morphology.

[0044] In some specific embodiments, the temperature of the first stage reaction is -20°C, -15°C, -10°C, -5°C, or 0°C, or can be a range consisting of any of the above values; the temperature of the second stage reaction is 20°C, 21°C, 22°C, 23°C, 24°C, or 25°C, or can be a range consisting of any of the above values.

[0045] In some embodiments of the present application, in the method for preparing lithium sulfide, the reaction of hexamethyldisilathioane with a weakly basic lithium salt is carried out in a single reaction stage, and the temperature of the reaction stage is between -20°C and 25°C. By carrying out the reaction of hexamethyldisilathioane with a weakly basic lithium salt in the single reaction stage, the process can be simplified and the process cost can be reduced. In some specific embodiments, the temperature of the reaction stage is -20°C, -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, or 25°C, or can be within a range consisting of any of the above values.

[0046] In some embodiments of the present application, the reaction time of the first stage reaction is 2 hours to 4 hours, and the reaction time of the second stage reaction is 2 hours to 5 hours. It is understood that in the synthesis process of lithium sulfide, the reaction time determines whether the reaction is complete. The first stage reaction is a low-temperature reaction (reaction temperature is -20°C to 0°C). Low temperature conditions can avoid the formation of by-products caused by violent reactions. The second stage reaction is a room temperature reaction (reaction temperature is 20°C to 25°C). This room temperature reaction can ensure the complete reaction and is conducive to promoting the growth of lithium sulfide crystals.

[0047] In some embodiments of the present application, the method for preparing lithium sulfide comprises the following steps: At room temperature, in an inert gas atmosphere, the weakly alkaline lithium salt and the organic solvent are mixed to obtain a mixed solution, and the mixture is stirred and cooled to -20°C to 0°C; Adding hexamethyldisilathioethane to the mixed solution, and performing a first-stage reaction at a reaction temperature of -20°C to 0°C; Conducting the second stage reaction at a reaction temperature of 20°C to 25°C, and obtaining crude lithium sulfide after the reaction is completed; and The crude lithium sulfide product is dried and calcined to obtain lithium sulfide.

[0048] In some embodiments of the present application, the first-stage reaction specifically includes: slowly adding the hexamethyldisilathione to the mixture of the weakly alkaline lithium salt and the organic solvent, and controlling the temperature of the addition process to be between -20°C and 0°C for the reaction; the second-stage reaction specifically includes: after the addition of the hexamethyldisilathione in the first-stage reaction is completed, heating the mixture to 20°C to 25°C for a constant temperature reaction.

[0049] In some embodiments of the present application, after the second stage reaction is completed, the solvent and by-products in the reaction system are removed by distillation under reduced pressure to obtain crude lithium sulfide.

[0050] In some embodiments of the present application, after obtaining the crude lithium sulfide, the drying conditions for drying the crude lithium sulfide are as follows: drying temperature of 50°C to 100°C, drying vacuum of -0.08 Mpa to -0.1 Mpa, and drying time of 1 h to 3 h.

[0051] In some embodiments, the drying temperature is 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, or 100°C, or any range thereof. In some embodiments, the drying vacuum is -0.08 MPa, -0.085 MPa, -0.09 MPa, -0.095 MPa, or -0.1 MPa, or any range thereof. In some embodiments, the drying time is 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, or any range thereof.

[0052] In some embodiments of the present application, after obtaining the crude lithium sulfide, the crude lithium sulfide is calcined under the following calcination conditions: calcination temperature is 400° C. to 800° C., and calcination time is 1 h to 5 h.

[0053] In some specific embodiments, the calcination temperature is 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or 800°C, or can be a range consisting of any of the above values; the calcination time is 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h, or can be a range consisting of any of the above values.

[0054] The present application also provides lithium sulfide, which is prepared by the lithium sulfide preparation method described in any of the aforementioned embodiments.

[0055] The preparation method of lithium sulfide provided in this application is described in detail below with reference to specific examples.

[0056] Example 1 The method for preparing lithium sulfide provided in Example 1 includes the following steps (1) to (5).

[0057] Step (1) At room temperature, 2 mol of lithium acetate, 300 g of tetrahydrofuran, and 100 g of ethylene glycol dimethyl ether were added to a dry reaction kettle in an argon atmosphere, and the mixture was stirred and cooled to -10°C.

[0058] Step (2) Control the temperature at -10°C and slowly add 1.1 mol of hexamethyldisilathioethane dropwise for about 3 hours.

[0059] After the addition in step (3) is completed, the temperature is raised to 25°C and the reaction is maintained for 2 h.

[0060] After the reaction in step (4) is completed, the solvent, the by-product trimethylsiloxyacetate and the unreacted hexamethyldisilathane are removed by distillation under reduced pressure to obtain crude lithium sulfide.

[0061] Step (5) calcining the crude lithium sulfide at 600° C. for 3 h under an inert atmosphere to obtain high-purity lithium sulfide with a yield of 99.95% and a purity of 98.12%.

[0062] Examples 2 to 20, Comparative Examples 1 to 3 The preparation methods for lithium sulfide provided in Examples 2 to 20 and Comparative Examples 1 to 3 are essentially the same as those in the Examples, with the differences shown in Table 1. In Table 1, the molar content of the lithium salt in the reactants of Examples 1 to 20 and Comparative Examples 1 to 3 is the same, 2 mol, and the sulfur source is hexamethyldisilathione; Examples 9-10 and Comparative Examples 1-3 all utilize a single solvent; and Example 18 is conducted in a single reaction stage at a reaction temperature of -10°C.

[0063] Table 1

[0064] Furthermore, the present application measured the purity and yield of the lithium sulfide prepared in Examples 1 to 20 and Comparative Examples 1 to 3, and the results are shown in Table 2.

[0065] Table 2

[0066] By comparing Examples 1-20 with Comparative Examples 1-3, it can be seen that in the preparation method of lithium sulfide of Examples 1-20 of the present application, when hexamethyldisilathane is used as the sulfur source and a weakly alkaline lithium salt such as lithium acetate, lithium propionate or lithium butyrate is used as the lithium source, the purity and yield of lithium sulfide can be significantly improved compared with the lithium salts of Comparative Examples 1-3 (such as lithium hydroxide, lithium chloride, lithium fluoride, etc.).

[0067] It can be seen from Example 1 and Examples 11-17 that when other reaction conditions are the same, within the range of the molar ratio of hexamethyldisilathione to the lithium salt being greater than 2:1 and less than or equal to 2:1.3, Examples 1 and Examples 11-15 can improve the purity and yield of lithium sulfide compared to Examples 16-17, and when the molar ratio of hexamethyldisilathione to the lithium salt is 2:1.1, the purity and yield of lithium sulfide reach the optimal value.

[0068] As can be seen from Examples 1-20, when other reaction conditions are the same, the mixture of the first and second solvents used in Examples 1-8 and Examples 11-20 can significantly improve the purity and yield of lithium sulfide compared to the single solvent (THF or DME) used in Examples 9-10. Furthermore, as can be seen from Examples 1 and Examples 5-8, when other reaction conditions are the same, the purity and yield of lithium sulfide can be further improved when a mixture of the first and second solvents is used within a mass ratio of the first and second solvents ranging from (2:1) to (4:1). For example, compared to Examples 7-8, the purity and yield of lithium sulfide prepared in Examples 1 and Examples 5-6 were significantly improved. Furthermore, within a mass ratio of the first and second solvents ranging from (2:1) to (4:1), when other reaction conditions are the same, the purity and yield of lithium sulfide reach optimal values ​​when the mass ratio of the first and second solvents is 3:1, as in Example 1.

[0069] It can be seen from Example 1 and Example 18 that, when other reaction conditions are the same, the two-stage reaction adopted in Example 1 can significantly improve the purity and yield of lithium sulfide compared to the single-stage reaction in Example 18. In addition, it can be seen from Examples 1-17 and Examples 19-20 that when a two-stage reaction is adopted, the temperature of the first-stage reaction is -20°C to 0°C and the temperature of the second-stage reaction is 20°C to 25°C, and lithium sulfide has a relatively high purity and yield. Further, it can be seen from Example 1 and Examples 11-12 that when the temperature of the first-stage reaction is -10°C and the temperature of the second-stage reaction is 25°C, the purity and yield of lithium sulfide reach the optimal value, as shown in Example 1.

[0070] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more features. In the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0071] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0072] The embodiments, implementation methods and related technical features of the present application can be combined and replaced with each other without conflict.

[0073] The above are merely preferred embodiments of the present application and do not constitute any form of limitation to the present application. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present application without departing from the content of the technical solution of the present application are still within the scope of the technical solution of the present application.

Claims

1. A method for preparing lithium sulfide, characterized in that: Lithium sulfide is prepared by reacting hexamethyldisilathione and a weakly basic lithium salt in an organic solvent, wherein the pKa range of the weakly basic lithium salt is 4.5-5.

5.

2. The method for preparing lithium sulfide according to claim 1, wherein The weakly alkaline lithium salt is selected from one of lithium acetate, lithium butyrate, lithium isobutyrate, lithium levulinate and lithium propionate.

3. The method for preparing lithium sulfide according to claim 1, wherein The organic solvent is selected from at least one of tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.

4. The method for preparing lithium sulfide according to claim 1, wherein The organic solvent includes a first solvent and a second solvent, the first solvent is selected from at least one of tetrahydrofuran and 2-methyltetrahydrofuran, and the second solvent is selected from at least one of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.

5. The method for preparing lithium sulfide according to claim 4, characterized in that: The first solvent is tetrahydrofuran, and the second solvent is ethylene glycol dimethyl ether; or the first solvent is 2-methyltetrahydrofuran, and the second solvent is diethylene glycol dimethyl ether.

6. The method for preparing lithium sulfide according to claim 4, characterized in that: The mass ratio of the first solvent to the second solvent is (2:1) to (4:1).

7. The method for preparing lithium sulfide according to claim 1, characterized in that: The reaction of hexamethyldisilathione with the weakly alkaline lithium salt includes a first-stage reaction and a second-stage reaction. The temperature of the first-stage reaction is -20°C to 0°C, and the temperature of the second-stage reaction is 20°C to 25°C.

8. The method for preparing lithium sulfide according to claim 1, wherein The molar ratio of the hexamethyldisilathane to the weakly basic lithium salt is greater than 2:1 and less than or equal to 2:1.

3.

9. The method for preparing lithium sulfide according to claim 1, wherein: The following steps are involved: At room temperature, in an inert gas atmosphere, the weakly alkaline lithium salt and the organic solvent are mixed to obtain a mixed solution, and the mixture is stirred and cooled to -20°C to 0°C; Adding hexamethyldisilathioethane to the mixed solution, and performing a first-stage reaction at a reaction temperature of -20°C to 0°C; The second stage reaction is carried out at a reaction temperature of 20°C to 25°C. After the reaction is completed, crude lithium sulfide is obtained; as well as The crude lithium sulfide product is dried and calcined to obtain lithium sulfide.

10. The method for preparing lithium sulfide according to claim 9, characterized in that: The reaction time of the first stage reaction is 2 h to 4 h, and the reaction time of the second stage reaction is 2 h to 5 h.

11. The method for preparing lithium sulfide according to claim 9, characterized in that: In the step of drying and calcining the crude lithium sulfide to obtain lithium sulfide, the drying conditions are as follows: drying temperature is 50° C. to 100° C., drying vacuum is -0.08 Mpa to -0.1 Mpa, and drying time is 1 h to 3 h.

12. The method for preparing lithium sulfide according to claim 9, characterized in that: In the step of drying and calcining the crude lithium sulfide to obtain lithium sulfide, the calcination conditions are as follows: the calcination temperature is 400° C. to 800° C., and the calcination time is 1 h to 5 h.

13. A lithium sulfide, characterized in that: The lithium sulfide is prepared by the preparation method of any one of claims 1 to 12.

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