Preparation methods of lithium sulfide and lithium sulfide

Abstract

This application relates to a method for preparing lithium sulfide and the lithium sulfide itself. In this method, lithium sulfide is prepared by reacting hexamethyldisilazane with a weakly basic lithium salt in an organic solvent. The pKa of the weakly basic lithium salt is in the range of 4.5 to 5.5. By using hexamethyldisilazane with a weakly basic lithium salt with a pKa of 4.5 to 5.5 as a raw material in an organic solvent to prepare lithium sulfide, this application provides a simple, efficient, low-cost, and high-purity method for preparing lithium sulfide.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, specifically to a method for preparing lithium sulfide and lithium sulfide. Background Technology

[0002] Lithium sulfide (Li₂S), as 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 method involves directly mixing and reacting metallic lithium with elemental sulfur. While the raw material cost is low, the reaction conditions are demanding, requiring a high-temperature and high-pressure environment. Furthermore, byproducts are easily generated 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 solvents are flammable, explosive, and volatile, causing serious environmental pollution, and the purification process is complex.

[0005] Method 3: High temperature and high pressure method. While the process is simple, it involves reactions under high temperature and high pressure conditions, but requires sophisticated equipment, makes reaction conditions difficult to control, and poses safety hazards.

[0006] Method 4: Ball milling. While the mechanical ball milling process for preparing lithium sulfide is simple and environmentally friendly, it suffers from high raw material costs (e.g., using lithium hydride), long reaction time, low conversion rate, and the presence of impurities such as lithium polysulfides in the product, making purification difficult.

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

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

[0009] In addition, there are some improved methods in the existing technology, such as the preparation of lithium sulfide by reacting carbon monoxide with anhydrous lithium sulfate. Although this method avoids the use of hydrogen sulfide, the reaction conditions are still relatively harsh and the raw material cost is high. Another example is the preparation of high-purity lithium sulfide through specific processes. Although the purity is high, the process is complex and difficult to scale up for industrial production. Summary of the Invention

[0010] This application provides a method for preparing lithium sulfide and lithium sulfide, aiming to overcome the shortcomings of the prior art and achieve a simple, efficient, low-cost, and high-purity method for preparing lithium sulfide.

[0011] To achieve the above objectives, according to a first aspect of this application, a method for preparing lithium sulfide is provided, wherein lithium sulfide is prepared by reacting hexamethyldisilazane and a weakly basic lithium salt in an organic solvent, wherein the pKa of the weakly basic lithium salt is in the range of 4.5 to 5.5.

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

[0013] In some embodiments of this 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 this application, the organic solvent includes a first solvent and a second solvent, wherein 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 this 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 this application, the mass ratio of the first solvent to the second solvent is (2:1) to (4:1).

[0017] In some embodiments of this application, the reaction of hexamethyldisiloxane with the weakly basic lithium salt includes a first-stage reaction and a second-stage reaction, wherein 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 this application, the molar ratio of the hexamethyldisiloxane and the weakly basic lithium salt is greater than 2:1 and less than or equal to 2:1.3.

[0019] In some embodiments of this application, the method for preparing the lithium sulfide includes the following steps:

[0020] At room temperature, the weakly basic lithium salt and the organic solvent are mixed in an inert gas atmosphere to obtain a mixture, which is then stirred and cooled to -20°C to 0°C.

[0021] The hexamethyldisilazane was added to the mixture, and the first stage reaction was carried out at a reaction temperature of -20°C to 0°C.

[0022] The second stage reaction was carried out at a reaction temperature of 20℃~25℃. After the reaction was completed, crude lithium sulfide was obtained; and

[0023] The crude lithium sulfide was dried and calcined to obtain lithium sulfide.

[0024] In some embodiments of this 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.

[0025] In some embodiments of this 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℃~100℃, drying vacuum degree is -0.08 MPa~-0.1 MPa, and drying time is 1 h~3 h.

[0026] In some embodiments of this application, the step of drying and calcining the crude lithium sulfide to obtain lithium sulfide is performed under the following calcination conditions: calcination temperature is 400℃~800℃, and calcination time is 1 h~5 h.

[0027] According to a second aspect of this application, a lithium sulfide is provided, which is prepared by any of the preparation methods described above.

[0028] Other features and advantages of this application will be described in detail in the following detailed description section.

[0029] Beneficial effects:

[0030] In the lithium sulfide preparation method of this application embodiment, hexamethyldisilazane is used as the sulfur source and a weakly basic lithium salt with a pKa of 4.5 to 5.5 is used as the lithium source. Compared with traditional lithium salts (such as lithium hydroxide, lithium chloride, etc.), in the reaction process of hexamethyldisilazane and weakly basic lithium salt in this application, the weakly basic lithium salt with a pKa of 4.5 to 5.5 can avoid excessive hydrolysis of lithium sulfide due to the generation of by-products such as water, and can also avoid the generation of colloidal by-products, thereby improving the low purity problem of traditional lithium sulfide synthesis routes. Detailed Implementation

[0031] The technical solutions in the embodiments of this application will be clearly and completely described below. It is understood that the described embodiments are merely a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0032] The lithium salts used in the traditional synthesis of lithium sulfide are typically lithium hydroxide or lithium chloride. In the reaction process where lithium hydroxide is used as the lithium source to synthesize lithium sulfide, the ionization of lithium hydroxide produces OH-. -This can lead to the formation of water, which in turn causes lithium sulfide to hydrolyze, thus reducing the purity of lithium sulfide. Furthermore, in the process of synthesizing lithium sulfide using lithium chloride as a lithium source, the ionization of lithium chloride produces Li₂. + It is easy to form colloidal aggregates, resulting in gelatinous byproducts, which also reduce the purity of lithium sulfide.

[0033] To address the aforementioned problems in the prior art, this application provides a method for preparing lithium sulfide. In this method, hexamethyldisilazane and a weakly basic lithium salt are reacted in an organic solvent to obtain lithium sulfide, wherein the pKa of the weakly basic lithium salt is 4.5~5.5.

[0034] In the lithium sulfide preparation method of this application embodiment, hexamethyldisilazane is used as the sulfur source and a weakly basic lithium salt with a pKa of 4.5 to 5.5 is used as the lithium source. Compared with traditional lithium salts (such as lithium hydroxide, lithium chloride, etc.), in the reaction process of hexamethyldisilazane and weakly basic lithium salt in this application, the weakly basic lithium salt with a pKa of 4.5 to 5.5 can avoid excessive hydrolysis of lithium sulfide due to the generation of by-products such as water, and can also avoid the generation of colloidal by-products, thereby improving the low purity problem of traditional lithium sulfide synthesis routes.

[0035] In this application, pKa represents the ability of an acid to dissociate hydrogen ions, and pKa is the negative logarithm of the dissociation constant (Ka) of an acid. The pKa value is closely related to the strength of the acid. The smaller the pKa value, the larger the corresponding Ka value, indicating that the acid dissociates hydrogen ions more easily in water and the stronger the acidity; conversely, the larger the pKa value and the smaller the Ka value, the weaker the acidity.

[0036] In some embodiments of this application, a weakly alkaline lithium salt with a pKa of 4.5 to 5.0 is used as the lithium source.

[0037] In some embodiments of this application, the weakly basic lithium salt is selected from lithium acetate, lithium butyrate, lithium isobutyrate, lithium levulinate, and lithium propionate. Specifically, lithium acetate has a pKa value of approximately 4.76, lithium butyrate approximately 4.83, lithium isobutyrate approximately 4.86, lithium levulinate approximately 4.5, and lithium propionate approximately 4.88. Using the above lithium salts to synthesize lithium sulfide further avoids the formation of byproducts, thereby further improving the purity of lithium sulfide.

[0038] In some embodiments of this application, the weakly basic lithium salt is selected from lithium acetate or lithium propionate. When lithium acetate or lithium propionate is used as the lithium source, it can directionally cleave the S-Si bond during the synthesis of lithium sulfide, avoiding the formation of by-products and thus improving product purity. At the same time, using lithium acetate or lithium propionate makes the synthesis reaction conditions of lithium sulfide mild and the operation simple.

[0039] In some embodiments of this application, taking lithium acetate as an example of a weakly basic lithium salt, the reaction process of hexamethyldisilazane and lithium acetate to generate lithium sulfide is as follows: Among them, by-products It can be removed during the reaction process by means of vacuum distillation or other methods.

[0040] In some embodiments of this application, the molar ratio of the hexamethyldisiloxane to the weakly basic lithium salt is 2:1.

[0041] In some embodiments of this application, the molar ratio of hexamethyldisilazane to the weakly basic lithium salt is greater than 2:1 and less than or equal to 2:1.3. A slight excess of hexamethyldisilazane can improve the reaction rate and conversion. Furthermore, after the reaction is complete, excess hexamethyldisilazane can be removed by vacuum distillation without affecting the purity of lithium sulfide. In some specific embodiments, the molar ratio of hexamethyldisilazane to the weakly basic lithium salt can be 2:1.1, 2:1.2, or 2:1.3.

[0042] In some embodiments of this application, the organic solvent is selected from at least one of tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-MeTHF, where Me represents methyl), diethylene glycol dimethyl ether (DME), and diethylene glycol dimethyl ether (DEGDME). These solvents can stabilize the intermediates generated during lithium sulfide synthesis, thereby suppressing side reactions. Specifically, in the synthesis of lithium sulfide, taking lithium acetate as the lithium source as an example, when hexamethyldisilazane reacts with lithium acetate, the generated intermediates Me3Si-SLi and Me3Si-OAc are prone to further condensation or decomposition. The lone pair electrons of polar solvents (such as THF) react with Li... + Coordination forms a stable solvated shell (e.g., [Li(THF)4]). + ), to prevent Li + With siloxane anions (Me3Si-O) - The two compounds directly combine to form a gel-like substance. Ether solvents (such as DME) form weak hydrogen bonds (CH···O) with silane groups (Me3Si-) through 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.

[0043] In some embodiments of this application, the organic solvent includes a first solvent and a second solvent, wherein 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. By employing a mixed solvent of the first and second solvents, the combined use of the first and second solvents can further stabilize the intermediates generated during the lithium sulfide synthesis process, thereby further suppressing the occurrence of side reactions during lithium sulfide synthesis.

[0044] In some embodiments of this application, the organic solvent is selected from tetrahydrofuran and ethylene glycol dimethyl ether, or from 2-methyltetrahydrofuran and diethylene glycol dimethyl ether. When either of the above two combinations of organic solvents is used, the synergistic effect of lithium salt selection with either of the above combinations can greatly reduce the probability of by-product formation, which is beneficial to further improving the purity of lithium sulfide.

[0045] 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 the mixed solvent in this embodiment is as follows: During the reaction of hexamethyldisilazane with lithium acetate, the intermediates Me3Si-SLi and Me3Si-OAc generated in the reaction are prone to condensation or decomposition, which may produce ions such as Li + and Me3Si-O - The silane group (Me3Si-). The lone pair of electrons of THF in the reaction system will react with Li. + Coordination forms a stable solvated shell (e.g., [Li(THF)4]). + ), to prevent Li + With Me3Si-O - They directly combine to form a gel-like substance. Furthermore, DME forms weak hydrogen bonds (CH···O) with silane groups (Me3Si-) through oxygen atoms, thereby inhibiting the self-condensation reaction of Me3Si-OAc.

[0046] In some embodiments of this 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 larger proportion, due to its higher dielectric constant, excessive polarization can lead to side reactions; if the second solvent accounts for a larger proportion, due to its lower dielectric constant, it can reduce the chemical reaction rate during lithium sulfide synthesis. Therefore, by setting the mass ratio of the first solvent to the second solvent within the above range, it is possible to increase the chemical reaction rate during lithium sulfide synthesis while avoiding side reactions.

[0047] In some embodiments of this application, in the method for preparing lithium sulfide, the reaction of hexamethyldisiloxane with a weakly basic 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.

[0048] It is understandable that the S-Si bond (bond energy 310 kJ / mol) in hexamethyldisilazane will randomly break under high temperature (above room temperature) or strong alkaline conditions, generating siloxanes and forming a gel-like polymer. In this application, taking the reaction of hexamethyldisilazane with lithium acetate as an example, in the above embodiments, by dividing the synthesis of lithium sulfide into two reaction stages, in the first stage reaction, under a low temperature environment of -20℃ to 0℃, compared to a high temperature environment (above room temperature) or strong alkaline conditions, the breaking rate constant (k) of the S-Si bond in hexamethyldisilazane decreases by 10%. 3 This allows for controlled S-Si bond breaking, preventing excessive breakage. Furthermore, intermediates generated during the reaction (e.g., Me3Si-OAc) are prone to polymerization at high temperatures. In this embodiment, the first-stage reaction is conducted at a low temperature of -20°C to 0°C, which inhibits intermediate polymerization and reduces byproduct formation, thereby further improving the purity of lithium sulfide. In the second-stage reaction, a room temperature environment of 20°C to 25°C promotes the growth of lithium sulfide crystals, facilitating the formation of lithium sulfide with good crystal morphology, thus resulting in lithium sulfide with excellent morphology.

[0049] In some specific embodiments, the temperature of the first stage reaction is -20℃, -15℃, -10℃, -5℃, or 0℃, or can be any range of the above values; the temperature of the second stage reaction is 20℃, 21℃, 22℃, 23℃, 24℃, or 25℃, or can be any range of the above values.

[0050] In some embodiments of this application, in the method for preparing lithium sulfide, the reaction between hexamethyldisilazane and a weakly basic lithium salt is carried out in one reaction stage at a temperature of -20°C to 25°C. By carrying out the reaction between hexamethyldisilazane and the weakly basic lithium salt in this single reaction stage, the process can be simplified and the process cost reduced. In some specific embodiments, the temperature of the above 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 any range of the above values.

[0051] In some embodiments of this 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. It is understood that in the synthesis of lithium sulfide, the reaction time determines whether the reaction is complete. The first stage reaction is a low-temperature reaction (reaction temperature -20℃ to 0℃), which avoids vigorous reaction leading to the formation of byproducts. The second stage reaction is a room-temperature reaction (reaction temperature 20℃ to 25℃), which ensures complete reaction and promotes the growth of lithium sulfide crystals.

[0052] In some embodiments of this application, the method for preparing lithium sulfide includes the following steps:

[0053] At room temperature, the weakly basic lithium salt and the organic solvent are mixed in an inert gas atmosphere to obtain a mixture, which is then stirred and cooled to -20°C to 0°C.

[0054] The hexamethyldisilazane was added to the mixture, and the first stage reaction was carried out at a reaction temperature of -20°C to 0°C.

[0055] The second stage reaction was carried out at a reaction temperature of 20℃~25℃. After the reaction was completed, crude lithium sulfide was obtained; and

[0056] The crude lithium sulfide was dried and calcined to obtain lithium sulfide.

[0057] In some embodiments of this application, the first stage reaction specifically includes: slowly adding hexamethyldisiloxane dropwise to the mixture of the weakly basic lithium salt and the organic solvent, with the temperature of the dropwise addition process controlled at -20°C to 0°C for the reaction; the second stage reaction specifically includes: after the dropwise addition of hexamethyldisiloxane in the first stage reaction is completed, raising the temperature to 20°C to 25°C for a constant temperature reaction.

[0058] In some embodiments of this application, after the second-stage reaction is completed, the solvent and byproducts in the reaction system are removed by vacuum distillation to obtain crude lithium sulfide.

[0059] In some embodiments of this application, after obtaining crude lithium sulfide, the drying conditions for drying the crude lithium sulfide are as follows: drying temperature is 50℃~100℃, drying vacuum degree is -0.08 MPa~-0.1 MPa, and drying time is 1 h~3 h.

[0060] In some specific embodiments, the drying temperature is 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, or 100℃, or any range of the above values. In some specific embodiments, the drying vacuum degree is -0.08 MPa, -0.085 MPa, -0.09 MPa, -0.095 MPa, or -0.1 MPa, or any range of the above values. In some specific embodiments, the drying time is 1 h, 1.5 h, 2 h, 2.5 h, or 3 h, or any range of the above values.

[0061] In some embodiments of this application, after obtaining crude lithium sulfide, the calcination conditions for calcining the crude lithium sulfide are as follows: calcination temperature is 400℃~800℃, and calcination time is 1 h~5 h.

[0062] In some specific embodiments, the calcination temperature is 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, or 800℃, or can be any range 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 any range of the above values.

[0063] This application also provides a lithium sulfide, which is prepared by the lithium sulfide preparation method described in any of the foregoing embodiments.

[0064] The preparation method of lithium sulfide provided in this application will be described in detail below with reference to specific embodiments.

[0065] Example 1

[0066] The method for preparing lithium sulfide provided in Example 1 includes the following steps (1) to (5).

[0067] Step (1) At room temperature, add 2 mol lithium acetate, 300 g tetrahydrofuran, and 100 g ethylene glycol dimethyl ether to a dry reaction vessel under an argon atmosphere, and stir to cool to -10℃.

[0068] Step (2) Control the temperature to -10℃ and slowly add 1.1 mol of hexamethyldisiloxane for about 3 hours.

[0069] After step (3) is completed, heat to 25℃ and keep the temperature for 2 hours.

[0070] After the reaction in step (4) is completed, the solvent, byproduct trimethylsiloxane and unreacted hexamethyldisiloxane are removed by vacuum distillation to obtain crude lithium sulfide.

[0071] Step (5) The crude lithium sulfide was calcined 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%.

[0072] Examples 2 to 20, Comparative Examples 1 to 3

[0073] The preparation methods of lithium sulfide provided in Examples 2 to 20 and Comparative Examples 1 to 3 are basically the same as those in the examples, with the differences shown in Table 1. In Table 1, the molar content of lithium salt in the reactants of Examples 1 to 20 and Comparative Examples 1 to 3 is the same, which is 2 mol, and the sulfur source is hexamethyldisilazane in all examples; Examples 9-10 and Comparative Examples 1-3 all use a single solvent; Example 18 is carried out in a single reaction stage at a reaction temperature of -10°C.

[0074] Table 1

[0075]

[0076] Furthermore, this application determined the purity and yield of lithium sulfide prepared in Examples 1 to 20 and Comparative Examples 1 to 3, and the results are shown in Table 2.

[0077] Table 2

[0078]

[0079] By comparing Examples 1-20 with Comparative Examples 1-3, it can be seen that in the lithium sulfide preparation method of Examples 1-20 of this application, when hexamethyldisiloxane is used as the sulfur source and a weakly basic 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 (such as lithium hydroxide, lithium chloride, lithium fluoride, etc.) of Comparative Examples 1-3.

[0080] As can be seen from Examples 1 and 11-17, when other reaction conditions are the same, within the range of a molar ratio of hexamethyldisiloxane to lithium salt greater than 2:1 and less than or equal to 2:1.3, Examples 1 and 11-15 can improve the purity and yield of lithium sulfide compared to Examples 16-17. Furthermore, when the molar ratio of hexamethyldisiloxane to lithium salt is 2:1.1, the purity and yield of lithium sulfide reach the optimal values.

[0081] As can be seen from Examples 1-20, when other reaction conditions are the same, compared with the single solvent (THF or DME) used in Examples 9-10, 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. Furthermore, as can be seen from Examples 1 and Examples 5-8, when other reaction conditions are the same, using a mixed solvent of the first and second solvents, within a mass ratio of (2:1) to (4:1) between the first and second solvents, the purity and yield of lithium sulfide can be further improved. For example, compared with Examples 7-8, the purity and yield of lithium sulfide prepared in Examples 1 and Examples 5-6 are significantly improved. Further, within a mass ratio of (2:1) to (4:1) between the first and second solvents, when other reaction conditions are the same, the purity and yield of lithium sulfide reach their optimal values ​​when the mass ratio of the first and second solvents is 3:1, as in Example 1.

[0082] As can be seen from Examples 1 and 18, when other reaction conditions are the same, the two-stage reaction used in Example 1 significantly improves the purity and yield of lithium sulfide compared to the single-stage reaction in Example 18. Furthermore, as can be seen from Examples 1-17 and 19-20, when using the two-stage reaction, with the first stage reaction temperature at -20°C to 0°C and the second stage reaction temperature at 20°C to 25°C, lithium sulfide exhibits relatively high purity and yield. Further, as can be seen from Examples 1 and 11-12, when the first stage reaction temperature is -10°C and the second stage reaction temperature is 25°C, the purity and yield of lithium sulfide reach their optimal values, as in Example 1.

[0083] In the description of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying 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, "multiple" means two or more, unless otherwise explicitly specified.

[0084] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0085] The embodiments, implementation methods, and related technical features of this application can be combined and substituted for each other without conflict.

[0086] The above are merely preferred embodiments of this application and are not intended to limit this application in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

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

5. The organic solvent includes a first solvent and a second solvent, wherein 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; the mass ratio of the first solvent and the second solvent is (2:1) to (4:1). The reaction between hexamethyldisiloxane and the weakly basic lithium salt includes a first stage reaction and a second stage reaction. The temperature of the first stage reaction is -20℃ to 0℃, and the temperature of the second stage reaction is 20℃ to 25℃.

2. The method for preparing lithium sulfide according to claim 1, characterized in that, The weakly basic 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, 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.

4. The method for preparing lithium sulfide according to claim 1, characterized in that, The molar ratio of the hexamethyldisiloxane to the weakly basic lithium salt is greater than 2:1 and less than or equal to 2:1.

3.

5. The method for preparing lithium sulfide according to claim 1, characterized in that, Includes the following steps: At room temperature, the weakly basic lithium salt and the organic solvent are mixed in an inert gas atmosphere to obtain a mixture, which is then stirred and cooled to -20°C to 0°C. The hexamethyldisilazane was added to the mixture, and the first stage reaction was carried out at a reaction temperature of -20°C to 0°C. The second stage reaction was carried out at a reaction temperature of 20℃~25℃. After the reaction was completed, crude lithium sulfide was obtained. as well as The crude lithium sulfide was dried and calcined to obtain lithium sulfide.

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

7. The method for preparing lithium sulfide according to claim 5, 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℃~100℃, drying vacuum degree is -0.08 MPa~-0.1 MPa, and drying time is 1 h~3 h.

8. The method for preparing lithium sulfide according to claim 5, characterized in that, 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℃~800℃, and calcination time is 1 h~5 h.

9. A lithium sulfide, characterized in that, It is prepared by the method for preparing lithium sulfide according to any one of claims 1 to 8.

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