Preparation method of lithium sulfide

Abstract

The invention provides a preparation method of lithium sulfide, which is low in cost, simple in process and high in product purity. The preparation method comprises the following steps: S10, drying lithium hydride; s20, in an inert atmosphere, adding the dried lithium hydride into a heating closed reaction kettle, stirring the lithium hydride, and heating the lithium hydride to a target reaction temperature at the same time; s30, keeping stirring the lithium hydride at the target reaction temperature, injecting hydrogen sulfide gas into the heating closed reaction kettle for multiple times, closing the heating closed reaction kettle after each time of injection of the hydrogen sulfide gas, monitoring the pressure in the heating closed reaction kettle in real time, and stopping heating after the pressure in the heating closed reaction kettle stops increasing; all gases in the heating closed reaction kettle are pumped out in a vacuum pumping mode, hydrogen sulfide gas is continuously injected into the heating closed reaction kettle for the next time after gas is pumped out every time until the total gas amount of hydrogen sulfide injected into the heating closed reaction kettle reaches the target total gas amount, and a lithium sulfide product is obtained.

Description

Technical Field

[0001] This application relates to the field of lithium sulfide preparation technology, and in particular to a method for preparing lithium sulfide. Background Technology

[0002] All-solid-state batteries based on sulfide electrolytes hold promise for achieving a balance between high safety and high specific energy, representing a significant direction for next-generation battery technology. Lithium sulfide, as a key raw material for synthesizing sulfide electrolytes, has attracted widespread attention. The low-cost preparation of high-purity lithium sulfide is crucial for the large-scale application of all-solid-state batteries.

[0003] Currently, various processes for producing lithium sulfide have been reported, but these processes suffer from the following problems: First, they generally require high-temperature and high-pressure processes, resulting in high energy consumption, high requirements for operating condition control, high production costs, and difficulty in scaling up production. Second, current lithium sulfide preparation processes involve complex separation and purification, leading to low production efficiency and difficulty in mass production. Third, current lithium sulfide preparation processes generate impurities and water during the reaction process, affecting the quality and purity of lithium sulfide.

[0004] Therefore, a new method for preparing lithium sulfide is urgently needed. Summary of the Invention

[0005] To address the problems of high energy consumption due to high temperature and pressure, complex separation and purification processes, low production efficiency, and low purity of initial products containing many impurities and moisture in current lithium sulfide preparation processes, this application provides a method for preparing lithium sulfide, comprising:

[0006] S10: Vacuum-dried lithium hydride;

[0007] S20: Under an inert atmosphere, the dried lithium hydride is added to a heated and sealed reaction vessel, and the lithium hydride is stirred while being heated to the target reaction temperature.

[0008] S30: At the target reaction temperature, keep the lithium hydride stirred and repeatedly inject hydrogen sulfide gas into the heated sealed reactor. After each injection of hydrogen sulfide gas, seal the heated sealed reactor and monitor the pressure inside the reactor in real time. When the pressure inside the heated sealed reactor stops increasing, extract all the gas from the heated sealed reactor using a vacuum pump. After each extraction, continue injecting hydrogen sulfide gas into the heated sealed reactor until the total amount of hydrogen sulfide gas injected into the heated sealed reactor reaches the target total amount, thus obtaining the lithium sulfide product.

[0009] Each extraction includes hydrogen gas. The target total gas volume is greater than or equal to the amount of hydrogen sulfide gas required for the complete reaction of lithium hydride to ensure that the lithium hydride reacts completely with the hydrogen sulfide gas. The target reaction temperature is 170℃~250℃.

[0010] In some optional embodiments of this application, the target reaction temperature is 190°C to 230°C.

[0011] In some optional embodiments of this application, the stirrer speed is 300 rpm to 1000 rpm during the stirring process.

[0012] In some optional embodiments of this application, the rotational speed is 400 rpm to 800 rpm.

[0013] In some optional embodiments of this application, in step S10, lithium hydride is dried by vacuum drying, with a vacuum drying temperature of 60°C to 120°C and a vacuum drying time of 6h to 12h.

[0014] In some optional embodiments of this application, in step S30, 1.4L to 2.2L of hydrogen sulfide gas at room temperature and pressure is injected for each gram of lithium hydride.

[0015] In some optional embodiments of this application, step S30 further includes: under an inert atmosphere and with the temperature inside the heated sealed reactor reduced to room temperature, removing the lithium sulfide product obtained from the reaction from the heated sealed reactor and crushing it to obtain lithium sulfide powder.

[0016] In some optional embodiments of this application, the lithium sulfide product has a lithium sulfide purity greater than or equal to 99.9%.

[0017] In some optional embodiments of this application, in step S30, the amount of hydrogen sulfide gas injected into the heated sealed reactor is the same each time.

[0018] In some optional embodiments of this application, the heated sealed reactor is equipped with a pressure sensor for detecting the gas pressure inside the heated sealed reactor.

[0019] Beneficial effects:

[0020] This application provides a method for preparing lithium sulfide. The reaction temperature required in the preparation process is below 500℃, resulting in low energy consumption, simple operating conditions, and low production costs suitable for large-scale production. This application employs a one-step gas-solid reaction method to prepare lithium sulfide. The preparation process does not involve solvents and eliminates the need for complex separation and purification processes, resulting in high-efficiency production suitable for batch production. The lithium sulfide preparation method of this application allows for the complete reaction of lithium hydride in the reaction vessel by repeatedly adding hydrogen sulfide gas combined with stirring the solid reactants, producing high-purity lithium sulfide in one step. The product consists of clean hydrogen gas in addition to solid lithium sulfide, without producing other solid impurities or water. Attached Figure Description

[0021] Figure 1These are the XRD characterization spectra of the lithium sulfide products and lithium sulfide standards obtained in Examples 1 to 3 of this application;

[0022] Figure 2 This is the XRD characterization spectrum of the lithium sulfide product obtained in Comparative Example 1 of this application;

[0023] Figure 3 This is the XRD characterization spectrum of the lithium sulfide product obtained in Comparative Example 2 of this application. Detailed Implementation

[0024] This application provides a method for preparing lithium sulfide, comprising:

[0025] S10: Dry lithium hydride;

[0026] S20: Under an inert atmosphere, the dried lithium hydride is added to a heated and sealed reaction vessel, and the lithium hydride is stirred while being heated to the target reaction temperature.

[0027] S30: At the target reaction temperature, keep the lithium hydride stirred and repeatedly inject hydrogen sulfide gas into the heated sealed reactor. After each injection of hydrogen sulfide gas, seal the heated sealed reactor and monitor the pressure inside the reactor in real time. When the pressure inside the heated sealed reactor stops increasing, extract all the gas from the heated sealed reactor using a vacuum pump. After each extraction, continue injecting hydrogen sulfide gas into the heated sealed reactor until the total amount of hydrogen sulfide gas injected into the heated sealed reactor reaches the target total amount, thus obtaining the lithium sulfide product.

[0028] Each extraction includes hydrogen gas. The target total gas volume is greater than or equal to the amount of hydrogen sulfide gas required for the complete reaction of lithium hydride to ensure that the lithium hydride reacts completely with the hydrogen sulfide gas. The target reaction temperature is 170℃~250℃.

[0029] This application provides a method for preparing lithium sulfide. The reaction temperature required in the preparation process is below 500℃, resulting in low energy consumption, simple operating conditions, and low production costs suitable for large-scale production. This application employs a one-step gas-solid reaction method to prepare lithium sulfide. The preparation process does not involve solvents and eliminates the need for complex separation and purification processes, resulting in high-efficiency production suitable for batch production. The lithium sulfide preparation method of this application allows for the complete reaction of lithium hydride in the reaction vessel by repeatedly adding hydrogen sulfide gas combined with stirring the solid reactants, producing high-purity lithium sulfide in one step. The product consists of clean hydrogen gas in addition to solid lithium sulfide, without producing other solid impurities or water.

[0030] The reaction equations involved in the preparation method of lithium sulfide in this application are as follows:

[0031] 2LiH + H2S → Li2S + 2H2 (Equation 1)

[0032] As can be seen from the reaction equation, this is a solid-gas reaction, ultimately producing solid lithium sulfide and gaseous hydrogen. The entire preparation process involves a single reaction formula, and the products are a single solid and gas phase, eliminating the need for complex subsequent separation and purification steps. High-purity hydrogen sulfide can be obtained, and relatively pure hydrogen can also be collected and utilized during the reaction. The reaction equation shows that one mole of hydrogen sulfide gas corresponds to two moles of hydrogen gas. That is, in a closed reaction environment, the reaction in Equation 1 allows the ambient pressure to gradually increase. Once the lithium hydride reacts completely, no further replenishment of hydrogen sulfide gas is needed, hydrogen is no longer produced, and the pressure in the reaction environment no longer increases.

[0033] In some optional embodiments of this application, the target reaction temperature is 190°C to 230°C.

[0034] In some embodiments, the target reaction temperature is 170°C, 180°C, 190°C, 200°C, 210°C, 220°C, or 230°C.

[0035] In some optional embodiments of this application, the stirrer speed is 300 rpm to 1000 rpm during the stirring process.

[0036] In some optional embodiments of this application, the rotational speed is 400 rpm to 800 rpm.

[0037] In some embodiments, the rotational speed is 400 rpm, 500 rpm, 600 rpm, 700 rpm, or 800 rpm.

[0038] In some optional embodiments of this application, in step S10, the vacuum drying temperature is 60°C to 120°C, and the vacuum drying time is 6h to 12h.

[0039] In some optional embodiments of this application, in step S30, 1.4L to 2.2L of hydrogen sulfide gas at room temperature and pressure is injected for each gram of lithium hydride.

[0040] In some optional embodiments of this application, step S30 further includes: under an inert atmosphere and with the temperature inside the heated sealed reactor reduced to room temperature, removing the lithium sulfide product obtained from the reaction from the heated sealed reactor and crushing it to obtain lithium sulfide powder.

[0041] In some optional embodiments of this application, the lithium sulfide product has a lithium sulfide purity greater than or equal to 99.9%.

[0042] In some optional embodiments of this application, in step S30, the amount of hydrogen sulfide gas injected into the heated sealed reactor is the same each time.

[0043] In some optional embodiments of this application, the heated sealed reactor is equipped with a pressure sensor for detecting the gas pressure inside the heated sealed reactor. [Specific Implementation Examples]

[0045] The following specific embodiments and comparative examples illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0046] I. Modification of sulfide solid electrolytes in examples and comparative cases:

[0047]

Example 1

[0048] S10: Vacuum-dried lithium hydride, specifically, 25g of lithium hydride (LiH) powder is placed in a vacuum drying oven and then vacuum-dried at 100°C for 10 hours;

[0049] S20: Under an inert atmosphere, 25g of dried lithium hydride (LiH) is added to a 2L heated sealed reactor. While stirring the lithium hydride, the lithium hydride is heated to the target reaction temperature of 210°C. The heated sealed reactor is equipped with a turbine stirrer and a pressure sensor. The stirring speed in step S20 is 600 rpm.

[0050] S30: At the target reaction temperature of 210°C, lithium hydride is stirred at a speed of 600 rpm, and hydrogen sulfide gas is injected into the heated sealed reactor multiple times. After each injection of 2L of hydrogen sulfide gas, the heated sealed reactor is sealed and the pressure inside the reactor is monitored in real time. When the pressure inside the heated sealed reactor stops increasing, all the gas in the heated sealed reactor is extracted by vacuum pumping. The extracted gas includes the gaseous reaction product hydrogen. After each extraction of hydrogen gas, the next injection of 2L of hydrogen sulfide gas into the heated sealed reactor is carried out until the total amount of hydrogen sulfide gas injected into the heated sealed reactor reaches the target total amount of gas, and lithium sulfide product is obtained. In Example 1, the process of injecting 2L of hydrogen sulfide gas and extracting all the gas from the heated sealed reactor after the pressure inside the heated sealed reactor stops increasing (i.e., stops increasing) is repeated 20 times.

[0051] After completing 20 cycles of injecting and evacuating hydrogen sulfide gas, the lithium sulfide product was removed from the reactor under an inert atmosphere after the temperature in the heated sealed reactor dropped to room temperature. The product was then crushed and refined to obtain lithium sulfide powder.

[0052]

Example 2

[0053] S10: Vacuum-dried lithium hydride, specifically, 25g of lithium hydride (LiH) powder is placed in a vacuum drying oven and then vacuum-dried at 100°C for 10 hours;

[0054] S20: Under an inert atmosphere, 25g of dried lithium hydride (LiH) is added to a 2L heated sealed reactor. While stirring the lithium hydride, the lithium hydride is heated to the target reaction temperature of 190°C. The heated sealed reactor is equipped with a turbine stirrer and a pressure sensor. The stirring speed in step S20 is 800 rpm.

[0055] S30: At the target reaction temperature of 190°C, lithium hydride is stirred at 800 rpm, and hydrogen sulfide gas is injected into the heated sealed reactor multiple times. After each injection of 2L of hydrogen sulfide gas, the heated sealed reactor is sealed and the pressure inside the reactor is monitored in real time. When the pressure inside the heated sealed reactor stops increasing, all the gas in the heated sealed reactor is extracted by vacuum pumping. The extracted gas includes the gaseous reaction product hydrogen. After each extraction of hydrogen gas, the next injection of 2L of hydrogen sulfide gas into the heated sealed reactor is carried out until the total amount of hydrogen sulfide gas injected into the heated sealed reactor reaches the target total amount of gas, and lithium sulfide product is obtained. In Example 2, the process of injecting 2L of hydrogen sulfide gas is repeated 20 times and all the gas is extracted from the heated sealed reactor after the pressure inside the heated sealed reactor stops increasing (i.e., stops increasing).

[0056] After completing 20 cycles of injecting and evacuating hydrogen sulfide gas, the lithium sulfide product was removed from the reactor under an inert atmosphere after the temperature in the heated sealed reactor dropped to room temperature. The product was then crushed and refined to obtain lithium sulfide powder.

[0057]

Example 3

[0058] S10: Vacuum-dried lithium hydride, specifically, 25g of lithium hydride (LiH) powder is placed in a vacuum drying oven and then vacuum-dried at 100°C for 10 hours;

[0059] S20: Under an inert atmosphere, 25g of dried lithium hydride (LiH) is added to a 2L heated sealed reactor. While stirring the lithium hydride, the lithium hydride is heated to the target reaction temperature of 230°C. The heated sealed reactor is equipped with a turbine stirrer and a pressure sensor. The stirring speed in step S20 is 400 rpm.

[0060] S30: At the target reaction temperature of 230°C, lithium hydride is stirred at a speed of 400 rpm, and hydrogen sulfide gas is injected into the heated sealed reactor multiple times. After each injection of 2L of hydrogen sulfide gas, the heated sealed reactor is sealed and the pressure inside the reactor is monitored in real time. When the pressure inside the heated sealed reactor stops increasing, all the gas in the heated sealed reactor is extracted by vacuum pumping. The extracted gas includes the gaseous reaction product hydrogen. After each extraction of hydrogen gas, the next injection of 2L of hydrogen sulfide gas into the heated sealed reactor is carried out until the total amount of hydrogen sulfide gas injected into the heated sealed reactor reaches the target total amount of gas, and lithium sulfide product is obtained. In Example 3, the process of injecting 2L of hydrogen sulfide gas is repeated 20 times and all the gas is extracted from the heated sealed reactor after the pressure inside the heated sealed reactor stops increasing (i.e., stops increasing).

[0061] After completing 20 cycles of injecting and evacuating hydrogen sulfide gas, the lithium sulfide product was removed from the reactor under an inert atmosphere after the temperature in the heated sealed reactor dropped to room temperature. The product was then crushed and refined to obtain lithium sulfide powder.

[0062] Comparative Example 1

[0063] S10: Vacuum-dried lithium hydride, specifically, 25g of lithium hydride (LiH) powder is placed in a vacuum drying oven and then vacuum-dried at 100°C for 10 hours;

[0064] S20: Under an inert atmosphere, 25g of dried lithium hydride (LiH) is added to a 2L heated sealed reactor. While stirring the lithium hydride, the lithium hydride is heated to the target reaction temperature of 210°C. The heated sealed reactor is equipped with a turbine stirrer and a pressure sensor. The stirring speed in step S20 is 600 rpm.

[0065] S30: At the target reaction temperature of 210℃, lithium hydride is stirred at a speed of 600 rpm, and hydrogen sulfide gas is injected into the heated sealed reactor multiple times. After each injection of 2L of hydrogen sulfide gas, the heated sealed reactor is sealed and the pressure inside the reactor is monitored in real time. When the pressure inside the heated sealed reactor stops increasing, all the gas in the heated sealed reactor is extracted by vacuum pumping. The extracted gas includes the gaseous reaction product hydrogen. After each extraction of hydrogen gas, the next injection of 2L of hydrogen sulfide gas into the heated sealed reactor is carried out until the total amount of hydrogen sulfide gas injected into the heated sealed reactor reaches the target total amount of gas, and lithium sulfide product is obtained. In Comparative Example 1, the process of injecting 2L of hydrogen sulfide gas is repeated 17 times and all the gas is extracted from the heated sealed reactor after the pressure inside the heated sealed reactor stops increasing (i.e., stops increasing).

[0066] After completing 17 cycles of injecting hydrogen sulfide gas and then evacuating it, once the temperature in the heated sealed reactor has dropped to room temperature, the lithium sulfide product is removed from the reactor under an inert atmosphere and then crushed and refined to obtain lithium sulfide powder.

[0067] Comparative Example 2

[0068] S10: Vacuum-dried lithium hydride, specifically, 25g of lithium hydride (LiH) powder is placed in a vacuum drying oven and then vacuum-dried at 100°C for 10 hours;

[0069] S20: Under an inert atmosphere, 25g of dried lithium hydride (LiH) is added to a 2L heated sealed reactor. While stirring the lithium hydride, the lithium hydride is heated to the target reaction temperature of 100°C. The heated sealed reactor is equipped with a turbine stirrer and a pressure sensor. The stirring speed in step S20 is 600 rpm.

[0070] S30: At the target reaction temperature of 100℃, lithium hydride is stirred at a speed of 600 rpm, and hydrogen sulfide gas is injected into the heated sealed reactor multiple times. After each injection of 2L of hydrogen sulfide gas, the heated sealed reactor is sealed and the pressure inside the reactor is monitored in real time. When the pressure inside the heated sealed reactor stops increasing, all the gas in the heated sealed reactor is extracted by vacuum pumping. The extracted gas includes the gaseous reaction product hydrogen. After each extraction of hydrogen gas, the process of injecting 2L of hydrogen sulfide gas into the heated sealed reactor continues until the total amount of hydrogen sulfide gas injected into the heated sealed reactor reaches the target total amount of gas, and lithium sulfide product is obtained. In Comparative Example 2, the process of injecting 2L of hydrogen sulfide gas is repeated 20 times until the pressure inside the heated sealed reactor stops increasing (i.e., stops increasing) and then all the gas is extracted from the heated sealed reactor.

[0071] After completing 20 cycles of injecting and evacuating hydrogen sulfide gas, the lithium sulfide product was removed from the reactor under an inert atmosphere after the temperature in the heated sealed reactor dropped to room temperature. The product was then crushed and refined to obtain lithium sulfide powder.

[0072] II. Test methods and equipment:

[0073] 1. XRD characterization methods and equipment

[0074] Under an inert atmosphere, the sample was placed on the XRD sample stage, protected with a polyimide film, and the phase structure of the material was characterized by X-ray diffraction (XRD, D8 Advance, Bruker). The diffraction angle range was 10°-80°, and the scanning speed was 5°min.

[0075] 2. Lithium sulfide purity test

[0076] After lithium sulfide was digested in an acidic solution, the impurity elements of lithium sulfide were tested by inductively coupled plasma optical emission spectrometry (ICP-OES, iCAP PRO DUO, Thermo Scientific), and the purity of lithium sulfide was analyzed by combining the XRD test results.

[0077] Table 1. Electrolyte ionic conductivity in the examples and comparative examples.

[0078]

[0079] From the data in Table 1 and Figures 1 to 3 The following conclusions can be drawn:

[0080] Figure 1 As can be seen from the XRD spectra of the lithium sulfide products and lithium sulfide standards in Examples 1 to 3, Figure 1 In summary, all three examples synthesized high-purity (purity greater than 99.9%) lithium sulfide.

[0081] Figure 2 As can be seen from the XRD pattern of the lithium sulfide product in Comparative Example 1, in addition to the characteristic peaks of lithium sulfide, characteristic peaks of lithium hydride also appeared. Example 1 and Comparative Example 1 were identical in all reaction conditions except for the amount of hydrogen sulfide gas injected. The reason for the presence of lithium hydride characteristic peaks in Comparative Example 1 is that, during the preparation of lithium sulfide, the total amount of hydrogen sulfide injected into the heated and sealed reactor was insufficient, resulting in incomplete reaction of lithium hydride and the presence of lithium hydride (LiH) impurity phase in the synthesized lithium sulfide (Li₂S). The purity of lithium sulfide in the lithium sulfide product of Comparative Example 1 was lower than that in Examples 1 to 3.

[0082] The reaction conditions for Comparative Example 2 and Example 1 were identical except for the reaction temperature. Figure 3 As can be seen, due to the low reaction temperature, some lithium hydride did not react completely, and the resulting lithium sulfide product also contained the LiHS impurity phase. The purity of lithium sulfide in the lithium sulfide product of Comparative Example 2 was further reduced compared to Comparative Example 1, and was much lower than the purity of lithium sulfide in Examples 1 to 3. This indicates that the reaction temperature in the examples of this application was below 150°C, and the gas-solid reaction was not complete.

[0083] In Examples 1 to 3, the lithium sulfide product of Example 1 had the highest lithium sulfide purity, indicating that higher reaction temperature and higher rotation speed can result in the highest lithium sulfide purity in the produced lithium sulfide product. Conversely, lithium sulfide obtained with high rotation speed and lower reaction temperature, or low rotation speed and higher reaction temperature, also had high purity, but lower than the lithium sulfide purity of Example 1.

[0084] This invention uses a strong reducing agent LiH and a weak acid H2S reaction. This reaction is exothermic and has high reactivity. It can achieve a rapid and efficient gas-solid reaction within a temperature range of 170℃-250℃, without the need for high temperature and high pressure processes. This results in low energy consumption and simple operating conditions, which greatly reduces the production cost of lithium sulfide.

[0085] It should be noted that, in this document, "comprising," "including," or any other variation thereof is intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0086] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0087] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the scope of protection of this application.

Claims

1. A method for preparing lithium sulfide, characterized in that, include: S10: Dry lithium hydride; S20: Under an inert atmosphere, the dried lithium hydride is added to a heated and sealed reaction vessel, and the lithium hydride is stirred while being heated to the target reaction temperature. S30: At the target reaction temperature, lithium hydride is stirred continuously, and hydrogen sulfide gas is injected multiple times into the heated sealed reactor. After each injection of hydrogen sulfide gas, the heated sealed reactor is sealed, and the pressure inside the reactor is monitored in real time. When the pressure inside the heated sealed reactor stops increasing, all gas in the heated sealed reactor is extracted by vacuum pumping. After each extraction, hydrogen sulfide gas is injected into the heated sealed reactor again until the total amount of hydrogen sulfide gas injected into the heated sealed reactor reaches the target total amount, thus obtaining the lithium sulfide product. The gas extracted each time includes hydrogen gas. The target total gas volume is greater than or equal to the amount of hydrogen sulfide gas required for the complete reaction of the lithium hydride to ensure that the lithium hydride reacts completely with the hydrogen sulfide gas. The target reaction temperature is 170℃~250℃.

2. The method for preparing lithium sulfide according to claim 1, characterized in that, The target reaction temperature is 190℃~230℃.

3. The method for preparing lithium sulfide according to claim 1, characterized in that, During the mixing process, the stirring speed is 300 rpm to 1000 rpm, preferably 400 rpm to 800 rpm.

4. The method for preparing lithium sulfide according to claim 1, characterized in that, In step S10, lithium hydride is dried by vacuum drying at a temperature of 60°C to 120°C for a duration of 6 to 12 hours.

5. The method for preparing lithium sulfide according to claim 1, characterized in that, In step S30, each gram of lithium hydride corresponds to the injection of 1.4L to 2.2L of hydrogen sulfide gas at room temperature and pressure.

6. The method for preparing lithium sulfide according to claim 1, characterized in that, Step S30 further includes: under an inert atmosphere and with the temperature inside the heated sealed reactor reduced to room temperature, removing the lithium sulfide product obtained from the reaction from the heated sealed reactor and crushing it to obtain lithium sulfide powder.

7. The method for preparing lithium sulfide according to claim 1, characterized in that, The lithium sulfide product has a lithium sulfide purity greater than or equal to 99.9%.

8. The method for preparing lithium sulfide according to claim 1, characterized in that, In step S30, the amount of hydrogen sulfide gas injected into the heated sealed reactor is the same each time.

9. The method for preparing lithium sulfide according to claim 1, characterized in that, The heated sealed reactor is equipped with a pressure sensor for detecting the gas pressure inside the reactor.

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