A method for preparing lithium sulfide

Abstract

The present invention provides a method for preparing lithium sulfide, the method comprising the following steps: (1) preparing lithium nitride by reacting cheap nitrogen with metallic lithium in the presence of an inert atmosphere or under vacuum conditions, and controlling the residual amount of metallic lithium in the lithium nitride to be within a preset safety threshold; (2) mixing the lithium nitride obtained in step (1) with elemental sulfur in a certain proportion to react and obtain lithium sulfide. The present invention adopts a two-step method to prepare lithium sulfide, which has the following advantages: 1. The two-step method avoids the danger of explosion caused by violent reaction by directly mixing metallic lithium and elemental sulfur using a high-temperature melting method, and safety is guaranteed; 2. Lithium nitride is prepared using cheap nitrogen, which can be mass-produced and all processes do not require high-temperature treatment, with low energy consumption and obvious low-cost advantages; 3. In the preparation process of lithium sulfide, nitrogen is released, hydrogen is not used, and no dangerous gases such as hydrogen sulfide are generated, which is green, safe and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic material synthesis and preparation, and relates to a method for preparing lithium sulfide, and specifically to a method for preparing lithium sulfide powder with low cost, low energy consumption and large-scale production. Background Art

[0002] In recent years, new energy technologies are developing rapidly. Among them, all-solid-state batteries with higher energy density and better safety have attracted the attention and investment of both academia and industry. The core of all-solid-state batteries is solid electrolyte materials, among which sulfide solid electrolytes are considered to be the most likely solid electrolyte materials for industrialization due to their high room temperature conductivity and strong processability. Therefore, they are vigorously developed by companies represented by Toyota and Solid Power.

[0003] The key raw material for synthesizing sulfide solid electrolytes is lithium sulfide. At present, the main production methods of lithium sulfide include high-temperature reduction of lithium sulfate, liquid-phase sol-gel distillation, molten metal lithium and sulfur methods, etc. On the one hand, these technologies require high temperatures, high energy consumption, and low purity of reaction products; on the other hand, lithium sulfide itself is sensitive to moisture, and the control of reaction conditions and moisture during the liquid-phase preparation process is very strict, and the remaining liquid from the reaction pollutes the environment; the preparation of lithium sulfide by the melting method has a violent reaction, is prone to explosion, and has great safety hazards. It is precisely because of the constraints of preparation technology that the price of lithium sulfide remains high. The price of lithium sulfide accounts for about 1 / 3 of the preparation cost of sulfide solid electrolytes, which greatly limits the large-scale industrial application of sulfide materials.

[0004] Based on the above points, it is necessary to develop low-cost, low-energy consumption technology for large-scale preparation of lithium sulfide. Summary of the invention

[0005] In view of the problems existing in the mainstream technology for synthesizing lithium sulfide, the present invention provides a method for preparing lithium sulfide on a large scale with low cost and low energy consumption, which solves the problems of high energy consumption, high cost and potential safety hazards in the mainstream technology for synthesizing lithium sulfide.

[0006] To achieve this object, the present invention adopts the following technical solutions:

[0007] In a first aspect, the present invention provides a method for preparing lithium sulfide, the method comprising the following steps:

[0008] (1) reacting metallic lithium with nitrogen gas in the presence of an inert atmosphere or under vacuum conditions to prepare lithium nitride, and controlling the residual amount of metallic lithium in the lithium nitride to be within a preset safety threshold range;

[0009] (2) The lithium nitride obtained in step (1) is mixed with elemental sulfur to react to obtain lithium sulfide.

[0010] As a preferred embodiment of the present invention, the metallic lithium in step (1) comprises any one of lithium block, lithium sheet, lithium foil, lithium strip or lithium powder, or a combination of at least two thereof.

[0011] As a preferred embodiment of the present invention, the inert atmosphere in step (1) comprises any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

[0012] As a preferred embodiment of the present invention, the vacuum degree under the vacuum conditions in step (1) is ≤0.1 Pa.

[0013] As a preferred embodiment of the present invention, the molar ratio of nitrogen to metallic lithium in step (1) is 3:20-1:6.

[0014] As a preferred embodiment of the present invention, the reaction time in step (1) is 6-48 hours.

[0015] As a preferred embodiment of the present invention, in the reaction process of step (1), the water content is controlled to be ≤0.1 ppm and the oxygen content is controlled to be ≤0.1 ppm.

[0016] As a preferred embodiment of the present invention, the safety threshold range described in step (1) is that the residual amount of metallic lithium in lithium nitride is in the range of 0-10wt%.

[0017] As a preferred embodiment of the present invention, after lithium nitride is prepared in step (1), the process further includes mechanically crushing the lithium nitride.

[0018] As a preferred embodiment of the present invention, the mechanical pulverization is ball milling pulverization.

[0019] As a preferred embodiment of the present invention, the mechanical pulverization is carried out in the presence of an inert atmosphere and / or in a sealed environment.

[0020] As a preferred embodiment of the present invention, the inert atmosphere includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

[0021] As a preferred embodiment of the present invention, the ball milling speed in the ball milling is 100-550 rpm, and the ball milling time is 1-24 hours, preferably 4-8 hours.

[0022] As a preferred embodiment of the present invention, the molar ratio of lithium nitride to elemental sulfur in step (2) is 2:3.

[0023] As a preferred embodiment of the present invention, the mixing in step (2) is mechanical mixing, including any one of ball milling mixing, gas mixing or mechanical shaking, or a combination of at least two of them.

[0024] As a preferred embodiment of the present invention, the mixing in step (2) is carried out in the presence of an inert atmosphere and / or under vacuum conditions.

[0025] As a preferred embodiment of the present invention, the inert atmosphere includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

[0026] As a preferred embodiment of the present invention, the vacuum degree under the vacuum conditions is ≤0.1 Pa.

[0027] As a preferred embodiment of the present invention, when the mixing is ball milling mixing, the ball milling speed is 100-550 rpm, the ball-to-material ratio is 50:1-5:1, and the ball milling time is 1-24 h.

[0028] As a preferred embodiment of the present invention, the particle size of the ball milling balls used in the ball milling is 4-30 mm.

[0029] As a preferred embodiment of the present invention, step (2) also includes a process of crushing the obtained lithium sulfide to prepare lithium sulfide powder.

[0030] As a preferred embodiment of the present invention, the crushing is carried out in the presence of an inert atmosphere, and the inert atmosphere includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

[0031] As a preferred embodiment of the present invention, the crushing includes any one of manual grinding, mechanical ball milling or air flow crushing, or a combination of at least two of them.

[0032] As a preferred embodiment of the present invention, the crushing is followed by sieving to obtain powder with a particle size D50 of 1-50 μm.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The method of the present invention does not use a high-temperature treatment process, has lower energy consumption, and does not use a high-temperature melting process, thereby avoiding the danger of explosion caused by violent reactions;

[0035] (2) The present invention uses metallic lithium and nitrogen as raw materials to synthesize lithium nitride, which is low-cost and pollution-free. In the presence of an inert atmosphere or under vacuum conditions, nitrogen is introduced into a closed space containing metallic lithium. The reaction is easy to control and has a large output. It is suitable for large-scale preparation of cheap lithium nitride, which has a significant cost advantage over the existing market price of high-purity lithium nitride (about RMB 30,000 / kg). In addition, the lithium nitride prepared by the method described in the present invention has a lower purity requirement, which further reduces the preparation cost.

[0036] (3) The present invention regulates the amount of nitrogen used, the pressure and the reaction time in the synthesis process of lithium nitride, and thus makes the residual amount of metallic lithium in the prepared lithium nitride within a preset safety threshold range. In the subsequent process of mixing with elemental sulfur to prepare lithium sulfide, the residual lithium in the lithium nitride of 0-10wt% reacts with the elemental sulfur at a faster rate, releases heat, and accelerates the reaction of lithium nitride and elemental sulfur, so that the synthesis rate of lithium sulfide in the overall process is faster; and because there is ≤10wt% metallic lithium in the lithium nitride, the metallic lithium reacts quickly with the elemental sulfur, only releasing heat without generating gas. Under the same conditions, the amount of nitrogen released by the reaction of lithium nitride and elemental sulfur is reduced (less than 10% N2 is generated), thereby reducing the gas pressure in the reaction space, so that the pressure in the reaction space during the reaction of lithium nitride and elemental sulfur is controlled within a safe range of <0.01 MPa, thereby eliminating the risk of explosion and increasing the safety of the reaction.

[0037] (4) The method of the present invention does not produce any toxic gas during the whole process, is green and environmentally friendly, and can prepare dozens of kilograms of high-purity lithium sulfide powder at a time, which can be used for large-scale industrial production. At the same time, the method of the present invention does not use hydrogen and does not release hydrogen sulfide gas, so there is no danger of explosion, poisoning, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the XRD pattern of the lithium nitride powder prepared in Example 1 of the present invention;

[0039] Figure 2 This is a SEM image of the lithium nitride powder prepared in Example 1 of the present invention;

[0040] Figure 3 This is the XRD pattern of the lithium sulfide powder prepared in Example 1 of the present invention;

[0041] Figure 4 This is a SEM image of the lithium sulfide powder prepared in Example 1 of the present invention. Implementation

[0042] In order to better illustrate the present invention and facilitate understanding of the technical solution of the present invention, the present invention is further described in detail below. However, the following embodiments are only simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0043] The specific implementation of the present invention provides a method for preparing lithium sulfide, which comprises the following steps:

[0044] (1) reacting metallic lithium with nitrogen gas in the presence of an inert atmosphere or under vacuum conditions to prepare lithium nitride, and controlling the residual amount of metallic lithium in the lithium nitride to be within a preset safety threshold range;

[0045] (2) The lithium nitride obtained in step (1) is mixed with elemental sulfur to react to obtain lithium sulfide.

[0046] The raw materials used for synthesizing lithium nitride in the present invention are metallic lithium and nitrogen. The obtained lithium nitride is reacted with sulfur powder to generate lithium sulfide again while releasing nitrogen. The specifically designed reactions are:

[0047] 3Li+N2——2Li3N

[0048] 2Li3N+3S——3Li2S+N2

[0049] The method of the present invention first uses metallic lithium and nitrogen as raw materials to synthesize lithium nitride, which is low-cost and pollution-free. In the presence of an inert atmosphere or under vacuum conditions, nitrogen is introduced into a closed space containing metallic lithium, and the reaction is easy to control and has a large output, which is suitable for large-scale preparation of cheap lithium nitride. At the same time, the method of the present invention can control the desired content of metallic lithium in the prepared lithium nitride.

[0050] The residual amount of metallic lithium in the lithium nitride prepared by the method described in the present invention is regulated within a preset safety threshold range. During the subsequent mechanical mixing of lithium nitride and elemental sulfur, the heat generated can enable a small amount of residual metallic lithium to react completely with the elemental sulfur, which will not affect the yield and quality of lithium sulfide, and can reduce the subsequent release of nitrogen, further reducing the pressure in the reaction space under the same conditions, so that the pressure in the reaction space is controlled within a safe range of <0.01 MPa, thereby eliminating the risk of explosion and increasing safety.

[0051] The lithium nitride prepared by the present invention is reacted with sulfur powder in the presence of an inert atmosphere and / or under vacuum conditions to directly prepare lithium sulfide. All processes of the present invention are not subjected to high-temperature treatment, and the energy consumption is low. The lithium nitride is synthesized by direct reaction of metallic lithium with cheap nitrogen, which has a huge cost advantage, and lithium sulfide can be produced on a large scale, with an obvious low-cost advantage; and no toxic and harmful gases such as hydrogen sulfide are generated during the preparation process, which is green, safe and environmentally friendly.

[0052] As a preferred embodiment of the present invention, the metallic lithium in step (1) comprises any one of a lithium block, a lithium sheet, a lithium foil, a lithium strip or a lithium powder, or a combination of at least two of them. Typical but non-limiting examples of the combination include: a combination of a lithium block and a lithium sheet, a combination of a lithium sheet and a lithium foil, a combination of a lithium strip and a lithium powder, a combination of a lithium block, a lithium sheet and a lithium foil, a combination of a lithium foil, a lithium strip and a lithium powder, etc.

[0053] In the present invention, when the metallic lithium is lithium powder, the particle size thereof is ≤100 μm.

[0054] As a preferred embodiment of the present invention, the inert atmosphere in step (1) comprises one or any one or a combination of at least two of helium, neon, argon, krypton or xenon.

[0055] As a preferred embodiment of the present invention, the vacuum degree under the vacuum conditions in step (1) is ≤0.1 Pa, such as 0.1 Pa, 0.08 Pa, 0.06 Pa or 0.04 Pa, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] As a preferred embodiment of the present invention, the molar ratio of nitrogen to metallic lithium in step (1) is 3:20-1:6, i.e., 9 / 60-10 / 60, specifically 9 / 60, 9.2 / 60, 9.4 / 60, 9.6 / 60, 9.8 / 60, 10 / 60, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0057] As a preferred embodiment of the present invention, the reaction time in step (1) is 6-48 h, for example, 6 h, 8 h, 10 h, 14 h, 16 h, 18 h, 20 h, 24 h, 26 h, 28 h, 30 h, 34 h, 36 h, 38 h, 40 h, 44 h, 46 h or 48 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0058] The present invention regulates the amount of nitrogen used, the pressure and the reaction time in the lithium nitride synthesis process, and thus the residual amount of metallic lithium in the prepared lithium nitride is within a preset safety threshold range.

[0059] As a preferred embodiment of the present invention, in the reaction process of step (1), the water content is controlled to be ≤0.1 ppm and the oxygen content is controlled to be ≤0.1 ppm.

[0060] As a preferred embodiment of the present invention, the safety threshold range described in step (1) is 0-10wt% of the metallic lithium content in lithium nitride, such as 10wt%, 8wt%, 6wt%, 4wt%, 2wt% or 1wt%, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0061] In the present invention, the residual amount of metallic lithium in the prepared lithium nitride is controlled within a preset safety threshold range (0-10wt%). If the residual amount of metallic lithium is too high, the purity of the lithium sulfide will be reduced when it is subsequently mechanically mixed with elemental sulfur to prepare lithium sulfide. At the same time, if the residual amount of metallic lithium is too high, it will react violently with elemental sulfur during high-speed ball milling to release a large amount of heat, causing excessive air pressure inside the ball mill, which is dangerous.

[0062] As a preferred embodiment of the present invention, after lithium nitride is prepared in step (1), the process further includes mechanically crushing the lithium nitride.

[0063] As a preferred embodiment of the present invention, the mechanical pulverization is ball milling pulverization.

[0064] As a preferred solution of the present invention, the ball milling is carried out in the presence of an inert atmosphere and / or in a sealed environment.

[0065] As a preferred solution of the present invention, the inert atmosphere includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

[0066] As a preferred embodiment of the present invention, the ball milling speed in the ball milling is 100-550 rpm, for example, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm or 550 rpm, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the ball milling time is 1-24h, for example, 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, etc., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable, preferably 4-8h.

[0067] As a preferred embodiment of the present invention, the molar ratio of lithium nitride to elemental sulfur in step (2) is 2:3.

[0068] As a preferred embodiment of the present invention, the mixing in step (2) is mechanical mixing, including any one of ball milling mixing, gas mixing or mechanical shaking, or a combination of at least two thereof.

[0069] As a preferred embodiment of the present invention, the mixing in step (2) is carried out in the presence of an inert atmosphere and / or under vacuum conditions.

[0070] As a preferred solution of the present invention, the inert atmosphere includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

[0071] As a preferred solution of the present invention, the vacuum degree under the vacuum conditions is ≤0.1 Pa, such as 0.1Pa, 0.08Pa, 0.06Pa or 0.04Pa, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0072] As a preferred embodiment of the present invention, when the mixing is ball milling mixing, the ball milling speed is 100-550rpm, for example, 100rpm, 150rpm, 200rpm, 250rpm, 300rpm, 350rpm, 400rpm, 450rpm, 500rpm or 550rpm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable; the ball-to-material ratio is 50:1-5:1, for example, 50:1, 40:1, 30:1, 20:1, 10:1 or 5:1, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable; the ball milling time is 1-24h, for example, 1h, 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h or 24h, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are equally applicable.

[0073] As a preferred embodiment of the present invention, the particle size of the ball milling balls used in the ball mill is 4-30 mm, for example, 4 mm, 6 mm, 8 mm, 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, 20 mm, 22 mm, 24 mm, 26 mm, 28 mm or 30 mm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0074] As a preferred embodiment of the present invention, step (2) also includes a process of crushing the obtained lithium sulfide to produce lithium sulfide powder.

[0075] As a preferred embodiment of the present invention, the crushing is carried out in the presence of an inert atmosphere, and the inert atmosphere includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

[0076] As a preferred solution of the present invention, the crushing includes any one of manual grinding, mechanical ball milling or air flow crushing, or a combination of at least two of them.

[0077] As a preferred embodiment of the present invention, the crushing is followed by sieving to obtain a powder with a particle size D50 of 1-50 μm, such as 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm or 50 μm, etc., but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0078] Furthermore, the preparation method of the present invention comprises:

[0079] (1) reacting metallic lithium with nitrogen in the presence of an inert atmosphere or under vacuum conditions to prepare lithium nitride, controlling the molar ratio of nitrogen to metallic lithium to be 3:20-1:6, reacting for 6-48 hours, controlling the water content to be ≤0.1ppm and the oxygen content to be ≤0.1ppm during the reaction, and thereby controlling the residual amount of metallic lithium in the lithium nitride to be 0-10wt%;

[0080] (2) The lithium nitride obtained in step (1) is mixed with elemental sulfur in a molar ratio of 2:3 and mixed in the presence of an inert atmosphere and / or under vacuum conditions to react to obtain lithium sulfide.

[0081] The following are typical but non-limiting embodiments of the present invention: Example

[0082] This embodiment provides a method for preparing lithium sulfide, the method comprising the following steps:

[0083] (1) Synthesis of lithium nitride: 50 g of lithium metal sheet was placed in a glove box under an argon protective atmosphere, the water and oxygen contents in the glove box were both ≤ 0.1 ppm, high-purity nitrogen (> 99.999%) was continuously introduced, and the molar ratio of nitrogen to lithium metal was > 1:6. After 12 hours of reaction, brown lithium nitride was obtained; after grinding, the obtained lithium nitride block was ground into powder, and the XRD and SEM images of the obtained lithium nitride were as follows: Figure 1 and Figure 2 As shown; the residual amount of metallic lithium in the obtained lithium nitride is ≤2wt%;

[0084] (2) Synthesis of lithium sulfide: In an inert atmosphere protected glove box, 34.83 g of lithium nitride obtained in step (1) and 48.105 g of sublimated sulfur powder were weighed in a molar ratio of 2:3, and placed in a 250 mL stainless steel ball mill with a ball-to-material ratio of 20:1. The ball mill was tightened and ball milled at 450 rpm for 6 h. After the ball milling was completed, the ball mill was opened, the product was taken out, ground, and passed through a 400 mesh sieve to obtain lithium sulfide powder, whose XRD and SEM images were shown as follows: Figure 3 and Figure 4 shown.

[0085] The yield of lithium sulfide obtained in this embodiment is >98%. Example

[0086] This embodiment provides a method for preparing lithium sulfide, the method comprising the following steps:

[0087] (1) Synthesis of lithium nitride: 100 g of lithium metal foil is placed in a reaction chamber under an argon protective atmosphere, the water and oxygen contents in the chamber are both ≤0.1 ppm, high-purity nitrogen (>99.999%) is continuously introduced, and the molar ratio of nitrogen to lithium metal is 1:6. After 18 hours of reaction, brown lithium nitride is obtained; after grinding, the obtained lithium nitride block is ground into powder, and the residual amount of lithium metal in the obtained lithium nitride is ≤1wt%;

[0088] (2) Synthesis of lithium sulfide: In a glove box protected by an inert atmosphere, 69.66 g of lithium nitride obtained in step (1) and 96.21 g of sublimated sulfur powder were weighed in a molar ratio of 2:3, and placed in a 500 mL stainless steel ball mill with a ball-to-material ratio of 25:1. The ball mill was tightened and ball milled at a speed of 500 rpm for 10 h. After the ball milling was completed, the ball mill was unscrewed, the product was taken out, ground, and passed through a 400 mesh sieve to obtain lithium sulfide powder.

[0089] The yield of lithium sulfide obtained in this embodiment is >99%. Example

[0090] This embodiment provides a method for preparing lithium sulfide, the method comprising the following steps:

[0091] (1) Synthesis of lithium nitride: 500g of lithium metal strip was laid flat in a reaction chamber under an argon protective atmosphere. The water and oxygen contents in the chamber were both ≤0.1ppm. High-purity nitrogen (>99.999%) was continuously introduced. The molar ratio of nitrogen to lithium metal was between 3:20 and 1:6. After 24h of reaction, brown lithium nitride was obtained. The residual amount of lithium metal in the obtained lithium nitride was ≤5wt%;

[0092] (2) Synthesis of lithium sulfide: In a reaction chamber protected by an inert atmosphere, 4 portions of lithium nitride obtained in step (1) and sublimed sulfur powder were weighed in a molar ratio of 2:3, each portion of 69.66 g of lithium nitride obtained in step (1) and 96.21 g of sublimed sulfur powder, and were placed in 4 500 mL stainless steel ball mills, respectively, with a ball-to-material ratio of 25:1. The ball mills were tightened and ball milled at 350 rpm for 12 h. After the ball milling was completed, the ball mill was unscrewed, the product was taken out, ground, and passed through a 400-mesh sieve to obtain lithium sulfide powder.

[0093] The yield of lithium sulfide obtained in this embodiment is >98%. Example

[0094] This embodiment provides a method for preparing lithium sulfide, the method comprising the following steps:

[0095] (1) Synthesis of lithium nitride: 10 g of lithium metal sheet was placed in a sealed can with an air valve, vacuumed, and high-purity nitrogen (>99.999%) was slowly introduced into the can through the air valve to ensure that the pressure was >0.01 MPa, and the molar ratio of nitrogen to lithium metal was 3:20. After 8 hours of reaction, brown lithium nitride was obtained, and the residual amount of lithium metal in the obtained lithium nitride was ≤10wt%;

[0096] (2) Synthesis of lithium sulfide: In a reaction chamber protected by an inert atmosphere, 3.483 g of lithium nitride obtained in step (1) and 4.8105 g of sublimated sulfur powder were weighed in a molar ratio of 2:3 and placed in a 100 mL stainless steel ball mill with a ball-to-material ratio of 15:1. The ball mill was tightened and ball milled at 350 rpm for 12 h. After the ball milling was completed, the ball mill was opened, the product was taken out, ground, and passed through a 400-mesh sieve to obtain lithium sulfide powder.

[0097] The yield of lithium sulfide obtained in this embodiment is >97%. Example

[0098] This embodiment provides a method for preparing lithium sulfide, the method comprising the following steps:

[0099] (1) Synthesis of lithium nitride: 10 g of lithium metal sheet was placed in a sealed can with an air valve, vacuumed, and high-purity nitrogen (>99.999%) was slowly introduced into the can through the air valve to ensure that the pressure was >0.01 MPa, and the molar ratio of nitrogen to lithium metal was between 3:20 and 1:6. After 8 hours of reaction, brown lithium nitride was obtained, and the residual amount of lithium metal in the obtained lithium nitride was ≤3wt%;

[0100] (2) Synthesis of lithium sulfide: In a reaction chamber protected by an inert atmosphere, 3.483 g of lithium nitride obtained in step (1) and 4.8105 g of sublimated sulfur powder were weighed in a molar ratio of 2:3 and placed in a 50 mL stainless steel metal can with a ball-to-material ratio of 5:1. The metal can was tightened and placed in a vibration device, and vibrated and mixed for 12 hours at a fixed frequency of 115 V / 60 Hz. After the vibration mixing was completed, the metal can was unscrewed, the product was taken out, ground, and passed through a 400-mesh sieve to obtain lithium sulfide powder.

[0101] The yield of lithium sulfide obtained in this embodiment is >97%.

[0102] Comparative Example 1:

[0103] This comparative example provides a method for preparing lithium sulfide, which is the same as the method in Example 1, except that the molar ratio of nitrogen to metallic lithium in step (1) is exactly 1:6, and the metallic lithium and nitrogen are not completely reacted. Because after the surface layer of the metallic lithium and the nitrogen are completely reacted, the inner layer of metallic lithium is not completely reacted, and the total residual amount of metallic lithium is greater than 15%. When it is subsequently ball-milled with elemental sulfur, a large amount of heat is generated, and the temperature of the ball mill is too high, which poses a safety hazard. In addition, there is too much metallic lithium that has not reacted completely, and the subsequently produced lithium sulfide contains obvious impurities, which affects the purity of the material.

[0104] The XRD result of the lithium sulfide finally obtained in this comparative example showed that there were obvious impurities and the purity was too low.

[0105] The applicant declares that the present invention illustrates the detailed process equipment and process flow of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed process equipment and process flow, that is, it does not mean that the present invention must rely on the above-mentioned detailed process equipment and process flow to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing lithium sulfide, characterized in that: The method comprises the following steps: (1) reacting metallic lithium with nitrogen gas in the presence of an inert atmosphere or under vacuum conditions to prepare lithium nitride, and controlling the residual amount of metallic lithium in the lithium nitride to be within a preset safety threshold range; (2) mixing the lithium nitride obtained in step (1) with elemental sulfur to react and obtain lithium sulfide; The method does not use hydrogen; The safety threshold range described in step (1) is that the residual amount of metallic lithium in lithium nitride is in the range of 0-10wt% and does not include 0.

2. The preparation method according to claim 1, characterized in that: The metallic lithium in step (1) includes any one of lithium block, lithium sheet, lithium foil, lithium strip or lithium powder, or a combination of at least two of them.

3. The preparation method according to claim 1, characterized in that: The inert atmosphere in step (1) includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

4. The preparation method according to claim 1, characterized in that: The vacuum degree under the vacuum conditions in step (1) is ≤0.1 Pa.

5. The preparation method according to claim 1, characterized in that: In step (1), the molar ratio of nitrogen to metallic lithium is 3:20-1:

6.

6. The preparation method according to claim 1, characterized in that: The reaction time in step (1) is 6-48h.

7. The preparation method according to claim 1, characterized in that: During the reaction in step (1), the water content is controlled to be ≤0.1 ppm and the oxygen content is controlled to be ≤0.1 ppm.

8. The preparation method according to claim 1, characterized in that: After lithium nitride is prepared in step (1), the process further includes mechanically crushing the lithium nitride.

9. The preparation method according to claim 8, characterized in that: The mechanical pulverization is ball milling pulverization.

10. The preparation method according to claim 8, characterized in that: The mechanical pulverization is performed in the presence of an inert atmosphere and / or in a sealed environment.

11. The preparation method according to claim 10, characterized in that: The inert atmosphere includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

12. The preparation method according to claim 9, characterized in that: The ball milling speed in the ball milling is 100-550 rpm, and the ball milling time is 1-24 h.

13. The preparation method according to claim 12, characterized in that: The ball milling time in the ball milling is 4-8h.

14. The preparation method according to claim 1, characterized in that: In step (2), the molar ratio of lithium nitride to elemental sulfur is 2:

3.

15. The preparation method according to claim 1, characterized in that: The mixing in step (2) is mechanical mixing, including any one of ball milling mixing, gas mixing or mechanical shaking, or a combination of at least two of them.

16. The preparation method according to claim 1, characterized in that: The mixing in step (2) is performed in the presence of an inert atmosphere and / or under vacuum conditions.

17. The preparation method according to claim 16, characterized in that: The inert atmosphere includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

18. The preparation method according to claim 16, characterized in that: The vacuum degree under the vacuum conditions is ≤0.1Pa.

19. The preparation method according to claim 15, characterized in that: When the mixing is ball milling mixing, the ball milling speed is 100-550 rpm, the ball-to-material ratio is 50:1-5:1, and the ball milling time is 1-24 h.

20. The preparation method according to claim 15, characterized in that: The particle size of the ball milling balls used in the ball milling is 4-30 mm.

21. The preparation method according to claim 1, characterized in that: Step (2) also includes the process of crushing the obtained lithium sulfide to prepare lithium sulfide powder.

22. The preparation method according to claim 21, characterized in that: The fragmentation is performed in the presence of an inert atmosphere, which includes any one of helium, neon, argon, krypton or xenon, or a combination of at least two of them.

23. The preparation method according to claim 21, characterized in that: The crushing includes any one of manual grinding, mechanical ball milling or air flow pulverization or a combination of at least two of them.

24. The preparation method according to claim 21, characterized in that: The crushing is followed by sieving to obtain powder with a particle size D50 of 1-50 μm.

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