A method for preparing lithium sulfide for solid electrolytes

Abstract

This invention discloses a method for preparing lithium sulfide for solid electrolytes, belonging to the field of lithium sulfide preparation technology. This invention involves the staged control of hydrogen sulfide and hydrogen gas. In the first stage, a sulfidation reaction occurs on the surface of lithium hydroxide. In the second stage, the sulfidation reaction proceeds from the surface of lithium hydroxide inwards, reducing the content of intermediate sulfidation reaction products to obtain lithium sulfide. The preparation method according to this invention reduces the densification tendency caused by excessively rapid sulfidation of the LiOH surface; increases the degree of internal conversion of LiOH to Li₂S; and reduces residual LiOH, LiHS, and other substances in the product that are detrimental to the synthesis of downstream solid electrolytes.

Description

Technical Field

[0001] This invention relates to the field of lithium sulfide preparation technology, and more specifically to a method for preparing lithium sulfide for solid electrolytes. Background Technology

[0002] Lithium sulfide (Li₂S) is one of the key raw materials in sulfide solid electrolyte systems and can be used to prepare sulfide solid electrolytes such as Li₃PS₄, LPSCl, and LGPS. The purity, residual alkaline substances, oxygen- and water-containing impurities, surface state, and particle uniformity of Li₂S directly affect the target crystal phase formation, ionic conductivity, interfacial stability, and batch consistency of the subsequent sulfide electrolyte. Existing patents have also explicitly used Li₂S as a raw material for sulfide solid electrolytes, indicating that the quality control of Li₂S has a significant impact on the performance of the subsequent solid electrolyte.

[0003] Currently, there are many methods for preparing lithium sulfide. The existing lithium sulfide preparation routes can be broadly classified into: lithium salt reduction method, direct lithium metal sulfidation method, gas-solid sulfidation method, and organic solvothermal method.

[0004] High-temperature reduction of oxygen-containing lithium salts typically uses lithium sulfate, lithium carbonate, and other oxygen-containing lithium salts as starting materials. By adding carbonaceous reducing agents, organic reducing agents, or sulfur sources, the reaction is carried out at high temperatures under inert, reducing, or vacuum conditions to ultimately obtain lithium sulfide. This route is characterized by a wide availability of raw materials and a relatively mature foundation in traditional inorganic salt processes, theoretically possessing certain scale-up potential. However, its disadvantages are also quite obvious: under high-temperature conditions, the system is prone to uneven mixing, insufficient localized reactions, or residual carbon problems; if carbonaceous reducing agents are used, subsequent product purification is more difficult, hindering the acquisition of higher purity and lower impurity lithium sulfide.

[0005] The direct sulfidation route of lithium metal uses lithium metal as the lithium source, reacting it directly with sulfur vapor, hydrogen sulfide, or other sulfur-containing reactants to produce Li₂S. The advantages of this route are a short reaction path, fewer theoretical byproducts, and potentially higher product purity. However, due to the extremely high reactivity of lithium metal, it has very stringent requirements regarding water, oxygen, and operational safety. Furthermore, the high cost of raw materials, equipment requirements, and difficulties in large-scale safety control limit its application in large-scale lithium sulfide production.

[0006] The gas-solid sulfidation route primarily uses LiOH or its hydrate as the lithium source and H2S, sulfur vapor, or a hydrogen-sulfur atmosphere as the sulfidation medium to generate Li2S through a gas-solid contact reaction. The advantages of this route are: relatively low reaction temperature, readily available lithium source, and easy coupling with equipment such as fixed-bed, fluidized-bed, moving-bed, and rotary reactors, possessing potential for continuous and large-scale production. However, this route also presents significant process challenges. The reaction of LiOH with H2S generates water; if this byproduct water is not removed promptly, it will affect the reaction equilibrium and product purity. Furthermore, a Li2S layer easily forms on the particle surface, hindering further gas diffusion into the particle interior, resulting in residual LiOH or LiHS inside. This creates a structure where the outer layer is sulfided and the inner layer is incompletely reacted, affecting the purity of Li2S. Moreover, the residual substances inside may further form oxygen-containing secondary phases such as Li2CO4 and Li2SO4 during subsequent storage or use, thus affecting powder stability. Additionally, bed structure, particle size, gas flow direction, and local sulfidation rate all significantly affect the final conversion uniformity. If Li2S is prepared according to the above preparation method, for the subsequent synthesis of sulfide solid electrolytes, if there are still unreacted lithium sources or intermediates inside Li2S, it may lead to local compositional inhomogeneity when reacting with raw materials such as P2S5 and LiCl, increasing the risk of secondary phase formation and affecting the formation of the target electrolyte phase and ionic conductivity.

[0007] The organic solvothermal method prepares lithium sulfide by reacting lithium-containing and sulfur-containing compounds in an anhydrous solvent medium, typically an organic solvent. The advantages of this method are its simplicity, controllable particle size, and low energy consumption. The disadvantages include high requirements for the anhydrous solvent system, complex process, and high costs associated with the recovery, residue management, and safety control of the organic solvent. Furthermore, the dehydration and post-treatment processes in the liquid phase become more cumbersome during scale-up. Summary of the Invention

[0008] To address the above problems, this invention provides a method for preparing lithium sulfide for solid electrolytes.

[0009] While there are many existing methods for preparing lithium sulfide, the core challenges for battery-grade Li2S lie in: how to reduce residual LiOH, LiHS, and other undesirable substances while ensuring the completeness of the reaction during preparation; how to remove byproduct water in a timely manner during sulfidation to avoid its impact on equilibrium and product quality; how to balance the surface reaction rate with the depth of internal particle conversion to avoid the formation of a structure where the outer layer is sulfided and the inner layer is not fully reacted; and how to ensure product purity while also considering the feasibility of continuous and large-scale production.

[0010] This invention reduces the densification tendency caused by excessively rapid sulfidation of LiOH surface by controlling the staged ratio of hydrogen sulfide and hydrogen; it increases the internal conversion degree of LiOH to Li2S, and reduces residual LiOH, LiHS and other substances in the product that are not conducive to the synthesis of downstream solid electrolytes; according to the method of this invention, battery-grade Li2S powder that is more suitable as a precursor for sulfide solid electrolytes is obtained, improving product purity and batch consistency.

[0011] The first objective of this invention is to provide a method for preparing lithium sulfide, comprising the following steps: Lithium hydroxide is subjected to dehydration and pre-activation treatment to obtain pre-activated lithium hydroxide.

[0012] Using hydrogen sulfide and hydrogen as a mixed gas, pre-activated lithium hydroxide undergoes a first-stage reaction at a first temperature, causing sulfidation on the surface of the lithium hydroxide. After the first-stage reaction, the temperature is raised to a second temperature for a second-stage reaction, causing sulfidation inside the lithium hydroxide to obtain lithium sulfide. During the second-stage reaction, the content of sulfidation reaction intermediates and unreacted lithium hydroxide is reduced. For example, the intermediate product is LiHS, which may originate from the staged transformation during the reaction of LiOH and H2S, ultimately yielding lithium sulfide suitable for use as a sulfide solid electrolyte. In the first-stage reaction, hydrogen sulfide accounts for 1%–20% of the volume fraction of the mixed gas; the total flow rate of the mixed gas is 250 mL / min–350 mL / min. The first temperature is 100℃–200℃.

[0013] In the second stage of the reaction, hydrogen sulfide accounts for 20%–90% of the volume fraction of the mixed gas; the total flow rate of the mixed gas is 350 mL / min–450 mL / min; and the second temperature is 350℃–500℃. The gas flow rate can be controlled by a gas flow meter.

[0014] This invention sets up two-stage atmosphere control based on the reaction characteristics and control objectives of different stages in the gas-solid reaction of LiOH and H2S to prepare lithium sulfide.

[0015] First, the first stage uses a lower H2S ratio and a higher H2 ratio, mainly to control the initial sulfidation rate of LiOH surface, avoid the rapid formation of a dense Li2S layer on the particle surface, thereby reducing the structural inhomogeneity problem of the outer layer being sulfided and the inner layer not being fully reacted, and improving the uniformity of subsequent H2S diffusion into the particle interior.

[0016] The second stage increases the H2S ratio, primarily to drive the main sulfidation reaction further into the particles, improving the overall conversion rate and reducing LiOH and LiHS residues. Simultaneously, the system is purged to continuously remove byproduct water and H2S that may be generated from LiHS desorption, thereby reducing residual intermediates and unstable sulfur-containing substances on the surface and improving product purity.

[0017] If only one stage is used, such as omitting the first stage, the initial sulfidation of the particle surface may be too rapid, increasing the internal LiOH / LiHS residue. If the second stage is omitted, the reaction process may be slow, resulting in higher levels of residual LiOH, by-product water, and LiHS, affecting product purity and surface stability. Further subdividing it into three or more stages increases the complexity of industrial control, while the marginal improvement in purity may be limited. Therefore, this invention employs a two-stage approach, primarily to achieve a balance between conversion uniformity, product purity, post-treatment effects, and industrial implementation complexity.

[0018] In this invention, the volume fraction of H2S in two stages was determined by combining the reaction characteristics of different stages in the gas-solid reaction of LiOH and H2S, as well as the requirements for product purity control.

[0019] The first stage is mainly used to control the initial sulfidation rate of LiOH surface, so a lower H2S volume fraction is preferred. If the H2S content in the first stage is too high, exceeding the above parameter range, a relatively dense Li2S layer will easily form rapidly on the particle surface, thereby hindering the subsequent diffusion of H2S into the particle interior.

[0020] The second stage primarily drives the main sulfidation process; therefore, increasing the H2S volume fraction is preferable. Increasing the H2S partial pressure in this stage enhances the driving force for H2S diffusion into the particle interior and continuous sulfidation, thereby reducing LiOH and LiHS residues. If the H2S content is too low in this stage (less than 20%), it may lead to insufficient internal conversion and increased LiOH / LiHS residues. Long-term use of pure H2S may increase tail gas treatment pressure, equipment corrosion, and the difficulty of continuous control. In the second stage, as the H2S ratio increases, the reaction rate of LiOH to Li2S increases accordingly, and the rate of by-product water generation also increases. Simultaneously, it helps to remove by-product water, residual H2S, and H2S that may be generated by LiHS desorption, thereby reducing residual intermediates and unstable sulfur-containing substances on the surface, and preventing the existence of incompletely converted areas.

[0021] In this invention, the setting of the H2S volume fraction at each stage takes into account not only the conversion law of the gas-solid reaction between LiOH and H2S, but also factors such as raw material utilization rate, tail gas treatment load, and production cost in industrial production. A balance needs to be struck between ensuring the reaction proceeds fully and reducing the amount of H2S used.

[0022] If the reaction temperature in the first or second stage is lower than the above parameter range, the overall reactivity of the system may be insufficient, and the reaction rate between LiOH and H2S will decrease significantly. In this case, the diffusion of H2S into the particle interior and the conversion of LiOH to Li2S are slower, which can easily lead to a significant extension of the reaction time and increase the residue of raw materials or intermediates such as LiOH or LiHS, thereby affecting the integrity and effective purity of Li2S conversion.

[0023] If the reaction temperature in the first or second stage exceeds the above parameter range, although the local reaction rate will be further increased, it may also bring a series of adverse effects. First, at higher temperatures, a thicker Li2S layer is more likely to form rapidly on the particle surface, thus exacerbating the structural inhomogeneity problem of the outer layer being sulfided and the inner layer not being fully reacted. Second, under high temperature conditions, sintering, agglomeration, or particle growth are more likely to occur between particles, leading to a decrease in powder dispersibility, which is not conducive to the uniform mixing and reaction of the subsequent sulfide solid electrolyte.

[0024] In a preferred embodiment of the present invention, the reaction time in the first stage reaction is 1h to 3h.

[0025] In a preferred embodiment of the present invention, the reaction time in the second stage reaction is 5h to 9h.

[0026] In a preferred embodiment of the present invention, the method for the second stage reaction is as follows: the reaction is carried out for 2 to 3 hours under the reaction conditions where the volume fraction of hydrogen sulfide in the mixed gas is 60% to 65% and the second temperature is 350°C to 400°C; then the reaction is carried out for 3 to 6 hours under the reaction conditions where the volume fraction of hydrogen sulfide in the mixed gas is 75% to 80% and the second temperature is 370°C to 450°C.

[0027] The main function of the second stage is to drive the LiOH particles from the surface inwards to continue their conversion into Li2S. Although an initial Li2S layer has formed on the particle surface after the first stage, incompletely converted LiOH or LiHS intermediates may still exist inside the particles. If the second stage is raised to a high temperature all at once and a high proportion of H2S is introduced all at once, although the reaction rate can be increased, it may also cause the surface reaction to accelerate further, which in turn increases the resistance to the gas diffusion into the interior, resulting in incomplete internal conversion.

[0028] Therefore, in the second stage, the present invention preferably employs a segmented heating and segmented increase in the H2S ratio, allowing the reaction to gradually transition from a gentle progression to full conversion. This enables H2S to diffuse more uniformly into the particle interior, reducing localized excessively rapid sulfidation and surface densification, thereby reducing LiOH / LiHS residue and improving the effective purity and conversion uniformity of Li2S.

[0029] In a preferred embodiment of the present invention, in the first stage reaction, hydrogen sulfide accounts for 5% to 10% of the volume fraction of the mixed gas.

[0030] In a preferred embodiment of the present invention, in the second stage reaction, hydrogen sulfide accounts for 60% to 80% of the volume fraction of the mixed gas.

[0031] If the H2S content is too low, the effective sulfidation driving force in the system will be insufficient, which will easily lead to incomplete conversion of LiOH to Li2S. This will result in the residue of raw materials or intermediates such as LiOH and LiHS, affecting the effective purity and conversion uniformity of Li2S. It may also cause the reaction time to be prolonged and the production efficiency to decrease.

[0032] If the H2S content is too high, although it can increase the local sulfidation rate, it will significantly increase the amount of H2S used and increase production costs. At the same time, excess unreacted H2S will enter the tail gas system, increasing the processing pressure of tail gas absorption, tail gas circulation and tail gas purification devices, increasing the risk of equipment corrosion and environmental load, which is not conducive to continuous and stable production.

[0033] Through the above methods, the present invention can improve the uniformity of Li2S conversion and product purity, while minimizing the amount of H2S used, reducing production costs, and alleviating the operating pressure of the tail gas absorption and tail gas treatment system, making it more suitable for continuous and large-scale industrial production.

[0034] In a preferred embodiment of the present invention, the pre-activation treatment method is as follows: under the action of hydrogen, in a reaction system, pre-activation treatment is carried out at 100℃~180℃ for 0.5h~3h to obtain pre-activated lithium hydroxide.

[0035] In a preferred embodiment of the present invention, the lithium hydroxide is anhydrous lithium hydroxide or lithium hydroxide monohydrate.

[0036] The lithium sulfide prepared by this invention has a purity of 90% to 99.99%. The aforementioned lithium sulfide can be used to prepare sulfide solid electrolytes, for example, by combining lithium sulfide with phosphorus pentasulfide, lithium chloride, and other raw materials to synthesize the desired sulfide solid electrolyte.

[0037] Compared with the prior art, the present invention has the following beneficial effects: This invention employs a staged, proportionally controlled method to regulate the ratio of hydrogen sulfide and hydrogen. In the first stage, with low H2S and high H2, a uniform surface nucleation layer is slowly formed. The low-speed sulfidation in this first stage prevents water from being unable to be carried away in time. In the second stage, the H2S ratio is increased, propelling the reaction inward and enhancing the internal conversion of LiOH to Li2S. Furthermore, by increasing the gas flow rate into the reaction system, the scavenging capacity is simultaneously improved, enhancing the removal of byproduct water and residual gas, and preventing byproduct water from accumulating on the particle surface or inside the bed. This reduces the adverse effects of moisture on the Li2S surface state, promotes the continued diffusion of H2S into the particle interior, and improves the conversion of LiOH to Li2S and the purity of the final product. During the reaction, the temperature is increased from a first temperature to a second temperature. The first temperature inhibits excessively rapid surface densification, while the second temperature promotes internal reaction and treats any remaining unreacted raw materials.

[0038] The preparation method of this invention is more suitable for continuous scale-up. Firstly, this invention primarily completes the sulfidation reaction through continuous gas supply, without involving the mixing and high-temperature decomposition of large amounts of solid sulfur sources, carbon sources, or thiourea, making it suitable for industrial continuous equipment such as rotary kilns or continuous tubular furnaces. The H2S / H2 ratio is easier to control, facilitating process stabilization. Secondly, this invention adjusts the H2S / H2 atmosphere composition in stages. Compared to existing technologies that rely on high-temperature drives above 500°C, the main reaction temperature of this invention is lower, which helps reduce furnace heat load, H2S high-temperature corrosion, equipment material wear, and the risks of long-term operation, making it more suitable for continuous and stable operation. Furthermore, in existing large-scale production, using pure H2S easily leads to the formation of an uneven structure with an outer Li2S layer and an inner LiOH / LiHS layer due to rapid sulfidation of the particle surface. Moreover, hydrogen sulfide is expensive, and using pure hydrogen sulfide would increase synthesis costs. This invention uses a low H2S concentration in the first stage to control the initial surface sulfidation rate, and increases the H2S ratio in the second stage to promote continued internal conversion. Therefore, it is more conducive to improving the overall conversion uniformity in large-scale beds, reducing residual LiOH and LiHS, and improving batch consistency. Furthermore, by using lower-cost hydrogen, material costs are reduced while ensuring product purity.

[0039] This invention uses lithium hydroxide (LiOH) as a raw material and obtains battery-grade Li2S powder through two stages of atmosphere control under strictly isolated water and oxygen conditions. H2 is used not only as a protective or diluting gas but also as a reaction atmosphere control component, working in conjunction with H2S to control the reaction rate, surface reaction mode, and internal particle conversion process at different stages. This suppresses excessively rapid densification of the particle surface, reduces residual LiOH, LiHS, and other intermediate or detrimental substances, and improves the purity, conversion uniformity, and batch stability of the obtained Li2S, resulting in lithium sulfide powder suitable for sulfide solid electrolyte systems. Attached Figure Description

[0040] Figure 1 The image shows the lithium sulfide product prepared in Example 4.

[0041] Figure 2 The image shows a SEM image of the lithium sulfide product prepared in Example 4.

[0042] Figure 3 This is the XRD pattern of Example 4.

[0043] Figure 4 This is the XRD plot of Comparative Example 2. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] This invention provides a method for preparing lithium sulfide for solid electrolytes based on a staged ratio control of hydrogen / hydrogen sulfide. The method uses lithium hydroxide (LiOH) as a raw material and, under strictly isolated conditions of water and oxygen, obtains battery-grade Li₂S powder through three stages of atmosphere control. H₂ is used not only as a protective or diluting gas but also as a reaction atmosphere control component, working in conjunction with H₂S to control the reaction rate, surface reaction mode, and internal particle conversion process at different stages. This suppresses excessively rapid densification of the particle surface, reduces residual LiOH, LiHS, and other intermediate or detrimental substances, and improves the purity, conversion uniformity, and batch stability of the obtained Li₂S, resulting in lithium sulfide powder suitable for sulfide solid electrolyte systems.

[0046] 1. Raw material preparation: Lithium hydroxide is used as the lithium source, which can be anhydrous lithium hydroxide (LiOH) or lithium hydroxide monohydrate (LiOH·H2O), preferably anhydrous lithium hydroxide. The lithium source is placed in a vacuum drying oven and dried at 120°C for 6 hours to remove free water and surface adsorbed water from the raw material.

[0047] 2. Pretreatment: The entire reaction system is purged to remove oxygen and water vapor from the air. The purging gas can be nitrogen, argon, hydrogen, or a combination thereof, preferably an inert gas. The purpose of this step is primarily to further remove weakly bound water from the surface of the raw materials, while simultaneously ensuring a uniform temperature distribution.

[0048] 3. Pre-activation treatment: At 100℃~180℃, preferably 130℃~150℃, pre-activation is performed by introducing hydrogen or a hydrogen-based mixture for 0.5~3 hours. A very low proportion of H2S may be included if necessary, but a low H2S content is preferred to avoid excessively rapid sulfidation of the lithium source surface during this stage.

[0049] 4. First-stage reaction: After pre-activation, a first-stage H2S / H2 mixture (H2S volume fraction: 1–20 vol%, preferably 5%–10%) is introduced into the reactor to induce an initial sulfidation reaction on the surface of the lithium source particles. The purpose of this stage is not to complete the entire conversion at once, but to control the surface reaction rate using a lower H2S content, forming a relatively uniform initial Li2S layer on the particle surface. This avoids the rapid formation of an excessively thick and dense layer on the surface, which would hinder subsequent gas diffusion into the particle interior. The reaction temperature is 100–200℃, preferably 160–180℃.

[0050] 5. Second-stage reaction: Increasing the proportion of H2S in the gas mixture utilizes a higher sulfidation reaction driving force to propel the reaction front from the particle surface inwards, thereby improving the overall conversion rate and reducing unreacted lithium source residue. This also reduces the content of residual LiOH, LiHS, and other surface-labile substances, improving surface uniformity and product stability. Temperature: 350–500℃, preferably 350–450℃. H2S volume fraction: 20–90 vol%, preferably 60%–80%.

[0051] 6. Post-processing: The reactor is cooled under nitrogen or argon atmosphere. Once the temperature drops to room temperature, battery-grade Li₂S is obtained.

[0052] The preparation method of lithium sulfide for solid electrolyte of the present invention will be described in detail below through specific embodiments.

[0053] Example 1 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 4.80g of anhydrous lithium hydroxide (LiOH) and place it in a vacuum drying oven. Dry it at 120℃ for 6 hours to remove free water and surface-adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0054] 2. The dried LiOH is loaded into a tube furnace and the reactor is pre-activated under a hydrogen atmosphere and kept at 140°C for 1 hour.

[0055] 3. Proceed to the first stage of initial surface vulcanization reaction. Maintain the reaction temperature at 160℃, introduce an H2S / H2 mixture with a volume fraction of 5 vol% for H2S and 95 vol% for H2, control the total flow rate at 300 mL / min, and allow the reaction time to be 2 hours.

[0056] 4. Proceed to the second stage of deep conversion reaction. Raise the reactor temperature directly to 370℃, switch the reaction atmosphere to an H2S / H2 mixture, with H2S volume fraction of 60 vol% and H2 volume fraction of 40 vol%, and control the total flow rate at 350 mL / min. React under these conditions for 5 hours.

[0057] 5. After the reaction is complete, stop the H2S / H2 supply, cool down under nitrogen protection, and obtain Li2S powder sample.

[0058] Example 2 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 8.39 g of lithium hydroxide monohydrate (LiOH·H2O), place it in a vacuum drying oven, and dry it at 120℃ for 6 hours to remove free water and surface adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0059] 2. The dried LiOH is loaded into a tube furnace and the reactor is pre-activated under a hydrogen atmosphere and kept at 150°C for 2 hours.

[0060] 3. Enter the first stage of initial surface curing. Maintain the reaction temperature at 160℃, introduce a mixture of H2S / H2 gas, wherein the volume fraction of H2S is 8 vol% and the volume fraction of H2 is 92 vol%, the total flow rate is controlled at 300 mL / min, and the reaction time is 1 h.

[0061] 4. Proceed to the second stage of deep conversion reaction. Raise the reaction temperature to 350℃, switch the atmosphere to an H2S / H2 mixture, with H2S volume fraction of 75 vol% and H2 volume fraction of 25 vol%, and control the total flow rate at 350 mL / min. React under these conditions for 5 hours.

[0062] 5. After the reaction is complete, stop the H2S / H2 supply, cool down under nitrogen protection, and obtain Li2S powder sample.

[0063] Example 3 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 4.80g of anhydrous lithium hydroxide (LiOH) and place it in a vacuum drying oven. Dry it at 120℃ for 6 hours to remove free water and surface-adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0064] 2. The dried LiOH is loaded into a tube furnace and the reactor is pre-activated under a hydrogen atmosphere and kept at 130°C for 1 hour.

[0065] 3. Enter the first stage of initial surface vulcanization. Raise the reaction temperature to 150℃, introduce a mixture of H2S / H2 gas, wherein the volume fraction of H2S is 3 vol%, the volume fraction of H2 is 97 vol%, the total flow rate is 300 mL / min, and the reaction is carried out for 1 hour.

[0066] 4. Proceed to the second stage of deep conversion reaction. First, maintain the reaction temperature at 350℃, adjust the mixed gas composition to H2S 60 vol%, H2 40 vol%, and the total flow rate to 350 mL / min, and react for 2 hours. Then, raise the reaction temperature to 370℃, adjust the mixed gas composition to H2S 75 vol%, H2 25 vol%, and the total flow rate to 350 mL / min, and continue the reaction for 3 hours.

[0067] 5. After the reaction is complete, stop the H2S / H2 supply, cool down under nitrogen protection, and obtain Li2S powder sample.

[0068] Example 4 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 4.80g of anhydrous lithium hydroxide (LiOH) and place it in a vacuum drying oven. Dry it at 120℃ for 6 hours to remove free water and surface-adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0069] 2. The dried LiOH is loaded into a tube furnace and the reactor is pre-activated under a hydrogen atmosphere and kept at 150°C for 1.5 hours.

[0070] 3. Enter the first stage of initial surface curing. Maintain 170℃, introduce H2S / H2 mixed gas, where H2S is 10 vol% and H2 is 90 vol%, with a total flow rate of 350 mL / min, and react for 1.5 h.

[0071] 4. Proceed to the second stage of the deep conversion reaction. Heat to 400℃, introduce an H2S / H2 mixture (65 vol% H2, 35 vol% H2, total flow rate 400 mL / min), and react for 2 hours. Then heat to 450℃, introduce an H2S / H2 mixture (80 vol% H2, 20 vol% H2, total flow rate 450 mL / min), and react for 3 hours.

[0072] 5. After the reaction is complete, stop the supply of H2S / H2, and cool down under the protection of an inert gas (such as argon or nitrogen) to obtain a Li2S powder sample with a purity of 99.99%.

[0073] Example 5 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 8.39 g of lithium hydroxide monohydrate (LiOH·H2O), place it in a vacuum drying oven, and dry it at 120℃ for 6 hours to remove free water and surface adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0074] 2. The dried LiOH is loaded into a tube furnace and the reactor is pre-activated under a hydrogen atmosphere and kept at 100°C for 3 hours.

[0075] 3. Enter the first stage of initial surface curing. Maintain the reaction temperature at 200℃, introduce a mixture of H2S / H2 gas, wherein the volume fraction of H2S is 1 vol% and the volume fraction of H2 is 99 vol%, the total flow rate is controlled at 310 mL / min, and the reaction time is 2 h.

[0076] 4. Proceed to the second stage of deep conversion reaction. Raise the reaction temperature to 350℃, switch the atmosphere to an H2S / H2 mixture, with H2S volume fraction of 20 vol% and H2 volume fraction of 80 vol%, and control the total flow rate at 340 mL / min. React under these conditions for 9 hours.

[0077] 5. After the reaction is complete, stop the H2S / H2 supply, cool down under nitrogen protection, and obtain Li2S powder sample.

[0078] Example 6 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 8.39 g of lithium hydroxide monohydrate (LiOH·H2O), place it in a vacuum drying oven, and dry it at 120℃ for 6 hours to remove free water and surface adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0079] 2. The dried LiOH is loaded into a tube furnace and the reactor is pre-activated under a hydrogen atmosphere and kept at 180°C for 0.5 h.

[0080] 3. Enter the first stage of initial surface vulcanization. Maintain the reaction temperature at 100℃, introduce H2S / H2 mixed gas, wherein the volume fraction of H2S is 20 vol%, the volume fraction of H2 is 80 vol%, the total flow rate is controlled at 290 mL / min, and the reaction time is 3 h.

[0081] 4. Proceed to the second stage of deep conversion reaction. Raise the reaction temperature to 500℃, switch the atmosphere to an H2S / H2 mixture, where the volume fraction of H2S is 90 vol% and the volume fraction of H2 is 10 vol%, and control the total flow rate at 370 mL / min. React under these conditions for 6 hours.

[0082] 5. After the reaction is complete, stop the H2S / H2 supply, cool down under nitrogen protection, and obtain Li2S powder sample.

[0083] Example 7 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 4.80g of anhydrous lithium hydroxide (LiOH) and place it in a vacuum drying oven. Dry it at 120℃ for 6 hours to remove free water and surface-adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0084] 2. The dried LiOH is loaded into a tube furnace and the reactor is pre-activated under a hydrogen atmosphere and kept at 150°C for 1.5 hours.

[0085] 3. Enter the first stage of initial surface curing. Maintain 170℃, introduce H2S / H2 mixed gas, where H2S is 10 vol% and H2 is 90 vol%, with a total flow rate of 250 mL / min, and react for 1.5 h.

[0086] 4. Proceed to the second stage of the deep conversion reaction. Heat to 370℃, introduce an H2S / H2 mixture (62 vol% H2, 38 vol% H2, total flow rate 400 mL / min), and react for 2.5 h. Then heat to 380℃, introduce an H2S / H2 mixture (78 vol% H2, 22 vol% H2, total flow rate 450 mL / min), and react for 6 h.

[0087] 5. After the reaction is complete, stop the H2S / H2 supply, cool down under nitrogen protection, and obtain Li2S powder sample. Comparative Example 1 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 4.80g of anhydrous lithium hydroxide (LiOH) and place it in a vacuum drying oven. Dry it at 120℃ for 6 hours to remove free water and surface-adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0088] 2. The dried LiOH was loaded into a tube furnace and, after being replaced with hydrogen, a fixed H2S / H2 mixture was directly introduced at 350°C, wherein H2S was 30 vol% and H2 was 70 vol%, and the total flow rate was 300 mL / min. The reaction was carried out continuously for 6 hours.

[0089] 3. After the reaction was completed, the H2S / H2 supply was stopped, and the temperature was lowered under nitrogen protection to obtain Li2S powder sample with a purity of 78.3%.

[0090] Comparative Example 2 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 4.80g of anhydrous lithium hydroxide (LiOH) and place it in a vacuum drying oven. Dry it at 120℃ for 6 hours to remove free water and surface-adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0091] 2. The dried LiOH was loaded into a tube furnace, and after being replaced with hydrogen, a high concentration of H2S atmosphere was directly introduced at 350℃ to carry out the reaction. The volume fraction of H2S was 90 vol%, and the remainder was hydrogen. The total flow rate was 300 mL / min, and the reaction was carried out continuously for 6 hours.

[0092] 3. After the reaction is complete, stop the H2S / H2 supply, cool down under nitrogen protection, and obtain Li2S powder sample.

[0093] Comparative Example 3 A method for preparing lithium sulfide for solid electrolytes includes the following steps: 1. Weigh 4.80g of anhydrous lithium hydroxide (LiOH) and place it in a vacuum drying oven. Dry it at 120℃ for 6 hours to remove free water and surface-adsorbed water from the raw material. After drying, transfer the raw material to a glove box for later use.

[0094] 2. The dried LiOH is loaded into a tube furnace and the reactor is pre-activated under a hydrogen atmosphere and kept at 140°C for 1 hour.

[0095] 3. Proceed to the first stage of initial surface vulcanization reaction. Maintain the reaction temperature at 160℃, introduce a mixture of H2S / H2 gas, wherein the volume fraction of H2S is 5 vol% and the volume fraction of H2 is 95 vol%, the total flow rate is controlled at 300 mL / min, and the reaction time is 2 h.

[0096] 4. Proceed to the second stage of deep conversion reaction. Raise the reactor temperature to 370℃, switch the reaction atmosphere to an H2S / H2 mixture, with H2S volume fraction of 30 vol% and H2 volume fraction of 70 vol%, and control the total flow rate at 350 mL / min. React under these conditions for 5 hours.

[0097] 5. After the reaction is complete, stop the supply of H2S / H2, cool down under nitrogen protection, and obtain Li2S powder sample with a product purity of 89.1%.

[0098] Figure 1 The image shows the lithium sulfide product prepared in Example 4. The generated powder is pure white.

[0099] Figure 2 The image shows a SEM image of the lithium sulfide prepared in Example 4. SEM is mainly used to observe the microstructure, particle agglomeration state, and particle uniformity of the obtained Li2S powder. The SEM shows that the sample particles have relatively clear boundaries, fewer hard agglomerates, and no obvious sintering necks or large dense agglomerates. This indicates that the staged H2S / H2 atmosphere control in this application is beneficial to reducing particle adhesion caused by high-temperature sintering, rapid surface sulfidation, and retention of by-product water, thereby improving powder dispersibility and particle size distribution uniformity.

[0100] Figure 3 The XRD pattern of lithium sulfide in Example 4 is shown. XRD characterization analysis of the obtained lithium sulfide sample revealed that the positions of the main diffraction peaks were essentially consistent with the characteristic peak positions in the Li₂S standard card, indicating that the main crystalline phase of the obtained product was lithium sulfide. Simultaneously, no obvious characteristic diffraction peaks corresponding to LiOH, Li₂CO₃, Li₂SO₄, or other impurities were observed within the detection range, indicating that no obvious crystalline impurity phases were detected in the sample. These results demonstrate that the staged H₂S / H₂ reaction atmosphere control method employed in this application can promote the complete conversion of LiOH to Li₂S and helps reduce unreacted lithium sources and byproduct residues, thereby obtaining lithium sulfide products with high crystalline purity.

[0101] Table 1. Purity of different lithium sulfides As shown in Table 1, the lithium sulfide prepared by this invention has high purity, indicating that the purity of the lithium sulfide prepared by this invention is high. The purity of Examples 1 to 4 all reach over 98%, with Example 4 reaching 99.99%, significantly higher than the comparative example. This demonstrates that the preparation method of this invention can effectively promote the complete conversion of raw materials to lithium sulfide, reduce unreacted raw materials and by-product residues, thereby improving the purity of the lithium sulfide product. In contrast, the comparative example, due to unreasonable reaction conditions, atmosphere control, or process parameters, resulted in insufficient sulfidation, leading to more impurities in the product and a significant decrease in purity. Therefore, this invention demonstrates a significant advantage in improving the purity of lithium sulfide.

[0102] The purity of lithium sulfide prepared in Comparative Example 1 was 78.3%, mainly because the H2S concentration was low and there were unreacted LiOH raw materials, which led to a decrease in purity.

[0103] The lithium sulfide prepared in Comparative Example 2 had a purity of 97.6%, corresponding to Figure 4 The XRD pattern of the lithium sulfide sample prepared in Comparative Example 2 shows that the main diffraction peak positions are basically consistent with those of the Li₂S standard card, indicating that the main phase of the product is lithium sulfide. However, an additional diffraction peak appears near 2θ≈32°, suggesting that a small amount of crystalline impurity phase or surface byproducts may exist in the lithium sulfide prepared in Comparative Example 2. This impurity peak may originate from incompletely converted lithium source, intermediate residues, or an oxygen-containing lithium salt secondary phase formed after the lithium sulfide prepared in Comparative Example 2 comes into contact with trace amounts of water and oxygen during the preparation process.

[0104] The product obtained in Comparative Example 3 has a lower purity. This is because although Comparative Example 3 also adopted a staged reaction, the H2S content in the second stage was low, resulting in insufficient diffusion of H2S into the particle interior. The conversion rate of LiOH and LiHS inside the particle decreased. At this time, raw materials or intermediates such as LiOH and LiHS may remain inside the particle, reducing the actual effective purity of Li2S and the overall conversion integrity.

[0105] Table 2. ICP results of lithium sulfide in Example 4 As shown in Table 2, the ICP test results indicate that the overall content of metal impurities in the lithium sulfide sample obtained in Example 4 is low. Specifically, the Mg content is 2 ppm, Na content is 16 ppm, K content is 11 ppm, Ca content is 3 ppm, Al content is 5 ppm, and Cu, Ni, and Ti were not detected. These results demonstrate that the staged H2S / H2 atmosphere control method described in this application for preparing lithium sulfide does not significantly introduce transition metal impurities or other high-content metal impurities, and the resulting product exhibits a good level of metal impurity control.

[0106] Analysis of impurity sources suggests that alkali metal impurities such as Na and K likely originate primarily from trace amounts introduced from the lithium hydroxide raw material itself. The low levels of impurities such as Mg, Ca, and Al indicate minimal metal contamination of the sample from the reaction apparatus, gas pipelines, and post-processing. The absence of detected Cu, Ni, and Ti further demonstrates that the process did not significantly introduce impurities from equipment wear or metal corrosion during the reaction.

[0107] Therefore, the ICP results demonstrate that the preparation method described in this application can effectively control the introduction of metal impurities while obtaining the Li2S main phase product, which is beneficial for preparing lithium sulfide that meets the requirements of sulfide solid electrolyte precursors. This result also indirectly illustrates that the use of a lower temperature gas-solid reaction and a staged atmosphere control method in this application helps reduce the risks of equipment and material contamination, solid reducing agent residue, or the introduction of exogenous metal impurities during high-temperature reactions.

[0108] The following comparison with existing direct lithium sulfide methods further illustrates the preparation principle and advantages of the embodiments of the present invention.

[0109] First, in existing technologies for preparing lithium sulfide, hydrogen sulfide and nitrogen are introduced sequentially during the lithium sulfide formation process. Nitrogen in these processes primarily serves as an inert purge gas or protective gas, its role being mainly to dilute the atmosphere, remove byproduct water, and replace residual H2S; it does not participate in the regulation of the reaction atmosphere itself. Second, in this invention, H2 and H2S together constitute the reaction atmosphere. By altering the actual partial pressure of H2S and the reaction environment, the sulfidation rate on the LiOH particle surface, the product layer formation rate, and the residual status of intermediate substances are affected. For the small amount of free sulfur or reactive sulfur that may be generated at high temperatures, hydrogen may react with it to form H2S under higher temperature conditions, which can then be carried out with the tail gas or re-participate in the sulfidation reaction, thereby reducing the residual free sulfur.

[0110] From a mechanistic perspective, the reaction of LiOH with H2S to prepare Li2S is not a simple homogeneous process, but rather a typical gas-solid reaction. In the early stages of the reaction, a Li2S layer is preferentially formed on the surface of the LiOH particles. If the initial H2S concentration is high, the surface reaction may be too rapid, potentially forming a relatively dense product layer that hinders the further diffusion of H2S into the particle interior. This results in residual LiOH or LiHS and other raw materials or intermediates inside the particle, leading to a decrease in product purity.

[0111] The staged reaction of this invention can reduce the problem of incomplete internal reaction caused by rapid surface densification, and reduce residual intermediate or unfavorable substances such as LiOH and LiHS. At the same time, hydrogen may react with free sulfur or active sulfur substances to form H2S under higher temperature conditions, which can be carried out with the tail gas or re-participate in the sulfidation reaction, thereby reducing sulfur residue. It also reduces the risk of hydrolysis, agglomeration or impurity phases caused by the retention of by-product water in local reaction zones.

[0112] If only pure hydrogen sulfide gas is introduced for a single reaction step in the preparation of lithium sulfide, the H2S concentration in the reaction atmosphere will remain consistently high. This will cause rapid sulfidation preferentially to occur on the surface of the LiOH particles, forming a Li2S product layer. If the surface reaction is too fast, a denser Li2S layer may form on the particle surface, hindering the further diffusion of H2S into the particle interior, thus resulting in the retention of intermediates such as LiOH or LiHS inside the particle.

[0113] In the first reaction stage of this invention, a mixture of low-proportion H2S and high-proportion H2 is used to reduce the actual concentration of H2S in the initial stage, control the sulfidation rate of LiOH surface, and make the particle surface form a relatively uniform and thin initial sulfidation layer first, rather than rapidly forming a thicker product layer under pure H2S conditions.

[0114] After the initial surface sulfidation in the first reaction stage is completed, the proportion of H2S is increased to enter the second reaction stage, the conversion stage. This enhances the sulfidation reaction conditions while maintaining a relatively uniform surface reaction, pushing the reaction further into the particle interior and increasing the overall conversion degree of LiOH to Li2S. Furthermore, the reaction of hydrogen with free sulfur or reactive sulfur substances at high temperatures further reduces the risk of residual sulfur substances in the reaction system.

[0115] Furthermore, from an industrial perspective, this invention, employing a staged H2S / H2 mixed gas, offers certain economic and environmental safety advantages. If a pure H2S reaction is used, the entire reaction stage relies on H2S as the reactant gas. H2S incurs high costs in storage and transportation, leak monitoring, tail gas absorption, alkali consumption, waste liquid disposal, and safety interlocking. In this invention, H2 can handle reaction atmosphere control and purging / carry-out functions, matching the H2S usage to the actual needs of different reaction stages, thus avoiding the tail gas treatment load and environmental pressure caused by excessive gas supply in the one-step pure H2S process.

[0116] Secondly, in existing technologies, the preparation of lithium sulfide involves a mixture of lithium source, elemental sulfur, and reducing agents. The reaction mechanism is a high-temperature reducing sulfidation system involving a solid sulfur source, essentially a redox reaction. This invention uses lithium hydroxide and hydrogen sulfide as raw materials, with the reaction equation: 2LiOH + H₂S = Li₂S + 2H₂O. This is a neutralization / dehydration sulfidation reaction between an acidic gas and an alkaline lithium source. This invention utilizes the low-temperature gas-solid reaction of gaseous H₂S with LiOH to prepare Li₂S.

[0117] If hydrogen is chosen as the reducing agent, its main role is as a reducing gas to drive the redox process. This is because, in the absence of a reducing agent, elemental sulfur converts to sulfur (S). 2- The conversion is quite difficult, and the reaction usually requires a high temperature. Moreover, when the sulfur source is elemental sulfur, the oxidation state of sulfur needs to be converted from 0 to -2 in Li2S, thus requiring the participation of a reducing agent (such as hydrogen).

[0118] In this invention, lithium hydroxide is reacted with a mixture of H2S and H2. Since the sulfur in H2S is already at a -2 valence, consistent with the valence state of sulfur in Li2S, the main reaction does not involve the reduction of sulfur from 0 to -2 valence, but is more akin to the acid-base neutralization reaction between acidic gas H2S and basic LiOH. In this invention, H2 is mainly used to coordinate with H2S to adjust the composition of the reaction atmosphere, and to continuously remove residual H2S, byproducts, and H2S that may be generated by the desorption of LiHS during the post-treatment stage. Simultaneously, it reacts with free sulfur or active sulfur substances, thereby reducing residual intermediates and unstable sulfur-containing substances in the product.

[0119] Third, in existing technologies for preparing lithium sulfide, thiourea and lithium hydroxide are first subjected to a heat treatment under a first condition to obtain a mixture. Then, the mixture is reacted with hydrogen sulfide under a second condition to obtain lithium sulfide. Thiourea is an organic sulfur source containing C, N, and S, and may decompose, complex, or generate sulfur-containing intermediates during heating. While it can provide a sulfur source, it may also introduce carbon-containing, nitrogen-containing, or organic decomposition residues. The sulfur source in this invention is H2S. The byproduct system is relatively simple and controllable, mainly requiring control of byproduct water, residual H2S, and possible LiHS intermediates. There is no risk of C and N residues due to thiourea decomposition, making it more suitable for low-impurity control of battery-grade Li2S.

[0120] In existing technologies, the reaction temperature for the second condition is 500℃ to 760℃, which may lead to the following problems: higher energy consumption, higher requirements for equipment temperature resistance and sealing; the use of H2S at high temperatures places higher demands on equipment corrosion, safety interlocks, and exhaust gas treatment; within this temperature range, Li2S powder is prone to sintering, particle growth, or hard agglomeration; thiourea thermal decomposition products may bring risks of residual carbon, residual nitrogen, or other impurities; and side reactions and surface state changes are more difficult to control at high temperatures. However, according to the preparation method of this invention, particle size and agglomeration are more controllable, and the low-temperature reaction reduces high-temperature sintering, particle growth, and hard agglomeration; the staged H2S / H2 atmosphere control helps reduce particle adhesion caused by high-temperature sintering, rapid surface sulfidation, and by-product water retention, thereby improving powder dispersibility and particle size distribution uniformity. Furthermore, residues are more controllable; the staged H2S / H2 atmosphere helps reduce the residue of LiOH, LiHS, and unstable sulfur-containing substances on the surface, and moisture and by-products are more controllable.

[0121] The lithium sulfide prepared in the embodiments of this invention is mainly used in sulfide solid electrolytes and related solid battery material systems, and is particularly suitable as a key lithium source for sulfide solid electrolytes such as Li3PS4, LPSCl, and LGPS. Compared with ordinary industrial-grade lithium sulfide, the lithium sulfide obtained in this invention has the following application advantages:

[0122] First, this invention improves the uniformity of LiOH to Li2S conversion and reduces the content of residual LiOH, LiHS, and unstable sulfur-containing species on the surface by controlling the H2S / H2 atmosphere in stages. This feature helps reduce the formation of secondary phases caused by local compositional deviations of raw materials during downstream electrolyte synthesis, and improves the stability of the target phase formation in the sulfide solid electrolyte. Second, this invention employs a relatively low-temperature gas-solid reaction route, which reduces high-temperature sintering and hard agglomeration, resulting in lithium sulfide powder with better dispersibility and adaptability to subsequent processing. This feature facilitates sufficient contact between lithium sulfide and raw materials such as P2S5, LiCl, and LiBr during ball milling, mixing, or heat treatment, improving reaction uniformity and reducing local compositional inhomogeneities caused by raw material particle agglomeration.

[0123] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0124] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing lithium sulfide for solid electrolytes, characterized in that, Includes the following steps: Lithium hydroxide is subjected to dehydration and pre-activation treatment to obtain pre-activated lithium hydroxide; Using hydrogen sulfide and hydrogen as a mixed gas, a first-stage reaction is carried out on pre-activated lithium hydroxide at a first temperature, causing a sulfidation reaction on the surface of the lithium hydroxide; after the first-stage reaction is completed, the temperature is raised to a second temperature to carry out a second-stage reaction, causing a sulfidation reaction inside the lithium hydroxide, thus obtaining lithium sulfide. In the first stage of the reaction, hydrogen sulfide accounts for 1% to 20% of the volume fraction of the mixed gas; the total flow rate of the mixed gas is 250 mL / min to 350 mL / min; and the first temperature is 100℃ to 200℃. In the second stage reaction, hydrogen sulfide accounts for 20% to 90% of the volume fraction of the mixed gas; the total flow rate of the mixed gas is 350 mL / min to 450 mL / min; and the second temperature is 350℃ to 500℃.

2. The method for preparing lithium sulfide for solid electrolytes according to claim 1, characterized in that, In the first stage of the reaction, the reaction time is 1 hour to 3 hours.

3. The method for preparing lithium sulfide for solid electrolytes according to claim 1, characterized in that, In the second stage of the reaction, the reaction time is 5 to 9 hours.

4. The method for preparing lithium sulfide for solid electrolytes according to claim 3, characterized in that, The second stage reaction method is as follows: under the reaction conditions of hydrogen sulfide accounting for 60% to 65% of the volume of the mixed gas and a second temperature of 350℃ to 400℃, the reaction is carried out for 2 to 3 hours; then, under the reaction conditions of hydrogen sulfide accounting for 75% to 80% of the volume of the mixed gas and a second temperature of 370℃ to 450℃, the reaction is carried out for 3 to 6 hours.

5. The method for preparing lithium sulfide for solid electrolytes according to claim 1, characterized in that, In the first stage of the reaction, hydrogen sulfide accounts for 5% to 10% of the volume fraction of the mixed gas.

6. The method for preparing lithium sulfide for solid electrolytes according to claim 1, characterized in that, In the second stage of the reaction, hydrogen sulfide accounts for 60% to 80% of the volume fraction of the mixed gas.

7. The method for preparing lithium sulfide for solid electrolytes according to claim 1, characterized in that, The pre-activation treatment method is as follows: under the action of hydrogen, the dehydrated lithium hydroxide is pre-activated at 100℃~180℃ for 0.5h~3h to obtain pre-activated lithium hydroxide.

8. The method for preparing lithium sulfide for solid electrolytes according to claim 1, characterized in that, Lithium hydroxide is either anhydrous lithium hydroxide or lithium hydroxide monohydrate.

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