Lithium sulfide, method for preparing the same, and use thereof

Abstract

The application discloses lithium sulfide, a preparation method and application thereof, and belongs to the technical field of inorganic material synthesis. The technical scheme comprises the following steps: removing the crystal water in LiOH H2O under the protection of an inert atmosphere, and then passing H2S into the LiOH at a flow rate of 0.1-0.5 L / min.g LiOH at 100-150 DEG C to complete the surface activation of the LiOH; the main reaction is carried out at 150-250 DEG C, the H2S partial pressure is kept at 0.05-0.3 MPa during the main reaction process, and the reaction sub-step and the dehydration sub-step are alternately carried out every Δt during the period, until the H2S breakthrough rate in the tail gas is greater than or equal to 95%; the H2S atmosphere is maintained, and the LiSH is made to occur the desulfurization reaction to be converted into Li2S at 250-350 DEG C, until the characteristic peak of the LiSH in the tail gas disappears. The application is applied to the sulfide solid electrolyte and the lithium-sulfur battery positive electrode raw material aspect, solves the problems that the existing lithium sulfide preparation method has low sulfuration efficiency and high energy consumption, and has the characteristics of high sulfuration efficiency and product purity.

Description

Technical Field

[0001] This invention belongs to the field of inorganic material synthesis technology, and particularly relates to a lithium sulfide, its preparation method and application. Background Technology

[0002] Lithium sulfide (Li₂S) is a core raw material for preparing sulfide solid electrolytes (such as Li₆PS₅Cl and Li₃PS₄) and the cathode of lithium-sulfur batteries. Its purity and conversion rate directly determine the ionic conductivity and cycle stability of solid-state batteries. Industrial-grade Li₂S needs to have a purity of over 99.9 wt%, but currently, the mainstream synthesis routes for Li₂S generally suffer from insufficient purity and low conversion rates.

[0003] The gas-solid reaction of LiOH as a solid raw material with H2S gas is currently the most industrially promising route for Li2S preparation, with the core reaction being: 2LiOH + H2S → Li2S + 2H2O. However, existing patents and literature reveal the following common shortcomings: (1) The water vapor inhibition effect leads to low conversion rate The forward reaction produces H2O(g). As the reaction proceeds, the partial pressure of water vapor in the system continues to rise. According to Le Chatelier's principle, the accumulation of water vapor will significantly inhibit the forward reaction, making it difficult for the LiOH conversion rate to exceed 90%. The residual LiOH remains in the product as an impurity.

[0004] (2) Accumulation of contaminants from LiSH intermediates Under conditions where water vapor is not removed in time, the reaction intermediate lithium hydrosulfide (LiSH) accumulates in large quantities and is difficult to completely convert into Li2S, resulting in a high LiSH content in the product, which directly affects the purity of the product.

[0005] (3) Product shell passivation hinders mass transfer The dense Li2S product layer is deposited on the surface of LiOH particles, forming a diffusion resistance shell that prevents the inner LiOH layer from fully contacting H2S, further reducing the conversion rate.

[0006] Existing technologies (such as CN120191895B and CN121341954A) typically employ overall heating and dehydration after the reaction or continuous purging with dry H2S. However, the following problems still exist: post-dehydration cannot eliminate the inhibition of reaction equilibrium by water vapor in real time; high-temperature overall dehydration easily leads to product sintering and agglomeration, reducing subsequent processing performance; continuous high-flow-rate H2S purging increases the burden of tail gas treatment and has limited dehydration efficiency; and it fails to achieve precise control over the differences in water vapor generation rates at different reaction stages.

[0007] Chinese patent CN122079082A discloses a method for preparing lithium sulfide by one-step continuous dehydration sulfidation of lithium hydroxide monohydrate, which adopts a gradient temperature increase and continuous dehydration design. However, the dehydration reaction and the formation of the final product lithium sulfide still occur in the same stage, and the raw materials are not pre-activated on the surface, resulting in low efficiency of the entire sulfidation reaction, relatively long reaction time (6-22h), and high energy consumption. Summary of the Invention

[0008] In view of the shortcomings of the existing technology, the technical problem to be solved by the present invention is that the existing lithium sulfide preparation methods have low sulfidation efficiency and high energy consumption. The present invention proposes a lithium sulfide with high sulfidation efficiency and high product purity, its preparation method and application.

[0009] To solve the aforementioned technical problem, the technical solution adopted by the present invention is as follows: The present invention provides a method for preparing lithium sulfide, including a raw material pretreatment and activation stage, a main reaction enhancement stage, and an intermediate elimination and purification stage.

[0010] The above preparation method first pre-activates the surface of the raw materials and separates the dehydration and lithium sulfide generation reactions, which effectively improves the sulfidation efficiency, shortening it from 6-22 hours in the existing technology to 2-6 hours.

[0011] The raw material pretreatment and activation stage includes: after removing the water of crystallization from LiOH•H2O under an inert atmosphere, H2S is introduced at 100-150℃ at a flow rate of 0.1-0.5 L / min•g LiOH to complete the surface activation of LiOH.

[0012] The above-mentioned raw material pretreatment process first removes the water of crystallization in LiOH•H2O to avoid the influence of water vapor on subsequent reactions. Then, the surface of LiOH is activated under a low-flow-rate H2S atmosphere to eliminate the small amount of lithium carbonate generated on the surface of LiOH due to contact with air during storage and transfer, thereby reducing the reaction barrier.

[0013] The above technical solution limits the activation temperature to 100-150℃ because, within this temperature range, the water of crystallization in LiOH•H2O can be rapidly released and evaporated as water vapor, without recombining with LiOH. It is understood that the activation temperature can also be any value within 110℃, 120℃, 130℃, 140℃, or a range thereof.

[0014] The aforementioned technical solution also limits the H2S flow rate to 0.1-0.5 L / min•g LiOH. This is because if the H2S flow rate is below 0.1 L / min•g LiOH, the reaction efficiency is too low, leading to decreased production efficiency. If the H2S flow rate is above 0.5 L / min•g LiOH, the reaction rate is too fast, resulting in the generation of large amounts of water vapor, increasing the difficulty of drainage, and reducing the utilization rate of hydrogen sulfide. It can be understood that the H2S flow rate can also be 0.2 L / min•g LiOH, 0.3 L / min•g LiOH, 0.4 L / min•g LiOH, or any value within this range.

[0015] In some embodiments, the raw material pretreatment and activation stage, the main reaction enhancement stage, and the intermediate elimination and purification stage are carried out in a reactor, and the reactor is designed to have a pressure ≥0.5 MPa.

[0016] The reactor described above is a conventional reactor, requiring only compliance with H2S corrosion resistance, pressure requirements, and airtightness. Specifically, it uses H2S corrosion-resistant materials (316L stainless steel or Hastelloy C-276), with a design pressure ≥0.5MPa. Additionally, it can be equipped with a programmed temperature control system (accuracy ±2°C) for more precise temperature control.

[0017] In some embodiments, the raw material pretreatment and activation stage includes: heating to 100-150°C at 2-5°C / min under Ar or N2 protection, holding at the temperature for 0.5-1h to remove the water of crystallization in LiOH•H2O; simultaneously condensing and capturing the volatile water vapor to reduce the relative humidity in the reactor to ≤5%; and continuously introducing H2S at a flow rate of 0.1-0.5L / min•g LiOH for 15-30min to complete the surface activation of LiOH.

[0018] The aforementioned water vapor condensation and capture employs a condenser trap, which is located downstream of the reactor outlet. The condensation temperature is -20 to 0°C, and the capture efficiency is ≥95%. Additionally, a molecular sieve drying column, employing a 3Å molecular sieve, is connected in series after the condenser trap to further reduce the moisture content in the carrier gas to ≤1 ppm.

[0019] The main reaction enhancement stage includes: the main reaction is carried out at 150-250℃, the H2S partial pressure is maintained at 0.05-0.3MPa during the main reaction, and the reaction sub-step and dehydration sub-step are alternated every Δt until the H2S penetration rate in the tail gas is ≥95%.

[0020] The above-mentioned main reaction enhancement stage separates dehydration and reaction, which can realize the drainage and lithium sulfide generation in two stages, avoiding the decrease in production efficiency and increase in energy consumption caused by the water vapor generated in the forward reaction and the reverse reaction of product Li2S.

[0021] The above technical solution limits the reaction temperature of the main reaction enhancement stage to 150-250℃. This is because if the reaction temperature is below 150℃, the water vapor discharge rate is low, making reverse reactions more likely and prolonging the reaction time. If the reaction temperature is above 250℃, LiSH will further decompose into Li2S, meaning the dehydration reaction of LiOH and the formation of Li2S will occur simultaneously in the same space, increasing the probability of reverse reactions between Li2S and water, reducing production efficiency, and causing material agglomeration and incomplete internal reactions due to multiple crystal decomposition and fusion processes. It can be understood that the reaction temperature can also be any value within the range of 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, 230℃, 240℃, etc.

[0022] In some embodiments, Δt is selected from any value between 10 and 30 min. It is understood that Δt can also be any point value within the range of 12 min, 14 min, 16 min, 18 min, 20 min, 22 min, 24 min, 26 min, 28 min, and 12 min.

[0023] In some embodiments, the reaction sub-step includes: maintaining an H2S atmosphere, with H2S reacting with LiOH Δt1; the dehydration sub-step includes: switching to an inert atmosphere while simultaneously extracting and condensing water vapor in the system, thereby reducing the partial pressure of water vapor in the reactor to ≤0.5 kPa.

[0024] In some embodiments, the duration Δt1 of the reaction sub-step is selected from any value between 8 and 25 min, and the duration Δt2 of the dehydration sub-step is selected from any value between 2 and 5 min.

[0025] The switching between the above reaction sub-steps and dehydration sub-steps can be achieved through a gas switching valve group, which is a pneumatic three-way / four-way valve with a response time ≤1s, enabling rapid switching between H2S atmosphere and inert carrier gas.

[0026] The intermediate elimination and purification stage includes: maintaining an H2S atmosphere and causing LiSH to undergo a dehydrosulfidation reaction at 250-350℃ to convert it into Li2S, until the characteristic peak of LiSH in the tail gas disappears.

[0027] The above technical solution limits the reaction temperature for the intermediate elimination and purification stage to 250-350℃. This is because if the reaction temperature is below 250℃, the rate of LiSH to Li2S conversion is low, reducing production efficiency. If the reaction temperature is above 350℃, it wastes energy and increases the probability of side reactions, reducing product purity. Generally, above 400℃, hydrogen sulfide begins to decompose, producing H2 and S. Elemental S can continue to react with LiSH to generate Li2S. x (Lithium polysulfide). It can be understood that the reaction temperature can also be any value within the range of 260℃, 270℃, 280℃, 290℃, 300℃, 310℃, 320℃, 330℃, 340℃.

[0028] In some embodiments, the intermediate elimination and purification stage includes: maintaining an H2S atmosphere, heating to 250-350°C at 2-5°C / min, at which temperature, LiSH undergoes a dehydrosulfide reaction to be converted into Li2S; simultaneously removing water vapor and H2S decomposition products; holding at the temperature for 1-2 hours until the characteristic peak of LiSH in the tail gas disappears; cooling to room temperature and discharging under an inert atmosphere to obtain the Li2S product.

[0029] The characteristic peak detection of LiSH in the exhaust gas mentioned above can be achieved using an online FTIR detection cell. The online FTIR detection cell is used for real-time monitoring of LiSH (1170 cm⁻¹) in the exhaust gas. -1 ), H2O (3657cm) -1 H2S (2611cm) -1 Characteristic peaks can be used to determine the reaction endpoint.

[0030] This invention provides a method for preparing Li2S by in-situ segmented removal of water vapor to enhance gas-solid reaction. By removing the generated water vapor from the reaction system in real time and in stages during the reaction, the inhibitory effect of water vapor on the reaction equilibrium is fundamentally eliminated. At the same time, segmented temperature control promotes the complete conversion of LiSH intermediate, ultimately achieving: LiOH conversion rate ≥99%, Li2S purity ≥99.9wt%, and LiSH residue ≤0.05wt%.

[0031] The above preparation method solves the problems of difficult dehydration and low conversion rate and low purity caused by water vapor inhibition during the gas-solid reaction process using LiOH and hydrogen sulfide as raw materials, and has the following characteristics: (1) Significantly improved conversion rate: By removing water vapor in situ in real time and eliminating reaction equilibrium inhibition, the conversion rate of LiOH is increased from 87-93% in the existing technology to ≥99%; (2) The vulcanization efficiency is improved, shortening the time from 6-22 hours in the existing technology to 2-6 hours; (3) The purity of the product reaches the battery grade: the purity of Li2S is stably above 99.9wt%, which meets the requirements for the preparation of solid electrolytes; (4) Complete elimination of LiSH intermediates: segmented temperature control and a third-stage specialized purification process reduced LiSH residue to ≤0.05 wt%; (5) No sintering agglomeration: avoids sintering caused by high-temperature overall post-processing, and the BET specific surface area of ​​the product is increased by about 1 time; (6) Improved H2S utilization: The on-demand dehydration mode reduces the amount of inert gas purging, increasing the effective utilization rate of H2S by approximately 10-15%; (7) Closed-loop automated control can be realized: If related detection and control equipment is further coupled, closed-loop control logic based on online moisture detection can be realized, which is suitable for industrial continuous production.

[0032] In another aspect, the present invention provides lithium sulfide prepared by the preparation method described in any of the above technical solutions.

[0033] In some embodiments, the lithium sulfide purity is ≥99.9wt% and the residual LiSH content is ≤0.05wt%.

[0034] The present invention also provides the application of lithium sulfide in battery materials according to any of the above technical solutions, wherein lithium sulfide is used as an electrolyte in battery materials.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention provides a method for preparing lithium sulfide, which breaks down the traditional "one-step" H2S gas-solid reaction into three functional stages. Each stage uses a different combination of temperature, H2S partial pressure and water vapor removal to achieve in-situ continuous removal of water vapor, so that the water vapor partial pressure in the reactor is always maintained below the inhibition threshold, fundamentally eliminating the inhibitory effect of water vapor on the reaction equilibrium. At the same time, the segmented temperature control promotes the complete conversion of LiSH intermediate. This invention provides a method for preparing lithium sulfide, which first pre-activates the surface of the raw materials and separates the dehydration and lithium sulfide formation reactions, effectively improving the sulfidation efficiency from 6-22 hours in the prior art to 2-6 hours. This invention provides a lithium sulfide with a purity ≥99.9wt% and a LiSH residue content ≤0.05wt%. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the connection of the preparation apparatus provided in an embodiment of the present invention. Detailed Implementation

[0037] The technical solutions in specific embodiments of the present invention will now be described in detail and completely with reference to the accompanying drawings. Obviously, the described embodiments are merely some specific implementations of the overall technical solution of the present invention, and not all implementations. Based on the overall concept of the present invention, all other embodiments obtained by those skilled in the art fall within the protection scope of the present invention.

[0038] The existing methods for preparing lithium sulfide have the problems shown in Table 1.

[0039] Table 1. Problems with existing lithium sulfide preparation methods

[0040] To address the above problems, this invention breaks down the traditional one-step H2S gas-solid reaction into three functional stages. Each stage employs differentiated combinations of temperature, H2S partial pressure, and water vapor removal. Furthermore, an independent drying and dehydration bypass enables continuous in-situ removal of water vapor, ensuring that the water vapor partial pressure within the reactor remains below the inhibition threshold. The specific solution is as follows: 1. A three-stage in-situ segmented dehydration reaction method is adopted. Step 1: Raw material pretreatment and activation stage (first stage, T1=100-150℃) (1) Place LiOH•H2O or anhydrous LiOH powder (particle size D) 50 ≤50μm) are placed in a closed reactor with a side-channel drying and dehydration bypass; (2) Under an inert atmosphere (Ar or N2), the temperature is increased to 100-150℃ at 2-5°C / min and held for 0.5-1h to remove the water of crystallization in LiOH•H2O; (3) Simultaneously turn on the bypass condenser (temperature setting -20 to 0℃) to condense and capture the volatile water vapor, so that the relative humidity in the reactor drops to ≤5%; (4) Switch the atmosphere to H2S (purity ≥99.9%) and introduce it at a low flow rate (0.1-0.5L / min•g_LiOH) to complete the surface activation for 15-30min.

[0041] Step 2: Main reaction enhancement stage (second stage, T2=150-250℃) (1) Increase the temperature at 3-8℃ / min to the main reaction temperature of 150-250℃ (preferably 180-220℃); (2) Maintain the partial pressure of H2S at 0.05-0.3MPa (preferably 0.1-0.2MPa); (3) Key operation: Perform the "reaction-dehydration" alternating cycle once every Δt = 10-30 min; (4) Reaction sub-step (lasting Δt1 = 8-25 min): Close the bypass, maintain the H2S atmosphere, and allow H2S to fully react with LiOH; (5) Dehydration sub-step (lasts Δt2=2-5min): Switch to inert gas carrier gas and simultaneously turn on the bypass condenser to extract and condense the water vapor accumulated in the system, so that the water vapor partial pressure in the reactor drops to ≤0.5kPa; (6) Repeat the above alternating cycle 5-15 times until the exhaust gas detector shows H2S penetration rate ≥95% (indicating that most of LiOH has been converted). (7) The goal of this stage is to achieve a LiOH → Li2S + LiSH mixture with a LiOH conversion rate of ≥95%.

[0042] Step 3: Intermediate elimination and purification stage (third stage, T3=250-350℃) (1) Maintain the H2S atmosphere and raise the temperature to 250-350°C (preferably 280-320°C) at a rate of 2-5°C / min. (2) At this temperature, LiSH undergoes a dehydrosulfide reaction and is completely converted to Li2S: 2LiSH→Li2S+H2S↑ (3) Simultaneously open the bypass to continuously remove trace amounts of water vapor and residual H2S decomposition products; (4) Keep warm for 1-2 hours until the characteristic peak of LiSH in the exhaust gas (online FTIR detection, 1170 cm⁻¹) is reached. -1 )disappear; (5) Cool down to room temperature and discharge the product under an inert atmosphere to obtain high-purity Li2S product.

[0043] 2. The apparatus used in the above preparation method like Figure 1 As shown, this device is a gas-solid reaction device with an in-situ segmented dehydration bypass, and includes the following functional modules: (1) Reactor: It can be a gas-solid reaction closed container such as a fixed bed, fluidized bed, moving bed or conveying bed. The inner wall is made of H2S corrosion resistant material (316L stainless steel or Hastelloy C-276). The design pressure is ≥0.5MPa and it is equipped with a programmed temperature rise control system (accuracy ±2℃). (2) Gas switching valve group: a pneumatic three-way valve / four-way valve with a response time ≤1s, which can be any type of ball valve, shut-off valve, plug valve, etc., to realize the rapid switching between H2S atmosphere and inert carrier gas; (3) Dehydration bypass condenser: The front end uses a low-temperature cold trap to condense and capture water vapor, and the rear end is connected to a steam-water separator. The demisting droplet is set downstream of the reactor outlet, and the condensation temperature is [not specified]. At 20–0℃, the collection efficiency is ≥95%; (4) Molecular sieve drying column: one or more types of molecular sieves, such as 3Å molecular sieve, 4Å molecular sieve, 5Å molecular sieve, and 13X molecular sieve, are connected in series after the condenser to further reduce the moisture content in the carrier gas to ≤1ppm; (5) Online moisture analyzer: measuring range 0-100%RH or 0-100kPa water vapor partial pressure, response time ≤5s; (6) Online FTIR detection cell: used for real-time monitoring of LiSH (1170 cm⁻¹) in exhaust gas. -1 ), H2O (3657cm) -1 H2S (2611cm) -1 Characteristic peaks can be used to determine the reaction endpoint. (7) PLC control system: Based on the moisture detector and FTIR signal, automatically execute the "reaction-dehydration" alternating switching logic.

[0044] To provide a clearer and more detailed description of the lithium sulfide, its preparation method, and its applications provided in the embodiments of the present invention, the following description will be based on specific embodiments.

[0045] Example 1 Small-scale verification of fixed bed foundation (1) Raw material preparation and filling Raw material specifications: LiOH•H2O (purity ≥99.5wt%, D 50 =15μm, BET≥8m 2 / g) Feed amount: 100g LiOH•H2O (equivalent to 83.5g of anhydrous LiOH, 3.48mol) Pretreatment dehydration: Fixed bed reaction tube (Ø25mm×300mm, 316L stainless steel), N2 atmosphere (≥99.999%, 500mL / min), heat up to 120°C at 5℃ / min, hold for 60min; after the outlet dew point ≤-40°C, proceed to the reaction stage; Bed filling: Quartz wool is used for upper and lower support, with a material layer height of about 80mm and a porosity of about 0.45.

[0046] (2) Gas ratio and flow rate parameters Table 2

[0047] Molar ratio control: n(H2S):n(LiOH)=1.05:1; Reaction formula 2LiOH+H2S→Li2S+2H2O, theoretically 1.74mol of H2S is required, but in practice 1.83mol is introduced (5% excess).

[0048] (3) Segmented reaction operation procedure Stage I Pretreatment Activation (100-150°C): After the furnace temperature is raised to 100°C, switch to H2S / N2 mixed gas (10 vol%, 500 mL / min) and maintain for 30 min; when the H2S concentration at the outlet decreases by ≥5 vol% compared to the inlet, confirm that the surface activation is complete, and raise the temperature to 150°C at 3°C / min to prepare for the main reaction; Stage II Main Reaction Enhancement (150-250°C): Switch to 20 vol% H2S (500 mL / min), and slowly increase the temperature at 2°C / min; Dehydration Cycle: When the outlet P(H2O) ≥ 0.5 kPa, the PLC triggers the dehydration program: close the H2S inlet valve → switch to pure N2 purging (500 mL / min) → open the bypass valve V1 (-10°C condenser); purge until P(H2O) ≤ 0.1 kPa (approximately 8-12 min) → close V1 → restore the H2S / N2 mixture; repeat the "reaction-dehydration" cycle 4-6 times, with a cumulative main reaction time of approximately 120 min.

[0049] Stage III intermediate elimination (250-350°C): Switch to 15 vol% H2S (500 mL / min), increase the temperature to 300°C at 3°C / min, and hold for 60 min; increase the temperature to 350°C and hold for 30 min; if the outlet H2S < 0.5 vol% (NIR detection) and P(H2O) < 0.05 kPa, the reaction is considered complete; Cooling and discharge: Cool to room temperature under pure N2 protection, and discharge through a sealed glove box (H2O < 0.1 ppm, O2 < 0.1 ppm).

[0050] (4) Online monitoring indicators and control conditions Table 3

[0051] (5) Post-processing and testing characterization The sample was manually ground in a glove box using an agate mortar and pestle, sieved through a 200-mesh sieve, and then tested for crystal structure analysis (XRD phase analysis), elemental analysis (ICP-OES), moisture content testing (Karl Fischer method), and specific surface area testing (BET analyzer).

[0052] Example 2 Closed-loop automatic control verification (1) Raw material preparation and filling Raw material specifications: Anhydrous LiOH (purity ≥ 99.8 wt%), D 50 =10μm, BET≥12m 2 / g, after ball milling activation treatment); Feed amount: 200g (8.33mol) of anhydrous LiOH; Pretreatment: N2 (800 mL / min), room temperature → 150°C (5°C / min), keep warm for 30 min (to remove adsorbed water); Bed specifications: Ø40mm×400mm reaction tube, material layer height approximately 100mm.

[0053] (2) Gas ratio and flow rate parameters Table 4

[0054] Molar ratio control: n(H2S):n(LiOH)=1.05:1, theoretically 4.17mol of H2S is required, but 4.38mol is actually introduced.

[0055] (3) Segmented reaction operation procedure Stage I pretreatment activation (100-150°C): Switch to 10 vol% H2S, 800 mL / min, maintain for 40 min, confirm activation is complete when H2S at the outlet drops by ≥5 vol%, then increase the temperature to 150°C at 3°C / min. Stage II main reaction enhancement (150-250°C): Fully automatic PLC closed-loop control; IF P(H2O)_outlet≥0.5kPa THEN Turn off MFC-H2S → Start pure N2 purging (800 mL / min) → Open bypass valve V1 IF P(H2O)_outlet≤0.1kPa OR timing≥15min THEN Turn off V1 → Restore 20 vol% H2S (800 mL / min) END IF END IF Response completion determination logic (automatic execution): IF H2S_outlet<0.5vol% AND P(H2O)<0.05kPa AND T_bed≥300°C AND cumulative reaction time≥90min THEN Trigger Stage III Heating Program END IF The main reaction stage involves automatic dehydration cycles of 6-8 times, with a total main reaction time of approximately 150 minutes. Stage III intermediate elimination (250-350°C): Automatically switch to 15 vol% H2S (800 mL / min), heat up to 320°C at 3°C / min, and hold for 75 min; if outlet H2S < 0.5 vol% and P(H2O) < 0.05 kPa, automatically trigger cooling.

[0056] (4) Online monitoring indicators and control conditions Table 5

[0057] (5) Post-processing The sample was manually ground in a glove box using an agate mortar and pestle, sieved through a 200-mesh sieve, and then tested for crystal structure analysis (XRD phase analysis), elemental analysis (ICP-OES), moisture content testing (Karl Fischer method), and specific surface area testing (BET analyzer).

[0058] Example 3 10kg scale-up engineering verification (1) Raw material preparation and filling Raw material specifications: LiOH•H2O (industrial grade, purity ≥99.0wt%, D) 50 =20μm, after being pulverized by airflow to D50=8μm before use); Feed amount: 10kg LiOH•H2O (equivalent to 8.35kg of anhydrous LiOH, 348.6mol); Pretreatment dehydration: Equipment: Horizontal tube furnace (Ø150mm×1500mm, 3-zone independent temperature control); N2 flow rate: 10 L / min (purity ≥ 99.999%); Heating program: room temperature → 80°C (2°C / min) → hold for 30 min → 120°C (1°C / min) → hold for 120 min; Completion criteria: outlet dew point ≤ -45°C, water content < 10 ppm; Bed filling: Fill in layers (approximately 1 kg per layer), with stainless steel wire mesh (40 mesh) laid between layers to ensure uniform gas distribution.

[0059] (2) Gas ratio and flow rate parameters Table 6

[0060] Molar ratio control: n(H2S):n(LiOH) = 1.05:1, theoretically requiring 174.3 mol of H2S, but actually introducing 183.0 mol; gas hourly space velocity ≈ 500 h⁻¹ -1 This ensures sufficient gas-solid contact.

[0061] (3) Segmented reaction operation procedure Stage I Pretreatment Activation (100-150°C): The furnace temperature in all three zones is raised to 100°C (temperature difference <5°C), 10 vol% H2S is switched on (10 L / min), and gas is circulated for 60 min; when the outlet H2S decreases by ≥4 vol%, activation is confirmed to be complete; the three zones are then coordinated to raise the temperature to 150°C (2°C / min, temperature difference between zones <10°C). Stage II Main Reaction Enhancement (150-250°C): Fully Automatic PLC + Safety Interlock Heating strategy (stepwise control): 150°C → 180°C (1°C / min) → Hold for 30 min 180°C → 200°C (1°C / min) → Hold for 60 min 200°C → 250°C (0.5°C / min) → Hold for 30 min Dehydration cycle: P(H2O) trigger threshold: ≥0.4kPa (smaller tests are more sensitive to prevent moisture accumulation inside the bed). Purge flow rate: 215 L / min pure N (higher than the reaction flow rate to accelerate dehydration) Condensation trap: Dual parallel circuit (-15°C, 5L capacity per circuit), alternating drainage. Single dehydration time: 15-20 minutes, approximately 10-15 cycles. Total main reaction time: approximately 240 minutes Stage III intermediate elimination (250-350°C): Switch to 15 vol% H2S (10 L / min), heat to 300°C (2°C / min), hold for 90 min; then heat to 350°C, hold for 60 min; multi-point temperature uniformity verification: temperature difference between the upper / middle / lower points of the bed <15°C (4) Online monitoring indicators and control conditions Table 7

[0062] Cooling and discharge: Pure N2 (10L / min) is cooled to 60°C at 3°C / min and allowed to cool naturally to room temperature; N2 positive pressure (0.02MPa) protection is applied, and the material is transferred to a sealed silo.

[0063] (5) Post-processing and testing characterization The sample was manually ground in a glove box using an agate mortar and pestle, sieved through a 200-mesh sieve, and then tested for crystal structure analysis (XRD phase analysis), elemental analysis (ICP-OES), moisture content testing (Karl Fischer method), and specific surface area testing (BET analyzer).

[0064] Comparative Example 1 Traditional one-step H2S gas-solid reaction (no segmented dehydration, no segmented temperature zone) (1) Raw material specifications and pretreatment Raw material specifications: LiOH•H2O (purity ≥99.5wt%, D 50 =15μm, BET≥8m 2 / g); Feed amount: 100g LiOH•H2O (equivalent to 83.5g of anhydrous LiOH, 3.48mol); Reactor specifications: Ø25×300mm quartz fixed-bed tube furnace; Bed height: Approximately 80mm; Gas seal: Standard flange seal, without bypass condensate trap.

[0065] (2) Gas ratio parameters: Table 8

[0066] (3) Segmented operation procedure Step 1: Filling and Airtightness Test Pre-dried LiOH (100g) was placed into the reaction tube in a glove box; the flange was sealed, and N2 was purged for 5 min (200mL / min) to check the airtightness; the tail gas was connected to the NaOH alkaline absorption tower (10wt%, 1L).

[0067] Step 2: Rapidly heat to high temperature Programmed temperature rise: room temperature → 350°C, heating rate 5°C / min, N2 protection (200mL / min); directly rise to 350°C, without lingering in the 100-150°C or 150-250°C range; after reaching 350°C, maintain constant temperature for 15min.

[0068] Step 3: Single-stage high-temperature reaction Atmosphere switching: H2S / N2 mixed gas (20 / 80 vol%), total flow rate 200 mL / min; reaction temperature: 350°C, constant temperature throughout.

[0069] No dehydration cycle is set, and the temperature is not adjusted.

[0070] Observations: In the initial stage of the reaction (0-20 min), there was significant exothermic reaction, and the bed temperature locally rose to 375-390°C (hot spot effect), and the LiOH particles sintered rapidly; the outlet H2S concentration was monitored by an online NIR analyzer, and the reaction was terminated when the outlet H2S ≥ 18 vol%.

[0071] Step 4: Cooling Switch to pure N2 and the program will cool down to room temperature.

[0072] (4) Post-processing After being removed from the glove box, the product appears grayish-white to pale yellow (containing LiSH intermediates and unreacted LiOH), and shows significant clumping.

[0073] Manually grind and crush the material, pass it through a 200-mesh sieve, and take samples for XRD, ICP-OES, moisture, and BET analysis.

[0074] Comparative Example 2 Post-dehydration only (1) Raw material specifications and pretreatment Raw material specifications: Anhydrous LiOH (purity ≥ 99.8 wt%), D 50 =10μm, BET≥12m 2 / g, after ball milling activation treatment); Feed amount: 200g (8.33mol) of anhydrous LiOH; Reaction tube specifications: Ø40×400mm quartz tube fixed bed; Bed height: Approximately 80mm; Carrier gas: High-purity N2 (purity ≥ 99.999 vol%).

[0075] (2) Gas proportioning parameters Reaction phase (maintained constant temperature throughout, without segmented control): Table 9

[0076] (3) Segmented operation procedure Step 1: Loading and airtightness testing 200g LiOH•H2O was evenly packed into a Ø40×400mm quartz tube, and both ends were sealed with quartz wool; N2 (500mL / min) was introduced, and a leak test (soap water method) was performed to confirm that the system was airtight; the bypass valve V1 (condensate trap bypass) was closed, and the bypass dehydration circuit was not opened throughout the process.

[0077] Step 2: Heating and preheating (without pre-drying) The temperature was increased to 200°C at a rate of 5°C / min, with N2 protection throughout (500 mL / min); after reaching 200°C, the temperature was stabilized for 10 min, and the initial bed state was recorded.

[0078] Step 3: Continuous reaction at constant temperature (no in-situ dehydration) Switch the gas source: H2S / N2 mixture (20 / 80 vol%), flow rate 500 mL / min; continuously introduce for 180 min without any interruption or bypass switching; record the outlet H2S concentration and outlet H2O partial pressure every 30 min (record only, do not trigger dehydration); observe the trend of outlet H2O partial pressure change (the expected peak appears in the reaction 30–60 min range). Step 4: Centralized dehydration in the back end After reacting for 180 min, the gas source was switched to pure N2 (800 mL / min, increasing the flow rate to enhance purging); the temperature was increased to 300°C at 5°C / min, and N2 was continuously purged at 300°C for 60 min; the partial pressure of H2O at the outlet was monitored, and the dehydration curve was recorded (a large moisture release peak was expected); after 60 min, the temperature was lowered, and N2 protection was maintained throughout the process until room temperature.

[0079] Step 5: Unloading and Product Collection Unload the product in a glove box (H2O < 0.1 ppm, O2 < 0.1 ppm); weigh the product and record its appearance (color, degree of agglomeration).

[0080] (4) Post-processing After being removed from the glove box, the product appears grayish-white to pale yellow (containing LiSH intermediates and unreacted LiOH), and shows significant clumping.

[0081] Manually grind and crush the material, pass it through a 200-mesh sieve, and take samples for XRD, ICP-OES, moisture, and BET analysis.

[0082] Comparative Example 3 Similar to Example 1, except that no pre-activation step is set.

[0083] Performance testing The purity and conversion rate of the products in the examples and comparative examples are shown in Table 10.

[0084] Table 10

[0085] Based on the table above, comparing Comparative Example 1 (single-stage 350°C) with Example 1 (three-stage 100→250→350°C), it is clear that a gradient temperature zone is a necessary condition for suppressing high-temperature side reactions and maintaining the active specific surface area of ​​particles, and cannot be replaced by a single-stage high temperature. Main analysis: Single-stage high temperature leads to locally higher temperatures in the hotspot region (up to 390°C), resulting in particle densification (BET < 0.5m). 2 / g), disproportionation byproducts such as Li2S2 / Li2O accumulated to 7.5wt%.

[0086] Comparative Example 2 (one-step dehydration at the back end) vs. Examples 1-3 (in-situ segmented dehydration) shows that dehydration must be carried out in-situ, in real time, and concurrently with the reaction. Post-processing dehydration cannot replace in-situ dehydration; "in-situ" is an independent and essential technical feature. The main reason is that during the reaction stage, the H2O partial pressure peak reaches 3.5-5.2 kPa, and the LiSH intermediate solidifies and encapsulates under high water vapor conditions, forming a dense shell. The concentrated dehydration at 300°C / 60 min at the back end cannot reverse the passivation of the formed shell, resulting in a LiSH residue as high as 4.21 wt%.

[0087] In summary, based on the complete experimental data from Examples 1-3 (verification group) and Comparative Examples 1-2 (control group), the following technical conclusions are drawn: The synergistic method of "three-stage gradient temperature zone + in-situ water vapor segmented removal" is a necessary and sufficient technical condition for achieving high conversion and high purity Li2S preparation. This process is scalable.

Claims

1. A method for preparing lithium sulfide, characterized in that, It includes the raw material pretreatment and activation stage, the main reaction enhancement stage, and the intermediate elimination and purification stage; The raw material pretreatment and activation stage includes: after removing the water of crystallization from LiOH•H2O under an inert atmosphere, H2S is introduced at 100-150℃ at a flow rate of 0.1-0.5 L / min•g LiOH to complete the surface activation of LiOH; The main reaction enhancement stage includes: the main reaction is carried out at 150-250℃, during which the H2S partial pressure is maintained at 0.05-0.3MPa, and the reaction sub-steps and dehydration sub-steps are alternated every Δt until the H2S penetration rate in the exhaust gas is ≥95%; The intermediate elimination and purification stage includes: maintaining an H2S atmosphere and causing LiSH to undergo a dehydrosulfidation reaction at 250-350℃ to convert it into Li2S, until the characteristic peak of LiSH in the tail gas disappears; The reaction sub-steps include: maintaining an H2S atmosphere, with H2S reacting with LiOH Δt1; the dehydration sub-steps include: switching to an inert atmosphere, while simultaneously extracting and condensing water vapor in the system, reducing the partial pressure of water vapor in the reactor to ≤0.5kPa.

2. The preparation method according to claim 1, characterized in that, The raw material pretreatment and activation stage, the main reaction enhancement stage, and the intermediate elimination and purification stage are carried out in the reactor, and the reactor is designed to have a pressure ≥0.5MPa.

3. The preparation method according to claim 2, characterized in that, The raw material pretreatment and activation stage includes: under Ar or N2 protection, heating to 100-150℃ at 2-5℃ / min and holding for 0.5-1h to remove the water of crystallization in LiOH•H2O; at the same time, condensing and capturing the volatile water vapor to reduce the relative humidity in the reactor to ≤5%; and continuously introducing H2S at a flow rate of 0.1-0.5L / min•g LiOH for 15-30min to complete the surface activation of LiOH.

4. The preparation method according to claim 1, characterized in that, Δt is selected from any value between 10 and 30 min.

5. The preparation method according to claim 1, characterized in that, The duration of the reaction sub-step Δt1 is selected from any value between 8 and 25 min, and the duration of the dehydration sub-step Δt2 is selected from any value between 2 and 5 min.

6. The preparation method according to claim 1, characterized in that, The intermediate elimination and purification stage includes: maintaining an H2S atmosphere, heating to 250-350℃ at 2-5℃ / min, at which temperature, LiSH undergoes a dehydrosulfide reaction to be converted into Li2S; simultaneously removing water vapor and H2S decomposition products; holding at the temperature for 1-2 hours until the characteristic peak of LiSH in the tail gas disappears; cooling to room temperature and discharging under an inert atmosphere to obtain the Li2S product.

7. The lithium sulfide prepared by the preparation method according to any one of claims 1-6, characterized in that, Lithium sulfide purity ≥ 99.9 wt%, LiSH residue ≤ 0.05 wt%.

8. The application of lithium sulfide in battery materials according to claim 7, characterized in that, Lithium sulfide is used as an electrolyte in battery materials.

Images