Lithium sulfide, preparation method thereof and solid-state battery

Abstract

The invention provides lithium sulfide, a preparation method thereof and a solid-state battery, and belongs to the technical field of batteries, and the preparation method of the lithium sulfide comprises the following steps: performing hydrosulfide reaction on water-containing hydrosulfide and lithium salt dissolved in a first solvent under the protection of inert gas to obtain a first lithium hydrosulfide suspension, and performing solid-liquid separation to obtain a first lithium hydrosulfide solution, the first solvent comprises an aprotic polar organic solvent; decompressing and dewatering the first lithium hydrosulfide solution to obtain a second lithium hydrosulfide suspension, and performing solid-liquid separation to obtain a second lithium hydrosulfide solution in which the water content is 0.05-2%; and desulfurizing the second lithium hydrosulfide solution to obtain a lithium sulfide suspension, and carrying out solid-liquid separation to obtain lithium sulfide. According to the present invention, the low-cost water-containing hydrosulfide is selected as the raw material, the pressure reducing water removal process is added to remove the impurities, and then the desulfurization is performed to obtain the high-purity lithium sulfide;

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a lithium sulfide and its preparation method, and a solid-state battery. Background Technology

[0002] In recent years, secondary batteries have been widely used and developed as a power source for portable electronic communication devices such as portable cameras, mobile phones, and laptops, as well as vehicles such as hybrid electric vehicles and electric vehicles. Lithium-ion secondary batteries, characterized by high operating voltage, high energy density, fast charging, and lightweight design, have been extensively studied. Among them, all-solid-state batteries have superior safety, energy density, and lifespan compared to liquid batteries, making them a research hotspot. Sulfide-based solid electrolytes are mainly prepared from lithium sulfide (Li₂S); however, lithium sulfide cannot be prepared from natural minerals and must be synthesized artificially.

[0003] Initially, industrial-scale production of lithium sulfide mainly involved methods such as carbothermal reduction, ball milling, metathesis, and gas-solid reaction. However, these methods suffer from problems such as difficulty in controlling impurity content, low safety, and low conversion and yield rates. To address these issues, related technologies employ the hydrosulfidation reaction of hydrides with lithium salts to prepare lithium hydrides, followed by desulfurization to obtain lithium sulfide. However, this method uses anhydrous raw materials with high costs, and the purity of the resulting lithium sulfide is relatively low. Summary of the Invention

[0004] This application provides a lithium sulfide, a method for preparing the same, and a solid-state battery, aiming to solve the problems of high cost of anhydrous raw materials and low purity of lithium sulfide obtained in the existing process of preparing lithium sulfide by hydrogen sulfide reaction.

[0005] In a first aspect, embodiments of this application provide a method for preparing lithium sulfide, comprising: Aqueous hydrosulfide is reacted with lithium salt dissolved in a first solvent under inert gas protection to obtain a first lithium hydrosulfide suspension. After solid-liquid separation, a first lithium hydrosulfide solution is obtained. The first solvent includes an aprotic polar organic solvent. The first lithium hydrosulfide solution was dehydrated under reduced pressure to obtain a second lithium hydrosulfide suspension. After solid-liquid separation, a second lithium hydrosulfide solution was obtained. The water content in the second lithium hydrosulfide suspension was 0.05%~2%. The second lithium hydrosulfide solution was desulfurized under reduced pressure to obtain a lithium sulfide suspension. After solid-liquid separation, lithium sulfide was obtained.

[0006] This application first obtains a lithium hydrosulfide suspension through a low-cost hydrosulfide and lithium salt hydrosulfide reaction. After solid-liquid separation, a first lithium hydrosulfide solution is obtained. Second, based on the low-cost hydrosulfide, the first lithium hydrosulfide solution is subjected to dehydration under reduced pressure. As water is removed, impurities in the first lithium hydrosulfide solution continuously precipitate out. The water content of the second lithium hydrosulfide suspension is controlled at 0.05%~2%, thereby significantly removing impurities from the first lithium hydrosulfide solution and obtaining a high-purity second lithium hydrosulfide solution. This provides a guarantee for the preparation of high-purity lithium sulfide. Furthermore, dehydration under reduced pressure can efficiently remove water while lowering the dehydration temperature, reducing the decomposition of aprotic polar organic solvents. Finally, the purified second lithium hydrosulfide solution is desulfurized to obtain the target high-purity lithium sulfide product.

[0007] Optionally, the water content in the second lithium hydrosulfide suspension is 0.05% to 1%.

[0008] This application further controls the water content in the second lithium hydride suspension so that 99.5% to 99.9% of the impurities are converted into precipitates and removed during the dehydration process under reduced pressure, thereby making the content of cationic impurities in the second lithium hydride solution <200ppm.

[0009] Optionally, the pressure for dewatering under reduced pressure is -0.04 MPa to -0.10 MPa; and / or the temperature for dewatering under reduced pressure is 80℃ to 140℃.

[0010] This application achieves efficient removal of moisture while minimizing the decomposition loss of aprotic polar organic solvents by rationally setting the pressure and temperature for decompression and dehydration.

[0011] Optionally, the desulfurization method is vacuum desulfurization, the temperature of vacuum desulfurization is 110℃~135℃; and / or, the time of vacuum desulfurization is 1h~10h; and / or, the water content of the lithium sulfide suspension is <0.5%.

[0012] In this application, desulfurization is performed under reduced pressure, maintaining the desulfurization temperature at 110℃~135℃. This facilitates the desulfurization of the second lithium hydride solution while minimizing the decomposition of aprotic polar organic solvents. This significantly reduces the organic content in the lithium sulfide product and minimizes the loss of aprotic polar organic solvents, increasing their reuse rate. By rationally controlling the desulfurization time, lithium hydride is fully converted to lithium sulfide, avoiding increased energy consumption and reduced production efficiency caused by prolonged reaction times. Maintaining a low water content in the lithium sulfide suspension prevents the degradation of the generated lithium sulfide by excessive water content, improving the purity and yield of lithium sulfide. Compared to desulfurization processes at atmospheric pressure and 170℃~180℃, the desulfurization and low-temperature desulfurization method in this application significantly reduces energy consumption.

[0013] Optionally, in the step of reacting an aqueous hydrosulfide with a lithium salt dissolved in an aprotic polar organic solvent under an inert gas atmosphere to obtain a first lithium hydrosulfide suspension: the molar ratio of lithium salt to aqueous hydrosulfide is 1~1.5:1; and / or, the reaction temperature of the hydrosulfide reaction is 50℃~140℃, and the reaction time is 1h~10h; and / or, the aprotic polar organic solvent includes at least one of dimethyl sulfoxide, dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropionamide, N-methylpyrrolidone, N-alkylcaprolactam, and N-alkylpyrrolidone; and / or, the aqueous hydrosulfide includes at least one of potassium hydrosulfide and sodium hydrosulfide; and / or, the lithium salt includes lithium chloride.

[0014] This application employs an appropriate excess of lithium salt to ensure the complete conversion of hydrosulfide to lithium sulfide while avoiding an increase in impurities in the first lithium hydrosulfide suspension caused by excessive lithium salt. By rationally controlling the reaction temperature and time of the hydrosulfide reaction, the application ensures the smooth and complete progress of the hydrosulfide reaction while reducing the decomposition of aprotic polar organic solvents caused by high temperatures. By rationally selecting the types of aprotic polar organic solvents, the application promotes the smooth and complete progress of the hydrosulfide reaction and avoids the hydrolysis of the generated lithium hydrosulfide, while ensuring that the byproducts are insoluble and facilitate solid-liquid separation. Hydrous potassium hydrosulfide and hydrous sodium hydrosulfide have good dissociation capabilities for sulfide ions, ensuring efficient hydrosulfide reaction at a low cost. By rationally selecting the types of lithium salts, lithium salts that are easily dissociated in aprotic polar organic solvents are chosen to provide lithium ions for the hydrosulfide reaction and promote its progress.

[0015] Optionally, the second lithium hydrosulfide solution is desulfurized to obtain a lithium sulfide suspension, and after solid-liquid separation, lithium sulfide is obtained, including: desulfurizing the second lithium hydrosulfide solution to obtain a lithium sulfide suspension, separating the solid and liquid to obtain a first solid, washing the first solid to obtain lithium sulfide and washing liquid.

[0016] This application improves the purity of lithium sulfide by washing the first solid to remove any impurities that may be present in it.

[0017] Optionally, the washing temperature is 25℃~120℃; and / or, the washing time is 15min~300min; and / or, the washing solvent is the aprotic polar organic solvent.

[0018] This application achieves efficient impurity removal by rationally setting the washing temperature and washing time, and through the synergistic effect of the washing temperature and washing time; by using aprotic polar organic solvent as the washing solvent, it can avoid introducing additional solvent while achieving efficient impurity removal, and the resulting washing liquid can be recycled to avoid waste of washing solvent.

[0019] Optionally, the washing liquid is used as the first solvent; and / or, the aqueous hydrosulfide is reacted with the lithium salt dissolved in the first solvent under an inert gas atmosphere to obtain a first lithium hydrosulfide suspension. After solid-liquid separation, a second solid is obtained, and the washing liquid is used to wash the second solid; and / or, the second lithium hydrosulfide solution is desulfurized under reduced pressure to obtain a lithium sulfide suspension. After solid-liquid separation, a recovery liquid is obtained, and the recovery liquid is used as the first solvent; and / or, the first lithium hydrosulfide solution is dehydrated under reduced pressure to obtain a second lithium hydrosulfide suspension. After solid-liquid separation, a third solid is obtained, and the third solid is used as the lithium salt.

[0020] This application avoids wasting washing solvent by using the washing liquid as the first solvent; it separates the first lithium hydrosulfide suspension into a second solid and washes the second solid to achieve its utilization; by separating the lithium hydrosulfide suspension into a recovered liquid, on the one hand, the depressurization dehydration process removes a large number of impurities, making the main component of the recovered liquid a non-proton polar organic solvent with few impurities, and the possible trace impurities do not affect its recycling; on the other hand, the depressurization dehydration and desulfurization processes can reduce the decomposition of non-proton polar organic solvents, so the recovered liquid can be used as the first solvent and can be reused many times, thus constructing a solvent recycling production process; the third solid is used as a lithium salt, and lithium sulfide can provide lithium ions for the hydrosulfide reaction, thereby forming a closed loop of lithium ions in the reaction system.

[0021] Secondly, embodiments of this application provide a lithium sulfide prepared using the lithium sulfide preparation method provided in the first aspect of this application. The lithium sulfide has a D10 particle size of 0.7 μm to 0.9 μm, a D50 particle size of 6.5 μm to 8.5 μm, and a D100 particle size of 19 μm to 21 μm.

[0022] In this application, lithium sulfide obtained through a specific method exhibits a relatively concentrated particle size distribution and an appropriate particle size, ensuring a high specific surface area while preventing particle agglomeration. Furthermore, the lithium sulfide exhibits high crystallinity and an excellent crystal structure, thereby improving battery performance.

[0023] Optionally, the lithium sulfide has a metal-based purity >99.9%; and / or, the lithium sulfide has a cationic impurity content <500ppm; and / or, the lithium sulfide has a lithium sulfite content <0.05% and a lithium sulfate content <0.03%.

[0024] The lithium sulfide prepared by this application through a specific preparation method has extremely high purity and extremely low content of cationic impurities, resulting in high purity of lithium ions and avoiding interference of impurity cations with lithium ions. In addition, the lithium sulfide contains less lithium sulfite and lithium sulfate. When lithium sulfide is applied to solid electrolyte membranes, it can improve the stability of solid electrolyte membranes and their ability to transport lithium ions.

[0025] Thirdly, embodiments of this application provide a solid-state battery, including a solid electrolyte membrane, wherein the solid electrolyte membrane includes lithium sulfide prepared by the lithium sulfide preparation method provided in the first aspect of this application or lithium sulfide provided in the second aspect of this application.

[0026] In this application, lithium sulfide is applied to the solid electrolyte membrane to improve the stability of the solid electrolyte membrane and its ability to transport lithium ions, thereby improving the performance of the battery. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is the process flow of the lithium sulfide preparation method provided in the embodiments of this application. Figure 1 ; Figure 2 This is the process flow of the lithium sulfide preparation method provided in the embodiments of this application. Figure 2 . Detailed Implementation

[0029] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0030] This application provides a lithium sulfide, its preparation method, and an all-solid-state battery. Detailed descriptions are provided below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in a range format; it should be understood that the description in a range format is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0031] The technical solution of this application is as follows: Firstly, please refer to Figure 1 The embodiments of this application provide a method for preparing lithium sulfide, comprising: Aqueous hydrosulfide is reacted with lithium salt dissolved in a first solvent under inert gas protection to obtain a first lithium hydrosulfide suspension. After solid-liquid separation, a first lithium hydrosulfide solution is obtained. The first solvent includes an aprotic polar organic solvent. The first lithium hydrosulfide solution was dehydrated under reduced pressure to obtain a second lithium hydrosulfide suspension. After solid-liquid separation, a second lithium hydrosulfide solution was obtained. The water content in the second lithium hydrosulfide suspension was 0.05%~2%. The second lithium hydrosulfide solution was desulfurized to obtain a lithium sulfide suspension. After solid-liquid separation, lithium sulfide was obtained.

[0032] In this application, firstly, hydrosulfide and lithium salt are used as raw materials. Under the protection of an aprotic polar organic solvent and an inert gas, a hydrosulfide reaction is carried out to convert the lithium salt into lithium hydrosulfide dissolved in the aprotic polar organic solvent. After solid-liquid separation, a first lithium hydrosulfide solution is obtained. In this process, hydrosulfide is used as a raw material. On the one hand, the presence of a small amount of water can promote the smooth progress of the hydrosulfide reaction. On the other hand, hydrosulfide can be produced on a large scale and has low cost, thereby significantly reducing the cost of raw materials. Secondly, using low-cost hydrosulfide, the obtained first lithium hydrosulfide solution was subjected to dehydration under reduced pressure. On the one hand, as water was removed (which carried away some aprotic polar organic solvent), impurities in the first lithium hydrosulfide solution continuously precipitated. Simultaneously removing water and impurities from the lithium hydrosulfide solution significantly reduced the impurity ion content in the second lithium hydrosulfide solution. The water content of the second lithium hydrosulfide suspension was controlled at 0.05%~2%. This low water content allowed a large amount of impurities to be converted into precipitates and removed during the dehydration process. After solid-liquid separation, a high-purity second lithium hydrosulfide solution was obtained, ensuring the preparation of high-purity lithium sulfide. On the other hand, reduced pressure not only better removed water but also lowered the dehydration temperature while efficiently removing water, reducing the decomposition of aprotic polar organic solvents. Next, the impurity-removed second lithium hydrosulfide solution was desulfurized to obtain the target lithium sulfide product, which is insoluble in aprotic polar organic solvents. After solid-liquid separation, high-purity lithium sulfide was obtained.

[0033] It is understood that this application prepares high-purity lithium sulfide by liquid phase method. This method does not use hydrogen sulfide and metallic lithium as limiting raw materials, but uses highly safe and readily available hydrosulfide and lithium salt. Moreover, the preparation process is green, energy-efficient, and can be continuously produced, and the resulting lithium sulfide product has high purity.

[0034] In some embodiments, the water content in the second lithium hydrosulfide suspension is 0.05% to 1%, for example, it can be 0.05%, 0.1%, 0.3%, 0.5%, 0.8%, 1%, etc.

[0035] In this application, by controlling the water content in the second lithium sulfide suspension to a lower level, the lower water content allows 99.5% to 99.9% of the impurities to be converted into precipitates and removed during the dehydration process under reduced pressure, thereby making the content of cationic impurities in the second lithium sulfide solution <200ppm (cationic impurities mainly refer to the cations in the hydrosulfide and a small amount of impurities present in the raw materials).

[0036] In some embodiments, the pressure for dewatering is -0.04MPa to -0.10MPa, for example, -0.04MPa, -0.05MPa, -0.06MPa, -0.07MPa, -0.08MPa, -0.09MPa, -0.10MPa, etc.

[0037] In this application, by setting the pressure of dewatering to -0.04MPa to -0.10MPa, the appropriate negative pressure ensures efficient removal of water while reducing the decomposition loss of aprotic polar organic solvents.

[0038] In some embodiments, the temperature for dewatering under reduced pressure is 80℃~140℃, for example, it can be 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, etc.

[0039] Understandably, by properly controlling the temperature of dewatering under reduced pressure, a relatively low temperature can reduce the decomposition loss of aprotic polar organic solvents while removing water.

[0040] Understandably, by controlling the pressure, temperature, and time of dewatering, the water content in the second lithium hydride suspension can be controlled within the desired range.

[0041] In some embodiments, the desulfurization method is vacuum desulfurization, and the temperature of vacuum desulfurization is 110℃~135℃, for example, 110℃, 120℃, 130℃, 135℃, etc.

[0042] In this application, desulfurization is performed under reduced pressure, maintaining the desulfurization temperature at 110℃~135℃. This facilitates the successful desulfurization of the second lithium hydride solution while simultaneously reducing the decomposition of aprotic polar organic solvents. This not only significantly reduces the organic matter content in the lithium sulfide product but also minimizes the loss of aprotic polar organic solvents, increasing their reuse frequency. Furthermore, the relatively lower operating temperature results in lower energy consumption and less stringent safety requirements for equipment, further reducing costs and achieving green, low-cost, and high-purity lithium sulfide production. Currently, commonly used desulfurization methods operate at 170℃~180℃ under normal pressure, resulting in high energy consumption. This application employs reduced pressure desulfurization, lowering the temperature to 135℃ or below, significantly reducing energy consumption.

[0043] For example, the temperature for desulfurization under reduced pressure is 120℃~135℃.

[0044] In some embodiments, the desulfurization time is 1h to 10h, for example, it can be 1h, 3h, 5h, 8h, 10h, etc.

[0045] Understandably, by controlling the desulfurization time within a suitable range, not only can lithium hydrosulfide be fully converted into lithium sulfide, but the increased energy consumption and reduced production efficiency caused by a longer reaction time can also be avoided.

[0046] For example, the desulfurization time is 2h to 6h.

[0047] For example, the pressure for desulfurization is low, ranging from -0.09 MPa to -0.10 MPa.

[0048] In some embodiments, the water content of the lithium sulfide suspension is <0.5%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.49%, etc.

[0049] Understandably, by controlling the water content of the lithium sulfide suspension to a low level, the damage caused by excessive water content to the generated lithium sulfide can be avoided, thereby improving the purity and yield of lithium sulfide.

[0050] It is understandable that by controlling the pressure, temperature, and time of desulfurization, the water content in the lithium sulfide suspension can be controlled within the required range.

[0051] In some embodiments, in the step of reacting an aqueous hydrosulfide with a lithium salt dissolved in an aprotic polar organic solvent under an inert gas atmosphere to obtain a first lithium hydrosulfide suspension, the molar ratio of lithium salt to aqueous hydrosulfide is 1 to 1.5:1, for example, it can be 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, etc.

[0052] In this application, by controlling the molar ratio of lithium salt to aqueous hydrosulfide at 1 to 1.5:1, an appropriate excess of lithium salt can ensure that the hydrosulfide is fully converted into lithium sulfide, while avoiding the increase in impurity content in the first lithium hydrosulfide suspension caused by excessive lithium salt, which would affect the purity of lithium sulfide.

[0053] For example, the molar ratio of lithium salt to aqueous hydrosulfide is 1.1 to 1.4:1.

[0054] In some embodiments, the reaction temperature of the hydrogen sulfide reaction is 50℃~140℃, and the reaction time is 1h~10h. For example, the reaction temperature of the hydrogen sulfide reaction can be 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, etc., and the reaction time can be 1h, 3h, 5h, 8h, 10h, etc.

[0055] It is understandable that by reasonably controlling the reaction temperature and reaction time of the hydrosulfurization reaction, the decomposition of aprotic polar organic solvents caused by high temperature can be reduced while ensuring that the hydrosulfurization reaction proceeds smoothly and fully.

[0056] For example, the reaction time for the hydrogenation reaction is 2h to 4h.

[0057] In some embodiments, the aprotic polar organic solvent includes at least one of dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), 3-methoxy-N,N-dimethylpropionamide (DMPA), N-methylpyrrolidone (NMP), N-alkylcaprolactam, and N-alkylpyrrolidone; preferably N-methylpyrrolidone.

[0058] Understandably, by rationally setting the types of aprotic polar organic solvents, firstly, the aforementioned aprotic polar organic solvents can dissolve hydrides and lithium salts to a certain extent, thereby promoting the smooth and complete progress of the hydride reaction; secondly, they can dissolve lithium hydrides but not byproducts, facilitating solid-liquid separation; and thirdly, the aprotic properties can prevent the hydrolysis of the generated lithium hydrides.

[0059] For example, the aprotic polar organic solvent is N-methylpyrrolidone.

[0060] In some embodiments, the aqueous hydrosulfide includes at least one of potassium hydrosulfide and sodium hydrosulfide.

[0061] Understandably, hydrated hydrosulfide is set to include at least one of potassium hydrosulfide and sodium hydrosulfide. On the one hand, potassium hydrosulfide and sodium hydrosulfide have good dissociation capabilities for hydrogen sulfide ions, ensuring efficient hydrosulfidation reaction; on the other hand, potassium hydrosulfide and sodium hydrosulfide are readily available and inexpensive. Understandably, when the hydrated hydrosulfide is potassium hydrosulfide, the impurity ion in the first lithium hydrosulfide suspension is potassium ion; when the hydrated hydrosulfide is sodium hydrosulfide, the impurity ion in the first lithium hydrosulfide suspension is sodium ion.

[0062] In some embodiments, the lithium salt includes lithium chloride.

[0063] It is understandable that by rationally setting the types of lithium salts and selecting lithium salts that are easily dissociated in aprotic polar organic solvents, lithium ions can be provided for the hydrosulfidation reaction, thus promoting the hydrosulfidation reaction.

[0064] In some embodiments, the second lithium hydrosulfide solution is desulfurized under reduced pressure to obtain a lithium sulfide suspension. After solid-liquid separation, lithium sulfide is obtained, comprising: The second lithium hydrosulfide solution was desulfurized under reduced pressure to obtain a lithium sulfide suspension. After solid-liquid separation, a first solid was obtained. The first solid was washed to obtain lithium sulfide and washing liquid.

[0065] In this application, the purity of lithium sulfide is further improved by washing the first solid to remove any impurities that may be present in the first solid.

[0066] In some embodiments, the washing temperature is 80℃~120℃, for example, it can be 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 95℃, 115℃, 120℃, etc.

[0067] In this application, by setting the washing temperature to 80℃~120℃, the relatively high washing temperature can not only increase the solubility of impurities, thereby increasing the purity of the product, but also increase the desorption rate of impurities and improve the impurity removal efficiency.

[0068] In some embodiments, the washing time is 15 min to 300 min, for example, it can be 15 min, 50 min, 100 min, 150 min, 200 min, 250 min, 300 min, etc.

[0069] It is understandable that selecting an appropriate washing time based on the washing temperature, and achieving efficient impurity removal through the coordinated use of washing temperature and washing time.

[0070] In some embodiments, the washing solvent is an aprotic polar organic solvent.

[0071] It is understandable that by using aprotic polar organic solvents as washing solvents, impurities can be removed efficiently while avoiding the introduction of additional solvents, making the reaction system more homogeneous. At the same time, the resulting washing liquid can be recycled, avoiding the waste of washing solvents.

[0072] In some embodiments, the washing liquid is used as a first solvent.

[0073] In this application, by using the washing solution as the first solvent, the waste of washing solvent can be avoided, and the small amount of impurities in the washing solution does not affect the reaction or the purity of the reaction product.

[0074] Aqueous hydrosulfide is reacted with lithium salt dissolved in a first solvent under inert gas protection to obtain a first lithium hydrosulfide suspension. After solid-liquid separation, a second solid is obtained, and the washing liquid is used to wash the second solid.

[0075] It is understandable that by separating the first lithium hydrosulfide suspension into a solid and liquid state to obtain a second solid, and then washing the second solid, the second solid can be sold or utilized, thereby improving the utilization rate of the product.

[0076] For example, when the hydrated hydrosulfide is sodium hydrosulfide and the lithium salt is lithium chloride, the hydrated sodium hydrosulfide and lithium chloride undergo a hydrosulfide reaction to produce lithium hydrosulfide and sodium chloride, that is, the second solid is sodium chloride, which is then washed and sold externally.

[0077] The second lithium hydride solution is desulfurized to obtain a lithium sulfide suspension. After solid-liquid separation, a recovered liquid is obtained, which is used as the first solvent. That is, the first solvent includes an aprotic polar organic solvent, the recovered liquid, and the washing liquid.

[0078] Understandably, by separating the lithium sulfide suspension into solid and liquid components to obtain the recovered liquid, on the one hand, the decompression dehydration process removes a large number of impurities, making the main component of the recovered liquid aprotic polar organic solvent with fewer impurities. At the same time, the very small amount of impurities that may exist do not affect its recycling. On the other hand, the decompression dehydration and desulfurization processes can reduce the decomposition of aprotic polar organic solvents. Therefore, the recovered liquid can be used as the primary solvent and can be reused multiple times, thereby constructing a solvent recycling production process and reducing costs.

[0079] The first lithium hydrosulfide solution was dehydrated under reduced pressure to obtain a second lithium hydrosulfide suspension. After solid-liquid separation, a third solid was obtained, which was used as a lithium salt.

[0080] It is understandable that during the dehydration process, lithium hydrosulfide will be desulfurized, resulting in the presence of lithium sulfide in the third solid. Simultaneously, the hydrolysis of lithium hydrosulfide may occur, resulting in the presence of lithium hydroxide in the third solid. When the third solid is used as a lithium salt, lithium sulfide can provide lithium ions for the hydrosulfide reaction, thereby forming a closed loop of lithium ions in the reaction system.

[0081] For example, when the hydrated hydrosulfide is hydrated sodium hydrosulfide and the lithium salt is lithium chloride, the hydrated sodium hydrosulfide and lithium chloride undergo a hydrosulfide reaction to generate lithium hydrosulfide and sodium chloride. That is, the first lithium hydrosulfide suspension includes the first lithium hydrosulfide solution and sodium chloride. The first lithium hydrosulfide solution undergoes dehydration under reduced pressure, which may be accompanied by the desulfurization of a small amount of lithium hydrosulfide. Therefore, a large amount of sodium chloride and a small amount of lithium sulfide are precipitated during dehydration under reduced pressure. That is, the third solid includes a large amount of sodium chloride and a small amount of lithium sulfide. The third solid contains lithium sulfide, which can provide lithium ions. Therefore, the third solid can be used as a lithium salt.

[0082] For example, such as Figure 2 As shown, the preparation method of lithium sulfide includes: Aqueous hydrosulfide is reacted with lithium salt dissolved in a first solvent under inert gas protection to obtain a first lithium hydrosulfide suspension. After solid-liquid separation, a first lithium hydrosulfide solution and a second solid are obtained. The first solvent includes an aprotic polar organic solvent. The first lithium hydrosulfide solution was dehydrated under reduced pressure to obtain a second lithium hydrosulfide suspension. After solid-liquid separation, a second lithium hydrosulfide solution and a third solid were obtained. The third solid was used as a lithium salt. The second lithium hydrosulfide solution is desulfurized to obtain a lithium sulfide suspension. After solid-liquid separation, a first solid and a recovered liquid are obtained. The main component of the recovered liquid is an aprotic polar organic solvent. The first solid is washed with a new aprotic polar organic solvent to obtain lithium sulfide and a washing liquid. The recovered liquid and a portion of the washing liquid are used as the first solvent, and the other portion of the washing liquid is used to wash the second solid.

[0083] Secondly, embodiments of this application provide a lithium sulfide prepared using the lithium sulfide preparation method provided in the first aspect of this application. The lithium sulfide has a D10 particle size of 0.7 μm to 0.9 μm, a D50 particle size of 6.5 μm to 8.5 μm, and a D100 particle size of 19 μm to 21 μm.

[0084] In this application, lithium sulfide obtained through a specific method exhibits a relatively concentrated particle size distribution and an appropriate particle size, ensuring a high specific surface area while preventing particle agglomeration. Furthermore, the lithium sulfide exhibits high crystallinity and an excellent crystal structure, thereby improving battery performance.

[0085] In some embodiments, the metal-based purity of lithium sulfide is >99.9%.

[0086] The lithium sulfide prepared by the specific preparation method of this application has a metal-based purity of >99.9%, which further demonstrates that the lithium sulfide prepared in this application has high purity.

[0087] In some embodiments, the content of cationic impurities in lithium sulfide is <500 ppm, and the content of sodium or potassium ions is <200 ppm.

[0088] The lithium sulfide prepared by the specific preparation method of this application has extremely low content of cationic impurities, resulting in high purity of lithium ions and avoiding interference of impurity cations with lithium ions. When lithium sulfide is applied to solid electrolyte membranes, it can improve the ability of solid electrolyte membranes to transport lithium ions.

[0089] In some embodiments, the lithium sulfide contains <0.05% lithium sulfite and <0.03% lithium sulfate.

[0090] It is understandable that the lithium sulfide obtained in this application contains relatively low amounts of lithium sulfite and lithium sulfate. When lithium sulfide is applied to a solid electrolyte membrane, it results in better stability of the solid electrolyte membrane and a stronger ability to transport lithium ions.

[0091] Thirdly, embodiments of this application provide a solid-state battery, including a solid electrolyte membrane, wherein the solid electrolyte membrane includes lithium sulfide prepared by the lithium sulfide preparation method provided in the first aspect of this application or lithium sulfide provided in the second aspect of this application.

[0092] In this application, lithium sulfide is applied to the solid electrolyte membrane to improve the stability of the solid electrolyte membrane and its ability to transport lithium ions, thereby improving the performance of the battery.

[0093] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0094] Example 1 This embodiment provides a method for preparing lithium sulfide, including: (1) Sodium hydrosulfide containing water and lithium chloride dissolved in the first solvent are subjected to hydrosulfide reaction under inert gas protection to obtain a first lithium hydrosulfide suspension (water content of 7%~8%). After solid-liquid separation, a first lithium hydrosulfide solution and a second solid are obtained. The first solvent includes N-methylpyrrolidone (NMP).

[0095] The molar ratio of lithium chloride to hydrated sodium hydrosulfide is 1.3:1, the reaction temperature of the hydrosulfide reaction is 50℃, and the reaction time is 3h.

[0096] (2) The first lithium hydrosulfide solution is dehydrated under reduced pressure to obtain a second lithium hydrosulfide suspension. After solid-liquid separation, a second lithium hydrosulfide solution and a third solid are obtained. The third solid is used as lithium chloride. It is understood that the use of the third solid as lithium chloride does not mean that the composition of the third solid is lithium chloride, but rather that the third solid can provide lithium ions.

[0097] The temperature for dehydration under reduced pressure was 120℃, the pressure for dehydration under reduced pressure was -0.09MPa, the water content in the second lithium hydride suspension was 1%, and the water content was determined using a Karl Fischer moisture analyzer.

[0098] (3) The second lithium hydride solution is desulfurized under reduced pressure to obtain a lithium sulfide suspension. After solid-liquid separation, the first solid and the recovered non-proton polar organic solvent are used to wash the first solid with NMP to obtain lithium sulfide and washing liquid. The recovered non-proton polar organic solvent and a part of the washing liquid are used as the first solvent, and the other part of the washing liquid is used to wash the second solid.

[0099] The desulfurization temperature was 125℃, the desulfurization time was 4h, the desulfurization pressure was -0.10MPa, and the water content of the lithium sulfide suspension was <0.5%.

[0100] The NMP washing temperature for the first solid was 105°C, and the washing time was 100 min.

[0101] Example 2 This embodiment provides a method for preparing lithium sulfide. Compared with Example 1, the only difference is that the temperature for dehydration under reduced pressure in step (2) is 140°C and the pressure for dehydration under reduced pressure is -0.08 MPa, so that the water content in the second lithium sulfide suspension is 0.05%. The rest is roughly the same as in Example 1, and will not be repeated here.

[0102] Example 3 This embodiment provides a method for preparing lithium sulfide. Compared with Example 1, the only difference is that the temperature for dehydration under reduced pressure in step (2) is 80°C, the pressure for dehydration under reduced pressure is -0.10 MPa, and the time for dehydration under reduced pressure is twice that of Example 1, so that the water content in the second lithium sulfide suspension is 2%. The rest is roughly the same as in Example 1, and will not be repeated here.

[0103] Example 4 This embodiment provides a method for preparing lithium sulfide. Compared with Example 1, the only difference is that the temperature for dehydration under reduced pressure in step (2) is 160°C, the pressure for dehydration under reduced pressure is -0.05MPa, and the time for dehydration under reduced pressure is shortened so that the water content in the second lithium sulfide suspension is 1%. The rest is roughly the same as in Example 1, and will not be repeated here.

[0104] Example 5 This embodiment provides a method for preparing lithium sulfide. Compared with Example 1, the only difference is that the desulfurization temperature in step (3) is 135°C and the desulfurization pressure is -0.08MPa. The rest is roughly the same as in Example 1, and will not be repeated here.

[0105] Example 6 This embodiment provides a method for preparing lithium sulfide. Compared with Example 1, the only difference is that the desulfurization temperature in step (3) is 110°C. The rest is roughly the same as in Example 1 and will not be repeated here.

[0106] Example 7 This comparative example provides a method for preparing lithium sulfide. Compared with Example 1, the only difference is that the desulfurization temperature in step (3) is 160°C and the desulfurization pressure is -0.05MPa. The other steps are roughly the same as in Example 1 and will not be repeated here.

[0107] Comparative Example 1 This comparative example provides a method for preparing lithium sulfide. Compared with Example 1, the only difference is that the temperature for dehydration under reduced pressure in step (2) is 70°C, the pressure for dehydration under reduced pressure is -0.08 MPa, and the time for dehydration under reduced pressure is twice that of Example 1, so that the water content in the second lithium sulfide suspension is 4.5%. The rest is roughly the same as in Example 1, and will not be repeated here.

[0108] Comparative Example 2 This comparative example provides a method for preparing lithium sulfide. Compared with Example 1, the only difference is that the depressurization dehydration process in step (2) is not performed. Instead, the first lithium sulfide solution is directly subjected to the depressurization desulfurization process in step (3). The rest is roughly the same as in Example 1, and will not be repeated here.

[0109] Comparative Example 3 This comparative example provides a method for preparing lithium sulfide, comprising: (1) Sodium hydrosulfide and lithium chloride dissolved in the first solvent are subjected to hydrosulfide reaction under inert gas protection to obtain a first lithium hydrosulfide suspension. After solid-liquid separation, a first lithium hydrosulfide solution and a second solid are obtained. The first solvent includes N-methylpyrrolidone (NMP).

[0110] The molar ratio of lithium chloride to sodium hydrosulfide is 1.3:1, the reaction temperature of the hydrosulfide reaction is 50℃, and the reaction time is 3h.

[0111] (3) The first lithium hydrosulfide suspension is desulfurized under reduced pressure to obtain lithium sulfide suspension. After solid-liquid separation, the first solid and the recovered liquid are obtained. The first solid is washed with NMP to obtain lithium sulfide and washing liquid. The recovered liquid and part of the washing liquid are used as the first solvent, and the other part of the washing liquid is used to wash the second solid.

[0112] The desulfurization temperature was 125℃, the desulfurization time was 4 hours, and the dewatering pressure was -0.10MPa.

[0113] The NMP washing temperature for the first solid was 105°C, and the washing time was 100 min.

[0114] The lithium sulfides prepared in Examples 1-7 and Comparative Examples 1-3 were subjected to performance tests, and the results are shown in Table 1.

[0115] Yield testing was performed using the formula: Yield = (Dried product / Theoretical output from feed) x 100%. Sodium ion content, other cationic impurities (including magnesium, iron, calcium, aluminum, silicon, etc.) content, and lithium-sulfur ratio were determined using ICP testing.

[0116] Table 1

[0117] As shown in Table 1, the data from Examples 1-3 and Comparative Example 1 indicate that when the water content in the second lithium sulfide suspension obtained by the vacuum dehydration process is controlled to be 0.05%-2%, the yield and purity of the obtained lithium sulfide are relatively high. In particular, when the water content in the second lithium sulfide suspension is 0.05%-1%, the purity of the obtained lithium sulfide is significantly improved. The lithium sulfide prepared in Examples 1-3 has a lithium sulfite content and a lithium sulfate content of less than 0.03% (the lithium sulfite content and lithium sulfate content were quantitatively detected by ion chromatography). The low impurity content results in a metal-based purity of lithium sulfide higher than 99.9%. Meanwhile, the lithium sulfide obtained in Examples 1-2 has a D10 particle size of 0.7μm-0.9μm, a D50 particle size of 6.5μm-8.5μm, and a D100 particle size of 19-21μm, indicating that the lithium sulfide product has a relatively small particle size and a uniform particle size distribution. When the water content in the resulting lithium hydride second suspension is 4.5%, the lithium-sulfur ratio of the obtained lithium sulfide is as high as 7.6, indicating a significant decrease in purity. Simultaneously, the impurity content in the obtained lithium sulfide is significantly higher. This is mainly because excessive water content in the lithium hydride second suspension leads to the formation of lithium hydroxide. Higher water content results in a higher impurity content in the lithium hydride second solution, leading to a higher content of cationic impurities in the obtained lithium sulfide, thus affecting the purity of the product. Data from Example 4 shows that when the dehydration temperature exceeds 150°C, the yield of lithium sulfide decreases significantly. This may be because higher dehydration temperatures cause the desulfurization reaction to proceed prematurely, resulting in the decomposition of a large amount of lithium hydride during the dehydration process, thus significantly reducing the lithium sulfide yield. Furthermore, higher temperatures affect the precipitation of impurities, resulting in lower purity of the lithium sulfide.

[0118] Data from Examples 5-7 show that when the desulfurization temperature is between 110°C and 135°C, a better desulfurization effect can be achieved, resulting in lithium sulfide products with higher purity and yield. However, when the desulfurization temperature is higher, the desulfurization reaction proceeds too quickly, resulting in a higher impurity content and relatively lower purity in the lithium sulfide.

[0119] As can be seen from the data in Comparative Example 2, when the dewatering step is not performed, the presence of water introduces more impurities, resulting in a lithium-sulfur ratio of up to 8.62, a sodium ion content of up to 3512 ppm, and other cationic impurities content of up to 287 ppm. This further illustrates that by removing water under reduced pressure, the solubility of impurity cations in the second lithium sulfide solution decreases as the water content decreases, thereby improving the purity of the lithium sulfide product.

[0120] As can be seen from the data in Comparative Example 3, when using anhydrous raw materials, although the purity of lithium sulfide products is high, the yield drops significantly, energy consumption is high, and the production rate is low, making it unsuitable for large-scale production.

[0121] In summary, this application significantly reduces the content of cationic impurities by adding a vacuum dehydration process and controlling the water content of the second lithium sulfide suspension obtained by vacuum dehydration. Finally, high-purity lithium sulfide is obtained through vacuum desulfurization.

[0122] The foregoing has provided a detailed description of a lithium sulfide and its preparation method, as well as an all-solid-state battery, provided by the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing lithium sulfide, characterized in that, include: Aqueous hydrosulfide is reacted with lithium salt dissolved in a first solvent under inert gas protection to obtain a first lithium hydrosulfide suspension. After solid-liquid separation, a first lithium hydrosulfide solution is obtained. The first solvent includes an aprotic polar organic solvent. The first lithium hydrosulfide solution is dehydrated under reduced pressure to obtain a second lithium hydrosulfide suspension. After solid-liquid separation, a second lithium hydrosulfide solution is obtained. The water content in the second lithium hydrosulfide suspension is 0.05%~2%. The second lithium hydrosulfide solution was desulfurized to obtain a lithium sulfide suspension. After solid-liquid separation, lithium sulfide was obtained.

2. The method for preparing lithium sulfide according to claim 1, characterized in that, The water content in the second lithium hydrosulfide suspension is 0.05% to 1%.

3. The method for preparing lithium sulfide according to claim 1, characterized in that, The pressure for dewatering is -0.04 MPa to -0.10 MPa; and / or, The temperature for dewatering under reduced pressure is 80℃~140℃.

4. The method for preparing lithium sulfide according to any one of claims 1 to 3, characterized in that, The desulfurization method is vacuum desulfurization, and the vacuum desulfurization temperature is 110℃~135℃; and / or, The desulfurization time is 1 hour to 10 hours; and / or, The water content of the lithium sulfide suspension is <0.5%.

5. The method for preparing lithium sulfide according to any one of claims 1 to 4, characterized in that, In the step of reacting an aqueous hydrosulfide with a lithium salt dissolved in an aprotic polar organic solvent under an inert gas atmosphere to obtain a first lithium hydrosulfide suspension: The molar ratio of the lithium salt to the aqueous hydrosulfide is 1~1.5:1; and / or, The hydrosulfurization reaction is carried out at a temperature of 50℃ to 140℃ for a reaction time of 1 h to 10 h; and / or, The aprotic polar organic solvent includes at least one selected from dimethyl sulfoxide, dimethylformamide, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropionamide, N-methylpyrrolidone, N-alkylcaprolactam, and N-alkylpyrrolidone; and / or, The hydrated hydrosulfide includes at least one of potassium hydrosulfide and sodium hydrosulfide; and / or, The lithium salt includes lithium chloride.

6. The method for preparing lithium sulfide according to any one of claims 1 to 5, characterized in that, The process of desulfurizing the second lithium hydrosulfide solution to obtain a lithium sulfide suspension, followed by solid-liquid separation to obtain lithium sulfide, includes: The second lithium hydrosulfide solution is desulfurized to obtain the lithium sulfide suspension. After solid-liquid separation, a first solid is obtained. The first solid is washed to obtain the lithium sulfide and the washing liquid.

7. The method for preparing lithium sulfide according to claim 6, characterized in that, The washing temperature is 80℃~120℃; and / or, The washing time is 15 min to 300 min; and / or, The washing solvent is the aprotic polar organic solvent.

8. The method for preparing lithium sulfide according to claim 6, characterized in that, The washing solution is used as the first solvent; and / or, The process involves reacting the aqueous hydrosulfide with a lithium salt dissolved in a first solvent under an inert gas atmosphere to obtain a first lithium hydrosulfide suspension. After solid-liquid separation, a second solid is obtained, and the washing liquid is used to wash the second solid; and / or, The second lithium hydride solution is desulfurized under reduced pressure to obtain a lithium sulfide suspension. After solid-liquid separation, a recovered liquid is obtained, which is used as the first solvent; and / or, The first lithium hydrosulfide solution is dehydrated under reduced pressure to obtain a second lithium hydrosulfide suspension. After solid-liquid separation, a third solid is obtained, which is used as the lithium salt.

9. A lithium sulfide, characterized in that, The lithium sulfide is prepared by the method according to any one of claims 1 to 8, wherein the D10 particle size is 0.7 μm to 0.9 μm, the D50 particle size is 6.5 μm to 8.5 μm, and the D100 particle size is 19 μm to 21 μm.

10. The lithium sulfide according to claim 9, characterized in that, The lithium sulfide has a metal-based purity >99.9%; and / or, The lithium sulfide contains <500 ppm of cationic impurities; and / or, The lithium sulfide has a lithium sulfite content of <0.05% and a lithium sulfate content of <0.03%.

11. A solid-state battery, characterized in that, The solid electrolyte membrane includes lithium sulfide prepared by the method of preparing lithium sulfide according to any one of claims 1 to 8 or lithium sulfide according to any one of claims 9 to 10.

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