Preparation method of lithium sulfide material

Abstract

The invention relates to the technical field of battery materials, in particular to a preparation method of a lithium sulfide material. The preparation method of the lithium sulfide material comprises the following steps: S1, mixing lithium carbonate and sodium sulfide, heating to a first heating temperature to melt lithium carbonate and react with sodium sulfide, separating out a solid phase, and collecting a first solid; s2, the first solid is heated to a second heating temperature, the second heating temperature is higher than the melting point of sodium carbonate and lower than the melting points of lithium sulfide and sodium sulfide, a solid phase is separated out, and a second solid is collected; s3, the second solid is heated to a third heating temperature, the third heating temperature is higher than the melting point of lithium sulfide and lower than the melting point of sodium sulfide, a liquid phase is separated out, and a liquid lithium sulfide material is prepared; and S4, carrying out curing treatment on the liquid lithium sulfide material to prepare a solid lithium sulfide material. The preparation method improves the reaction conversion rate, simplifies the process flow, reduces the cost and improves the product purity.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, and in particular to methods for preparing lithium sulfide materials. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and drones, the demand for energy storage batteries is constantly increasing, placing higher requirements on their energy density and safety.

[0003] Among numerous battery materials, lithium sulfide (Li2S) exhibits enormous application potential. It is not only the cathode material for high-capacity lithium-sulfur batteries, but also a raw material for preparing sulfide solid electrolytes in high-energy-density, high-safety solid-ion batteries.

[0004] However, in traditional battery-grade lithium sulfide preparation methods, dry synthesis has a long process flow, many side reactions, and a complicated impurity removal process; wet synthesis requires the use of a large amount of organic solvents, which not only increases costs and environmental pressure, but also makes it difficult to remove by-products, ultimately affecting product purity.

[0005] Furthermore, lithium sulfide is chemically reactive and unstable in air, so anhydrous and oxygen-free conditions must be ensured during its preparation. At the same time, battery-grade lithium sulfide requires high purity to prevent impurities from affecting the battery's electrochemical performance. Summary of the Invention

[0006] Therefore, it is necessary to provide a method for preparing lithium sulfide materials to solve the above-mentioned technical problems.

[0007] A first aspect of this application provides a method for preparing lithium sulfide material, the method comprising the following steps: S1, mixing lithium carbonate and sodium sulfide, heating to a first heating temperature to melt the lithium carbonate and react it with the sodium sulfide, separating the solid phase, and collecting the first solid; S2, heating the first solid to a second heating temperature, the second heating temperature being higher than the melting point of sodium carbonate and lower than the melting points of lithium sulfide and sodium sulfide, separating the solid phase, and collecting the second solid; S3, heating the second solid to a third heating temperature, the third heating temperature being higher than the melting point of lithium sulfide and lower than the melting point of sodium sulfide, separating the liquid phase, and preparing a liquid lithium sulfide material; S4, solidifying the liquid lithium sulfide material to prepare a solid lithium sulfide material.

[0008] In some embodiments, step S1 satisfies at least one of the following conditions: (1) the molar ratio of lithium carbonate to sodium sulfide is 1:(1.001~1.1); (2) the total amount of metal impurities in lithium carbonate is ≤50 ppm; (3) the total amount of metal impurities in sodium sulfide is ≤50 ppm; (4) the mixing method includes at least one of mechanical crushing, spraying and ball milling; (5) the first heating temperature is 600℃~800℃; (6) the reaction time of lithium carbonate and sodium sulfide is 1h~6h.

[0009] In some embodiments, step S2 satisfies at least one of the following conditions: (1) the second heating temperature is 850°C to 940°C; (2) the holding time after heating to the second heating temperature is 0.5h to 3h.

[0010] In some embodiments, step S3 satisfies at least one of the following conditions: (1) the third heating temperature is 940°C to 950°C; (2) the holding time after heating to the third heating temperature is 10 min to 60 min.

[0011] In some implementations, the curing process in step S4 is cooling crystallization.

[0012] In some embodiments, step S4 specifically includes the following steps: S41, cooling the liquid lithium sulfide material to a first cooling temperature, which is lower than the freezing point of lithium sulfide, separating the solid phase, and preparing a third solid; S42, cooling the third solid to a second cooling temperature, which is lower than the first cooling temperature, separating the solid phase, and preparing a solid lithium sulfide material.

[0013] In some embodiments, at least one of the following conditions is met: (1) the first cooling temperature is 700°C to 900°C; (2) the holding time of the first cooling temperature is 1h to 3h; (3) the second cooling temperature is 200°C to 600°C; (4) the holding time of the second cooling temperature is 0.5h to 3h.

[0014] In some embodiments, after step S4, the preparation method further includes the following step: S5, pulverizing the solid lithium sulfide material to prepare lithium sulfide powder.

[0015] In some embodiments, the pulverization method includes at least one of mechanical pulverization, air jet milling, and ball milling.

[0016] In some embodiments, the preparation method is carried out under an inert or reducing atmosphere.

[0017] Compared with traditional technologies, the method for preparing lithium sulfide materials provided in some embodiments of this application has at least the following beneficial effects:

[0018] First, in the reaction stage (step S1), low-cost and high-purity lithium carbonate and sodium sulfide are selected as starting materials. The lithium carbonate and sodium sulfide are mixed and heated to the first heating temperature. The lower melting point of lithium carbonate causes it to melt, while the higher melting point of sodium sulfide dissolves in the molten lithium carbonate, forming a molten reaction system. The reaction equation is Li₂CO₃(l) + Na₂S(s) → Na₂CO₃(s) + Li₂S(s). Since the melting point of the byproduct sodium carbonate is much higher than the reaction temperature, sodium carbonate continuously precipitates in solid form during the reaction, continuously driving the reaction forward, thus achieving a high conversion rate.

[0019] Secondly, in the purification stage (steps S1 to S3), a gradient heating method is used. Utilizing the melting point differences between the components in the reaction system, the impurity removal process is completed without introducing solvents, reducing production costs and environmental pressure, and achieving efficient removal of byproducts. Specifically, in step S1, after the reaction stage, the solid product generated is separated through solid-liquid separation to remove the unreacted liquid lithium carbonate from the reaction system. In step S2, the temperature is raised to a second heating temperature, which is higher than the melting point of sodium carbonate but lower than the melting points of lithium sulfide and sodium sulfide, thereby melting the sodium carbonate and converting it into a liquid phase. Through solid-liquid separation, the solid phase is separated, removing the liquid sodium carbonate. In step S3, the temperature is further raised to a third heating temperature, which is higher than the melting point of lithium sulfide but lower than the melting point of sodium sulfide, thereby melting the lithium sulfide and converting it into a liquid phase. The sodium sulfide raw material remains solid, and through solid-liquid separation, the liquid phase is separated, obtaining liquid lithium sulfide material and removing the solid sodium sulfide.

[0020] Finally, in the product forming stage (step S4), the liquid lithium sulfide material is solidified to obtain the solid lithium sulfide material.

[0021] The above preparation method simplifies the process flow, eliminates the need for purification materials such as organic solvents, and can be operated under anhydrous and oxygen-free conditions throughout the entire process. This effectively reduces the introduction of impurities and the decomposition of products, resulting in a significant improvement in product purity, which meets the requirements of battery-grade lithium sulfide. Attached Figure Description

[0022] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0023] Figure 1 This is a schematic flowchart of a method for preparing lithium sulfide according to one embodiment of this application. Detailed Implementation

[0024] Reference will now be made to detailed embodiments of this application, one or more of which are described below. Each example is provided for explanation and not for limitation of this application. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made to this application without departing from its scope or spirit. For example, features described or illustrated as part of one embodiment may be used in another embodiment to produce further embodiments.

[0025] Therefore, this application is intended to cover such modifications and variations falling within the scope of the appended claims and their equivalents. Other objects, features, and aspects of this application are disclosed in or will be apparent from the following detailed description. It will be understood by those skilled in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of this application.

[0026] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0027] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0028] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0029] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0030] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0031] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0032] The first aspect of this application, as Figure 1 As shown, a method for preparing lithium sulfide material is provided, the method comprising the following steps:

[0033] S1. Mix lithium carbonate and sodium sulfide, heat to the first heating temperature to melt the lithium carbonate and react with the sodium sulfide, separate the solid phase, and collect the first solid.

[0034] S2. The first solid is heated to a second heating temperature, which is higher than the melting point of sodium carbonate but lower than the melting points of lithium sulfide and sodium sulfide. The solid phase is separated and the second solid is collected.

[0035] S3. The second solid is heated to a third heating temperature, which is higher than the melting point of lithium sulfide but lower than the melting point of sodium sulfide, and the liquid phase is separated to prepare liquid lithium sulfide material.

[0036] S4. Solidify the liquid lithium sulfide material to prepare a solid lithium sulfide material.

[0037] The method for preparing lithium sulfide materials provided in some embodiments of this application has at least the following beneficial effects:

[0038] First, in the reaction stage (step S1), low-cost and high-purity lithium carbonate and sodium sulfide are selected as starting materials. The lithium carbonate and sodium sulfide are mixed and heated to the first heating temperature. The lower melting point of lithium carbonate causes it to melt, while the higher melting point of sodium sulfide dissolves in the molten lithium carbonate, forming a molten reaction system. The reaction equation is Li₂CO₃(l) + Na₂S(s) → Na₂CO₃(s) + Li₂S(s). Since the melting point of the byproduct sodium carbonate is much higher than the reaction temperature, sodium carbonate continuously precipitates in solid form during the reaction, continuously driving the reaction forward, thus achieving a high conversion rate.

[0039] Secondly, in the purification stage (steps S1 to S3), a gradient heating method is used. Utilizing the melting point differences between the components in the reaction system, the impurity removal process is completed without introducing solvents, reducing production costs and environmental pressure, and achieving efficient removal of byproducts. Specifically, in step S1, after the reaction stage, the solid product generated is separated through solid-liquid separation to remove the unreacted liquid lithium carbonate from the reaction system. In step S2, the temperature is raised to a second heating temperature, which is higher than the melting point of sodium carbonate but lower than the melting points of lithium sulfide and sodium sulfide, thereby melting the sodium carbonate and converting it into a liquid phase. Through solid-liquid separation, the solid phase is separated, removing the liquid sodium carbonate. In step S3, the temperature is further raised to a third heating temperature, which is higher than the melting point of lithium sulfide but lower than the melting point of sodium sulfide, thereby melting the lithium sulfide and converting it into a liquid phase. The sodium sulfide raw material remains solid, and through solid-liquid separation, the liquid phase is separated, obtaining liquid lithium sulfide material and removing the solid sodium sulfide.

[0040] Finally, in the product forming stage (step S4), the liquid lithium sulfide material is solidified to obtain the solid lithium sulfide material.

[0041] The above preparation method simplifies the process flow, eliminates the need for purification materials such as organic solvents, and can be operated under anhydrous and oxygen-free conditions throughout the entire process. This effectively reduces the introduction of impurities and the decomposition of products, resulting in a significant improvement in product purity, which meets the requirements of battery-grade lithium sulfide.

[0042] The chemical reaction equation for steps S1 to S3 as a whole is Li2CO3(l) + Na2S(l) → Na2CO3(s) + Li2S(l), which is the reaction in which sodium carbonate solid is precipitated in the molten state.

[0043] In some embodiments, in step S1, the molar ratio of lithium carbonate to sodium sulfide is 1:(1.001~1.1). Exemplarily, in step S1, the molar ratio of lithium carbonate to sodium sulfide can be, but is not limited to, 1:1.001, 1:1.01, or 1:1.1. Thus, an excess of sodium sulfide is beneficial for achieving efficient conversion of lithium carbonate.

[0044] In some embodiments, in step S1, the total amount of metal impurities in lithium carbonate is ≤50 ppm.

[0045] In some embodiments, in step S1, the total amount of metallic impurities in sodium sulfide is ≤50 ppm.

[0046] Therefore, using high-purity lithium carbonate or sodium sulfide as starting materials is beneficial to improving the purity of lithium sulfide material products.

[0047] In some embodiments, in step S1, the mixing method includes at least one of mechanical crushing, spraying, and ball milling.

[0048] In some embodiments, in step S1, the first heating temperature is 600°C to 800°C. Exemplarily, the first heating temperature can be, but is not limited to, 600°C, 650°C, 700°C, 750°C, or 800°C. Within the aforementioned first heating temperature range, lithium carbonate can melt and form a liquid-solid reaction interface, improving the reaction conversion efficiency. Simultaneously, since the first heating temperature is lower than the melting points of the byproduct sodium carbonate, the target product lithium sulfide, and the raw material sodium sulfide, these substances exist in solid form or precipitate during the reaction. At the end of the reaction, a separable solid-liquid mixture is formed, facilitating the subsequent removal of unreacted lithium carbonate raw materials and improving product purity.

[0049] In some embodiments, in step S1, the reaction time between lithium carbonate and sodium sulfide is 1 h to 6 h. Exemplarily, the reaction time between lithium carbonate and sodium sulfide can be, but is not limited to, 1 h, 2 h, 3 h, 4 h, 5 h, or 6 h.

[0050] In some embodiments, in step S2, the second heating temperature is 850°C to 940°C. Exemplarily, the second heating temperature can be, but is not limited to, 850°C, 860°C, 870°C, 880°C, 890°C, 900°C, 910°C, 920°C, 930°C, and 940°C. Within the above-mentioned second heating temperature range, the byproduct sodium carbonate can be melted into a flowable liquid phase, while lithium sulfide and sodium sulfide remain in a stable solid state, forming a separated solid-liquid mixture system. This facilitates subsequent removal of the byproduct sodium carbonate, improving the purity of the product.

[0051] In some embodiments, in step S2, the holding time after heating to the second heating temperature is 0.5h to 3h. For example, the holding time after heating to the second heating temperature can be, but is not limited to, 0.5h, 1h, 1.5h, 2h, 2.5h, or 3h.

[0052] In some embodiments, in step S3, the third heating temperature is 940°C to 950°C. Exemplarily, the third heating temperature can be, but is not limited to, 940°C, 941°C, 942°C, 943°C, 944°C, 945°C, 946°C, 947°C, 948°C, 949°C, or 950°C. Within the aforementioned range of the third heating temperature, the target product lithium sulfide melts into a liquid phase, while the excess raw material sodium sulfide remains solid, forming a separated solid-liquid mixture system. This facilitates the subsequent removal of excess raw material sodium sulfide, improving the purity of the product.

[0053] In some embodiments, in step S3, the holding time after heating to the third heating temperature is 10 min to 60 min. For example, the holding time after heating to the third heating temperature can be, but is not limited to, 10 min, 20 min, 30 min, 40 min, 50 min, or 60 min.

[0054] In some embodiments, in step S4, the curing process is performed by cooling crystallization.

[0055] In some implementations, step S4 specifically includes the following steps:

[0056] S41. Cool the liquid lithium sulfide material to a first cooling temperature, which is lower than the freezing point of lithium sulfide, and separate the solid phase to prepare a third solid.

[0057] S42. Cool the third solid to a second cooling temperature, which is lower than the first cooling temperature, and separate the solid phase to prepare a solid lithium sulfide material.

[0058] Thus, by using a gradient cooling method to remove impurities, low-melting-point impurities are removed in the high-temperature range, and low-boiling-point impurities (elemental sulfur) are removed in the medium- and low-temperature range, further improving the purity of the solid-phase lithium sulfide product. Specifically, in step S41, low-melting-point impurities remaining in the molten liquid phase are removed; in step S42, the low-boiling-point impurities that condense from the atmosphere due to the cooling of the system are mainly removed, thereby achieving stepwise and in-depth removal of impurities from different sources, further improving the purity of the solid-phase lithium sulfide product.

[0059] In some embodiments, in step S41, the first cooling temperature is 700°C to 900°C. Exemplarily, the first cooling temperature can be, but is not limited to, 700°C, 750°C, 800°C, 850°C, or 900°C. Within the aforementioned first cooling temperature range, the first cooling temperature is below the freezing point of lithium sulfide. High-purity lithium sulfide will crystallize and precipitate first to form a solid phase, while low-melting-point impurities, because they have not yet reached their freezing point, will be enriched in the undried liquid phase. Separating the solid phase and removing the liquid phase further improves the product purity.

[0060] In some embodiments, in step S41, the holding time for the first cooling temperature is 1 hour to 3 hours. For example, the holding time for the first cooling temperature can be, but is not limited to, 1 hour, 2 hours, or 3 hours.

[0061] In some embodiments, in step S42, the second cooling temperature is 200°C to 600°C. Exemplarily, the second cooling temperature can be, but is not limited to, 200°C, 300°C, 400°C, 500°C, or 600°C. Within the aforementioned range of second cooling temperatures, which is lower than the first cooling temperature, the third solid obtained in step S41 continues to be cooled. During this process, low-boiling-point impurities condense from the reaction atmosphere onto the product surface to form a liquid phase. The solid phase is separated, and the liquid phase is removed, further improving product purity.

[0062] In some embodiments, in step S42, the holding time for the second cooling temperature is 0.5h to 3h. Exemplarily, the holding time for the second cooling temperature can be, but is not limited to, 0.5h, 1h, 1.5h, 2h, 2.5h, or 3h.

[0063] In some embodiments, after step S4, the preparation method further includes the following steps:

[0064] S5. Crush solid lithium sulfide material to prepare lithium sulfide powder.

[0065] In this way, high-purity lithium sulfide in bulk or granular form is transformed into fine powder, thereby meeting the practical application requirements as a battery material.

[0066] In some embodiments, in step S5, the pulverization method includes at least one of mechanical pulverization, air jet milling, and ball milling.

[0067] In some embodiments, the preparation method is carried out entirely under an inert or reducing atmosphere. This isolates water and oxygen during synthesis and purification, improving the purity of the product. For example, the inert atmosphere may include argon, and the reducing atmosphere may include nitrogen.

[0068] It is understood that the aforementioned lithium sulfide material can be used in batteries. Lithium sulfide can be used directly as a battery material or as a raw material to prepare a solid electrolyte. For example, the battery includes a solid electrolyte, which is prepared by sintering a mixture of lithium sulfide, P2S5, and LiCl.

[0069] The present application will be further described below with reference to specific embodiments and comparative examples.

[0070] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0071] Example 1

[0072] This embodiment provides a method for preparing lithium sulfide materials.

[0073] (1) Lithium carbonate and anhydrous sodium sulfide are purified by recrystallization until the total amount of metal impurities in each raw material is controlled within 50 ppm, and then set aside.

[0074] (2) Weigh 5 kg of lithium carbonate and 5.81 kg of anhydrous sodium sulfide (molar ratio of 1:1.1), place them in a vertical ball mill and ball mill until they are mixed evenly to obtain a mixture.

[0075] (3) The mixture was fed into the heating furnace tube, nitrogen gas was introduced, and the temperature was raised to 700℃ for 3 hours. After the reaction was completed, no obvious fluid was observed. The mixture was filtered to separate the solid phase and obtain the first solid.

[0076] (4) Under the protection of nitrogen atmosphere, the first solid is heated to 900℃ and held for 2 hours. At this temperature, the byproduct sodium carbonate melts to form a liquid phase. After filtration, the solid phase is separated to obtain the second solid.

[0077] (5) Under the protection of nitrogen atmosphere, the second solid is heated to 945℃ and held for 30 min. At this temperature, the target product lithium sulfide melts into liquid, while the excess raw material sodium sulfide remains solid. After filtration, the liquid phase is separated to obtain liquid lithium sulfide material.

[0078] (6) Under the protection of nitrogen atmosphere, the liquid lithium sulfide material is cooled to 800℃ and kept at that temperature for 1 hour. The solid phase is separated and the liquid phase is removed to obtain the third solid.

[0079] (7) Under the protection of nitrogen atmosphere, the third solid is cooled to 400℃ and kept at that temperature for 1 h. The solid phase is separated, the liquid phase is removed, and the solid phase is cooled to room temperature to obtain solid block lithium sulfide.

[0080] (8) Under the protection of nitrogen atmosphere, solid block lithium sulfide tablets are crushed to obtain lithium sulfide powder.

[0081] Testing revealed that the impurity in the lithium sulfide powder was sodium, with a content of 0.5 ppm. The lithium sulfide powder prepared in this embodiment meets the 99.99% content requirement for battery-grade lithium sulfide powder.

[0082] Example 2

[0083] The preparation method of lithium sulfide material in this embodiment is basically the same as that in Example 1, except that:

[0084] In step (3), the first heating temperature is 600℃ and the reaction time is 6h.

[0085] Example 3

[0086] The preparation method of lithium sulfide material in this embodiment is basically the same as that in Example 1, except that:

[0087] In step (3), the first heating temperature is 800℃ and the reaction time is 1h.

[0088] Example 4

[0089] The preparation method of lithium sulfide material in this embodiment is basically the same as that in Example 1, except that:

[0090] In step (4), the second heating temperature is 850℃ and the holding time is 3h.

[0091] Example 5

[0092] The preparation method of lithium sulfide material in this embodiment is basically the same as that in Example 1, except that:

[0093] In step (4), the second heating temperature is 950℃ and the holding time is 3h.

[0094] Example 6

[0095] The preparation method of lithium sulfide material in this embodiment is basically the same as that in Example 1, except that:

[0096] In step (2), 5 kg of lithium carbonate and 5.29 kg of anhydrous sodium sulfide are weighed, with a molar ratio of lithium carbonate to sodium sulfide of 1:1.001.

[0097] Example 7

[0098] The preparation method of lithium sulfide material in this embodiment is basically the same as that in Example 1, except that:

[0099] In steps (6) and (7), the first solution is directly cooled to room temperature to obtain solid block lithium sulfide.

[0100] Comparative Example 1

[0101] This comparative example provides a method for preparing lithium sulfide materials.

[0102] (1) Lithium carbonate and anhydrous sodium sulfide are purified by recrystallization until the total amount of metal impurities in each raw material is controlled within 50 ppm, and then set aside.

[0103] (2) Weigh 5 kg of lithium carbonate and 5.81 kg of anhydrous sodium sulfide (molar ratio of 1:1.1), place them in a vertical ball mill and ball mill until they are mixed evenly to obtain a mixture.

[0104] (3) The mixture was fed into the heating furnace tube, nitrogen gas was introduced, and the temperature was raised to 700℃ for 3 hours. After the reaction was completed, no obvious fluid was observed. The mixture was filtered to separate the solid phase and obtain the first solid.

[0105] (4) Under the protection of nitrogen atmosphere, the first solid is directly cooled to room temperature to obtain solid lithium sulfide material.

[0106] (5) Under the protection of nitrogen atmosphere, the solid block lithium sulfide tablets are crushed to obtain lithium sulfide powder.

[0107] Performance testing

[0108] Purity test: Weigh the lithium sulfide powder samples prepared in the above examples and comparative examples, and determine the impurity content and purity of the lithium sulfide materials by inductively coupled plasma atomic emission spectrometry (the content is calculated by the metal difference method).

[0109] Table 1

[0110]

[0111] As shown in Table 1, by comparing Examples 1-7 and Comparative Example 1, it can be seen that the lithium sulfide material preparation method provided in some embodiments of this application produces lithium sulfide material with purity that meets the requirements for battery-grade lithium sulfide.

[0112] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0113] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical concept of this application, and these modifications and improvements all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for preparing lithium sulfide material, characterized in that, Includes the following steps: S1. Lithium carbonate and sodium sulfide are mixed and heated to a first heating temperature to melt the lithium carbonate and react with the sodium sulfide, separating the solid phase and collecting the first solid. S2. The first solid is heated to a second heating temperature, which is higher than the melting point of sodium carbonate and lower than the melting points of lithium sulfide and sodium sulfide, to separate the solid phase and collect the second solid. S3. The second solid is heated to a third heating temperature, which is higher than the melting point of lithium sulfide and lower than the melting point of sodium sulfide, and the liquid phase is separated to prepare liquid lithium sulfide material. S4. The liquid lithium sulfide material is solidified to prepare a solid lithium sulfide material.

2. The method for preparing lithium sulfide material according to claim 1, characterized in that, Step S1, at least one of the following conditions must be met: (1) The molar ratio of lithium carbonate to sodium sulfide is 1:(1.001~1.1). (2) The total amount of metallic impurities in the lithium carbonate is ≤50 ppm; (3) The total amount of metallic impurities in the sodium sulfide is ≤50 ppm; (4) The mixing method includes at least one of mechanical crushing, spraying and ball milling; (5) The first heating temperature is 600℃~800℃; (6) The reaction time between the lithium carbonate and the sodium sulfide is 1h to 6h.

3. The method for preparing lithium sulfide material according to claim 1, characterized in that, Step S2, at least one of the following conditions must be met: (1) The second heating temperature is 850℃~940℃; (2) The holding time after heating to the second heating temperature is 0.5h~3h.

4. The method for preparing lithium sulfide material according to claim 1, characterized in that, Step S3, at least one of the following conditions must be met: (1) The third heating temperature is 940℃~950℃; (2) The holding time after heating to the third heating temperature is 10 min to 60 min.

5. The method for preparing lithium sulfide material according to claim 1, characterized in that, In step S4, the curing process is performed by cooling crystallization.

6. The method for preparing lithium sulfide material according to claim 5, characterized in that, Step S4 specifically includes the following steps: S41. Cool the liquid lithium sulfide material to a first cooling temperature, which is lower than the freezing point of lithium sulfide, separate the solid phase, and prepare a third solid. S42. Cool the third solid to a second cooling temperature, which is lower than the first cooling temperature, and separate the solid phase to prepare a solid lithium sulfide material.

7. The method for preparing lithium sulfide material according to claim 6, characterized in that, At least one of the following conditions must be met: (1) The first cooling temperature is 700℃~900℃; (2) The holding time at the first cooling temperature is 1h to 3h; (3) The second cooling temperature is 200℃~600℃; (4) The heat preservation time at the second cooling temperature is 0.5h to 3h.

8. The method for preparing lithium sulfide material according to any one of claims 1 to 7, characterized in that, After step S4, the following steps are also included: S5. Crush the solid lithium sulfide material to prepare lithium sulfide powder.

9. The method for preparing lithium sulfide material according to claim 8, characterized in that, The pulverization method includes at least one of mechanical pulverization, air jet milling, and ball milling.

10. The method for preparing lithium sulfide material according to any one of claims 1 to 7, characterized in that, The preparation method is carried out under an inert or reducing atmosphere.

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