A method for preparing lithium sulfide and applications thereof

Abstract

The application relates to a preparation method and application of lithium sulfide, which comprises the following steps: S1, mixing lithium sulfate and a carbon source after drying and ball milling, and carrying out a carbonization reaction on the obtained material under inert gas protection or in a vacuum environment; S2, mixing the carbonization product obtained in S1 with sulfur powder, ball milling, and calcining the obtained material under inert gas protection or in a vacuum environment; and S3, dissolving the material obtained in S2 in an alcohol solvent, filtering and drying to obtain lithium sulfide. In S3, the material obtained in S2 is dissolved, filtered and dried, and then calcined to obtain lithium sulfide. The mass ratio of the lithium sulfate to the carbon source is (1-1.4):1. In S1, the average particle size of the lithium sulfate and the carbon source after ball milling is 50-100 um. In S1, the carbonization reaction temperature is 250-280 DEG C. The application selects raw materials including lithium sulfate, a carbon source and sulfur powder, the raw materials are easy to obtain, the production cost is low, the method is simple, the period is short, the material does not need to be purified, high-purity lithium sulfide is finally obtained, and the purity reaches more than 99.9%.

Description

Technical Field

[0001] This application relates to the field of battery materials technology, specifically to a method for preparing lithium sulfide and its application. Background Technology

[0002] Energy storage technology, as a key supporting technology in important fields such as portable electronic devices, electric vehicles, rail transportation, space technology, and grid energy storage, is of great significance to promoting my country's economic and social development. Lithium-sulfur batteries are considered one of the most promising systems in high-energy-density battery technology, and solid-state batteries are an important future development direction in the battery field. Solid-state electrolytes are the core component of all-solid-state lithium batteries and will replace liquid electrolytes in the future. They determine the battery's ion conductivity, interface stability, and process feasibility. Sulfide solid electrolytes with high ionic conductivity are key materials for constructing next-generation high-energy-density and high-safety all-solid-state batteries. Lithium sulfide, as a raw material required for the synthesis of sulfur-based solid electrolytes and lithium-sulfur battery composite cathodes, plays a crucial role in improving the electrolyte, electrode materials, and battery electrochemical performance due to its purity.

[0003] Currently, the main methods for preparing lithium sulfide are solid-phase synthesis and liquid-phase synthesis. Solid-phase synthesis mainly includes three methods: carbothermic reduction, magnesothermic reduction, and ball milling of elemental lithium and elemental sulfur. Magnesothermic reduction mainly uses magnesium as a reducing agent to react with lithium sulfate at 550℃ to prepare lithium sulfide. However, because the reaction temperature can reach 1500℃ instantaneously, it is prone to explosion, posing a significant safety hazard. Ball milling of elemental lithium and elemental sulfur is a simple synthesis method, but it has disadvantages such as expensive raw materials, frequent loading and unloading during ball milling, low synthesis conversion rate, and long reaction time. Carbothermic reduction of lithium sulfate is currently a relatively common commercial method for preparing lithium sulfide due to its low cost, low process cost, and minimal emission of toxic gases. Liquid-phase synthesis is mainly a solvent method, which has a complete reaction and easy product purification. However, organic solvents are flammable, explosive, and volatile, causing serious environmental pollution and are difficult to recycle.

[0004] Lithium sulfide is prepared using the carbothermal reduction method. Based on existing research, thermodynamic calculations and analysis of the pyrolysis reaction between lithium sulfate and carbon show that the main reaction for lithium sulfide formation occurs at calcination temperatures above 660℃. However, severe side reactions still occur under these conditions, primarily the formation of Li₂O or Li₂CO₃, further reducing the conversion rate of the target product. Current techniques employ sulfur supplementation during the carbothermal reduction process to suppress these side reactions, but the effect is not ideal, resulting in a low conversion rate of the target product. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide a method for preparing lithium sulfide and its application, which improves the purity of lithium sulfide and reduces production costs.

[0006] To address the problems of the prior art, this application provides a method for preparing lithium sulfide, comprising the following steps:

[0007] S1: After drying, lithium sulfate and carbon source are ball-milled and mixed. The resulting material is then subjected to a carbonization reaction under inert gas protection or in a vacuum environment.

[0008] S2: Mix the carbonized product obtained in S1 with sulfur powder, ball mill it, and calcine the resulting material under inert gas protection or vacuum environment.

[0009] S3: Dissolve the material obtained in S2 in an alcohol solvent, filter and dry to obtain lithium sulfide.

[0010] Preferably, in step S3, the material obtained in step S2 is dissolved, filtered, dried, and then calcined to obtain lithium sulfide.

[0011] Preferably, the mass ratio of lithium sulfate to the carbon source is (1-1.4):1.

[0012] Preferably, the average particle size of the lithium sulfate and the carbon source after ball milling in S1 is 50-100 μm.

[0013] Preferably, the carbonization reaction temperature in S1 is 250–280°C.

[0014] Preferably, the mass ratio of the carbonization product to the sulfur powder is (1-10):1.

[0015] Preferably, the average particle size of the carbonized product and the sulfur powder after ball milling in S2 is 40-80 μm.

[0016] Preferably, the calcination temperature in S2 is 690–850°C, and more preferably 800–820°C.

[0017] Preferably, the calcination temperature in S3 is 300–600°C.

[0018] This application also provides the application of lithium sulfide prepared according to the above-described method in lithium-sulfur batteries.

[0019] This application also provides the application of lithium sulfide prepared according to the above-described method in solid-state batteries.

[0020] Compared with existing technologies, the beneficial effects of the technical solution in this application are as follows:

[0021] 1. The raw materials used in this application include lithium sulfate, carbon source and sulfur powder. The raw materials are readily available, the production cost is low, the method is simple, the cycle is short, the materials do not need to be purified, and finally high-purity lithium sulfide is obtained with a purity of over 99.9%.

[0022] 2. This application employs a two-step ball milling method. In step S1, ball milling enhances the solid-solid contact between lithium sulfate and the carbon source, resulting in uniform mixing of the reactants. In step S2, the ball-milled sulfur powder comes into full contact with the carbonization products. This not only replenishes the sulfur lost during sintering, preventing a decrease in material purity and crystallinity due to insufficient sulfur at high temperatures, but also suppresses side reactions, improves the conversion rate of lithium sulfide, and shortens the reaction time.

[0023] 3. This application provides a reasonable and effective sulfur supplementation temperature range. Since the generation of lithium sulfide at temperatures above 700°C involves serious side reactions, leading to sulfur volatilization and the formation of lithium oxide, the conversion rate of the target product is reduced. Therefore, the addition ratio of sulfur powder is adjusted within this temperature range to suppress the occurrence of side reactions and thereby improve the conversion rate of lithium sulfide.

[0024] 4. The high-purity lithium sulfide obtained in this application has fewer impurities, meaning fewer byproducts generated during carbothermic reduction, including lithium oxide, lithium carbonate, carbon black, and sublimed sulfur. This fundamentally improves the purity of lithium sulfide, and also results in higher crystallinity and yield, leading to excellent performance in battery applications. The solid electrolyte synthesized from the lithium sulfide obtained in this application has high conductivity and exhibits high cycle performance when assembled into lithium batteries. Attached Figure Description

[0025] Figure 1 The image shows the XRD pattern of lithium sulfide prepared in Example 1.

[0026] Figure 2 The image shows the XRD pattern of lithium sulfide prepared in Example 2.

[0027] Figure 3 This is a scanning electron microscope image of lithium sulfide prepared in Example 1.

[0028] Figure 4 This is a scanning electron microscope image of lithium sulfide prepared in Example 2.

[0029] Figure 5 The graph shows the cycle number, capacity, and coulombic efficiency performance of the solid electrolyte battery synthesized in Example 1.

[0030] Figure 6 The XRD patterns of Li2S prepared in Example 1 and Comparative Example 3 are shown.

[0031] Figure 7 The graph shows the cycle number, capacity, and coulombic efficiency performance of the solid electrolyte battery synthesized in Example 2.

[0032] Figure 8 The XRD patterns of Li6PS5Cl prepared in experimental group 1 and experimental group 2 are shown. Detailed Implementation

[0033] To further understand this application, preferred embodiments are described below with reference to examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of this application and not for limiting this application. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

[0034] This application provides a method for preparing lithium sulfide, comprising the following steps:

[0035] S1: After drying, lithium sulfate and a carbon source are ball-milled and mixed. The mass ratio of lithium sulfate to carbon source is (1-1.4):1. The preferred ball milling speed is 120 rpm / min, the ball-to-material ratio is (25-40):1, preferably 30:1, and the ball milling time is 1-3 hours. The resulting material is then subjected to a carbonization reaction under inert gas protection at a reaction temperature of 250-280℃ for 3-5 hours. In this step, ball milling ensures sufficient contact between lithium sulfate and carbon source at the microscopic scale, which is beneficial for the solid-phase reaction.

[0036] Carbon sources include at least one of glucose, sucrose, fructose, maltose, or citric acid, and all listed carbon sources are renewable energy sources.

[0037] S2: Mix the carbonized product obtained in S1 with sulfur powder, preferably at a mass ratio of (1-10):1. Excessive use of sulfur powder can lead to waste and environmental pollution. Ball mill the mixture, preferably at a speed of 120 rpm / min, with a ball-to-material ratio of (25-40):1, preferably 30:1, for 1-3 hours. Calcine the resulting material under inert gas protection or in a vacuum environment at a temperature of 690-850℃, preferably 800-820℃, for 4-6 hours. At temperatures above 820℃, severe side reactions occur, primarily involving the reaction of lithium sulfate with carbon or carbon monoxide. These side reactions are as follows:

[0038] Li2SO4+3C=S(g)+3CO(g)+Li2O,

[0039] Li2SO4+3CO(g)=S+3CO2+Li2O,

[0040] This leads to sulfur volatilization and lithium oxide formation, reducing the conversion rate of the target product. Below 690℃, the main reaction between lithium sulfate and carbon is incomplete, resulting only in a portion of crude lithium sulfide with low crystallinity and many impurities. Therefore, setting an appropriate temperature and the amount of sulfur powder added has a significant impact on the synthesis of the target product. This step can compensate for the sulfur loss during subsequent reactions, suppress side reactions, and the ball-milled sulfur powder has more thorough contact with the reactants, which is conducive to a complete reaction.

[0041] The calcination time in S2 of this application is also an important factor affecting the synthesis of lithium sulfide. If the calcination time is greater than 6 hours, it prolongs the reaction time of more side reactions and reduces the purity of lithium sulfide. If the calcination time is less than 4 hours, the main reaction is incomplete, which also reduces the conversion rate of lithium sulfide.

[0042] S3: Dissolve the material obtained in S2 in an alcohol solvent, preferably anhydrous ethanol, with a mass ratio of material to alcohol solvent of 1:(15-30), preferably 1:(20-25). Filter to remove impurities with a particle size greater than 3 μm to prevent excessive impurities from affecting product purity. This process improves the uniformity of the obtained lithium sulfide. Collect the supernatant and dry it at a temperature ≤150℃, preferably 100-130℃, to obtain lithium sulfide.

[0043] Preferably, in step S3, the material obtained in step S2 is dissolved, filtered, dried, and then calcined at a temperature of 300–600°C, preferably 450–560°C, to obtain lithium sulfide. The purpose of calcination in step S3 is to remove remaining impurities and to break down the hydrogen bonds and chemical bonds formed by van der Waals forces or complexations after the impurities and lithium sulfide dissolve in alcohol solvents, thereby increasing the purity of the obtained lithium sulfide and improving the electrochemical performance of the material.

[0044] In summary, this application employs a two-step ball milling method. Step S1 ball milling coats lithium sulfate particles onto the surface of carbon, increasing the reaction contact area. Mixing reactants with a solvent can leave residues, affecting the performance of the synthesized material; dry ball milling avoids introducing impurities. Step S2 ball milling ensures sufficient contact between the carbonization product and sulfur powder, resulting in better sulfur replenishment and a more complete reaction, thus improving the conversion rate of lithium sulfide. While existing technologies may use single-step dry ball milling, it has several drawbacks. Single-step ball milling involves mixing three materials, and the temperature reaches the melting point of sulfur during carbonization and calcination, leading to sulfur volatilization and failing to replenish sulfur, thus reducing the conversion rate of lithium sulfide. Furthermore, single-step ball milling introduces three components, reducing the contact area of ​​the reactants. Although the carbonization and lithium sulfide synthesis reactions theoretically do not occur at the same temperature, in practice they often occur simultaneously, leading to incomplete or insufficient reactions.

[0045] Example 1

[0046] A method for preparing lithium sulfide includes the following steps:

[0047] S1: 5.5g of lithium sulfate monohydrate (AR grade) and 4.3g of sucrose (AR grade) were dried and then ball-milled together at 120 rpm / min, with a ball-to-material ratio of 30:1, for 2 hours. The resulting material was then transferred to a tube furnace and carbonized under argon protection at 280℃ for 5 hours.

[0048] S2: Mix 7.2g of the carbonized product obtained in S1 with 1.6g of sulfur powder, and ball mill at 120rpm / min with a ball-to-material ratio of 30:1 for 2 hours. Transfer the resulting material into a tube furnace and calcine under argon protection at a heating rate of 5℃ / min until it reaches 810℃ and remains constant for 6 hours.

[0049] S3: In an argon-filled glove box, the material obtained in S2 was dissolved in anhydrous ethanol at a solid-liquid mass ratio of 1:20. After complete dissolution, the mixture was centrifuged and filtered at 8000 rpm for 10 min. This process was repeated twice. The supernatant was collected and dried under vacuum at 120°C for 12 h. Then, it was calcined at 500°C to obtain lithium sulfide.

[0050] Example 2

[0051] A method for preparing lithium sulfide includes the following steps:

[0052] S1 and S2 are the same as S1 and S2 in Example 1.

[0053] S3: In an argon-filled glove box, the material obtained in S2 was dissolved in anhydrous ethanol at a solid-liquid mass ratio of 1:20. After complete dissolution, the mixture was centrifuged and filtered at 8000 rpm for 10 min. This process was repeated twice. The supernatant was collected and dried under vacuum at 120°C for 12 h to obtain lithium sulfide.

[0054] Example 3

[0055] A method for preparing lithium sulfide includes the following steps:

[0056] S1 is the same as S1 in Example 1.

[0057] S2: Mix 7.2g of the carbonized product obtained in S1 with 1.6g of sulfur powder, and ball mill at 120rpm / min with a ball-to-material ratio of 30:1 for 2 hours. Transfer the resulting material into a tube furnace and calcine under argon protection at a heating rate of 5℃ / min until it reaches 750℃ and remains constant for 6 hours.

[0058] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0059] Example 4

[0060] A method for preparing lithium sulfide includes the following steps:

[0061] S1 is the same as S1 in Example 1.

[0062] S2: Mix 7.2g of the carbonized product obtained in S1 with 1.6g of sulfur powder, and ball mill at 120rpm / min with a ball-to-material ratio of 30:1 for 2 hours. Transfer the resulting material into a tube furnace and calcine under argon protection at a heating rate of 5℃ / min until it reaches 850℃ and remains constant for 6 hours.

[0063] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0064] Example 5

[0065] A method for preparing lithium sulfide includes the following steps:

[0066] S1 is the same as S1 in Example 1.

[0067] S2: Mix 7.2g of the carbonized product obtained in S1 with 1.6g of sulfur powder, and ball mill at 120rpm / min with a ball-to-material ratio of 30:1 for 2 hours. Transfer the resulting material into a tube furnace and calcine under argon protection at a heating rate of 5℃ / min until it reaches 810℃ and remains there for 8 hours.

[0068] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0069] Example 6

[0070] A method for preparing lithium sulfide includes the following steps:

[0071] S1 is the same as S1 in Example 1.

[0072] S2: Mix 7.2g of the carbonized product obtained in S1 with 3.2g of sulfur powder, and ball mill at 120rpm / min with a ball-to-material ratio of 30:1 for 2 hours. Transfer the resulting material into a tube furnace and calcine under argon protection at a heating rate of 5℃ / min until it reaches 810℃ and remains constant for 6 hours.

[0073] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0074] Example 7

[0075] A method for preparing lithium sulfide includes the following steps:

[0076] S1 is the same as S1 in Example 1.

[0077] S2: Mix 7.2g of the carbonized product obtained in S1 with 0.8g of sulfur powder and ball mill for 2 hours. Transfer the resulting material into a tube furnace and calcine it under argon protection at a heating rate of 5℃ / min until it reaches 810℃ and remains constant for 6 hours.

[0078] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0079] Comparative Example 1

[0080] A method for preparing lithium sulfide includes the following steps:

[0081] S1 is the same as S1 in Example 1.

[0082] S2: 7.2g of the carbonized product obtained in S1 was calcined under argon protection at a heating rate of 5℃ / min, and kept at a constant temperature of 810℃ for 6h.

[0083] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0084] Comparative Example 2

[0085] A method for preparing lithium sulfide includes the following steps:

[0086] S1 is the same as S1 in Example 1.

[0087] S2: The carbonized product obtained in S1 was mixed with 1.6g of sulfur powder and ball-milled at a speed of 120rpm / min, a ball-to-material ratio of 30:1, and a milling time of 2h. The resulting material was then transferred to a tube furnace and calcined under argon protection at a heating rate of 5℃ / min until it reached 600℃ and remained at that temperature for 6h.

[0088] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0089] Comparative Example 3

[0090] A method for preparing lithium sulfide includes the following steps:

[0091] S1: Disperse 5.5g lithium sulfate (AR grade) and 4.3g sucrose (AR grade) in isopropanol, mix for 15 minutes using a high-speed mixer, filter, press the filter cake into small pieces and place them in a crucible, place the crucible in a tube furnace, and carry out the carbonization reaction under argon protection at a reaction temperature of 280℃ for 5 hours.

[0092] S2: The product obtained in S1 was mixed with 1.6g of sulfur powder and ball-milled at a speed of 120rpm / min, a ball-to-material ratio of 30:1, and a milling time of 2h. The resulting material was then transferred to a tube furnace and calcined under argon protection at a heating rate of 5℃ / min until it reached 810℃ and remained at that temperature for 6h.

[0093] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0094] Comparative Example 4

[0095] A method for preparing lithium sulfide includes the following steps:

[0096] S1 and S2 are consistent with Comparative Example 3.

[0097] S3: Lithium sulfide is obtained by drying under vacuum at 120°C without calcination.

[0098] Comparative Example 5

[0099] A method for preparing lithium sulfide includes the following steps:

[0100] S1 is the same as S1 in Example 1.

[0101] S2: The carbonized product obtained in S1 and 1.6g of sulfur powder were ball-milled separately at a speed of 120rpm / min, a ball-to-material ratio of 30:1, and a milling time of 2h. The resulting carbonized product and sulfur powder were then placed in a tube furnace and calcined under argon protection. The sulfur powder was positioned closer to the side where argon was introduced, and the resulting carbonized product was positioned closer to the side where argon was expelled. The calcination heating rate was 5℃ / min, and the temperature was raised to 810℃ and held constant for 6h.

[0102] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0103] Comparative Example 6

[0104] A method for preparing lithium sulfide includes the following steps:

[0105] S1: 5.5g of lithium sulfate monohydrate (AR grade), 4.3g of sucrose (AR grade), and 1.6g of sulfur powder were dried and then ball-milled together at 120 rpm / min, a ball-to-material ratio of 30:1, and a milling time of 2 hours. The resulting material was then transferred to a tube furnace and subjected to a carbonization reaction under argon protection at 280℃ for 5 hours.

[0106] S2: Calcination under argon protection, with a heating rate of 5℃ / min, heated to 810℃ and held at that temperature for 6 hours.

[0107] S3 is the same as S3 in Example 1, and lithium sulfide is obtained.

[0108] (1) Purity analysis:

[0109] The purity of lithium sulfide prepared in Examples 1, 2 and 3 can be determined by elemental analysis or by X-ray diffraction.

[0110] The sample stage was cleaned with anhydrous ethanol to prevent cross-contamination. 50 mg of the lithium sulfide sample to be tested was weighed and poured into the sample stage, covering the entire area to prevent the test from reaching the substrate. A polyimide film was then placed over the sample stage surface to prevent contact with air. All the above procedures were performed under an argon protective atmosphere, with water and oxygen content below 1 ppm.

[0111] The X-ray diffraction pattern of Example 1 is as follows: Figure 1 As shown, the X-ray diffraction pattern of Example 2 is as follows. Figure 2 As shown, Figure 6 The images show the XRD patterns of lithium sulfide prepared in Example 1 and Comparative Example 3. Figure 6 As shown. Both Examples 1 and 2 yielded high-purity nano-sized lithium sulfide. Because step S3 of Example 1 involved calcination, the resulting lithium sulfide contained fewer impurities than that of Example 2. Figure 6 As shown, compared with the lithium sulfide prepared in Example 1, the lithium sulfide prepared by the wet method in Comparative Example 3 has poorer crystallinity and less obvious characteristic peaks, thus affecting the electrochemical performance of the synthesized sulfide solid electrolyte. This is reflected in the subsequent cycling performance diagram. Figure 7 This has also been verified in [the study].

[0112] The lithium sulfide materials prepared in Examples 1 and 2 were characterized using scanning electron microscopy (SEM), and the results are as follows: Figure 3 and Figure 4 As shown.

[0113] (2) Conversion rate analysis:

[0114] The conversion rates of lithium sulfide in the examples and comparative examples were calculated, and the results are shown in Table 1.

[0115] Table 1

[0116]

[0117]

[0118] Conversion rate = Actual lithium sulfide mass / Theoretical lithium sulfide mass, where theoretical lithium sulfide mass = Lithium sulfate monohydrate mass / Lithium sulfate monohydrate relative molecular mass * Lithium sulfide relative molecular mass.

[0119] As shown in Table 1, the lithium sulfide conversion rates of Examples 1-6 of this application are higher than those of the comparative examples. In Example 2, the conversion rate is slightly lower than that of Example 1 because calcination was not performed in S3. In Examples 3 and 4, the calcination temperature in S2 is in the range of 690-850°C, not in the range of 800-820°C, therefore the conversion rate is lower than that of Example 1. In Example 5, the calcination time in S2 is longer than that in Example 1, resulting in slightly more side reactions, thus the conversion rate is lower than that of Example 1. In Example 6, the increased amount of sulfur powder inhibits side reactions, but also accelerates the volatilization rate, carrying away the effective product, resulting in a lower conversion rate than that of Example 1. In Example 7, the relatively small amount of sulfur powder is added, resulting in a lower conversion rate than that of Example 1.

[0120] In Comparative Examples 1, no sulfur powder was added, leading to sulfur volatilization and lithium oxide formation, which reduced the lithium sulfide conversion rate. In Comparative Example 2, the calcination temperature in S2 was lower, resulting in a lower conversion rate than in Example 1. Comparative Examples 3 and 4 used wet mixing, which resulted in solvent residue, affecting the performance of the synthesized materials. In Comparative Example 5, the carbonized product and sulfur powder were ball-milled separately and placed separately with gas introduced to supplement sulfur; however, the contact between the reactants and sulfur powder was insufficient, resulting in a less effective sulfur supplementation than in this application, and its conversion rate was lower than in Example 1. In Comparative Example 6, only one ball milling was performed; the carbonization and calcination process caused sulfur volatilization, failing to achieve the desired sulfur supplementation effect, and its conversion rate was lower than in Example 1.

[0121] (3) Electrochemical performance analysis:

[0122] Application of lithium sulfide prepared according to the method of this application in solid-state batteries.

[0123] Experimental group 1 was set up to synthesize the sulfide solid electrolyte Li6PS5Cl from the lithium sulfide prepared according to Example 1. The experimental raw materials were self-made lithium sulfide, purchased lithium sulfide (Li2S, ≥99.9%, Aladdin), phosphorus pentasulfide (P2S5, 99%, Mucklin), and lithium chloride (LiCl, 99.99%, Aladiin) powders. First, the raw materials were weighed according to the molar ratio of LiPS5Cl, and then the mixed powder was ball-milled using a vacuum zirconia ball mill. The mass ratio of raw materials to zirconia ball beads (10 mm in diameter) was approximately 1:30, the ball milling speed was 380 r / min, the ball milling interval was changed every 20 min, and the ball milling time was 20-24 h. The precursor powder sample was placed in a quartz crucible (35 mL), heated at a rate of 5 °C / min, sintered at 550 °C, held at that temperature for 6 h, and then naturally cooled to room temperature with the furnace to obtain the Li6PS5Cl solid electrolyte. All the above operations were carried out under an argon protective atmosphere, and the water and oxygen content was less than 1 ppm.

[0124] Experimental group 2 was set up, using commercially available lithium sulfide (Li2S, ≥99.9%, Aladdin) to synthesize a sulfide solid electrolyte, Li6PS5Cl. The preparation process of this commercially available lithium sulfide employed a wet mixing method.

[0125] The purity of the solid electrolyte Li6PS5Cl prepared in Example 1 and Example 2 was determined by X-ray diffraction. The results are as follows: Figure 8 As shown, the lithium sulfide prepared in Example 1 synthesized into a sulfide solid electrolyte Li6PS5Cl with higher purity, indicating that the lithium sulfide provided in this application has high purity and is more suitable for solid-state batteries.

[0126] Based on the formula for calculating ionic conductivity σ = L / RS, the calculated ionic conductivity of the electrolytes in experimental group 1 and experimental group 2 is 3.42 × 10⁻⁶. -3 Scm -1 and 3.03×10 -3 Scm -1 The electronic conductivity is 9.15 × 10⁻⁶. -10 Scm -1 and 1.58×10 -9 S cm -1 The lithium sulfide prepared according to the method of this application performs better than commercially available lithium sulfide in solid-state batteries.

[0127] Charge-discharge cycle test:

[0128] The battery capacity of three experimental groups was measured using electrochemical constant current charge / discharge technology. The positive electrode of the battery was NCM811@LiNbO3, and the active material loading was 31.85 mg / cm³. -2 The negative electrode uses a lithium-indium alloy, with an electrochemical testing window of 1.88-3.78V.

[0129] The room-temperature cycling performance of an all-solid-state lithium battery assembled using lithium sulfide as a solid electrolyte, prepared according to the method of this application, is shown in the figure below. Figure 5 As shown, the discharge capacity at 0.5C and room temperature (25℃) is 95mAh g. -1 It can stably cycle for 200 times with a capacity retention rate of ≥90%.

[0130] The room temperature cycling performance of an all-solid-state lithium battery assembled using commercially available lithium sulfide (Li2S, ≥99.9%, Aladdin) as the solid electrolyte is shown in the figure. Figure 7 As shown, the initial discharge capacity at room temperature (25°C) under 0.5C conditions is 120mAh / g, the capacity begins to decay after 20 cycles, and the capacity retention rate is less than 60% after 130 cycles.

[0131] Compared to the solid electrolyte prepared in Example 1, the solid electrolyte prepared with commercially available lithium sulfide showed a significant decrease in cycle performance. The results verified that the solid electrolyte prepared in Example 1 has good rate performance, and the lithium sulfide prepared in Example 1 has better electrochemical performance in practical applications.

[0132] The above description of the embodiments is only for the purpose of helping to understand the method and core idea of ​​this application. It should be noted that for those skilled in the art, several improvements and modifications can be made to this application without departing from the principle of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A method for preparing lithium sulfide, characterized in that, Includes the following steps: S1: After drying lithium sulfate and carbon source, they are ball-milled and mixed at a ball-to-material ratio of (25-40):

1. The average particle size of the lithium sulfate and carbon source after ball milling is 50-100 μm. The resulting material is carbonized under inert gas protection or vacuum environment at a carbonization reaction temperature of 250-280℃. S2: Mix the carbonized product obtained in S1 with sulfur powder, wherein the mass ratio of the carbonized product to the sulfur powder is (1~10):1, and ball mill it according to the ball-to-material ratio (25~40):

1. The average particle size of the carbonized product and the sulfur powder after ball milling is 40~80um. Calcine the obtained material under inert gas protection or vacuum environment at a calcination temperature of 800~820℃ for 4-6 hours. S3: Dissolve the material obtained in S2 in an alcohol solvent, filter and dry it, and then calcine it at a temperature of 300~600℃ to obtain lithium sulfide.

2. The method for preparing lithium sulfide according to claim 1, characterized in that, The mass ratio of lithium sulfate to the carbon source is (1~1.4):1.

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