Lithium sulfide and two-step metathesis preparation method and application in all-solid-state batteries

Abstract

The application discloses a lithium sulfide and a two-step metathesis preparation method and application in a full solid-state battery, and belongs to the technical field of solid-state batteries. The preparation method adopts a two-step decomposition synthesis technology, lithium carbonate and ammonium thiocyanate are used as raw materials, the raw materials are uniformly mixed and then placed in a high-temperature reactor, a step-by-step sintering process is completed under an inert gas atmosphere, and through accurate control of temperature and time, the full decomposition and conversion of the raw materials are realized; after the reaction, the product is cooled to room temperature to obtain a high-purity lithium sulfide material. In the method for preparing the lithium sulfide, the raw material cost is low, the reactant formula is simple, the reaction process is free of side reactions, the finally generated product is low in impurities, high in purity and good in crystallinity.

Description

Technical Field

[0001] This invention belongs to the field of all-solid-state battery technology, specifically relating to a lithium sulfide preparation method and its application in all-solid-state batteries. Background Technology

[0002] In recent years, with the booming development of new energy vehicles and other fields, a series of problems with traditional lithium-ion batteries, such as low energy density, poor safety, short driving range, low charging rate, and poor low-temperature performance, have gradually been exposed, causing great inconvenience to daily life. Against this backdrop, all-solid-state batteries equipped with non-flammable solid-state electrolytes, with their advantages of high energy density, high safety factor, simple battery system design, and compatibility with fast charging technology, are expected to become the ultimate solution for future power batteries. Solid-state electrolytes are classified into oxide solid-state electrolytes, sulfide solid-state electrolytes, halide solid-state electrolytes, and polymer solid-state electrolytes. Among them, sulfide solid-state electrolytes have extremely high ionic conductivity (>10⁻⁶). -3 The advantages of cold pressing (S / cm) and the ability to form a good interface with the electrode have attracted great attention from researchers.

[0003] Sulfide solid electrolytes are mainly classified into glassy phase type (Li3PS4), glass-ceramic phase type (Li2S-P2S5), sterhenite type (Li6PS5Cl), and sulfide crystalline lithium superion conductor type (Li 3.25 Ge 0.25 P 0.75 S4) and LGPS type (Li 10 GeP2S 12 Sulfur has low electronegativity and a large ionic radius, resulting in a weak bond between sulfur and lithium, which creates more lithium-ion transport channels, leading to a room-temperature ionic conductivity as high as 10⁻⁶. -2 Its S / cm is comparable to that of traditional liquid electrolytes.

[0004] High-purity, highly crystalline lithium sulfide (Li₂S) is an essential material for the synthesis of sulfide solid-state electrolytes. However, due to the complex preparation process, high energy consumption, and high sensitivity to moisture, additional costs are often incurred during synthesis, purification, storage, and transportation of lithium sulfide. The scarcity of raw materials, complex synthesis steps, stringent purification processes, and safety and environmental pressures contribute to the persistently high cost of lithium sulfide. Therefore, exploring a low-cost, large-scale synthesis route for high-purity, highly crystalline lithium sulfide is crucial for advancing the commercialization of sulfide solid-state electrolytes and all-solid-state batteries. The initial method for synthesizing lithium sulfide was to directly synthesize lithium metal or lithium hydride with sublimed sulfur. Subsequently, researchers explored new preparation processes, such as the reaction of lithium metal with tetrahydrofuran solution of hydrogen sulfide, the direct reaction of lithium carbonate with hydrogen sulfide gas, and the decomposition of lithium thiohydride into ethanol adducts by lithium ethoxylate. Specific synthesis methods for lithium sulfide mainly include mechanical ball milling, liquid solvent method, metathesis reaction method, and high-temperature carbothermal method. These preparation methods have problems such as long preparation cycle, use of organic solvents or flammable and explosive materials, release of toxic gases, and limited crystallinity and purity of the prepared products. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a lithium sulfide preparation method and its application in all-solid-state batteries, so as to solve the problems of high raw material cost, long preparation cycle, flammable and explosive raw materials, and defects in the crystallinity and purity of the final lithium sulfide obtained in the prior art.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A two-step metathesis preparation method for lithium sulfide includes:

[0008] Lithium carbonate and ammonium thiocyanate are mixed as raw materials to obtain a mixture, and the mixture is sintered in an inert atmosphere to obtain lithium sulfide. The sintering is divided into two stages: the temperature of the first stage is 150℃~250℃ and the holding time is 3h~5h; the temperature of the second stage is 650℃~750℃ and the holding time is 8h~12h. During the sintering process, a flowing inert gas is introduced.

[0009] In the first stage, ammonium thiocyanate and lithium carbonate undergo a decomposition reaction to produce ammonium carbonate and lithium thiocyanate; in the second stage, lithium thiocyanate and lithium carbonate react to produce lithium sulfide, and ammonium carbonate decomposes into a byproduct. The byproduct and the process products of the reaction are gaseous.

[0010] A further improvement of the present invention is that:

[0011] Preferably, the molar ratio of lithium carbonate and ammonium thiocyanate is 1:(1.2~1.5).

[0012] Preferably, the heating rate during the sintering process is 1℃ / min to 3℃ / min.

[0013] Preferably, during the heating process from the first stage to the second stage, when the temperature is raised to between 400℃ and 500℃, the heating rate is 5℃ / min to 10℃ / min.

[0014] Preferably, lithium sulfide is obtained by air cooling of the sintered product.

[0015] Preferably, when mixing lithium carbonate and ammonium thiocyanate, the mixing is carried out by grinding, ball milling or mechanical crushing.

[0016] Preferably, the mixture is reacted in a container, which is in a reaction chamber filled with a flowing inert gas; the upper part of the container is provided with a top cover with holes.

[0017] Preferably, the flow rate of the inert gas is 10-100 mL / min.

[0018] A lithium sulfide prepared by any one of the two-step metathesis preparation methods described above.

[0019] An application of the aforementioned lithium sulfide in all-solid-state batteries, used to prepare sulfide solid electrolytes.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] This invention discloses a two-step metathesis preparation method for lithium sulfide. The method uses lithium carbonate and ammonium thiocyanate as raw materials, mixes them uniformly, and then performs a stepped heating sintering process under an inert gas atmosphere. After stepped heating and holding at that temperature, the product is cooled to room temperature to obtain high-purity lithium sulfide material. The specific advantages of this invention are:

[0022] (1) The lithium carbonate and ammonium thiocyanate used in the preparation process are non-toxic and harmless, and the synthesis cost is low. As the only additives in the preparation process are the reactants themselves, no other raw materials are added to promote the reaction, thus avoiding the introduction of impurities due to the introduction of other substances in the entire preparation process, resulting in high purity and good crystallinity of the prepared product.

[0023] (2) In the preparation process of this invention, the reaction process is divided into two stages, namely 150℃~250℃ and 650℃~750℃. The temperature of the first stage can ensure that ammonium thiocyanate melts into a molten state first, so as to promote the full reaction of the subsequent reaction. After the set temperature is maintained for a set time, the temperature is slowly increased according to the set temperature. As the temperature increases, the reaction is further promoted. Lithium carbonate reacts to generate lithium sulfide solid phase. After the set temperature is maintained for a set time, crystalline lithium sulfide phase is generated.

[0024] (3) The entire preparation process has simple equipment requirements, good reproducibility, easy operation, and is convenient for large-scale industrial production.

[0025] (4) Using inexpensive lithium carbonate and ammonium thiocyanate as raw materials, the method has the advantages of low cost, simple reactant formulation, no side reaction in the reaction process, few impurities in the product and easy removal. The lithium sulfide product obtained by this method has high purity and crystallinity.

[0026] The second aspect of the present invention discloses a lithium sulfide obtained by the above-mentioned two-step metathesis method. The lithium sulfide obtained by this method has good crystallinity, high purity (above 97%), and fine and uniform particles.

[0027] The third aspect of the present invention discloses the application of lithium sulfide in all-solid-state batteries for preparing sulfide solid electrolytes. Due to the high purity of lithium sulfide, the sulfide solid electrolytes have better crystallinity and achieve higher room temperature ionic conductivity. Solid-state batteries equipped with this electrolyte can achieve a high capacity of 217.34 mAh / g and an initial charge-discharge efficiency of 89.09% at 0.1C, as well as excellent rate performance. Attached Figure Description

[0028] Figure 1 This is a reaction flow diagram of the present invention;

[0029] Figure 2 This is a schematic diagram of the reaction chamber of the present invention;

[0030] Among them, 1. reaction chamber; 2. container; 3. inlet; 4. outlet; 5. hole; 6. top cover; 7. mixture.

[0031] Figure 3 The image shows the XRD pattern (X-ray diffraction pattern) of the lithium sulfide product in Example 1; where au is the relative intensity of the X-ray diffraction peak, abbreviation for Arbitrary Unit, and PDF is the powder diffraction file.

[0032] Figure 4 The images show the microstructure of the product obtained in Example 1; where (a) is a SEM (Scanning Electron Microscope Image) image of commercial lithium sulfide; (b) is a SEM image of lithium sulfide synthesized in Example 1; (c) is a SEM image of a single lithium sulfide particle synthesized in Example 1; and (d) is an EDS (Energy Dispersive Spectrum) image of a single lithium sulfide particle synthesized in Example 1.

[0033] Figure 5 Comparison of particle size distribution between lithium sulfide synthesized from ammonium thiocyanate in a laboratory and commercial lithium sulfide;

[0034] (a) represents laboratory-synthesized lithium sulfide; (b) represents commercially available lithium sulfide.

[0035] Figure 6 The image shows the EIS (Electrochemical Impedance Spectroscopy) spectrum of the electrolyte material in the application example, where the ionic conductivity σ is... ion =7.43 mS / cm, where ion represents ion.

[0036] Figure 7 The image shows the XRD pattern of the electrolyte material in the application example, where BG is the background peak of the plastic wrap, abbreviated as Background.

[0037] Figure 8 This is the first charge-discharge curve of the all-solid-state battery in the application example.

[0038] Figure 9 The data shows the rate performance curves of the all-solid-state battery at different current densities in the application example. Detailed Implementation

[0039] The present invention will now be described in further detail with reference to the accompanying drawings:

[0040] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions mentioned in the specification are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0041] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0042] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0043] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0044] As the background section addresses, lithium sulfide is a key material for synthesizing sulfide solid electrolytes with high ionic conductivity. Existing methods for synthesizing lithium sulfide include direct synthesis from lithium metal and sulfur powder, direct synthesis from the reaction of hydrogen sulfide and lithium salts, and the carbon reduction of lithium sulfate. However, lithium metal is flammable and explosive, compromising the safety of the preparation process; hydrogen sulfide is a highly toxic gas, resulting in high costs for exhaust gas treatment; and the carbon reduction of lithium sulfate method easily introduces impurities, reducing the purity of the final lithium sulfide. Therefore, existing methods suffer from high cost, low safety, and low purity of lithium sulfide. To address these issues, this invention discloses a lithium sulfide preparation method using a two-step metathesis process and its application in all-solid-state batteries.

[0045] The first aspect of this invention discloses a two-step metathesis preparation method for lithium sulfide. The preparation process is as follows: lithium carbonate and ammonium thiocyanate are mixed as raw materials to obtain a mixture 7, and the mixture 7 is sintered in an inert atmosphere to obtain lithium sulfide. The sintering process is divided into two stages: the temperature of the first stage is 150℃~250℃ and the holding time is 3h~5h, and the temperature of the second stage is 650℃~750℃ and the holding time is 8h~12h. During the reaction, a flowing inert gas is introduced.

[0046] In the process, in the first stage, ammonium thiocyanate and lithium carbonate undergo a decomposition reaction to produce ammonium carbonate and lithium thiocyanate; in the second stage, lithium thiocyanate and lithium carbonate react to produce lithium sulfide, and ammonium carbonate decomposes into a byproduct. The byproduct and the process products of the reaction are in the gaseous state.

[0047] See Figure 1The method uses lithium carbonate and ammonium thiocyanate as raw materials. After the raw materials are mixed evenly, lithium sulfide products are obtained by sintering under an inert atmosphere through a step-by-step heating method. In the above process, the first stage is the low-temperature decomposition stage. First, lithium carbonate and ammonium thiocyanate are mixed evenly and then sintered by step-by-step heating. The temperature in this stage is controlled at 150℃~250℃ and held for 3~5 hours. In this process, ammonium thiocyanate (NH4SCN) and some lithium carbonate (Li2CO3) undergo a metathesis reaction to produce ammonium carbonate ((NH4)2CO3) and lithium thiocyanate (LiSCN). The ammonium carbonate continues to decompose to produce water (H2O), carbon dioxide (CO2), and ammonia (NH3), thus avoiding the need for high temperatures for lithium carbonate to decompose. The second stage is the high-temperature synthesis stage, which is the key to solid-phase reaction synthesis. The temperature is significantly increased to 650℃~750℃ and maintained for a long time of 8~12 hours. During this process, lithium thiocyanate, water, and the remaining lithium carbonate react to produce lithium sulfide (Li2S), carbon dioxide, and cyanic acid (HOCN). Cyanic acid and ammonia continue to react to produce urea OC(NH2)2, and urea can decompose into a gaseous state at high temperatures. In this process, it can be seen that except for lithium sulfide, which is solid, all other by-products are gaseous. The final urea can also decompose into a gaseous state and be volatilized and removed. Therefore, the two-step metathesis reaction can obtain high-purity lithium sulfide. In the second stage, at this high temperature, the final product lithium sulfide is generated, and the reaction is ensured to be complete to obtain a pure phase. After the reaction gradually generates polycrystalline lithium sulfide, it is kept at this temperature for a certain period of time to ensure that the reactants react fully, while allowing the crystals to grow more fully and have better crystallinity, thus obtaining a highly crystalline product.

[0048] The first stage of heat preservation lasts for 3-5 hours (h is an abbreviation for hour); the second stage lasts for 8-12 hours. During the first stage, the molten ammonium thiocyanate reacts fully with the solid lithium carbonate to form a crystalline phase. Heat preservation for a period ensures the ammonium thiocyanate melts completely, guaranteeing a complete reaction and maintaining the system in a solid-liquid coexistence or highly diffusive solid phase state. As the temperature increases, the reaction continues, reaching the second stage. After the reaction is complete, heat preservation for a period promotes the continued growth of the already crystallized crystals, improving their purity. For example, the first stage heat preservation time can be 3, 4, or 5 hours, and the second stage heat preservation time can be 8, 9, 10, or 12 hours.

[0049] Since the reaction products are mostly gaseous, they are efficiently removed under continuous purging with an inert gas flow, promoting the irreversible reaction. On the other hand, purging with an inert gas flow can prevent the CO2 generated in the reaction from reacting with the product Li2S, thus avoiding affecting the product formation rate.

[0050] Since lithium carbonate decomposes only above 1000℃, traditional high-temperature carbothermal methods require reactions above 1000℃, significantly increasing energy consumption and leading to lithium volatilization losses. Liquid-phase methods require organic solvents such as tetrahydrofuran, posing flammability risks and solvent residue pollution. This solution achieves gradual decomposition and reaction of raw materials through staged temperature control. A two-stage stepped heat treatment precisely matches the kinetic and thermodynamic requirements of different reaction steps. The first stage utilizes low-temperature melting to induce metathesis, allowing lithium carbonate to react with ammonium thiocyanate without high temperatures, generating the active intermediate LiSCN and in-situ volatile ammonium carbonate. The second stage uses high-temperature driven deep solid-liquid reaction to generate Li₂S, while an inert gas flow continuously removes all gaseous byproducts, making the reaction irreversible and spontaneously clearing impurities, avoiding the formation of byproducts at high temperatures. Furthermore, the entire process is a solid-phase reaction system, requiring no solvent, significantly improving product crystallinity and eliminating the need for additional purification steps.

[0051] In some embodiments of the present invention, the molar ratio of lithium carbonate to ammonium thiocyanate ranges from 1:(1.2 to 1.5), and exemplaryly, this molar ratio can be 1:1.2, 1:1.3, 1:1.4, and 1:1.5. Since the reaction molar ratio of lithium carbonate to ammonium thiocyanate is 1:1, an appropriate excess of ammonium thiocyanate can ensure that the lithium source is fully sulfided, thereby improving the conversion rate and purity of the final product.

[0052] In some embodiments of the present invention, the heating rate of the sintering process is 1°C / min to 3°C / min, where min is an abbreviation for minutes. The sintering process covers the complete thermal journey from room temperature to the end of the second stage holding period. A slower heating rate throughout the sintering process allows sufficient time for decomposition at each stage, ensuring a complete reaction, facilitating the stable release of reactant gases, preventing material splashing or deterioration of crystal morphology due to sudden temperature changes, and ensuring the uniformity of the product morphology. It should be understood that this heating rate is limited to all heating sections except the isothermal section, specifically referring to the rate of temperature change in each heating section, excluding the temperature holding state during the holding period.

[0053] Furthermore, during the heating process from the first stage to the second stage, when the temperature is raised to between 400℃ and 500℃, the heating rate is 5℃ / min to 10℃ / min. This is because carbon and nitrogen organic matter will undergo carbonization at around 450℃, resulting in impurity residues that affect the purity of lithium sulfide products. To avoid this process, the temperature is raised rapidly to reduce the time spent at 450℃.

[0054] In some embodiments of the present invention, the method further includes: rapid air cooling after sintering to refine the lithium sulfide product grains. This product, when exiting the furnace, is a brittle solid in blocky or agglomerated form with a dense surface and potentially microporous internal structures. If left in a high-temperature zone for an extended period, it exhibits thermodynamic instability and is prone to secondary crystallization, resulting in a significant increase in average grain size and a sharp decrease in specific surface area. Refining the grains improves its contact area and reactivity in subsequent electrolyte synthesis. Air cooling, as the final stage of thermal management, forms a closed loop with the temperature regime of the two-stage sintering—the first stage of low-temperature holding ensures the full decomposition of ammonium thiocyanate and the in-situ generation of lithium thiocyanate; the second stage of high-temperature holding drives the metathesis reaction to complete and achieve preliminary crystallization; while air cooling immediately "freezes" this crystalline state after the reaction terminates, preventing grain aggregation and growth at high temperatures.

[0055] In some embodiments of the present invention, both lithium carbonate and ammonium thiocyanate are subjected to vacuum drying. Specifically, before mixing lithium carbonate and ammonium thiocyanate, they are vacuum dried by placing them separately in a vacuum drying oven at 80°C to 90°C for 12 to 24 hours before use. Drying ensures the accuracy of the product dosage in subsequent use. Furthermore, since both lithium carbonate and ammonium thiocyanate have a certain degree of hydrolysis, drying is performed at the initial stage of raw material use to ensure the quality of subsequent reactions, avoid hydrolysis, improve subsequent grinding and dispersibility and material purity, and prevent moisture from interfering with the reaction and generating impurities. For example, the drying temperature can be any value between 80°C, 82°C, 85°C, 87°C, 90°C, or 80°C to 90°C; the drying time can be any value between 12 hours, 15 hours, 18 hours, 20 hours, 24 hours, or 12 to 24 hours. In some embodiments, the drying conditions can be a combination of any two of the above-mentioned temperature and time values.

[0056] In some embodiments of the present invention, the mixing of lithium carbonate and ammonium thiocyanate can be carried out by grinding, ball milling, acoustic resonance, or mechanical crushing, until the ammonium thiocyanate crystals are uniformly dispersed in the lithium carbonate powder. The specific mixing time and particle size can be determined according to requirements, specifically ranging from 0.2 μm to 15 μm, preferably from 0.2 μm to 10 μm, more preferably from 0.2 μm to 1 μm, and most preferably from 0.2 μm to 0.7 μm. These methods aim to achieve uniform mixing of raw materials at the molecular level, increase the reaction contact area, and thus optimize the efficiency and uniformity of the subsequent sintering reaction. Furthermore, the grinding time can be from 15 min to 60 min. For example, the grinding time can be any one of 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, or 60 min. Generally, the smaller the particle size, the more beneficial it is for the subsequent melting reaction and the earlier the crystal formation occurs. In some embodiments, if manual grinding is used, the raw materials on the mortar wall need to be scraped off and remixed every 5 minutes to ensure that all raw materials are mixed.

[0057] Some embodiments of the present invention are described below. Figure 2 The mixture 7 reacts in container 2, which is placed in reaction chamber 1. Reaction chamber 1 is filled with a flowing inert gas. The flowing gas can promptly carry away the gaseous byproducts generated during the reaction, shifting the reaction equilibrium towards the positive direction and preventing the gas from re-condensing and contaminating the product. The flowing inert gas flows in from inlet 3 and out from outlet 4 of reaction chamber 1. By placing the reaction container 2 in a large inert reaction environment, it is ensured that during the reaction in container 2, the gaseous reaction products can be quickly discharged from container 2, enter the entire reaction chamber 1, and flow out of reaction chamber 1 with the flowing inert gas. Exemplarily, the inert reaction environment can be nitrogen or argon.

[0058] The sintering process can be carried out in various equipment such as box furnaces, tube furnaces, Joule flash evaporators, electric arc melting furnaces, and microwave sintering furnaces. When selecting an equipment, factors such as temperature control accuracy, atmosphere sealing, and process adaptability must be considered. The entire sintering process must be conducted in an inert gas atmosphere (such as argon). This is because lithium sulfide products are extremely sensitive to water and oxygen; an inert atmosphere effectively prevents oxidation and hydrolysis, which is crucial for obtaining high-purity products.

[0059] Furthermore, the upper part of the container 2 is provided with a top cover 6 with holes 5, which allows the reaction to proceed in a semi-open inert gas atmosphere. This allows the gases produced by the decomposition of ammonium thiocyanate (such as ammonia) to be discharged smoothly, maintaining the system pressure balance, while also preventing external air backflow to the maximum extent and maintaining the purity of the inert atmosphere inside the reaction chamber 1. During the solid-phase reaction of lithium carbonate and ammonium thiocyanate, the mixture 7 decomposes upon heating, producing byproducts such as sulfur-containing gases and ammonia. When the top cover 6 of the container 2 has holes 5, the gaseous substances generated by the reaction can slowly escape outward through the holes 5, preventing abnormal pressure rise inside the container 2 that could lead to seal failure or rupture of the container 2. At the same time, the inert gas continuously introduced into the reaction chamber 1 can permeate back into the container 2 in small amounts through the holes 5, forming a weak convection from top to bottom inside the container, creating a dynamic gas exchange mechanism. This maintains the oxygen-free environment required for the reaction and achieves the controlled emission of byproducts. The flow rate of the flowing inert gas is 10-100 mL / min. During this process, the flowing inert gas does not directly contact the surface of the mixture 7, but achieves internal and external mass exchange through the holes 5 opened on the top cover 6. Therefore, its flow rate design needs to take into account both the exhaust driving force and the maintenance of the micro-positive pressure inside the container 2.

[0060] It should be understood that both the number and size of the holes 5 mentioned above need to be matched with the flow rate. This flow rate or volume must ensure that the gaseous byproducts can be fully discharged under the condition that the entire reaction system is inert, so as to ensure that the entire reaction can proceed smoothly and improve the purity of the reaction products.

[0061] In some embodiments of the present invention, container 2 is a corrosion-resistant quartz glass tank. Since lithium sulfide and ammonium thiocyanate are corrosive, in order to avoid corroding container 2, generating impurities, and affecting the purity of the reaction products, container 2, which is corrosion-resistant and will not react with the reaction raw materials and reaction products, is selected.

[0062] The second aspect of this invention discloses a lithium sulfide generated by the above-mentioned two-step metathesis method, which has high purity, reaching over 98%, and fine and uniform particles.

[0063] A third aspect of the present invention discloses an application of lithium sulfide, which can be used as a raw material for the synthesis of sulfide solid electrolytes, specifically, applicable to Li 5.5 PS 4.5 Cl 1.5 Li 5.5 PS 4.5 Cl 0.7 Br 0.8 Li7P3S 11 Li 10 GeP2S 12Sulfide solid electrolytes such as Li4SnS4 can be used to prepare ternary high-nickel all-solid-state batteries.

[0064] The Li partial molar ratio described 5.5 PS 4.5 Cl 1.5 Solid electrolytes are prepared by ball milling and sintering. Li2S, LiCl and P2S5 are weighed in the corresponding stoichiometric ratio and ball-milled at 600 rpm (Revolutions Per Minute) for 10 h. The resulting precursor powder is placed in a vacuum ampoule and sintered at 550 °C for 10 h. The resulting sulfide electrolyte powder is then ground.

[0065] The following detailed explanation is further illustrated with specific examples.

[0066] Example 1

[0067] Lithium carbonate and ammonium thiocyanate were dried separately in a vacuum drying oven at 80℃ for 24 hours. Lithium carbonate and ammonium thiocyanate were weighed into a mortar at a molar ratio of 1:1.2 and ground thoroughly for 15 minutes until uniformly mixed, forming a white powder. This white powder was placed in a nitrogen-filled tube furnace and sintered using a stepped heating method to obtain lithium sulfide. The first step temperature was 250℃, held for 4 hours, which resulted in partial lithium sulfide formation. The second step temperature was 650℃, held for 10 hours, with a heating / cooling rate of 3℃ / min for each step. After cooling to room temperature, a white, brittle solid was formed and ground into a fine solid powder in a mortar. The lithium sulfide purity was over 99%. During this process, when the temperature reached 400℃, the heating rate was increased to 7℃ / min until reaching 500℃, at which point the original heating rate was returned. The flow rate of the inert gas in the tube furnace was 50 mL / min.

[0068] The XRD pattern and SEM image of the obtained lithium sulfide are shown in the figure. Figure 3 and Figure 4 .from Figure 3 The XRD pattern shows that after holding at 650℃, lithium sulfide with almost no impurities was completely formed, and the material exhibits excellent crystallinity. Figure 4 The SEM images show that, compared to Figure 4 The commercial lithium sulfide shown in (a) is the present invention. Figure 4 The lithium sulfide grains shown in Figure (b) are more uniform, more fully crystallized, and have fewer impurities; Figures (c) and (d) show that sulfur is evenly distributed in the material.

[0069] See Table 1 below for particle size distribution data, where HM stands for Homemade (laboratory-made) and CM stands for Commercial (commercially purchased lithium sulfide); (See attached table for details). Figure 5 The particle size distributions of lithium sulfide synthesized from ammonium thiocyanate in the laboratory and commercial lithium sulfide show that for the fine particle segments (D10, D30, and D50), Li2S-HM is significantly smaller than Li2S-CM, with a difference of over 10 times at D50. This indicates that the lithium sulfide synthesized from ammonium thiocyanate is predominantly fine-particle, with an overall average particle size much finer than that of commercial lithium sulfide. For the medium particle segment (D70), Li2S-HM still exhibits extremely fine characteristics, with an average particle size of 0.682 μm, while commercial lithium sulfide is close to 6 μm, indicating a significantly coarser particle size in the medium particle segment. For the coarse particle segment, Li2S-HM contains a small number of large particles. Therefore, the overall particle size of lithium sulfide prepared by the method of this invention is much smaller than that of commercial lithium sulfide, with 70% of the cumulative particles maintaining ultrafine characteristics.

[0070] Table 1 Particle size distribution parameters

[0071]

[0072] Example 2

[0073] Lithium carbonate and ammonium thiocyanate were dried separately in a vacuum drying oven at 80℃ for 24 hours. Lithium carbonate and ammonium thiocyanate were weighed into a mortar at a molar ratio of 1:1.5 and ground thoroughly for 15 minutes until uniformly mixed, forming a white powder. This white powder was placed in a nitrogen-filled tube furnace and sintered using a stepped heating method to obtain lithium sulfide. The first step temperature was 250℃ for 4 hours, and the second step temperature was 650℃ for 10 hours, with a heating / cooling rate of 3℃ / min for each step. After cooling to room temperature, a white, foamy, brittle solid was formed. This solid was then ground into a fine powder in a mortar, achieving a lithium sulfide purity of over 98%. During this process, the heating rate was increased to 6℃ / min when the temperature reached 400℃, and then returned to the original rate when the temperature reached 500℃. The flow rate of the inert gas in the tube furnace was 50 mL / min.

[0074] Example 3

[0075] Lithium carbonate and ammonium thiocyanate were dried separately in a vacuum drying oven at 80℃ for 24 hours. Lithium carbonate and ammonium thiocyanate were weighed into a mortar at a molar ratio of 1:1.2 and ground thoroughly for 15 minutes until uniformly mixed, resulting in a white powder. This white powder was placed in a nitrogen-filled tube furnace and sintered using a stepped heating method to obtain lithium sulfide. The first step temperature was 150℃ for 4 hours, and the second step temperature was 650℃ for 10 hours, with a heating / cooling rate of 3℃ / min for each step. After cooling to room temperature, a yellowish-white, foamy, brittle solid (with a purity lower than white) was formed. This solid was ground into a fine powder in a mortar, achieving a lithium sulfide purity of over 97%. During this process, the heating rate was increased to 6℃ / min when the temperature reached 400℃, and then returned to the original heating rate when the temperature reached 500℃. The flow rate of the inert gas in the tube furnace was 80 mL / min.

[0076] Example 4

[0077] Lithium carbonate and ammonium thiocyanate were dried separately in a vacuum drying oven at 80℃ for 24 hours. Lithium carbonate and ammonium thiocyanate were weighed into a mortar at a molar ratio of 1:1.5 and ground thoroughly for 15 minutes until uniformly mixed, forming a white powder. This white powder was placed in a nitrogen-filled tube furnace and sintered using a stepped heating method to obtain lithium sulfide. The first step temperature was 150℃ for 4 hours, and the second step temperature was 650℃ for 10 hours, with a heating / cooling rate of 3℃ / min for each step. After cooling to room temperature, the product formed a yellowish-brown, foamy, brittle solid, which was then ground into a fine solid powder in a mortar. The lithium sulfide purity was over 97%. During this process, when the temperature reached 400℃, the heating rate was increased to 5℃ / min until reaching 500℃, at which point the original heating rate was returned. The flow rate of the inert gas in the tube furnace was 20 mL / min.

[0078] Example 5

[0079] Lithium carbonate and ammonium thiocyanate were dried separately in a vacuum drying oven at 85℃ for 20 hours. Lithium carbonate and ammonium thiocyanate were weighed into a mortar at a molar ratio of 1:1.3 and ground thoroughly for 30 minutes until uniformly mixed, forming a white powder. This white powder was placed in a nitrogen-filled tube furnace and sintered using a stepped heating method to obtain lithium sulfide. The first step temperature was 200℃ for 3 hours, and the second step temperature was 750℃ for 8 hours, with a heating / cooling rate of 1℃ / min for each step. After cooling to room temperature, the product formed a yellowish-brown, foamy, brittle solid, which was then ground into a fine solid powder in a mortar. The lithium sulfide purity was over 97%. During this process, when the temperature reached 400℃, the heating rate was increased to 10℃ / min, and then adjusted back to the original heating rate when the temperature reached 500℃. The flow rate of the inert gas in the tube furnace was 50 mL / min.

[0080] Example 6

[0081] Lithium carbonate and ammonium thiocyanate were dried separately in a vacuum drying oven at 90℃ for 12 hours. Lithium carbonate and ammonium thiocyanate were weighed into a mortar at a molar ratio of 1:1.5 and ground thoroughly for 60 minutes until uniformly mixed, forming a white powder. This white powder was placed in a nitrogen-filled tube furnace and sintered using a stepped heating method to obtain lithium sulfide. The first step temperature was 250℃ for 5 hours, and the second step temperature was 700℃ for 12 hours, with a heating / cooling rate of 2℃ / min for each step. After cooling to room temperature, the product formed a yellowish-brown, foamy, brittle solid, which was then ground into a fine solid powder in a mortar. The lithium sulfide purity was over 98%. During this process, when the temperature reached 400℃, the heating rate was increased to 7℃ / min until reaching 500℃, at which point the original heating rate was returned. The flow rate of the inert gas in the tube furnace was 100 mL / min.

[0082] Application examples

[0083] The lithium sulfide powder synthesized in Example 1 was mixed in a molar ratio of Li₂S:P₂S₅:LiCl = 2:0.5:1.5 and ball-milled at 600 rpm for 10 min of forward rotation, 10 min of reverse rotation, and 5 min of interval, repeated 30 times to obtain a mixture. The mixture was then ground, pressed into tablets, and encapsulated in a vacuum quartz tube. The tablets were then heated at 550°C for 10 hours. The resulting shrunken solid was thoroughly ground into powder, which is LiCl. 5.5 PS 4.5 Cl 1.5 Solid electrolyte.

[0084] See Figure 6 EIS diagram and Figure 7 XRD patterns, based on Figure 6The ohmic impedance value of the EIS spectrum was obtained, and the ionic conductivity was calculated according to the formula σ=L / RS, where σ It is the ionic conductivity. L Let R be the length of the conductor, R be the ohmic resistance, and S be the cross-sectional area of ​​the conductor. From this, we can obtain that the ionic conductivity of the sulfide electrolyte is as high as 7.43 mS / cm. Figure 7 The XRD pattern shows that the synthesized sulfide electrolyte has good crystallinity with almost no impurity phase formation. Following the lithium-indium alloy-lithium-phosphorus-sulfur-chloride-lithium-indium-chloride-high-nickel ternary cathode (LiIn-LPSC-LIC-Ni88) structure from negative to positive electrode, an all-solid-state battery was assembled with an active material areal loading of 8.92 mg / cm³. 2 The first charge / discharge curves and rate performance curves are shown below. Figure 8 and Figure 9 .from Figure 8 It can be seen that at 0.1C, this solid-state battery achieves a high capacity of 217.34 mAh / g and an initial charge-discharge efficiency of 89.09%. Figure 9 The excellent rate performance demonstrates the feasibility of charging and discharging the battery under high current.

[0085] Test case

[0086] The purity of lithium sulfide was tested using the barium sulfate gravimetric method. 100 mg of lithium sulfide powder synthesized in Examples 1-6 was weighed, dissolved in 50 mL of 5% hydrogen peroxide, stirred and heated to fully oxidize, and then an excess of 0.05 mol / L barium chloride solution was added. After filtration, washing, drying, and ignition, the product was weighed. The sulfur content in lithium sulfide was calculated based on the mass of barium sulfate, and the purity of the product was then calculated. The test results are shown in Table 2. As can be seen from Table 2, the lithium sulfide powder prepared by this invention has high purity, all above 97%.

[0087] Table 2. Purity of lithium sulfide powders obtained in Examples 1-6

[0088]

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A two-step metathesis process for the preparation of lithium sulfide, characterized in that, The application relates to a lithium sulfide preparation method. The lithium carbonate and the ammonium thiocyanate are mixed as raw materials to obtain a mixture, and the mixture is sintered under an inert atmosphere to obtain lithium sulfide; The sintering is divided into two stages: the temperature of the first stage is 150-250 DEG C, the holding time is 3-5 h, the temperature of the second stage is 650-750 DEG C, and the holding time is 8-12 h; and a flowing inert gas is introduced during the sintering process; In the first stage, the ammonium thiocyanate and the lithium carbonate generate a decomposition reaction to generate ammonium carbonate and lithium thiocyanate; in the second stage, the lithium thiocyanate and the lithium carbonate generate a reaction to generate lithium sulfide, and the ammonium carbonate is decomposed into by-products; and the by-products and the process products in the reaction process are gaseous.

2. The process according to claim 1, characterized in that, The mixing molar ratio of the lithium carbonate and the ammonium thiocyanate is 1: (1.2-1.5).

3. The process for the preparation of lithium sulfide in two steps by recomplexation according to claim 1, characterized in that, The heating rate of the sintering process is 1-3 DEG C / min.

4. The process according to claim 3, characterized in that, During the heating process from the first stage to the second stage, when the temperature is heated to 400-500 DEG C, the heating rate is 5-10 DEG C / min.

5. The process for the preparation of lithium sulfide in two steps by recomplexation according to claim 1, characterized in that, The product after sintering is obtained by air cooling to obtain lithium sulfide.

6. The process according to claim 1, characterized in that, When the lithium carbonate and the ammonium thiocyanate are mixed, the mixing is achieved through a grinding method or a ball milling method.

7. The method of claim 1, wherein the two-step metathesis process for the production of lithium sulfide is characterized by, The mixture is reacted in a container, the container is in a reaction box, the reaction box is filled with a flowing inert gas, and the upper part of the container is provided with a top cover with holes.

8. The process according to claim 1, characterized in that, The flow rate of the flowing inert gas is 10-100 mL / min.

Images