A method for preparing lithium sulfide using diethyl sulfide as a sulfur source, and products and applications thereof

Abstract

The application provides a method for preparing lithium sulfide by using diethyl sulfide as a sulfur source, and a product and application thereof, and belongs to the technical field of compound synthesis. The method uses diethyl sulfide as a sulfur source and lithium metal as a lithium source. The specific steps include: preparing a substituted biphenyl lithium complex; adding diethyl sulfide dropwise into the substituted biphenyl lithium complex system, and performing a reduction reaction under the condition of 60-70 DEG C, and then performing solid-liquid separation, washing, vacuum distillation impurity removal and drying to obtain high-purity lithium sulfide. The application innovatively adopts a washing-vacuum distillation composite purification process, the obtained product has a purity of greater than or equal to 99.9%, water content of less than or equal to 30 ppm and D50 particle size of less than or equal to 5 mu m, the reaction condition is mild, the by-product is easy to handle, and the cost is controllable, the problems such as high toxicity of raw materials and difficulty in removing by-products in the prior art are effectively solved, the method is suitable for preparation of an electrolyte precursor of a full solid battery, and has industrialization amplification potential.

Description

Technical Field

[0001] This invention belongs to the field of compound synthesis technology, specifically relating to a method for preparing lithium sulfide using diethyl sulfide as a sulfur source, its products, and applications. Background Technology

[0002] Li₂S is a typical inorganic compound, belonging to the binary lithium salt class, and has a face-centered cubic crystal structure. At room temperature and pressure, Li₂S is a white or pale yellow crystal with a melting point of approximately 938℃ and a density of approximately 1.67 g / cm³. 3 Li₂S possesses high thermal and chemical stability. It is relatively stable in an inert atmosphere, does not readily react with oxygen at room temperature, exhibits reducing properties at high temperatures, and can react with water to produce lithium hydroxide and hydrogen sulfide gas, demonstrating strong hydrolytic activity. Therefore, its preparation, storage, and application processes must strictly control environmental humidity and oxygen content. Li₂S is a functional material that combines high theoretical specific capacity, high energy density, and interfacial stability, showing broad application prospects in multiple high-performance fields, and playing a particularly important role in electrochemical energy storage systems. In next-generation battery systems such as lithium-sulfur batteries and all-solid-state batteries, Li₂S can serve as a precursor for cathode materials and can also participate in the construction of composite solid-state electrolytes under certain conditions. The charging and excitation process of Li₂S typically involves electrochemical reactions in lithium-ion batteries. During charging, lithium ions migrate from the negative electrode to the positive electrode, while during excitation, electron transfer and chemical reactions also affect the lithiation process. Its conductivity significantly improves under high-temperature conditions, enabling it to form good interfacial matching with various sulfide electrolytes, making it a crucial fundamental material for achieving a balance between high energy density, safety, and lifespan. Beyond battery systems, Li₂S plays a unique role in thermoelectric materials, organic synthesis, and functional ceramics. In thermoelectric conversion, introducing Li₂S into solid solutions such as Li-Sn-S can effectively improve carrier mobility and the figure of merit (ZT), making it suitable for high-temperature thermoelectric devices. In fine chemicals and pharmaceutical synthesis, Li₂S, as a highly reactive sulfur source, can be used to construct various sulfur-containing organic molecules, such as thioethers, thioamides, and ligand-based functional materials, exhibiting unique advantages in highly selective synthesis and directed catalytic reactions.

[0003] In battery technology, Li₂S applications are concentrated in lithium-sulfur batteries and all-solid-state battery systems. Unlike lithium metal anodes, Li₂S exhibits higher chemical stability and lower reactivity, which helps improve the safety of battery assembly and avoids safety risks such as dendrite formation and short circuits caused by lithium metal. In lithium-sulfur batteries, Li₂S can serve as a pre-lithiated cathode precursor, with a theoretical specific capacity far exceeding that of traditional oxide or phosphate cathode materials, significantly improving overall energy density. In all-solid-state systems, Li₂S exhibits good interface compatibility with typical sulfide electrolytes, making it suitable for constructing continuous ion channel structures, which is beneficial for improving charge transfer efficiency and interface stability. These composite battery structures are particularly suitable for applications with extremely high requirements for energy density, safety, and stability, such as aerospace, military equipment, and high-end electric vehicles.

[0004] However, high-performance battery applications place stringent requirements on the purity and structure of Li₂S materials. Trace impurities, such as Li₂CO₃, LiOH, and Li₂SO₄, can interfere with electrode interface stability, increase the tendency for side reactions, and thus affect battery cycle life and coulombic efficiency. Therefore, reaction conditions must be strictly controlled during material synthesis to ensure product purity and achieve uniform particle size distribution, pure crystal form, and the absence of impurity phases. High-purity Li₂S materials should also possess good micro / nano structure control capabilities to form a large contact area electrode interface with the electrolyte, thereby improving reaction efficiency.

[0005] Currently, there are various methods for synthesizing Li2S, including solid-phase reaction, solution method, gas-phase method and carbon reduction method.

[0006] The basic process of the solid-state reaction method involves reacting lithium metal or its compounds with sulfur at high temperatures to produce Li₂S. The reaction is typically carried out in an inert atmosphere (such as nitrogen or argon). The temperature range for this reaction is controlled between 400-800℃, primarily to avoid vigorous reaction or imbalance of reactant proportions due to sulfur evaporation. The advantages of this method are its relative simplicity, low equipment requirements, and the wide availability and low cost of raw materials, making it suitable for batch reactions and a commonly used method in laboratory and early-stage engineering preparations. However, this method also has certain limitations: for example, the reaction at high temperatures can easily introduce byproducts; the reaction process is vigorous, especially when using lithium metal as a raw material, posing significant safety risks; and to improve the synthesis quality, auxiliary methods such as mechanical ball milling, cold pressing, and inert encapsulation are often introduced to improve the reaction interface, uniformity, and safety, but these methods increase the complexity of the process to some extent.

[0007] Solution-based methods primarily involve the reaction of a lithium source (such as LiOH or Li₂CO₃) with a sulfur source (such as Na₂S or CS₂) in a solvent to generate Li₂S precipitate, which is then obtained through heat treatment. This method is typically carried out under relatively mild conditions, facilitating reaction control and morphology adjustment. It is particularly suitable for preparing specific structures such as nanoparticles, spherical or sheet-like structures, and helps improve the dispersibility and interfacial reaction performance of materials in subsequent applications. However, this method may introduce more impurities, requiring additional purification steps to improve product quality. Furthermore, the post-processing steps are cumbersome, often involving multiple processes such as solvent removal, washing, and drying.

[0008] The gas-phase reaction method typically uses sulfide gases such as hydrogen sulfide (H2S) and carbon disulfide (CS2) to react with lithium vapor or lithium compounds in a high-temperature atmosphere to produce Li2S. Although it can produce products with high purity, the equipment required for the reaction process is complex and expensive, and it places high demands on the system's sealing and reaction control. Furthermore, the hydrogen sulfide gas used in the reaction is highly toxic, posing significant safety risks.

[0009] The carbon reduction method typically uses lithium sulfate (Li₂SO₄) as the lithium source, which reacts with a carbon source (usually activated carbon, carbon black, or polymeric carbon precursor) at high temperatures to produce Li₂S, releasing gases such as CO or CO₂. The reaction is usually carried out in an inert atmosphere (such as Ar or N₂) at 700-900℃, offering advantages such as simple operation and inexpensive raw materials. However, the generated gases pose a challenge to the sealing of the equipment, and controlling residual carbon impurities is difficult, requiring additional heat treatment and post-purification processes.

[0010] While existing methods can yield relatively pure Li₂S to a certain extent, effectively controlling impurity formation, improving Li₂S purity, and ensuring the controllability and economy of the synthesis process remain pressing challenges. Furthermore, since the performance of high-purity Li₂S is significantly influenced by the synthesis process and reaction conditions, in-depth research into its synthesis methods and mechanisms, and the exploration of more efficient synthetic routes, are of great importance for improving the quality of Li₂S and its applications in various fields.

[0011] Relevant patent documents retrieved:

[0012] Publication number CN111517288A, publication date August 11, 2020, discloses a method for directly synthesizing lithium sulfide from a lithiation solution and elemental sulfur as raw materials, comprising the following steps: preparing a lithiation solution, including a lithium metal-aromatic compound organic ether solution, a lithium iodide solution, and a n-butyllithium solution; adding elemental sulfur to the lithiation solution and mixing; and subjecting the above mixed solution to a reaction at room temperature, separation of the precipitate, drying, and heat treatment to obtain lithium sulfide. The organic ether solvent used in this invention is selected from at least one of the following: monoethers such as diethyl ether, diphenyl ether, and divinyl ether; mixed ethers such as methyl ethyl ether, ethyl vinyl ether, and anisole; ethers formed from polyols such as ethylene glycol dimethyl ether and ethylene glycol monomethyl ether; cyclic ethers such as tetrahydrofuran; and thioethers such as methyl ethyl sulfide, but not limited to the ethers listed above. The aromatic compound is selected from at least one of the following: monocyclic aromatic hydrocarbons such as benzene, toluene, xylene, ethylbenzene, cumene, and styrene; biphenyls such as biphenyl and p-terphenyl; fused-ring aromatic hydrocarbons such as naphthalene and anthracene; polyphenylene aliphatic hydrocarbons such as diphenylmethane; and non-benzene aromatic hydrocarbons such as azurite. This method for synthesizing lithium sulfide uses inexpensive and readily available raw materials, has a simple process, produces no harmful gases, and the synthesis process is mild and controllable. However, the purity of the lithium sulfide obtained by this invention does not meet the requirements.

[0013] Relevant patent documents retrieved:

[0014] Publication number CN120208166A, publication date June 27, 2025, discloses a method for synthesizing nano-sized lithium sulfide. The method includes: dissolving lithium sulfide raw material in an alcohol solvent by stirring, then separating to obtain a lithium sulfide alcohol solution; evaporating and crystallizing the lithium sulfide alcohol solution and drying to obtain lithium sulfide crystals; mixing the lithium sulfide crystals with a sulfur source and calcining at 550℃-850℃ to obtain nano-sized lithium sulfide. The sulfur source includes one of elemental sulfur, thiols, thiophenols, thioethers, thiocarboxylic acids, thioamides, and thiocyanates. The thiols include isobutanol sulfide. The present invention directly synthesizes nano-sized lithium sulfide in one step via solid-state sintering. The method is simple, low-cost, and suitable for large-scale industrial production. However, the synthesis process requires high temperature conditions of 550℃-850℃, and the water content of the obtained lithium sulfide cannot better meet the requirements. The thiophenolic compounds include toluenethiophenol or naphthiophenol; the thioether compounds include dibenzyl sulfide or diethyl sulfide; the thiocarboxylic acid compounds include thiobenzoic acid; the thioamide compounds include thiourea or thioacetamide; and the thiocyanate compounds include ammonium thiocyanate.

[0015] Therefore, there is a need to develop a lithium sulfide synthesis method that uses low-toxicity raw materials, allows for controllable reactions, simplifies purification, produces high-purity products, and has controllable costs. Summary of the Invention

[0016] Based on the shortcomings of existing technologies, such as high toxicity of raw materials, difficulty in removing by-products, low product purity, and high preparation costs, this invention uses low-toxicity diethyl sulfide as a sulfur source and metallic lithium as a lithium source. Through precise control of lithium source dosage, optimization of reaction parameters, and innovation in purification processes, it achieves efficient synthesis of lithium sulfide with a product purity of over 99.9%. Moreover, the process is highly stable and safe, and has the potential for industrial scale-up.

[0017] In order to achieve the above objectives, the present invention aims to provide:

[0018] This invention provides a method for preparing lithium sulfide using diethyl sulfide as a sulfur source, and related technologies, to solve the technical problems of high raw material toxicity, difficulty in removing by-products, low product purity, and high preparation cost in the prior art, or a combination thereof.

[0019] This invention utilizes low-toxicity diethyl sulfide as a sulfur source and metallic lithium as a lithium source. Through precise control of lithium source dosage, optimization of reaction parameters, and innovation in purification processes, a high-purity lithium sulfide with low water content has been obtained. This sulfide can be directly applied to high-end fields such as all-solid-state batteries and lithium-sulfur batteries. It is of great significance and has broad prospects for industrial application, especially for breaking through the industrialization bottleneck of all-solid-state batteries.

[0020] Terminology Explanation:

[0021] Unless otherwise defined, all technical terms in this document have the same meanings as commonly understood by one of ordinary skill in the art to which the subject matter of the claims pertains. Unless otherwise stated, all patents, patent inventions, and publications cited in this document are incorporated herein by reference in their entirety. If multiple definitions exist for terms in this document, the definitions in this chapter shall prevail.

[0022] It should be understood that the above brief description and the following detailed description are exemplary and for illustrative purposes only, and do not limit the subject matter of the invention in any way. In this invention, the singular is used in conjunction with the plural unless otherwise specifically stated. It should also be noted that, unless otherwise stated, the use of “or” or “or” means “and / or”. Furthermore, the use of the term “comprising” and other forms such as “including,” “containing,” and “contains” are not limiting.

[0023] Unless otherwise stated, conventional methods within the scope of the art, such as mixing and stirring, shall be used.

[0024] Unless specifically defined herein, the use of various commercially available products herein employs standard techniques. For example, they may be implemented in a manner known in the art or as described in this invention. The techniques and methods described herein can generally be implemented according to conventional methods well known in the art, based on the descriptions in the various summary and more specific documents cited and discussed in this specification.

[0025] The terms “optional / arbitrary” or “optionally / arbitrarily” mean that the event or situation described below may or may not occur, including both the occurrence and non-occurrence of the event or situation.

[0026] In a first aspect, the present invention provides a method for preparing lithium sulfide using diethyl sulfide as a sulfur source.

[0027] The method includes the following steps:

[0028] S1. Preparation of lithium complex: Under an inert gas atmosphere, substituted biphenyls were dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution; metallic lithium was added to the solution and stirred at room temperature to obtain a lithium complex solution;

[0029] S2, Reduction reaction: Diethyl sulfide is added dropwise at a constant rate to the lithium complex solution prepared in step S1 to carry out the reduction reaction, and a suspension is obtained;

[0030] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration to collect the solid precipitate; the solid precipitate is washed to obtain the washed solid precipitate.

[0031] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation to obtain the pre-product.

[0032] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven for drying to obtain a high-purity lithium sulfide product.

[0033] in:

[0034] The inert gas mentioned in step S1 above is argon;

[0035] The substituted biphenyl mentioned in step S1 above is one or more of 4,4′-dimethylbiphenyl, 2-methylbiphenyl, or 3,3′,4,4′-tetramethylbiphenyl;

[0036] The drying process described in step S1 above is performed using a molecular sieve; the molecular sieve is a 4A molecular sieve, and the moisture content of the dried ethylene glycol dimethyl ether needs to be controlled below 30 ppm;

[0037] The concentration of the substituted biphenyl solution mentioned in step S1 above is 0.5-1.5 mol / L; preferably 0.8-1.2 mol / L; and even more preferably 1.0-1.2 mol / L.

[0038] As a further preferred embodiment, the concentration of the substituted biphenyl solution is any point or range between 0.5 and 1.5 mol / L, and can be selected from 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, or 1.5 mol / L;

[0039] As a further preferred embodiment, the concentration of the substituted biphenyl solution is any value or range between 0.5-1.5 mol / L, and can be selected from 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.1 mol / L or 1.2 mol / L;

[0040] As a further preferred embodiment, the concentration of the substituted biphenyl solution is any value or range between 0.5-1.5 mol / L, and can be selected from 1.0 mol / L, 1.1 mol / L or 1.2 mol / L;

[0041] As a further preferred embodiment, the concentration of the substituted biphenyl solution is any value or range between 0.5-1.5 mol / L, and may be selected from 1.0 mol / L.

[0042] The molar ratio of metallic lithium to substituted biphenyl is 1:1-1.2; preferably 1:1-1.1.

[0043] As a further preferred embodiment, the molar ratio of lithium metal to substituted biphenyl is any point or range between 1:1 and 1.2, and can be selected from 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.1, 1:1.11, 1:1.12, 1:1.13, 1:1.14, 1:1.15, 1:1.16, 1:1.17, 1:1.18, 1:1.19 or 1:1.2;

[0044] As a further preferred embodiment, the molar ratio of lithium metal to substituted biphenyl is any point or range between 1:1 and 1.2, and can be selected from 1:1, 1:1.01, 1:1.02, 1:1.03, 1:1.04, 1:1.05, 1:1.06, 1:1.07, 1:1.08, 1:1.09, 1:1.1, 1:1.11, or 1:1.12;

[0045] As a further preferred embodiment, the molar ratio of lithium metal to substituted biphenyl is any point or range between 1:1 and 1.2, and can be selected from 1:1, 1:1.1, 1:1.11 or 1:1.12;

[0046] As a further preferred embodiment, the molar ratio of lithium metal to substituted biphenyl is any point or range between 1:1 and 1.2, and can be selected from 1:1.

[0047] The stirring time in step S1 above is 2-4 hours; preferably 2.5-3.5 hours.

[0048] As a further preferred embodiment, the stirring time is any value or range between 2 and 4 hours, and can be selected from 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, 3.5 hours, 3.6 hours, 3.7 hours, 3.8 hours, 3.9 hours, or 4.0 hours.

[0049] As a further preferred embodiment, the stirring time is any value or range between 2 and 4 hours, and can be selected from 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, or 3.5 hours.

[0050] As a further preferred embodiment, the stirring time is any value or range between 2 and 4 hours, and can be selected from 3.0 hours, 3.1 hours, 3.2 hours, 3.3 hours, 3.4 hours, or 3.5 hours;

[0051] As a further preferred embodiment, the stirring time is any value or range between 2 and 4 hours, and can be selected from 3.0 hours.

[0052] The lithium complex obtained in step S1 above is the core catalyst used in the above method. It is generated by the electron transfer reaction between substituted biphenyl and metallic lithium. The introduction of methyl substituents can optimize the electron cloud distribution, enhance the electron transfer ability and catalytic activity of the complex, and significantly reduce the breaking energy barrier of the CS bond in diethyl sulfide. Moreover, this type of complex has excellent stability and can exist stably at a reaction temperature of 60-70℃ without obvious decomposition, which ensures the efficient progress of the reaction.

[0053] The dropping rate of the diethyl sulfide mentioned in step S2 above is 0.5-1 mL / min, preferably 0.6-0.8 mL / min;

[0054] As a further preferred embodiment, the dropping rate of the diethyl sulfide is any point or range between 0.5 and 1 mL / min, and can be selected from 0.5 mL / min, 0.6 mL / min, 0.7 mL / min, 0.8 mL / min, 0.9 mL / min or 1.0 mL / min;

[0055] As a further preferred embodiment, the dropping rate of the diethyl sulfide is any value or range between 0.5 and 1 mL / min, and can be selected from 0.6 mL / min, 0.7 mL / min or 0.8 mL / min;

[0056] As a further preferred embodiment, the dropping rate of the diethyl sulfide is any value or range between 0.5 and 1 mL / min, and can be selected from 0.8 mL / min.

[0057] Preferably, the diethyl sulfide is added dropwise using a constant-pressure dropping funnel to avoid excessive local reaction that could trigger side reactions.

[0058] The molar ratio of diethyl sulfide to lithium metal mentioned in step S2 above is 1:4-4.5;

[0059] As a further preferred embodiment, the molar ratio of the diethyl sulfide to lithium metal is any point or range between 1:4 and 4.5, and can be selected from 1:4, 1:4.1, 1:4.2, 1:4.3, 1:4.4 or 1:4.5;

[0060] As a further preferred embodiment, the molar ratio of the diethyl sulfide to lithium metal is any point or range between 1:4 and 4.5, and can be selected from 1:4.2, 1:4.3, 1:4.4 or 1:4.5;

[0061] As a further preferred embodiment, the molar ratio of the diethyl sulfide to lithium metal is any value or range between 1:4 and 4.5, and can be selected from 1:4.2.

[0062] The temperature of the reduction reaction described in step S2 above is 60-70℃;

[0063] As a further preferred embodiment, the temperature of the reduction reaction is any point or range between 60-70°C, and can be selected from 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C or 70°C.

[0064] As a further preferred embodiment, the temperature of the reduction reaction is any point or range between 60-70°C, and can be selected from 62°C, 63°C, 64°C, 65°C, 66°C or 67°C.

[0065] As a further preferred embodiment, the temperature of the reduction reaction is any point or range between 60-70°C, and can be selected from 65°C.

[0066] The reduction reaction in step S2 above takes 3-5 hours;

[0067] As a further preferred embodiment, the reduction reaction time is any value or range between 3 and 5 hours, and can be selected from 3 hours, 3.2 hours, 3.5 hours, 3.8 hours, 4.0 hours, 4.2 hours, 4.5 hours, 4.8 hours or 5 hours;

[0068] As a further preferred embodiment, the reduction reaction time is any value or range between 3 and 5 hours, specifically 3.5 hours, 3.8 hours, 4.0 hours, 4.2 hours, or 4.5 hours.

[0069] As a further preferred embodiment, the reduction reaction time is any value or range between 3 and 5 hours, and can be selected from 4.0 hours.

[0070] Diethyl sulfide undergoes a reduction reaction with metallic lithium under the catalysis of a lithium complex. The CS bond breaks, generating a solid precipitate of lithium sulfide and ethane gas. The core reaction equation is as follows:

[0071] (C2H5)2S+4Li→2Li2S↓+2C2H6↑

[0072] The above equation represents the core reaction for the synthesis of lithium sulfide from diethyl sulfide and metallic lithium. (C₂H₅)₂S serves as the sulfur source, Li as the lithium source and reducing agent, and the Li-4,4′-dimethylbiphenyl, Li-2-methylbiphenyl, or Li-3,3′,4,4′-tetramethylbiphenyl lithium complexes prepared in step S1 act as catalysts. Compared to the unsubstituted Li-biphenyl system, the electron-donating effect of the methyl substituent optimizes the radical anionic structure of the complex, enhances the electron transfer efficiency to the diethyl sulfide CS bond, further weakens the CS bond energy (reducing it from approximately 330 kJ / mol to 260-290 kJ / mol), significantly lowers the activation energy, and promotes efficient CS bond cleavage under mild conditions of 60-70℃. In this catalytic process, the lithium complex only participates in electron transfer without altering its chemical properties. After the reaction, it can be recovered through washing and distillation processes, achieving a recovery rate of over 88%, which is 3-5 percentage points higher than the traditional Li-biphenyl system, further reducing catalyst consumption costs. In the reaction, sulfur is retained from the -2 valence in diethyl sulfide to the -2 valence in lithium sulfide, while lithium metal is oxidized from 0 valence to +1 valence. The electron transfer process is stable and controllable under the mediation of a catalyst, and the sulfur conversion rate can reach over 97%.

[0073] The vacuum degree of vacuum filtration mentioned in step S3 above is 0.006-0.06 MPa;

[0074] As a further preferred embodiment, the vacuum degree of the vacuum filtration is any point or range value between 0.006 and 0.06 MPa, and can be selected from 0.006 MPa, 0.008 MPa, 0.01 MPa, 0.012 MPa, 0.015 MPa, 0.02 MPa, 0.025 MPa, 0.03 MPa, 0.035 MPa, 0.04 MPa, 0.045 MPa, 0.05 MPa, 0.055 MPa or 0.06 MPa;

[0075] As a further preferred embodiment, the vacuum degree of the vacuum filtration is any point or range value between 0.006 and 0.06 MPa, and can be selected from 0.03 MPa, 0.035 MPa, 0.04 MPa, 0.045 MPa, 0.05 MPa, 0.055 MPa or 0.06 MPa;

[0076] As a further preferred embodiment, the vacuum degree of the vacuum filtration is any point or range value between 0.006-0.06 MPa, and can be selected from 0.03 MPa, 0.035 MPa or 0.04 MPa;

[0077] As a further preferred embodiment, the vacuum degree of the vacuum filtration is any point or range between 0.006 and 0.06 MPa, and can be selected from 0.03 MPa;

[0078] The washing described in step S3 above is performed using anhydrous tetrahydrofuran.

[0079] The washing process is repeated 2-3 times, with each wash lasting 20-30 minutes.

[0080] The amount of anhydrous tetrahydrofuran used is 3-5 times the mass of the solid phase precipitate to ensure that residual impurities are fully dissolved and removed.

[0081] As a further preferred embodiment, the amount of anhydrous tetrahydrofuran is any value or range between 3 and 5 times the mass of the solid precipitate, and can be selected from 3 times, 3.2 times, 3.5 times, 3.8 times, 4.0 times, 4.2 times, 4.5 times, 4.8 times or 5 times.

[0082] As a further preferred embodiment, the amount of anhydrous tetrahydrofuran used is any value or range between 3 and 5 times the mass of the solid precipitate, and can be selected from 3.5 times, 3.8 times, 4.0 times, 4.2 times or 4.5 times.

[0083] As a further preferred embodiment, the amount of anhydrous tetrahydrofuran used is any value or range between 3 and 5 times the mass of the solid phase precipitate, and can be selected from 4.0 times, 4.2 times or 4.5 times.

[0084] As a further preferred embodiment, the amount of anhydrous tetrahydrofuran is any value or range between 3 and 5 times the mass of the solid phase precipitate, and can be selected from 4.0 times.

[0085] The vacuum degree of vacuum distillation described in step S4 above is 0.001-0.005 MPa;

[0086] As a further preferred embodiment, the vacuum degree of the vacuum distillation is any point or range value between 0.001 and 0.005 MPa, which can be selected from 0.001 MPa, 0.002 MPa, 0.003 MPa, 0.004 MPa or 0.005.

[0087] As a further preferred embodiment, the vacuum degree of the vacuum distillation is any point or range value between 0.001 and 0.005 MPa, which can be selected from 0.002 MPa, 0.003 MPa or 0.004 MPa;

[0088] As a further preferred embodiment, the vacuum degree of the vacuum distillation is any point or range between 0.001 and 0.005 MPa, and can be selected from 0.003 MPa.

[0089] The temperature of vacuum distillation in step S4 above is 120-150℃;

[0090] As a further preferred embodiment, the temperature of the vacuum distillation is any point or range between 120-150℃, and can be selected from 120℃, 121℃, 122℃, 123℃, 124℃, 125℃, 126℃, 127℃, 128℃, 129℃, 130℃, 131℃, 132℃, 133℃, 134℃, 135℃, 136℃, 137℃, 138℃, 139℃, 140℃, 141℃, 142℃, 143℃, 144℃, 145℃, 146℃, 147℃, 148℃, 149℃ or 150℃;

[0091] As a further preferred embodiment, the temperature of the vacuum distillation is any point or range between 120-150°C, and can be selected from 130°C, 131°C, 132°C, 133°C, 134°C, 135°C, 136°C, 137°C, 138°C, 139°C or 140°C.

[0092] As a further preferred embodiment, the temperature of the vacuum distillation is any point or range between 120-150°C, and can be selected from 135°C, 136°C, 137°C, 138°C, 139°C or 140°C.

[0093] As a further preferred embodiment, the temperature of the vacuum distillation is any point or range between 120-150°C, and can be selected from 140°C.

[0094] The vacuum distillation time described in step S4 above is 2-3 hours;

[0095] As a further preferred embodiment, the vacuum distillation time is any value or range between 2 and 3 hours, and can be selected from 2 hours, 2.1 hours, 2.2 hours, 2.3 hours, 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, 2.8 hours, 2.9 hours, or 3.0 hours.

[0096] As a further preferred embodiment, the vacuum distillation time is any value or range between 2 and 3 hours, and can be selected from 2.4 hours, 2.5 hours, 2.6 hours, 2.7 hours, or 2.8 hours.

[0097] As a further preferred embodiment, the vacuum distillation time is any value or range between 2 and 3 hours, and can be selected from 2.5 hours, 2.6 hours, or 2.7 hours.

[0098] As a further preferred embodiment, the vacuum distillation time is any value or range between 2 and 3 hours, and can be selected from 2.5 hours.

[0099] In step S4 above, the vacuum distillation process adopts a programmed temperature rise mode, with the temperature rise rate controlled at 5℃ / min to avoid local overheating that could lead to agglomeration of lithium sulfide particles.

[0100] The purpose of vacuum distillation in step S4 above is to remove residual solvent and trace amounts of lithium polysulfide byproducts.

[0101] The drying temperature described in step S5 above is 100-120℃;

[0102] As a further preferred embodiment, the drying temperature is any point or range between 100-120℃, and can be selected from 100℃, 101℃, 102℃, 103℃, 104℃, 105℃, 106℃, 107℃, 108℃, 109℃, 110℃, 111℃, 112℃, 113℃, 114℃, 115℃, 116℃, 117℃, 118℃, 119℃ or 120℃;

[0103] As a further preferred embodiment, the drying temperature is any point or range between 100-120℃, and can be selected from 105℃, 106℃, 107℃, 108℃, 109℃, 110℃, 111℃, 112℃, 113℃, 114℃ or 115℃.

[0104] As a further preferred embodiment, the drying temperature is any point or range between 100-120°C, and can be selected from 108°C, 109°C, 110°C, 111°C or 112°C.

[0105] As a further preferred embodiment, the drying temperature is any point or range between 100-120°C, and may be selected from 110°C.

[0106] The drying time in step S5 above is 4-6 hours;

[0107] As a further preferred embodiment, the drying time is any value or range between 4 and 6 hours, and can be selected from 4 hours, 4.1 hours, 4.2 hours, 4.3 hours, 4.4 hours, 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours, 5.0 hours, 5.1 hours, 5.2 hours, 5.3 hours, 5.4 hours, 5.5 hours, 5.6 hours, 5.7 hours, 5.8 hours, 5.9 hours, or 6.0 hours.

[0108] As a further preferred embodiment, the drying time is any value or range between 4 and 6 hours, and can be selected from 4.5 hours, 4.6 hours, 4.7 hours, 4.8 hours, 4.9 hours, 5.0 hours, 5.1 hours, 5.2 hours, 5.3 hours, 5.4 hours, or 5.5 hours.

[0109] As a further preferred embodiment, the drying time is any value or range between 4 and 6 hours, and can be selected from 5.0 hours, 5.1 hours, 5.2 hours, 5.3 hours, 5.4 hours, or 5.5 hours;

[0110] As a further preferred embodiment, the drying time is any value or range between 4 and 6 hours, and may be selected from 5.0 hours.

[0111] As some preferred embodiments, the method for preparing lithium sulfide using diethyl sulfide as a sulfur source is described.

[0112] The method includes the following steps:

[0113] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 4,4′-dimethylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 0.5-1.5 mol / L; metallic lithium (purity ≥99.9%) was added to the solution, and the mixture was stirred at room temperature for 2-4 h to obtain a Li-4,4′-dimethylbiphenyl lithium complex solution; the molar ratio of metallic lithium to substituted biphenyl was 1:1-1.2.

[0114] S2. Reduction reaction: Diethyl sulfide is added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.5-1 mL / min to carry out the reduction reaction. The temperature of the reaction system is maintained at 60-70℃, and the reaction is stirred for 3-5 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal is 1:4-4.5.

[0115] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.006-0.06 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, the amount of anhydrous tetrahydrofuran being 3-5 times the mass of the solid precipitate, the washing number being 2-3 times, and the washing time for each washing being 20-30 min, to obtain the washed solid precipitate;

[0116] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation. The heating rate is controlled at 5℃ / min. The mixture is kept at a vacuum of 0.001-0.005MPa and a distillation temperature of 120-150℃ for 2-3 hours to obtain the pre-product.

[0117] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 100-120℃ for 4-6 hours to obtain a high-purity lithium sulfide product.

[0118] As a preferred embodiment, the method for preparing lithium sulfide using diethyl sulfide as a sulfur source is described.

[0119] The method includes the following steps:

[0120] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 4,4′-dimethylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 1.0 mol / L; metallic lithium (purity ≥99.9%) was added to the solution, and the mixture was stirred at room temperature for 3 h to obtain a Li-4,4′-dimethylbiphenyl lithium complex solution; the molar ratio of metallic lithium to substituted biphenyl was 1:1;

[0121] S2. Reduction reaction: Diethyl sulfide was added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.8 mL / min to carry out the reduction reaction. The temperature of the reaction system was maintained at 65℃, and the reaction was stirred for 4 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal was 1:4.2.

[0122] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.03 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, the amount of anhydrous tetrahydrofuran being 4 times the mass of the solid precipitate, the washing is performed 3 times, and the washing time is 20 min per wash, to obtain the washed solid precipitate.

[0123] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation. The heating rate is controlled at 5℃ / min. The mixture is kept at a vacuum of 0.003MPa and a distillation temperature of 140℃ for 2.5h to obtain the preproduct.

[0124] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 110°C for 5 hours to obtain a high-purity lithium sulfide product.

[0125] As another preferred embodiment, the method for preparing lithium sulfide using diethyl sulfide as a sulfur source is described.

[0126] The method includes the following steps:

[0127] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 2-methylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 0.5-1.5 mol / L; lithium metal (purity ≥99.9%) was added to the solution, and the mixture was stirred at room temperature for 2-4 h to obtain a Li-2-methylbiphenyl lithium complex solution; the molar ratio of lithium metal to substituted biphenyl was 1:1-1.2.

[0128] S2. Reduction reaction: Diethyl sulfide is added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.5-1 mL / min to carry out the reduction reaction. The temperature of the reaction system is maintained at 60-70℃, and the reaction is stirred for 3-5 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal is 1:4-4.5.

[0129] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.006-0.06 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, 2-3 times, with each washing time being 20-30 min, to obtain the washed solid precipitate.

[0130] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation. The heating rate is controlled at 5℃ / min. The mixture is kept at a vacuum of 0.001-0.005MPa and a distillation temperature of 120-150℃ for 2-3 hours to obtain the pre-product.

[0131] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 100-120℃ for 4-6 hours to obtain a high-purity lithium sulfide product.

[0132] As a preferred embodiment, the method for preparing lithium sulfide using diethyl sulfide as a sulfur source is described.

[0133] The method includes the following steps:

[0134] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 2-methylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 1.0 mol / L; lithium metal (purity ≥99.9%) was added to the solution, and the mixture was stirred at room temperature for 3 h to obtain a Li-2-methylbiphenyl lithium complex solution; the molar ratio of lithium metal to substituted biphenyl was 1:1;

[0135] S2. Reduction reaction: Diethyl sulfide was added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.8 mL / min to carry out the reduction reaction. The temperature of the reaction system was maintained at 65℃, and the reaction was stirred for 4 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal was 1:4.2.

[0136] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.03 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, the amount of anhydrous tetrahydrofuran being 4 times the mass of the solid precipitate, the washing is performed 3 times, and the washing time is 20 min per wash, to obtain the washed solid precipitate.

[0137] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation. The heating rate is controlled at 5℃ / min. The mixture is kept at a vacuum of 0.003MPa and a distillation temperature of 140℃ for 2.5h to obtain the preproduct.

[0138] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 110°C for 5 hours to obtain a high-purity lithium sulfide product.

[0139] As another preferred embodiment, the method for preparing lithium sulfide using diethyl sulfide as a sulfur source is described.

[0140] The method includes the following steps:

[0141] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 3,3′,4,4′-tetramethylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 0.5-1.5 mol / L; lithium metal (purity ≥99.9%) was added to the solution, and the mixture was stirred at room temperature for 2-4 h to obtain a Li-3,3′,4,4′-tetramethylbiphenyl lithium complex solution; the molar ratio of lithium metal to substituted biphenyl was 1:1-1.2.

[0142] S2. Reduction reaction: Diethyl sulfide is added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.5-1 mL / min to carry out the reduction reaction. The temperature of the reaction system is maintained at 60-70℃, and the reaction is stirred for 3-5 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal is 1:4-4.5.

[0143] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.006-0.06 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, 2-3 times, with each washing time being 20-30 min, to obtain the washed solid precipitate.

[0144] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and vacuum distilled. The distillation is carried out at a vacuum of 0.001-0.005 MPa and a distillation temperature of 120-150℃ for 2-3 hours to obtain the pre-product.

[0145] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 100-120℃ for 4-6 hours to obtain a high-purity lithium sulfide product.

[0146] As a preferred embodiment, the method for preparing lithium sulfide using diethyl sulfide as a sulfur source is described.

[0147] The method includes the following steps:

[0148] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 3,3′,4,4′-tetramethylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 1.0 mol / L; lithium metal (purity ≥99.9%) was added to the solution, and the mixture was stirred at room temperature for 3 h to obtain a Li-3,3′,4,4′-tetramethylbiphenyl lithium complex solution; the molar ratio of lithium metal to substituted biphenyl was 1:1.

[0149] S2. Reduction reaction: Diethyl sulfide was added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.8 mL / min to carry out the reduction reaction. The temperature of the reaction system was maintained at 65℃, and the reaction was stirred for 4 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal was 1:4.2.

[0150] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.03 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, the amount of anhydrous tetrahydrofuran being 4 times the mass of the solid precipitate, the washing is performed 3 times, and the washing time is 20 min per wash, to obtain the washed solid precipitate.

[0151] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation. The heating rate is controlled at 5℃ / min. The mixture is kept at a vacuum of 0.003MPa and a distillation temperature of 140℃ for 2.5h to obtain the preproduct.

[0152] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 110°C for 5 hours to obtain a high-purity lithium sulfide product.

[0153] Secondly, the present invention provides: a lithium sulfide prepared by the above method, wherein the lithium sulfide has a purity ≥99.9%, a moisture content ≤30ppm, a D50 particle size ≤5μm and a whiteness ≥80.

[0154] Thirdly, the present invention provides the application of lithium sulfide prepared by the above method in the preparation of lithium-sulfur batteries or semiconductor electronics.

[0155] Examples 1-13 of this invention at least support the protection range of the following: type of substituted biphenyl, molar ratio of lithium metal to substituted biphenyl, concentration of substituted biphenyl, stirring time, molar ratio of diethyl sulfide to lithium metal, reduction reaction temperature, stirring time of reduction reaction, vacuum degree of filtration, vacuum degree of distillation, and distillation time.

[0156] The term "substituted biphenyl" is derived from the common feature "substituted biphenyl" in the foregoing explanation and / or examples 1-13, which are 4,4′-dimethylbiphenyl, 2-methylbiphenyl, or 3,3′,4,4′-tetramethylbiphenyl. Therefore, those skilled in the art can reasonably infer that the subordinate concepts of the technical feature "substituted biphenyl," substantially equivalent technical means, and technical means that can replace substituted biphenyl within the scope of conventional technical means and common knowledge based on the existing technical level should all fall within the protection scope of this invention. For example, replacing substituted biphenyl with other trisubstituted or tetrasubstituted biphenyls while keeping other technical features unchanged still falls within the protection scope of this invention.

[0157] The "molar ratio of lithium metal to substituted biphenyl" mentioned above is derived from the common feature "1:1-1.2" summarized from the corresponding technical features of 1:1, 1:1.1, 1:1.2, etc., explained above and / or in Examples 1-13. Therefore, those skilled in the art can reasonably infer that the subordinate concepts of the technical feature "molar ratio of lithium metal to substituted biphenyl," the substantially equivalent technical means, and the technical means that can replace the molar ratio within the scope of conventional technical means and common knowledge based on the existing technical level should all fall within the protection scope of this invention. For example, replacing the molar ratio with 1:1.02, 1:1.05, or 1:1.08 while keeping other technical features unchanged still falls within the protection scope of this invention.

[0158] The "preparation of biphenyl substituted concentration" is derived from the aforementioned explanation and / or the corresponding technical features in Examples 1-13, such as 0.5 mol / L, 1 mol / L, and 1.5 mol / L, summarized by the common feature "0.5-1.5 mol / L". Therefore, those skilled in the art can reasonably infer that the subordinate concept of the technical feature replacing the biphenyl concentration, the substantially equivalent technical means, and the technical means that can replace the concentration within the scope of conventional technical means and common knowledge based on the existing technical level should all fall within the protection scope of this invention. For example, replacing the concentration with 0.6 mol / L, 1.0 mol / L, etc., while keeping other technical features unchanged, still falls within the protection scope of this invention.

[0159] The "stirring reaction time" mentioned above is derived from the common feature "2-4h" summarized by the corresponding technical features of 2h, 3h, 4h, etc., in the foregoing explanation and / or Examples 1-13. Therefore, those skilled in the art can reasonably infer that the subordinate concept of the technical feature stirring reaction, the substantially equivalent technical means, and the technical means that can replace biphenyl within the scope of conventional technical means and common knowledge based on the existing technical level should all fall within the protection scope of this invention. For example, replacing the time with 2.5h, 2.8h, 3.5h, etc., while keeping other technical features unchanged, still falls within the protection scope of this invention.

[0160] The "molar ratio of diethyl sulfide to lithium metal" mentioned above is derived from the corresponding technical features of 1:4, 1:4.2, 1:4.5, etc., explained above and / or in Examples 1-13, summarized by the common feature "1:4-4.5". Therefore, those skilled in the art can reasonably infer that the technical feature of the molar ratio of diethyl sulfide to lithium metal is a subordinate concept, a substantially equivalent technical means, or a technical means that can replace the molar ratio within the scope of conventional technical means and common knowledge based on the existing technical level, and should all fall within the protection scope of this invention. For example, replacing the molar ratio with 1:4.1 or 1:4.3 while keeping other technical features unchanged still falls within the protection scope of this invention.

[0161] The "reduction reaction temperature" mentioned above is derived from the aforementioned explanation and / or the corresponding technical features of 60℃, 65℃, 70℃, etc. in Examples 1-13, summarized by the common feature "60-70℃". Therefore, those skilled in the art can reasonably infer that the subordinate concept of the technical feature reaction temperature, the substantially equivalent technical means, and the technical means that can replace the reduction reaction temperature based on the existing technical level within the scope of conventional technical means and common knowledge should all fall within the protection scope of this invention. For example, replacing the temperature with 62℃ or 68℃ while keeping other technical features unchanged still falls within the protection scope of this invention.

[0162] The "reduction reaction stirring time" mentioned above is derived from the common feature "3-5h" summarized by the corresponding technical features of 3h, 4h, and 5h in the foregoing explanation and / or Examples 1-13. Therefore, those skilled in the art can reasonably infer that the subordinate concept of the technical feature reaction temperature, the substantially equivalent technical means, and the technical means that can replace the reduction reaction stirring time based on the existing technical level within the scope of conventional technical means and common knowledge should all fall within the protection scope of this invention. For example, replacing the time with 3.2h or 4.2h while keeping other technical features unchanged still falls within the protection scope of this invention.

[0163] The "vacuum degree of filtration" mentioned above is summarized from the common feature "0.006-0.06MPa" such as 0.006MPa, 0.03MPa, and 0.05MPa in the foregoing explanation and / or the corresponding technical features in Examples 1-13. Therefore, those skilled in the art can reasonably infer that the subordinate concept of the technical feature vacuum degree of filtration, the substantially equivalent technical means, and the technical means that can replace the vacuum degree of filtration based on the existing technical level within the scope of conventional technical means and common knowledge should all fall within the protection scope of this invention. For example, replacing the vacuum degree with 0.02MPa or 0.06MPa while keeping other technical features unchanged still falls within the protection scope of this invention.

[0164] The "distillation vacuum degree" mentioned above is derived from the common feature "0.001-0.005MPa" such as 0.001MPa, 0.003MPa, and 0.005MPa in the foregoing explanation and / or the corresponding technical features in Examples 1-13. Therefore, those skilled in the art can reasonably infer that the subordinate concept of the technical feature distillation vacuum degree, the substantially equivalent technical means, and the technical means that can replace the distillation vacuum degree based on the existing technical level within the scope of conventional technical means and common knowledge should all fall within the protection scope of this invention. For example, replacing the vacuum degree with 0.002MPa or 0.004MPa while keeping other technical features unchanged still falls within the protection scope of this invention.

[0165] The "distillation temperature" mentioned above is a generalization derived from the common feature "120-150℃" such as 120℃, 130℃, and 150℃ in the foregoing explanation and / or the corresponding technical features in Examples 1-13. Therefore, those skilled in the art can reasonably infer that the subordinate concept of the technical feature distillation temperature, the substantially equivalent technical means, and the technical means that can replace the distillation temperature within the scope of conventional technical means and common knowledge based on the existing technical level should all fall within the protection scope of this invention. For example, replacing the distillation temperature with 135℃ or 145℃ while keeping other technical features unchanged still falls within the protection scope of this invention.

[0166] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0167] 1. This invention uses diethyl sulfide as the sulfur source, which, compared to traditional dimethyl sulfide, has lower toxicity, lower volatility, and higher chemical stability during the reaction, effectively inhibiting the occurrence of side reactions in sulfide polymerization. Simultaneously, using Li-4,4′-dimethylbiphenyl, Li-2-methylbiphenyl, or Li-3,3′,4,4′-tetramethylbiphenyl lithium complexes as catalysts, the electron-donating effect of the methyl substituents significantly enhances the catalytic activity, and the catalytic activity is clearly correlated with the number and position of the substituents: the tetramethyl-substituted (3,3′,4,4′-position) complex has the strongest electron-donating effect, enabling the diethyl sulfide to... The CS bond breaking energy of the first complex is reduced to 260-270 kJ / mol, with a sulfur conversion rate of 97.5%-98.0%, and the equilibrium time is shortened to 3-3.5 h. The 4,4′-dimethyl substituted complex is the next best, with a CS bond breaking energy of 275-285 kJ / mol, a sulfur conversion rate of 96.0%-97.0%, and an equilibrium reaction time of 3.5-4 h. The 2-methyl substituted complex (monosubstituted) has slightly lower catalytic activity, with a CS bond breaking energy of 285-290 kJ / mol, a sulfur conversion rate of 95.0%-96.0%, and an equilibrium reaction time of 4-4.5 h. The catalytic performance of these three complexes is significantly better than that of the unsubstituted Li-biphenyl system (sulfur conversion rate of 92%, equilibrium time of over 5 h) and other synthetic techniques.

[0168] 2. High-purity metallic lithium is selected as the lithium source, and the molar ratio of metallic lithium to diethyl sulfide is precisely controlled at 1:4-1:4.5, with the lithium excess ratio controlled at 10%-15%. Compared with the 5% lithium excess ratio in the existing technology, this ratio design can significantly improve the conversion efficiency of the sulfur source, suppress the formation of lithium polysulfide byproducts, and avoid excessive consumption of lithium source, thereby reducing preparation costs; high-purity metallic lithium can reduce the introduction of impurities and further improve the purity of the product.

[0169] 3. An innovative "washing-vacuum distillation" composite purification process is adopted. First, most of the residual biphenyls and sulfides are removed by washing with anhydrous tetrahydrofuran, and then trace amounts of lithium polysulfides and solvent residues are removed by vacuum distillation. Compared with the traditional high-temperature heat treatment impurity removal process, this composite process can effectively avoid the agglomeration of lithium sulfide particles, ensure the uniformity of product particle size, and further improve the product purity to over 99.9%.

[0170] 4. The reaction conditions are mild and controllable, and the entire process is carried out at 60-70℃ in an anhydrous and oxygen-free atmosphere. No high-temperature and high-pressure equipment is required. The process has strong compatibility and high controllability. The by-product is ethane gas, which can be discharged in compliance with standards after absorption and treatment with dilute sulfuric acid. It conforms to the concept of green chemical production and has the technical foundation for large-scale industrial production. Attached Figure Description

[0171] Figure 1 SEM image of lithium sulfide prepared in Example 13;

[0172] Figure 2 The image shows the XRD pattern of lithium sulfide prepared in Example 13, where Li2S-PDF#00-023-0369 is the lithium sulfide standard card. Detailed Implementation

[0173] The following non-limiting embodiments are intended to enable those skilled in the art to gain a more comprehensive understanding of the present invention, but do not limit the invention in any way. The following content is merely an exemplary description of the scope of protection claimed by the present invention, and those skilled in the art can make various changes and modifications to the present invention based on the disclosed content, and such changes should also fall within the scope of protection claimed by the present invention.

[0174] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, all instruments, devices, equipment, reagents, products, etc., used in the embodiments of the present invention are obtained through conventional commercial means.

[0175] The lithium metal used in the following examples is lithium metal sheet with a purity of ≥99.9% and a thickness of 0.1-0.3 mm.

[0176] This invention provides a method for preparing lithium sulfide using diethyl sulfide as a sulfur source, comprising the following steps:

[0177] S1. Preparation of lithium complex: Under an inert gas atmosphere, substituted biphenyls were dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution; metallic lithium was added to the solution and stirred at room temperature to obtain a lithium complex solution;

[0178] The substituted biphenyl is one or more of 4,4′-dimethylbiphenyl, 2-methylbiphenyl, or 3,3′,4,4′-tetramethylbiphenyl;

[0179] The drying process is carried out using a molecular sieve; the molecular sieve is a 4A molecular sieve, and the moisture content of the dried ethylene glycol dimethyl ether needs to be controlled below 30 ppm.

[0180] The concentration of the substituted biphenyl solution mentioned in step S1 above is 0.5-1.5 mol / L; preferably 0.8-1.2 mol / L; and even more preferably 1.0-1.2 mol / L.

[0181] The lithium metal mentioned in step S1 has a purity of ≥99.9% and a thickness of 0.1-0.3 mm;

[0182] The molar ratio of metallic lithium to substituted biphenyl is 1:1-1.2; preferably 1:1-1.1.

[0183] The stirring time is 2-4 hours; preferably 2.5-3.5 hours.

[0184] The lithium complex obtained in this step is the core catalyst used in the above method. It is generated by the electron transfer reaction between substituted biphenyl and metallic lithium. The introduction of methyl substituents can optimize the electron cloud distribution, enhance the electron transfer ability and catalytic activity of the complex, and significantly reduce the breaking energy barrier of the CS bond in diethyl sulfide. Moreover, this type of complex has excellent stability and can exist stably at a reaction temperature of 60-70℃ without obvious decomposition, which ensures the efficient progress of the reaction.

[0185] S2, Reduction reaction: Diethyl sulfide is added dropwise at a constant rate to the lithium complex solution prepared in step S1 to carry out the reduction reaction, and a suspension is obtained;

[0186] The dropping rate of the diethyl sulfide is 0.5-1 mL / min, preferably 0.6-0.8 mL / min;

[0187] The diethyl sulfide is added dropwise using a constant-pressure dropping funnel to avoid excessive local reaction and side reactions; the molar ratio of diethyl sulfide to lithium metal is 1:4-4.5.

[0188] The reduction reaction is carried out at a temperature of 60-70℃ for 3-5 hours.

[0189] In this step, diethyl sulfide and metallic lithium undergo a reduction reaction catalyzed by a lithium complex. The CS bond breaks, generating lithium sulfide solid precipitate and ethane gas. The core reaction equation is as follows:

[0190] (C2H5)2S+4Li→2Li2S↓+2C2H6↑

[0191] The above equation represents the core reaction for the synthesis of lithium sulfide from diethyl sulfide and metallic lithium. (C₂H₅)₂S serves as the sulfur source, Li as the lithium source and reducing agent, and the Li-4,4′-dimethylbiphenyl, Li-2-methylbiphenyl, or Li-3,3′,4,4′-tetramethylbiphenyl lithium complexes prepared in step S1 act as catalysts. Compared to the unsubstituted Li-biphenyl system, the electron-donating effect of the methyl substituent optimizes the radical anionic structure of the complex, enhances the electron transfer efficiency to the diethyl sulfide CS bond, further weakens the CS bond energy (reducing it from approximately 330 kJ / mol to 260-290 kJ / mol), significantly lowers the activation energy, and promotes efficient CS bond cleavage under mild conditions of 60-70℃. In this catalytic process, the lithium complex only participates in electron transfer without altering its chemical properties. After the reaction, it can be recovered through washing and distillation processes, achieving a recovery rate of over 88%, which is 3-5 percentage points higher than the traditional Li-biphenyl system, further reducing catalyst consumption costs. In the reaction, sulfur is retained from the -2 valence in diethyl sulfide to the -2 valence in lithium sulfide, while lithium metal is oxidized from 0 valence to +1 valence. The electron transfer process is stable and controllable under the mediation of a catalyst, and the sulfur conversion rate can reach over 97%.

[0192] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration to collect the solid precipitate; the solid precipitate is washed to obtain the washed solid precipitate.

[0193] The vacuum filtration vacuum degree is 0.006-0.06 MPa; the washing is performed using anhydrous tetrahydrofuran.

[0194] The washing process is repeated 2-3 times, with each wash lasting 20-30 minutes.

[0195] The amount of anhydrous tetrahydrofuran used is 3-5 times the mass of the solid phase precipitate to ensure that residual impurities are fully dissolved and removed.

[0196] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation to obtain the pre-product.

[0197] The vacuum degree of the vacuum distillation is 0.001-0.005 MPa; the temperature of the vacuum distillation is 120-150℃; and the time of the vacuum distillation is 2-3 hours.

[0198] The vacuum distillation process uses a programmed temperature rise mode with a heating rate controlled at 5℃ / min to avoid local overheating that could lead to agglomeration of lithium sulfide particles. The purpose of vacuum distillation is to remove residual solvent and trace amounts of lithium polysulfide byproducts.

[0199] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven for drying to obtain a high-purity lithium sulfide product.

[0200] The drying temperature is 100-120℃; the drying time is 4-6 hours.

[0201] The obtained lithium sulfide has a purity of ≥99.9%, a moisture content of ≤30ppm, a D50 particle size of ≤5μm, and a whiteness of ≥80.

[0202] As some preferred embodiments, the method for preparing lithium sulfide using diethyl sulfide as a sulfur source includes the following steps:

[0203] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 4,4′-dimethylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 0.5-1.5 mol / L; metallic lithium was added to the solution and stirred at room temperature for 2-4 h to obtain a Li-4,4′-dimethylbiphenyl lithium complex solution; the molar ratio of metallic lithium to substituted biphenyl was 1:1-1.2.

[0204] S2. Reduction reaction: Diethyl sulfide is added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.5-1 mL / min to carry out the reduction reaction. The temperature of the reaction system is maintained at 60-70℃, and the reaction is stirred for 3-5 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal is 1:4-4.5.

[0205] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.006-0.06 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, the amount of anhydrous tetrahydrofuran being 3-5 times the mass of the solid precipitate, the washing number being 2-3 times, and the washing time for each washing being 20-30 min, to obtain the washed solid precipitate;

[0206] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation. The heating rate is controlled at 5℃ / min. The mixture is kept at a vacuum of 0.001-0.005MPa and a distillation temperature of 120-150℃ for 2-3 hours to obtain the pre-product.

[0207] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 100-120℃ for 4-6 hours to obtain a high-purity lithium sulfide product.

[0208] As another preferred embodiment, the method for preparing lithium sulfide using diethyl sulfide as a sulfur source includes the following steps:

[0209] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 2-methylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 0.5-1.5 mol / L; metallic lithium was added to the solution and stirred at room temperature for 2-4 h to obtain a Li-2-methylbiphenyl lithium complex solution; the molar ratio of metallic lithium to substituted biphenyl was 1:1-1.2.

[0210] S2. Reduction reaction: Diethyl sulfide is added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.5-1 mL / min to carry out the reduction reaction. The temperature of the reaction system is maintained at 60-70℃, and the reaction is stirred for 3-5 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal is 1:4-4.5.

[0211] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.006-0.06 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, 2-3 times, with each washing time being 20-30 min, to obtain the washed solid precipitate.

[0212] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation. The heating rate is controlled at 5℃ / min. The mixture is kept at a vacuum of 0.001-0.005MPa and a distillation temperature of 120-150℃ for 2-3 hours to obtain the pre-product.

[0213] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 100-120℃ for 4-6 hours to obtain a high-purity lithium sulfide product.

[0214] In another preferred embodiment, the method for preparing lithium sulfide using diethyl sulfide as a sulfur source includes the following steps:

[0215] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 3,3′,4,4′-tetramethylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 0.5-1.5 mol / L; metallic lithium was added to the solution and stirred at room temperature for 2-4 h to obtain a Li-3,3′,4,4′-tetramethylbiphenyl lithium complex solution; the molar ratio of metallic lithium to substituted biphenyl was 1:1-1.2.

[0216] S2. Reduction reaction: Diethyl sulfide is added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.5-1 mL / min to carry out the reduction reaction. The temperature of the reaction system is maintained at 60-70℃, and the reaction is stirred for 3-5 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal is 1:4-4.5.

[0217] S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.006-0.06 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, 2-3 times, with each washing time being 20-30 min, to obtain the washed solid precipitate.

[0218] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and vacuum distilled. The distillation is carried out at a vacuum of 0.001-0.005 MPa and a distillation temperature of 120-150℃ for 2-3 hours to obtain the pre-product.

[0219] S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 100-120℃ for 4-6 hours to obtain a high-purity lithium sulfide product.

[0220] The technical solution of the present invention will be described below with reference to specific embodiments:

[0221] Example 1: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0222] Includes the following steps:

[0223] S1. Preparation of the lithium complex (catalyst system construction): Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 4,4′-dimethylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieves (moisture content < 30 ppm) to prepare a 1.0 mol / L solution of 4,4′-dimethylbiphenyl. Then, lithium metal was added as the lithium source, controlling the molar ratio of lithium metal to 4,4′-dimethylbiphenyl at 1:1.1. The reaction was stirred at room temperature for 3 h until the solution turned deep blue, yielding a Li-4,4′-dimethylbiphenyl lithium complex solution (catalyst concentration 1.0 mol / L). At this catalyst concentration, rapid conversion of diethyl sulfide can be achieved while avoiding side reactions caused by excess catalyst.

[0224] S2. Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 0.8 mL / min to the Li-biphenyl radical anion solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.1. The temperature of the reaction system was maintained at 65℃ and the reaction was stirred for 4 h to obtain a suspension.

[0225] S3. Solid-liquid separation and preliminary purification: The reaction suspension obtained in step S2 is vacuum filtered, and the vacuum degree is controlled at 0.03 MPa. The solid precipitate is collected. The solid precipitate is washed three times with anhydrous tetrahydrofuran, with each washing time being 25 min. The amount of anhydrous tetrahydrofuran used is 4 times the mass of the solid precipitate.

[0226] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and heated to 130°C at a heating rate of 5°C / min. The precipitate is then distilled under a vacuum of 0.003 MPa for 2.5 hours.

[0227] S5. Drying and finished product preparation: The product after distillation in step S4 is placed in a vacuum drying oven and dried at 110°C for 5 hours to obtain a high-purity lithium sulfide product.

[0228] Testing revealed that the Li-4,4′-dimethylbiphenyl lithium complex catalyst used in this embodiment achieved a sulfur conversion rate of 96.8% for diethyl sulfide. The prepared lithium sulfide product had a purity of 99.93%, a moisture content of 22 ppm, a D50 particle size of 3.2 μm, and a whiteness of ≥80. All indicators met the requirements for preparing electrolytes for all-solid-state batteries.

[0229] Example 2: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0230] Includes the following steps:

[0231] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 2-methylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieve (moisture content < 30 ppm) to prepare a 0.5 mol / L solution of 2-methylbiphenyl; then, lithium metal was added as the lithium source, and the molar ratio of lithium metal to 2-methylbiphenyl was controlled at 1:1.0. The reaction was stirred at room temperature for 2 h until the solution turned dark blue, thus obtaining the Li-2-methylbiphenyl lithium complex solution;

[0232] S2. Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 0.5 mL / min to the Li-biphenyl radical anion solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.0. The temperature of the reaction system was maintained at 60℃. The reaction was stirred for 3 h to obtain a suspension.

[0233] S3. Solid-liquid separation and preliminary purification: The reaction suspension obtained in step S2 is vacuum filtered, and the vacuum degree is controlled at 0.006 MPa. The solid precipitate is collected. The solid precipitate is washed twice with anhydrous tetrahydrofuran, with each washing time being 20 min. The amount of anhydrous tetrahydrofuran used is 3 times the mass of the solid precipitate.

[0234] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and heated to 120°C at a heating rate of 5°C / min. It is then distilled under a vacuum of 0.001 MPa for 2 hours.

[0235] S5. Drying and product preparation: The product after distillation in step S4 is placed in a vacuum drying oven and dried at 100°C for 4 hours to obtain a high-purity lithium sulfide product.

[0236] Testing revealed that this embodiment used a Li-2-methylbiphenyl lithium complex as a catalyst, with a sulfur conversion rate of 95.5% for diethyl sulfide. The prepared lithium sulfide product had a purity of 99.90%, a moisture content of 28 ppm, a D50 particle size of 4.5 μm, and a whiteness ≥80, meeting the requirements for preparing all-solid-state battery electrolytes.

[0237] Example 3: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0238] Includes the following steps:

[0239] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 3,3′,4,4′-tetramethylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieve (moisture content < 30 ppm) to prepare a solution with a 3,3′,4,4′-tetramethylbiphenyl concentration of 1.5 mol / L; then, lithium metal was added as the lithium source, and the molar ratio of lithium metal to 3,3′,4,4′-tetramethylbiphenyl was controlled at 1:1.2. The reaction was stirred at room temperature for 4 h until the solution turned dark blue, thus obtaining the Li-3,3′,4,4′-tetramethylbiphenyl lithium complex solution;

[0240] S2. Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 1.0 mL / min to the Li-biphenyl radical anion solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.2. The temperature of the reaction system was maintained at 70℃. The reaction was stirred for 5 h to obtain a suspension.

[0241] S3. Solid-liquid separation and preliminary purification: The reaction suspension obtained in step S2 is vacuum filtered, and the vacuum degree is controlled at 0.06 MPa. The solid precipitate is collected. The solid precipitate is washed three times with anhydrous tetrahydrofuran, with each washing time being 30 min. The amount of anhydrous tetrahydrofuran used is 5 times the mass of the solid precipitate.

[0242] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and heated to 150°C at a heating rate of 5°C / min. It is then distilled under a vacuum of 0.005 MPa for 3 hours.

[0243] S5. Drying and finished product preparation: The product after distillation in step S4 is placed in a vacuum drying oven and dried at 120°C for 6 hours to obtain a high-purity lithium sulfide product.

[0244] Testing revealed that this embodiment used a Li-3,3′,4,4′-tetramethylbiphenyl lithium complex as a catalyst, with a sulfur conversion rate of 97.8% for diethyl sulfide. The prepared lithium sulfide product had a purity of 99.95%, a moisture content of 20 ppm, a D50 particle size of 2.8 μm, and a whiteness ≥78. All these indicators were superior to the standards for preparing electrolytes for all-solid-state batteries.

[0245] Example 4: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0246] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 4,4′-dimethylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieve (moisture content < 30 ppm) to prepare a solution with a 4,4′-dimethylbiphenyl concentration of 1.2 mol / L; then, lithium metal was added as the lithium source, and the molar ratio of lithium metal to 4,4′-dimethylbiphenyl was controlled at 1:1.05. The reaction was stirred at room temperature for 3.5 h until the solution turned dark blue, thus obtaining the Li-4,4′-dimethylbiphenyl lithium complex solution;

[0247] S2. Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 0.7 mL / min to the Li-4,4′-dimethylbiphenyl lithium complex solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.05. The system temperature was maintained at 68℃ and the reaction was stirred for 4.5 h to obtain a suspension.

[0248] S3. Solid-liquid separation and preliminary purification: The reaction suspension obtained in step S2 is vacuum filtered, and the vacuum degree is controlled at 0.06 MPa. The solid precipitate is collected. The solid precipitate is washed three times with anhydrous tetrahydrofuran, with each washing time being 30 min. The amount of anhydrous tetrahydrofuran used is 5 times the mass of the solid precipitate.

[0249] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and heated to 125°C at a heating rate of 5°C / min. It is then distilled under a vacuum of 0.002 MPa for 2 hours.

[0250] S5. Drying and product preparation: The product after distillation in step S4 is placed in a vacuum drying oven and dried at 105℃ for 5 hours to obtain a high-purity lithium sulfide product.

[0251] Test results: In this example, 4,4′-dimethylbiphenyl lithium complex was used as a catalyst, and the sulfur conversion rate of diethyl sulfide was 96.5%. The prepared lithium sulfide product had a purity of 99.92%, a moisture content of 25 ppm, a D50 particle size of 3.5 μm, and a whiteness ≥82. All indicators are superior to the preparation standards of all-solid-state battery electrolytes.

[0252] Example 5: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0253] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 2-methylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieve (moisture content < 30 ppm) to prepare a 0.8 mol / L solution of 2-methylbiphenyl; then, lithium metal was added as the lithium source, and the molar ratio of lithium metal to 2-methylbiphenyl was controlled at 1:1.0. The reaction was stirred at room temperature for 2.5 h until the solution turned dark blue, thus obtaining the Li-2-methylbiphenyl lithium complex solution;

[0254] S2. Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 0.5 mL / min to the Li-2-methylbiphenyl lithium complex solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.0. The system temperature was maintained at 62℃ and the reaction was stirred for 3.5 h to obtain a suspension.

[0255] S3. Solid-liquid separation and preliminary purification: The reaction suspension obtained in step S2 is vacuum filtered, and the vacuum degree is controlled at 0.03 MPa. The solid precipitate is collected. The solid precipitate is washed three times with anhydrous tetrahydrofuran, with each washing time being 25 min. The amount of anhydrous tetrahydrofuran used is 4 times the mass of the solid precipitate.

[0256] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and heated to 120°C at a heating rate of 5°C / min. It is then distilled under a vacuum of 0.001 MPa for 2 hours.

[0257] S5. Drying and product preparation: The product after distillation in step S4 is placed in a vacuum drying oven and dried at 100°C for 4.5 hours to obtain a high-purity lithium sulfide product.

[0258] Test results: In this embodiment, 2-methylbiphenyl lithium complex was used as a catalyst, and the sulfur conversion rate of diethyl sulfide was 95.8%. The prepared lithium sulfide product had a purity of 99.91%, a moisture content of 26 ppm, a D50 particle size of 4.2 μm, and a whiteness of ≥80. All indicators were superior to the preparation standards of all-solid-state battery electrolytes.

[0259] Example 6: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0260] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 3,3′,4,4′-tetramethylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieve (moisture content < 30 ppm) to prepare a solution with a 3,3′,4,4′-tetramethylbiphenyl concentration of 1.4 mol / L; then, lithium metal was added as the lithium source, and the molar ratio of lithium metal to 3,3′,4,4′-tetramethylbiphenyl was controlled at 1:1.15. The reaction was stirred at room temperature for 4 h until the solution turned dark blue, thus obtaining the Li-3,3′,4,4′-tetramethylbiphenyl lithium complex solution;

[0261] S2. Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 0.9 mL / min to the Li-3,3′,4,4′-tetramethylbiphenyl lithium complex solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.18, the system temperature was maintained at 72℃, and the reaction was stirred for 5 h to obtain a suspension.

[0262] S3. Solid-liquid separation and preliminary purification: The reaction suspension obtained in step S2 is vacuum filtered, and the vacuum degree is controlled at 0.03 MPa. The solid precipitate is collected. The solid precipitate is washed three times with anhydrous tetrahydrofuran, with each washing time being 25 min. The amount of anhydrous tetrahydrofuran used is 4 times the mass of the solid precipitate.

[0263] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and heated to 145°C at a heating rate of 5°C / min. It is then distilled under a vacuum of 0.004 MPa for 2.8 hours.

[0264] S5. Drying and product preparation: The product after distillation in step S4 is placed in a vacuum drying oven and dried at 115°C for 5.5 hours to obtain a high-purity lithium sulfide product.

[0265] Test results: In this embodiment, 3,3′,4,4′-tetramethylbiphenyl lithium complex was used as a catalyst, and the sulfur conversion rate of diethyl sulfide was 97.6%. The prepared lithium sulfide product had a purity of 99.94%, a moisture content of 21 ppm, a D50 particle size of 3.0 μm, and a whiteness of ≥82. All indicators are superior to the preparation standards of all-solid-state battery electrolytes.

[0266] Example 7: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0267] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 4,4′-dimethylbiphenyl and 2-methylbiphenyl in a molar ratio of 1:1 were dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieve (moisture content < 30 ppm) to prepare a solution with a total concentration of 1.0 mol / L of 4,4′-dimethylbiphenyl and 2-methylbiphenyl. Subsequently, lithium metal was added as a lithium source, and the molar ratio of lithium metal to the mixture of 4,4′-dimethylbiphenyl and 2-methylbiphenyl was controlled at 1:1.1. The mixture was stirred at room temperature for 3 h until the solution turned dark blue, thus obtaining a mixed biphenyl lithium complex solution.

[0268] S2. Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 0.75 mL / min to the mixed lithium biphenyl complex solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.18. The system temperature was maintained at 65℃ and the reaction was stirred for 4 h to obtain a suspension.

[0269] S3-S5 are the same as in Example 1.

[0270] Test results: In this example, a mixed lithium biphenyl complex of 4,4′-dimethylbiphenyl and 2-methylbiphenyl was used as a catalyst, and the sulfur conversion rate of diethyl sulfide was 96.2%. The prepared lithium sulfide product had a purity of 99.92%, a moisture content of 24 ppm, a D50 particle size of 3.8 μm, and a whiteness ≥81. All indicators are superior to the preparation standards of all-solid-state battery electrolytes.

[0271] Example 8: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0272] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 4,4′-dimethylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieve (moisture content < 30 ppm) to prepare a 1.0 mol / L solution of 4,4′-dimethylbiphenyl; then, lithium metal was added as the lithium source, and the molar ratio of lithium metal to 4,4′-dimethylbiphenyl was controlled at 1:1.1. The reaction was stirred at room temperature for 3 h until the solution turned dark blue, thus obtaining a lithium 4,4′-dimethylbiphenyl complex solution;

[0273] S2, Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 0.6 mL / min to the 4,4′-dimethylbiphenyl lithium complex solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.02. The system temperature was maintained at 63℃ and the reaction was stirred for 3.8 h to obtain a suspension.

[0274] S3-S5 are the same as in Example 1.

[0275] Test results: In this example, 4,4′-dimethylbiphenyl lithium complex was used as a catalyst, and the sulfur conversion rate of diethyl sulfide was 96.3%. The prepared lithium sulfide product had a purity of 99.91%, a moisture content of 27 ppm, a D50 particle size of 3.6 μm, and a whiteness of ≥80. All indicators were superior to the preparation standards of all-solid-state battery electrolytes.

[0276] Example 9: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0277] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 3,3′,4,4′-tetramethylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieve (moisture content < 30 ppm) to prepare a solution with a 3,3′,4,4′-tetramethylbiphenyl concentration of 1.5 mol / L; then, lithium metal was added as the lithium source, and the molar ratio of lithium metal to 3,3′,4,4′-tetramethylbiphenyl was controlled at 1:1.1. The reaction was stirred at room temperature for 3 h until the solution turned dark blue, thus obtaining a 3,3′,4,4′-tetramethylbiphenyl lithium complex solution;

[0278] S2. Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 0.9 mL / min to the 3,3′,4,4′-tetramethylbiphenyl lithium complex solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.15. The system temperature was maintained at 68℃ and the reaction was stirred for 3.3 h to obtain a suspension.

[0279] S3 is the same as in Example 1;

[0280] S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and heated to 140°C at a heating rate of 5°C / min. It is then distilled under a vacuum of 0.003 MPa for 2.5 hours.

[0281] S5 is the same as in Example 1;

[0282] Test results: In this embodiment, 3,3′,4,4′-tetramethylbiphenyl lithium complex was used as a catalyst, and the sulfur conversion rate of diethyl sulfide was 97.7%. The prepared lithium sulfide product had a purity of 99.94%, a moisture content of 20 ppm, a D50 particle size of 2.9 μm, and a whiteness ≥80. All indicators were superior to the preparation standards of all-solid-state battery electrolytes.

[0283] Example 10: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0284] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere (H2O / O2 < 1 ppm), 2-methylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through 4A molecular sieve (moisture content < 30 ppm) to prepare a 1.1 mol / L solution of 2-methylbiphenyl; then, lithium metal was added as the lithium source, and the molar ratio of lithium metal to 2-methylbiphenyl was controlled at 1:1.1. The reaction was stirred at room temperature for 3 h until the solution turned dark blue, thus obtaining the 2-methylbiphenyl lithium complex solution;

[0285] S2, Reduction reaction: Diethyl sulfide was slowly added dropwise at a rate of 0.9 mL / min to the 2-methylbiphenyl lithium complex solution prepared in step S1 using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.0. The system temperature was maintained at 61℃ and the reaction was stirred for 4.3 h to obtain a suspension.

[0286] S3-S5 are the same as in Example 1.

[0287] Test results: In this embodiment, 2-methylbiphenyl lithium complex was used as a catalyst, and the sulfur conversion rate of diethyl sulfide was 95.9%. The prepared lithium sulfide product had a purity of 99.90%, a moisture content of 29 ppm, a D50 particle size of 4.3 μm, and a whiteness of ≥82. All indicators were superior to the preparation standards of all-solid-state battery electrolytes.

[0288] Example 11: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0289] S1. Preparation of the lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 3,3′,4,4′-tetramethylbiphenyl was dissolved in ethylene glycol dimethyl ether dried through a 4A molecular sieve to prepare a 1.5 mol / L solution. High-purity lithium metal was added, and the molar ratio of lithium metal to 3,3′,4,4′-tetramethylbiphenyl was controlled at 1:1.2. The mixture was stirred at room temperature for 4 h to obtain a deep blue Li-3,3′,4,4′-tetramethylbiphenyl lithium complex solution.

[0290] S2. Reduction reaction: Diethyl sulfide was slowly added dropwise to the above catalyst solution at a rate of 1.0 mL / min using a constant pressure dropping funnel, and the molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.20. The temperature of the reaction system was strictly maintained at 70℃. After stirring for 3.0 h, the reaction was complete, and a suspension was obtained.

[0291] S3. Solid-liquid separation and preliminary purification: The obtained suspension was vacuum filtered (vacuum degree 0.04 MPa), and the solid precipitate was washed three times with anhydrous tetrahydrofuran (30 min each time, solvent volume 5 times the solid mass). The washed filter cake was then transferred to a vacuum distillation apparatus.

[0292] S4. Vacuum distillation for deep impurity removal: The temperature is increased to 145℃ at a programmed rate of 5℃ / min, and distilled under a vacuum of 0.004 MPa for 3 h.

[0293] S5. Drying and Finished Product Preparation: Finally, the product was dried in a vacuum drying oven at 115℃ for 6 h to obtain high-purity lithium sulfide powder.

[0294] Test results: The sulfur conversion rate reached 98.2%, the product purity was as high as 99.96%, the moisture content was as low as 18 ppm, the D50 particle size was 2.5 μm, the whiteness was ≥85, and the catalyst recovery rate reached 90%. This example showed the best performance in terms of conversion efficiency, product purity, and particle size control.

[0295] Example 12: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0296] S1. Preparation of the lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 4,4′-dimethylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to prepare a 1.0 mol / L solution. Lithium metal was added, controlling the molar ratio of lithium metal to 4,4′-dimethylbiphenyl to be 1:1.1. The mixture was stirred at room temperature for 3.5 h to obtain a Li-4,4′-dimethylbiphenyl lithium complex solution.

[0297] S2, Reduction reaction: Diethyl sulfide was added dropwise at a rate of 0.8 mL / min, and its molar ratio with lithium metal was controlled at 1:4.10. The temperature of the reaction system was maintained at 67℃, and the reaction was stirred for 3.5 h to obtain a suspension.

[0298] S3. Solid-liquid separation and preliminary purification: After the reaction, solid-liquid separation was performed, and the solid was washed three times with anhydrous tetrahydrofuran. Then, deep impurity removal was carried out by vacuum distillation: the temperature was increased to 140℃ at 5℃ / min, and distillation was carried out at a vacuum of 0.003 MPa for 3 hours.

[0299] S5. Drying and product preparation: Finally, the product was vacuum dried at 110℃ for 5 h to obtain the product.

[0300] Test results: Sulfur conversion rate was 97.1%, product purity was 99.94%, moisture content was 19 ppm, D50 particle size was 3.0 μm, and whiteness was ≥83. This example achieved excellent particle size distribution while maintaining high purity.

[0301] Example 13: A method for preparing lithium sulfide using diethyl sulfide as a sulfur source

[0302] S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 3,3′,4,4′-tetramethylbiphenyl and 4,4′-dimethylbiphenyl were mixed in a molar ratio of 2:1 and dissolved in dry ethylene glycol dimethyl ether to prepare a solution with a total concentration of 1.3 mol / L. Metallic lithium was added, and the molar ratio of metallic lithium to total biphenyl was controlled at 1:1.15. The mixture was stirred at room temperature for 3.5 h to obtain a mixed lithium complex solution.

[0303] S2, Reduction reaction: Diethyl sulfide was added dropwise at a rate of 0.9 mL / min, and its molar ratio with lithium metal was controlled at 1:4.18. The temperature of the reaction system was maintained at 69℃, and the reaction was stirred for 3.2 h to obtain a suspension.

[0304] S3. Solid-liquid separation and preliminary purification: After the reaction, solid-liquid separation was performed, and the solid was washed three times with anhydrous tetrahydrofuran. Then, deep purification was carried out by vacuum distillation: the temperature was increased to 142℃ at 5℃ / min, and distillation was carried out at a vacuum of 0.0035 MPa for 2.8h.

[0305] S5. Drying and product preparation: Finally, the product was vacuum dried at 112℃ for 5.5h to obtain the product.

[0306] Test results: Sulfur conversion rate was 98.0%, product purity was 99.95%, moisture content was as low as 17 ppm, D50 particle size was 2.7 μm, and whiteness was ≥84. This embodiment achieved an optimal balance in conversion rate, purity, and particle size through a mixed catalyst system, and based on… Figure 1 It is known that the product's D50 is 2.7 μm, with a distribution range of 1.0-5.0 μm, which meets the control requirements within 5 μm. Figure 2 XRD analysis showed that the characteristic diffraction peaks of the obtained product were completely matched with the lithium sulfide standard card (Li2S-PDF#00-023-0369), with no impurity peaks and high crystallinity.

[0307] Comparative Example 1:

[0308] The only difference from Example 1 is that ethylene glycol dimethyl ether is replaced with dimethyl sulfide (DMS). All other steps, material ratios and reaction conditions are exactly the same as in Example 1.

[0309] An increase in system viscosity and the formation of polymeric byproducts were observed during the reaction.

[0310] The test results showed that the sulfur conversion rate decreased significantly to 90.5%, the product purity was only 99.85%, the moisture content increased to 40 ppm, the D50 particle size increased to 7.2 μm, and the product whiteness decreased. This indicates that dimethyl sulfide has poor stability in this system, many side reactions, and is difficult to purify.

[0311] Comparative Example 2:

[0312] The only difference from Example 1 is that step S1 is omitted; the specific steps are as follows:

[0313] S1. Reduction reaction: Diethyl sulfide was slowly added dropwise to 4,4′-dimethylbiphenyl and lithium metal at a rate of 0.8 mL / min using a constant pressure dropping funnel. The molar ratio of diethyl sulfide to lithium metal was controlled at 1:4.1. The temperature of the reaction system was maintained at 65℃ and the reaction was stirred for 4 h to obtain a suspension.

[0314] S2. Solid-liquid separation and preliminary purification: The reaction suspension obtained in step S1 is vacuum filtered, and the vacuum degree is controlled at 0.03 MPa. The solid precipitate is collected. The solid precipitate is washed three times with anhydrous tetrahydrofuran, with each washing time being 25 min. The amount of anhydrous tetrahydrofuran used is 4 times the mass of the solid precipitate.

[0315] S3. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S2 is placed in a vacuum distillation apparatus and heated to 130°C at a heating rate of 5°C / min. The precipitate is then distilled under a vacuum of 0.003 MPa for 2.5 hours.

[0316] S4. Drying and finished product preparation: The product after distillation in step S3 is placed in a vacuum drying oven and dried at 110°C for 5 hours to obtain a high-purity lithium sulfide product.

[0317] The other steps are the same as in Example 1.

[0318] The test results showed that the sulfur conversion rate was 92.0%, and the reaction time needed to be extended to more than 5 hours to reach equilibrium. The product purity was 99.82%, the moisture content was 38 ppm, and the D50 particle size was 6.8 μm. This demonstrates that methyl substituents are crucial for improving catalyst activity and reaction efficiency.

[0319] Comparative Example 3:

[0320] The difference from Example 1 is that in step S2, the molar ratio of lithium metal to diethyl sulfide is controlled to be 3.8:1 (lithium deficiency), while the remaining steps and reaction conditions are the same as in Example 1.

[0321] Test results: The sulfur conversion rate dropped significantly to 89.2%, and obvious lithium polysulfides (Li2S) were detected in the product. x Impurities (x>1) caused the final product purity to drop to 99.70%, moisture content to 42 ppm, and D50 particle size to increase to 9.0 μm. This demonstrates that the molar ratio range of 1:4 to 1:4.5 in this invention is crucial for ensuring complete reaction and suppressing byproducts.

[0322] Comparative Example 4:

[0323] The only difference from Example 1 is that the vacuum distillation step is omitted, that is, after washing with anhydrous tetrahydrofuran (3 times), the product is directly vacuum dried at 110°C. The remaining steps and reaction conditions are the same as in Example 1.

[0324] Test results: Although the sulfur conversion rate was similar to that of Example 1 (96.5%), trace amounts of biphenyl and lithium polysulfides remained in the product, resulting in a purity of only 99.88%, a moisture content of 35 ppm, an increased D50 particle size to 6.5 μm, and a product whiteness of only 78. This indicates that the "washing-vacuum distillation" combined purification process is indispensable for removing trace impurities, controlling particle size, and improving product purity and appearance.

[0325] Effect detection:

[0326] 1. Conversion rate: determined by gravimetric method;

[0327] 2. Product purity: determined by the difference method;

[0328] 3. Moisture content: Measured using a Karl Fischer moisture analyzer;

[0329] 4. D50 particle size: determined using a laser particle size analyzer;

[0330] 5. Whiteness: Measured using a whiteness meter.

[0331] The test results are shown in Table 1 below:

[0332] Table 1

[0333]

[0334] According to the test results in Table 1 above, the lithium sulfide prepared by Examples 1-13 of this invention using a specific catalyst system exhibits the following characteristics: sulfur conversion rate (≥95%), product purity (≥99.90%), moisture control (≤30 ppm), and ultrafine particle size (D50≤5.0μm). In particular, Examples 11-13, using a highly active catalyst system and optimized reaction and purification parameters, achieved optimal levels in the core indicators of sulfur conversion rate (≥97.1%), product purity (≥99.94%), moisture control (≤20 ppm), and ultrafine particle size (D50≤3.0μm), which are comprehensively superior to the general examples.

[0335] However, changing the type of catalyst, the type of sulfur source, or the lithium-sulfur molar ratio in the comparative examples will affect the performance of the prepared lithium sulfide. For example, using diethyl sulfide (Comparative Example 3 vs Example 1), methyl-substituted biphenyl catalyst (Comparative Example 4 vs Example 1), a specific lithium-sulfur molar ratio (Comparative Example 5 vs Example 1), and the "washing-vacuum distillation" composite purification process (Comparative Example 6 vs Example 1) are all indispensable key elements for the excellent technical effect of this invention. Any change in key conditions will lead to a significant decrease in product performance.

[0336] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing lithium sulfide using diethyl sulfide as a sulfur source, characterized in that: The method includes the following steps: S1. Preparation of lithium complex: Under an inert gas atmosphere, substituted biphenyls were dissolved in dried ethylene glycol dimethyl ether to obtain a substituted biphenyl solution; metallic lithium was added to the solution and stirred at room temperature to obtain a lithium complex solution; S2, Reduction reaction: Diethyl sulfide is added dropwise at a constant rate to the lithium complex solution prepared in step S1 to carry out the reduction reaction, and a suspension is obtained; S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration to collect the solid precipitate; the solid precipitate is washed to obtain the washed solid precipitate. S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation to obtain the pre-product. S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven for drying to obtain a high-purity lithium sulfide product. The substituted biphenyl mentioned in step S1 is one or more of 4,4′-dimethylbiphenyl, 2-methylbiphenyl, or 3,3′,4,4′-tetramethylbiphenyl; The molar ratio of diethyl sulfide to lithium metal in step S2 is 1:4-4.5; In step S4, the vacuum distillation process adopts a programmed temperature rise mode, with the temperature rise rate controlled at 5℃ / min.

2. The method according to claim 1, characterized in that: The substituted biphenyl mentioned in step S1 is 3,3′,4,4′-tetramethylbiphenyl.

3. The method according to claim 1, characterized in that: The drying process described in step S1 involves using molecular sieves, and the moisture content of the dried ethylene glycol dimethyl ether must be controlled below 30 ppm.

4. The method according to claim 3, characterized in that: The molecular sieve mentioned is 4A molecular sieve.

5. The method according to claim 3, characterized in that: The concentration of the substituted biphenyl solution is 0.5-1.5 mol / L.

6. The method according to claim 5, characterized in that: The concentration of the substituted biphenyl solution is 0.8-1.2 mol / L.

7. The method according to claim 6, characterized in that: The concentration of the substituted biphenyl solution is 1.0 mol / L.

8. The method according to claim 1, characterized in that: The molar ratio of metallic lithium to substituted biphenyl is 1:1-1.

2.

9. The method according to claim 8, characterized in that: The molar ratio of metallic lithium to substituted biphenyl is 1:1-1.

1.

10. The method according to claim 9, characterized in that: The molar ratio of metallic lithium to substituted biphenyl is 1:

1.

11. The method according to claim 1, characterized in that: The stirring time mentioned in step S1 is 2-4 hours.

12. The method according to claim 1, characterized in that: The dropping rate of the diethyl sulfide described in step S2 is 0.5-1 mL / min.

13. The method according to claim 12, characterized in that: The dropping rate of the diethyl sulfide described in step S2 is 0.6-0.8 mL / min.

14. The method according to claim 13, characterized in that: The dropping rate of the diethyl sulfide described in step S2 is 0.8 mL / min.

15. The method according to claim 1, characterized in that: The molar ratio of diethyl sulfide to lithium metal in step S2 is 1:4.

2.

16. The method according to claim 1, characterized in that: The temperature of the reduction reaction described in step S2 is 60-70℃.

17. The method according to claim 16, characterized in that: The reduction reaction in step S2 is carried out at a temperature of 65°C.

18. The method according to claim 1, characterized in that: The reduction reaction in step S2 takes 3-5 hours.

19. The method according to claim 1, characterized in that: The vacuum degree of vacuum filtration in step S3 is 0.006-0.06 MPa.

20. The method according to claim 1, characterized in that: The washing described in step S3 is performed using anhydrous tetrahydrofuran; the washing is performed 2-3 times, and each washing session lasts 20-30 minutes.

21. The method according to claim 20, characterized in that: The amount of anhydrous tetrahydrofuran used is 3-5 times the mass of the solid phase precipitate.

22. The method according to claim 21, characterized in that: The amount of anhydrous tetrahydrofuran used is 4.0 times the mass of the solid phase precipitate.

23. The method according to claim 1, characterized in that: The vacuum degree of the vacuum distillation described in step S4 is 0.001-0.005 MPa.

24. The method according to claim 1, characterized in that: The temperature of vacuum distillation in step S4 is 120-150℃; the time of vacuum distillation is 2-3 hours.

25. The method according to claim 1, characterized in that: The drying temperature in step S5 is 100-120℃; the drying time is 4-6 hours.

26. The method according to any one of claims 1-25, characterized in that: Includes the following steps: S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 4,4′-dimethylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 0.5-1.5 mol / L; metallic lithium was added to the solution and stirred at room temperature for 2-4 h to obtain a Li-4,4′-dimethylbiphenyl lithium complex solution; the molar ratio of metallic lithium to substituted biphenyl was 1:1-1.

2. S2. Reduction reaction: Diethyl sulfide is added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.5-1 mL / min to carry out the reduction reaction. The temperature of the reaction system is maintained at 60-70℃, and the reaction is stirred for 3-5 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal is 1:4-4.

5. S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.006-0.06 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, the amount of anhydrous tetrahydrofuran being 3-5 times the mass of the solid precipitate, the washing number being 2-3 times, and the washing time for each washing being 20-30 min, to obtain the washed solid precipitate; S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation. The heating rate is controlled at 5℃ / min. The mixture is kept at a vacuum of 0.001-0.005MPa and a distillation temperature of 120-150℃ for 2-3 hours to obtain the pre-product. S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 100-120℃ for 4-6 hours to obtain a high-purity lithium sulfide product.

27. The method according to any one of claims 1-25, characterized in that: Includes the following steps: S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 2-methylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 0.5-1.5 mol / L; metallic lithium was added to the solution and stirred at room temperature for 2-4 h to obtain a Li-2-methylbiphenyl lithium complex solution; the molar ratio of metallic lithium to substituted biphenyl was 1:1-1.

2. S2. Reduction reaction: Diethyl sulfide is added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.5-1 mL / min to carry out the reduction reaction. The temperature of the reaction system is maintained at 60-70℃, and the reaction is stirred for 3-5 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal is 1:4-4.

5. S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.006-0.06 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, 2-3 times, with each washing time being 20-30 min, to obtain the washed solid precipitate. S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus for vacuum distillation. The heating rate is controlled at 5℃ / min. The mixture is kept at a vacuum of 0.001-0.005MPa and a distillation temperature of 120-150℃ for 2-3 hours to obtain the pre-product. S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 100-120℃ for 4-6 hours to obtain a high-purity lithium sulfide product.

28. The method according to any one of claims 1-25, characterized in that: Includes the following steps: S1. Preparation of lithium complex: Under an anhydrous and oxygen-free argon atmosphere, 3,3′,4,4′-tetramethylbiphenyl was dissolved in dry ethylene glycol dimethyl ether to obtain a substituted biphenyl solution with a concentration of 0.5-1.5 mol / L; metallic lithium was added to the solution and stirred at room temperature for 2-4 h to obtain a Li-3,3′,4,4′-tetramethylbiphenyl lithium complex solution; the molar ratio of metallic lithium to substituted biphenyl was 1:1-1.

2. S2. Reduction reaction: Diethyl sulfide is added dropwise to the lithium complex solution prepared in step S1 at a constant rate of 0.5-1 mL / min to carry out the reduction reaction. The temperature of the reaction system is maintained at 60-70℃, and the reaction is stirred for 3-5 h to obtain a suspension. The molar ratio of diethyl sulfide to lithium metal is 1:4-4.

5. S3. Solid-liquid separation and preliminary purification: The suspension obtained in step S2 is subjected to vacuum filtration, with the vacuum degree controlled at 0.006-0.06 MPa, and the solid precipitate is collected; the solid precipitate is washed with anhydrous tetrahydrofuran, 2-3 times, with each washing time being 20-30 min, to obtain the washed solid precipitate. S4. Vacuum distillation for deep impurity removal: The solid precipitate washed in step S3 is placed in a vacuum distillation apparatus and vacuum distilled. The distillation is carried out at a vacuum of 0.001-0.005 MPa and a distillation temperature of 120-150℃ for 2-3 hours to obtain the pre-product. S5. Drying and finished product preparation: The preproduct obtained in step S4 is placed in a vacuum drying oven and dried at 100-120℃ for 4-6 hours to obtain a high-purity lithium sulfide product.

29. The lithium sulfide prepared by the method according to any one of claims 1-28, characterized in that: The lithium sulfide has a purity of ≥99.9%, a moisture content of ≤30ppm, a D50 particle size of ≤5μm, and a whiteness of ≥80.

30. The use of lithium sulfide as described in claim 29 in the preparation of lithium-sulfur batteries or semiconductor electronic materials.

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