A low-cost method for preparing lithium sulfide and its application

Abstract

This invention discloses a low-cost method for preparing lithium sulfide and its application. The low-cost lithium sulfide is prepared by a solid-phase reaction of a lithium source and thiocyanate. The process involves refining and uniformly mixing the lithium source, a small amount of lithium hydroxide, and thiocyanate, followed by a solid-phase reaction at a specific temperature. This technical solution utilizes a small amount of lithium hydroxide combined with lithium carbonate, where lithium hydroxide dissociates into trace amounts of hydroxide ions. These ions accelerate the hydrolysis of HOCN / HNCO into NH3 and CO2 via alkaline catalysis, rapidly consuming the urea precursor. Simultaneously, the weak alkalinity of the system converts cyanic acid into negatively charged cyanate ions, which, through electrostatic repulsion, prevent the dimerization of isocyanate molecules to form urea. The addition of weakly polarized lithium ions further enhances the process, ultimately achieving efficient decomposition of HOCN and reducing urea production. This technical route features a simple preparation process and produces no solid waste.

Description

Technical Field

[0001] This invention relates to the field of low-cost lithium sulfide technology for lithium-ion batteries, and particularly to a low-cost lithium sulfide, its preparation method, and its application. Background Technology

[0002] Sulfide electrolytes are considered one of the most ideal electrolyte materials for solid-state batteries due to their high ionic conductivity and good mechanical properties. Their ionic conductivity can reach or even exceed that of liquid electrolytes, giving sulfide solid-state batteries significant advantages in terms of energy density and power density.

[0003] However, the high price of lithium sulfide, the core raw material for sulfide electrolytes, has hindered the commercialization of sulfide solid-state batteries.

[0004] Currently, there are three main methods for synthesizing lithium sulfide: (1) Direct solid-phase reaction of lithium with sulfur - lithium foil or lithium scrap reacts with elemental sulfur under an inert atmosphere. The advantages are high product purity and simple process. The disadvantages are that lithium is active, flammable and easily oxidized, the operation is dangerous, and the cost of lithium is high. (2) Gas / liquid phase method of hydrogen sulfide reacting with lithium or lithium compounds (such as LiOH, Li2CO3) - dry hydrogen sulfide gas reacts with lithium powder or lithium hydroxide under heating to generate lithium sulfide. The advantages are that it can be scaled up and the reactants are mixed more evenly. The disadvantages are that hydrogen sulfide gas is used for the reaction of lithium powder or lithium hydroxide under heating. The substance is highly toxic and corrosive, requiring extremely high standards for equipment sealing and exhaust gas treatment, posing safety hazards; (3) Low-temperature reaction of lithium with sulfur in organic solvents or Li2S·xH2O dehydration method - n-BuLi reacts with sulfur in anhydrous solvents such as THF to generate Li2S and then separates it, or soluble polysulfides are first precipitated with lithium salts to obtain hydrated lithium sulfide and then dehydrated under high temperature and vacuum. The former is suitable for laboratory preparation of high-purity small-batch samples, but the cost is high and the solvent needs to be strictly dehydrated. The latter has relatively cheap raw materials and can be mass-produced, but dehydration is very easy to leave residual oxygen / water, which leads to product oxidation and hydrolysis, and the purity is difficult to control. In industry, there is a tendency to improve the solid phase method or gas phase method and combine it with a strict inert atmosphere and post-treatment to ensure purity and safety.

[0005] In the existing technology, the article "Li2CO3-Derived Low-Cost Li2S for Sulfide Solid Electrolytes Exceeding 11 mScm" describes a solution. -1The method disclosed involves mixing lithium carbonate and ammonium thiocyanate in a specific molar ratio and then ball-milling them until homogeneous. The mixed powder is then pressed into tablets using a stainless steel mold under 400 MPa pressure, placed in a tube furnace, and sintered at 450°C for 5 hours under an argon atmosphere, with exhaust gas collected and treated simultaneously. The sintered product is then intermittently ball-milled again for 2 hours with the ball-to-material ratio remaining constant, followed by holding at 650°C for 5 hours to complete crystal growth and polysulfide removal. A brittle, hard white solid is finally obtained, which, after thorough grinding, yields lithium sulfide powder for subsequent experimental use.

[0006] In the above technology, the stainless steel mold pressing process is mainly used to ensure that the materials are mixed evenly and in close contact, thereby improving the reactivity. This process can also be achieved by finely controlling the particle size of the raw materials to a certain extent. In addition, the pressing and sintering process requires additional equipment and costs. Finally, the chemical formulas for the reactions in the synthesis of this technical route are as follows:

[0007] Li₂CO₃ + NH₄SCN → Li₂S + CO₂↑ + NH₃↑ + HCNO / HOCN↑ (with small amounts of COS and CS₂); HCNO is present in the intermediate products, and HCNO or cyanic acid (HOCN): exists in an isomeric equilibrium (HOCN <=> HNCO isocyanate, which is thermodynamically more stable). Both are collectively called cyanates and are precursors to urea. A side reaction in urea formation (the core of which needs to be suppressed) involves the dimerization of two isocyanate molecules to form urea: 2HNCO > (NH₂)₂CO. This reaction is an intermolecular nucleophilic addition and is the root cause of excessive urea residue in the system. Therefore, this technical route will result in some urea residue.

[0008] Our company has discovered that the addition of small amounts of lithium hydroxide can inhibit urea production. The mechanism of action of lithium hydroxide mainly involves the following steps:

[0009] 1. Alkaline catalysis: Accelerates the hydrolysis and decomposition of HOCN / HNCO (main function)

[0010] Lithium hydroxide is a weakly basic hydroxide that dissociates in trace amounts, acting as a base catalyst to activate cyanic acid molecules and significantly accelerate hydrolysis and decomposition.

[0011] Stepwise hydrolysis reaction:

[0012] 1) Base deprotonation activation: HNCO + OH - —[NCO] - +H2O

[0013] Isocyanate loses a proton to hydroxide ions to generate cyanate anions, which significantly enhances its reactivity.

[0014] 2) Alkaline hydrolysis of cyanate ion: [NCO] -+2H₂O—NH₃+CO₂

[0015] It can be recycled and regenerated, requiring only a small amount to continue catalysis.

[0016] Overall hydrolysis reaction: HNCO + H2O → NH3 + CO2

[0017] Results: Free HNCO / HOCN in the system was rapidly consumed, and the precursor concentration decreased significantly.

[0018] 2. Inhibit dimerization: kinetically block urea formation.

[0019] Urea is a dimerization product between two HNCO molecules, and the reaction depends on a neutral / weakly acidic environment and a high concentration of free urea.

[0020] Lithium hydroxide provides a weakly alkaline environment, altering the molecular charge configuration: most of the HNCO is converted to the negatively charged [NCO]. - Like charges repel each other, preventing intermolecular dimerization between anions and directly blocking the basic reaction of urea synthesis; at the same time, the precursor is rapidly hydrolyzed and consumed, resulting in extremely low concentrations of free HNCO, which further inhibits the dimerization of urea from a kinetic perspective.

[0021] Under the dual effect, urea formation is significantly inhibited, and the final residue can be reduced to <1%; finally, the small amount of residual urea is further decomposed by high-temperature post-treatment.

[0022] Our company proposes a low-cost method for preparing and applying lithium sulfide. The core of this method is to first mix a small amount of lithium hydroxide with ammonium thiocyanate. By utilizing the two core mechanisms of lithium hydroxide mentioned above, the formation of urea is inhibited in situ, thereby reducing the content of impurities such as urea in lithium sulfide and improving its purity. Summary of the Invention

[0023] The purpose of this invention is to provide a low-cost method for preparing lithium sulfide and its application. The core method is to first mix a small amount of lithium hydroxide with ammonium thiocyanate; and to use the two core mechanisms of lithium hydroxide mentioned above to inhibit the formation of urea in situ, thereby reducing the content of impurities such as urea in lithium sulfide and improving its purity.

[0024] To achieve the above objectives, the present invention adopts the following technical solution:

[0025] Firstly, this invention provides a low-cost method for preparing lithium sulfide and its application. The core of this method is to first mix a small amount of lithium hydroxide with ammonium thiocyanate; then, by utilizing the two core mechanisms of lithium hydroxide described above, the generation of urea is inhibited in situ, thereby reducing the content of impurities such as urea in lithium sulfide and improving its purity.

[0026] As a specific technical solution, this low-cost lithium sulfide is prepared by solid-phase reaction of a small amount of lithium hydroxide a with lithium source b and a slightly excess of thiocyanate c. The lithium source and thiocyanate of the raw materials are refined, uniformly mixed, and then reacted in a solid-phase atmosphere at a certain temperature; where a+b=100%, 0≤a≤10%, 90%≤a≤100%; (a+b):c=1:(1~1.2); a and b are the molar ratio of lithium; c is the corresponding molar ratio of thiocyanate. Where 'a' can be 0%, 1%, 2%, 5%, 8%, 10%, or any of these percentages; where 'b' can be 90%, 92%, 94%, 96%, 98%, 100%, or any of these percentages; 'c' is an excess of thiocyanate designed to ensure sufficient reaction of the lithium source, with the excess ratio preferably not exceeding 1.2; experiments have shown that the higher the excess ratio, the longer the post-processing time and the more impurities in the product; the lower the excess ratio, the less consistent the reaction, and the more residual lithium carbonate will be.

[0027] Secondly, the present invention provides a method for preparing the above-mentioned low-cost lithium sulfide, comprising the following steps:

[0028] This invention also discloses a low-cost method for preparing lithium sulfide, characterized by comprising the following steps:

[0029] Its characteristic includes the following steps:

[0030] S1. Remove impurities and water from the above raw materials and dry them; refine the above raw materials and control the particle size D50≤10μm;

[0031] S2. To better suppress the generation of urea byproducts during the synthesis of lithium sulfide, a small amount of refined lithium hydroxide and refined ammonium thiocyanate are mixed uniformly first, and then further mixed with a lithium source (such as lithium carbonate) in proportion.

[0032] S3. After mixing the above raw materials, place them in an inert gas atmosphere and sinter them at a high temperature for a certain time while ensuring a certain gas flow rate; after sintering the above materials in a low temperature section, a medium temperature section, and a high temperature section (post-processing section) for a certain time; after refining the lithium sulfide into a certain particle size, the product lithium sulfide is obtained.

[0033] As a specific technical solution, in step S1 of this low-cost lithium sulfide preparation method, the drying and dehydration temperature is ≤300℃, specifically 100℃, 200℃, 300℃ or any value therein; the processing time is ≤12h: any value among 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 16, 18, 20, 24.

[0034] As a specific technical solution, in step S1 of this low-cost lithium sulfide preparation method, the particle size is controlled to be ≤10μm: specifically, it can be any value among 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10μm.

[0035] As a specific technical solution, in step S2 of this low-cost lithium sulfide preparation method, the molar ratio of the solution can be the molar ratio required by claim 1 or any number of molar ratios.

[0036] As a specific technical solution, in step S3 of this low-cost lithium sulfide preparation method...

[0037] The sintering temperatures are as follows: low-temperature sintering temperature: 150℃ ≤ sintering temperature ≤ 250℃, 1 ≤ sintering time ≤ 24; medium-temperature sintering temperature: 350℃ ≤ sintering temperature ≤ 550℃, 1 ≤ sintering time ≤ 24; post-treatment high-temperature sintering temperature: 500℃ ≤ sintering temperature ≤ 900℃, 1 ≤ sintering time ≤ 24; the refinement method is the same as that of claim 8; the low-temperature sintering is defined as: 150℃ ≤ sintering temperature ≤ 250℃, 1 ≤ sintering time ≤ 24; specifically, it can be any value among 150℃, 200℃, and 250℃; the sintering time is 1h ≤ sintering time ≤ 24h: specifically, it can be 4h, 8h, 12, or 16h. The temperature can be any value among 350℃, 20h, and 24h; the medium-temperature sintering is defined as: 350℃ ≤ sintering temperature ≤ 550℃, specifically any value among 350℃, 400℃, 450℃, and 550℃; 1 ≤ sintering time ≤ 24h; the sintering time is 1h ≤ sintering time ≤ 24h, specifically any value among 4h, 8h, 12, 16h, 20h, and 24h; the high-temperature post-treatment sintering section temperature is 500℃ ≤ sintering temperature ≤ 900℃, 1 ≤ sintering time ≤ 24h; specifically any value among 500℃, 600℃, 700℃, 800℃, and 900℃; 1 ≤ sintering time ≤ 24h; the sintering time is 1h ≤ sintering time ≤ 24h.

[0038] Thirdly, the present invention also provides a low-cost method for preparing lithium sulfide and its future application in solid electrolytes and batteries, wherein the battery includes any one of lithium-ion batteries, solid-state batteries, and semi-solid-state batteries.

[0039] Compared with existing technologies, the core is to first mix a small amount of lithium hydroxide with ammonium thiocyanate; utilize the two core mechanisms of lithium hydroxide mentioned above to inhibit the formation of urea in situ, reduce the content of impurities such as urea in lithium sulfide, and improve purity. Detailed Implementation

[0040] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] Unless otherwise specified, the experimental methods used in the examples and comparative examples are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0042] The present invention will be further described in detail below through detailed embodiments.

[0043] Example 1

[0044] This embodiment provides a low-cost method for preparing lithium sulfide, wherein lithium hydroxide is 0.02 mol, lithium carbonate is 0.49 mol, and ammonium thiocyanate is 1.1 mol; the particle size of the raw materials is D50≤1μm; the method for preparing this low-cost lithium sulfide is as follows:

[0045] S1. Remove impurities and moisture from the above raw materials and dry them; refine the above raw materials and control the particle size D50≤1μm;

[0046] S2. To better suppress the generation of urea byproducts during the synthesis of lithium sulfide, a small amount of refined lithium hydroxide and refined ammonium thiocyanate are mixed uniformly first, and then further mixed with a lithium source (such as lithium carbonate) in proportion.

[0047] S3. After mixing the above raw materials, place them in an inert gas atmosphere and sinter them at a high temperature for a certain time while ensuring a certain gas flow rate; after sintering the above materials in a low temperature section, a medium temperature section, and a high temperature section (post-processing section) for a certain time; after refining the lithium sulfide into a certain particle size, the product lithium sulfide is obtained.

[0048] Example 2

[0049] This embodiment provides a low-cost method for preparing lithium sulfide, wherein lithium hydroxide is 0.04 mol, lithium carbonate is 0.48 mol, and ammonium thiocyanate is 1.1 mol; the particle size of the raw materials is D50≤1μm; the method for preparing this low-cost lithium sulfide is as follows:

[0050] S1. Remove impurities and water from the above raw materials and dry them; refine the above raw materials and control the particle size D50≤1μm;

[0051] S2. To better suppress the generation of urea byproducts during the synthesis of lithium sulfide, a small amount of refined lithium hydroxide and refined ammonium thiocyanate are mixed uniformly first, and then further mixed with a lithium source (such as lithium carbonate) in proportion.

[0052] S3. After mixing the above raw materials, place them in an inert gas atmosphere and sinter them at a high temperature for a certain time while ensuring a certain gas flow rate; after sintering the above materials in a low temperature section, a medium temperature section, and a high temperature section (post-processing section) for a certain time; after refining the lithium sulfide into a certain particle size, the product lithium sulfide is obtained.

[0053] Example 3

[0054] This embodiment provides a low-cost method for preparing lithium sulfide, wherein lithium hydroxide is 0.06 mol, lithium carbonate is 0.47 mol, and ammonium thiocyanate is 1.1 mol; the particle size of the raw materials is D50≤1μm; the method for preparing this low-cost lithium sulfide is as follows:

[0055] S1. Remove impurities and water from the above raw materials and dry them; refine the above raw materials and control the particle size D50≤1μm;

[0056] S2. To better suppress the generation of urea byproducts during the synthesis of lithium sulfide, a small amount of refined lithium hydroxide and refined ammonium thiocyanate are mixed uniformly first, and then further mixed with a lithium source (such as lithium carbonate) in proportion.

[0057] S3. After mixing the above raw materials, place them in an inert gas atmosphere and sinter them at a high temperature for a certain time while ensuring a certain gas flow rate; after sintering the above materials in a low temperature section, a medium temperature section, and a high temperature section (post-processing section) for a certain time; after refining the lithium sulfide into a certain particle size, the product lithium sulfide is obtained.

[0058] Example 4

[0059] This embodiment provides a low-cost method for preparing lithium sulfide, wherein lithium hydroxide is 0.08 mol, lithium carbonate is 0.46 mol, and ammonium thiocyanate is 1.1 mol; the particle size of the raw materials is D50≤1μm; the method for preparing this low-cost lithium sulfide is as follows:

[0060] S1. Remove impurities and water from the above raw materials and dry them; refine the above raw materials and control the particle size D50≤1μm;

[0061] S2. To better suppress the generation of urea byproducts during the synthesis of lithium sulfide, a small amount of refined lithium hydroxide and refined ammonium thiocyanate are mixed uniformly first, and then further mixed with a lithium source (such as lithium carbonate) in proportion.

[0062] S3. After mixing the above raw materials, place them in an inert gas atmosphere and sinter them at a high temperature for a certain time while ensuring a certain gas flow rate; after sintering the above materials in a low temperature section, a medium temperature section, and a high temperature section (post-processing section) for a certain time; after refining the lithium sulfide into a certain particle size, the product lithium sulfide is obtained.

[0063] Example 5

[0064] This embodiment provides a low-cost method for preparing lithium sulfide, wherein lithium hydroxide is 0.1 mol, lithium carbonate is 0.45 mol, and ammonium thiocyanate is 1.1 mol; the particle size of the raw materials is D50≤1μm; the method for preparing this low-cost lithium sulfide is as follows:

[0065] S1. Remove impurities and water from the above raw materials and dry them; refine the above raw materials and control the particle size D50≤1μm;

[0066] S2. To better suppress the generation of urea byproducts during the synthesis of lithium sulfide, a small amount of refined lithium hydroxide and refined ammonium thiocyanate are mixed uniformly first, and then further mixed with a lithium source (such as lithium carbonate) in proportion.

[0067] S3. After mixing the above raw materials, place them in an inert gas atmosphere and sinter them at a high temperature for a certain time while ensuring a certain gas flow rate; after sintering the above materials in a low temperature section, a medium temperature section, and a high temperature section (post-processing section) for a certain time; after refining the lithium sulfide into a certain particle size, the product lithium sulfide is obtained.

[0068] Comparative Example 1

[0069] This embodiment provides a low-cost method for preparing lithium sulfide, using 0.5 mol of lithium carbonate and 1.1 mol of ammonium thiocyanate; the raw material particle size is D50≤1μm; the method for preparing this low-cost lithium sulfide is as follows:

[0070] S1. Remove impurities and water from the above raw materials and dry them; refine the above raw materials and control the particle size D50≤1μm;

[0071] S2. Mix further with a lithium source (such as lithium carbonate) in a certain proportion;

[0072] S3. After mixing the above raw materials, place them in an inert gas atmosphere and sinter them at a high temperature for a certain time while ensuring a certain gas flow rate; after sintering the above materials in a low temperature section, a medium temperature section, and a high temperature section (post-processing section) for a certain time; after refining the lithium sulfide into a certain particle size, the product lithium sulfide is obtained.

[0073] The products from Examples 1-5 and Comparative Example 1 were tested using ICP, with a focus on monitoring the elemental content of N, C, and O, as well as the purity of lithium sulfide. The experimental steps are as follows:

[0074] Sample pretreatment: Accurately weigh an appropriate amount of lithium sulfide sample, digest it at low temperature using an acid dissolution system, and after the sample is completely dissolved and cooled, make up to volume to prepare the test solution. At the same time, prepare blank control solution and a series of standard solutions.

[0075] Instrument testing: Start the ICP instrument, adjust the instrument parameters, and measure the blank solution, standard solution, and sample solution in sequence to establish a standard curve.

[0076] Data determination: The content of N, C and O impurity elements in the samples was mainly detected. Combined with the detection results of lithium and sulfur elements, the purity of lithium sulfide was calculated. Each group of samples was tested in parallel for 3 times and the average value was taken.

[0077] Table 1 Test data of batteries made in different embodiments

[0078] Example Lithium sulfide purity Nitrogen content Carbon content Oxygen content Other elements 1 99.10% 0.28% 0.12% 0.34% 0.16% 2 99.20% 0.23% 0.10% 0.33% 0.14% 3 99% 0.37% 0.16% 0.39% 0.08% 4 98.75% 0.47% 0.20% 0.46% 0.12% 5 98.43% 0.61% 0.31% 0.48% 0.17% Comparative Example 1 98.20% 0.70% 0.30% 0.40% 0.40%

[0079] As shown in Table 1 above, the comparative examples without lithium hydroxide have a lithium sulfide purity of 98.2%, a nitrogen content of 0.7%, a carbon content of 0.3%, an oxygen content of 0.4%, and a total content of other elements of 0.4%. Adding lithium hydroxide effectively inhibits urea residue, resulting in higher lithium sulfide purity and correspondingly lower nitrogen, carbon, and oxygen content. In Example 1, with a lithium hydroxide content of 0.02 mol, the lithium sulfide purity is 99.1%, with a nitrogen content of 0.28%, a carbon content of 0.12%, an oxygen content of 0.34%, and a total content of other elements of 0.16%. In Example 2, with a lithium hydroxide content of 0.04 mol, the lithium sulfide purity is 99.2%, with a nitrogen content of 0.23%, a carbon content of 0.10%, an oxygen content of 0.33%, and a total content of other elements of 0.4%. The purity of lithium sulfide was 99% when the lithium hydroxide content was 0.14% in Example 3, with nitrogen content of 0.37%, carbon content of 0.16%, oxygen content of 0.39%, and total content of other elements of 0.08% when the lithium hydroxide content was 0.06 mol in Example 4, with nitrogen content of 0.47%, carbon content of 0.2%, oxygen content of 0.46%, and total content of other elements of 0.12% when the lithium hydroxide content was 0.1 mol in Example 5, with lithium hydroxide content of 98.43% in Example 5, with nitrogen content of 0.61%, carbon content of 0.3%, oxygen content of 0.17%, and total content of other elements of 0.4% when the lithium hydroxide content was 0.1 mol in Example 6. The experimental results show that the addition of a small amount of lithium hydroxide can effectively inhibit the generation and residue of urea molecules and further improve the purity of lithium sulfide.

[0080] The present invention provides a low-cost method for preparing lithium sulfide and its application, which can be used in batteries such as lithium-ion batteries, solid-state batteries, semi-solid-state batteries, and negative electrode-free batteries.

[0081] The above embodiments are merely illustrative of the concept and technical solution of the present invention and are not intended to limit the present invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

[0082] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing low-cost lithium sulfide and its application, wherein the low-cost lithium sulfide is prepared by a solid-phase reaction of a small amount of lithium hydroxide a with a lithium source b and a slightly excess of thiocyanate c. The lithium source and thiocyanate are refined, uniformly mixed, and then reacted in a solid-phase atmosphere at a certain temperature; wherein a+b=100%, 0≤a≤10%, 90%≤b≤100%; (a+b):c=1:(1~1.2); a and b are the molar ratio of lithium; c is the corresponding molar ratio of thiocyanate.

2. The method for preparing low-cost lithium sulfide according to claim 1, characterized in that... The lithium source can be one or more of lithium oxide, lithium carbonate, lithium hydroxide, lithium acetate, lithium formate, and tert-butyllithium; when the lithium source is lithium carbonate, there is less solid waste and it is easier to handle.

3. The method for preparing low-cost lithium sulfide according to claim 1, characterized in that, The thiocyanate can be one or more of ammonium thiocyanate, sodium thiocyanate, potassium thiocyanate, lithium thiocyanate, thiocyanic acid, etc.

4. The method for preparing low-cost lithium sulfide according to claim 1, characterized in that, The inert atmosphere is mainly composed of one or more of nitrogen, helium, neon, argon, krypton, and xenon.

5. According to the method for preparing low-cost lithium sulfide as described in claim 1, the solid-state sintering at a certain temperature can be configured with a reaction curve according to actual reaction process requirements; the overall temperature range is ≤900℃.

6. A low-cost method for preparing lithium sulfide, characterized in that... Includes the following steps: S1. Remove impurities and water from the above raw materials and dry them; refine the above raw materials and control the particle size D50≤10μm; S2. To better suppress the generation of urea byproducts during the synthesis of lithium sulfide, a small amount of refined lithium hydroxide and refined ammonium thiocyanate are mixed uniformly first, and then further mixed with a lithium source (such as lithium carbonate) in proportion. S3. After mixing the above raw materials, place them in an inert gas atmosphere and sinter them at a high temperature for a certain time while ensuring a certain gas flow rate; after sintering the above materials in a low temperature section, a medium temperature section, and a high temperature section (post-processing section) for a certain time; after refining the lithium sulfide into a certain particle size, the product lithium sulfide is obtained.

7. The preparation method according to claim 6, wherein the dehydration drying in step S1 of the preparation method is mainly used to remove some volatile water and volatile impurities, and the drying temperature is 80 ≤ drying temperature ≤ 300℃ and the drying time is 0 ≤ drying time ≤ 24h.

8. The preparation method according to claim 6, wherein the refining treatment in step S2 of the preparation method can be dry grinding (sand milling), air jet milling, wet grinding (sand milling), mechanical milling, ball milling, etc.; in step S2, the mixing ratio is added according to claim 1.

9. The preparation method according to claim 6, characterized in that, In step S3, the sintering temperature in the low-temperature section is: 150℃≤sintering temperature≤250℃, 1≤sintering time≤24; the sintering temperature in the medium-temperature section is: 350℃≤sintering temperature≤550℃, 1≤sintering time≤24; the sintering temperature in the high-temperature section of the post-treatment is: 500℃≤sintering temperature≤900℃, 1≤sintering time≤24; the refinement method is the same as that in claim 8.

10. A low-cost lithium sulfide material according to claim 1 or a low-cost lithium sulfide material prepared by any one of claims 1 to 9, and a sulfide solid electrolyte prepared therefrom, and the sulfide electrolyte prepared therefrom can be matched with a solid positive electrode, a solid negative electrode, and an electrolyte layer to assemble into a solid-state battery system, and its application in electrode sheets, batteries, battery packs, and electrical devices, wherein the battery includes any one of lithium-ion batteries, solid-state batteries, and semi-solid-state batteries.