Preparation method of lithium sulfide powder, lithium sulfide powder and application

Abstract

The invention relates to the technical field of battery raw materials, in particular to a preparation method of lithium sulfide powder, the lithium sulfide powder and application, and the preparation method comprises the following steps: uniformly mixing lithium sulfate and a carbon source according to a preset proportion to obtain a first mixture; performing first heat treatment on the first mixture in inert gas to obtain a second mixture; and performing second heat treatment on the second mixture in reducing gas to obtain the lithium sulfide powder. The product obtained by the preparation method disclosed by the invention is the lithium sulfide powder, and the obtained lithium sulfide powder has the advantages of less oxygen and carbon impurities, higher purity and high reaction activity, and meets the synthesis requirements of the electrolyte; according to the preparation method, in the process of preparing lithium sulfide, toxic gas and organic solvent are not used, the reaction temperature is low, the energy consumption is low, the requirement on production equipment is low, the process is simple, the cost is low, harmful gas emission is avoided, safety and environment friendliness are achieved, and industrialization is easy to achieve.

Description

Technical Field

[0001] The present invention relates to the technical field of battery raw materials, and in particular to a preparation method of lithium sulfide powder, the lithium sulfide powder and applications thereof. Background Art

[0002] With the continuous growth in sales of new energy vehicles, safety accidents involving power batteries have also occurred frequently. The liquid electrolytes used in existing power batteries are highly flammable, which is one of the key factors affecting their safety. All-solid-state batteries use non-flammable solid electrolytes to replace liquid electrolytes, which is expected to fundamentally solve the safety problem and is considered to be the most promising new generation of power battery technology. Solid-state electrolyte materials, as the core materials of solid-state batteries, contain huge market opportunities. Among them, sulfides are considered to be the solid-state electrolyte materials with the most application potential in the field of all-solid-state batteries. High-purity Li2S is the key basic raw material for the synthesis of sulfide solid electrolytes, but because it is extremely easy to absorb moisture and hydrolyze, it is difficult to prepare it by engineering. The high cost has become the main obstacle to the application of sulfide solid electrolytes. It is particularly urgent to develop a low-cost and large-scale preparation technology for Li2S.

[0003] Existing lithium sulfide raw material preparation technologies mainly include elemental chemical method, H2S gas phase synthesis method, organic synthesis method, carbon thermal reduction method and gas phase reduction method. The main problem of the elemental chemical method is that the metallic Li is relatively active and dangerous, the product stoichiometry is difficult to control, and polysulfides are easily formed. The main problem of the H2S gas phase synthesis method and the organic synthesis method is that a large amount of toxic and harmful H2S gas is required. The carbon thermal reduction method requires the addition of an excessive amount of C source during the reaction, and the content of impurities such as oxygen and carbon in the product is relatively high. The main problem of the gas phase reduction method is the use of toxic gas CO, the high reaction temperature, high energy consumption, the product is a hardened block, and the reaction activity is low. Summary of the Invention

[0004] (1) Purpose of the invention

[0005] The purpose of the present invention is to provide a preparation method of lithium sulfide powder, which avoids the use of toxic and harmful gases and organic solvents, has high product reactivity, is simple in process, safe, efficient and easy to produce on a large scale, and provides lithium sulfide powder and its application.

[0006] (2) Technical solution

[0007] To solve the above problems, the present invention provides a method for preparing lithium sulfide powder, comprising:

[0008] Evenly mixing lithium sulfate and a carbon source in a predetermined ratio to obtain a first mixture;

[0009] subjecting the first mixture to a first heat treatment in an inert gas to obtain a second mixture;

[0010] The second mixture is subjected to a second heat treatment in a reducing gas to obtain lithium sulfide powder.

[0011] In another aspect of the present invention, preferably,

[0012] The water content of the lithium sulfate is less than 1%; the carbon source includes at least one of carbon powder, carbon black, activated carbon or biomass carbon.

[0013] In another aspect of the present invention, preferably,

[0014] The preset ratio includes a molar ratio of lithium sulfate to carbon source of 1:1.8 to 1:1.95.

[0015] In another aspect of the present invention, preferably,

[0016] The step of uniformly mixing the lithium sulfate and the carbon source in a preset ratio further comprises:

[0017] Grinding the lithium sulfate and the carbon source, sieving and uniformly mixing to obtain a first mixture;

[0018] The powder particle size D90 of the first mixture is less than 70 μm.

[0019] In another aspect of the present invention, preferably,

[0020] The inert gas is N2 gas or Ar gas.

[0021] In another aspect of the present invention, preferably,

[0022] The reducing gas is H2 gas, a mixture of H2 and an inert gas, or NH3 decomposition gas.

[0023] In another aspect of the present invention, preferably,

[0024] The temperature of the first heat treatment is 700° C.-858° C., and the time of the first heat treatment is 1 hour-10 hours;

[0025] The temperature of the second heat treatment is 800° C.-937° C., and the time of the second heat treatment is 1 hour-6 hours.

[0026] In another aspect of the present invention, preferably,

[0027] The temperature of the first heat treatment is 750° C.-850° C., and the time of the first heat treatment is 2 h-4 h;

[0028] The temperature of the second heat treatment is 900° C.-930° C., and the time of the second heat treatment is 1 hour-2 hours.

[0029] In another aspect of the present invention, preferably,

[0030] A lithium sulfide powder is prepared by the above-mentioned preparation method, wherein the oxygen content of the lithium sulfide powder is ≤0.5wt%, the carbon content of the lithium sulfide powder is ≤0.4wt%, and the total content of lithium and sulfur elements in the lithium sulfide powder is ≥99wt%.

[0031] In another aspect of the present invention, preferably,

[0032] A lithium sulfide powder prepared by the preparation method described above and / or an application of the lithium sulfide powder described above in the field of solid electrolyte raw materials for lithium-ion batteries.

[0033] (3) Beneficial effects

[0034] The above technical solution of the present invention has the following beneficial technical effects:

[0035] The product obtained by the preparation method of the present invention is lithium sulfide powder. The obtained lithium sulfide powder has less oxygen and carbon impurities, high purity, high reaction activity, and meets the synthesis requirements of the electrolyte. The preparation method of the present invention avoids the use of toxic gases and organic solvents during the preparation of lithium sulfide, has a low reaction temperature, low energy consumption, low requirements for production equipment, simple process, low cost, no harmful gas emissions, is safe, environmentally friendly, and easy to industrialize. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is an overall flow chart of a preparation method according to an embodiment of the present invention.

[0037] Figure 2 This is the XRD phase diffraction pattern of the Li2S powder obtained in Example 1 of the present invention.

[0038] Figure 3 This is a SEM scanning electron microscope image of the Li2S powder obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the present invention more clearly understood, the present invention will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present invention.

[0040] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0041] In the description of the present invention, it should be noted that the terms "first", "second" and "third" are only used for descriptive purposes and should not be understood as indicating or implying relative importance.

[0042] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0043] The present invention provides a method for preparing lithium sulfide powder. Figure 1 The overall flow chart of the preparation method of one embodiment of the present invention is shown as follows: Figure 1 Shown, including:

[0044] The lithium sulfate and the carbon source are uniformly mixed in a preset ratio to obtain a first mixture. The specific contents of the lithium sulfate and the carbon source are not limited here. Optionally, in this embodiment, the water content of the lithium sulfate is less than 1%. The carbon source includes at least one of carbon powder, carbon black, activated carbon, or biomass carbon. Further, the biomass carbon includes sucrose, glucose, etc. The specific contents of the preset ratio are also not limited here. Optionally, in this embodiment, the preset ratio includes a molar ratio of lithium sulfate to carbon source of 1:1.8 to 1:1.95. By strictly controlling the water content of the lithium sulfate to below 1%, the adverse effects of water on the reaction, such as reducing the reaction rate, inducing side reactions, or causing impure products, can be avoided. By precisely controlling the molar ratio of lithium sulfate to carbon source within the range of 1:1.8 to 1:1.95, the amount of carbon source added is lower than the molar ratio of 1:2 theoretically required for the carbothermal reduction reaction, which will promote the complete reaction of the carbon source with the excess lithium sulfate raw material at high temperature and avoid carbon residue. When the amount of carbon source added is too small, too much unreacted lithium sulfate will remain in the lithium sulfide crude material after the first heat treatment, which will increase the time required for the second heat treatment reaction and the generated water vapor, which is not conducive to the synthesis of high-purity lithium sulfide. By precisely controlling the molar ratio of lithium sulfate to carbon source within the range of 1:1.8 to 1:1.95, it can be ensured that the stoichiometric ratio between the mixture is close to the optimal reaction ratio. After the first heat treatment, there is less lithium sulfate, and a higher purity lithium sulfide product can be obtained, reducing the introduction of impurities. Further, in this embodiment, the lithium sulfate and carbon source are mixed uniformly according to the preset ratio and further include:

[0045] The lithium sulfate and the carbon source are ground, sieved, and uniformly mixed to obtain a first mixture. The specific grinding method and the mixing method are not limited herein. Optionally, the two raw material powders, which have been sieved separately, are placed in a high-speed mixer and uniformly mixed. The powder particle size D90 of the first mixture is less than 70 μm. The powder particle size D90 means that the number of particles of the first mixture with a size less than 70 μm reaches 90%. Grinding refines the particles of the lithium sulfate and the carbon source, which significantly increases the contact area between the two. The increase in contact area facilitates a more complete and rapid chemical reaction between the two, thereby improving reaction efficiency.

[0046] The first mixture is subjected to a first heat treatment in an inert gas to obtain a second mixture; the specific content of the inert gas is not limited here, nor is the specific content of the first heat treatment. Optionally, in this embodiment, the inert gas is N2 gas or Ar gas, the temperature of the first heat treatment is 700℃-858℃, and the time of the first heat treatment is 1h-10h; further, the temperature of the first heat treatment is 750℃-850℃, and the time of the first heat treatment is 2h-4h; the first mixture is transferred to a tubular furnace and protected by an inert gas, and then gradually heated to the set temperature for the first heat treatment. The temperature of the first heat treatment can make the carbon thermal reduction reaction of lithium sulfate proceed rapidly, while also avoiding the adverse effects of local melting and agglomeration of lithium sulfate powder on the reaction;

[0047] The second mixture is subjected to a second heat treatment in a reducing gas to obtain lithium sulfide powder. The specific content of the reducing gas is not limited here, nor is the specific content of the second heat treatment. Optionally, the reducing gas is H2 gas, a mixture of H2 and an inert gas, or NH3 decomposition gas. Further, the reducing gas is H2 gas, a mixture of H2 and N2 gas, a mixture of H2 and Ar gas, a mixture of H2, N2 gas and Ar gas, or NH3 decomposition gas; the temperature of the second heat treatment is 800°C-937°C, and the time of the second heat treatment is 1h-6h. The temperature of the second heat treatment is 900°C-930°C, and the time of the second heat treatment is 1h-2h. The temperatures of the first heat treatment and the second heat treatment are both lower than the melting point of lithium sulfide to prevent the lithium sulfide from melting and agglomerating. The resulting lithium sulfide powder has high reaction activity and meets the synthesis requirements of the electrolyte.

[0048] After the first heat treatment is completed, the inert gas introduced is converted into a reducing gas through a three-way valve, and the second heat treatment is carried out after the temperature is raised to the set temperature. After the second heat treatment is completed, the gas in the tube furnace is converted into an inert gas to reduce the amount of reducing gas, and after cooling to room temperature, it is sealed and transferred to a glove box protected by inert gas. Furthermore, the reducing gas is NH3 decomposition gas. Since it is very dangerous to directly use pure H2 gas as a reducing gas in the reaction, the use of low-cost and easy to stably supply NH3 decomposition gas (the volume ratio of H2 to N2 is 3:1) can improve the efficiency and safety of the reduction reaction. At the same time, N2 gas is introduced as an inert gas that does not participate in the reaction, and can also quickly take away a small amount of water vapor generated by the reaction;

[0049] A lithium sulfide powder is prepared by the above-mentioned preparation method, wherein the oxygen content of the lithium sulfide powder is ≤0.5wt%, the carbon content of the lithium sulfide powder is ≤0.4wt%, and the total content of lithium and sulfur elements in the lithium sulfide powder is ≥99wt%.

[0050] A lithium sulfide powder prepared by the preparation method described above and / or an application of the lithium sulfide powder described above in the field of solid electrolyte raw materials for lithium-ion batteries.

[0051] To avoid the complex process of removing residual carbon, the present preparation method utilizes a carbothermal reduction reaction between lithium sulfate and an insufficient amount of a carbon source at a temperature below the melting point of lithium sulfate (859°C). Because the amount of added carbon powder is less than the theoretical molar amount required for a complete reaction, the lithium sulfate completely consumes the carbon source during the carbothermal reduction reaction, eliminating the need for subsequent carbon removal. The resulting second mixture after the first reaction is a crude lithium sulfide material containing only a small amount of unreacted lithium sulfate.

[0052] The present invention uses reducing gas H2 to perform a high-temperature reduction reaction on a small amount of unreacted lithium sulfate in the second mixture, thereby reacting the small amount of lithium sulfate to obtain lithium sulfide. The reaction formula is Li2SO4+4H2=Li2S+4H2O. H2 gas is non-toxic, clean and environmentally friendly. At the same time, H2 has strong reducing ability and a lower reaction temperature, which can save energy and obtain a highly active powder. A large amount of water is produced during the H2 gas reduction reaction of lithium sulfate. If this high-temperature water vapor is not discharged in time, it will undergo a hydrolysis reaction with the newly generated Li2S: Li2S+H2O=LiOH+H2S. The generated impurity phase LiOH will reduce the performance of the final lithium sulfide product. It is difficult to obtain a high-purity lithium sulfide sample by selecting different reaction temperatures for the direct H2 reduction reaction. As shown in a comparative example of the present invention, when lithium sulfate is directly reduced using NH3 decomposition gas (H2 to N2 volume ratio of 3:1) at 850°C, 7.5% of the oxygen content remains after 10 hours; as shown in another comparative example of the present invention, when the gas phase reduction temperature is increased to 950°C, the product is in a hardened block after 4 hours, and the oxygen content is still as high as 8.6%. Therefore, it is difficult to achieve the preparation of low-oxygen lithium sulfide by directly using H2-containing reducing gas at high temperature to reduce lithium sulfate. In the present invention, the lithium sulfate has been mostly converted into lithium sulfide with a higher melting point after the first heat treatment. At this time, the reducing gas containing H2 is introduced into the reaction system for the second heat treatment. At a temperature below the melting point of lithium sulfide (938°C), the H2 gas can quickly convert the small amount of lithium sulfate remaining in the lithium sulfide crude material obtained in the first step into lithium sulfide. Since the amount of lithium sulfate that needs to be reduced is small, the small amount of water vapor produced by the reaction can be quickly carried out with the reaction gas, avoiding its reaction with the newly generated lithium sulfide and suppressing the generation of LiOH impurity phase. At the same time, the temperatures of the above two steps of heat treatment are controlled below the melting point of the mixture, avoiding sintering agglomeration or liquid phase melting process between powder particles, ensuring the smooth flow of powder solid-solid reaction and gas-solid reaction channels. On the one hand, it greatly improves the reaction rate and ensures the complete reaction. On the other hand, it keeps the lithium sulfide product in a powder state with good reaction activity.

[0053] Example 1

[0054] 100g of anhydrous lithium sulfate powder and 20.2g of carbon powder, each sieved through a 200-mesh sieve, were weighed in a molar ratio of 1:1.9. The two materials were placed in a high-speed mixer and mixed for 10 minutes before taking out to obtain a mixture. The mixture was then poured into an alumina crucible and transferred to a tubular furnace filled with Ar gas for the first heat treatment. The Ar gas flow rate was set to 5L / min, and the mixture was heated to 800°C at a heating rate of 5°C / min and kept warm for 3 hours. After the first heat treatment, the gas introduced into the tubular furnace was converted to NH3 decomposition gas at a gas flow rate of 5L / min and heated to 920°C at a heating rate of 5°C / min and kept warm for 1.5 hours. After the second heat treatment was completed, the mixture was cooled to room temperature, and the third mixture was sealed and transferred to an argon glove box. The powder was taken out to obtain lithium sulfide powder. Figure 2 This is the XRD phase diffraction pattern of the Li2S powder obtained in Example 1 of the present invention. The synthesized sample is pure phase Li2S without the presence of other impurities. Figure 3 This is a SEM scanning electron microscope image of the Li2S powder obtained in Example 1 of the present invention. The synthesized powder has a uniform particle size distribution, no agglomeration phenomenon, and good reaction activity.

[0055] Example 2

[0056] 100g of anhydrous lithium sulfate powder and 21.3g of carbon black, each passed through a 200-mesh sieve, were weighed in a molar ratio of 1:1.95. The two materials were placed in a high-speed mixer and mixed for 10 minutes before removal to obtain a mixture. The mixture was then poured into an alumina crucible and transferred to a tubular furnace filled with Ar gas for a first heat treatment. The Ar gas flow rate was set to 5L / min, and the mixture was heated to 850°C at a heating rate of 5°C / min and held at that temperature for 4 hours. After the first heat treatment, the gas introduced into the tubular furnace was converted to NH3 decomposition gas at a gas flow rate of 5L / min, and heated to 930°C at a heating rate of 5°C / min and held at that temperature for 2 hours. After the second heat treatment, the mixture was cooled to room temperature and the third mixture was sealed and transferred to an argon glove box. The powder was removed to obtain lithium sulfide powder.

[0057] Example 3

[0058] 100g of anhydrous lithium sulfate powder and 19.6g of activated carbon, both sieved through a 200-mesh sieve, were weighed in a molar ratio of 1:1.8. The two materials were placed in a high-speed mixer and mixed for 10 minutes before removal to obtain a mixture. The mixture was then poured into an alumina crucible and transferred to a tubular furnace filled with N2 gas for a first heat treatment. The N2 gas flow rate was set to 5 L / min, and the mixture was heated to 750°C at a heating rate of 5°C / min and held at that temperature for 2 hours. After the first heat treatment, the gas introduced into the tubular furnace was converted to NH3 decomposition gas at a gas flow rate of 5 L / min, and heated to 900°C at a heating rate of 5°C / min and held at that temperature for 1 hour. After the second heat treatment, the mixture was cooled to room temperature and the third mixture was sealed and transferred to an argon glove box. The powder was removed to obtain lithium sulfide powder.

[0059] Example 4

[0060] 100g of anhydrous lithium sulfate powder and 49.2g of sucrose, both passed through a 200-mesh sieve, were weighed in a molar ratio of 1:1.9. The two materials were placed in a high-speed mixer and mixed for 10 minutes before removal to obtain a mixture. The mixture was then poured into an alumina crucible and transferred to a tubular furnace filled with N2 gas for a first heat treatment. The N2 gas flow rate was set to 5L / min, and the mixture was heated to 850°C at a heating rate of 5°C / min and held at that temperature for 2 hours. After the first heat treatment, the gas introduced into the tubular furnace was converted to NH3 decomposition gas at a gas flow rate of 5L / min, and heated to 900°C at a heating rate of 5°C / min and held at that temperature for 2 hours. After the second heat treatment, the mixture was cooled to room temperature and the third mixture was sealed and transferred to an argon glove box. The powder was removed to obtain lithium sulfide powder.

[0061] Example 5

[0062] 100g of anhydrous lithium sulfate powder and 20.2g of carbon powder, each passed through a 200-mesh sieve, were weighed in a molar ratio of 1:1.85. The two materials were placed in a high-speed mixer and mixed for 10 minutes before being taken out to obtain a mixture. The mixture was then poured into an alumina crucible and transferred to a tubular furnace filled with N2 gas for the first heat treatment. The N2 gas flow rate was set to 5L / min, and the mixture was heated to 700°C at a heating rate of 5°C / min and kept warm for 10 hours. After the first heat treatment, the gas introduced into the tubular furnace was converted to a mixture of H2 and inert gas (H2 to Ar gas volume ratio of 3:1) with a gas flow rate of 5L / min and heated to 800°C at a heating rate of 5°C / min and kept warm for 6 hours. After the second heat treatment reaction was completed, the mixture was cooled to room temperature, and the third mixture was sealed and transferred to an argon glove box. The powder was taken out to obtain high-purity lithium sulfide powder.

[0063] Example 6

[0064] 100g of anhydrous lithium sulfate powder and 20.7g of carbon powder, each weighed through a 200-mesh sieve, were weighed in a molar ratio of 1:1.9. The two materials were placed in a high-speed mixer and mixed for 10 minutes before taking out to obtain a mixture. The mixture was then poured into an alumina crucible and transferred to a tubular furnace filled with Ar gas for the first heat treatment. The Ar gas flow rate was set to 5L / min, and heated to 720°C at a heating rate of 5°C / min, and kept warm for 6h. After the first heat treatment, the gas introduced into the tubular furnace was converted to a mixture of H2 and inert gas (H2 and Ar gas volume was 2:1), with a gas flow rate of 5L / min, and heated to 860°C at a heating rate of 5°C / min, and kept warm for 4h. After the second heat treatment was completed, the mixture was cooled to room temperature, and the third mixture was transferred to an argon glove box in a sealed manner. The powder was taken out to obtain high-purity lithium sulfide powder.

[0065] Example 7

[0066] 100g of anhydrous lithium sulfate powder and 20.2g of activated carbon, which have passed through a 100-mesh sieve, were weighed in a molar ratio of 1:1.85. The two materials were placed in a high-speed mixer and mixed for 10 minutes before taking out to obtain a mixture. The mixture was then poured into an alumina crucible and transferred to a tubular furnace filled with N2 gas for the first heat treatment. The N2 gas flow rate was set to 5L / min, and the mixture was heated to 858°C at a heating rate of 5°C / min and kept warm for 1 hour. After the first heat treatment, the gas introduced into the tubular furnace was converted to a mixture of H2 and inert gas (the volume of H2 and N2 gas was 2:1, the gas flow rate was 5L / min, and the mixture was heated to 937°C at a heating rate of 5°C / min and kept warm for 4 hours. After the second heat treatment reaction was completed, the mixture was cooled to room temperature, and the third mixture was sealed and transferred to an argon glove box. The powder was taken out to obtain lithium sulfide powder.

[0067] Comparative Example 1

[0068] 100g of anhydrous lithium sulfate powder and 21.8g of carbon powder, both passed through a 200-mesh sieve, were weighed in a 1:2 molar ratio. The two materials were placed in a high-speed mixer and mixed for 10 minutes before removal to obtain a mixture. This mixture was then poured into an alumina crucible and transferred to a tubular furnace filled with Ar gas for a carbothermal reduction reaction. The Ar gas flow rate was set at 5 L / min, and the temperature was increased to 850°C at a rate of 5°C / min for 4 hours. After the reaction was completed, the temperature was cooled to room temperature, and the sample was sealed and transferred to an argon glove box. The powder was removed to obtain lithium sulfide powder.

[0069] Comparative Example 2

[0070] 100g of anhydrous lithium sulfate powder, passed through a 200-mesh sieve, was weighed and poured into an alumina crucible. The crucible was then transferred to a tubular furnace flowing with NH3 decomposition gas for direct reduction. The gas flow rate was set at 5 L / min. The temperature was heated to 850°C at a rate of 5°C / min and held for 10 hours. After the reaction was complete, the sample was cooled to room temperature and sealed in an argon glove box. The powder was removed to obtain lithium sulfide powder.

[0071] Comparative Example 3

[0072] 100g of anhydrous lithium sulfate powder, passed through a 200-mesh sieve, was weighed and poured into an alumina crucible. The crucible was then transferred to a tubular furnace flowing with NH3 decomposition gas for direct reduction. The gas flow rate was set at 5 L / min. The temperature was heated to 950°C at a rate of 5°C / min and held for 4 hours. After the reaction was complete, the sample was cooled to room temperature and sealed in an argon glove box. The powder was removed to obtain lithium sulfide powder.

[0073] Related embodiment detection method

[0074] Oxygen content test: Use an oxygen content analyzer for testing. Take 1g of the final lithium sulfide sample and grind it evenly in a glove box. Then, transfer it to a glove box equipped with an oxygen content analyzer. Then, accurately weigh 0.02g of lithium sulfide powder sample and put it into a special nickel bag for testing. After covering it tightly, put it into the oxygen content analyzer for testing. The sample is tested 3 times, and the average value is taken if there is no abnormality.

[0075] Carbon and sulfur content test: Use a carbon and sulfur analyzer for testing. Weigh the final lithium sulfide sample in the glove box (0.1g for carbon content analysis and 0.025g for sulfur content analysis) and put it into a special alumina crucible for testing. Then, add pure iron flux and tungsten particles to the crucible in sequence. After taking out the sample crucible from the glove box, quickly put it into the carbon and sulfur analyzer for testing. The sample is tested 3 times, and the average value is taken if there is no abnormality.

[0076] Lithium content test: ICP-OES electron coupled emission spectrometer is used for testing. 5.0 g of the final lithium sulfide sample is weighed in the glove box and transferred into a glass beaker. The sample is then taken out of the glove box and 40 ml of hydrochloric acid and 10 ml of nitric acid are added to dissolve the sample. The sample is then accurately titrated into a 100 ml volumetric flask with deionized water. The fixed volume solution is then tested by ICP-OES equipment. The sample is tested 3 times, and the average value is taken if no abnormality is found.

[0077] Table 1 shows the test results of oxygen content, carbon content, and total lithium-sulfur content of the lithium sulfide powders prepared in Examples 1-7 of the present invention and Comparative Examples 1-3.

[0078]

[0079]

[0080] In summary, the lithium sulfide obtained by the preparation method of the present invention has low carbon and oxygen contents, a high total lithium-sulfur content, and a uniformly dispersed, non-agglomerated powder, meeting the requirements of a sulfide electrolyte. Furthermore, the preparation method is simple in synthesis, uses no toxic or hazardous gases, and is scalable, providing a good foundation for the large-scale production of sulfide solid electrolyte materials.

[0081] It should be understood that the above-described specific embodiments of the present invention are merely illustrative or illustrative of the principles of the present invention and do not constitute limitations of the present invention. Therefore, any modifications, equivalent substitutions, improvements, etc. made without departing from the spirit and scope of the present invention should be included within the scope of protection of the present invention. In addition, the appended claims are intended to cover all variations and modifications that fall within the scope and metes and bounds of the appended claims, or equivalents thereof.

[0082] The present invention has been described above with reference to the embodiments thereof. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention. The scope of the present invention is defined by the appended claims and their equivalents. Those skilled in the art may make various substitutions and modifications without departing from the scope of the present invention, and such substitutions and modifications are intended to fall within the scope of the present invention.

[0083] Although the embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.

[0084] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing lithium sulfide powder, characterized in that: include: Evenly mixing lithium sulfate and a carbon source in a predetermined ratio to obtain a first mixture; subjecting the first mixture to a first heat treatment in an inert gas to obtain a second mixture; The second mixture is subjected to a second heat treatment in a reducing gas to obtain lithium sulfide powder.

2. The preparation method according to claim 1, wherein: The water content of the lithium sulfate is less than 1%; the carbon source includes at least one of carbon powder, carbon black, activated carbon or biomass carbon.

3. The preparation method according to claim 1, wherein: The preset ratio includes a molar ratio of lithium sulfate to carbon source of 1:1.8 to 1:1.

95.

4. The preparation method according to claim 1, characterized in that The step of uniformly mixing the lithium sulfate and the carbon source in a preset ratio further comprises: Grinding the lithium sulfate and the carbon source, sieving and uniformly mixing to obtain a first mixture; The powder particle size D90 of the first mixture is less than 70 μm.

5. The preparation method according to claim 1, characterized in that The inert gas is N2 gas or Ar gas.

6. The preparation method according to claim 1, wherein: The reducing gas is H2 gas, a mixture of H2 and an inert gas, or NH3 decomposition gas.

7. The preparation method according to claim 1, characterized in that The temperature of the first heat treatment is 700° C.-858° C., and the time of the first heat treatment is 1 hour-10 hours; The temperature of the second heat treatment is 800° C.-937° C., and the time of the second heat treatment is 1 hour-6 hours.

8. The preparation method according to claim 7, characterized in that The temperature of the first heat treatment is 750° C.-850° C., and the time of the first heat treatment is 2 h-4 h; The temperature of the second heat treatment is 900° C.-930° C., and the time of the second heat treatment is 1 hour-2 hours.

9. A lithium sulfide powder, characterized in that: The lithium sulfide powder is prepared by the preparation method according to any one of claims 1 to 8, wherein the oxygen content of the lithium sulfide powder is ≤0.5wt%, the carbon content of the lithium sulfide powder is ≤0.4wt%, and the total content of lithium and sulfur elements in the lithium sulfide powder is ≥99wt%.

10. Use of the lithium sulfide powder prepared by the preparation method according to any one of claims 1 to 8 and / or the lithium sulfide powder according to claim 9 in the field of raw materials for solid electrolytes of lithium-ion batteries.

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