Lithium sulfide powder and preparation method thereof, sulfide electrolyte and preparation method thereof, and solid-state battery

Abstract

The invention provides lithium sulfide powder and a preparation method thereof, sulfide electrolyte and a preparation method thereof, and a solid-state battery. The purity of the lithium sulfide powder is greater than or equal to 99.5%, the whiteness is greater than or equal to 83%, the oxygen mass content is less than or equal to 0.3%, the carbon mass content is less than or equal to 0.2%, and the metal impurity mass content is less than or equal to 0.1%. And the ratio of (Dv90-Dv10) / Dv50 of the lithium sulfide powder is 3-5. The lithium sulfide powder is high in purity and whiteness and few in impurity, and is matched with (Dv90-Dv10) / Dv50 = 3-5, so that the high-purity powder can be tableted and calcined when being used for preparing sulfide electrolyte, gaps among large particles are effectively filled with small particles, residual gaps are further filled with medium particles, close packing is formed, and the sulfide electrolyte is prepared. Therefore, the ionic conductivity of the sulfide electrolyte obtained after sintering is relatively high, so that the rate capability and the cycle performance of the solid-state battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of solid-state battery materials, in particular to a lithium sulfide powder and a preparation method thereof, a sulfide electrolyte and a preparation method thereof, and a solid-state battery. BACKGROUND

[0002] Li2S is one of the key raw materials of sulfide electrolyte, and its purity has a great influence on the performance of the prepared sulfide electrolyte. The existing methods for preparing lithium sulfide are: metal lithium and sulfur ball milling method, the reaction is very violent, only suitable for small batch preparation, and there are difficulties in mass production; lithium salt and hydrogen sulfide method, which needs toxic gas, and the safety has not been solved; double decomposition method, which needs to use a large amount of solvent, which is toxic and harmful to the environment, and the impurities in the product are difficult to remove, affecting the subsequent use.

[0003] In the prior art, the technical personnel pay more attention to the purity of the lithium sulfide powder, but even if the lithium sulfide with high purity is prepared, the ionic conductivity of the sulfide electrolyte prepared finally is still low. SUMMARY

[0004] The present application is carried out in view of the above-mentioned problems, and aims to provide a lithium sulfide powder and a preparation method thereof, a sulfide electrolyte and a preparation method thereof, and a solid-state battery, which aims to prepare a sulfide electrolyte with higher ionic conductivity, so as to improve the rate performance and cycle performance of the solid-state battery.

[0005] In a first aspect, the present application provides a lithium sulfide powder, the purity of the lithium sulfide powder is ≥99.5%, the whiteness is ≥83%, the oxygen mass content is ≤0.3%, the carbon mass content is ≤0.2%, and the metal impurity mass content is ≤0.1%. The (Dv90-Dv10) / Dv50 of the lithium sulfide powder is 3-5.

[0006] In the above technical solution, the purity and whiteness of the lithium sulfide powder are high, the impurities are less, and the (Dv90-Dv10) / Dv50 is 3-5, which can make the powder with high purity effectively fill the gaps between large particles when preparing the sulfide electrolyte and pressing and calcining, and the medium particles further fill the remaining gaps, so as to form a close packing, so that the ionic conductivity of the sulfide electrolyte obtained after sintering is high, and the electronic conductivity is low, thereby improving the rate performance and cycle performance of the solid-state battery.

[0007] In some embodiments, the chemical formula of the lithium sulfide powder is Li x S, 1.900≤x≤2.100; optionally, 1.990≤x≤2.010.

[0008] In the above technical solution, the ratio of lithium to sulfur in the lithium sulfide powder has a certain deviation, but the deviation is very small. When used to prepare sulfide electrolyte, the ionic conductivity of the sulfide electrolyte is higher.

[0009] In some embodiments, the whiteness of lithium sulfide powder is 83%~85%, the oxygen content is ≤0.25% by mass, the carbon content is ≤0.17% by mass, and the metal impurity content is ≤0.1% by mass.

[0010] In the above technical solution, further controlling the content of oxygen and carbon impurities to be lower, and controlling the whiteness within this range, can further improve the purity of lithium sulfide powder, which is beneficial for preparing sulfide electrolytes with better ionic conductivity.

[0011] In some embodiments, the lithium sulfide powder has a Dv10 of 0.1 μm to 2 μm, a Dv50 of 2 μm to 6 μm, and a Dv90 of 9 μm to 15 μm.

[0012] In the above technical solution, the particle size distribution of lithium sulfide is within the above range, which is beneficial to control the (Dv90-Dv10) / Dv50 of lithium sulfide powder to be 3~5, so as to match the composition of high-purity lithium sulfide powder, thereby improving the ionic conductivity of the prepared sulfide electrolyte.

[0013] Secondly, this application provides a method for preparing lithium sulfide powder, comprising: S1, mixing a lithium source and a first carbon material using a first airflow crushing process, and then sintering the mixture under an inert atmosphere to form crude lithium sulfide, wherein the lithium source includes at least one of lithium sulfate, lithium sulfite, and lithium thiosulfate, and the temperature of the first sintering is lower than the melting point of the lithium source; S2, mixing the crude lithium sulfide, a second carbon material, and sulfur powder, and then sintering the mixture under an inert atmosphere to form lithium sulfide material; subjecting the lithium sulfide material to a second airflow crushing and sieving process, and collecting the undersize material to obtain lithium sulfide powder.

[0014] In the above technical solution, after the first sintering, carbon materials and sulfur powder are added for a second sintering, which can convert impurities (lithium carbonate and lithium oxide) in the crude product into lithium sulfide, resulting in higher purity and lower impurity content in the obtained lithium sulfide powder. Furthermore, before the first sintering, the lithium source and the first carbon material are mixed by airflow crushing, which increases the mixing uniformity and contact between the carbon material and the lithium source, allowing for a more complete subsequent reaction. The temperature of the first sintering is controlled to be lower than the melting point of the lithium source, so as to maintain the morphology of the lithium sulfide after sintering and control the particle size. During the second sintering, sulfur first transforms into a molten state, coating and binding the raw materials, preventing further growth of lithium sulfide particles. After the second sintering, airflow crushing and sieving are performed, ultimately controlling the particle size distribution (Dv90-Dv10) / Dv50 of the lithium sulfide powder within the range of 3-5. This results in a sulfide electrolyte prepared from this powder with higher ionic conductivity and lower electronic conductivity, thereby improving the rate performance and cycle performance of solid-state batteries. Furthermore, this method eliminates the need for washing and requires raw materials of high purity, enabling large-scale industrial production and reducing preparation costs.

[0015] In some embodiments, the conditions for the first airflow crushing in step S1 include: performing the process using an airflow mill at a pressure of 0.5 MPa to 0.7 MPa for 20 to 40 minutes. By performing airflow crushing and mixing of the lithium sulfide powder under the above conditions, the mixing of the first carbon material and the lithium source can be more uniform and the contact more sufficient, so that fewer impurities are generated during the first sintering, thereby ultimately improving the purity of the lithium sulfide powder.

[0016] In some embodiments, the conditions for the second airflow crushing in step S2 include: 10 to 20 minutes of airflow milling at a pressure of 0.3 MPa to 0.5 MPa. In step S2, the sieve used for screening is 200 to 400 mesh. By performing airflow crushing and screening under the above conditions, in conjunction with the aforementioned first airflow crushing, primary sintering, and secondary sintering, it is easier to control the particle size distribution (Dv90-Dv10) / Dv50 of the lithium sulfide powder within the range of 3 to 5.

[0017] In some embodiments, the conditions for a single sintering in step S1 include: a sintering temperature of 700°C to 800°C, a sintering time of 1 h to 5 h, and a first flow rate of inert gas of 1 L / min to 5 L / min.

[0018] In the above technical solution, controlling the sintering within this temperature and time range in one sintering stage is beneficial for allowing the lithium source (at least one of lithium sulfate, lithium sulfite, and lithium thiosulfate) to react fully with the carbon material, so as to maintain the morphology of lithium sulfide after sintering and facilitate subsequent particle size control; in addition, controlling the flow rate of the inert atmosphere within this range is beneficial for carrying out the reaction product carbon dioxide, so as to reduce the content of impurity lithium carbonate in the crude lithium sulfide product.

[0019] In some embodiments, the conditions for secondary sintering in step S2 include: a sintering temperature of 800℃~1000℃ and a sintering time of 1h~4h.

[0020] In the above technical solution, the secondary sintering is controlled within the temperature and time range, which allows sulfur to react with the second carbon material to obtain carbon disulfide, and allows carbon disulfide to react with lithium carbonate and lithium oxide, thereby reducing impurities in the lithium sulfide material and making it more pure.

[0021] In some embodiments, in step S2, the mass percentage of the second carbon material is 0.1% to 5% of the crude lithium sulfide mass, and the mass percentage of the sulfur powder is 0.6% to 40% of the crude lithium sulfide mass.

[0022] In the above technical solution, the addition amounts of the second carbon material and sulfur powder are within the above ranges, which can make the reaction of lithium carbonate and lithium oxide in the crude lithium sulfide more complete, resulting in lithium sulfide material with higher purity.

[0023] In some embodiments, in step S2, the material for secondary sintering is a material that is mixed with crude lithium sulfide, a second carbon material, and sulfur powder and then pressed into sheets.

[0024] In the above technical solution, the material for secondary sintering is a mixture after tableting (a mixture of crude lithium sulfide, second carbon material, and sulfur powder). After tableting, the second carbon material, crude lithium sulfide, and sulfur powder can be in closer contact, which is conducive to the more complete reaction between the generated carbon disulfide and the impurities in the crude lithium sulfide. This results in higher purity of the lithium sulfide material, lower carbon content, oxygen content, and metal impurity content, and also higher whiteness.

[0025] In some embodiments, in step S1, the first carbon material includes inorganic carbon and / or inorganic carbon carbon carbonized from an organic carbon source.

[0026] In the above technical solutions, either inorganic carbon is added directly, or an organic carbon source is added, and the inorganic carbon formed after carbonization can be used as the material of this application for the preparation of crude lithium sulfide.

[0027] In some embodiments, the first carbon material comprises inorganic carbon carbonized from an organic carbon source. Before step S1, the method further includes: mixing a lithium source with an organic carbon source and carbonizing the organic carbon source in an inert atmosphere to carbonize the organic carbon source into inorganic carbon.

[0028] In the above technical solution, using organic carbon source to form inorganic carbon after carbonization as the first carbon material can make the distribution of lithium source (lithium sulfate and / or lithium sulfite) and first carbon material more uniform. After carbonization, crushing and mixing are carried out, followed by a first sintering, which is beneficial to control the particle size distribution of lithium sulfide. Combined with subsequent secondary sintering, second airflow crushing and screening, it is beneficial to obtain lithium sulfide powder with high purity and particle size distribution within a certain range.

[0029] In some embodiments, the carbonization temperature is 250°C to 350°C, the carbonization time is 3h to 5h, and the second flow rate of the inert gas is 0.5 L / min to 2L / min.

[0030] In the above technical solution, the carbonization temperature, time, and inert atmosphere flow rate are controlled within this range, which can make the carbonization of the organic carbon source more complete and the carbonization relatively slow, so that the distribution between the first carbon material and the lithium source is more uniform, which is beneficial to the subsequent preparation of lithium sulfide.

[0031] Thirdly, this application provides a method for preparing a sulfide electrolyte, which involves mixing lithium halide, phosphorus pentasulfide, and lithium sulfide powder provided in the first or second aspect, pressing the mixture into tablets, and then calcining it.

[0032] Lithium sulfide solid electrolyte is prepared by pressing high-purity lithium sulfide powder with a particle size distribution within a certain range into tablets and then calcining it. During tableting, small particles can effectively fill the gaps between large particles, and medium-sized particles can further fill the remaining gaps, thus forming a close packing. This results in the calcined sulfide electrolyte having higher ionic conductivity and lower electronic conductivity, thereby improving the rate performance and cycle performance of solid-state batteries.

[0033] Fourthly, this application provides a sulfide electrolyte with an ionic conductivity of 10 mS / cm to 12 mS / cm and an electronic conductivity of 1×10⁻⁶ mS / cm. -9 S / cm ~2×10 -9 S / cm.

[0034] Fifthly, this application provides a solid-state battery, including the sulfide electrolyte provided in the third aspect. Attached Figure Description

[0035] Figure 1 The X-ray diffraction pattern of the lithium sulfide powder provided in Example 1 of this application is shown.

[0036] Figure 2 The X-ray diffraction pattern of lithium sulfide powder provided in Comparative Example 1 of this application.

[0037] Figure 3 XPS images of lithium sulfide powder provided in Example 1 and Comparative Example 2 of this application. Detailed Implementation

[0038] The following detailed description, with appropriate reference to the accompanying drawings, discloses the lithium sulfide powder and its preparation method, the sulfide electrolyte and its preparation method, and embodiments of the solid-state battery of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0039] The "scope" disclosed in this application is defined by a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude endpoints, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope. It should be noted that "and / or" in this application, such as "feature 1 and / or feature 2," refers to three possibilities: feature 1 alone, feature 2 alone, or feature 1 plus feature 2.

[0040] In addition, in the description of this application, unless otherwise stated, "one or more" means two or more; the range of "numerical value a to numerical value b" includes the two endpoints "a" and "b"; and "unit of measurement" in "numerical value a to numerical value b + unit of measurement" represents the "unit of measurement" of both "numerical value a" and "numerical value b".

[0041] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions. Unless otherwise specified, all technical features and optional technical features of this application can be combined to form new technical solutions. Unless otherwise specified, all steps of this application can be performed sequentially or randomly, preferably sequentially.

[0042] In existing technologies, lithium sulfide is typically prepared via carbon reduction. Specifically, lithium sulfate (Li₂SO₄) reacts with carbon materials (Li₂SO₄ + 2C = Li₂S + 2CO₂). The raw materials are non-toxic and harmless, and the equipment is compatible with existing conventional sintering equipment, requiring no modification. However, due to inherent limitations, the traditional carbothermal reduction reaction results in the presence of small amounts of lithium carbonate and lithium oxide impurities in the produced lithium sulfide, which are difficult to remove. Using conventional organic solvents for purification requires additional distillation equipment, significantly increasing the cost of solvent use and recovery, which is uneconomical. More importantly, the use of solvents leads to a substantial increase in the solvent content in the material, necessitating additional sintering for removal. Furthermore, this process introduces oxygen elements, generating oxygen-containing impurities, further affecting its performance and subsequent use.

[0043] In the existing technology, although some lithium sulfide powders have high purity, their particle size distribution is concentrated and the particle size is relatively uniform. When used to prepare sulfide electrolytes, the cycle performance and rate performance of the battery are still not good.

[0044] Therefore, this application provides a lithium sulfide powder that meets the following requirements: purity ≥ 99.5%, whiteness ≥ 83%, oxygen content ≤ 0.3% by mass, carbon content ≤ 0.2% by mass, and metal impurity content ≤ 0.1% by mass. The ratio of (Dv90-Dv10) / Dv50 of the lithium sulfide powder is 3~5. This lithium sulfide powder has high purity and whiteness, and fewer impurities. Combined with (Dv90-Dv10) / Dv50 = 3~5, the high-purity powder allows for effective filling of the gaps between large particles and further filling of the remaining gaps during the pressing and calcination of the sulfide electrolyte, resulting in a dense packing. This leads to a higher ionic conductivity and lower electronic conductivity in the sintered sulfide electrolyte, thereby improving the rate performance and cycle performance of solid-state batteries.

[0045] As an example, the purity of the lithium sulfide powder is 99.5%, 99.6%, 99.7%, 99.8%, 99.9%, or 100%, and any value within any two adjacent ranges. The whiteness is 83%, 84%, 85%, 86%, 87%, 88%, 89%, or 90%, and any value within any two adjacent ranges. The oxygen content is 0%, 0.01%, 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, or 0.3%, and any value within any two adjacent ranges. The carbon content is 0%, 0.01%, 0.05%, 0.1%, 0.15%, or 0.2%, and any value within any two adjacent ranges. The metal impurity content is 0%, 0.01%, 0.03%, 0.05%, 0.07%, or 0.1%, and any value within any two adjacent ranges. Optionally, the lithium sulfide powder has a whiteness of 83%~85%, an oxygen content of ≤0.25% by mass, a carbon content of ≤0.17% by mass, and a metal impurity content of ≤0.1% by mass. The (Dv90-Dv10) / Dv50 value of the lithium sulfide powder is 3, 3.5, 4, 4.5 or 5, or any value within two adjacent value ranges.

[0046] In some embodiments, the chemical formula of lithium sulfide powder is Li x S, 1.900≤x≤2.100; optionally, 1.990≤x≤2.010. In this lithium sulfide powder, the ratio of lithium to sulfur elements has a certain deviation, but the deviation is very small. When used to prepare sulfide electrolytes, the ionic conductivity of the sulfide electrolytes is higher.

[0047] In this application, the lithium sulfide powder has a Dv10 of 0.1 μm to 2 μm, a Dv50 of 2 μm to 6 μm, and a Dv90 of 9 μm to 15 μm. The particle size distribution of lithium sulfide within these ranges facilitates control of the (Dv90-Dv10) / Dv50 ratio of the lithium sulfide powder to 3 to 5, allowing for better compatibility with the components of high-purity lithium sulfide powder and thus improving the ionic conductivity of the prepared sulfide electrolyte.

[0048] As an example, the Dv10 of the lithium sulfide powder is 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, or 2 μm, or any value within two adjacent ranges; the Dv50 is 2 μm, 3 μm, 4 μm, 5 μm, or 6 μm, or any value within two adjacent ranges; and the Dv90 is 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm, or any value within two adjacent ranges. Furthermore, the particle size selection described above can result in (Dv90-Dv10) / Dv50 = 3~5.

[0049] In this application, the aforementioned lithium sulfide powder can be used to prepare sulfide electrolytes. Specifically, lithium halide, phosphorus pentasulfide, and lithium sulfide powder are mixed, pressed into tablets, and then calcined. By using high-purity lithium sulfide powder with a particle size distribution within a certain range for tableting and calcination, a lithium sulfide solid electrolyte is prepared. During tableting, small particles can effectively fill the gaps between large particles, and medium-sized particles can further fill the remaining gaps, thereby forming a close packing. This results in a sulfide electrolyte with high ionic conductivity and low electronic conductivity after calcination, which can improve the rate performance and cycle performance of solid-state batteries.

[0050] Optionally, lithium halide, phosphorus pentasulfide, and lithium sulfide are mixed in a molar ratio of (2~3):1:(4~5), and uniformly mixed using a mortar and pestle for 0.5h~2h; then the material is transferred to a ball mill jar for high-energy ball milling for 4h~8h. Finally, the mixed electrolyte powder is pressed into tablets, then calcined at 500℃~600℃ for 1h~3h, and crushed and granulated to obtain sulfide solid electrolyte powder. The lithium halide can be lithium chloride or / and lithium bromide. For example, lithium chloride, phosphorus pentasulfide, and lithium sulfide are mixed in a molar ratio of 4:1:3, and sintered to obtain Li5.5PS4.5Cl1.5 electrolyte material; lithium chloride, phosphorus pentasulfide, and lithium sulfide are mixed in a molar ratio of 5:1:2, and sintered to obtain Li6PS5Cl electrolyte material.

[0051] The sulfide electrolytes prepared by this method exhibited ionic conductivity of 10 mS / cm to 12 mS / cm and electronic conductivity of 1 × 10⁻⁶ mS / cm. -9 S / cm ~2×10 -9 S / cm. This sulfide electrolyte has high ionic conductivity and low electronic conductivity, which can improve the rate performance and cycle performance of solid-state batteries.

[0052] The aforementioned sulfide electrolyte powder can be pressed into sheets to prepare sulfide electrolyte membranes, which can then be combined with negative and positive electrode sheets to prepare solid-state batteries.

[0053] Having introduced lithium sulfide powder above, the preparation method of lithium sulfide powder will be introduced below.

[0054] This application provides a method for preparing lithium sulfide, which can improve the purity of lithium sulfide without the need for solvent purification. Furthermore, by controlling the preparation process, this application ensures that the particle size distribution of the obtained lithium sulfide is within a certain range, thereby enabling the sulfide electrolyte prepared from this material to have higher ionic conductivity and lower electronic conductivity, thus improving the rate performance and cycle performance of solid-state batteries.

[0055] This application provides a method for preparing lithium sulfide powder, comprising: S1. The lithium source and the first carbon material are mixed by first airflow crushing and sintering under an inert atmosphere to form crude lithium sulfide. The lithium source includes at least one of lithium sulfate, lithium sulfite and lithium thiosulfate. The temperature of the first sintering is lower than the melting point of the lithium source.

[0056] S2. After mixing the crude lithium sulfide with the second carbon material and sulfur powder, the mixture is sintered again under an inert atmosphere to form lithium sulfide material. The lithium sulfide material is then subjected to second airflow crushing and sieving, and the undersize material is taken to obtain lithium sulfide powder.

[0057] In the above technical solution, after the first sintering, carbon materials and sulfur powder are added for a second sintering, which can convert impurities (lithium carbonate and lithium oxide) in the crude product into lithium sulfide, resulting in higher purity and lower impurity content in the obtained lithium sulfide powder. Furthermore, before the first sintering, the lithium source and the first carbon material are mixed by airflow crushing, which increases the mixing uniformity and contact between the carbon material and the lithium source, allowing for a more complete subsequent reaction. The temperature of the first sintering is controlled to be lower than the melting point of the lithium source, so as to maintain the morphology of the lithium sulfide after sintering and control the particle size. During the second sintering, sulfur first transforms into a molten state, coating and binding the raw materials, preventing further growth of lithium sulfide particles. After the second sintering, airflow crushing and sieving are performed, ultimately controlling the particle size distribution (Dv90-Dv10) / Dv50 of the lithium sulfide powder within the range of 3-5. This results in a sulfide electrolyte prepared from this powder with higher ionic conductivity and lower electronic conductivity, thereby improving the rate performance and cycle performance of solid-state batteries. Furthermore, this method eliminates the need for washing and requires raw materials of high purity, enabling large-scale industrial production and reducing preparation costs.

[0058] In S1, in addition to adding at least one of lithium sulfate, lithium sulfite, and lithium thiosulfate, a small amount of lithium carbonate and / or lithium hydroxide may be added to supplement the lithium source. Among these, lithium sulfate, lithium sulfite, lithium thiosulfate, and lithium carbonate are preferably anhydrous lithium sulfate, anhydrous lithium sulfite, anhydrous lithium thiosulfate, and anhydrous lithium carbonate; in other embodiments, hydrates may also be used.

[0059] When the first carbon material is added, the molar ratio of Li to C in the lithium source and the first carbon material is 1:1 to 1:1.25; for example, the molar ratio of Li to C is 1:1, 1:1.05, 1:1.1, 1:1.15 or 1:1.2, and any value in any two adjacent numerical ranges.

[0060] In some embodiments, the conditions for the first sintering in step S1 include: a sintering temperature of 700°C to 800°C, a sintering time of 1 h to 5 h, and a first flow rate of inert gas of 1 L / min to 5 L / min. Controlling the first sintering within this temperature and time range is beneficial for allowing the lithium source (at least one of lithium sulfate, lithium sulfite, and lithium thiosulfate) to react fully with the carbon material, thus maintaining the morphology of lithium sulfide after sintering and facilitating subsequent particle size control. Furthermore, controlling the inert atmosphere flow rate within this range helps to carry away the reaction product carbon dioxide, resulting in a lower content of lithium carbonate impurities in the crude lithium sulfide product.

[0061] As an example, the sintering temperature for a single sintering is 700℃, 720℃, 740℃, 760℃, 780℃, or 800℃, and any value within two adjacent ranges; the sintering time for a single sintering is 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, or 5h, and any value within two adjacent ranges; the first flow rate of the inert gas is 1 L / min, 1.5 L / min, 2 L / min, 2.5 L / min, 3 L / min, 3.5 L / min, 4 L / min, 4.5 L / min, or 5 L / min, and any value within two adjacent ranges. Optionally, the conditions for a single sintering include: a sintering temperature of 750℃~800℃, a heating rate of 5℃ / min~10℃ / min, a sintering time of 1h~3h, and a first flow rate of the inert gas of 2 L / min~3 L / min.

[0062] The inert atmosphere can be at least one of nitrogen, argon, helium, and neon. The equipment for primary sintering can be a tube furnace or a rotary furnace.

[0063] In this application, the first carbon material can be either directly added inorganic carbon or prepared by carbonizing an organic carbon source into inorganic carbon, which will be explained below.

[0064] In some embodiments, the first carbon material is inorganic carbon directly added, and the method for preparing crude lithium sulfide includes: mixing a lithium source with the first carbon material (inorganic carbon) using a first air jet mill, and then sintering it once under an inert atmosphere (sintering temperature of 700℃~800℃, sintering time of 1h~5h, and first flow rate of inert gas of 1 L / min~5L / min) to form crude lithium sulfide. Optionally, the conditions for the first air jet milling include: 20min~40min under a pressure of 0.5MPa~0.7MPa using an air jet mill.

[0065] In this application, inorganic carbon can be one or more of the following: multi-walled carbon nanotubes, single-walled carbon nanotubes, graphene, activated carbon, biochar, carbon black, hard carbon, soft carbon, amorphous carbon, Super-P, and carbon fiber.

[0066] In another embodiment, the first carbon material is prepared by carbonizing an organic carbon source into inorganic carbon. Before step S1, the method further includes: mixing a lithium source with an organic carbon source, carbonizing the organic carbon source into inorganic carbon in an inert atmosphere; then performing a first gas flow crushing and mixing, and sintering once in an inert atmosphere (sintering temperature of 700℃~800℃, sintering time of 1h~5h, and first flow rate of inert gas of 1 L / min~5L / min) to form crude lithium sulfide. Optionally, the conditions for the first gas flow crushing include: performing the process by an airflow mill at a pressure of 0.5Mpa~0.7Mpa for 20min~40min.

[0067] In the above technical solution, using inorganic carbon formed by carbonization of organic carbon source as the first carbon material can make the distribution of lithium source (lithium sulfate and / or lithium sulfite) and first carbon material more uniform. Furthermore, crushing and mixing after carbonization can make the mixing of first carbon material and lithium source more uniform and the contact more sufficient. Then, a first sintering is performed, which is beneficial to the subsequent control of lithium sulfide particle size distribution. Combined with the subsequent second sintering, it is beneficial to obtain lithium sulfide powder with high purity and particle size distribution within a certain range.

[0068] Optionally, the carbonization temperature is 250℃~350℃, the carbonization time is 3h~5h, and the second flow rate of the inert gas is 0.5 L / min~2L / min.

[0069] As an example, the carbonization temperature is 250°C, 270°C, 290°C, 310°C, 330°C, or 350°C, and any value within two adjacent numerical ranges; the carbonization time is 3h, 3.5h, 4h, 4.5h, or 5h, and any value within two adjacent numerical ranges; and the second flow rate of the inert gas is 0.5 L / min, 1 L / min, 1.5 L / min, or 2 L / min, and any value within two adjacent numerical ranges. Optionally, the carbonization conditions include: a carbonization temperature of 270°C to 330°C, a heating rate of 5°C / min to 10°C / min, a sintering time of 3h to 5h, and a second flow rate of the inert gas of 0.5 L / min to 1 L / min.

[0070] Optionally, the second flow rate is lower than the first flow rate. The lower first flow rate can better maintain the inert atmosphere environment in the atmosphere furnace, so as to avoid carbon loss to a certain extent, and also make the atmosphere flow rate relatively low. The higher second flow rate can make the carbon dioxide (Li2SO4+2C=Li2S+2CO2) generated in the process of preparing lithium sulfide be carried out in time, reducing the generation of impurities.

[0071] In this application, a lithium source and an organic carbon source are dissolved in water (preferably deionized water) and stirred magnetically or mechanically for 6 to 24 hours. The mixture is then spray-dried or the solvent is evaporated to obtain a precursor. This precursor is then ground in a mortar to obtain a fine product. The precursor is carbonized in an inert atmosphere to convert the organic carbon source into inorganic carbon. A first airflow mixing process is then performed (using an airflow mill at a pressure of 0.5 MPa to 0.7 MPa for 20 to 40 minutes), followed by a first sintering process in an inert atmosphere (sintering temperature of 700°C to 800°C, sintering time of 1 to 5 hours, and a first inert gas flow rate of 1 L / min to 5 L / min) to form crude lithium sulfide.

[0072] As an example, the pressure of the first air jet milling is 0.5 MPa, 0.55 MPa, 0.6 MPa, 0.65 MPa, or 0.7 MPa, or any value within two adjacent ranges. The time for the first air jet milling is 20 min, 25 min, 30 min, 35 min, or 40 min, or any value within two adjacent ranges.

[0073] In some embodiments, the conditions for secondary sintering in step S2 include: a sintering temperature of 800℃~1000℃ and a sintering time of 1h~4h. Controlling the secondary sintering within this temperature and time range allows sulfur to react with the second carbon material to obtain carbon disulfide, and allows carbon disulfide to react with lithium carbonate and lithium oxide, thereby reducing impurities in the lithium sulfide material and increasing its purity.

[0074] As an example, the sintering temperature for secondary sintering is 800℃, 850℃, 900℃, 950℃, or 1000℃, or any value within two adjacent ranges; the sintering time for secondary sintering is 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, or 4h, or any value within two adjacent ranges. Optionally, the conditions for secondary sintering include: a sintering temperature of 850℃~950℃, a heating rate of 10℃ / min~15℃ / min, and a sintering time of 1h~3h.

[0075] In this application, during the secondary sintering in step S2, the mass percentage of the second carbon material is 0.1% to 5% of the crude lithium sulfide mass, and the mass percentage of sulfur powder is 0.6% to 40% of the crude lithium sulfide mass. The addition amounts of the second carbon material and sulfur powder are within the aforementioned ranges, which allows for a more complete reaction between lithium carbonate and lithium oxide in the crude lithium sulfide, resulting in a lithium sulfide material with higher purity.

[0076] As an example, the mass percentage of the second carbon material is 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5% of the crude lithium sulfide mass, and any value within two adjacent numerical ranges; the mass percentage of the sulfur powder is 0.6%, 1%, 5%, 10%, 20%, 25%, 30%, 35%, or 40% of the crude lithium sulfide mass, and any value within two adjacent numerical ranges. Optionally, the mass percentage of the second carbon material is 1% to 5% of the crude lithium sulfide mass, and the mass percentage of the sulfur powder is 10% to 40% of the crude lithium sulfide mass.

[0077] Optionally, the second carbon material can be at least one of natural graphite powder, artificial graphite powder, lignin-based hard carbon, pitch-based hard carbon anode, and multi-walled carbon nanotubes; the sulfur powder can be sublimated sulfur powder.

[0078] In this application, the second carbon material, crude lithium sulfide, and sublimed sulfur powder can be ground and mixed first, then pressed into sheets, and then sintered in a covered crucible. The material for secondary sintering is the mixture after pressing. Pressing allows the second carbon material, crude lithium sulfide, and sulfur powder to come into closer contact, which is beneficial for the reaction between the generated carbon disulfide and impurities in the crude lithium sulfide to be more complete. This results in higher purity of the lithium sulfide material, lower carbon content, oxygen content, and metal impurity content, and higher whiteness.

[0079] After the second sintering, a second airflow pulverization and sieving process is performed. The conditions for the second airflow pulverization include: pulverizing in an airflow mill at a pressure of 0.3 MPa to 0.5 MPa for 10 to 20 minutes. The sieving screen is 200 mesh to 400 mesh. By performing airflow pulverization and sieving under the above conditions, in conjunction with the first airflow pulverization, primary sintering, and secondary sintering, it is easier to control the particle size distribution (Dv90-Dv10) / Dv50 of the lithium sulfide powder within the range of 3 to 5.

[0080] As an example, the pressure of the second airflow pulverization is 0.3 MPa, 0.35 MPa, 0.4 MPa, 0.45 MPa, or 0.5 MPa, or any value within two adjacent ranges. The pulverization time of the second airflow is 10 min, 13 min, 18 min, or 20 min.

[0081] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0082] Example 1 This embodiment provides a method for preparing lithium sulfide powder, including the following steps: (1) Raw material mixing: Weigh industrial grade anhydrous lithium sulfate and glucose with a molar ratio of Li to C of 1:1.1, dissolve them in 500 mL of deionized water, mechanically stir the solution at 120 °C to allow the water to gradually evaporate, and then grind and pulverize it using a mortar and pestle.

[0083] (2) Carbonization: The product of step (1) is placed in a nitrogen tube furnace at 250°C, and the air is evacuated and replenished three times to exhaust the air. The furnace is kept at a gas flow rate of 0.5 L / min for 2 hours to carbonize the glucose into inorganic carbon. After cooling, the product is taken out.

[0084] (3) Mixed reaction: The product of step (2) was placed in an air jet mill for first air jet crushing (pressure 0.5 MPa, time 40 min), and then placed in a nitrogen tube furnace with a flow rate of 3 L / min and a heating rate of 10 °C / min. After holding at 750 °C for 3 h, it was taken out to obtain crude lithium sulfide.

[0085] (4) The product of step (3), graphite powder (2% of the mass of crude lithium sulfide) and sublimed sulfur (30% of the mass of crude lithium sulfide) are mixed, ground and mixed thoroughly, pressed into tablets, and sintered at 900°C for 2 hours to obtain lithium sulfide material.

[0086] (5) Place the product from step (4) into an air jet mill for a second air jet milling (pressure 0.4 MPa, time 15 min), and then sieve it (sieve mesh number 400 mesh) to obtain lithium sulfide powder.

[0087] Example 2 This embodiment provides a method for preparing lithium sulfide powder, including the following steps: (1) Weigh industrial grade anhydrous lithium sulfate and glucose in a molar ratio of Li to C of 1:1.1, dissolve them in 500 mL of deionized water, mechanically stir the solution at 120 °C to allow the water to gradually evaporate, and then grind them into powder using a mortar and pestle.

[0088] (2) Place the product of step (1) in a nitrogen tube furnace at 300℃, remove and replenish the air three times to exhaust the air, keep it at a gas flow rate of 0.5L / min for 1h to carbonize the glucose into inorganic carbon, and take it out after cooling.

[0089] (3) The product of step (2) is placed in an air jet mill for first air jet crushing (pressure is 0.6 MPa, time is 30 min), and then placed in a nitrogen tube furnace with a flow rate of 3 L / min and a heating rate of 10 °C / min. After being kept at 800 °C for 2 h, it is taken out to obtain crude lithium sulfide.

[0090] (4) The product of step (3), graphite powder (2% of the mass of crude lithium sulfide) and sublimed sulfur (30% of the mass of crude lithium sulfide) are mixed, ground and mixed thoroughly, pressed into tablets, and sintered at 900°C for 2 hours to obtain lithium sulfide material.

[0091] (5) Place the product from step (4) into an air jet mill for a second air jet milling process (pressure 0.5 MPa, time 10 min), and then sieve it (sieve mesh number 200 mesh). Take the sieve material to obtain lithium sulfide powder.

[0092] Example 3 This embodiment provides a method for preparing lithium sulfide powder, including the following steps: (1) Weigh industrial grade anhydrous lithium sulfate and glucose in a molar ratio of Li to C of 1:1.2, dissolve them in 500 mL of deionized water, spray dry to obtain a mixture, and then grind and pulverize it using a mortar and pestle.

[0093] (2) Place the product of step (1) in a nitrogen tube furnace at 300℃, remove and replenish the air three times to exhaust the air, keep it at a gas flow rate of 0.5 mL / min for 2 hours to carbonize the glucose into inorganic carbon, and take it out after cooling.

[0094] (3) The product of step (2) is placed in an air jet mill for first air jet crushing (pressure 0.7 MPa, time 20 min), and then placed in a nitrogen tube furnace with a flow rate of 3 L / min and a heating rate of 10 °C / min. After holding at 750 °C for 3 h, it is taken out to obtain crude lithium sulfide.

[0095] (4) The product of step (3), graphite powder (5% of the mass of crude lithium sulfide) and sublimed sulfur (40% of the mass of crude lithium sulfide) are mixed, ground and mixed thoroughly, pressed into tablets, and sintered at 900°C for 2 hours to obtain lithium sulfide material.

[0096] (5) The product of step (4) is placed in an air jet mill for a second air jet milling (pressure is 0.3 MPa, time is 20 min), and then sieved (sieve mesh is 325 mesh) and the sieved material is taken to obtain lithium sulfide powder.

[0097] Example 4 Example 4 is basically the same as Example 1, except that: (1)-(3) Weigh industrial-grade anhydrous lithium sulfate and industrial-grade activated carbon with a molar ratio of Li to C of 1:1.1. Place the industrial-grade anhydrous lithium sulfate and industrial-grade activated carbon in an air jet crusher for the first air jet crushing (pressure of 0.5 MPa, time of 40 min). Then place them in a nitrogen tube furnace with a flow rate of 3 L / min and a heating rate of 10 °C / min. After holding at 750 °C for 3 h, take them out to obtain crude lithium sulfide.

[0098] Example 5 Example 5 is basically the same as Example 1, except that: The nitrogen flow rate in both steps (2) and (3) is 1 L / min.

[0099] Example 6 Example 6 is basically the same as Example 1, except that: Step (4) Add 2% graphite powder and 30% sublimed sulfur of the crude lithium sulfide product, and mix with the crude lithium sulfide product. After thorough grinding and mixing, sinter at 900℃ for 2 hours to obtain lithium sulfide material.

[0100] Example 7 Example 7 is basically the same as Example 1, except that: In step (3), the pressure of the first airflow breakup is 0.45 MPa and the time is 30 min.

[0101] Example 8 Example 8 is basically the same as Example 1, except that: In step (3), the pressure of the first airflow breakup is 0.75 MPa and the time is 30 min.

[0102] Example 9 Example 9 is basically the same as Example 1, except that: In step (5), the pressure of the second airflow breakup is 0.25 MPa and the time is 30 min.

[0103] Example 10 Example 10 is basically the same as Example 1, except that: In step (5), the pressure of the second airflow breakup is 0.55 MPa and the time is 30 min.

[0104] Example 11 Example 11 is basically the same as Example 1, except that: In step (3), the temperature is maintained at 650℃ for 3 hours.

[0105] Example 12 Example 12 is basically the same as Example 1, except that: In step (3), the temperature is maintained at 850℃ for 3 hours.

[0106] Example 13 Example 13 is basically the same as Example 1, except that: In step (4), sintering is carried out at 750℃ for 2 hours.

[0107] Example 14 Example 14 is basically the same as Example 1, except that: In step (3), the temperature is kept at 1050℃ for 2 hours.

[0108] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that step (4) was not performed.

[0109] Comparative Example 2 Commercially available lithium sulfide powder (Aladdin lithium sulfide, product number L299275).

[0110] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that, (3) Mixing reaction: The product of step (2) is placed in a ball mill for ball milling (the grinding atmosphere is an inert atmosphere, the ball-to-material ratio is 10:1, the rotation speed is 400 rpm, and the time is 60 min). Then it is placed in a nitrogen tube furnace with a flow rate of 3 L / min and a heating rate of 10 °C / min. After holding at 750 °C for 3 h, it is taken out to obtain crude lithium sulfide.

[0111] Comparative Example 4 Comparative Example 4 is basically the same as Example 1, except that graphite powder is not added in step (4).

[0112] Comparative Example 5 Comparative Example 5 is basically the same as Example 1, except that, (5) Place the product from step (4) into a ball mill for ball milling (the grinding atmosphere is an inert atmosphere, the ball-to-material ratio is 10:1, the rotation speed is 400 rpm, and the time is 60 min), and then sieve it (the mesh size of the sieve is 400 mesh), and take the sieve material to obtain lithium sulfide powder.

[0113] Comparative Example 6 Comparative Example 6 is basically the same as Example 1, except that, (3) Mixed reaction: The product of step (2) was placed in an air jet mill for first air jet crushing (pressure 0.5 MPa, time 40 min), and then placed in a nitrogen tube furnace with a flow rate of 3 L / min and a heating rate of 10 °C / min. After holding at 900 °C for 3 h, it was taken out to obtain crude lithium sulfide.

[0114] Figure 1 The X-ray diffraction pattern of the lithium sulfide powder provided in Example 1 of this application is shown below. Figure 1 It can be seen that the lithium sulfide powder provided in Example 1 of this application has the same crystal form as the standard lithium sulfide powder, indicating that this application has prepared high-purity lithium sulfide powder.

[0115] Figure 2 The X-ray diffraction pattern of the lithium sulfide powder provided in Comparative Example 1 of this application is shown below. Figure 2 It can be seen that the lithium sulfide powder provided in Comparative Example 1 of this application has impurities, indicating that the purity of the lithium sulfide powder provided in Comparative Example 1 of this application is low.

[0116] Figure 3 XPS images of lithium sulfide powder provided in Example 1 and Comparative Example 2 of this application, from Figure 3 It can be seen that the XPS binding energy of the Li element in the lithium sulfide powder provided in this application has shifted, indicating that the chemical environment of the lithium atom has changed. This is due to the change in the ratio of lithium to sulfur. Combined with the subsequent lithium-sulfur ratio test, it can be determined that the chemical formula of the lithium sulfide powder provided in Example 1 of this application is Li. 1.994 S.

[0117] Lithium sulfide powders from Examples 1-6 and Comparative Examples 1-4 were used to prepare sulfide electrolytes, and the specific preparation methods are as follows: LiCl, P2S5, and the Li2S material prepared above were mixed in a molar ratio of 3:1:4 and uniformly mixed in a grinding jar for 0.5 h. The mixture was then transferred to a ball mill and ball-milled for 4 h (inert atmosphere, ball-to-material ratio of 10:1, rotation speed of 600 rpm, and time of 60 min). Finally, the mixed electrolyte powder was calcined at 500℃ for 2 h, and then crushed and granulated to obtain the sulfide electrolyte.

[0118] The lithium sulfide powder and sulfide electrolyte were tested separately, and the results are shown in Tables 1 and 2. The testing methods are as follows: (1) Whiteness of lithium sulfide powder: a. Sample preparation: In an argon-filled glove box, press lithium sulfide powder into discs (pressure 8t, pressing time 3min). b. Instrument calibration: In the glove box, calibrate the benchtop spectrophotometer using a standard white plate. c. Measurement: Place the pressed lithium sulfide discs onto the instrument's measuring aperture. Adjust the measuring aperture to ensure complete coverage of the measured area. Select the light source (D65, simulated sunlight) and the observer's viewing angle (10° angle with the vertical direction). Start the measurement; the instrument will automatically record the spectral reflectance data. d. Data calculation and expression: Based on the spectral data, calculate the whiteness value of the lithium sulfide powder according to the Hunter whiteness formula.

[0119] (2) Oxygen content of lithium sulfide powder: The inert gas melting-infrared absorption method was used for testing. In a glove box filled with argon, lithium sulfide powder was made into a sample capsule with high-purity nickel and sealed tightly. Then it was transferred to the instrument and melted at high temperature by heating the graphite crucible with a pulse furnace. The oxygen element was converted into CO2 by reacting with carbon. Then the CO2 content was accurately measured by an infrared detector, and the oxygen content was calculated.

[0120] (3) Carbon content of lithium sulfide powder: The high-frequency combustion-infrared absorption method was used for testing. In a glove box filled with argon, lithium sulfide powder was made into a sample capsule with high-purity nickel and sealed tightly. Then it was transferred to the instrument and heated in the high-frequency furnace to burn in the oxygen flow. The carbon element was converted and oxidized into CO2 gas. Then the CO2 content was accurately determined by the infrared detector, and the carbon content was calculated.

[0121] (4) Content of metal impurities: According to the test standards of EPA 6010D-2018 and JY / T 0567-2020, aqua regia was used as the digesting agent and the lithium sulfide powder was digested under high temperature and high pressure using microwave digestion method. The content of each metal impurity element was tested by inductively coupled plasma-atomic emission spectrometry (ICP-AES) to obtain the total content of metal impurity elements.

[0122] (5) Purity of lithium sulfide powder: According to the testing standards of EPA 6010D-2018 and JY / T 0567-2020, aqua regia was used as the digesting agent, and the lithium sulfide powder was digested under high temperature and high pressure using microwave digestion. The sulfur content was tested by inductively coupled plasma-atomic emission spectrometry (ICP-AES) to obtain the mass of lithium sulfide. Then, the purity of lithium sulfide powder was obtained by dividing this mass by the mass of the sample.

[0123] (6) Value of (Dv90-Dv10) / Dv50: Refer to GB / T19077-2016, use an instrument for particle size distribution laser diffraction (such as Bettersize2600 laser particle size analyzer from Dandong Better Instrument Co., Ltd.) to measure the particle size distribution, obtain the values ​​of Dv10, Dv50 and Dv90 respectively, and calculate the value of (Dv90-Dv10) / Dv50.

[0124] (7) Lithium-sulfur molar ratio: According to the EPA 6010D-2018 and JY / T 0567-2020 test standards, aqua regia was used as the digesting agent, and lithium sulfide powder was digested under high temperature and high pressure using microwave digestion method. The lithium and sulfur content was tested by inductively coupled plasma-atomic emission spectrometry (ICP-AES) and the lithium-sulfur molar ratio was calculated.

[0125] (8) Ionic conductivity test: 0.215g of sulfide electrolyte was placed in a φ10cm battery mold and pressed for 10min under 4T pressure to form an electrolyte sheet. Carbon-coated aluminum foil was placed on two layers of the electrolyte sheet, pressed for 2T, and held for 30s. After assembling the mold, the mold was placed at 30℃ for 2h and then the impedance test was performed to calculate the ionic conductivity.

[0126] (9) Electronic conductivity test: The assembled mold battery in (8) is subjected to a constant potential current test at a voltage of 0.05V; the test duration is 1500s, and the average value of the data in the last 100s is taken as the steady-state current to calculate the electronic conductivity.

[0127] (10) Solid-state battery performance testing: (10.1) Fabrication of solid-state batteries: Preparation of the electrolyte layer: The sulfide electrolytes provided in the aforementioned examples and comparative examples were used to compress the powder into tablets to obtain electrolyte layers.

[0128] Preparation of the negative electrode sheet: Micron-sized silicon, sulfide electrolyte (using the sulfide electrolytes provided in the aforementioned examples and comparative examples respectively), and polystyrene-butadiene copolymer were dissolved in butyl butyrate at a mass ratio of 70:30:5. The mixture was magnetically stirred for 24 hours to obtain a negative electrode slurry. The negative electrode slurry was coated onto copper foil and dried to form a negative electrode sheet.

[0129] Preparation of c positive electrode: NCM811, sulfide electrolyte, and nitrile rubber were dissolved in xylene at a mass ratio of 85:15:2:3 and magnetically stirred for 24 hours to obtain a positive electrode slurry. The positive electrode slurry was then coated onto aluminum foil, dried, and cut into sheets to obtain the positive electrode sheet.

[0130] Fabrication of solid-state batteries: In the molded battery, the negative electrode and positive electrode are placed on both sides of the pressed electrolyte layer, sealed and assembled, and then pressurized to 4T and held for 10 minutes to obtain a solid-state battery.

[0131] (10.2) Rate performance test: Connect the mold battery to the Blue Battery Tester, charge it to 4.25V with a constant current of 0.1C, let it stand for 5 minutes, and then discharge it to 1.2V with a constant current of 0.1C. The resulting discharge capacity is recorded as C0. Then charge it to 4.25V with a constant current of 1C, let it stand for 5 minutes, and then discharge it to 1.2V with a constant current of 1C. The resulting discharge capacity is recorded as C1. Rate performance = 1C / 0.1C = (C1 / C0)*100%.

[0132] (10.3) Cyclic performance test: Connect the mold battery to the Blue Electric Tester, charge it to 4.25V with 1C constant current, let it stand for 5 minutes, and then discharge it to 1.2V with 1C constant current. The resulting capacity is recorded as the initial discharge capacity C0. After 100 cycles, test the discharge capacity C2 of the 100th cycle. 1C capacity retention rate = (C2 / C0)*100%.

[0133] Table 1 Parameters of Lithium Sulfide Powder

[0134] Table 2. Parameters of sulfide electrolytes and performance of solid-state batteries

[0135] In conjunction with the embodiments, as can be seen from Tables 1 and 2, the lithium sulfide powder provided in Embodiments 1 to 14 of this application has higher purity, lower carbon content, oxygen content, and metal impurity content, and higher whiteness. Furthermore, the (Dv90-Dv10) / Dv50 of the lithium sulfide powder is 3 to 5, which can result in higher ionic conductivity and lower electronic conductivity of the sulfide electrolyte prepared from the lithium sulfide powder. Using the sulfide electrolyte to prepare the battery can result in better rate performance (higher 1C retention rate) and better cycle performance (higher capacity retention rate) of the final solid-state battery.

[0136] A comparison of Examples 1 and 4 shows that the method provided in this application can still achieve high purity of lithium sulfide powder even when using industrial-grade anhydrous lithium sulfide and activated carbon to prepare lithium sulfide powder. The ionic conductivity of the sulfide electrolyte prepared using this lithium sulfide powder is still high, while the electronic conductivity is low. When using this sulfide electrolyte to prepare a battery, the final battery has good cycle performance and rate performance.

[0137] A comparison of Examples 1 and 7 with Example 8 reveals that, compared to Example 1, the lower pressure of the first airflow pulverization in Example 7 leads to incomplete reaction between the carbonized inorganic carbon and lithium sulfate, resulting in relatively lower purity of the product. Furthermore, it results in larger lithium sulfide particles, leading to lower ionic conductivity in the sulfide solid electrolyte prepared from this lithium sulfide material, and consequently, slightly poorer cycle performance and rate capability of the resulting battery. In Example 8, the purity and particle size distribution of the lithium sulfide material are more reasonable, but the higher airflow pressure of the first airflow pulverization actually increases the preparation cost.

[0138] A comparison of Examples 1 and 9 with Example 10 shows that, compared to Example 1, the lower pressure of the second airflow pulverization in Example 9 results in larger lithium sulfide material particles with greater variation in particle size distribution. This leads to lower ionic conductivity in the sulfide solid electrolyte prepared from this lithium sulfide material, resulting in slightly poorer cycle performance and rate capability of the battery. In Example 10, the purity and particle size distribution of the lithium sulfide material are more reasonable, but the higher airflow pressure of the second airflow pulverization actually increases the preparation cost.

[0139] A comparison of Examples 1 and 11 with Example 12 shows that, compared to Example 1, the reaction temperature between the carbonized inorganic carbon and lithium sulfate in Example 11 was lower, making it more difficult to control the morphology of lithium sulfide. This resulted in larger lithium sulfide particles and lower purity. Consequently, the sulfide solid electrolyte prepared using this lithium sulfide material had lower ionic conductivity, leading to slightly poorer cycle performance and rate capability of the resulting battery. In Example 12, the reaction temperature between the carbonized inorganic carbon and lithium sulfate was higher, resulting in higher purity and a more reasonable particle size distribution of the lithium sulfide material. However, the higher reaction temperature increased the preparation cost.

[0140] Comparing Examples 1 and 13 with Example 14, it can be seen that, compared to Example 1, the sintering temperature of the crude lithium sulfide mixed with carbon and sulfur in Example 13 is lower, resulting in lower purity of the product. The sulfide solid electrolyte prepared using this lithium sulfide material has lower ionic conductivity, and the cycle performance and rate performance of the resulting battery are slightly worse. In Example 14, the sintering temperature of the crude lithium sulfide mixed with carbon and sulfur is higher, resulting in higher purity and a more reasonable particle size distribution of the lithium sulfide material. However, the higher reaction temperature leads to increased preparation costs.

[0141] In Comparative Example 1, the purity of crude lithium sulfide is low. When crude lithium sulfide is used to directly prepare sulfide electrolyte, the resulting electrolyte powder has low ionic conductivity and high electronic conductivity. Using this sulfide electrolyte to prepare a battery results in poor rate performance and cycle performance.

[0142] In Comparative Example 2, although the lithium sulfide powder from the commercially available Aladdin product has high purity, its particle size distribution is relatively small, with (Dv90-Dv10) / Dv50=2.428. When used to prepare sulfide electrolyte, the ionic conductivity of the sulfide electrolyte is low. When using this sulfide electrolyte to prepare a battery, the rate performance and cycle performance of the battery are poor.

[0143] In Comparative Example 3, after the organic carbon source was carbonized, the product was not subjected to air jet crushing, but instead ball milling and mixing. The mixing effect was poor, resulting in slightly lower purity of lithium sulfide powder and larger particle size with a smaller particle size distribution difference (Dv90-Dv10) / Dv50=2.51. When used to prepare sulfide electrolyte, the ionic conductivity of the sulfide electrolyte was low. When using the sulfide electrolyte to prepare batteries, the rate performance and cycle performance of the resulting batteries were poor.

[0144] In Comparative Example 4, when processing crude lithium sulfide, only sublimed sulfur was added without adding graphite powder, which failed to achieve the desired impurity removal effect. The low purity of the lithium sulfide powder resulted in low ionic conductivity and high electronic conductivity of the sulfide electrolyte. Using this sulfide electrolyte to prepare batteries ultimately led to poor cycle performance and rate performance of the batteries.

[0145] In Comparative Example 5, after ball milling and sieving, lithium sulfide material was not subjected to air jet crushing. The resulting lithium sulfide powder had a large particle size and a small particle size distribution difference, with (Dv90-Dv10) / Dv50=2.03. When used to prepare sulfide electrolyte, the ionic conductivity of the sulfide electrolyte was low. When using the sulfide electrolyte to prepare a battery, the rate performance and cycle performance of the battery were poor.

[0146] In Comparative Example 6, when crude lithium sulfide was obtained in step (2), the sintering temperature exceeded the melting point of lithium sulfate, resulting in low purity and small particle size distribution of the obtained lithium sulfide powder. After using it to prepare sulfide electrolyte, the ionic conductivity of the sulfide electrolyte was low and the electronic conductivity was high. Using the sulfide electrolyte to prepare the battery ultimately led to poor cycle performance and rate performance of the battery.

[0147] 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 lithium sulfide powder, characterized in that, The lithium sulfide powder has a purity of ≥99.5%, whiteness of ≥83%, oxygen content of ≤0.3% by mass, carbon content of ≤0.2% by mass, and metal impurity content of ≤0.1% by mass. The ratio of (Dv90-Dv10) / Dv50 of the lithium sulfide powder is 3~5.

2. The lithium sulfide powder as described in claim 1, characterized in that, The chemical formula of the lithium sulfide powder is Li. x S, 1.900 ≤ x ≤ 2.100; alternatively, 1.990 ≤ x ≤ 2.

010.

3. The lithium sulfide powder as described in claim 1, characterized in that, The lithium sulfide powder has a whiteness of 83%~85%, an oxygen content of ≤0.25% by mass, a carbon content of ≤0.17% by mass, and a metal impurity content of ≤0.1% by mass. Or / and, the lithium sulfide powder has a Dv10 of 0.1μm to 2μm, a Dv50 of 2μm to 6μm, and a Dv90 of 9μm to 15μm.

4. A method for preparing lithium sulfide powder, characterized in that, include: S1. The lithium source and the first carbon material are mixed by first airflow crushing and sintering under an inert atmosphere to form crude lithium sulfide. The lithium source includes at least one of lithium sulfate, lithium sulfite and lithium thiosulfate. The temperature of the first sintering is lower than the melting point of the lithium source. S2. After mixing the crude lithium sulfide, the second carbon material, and the sulfur powder, the mixture is sintered again under an inert atmosphere to form lithium sulfide material. The lithium sulfide material is then subjected to second airflow crushing and sieving, and the undersize material is taken to obtain lithium sulfide powder.

5. The preparation method according to claim 4, characterized in that, In step S1, the conditions for the first airflow pulverization include: 20 min to 40 min by using an airflow pulverizer under a pressure of 0.5 MPa to 0.7 MPa; Or / and, in step S2, the conditions for the second airflow agitation include: 10 min to 20 min by airflow agitator under a pressure of 0.3 MPa to 0.5 MPa; Or / and, in step S2, the sieve used for screening is 200 mesh to 400 mesh.

6. The preparation method according to claim 4, characterized in that, In step S1, the conditions for the first sintering include: a sintering temperature of 700℃~800℃, a sintering time of 1h~5h, and a first flow rate of inert gas of 1 L / min~5L / min. Or / and, in step S2, the conditions for the secondary sintering include: a sintering temperature of 800℃~1000℃ and a sintering time of 1h~4h.

7. The preparation method according to claim 4, characterized in that, In step S2, the mass percentage of the second carbon material is 0.1% to 5% of the mass of the crude lithium sulfide, and the mass percentage of the sulfur powder is 0.6% to 40% of the mass of the crude lithium sulfide. Or / and, in step S2, the material for secondary sintering is a material that is mixed with crude lithium sulfide, second carbon material and sulfur powder and then pressed into sheets.

8. The preparation method according to any one of claims 4 to 7, characterized in that, In step S1, the first carbon material includes inorganic carbon and / or inorganic carbon carbon carbonized from an organic carbon source; Optionally, the first carbon material comprises inorganic carbon carbonized from an organic carbon source. Before step S1, the method further includes: mixing the lithium source with the organic carbon source and carbonizing the organic carbon source in an inert atmosphere to carbonize the organic carbon source into inorganic carbon. Optionally, the carbonization temperature is 250℃~350℃, the carbonization time is 3h~5h, and the second flow rate of the inert gas is 0.5 L / min~2L / min.

9. A method for preparing a sulfide electrolyte, characterized in that, Lithium halide, phosphorus pentasulfide, and lithium sulfide powder according to any one of claims 1 to 3 and lithium sulfide powder prepared by any one of claims 4 to 8 are mixed, pressed into tablets, and then calcined.

10. A sulfide electrolyte prepared by the method of claim 9, characterized in that, The ionic conductivity of the sulfide electrolyte is 10 mS / cm to 12 mS / cm; the electronic conductivity of the sulfide electrolyte is 1×10⁻⁶ mS / cm. - 9 S / cm ~2×10 -9 S / cm.

11. A solid-state battery, characterized in that, Includes the sulfide electrolyte of claim 10.

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