Method for producing lithium sulfide, lithium sulfide, sulfide solid electrolyte, and battery

Abstract

The application provides a preparation method of lithium sulfide, and lithium sulfide, a sulfide solid-state electrolyte and a battery, and comprises the following steps: mixing lithium sulfate and a soluble organic carbon source in water, and obtaining a first precursor after spray drying; and performing sintering treatment on the first precursor and an organic sulfur source to obtain lithium sulfide; wherein the molar ratio of the lithium sulfate to the soluble organic carbon source is 1:(3-3.85). The organic sulfur source can provide an additional S source, positively promotes the reaction of the carbon source and the lithium sulfate, greatly reduces the generation of Li2O, and thus is beneficial to improving the purity of the Li2S product.

Description

Technical Field

[0001] This invention belongs to the field of secondary battery technology, specifically relating to a method for preparing lithium sulfide, as well as lithium sulfide, sulfide solid electrolyte, and battery. Background Technology

[0002] Sulfide solid electrolytes have shown great promise in all-solid-state batteries due to their advantages such as high conductivity, good thermal stability, and wide electrochemical window. Sulfide solid electrolytes are mainly prepared using Li₂S, P₂S₅, and dopants through high-energy ball milling and heat treatment. Li₂S is one of the key raw materials for sulfide solid electrolytes, and its purity directly affects the performance of the electrolyte.

[0003] Currently, lithium sulfide production is mainly based on the solid-phase method of carbothermic reduction of lithium sulfate. However, this process generates a large amount of Li₂O as a byproduct, resulting in impurities in the Li₂S product and ultimately affecting the performance of sulfide solid electrolytes using Li₂S. Therefore, how to further improve the purity of Li₂S is a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0004] This invention provides a method for preparing lithium sulfide. The organic sulfur source can provide an additional S source, which positively promotes the reaction between the carbon source and lithium sulfate, greatly reducing the production of Li2O, thereby improving the purity of the Li2S product.

[0005] The present invention also provides a lithium sulfide prepared by the above preparation method. This lithium sulfide has the advantage of high purity and can be directly used as a raw material for sulfide solid electrolytes, which is beneficial to improving the performance of sulfide solid electrolytes.

[0006] The present invention also provides a sulfide solid electrolyte, which is prepared from the above-mentioned lithium sulfide and has excellent lithium-ion conductivity.

[0007] The present invention also provides a battery that, due to including the above-mentioned sulfide solid electrolyte, has excellent electrochemical performance.

[0008] In a first aspect, the present invention provides a method for preparing lithium sulfide, comprising the following steps: mixing lithium sulfate and a soluble organic carbon source in water, and spray drying the mixture to obtain a first precursor;

[0009] The first precursor and the organic sulfur source are sintered to obtain lithium sulfide.

[0010] The molar ratio of lithium sulfate to the soluble organic carbon source is 1:(3-3.85).

[0011] In the preparation method described above, the soluble organic carbon source includes at least one of glucose, sucrose, and citric acid.

[0012] In the preparation method described above, the organic sulfur source includes at least one of thioacetamide and thiourea.

[0013] In the preparation method described above, the particle size of the first precursor is 15–25 μm.

[0014] In the preparation method described above, the molar ratio of lithium sulfate to the soluble organic carbon source is 1:(3-3.85).

[0015] In the preparation method described above, the amount of the organic sulfur source added is 1 to 10 wt% of the mass of the first precursor.

[0016] In the preparation method described above, the spray drying temperature is 200℃~230℃; and / or,

[0017] The sintering process is carried out in an inert atmosphere or a reducing atmosphere;

[0018] The sintering process is carried out at a temperature of 760℃ to 820℃ for 4 to 7 hours.

[0019] In a second aspect, the present invention provides a lithium sulfide prepared by the preparation method described in the first aspect.

[0020] The lithium sulfide as described above, wherein the purity of the lithium sulfide is not less than 99.5%.

[0021] In a third aspect, the present invention provides a method for preparing a sulfide solid electrolyte, wherein lithium sulfide, P2S5 and LiCl described in the second aspect are mixed in a certain proportion and ball-milled, and then sintered to obtain a sulfide solid electrolyte.

[0022] A fourth aspect of the present invention provides a battery comprising the sulfide solid electrolyte described in the third aspect.

[0023] The implementation of this invention has at least the following beneficial effects:

[0024] The lithium sulfide preparation method provided by this invention utilizes an organic sulfur source to provide additional sulfur (S) source, which positively promotes the reaction between the carbon source and lithium sulfate, significantly reducing the generation of Li₂O during the reaction and thus improving the purity of the Li₂S product. When this lithium sulfide is applied to the preparation of sulfide solid electrolytes, it significantly improves the lithium-ion conductivity of the sulfide solid electrolyte. Introducing this sulfide solid electrolyte into batteries is beneficial for improving battery performance. Attached Figure Description

[0025] Figure 1 This is the XRD pattern of lithium sulfide in Example 2 of the present invention;

[0026] Figure 2 This is the XRD pattern of lithium sulfide in Comparative Example 1 of the present invention;

[0027] Figure 3 This is a SEM image of the first precursor in Embodiment 1 of the present invention;

[0028] Figure 4 This is a SEM image of lithium sulfide in Comparative Example 5 of this invention;

[0029] Figure 5 This is the XRD pattern of lithium sulfide in Comparative Example 4 of this invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0031] In a first aspect, the present invention provides a method for preparing lithium sulfide, comprising the following steps: mixing lithium sulfate and a soluble organic carbon source in water, and spray drying the mixture to obtain a first precursor; and sintering the first precursor and the organic sulfur source to obtain lithium sulfide.

[0032] In this invention, a soluble organic carbon source is used as the carbon source. Lithium sulfate and the soluble organic carbon source are mixed in water to form an aqueous solution containing lithium sulfate and the carbon source. After spray drying, the water evaporates, and the organic carbon source coats the surface of the lithium sulfate, forming a first precursor. Mixing in water facilitates the uniform mixing of lithium sulfate and the soluble organic carbon source, resulting in a tight bond between the soluble organic carbon source and lithium sulfate after spray drying, which promotes uniform coating and improves the conversion efficiency of lithium sulfide.

[0033] During the sintering process, the soluble organic carbon source undergoes carbonization, first converting into carbon. Carbon then reacts with lithium sulfate as a reducing agent, specifically: Li₂SO₄ + 2C = Li₂S + 2CO₂. Simultaneously, a side reaction occurs during the reaction of carbon as a reducing agent with lithium sulfate: 2Li₂SO₄ + 5C = Li₂O + Li₂S + SO₂ + 5CO, generating a large amount of byproduct Li₂O.

[0034] During sintering, the organic sulfur source reacts with moisture upon heating to generate hydrogen sulfide. Hydrogen sulfide then reacts with the byproduct Li₂O: H₂S + Li₂O = Li₂S + H₂O. This process removes excess Li₂O, improving both the purity and conversion efficiency of lithium sulfide. Furthermore, organic sulfur can decompose at high temperatures into reducing gases such as H₂S and NH₄. These gases lower the reaction temperature to some extent, inhibiting side reactions and further enhancing the purity of lithium sulfide.

[0035] According to the research of the present invention, the lithium sulfide prepared by the above method has high purity. This is because, compared with the existing technology of directly mixing carbon materials (such as porous carbon, graphene, carbon nanotubes, carbon fibers, carbon black, graphite) with lithium sulfate for sintering, on the one hand, the present invention, by mixing in water first and then spray drying, allows lithium sulfate and soluble organic carbon sources to contact more evenly, which positively promotes the formation of lithium sulfide; on the other hand, by adding an organic sulfur source during the sintering process, it can provide additional S source and remove the byproduct Li2O, thereby improving the purity of lithium sulfide.

[0036] The present invention does not limit the specific type of soluble organic carbon source. For example, in some embodiments, the soluble organic carbon source includes at least one of glucose and sucrose.

[0037] This invention does not limit the specific type of organic sulfur source. For example, in some embodiments, the organic sulfur source includes at least one of thioacetamide and thiourea. When the organic sulfur source is thioacetamide, during the sintering process, thioacetamide reacts with moisture upon heating: CH3CSNH2 + H2O = CH3CONH2 + H2S, H2S + Li2O = Li2S + H2O, which can maximize the removal of the byproduct Li2O, thereby improving the purity of Li2S.

[0038] In this invention, the particle size of the first precursor is 15 to 25 μm, for example, 15 μm, 20 μm, 25 μm or any combination thereof.

[0039] This invention does not limit the amount of reactants added. For example, in some embodiments, the molar ratio of lithium sulfate to a soluble organic carbon source is 1:(3 to 3.85), such as 1:3, 1:3.2, 1:3.3, 1:3.4, 1:3.5, 1:3.6, 1:3.7, 1:3.8, 1:3.85, or any combination thereof. And / or, the amount of organic sulfur source added is 1 to 10 wt% of the mass of the first precursor, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any combination thereof.

[0040] This invention does not limit the conditions for spray drying and sintering. For example, in some embodiments, the spray drying temperature is 200℃ to 230℃, such as 200℃, 210℃, 220℃, 230℃, or any combination thereof; the sintering process is carried out in an inert or reducing atmosphere, the sintering temperature is 760℃ to 820℃, such as 760℃, 780℃, 800℃, 820℃, or any combination thereof, and the time is 4 to 7 hours, such as 4 hours, 5 hours, 6 hours, 7 hours, or any combination thereof. By adjusting the equipment used for spray drying, it is beneficial to adjust the particle size of the first precursor to 15 to 25 μm.

[0041] After sintering, the organic sulfur source is ground to finally obtain lithium sulfide.

[0042] In a second aspect, the present invention provides a lithium sulfide prepared by the preparation method provided in the first aspect. Because it is prepared by the above method, the lithium sulfide possesses advantages such as high purity.

[0043] In some embodiments, the purity of lithium sulfide is not less than 99.5%.

[0044] In a third aspect, the present invention provides a method for preparing a sulfide solid electrolyte, wherein lithium sulfide, P2S5 and LiCl provided in the second aspect are mixed in a certain proportion and subjected to ball milling, followed by solid-state sintering to obtain a sulfide solid electrolyte.

[0045] The ratio of lithium sulfide, P2S5, and LiCl is adjusted according to the stoichiometric ratio of the sulfide solid electrolyte. For example, if the chemical formula of the sulfide solid electrolyte is Li... 5.5 PS 4.5 Cl 1.5 / Li6PS5Cl, then lithium sulfide, P2S5 and LiCl are mixed according to the stoichiometric ratio, and ball milling and solid-state sintering are performed in sequence to obtain sulfide solid electrolyte. The solid-state sintering is carried out under an inert atmosphere at a temperature of 500 to 550°C, for example 500°C, 520°C, 540°C, 550°C or any combination thereof, for a time of 4 to 6 hours, for example 4 hours, 5 hours, 6 hours or any combination thereof.

[0046] A fourth aspect of the present invention provides a battery comprising the sulfide solid electrolyte provided in the third aspect.

[0047] The present invention will be further described below through specific embodiments and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, all of which are commercially available, and the reagents and materials involved can also be synthesized by conventional synthetic methods.

[0048] Example 1

[0049] 1) The raw materials Li2SO4 and glucose were dissolved in an aqueous solution at a molar ratio of Li2SO4:C = 1:3 and then spray-dried to obtain the first precursor; wherein the spray drying temperature was 220℃.

[0050] 2) The first precursor in step 1) and thioacetamide were mechanically mixed and sintered at 780°C for 7 hours to obtain the crude product; wherein the amount of thioacetamide added relative to the first precursor was 8%.

[0051] 3) The crude product is ground in a crusher to obtain lithium sulfide in this embodiment.

[0052] Example 2

[0053] The preparation process is basically the same as in Example 1, except that:

[0054] Replace "Add raw material Li2SO4 and glucose to aqueous solution in a molar ratio of Li2SO4:C = 1:3" in step 1) with "Add raw material Li2SO4 and glucose to aqueous solution in a molar ratio of Li2SO4:C = 1:3.25"; replace "Sinter at 780℃ for 7 hours" in step 2) with "Sinter at 800℃ for 6 hours"; replace "The amount of thioacetamide added relative to the first precursor is 8%" with "The amount of thioacetamide added relative to the first precursor is 5%"; and keep other conditions unchanged to obtain lithium sulfide of this embodiment.

[0055] Example 3

[0056] The preparation process is basically the same as in Example 1, except that:

[0057] Replace "Add raw material Li2SO4 and glucose to the aqueous solution to dissolve in a molar ratio of Li2SO4:C = 1:3" in step 1) with "Add raw material Li2SO4 and glucose to the aqueous solution to dissolve in a molar ratio of Li2SO4:C = 1:3.5"; replace "Sinter at 780℃ for 7 hours" in step 2) with "Sinter at 820℃ for 6 hours"; replace "The amount of thioacetamide added relative to the first precursor is 8%" with "The amount of thioacetamide added relative to the first precursor is 2%"; and keep other conditions unchanged to obtain lithium sulfide of this embodiment.

[0058] Example 4

[0059] The preparation process is basically the same as in Example 1, except that:

[0060] By replacing glucose with sucrose while keeping other conditions unchanged, lithium sulfide was obtained as described in this embodiment.

[0061] Example 5

[0062] The preparation process is basically the same as in Example 1, except that:

[0063] By replacing thioacetamide with thiourea while keeping other conditions unchanged, lithium sulfide was obtained in this embodiment.

[0064] Example 6

[0065] The preparation process is basically the same as in Example 1, except that:

[0066] In step 1), replace "add raw material Li2SO4 and glucose to the aqueous solution to dissolve in a molar ratio of Li2SO4:C = 1:3" with "add raw material Li2SO4 and glucose to the aqueous solution to dissolve in a molar ratio of Li2SO4:C = 1:3.85"; in step 2), replace "the amount of thioacetamide added relative to the first precursor is 8%" with "the amount of thioacetamide added relative to the first precursor is 10%", and keep other conditions unchanged to obtain lithium sulfide of this embodiment.

[0067] Comparative Example 1

[0068] The preparation process is basically the same as in Example 1, except that:

[0069] Remove the thioacetamide in step 2), and directly sinter the first precursor at 820°C for 5 hours, keeping other conditions unchanged, to obtain the lithium sulfide of this comparative example.

[0070] Comparative Example 2

[0071] 1) The raw materials Li2SO4 and glucose were mechanically mixed with thioacetamide in a molar ratio of Li2SO4:C = 1:3, and sintered at 780℃ for 7 hours to obtain the crude product; wherein the thioacetamide accounted for 8% of the total mass of Li2SO4 and glucose.

[0072] 2) The crude product was ground in a crusher to obtain the lithium sulfide of this comparative example.

[0073] Comparative Example 3

[0074] The preparation process is basically the same as in Example 1, except that:

[0075] Replace glucose in step 1) with carbon fiber (VGCF) and mix by mechanical stirring; keep other conditions unchanged to obtain lithium sulfide of this comparative example.

[0076] Comparative Example 4

[0077] The preparation process is basically the same as in Example 1, except that:

[0078] Replace "Add raw material Li2SO4 and glucose to aqueous solution in a molar ratio of Li2SO4:C = 1:3" in step 1) with "Add raw material Li2SO4 and glucose to aqueous solution in a molar ratio of Li2SO4:C = 1:2"; keep other conditions unchanged to obtain lithium sulfide of this comparative example.

[0079] Comparative Example 5

[0080] The preparation process is basically the same as in Example 1, except that:

[0081] Replace "Add raw material Li2SO4 and glucose to the aqueous solution to dissolve in a molar ratio of Li2SO4:C = 1:3" in step 1) with "Add raw material Li2SO4 and glucose to the aqueous solution to dissolve in a molar ratio of Li2SO4:C = 1:4"; keep other conditions unchanged to obtain lithium sulfide in this embodiment.

[0082] Test case

[0083] 1. Li2S purity test

[0084] A 37% formalin solution was diluted to 10% with ultrapure water and then degassed for 10 minutes using an ultrasonic cleaner and a suction device to obtain a 10% formalin aqueous solution.

[0085] Weigh 0.2g of lithium sulfide from the above examples and comparative examples, add 100mL of 10% (volume concentration) formalin solution to obtain a solution, and use liquid chromatography (HPLC) to test the sulfite ions, sulfate ions, and thiosulfate ions in the solution, and use the absolute calibration curve method for quantitative testing.

[0086] Based on the mass of the precipitate containing S anions, the number of moles of S in the total precipitate is calculated, and the actual mass of Li₂S is calculated. The purity of Li₂S is then calculated by dividing the actual mass of Li₂S by 0.2g and multiplying by 100%.

[0087] 2. Performance testing of sulfide solid electrolytes

[0088] Preparation of sulfide solid electrolytes: according to Li 5.5 PS 4.5 Cl 1.5 The stoichiometric ratios of lithium sulfide, P2S5, and LiCl in the examples and comparative examples were mixed in proportion and ball-milled. After solid-state sintering, a sulfide solid electrolyte was obtained.

[0089] The solid-state sintering treatment was carried out under an inert atmosphere at a temperature of 520℃ for 5 hours.

[0090] The prepared sulfide solid electrolyte was subjected to the following tests:

[0091] Lithium-ion conductivity test: 0.22g of sulfide solid electrolyte was cold-pressed at 4T in a φ10mm mold and kept at the temperature for 10min. The impedance test was performed using carbon-coated aluminum foil as the current collector. The test frequency was 106~1Hz.

[0092] Electronic conductivity test: The IT curve of the sulfide solid electrolyte was tested with Li metal current collector on one side. The test voltage was 0.05V and the test time was 1500s.

[0093] 4. Battery performance

[0094] The positive electrode material NCM811, electrolyte material, and binder (80:15:5) were mixed in butyl butyrate solvent to form a positive electrode slurry, which was then coated on aluminum foil and cut into φ9cm positive electrode sheets using a sampler.

[0095] Weigh 0.15g of Li6PS5Cl into the battery mold and pre-press it under 3T pressure; place the weighed electrode sheet on one side of the mold; place the cut In foil sheet on the other side of the electrolyte; after pressing under 4T pressure, assemble the mold battery, remove the glove box and assemble the pressure device.

[0096] Among them, the electrical performance test parameters are: cutoff voltage: 1.9~3.65V, multiplier: 0.05C / 0.05C.

[0097] The results are shown in Table 1.

[0098] Table 1

[0099]

[0100] according to Figure 4 It can be seen that the C in Comparative Example 5 was not completely consumed, and there was a significant excess. According to... Figure 5 It can be seen that the lithium sulfide product of Comparative Example 4 has a weak lithium sulfide peak intensity in XRD test, with only a small amount of lithium sulfide generated and a large amount of raw material Li2SO4 present.

[0101] As shown in Table 1, the lithium sulfide preparation method provided by the present invention can produce high-purity lithium sulfide by introducing spray drying and organic sulfur, which is beneficial to improving the lithium-ion conductivity of the sulfide solid electrolyte and ensuring electronic insulation. Applying this sulfide solid electrolyte to batteries can help improve the discharge capacity.

[0102] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A method for preparing lithium sulfide, characterized in that, The process includes the following steps: mixing lithium sulfate and a soluble organic carbon source in water, followed by spray drying to obtain the first precursor; The first precursor and the organic sulfur source are sintered to obtain lithium sulfide. Wherein, the molar ratio of lithium sulfate to the soluble organic carbon source is 1:(3~3.85). The amount of the organic sulfur source added is 1 to 10 wt% of the mass of the first precursor.

2. The preparation method according to claim 1, characterized in that, The soluble organic carbon source includes at least one of glucose, sucrose, and citric acid; and / or, The organic sulfur source includes at least one of thioacetamide and thiourea.

3. The preparation method according to claim 1, characterized in that, The particle size of the first precursor is 15~25μm.

4. The preparation method according to any one of claims 1-3, characterized in that, The sintering process is carried out in an inert atmosphere or a reducing atmosphere; The sintering process is carried out at a temperature of 760℃~820℃ for 4~7 hours.

5. The preparation method according to any one of claims 1-3, characterized in that, The spray drying temperature is 200℃~230℃.

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