Lithium sulfide and preparation method thereof

Abstract

The invention discloses lithium sulfide and a preparation method thereof. The preparation method comprises the following steps: (1) carrying out ball-milling mixing on iron powder, sodium sulfide and lithium sulfate in a first inert atmosphere to obtain a mixture; (2) calcining the mixture in a second inert atmosphere for the first time to obtain a reaction material; (3) stirring and washing the reaction material with an alcohol solvent in a third inert atmosphere, filtering to obtain filtrate and a filter cake, performing reduced pressure distillation on the filtrate to obtain a lithium sulfide crude product, washing the filter cake with deionized water, and filtering to obtain a solid by-product; and (4) carrying out secondary calcination on the lithium sulfide crude product in a fourth inert atmosphere to obtain lithium sulfide. The preparation method provided by the invention has the advantages of few synthesis steps, simple product purification and environmental protection.

Description

Technical Field

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

[0002] Lithium sulfide, a white to yellow crystal with an inverse fluorite structure and the molecular formula Li2S, can be used directly as the cathode material for lithium-sulfur batteries and is also a key raw material for the synthesis of sulfide solid electrolytes. Recent reports have shown that sulfide solid electrolytes prepared using lithium sulfide exhibit high ionic conductivity. Current methods for synthesizing lithium sulfide can be broadly categorized into ball milling, solvent processing, and high-temperature and high-pressure methods.

[0003] The ball milling method refers to mixing elemental sulfur and metallic lithium / lithium hydride in proportion under an inert atmosphere and then subjecting them to a mechanical ball milling reaction to obtain lithium sulfide. CN201911128024.4 reports that under the protection of an inert atmosphere, silicon sulfide and lithium oxide are added to a sealed ball mill jar and ball milled for a certain period of time, the solid product in the ball mill jar is taken out, the excess silicon sulfide is recovered, and the remaining solid product is separated to obtain lithium sulfide powder. CN202010765232.1 uses lithium-containing compounds, elemental sulfur and hydrogen as raw materials and simple mechanical ball milling to synthesize high-purity lithium sulfide powder. This method is simple and environmentally friendly, but the reaction time is long, the conversion rate is low, and the resulting product contains miscellaneous substances.

[0004] The solvent method involves mixing lithium / lithium compounds and sulfur / sulfur compounds in a solvent medium to produce lithium sulfide. CN202011457808.4 Under an inert atmosphere, a lithium source compound and a sulfur source compound are weighed and their respective alcoholic solutions are prepared. The alcoholic solution of the lithium source compound is then added to the alcoholic solution of the sulfur source compound. After magnetic stirring, the fully reacted product is centrifuged and the supernatant is collected. The supernatant is then transferred to a tube furnace and heated for crystallization to obtain a crude lithium sulfide product, which is then processed to obtain high-purity lithium sulfide. This reaction is fully and completely liquid-phase, leaving few impurities, and making the product easy to purify. However, there are issues such as the flammability, explosiveness, volatility, and severe environmental pollution of the organic solvent.

[0005] The high temperature and high pressure method refers to the preparation of lithium sulfide by reduction or gas phase reaction of lithium / lithium compounds and sulfur / sulfur compounds under high temperature and high pressure in an inert / reducing protective atmosphere. CN201910993364.7 uses a lithium sulfide precursor (one or more of lithium sulfate, lithium sulfite, lithium bisulfate, and lithium dithionate) to react with a related reducing agent at high temperature to prepare a substance containing lithium sulfide, and then the lithium sulfide in the mixture is leached and purified, and finally a lithium sulfide product with a purity of more than 99.9% and controllable morphology is obtained by spray drying. The process of this method is simple, no harmful gases are generated, and the advantages of high temperature and high pressure closed reactions are effectively utilized to avoid leakage of harmful solvents, but high temperature and high pressure will make the working conditions difficult to control.

[0006] In summary, the shortcomings of different methods for preparing lithium sulfide make its industrialization difficult and the cost remains high. Therefore, the continuous development of low-cost, efficient and green lithium sulfide preparation methods is of great significance to the sustainable development of batteries. Summary of the Invention

[0007] In view of the above problems, the object of the present invention is to provide a lithium sulfide and a preparation method thereof, which has the advantages of low raw material cost, fewer synthesis steps, simple product purification, and environmental protection.

[0008] To achieve the above object, the present invention provides a method for preparing lithium sulfide, comprising the steps of: (1) ball-milling iron powder, sodium sulfide, and lithium sulfate in a first inert atmosphere to obtain a mixture; (2) calcining the mixed material once in a second inert atmosphere to obtain a reaction material; (3) The reaction material is stirred and washed with an alcohol solvent in a third inert atmosphere, and then filtered to obtain a filtrate and a filter cake. The filtrate is subjected to reduced pressure distillation to obtain crude lithium sulfide. The filter cake is washed with deionized water and then filtered to obtain a solid by-product; (4) The crude lithium sulfide is subjected to a second calcination in a fourth inert atmosphere to obtain lithium sulfide.

[0009] Compared with the prior art, the present invention uses iron powder, sodium sulfide and lithium sulfate as raw materials to prepare lithium sulfide. Among them, the iron powder has a low cost, and valuable solid by-products such as iron oxide and ferrosoferric oxide are obtained during the preparation process. Sodium sulfide can be used as a reducing agent and can also increase the source of sulfur in the reaction system. In addition, the purification method of the present invention is simple, and the solvent in the purification process can be recovered and reused, which is green and environmentally friendly. At the same time, the preparation method of the present invention is simple, environmentally friendly, and easy to industrialize.

[0010] Furthermore, the molar ratio of lithium sulfate, sodium sulfide and iron powder of the present invention is 1:0.5~2:3~8. Preferably, the molar ratio of lithium sulfate, sodium sulfide and iron powder is 1:0.5~1:3~5. As an example, the molar ratio of lithium sulfate, sodium sulfide and iron powder can be, but is not limited to, 1:0.5:3, 1:0.5:3.5, 1:0.5:4, 1:0.5:4.5, 1:0.5:5, 1:0.5:5.5, 1:0.5:6, 1:0.5:6.5, 1:0.5:7, 1:0.5:7.5, 1:0.5:8, 1:1:3, 1:1:3.5, 1:1:4, 1:1:4.5, 1:1:5, 1:1:5.5, 1:1:6, 1:1:6.5, 1:1:7, 1:1:7.5, 1:1:8, 1:2:3, 1:2:3.5, 1:2:4, 1:2:4.5, 1:2:5, 1:2:5.5, 1:2:6, 1:2:6.5, 1:2:7, 1:2:7.5, 1:2:8.

[0011] Furthermore, the rotation speed of the ball mill of the present invention is 400 rpm to 700 rpm. As an example, the rotation speed of the ball mill can be but is not limited to 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm, 650 rpm, and 700 rpm.

[0012] Furthermore, the ball milling time of the present invention is 1 hour to 10 hours, preferably, the ball milling time is 2 hours to 5 hours. As an example, the ball milling time can be, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, and 10 hours. By controlling the ball milling speed and ball milling time of the present invention within this range, the particle size of the iron powder and lithium sulfate is effectively reduced and the mixing uniformity is improved, thereby ensuring the conversion rate of the subsequent reduction reaction.

[0013] Furthermore, the primary calcination temperature of the present invention is 500° C. to 850° C., preferably, the primary calcination temperature is 650° C. to 820° C. As an example, the primary calcination temperature can be, but is not limited to, 500° C., 550° C., 600° C., 650° C., 700° C., 750° C., 800° C., or 850° C.

[0014] Furthermore, the primary calcination time of the present invention is 1 hour to 10 hours, preferably, the primary calcination time is 2 hours to 4 hours. As an example, the primary calcination time can be, but is not limited to, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0015] Furthermore, in the primary calcination of the present invention, the reaction between iron powder and lithium sulfate is as follows: 2Li2SO4+ Na2S + Fe = 2Li2S + Na2SO4+ Fe2O3 2Li2SO4+ Na2S + 3Fe = Li2S + Na2SO4+ Fe3O4 Furthermore, the mass ratio of the alcohol solvent to the reactants of the present invention is 30 to 100:1. By way of example, the mass ratio of the alcohol solvent to the reactants of the present invention can be, but is not limited to, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, 90:1, 95:1, or 100:1. Controlling the mass ratio of the alcohol solvent to the reactants within this range maximizes the retention of crude lithium sulfide while effectively removing solid byproduct impurities.

[0016] Furthermore, the alcohol solvent of the present invention is selected from at least one of methanol, ethanol, ethylene glycol, n-propanol, and n-butanol. Preferably, the alcohol solvent of the present invention is selected from ethanol.

[0017] Furthermore, the stirring and washing time of the present invention is 5 min to 30 min. As an example, the stirring and washing time of the present invention is 5 min, 10 min, 15 min, 20 min, 25 min, and 30 min.

[0018] Furthermore, the temperature of the vacuum distillation of the present invention is 45°C to 55°C. Preferably, the temperature of the vacuum distillation is 50°C. As an example, the temperature of the vacuum distillation can be, but is not limited to, 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, or 55°C.

[0019] Furthermore, the temperature of the secondary calcination of the present invention is 200° C. to 500° C., preferably, the temperature of the secondary calcination of the present invention is 200° C. to 350° C. As an example, the temperature of the secondary calcination of the present invention can be, but is not limited to, 200° C., 220° C., 240° C., 250° C., 260° C., 280° C., 300° C., 320° C., 340° C., 350° C., 360° C., 380° C., 400° C., 420° C., 440° C., 450° C., 460° C., 480° C., and 500° C. At this temperature, the residual solvent in the crude lithium sulfide product can be effectively removed, thereby improving the purity of the lithium sulfide.

[0020] Furthermore, the secondary calcination time of the present invention is 1h~10h. Preferably, the secondary calcination time of the present invention is 2h~4h. As an example, the secondary calcination time of the present invention can be but is not limited to 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h.

[0021] Furthermore, the first inert atmosphere, the second inert atmosphere, the third inert atmosphere and the fourth inert atmosphere of the present invention are each independently selected from at least one of nitrogen and argon.

[0022] Another aspect of the present invention provides lithium sulfide, which is prepared using the aforementioned preparation method. The lithium sulfide prepared using the preparation method of the present invention is battery-grade lithium sulfide and can be directly used in batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the XRD pattern of lithium sulfide prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0024] In order to better illustrate the purpose, technical solutions and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following implementation method is a further explanation of the present invention and should not be used as a limitation of the present invention.

[0025] Example 1 This embodiment provides a method for preparing lithium sulfide, comprising the steps of: (1) 7.65 g of iron powder, 5 g of lithium sulfate, 2 g of sodium sulfide and 250 g of zirconium oxide grinding balls were placed in a ball mill and ball milled under argon atmosphere to obtain a mixture. The ball milling speed was 600 rpm and the ball milling time was 2 h.

[0026] (2) The mixture was placed in a tubular furnace and calcined at 750 °C for 3 h under argon atmosphere to obtain 1.2 g of reaction material; (3) Under nitrogen protection, 60 g of anhydrous ethanol was added to the reaction material, stirred and washed for 20 minutes, and the filtrate and filter cake were filtered. The filtrate was subjected to vacuum distillation to obtain crude lithium sulfide. The vacuum distillation temperature was 50 ° C. The filter cake was washed with deionized water and filtered to obtain solid by-products of iron oxide and ferrosoferric oxide.

[0027] (4) The crude lithium sulfide was transferred to a tubular furnace and calcined at 250 °C for 3 h under argon atmosphere to obtain 1.07 g of lithium sulfide.

[0028] Figure 1 The XRD pattern of lithium sulfide obtained in Example 1 proves that lithium sulfide is obtained by the preparation method of the present invention.

[0029] Example 2 This embodiment provides a method for preparing lithium sulfide, comprising the steps of: (1) 10.2 g of iron powder, 5 g of lithium sulfate, 2 g of sodium sulfide and 300 g of zirconium oxide grinding balls were placed in a ball mill and ball milled under argon atmosphere to obtain a mixture. The ball milling speed was 600 rpm and the ball milling time was 2 h.

[0030] (2) The mixture was placed in a tubular furnace and calcined at 750 °C for 3 h under argon atmosphere to obtain 1.06 g of reaction material; (3) Under nitrogen protection, 60 g of anhydrous ethanol was added to the reaction material, stirred and washed for 30 minutes, and the filtrate and filter cake were filtered. The filtrate was subjected to vacuum distillation to obtain crude lithium sulfide. The vacuum distillation temperature was 50 ° C. The filter cake was washed with deionized water and filtered to obtain solid by-products of iron oxide and ferrosoferric oxide.

[0031] (4) The crude lithium sulfide was transferred to a tubular furnace and calcined at 250 °C for 3 h under argon atmosphere to obtain 0.95 g of lithium sulfide.

[0032] Example 3 This embodiment provides a method for preparing lithium sulfide, comprising the steps of: (1) 12.75 g of iron powder, 5 g of lithium sulfate, 3.5 g of sodium sulfide and 350 g of zirconium oxide grinding balls were placed in a ball mill and ball milled under argon atmosphere to obtain a mixture. The ball milling speed was 700 rpm and the ball milling time was 1 h.

[0033] (2) The mixture was placed in a tube furnace and calcined at 750 °C for 3 h under argon atmosphere to obtain 1.14 g of reaction material; (3) Under nitrogen protection, 60 g of anhydrous ethanol was added to the reaction material, stirred and washed for 20 minutes, and the filtrate and filter cake were filtered. The filtrate was subjected to vacuum distillation to obtain crude lithium sulfide. The vacuum distillation temperature was 50 ° C. The filter cake was washed with deionized water and filtered to obtain solid by-products of iron oxide and ferrosoferric oxide.

[0034] (4) The crude lithium sulfide was transferred to a tubular furnace and calcined at 250 °C for 3 h under argon atmosphere to obtain 1 g of lithium sulfide.

[0035] Example 4 This embodiment provides a method for preparing lithium sulfide, comprising the steps of: (1) 7.65 g of iron powder, 5 g of lithium sulfate, 2 g of sodium sulfide and 250 g of zirconium oxide grinding balls were placed in a ball mill and ball milled under argon atmosphere to obtain a mixture. The ball milling speed was 700 rpm and the ball milling time was 2 h.

[0036] (2) The mixture was placed in a tubular furnace and calcined at 820°C for 3 h under argon atmosphere to obtain 1.4 g of reaction material; (3) Under nitrogen protection, 45 g of anhydrous ethanol was added to the reaction material, stirred and washed for 20 minutes, and the filtrate and filter cake were filtered. The filtrate was subjected to vacuum distillation to obtain crude lithium sulfide. The vacuum distillation temperature was 50 ° C. The filter cake was washed with deionized water and filtered to obtain solid by-products of iron oxide and ferrosoferric oxide.

[0037] (4) The crude lithium sulfide was transferred to a tubular furnace and calcined at 250 °C for 3 h under argon atmosphere to obtain 1.23 g of lithium sulfide.

[0038] Example 5 This embodiment provides a method for preparing lithium sulfide, comprising the steps of: (1) 7.65 g of iron powder, 5 g of lithium sulfate, 2 g of sodium sulfide and 250 g of zirconium oxide grinding balls were placed in a ball mill and ball milled under argon atmosphere to obtain a mixture. The ball milling speed was 700 rpm and the ball milling time was 1 h.

[0039] (2) The mixture was placed in a tubular furnace and calcined at 750°C for 4 h under argon atmosphere to obtain 1.08 g of reaction material; (3) Under nitrogen protection, 60 g of anhydrous ethanol was added to the reaction material, stirred and washed for 10 minutes, and the filtrate and filter cake were filtered. The filtrate was subjected to vacuum distillation to obtain crude lithium sulfide. The vacuum distillation temperature was 50 ° C. The filter cake was washed with deionized water and filtered to obtain solid by-products of iron oxide and ferrosoferric oxide.

[0040] (4) The crude lithium sulfide was transferred to a tube furnace and calcined at 250 °C for 3 h under argon atmosphere to obtain 0.87 g of lithium sulfide.

[0041] Example 6 This embodiment provides a method for preparing lithium sulfide, comprising the steps of: (1) 7.65 g of iron powder, 5 g of lithium sulfate, 3 g of sodium sulfide and 250 g of zirconium oxide grinding balls were placed in a ball mill and ball milled under argon atmosphere to obtain a mixture. The ball milling speed was 500 rpm and the ball milling time was 2 h.

[0042] (2) The mixture was placed in a tubular furnace and calcined at 820°C for 2 h under argon atmosphere to obtain 1.15 g of reaction material; (3) Under nitrogen protection, 80 g of anhydrous ethanol was added to the reaction material, stirred and washed for 20 minutes, and the filtrate and filter cake were filtered. The filtrate was subjected to vacuum distillation to obtain crude lithium sulfide. The vacuum distillation temperature was 50 ° C. The filter cake was washed with deionized water and filtered to obtain solid by-products of iron oxide and ferrosoferric oxide.

[0043] (4) The crude lithium sulfide was transferred to a tubular furnace and calcined at 300 °C for 2 h under argon atmosphere to obtain 1.01 g of lithium sulfide.

[0044] Example 7 This embodiment provides a method for preparing lithium sulfide, comprising the steps of: (1) 12.75 g of iron powder, 5 g of lithium sulfate, 2 g of sodium sulfide and 350 g of zirconium oxide grinding balls were placed in a ball mill and ball milled under argon atmosphere to obtain a mixture. The ball milling speed was 700 rpm and the ball milling time was 4 h.

[0045] (2) The mixture was placed in a tube furnace and calcined at 820°C for 4 h under argon atmosphere to obtain 1.26 g of reaction material; (3) Under nitrogen protection, 90 g of anhydrous ethanol was added to the reaction material, stirred and washed for 30 minutes, and the filtrate and filter cake were filtered. The filtrate was subjected to vacuum distillation to obtain crude lithium sulfide. The vacuum distillation temperature was 50 ° C. The filter cake was washed with deionized water and filtered to obtain solid by-products of iron oxide and ferrosoferric oxide.

[0046] (4) The crude lithium sulfide was transferred to a tubular furnace and calcined at 350 °C for 2 h under argon atmosphere to obtain 1.11 g of lithium sulfide.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the scope of protection of the present invention. Although the present invention is described in detail with reference to the preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing lithium sulfide, characterized in that: Including steps: (1) ball-milling iron powder, sodium sulfide, and lithium sulfate in a first inert atmosphere to obtain a mixture; (2) calcining the mixed material in a second inert atmosphere to obtain a reaction material; (3) stirring and washing the reaction material with an alcohol solvent in a third inert atmosphere, filtering to obtain a filtrate and a filter cake, performing vacuum distillation on the filtrate to obtain crude lithium sulfide, and washing the filter cake with deionized water and filtering to obtain a solid by-product; (4) The crude lithium sulfide is subjected to a second calcination in a fourth inert atmosphere to obtain lithium sulfide.

2. The method for preparing lithium sulfide according to claim 1, wherein The molar ratio of the lithium sulfate, the sodium sulfide and the iron powder is 1:0.5-2:3-8.

3. The method for preparing lithium sulfide according to claim 1, wherein The ball milling speed is 400 rpm to 700 rpm, and the ball milling time is 1 h to 10 h.

4. The method for preparing lithium sulfide according to claim 1, wherein The temperature of the primary calcination is 500° C. to 850° C., and the time of the primary calcination is 1 hour to 10 hours.

5. The method for preparing lithium sulfide according to claim 1, wherein The mass ratio of the alcohol solvent to the reaction material is 30-100:

1.

6. The method for preparing lithium sulfide according to claim 1, characterized in that: The alcohol solvent is selected from at least one of methanol, ethanol, ethylene glycol, n-propanol and n-butanol.

7. The method for preparing lithium sulfide according to claim 1, characterized in that: The stirring washing time is 5 min to 30 min, and the temperature of the reduced pressure distillation is 45° C. to 55° C.

8. The method for preparing lithium sulfide according to claim 1, characterized in that: The temperature of the secondary calcination is 200° C. to 500° C., and the time of the secondary calcination is 1 hour to 10 hours.

9. The method for preparing lithium sulfide according to claim 1, wherein: The first inert atmosphere, the second inert atmosphere, the third inert atmosphere and the fourth inert atmosphere are each independently selected from at least one of nitrogen and argon.

10. Lithium sulfide, characterized in that The method is prepared according to any one of claims 1 to 9.

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