Process for directly synthesizing battery-grade lithium sulfide

Abstract

The invention discloses a process for directly synthesizing battery-grade lithium sulfide, which comprises the following steps: enabling metal lithium and sulfur to directly react in an inert gas atmosphere under the conditions of 30-350kPa and 945-1320 DEG C to generate a reaction product A containing lithium sulfide and lithium polysulfide; the molar ratio of metal lithium to sulfur is 1: (15-32); reducing the temperature of the reaction product A to 390-705 DEG C, carrying out countercurrent contact reaction on the reaction product A and hydrogen at 20-65 DEG C, and converting lithium polysulfide into lithium sulfide to obtain a reaction product B; and cooling and crushing the reaction product B to obtain the battery-grade lithium sulfide. The method is low in raw material cost, high in product purity and capable of fully recovering heat energy.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy solid-state batteries, and in particular to a process for directly synthesizing battery-grade lithium sulfide. Background Art

[0002] All-solid-state lithium-ion batteries have high safety performance and excellent electrochemical properties due to the use of non-flammable solid electrolytes. Sulfide solid electrolytes have attracted widespread attention among several types of solid electrolytes because of their high ionic conductivity. Lithium sulfide (Li2S) is a key raw material for the preparation of sulfide electrolytes for solid-state batteries. A 1GWh solid-state battery based on Li6PS5Cl (LPSC) electrolyte consumes 400-450 kg of Li2S. The current kilogram-level bulk purchase price is 6000-7000 yuan / kg, accounting for 99% of the cost of LPSC electrolyte raw materials. The high price limits its widespread application in the market and hinders the rapid development of sulfide solid-state batteries. Therefore, exploring low-cost large-scale synthesis of battery-grade lithium sulfide has become one of the key factors for the industrialization of sulfide solid electrolytes.

[0003] At present, the industrial production method of Li2S is carbon thermal reduction (Li2SO4+2C→Li2S+2CO2), which has many by-products and emits CO2. Other synthesis methods include double decomposition (2LiCl+Na2S→Li2S+2NaCl), solid phase reaction (2LiOH+H2S→Li2S+H2O or Li2CO3+H2S→Li2S+H2O+CO2), etc. Double decomposition reaction and gas-solid phase reaction are not thorough, and the product purity cannot meet the requirements. Double decomposition reaction requires a large amount of organic solvents, which pollutes the environment. High temperature reaction has high requirements for reaction equipment and has certain safety risks. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention aims to provide a process for directly synthesizing battery-grade lithium sulfide.

[0005] In order to achieve the above object, the present invention adopts the following technical solution:

[0006] A process for directly synthesizing battery-grade lithium sulfide comprises the following steps:

[0007] S1. Directly react metallic lithium and sulfur in an inert gas atmosphere at 30-350 kPa and 945-1320°C to generate a reaction product A containing lithium sulfide and lithium polysulfide; the molar ratio of metallic lithium to sulfur is 1:15-32. The main reaction process includes:

[0008] S+2Li→Li2S

[0009] xS+2Li→Li2Sx

[0010] S2, after reducing the temperature of the reaction product A obtained in step S1 to 390-705°C, the reaction is carried out in a countercurrent contact reaction with hydrogen at 20-65°C to convert lithium polysulfide into lithium sulfide to obtain a reaction product B. The main reaction process includes:

[0011] (x-1)H2+Li2Sx→(x-1)H2S+Li2S

[0012] S3. The reaction product B obtained in step S2 is cooled and crushed to obtain battery-grade lithium sulfide.

[0013] Furthermore, in step S1, the purity of sulfur is above 99.95%, and metallic lithium is obtained by electrolyzing lithium chloride; the mixed gas of sulfur-containing vapor and inert gas remaining after the reaction of sulfur and metallic lithium enters the sulfur recovery system after waste heat recovery and cooling, and the sulfur recovered by the sulfur recovery system and the liquid sulfur generated by condensation of the mixed gas during the waste heat recovery and cooling process are returned to participate in the reaction of metallic lithium.

[0014] Furthermore, in step S1, a waste heat boiler is used to recover waste heat from the mixed gas containing sulfur steam and inert gas, and saturated steam is produced as a by-product. The pressure of the saturated steam is 0.3-4MPa, and the mixed gas after waste heat recovery is cooled to 70-145°C using circulating cooling water.

[0015] Furthermore, in step S2, the hydrogen-containing tail gas generated by the countercurrent contact reaction between the reaction product A and hydrogen enters the sulfur recovery system, and the sulfur recovered by the sulfur recovery system is returned to participate in the reaction of the metallic lithium.

[0016] Furthermore, in step S1, the inert gas includes at least one of argon, helium and neon, and the oxygen content is less than 210 ppm, and the nitrogen content is less than 0.05%.

[0017] Furthermore, in step S2, saturated steam or a waste heat boiler is used to recover waste heat from the reaction product A, and superheated steam or saturated steam is produced as a by-product.

[0018] Furthermore, in step S2, the molar ratio of the hydrogen to the sum of lithium sulfide and lithium polysulfide in the reaction product A is 1:0.3-10, and the mass content of hydrogen sulfide in the hydrogen-containing tail gas produced by the countercurrent contact reaction of the hydrogen and the reaction product A is 30-65%.

[0019] Furthermore, in step S3, the reaction product B is cooled to 30-55° C., and after air flow pulverization and iron removal, battery-grade lithium sulfide is obtained.

[0020] Furthermore, the sulfur recovery system adopts a combination of a two-stage Claus process and a super Claus process or a combination of a three-stage Claus process and a super Claus process to achieve sulfur recovery. The main reaction process includes:

[0021] 2H2S+3O2→2SO2+2H2O

[0022] SO2+2H2S→3S+2H2O

[0023] 2H2S+O2→2H2O+2S

[0024] Furthermore, in step S1, the sulfur is stored in a liquid sulfur storage system, and the liquid sulfur storage system includes a liquid sulfur pool, and the liquid sulfur pool uses a steam jacket to heat the sulfur to 115-140°C.

[0025] The beneficial effects of the present invention are:

[0026] 1. The present invention uses sulfur and metallic lithium to directly produce battery-grade lithium sulfide, and the raw material cost is low;

[0027] 2. The present invention uses sulfur with a purity of 99.95% to directly react with metallic lithium obtained by lithium chloride electrolysis. The product has high purity and can meet the production needs of downstream sulfide electrolytes and sulfide solid-state batteries.

[0028] 3. The present invention strictly controls the reaction temperature of sulfur and metallic lithium to 945-1320°C. At this time, sulfur and metallic lithium react in gas-liquid phase (sulfur is in gas phase, metallic lithium is in liquid phase), with full contact and high conversion rate.

[0029] 4. The present invention adds excess sulfur and uses sulfur vaporization to take away the reaction heat of metallic lithium and sulfur, thereby maintaining the heat balance of the reaction, increasing the reaction rate, and controlling side reactions; and a small amount of lithium polysulfide generated due to excess sulfur is removed by hydrogenation reduction to improve the purity of the product;

[0030] 5. The present invention strictly controls the nitrogen and oxygen content in the inert atmosphere to ensure the quality of lithium sulfide;

[0031] 6. In the present invention, the reaction tail gas of metallic lithium and sulfur and the reaction tail gas reduced by hydrogen adopt a sulfur recovery system to recover sulfur, which can further improve the utilization rate of raw materials and make the consumption of metallic lithium and sulfur per unit product lithium sulfide close to the theoretical value;

[0032] 7. The present invention fully recovers the reaction heat, and the recovered heat can be used for sulfur melting or external steam, thereby effectively reducing carbon emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a schematic diagram of the device structure of Example 3 of the present invention. DETAILED DESCRIPTION

[0034] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0035] Example 1

[0036] This embodiment provides a process for directly synthesizing battery-grade lithium sulfide, comprising the following steps:

[0037] S1. Directly react metallic lithium and sulfur in an inert gas atmosphere at 30 kPa and 945° C. to generate a reaction product A containing lithium sulfide and lithium polysulfide; the molar ratio of metallic lithium to sulfur is 1:15. The sulfur is stored in a liquid sulfur storage system, which includes a liquid sulfur pool. The liquid sulfur pool uses a steam jacket to heat the sulfur to 115° C. to prevent the liquid sulfur from solidifying.

[0038] The mixed gas containing sulfur steam and inert gas produced by the reaction is recovered by waste heat boiler, and saturated steam is produced as a by-product, and the pressure of saturated steam is 0.3MPa. The mixed gas after waste heat recovery is cooled to 70°C by circulating cooling water, and then enters the sulfur recovery system. The sulfur recovered by the sulfur recovery system and the liquid sulfur condensed during waste heat recovery and cooling are returned to the liquid sulfur storage system to continue to participate in the reaction of metallic lithium.

[0039] The inert gas is argon, with an oxygen content of 10 ppm and a nitrogen content of <0.05%.

[0040] S2. After the temperature of the reaction product A obtained in step S1 is reduced to 390° C. by waste heat recovery, the reaction product A is subjected to countercurrent contact reaction with hydrogen at 20° C. to convert lithium polysulfide into lithium sulfide to obtain a reaction product B, wherein the molar ratio of the hydrogen to the sum of lithium sulfide and lithium polysulfide in the reaction product A is 1:10. The hydrogen-containing tail gas produced by the reaction has a hydrogen sulfide content of 65% and enters the sulfur recovery system. The sulfur recovered by the sulfur recovery system is returned to the liquid sulfur storage system to continue to be used in the reaction of the metallic lithium.

[0041] In this embodiment, the reaction product A uses a waste heat boiler to recover waste heat and produce saturated steam as a by-product.

[0042] S3. After the reaction product B obtained in step S2 is cooled to 30° C., it is subjected to air flow pulverization and iron removal to obtain battery-grade lithium sulfide.

[0043] In this embodiment, the sulfur recovery system combines a three-stage conventional Claus process and a super Claus process for sulfur recovery.

[0044] Example 2

[0045] This embodiment provides a process for directly synthesizing battery-grade lithium sulfide, comprising the following steps:

[0046] S1. Directly react metallic lithium and sulfur in an inert gas atmosphere at 350 kPa and 1320° C. to generate a reaction product A containing lithium sulfide and lithium polysulfide; the molar ratio of metallic lithium to sulfur is 1:32. The sulfur is stored in a liquid sulfur storage system, which includes a liquid sulfur pool. The liquid sulfur pool uses a steam jacket to heat the sulfur to 140° C. to prevent the liquid sulfur from solidifying.

[0047] The mixed gas containing sulfur steam and inert gas produced by the reaction is recovered by waste heat boiler, and saturated steam is produced as a by-product, and the pressure of saturated steam is 4MPa. The mixed gas after waste heat recovery is cooled to 145°C by circulating cooling water, and then enters the sulfur recovery system. The sulfur recovered by the sulfur recovery system and the liquid sulfur condensed during waste heat recovery and cooling are returned to the liquid sulfur storage system to continue to participate in the reaction of metallic lithium.

[0048] The inert gas is helium, with an oxygen content of 5 ppm and a nitrogen content of <0.02%.

[0049] S2. After the temperature of the reaction product A obtained in step S1 is reduced to 705° C. by waste heat recovery, the reaction product A is subjected to countercurrent contact reaction with hydrogen at 65° C. to convert lithium polysulfide into lithium sulfide to obtain a reaction product B, wherein the molar ratio of the hydrogen to the sum of the lithium sulfide and the lithium polysulfide in the reaction product A is 1:0.3. The hydrogen-containing tail gas produced by the reaction has a hydrogen sulfide content of 30% and enters the sulfur recovery system. The sulfur recovered by the sulfur recovery system is returned to the liquid sulfur storage system to continue to be used in the reaction of the metallic lithium.

[0050] In this embodiment, the reaction product A utilizes saturated steam to recover waste heat and produces superheated steam as a by-product.

[0051] S3. After the reaction product B obtained in step S2 is cooled to 55° C., it is subjected to air flow pulverization and iron removal to obtain battery-grade lithium sulfide.

[0052] In this embodiment, the sulfur recovery system combines a two-stage conventional Claus process and a super Claus process to perform sulfur recovery.

[0053] Example 3

[0054] This embodiment provides a device for implementing the methods of Embodiment 1 and Embodiment 2, such as Figure 1 As shown, it includes a reaction system, a waste heat recovery system 1, a liquid sulfur storage system, a sulfur recovery system, a cooling system 1, a waste heat recovery system 2, a hydrogenation system and a cooling system 2.

[0055] Metallic lithium and sulfur react in the reaction system, and metallic lithium is obtained by electrolyzing lithium chloride. The reaction product A obtained by the reaction of metallic lithium and sulfur enters the waste heat recovery system 1 for waste heat recovery, and the remaining mixed gas containing sulfur vapor and inert gas enters the waste heat recovery system 2 for waste heat recovery, then enters the cooling system 1 for cooling, and then enters the sulfur recovery system to recover sulfur. The liquid sulfur condensed in the waste heat recovery system 2 and the cooling system 1 returns to the liquid sulfur storage system. The reaction product A after waste heat recovery by the waste heat recovery system 1 enters the hydrogenation system, and reacts with high-purity hydrogen in countercurrent contact. The obtained reaction product B enters the cooling system 2 for cooling, and further gas flow crushing and iron removal are used to obtain battery-grade lithium sulfide, and the generated hydrogen-containing tail gas enters the sulfur recovery system to recover sulfur. The sulfur recovered by the sulfur recovery system is returned to the liquid sulfur storage system. Industrial sulfur can be added to the liquid sulfur storage system in a timely manner according to the reaction needs.

[0056] Filtering equipment and overflow equipment can be further installed in the liquid sulfur storage system to ensure the quality of liquid sulfur. Jacket insulation and precision filtering equipment can be installed on the liquid sulfur transportation pipeline between the liquid sulfur storage system and the reaction system to ensure that the liquid sulfur does not solidify and the sulfur content is greater than 99.95%.

[0057] When the amount of lithium metal added is 15 kg / h and the amount of industrial sulfur (purity 99.95%) added is 34.6 kg / h, 49.1 kg / h of battery-grade lithium sulfide can be obtained. When the amount of lithium metal added is 120 kg / h and the amount of industrial sulfur (purity 99.95%) added is 277.3 kg / h, 392 kg / h of battery-grade lithium sulfide can be obtained.

[0058] For those skilled in the art, various corresponding changes and modifications can be made according to the above technical solutions and concepts, and all of these changes and modifications should be included in the protection scope of the claims of the present invention.

Claims

1. A process for directly synthesizing battery-grade lithium sulfide, characterized in that: The following steps are involved: S1. Directly react metallic lithium and sulfur in an inert gas atmosphere at 30-350 kPa and 945-1320° C. to generate a reaction product A containing lithium sulfide and lithium polysulfide; the molar ratio of metallic lithium to sulfur is 1:15-32; S2, after reducing the temperature of the reaction product A obtained in step S1 to 390-705° C., reacting the reaction product A with hydrogen at 20-65° C. in a countercurrent manner to convert the lithium polysulfide into lithium sulfide, thereby obtaining a reaction product B; S3. The reaction product B obtained in step S2 is cooled and crushed to obtain battery-grade lithium sulfide.

2. The process according to claim 1, characterized in that In step S1, the purity of sulfur is above 99.95%, and metallic lithium is obtained by electrolyzing lithium chloride; the remaining mixed gas of sulfur-containing vapor and inert gas after the reaction of sulfur and metallic lithium enters the sulfur recovery system after waste heat recovery and cooling, and the sulfur recovered by the sulfur recovery system and the liquid sulfur generated by condensation of the mixed gas during the waste heat recovery and cooling process are returned to participate in the reaction of metallic lithium.

3. The process according to claim 2, characterized in that In step S1, waste heat boiler is used to recover waste heat from the mixed gas of sulfur-containing steam and inert gas, and saturated steam is produced as a by-product. The pressure of saturated steam is 0.3-4MPa. The mixed gas after waste heat recovery is cooled to 70-145°C by circulating cooling water.

4. The process according to claim 1, characterized in that In step S2, the hydrogen-containing tail gas generated by the countercurrent contact reaction between the reaction product A and hydrogen enters the sulfur recovery system, and the sulfur recovered by the sulfur recovery system is returned to participate in the reaction of the metallic lithium.

5. The process according to claim 1, characterized in that In step S1, the inert gas includes at least one of argon, helium and neon, and the oxygen content is less than 210 ppm and the nitrogen content is less than 0.05%.

6. The process according to claim 1, characterized in that In step S2, saturated steam or a waste heat boiler is used to recover waste heat from the reaction product A, and superheated steam or saturated steam is produced as a by-product.

7. The process according to claim 1, characterized in that In step S2, the molar ratio of the hydrogen to the sum of lithium sulfide and lithium polysulfide in the reaction product A is 1:0.3-10, and the mass content of hydrogen sulfide in the hydrogen-containing tail gas generated by the countercurrent contact reaction of the hydrogen and the reaction product A is 30-65%.

8. The process according to claim 1, characterized in that In step S3, the reaction product B is cooled to 30-55° C., and after air flow pulverization and iron removal, battery-grade lithium sulfide is obtained.

9. The process according to claim 2 or 4, characterized in that The sulfur recovery system adopts a combination of a two-stage Claus process and a super Claus process or a combination of a three-stage Claus process and a super Claus process to achieve sulfur recovery.

10. The process according to claim 1, characterized in that In step S1, the sulfur is stored in a liquid sulfur storage system, which includes a liquid sulfur pool. The liquid sulfur pool uses a steam jacket to heat the sulfur to 115-140°C.

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