A preparation method of lithium bis(fluorosulfonyl)imide

Abstract

The present invention relates to the technical field of lithium bis(fluorosulfonyl)imide preparation, and discloses a preparation method of lithium bis(fluorosulfonyl)imide; the method comprises the following steps: S1, preparing sulfuryl fluoride; using calcium fluoride and sulfur trioxide as raw materials, reacting at high temperature in the presence of a catalyst to obtain a mixed gas containing sulfuryl fluoride; the mixed gas is processed to obtain gaseous sulfuryl fluoride; S2, preparing lithium bis(fluorosulfonyl)imide; introducing the gaseous sulfuryl fluoride obtained in step S1 into an organic solvent containing lithium nitride, reacting to obtain a slurry; separating the solid and liquid of the slurry to obtain a first filtrate, concentrating the first filtrate and crystallizing to obtain a crystalline slurry; filtering the crystalline slurry to obtain lithium bis(fluorosulfonyl)imide. When preparing sulfuryl fluoride, the present invention uses potassium fluoride as a catalyst, and the reaction temperature and pressure are significantly lower than the data of the prior art, and the sulfuryl fluoride yield is above 93%; the calcium fluoride raw material is cheap, and lithium bis(fluorosulfonyl)imide is prepared by a two-step method, and the overall process route has good economic benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of lithium bis(fluorosulfonyl)imide, and particularly to a method for preparing lithium bis(fluorosulfonyl)imide. Background Art

[0002] Lithium bis(fluorosulfonyl)imide, as a new type of lithium battery electrolyte, has high conductivity, high thermal stability and chemical stability, excellent high and low temperature performance, and can effectively improve the safety and cycle life of lithium batteries. It is a next-generation functional lithium salt expected to replace lithium hexafluorophosphate.

[0003] Among many preparation process methods of lithium bis(fluorosulfonyl)imide, the method of using sulfuryl fluoride as a raw material combined with an amine source to prepare lithium bis(fluorosulfonyl)imide is one of the important routes. However, sulfuryl fluoride raw materials are not easily available and the market price is relatively high. Using relatively basic fluorine raw materials to first prepare sulfuryl fluoride and then further synthesize lithium bis(fluorosulfonyl)imide has better economic benefits. Calcium fluoride is one of the most basic fluorine raw materials, which is derived from natural fluorite and is inexpensive. In the last century, American factories have studied the preparation of sulfuryl fluoride from calcium fluoride, but the reaction conditions are harsh and the yield is low, so this method has not been popularized. For example, the US patent "Preparation of sulfuryl fluoride" with the publication number US3146068A reacts calcium fluoride and sulfur trioxide at a temperature of 600 - 800 °C and a pressure of 500 - 2000 p.s.i.g (equivalent to 34 - 138 atmospheres) to obtain a mixture of sulfuryl fluoride, silicon tetrafluoride and sulfur trioxide, and the reaction conversion rate is less than 30%. The US patent "Method for production of sulfuryl fluoride" with the publication number US3132925A passes gaseous sulfur trioxide through calcium fluoride heated to 300 - 600 °C with a contact time controlled to be 12 - 24 seconds to obtain a mixture of sulfuryl fluoride, silicon tetrafluoride and sulfur dioxide, and the highest reaction yield is 85%.

[0004] Therefore, there is an urgent need for a method for preparing lithium bis(fluorosulfonyl)imide to solve the above technical problems. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above deficiencies and provide a method for preparing lithium bis(fluorosulfonyl)imide, which first uses calcium fluoride to prepare sulfuryl fluoride and then further synthesizes lithium bis(fluorosulfonyl)imide.

[0006] To achieve the above purpose, the present invention is implemented according to the following technical scheme:

[0007] A method for preparing lithium bis(fluorosulfonyl)imide, comprising the following steps:

[0008] S1, preparing sulfuryl fluoride

[0009] Using calcium fluoride and sulfur trioxide as raw materials, a sulfuryl fluoride-containing mixed gas is prepared by high-temperature reaction in the presence of a catalyst; the mixed gas is processed to obtain gaseous sulfuryl fluoride;

[0010] The reaction equation of calcium fluoride and sulfur trioxide is: CaF2 + 2SO3 → SO2F2 + CaSO4;

[0011] S2, for preparing lithium bis(fluorosulfonyl)imide

[0012] The gaseous sulfuryl fluoride obtained in step S1 is introduced into an organic solvent containing lithium nitride, and after reaction, a slurry is obtained; the slurry is separated into solid and liquid to obtain a first filtrate, and the first filtrate is concentrated and crystallized to obtain a crystalline slurry; the crystalline slurry is filtered to obtain lithium bis(fluorosulfonyl)imide;

[0013] The reaction equation of sulfuryl fluoride and lithium nitride is: 2SO2F2 + Li3N → LiN(SO2F)2 + 2LiF.

[0014] Preferably, the catalyst is potassium fluoride, and the dosage of the catalyst is 5-10% of the amount of substance of calcium fluoride. Preferably, the molar ratio of calcium fluoride to sulfur trioxide is 1:(2.5-3.0).

[0015] Preferably, in step S1, the reaction temperature is 300-350 °C, and the reaction pressure does not exceed 0.6 MPa;

[0016] In step S1, calcium fluoride and the catalyst are mixed evenly at room temperature, and after heating up in a reaction furnace, sulfur trioxide vapor at the same temperature as the reaction furnace is introduced, and the gas-solid contact time is greater than 30 seconds.

[0017] During the reaction, the reaction bed of the reaction furnace is continuously turned over to make the solid and gas fully contact and reduce the encapsulation of calcium fluoride and potassium fluoride by calcium sulfate.

[0018] Preferably, the sulfuryl fluoride-containing mixed gas is cooled, washed with water, and condensed to obtain sulfuryl fluoride.

[0019] The raw material calcium fluoride often contains a small amount of iron oxide and silicon dioxide impurities. After the reaction, iron oxide is converted into iron sulfate, and silicon dioxide is converted into silicon tetrafluoride gas.

[0020] The mixed gas obtained after the reaction contains excessive sulfur trioxide, impurity silicon tetrafluoride, and by-product sulfur dioxide. The mixed gas is cooled, washed with water, and condensed to remove sulfur trioxide, silicon tetrafluoride, and sulfur dioxide impurities in sequence to obtain high-purity sulfuryl fluoride.

[0021] Preferably, a solid mixture is also obtained after the reaction in step S1. The solid mixture is soaked in water and filtered to obtain a second filtrate, and the second filtrate is concentrated to obtain potassium fluoride.

[0022] The solid mixture after the reaction is calcium sulfate and potassium fluoride. It is soaked in water and filtered, and the recovered potassium fluoride from the concentrated filtrate can be reused.

[0023] In the present invention, the catalytic principle of potassium fluoride is that the crystal lattice energy of potassium fluoride is smaller than that of calcium fluoride (the melting point of potassium fluoride is 858 °C, and the melting point of calcium fluoride is 1402 °C). Under high-temperature conditions, fluoride ions (F - ) are more likely to break away from the lattice binding and combine with sulfur in sulfur trioxide to form sulfuryl fluoride and leave the system in the form of gas. And the defective potassium fluoride lattice is unstable and then combines with F in calcium fluoride - to combine.

[0024] Preferably, the mass ratio of lithium nitride to the organic solvent is (0.05 - 0.1):1; the molar ratio of sulfuryl fluoride to lithium nitride is (2.1 - 3):1. The excessive sulfuryl fluoride during the reaction process can be recovered and reused.

[0025] Preferably, the organic solvent is an organic solvent that can dissolve lithium bis(fluorosulfonyl)imide but cannot dissolve lithium fluoride; the reaction temperature for the reaction of sulfuryl fluoride gas with lithium nitride in step S2 is -20 °C to 30 °C, and the reaction time is 12 - 48 h.

[0026] Specifically, the organic solvent is one of dimethyl carbonate, diethyl carbonate, diethyl ether, and ethyl acetate.

[0027] Preferably, in step S2, the crystallization process is as follows: After adding an antisolvent to the concentrated first filtrate, stir and crystallize for 6 - 12 h. The volume of the concentrated first filtrate is 40 - 50% of the original volume of the first filtrate.

[0028] Preferably, the antisolvent is one of dichloromethane, dichloroethane, carbon tetrachloride, chloroform, and toluene; the addition amount of the antisolvent is 6 - 10 times the theoretical mass of the lithium salt. The theoretical lithium salt here refers to the theoretical value of lithium bis(fluorosulfonyl)imide, that is, the theoretical value of lithium bis(fluorosulfonyl)imide calculated according to the reaction equation of sulfuryl fluoride and lithium nitride with all lithium nitride reacted.

[0029] The antisolvent can reduce the solubility of the lithium bis(fluorosulfonyl)imide product in the organic solvent and facilitate the precipitation of the product.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] In the present invention, potassium fluoride is used as a catalyst in the preparation of sulfuryl fluoride, and the reaction temperature and pressure are significantly lower than the data of the prior art. The yield of sulfuryl fluoride is above 93%; calcium fluoride raw materials are cheap, and lithium bis(fluorosulfonyl)imide is prepared by a two-step method, and the overall process route has good economic benefits. Specific Embodiments

[0032] A preparation method of lithium bis(fluorosulfonyl)imide, comprising the following steps:

[0033] The first step is to prepare sulfuryl fluoride

[0034] Using calcium fluoride and sulfur trioxide as raw materials, potassium fluoride as a catalyst, reacting at high temperature to obtain a high-temperature mixed gas containing sulfuryl fluoride, and also obtaining a solid mixture.

[0035] The chemical reaction is CaF2 + 2SO3 → SO2F2 + CaSO4.

[0036] The molar ratio of calcium fluoride to sulfur trioxide is 1:(2.5 - 3.0), and the dosage of the catalyst potassium fluoride is 5 - 10% of the amount of substance of calcium fluoride.

[0037] The raw material calcium fluoride and the catalyst potassium fluoride are first mixed evenly at room temperature, then put into a tubular reaction furnace and heated to 300 - 350 °C, and then sulfur trioxide vapor at the same temperature is introduced, with the pressure not exceeding 0.6 MPa (equivalent to 6 atmospheres), and the gas-solid contact time is greater than 30 seconds.

[0038] During the reaction process, the reaction bed of the tubular reaction furnace is continuously turned over to make the solid and gas fully contact, and reduce the encapsulation of calcium sulfate on calcium fluoride and potassium fluoride.

[0039] The raw material calcium fluoride often contains a small amount of iron oxide and silicon dioxide impurities. After the reaction, iron oxide is converted into iron sulfate, and silicon dioxide is converted into silicon tetrafluoride gas.

[0040] The high-temperature mixed gas after the reaction contains excessive sulfur trioxide, impurity silicon tetrafluoride and by-product sulfur dioxide. The mixed gas is cooled, washed with water, and condensed to remove sulfur trioxide, silicon tetrafluoride and sulfur dioxide impurities in turn to obtain high-purity sulfuryl fluoride.

[0041] The solid mixture after the reaction is calcium sulfate and potassium fluoride. It is soaked in water and filtered, and the potassium fluoride recovered by concentrating the filtrate can be reused.

[0042] The catalytic principle of potassium fluoride is that the crystal lattice energy of potassium fluoride is smaller than that of calcium fluoride (the melting point of potassium fluoride is 858 °C, and the melting point of calcium fluoride is 1402 °C). Under high-temperature conditions, fluoride ions (F - ) are more likely to break away from the lattice binding and combine with sulfur in sulfur trioxide to form sulfuryl fluoride and leave the system in the form of gas, and the defective potassium fluoride lattice is unstable and then combines with F in calcium fluoride - again.

[0043] The second step is to prepare lithium bis(fluorosulfonyl)imide

[0044] The sulfuryl fluoride gas obtained in the first step is introduced into an organic solvent in which lithium nitride is dispersed. After the reaction, a slurry is obtained. The solid-liquid separation is carried out to obtain a filtrate. The filtrate is concentrated to obtain a concentrated solution. The concentrated solution is stirred and crystallized under the condition of a precipitating agent to obtain a crystalline slurry, and lithium bis(fluorosulfonyl)imide crystals are separated from the crystalline slurry.

[0045] The chemical reaction is 2SO2F2 + Li3N → LiN(SO2F)2 + 2LiF.

[0046] The mass ratio of lithium nitride to the organic solvent is (0.05 - 0.1):1.

[0047] The molar ratio of sulfuryl fluoride to lithium nitride is (2.1 - 3):1, and the excessive sulfuryl fluoride can be recycled and reused.

[0048] The reaction temperature is -20°C to 30°C, and the reaction time is 12 to 48 h.

[0049] The organic solvent can dissolve lithium bis(fluorosulfonyl)imide well but does not dissolve lithium fluoride, and is selected from one of dimethyl carbonate, diethyl carbonate, and diethyl ether.

[0050] The volume of the concentrated solution is 40 - 50% of the original volume of the filtrate.

[0051] The precipitating agent can reduce the solubility of lithium bis(fluorosulfonyl)imide product in the organic solvent and facilitate the precipitation of the product. It is selected from one of dichloromethane, dichloroethane, carbon tetrachloride, and chloroform, and the addition amount is 6 - 10 times the mass of the theoretical lithium salt.

[0052] The crystallization process is to stir and crystallize for 6 - 12 h after adding the precipitating agent.

[0053] The following further describes the present invention with specific embodiments. The schematic embodiments and explanations of the present invention are used to explain the present invention, but do not limit the present invention. In the following embodiments, sulfur trioxide vapor is circulated and introduced, so the gas-solid contact time must be greater than 30 s, which is not emphasized in the following embodiments.

[0054] Example 1:

[0055] A preparation method of lithium bis(fluorosulfonyl)imide includes the following steps:

[0056] The first step is to prepare sulfuryl fluoride

[0057] Pre-mix 300 g of calcium fluoride and 12 g of potassium fluoride evenly in advance, put them into the dry tubular reaction furnace A, and close and heat up to 350 °C; heat sulfur trioxide to 350 °C in another container B to form a gas (obtain sulfur trioxide vapor), and introduce it into the tubular reaction furnace A with a flow rate of 3 L / min. At the same time, continuously turn the reaction bed of the tubular reaction furnace A. The reacted mixed gas is then returned to the container B for heating up, and new sulfur trioxide vapor is replenished and introduced into the tubular reaction furnace A again for circulation. The total amount of sulfur trioxide introduced is 770 g. After stopping the replenishment of new sulfur trioxide, continue to circulate for 30 min. The process pressure does not exceed 0.6 MPa all the time. Cool the reacted mixed gas to room temperature, separate out the sulfur trioxide liquid, then remove silicon tetrafluoride and part of sulfur dioxide through a water scrubber, and then introduce it into a -30 °C cold trap to remove sulfur dioxide and water vapor, obtaining 368 g of gas sulfuryl fluoride with a yield of 93.8% and a purity of 99.6%.

[0058] Step 2: Prepare lithium bis(fluorosulfonyl)imide

[0059] Disperse 20 g of lithium nitride into 400 g of dimethyl carbonate solvent, cool to -20 °C, then introduce 124 g of the gas sulfuryl fluoride obtained in the first step, and then heat to 30 °C for reaction for 24 h to obtain a slurry. Then filter to obtain a clear filtrate. Concentrate the clear filtrate at 60 °C and -0.098 Mpa to obtain a concentrated solution. The volume of the concentrated solution is 40% of the original volume of the clear filtrate; then add 650 g of dichloromethane, stir and crystallize for 10 h, filter, wash the filter cake three times with dichloromethane slurry, each time adding dichloromethane with a mass 1 time that of the filter cake. The obtained powder is dried in nitrogen at 60 °C for 8 h to obtain 79.9 g of lithium bis(fluorosulfonyl)imide powder with a yield of 74.4%. The 19F NMR test is 51.8 ppm (solvent deuterated acetonitrile, internal standard CCl3F), and the purity is 99.96%.

[0060] Example 2:

[0061] A preparation method of lithium bis(fluorosulfonyl)imide, comprising the following steps:

[0062] Step 1: Prepare sulfuryl fluoride

[0063] Pre-mix 300 g of calcium fluoride and 22 g of potassium fluoride evenly in advance, put them into the dry tubular reaction furnace A, close it and heat up to 300 °C; heat sulfur trioxide to 300 °C in another container B to form a gas (obtain sulfur trioxide vapor), and introduce it into the tubular reaction furnace A with a flow rate of 3 L / min. At the same time, continuously turn the reaction bed of the tubular reaction furnace A. The reacted mixed gas is then returned to the container B to be heated up, new sulfur trioxide vapor is supplemented and introduced into the tubular reaction furnace A again, and the cycle is carried out. The total amount of sulfur trioxide introduced is 920 g. After stopping the supplement of new sulfur trioxide, continue the cycle for another 30 min. The process pressure does not exceed 0.6 MPa all the time. Cool the reacted mixed gas to room temperature, separate out the sulfur trioxide liquid, then remove silicon tetrafluoride and part of sulfur dioxide through a water scrubber, and then introduce it into a -30 °C cold trap to remove sulfur dioxide and water vapor, obtaining 379 g of sulfuryl fluoride with a yield of 96.6% and a purity of 99.5%.

[0064] Step 2, prepare lithium bis(fluorosulfonyl)imide

[0065] Disperse 40 g of lithium nitride in 400 g of diethyl ether solvent, cool it to -10 °C, then introduce 351 g of the sulfuryl fluoride gas obtained in the first step, and then heat it to 25 °C for reaction for 24 h to obtain a slurry. Then filter to obtain a clear filtrate. Concentrate the clear filtrate at 30 °C and -0.098 Mpa to obtain a concentrated solution. The volume of the concentrated solution is 50% of the original volume of the clear filtrate; then add 2140 g of carbon tetrachloride, stir and crystallize for 12 h, filter, wash the filter cake three times with carbon tetrachloride slurry, each time adding carbon tetrachloride with a mass 1 time that of the filter cake. The obtained powder is dried in nitrogen at 60 °C for 8 h to obtain 203.7 g of lithium bis(fluorosulfonyl)imide powder with a yield of 94.8%. The 19F NMR test is 51.8 ppm (solvent deuterated acetonitrile, internal standard CCl3F), and the purity is 99.97%.

[0066] Example 3:

[0067] A preparation method of lithium bis(fluorosulfonyl)imide, comprising the following steps:

[0068] Step 1, prepare sulfuryl fluoride

[0069] Pre-mix 300 g of calcium fluoride and 17 g of potassium fluoride evenly, put them into a dry tubular reaction furnace A, close it and heat up to 330 °C; heat sulfur trioxide to 330 °C in another container B to form a gas (obtain sulfur trioxide vapor), and introduce it into the tubular reaction furnace A with a flow rate of 3 L / min. At the same time, continuously turn the reaction bed of the tubular reaction furnace A. The reacted mixed gas is then returned to the container B for heating up, and new sulfur trioxide vapor is supplemented and introduced into the tubular reaction furnace A again for circulation. The total amount of sulfur trioxide introduced is 831 g. After stopping the supplement of new sulfur trioxide, continue to circulate for 30 min. The pressure during the process does not exceed 0.6 MPa all the time. Cool the reacted mixed gas to room temperature, separate out the sulfur trioxide liquid, then remove silicon tetrafluoride and part of sulfur dioxide through a water scrubber, and then introduce it into a -30 °C cold trap to remove sulfur dioxide and water vapor, obtaining 372 g of gaseous sulfuryl fluoride with a yield of 94.9% and a purity of 99.6%.

[0070] Step 2: Prepare lithium bis(fluorosulfonyl)imide

[0071] Disperse 30 g of lithium nitride into 400 g of ethyl acetate solvent, cool it to 0 °C, then introduce 229 g of the gaseous sulfuryl fluoride obtained in the first step, and then heat it to 30 °C for reaction for 24 h to obtain a slurry. Then filter to obtain a clear filtrate. Concentrate the clear filtrate at 50 °C and -0.098 Mpa to obtain a concentrated solution. The volume of the concentrated solution is 45% of the original volume of the clear filtrate; then add 1290 g of toluene, stir and crystallize for 6 h, filter, wash with toluene slurry three times, each time adding toluene with a mass 1 time that of the filter cake, and dry the obtained powder in nitrogen at 60 °C for 8 h to obtain 138.1 g of lithium bis(fluorosulfonyl)imide powder with a yield of 85.7%. The 19F NMR test is 51.8 ppm (solvent deuterated acetonitrile, internal standard CCl3F), and the purity is 99.96%.

[0072] The technical solution of the present invention is not limited to the limitations of the above specific embodiments. Any technical deformation made according to the technical solution of the present invention falls within the protection scope of the present invention.

Claims

1. A preparation method of lithium bis(fluorosulfonyl)imide, characterized in that: It includes the following steps: S1. Prepare sulfuryl fluoride Using calcium fluoride and sulfur trioxide as raw materials, react at high temperature in the presence of a catalyst to obtain a mixed gas containing sulfuryl fluoride; the mixed gas is processed to obtain gaseous sulfuryl fluoride; the catalyst is potassium fluoride, and the dosage of the catalyst is 5-10% of the amount of substance of calcium fluoride; S2. Prepare lithium bis(fluorosulfonyl)imide Pass the gaseous sulfuryl fluoride obtained in step S1 into an organic solvent containing lithium nitride, and after reaction, obtain a slurry; separate the solid and liquid of the slurry to obtain a first filtrate, concentrate the first filtrate and crystallize to obtain a crystalline slurry; filter the crystalline slurry to obtain lithium bis(fluorosulfonyl)imide; The molar ratio of the calcium fluoride to the sulfur trioxide is 1:(2.5-3.0); In step S1, the reaction temperature is 300-350 °C, and the reaction pressure does not exceed 0.6 MPa; In step S1, the calcium fluoride and the catalyst are mixed evenly at room temperature, after heating up in a reaction furnace, sulfur trioxide vapor at the same temperature as the reaction furnace is introduced, and the gas-solid contact time is greater than 30 seconds.

2. The preparation method of lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The mixed gas containing sulfuryl fluoride is cooled, washed with water, and condensed to obtain sulfuryl fluoride.

3. A preparation method of lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: After the reaction in step S1, a solid mixture is also obtained. The solid mixture is soaked in water and filtered to obtain a second filtrate, and the second filtrate is concentrated to obtain potassium fluoride.

4. A preparation method of lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The mass ratio of the lithium nitride to the organic solvent is (0.05-0.1):1; the molar ratio of the sulfuryl fluoride to the lithium nitride is (2.1-3):

1.

5. A preparation method of lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The organic solvent is an organic solvent that can dissolve lithium bis(fluorosulfonyl)imide but does not dissolve lithium fluoride; in step S2, the reaction temperature for the reaction of sulfuryl fluoride gas with lithium nitride is -20 °C to 30 °C, and the reaction time is 12-48 h.

6. The preparation method of lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: In step S2, the crystallization process is: adding a precipitant to the concentrated first filtrate and stirring for crystallization for 6-12 h.

7. A method for preparing lithium bis(fluorosulfonyl)imide according to claim 6, characterized in that: The precipitant is one of dichloromethane, dichloroethane, carbon tetrachloride, chloroform, toluene; the addition amount of the precipitant is 6-10 times the mass of the theoretical lithium salt.