Refining method of ultra-pure lithium bis (fluorosulfonyl) imide

Abstract

The invention belongs to the field of chemical purification, and relates to a method for refining ultra-pure lithium bis (fluorosulfonyl) imide, which comprises the following steps of: adding a crude product of lithium bis (fluorosulfonyl) imide with the mass percentage of more than or equal to 90 percent into a crystallizer, heating until the crude product is completely molten into a liquid state, controlling the cooling rate at 5-20K / h, cooling to 90-120 DEG C, keeping the temperature constant, and discharging uncrystallized mother liquor (recrystallizing until the purity of the raw material is reached, thereby obtaining the ultra-pure lithium bis (fluorosulfonyl) imide. Returning to the raw material tank, and discharging the uncrystallized mother liquor out of the system after the purity is lower than 75%; the temperature rise rate is 0.1 K / h to 30 K / h; the temperature of the crystallizer is raised to 125-130 DEG C, the temperature is kept constant, sweat is discharged, the temperature of the crystallizer is raised to 130 DEG C or above, crystals are completely melted and then collected as a product, and the mass percentage content of lithium bis (fluorosulfonyl) imide in the final product is larger than or equal to 99.99%. The method provided by the invention has the advantages of low operation temperature, high efficiency, greenness, safety, no additional solvent, no discharge of three wastes, no side reaction, and high purity and yield of the final product.

Description

Technical Field

[0001] The invention belongs to the field of chemical purification and relates to a preparation method of lithium bis(fluorosulfonyl)imide, in particular to a purification method of ultra-high-purity lithium bis(fluorosulfonyl)imide. Background Art

[0002] The melting point of lithium bis(fluorosulfonyl)imide is 124-128°C. It is a colorless to light yellow liquid at room temperature. It does not decompose below 200°C and has the characteristics of high thermal stability, high conductivity and low volatility. It is often used in the electrolyte of lithium-ion batteries. As an electrolyte additive, it can effectively reduce the resistance of the SEI layer on the electrode surface, improve low-temperature discharge and high-temperature storage performance, thereby improving the battery capacity and electrochemical performance. It also has a wide electrochemical window and can operate within a higher voltage range to provide higher energy output. Studies have shown that the use of high concentrations of LiFSI can effectively inhibit the growth of lithium dendrites, which is crucial to improving the cycle stability and safety of metal lithium batteries. With the reduction of production costs and the maturity of technology, it is expected to achieve wider commercial applications in the next few years, making an important contribution to the improvement of lithium battery performance. At present, lithium bis(fluorosulfonyl)imide is often purified by crystallization or a combination of synthesis and distillation and crystallization, as follows:

[0003] Chinese patent CN117246982A discloses "Lithium bis(fluorosulfonyl)imide and method for purifying lithium bis(fluorosulfonyl)imide". This method adds an organic ammonium salt to a mixture containing lithium bis(fluorosulfonyl)imide to obtain an intermediate mixture through reaction; under alkaline conditions, the intermediate mixture is reacted with lithium ions to obtain lithium bis(fluorosulfonyl)imide. The intermediate mixture is contacted with a decolorizing agent and a cleaning agent to adsorb and remove colored impurities and metal ions. However, this method is cumbersome and costly, and the purity and yield of the final product are not mentioned.

[0004] Chinese patent CN115259113A discloses "a method and device for continuous purification of lithium bis(fluorosulfonyl)imide", wherein a lithium bis(fluorosulfonyl)imide solution is contacted with a dissolving agent in at least one group of hollow fiber membrane components to form a crystallization solution, and then the formed crystallization solution is matured in a crystallizer, and after maturation, a lithium bis(fluorosulfonyl)imide finished product is obtained by vacuum filtration. This method requires the addition of a dissolving agent to lithium bis(fluorosulfonyl)imide, which introduces a new organic solvent, causing environmental pollution, and the subsequent solvent recovery problem needs to be considered, increasing costs.

[0005] The Chinese patent CN115159479A discloses a method for preparing lithium bis(fluorosulfonyl)imide and the Chinese patent CN117699748A discloses a method for preparing high-purity lithium bis(fluorosulfonyl)imide. Both of them are to add sulfamic acid, thionyl chloride and chlorosulfonic acid into a reaction kettle for reaction, and then react with an alkaline lithium source in a non-benign solvent of lithium bis(fluorosulfonyl)imide. After the reaction is completed, the solid-liquid separation is performed to obtain a solid crude product; then washing, drying and recrystallization are performed to obtain lithium bis(fluorosulfonyl)imide. The purity can reach more than 99.9%, and the total yield is not less than 90%. This method is complex, has high energy consumption and cost, introduces new organic solvents, causes serious environmental pollution, and has low purity.

[0006] Chinese patent CN112645294A discloses a method for preparing high-purity lithium bisfluorosulfonyl imide salt and Chinese patent CN116374964A discloses a method for preparing high-purity lithium bisfluorosulfonyl imide. The method comprises adding silicon-lithium alloy or alkyl lithium to an organic solution of bisfluorosulfonyl imide for reaction, and then distilling, filtering and drying the resulting material to obtain a finished product. However, the lithium bisfluorosulfonyl imide product obtained by the above process has low purity and also introduces new organic solvents such as tetrahydrofuran, petroleum ether, and n-hexane. Subsequent solvent recovery will increase costs.

[0007] Chinese patent CN117819494A discloses "a method for purifying lithium bis(fluorosulfonyl)imide", wherein crude lithium bis(fluorosulfonyl)imide is dissolved in an organic solvent, mixed with a dehydrating agent and stirred, the organic solvent is removed by vacuum distillation, and then added to an organic solvent with a lower polarity, and battery-grade lithium bis(fluorosulfonyl)imide is obtained by ultrasonic crystallization. The distillation process of this method has high energy consumption, which increases the cost, and the product purity is low, and the yield is not mentioned.

[0008] Chinese patent CN114852977A discloses "a method for purifying high-purity lithium bis(fluorosulfonyl)imide", which involves mixing lithium bis(fluorosulfonyl)imide salt with an organic solvent until fully dissolved, filtering, and then purifying it by combining gradient cooling crystallization and low-temperature recrystallization. This method does not mention the purity of the crude lithium bis(fluorosulfonyl)imide, the process is time-consuming, and the introduction of organic solvents causes serious environmental pollution.

[0009] Most of the above methods use solution crystallization or synthesis combined with vacuum distillation and crystallization to prepare high-purity lithium bis(fluorosulfonyl)imide. However, the processes are complex and time-consuming. At the same time, organic solvents are introduced, which seriously pollutes the environment. Solvent recovery and treatment issues need to be considered later, resulting in high costs and energy consumption. Summary of the invention

[0010] In order to overcome the shortcomings of the prior art such as complex operation, high production cost, low economic benefit, low product yield and purity, the present invention provides a method for refining ultra-high purity lithium bisfluorosulfonyl imide, which can prepare an ultra-high purity lithium bisfluorosulfonyl imide product with a purity of more than 99.99% by melt crystallization, which is superior to most purification processes of lithium bisfluorosulfonyl imide; and the method is simple in process, highly efficient and energy-saving, environmentally friendly, and does not produce three wastes, which is in line with the development direction of green chemical industry.

[0011] In order to achieve the above object, the present invention adopts the following technical solutions:

[0012] A method for refining ultra-high purity lithium bis(fluorosulfonyl)imide comprises the following steps:

[0013] 1) The temperature of the melt crystallizer is raised to 130° C., crude lithium bis(fluorosulfonyl)imide with a mass percentage of ≥90% is added into the crystallizer, and heated until it is completely melted into a liquid state, the cooling source controls the cooling rate to be 5 to 20 K / h, the final cooling temperature is 90 to 120° C., the temperature is kept constant for 0.5 to 2 hours, and the uncrystallized mother liquor is discharged;

[0014] 2) The crystals in the melt crystallizer are heated at a heating rate of 0.1 to 30 K / h to sweat, the final temperature is 125 to 130° C., the temperature is kept constant for 0.5 to 2 hours, the sweating liquid is discharged, and finally the melt crystallizer is heated to above 130° C., the crystals are completely melted and then collected to obtain an ultra-high purity lithium bis(fluorosulfonyl)imide product, wherein the mass percentage of lithium bis(fluorosulfonyl)imide is ≥99.99%.

[0015] Furthermore, in step 1), the heat transfer temperature difference between the cooling source and the melt is controlled to be less than 5°C.

[0016] Furthermore, in step 1), the cooling rate of the cold source is 5 to 15 K / h, the final temperature of the cooling is 90 to 110° C., and the temperature is maintained at a constant level for 0.5 to 1 hour.

[0017] Furthermore, the uncrystallized mother liquor discharged in step 1) is recrystallized to the purity of the raw material and returned to the raw material tank as the raw material of step 1), and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%.

[0018] Furthermore, in step 2), the heating rate is 5 to 30 K / h, the final temperature is 127 to 130° C., and the temperature is maintained at a constant level for 0.5 to 1 h.

[0019] Furthermore, in step 2), the sweating liquid from the crystals in the melt crystallizer during the period of heating and sweating to the final temperature is returned to step 1) as raw material.

[0020] The advantages and beneficial effects of the present invention are:

[0021] 1. The present invention adopts a melt crystallization process to increase the purity of the product to more than 99.99%, solving the industry problem of those skilled in the art in improving the purity of lithium bis(fluorosulfonyl)imide and having a strong market competitive advantage. The process of the present invention is flexible and can be adjusted according to actual needs.

[0022] 2. After the raw materials of the process of the present invention enter the separation process, the lithium bis(fluorosulfonyl)imide materials obtained in each step can be reused, recovered and re-purified, which is efficient and energy-saving and easy to industrialize. Compared with the currently commonly used synthesis, vacuum distillation and other processes, it has obvious advantages in equipment investment and operating energy consumption. The theoretical recovery rate can reach 99%, and high-purity lithium bis(fluorosulfonyl)imide can be stably produced. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the best implementation case.

[0024] Example 1

[0025] In a 500ml melt crystallizer, 505.3g of crude lithium bis(fluorosulfonyl)imide with a content of 91.2% is put into the melt crystallizer, and the temperature is raised to 130°C to melt all the materials into liquid state, and then the temperature is lowered at a cooling rate of 8K / h, and the final temperature of the cooling is 95°C, and the temperature is kept constant for 0.5h; the uncrystallized mother liquor is discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%). The crystals in the melt crystallizer are heated to 128°C at a heating rate of 5K / h, and the temperature is raised to sweat, and the temperature is kept constant for 0.5h, and the sweating liquid is discharged to the raw material tank and used as raw material; finally, the melt crystallizer is heated to above 130°C, and the crystals are completely melted and collected to obtain 298.77g of ultra-high-purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide is 99.99%, and the total yield is 64.83%.

[0026] Example 2

[0027] In a 500ml melt crystallizer, 498.3g of crude lithium bis(fluorosulfonyl)imide with a content of 95% was added, and the temperature was raised to 130°C to melt all the materials into liquid state, and then the temperature was lowered at a cooling rate of 10K / h, and the final temperature of the cooling was 97°C, and the temperature was kept constant for 0.5h; the uncrystallized mother liquor was discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor was discharged from the system after the purity was lower than 75%). Then the material was raised to 128°C at a heating rate of 6K / h, and the temperature was raised to sweat, and the temperature was kept constant for 0.5h, and the sweating liquid was discharged to the raw material tank and used as raw material; finally, the melt crystallizer was heated to above 130°C, and the crystals were completely melted and collected to obtain 369.42g of ultra-high purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide was 99.99%, and the total yield was 78.03%.

[0028] Example 3

[0029] In a 500ml melt crystallizer, 460g of crude lithium bis(fluorosulfonyl)imide with a content of 98.64% is put into the melt crystallizer, and the temperature is raised to 130°C to melt all the materials into liquid state, and then the temperature is gradually lowered at a cooling rate of 12K / h, and the final temperature of the cooling is 98°C, and the temperature is kept constant for 0.5h; the uncrystallized mother liquor is discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%). Then the material is raised to 129°C at a heating rate of 7K / h, and the temperature is raised to sweat, and the temperature is kept constant for 0.5h, and the sweating liquid is discharged to the raw material tank and used as raw material; finally, the melt crystallizer is heated to above 130°C, and the crystals are completely melted and collected to obtain 383.91g of ultra-high-purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide is 99.99%, and the total yield is 84.6%.

[0030] Example 4

[0031] In a 500ml melt crystallizer, 484g of crude lithium bis(fluorosulfonyl)imide with a content of 99.2% is put into the melt crystallizer, and the temperature is raised to 130°C to melt all the materials into liquid state, and then the temperature is lowered at a cooling rate of 15K / h. When the crystals are about to precipitate, the cooling rate is controlled to 8°C / h, and the final temperature of the cooling is 100°C, and the temperature is kept constant for 0.5h; the uncrystallized mother liquor is discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%). Then the material is raised to 130°C at a heating rate of 8K / h, and the temperature is raised to sweat, and the temperature is kept constant for 0.5h, and the sweating liquid is discharged to the raw material tank and used as raw material; finally, the melt crystallizer is heated to above 130°C, and the crystals are completely melted and collected to obtain 426.59g of ultra-high-purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide is 99.99%, and the total yield is 88.84%.

[0032] Example 5

[0033] In a 500ml melt crystallizer, 511g of crude lithium bis(fluorosulfonyl)imide with a content of 99.7% is put into the melt crystallizer, and the temperature is raised to 130°C to melt all the materials into liquid state, and then the temperature is lowered at a cooling rate of 15K / h, and the final temperature is 100°C, and the temperature is kept constant for 0.5h; the uncrystallized mother liquor is discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%). Then the material is raised to 130°C at a heating rate of 8K / h, and the temperature is kept constant for 0.5h, and the sweating liquid is discharged to the raw material tank and used as raw material; finally, the melt crystallizer is heated to above 130°C, and the crystals are completely melted and collected to obtain 463.15g of ultra-high purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide is 99.99%, and the total yield is 90.9%.

[0034] Comparative Example 1

[0035] In a 500ml melt crystallizer, 505.3g of crude lithium bis(fluorosulfonyl)imide with a content of 91.2% is put into the melt crystallizer, and the temperature is raised to 130°C to melt all the materials into liquid state, and then the temperature is lowered at a cooling rate of 8K / h, and the final temperature of the cooling is 85°C, and the temperature is kept constant for 0.5h; the uncrystallized mother liquor is discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%). The crystals in the melt crystallizer are heated to 128°C at a heating rate of 5K / h, and the temperature is raised to sweat, and the temperature is kept constant for 0.5h, and the sweating liquid is discharged to the raw material tank and used as raw material; finally, the melt crystallizer is heated to above 130°C, and the crystals are completely melted and collected to obtain 292.59g of ultra-high-purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide is 99.7%, and the total yield is 63.3%.

[0036] Comparative Example 2

[0037] In a 500ml melt crystallizer, 505.3g of crude lithium bis(fluorosulfonyl)imide with a content of 91.2% is put into the melt crystallizer, and the temperature is raised to 130°C to melt all the materials into liquid state, and then the temperature is lowered at a cooling rate of 8K / h, and the final temperature of the cooling is 121°C, and the temperature is kept constant for 0.5h; the uncrystallized mother liquor is discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%). The crystals in the melt crystallizer are heated to 128°C at a heating rate of 5K / h, and the temperature is raised to sweat, and the temperature is kept constant for 0.5h, and the sweating liquid is discharged to the raw material tank and used as raw material; finally, the melt crystallizer is heated to above 130°C, and the crystals are completely melted and collected to obtain 170.53g of ultra-high-purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide is 99.99%, and the total yield is 37%.

[0038] Comparative Example 3

[0039] In a 500ml melt crystallizer, 505.3g of crude lithium bis(fluorosulfonyl)imide with a content of 91.2% is put into the melt crystallizer, and the temperature is raised to 130°C to melt all the materials into liquid state, and then the temperature is lowered at a cooling rate of 8K / h, and the final temperature of the cooling is 95°C, and the temperature is kept constant for 0.5h; the uncrystallized mother liquor is discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%). The crystals in the melt crystallizer are heated to 124°C at a heating rate of 5K / h, and the temperature is raised to sweat, and the temperature is kept constant for 0.5h, and the sweating liquid is discharged to the raw material tank and used as raw material; finally, the melt crystallizer is heated to above 130°C, and the crystals are completely melted and collected to obtain 303.52g of ultra-high-purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide is 99.6%, and the total yield is 65.6%.

[0040] Comparative Example 4

[0041] In a 500ml melt crystallizer, 505.3g of crude lithium bis(fluorosulfonyl)imide with a content of 91.2% is put into the melt crystallizer, and the temperature is raised to 130°C to melt all the materials into liquid state, and then the temperature is lowered at a cooling rate of 8K / h, and the final temperature of the cooling is 95°C, and the temperature is kept constant for 0.5h; the uncrystallized mother liquor is discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%). The crystals in the melt crystallizer are heated to 131°C at a heating rate of 5K / h, and the temperature is raised to sweat, and the temperature is kept constant for 0.5h, and the sweating liquid is discharged to the raw material tank and used as raw material; finally, the melt crystallizer is heated to above 130°C, and the crystals are completely melted and collected to obtain 233.71g of ultra-high-purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide is 99.99%, and the total yield is 50.71%.

[0042] Comparative Example 5

[0043] In a 500ml melt crystallizer, 505.3g of crude lithium bis(fluorosulfonyl)imide with a content of 91.2% is put into the melt crystallizer, and the temperature is raised to 130°C to melt all the materials into liquid state, and then the temperature is lowered at a cooling rate of 16K / h, and the final temperature of the cooling is 95°C, and the temperature is kept constant for 0.5h; the uncrystallized mother liquor is discharged (recrystallized to the purity of the raw material, returned to the raw material tank, and the uncrystallized mother liquor is discharged from the system after the purity is lower than 75%). The crystals in the melt crystallizer are heated to 128°C at a heating rate of 5K / h, and the temperature is raised to sweat, and the temperature is kept constant for 0.5h, and the sweating liquid is discharged to the raw material tank and used as raw material; finally, the melt crystallizer is heated to above 130°C, and the crystals are completely melted and collected to obtain 279.1g of ultra-high-purity lithium bis(fluorosulfonyl)imide product, wherein the product purity of lithium bis(fluorosulfonyl)imide is 99.3%, and the total yield is 60.14%.

[0044] Table 1 Purity and yield of Examples 1 to 5 and Comparative Examples 1 to 5

[0045]

[0046]

[0047] The above contents are only preferred examples of the present invention and are not intended to limit the protection scope of the present application. For ordinary technicians in this field, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scopes, which should all be included in the protection scope of the present application.

Claims

1. A method for refining ultra-high purity lithium bis(fluorosulfonyl)imide, characterized in that: The following steps are involved: 1) The temperature of the melt crystallizer is raised to 130° C., crude lithium bis(fluorosulfonyl)imide with a mass percentage of ≥90% is added into the crystallizer, and heated until it is completely melted into a liquid state, the cooling source controls the cooling rate to be 5 to 20 K / h, the final cooling temperature is 90 to 120° C., the temperature is kept constant for 0.5 to 2 hours, and the uncrystallized mother liquor is discharged; 2) The crystals in the melt crystallizer are heated at a heating rate of 0.1 to 30 K / h to sweat, the final temperature is 125 to 130° C., the temperature is kept constant for 0.5 to 2 hours, the sweating liquid is discharged, and finally the melt crystallizer is heated to above 130° C., the crystals are completely melted and then collected to obtain an ultra-high purity lithium bis(fluorosulfonyl)imide product, wherein the mass percentage of lithium bis(fluorosulfonyl)imide is ≥99.99%.

2. The refining method according to claim 1, characterized in that: In step 1), the heat transfer temperature difference between the cooling source and the melt is controlled to be less than 5°C.

3. The refining method according to claim 1, characterized in that: Step 1) The cooling rate of the cold source is 5 to 15 K / h, the final temperature is 90 to 110° C., and the temperature is kept constant for 0.5 to 1 hour.

4. The refining method according to claim 1, characterized in that: The uncrystallized mother liquor discharged from step 1) is recrystallized to the purity of the raw material and returned to the raw material tank as the raw material of step 1). The uncrystallized mother liquor is discharged from the system after the purity is lower than 75%.

5. The refining method according to claim 1, characterized in that: Step 2) The heating rate is 5 to 30 K / h, the final temperature is 127 to 130°C, and the temperature is maintained at a constant level for 0.5 to 1 hour.

6. The refining method according to claim 1, characterized in that: In step 2), the sweating liquid from the crystals in the melt crystallizer during the period of heating and sweating to the final temperature is returned to step 1) as raw material.

Images