Preparation method of lithium bis (fluorosulfonyl) imide liquid salt

Abstract

The invention relates to a preparation method of lithium bis (fluorosulfonyl) imide liquid salt, which comprises the following steps: step 1, reacting hexamethyldisilazane, fluorosulfonic acid and organic alkali serving as raw materials in the presence of a first solvent and in an inert gas atmosphere, and removing a reaction solvent by reduced pressure distillation after the reaction is finished, washing the concentrated solution with water, and drying to obtain organic alkali salt of bis (fluorosulfonyl) imide; and 2, reacting the organic alkali salt of the imidodisulfuryl fluoride with an alkaline lithium source in the presence of a second solvent, and after the reaction is finished, filtering, crystallizing and drying to obtain the high-purity lithium imidodisulfuryl fluoride, and 3, adding the obtained lithium bis (fluorosulfonyl) imide into DMC (dimethyl carbonate), and dissolving to prepare a DMC solution with the concentration of about 30% so as to obtain the lithium bis (fluorosulfonyl) imide liquid salt. The method overcomes the problems of high production cost, complex process, low yield and purity and the like caused by production of a large amount of water, acid gas and organic matters in the preparation process of the lithium bis (fluorosulfonyl) imide liquid salt and many purification steps in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery electrolyte preparation technology, specifically relating to a method for preparing lithium bisfluorosulfonylimide liquid salt using hexamethyldisilazane, fluorosulfonic acid, triethylamine, etc. as raw materials. Background Technology

[0002] With the rapid development of lithium-ion battery technology, higher requirements have been placed on the safety and energy density of electrolytes. Lithium bisfluorosulfonylimide (LiFSI), as a novel electrolyte solute, exhibits superior thermal stability and higher conductivity compared to traditional lithium hexafluorosulfonate (LiPF6). Therefore, LiFSI has the potential to become the best alternative to LiPF6, whether used as a main salt additive or a core solute. However, the purity of the electrolyte solute has a significant impact on the overall performance of the battery; impurities can affect the irreversible capacity of the battery and may also pose safety hazards.

[0003] Currently, the main methods for preparing lithium difluorosulfonylimide involve synthesizing dichlorosulfonylimide acid from sulfonium chloride, aminosulfonic acid, and chlorosulfonium, then fluorinating the dichlorosulfonylimide acid to difluoroxanimide acid, reacting the difluoroxanimide acid with a lithium source to obtain lithium difluoroxanimide, and finally purifying it to obtain LiFSI. However, these methods have some problems, such as the generation of acidic gases and organic matter during the reaction, requiring additional dehydration and purification steps, which increases production costs and complexity. Several invention patents have been developed to address the problems in the preparation of lithium difluorosulfonylimide. For example, CN116654883A discloses a method for preparing lithium difluorosulfonylimide from methylsilazane. This method uses thioyl fluoride, methylsilazane, basic lithium, and resin-based diacid adsorbent as raw materials to synthesize lithium difluorosulfonylimide through reaction; however, there is still room for improvement in optimizing the reaction conditions to further improve the yield and purity of lithium difluorosulfonylimide. CN120157091A discloses a method for preparing liquid lithium bis(fluorosulfonyl)imide. This method uses bis(fluorosulfonyl)imide acid and esters as raw materials, mixes them to form a mixture, and then adds lithium carbonate dropwise to the mixture to react, yielding a liquid lithium bis(fluorosulfonyl)imide solution. The product obtained by this method does not require additional dehydration, thus improving product quality. The synthesis process is also simple. However, there is still room for improvement in optimizing the reaction conditions to further enhance the product yield and purity.

[0004] Existing technologies for preparing lithium bis(fluorosulfonyl)imide liquid salts often suffer from the following drawbacks: 1) In the traditional method for preparing lithium bis(fluorosulfonyl)imide liquid salt, a large amount of water, acidic gas and organic matter are generated during the reaction process, which requires additional dehydration and purification steps, increasing production costs and complexity; 2) Some preparation methods use flammable and explosive hydrogen fluoride or hydrogen, posing safety hazards and making it difficult to meet the safety requirements for lithium battery electrolyte preparation. 3) In the existing technology, the purity and yield of lithium bis(fluorosulfonyl)imide need to be improved, especially in the preparation process, it is difficult to effectively control reaction conditions such as temperature and time, resulting in low product purity and yield. 4) In the existing technology, the preparation process of lithium bisfluorosulfonylimide liquid salt is relatively complex and needs to be further simplified to reduce costs and improve production efficiency.

[0005] Therefore, there is an urgent need to develop and research a new method for preparing lithium bis(fluorosulfonyl)imide liquid salt to improve the yield and purity of lithium bis(fluorosulfonyl)imide liquid salt, simplify the production process, reduce costs, and ensure safety. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing lithium bis(fluorosulfonyl)imide liquid salt through organic synthesis using hexamethyldisilazane, fluorosulfonic acid, triethylamine, etc. This method overcomes the problems of existing technologies, such as the generation of large amounts of water, acidic gases, and organic matter during the preparation of lithium bis(fluorosulfonyl)imide liquid salt, high production costs due to multiple purification steps, complex processes, and low yields and purity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a liquid salt of lithium bis(fluorosulfonyl)imide includes the following steps: Step 1: The raw materials hexamethyldisilazane, fluorosulfonic acid and organic base are reacted in the presence of the first solvent and in an inert gas atmosphere. After the reaction is completed, the reaction solvent is removed by vacuum distillation. The concentrated liquid is washed with water and dried to obtain the organic base salt of difluorosulfonylimide. Step 2: The organic base salt of bis(fluorosulfonyl)imide is reacted with an alkaline lithium source in the presence of a second solvent. After the reaction is completed, the mixture is filtered, crystallized, and dried to obtain high-purity lithium bis(fluorosulfonyl)imide.

[0008] Step 3: Add the obtained lithium bis(fluorosulfonyl)imide to DMC (dimethyl carbonate) to dissolve and prepare a DMC solution of 30±5%. After filtration, the liquid salt of lithium bis(fluorosulfonyl)imide is obtained.

[0009] To further promote the forward reaction, preferably, in step one, the hexamethyldisilazane, fluorosulfonic acid, and organic base are mixed in a molar ratio of 1:(2-2.5):(1-1.5).

[0010] To further improve product purity and yield, specifically, the organic base in step one can be selected from one or two of triethylamine and pyridine. More preferably, the organic base is triethylamine. Compared with pyridine, triethylamine can promote the forward reaction more effectively, resulting in higher product purity and yield, with a product purity of over 95% and a yield of up to 97%.

[0011] Furthermore, in step one, the first solvent may be selected from one or more of acetonitrile, propionitrile, isopropionitrile, diethyl ether, propyl ether, isopropyl ether, tetrahydrofuran, acetone, butanone, methyl isobutyl ketone, and methylpyrrolidone, and the amount of the first solvent added is 2-3 times the mass of hexamethyldisilazane.

[0012] To further improve reaction efficiency, preferably, in step one, the reaction conditions are as follows: under nitrogen protection, the reaction is carried out at 0-20°C for 4-6 hours.

[0013] To further improve the purity and yield of the product, the organic base salt of bis(fluorosulfonyl)imide obtained at the end of step one reaction was distilled under reduced pressure to remove the solvent and obtain the organic base salt of bis(fluorosulfonyl)imide.

[0014] To further promote the forward reaction, preferably, in step two, the organic base salt of bis(fluorosulfonyl)imide is mixed with the alkaline lithium source in a molar ratio of 1:(0.5-1.5).

[0015] To further improve the purity and yield of bis(fluorosulfonyl)imide alkali metal salt, preferably, the alkali metal source can be selected from one or two of alkali metal carbonates and alkali metal hydroxides; the alkali metal carbonate can be lithium carbonate, etc., and the alkali metal hydroxide can be lithium hydroxide, etc. More preferably, the alkali metal source is an alkali metal carbonate.

[0016] Furthermore, in step two, the second solvent may be selected from one or more of acetonitrile, propionitrile, isopropionitrile, n-hexane, ethanol, methanol, diethyl ether, propyl ether, isopropyl ether, tetrahydrofuran, acetone, butanone, methyl isobutyl ketone, and methyl pyrrolidone, and the amount of the second solvent added is 1-10 times the mass of the alkaline lithium source.

[0017] To further improve the reaction rate, preferably, in step two, the reaction is carried out at a temperature of 20-40℃ for 2-4 hours. In step three, the dissolution temperature is room temperature (25±5℃).

[0018] As one preferred method, the organic base salt of bis(fluorosulfonyl)imide can be mixed with an alkaline lithium source at a molar ratio of 1:0.6, an appropriate amount of a second solvent can be added, the reaction temperature can be controlled at around 20°C, and the reaction can be stirred for 2 hours.

[0019] This invention provides a method for preparing lithium bis(fluorosulfonyl)imide liquid salt from hexamethyldisilazane via organic synthesis. Compared with the prior art, the synthesis method of this invention has the following advantages and beneficial effects: 1) This invention uses a novel combination of raw materials such as hexamethyldisilazane, fluorosulfonic acid, triethylamine, and acetonitrile, which improves the safety of the preparation process and meets the safety requirements for the preparation of lithium battery electrolytes; 2) This invention prepares the organic base salt of bis(fluorosulfonyl)imide in one step, which reduces the generation of water, acidic gas and organic matter during the reaction process, simplifies the subsequent dehydration and purification steps, and reduces production costs and complexity. 3) This invention utilizes the reaction of triethylamine salt with an alkaline lithium source to generate lithium difluorosulfonylimide, avoiding the complex reaction condition control in traditional methods and improving the purity and yield of the product. 4) This invention achieves high purity (up to 99%) and high yield (up to 96.96%) of lithium bisfluorosulfonylimide, meeting the stringent requirements for electrolyte solute purity in lithium battery electrolyte preparation. 5) The preparation method of the present invention is simple to operate, easy to industrialize, and has good economic benefits and practical value, providing a new idea for the industrial application of lithium bis(fluorosulfonyl)imide. Detailed Implementation

[0020] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0021] In the following examples, all raw materials used are commercially available and can be prepared using conventional techniques in the art.

[0022] Example 1 A method for preparing lithium bis(fluorosulfonyl)imide liquid salt using hexamethyldisilazane, fluorosulfonic acid, triethylamine, acetonitrile, etc. as raw materials, specifically includes the following steps: 1) Mix 100 g of hexamethyldisilazane, 130 g of fluorosulfonic acid, and 69 g of triethylamine in a molar ratio of 1:2.1:1.1, and introduce 200 g of acetonitrile. React at 5 °C for 5 hours under a nitrogen atmosphere. Remove the acetonitrile by vacuum distillation of the reaction solution, wash the concentrated solution with water, and dry to obtain 170 g of triethylamine salt of difluorosulfonylimide, with a yield of 97%.

[0023] 2) The obtained triethylamine salt of bis(fluorosulfonyl)imide was mixed with 23 g of lithium carbonate. 200 g of acetonitrile was added, and the reaction temperature was controlled at 25 °C. The mixture was stirred for 3 hours. After the reaction was completed, the mixture was filtered, concentrated, and 350 g of dichloromethane was added to crystallize the mixture. After filtration, the crystals were dried under vacuum at 60 °C for 4 hours to obtain 109 g of lithium bis(fluorosulfonyl)imide, with a yield of 96.7% and a purity of 99%.

[0024] 3) The obtained lithium difluorosulfonylimide was dissolved in 255g of DMC (dimethyl carbonate) at 25℃, and the solution was filtered to obtain liquid salt of lithium difluorosulfonylimide.

[0025] Example 2 A method for preparing lithium bis(fluorosulfonyl)imide liquid salt using hexamethyldisilazane, fluorosulfonic acid, triethylamine, acetonitrile, etc. as raw materials, specifically includes the following steps: 1) Mix 120 g of hexamethyldisilazane, 150 g of fluorosulfonic acid, and 75 g of triethylamine in a molar ratio of 1:2:1, and introduce 240 g of acetonitrile. React at 10 °C for 6 hours under a nitrogen atmosphere. Remove the acetonitrile by vacuum distillation of the reaction solution, wash the concentrated solution with water, and dry to obtain 200 g of triethylamine salt of difluorosulfonylimide, with a yield of 95%.

[0026] 2) To generate lithium bisfluorosulfonylimide by reacting the triethylamine salt of bisfluorosulfonylimide with an alkaline lithium source, the following steps were performed: 17 g of the obtained triethylamine salt of bisfluorosulfonylimide was mixed with 150 g of acetonitrile, and the reaction temperature was controlled at 20 °C. The mixture was stirred for 2 hours. After the reaction was completed, the mixture was filtered, concentrated, and 400 g of dichloromethane was added to crystallize the crystals. After filtration, the crystals were dried under vacuum at 60 °C for 4 hours to obtain 123 g of lithium bisfluorosulfonylimide, with a yield of 93% and a purity of 96%.

[0027] 3) The obtained lithium difluorosulfonylimide was dissolved in 290g of DMC (dimethyl carbonate) at 25℃, and the solution was filtered to obtain liquid salt of lithium difluorosulfonylimide.

[0028] Example 3 A method for preparing lithium bis(fluorosulfonyl)imide liquid salt using hexamethyldisilazane, fluorosulfonic acid, triethylamine, diethyl ether, etc. as raw materials, specifically includes the following steps: 1) Mix 100 g of hexamethyldisilazane, 130 g of fluorosulfonic acid, and 69 g of triethylamine in a molar ratio of 1:2.1:1.1 and introduce 200 g of diethyl ether. React at 10 °C for 6 hours under a nitrogen atmosphere. Remove the diethyl ether by vacuum distillation of the reaction solution, wash the concentrated solution with water, and dry to obtain 166 g of triethylamine salt of difluorosulfonylimide, with a yield of 95%.

[0029] 2) The obtained triethylamine salt of bis(fluorosulfonyl)imide was mixed with 22 g of lithium carbonate. 200 g of methanol was added, and the reaction temperature was controlled at 25 °C. The mixture was stirred for 3 hours. After the reaction was completed, the mixture was filtered, concentrated, and 350 g of dichloromethane was added to crystallize the mixture. After filtration, the crystals were dried under vacuum at 60 °C for 4 hours to obtain 104.5 g of lithium bis(fluorosulfonyl)imide, with a yield of 95% and a purity of 97%.

[0030] 3) The obtained lithium difluorosulfonylimide was dissolved in 255g of DMC (dimethyl carbonate) at 25℃, and the solution was filtered to obtain liquid salt of lithium difluorosulfonylimide.

Claims

1. A method for preparing a liquid salt of lithium bis(fluorosulfonyl)imide, characterized in that, Includes the following steps: Step 1: The raw materials hexamethyldisilazane, fluorosulfonic acid and organic base are reacted in the presence of the first solvent and in an inert gas atmosphere. After the reaction is completed, the reaction solvent is removed by vacuum distillation. The concentrated liquid is washed with water and dried to obtain the organic base salt of difluorosulfonylimide. Step 2: React the organic base salt of bis(fluorosulfonyl)imide with an alkaline lithium source in the presence of a second solvent. After the reaction is complete, filter, crystallize, and dry to obtain lithium bis(fluorosulfonyl)imide. Step 3: Add the obtained lithium bis(fluorosulfonyl)imide to DMC (dimethyl carbonate) to dissolve and prepare a DMC solution of 30±5%. After filtration, the liquid salt of lithium bis(fluorosulfonyl)imide is obtained.

2. The method for preparing lithium bis(fluorosulfonyl)imide liquid salt as described in claim 1, characterized in that, In step one, the molar ratio of hexamethyldisilazane, fluorosulfonic acid and organic base is 1:(2-2.5):(1-1.5).

3. The method for preparing lithium bis(fluorosulfonyl)imide liquid salt as described in claim 1, characterized in that, The organic base mentioned in step one is selected from one or both of triethylamine and pyridine.

4. The method for preparing lithium bis(fluorosulfonyl)imide liquid salt as described in claim 1, characterized in that, In step one, the first solvent is selected from one or more of acetonitrile, propionitrile, isopropionitrile, diethyl ether, propyl ether, isopropyl ether, tetrahydrofuran, acetone, butanone, methyl isobutyl ketone, and methyl pyrrolidone.

5. The method for preparing lithium bis(fluorosulfonyl)imide liquid salt as described in claim 1, characterized in that, In step one, the reaction conditions are: reaction at 0-20°C for 4-6 hours under nitrogen protection.

6. The method for preparing lithium bis(fluorosulfonyl)imide liquid salt as described in claim 1, characterized in that, In step two, the molar ratio of the organic base salt of bis(fluorosulfonyl)imide to the alkaline lithium source is 1:(0.5-1.5).

7. The method for preparing lithium bis(fluorosulfonyl)imide liquid salt as described in claim 1, characterized in that, In step two, the alkali metal source is selected from one or both of alkali metal carbonates and alkali metal hydroxides.

8. The method for preparing lithium bis(fluorosulfonyl)imide liquid salt as described in claim 1, characterized in that, In step two, the second solvent is selected from one or more of acetonitrile, propionitrile, isopropionitrile, n-hexane, ethanol, methanol, diethyl ether, propyl ether, isopropyl ether, tetrahydrofuran, acetone, butanone, methyl isobutyl ketone, and methyl pyrrolidone.

9. The method for preparing the lithium bis(fluorosulfonyl)imide liquid salt as described in claim 1, characterized in that, In step two, the reaction is carried out at a temperature of 20-40℃ for 2-4 hours.

10. The method for preparing the lithium bis(fluorosulfonyl)imide liquid salt according to claim 1, characterized in that, In step three, the dissolution temperature is 25±5℃.