Preparation method of liquid lithium bis (fluorosulfonyl) imide

Abstract

The invention provides a preparation method of liquid-state lithium bis (fluorosulfonyl) imide, and relates to the technical field of organic synthesis.The preparation method comprises the steps that bis (fluorosulfonyl) imide acid, ester substances and a non-aqueous solvent are mixed to form a mixed solution, and lithium carbonate is dropwise added into the mixed solution for a reaction to obtain a liquid-state lithium bis (fluorosulfonyl) imide solution. According to the invention, the imidodisulfuryl fluoride acid and the ester substance are used as raw materials, and the obtained liquid imidodisulfuryl fluoride lithium product does not need to be subjected to additional water removal, so that the quality of the product is improved, and meanwhile, the synthesis process is simple.

Description

Technical Field

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

[0002] Lithium bis(fluorosulfonyl)imide (LiFSI), as a new type of lithium salt, exhibits excellent comprehensive performance. Compared with traditional lithium hexafluorophosphate, LiFSI has a larger anion radius, which enables it to dissociate lithium ions more effectively, thereby improving the conductivity of the electrolyte. In addition, its decomposition temperature exceeds 200 °C, showing excellent thermal stability, which helps to enhance the high-temperature resistance of the electrolyte. At low temperatures, LiFSI can improve the discharge charge performance, while at high temperatures, it can maintain the stability of the capacitance, thus improving the high and low temperature performance of lithium batteries. Therefore, the electrolyte using LiFSI can significantly extend the cycle life of the battery, improve the rate performance and safety, which highly conforms to the future development trend of lithium batteries.

[0003] Although LiFSI has excellent performance and meets the requirements of the future new energy industry development, the cost has always been the main limiting factor for LiFSI to replace LiPF6. Especially for solid LiFSI, the synthesis process is complex, and a large amount of solvent purification is required in the later stage. The final product has the problem of solvent residue, which seriously affects the product quality and cost control. Therefore, the existing technology needs to be further developed. Summary of the Invention

[0004] In view of the various deficiencies of the prior art, in order to solve the above problems, a preparation method of liquid lithium bis(fluorosulfonyl)imide is now proposed, and the following technical solutions are provided: A preparation method of liquid lithium bis(fluorosulfonyl)imide, the preparation method comprising: mixing bis(fluorosulfonyl)imide acid, an ester substance and a non-aqueous solvent to form a mixed solution, and dropping lithium carbonate into the mixed solution for reaction to obtain a liquid lithium bis(fluorosulfonyl)imide solution.

[0005] Further, the pH value of the mixed solution formed by mixing bis(fluorosulfonyl)imide acid, an ester substance and a non-aqueous solvent is 2-3.

[0006] Further, the mass ratio of bis(fluorosulfonyl)imide acid to the non-aqueous solvent is 1:(5.94-9).

[0007] Further, the dropping time of lithium carbonate is 4-6 h.

[0008] Further, the temperature of the in-situ synthesis is 30-40 °C.

[0009] Further, the molar ratio of bis(fluorosulfonyl)imide acid, lithium carbonate to the ester substance is (2.02-2.04):1:(1.0-1.05).

[0010] Further, the ester substance is trimethyl orthoformate, triethyl orthoformate or tripropyl orthoformate.

[0011] Further, the non-aqueous solvent is at least one of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and propylene carbonate.

[0012] Further, after the in-situ synthesis is completed, post-treatment is carried out. The post-treatment includes filtration, and the filtrate after filtration is concentrated under vacuum negative pressure conditions.

[0013] Beneficial effects: 1. Compared with the prior art where water needs to be removed by adding a water remover after the preparation of lithium bis(fluorosulfonyl)imide, the present invention uses bis(fluorosulfonyl)imide acid and an ester substance as raw materials therein, and utilizes the acidic characteristics of bis(fluorosulfonyl)imide acid to promote the in-situ hydrolysis of orthoformate. The obtained liquid lithium bis(fluorosulfonyl)imide product does not require additional water removal, and only needs to be simply deacidified subsequently to obtain a qualified product, improving the quality of the product while the synthesis process is simple.

[0014] 2. The present invention has no other side reactions, and the by-products can be separated by simple distillation subsequently, with simple operation, low cost, and being green and environmentally friendly. Description of the Drawings

[0015] Figure 1 is a reaction schematic diagram for preparing liquid lithium bis(fluorosulfonyl)imide in Example 1 of the present invention. Detailed Embodiments

[0016] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Based on the embodiments in this application, other similar embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

[0017] According to an embodiment of the present invention, a method for preparing liquid lithium bis(fluorosulfonyl)imide is provided. The preparation method includes: mixing bis(fluorosulfonyl)imide acid, an ester substance, and a non-aqueous solvent to form a mixed solution, and dropping lithium carbonate into the mixed solution to obtain an anhydrous liquid lithium bis(fluorosulfonyl)imide solution. The present invention uses bis(fluorosulfonyl)imide acid and an ester substance as raw materials therein, and the obtained liquid lithium bis(fluorosulfonyl)imide product does not require additional water removal, improving the quality of the product while the synthesis process is simple.

[0018] The ester substance is trimethyl orthoformate, triethyl orthoformate (EMC) or tripropyl orthoformate. Under neutral or alkaline conditions, the reaction of orthoester substances with water is relatively slow, with a small amount of hydrolysis reaction occurring and the reaction with water being incomplete. Moreover, there are many side reactions under alkaline conditions, and transesterification will occur with anhydrous solvents. Due to the relatively large spatial position of orthoacetate substances and orthopropionate substances, the reaction is slower. However, through experiments, it is found that due to the small steric hindrance of the formate ester structure in orthoformate substances, they are easily hydrolyzed under acidic conditions, and even if the reaction system contains a few hundred ppm of trace water, it is easily reacted away.

[0019] Furthermore, the ester substance is preferably triethyl orthoformate. Compared with trimethyl orthoformate and tripropyl orthoformate, the product when using triethyl orthoformate is ethanol. Ethanol has a moderate boiling point and is easy to evaporate and separate. At the same time, the molecular structure chain length of ethanol is moderate, with a certain steric hindrance effect, and it is not easy to undergo transesterification in non-aqueous solvents such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, and propylene carbonate, and will not affect the quality of liquid lithium bis(fluorosulfonyl)imide. However, the product methanol of trimethyl orthoformate is prone to transesterification, and the product propanol of tripropyl orthoformate has a relatively high boiling point and is not easy to distill out. Therefore, the reaction effect is not as good as that of triethyl orthoformate.

[0020] Example 1 Under nitrogen protection, 181.14 g (1 mol) of bis(fluorosulfonyl)imide acid, 74.1 g (0.5 mol) of triethyl orthoformate, and 1087 g of ethyl methyl carbonate were respectively weighed and added into a 2 L four-necked flask. After stirring evenly, the materials were heated to 35 °C. 36.2 g (0.49 mol) of lithium carbonate was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and the addition was completed in 5 h. After the addition of lithium carbonate was completed, the pH value was detected to be 2, and the temperature was kept at 35 °C for another 2 h. The water content of the reaction solution was sampled and detected to be 22 ppm. The reaction was completed. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated at 40 °C under a negative pressure of -0.098 MPa. When the concentration of LiFSI reached about 45%, 300 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% to notify the concentration. 623.1 g of liquid lithium bis(fluorosulfonyl)imide was obtained, and the water content was detected to be 17 ppm. The specific preparation schematic diagram is as Figure 1 shown.

[0021] Example 2 Under nitrogen protection, 181.14 g (1 mol) of bis(fluorosulfonyl)imide acid, 80.14 g (0.5 mol) of tripropyl orthoformate, and 1087 g of ethyl methyl carbonate were weighed and added into a 2 L four-necked flask. After stirring evenly, the material was heated to 35 °C. 36.2 g (0.49 mol) of lithium carbonate was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and the addition was completed in 5 h. After the addition of lithium carbonate was completed, the pH value was detected to be 3, and it was kept warm at 35 °C for 2 h. The water content of the reaction solution was sampled and detected to be 35.9 ppm. The reaction was completed. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated at 40 °C under a negative pressure of -0.098 MPa. When the concentration of LiFSI reached about 45%, 300 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was stopped. 622.9 g of liquid lithium bis(fluorosulfonyl)imide was obtained, and the water content was detected to be 24.3 ppm.

[0022] Example 3 Under nitrogen protection, 181.14 g (1 mol) of bis(fluorosulfonyl)imide acid, 76.3 g (0.515 mol) of triethyl orthoformate, and 1087 g of ethyl methyl carbonate were weighed and added into a 2 L four-necked flask. After stirring evenly, the material was heated to 38 °C. 36.2 g (0.49 mol) of lithium carbonate was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and the addition was completed in 6 h. After the addition of lithium carbonate was completed, the pH value was detected to be 1, and it was kept warm at 38 °C for 2 h. The water content of the reaction solution was sampled and detected to be 12.6 ppm. The reaction was completed. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated at 40 °C under a negative pressure of -0.098 MPa. When the concentration of LiFSI reached about 45%, 300 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was stopped. 623.4 g of liquid lithium bis(fluorosulfonyl)imide was obtained, and the water content was detected to be 8.6 ppm.

[0023] Example 4 Under nitrogen protection, 132.78 g (0.674 mol) of bis(fluorosulfonyl)imide acid, 35.39 g of trimethyl orthoformate (0.3335 mol), and 1195.02 g of propylene carbonate were weighed and added into a 2 L four-necked flask. After stirring evenly, the temperature of the materials was raised to 35 °C. 24.64 g (0.3335 mol) of lithium carbonate was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and the addition was completed in 4 h. After the addition of lithium carbonate was completed, the pH value was detected to be 3, and it was kept warm at 40 °C for 2 h. The water content of the reaction solution was sampled and detected to be 35.2 ppm. The reaction was ended. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated at 40 °C under a negative pressure of -0.098 MPa. When the concentration of LiFSI reached about 45%, 300 g of propylene carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was stopped, obtaining 415.6 g of liquid lithium bis(fluorosulfonyl)imide, and the water content was detected to be 26.6 ppm.

[0024] Comparative Example 1 Under nitrogen protection, 36.2 g (0.49 mol) of lithium carbonate, 74.1 g (0.5 mol) of triethyl orthoformate, and 1087 g of ethyl methyl carbonate were weighed and added into a 2 L four-necked flask. After stirring evenly, the temperature of the materials was raised to 35 °C. 181.14 g (1 mol) of bis(fluorosulfonyl)imide acid was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and the addition was completed in 5 h. After the addition of bis(fluorosulfonyl)imide acid was completed, it was kept warm at 35 °C for 2 h. The water content of the reaction solution was sampled and detected to be 5853 ppm. The reaction was ended. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated at 40 °C under a negative pressure of -0.098 MPa. When the concentration of LiFSI reached about 45%, 300 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was stopped, obtaining 623.4 g of liquid lithium bis(fluorosulfonyl)imide, and the water content was detected to be 5264 ppm.

[0025] Comparative Example 2 Under nitrogen protection, 36.2 g (0.49 mol) of lithium carbonate, 88.9 g (0.6 mol) of triethyl orthoformate, and 1087 g of ethyl methyl carbonate were weighed separately and added into a 2 L four-necked flask. After stirring evenly, the material was heated to 35 °C. 181.14 g (1 mol) of bis(fluorosulfonyl)imide acid was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and the addition was completed in 5 h. After the addition of bis(fluorosulfonyl)imide acid was completed, keep warm at 35 °C for 2 h. The water content in the reaction solution was sampled and detected to be 5528 ppm. The reaction was completed. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated under the conditions of 40 °C and -0.098 MPa negative pressure. When the concentration of LiFSI reached about 45%, 300 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was stopped. 623.4 g of liquid lithium bis(fluorosulfonyl)imide was obtained, and the water content was detected to be 5141 ppm.

[0026] Comparative Example 3 Under nitrogen protection, 620 g of liquid lithium bis(fluorosulfonyl)imide containing water with a pH value of 7 and a water content of 4960 ppm was weighed and added into a 1 L four-necked flask. After stirring evenly, the material was heated to 35 °C. 74.1 g of triethyl orthoformate was weighed and slowly added dropwise into the liquid lithium bis(fluorosulfonyl)imide solution. The dropping time was 6 h. After the addition was completed, keep warm at 35 °C for 2 h. The water content in the reaction solution was sampled and detected to be 4537 ppm.

[0027] Comparative Example 4 Under nitrogen protection, 172.1 g (0.95 mol) of bis(fluorosulfonyl)imide acid, 88.9 g (0.6 mol) of triethyl orthoformate, and 1087 g of ethyl methyl carbonate were weighed separately and added into a 2 L four-necked flask. After stirring evenly, the material was heated to 37 °C. 36.2 g (0.49 mol) of lithium carbonate was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and the addition was completed in 5 h. After the addition of lithium carbonate was completed, the pH value was detected to be 9, and continue to keep warm at 37 °C for 2 h. The water content in the reaction solution was sampled and detected to be 2145.2 ppm. The reaction was completed. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated under the conditions of 40 °C and -0.098 MPa negative pressure. When the concentration of LiFSI reached about 45%, 300 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was stopped. 623.4 g of liquid lithium bis(fluorosulfonyl)imide was obtained, and the water content was detected to be 1928.6 ppm.

[0028] Comparative Example 5 Under nitrogen protection, 172.1 g (0.95 mol) of bis(fluorosulfonyl)imide acid, 74.1 g (0.5 mol) of triethyl orthoformate, and 1087 g of ethyl methyl carbonate were weighed and added into a 2 L four-necked flask. After stirring evenly, the material was heated to 40 °C. 36.2 g (0.49 mol) of lithium carbonate was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and complete the addition in about 1 h. After the addition of lithium carbonate was completed, keep the temperature at 40 °C for 2 h. The pH value was detected to be 9, and the water content of the reaction solution was sampled and detected to be 2126.1 ppm. The reaction was completed. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated under the negative pressure conditions of 34 °C and -0.098 MPa. When the concentration of LiFSI reached about 45%, 400 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was stopped. 622.3 g of liquid lithium bis(fluorosulfonyl)imide was obtained, and the water content was detected to be 1934.3 ppm.

[0029] Comparative Example 6 Under nitrogen protection, 182.04 g (1.005 mol) of bis(fluorosulfonyl)imide acid, 74.1 g (0.5 mol) of triethyl orthoformate, and 1087 g of ethyl methyl carbonate were weighed and added into a 2 L four-necked flask. After stirring evenly, the material was heated to 37 °C. 36.95 g (0.5 mol) of lithium carbonate was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and complete the addition in 5 h. After the addition of lithium carbonate was completed, keep the temperature at 37 °C for 2 h. The pH value was detected to be 5, and the water content of the reaction solution was sampled and detected to be 940.5 ppm. The reaction was completed. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated under the negative pressure conditions of 34 °C and -0.098 MPa. When the concentration of LiFSI reached about 45%, 400 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was stopped. 621.8 g of liquid lithium bis(fluorosulfonyl)imide was obtained, and the water content was detected to be 716.2 ppm.

[0030] Comparative Example 7 Under nitrogen protection, 181.14 g (1 mol) of bis(fluorosulfonyl)imide acid, 74.1 g (0.5 mol) of triethyl orthoformate, and 1087 g of ethyl methyl carbonate were weighed and added into a 2 L four-necked flask. After stirring evenly, the material was heated to 50 °C. 36.2 g (0.49 mol) of lithium carbonate was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and the addition was completed in 5 h. After the addition of lithium carbonate was completed, keep it warm at 50 °C for 2 h. The water content of the reaction solution was sampled and detected to be 5.2 ppm. The reaction was completed. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated at 40 °C under a negative pressure of -0.098 MPa. When the concentration of LiFSI reached about 45%, 300 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was stopped. 623.4 g of liquid lithium bis(fluorosulfonyl)imide was obtained, and the water content was detected to be 4.6 ppm, and the content of diethyl carbonate was 3.2%.

[0031] Comparative Example 8 Under nitrogen protection, 181.14 g (1 mol) of bis(fluorosulfonyl)imide acid, 88.125 g (0.5 mol) of triethyl orthopropionate, and 1087 g of ethyl methyl carbonate were weighed and added into a 2 L four-necked flask. After stirring evenly, the material was heated to 35 °C. 36.2 g (0.49 mol) of lithium carbonate was weighed and slowly and evenly added into the four-necked flask. During the addition process, pay attention to controlling the feeding time, and the addition was completed in 5 h. After the addition of lithium carbonate was completed, the pH value was detected to be 2, and it was kept warm at 35 °C for 2 h. The water content of the reaction solution was sampled and detected to be 1362 ppm. The reaction was completed. The reaction solution was filtered under nitrogen protection in a glove box, and then distilled and concentrated at 40 °C under a negative pressure of -0.098 MPa. When the concentration of LiFSI reached about 45%, 300 g of ethyl methyl carbonate was added, and the concentration was continued to be concentrated to 30% and then the concentration was notified to be stopped. 622.9 g of liquid lithium bis(fluorosulfonyl)imide was obtained, and the water content was detected to be 1180 ppm.

[0032] It can be seen from the examples and comparative examples that, firstly, the addition sequence and mass ratio of difluoromethanesulfonimide acid and lithium carbonate are crucial. Only when lithium carbonate is added dropwise to the mixed solution of difluoromethanesulfonimide acid and the pH of the reaction solution is ensured to be ≤ 3, the obtained liquid lithium difluoromethanesulfonimide has less water content and no subsequent water removal is required. In addition, in Comparative Example 3, triethyl orthoformate was added after preparing liquid lithium difluoromethanesulfonimide by the prior art, and the water content of the obtained product was 4537 ppm, which was more than 200 times the water content in Example 1. In Example 1, liquid lithium difluoromethanesulfonimide was prepared in-situ and water was removed in one step. In addition, the dosage of each raw material will also affect the water content of liquid lithium difluoromethanesulfonimide. The present invention explores the corresponding addition amount of raw materials, so that the prepared liquid lithium difluoromethanesulfonimide does not need to be dehydrated. Finally, Comparative Example 7 shows that the reaction temperature cannot be too high, otherwise transesterification reaction will occur, ultimately affecting the product quality.

[0033] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing liquid lithium bis(fluorosulfonyl)imide, characterized in that: The preparation method comprises: The bisfluorosulfonyl imide acid, the ester substance and the non-aqueous solvent are mixed to form a mixed solution, and lithium carbonate is added dropwise to the mixed solution to react and obtain a liquid bisfluorosulfonyl imide lithium solution.

2. The method for preparing liquid lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The pH value of the mixed solution formed by mixing the bisfluorosulfonyl imide acid, the ester substance and the non-aqueous solvent is 2-3.

3. The method for preparing liquid lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The mass ratio of the bisfluorosulfonyl imide acid to the non-aqueous solvent is 1:(5.94-9).

4. The method for preparing liquid lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The lithium carbonate is added dropwise for 4-6 hours.

5. The method for preparing liquid lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The temperature of the in-situ synthesis is 30-40°C.

6. The method for preparing liquid lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The molar ratio of the bis(fluorosulfonyl)imidic acid, lithium carbonate and ester substance is (2.02-2.04):1:(1-1.05).

7. The method for preparing liquid lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The ester substance is trimethyl orthoformate, triethyl orthoformate or tripropyl orthoformate.

8. The method for preparing liquid lithium bis(fluorosulfonyl)imide according to claim 1 or 7, characterized in that: The ester substance is triethyl orthoformate.

9. The method for preparing liquid lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: The non-aqueous solvent is at least one of ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate and propylene carbonate.

10. The method for preparing liquid lithium bis(fluorosulfonyl)imide according to claim 1, characterized in that: After the in-situ synthesis is completed, post-treatment is performed, and the post-treatment includes filtration, and the filtrate after filtration is concentrated under vacuum negative pressure conditions.

Images