A method for removing fluorosulfonic acid from bisfluorosulfone imides

Abstract

The application discloses a method for removing fluorosulfonic acid in bisfluorosulfonylimide, and the method comprises the following steps: reacting crude bisfluorosulfonylimide containing fluorosulfonic acid with inorganic acid salt or organic acid salt, and distilling the reaction product to remove fluorosulfonic acid in the bisfluorosulfonylimide. The application effectively solves the problem that fluorosulfonic acid is difficult to be completely removed in the prior art, and has the advantages of simple operation, low cost, high efficiency and good effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ion batteries, in particular to a method for removing fluorosulfonic acid in bisfluorosulfonylimide. BACKGROUND

[0002] In recent years, lithium ion batteries have attracted widespread attention due to their higher energy density than other traditional ion batteries. With the rapid development of its application field, people have put forward higher requirements for the energy density, rate performance, applicable temperature, cycle life and safety of lithium ion batteries. As an excellent additive, bisfluorosulfonylimide lithium can significantly improve the performance of lithium ion batteries, and its demand is also increasing.

[0003] Bisfluorosulfonylimide (HFSI) is one of the main raw materials for preparing bisfluorosulfonylimide lithium. In industry, bisfluorosulfonylimide is mainly prepared by fluorination of bischlorosulfonylimide or directly using fluorosulfonic acid. However, there is chlorosulfonic acid residue in the preparation process of bischlorosulfonylimide, which can further generate fluorosulfonic acid in the fluorination process to prepare bisfluorosulfonylimide, so that the product bisfluorosulfonylimide contains a certain amount of fluorosulfonic acid. When fluorosulfonic acid is used as a raw material to prepare bisfluorosulfonylimide, fluorosulfonic acid will inevitably be left over. When bisfluorosulfonylimide containing fluorosulfonic acid enters the next salt formation process to generate bisfluorosulfonylimide lithium, fluorosulfonic acid will generate lithium fluorosulfonate, which has poor hydrolysis stability and is easy to hydrolyze with trace water in bisfluorosulfonylimide lithium to generate lithium fluoride, lithium sulfate, hydrogen fluoride, etc., resulting in excessive anions such as fluorine ions and sulfate ions and acidity. However, with the rapid development of the lithium ion battery market, the requirements for electrolyte preparation process and product quality are also becoming more and more stringent, and there are higher requirements for the content of anions and cations. Therefore, the purification of bisfluorosulfonylimide is particularly important in the process. At present, rectification is mainly used in industry to remove impurities such as fluorosulfonic acid, but since the boiling points of fluorosulfonic acid (165.5℃) and bisfluorosulfonylimide (170℃) are close, the required device and conditions for rectification are harsh and difficult to control.

[0004] CN113104823A discloses a synthesis method of bisfluorosulfonylimide. The invention uses rectification for purification, and the purification method is: fluorination with high-purity bischlorosulfonylimide and hydrogen fluoride, after the reaction is completed, vacuum rectification is carried out under the condition of 25mmHg, and the 60℃ fraction is collected to obtain bisfluorosulfonylimide. The disadvantage is that bischlorosulfonylimide needs to be purified by rectification to remove chlorosulfonic acid and other impurities, which is relatively cumbersome.

[0005] After using a decontaminating agent to reduce the content of fluorosulfonic acid in bisfluorosulfonylimide, then rectification, it is beneficial to reduce the difficulty of rectification, reduce equipment investment, and improve the purity of bisfluorosulfonylimide. Therefore, it is a research hotspot to use a decontaminating agent to reduce the content of chlorides / fluorosulfonic acid in bisfluorosulfonylimide.

[0006] CN113912028A discloses a purification method of a bisfluorosulfonylimide, a certain amount of acid or organic acid salt is added as a impurity remover in the crude product to reduce the chloride content in the bisfluorosulfonylimide to achieve the purpose of purification. The salt added in the bisfluorosulfonylimide is an alkali metal salt of an organic acid, the alkali metal salt is one or several of oxalate alkali metal salt, citric acid alkali metal salt, tartaric acid alkali metal salt, ascorbic acid alkali metal salt, benzoic acid alkali metal salt, and salicylic acid alkali metal salt. The invention can reduce the chloride in the bisfluorosulfonylimide to below 10 ppm by one distillation or rectification, solves the problem of sublimation residue of chloride in the past, and improves the quality of bisfluorosulfonylimide. The disadvantage is that the amount of organic acid salt or acid used in the invention is large, the cost is higher than that of inorganic acid, and the organic acid is not stable at high temperature, which can easily introduce new impurities. SUMMARY

[0007] The purpose of the present application is to overcome the shortcomings of the prior art, and to provide a method for removing fluorosulfonic acid from bisfluorosulfonylimide, which is simple to operate, low in cost, high in efficiency and good in effect.

[0008] To solve the above technical problems, the present application is realized by the following technical scheme: a method for removing fluorosulfonic acid from bisfluorosulfonylimide, the crude bisfluorosulfonylimide containing fluorosulfonic acid is reacted with an inorganic acid salt or an organic acid salt, and the reaction product is distilled to remove the fluorosulfonic acid in the bisfluorosulfonylimide.

[0009] As a preferred embodiment of the present application, the inorganic acid salt is at least one of sulfate, halide or bisulfate; the inorganic acid salt is more preferably at least one of sodium chloride, potassium fluoride, potassium sulfate, and magnesium sulfate.

[0010] As a preferred embodiment of the present application, the organic acid salt is at least one of oxalate, benzoate, stearate, and citrate; the organic acid salt is more preferably at least one of sodium stearate and sodium benzoate.

[0011] As a preferred embodiment of the present application, the molar ratio of the inorganic acid salt or the organic acid salt to the fluorosulfonic acid in the crude bisfluorosulfonylimide is 0.1-3:1, and more preferably 0.5-2:1.

[0012] As a preferred embodiment of the present application, the reaction time is 0.5-5h, and the reaction temperature is 20-60℃.

[0013] As a preferred embodiment of the present application, the distillation is reduced pressure distillation; the temperature of the reduced pressure distillation is preferably 60-130℃, and the pressure is preferably 0-30KPa.

[0014] In view of the problem that the product obtained by the existing preparation process of bisfluorosulfone imide is mixed with fluorosulfonic acid which is difficult to remove and further affects the performance of lithium ion batteries, the inventors find in the research process that the fluorosulfonic acid can be effectively removed by a double decomposition reaction after the crude bisfluorosulfone imide containing fluorosulfonic acid is mixed with a small amount of specific inorganic acid salt or organic acid salt, the distillation efficiency of bisfluorosulfone imide is increased, and high-purity bisfluorosulfone imide can be obtained by simple distillation. The present application has the advantages of simple operation, low cost, high efficiency, good effect and the like.

[0015] In the present application, the amount of inorganic acid salt or organic acid salt has a greater effect on the removal of fluorosulfonic acid. If the amount is too low, the removal efficiency of fluorosulfonic acid is reduced. If the amount is too high, the yield of bisfluorosulfone imide is low. Therefore, the molar ratio of the inorganic acid salt or organic acid salt to fluorosulfonic acid in the crude bisfluorosulfone imide is 0.1-3:1, and more preferably 0.5-2:1. In actual operation, in order to ensure the appropriate amount, the content of fluorosulfonic acid can be detected first, and then the inorganic acid salt or organic acid salt can be added according to the content.

[0016] Compared with the prior art, the present application has the following advantages:

[0017] 1. High efficiency and good effect. The specific inorganic acid salt or organic acid salt which can react with fluorosulfonic acid by double decomposition reaction is added to effectively remove fluorosulfonic acid, increase the distillation efficiency of bisfluorosulfone imide, and the yield of bisfluorosulfone imide after purification is more than 93%, and no fluorosulfonic acid is detected in the purified bisfluorosulfone imide;

[0018] 2. Simple process. Since only fluorosulfonic acid and bisfluorosulfone imide have close boiling points in the system, the distillation difficulty is greatly reduced after the fluorosulfonic acid is treated, the equipment investment is reduced, and the distillation operation is greatly simplified. At the same time, the purification process of bisfluorosulfone imide is also simplified, and the bisfluorosulfone imide can be used for fluorination after simple solid-liquid separation, which significantly simplifies the production process of bisfluorosulfone imide;

[0019] 3. Green and environmentally friendly, low cost. The present application uses specific inorganic acid salt or organic acid salt, reduces the amount, improves the purification efficiency, and significantly reduces the discharge of three wastes and production cost. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 The fluorine spectrum of the crude bisfluorosulfone imide of Example 1.

[0021] Figure 2 The fluorine spectrum of the purified bisfluorosulfone imide obtained in Example 1. DETAILED DESCRIPTION

[0022] The technical solutions of the present application are further clearly and completely described below in combination with examples. Obviously, the described examples are only some of the examples of the present application, but not all.

[0023] In order to compare the removal effect, the crude bisfluorosulfonylimide with a fluorosulfonic acid content of 16 mmol is selected in the examples, and the fluorosulfonic acid content is confirmed by nuclear magnetic fluorine spectrum.

[0024] Example 1

[0025] 20 g of the crude bisfluorosulfonylimide (with a fluorosulfonic acid content of 16 mmol according to fluorine spectrum) is weighed, 16 mmol of sodium chloride is added, and after stirring at 30°C for 1.5 h, distillation is carried out under reduced pressure at 100 Pa and 100°C, the distillate is collected, 18.2 g of bisfluorosulfonylimide is obtained, the yield is 99%, and the obtained bisfluorosulfonylimide is analyzed by nuclear magnetic fluorine spectrum, and no fluorosulfonic acid peak is found in the fluorine spectrum.

[0026] Example 2

[0027] 20 g of the crude bisfluorosulfonylimide (with a fluorosulfonic acid content of 16 mmol according to fluorine spectrum) is weighed, 20 mmol of potassium fluoride is added, and after stirring at 25°C for 0.5 h, distillation is carried out under reduced pressure at 1000 Pa and 120°C, the distillate is collected, 17.5 g of bisfluorosulfonylimide is obtained, the yield is 95%, and the obtained bisfluorosulfonylimide is analyzed by nuclear magnetic fluorine spectrum, and no fluorosulfonic acid peak is found in the fluorine spectrum.

[0028] Example 3

[0029] 20 g of the crude bisfluorosulfonylimide (with a fluorosulfonic acid content of 16 mmol according to fluorine spectrum) is weighed, 9 mmol of potassium sulfate is added, and after stirring at 50°C for 1 h, distillation is carried out under reduced pressure at 100 Pa and 100°C, the distillate is collected, 18.3 g of bisfluorosulfonylimide is obtained, the yield is 99%, and the obtained bisfluorosulfonylimide is analyzed by nuclear magnetic fluorine spectrum, and no fluorosulfonic acid peak is found in the fluorine spectrum.

[0030] Example 4

[0031] 20 g of the crude bisfluorosulfonylimide (with a fluorosulfonic acid content of 16 mmol according to fluorine spectrum) is weighed, 10 mmol of magnesium sulfate is added, and after stirring at 40°C for 2 h, distillation is carried out under reduced pressure at 100 Pa and 80°C, the distillate is collected, 17.6 g of bisfluorosulfonylimide is obtained, the yield is 96%, and the obtained bisfluorosulfonylimide is analyzed by nuclear magnetic fluorine spectrum, and no fluorosulfonic acid peak is found in the fluorine spectrum.

[0032] Example 5

[0033] Take 20g of crude difluorosulfimide (fluorine spectrum fluorosulfonic acid content is 16mmol), add 20mmol of sodium stearate, stir at 20℃ for 3h, then distill under reduced pressure at 1000Pa, 120℃, collect the fraction, get 17.1g of difluorosulfimide, yield 93%, the obtained difluorosulfimide is analyzed by fluorine nuclear magnetic resonance, and no fluorosulfonic acid peak is found in the fluorine spectrum.

[0034] Example 6

[0035] Take 20g of crude difluorosulfimide (fluorine spectrum fluorosulfonic acid content is 16mmol), add 20mmol of sodium stearate, stir at 20℃ for 3h, then distill under reduced pressure at 1000Pa, 120℃, collect the fraction, get 17.1g of difluorosulfimide, yield 93%, the obtained difluorosulfimide is analyzed by fluorine nuclear magnetic resonance, and no fluorosulfonic acid peak is found in the fluorine spectrum.

Claims

1. A method for removing fluorosulfonic acid from bisfluorosulfonyl imide, characterized by, The crude bifluorosulfonylimide containing fluorosulfonic acid is reacted with an inorganic acid salt or an organic acid salt, the reaction product is distilled to remove fluorosulfonic acid in the bifluorosulfonylimide, the inorganic acid salt is one of sodium chloride, potassium fluoride, potassium sulfate, magnesium sulfate, and the organic acid salt is at least one of sodium stearate and sodium benzoate.

2. The method of removing fluorosulfonic acid from bisfluorosulfonyl imide according to claim 1, characterized by, The molar ratio of the inorganic acid salt or the organic acid salt to fluorosulfonic acid in the crude bifluorosulfonylimide is 0.1-3:

1.

3. The method of removing fluorosulfonic acid from bisfluorosulfone sulfimide according to claim 1, characterized by, The reaction time is 0.5-5 h and the reaction temperature is 20-60℃.

4. The method of removing fluorosulfonic acid from bisfluorosulfone sulfimine according to claim 1, wherein The distillation is reduced pressure distillation.

5. The method of removing fluorosulfonic acid from bisfluorosulfonyl imide according to claim 4, wherein The reduced pressure distillation temperature is 60-130℃ and the pressure is 0-30 KPa.

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